The pilot control system of the excavator is mainly composed of a pilot pump, an accumulator, a safety lock valve, a working device and a rotary pilot control valve, a traveling pilot control valve, a boom bucket and a traveling PPC shuttle valve, a stick and a rotary PPC shuttle valve , A pilot filter element and a pilot overflow valve are also installed on the pilot pump. Among them, the pilot control valve is one of the main hydraulic components of the system.
There are 3 pilot control valves in the whole vehicle. Among them, the boom pilot valve and the bucket pilot valve share the next valve body, which is controlled by the right joystick in the cab. The stick pilot valve and the swing pilot valve share the same valve body. Joystick control, the left and right travel pilot valves share a valve body, which is controlled by the left and right travel joysticks in the cab.
The structure of the working device is basically the same as the PPC valve for rotation and the PPC valve for walking, except that the former adds a shock absorber piston and a shock absorber spring, as shown in Figure 3-27.
1 a spool valve: 2-adjusting spring; 3-return spring; 4-shock absorber piston; 5-shock absorber spring;
6—plunger; 7—pressure plate; 8—control lever; 9—universal joint; 10—mounting plate;
11—guide sleeve; 12—valve body; 13—spring seat
Figure 3-27 Working device and pilot control direction for rotation
The function of the shock absorber piston 4 is to move the piston 4 along with the plunger 6 when the joystick is suddenly pulled to prevent time lag. During fine-tuning control, the shock absorber piston 4 does not move with the plunger 6 to ensure fine-tuning performance.
The pilot joystick has three positions: neutral, jog, and full. The working principle of the pilot valve is shown in Figure 3-28.
① The control lever is in the neutral position, and the Pi and P2 ports of the control valves A and B and the PPC valve are all connected to the fuel tank through the fine control holes f and F in the spool valve 1.
② Slightly pull the joystick (inching), when the pressure plate 7 starts to push the plunger 6, the spring seat 13, the adjusting spring 2 push the slide valve 1 downward, and the fine control hole f and the oil return chamber D are cut off at this time , And the hole f is in communication with the pressure chamber Pp of the pilot pump. The pilot pressure oil flows from the pilot pump through the P port, the oil hole f, and the Pi port to the main operating valve A chamber. When the pressure at the Pi port increases, the slide valve 1 is pushed back , The oil hole f cuts off the pressure chamber Pp and communicates with the oil return chamber D. The spool valve 1 moves up and down until the force of the adjusting spring 2 and the pressure of the Pi port are balanced, the spool valve 1 is in a certain equilibrium position. The positional relationship between the spool valve 1 and the valve body 12 changes only when the shock absorber piston 4 contacts the plunger 6. Therefore, the compression amount of the adjusting spring 2 is proportional to the stroke of the pilot control valve rod, and the pressure of the oil port Pi is also proportional to the stroke of the pilot control valve rod. In this way, when the pressure in the oil chamber A where the spool of the main operating valve moves is balanced with the return spring force of the main operating valve, the pressure oil in the oil chamber B flows back to the return chamber D through the P2 port and the oil hole P. .
When the joystick returns, the spool valve 1 pushes up under the combined action of the force of the return spring 3 and the pressure of the Pi port
Shift, the oil hole f is connected to the oil return cavity D. When the pressure of the P] port drops too fast, the spool valve 1 moves downward under the action of the adjusting spring 2, and the oil hole f is connected to the pressure chamber Pp until the pressure of the Pi port returns to the pressure corresponding to the position of the pilot lever. Spool valve 1 is in the equilibrium position. At the same time, the pressure oil in the oil return cavity D enters the main operation valve B cavity through the fine control holes F and P2.
1 a spool valve; 2 an adjustment spring; 3 a return spring; 4-shock absorber piston; 5-shock absorber spring; 6-plunger;
7—pressure plate; 12—valve body; 13—spring seat; A, B, P, T, Pi, P2—oil port;
f. Fine control hole; Pp—pressure chamber; D—oil return chamber Figure 3-28 Working principle of pilot control valve
③ With the joystick at the full stroke position, the pressure plate 7 pushes the plunger 6 downwards, the shock absorber piston 4 also moves downwards, and pushes the slide valve 1 downwards, the oil hole f cuts off the oil return chamber D and The pressure chambers Pp are connected. Therefore, the pressure oil from the pilot pump flows to the A chamber through the holes f and Pl, pushing the control valve spool to move. The return oil from the B cavity flows from the P2 port to the oil return cavity D through the oil hole F. The time lag of the sudden operation of the joystick is prevented by the shock-absorbing piston.
