GB2276214A

GB2276214A - Bearing mounting

Info

Publication number: GB2276214A
Application number: GB9404874A
Authority: GB
Inventors: Peter Harrison
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-18
Filing date: 1994-03-14
Publication date: 1994-09-21
Anticipated expiration: 2014-03-14
Also published as: GB9305594D0; GB2276214B; GB9404874D0

Abstract

A shaft 5 is conventionally mounted in the bore of the inner race 2 of a rolling bearing 1. The outer race 4 is mounted in a polypropylene mounting bush 6. This has an internal shoulder 7 against which the outer race abuts and an external taper 8, the shoulder 7 being at the large diameter end 9 of the taper. At the small diameter end 10 of the taper, the bush has an external lip 11. The bush is received in a tapered housing 12 in a light alloy casting 13. At the small diameter end of the housing, it has an under-cut 14 into which the external lip on the bush snaps on insertion of the bush from the large diameter end of the housing. <IMAGE>

Description

BEARING MOUNTING The present invention relates to a mounting for a bearing.

In many light engineering products, there is the requirement to mount a rolling element bearing in a light alloy casting for a rotating component. For instance, in a fractional horse-power electric motor, the body of the motor usually is of at least one light alloy casting - typically a pressure die casting - and the rotor is mounted in the body on a shaft journalled in the casting(s) via ball bearings.

It is impractical to cast the light alloy, e.g. aluminium silicon-alloy LM2, to sufficiently tight tolerances to receive an outer race of a bearing. A casting tolerance of 0.05mm (0.002") is achievable. However for a nominal 25mm (1.0") diameter, the housing of a bearing race requires to be held to a tolerance one order of magnitude less, that is a tolerance of 0.005mm (2/lOth of a thousandth of an inch).

In practice such a housing can be produced only by machining the casing. This is an operation whose cost it would be convenient to avoid, since then production of the motor could be reduced to assembly of bought in parts.

The object of the invention is to improve the mounting of bearings in castings, in particular but not exclusively in light alloy castings for electric motors.

The object of the invention is met by mounting a bearing race in a plastics material bush received in a housing in the casting, both the bush and the housing being complementarily tapered.

Accordingly in one aspect, the invention provides a bearing mounting bush of plastics material, sized internally to receive the journal bearing and tapered externally to fit the housing.

One important preferred feature of the bush is that it includes an external lip at the smaller diameter end of its taper, the external lip being receivable in an increased diameter section, called an "under-cut section" although it may be cast, at the smaller diameter end of the housing's taper, to inhibit removal of the bush from the housing.

Preferably the under-cut section acts to restrict the bush radially. Conveniently, the lip is tapered at its end external diameter to aid insertion of the bush into the housing.

In one embodiment, the bush has a plain internal bore at the lip end of-the bush, whereby the bore is restricted in the region of the lip, when the lip is restricted in diameter on receival of the lip in the under-cut section of the bore. Such a bush may have a relieved internal bore at the lip end of the bush, whereby the bore is not restricted when the lip is restricted in diameter on receival of the lip in the under-cut section of the bore. More usually, the internal bore of the bush is of uniform diameter.

In another embodiment, the bush has an inwardly extending shoulder at the larger diameter end of its taper, against which the journal bearing can abut in use, for axial location of the bearing. The inwardly extending shoulder may have sufficiently small inwards extent that the journal bearing can be pushed past it on assembly of the bearing into the bush.

Conveniently, the bush includes a stepped bore for receiving an oil seal in addition to the bearing. An inwards extending flange may be provided at the external lip for defining the bore step.

Usually, the bush is of injection moulded plastics material. Other materials are envisaged to be suitable. Due to shrinkage, the taper may not be even in particular locally to the inwardly extending shoulder, when provided. In this case, the tapered housing preferably mirrors the contour of the taper.

According to a second aspect of the invention, there is provided the combination of a bush of the first aspect of the invention with a journal bearing and a body having a housing: the bearing being fitted in the mounting bush and the housing having a tapered bore into which the mounting bush is fitted, the tapered bore and the external surface of the mounting bu h being complementarily tapered.

Where the bush has an external lip, the housing has an increased diameter section, its "under-cut section", at the smaller diameter end of the housing's taper to receive the lip and inhibit removal of the bush from the housing. Preferably the under-cut section has a restrictive diamater compared with that of the lip, to hold the bush restrict the lip inwardly.

