1. Applicability of Driving Index
WLTP-06-16e
Study on
Applicability of Driving Index
(defined in SAE J2951)
to WLTC

2. < Background >
It is quite reasonable to have tolerance for each set point under the emission/fuel consumption test procedure from the view points of testing practicability. On the other hands, the tolerance have a possibility to create test result variations. These variations may cause inappropriate information to customer and/or unfair competitions.
WLTP has been trying to narrow the tolerance and to stringent the test procedure, however, it still has a room for data variations.
European commission has been reviewing all possible flexibilities in the WLTP gtr and their studies are under going with support of TNO and TUG.
Japan focus on driving tracability as one of the most significant factors since new test cycle profile has changed to micro-transient mode from trapezium mode.

3. Trace technique ： Normal (keep the target trace as much as possible),
< Overall Test Plan >
Test vehicles：
Trace technique ： Normal (keep the target trace as much as possible),
Smoothing, Rough, Rough-2 (see below)
# of Tests ：
Vehicle A：1.3L, Gasoline, CVT, have few difficulty to follow the trace
Vehicle B：0.66L, Gasoline, CVT, have difficulty to follow the trace
 study how to treat WOT driving portions
Vehicle C：2.0L, Gasoline, 6MT
 study how to treat gear shift portions
Vehicle condition
Normal-1
Smooth
Rough-1
Rough-2 (Slightly)
Cold 1 -
Hot 2
Smoothing
Rough
higher than target
lower than target
Smooth acceleration
Rough pedal operation

4. < Conclusion >
It was observed that drive trace indexes are able to detect the unexpected driving technique (smooth or rough) and to eliminate the inappropriate cycle trace by applying the appropriate criteria. (ASCR and RMSSE are possible candidate indexes, on the other hands, ER, DR and EER have weakness due to offset of positive and negative side)
It was observed that special treatment during wide-open-throttle operation is necessary.
More study on how to treat gear shift events is required.
It was observed that negative side (smooth driving) drive trace index has slight correlation with FC value, on the other hands, positive side (rough driving) has no correlation with FC value.

5. < Request to all CPs >
Evaluate the drive trace index (provide calculation tool, if necessary).
Speed sampling rate : 10Hz (  need to modify gtr description).
< Next Actions >
Provide specific procedure for WOT operation and gear shift events.
Propose driving index criteria for test validity.
Collaborate “normalization procedure” with TUG.

6. Driving Indexes defined in SAE J2951
Engine force
FENG = [F0 + F1*V + F2*V * ETW * a]+
Engine work increment
Wi = FENGi * di
Cycle energy (CE)
CE = ΣWi = Σ[(F0 + F1*Vi + F2*Vi * ETW * ai) * di]+
Energy rating (ER)
ER = (CED - CET) / CET*100
Distance rating (DR)
DR = (DD - DT) / DT*100
Energy economy rating (EER)
EER = [1 – (DR / ) / (ER / )] * 100
Combined ER and DR
Absolute speed change rating (ASCR)
ASCR = (ASCD - ASCT) / ASCT * 100
ASC = ⊿t*Σ|ai|
Integrate the acceleration (= speed fluctuation)
Root mean squared speed error (RMSSE)
RMSSE = √(Σ(VDi - VTi)2) / N)
Integrate the difference between target speed and actual speed

7. Test results-1 (Vehicle A)
Energy rating [ER]
Distance rating [DR]
rough
smooth
smooth
rough
depends on number of opportunity to acceleration
Energy economy rating [EER]
Absolute speed change rating [ASCR]
obvious difference
rough
smooth
rough
smooth

8. Test results (Vehicle A)
Root mean squared speed error [RMSSE]
Impact on fuel economy
RMSSE becomes higher value when Smoothing/Rough driving
worse
better
ER, DR, EER，ASCR and RMSSE became closer to zero when the vehicle follow the target speed (Normal driving).
In case of a smoothing or rough driving, those index values became higher or lower value. This indicates that there is a possibility to detect the inappropriate driving.

9. Driving indexes and fuel economy impact (vehicle A)
●LOW hot ▲MID hot ■HIGH hot ◆ExHIGH hot ●LMH hot ▲LMHxH hot ○LOW cold △MID cold □HIGH cold ◇ExHIGH cold ●LMH cold ▲LMHxH cold
Energy rating [ER]
Distance rating [DR]
Energy economy rating [EER]
Possible criteria
Possible criteria
worse
better
worse
better
worse
better
linear relationship
linear relationship
Absolute speed change rating [ASCR]
Root mean squared speed error [RMSSE]
Possible criteria
Possible criteria
worse
better
worse
better

10. Summary (Vehicle A) ER DR Smooth driving: Negative value
Rough driving: Positive value
Index value varies depend on each phase DR
Smooth driving: Positive value
Rough driving: Negative value
Difficult to detect inappropriate driving technique
EER
Almost same characteristics as ER
a significant difference according to driving techniques
linear relationship to fuel economy impact (only smooth driving)
ASCR
RMSSE

