GB2190434A

GB2190434A - Sintered bearings

Info

Publication number: GB2190434A
Application number: GB08611206A
Authority: GB
Inventors: Georg Strobl
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1986-05-08
Filing date: 1986-05-08
Publication date: 1987-11-18
Also published as: GB8611206D0

Abstract

A sintered cylindrical bearing (10) particularly for an electric motor has a continuous or interrupted groove (15) in at least one and preferably in each of two opposite end faces. A radially inner bearing portion (17) can thus be deformed, even to the extent of being plastically deformed, relative to a radially outer bearing portion (16) to allow for slight bearing misalignment. Ribs (19) may extend in the grooves (15). <IMAGE>

Description

SPECIFICATION Sintered Bearings This invention relates to sintered bearings, and particularly to sintered cylindrical bearings, the term "cylindrical" being used herein to include so-called flanged bearings but to exclude so-called spherical bearings.

Where a shaft is supported for rotation in two bearings good bearing alignment is essential.

Bearings have to be made to tight tolerances and accurate alignment of cylindrical bearings has always posed problems. It has therefore become quite common to use self-aligning spherical bearings but assembly of such bearings is comparatively expensive. Moreover, cylindrical bearings are able to take some loads better than spherical bearings.

The present invention therefore seeks to provide an improved cylindrical bearing in which alignment is not quite as crucial as heretofore.

According to the invention there is provided a sintered cylindrical bearing having a continuous or interrupted annular groove in at least one of two opposite end faces, the groove or the grooves serving to define a radially outer bearing portion, a radially inner bearing portion and an integral web portion therebetween so that in use the inner bearing portion is capable of being deformed relative to the outer bearing portion to cause slight displacement of the axis of the inner bearing portion relative to axis of the outer bearing portion.

Preferred and/or optional features of the invention are set forth in claims 2 to 10 inclusive and the invention in a further aspect is set forth in claim 12.

The use of sintered cylindrical bearings in accordance with the invention allows a limited degree of self-alignment. Moreover, the groove or grooves provide the bearing with an increased surface area for dissipating heat generated therein.

Also, when the bearing is press-fitted into a cylindrical bearing seat to form an interference fit therewith any reduction in internal diameter of the bearing should be localised in the region of the web portion. When two grooves are provided any reduction in internal diameter should therefore occur at a position intermediate the ends of the bearing and this is much preferred over the slight taper which commonly results from forcing conventional cylindrical bearings into a cylindrical bearing seat.

The ribs referred to in claim 4 give the bearing added strength and enable it to be made to a required strength with the minimum of material.

The axial length of the inner and outer bearing portions need not be identical and can be independently optimized.

The invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a plan view of one embodiment of a sintered cylindrical bearing according to the invention; Figure 2 is a section taken along the line Il-Il of Figure 1 showing the bearing mounted as inference fit in a cylindrical bearing seat, Figure 3 is a section, similar to that in Figure 2, of another embodiment of a sintered cylindrical bearing according to the invention, and Figure 4 is a section, again similar two that in Figure 2, of yet another embodiment of a sintered cylindrical bearing according to the invention.

Referring to Figures 1 and 2, there is shown therein a cylindrical bearing 10 of sintered metal, such as of sintered iron or sintered bronze with or without additives. The bearing 10 has a cylindrical outer surface 11, a cylindrical through bore 12 and end faces 13 and 14. An annular groove 15isformed in each end face 13, 14. The grooves 15 are concentric with the axis of the bearing 10 and are aligned with one another so that the internal radii and the externai radii of the two grooves 15 are identical. The two grooves 15 serve to define a radially outer bearing portion 16, a radially inner bearing portion 17, and an integral radially extending web portion 18therebetween.

The two grooves 15 are of equal depth and in the particular embodiment shown the depth of each groove is equivalent to about one third of the axial length of the bearing.

The base of each groove 15 has a plurality of integral radially extending angularly spaced ribs 19.

As shown these ribs 19 have a height which corresponds to about ha If the depth of the groove 19 but they could of smaller or greater height and could for example extend from the top to the base of each groove. The ribs 19 give the bearing added strength but are not essential.

The grooves 15 and ribs 19 are formed by appropriate tools in a pressing stage during the manufacture of the bearing 10.

Figure 2 shows the bearing 10 mounted as an interference fit in a cylindrical bearing seat 20 formed, for example, in a casing, frame or end cap of a permanent magnet direct current electric motor.

