TECHNICAL FIELD OF THE INVENTION

The present invention relates to a rolling bearing assembly. Besides, the present invention relates to a method for assembling such a rolling bearing assembly. The present invention can be used for example in a wheel of a two- wheels vehicle, such as a motorcycle or a bicycle. BACKGROUND ART OF THE INVENTION

EP-A-0 495 323 discloses a ball bearing assembly comprising a ball bearing having an inner ring and an outer ring, a target rotatable around an axis of rotation of the ball bearing, and a sensor unit holding a sensing element for detecting or reading the target. The target is secured to the inner ring, whereas the sensor unit is secured to the outer ring. A clearance or gap is arranged between the sensing element and the target. The target may be, for instance, of the magnetic or optical kind. A seal is fastened to the inner ring and it extends up to the outer ring. Thus, a portion of the seal cooperates with the outer ring so as to prevent ingress of contaminants inside the ball bearing.

The gap between the sensing element and the target is not sealed with respect to the exterior of the ball bearing. Hence, exterior contaminants can ingress the gap and accumulate therein. Eventually, the accumulated contaminants can impede or even thwart the reading of the rotating target by the sensing element. Hence, the accumulated contaminants can hinder the calculation of the rotation speed .

Moreover, the contaminants accumulated in the gap may induce undesirable frictions between the opposing surfaces of the target and of the sensing element. Such undesirable frictions may eventually cause wearing of these opposing surfaces, hence reduce the service life of the ball bearing assembly. SUMMARY OF THE INVENTION

On object of the present invention is to overcome the aforementioned drawback, by providing a rolling bearing assembly having a structure and an arrangement preventing the ingress of exterior contaminants into a gap between its target and its sensing element.

To achieve this object, the subject matter of the present invention is a rolling bearing assembly comprising:

a rolling bearing having an inner ring and an outer ring,

a target rotatable around an axis of rotation of the rolling bearing,

- a sensor unit including at least one sensing element, the sensing element being arranged to read the target with a gap between the sensing element and the target,

wherein:

the target is fast in rotation with the outer ring,

- the sensor unit is fixed relative to the inner ring,

the rolling bearing assembly further comprises a sealing member in the general shape of a ring, the sealing member being fast in rotation with the outer ring , the sensor u n it com prising a seal ing surface adapted to cooperate with the sealing member, so as to seal the gap against exterior contaminants.

The cooperation of the sealing member and the sealing surface into the rolling bearing assembly permits to seal the gap against exterior contaminants.

According to advantageous but optional features, considered on their own or in any technical feasible combination:

- The sealing member is in contact with the sealing surface.

- A tight clearance separates the sealing member from the sealing surface.

- The seal ing surface is a radial surface in the shape of a cyl inder, the sensing element being arranged to read in a direction perpendicular to the axis of rotation.

- The sealing surface is an axial surface in the shape of an annulus, the sensing element being arranged to read in a direction parallel to the axis of rotation. - The sensor unit comprises a sensor body and a separate part which is secured to the sensor body, the sealing surface being formed onto the separate part.

- The sealing surface is formed by a surface of a body of the sensor unit. - The sealing member has an outer diameter approximately equal to the outer diameter of the outer ring.

- The sealing member has an outer diameter larger than the outer diameter of the outer ring, the sealing member extending, along a direction perpendicular to the axis of rotation, partially in front of the outer ring.

- The outer ring extends at least partially beyond the sensor unit along a direction perpendicular to the axis of rotation.

- The rolling bearing assembly further comprises a ring-shaped seal fast in rotation with the outer ring, the target being secured to or integral with the ring- shaped seal.

- The sealing member includes an elastomeric material.

- The sealing member includes a metallic material.

- The sealing member is made of a labyrinth seal.

- The sensor unit has a generally rotational symmetry around the axis of rotation.

Besides, a subject matter of the present invention is a method for assembling a rolling bearing assembly to a rotating body having a shaft and a hub, like a wheel, wherein the method comprising the steps of:

- securing the inner ring to the shaft;

- placing the sealing member around the shaft and past the sensor unit; - press-fitting the outer ring into the hub;

- securing the sealing member to the hub, so as to fasten in rotation the sealing member with the outer ring;

- securing sensor unit onto the shaft.

