The variable servo piston 1 is connected with the valve plate 6 through the connecting rod 5. Therefore, when the servo piston 1 is moved, the valve plate 6 changes the inclination angle of the cylinder 7, which causes the displacement of the hydraulic motor to change, and finally the walking speed is generated. Variety. .
When low-speed or medium-speed travel is selected, the pump valve controller (PVC) does not send electronic control signals to the travel (high-low-speed) solenoid valve. Therefore, the pilot pressure oil that changes the speed cannot flow from the port SH to the variable servo Piston 1, so that the valve core 3 is kept downward under the action of the spring 2, so the pressure oil P from the motor oil port flows into the oil chambers B and C.
Since the area of the oil chamber C receiving pressure oil is larger than that of the oil chamber B, the variable servo piston 1 moves upward to increase the inclination angle of the swash plate to the maximum. At this time, the stroke of the motor plunger increases, that is, the displacement of the walking motor increases, and the travel The motor rotates at a low speed,
thus realizes low-speed and medium-speed walking mode. In the low-speed travel mode, the flow rate of the hydraulic pump is reduced by about 40%. Therefore,
Hitachi excavator hydraulic motor running at low speed.
When the high-speed travel mode needs to be selected for light-load travel, the pump valve controller (PVC) sends an electronic control signal to the travel (high-low-speed) solenoid valve, so the pilot pressure oil that changes the speed flows into the oil chamber C from the oil port SH. Move the spool 3 upwards. Then, the pressure oil in the oil chamber C is discharged through the inner passage of the valve core 3. As the pressure oil P from the motor oil port flows into the oil chamber B, the servo piston 1 moves downward, reducing the inclination angle of the cylinder 7, and the stroke of the motor plunger is reduced, and the traveling motor rotates at a higher speed to achieve a high speed. Way of walking.
When the walking load is large, PVC stops sending control signals to the proportional solenoid valve, so the inclination angle of the cylinder increases and the walking speed is reduced to reduce the walking load.
