GB2100365A

GB2100365A - A linear recirculating rolling bearing

Info

Publication number: GB2100365A
Application number: GB8123468A
Authority: GB
Original assignee: SKF Kugellagerfabriken GmbH
Current assignee: SKF GmbH
Priority date: 1981-05-09
Filing date: 1982-05-10
Publication date: 1982-12-22
Also published as: DE3118386A1; FR2505424A1; FR2505424B1; GB2100365B

Abstract

A linear recirculating rolling bearing has a cage (12) with rails (17) disposed in slots (16) for the transmission of radial loads between the shaft (13) and the housing (10) via the rolling bodies (20). For the transmission of torque, a groove (26) is provided in the shaft (13) and one rail (17) has its radially inner surface radially inwardly offset by distance A. All the slots (16) in the cage (12) in which the rails (17) are disposed are made the same. <IMAGE>

Description

SPECIFICATION A linear recirculating rolling bearing This invention concerns a linear recirculating rolling bearing comprising a cage providing a plurality of endless paths in each of which is accommodated a plurality of rolling bodies for recirculation between a first longitudinally extending portion of the path in which, in use of the bearing, the rolling bodies are subject to loads directed radially of the cage and a second longitduinaliy extending portion of the path in which, in use of the bearing, the rolling bodies are not subject to loads directed radially of the cage, the cage having a plurality of longitudinally extending slots in its radially outer surface, which slots open one into the first portion of each path, and a plurality of rails are disposed longitudinally of the cage and one in each slot, each rail providing a longitudinal radially inwardly facing raceway surface for rolling bodies to roll along in the first portion of the paths and transmit loads radially of the cage, and the rolling bodies in the first portion of at least one path are arranged to roll along a longitudinal raceway surface offset radially inwardly relative to the raceway surfaces of the first portions of other paths.

A bearing having these features is disclosed in published specification DE 28 49 758. In this bearing one or more pins extend radially through the housing and engage in annular recesses in one of the rails so fixing that rail longitudinally and rotationally with respect to the housing. This rail provides a longitudinal raceway surface offset radially inwardly relative to the raceway surfaces of the first portions of other paths. A shaft extending through the bore of the annular cage has a longitudinal groove in its outer surface.

Rolling bodies rolling on the raceway surface of that rail also roll along the groove in the shaft so that torque can be transmitted.

The pin or pins engaging the rail are quite large and the rail engaged by the pin has to be wide to accommodate the pin, wider in fact than the other rails which just transmit forces radially of the cage. This means that the bearing cannot readily be used as just a linear recirculating rolling bearing, Because of the wider rail, a wider slot must be provided in the cage to accommodate the rail which weakens the cage.

Where several pins extend through the housing to engage in recesses in one and the same torque transmitting rail, care must be taken to ensure that the distance between the bores in the housing matches the distance between the recesses in the rail otherwise the pins will not fit properly and there will be distortion. This means that the manufacture of this bearing is more costly.

A different cage must be produced for each size of bearing having the torque transmitting rails so that the cage has only this specific use. This in turn means that the cage cannot be produced in large numbers by, for example, injection moulding in order to keep the unit cost down.

The subject of this invention is a linear recirculating rolling bearing in which the cage can be produced in large numbers and can be used for a bearing which transmits only radial loads and also for a bearing which can transmit torque between the shaft and housing as well. The assembly of this bearing is also simple.

The invention resides in the feature that the cage has slots which are all the same as each other.

By fitting one or more rails which can transmit torque into respective slots in the cage, a bearing is produced which can transmit radial loads and torque without the cage having to be modified.

The linear recirculating rolling bearing which can transmit only radial loads can be converted into one which can transmit torque as well simply be replacing one or more of the rails with torquetransmitting rails. Since the cage can be used for both types of bearing, large numbers of the cage can be produced and thus the unit cost kept low.

The cage may be disposed in the cylindrical bore of a housing and all the rails contact and conform to the bore surface. This construction is economical to manufacture since the rails can be easily shaped to conform with the bore surface.

