WO2012176013A1

WO2012176013A1 - Sensor unit for sensing the angular position of a rotatable element with respect to a fixed element and bearing assembly comprising such a sensor unit

Info

Publication number: WO2012176013A1
Application number: PCT/IB2011/001776
Authority: WO
Inventors: Franck Landrieve
Original assignee: Aktiebolaget Skf
Priority date: 2011-06-23
Filing date: 2011-06-23
Publication date: 2012-12-27

Abstract

This sensor unit (10) for sensing the angular position of a rotating element (4) with respect to a fixed element (2), comprises a coder element which is fast in rotation with the rotatable element (4), adapted to generate magnetic field variations as a function of its angular position, and a sensing element (20), fast with the fixed element (2), adapted to sense the magnetic field variations. The sensing element (20) extends in a limited angular sector of an annular gap extending between the rotatable element (4) and the fixed element (2). The sensing element can comprise an inductive sensor having a coil and flux concentrators. The sensor may comprise a single magnet oriented tangentially, or two radially aligned, oppositely arranged magnets.

Description

SENSOR UNIT FOR SENSING THE ANGULAR POSITION OF

A ROTATABLE ELEMENT WITH RESPECT TO A FIXED ELEMENT AND BEARING ASSEMBLY COMPRISING SUCH A SENSOR UNIT TECHNICAL FIELD OF THE INVENTION

The present invention relates to a sensor unit for sensing the angular position of a rotatable element with respect to a fixed element. The invention also concerns a bearing assembly, in particular of the rolling type, comprising such a sensor unit. BACKGROUND OF THE INVENTION

Sensor units for sensing the angular position of a rotatable element often include induction sensors, for example known from US-5 309 094, involving a coder element, adapted to generate magnetic field variations and a sensing element adapted to determine, on the basis of a sensing of the magnetic field variations, the angular position of the rotating element.

The coder element is generally a magnetic ring formed by several magnets having inverted polarities along the circumference of the ring. The sensing element is generally an annular coil in which an annular magnetic core is mounted, the coil facing the whole of the circumference of the coder element.

This annular structure is relatively bulky and provokes issues when it must be integrated in some places of automotive vehicles, such as front wheels of motorcycles, where there is not much space to do so.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a sensor unit for sensing the angular position of the element rotating with respect to a fixed element, which is more compact than the sensor devices of the prior art.

To this end, the invention concerns a sensor unit for sensing the angular position of a rotatable element with respect to a fixed element, comprising a coder element which is fast in rotation with the rotatable element, adapted to generate magnetic field variations as a function of its angular position, and a sensing element, fast with the fixed element, adapted to sense the magnetic field variations. This sensor device is characterized in that the sensing element extends in a limited angular sector of an annular gap defined between the rotating element and the fixed element.

Thanks to the invention, the non-rotatable part of the sensor is much smaller than an annular coil for sensing the magnetic field variations. This permits to mount the sensing element in a relatively small space and therefore to save the space for other components or functions, for example signal processing functions.

According to further aspects of the invention, which are advantageous but not compulsory, such a sensor unit may incorporate one or several of the following features:

- The sensing element is mounted on a printed circuit board fast with the fixed element and which comprises means for processing and transmitting data delivered by the sensing element.

- The printed circuit board has an annular shape centered around the rotation axis of the rotatable element.

- The sensing element includes one magnet having its poles oriented substantially tangentially to the circumference of the printed circuit board,

- The magnet is fast with two non-rotative flux concentrators, a coil is mounted and connected to the printed circuit board, along an axis radial to the rotation axis of the rotatable element, on an opposite side of the printed circuit board with respect to the magnet and

- The coder element comprises a rotatable inner flux concentrator and a rotatable outer flux concentrator concentric to the inner rotatable flux concentrator.

- Each non-rotating flux concentrator comprises an outer concentrating plate and an inner concentrating plate, both extending parallel to the rotation axis of the rotatable element.

