In order to understand and design the hydraulic system of excavator, we must first analyze the working process of hydraulic excavator and understand the operation requirements of excavator. It is necessary to master the flow, force and power requirements of each hydraulic action element, the compound action requirements of the hydraulic action element matching each other, and the flow distribution and power distribution of the oil pump when supplying oil to each hydraulic element at the same time.
The following basic actions of full bucket lift rotation are explained.
After excavation, the arm cylinder will lift the arm up, lift the bucket, and turn the hydraulic motor to make the turntable turn to the earth unloading place, which is mainly the compound action of the arm and the rotation. When the lifting and turning of the arm are operated at the same time, the two require matching in speed, and when turning to the specified unloading position, the arm and bucket are automatically raised to the correct unloading height. Because the rotation angle required for unloading is different, it varies with the position of the excavator relative to the dump truck, so the relative relationship between the lifting speed and the rotary speed of the arm can be adjusted. If the unloading angle is large, the rotation speed is faster and the lifting speed of the arm is slower.
Because of the large inertia, the oil pressure will rise very high in the rotary starting, which may overflow from the relief valve. At this time, the overflow oil should be supplied to the arm. In addition to the lifting of the moving arm, the bucket rod should be placed at the same time, and sometimes the bucket should be adjusted. In this case, the rotary arm, the bucket rod and the bucket are combined.
Because of the high pressure of the cylinder of the arm when the full bucket is raised, the flow rate of the variable pump is reduced. In order to make the lifting and rotating of the arm and the outside of the bucket rod cooperate with each other, one pump is used to supply the arm cylinder, and the other pump has some oil supply arms besides the rotary and bucket rod. However, due to the high oil pressure of the arm lift, the one-way valve is closed most of the time, and the left pump is only for rotation and bucket rod.
Three pump system oil supply, each pump supply a hydraulic action element, no interference. Generally, the flow rate required for rotary motion is small, and a smaller flow pump should be used. If driven by a large flow pump, the rotation inertia is very large and the power loss is large in the process of starting and braking.