WO1999056029A1

WO1999056029A1 - Cage with improved mass distribution, and ball bearing comprising such cage

Info

Publication number: WO1999056029A1
Application number: PCT/NL1999/000251
Authority: WO
Inventors: Yannick Pierre Hubert Fierling
Original assignee: Skf Engineering & Research Centre B.V.
Priority date: 1998-04-28
Filing date: 1999-04-28
Publication date: 1999-11-04
Also published as: AU3540099A; NL1009025C2

Abstract

A cage for a ball bearing comprises a ring-shaped element provided with prongs (2, 3) which extend with respect to the ring-shaped element (1), cage pockets (4) being enclosed between adjacent pairs of prongs (2, 3), and said pairs of prongs each defining an opening (5) through which a ball element may be accommodated in the cage pocket (4) by snapping in in the axial direction with respect to the ring-shaped element, said ring-shaped element having opposite sides (16, 17) facing away from each other in axial direction with respect to said element (1), and the prongs (2, 3) being situated on one side of the ring-shaped element. The other side (16) of the ring-shaped element (1), facing away from said one side (16), is provided with recesses (13), each of said recesses (13) being located between two adjacent cage pockets (4) and stretching over the full thickness in the radial direction of the ring-shaped element (1).

Description

1

Cage with improved mass distribution, and ball bearing comprising such cage

The invention is related to a cage for a ball bearing, comprising a ring-shaped element provided with prongs which extend with respect to the ring-shaped element, cage pockets being enclosed between adjacent pairs of prongs, and said pairs of prongs each defining an opening through which a ball may be accommodated in the cage pocket by snapping in in the axial direction with respect to the ring-shaped element, said ring-shaped element having opposite sides facing away from each other in axial direction with respect to said element, and the prongs being situated on one side of the ring-shaped element.

Such cage, which is generally known, and the balls are assembled by pressing them together, such that said balls all at the same time snap into the respective pockets. The pockets are shaped in such a way that the cage is fully supported by the balls, which means that no direct contact between the cage and the inner ring or outer ring of the bearing exists.

By means of the cage, the balls are held at predetermined intervals. In turn, the cage is supported by the balls in such a way that no contact exists between the cage and the rings of the bearing in question. As a result of the engagement of the cage with all balls, the cage is subjected to varying load. Said loads are caused by the conditions to which the bearing as a whole is subjected, i.e. misalignment and the loads on the (rotating) inner ring such as radial thrust load and acceleration. These conditions lead to the development of a pattern of contact forces between the cage, in particular the cage pockets, and the associated balls.

In service of the bearing in question, the cage is rotated together with the rotating movement of the balls around the axis of the bearing. As a result, the cage is exposed to centrifugal forces due to its rotational movement, and to impacts caused by the relative motions of the balls in the respective cage pockets. Having an offset between the centre of mass of the cage and the center-line of the bearing is an important factor of the cage instability. This offset creates wobbling and whirl. This unstable running behaviour leads to additional impact forces between the balls and the cage. As a result, the performance of the bearing is deteriorated, and the cage is subjected to excessive wear. 2

The object of the invention is to provide a ball guided cage for a ball bearing which has a better performance. This object is achieved in that the other side of the ring-shaped element, facing away from said one side containing the prongs, is provided with recesses, each of said recesses being located between two adjacent cage pockets and stretching over the full thickness in the radial direction of the ring- shaped element.

As a consequence of the particular, radially extending recesses of the cage according to the invention, several advantages are obtained.

First of all, in comparison to the prior art cages, the side of the cage opposite the side where the cage pocket openings are situated, has a reduced mass, which means that the centre of gravity of the cage is shifted more towards the centre of the bearing center-line.

As a result, the offset between the centre of mass of the cage and the bearing center-line is smaller. Consequently, a more stable running behaviour is obtained. According to a further advantage, the radially running recesses provide a relative flexibility of the ring-shaped element, in the areas between the cage pockets. This flexibility plays a role with respect to the behaviour of the cage at the stage of snapping in the balls into the corresponding cage pockets. Also, said flexibility influences the holding capacity of the cage pockets. In particular the force which is exerted by the prongs on a ball in the corresponding cage pocket, which force determines the holding capacity, depends to some extend on the flexibility of the cage.

As an illustration, in case the ring-shaped element of the cage has a high stiffness, the prongs themselves should be able to deform sufficiently upon snapping in a ball into the corresponding cage pockets. This entails a certain level of flexibility of the prongs. Said flexibility should however not become too exaggerate, as the holding capacity of the prongs would decrease therewith.

