WO2015166100A2

WO2015166100A2 - Bearing assembly with integrated generator

Info

Publication number: WO2015166100A2
Application number: PCT/EP2015/059622
Authority: WO
Inventors: Nicolaas DEN HAAK; Georgo Angelis; Gertjan Van Amerongen
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2014-05-02
Filing date: 2015-05-01
Publication date: 2015-11-05
Anticipated expiration: 2016-11-02
Also published as: WO2015166100A3

Abstract

The invention resides in a bearing assembly with integrated generator, comprising a bearing having an inner ring, an outer ring (420) and at least one row of rolling elements (431, 432) arranged in a radial gap between the inner and outer rings, and further comprising a generator. The generator (360) comprises a stator and a first magnetic rotor (20), whereby the stator is mounted to a non-rotational part of the bearing assembly and comprises a coil with at least one winding. According to the invention, the assembly further comprises a target ring (470) made of an electrically conductive material, which is mounted to or is formed by a rotational part of the bearing assembly and is thus rotatable about the bearing axis of rotation. Furthermore, the first magnetic rotor is rotationally mounted to the stator and is rotatable about a first axis of rotation, which is different from the bearing axis of rotation. The first magnetic rotor comprises a plurality of magnets arranged with alternating polarities along a periphery of the first magnetic rotor, whereby said periphery may face a target surface of the target ring. As the target ring rotates, eddy currents are induced in the target surface, which generate oppositely polled magnetic fields. A contact-free magnetic coupling is thus formed between the rotating target ring (470) and the first magnetic rotor (20), which causes the first magnetic rotor to rotate with the target ring.

Description

Bearing assembly with integrated generator

FIELD OF THE INVENTION

The invention relates to a bearing assembly comprising a rolling element bearing 5 and means for generating electrical energy from rotation of the bearing.

BACKGROUND TO THE INVENTION

An example of such a bearing assembly is disclosed in EP 1292831 . The assembly comprises a wireless self-powered sensor unit which is electrically i o powered by an integrated generator. Electric power is generated via electromechanical energy conversion using permanent magnets, an armature winding and a target wheel that is mounted to and rotates with one of the bearing rings. In one example, the generator comprises a stator formed by a winding that encircles a magnetic core, whereby the target wheel is a toothed wheel. The

15 rotating target wheel causes a change in magnetic flux in an air gap between the magnetic core and the teeth of the wheel, producing an electric current in the winding. In an alternative example, the target wheel is formed by a magnetized ring whose rotation induces an electric current in the winding of the stator.

20 The toothed wheel or magnetized ring therefore has a diameter which is governed by the diameter of the bearing ring to which it is mounted. Therefore, if the solution is to be integrated in bearings of different size, it is necessary to execute the toothed wheel or magnetized ring in a range of diameters. These components of the generator are relatively expensive. Furthermore, if the bearing has a large

25 diameter, the toothed wheel or magnetized ring will add considerably to the rotating mass, leading to higher friction losses.

There is thus room for improvement.

30 SUMMARY OF THE INVENTION

The invention resides in a bearing assembly with integrated generator, comprising a bearing having an inner ring, an outer ring and at least one row of rolling elements arranged in a radial gap between the inner and outer rings, and further comprising a generator. The generator comprises a stator and a first magnetic rotor, whereby the stator is mounted to a non-rotational part of the bearing assembly and comprises a coil with at least one winding. According to the invention, the assembly further comprises a target ring made of an electrically conductive material, which is mounted to or is formed by a rotational part of the bearing assembly and is thus rotatable about the bearing axis of rotation. Furthermore, the first magnetic rotor is rotationally mounted to the stator and is rotatable about a first axis of rotation, which is different from the bearing axis of rotation. The first magnetic rotor comprises a plurality of magnets arranged with alternating polarities along a periphery of the first magnetic rotor, and is arranged such that magnetic field lines from the plurality of magnets intersect the target surface. As the target ring rotates, eddy currents are induced in the target surface, which generate oppositely polled magnetic fields. A contact-free magnetic coupling is thus formed between the rotating target ring and the first magnetic rotor, which causes the first magnetic rotor to rotate with the target ring.

The first magnetic rotor is mounted to a non-rotational part of the bearing and can have a diameter that is considerably smaller than the bearing mean diameter. In one example, the first magnetic rotor has a diameter which is smaller than the radial gap between the inner and outer bearing rings and is arranged entirely within the radial gap. The first magnetic rotor is therefore low in weight and can be implemented in bearing assemblies of various sizes.

In a first embodiment, the target ring of the generator is a separate part that is mounted to one of the inner ring or the outer ring, depending on which is rotational during bearing operation. The separate target ring may also be mounted to a cage or a guide ring that retains or guides the at least one row of rolling elements. Suitably, the separate target ring has a flat target surface and is thus of straightforward construction, making it inexpensive to manufacture for a variety of bearing sizes.

