GB2306417A - Vehicle wheel steering arrangement - Google Patents

Abstract

A steering arrangement allows the steering rod 7 to be turned to full lock only against the force of a spring 11. As soon as the steering wheel is released, the spring 11 will move the steered wheels to a position less than the full lock. This enables the driver to turn the wheels to full lock, by overcoming the spring force but prevents full lock being applied accidentally or when the steering wheel is released.

Description

A VEHICLE WHEEL STEERING ARRANGEMENT This invention relates to a vehicle wheel steering arrangement for determining the maximum extent to which the steered wheels can be turned.

It is desirable that the steerable wheels (normally the front wheels) of a vehicle be turned as far as possible, because this has the desirable effect of reducing the turning circle of the vehicle. However, it is not always possible to achieve as large a turning angle as might be desired, because the wheels must not foul the vehicle bodywork in their extreme positions. It is normally necessary to set the maximum angle of turn of the wheels such that when the wheels are fitted with snow chains and are at one or other limit of the up and down suspension travel, they remain clear of the bodywork.

As a result, the maximum turning angle permitted when the vehicle is in its normal position on a level road has to be significantly less than could be used if these constraints did not have to be taken into account.

European Patent specification 0 614 796 discloses one solution to this problem. In that specification a fixed abutment is mounted on each tie rod, in such a way that the abutment makes contact with the end of the steering rod housing to limit the movement of this rod when the vehicle wheel is in the full hang or full rebound position.

The present invention represents another. different solution to the same problem.

According to the invention, there is provided a vehicle wheel steering mechanism comprising a steering rod reciprocable in a steering rod housing and movable transversely of the vehicle when a steering wheel of the vehicle is turned, tie rods connected to opposite ends of the steering rod and connectable to the wheels to be steered, and springs at each end of the arrangement mounted, between the rod and the housing, the springs being arranged, when stressed, to tend to centre the steering rod in the housing.

The springs are preferably compression springs, and they can be mounted at the ends of the housing.

With this arrangement, when the steering wheel is turned gently, without applying extreme force, the transverse movement of the steering rod will be restricted when the compression spring at one end is trapped between the steering rod and the housing, and this will limit the steering movement, under those conditions. However, by applying more force to the steering wheel, it will be possible to compress the trapped spring to allow the wheel to turn further and this is the situation which will occur during, for example, parking manoeuvres.

Preferably the steering rod itself will have shoulders at each end, facing corresponding shoulders on the steering rod housing. The springs are preferably held against the shoulder on the steering rod housing, and the shoulder at one end of the rod will come into contact with the spring, so that the spring is trapped between the shoulder on the rod and the shoulder on the housing, at one end of the steering rod housing. The spring at the other end of the housing will be trapped between the steering rod shoulder and the housing shoulder at the opposite extreme of steering travel.

The spring rate of the springs will be chosen so that the driver experiences steering resistance when a spring is trapped between the steering rod shoulder and the rod housing shoulder, but so that the driver can overcome this resistance by a reasonable amount of additional turning force applied to the steering wheel.

The steering arrangement is preferably a rack and pinion arrangement and the steering rod is a steering rack.

The steering wheel arrangement is preferably for steering the front wheels of a vehicle.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates a motor vehicle steering apparatus according to this invention; Figure 2 shows a detail of one end of a steering housing; and Figures 3a and 3b show two alternative conditions of the steering housing of the invention.

Figure 1 shows in general form, a motor vehicle steering apparatus. A steering column 1 is connected via a universal joint 2 to a rack and pinion steering gear contained in a steering housing 3. Each end (only one end is visible) of the steering housing 3 is covered by a corrugated rubber protective boot 4 which also covers a ball and socket hinged joint 5 shown in Figures 2 and 3 which attaches, in a hinged manner, a tie rod 6 to a steering rod 7. The steering rods are driven by the rack and pinion steering gear. The tie rods 6 are attached in hinged manner at their other ends to steering arms 15 (one only shown) via further ball and socket joints, and the arms 15 are mounted on wheels 14.

