TECHNICAL FIELD OF THE INVENTION

This invention relates to an encoder washer to be used with a bearing assembly and to a bearing assembly comprising such an encoder washer.

BACKGROUND OF THE INVENTION

In the field of bearings, it is known to use a sensor to determine a rotation parameter of a rotating ring. The accuracy of this determination is highly dependent on the thickness of the air gap between an encoder washer, fast in rotation with the rotatable ring, and the sensor. On the other hand, because of the tolerances in the manufacturing of the respective parts of the bearing, of the encoder washer and of the sensor, the thickness of the air gap might vary substantially of several tenth of a millimeter for an air gap having a nominal thickness of a few millimeters. This might lead to improper working of the sensing assembly constituted of the encoder washer and the corresponding sensor.

SUMMARY OF THE INVENTION

The invention aims at solving these problems with a new encoder washer with which variations of the thickness of an air gap can be accommodated.

To this end, the invention concerns an encoder washer, comprising a magnetic body and adapted to be mounted on a rotatable ring of a bearing assembly in a position where a surface of this magnetic body defines an air gap with a sensor of the bearing assembly, wherein the surface of the magnetic body is provided with at least one groove defining two edges with said surface, said two edges being located between two lateral edges of said surface or between a radial inner edge and a radial outer edge of said surface.

Thanks to the invention, the two edges defined by the groove and the surface of the magnetic body modify the magnetic field generated by the magnetic body in the air gap, in such a way that the intensity of this magnetic field is not drastically modified by a slight modification of the air gap thickness.

According to further aspects of the invention, which are advantageous but not compulsory, the encoder washer might incorporate one or several of the following features:

- The washer includes an armature to hold the magnetic body with respect to the rotating ring and the magnetic body is mounted on this armature. In such a case, the groove advantageously can extend from the above-mentioned surface to a face of the armature. - The groove has a rectangular cross section, a rounded cross section or a V- shaped cross section.

- The groove is provided in a median zone between two lateral edges of the surface or between the radial inner edge and the radial outer edge of the surface.

The invention also concerns a bearing assembly which comprises a bearing, with an inner ring and an outer ring and at least a sensor fast in rotation with a first ring, amongst the inner and outer rings. This rolling bearing assembly also comprises an encoder washer as mentioned here-above which is fast in rotation with the second one of the inner and outer rings.

Advantageously, the amplitude of a magnetic field in an air gap defined between the sensor and the surface of the encoder washer magnetic body varies by less than 10%, preferably by about 5%, when the thickness of the air gap varies by plus or minus 0,4 mm around a nominal value between 0.5 and 5 mm.

This amplitude can also vary by less than 7%, preferably by about 2%, when the thickness of the air gap varies by plus or minus 0,2 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better 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 sectional view of a rolling bearing assembly according to the invention,

figure 2 is an enlarged view of detail II on figure 1 ,

figure 3 is a perspective view of an encoder washer according to the invention, used in the rolling bearing assembly of figures 1 and 2,

figure 4 is an enlarged cross-section along line IV-IV on figure 3,

figure 5 is a representation of the amplitude of a magnetic field within an air gap of the assembly of figures 1 and 2, as a function of an air gap thickness variation, and

figures 6 to 9 are cross-sections similar to figure 4 for a second, a third, a fourth and a fifth embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The rolling bearing assembly 1 represented on figure 1 includes a rolling bearing 2 having a fixed outer ring 4 and an inner ring 6 rotatable around a central axis X2 of rolling bearing 2. Several balls 8 are installed within a chamber 10 defined between rings 4 and 6 and held in position within this chamber by a cage 12. These balls constitute rolling bodies for rolling bearing 2. The invention can also be implemented with another type of rolling bearing, e.g. a roller bearing or a needle bearing, or with a plain bearing.

In the present description, unless otherwise specified, the words "axial", "radial",

"axially" and "radially" are defined in relation to axis X2. A direction is "axial" when it is parallel to axis X2 and a direction or an axis is "radial" when it is perpendicular to and secant with such this axis.

An encoder washer 20 is fast in rotation with inner ring 6. Encoder washer 20 includes a metallic armature 22 and a magnetic body 24 mounted on this armature. Armature 22 is used to hold encoder washer 20 onto inner ring 6. Magnetic body 24 is made in a magnetic material such as ferrite, e.g. plasto-ferrite or elasto-ferrite, or a rare earth, such as NdFeB or Sm2Co17. This magnetic body is polarized in order to constitute several North and South magnetic poles distributed around a central axis X20 of encoder washer 20 which is superimposed with axis X2 when encoder washer 20 is mounted on inner ring 6.

