WLTP. Proposal for a downscaling procedure for the extra high speed phases of the WLTC for low powered vehicles within a vehicle class

Transcription

1 WLTP Proposal for a downscaling procedure for the extra high speed phases of the WLTC for low powered vehicles within a vehicle class Technical justification Heinz Steven

2 Introduction The WLTP vehicle classification is based on the ratio between rated power and kerb mass (pmr). Based on an analysis of the dynamics of the in-use data the following classification was agreed: 1. Class 1: pmr <= 22 W/kg, 2. Class 2: 22 W/kg < pmr <= 34 W/kg, 3. Class 3: pmr > 34 W/kg. Consequently, 3 different WLTC versions were developed according to the dynamic potentials of the different classes. The maximum speeds of the different cycle versions and phases are shown in Table 1. 2

3 Introduction Vehicle class Cycle version v_max for cycle phase in km/h low medium high extra high / Table 1 During the validation 2 phase some vehicles with pmr values close to the borderlines had problems to follow the cycle speed trace within the tolerances (+/- 2 km/h, +/- 1 s). The question to be answered for the GTR is, how to proceed with such vehicles. 3

4 Introduction Three possibilities were discussed: 1. Follow the trace as good as possible, 2. Apply a cap on the maximum speed of the vehicle, 3. Downscale the cycle for those sections where the driveability problems occur (see figures 1 and 2). The first possibility can lead to excessively high percentages of wide open throttle (wot) operation and would create a burden for those vehicles compared to vehicles without driveability problems. The second possibility was found to be not very effective. It works for some vehicle configurations but does not work for others. The third possibility was found to be more effective and the technical justification is given in this presentation. 4

5 vehicle speed in km/h 140 Downscaling example for class 3 versions 5.1 and v_set version v_downscaled time in s Figure 1 5

6 vehicle speed in km/h Downscaling example for class 2 version WLTC class 2, version 2 v_downscaled time in s Figure 2 6

7 Introduction The downscaling method is described in the Proposal for a downscaling procedure for the extra high speed phases of the WLTC for low powered vehicles within a vehicle class from The determination of the downscaling factor could be finalised for class 3 vehicles but needs to be extended to class 2 vehicles. The following elaborations are therefore related to class 3 vehicles only. Furthermore it needs to be evaluated whether the method should also be applied to class 1 vehicles. 7

8 Calculations performed for the downscaling method The development of a proposal for downscaling factors is based on calculations performed with a modified version of the WLTP gearshift calculation tool, which provides also estimates of the CO2 emissions. The calculations were performed for a series of class 3 vehicles with maximum speeds between 90 km/h and 250 km/h. The maximum speeds were calculated from the transmission data and the default values for the driving resistance coefficients provided by the model. Since these coefficients are based on existing European legislation and thus do not reflect the modifications currently discussed within the GTR development process, calculations were performed with varied driving resistance coefficients for some vehicles. 8

9 Calculations performed for the downscaling method These driving resistance coefficients were chosen from a datapool provided by vehicle manufacturers, TUG and TNO. For the calculations min, ave and max values for f 0, f 1 and f 2 were used for the following vehicle categories: Subcompact cars, Compact cars, Medium cars, Large cars, Small N1, Medium N1, Large N1. According to the aim of the analysis the focus was set on subcompact and compact cars and N1 vehicles. 9

10 Influencing parameter for the driveability of the WLTC From previous investigations is known that possible driveability problems for class 3 vehicles are related to the following time periods in the extra high speed phase (see figure 1): 1. From 1560 s to 1583 s, 2. From 1650 s to 1669 s and 3. From 1712 s to 1724 s. The maximum set speed of the extra high speed phase of the cycle (131.3 km/h) is reached at 1724 s. In order to find an appropriate solution for vehicles with driveability problems one need to know the most influencing parameters. The most important parameter is the ratio between the power demand and the available power. 10

