Wheel hub unit

Abstract

Wheel hub unit (2) for vehicles, comprising: - a radially outer ring (6), - a radially inner ring (7), several rolling elements (8) arranged between the inner and outer rings to enable their relative rotation about an axis of rotation (A), and - a sealing device (40) extending axially symmetrically about the axis of rotation (A), comprising a shaped shield (45) which is press-fitted to the radially inner ring (7) and is provided with an annular flanged section (46) extending perpendicular to the axis of rotation (A) and with a tubular mounting section (47) extending parallel to the axis of rotation (A) and rigidly connected to the annular flanged section (46), wherein: - the tubular mounting section (47) is keyed onto a mounting seat (7') of the radially inner ring (7) and has a circumferentially constant first inclination (a) with respect to the axially inwardly directed axis of rotation (A),and- the annular flanged section (46) has a second inclination (b) with respect to the tubular section (47), which is constant around its circumference.

Description

Technical FieldThe present invention relates to a wheel hub unit for vehicles.Prior ArtIn the prior art, a wheel hub unit comprises a flanged rotating hub mechanically connected to a rotating element of the motor vehicle, for example the wheel or disc of a braking element, and a rolling bearing, which in turn comprises an outer ring, a pair of inner rings, one of which may be the flanged hub itself, and a plurality of rolling elements, for example balls. All these components have an axial symmetry about the axis of rotation of the rotating elements, for example the flanged hub and the inner rings of the rolling bearing.The rolling bearings also have sealing devices (both in the direction of the axially outer side and in the direction of the axially inner side of the wheel hub unit) to protect the raceways and rolling elements from contaminants from the outside and to provide a seal for the grease. Typically, such sealing devices are formed from an elastomeric insert co-molded with a first molded metal shield and press fit onto one of the rings of the bearing unit, for example the stationary radially outer ring. The elastomer insert is provided with contact sealing lips which ensure sealing by means of sliding contact with a rotating metal surface. Normally, this metal surface belongs to a second shaped metal shield which is press fit to the other ring of the bearing unit, for example the flanged radially inner rotating ring. The second molded shield may include, for example, an annular flanged portion and a tubular mounting portion that are connected together in an L-shape.The second shaped shield is mounted by means of a tool on a cylindrical seat of the flanged radially inner ring, the shield being pushed axially into its final position using a standardized mounting method. The press-fit assembly guarantees a long-term stable end position.However, during the press-fit assembly operation, the molded shield always undergoes some degree of plastic deformation. The most important factors affecting this deformation are the values of the press fit between the shield and the inner ring, as well as the diameter, shape and thickness of the shield.Under conditions of very severe press fit, plastic deformation is maximized. More specifically, the tubular part is deformed. This portion is no longer cylindrical by 360°, but rather becomes conical, which is:a reduction of the contact zone. The contact between the tubular portion of the shield and the cylindrical seat of the inner ring is no longer guaranteed over the entire axial length of the tubular part, but is substantially reduced and concentrated on the zone of connection between the tubular portion and the annular flanged portion of the shield,an uneven contact zone. Moreover, due to structural instabilities ("buckling") of the tubular portion of the shield and unavoidable errors in squareness and axiality that occur during the assembly process, it is not guaranteed that a reduced contact is uniform through 360°.Moreover, conditions of very strong press fit result in plastic deformation of the annular flanged portion, which after assembly no longer runs perpendicular to the axis of the rolling bearing.The plastic deformation of the shield affects the static seal between the shield itself and the inner ring, resulting in the following:reduced sealing performance against contaminants from the outside and consequently corrosion and a shorter service life of the bearings,Inability to keep the base oil of the grease inside the bearing. This effect creates problems during bearing storage and / or operation of the bearing, and oil loss can reduce the performance of the bearing itself.Moreover, the plastic deformation of the shield affects the friction torque of the sealing device because the mutual position between the second shield and the contact lips of the first shield moves away from the target conditions. This means that:the contact pressure of the lips is influenced,an undesired contact and / or press fit may occur between the second shield and the elastomer insert of the first shield of the sealing device.One solution to these problems could be to reduce the interference fit between the shield and the inner ring; in this case, the plastic deformations described above would be less pronounced due to the conditions of low interference fit. However, the press fit must not be reduced too much, since during operation there is a risk of axial slipping of the shield, wherein vibrations, deformations of the components under load and temperature are factors which contribute to the slipping of the shield. Therefore, a minimum pull-out force is required for pulling the shield out of its seat, thereby limiting the minimum usable press-fit values.Summary of the InventionIt is an object of the present invention to provide a wheel hub unit for vehicles which overcomes the disadvantages of the prior art and which is simple and cost-effective to produce.The present invention therefore provides a wheel hub unit for vehicles having the features set out in the appended claims.Brief Description of the DrawingsThe invention will now be described with reference to the accompanying drawings which show a non-limiting exemplary embodiment of the invention and in which:FIG. 1 is a schematic radial cross section of a preferred embodiment of a wheel hub unit according to the present invention,FIG. 2 is an enlarged view of a detail of the wheel hub unit in FIG. 1 ,FIG. 3 is a schematic view of a shield of the wheel hub unit in FIG. 1 in a first embodiment of the shield, andFIG. 