WO2013098584A1

WO2013098584A1 - Bearing assembly and rotary electric machine comprising such a bearing

Info

Publication number: WO2013098584A1
Application number: PCT/IB2011/003321
Authority: WO
Inventors: Sylvain Chaussat; Benoît Locher
Original assignee: Aktiebolaget Skf
Priority date: 2011-12-28
Filing date: 2011-12-28
Publication date: 2013-07-04

Abstract

This bearing assembly (A) comprises a bearing with a first rotatable ring and a second fixed ring, an encoder washer fast in rotation with the rotatable ring, at least one sensor (60) adapted to detect a rotation parameter of the encoder washer, a sensor body (70) for holding the sensor, an electrically conductive mounting flange (80) for holding the sensor body in position with respect to the second ring and a multiconductor electric cable (76) electrically connected to the sensor. The sensor body comprises a printed circuit board (72). A shielding conductor (762) of the electric cable (76) is electrically connected to a conductive track (726) of the printed circuit board and the conductive track of the printed circuit board (72) is electrically connected to the mounting flange (80) when this flange holds the sensor body (70) with respect to the second ring (12).

Description

BEARING ASSEMBLY AND ROTARY ELECTRIC MACHINE

COMPRISING SUCH A BEARING

TECHNICAL FIELD OF THE INVENTION

This invention relates to a bearing assembly for rotatively holding a rotating part with respect to a support member. Such a bearing assembly includes, amongst others, at least one sensor adapted to detect a rotation parameter of an encoder washer and a cable connected to such a sensor. This invention also relates to an electric machine, such as an electric motor, including, amongst others, a bearing assembly as mentioned here-above.

BACKGROUND OF THE INVENTION

Generally speaking, a bearing comprises an inner ring and an outer ring adapted to rotate around a rotation axis, one with respect to the other. In a plain bearing, the two rings are in sliding contact. In a rolling bearing, several rolling bodies are installed between the two rings. These rolling bodies can be balls, rollers or needles. Thus, a rolling bearing can be, for instance, a ball bearing, a roller bearing or a needle bearing.

In the field of bearings, it is known to use a tachometer in order to determine the rotation speed of a rotating part. As explained in EP-A-1 933 155, one can use an encoder washer with magnetic poles fast in rotation with a rotatable ring of a bearing, and one or several sensors distributed around the encoder washer or located in front of it. The or each sensor must be connected to an electronic control unit for providing this unit for a signal representative of a rotation parameter of the encoder washer. Each sensor is thus connected, either directly or via a printed circuit board, to a cable which is advantageously shielded in order to reduce EMI (Electromagnetic interference) noise, in the electrical signals emitted by the sensors. A shielding conductor is then integrated to the cable which is a multiconductor cable, this shielding being, for example, an annular conductive sleeve integrated in the outer insulating sheath of the electric cable.

It is known from JP-A-2007/024778 to couple a magnetic sensor of a rotary bearing to a noise filter. A frame grounding wire is used and it must be installed by hand within the housing of the sensor which is cumbersome and needs a highly qualified manpower.

SUMMARY OF THE INVENTION

The invention aims at solving these problems with a new bearing assembly which facilitates the connection of a shielding conductor to a grounded part.

To this end, the invention concerns a bearing assembly for rotatively holding a rotative part with respect to a support member, this bearing assembly comprising a bearing with a first rotatable ring and a second fixed ring, an encoder washer fast in rotation with the rotatable ring, at least one sensor adapted to detect a rotation parameter of the encoder washer, a sensor body for holding the sensor, this sensor body comprising a printed circuit board or PCB, an electrically conductive mounting flange for holding the sensor body in position with respect to the second ring and a multiconductor electric cable electrically connected to the sensor. According to the invention, at least one shielding conductor of the electric cable is electrically connected to at least one conductive track of the PCB and this at least one conductive track is electrically connected to the mounting flange when this flange holds the sensor body with respect to the second fixed ring.

Thanks to the invention, grounding of the shielding conductor occurs through the conductive track of the PCB and the mounting flange which is itself grounded due to its mounting on a supporting part of the bearing assembly. Thus, grounding of the shielding conductor is obtained automatically, as soon as the mounting flange is fixed on the support member.

