Hydraulic System Control for a Hybrid Continuously Variable Transmission Based on an Electric Oil Pump

An electric oil pump (EOP) for the hydraulic system of a continuously variable transmission (CVT) based hybrid electric vehicle is developed by considering the arrangement of structures and the realization of an electric drive mode (EDM). The basic parameters required for the EOP motor are obtained by analyzing the flow rate and pressure of CVT. Then, the EOP motor is designed and developed. Current-pressure characteristics of different solenoid valves are measured and analyzed for designing the CVT speed ratio controller. The speed ratio controller, pressure controller, and EOP control strategy are analyzed in detail with the use of EOP as the power source of the hydraulic system only. The performances of the speed ratio controller and the EOP control strategy are verified on a test bench. Experimental results show that the steady-state error of the speed ratio controller is minimal, and the response time of speed ratio from 0.7 to 1.4 can be shortened approximately 0.49 s to 1.40 s by increasing the EOP speed from 1000 to 2500 r/min. The actual EOP speed can also be adjusted by the demand of system flow to save the maximum amount of energy.