The hydraulic system of the excavator is a combination of various hydraulic components organically connected with pipelines according to the transmission requirements of the excavator working device and each mechanism. It mainly includes the hydraulic oil tank, the main pump, the multi-way valve, the pipeline and the oil cylinder, the motor, and other parts of the execution of each action. Its function is to use oil as the working medium, then use of hydraulic pump to convert the mechanical energy of the engine into hydraulic energy and transfer it, and then through the hydraulic cylinder and hydraulic motor to turn the hydraulic energy back into mechanical energy, to achieve various actions of the excavator.
Working principle
The excavator hydraulic system is composed of some basic circuits and auxiliary circuits, which include a working circuit, a pressure limiting circuit, an unloading circuit, a buffer circuit, a throttle speed regulation, and throttle limiting circuit, a walking speed limiting circuit, and pilot valve control circuit. Its components are mainly composed of a working pump, supplement oil pump, pilot control valve, distribution valve, safety valve, boom cylinder, boom cylinder, bucket cylinder, oil tank, and related pipelines. In the working process of the excavator hydraulic system, the hydraulic oil is drawn from the bottom of the tank through the oil filter by the working pump, and the hydraulic oil with a certain pressure is output from the oil pump into a set of parallel distribution valves. The corresponding action is realized through the handle - → pilot valve - → working valve group. The total pressure of the whole system is limited by the total safety valve on the total oil circuit. The safety valve of each working oil circuit plays the role of overload protection and oil supplement for the corresponding oil circuit respectively.
Basic requirement
The action of a hydraulic excavator is complex, where the mechanism often starts, braking, reverses, load changes, impact and vibration frequently, and field operation, temperature, and geographical location change greatly, so according to the working characteristics and environmental characteristics of the excavator, the excavator hydraulic system should meet the following requirements:
1) To ensure that the excavator arm, bucket rod, and bucket can operate separately, or can cooperate to achieve compound action.
2) The action of the working device and the rotation of the turntable can be carried out both individually and in combination to improve the productivity of the excavator.
3) The left and right tracks of the crawler excavator are driven respectively, making the excavator easy to walk, flexible to turn, and can be turned on the spot to improve the flexibility of the excavator.
4) Ensure that all actions of the excavator are reversible and continuously variable.
5) Ensure the safe and reliable work of the excavator, and each actuator (hydraulic cylinder, hydraulic motor, etc.) has good overload protection; the Rotary mechanism and walking device have reliable braking and speed limit; Prevent the boom from falling fast due to its weight and the whole machine speeding slope.
The excavator hydraulic system should be:
1) High transmission efficiency to give full play to the power and fuel economy of the engine.
2) The hydraulic system and hydraulic components have sufficient reliability under the action of large load changes and sharp vibration shocks.
3) Adjust the lightweight vibration-resistant cooler to reduce the total heat of the system, so that the hydraulic oil temperature does not exceed 80 degrees when the main engine continues to work, or the temperature rise does not exceed 45 degrees.
4) Because the excavator operation site is dusty, the hydraulic oil is easy to be polluted, so the sealing performance of the hydraulic system is better, the sensitivity of the hydraulic components to oil pollution is low, and the entire hydraulic system should be equipped with an oil filter and dustproof device.
5) A hydraulic or electro-hydraulic servo control device is used to set up an automatic control system for the excavator, thereby improving the technical performance of the excavator and reducing the labor intensity of the driver.
System type
According to the characteristics of hydraulic pumps, the hydraulic system used by hydraulic excavators is roughly divided into three types: quantitative system, variable system, and quantitative and variable system.
Quantitative system
In the quantitative system used by hydraulic excavators, the flow is constant, that is, the flow does not change with the load, and the speed is usually adjusted by throttling. According to the quantity and combination form of oil pumps and circuits in the quantitative system, it can be divided into single pump single loop, double pump single loop quantitative system, double pump double loop quantitative system, and multi-pump multi-loop quantitative system.
Variable system
In the variable system used in hydraulic excavators, step-less speed regulation is realized by volume variable, and there are three adjustment methods: variable pump-quantitative motor speed regulation, quantitative pump-variable motor speed regulation, and variable pump-variable motor speed regulation.
The variable system adopted by hydraulic excavators mostly adopts the combination of variable pumps and quantitative motors to realize stepless variables, and all of them are double pumps and double circuits. According to whether the variables of the two circuits are related, they can be divided into two kinds: sub-power variable system and total power variable system. Each oil pump of the sub-power variable system has a power regulating machinery, and the flow change of the oil pump is only affected by the pressure change of the circuit in which it is located, which has nothing to do with the pressure change of the other circuit, that is, the oil pumps of the two circuits independently carry out constant power regulating variables, and the two oil pumps each have a bucket of engine output power; The two oil pumps in the full power variable system are balanced by a total power regulating mechanism, so that the pendulum Angle of the two oil pumps is always the same, the synchronization variable and the flow rate are equal. What determines the flow rate change is the total pressure of the system, and the power of the two oil pumps is not the same in the range of variables. The regulating mechanism has two forms mechanical linkage and hydraulic linkage.
