A bearing assembly with a protective cover for an encoder

The present invention relates to a bearing assembly with a protective cover for a magnetic encoder.

In order to detect the relative speed of rotation between the rotating race and the stationary race of a bearing assembly, detecting devices are conventionally used comprising a magnetic encoder mounted on a rotating bearing race and a sensor that is fitted on a stationary part at a location facing the encoder at a preset distance. Electric signals generated by the sensor due to the rotation of the encoder are transmitted to a processing unit, which provides information on the rotation (rotational speed, angular position, etc.) of the rotating member. With hub-bearing units, the processing unit mounted on board of the vehicle provides information on the rotation of the wheels.

US 6 939 050 discloses a cover of non- ferromagnetic material mounted on the outer, stationary bearing race to protect the encoder and seal the bearing from the axially inner side (or inboard side). The encoder is associated with a sealing device that limits the radial size of the encoder.

It is an object of the present invention to increase the intensity of the magnetic field generated by the encoder, so that the associated sensor will be capable of picking up magnetic pulses which are strong enough, although the cover is interposed between the encoder and the sensor. It is also desired to have more freedom in choosing the position where the sensor is to be mounted, without needing to locate it exactly in front of the middle of the radial extension of the encoder, where the magnetic field is maximum, at equal distance.

The above and other objects and advantages, that will be better understood in the following, are accomplished, in accordance with the invention, by a bearing assembly having the features defined in the appended claims.

A few preferred but not limiting embodiments of the invention will now be described,

reference being made to the accompanying drawings, in which: figure 1 is an axial cross sectional view of a hub-bearing assembly according to a first embodiment of the invention; figure 2 is an enlarged view of a detail of figure 1 ; figure 3 is an axial cross sectional view of a hub-bearing assembly according to a second embodiment of the invention; figure 4 is view similar to figure 2 of a detail of third embodiment of the invention; and figures 5, 6, 7 and 8A-8C are axial cross sectional views of further embodiments of the invention.

Referring initially to figure 1, a hub-bearing assembly is designated overall at 10 with an outer, stationary bearing race 11 fixable to the suspension standard of a motor vehicle, and a radially inner rotatable hub 12 forming a radial flange 13 to be fastened to a wheel (not shown) of a vehicle. An inner bearing race 15 is fixed on the axially inner side, or inboard side of the hub 12, by rolling an edge 14 thereof. The outer race 11 forms radially outer raceways 16, 17 for two sets of rolling bodies 18, 19, in this example balls, whereas radially inner raceways 20 and 21 are formed by the hub 11 and the inner race 15, respectively.

Whereas a conventional sealing device 22 is provided at the axially outer side (outboard side) of the assembly in order to seal the annular space between the outer race 11 and the hub 12, a device of this kind is absent on the inboard side of the assembly. On this side, located in the annular gap between the bearing races 11 and 15 is a magnetic encoder 23 in form of an annular disc fixed to a supporting ring 24 having an L-shaped cross section and mounted on the inner bearing race 15. As shown more clearly in figure 2, the supporting ring 24 has a cylindrical portion 25 forcefully fixed onto the outer cylindrical surface 26 of the inner race 15, and a flange 27 extending in a radially outer direction from the axially inner end of cylindrical portion 25. The annular encoder 23 is fitted on the axially inner side 28 of the flange 27, and extends radially up to near the inner cylindrical surface 29 of the outer race 11. The radial gap Gl between the inner surface 29 of the outer race and the outer peripheral edge of the encoder may be kept as narrow as about 0.2 mm, so as to avoid

any contact between the rotating encoder 23 and the non-rotating outer race 11 , also in case the encoder is mounted with some defect and/or under the action of high external loads, particularly lateral loads which tend to deflect the bearing in an axial plane.

A protective cover 30 made of non- ferromagnetic material (for example aluminium, copper, or the like) is applied on the inboard side of the hub-bearing assembly to protect the encoder and seal the bearing, leaving a minimum axial gap G2 between the cover 30 and the axially inner side of the encoder.

The cover 30 has a radial peripheral portion 31 axially abutting against the side surface 32 of the outer race 11 facing the inboard side and, in the preferred embodiment shown in the drawings, an axial cylindrical edge 33 that is forcedly fitted on the outer cylindrical surface 34 of the bearing outer race.

