Hydraulic excavator hydraulic system has many forms and types, can be classified from different angles. From the form of multi-way valve can be divided into two categories: medium open system and closed load sensing pressure compensation system; from the form of pump, there are quantitative pump and variable pump; pump control mode is also many, and according to the number of pumps can also be divided into single pump, double pump, three pump and multi pump.
1.Medium open system
The system adopts three-position six-way valve, which is characterized by two oil supply routes, one is through oil supply road, the other is parallel oil supply road. This kind of oil path speed regulation mode is that the oil intake throttling and the bypass throttling act at the same time, and its speed regulation characteristics are affected by the load pressure and the oil pump flow rate, so the valve system has poor operation performance, speed regulation performance and fine adjustment performance. At the same time, the hydraulic action elements of the oil circuit system interfere with each other when they are combined together, which makes the compound action manipulation very difficult. It is very important for the hydraulic excavator to adjust the speed and the compound action maneuverability. This is a big disadvantage of the median form system.
2.Closed Load Sensor Pressure Compensation System
The closed oil circuit can supply all hydraulic action elements with one pump at the same time. The speed of each hydraulic component is only related to the stem stroke of the control valve, and has nothing to do with the pump flow of the load.
The comparison between open and closed oil circuits: the main problem of open oil circuits is that the speed regulation characteristics of valves fluctuate with the load, the multi-load work interferes with each other at the same time, and the maximum speed of hydraulic components can not be set arbitrarily. These problems can be solved by using closed oil circuit, and they have strong adaptability to various auxiliary devices. According to the needs of auxiliary devices, the complete compensation characteristics can be realized by adjusting the compensation degree, which is close to the open oil circuit characteristics and the intermediate state characteristics. The main problem of closed oil circuit is poor dynamic performance.
3.Quantitative and variable pumps
The quantitative pump is simple in structure and easy to manufacture. It is used for micro excavators with low price. But the quantitative pump angle power is large, the engine power is high, the engine power utilization ratio is low, and the productivity is affected. At the same time, the quantitative pump can not supply oil according to the required variable flow rate, the power loss is large, the fuel consumption is high, the economy is poor and the discharge is not good, so the variable pump should be used in the operation requirement of excavator.
4.Oil pump control mode
There are three kinds of energy saving control methods: negative flow control, positive flow control and load sensitive pressure compensation control. At present, excavators choose one of the control methods to achieve energy saving requirements.
The control modes that match the engine are pressure induction control and speed induction control. At present, excavators generally have these two control modes. In addition, the general hydraulic excavator also has working condition control, automatic idle speed control, control and automatic cutting control.