WO2012160028A1

WO2012160028A1 - Lightweight bearing

Info

Publication number: WO2012160028A1
Application number: PCT/EP2012/059384
Authority: WO
Inventors: Richard Schaake
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2011-05-20
Filing date: 2012-05-21
Publication date: 2012-11-29
Anticipated expiration: 2013-11-20
Also published as: WO2012160026A1

Abstract

The invention relates to a rolling element bearing (1) comprising an outer bearing ring (2) and an inner bearing ring (3), wherein rollers (4) are arranged between the bearing rings (2, 3). Each bearing ring is predominantly made of a polymer material, wherein a raceway (5, 6) for the rollers (4) is established by at least one raceway element (7, 8) which is connected with the outer bearing ring (2) and/or with the inner bearing ring (3). To obtain a light but stable design of the bearing, the invention proposes that the raceway element (7, 8) consists of at least two layers (9, 10), wherein a first layer (9) being remote from a raceway surface (11) comprises a carbon fiber material (12) and wherein a second layer (10) forming the raceway surface (11) comprises a lightweight material with good tribological properties.

Description

Lightweight Bearing

Technical Field

The invention relates to a rolling element bearing comprising a bearing ring that is made of a polymer base body, which has a raceway element made of a different material that is joined to the polymer base body.

Background

Rolling element bearings of the kind mentioned above are well known in the art. One example is known from US5845998, which discloses a ball bearing assembly comprising a polymer outer bearing ring that is moulded over and partially encloses a metal annular outer raceway. The metal raceway ensures that the bearing has sufficient stability and durability to guarantee a proper operation and a satisfactory bearing life. By this design, the weight of the rolling element bearing can be reduced significantly as a relatively light material can be used for the base bodies of the bearing rings. Only the raceway elements are made of steel. With respect to the question of weight of the rolling element bearing, the raceway element made of sheet metal has disadvantages as the weight of the sheet metal element is still quite high. It is an o b j e c t of the present invention to propose a rolling element bearing of the kind mentioned above which has a comparable stiffness and durability but which is significantly lighter.

Summary of the invention

A s o l ut i o n according to the invention is characterized in that the raceway element consists of at least two layers, wherein a first layer - being remote from a raceway surface - comprises a carbon fiber material and wherein a second layer - forming the raceway surface - comprises a lightweight material with good tribological properties. A material with good tribological properties is to be understood as a wear-resistant material.

According to a preferred embodiment, the second layer is formed by or comprises aramid, specifically aramid fibers, which are embedded in polyamide (PA).

In further embodiment, the second layer is formed by a layer of ceramic material.

In a still further embodiment, the second layer is formed by or comprises polyethylene (PE) or polytetrafluorethylene (PTFE), specifically polyethylene (PE) or polytetrafluorethylene (PTFE) fibers, which are embedded in polyamide (PA). The polyamide is preferably polyamide PA 6.6 (trademark "Nylon") or PA 6. The polyamide can contain glass fiber material. The carbon fiber material of the first layer is preferably arranged in a corrugated manner when seen in an axial direction of the raceway element. The carbon fiber material is preferably a two-dimensional plane material which is folded into the corrugated shape. The corrugated carbon fiber material can have sections running perpendicular to the raceway surface; alternatively the sections can run under a small angle of up to 30° relative to the perpendicular. Preferably, the corrugated carbon fiber material has a substantially rectangular shape, seen in the axial direction of the raceway element.

The carbon fiber material is suitably embedded in a thermoplastic material, specifically in polyamide (PA), especially in polyamide PA 6.6 or polyamide PA 6. The first layer and the second layer of the raceway element can be joined to each other in situ by an injection moulding process. Preferably, the base body of the bearing ring is moulded to the raceway element in the same moulding process. Alternatively, the raceway element can be bonded to the bearing ring, especially by means of an adhesive.

The base body of the inner bearing ring and/or the outer bearing ring can consist of polyamide (PA), especially of polyamide PA 6.6. Thus, the bearing becomes very light. A further embodiment for ensuring a low weight of the bearing is that the rolling elements consist of ceramic material.

Thus, the above proposal suggests the replacement of a sheet metal raceway element by a combination of a tribological layer supported by a carbon fiber composite foundation.