Each end of the steering housing 3 is provided with a tubular end extension 8 outboard of an end wall 9. The end wall 9 has a hole through it for passage of the steering rod 7, and the rod 7 ends in a head 10 which is a sliding fit within the extension 8 and which has a socket forming part of the ball and socket joint 5. A ball on the end of the tie rod 6 is received within this socket.

A compression spring 11 is fitted in the tubular end extension 8 and is arranged so that when the steering rod 7 is moved to the left (as seen in Figure 2), the spring 11 is compressed between the head 10 and the wall 9.

The operation of this steering apparatus is illustrated with reference to Figures 3a and 3b.

Figure 3a shows the entire steering housing 3 with a rack and pinion housing 12 to which the steering column 1 is connected. It has to be appreciated that the steering rods 7 at the two ends are at opposite ends of a single rack, so that when one rod 7 moves to the right a certain distance, then the other rod 7 also moves to the right by the same distance Figure 3a shows the situation when the steered wheels are in the "straight ahead" position. In this situation, the ends 103 and 203 of the rack are symmetrical to one another. The springs 11 are untensioned, because the distance between the walls 9 and the heads 10 is greater than the relaxed length of the springs 11. It will also be evident from Figure 3a that some movement of the steering rods 7 to either side of the "straight ahead" position is possible without causing the springs 11 to exert any force on the heads.Under these conditions which represent normal driving at speed, the steering of the vehicle will be no different from that of a conventional vehicle.

However, when the steering angle becomes more acute, as can be seen in Figure 3b, the distance between the head 10 at the end 103 and the adjacent wall 9 will diminish to a stage where it is less than the relaxed length of the spring 11. When this occurs, further turning of the steering wheel will cause compression of the spring 11 which will be evident to the driver as a resistance to turning.

At low speeds, such as encountered during parking manouvres, this increased resistance does not matter and can be overcome by the driver who can thus turn the steered wheels to the "full lock" position. However, any attempt to turn the wheels so far whilst driving at speed would very quickly be signalled to the driver who would thus be prevented from turning the wheels to an extreme position.

If the steering wheel is released under these conditions, the spring 11 will have the effect of returning the steered wheels to a less acute position. The effect of the spring therefore will be to prevent full lock being applied unless a driver is actually holding the steering wheel and positively applying full lock. When the suspension is in a "full hang" condition, this will not be the case and therefore the wheels will be prevented from travelling to their full lock position when they are also in the full hang position. The full lock available under normal suspension loadings is therefore significantly greater than that available at full hang and therefore full lock can be relatively extreme resulting in a small turning circle for the vehicle.

As can be seen from Figure 3b, only one spring 11 is active at any one time, but springs are required at both ends of the rack to produce the same effect in both directions.

Alternatively, however, it may be possible to arrange a double acting spring or two separate springs at one end of the steering assembly, so that both pushing and pulling of the rack is achieved from one end.

Claims (6)

Claims

1. A vehicle wheel steering mechanism comprising a steering rod reciprocable in a steering rod housing and movable transversely of the vehicle when a steering wheel of the vehicle is turned1 tie rods connected to opposite ends of the steering rod and connectable to the wheels to be steered, and springs mounted between the rod and the housing, the springs being arranged, when stressed, to tend to centre the steering rod in the housing.

2. A steering mechanism as claimed in Claim 1, wherein the springs are compression springs.

3. A steering mechanism as claimed in Claim 1 or Claim 2, wherein the springs are mounted at the ends of the housing, between internal shoulders in the housing and shoulders at the ends of the rods.

4. A steering mechanism as claimed in any preceding claim, which is a rack and pinion steering mechanism.

5. A steering mechanism as claimed in any preceding claim, for steering the front wheels of a motor vehicle.

6. A vehicle wheel steering mechanism substantially as herein described with reference to the accompanying drawings.