RUNNING SPEED CHANGING DEVICE

摘要

PROBLEM TO BE SOLVED: To perform slight operation a hydraulic motor for running and to control deceleration with ease by controlling the high speed/low speed changing of the hydraulic motor for running not only by sensing the pump pressure of a main pump but also the pilot secondary pressure according to the displacement of the running operation means. SOLUTION: When the pump pressure of a main pump 2 is in a low pressure range, an automatic two-speeds change over valve 46 opens an oil passage 44 for supplying a signal pressure. If a remote control valve 30 is operated in this state by operating an operation lever 32 to slightly operate a hydraulic motor 12 for running, the pilot secondary pressure is supplied to the pilot port of a capacity change over valve 26 by a pilot pump 4. At this time, the capacity change over valve 26 is in a low speed position when the secondary pressure is less than a setting value and the pump pressure is supplied to a piston 20 for low speed thereby to drive the hydraulic motor 12 for running at a large capacity and a low speed. On the other hand, an oil passage 28 of a piston 18 side for high speed is connected to a tank T thereby to perform slight operation of the hydraulic motor 12 for running with ease.