WLTP-DHC-10-15
WLTP
H.S.
Comparison of WLTP unified database
distributions and WLTC rev2 distributions
Heinz Steven
08.10.2011
1
Overview
H.S.
• The comparison includes the following aspects
• Different acceleration classification systems (km/h/s
versus m/s²),
• Consideration of idling phases,
• Consideration of negative accelerations,
• Discussion of database for extra high speed part,
• Further discussion point
• Selection approach for short trips,
• The following figures show the comparison of acceleration
distributions of the unified WLTP database and WLTC rev2
for the different speed parts. The distributions of the unified
WLTP database were delivered by JARI, they contain also the
idling phases.
2
Comparison of acc distributions, low
H.S.
100%
90%
80%
unified WLTP distribution
cum frequency
70%
low, with idle
WLTC rev2, low
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 1
1.5
2.0
3
Comparison of acc distributions,
medium
H.S.
100%
90%
80%
unified WLTP distribution
cum frequency
70%
medium, with idle
WLTC rev2, medium
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 2
1.5
2.0
4
Comparison of acc distributions, high
H.S.
100%
90%
80%
unified WLTP distributions
cum frequency
70%
high, with idle
WLTC rev2, high
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 3
1.5
2.0
5
Comparison of acc distributions, extra
high
H.S.
100%
90%
80%
unified WLTP distributions
cum frequency
70%
extra high, with idle
WLTC rev2, extra high
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 4
1.5
2.0
6
Observations, remarks, questions
H.S.
• Only 30% of the operation time or even less is related to
positive accelerations.
• Where is the justification to include the idling phases in the
distributions and the least square calculation?
• The WLTC rev2 distributions for the low and the medium
speed parts show lower dynamics in the positive
acceleration sections than the database distributions.
• For the high and extra high speed parts it is the opposite, but
less pronounced.
• Deviations to lower dynamics have the same influence on the
least square sum as deviations of the same order to higher
dynamics.
• This led to the differences shown in the comparison.
7
Observations, remarks, questions
H.S.
• This situation is unsatisfactory, especially because the
acceleration phases determine the major parts of the CO2
and NOx emissions in real traffic.
• Figure 5 shows results of PEMS measurements performed
with 3 different EURO 4 Diesel vehicles in Stuttgart within a
project sponsored by LUBW.
• The routes driven were related to the low speed part. The
idling and deceleration phases determine about 10% of CO2
and NOx emissions each, the by far most important phase is
the acceleration phase.
• In this context, the situation will not be improved enough, if
the idling phases are disregarded for the analysis (see
figures 6 and 7).
8
PEMS measurement results in real
traffic
100%
0.1%
9.7%
90%
H.S.
18.6%
10.1%
23.9%
80%
70%
25.2%
45.6%
acceleration
Percentage
60%
49.2%
cruise
50%
40%
stop
deceleration
52.0%
32.7%
PEMS measurements, averages of 3
EURO 4 Diesel vehicles
30%
34.2%
30.6%
20%
10%
23.5%
24.0%
10.4%
10.0%
CO2
NOx
0%
duration
distance
Figure 5
9
Comparison of acc distributions, low
H.S.
100%
90%
unified WLTP distributions
80%
cum frequency
70%
low, without idle
WLTC rev2, low
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 6
1.5
2.0
10
Comparison of acc distributions,
medium
H.S.
100%
90%
unified WLTP distributions
80%
cum frequency
70%
medium, without idle
WLTC rev2, medium
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 7
1.5
2.0
11
Comparison of acc distributions,
medium
H.S.
100%
90%
unified WLTP distributions
80%
cum frequency
70%
medium, without idle
WLTC rev2, medium
60%
50%
40%
30%
20%
10%
0%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
acceleration in m/s²
1.0
Figure 7
1.5
2.0
12
Observations, remarks, questions
H.S.
• The development approach should be related to the positive
acceleration section instead.
• When focussing on this section the lower dynamics of the
WLTC rev2 in comparison to the database distributions for
low and medium speeds becomes more obvious (see figures
8 and 9).
• But the different acceleration classification systems used by
JARI and JRC/Steven become important within this context,
especially for the high and extra high speed parts (see figure
10).
13
Comparison of acc distributions, low
H.S.
