GB2196067A

GB2196067A - Thrust bearings

Info

Publication number: GB2196067A
Application number: GB08624286A
Authority: GB
Inventors: Ronald Francis Hamblin
Original assignee: Svenska Kullagerfabriken AB
Current assignee: SKF AB
Priority date: 1986-10-09
Filing date: 1986-10-09
Publication date: 1988-04-20
Anticipated expiration: 2006-10-09
Also published as: GB8624286D0; GB2196067B

Abstract

A blind jam pot thrust bearing assembly in which an end of an upright shaft (30) is engaged in two spaced apart bearings (12, 13) in a housing (10) closed at the lower end thereof. The upper bearing (12) transmits downward thrust from the shaft to the housing, and the lower bearing (13) is self-aligning and comprises an inner bearing ring (40) locked to the shaft and an outer bearing ring (41) mounted as a sliding fit in the housing. A thrust ring (45) on the outer bearing ring has a frusto-conical upper surface (47) engaged by radial pins (50) in the wall of the housing to transmit to the housing any upward thrust acting on the shaft and lower bearing. <IMAGE>

Description

SPECIFICATION Thrust bearing assembly This invention relates to a thrust bearing assembly, and is concerned more particularly with a so-called Jam Pot assembly in which an end of a shaft is engaged in thrust bearings supported in a blind Jam Pot housing, that is a tubular housing closed at one end, which encloses the end of the shaft and the thrust bearings. The housing may be fixed and the shaft rotatably mounted by the bearings in the stationary housing, or alternatively the shaft may be fixed and the housing rotatably mounted by the bearings on the fixed shaft.

In heavy engineering there is a need for Jam Pot assemblies in which heavy section bearings are mounted on a shaft as a bench operation. The whole shaft assembly has then to be lifted and lowered into an oil-containing Jam Pot housing. In this method of assembly it is difficult to prevent the two major components, that is the shaft and the housing, coming apart during subsequent handling and in service where secondary forces can arise causing separation.

It is known to provide a Jam Pot assembly with a double row thrust bearing adjacent the open end of the housing and a self-aligning bearing adjacent the closed end of the housing, the double row thrust bearing having the inner and outer bearing rings clamped to the shaft and housing respectively, and the selfaligning bearing having the inner bearing ring clamped to the end of the shaft and the outer bearing ring mounted as a sliding fit in a bore in the housing. The double row thrust bearing resists thrust in either of the axial directions, and the self-aligning bearing resists only radial load. Because the double row thrust bearing is bi-directional it has a low thrust carrying capacity and hence low efficiency relative to size compared to a uni-directional thrust bearing.

Also the double row thrust bearing creates mounting and dismounting problems with the required interference fit of the outer bearing ring.

According to the present invention there is provided a blind Jam Pot thrust bearing assembly in which an end of a shaft is engaged in two spaced apart rolling bearings in a housing closed at one end thereof, wherein the first bearing at the open end of the housing comprises inner and outer bearing rings abutting opposing shoulders on the shaft and housing respectively and is adapted to transmit to the housing thrust acting on the shaft in the direction towards the closed end of the housing, or alternatively to transmit to the shaft thrust acting on the housing in the direction towards the open end thereof, the second bearing comprises an inner bearing ring locked onto the shaft and an outer bearing ring mounted in a cylindrical bore in the housing and is adapted to transmit to the shaft thrust acting on the outer bearing ring jn the direction towards the closed end of the housing, or alternatively to transmit to the outer bearing ring thrust acting on the shaft in the direction towards the open end of the housing, and the housing is provided with locating means movable into engagement with the outer bearing ring of the second bearing to prevent axial movement of the shaft in the direction away from the closed end of the housing, or alternatively movement of the housing in the direction away from the shaft, whereby the shaft and housing are held in position relative to one another.