- The sensing element comprises a core inserted in the coil along a longitudinal axis of the coil.

- Each of the rotatable inner and outer flux concentrators comprise teeth extending parallel to the rotation axis of the rotatable element and respectively radially facing, when rotating, the inner and outer concentrating plates of the non-rotating flux concentrators.

- The respective teeth of the rotatable flux concentrators are angularly offset so that when a tooth of the inner flux concentrator radially faces the inner plate of a first non- rotative flux concentrator and a first end of the core, a tooth of the outer flux concentrator radially faces the outer plate of the second non-rotative flux concentrator and a second end of the core.

- The rotatable flux concentrators are mounted in a non-magnetic holder fast in rotation with the rotatable element.

- The sensing element comprises two magnets oriented parallel to an axis radial to the rotation axis of the rotatable element, said magnets having their poles inversely oriented parallel to the radial axis, - A magnetic core is inserted in a coil mounted between the two magnets and connected to the printed circuit board,

- The coder element includes a rotatable flux concentrator fast with the rotatable element and

- Two opposite poles of the magnets are connected to each other, on an opposite side of the sensing element with respect to the rotatable flux concentrator, by a magnetized element.

- The rotatable flux concentrator comprises teeth extending parallel to the rotation axis of the rotatable element and radially facing, when rotating, outer poles of the magnets and an outer end of the core.

- The teeth of the rotatable flux concentrator are angularly offset so that when rotating a tooth radially and alternatively faces the north pole of a first magnet and the outer end of the core, or the outer end of the core and the south pole of the second magnet.

- The printed circuit board comprises means to measure, on the basis of an electrical current generated in the coil, the rotation speed of the rotating element with respect to the fixed element.

- The printed circuit board comprises means to electrically feed the means for processing and transmitting the data delivered by the sensing element with an electrical current generated in the coil.

The invention also concerns a bearing assembly comprising in particular a rolling bearing including a fixed ring fast with a fixed element, a rotatable ring fast with a rotatable element and rolling elements, and a sensor unit as mentioned here-above.

According to further aspects of the invention which are advantageous but not compulsory, such a bearing assembly may incorporate one or several of the following features:

- The bearing is of the rolling type and comprises rolling elements located between the fixed ring and the rotatable ring.

- The rolling elements are balls which travel along raceways arranged on the fixed ring and the rotatable ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in correspondence with annexed figures, as an illustrative example. In the annexed figures:

- Figure 1 is an exploded perspective view of a rolling bearing assembly comprising a sensor unit according to a first embodiment of the invention. Figure 2 is a sectional view of a portion of the rolling bearing assembly of figure 1 , along a longitudinal plane.

Figure 3 is a perspective view, at a larger scale, of detail III on figure 1 of a portion of a sensor unit according to a first embodiment of the invention.

- Figure 4 is a view of a portion of the sensor device of figure 4, from a different angle, a flux concentrator being partially exploded.

Figure 5 is a sectional view of the rolling bearing assembly of figure 2, along plane V on figure 2, in a first configuration.

Figure 6 is a view similar to figure 5, for a second configuration.

- Figure 7 is a partially exploded perspective view of a rolling bearing assembly comprising a sensor unit according to a second embodiment of the invention. Figure 8 is a perspective view, at a larger scale, of detail VIII on figure 7 of the portion of the sensor unit of figure 7.

Figure 9 is a sectional view, along the longitudinal plane, of the rolling bearing assembly of figure 7.

Figure 10 is a sectional view, along plane X on figure 9, of the rolling bearing assembly of figure 9, in a first configuration.

Figure 1 1 is a sectional view similar to figure 10, for a second configuration. DETAILED DESCRIPTION OF SOME EMBODIMENTS

The rolling bearing assembly A represented on figure 1 is adapted to be mounted on an automotive vehicle, such as a motorcycle.