Also the radial distance of the raceway surface of each rail from the shaft can be adjusted by altering the radial thickness of the rail.

One of the rails may have two radially opposed longitudinal raceway surfaces, which rail can be disposed in its slot in either one of two positions, in one position the rail provides the or one of the radially inwardly facing and offset longitudinal raceway surfaces and in the other position the rail provides a radially inwardly facing but not offset longitudinal raceway surface.

This feature means that all the rails can be made the same and the manufacture of the linear bearing and stock keeping of all the components-rails, cage and rolling bodies-are simplified. Also the bearing is easily adaptable, it being converted from one which can transmit only radial loads to one which can transmit also torque by simply turning over one or more rails so that the radially inwardly offset raceway surface of each rail faces radially inwardly. The reverse is also true, by simply turning over the torque transmitting rails so that the radially inwardly offset raceway surface of each of those rails faces radially outwardly.In the former condition, with the radially inwardly offset raceway surface of the or each of the torque transmitting rails facing radially inwardly, there must of course be a corresponding number of grooves in the shaft for rolling bodies as there are offset raceway surfaces.

In a construction in which there are at least three rails which transmit only radial forces, and these rails are evenly spaced in their respective grooves around the cage, and there are one or more torque transmitting rails having their radially inwardly offset raceway surfaces facing radially inwardly and the radial depth of the groove in the shaft for each torque transmitting rail in greater than the radial distance of the offset, then no radial force is transmitted by the or each torque transmitting rail from the shaft to the housing.

The at least three rails transmitting only radial forces guide the shaft centrally in the bore of the housing. Thus the or each torque transmitting rail can transmit relatively high torques since it does not or they do not have to transmit radial forces as well.

The cage may be disposed in the bore of a housing and one rail may provide the radially inwardly offset raceway surface, which rail has a radially outwardly extending projection engaging in a recess in the bore of the housing. With this construction the torque forces can be transmitted directly between the rail and the housing so that the relatively delicate cage is not loaded.

Additionally the projection may extend longitudinally and provide a radially outwardly facing longitudinal raceway surface. Thus a simple and economic construction is provided in which the rail is reversible and also is able to transmit torque.

The radially inwardly offset raceway surface may be of open channel section. With this feature, the circumferential forces transmitted by the shaft through the rolling bodies to the torque transmitting rail are taken up by the side walls of the channel raceway surface. This means that greater torques can be transmitted by the bearing.

One of the rails may have two radially opposed longitudinal raceway surfaces each formed as a longitudinal groove, which rail can be disposed in its slot with either one of the two raceway grooves facing radially outwardly, and at least one pin may extend through the housing and its radially inner end conform in shape and size to and engage in the radially outwardly facing raceway groove of the rail to prevent relative rotation between the housing and the cage. The construction provides a relatively simple means of holding the rail, which is able to transmit radial forces and/or torque, rotationally stationary relative to the housing.

The radially inwardly offset longitudinal raceway may be provided by a strip of material secured to one of the rails. This feature enables all the rails to be of the same size and shape and so they can be produced in large numbers thus keeping their cost down.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which: Figure 1 is a section on I-I of the linear recirculating rolling bearing shown in Figure 2; Figure 2 is a partial longitudinal section of the linear recirculating rolling bearing shown in Figure 1;and Figures 3, 4 and 5 are each part of a crosssection of different linear recirculating rolling bearings.

The linear recirculating rolling bearing shown in Figures 1 and 2 comprises a sleeve or housing 10 having a cylindrical bore 1 an annular cage 12 disposed in the bore 11 and a shaft 13 extending through the bore of the cage 12.

The cage 12 is a two part cage having an outer part 14 and an inner part 15, both made from an elastic material such as plastics by injection moulding. The two parts 14 and 1 5 are assembled by pushing them together axially and they fit together in a known manner.

The cage 12 has six evenly circumferentially spaced longitudinally extending slots 1 6 in its radially outer surface, each slot being the same as the other. Into the slots 1 6 are fitted, one into each slot, rails 1 7.