In prior art cages, the required flexibility is obtained by providing prongs having a relatively great length. Shorter prongs are too stiff, and would give rise to unacceptable stress concentrations at specific spots in the cage pockets when snapping the balls into the pockets, leading to early failure of the cage.

By providing some of the flexibility, which is necessary for pressing in the balls, in the ring-shaped element, the prongs can be made somewhat stiffer, and 3 therefore shorter, without causing too high stress concentrations upon snapping in of the balls in the cage pockets.

The circumstance that the prongs can be made somewhat shorter brings an additional advantage, in that it also influences the mass distribution of the cage. In particular, the parts of the ring-shaped element which are situated between the cage pockets can now be made to lie further towards the side of the ring-shaped element where the prongs extend. Such lay-out brings an extra shift of the centre of gravity of the cage mass towards the centres of the pockets, which centres defines the plane in which the supporting forces exerted by the balls on the cage are situated. Said circumstance can be distinguished in particular in an embodiment wherein the prongs each extend from an intermediate prong body, said intermediate prong bodies being situated between two adjacent cage pockets each, and at least one prong body being provided with a recess. Said intermediate prong bodies are connected to the roots of two adjoining prongs, a recess being provided in said prong body at the side thereof facing away from the prongs.

In axial direction, the root of each prong is at a distance from the bottom of the cage pockets, said bottom lying opposite the opening defined by the prongs.

By selecting a design wherein the roots of the prongs are at a relatively large distance of the cage bottom, the optimal combination of mass distribution and supporting forces for the cage may be obtained.

As an approximation, the dimension of a prong in axial direction is about the same as the depth in axial direction of a recess.

In a particular embodiment, which has advantages from the point of view of manufacturing the bearing, each recess has a relatively deep, central part, and by two radially opposed, relatively shallow parts, which enclose the central part. This embodiment also has the advantage that a proper balance is ensured between the required holding capacity of the prongs on the balls, and the necessary flexibility for snapping in the balls into said cage pockets.

The invention is furthermore related to a ball bearing, comprising an inner ring, an outer ring which each define a raceway, a set of balls which are in rolling contact with the raceways of the rings, and a cage, comprising a ring-shaped element provided with prongs which extend with respect to the ring-shaped element, cage pockets being enclosed between adjacent pairs of prongs, and said pairs of prongs 4 each defining an opening through which a ball element may be accommodated in the cage pocket by snapping in in the axial direction with respect to the ring-shaped element, said ring-shaped element having opposite sides facing away from each other in axial direction with respect to said element, and the prongs being situated on one side of the ring-shaped element, said cage being supported by the balls accommodated in the cage pockets, in such a way that no supporting contact exists between the cage and the rings.

According to the invention, the other side of the ring-shaped element, facing away from said one side, is provided with recesses, each of said recesses being located between two adjacent cage pockets and stretching over the full thickness in the radial direction of the ring-shaped element.

The invention will now be described further with reference to the figures.

Figure 1 shows a cage according to the invention, in perspective view.

Figure 2 shows a developed view of a part of the cage, together with balls. Figure 3 shows a bearing with axis and center-line.

The cage shown in figure 1 comprises a ring-shaped element, provided with pairs of prongs 2, 3, whereby each pair of prongs 2, 3 encloses a cage pocket. Said cage is coaxial to the axis 21 of the bearing into which the cage is to be applied (see figure 3). Between adjoining prongs 2, 3 of adjoining cage pockets, prong bodies 9 have been provided. The prongs 2, 3 have a root 10 at the level of the axial sides 16 of the ring-shaped element 1.

At the other axial side 17 of the ring-shaped element, the prong bodies 9 have recesses 13, which run the full thickness in radial direction of the ring-shaped element 1.

As shown in figure 2, each recess 13 may comprise a relatively deep central part 14, enclosed between more shallow, radially opposed parts 15.

The recesses 13, 14, 15 provide the ring-shaped element 1 with a certain amount of flexibility, which is helpful for snapping in the balls 6 in their respective cage pockets 4.

As a result of this flexibility, the prongs 2, 3 themselves may be carried out somewhat shorter and thereby stiffer. Despite of this short dimension of the prongs 2, 3, no unacceptable stress concentration, when snapping the ball into pocket, would 5 occur within the wall of the cage pockets 4, thanks to the flexibility added by the recesses 13-15.

The particular embodiment of the present cage with the recesses 13-15, provides the advantage that the centre of gravity of the cage comes rather close to the bearing center-line 20, as defined in figure 3. Thus, upon rotation the cage is loaded advantageously by the balls and the centrifugal forces, that is without large disturbing forces. Thereby, a smooth running behaviour is ensured.