Assembly A comprises a shaft 2, adapted to be fixed to a non-shown fork of a motorcycle and a hub 4, adapted to be fast in rotation with a non-shown wheel of the motorcycle, so that it rotates with respect to shaft 2 along a longitudinal axis X-X' of shaft 2.

Rotation of hub 4 with respect to shaft 2 is allowed by a rolling bearing 6. Rolling bearing 6 comprises an inner ring 60, an outer ring 62 and rolling elements, such as balls 64. Inner ring 60 is fixed to a sleeve 8, which is mounted on shaft 2. Inner ring 60 is mounted on an outer peripheral surface 80 of sleeve 8 and positioned against a shoulder 82 of sleeve 8, which delimits peripheral surface 80 with respect to a peripheral surface 84, which has a greater outer diameter than peripheral surface 80.

Outer ring 62 is fast in rotation with hub 4 and mounted on an inner peripheral surface 40 of hub 4. An annular gap G extends between surfaces 40 and 84.

Rolling bearing assembly A is equipped with a sensor unit 10, adapted to detect or sense the angular position of hub 4 with respect to shaft 2 in order to determine the rotation speed of hub 4 and the speed of the motorcycle. Sensor unit 10 comprises a coder element 12 which includes an inner flux concentrator 100 and an outer flux concentrator 120 fast with a flux concentrator holder 130. Flux concentrator 100 and 120 are concentric rings respectively equipped with spaced respective teeth 101 and 121 distributed regularly around their circumferences. Teeth 101 and 121 extend parallel to axis X-X'. Teeth 101 of inner flux concentrator are angularly offset with respect to teeth 121 of outer flux concentrator 120. Holder 130 includes a first part 131 on which flux concentrators 100 and 120 are axially positioned, and a second part 132 fast with first part 131 , which comprises a positioning hole 133 for angularly position inner flux concentrator 100 and outer flux concentrator 120 with respect to each other. Each of flux concentrators 100 and 120 comprises a positioning pin 103 and 123 adapted to cooperate with positioning hole 133.

Coder element 12 of sensor unit 10 is fast in rotation with hub 4 thanks to a clipping member 135, extending from holder 130 along axis X-X', and fixed to outer ring 62.

Sensor unit 10 further includes an induction sensing element 20. Sensing element

20 is mounted on a printed circuit board (PCB) 30 which comprises means for processing and transmitting the data delivered by sensor unit 10. PCB 30 has a radial annular shape centered around axis X-X' and extends on an area axially facing coder element 12. On a first surface 301 of PCB 30 oriented towards coder element 12, sensing element 20 comprises a coil 201 in which a core 203 is inserted. Core 203 may be made of a ferromagnetic material such as ferrite, and has a cylindrical shape extending along an axis X201 perpendicular to axis X-X' and parallel to surface 301.

On a surface 303 of printed circuit board 30 opposed to surface 301 , sensing element 20 is equipped with a magnet 205, which has substantially the shape of a parallelepiped extending along a longitudinal axis X205 perpendicular to axis X201. Axis X205 joins the north and south poles of magnet 205. Magnet 205 is positioned with respect to coil 201 so that magnet 205 and coil 201 form a cross, when viewed along axis X-X'. As magnet 205 is not visible on sectional plane V, it is represented in discontinuous lines on figures 5 and 6.

Magnet 205 is fast with printed circuit board 30 by two non-rotating flux concentrators 207 and 209, so that axis X205 is parallel to surface 303. Each of concentrators 207 and 209 comprises respective radially extending outer flux concentrating plates 2070 and 2090 and radially extending inner flux concentrating plates 2072 and 2092. Outer plates 2070 and 2090 extend parallel to axis X-X' towards coder elements 12 in the vicinity of an outer peripheral edge 305 of printed circuit board 30, radially outside this edge with respect to axis X-X'. Inner concentrating plates 2072 and 2092 extend parallel to axis X-X' towards coder element 12 in the vicinity of an inner peripheral edge 307 of printed circuit board 30, radially inside this edge with respect to axis X-X'.