Each rail 1 7 has a groove in each of its sides into which snap projections from the sides of the slot of the cage to hold the rails in place. Each rail 1 7 is symmetrical and has a longitudinal groove 1 8 in its convexly curved radially inwardly facing surface and a longitudinal groove 1 9 in its convexly curved radially outwardly facing surface, the radially outwardly facing surface of each rail bearing on the bore 11 of the housing 20.

The linear recirculating rolling bearing has a plurality (six in this embodiment) of endless paths.

In each path are accommodated a plurality of rolling bodies 20-balls in this embodiment and all of the same size-for recirculation between a first longitudinally extending portion 21 of the path and a second longitudinally extending portion 22 of the path. The two portions 21 and 22 are interconnected at each end by reversal portions 23.

In the first portion 21 of each path, in use of the bearing, the balls 20 are subject to loads directed radially of the cage 12 and in the second portion 22 of each path, in use of the bearing, the balls 20 are not subject to loads directed radially of the cage. For five of the paths, in the first portion 21 of the path, and in use of the bearing, the balls 20 run on the outer surface of the shaft 13 and in the groove 18 of the respective rail 17.

In the final path, the rail 17 has a strip 24 of material such as steel, secured by for example adhesive, to the radially inwardly facing surface of the rail, which strip provides a longitudinal groove 25 radially inwardly offset by an amount A from the grooves 1 8 of the other rails. The balls 20 which, in use, of the bearing, roll in the groove 25 also roll in a longitudinal groove 26 provided in the outer surface of the shaft 1 3. The radial depth of the groove 26 in the shaft 13 is equal to the radial offset A of the groove 25. The rail 17 plus the strip 24 can thus transmit torque as well as radial loads. The other rails 17, being symmetrical, can be turned over so that when the wear on groove 18 is unacceptable, the rail can be turned over to present the groove 19 for the balls 20 to roll on. This prolongs the useful life of the rails 1 7.

The housing 10 has two longitudinally aligned and spaced radially extending bores 27 and two pins 28 are disposed one in each bore. The radially inner end 29 of each pin 28 is of the same shape and size as and engages in the groove 1 9 in the radially outwardly facing surface of the rail 1 7 having the strip 24. Thus relative rotation between the cage 12 and the housing 10 is prevented.

In the outer end of each bore 27 an elastic pad 30 of, for example, plastics is secured abutting the radially outer end of the pin 28 and urging the pin radially inwardly into the groove 19 of the rail 17 having the strip 24. In the event of a very high torque being transmitted through the rail 17 having the strip 24, the pin 28 is pushed by the circumferential forces acting on the inner end 29 outwardly against the pad 30. The inner end 29 of the pin 28 is thus forced out of the groove 19 in the rail 1 7 having the strip 24 so leaving the cage 1 2 free to rotate. This then provides a safety measure preventing large torques from overloading the rail 1 7 having the strip 24.

Figure 3 shows part of a linear recirculating rolling bearing similar to that of Figures 1 and 2 and includes a sleeve or housing 31 with a cylindrical bore 32, a two part annular plastics cage 33 and a shaft 34. The cage 33 has a plurality of longitudinal slots 35 in its radially outer surface, each the same as the other, and longitudinal rails 36 are disposed one in each of all but one of the slots, a rail 37 being disposed in the last slot. Rails 36 are symmetrical and the radially inwardly and outwardly facing surfaces 38 and 39 respectively are concave in section with the radially inner surface 38 co-axial with the shaft. Rail 37 is symmetrical, has longitudinal radially inwardly and outwardly extending projections 40 and 41 respectively each having a groove 42, 43 in its radially facing surface.The radially outwardly extending projections 41 engages in a longitudinal groove 44 in the bore 32 of the housing 31. The groove 42 in the projection 40 is radially inwardly offset, by an amount B, from the surfaces 38 of the rails 36, and is radially aligned with a longitudinal groove 45 in the shaft 34. The radial depth of the groove 45 is the same as or greater than the amount of radial offset B.

