PURPOSE: To secure a sufficient flow rate control range with respect to the spool stroke of a changeover valve even when an engine speed for driving a variable discharge pump is low and a discharge quantity is small in a controller which control the discharge a pressure of the above variable discharge pump by a regulator.
CONSTITUTION: The spring force of the spring 38 of a valve 37 constituting a regulator can be regulated by means of a cylinder 41 linked to a throttle lever 42 for controlling an engine. The cylinder 41 is operated and the spring force of the spring 38 is relatively weakened when the throttle lever 42 is laid in the direction for decreasing rotational speed of the engine. Thereby the valve 37 is switched and the gain of controlled flow rate is sufficiently secured even when the discharge quantity of a variable discharge pump 1 is small and a variable rate of load pressure is small.
YONEKUBO YOSHITAKE
NAITO HISATO
