Construction Machine

Construction machine comprising:

• an engine;
• a hydraulic oil tank that stores hydraulic oil;
• a hydraulic pump that is driven by the engine and delivers the hydraulic oil in the hydraulic oil tank as pressure oil;
• a boom cylinder that is operated by the pressure oil delivered by the hydraulic pump;
• a directional control valve of an open-center type that controls a flow of the pressure oil;
• an operating device that performs switching operation of the directional control valve;
• and a boom that rotates in vertical directions through extension and contraction of the boom cylinder, the construction machine performing jack-up operation to lift a vehicle body up by use of a boom lowering motion of the boom,
• wherein the construction machine includes:
• a body weight acquisition device that acquires a weight of the vehicle body;
• a manipulated variable detector that detects a manipulated variable of the operating device;
• a delivery pressure detector that detects a delivery pressure of the hydraulic pump;
• a center bypass selector valve that is installed midway through a center bypass duct and downstream of the directional control valve, the center bypass duct connecting the hydraulic pump to the hydraulic oil tank, the center bypass selector valve having valve-opening area characteristics capable of fully closing the center bypass duct;
• a center-bypass-selector-valve operating valve that performs switching operation of the center bypass selector valve;
• and
• a controller that controls operation of the center bypass selector valve on the basis of the weight of the vehicle body acquired by the body weight acquisition device, the manipulated variable of the operating device detected by the manipulated variable detector, and the delivery pressure of the hydraulic pump detected by the delivery pressure detector, and
• wherein the controller includes:
• a storage section that stores a first relationship between manipulated variables of the operating device for the boom lowering motion preset for each weight of the vehicle body and target delivery pressures of the hydraulic pump;
• a target delivery pressure computation section that applies the weight of the vehicle body acquired by the body weight acquisition device, and the manipulated variable of the operating device detected by the manipulated variable detector, to the first relationship stored in the storage section in order to calculate a target delivery pressure of the hydraulic pump;
• and
• a feedback control section that performs feedback control on the center bypass selector valve through the center-bypass-selector-valve operating valve such that the delivery pressure of the hydraulic pump detected by the delivery pressure detector agrees with the target delivery pressure of the hydraulic pump calculated by the target delivery pressure computation section.