100%
90%
80%
cum frequency
70%
low, Jari, km/h/s
60%
low, Steven, m/s²
50%
WLTC rev2, low, km/h/s
unified WLTP distributions
WLTC rev2, low, m/s²
40%
30%
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 8
2.5
14
Comparison of acc distributions,
medium
H.S.
100%
90%
80%
cum frequency
70%
medium, Jari, km/h/s
60%
medium, Steven, m/s²
WLTC rev2, medium, km/h/s
50%
unified WLTP distributions
WLTC rev2, medium, m/s²
40%
30%
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 9
2.5
15
Comparison of acc distributions, high
and extra high
H.S.
100%
90%
80%
70%
cum frequency
high, Jari, km/h/s
60%
extra high, Jari, km/h/s
50%
high, Steven, m/s²
40%
extra high, Steven, m/s²
30%
unified WLTP distributions
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 10
2.5
16
Further analysis
H.S.
• In order to further check these observations additional
analysis work was performed by developing regional cycles
for the EU and the US. The key parameters of these cycles
are tabled in Annex A.
• Figures 11 to 14 show the results for the positive acceleration
sections and the different speed parts.
• First of all it needs to be mentioned that the distributions for
the unified WLTP database and the EU regional database are
pretty close together, while the distributions of the regional
US database show higher dynamics for the low and medium
speed parts and less pronounced for the high speed part.
The distributions for the extra high speed parts are almost
identical.
• The corresponding distributions for the candidate cycles
show different trends.
17
Comparison between regions, low
H.S.
100%
90%
low, EU DB
80%
low, WLTP DB
low, US DB
70%
cum frequency
WLTC rev2
WLTC EU regional
60%
WLTC US regional
50%
40%
30%
20%
10%
0%
0
0.5
1
a in m/s²
1.5
Figure 11
2
18
Comparison between regions, medium
H.S.
100%
90%
medium, EU DB
80%
medium, WLTP DB
medium, US DB
70%
cum frequency
WLTC rev2
WLTC EU regional
60%
WLTC US regional
50%
40%
30%
20%
10%
0%
0
0.5
1
a in m/s²
1.5
Figure 12
2
19
Comparison between regions, high
H.S.
100%
90%
high, EU DB
80%
high, WLTP DB
high, US DB
70%
cum frequency
WLTC rev2
WLTC EU regional
60%
WLTC US regional
50%
40%
30%
20%
10%
0%
0
0.5
1
a in m/s²
1.5
Figure 13
2
20
Comparison between regions, extra
high
H.S.
100%
90%
extra high, EU DB
80%
extra high, WLTP DB
extra high, US DB
70%
cum frequency
WLTC rev2
WLTC EU regional
60%
WLTC US regional
50%
40%
30%
20%
10%
0%
0
0.5
1
a in m/s²
1.5
Figure 14
2
21
Observations, remarks, questions
H.S.
• In case of the low speed part the WLTC rev2 is less dynamic,
the regional candidates are more dynamic compared to the
database distributions.
• The results for the medium speed part show a different
picture: WLTC rev2 once again less dynamic, EU regional in
the lower acceleration area more dynamic, in the higher
acceleration area good coincidence, US regional with an
overall very good fit to the database.
• High speed part: WLTC rev2 and EU regional in the lower
acceleration area more dynamic, in the higher acceleration
area good coincidence, US regional less dynamic than the
database.
• Extra high speed part: WLTC rev2 more dynamic in the
middle, EU regional more dynamic and the US regional with a
good fit to the corresponding database.
22
Application of a modified approach
H.S.
• These results underline the need for an alternative
development approach.
• In a further step the cycle development approach was
modified in that way that the v, a distributions were limited to
positive accelerations only. An alternative cycle was then
developed based on these distributions.
• Comparisons of the resulting acceleration distributions with
the database distributions are shown in figures 15 to 18.
• In these figures two versions of the alternative cycle are
shown: “original” and “modified”.
• “Modified” means, that the following modifications were
applied to the original ST:
 No decelerations within a ST below 10 km/h,
 Accelerations were limited to +/- 2 m/s².
23
H.S.
Comparison for pos. acc, low
100%
90%
80%
cum frequency
70%
low, WLTP
60%
WLTC rev2, low
50%
WLTC cand pos acc only, orig
unified WLTP distributions
WLTC cand pos acc only, modified
40%
30%
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 15
2.5
24
Comparison for pos. acc, medium
H.S.
