Hydraulic circuit for a construction machine

Abstract

Provide a hydraulic circuit that can prevent damage to the oil cooler while suppressing excessive rise in the temperature of the operating oil. The hydraulic circuit includes a control valve that controls supply of operating oil from the hydraulic pump to the work tool; a first return pipeline that connects the control valve with the operating oil tank; an oil cooler disposed in the first return pipeline on a downstream side of a first check valve; a second return conduit that branches from the first return pipeline and extends to the operating oil tank without passing through the oil cooler; a third return pipeline that branches from the pipeline and extends to the first return pipeline between the first check valve and the oil cooler; a solenoid valve disposed in the third return pipeline; an operating device that outputs an operating signal of the work tool; a controller that opens the control valve and the solenoid valve based on the signal output from the operating device; and an operating oil temperature sensor. The controller reduces the amount of operating oil passing through the oil cooler when a temperature detected by the temperature sensor is less than a predetermined value.