GB2050271A

GB2050271A - Vehicle steering assemblies

Info

Publication number: GB2050271A
Application number: GB8016418A
Authority: GB
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1979-05-22
Filing date: 1980-05-19
Publication date: 1981-01-07
Also published as: GB2050271B; DE2920637A1; FR2457206B3; FR2457206A1

Abstract

In a motor vehicle steering assembly, for protecting shock sensitive, precision- made and expensive components such as the steering gearbox against impact damage originating at the vehicle's steered wheels, the invention provides at least one force transmission element or buffer member in the steering assembly, between the steering gearbox and steering arms of the steering linkage and which is arranged in use to yield axially when subjected to an axially directed shock- like force exceeding a predetermined maximum service force. In Figure 1 a tie rod coupled by a ball joint 4 to a track rod or a toothed rack includes two parts 1,3 connected by a prestressed resilient body made of rubber or plastics material. In an alternative construction the steering linkage includes a ball joint having a ball socket axially supported in a joint housing by a plastically deformable member. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicle steering assemblies This invention concerns vehicle steering mechanisms.

It is common knowledge that the steering effort applied by the driver of a motor vehicle to the steering wheel is transmitted by way of a steering shaft to a steering mechanism, usually a steering gearbox, which converts this effort into to-and-fro forces which are transmitted to steering arms by way of track rods. The steering arms are secured to swivel bearings of the steerable wheels of the motor vehicle and turn the steerable wheels about the steering pivot, often referred to as the centre of rotation, until the desired angle of steering lock is obtained.

Two principal types of steering mechanisms are in common use, of which one produces a rotary movement responsive to rotation of the steering shaft, which is converted by means of a drop arm and a steering control arm into linear displacement of a track rod; and of which the other type has a steering gearbox including a pinion engaged with a toothed rack, whereby rotary movements imparted to the pinion by the steering shaft are converted to linear displacements of the rack and hence to track rods connected to the ends of the rack.

The need to provide steering mechanisms with teeth makes them relatively expensive components to construct.

It is therefore the aim of the present invention to provide means for protecting against shock-like overload, the shock-sensitive steering mechanism which forms part of a steering linkage arranged between a steering shaft and the steerable wheels of a motor vehicle, and which, compared with the other components, is structurally expensive, thus to prevent consequential damage to the teeth of the steering mechanism when the vehicle wheel abruptly introduces large forces into the steering linkage in the event, for example, of slight accidents or of skidding onto the edges of curbs or other obstacles.

The present invention accordingly provides a shock overload protection device for protecting against shock-like overload, the relatively shocksensitive steering gearbox which is arranged between the conventional steering shaft and the steerable wheels of a motor vehicle, and which, compared with other components of the assembly such as the steering linkage, constitutes the weakest component with respect to steerability and is structurally expensive, characterised in that there is disposed in the steering assembly, between the steering gearbox and steering arms of the steering linkage, at least one force transmission element or buffer member which ia arranged in use to yield axially when subjected to an axially directed shocklike force exceeding a predetermined maximum permissible limit.

The device provided by the invention is most conveniently embodied in a steering linkage which may include a single drop arm actuated track rod or a pair of rack actuated track rods, the track rods in either case being liable to experience axial forces, the effects of which are buffered and reduced as by arranging the overload protection device in series with the or each track rod.

The invention will be described further, by way of example, with reference to the accompanying generally diagrammatic drawings, in which: Figure 1 is an elevation, partly in axial section, of a part of one steering linkage embodying the invention; and Figure 2 is an axial section of part of another steering linkage.

Force transmission elements are illustrated in the drawings as being disposed in the steering linkage of a motor vehicle between the steering arms and the steering gearbox, that is to say, the toothed rack or the drop arm, and which yield when a predetermined shock-like force is exceeded which is distinctly larger than the maximum force occuring during normal operation, but which is smaller than the force required to damage the steering mechanism, this resilience being effected either by plastic deformation, sliding or by overcoming the force of a prestressed spring device. Either one or two yielding force transmission elements of this kind are used according to the construction of the steering linkage and according to the place of installation.

Referring to Figure 1, an axial force transmitting portion of the steering linkage includes a yielding force transmission element located between the conventional steering arm and the steering gearbox.

In the illustrated embodiment, the force transmission element is one of two outer track arms connected by way of an axial joint or tube joint 4 to a track rod (not shown) orto a toothed rack. The other outer track arm is constructed in the same manner.

This yielding force transmission element is of twopart construction. It comprises a first part 1 for connection to the steering arm (not shown) and a second part 3 which is axially contiguous thereto and which leads to the main steering linkage (also not shown). The end of one of the parts 1 and 3, shown in the present instance as being the part 1, is axially overlapped by the end of the other part 3, and is rigidly embraced in a pincer-like or sleeve-like manner by an interposed, prestressed resilient intermediate body 2 made from rubber, plastics material or a similar material, so that a coupling is created which transmits axial forces between the two parts.

In the illustrated embodiment, the enclosed end of the part 1 has radially outwardly extending projections 11 which can be, for example, in the form of continuous annular tori. By appropriately selecting the material of the intermediate body 2, the strength of this coupling can be adapted to prevailing requirements by the type of construction and the number of the projections.

