GB1604879A - Bearing arrangements - Google Patents

Description

(54) BEARING ARRANGEMENTS (71) We, RANSOME HOFFMANN POLLARD LIMITED, a British Company, of New Street, Chelmsford, Essex, CMl lPU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to bearing arrangements for supporting rotatable members referred to hereinafter as spindles or shafts. The invention is particularly, but not solely, concerned with bearing arrangements supporting spindles of machine tools such as lathes or milling machines.

According to the present invention a bearing arrangement comprises a pair of tapered roller bearings or angular contact ball bearings with inner races mounted for rotation with a shaft or spindle and stationary outer races, means for restraining the races of the bearings from movement in a direction parallel to the axis of rotation and adjustment means for subjecting the outer race of at least one of said bearings to a pre-load variable compressive force directed radially inwards towards the axis of rotation and acting uniformly over the whole circumference.

The invention also provides a method of controlling the loading on a shaft or spindle of a machine tool supported for rotation by the inner races of a pair of tapered roller bearings or angular contact ball bearings; said method comprising subjecting the stationary outer race of at least one of said bearings to a pre-load variable compressive force directed radially inwards towards the axis of rotation and acting uniformly over the whole circumference while restraining the races of the bearings from moving parallel to the axis of rotation.

The bearings may be in closely adjacent side-by-side e.g. abutting relationship or spaced apart in a direction parallel to the axis of rotation. The variable pre-load force can be applied to one or both bearings.

Nevertheless, the bearing arrangement can also employ additional non-adjustable bearings.

Concentricity between the axes or rotation of the shaft or spindle and the bearing or bearings is maintained at all times and the adjustment controls the loading on the shaft during operation.

The present invention also provides an assembly composed of a spindle or shaft of a machine tool, e.g. supporting a chuck or the like, the spindle being supported for rotation in a housing containing a bearing arrangement constructed in accordance with the invention.

In certain embodiments of the invention the adjustment means is fluid-operated and a chamber is provided for receiving pressure medium, hydraulic or pneumatic, used to exert the necessary compressive force on the bearings or on an associated one of the bearings. The chamber can then be defined by the outer race of the bearing to be adjusted or by some other component such as by the yieldable e.g. flexible resilient wall of a member contacting the outer race.

In other embodiments the adjustment means is mechanical and can, for example, be one or more tapered sleeves or the like forced between the outer race to be adjusted and some abutment such as part of a housing.

In this case, it may be desirable to provide a tapered profile or inclined external surface for the or each outer race to be adjusted.

Shallow recesses in the sleeve or sleeves and in the outer race or races can usefully form lubrication pockets to store lubricant acting on the sleeve or sleeves to reduce sliding friction.

The invention may be understood more readily and various other features of the invention may become apparent from consideration of the following description.

Embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings, wherein Figures 1 to 3, are schematic sectional side views of respective bearing arrangements made in accordance with the invention.

In Figures 1 to 3, various bearing arrangements each having a pair of bearings, are each shown as rotatably supporting a shaft or spindle. It is assumed for the purpose of exemplification that the spindle forms part of a machine, such as a milling machine or a lathe, and that the bearing designated A is closest to the workpiece, e.g., to the chuck of the machine, while the bearing designated B is remote from the workpiece and nearer to the drive means. During a typical machining operation the spindle 1 can rotate at speeds over the range from a few r.p.m., up to several thousand r.p.m.

Referring now to Figure 1, the spindle 1 is supported for rotation by the bearings A, B in a housing 2. The housing 2 can form the headstock casing of a lathe and in this case the spindle 1 can support a chuck denoted C.

The bearings A, B are angular-contact ball bearings each composed of an inner ring or raceway 7, an outer ring or raceway 9 and balls 11 therebetween. A cage 15 serves to space and locate the balls 11 of each bearing A, B. The outer ring 9 of each bearing A, B has a relieved portion or counterbore 13 facing outwardly of the overall bearing arrangement and permitting the rings 7, 9 to be separated during assembly and disassembly by relative axial movement in the direction as is known per se. The inner rings 7 of the bearings A, B are fitted to the spindle 1 and a sleeve 19 serves to space the rings 7 apart axially of the spindle 1. A shoulder 18, or similar abutment, formed by the spindle 1 engages on the outer face of the ring 7 of the bearing A while a locking ring 20 in screw-threaded engagement with a portion of the spindle 1 engages on the outer face of the ring 7 of the bearing B. The components 19, 18 and 20 thus retain the rings and prevent movement axially of the spindle 1. The rings 7 can however be directly secured to the spindle 1 in other ways. The outer rings 9 of the bearings A, B are similarly located to restrain axial movement. More particularly, the rings 9 of the bearings A, B engage on a sleeve 21 and are retained outwardly by axial flanges 3 of covers 10, 26 detachably secured to the housing 2 for example with screws (not shown). Conveniently, the covers 10, 26 have packings 4, or labyrinth seals, engaging on portions of the spindle 1 to seal off the bearing arrangement and retain lubricant therein.

