Technical Field

The invention relates to a bearing arrangement, comprising a rolling element bearing with an inner bearing ring and an outer bearing ring between which rolling elements are arranged, wherein the rolling element bearing supports a first machine part rotatable relative to a second machine part around an axis of rotation, wherein means are provided to establish an electrical connection between the inner bearing ring and the outer bearing ring and/or between the first and second machine parts.

Background

In some bearing applications it is important to make sure that an electrical current can flow from the supported rotating shaft to the housing in which the shaft is supported by means of the bearing. Here, problems can occur when the electrical current passes the contact between the rolling elements and the raceways of the bearing. Different possibilities are known to allow the flow of an electrical current at a predetermined location remote form the contact area of the rolling elements and the raceways to ensure a proper lifetime of the bearing, i.e. to conduct a current from the shaft to the housing. In particular, electric motors and generators create unwanted voltages on the shaft leading to bearing damage or electromagnetic interference. Grounding the shaft would solve these issues and there are various solutions for this, with each solution having its own drawbacks.

Pre-know solutions are based, for example, on spring loaded graphite brushes, fibrous brushes and conductive grease. Alternatively, it is possible to avoid problems by insulating the bearing, e.g. means of hybrid bearings or insulated bearing rings.

US 5 139 425 A discloses such a solution. Here a rolling element bearing is shown with rotating electrical contacts which comprises inner and outer races gripping around the rolling elements; means are provided which permit the passage of an electrical current between two mechanical components, of which one is rotationally moveable in relation to the other. For this purpose one conductive cartridge of generally annular form is mounted substantially in a frontal radial plane of the bearing. The cartridge comprises two conductive armatures, one being able to rotate in relation to the other, each armature being integral with one of the races of the rolling mechanism and one conductive element pressed against one of the armatures by one conductive elastic element in contact with the other armature.

Also DE 101 10 067 Al shows a bearing with electrical connection between the bearing rings, which has a one-piece element of linear spring elastic material in curved form in direct pressured electrical contact with bearing rings.

Similar and other solutions are shown in US 5 454 724 A, US 3 564 477 A and US 3 581 267 A. All the pre-known solutions are not yet fully satisfactory with regard to the reliability of the conduction of an electrical current, especially when it comes to wear during the operation of the bearing arrangement. Thus, the durability of the means is often not sufficient. Finally, in some cases costly elements are necessary to realize a proper conduction of the electrical current around the bearing.

Thus, it is an o bj e c t of the present invention to further develop a bearing arrangement of the kind mentioned above so that a reliable and durable electrical connection between the two machine parts is established. Also, the device necessary for doing so should be realized in an economic manner. Thus, it is an aim to propose a proper solution by which currents can be conducted from a motor shaft to the ground.

Summary of the invention

The s o l u t i o n according to the invention is characterized in that the means to establish the electrical connection comprise at least one electrical conductive brush element, wherein the brush element is pivotably arranged at one of the bearing rings so that it can swivel around a pivot axis which is parallel to the axis of rotation, wherein the brush element has a contact section which can slide on one of the machine parts or one of the bearing rings.

The first machine part is preferably a rotating shaft, the second machine part is preferably a housing. The brush element consists preferably of a solid electrically conductive material, specifically of graphite material. Here, the brush element can be designed as a one-piece block-shaped element.

The brush element is preferably biased by means of a spring element so that its contact section is pressed against one of the machine parts or one of the bearing rings. The direction of the pressing force is thus preferably radially inwards. The spring element is preferably a garter spring.

A preferred embodiment provides that more than one brush element is arranged pivotably at one of the bearing rings. The brush elements are preferably arranged equidistantly around the circumference of the bearing ring. Hereby, all brush elements can be biased by a single spring element, preferably by a single garter spring.

A specifically preferred embodiment is characterized in that two brush elements which are adjacent in circumferential direction are designed in such a manner that a first brush element has a protrusion which can be brought into engagement with a blocking area which is arranged at the adjacent second brush element so that the second brush element can pivot with its contact section against one of the machine parts or one of the bearing rings only when the first brush element has swivelled due to wear around a predetermined angle around the pivot axis. By this design a second (fresh) brush element comes into engagement only when a first (old) brush element is worn out. So, the lifetime of the arrangement can be significantly enhanced.

This principle can be further developed in such a manner that a series of brush elements is arranged and always a subsequent (fresh) brush element comes into engagement when the antecedent (old) brush element is worn out. Thus, is can be provided that more than two brush elements are arranged, wherein a respective adjacent brush element can pivot with its contact section against one of the machine parts or one of the bearing rings only when the preceding adjacent brush element has swivelled due to wear around the predetermined angle around the pivot axis.

