1. Basic circuit The basic circuit is composed of one or several hydraulic components, which can complete specific functions and is the basic unit of the system.
2. Pressure limiting circuit The pressure limiting circuit is used to limit the pressure so that it does not exceed a certain set value, so that the system and components are not damaged due to overload.
Digging manipulator arm and stick cylinder inlet and return circuits are often paired with parallel pressure limiting valves (overload valves) to limit the maximum locking pressure of the hydraulic cylinder in the locked state; if this pressure is exceeded, the pressure limiting valve opens , Unloading, protecting hydraulic components and pipelines from damage. For example, when the excavator bucket is digging, the boom must be stressed. In order to maintain normal operation, the boom hydraulic cylinder is in a "non-working state", but it must have a sufficient locking force to resist stretching or compression. The blocking pressure sometimes exceeds the maximum working pressure of the system. When the blocking pressure is greater than the set value of the overload valve, the overload valve opens and returns oil to the tank. In theory, the setting pressure of this pressure limiting valve can be independent of the pressure of the hydraulic system. Moreover, the higher the setting pressure, the greater the locking force, which is beneficial to mechanical operations. However, the effect of excessively high setting pressure The strength of the hydraulic components and the safety of the hydraulic lines. In general, the set pressure of the overload valve is 1.25 times the system pressure.
Speed limit circuit Speed limit circuit is used to ensure the safety of the operation. In order to prevent the boom from dropping too fast due to its own weight, the one-way throttle valve is installed on the return path of the large cavity of the boom cylinder. The corresponding return path of the digging motor arm, arm, and bucket directional valve is equipped with a throttle oil path, which can also prevent the boom, arm, and bucket from falling too fast due to their own weight.
Speed limit circuit
Speed limit circuit is used to ensure the safety of the operation. In order to prevent the boom from dropping too fast due to its own weight, the one-way throttle valve is installed on the return path of the large cavity of the boom cylinder. The corresponding return path of the digging motor arm, arm, and bucket directional valve is equipped with a throttle oil path, which can also prevent the boom, arm, and bucket from falling too fast due to their own weight.
Rotary mechanism brake circuit and buffer circuit
When the excavator rotates, the moment of inertia is large, and the starting and braking are frequent. A special circuit should be used to ensure safety and protect the components.
(1) Brake circuit
Rotary mechanism often uses hydraulic brake, mechanical brake and machine hydraulic brake.
Hydraulic braking is to achieve rapid braking by cutting off the inlet and outlet oil paths of the rotary motor and generating a large back pressure on the oil return path. The braking force is large. The braking of Yuchai excavator's rotary motor and walking motor is hydraulic brake.
(2) Buffer circuit
In order to reduce the excessive impact during braking, two buffer valves are installed on the inlet and outlet oil paths of the rotary motor. When the rotary motor suddenly stops or reverses, the pressure oil in the high-pressure oil path of the motor is discharged from the buffer valve back to the oil tank. The oil circuit is filled by the oil supply circuit through the check valve, thus eliminating the hydraulic shock.
The slewing motor of the excavator adopts such a buffer circuit of two buffer valves and two one-way charge valves. The setting pressure of the buffer valve is equal to the rated working pressure of the rotary motor. The charge pressure of the one-way charge valve is determined by the return circuit The back pressure valve is provided, and the back pressure for oil supplement is generally 0.3-0.5MPa.
