Patent ID: 8266903

Claim:
An engine lag down control system for construction machinery provided with an engine, a main pump driven by said engine, a torque regulating means for regulating a maximum pump torque of said main pump, a hydraulic actuator driven by pressure fluid delivered from said main pump, and a control device for controlling said hydraulic actuator, said engine lag down control system comprising: a first torque control means for controlling said torque regulating means to a predetermined low pump torque lower than the maximum pump torque when a non-operated state of said control device has continued beyond a predetermined monitoring time, and a second torque control means for controlling said torque regulating means to the predetermined low pump torque or to a pump torque around of the predetermined low pump torque for a predetermined holding time subsequent to an operation of said control device from the non-operated state while said torque regulating means is being controlled by said first torque control means, to control small a temporary reduction in engine revolutions that occurs upon operation of said control device from the non-operated state, wherein: said engine lag down control system is provided with a third torque control means for controlling said torque regulating means such that from a time point of a lapse of the predetermined holding time, the pump torque of said main pump gradually increases at a predetermined torque increment rate as time goes on, and further wherein: said engine lag down control system is provided with a speed sensing control means having a torque correction computing unit, which determines a torque correction value corresponding to a revolution deviation of an actual number of revolutions of said engine from a target number of revolutions of said engine, for determining a target value for the maximum pump torque, which is controlled by said first torque control means, on a basis of the torque correction value determined by said torque correction computing unit, and said predetermined torque increment rate is determined on the basis of said torque correction value.