Structure and working principle of Hitachi excavator hydraulic control system

Structure and working principle of Hitachi excavator hydraulic control system

by Weston Gao on April 29, 2022 Categories: Repair Technology

1. The composition of the main hydraulic circuit system
Hitachi excavator main hydraulic circuit system is composed of main hydraulic system and pilot circuit system. The main hydraulic circuit supplies the hydraulic oil of the pump to the actuators of each operating function.

2. The composition of the pilot circuit hydraulic operating system
The hydraulic system is composed of one engine, one main pump, one pilot pump, one control valve and four hydraulic cylinders, one rotary motor and two traveling motors. The pump is driven by the engine through the input shaft. .The hydraulic oil of the main pump flows to each actuator through the control valve. The hydraulic oil of the pilot pump flows into the pilot circuit.

3. Main circuit
①. Main hydraulic circuit
The main hydraulic circuit is composed of suction circuit, output circuit, oil return circuit and brand friend circuit. The hydraulic system consists of one main pump, one control valve, one traveling motor and four hydraulic cylinders.
The main pump is an oblique shaft type variable displacement axial piston pump, which is driven by the engine (the engine speed ratio is 1.0)
②. Attraction circuit and output circuit
The pump sucks the oil in the hydraulic oil tank through the suction oil filter, the oil flows from the pump into the control valve, and then is released from the oil tank port, and the oil released by the main pump flows to each actuator through the control valve.
The control valve controls various hydraulic functions, and the return oil from each actuator flows back to the hydraulic oil tank through the control valve and the hydraulic oil cooler.
③. Oil return circuit
All the oil released by each actuator flows back to the hydraulic tank through the control valve. There are bypass check valves in the oil return circuit, and the set pressures are 9.8×10^4pa and 4×9.8×10^4pa respectively. Usually the return oil flows back to the hydraulic oil tank through the hydraulic oil cooler and the left control valve. When the oil temperature is low, the viscosity becomes high, and the resistance when passing through the oil cooler also increases.
When the oil pressure exceeds 9.8×10" 4pa, the return oil flows directly back to the hydraulic oil tank, which can raise the oil temperature to an appropriate height in a short time.
When the oil cooler is blocked, the return oil flows directly back to the hydraulic tank through the bypass check valve.
When the bypass check valve is blocked, it is located between the cooler and the hydraulic oil tank, and its set pressure is 4×9.8×10^4pa.
There is a direct-flow oil filter in the hydraulic box. The oil flowing from the control valves on the left and right sides is combined and filtered by the direct-flow oil filter. There is a bypass safety valve in the direct-flow oil filter. When the filter element is blocked, the differential pressure reaches At 9.8×10^4pa, the bypass safety valve is opened, and the oil flows directly back to the hydraulic oil tank.
④. Oil drain circuit
The oil leaking from the motor and brake valve, as well as the oil in the lubricating oil circuit, all accumulate and flow back to the operating oil tank through the oil drain circuit.
⑤. Travel motor oil drain circuit
The oil leaking from the left and right walking motors is discharged from the oil discharge ports of each motor casing, and after the confluence, passes through the central joint and flows back to the hydraulic oil tank through the DC oil filter.
⑥. Rotary motor oil drain circuit
After the oil leaked from the rotary motor is discharged, it flows back to the hydraulic oil tank through the DC oil filter together with the oil discharged from the walking circuit.
⑦. Output pressure control
The unloading safety valve in the control valve keeps the output pressure of the pump constant. All operations were operated at a set pressure of 330×9.8×10^4Pa.
During the excavation operation, the set pressure became 370×9.8×10^4Pa.
The Langyong cut-off safety valve releases the high pressure oil into the hydraulic oil tank to prevent the oil pressure system and the engine from being overloaded.
⑧. Pilot circuit
The pilot circuit is composed of suction and oil discharge circuits. The pilot system includes a pilot pump, a flush valve, a safety valve, 2 high-speed solenoid valves, 3 pilot valves and a solenoid valve device.
After the hydraulic tank oil is sucked out, it flows to the pilot pump through the suction oil filter. The oil released by the pilot pump flows to the pilot valve through the solenoid valve unit and the safety valve. Return oil from the actuator flows through the hydraulic components to the hydraulic tank.
⑨. Oil suction circuit, oil delivery circuit and oil return circuit
The pilot pump sucks oil in the hydraulic mailbox through the suction filter. The oil discharged from the pilot pump is filtered by the pilot oil filter and then flows to the solenoid valve. The solenoid valve unit has a pilot safety valve that controls the pilot circuit pressure.
The pilot oil is divided into two paths, one flows into the safety valve, the other flows into the control valve travel motor, and is injected into the rotary motor through the solenoid valve device.
The oil from the safety valve flows through the oil filter to the 3 pilot valves. The oil from the 3 pilot valves flows to the hydraulic oil tank through the safety valve.
⑩. Control system
The control system is composed of a hydraulic system and an electrical system, and uses various sensors and solenoid valves to monitor and control various operational data. These data are turned into electrical signals and sent to the computer, which processes and controls the actuators to work in the most appropriate state.
The control system mainly controls the main pump and control valve to form various characteristic actions, so that the performance
be further improved.
. Pump control system
(1) Load sensing control
The function of this system is to save energy and improve fretting operability, adjust the flow of the main pump according to the load of the actuator, and keep the differential pressure between the two control valves constant.
(2) Speed ​​sensor control
The function of the system is to improve the production capacity and operation performance on high ground, adjust the flow of the main pump according to the change of engine speed, and change the input torque of the pump to improve the efficiency of the engine.
①②. Valve control system
(1) Diversion control system
The system improves compliance operation, workload and inching operability, and adjusts the variable pressure compensation valve appropriately according to the actuator load.
(2) Job selection control system
The system is used to control the variable pressure compensation valve to make the actuator speed in the most appropriate situation to carry out the action required for various jobs.
①③. Walking motor control system
There are three kinds of walking speeds: high-speed, low-speed, and medium-speed, and the most appropriate walking speed can be selected according to the working situation. The travel speed is controlled by the change of the driving angle of the combined travel motor and the adjustment of the variable pressure compensation valve.
①④. Other control systems
(1) Insurance circuit of parking brake
The parking brake is released only during swivel and forearm backhoe operations, and the parking brake function is used in all other situations.
(2) Warm-up control system
When the oil temperature is below 30 ° to start the engine, the minimum pump flow and the increase of the engine speed will make the engine and hydraulic system run fast.
(3) Power supercharger control system
The system applies back pressure to the safety valve, instantly increases the set pressure of the safety valve, and increases the operating power in a short time.

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