The energy-saving hydraulic system commonly used in medium-sized excavators mainly includes positive flow control system, negative flow control system and load sensing system.
In the positive flow control system, the displacement of the hydraulic pump is proportional to the output pressure of the pilot control handle, which can effectively eliminate the air flow loss when the control handle is in the middle position. When the handle starts to operate, the pilot pressure rises and the control pump displacement increases. In this process, the bypass throttling is still needed to increase the pump output pressure to meet the load pressure.
The negative flow control system is equipped with a flow detection device on the bypass oil return path. By detecting the pressure of the bypass oil return of the control valve, the demand of the system for hydraulic oil can be judged, and then the variable mechanism of the hydraulic pump can be controlled, so that the pump displacement and the bypass oil return pressure have a double linear relationship.
The main characteristic of the load sensing control system is to use the pressure compensation method to distribute the flow. It can use one oil pump to supply oil to all hydraulic components at the same time. In order to keep the pressure difference between the front and back of the main control valve as a constant value, the pressure compensation is adopted at the outlet of the main valve. The flow into the actuator of the excavator is only determined by the opening area of the main control valve core, which has nothing to do with the load. At the same time, it also ensures that each actuator can work independently without affecting each other.
