Patent ID: 8371117

Claim:
A torque control apparatus for a construction machine three-pump system having a prime mover; a first variable displacement hydraulic pump and a second variable displacement hydraulic pump that are driven by the prime mover; a third variable displacement hydraulic pump that is driven by the prime mover; instruction means for prescribing a target rotation speed of the prime mover; a prime mover control device for controlling the rotation speed of the prime mover in accordance with the target rotation speed prescribed by the instruction means; a first regulator which controls absorption torques of the first and second hydraulic pumps by controlling the displacements of the first and second hydraulic pumps in accordance with the delivery pressures of the first and second hydraulic pumps; and a second regulator which controls an absorption torque of the third hydraulic pump by controlling the displacement of the third hydraulic pump in accordance with the delivery pressure of the third hydraulic pump, the torque control apparatus comprising: a pressure sensor for detecting the delivery pressure of the third hydraulic pump; and control means for computing a maximum absorption torque (Tn) available to the first and second hydraulic pumps that is obtained by subtracting a calculated absorption torque of the third hydraulic pump from a pump base torque (Tr), which is a total absorption torque available to the first, second, and third hydraulic pumps, in accordance with the target rotation speed prescribed by the instruction means and the delivery pressure of the third hydraulic pump that is detected by the pressure sensor, and outputting a control signal according to the computation result; wherein the first regulator controls the displacements of the first and second hydraulic pumps in accordance with the control signal to ensure that the absorption torques of the first and second hydraulic pumps do not exceed the maximum absorption torque (Tn) computed by the control means.