GB1604411A

GB1604411A - Bearing arrangements

Info

Publication number: GB1604411A
Application number: GB8095/77A
Authority: GB
Original assignee: Ransome Hoffmann Pollard Ltd
Current assignee: Pilgrim House Group Ltd
Priority date: 1978-05-23
Filing date: 1978-05-23
Publication date: 1981-12-09

Description

(54) BEARING ARRANGEMENTS (71) We, RANSOME HOFFMANN POL LARD LIMITED, a British Company, of New Street, Chelmsford, Essex, CM 1 1 PU, 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.

In known bearing arrangements for machine tools, the bearings are subjected to dynamic axial loading forces and it is generally desirable to provide a compensatory variable pre-load force. It has been known in the past to utilize tapered roller bearings in a bearing arrangement for a machine tool spindle and to subject such bearings to an axial pre-load force. Examples of these known bearing arrangements are described in UK Patent Specifications 858914 and 1373861.

According to the present invention a bearing arrangement comprises a pair of bearings with inner races mounted for rotation with a shaft or spindle, non-rotatable outer races which are relatively displaceable in a direction parallel to the axis of rotation and balls as rolling elements between the races, and adjustment means disposed at least partly between the bearings for subjecting the outer race of at least one of the bearings to a force in a direction substantially parallel to the axis of rotation which force is variably adjustable during operation while the shaft is rotating to impose additional controlled load on the bearing, wherein the bearings support the shaft within a housing, the outer race of said at least one of the bearings is directly received for sliding in the housing and the adjustment means is located within the housing and is independent of the shaft or of parts rotatable therewith.

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

As will become apparent hereinafter the invention also provides a method of controlling the loading on a shaft or spindle of a machine tool supported for rotation within a housing by the inner races of a pair of ball bearings during operation and by utilizing adjustment means located in the housing at least partly between the bearings and independent of the shaft or parts rotating therewith; said method comprising subjecting the non-rotatable outer race of at least one of the bearings which is directly received for sliding in the housing to a force directed substantially parallel to the axis of rotation and varying the force while the shaft is rotating to impose additional controlled load on the bearing.

In general, it has been found that applying a dynamically variable force to a ball bearing in accordance with the invention provides better results than the prior art tapered roller bearings where the rollers tend to be subjected to a wedging action when the races thereof are displaced axially.

Although the or each ball bearing of a bearing arrangement constructed in accordance with the invention is preferably an angular-contact bearing it is possible to use radial contact bearings.

The outer races of the bearings are normally displaced away from one another when the adjustable force increases. It is also possible to restrain the outer race of the other bearing from movement. In one embodiment of the invention it is possible to provide a differential force to displace both the outer races by different amounts. In this way the bearings can be subjected to different preload forces.

The means for adjusting the pre-load force may be fluid, i.e. hydraulically or pneumatically operated or mechanically operated. In the former case, at least one chamber for receiving pressure medium can be provided in the housing of the bearing arrangement. A member such as an annular piston subjected to the pressure medium can then move and displace one of the outer races of the bearings. At least one of the outer races can be subjected to additional spring force opposing the force applied by the adjustment means.

In accordance with further features of the invention, a spring-steel diaphragm can be located in the chamber and/or restriction means, such as a nozzle, may be disposed in the fluid flow path.

In embodiments of a mechanically-operated adjustment means, a pair of pressure members can be relatively displaced to engage and apply force to one of the outer races of the bearings.

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: Figure 1 to 5, are schematic sectional side views of respective bearing arrangements made in accordance with the invention; and Figure 6 is a side view of one of the pressure members used in the bearing arrangement shown in Figure 5.

Throughout the accompanying drawings and following description like reference numerals are used to identify like or equivalent parts. In Figures 1 to 5 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.

During operation, the spindle 1 is subjected to a reactive force with an axial component and the bearing A is subjected to a higher axial loading than the bearing B. In accordance with the invention one or both bearings A, B can be subjected to an additional adjustable axial loading force. In the case where the bearing A is depicted as being subjected to pre-loading it should be understood that the overall arrangement can be reversed so that the bearing B is subjected to the pre-loading and vice versa.

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 race 7, an outer ring or race 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 screwthreaded engagement with a portion of the spindle I engages on the outer face of the ring 7 of the bearing B. The components 19, 18, and 20 thus retain the rings 7 and prevent movement axially of the spindle 1. The rings 7 can however be directly secured to the spindle I in other ways. The outer rings 9 of the bearings A, B are similarly located to the housing 2. As illustrated, the ring 9 of the bearing B locates in a recess 8 and is retained by an axial flange 3 of a cover 10 detachably secured to the housing 2. The outer ring 9 of the bearing A is allowed to move axially of the spindle I and is operably associated with means for effecting this movement to thereby adjust the axial loading of the bearing A. A further cover 26, complementary to the cover 10, is detachably secured to the housing 2 and has an axial flange 3' serving to limit the outward extent of axial movement of the ring 9. Conveniently, the covers 10, 26 have packings 4, or labyrinth seals, engaging on portions of the spindle I to seal off the bearing arrangement and retain lubricant therein. The means for adjusting the loading of the bearing A operates hydraulically or pneumatically and a path 23, which may be a conduit or a channel for example, serves to convey pressure medium P to a chamber 5.

