Hitachi excavator gear pump (HY/ZFS11/16.8L) is used to supply pilot pump oil. The gear on the main pump drives the gear pump at engine speed. The pilot oil pressure is set to 5.2kPa by the pilot pressure regulator.
One of the two gears is driven by the engine through the pump transmission, thereby driving the other gear. The working principle of the gear pump is shown in Figure 2-41.
The inlet oil fills the rotating tooth groove and squeezes to the outside of the gear along the inner surface of the casing.
The oil between the output side and the suction side can only be discharged when the two gears mesh. The output pressure is set to a safe pressure of 5.2kPa, and the compressed oil is delivered to the main pump and the pilot circuit.
1. The structure and principle of the rotating motor assembly
(1) The structure of the rotating motor assembly
The rotating motor assembly includes a valve cover part, a rotating motor part and a rotating reduction gear part. The valve cover includes rotary parking brake, cross safety valve and auxiliary valve. The structure of the rotating motor assembly is shown in Figure 2-42.
The rotary motor is a swash plate type axial piston motor. The rotating motor is composed of a swash plate, a hydraulic cylinder group, a piston with a spacer, a valve plate, a parking brake and a motor housing.
Each piston is equipped with brake shoes, and 9 pistons with brake shoes are inserted in the hydraulic cylinder. Nine pistons are supported by the swash plate and slide on the angular surface of the swash plate. The hydraulic pressure causes the piston to perform linear reciprocating motion in the hydraulic cylinder group, generating a rotational force to make the hydraulic cylinder rotate.
Since the hydraulic cylinder group is connected to the output shaft with a needle, the rotational force of the hydraulic cylinder group is transmitted to the output shaft. The rotating force of the output shaft is transmitted to each rotating gear through the rotating reduction gear.
(2) Working principle of rotating motor
The casing part includes an anti-cavitation valve and a cross safety valve. The high-pressure oil enters the rotating motor through port A or port B along with the direction of rotation. The oil path of the high pressure port and low pressure port of the rotating motor is shown in Figure 2-43.
Each piston is connected to the slider with a ball or socket joint. When oil is squeezed into the top of the piston, the slider slides around the thrust plate, causing the motor to rotate. The protective enclosure fixes the slider against the plate with spring force. The oil flows into or out of the piston through the fixed valve plate.
The rotary motor is a fixed displacement motor, and its rotation speed increases or decreases according to the amount of oil delivered to the rotary motor.
2. Brake valve
(1) Safety valve operation
The brake valve structure is shown in Figure 2-44.
When the lever is neutral, the oil pressure at the P port is equal to the oil pressure at the R port. The oil pressure of the P port rises, the pressure area of the plunger, the pressure of the P port, the elastic force of the spring, and the pressure of the g chamber are balanced, and the safety valve starts to operate.
When Huozhai 21 and 7 move, the pressure in chamber g changes, so the safety pressure is affected by the spring and piston.
As the pistons 21 and 7 move, the safety pressure rises from P1 to P, and the pressure (P2) and spring force change accordingly.
(2) Pressure lifting operation of safety valve
When the pressure in the P port increases, oil pressure is generated in the g chamber, which promotes the balance between the force of the spring and the pressure (Pa), and then the piston 21 moves to the left.
The safety valve works (released) under the safety pressure of P1, and the piston 7 moves to the left. The piston 21 forces the oil flow to the R port through the orifice. When the piston 21 reaches the top of the stroke, the pressure in the g chamber is greater than the elastic force of the spring, so the piston 7 moves to the right. The piston 7 starts to move, and the h chamber and the piston 7 are dumped on the sliding surface through the groove. The pressure of the safety valve set in chamber g slowly rises from P2 to P.
The piston 7 reaches the adjusting socket, and the oil pressure in the g chamber reaches a safe set pressure. The working process of the safety valve is shown in Figure 2-45.
(3) When the pressure of the safety valve is reduced
When the oil pressure at the P port becomes 0, the oil pressure in the g chamber rises to the tank pressure. The plunger 9 moves to the right, the piston 7 is pushed to the left by the spring 16, the piston 21 is pushed to the right by the spring 1, and the one-way valve 2 is opened while sucking oil from the R port, and the piston 21 returns to the original port.
3. The function of preventing cavitation
When the rotating motor rotates, if the control valve is in a neutral state, the weight of the upper structure will make the device continue to rotate, and the pressure on port B will also continue to rise. At this time, the B port safety valve should be opened to prevent the circuit from being affected by high pressure. In this way, cavitation will occur at port A. Therefore, oil should be supplied immediately after the control valve is closed. Open the supplementary plunger, and the oil flows through the oil return path to supplement the oil supply, thereby avoiding cavitation.
