Bearing assembly

The present invention relates to a bearing assembly and, in particular, to a bearing assembly suitable for providing a pre-loaded, self-sealed, removable and re-mountable bearing unit adapted to operate under axial loads.

In conventional bearing assemblies adapted to operate under axial loads with a rotating shaft, the bearing assemblies are generally mounted with internal radial and axial clearance. The outer rings are generally mounted with a radially loose fit in the housing so as not to transmit any radial load to the bearing whilst the inner race is securely mounted on the shaft which is to rotate relative to the housing. Between the inner and outer races solid rolling elements are provided which will be submitted to varying amounts of skew in any unloaded bearing row, depending on the amount of radial clearance in the bearing assembly. Skewing often results in the oil film between the rolling elements and their respective races being broken. This in turn may result in metal to metal contact which will cause the bearing assembly to deteriorate more quickly than would otherwise be the case.

According to the present invention, there is provided a bearing assembly for mounting in a housing, the bearing assembly comprising at least one bearing row which includes an inner race, an outer race, and a plurality of rolling elements located therebetween, said bearing assembly further comprising means which permits relative axial movement between the housing and at least one outer race, but prevents relative circumferential movement between the housing and said at least one outer race; and a seal provided at one or both ends of the bearing assembly, said seal having engagement means for engaging with one or both of a respective outer race and a respective inner race, wherein said engagement means permits relative axial movement between said seal and said respective outer race, inner race or both.

Preferably, the means includes axial biasing or preloading means, which may preferably be biased away from the bearing assembly, at one or both ends of the bearing assembly. When the bearing assembly is mounted in a housing, the or each biasing means may act against an axially facing surface of the housing, preferably via the or each seal and thus may act to maintain a bearing row of the bearing assembly correctly seated even when it is unloaded. By maintaining any unloaded bearing rows correctly seated during operation of the bearing assembly, skewing of the unloaded bearing row is prevented; skewing may result in a breakdown of lubrication between rolling elements and races which will result in metal to metal contact and thus early deterioration of the bearing row. It is thus advantageous if such skewing can be avoided. The or each biasing means may act to apply a preload to the bearing assembly, thereby preventing skewing of any unloaded bearing rows.

Preferably the bearing assembly is adapted to work purely under an axial load and especially in circumstances involving large axial loads such as those encountered in rolling mills. In these circumstances the bearing assembly may, for example, take the form of an angular contact ball bearing, a spherical thrust bearing assembly or a tapered roller bearing. It is advantageous for the bearing assembly to be adapted to work purely under an axial load because in this situation there need be no engagement between the radially outer surface of the bearing assembly and the adjacent radially inner surface of the housing, which might reduce the freedom of axial movement of the or each outer race of the bearing assembly.

In order to seal the bearing assembly, a seal is provided at one or both ends of the bearing assembly. Ideally, the seal may be a single annular component having a static radially outer sealing element at an outer circumferential edge region of the seal and a dynamic, internal sealing element at a radially inner edge region of the seal. In this way, two separate sealing functions are met in a single component. Preferably, the engagement means permits relative axial movement between its respective bearing row and the static sealing element. The engagement means may detachably secure the seal to the bearing assembly or alternatively the engagement means may provide only a loose fit onto the bearing assembly. In this way, the bearing assembly may be sold and mounted as a single unit. Where the or each seal attaches to the outer race, the engagement means is arranged to allow relative axial movement between the outer race and the or each seal. In this way, when the bearing assembly is mounted within a housing, the static sealing element may remain substantially static with respect to the housing, while the outer race may move relative to the housing and the sealing element in an axial direction in order, for example, to absorb alternating axial loads transmitted to the bearing assembly. Ensuring the static sealing element remains substantially static with respect to the housing regardless of any movement of the outer race is advantageous because the effectiveness of a static sealing element is impaired unless it does in fact remain static with respect to the surface which it is sealing.

Where the bearing assembly includes an axial biasing means and a seal located at the same end, the axial biasing means is preferably located between the outer race and the seal and acts to bias the seal away from the outer race. Preferably, a biasing means and a seal are provided at both ends of the bearing assembly. By this arrangement, the opposing seals may be biased axially outwardly against the housing in static relation thereto while the outer race has limited freedom of movement axially between the seals, relative to the housing and the seals. In this arrangement the biasing means continues to act against an axially facing surface of the housing albeit that the action is via the seal. The bearing assembly may be a two row tapered bearing assembly having a double inner race and a pair of outer rings forming the outer race, the assembly being arranged such that the larger diameter ends of the tapered rollers face axially inwardly towards the axial centre of the bearing assembly. In this way each biasing means acts to preload its respective bearing row of inner race, outer ring and tapered rollers.

The static sealing element preferably comprises a flexible axial lip which is axially directed and seals against an axially directed surface of the housing. This is advantageous because it enables the biasing means to positively clamp the flexible axial lip against the surface to be sealed. The static sealing element may further comprise a flexible radial lip which can provide a secondary sealing action. Furthermore, the or each seal may further comprise a circular axially outwardly projecting ridge. This ridge can provide an additive barrier against contaminants, especially when an outer race locking pin is used to lock the outer race in a circumferentially fixed position relative to the housing.

Preferably, the or each seal is similar to the seal as described in co-pending European Patent Application No. EP-A-0737821, filed in the name of the present Applicant. In this case though the seal is adapted by omitting the attachment means, in the form of an inner shoulder for example, which attaches to the outer race in a manner preventing or restricting relative axial movement between the seal and the bearing assembly. In this way, the numerous advantages of the present invention as set out above may be enjoyed together with the advantages provided by the seal described in EP-A-0737921.

