Wheel hub bearing unit for vehicles and associated method

A wheel hub bearing unit including a plurality of rolling bodies disposed between annular elements. One of the annular elements is a rotating element that includes a spindle on a side facing the outboard side of the vehicle having a mounting flange adapted to receive a vehicle wheel. A frontal surface of the mounting flange is covered by a layer of UV photopolimerizable synthetic plastic material having a predetermined thickness deposited on the frontal surface of the flange in the non-polimerized state by a mixed air spraying nozzle, by rotating the wheel hub bearing unit about a symmetry axis thereof with the nozzle arranged at a radial distance from a peripherally outer edge of the flange, and has a spraying axis which forms, with the symmetry axis, an angle from 20° to 80°; the synthetic plastic material being sprayed by the nozzle at a temperature higher than the room temperature.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a wheel hub bearing unit for vehicles. The invention also relates to a method for manufacturing a wheel hub bearing unit for vehicles. Here and below, “run-out” means the rotation oscillation allowed for the outboard flange of the unit, intended to receive in use a vehicle wheel.

PRIOR ART

As it is known from US2010/0301666A1, for example, a wheel hub bearing unit comprises a radially outer annular element or member provided radially on the inside with first rolling tracks, a radially inner annular element or member provided radially on the outside with second rolling tracks facing and opposite to the first rolling tracks and a plurality of rolling bodies interposed between the radially inner and outer elements and engaging the rolling tracks. One of the annular elements, which acts in use as a rotating element, generally consisting of the radially inner member, comprises a spindle provided, on the outboard side of the unit, with a mounting flange for a vehicle wheel and a possible cylindrical guiding collar which axially protrudes from the mounting flange, on the side opposite to the spindle, with which it is coaxial.

In use, both the collar (when present) and the mounting flange are subject to coming in contact with several contaminants (water, mud, dust, sand) and, during the wheel mounting and dismounting operations, for example when changing the tires, are subject to chafing. These parts of the wheel hub bearing unit may thus be easily subject to corrosion, with formation of rust.

A solution known in the art is to coat at least a frontal surface of the mounting flange with a protective metal layer, e.g. a galvanic coating of zinc, which acts as a sacrificial anode. However, this solution has the drawback of needing to carry out the galvanic coating on the annular element provided with the flange before it is mounted on the wheel hub bearing unit. Once mounted, the wheel hub bearing unit must be tested to verify the matching to the required run-out tolerances thereof, which operation often requires to carry out mechanical machining on the flange to remove superficial parts in order to reduce the oscillations within acceptable limits (in essence, a sort of balancing is carried out, such as that which is carried out on tires, but removing material instead of adding counterweights); it follows that part of the protective layer is removed, with the consequent possibility of starting rust.

The solution known from US2010/0301666A1, instead, provides for covering with a protective layer, after mounting the wheel hub bearing unit, the guiding collar only, which is definitely one of the most exposed parts, by applying a layer of photopolimerizable (in this case UV polimerizable) synthetic material. According to this solution, only the collar is coated, since the known methods of applying photopolimerizable products do not ensure obtaining coating layers of even thickness. Therefore, if these were also applied on the flange, it would be liable to exceed the allowed run-out tolerances, since the presence of non-uniform coating layers could produce the triggering of vibrations and oscillations, resulting in the generation of undesired noise.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a wheel hub bearing unit protected from corrosion over the entire mounting flange and respecting the run-out tolerances required. It is also an object of the invention to provide a method for manufacturing such a wheel hub bearing unit.

According to the invention, a wheel hub bearing unit and a manufacturing method for such a wheel hub bearing unit are thus provided, having the features set forth in the appended claims.

DETAILED DESCRIPTION

With reference toFIG. 1, numeral1indicates a wheel hub bearing unit for vehicles as a whole. The wheel hub bearing unit1comprises, in the non-limiting embodiment shown, a radially outer annular element or member or ring2provided radially on the inside with first rolling tracks3, a radially inner annular element or member or ring provided radially on the outside with second rolling tracks5facing and opposite to the first rolling tracks3and a plurality of rolling bodies interposed between the radially outer2and inner3elements and engaging the rolling tracks3and5, in this case forming two crowns of balls.

