6d TEMP, WLTP, RDE and PEMS. Part I: Measurement of consumption and emissions

Since September 1, 2017, new passenger car models to be newly certified in the EU have been subject to a new procedure for the measurement of consumption and emissions – the WLTP (Worldwide Harmonized Light Vehicles Test Procedure). On September 1, 2018, this test will become mandatory for all newly registered passenger cars (for vans with commercial use there will be other timelines) and will thus gradually replace the New European Driving Cycle (NEDC).

Alongside the new WLTP dynamometer driving cycle, there will be an additional on-road measurement to guarantee compliance with the new Euro 6d-TEMP emissions standard. Called Real Driving Emissions (RDE), the purpose of the additional procedure is to validate the emissions values measured on the dynamometer under real driving conditions. The "road emissions value", including a measuring tolerance, must not exceed 2.1 times the laboratory limit for nitrogen oxides.

What is a driving cycle?

A test procedure for a dynamometer includes not only the defined driving cycle, but also the specification of parameters under which the test must be performed. The driving cycle itself defines a standardized speed profile that is simulated with the vehicle on the dynamometer, i.e. in the laboratory. The parameters include, for example, the test temperature, specification of the vehicle test weight and the state of charge of the vehicle battery. Consumption and emissions are measured on the basis of these legally set parameters.

Why dynamometer and not on the road?

The fundamental question asked by experts in Germany and France, for example, already in the 1960s was: How can it be guaranteed across manufacturers, brands and national borders that vehicles comply with emissions limits? Initially, the focus was not on measuring the fuel consumption. The idea of doing so led in 1970 to the first standardized emissions regulations for passenger cars in the European Community. These were superseded in 1992 by the "New European Driving Cycle" (NEDC), which was in force until August 31, 2017.

This involves precisely defined driving cycles being run on standardized and calibrated dynamometers under laboratory conditions and approved by an accredited "Technical Service" (e.g. in Germany: TÜV, DEKRA). The advantage: The results of the tests are comparable and reproducible across all manufacturers and dynamometers.

Which vehicles undergo the test procedure?

New vehicle models of all manufacturers within a new model series must undergo the driving cycle (formerly NEDC, now WLTP). A frequent misunderstanding: What is tested is not each individual vehicle delivered to a customer, but each new model with every available engine/transmission combination (i.e. constellations that can have impacts on consumption and emissions).

What is measured?

What is measured is the fuel consumption and the emissions as well as, in the case of hybrid and electric vehicles, the electric range.

• If the results meet the limits required by the EU in the form of the so-called Euro-X standards, the competent national authority (in our case the German Federal Motor Transport Authority/KBA) issues a so-called type approval for a regional territory, in this case the EU. This means that, once type-approved, this precise model can be sold in that territory and used on the road.

• The type approval with the certified technical consumption figures is used in many EU states to calculate, for example, the motor vehicle tax or is used as the basis for the assignment of an environment sticker.

• Also from the certification results, the EU Commission calculates an average EU fleet CO₂ emissions value based on total sales of the models. To achieve the EU's climate protection goals from 2020, this value should be below 95 g/km. In other regions of the world, there are different limits.

• The consumption and emissions values from the test cycle must also be published in various advertising and communications activities, such as brochures, websites or exhibits in showrooms. All manufacturers are obliged to disclose the results – this is what we call "labeling". For car-makers, this is regulated, for example in Germany, by the Passenger Car Energy Consumption Labeling Ordinance (Pkw-EnVKV), the national implementation of European directive 1999/94/EC on "the availability of consumer information on fuel economy and CO₂ emissions in respect of the marketing of new passenger cars". Yet mandatory labeling applies not only to car-makers: Similar labelling requirements are also applied to manufacturers of refrigerators or washing machines in the European Union.

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