GB2335400A - Motor vehicle hub assembly - Google Patents

Abstract

The hub assembly comprises a wheel (1) and hub (2) with a brake disc (3) sandwiched therebetween under compressive engagement; raised annular contact surfaces (11, 12) are provided for contact between these respective components (1, 2, 3) in order to limit the areas of these components (1, 2, 3) which require accurate machining and to provide preferential distortion control in order to ensure that braking surfaces (7) are presented appropriately to a brake caliper. The outer contact surface (11) is higher than the inner one (12) thereby ensuring preferential distortion in the region of this inner ring (12) such that distortion of the braking surfaces (7) is minimized.

Description

2335400 A Motor Vehicle Hub Assembly The present invention relates to a

motor vehicle hub assembly and more particularly to a hub assembly including a disc brake element.

A conventional hub assembly comprises a hub and wheel secured together with studs extending from the hub through apertures in the wheel.

The assembly is subject to a compressive force applied by nuts secured on these respective studs. Furthermore, sandwiched between the hub and the wheel is a brake element, generally either a disc or a drum, which also includes apertures to allow passage of the hub studs therethrough.

Flats about these respective studs and apertures through the assembly are generally brought into compressive abutment by securing the nuts on the studs. Thus, it is necessary to accurately machine these respective flat abutment surfaces for the wheel, the brake element and hub. Otherwise, there is a possibility of disc or drum distortion or mis- alignment and therefore brake judder during operation. Furthermore, it will be appreciated that these abutment surfaces may become distorted through heat cycling, wear or may simply be contaminated by debris during maintenancelassembly.

Known hub assemblies are generally fabricated to produce a non-convex mounting base. Such fabrication requires a high quality, well controlled i machining process to achieve the necessary flat contact. Such requirements can lead to increased manufacturing costs or potential increased failure of the hub assembly in use through brake judder etc.

It is an object of the present invention to provide a hub assembly which 5 substantially reduces the above-mentioned problems.

In accordance with the present invention, there is provided a hub assembly including a first element and a second element, said first element and said second element being secured together under a compressive force by compression means, at least one of said members having inner and outer raised annular contact surfaces formed thereon arranged to contact the other of said members and a depression between the contact surfaces arranged not to contact the other of said members, wherein the compression means are arranged radially inside the outer contact surface and the outer contact surface is higher than the inner contact surface such that on securing together of the elements the outer contact surface comes into contact with said other member before the inner contact surface.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

3- Figure 1 is a part cross-section of a wheel hub assembly in accordance with a first embodiment; Figure 2 is a perspective view of the wheel hub illustrated in Figure 1; Figure 3 is a perspective view of a brake disc element illustrated in 5 Figure 1; Figure 4 is a part cross-section illustrating an alternative embodiment of the present invention; and Figure 5 is a part schematic plan view of the embodiment shown in Figure 4 in the plane A-A.

The manner of assembly of a motor vehicle wheel to a hub is well known. Generally, the hub is coupled to the axle or drive shaft and includes a number of studs which protrude through apertures in the wheel and, with disc brake systems, apertures within the disc element whereby the hub assembly of the wheel, brake element and hub is secured with a number of compressive nuts acting upon screw threads of respective studs.

In Figure 1, illustrating a part cross-section of a hub assembly in accordance with the present invention, it can be seen that a wheel 1 is coupled to a hub 2 with a brake disc element 3 sandwiched therebetween.

The whole assembly of the wheel 1, hub 2 and brake element 3 is secured together under compressive engagement by a stud 4 extending from the hub 2 and a nut 5 secured to the stud 4 through a screw thread 6. Thus, the nut 5 is tightened onto the stud 4 to compress the wheel 1, the brake element 3 5 and hub 2 into a robust engagement.

As indicated above, the juxtaposed interface surfaces of the wheel 1, brake element 3 and hub 2 have traditionally been notionally flat but, due to the-limitations of the manufacturing process, obtaining flat surfaces has been difficult, a problem exacerbated by thermal cycling, distortion due to compressive effect of the stud/nut and wear etc. Of most concern is overtightening with the compressive stud 41nut 5 as this can distort the hub assembly.