4 is a schematic view of the shield in FIG. 3 in a second embodiment of the shield.Detailed DescriptionReferring to FIG. 1, a wheel hub assembly 2 according to the present invention includes a rolling bearing 3, which in the illustrated example is a bearing having two rows of rolling elements (balls).The wheel hub 2 is configured to rotatably support a wheel (not illustrated) of a vehicle about a rotational axis A.The wheel hub unit 2 includes:a radially outer ring 6,a radially inner ring 7, anda plurality of rolling elements 8 comprising, in the example shown, two rows of balls arranged side by side, arranged between the inner ring 7 and the outer ring 6, in order to allow the relative rotation of the balls.Throughout the present specification and in the claims, terms and expressions indicating positions and orientations, such as "radial" and "axial", are to be understood with respect to the central rotational axis A of the rolling bearing 3. On the other hand, expressions such as "axially outer" and "axially inner" refer to the assembled state of the wheel hub unit, and in this case, refer to a wheel side and a side opposite to the wheel side, respectively.The rings 6 and 7 and the rolling elements 8 are part of the rolling bearing 3. In the illustrated non-limiting example, the rolling bearing 3 is a "third generation" bearing and therefore directly forms the entire wheel hub unit 2, since the radially outer ring 6 comprises a known flange 9 used for attachment to the knuckle (not illustrated for simplicity) and integral with the outer ring 6, and since the radially inner ring 7 comprises a known flange 10 used for attachment of the wheel of the vehicle (not illustrated for simplicity) and integral with the radially inner ring 7, in particular at its axial end 11 opposite the flange 9 and at a second end 12 of the radially inner ring 7.In the illustrated, non-limiting, preferred example, the radially inner ring 7 is also divided according to a known configuration into two separate elements which are angularly and rigidly coupled to each other, one element being an annular element formed by the ends 11, 12 and the integral flange 10, and the other element being a known small inner ring 13 driven onto the end 12 so as to axially abut an axial shoulder 14 of the radially inner ring 7 directed towards the end 12.The rolling bearing further includes an axially outer sealing device 40 and an axially inner sealing device 50.Referring to FIG. 2, the sealing device 40 is arranged symmetrically about the axis of rotation A of the rolling bearing and may include:a first shaped metal shield 41 press fit to the radially outer ring 6,a second shaped shield 45 which is L-shaped and is also made of metal. The second shaped shield 45 is press-fitted to the radially inner ring 7 and is provided with an annular flanged portion 46 perpendicular to the axis of rotation A of the rolling bearing and a tubular mounting portion 47 parallel to the axis of rotation A and rigidly connected to the annular flanged portion 46. The radially inner end of the annular flanged portion 46 has a connecting arc portion 46' with the tubular portion 47. The tubular mounting portion 47, in turn, has at its axially inner end, which is opposite the curved portion 46', an end edge 47' which is tapered at its radially outer portion,an elastomer insert 42 co-moulded on the first metal shield 41 and provided with an axial lip 43 and with a first radial lip 48 and a second radial lip 49 for retaining the grease, which are arranged axially inside the first radial lip 48. All the lips are contact lips and produce sliding contact: the axial lip 43 against the annular flanged portion 46 of the second shaped shield 45 and the radial lips 48, 49 against the tubular portion 47 of the second shaped shield 45.The second shaped shield is mounted on a mounting seat 7' of the radially inner ring 7 by means of a tool which presses the shield axially into its final position using a standardized mounting method. The press-fit assembly guarantees a long-term stable end position of the shaped shield 45.According to the present invention, the wheel hub unit 2 is characterized in that the axially outer sealing device 40, and more specifically the second shaped shield 45, has characteristics capable of eliminating the problem of plastic deformation of the second shaped shield 45.With reference to Figure 3, the second shaped shield 45 is characterized by a geometry suitable for minimizing the effects of plastic deformations when the shield is mounted on the radially inner ring 7. The effects of the undesirable deformations of the tubular mounting portion 47 and the annular flanged portion 46 are minimized over the entire range of press-fit variation.In particular, according to the present invention:the tubular mounting portion 47 is keyed onto the mounting seat 7' of the radially inner ring and has a first circumferentially