Patent ID: 6925799

Claim:
In a speed control apparatus for a hydraulic actuator which includes a hydraulic source, the actuator connected with the hydraulic source and driven based on a supply of an operation oil, a direction switching valve which is switchably installed in a flow path between the hydraulic source and the actuator, and an inclination piston which is installed between a parallel flow path in parallel connected with a flow path in a supply side of the actuator and the actuator for thereby controlling an inclination angle of an inclination plate of the actuator, the speed control apparatus for the hydraulic actuator, comprising: a multi-step adjusting inclination piston which is driven when an operation oil is supplied, and adjusts the inclination angle of the inclination plate of the actuator based on multiple steps; and a multi-step adjusting control valve which is switchably installed in a flow path between the parallel flow path and the multi-step adjusting inclination piston, controls an operation oil supplied to the multi-step adjusting inclination piston, and adjusts a speed of the actuator, wherein said multi-step adjusting control valve is formed of: a first zone in which as the multi-step adjusting control valve is switched by a signal pressure which is externally supplied, an operation oil is supplied to the inclination piston, and the actuator is rotated at a high speed; a second zone in which in the case that a pressure of an operation oil supplied to the actuator exceeds a first set pressure, an operation oil is concurrently supplied to the inclination piston and the multi-step adjusting inclination piston, and the actuator is rotated at an intermediate speed; and a third zone in which in the case that a pressure of an operation oil supplied to the actuator exceeds a second set pressure, an operation oil is drained from the inclination piston, and the actuator is rotated at a low speed.