11 Influencing parameter for the driveability of the WLTC The power demand can easily be calculated from the driving resistance coefficients, the mass of the vehicle and the cycle parameter vehicle speed and acceleration. P_demand = (f 0 *v + f 1 *v 2 + f 2 *v 3 )/ kr*m test *a*v/3600 with v vehicle speed in km/h, a acceleration in m/s², m test test mass in kg and P in kw. kr represents the rotational inertia and was set to 1,1. The available power depends on the full load power curve (wot curve) and the transmission design. Average wot curves for Petrol and Diesel vehicles as provided by Stefan Hausberger were used for the calculations. The transmission designs were taken from manual transmission vehicles either from the WLTP in-use databse or the validation 2 database. 11

12 Influencing parameter for the driveability of the WLTC In some cases the transmission design was modified in order to assess the influence on driveability. For the available power a safety margin of 10% was applied to the wot curves. In order to illustrate the power demand and the available power both values were calculated for each second of the WLTC and plotted against the vehicle speed. The driveability was checked by a comparison of the actual speed, the set speed and the tolerance band. Figures 3 and 4 show an example of an average medium sized car from the EU WLTP database. P_max represents the available wot power (90% of the original curve) in the different gears, P_res represents the driving resistance power for constant speeds and P_tot includes also the acceleration power. 12

13 vehicle speed in km/h delta v in km/h Speed trace of the extra high speed phase for an average European car veh 130, SLO in-use 30, RL medium ave, 0% DSC, rated power = 74 kw, v_max = 179 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 3 13

14 P in kw Corresponding power values for an average European car 70 P_max P_res 60 P_tot act 1560 s to 1583 s act 1650 s to 1669 s 50 act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s veh 130, SLO in-use 30, RL medium ave, 0% DSC, rated power = 74 kw, v_max = 179 km/h vehicle speed in km/h Figure 4 14

15 Influencing parameter for the driveability of the WLTC The 3 periods of the extra high speed phase, that are critical for the driveability are separately highlighted. It can clearly be seen that this vehicle has always more power available than required and that wot operation is negligible. This result is representative for the major part of the European car market. Similar results were found for a relatively low powered European compact car (figures 5 and 6), although the requested power values are closer to the available power values in this case. But the situation can be different for low powered N1 vehicles, especially with the increased test mass. Figures 7 and 8 show an example from the EU in-use database, where the power request exceeds the available power for the first critical time period, but the vehicle speed can still be kept within the tolerances. 15

16 vehicle speed in km/h delta v in km/h Speed trace of the extra high speed phase for a European compact car veh 40, BE in-use 2, RL compact ave, 0% DSC, rated power = 50 kw, v_max = 158 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 5 16

17 P in kw Corresponding power values for a European compact car P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s set 1650 s to 1669 s set 1712 s to 1724 s veh 40, BE in-use 2, RL compact ave, 0% DSC, rated power = 50 kw, v_max = 158 km/h vehicle speed in km/h Figure 6 17

18 vehicle speed in km/h delta v in km/h Speed trace of the extra high speed phase for a European N1 vehicle veh 136, UK in-use veh 1, default RL small N1 min, rated power = 63 kw, v_max = 153 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 7 18

19 P in kw Corresponding power values for a European N1 vehicle 70 P_max P_res 60 P_tot act 1560 s to 1583 s act 1650 s to 1669 s 50 act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s veh 136, UK in-use veh 1, default RL small N1 min, rated power = 63 kw, v_max = 153 km/h vehicle speed in km/h Figure 8 19

20 Influencing parameter for the driveability of the WLTC If the max values for the RL coefficients are used, the maximum speed of the vehicle decreases from 153 km/h to 147 km/h and speed tolerance violations occur in the first critical period, but not in the other two periods (see figures 9a and 10a). That means this vehicle does not have any problems to reach the maximum cycle speed and demonstrates the ineffectiveness of a maximum speed cap. With a downscaling factor of only 6% the driveability problems could be reduced to that extend that the speed tolerance violations disappear (see figures 9b and 10b). 20

