| 摘要 |
PURPOSE:To enhance the turning characteristic of a tractor, by providing a relief valve for restraining the internal pressure of a hydraulic mechanism which is adapted to actuate when the steering angles of both right and left steered wheels reach to the limit of a predetermined range, to a value less than a predetermined value. CONSTITUTION:When a steering wheel 1 is turned to the left or the right, a control valve 18 is changed over from its neutral position, and therefore, a power steering mechanism 17 turns a pit man arm 21 to the left or the right. When the amount of turning of the pit man arm 21 reaches the limit of a predetermined range, a solenoid valve 27 is changed over into a circuit for one of the hydraulic cylinder 10 sides from its neutral position. The pressure of hydraulic oil in a high pressure circuit, flowing from a hydraulic pump 24 into a control valve 18, becomes higher than a predetermined value and therefore, the hydraulic oil is fed under pressure from the solenoid valve 27 into one of the hydraulic cylinders 10 which therefore extends its piston 11 outward. With this arrangement, a retractable member 13, a king pin 12 and a bearing member 15 are simultaneously pushed out to further increase the angle between a drag rod and a knuckle arm 16, thereby it is possible to further increase the steering angle. |
