ANTI-SKID DEVICE

The present invention refers to an anti-skid device to as- sist motorvehicles, and particularly cars, driving on snow or other low-friction terrain, such as for example sand, mud, grass .

The use of so-called snow chains is widely known to the public of motorists, where "snow chains" normally indicates both conventional snow chains formed by chain lengths variously joined to each other, still widely used, especially on heavy- duty vehicles, and the number of variously formed devices which have been introduced on the market with the main objective of simplifying and speeding up the process of mounting them on the wheel, and also of enabling the user to carry out this operation with no particular difficulty and without getting excessively soiled.

As a matter of fact, the mounting of conventional snow chains necessarily requires chains to be joined on the inner side of tyres, having previously fitted the chains on the tyres, with a particularly awkward operation when it is performed on snow-covered roads and at low temperatures, and virtually impossible to be performed without getting remarkably dirty.

Companies in this field have hence long focussed on alter- native solutions to the conventional snow-chain, capable of solving or at least of reducing the above-mentioned problems. The solutions suggested so far can be substantially divided into two broad categories: conventional-design snow-chains, i.e. requiring some sort of joining device on the inner side of the tyre, wherein, however various types of devices are provided to speed up and simplify the arrangement of the chain on the tyre, and consequently the joining and tensioning of the same,- and snow chains which are mounted only on the outer side of the wheel and which are generally equipped with a central plate from which between 3 and 6 radial arms project, which extend at least partly on the tyre tread with a curved portion thereof, said portion being equipped with gripping means for snow-covered or

low-friction terrain.

Despite its higher cost, this last device category has met with remarkable market interest, precisely due to the fact that mounting thereof is performed exclusively on the outer side of the wheel and can further be performed without any need to move the vehicle, considering that the device does not fully enclose the outer tyre circumference, but consists of a discrete number of arms, whose pitch is normally wider than the tyre portion resting on the ground. Fitting the above-mentioned devices on the wheel is currently achieved by means of two different mechanical solutions. In a former solution the central plate makes up the mechanical support of the device and is therefore steadily joined to the wheel hub or to the fixing nuts of the same. The joining of the device normally requires one or more specific supports to be previously mounted on the wheel, whereon the snow chain is then mounted with quick-fitting means. Precisely due to this type of joining, in addition to the cost which is remarkably higher than that of conventional chains, this solution has not met with widespread diffusion, albeit among the users who make very frequent use of such device during the winter season and therefore readily accept the limitations due to the need to pre-tnount the supports on the wheels and to the presence of the same also when the snow chain is not in use. On the contrary, the device has not found the favour of the general public of users who make only occasional use of snow chains, precisely because pre- mounting of the supports is not a quick operation, it requires lifting of the car and use of tools and cannot therefore be quickly completed only when use of the chains becomes necessary. Such type of mechanical solution is consequently not suitable for impromptu use of snow chains, that is, only in case of real need.

In a second type of solution, the mechanical support of the device is instead demanded to the same arms, which for this rea- son have a J-shaped end portion partially surrounding the tyre, extending also on the inner side of the same and thereby guaranteeing the fastening of the arm, and hence of the device, to the

tyre. The central plate in this case hence represents only a necessary element of connection and mechanical support among the various arms and does not have instead any element of connection with the wheel, against which it simply rests. In actual fact, devices of the above-described solution of the second type are also known which employ, in addition to the J-shaped arm, an additional fitting device of the above-said disc to the wheel; such fitting, however, does not require any preliminary mounting, since it is not responsible for guaranteeing the entire me- chanical support of the device, but more simply that of keeping the disc supporting the J-shaped arms in a stable position; as a matter of fact, such fitting often consists of one of the bolts which secure the wheel to the vehicle. Mounting on the tyre of this second type of snow chain is of course much simplified, since it does not require any preliminary arrangement of the wheel or of the tyre and it can therefore be performed only when needed, nevertheless allowing to always operate exclusively on the outer side of the tyre.

