GB2347906A

GB2347906A - A suspension strut

Info

Publication number: GB2347906A
Application number: GB9916431A
Authority: GB
Inventors: Jer Me Kieffer
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1999-03-19
Filing date: 1999-07-13
Publication date: 2000-09-20
Also published as: GB9906448D0; GB9916431D0

Abstract

A suspension strut for a motor vehicle characterised by an armature 24 located around an inner annulus 22 and an outer annulus 26, whereby spring forces are transmitted to the vehicle body via the armature 24 and the outer annulus 26 and damper forces are transmitted to the body via the inner annulus 22, the armature 24 and the outer annulus 26. A further embodiment is disclosed in figures 4 and 5.

Description

SUSPENSION STRUT This invention relates to a suspension strut such as a Macpherson strut, for a motor vehicle.

According to the present invention there is provided a suspension strut, such as a Macpherson strut, for a motor vehicle, comprising a damper member mounted generally concentrically within a spring and extending therethrough to an end, an inner generally annular elastomeric member located concentrically and axially with the damper member where its end extends through the spring, a relatively rigid armature located generally around the periphery of the inner annulus and arranged to receive forces imposed by the spring and an outer generally annular elastomeric component located at the periphery of the armature and arranged to bear on the body of the vehicle to which the strut is to be mounted, whereby the spring forces are transmitted to the vehicle body generally via the armature and the outer annular member and damper forces are transmitted to the body via the inner annular member, the armature and the outer annular member.

A strut embodying the invention is described by way of example with reference to the drawings in which: Figure 1 is a schematic cross sectional view of a prior art upper strut mount; Figure 2 is a schematic cross sectional view of a strut in accordance with the invention mounted to a vehicle; Figure 3 is a schematic cross sectional view of the strut of Figure 2 separated from a vehicle ; Figure 4 is a schematic cross sectional view of an alternative strut separated from a vehicle; and Figure 5 is a schematic cross sectional view of the strut of Figure 4 mounted to a vehicle.

With reference to Figure 1, the prior art strut generally comprises a damper 2 mounted concentrically within a spring 3. In the diagram, only the upper part of the damper 2 and the uppermost coil of the coil spring 3 are shown. The lower parts of the damper 2 and coil spring 3 are attached to a moving part of the vehicle suspension and the upper part of the damper 2 passes through an aperture 4 formed in a suspension turret 6 of the vehicle body. The strut thus provides damping and spring forces between the moveable suspension component and the relatively fixed suspension turret 6.

An important function of the upper strut mount shown in Figure 1 is to reduce the transmission of vibration from the suspension to the vehicle body. To achieve this, an annulus 8 of elastomeric material is interposed between the undersurface of the turret 6 and an armature 10 which is rigidly fixed both to the damper 2 and to a spring plate 12 which carries the load of the spring 3.

Although this arrangement is simple, it is less effective because the elastomeric annulus 8 carries the load imposed by the spring and thus carries the weight of the vehicle. Since the annulus 8 is therefore under high loads from the spring, it cannot be optimised to provide good vibration filtration for the damper 2.

An alternative is to mount the spring separately using a separate bearing point on the vehicle body. This allows the use of a separate elastomeric component. However, this has the disadvantage that the spring is separate from the damper prior to mounting on the vehicle and thus is more difficult to assemble to the vehicle during vehicle manufacture.

With reference to Figure 2, in a strut in accordance with the invention, the upper part of a damper 2 passes through an aperture 4 in a suspension turret 6 forming part of the vehicle body or chassis. A collar 20 is rigidly fixed to the damper 2 and acts on the lower surface of an inner, elastomeric annulus 22 which is located generally concentrically with the damper 2. The damper is generally enclose in a bellows arrangement 23.

The outer perimeter of the inner annulus 22 is surrounded by an armature 24 which in turn, is surrounded by an outer elastomeric annulus 26. The armature 24 is relatively rigid. Typically it is formed from a metal such as steel.

The combination of the inner annulus 22, the armature 24 and the outer annulus 26, is shaped to be a vertical sliding fit in the inner surface of the suspension turret 6. As will be described below, this construction allows vibration of the damper 2 to be filtered by the inner annulus 22 so that it does not pass to the vehicle body via suspension turret 6.

The spring 3 is located in the underside of a spring mount 28. The upper surface of the spring mount 28 holds bearings 30 which allow rotational movement of the spring mount 28 relative to a lower extension of the armature 24. The bearings 30 also transmit axial forces from the spring via the spring mount 28 to the armature 24. Thus, the top of the spring 3, the spring mount 28 and the armature 24 are generally rigidly connected.

From inspection of the Figure, it will be noted that the outer annulus 26 has a"top hat"configuration having an upper section 30 with a generally vertical outer surface and a lower section 32 with a generally horizontal upper surface. It will also be noted that the armature 24 also follows this general configuration.

Thus, axial movement of the spring is generally resisted by the lower section 32 of the outer annulus 26 and radial movement is resisted generally by the upper section 30 of the outer annulus 26. It is the outer annulus 26 which largely performs the function of filtering vibrations from the spring to prevent these being transmitted to the suspension turret 6. Such vibrations are not imposed on the inner annulus 22.

It will be appreciated therefore that two different elastomeric components 22,26 perform the respective functions of filtering vibrations from the damper 2 and filtering vibrations from the spring 3. Thus each of these two components may by optimised in shape and/or material selection to provide improved damping on the prior art.

However, the disadvantage of separate mountings for the spring and damper respectively have been avoided.

Figure 3 shows the mount of Figure 2 separated from the vehicle.

