A distributed control system for an automatic mechanical transmission of a fuel cell city bus

This paper proposes a study on the distributed control system of a non-clutch automatic mechanical transmission for an electrified power-train applied on a fuel cell city bus. The control system is composed of three electronic controllers, the vehicle control unit (VCU), the electric motor control unit (MCU) and the transmission control unit (TCU). The vehicle can accelerate or decelerate, the electric motor can drive, slide or brake, and the transmission can upshift or downshift. Therefore, there are twelve possible operation modes. Removing the unreasonable modes, four modes need to be considered. A two-layer control strategy based on the four modes is designed, including a two-parameter optimal shift decision strategy and a shift process control strategy with a sliding mode control algorithm. Simulation results show that, compared to the energy consumption in a non-shift strategy, the energy consumption can be reduced by 5.3% and 7.0% with the AMT system in cases of being without and with automatic shifting strategies in the braking process, respectively. Experiments on test bench show that, the upshifting process lasts about 2.09s, and the downshifting process lasts about 1.59s. The time can be reduced by enlarging the torque rate limitations of the electric motor during dynamic process, and by improving the performance of the stepping motor and the mechanical system of the transmission.