1. HDV CO2 verification test (“SiCo”)
HDV CO2 Editing board

2. Overview on the Method
Measurement of torque on driven axle and of fuel flow shall allow accurate verification of drive train efficiency without the uncertainties related to the chassis dynamometer calibration. Main uncertainty is power demand of auxiliaries.
Method under consideration:
Comparison of simulated and measured specific fuel consumption [g/kWh]
Differential
Engine
Gearbox
Fuel flow
Aux.
Test point areas calculated by VECTO ex-ante from vehicle specific load points in CO2 cycles
Options:
Selected steady state points (closest to VECTO simulation, no transient effects in engine operation, no torque interruption during gear shifts etc.)
WHVC with road gradients as developed in HDH-HILS and/or CO2 test cycles (may be used also to assess efficiencies for future technologies not covered by VECTO)
PEMS tests (with torque measurement at axle): not in actual test program but may be analysed if 2) shows good results
Wheel Power

3. Overview possible testing concepts
VECTO reference results generated “ex-ante” together with the official CO2 values
Testing of full vehicle drivetrain efficiency on a chassis dynamometer
Comparison with VECTO results on basis of “g_fuel / kWh_wheel”
Required measurement data:
Fuel mass flow (external measurement device)
Torque at driven axle (external measurement device)
Engine speed and cardan speed (external measurement device or CAN)
Drivetrain oil temperatures (gear box, axle, others?)
Other parameters for verification of boundary conditions for valid measurement data (engine cooling fan speed, others?)
Energy content (lower heating value) of test fuel
Test option 1: Steady state points defined by gear, engine speed and wheel power
Test option 2: Implicit verification of CdxA value (combination of chassis dyno testing with full vehicle air drag test)
Test option 3: Transient chassis dyno testing, e.g. WHVC according to “HILS” procedure

4. Description “Option 1”: Steady state points
For each applicable mission profile VECTO shall determine 12 steady state points:
3 most frequent gears x 4 most relevant drivetrain operation points (engine speed, wheel power) in terms of contribution to overall fuel consumption
Grid resolution e.g. 50 rpm x 20 kW, tested points shall differ by min. 100 rpm and 40 kW
 testing points depend on particular vehicle configuration and on chassis dyno operator; thus for one engine a huge number of possible test points is expected what prevents against unwanted specific optimisations. If necessary random offsets could be added in VECTO ex-ante selection.
Example: delivery truck 12t GVW, mission profile „long haul“, gear 6:

5. Description “Option 1”: Steady state points
Test execution on the chassis dyno:
Testing to be performed with newly produced vehicle out of production (comparable run-in as in component tests, series equipment (e.g. oils), etc.)  comparability of component data of vehicle to the certified data
Deactivation of auxiliaries t.b.d. (main open issue: engine cooling fan)
Warm-up of vehicle in order to get all relevant temperatures into a window comparable to component testing e.g.:
Engine oil (window t.b.d.)
Gearbox oil (77 – 87°C)
Axle oil (60 – 70°C)
60s of measurement time = 1 “repetition”; number of required repetitions per steady state point t.b.d. (e.g. min=3 or minimum required number to be calculated based on variance of g/kWh of repetitions)
“Valid” repetition: During full 60s all temperatures are inside target window and engine speed and wheel power are completely within 50 rpm x 20 kW window (possibly more stringent definition for stability of constant point t.b.d.)

6. Description “Option 1”: Steady state points
Verification of measured value (average of all valid repetitions) with VECTO reference by comparison with interpolated value from VECTO results for 4 corner points
VECTO ex-ante result for corner points x x
Measured point to be interpolated from corner points
P_wheel
20 kW
50 rpm
n_engine
Pass/Fail criteria may be similar to actual WLTP proposal for CO2:
Define maximum deviation (per point or for weighted average)
If first test fails, second test is run, then third, if average of tests fails then vehicle has failed
Tbd: allow test of 2nd and 3rd vehicle or switch directly to component tests?

7. Description “Option 2”: Implicit verification of CdxA value
Idea: Possibility to verify certified CdxA value without publishing of particular value
Approach
Step 1: VECTO ex-ante reports FC [kg/h] for 85km/h constant speed driving and the corresponding engine speed [rpm] and rolling resistance drag power [kW]
Step 2: Determination of CdxA value of the COP tested vehicle via full vehicle air drag test
Step 3: Chassis dyno testing in the steady state operation point defined by engine speed and wheel power (sum of measured CdxA value and pre-defined rolling resistance drag power)
Step 4: Comparison of fuel consumption in [kg/h]
“Option 2” can supplement “Option 1” and “Option 3” testing

8. Description “Option 3”: WHVC (1) and/or CO2 test cycle(s)
Comparison of g/kWh fuel flow as option 1 but using transient cycles.
WHVC and/or CO2 test cycles relevant for the vehicle (shortened where necessary) can be measured on chassis dyno instead of steady state points.
Speed trajectories, gear shift points and average fuel flow to be calculated ex-ante by VECTO. To allow tolerances in engine speed and wheel power again results for offsets of +/-50 rpm and +/-20 kW can be computed.
kWh wheel power gained from torque and rpm measurement at the wheel. Fuel flow from fuel flow meter  g/kWh
+ covers more load points, due to dependency on vehicle configuration high variability of engine loads within engine family
Includes transient effects not simulated accurately by VECTO (influence on fuel flow to be analysed)
Auxiliary engagement and temperature levels may be harder to control than in steady state points
+ option may be used also to treat new technologies not yet covered by VECTO (“WHVC correction factor”)
(1)…World harmonized heavy Duty vehicle Cycle (WHVC) was basis for WHTC. In HDH-HILS development the WHVC road gradients were added to meet power distribution in WHTC.

9. Preliminary findings from MB Atego testing at TUG chassis dyno

10. Measured steady state points
47 different steady state points in 5 gears (gear 2 to gear 6)
2 to 8 repetitions per point (some points by intention measured also with “too low” and “too high” temperatures in the drivetrain (gearbox, axle))

11. Plausibility checks for measured quantities (examples)
Comparison of traction force from chassis dyno with “traction force” calculated from Kistler torque
 Plausible correlation (difference of approx. 500N correlates to rolling resistance as determined by „Loss Run“)
Wheel slip calculated from roller speed and cardan speed (ECU-CAN) shows plausible correlation with traction force from chassis dyno

12. First results: Repeatability of steady state points
Repeatability of single repetitions worse than expected
Example point: XXXX rpm, YY kW
1 dot = 1 „repetition“ (60s average)
„g/kWh“ calculated considering wheel power and fan power from propeller curve
 No correlation of g/kWh with drivetrain temperature!?
Spread of g/kWh of single repetitions for steady state points where ≥ 4 repetitions have been measured:

13. First results: Repeatability of transient tests
Repeatability of single repetitions of transient tests better than expected

14. Planned further steps MB Atego:
Component tests to generate VECTO input data ongoing
Comparison of measurement results with VECTO reference by Daimler (using actual component data as input for VECTO) planned until Mid 2015
Scania truck:
Vehicle already tested on Scania chassis dyno
Vehicle will be retested on TUG chassis dyno in April (to check reproducibility of methods)
Comparison of measurement results with VECTO reference (input data for similar vehicle components) open
MAN truck:
Chassis dyno tests announced for April/May
Analyse deviations
Check options for improvement of testing method(s)
Define common test procedure for the pilot phase
Definition of overall tolerances to be based on more test data from pilot phase