GB2124167A

GB2124167A - Vehicle steering mechanisms

Info

Publication number: GB2124167A
Application number: GB08315745A
Authority: GB
Inventors: Shoichi Sano; Yoshimi Furkawa
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1982-06-09
Filing date: 1983-06-08
Publication date: 1984-02-15
Also published as: FR2528373B1; FR2528373A1; GB8315745D0; GB2124167B

Abstract

A steering mechanism in a vehicle having front and rear wheels capable of being steered, wherein the rear wheel castor trail (I) and/or the rear wheel king pin offset (e) is set negative. As in this mechanism the point of intersction (c) as viewed from the side between the rear wheel king pin centre line (K) and a road surface (G) is to the rear of the rear wheel central grounding point (g), and/or the point of intersection (k) as viewed from the rear, or the front, of the rear wheel king pin centre line (K) and the road surface (G) is outboard of the rear wheel central grounding point (g), the force required for steering the rear wheels is minimised, and therefore the required steering force as whole is minimised, without recourse to provision of a powered steering mechanism. <IMAGE>

Description

SPECIFICATION Vehicle steering mechanisms This invention relates to vehicle steering mechanisms and is particularly concerned with steering mechanisms in which both front and rear road wheels are steerable through steering operation of a steering wheel. Throughout, description will be made with reference to the front and rear of a vehicle as determined by the intended direction of forward running of the vehicle.

It has already been proposed that in a vehicle both the front and the rear wheels are steered by operating the vehicle steering wheel. In one particular proposal the rear wheels are steered in the same direction as the front wheels within a relatively small steering angle range on either side of straight ahead, this being the range that is used in general during high speed running of the vehicle, whereas upon rotation of the steering wheel beyond this small steering angle range to a large steering angle such as used during low speed running of the vehicle, the rear wheels are steered in the opposite direction to the front wheels.As a result not only is a good steering attained while the vehicle is running at high speed, but also since a small radium of gyration is obtained at a large turning angle of the steering wheel when executing a U-turn or during vehicle movement into or out of a parking space, operation of the vehicle in general is enhanced.

According to the present invention there is provided a steering mechanism in a vehicle having front and rear wheels capable of being steered, wherein at least one of a rear wheel castor trail and a rear wheel king pin offset is set negative. In this mechanism, as a point of intersection as viewed from the side between a rear wheel king pin centre line and a road surface is to the rear of a rear wheel central grounding point, and/or a point of intersection as viewed from the rear (or the front) of the rear wheel king pin centre line and the road surface is outboard of the rear wheel central grounding point, the force required for steering the rear wheels is minimised, and therefore the required steering force as a whole is minimised, without recourse to provision of a powered steering mechanism.

For a better understanding understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an explanatory plari view of a vehicle equipped with a steering mechanism in which the front and rear wheels are steered; Figure 2 is a side view of the vehicle of Fig. 1; Figure 3 is a rear view; Figure 4 is a perspective view on a larger scale of a detail of rear wheel steering mechanism of the vehicle; Figure 5 is a side view on a larger scale showing steering geometry of one of the rear wheels of the vehicle; and Figure 6 is a rear view on the same scale as Fig. 5 and also showing the steering geometry.

Referring first to Figs. 1 and 2, a steering motion of a steering wheel 1 is converted to transverse motion of two tie rods 4 for steering two front wheels 3 through a rack and pinion type steering arrangement 2 which, for example, is provided internally with a power cylinder, the front wheels 3 being steered by a resulting pivotal movement of two knuckle arms 5 connected to the outer ends of the tie rods 4.

A linkage 6 is connected to an approximately central part of the steering arrangement 2. To this end, a shaft 9 of the linkage 6 is connected through a universal joint 8 to a shaft 7 of a driven pinion, the shaft 9 extending rearwardly from the joint 8. The driven pinion is in mesh through an idler gear (not shown) with the rack (also not shown) of the steering arrangement 2.

A shaft 1 2 (Fig. 3) which constitutes an input portion of the steering mechanism for two rear wheels 11 is connected to the shaft 9 through a universal joint 10.

The shaft 1 2 is disposed on the longitudinal centre line of the vehicle body inclined downwarely to the rear. A crank 1 3 is provided at the rear end of the shaft 1 2 with the crank pin 14 thereof projecting rearwards. The shaft 1 2 is disposed in and supported by a sleeve 1 6 which is fast with a lower arm bracket 1 5 for the rear wheels, the bracket 1 5 being attached to a cross member of a body frame (not shown) of the vehicle.

