Abstract: Conventionally, continuously variable transmission (CVT) improves fuel economy by ensuring the engine works under a high efficiency condition. However, this method does not pay any attention to the CVT efficiency. The CVT efficiency changes from 70% to 95% with its work condition, which also has considerable influences on fuel consumption of the system. Based on the analysis of how CVT efficiency and engine efficiency influence the fuel consumption of the system, an optimal economy control method with consideration of both engine and CVT efficiency is proposed. An optimal algorithm is proposed to calculate the combinations between the engine torque and CVT ratio in order to achieve the highest overall efficiency of engine and transmission system. A simulation model is built to validate the optimal algorithm. Experiment under several static vehicle speeds are also carried out to validate the control method. Simulation and experiment results indicate that fuel consumption of the system is reduced by more than two percent after the optimization.

Key words: Efficiency, Optimal economy control, Continuously variable transmission