In order that the present invention may be better understood, embodiments thereof will now be described by way of example only, with reference to the accompanying drawings in which:- <ul id="ul0001" list-style="none"><li>Figure 1 is a diagrammatical, cross-sectional view of a bearing assembly according to the present invention, showing the bearing assembly being mounted;</li><li>Figure 2 is a view similar to Figure 1 showing another bearing assembly according to the present invention when correctly mounted;</li><li>Figure 3 is a view similar to Figures 1 and 2 showing another bearing assembly according to the present invention when correctly mounted and locked; and</li><li>Figure 4 is a diagrammatical, cross-sectional view showing the locking mechanism of Figure 3 in greater detail.</li></ul>

The bearing assembly shown in Figure 1 comprises an inner race 10, an outer race in the form of a pair of outer rings 12, 13 and rolling elements in the form of tapered rolling elements 14, 15. The inner race 10 is securely mounted on a shaft 2, while the outer rings 12, 13 are mounted within the housing 1 in a manner which allows limited, relative axial movement between the housing 1 and the outer rings 12, 13. The radial gap 1 1 between the outer rings 12, 13 and the housing 1 has been enlarged for the sake of clarity. In reality the radial gap 11 would be much smaller than it appears in the Figures. Each outer ring 12, 13 includes axial biasing means in the form of a plurality of axial spring systems 22, 23 respectively. Each axial spring system 22, 23 may be attached to a seal 30 by means of suitable seal attachment means (not shown). There is a small space between each seal 30 and the face of its respective outer ring 12, 13 as shown in the Figures, although in reality the space will be much smaller than it appears. Each seal 30 is preferably substantially as described in co-pending European Patent Application No. EP-A-0737821 filed in the name of the present applicant and incorporated herein by reference. Unlike the seal described in EP-A-0737821, the outer static sealing element preferably does not include a ridge for engagement in grooves commonly provided in the radially outwardly facing shoulder portion 12a, 13a of the respective outer ring 12, 13. In this way the means for preventing relative axial movement between the seal 30 and the outer ring is omitted.

Each seal 30 has a substantially rigid casing 32, made for example of steel, which is generally planar and ring shaped to enable the seal 30 to be located around the shaft 2. On the axially outwardly facing surface of the casing 32 a coating 31 of rubber or other similar resilient material is provided. Projecting axially outwardly from the seal is a small sealing ridge 38 which may define a continuous circular sealing ridge on the axially outer surface of the seal 30. At the radially inner edge of the seal 30, there is provided a dynamic sealing element 39, and at the radially outer edge of the seal 30 a static sealing element 40.

The dynamic sealing element 39 has two sealing lips 39a, 39b of which one is preferably made from rubber or another similar resilient material and the other 39b is preferably an elastohydro-dynamic (EHD) lip of the type described in detail in EP 0304160 the content of which is incorporated herein by reference.

The static sealing element may also include two sealing lips 35, 36 (as shown on the seal at the left of Figure 1) or it may include only one lip 35. Both lips 35, 36 are made of rubber or other similar resilient material, and one lip 35 extends radially upwardly and axially outwardly to seal against an axially facing surface of the housing 1, 1a. The other lip 36 extends radially outwardly to at least partially seal against a radially inwardly facing surface of the main part 1 of the housing. This additional radial lip 36 is optional (and is thus not shown on the seal 30 at the right of Figure 1).

Biasing means in the form of a plurality of springs 22, 23 are provided in small axially extending pockets formed in the outer rings 12, 13. The springs 22, 23 act between the seals 30 and the respective outer ring 12, 13.

In order to mount the bearing assembly of Figure 1, it is firstly necessary to mount the assembly in the housing. Thereafter, a locking member 1a which essentially forms a part of the housing 1, 1a is screwed or otherwise clamped into and against the main part 1 of the housing as is shown in Figure 2. A compressible sealing gasket 50 or any other suitable gasket device is provided between the locking member 1a and the main part 1 of the housing where these two components axially abut one another. This gasket 50 provides the axial clearance, and therefore the necessary radial clearance in the bearing assembly, to perform properly when in use. This axial clearance will also enable the spring system to operate. When the bearing assembly is clamped in position by the locking member 1a, the springs 22, 23 press the seals 30 into tight sealing engagement with the housing 1, 1a. Small axial movements of the outer rings 12, 13 (of the order of a few tenths of a millimetre - i.e. within the range 0.1 - 1.0 mm) may be permitted with this arrangement. These small axial movements though do not affect the engagement of the seals 30 with the housing 1, 1a by virtue of the biasing means 22,23. Where the inner race 10 is initially a loose fit, in order to maintain it firmly in place on the shaft 2 during use, an inner ring locking key 52 is firmly mounted onto the shaft 2.

Figure 3 shows one of the outer rings 12 rotationally secured to the locking member 1a by means of a locking pin 54. A locking pin may also be used in a similar way between the other outer ring 13 and the main part 1 of the housing. In order to maintain a good seal when using a locking pin it will be noted that the sealing ridge 38 (fully compressed in Figure 3) is located adjacent but radially inwardly of the locking pin 54 (i.e. below the locking pin 54 as shown in Figure 3). Furthermore, an additive annular sealing element 56 is provided within the seal 30 where the locking pin passes through the seal 30. This is more clearly seen in Figure 4.

Although the invention has been particularly described in relation to a tapered roller bearing assembly, it will be understood that it is equally applicable to other forms of bearing assembly.