[1] Xihua Univ, Sch Automobile & Transportat, Chengdu 610039, Peoples R China
[2] Chongqing Univ, State Key Lab Mech Transmiss, Chongqing 400044, Peoples R China
[3] Univ Calif Berkeley, Energy Controls & Applicat Lab, Berkeley, CA 94720 USA
[4] Newcastle Univ, Sch Elect & Elect Engn, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England