WO2013098583A1

WO2013098583A1 - Bearing assembly and rotary electric machine comprising such a bearing

Info

Publication number: WO2013098583A1
Application number: PCT/IB2011/003320
Authority: WO
Inventors: Sylvain Chaussat
Original assignee: Aktiebolaget Skf
Priority date: 2011-12-28
Filing date: 2011-12-28
Publication date: 2013-07-04

Abstract

This bearing assembly (A) for rotatively holding a shaft (2) with respect to a fixed element (4, 30) comprises a bearing (10) with a rotatable inner ring (14) and a fixed outer ring (12) to be immobilized within a housing (4A) of said fixed element (4, 30), an encoder washer (50) fast in rotation with the rotatable ring (14), at least one sensor (60) adapted to detect at least one rotation parameter of the encoder washer (50), a sensor body (70) for holding said sensor (60), an annular flange (80) for mounting said sensor body (70) with respect to said fixed outer ring (12), and an output electric cable (76) electrically connected to the sensor body (70) for transmitting output signals delivered by the sensor (60) to a reception device. The annular flange (80) comprises a recess (880) adapted to accommodate the output electric cable (76), said recess (880) having a depth (D88) slightly inferior to the diameter (D76) of the cable (76) The fixed element (4, 30) comprises a flat annular surface (32) adapted to cooperate with a flat annular surface (810) of the annular flange (80) on which the recess (880) is provided The cable (76) is pressed between the recess (880) and the flat annular surface (32) of the fixed element remotely from the electrical connections between the cable (76) and the sensor body (70).

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 shaft with respect to a fixed element. Such a bearing assembly includes, amongst others, at least one sensor adapted to detect a rotation parameter of an encoder washer.

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 shaft supported by a bearing with respect to a supporting member, such as the casing of an electric machine. As explained in EP-A-1 933 155, one can use an encoder washer with magnetic poles fast in rotation with a rotating ring of a bearing, and one or several sensors distributed around the encoder washer or located in front of it. An air gap is provided between the encoder washer and the or each sensor. Detection of a rotation parameter of the encoder washer occurs through this air gap, thanks to the variation of a magnetic field generated by the encoder washer.

Such tachometers are equipped with an output cable adapted to transmit, to a reception device such as a dashboard of a vehicle, the rotation parameter detected by the tachometer. This cable generally comprises several wires connected to a printed circuit board of the tachometer by soldering. These wires can be a ground connection wire, a power supply wire and electrical signal transmission wires. The fact that the wires are connected to the printed circuit board by soldering implies that this connection could be damaged and needs to be protected but also remain easy to handle, for example in the automotive market.

It is known to overmould the cable and its connection area with plastic or elastomeric material, or to use polymeric covers or guiding means. These techniques do not provide a satisfying protection to the connection between the output cable and the tachometer. In case an undesired traction or force is exerted on the cable, this force is transmitted to the soldered part, whose mechanical resistance is low, even with the techniques previously mentioned.

SUMMARY OF THE INVENTION

The invention aims at solving these problems with a new bearing assembly whose output cable is connected to the sensor unit in a more robust and reliable way than in the prior art.

To this end, the invention concerns a bearing assembly for rotatively holding a shaft with respect to a fixed element, said bearing assembly comprising a bearing with a rotatable inner ring and a fixed outer ring to be immobilized within a housing of said support member, an encoder washer fast in rotation with the rotatable ring, at least one sensor adapted to detect at least one rotation parameter of the encoder washer, a sensor body for holding said sensor, an annular flange for mounting said sensor body with respect to said fixed outer ring, and an output electric cable electrically connected to the sensor body for transmitting output signals delivered by the sensor to a reception device. This bearing assembly is characterized in that the annular flange comprises a recess adapted to accommodate the output electric cable, said recess having a depth slightly inferior to the diameter of the cable, while the fixed element comprises a flat annular surface adapted to cooperate with a flat annular surface of the annular flange on which the recess is provided, and while the cable is pressed between the recess and the flat annular surface of the fixed element, remotely from the electrical connections between the cable and the sensor body.

Thanks to the invention, the stresses that may be exerted on the output cable are transmitted to a portion of the cable which is remote from the fragile soldered connections between the cable and the sensor body. The rigid parts which press the cable will resist against a sideward traction of the cable. This improves the robustness and the service life of the output cable.

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 and centered on the axis of rotation. A "radially inner" part is closer to this axis, along a radial direction, than a "radially outer" part. 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 recess has the shape of a cylinder having a longitudinal axis aligned with the axis of the cable.

- The width of the recess on the side of the flat annular surface of the flange is slightly inferior to the diameter of the cable.

- The flat annular surface of the fixed element is located on a spacer ring fast with a support member of the rotating shaft.

- The annular flange is a molded part. Alternatively, the annular flange is a stamped part.

The invention also concerns a rotary electric machine, such an electric motor, having a casing supporting a rotating shaft. According to the invention, this rotary electric machine includes at least one 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 front view along rotation axis of bearing assembly of figure 1 , of a sensor body belonging to said bearing assembly, mounted in a support flange,

- figure 3 is a sectional view of a portion of the bearing assembly of figure 1 , along plane III,

- figure 4 is a perspective view, in another direction, of an annular flange belonging to the bearing assembly of figure 1 ,

- figure 5 is a sectional view, along plane V, of the support flange of figure 2.