That is to say, the under-cut for the lip of the bush is sized and shaped to cause inwards deformation of the lip and possibly an end portion of the inside of the bush which is sized to receive the bearing - the deformation being from the free state of the bush. The deformation can act to locate the bearing at its end opposite from its abutment with the inwardly extending shoulder of the bush.

Conveniently, the end external diameter of the lip is no bigger than the orifice of the housing opposite from its undercut.

The invention is particularly suitable where the body is as cast in a light alloy casting, having the tapered housing cast in it.

A particular feature of the invention is that the body can have a location for a complementary location on another body having another tapered housing for another bush, both bearings journalling a common shaft, the tapers in the housings having their larger diameter ends towards the locations.

According to a third aspect of the invention, two alternative methods of mounting a journal bearing in a tapered housing via a bush are provided. The first method consists in the steps of: fitting the bearing into a mounting bush and fitting the bush with the bearing to the tapered housing .

The second method consists in the steps of: fitting the bush into the tapered housing and fitting the bearing to the bush.

Tests have established that bearings can be mounted using identical bushes and housing bore sizes varying across the tolerance range expected in die casting, without slack in location of the race and without tightness in the bearing. It is believed that this is achieved as a result of residual stress remaining in the bush after fitting, particularly as a result of snapping of the external lip of the bush into the under-cut of the housing. It is thought likely that some degree of plastic deformation of the bush occurs.

To help understanding of the invention, various specific embodiments thereof will now be described by way of example and with reference to the accompanying drawing, in which: Figure 1 is a cross-sectional view of a bearing mounted in a housing via a bush in accordance with the invention, Figure 2 is a similar view of the bush of Figure 1 before mounting, Figure 3 is a view 8;m; lar to Figure 1 schematically showing an electric motor rotor mounted in body castings via bushes of the invention, Figure 4 is a view similar to Figure 2 of one of the bushes of Figure 3, Figure 5 is a similar view of the other bush of Figure 3, Figures 6, 7 & 8 show bushes suitable for retaining oil seals in addition to bearings, the top portion of each Figure showing the bearings and the seals in the bushes, whilst the bottom portions show the free state of the bushes.

Referring first to Figure 1, the bearing 1 has an inner race 2, rolling balls 3 and an outer race 4. A shaft 5 is conventionally mounted in the bore of the inner race. The outer race is mounted in a polypropylene mounting bush 6.

This has an internal shoulder 7 against which the inner race abuts and an external taper 8, the shoulder 7 being at the large diameter end 9 of the taper. At the small diameter end 10 of the taper, the bush has an external lip 11. The bush is received in a tapered housing 12 in a light alloy casting 13. At the small diameter end of the housing, it has an under-cut 14 into which the external lip on the bush snaps on insertion of the bush from the large diameter end 15 of the housing.

Figure 2 shows the bush before mounting in more detail.

The internal diameter 21 of the bu h is parallel and nominally the same size as the outer diameter of the outer race, within a tolerance 0.002mm, such that the bearing can be fitted to the bush by hand. The external taper 8 is at 5 to the central axis 22 of the bush. At the large diameter end 9 of the taper, due to differential shrinkage along the majority of the length of the taper and in the short region of the internal shoulder 7, the taper is slightly steeper. The external surface 23 of the lip 11 is also tapered in the same direction as the taper 8, but more steeply at 15 to the axis 22. The outside diameter of the lip at its end edge 24 is thus able to be substantially the same diameter as the outside diameter of the bush at its opposite end 25, which enables the bush to be readily inserted into the housing 12. The step 26, of the bush is at 75 to the axis 22.

The actual taper of the housing 12 is matched in its angle of taper to that of the bush, including the steepening at the end 9. The under-cut 14 is at 45 to the central axis of the housing and has no step from the tapered housing bore. The nominal external diameter of the bush at its large end 9 is equal to the internal diameter of the housing at its large diameter mouth 27 of the housing.

Prior to insertion, the bearing 1 is pushed into the mounting bush 6. Then the bush with its bearing is pushed into the housing 12 in the casting 13, so far that the lip 11 snaps into the under-cut 14. Since there is no step in the housing at the under-cut, the material of bush in the region of the lip 11 deforms inwardly at 29 with respect to the original internal diameter 21 of the bush. The components are dimensioned so that the corner between the housing bore and the undercut is aligned with the edge 27 ol the bearing. The result is that the deformed material 29 captivates the bearing race against the shoulder 7.

