Power Control Strategy and Performance Evaluation of a Novel Two-pump Hydraulic Control Unit for BEVs

Abstract

A hydraulic control unit system with a mechanical oil pump (MOP) and an electric oil pump (EOP) was newly designed for the lubrication and clutch-to-clutch control of a two-speed dedicated electric transmission for battery electric vehicles (BEVs), in order to solve the high-cost, poor-noise and high-energy-consumption problem exposed in previous single-EOP design with big displacement. The driving motor for BEVs can’t idle like the combustion engine when the vehicle stops still, so an EOP with small displacement is required to supply enough fluid to start the vehicle except to a low-cost MOP. Four control algorithms for the two-pump system were developed as well as the main line pressure control strategy, which were confirmed by a Hardware-in-the-Loop (HIL) test bench. The simulated and tested total pump energy consumption in a driving circle WLTC shows that the equal-power control algorithm and the transient on-demand control algorithm can obtain better performance for saving energy consumption. Several oil displacement parameter groups for the MOP and the EOP are discussed, and the results show that proper displacement group for the EOP and the MOP can obtain good balance for the total cost and the performance with the combination of proper two-pump control strategies.