A sensor unit 40 is mounted on outer ring 4 and includes at least one sensor cell 42 arranged in a sensor body 44 and connected to a printed circuit board 46 which is connected to a non represented electronic control unit via a cable 47. An air gap G is defined between a radial outer surface 26 of magnetic body 24 and a face 48 of sensor cell 42 oriented towards encoder washer 20. e _G denotes the radial thickness of air gap G, that is the radial distance between surface 26 and face 48.

Surface 26 extends, axially along axis X20, between a first lateral edge 262 and a second lateral edge 264.

A peripheral groove 265 is formed in outer surface 26 in a central zone of this surface that is in a zone Z ₂₆ median between edges 262 and 264. Groove 265 forms with outer surface 26 two edges 266 and 268 which are circular and parallel to edges 262 and 264 and located between edges 262 and 264 along axis X20.

Thus, surface 26 is divided into two annular sub-surfaces 26A and 26B which extend on either side of groove 265, respectively between edges 262 and 266 and edges 264 and 268.

Thanks to this configuration of outer surface 26, the magnetic field created by the succession of North and South poles of magnetic body 24 rotating around axes X2 and X20 is less influenced, by variations of the radial thickness e _G , than in case where outer surface 26 would extend continuously between edges 262 and 264. Figure 5 shows with curves C1 , C2, C3 and C4, four examples of the variation of the amplitude A or intensity of the magnetic field generated in an air gap G of a bearing of the prior art, as a function of the air gap thickness variation with respect to a nominal thickness of 1.2 mm. If one considers a thickness variation range between - 0,4 mm and + 0,4 mm, then the variation in the magnetic field amplitude A on curves C1 to C4 is about 24% of its value when the air gap thickness e _G equals the nominal value, that is when this variation is null. Such an amplitude variation could cause problems for the detection of the magnetic field.

Curves C'1 , C'2, C'3 and C'4 show values measured for four encoder washers embodying the invention. In this case, over the same air gap thickness variation range, between - 0,4 mm and + 0,4 mm with respect to value the nominal value, the magnetic field amplitude A variation is of about 5% for each of these curves.

The same kind of result can be obtained experimentally for a nominal value of the air gap thickness e _G between 0.5 and 5 mm: the magnetic field amplitude varies by less than 10%, preferably about 5%, on an air gap thickness range of ± 0,4 mm.

One can also notice on curves C'1 to C'4 that, in the air gap thickness variation range of ± 0,2 mm, the magnetic field amplitude varies by about 2%. Actually, for an air gap thickness e _G between 0.5 and 5 mm, the magnetic field amplitude varies by less than 7%, preferably by about 2%.

The second to fifth embodiments represented on figures 6 to 9 also embody the invention. On this figures, the same references are used to identify the same features as in the first embodiment. Here-after, only the differences between these embodiments and the first embodiment are mentioned.

In the embodiment of figure 6, the groove 265 has a curved section, as opposed to the rectangular cross-section of the groove 265 of the first embodiment.

In the third embodiment, the groove 265 has a V-shaped cross-section.

In the fourth embodiment, the groove 265 extends up to a face 222 of the armature 22 of the encoder body oriented towards the sensor cell. In other words, the magnetic body 22 is divided by the groove 265 into two separate sub-bodies 24A and 24B.

In the embodiments of figures 1 to 8, the encoder washer 20 is adapted to a sensor cell 42 whose reading direction is radial with respect to axis X2. In these embodiments, the surface 26 defining the air gap G is the outer radial surface of the body 24.

In the embodiment of figure 9, the encoder washer 20 is adapted to cooperate with a non represented sensor cell whose reading direction is parallel to the central axis of the bearing. In such a case, the surface 26 of the magnetic body 24, which defines an air gap, is a lateral surface of this body which extends between a radial inner edge 262 and a radial outer edge 264. As in the first embodiment, a rectangular shaped grove 265 is defined between two edges 266 and 268 of surface 26 which is divided into two subsurfaces 26A and 26B. Edges 266 and 268 are located in a median zone Z ₂ 6 of surface 26, between axes 262 and 264 along an axis Y2 which is radial with respect to axis X2.

The respective shapes represented on figures 4 and 6 to 9 induce different magnetic field repartitions in the corresponding air gaps.

The invention can be implemented with a sensor unit 40 having one or several sensor cells 42.

The invention has been represented on the figures in case the rotatable ring of a bearing is its inner ring. The invention also applies to the case where the rotatable ring is the outer ring of a bearing.

According to a non represented alternative embodiment, the magnetic body can be provided with several grooves, each of these grooves defining two edges with the surface of the magnetic body which defines the air gap.

The invention can be implemented with several types of sensors, namely a position sensor, a speed sensor, an ABS sensor, a crankshaft and transmission sensor and/or a motor control or commutation sensor.

The respective features of the embodiments considered in this description can be combined.

The invention can be implemented with a rolling bearing or a plain bearing.