The connection between the two parts 1 and 3 is dimensioned such that, taking into account any safety factors appropriate to predictable normal stresses of travelling, a rigid connection exists which ensures precise transmission of the steering forces applied. However, as soon as shock-like forces larger than the pre-determined limiting values are intro duced into the steering linkage, for example upon one of the two steerable vehicle wheels skidding onto the edge of a curb, the adhesion between the enclosed first part 1 of the force transmission element and the prestressed resilient body 2 surrounding it is overcome, so that the part 1 is displaced axially within the resilient member and energy-absorbing work is performed in the resilient member 2 as required to take up the shock.The leading edge of the shock-like force pulse introduced into the linkage is thereby flattened, so that the impact force acting upon the steering gearbox is reduced to harmless values as a result of the consequently lower accelerations of the masses connecting it to the wheels. Although in Figure 1, the yielding force transmission element is constructed to be substantially unidirectional in its action, that is to say, axially directed forces can displace the first part 1 only towards the right, it is alternatively a simple matter to construct the force transmission element symmetrically, so that it is effective in both directions.

As an alternative to the use of linkage parts for transmitting axial forces, it is possible to arrange for axial joints disposed in the steering linkage to be in the form of yielding force transmission elements.

For example, convenient joints are usually present between the toothed rack and the outer track rods in a rack-and-pinion steering mechanism, or between the track rod and the outer track arms in a drop arm mechanism. An axial joint or ball joint of this kind is shown diagrammatically in Figure 2, an outer track rod or track arm being designated 5. The cooperating toothed rack or centre track rod (not shown) is screwed into the right hand portion of the housing 6 of the ball joint. A ball joint normally comprises a ball head 51 connected to the track rod or track arm and a bearing socket 61 which is made from a plastics material conveniently of a solid, self-lubricating character and which is let into the housing of the ball joint.In the present embodiment, in order to be able to act as a force transmission element which yields under the action of excessive forces, the bearing socket 61 receiving the ball head 51 is axially supported relative to the housing 6 of the axial joint by way of a plastically deformable buffer member 7 in the form of a sleeve or bush. A closure cover of steel plate is disposed between the bearing socket 61 and the buffer member 7. Alternatively, a prestressed spring device, such as a cup spring, may be fitted instead of a plastically deformable buffer member.Under the normal stresses occuring during operation, a rigid connection exists between the ball head 51 and the housing 6 of the ball joint, and thus between the outer track rod or track arm 5 and the toothed rack or centre track rod as the case may be, so that it is ensured that normal steering forces originating from the steering gear box are transmitted with precision to the steering linkage. The buffer member 7 or the prestressed spring device yields axially only when the above mentioned limiting values are exceeded, so that any shock-like forces transmitted to the steering gearbox are appropriately reduced.

It will be appreciated that the measures proposed by the invention do not preclude damage within the steering transmission system caused by overstress.

However, the consequential damage is reduced to a considerable extent, since the high-grade components, especiaily the steering gearbox and its teeth, are protected against damage. Thus, in the event of damage, it is only necessary to change the defective yieldable force transmission elements or buffers, which are relatively easily accessible.

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Claims

1. A steering assembly shock overload protection device for protecting against shock-like overload, the relatively shock-sensitive steering gearbox which is arranged between the conventional steering shaft and the steerable wheels of a motor vehicle, and which, compared with other components of the assembly such as the steering linkage, constitutes the weakest component with respect to steerability and is structurally expensive, characterised in that there is disposed in the steering assembly, between the steering gearbox and steering arms of the steering linkage, at least one force transmission element or buffer member which is arranged in use to yield axially when subjected to an axially directed shock-like force exceeding a predetermined maximum permissible limit.

2. A steering linkage including a single drop arm actuated track rod or a pair of rack actuated track rods, said track rods being arranged to transmit axial forces, in which the or each track rod incorporates a force transmission or buffer member as claimed in claim 1.

3. A steering linkage as claimed in claim 2, in which the track rod or track rods are components of a steering trapeze.

4. A steering linkage as claimed in claim 2 or claim 3, in which each of the yielding force transmission elements or buffer members comprises a first part for direct or indirect connection to a steering arm and a second part which is axially contiguous to the first part and leads to the remainder of the steering linkage, the end of one of said parts being axially overlapped and rigidly embraced or gripped by the end of the other of said parts by way of an interposed, prestressed resilient intermediate body.

5. A steering linkage as claimed in claim 4, in which the enclosed end of said one part has at least one radially outwardly directed projection.

6. A steering linkage as claimed in claim 5, in which the projection is in the form of a continuous annular torus.

7. A steering linkage as claimed in any one of the preceding claims, in which the yielding force transmission element or buffer member is constructed so as to be effective in both directions in which force is applied.

8. A steering linkage comprising outer track rods connected by way of inner axial joints or ball joints to a toothed rack or to a centre track rod and in which at least some of said joints incorporate axially yielding force transmission elements or buffer members as claimed in claim 1.

9. A steering linkage as claimed in claim 8, in which a ball socket receiving a ball head of a ball joint is supported relative to the joint housing by way of a plastically deformable buffer member or by a prestressed spring device.

10. Steering linkages incorporating yielding force transmission elements or buffer members substantially as hereinbefore described with refer ence to and as illustrated in the accompanying drawings.