GB2166813A - Tapered roller bearing assembly - Google Patents

Abstract

A tapered roller bearing assembly, particularly for the pilot position in automotive gearboxes, in which the cage 17 is provided, adjacent the large end faces of the rollers 16 with a ring portion 27 which defines an outwardly-facing surface 21 which is urged against the tapered outer raceway 14 of the bearing to thereby form an oil seal which acts to allow oil to collect in an annular space 18. The large end faces of the rollers pass through this space and are thereby lubricated. The surface 21 may be plain or may be embossed with an oil-retaining pattern, two examples of which are described. <IMAGE>

Description

SPECIFICATION Improvements relating to tapered roller bearings This invention relates to tapered roller bearings, particularly of the type for use in the pilot position in gearboxes for automotive vehicles.

Figure 1 of the accompanying drawings is a transverse section through a typical gearbox arrangement in which the pilot bearing is coaxially located between the input shaft and the output shaft.

The illustrated gearbox comprises an input shaft 1, coaxial output shaft 2 and parallel layshaft 3. The input and output shafts are rotatably mounted in respective roller bearings 4 and 5 and are rotatably mounted with respect to one another by means of a pilot bearing 6 mounted within a cavity 10 formed in the end of the input shaft. Drive from the input shaft to the layshaft is transmitted by means of constant mesh gears 7 and 8. Drive from the layshaft to the output shaft is transmitted by way of a selected one of a number of synchromesh coupling arrangements 9.

When the gearbox is engaged in one of the low-speed ratios, the drive is transmitted from the constant-mesh gear 7 on the input shaft to the constant-mesh gear 8 on the layshaft and then through the selected one of the pairs of output gears to the output shaft. In these circumstances, the output shaft rotates at a lower speed than the input shaft and the pilot bearing 6 accommodates this relative rotation while supporting forces transmitted between shafts 1 and 2 resulting from gear loads.

It is customary in such gearboxes to use single helical gears in all positions to achieve quiet and smooth operation. It is also customary to arrange the design so that the axial forces, induced in the input and output shafts by driving forces transmitted through the helical gears, are directed away from the pilot bearing and are supported by the other bearings 4 and 5 on these two shafts. This means that a bearing of comparatively small size may be used in the pilot position since it is not normally exposed to heavy axial forces.

The pilot bearing is effectively enclosed between the input and output shafts and a synchromesh coupling arrangement is provided to allow the direct connection of these two shafts. Consequently, the pilot bearing is shielded from the spray of lubricating oil that normally pervades the interior of the gearbox during operation. It is therefore usual to make some special provision for feeding oil to the pilot bearing.

One such method is to provide a number of drilled holes 11 extending radially inwards from the roots of the teeth on the constantmesh input-shaft gear 7 to connect with the cavity 10 in the end of the input shaft. In operation, the meshing of the gears forces small amounts of oil radially inwards through these holes, from where it flows axially through the pilot bearing to return to the gearbox casing.

Although the flow of oil achieved in this way may be restricted and intermittent it is usually sufficient to maintain effective lubrication of the pilot bearing under normal operating conditions.

In recent years, the increasing use of towed trailers, caravans, etc., has resulted in the more frequent use of gearboxes under conditions of reversed loading, as for example when the vehicle and its towed load descend a steep hill in low gear, using the engine as a means of braking. Under these conditions the axial forces induced by the helical gears are in the opposite directions to those normally applied and therefore the pilot bearing can be subjected to heavy axial forces.

It has been found that, in some cases, the increased demands on lubrication caused by this abnormal operating condition have not been satisfactorily fulfilled by the normal provision for pilot bearing lubrication as described earlier. Consequently, the pilot bearing has sometimes sustained damage in the form of wear or scoring of the bearing surfaces.

The present invention seeks to provide an improved bearing design for use in the pilot position, with provision for better retention of lubricating oil.

According to the invention there is provided a tapered roller bearing assembly comprising inner and outer bearing rings respectively defining inner and outer raceways, a set of tapered rollers and associated cage rotatably mounted between the raceways, said cage having a generally radially outwards-facing surface which bears against and is movable across a concave surface of the bearing in such a way as to define an oil seal operable to form, during use of the bearing an annular oil reservoir behind such seal. Said surface on the cage may be a plain surface, but is preferably formed with an embossed pattern to assist oil retention. Any effective pattern can be used for this purpose, and two such are to be described hereinafter by way of example.

