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Recently even for medium or heavy duty commercial vehicles (MD/HD CVs), hybrid electric vehicles (HEVs) or electric vehicles (EVs) have been launching in the world. In the current status, parallel type of HEV shows the most practicality in market. In that case, the optimal engine adaptation and the highly efficient brake energy recovery are the keys for efficient HEV. The EV application for MD/HD CVs is also the possible solution in the near future if some issues are cleared. Therefore it is hard to decide the most possible case for future CVs only from the existing point of view. The conceptual new name of “XEV” will be suitable to express those possible cases generically. The improvement of energy storage system (ESS) will have been the most prioritized issue for “XEV” for a while.

In recent years, attention has focused on smokeless, sulfur-free dimethyl ethyl (DME) as a clean fuel for heavy-duty diesel vehicles [1]. In this development, the DME engine applied for 20-ton GVW truck was developed under the auspices of the Ministry of Land, Infrastructure and Transport of Japan, the first known instance worldwide. With careful design of the fuel system considering DME's unique fuel characteristics and suitable combustion improvement, higher torque was obtained with DME, compared to diesel fueling. and also use of the proper EGR and catalyst, exhaust emissions levels were generally less than one-fourth of new long-term regulation value promulgated in 2005 Japan.