Presentation on theme: "WLTP-08-10 1 Elaborated by the WLTP downscaling issues task force 01.11.2014 OIL #5 Proposal for modifications of the calculation parameter/coefficients."— Presentation transcript:
WLTP-08-10 1 Elaborated by the WLTP downscaling issues task force 01.11.2014 OIL #5 Proposal for modifications of the calculation parameter/coefficients r 0, a 1 and b 1
Determination of the downscaling factor 2 The downscaling procedure is specified in GTR 15 in paragraph 7 of annex 1. The method as such is agreed, but paragraph 7.3 “Determination of the downscaling factor” needs to be amended. India requests modifications of the calculation parameter/coefficients r 0, a 1 and b 1 and made already a proposal for amendments (see WLTP-DHC-18-05). This issue is related to # 5 of WLTP-05-04. Calculations based on the Indian amendment proposal were performed for a series of class 3 vehicles. In figure 1 the resulting downscaling factor curve is compared to the current GTR curve.
Comparison current GTR – Indian proposal 3 Figure 1
Approach for a compromise proposal 4 In order to find a compromise proposal the following approach was chosen and applied to class 3 vehicles. The downscaling method uses the ratio between the maximum required power of the cycle phases where the downscaling is to be applied and the rated power of the vehicle. This ratio is independent of the transmission design, which is necessary in order to make the method applicable for any kind of transmission. But in order to better consider the influence of the transmission design, the necessary downscaling factor was related to the power available in second 1566 of the WLTC instead of rated power.
Approach for a compromise proposal 5 Second 1566 is the time, at which the maximum power is required within the cycle for class 3 vehicles. The calculation was performed for 81 vehicles of the development database. The rated power to kerb mass ratio of these vehicles varies between 34,1 kW/t to 52 kW/t and includes different transmission designs. The results are shown in figure 2. As expected, the correlation is much better than for rated power. The correlation function is f_DSC = 0,4554*Pnec/Pavailable – 0,51
Approach for a compromise proposal 7 In order to reestablish the relationship with Pnec/Prated, the correlation between Pnec/Pavailable and Pnec/Prated was calculated (see figure 3). By using the regression curve between both values (the green curve in figure 3) in order to replace Pnec/Pavailable by Pnec/Prated one gets a new curve for f_DSC. But since a significant number of vehicles (14 of 81) have ratios above the regression curve, it can be expected that f_DSC based on the regression line will not be sufficient, especially, when the wot percentage is considered as additional requirement.
Compromise proposal 8 Therefore the average between the regression curve and the upper envelope curve is proposed as compromise. It is the blue curve in figure 3 and it results in the green f_DSC curve in figure 4. This curve is close to the Indian proposal, but starts at a 3% higher power ratio (87% instead of 84%).
Consequence for class 3 M1 vehicles 11 The calculation parameter/coefficients r 0, a 1 and b 1 of the new proposal are as follows: r 0 = 0.867, a 1 = 0.588, b 1 = -0.51; The new function for f_DSC was applied on the gearshift prescription development database, but without the artificial vehicle configurations, used for the development of the downscaling method. The remaining sample consists of 128 vehicles from the WLTP in-use database, 24 vehicles from validation 2 and 16 other modern class 3 M1 vehicles. The power to mass ratios range from 36,5 kW/t to 137 kW/t.
Consequence for class 3 M1 vehicles 12 None of them gets downscaling following the current GTR. With the new proposal the downscaling factor is higher than 1% for 2 vehicles, both from the Indian in- use database. In one case (rated power = 26 kW) the vehicle would have 11 s of speed trace violations and 20,7% wot operation in the extra high speed phase. With the new proposal f_DSC is 6%, which reduces the speed violations to 0 and the wot operation to 14,9%. In the other case (rated power 35 kW) no speed trace violations are to be expected even without downscaling, but the new f_DSC of 2% reduces the wot operation in extra high from 19,5% to 16,4%.
Consequence for class 3 M1 vehicles 13 There is still one borderline case (rated power 35 kW), which does not get downscaling by the new requirements (f_DSC = 0,6%), but for which a high wot operation percentage in extra high can be expected (17,3%). This vehicle is from the validation 2 database from India.
Consequence for class 3 N1 vehicles 14 As one could expect, tor N1 vehicles the consequences of the new downscaling requirements are much higher. The corresponding database with artificial vehicle configurations excluded consists of 24 vehicles from the WLTP in-use database, 5 vehicles from validation 2 and 1 other vehicle. The power to mass ratios range from 34,4 kW/t to 64,6 kW/t. For 4 vehicles speed trace violations between 6 s and 11 s are to be expected. These vehicles would get downscaling factors of 2% to 3% according to the current GTR, but this would not fully eliminate the speed trace violations (still between 3 s and 9 s.
Consequence for class 3 N1 vehicles 15 Also the wot operation percentage would only slightly be reduced by the current downscaling factors. These percentages are 22% to 25% for 3 vehicles from the validation 2 database and 31% for the other vehicle, if no downscaling is applied. The other vehicle is a N1 vehicle with 3500 kg GVM and default road load values from the current GTR. The wot operation percentages will be reduced to 19,8% to 20,4% for the 3 validation 2 vehicles and to 27,9% for the other vehicle. With the new DSC requirements the f_DSC values would be 10% to 11% for these 4 vehicles.
Consequence for class 3 N1 vehicles 16 This reduces the speed trace violations completely and the wot operation percentages to 11% to 19,8%. The higher value belongs to the vehicle with the default road load values. But 12 other vehicles would also get downscaling between 1 % and 7% according to the new requirements (2 vehicles from Japan, 1 from India and 9 from Europe). 8 of these vehicles have high wot operation percentages, which are significantly reduced by the new requirements, except for one case.
Consequence for class 3 N1 vehicles 17 That means that the new requirements reduce the risk for speed trace violations and high wot operation percentages for some N1 vehicle configurations, but could lead to advantages for other N1 vehicle configurations. These might lead to a reduction of the maximum cycle speed by up to 2,5 km/h. The reduction of the CO2 emissions is expected to be less than 1%.
Application of the new approach to class 2 vehicles 18 The same approach as described for class 3 vehicles was applied to 105 class 2 vehicles in the gearshift prescription development database. The results are shown in figure 5. Figure 6 shows the correlation between Preq/Pavailable and Preq/Prated and figure 7 shows the results on the basis of Preq/Prated.
Application of the new approach to class 1 vehicles 22 Finally the new approach was applied to 34 class 1 vehicles in the gearshift prescription development database. The results are shown in figure 8. Figure 9 shows the correlation between Preq/Pavailable and Preq/Prated and figure 10 shows the results on the basis of Preq/Prated.
Proposal for new r 0, a 1 and b 1 values 26 The task force came to the conclusion, that the outlined approach results in downscaling requirements, which are better balanced than the current requirements with respect to driveability issues and wot operation. The task force therefore proposes an amendment of the calculation parameter/coefficients r 0, a 1 and b 1 as follows: Class 1:r 0 = 0.978, a 1 = 0.680, b 1 = -0.665, Class 2:r 0 = 0.866, a 1 = 0.606, b 1 = -0.525, Class 3:r 0 = 0.867, a 1 = 0.588, b 1 = -0.510. This proposal will be presented at WLTP IG #8 in order to be adopted.
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