AN EXAMINATION OF VEHICLE NOISE TEST PROCEDURES

Transcription

1 TRL Limited PUBLISHED PROJECT REPORT PPR044 AN EXAMINATION OF VEHICLE NOISE TEST PROCEDURES by G. Watts, P. Nelson, C. Treleven and M. Balsom Prepared for: Project Record: Client: Vehicle Noise - Assessment of Test Procedures and New Technologies, S0128/VB Cleaner Fuels and Vehicles Division, Environmental Standards Branch, Department for Transport (Mr I Turner) Copyright TRL Limited May 2005 This report, prepared for Mr Ian Turner, Cleaner Fuels and Vehicles Division. The views expressed are those of the authors and not necessarily those of Cleaner Fuels and Vehicles Division. Published Project Reports are written primarily for the customer rather than for a general audience and are published with the customer s approval. Project Manager Approvals Quality Reviewed

2 This report has been produced by TRL Limited as part of a Contract placed by Cleaner Fuels and Vehicles Division. Any views expressed are not necessarily those of Cleaner Fuels and Vehicles Division. TRL is committed to optimising energy efficiency, reducing waste and promoting recycling and re-use. In support of these environmental goals, this report has been printed on recycled paper, comprising 100% postconsumer waste, manufactured using a TCF (totally chlorine free) process.

3 CONTENTS Executive summary i 1 Introduction 1 2 Background and literature review Conceptual framework Vehicle operations in urban areas Perception of vehicle noise Consideration of stationary and low speed test methods 10 3 Selection of candidate test procedures Basic requirements of a test method The test programme for stationary and low speed operations The test programme for pass-by operations 22 4 Measurement programme Test methods Measurement set up and equipment development Vehicle description, loading and modifications to the test procedures 34 5 Results and analysis Results Analysis 39 6 GRB Test Programme Results Analysis 61 7 Regulatory impact assessment (RIA) Introduction The proposed new noise test How much stricter are the options for the proposed new test? Benefits of the options Information from the Highways Agency Costs to industry Benefit cost ratio Other issues M2, M3, N2 and N3 vehicles Recommended Option Significance and relevance of this RIA 76 8 Summary and Conclusions Further work 83 Acknowledgements 87 References 88 Appendix A. Results of Vehicle tests 91 Appendix B. Summary of Pull-away From Rest Test Results 117 Appendix C. Comparison of test results 119 TRL Limited PPR044

4 Appendix D. Results of ACEA test programme 123 Appendix E. Results of SAE test programme 125 Appendix F. List of acronyms 126 TRL Limited PPR044

5 Executive summary Since the early 1970's new motor vehicles have been subject to type approval test procedures that limit noise emission. Since the regulations were first introduced, the limits imposed have been progressively tightened with the overall objective of reducing the levels of traffic noise and the associated impact of traffic noise on people. However, despite the dramatic reductions achieved in power train noise from vehicles for the conditions imposed by the type approval test, traffic noise levels in the UK and Europe do not appear to have fallen significantly. Several studies suggest that the noise from traffic, i.e. after correcting for traffic flow and speed, has either remained virtually constant, or has, under certain conditions risen, over the past twenty years. The lack of a closer correlation between type approval noise limits and traffic noise emission levels has been attributed, in part, to the test procedure that is used for type approval. It is argued that changes are needed so that the test procedure is made more representative of vehicle operations in real road situations. It is clear that future vehicle noise test procedures will need to ensure that there is a better degree of discrimination between noisy and relatively quiet vehicles for conditions representative of noise intrusion in residential areas. This may require vehicles to be tested under a variety of operating conditions representative of normal driving. Future testing will also need to ensure that appropriate examination of both power unit and rolling noise components are considered and with the emergence of alternative fuelled and hybrid powered vehicles, any future test procedure should also be appropriate for new and emerging vehicle technologies. Given the broad range of options that are presently being considered by regulatory and standards authorities, the Department for Transport commissioned TRL to examine the technical issues associated with the range of test procedures that could be considered for future vehicle noise testing. In summary, the objectives of the study are to: To produce a critical assessment of the proposed UN-ECE test procedures and their potential effectiveness in meeting the aim of reducing road traffic noise nuisance. To produce an assessment of test procedures not currently included in these new proposals and to examine each procedure s ability to distinguish between different types of quiet or new technology vehicle from relatively noisy vehicles. To provide indicative noise limit levels on the proposed test. To produce an assessment of the costs to UK industry, the UK consumer and the general public resulting directly or indirectly from the impact of the proposals and any recommendations to change these. Provide vehicle noise emissions data that could be used for the purposes of modelling road traffic noise This report provides the results of this study. It begins with a comprehensive review of the issues associated with changing the vehicle noise type approval test procedure. It includes an assessment of results from drive cycle and perception studies and provides an overview of both current and proposed test procedures and related research studies. This information has been assessed to help define a range of candidate test procedures that have been examined further as part of a measurement programme using a carefully selected sample of vehicles. The test procedures examined include both the current and proposed new test procedures as well as exploring a range of additional test procedures designed to expose noise emission from different types of vehicle operation that are not currently covered in the proposals. These test procedures have examined noise from typical low speed operations as well as noise from stationary vehicles. Noise from vehicles idling, noise from the operation of the air brakes exhaust noise and noise from ancillary equipment such as hydraulic tailgate operation have been measured as part of this programme. The vehicle sample selected included five HGV s, four buses, five minibuses, four vans, five cars, two sports cars and one 4x4. The results from the test programme have indicated the limitations and advantages of the various test procedures and exposed questions of interpretation of the test methods, TRL Limited i PPR044

6 some of which have already been addressed by the relevant standards committees. The results been analysed to investigate a broad range of issues associated with changing the test procedure and have focussed on providing answers to the questions posed by the main objectives of the study. The measurement programme has enabled comparisons to be drawn between the different test methods and issues of repeatability, reproducibility and the degree to which the tests are representative of real situations have been examined. By combining the data obtained with that of a survey being conducted by the Groupe de Rapporteur du Bruit (GRB) it has been possible to speculate on the limit values that could be employed if the proposed test procedure is introduced. Modelling techniques have been used to investigate the benefits, in terms of controlling traffic noise levels, of reducing the type approval noise limits associated with the proposed test procedure. The overall costs and benefits of the proposed changes have been evaluated as part of a Regulatory Impact Assessment. The main conclusions are as follows: Assessment of the proposed UN-ECE test procedure The proposed test condition which involves the measurement of the maximum A-weighted level at moderate acceleration (typically 1 to 2 m s -2 ) and at a cruise-by speed of 50 km/h appears to be appropriate for assessing the noise impact of vehicles under typical urban driving conditions. The current test involves full throttle acceleration in a low gear so acceleration rates and engine speeds are relatively high. Such test conditions are more likely to be representative of the worst case driving conditions than the average condition represented in the proposed test. Consequently the proposed test should more fairly represent the noise impact of a vehicle under urban driving conditions where the vehicle operation is largely constrained by speed limits, presence of junction controls and other road users. However, it is clear, that with the introduction of the new test, which is intended to expose propulsion and rolling noise, there is a need to consider revising the specification of the International Organisation of Standardisation (ISO) so that it is a more representative surface. It has been noted that a subgroup of ISO WG42 is planning to revise the current test surface specification. It is hoped that a new surface will emerge from the group that better represents the rougher surfaces found in the UK. In the event that the ISO surface is replaced by a test surface that represents average UK road conditions then the proposed test method becomes appropriate for controlling both propulsion and tyre/road noise. To meet lower limit values manufactures will then need to consider reducing both of these main sources of vehicle noise. However, adopting the proposed method and imposing limit values at levels which would pass most vehicles that meet the current standard may lead to poor control of noise levels under worst case driving conditions. It has been shown that three M1 vehicles that failed the current test would actually pass the proposed test if the L urban value was set above 69 db(a), i.e. a level where 70 % of current vehicles would fail. This argues for retaining the current test (or imposing a similar test) in order to control noise at high engine speeds. Annex 10 would be the appropriate place in the regulation to require additional testing to ensure noise levels were acceptable under more extreme conditions than the proposed test condition. Assessment of other test procedures Generally all the tests examined have indicated a good degree of repeatability. However, for a test designed to represent a vehicle accelerating from a stationary condition, such as might occur at a junction or traffic light, there were some problems obtaining consistent results. Of particular interest was the fact that vehicles tested using this low speed test were ranked differently than when tested using the current or proposed pass-by test. This suggests that this type of low speed test is exposing some aspects of noise generation that is not being picked up by the other test conditions. A review of earlier studies examining the subjective assessment of the noisiness of different vehicle operations has indicated the importance of this operating condition. However, if a low speed test of this type is to be included in future revisions of the standard test method then further work is needed on the TRL Limited ii PPR044

7 specification of the driving condition and, of course, additional data would be needed to define appropriate limit values. Exhaust test results show that there is no real advantage in carrying out a slow or rapid change in the engine speed as in the current ISO 5130 exhaust test. Overall the ranking of exhaust noise levels for the vehicles tested did not correspond closely with either stationary or moving tests. Therefore, the use of a slow sweep type of test for use in controlling noise emission in the environment under normal driving conditions is limited apart from identifying faulty exhaust systems. Generally with the slow whole vehicle engine sweep test results for light vehicles and buses were well correlated with the corresponding results for the moving tests. For the heavy vehicles tested, the correlations were less good although the sample size available was small. It was found that measurements taken close to the vehicle (i.e. 2m) are reasonably representative of the total noise from the vehicle measured at 7m. Therefore the test could potentially be carried out under restricted space conditions as part of in-service testing of vehicles. When the results for vehicles idling were examined and for the heaviest vehicles large differences of the order of 15 db(a) were noted in the results. One vehicle was particularly noisy at idle but performed reasonably well on the pass-by tests. The use of an idle test as a means of licensing heavy vehicles for delivering to noise sensitive areas would be worthy of further consideration in view of the prevalence of this operating condition. The measurements taken of air brake noise revealed that of the nine vehicles tested, three gave results that exceeded the proposed limit value set for air brake noise measured at 7m. Low values of air brake noise are particular relevant to quiet operations at depots and supermarkets especially if deliveries are made in the evening or at night. As for noise at idle a case could be made for controlling this source of noise through an appropriate licensing system. A test on ancillary equipment involved tailgate operation on a delivery truck, automatic door operation and kneel operation on buses. The kneel operation on a single deck bus produced the highest level of 73.3 db(a) at 7m. The findings suggest that ancillary equipment is an important noise source which should be considered when designing vehicles for quiet operation. Results for alternative fuelled vehicles There was no consistent pattern in the results for Compressed Natural Gas (CNG) vehicles and their diesel equivalents. This might suggest that for the vehicles studied there is no distinct advantage in preferring these vehicles in order to reduce community noise impact. However, a larger sample and greater examination of existing data is required before definite conclusions can be drawn. An electric van produced levels of 68.8 and 68.2 db(a) on the current test and proposed tests respectively. The diesel equivalent van produced significantly higher levels of 75.6 and 71.4 db(a) respectively. It can be seen that both under average and extreme driving conditions the electric equivalent van has a distinct noise advantage. Currently there are few electric vehicles in use but these results argue for a careful consideration of the merits of promoting their use in the future. Indicative noise limits for the proposed test procedure In order to set appropriate limit values for the new test it is appropriate to consider technical equivalence to the current standard. However, it is clear from the scatter plots of L current against L urban that, although there is a trend for the proposed test to give lower noise levels than the current method, there is no one-to-one correspondence that could be used to reliably establish a set of new limit values. Since no exact technical equivalence exists it is difficult to decide an appropriate limit value based on a purely statistical analysis of test values. In GRB it was agreed that the way forward was to examine the costs and benefits of applying various limit values and to make a decision on the appropriate limit value informed by a knowledge of the trend between costs and benefits. The benefits in terms of traffic noise reduction of lowering L urban of light vehicles by a significant amount (3dB(A)) TRL Limited iii PPR044

8 have been discussed in this report and without an appropriate test surface they are predicted to be small (less than approximately 0.5 db(a)). Recently GRB data for M2, M3, N2 and N3 category vehicles has become available. It is likely that in order to set limit values for these heavier vehicles a similar approach to the analysis of the data will be taken. Costs and benefits to UK industry, consumers and the general public of introducing the proposed test method The Regulatory Impact Assessment (RIA) portion of this report recommends that the proposed new ECE vehicle noise test be adopted by the UK. The new test should start as soon as possible, e.g. in 2007, with noise limits that are equivalent to those currently in use with the old test. A tightening in 2010 by 2 db should then occur. The benefit to the UK of each 1dB reduction in noise measured at dwellings was found to be at least 524 million per annum. If the new ECE test were to reduce real noise from road traffic by 2dB, this would mean an annual benefit of 1048 million and a minimum benefit cost ratio of 116. This figure is far higher than that from most public investment projects available to governments. However, a reduction of 2dB in the limits for the new ECE test is likely to result in a much smaller reduction in real noise from road traffic than 2dB, because the test surface that is currently use in the test is unrepresentative of real roads in the UK. Although work is in hand to specify a new test surface that is more representative it is likely to be some time before the specification is available as a standard. Given this concern over the surface, it can be stated that the minimum benefit cost ratio of the proposed new test therefore lies somewhere in the range of This RIA should be completed when the GRB sets numerical values for the noise limits to be used with the new test. In addition, data needs to be collected on the proportion of the road network that is coated with each type of thin surface course. Vehicle noise emission data for modelling purposes The data collected in the current project will be used in the follow-up project to Harmonoise called IMAGINE (Improved Methods for the Assessment of the Generic Impact of Noise in the Environment). The project started in December 2003 and was funded under the 6 th EC framework programme (CT ) and by Department for Transport (DfT). TRL are playing an active part in refining the source model which forms a major part of the overall project. TRL Limited iv PPR044