A result of the fact that the prongs 2, 3 can be relatively short, the axial side 16 of the prong bodies 9 may extend rather far into the direction of the openings 5 of the cage pockets 4. Thereby as well, a advantageous effect of the centre of gravity of the cage is obtained.

The dimension of the recesses 13, in particular of the shallower part 15 thereof, has been indicated by letter a, the dimension in axial direction of the prongs have been indicated by b. The dimensions a and b may be of the same order of magnitude, so as to obtain the desired effect. According to the invention, each cage pocket 4 may be considered to be comprised of a holding element, which holding elements are mutually connected by bridge elements which comprise the prong bodies 9 and prongs 2, 3. Said holding elements extend further in axial direction than said bridge elements.

Alternatively, the dimensions a and b may be inversely proportional, in the sense that a may become relatively large and b relatively small.

Claims

6Claims

1. Cage for a ball bearing, comprising a ring-shaped element (1) provided with prongs (2, 3) which extend with respect to the ring-shaped element (1), cage pockets (4) being enclosed between adjacent pairs of prongs (2, 3), and said pairs of prongs (2, 3) each defining an opening (5) through which a ball element (6) may be accommodated in the cage pocket by snapping in in the axial direction with respect to the ring-shaped element (1), said ring-shaped element (1) having opposite sides (16, 17) facing away from each other in axial direction with respect to said element, and the prongs (2, 3) being situated on one side (16) of the ring-shaped element (1), characterized in that the other side (17) of the ring-shaped element (1), facing away from said one side (16), is provided with recesses (13), each of said recesses (13) being located between two adjacent cage pockets (4) and stretching over the full thickness in the radial direction of the ring-shaped element (1).

2. Cage according to claim 1, wherein the prongs (2, 3) each extend from an intermediate prong body (9), said intermediate prong bodies (9) being situated between two adjacent cage pockets (4) each, and at least one prong body (9) being provided with a recess (13).

3. Cage according to claim 2, wherein each intermediate prong body (9) is connected to the roots (10) of two adjoining prongs (2, 3), a recess (13) being provided in said prong body (9) at the side thereof facing away from the prongs (2, 3).

4. Cage according to claim 3, wherein, in axial direction, the root (10) of each prong (2, 3) is at a distance from the bottom (11) of the cage pockets (4), said bottom (11) lying opposite the opening (5) defined by the prongs (2, 3).

5. Cage according to claim 3 or 4, wherein the dimension b of a prong (2, 3) in axial direction is about the same as the depth a in axial direction of a recess (13). 7

6. Cage according to claim 3 or 4, wherein the dimension b of a prong (2, 3) in axial direction is about inversely proportional to the depth a in axial direction of a recess (13).

7. Cage according to any of claims 2-6, wherein each recess (13) has a relatively deep, central part (14), and by two radially opposed, relatively shallow parts (15), which enclose the central part (14).

8. Cage according to any of the preceding claims, wherein between all adjacent cage pockets (4), recesses (13) have been provided.

9. Ball bearing, comprising an inner ring, an outer ring which each define a raceway, a set of balls which are in rolling contact with the raceways of the rings, and a cage according to any of the preceding claims, comprising a ring-shaped element (1) provided with prongs (2, 3) which extend with respect to the ring-shaped element (1), cage pockets (4) being enclosed between adjacent pairs of prongs (2, 3), and said pairs of prongs (2, 3) each defining an opening (5) through which a ball element (6) may be accommodated in the cage pocket by snapping in in the axial direction with respect to the ring-shaped element (1), said ring-shaped element (1) having opposite sides facing away from each other in axial direction with respect to said element, and the prongs (2, 3) being situated on one side of the ring-shaped element (1), said cage being supported by the balls accommodated in the cage pockets, in such a way that no supporting contact exists between the cage and the rings, characterized in that the other side of the ring-shaped element (1), facing away from said one side, is provided with recesses (13), each of said recesses (13) being located between two adjacent cage pockets (4) and stretching over the full thickness in the radial direction of the ring-shaped element (1).

10. Cage for a ball bearing, said cage comprising a ring-shaped element (1) which has two axial sides (16, 17) and which comprises consecutive holding elements, each defining a cage pocket (4) opening out on a first side (16) of the ring- shaped element (1), and bridge elements (9) each connecting two adjacent holding 8 elements, characterized in that, at the second axial side (17) the holding elements extend further in axial direction than the bridge elements (9).