In the present description, the words "axial", "radial", "axially" and "radially" relate to the axis of rotation of the rotatable ring with respect to the fixed ring of the bearing or the axis of rotation of the encoder washer. A direction is "axial" when it is parallel to such an axis and "radial" when it is perpendicular to and secant with such an axis. A surface is "axial" when it is perpendicular to an axial direction and "radial" when it is perpendicular to a radial direction. A rotation parameter is representative of the rotation movement of the encoder washer. Such a parameter can be an angle, a speed, a displacement, an acceleration or a vibration.

According to further aspects of the invention which are advantageous but not compulsory, this bearing assembly can incorporate one or several of the following features, taken in any admissible configuration:

- The mounting flange is provided with at least one conductive pad and a portion of the conductive track of the printed circuit board lies against one such pad.

- The portion of the conductive track which lies against the pad is an eyelet and a screw crosses this eyelet, is screwed in a threaded hole of the pad and pushes the eyelet against the conductive pad.

- Alternatively, the sensor body is immobilized on the flange by at least one conductive screw or pin which crosses an eyelet forming a part of the conductive track. When a screw is used, it can be threaded into a pad of the flange. When a pin is used, it can be swaged on the flange.

- The sensor body and the flange are annular and centered on a rotation axis of the rotatable ring and the flange has a first inner skirt and a second outer skirt which define, between them and with a bottom wall of the flange, an annular recess for accommodating at least a part of the sensor body.

The PCB is received in the volume defined between the radially inner and outer skirts and the conductive track is connected to the mounting flange within this volume.

- The pad holds the PCB in position within the volume defined between the inner and outer skirts.

The invention also concerns a rotary electric machine, such as an electric motor, having a casing supporting a rotating shaft. According to the invention, this rotary electric machine includes a bearing assembly as mentioned here-above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be well understood on the basis of the following description which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures:

- figure 1 is a perspective exploded view of a support member, a shaft and a bearing assembly according to the invention,

- figure 2 is a perspective view, in another direction, of a mounting flange, a PCB and a synthetic ring of the bearing assembly represented on figure 1 ,

- figure 3 is a partial axial cut view of the elements represented on figure 1 , in the plane of an end of a cable represented on this figure, and

- figure 4 is an enlarged view of detail IV on figure 3.

DESCRIPTION OF SOME EMBODIMENTS

The rolling bearing assembly A represented on the figures is used to rotatively hold a rotating shaft 2 with respect to a support member 4 forming part of the casing 6 of a non further represented electric motor M. Rotating shaft 2 has a corrugated central opening 2A which is centered on an axis X2 and adapted to accommodate a non-represented shaft extending within casing 6 and supporting a rotor of motor M.

Figure 1 shows support member 4 mounted on casing 6. Alternatively, these two parts can be integral with each other.

Bearing assembly A includes a ball bearing 10 with a fixed outer ring 12 and a rotatable inner ring 14. Some balls 16 are located in a rotation chamber 18 defined between respective raceways of rings 12 and 14, as shown on figures 3 and 4. X10 denotes the rotation axis of inner ring 4 with respect to outer ring 12 in bearing 10. In mounted configuration of bearing assembly A, axis X10 is superimposed with a central axis XA of bearing assembly A. Support member 4 is provided with a circular opening 4A centered on an axis X4 which is superimposed with axis XA in mounted configuration of bearing assembly A with respect to support member 4.

Bearing assembly A also includes a snap ring or circlip 20 which is accommodated within an inner circumferential groove 4B of support member 4, next to housing 4A. Thus, when in position within groove 4B, snap ring 20 holds bearing 10 within housing 4A.

Snap ring 20 is optional and can be omitted in an alternative embodiment, e.g. when outer ring 12 is press-fitted within housing 4A.

Bearing assembly A also includes a spacer ring 30 adapted to be mounted on an outer collar 4C of support member 4 via six screws 40. Spacer ring 30 has a flat side surface 32 which is oriented opposite to support member 4 when spacer ring 30 is mounted onto support member 4. Spacer ring 30 is optional insofar as it can be omitted if support member 4 has a flat surface analogous to surface 32.

