Method for controlling speed ratio of hybrid electric vehicle in driving process

A method for controlling the speed ratio of a hybrid electric vehicle in the driving process comprises the steps that S1, a signal related to speed ratio control is received; S2, an efficiency graph of an engine and an efficiency graph of a motor are measured through experiments and optimal economical curves of the graphs are made respectively; S3, the optimal economical rotating speed of the engine under the required power and the optimal economical rotating speed of the motor under the required power are respectively calculated; S4, considering the required power ratios of the engine and the motor and influence, caused by the rotating speed, on the efficiency, the target rotating speed is calculated; S5, the target speed ratio is calculated through the target rotating speed, the vehicle speed and the main speed reducing ratio; S6, the target speed ratio is sent to a speed ratio control actuator to be executed. According to the method for controlling the speed ratio of the hybrid electric vehicle in the driving process, when the vehicle is driven in a hybrid mode, the ratios of work of the engine and work of the motor and different influences, caused by the rotating speed, on the efficiency of the engine and the efficiency of the motor are fully considered, so that the optimized target speed ratio is obtained, and the method enables the economical efficiency of the vehicle to be improved.