PLASTICS HOUSING THRUST BEARING WITH COMPLETE SEALING

Abstract: A thrust ball bearing (10) for a McPherson strut provides rubbing seals that are integral with rigid plastics housings by making a pair of sealing flanges (38,40) on an upper housing (20) flexible enough to continuously engage a pair of sloped seal surfaces (26,28) on a lower housing (18).

Description: This invention relates to thrust bearings in general, and specifically to a thrust bearing that has, in addition to a complement of rolling elements, two rigid plastics moulded housings, as specified in the preamble of claim 1, for example as disclosed in FR-A-2 375 484. Background of the Invention The addition of a rolling element thrust bearing at the turning junction between a front McPherson strut mount and the vehicle body provides a steering feel superior to a plain bearing, and several designs have been proposed therefor. An important design objective is to minimize components and provide unitary construction for ease of handling, since a rolling element bearing is inherently more expensive and more difficult to handle than a plain bearing. But rigorous sealing of the rolling elements still has to be provided, because of the harsh, under-body environment. One approach to unitary construction and simplification is to provide two basic housing units which snap together, sandwiching a complement of bearing balls between them as a unit. Several examples of such a bearing are disclosed in US-A-4,497,523 (Lederman). One or more of the housings may be moulded of rigid plastics material, which is strong enough to provide an integral pathway trough for a stamped metal race that in turn supports the balls. An example is shown in Figure 2 of US-A-4,497,523, where separate soft rubber O rings are used to seal each side of the bearing balls. In an alternative embodiment, Figure 5, one of the housings is itself moulded of softer rubber, which allows a pair of soft rubber sealing lips to be integrally moulded with it. Another approach to component minimization and unitary construction may be seen in US-A- 4,541,744 (Lederman). There, both housings are moulded of rigid plastics material, and snap-fit together with a ball-separating cage to create a unit. Sealing rings are eliminated by creating a labyrinth seal with flanges and grooves integrally moulded to the housings. Of course, a labyrinth seal is not a complete or continuous seal, but rubbing seal friction is eliminated, and a labyrinth seal may be sufficient in certain applications. Summary of the Invention A thrust bearing according to the present invention is characterised by the features specified in the characterising portion of claim 1. The invention provides a ball thrust bearing in which the only basic components, other than the ball complement itself, are first and second housings moulded of a plastics material rigid enough to support the ball complement. Despite the rigidity of the plastics material, other structure moulded integrally with the housings also provides a complete rubbing seal bordering the ball complement. The first, lower housing is generally annular in shape, with a central, trough-shaped pathway that supports a metal race liner which, in turn, supports the lower side of the bearing ball complement. The pathway is bordered by a pair of seal surfaces, the inner one of which is sloped radially inwards and axially downwards, while the outer one is sloped radially outwards and axially downwards. The second, upper housing is moulded of the same material, with the same type of central pathway. The pathway of the upper housing is bordered by integrally-moulded, generally cylindrical, inner and outer sealing flanges. The sealing flanges are sufficiently long and thin as to be partially flexible, despite the rigidity of the plastics material from which they are moulded. The sealing flanges are also sufficiently long enough to assure that the lower edges thereof will contact a respective sloped sealing surface on the lower housing with axial and radial interference when the bearing is assembled. In addition, in the embodiment disclosed, the sealing flanges themselves are bordered by cylindrical, inner and outer shielding walls that create a slight radial and axial clearance with the lower housing when the bearing is assembled. When the bearing is assembled, the resulting contact of the edges of the upper housing sealing flange edges with the lower housing sealing surfaces assures a complete, continuous seal interface around the bearing balls. Variations in the axial and radial position of the assembled housings are compensated for by the slope of the sealing surfaces, which will spread the sealing flanges apart to a greater or lesser degree, maintaining continuous contact. In addition, the shielding flanges on the upper race protect the sealing flanges, and create a labyrinth seal bordering the rubbing seal. It is, therefore, an object of the invention to provide for a complete, continuous contact seal in a ball thrust bearing having rigid plastics housings, without providing softer material seals as separate components. It is another object of the invention to provide such a complete, continuous seal by moulding partially-flexible, axially-depending cylindrical sealing flanges on one housing bordering its pathway that engage a pair of outwardly-sloped sealing surfaces bordering the pathway of the other housing to create an assured seal. Description of the Preferred Embodiment These and other objects and features of the invention will appear from the following written description, and from the accompanying drawings, in which: Figure 1 is a perspective cross-sectioned view of a preferred embodiment of the invention; Figure 2 is an exploded and