WLTP and RDE – Emission testing for motor vehicles with constantly increasing requirements.
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WLTP and RDE – Emission testing for motor vehicles with constantly increasing requirements.

The test routines used in the new WLTP procedure are designed to reproduce the driving data more realistically. Four vehicle classes are defined, which differ according to the power-to-weight ratio. The driving profile in the WLTC (Worldwide harmonized Light vehicles Test Cycle) is based on real driving data, which was calculated as an average from surveys in 14 countries.

In addition, not only a standard vehicle model is tested, but all engine-transmission combinations must be assessed separately. The effects of variant diversity due to optional equipment are interpolated or calculated. In addition, the procedures are becoming stricter with the WLTP 2nd Act in 2019 and RDE 2 in 2020. This also results in a need for changes to existing whole vehicle type approvals, which must be realized in vehicle homologation.

WLTP 2nd Act as of 2019

Since January 2019, the second part of the WLTP (WLTP 2nd Act) has been defined and from 01.09.2019, all new vehicles registered in the EU must meet the requirements of the new procedure. For example, the usage of the air conditioning system is now included in the tests, a stricter measurement procedure for fuel evaporation in gasoline engines applies and the shift point calculation for manual transmissions is subject to changed specifications. It was therefore necessary for all vehicles approved according to the previous WLTP procedure to be provided with updated type approval documents by September 2019.

The measurement results for carbon monoxide, nitrogen oxides and soot particles usually differ considerably between the WLTP and RDE procedures. On the basis of the currently valid Euro 6d TEMP emissions standard, petrol-powered passenger cars may emit 60 mg/km NOx on the WLTP test stand, whereas the RDE limit value is 126 mg/km. According to WLTP, a limit value of 80 mg/km NOx applies to diesel passenger cars, which can be 168 mg/km NOx in the RDE process.

WLTP and RDE have different results

Stricter RDE limits as of 2020

For the evaluation of the RDE, the test route is largely freely definable. The minimum distance specified is 16 kilometres in the city, cross-country and on the motorway. The test drive should last between 1.5 and 2 hours and cover as wide a range as possible of different driving profiles and driving styles. The individual RDE test drives are not comparable or reproducible due to traffic-related conditions such as different traffic lights or changing traffic intensity. The basic principle is that the test driver performs a test drive in the same way as any other driver would.

RDE 2 will come into force on 01.01.2020. Then the values of new types measured during on-road driving may no longer exceed those measured on the WLTP test stand. This also applies to new approvals from January 2021. The measurement tolerance of the mobile measuring device PEMS (Portable Emission Measurement System) is taken into account by a 43 % surcharge on the WLTP limit value; for particles, a 50 % surcharge on the WLTP limit value is applied as the measurement tolerance.

RDE 2 closes the gap between WLTP and road driving

Increasing complexity of emission approvals

The constant need to adapt these documents and the complex interaction between technical services and various authorities in order to obtain system and whole vehicle type approvals bear considerable potential for errors.

The set-up and implementation of a multi-level, structured document examination system for test and approval documents in the context of emission type approvals can ensure the identification of any necessary corrections in the type approval-relevant documents and create trust and confidence in the cooperation with the approving authorities.

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Marco Mauler

Marco Mauler
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