Typically for a nominal 25mm bore, a lmm reduction due to the deformation can be achieved. The bearing will be held against normal working axial loads on the bearing.

Tests have shown that the bush as assembled in Figure 3 can resist the design axial loads of the bearing.

Tests have also shown that plastic flow in the bush during mounting enables the bearing to be pushed in to a design position despite normal casting tolerances in the tapered bore.

Turning now to Figures 3, 4 & 5, the motor there shown has a rotor 51 on shaft 52. The stator is omitted for clarity, but is contained within body castings 53,54. These have complementary locating formations 55,56 at a joint 57.

Bearing mounting bores 58,59 are provided in castings, each having a long shallowly tapered portion 60 and a short steeply tapered, "under-cut" portion 61. In order to avoid any possibility of eccentricity of the bearing locating borf portions 60 with respect to the body locating formations 55,56, as a result of mould part misalignment, both bore portions 60 and locations 55,56 being formed in the casting process, both are formed in the respective body castings 53,54 by the same body mould part. This results in the lonc bearing locating bore portions being on the same side of thf casting joint lines, at the narrowest place between the borz portions 60,61, as the locations and being directed inwardly of the motor.

The rotor is balanced with its bearings 62,63 already mounted on the shaft 52, with the result that the bearings have bearing bushes 64,65 fitted after balancing and from opposite ends of the shaft. The arrangement needs to result in the external tapers of the bushes tapering inwardly away from the rotor to match the housing tapers 60. Thus shoulders such as 7 cannot be provided.

The bushes 64,65 are fitted to the casting bodies 53,54 prior to fitting of the bearings to them by means of drifts (not shown), which replicate the bearings and prevent the bushes collapsing on insertion of the bushes. Once the lips 66,67 of the bushes have snapped into the under-cuts 61, the drifts can be withdrawn and the bearings fitted in their place, without the force needed to snap the lips into the under-cuts. To provide positive location of the commutator end of the rotor, its end bush 65 is provided with a very small, O.Olmm high, ridge 68 in its bore at its large outer diameter end. This allows the bearing 63 to be pushed in, but restrains its free removal. The other side of the bearing is restrained against the inwards deformation 69 of the lip. The other bush 64 has no such ridge to allow its bearing 62 to move axially with thermal expansion of the rotor. For this clearance 70 is provided between it and the bush deformation 69.

Turning on to Figure 6, the bush 100 there shown has a stepped bore, for accommodation of a bearing 101 and an oil seal 102. The former is fitted to a larger diameter portion 103 of the bore and the latter to a smaller diameter portion 104. Typically the bush 100 can be fitted with a drift, which is then removed. The oil seal is then pushed in against the bush deformation 105 and the bearing is pushed in against the step between the bore portions.

The bush 110 of Figure 7 has an initial internal tapered relief 111 at its lip 112. This results in a plain bore within the lip after fitting of the bush. Thus the oil seal 113 can be fitted from the lip end of the bush; whilst the bearing 114 can be fitted to the larger diameter bore at the other end.

The bush 120 of Figure 8 has a double step 121,122, and does not rely on deformation at its lip to provide positive location of the oil seal 123 and the bearing 124.

The invention is not intended to be restricted to the details of the above described embodiments. For instance in respect of the bush of Figures 1 & 2, it is envisaged that the bore of the bush may have a small moulded-in lip at its end opposite from the shoulder to aid axial retention of the bearing race in the bush. Further as an addition or an alternative to the external lip on the bush at the smaller end of the taper, an external lip may be provided at the larger end of the taper, particularly if the internal shoulder were provided at the end of the bush having the smaller end of the taper.

Whilst the above embodiments show the bush of the invention in use with rolling element bearings, it may equally be used with plain bearings.

Claims

CLAIMS:

1. A bush for mounting a journal bearing in a tapered housing, the bush being of plastics material, being sized internally to receive the journal bearing and being tapered externally to fit the housing.

