Hitachi excavators have a torsion control valve (TVC valve), a stick flow solenoid valve, and a solenoid valve group consisting of a secondary overflow?CO cancellation solenoid valve, a rotary brake solenoid valve, and a traveling speed solenoid valve. The structure of the solenoid valve is basically the same, consisting of iron core, coil, spring, valve core, push rod and valve body.
1. Solenoid valve in solenoid valve group
The structure and working principle of the solenoid valve in the solenoid valve group are shown in Figure 3-29.
① When the solenoid valve is not energized, the controller does not send out signal current, the coil is not energized, and the solenoid valve does not operate. Therefore, the P port is closed and the pressure oil from the pilot pump cannot flow to the actuator. At the same time, the oil from the actuator flows to the oil tank through the A port and T port.
② When the solenoid valve is energized, the controller sends out a signal current, the coil is energized, and the solenoid valve acts. Therefore, the pressure oil from the pilot pump flows from port P to port A, and then flows into the actuator to complete the required action. At the same time, the T port is closed and the hydraulic oil does not flow back to the tank.
2. Stick half-flow solenoid valve
The structure and working principle of the stick half-flow solenoid valve are shown in Figure 3-30.
1—Plug; 2—Iron core; 3—Coil; 4—Push rod; 5—Spring; 6—Spool; 7—Valve body; 8-Screw plug Figure 3-30 Structure and operation of stick semi-flow solenoid valve principle
① When the solenoid coil is not energized, since the controller does not send out signal current, the P port is connected with the S port, and the pressure oil from the PPC valve flows to the control valve.
② When the solenoid coil is energized, the controller sends out a signal current, the P port is closed, and the pressure oil from the PPC valve does not flow to the control valve. At the same time, the S port is connected to the T port, and the pressure oil from the control valve is discharged into the oil tank.