9 1 Introduction Since the early 1970's new motor vehicles have been subject to type approval test procedures that limit noise emission. Since the regulations were first introduced, the limits imposed have been progressively tightened with the overall objective of reducing the levels of traffic noise and the associated impact of traffic noise on people. However, despite the dramatic reductions achieved in power train noise from vehicles for the conditions imposed by the type approval test, traffic noise levels in the UK and Europe do not appear to have fallen significantly. The lack of a closer correlation between type approval noise limits and traffic noise emission levels has been attributed, in part, to the test procedure that is used for type approval. It is argued that changes are needed so that the test procedure is made more representative of vehicle operations in real road situations. Recently work has been carried out to develop the vehicle noise test procedure. For example, ISO Working Group TC 43/SC1/WG42 is revising the basic test method described in the original ISO standard (ISO 362). Concurrently, the UN-ECE WORKING GROUP WP29/GRB is updating its method of testing road vehicles (Regulation 51). It is anticipated that the revision of Regulation 51 will be adopted by the European Commission as the basis for an updated EU Directive. This will require the involvement of a European Union Working Group WG8: Road traffic. It is clear that future vehicle noise test procedures will need to ensure a greater degree of correspondence between test results and noise generation in practice. In other words, test procedures will need to offer a better degree of discrimination between noisy and relatively quiet vehicles for conditions representative of noise intrusion in residential areas. This may require vehicles to be tested under a variety of operating conditions representative of normal driving. Future testing will also need to ensure that appropriate examination of both power unit and rolling noise components are considered and with the emergence of alternative fuelled and hybrid powered vehicles, any future test procedure should also be appropriate for new and emerging vehicle technologies. Given the broad range of options that are presently being considered by regulatory and standards authorities, the Department for Transport commissioned TRL to examine the technical issues associated with the range of test procedures that could be considered for future vehicle noise testing. In summary, the objectives of the study are to: Produce a critical assessment of the proposed UN-ECE test procedures and their potential effectiveness in meeting the aim of reducing road traffic noise nuisance: Produce an assessment of issues not currently included in the new ECE/EU proposals Provide an assessment of each procedure's ability to distinguish between different types of quiet or new technology vehicles from relatively noisy vehicles and accordingly provide indicative noise level limit values. Produce an assessment of the costs to UK industry, the UK consumer and general public resulting directly or indirectly from the impact of these UN-ECE proposals and any recommendations to change these. Provide vehicle noise emissions data that could be used for the purposes of modelling road traffic noise. The programme of work has been divided into essentially two parts; a preliminary stage that includes a review of relevant information and a definition of a programme of measurements, and a second stage which included the measurement programme and the bulk of the analysis. This report describes the results of the study. It describes the technical review that was carried out and how this was used to determine the test programme and rationale underpinning the selection of the vehicle sample. It describes the comprehensive test programme that was undertaken and the results obtained. It also provides guidance on the most appropriate test procedures to use for vehicle type approval testing and indicates the noise level limits that should be achievable for different vehicle types. The costs and benefits of the proposed changes are defined and evaluated in a Regulatory Impact Assessment (RIA). TRL Limited 1 PPR044

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11 2 Background and literature review The main objective of the study is to identify a suitable test procedure or procedures that allow a proper evaluation of the noisiness of a vehicle when it is operating under real driving conditions in the community. The literature review was undertaken mainly to establish relevant background information but also to help determine a range of candidate test procedures taking into account information from drive cycles and perception studies. These candidate test procedures would then be examined in more detail as part of a test programme involving a sample of vehicles, chosen to be representative of the vehicle fleet. It was anticipated that a single test procedure would be unlikely to cover all vehicle operations and so, initially, the study focussed on establishing typical operations representative of both low speed/stationary conditions, that might be encountered in congested urban streets, as well as the range of drive-by conditions that tend to occur on main roads and in suburban and less congested roads. This section describes the main aspects of the review that was carried out. It begins with establishing a framework embracing the important factors affecting noise annoyance from individual vehicles and then critically examines the literature available on vehicle operations in different traffic conditions and the results of relevant perception studies. A summary of existing and proposed test procedures is included. 2.1 Conceptual framework At the outset it is useful to consider, in a broad sense, how individual vehicles operating under different driving conditions relate to community annoyance. A framework for viewing this relationship will assist in the development of both the study design adopted for this project and the development of an appropriate strategy for vehicle noise test procedures. For a vehicle noise test procedure to be relevant it must cover the operations that cause annoyance or disturbance in the community. The relative importance of any operating condition will depend on the amount of time that operating condition is maintained and the noise level emitted. The noise impact (NI) of a vehicle can be considered to be dependent on the number of people bothered by the various vehicle operations and the time for which these operations take place. This can be expressed as: NI = t i n i (2.1) i Where t i is the fraction of the time a particular operation takes place and n i is the number of people bothered by the noise produced during operation i. If we assume that the density of population is uniform across the network of roads where the vehicle operates then we can expect the number of people bothered to be simply related to the noise level L i during pass-by for vehicle operation i. It has been found from social surveys of noise exposure that the percentage of persons annoyed is related to the average noise over an average typical day. The percentage is always monotonically related to level. Typically the percentage bothered increases slowly for increases in noise level at low noise levels but then larger increases are observed for similar increases at higher levels. In addition, the louder the level of noise the larger the noise footprint i.e. the area within which residents will notice the noise and be affected will be greater. For these two reasons it would be reasonable to expect that the numbers bothered to increase approximately exponentially with the level of noise emitted. To a reasonable approximation this can be expressed as a parabolic curve though the exact form of the curve is not critical to the understanding. Hence the number bothered is given by: i i i i i 2 i n = + L + L (2.2) The constants i, i and i will depend on the types of operation since it might be expected that some operations produce more irritation than others at the same overall noise level. However, the A- TRL Limited 3 PPR044

12 weighted level is highly correlated with perceived noisiness so that the constants may not vary greatly between operations. If this is assumed we can simplify the expression of noise impact to: NI = i t i 2 ( + L + L ) Because of the squared value in the expression we can see that the largest contribution to the NI will come from operations that are particularly noisy especially if they also last a significant fraction of the time. Conversely quiet events lasting a small fraction of time will almost certainly be insignificant. In order to advise on the extent to which current and new tests reflect the impact on the community it is important to carefully consider the inclusion of operations that contribute significantly to the NI value. To do this, data are needed of the frequency of various vehicle operations and the associated noise levels in places where people live and to a lesser extent where they work, since it is at home in the early morning and the evening and at night where most disturbance occurs. For this reason it is important to consider operations in residential areas which will usually be in suburban areas rather than town or city centres. It is likely that steady (or nearly steady speeds) occur frequently and should certainly be considered for representative test procedures. However, there is a need to determine the frequency of various steady speeds in typical residential areas in order to choose the most appropriate and representative values for the standard test. Other types of operation such as rapid acceleration, braking and idling are likely to occur less frequently than steady speeds unless traffic conditions are congested. However, these types of operation can also produce intrusive noise levels in the community and, therefore, may need to be considered as part of a future test procedure. It is important therefore to consider what would be a representative level of acceleration or braking although it should be acknowledged that conditions other than Wide Open Throttle (WOT) may be difficult to reproduce accurately under standard test conditions. A statistical approach could be used to overcome this type of problem that would involve testing over a range of acceleration conditions and then using the implied relationship to normalise the data to a typical acceleration value. To obtain t i it is necessary to obtain the acceleration and distribution of speeds on the road network in or near residential areas. Noise levels and perceived noisiness have been assessed in jury experiments and this information can be used to inform decisions about appropriate test procedures. i i (2.3) 2.2 Vehicle operations in urban areas Information on urban drive cycles provide insight into the range and frequency of different vehicle operations in practice. It was anticipated that this information would help to establish the most appropriate vehicle operations to use in standard testing. An investigation in Japan in 1995 examined driving conditions in urban areas. The results of this work were presented at the 26 th -30 th session meetings of GRB (JAMA, 2001). The study included tests on 12 vehicles (5 cars, 5 light commercial vehicles, 2 heavy commercial vehicles). Measurements were taken of vehicle speed, acceleration, engine speed and load while driving in urban areas. No precise information on low speed driving was included in the meeting reports, except to say that it was found that a vehicle speed of 50 km/h occurred most frequently during urban driving. Information on drive cycle statistics was included in an informal paper presented by the expert from the Netherlands at the 34 th session meeting GRB (Informal document number 9, 2001). It was recommended to use a drive-by test at 50 km/h, and second test involving an acceleration from a lower speed in the range km/h. The justification for his proposal was based on drive cycle information. The key points that emerged from the presentation of the paper were: A speed of 50 km/h cruising has a "45% relevance to the noise problem relative to other driving states". See Table 2.1 that has been reproduced from the presentation. It should be noted that the TRL Limited 4 PPR044

13 table also shows that a medium acceleration from km/h and acceleration from traffic lights account, when combined, to about 15% of driving. Data from the European Automobile Manufacturers Association (ACEA) showing vehicle speed distribution for medium driving behaviour on a main street also indicated that the most frequently occurring speed was 50 km/h. Data from M+P, a firm of acoustic consultants in The Netherlands, showed average vehicle speed/acceleration distributions (based on an average of 11 vehicles) for normal driving behaviour in a main street and residential area. The distribution shows that low speed accelerations account for a significant proportion of total driving. Figure 2.1 shows the distribution presented by M+P. Table 2.1: Representativity for traffic noise situations Circumstances to be covered by noise test: % of relevance for noise problem 50 km/h 2 nd gear heavy acceleration 5 50 km/h cruising km/h low acceleration km/h cruising 10 Traffic light medium acceleration 5 Cruising 30 km/h km/h 2 nd gear medium acceleration 10 Sum total 100% Figure 2.1: Representativity for traffic noise situations: Vehicle speed/acceleration distribution for normal driving behaviour on a main street and residential area (Based on an average of 11 vehicles) (Source: M+P) TRL Limited 5 PPR044

14 The expert from Germany made a presentation at the same meeting (Informal document No.11, 2001) regarding the noise emission of motor vehicles and the information from drive cycle studies. The key points of the presentation, which relate to the bar chart shown in Figure 2.2 were: Due to stop/start conditions plots of vehicle speed distribution curves show that 0 km/h is the dominant speed on main streets with traffic lights having a speed limit of 50 km/h. The second most dominant speed is 50 km/h. 25 km/h is the dominant speed on residential streets with a speed limit of 30 km/h. 40 km/h is the dominant speed on residential streets with a speed limit of 50 km/h 25% 20% main streets, speed limit 50 km/h, traffic lights residential streets, speed limit 30 km/h frequency 15% 10% residential streets, speed limit 50 km/h 5% 0% vehicle speed in km/h Figure 2.2: Vehicle speed distributions (Source: RWTÜV) Drive cycle data obtained by TRL have been largely related to projects concerned with examining the influence of traffic calming schemes on vehicle operation. Clearly the use of drive cycle statistics determined from vehicles involved in traffic management and calming schemes must be used with caution in relation to this study since the modes of operation of the vehicles are deliberately constrained by the traffic calming methods employed. Drive cycle and speed profile information was available in several projects for the periods before any schemes were implemented, e.g. Cloke et al (1999), Boulter (2000), Boulter et al (2001). However, the prime focus of this aspect of the project was to establish data on low speed accelerations, either from stationary vehicles or from a low speed in different traffic situations. A TRL study by Barlow and Green (2003) for CLT Division, DfT looked at realistic drive cycles with regards to traffic management and air quality, including data on traffic accelerations. The study included the measurement of drive cycles within 6 different cities for a wide range of traffic management options. Of specific relevance to this project were the drive cycles on those roads featuring urban traffic control measures such as SCOOT controlled traffic lights and on those roads without traffic control but classified as being congested urban roads. Four different classes of vehicle were used; a passenger TRL Limited 6 PPR044

15 car, a light goods vehicle, a heavy goods vehicle and a range of buses. Table 2.2 summarises the acceleration information obtained. Table 2.2: Acceleration rates in urban areas Vehicle type Urban traffic control cycle accelerations Average (m/s 2 ) Maximum (m/s 2 ) Congested urban cycle accelerations Average (m/s 2 ) Maximum (m/s 2 ) M N M N M1 - Ford Mondeo N1 - Ford Transit N3-17 tonne Ford Cargo rigid flatbed loaded to approximately 12 tonnes M3: Dennis single-decker (36 seats) / Dennis Dart single-decker (28 or 35 seats) / Volvo Olympian doubledecker (68 seats) / Volvo B10B LE single decker (39 seats) / Excel single-decker (39 seats). The results given in Table 2.2 show that in areas subject to 'urban traffic controls' and in congested traffic the average accelerations for all vehicle classes examined are very similar. This is indicative of the fact that vehicles operating within the confines of a stream of traffic tend to adopt similar speeds and accelerate at similar rates irrespective of the type of vehicle and engine power. Differences in the rates of acceleration were noted, however, when comparing the maximum rates for different vehicle types. Maximum accelerations tend to occur in situations where the road ahead is relatively traffic free and under these conditions the vehicles with the greater power to weight tend to accelerate more rapidly as indicated in the table. Overall the table appears to indicate that a rate of acceleration in the range of m/s 2 would be appropriate as a general indicator for low speed operation in urban traffic. A value chosen within this range could, therefore, be used as a target acceleration for a low speed 'type approval' test. ISO 362 Part 1 procedure is based on the initial data developed by RWTÜV Fahrzeug GmbH (formerly FIGE). This work was further developed by the European Automobile Manufacturers Association (ACEA) based on the premise that in urban traffic vehicles are frequently driven under a partial throttle and engine load condition on main urban roads at speeds near 50km/h.. Data were obtained from 50 vehicles that showed that the most frequently used gears were 3 rd and 4 th rather than 2 nd which has been the original test condition. The actual in-use acceleration rate was shown to be lower than the high rate developed in 2 nd gear. Some further improvements were made following the report of test results by Japan at the 35 th GRB that indicated the usefulness of part loading light commercial vehicles. For trucks the proposal was for WOT test conditions but that loading should be introduced to improve the correlation between test results and those obtained in actual use. Part 2 of ISO 362 is a proposal to extend the operating test conditions to include lower speeds and higher acceleration levels found in residential streets as opposed to main urban roads. The current evidence presented by de Graaff and van Blokland (2002) at the December meeting of ISO WG42 is based on results provided by the Japan Automobile Manufacturers Association (JAMA) and by Sandberg and Stevens (2002). The results from JAMA show a frequency distribution of the speeds of passenger cars in urban traffic (see Figure 2.3). It can be seen that the percentage of time that vehicles are operating in the speed range of 0 to 40km/h is 47.5% compared with 52.5% operating between 40km/h and above. TRL Limited 7 PPR044