21 vehicle speed in km/h delta v in km/h Speed trace of the exhigh speed phase for a N1 vehicle with increase RL veh 136, UK in-use veh 1, default RL small N1 max, rated power = 63 kw, v_max = 147 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 9a 21

22 P in kw Corresponding power values for a N1 vehicle with increased RL 70 P_max P_res 60 P_tot act 1560 s to 1583 s act 1650 s to 1669 s 50 act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s veh 136, UK in-use veh 1, default RL small N1 max, rated power = 63 kw, v_max = 147 km/h vehicle speed in km/h Figure 10a 22

23 vehicle speed in km/h delta v in km/h Speed trace of the exh phase for a N1 vehicle with increase RL, with DSC veh 136, UK in-use veh 1, default RL small N1 max 6% DSC, rated power = 63 kw, v_max = 147 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 9b 23

24 P in kw Corresponding power values for a N1 vehicle with increased RL, with DSC 70 P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s veh 136, UK in-use veh 1, default RL small N1 max 6% DSC, rated power = 63 kw, v_max = 147 km/h vehicle speed in km/h Figure 10b 24

25 Influencing parameter for the driveability of the WLTC Figures 11 and 12 show results for a N1 vehicle from the Indian in-use database. Although this vehicle has a maximum speed of only 132 km/h, it has no driveability problems and can easily reach the maximum speed of the cycle. The reason is that the maximum vehicle speed is not determined by the power demand but by engine speed limitation and that the transmission is designed such, that the highest power demand in the first critical period coincides with the maximum of the wot curve in highest gear. 25

26 vehicle speed in km/h delta v in km/h Speed trace of the exh speed phase for a N1 vehicle from Indian in-use DB IN veh 18, D, veh 125, RL small N1 ave, 0% DSC, rated power = 65 kw, v_max = 132 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 11 26

27 P in kw Corresponding power values for a N1 vehicle from Indian in-use DB 70 P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s IN veh 18, D, veh 125, RL small N1 ave, 0% DSC, rated power = 65 kw, v_max = 132 km/h vehicle speed in km/h Figure 12 27

28 Influencing parameter for the driveability of the WLTC The situation gets different, if the driving resistance is increased to that extend, that the maximum speed (although still the same value) is now determined by the available power (see figures 13a and 14a). The power demand exceeds now the available power in the critical periods 1 and 3 and the maximum speed of the cycle is no longer reached. Figures 13b and 14b show the results for a downscaling factor of 11.8%. The driveability problems disappeared completely. 28

29 vehicle speed in km/h delta v in km/h Speed trace of the exhigh speed phase for a N1 vehicle with increase RL IN veh 18, D, veh 125, RL medium N1 max, 0% DSC, rated power = 65 kw, v_max = 132 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 13a 29

30 P in kw Corresponding power values for a N1 vehicle with increased RL 70 P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s IN veh 18, D, veh 125, RL medium N1 max, 0% DSC, rated power = 65 kw, v_max = 132 km/h vehicle speed in km/h Figure 14a 30

31 vehicle speed in km/h delta v in km/h Speed trace of the exh phase for a N1 vehicle with increase RL, 11.8% DSC veh 125, RL medium N1 max, 11.8% DSC, rated power = 65 kw, v_max = 132 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 13b 31

32 P in kw Corresponding power values for a N1 vehicle with increased RL, 11.8% DSC 70 P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s 40 set 1650 s to 1669 s set 1712 s to 1724 s veh 125, RL medium N1 max, 11.8% DSC, rated power = 65 kw, v_max = 132 km/h vehicle speed in km/h Figure 14b 32

33 Influencing parameter for the driveability of the WLTC Figures 15 and 16 show the results for a M1 vehicle from the Indian in-use database modelled with relatively low driving resistance. Although this vehicle has a relatively high maximum vehicle speed and reaches the maximum speed of the cycle without problems, serious problems occur at the other two critical cycle periods, because the high power demand coincides with a local minimum of the available power. 33