100%
90%
80%
cum frequency
70%
medium, WLTP
60%
WLTC rev2, medium
50%
WLTC cand pos acc only, modified
unified WLTP distributions
WLTC cand pos acc only, orig
40%
30%
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 16
2.5
25
H.S.
Comparison for pos. acc, high
100%
90%
80%
cum frequency
70%
high, WLTP
WLTC rev2, high
60%
WLTC cand pos acc only, modified
WLTC cand pos acc only, orig
50%
40%
30%
unified WLTP distributions
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 17
2.5
26
Comparison for pos. acc, extra high
H.S.
100%
90%
80%
cum frequency
70%
extra high, WLTP
60%
WLTC rev2, extra high
50%
WLTC cand pos acc only, modified
WLTC cand pos acc only, orig
40%
30%
unified WLTP distributions
20%
10%
0%
0.0
0.5
1.0
1.5
acceleration in m/s²
2.0
Figure 18
2.5
27
Application of a modified approach
H.S.
• These modifications do not deteriorate the cycle dynamics
but improve the driveability significantly.
• The acceleration distributions of the modified approach
(consideration of only positive accelerations) for the low and
medium parts fit significantly better to the database
distributions than the WLTC rev2 distributions.
• For the high speed part the modified approach results in
slightly higher dynamics than the WLTC rev2.
• The acceleration distribution of the modified approach are
significantly more dynamic than the WLTC rev2 distribution
and the corresponding database distribution.
• But as already stated in a previous presentation, alternative
assessment criteria should be used for the extra high speed
part, because - due to the time limitations – this part cannot
cover the whole driving condition range of the database.
28
Conclusions, recommendations
H.S.
• The cycle development approach should be modified in that
way that negative accelerations should be disregarded.
• The classification steps for the acceleration distributions
should be smaller than 1 km/h/s (at least 0,5 km/h/s). A change
to the m/s² unit and 0,1 m/s² steps would be even more
preferable.
• It is highly recommended to include the v, v*a_pos
distributions in the analysis and development process.
• It is recommended to modify the short trips in order to avoid
driveability problems:
 No decelerations within a ST below 10 km/h,
 Limit accelerations to +/- 2 m/s².
29
Conclusions, recommendations
H.S.
• It is recommended to apply the original approach for the
determination of the different short trip durations for the low
speed part.
• This approach was already applied to the idling phases
duration determination for WLTC rev2 in order to avoid too
long idling phases.
• The same argument is also valid for the short trips. It would
ease a better balance between the short trips and avoid too
short ST.
30
Annex A, Key cycle parameter
H.S.
• The key cycle parameter for the WLTC rev2 and the EU and
US regional candidate cycles are listed in the following
tables.
31
Comparison of key cycle parameter
H.S.
duration in s
v_ave in km/h
speed class
WLTC rev2 EU cand US cand WLTC rev2 EU cand US cand
low
589
620
375
18.2
20.3
20.1
medium
433
323
419
41.6
39.9
42.3
high
455
369
416
55.5
56.1
58.6
extra high
323
488
590
86.0
90.4
87.8
p_stop
number of ST
WLTC rev2 EU cand US cand WLTC rev2 EU cand US cand
low
25.3%
19.0% 25.3%
5
6
5
medium
11.1%
8.6%
15.3%
1
1
3
high
6.6%
4.3%
6.7%
1
1
1
extra high
2.2%
1.4%
2.2%
1
1
1
speed class
Table 1
32
Comparison of key cycle parameter
H.S.
a_max in m/s²
a_pos_ave in m/s²
WLTC rev2 EU cand US cand WLTC rev2 EU cand US cand
low
1.47
1.65
2.10
0.47
0.49
0.61
medium
1.50
1.64
2.05
0.42
0.39
0.56
high
1.82
1.73
1.46
0.58
0.45
0.37
extra high
2.06
1.76
1.82
0.47
0.37
0.29
speed class
v*a_pos_ave in m²/s³
RPA in kWs(kg*km)
WLTC rev2 EU cand US cand WLTC rev2 EU cand US cand
low
2.81
3.35
4.35
0.157
0.224
0.331
medium
4.38
4.51
6.53
0.148
0.166
0.256
high
6.73
5.45
5.60
0.138
0.187
0.181
extra high
9.22
7.82
5.98
0.117
0.157
0.118
speed class
Table 2
33