Electro-hydraulic control system can be divided into two types: valve control and pump control. The valve-controlled hydraulic system has fast response and high precision. The same power source can control multiple actuators, but the throttling loss is large and the energy efficiency is low. Compared with the valve control system, the closed pump control system has almost no throttling loss, and has the advantages of integration of drive and dynamic energy recovery, which can greatly reduce the heating and installed power of the system. It is the development direction of electro-hydraulic control technology at present.
According to the different actuators, the closed pump control system is composed of pump control motor and pump control cylinder. The closed pump control motor is mainly used in high power walking and rotary system, and the technology has been relatively mature. The pump control cylinder system includes two kinds of pump control symmetrical cylinder and pump control single outlet cylinder. The research of pump control symmetrical cylinder started earlier and has been improved day by day, and has been widely used in aircraft control system. The use of closed pump control cylinder technology in hydraulic construction machinery can not only simplify the hydraulic circuit, reduce the weight of the whole machine, recover the kinetic energy, but also greatly improve the energy utilization ratio of the machine.
After many years of development, although many advances have been made in pump-controlled single-bar hydraulic cylinder technology, there is still no good solution to the flow asymmetry problem caused by the area difference of single-bar hydraulic cylinder. Although the scheme of not long hydraulic one-way valve has achieved good results in the system with constant load force direction, when used in the system with frequent change of load force direction such as excavator bucket rod, there are problems such as sudden change of hydraulic cylinder speed and pressure and poor stability of the system, which affect the practical application.