In a second embodiment, the target ring is formed by a rotational part of the bearing assembly. The target surface may thus be a surface of the rotational bearing ring or of the cage or guide ring. The advantage of the second embodiment is that the need for a separate target ring is eliminated.

When the target ring is a separate part or when the target surface is a surface of the cage/guide ring, the target ring or cage/guide ring is preferably made of a paramagnetic material such as aluminium or copper. The advantage of a paramagnetic material is that the low electrical resistance optimises the generation of eddy currents. When the target surface is a surface of a bearing ring, the target ring is made of bearing steel. This is a magnetically conductive material and has a higher resistivity than e.g. aluminium, meaning that relatively lower eddy currents are generated, leading to a relatively weaker magnetic coupling. The potential generating power is therefore relatively less, due to the lower rotational speed of the first magnetic rotor, but may nevertheless be sufficient to power a low energy consumer such as a temperature sensor.

A further drawback of bearing steel is that it magnetically attracts the magnets of the first magnetic rotor. Even when the target ring is a separate part made of paramagnetic material, which is magnetically non-conductive, it is likely that the underlying bearing steel will still exert a magnetic attraction. In effect, the attraction force will increase the radial load on a bearing or bearings that rotationally support the first magnetic rotor, leading to an increase in friction. Thus, in a further development, the stator comprises a ferromagnetic body, which is arranged opposite from the target surface, such that the first magnetic rotor lies between the laminated body and the target surface. The ferromagnetic body is configured to exert an attraction force on the first magnetic rotor which cancels out the attraction force exerted by the steel of or close to the target surface. Preferably, the ferromagnetic body has a laminated structure, to suppress the generation of eddy currents in the body and minimise eddy current losses. Suitably, the magnets of the first magnetic rotor are arranged radially to the first axis of rotation with regard to their North-South orientation and the magnetic rotor preferably comprises at least six magnets. In one example of a bearing assembly according to the invention, the generator comprises only a first magnetic rotor whose rotation induces an electrical current in the coil of the stator. In a further example, the generator comprises a second magnetic rotor coupled to the first, whereby rotation of the second magnetic rotor (about the first axis of rotation) induces an electrical current in the stator coil. Suitably, the second magnetic rotor comprises one or more magnets with a radial N-S orientation relative to the first axis of rotation.

In some examples, the generator comprises a claw pole generator, whereby the stator comprises a yoke with a number of claws that form at least part of a circle.

When the generator comprises a second magnetic rotor, the one or more magnets of the second rotor are arranged to rotate within the claws. When the claw pole generator comprises only a first magnetic rotor, the magnets of the first rotor are arranged to rotate within the claws and are partly surrounded by the claws. The yoke is free of claws where the magnets face the target surface.

A bearing assembly according to the invention may comprise any type of rolling element bearing, such as a deep groove ball bearing or a tapered roller bearing or spherical roller bearing. Further, the bearing may comprise one or more rows of rolling elements. The generator is arranged at an axial side of the rolling elements. When the bearing comprises two axially spaced rows of rolling elements, the generator may be arranged between the two rows. When the generator is arranged at an axially outer side of the rolling elements, the target ring may comprise a radially extending flange part. An advantage of the flange part is that it may form part of a seal that encloses the radial gap between the bearing rings. The target ring may additionally comprise a cylindrical part whose radial surface forms target surface, whereby the first magnetic rotor is arranged such that the first axis of rotation is parallel to the bearing axis of rotation. Alternatively, the axially inner surface of the flange part may serve as the target surface, whereby the first magnetic rotor is arranged such that the first axis of rotation is perpendicular to the bearing axis of rotation.

Suitably, a bearing assembly according to the invention further comprises at least on sensor which is powered by the generator. The sensor may be a temperature sensor, a vibration sensor, an acoustic emission sensor, a displacement sensor or any other type of sensor which is useful for monitoring the condition of the bearing or the condition of a lubricant within the bearing. As a result of the invention, the sensor can be powered for the lifetime of the bearing.

A bearing assembly according to the invention has further advantages, which will become apparent from the following detailed description and accompanying figures.

DESCRIPTION OF THE FIGURES

In the following, the invention is described with reference to the accompanying drawings, in which:

Fig.1 shows a cross-section of a first example of a bearing assembly according to the invention comprising a generator with a magnetic rotor and a target ring

Fig. 2 shows an exploded, perspective view of the magnetic rotor and a target surface of the target ring;

Fig. 3 shows a perspective view of a generator that may be used in a bearing assembly according to the invention.

Fig. 4 shows a perspective cut view of part of a second example of a bearing assembly according to the invention, comprising the generator of Fig. 3.