The stiffness of the carbon fiber composite foundation is significantly improved by the mentioned corrugation, especially linear corrugation, of the fibers. The corrugating or folding process can be done with conventional manufacturing techniques. For the production of the corrugated structure, preferably a woven cloth or unidirectional prepreg of carbon fiber material is employed which is then folded to the desired shape. The carbon fiber material can be a prepreg. The carbon fiber can be a single tow or tape.

A carbon fiber material is preferred which has at least 1 % strain at break. The yarn may be twisted to improve and to facilitate the folding process.

With respect to the tribological layer, aramid embedded in polyamide (PA) is preferred which is overmoulded with polyamide PA 6.6 with glass fibers. Aramid fibers have a good compatibility with polyamide. But also other materials can be used like polyethylene (PE) or polytetrafluorethylene (PTFE). In the latter case it has to be stated that the compatibility is not as good as in the case of aramid.

The orientation of the corrugation is important to improve the stiffness of the rolling element bearingin the desired load or stress direction. Basically, it is aimed to orient the corrugated carbon fiber material so that the bending stiffness of the raceway is increased. If fibers in the second layer are employed, they are preferably oriented in the rolling direction and have a lower stiffness than the carbon fibers. Furthermore, they have preferably good anti-wear and fatigue properties. Those fibers in the tribological layer should have a sufficient elasticity to transverse compressive loads and are therefore preferably polymer fibers.

The raceway thickness depends on the selection of the carbon fibers, of the tribological material and the contact geometry and distance of the corrugated structure, i. e. between the folded carbon fibers sections. The thickness should be as thin as possible as to distribute the contact load across several carbon fibers to avoid stress concentrations.

Basically, the proposal can be employed for all kinds of bearings (ball bearings and roller bearings). Preferred applications are such bearings which have low hoop stresses during operation. Also a beneficial manufacturing becomes possible when the bearing parts (bearing rings) are made of a polymer material, e. g. polyamide PA 6.6 with glass fibers. The proposed roller (or ball) bearing is preferably employed in such applications in which a very low weight of the bearing is required which must have a high stability and durability.

Brief description of the drawings

The drawings show an embodiment of the invention.

Fig. 1 shows a radial cross section through a rolling element bearing and Fig. 2 shows an enlarged view of cross section A-B according Fig. 1 without rolling elements.

Detailed description of the invention

In Fig. 1 a rolling element bearing 1 - being an angular contact ball bearing in the present example - is shown. The bearing 1 has an outer bearing ring 2 and an inner bearing ring 3, between which rolling elements (balls) 4 are arranged in a well-known manner. The bearing rings 2, 3 are made of a polymer material; more specifically, polyamide PA 6.6 is used in which glass fibers are embedded. To establish a hard and durable outer raceway 5 in the outer bearing ring 2 and an inner raceway 6 in the inner bearing ring 3 for the balls 4, specially adapted raceway elements 7 and 8 provided on the bearing rings 2, 3.

The specific design of the raceway elements 7, 8 becomes apparent from Fig. 2, which shows an enlarged view of the section A-B according Fig. 1 of the bearing. Thus, the axial direction a stands perpendicular to the plane of projection.

Here, it can be seen that the inner raceway element 8 (the same applies for the outer raceway element 7) is a two layer element. A first layer 9 is arranged remote from the raceway surface 11 and a second layer 10 forms the raceway surface 11. The two layers are produced in situ by means of an injection moulding process. The first layer 9 comprises a carbon fiber material 12 which is corrugated in the depicted manner. This is a schematical depiction only, but a folded structure which is - as shown - substantially rectangular is preferred. That is, essentially linear sections 13 extending perpendicular to the raceway surface 11 and having a certain height h are connected by connection sections 14, so that a certain distance d between the linear sections 13 is established.

A perpendicular orientation of the sections 13 is not mandatory but an angle a of up to 30° between the orientation of the sections 13 and the perpendicular to the raceway surface 11 is preferred. In the depicted embodiment the angle a is very small (almost 0°).

The height h of the corrugated structure is preferably maximized to maximize the bending stiffness of the carbon fiber material 12. The distance d between the sections 13 is preferably minimized to distribute the contact forces in an optimal manner.

The space between the carbon fiber material 12 is filled with polymer material, in the present embodiment with polyamide (PA).

