This paper presents an optimal approach for the design of gear ratios and gear shifting strategy for parallel hybrid electric vehicle (HEV) equipped with automated manual transmission (AMT). For this purpose, an AMT model is firstly provided and integrated with a pre-transmission parallel HEV model to develop a comprehensive simulation tool for vehicle powertrain performance evaluation. Using genetic algorithm (GA), an optimization problem is then formulated for the optimal design of the AMT variables including its gear ratios as well as the variables defined for the gear shifting strategy. A weighted aggregation of the HEV fuel consumption and emissions is also employed as the fitness function. In addition, the vehicle driving performance characteristics are considered as the optimization constraints. To optimize the gearshift strategy and gear ratios, GA optimization process is performed for several traffic conditions. The results show that the approach is quite effective. A considerable improvement is achieved at congested condition due to its sensitivity to the stop-start operation of the vehicle.

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