16 The frequency distribution peaks at 50km/h and there is a minor peak at 25km/h. Results showed that at 50km/h all the cars were travelling in 3 rd or 4 th gear while at 25km/h the majority of these vehicles were travelling in 1 st or 2 nd gear Frequency (%) Speed (km/h) Figure 2.3: Speed distribution of passenger cars in urban traffic (Source: JAMA) The data published by Sandberg and Stevens (2002) is limited to a single car with a power output of 90kW. The driver is reported to have medium driving behaviour. In main streets the peak in the speed distribution occurred at 45km/h while in residential streets the peak occurred at 35km/h. Further data produced by Le Salver (2001) shows the speed-acceleration distribution in urban areas presumably for light vehicles. This clearly shows that as speeds increase acceleration rates tend to decrease. For example at 30km/h the acceleration rate tends to average at 1.5m/s 2 while at the higher speed of 50km/h the average acceleration is approximately 0.5m/s 2. De Graff and van Blokland (2002) also provide data for the noise emission of 13 vehicles in urban driving. This shows that the average noise level for the 20-30km/h speed range did not correlate very closely with the average level produced between 40 to 50km/h. From these data and a consideration of the annoyance produced, the authors argue that there is a need for a Part 2 to cover operations in residential streets. They state that the noise emission under tests defined in Parts 1 and 2 are not well correlated so the additional test is necessary although no data has yet been provided. The main conclusions from the studies of drive cycles are that in urban areas: the most likely speed is close to 50 km/h and that acceleration rates are low and generally less than 1 m/s Perception of vehicle noise The main objective of any vehicle noise type approval or in-service test is to limit or control the degree of nuisance/annoyance caused by both individual vehicles and traffic streams. Ultimately, therefore, the effectiveness of any test procedure must be judged against its ability to reduce noise annoyance in the community. It is often argued that the current test procedures do not adequately address these issues. This, of course, lends support to the case to change the test procedure. It is important therefore to examine the available information from research into the relationships between vehicle noise, mode of operation (i.e. low speed/stationary) and subjective nuisance/annoyance. This evidence should help to define an appropriate range of test procedures that could be examined further in the measurement programme. TRL Limited 8 PPR044

17 (i) Jury experiments Jury experiments involve exposing human subjects to actual noise from vehicles undergoing different operations and obtaining their judgements on relative noisiness using some form of rating scale. Previous jury assessments of vehicle noise were carried out in 1959 by the National Physical Laboratory and by MIRA in 1960 (Mills and Robinson, 1961). These early studies examined the relationships between subjective noisiness and different physical measures of the noise. This work led to the adoption of the db(a) scale for all vehicle and traffic noise assessments. More recently, a large-scale jury experiment was carried out by TRL (Watts and Nelson, 1993). Although this was also primarily concerned with establishing scales of noise which best related to listeners' perception of noisiness it was possible to use the data obtained to yield a rank ordering of the noisiness of different vehicle operations. The study involved the rating of 25 vehicles including 8 heavy goods vehicles with a gross allowable vehicle weight between 16 and 38 tonnes, 8 medium sized goods vehicles (7.5 and 16 tonnes) and 9 passenger cars with a engine powers ranging between kW. Approximately 70,000 ratings were made of some 2250 individual pass-by events. In order to examine the responses of people exposed to noise heard indoors as well as outdoors a single storey building was constructed alongside the TRL test track with a listening room to accommodate juries located indoors. The juries assessed the pass-by noise of all vehicles for the following conditions: Low, medium and high steady speeds, using different gears and engine speed to produce a wide range of noise levels and spectra. Maximum acceleration from a steady entry speed to simulate approximate type approval test conditions (ISO R362, 1964) for each vehicle class. Idling condition lasting approximately 15s. Pull-away from rest. It is interesting to note in that it was found that the vehicle operation described as pulling away from rest was consistently rated highly on the noisiness rating scale. This was true for all vehicle groups and for respondents located both indoors and outdoors. For this mode of operation the drivers were instructed to pull away in a "normal" fashion so that the ratings were not affected by excessive revving of the engine or the noise produced by wheel spin. Nevertheless, for this operation, it is expected that the load on the engine is relatively high and therefore it is reasonable to expect that the noise generated and hence the corresponding subjective noisiness ratings were high. The study also indicated that for the 8 heavy vehicles tested the ranking of vehicles by subjective noisiness for the moving acceleration test procedure, which approximated to the test procedure described in ISO 362, was similar to the ranking on noisiness for other test conditions. These other test conditions included steady speeds, idle, pull-away from rest and 3 steady speeds. The mean noisiness rating under acceleration was the highest for any other test condition. Hence it would appear from this data that the current ISO 362 test should give a reasonable indication of the potential to cause noise nuisance in the community. However for light and medium goods vehicles this relationship was not nearly so strong. The mean noisiness rating under acceleration was not as high as pulling away from rest or driving at a steady speed in a low gear. This indicates the need for more than one test condition when determining the noisiness characteristics of these lighter vehicles. The jury experiment also revealed that the correlations between subject s ratings of noisiness and Sound Exposure Levels (SEL) were often higher than the corresponding maximum level, although not statistically significant except in one case. The higher correlation may result because SEL is a measure of total sound energy and depends on both maximum level attained during pass-by and also the duration of the event. It is possible that that the duration of the noisy portion of the events had some significant effect on ratings, and therefore the SEL accounts for some of the variation in the scores not reflected in measures of maximum level. In addition, the maximum level can obviously be influenced TRL Limited 9 PPR044

18 by very short duration events that may not be fully perceived by the listener. Clearly there is a need to consider the inclusion of SEL measurements in new test procedures. (ii) Social surveys While jury studies provide an opportunity to examine, in some detail, the relationships between physical noise levels and subjective ratings for particular vehicles and operations, they are limited to the extent that the ratings can only be used to provide an indication of relative noisiness. It would be clearly more beneficial if ratings of 'annoyance' could be obtained. Unfortunately, attempting to obtain a direct measure of annoyance may cause confusion in an experimental situation since listeners are rarely truly "annoyed" since they are being paid for their time, or have volunteered and are therefore "interested". Social surveys, however, are normally conducted in the community where respondents can, more readily, provide a reasonable indication of their annoyance with the vehicle and traffic noise that they experience. With regard to this study it is important to note that respondents can only give an overview of their annoyance. Consequently, it is not normally possible to examine annoyance reactions to specific vehicle operations. In the national survey carried out in the 1970's and reported by Morten et al (1978), it was indicated that noise from motorcycles produced the highest levels of annoyance of any particular vehicle category even though there were relatively few motorcycles in the traffic stream. Lorries were also rated highly as was peripheral types of traffic noise such as brake or tyre squeal, car horns and doors being slammed. It is clear from this analysis that people tend to give high ratings to noises that are associated with unsociable or inconsiderate behaviour by drivers/passengers. Unfortunately these types of noise sources are not usually amenable to control through vehicle noise testing. A recent national survey carried out by BRE also asked respondents to rate the degree of bother annoyance or disturbance caused by a wide range of specific road traffic noise sources (Building Research Establishment, 2002). Regarding the issue related to low speed/stationary vehicle operations the results showed that there was a relatively high degree of annoyance caused by 'engine revving' (19% bothered to some extent) and vehicles starting/ stopping/ticking over at traffic lights, crossings etc.(13% bothered to some extent). Interestingly the noise from private cars, heavy lorries and motorcycles were each given a similar rating which differs from the results of the national survey conducted in the 1970's where motorcycle noise was given the highest rating. Of the peripheral sources examined, music from vehicles, car alarms and brake squeal were rated highly in the survey reported in Information is also provided in the position paper by van Donegen presented at the GRB meeting in February They examined the community annoyance caused by free-flowing traffic and interrupted traffic flows with traffic accelerating from standstill to free flow speeds. The data was collected from a total of over 5,000 respondents in 10 urban areas. They concluded that, where the average noise levels (L Aeq ) were the same, an interrupted traffic condition produced more highly annoyed residents than under the free flow conditions. The percentage of highly annoyed people exposed to freely flowing traffic at a L dn of 65.5dB(A) was 27.6%. The percentage highly annoyed by interrupted traffic when corrections were made for differences in average noise exposure was 33.6% level. Although this was a modest increase of 6% it was found to be statistically significant. They also concluded that in the Netherlands most noise annoyance is caused by roads with a maximum speed of 50km/h. Eight percent were highly annoyed by noise from such roads. Four percent were highly annoyed by noise from roads with a speed limit of 80 or km/h. 2.4 Consideration of stationary and low speed test methods There are essentially three main objectives that have been identified for a low speed/stationary test. These are: 1. To provide a test procedure suitable for inclusion as part of vehicle noise type approval that adequately addresses the noise generated by vehicles involved in low speed manoeuvring and whilst stationary. TRL Limited 10 PPR044

19 2. To provide a simple means of establishing noise emission factors for in-service vehicles. This information could have future application in the development of a certification scheme for quiet vehicles. 3. To provide an effective means of identifying noisy vehicles in-service that could be used as part of routine testing and/or for enforcement processes. The three objectives listed above may appear, at first sight, to require similar vehicle operations and measurement methods. However, there are differences in the test conditions and the objectives of the test and this could have a significant bearing on the type of test that could be carried out or would be relevant to a particular application. For example, measurements from a stationary vehicle offer potential advantages for in-service testing in that they can be taken, with safety, relatively close to the vehicle and in an area where space is limited. Tests on a moving vehicle would normally require a reasonable separation between the vehicle and measurement locations and a larger test site to accommodate the chosen mode of operation of the vehicle. The main advantage of taking measurements in close proximity to the test vehicle is that the effect of external parasitic noise is removed. Consequently, as indicated above, it is a technique that is suited to in-service testing where the test would need to be carried out in a variety of non-standard acoustic environments such as a test bay or forecourt in a garage. Close proximity measurements therefore provide an opportunity for the development of a procedure that could be used as part of an annual vehicle MOT test, or it could be used to identify excessively noisy vehicles as part of an in-service enforcement programme. Clearly, for these applications the test would need to be very simple, make use of low cost equipment, and provide reproducible results independent of the acoustic environment. The main disadvantage of close proximity measurements is that they cannot be related simply to the noise from the whole vehicle. For example, a simple tailpipe measurement will not necessarily be a good measure of noise radiated by the engine and vice versa. This raises issues associated with how representative such a test is in relation to the total noise generated by the vehicle in real road situations. When vehicles are being tested for type approval, a different set of conditions applies. Type approval occurs at registered test sites, where the acoustic conditions are closely controlled and where high quality equipment is available for use by experienced measurement technicians. In this test environment, there are clearly greater opportunities to ensure that the mode of operation of the vehicle, the location of microphones, and the analysis and interpretation of the data is tailored to the overall objectives of the test. Under these conditions, even relatively complex vehicle operations can be undertaken by experienced drivers to produce highly repeatable results. Furthermore, with the strict requirements attached to the quality of the equipment used and the standardisation of the test site itself, the results can be expected to attain a high degree of reproducibility at other type approval test sites. The question that remains is to ensure that the mode of operation of the vehicle and the measurements taken produce results that are representative of noise generation in real road conditions. Finally it should be noted that when the objective of the test is intended to identify particularly quiet vehicles that could be licensed to operate in noise sensitive areas, other 'ancillary' noise sources may also need to be considered. These could include noise from refrigeration units fitted to commercial vehicles, compressed air noise and noise from the use of hydraulic machinery such as tail lifts Review of low speed and stationary vehicle test methods (i) International standard ISO 5130 The International Standard ISO 5130 "Acoustics - Measurement of noise emitted by stationary road vehicles - Survey method" (1982) was developed in the late 70's and published in 1982 (International Organisation for Standardisation, 1982). The standard was based on the need to undertake roadside checks of the acoustical condition of vehicle exhaust systems at a time when this was a dominating TRL Limited 11 PPR044