With the Pot assembly of the present invention, the outer bearing ring of the first bearing may be mounted in the housing as a separate component, the other components of the first bearing and the second bearing mounted on the shaft as a bench operation, and then the assembly fitted as a unit into the housing. The Pot assembly thus has the advantage over the known Pot assemblies that the outer bearing ring of the first bearing can be mounted as a force fit in the housing. In prior known pot assemblies the outer bearing rings are a sliding fit within the bore of the housing and in operation the outer bearing rings may creep relative to the housing and thereby cause wear. The pot assembly of the invention also has the advantage that, upon dismantling for repair or maintenance, the outer ring of the first bearing can remain undisturbed in the housing.

A separate single direction tapered roller thrust bearing can conveniently be used for the main thrust bearing at the open end of the housing, since the locating means ensure that the shaft and the housing are securely held together against axial thrust in either direction.

The locating means are preferably adapted to apply to the outer bearing ring of the second bearing a locating thrust directed inwardly towards the closed end of the housing, the locating thrust being transmitted through the second bearing to the shaft and exerting a pre-load on the first bearing The locating means can conveniently comprise a plurality of pins mounted in apertures in the wall of the housing, the inner ends of the pins being engaged against a cam surface on the outer bearing ring of the second bearing or against a cam surface on an annular spacer abutting the outer bearing ring of the second bearing.

One construction of a blind Jam Pot thrust bearing assembly supporting a rotary shaft in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which shows the bearing assembly and shaft in axial section.

As shown in the drawing, the bearing assembly comprises a housing 10 which is open at the top and closed at the bottom thereof, and the shaft 11 extends vertically down wards into the housing with its lower end rotatably mounted therein by a roller thrust bear ing 12 adjacent the open upper end of the housing and a self-aligning roller bearing 13 positioned below and spaced from the thrust bearing 12.

The housing 10 has an upright tubular section 15 and a base section 16 which closes the bottom end of the tubular section. The tubular section 15 has its lower end portion stepped radially inwards to define an upper cylindrical bore 17 which receives the thrust bearing 12 and a lower cylindrical bore 18 which is of smaller diameter than that of the bore 17 and which receives the self-aligning bearing 13. An internal shoulder 19 is formed at the junction of the bores 17, 18 and an external shoulder 20 is formed at the stepped portion of the housing.The tubular section 15 is formed with three radial apertures 21 which open into the lower bore 18 adjacent the upper end thereof, the three apertures 21 being spaced at equal intervals around the housing, and the external shoulder 20 of the stepped portion of the tubular section 15 is formed with three axial-extending apertures 22 which open one into each of the three radial apertures 21. The parts of the housing formed with the apertures 21, 22 have a thicker wall than the remainder of the housing for strength purposes. The upper end of the tubular section 15 is fitted with an annular end cap 25, the inner periphery of which is fitted with a rubber sealing ring 26 in sliding sealing contact with the shaft 11.The base section 16 projects radially outwards beyond the tubular section 15 to form a radial flange 27 which is provided with apertures (not shown) for bolting the housing onto a support.

The lower end portion of the shaft 11 is stepped to form a cylindrical journal 30 of smaller diameter than that of the shaft and cooperating therewith to form a shoulder 31, and a cylindrical journal 32 of smaller diameter than that of the journal 30 and co-operating therewith to form a shoulder 33 as shown in the left hand side of the Figure. The journal 32 may be made longer than necessary to accommodate the bearing 13 and fitted with an annular spacer 34 which abuts the shoulder between the journals 30, 33 as shown in the right hand side of the Figure, the spacer 34 having a function as explained hereinafter.

The roller thrust bearing 12 comprises an inner bearing ring 35 mounted on the journal 30 and abutting against the shoulder 31, an outer bearing ring 36 mounted in the upper bore 17 of the housing and abutting against the internal shoulder 19 on the housing, and tapered rollers 37 between the bearing rings 35, 36. The bearing 12 is adapted to transmit to the housing any downward thrust exerted on the shaft 11.

