Patent ID: 7497081

Claim:
A hydraulic fluid supply structure comprising: a discharge line fluidly connected to a discharge port of a hydraulic pump body and regulated to have a first pressure value; an external hydraulic fluid extraction line for supplying the hydraulic fluid to a raising and lowering hydraulic actuator for raising and lowering a working machine, the external hydraulic fluid extraction line being fluidly connected to the discharge line through a resistance valve; a PTO hydraulic fluid line for supplying the hydraulic fluid to a hydraulic operating type clutch mechanism for engaging or disengaging power transmission to the working machine, the PTO hydraulic line being fluidly connected to the discharge line through a throttle valve; a PTO relief valve for regulating the pressure of the PTO hydraulic fluid line at a second pressure value lower than the first pressure value; and a PTO switching valve interposed in the PTO hydraulic fluid line so as to turn ON/OFF the supply of the hydraulic fluid to the hydraulic clutch mechanism; wherein: the PTO switching valve is configured to block a primary side line, out of the PTO hydraulic fluid line, positioned on the upstream side from the PTO switching valve, when the supply of hydraulic fluid to the hydraulic clutch mechanism is turned OFF, the PTO relief valve is interposed in a secondary side line of the PTO hydraulic fluid line positioned on a downstream side from the PTO switching valve, the throttle valve includes a valve body interposed in the PTO hydraulic fluid line in a movable manner along the axis line direction so as to divide the PTO hydraulic fluid line into a primary space fluidly connected to the discharge line and a secondary space fluidly connected to the PTO switching valve through a throttle hole, a biasing member for biasing the valve body towards the primary space, and a valve seat member, and the valve body is seated at the valve seat member so that the throttle hole is sealed by the valve seat member when the hydraulic pressure of the discharge line is higher than a third pressure value defined by a resultant force of the hydraulic pressure in the secondary space, which is fluidly connected to the discharge line through the throttle hole, and the biasing force of the biasing member, the third pressure value being lower than the first pressure value and higher than the second pressure value.