Owing to the above described arrangement, in accordance with the invention the radial size of the encoder is increased, thereby exploiting practically all the space between the bearing races 11 and 15. As a result, a more intense magnetic field is generated. This allows also the designer to have more freedom in positioning the sensor (not shown), which will not necessarily have to be facing the encoder exactly at half its radial extension, where the magnetic field is at its maximum intensity, at equal distance from the encoder. Owing to the invention, the sensor may instead be located also at radially outer or inner positions, as indicated at P in figure 2, according to requirements and available space. In this way, even though the sensor may not be positioned exactly in front of the mid portion of the encoder, it will nevertheless be able to pick up a magnetic signal being intense enough to generate an electric signal clearly indicating rotation parameters of the hub.

With the hub-bearing units of the general design discussed herein, the side surface 32 is conventionally machined with high accuracy since it serves as a reference surface for fitting the encoder in the hub-bearing unit and, as said above, for determining the correct axial position of the cover 30. In this way an accurately sized minimum axial gap G2 is achieved, allowing to reduce the overall distance between the encoder and the sensor (not shown). Since a sealing device has no longer to be fitted in the inner cylindrical surface 29

of the outer race, machining of this surface can be dispensed with, which is advantageous since it eliminates a conventionally required step. Moreover, in the hub-bearing assembly according to the invention, with respect to the prior art there is also eliminated the sealing device arranged on the inboard side of the assembly. This reduces rolling friction of the assembly and cuts down manufacturing and assembling costs of a sealing device. Finally, the axial dimension of the outer 11 and inner 15 bearing races on the inboard side may be reduced, since it is not necessary to accommodate a sealing device, but only the encoder 23, which takes up a rather limited axial space. This helps to make the assembly lighter and axially compact. As an alternative, at equal axial bulk, the two sets of rolling bodies may be further spaced apart, thereby gaining a greater rigidity of the assembly as a whole concerning bending in an axial plane. This prevents any contact between the peripheral edge of the encoder and the inner cylindrical surface 29 of the outer race.

In the embodiment shown in figure 3, the cover 30 forms a radially outer extension or flange 35 interposed between the bearing outer race 11 and the suspension standard 36. The flange 35, by covering the inboard side of the outer race flange 11a, serves to prevent the suspension from contacting the bearing, and therefore avoid electrolytic corrosion at the interface between two bodies made of different metals, which would otherwise render the bearing unit difficult to remove from the suspension.

It is to be understood that invention is not limited to the embodiments described and illustrated herein, which are to be considered as examples of the assembly; rather, the invention can undergo modifications concerning shape and arrangement of parts, constructional and functional details, as will be apparent to those skilled in the art. As an example, the protective cover may not have the peripheral edge 33, as shown in the embodiment of figure 4. Here, the cover 30 is fitted directly on the side surface 32 of the outer race 11 for instance by brazing or soldering or welding or glueing, without requiring any machining of the outer cylindrical surface 34 of the outer bearing race in order to fit the cover to the bearing, and therefore without forming the step visible in figure 2.

Further, the invention is applicable also to bearing assemblies different from the kinds illustrated in figures 1 and 3. For example, as shown in the embodiment of figure 5, the

invention may be applied to bearing assemblies for virtually any rotating member for which a rotation feedback is needed (e.g. angular position, rotational speed, etc.). Figure 5 shows a cover 30 fitted to a bearing unit having a single set of rolling bodies, in this example a deep groove ball bearing unit. In the variant embodiment of figure 6, the peripheral edge 33 extends forming a skirt over the outer cylindrical surface 34 to be interposed between the bearing outer race 11 and the bearing housing (not shown). In the example of figure 7, the skirt 33 is prolonged on the side of the bearing opposite the side with the encoder, and forms a radially outer flange 38 that provides a means for mounting the bearing unit to a support S such as a wall, or a housing to which the cover is to be secured in any known manner. As an alternative or in addition to any of the above cited means of fastening the cover to the side of the bearing where the encoder is fitted, the cover can also be fastened to the bearing on the opposite side. In the embodiments of figures 8A, 8B and 8C, the cover 30 is fastened to the bearing by means of radially inwardly projecting portions 37, for example in the form of circumferentially adjacent tabs that extend from the skirt 33 and are bent against or towards the side of the bearing opposite to the side where the encoder is fitted. The radial extent of the tabs 37 provides different degrees of sealing action on that side of the bearing.