The chamber 5 is of annular shape and is defined between a piston 21 and a block 6 secured to the housing 2. Instead of a block 6 an integral extension of the housing 2 can provide the chamber-defining wall complementary to the working surface of the piston 21. The piston 21 has an external face 28 in sliding contact with a wall of the housing 2, which also slidably contacts the movable ring 9 of the bearing A, and an internal face 29 in sliding contact with a wall of the block 6. 0ring seals 24, 25 engage the respective sliding surfaces and seal the chamber 5. The piston 21 engages on the ring 9 and the movement of the piston 21 is transferred to the ring 9.

During use, pressure medium P is supplied to the chamber 5 to displace the piston 21 and hence the ring 9 of the bearing A axially of the spindle 1 to load the bearing A. Normally pressure medium would be present in the chamber 5 at all times and a small shoulder or step in the chamber-defining wall of the block 6 or its equivalent can ensure there is a minimum pre-load force even if the pressure in the paths should fall or even fail. The pressure medium can inherently provide resilient damping for shock-loads and the damping effect can be enhanced by providing a restriction, such as a nozzle, in the pressure medium flow path. The minimum pre-load force and resilient damping effects can also be enhanced by arranging an annular spring-steel diaphragm in the chamber 5 to receive the pressure medium. The scrap view at Figure la depicts this modification where the diaphragm is denoted D.

Figure 2 depicts an arrangement wherein the outer rings 9 of both bearings A and B are moved and displaced apart by the application of pressure medium but are subjected to an opposing spring force tending to move them together. In this modified arrangement two chambers 5, 5' are provided each defined between a wall of the housing 2 and a respective piston 21, 21'. The sliding faces and seals of the pistons 21, 21' are denoted 28, 29, 28', 29' and 24, 25, 24', 25' respectively. The pressure medium P is conveyed to the chambers 5, 5' via a common path 23 and the path 23 leads to a port 14 for receiving a hose connector or the like. The outer face of the ring 9 of the bearing A is subjected to the force of a compression spring 16 located between the flange 3' of the cover 26 and a pressure pad or washer 17. The chambers 5, 5' are of different size and the piston 21 has a greater working area than the piston 21'. This differential ensures that the displacement force produced by the piston 21 is greater than that produced by the piston 21'. The force of the spring 16 tends to oppose the displacement of the piston 21 and can be designed to balance out the displacement force on the piston 21 when the spindle 1 is not subjected to axial loading.

In the arrangements shown in Figures I and 2 the bearings A, B are disposed quite close together and may be at the end of the spindle 1 remote from the drive means thereof. The other end of the spindle 1 may also be supported by a similar arrangement provided with means for adjustably preloading one or both bearings. In this way differential preloading can be provided at the ends of the spindle 1. Alternatively, the individual bearings A, B can be spaced apart in another arrangement as depicted in Figure 3. The spacing sleeve 19 in the Figure 3 arrangement is prolonged and the bearing A is fixed in position while the outer ring 9 of the bearing B is adjustable to pre-load the bearing B. The means for adjusting the ring 9 of the bearing B takes the same form as in the Figure 1 arrangement and serves to urge the rings 9 of the bearings A, B apart.

In the arrangement described hereinbefore and shown in Figures 1 to 3, the means for adjustably pre-loading one or both bearings employs gaseous or liquid pressure medium.

Figures 4 to 6 collectively depict analogous arrangements wherein the adjustable preloading is effected mechanically. In the arrangement shown in Figure 4, the bearing A has its outer ring 9 adjustable axially of the spindle 1. A pair of annular pressure members 30, 31 are located to engage the respective inner faces of the rings 9 of the bearings A, B. The pressure members 30, 31 have tapered facing surfaces which converge towards the spindle 1. A set of balls 22 located and spaced by a cage 27 seats in the tapered gap 32 between the pressure members 30, 31 and the balls 22 can be urged inwardly of the gap 32 and towards the spindle 1. The ring 9 of the bearing B is held between the pressure member 31 and the flange 3 of the cover 10 while the ring 9 of the bearing A can be move towards the flange 3' of the other cover 26.

Depending on the distance by which the balls 22 are forced radially inwards towards the spindle 1, the ring 9 of the bearing A can be moved through a certain distance to produce a corresponding pre-loading of the bearing A in a manner analogous to the other embodiments. A recess 34 in the housing 2 serves to accommodate a mechanism for moving the balls 22 in and out of the gap 32.

