Hitachi excavator brake valve
(1) Working principle
Brake valve outlet charge valve and safety valve, the principle is shown in Figure 5-7. When the slewing motion stops, if the upper slewing platform is still rotating due to the inertial force of the slewing, the slewing motor will continue to rotate and suck oil from the oil pump, thereby forming cavitation in the motor. The charge valve draws hydraulic oil in the oil return (oil port C) to compensate for the lack of hydraulic oil in the motor, which can prevent the generation of cavitation and also allow the upper turntable to rotate smoothly.
(2) Safety valve
The structure of safety valve is shown in Figure 5-8. When the slewing operation starts or stops, the oil pressure in the slewing oil circuit rises, and the safety valve can prevent the oil pressure in the pipeline from rising above the specified pressure.The pressure P of the oil port P and the pressure of the pressure zone A2 will The plug 5 is pushed to the left, but the plunger 5 is pushed back to the right by the force of the spring 8, the pressure p of the oil chamber g, and the pressure of the pressure zone A3.
The oil chamber g communicates with the oil port P through a small hole m. When the force on the left is higher than the force on the right, the safety valve starts to move.
(1) Action when the pressure rises. When the pressure p of the oil port P increases, the pressure p of the oil chamber g also increases accordingly. Because the oil chamber g communicates with the oil port P through the small hole m of the plunger, the increased pressure acts on the pressure receiving area A4 of the piston 2. When the force pushing the piston 9 to the left exceeds the force of the spring 1, the piston 9 moves to the left, and the pressure p of the oil chamber g drops below the pressure P. Then, the plunger 5 moves to the left, the oil port P and the oil port R communicate, and the pressure of the oil port P drops
When the pressure at port P drops, plunger 5 returns to the right, the passage between port P and port B is shut off, and the pressure P at port P and the pressure p in chamber g rise until The piston 9 starts to move to the left again. This action is repeated until the piston 9 reaches the end of the stroke
When the piston 9 moves to the left, the oil behind the piston 2 is squeezed out through the small hole n, and slowly flows back to the oil port R, so that the overflow pressure slowly increases.
When the piston 9 reaches the end of the stroke, the piston 2 starts to move to the right, which is the result of the force generated by the pressure p in the oil chamber g acting on the pressure-receiving area A1. At the same time, the spring 8 is compressed. When the piston 4 starts to move to the right, the oil remaining in the oil chamber leaks out through the oil groove h on the sliding surface between the adjustment valve 10 and the piston 2. Therefore, the pressure p of the oil chamber g gradually increases until the piston 2 reaches the end of the stepped hole of the adjustment valve 10. As the spring is compressed, its spring force increases, so the overflow pressure slowly rises. When the piston 2 reaches the end of the stepped hole of the adjustment valve 10, it can no longer move to the right, and the pressure of the oil chamber g becomes equal to the prescribed pressure p. After reaching this position, the continuous overflow action begins
(2) The action of pressure reduction. When the pressure P of the oil port P drops, the pressure P of the oil chamber g also drops to the tank pressure, the plunger 5 moves to the right, closes the valve seat 6, the piston 2 is pushed by the spring 8 to the original position on the left, the piston 2 is The spring 1 is pushed to the right. At the same time, the check ball valve installed on the sleeve 3 is opened to obtain oil from the oil port R, which prevents a vacuum from appearing behind the piston 2, which helps the piston 2 return immediately without delaying time.