The anti-skid device of the present invention ranks in this last type of devices and intends to solve the main problems encountered by known-type devices, which problems will be illustrated in the following with reference to some specific prior art documents.

US-A-4287926 describes a 3 -armed anti-skid device of the general type illustrated above. Two arms are directly pivoted about a central plate, simply resting on the side of the tyre, while a third arm is engaged with the same central pivot with radial slack, so as to allow tightening of the device on the tyre by means of suitable leverages. The 3 arms are guided by suitable ribs formed on the central plate so as to be able to perform exclusively radial movements.

GB-A-2272193 describes another anti-skid device of the type highlighted above, equipped, however, with an even number of pairs of J-shaped arms (4 in the drawings) , each pair being mounted on a respective hub, in respect whereof the arms are capable of performing only rectilinear translation movements getting mutually closer/further away.

The hubs of the different pairs of arms are mounted on a single pivot and can rotate in respect thereof from a collapsed position, wherein each arm of any pair is overlaid by the corresponding arm of another pair, up to the operating position wherein the different arms are circumferentially arranged along the tyre at an even distance from one another. Mounted on the central pivot, furthermore, there are toothed wheels which cooperate with a rack portion of each arm, so as to be able to move the arms in a radial direction, in order to tighten the same against the tyre and viceversa, with the movement of a single lever connected to said pivot.

EP-A-0147272 introduces an improvement to the anti-skid device disclosed in the above-described British patent, consisting in providing each individual arm with additional radial mobil- ity, which mobility comes into play when the gripping lug of the arm (i.e. the horizontal portion of the arm covering the tyre tread and comprising suitable means for gripping the snow) rests on the ground, to compensate the simultaneous tyre squashing, which mobility was instead not disclosed in the previous patent. Such result is achieved by means of a mechanism which allows to decouple the arm from the toothed wheel/rack coupling in its movements coming closer to the centre of the wheel. In this patent the option is also described of making the gripping lugs swing about a horizontal axis, with respect to the J-shaped arm supporting said gripping lugs, so as to reduce the angle of incidence thereof upon impact with the ground.

However, the known devices described above, although they all achieve the result of allowing quick fitting on the wheel by operating exclusively on the outer side of the wheel, are not free from faults and drawbacks.

A first drawback occurs due to the fact that mounting of the device and tightening of the same on the tyre calls for manual adjustment of the arm position, both along the circumference and in a radial direction, and requires the use of tools and of toothed wheel/rack assemblies in order to accomplish suitable tightening of the device on the tyre. These solutions hence all have the drawback of requiring certain manual dexterity on the

part of the user, of increasing mounting times and, finally, they complicate the structure of the device, which as a result is more prone to wear and failures due to deposits of dirt or rust formation in its mobile components. A second drawback lies in the fact that the arms of known devices are mechanically linked to one another in a direct manner; the shifting of an arm position therefore directly affects that of the other arms. This creates problems both during the mounting step and, especially, during use of the device. As a matter of fact, whereas during mounting there is simply the drawback of having to determine the final correct position of all arms simultaneously, during vehicle running, shifting of the arm resting on the ground - due to the effect of the tyre being squashed - at least partly affects the position of the other arms and hence determines a substantial instability of the device. Said drawback is particularly evident in the first two cited devices, where the device does not have inner degrees of freedom and hence the entire shifting of the ground-resting arm affects the other arms. However, the drawback is nevertheless evident also in the device described in EP-A-0147272, where in fact the reaction force of the spring allowing the shifting in a centripetal direction of the arm in contact with the ground is in any case released on the central pivot of the device and con- osequently, since such pivot is not fixed to the wheel in any way, on the other arms. This determines a continuous shifting of the arms not resting on the ground with respect to the tyre and thereby a faster deterioration both of the device and of the tyre .

