Abstract: In this paper, the mechanical innovative design method is applied to the structural analysis of single-motor parallel hybrid powertrain system for expanding the transmission system structure of hybrid electric vehicle. Firstly, two representative transmission structures of single-motor parallel hybrid electric vehicle are analysed with their mechanical topology structure obtained. With mechanical innovative design method, the kinematic chains of mechanical topology structure are obtained by applying generalization rules, and the generalized kinematic chains are acquired according to the members of kinematic chain links and kinematic pairs. By adopting specific program the feasible and specific kinematic chain map meeting design constraints is found from the generalized kinematic chain plots, and after eliminating those with same configurations, 12 feasible and specific kinematic chains are obtained, which are then converted into corresponding schematic diagram of plenary gear set by using concretization rules. Finally, through the analyses on power input/output distribution and operation modes, 132 feasible structures for the transmission system of single-motor parallel hybrid electric vehicle are obtained, from which a new configuration is chosen with its energy flows in six basic operation modes analyzed to get 15 combinations of clutch and brake state, verifying the feasibility of applying mechanical innovative design method to the structural design of hybrid powertrain system

Key words: hybrid electric vehicle, mechanical innovative design, structural design, operation mode, energy flow