According to an advantageous but optional feature, the method further comprises the step of appropriately bending a cable of the sensor unit, so as to engage the sealing member around the cable and around the shaft. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be well understood on the basis of the following description, which is given as an illustrative example, without restricting the scope of the invention, and in relation with the annexed drawings among which:

- figure 1 is a cross-section of a rolling bearing assembly according to the present invention;

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

- figure 3 is a view, at a smaller scale, of a hub and a fork of a two-wheels vehicle, the hub comprising the rolling bearing assembly of figure 1 ;

- figure 4 is a perspective view of the rolling bearing assembly in a disassembled state during a step of an assembling method according to the present invention; and

- figure 5 is a perspective view, at an angle different from figure 4, of the rolling bearing assembly of figure 4 during a subsequent step of the assembling method.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Figures 1 and 2 depict a rolling bearing assembly 1 comprising a ball bearing 2 which has an inner ring 21 and an outer ring 22. Ball bearing 2 includes balls 23 arranged to roll between inner ring 21 and outer ring 22. Rolling bearing assembly 1 is shown in its service state, after completion of an assembling method according to the present invention and hereafter described in relation with figures 4 and 5.

In this service state, inner ring 21 is secured to a shaft 3 and outer ring 22 is secured to a hub 4 of a not-shown wheel belonging for instance to a not-shown two-wheels vehicle, such as a motorcycle or a bicycle. Outer ring 22 can be press-fitted into a cylindrical bore 40 of hub 4. Outer ring 22 is hence fast in rotation with hub 4. Outer ring 22 and hub 4 are intended to rotate around an axis X ₂ -X'2 of rotation of the ball bearing 2, whereas inner ring 21 and shaft 3 are intended to remain static.

Two ring-shaped seals 50 and 51 are mounted between inner ring 21 and outer ring 22, one on each axial face of ball bearing 2. Ring-shaped seals 50 and 51 are secured to outer ring 22. As known per se, ring-shaped seals 50 and 51 prevent ingress of exterior contaminants inside ball bearing 2. Also, ring-shaped seals 50 and 51 prevent leaks of lubricating fluid outside of ball baring 2.

Roll ing bearing assembly 1 further comprises a target 5, in the form of an encoder washer, which is attached to or integral with ring-shaped seal 50. Since ring-shaped seal 50 is secured to outer ring 22 and target 5 is attached to ring- shaped seal 50, target 5 is fast in rotation with outer ring 22. Therefore, target 5 is rotatable around axis X ₂ -X' ₂ . Target 5 has a generally rotational symmetry around axis X ₂ -X'2 and, more accurately, the shape of an annulus.

Rolling bearing assembly 1 also comprises a sensor unit 6 which holds a sensing element or sensor 61 . Sensor 61 is arranged to detect or read target 5, along an axial direction. To achieve this function, sensor 61 extends approximately at the same position than target 5 along a direction Y ₂ -Y' ₂ , which is radial with respect to axis X ₂ -X' ₂ . Along an axial direction parallel to axis X ₂ - X' ₂ , sensor 61 is mounted so that sensor 61 and target 5 are separated by a gap 1 1 which is less than the maximum sensing distance of sensor 61 .

Target 5 can comprise a magnetic material and sensor 61 can perform a magnetic detection of target 5, for instance by detecting the intensity or the variation of the magnetic field generated by target 5.

In the present application, the term "axial" refers to a direction which is parallel to the axis of rotation X ₂ -X' ₂ of ball bearing 2. The term "radial" refers to a d i rection wh ich is perpend icu lar to the axis of rotation X ₂ -X' ₂ , l ike rad ial direction Y ₂ -Y' ₂ at figure 1 . Conversely, a surface is said to be "axial" or "radial" by reference to a d irection wh ich is local ly or g lobally perpend icular to th is surface.