In accordance with the invention the bearings A, B are operably associated with means for adjustably pre-loading the bearings A, B in a radial sense. A shaped cylindrical member 22 surrounds the assembly 9, 21 3 and is located by the covers 26, 0 and the housing 2. This member 23 which is here of unitary or integral form, has two recesses which form chambers 5, 6 for receiving hydraulic or pneumatic pressure medium. A path 23, which may be a conduit or a channel, for example, leads to a groove 33 in the member 22 which communicates with both the chambers 5, 6. The walls 50 of the member 22 inwardly defining the chambers 5, 6 are relieved as at 24 and the material of the member 22 is resiliently flexible. Thus when pressure medium is supplied to the chambers 5, 6 the inner defining walls 50, which are located around the rings 9, tend to flex inwardly to compress the bearings A, B radially. The pressure medium can inherently provide resilient damping for shock loads on the spindle 1 and the damping effect can be enhanced by providing a restriction in the fluid flow path.

Figure 2 depicts a modified arrangement where the bearings A, B are located close together with their rings 7, 9 in respective direct engagement. For convenience like reference numerals denote similar parts to the arrangement shown in Figure 1. In contrast to Figure 1, the member 22 and the sleeves 19, 21 are omitted and the rings 7, 9 respectively abut one another. The rings 9 are axially located between the flange 3 of the cover 26 and a shoulder 48 of the housing 2. Small chamber 5, 6 are formed between the housing 2 or a part thereof and the rings 9 of the bearings A, B. O-ring seals 33, 34 serve to seal these chambers 5, 6 and here the pressure medium P directly compresses the bearings A, B radially.

Instead of employing a gaseous or liquid pressure medium to compress the bearings A, B a mechanical system can be used.

Figure 3 depicts an embodiment of a mechanical system for pre-loading the bearings which is otherwise analogous to Figure 2.

For convenience like reference numerals again denote like parts. In the Figure 3 arrangement the outer peripheral surfaces of the ring 9 are machined or otherwise treated to adopt a slight inclination relative to the axis of rotation. Tapered sleeves 40, 41, 42 extend between the rings 9 and the housing 2 or a part thereof and the ring 42 is located again on a shoulder of the flange 3 of the cover 10. The flange 3 of the cover 26 engages the ring 9 of the bearing A and a mechanism M (not shown in detail) carried by the housing 2 or by the cover 26 which may in fact be integral with the housing 2, serves to exert lateral force over the outer end of the sleeve 40. One form of mechanism M may utilize a cam driven by gearing to displace the sleeve 40 by an adjustable amount. The sleeves 40-42 and the housing 2, or a part thereof, are provided with shallow recesses which form pockets 45 for receiving lubricant from a path 46.

The lubricant in the pockets 45 serves to reduce sliding friction and by displacing the sleeves 40, 41 axially the bearings A, B can be compressed as before to an adjustable extent.

WHAT WE CLAIM IS: 1. A bearing arrangement comprising a pair of tapered roller bearings or angular contact ball bearings with inner races mounted for rotation with a shaft or spindle and stationary outer races, means for restraining the races of the bearings from movement in a direction parallel to the axis of rotation and adjustment means for subjecting the outer race of at least one of said bearings to a pre-load variable compressive force directed radially inwards towards the axis of rotation and acting uniformly over the whole circumference.

2. An arrangement according to claim 1, wherein the bearings support said shaft within a housing and the adjustment means is located within said housing.

3. An arrangement according to claim 1 or 2, wherein said adjustment means subjects the outer races of both bearings to said force.

4. An arrangement according to any one of claims 1 to 3, wherein said adjustment means is fluid operated.

5. An arrangement according to any one of claims 1 to 3, wherein the adjustment means is mechanically operated.

6. An arrangement according to claim 4, wherein said adjustment means includes at least one chamber for receiving pressure medium, said chamber being at least partly defined by the outer surface of the outer race of said at least one bearing.

7. An arrangement according to claim 4, wherein said adjustment means includes at least one chamber for receiving pressure medium, said chamber being at least partly defined by a flexible resilient wall of a member contacting the outer race of said at least one bearing.

8. An arrangement according to claim 5, wherein said adjustment means includes one or more tapered sleeves displaceable in a direction parallel to the axis of rotation and contacting the outer race of said at least one bearing.

9. An arrangement according to claim 8, wherein the outer race of said at least one bearing has a tapered outer surface contacted by said sleeve or sleeves.

10. An arrangement according to claim 8 or 9, and further comprising lubrication pockets which serve to reduce sliding friction as the or each sleeve is displaced.

11. An arrangement according to any one of the preceding claims, wherein the pair of bearings are spaced apart in a direction parallel with the axis of rotation.

12. An arrangement according to any one of claims 1 to 10, wherein the pair of bearings are in side-by-side closely adjacent relationship.

13. A bearing arrangement substantially as described with reference to, and as illustrated in, Figure 1, 2 or 3 of the accompanying drawings.

14. An assembly composed of a spindle or shaft of a machine tool supported for rotation in a housing by a bearing arrangement according to any one of the preceding

Claims (1)

1. claims.

   15. A method of controlling the loading on a shaft or spindle of a machine tool supported for rotation by the inner races of a pair of tapered roller bearings or angular contact ball bearings; said method comprising subjecting the stationary outer race of at least one of said bearings to a preload variable compressive force directed radially inwards towards the axis of rotation and acting uniformly over the whole circumference while restraining the races of the bearing from moving parallel to the axis of rotation.