According to the characteristics of hydraulic pump, there are two types of hydraulic system used in hydraulic excavator: quantitative system and variable system.
1. Quantitative system. In the quantitative system of hydraulic excavator, the flow rate is constant, that is, the flow rate does not change with the load, and the speed is usually regulated by throttling. According to the quantity and combination form of oil pump and circuit in quantitative system, it can be divided into single pump single circuit quantitative system, double pump single circuit quantitative system, double pump double circuit quantitative system and multi pump multi circuit quantitative system.
2. Variable system. In the variable system of hydraulic excavators, the volume variable is used to realize the stepless speed regulation. There are three kinds of regulation modes: variable pump variable motor speed regulation, quantitative pump variable motor speed regulation, variable pump variable motor speed regulation. The variable system of hydraulic excavator mostly adopts the combination of variable pump and certain motor to realize stepless variable, and all of them are double pump and double loop. According to whether the variables of the two loops are related or not, it can be divided into two kinds: partial power variable system and full power variable system. Each oil pump in the variable power system has a power regulating mechanism. The flow change of the oil pump is only affected by the pressure change of its own circuit, and has nothing to do with the pressure change of the other circuit. That is to say, the oil pumps in the two circuits adjust the variable power independently, and each oil pump has a bucket of engine output power. The two oil pumps in the full power variable system are balanced and regulated by a total power regulating mechanism, so that the power of the two oil pumps is different in the variable range. Its regulating mechanism has two forms: mechanical linkage and hydraulic linkage.