1. Status report about the work of the task force on gearshift issues
WLTP-16-10e-Rev1
Cycle / gearshifting
Status report about the work of the task force on gearshift issues
Heinz Steven 1

2. Meetings and audio-web telcos
After WLTP IWG #15 at the gearshift issues task force had the following meetings:
Face to face meeting at in Brussels,
Audio-web telco at
On the following slides the proposed amendments to the GTR text are written
in green, if they are already incorporated by the drafting coordinator,
in red, if they still need to be considered by the drafting coordinator and
In pink, if they were added in revision 1.
Modified or added text in revision 1 is written in brown. 2

3. Annex 2, paragraph 2 (g) (n/v)i
Annex 2, paragraph 2 “Required data and precalculations”
(e) ndvi (n/v)i , the ratio obtained by dividing the engine speed n by the vehicle speed v for each gear i, for i to ngmax, min-1/(km/h). (n/v)i shall be calculated according to the equations in paragraph of this Regulation; 3

4. Calculation procedure for (n/v)i
In paragraph 3 “Definitions”, 3.2 “Road load and dynamometer settings” the following sub-paragraph was added:
“n/v ratio” means the engine rotational speed divided by vehicle speed in a specific gear. The n/v ratios shall be calculated using the following equation:
where:
n is engine speed, min-1;
v is the vehicle speed, km/h;
ri is the transmission ratio in gear i;
raxle is the axle transmission ratio. 4

5. Calculation procedure for (n/v)i
Udyn is the dynamic rolling circumference of the tyres of the drive axle. Udyn is calculated using the following equation:
where:
H/W is the aspect ratio, e.g. "45" for a 225/45 R17 tyre;
W is the tyre width, mm; e.g. "225" for a 225/45 R17 tyre;
R is the rim diameter, inch; e.g. "17" for a 225/45 R17 tyre.
Udyn shall be rounded to whole millimeters. 5

6. Annex 2, paragraph 2 (g) nmax
The (n/v) definition was proposed at the GSTF meeting in Brussels. The Japanese colleagues still had scrutiny reservations. At the audio-web telco at the proposal was accepted by the GSTF.
Annex 2, paragraph 2 “Required data and precalculations”
nmax
Obvious errors in the formulas, like missing closing brackets, were corrected. 6

7. Annex 2, paragraph 2 (h) Pwot(n)
Annex 2, paragraph 2 “Required data and precalculations” (h) shall be amended as follows:
(h) Pwot(n), the full load power curve over the engine speed range. from nidle nmin_drive to nrated or nmax, or (n/v)(ngvmax) × vmax, whichever is higher.
(n/v)(ngvmax) is the ratio obtained by dividing the engine speed n by the vehicle speed v for the gear ngvmax, min-1/(km/h);
The power curve shall consist of a sufficient number of data sets (n, Pwot) so that the calculation of interim points between consecutive data sets can be performed by linear interpolation. 7

8. Annex 2, paragraph 2 (h) Pwot(n)
Pwot(n), (continued)
Deviation of the linear interpolation from the full load power curve according to Regulation No. 85 shall not exceed 2 per cent. The first data set shall be at nidle nmin_drive of ngear > 2 (see (k) below) or lower. The last data set shall be at nrated or nmax, or (n/v)(ngvmax) × vmax, whichever is higher.
Data sets need not be spaced equally.
The full load power at engine speeds not covered by Regulation No. 85 (e.g. nidle) shall be determined according to the method described in Regulation No. 85; 8

9. Annex 2, paragraph 2 (h) gear specific Pwot(n) curves
In the context of annex 2, paragraph 2, (h) Pwot(n), the use of gear specific Pwot(n) curves was discussed on request of some manufacturers.
Henrik Malberg gave a presentation in which he compared the consequences for the gear choice with the current prescriptions (one fixed wot curve).
Since one could conclude from the comparison that the gear choice would not be influenced significantly for the usual application of power limitations in first and second gear, the group decided to keep the current prescriptions. 9

