Construction Machine

Abstract

Provided is a construction machine having a front work implement to be coupled with an attachment via a quick hitch, a directional control valve that controls pressurized fluid delivered from a hydraulic pump and drives an actuator of the front work implement, and an operation lever that operates the directional control valve. The construction machine also includes a lock port to be connected to a lock-side hydraulic chamber of a lock cylinder of the quick hitch, an unlock port to be connected an unlock-side hydraulic chamber of the lock cylinder, a selector valve that switches connection destinations of the lock port and the unlock port to any one of the hydraulic pump and a reservoir, a switch that operates the selector valve, a pilot drive type relief valve disposed in a hydraulic line connecting the hydraulic pump and the selector valve, and a relief pilot line that connects, to a hydraulic chamber of the relief valve, a hydraulic line to be boosted as a result of an operation of the operation lever.

1 . A construction machine having
 a front work implement that is to be coupled with an attachment via a quick hitch,   an actuator that drives the front work implement,   a reservoir that holds hydraulic operating fluid,   a hydraulic pump that delivers the hydraulic operating fluid drawn from the reservoir,   a directional control valve that controls pressurized fluid delivered from the hydraulic pump and drives the actuator, and   an operation lever that operates the directional control valve,   the construction machine comprising:   a lock port that introduces the pressurized fluid from the hydraulic pump into a lock-side hydraulic chamber of a lock cylinder of the quick hitch when the attachment is grasped by an operation of the lock cylinder;   an unlock port that introduces the pressurized fluid from the hydraulic pump into an unlock-side hydraulic chamber of the lock cylinder of the quick hitch when a grasp state of the attachment is released by an operation of the lock cylinder;   a selector valve that switches connection destinations of the lock port and the unlock port to any one of the hydraulic pump and the reservoir;   a switch that operates the selector valve;   a pilot drive type relief valve that is disposed in a hydraulic line connecting the hydraulic pump and the selector valve to each other; and   a relief pilot line that connects, to a hydraulic chamber of the relief valve, a hydraulic line that is boosted as a result of an operation of the operation lever.   
     
     
         2 . The construction machine according to  claim 1 , wherein
 the selector valve is connected to a delivery line of the hydraulic pump that connects the hydraulic pump and the directional control valve, and   the hydraulic line is the delivery line of the hydraulic pump.   
     
     
         3 . The construction machine according to  claim 1 , comprising:
 a pilot pump that delivers pilot fluid; and   a pilot valve that is operated by the operation lever, reduces a pressure of the pilot fluid, and outputs a pilot pressure that drives the directional control valve, wherein   the hydraulic line is a pilot line that connects the pilot valve to a hydraulic chamber of the directional control valve.   
     
     
         4 . The construction machine according to  claim 1 , comprising:
 a check valve that is disposed between the hydraulic pump and the selector valve and prevents release of the pressurized fluid from the lock-side hydraulic chamber when the lock port and the hydraulic pump are in a connected state via the selector valve.