PUMP CONTROL CIRCUIT FOR CONSTRUCTION MACHINE

摘要

PROBLEM TO BE SOLVED: To improve the operating ability of a pump control circuit, and to make the control of a pump possible even in case of the occurrence of electrical trouble by varying the tilting angle of the variable displacement type pump from pure hydraulic control into pure electric control. SOLUTION: External signal pressure (a) is made to act on a regulator 17 from a hydraulic source 18 through a proportional pressure reducing valve 19 to carry out the maximum flow rate control of a pump 11. The self pressure (b) of the pump 11 is made to act on a regulator 17 to carry out the fixed horse-power control of the pump 11. The pressure of the hydraulic source 18 is selected into high and low pressures by a solenoid change-over valve 20 and made to act as signal pressure (c) on the regulator 17 for carrying out the horse-power shift control of the pump 11.