1. WLTP-11-12e
Christoph Lueginger (BMW), Céline Vallaude (UTAC), Folko Rohde (VW) on behalf of Annex 4 taskforce
wind tunnel method
road load determination with A wind tunnel And a Flat belt or Chassis dynamometer

2. wind tunnel Method Introduction
Within the Annex 4 Taskforce, the Wind Tunnel Method has been developed as an alternative method for road load determination with a) A wind tunnel + flat belt b) A wind tunnel + chassis dynamometer
At IWG #8 in Poona, the first GTR Draft with the principle ideas of the Wind Tunnel Method has been presented
At IWG #10 in Stockholm, the finalized GTR proposal for the Wind Tunnel Method + Flat Belt has been discussed and adopted in principle by IWG
Open Issues: 1) Adoption of tolerances for the approval of facilities 2) GTR proposal for Wind Tunnel Chassis Dyno
Source: VW
Source: BMW
WLTP-11-12e - Wind Tunnel Method,

3. flat belt plus wind tunnel Method GTR Text – Approval of facilities
comparison coast down to wind tunnel method required (adopted)
6.2. Approval of facilities by the responsible authority
The results of the wind tunnel method shall be compared to those obtained using the coast down method to demonstrate qualification of the facilities.
Three vehicles shall be selected by the responsible authority. These vehicles should cover the range of vehicles (e.g. size, weight) planned to be measured with the facilities concerned.
Two separate coast down tests shall be performed with each of the three vehicles according to paragraph 4.3. of this Annex, and the resulting road load coefficients f0, f1 and f2 shall be determined according to that paragraph and corrected according to paragraph The coast down result of a test vehicle shall be the average of its two separate coast downs. If more than two coast down tests are necessary to fulfill the approval of facilities criteria, all valid tests shall be averaged.
Measurement with the wind tunnel method according to the following paragraphs shall be performed on the same three vehicles in the same vehicle conditions, and the resulting road load coefficients f0, f1 and f2 shall be determined. If the alternative preconditioning in paragraph is used, it shall be used for the approval of the facilities as well.
3 vehicles are tested,
selected by authority (adopted)
2 complete coast down tests with each vehicle
(adopted)
If more than two coast down tests are needed, they shall all be considered (recommendation of Annex 4 taskforce)
and wind tunnel method measurement under identical vehicle conditions
(adopted)
WLTP-11-12e - Wind Tunnel Method,

4. flat belt plus wind tunnel Method
GTR Text – Approval of facilities, criteria
Approval criteria
The facility or combination of facilities used shall be approved if the following two criteria are met:
(a) The difference in cycle energy, expressed as , between the wind tunnel method and the coast down method shall be within ± [5] % for each of the three vehicles k, according to the following equation:
where:
εk is the difference in cycle energy for vehicle k between the wind tunnel method and the coast down method, per cent;
Ek,WTM is the cycle energy over a complete Class 3 WLTC  for vehicle k calculated with the road load derived from the wind tunnel method (WTM), calculated according to paragraph 5 of Annex 7, J;
Ek,coastdown is the cycle energy over a complete Class 3 WLTC for vehicle k calculated with the road load derived from the coast down method, calculated according to paragraph 5 of Annex 7, J.;
(b) The average of the three differences shall be within [2] %.
The facility may be used for road load determination for a maximum of [two]  years after the approval has been granted.
Each combination of roller chassis dynamometer or flat belt and wind tunnel shall be approved separately.
allowed deviation of one vehicle lower than 5% cycle energy
(to be adopted at IWG #11)
cycle energy basis for criterion is full WLTC
on average of three vehicles max. 2% deviation (to be adopted at IWG #11)
re-approval every two years
(adopted)
WLTP-11-12e - Wind Tunnel Method,

5. flat belt plus wind tunnel Method Conclusion
The GTR text of the method was discussed intensively and developed together within the Annex 4 group and achieved a high acceptance.
The principle idea of this new method is to frequently approve equivalency of the used combination of wind tunnel and flat belt/chassis dyno every two years.
The tolerances for the approval of facilities are based on the validation measurements and are very stringent compared to other methods.
The proposed tolerances for the approval of facilities (< 5 % for a single car, < 2 % in average for the three tested cars) have been discussed and accepted in the Annex 4 taskforce.
1) The Annex 4 taskforce recommends the adoption of the proposed tolerances.
2) The chassis dyno part shall be adopted separately at the next IWG.
WLTP-11-12e - Wind Tunnel Method,