WLTP
H.S.
Further modifications on the gearshift
calculation tool
Heinz Steven
09.03.2013
1
Background
H.S.
• In order to take into account the technical progress and the
increased variety of transmission design (e.g. 4-speed up to 7speed gearboxes) shift points at fixed vehicle speeds are no
longer appropriate.
• In order to reflect practical use as well as fuel efficient driving
behaviour as much as possible, the prescriptions are based
on the balance between the power required for driving
resistance and acceleration and the power provided by the
engine in all possible gears at a specific cycle phase.
• In order to cover the wide range of rated engine speeds (e.g.
3200 to 8000 min-1) depending of the engine technology, a
calculation tool was developed which is based on normalised
engine speeds (normalised to the span between idling speed
and rated engine speed) and normalised full load power
curves (normalised to rated power) versus normalised engine
speed.
2
H.S.
Input data
parameter
Prated
unit
kW
s
min-1
nidle
min-1
-1
nmin_drive
min
mt
kg
ngmax
Idling speed, the engine speed when the gear lever is in neutral and the vehicle is not
in motion.
minimum engine speed for gear numbers ≥ 3 when the vehicle is in motion. The
minimum value is determined by n idle + 0,125×(s - nidle). Higher values can be required
by the manufacturer.
test mass of the vehicle
number of foreward gears
ndvi
min-1/(km/h)
f0
N
f1
N/(km/h)
f2
N/(km/h)2
Pwot(nnorm)/Prated
definition/description
The maximum power of the engine as declared by the manufacturer.
Rated engine speed, the engine speed at which an engine develops its maximum
power. If the maximum power is developed over an engine speed range, s is
determined by the mean of this range.
ratio of engine speed and vehicle speed for gear i, i = 1 to ng max
driving resistance coefficients as defined in Annex 4
Normalised full load power curve as function of normalised engine speed
nnorm = (n - nidle)/(s - nidle)
3
Modifications performed during
validation 2
H.S.
• This calculation tool was used during validation 2 of the WLTP
project.
• Some comments were already made within the validation 2
time period and led to the following modifications for the 2.
version of the tool in conjunction with the implementation of
the modified cycle versions for low powered vehicles:
 options for the choice of lower n_min_drive values (for
gears >= 3) for sensitivity studies but not for validation 2,
 n_min_2 was added as input parameter. n_min_2 is the
minimum engine speed in gear 2. n_min_2 was defined as
1,25*idling_speed.
 It is now recommended to set n_min_2 to
1,15*idling_speed. The minimum value that can be used for
the calculation is 1,1*idling_speed.
4
Modifications performed during
validation 2
H.S.
 The safety margin accounting for the difference between
stationary wot power curve and the power available during
transient conditions could be chosen as input parameter in
the 1. version.
 The choice of 90% was recommended. The safety margin
was then set to 90% and cannot be changed any more in
the 2. version.
5
Summary of discussion points
H.S.
• The comments after validation 2 can be summarised as follows:
• Input data:
 Default values for the full load power curve and for driving
resistance coefficients should not be provided in a final
version.
 The safety margin for the full load power curve needs to be
updated/improved, the input data for the curve need to be
simplified.
 Uniform input data for a vehicle family.
6
Summary of discussion points
H.S.
• Downshifts:
 Downshift to 1. gear: Although the number of downshifts to
the 1. gear within a short trip were reduced with version 2
compared to version 1, there is still a need for further
improvement.
 Downshifts by more than 2 gears.
• Approach
 The current approach aimes at a compromise between
economic driving and representativity with respect to in-use
data,
 The current n_min_drive concept is a bit more favourable
for Diesel engines compared to Petrol engines.
7
Summary of discussion points
H.S.
• As a consequence the number of shift points is higher
compared to a vehicle speed based system.
• It should be assessed, how the number of shift points
correlates with the in-use data and whether or to what extent it
could be reduced by an increase of engine speeds.
8
Modifications made for the 3. version
H.S.
• For the 3. version of the calculation tool, which is not yet
distributed, the following modifications were made:
 An additional safety margin can be applied on the wot
power curve, additional to the 10% default margin.
 The additional safety margin is fully applied at idling speed
and then linearily reduced to 0 at rated speed.
 As an example, if one chooses 10% for the additional
margin, the effective safety margin at idling speed is 20%
and at rated speed or higher speeds 10%.
 In order to avoid downshifts to the 1. gear within a short
trip, the choice of n_min_2 was deleted and replaced by
the following requirements:
9
Modifications made for the 3. version
H.S.
 The minimum engine speed in 2. gear during acceleration
phases starting from standstill is determined by the
maximum of
 1,15*idling_speed or
 0,03*(rated_speed –idling_speed) + idling_speed
 The minimum vehicle speed at which the 2. gear during
deceleration phases or acceleration phases within a short
trip will be kept is detemined by a theoretical
corresponding engine speed of 0,9*idling_speed.
 If this is fulfilled, the 2. gear is kept and the engine speed
is set to the maximum as defined in the first bullet point on
this slide as long as this value exceeds the theoretical
corresponding engine.
 In order to avoid engine stalling, the clutch is disengaged.
10
Modifications made for the 3. version
H.S.
 The application of a maximum speed cap was implemented
into the tool. In cases where the original cycle speed
exceeds the cap, the cycle speed is limited to the cap.
 In addition to that the calculation tool was further modified
in that way, that it reduces the vehicle speed in cases
where the required acceleration exceeds the available
acceleration power and where the maximum speed of the
vehicle is lower than the cycle speed.
 In order to enable the assessment of speed caps versus
cycle downscaling, the latter was implemented as
additional option for the extra high speed phases of the
class 2 and class 3 cycles.
 But the downscaling is restricted to the time sections with
high speeds within the extra high speed phases (see
figures 1 and 2).
11
Downscaling example for class 3
versions 5.1 and 5.3
H.S.
140
120
vehicle speed in km/h
100
80
v_set version 5.3
60
v_downscaled
40
20
0
1440
1500
1560
1620
time in s
1680
1740
Figure 1
1800
12
Downscaling example for class 2
version 2
H.S.
140
120
vehicle speed in km/h
100
80
60
WLTC class 2, version 2
40
v_downscaled
20
0
1440
1500
1560
1620
time in s
1680
1740
Figure 2
1800
13
Remaining issues
H.S.
• The remaining issues that are not yet delt with are:
 The safety margin for the full load power curve needs to be
updated/improved, the input data for the curve need to be
simplified.
 Uniform input data for a vehicle family.
 The current n_min_drive concept is a bit more favourable
for Diesel engines compared to Petrol engines.
 The current approach aims at a compromise between
economic driving and representativity with respect to inuse data. As a consequence the number of shift points is
higher compared to a vehicle speed based system.
 It should be assessed, how the number of shift points
correlates with the in-use data.
14