Patent ID: 8910473

Claim:
A pipe layer comprising: an engine; a hydraulic pump driven by the engine; a hydraulic motor driven by hydraulic fluid discharged from the hydraulic pump; a winch driven by the hydraulic motor; a winch operation member for operating the winch; a pump hydraulic circuit connected to the hydraulic pump and through which the hydraulic fluid discharged from the hydraulic pump passes; a drive hydraulic circuit connected to the hydraulic motor and through which hydraulic fluid for driving the hydraulic motor passes; a warm-up hydraulic circuit provided with a pressure loss portion and through which hydraulic fluid for warming up the hydraulic motor passes; a flow rate control unit provided between the pump hydraulic circuit and the drive hydraulic circuit, and configured to adjust a flow rate of hydraulic fluid fed from the pump hydraulic circuit to the drive hydraulic circuit in response to an inputted pilot pressure; a drive pilot pressure control unit configured to adjust a pilot pressure inputted to the flow rate control unit in response to an operation of the winch operation member; a flow channel open/close unit provided between the pump hydraulic circuit and the warm-up hydraulic circuit, and configured to be switched between an open state in which the pump hydraulic circuit and the warm-up hydraulic circuit are allowed to communicate and a closed state in which the pump hydraulic circuit and the warm-up hydraulic circuit are disconnected in response to an inputted pilot pressure; a warm-up pilot pressure control unit configured to, when a warm-up start state occurs under a necessary condition that the winch operation member is in a neutral position, adjust the pilot pressure inputted to the flow channel open/close unit so that the flow channel open/close unit is switched to the open state; and a pump displacement adjustment unit configured to, when the flow channel open/close unit is in the closed state, adjust a displacement of the hydraulic pump so that a differential pressure between the pump hydraulic circuit and the drive hydraulic circuit becomes constant at a predetermined set pressure, and when the flow channel open/close unit is in the open state, adjust the displacement of the hydraulic pump so that a differential pressure between the pump hydraulic circuit and the warm-up hydraulic circuit becomes constant at a predetermined set pressure.