Effect of gear shift and engine start losses on control strategies for hybrid electric vehicles

In this paper, energetic loss models in the events of shifting gear and starting engine in a parallel Hybrid Electric Vehicle equipped with an Automated Manual Transmission (AMT) will be introduced. The optimal control algorithm for the start-stop, power split and gear shift problem based on Dynamic Programming-Pontryagin's Minimum Principle control approach is used to evaluate the effect of gear shift and engine start losses on the optimal solution. Furthermore, with preview route information available, a model predictive control algorithm is utilized to investigate the achievable fuel savings with respect to the prediction horizon. Under influence of the gear shift loss, simulation results of the prototype hybrid passenger car disclose a superior fuel efficiency property of the powershift AMT over its normal AMT counterpart. Sensitivity analysis of the traction force interruption time in a gear shift process can give a new perception on fuel economy benefit of powershift transmissions (e.g. automatic, dual clutch, powershift AMT, etc.) over a normal AMT. The study also reveals a minimum prediction length of 4s required for the design of such a realtime implementable controller to get the possible maximum fuel economy level under the impact of the engine start loss.