cross-sectioned view of the various components of the bearing; Figure 3 shows a portion of a McPherson strut with the bearing installed; Figure 4 is a cross-sectional view showing a condition where the bearing is heavily loaded; Figure 5 is a view like Figure 4 showing a condition of radial mis-alignment. Referring first to Figures 1 and 3, a preferred embodiment of the ball thrust bearing of the invention, designated generally at 10, is installed between relatively turnable lower 12 and upper 14 plates of a McPherson strut. Bearing 10 is subjected to dirt, water, road spray and salt, so rigorous sealing is needed. As plates 12 and 14 turn, they are also subject to heavy, shifting strut loads that compress the components of bearing 10, loads that may also have a radial component tending to misalign the components of bearing 10. So any seal in bearing 10 must withstand those forces, and still maintain the sealing contact. The preferred embodiment of bearing 10 does so with a minimal number of components. The basic components include a full complement of bearing balls 16 arranged in a circle about a central axis of bearing 10, a lower housing designated generally at 18, and an upper housing designated generally at 20. Details of the basic components are described next. Referring next to Figures 1 and 2, lower housing 18 is generally annular in shape, and is moulded in one piece of a rigid plastics material. It includes a generally trough-shaped central pathway 22 of symmetrical cross-section that conforms to and supports a stamped steel race liner 24. It is the race liner 24 that directly contacts the lower axial side of the ball complement 16, but the moulded pathway 22 must be rigid enough to at least indirectly support the loads seen by the balls 16 without deforming to a great extent. The pathway 22 is bordered by a pair of troughs of asymmetrical cross-section comprised of inner and outer steeply-sloped sealing surfaces 26 and 28 respectively, which merge into an innermost and an outermost upstanding lip 30 and 32 respectively. Inner seal surface 26 is sloped radially inwards and axially downwards, while outer seal surface 28 is sloped radially outwards and axially downwards. Since none of the surfaces of lower housing 18 have any return bends or undercuts relative to the axis of bearing 10, it may be moulded by a single pair of mould halves that part along that axis, known as by-pass moulding. Still referring to Figures 1 and 2, upper housing 20 is moulded of the same material and has an identically shaped pathway 34, which supports an identical race liner 36 for the upper axial side of the ball complement 16. However, upper housing pathway 34 is located higher up within bearing 10 than is lower housing pathway 22, off-centre. Stated differently, the location of the central plane of the ball complement 16 measured from the bottom of bearing 10, indicated at X in Figure 1, is more than half of the total height H of bearing 10, which serves a purpose described below. Upper housing pathway 34 is also bordered by a pair of generally cylindrical sealing flanges, specifically an inner flange 38 and an outer flange 40. Although they are integrally moulded of the same rigid plastics material as upper housing 20, flanges 38 and 40 are sufficiently long and thin as to be partially flexible. The sealing flanges 38 and 40 are each also sufficiently long enough to assure that their lower edges contact a respective sloped sealing surface 26 and 28 on lower housing 18 with a slight axial and radial interference. In the embodiment disclosed, the sealing flanges 38 and 40 are themselves bordered by inner and outer, generally cylindrical shielding walls 42 and 44. Inner shielding wall 42 is longer than the sealing flange 38, and is barbed at its lower edge. Outer shielding wall 44 is approximately the same length as outer sealing flange 40. As with lower housing 18, the surfaces of lower housing 20 are configured so that it can be effectively by-pass moulded. Whilst the barbed lower edge of inner shielding wall 42 does present an undercut, it is long enough to be flexible enough to pop out of the mould without damage. The assembled housings 18 and 20 co-operate with one another to provide sealing as is next described. Referring next to Figures 1, 4 and 5, bearing 10 is assembled by pushing the housings 18 and 20 axially together, sandwiching the ball complement 16 between the race liners 24 and 36. The barbed lower edge of inner shielding wall 42 snaps past the inner diameter of lower housing 18, thereby retaining all components together as a unit. The lower edge of each sealing flange 38 and 40 engages a respective sealing surface 26 and 28, giving a complete seal interface surrounding the ball complement 16. Because of the deliberate axial interference and the slope of the seal surfaces 26 and 28, they spread the flanges 36 and 40 radially apart slightly from their free moulded state. By placing the upper housing pathway 34 high, and by steeply sloping the lower housing seal surfaces 26 and 28, it is assured that the sealing flanges 38 and 40 are relatively long compared to their thickness, which adds to their flexibility. That flexibility, in turn, helps assure that the seal is maintained under all conditions. Thus, in Figure 4, the condition is shown where the housings 18 and 20 have been pushed closer together by a compressive load. The edges of the sealing flanges 38 and 40 have simply moved farther down the respective sloped sealing surfaces 26 and 28, spreading them radially apart farther. Furthermore, as seen in Figure 5, should a radial load shift the lower housing 20 radially to the right slightly, the misalignment is compensated for by the inner sealing flange 38 flexing