Technical Standards

Phase 2 standards apply to the same types and classes of diesel engine heavy-duty vehicles (GVW >= 3.5 t), including regular trucks, tractor trucks, transit buses and general (non-transit) buses. Like Phase 1, the updated standards are also applicable to non-type-approved diesel vehicles that are equipped with CO or other pollutant emissions control devices.

Japanese regulators tightened Phase 1 standards by raising the fuel economy targets. When the Phase 2 targets are fully met, the fleet average fuel economy is estimated to be:

For trucks, 7.63 km/L, a 13.4% improvement over the 2015 baseline at 6.72 km/L.

For buses, 6.52 km/L, a 14.3% improvement over the 2015 baseline at 5.71 km/L.

Table 1 summarizes the average Model Year 2015 baseline fuel consumption values (kilometers per liter of fuel consumed), 2025 requirements, and the percentage improvement between 2015 and 2025 for the major truck and bus categories. Average fuel efficiency values are based on weighting from 2014 sales data that the Japanese MLIT referred to in their regulatory document.

A detailed breakdown of standards for different heavy-duty vehicle types and classes is summarized in the following tables. Each manufacturer is required to meet the fuel efficiency target in all categories.

Testing

The Phase 2 standards retain the existing test cycles for heavy-duty vehicles but modify some of the weighting and load factor assumptions to better reflect real-world driving conditions. The test cycles include a JE05 test for urban driving simulation and an interurban transient test. Compliance is determined by aggregating the fuel economies measured under these test cycles, based on weighting factors that reflect assumptions about the operating environments and use cases of different classes of vehicles. The Phase 2 standards include new percentage weights for interurban driving conditions and variable load factors (cargo mass and passengers) that better reflect real-world driving conditions. Table 6 summarizes changes to these two parameters for different vehicle classes and types.

The Phase 2 standards include several other modifications to certification protocols and simulation models:

• Additional test points to the steady-state engine fuel map: increased from the prior 31 points (6 RPM x 5 torque points plus one idle) to 51 points (10 RPM x 5 torque points plus one idle point);
• Incorporated confirmed data for aerodynamic and rolling resistance into the simulation;
• Changed the manual transmission shifting algorithm by making minor adjustments to engine rotation speeds;
• For Automated Manual Transmission (AMT) vehicles, gear positions are calculated second-by-second;
• Introduced a new function to estimate inertial mass corresponding to the drive system to be used to estimate air resistance from the coast down test;
• Introduced a 3% correction factor for the urban driving mode to capture the effects of transient engine operation.

Compliance

Similar to Phase 1, compliance with the Phase 2 standards is measured by reference to the individual fuel economy targets for each vehicle class, gross vehicle weight, and for lighter trucks, rated cargo load. Japan had introduced a cross-category crediting system that allowed transfer of half the emissions reductions from vehicles that overachieve the fuel economy targets to vehicles that fail to achieve the targets. This credit system will be kept under the Phase 2 standards.