JPS6428200A - Controller for hydraulic winch - Google Patents

Abstract

PURPOSE: To prevent the damaging of a motor by switching a capacity changeover valve following an increase in the load pressure of the motor, and operating an over relief valve by a low pressure during the transition period of the switching thereof for reducing or stopping from high-speed lowering. CONSTITUTION: When a high/low speed selecting valve 8 is placed in a low-speed position, low-speed raising/lowering is performed by a direction switching valve 3 and, when it is placed in a high-speed position, high-speed low torque lowering is performed at the time of low load application, low-speed high torque raising is automatically performed at the time of heavy load application, and high-speed low torque lowering is performed at the time of lowering. Here, for making a reduction or stop from high-speed lowering, a capacity changeover valve 9 is switched following an increase in the load pressure of a motor 5, the motor 5 is automatically switched to a large capacity and, during the transition period thereof, an over load relief valve 7 is operated by a pressure lower than a motor allowable pressure, and a motor load pressure is surely prevented from exceeding the allowable pressure. Thus, the damaging of the motor is prevented.