The new WLTP test cycle: Closer to real-world consumption

In 2017, a new procedure for consumption/exhaust testing is scheduled to be introduced in the automotive industry. The goal of the new WLTP cycle (Worldwide Harmonized Light Vehicle Test Procedure) is to harmonise testing procedures around the world. It is intended to deliver more realistic test results than the previous NEDC procedure (New European Driving Cycle), which was adopted in 1992 and introduced by the European Commission in 1996.
The NEDC took over from the Euromix method with its constant driving at 90 and 120 km/h and for the first time included precisely defined driving cycles to be carried out on standardised and calibrated test rigs. The advantage: the results of the tests are comparable and reproducible across all manufacturers and test rigs. And it is not just the fuel consumption that is measured, but also the emissions, such as those of nitrogen oxides and particulates. This made it possible for the first time to set legal limits.
Yet the NEDC also has a number of drawbacks. For example, the effect of a car's aerodynamics - a key efficiency factor in real-world inter-city driving - is under-represented at the comparatively low speeds in the NEDC. Also, there is this: the NEDC does not apply in key markets outside Europe. While important regions such as the USA/Canada or Japan have their own cycles, China has additional procedures on top of the NEDC. In the case of a globally active automaker, this results in tremendous expenditure on testing and development as well as in a multiplicity of technical variants of automobiles that are to all intents and purposes identical.
For all these reasons, Mercedes-Benz has from the outset supported the efforts to introduce a more realistic and, if possible, globally valid test cycle.
The WLTP in comparison with the NEDC
Cycle
WLTP
NEDC
Starting temperature
Cold
Cold
Cycle time/duration
min
30
20
Percentage of stops
%
13
25
Cycle length
km
23.5
11
Average speed
km/h
46.6
34
Max. speed
km/h
131
120
Average driving power
kW
7
4
Max. driving power
kW
47
34
Optional equipment of the specific model
is taken into consideration for weight, aerodynamics, rolling resistance
only wheels& tyres
Climate control
no
no
Test temperature
°C
23
25 +/- 5
Temperature for additional EU test
°C
14
-
Test weight
Vehicle weight plus representative payload
Inertia weight class
Other changes compared with NEDC in relation to
preconditioning, driving resistances, plug-in hybrids
-

Limitations of a standardised cycle: between local and global
The WLTP is closer to what happens in real-world traffic and offers a more precise test method than the current NEDC. It defines clear boundary conditions for testing and thus delivers results that are more accurate, more consistent and more reproducible. Even so: a standardised cycle cannot fully cover the range of real-world consumptions and emissions around the globe. For example, there is too much difference in
  • climatic conditions between the tropical regions in Asia and the long winters in Russia. There are also seasonal variations
  • traffic conditions and traffic density in mega cities compared with little-used motorways or country roads
  • road profiles from the mountainous regions of Switzerland to the lowland plains of northern Germany
  • vehicles - from small compacts in India to full-grown SUVs and pick-ups
  • driving habits and driver temperaments
  • use of ancillary consumers such as air conditioning or lighting.
In addition, it is planned in Europe to introduce a measuring procedure for Real Driving Emissions (RDE). This, too, is actively supported by Mercedes-Benz. It uses a portable emissions measurement system (PEMS) for measuring the pollutant emissions during real-world vehicle operation.
CO2 emissions of Mercedes-Benz: almost halved since 1995
European legislation has set challenging targets for the further reduction of consumption and CO2 emissions in road traffic: by 2020, the average emissions of the new-vehicle fleet must fall to 95 g CO2/km (corresponding to 4.0 litres of petrol or 3.5 litres of diesel/100 km) - measured according to NEDC. The method for converting the NEDC targets to future valid WLTP targets is currently being developed under the aegis of the EU Commission. There applies the principle of "comparable stringency", which means that the introduction of the WLTP should not result in any tightening of targets for manufacturers.
Mercedes-Benz is on the right track. In two decades since 1995, the average consumption of the passenger car fleet has fallen by almost half from 9.2 litres/100 km (230 g CO2 /km) to 5.0 litres (125 g CO2/km). Already today, Mercedes-Benz Cars has 68 models that emit less than 120 g/km – and 108 models with the efficiency label A+ or A.
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