OIL PRESSURE CONTROL DEVICES FOR TRAVELLING SPEED CONTROL IN EXCAVATOR

摘要

The system for controlling running speed by two speeds of high and low, has a velocity-constant type hydraulic motor to get high torque in high speed and preventing power decreasing in low speed by cutting the maximum flow rate of a main pump and keeping the maximum rpm of engine in low-speed controlling. The system comprises a velocity-constant type hydraulic motor (11) connected with the main pump (13) and an oil tank (14) via direction change valve (12); means for controlling running controlling piston (16) to control negative pilot spool (15) mounted in a pump regulator of the motor (11). The means for controlling the piston (16), comprises a pilot line (19) connected with pilot pump (18) and the piston (16) via speed-change valve (17); a negative pilot line (20) connected with the tank (14) and the piston (16).