The self-aligning bearing 13 comprises an inner bearing ring 40 mounted on the journal 32, an outer bearing ring 41 mounted in the lower bore 18 of the housing, and two rows of barrel rollers 42 between the bearing rings 40, 41. The inner bearing ring 40 is clamped against the shoulder 33 by a locking ring 43 screwed onto a screw-thread on the lower end of the journal 32, but the outer bearing ring 41 is free to float axially in the bore 18 in accordance with the axial position of the shaft relative to the housing. The bearing 13 has self-aligning properties which compensates for any small misalignment of the shaft and housing. The self-aligning bearing 13 also has the property of transmitting axial thrust in both directions between its inner and outer bearing rings, which property is utilised as hereinafter explained.

A frusto-conical annular disc 45 is mounted as a sliding fit in the bore 18 of the housing above the self-aligning bearing 13, the inner periphery of the disc 45 being spaced with small clearance from the journal 30. The disc 45 has an annular base 46 which abuts against the outer bearing ring 41 of the bearing 13 and the disc 45 is arranged so that its external conical surface 47 faces the radial apertures 21. The angle of inclination of the conical surface 47 relative to the axes of the radial apertures 20 is approximately 15 degrees.

Three locating pins 50 are mounted one in each of the radial apertures 21. Each pin 50 has a central cylindrical portion which is a sliding fit within its radial aperture 21, an inner tapered portion having a flat surface 51 which engages against the conical external surface 47 of the annular disc 45, and an outer portion having a flat surface 52 facing the associated axial aperture 22. Each radial aperture 21 is fitted with an 0 ring seal 53 which engages the central cylindrical portion of the pin 50 to provide an oil tight seal. Three locking pins 54 are screwed into the three axial apertures 22 respectively with the inner end of each locking pin abutting the flat surface 52 on the associated locating pin 50. The locking pins are secured in position by lock nuts 55.

The shaft is mounted in the Jam Pot assembly by first of all detaching the end cap 25 from the housing 10 and positioning the end cap around the shaft. The inner ring 35 and the roller set 37 of the thrust bearing 12 are then fitted on the journal 30 with the inner bearing ring 35 abutting the shoulder 31, the annular disc 45 positioned around the journal 30 with its conical end projecting away from the end of the shaft, the self-aligning bearing 13 fitted on the journal 32, and the locking ring 43 screwed onto the end of the journal 32 to clamp the inner bearing ring 40 of bearing 13 against the shoulder 33.The outer bearing ring 36 of bearing 12 is fitted as a force fit into the bore 17 and is abutted against shoulder 19, the shaft and bearings inserted into the housing to engage the outer bearing ring 41 of the self-aligning bearing as a sliding fit in the bore 18, and the shaft and bearings lowered to engage the rollers 37 of the thrust bearing 12 against the outer ring 36. The weight of the shaft is then supported by the thrust bearing on the housing 10 with zero clearance in the.thrust bearing. The Jam Pot assembly is then capable of resisting downward thrust in the direction of arrow A in the drawing, but any side thrust in the direction of arrow B would tend to cause the shaft to lift due to the inclination of the rollers of the thrust bearing relative to the axis of the shaft.

In accordance with the present invention, the shaft is held in position within the housing by inserting the locating pins 50 in the apertures 21 to engage the surfaces 51 against the conical surface 47 on the annular disc 45 and thereby move the disc 45 downwards against the outer bearing ring 41 of the selfaligning bearing. The locating pins 50 are secured in position by screwing the locking pins 54 into engagement with the flat surfaces 52 on the pins 50. The locating pins and the annular disc 45 then form a fixed abutment on the housing and any upward thrust on the shaft is resisted by the thrust resisting properties of the self-aligning bearing which abuts the disc 45.

The locating pins 50 may be pressed inwards against the cam surface formed by the frusto-conical surface on the disc 45 so as to force the disc downwards and thereby apply a downwards thrust to the outer bearing ring of the self-aligning bearing. The thrust is transmitted through the bearing to the shaft and thereby exerts a pre-load on the thrust bearing 12.