- Figure 6 is a perspective view of a bearing assembly according to a second embodiment of the invention.

DESCRIPTION OF SOME EMBODIMENTS

The rolling bearing assembly A represented on the figures is used to rotatively hold a rotatable 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 nonrepresented 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 rotating 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.

Bearing assembly A also includes several sensors adapted to detect a rotation parameter of encoder washer 50. One of these sensors is visible on figures 3 and 4 with reference 60. Actually, several sensors can be distributed around axis XA. These sensors 60 are installed within a sensor body 70 formed of a printed circuit board 72 and a synthetic ring 74 provided with respective housings for the sensors 60. An electric cable 76 is connected to PCB 72 and enables to feed it with electric power and convey output signals of sensors 60. The electrical connections between cable 76 and PCB 72 are located within synthetic ring 74.

Bearing assembly A also includes an annular 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, X70 and X80 respectively denote the central axis of spacer ring 30, encoder washer 50, sensor body 70 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.

In the vicinity of the connection between electric cable 76 and PCB 72, external flat annular band 81 comprises a radial portion 88 which has the shape of bottom wall 83 and which extends radially to axis X80. Electric cable 76 is guided through radial portion 88 which comprises a recess 880 adapted to accommodate electric cable 76. Recess 880 has substantially a cylindrical shape corresponding to the shape of electric cable 76 and centered around a longitudinal axis X88.

Recess 880 extends from a flat annular surface 810 of external flat annular band 81 in radial portion 88. Recess 880 is therefore remote from the electrical connections between electrical cable 76 and PCB 74.

The depth D88 of recess 880, from surface 810 to the bottom of recess 880, is slightly inferior to the diameter D76 of electric cable 76. A small radial portion of electric cable 76 therefore protrudes from surface 810 when cable 76 is received in recess 880.

When assembly A is mounted, annular flange 80 is pressed against spacer 30 by screws 40 along axis X80. Therefore, surfaces 810 and 32 are pressed against each other. The protruding portion of electric cable 76 permits a pressing of cable 76 between recess 880 and surface 32. As recess 880 is located remotely from the electric connections between electric cable 76 and PCB 72, undesired tractions or efforts that may be exerted on electric cable 76 are transmitted to radial portion 88 and are not exerted on the electrical connections between cable 76 and PCB 72. This improves the robustness and the reliability of electric cable 76.

As shown on figures 4 and 5, recess 880 has the shape of a cylinder whose longitudinal axis is aligned with the longitudinal axis of electric cable 76. In addition, the width W88 of recess 880 on the side of surface 810 is slightly inferior to the diameter D76 of cable 76. This geometry, together with the fact that electric cable 76 has the property to elastically deform, allows a pinching and a pressing of electric cable 76 in recess 880. This permits to further concentrate undesired forces exerted on electric cable 76 on radial portion 88.

In the embodiment represented on figures 1 to 5, annular flange 80 is a molded part. In a second embodiment represented on figure 6, only the differences from the first embodiment are detailed. In this embodiment, annular flange 80 is a stamped metal sheet part. Recess 880 is formed by a curved portion 812 of external flat annular band 81 . The curved portion 812 which forms recess 880 permits to accommodate cable 76 to allow a pressing of electric cable 76 between recess 880 and surface 32.

According to a non shown embodiment of the invention, electric cable 76 may be pressed between recess 880 and a flat annular surface which may not be provided on spacer 30 but on support member 4.

Claims

1 . - Bearing assembly (A) for rotatively holding a shaft (2) with respect to a fixed element (4, 30), said bearing assembly comprising:

- a bearing (10) with a rotatable inner ring (14) and a fixed outer ring (12) to be immobilized within a housing (4A) of said fixed element (4, 30),

- an encoder washer (50) fast in rotation with the rotatable ring (14),

- at least one sensor (60) adapted to detect at least one rotation parameter of the encoder washer (50),

- a sensor body (70) for holding said sensor (60),

- an annular flange (80) for mounting said sensor body (70) with respect to said fixed outer ring (12),

- an output electric cable (76) electrically connected to the sensor body (70) for transmitting output signals delivered by said sensor (60) to a reception device, wherein:

- the annular flange (80) comprises a recess (880) adapted to accommodate the output electric cable (76), said recess (880) having a depth (D88) slightly inferior to the diameter (D76) of the cable (76),

- the fixed element (4, 30) comprises a flat annular surface (32) adapted to cooperate with a flat annular surface (810) of the annular flange (80) on which the recess (880) is provided,

- the cable (76) is pressed between the recess (880) and the flat annular surface (32) of the fixed element remotely from the electrical connections between the cable (76) and the sensor body (70).

2. - Bearing assembly according to claim 1 , wherein the recess (880) has the shape of a cylinder having a longitudinal axis (X88) aligned with the axis of the cable (76).

3. - Bearing assembly according to claim 2, wherein the width of the recess (880) on the side of the flat annular surface (810) of the flange (80) is slightly inferior to the diameter (D76) of the cable (76).

4. - Bearing assembly according to one of the previous claims, wherein the flat annular surface (32) of the fixed element (4, 30) is located on a spacer ring (30) fast with a support member (4) of the rotating shaft (2).

5. - Bearing assembly according to one of the previous claims, wherein the annular flange (80) is a molded part.

6. - Bearing assembly according to one of claim 1 to 4, wherein the annular flange (80) is a stamped part.

7. - A rotary 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.