20 noise source. The standard has not been revised since 1982 although there are now proposals for amendments. Section 6 of the original Standard deals with the procedures required for the testing of exhaust noise. For the exhaust noise test the Standard requires the measurement of the maximum noise level from a stationary vehicle at a point 0.5m from the exhaust outlet, while the engine speed is allowed to rapidly decelerate from a specified engine speed. The initial engine speed is defined as a fraction of the engine speed, n, at which maximum power is produced. For all vehicles other than motorcycles the initial engine speed for the test is specified as 0.75n. The microphone used for this is required to be placed with its most sensitive axis parallel to the ground and pointing at the exhaust outlet making an angle of 45 degrees with the vertical plane containing the direction of the gas flow. In November 2002, a proposal to carry out work to modify the procedure for testing the noise emitted by stationary vehicles was submitted to the ISO Secretariat by Technical Committee 43/SC1. This was accepted and included as a work item to be considered by the ISO Working Group 42. There are several technical reasons to revise ISO5130. Firstly, there has been continuous development of vehicle technology. This includes the reduction of exhaust noise and the design of vehicle exhaust systems so the need for a test designed to purely examine exhaust condition noise needs to be questioned. Other important vehicle design changes include the incorporation of engine protection systems that limit engine speed while stationary. Many current vehicle designs include this technology which restricts the ability to obtain an operating test point of 0.75n. In addition, changes to the design and positioning of the exhaust outlet on many vehicles require a new approach to the positioning of the measurement microphone. It is also clear that the application of the method has exposed some difficulties. A particular problem in using the method for in-service testing is to obtain reliable measurement of the engine speed. For example, not all vehicles are fitted with accurate tachometers. For those that are, the question arises as to whether it is implicitly correct, in a regulatory test where prosecutions may result, to use the vehicle's instrumentation to set the initial engine speed condition. An alternative is to use a remote system designed specifically for conformity checking that can be calibrated independently. However, this introduces additional complexity to the test and additional costs. A further concern over the use of the method arises because it is not clear whether the mode of operation of the vehicle will give rise to noise levels, at the prescribed measurement positions, that are well correlated with the noise generated by vehicles undergoing the type approval test. In fact the Standard currently states that "the values obtained using the method are not representative of the total noise emitted by vehicles in motion". The application of the standard has also exposed inaccuracies for vehicles with rear- or mid engine, as the engine noise could be the dominating noise source thereby interfering with the original intent of the measurement (Ehinger, 1999). In such cases, flexible shields could be used to separate the different noise sources during the test but this would add complexity and potential measurement variability. For vehicles with front mounted engines, typically the engine and exhaust noise levels tend to be approximately the same order. Thus, it should be possible to detect changes in both noise sources, if improved microphone positions are chosen. ISO report that investigations have shown that the noise level close to the exhaust pipe is very much dependent on engine speed and can vary as much as 20 db over a typical range of operating engine speeds. Because the exhaust system is effectively an acoustic tuning element, resonance can occur at specific engine speeds that can give rise to variable results that are dependent on the rate of change of engine speed employed during the tests. To overcome some of these problems, in its position paper issued in November 2002, ISO suggest modifying the vehicles operation to incorporate an engine 'sweep' test similar to that advocated by the Society of Automotive Engineers (SAE) (International Standards Organisation, 2002). In this test the engine speed is increased gradually from idle to the maximum possible speed (not exceeding 75% of TRL Limited 12 PPR044

21 the maximum power engine speed) and then held at that speed for 1-2 seconds. Then the throttle control is rapidly released and the engine speed allowed to return to idle. The sweep test was specifically designed for detecting exhaust system resonance. SAE recommend that the change from idle to 0.75 rated engine speed should occur over a period of seconds. Some engines exhibit sensitivity to the rate of increase and the longer time interval helps to reduce run-to-run variability. It is argued that the sweep test presents technical and practical advantages that can reduce test time and provide a comprehensive evaluation of exhaust system noise performance across a range of engine operation conditions (Society of Automotive Engineers, 1998). (ii) UN-ECE The United Nations Economic Commission for Europe (UN-ECE) have produced their own version of a vehicle noise testing standard. The Groupe de Rapporteurs du Bruit (GRB) produced Regulation 51 in October 1995 that deals with the specification of the test method for both pass-by and stationary vehicles. This method is commonly used outside of the European Union although it is very similar to the EU type approval method. The method specified for the testing of stationary vehicles is identical to that in the current EU Directive (See section 2.2.3). GRB is, however, in the process of revising Regulation 51 and it is anticipated that further proposals on low speed/stationary testing will be made in the near future. (iii) EU Directive 70/157/EEC EU Directive 70/157/EEC (Amended by 73/350/EEC, 77/212/EEC, 81/334/EEC, 84/372/EEC, 84/424/EEC, 87/354/EEC, 89/491/EEC and 92/97/EEC) deals specifically with the permissible sound levels for all road vehicles other than motorcycles (European Communities, 1970). The Directive is primarily concerned with specifying the type-approval noise testing procedure and limit values. There are, as yet, no EU Regulations covering low speed/stationary testing of motor vehicles. However, the Directive does include a section dealing with measurements of noise from a stationary vehicle. The test procedure is virtually identical to the close-proximity exhaust noise test specified in ISO 5130 which is described in Section The Directive requires that the test site is a hard, flat and reflective surface and that the edges of the test site form a rectangle, the sides of which are at least 3m from the edges of the test vehicle. The rectangle must not contain any significantly reflecting obstacles. It is also stipulated that the engine speed indicator should have an accuracy of better than 3%. The Directive provides details on the measurement procedures to adopt when there is more than one exhaust outlet or if the standard measurement position cannot be achieved due to fixed obstacles on the vehicle. A measurement procedure for the measurement of exhaust noise from a vertical stack is also defined. At least three repeat tests are performed and the test is considered valid provided the levels measured during 3 consecutive tests do not differ by more than 2dB(A). The noise level readings are rounded to the nearest db and the highest level of the 3 valid results is taken as the result. It should be noted that this differs from ISO5130 in that the final result is determined from the arithmetic mean of three tests, within a range of less than 2dB(A). (iv) Other measurement procedures The EEC, ECE and ISO test procedures described above specify close proximity measurement procedures for noise generated at the exhaust outlet. Although these procedures are not used widely, some countries have introduced regulations and limit values which are based upon these standards (Eiser and Scott, 1994; Berge, 1996; Tukker, 1977). Morrison and Nelson (1985) have examined the correlation between noise levels generated by stationary vehicles and pass-by noise levels obtained during type approval testing. Both petrol powered cars and petrol and diesel powered trucks were examined. TRL Limited 13 PPR044

22 Measurements were carried out according to the procedures specified in EEC Directive and also according to the exhaust noise test of ISO A further series of test were carried out with the vehicle stationary. For diesel powered vehicles the engine operations examined were: Engine accelerated rapidly from idle to Governor Run Out (GRO). Gradual acceleration from idle to GRO. This was described as a quasi steady state test. Engine operated at a steady speed set at 0.75 of the rated speed. From tests carried out as part of this study, it was found that the most appropriate measuring point was midway between the exhaust outlet and the centre of the engine. The microphone should be positioned at distance of 2 m from the centre-line of the vehicle and a height of 1.2 m above the test surface. By examining the three modes of operation listed above, it was shown that both the quasi steady state and steady state tests, including the ISO 5130 exhaust noise test, gave results which were poorly correlated with the drive by type approval test. In addition, it was stated that the ISO 5130 test was not suitable for assessing total vehicle noise due to the dominance of the exhaust noise at the microphone position specified for this test. The most promising approach proved to be the transient acceleration test up to GRO for diesels. The principal advantage of this test appeared to be associated with the fact that the engine was effectively under some load during the test, due to the inertial forces associated with accelerating the engine. It was concluded that, although the engine was operating 'freely' under these conditions, the combination of the rapid acceleration of the engine coupled with the presence of some inertial load gave a better degree of representation of the moving vehicle acceleration test. For the diesel powered vehicles the correlation between drive-by and transient test results was good with a correlation coefficient of 0.89 indicating approximately 80% of the observed variance in driveby levels explained. By comparing the drive-by results with the ISO 5130 test results for the diesel group the correlation was found to be poorer (r = 0.77) although the significance of the differences in the correlation coefficients was not tested. However, it was also pointed out that because the ISO test requires the microphone to be placed close to the exhaust outlet it would not necessarily be able to detect changes in the noise emission from other sources. For example, noise from a blowing exhaust manifold or as a result of the deterioration of noise shields, enclosures etc., positioned around an engine. It was concluded, therefore that, in view of the indicated high degree of correlation found between the transient test levels and the drive-by levels, for diesel powered vehicles, the transient test was the most appropriate of those examined. It was also stated that the test procedure was simple to carry out and appeared to give repeatable results at a variety of roadside locations, i.e. non-standard locations. Earlier studies reported by Ellis and Waters compared the results of measurements taken on petrol and diesel powered vehicles under both drive-by and stationary test conditions (Ellis and Waters, 1978). In this study, the drive-by measurements were taken according to the procedure given in BS 3425:1966 which is closely similar to the acceleration test condition defined by current EU Directives (British Standards Institution, 1966). The stationary tests were carried out using a "free acceleration test". This test requires the driver of the vehicle to fully depress the accelerator pedal on the vehicle and then release it quickly. The noise is measured at a distance of 7.5 m from the centre-line of the vehicle with the microphone located in line with the exhaust outlet. The free acceleration test is therefore similar to that recommended by Morrison and Nelson (1985) in that it relies on the philosophy that the inertia load of the engine is sufficient to reproduce the full load operation of the vehicle drive past test. The test did not, however, define a maximum engine speed condition which may have affected the degree of repeatability achievable using the test. Furthermore, the measurements were not taken in close proximity to the vehicle. This would effectively mean that it could not be considered realistically for roadside noise measurements where intrusive noise from other noise sources could be a problem. The results obtained using this test do, however, support the TRL Limited 14 PPR044

23 results obtained by Morrison and Nelson by showing that there is a reasonably high correlation between pass-by noise and the noise generated during a transient free acceleration. More recently TRL has carried out a comprehensive study of vehicle noise test procedures that would be suitable for in-service applications (Harris and Nelson, 1995; Harris, Nelson and Stait, 1997). Again the suitability of a test method was judged by its ability to produce repeatable results in a variety of non-standard acoustic environments and that the results produced were correlated with drive-by type approval levels. The reason why a high correlation is considered necessary for an inservice test is because it does not seem feasible to introduce regulations whereby a vehicle could be found to fail an in-service noise test and yet comfortably pass the type approval test. Without an adequate degree of correlation between the two types of measurement it would be necessary to set the limits for in-service noise levels at a very high level which would, in turn, reduce the effectiveness of the test procedure in identifying vehicles producing excessive noise in-service. Additionally, the study examined the test site conditions needed to ensure that the results taken in close proximity to the vehicle were not affected by external noise sources and reflections from walls/facades etc. It was found that the minimum requirements for the test location should be a flat hard surface with no reflecting facades, buildings etc. within 5 m of the external sides of the vehicle. With these minimum test site conditions, in-service tests on vehicles can be carried out with acceptable repeatability in an outdoor location such as an open space on a garage forecourt, or at the roadside. It was found that the method of measurement should use a microphone located midway between the centre of the engine (i.e. taken to be the crankshaft centre-line for transversely mounted engines or the midpoint of the crankshaft for in-line engine configurations) and the exhaust outlet. The distance of the microphone from the centre-line of the vehicle should be 2.0 m and the height of the microphone above the surface should be 1.2 m. When considering the vehicle operation, it was found that for diesel powered vehicles, the engine should be accelerated rapidly from idle to governor run out and the maximum noise level determined during the transient. For petrol powered vehicles, the engine should be accelerated rapidly under full throttle from idle to approximately 4500 rpm and measurements taken of the peak noise level at the point where the engine speed reached 4000 rpm. To carry out this form of measurement an appropriate tachometer device would be needed to trigger the measurement of the test sound level when an engine speed of 4000 rpm is reached. It was noted, however, that the tests on petrol powered cars were inherently more difficult to achieve with an acceptable degree of repeatability. (v) Ancillary noise sources A possible important consideration for commercial vehicles operating in urban areas is the noise produced from ancillary equipment such as hydraulic lifting gear, refrigeration unit compressor motors and noise from air brakes and other compressed air sources. These ancillary sources are likely to be most important when other noise sources emanating from the vehicle are not operating, or are at a low level due to the mode of operation, for example when the vehicle is stationary. The EU has proposed a type approval test procedure for air brake noise and TRL has examined the proposals by carrying out a small programme of tests using the proposed method. It was found that measurements of air venting noise during the operation of the parking brake and the pressure regulator were relatively easy to carry out and gave repeatable results. However, the noise produced by operating the service brake was more difficult to accomplish with acceptable repeatability due to ambiguities associated with the mode of operation. Overall the air brake noise levels measured in the study were well in excess of the limit values that were proposed at that time. Literature searches have thus far not uncovered publications concerned with the measurement of other ancillary vehicle noise sources and there are no proposals at present to develop standard measurement techniques for these sources. It is possible, however, that stationary test procedures could be adapted to include measurements from hydraulic tail lifts and refrigeration units and the measurement programme discussed later in this report provides an opportunity to examine possible procedures. TRL Limited 15 PPR044

24 2.4.2 Review of drive-by test methods (i) International Standard ISO 362 The basic aim of this type of test method is to measure the maximum power train noise a vehicle is capable of producing. For this reason a Wide Open Throttle (WOT) procedure is adopted. During this type of driving the engine develops close to maximum power and the resulting noise is dominated by power train noise (engine, exhaust, transmission, air intake, fan etc). The first test procedure was an ISO recommended test procedure ISO R 362 produced in the 1950 s. However it was not until 1964 that the first official version was published. The first international regulation to control noise from vehicles was in 1969 ECE Regulation 9 and was superseded by regulation 51. These used ISO R 362 as the basis for the measurement method. A year later the EEC (European Economic Commission) established the directive for harmonising member state s regulations (Directive 70/157/EEC) again based on ISO R 362. In 1981 ISO R 362 was upgraded to a full standard ISO 362. The current UN-ECE regulations were published in 1996 (UN-ECE, 1996) and follow the ISO 362 test method and setting limit values of 74 db(a) for passenger vehicles with less than 10 seats and 80dB(A) for vehicles with an engine power of 150kW. The testing procedure requires the unladen vehicle to approach a line crossing the test track 10m ahead of the microphone position. When this line is reached, the vehicle is accelerated with WOT until it has passed 10m beyond the microphone location, when the throttle is closed. The initial constant speed is generally 50km/h for cars using 2 nd and/or 3 rd gear. For heavy vehicles the approach speed is in the range 15-50km/h using a wide selection of gears. The maximum noise level at microphones set at 7.5 from the centre of the test lane on each side of the vehicle and at a height of 1.2m is recorded. Repeat runs are carried out and a reading is considered valid if the difference between two consecutive measurements on the same side of the vehicle is not more than 2dB(A). The highest sound level is recorded to obtain a final maximum level. The test surface should conform to ISO (ISO, 1991). This fine graded surface was developed to test the noise emitted from the power unit related sources on the vehicle and therefore the contribution from tyre/road noise was minimised. This was achieved by limiting the texture depth by specifying a small maximum chipping size of 8mm and placing a lower limit of 0.4mm on the mean value. In addition a reflective low absorption surface was specified with a normal incidence sound absorption value ( ) of less than 0.1. In practice this surface does produce low levels of tyre noise during the test although there remain some problems associated with powerful unladen vehicles where excessive torque at the wheels can induce tyre slip and relatively high noise levels. (ii) Proposed amendments to ISO 362 In September 2002 an ISO working draft was circulated within committee ISO-WG42 which set down both a WOT test and steady cruise-by condition (ISO, 2002). The WOT procedure for light vehicles involved a steady approach speed of 50km/h while for heavy vehicles the approach speed was set lower at 35km/h. For light vehicles gears are chosen so as to achieve a close match with a reference acceleration that is based on the power to weight ratio of the vehicle. This reference acceleration takes into account the target acceleration, which is based on 95 th percentile acceleration rates observed in urban traffic. Because of the constraining effects of traffic and posted speed limits this is typically relatively low at 0.8 to 1.3m/s for light vehicles on main urban roads. For heavy vehicles the gear is selected by requirements on engine speed. In addition there is also a steady speed cruise-by test for light vehicles. For the steady speed test for light vehicles the requirement is for a TRL Limited 16 PPR044