Non-rotating flux concentrator 207 comprises a fastening plate 2074 on which the north pole N of magnet 205 is fixed. In the same way, non-rotating flux concentrator 209 comprises a fastening plate 2094 on which the south pole S of magnet 205 is fixed.

Sensing element 20 is housed into a circular sensing element holder 22, which is mounted on surface 84 of sleeve 8 and positioned against a stop 86 opposed to shoulder 82 along axis X-X'.

Printed circuit board 30 is equipped with components adapted to process data delivered by sensing element 20. For example, printed circuit board 30 can comprise microprocessors and memories. Printed circuit board 30 also comprises means to transmit, to a non-shown dashboard of the motorcycle, data delivered by sensing element 20 or calculated by the components of printed circuit board 30, generally parameters representative of the rotation speed of hub 4. To transmit such parameters, printed circuit board 30 can include a non represented radio signals emitter, and an antenna 310 connected to printed circuit board 30. Antenna 310 is housed in a groove 88 realized on surfaces 80 and 84 between stop 86 and an axial end 89 of sleeve 8 close to bearing 6. Antenna 310 extends partially outside a volume delimited by hub 4. This structure avoids blocking of radio signals by hub 4, which is generally metallic and may act as a faraday cage.

Rolling bearing assembly A works in the following way: while coder element 12 rotates with respect to sensing element 20, teeth 101 and 121 come close to concentrating plates 2070, 2072, 2090 and 2092. Teeth 101 and 121 extend on delimited angular sector and are angularly offset with respect to each other so as to achieve the two following configurations, which are obtained during a determined portion of a turn of coder element 12 with respect to sensing element 20.

In the first configuration represented on figure 5, a tooth 121 of outer flux concentrator 120 faces outer concentrating plate 2070 of flux concentrator 207 and an outer end 2030 of core 203 oriented opposite to axis X-X'. At the same time, outer concentrating plate 2090, opposed to plate 2070 with respect to outer core end 2030 faces mainly an empty space of outer flux concentrator 120. A tooth 101 of inner flux concentrator 100 faces an inner end 2032 of core 203 and the inner concentrating plate 2092 of non-rotating flux concentrator 209. At the same time, inner concentrating plate 2072 faces mainly an empty space of inner flux concentrator 100. The respective angular extensions of teeth 101 and 121 and their relative angular offset permit that the north pole N of magnet 205 is magnetically connected to outer end 2030 via external plate 2070 and tooth 121 , while south pole S of magnet 205 is magnetically connected to inner end 2032 via inner plate 2092 and tooth 101 . These magnetic connections induce a magnetic field represented by line B1 on figure 5, which originates from north pole N, crosses core 203 along axis X201 from outer end 2030 to inner end 2032 and ends on south pole S. This magnetic field B1 induces an electrical potential difference between the ends of coil 201 and therefore an electrical current.

When the rotation of coder element 12 goes further, a second configuration, corresponding to a second relative position of coder element 12 and sensing element 20, is obtained. In this configuration represented on figure 6, the respective positions of teeth 101 and 121 with respect to concentrating plates of flux concentrators 207 and 209 are inverted with respect to the configuration of figure 5. In other words, a tooth 121 now faces outer end 2030 and outer concentrating plate 2092, while a tooth 101 faces inner end 2032 and inner concentrating plate 2072. This means that north pole N of magnet 205 is now connected to inner end 2032, while south pole S is connected to outer end 2030. The magnetic field obtained in this case is represented by line B2, on figure 6, which crosses core 203 from inner end 2032 to outer end 2030, in the opposite direction with respect to the configuration of figure 5. The induced electrical current passing in coil 201 is therefore inverted with respect to the one which passes in the configuration of figure 5.

The two previous configurations induce a high efficiency of induced electrical current generation. Between these two configurations, transient periods take place. The generation of successive alternating magnetic fields B1 and B2 induces an alternating electrical current passing in coil 201 .

