GB2034648A

GB2034648A - Vehicle steering system

Info

Publication number: GB2034648A
Application number: GB7937874A
Authority: GB
Original assignee: Centro Ricerche Fiat SCpA
Current assignee: Centro Ricerche Fiat SCpA
Priority date: 1978-11-14
Filing date: 1979-11-01
Publication date: 1980-06-11
Also published as: JPS5572462A; FR2441527A1; IT1108187B; DE7932015U1; DE2945800A1; IT7869594A0

Abstract

A vehicle with two, independently- suspended, steerable wheels (12) is provided with a steering system in which rotation of a steering shaft causes angular displacement of a control lever (38). The control lever (38) is coupled to each of the steerable wheels (12) via a respective rod (50, 52) and steering arm (58, 60) which lie in the same horizontal plane as the control lever (38). The control lever (38) extends forwardly of a line (A) connecting the centres of the steerable wheels (12) and is rotatable about an axis adjacent its front end. The angles between each rod (50, 52) and the control lever (38) and between each rod (50, 52) and its associated steering arm (58, 60) are substantially equal to 90 DEG during straight line motion of the vehicle. The particular geometry of the steering system elements ensures that high steering angles are possible with a minimum of tyre slip or distortion. <IMAGE>

Description

SPECIFICATION Vehicle steering system The present invention relates to a vehicle having a pair of independently-suspended wheels which are mounted on stub axles and are steerable by a steering system of the vehicle, this steering system comprising a steering shaft coupled via a reduction mechanism to an angularly displaceable control lever which, in turn, is coupled to the stub axle of each steerable wheel via a respective rod and steering arm.

The object of the present invention is to provide a steering system of simple form which makes it possible to obtain high steering angles whilst maintaining within acceptable limits the values of the displacement between the point of intersection of the extensions of the axis of rotation of the steerable wheels and the instantaneous axis of rotation of the vehicle. As is known, this displacement is undesirable since it causes the tyres of the steerable wheels to distort or slip on the road surface during cornering.

This object is achieved, in accordance with the present invention, by the provision of a vehicle having a steering system of the form described above, in which: the control lever, the two rods and the two steering arms are substantially arranged in a common horizontal plane; the control lever extends forwardly of a line connecting the centres of the steerable wheels, and is angularly displaceable about an axis situated in the region of the forward end of the lever; the centres of rotation of the two steering arms are situated on opposite sides of their corresponding rods to the axis of rotation of the control lever; the rods are articulated to the control lever about respective axes adjacent to the line connecting the centres of the steerable wheels; and the angles comprised between each rod and the control lever and between each rod and its associated steering arm are substantially equal to 90 during straight-line motion of the vehicle.

Due to such an arrangement of the- steering system, when the wheels are turned to high steering angles the effective length of each steering arm (that is, the projection of this steering arm on a line normal to its corresponding rod) is only reduced by a small amount compared to the effective length of the steering arm when the vehicle is moving in a straight line. As a result, high steering angles can be achieved without involving excessive increases in the forces acting on the components of the steering system. This has the advantage of making it possible to minimise the dimensions of the steering system components.

Avehicle steering system embodying the invention will now be particularly described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a part cut-away side elevation of a vehicle showing the general disposition of the steering system; Figure2 is a plan view corresponding to Figure 1; Figure 3 is a diagrammatic plan view to an enlarged scale of part of the steering system shown in Figures 1 and 2, and Figure 4 is an enlarged view of part of Figure 3.

Shown in Figures 1 and 2, is a bus 10 of a known type used for passenger transport. The bus 10 has a pair of steerable front wheels 12, a pair of steerable rear wheels 14, and a pair of non-steerable rear wheels 16 which form the driving wheels of the bus.

The wheels 12, 14 and 16 are suspended on the body of the bus 10 in independent manner. In particular, each front wheel 12 is suspended, in a manner known per se, by means of a wishbone 18 pivoted on the bus body and a telescopic shock absorber 20.

The front wheels 12 are situated rearwardly of the driving seat 22 considered relative to the normal direction of movement of the bus 10.

The steering system for the wheels 12 comprises an articulated steering shaft 24 carrying at its upper end a steering-wheel 26 situated in front of the seat 22.

