Regulation of fuel consumption in Japan is directly linked to Japan’s commitment under the Kyoto Protocol to reduce greenhouse gases.1 In Japan, heavy-duty trucks account for 25 percent of the greenhouse gases generated by automotive sources. The “Top-Runner Standard” for measuring fuel consumption was started for heavy-duty trucks in 2006, with a target implementation date of 2015. The vehicle manufacturer is the regulated entity. In Japan the engine and heavy-duty vehicle manufacturers are integrated and few in number, so the point of regulation is more obvious than in the United States.
As in Europe, the process began with collaborative meetings with the heavy-duty truck manufacturers to collect data on vehicles and technologies that could improve fuel consumption. However, unlike in Europe, the primary focus in Japan is on improvements due to changes in engine technology only, rather than to the whole vehicle, and the metric used is “kilometers/liter,” with differing standards for different weight classes (Figure 3-2).
Fuel consumption is evaluated through computer simulation based on a combination of an urban duty cycle defined in JE005, used for emissions testing, and an interurban cycle developed for fuel economy testing. The simulation tool, which is available online for manufacturers to use, requires vehicle specifications and engine fuel maps as input data. An overview of the simulation methodology is given in Figures 3-3 and 3-4.
The vehicle simulation tools used by Japan’s Ministry of Land, Infrastructure, Transport, and Tourism evaluate the fuel consumption and performance of conventional vehicles. The software, available in both FORTRAN and C++, allows users to modify the transmission ratio, the final drive ratio, the wheel radius, and the main engine characteristics (including wide-open-throttle and closed-throttle torque curves as well as fuel rate map). However, it forces most of the remaining parameters to remain constant. As such the vehicle characteristics (weight, frontal area, drag coefficient) or component losses (efficiencies) cannot be modified. Moreover, advanced shifting control algorithms that might be available cannot be implemented. The impact of active regeneration of diesel particle filters is handled by calculating the ratio of vehicles with this feature to those without it (Sato, 2007). Overall, the tool allows evaluation of new engine technologies while keeping the rest of the power train and vehicle unchanged. Finally, only two drive cycles can currently be selected.
Because the Japanese program focuses on engines, new methodologies for measurement must be developed as new technologies are introduced to account for their contribution to improving fuel consumption. There is currently no provision in the simulations to take these contributions into account.
Because of the large reductions in fuel consumption achievable with hybrid electric trucks, a measurement method for this technology was included in the Japanese regulation. To measure the contribution of hybrid technology, the Japanese developed hardware-in-the-loop simulation (HILS) testing (Figure 3-5; see also Appendix H) and used it for measuring emissions, as well as calculating fuel consumption. HILS substitutes for the conversion program (see Figure 3-4) used in the process for nonhybrid vehicles (Morita et al., 2008). Details of the method and validation are available in Morita et al. (2008). The HILS approach was recently recommended for further study and potentially wider implementation (in Europe and beyond) for hybrid vehicles by an international committee of engine and vehicle manufacturers.
The Kyoto Protocol, an international agreement linked to the United Nations Framework Convention on Climate Change, sets binding targets for 37 industrialized countries and the European community for reducing greenhouse gas emissions by an average of 5 percent against 1990 levels over the 5-year period 2008-2012.