25 pass-by at 50km/h with the same gears as selected for the acceleration test. Note that there is no requirement for a steady speed test for heavy vehicles. In addition to the introduction of the steady speed test for light vehicles there is also a requirement to load the heavier vehicles to produce a more typical test condition. For light vehicles an overall level L urban is derived from combining the results from the WOT and steady speed components of the test results. For heavy vehicles the WOT value is simply reported. It is argued, in the introduction to Part 1, that the level L urban is equivalent to the noise emitted when the vehicle is accelerating under the constraints of urban traffic. It also states that The test guarantees an excitation of all relevant noise sources and the final test result will reflect a composition of these sources at a compromise between normal urban use and worst case. It has been argued that in the case of many light vehicles the full acceleration potential of the vehicle is rarely used under the constraining influence of urban traffic and therefore the noise level measured under current WOT test was not representative of normal driving. In the proposed revision the result of combining the WOT result with a steady speed test result is considered to be more indicative of the noise produced in urban areas. The more powerful the car when compared with its mass the more the overall result L urban is weighted towards the steady speed result. In the case of heavy vehicles the situation is different as the power to weight ration is much smaller and full throttle acceleration is often used in urban situations so that the need to weight the results with steady speed values is not considered necessary. (iii) Further proposals to revise ISO362 Amendments to ISO 362 have been proposed by van Blokland (2002). The proposal includes a procedure for light vehicles (Part 2) that complements Part 1. The scope of Part 2 is the noise production of road vehicles under conditions of low speed driving and medium to high acceleration. The vehicles included in the test would be M1 and N1 i.e. passenger vehicles with less than 10 seats and light goods vehicles with a maximum authorised mass of less than 3,500 kg. The proposal is for a lower approach speed of 30km/h but the reference acceleration would be higher than for Part 1 and would be based on further analysis of the available drive cycle data. It is argued that in residential streets, as opposed to main urban roads, speeds are lower but acceleration rates are higher and typically from 1.5 to 2.5 m/s 2. It will be remembered from a discussion of Part 1 that the acceleration range in urban streets is typically 0.8 to 1.3m/s 2 so it is argued that the results from Part 2 tests should be sufficiently different from those from Part 1 to justify its consideration. A further proposal has been made by Sandberg and Steven (Sandberg and Steven, 2002). This takes a different approach for light vehicles except motorcycles. The basis of the test is an acceleration test at different throttle openings so that a series of readings of noise level against acceleration rate and entry speed can be mapped. Levels can then be determined by multiple regression analysis and normalised to a standard set of speed and acceleration conditions typical of urban driving conditions. The speed range covers 15 to 30km/h and the acceleration range is from 1 to 2.5m/s 2 so that the conditions covered include those test conditions proposed by de Graff and van Blokland in residential streets. A further test condition would be a coast-by test according to ISO/DIS (iv) Coast-by test ISO/DIS This method examines the contribution of the noise from tyres running on the standard ISO surface (ISO, 2002). The test procedure is similar in many aspects to that described for the steady speed cruise-by test in the proposed ISO 362 Part 1. However, when the front of the vehicle reaches the line 10m in front of the microphone the vehicle must be in neutral gear with the engine switched off. A reference speed of 80km/h are given for tyres fitted to passenger cars and light commercial vehicles (C1 and C2) and a number of tests are carried out in the speed range from 70 to 90km/h. In the case of tyres for heavier vehicles (C3) the reference speed is lower at 70km/h and the speed range is 60 to 80km/h. At least four measurements are made at test speeds lower than the relevant reference speed and at least four measurements at test speeds higher than the reference speed. The speeds TRL Limited 17 PPR044

26 should be approximately equally spaced over the relevant test range. The maximum noise level in db(a) is recorded during each coast-by on each side of the vehicle. A regression analysis is then performed between these maximum levels and the logarithm of the speed during pass-by. The value at the relevant reference test speed is then determined. In the EC directive 2001/43/EC limit values are given for various categories of tyre. For the narrowest C1 tyre (145mm) the current limit value is 72dB(A) while for the widest tyre in this category (215mm) the limit value is 76dB(A). The highest limit value in class C2 is 78dB(A) and in class C3 it is 79dB(A). (v) Other measurement procedures and relevant research The EEC, ECE and ISO test procedures described above for pass-by noise tests are widely used. However, there is considerable research evidence that the ISO test surface is not representative for the measurement of tyre road noise. The directive 2001/43/EC anticipates a change of test surface for in Annex VI it notes that: If a different test surface is defined by ISO, in the future, the reference standard will be amended accordingly. TRL have carried out a study involving different combinations of tyres and road surface types including ISO The results demonstrate some of the inadequacies of the ISO surface for tyre noise type approval testing (Phillips et al, 2002). In this study coast by measurements were carried out at a speed of 80km/h on the ISO and a Hot Rolled Asphalt (HRA) surface. It was found that for the 12 tyres tested there was a very low correlation between maximum pass-by levels on the two surfaces (r=0.02). HRA, and surfaces with similar textures are commonly used in the UK on both urban and rural main roads and so the lack of a correlation between the standard surface and these more coarsely textured surfaces is of some concern. It should be noted, however, that road surfaces are continually being replaced through normal maintenance programmes and the current policy is to use lower noise surfaces where possible. Generally this means using materials with finer aggregates. This may help, in the longer term, to improve the correlation between noise generated on the standard ISO surface and that developed on real roads although it is unlikely that the correlation will improve greatly. Given this general concern over the use of the ISO surface for tyre noise testing, there is an action within ISO WG42 to develop a test surface that is more typical of normal roads. The Nordic traffic noise prediction model Nord 2000 refers to a method NT ACOU 105 for the measurement of pass-by noise emission of vehicles on real roads and unlike the methods described above it involves the measurement of the sound exposure level, SEL, rather than the maximum level. Using an appropriate propagation model it is possible to calculate the sound power level of passing vehicles. The latter together with source height and directivity can be used as an input to traffic noise prediction model. Measurements are carried out in each third-octave band from 25Hz to 10kHz over the test section. The sample length over which sound exposure is determined depends on the distance of the measurement position from the centre of the track d and the length of the vehicle. Figure 2.4 shows the measurement set-up where d is 7.5m and the vehicles measured have an overall length of less than 10m. For these vehicles that are shorter than 10m, the measurements are started when the centre of the vehicle is at a distance of 2d in front of the normal from the microphones to the road. For vehicles with length greater than 10m the distance to the microphone is increased to 3d. The sampling period stops when the centre of the vehicle is at the same distance behind the microphone. Note that the distance d can be set at any value between 7.5 and 15m. Other differences are the use of two microphone heights of 0.2m and 4m. The low height is used to guarantee that the direct and reflected rays are in phase at low frequencies whatever the height of the source and the higher position is used to minimise excess attenuation at high frequencies. The measurement result is normalised to d=10m and an angle of integration of 2.75 radians or degrees. Although the measurements are taken at two heights only one value is used for the calculation of sound power. In order not to underestimate the sound power level the SEL value giving the highest sound power level is selected. However, due to wind and other background noise problems at low frequencies and high receiver heights the level at the lowest microphone is used below 100Hz. TRL Limited 18 PPR044

27 End of site 30m Start of site 7.5m 15m Microphones at 0.2m and 4m Figure 2.4: Location of microphones at the test site In the Harmonoise project a revision of the standard has been proposed. It was felt that because the 1.2m high microphone height is so widely used in standard test procedures that this should be retained. At low heights there is also the potential problem of large ground absorption effects. It was considered that the 4m high microphone position was too high and that screening of the low subsources by the vehicle body may occur. For this reason it is now proposed that the highest microphone should be placed at the lower height of 3m. The Japanese test procedure TRIAS involves measurement under the three conditions of moving acceleration (similar to ISO 362), steady speed and idling. For the steady speed test the vehicle is driven past the microphone in an appropriate gear at the lower of the steady speeds corresponding to 60% rated engine speed or 35km/h. There is also a reference to a Japanese higher speed cruise-by test. TRL Limited 19 PPR044

28 3 Selection of candidate test procedures The information gained from the literature review provides an important ingredient in establishing the design of the measurement programme that is described in detail in the next section. Primarily it has helped to rationalise the choice of a list of candidate test procedures that should be included in the programme. This section summarises the main factors affecting the decisions taken. 3.1 Basic requirements of a test method Fundamentally any viable test procedure has to satisfy some fundamental objectives and these should be taken fully into account when considering possible candidate test methods. They can be summarised as follows: The test should offer a high degree of repeatability. This generally means the test should be as simple to carry out as possible. Overly complex tests tend to produce difficulties in achieving repeatable results. They also tend to be more expensive to carry out. The test should provide reproducible results. This means the test when carried out on the same vehicle at different locations with different equipment and personnel should give acceptably similar results. Clearly, this objective also points to a relatively simple test but also involves other issues such as the standardisation of the test site. This, of course, has implications for in-service testing and vehicle certification applications where fully standardised test site conditions will be difficult to achieve. The test should be representative of real road conditions. This objective refers to the need to ensure that the results obtained relate closely to the noise generated by vehicles when operating in-service. A close correlation with in-service noise will help to ensure that reducing limit values under the test will have a corresponding benefit in terms of reducing noise impact from traffic. It is potentially the most difficult of the primary objectives and to some extent achieving a representative test will tend to increase difficulties regarding repeatability and reproducibility. The key to achieving this objective is to ensure that the mode of operation of the vehicle is sufficiently representative of on-road conditions and that the measurement positions and analysis procedures employed provide a reasonable assessment of the total noise that is generated during the test. A further general point that needs to be considered follows from the points made when describing the conceptual framework in section 2.1. The conceptual framework showed that the noise impact of a vehicle operation is a product of the fraction of time it is operating and the noise level produced. From equation 2.3 it can be seen that events which are relatively loud should be given particular attention especially if they are occur relatively frequently. But even when they do not the squared function of level implies that when selecting operations for type approval the bias should be towards the noisier events even if they do not occur most frequently. This would suggest that when choosing, for example, a rate of acceleration for the test a rate higher than the most frequent should be considered. 3.2 The test programme for stationary and low speed operations When considering the information available from research studies and from vehicle noise testing standards it is clear that most information relevant to stationary/low speed testing has, hitherto focused on testing stationary vehicles. Historically, stationary tests have been largely concerned with establishing the condition and effectiveness of the exhaust silencer rather than establishing noise levels that are representative of the total noise from the vehicle. This form of testing was introduced in the vehicle noise standards primarily to establish benchmarks for exhaust noise that could be used subsequently by relevant authorities to provide a physical measure of silencer condition as part of inservice testing and enforcement. It was noted, however, that very few countries have so far introduced any form of in-service enforcement procedure based on exhaust condition measurement. TRL Limited 20 PPR044

29 More recent research has attempted to provide a more comprehensive measure of in-service vehicle noise, again based on taking measurements from stationary vehicles. In this research the objective was to establish a measure of total noise from the vehicle that includes noise sources associated with the power unit as well as the exhaust silencer equipment. These studies have also examined the limitations that might be imposed on achieving reproducible results by the test site layout and general environmental conditions. It was assumed that in-service testing might be carried out in a variety of acoustically non-standard locations, which meant it was necessary to establish the minimum test site requirements for a valid test. To a large extent the issues of achieving both repeatable and reproducible results from in-service testing have now been largely overcome although there are remaining problems associated with testing ungoverned engines due to the potential of over-speeding the engine during the test causing damage. Additionally it was pointed out that changes in vehicle design may require a more complex test to accommodate all major noise sources. Other research reviewed on stationary testing pointed to the need to operate the vehicle's engine in a manner that would put some load on the engine during the test. It was felt that this would encourage higher noise levels and would be more representative of noise generated during normal driving. It has also been pointed out in the literature that exhaust noise can be tested more effectively by sweeping through the engine speed range in a controlled manner rather than allowing the engine speed to decay naturally as in the current test procedure. By using this slow 'sweep' test, it is argued that any exhaust resonance that occurs at particular engine speeds will be identified by the test. A review of information gleaned from social surveys and jury experiments have helped to identify the types of vehicle operations and noise sources that people judge to be particularly annoying or noisy. It is clear from the social surveys that people tend to give high annoyance ratings to noises that are associated with unsociable or inconsiderate behaviour by drivers/passengers. These types of noises include, slamming doors, sounding the horn, revving the engine, tyre squeal, the car radio. Unfortunately these types of noise sources are not usually amenable to control through vehicle noise testing although some could be treated through appropriate vehicle design. What is particularly interesting from the standpoint of establishing representative vehicle operations for inclusion in the measurement programme was that from both jury and social survey studies noise from vehicles idling and pulling away from rest are regarded as relatively intrusive operations. A study of drive cycle information also supported the need to include some form of low speed acceleration and/or stationary test in the programme of measurements. It would seem, therefore, for slow speed testing some form of low speed acceleration or pull away from rest operation should be included. An obvious difficulty with this form of test is that, to ensure repeatability, the vehicle loading and rate of acceleration would need to be clearly defined. In the jury experiments, drivers were instructed to carry out these manoeuvres using the gears and rate of acceleration they considered appropriate for the vehicle they were driving. Perhaps surprisingly, although this instruction would appear rather vague, drivers were able to achieve tolerably similar driving operations and noise generation during repeat testing. Nevertheless, achieving a more precise definition of the low speed acceleration or the pull away from rest operation is an important consideration that needs to be understood and specified if this type of test were to be incorporated in the type approval test. Bearing in mind the overall objectives of the study, the basic requirements for a suitable test regime and the results of the review of test procedures, drive cycle data and perception studies, a programme of testing focussing on low speed and stationary vehicle operations has been prepared. This is outlined below. Detailed descriptions of the test methods employed in the measurement programme which includes details of the vehicle operations measurement positions, sampling techniques etc. are described in Section 4. TRL Limited 21 PPR044