The lower end of the steering shaft 24 is connected to a steering box 36 via an actuator 28, a transvese bar 30, a servomechanism 32 known per se, and an articulated control bar 34 lying in the longitudinal median plane B of the bus 10 (see Figure 3).

The steering box 36 contains a reduction mechanism, known per se, which has a substantially vertical output shaft 42 arranged adjacent the longitudinal median plane B of the bus 10. The shaft 42 is connected to the forward end 40 of a control lever 38 which is arranged in front of the axis A extending between the centres of the wheels 12 (considered with respect to the normal direction of movement of the bus 10). When the bus 10 is moving in a straight line, the lever 38 lies parallel to the longitudinal median axis B of the bus 10.

The rear end of the control lever 38 has a cross-piece 44 to the opposite ends of which are articulated, by means of ball-and-socket joints 46 and 48, the ends of two rods 50 and 52 (see Figure 4).

The ends of the rods 50, 52 remote from the control lever 38 are articulated, by respective balland-socket joints 54 and 56, to the ends of two steering arms 58 and 60. The opposite ends of the steering arms 58,60 are rigidly connected in a manner known per se to the stub axles, not shown in the drawings, of the wheels 12.

The control lever 38, the rods 50, 52 and the steering arms 58, 60 are substantially arranged in a common horizontal plane.

The centres of rotation of the steering arms 58 and 60 (which correspond to the points where these steering arms 58, 60 are secured to the stub axles of the wheels 12) lie on opposite sides ofthe corresponding rods 50,52 to the output shaft 42 of the control lever 38.

The joints 46 and 48 which serve to articulate the rods 50 and 52 to the control lever 38, are situated adjacent the axis A connecting the centres of the wheels 12. When the bus 10 is moving in a straight line, these joints 46,48 are in mutual alignment in a direction parallel to the axis A and, in addition, the angles between each rod 50, 52 and the control lever 38, and between each rod 50, 52 and the corresponding steering arm 58, 60 approximate to 90 .

The steering system described above is particularly simple and makes it possible to achieve high steering angles for the wheels 12 (of the order of 60 ) with reduced displacement between the point of intersection of the extensions of the axes of rotation of the wheels 12 and the instantaneous axis of rotation of the bus (which in the present example lies on the extension of the line connecting the centres of rotation of the non-steerable rear wheels 16).

Furthermore, when the wheels 12 are set at their maximum steering angle (full lock), the effective length of the lever arms formed by the steering arms 58, 60 is only slightly reduced with respect to their effective length during straight-line motion of the bus 10. This may be seen from Figure 4, in which the rod 50 and the steering arm 58 are shown in continuous, dashed, and chain-dashed outlines respectively indicating their positions during straightline motion, and with full lock to the left and to the right. The effective length of the arm 58 with full lock set is indicated by distances C and D which, as shown, are at least equal to two thirds of the distance E representing the effective length of the arm 58 during straight-line motion. This reduces the magnitude of the forces required to be imparted to the rods 50,52 in order to obtain high steering angles, and thereby makes it possible to reduce the dimensions of the components of the mechanical transmission of the steering system; in particular, the size of the heads of the spherical joints 46 and 48 and 54 and 56 can be reduced.

The described steering system is particularly suitable for industrial vehicles.

Claims

1. Avehicle including a pair of independentlysuspended wheels mounted on stub axles and steerable by a steering system which comprises a steering shaft coupled via a reduction mechanism to an angularly displaceable control lever which, in turn, is coupled to the stub axle of each said wheel via a respective rod and steering arm, the steering system being so arranged that: the control lever, the rods and the steering arms lie substantially in a common horizontal plane.

the control lever extends forwardly of a line connecting the centres of the steerable wheels and is angularly displaceable about an axis situated in the region of the forward end of the lever, the centres of rotation of the steering arms are situated on opposite sides of their corresponding rods to the axis of rotation of the control lever, the rods are articulated to the control lever about respective axes adjacent to the line connecting the centres of the steerable wheels, and the angles comprised between each rod and the control lever and between each rod and its associated steering arm are substantially equal to 90 during straight-line motion of the vehicle.

2. Avehicle according to Claim 1, wherein said steerable wheels form the front wheels of the vehicle.

3. Avehicle steering system substantially as herein before described with reference to the accompanying drawings.