When separated from the vehicle, the spring 3 tends to pull the upper part of the damper 2 downward. It will be noted that in this configuration, the collar 20 is arranged to bear on a formation 40 on the upper surface of the spring mount 28 to contain the precompression of the spring 3. The cooperation between the lower surface of the collar 20 and the formation 40 serves two purposes.

Firstly, by limiting the downward movement of the strut 2 relative to the armature 24 under the force of the precompressed spring 3, damage to the inner annulus 30 is avoided.

Secondly, the formation 40 is chosen to cooperate with the collar 20 to radially align the strut 2 concentrically within the armature 24. This concentric positioning cannot be guaranteed in the prior art (Figure 1) since the upper formation of the spring 3 may not be consistent throughout manufacture. In this way, optimum positioning of the damper 2 within the turret 6 is achieved when the damper 2 is fixed in position by the application of a fixing nut 42 (Figure 2) applied to the threaded stud 44 at the top of the damper 2.

The preceding description has dealt primarily with the operation of the mount when the weight of the vehicle is bearing downwardly on the turret 6. However, during operation of the vehicle it is not uncommon that the forces are reversed (for example if the wheel suddenly passes over a depression in the road surface) and under these conditions, the damper 2 and spring 3 move downwardly away from the turret 6. To limit this downward movement, a bump stop 46 is secured under the fixing nut 42 and acts on the upper surface 48 of the turret 6. As mentioned above, the outer annulus 26 is arranged to be a sliding axial fit in the turret 6. Thus under the conditions described above, the inner annulus 22, the armature 24 and the outer annulus 26 may move vertically downward as a whole until the downward movement is restricted by the bump stop 46. As this happens, the lower part 32 of the outer annulus moves away from the vehicle body. It will be noted, however, that since the outer periphery of the upper section of 30 the outer annulus 26 has generally vertical sides, the damper 2 is maintained in good radial location within the turret 6. Thus when the downward movement of the suspension stops or the damping force of the damper 2 diminishes (which then allows relative movement between the spring and the upper part of the damper), the damper 2, spring 3 and associated elastomeric components 22,26 begin to move upwardly again and are accurately reseated in the turret 6. The outer annulus 26 then comes into contact again with the vehicle body. The lower section 32 of the outer annulus 26 reduces the shock of the contact made between the strut and the vehicle body as it moves upwardly again and thus a significant source of noise (in the prior art) is advantageously reduced.

With reference to Figure 4, an alternative arrangement for the armature is shown. The modified armature 24'is folded at 50 to form a re-entrant portion 52. This allows the mount to be reduced in height whilst still retaining the improved characteristics of the earlier-described embodiment.

At the distal or upper end of the re-entrant portion 52, an upwardly and radially inwardly directed surface 54 is formed. This co-operates with a surface 56 of a nut 58 fitted on to the threaded stud 44 of the damper 2. The surface 56 is directed generally downwardly and radially outwardly and acts to compress a portion 60 of the elastomeric material forming the inner annulus 22'and outer annulus 26'.

The compressed portion 60 may be used further to adjust the force/displacement characteristics of the upper strut mount and may be used in particular to introduce desirable non-linearities in the characteristic force/displacement curve.

A comparison between Figures 4 and 5 shows that when the strut is not mounted to a vehicle, the portion 60 acts to absorb the force due to the pre-compression of the spring 3.

It will be appreciated that the struts described above may be used in front suspension applications where it may be required to turn for steering purposes, or for other applications, such as rear suspension applications, where turning is not required.

Claims

CLAIMS 1. A suspension strut, such as a Macpherson strut, for a motor vehicle, comprising a damper member mounted generally concentrically within a spring and extending therethrough to an end, an inner generally annular elastomeric member located concentrically and axially with the damper member where its end extends through the spring, a relatively rigid armature located generally around the periphery of the inner annulus and arranged to receive forces imposed by the spring and an outer generally annular elastomeric component located at the periphery of the armature and arranged 'to bear on the body of the vehicle to which the strut is to be mounted, whereby the spring forces are transmitted to the vehicle body generally via the armature and the outer annular member and damper forces are transmitted to the body via the inner annular member, the armature and the outer annular member.
2. A suspension strut according to claim 1, including a spring mount interposed between the spring and the armature and which permits relative rotational movement generally about the axis of the strut between the spring and the armature.
3. A suspension strut according to claim 1 or claim 2, wherein the outer annulus is arranged to slide generally vertically within and relative to a similarly dimensioned part of the vehicle body.
4. A suspension strut according to claim 3, wherein the outer annulus is arranged to cooperate with the vehicle body to maintain the damper in a generally constant radial position during the sliding movement of the outer annulus relative to the vehicle body.
5. A suspension strut according to any preceding claim, in which the damper member carries a collar near its said end and the inner elastomeric member is located between the collar and the end.
6. A suspension strut according to any of claims 1 to 4, in which the damper member carries a collar near its said end which is arranged to cooperate with a formation on the spring mount to locate the damper generally concentrically within the armature when the strut is not fitted to a vehicle.
7. A suspension strut according to claim 6, wherein the inner elastomeric member is located between the collar and the said end.
8. A suspension strut according to any preceding claim, wherein the spring mount and the armature include bearing races and wherein the strut includes one or more bearing located between the races which permit relative rotational movement between the spring mount and the armature.
9. A suspension struct according to any preceding claim wherein the armature is arranged to co-operate with a surface fixed to the damper member to compress a portion of elastomeric material located between the inner annulus and the outer annulus.
10. A suspension strut constructed and arranged as described herein with reference to any of Figures 2 to 5 of the drawings.