Patent ID: 8162618

Claim:
A pump torque control method for a hydraulic construction machine comprising an engine, a fuel injector for controlling a revolution speed and an output of said engine, a fuel injector controller for computing a target fuel injection amount and controlling said fuel injector based on the target fuel injection amount, and at least one variable displacement hydraulic pump driven by said engine and driving actuators, wherein the control method comprises the steps of: driving a certain engine and collecting data of output torque for each target fuel injection amount in a reference condition, calculating an engine torque margin rate by the following formula from said output torque data, and then determining a relationship between said target fuel injection amount and said engine torque margin rate in advance of operation; engine torque margin rate(%)= Tx/T max*100, wherein Tx represents an output torque of the engine corresponding to each of target fuel injection amounts, and Tmax represents a maximum output torque of the engine corresponding to a maximum target fuel injection amount computing a current engine torque margin rate of said engine by referring the target fuel injection amount computed by said fuel injector controller to said relationship; and comparing the current engine torque margin rate with a target value of said engine torque margin rate preset as a value smaller than 100% and reducing a maximum absorption torque of said hydraulic pump when said current engine torque margin rate exceeds the preset target value thereby to control the maximum absorption torque of said hydraulic pump to return said current engine torque margin rate to the preset target value.