The Hitachi excavator parking brake is a wet multi-disc negative structure brake. The negative structure means that the brake is often braked by the spring. Once the pilot pressure oil enters the brake cylinder cavity, the brake is released.
When the engine is not rotating, the parking brake is automatically activated because the pilot pressure is 0.
The "ON-OFF" operation of the brake is to switch the electromagnetic switch by the brake according to an external signal. The external signal refers to the release stop signal. If the operating lever other than the rotation or excavation is manipulated, the signal center of the control valve will transmit the release signal to the SI port (see Figure 2-46), release the mechanical brake, and reduce the gear during the excavation operation. No load.
1. When the brake is "ON" (for operations other than rotation and forearm involvement)
When the control lever is in the neutral position, the signal pressure of the Sl port is not generated (the pressure of the brake signal is released), and the shuttle valve cuts off the port PG (the brake release pressure). On the other hand, open port B (brake hydraulic chamber), and directly connect to port D (in the motor box) through the shuttle valve.
In this state, the circular disc plate meshing with the circumference of the hydraulic cylinder group and the friction plate meshing with the inner side of the motor box will cause the spring force to act downward through the piston, as shown in Figure 2-46. Due to the force generated by this downward thrust, the motor spindle torque is applied to the circumferential part of the hydraulic cylinder group, and the reverse input torque is absorbed to lock the spindle.
2. When the brake is OFF (when rotating and forearm rolling operation)
When the control lever is operated, the SI port does not generate signal pressure (brake release signal pressure), the shuttle valve is squeezed down, and the PG port pressure (brake release pressure) is immediately introduced into port B (brake hydraulic cylinder chamber) through the check valve After the disc spring force is exceeded, the brake piston is pressed upward to release the braking force, as shown in Figure 2-47.
3. Rotate and shake the suppression valve
When the rotation control lever is in the neutral position, the control lever is OFF→the solenoid valve is OFF, the valve is OPEN, and the oil flows into the rotation and shaking suppression valve. When the rotary operation control lever is in the operating position, the control lever ON-solenoid valve ON-valve CLOSE-oil flows into the rotation and shaking suppression valve. The solenoid valve input signal system diagram is shown in Figure 2-48.
When the control lever is in the neutral position, the signal oil pressure (PS) closes the rotation and swing suppression valve (pilot change valve) and keeps the oil pressure of BM1 greater than AM; and the oil pressure of AM2 is greater than BM2. The flow direction of the motor hydraulic oil is shown by the dotted line in Figure 2-50 (a).
When the control lever is in the operating position, the oil pressure of BM2 is greater than AM2, which makes the valve slide valve move, and the oil of BM2 flows into AM2 through the orifice.
When the oil pressure of BM2 is greater than AM2, the spring in the valve moves to the slide valve, and the oil flow of AM2 flows into BM? through the orifice.
The flow of signal pressure (PS) makes the rotation and shaking suppression valve close, and the oil flow direction at this time is the same as that of the control operation. The working diagram of the suppression valve is shown in Figure 2-50(b).
4. Oil flow conditions
The oil flow is controlled by the control valve. When the control valve rotates clockwise to the neutral position, the valve opens. When turning counterclockwise to the neutral position, the valve opens. The solenoid valve slide valve moves to the left, and the PS signal pressure pushes the oil into the slide valve chamber. When the pressure is greater than the spring force, the slide valve is pushed to the right, thus blocking the BM1 oil flow. The hydraulic oil flow is shown in Figure 2-51.
5. Operation
Figure 2-52 shows the neutral state of the rotation and shaking suppression valve.
When pressure is generated at the oil inlet, the oil flows through the oil channel and the plunger "m" channel, and flows into the n chamber from the shaft core hole of the valve seat.
As shown in Figure 2-53, when the pressure P exceeds the set pressure of the spring, the plunger compresses the spring to move to the left.
The valve seat is pushed by the plunger and the compression spring moves to the left.
If the inertial load pressure ceases, the brake pressure at point Y decreases, and the situation P<P, appears, as shown in Figure 2-54 and Figure 2-55, the plunger moves to the right due to the elastic force of the spring. The movement of the valve seat is relatively delayed for the plunger.
Therefore, the valve seat part (t) is opened, and the oil inlet and the oil outlet form a circuit connected to the rotary motor through the internal oil passage, that is, the pressure of the oil inlet and the oil outlet are suddenly equal. When the Z point state occurs, due to AM The locking pressure of the port prevents the reverse rotation of the motor.