back in slightly, and the outer sealing flange 40 flexing out more, maintaining complete sealing contact. These same features could also compensate for axial and radial tolerance variations in the housings 18 and 20. Referring next to Figure 4, sealing is aided by the fact that the orientation of the flanges 38 and 40 and the sloped sealings surfaces 26 and 28 create, in effect, inner and outer grease reservoirs 46 and 48, from which wetting lubricant would be continually fed down into the sealing contact interface to reduce wear. In addition, the axial and radial clearance between the shielding walls 42 and 44, and the inner and outer lips 30 and 32 create a non-rubbing labyrinth seal at the inner and outer perimeter of the bearing 10, presenting a tortuous path to prevent abrasives entering and from reaching the sealing interface. The length of the seal surfaces 26 and 28 is sufficient that there is also an inner and outer gutter 50 and 52 created below the sealing interfaces that collect any abrasives that do enter, keeping them from the sealing interface. Any grease that does get through the sealing interface from the reservoirs 46 and 48 will tend to pack the gutters 50 and 52, protecting the outside of the sealing interface. Furthermore, the thicker shielding walls 42 and 44 protect the inner sealing flanges 38 and 40 from impact damage. Therefore, the particular structural features of just two by-pass mouldable plastics housings 18 and 20 co-operate in numerous ways to assure continuous sealing. Variations in the preferred embodiment could be made. Most generally, the housings 18 and 20 could be reversed, although the reservoirs 46 and 48 and the gutters 50 and 52 would not then work with the assistance of gravity. The housing pathways 22 and 34 could be oriented so as to place the ball pathway conventionally in the centre plane of bearing 10. Raising the ball complement 16 up, however, allows the seal surfaces 26 and 28 to slope down farther, thereby allowing the flanges 38 and 40 to be longer, which adds advantageously to their flexibility, as well as co-operating to create the grease reservoirs 46 and 48 and protective gutters 50 and 52. The shielding walls 42 and 44 and facing lips 30 and 32 are not necessary to the basic sealing function, but they are simple to integrally mould with the housings 18 and 20, and do provide the several advantageous features of impact protection and labyrinth seal. Thus, it will be understood that it is not intended to limit the invention as defined in the claims to just the specifice embodiment disclosed herein.

Claims: A bearing (10) having a circular complement of rolling elements (16) arranged about an axis of said bearing (10) for supporting an axial load, comprising: a first, generally annular housing (18) moulded of a rigid plastics material with an integrally moulded first pathway (22) for supporting one side of said rolling elements (16), and a second, generally annular housing (20) also moulded of a rigid plastics material with an integrally moulded second pathway (34) for supporting the other side of said rolling elements (16), said second pathway (34) further being bordered by inner and outer generally cylindrical, sealing flanges (38,40), integrally moulded from the same rigid plastics material as said second housing (20), said first pathway (22) being bordered by an inner, radially and axially-sloping seal surface (26), and an outer, radially and axially-sloping seal surface (28), said seal surfaces (26,28) being integrally moulded from the same rigid plastics material as said first housing (18); and said inner and outer sealing flanges (38,40) being sufficiently long and thin as to be partially flexible, whereby said flanges (38,40) contact the respective inner and outer sealing surfaces (26,28) of said first housing (18) with an axial and radial interference sufficient to, in turn, assure a continuous sealing interface therebetween, and complete sealing of said rolling elements (16) within said first and second housings (18,20), characterised in that the terminal edges of said flanges (38,40) contact the respective inner and outer sealing surfaces (26,28) of said first housing (18) with said axial radial interference. A bearing (10) according to claim 1, characterised in that said first housing is a lower housing (18) in which said first pathway (22) is located above a central plane of said bearing (10) and is bordered by said inner, radially inwardly and axially downwardly-sloping seal surface (26), and said outer, radially outwardly and axially downwardly-sloping seal surface (28); and said second housing is an upper housing (20) in which the lower edges of said inner and outer sealing flanges (38,40) flexibly contact said respective inner and outer sealing surfaces (26,28) of said lower housing (18) with said axial and radial interference. A bearing (10) according to claim 2, characterised in that , in said lower housing (18), said inner, radially inwardly and axially downwardly-sloping seal surface (26), and said outer, radially outwardly and axially downwardly-sloping seal surface (28), are both bordered respectively by an inner (30) and an outer (32) upstanding lip; and, in said upper housing (20), said inner and outer sealing flanges (38,40) are bordered by inner and outer cylindrical shielding walls (42,44) that create a slight radial and axial clearance with said inner and outer lips (30,32) of said lower housing (18), with said sealing interface further being protected by said shielding walls (42,44) and the slight clearance they create with said lips (30,32).

Inventors: STOWE, KEITH ALAN
Applicants: GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: B60G15
IPC codes: F16C33, B60G15, F16C19