1. College of Mechanical Engineering; Chongqing University; Chongqing 400044 China
2. Department of Mechanical Engineering; Northwestern University; Evanston IL60208 IL USA
3. State Key Lab of Mechanical Transmission; Chongqing University; Chongqing 400044 China
4. CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd; Qingdao 266031 China
5. China National Heavy Machinery Research Institute Co, Ltd; Shanxi 710032 China