This mechanism can take various forms but in this embodiment an adjustment ring 33 coaxial with the spindle 1 engages with its inner face 35 on the balls 22. The ring 33 is tapered axially so that the inner face 35 is inclined relative to the axis of the spindle 1.

The ring 33 is also externally threaded to mate with an internal threaded portion of the recess 34 and by rotating the ring 33 about the axis of the spindle 1, the balls 22 can be progressively forced into the gap 32 to displace the pressure member 30 and hence the outer ring 9 of the bearing A. The ring 33 has outer end portions in sliding engagement with faces of the recess 36 to hold and locate the ring 33 externally. The mechanism can be supplemented by suitable means (not shown) such as gearing, for rotating the ring 33.

In the arrangement shown in Figure 5, the pressure members 30, 31 of Figure 4 are replaced by pressure members 40, 41 a typical one of which is depicted in Figure 6.

The pressure members 40, 41 are again of generally annular form and abut one another and the inner faces of the rings 9 of the bearings A, B. The abutting faces 44 of the pressure members 40, 41 are shaped in a manner such that relative rotation between the members 40, 41 causes the surfaces 44 to slide across one another to axially displace the member 40 and thereby move the ring 9 of the bearing A. As shown in Figure 6, where the member 40 is depicted as typical of the one constructional configuration for the members 40 and 41, the face(s) 44 of the members 40, 41 are helical (in the sense of comprising one turn of a helix) with a step 45. The members 40, 41 thus collectively resemble a dog-clutch. Alternatively it may be possible to have the faces 44 simply planar and inclined to the axis of the members 40, 41. The outer peripheral surface of the member 40 is provided with a recess 42, such as a slot, engaged by a pin 43 or the like. The pin 43 serves to prevent rotation of the member 40 while permitting axial displacement as desired. The member 41 is, in contrast, rotatable and again a suitable mechanism is provided for rotating the member 41 to adjust the pre-loading of the bearing A. As shown in Figure 5, the drive or gearing mechanism for rotating the member 41 takes the form of a worm wheel 46 engaging a screw thread 45 provided on the outer periphery of the member 41.

Although the various bearing arrangements described hereinbefore have all employed angular-contact ball bearings A, B any arrangement can be modified to employ radial ball bearings.

WHAT WE CLAIM IS: 1. A bearing arrangement comprising a pair of bearings with inner races mounted for rotation with a shaft of spindle, non-rotatable outer races which are relatively displaceable in a direction parallel to the axis of rotation and balls as rolling elements between the races, and adjustment means disposed at least partly between the bearings for subjecting the outer race of at least one of the bearings to a force in a direction substantially parallel to the axis of rotation which force is variably adjustable during operation while the shaft is rotating to impose additional controlled load on the bearing wherein the bearings support the shaft within a housing, the outer race of said at least one of the bearings is directly received for sliding in the housing and the adjustment means is located within the housing and is independent of the shaft or of parts rotatable therewith.

2. An arrangement according to claim 1, wherein either or each of the bearings is an angular-contact ball bearing.

3. An arrangement according to claim I or 2, wherein the other bearing has its inner and outer races non-displaceable in a direction substantially parallel to the axis of rotation.

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

5. An arrangement according to any one of claims 1 to 3, wherein the operation ofsaid adjustment means to increase said force causes the corresponding outer races of the bearings to move apart.

6. An arrangement according to any one of claims 1 to 5, wherein said adjustment means is fluid operated.

7. An arrangement according to any one of claims I to 5, wherein said adjustment means is mechanically operated.

8. An arrangement according to claim 6, wherein said adjustment means includes at least one chamber for receiving pressure medium, said chamber being defined by means including the surface of an annular piston which is mounted for sliding and serves to apply force dependent on the pressure medium supplied to the chamber to the outer race of said at least one bearing.

9. An arrangement according to claim 6, where appended to claim 4, wherein said adjustment means includes chambers for receiving pressure medium, each chamber being defined by means including the surface of an annular piston which is mounted for sliding and serves to apply force, dependent on the pressure medium supplied to that chamber, to the outer race of one of the bearings operably associated therewith.

10. An arrangement according to claim 9, wherein the chambers and/or surfaces of the pistons have a different size so that differential force is applied to the associated outer races of the bearings.

11. An arrangement according to claim 9 or 10, wherein at least one of the outer races is additionally subjected to spring force opposing the force applied by the associated piston.

12. An arrangement according to claim 6, wherein at least one of the outer races is additionally subjected to spring force which tends to oppose the force applied by the adjustment means.

13. An arrangement according to claim 6, wherein said adjustment means includes at least one annular chamber for receiving pressure medium and an annular member which applies said force to said at least one outer race in dependence on the pressure medium in said chamber.

