Optimal Control Allocation-Based Automatic Transmission Upshift Control Strategy for Inertia Phase

The development of a vehicle equipped with a step-ratio automatic transmission (AT) requires manual calibration to enhance the shift quality. This involves labor-intensive iterations in a prototype vehicle to balance shift time, smoothness, and energy for every realizable gear combination. An improved shift control method is desired to deliver optimized shift quality with reduced calibration needs. This article proposes a hierarchical optimal control strategy for AT upshift aimed at optimizing shift time, comfort, and thermal loss during the inertia phase with minimal calibration effort for faster product development. The strategy consists of a static model-based predictive controller coupled with an optimal control allocation algorithm. The superimposed variable-gain feedback controller commands the AT input torque required to complete the inertia phase in the specified time. The optimal control allocation algorithm coordinates two clutches and the engine by solving a constrained quadratic programming problem to deliver the desired input torque, and minimize AT output torque tracking error and clutch power loss for shift comfort and thermal efficiency, respectively. The modulation of the off-going clutch allows fast, yet comfortable shifts as compared to the conventional shift control. The online performance of the control strategy is verified by realistic shift simulations and compared to the optimal profiles established through off-line control parameter optimization. The ease of shift calibration is demonstrated by setting different targets for shift time and output torque profile. The control robustness is verified against clutch torque and engine torque delivery errors.