11. Consideration of special treatment during wide-open-throttle
During acceleration events, vehicle B could NOT follow the target speed with wide open throttle (WOT) operation.
Need to consider how to treat in case of WOT operation.
Special treatment: treat as same speed as target speed during WOT operation. (index value will be over-evaluated when excluding all WOT portions from calculation)
unable to follow despite of WOT operation

12. Test results（Vehicle B）
Energy rating [ER]
Energy rating [ER] with special treatment
Distance rating [DR]
Distance rating [DR] with special treatment

13. Test results （Vehicle B）
Energy economy rating [EER]
[EER] with special treatment
decrease
Absolute speed change rating [ASCR]
ASCR with special treatment
not change so much

14. Test results (Vehicle B）
Root mean squared speed error [RMSSE]
RMSSE with special treatment
Special treatment is necessary
Impact on fuel economy
worse
better

15. Driving indexes(with special treatment) and fuel economy impact (vehicle B)
●LOW hot ▲MID hot ■HIGH hot ◆ExHIGH hot ●LMH hot ▲LMHxH hot ○LOW cold △MID cold □HIGH cold ◇ExHIGH cold ●LMH cold ▲LMHxH cold
Energy rating [ER] with special treatment
Distance rating [DR] with special treatment
Energy economy rating [EER] with special treatment
worse
better
worse
better
worse
better
linear relationship
Absolute speed change rating [ASCR] with special treatment
Root mean squared speed error [RMSSE] with special treatment
Possible criteria
Possible criteria
worse
better
worse
better

16. Driving indexes(without special treatment) and fuel economy impact (vehicle B)
●LOW hot ▲MID hot ■HIGH hot ◆ExHIGH hot ●LMH hot ▲LMHxH hot ○LOW cold △MID cold □HIGH cold ◇ExHIGH cold ●LMH cold ▲LMHxH cold
Energy rating [ER]
Distance rating [DR]
Energy economy rating [EER]
worse
better
worse
better
worse
better
Absolute speed change rating [ASCR]
Root mean squared speed error [RMSSE]
worse
better
worse
better
Need special treatment

17. Summary (Vehicle B) ER, DR, EER
with special treatment
ER, DR, EER
could not detect inappropriate driving technique, due to offset positive and negative side.
ASCR
ASCR won’t change much when special treatment was applied.
ASCR is able to detect the smooth and/or rough driving.
RMSSE
RMSSE need special treatment to detect the smooth and/or rough driving.
with special treatment

18. Test results (Vehicle C）
During gear shift events, no tolerance is required.
Treat as same speed as target speed during gear shift events±1sec.
gearshifting±1sec

19. Test results (Vehicle C）
Energy rating [ER]
Energy rating [ER] with special treatment
become worse!!
Distance rating [DR]
Distance rating [DR] with special treatment

20. Test results (Vehicle C）
Energy economy rating [EER]
[EER] with special treatment
become worse!!
Absolute speed change rating [ASCR]
ASCR with special treatment
become worse!!

21. Test results (Vehicle C）
Root mean squared speed error [RMSSE]
RMSSE with special treatment
変化小さい
Impact on fuel consumption
To treat as same speed as target speed during gear shift events is not effective.
More study for gear shift events is necessary.
worse
better

22. Driving indexes(with special treatment) and fuel economy impact (vehicle C)
●LOW hot ▲MID hot ■HIGH hot ◆ExHIGH hot ●LMH hot ▲LMHxH hot ○LOW cold △MID cold □HIGH cold ◇ExHIGH cold ●LMH cold ▲LMHxH cold
Energy rating [ER] with special treatment
Distance rating [DR] with special treatment
Energy economy rating [EER] with special treatment
worse
better
worse
better
worse
better
Absolute speed change rating [ASCR] with special treatment
Root mean squared speed error [RMSSE] with special treatment
worse
better
worse
better

23. Driving indexes(without special treatment) and fuel economy impact (vehicle C)
●LOW hot ▲MID hot ■HIGH hot ◆ExHIGH hot ●LMH hot ▲LMHxH hot ○LOW cold △MID cold □HIGH cold ◇ExHIGH cold ●LMH cold ▲LMHxH cold
Energy rating [ER]
Distance rating [DR]
Energy economy rating [EER]
worse
better
worse
better
worse
better
Absolute speed change rating [ASCR]
Root mean squared speed error [RMSSE]
Possible criteria
worse
better
worse
better
Possible criteria

24. Summary (Vehicle C)
with special treatment
It was observed that the treatment (same as target speed) doesn’t work for gear shift events.
More effective treatment during gear shift events is necessary to adopt driving index requirement.
with special treatment