Pump control apparatus for construction machine

A pump control apparatus for a construction machine, said pump control apparatus comprising:

• a prime mover;
• first, second, and third variable displacement pumps and a fixed displacement pilot pump, all driven by the prime mover;
• specifying means for specifying a target revolution speed of the prime mover;
• a control unit for controlling the revolution speed of the prime mover;
• a regulator used for the first and second pumps, the regulator controlling the input torques of the first and second pumps on the basis of the discharge pressures of the first, second, and third pumps;
• a regulator used for the third pumps, the regulator controlling the input torque of the third pump on the basis of the discharge pressure of the third pump;
• and
• limiting means for limiting the discharge pressure of the third pump, the discharge pressure being supplied to the regulator used for the first and second pumps,
• wherein:
• said regulator used for the first and second pumps includes varying mechanisms for varying the input torques of the first and second pumps by external command pressure;
• said pump control apparatus further includes:
• a controller for calculating torque control command pressure as the external command pressure, the torque control command pressure being supplied to the regulator used for the first and second pumps;
• torque control means for controlling the torque control command pressure;
• and
• pressure detection means for detecting the discharge pressure of the third pump;
• and
• said controller includes:
• a torque correction amount output unit for outputting torque correction amounts of the first and second pumps on the basis of the discharge pressure of the third pump detected by the pressure detection means;
• a reference torque output unit for outputting reference torque values of the first and second pumps on the basis of the target revolution speed of the prime mover specified by the specifying means;
• and
• an operation unit for calculating the torque control command pressure on the basis of an output value of the torque correction amount output unit and that of the reference torque output unit.