TITLE : "Method and apparatus for reducing the run-out" DESCRIPTION The invention may be used industrially in machines tools for machining, on an industrial scale, the hub and bearing assembly intended to support with its associated flange each wheel of motor vehicles and the associated brake disc, so that the surface of the said hub flange can be precisely machined, with the aim of reducing the so-called run-out or wobble due to the very small machining and mounting tolerances of the bearings and other parts of the assemblies in question. This technology is described, for example, in documents WO 00/74883 and WO 01/38025. Both these documents relate to the machining, for the abovementioned purposes, of an assembly formed by a ring which is able to be fixed to the suspension of the motor vehicle and which has mounted therein in a coaxially rotatable manner, via bearings, an axially hollow hub which may be connected, if necessary, to a splined rotating shaft and is provided at one end with a flange which is able to receive in a perpendicularly projecting manner stud bolts designed to pass through corresponding holes in the braking disc which is then fixed onto the said flange with its own screws, the said stud bolts being then used to fix to the hub, using special nuts, the rim of the vehicle wheel. The abovementioned patent applications envisage keeping immobilized the outer race of the bearing of the assembly, causing the hub to rotate about it axis and finally machining with the machine tool the visible surface of the hub flange on which the brake disc is then mounted. This technology has been recently refined with patent applications in the name of the Applicant, which envisage correctly preparing machining with the machine tool in accordance with the prior knowledge of the degree and nature of the run-out of the part to be machined, causing initially rotation of the outer race of the bearings relative to the hub which is temporarily kept still.

The means which roll inside the said race may consist equally well of rollers and/or balls which travel along the rolling paths of at least one pair of inner races which are passed through axially by the hub with the disc-carrying flange. The end of the hub which protrudes from these inner races is pressure-formed on the outside

thereof. In some assemblies, such as those described for example in the TIMKEN patent, the outer race of the bearing is provided integrally in the middle part with a flange for effecting fixing by means of screws or bolts onto the vehicle suspension.

In these cases, the inner races of the bearing are axially pre-stressed by the correct amount before pressure-flanging the end of the hollow hub of the assembly so that in the abovementioned machining step the assembly is already in the final working condition and does not need to be axially stressed.

In other assemblies, such as that illustrated in Figure 1 of the accompanying drawings, for which the apparatus according to the invention was devised, the outer race 1 of the bearing is without external flange in that it is intended to be press-fitted into a corresponding housing in the vehicle suspension. In these cases, the inner races 3,3'of the rolling means 2 of the bearing are not axially pre-stressed as in the case of the Timken patent mentioned above. The pressure-flanging of the end 204 of the hub 4, which with the annular step 104 opposes the said end 204 during axial containment of the races 3,3', is performed in conditions such that, between the said races 3,3', there exists a degree of axial play which is eliminated by the plastic and centripetal deformation to which the outer race 1 of the bearing is subjected when it is press-fitted into the corresponding support housing of the vehicle suspension.

In order to be able to subject the flange 304 of the hub 4 of the assemblies in question to the machining process described in the introduction of the present description, the invention envisages clamping the outer race 1 of the bearing of the said assemblies using self-centring means such as to subject this race 1 substantially to the same plastic deformation which it undergoes later when mounted in its working position, so as to eliminate any radial and axial play of the bearing, such that the assembly is machined with the aim of eliminating the run-out effects, substantially under the same conditions which exist during operation on the vehicle.

In order to be able to implement this method, the invention envisages clamping the outer race of the bearing using a self-centring spring clamp having a deformation which is fully and uniformly distributed within the round angle, with incisions open at both ends and suitably staggered with respect to each other, and

envisages insertion of this clamp inside an annular chamber, the inner wall of which is elastically deformable under the action of a pressurised fluid supplied into said chamber at pressure values such that the said spring clamp grips the whole of the periphery of the outer race 1 of the bearing and compresses it with the same centripetal pressure values to which this race will be subject when mounted in the working position.

Further characteristic features of the invention and the advantages arising therefrom will become clearer from the following description of a preferred embodiment thereof illustrated purely by way of a non-limiting example in the figures of the accompanying illustrative plates, in which : - Fig. 1 is a cross-sectional view along the axis of rotation of the apparatus according to the invention shown during the active stage of machining of the disc- carrying flange of the hub and bearing assembly of the type already considered; - Fig. 2 shows, cross-sectioned along the axis of rotation, the apparatus according to Figure 1 in the rest condition without the part to be machined; - Fig. 3 shows a perspective view of the spring clamp used in the apparatus according to the invention.