Specifically, two pairs of brush elements can be arranged, wherein the second one of each pair of adjacent brush elements can pivot with its contact section against one of the machine parts or one of the bearing rings only when the preceding adjacent first brush element has swivelled due to wear around the predetermined angle around the pivot axis.

For the support of the brush elements a swivel bearing for each brush element can be arranged which is formed by a holding element which has a pin-shaped section which is arranged in a bore in the brush element, wherein the holding element is fixed at one of the bearing rings. Thereby, the holding element can be arranged with a fixation section in a groove which is machined in the outer or inner circumference of the bearing ring. So an economical support of the brush elements is possible.

The present invention consists thus of one or more brushes, held to e.g. the non-locating bearing in an electric motor preferably by means of a wire and spring loaded onto the shaft by a garter spring.

The invention is specifically used for electric motors and generators in automotive applications. The main application of the present invention is automotive, but of course it is suitable also for other applications, e.g. for industrial installations. Beneficially, the axial length of the machine arrangement with the bearing arrangement in question is fairly small; this is always important in electric motors. No extra parts and limited extra handling are required. The costs are lower than mounting a separate brush holder as known from the state of the art.

Brief description of the drawings

Fig. 1 shows a radial cross sectional view through a first example of a bearing arrangement according to the invention, in which a shaft is supported in a housing by means of a rolling element bearing,

Fig. 2 shows in perspective view a second example of a rolling element bearing provided with four brush elements,

Fig. 3 shows the rolling element bearing according to Fig. 2, seen in the direction of the axis or rotation, wherein the brushes are new,

Fig. 4 shows in the depiction according to Fig. 3 a status where two of the brushes experienced wear and

Fig. 5 shows in the depiction according to Fig. 3 a status where the wear of the brushes has proceeded to a stage where two other brushes have come into engagement. Detailed description of the invention

In Fig.1 a bearing arrangement 1 is depicted which has a rolling element bearing 2 with an inner bearing ring 3 and an outer bearing ring 4. Between the bearing rings, rolling elements 5 are arranged. The rolling element bearing 2 is arranged in a bore of a second machine part, which is a housing and which is only indicated in the figure by reference numeral 7. Also, a rotating shaft, which is a first machine part, is only indicated in the figure by reference numeral 6.

As known in the art as such, means 8 are provided for establishment of an electrical connection between the two machine parts 6, 7 respectively between the two bearing rings 3, 4.

According to the present invention the means 8 to establish the electrical connection are designed in a special manner: They comprise at least one electrically conductive brush element 9. This brush element 9 is pivotably arranged at one of the bearing rings - in the shown embodiment at the outer bearing ring 4 - so that it can swivel around a pivot axis b; this pivot axis b is parallel to the axis a of rotation of the rolling element bearing 2. The brush element 9 has a contact section 10 which can slide on the machine part 6, i.e. on the shaft in the present case.

The brush element or brush elements 9 (graphite brushes in the present case) is or are biased to be pressed against the shaft 6 to establish a proper electrical connection. For doing so a spring element 11 is employed which is a garter spring in the present case. In Fig. 1 a sheet metal finger 19 (which is L-shaped in the cross section) is shown which is connected with a sealing element 20 that is mounted to the bearing outer ring 4. The sheet metal finger 19 serves for the fixation of the brush element 9 at the sealing element 20 and thus indirectly at the rolling element bearing 2. The brush element is pivotably attached to the sheet meal finger 19.

That is, Fig. 1 shows specifically an implementation where the at least one brush element 9 (brush pivot) is mounted to the sealing element 20, whereas the following figures use wires to arrange the brush elements 9 directly at the outer bearing ring.

In Fig. 2 the rolling element bearing 2 is shown which is equipped with four brush elements 9', 9", 9"' and 9"" which are arranged equidistantly around the circumference of the outer bearing ring 4. The four brush elements 9 are supported pivotably relative to the bearing outer ring 4 around the pivot axis b. The swivel bearing 14 for this purpose is realized by means of a bent wire. A holding element 15 has a section which runs in the direction of the pivot axis b and which enters into a bore 16 in the brush element 9. Furthermore, the holding element 15 has a fixation section 17 which runs also in the direction of the pivot axis b and which is fixed in a groove 18 in the radially outer circumference of the outer bearing ring 4.

A further beneficial feature of the proposed bearing arrangement becomes apparent from the synopsis of figures 3 to 5.