34 vehicle speed in km/h delta v in km/h Speed trace of the exh speed phase for a M1 vehicle from IN in-use DB , veh 225, RL default, 0% DSC, rated power = 26 kw, v_max = 143 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 15 34

35 P in kw Corresponding power values for a M1 vehicle from the IN in-use DB 30 P_max P_res 25 P_tot act 1560 s to 1583 s act 1650 s to 1669 s 20 act 1712 s to 1724 s set 1560 s to 1583 s 15 set 1650 s to 1669 s set 1712 s to 1724 s , veh 225, RL default, 0% DSC, rated power = 26 kw, v_max = 143 km/h vehicle speed in km/h Figure 16 35

36 Influencing parameter for the driveability of the WLTC Figures 17 and 18 show the results for the vehicle from the previous figures (15 and 16) but with a modified transmission design so that the maximum vehicle speed is engine speed limited to 106 km/h. This vehicle has no problems to follow the trace, except that the maximum speed is limited to 106 km/h. This vehicle would not need any downscaling because the maximum speed is driven at partial load conditions. The situation is totally different for the vehicle whose results are shown in figures 19 and 20. The maximum speed is also 106 km/h, but determind by the available power by using extremely high driving resistance coefficients. In this case downscaling would be needed because the wot operation in the extra high phase is extremely high (59%). 36

37 vehicle speed in km/h delta v in km/h Speed trace of the exh phase for a M1 vehicle with low RL petrol, class 3, 106 km/h, RL subcompact min, rated power = 26 kw, v_max = 106 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 17 37

38 P in kw Corresponding power values for a M1 vehicle with low RL 35 P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s 20 set 1650 s to 1669 s set 1712 s to 1724 s petrol, class 3, 106 km/h, RL subcompact min, rated power = 26 kw, v_max = 106 km/h vehicle speed in km/h Figure 18 38

39 vehicle speed in km/h delta v in km/h Speed trace of the exh phase for a M1 vehicle with extremely high RL veh 335, petrol, class 3, 106 km/h, RL compact max, rated power = 27.5 kw, v_max = 106 km/h v_downscale v tol_min tol_max v_orig delta v ,500 1,560 1,620 1,680 1,740 1,800 time in s Figure 19 39

40 P in kw Corresponding power values for a M1 vehicle with extremely high RL P_max P_res P_tot act 1560 s to 1583 s act 1650 s to 1669 s act 1712 s to 1724 s set 1560 s to 1583 s set 1650 s to 1669 s set 1712 s to 1724 s veh 335, petrol, class 3, 106 km/h, RL compact max, rated power = 27.5 kw, v_max = 106 km/h vehicle speed in km/h Figure 20 40

41 Analysis results The previously shown examples clearly demonstrate that the ratio between the power demand and the available power is the most important parameter for the forecast of driveability problems. The power demand can easily be calculated from the driving resistance coefficients, the mass of the vehicle and the cycle parameter vehicle speed and acceleration. The available power depends on the full load power curve (wot curve) and the transmission design. In order to find a solution that is also applicable to vehicles with automatic transmissions, parameter independent from the transmission design should be used for the forecast. Two parameters were included in the analysis. 41

42 Analysis results One parameter is the ratio between the driving resistance power at 130 km/h (almost the maximum vehicle speed of the original extra high speed cycle phase) and the rated power of the vehicle. It is called r_130 in the following. This parameter considers the vehicle mass only within the coast down measurements for the determination of the required driving resistance coefficients (f 0, f 1 and f 2 ). The other parameter is the ratio between the total required power at second 1566 of the first critical period of the extra high speed phase, which includes the vehicle mass directly via the required acceleration power. In a first step the r_130 was calculated for all vehicles in the calculation database. Figure 21 shows the v_max vehicle values versus r_130. The upper envelope can be approximated by a power function. The v_max_border curve will be explained later. 42