constant inclination a with respect to the axis of rotation A of the rolling bearing 3 (maintaining axial symmetry with respect to the axis of rotation A). This first inclination means that the end edge 47' is arranged radially inside the arc section 46'.the annular flanged portion 46 in turn has, with respect to the tubular portion 47, a respective second inclination b which is also circumferentially constant.Since the mounting tubular portion 47 and the annular flanged portion 46 are rigidly connected to each other, when the mounting tubular portion 47 is keyed onto the mounting seat 7', the mounting tubular portion 47 is deformed so as to completely simulate the mounting seat 7' (the tubular portion 47 therefore runs parallel to the rotational axis A of the rolling bearing 3) by rotating about a rotational center defined by the arc portion 46', while the mounting annular flanged portion 46 rotates about the same angle with respect to the arc portion 46' and is positioned in a plane perpendicular to the rotational axis A.Finite element simulations and experimental tests have shown that plastic deformation of the shield during assembly at the best is prevented with values of the first inclination a between 0.5° and 3°.A range of values for the second slope b may be defined as a function of the value of the first slope a. The same calculations and experimental evidence require that the following relationship be satisfied:If the first slope a is the maximum value, i.e. 3°, the second slope b is between 88.2° and 91.8°.Referring to FIG. 4, in another embodiment, the second shaped shield 45 could be C-shaped, i.e., could be provided with a second tubular portion 44 disposed radially outward of the mounting tubular portion 47.The geometric optimizations with which the effects of the plastic deformations are to be reduced remain unchanged, and therefore the following also applies to the configuration illustrated in FIG. 4 :the first inclination a between the tubular mounting portion 47 and the axis of rotation A of the rolling bearing 3 has a value between 0.5° and 3°,the second inclination b between the mounting tubular portion 47 and the flanged annular portion 46 takes the values defined by the aforementioned relationship:Moreover, in the case of the C-shaped second shaped shield 45, a third inclination c can be defined between the annular flanged portion 46 and the second tubular portion 44, which is also circumferentially constant. This third inclination is intended to ensure that the second tubular portion 44 is returned to a position parallel to the axis of rotation A of the rolling bearing 3 after assembly is completed. The improved results are obtained when a value of the third inclination c is at least 90°. In particular, the following relationship can be defined: wherein the parameter k is between 0% and 50% of the first inclination a.Advantageously, the second shaped shield 45 (in both of the described embodiments) is formed from sheet metal, for example AISI293 steel. The thickness of the tubular portion 47 and the thickness of the annular flanged portion 46 may be between 0.4 mm and 0.8 mm.The clamping action of the end edge 47' on the mounting seat 7' of the radially inner ring 7 is used to increase the extraction force of the shaped shield 45, thus realizing a greater extraction force with the same press fit.The press fit values (diametrical press fit between the tubular mounting portion 47 and the mounting seat 7') may be between 0.05 mm and 0.35 mm, these values being defined at the end edge 47'.And finally, the mounting seat 7' of the flanged radially inner ring 7 is preferably made of G55 / G70 series steel having a ground surface and a roughness Ra of at most 0.8.In short, the solution according to the invention has numerous advantages:friction torque values of the sealing device which are almost constant and repeatable, that is less affected by the differential sealing pressure on the contact lips due to the plastic deformation of the shaped shield 45,avoiding undesired contact between the rotating second shaped shield 45 and the non-rotating elements (first shaped shield 41 and elastomer insert 42) of the sealing device 40,The conical geometry facilitates the assembly process and brings about a self-alignment effect. Moreover, axial eccentricity errors of the annular flanged portion 46 of the shaped shield 45 are minimized.Since the static seal is distributed over the entire surface of the tubular mounting portion 47, its axial length can be minimized. As a result, the sealing devices can be axially more compact, and consequently the rolling bearing can offer more space for the rolling elements 8 (if the task is a higher stiffness) or can be more compact overall.The press fit between the mounting seat of the radially inner ring and the tubular portion of the shaped shield can be kept large enough to guarantee a high extraction force and to prevent slipping of the shield during operation.The non-deformed tubular portion and its end edge contribute to keeping the extraction force at a high value without the risk of the shield slipping during operation.In addition to the above-described embodiments, numerous further variants of the invention are possible. It is also understood that the embodiments are merely examples and do not limit the scope of the invention, its applications, or its possible configurations. Although the description given above enables those skilled in the art to practice the present invention in accordance with at least one of its exemplary embodiments, numerous variations of the described components could be used without thereby departing from the scope of the invention as defined in the appended claims, which are intended to be accorded the literal and / or legal equivalents thereof.