Sensor unit 6 is attached to shaft 3 by means of a sleeve 30. Sensor unit 6 and sleeve 30 both have a generally rotational symmetry around axis X ₂ -X' ₂ . The term "generally" refers to the overall shape, notwithstanding the local exceptions visible on figures 1 and 2. Indeed, sensor unit 6 also comprises a cable 63 which protrudes outwardly along a radial direction.

Cable 63 can transmit electric signals generated by sensor 61 while reading target 5. Sensor un it 6 can be secu red to sleeve 30 by overmold ing, gluing , welding or else. Cable 63 and sensor 61 are overmoulded onto a sensor body 62 of sensor unit 6.

Rolling bearing assembly 1 further comprises a sealing member 8 in the general shape of a ring. In the example of figures 1 and 2, the sealing member 8 is a lip seal. Sealing member 8 is mounted fast in rotation with outer ring 22. Indeed, sealing member 8 has a securing portion 83 which is adhered or overmoulded onto a flange 9. In turn, flange 9 is secured to the open end of bore 40, for instance by press-fitting or shrinking. Flange 9 has approximately an "L" cross-section in a plane comprising axis X2-X 2, like the plane of figure 1 or 2.

Besides, sealing member 8 has a lip 81 for contacting a sealing surface 78.

Sealing member 8 has a middle portion 82 for carrying lip 81 and securing portion 83. Sealing member 8 has a generally rotational symmetry around axis X ₂ -X'2- Along radial direction Y2-Y 2, lip 81 extends in the inner region, of smaller diameter, of sealing member 8, whereas securing portion 83 extends in the outer region, of larger diameter, of sealing member 8. Middle portion 82 is termed " m idd l e" , beca u se it extend s between l i p 81 and securing portion 83, substantially along radial direction Y2-Y'2-

Sealing surface 78 belongs to a separate part which is preferably cylindrical and which is itself secured to a shoulder 67 of sensor unit 6. In the example of figures 1 and 2, the separate part is in the form of a cylinder 7. The adjective separate means that it is distinct from sensor body 62. Sealing surface 78 is an axial surface in the shape of an annulus.

The material constituting cyl inder 7 is selected so that the surface roughness of the sealing surface 78 complies with the friction against sealing member 8, in order to limit the wear thereof and the loss of energy by friction. Preferably, the cylinder 7 is made of steel such as a steel for seal flinger. The sealing surface 78 can be formed by a layer of PTFE or any equivalent low- friction material.

Sealing surface 78 is adapted to cooperate with sealing member 8, in particular with lip 81 , so as to seal gap 1 1 against exterior contaminants. Lip 81 of sealing member 8 is in contact with sealing surface 78. In order it to withstand frictional forces, sealing member 8 includes an elastomeric material, in particular for lip 81 . Hence, the cooperation between sealing member 8 and sealing surface 78 is herein based on frictional contacts.

Cylinder 7 extends beyond shoulder 67 along an axial direction. On one end, cylinder 7 has a securing wing 71 for attaching cylinder 7 onto shoulder 67 of sensor unit 6. For instance, cylinder 7 can be shrunk or press-fitted on sensor unit 6 or attached thereto by any other equivalent means. On its other end, cylinder 7 has a cantilever wing 72 which axially protrudes towards outer ring 22 and between sealing member 8 and target 5. Cantilever wing 72 thus forms a chicane or labyrinth seal which further helps preventing ingress of exterior contaminants into gap 1 1 .

Sealing member 8 has an outer diameter D ₈ 3 which is approximately equal to the outer diameter D ₂ 2 of outer ring 22. Thus, rolling bearing assembly 1 can have a relatively compact structure or relatively small overall dimensions. Furthermore, bore 40 of hub 4 is relatively easy to machine. The hub can advantageously be made of aluminum.

Besides, sealing member 8 has an inner diameter D ₈ i which is slightly inferior to the diameter D62 of sensor unit 6, so that sealing member 8 contacts sealing surface 78. Thus, sealing member 8 can easily be engaged around sensor unit 6 so as to be placed between sensor unit 6 and ball bearing 2 as hereafter described in relation with figures 4 and 5.

