TECHNICAL FIELD OF THE INVENTION

The invention concerns an impulse ring for a sensor bearing unit and a sensor bearing unit comprising such an impulse ring.

BACKGROUND ART OF THE INVENTION

Today, sensor bearing units are commonly used in automotive industry, aeronautics and other technical fields. These units provide high quality signals and transmissions, while allowing integration in simpler and more compact apparatuses. Such sensor bearing units generally comprise a bearing, an impulse ring and detection means facing the impulse ring. The impulse ring comprises a target holder and a target including alternating North and South poles, whose number depends on the bearing size and particular applications. With a bearing having suitable dimensions, the impulse ring may be fixed to a rotating ring of this bearing, while the detection means may be fixed to a non rotating ring of this bearing.

The impulse ring comprises a magnetized portion, which is attached to a tubular portion of the holder of the impulse ring. Such a design is known from FR-A-2 884 367, in which the holder comprises an inner portion, which is attached to the inner ring of a bearing, a radial portion, and an outer tubular portion, which holds the magnetized portion. The radial portion and the outer tubular portion form a right angle, which can be damaged in case of high rotation speeds and vibrations during operation of the impulse ring. In addition, the available space to integrate the detection means is generally not large enough to permit a proper integration of some types of detection means.

SUMMARY OF THE INVENTION

The aim of the invention is to provide an impulse ring which has a holder which better undergoes high rotation speeds and vibrations, and provides a large space to integrate the detection means.

To this end, the invention concerns an impulse ring for a sensor bearing unit comprising a magnetized portion which generates a magnetic field adapted to be sensed by detection means, the magnetized portion being mounted on a holder fixed to a rotatable ring of a bearing of the sensor bearing unit, the holder comprising an outer tubular portion and a radial portion which define an inner housing in which the magnetized portion is fixed, whereas the holder comprises, at the intersection of the tubular portion with the radial portion of the holder, an inwardly protruding boss which extends on the whole circumference of the holder.

Thanks to the invention the mechanical resistance of the holder at high rotation speeds is improved, and the peak of magnetic field is shifted away from the radial portion of the holder, which permits a better integration of the sensing element. Moreover, less magnetized material is required, permitting a reduced weight and cost of the unit.

According to further aspects of the invention which are advantageous but not compulsory, such an impulse ring may incorporate one or several of the following features:

- The boss is formed by deformation of the transversal section of the holder, without changing its thickness with respect to the tubular portion and radial portion.

- The boss presents two annular surfaces which form a right angle between each other, and which form right angles with the tubular portion and the radial portion.

- The boss presents a cylindrical band attached to the radial portion and a frustoconical band attached to the tubular portion.

- The frustoconical band of the boss makes an angle with respect to an axial direction which is comprised between 45° and 75° , peferably equal to 60° .

- The radial portion of the holder is partially inclined with respect to a central axis of the impulse ring.

The invention also concerns a sensor bearing unit comprising a bearing and an impulse ring as mentioned here-above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in correspondence with the annexed figures, as an illustrative example, without restricting the object of the invention. In the annexed figures:

- figure 1 is a perspective view of a sensor bearing unit according to the invention, comprising an impulse ring according to the invention,

- figure 2 is an axial sectional view of the sensor bearing unit of figure 1 ,

- figure 3 is a sectional view at a larger scale of detail III on figure 2.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The sensor bearing unit 10 according to the invention represented on figures 1 to 3 is adapted to equip a non-shown apparatus, such as a motor, a brake system, a suspension system or any rotating machine, in particular for an automotive vehicle. Sensor bearing unit 10 comprises a bearing 20 including a rotating inner ring 22 and a stationary outer ring 24. Inner ring 22 rotates with respect to outer ring 24 around a central axis X-X'. Bearing 20 also comprises balls 26 located between inner ring 22 and outer ring 24. Alternatively, rollers or needles can be used as rolling elements for bearing 20, instead of balls 26.

Sensor bearing unit 10 also includes a magnetic impulse ring 40 mounted on inner ring 22, and which comprises a target holder 42 and a target formed by a magnetized portion 44. Target holder 42 is fixed to inner ring 22 and extends beyond outer ring 24, radially to axis X-X'.

Magnetized portion 44 is fixed to target holder 42 by press mounting or by overmoulding.

Target holder 42 is manufactured by stamping.

Impulse ring 40 generates a magnetic field adapted to be sensed by detection means 100, which are represented on figures 2 and 3 with phantom lines. For example, detection means 100 may include Hall-effect sensors. Detection means 100 may be fixed to outer ring 24 by non-shown fastening means.

Holder 42 comprises an outer tubular portion 420 and a radial portion 422. Outer tubular portion 420 and radial portion 422 define an inner housing H in which the magnetized portion 44 is fixed. At the intersection of the tubular portion 420 and radial portion 422, holder 42 comprises an inwardly protruding boss 430, which extends on the whole circumference of holder 42.

The boss 430 is formed by deformation of the transversal section of holder 42. In other words, the thickness of holder 42 in the area of boss 430 is the same as in the areas of radial portion 422 and tubular portion 420.

The boss 430 presents a cylindrical band 430a centered on axis X-X' which is attached to radial portion 422, and a frustoconical band 430b which is attached to tubular portion 420. The frustoconical band 430b makes an angle A, with respect to an axial direction Δ parallel to central axis X-X, which may be comprised between 45° and 75° , preferably equal to 60° .

Boss 430 permits to improve the mechanical resistance of holder 4 at high rotation speeds, such as at 22 000 rotations per minute (rpm).

Boss 430 also reduces the quantity of magnetized matter of the magnetized portion

44, with respect to target holders of the prior art. This permits to reduce the rotating weight of the impulse ring 40, thus its inertia.

Impulse ring 40 generates a magnetic field is represented by curved lines L1 on figures 2 and 3. The shape of the magnetic field depends on the shape and location of magnetized portion 44. In order to obtain a satisfying detection accuracy, detection means 100 must be placed in an area corresponding to the peak P of the magnetic field generated by magnetized portion 44. Peak P forms an annular shaped zone centered on axis X-X' and located axially between an axial edge 400 of impulse ring 40 and radial portion 422, and radially between outer ring 24 and magnetized portion 44. Thanks to boss 430, peak P is closer to axial edge 400 than to radial portion 422. Peak P is therefore axially shifted away from radial portion 422 in comparison with the impulse rings of the prior art. The space available to integrate detection means 100 is therefore larger.

As an optional aspect, radial portion 422 is partially inclined with respect to axis X-X'. In the example, radial portion 422 comprises three inclined sections 422a, 422b and 422c which improve the stiffness of holder 42.

According to a non-shown embodiment of the invention, the boss 430 may present two annular surfaces which form a right angle between each other, and which form right angles, respectively, with tubular portion 420 and radial portion 422.