Excavators basically adopt hydraulic transmission. According to the transmission requirements of various mechanisms and devices of excavators, the combination that organically connects various hydraulic components (including hydraulic pumps, hydraulic motors, hydraulic valves, hydraulic cylinders, etc.) with pipelines in a certain way is called the hydraulic system of excavators. The function of the hydraulic system is to take the mechanical energy of the engine as the medium, use the hydraulic pump to convert the mechanical energy of the engine into the hydraulic energy of the hydraulic system, and transmit it. Finally, it is converted into mechanical energy through the hydraulic cylinder or hydraulic motor to realize various working actions. According to different functions, the hydraulic system of excavator can be divided into three basic parts: walking device hydraulic system, slewing device hydraulic system and working device hydraulic system. The traveling device is the supporting part of the whole excavator. It is used to bear the self weight of the whole machine and the excavation reaction force of the working device, so that the whole machine can be stably supported on the ground; At the same time, we have to complete the walking task. Most of them adopt wheel type and crawler type, and are driven by walking hydraulic motor. The function of the slewing device is to complete the left and right slewing of the upper vehicle in the process of excavation and unloading. It is driven by the slewing hydraulic motor. The working device is mainly composed of bucket, bucket cylinder, stick, stick cylinder, boom and boom cylinder. It includes three hydraulic systems of bucket, stick and boom [1].
The hydraulic excavator has multiple actuators (bucket, stick, boom, swing and travel, etc.), multi degrees of freedom, a large number of hydraulic actuators, and the required actions are complex; In addition, it is necessary to start, brake and reverse frequently during the operation, with large changes in external load, frequent impact and vibration and poor working environment. Therefore, high requirements are put forward for the hydraulic system of excavator, mainly including the following aspects:
(1) The hydraulic excavator requires high handling performance. It requires micro movement during fine operation. When the productivity is high, it requires rapid action, and the speed regulation range is wide. The excavator operation objects and working conditions are changeable. Therefore, the speed regulation performance of each actuator is good.
(2) During the operation of hydraulic excavator, each hydraulic actuator can not only act independently, but also cooperate with each other for compound action. It is required that almost all bucket, stick, boom, rotation and walking can be compound action, and the forms of compound action are complex and diverse. The compound handling performance is required to be good, and the flow and power of each hydraulic actuator participating in the compound action should be reasonably distributed.
(3) Hydraulic excavator has high power, long operation time and high energy consumption, which requires high efficiency of hydraulic system, so as to reduce energy consumption and emission. At the same time, the system should have good heat dissipation performance, and the hydraulic oil temperature should not be too high. The loss of hydraulic components and pipelines should be reduced as much as possible, so the hydraulic system of hydraulic excavator must fully consider energy saving.
(4) Improve engine power utilization as much as possible, improve economy and reduce emissions. When the external load changes, the hydraulic system is required to have a good power match with the engine.
(5) In order to improve the operation efficiency and reduce the labor intensity of the driver, the operation is required to be flexible, simple and labor-saving.
(6) The mechanical work is required to be safe and reliable. Each hydraulic element shall be provided with good overload protection and buffer device. The traveling mechanism and rotary mechanism shall have reliable braking and speed limit to prevent the stick and boom from falling rapidly due to self weight and the whole machine from overspeed sliding.