2. A bush as claimed in claim 1, including an external lip at the smaller diameter end of its taper, the external lip being receivable in an increased diameter section (hereafter referred to as the "under-cut section") at the smaller diameter end of the housing's taper, to inhibit removal of the bush from the housing.

3. A bush as claimed in claim 2 t wherein the lip is tapered at its end external diameter to aid insertion of the bush into the housing.

4 . A bush as claimed in claim 2 or claim 3 f wherein the bush has a plain internal bore at the lip end of the bush, whereby the bore is restricted in the region of the lip, when the lip is restricted in diameter on receival of the lip in the under-cut section of the bore.

5 . A bush as claimed in claim 2 or claim 3 wherein the bush has a relieved internal bore at the lip end of the bush, whereby the bore is not restricted when the lip is restricted in diameter on receival of the lip in the under-cut section of the bore.

6. A bush as claimed in any one of claims 1 to 5, wherein the internal bore of the bush is of uniform diameter.

7. A bush as claimed in any preceding claim, including an inwardly extending shoulder at the large diameter end of its taper, against which the journal bearing can abut in use, for axial location of the bearing.

8. A bush as claimed in claim 7, wherein the inwardly extending shoulder has sufficiently small inwards extent that the journal bearing can be pushed past it on assembly of the bearing into the bush.

9. A bush as claimed in any preceding claim, including a stepped bore for receiving an oil seal in addition to the bearing.

10. A bush as claimed in claim 9 as appendant to claim 2 or any one of claims 3 to 8 as appendant to claim 2, including an inwards extending flange at the external lip for defining the bore step.

11. A bush as claimed in any preceding claim, wherein the bush is of injection moulded plastics material.

12. A bush as claimed in claim 8 as appendant to claim claim 7, wherein the external taper of the bush is steeper in the region of the inwardly external shoulder.

13. A bush as claimed in any one of claims 1 to 12, wherein the journal bearing is a rolling element bearing.

14. A bush as claimed in any preceding claim in combination with a journal bearing and a body having a housing: the bearing being fitted in the mounting bush and the housing having a tapered bore into which the mounting bush is fitted, the tapered bore and the external surface of the mounting bush being complementarily tapered.

15. The combination of claim 14, the bush being in accordance with claim 2 or any one of claims 3 to 13 as appendant to claim 2, wherein the housing has an increased diameter section (the "under-cut section") at the smaller diameter end of the housing's taper to receive the lip and inhibit removal of the bush from the housing.

16. The combination as claimed in claim 15, wherein the under-cut section of the housing has a restrictice diameter in comparison with that of the lip and acts to restrict the lip inwardly.

17. The combination as claimed in claim 15 or claim 16, wherein the end external diameter of the lip is no bigger than the orifice of the housing opposite from its undercut.

18. The combination as claimed in any one of claims 14 to 17, the bush being according to claim 12, wherein the housing has a more steeply tapered region complementary to the steeper region of the bushes taper.

19. The combination as claimed in any one of claims 14 to 18, wherein the body is as cast in a light alloy casting, having the tapered housing cast in it.

20. The combination as claimed in claim 19, wherein the body has a location for a complementary location on another body having another tapered housing for another bush according to claim 1 and its bearing, both bearings journalling a common shaft, the tapers in the housings having their larger diameter ends towards the locations.

21. A method of mounting a journal bearing in a tapered housing via a bush in accordance with claim 1, the method consisting in the steps of: fitting the bearing into a mounting bush and fitting the bush with the bearing to the tapered housing .

22. A method of mounting a journal bearing in a tapered housing via a bush in accordance with claim 1, the method consisting in the steps of: fitting the bush into the tapered housing and fitting the bearing to the bush.

23. A method as claimed in claim 22, wherein the bush is fitted to the housing with a drift, which is subsequently removed, prior to fitting of the bearing to the bush.

24. A bush for mounting a journal bearing in a tapered housing substantially as hereinbefore described with reference Figures 1 & 2, Figures 3, 4 & 5, Figure 6, Figure 7 or Figure 8 of the accompanying drawings.

25. A bush for mounting a journal bearing in a tapered housing in combination with a journal bearing and a body having the housing substantially as hereinbefore described with reference Figures 1 & 2, or Figures 3, 4 & 5.

26. A method of mounting a journal bearing in a tapered housing via a bush substantially as hereinbefore described with reference Figures 1 & 2, or Figures 3, 4 & 5