Characteristics of high energy-efficient Electro-hydraulic power source driven by servo motor and variable pump

An electro-hydraulic power source is a unit that provides power for a hydraulic system, whose energy efficiency determines the whole system's energy efficiency. The electro-hydraulic variable displacement proportional pump has the disadvantages of bad controllability, slow dynamic response in low-pressure condition, and high energy consumption in its non-working period (due to its electric motor still running at a rated speed). The electro-hydraulic variable displacement pump has some drawbacks regarding bad controllability. Aiming the above problems, a new electro-hydraulic power source based on pressure-controlled variable piston pump driven by a servo motor is developed in this paper. The pump's output pressure can be continuously controlled without throttle losses through changing a swash-plate angle of the pump, and the output flow can be continuously controlled by changing motor speeds. A simulation model is established based on the mathematical models of pressure-controlled pump and servo motor, and the characteristics of its constant pressure control and constant flow control are discussed. A test bench is built to study its characteristics of pressure control, flow control, and energy efficiency. The results show that: (1) the proposed power source can realize the pressure control of the system, the direct open-loop control performance of the electro-hydraulic pilot valve is better than that of the speed-variable proportional-integral closed-loop control; (2) the leakage caused by load pressure change can be supplemented by speed and the control accuracy error is lower than 0.2%; (3) under the situation of pressure maintaining without flow outputs, pressure unloading and constant pressure control operating, through controlling the motor speed, the energy consumption of the power source can be reduced by almost 30% compared to a traditional power source.