30 Outline test programme for stationary/low speed operations: Slow speed test: Pull away from rest with the vehicle laden. Measurements to be taken of both the maximum level and the Sound Exposure Level (SEL) Stationary tests: Exhaust noise test carried out according to ISO 5130 Exhaust noise test (ISO 5130) but using an engine sweep as defined by SAE Whole vehicle noise engine sweep test For M2, M3 and N2, N3 vehicles only - rapid acceleration to Governor Run Out (GRO) Air brake noise test according to EU Directive 92/97/EEC & EC Reg 51 (Ann. 6) Ancillary noise test on appropriate vehicles including engine idle test The main objective of including the low speed test is to examine the possibility of achieving a repeatable and reproducible test procedure based on a type of vehicle operation that has been shown from perception studies to cause relatively high levels of annoyance. The main difficulty envisaged was in specifying the mode of operation of the vehicle being tested and in ensuring that the procedure could produce repeatable results. The range of tests specified, with the vehicle stationary, have applications for both type approval and in-service testing. They cover tests for both exhaust condition and the whole vehicle. The engine sweep tests and rapid acceleration tests are intended to examine whether this form of test exposes aspects of noise emission not picked up by the exhaust condition test method. Air brake noise and ancillary noise tests will provide information on noise sources that may have an importance in causing annoyance in the community but as yet are not yet covered by type approval regulation in the UK. 3.3 The test programme for pass-by operations As with low speed and stationary testing, the basic requirements for a viable drive-by test are that it should be repeatable, give reproducible results at different test locations and be representative of noisy vehicle operations in practice. From drive cycle information it appears that over half the time light vehicles are operating at or above 40km/h and acceleration rates are relatively low. Under these conditions tyre road noise will contribute to the overall noise levels. Thus consideration should be given to testing at a steady speed pass-by at say 50km/h on a representative surface. Speeds below 40km/h occur just under half the time for light vehicles. Propulsion noise is relatively more important than rolling noise and vehicles are frequently accelerating in low gears. Average noise levels may not be as great as at higher steady speeds but nevertheless there is evidence that annoyance can be comparable. Therefore the noise impact at these higher engine speeds may be of a similar order and cannot be neglected. For heavy vehicles it is known that at speeds of approximately 50 km/h and below, propulsion noise dominates and noise levels are highest. In addition for these vehicles a greater proportion of the time is likely to be spent at these lower speeds and under acceleration because acceleration rates are relatively low. Therefore unlike the situation for light vehicles the noise impact will be greater at these lower speeds than at higher speeds. These vehicles are frequently operated under wide open throttle conditions. Therefore an acceleration test at say 35 km/h under WOT according to the proposed ISO procedure appears to be worthy of consideration. Although of lesser importance, a cruise by-test at 50 km/h in a gear appropriate for the speed would cover the constant speed portion of urban journeys. In the Dutch study it was mentioned that four percent were highly annoyed by noise from roads with a speed limit of 80 or km/h. This can be compared with the 8% who are seriously annoyed by TRL Limited 22 PPR044

31 noise from urban roads. If the percentages are significant then it would be necessary to introduce a test to control high speed rolling noise. The current tyre noise test carried out at 70 and 80km/h would be appropriate if the test surface was more representative e.g. HRA or Stone Mastic Asphalt (SMA). Further consideration should therefore be given to the inclusion of a high constant speed pass-by test. Ideally separate noise limits should be set for the acceleration test, which mainly examines the potential of the power train noise to emit noise, and the steady speed tests that mainly address tyre/road noise in the case of light vehicles. In the case of current light vehicles the pressure would clearly be to reduce the noise in the steady speed component of the test. For heavy vehicles the main pressure would still be to reduce noise under acceleration. In practice, it is necessary to take account of the current test methods that are being proposed or have been accepted. It may be possible to make amendments to approach the ideal conditions outlined above. Given the above, the following test methods were included in the main measurement programme: The current ECE 51 pass-by test The proposed ECE 51 pass-by test A cruise by test at 50 km/h for selected vehicles on surfaces that are typically found on main roads in the UK. It should be noted that the cruise by tests on different surfaces was included to provide further information on the relevance of the ISO standard surface which is currently used for vehicle noise testing. The review of previous research indicated that the relatively smooth texture of the ISO surface may not be representative of a broad range of surface types used on roads in the UK, such as Hot Rolled Asphalt (HRA) and Stone Mastic Asphalt (SMA). The proposed ECE 51 pass-by test method should address the power train noise component for heavy vehicles adequately. What is more uncertain is the test for lighter vehicles involving a two component test where one component is a steady speed test at 50km/h on the ISO surface. Despite these reservations it was felt important that vehicles are tested under this condition. Under all test conditions it was also felt important to measure both maximum levels, and where possible, SEL levels. It will then be possible to check the extent to which the two measuring methods agree. If there is not a close correlation this will argue for a further examination of the use of SEL. TRL Limited 23 PPR044

32 4 Measurement programme The measurement programme described in this section was mainly carried out at the Millbrook proving ground using a test site laid to the specifications of ISO (see Figure 4.1). Some measurements of cruise-by noise on different surfaces were carried out on the TRL test track. The measurement team, including drivers, involved staff from both TRL and Millbrook and apart from the cases where reproducibility issues were examined, the same staff were employed throughout the study. The section includes descriptions of the methods of measurement employed, including details of the equipment used, the commissioning studies carried out, and the vehicle sample selected. Figure 4.1: Millbrook test site 4.1 Test methods Test 1: UN ECE R51.02 A description of this test procedure is also given in section 2.3. The test procedure requires that the maximum noise level in db(a) is determined during pass-by operation with a microphone placed on either side of the vehicle at a distance of 7.5m from the vehicle centre line at a height of 1.2m. Vehicles are not loaded for this test procedure. The standard requires that A-weighted sound level of sound sources other than those of the vehicle to be tested and of wind effects must be at least 10dB(A) below the sound level produced by the vehicle. The test specification depends on a number of vehicle parameters including maximum power, vehicle mass, rated engine speed and number of gears. For manual transmission, tests are carried out in 2 nd, 3 rd or both these gears and at entry speeds of 50km/h or less. The entry engine speed is 50% or 75% of the rated engine speed (speed at which maximum power is developed). For this test the vehicle is operated under wide open throttle conditions (WOT). At least two measurements were made on each side of the vehicle. Results were considered valid if the difference between the two consecutive measurements on the same side of the vehicle were not more than 2dB(A). The test result recorded is the highest sound level. TRL Limited 24 PPR044

33 4.1.2 Test 2: Proposed UN ECE R51.02 The test procedure requires that the maximum noise level in db(a) is determined during pass-by operation with a microphone placed on either side of the vehicle at a distance of 7.5m from the vehicle centre line at a height of 1.2m. The test surface is that specified in ISO As in the previous test the A-weighted sound level of sound sources other than those of the vehicle to be tested and of wind effects must be at least 10dB(A) below the sound level produced by the vehicle. The test specification depends on a number of vehicle parameters including maximum power, vehicle mass, rated engine speed and number of gears. For manual transmission vehicles of type M1, N1 and M2Q3.5 tonne, tests are carried out typically in 3 rd and 4 th gears with the aim of achieving a reference acceleration depending on the power to mass ratio. This is typically around 1.3 m s -2. For these vehicles there is an additional requirement to test at a steady cruise by speed of 50 km/h ± 1 km/h. The results for the WOT and steady speed are then combined to yield a single db(a) level termed L urban. For heavier vehicles there is no requirement for a steady speed test. The acceleration test is carried out at WOT with an exit speed to the test site of 35±5 km/h. The gear selected is such that at exit the engine speed is a given fraction of the rated engine speed i.e. 0.7 to 0.75 for M2 and N2 vehicles and 0.85 to 0.89 for categories M3 and N3. Load conditions depend on vehicle category. For M1, M2 and M3 vehicles there is no requirement to add load. For N2 and N3 vehicles the total mass of the vehicles is 50kg per kw rated power. Note that for N1>2000kg there is some discussion in the informal GRB group of the load condition. However, the working assumption was to test these vehicles laden. At least four measurements were made on each side of the vehicle and in each gear for both the acceleration and steady speed tests. Results were deemed to be valid provided the difference between four measurements on the same side of the vehicle was not more than 2dB(A). Each test reading was rounded to the first decimal place. The results of each side were averaged separately. The intermediate result is the higher of these two averages. The final figure was obtained by rounding this intermediate value to the nearest integer Test 3: Pull away from rest This test procedure requires that the maximum noise level in db(a) is determined during an operation involving accelerating the vehicle from stationary. Microphones are placed on either side of the vehicle at a distance of 7.5m from the vehicle centre line at a height of 1.2m. The objective is to simulate the type of vehicle operation that commonly occurs at traffic lights and at road junctions. The test surface used was the ISO surface. To carry out the test, the vehicle is initially positioned with its front opposite the start line of the test strip, i.e. 10m downstream of the centre of the test site. When testing cars and light vans, 1st gear is selected and the vehicle is accelerated smoothly until the rear of the vehicle passes the stop line of the test strip. Having passed the stop line, the throttle setting is released. When testing other vehicles the gear selected will be that which is considered to be normal for the type of operation described in real driving situations, bearing in mind the loading conditions. During the test, the maximum noise level and the sound exposure level (SEL) is recorded at both microphone positions. Any noise generated by the air brakes is discarded. In addition measurements of the speed of the vehicle and the acceleration are taken during the drive-by. At least 20 individual readings of speed and acceleration are recorded. The test was repeated 8 times with the vehicle accelerating at different rates to cover a wide range of possible accelerating conditions. As a guide, the target speed range at the stop line position should be in the range km/h. However, it was realised that some vehicles may not be able to achieve the highest speeds in this range. In all cases the objective was to obtain a good spread of data over the range applicable for the vehicle under test. TRL Limited 25 PPR044

34 For each test run the complete time history of the noise level at both microphones and the speed and acceleration was recorded. To test for repeatability it was decided that an example of a car, bus and truck would be re-tested four times. For these selected vehicles the whole test procedure was repeated to produce 4 separate data sets of 8 measurements. For each vehicle tested the measurement protocol required the following information to be obtained: Values of the maximum and SEL noise levels at each microphone position, together with the average acceleration and the speed of the vehicle at the exit point of the test site. The evolution of speed and acceleration during each test A description of any problems encountered during testing including difficulties with achieving the required conditions and the precise instructions given to the driver Test 4 and 5: Cruise by at 50 km/h on HRA and SMA For vehicle categories M1 and N1 the maximum noise levels achieved during the cruise by test at 50km/h (described under Test 2) were measured on surfaces not specified in the proposed revision of ECE but typical of main roads in the UK. These tests were carried out at TRL on sections of hot rolled asphalt (HRA) and a thin surfacing i.e. stone mastic asphalt with 14mm maximum stone size (SMA14) Test 6: Exhaust test according to ISO 5130 This test was performed with the microphone placed 1m from the exhaust outlet and 45 degrees to the jet flow as specified in the standard. Where it was found that the required engine speed (i.e. 3/4 of the speed that produces the maximum power output) could not be achieved due to intervention by the engine management system then the measurements were taken according to the standard but at the maximum engine speed obtainable. Any departure from the requirements of the standard were noted on the data sheet and the maximum engine speed achieved was also reported. The test procedure requires that the maximum noise level in db(a) is determined during the operation cycle. In addition the following results were reported: A graph showing the change in noise level with time during the operation cycle For each test, the maximum noise level and the engine speed at which the maximum level is generated was tabulated. All valid test results were tabulated with decibel readings posted to the nearest 0.1dB(A). The noise results were averaged and rounded according to the procedure given in WP-025. It should be noted that at least three repeat tests are required to be performed and that a valid test can only result when three consecutive test results differ by less than 2dB(A). To test for repeatability, an example of a car, bus and two trucks selected by TRL were retested four times Test 7: Exhaust test with engine sweep according to SAE J1 492 The method specified in the SAE standard was used. This requires that the engine speed shall be gradually increased from idle to 3/4 of the engine speed at which the maximum rated power is obtained (rated engine speed) and then held constant at that speed for 1-2s. The throttle is then rapidly released and the engine is allowed to return to idle. (NB. The change from idle to 3/4 rated engine speed should occur over a 10-15s interval). Where it is found that the required maximum engine speed cannot be achieved due to intervention by the engine management system then the measurements were taken according to the standard but at the maximum engine speed obtainable. TRL Limited 26 PPR044