A third drawback finally lies in the fact that the degree of freedom provided in EP-A-0147272 - but not in the other two cited prior patents - to allow the arms to follow the deformation the tyre undergoes while resting on the ground provides a rectilinear shifting in a radial direction. Since the force acting on the arm lug upon the first contact with the ground has instead of course a tangential direction, it is evident that in this step the arm undergoes strong flexural stress, since there are no useful components of such force acting on the arm in the

radial direction in which said arm can actually move. This has two seriously negative effects. As a matter of fact, on the one hand the dimensioning of the arms, and consequently of the entire device, must be such as to support the flexural action arising in the arm, with a resulting greater weight and cost of the device. On the other hand, it is further evident that shifting of the arm in a radial direction occurs with delay over the time of the first impact, i.e. only when the tyre begins to "squash" the lug on the ground in a direction close to the ra- dial one; thus, a continuous impact action of the lugs on the ground is thereby determined, which dramatically reduces the lifetime of the device and seriously worsens vehicle driving comfort already at very low speeds .

Finally, a fourth drawback lies in the fact that known de- vices, when they grip the snow-covered ground, are subject - as already seen above - to a reaction force having a direction substantially tangential to the wheel, which force consequently tends to move the lug further away from the tyre surface and which can only be countered by the flexural resistance of the supporting arm. In any case, the tyre/lug adherence is lessened, with negative consequences both on traction effectiveness and on device stability, as well as on the resulting tyre wear.

The object of the present invention is hence that of offering an anti-skid device for vehicle wheels of the general type described above, which, however, is free from the above outlined drawbacks for the devices currently known and, in particular, a device of an extremely simple construction, of extremely simple mounting, of automatic centring and tightening and finally free from the above-described problems of the impact of the lugs dur- ing vehicle running thanks to a higher improved adjustment speed of the lug position to tyre deformations and thanks to a greater continuous adherence of the lugs to the tread surface.

These objects are achieved, according to the present invention, by means of an anti-skid device for vehicle wheels, of the type comprising a central support adjacent to the outer side of the wheel and three or more arms pivoted to said support which extend to surround the tyre by means of a J-shaped end thereof

tightening on the same, so as to fasten the anti-skid device to the wheel, characterised in that said tightening is achieved by- means of a rotation movement of said arms which causes said J- shaped ends to move closer to the wheel axis, rather than by the radial translation movement of said arms which is typical of known devices .

In a preferred embodiment of the invention, this result is achieved thanks to the fact that said arms are pivoted in an eccentric position in respect of the rotation axis of said wheel. Further features and advantages of the anti-skid device according to the present invention will in any case be more evident from the following detailed description of some preferred embodiments of the same, with reference to the accompanying drawings, wherein: fig- 1 is a front elevation view which shows diagrammati- cally one of the arms of the anti-skid device according to the present invention in a mounting position; fig. 2 is a side elevation view which shows diagrammati- cally the essential structure of the anti-skid device according to the present invention; fig. 3 is a side elevation view of a first embodiment of the anti-skid device according to the present invention in a mounting position; fig. 4 is a side elevation view of the device of fig. 3, in a tightened condition on the tyre,- fig. 5 is an enlarged-scale, detailed view which shows the detail of the inner end of one of the J-shaped arms ; fig. 6 is an enlarged-scale, detailed view which shows the orientation of the horizontal lug of one of the arms of the de- vice, during device use,- fig. 7 is a side elevation view of the device of fig. 3, which shows a possible irregular operative condition; fig. 8 is a side elevation view which shows a second embodiment of the anti-skid device according to the present inven- tion, in a tightened condition; fig. 9 is a side elevation view which shows a third embodiment of the anti-skid device according to the present invention

in a tightened condition; fig. 10 is a side elevation view which shows a fourth embodiment of the anti-skid device according to the present invention, wherein, for simplicity's sake, a single J-shaped arm is shown, in a mounting and tightened condition, respectively; fig. 11 is a side elevation view which shows a fifth embodiment of the anti-skid device according to the present invention, wherein, for simplicity's sake, a single J-shaped arm is shown, in a mounting and tightened condition, respectively. In figs. 1 and 2 the structure of the anti-skid device of the present invention is diagrammatically shown, which substantially comprises a central disc 1, whereon multiple arms 2 are hinged, having a J-shaped end, intended to accomplish the device fastening on tyre P and to support the ground gripping means . In the use position, disc 1 is adjacent to the outer side of tyre P whereon the device is mounted, while arms 2, according to a basic feature of the present invention, have their respective rotation centres 3 circumferentially arranged at an even distance from each other, in the proximity of the edge of disc 1. In other words, when the anti -skid device is mounted on tyre P, the rotation centres of arms 2 are offset with respect to the rotation centre of the wheel whereon tyre P is mounted, by a measure sufficient to cause the effects which will be described in detail in the following and, preferably, comprised between 1/4 and 4/5 of the wheel radius.

