Abstract: A vehicle four wheel steering system including a rear wheel steering mechanism with a power assist device. The rear wheel steering mechanism includes a steering rod extending transversely of the vehicle and having the opposite ends connected with tie rods which are in turn connected with knuckle arms of the rear wheels. The steering rod is provided with a power cylinder in which a piston is slidably disposed. The piston is provided on the steering rod and defines hydraulic chambers in the cylinder. A control valve is provided to control hydraulic oil supply to the power cylinder. The control valve has a casing which is connected with the steering rod through an interconnecting section and hydraulic oil passages are formed in the interconnecting section for passing hydraulic oil to and from the power cylinder.

Abstract: A working fluid passage supplying a fixed flow rate is divided into passages so that a flow rate ratio between the two passages is varied by a variable orifice valve based on a detection signal of a physical quantity factor which varies depending on travelling and steering conditions of the vehicle. The working fluid from one of the two passages is supplied to a steering assisting force generating mechanism through a changeover valve which changes over the passages in accordance with a direction of steering torque acting on the input shaft steering the vehicle, to generate the steering assisting force. The working fluid from the other passage is supplied to a steering reaction force generating mechanism through the changeover valve, and by generating the steering reaction force to the input shaft, the steering force is controlled to an adequate condition corresponding to the physical quantity factor.

Abstract: A four-wheel steering system comprises a steering wheel; a steering shaft which is connected to the steering wheel to be rotated in response to operation of the steering wheel and is provided with a first pinion fixedly mounted thereon; a rack bar which is supported for sliding motion in the transverse direction of the vehicle body, is provided with a first rack gear in mesh with the first pinion and a second rack gear, and is connected to the right and left front wheels by way of tie rods, a rear wheel turning force taking-out mechanism which includes a second pinion in mesh with the second rack gear on the rack bar and a rod member connected to the second pinion, and which converts the sliding motion of the rack bar into rotation of the rod member; and a rear wheel turning mechanism which is arranged to turn the rear wheels in response to rotation of the rod member.

Abstract: In a four-wheel steering apparatus of a vehicle for steering also the rear wheels in conformity with the steering of the front wheels by a steering wheel, a control force for a rear wheel steering device is mechanically taken out from a front wheel steering device and is suitably controlled in the intermediate portion and is transmitted as a steering control force to the rear wheel steering device, whereby the front wheels and the rear wheels are steered in the same direction when the absolute value of the steering angle of the front wheels is less than a predetermined value, and the rear wheels are steered in the direction reverse to the front wheels when the absolute value is greater than the predetermined value.

Abstract: The rear wheels of a vehicle are turned in response to the turning of the front wheels upon operation of the steering wheel. A rack member is provided to be operatively connected with a movable member of the front wheel steering system which is moved right and left in response to operation of the steering wheel so that the rack member is moved together with the movable member. The rack member is in mesh with a pinion fixed to an end of an output shaft whose rotation is transmitted to the rear wheel steering system as steering force for moving it by way of a transmission shaft.

Abstract: A four-wheel steering system for a vehicle comprising a steering mechanism including a steering wheel, a front wheel turning mechanism operatively connected to the steering mechanism to turn the front wheels according to the turning angle of the steering wheel, a rear wheel turning mechanism operatively connected to the steering mechanism to turn the rear wheels in response to operation of the steering wheel, and a rear wheel steering ratio changing mechanism for changing the ratio of the turning angle of the rear wheels to the turning angle of the steering wheel.