DETAILED DESCRIPTION

A first example of a bearing assembly with integrated generator according to the invention is shown. The assembly 100 comprises a deep groove ball bearing having an inner ring 1 1 0 and an outer ring 120 and a number of balls 130 arranged between an inner raceway 1 15 of the inner ring and an outer raceway 125 of the outer ring. The balls 130 are retained by a cage 140. In the depicted example, the inner ring 1 10 is rotational about a bearing axis of rotation 145 and the outer ring 120 is non-rotational. For condition monitoring purposes, the bearing assembly is further equipped with a sensor 150 for measuring an operating parameter of the bearing. In the depicted example, the sensor 1 50 is a temperature sensor. In many sensorized bearing applications, the sensor or sensors are battery- powered. Batteries have a limited operating life, meaning that replacement needs to take place after a certain time has elapsed. In many cases, however, replacement may be difficult and expensive to carry out. A bearing assembly according to the invention is therefore equipped with an integrated generator 160 based on electromagnetic induction for supplying the sensor 150 with electrical energy.

The generator 1 60 comprises a stator having a yoke 10 with a coil, which is mounted to the outer ring. According to the invention, the generator further comprises a magnetic rotor 20 that is rotationally supported relative to the stator and outer ring 120 by a bearing (not visible). The magnetic rotor 20 is caused to rotate via a magnetic coupling with a target ring 30 that is mounted to the rotatable inner ring 1 10. The theory behind the operating principle will be explained with reference to Figure 2, which shows a detailed view of the magnetic rotor and a target surface of the target ring.

The target ring is made of aluminium in the depicted example and has a target surface 30s. The magnetic rotor 20 is rotatable about an axis of rotation 20a and comprises a number of permanent magnets 22 with alternating polarities. The magnets 22 have a N-S orientation in radial direction relative to the rotation axis 20a, whereby a radial periphery of the magnetic rotor 20 faces the target surface 30s and is separated by a small air gap.

Initially, the magnetic rotor generates a static magnetic field. Magnetic field lines 4a, 4b of the magnet 22, which is arranged closest to the target surface 30s, permeate the target ring. During rotation of the bearing inner ring, the target surface moves in direction V1 . Moving an electrical conductor through a static magnetic field generates eddy currents. Opposed eddy current fields 5a, 5b are induced in the target surface 30s, which generate their own magnetic fields 6a, 6b. The magnetic field 6a located in a front position with respect to the direction of rotation of the target ring magnetically attracts the magnet 22 while the magnetic field 6b in a rear position magnetically repels the magnet. As a result, a force in direction V2 is exerted on the magnet 22, causing a rotational movement in direction V3 of the magnetic rotor 20. This movement is increased in that adjacent magnets have opposite polarities and are also repelled or attracted corresponding to the direction of rotation.

A further example of a generator that may be used in a bearing assembly according to the invention is depicted in Figure 3. In this example, the generator 360 comprises a first magnetic rotor 20, such as shown in Figure 2, and further comprises a second magnetic rotor 320. The first magnetic rotor has a plurality of magnets 22 with alternating polarities arranged around the periphery, which face a target surface (not shown). The second magnetic rotor 320 is mechanically coupled to the first magnetic rotor 20 and is rotational about the axis of rotation 20a. Suitably, the second magnetic rotor 320 also comprises plurality of magnets 22 with alternating polarities arranged around the radial periphery. The arrangement of the first and second magnetic rotors is rotationally mounted to the stator via bearings (not shown). In the depicted example, the generator comprises a claw pole generator, whereby the stator has a yoke 310 with a number of claws 31 2 arranged at intervals around a circumference of the yoke. The yoke further comprises a coil 315. The second magnetic rotor 320 is arranged within the claws 312 of the yoke 310. Thus, it is the rotation of the second magnetic rotor 320 which induces an electric current in the coil 31 5 due to electromagnetic induction.

Advantageously, the stator further comprises a laminated ferromagnetic body 31 7, which is arranged to face a radial periphery of the first magnetic rotor 20 at a side opposite from the radial periphery that faces the target surface. In other words, the first magnetic rotor 20 lies between the laminated ferromagnetic body 317 and the target surface. Let us assume that the target surface is a radially outer surface of an aluminium ring that is mounted to the bearing inner ring. Although the magnets 22 of the first magnetic rotor are not attracted by aluminium, the underlying bearing steel (which is a magnetic conductor) does exert an attraction force on the magnets. This attraction force will cause increased friction in the bearings that support the first and second magnetic rotors. The purpose of the laminated ferromagnetic body 317 is therefore to attract the magnets 22 of the first magnetic rotor 20 in an opposite direction, such that the net attraction force on the first magnetic rotor is zero. Suitably, the ferromagnetic body 317 has a laminated structure, to suppress the generation of eddy currents and minimise eddy current losses.