Balls 46 are accommodated for recirculation between first and second longitudinally extending portions of endless paths. In the first longitudinally extending portion of all the paths but one, the balls 46 roll on the radially outer surface of the shaft 34 and on the radially inner surface 38 of the respective rail 36 and transmit loads radially between the shaft and the rail, the rail transmitting loads radially between the balls and the housing 31. In the remaining endless path, the balls 46 in the first portion roll in the grooves 42 and 45 in the projection 40 of the rail 37 and in the shaft 34 respectively.

The rail 37 can transmit torque, and if the amount of radial offset B is the same as the radial depths of the groove 45 in the shaft 34, then the rail 37 can transmit radial loads as well. The rails 36 can transmit only radial loads.

A small rotational movement of the shaft 34 relative to the housing 31 may take place because, for example, of a change in direction of rotation of the torque being transmitted, and this small rotational movement can be accommodated by the balls 46 rolling circumferentially on the shaft 34 and on the concave surface 38 of the rails 36.

Since the rails 36 and 37 are symmetrical they can be turned over to present the other raceway surfaces 39 and 43, for the balls 46 to roll on.

The linear recirculating rolling bearing shown in Figure 4 comprises a sleeve or housing 47 having a circular bore 48, an annular two part plastics cage 49 disposed in the bore 48 of the housing 47, and a shaft 50 disposed in the bore of the annular cage 49. The bearing includes a plurality of endless paths and a plurality of rollers 51 are accommodated for recirculation between first and second longitudinally extending portions 52 and 53 of each path. In the first portion 52 of each path, in use of the bearing, the rollers 51 are subject to loads directed radially of the bearing and in the second portion 53 of each path, in use of the bearing, the rollers 51 are not subject to loads directed radially of the bearing.

Each roller 51 is the same shape and size as the others and has a central waisted portion 54, formed as the rotation of an arc, of the same radius as the shaft 50, about an axis, and cylindrical portions 55 extending one from each end of the waisted portion 54.

The cage 49 has a plurality of longitudinal slots 56 in its radially outer surface, all the same as each other and opening one into the first portion 52 of each path. A plurality of longitudinal rails 57 and 58 are disposed in the slots 56, rails 57 one in each of all but one of the slots 56 and rail 58 in the remaining slot. All the rails 57 and 58 have longitudinal grooves in their sides and the slots 56 have projections which snap into the grooves to hold the rails in place.

The rails 57 are symmetrical and each has an open channel section groove 59 in its radially inwardly facing surface and an open channel section groove 60 in its radially outwardly facing surface. In all but one of the endless paths, the rollers 51 in use of the bearing roll in the first portion 52 of each path on the cylindrical outer surface of the shaft 50 and in the channel section groove 59 in the rail 57. There is line contact between the centre waisted portion 54 of each of the rollers 51 and the cylindrical surface of the shaft 50, and line contact between each cylindrical end portion 55 of each of the rollers and the flat base of the open channel section grooves 59 in the rails 57.The rails 57 bear against the bore 48 of the housing 47 and so in use of the bearing radial loads are transmitted between the shaft 50 and the rollers 51, between the rollers 51 and the rails 57, and between the rails 57 and the housing 47.

The rail 58 is also symmetrical but is radially deeper than the rails 57. The rail 58 has an open channel section groove 61 in its radially inwardly facing surface and an open channel section groove 62 in its radially outwardly facing surface.

The rail 58 extends radially outwardly and engages in a longitudinal groove 63 in the bore 48 of the housing 47. The radially inner channel groove 61 in the rail 58 is radially inwardly offset relative to the grooves 59 in the rails 57, and is radially aligned with a longitudinal open channel section groove 64 in the shaft 50. In the first portion 52 of the remaining path the rollers 51, in use of the bearing, roll in the groove 61 in the rail 58 and in the groove 64 in the shaft 50. A leaf spring 79 is arranged in the groove 63 in the bore 48 of the housing 47 and engages the outer groove 62 in the rail 58, pressing the rail radially inwardly against the rollers 51, so that the rollers 51 are guided without play between the rail 58 and the shaft 50.