10. Annex 2, paragraph 2 (i) ngvmax
Annex 2, paragraph 2 “Required data and precalculations”
ngvmax
Add the following sentence at the end of this paragraph:
If, for the purpose of limiting the maximum vehicle speed, the maximum engine speed in the highest gear is limited to a value nlim which is lower than the engine speed, corresponding to the intersection of the road load power curve and the available power curve,
ngvmax = ngmax and vmax = nlim / (n/v)(ngmax).
Necessary to perform the required calculations. 10

11. Annex 2, paragraph 2 (j) exclusion of a crawler gear
Annex 2, paragraph 2 “Required data and precalculations”
(j) Exclusion of a crawler gear
In this paragraph the symbol mr is used for the mass in running order.
Since mr is used as symbol for the rotational mass in other parts of the GTR it is proposed to replace mr by mro. 11

12. Annex 2, paragraph 2 (k) nmin_drive
The discussion about this issue is related to the definition of nmin_drive for ngear > 2, which is currently as follows:
nmin_drive = nidle ×( nrated - nidle ).
Three main concerns with regard to this definition:
nmin_drive is very sensitive to variations of nidle, since nidle determines 87,5% of nmin_drive.
This definition does not take into account differences in the power and torque curves between vehicles with the same nominal power to mass ratio.
This definition favours vehicles with Diesel engines compared to Petrol engines. 12

13. Annex 2, paragraph 2 (k) nmin_drive
Some negative reactions from WLTP IWG members were obtained at the beginning of the discussions, since the first amendment proposals resulted too much in further reductions of fuel consumption and CO2 emissions not in line with actual practical use.
In this context the chairman reminded the group on one of the principles that were followed during the development process of the gearshift prescriptions.
This was the balance between economic driving behaviour, which can be expected to be more representative for the future, and the correlation of the average engine speeds, resulting from the gearshift prescriptions, with the average engine speeds in the WLTP in-use database. 13

14. Annex 2, paragraph 2 (k) nmin_drive
The chairman recommended, that this principle should also be kept for further modifications of the prescriptions.
Henrik Malberg presented a proposal, which is based on acceleration capability requirements which would replace nmin_drive.
Since the acceleration potential was tuned by the max torque to mass ratio in this proposal, significant differences were found between Diesel and Petrol vehicles.
Consequently, Petrol vehicles get a bonus and Diesel vehicles a malus with this tuning method and it was proposed to replace the max torque to mass ratio by max power to mass ratio. 14

15. Annex 2, paragraph 2 (k) nmin_drive
Finally a combination of these two approaches was found to fit better to the side conditions mentioned before with the following formula for the required acceleration:
areq = 6*Tmax/mtest + 15*Pmax/mtest + 0,4
But since this proposal could not be accepted by all GSTF members, this issue was still under discussion.
Currently, some GSTF members are working on modifications of the coefficients of the formula for the required acceleration in order to provide a more accepted solution without violating the side conditions. 15

16. Annex 2, paragraph 2 (k) nmin_drive
Alternative coefficients, supported by some OEMs are:
areq = 4*Tmax/mtest + 16*Pmax/mtest + 0,4
The following table shows the resulting average engine speeds (v > 1 km/h) per veh. and eng. class. 16

17. Annex 2, paragraph 2 (k) nmin_drive
One could conclude that proposal A leads to slight disadvantages for class 1 and 2 Diesel vehicles and slight advantages for class 1 and 2 Petrol vehicles.
Alternative B leads to slight advantages for both engine types in these classes.
For class 3 vehicles proposal A leads to significant disadvantages for Diesel and advantages for Petrol vehicles, while proposal B keeps the current situation on average for Diesel vehicles, but leads to a 3% decrease (on average) of the average engine speeds for Petrol vehicles.
This would avoid an nmin_drive increase for Diesel vehicles and reduce the imbalance between Petrol and Diesel vehicles compared to the current definition. 17