The second layer 10 is arranged on the first layer 9. The second layer functions as a tribological layer, i. e. the second layer 10 provides the raceway surface 1 1 and comprises a material with good tribological properties. This material with good tribological properties comprises presently aramid fibers, which are embedded in polyamide (PA). Polyamide can be used as the matrix material for the first and second layers of the raceway and as the material for the base bodies of the inner and outer bearing rings 2, 3, i. e. polyamide PA 6.6 in the present case. The two-layer raceway elements 8, 9 can be fixed with the base bodies of the bearing rings 2, 3 in a suitable manner. For example the raceway elements can be glued to the bearing rings. Also a form- fit connection can be contemplated. Preferably, the base body of the bearing ring is moulded to the raceway element.

Especially when used with ceramic rollers 4 a very light and stable rolling element bearing is obtained.

Reference Numerals:

1 Rolling element bearing

2 Outer bearing ring

3 Inner bearing ring

4 Rollers (balls)

5 Raceway

6 Raceway

7 Outer raceway element

8 Inner raceway element

9 First layer

10 Second layer

11 Raceway surface

12 Carbon fiber material

13 Linear section

14 Connection section a Axial direction h Height

d Distance a Angle

Claims

Patent Claims;

Rolling element bearing (1) comprising an outer bearing ring (2) and an inner bearing ring (3) between which rolling elements (4) are arranged, wherein at least one of the bearing rings (2, 3) comprises a base body made of a polymer material and wherein a raceway (5, 6) for the rolling elements (4) is established by at least one raceway element (7, 8) that is joined to the at least one bearing ring (2, 3), characterized in that the raceway element (7, 8) consists of at least two layers (9, 10), wherein a first layer (9) being remote from a raceway surface (11) comprises a carbon fiber material (12) and wherein a second layer (10) forming the raceway surface (11) comprises a lightweight material with good tribological properties.

Rolling element bearing according to claim 1, characterized in that the lightweight material with good tribological properties is or comprises aramid, specifically aramid fibers, which are embedded in polyamide (PA). Rolling element bearing according to claim 1, characterized in that the lightweight material with good tribological properties is or comprises polyethylene (PE), specifically polyethylene (PE) fibers, which are embedded in poly amide (PA).

Rolling element bearing according to claim 1, characterized in that the material with good tribological properties is or comprises polytetrafluorethylene (PTFE), specifically polytetrafluorethylene (PTFE) fibers, which are embedded in polyamide (PA).

5. Rolling element bearing according to one of claims 2 to 4, characterized in that the polyamide is polyamide PA 6.6 or polyamide PA 6.

6. Rolling element bearing according to claim 5, characterized in that the polyamide contains fiber material, especially glass fiber material.

7. Rolling element bearing according to one of claims 1 to 6, characterized in that the carbon fiber material (12) of the first layer (9) is arranged in a corrugated manner, viewed in the axial direction (a) of the raceway element (7, 8).

8. Rolling element bearing according to claim 7, characterized in that the carbon fiber material (12) is a two-dimensional plane material which is folded into the corrugated shape.

9. Rolling element bearing according to claim 7 or 8, characterized in that the corrugated carbon fiber material (12) has sections (13) running perpendicular to the raceway surface (1 1) or under an angle (a) of maximal 30° to the perpendicular of the raceway surface (11).

Rolling element bearing according to one of claims 7 to 9, characterized in that the corrugated carbon fiber material (12) has a substantially rectangular shape, viewed in the axial direction (a) of the raceway element (7, 8).

Rolling element bearing according to one of claims 7 to 10, characterized in that the carbon fiber material (12) is embedded in a thermoplastic material, specifically in polyamide (PA), especially in polyamide PA 6.6 or in polyamide PA 6.

Rolling element bearing according to one of claims 1 to 11, characterized in that the polymer material of the at least one bearing ring (2, 3) consists of polyamide (PA), especially of polyamide PA 6.6 or of polyamide PA 6.

Rolling element bearing according to one of claims 1 to 12, characterized in that the first and second layers (9, 10) are connected in situ by an injection moulding process.

14. Rolling element bearing according to one of claims 1 to 13, wherein the polymer material of the at least one bearing ring (2, 3) is joined to the at least one raceway element (7, 8) in a moulding process.

15. Rolling element bearing according to one of claims 1 to 13, characterized in that the raceway element (7, 8) is bonded to the at least one bearing ring (2, 3), especially by means of an adhesive.

Rolling element bearing according to one of claims 1 to 15, characterized in that the rolling elements (4) consist of ceramic material.