As said above, arms 2 are generally J-shaped, i.e. in the shape of a U having different-length arms, and hence have a horizontal portion or lug 2r intended to rest on the tread of the tyre and an end portion 2f which is joined to the inner side of the tyre to accomplish the fastening of the device to the wheel. In fig. 2 and in the subsequent side elevation figures, the inner portion 2f of course is not visible, since it is covered by the outer portion of arm 2, but the length thereof is anyway shown for clarity's sake by a shadowed area of the arm. On the outer side of the tyre, arms 2 further have an extension 2a, which is substantially perpendicular to arm 2, which acts as a control lever to determine the shifting of arms 2 from the

mounting position on tyre P, shown in fig. 2, wherein said arms have a direction substantially coinciding with a wheel radius, up until the tightening position, wherein arms 2 have been caused to rotate until they bring lugs 2r in contact with the tread of tyre P as shown, for example, in fig. 4. In the mounting position the entire end portion 2f of arms 2 is arranged outside the perimeter of tyre P, so that the anti-skid device of the present invention can be fitted without any problem on the tyre . A first embodiment of the present invention, which shows a practical application of the construction diagram shown above, is illustrated in figs. 3 and 4, in a mounting and in a tightened position on tyre P, respectively. In this embodiment, each of levers 2 have its inner end 4 shaped as a hook and is further equipped with a grooved pulley 5, pivoted idle about the free end of extension 2a. Upon mounting, a flexible elastic ring E is caused to pass outside hooks 4 and by this simple expedient the perfect radial position of all arms 2 is preserved, remarkably easing the fitting of the device on tyre P. Once the device has been fitted in position, the same elastic ring E is instead caused to pass through the groove of pulleys 5. The elastic return force of flexible ring 5 is sufficient to determine the shifting of levers 2 into the position shown in fig. 4, wherein all arms 2 and their corresponding ends 2f are correctly fitted on tyre P and lugs 2r are in contact with the tread of the same.

The fastening depth on tyre P of end portions 2f, shown in fig. 4 by letter h, is determined by the height of said portion and by the inclination taken up by arm 2 in a tightening posi- tion. As a matter of fact, such inclination causes a further coming closer of tip head 6 of end 2f to the centre of the wheel and hence improved fastening of the device on the tyre with respect to that of similar prior art devices. This feature is particularly interesting because it allows the device of the present invention to be used also by those types of vehicles, which are very popular on the market today, wherein useful space to fit the device (i.e. the distance in a vertical plane between

the tyre tread and the vehicle mudguard) is severely reduced, so much so that known devices cannot normally be employed by the same. As a matter of fact, the maximum fastening height of such devices, the other conditions being equal, is shown by segment n of fig. 3, which shows precisely the maximum fastening depth for a (known) fitting system, characterised by radial shifting of the J-shaped arms, where n < h. The length difference between segments n and h is of course rather modest, i.e. in the order of a few millimetres, but it is often sufficient to determine the difference between a condition of insufficient fastening of the device to the tyre and instead a condition of stable and satisfactory fastening. In order to ease sliding of tip head 6 on the tyre surface during tightening of the device and during use of the same and also in order to avoid any possible tyre de- terioration, such tip head is shaped as a small sphere, as can be better seen in the enlarged drawing of fig. 5.

