Abstract: Parallel hybrid electric vehicle is becoming an attractive technique in the research of automobile for the reason of environment and energy. Coordinated control issue is one of the difficult control issues of parallel hybrid electric system. On-board engine torque estimation is the key technology of coordinated control algorithm. Mean value SI engine modeling is introduced and an expression of the mean effective torque is derived on the basis of the model. The derivative result shows that main parameters which affect the mean effective torque are indicative efficiency, friction torque and pump torque, and product of volumetric efficiency and air pressure of manifold. Parameters of the expression are identified by experimental results of an electric-controlled SI engine. Calculation for steady and dynamic states is presented. Steady experiments at a throttle position of 10% and different speeds are performed on the engine. Comparison of experiment and calculation results shows all relative errors are within 7%. Moreover, dynamic experiments are carried out with a load of 40 N•m and a throttle step from 24% to 44%. Relative errors are less than 8.5%. Error analysis shows that on-board torque estimation based on the mean value SI engine model is acceptable.

Key words: Coordinated control, Mean value engine model, Torque estimation