Preferably means are provided for urging the surface on the cage against the concave surface in order to ensure correct contact between the two surfaces in all anticipated operating conditions of the bearing.

In the currently preferred embodiment of the invention the concave surface takes the form of part of the tapered outer raceway, such outer raceway either being formed integrally with the ring, or on a separate bearing ring fitted into the outer ring. In the particular example of the pilot bearing mentioned above, it is likely that the outer ring will itself be integral with the input shaft in which case it is likely that such a separate bearing ring will be fitted.

In order that the invention may be better understood an embodiment thereof will now be described by way of example only and with reference to Figures 2 to 6 of the accompanying drawings in which: Figure 2 is a part-sectional view of a gearbox pilot bearing made in accordance with the invention; Figure 3 is a diagrammatic sectional view of the cage forming part of the bearing of Figure 2; Figure 4 is a view of part of the exterior of the cage of Figure 3, showing a first embossed pattern; and Figures 5 and 6 are views similar to Figures 3 and 4 respectively, but showing a second embossed pattern.

Referring to Figure 2, the bearing comprises an outer ring 12 which may or may not be provided as an integral part of the input shaft as aforesaid, and an inner ring 13 which is seated on a reduced diameter end portion of the output shaft 2. Each of the rings 12, 13 is formed with a respective raceway 14, 15 between which is mounted a set of tapered rollers 16 and a cage 17.

The normal functions of the cage in a conventional tapered roller bearing are to retain the rollers prior to final assembly and to space the rollers apart during operation of the bearing. In the present bearing, however, the cage also has the function, cooperatively with the tapered outer raceway 14, of retaining lubricant in an annular space 18 through which the large end faces of the rollers pass and thus become lubricated.

This function of the cage 17 and the raceway 14 is accomplished by certain special features of the design which are here described.

The cage 17 is advantageously manufactured from a suitable polymer material by an injection-moulding process. The design provides a number of flexible fingers 19, integral with a ring portion 20 of the cage adjacent the small ends of the rollers. These fingers are designed to apply a force against the centre of the small end faces of some or all of the rollers. As an alternative to separate fingers, a continuous lip of similar section may be employed.

During operation of the bearing the relative sliding velocity of the roller at this point against the flexible fingers on the cage is minimal and therefore does not cause any significant amount of friction or wear at this position.

The reaction to the forces applied to the small end faces of the rollers causes the cage 17 to be urged axially in a leftwards direction thus tending to increase the gap formed between the small end ring portion 20 of the cage and the adjacent small end faces of the rollers. Movement of the cage in this direction is constrained by engagement of the tapered outer raceway 14 with a tapered land 21 on the outside surface of the large end ring portion 27 of the cage. The flexibility of the fingers 19 ensures that the land 21 is urged against the raceway 14 with a pressure sufficient to hold it in place during expected operating conditions.For example, the fingers are designed so that they can accommodate any variations in the relative axial positions of the cage and the tapered outer raceway due to differential thermal expansions of these components at the expected operating temperatures.

The components are designed to ensure that when the land on the cage engages the tapered outer raceway, as shown in Figure 2, a finite gap 22 is retained between the large end ring portion of the cage and the adjacent large end faces of the rollers.

The tapered land 21 on the large end ring portion of the cage is preferably provided with an embossed surface of one of a number of known forms that can be utilised effectively to prevent the loss of lubricant from the bearing at this point when the cage and the outer raceway rotate at different speeds.

One example of such an embossed surface is shown in Figures 3 and 4. The embossed pattern on the tapered land takes the form of a shallow helical groove 23 in a form similar to that of a screw thread. The axial force generated by the flexed fingers 19 at the small end of the cage causes the helical land between the adjacent turns of the helical groove to be lightly loaded in contact with the tapered outer raceway surface.

