Power-based control of an electric oil pump for an automatic-transmission-based hybrid electric vehicle

A power-based control algorithm for an electric oil pump for a six-speed automatic-transmission-based hybrid electric vehicle was proposed. The new technology estimates the viscosity factor without having to measure the temperature of the automatic transmission fluid and controls the electric oil pump based on the required power. The viscosity factor was determined on a three-dimensional (3D) map by measuring the steady-state line pressure and the power and speed of the electric oil pump. Using the viscosity factor, the electric oil pump was controlled to supply the target line pressure according to the command power that was determined from the 3D viscosity factor-line pressure-power map. To save energy, multi-stage control was suggested which was based on low power, high power and medium power, according to the driving conditions of the vehicle. The test results showed that the proposed control method based on the electric oil pump power properly followed the target line pressure regardless of the change in the temperature of the automatic transmission fluid. In addition, when the line pressure changed owing to the additional flow rate consumption, e.g. during engine clutch engagement, the power-based control method easily followed the line pressure using only the target power, without needing to set the driving speed of the electric oil pump for each temperature. It was also found that control based on the electric oil pump power could save the driving power of the electric oil pump, unlike the situation with speed-based control, considering the product deviations.