Pump control apparatus for hydraulic work machine, pump control method and construction machine

A pump control apparatus for a hydraulic work machine, comprising:

• a rotation speed setting device that sets a target rotation speed for an engine;
• a rotation speed control device that controls an engine rotation speed so as to adjust the engine rotation speed to the target rotation speed;
• a first variable hydraulic pump used to drive a work hydraulic actuator, driven by the engine;
• a second variable hydraulic pump used to drive a cooling fan, driven by the engine;
• a rotation speed detection device that detects an actual rotation speed of the engine;
• a correction torque calculation device that calculates a correction torque corresponding to a deviation of the actual rotation speed detected by the rotation speed detection device relative to the target rotation speed set by the rotation speed setting device;
• and
• a pump controller that controls an output flow rate of the first variable hydraulic pump and an output flow rate of the second variable hydraulic pump so as to ensure that a sum of an intake torque of the first variable hydraulic pump and an intake torque of the second variable hydraulic pump does not exceed an engine output torque determined in advance based upon the target rotation speed, wherein the pump controller
• a) controls the output flow rate of the second variable hydraulic pump based upon the target rotation speed and a target output flow rate of the second variable hydraulic pump assuring a required cooling air volume at the cooling fan;
• b) regulates the intake torque of the first variable hydraulic pump so that the intake torque of the first variable hydraulic pump remains unchanged even when an actual rotation speed of the engine fluctuates, by calculating the intake torque of the second variable hydraulic pump and subtracting the intake torque of the second variable hydraulic pump from the engine output torque determined in advance based upon the target rotation speed;
• and
• c) corrects the intake torque of the first variable hydraulic pump by using the correction torque calculated by the correction torque calculation device.