During operation of the gearbox, a small flow of oil is fed into the bearing through the radial holes 11 connecting with the roots of the input gear teeth. The normal tendency is for this oil to pass axially through the bearing and to be expelled by centrifugal action from the large end diameter of the tapered outer raceway. However, the engagement of the tapered land on the cage with the tapered outer raceway inhibits the loss of lubricant at this point. Furthermore, in one direction of relative rotation of these surfaces, the presence of the helical groove generates a positive pumping action that provides an effective seal against leakage at this position.

An alternative design, which is equally effective in either direction of relative rotation, provides an embossed surface on the tapered land of the cage in the form of a series of relieved areas 24 in the shape of isosceles triangles as shown in Figures 5 and 6.

In operation, when the cage and the raceway 14 experience relative rotation about their common axis, any lubricant present between the embossed land and the outer raceway is subjected to a hydrodynamic pumping action that inhibits leakage from the bear ing at this position.

Because of the orientation of the edges of the triangular relieved areas 24 on the cage land, this pumping action acts in the same direction regardless of the direction of relative rotation of the bearing components.

Various other forms of sculptured relief of the surface of the cage land could be used to achieve the effect described.

The use of one or other of these embodiments of the design provides a bearing construction in which the lubricant supplied to the bearing in operation fills the annular space 18 formed between the large end ring portion of the cage and the surface of the outer raceway against which the rollers are located. Thus the large ends of the rollers are lubricated by this reservoir of lubricant as the bearing rotates.

Any surplus lubricant passing through the bearing is free to escape from the opening formed by the bore 25 of the large end ring portion of the cage.

It is preferred that the internal surface of the bore 25 should be slightly tapered as shown in Figure 2, having its smallest diameter adjacent the large end face of the cage. This inhibits the dispersion of lubricant particles that may be directed radially outwards from the guiding rib 26 on the inner bearing ring 13.

The cage described can be formed by an injection-moulding operation using a fabricated mould designed to reproduce the required features including the flexible fingers, the sculptured surface and the tapered bore surface of the large end ring.

Claims (11)

1. A tapered roller bearing assembly comprising inner and outer bearing rings respectively defining inner and outer raceways, a set of tapered rollers and associated cage rotatably mounted between the raceways, said cage having a generally radially outwards-facing portion which bears against and is movable across a concave surface of the bearing in such a way as to define an oil seal operable to form, during use of the bearing, an annular oil reservoir behind such seal.

2. A bearing assembly as claimed in claim 1 wherein said portion takes the form of a plain surface.

3. A bearing assembly as claimed in claim 1 wherein said portion takes the form of a surface formed with an embossed pattern oper able to assist the retention of oil within said reservoir.

4. A bearing assembly as claimed in any one of claims 1 to 3 further comprising means for urging said portion on the cage against the concave surface of the bearing.

5. A bearing assembly as claimed in claim 4 wherein said concave surface of the bearing is tapered in the axial direction of the bearing and wherein said urging means comprises a number of flexible fingers which extend from said cage against one end of at least some of said rollers thereby to bias the cage in an axial direction and thus urge the outwards facing portion of the cage against the tapered concave surface of the bearing.

6. A bearing assembly as claimed in claim 4 wherein said concave surface of the bearing is tapered in the axial direction of the bearing and wherein said urging means comprises a flexible annular lip which extends from said cage against one end of at least some of said rollers thereby to bias the cage in an axial direction and thus urge the outwards facing portion of the cage against the tapered concave surface of the bearing.

7. A bearing assembly as claimed in any one of the preceding claims wherein said outwards facing portion is formed on an annular portion of the cage which lies adjacent the large end faces of the tapered rollers.

8. A bearing assembly as claimed in claim 7 and either one of claims 5 or 6 wherein said fingers or lip are or is biassed against the small end faces of all or some of said tapered rollers.

9. A bearing assembly as claimed in claim 8 wherein said fingers or lip are or is formed integrally with a further annular portion of the cage which lies adjacent the small end faces of the tapered rollers.

10. A tapered roller bearing as claimed in any one of the preceding claims wherein said concave surface of the bearing takes the form of a part of the outer raceway of the bearing.

11. A tapered roller bearing assembly substantially as hereinbefore described with reference to the accompanying drawings.