PURPOSE: To prevent hunting due to delays of the absorption torque control of a variable displacement hydraulic pump and lowering the real engine speed by changing the set pressure of a control valve with a positive and a negative deflection between a target engine speed and the real engine speed and the pressure in response to the working load of the pump.
CONSTITUTION: A target engine speed is detected by a sensor 37 and input to a controller 38. The real engine speed is input from an engine speed sensor 39 to the controller 38, while the pump discharge pressure is input from a pressure sensor 40 to the controller 38, and the controller 38 controls the supply of the current to a proportional solenoid 41a of a solenoid proportional pressure reducing valve 41. When the control pressure is not supplied from the solenoid proportional pressure reducing valve 41 to a third pressure receiving part 45 of a control valve 30, discharge quantity of a variable hydraulic pump 20 is controlled by the control valve 30 on the basis of a differential pressure between the pump discharge pressure and the load pressure, and when the control pressure is supplied from the solenoid proportional pressure reducing valve 41 to the third pressure receiving part 45 of the control valve 30, the set differential pressure of the control valve 30 is changed. Absorption torque of the variable displacement type hydraulic pump is thereby controlled.
AKIYAMA TERUO
ODA YASUSUKE
TAKEUCHI MASAMITSU
