So far, the hydraulic system of excavator is mainly composed of two parts: main hydraulic circuit and pilot hydraulic circuit. In the main hydraulic circuit, the multi-way valve is used to control the flow rate of the hydraulic pump output to the hydraulic actuator, and the multi-way valve itself is controlled by the pilot valve in the pilot circuit. According to the type of hydraulic pump, excavator hydraulic system is generally divided into quantitative system and variable system, in which variable system is widely used.
1.Excavator Quantitative Hydraulic System
Quantitative hydraulic system is mainly used in small tonnage excavator less than 13 tons. The hydraulic system uses external meshing gear hydraulic pump with working pressure of about 16 MPa.
The reason for the application of quantitative hydraulic system in small and medium excavators are as follows :1. The quantitative pump has simple structure, low price and reliable operation. 2.Because the pump often works under non-full load, the pump has a long life. 3. because the flow rate is fixed, the speed of the actuator is stable, and the track of the working device is easy to control, the excavation surface is good.
In the quantitative system, because the flow rate is fixed, the flow rate can not be changed when the load changes, the load hour can not improve the working speed, and the power can not be fully utilized. In order to meet the operational requirements, the engine of the quantitative system should be determined according to the maximum external load and operating speed. In general, the average load of a single pump quantitative system is about 60% of the maximum load, so the average power of the engine of the system is only about 60%. When the working mechanism of excavator needs to change speed because of the operation demand, it often needs to rely on the throttling the valve to achieve, the result is large calorific value and serious waste.
2.Excavator Variable Hydraulic System
Variable system has the following performance :1. The working speed and working force can be adjusted automatically, and the working force can be reduced and the working speed increased when the external load is large.2. Variable hydraulic pump often works at full load, engine power is fully utilized, stepless speed regulation can be realized by volume variable, which is widely used in excavator.