To instantaneously reduce excessive oil pressure acting on a hydraulic cylinder or the like steering rear wheels for making a driver aware of the occurrence of an anomaly in a circumference of front wheels or the rear wheels.
Hydrauhc oil 33 is supplied to a power steering device 18 through a main supply line 32 by a hydraulic pump 31 and by this, steering force of the front wheel 11 is supported. A branch port 37b of a flow dividing valve 37 provided in the main supply line and the hydraulic cylinder 28 steering the rear wheel 13 are connected by a branched supply pipe 38, and the hydraulic oil supplied to and discharged from the hydraulic cylinder is controlled by a valve unit 40 provided in the branched supply pipe. A front relief valve 46 returning hydraulic oil of a predetermined pressure or more to an oil tank 36 is provided in a first bypass pipe 43 bypassing the power steering device, an opening/closing valve is provided in a second bypass valve 44 connected in parallel with the first bypass pipe, and a pump relief valve 47 is provided in a pump bypass pipe 48 bypassing the hydraulic pump.
ENOMOTO MITSURU
HAGIHIRA SHINICHI
SASAKI KAZUHIRO
KAYABA INDUSTRY CO LTD
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