In Figure 1, M denotes the chuck which, in the known art, is intended to support coaxially the assembly or part P to be machined, so as to keep it fixed and so as to be able to rotate it, if necessary, about its axis. In the example in question the chuck M is arranged vertically and is designed to support the part to be machined with its top end, but it is understood that these conditions are purely exemplary and non-limiting. A cylindrical body 7 made of any material suitable for the purposes mentioned further below is fixed coaxially with its flange 107 on the top end of the chuck M, said chuck having an axial cavity 8 which has a diameter suitably greater than the outer diameter of the race 1 of the part P to be machined and which opens out on the top end of the said body 7, with a section 108 of larger diameter inside which an annular spring clamp 9, more clearly visible in Figure 3, is precisely seated, the internal diameter of said clamp being slightly greater than the outer diameter of the said race 1 so that the latter may be introduced into the clamp by automatic

systems easily and with a minimum amount of radial play. From Figure 3 it can be seen that the clamp 9 is nothing more than a bush with a round cross-section, made of any material which is sufficiently elastic and strong, of metal, of plastic and/or of any other suitable material, including a composite material, and provided heightwise with incisions 10,10'which are equally spaced angularly with respect to each other and have the same characteristics and which open out alternately at opposite ends of the bush and which with their other end terminate instead in respective holes 110, 110'having a diameter suitably greater than the thickness of the incisions and spaced for example by the same amount from the opposite ends of the bush; all of this so that the clamp thus formed is able to reduce its diameter in a manner uniformly distributed over its height should the same clamp be subjected externally to a centripetal pressure uniformly distributed within the round angle, whereas, when this pressure ceases, the clamp returns as a result of its own form-retaining memory into the original rest condition.

The clamp 9 has a height which is suitably greater than that of the race 1 of the part P and with one end rests on the step 11 present between the axial cavities 8, 108 of the body 7, while with the other end which is for example externally tapered, as indicated by 12, the same clamp projects from the seat 108 inside which it is retained by a flange or other suitable means 13 fixed to the body 7.

The axial cavity 8 of the body 7 receives coaxially a bush 14, which with its own tapered end section of suitable length enters inside the spring clamp 9 with a correct amount of radial play which leaves it free during the radial contraction and expansion movements. The race 1 of the part P which is inserted into the spring clamp 9 in the rest position must have a sufficiently symmetrical arrangement inside the said clamp and this is ensured by the aforementioned bush 14 on which the end of the race 1 which first enters into the clamp 9 rests.

When the part P is seated inside the clamp 9, the flange 304 of the hub 4 is sufficiently distant from the device in question and does not interfere at all with the latter when it is later rotated (see below).

An annular pressure chamber 15 is formed next to the spring clamp 9, all the

way around it, inside the body 7 of the device, said chamber having an arrangement symmetrical and centred with respect to the heightwise dimension of the said clamp and its wall 207 which makes contact with the clamp having flexibility and elasticity properties such that, by introducing into the said chamber 15 a fluid at suitable pressure values, said fluid deforms the said wall 207 and causes closing of the clamp 9 onto the race 1 of the part P with the desired pressure. Vice versa, when the chamber 15 is connected so as to be discharged, the clamp 9 returns as a result of its form-retaining memory into the rest position. If necessary, the body 7 may be surrounded by a protective cage (not shown), especially if the elasticity of the material which forms the body 7 is exploited in order to form the said movable wall 207. It is understood, however, that the pressure chamber 15 may be constructed adopting any suitable solution, with the wall 207 which may be made as one piece with the body 7 or which may be mounted separately, as indicated for example by 207'in Figure 2. In turn, the body 7 may be formed by several parts which, when assembled, result in the formation of the pressure chamber 15, all of which in a manner which is deducible and can be easily realized by persons skilled in the art.

Protective elements may be provided between the said flexible wall 207,207'of the annular pressure chamber 15 and the adjacent spring clamp 9 in order to prevent the direct contact of the said wall with the incisions 10,10'of the said clamp intended to close and open with closing and opening of the said clamp. These protective elements may for example consist of small segments which are made of steel or other suitable material and which are partially superimposed in an overlapping or fish-bone arrangement so as to be able to slide on top of each other.