Torque is transmitted between the shaft 50 and the rollers 51 in the groove 64 in the shaft, between those rollers 51 and the rail 58 and between the rail 58 and the housing 47.

Since all the rails 57 and 58 are symmetrical they are reversible and since the slots 56 are the same a rail 57 can be replaced by a rail 58 and vice versa.

The linear recirculating rolling bearing shown in Figure 5 comprises a sleeve or housing 65 having a cylindrical bore 66, an annular one piece plastics cage 67 in the bore 66 of the housing, and a shaft 68 extending through the bore of the cage.

The bearing comprises a plurality of endless paths and a plurality of balls 69 are accommodated in each path for recirculation between a first longitudinally extending portion 70 and a second longitudinally extending portion (not shown). In the first portion 70 in use of the bearing the balls 69 are subject to loads directed radially of the bearing, and in the second portion in use of the bearing the bails 69 are not subject to such loads. The cage 67 has a plurality of longitudinal slots 71 in its radially outer surface opening one into the first portion 70 of each path, all the slots being the same. A plurality of longitudinal rails (not shown) and rail 72 are disposed one in each slot 71 and bear against the cylindrical bore 66 of the housing 65.Each rail (not shown) and rail 72 has longitudinal grooves one in each side, and each slot 71 has projections which snap into each groove and hold the rail in the slot.

In all the paths but one, in the first portion 70 the balls 69 roll on the cylindrical surface of the shaft 68 and against the rail (not shown) so that radial loads are transmitted between the shaft 68 and the balls 69, between the balls 69 and the rail (not shown) and between the rail (not shown) and the housing 65.

Rail 72 has radially opposed open channel section longitudinal grooves 73 and opposed to the radially inner longitudinal groove is a longitudinal groove 74 in the shaft 68. The radially inner groove 73 in the rail 72 is radially inwardly offset relative to the grooves in the other rails (not shown). In the remaining path, the balls 69 in the first portion, in use of the bearing, roll in grooves 73 and 74 in the rail 72 and shaft 68 respectively.

The housing 65 has a radial aperture 75, and a pin 76 extends radially through the aperture and engages in the radially outer groove 73 in the rail 72. The cage 67 is thus prevented from rotating relative to the housing 65 and so torque can be transmitted between the shaft 68 and the balls 69 in the groove 74 in the shaft, between those balls 69 and the rail 72, between the rail and the pin 76 and between the pin and the housing 65.

The rail 72 can be reversed so that the balls 69 can roll along the outer cylindrical surface of the shaft 68. For this to be done a longitudinal recess 77 must be cut in the bore 66 of the housing 65.

The torque-transmitting rail 72 as shown in Figure 5 can then be converted into a rail transmitting only radial loads and engaging in the longitudinal recess 77 in the bore 66 of the housing 65 and thus preventing relative rotation between the cage 67 and the housing.

Claims

1. A linear recirculating rolling bearing comprising a cage providing a plurality of endless paths in each of which is accommodated a plurality of rolling bodies for recirculation between a first longitudinally extending portion of the path in which, in use of the bearing, the rolling bodies are subject to loads directed radially of the cage and a second longitudinally extending portion of the path in which, in use of the bearing, the rolling bodies are not subject to loads directed radially of the cage, the cage having a plurality of longitudinally extending slots in its radially outer surface, which slots open one into the first portion of each path, and a plurality of rails are disposed longitudinally of the cage and one in each slot, each rail providing a longitudinal radially inwardly facing raceway surface for rolling bodies to roll along in the first portion of the paths and transmit loads radially of the cage, and the rolling bodies in the first portion of at least one path are arranged to roll along a longitudinal raceway surface offset radially inwardly relative to the raceway surfaces of the first portions of other paths, wherein the slots are all the same as each other.

