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WLTP correction algorithms progress report from TUG (chassis dynamometer corrections) and TNO (coast down corrections) preliminary results (27.03.2014)

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Presentation on theme: "WLTP correction algorithms progress report from TUG (chassis dynamometer corrections) and TNO (coast down corrections) preliminary results (27.03.2014)"— Presentation transcript:

1 WLTP correction algorithms progress report from TUG (chassis dynamometer corrections) and TNO (coast down corrections) preliminary results (27.03.2014) TU Graz:Stefan Hausberger David Leitner TNO: Norbert Ligterink Rob Cuelenaere Pim van Mensch Content of TUG slides not yet discussed with TNO WLTP-06-31e

2 Chassis dynamometer corrections January 20, 2014 2

3 Correction algorithms for variations in the WLTP testing Methods drafted for chassis dynamometer test (TUG) Target is, to correct all test results to the target settings. Following deviations are analysed and lead to the listed correction methods: 1.Correct test results for imbalances in battery SOC as drafted in WLTP 2.Set up a vehicle specific Willans linear function (from WLTP subcycles) (k =  CO2/  kWh) from the SOC-corrected WLTC test data as basis for corrections of deviations in positive wheel power). 3.Deviation against target speed: calculate from driven speed profile the actual power at wheels [P (t) = (R 0 + R 1 *v+R 2 *v² + m*a) * v], Calculate difference in average positive power values January 20, 2014 3

4 Correction algorithms for variations in WLTP testing January 20, 2014 4

5 Example for results passenger car 1 with diesel engine 6 repetitions WLTC under normal conditions Measured CO2  SOC-corrected  complete correction January 20, 2014 5 Note: * tests 2, 3 and 4 were out of WLTP temperature range to test temperature correction * correction for road load settings not applied (no coast down after each test available)

6 Example for result passenger car 2 with diesel engine 5 repetitions with wide variations in temperature, SOC at start, driver Stepwise effects of correction functions Cumulative application of corrections against measured CO 2 Corr v-deviations Corr SOC Corr temp. January 20, 2014 6

7 5. Temperatures from preconditioning and soak January 20, 2014 7 This logarithmic function worked very well between 1°C < t test < 90°C for the vehicles tested yet, so it should be applicable for the WLTC tests. This correction must be the final one to avoid influences of SOC or speed deviations in the CO 2 -value.

8 Overview on sequence of corrections January 20, 2014 8 1) Measured values in WLTC: CO 2 [g], distance [km],  SOC [kWh], Oil temperature at start [°C] instantaneous velocity [km/h] to compute average P wheel [kW] per phase 2)  SOC correction: apply WLTP option (or detailed approach)  CO 2 SOC [g] = k engine x  SOC CO2 SOC_corr [g] = CO2 measured [g] +  CO 2 SOC [g] 3) Establish vehicle specific Willans linear equation from CO2 SOC_corr [g/h] and P wheel [kW] per phase 4) Wheel power correction 4.1) deviation against target speed at times with power > 0 4.2) deviations in road load settings at chassis dyno vs. target  CO 2 [g] = k x  W wheel [kWh] CO2 v_corr [g] = CO2 SOC_corr [g] +  CO 2 [g] 5) Distance correction: CO2 d_corr [g/km] = CO2 v_corr [g] / target distance [km] 6) Temperature correction: (different soak temperature): CO2 corr [g/km] = CO2 d_corr [g/km] x (1+  CO2 temp [%]/100)

9 P overrun January 20, 2014 9 ~12% for WLTP Optional: detailed approach for SOC correction (instead of WLTP method)

10 SOC correction effect for vehicle # 1 (diesel engine) Comparison of the SOC correction method of WLTP draft with detailed approach. Small differences but detailed method would be much more complex for type approval Simple approach as outlined in WLTP is good option. January 20, 2014 10

11 Coast down corrections January 20, 2014 11

12 Current WLTP coast down corrections are validated (no reasons found to augment existing methods) wind correction: (stationary method)  in principle correct, but large: source of uncertainty vehicle weight correction:  physically sound, measured effect is somewhat larger (f1?) tyre temperature correction:  magnitude reproduced, despite doubts on physical soundness air pressure correction:  limitation to f2 somewhat doubtful (role f1?), but effect reproduced road slope:  1/T average yield appropriate correction for sloping tracks tyre pressure correction: is based on a particular tyre pressure  role of f1 (in “f0 + f1*v + f2*v 2 ”) in the WLTP text could be reviewed January 20, 2014 12

13 WP 210 Correction parameters and algorithms for road load determination NoParameterMethodComments R1 rotational inertia correction Weigh the wheels and tyres and use 60% of the weight as rotational inertia, compensate on dynamometer. The rest of the driveline (after transmission) has a limited contribution, effect may vary somewhat with rim sizes and wheel type (secondary effect). January 20, 2014 13 Inertia of wheels and tyres (separate tests): o WLTP: “3% of unladen mass (UM=1201 kg)”  36.0 kg o normal wheels: 38.0 kg (56% of wheel weight) o 18” wheels: 54.4 kg (64% of wheel weight) o theoretical arguments leads to 60% - 70% of wheel weight from coast-down to chassis dynamometer

14 WP 210 Correction parameters and algorithms for road load determination NoParameterMethodComments R2 tyre pressure correction The rolling resistance is corrected for difference between pressures by: f0 final = f0 test * (P test /P set ) Apply per tyre, average the result. Current WLTP text is based on specific case. January 20, 2014 14 NoParameterMethodComments R4 tyre label correction f0 final = f0 test *(RRC class /RRC test ) Correct the actual tyre labels (Rolling Resistance Coefficients: RRC) back to the setpoint, or “class value” value, if RRC test < RRC class. Tyre aspects difficult to recover from vehicle tests: rely on tyre label testing for the appropriate corrections range in a single tyre label more than 10%  still a flexibility, to be corrected for. How to include f1 in rolling resistance corrections is under investigation.

15 WP 210 Correction parameters and algorithms for road load determination NoParameterMethodComments R10 air density correction   Use air pressure and water vapour pressure. (Water vapour pressure depends on relative humidity and temperature.) Partly included in WLTP, update with humidity. Air viscosity effects are ignored. January 20, 2014 15 air density  varies slightly with humidity: maximal 37.7% x 7.3% = 2.7% water vapour content at 40 o C difference of density    T 0 /T) * (P/P 0 ) * (1.00 – 0.38 * (RH/100) * (P vapour /P)) P vapour [bar] = 157001*10 -1730.63/(233.46+T[C]) Antoine equation T 0 = 293 K P 0 = 100 kPa humidity effect especially at high temperatures water vapour 37.7% lighter than dry air

16 Open issues, difficult to cover in simple corrections January 20, 2014 16 test track surface: large effect on rolling resistance (up to 24%) probably more so because of tyre tread and pressure difficult to correct for, road surface characteristics not known tyre pressure variations during coast down testing: (up to 15%) not fully fixed by conditioning (average: up 7% from ambient) can be controlled somewhat by intermediate driving/text execution variation in wind speed and direction during testing: (“gustiness”) wind has large effect  need for back and fro testing (a and b) small remainder of a and b average largely affected by minute-to-minute variations

17 preliminary results current status: final testing, reporting in progress thank you for your attention January 20, 2014 17


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