43 v_max vehicle in km/h v_max of the vehicle versus r_ y = x R² = v_max v_max_border downscaling analysis y = x % 20% 40% 60% 80% 100% 120% Pres at 130 km/h / Prated Figure 21 43

44 Analysis results 40 different vehicle configurations were chosen for the further analysis steps, mainly borderline cases. The downscaling factor (f_dsc) as described in [1] was determined by trial for the 40 vehicles and the results plotted against the above described parameters. The r_130 ranges from 46.6% to 118.5%. The results are shown in figure 22. f_dsc can be approximated by a 3 rd degree polynomial function. 79% of the f_dsc variance can be expained by r_130. The remaining 21% unexplained variance part seems quite high, but results from the fact, that the transmission design is disregarded. The ratio between the total required power at second 1566 of the first critical period of the extra high speed phase and the rated power shows a linear relationship with f_dsc, but the square of the correlation coefficient is only 74%. 44

45 downscaling factor Downscaling factor as function of r_130 50% 45% downscaling 40% 35% no problems 30% 25% necessary DSC factor y = x x x R² = % 15% Poly. (necessary DSC factor) 10% 5% 0% 0% 20% 40% 60% 80% 100% 120% Pres at 130 km/h / Prated Figure 22 45

46 Analysis results In a next step the regression function as shown in figure 22 was used for the f_dsc forecast and calculations for the 40 vehicle configurations and some additional configurations (in total 147 cases) were performed with the resulting f_dsc values, where necessary. One result was that vehicles, whose maximum vehicle speed is below the v_max_border line shown in figure 21, would not require any downscaling measure, because the cycle trace could be followed without any problems at speeds below the maximum vehicle speed and the maximum vehicle speed could be driven with partial load conditions. This condition was fulfilled for 20 of the 147 cases. For another 18 cases no downscaling was necessary, because the f_dsc resulting from the regression function was 0. 46

47 Analysis results The remaining 109 cases can be clustered as follows: For 17 cases the resulting f_dsc was below 5% and in 15 of these cases no speed tolerance violations occured. The speed tolerance violations for the other 2 cases occured only for 3 s. Therefore it is proposed in [1] to apply no downscaling, if r_130 is <= 68.7%. For another 92 cases speed trace violations were found without downscaling, but could completely be avoided by the application of the downscaling method. In the remaining 10 cases the downscaling reduced the number of speed tolerance violations significantly, but not completely. 8 of these cases were vehicles with 4speed gearboxes. All cases are related to transmission configurations as shown in figure

48 Analysis results For 43 cases the wot percentage of the extra high speed phase was higher than 35%. The downscaling led to a significant reduction of these percentages. The maximum f_dsc was 28.3%. The effects of the downscaling on the maximum speed of the cycle ranges from 0 (in cases where v_max vehicle was below v_max cycle) to a reduction of 6.8% (-8.7 km/h). The effects of the downscaling on the fuel consumption (FC) are also influenced by the transmission design and the resulting gear use. The relative difference to the case without downscaling ranges from +0.9% to - 5.6% with an average of - 1.6%. High reductions are quite often related to high wot percentages for the cases without downscaling. 48

49 Analysis results But compared to the deletion of the extra high speed phase the FC is on average 5.6% higher for the downscaled cycles. If the base cases without downscaling are included in the comparison of the FC with and without the extra high speed phase, the deletion of the extra high speed phase decreases the FC on average by 5.6% (range between -19.3% and +3.6%). More details can be found in the attached Excel file. The conclusions of the analysis results were used for the proposal for a downscaling procedure for the extra high speed phases of the WLTC for low powered vehicles within a vehicle class (see [1]). 49

50 References [1] H. Steven, Proposal for a downscaling procedure for the extra high speed phases of the WLTC for low powered vehicles within a vehicle class, [2] H. Steven, Modelling of fuel consumption and detection of driveability problems for borderline cars using speed caps and downscaling of sections of the extra high phase,