14. An arrangement according to claim 6, wherein said adjustment means comprises at least one chamber for receiving pressure

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. replaced by pressure members 40, 41 a typical one of which is depicted in Figure 6. The pressure members 40, 41 are again of generally annular form and abut one another and the inner faces of the rings 9 of the bearings A, B. The abutting faces 44 of the pressure members 40, 41 are shaped in a manner such that relative rotation between the members 40, 41 causes the surfaces 44 to slide across one another to axially displace the member 40 and thereby move the ring 9 of the bearing A. As shown in Figure 6, where the member 40 is depicted as typical of the one constructional configuration for the members 40 and 41, the face(s) 44 of the members 40, 41 are helical (in the sense of comprising one turn of a helix) with a step 45. The members 40, 41 thus collectively resemble a dog-clutch. Alternatively it may be possible to have the faces 44 simply planar and inclined to the axis of the members 40, 41. The outer peripheral surface of the member 40 is provided with a recess 42, such as a slot, engaged by a pin 43 or the like. The pin 43 serves to prevent rotation of the member 40 while permitting axial displacement as desired. The member 41 is, in contrast, rotatable and again a suitable mechanism is provided for rotating the member 41 to adjust the pre-loading of the bearing A. As shown in Figure 5, the drive or gearing mechanism for rotating the member 41 takes the form of a worm wheel 46 engaging a screw thread 45 provided on the outer periphery of the member 41. Although the various bearing arrangements described hereinbefore have all employed angular-contact ball bearings A, B any arrangement can be modified to employ radial ball bearings. WHAT WE CLAIM IS:

1. A bearing arrangement comprising a pair of bearings with inner races mounted for rotation with a shaft of spindle, non-rotatable outer races which are relatively displaceable in a direction parallel to the axis of rotation and balls as rolling elements between the races, and adjustment means disposed at least partly between the bearings for subjecting the outer race of at least one of the bearings to a force in a direction substantially parallel to the axis of rotation which force is variably adjustable during operation while the shaft is rotating to impose additional controlled load on the bearing wherein the bearings support the shaft within a housing, the outer race of said at least one of the bearings is directly received for sliding in the housing and the adjustment means is located within the housing and is independent of the shaft or of parts rotatable therewith.

medium and a spring-steel diaphragm is located in the chamber to receive the pressure medium.

15. An arrangement according to claim 6, wherein said adjustment means comprises at least one chamber for receiving pressure medium and there is further provided restriction means in the fluid flow path to the chamber.

16. An arrangement according to claim 15, wherein the restriction means is a nozzle.

17. An arrangement according to claim 7, wherein said adjustment means comprises a pair of pressure members relatively movable in a direction parallel to the axis of rotation to apply force to the outer race of the or each bearing.

18. An arrangement according to claim 17, wherein the pressure members are provided with facing surfaces which converge towards the axis of rotation and a set of balls is movable between said facing surfaces and generally radially of the axis of rotation to move the pressure members together or apart.

19. An arrangement according to claim 18, wherein the adjustment means further comprises a displaceable ring generally surrounding the set of balls and having an inner surface which contacts the set of balls whereby the ring is displaced to move the balls between the facing surfaces of the pressure members.

20. An arrangement according to claim 19, wherein the inner surface of the displaceable ring is inclined relative to the axis of rotation and the ring is displaceable in a direction parallel to the axis of rotation.

21. An arrangement according to claim 20, wherein the adjustment means further comprises gearing means which serves to rotate the ring to effect the axial displacement thereof.

22. An arrangement according to claim 17, wherein the pressure members are relatively rotatable about the axis of rotation and are provided with engaging surfaces shaped in a manner such that relative rotation between the members causes said relative movement in a direction parallel to the axis of rotation.

23. An arrangement according to claim 22, wherein the adjustment means further comprises gearing means which serves to rotate one of the pressure members and the other pressure member is inhibited from rotation but displaceable in a direction parallel to the axis of rotation to apply force to the outer race of said at least one bearing.

24. A bearing arrangement substantially as described with reference to. and as illustrated in, any one of Figures I to 4 of the accompanying drawings or Figures 5 and 6 of the accompanying drawings.

25. An assembly composed of a spindle for a machine tool rotatably supported by a bearing arrangement according to any one of the preceding claims.

26. A method of controlling the loading on a shaft or spindle of a machine tool supported for rotation within a housing by the inner races of a pair of'ball bearings during operation and by utilizing adjustment means located in the housing at least partly between the bearings and independent of the shaft or parts rotating therewith; said method comprising subjecting the non-rotatable outer race of at least one of the bearings which is directly received for sliding in the housing to a force directed substantially parallel to the axis of rotation and varying the force while the shaft is rotating to impose additional controlled load on the bearing.