The shaft may be fitted with the spacer ring 34 as shown in the right hand side of the Figure to facilitate fitting of the shaft in the housing. The ring 34 has an annular flange 56 which overlaps the annular disc 45 on the side thereof remote from the self-aligning bearing and thereby holds the disc 45 adjacent to the self-aligning bearing during the lowering of the shaft into the housing. There is then no risk of the disc 45 becoming jammed in the housing at a level above the apertures 21 in the housing.

The locating pins and frusto-conical disc in the embodiment described can be replaced by any other mechanical, hydraulic, pneumatic or electrical mechanism operable from outside the housing and after installation of the shaft and bearings in the housing, to provide an abutment engaging the upper end of the outer bearing ring of the self-aligning bearing or to exert a downward locating thrust on the outer bearing ring of the self-aligning bearing.

In the embodiment described above, the housing is fixed and the shaft is rotatably mounted in the bearing in the stationary housing. However, the shaft.may be fixed and the housing rotatably mounted by the bearings on the stationary shaft. The housing can then serve as the rotary hub of a wheel or tool secured to the housing.

Claims

1. A blind Jam Pot thrust bearing assembly in which an end of a shaft is engaged in two spaced apart rolling bearings in a housing closed at one end thereof, wherein the first bearing at the open end of the housing comprises inner and outer bearing rings abutting opposing shoulders on the shaft and housing respectively and is adapted to transmit to the housing thrust acting on the shaft in the direction towards the closed end of the housing, or alternatively to transmit to the shaft thrust acting on the housing in the direction towards the open end thereof, the second bearing comprises an inner bearing ring locked onto the shaft and an outer bearing ring mounted in a cylindrical bore in the housing and is adapted to transmit to the shaft thrust acting on the outer bearing ring in the direction towards the closed end of the housing, or alternatively to transmit to the outer bearing ring thrust acting on the shaft in the direction towards the open end of the housing, and the housing is provided with locating means movable into engagement with the outer bearing ring of the second bearing to prevent axial movement of the shaft in the direction away from the closed end of the housing, or alternatively movement of the housing in the direction away from the shaft, whereby the shaft and housing are held in position relative to one another.

2. A bearing assembly as claimed in claim 1, wherein said locating means are adapted to apply to the outer bearing ring of the second bearing a locating thrust directed inwardly towards the closed end of the housing, said locating thrust being transmitted through the second bearing to the shaft and exerting a pre-load on said first bearing.

3. A bearing assembly as claimed in claim 1 or 2, wherein said locating means comprises a plurality of pins mounted in apertures in the wall of the housing, the inner ends of the pins engaging against a cam surface on the outer bearing ring of the second bearing or against a cam surface on an annular disc abutting the outer bearing ring of the second bearing.

4. A bearing assembly as claimed in claim 3 and including an annular frusto-conical disc abutting the outer bearing ring of the second bearing at the end remote from the closed end of the housing, the external conical surface of the annular disc forming said cam surface.

5. A bearing assembly as claimed in claim 4, wherein the inner end portion of each of said pins is provided with a surface which is inclined relative to the axis of the pin and which engages against the external conical surface of the annular disc.

6. A bearing assembly as claimed in claims 3, 4 or 5, wherein the shaft is fitted with a spacer ring having a flange which overlaps the annular disc at the end thereof remote from the second bearing, said flange holding the annular disc in position adjacent the second bearing prior to movement of said pins against the cam- surface on the annular disc.

7. A bearing assembly as claimed in any of the preceding claims, wherein the second bearing is a double row self-aligning bearing.

8. A bearing assembly as claimed in any of the preceding claims, wherein the first bearing is a single direction tapered roller thrust bearing.

9. A blind Jam Pot thrust bearing assembly substantially as hereinbefore described with reference to the accompanying drawing.