During a turn of coder element 12 with respect to sensing element 20, the configurations of figures 5 and 6 are repeated a predetermined number of times depending on the respective number of teeth 101 and 121.

The measurement of the frequency of this alternative current gives, via electronic processing taking into account the number of teeth 101 and 121 , the angular position of hub 4 with respect to shaft 2, and the rotation speed of hub 4. With further electronic processing implemented in the components of printed circuit board 30, the speed of the motorcycle can be determined and transmitted via antenna 310.

The electrical current obtained in coil 201 also provides electric energy for directly or indirectly operating the processing and transmitting means implemented on printed circuit board 30. Transducers can be used to obtain from the output current of coil 201 a direct current to be delivered to the electronic components of printed circuit board 30. Given that the electrical power needs of the electronic components of printed circuit board 30 are relatively low, for example below 10^"4 W, there is not a need for high electrical current generation. The electrical current generated in coil 201 is therefore sufficient to operate the processing and transmitting means. In other words, the tachymeter bearing formed by rolling bearing 6 and sensor unit 10 is autonomous, as it generates itself the electrical energy needed to process and transmit the data delivered by sensor unit 10. Besides, the relatively small space occupied by sensing element 20 allows mounting it in a limited angular sector of annular gap G and to improve the compactness of 10 and rolling bearing assembly A, by mounting sensing element 20 on PCB 30.

A second embodiment of the invention is represented on figures 7 to 1 1. Elements similar to the first embodiment have the same references and work in the same way.

An induction sensing element 45 is mounted on printed circuit board 30. Sensing element 45 comprises a central coil 451 extending along a radial axis X451. A core 453 is inserted in coil 451 along axis X451 . Core 453 is cylindrical shaped and is similar to core 203. Sensing element 45 further includes two magnets 455 and 457, which have a substantial parallelepiped shape extending along axes X455 and X457 parallel to axis X451. A first magnet 455 is positioned on the left of coil 451 on figures 10 and 1 1 and a second magnet 457 is positioned on the right of coil 451 . Core 453 has an outer end 4530 and an inner end 4532 oriented towards axis X-X'. Magnet 455 has its north pole N oriented towards outer end 4530 and its south pole S oriented towards inner end 4532 oriented towards axis X-X'. Magnet 457 has an inverted arrangement. Its north pole N is oriented towards inner end 4532 while its south pole S is oriented towards outer end 4530.

A plate 459 made of a magnetic material magnetically connects the south pole S of magnet 455 to the north pole N of magnet 457. Magnets 455 and 457, coil 451 , core 453 and link plate 459 are housed in a casing 461 which is fast with printed circuit board 30 thanks to fastening means comprising pins 463 adapted to be inserted in holes 312 of PCB 30. Assembly A comprises a sensing element holder 22 in which printed circuit board 30 and sensing element 45 are mounted. Assembly A comprises also a coder element 50, which includes a single rotating flux concentrator 500. Flux concentrator 500 has teeth 502 similar to teeth 121 , which extend parallel to axis X-X' and so as to radially face outer end 4530 of core 453 while rotating. Flux concentrator 500 is fast in rotation with outer ring 62 thanks to a fastening edge 504. Printed circuit board 30 is equipped with the same type of components as in the first embodiment, including processing and transmitting means for the data delivered by sensor element 45. Printed circuit board 30 also comprises an antenna 310 adapted to emit radio signals for transmitting data. In this embodiment, assembly A works in the following way: when flux concentrator 500 rotates with respect to sensing element 45, a first configuration corresponding to a first relative position of teeth 502 with respect to magnets 455 and 457 occurs. In this configuration represented on figure 10, a tooth 502 faces the north pole N of magnet 455 and outer end 4530 of core 453. As flux concentrator 500 is made of a magnetic material, this means that north pole N of magnet 455 is magnetically connected to outer end 4530, while inner end 4532 is magnetically connected to link plate 459. A magnetic field represented by line B3 on figure 10 therefore exists in coil 451 . Line B3 originates from north pole N of magnet 455 and crosses core 453 from outer ring 4530 to inner end 4532. This magnetic field B3 induces an electrical potential difference between the ends of coil 451 and therefore creates an electrical current passing in coil 451.

