Multi-Performance Optimal Gearshift Schedule for Vehicle Adaptive to Curves of the Road 2018-01-1168
Gearshift schedule of stepped automatic transmission (SAT) determines the timing when the gearbox should be shifted from a certain gear position to an adjacent one, which directly affects the performance of complete vehicle. To optimize the comprehensive performance considering power performance, fuel economy, and driver’s performance expectation, the formulation of gearshift schedule needs to take into account a number of factors such as the expression of different performance indices, the identification of driver’s intention on each sub-performance, and the adaption to driving conditions especially the road slope and curve. Based on our previous work, this investigation is focused on the adaptability of the gearshift schedule to curves of the road that could ensure the safety of vehicle and meanwhile maintain an optimal comprehensive performance reflecting a specific driver’s performance expectation. The influence of curves on vehicle dynamics has been analyzed, an improved safe velocity model has been proposed, and a vehicle dynamic model considering the road curve has been built. The power performance index has been modified using the built vehicle dynamic model to construct the comprehensive performance evaluation function. While the improved safe velocity corresponding to various curves are used as one additional constraint to optimize the multi-performance gearshift schedules adaptive to the curves. To demonstrate the feasibility of the proposed approach, the power performance dominant gearshift schedules and the fuel economy dominant gearshift schedules corresponding to curve driving and straight road driving have been formulated, and these gearshift schedules have been compared via simulations of vehicle driving on curves with different turning radius. The simulation results show that the improved gearshift schedules considering the road curves could reduce the gearshift times, ensure driving safety and stability, and meanwhile maintain acceptable comprehensive performance to reflect driver’s intention.