35 Again any departures from the standard were noted in the comments on the data sheet and the maximum engine speed achieved was reported. The test procedure requires that the maximum noise level in db(a) is determined during the operation cycle. The following results were also reported: A graph showing the change in noise level with time during the operation cycle. For each test, the maximum noise level and the engine speed at which the maximum level is generated was tabulated. All valid test results were tabulated with decibel readings posted to the nearest 0.1dB(A). The noise level results were averaged according to the procedure given in the SAE standard. This requires that the reported sound level is the arithmetic average of the 2 highest noise levels that are within 2 db(a) of each other. To test for repeatability, an example of a car, bus and two trucks selected by TRL were retested four times Test 8: Whole vehicle noise during engine sweep test The engine sweep operation conformed to that described in The Society of Automotive Engineers Standard J1492 (Revision ). However, the procedure used in this study differed from the SAE standard in that it attempted to measure the noise from all major sources on the vehicle and not just exhaust noise. The test site used was the ISO standard site at Millbrook. The measurements were performed at the microphone positions shown in the array in Figure 4.2 with the vehicle stationary. As required by the standard, measurements were only taken in good weather conditions when wind gusts did not affect meter readings. Ambient noise was at least 10dB(A) below test levels. The vehicle operation used is similar to that specified in the SAE standard. For vehicles where the maximum engine speed is not controlled by some from of speed limiting device the engine speed was gradually increased from idle to 3/4 of the engine speed at which the maximum rated power is obtained and then held constant at that speed for 1-2s. The throttle was then rapidly released and the engine is allowed to return to idle. As in the exhaust noise tests, the change from idle to 3/4 rated engine speed occurred over a 10-15s interval. For governed engines the same test operations were applied although in this case the sweep covered the range from idle to governor run out speed or maximum limited speed. The maximum noise level in db(a) was determined during the operation cycle at each of the microphone positions shown in the array. NB. The 2m microphone positions were measured separately from the 7m microphone positions. The following results were reported: A graph showing the change in noise level with time during the operation cycle. For each test, the maximum noise level and the engine speed at which the maximum level is generated was tabulated for each microphone. All valid test results were tabulated with decibel readings posted to the nearest 0.1dB(A). To test for repeatability, an example of a car, bus and two trucks selected by TRL were retested four times. TRL Limited 27 PPR044

36 Mic 1 Mic 8 Mic m Mic m Mic 3 Mic 6 Mic 4 Mic 5 Figure 4.2: Microphone array positions Test 9: Rapid acceleration to governor run out (GRO) The measurements were performed with the vehicle stationary and at the microphone positions shown in the array in Figure 4.2. The method requires the test vehicles' engine to be accelerated as rapidly as possible. The engine is therefore accelerated rapidly (WOT) from idle to the maximum allowable speed and then the throttle released and the engine allowed to return to idle. The maximum noise level is recorded during the whole operation. The following results were also reported: A graph showing the change in noise level with time during the operation cycle at each microphone location. The maximum noise level at each microphone and the maximum speed achieved. All valid test results were tabulated with decibel readings posted to the nearest 0.1dB(A). To test for repeatability, an example of a bus and two trucks selected by TRL were re-tested four times. Comments about the operation of the test Test 10: Air brake test according to UN ECE R This test only applies to commercial vehicles fitted with air brakes. The air brake noise test is specified in Annexe 6 of the ECE regulation 51.The measurements were performed at the microphone positions 3 and 7 shown in the array in Figure 4.2. The maximum A-weighted noise level was measured during venting the pressure regulator and during the use of both the service and parking brakes. The sound during venting the pressure regulator is measured with the engine at idling speed. Before each measurement of both the service TRL Limited 28 PPR044

37 and parking brakes, the air-compressor unit was brought up to the highest permissible operating pressure, and then the engine switched off. Two measurements were taken at each microphone position for each condition tested. The maximum noise levels were reported to the nearest 0.1dB(A) and then adjusted as specified by the standard. In addition to the measurement of maximum noise, measurements were also taken of peak noise level. The following results were also reported: All noise levels taken at both microphones were tabulated separately for the operation of the parking and service brake. Test levels, including any adjustments made according to the standard, were also tabulated. To test for repeatability, examples of two buses and two trucks selected by TRL were retested four times. The measurement team were also required to comment on the operation of the test, the type of air brakes and any suppression equipment fitted Test 11: Ancillary noise The maximum noise was recorded during the operation of ancillary equipment such as hydraulic lifting gear and automatic doors. In the absence of any standard on the testing of ancillary noise sources, the measurements were performed at the microphone positions in the array in Figure 4.2. The highest A-weighted noise level and the SEL were measured at each microphone location during the operation of the ancillary device. All operations were carried out with the engine set at idling speed. For the operation of hydraulic equipment then the period of measurement encompassed the full range of operation. The possibility of dividing the measurement period to cover different operations was explored. For example, when operating hydraulic lifting gear it may be necessary to separate the lift operation from other operations. The following information was reported: The noise level at idle, as well as the maximum and SEL noise levels during the operation of the ancillary equipment was reported to the nearest 0.1dB(A). At least 4 repeat tests were completed and both the average and range determined for each microphone location. The measurement team were required to comment about the operation of the ancillary equipment (for example, whether lifting gear should be put under load), the repeatability of the results and whether any preconditioning might be needed in a type approval test environment. 4.2 Measurement set up and equipment development The range of tests defined for the study required that in some instances several data streams needed to be recorded simultaneously. In order to accommodate the large amount of data that needed to be recorded, the equipment developed for this study was based around a multi-channel real time logging system that enables up to 12 channels of data to be acquired simultaneously. Stop and start triggers were also included in the equipment set up so that the measurement period could be closely defined and controlled, where appropriate, by the movement of the test vehicle. This facility enabled measures such as the Sound Exposure Level (SEL) to be computed from the time history of measured levels. As well as logging noise levels measured using an array of, up to, 8 microphones it was also considered important to integrate engine speed and entry and exit speed into the data set that is collected for each vehicle. Apart from providing useful data for use subsequently in the analysis, it was envisaged that this information would also be needed following the completion of each test to establish that the requirements of the test had been met and to determine whether repeat runs were required. TRL Limited 29 PPR044

38 4.2.1 Test equipment development The measurement system chosen for the study was based on a real time data logger capable of collecting and storing acoustic data in both time and frequency domains simultaneously from several microphone inputs. Software programs were written initially to control the exact configuration of microphones, data analysis etc.. Five programs were written for this study by TRL and these are described briefly below. Program 1 - Four Microphone Test (for Tests 1, 2 and 3: pass-by and pull away from rest) It was decided that four microphones, three light gates 1 and a radar signal would be used for all Passby tests, and the Pull-away from rest test. Figure 4.3, discussed later, shows a typical layout. A program was therefore written and tested to control these items of equipment. Two of the TRL light gates were used in conjunction with the microphones for measuring SEL. The third light gate was programmed to trigger the measurement of vehicle speed using a radar system. The microphone data is acquired as fast A-weighted levels, and the maximum level for each microphone is measured. The microphone data is also sampled every 30 ms and stored in third octave bands for use in calculating the SEL. The radar data was sampled with distance rather than time, and provided speed measurements for every 0.5 m throughout the site. The program also controlled the storage and display of data following each test. Program 2 - Single Microphone Static Test (Tests 6 and 7: exhaust tests) For the single microphone static tests, a program was written to control a single microphone signal and the engine tachometer signal. No light gates were required for this test. The microphone fast A-weighted level and the tachometer rpm was sampled over time. The program then stores the sampled microphone and tachometer data. Program 3 - Eight Microphone Static Test (Test 8 and 9: vehicle noise engine sweep and rapid acceleration to GRO) The program written for the eight microphone static test was similar to the single microphone program (program 2). It samples the fast A-weighted levels from eight microphones and the engine speed tachometer signal as rpm. This data is then stored. Due to data capture and storage problems, the sampling rate and the microphone signal bandwidth were reduced. This restricted the third octave bands measured to the range, 16 Hz to 10 khz. This range is still more than adequate to cater for the range of frequencies generated by vehicle sources. Program 4 - Brake Venting Test (Test 10) The brake venting test program was written to acquire data from two microphones. The fast A-weighted microphone levels are sampled, and the data stored. Program 5 - Ancillary Noise Test (Test 11) The ancillary noise test program acquires data from eight microphones and stores the data in third octave bands. The fast A-weighted third octave bands are sampled for each microphone with respect to time, and the data stored. Due to the data capture and storage problems with eight microphones, the microphone bandwidth was reduced, but the sample rate remained at 30 ms, to comply with the 1 A light gate is a trigger device used to start and stop data sampling during a moving vehicle test. A light beam is directed across the track to a receiver. The beam is cut when the front of the vehicle moves through the light beam which activates the trigger. TRL Limited 30 PPR044

39 requirements for SEL calculations. This restricted the range of third octave bands measured to 16 Hz to 10 khz Equipment configuration for the moving vehicle tests Figure 4.3 shows a schematic of the layout of the microphones used for the moving vehicle tests and the positions of the light gates and radar system. Microphones were placed at 1.2m and 3m high at line PP. The microphones were located 7.5m from the centre of the test track. AAA AA PP BB BBB -20m -15m -10m 0 +10m +15m Length L (m) Radar Light Gate Light Gate Millbrook Trigger Start Trigger Microphones Stop Trigger Figure 4.3: Layout of microphones, light gates and radar for pass-by tests For the moving vehicle tests 1, 2 and 3 the logger/analyser was connected to four microphones, three light gate triggers and the vehicle speed signal. Two of the light gates (labelled Start trigger and Stop trigger ) were used to trigger the start and stop positions in the acoustic data acquisition time history. The third light gate (labelled Millbrook trigger was used to trigger the radar (vehicle speed) system. It should be noted that for measuring SEL it was required that the trigger was activated when the middle of the vehicle passed AAA and BBB. Consequently for this type of measurement the light gates were moved a distance of L/2 metres in front of these lines (where L is the vehicle length). A similar set-up was used for Test 3 - the pull-away from rest test condition. However, the start gate was placed at the -10m position with respect to the line PP (as for Tests 1 and 2) but the stop trigger was taken as the rear of the vehicle crossed the +10m position. For this test, therefore, the stop gate was therefore placed at 10+L metres from line PP Equipment configuration for the static tests Test 6 and Test 7 are exhaust condition tests, carried out with the vehicle stationary. They required the use of a single microphone placed close to the exhaust outlet, as shown in Figure 4.4. TRL Limited 31 PPR044

40 Figure 4.4: Stationary vehicle exhaust test For this study, the measurement microphone is to be placed at 0.5m from the tail pipe at 45 degrees to the direction of the main exhaust gas flow. For vehicles where the exhaust is located under the vehicle and where the standard 0.5m tailpipe position cannot be achieved, it was decided that the microphone would be placed at 0.5m from the edge of the vehicle, as shown in the diagram in Figure m 45 Exhaust 0.5m from vehicle edge Figure 4.5: Single microphone location for Test 6 and Test 7 Both Test 6 and Test 7 require that noise levels are logged together with the engine speed determined from a tachometer device 2. The maximum levels and associated engine speed for each test can then be determined from the stored data. It was noted that both Test 6 and Test 7 use the same measurement microphone layout and vehicle speed operating range. Consequently, in order to reduce the time needed to take the measurements, it was decided to combine Test 6 and Test 7 into one vehicle operation. Test 6 requires the engine speed to be increased from idle to target speed, held constant for a few seconds, and the allowed to rapidly return to idle. Test 7 differs from Test 6 only in that it requires the engine speed to be gradually increased from idle to a target speed, prior to rapid deceleration. By using the time traces stored in the logger system, tests 6 and 7 can be combined, and the resulting data analysed appropriately. An example of the microphone array (used as part of tests 8 and 9 and described in sections and 4.1.8, is shown in Figure It was a requirement to measure the engine speed independently from the vehicle's instrumentation using an appropriate tachometer device. For spark ignition vehicles this was achieved by attaching a probe to one of the HT leads. For diesel powered vehicles a reflective patch was placed on the engine flywheel. An optical sensor was used to generate a pulse during the passage of the patch. The signal was fed to the logger system (via a cable) and the revolutions per minute (rpm) were computed. TRL Limited 32 PPR044

41 Figure 4.6: Stationary eight microphone test set up During these tests, noise levels at each of the eight channels were logged together with the engine speed determined from the tachometer signal. During the development of the equipment for the eight microphone static tests, a problem arose when using the logger to record data from all microphone channels. This was found to be due to the large volume of data generated by the microphone array which led, on occasions, to a loss in synchronisation with the tachometer signal and an associated loss of some data. In order to minimise this 'drop out', the sampling interval was increased from 10ms to 50ms and the highest third octave band was reduced from 20kHz to 10kHz. Frequencies above 10kHz are found to make a minimal contribution to overall broad band noise levels and can therefore be safely neglected. This reduced the amount of data collected, and eased the data flow through the logger system. Test 10 is a static test of the noise from a vehicle s air brakes. For this test, all eight microphones are connected to the logger system, and the appropriate program loaded. This uses only 2 of the eight microphones, which are in positions 3 and 7 in Figure 5 above. The tachometer signal is not used in this test. Test 11 is a test of the noise generated by a vehicle s ancillary equipment and is carried out with the vehicle stationary. It uses the same eight microphone array as that used for Test 8 and Test 9, but as mentioned earlier it used a different logger program Commissioning TRL s logger system To ensure that the logger system developed by TRL was measuring accurately, a simple test was carried out where both the TRL logger system and the system used at Millbrook for type approval testing were used to measure pass-by noise on a test vehicle. The vehicle used for these tests was a petrol powered car. Two microphones were used on each side of the test track with one set connected to the TRL system and the other to Millbrook's analysers. The microphones on each side were placed close together at approximately 0.2m distance apart with the TRL microphones being placed at -0.2m of the centreline position PP on Figure 4.3, and the microphones connected to the Millbrook system being placed at 0m. The full results obtained from 4 repeat runs are listed in Table 4.1. It can be seen that for each test there was close agreement between the data from each system with the average difference of 0.16dB(A) and a maximum discrepancy being 0.6dB(A). As a result it was concluded that the TRL logger system was producing accurate measurements. TRL Limited 33 PPR044