The position of the pivoting centre 3 of arms 2 and the length of such arms determines the final position of arms 2 when lugs 2r are in contact with the tread of tyre P. In this posi- tion the angle formed by the arm (intended as the straight line joining pivoting centre 3 with lug 2r) with respect to a wheel radius passing through centre 3 is preferably between 30 and 85° and more preferably between 45° and 60°.

Even if it is not essential for the good operation of the device, in a preferred embodiment lug 2r does not rest on the tread with all its surface, but only with one of the two edges, and precisely the one downstream in the driving direction (i.e. upstream when following the direction of rotation of the wheel shown by arrow F in fig. 6) . As a matter of fact, thereby lug 2r has a sharp edge facing towards the surface of the low-adherence terrain and the other one towards the surface of the tread, and this on the one hand improves gripping of the anti-skid device on the ground and on the other hand prevents any possible sliding thereof on the tyre, further improving gripping of the de- vice on the ground, which remains nevertheless excellent even when the lug is arranged parallel to the tread surface. As a mater of fact, it must be stressed that, unlike what happens in

known devices, the reaction force which the snow-covered ground imparts on the lug in a direction tangential to the wheels determines - precisely thanks to the particular fastening of the corresponding support arm in a non-radial direction and with an eccentric pin - improved tightening of the lug on the tread.

From the preceding description, it can be noticed how the anti-skid device according to the present invention has fully achieved all the set objects. As a matter of fact, it has an extremely simple construction and is fitted very quickly and eas- ily on the tyre, whereon it tightens automatically, centring itself as soon as elastic ring E is positioned on pulleys 5, with no need any other intervention by the user. The device-mounting operation is hence much faster and more precise than that of known devices, indeed thanks to the fact that the individual arms move into the tightening position with a rotation movement and not a translation movement. Still thanks to the rotation ability of arms 2, any possible tyre diameter variation due to wear and tear, incorrect inflation pressure and the like is further automatically compensated. The full mutual independence of individual arms 2 allows the arms to follow with immediacy the cyclical deformation of the tyre resting on the ground without releasing any tension on the other arms, but simply with a further modest alternate rotation about the centre of rotation 3 beyond the normal tightening position. In this respect it will be noted that in the device of the present invention, unlike radial-arm known-type devices, arm 2 is oriented so that the force the ground imparts to lug 2r at the moment of the first impact has, from the start, a remarkable lever arm with respect to the centre of rotation 3 and hence im- mediately determines the rotation of arm 2 in the desired direction; the movement of arm 2 hence unfolds gradually and rapidly from the first impact with the ground and this allows to dramatically increase both driving comfort and gripping effectiveness of the device. At the same time, the structure considered above allows to reduce the weight and hence the cost of the device, which as a matter of fact can be dimensioned so as to be much lighter, having to endure much weaker flexural stresses

than known devices. Finally, the absence of impacts and of great flexural stresses within the device remarkably increases the useful life of the device.

In practical tests of the device described above, however, it was possible to ascertain that in specific acceleration conditions, irregular configurations of the device can be determined, for example such as the one diagrammatically shown in a wilfully exaggerated manner in fig.7, wherein the device loses its symmetrical configuration on the wheel, with a consequent offsetting of disc 1 with respect to the conventional concentric position to the wheel; it can be assumed that the technical causes of this phenomenon are the following. When the wheel is driven into rotation, the device is driven by friction by the tyre generating, upon contact of the lugs with the ground, a forward reaction force. During the acceleration step, due to the great inertia difference between the device and the vehicle whereon said device is mounted, the above-said reaction force determines thereon very different effects, so that the device tends to increase its speed more rapidly than the vehicle, mov- ing forward with respect to the wheel whereon it is mounted. This movement dissimilarity between the device and the wheel is of course countered by the device arms arranged behind the tyre, but since these are held in a correct position by the elastic return force of ring E, in conditions of fast acceleration it can lead to an excessive deformation of such ring by the arms arranged at the back, so that they take up the irregular position shown in fig. 7, even finally allowing the arms to pass over the tyre. Continuing to drive in these conditions, accidental uncoupling of the device from the tyre can hence occur. This problem can be by-passed in two different ways, or by any combination of the same. On the one hand, as a matter of fact, the device of the invention can be manufactured by adopting a large number of arms (for example 5 or 6 arms) , which means that there is always at least one arm, in the rear lower part of the tyre, capable of perfectly releasing on the wheel the reaction force caused by the impact of the device on the ground, with no opportunity for such arm to slide forward on the