In figures 3 to 5 the view of the rolling element bearing 2 is shown in different wear-out situations. In Fig. 3 all brush elements 9 are fresh and not yet worn out; here, only the contact sections 10 of the brush elements 9' and 9" ' are in engagement with the shaft 6. In Fig. 4 the two brush elements 9' and 9"' - which are in use simultaneously - are worn to a certain degree which is denoted by the dashed lines in the brush elements 9', 9"'. The degree of wear-out has advanced in Fig. 5; here the dashed lines denote a higher amount of material of the brush elements which has vanished due to wear.

Furthermore, as can be seen in the figures 2 to 5 two adjacent brush elements 9' and 9" on the one hand and 9"' and 9"" on the other hand cooperate by means of a protrusion 12 of the brush elements 9' and 9"' respectively and a corresponding blocking area 13 of the brush elements 9" and 9" " respectively. That is, the protrusion 12 holds in this status the adjacent brush element away from the shaft 6.

A first radius of the brush elements 9 (facing the shaft 6) conforms to the shaft, a second radius (running radially outwards) allows sufficient space for a press fit tool if the brush elements 9 are swivelled outwards (i.e. away from the shaft 6).

As can be seen in the synopsis of figures 3 to 5 as wear of the brush elements 9' and 9"' advances said brush elements pivot around the pivot axis b while - in figures 3 and 4 - the protrusion 12 is still engaged with the blocking area 13 of the adjacent brush element 9 and prevents that the adjacent brush element 9", 9" " comes into engagement with its contact section 10 with the shaft 6. Only when wear of the brush elements 9', 9"' is sufficiently advanced (see dashed lines in the brush elements 9' and 9"' in figures 4 and 5) the protrusion 12 comes out of engagement with the blocking area 13 and unblocks the adjacent brush element 9", 9"" (see status according to Fig. 5). Thus, in Fig. 5 the brush elements 9" and 9"" came into engagement with the shaft 6 with their respective contact section 10. Thus, the rolling element bearing 2 has four swivel-mounted conducting brush elements 9 with respective contact sections 10 (contacting lips) which are urged towards the shaft 6 by the garter spring 11. The arrangement of brush elements 9 is designed such that two of the contact sections 10 (on the brush elements 9' and 9"') are in contact with the shaft 6 at the same time. This first and third brush elements 9', 9" ' keep the second and fourth brush elements 9", 9" " out of contact with the shaft 6, until wear of the corresponding first and third contact sections allows the second and fourth brush elements 9 to swivel into a position where the contact sections engages the shaft 6.

In an alternative embodiment (not depicted) only one contact section at a time is in contact with the shaft 6. Wear of the first brush element 9' activates the subsequent brush element 9" into engagement whose wear activates brush element 9" ' whose wear activates brush element 9"" . Thus, here only one brush is in contact at a time, whereby wear of said brush activates the next brush and so on.

According to the preferred design of the proposed concept the wire (holding element 15) is staked into the slot (groove 17) in the outer diameter of the outer bearing ring 4 and acts as a centre of rotation for the graphite brushes 9. The brushes 9 have features to hold a garter spring 11 in place, which ensures brush contact with the shaft 6.

More (for example four) of these brushes 9 can be mounted to the side of a bearing, or a plastic spring guide could be used to reduce the number of brushes and thereby cost. The brushes 9 can be rotated out of the way to push on the inner ring to press it onto the shaft 6. In the embodiment depicted in Figs. 2 to 5, multiple (four) brushes 9 are mounted at the side of the bearing 2. Thus, the brushes 9 geometrically engage with one and other such that two of the brushes are in contact and keep the other two brushes out of contact, until a sufficient amount of wear has taken place.

It should be mentioned that the hinge is preferably attached to the outer ring or seal. The "outer ring" version is a straightforward implementation, but requires normally a certain modification of the outer ring. The "seal" version needs a suitable electrical contact to the outer ring and a respective design of the protruding part in the seal.

The benefit for having (at least) two sequential brush sets on the bearing is to have some redundancy in case the powder from the worn brushes blocked the motion of a brush. So, also in this case proper operation is ensured.

Reference Numerals:

1 Bearing arrangement

2 Rolling element bearing

3 Inner bearing ring

4 Outer bearing ring

5 Rolling element

6 First machine part (shaft)

7 Second machine part (housing)

8 Means to establish an electrical connection

9 Brush element

9', 9" Brush element

9"' 9"" Brush element

10 Contact section

11 Spring element

12 Protrusion

13 Blocking area

14 Swivel bearing

15 Holding element

16 Bore

17 Fixation section

18 Groove

19 Sheet metal finger

20 Sealing element a Axis of rotation

b Pivot axis