A further example of a bearing assembly according to the invention, incorporating a generator as shown in Figure 3, is depicted in Figure 4. In this example, the bearing assembly 400 comprises a spherical roller bearing with first and second rows 431 , 432 of spherical rollers. Each row of rollers is retained by a cage (not shown) and the bearing further comprises a floating guide ring 470, provided between the two roller sets at a radially outer side of the cages. The purpose of the guide ring is to ensure that unloaded rollers enter the bearing loaded zone in an optimal position. The generator 360 is integrated in an outer ring 420 of the bearing. The outer ring 420 has a lubrication groove 427 and typically has three oil holes (not shown) for enabling lubricant to be supplied to the bearing cavity. A further opening is provided in the groove 427, in which opening the generator 360 is mounted. The generator is arranged such that a radially outer surface of the first magnetic rotor 20 faces a radially outer surface of the guide ring 470, with a small air gap. The guide ring is made of paramagnetic material and the radially outer surface of the guide ring serves as the target surface in which opposed eddy current fields are generated when the guide ring rotates in the magnetic field from the magnetic rotor 20. In other examples, when a guide ring is not present, a target ring is mounted to one of the bearing cages or a surface of the bearing cage serves as the target surface. A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. The invention may thus be varied within the scope of the accompanying patent claims.

Claims

Patent Claims:

1 . Bearing assembly (100, 400) with integrated generator, comprising:

• an inner ring (1 10), an outer ring (120, 420) and at least one row of rolling elements (130, 431 , 432) arranged in an annular gap between the inner

5 and outer rings, and

• a generator (160, 360) for generating electrical energy based on electromagnetic induction, comprising a stator and a first magnetic rotor (20), whereby the stator is mounted to a non-rotational part of the bearing assembly and has a coil (315) with at least one winding,

i o characterized in that

the assembly further comprises a target ring (10, 470) made of an electrically conductive material, which is mounted to a rotational part of the bearing assembly and is rotatable about the bearing axis of rotation (145);

15 - the first magnetic rotor is rotationally supported relative to the stator and is rotatable about a first axis of rotation (20a), which is different from the bearing axis of rotation;

the first magnetic rotor (20) comprises a plurality of magnets (22) arranged with alternating polarities along a periphery of the first 20 magnetic rotor; and

the first magnetic rotor is arranged such that magnetic field lines (4a, 4b) from the plurality of magnets intersect a target surface (30s) of the target ring (30, 470).

25 2. Bearing assembly according to claim 1 , wherein the generator is at least partly arranged within the radial gap between the bearing rings.

3. Bearing assembly according to claim 1 or 2, wherein the first magnetic rotor (20) has a diameter which is smaller than the radial gap between the bearing

30 rings.

4. Bearing assembly according to any preceding claim, wherein the target surface (30s) is formed by a surface of one of: a cage (140) that retains the at least one row of rolling elements (130); a guide ring (470) that guides the at least one row of rolling elements (431 , 432); and one of the bearing rings which is rotational during bearing operation.

5. Bearing assembly according to any of claims 1 - 3, wherein the target ring (20) is a separate part.

6. Bearing assembly according to any preceding claim, wherein the target surface comprises a paramagnetic material.

7. Bearing assembly according to any preceding claim, wherein the target surface comprises a ferromagnetic material

8. Bearing assembly according to any preceding claim, wherein the stator comprises a ferromagnetic body (317), which is arranged opposite from the target surface (30s), such that the first magnetic rotor (20) lies between the ferromagnetic body and the target surface.

9. Bearing assembly according to claim 8, wherein the ferromagnetic body (317) has a laminated structure.

10. Bearing assembly according to any preceding claim, wherein the generator (360) further comprises a second magnetic rotor (320), coupled to the first magnetic rotor (20).

1 1 . Bearing assembly to any preceding claim, wherein the generator (360) comprises a claw pole generator, whereby the stator comprises a number of claws (312) which form at least part of a circle.

12. Bearing assembly according to claim 1 1 , wherein the first magnetic rotor (20) is partly surrounded by claws of the claw pole generator.

13. Bearing assembly according to claim 1 1 , dependent on claim 1 0, wherein the second magnetic rotor (320) is arranged within the claws (31 2) of the claw pole generator.

14. Bearing assembly according to any preceding claim having two axially spaced rows of rolling elements, wherein the generator (360) is arranged between the rows of rolling elements.

15. Bearing assembly according to claim 14, wherein the generator is integrated in an opening in the non-rotational bearing ring.

16. Bearing assembly according to any of claims 1 - 13, wherein the generator (160) is arranged an axially outer side of the at least one row of rolling elements (130).

17. Bearing assembly according to claim 16, wherein the target ring comprises a radially extending flange, which forms part of a seal for sealing the radial gap between the bearing rings.

18. Bearing assembly according to any preceding claim further comprising at least one sensor (150) which is powered by the generator (1 60, 360).