1. Starting note on gearshift issues
WLTP-14-05e
Cycle / gearshifting
Starting note on gearshift issues
Heinz Steven 1

2. Carry over item from phase 1b
According to the Excel sheet “WLTP Phase 2, working items and schedule “nmin_drive” is listed as carry over item from phase 1b.
It is further expressed that the work should be continued based on the latest VCC proposal.
The members of the phase 1b gearshift issues task force were already contacted and informed that the work needs to be continued on a short time base, because this task is dedicated to phase 2a. 2

3. Further issues to be discussed
Meanwhile OEMs and other parties started testing vehicles according to GTR #15 and, as could be expected, some people found problems.
These problems are mainly related to paragraph 4 of annex 2 of GTR #15 “Additional requirements for corrections and/or modifications of gear use”.
But in addition to that one OEM found driveability problems, which could be related to the low engine speed end of the wot power curve.
And one OEM brought up a problem, where the technical design of the drivetrain is not covered by annex 2 of GTR #15 at all. 3

4. Amendment for nmax
With the Informal document GRPE Rev.2 the text in annex 2 indent (g) was supplemented as follows:
(g) nmax
nmax_95, the minimum engine speed where 95 per cent of rated power is reached, min-1.
If nmax_95 is less than 65 per cent of nrated, nmax_95 shall be set to 65 per cent of nrated.
If 65 per cent of nrated x ndv3 / ndv2 < 1,1 x (nidle × ( nrated -nidle )), nmax_95 shall be set to ,1 x (nidle ×( nrated -nidle )) x ndv2 / ndv3
The text in red colour needs to be added in Informal document GRPE Rev.2. 4

5. Additional requirements, phases
Paragraph 4 of annex 2 of GTR #15 starts with the following:
The initial gear selection shall be checked and modified in order to avoid too frequent gearshifts and to ensure driveability and practicality.
An acceleration phase is a time period of more than 3 seconds with a vehicle speed ≥ 1 km/h and with monotonic increase of vehicle speed. A deceleration phase is a time period of more than 3 seconds with a vehicle speed ≥ 1 km/h and with monotonic decrease of vehicle speed.
It needs to be assessed, whether more than 3 s is appropriate or whether it needs to be reduced or deleted. 5

6. Additional requirements, rank order
Calculations for N2 vehicles with extremely “short” transmission ratios, where the maximum speed of the vehicle is determined by the engine speed limiter in the highest gear and not by the road load resistance led to inconsistencies in the gear sequence calculation.
In order to eliminate these inconsistencies, the rank order of the additional requirements for corrections and/or modifications of gear use need to be rearranged as follows:
(a), (b), (c), (d), (e), (f) --> (a), (b), (f), (c), (d), (e)
(a), (b) are related to accelerations, (c) to (d) are related to decelerations and (f) is related to the replacement of too short gear sequences. 6

7. Additional requirements, clearer text
And old (c), new (d) should be amended as follows:
……If the duration of a gear sequence is 2 seconds, it shall be replaced by gear 0 for the 1st second and for the 2nd second with the gear that follows after the 2 second period. The clutch shall be disengaged for the 1st second.
Example: A gear sequence 5, 4, 4, 2 shall be replaced by 5, 0, 2, 2.
It needs to be clarified that this requirement shall only be applied, if the gears before and after the 2 second period are > 0. 7

8. Additional requirements, clearer text
And old (e), new (f) should be amended as follows:
If the deceleration phase is the last part of a short trip shortly before a stop phase and the second gear gear in this phase would only be used for up to two seconds, the clutch may be either disengaged or the gear lever placed in neutral and the clutch left engaged. (Examples: A gear sequence of : 4, 0, 2, 2, 0 for the last 5 seconds before a stop phase shall be replaced by 4, 0, 0, 0, 0. A gear sequence of 4, 3, 3, 0 for the last 4 seconds before a stop phase shall be replaced by 4, 0, 0, 0.)
A downshift to first gear is not permitted during those deceleration phases.
The proposed modifications are indicated in red. 8

9. Driveability problems
One OEM reported driveability problems.
The problems are related to the low engine speed range, where the wot power increases rapidly with increasing engine speed.
Figure 1 shows an example.
Accelerations starting at engine speeds in the red part result in poor repeatability.
This issue should be more deeply discussed in the gearshift issues task force.
One solution could be to increase the safety margin for such parts of the wot curve. 9

10. Driveability problems
Figure 1 10

11. Gear specific wot power curves
One OEM reported, that there might be vehicles in future, that have gear specific wot power curves.
This is not covered by GTR #15.
In principle, this problem can be solved but makes things much more complex and complicated. 11

12. Combination of downscaling and speed cap
Another issue, that needs to be clarified, is an annex 1 related issue: the combination of downscaling and speed cap.
The authors interpretation of annex 1 of GTR #15 is as follows:
A vehicle gets downscaling, when the ratio between the maximum power required within the WLTC and rated power exceeds the threshold value listed in paragraph 8.3 of annex 1 of GTR #15.
This results in a modified (downscaled) cycle.
If the maximum speed of the cycle exceeds the maximum speed of the vehicle, paragraph 9 of annex 1 of GTR #15 needs to be applied. 12

13. Combination of downscaling and speed cap
This will then lead to a capped speed cycle based on the downscaled cycle.
It needs to be discussed, whether this interpretation is right or not and whether the text in annex 1 should be modified to be more precise. 13

14. Thank you for your attention!
End
Thank you for your attention! 14