TECHNICAL FIELD OF THE INVENTION

The invention relates to a rolling bearing assembly and to an electric motor comprising such a rolling bearing assembly.

BACKGROUND OF THE INVENTION

On rolling bearing assemblies equipped with sensor units, the rotating ring of the bearing must be blocked in axial translation with respect to the rotatable element of the assembly. This translation blocking is generally obtained with elastic rings mounted in specifically provided grooves. This solution implies supplementary productions costs.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a rolling bearing assembly in which the rotating ring of the bearing is blocked in axial translation in more simple way than in the prior art.

To this end, the invention concerns a rolling bearing assembly comprising a rotating element adapted to rotate with respect to a fixed element, a bearing having a rotating ring fast in rotation with the rotatable element and a fixed ring fast in rotation with the fixed element, and a sensor unit including an encoder fast in rotation with the rotatable element and a sensing element fixed with respect to the fixed element. This rolling bearing is characterized in that the encoder is mounted in or on the rotatable element so as to block the rotating ring in translation with respect to the rotatable element along the rotation axis of the rotatable element.

Thanks to the invention, the rotating ring of the bearing of the assembly is axially held in place thanks to the encoder of the sensor unit. This avoids providing the rotating ring of the bearing with specific fastening means with the rotatable element of the assembly.

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

- The rotating ring of the bearing is blocked in translation, on a side opposed to the encoder, by an axial surface of the rotatable element.

- The encoder comprises an axial planar surface adapted to exert an axial blocking contact on a corresponding axial lateral surface of the rotating ring of the bearing.

- The encoder comprises a stop surface protruding in a cavity of a cylindrical surface of a tubular portion of the rotatable element.

- The encoder is press fitted in or on a tubular portion of the rotatable element against an axial surface of the rotating ring of the bearing.

- The encoder comprises a frame and magnetic elements arranged around the rotation axis of the encoder.

- The rotating ring is the outer ring of the bearing.

- The rotating ring is the inner ring of the bearing.

- The sensing element is adapted to read the encoder along a radial direction.

The invention also concerns an electric motor characterized in that it comprises a rolling bearing assembly as mentioned here-above, and in that it comprises a magnetized ring fast in rotation with the rotatable element to form a rotor and electric coils fixed to the fixed element to form a stator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in correspondence with the annexed figures, as an illustrative example. In the annexed figures: - figure 1 is a longitudinal sectional view of a rolling bearing assembly according to a first embodiment of the invention;

- figure 2 is a view, at a larger scale, of detail II on figure 1 ;

- figure 3 is a view similar to figure 2, for a second embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Each electric motor M represented on one of figures 1 to 3 comprises a stator S including a housing 2 in which stator coils 22 are arranged. Stator S also includes a non- rotatable shaft 4 mounted in a hole 24 of housing 2. Non-rotatable shaft 4 defines a longitudinal axis X4.

Electric motor M also includes a rotor R which comprises a rotor shaft 6 adapted to rotate around non-rotatable shaft 4 around axis X4. Rotor R also comprises a tubular portion 8 which extends on the opposite side of rotor shaft 6 with respect to an end 62 which extends outside a casing 10 of electric motor M. Tubular portion 8 is centred around axis X4 and has a diameter superior to the diameter of rotor shaft 6.

Rotor R defines an annular internal volume V8 which extends axially from an internal surface of housing 2 and an axial bottom surface 82 of tubular portion 8. Internal volume V8 extends radially from a cylindrical outer peripheral surface 42 of shaft 4 and an inner cylindrical surface 84 of tubular portion 8 centred around axis X4. The adjectives "axially" and "radially" are defined with respect to the rotation axis X4 of electric motor M. An axial direction denotes a direction parallel to axis X4, while a radial direction defines a direction perpendicular to axis X4.

A rolling bearing 12 is mounted in internal volume V8 to permit the rotation between rotor R and stator S. Rolling bearing 12 comprises an inner ring 120 fixed on non-rotatable shaft 4, an outer ring 122 fast in rotation with rotor R and one row of balls 124 arranged between inner ring 120 and outer ring 122. According to a non-shown embodiment of the invention, rolling bearing 12 may comprise different rolling elements such as rollers or needles. The bearing 12 may also comprise several inner rings and/or several outer rings, as well as a plurality of rows of rolling element. In particular, the bearing may comprise one inner ring , one outer ring, and two rows of balls...