Outer ring 22 extends partially beyond sensor unit 6 along a radial direction, excepted where cable 63 extends outwardly from sensor body 62. Thus, a part of the axial, outside face 222 of outer ring 22 is clear from sensor unit 6 when seen along arrow on figure 1 . This permits to apply axial forces on outer ring 22 towards bore 40 so as to press-fit bal l bearing 2 into hub 4, as hereafter described in relation with figures 4 and 5.

Figure 3 depicts the rolling bearing assembly 1 in its assembled state into the hub 4 of a not shown wheel held by a fork 1 0. The assembled state of the rolling bearing assembly 1 as illustrated on figure 3 results from the completion of an assembling method according to the present invention which will be hereafter described.

Inner ring 21 , outer ring 22 and balls 23 are preassembled to form ball bearing 2. In an initial step, inner ring 21 is secured to shaft 3.

As illustrated on figure 4, the sealing member 8 is engaged onto cable 63. Then sealing member 8 is drawn around sensor unit 6 so as to be placed around shaft 3 between sensor unit 6 and ball bearing 2. In order to engage sealing member 8 past cable 63 and past sensor unit 6, cable 63 can be bent appropriately, as illustrated on figure 4.

Thereafter, outer ring 22 is press-fitted into hub 4, by means of a not shown tool which can apply axial forces on the axial, outside face 222 of outer ring 22 which is clear from sensor unit 6.

Sealing member 8 is then secured to the hub 4, so as to fasten in rotation sealing member 8 to outer ring 22. For instance, flange 9 can be press-fitted, shrunk or welded into bore 40.

At a next step, sensor unit 6 is secured on shaft 3, for instance by shrinking or snapping in sleeve 30 to shaft 3.

The completion of an assembling method according to the present invention results in a rolling bearing assembly 1 according to the present invention, like the one illustrated on figure 3.

According to a not shown embodiment, the sealing member can be separated from the sealing surface by a tight clearance. In such an embodiment, the sealing member and the sealing surface are not in contact, unlike sealing member 8 and sealing surface 78. This non-contacting sealing member can include a metallic material and/or be made of a labyrinth seal so as to provide several chicanes preventing ingress of exterior contaminants into the gap.

According to another not shown embodiment, the sealing surface 78 can be an axial surface in the shape of an annulus, the sensor being arranged to read along a direction perpendicular to the axis of rotation. This arrangement permits to reduce the overall dimensions of the rolling bearing assembly along a radial direction. Alternatively, the sealing surface 78 can have a frustoconical shape.

According to a further not shown embodiment, the sealing surface can be formed by a surface of the sensor unit, in particular of the sensor body 62, unlike sealing surface 78. In such an embodiment, the plastics material constituting the sensor body 62 must be selected so that the surface roughness of the sealing surface complies with the friction against the sealing member, in order to limit the wear thereof. For instance, the sensor unit can be made of or comprise a layer of hard, low-friction material such as PEEK or PTFE. These two embodiments avoid mounting and using a supplementary separate part, like cylinder 7.

According to another not shown embodiment, the sealing member can have an outer diameter which is larger than the outer diameter of the outer ring. In such an embodiment, the sealing member extends partially in front of the outer ring along a radial direction. Such an arrangement provides a high sealing for the gap.

The invention has been described with balls as rolling elements. However, other rolling elements may be contemplated to implement the present invention, like rollers or needles.

Besides, the target can be discrete instead of symmetric.

Moreover, means for remotely transmitting signals, like an antenna, can be used instead of cable 63, so as to reduce the overall dimensions of a rolling bearing assembly according to the present invention.

Instead of a magnetic detection of target 5 by sensor 61 , the rolling bearing assembly can comprise a sensing element performing an optical reading of a purposely designed target. Other kinds of reading may be contemplated.

A rolling bearing assembly according to the present invention prevents the ingress of exterior contaminants into the gap between the target and the sensing element. Hence, the detection or reading of the rotating target by the sensing element can be performed accurately. Furthermore, a rolling bearing assembly according to the present invention has a relatively longer service life, since the exterior contaminants can not accumulate in the gap.