Patent ID: 8578709

Claim:
An over-loading prevention device of construction machinery, comprising: a hydraulic pump which is driven by an internal-combustion engine; a control valve which controls supply of hydraulic pressure from the hydraulic pump to a hydraulic actuator and exhaust of hydraulic pressure from the hydraulic actuator; a control lever which outputs a pilot pressure to operate the control valve; a discharge-quantity control unit which performs constant-torque control which decreases a discharge quantity in proportion to an increase in a discharge pressure in the hydraulic pump to control an input torque of the hydraulic pump uniformly; an operation-state detection unit which detects the pilot pressure output from the control lever to determine an actuation speed of the control lever; and a control unit which outputs a control signal that sets the input torque of the hydraulic pump to a minimum torque value according to the constant-torque control, to the discharge-quantity control unit when it is determined based on the actuation speed determined by the operation-state detection unit that the control lever is operated over a predetermined speed, and subsequently the control unit changing a level of the control signal to a maximum torque value according to the constant-torque control, in accordance with a predetermined control pattern to raise the input torque of the hydraulic pump.