tyre and to pass over the same. On the other hand the device according to the invention can instead be equipped with additional elements suitable to limit, by means of different rigid end stops, the opening travel of arms 2 towards the mounting posi- tion or suitable to prevent the offsetting of the arm support disc with respect to the wheel .

In figs. 8 and 9 two further embodiments of the anti-skid device of the present invention are shown which incorporate two different types of these last devices and precisely: a bell jar 7 (fig. 8) which is steadily anchored to disc 1 and whose inner edge represents an end stop for the movement of pulleys 5, simultaneously protecting the device members,- a series of stops 8 (fig. 9) projecting from disc 1 and which can be quickly fitted to said disc, which accomplish an end stop directly on arms 2. This same result of limiting the opening travel of arms 2 can in any case be achieved also in other ways, for example restraining

^• disc 1 to a coaxial position to the wheel, by means of a pivot which is mounted on, bayonet-wise or being fitted on, a hollow hub of the same,- or by using a limited-extension elastic ring E, which becomes inextensible after a certain length, having incorporated a rigid cable of such determined length, so as to prevent too wide displacements of pulleys 5 and hence of arms 2.

In a fourth and fifth embodiment of the device of the present invention, shown in figs. 10 and 11, rather than by means of a tensioning element, such as for example the above-described elastic ring E, arms 2 are brought and held in a tightening position by means of pushing means. This solution allows to overcome at the origin the above-discussed problem of possible changes of the symmetrical and centred configuration of the de- vice with respect to the wheel during acceleration, considering that each individual arm 2 is constantly held in a correct position no longer by an elastic means, but by a substantially non- deformable pushing means .

In particular, in fig. 10 a device comprising a second disc 9 is shown, connected to disc 1 by means of a suitable ratchet 10. Arms 2 in this case have a simple transversal pin 11 capable of cooperating with slot-like cut-outs 12 formed on disc 9. By

rotating disc 9 with respect to disc 1, the pin 11 of each arm 2 (a single arm is shown for simplicity's sake both in this fig. 10 and in the subsequent fig. 11) moves along slot 12 bringing the arm from the mounting position M to the tightening position S . In this last position pin 11 lies in the broadest area of slot 12, so that arm 2 has the slack sufficient to be able to follow - by means of alternate rotation movements about pin 3 - the squashing of tyre P on the ground.

The same result is achieved, in the embodiment shown in fig. 11, by means of an articulated leverage 13 which drives the rotation of arm 2 between the mounting position M and the tightening position S. Similarly to what has been described above, the base lever of leverage 1 is fastened to a central pin 14 which is coaxial to disc 1 and connected to the same by means of a suitable ratchet which allows to lock all leverages 13 in the tightening position S of respective arms 2. In this case, too, the limited alternate rotation movement of arm 2 which is required to follow the squashing of the tyre is allowed by a slot 15 formed in a suitable position in one of the levers of lever- age 13.

The present invention has been described with reference to some preferred embodiments of the same and, in particular, with reference to a device consisting of 4 arms. It is clear, however, that the scope of protection of the invention is not lim- ited to said embodiments, which can instead be changed, both in the number of arms and in the shape, arrangement and system of tensioning/pushing of the arms, it being only necessary that the arrangement thereof is such as to allow a rotation movement of the arms, during the squashing of the tyre, rather than the movement in a radial direction typical of known devices, and that the pitch between one arm and the next is at least greater than the space taken up by the wheel portion resting on the ground, so as to allow to mount the device without having to move the vehicle. All these possible changes are within easy reach of a person skilled in the field and are therefore all to be considered within the scope of protection of the patent, provided they fall within the definitions of the invention con-

tained in the accompanying claims .