VIBRATION, NOISE AND RIDE QUALITY 1 Introduction 2 Road Traffic Noise
Degree of throttle openness New Result Full-throttle acceleration under current test method New test method Moderate acceleration equivalent (Calculated from full-throttle acceleration and constant speed) Engine speed (rpm) High speed A-weighted sound pressure level db Current Result WOT 75 70 65 60 55 50 45 40 35 30 25 20 ICEV1 ICEV2 HEV EV mode Background Noise 0 5 10 15 20 25 Vehicle speed km/h 30 35 Fig. 3 Difference in Noise Levels between Gasoline-engine Vehicles and HEV Electric Running Actual driving conditions in urban areas Fig. 2 Driving Conditions under both New and Old Test methods electricity requires drawing air into the fuel cell stack, and possible countermeasures to the unique noise issue recognition by pedestrians. When the R138 technical re- associated with this intake and discharge of air have quirements were discussed, the Japanese automobile been published (Fig. 4)(1). In HEVs, the unpleasant vibra- manufacturers who first commercialized vehicle ap- tions when the engine was started have already been proach alerting devices and the ministry that first estab- improved to the point of going unnoticed, and efforts lished the guidelines collaborated in leading the UN rule- have moved on to examining whether the number of cyl- making process as well as the creation of the ISO inders in the engine can be reduced to achieve even standard for the testing method. In the U.S. as well, the greater fuel efficiency. In older HEVs the combustion Pedestrian Safety Enhancement Act of 2010 was passed force of the engine generates vibrations when it was by Congress and signed into law in January 2011. started. However, in newer engines with a smaller num- Other future issues concerning vehicle noise regula- ber of cylinders, it is the vibration prior to combustion tions currently being discussed within the GRB include: that has become a problem, and reports on the mecha- improving the Additional Sound Emission Provisions nism causing these vibrations and possible countermea- (ASEP) testing methods added to R51-03, noise regula- sures have been published (Fig. 5)(2). The demand for fur- tions for in use vehicles, and developing different road ther improved fuel efficiency also remains strong for surface classifications to address the eventual wide- internal combustion engine (ICE) vehicles, and progress spread use of low-noise road surfaces. As a result, there on measures such as further lowering the lock-up speed are strong expectations for even further reductions in of the CVT and reducing friction continues to be made. road traffic noise. However, such measures have resulted in other unpleas- 3 Noise and Vibration of Vehicle Components ant phenomena, including a worsening of booming noise and self-excited vibrations from the clutch, and factor analysis and simulation technologies to find countermea- 3. 1. Powertrains sures are being developed(3)(4). Since the technologies that New vehicle vibration and noise technologies to ad- improve the fuel efficiency of ICE vehicles and HEVs dress fuel efficiency and environmental friendliness re- also strongly affect vibration and noise characteristics, main essential. At the same time, the search for new pos- the development of new vibration and noise technologies sibilities in automobiles is driving the examination of new that address fuel efficiency is expected to continue in the ideas for powertrains. future. As HEVs and EVs grow in popularity, automobile Reports on vehicles equipped with in-wheel motors manufacturers have launched FCVs, which use fuel cells (IWM) as the possible new form of next-generation pow- as their source of energy. FCVs share many vibration ertrain packaging have also been issued. IWM systems and noise issues with HEVs and EVs, but there are also place an electric motor within the wheel itself, resulting FCV- specific vibration and noise phenomena. Generating in constraints on design and vehicle packaging that differ Copyright 2016 Society of Automotive Engineers of Japan, Inc. All rights reserved
1 10 6 Pa 70 SPL db A 60 Experiment Prediction 0.00 50 40 30 20 0 125 Hz 200 Hz 315 Hz 400 Hz 613 Hz 800 Hz 1 000 Hz 2 000 Hz 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1 000 1 250 1 600 2 000 2 500 3 150 4 000 5 000 10 1/3 Octave Band Frequency Hz Fig. 8 Comparison of Wind Noise Prediction Analysis Results with Experimental Results 21 optimal structure of air conditioning devices since they generate noise in the vehicle interior. Nevertheless, it is still not easy to accurately calculate the wind noise for the entire vehicle system over the entire frequency range from low to high when the vehicle 4 000 Hz is traveling at high speed. At the research level, projects such as this using the K supercomputer have been making progress and it was reported that good accuracy has Fig. 9 Wind Noise Prediction Model 22 (21)(22) been obtained (Fig. 8) (Fig. 9). At the locations where actual wind noise research is being carried out, the reali- issue. The use of a wave-number filter and of methods ty is that a variety of different techniques are being de- that do not separate the sound and sound-like effects ployed depending on the different standpoints and pur- have both been reported, but it is expected that some poses of the research. new theoretical basis will have to be established in the Another issue confronting researchers as they pursue future. a better understanding and more precise analysis of the Obviously, this field of vehicle wind noise requires ex- mechanism of wind noise is the fact that the technologies pertise in both fluid dynamics and vibration noise, but as in this field straddle the line between fluid dynamics and mentioned previously, there are almost no engineers who vibration noise. At the current time, the theoretical sys- currently possess the necessary expertise in both these tem attempting to integrate these two areas is insuffi- areas. Consequently, it is thought that another challenge cient and very few researchers and engineers are equal- to solving this issue in the future will be the need to re- ly well-versed in both of these fields. From the standpoint form the educational system at universities and the of vibration noise engineers, the size and distribution of training methods for engineers at companies. vibration sources caused by air flow are important, but In recent years, there have also been reports on re- in the world of fluid dynamics the vibration sources are search into the unconventional characteristics of new often separated into sound and sound-like effects (pres- materials used in automobiles. These include the move sure fluctuations that do not become sound) for reasons away from the conventional sound insulation materials of computational efficiency and the analysis techniques made from fibers and urethane to the construction of being used. This poses no problem when all vibration acoustic circuits composed of a large number of fine sources and the whole transmission response system are structures, or even the periodic placement of materials in a uniform piece of air. However, in the case of vehicle with different acoustic impedances(23)(24). It is expected wind noise, the transmission system includes vibrations that in the near future materials such as these will be passing through the glass and steel sheet of the vehicle applied to actual products thanks to innovations in manu- body, so identifying the proper theory and methods facturing technologies such as 3D printing. needed to separate the vibration sources has become an Copyright 2016 Society of Automotive Engineers of Japan, Inc. All rights reserved
4 Sound Quality