The body 7 has, formed therein, one or more ducts 16 for connecting the chamber 15 to the source supplying pressurised fluid and, if the chuck M must be able to rotate, these ducts may for example be open on the flanged base 107 of the body 7 where they abut with an annular header 17 and an axial duct 117 which via a rotating distributor (not shown) is connected to the said source supplying or discharging the pressurised fluid.

By replacing the spring clamp 9 with other clamps which have a different

diameter it will be possible to use the same apparatus in order to machine parts P with a race 1 having a different outer diameter.

In the example shown in Figure 1, the holes 5 in the flange 304 are without the stud bolts which are intended to support the wheel of the motor vehicle and which pass through corresponding holes in the braking disc, so that the said flange is machined by a single U-shaped tool having a simplified shape. It is understood, however, that the form and number of the tools as well the form and/or composition of the flange 4 may be different from that shown, without departing from the scope of the invention.

With reference to Figure 1, a device for driving with friction the hub 4 is now described, said device being able to adapt automatically to any small errors in the coaxial alignment between the part P and the supporting and rotating system. The hub 4 has an axial cavity 6 usually provided with longitudinal grooves for mating, if necessary, with a rotating joint of the vehicle wheel and the said cavity 6 terminates in widened sections 106 and 206 at the ends, the widened section 206 being situated on the flange side and having a diameter which is normally larger. This having been stated, it can be seen that the driving device in question comprises a shank 18 for keying to the chuck for locking or rotating the hub 4 and this shank is axially aligned with a cylindrical head-piece 19 provided in the middle of the side facing the shank with an impression 20 in the form of a cone or a spherical cap engaged by a steel ball 21 which, together with the part opposite to that interacting with the said impression 20, co-operates with the small impression in the head of a mushroom piece 22 which is seated with the possibility of replacement in a corresponding axial seat 23 of the shank 18 and made for example with a self-lubricating material which is designed to wear during co-operation with the said ball. For this purpose, the mushroom piece 22 may be freely slidable inside the seat 23 and may if necessary be pushed towards the ball 21 by a small spring housed inside the said seat 23, not shown. The head- piece 19 is constrained to the shank 18 by means of three screws 24 which are equally spaced angularly at 120° from each other and which are each screwed by a predetermined amount into a threaded and blind hole 25 in the shank 18 and, with

their own head and stem, pass through the holes 26,26'formed in the head-piece 19 with sufficient radial play, the hole 26'opening out on the upper side of the said head- piece with a widened section 26"which houses a section of a cylindrical helical spring 27 which surrounds the screw 24 and with its other end rests on the shank 18. When the device is in the rest condition and owing to the effect of the spring 27 the head of the screw 24 rests on the step present between the holes 26, 26', the head-piece 19 is separated from the shank 18 by an amount slightly greater than the distance D defined in Figure 1 by the height of the part of the ball 21 emerging from the seat 20 and by the thickness of the head of the mushroom element 22.

The tapered and threaded end of an overturned mushroom element 30 is screwed inside a threaded, bottom, blind, axial seat 28 of the head-piece 19 and axially locked by means of at least one radial grub screw 29 or other suitable means, for example using adhesives, said mushroom element with its stem passing through the axial hole in a disc-shaped base-piece 31 which is made of metal or other suitable material and which has fixed to its bottom side an insert 32 of material with a high coefficient of friction, for example of the type used for the brake pads in motor vehicles. Resilient means are provided between the base-piece 31,32 and the head- piece 19, said means tending to keep the said base-piece in contact with the head of the mushroom element 30 and consisting, for example, of one or more bushes or rings 33 made of any suitable elastomer.

The operating principle of the device as described is simple and is obvious from Figure 1. After the part P has been gripped inside the spring clamp 9, the driving device is moved axially towards the said part, with the base-piece 31 which enters into the end seat 206 and with the head of the mushroom element 30 which enters into the axial cavity 6 of the hub 4. When the friction insert 32 of the base- piece 31 touches the bottom of the seat 206, the shank 18 is moved closer axially with a predetermined travel movement which causes the head of the mushroom element 30 to move away by a suitable amount from the said insert 32 and enter further into the axial cavity of the hub, against the elastic resistance of the elastomer pad 33 which is compressed, so as to fix the insert 32 in a condition where it is in

contact with the bottom of the seat 206 such as to ensure a substantial keyed connection between the hub and the driving device, while the head of the screw 24 is suitably moved away from the step present between the holes 26,26'so as to allow the whole assembly associated with the head-piece 19 to perform any oscillating movements about the ball 21 caused by the run-out and/or any misalignment of the part P with respect to the gripping clamp 9.