7 1 Almost invariably the interface surfaces between the wheel 1, the hub 2 and braking element 3 are either slightly convex or concave with the result that the compression provided by stud 4 and nut 5 distorts these components 1, 2, 3. If the braking element 3 is distorted, the actual braking surface 7 may be slightly out of alignment, askew or twisted. In disc brake systems, a caliper 10 is located so as to contact the braking surface 7 on either side of the disc 3 so, if the surfaces 7 are misaligned from the desired location or twisted or askew, the caliper 10 acting upon these surfaces 7 will not properly engage them and will therefore create uneven wear and, more importantly, braking judder due to induced vibration in the disc 3 and/or caliper 10.

As indicated above, provision of flat square contact surfaces on the wheel 1, element 3 and hub 2 is difficult due to the relatively large areas to be machined. In accordance with the present invention the contact areas of the respective wheel 1, hub 2 and brake element 3 are reduced to contact surfaces 11, 12 which are raised in the axial direction and which engage with one another.

It will be appreciated that in accordance with the present invention, a raised contact surface 11, 12 in one of the components 1, 2, 3 could engage with a flat control portion in an associated component 1, 2, 3 but, the principle of the invention is maintained in that only the flat control portion of the component 1, 2, 3 needs accurate machining for engagement with the raised contact surface 11, 12 of the other component 1, 2, 3. However, normally opposed raised contact surfaces 11, 12 will engage each other to increase the depth of any recess, groove, or lower non-contact area 13 about these portions 11, 12 able to accommodate distortion.

By provision of raised contact surfaces 11, 12 within the hub assembly, there are also provided recesses 13 about these raised contact surfaces 11, 12 into which any local distortion of the hub 2, caused when the studs 4 and -6" nuts 5 are tightened, is located rather than upon the raised contact surfaces 11, 12. It will be appreciated that the grooved areas or recesses 13 about the contact surfaces 11, 12 are relatively unsupported and thus preferential deformation takes place in these areas 13. However, the degree of globalised distortion within the hub assembly should be within limits such that the only contact between the hub 2, braking element 3 and wheel 1 is through the contact surfaces 11, 12.

In order to further control distortion between the hub 2, wheel 1 and disc element 3, the contact surfaces comprise two concentric raised rings 11, 12. An outer ring 11 towards the periphery of the hub 2, wheel 1 and braking element 3 and an inner ring 12 on the other side of the studs 4 towards the centre of the hub 2, wheel 1 and element 3. The outer ring 11 is higher than the inner ring 12 in order that initial contact, upon assembly of the hub assembly, takes place with this outer ring 11 and a clearance gap is left between the wheel 1, hub 2 and element 3. This clearance gap is required so that any distortion during clamp-up with the studs 4 and nuts 5 will not effect the "run-ouC of a disc braking surfaces 7. Again, the provision of the clearance gap provides for preferential distortion under the compressive force of the nut 5 on the stud 4, in order to ensure accurate assembly about the outer ring. Typically, the gap should be at least 60 gm, but obviously it depends upon the materials used to construct the wheel 1, the hub 2 and element 3. In effect, all distortion due to nut 5 and stud 4, clamp-up of the hub 2, braking element 3 and wheel 1, takes place in the area denoted by broken line 8 with the outer ring remaining substantially perpendicular and so the braking surface 7 being presented substantially in the most desirable orientation with regard to its braking caliper 10.

It will be appreciated than the preferential distortion described above would also occur if the studs 4 where situated radially inwards of both raised contact surfaces, rather than between them.

Figure 2 illustrates in perspective the hub 2 illustrated in Figure 1.

The raised contact surfaces 11, 12 are depicted by shaded areas. Thus, it will be noted that the studs 4 mounted in the hub 2 are located between the outer mounting ring 11 and the inner mounting ring 12 in order to provide the distortional benefits as described above.

In Figure 3, the braking element 3 illustrated is that depicted in Figure 1. This braking element 3 takes the form of a disc bell with apertures 9 through which the studs 4 protrude. The shaded areas illustrate the raised contact surfaces 11, 12 used for engagement between a wheel 1 and the braking element 3. It will be appreciated that on the rear side of the element 3 similar concentric rings of contact surfaces 11, 12 will be located to engage corresponding portions of the hub 2.

It will also be appreciated by those skilled in the art that by provision of continuous concentric mounting portions 11, 12 manufacture of those components 1, 2, 3 which incorporate the contact surfaces 11, 12 is made easy. Typically a quick, rough initial cut will be made to create the basic mounting portion proffle and high tolerance, fine machining is used only on the mounting portions 11, 12 to achieve the best alignment and so braking surface 7 run-out tolerance possible.