A joint member 17, which is generally of inverted T-shape in front view is loosely mounted on the crank pin 14 at its upper portion 1 8. Rear wheel steering tie rods 20 are connected and supported through respective ball joints 21 to upper surfaces 1 9a of projecting portions 19 which constitute right and left lower portions of the joint member 1 7.

A link bracket 22 is fixedly suspended from a vehicle floor panel (not shown) at one side of the floor panel in a position rearer than the joint member 1 7. A first link 23 is suspended from the bracket 22 pivotably through a pivot pin 23a constituted by a bolt and nut. To the lower portion of the link 23 is pivoted, by a pivot pin 23b also constituted by a bolt and nut, an arm 24 which functions as a second link.The arm 24 is formed sufficiently long beyond the centre line with respect to the right and left of the vehicle body, and its fore portion 24a is secured fast by two bolts 25 to rear faces 19b of the right and left projecting portions 1 9 of the joint member 1 7. By such a construction, the joint member 1 7 is allowed to perform a composite pivotal motion consisting of vertical and transverse motions along with a cranking motion of the crank pin 14.

In the drawings, the reference numerals 26, 26 denote knuckle arms respectively connected to the outer ends of the rear wheel steering tie rods 20, and the numerals 27, 27 denote respective lower arms for the rear wheels 11.

In operation of the steering mechanism the rear wheels 11 are steered in the same direction as the front wheels 3 by turning the steering wheel 1 within a relatively small steering angle range on either side of straight ahead, whereas upon rotation of the steering wheel beyond this small steering angle range to a large steering angie, the rear wheels are steered in the opposite direction.

As shown in Fig. 5, the distance between a castor point which is a point of intersection between a king pin centre line K of the rear wheel 11 and a road surface G-and a central grounding point g of the rear wheel 11, namely, a castor trail I, when viewed from the side of the vehicle, is set negative, point c being to the rear of point g. As a result, the returning force (=. steering holding force 6 steering force) about the king pin centre line K can be rendered zero or negative while cancelling the self-aligning torque mainly during vehicle running, that is, the steering force required for steering the rear wheels 11 can be reduced and thus the steering force required as a whole can be reduced.The castor angle 8 is positive, the king pin centre line K being inclined rearwarely in the direction from bottom to top of the king pin.

As shown in Fig. 6, the distance between a point of intersection which is between the king pin centre line K of the rear wheel 11 and the road surface G- and the central grounding point g, namely, a king pin offset e, when viewed from the rear (or the front) of the vehicle, is set negative, point k, being outboard of point g. This also has the result that the steering force required for steering the rear wheels 11 can be reduced and the steering force required as a whole can therefore be decreased.

In general, if there exists a king pin inclination angle a, there occurs a vertical movement of the vehicle body upon steering except when the central grounding point g of the rear wheel 1 coincides with the point of intersectionk between the king pin centre line K and the road surface G. This means that if the offset e is positive, the vehicle body rises upon steering and the following force acts on the hands of the driver who is trying to turn the steering wheel 1::

Amount of rise of vehicle body Axial load X perimeter] Turning distance of hand on steering wheel Therefore, if the offset e is set negative, the vehicle body descends upon steering and the value of the above force becomes negative, so that the force acting at the steering wheel 1 becomes lighter.

If the king pin offset e of the rear wheel 11 is set negative, the steering force as a whole can be reduced.

It will be understood that if either the castor trail I or the king pin offset e of the rear wheel 11 is set negative, the steering force can be reduced to a considerable extent, and that if both the castor trail and the king pin offset e of the rear wheel 11 are set negative, a further reduction of the steering force can be attacined by a cooperative effect. Thus it is possible to reduce the steering force for the rear wheels and hence the steering force as a whole merely by giving some consideration to the geometry of the rear wheels without the need to provide the rear wheel steering mechanism with any form of powered drive.

Claims

1. A steering mechanism in a vehicle having front and rear wheels capable of being steered, wherein at least one of a rear wheel castor trail and a rear wheel king pin offset is set negative.

2. A steering mechanism as claimed in claim 1, wherein both said rear wheel castor trail and said rear wheel king pin offset are set negative.

3. A steering mechanism substantially as hereinbefore described with reference to the accompanying drawings.

4. A steering mechanism in a vehicle having front and rear wheels capable of being steered, wherein a point of intersection as viewed from the side between a rear wheel king pin centre line and a road surface is to the rear of a rear wheel central grounding point, and/or a point of intersection as viewed from the rear (or the front) of the rear wheel king pin centre line and the road surface is outboard of the rear wheel central grounding point.