In press-fitting the bearing 10 into the bearing seat 20 the outside diameter of the bearing 10 is reduced slightly. There will be a consequential reduction in the diameter of the bearing bore 12 but it is believed that this latter reduction will be localised in the region of the web portion 18, i.e. in the embodiment shown midway or substantially midway between the ends of the bore 12. Such a localised reduction in diameter of the bore 12 is shown in Figure 2 to an exaggerated extent for purposes of illustration and it will be appreciated by those skilled in the art that this localised reduction is ideally positioned for journalling a shaft (not shown).

The radially outer and radially inner portions 16 and 17, respectively, of the bearing 10 are, as shown, of equal axial length. However, this is not essential and the axial length of the two portions 16 and 17 could be independently optimized in respect of the outer portion 16 in accordance with for example the material of the bearing support and in respect of the inner portion in accordance with for example the load to be applied, the type of lubrication impregnated in the bearing, the material of the shaft to be journalled and/or the material of the bearing.

The principal advantage of the bearing 10 over and above known cylindrical bearings is that the inner bearing portion 17 is capable of undergoing deformation, even to the extent of plastic deformation, in relation to the outer bearing portion 16 to cause slight angular displacement of the axis of the inner bearing portion relative to the axis of the outer bearing portion to provide for slight misalignment between two bearings.

The bearing 10 has the added advantage, however, that the grooves 15 and, if provided, the ribs 19 provide the bearing with an increased surface area for dissipating heat generated therein.

An axial end face of the inner bearing portion 17 can be used to support a thrust washer mounted about a shaftjournalled in the bearing 10. Provided that the thrust washer has a diameter greater than the outer diameter of the inner bearing portion 17 and less than the inner diameter of the outer bearing portion 16 the thrust washer will make only surface contact with the bearing 10 and will not dig into it.

This will have the effect of keeping friction to a minimum.

Figure 3 shows a flanged cylindrical bearing 20 which differs from the bearing 10 shown in Figures 1 and 2 only in that it has an integral outwardly extending flange 21 at one end. This bearing 30 would be press-fitted into a bearing seat but a bearing similar two that shown in Figure 3 could be "rivetted" in a plate-like bearing support by radially outwardly deforming the outer bearing portion at the axial end the bearing remote from the flange 21.

In this latter case there will, of course, be no bore contraction.

Figure 4 shows a blind cylindrical bearing 30. This differs from the bearing shown in Figures 1 and 2 only in that it has an integral cover portion 31 closing one end of the bore 32. This bearing 30 can serve both as a radial bearing and as a thrust bearing by taking axial thrust on the cover portion 31 and is preferably used in conjunction with a shaft having a part spherical end.

The above embodiments are given by way of example only and it will be apparent to persons skilled in the art that various modifications can be made without departing from the scope of the invention. For example, each of the bearings described above could be provided with an annular groove in only one of its end faces. In any event however it is desirable that the depth of the groove or the combined depth of the two grooves, when provided, is equivalent to at least 30 percent of the axial length of the outer bearing portion.

Claims

1. sintered cylindrical bearing having a continuous or interrupted annular groove in at least one of two opposite end faces, the groove or grooves serving to define a radially outer bearing portion, a radially inner bearing portion and an integral web portion therebetween so that in use the inner bearing portion is capable of being deformed relative to the outer bearing portion to cause slight displacement of the axis of the inner bearing portion relative to the axis of the outer bearing portion.

2. The bearing of claim 1, wherein the depth of the groove or the combined depth of two grooves, one in each end face, is equivalent to at least 30 percent of the axial length of the outer bearing portion.

3. The bearing of claim 1 or claim 2, wherein the groove or grooves have been formed in the bearing in a pressing stage during the manufacture of the bearing.

4. The bearing of anyone of claims 1 to 3, having a plurality of integral angularly spaced radially extending ribs in the groove or in one or both grooves where two such grooves are provided.

5. The bearing of claim 4, wherein the height of the ribs is less than the depth of the respective groove.

6. The bearing of anyone of the preceding claims, wherein a continuous or interrupted annular groove is provided in each of its two opposite end faces.

7. The bearing of claim 6, wherein the depth of the two grooves is identical.

8. The bearing of claim 6 or claim 7, wherein the two grooves have identical inner radii and identical outer radii.

9. The bearing of anyone of the preceding claims, wherein the axial length of the inner bearing portion is identical to the axial length of the outer bearing portion.

10. The bearing of anyone of claims 1 to 8, wherein the axial length of the inner bearing portion is different from the axial length of the outer bearing portion.

11. A sintered cylindrical bearing substantially as hereinbefore described with reference to Figures 1 and 2, Figure 3, or Figure 4 of the accompanying drawings.

12. An electric motor having a motor shaft journalled at least at one end in a bearing as set forth in anyone of the preceding claims.

13. An electric motor according to claim 12, wherein the motor is a fractional horsepower permanent magnet direct current motor.