1 1 1 It-will be appreciated that the mounting portions 11, 12 of both the hub 2 and the braking element 3 disc are fully machined so the height of the clearance groove is kept to a minimum. Thus, the rigidity and strength of both the hub 2 and the braking disc 3 element are not compromised.

Essentially, the raised mesa mounting portions 11, 12 will only have a height of a few mm which will have a limited effect upon the strength of the hub 2 and braking element 3 components as these usually have a significantly greater thickness. However, care should be made to ensure that the raised mounting portions have chamfered edges to reduce stress concentration.

Rather than present the raised contact surfaces concentrically about the rotation axis of the hub assembly it is possible as depicted in Figure 4 and Figure 5 to arrange- for outer and inner mounting ring portions 21, 22 to be located about each compressive stud 41nut 5 of the assembly. Thus, again " 9 1 distortion is preferentially retained within the groove centre of such concentric mounting rings 21 whilst the actual flats of the ring 21 are engaged substantially parallel to one another and so ensuring that the braking surface 7 is also properly aligned within its caliper 10. Again the outer rings 21 are initially higher than the inner ones 22, although they are shown under compression with both rings 21, 22 having been brought into contact on tightening of the nuts 5.

As an alternative to flat-topped mounting portions, it will be appreciated that a multiplicity of rib portions with rounded or pointed peaks could be used for each contact surface. In such circumstances, it is the configuration of the rounded peaks or points which must be accurately controlled to achieve the desired orientation of the brake element and subsequently the braking surface. In particular, a rib could be provided in close association and concentricity around each stud 4 mounting into the hub 2 to achieve the desired effect with other raised portions located in between, if necessary, in order to maintain the correct hub assembly configuration. The tips of the ribs and the other raised portions are accurately machined as required whilst the grooves requiring only rough machining as their surfaces are not critical to alignment and run-out for the brake surface 7 in relation to its brake caliper 10.

Claims (14)

1. A hub assembly including a first element and a second element, said first element and said second element being secured together under a compressive force by compression means, at least one of said members having inner and outer raised annular contact surfaces formed thereon arranged to contact the other of said members and a depression between the contact surfaces arranged not to contact the other of said members, wherein the compression means are arranged radially inside the outer contact surface and the outer contact surface is higher than the inner contact surface such that on securing together of the elements the outer contact surface comes into contact with said other member before the inner contact surface.

2. An assembly according to claim 1 further comprising a third element, at least one of the second and third elements having inner and outer i 1 raised annular contact surfaces formed thereon arranged to contact the other of said second and third members and a depression between the contact surfaces arranged not to contact the other of said second and third members, wherein the compression means are arranged radially inside the outer contact surface and the outer contact surface is higher than the inner contact surface such that on securing together of the elements the outer contact surface comes into contact with said other member before the inner contact surface.

3. A hub assembly as claimed in claim 1 or claim 2 wherein one of the elements is a wheel.

4. A hub assembly as claimed in any preceding claim wherein one of the elements is a hub.

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5. A hub assembly as claimed in any preceding claim wherein one of the elements is a brake element.

6. A hub assembly as claimed in claim 5 wherein said one of the elements is a brake disc.

7. A motor vehicle hub assembly as claimed in any foregoing claim wherein the compression means comprises a plurality of compression members and a respective pair of such raised contact surfaces are located about each of said compression members.

8. A hub assembly as claimed in any one of claims 1 to 6 wherein said raised contact surfaces are concentric with the axis of rotation of the hub assembly.

9. A hub assembly according to claim 8 wherein the compression means comprises a plurality of compression members each of which is arranged radially inside the outer raised contact surface.

10. A hub assembly according to claim 8 or claim 9 wherein the compression means are arranged between the inner and outer contact surfaces.

11. A hub assembly according to claim 8 or claim 9 wherein the compression means are arranged radially inside both the inner and outer contact surfaces.

12. A vehicle wheel hub assembly according to any foregoing claim.

13. A hub assembly substantially as hereinbefore described with reference to the accompanying drawings.

14. A vehicle wheel hub assembly substantially as hereinbefore described with reference to the accompanying drawings.

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