One of the annular elements2,4, which acts in use as a rotating element, generally consisting of the radially inner member and, in the non-limiting embodiment, precisely consisting of the inner ring4, comprises a spindle7provided, on the outboard side of unit1, i.e. towards the parts of spindle7and unit1intended to be facing in use the outboard side of the vehicle, with a mounting flange8for a vehicle wheel, (known and not shown for simplicity).

Ring4is also preferably provided with a cylindrical guiding or pilot collar or annular sleeve-like portion9, which axially protrudes from the mounting flange8, on the side opposite to spindle7, with which it is coaxial. The collar or sleeve-like portion9has the function, in use, to receive the brake disc or drum and the wheel, the latter being then fixed to flange8, which is for this purpose provided with a plurality of through holes10arranged in a crown.

Towards the outboard side, flange8is delimited by a flat frontal surface11interrupted only by the holes10that come out therethrough. From such a surface11, the collar or pilot portion9, which is delimited radially on the outside by a lateral peripheral surface12, overhangingly perpendicularly extends.

Rings2and4are coaxial with spindle7and the collar or pilot portion9and all these elements are coaxial with a symmetry axis A of unit1.

According to the invention, at least the frontal surface11of the mounting flange8is entirely covered by a layer13of UV photopolimerizable synthetic plastic material, diagrammatically shown out of scale in broken lines inFIG. 1. Layer13has a predetermined thickness and, according to the invention, it has been deposited on the frontal surface11of flange8in the non-polimerized state by means of (FIG. 2) a mixed air spraying nozzle14with a tolerance not exceeding 5 microns on the predetermined thickness.

At least the lateral peripheral surface12of the collar or sleeve portion9is also entirely covered by the same layer13of UV photopolimerizable synthetic plastic material which covers the frontal surface11of the mounting flange8and which has been formed simultaneously on flange8and collar9by means of the mixed air spraying nozzle14with a tolerance not exceeding 5 microns on the predetermined thickness on both flange8and collar9.

The predetermined thickness of the layer13of UV photopolimerizable synthetic plastic material is from 30 to 40 microns.

Thereby, the wheel hub bearing unit1has a run-out tolerance lower than or equal to 15 microns.

The through holes10pass through the layer13of UV photopolimerizable synthetic plastic material, since they were not affected by the step of spraying.

The wheel hub bearing unit1is made by means of a method in several steps, the main step of which is shown inFIG. 2.

Firstly, the wheel hub bearing unit1is completely assembled and, optionally, when needed, a mechanical machining with chip removal is carried out on the frontal surface11of flange8, so as to make unit1fall within an allowed run-out tolerance. Such a mechanical machining is generally carried out with a tolerance equal to or lower than 10 microns.

The wheel hub bearing unit1completely assembled and already mechanically machined on surface11, thus falling within the allowed run-out tolerances, is then taken to and mounted on an apparatus (diagrammatically shown inFIG. 2and indicated at15as a whole).

Apparatus15comprises nozzle14, a support16and an engine17, diagrammatically shown as a block. The wheel hub bearing unit1is mounted on support16so as that the annular element4, intended in use to be the rotating element of unit1, is idly carried by support16, which has a high stiffness, so as to avoid possible vibrations. For example, the annular element2is angularly fixed so as to be integral with support16, which is stationary. In the non-limiting embodiment shown, the annular element2is also provided with a flange18for fixing, in use, unit1on the strut of a vehicle suspension and therefore flange18may be used for integrally fixing unit1to support16. If flange18is not present, a different fixing system will be used, as apparent to those skilled in the art and thus not described.