42 Table 4.1: Results from Commissioning trials. Entry conditions Left Side Right Side Exit conditions Engine Speed Velocity Millbrook TRL Millbrook TRL Engine Speed Velocity RPM Km/h db(a) db(a) db(a) db(a) RPM km/h Vehicle description, loading and modifications to the test procedures The vehicles selected for testing were chosen to cover a wide range of sizes and propulsion units. In some cases alternative fuelled vehicles were included so comparisons could be made with diesel and petrol powered equivalents Vehicles Table 4.3 provides a brief description of each vehicle tested, some relevant vehicle and engine parameters and the additional loading applied in each case. It can be seen that in total the vehicle sample includes five HGV s, four buses, 5 minibuses, four vans and eight cars. The main measurement programme was carried out during The vehicles tested during 2004 include an electric powered van, a dual fuel car, two diesel powered buses, diesel powered minibuses and high performance sports cars. It should be noted that all vehicles are categorised for the purpose of type approval according to their use and carrying capacity. The following definitions, shown in Table 4.2, are used within the EU and apply throughout this report: Table 4.2: Vehicle category classifications Category M1 M2 M3 N1 N2 N3 Classification Vehicles used for the carriage of passengers and comprising not more than eight seats in addition to the driver's seat Vehicles used for the carriage of passengers, comprising more than eight seats in addition to the driver's seat, and having a maximum mass not exceeding 5 tonnes Vehicles used for the carriage of passengers, comprising more than eight seats in addition to the driver's seat, and having a maximum mass exceeding 5 tonnes Vehicles used for the carriage of goods and having a maximum mass not exceeding 3.5 tonnes Vehicles used for the carriage of goods and having a maximum mass exceeding 3.5 tonnes but not exceeding 12 tonnes Vehicles used for the carriage of goods and having a maximum mass exceeding 12 tonnes TRL Limited 34 PPR044

43 4.3.2 Vehicle loading For determining the load conditions for Test 2 for N2 and N3 vehicles, the formula in the proposed revision of regulation ECE R51.02 was used. The load on the rear axle with a tolerance of ± 5% is given as: Load = 50 * Rated Power (in kw) Note that where this calculated added load is greater than the maximum axle weight, the proposed standard test requires that the vehicle is loaded to achieve 75% of maximum axle weight of the rear axle. The calculated added load was greater than the maximum axle weight in the case of all the N2 and N3 vehicles. For N1 vehicles over 2500 kg, the load added is half the payload of the vehicle. For N1 less than 2500 kg, the vehicle was tested unladen. TRL Limited 35 PPR044

44 Vehicle Number Table 4.3: Description of vehicles tested Category Type Engine Unladen Weight (kg) Load Added (kg) No. of Axles Rated Engine Speed (RPM) Rated Power (kw) Power to Mass Ratio 1 N3 Rigid Diesel N3 Rigid CNG * (1) N3 Tractor Unit CNG * (1) N3 Tractor Unit Diesel * (1) N2 Rigid Diesel N1 >2500kg 7 N1 >2500kg 8 N1 <2500kg 9 N1 <2500kg Van Diesel Van Diesel Van Diesel * (4) Van Electric N/A M3 Bus Diesel M3 Bus CNG M3 * (2) Bus Diesel M3 * (2) Bus Diesel M2 Minibus Diesel M2 Minibus LPG M2 * (3) <3500kg 17 M2 * (3) <3500kg 18 M2 * (3) <3500kg Minibus Diesel Minibus Diesel Minibus Diesel M1 Car Diesel M1 Car LPG M1 Car Petrol M1 4x4 Diesel M1 Car LPG M1 Car Petrol M1 Sports Car Petrol M1 Sports Car Petrol (1) The vehicle was equipped with three axles. During the tests the wheels of only two axles were in contact with the ground. (2) Tested to the new requirements for automatic gearbox M3 vehicle with 30 km/h and 40 km/h exit speeds. (3) Tested to light vehicle test due to change in weight definitions for M2 vehicles. (4) In cases where no load is added the mass of an average driver is given for consistency TRL Limited 36 PPR044

45 4.3.3 Changes to the test procedures A number of changes were made to the test procedures during the period of testing. This followed decisions made in the ISO committee WG42 and subsequently in the GRB group. (i) Weight classification changes for minibuses It should be noted that Table 4.3 shows two diesel minibuses (vehicles 14 and 16). The first of these, vehicle 14, was tested in 2003 using the loading conditions and test procedure specified for heavy vehicles whereas the tests carried out on vehicle 16, in 2004, followed the procedure for light vehicles. This change in the method of testing follows a division in the weight classification for this type of vehicle that occurred during this period i.e. for M2 vehicles <3500kg the test procedure follows that of M1 vehicles. Heavier M2 vehicles are only required to be tested under the acceleration conditions specified for M3 vehicles. (ii) Buses fitted with automatic gearboxes Changes were also introduced during the measurement programme in the method for testing buses fitted with automatic transmissions. Difficulties were encountered initially in achieving the correct engine speeds during acceleration testing due to the vehicle automatically changing gear during the test. At the time when the tests were carried out an exit speed of 35 km/h + 5 km/h was specified. This changed during the measurement programme such that it is now necessary to test buses with automatic transmissions under two conditions where the exit speed is set at, 30 km/h and 40km/h. The test result being taken using the condition that generates the highest engine speed during the test. This revised test procedure was used on the two buses tested in 2004 (vehicles 12 and 13). (iii) Measurement of exhaust noise During the measurements of exhaust noise it was found that neither the existing or revised ISO 5130 nor the proposed draft regulations R51.02 dealt adequately with the problem of measuring close to an exhaust outlet that is positioned under the vehicle chassis. The difficulty arises since it can be impossible, in these situations, to position the measurement microphone at the required distance of 0.5 metres from the exhaust orifice and at an angle of 45 degrees to the direction of gas flow. This issue was raised in discussion at an ISO WG42 meeting. While this matter was being resolved by ISO it was decided that, for this project, measurements would be taken at the nearest position to that required in the standard bearing in mind that the microphone should not be located closer than 0.5m from any vehicle component. (NB. This latter requirement was found in a copy of an amendment of the regulation R51.02 held by Millbrook 3 ). Given these requirements it was found that this could only be achieved by moving the microphone to the nearest vehicle contour on the near-side of the vehicle and then displacing the microphone a further 0.5m beyond this boundary. Figure 4.7 illustrates the problem and the interpretation made by TRL for the correct microphone position. This position is labelled original position in the diagram. 3 However, the wording does NOT appear in the proposed draft revision of R51.02 or ISO TRL Limited 37 PPR044

46 Exhaust Outlet 0.5m 45º > 0.2m Revised Position 0.5m Original Position Figure 4.7: Position of microphone for static engine tests. Since making this judgement, the ISO WG42 have recently decided that where the exhaust outlet is positioned under the vehicle the microphone position should be that shown in Figure 4.7, labelled revised position. The revised microphone position was defined by taking a distance of 0.5m from the exhaust outlet perpendicular to the nearest vehicle contour, with an additional condition that the microphone had to be a minimum of 0.2m from the vehicle contour. For example, if the exhaust position was less than 0.3m under the vehicle body then the position would be 0.5m from the exhaust outlet. If however, the exhaust outlet was greater than 0.3m under the body, then the microphone would be placed at 0.2m from the vehicle contour, in a line perpendicular to the vehicle contour. TRL Limited 38 PPR044

47 5 Results and analysis 5.1 Results Appendix A provides results for all tests carried out on the trucks, vans, buses, minibuses and cars respectively. It should be noted that the results posted in the tables are the final test results obtained according to the procedures specified in the standards and proposed methods. They have therefore been subject to the averaging and rounding procedures specified in these standards. The raw data obtained from the actual test runs are not included in this report for reasons of brevity. A further point to note from the tabulated data set is that an additional test result for engine noise at idle has been included for the trucks tested. This data is tabulated as part of test 8 in Appendix A. This test was included as it was thought that the values obtained would be of relevance for assessing the noise impact of trucks operating in a noise sensitive urban environments. Appendix B provides a summary of the regression analyses carried out for the pull-away from rest test (Test 3). It also contains graphs showing the regression lines obtained for each vehicle tested. Appendix C provides the test results of each vehicle and test in graphical form so comparisons between vehicles of a similar type can be made more easily. 5.2 Analysis Since the programme of measurements have generated a very large data set it is useful to begin the process of analysis with an overview of the main objectives. This will help to refine the process and target the issues of main concern General considerations It has been argued that an appropriate test for type approval should expose the major vehicle noise sources. To this end Test 2 for light vehicles involves a steady speed component which is intended to expose tyre noise. It will be instructive therefore to compare the ranking of these vehicles on the results from the current test procedure (Test 1) that essentially measures power train noise to the ranking obtained from the testing under the proposed procedure (Test 2) that should produce an overall measure of vehicle noise. Similar rankings may indicate that the proposed amendments to the test method are superfluous although a larger vehicle sample would be needed to confirm such a finding. Such analyses could provide useful information on the overall validity of the test methods. It was noted earlier that the stationary tests may be used for different purposes that include type approval, national certification and in use testing. It would be of considerable interest therefore to determine the extent to which stationary or low speed manoeuvring tests correlate with pass-by tests. Good agreement (especially with Test 2) could strengthen the argument for the introduction of such tests since the results may be used to indicate noise produced under typical urban driving conditions. A further consideration is the repeatability of the results of the test procedures. An analysis of the variation of test results will indicate the repeatability of the test. The pull away from rest test is a new test idea that attempts to simulate a frequently occurring driving condition in urban areas. The driving condition for this test is not straightforward and so an analysis of the experience gained in carrying out this test on a range of vehicles will be useful in guiding any further development of this procedure. Issues of repeatability and reproducibility are particularly important when considering a new form of test procedure. An additional consideration for Test 3 is the need to determine a suitable acceleration to which results should be normalised for comparison TRL Limited 39 PPR044

48 purposes. It may be necessary to consider a different normalisation for different vehicle classes. Information gleaned from urban drive cycle statistics will help to provide appropriate values. For the stationary tests a large amount of data has been collected for each vehicle using an array of microphone positions. It would be advantageous to be able to use microphones only in the near field especially when testing in less than ideal conditions e.g. at the roadside or on a garage forecourt and so an examination of the correlation between different measurement positions is needed. Other issues that need to be considered include an examination of the effects of using vehicles with alternative fuels and examining the importance of other, non-regulated, sources of noise on the vehicle such as air brake noise. The issue of alternative fuels has particular importance as it is often claimed that such vehicles emit lower noise than petrol or diesel powered equivalent vehicles. In summary the main points that need to be addressed by the analysis are: Assess changes to the test conditions reflecting the problems in testing identified in this study. For Test 3, the pull away from rest test, assess any issues associated with driving this test condition and determine the likely repeatability and reproducibility of the test method. Compare the ranking of test results from the current test procedure (Test 1) that essentially measures power train noise to the ranking obtained from the testing under the proposed procedure (Test 2) which has been designed to produce a measure of overall vehicle noise. Significant differences would suggest the new test is exposing tyre/road noise to a greater extent in the new test method. On the other hand very close agreement would question the need for the new test procedure as currently specified. Determine the extent to which stationary or low speed manoeuvring tests correlate with passby tests. Good agreement (especially with Test 2) could strengthen the argument for the introduction of such tests since the results from type approval could then be used to indicate noise produced under typical urban driving conditions. Poor agreement would indicate that the low speed/static tests were exposing noise generation characteristics that were not being tested during the drive-by tests. For the stationary test with microphone arrays (Test 8) analyse the correlation between levels measured at positions located close to the vehicle and those measured further away. Assess the influence of alternative fuelled vehicles on noise levels using the different test methods. Assess the importance of other vehicle noise sources, e.g. air brake noise. These highlighted issues are analysed and discussed in the following sections Assessment of the changes to the test procedure It was pointed out in section that initially there were some problems in achieving the proposed test procedures with some of the vehicles tested. (i) Position of microphone for exhaust tests Of the six vehicles tested in 2004 only Vehicle 12 and Vehicle 13 were found to have an exhaust orifice located underneath the vehicle. However, in the case of Vehicle 12 the exhaust orifice exited just at the edge of the side panel of the vehicle (See Figure 5.1). This geometry again raises a question of interpretation of where the measurement microphone should be located. The current draft regulations do not make clear whether an exhaust which is below the vehicle body but just reaches the edge of the vehicle is classed as being under the vehicle body or external to it. The problem is TRL Limited 40 PPR044

49 illustrated in the diagram given in Figure 5.2 where, for this geometry, two possible microphone positions can be deduced from the current wording in the standard. Figure 5.1: Vehicle 12 exhaust location From a practical standpoint the microphone located at 45 degrees to the gas flow is a more sensible position as there is a risk that with the microphone positioned at right angles to the vehicle body, as described in the draft standard, there could be damage caused to the microphone from the exhaust gases. The gas flow itself could also create unrepresentative pressure fluctuations at the microphone leading to erroneous results. Exhaust Outlet 45º 0.5m 0.5m Microphone position where exhaust under body Microphone position where exhaust at edge of body Figure 5.2: Microphone positions where exhaust is under the vehicle body and at edge of vehicle body. However, despite these concerns, in this case, when testing Vehicle 13, measurements were taken at both microphone positions shown in Figure 5.2. This is because the tailpipe bends downwards at the edge of the vehicle, and so the microphone was not directly in the gas stream in either case. When comparing the results obtained at the two microphone positions, the results at 45 degrees were, on average, 0.9 db(a) higher than the corresponding values taken at the 0 degree position. Both sets of measurements produced highly repeatable results and there was no evidence of gas flow induced noise. However, the higher values generally found at 45 degrees to the gas flow supports the contention that this is a more suitable position for testing in such cases. Clearly, the issue of microphone placement in the draft standard still requires some consideration to avoid such ambiguities occurring in practice. TRL Limited 41 PPR044