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 excavation are explained.
Usually the bucket hydraulic cylinder or bucket rod hydraulic cylinder are separately excavated, or the two are combined to excavate. In the excavation process, the bucket and bucket rod have compound action, if necessary, with arm action.
When leveling the land and cutting the slope, the arm and the rod must be operated simultaneously so that the tip of the bucket can move along a straight line. At this time, the bucket rod is recovered and the arm is raised.
In order to improve the cutting speed, double pump combined flow is generally used when bucket rod is used for excavation, and three pump combined flow is used individually. When the bucket is excavated separately, double pump confluence is also used. The following three pump system is used to explain the oil supply situation of oil pump flow distribution and split-flow oil line connection during compound operation mining.
When the bucket rod and bucket are excavated by combined motion, when the oil pressure of the bucket rod is close to the pressure of the relief valve, the original overflow oil is used effectively for the bucket. When the bucket rod and the arm compound action, because the arm only plays the role of adjusting the position, mainly the bucket rod excavation, so the bucket rod priority confluence, double pump oil supply.
When the moving arm, bucket rod and bucket are combined, in order to prevent the action of the same pump from interfering with each other, the pump of the three pump system has a hydraulic action element alone. It is necessary to use throttling and other measures to distribute the flow rate, which is the same as the three pump system.
In order to effectively dig vertically, it is required to provide pressure oil to the rotary motor, produce rotary force, and keep the bucket close to the side wall for excavation, so it is necessary to supply oil and move together with the bucket rod at the same time. When the rotary and bucket rod shrink at the same time, the rotary priority oil circuit should be used to supply oil from the same pump, otherwise, the oil flow pressure is low, which makes it difficult to stick to the side wall when digging.
Variable throttle valve is arranged on the return line of the piston rod end of the bucket rod cylinder. The opening size and throttle degree of the valve are controlled by the rotary pilot pressure. If the rotary pilot pressure is large and the throttle is large, the return oil pressure of the bucket cylinder increases, which increases the pump oil supply pressure. Therefore, with the increase of the stroke of the rotary joystick, the oil pressure of the rotary motor increases and the rotary force increases.