Rack and pinion steering device

Claim 1

A rack and pinion device comprising: a gear housing; a pinion rotatably supported within said gear housing and connected during use of the device to a steering shaft of a vehicle; a rod-like rack connected during use of the device to a steering lever mechanism of the wheels of the vehicle, said rack having a lengthwise axis and having a group of rack teeth meshed with said pinion; and a spring device in contact with the back of said rack on the side opposite said pinion to resiliently bias said rack against said pinion; wherein said group of rack teeth includes, in symmetrical relation on opposite sides of the lengthwise center thereof, a first rack teeth portion near to and a second rack teeth portion far from said center respectively, said second rack teeth portion having a reference pitch line which is inclined so as to approach the lengthwise axis of said rack in a direction extending away from the adjacent first rack teeth portion to enable said rack to undergo flexure displacement in response to a bending pressure exerted thereon by said spring device, said spring device comprises a cylinder connected to said gear housing, said cylinder having an axis perpendicular to the axis of said pinion and defining a cylinder space which is open at one end to said rack, an end member for closing the other end of said cylinder space, a plunger slidably mounted within said cylinder space and having one end thereof in frictional engagement with the back of said rack, and first and second springs retained between said plunger and said end member to resiliently bias said plunger against said rack, and wherein the effective distance through which said first spring acts is relatively small with respect to the effective distance through which said second spring acts so that if an amount of flexure displacement in said rack is less than a predetermined value, the resultant pressure of said first and second springs is applied to said rack whereas if the amount of flexure displacement exceeds a predetermined value, only the pressure of said second spring is applied to said rack.