1. WLTP rev1e
BMW,
Christoph Lueginger
WLTP Road Load Family
Proposal on a family definition for road load determination

2. The road load influences
WLTP Road Load Family
The road load influences
influences on road load
assessed by
mass
combined approach
rolling resistance
aerodynamics
drivetrain type (2WD/4WD)
defined in
road load family
drivetrain losses
Annex 4
gearbox type
electric machine
uses interpolation family definition, if not decoupled
not relevant
for road load
The engine has no influence on the road load values (f0,f1,f2), as it is decoupled, apart from:
weight, aerodynamic (and indirectly rolling resistance) influences.  But they are covered by the calculation of the individual road load coefficients!
As the test vehicle selection is based on a worst case approach (already defined in Annex 4), drivetrain losses are considered properly anyway.
WLTP Road Load Family, BMW,

3. WLTP Road load family Introduction
Road load testing for each interpolation family causes a lot of effort, although differences between interpolation families could be calculated easily, as long as they are related to road load (i.e. RR, mass, aerodynamics).
Introducing a road load family can be done quite easily, as it uses available definitions.
The only new part, which needs a definition, is the allowed interpolation range. It has to be slightly bigger than the allowed range for the interpolation family to include for mass and aerodynamic differences of different engines.
Conforming that interpolation range and the concept itself, it was agreed to perform validation tests. See minutes of Geneva-meeting 06/2014:
WLTP Road Load Family, BMW,

4. performed measurements
WLTP road load Family
Validation Program, introduction
Four vehicles have been selected (from what was available!) and some road load parameters have been adjusted in order to cover the needed range as good as possible and within the constraints of the road load family criteria (e.g. n/v was 11%, same drivetrain: RWD, AT).
performed measurements
selection
coast down
1-2 tests, average taken, 11/2014 and 03/2015
weight
adjusted within vehicle limits, to get an equal distribution
aerodynamic drag
as it is
rolling resistance (according to GTR)
wheels selected within optional equipment
vehicle
318dA
weight 
aero RR
vehicle
320dA
weight 
aero  RR
vehicle
328iA
weight 
aero  RR 
vehicle
435iA
weight 
aero  RR 
WLTP Road Load Family, BMW,

5. Validation Program, validated range
WLTP road load Family
Validation Program, validated range
Proposed maximum range of 35% was validated as far as it was possible with the available vehicles.
WLTP Road Load Family, BMW,

6. Validation Program, road load comparison
WLTP road load Family
Validation Program, road load comparison
Not only the values, but also the shape matches very well between coast down and calculated result.
Please notice, that here only F1F1F2 is shown, mass influence has to be considered on top.
WLTP Road Load Family, BMW,

7. Validation Program, result and conclusion
WLTP road load Family
Validation Program, result and conclusion
 Calculation of road load is at least as accurate as coast down testing, and very close to its result (0% and 0.5% cycle energy). Difference can be a result of coast down variance as well.
 This maximum error of 0.08 MJ corresponds to approx. 0.5 g/km CO2 within WLTP.
 Road load family is validated!
WLTP Road Load Family, BMW,

8. from WLTP-DTP-LabProcICE-172 - Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family
definition proposal
Starting from the interpolation family and dropping the engine related issues (decoupled parts).
Input of Japan can be included in the definition, if not already covered by other parts of the GTR.
Fine-tuning can be still done.
from WLTP-DTP-LabProcICE Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family, BMW,

9. from WLTP-DTP-LabProcICE-172 - Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family
proposal for inclusion in Annex 4
Use vehicle definition for interpolation family as a starting point, but select test vehicles from road load family instead.
from WLTP-DTP-LabProcICE Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family, BMW,

10. WLTP Road Load Family Conclusion, proposal
The family definition and its inclusion in Annex 4 is straight forward by using existing definitions and formulas. Improvement of the wording is welcomed of course.
The interpolation range covers to a huge extend the already existing range for an interpolation family and an "add-on" for differences resulting from different engines to be included in one road load family (weight, aerodynamics).  Therefore the range is no extended significantly.
Additionally, the concept was validated by testing, which shows a very good accuracy of the calculation method.
The Annex 4 taskforce recommends the following:
Adopt the family description and add it as a new paragraph 5.7.
Adopt the way of including it into the GTR, Annex 4,
Adopt the maximum interpolation range of 35% cycle energy.
WLTP Road Load Family, BMW,

11. from WLTP-DTP-LabProcICE-172 - Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family
Backup
Backup
from WLTP-DTP-LabProcICE Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family, BMW,

12. from WLTP-DTP-LabProcICE-172 - Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family
Calculation of road load influences, Annex 7
Calculation of road load for individual vehicles in the CO2 vehicle family
Calculation of cycle energy per phase
Calculation of the CO2 value for an individual vehicle by the CO2 interpolation method
Formulas for road load family
Formulas for both families
Formulas for CO2-family
from WLTP-DTP-LabProcICE Comparison RLD flatbelt_VW.pdf
WLTP Road Load Family, BMW,

13. CO2-influence of road load family
WLTP Road load family
CO2-influence of road load family
Delta cycle energy WLTC
Delta CO2 for an average vehicle
Road load family
35%  approx. 5 MJ
approx. 38 g/km*
CO2 family
max. approx. 3.8 MJ
max. 30 g/km or 20 %
The theoretical CO2-range of the road load family is higher, which is in the order of the additional road load difference resulting from different engine mass (e.g. 4cyl / 6cyl / gasoline / Diesel) or aerodynamic influence (radiator areas).
(*) The CO2 range of ~ 38 g/km is a theoretical value, as different engines are included in a road load family, that are obviously in separate CO2-families.
CO2-influence derived from GTR Willans factors and confirmed with BMW simulations: Willans for Diesel..gasoline: g CO2 / MJ  g CO2 / 23.3 km * 5 MJ = g/km
5 MJ or 35 % as a road load range for the road load family is a reasonable tolerance, which allows to include all similar vehicles into one family. Thus reducing test effort but ensuring that misuse is impossible.
WLTP Road Load Family, BMW,