Bearing assembly A also includes an encoder washer 50 formed of a bipolar permanent magnet ring 52 and a ferromagnetic armature 54. Encoder washer 50 is fixedly mounted on inner ring 14. This is obtained by engaging an annular skirt 542 of armature 54 within a radial inner groove 142 of inner ring 14.

Bearing assembly A also includes five sensors 60 adapted to detect a rotation parameter of encoder washer 50. These sensors 60 are installed within a sensor body 70 formed of a printed circuit board or PCB 72 and a synthetic ring 74 provided with respective housings 742 for the sensors 60. Each sensor 60 is provided with three connecting pins 62 which connect this sensor to some conductive tracks printed on PCB 72. These conductive tracks are not shown on figures 1 and 2, for the sake of simplicity. PCB 72 is annular and centered on a central axis X70 of sensor body 70. Synthetic ring 74 is centered on the same central axis when items 72 and 74 are assembled together in order to constitute sensor body 70.

An electric cable 76 is connected to PCB 72 and enables to feed its electronic components with electric power and to convey output signals of sensors 60. Cable 76 is thus, at least indirectly, connected to sensors 60. Electric cable 76 is a multiconductor cable and it includes a shielding conductor 762 which is electrically connected to a conductive pin 722 fixed on PCB 72. Electric cable 76 includes several other conductors 764 which are connected to other pins 724 fixed on PCB 72. On figure 2, the connections between cables 764 and pins 724 are, for the sake of clarity, not visible since they occur on the hidden side of PCB 72. Shielding conductor 762 can be embedded within an outer sheath 766 of electric cable 76. Alternatively, this conductor can be installed amongst the other conductors, in the center of this sheath.

A conductive electric track 726 extends from pin 722 on the side of PCB 72 visible on figure 2. Opposite to pin 722, track 726 ends with and an eyelet 728 which surrounds a throughhole 729 which goes from the side of PCB 72 visible on figure 2 to the side of this PCB visible on figure 1 . Eyelet 728 is a part of track 726 and made of an electrically conductive material, as track 726. This eyelet covers the edge of throughhole 729 and extends on both sides of PCB 72. In other words, eyelet 728 is continuous between its two parts lying respectively on the two sides of PCB 72. Thus, eyelet 728 is adapted to convey electricity from one side of PCB 72 to the other side.

Bearing assembly A also includes an annular, electrically conducting flange 80 which is designed to be mounted onto spacer ring 30 and support member 4 thanks to the set of screws 40. To this end, flange 80 includes a radially external flat annular band 81 provided with several oblong holes 82 adapted to be aligned with respective holes 34 of spacer ring 30 and threaded holes 4D of support member 4. Screws 40 are used to immobilize flange 80 on spacer ring 30 and support member 4. The fact that openings 82 are oblong allows to adjust the angular orientation of flange 80, around axis XA, with respect to items 4 and 30.

Items 2, 4, 12, 14, 16, 20 and 80 are made of ferromagnetic materials, such as steel.

X30, X50 and X80 respectively denote the central axis of spacer ring 30, encoder washer 50 and flange 80. These axes and axis X2 are superimposed with axis XA in the mounted configuration of bearing assembly A.

Flange 80 has a bottom wall 83 which is parallel to band 81 and perpendicular to axis X80. Bottom wall 83 is radially inside band 81 and offset, along axis X80, with respect to band 81 . A circular wall 84 connects these two parts of flange 80 which is integral.

The face of flange 80 visible on figure 1 is the outer face of this flange, insofar as it is oriented towards the outside of bearing assembly A in the mounted configuration. The inside face of flange 80 is visible on figure 2. The inner radial edge of flange 80 is defined by a first skirt 85 which is cylindrical, circular and centered on axis X80. This skirt extends, along axis X80, from bottom wall 83 towards a continuous free circular edge 852 visible from the inside face of flange 80.

A second skirt 86 is centered on axis X80 and formed by three parts 86A, 86B, 86C. In other words, skirt 86 is not fully circular and it is interrupted by three openings 87. On figure 2, some phantom lines show the trace of skirt 86 if it were continuous around axis X80. According to an alternative embodiment of the invention, skirt 86 can be circular and continuous around axis X80. In such a case, its free edge follows the phantom lines on figure 2.