When the rotation of coder element 50 with respect to sensing element 45 goes further, a second configuration corresponding to a second relative position of coder element 50 with respect to sensing element 45 is obtained. In this configuration represented on figure 1 1 , a tooth 502 of flux concentrator 500 faces outer end 4530 and south pole S of magnet 457, while the north pole N of magnet 457 faces an empty space of flux concentrator 500.

Outer ring 4530 is therefore magnetically connected to the south pole S of magnet 457. As the south pole S of magnet 455 and the north pole N of magnet 457 are magnetically connected, magnet 455 and link plate 459 act as a north pole N together with the north pole N of magnet 457.

A magnetic field is therefore generated in coil 451. This magnetic field is represented by line B4 on figure 1 1 , which originates from a north pole formed by magnet 455, connects plate 459 and north pole N of magnet 457. Line B4 crosses core 453 from inner end 4532 to outer end 4530 and ends at the south pole S of magnet 457 via tooth 502. This provokes a potential difference between outer end 4530 and inner end 4532 and the generation of an induced electrical current in coil 451 . As the direction of the magnetic field B4 is inverted with respect to the direction of magnetic field B3, the electrical current obtained in the configuration of figure 1 1 is inverted with respect to the one obtained in the configuration of figure 10.

Thus, in the same way as in the first embodiment, rotation of coder element 50 with respect to sensing element 45 induces the generation of an induced alternative electrical current passing in coil 451. This electrical alternative current is processed in the same way as in the first embodiment in order to determine parameters representing the rotation speed of hub 4. These parameters are transmitted thanks to means implemented in printed circuit board 30. In the same way as in the first embodiment, this alternative current is used to electrically power the electronic components of printed circuit board 30. The structure of sensing element 45, which extends on a limited angular sector of annular gap G, improves the compactness of sensor unit 10 and assembly A.

According to an alternative non-shown embodiment of the invention, inner ring 60 of rolling bearing 6 may be the rotating ring while outer ring 62 may be the fixed ring.

The invention can be implemented in any kind of bearing, for instance a rolling bearing, such as a ball bearing, or a plain bearing.

Claims

1. A sensor unit (10) for sensing the angular position of a rotatable element (4) with respect to a fixed element (2), comprising:

- a coder element (12 ; 50) which is fast in rotation with the rotatable element (4), adapted to generate magnetic field variations as a function of its angular position,

a sensing element (20; 45), fast with the fixed element (2), adapted to sense the magnetic field variations,

wherein the sensing element (20; 45) extends in a limited angular sector of an annular gap (G) defined between the rotatable element (4) and the fixed element (2).

2. Sensor unit according claim 1 , wherein the sensing element (20; 45) is mounted on a printed circuit board (30) fast with the fixed element (2) and which comprises means for processing and transmitting data delivered by the sensing element (20; 45).

3. Sensor unit according to claim 2, wherein the printed circuit board (30) has an annular shape centered around the rotation axis (Χ-Χ') of the rotating element (4).

4. Sensor unit according to claim 3, wherein

- the sensing element (20) includes one magnet (205) having its poles (N, S) oriented substantially tangentially to the circumference of the printed circuit board (30),

- said magnet (205) is fast with two non-rotative flux concentrators (207, 209), a coil (201 ) is mounted and connected to the printed circuit board (30), along an axis (X201 ) radial to the rotation axis (Χ-Χ') of the rotatable element (4), on an opposite side (303) of the printed circuit board (30) with respect to the magnet (205) and

- the coder element (12) comprises a rotatable inner flux concentrator (100) and a rotatable outer flux concentrator (120) concentric to the inner rotatable flux concentrator (100).

