WLTP: New certification regulations.
From 1 September 2017, the WLTP will be introduced. This new procedure for consumption and emissions tests is designed to deliver test results that more accurately reflect real driving behaviour than the previous NEDC. From September 2017, all newly developed vehicles and vehicles with new powertrains will be certified under WLTP. From September 2018, the WLTP will then apply to all other newly registered vehicles. Between now and August 2018, therefore, Mercedes-Benz will certify its passenger car portfolio under WLTP. In the transitional period, vehicles with WLTP and NEDC will be simultaneously available. In addition, there will be a NEDC consumption value that is based on the WLTP and which will also be higher. This value will be used in sales documents until 2020.
Efficiency factors left out of consideration.
Since vehicles are becoming more and more efficient, this lowers the values measured in the test cycle. At the same time, if the higher consumption due to comfort/convenience functions not covered by the NEDC remains constant, the difference increases as a percentage. While other technical factors play only a minor or even no role on the dynamometer, they have a considerable effect under real driving conditions. For example, aerodynamics, a key efficiency factor in long-distance driving, is left out of consideration in the NEDC. The WLTP takes account of all optional extras with an influence on vehicle aerodynamics, rolling resistance, vehicle mass or power consumption. The only exception in the first stage of the WLTP is the air conditioner. This means that, in most cases, WLTP consumption values will be higher, yet more realistic.
The NEDC is outdated.
The first European driving cycle came into effect in 1970. In 1992, the NEDC was extended beyond urban traffic. This New European Driving Cycle (NEDC) is the currently valid test cycle. The results are comparable and reproducible across all manufacturers. However, a test cycle cannot reflect what happens under real driving conditions. There is a discrepancy due to factors such as driving style, use of comfort/convenience functions or increased rolling resistance as a result of additional weight. Many CO2 reduction technologies often have a stronger impact on the dynamometer than on the road, such as a start/stop system. Continuous technological advances mean that the NEDC is now outdated. The WLTP (Worldwide Harmonized Light-Duty Vehicles Test Procedure) has been created with the goal of establishing a globally valid test cycle.
The key innovations.
In contrast to the NEDC, the WLTP driving cycle lasts ten minutes longer and includes only 13 percent stopping time. The length of the entire cycle is 23.5 kilometres, i.e. over twice as long as the 11 kilometres of the NEDC. The WLTP includes higher average speeds up to 131 km/h, subjects the vehicle to stronger variations in speed and imposes significantly stricter test conditions. In addition, unlike previously, it is not just the basic variant of a model that is tested, but additional equipment and optional extras are taken into consideration. The shift points are calculated in advance and are specific to the vehicle and its powertrain. Vehicles with manual transmission benefit from this specific method of calculation as opposed to the fixed shift points in the NEDC.
The new speed profile.
The greatest drawback of the NEDC is the high proportion of driving at constant speed (40 percent) and the relatively low proportion of acceleration events (21 percent). The NEDC therefore represents, above all, an urban driving cycle that delivers scarcely realistic values. The new WLTP, on the other hand, includes four different phases: up to 60, up to 80, up to 100 and above 130 km/h. These simulate urban, extra-urban and motorway driving. The differences between the test procedures are made clear by the chart opposite. The result is a test procedure that delivers significantly more realistic results in the interests of the end customer.