Flange 80 is provided with a groove 88, which extends in a radial direction with respect to axis X80 and is adapted to accommodate a part of cable 76. Groove 88 defines a reception zone for an end of cable 76 to be connected to PCB 72.

Flange 80 is provided with three bracing pads 89A, 89B and 89C regularly distributed, at 120°, around axis X80, on the side of bottom wall 83 oriented towards skirts 85 and 86. 89A denotes the bearing pad which is closest to groove 88. Each bracing pad is provided with a threaded hole 892 adapted to receive the stem of a respective screw 90A, 90B or 90C. Each screw 90A, 90B or 90C is supposed to go through sensor body 70 in order to immobilize it onto flange 80. Synthetic ring 74 is provided with three openings 744A, 744B and 744C designed to accommodate the heads of screws 90A, 90B and 90C and to be respectively crossed by screws 90A, 90B, 90C. One opening 744A is supposed to be aligned with hole 729 in PCB 72, whereas the other two openings 744B and 744C are supposed to be aligned with notches 727 provided on the outer edge of PCB 72.

On figure 2, screws 90A, 90B and 90C are represented between PCB 72 and synthetic ring 74 for the compactness of this figure. Actually, they are inserted within openings 744A, 744B and 744C from the side of synthetic ring 74 visible on figure 2 and they go through PCB 72 in order to be screwed into threaded holes 892.

Skirt 85 is radially inside skirt 86. In other words, skirt 85 is a radially inner skirt and skirt 86 is a radially outer skirt with respect to axis X80. Skirts 85 and 86 define, radially between them and axially with bottom wall 83, a volume V8 adapted to accommodate a part of sensor body 70. Actually, depending on the length of skirts 85 and 86 along axis X80, volume V8 can accommodate at least PCB 72 and a part of synthetic ring 74 or the totality of sensor body 70.

Pads 89A, 89B and 89C are located within volume V8.

As shown on figures 3 and 4, it is possible to insert sensor body 70 in volume V8 and to immobilize it with screws 90A, 90B and 90C and, possibly, with a non represented quantity of glue. Then, sensor body 70 is held in position by flange 80, with respect to support member 4 and fixed ring 12 received within opening 4A, when flange 80 is mounted onto support members 4 via items 30 and 40.

In this configuration, screw 90A pushes eyelet 728 against pad 89A, which induces an electrical contact between track 726 and flange 80. Thus, when sensor body 70 is mounted onto flange 80, conductive track 726 is electrically connected to annular flange 80 via eyelet 728. On the other hand, in the mounted configuration of bearing assembly A, flange 80 is electrically grounded via its electrical connection to support member 4 through spacer ring 30 and screws 40. Actually, items 4, 30, 40 and 80 are made of electrically conductive materials and casing 6 is grounded by construction of motor M.

Therefore, when sensor body 70 is partially or totally received within volume V8, shielding cable 762 is automatically grounded via pin 722, conductive track 726, annular flange 80, screws 40, spacer 30 and support member 4.

This facilitates mounting of bearing assembly A and guarantees that a proper protection against EMI noise is obtained via shielding conductor 762, irrespective of the qualification and care of the operator.

In the embodiment represented on the figures, screws 90A, 90B and 90C exert on

PCB 72 an effort E1 pushing this PCB against bracing pad 89A, 89B and 89C, which guarantees an electric contact between eyelet 728 and pad 88A. In this embodiment, screws 90A, 90B and 90C do not need to be electrically conductive.

According to an alternative embodiment, eyelet 728 does not extend radially around the edge of throughhole 729 and on the side of PCB 72 visible on figure 1 . In this case, screw 90A is electrically conductive and its head comes into contact against eyelet 728 whereas its stem is in electrical contact within the corresponding pad 88. This induces an electric contact between eyelet 728, thus track 726, and flange 80. Thus, shielding conductor 762 is grounded via items 722, 726, 90A, 80, 40, 30 and 4.