5. Sensor unit according to claim 4, wherein each non-rotating flux concentrator

(207, 209) comprises an outer concentrating plate (2070, 2090) and an inner concentrating plate (2072, 2092), both extending parallel to the rotation axis (Χ-Χ') of the rotating element (4).

6. Sensor unit according to claim 5, wherein the sensing element (20) comprises a core (203) inserted in the coil (201 ) along a longitudinal axis (X201 ) of the coil (201 ).

7. Sensor unit according to claim 6, wherein each of the rotatable inner and outer flux concentrators (100, 120) comprise teeth (101 , 121 ) extending parallel to the rotation axis (Χ-Χ') of the rotatable element (4) and respectively radially facing, when rotating, the inner and outer concentrating plates (2072, 2092, 2070, 2090) of the non-rotating flux concentrators (207, 209).

8. Sensor unit according to claim 7, wherein the respective teeth (101 , 121 ) of the rotating flux concentrators (100, 120) are angularly offset so that when a tooth (101 ) of the inner flux concentrator (100) radially faces the inner plate (2072) of a first non-rotative flux concentrator (207) and a first end (2032) of the core (203), a tooth (121 ) of the outer flux concentrator (120) radially faces the outer plate (2090) of the second non-rotative flux concentrator (209) and a second end (2030) of the core (203).

9. Sensor unit according to claim 8, wherein the rotatable flux concentrators (100,

120) are mounted in a non-magnetic holder (130) fast in rotation with the rotatable element (4).

10. Sensor unit according to one of claims 2 and 3, wherein

- the sensing element (45) comprises two magnets (455, 457) oriented parallel to an axis (X451 ) radial to the rotation axis (Χ-Χ') of the rotating element (4), said magnets having their poles inversely oriented parallel to the radial axis (X451 ),

- a magnetic core (453) is inserted in a coil (451 ) mounted between the two magnets (455, 457) and connected to the printed circuit board (30),

- the coder element (50) includes a rotatable flux concentrator (500) fast with the rotatable element (4) and

- two opposite poles (N, S) of the magnets (455, 457) are connected to each other, on an opposite side of the sensing element (45) with respect to the rotating flux concentrator (500), by a magnetic element (459).

1 1 . Sensor unit according to claim 10, wherein the rotatable flux concentrator (500) comprises teeth (502) extending parallel to the rotation axis (Χ-Χ') of the rotatable element (4) and radially facing, when rotating, outer poles of the magnets (455, 457) and an outer end (4530) of the core (453).

12. Sensor unit according to claim 1 1 , wherein the teeth (502) of the rotating flux concentrator (500) are angularly offset so that, when rotating, a tooth (502) radially and alternatively faces the north pole (N) of a first magnet (455) and the outer end (4530) of the core (453), or the outer end (4530) of the core (453) and the south pole (S) of the second magnet (457).

13. Sensor unit according to claims 4 and 10, wherein the printed circuit board (30) comprises means to measure, on the basis of an electrical current generated in the coil (201 ; 451 ), the rotation speed of the rotating element (4) with respect to the fixed element (2).

14. Sensor unit according to claims 4 and 10, wherein the printed circuit board (30) comprises means to electrically feed the means for processing and transmitting the data delivered by the sensing element (20; 45) with an electrical current generated in the coil (201 ; 451 ).

15. Bearing assembly (A) comprising a bearing (6) including a fixed ring (60) fast with a fixed element (2), a rotatable ring (62) fast with a rotatable element (4), and a sensor unit (10) according to one of the previous claims.

16. Bearing assembly (A) according to claim 15 wherein the bearing (6) is of the rolling type and comprises rolling elements (64) located between the fixed ring (60) and the rotatable ring (62).

17. Bearing assembly according to claim 16 wherein the rolling elements are balls (64) which travel along raceways arranged on the fixed ring (60) and the rotatable ring (62).