| As a new type of public transportation tool, the hybrid electric bus attracts people's attention since its better fuel economy and emission performances. Series powertrain has good performances at low speed, and the parallel behaviors are desired at high speed. The series-parallel hybrid bus inherits the advantages from both systems. It is therefore suitable for variable driving cycle conditions, such as transit bus city driving cycle. Presently, much more transit bus adopts manual transmission and the duty-heavy automatic mechanical transmission (AMT) technology is also not mastered by the native manufactures. Based on such a background, this paper presents a post-transmission coupled series-parallel configurations switchable hybrid electric powertrain in which the manual transmission is employed. This manual transmission is replaceable with the automatic transmission.Now, this system is successfully applied in SWB6116HEV hybrid electric bus. Based on this hybrid bus, the paper put the research emphasis on powertrain configuration & size design, the energy management strategy (EMS) design as well as its optimization, and the experimental validation.Numerical simulation is an effective approach to evaluate vehicle performances, analyze vehicle characteristics and optimize control parameters. Based on the previous researches, this paper builds up the numerical models of each components, including powertrain and transmission systems, and vehicle dynamics. A general simulation program for series-parallel hybrid electric vehicles is coded in Matlab/Simulink software environment. This model is used to evaluate the EMS performances and the optimization of the control parameters.EMS is a critical technology of fuel economy improvement for HEVs. It is essential in control system of the hybrid powertrain. This paper presents an engine-operation-optimization based multi-modes control strategy in order to reduce the fuel consumption as well as the emission pollution while satisfy the drive abilities. Based on the finite state machine theory, the EMS is coded in software Matlab/ Stateflow and validated in the simulation program described above. As to this EMS, some control parameters, such as the battery charge state threshold for series charge operation and the current engine"on-off"state, etc., are innovationally introduced to satisfy the requirements on charge sustaining and reduction on engine"on-off"operations.Energy management control parameter optimization is an important issue which affects the performances of vehicle in depth. With the goal to reduce the fuel consumption while sustaining the battery charge state, an objective function using the penalty function approach has been built up. The control parameters of SWB6116HEV were optimized via the real-valued genetic algorithm in which the mathematical crossover and mutation operators are employed.On the basis of the prototype with AMT, this paper theoretically studies the optimal fuzzy logic based EMS for the series-parallel hybrid electric vehicles. Two fuzzy controllers in series are included in the EMS to decide the configuration and distribute the torques in parallel configuration, respectively. The simulation results identify its feasibility.Last, the configuration of the CAN-based control network and the development approach of the VCU for the series-parallel hybrid bus are introduced in this paper. Moreover, a CAN-based Assist & Collection System is developed to help the driver to drive a vehicle tracking the referenced speed profile during a driving cycle test, and to collect the data about fuel consumption and drive abilities. The road test results identify that the required drive abilities are satisfied and the fuel consumption is reduced by 21.3% on average compared with that of a conventional baseline bus.
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