Worldwide Harmonized Light Vehicles Test Cycle (WLTC)

Background

The Worldwide harmonized Light vehicles Test Cycles (WLTC) are chassis dynamometer tests for the determination of emissions and fuel consumption from light-duty vehicles. The tests have been developed by the UN ECE GRPE (Working Party on Pollution and Energy) group [2624]. The WLTC cycles are part of the Worldwide harmonized Light vehicles Test Procedures (WLTP), published as UNECE Global technical regulation No 15 (GTR 15) [3553]. While the acronyms WLTP and WLTC are sometimes used interchangeably, the WLTP procedures define a number of other procedures—in addition to the WLTC test cycles—that are needed to type approve a vehicle.

The WLTP replaces the European NEDC based procedure for type approval testing of light-duty vehicles [3635][4056][4057], with the transition from NEDC to WLTP occurring over 2017-2019. The WLTP is also introduced for vehicle certification in Japan.

The WLTP procedures includes several WLTC test cycles applicable to vehicle categories of different power-to-mass (PMR) ratio, Table 1. The PMR parameter is defined as the ratio of rated power (W) / curb mass (kg) [3553]. The curb mass (or kerb mass) means the “unladen mass”, not including the driver, as defined in ECE R83 [3903]. However, EU regulations [3635] appear inconsistent with GTR 15 and replace the curb mass with “mass in running order”, which includes the driver and is 75 kg higher.

The cycle definitions may also depend on the maximum speed (v_max), which is the maximum speed of the vehicle as declared by the manufacturer (ECE R68) and not any use restriction or safety based limitation. Cycle modifications are allowed to accommodate drivability problems for vehicles with power to mass ratios close to the borderlines or with maximum speeds limited to values below the maximum speed required by the cycle.

WLTC Test Cycles

Class 3 Cycle

With the highest power-to-mass ratio, Class 3 is representative of vehicles driven in Europe and Japan. Class 3 vehicles are divided into 2 subclasses according to their maximum speed: Class 3a with v_max < 120 km/h and Class 3b with v_max ≥ 120 km/h. Selected parameters of the Class 3 cycles are given in Table 2, and the vehicle speed for Class 3b is shown in Figure 1 (in this representation, Class 3a trace would look very similar).

Class 2 Cycle

Class 2 is representative of vehicles driven in India and of low power vehicles driven in Japan and Europe. Selected parameters of the Class 2 cycle are given in Table 3, and the vehicle speed is shown in Figure 2.

Class 1 Cycle

With the lowest power-to-mass ratio, Class 1 is representative of vehicles driven in India. Selected parameters of the Class 1 cycle are given in Table 2, and the vehicle speed is shown in Figure 3.

Cycle Modifications

For some vehicles, it may not be possible to follow speed/time requirements of the cycle. The reasons for this are:

1. Vehicles with power to mass ratios close to the borderlines between Class 2 and Class 3 vehicles or very low powered vehicles in Class 1 may not be able to achieve the accelerations required to maintain cycle speed. In these cases, a downscaling procedure can be applied to reduce the maximum acceleration rates to improve driveability. A consequence of this procedure is a reduction of maximum cycle speeds.
2. Some vehicles may have a maximum speed limited to a value lower than the maximum speed of the downscaled cycle. In these cases, the vehicle shall be driven with its maximum speed in those cycle periods where the cycle speed is higher than the maximum speed of the vehicle. An example of vehicles for which this applies is Class 3a vehicles over the Extra-High 3 phase.
3. Some vehicles may not be able to follow the speed trace of the downscaled cycle within the required tolerance for specific periods. In these cases the vehicle shall be driven with the accelerator control fully activated during these periods. In these cases, driving trace violations are permitted.

Tests for Hybrid & Electric Vehicles

The WLTP includes special provisions for testing of various categories of hybrid-electric and electric vehicles: OVC-HEVs (off-vehicle chargeable hybrid electric vehicles); NOVC-HEV (not off-vehicle chargeable hybrid electric vehicles); and PEV (pure electric vehicles).

All OVC-HEVs, NOVC-HEVs and PEVs are classified as Class 3 vehicles. Emissions and a number of other parameters are tested over the respective Class 3 (Class 3a or Class 3b) cycle, in both charge-depeting and charge-sustaining modes. In addition, certain parameters are tested over WLTC city cycles, composed of the low and medium speed phases only. The test matrix is summarized in Table 5.