2. A bearing as claimed in claim 1, wherein the cage is disposed in the cylindrical bore of a housing and all the rails contact and conform to the bore surface.

3. A bearing as claimed in claim 1 or 2, wherein one of the rails has two radially opposed longitudinal raceway surfaces, which rail can be disposed in its slot in either one of two positions, in one position the rail provides the or one of the radially inwardly facing and offset longitudinal raceway surfaces and in the other position the rail provides a radially inwardly facing but not offset longitudinal raceway surface.

4. A bearing as claimed in claim 1, wherein the cage is disposed in the bore of a housing and one rail provides the radially inwardly offset raceway surface, which rail has a radially outwardly extending projection engaging in a recess in the bore of the housing.

5. A bearing as claimed in claim 4, wherein the projection extends longitudinally and provides a radially outwardly facing longitudinal raceway surface.

6. A bearing as claimed in any preceding claim, wherein the radially inwardly offset raceway surface is of open channel section.

7. A bearing as claimed in claim 2, wherein one of the rails has two radially opposed longitudinal raceway surfaces each formed as a longitudinal groove, which rail can be disposed in its slot with either one of the two raceway grooves facing radially outwardly, and at least one pin extends through the housing and its radially inner end conforms in shape and size to and engages in the radially outwardly facing raceway groove of the rail to prevent relative rotation between the housing and the cage.

8. A bearing as claimed in claim 1, wherein the radially inwardly offset longitudinal raceway surface is provided by a strip of material secured to one of the rails.

9. A linear recirculating rolling bearing substantially as herein described with reference to and as shown in Figures 1 and 2, or with reference to and as shown in Figure 3, or with reference. to and as shown in Figure 4, or with reference to and as shown in Figure 5 of the accompanying drawings.

10. Rolling bearing, provided with endless rolling body rows distributed on the circumference, for longitudinal movements of a machine part or the like on a shaft, comprising a cage sleeve with radially outwardly throughpassing openings arranged on its circumference, in each of which there is inserted a loaded accommodating track rail per rolling body row, the loaded rolling bodies of each rolling body row being arranged between a longitudinally extending, radially inwardly facing track of the relevant track rail and the shaft, characterised in that the rolling bodies of all rolling body rows of the cage sleeve have one and the same diameter and in that at least one of the track rails inserted into the mutually similarly formed openings of the cage sleeve is provided, for the transmission of a torque, with a track offset radially inwards in relation to the tracks on the other track rails.

11. Rolling body according to claim 10, characterised in that the cage sleeve is surrounded by a housing with a cylindrical bore on which all the track rails of the cage sleeve are arranged in radially supporting manner.

12. Rolling bearing according to claim 10 or 11, characterised in that at least one of the track rails comprises, as well as a track conforming with the form and position of the tracks of the other track rails, the radially offset track on the radially opposite side and in that this track rail is insertable according to choice with the one or the other track facing radially inwards into one of the openings of the cage sleeve.

13. Rolling bearing according to one of the preceding claims 10, 11 and 12, characterised in that the track rail provided with the radially offset track comprises at least one radially outwardly facing projection held fast on the circumference in a radial depression in the housing.

14. Rolling bearing according to claims 12 and 13, characterised in that a single radial projection extending in the longitudinal direction on at least one track rail carries the radially outer track of this track rail.

1 5. Rolling bearing according to one of the preceding claims 10 to 14, characterised in that at least the radially inwardly offset track is made in channel form.

1 6. Rolling bearing according to one of the preceding claims 10 to 15, characterised in that at least one pin directed radially inwards in the housing is made fast in the circumferential direction, and its radially inwardly pointing end is arranged engaging in shape-locking manner in the outer track of a track rail of the cage sleeve.

1 7. Rolling bearing according to one of the preceding claims 10 to 16, characterised in that the radial offsetting of the radially inwardly offset track of the torque-transmitting track rail is produced by a layer, for example sheet metal, secured on the track of the other track rails, with a thickness corresponding to this offsetting.