Engine17is connected by means of a transmission system, apparent to those skilled in the art and thus not shown for simplicity, to the annular element2, so as to cause element2, and flange8and collar9therewith, to rotate about symmetry axis A when engine17is actuated.

Nozzle14is a mixed air spraying nozzle, of the so-called AIRMIX® type. It is serviced by a known power supply system19, diagrammatically shown as blocks inFIG. 2, comprising a compressed air feeding line20and a pressurized line21for supplying a product to be sprayed by means of nozzle14, which line21is thus equipped with a pump22, which draws from a tank23.

According to the invention, the method for obtaining the wheel hub bearing unit thus comprises, temporally in sequence after the step of machining by chip removal the parts of surface11, a step of coating the frontal surface11of flange8with a layer13of a UV photopolimerizable synthetic plastic material, indicated by26and contained within tank23, which is deposited on the frontal surface11of flange8(and on the surface12of collar9) in the non-polimerized state by means of the mixed air spraying nozzle14.

According to the main feature of the invention, in order to obtain a layer13of even thickness unless having very tight tolerances, the step of spraying deposition of the photopolimerizable material in the non-polimerized state is carried out by rotating the hub bearing unit1about the symmetry axis A thereof at a predetermined speed, while keeping the frontal surface11of flange8exposed towards the spraying nozzle14; and, in combination, by arranging the mixed air spraying nozzle14at a predetermined radial distance “a” from a peripherally outer edge24of the mounting flange, also arranging nozzle14with a spraying axis B thereof that forms, with the symmetry axis A of the wheel hub bearing unit1, an angle α different from both zero and 90° and comprised between 20° and 80°, in a plane containing both axes A and B.

Here and below, “spraying axis” means the symmetry axis of a jet25of photopolimerizable material and along which the photopolimerizable material itself, in the liquid state and mixed with air, is projected towards flange8and, in the example shown, also towards the collar or pilot sleeve-like portion9, to form layer13on the surfaces11and12.

Furthermore, the UV photopolimerizable synthetic plastic material26is sprayed by nozzle14at the liquid state, but at a temperature higher than the room temperature, in particular from 40° C. to 60° C., so as to adjust the viscosity thereof to a desired level.

With the combination of such expedients, a layer13of UV photopolimerizable synthetic plastic material26which is absolutely even in thickness (but totally unconceivable a priori) is surprisingly obtained.

To this purpose, moreover, the predetermined radial distance “a” is chosen so as to be from 15 to 30 mm, while the predetermined rotation speed of the wheel hub bearing unit1is kept from 45 to 75 RPM; the UV photopolimerizable synthetic plastic material26is then sprayed by nozzle14towards flange8(and collar9) over a time ranging from 6 to 12 seconds.

The photopolimerizable material26used according to the invention consists of a solvent-free, water-based paint containing substituted tri-acrylates, for example it is the product EU-17-7001/0 from Lankwitzer, available on the market.

After the step of spraying shown inFIG. 2, the layer13of UV photopolimerizable synthetic plastic material26is irradiated by means of UV over a time ranging from 10 to 15 seconds, by operating according to known techniques, thus apparent for those skilled in the art, which are not described for simplicity.

In order to achieve the desired results, nozzle14has an outlet opening “b” with a passage section from 0.4 to 1.4 mm wide; furthermore, the UV photopolimerizable synthetic plastic material26is atomized in nozzle14by an air flow F (FIG. 2), indicated by the arrow, at a pressure from 2 to 10 bars, thus feeding compressed air in line20at a pressure from 2 to 10 bars. The material26itself is also fed by pump22at a pressure from 2 to 10 bars.

Thereby, a layer13of thickness from 30 to 40 microns is deposited, having a tolerance (i.e. an allowed thickness variation) lower than 5 microns which, when added to the allowed tolerance for the tool machining step (equal to or lower than 10 microns), finally provides a unit1protected from corrosion over all the surfaces11and12, by means of the layer13of photopolimerized material16and which falls within the most severe run-out tolerances, thus remaining below 15 microns.