According to another alternative embodiment of the invention, some pins can be used instead of screws 90A, 90B and 90C. In this case, these pins can be swaged onto annular flange 80.

The invention is represented on figure 2 in case five sensors are mounted on PCB 72. Actually, any number of sensors can be used.

In the embodiments considered here-above, the electric connection between conductive track 726, on the one hand, and annular flange 80, on the other hand, takes place within the volume V8 defined between skirts 85 and 86 and in the vicinity of bottom wall 83. Thus, this electric connection is efficiently protected against shocks and pollution.

The three pads 89A, 89B and 89C cooperate to hold sensor body 70, in particular its PCB 72, in position within volume V8, while keeping a distance between PCB 72 and bottom wall 83, which allows some room for electronic components mounted on PCB 72 and non represented on figure 1 . This space is also available for receiving a quantity of glue to immobilize sensor body 70 with respect to annular flange 80.

The invention is described here-above in case one uses a ball bearing. Other types of rolling bearings, including roller bearings and needle bearings, can be considered. It is also possible to use a plain bearing. Openings 87 allow a direct contact between sensor body 70 and the radial surface of housing 4A. This facilitates centering of sensor body 70 with respect to axis X4.

The number of pads 89A, 89B, 89C can be different from three.

The invention is represented on the figures in case one shielding cable 762 is connected to one conductive track 726. However, according to alternative embodiments, several shielding conductors and/or several conductive tracks might be used.

Claims

1 . - A bearing assembly (A) for rotatively holding a rotating part (2) with respect to a support member (4), this bearing assembly comprising:

- a bearing (10) with a first rotatable ring (14) and a second fixed ring (12),

- an encoder washer (50) fast in rotation with the rotatable ring,

- at least one sensor (60) adapted to detect a rotation parameter of the encoder washer,

- a sensor body (70) for holding the sensor, this sensor body comprising a printed circuit board (72),

- an electrically conductive mounting flange (80) for holding the sensor body in position with respect to the second ring (12)

- a multiconductor electric cable (76) electrically connected to the sensor wherein at least one shielding conductor (762) of the electric cable (76) is electrically connected to at least one conductive track (726) of the printed circuit board (72) and the at least one conductive track of the printed circuit board (72) is electrically connected to the mounting flange (80), when this flange holds the sensor body (70) with respect to the second fixed ring (12).

2. - Bearing assembly according to claim 1 , wherein the mounting flange (80) is provided with at least one conductive pad (89A, 89B, 89C) and a portion (728) of the conductive track (726) of the printed circuit board (72) lies against one pad (89A).

3. - Bearing assembly according to claim 2, wherein the portion of the conductive track (726) which lies against the pad (89A) is an eyelet (728) and wherein a screw (90A) crosses this eyelet and is screwed in a threaded hole (892) of the pad and pushes (E1 ) the eyelet against the conductive pad.

4. - Bearing assembly according to claim 1 , wherein the sensor body (70) is immobilized on the flange by at least one conductive screw (90A) or pin which crosses an eyelet (728) forming a part of the conductive track (728).

5. - Bearing assembly according to claim 4, wherein the screw (90A) is threaded into a pad (89A) of the flange (80).

6. - Bearing assembly according to claim 4, wherein the pin is swaged on the flange (80).

7. - Bearing assembly according to any preceding claim, wherein the sensor body (70) and the flange (80) are annular and centered on a rotation axis (X10) of the rotatable ring (14) and wherein the flange has a first inner skirt (85) and a second outer skirt (86) which define, between them and with a bottom wall (83) of the flange, an annular recess (V8) for accommodating at least a part (72) of the sensor body.

8. - Bearing assembly according to claim 7, wherein the PCB (72) is received in the volume (V8) defined between the inner and outer skirts (85, 86) and the conductive track (726) is connected to the mounting flange (80) within this volume.

9. - Bearing assembly according to one of claims 2, 3 and 5 and to claim 8, wherein the pad (89A) holds the printed circuit board (72) in position within the volume (V8) defined between the inner and outer skirts (85, 86).

10. - An electric machine, in particular an electric motor (M), having a casing (6) supporting a rotating shaft (2), wherein it includes at least one bearing assembly (A) according to any preceding claim.