1. Hitachi excavator main hydraulic circuit
The main hydraulic circuit is composed of a suction circuit, an output circuit, an oil return circuit and an oil discharge circuit. The structure diagram is shown in Figure 2-2. The hydraulic system has one main pump, one control valve, one traveling motor and four hydraulic cylinders.
Control valve hydraulic oil cooler hydraulic oil tank|suction oil filter) Main probe 57 Figure 2-2 Main hydraulic circuit structure block diagram The main pump is a bent-axis variable displacement axial piston pump, which is driven by the engine (engine speed ratio 1.0).
2. Suction circuit and output circuit
The pump sucks the oil from the hydraulic oil tank through the suction filter, and the oil flows from the pump into the control valve and then discharges from the oil tank port. The oil discharged from the main pump flows to each actuator through the control valve.
The control valve controls various hydraulic functions. 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 line
All the oil released by each actuator flows back into the hydraulic oil tank through the control valve.
There is a bypass check valve in the oil return path, and its set pressure is 9.8×10Pa and 4×9.8×10Pa respectively. Normally, 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 higher, and the resistance when passing through the oil cooler also increases.
When the oil pressure exceeds 9.8×10Pa, 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 oil tank through the bypass check valve.
The bypass check valve is located between the cooler and the hydraulic oil tank, and its set pressure is 4×98×10Pa.
A DC oil filter is installed in the hydraulic oil tank. As shown in Figure 2-3, the oil flowing from the control valves on the left and right sides merges and is 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 and the differential pressure reaches 9.8×10Pa, the bypass safety valve opens and the oil flows directly back to the hydraulic oil tank.
4. Oil drain circuit
The oil leaking inside the motor and brake valve and the oil in the lubricating oil circuit are all accumulated and flow back to the operating oil tank through the oil drain circuit.
5. Traveling motor oil drain circuit
As shown in Figure 2-4, the oil leaking from the two walking motors on the left and right is discharged from the oil outlet of each motor housing, and flows back to the hydraulic oil tank through the DC filter through the central joint after merging.
6. Rotating motor oil drain circuit
After the oil leaking from the rotating 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. The oil output pressure control diagram is shown in Figure 2-5.
7. Output pressure control
The unloading safety valve in the control valve keeps the output pressure of the pump constant. All operations are operated at a set pressure of 330×9.8×10Pa.
During the excavation operation, the set pressure becomes 370×9.8×10Pa.
The surge stop safety valve releases high-pressure oil into the hydraulic oil tank to prevent the hydraulic system and the engine from being overloaded.
8. Pilot circuit
The pilot circuit is composed of a suction circuit and an oil output circuit. The block diagram is shown in Figure 2-6. The pilot system has a pilot pump, a buffer valve, a safety valve, 2 high-speed solenoid valves, 3 pilot valves, and solenoid valve devices (including EHC valves and 1 pressure reducing valve).
After the oil in the hydraulic oil tank is sucked out, it flows to the pilot pump through the suction filter. The oil discharged by the pilot pump flows to the pilot valve through the solenoid valve device and the safety valve. The return oil from the actuator flows to the hydraulic oil tank through the hydraulic components.
1. Oil suction line, oil delivery line and oil return line
The pilot pump sucks the oil from the hydraulic oil tank through the suction filter. The oil discharged by the pilot pump flows to the solenoid valve after being filtered by the pilot oil filter. There is a pilot safety valve in the solenoid valve device that controls the pressure of the pilot circuit, as shown in Figure 2-7.
The pilot oil is divided into two paths, one flows into the safety valve, the other flows into the control valve, the traveling motor, and is injected into the rotating 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 back to the hydraulic oil tank through the safety valve.
2. Control system
The control system is a combination of Hitachi excavator hydraulic system and electrical system, using various sensors and solenoid valves to monitor and control various operating data. These data are converted into electrical signals and sent to the computer, where the computer processes and controls each actuator 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 is further improved.
3. Pump control system
(1) Load sensing control The function of this system is to save energy and improve micro-operation, adjust the flow of the main pump according to the load of the actuator, so that the differential pressure between the two control valves is kept constant.
(2) Speed sensor control The function of this system is to improve production capacity and operating performance on high ground, adjust the main pump flow according to the change of engine speed, and change the pump input torque to improve the efficiency of the engine.
4. Valve control system
(1) Diverting control system This system can improve compound operation, workload and micro-operation, and adjust the variable pressure compensation valve appropriately according to the load of the actuator.
(2) Job selector control system This system is used to control the variable pressure compensation valve, so that the actuator speed can implement the actions required for various jobs under the most appropriate conditions.
5. Walking motor control system
There are three kinds of walking speeds: high speed, medium speed and low speed, and the most appropriate walking speed can be selected according to the operating conditions. The walking speed is controlled by the change of the driving angle of the combined walking motor and the adjustment of the variable pressure compensation valve.
6. Other control systems
(1) The safety circuit of the parking brake releases the parking brake only during rotation and forearm backhoe operation, and has the parking brake function under any other conditions.
(2) Warm-up control system When the oil temperature is 30°C to start the engine, the minimum pump flow rate and engine speed will automatically increase so that the engine and hydraulic system will warm up quickly.
(3) Power booster control system This 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.
