During the operation of construction machinery, various complex operating environments will be encountered. At this time, variable pumps need to be used to adjust the displacement to adapt to different scenarios. In order to improve the efficiency of energy utilization, we innovatively adopted the volume speed regulation method to replace the traditional throttling speed regulation. It is precisely because of these significant advantages that variable pumps have been widely used. In terms of control methods, the development of variable pumps has shown diversification, mainly including three basic types: throttling control, LS load sensitive control and LUDV control.
1) Throttling control
In hydrostatic transmission control, throttling control is a relatively classic system control method. According to the variable control method of the pump, it can be subdivided into two throttling control modes: "positive flow" and "negative flow". This control mode was originally applied to the hydraulic system of excavators and can effectively reduce power loss. When working, the stroke of the pilot pressure control valve core is proportional to the output flow of the pump, so it is called "positive flow" control. However, the valve group design of the positive flow control hydraulic system is quite complex, which affects the response speed of the system to a certain extent.
2) LS load-sensitive control
The core principle of LS load-sensitive control is that when the external load changes, the system can automatically adjust the flow of the pump and valve to ensure that the hydraulic system can provide appropriate flow and pressure according to the load conditions, thereby improving the efficiency of the entire system. This control method regulates the pump displacement by pressure difference. When the pressure difference loses balance with the spring force on the control valve, the valve core of the control valve will be displaced, thereby changing the pump displacement.
3) LUDV control
In actual operation, the operator controls the movement of the excavator through the hydraulic joystick. The amount of oil required by the hydraulic system is provided by the main pump, which distributes hydraulic oil to the branches of each actuator through the main oil circuit. Each branch is equipped with a three-position six-way solenoid valve to generate a valve back pressure drop to match the working pressure required by the actuator. The system feeds back the maximum load pressure to the variable mechanism of the load-sensitive pump through the pilot oil circuit and compares it with the outlet pressure of the pump. According to the relationship between the load pressure and the outlet pressure of the pump, the load-sensitive pump will adjust its output flow accordingly to ensure the stable operation of the system. In the application of LUDV load sensing system, when multiple actuators work simultaneously or jointly, the main pump will supply pressure according to the continuous adjustment of multiple control valves to ensure the highest load pressure provided to the actuator.