18. Annex 2, paragraph 2 (k) nmin_drive
The Japanese colleagues expressed reservation on proposal A so far and stated, that this proposal could only be accepted as an option in addition to the current definition of nmin_drive.
There might now a possibility to agree on a compromise proposal but the GSTF would still need some time for assessment and discussions. 18

19. Consequences of annex 2 requirement options for family definitions
In Annex 2, paragraph 2 “Required data and precalculations”, (k) Definition of nmin_drive the manufacturer may request higher values than specified.
In Annex 2, paragraph 3.4 “Calculation of available power” the manufacturer may apply an additional power safety margin (ASM).
If these requests are used, this has consequences for the family definition in paragraph of the GTR. 19

20. Consequences for family definitions
Therefore, the following text was added at the end of paragraph 5.6.1:
If an alternative parameter such as a higher nmin_drive, as defined in the last sentence of paragraph 2.(k) of Annex 2, or ASM, as defined in paragraph 3.4. of Annex 2 is used, this parameter must be the same within an interpolation family. 20

21. Annex 2, paragraph 3.4 ASM
Annex 2, paragraph 3.4 “Calculation of available power”
Paragraph 3.4 reads:
The available power for each possible gear i and each vehicle speed value of the cycle trace, vj, shall be calculated using the following equation:
where:
Prated is the rated power, kW;
Pwot is the power available at ni,j at full load condition from the full load power curve; 21

22. Annex 2, paragraph 3.4 ASM where (continued):
SM is a safety margin accounting for the difference between the stationary full load condition power curve and the power available during transition conditions. SM is set to 10 per cent;
ASM is an additional exponential power safety margin, which may be applied at the request of the manufacturer. ASM is fully effective between nidle and nstart nASM_start, and approaches zero exponentially at nend nASM_end as described by the following requirements: 22

23. Annex 2, paragraph 3.4 ASM ASM (continued):
If ni,j ≤ nASM_start, then ASM = ASM0;
If ni,j > nASM_start, then:
ASM = ASM0 × exp(ln(0.005/ASM0) × (nASM_start – n)/(nASM_start – nASM_end))
ASM0, nASM_start and nASM_end shall be defined by the manufacturer but shall fulfil the following conditions:
nASM_start ≥ nidle,
nASM_start < nASM_end < nrated > nstart,
ASM0 ≤ 0.5. 23

24. Annex 2, paragraph 3.4 ASM
At the meeting in Brussels at Kostis Anagnostopoulos proposed to replace the current exponential function for the ASM by a sigmoid function, in order to reduce the “edge” effect of the exponential function.
This proposal was taken on board, but the GSTF asked for time for scrutiny, because most members were not familiar with this function.
Henrik Malberg prepared a presentation for the audio-web telco at , in which he applied both approaches on different example engines and concluded, that both approaches are acceptable, because they lead to similar results. 24

25. Annex 2, paragraph 3.4 ASM
But he asked the group, whether it would be more straightforward, that the manufacturer provides the ASM as datasets together with the Pwot curve.
The GSTF agreed and therefore proposes a new approach for ASM:
ASM is an additional exponential power safety margin, which may be applied at the request of the manufacturer.
When requested, the manufacturer has to provide the ASM values (in per cent reduction of the wot power) together with the data sets for Pwot(n) as shown in table A2-1. Linear interpolation shall be used between consecutive data points. ASM is limited to 50 per cent. 25

26. Annex 2, paragraph 3.4 ASM
The application of an ASM requires the approval of the responsible authority.
Table A2-1 26

27. Annex 2, paragraph 3.4 Pwot(n)
Pwot(n) (continued):
If aj > 0 and i = 1 or i = 2 and Pavailable_i,j < Prequired,j, ni,j shall be increased by increments of 1 min-1 until Pavailable_i,j = Prequired,j, and the clutch shall be disengaged.
Proposal:
This text can be deleted, since Pwot(n) is only defined from nmin_drive for ng > 2 on. 27