Claims

A wheel hub unit (2) for vehicles, comprising: - a radially outer ring (6), - a radially inner ring (7), a plurality of rolling elements (8) arranged between the inner and outer rings to make them relatively rotatable with respect to an axis of rotation (A), and - a sealing device (40) axially symmetric with respect to the axis of rotation (A) and having a shaped shield (45) mounted with an interference fit on the radially inner ring (7) and provided with an annular flanged portion (46) perpendicular to the axis of rotation (A) and a tubular mounting portion (47) parallel to the axis of rotation (A) and integral with the annular flanged portion (46), the wheel hub unit (2) being characterized in that, wherein: - the mounting tubular portion (47) is keyed onto a mounting seat (7') of the radially inner ring (7) and has, with respect to the axis of rotation (A) and axially inwards, a first inclination (a) which is circumferentially constant, and - the flanged annular portion (46) has, with respect to the mounting tubular portion (47), a second inclination (b) which is circumferentially constant.The wheel hub unit (2) according to claim 1, wherein the first inclination (a) between the mounting tubular portion (47) and the rotation axis (A) is between 0.5° and 3°.The wheel hub unit (2) according to claim 2, wherein the second inclination (b) between the mounting tubular portion (47) and the flanged annular portion (46) is defined by the following relationship: 90° - 60% a < b < 90° + 60% a The wheel hub unit (2) according to claim 3, wherein the shaped shield (45) is provided with a second tubular portion (44) that lies radially outside with respect to the mounting tubular portion (47), the second tubular portion (44) having a third inclination (c) that is circumferentially constant with respect to the flanged annular portion (46).The wheel hub unit (2) according to claim 4, wherein the third inclination (c) between the second tubular portion (44) and the annular flanged portion (46) is defined by the following relationship: c = 90° + k wherein k is a parameter between 0% and 50% of the first inclination (a).Wheel hub unit (2) according to one of the preceding claims, wherein the tubular mounting portion (47) has an axially inner end edge (47').The wheel hub unit (2) according to any one of the preceding claims, wherein the shaped shield (45) is made of sheet metal and the thicknesses of the tubular mounting portion (47) and the annular flanged portion (46) are between 0.4 mm and 0.8 mm.Wheel hub unit (2) according to claim 6, wherein the diametrical press fit between the tubular mounting portion (47) and the mounting seat (7') at the end edge (47') is between 0.05 mm and 0.35 mm.Wheel hub unit (2) according to any of the preceding claims, wherein the mounting seat (7') of the radially inner ring (7) is made of steel and has a roughness Ra of at most 0.8.

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