The United Nations Economic Commission for Europe (UNECE) have recently published amendments to their Regulations on emissions and fuel consumption to introduce an alternative test procedure for the testing of externally chargeable hybrid electric vehicles (i.e. hybrid electric vehicles which have an off vehicle charging (OVC) capability).
Previously, the ECE Regulations on CO2 emissions and fuel consumption (ECE 101.00) and on pollutant emissions (ECE 83.05) specified that externally chargeable hybrid electric vehicles should be subjected to three separate tests:
- An emissions and fuel consumption test with the vehicle's battery at its maximum state of charge.
- An emissions and fuel consumption test with the vehicle's battery at its minimum state of charge.
- A range test to determine the pure electric driving range of the vehicle.
A weighted average of the emissions and fuel consumption results from the first two tests is then calculated, utilising a formula which takes into account the result of the range test.
Whilst these test procedures and formulae have provided realistic and representative emissions and fuel consumption figures for externally chargeable hybrid electric vehicles that utilise a simple control strategy (i.e. where the vehicle runs in pure electric mode until the battery reaches a minimum state of charge and then starts the internal combustion engine), they penalise externally chargeable hybrid electric vehicles that utilise more complex control strategies (i.e. where the internal combustion engine is run in conjunction with the electric motor during periods of high energy demand).
Supplement 8 to ECE 83.05 and Supplement 8 to ECE 101.00 introduce a new, alternative test procedure for such vehicles which takes into account these more complex control strategies. Under this new test procedure, the emissions and fuel consumption test with the vehicle's battery at its minimum state of charge is still carried out, but the other tests are replaced with an "OVC" range test.
For the "OVC" range test, the vehicle begins the test with a fully charged battery and is driven over consecutive European drive cycles until the battery reaches its stable minimum state of charge (defined as the point where the battery is no longer being discharged during the drive cycle). Emissions and fuel consumption results are measured and recorded for each of the European drive cycles that the vehicle completes, and are then averaged. A weighted average of these results and those from test with the battery at its minimum state of charge is then calculated, utilising a formula which takes into account the range measured during the "OVC" range test.
To ensure that this test procedure does not lead to a relaxation in the pollutant emissions requirements, it is specified that the emissions results recorded for each drive cycle must meet the applicable pollutant emissions limits. Also, even though the result from the pure electric driving range test is no longer required for the formulae, it is still necessary to carry out the pure electric driving range test on externally chargeable hybrid electric vehicles for reference purposes.