28. Annex 2, paragraph 3.4 Driveability problems
One OEM reported at the last meeting about driveability problems at low engine speeds.
Other OEMs did not experience similar problems and it was mentioned that this problem could be solved by the application of the additional safety margin (ASM).
The chairman proposed to close this item with the recommendation to apply the ASM in such cases.
This proposal was accepted by the GSTF. 28

29. Annex 2, paragraphs 3.3 and 3.5
Annex 2, paragraph 3.5 “Determination of possible gears to be used”
Paragraph 3.5 reads:
The possible gears to be used shall be determined by the following conditions:
(a) The conditions of paragraph 3.3. are fulfilled, and
Pavailable,i,j ≥ Prequired,j
Since the available power can only be calculated from nmin_drive of ngear > 2 on, (b) needs to be modified as follows:
(b) if ni,j ≥ nmin_drive of ngear > 2, Pavailable,i,j ≥ Prequired,j 29

30. Annex 2, paragraphs 3.3 and 3.5
Paragraph 3.3, “Selection of possible gears with respect to engine speed” reads:
The following gears may be selected for driving the speed trace at vj:
(a) All gears i < ngvmax where nmin_drive ≤ ni,j ≤ nmax_95,
(b) All gears i ≥ ngvmax where nmin_drive ≤ ni,j ≤ nmax(ngvmax)
It could happen that paragraph 3.3 allows only the highest gear, because nmax_95 is exceeded in the next lower gear, but paragraph 3.5 (b) is not fulfilled.
A violation of paragraph 3.5 (b) Pavailable,i,j ≥ Prequired,j was accepted in the calculation tool up to now but has to be avoided, because it could cause negative effects on the driveability (see figure 1). 30

31. Annex 2, paragraphs 3.3 and 3.5
Therefore the following sentence should be added in order to close this gap:
If paragraph 3.5 (b) Pavailable,i,j ≥ Prequired,j can only be fulfilled by using a gear, where paragraph 3.3 (a) cannot be fulfilled, because the corresponding engine speed exceeds nmax_95, this shall be accepted as long as the engine speed does not exceed nrated.
If paragraph 3.5 (b) Pavailable,i,j ≥ Prequired,j can only be fulfilled in a gear in which nrated is exceeded, the next higher gear shall be used.
The justification for this amendment is shown in figure 1 (second 1567 to 1572). 31

32. n, v and P values vs t for a N1 vehicle
According to the proposal for an amendment of paragraph 3.5
Figure 1 32

33. Conclusions from figure 1
The time section from second 1557 to 1572 demonstrates the necessity for the amendment proposal for paragraph 3.5 (see slide 29).
The required power is only provided in 5th gear although the engine speeds exceed nmax_95.
At second 1566 even the 4th gear would be required by paragraph 3.5 (b), but in this case the engine speed exceeds nrated.
Therefore the 5th gear is chosen.
The lack of the necessary power for just one second will certainly not lead to a violation of the tolerances of the vehicle speed trace. 33

34. Annex 1, paragraphs 1 and 2
Annex 1, paragraphs 1 and 2 are related to the vehicle classification.
The current text specifies that the classification is based on the test vehicle’s rated power to mass in running order ratio.
The Japanese colleagues require that the classification shall be based on the test vehicle’s rated power to kerb mass ratio, because this was the basis for the determination of the borderlines between the classes in the WLTP in-use database. 34

35. Annex 1, paragraphs 1 and 2
Since kerb mass is not defined in the GTR, the Japanese colleagues accepted the proposal to replace “mass in running order” by “mass in running order – 75 kg” in both paragraphs.
This proposal was supported by the GSTF. 35

36. Round robin test for calculation tools
At the last meeting Christoph Lueginger proposed a round robin test for gearshift calculation tools in order to check the tools as well as the common understanding of the text in annex 2.
This proposal was welcomed by the GSTF.
Christoph sent already the data of example vehicles to the GSTF members and asked for data from other members who would like to participate.
It was agreed in the GSTF that a more specific roadmap for this test should be elaborated by Christoph Lueginger and the chairman. 36

37. Thank you for your attention!
End
Thank you for your attention! 37