International: Light-duty: WLTP

Background
The Worldwide Harmonized Light Vehicles Test Procedure (WLTP) is a chassis dynamometer test cycle for the determination of emissions and fuel consumption from light-duty vehicles. At its November 2007 session, the World Forum for Harmonization of Vehicles Regulations (WP.29) of the UNECE established an informal group under its Working Party on Pollution and Energy (GRPE) to prepare a road map for the development of a WLTP. This road map was proposed in 2009 and called for the development of a Global Technical Regulation (GTR) for light-duty vehicles, similar to regulations developed earlier for motorcycles (GTR no. 2, WMTC) and heavy-duty vehicles (GTR no. 4, WHDC). A UN GTR specifies globally harmonized performance-related requirements and test procedures, but not the administrative provisions for certification by individual countries and their mutual recognition. Member countries (“contracting parties”) that adopt the GTR are obliged to incorporate the GTR into their national laws.

On 14 November 2013, after four years of work, the formal text for the WLTP was adopted by the GRPE. The decision must be confirmed by the WP.29 at its March 2014 session. If the WP.29 does confirm the GRPE decision, the WLTP will be complete and ready to be implemented by individual countries. When finalized, the WLTP test is expected to replace the European NEDC procedure for type approval testing of light-duty vehicles. Meanwhile, the contracting parties that adopt the GTR can start preparations to implement it into their national law. This process has already started in the EU, and a simulation-based correlation exercise has been initiated by the European Commission to convert the CO2 targets set under the NEDC into targets for the GTR test procedure.

The development of the WLTP comprised two main elements:
 * Development of a harmonized driving cycle representative of world average driving conditions (internally referred to as the DHC)
 * Development of a harmonized test procedure that sets the conditions, requirements, tolerances, etc. for the emissions test (internally referred to as the DTP)

Harmonized Driving Cycles
Driving cycles are an essential element for the measurement of fuel consumption and emissions. Currently, each region uses its own driving cycle, varying from a stylized, less dynamic driving pattern—e.g., the NEDC in Europe—to a more dynamic driving pattern such as the US06 cycle used in the United States. The characteristics of a driving pattern, such as average speed, dynamic behavior, and length and number of stops, all have an effect on the resulting emissions and fuel consumption.

Since the WLTP was intended to harmonize test procedures worldwide, the GRPE’s task scope included development of a new cycle representing typical driving characteristics around the world. This is referred to as the World Harmonized Light-duty Vehicle Test Cycle, or WLTC. The real-world driving data used as input for this development came from five different regions: the European Union plus Switzerland, the United States, India, Korea, and Japan.

Three different driving cycles were developed representing three different vehicle classes, based upon a vehicle’s power-to-mass (PMR) ratio and its maximum speed. The PMR parameter is defined as the ratio of rated power (W) / curb mass (kg). The curb mass (or kerb mass) means the “unladed mass” as defined in ECE R83. 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.

Class 3 Cycle
With the highest power-to-mass ratio, Class 3 is representative of vehicles driven in Europe and Japan. Selected parameters of the Class 3 cycle (Version 5) are given in the following table, and the vehicle speed and acceleration are shown in Figure 1.

Figure 1. WLTP Cycle for Class 3 Vehicles

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 (Version 1.4) are given in the table below, and the vehicle speed and acceleration are shown in Figure 2.

Figure 2. WLTP Cycle for Class 2 Vehicles

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 (Version 1.4) are given in Table 2, and the vehicle speed and acceleration are shown in Figure 3.

Figure 3. WLTP Cycle for Class 1 Vehicles

Harmonized Test Procedure
In addition to the driving cycle, a test procedure is needed to prescribe test conditions, requirements, tolerances, and so on. The procedure covers everything from the preparation of the test vehicle and measurement equipment to how the test is to be conducted and the results calculated. Development of the WLTP test procedure started by analyzing current emission statutes and regulations, along with related standards. The best features of each were identified and were used to pattern each section of the GTR.

Links
ICCT Policy Update, World-Harmonized Light-Duty Vehicles Test Procedure, Nov 2013

Worldwide harmonized Light vehicles Test Procedure on UNECE website

UN ECE GRPE (Working Party on Pollution and Energy)