Rotor R further includes a magnetized ring 14 mounted on an outer peripheral surface 86 of tubular portion 8, so as to radially face stator coils 22. The rotation of rotor R is driven by the magnetic attraction between stator coils 22 and magnetized ring 14, this magnetic attraction being created by stator coils 22, which are fed with electrical current.

Electric motor M also comprises a sensor unit 16 for sensing the angular position or the rotational speed of rotor R with respect to stator S. Sensor unit 16 comprises an encoder ring 160 fast in rotation with rotor R, and a sensing element 162. Encoder ring 160 produces magnetic field variations which are detected by a sensing element 162 which is fixed with respect to stator S. Sensing element 162 is housed in a sensor body 164 which includes data processing means and a connection area in which a connector can be plugged. Sensing element 162 is fixed to inner ring 120 thanks to fastening means comprising an axially extending member 162a having a terminal bulge 162b, adapted to be received in a circular groove 120b provided on the inner side of the inner ring 120 with respect to axis X4.

The assembly of non-rotatable shaft 4, rolling bearing 12, rotor shaft 6, tubular portion 8 and sensor unit 16 forms a rolling bearing assembly. In the case stator coils 22 are fixed to non-rotatable shaft 4 and a magnetized ring 14 is fixed to rotor shaft 6, the assembly forms an electric motor M having a rotor R and a stator S.

According to an non-shown embodiment of the invention, the rolling bearing assembly formed by non-rotatable shaft 4, rotor shaft 6, tubular portion 8, rolling bearing 12 and sensor unit 16 may be used in a different application, such as, for example, a wheel of an automotive vehicle or a motorcycle.

A first embodiment of the invention is represented on figures 1 and 2. Encoder 160 comprises a ring-shaped frame 160a fast in rotation with outer ring 122. Magnetic elements 160b, such as permanent magnets, are fixed on the inner side of frame 160a and are distributed around axis X4. Optionally, frame 160a may be made of a metallic material.

Encoder ring 160 comprises a fastening collar 160c adapted to be received in a corresponding recess 122b provided on lateral surface 122a of outer ring 122. Magnetic elements 160b are oriented towards axis X4, so that sensing element 162 detects the magnetic field variations generated by the rotation of encoder ring 160 along a radial direction.

Encoder 160 is fast in rotation with rotor R, thanks to a stop surface 160d of frame 160a, which radially protrudes in a cavity 84a provided in inner surface 84 of tubular portion 8. Frame 160a comprises an axial lateral surface 160e which is planar and cooperates with lateral surface 122a of outer ring 122. The contact between surface 160e and surface 122a permits to block the translation of outer ring 122 along axis X4 with respect to tubular portion 8.

A second embodiment of the invention is represented on figure 3. In this embodiment, elements similar to the first embodiment have the same references and work in the same way. This embodiment differs from the first embodiment by the fact that frame 160a does not comprise any stop surface 160d, and inner surface 84 does not comprise any cavity 84a. Frame 160a is directly press-fitted against the inner surface 84 of tubular portion 8.

Encoder 160 is press-fitted in tubular portion 8, so that axial surface 160e cooperates with lateral surface 122a of outer ring 122, in order to block axial translation of outer ring 122 with respect to tubular portion 8.

According to a non-shown embodiment of the invention, encoder ring 160 may not comprise any frame 160a. In such a case, magnetic elements 160b may be directly press- fitted in tubular portion 8 or be specifically produced so as to comprise stop surfaces to be received in cavity 84a. According to a non-shown embodiment of the invention, the rolling bearing assembly formed by non-rotatable shaft 4, rotor shaft 6, tubular portion 8, rolling bearing 12 and sensor unit 16 may be inverted. Inner ring 120 may be the rotating ring of rolling bearing 12, and encoder 160 may be fast in rotation with inner ring 120. In such a case, encoder 160 may be adapted to block in axial translation inner ring 120 is a way similar to the embodiments of figures 1 to 3.

In the embodiments described above, the magnetized ring 14 is preferably obtained from the magnetization of a ring previously overmoulded onto the shaft.

Alternatively, the magnetized ring 14 may be obtained by inserting a plurality of permanent magnets in slots arranged on the shaft, or by attaching the permanent magnets directly onto the shaft, preferably by gluing. Such permanent magnets can advantageously be made from rare earth materials.