LU85324A1 - SELF-SUPPORTING TIRE - Google Patents

Abstract

The tyre comprises a radial carcass having at least two piles 1,2 or groups of plies between which is incorporated, in each sidewall of the tyre, a supporting component (10) made of a soft elastomeric material, of lenticular cross-sectional shape, which extends from a filler (8) (which overlies the bead core (3)) to a location under the belt (5,6,7) which underlies the tread band (4). The elastomeric material of component (10) has an ISO hardness not exceeding 47 and a thermal stability not less than 20 minutes for a temperature increase not exceeding 25 DEG C. Instead of the load, in the deflated tyre, being borne by the material of the sidewalls, the component (10) tends to maintain the tyre shape. <IMAGE>

Description

SELF-SUPPORTING TIRE

The present invention relates to self-supporting tires, that is to say tires which are capable of continuing their race over an appreciable distance and at a non-negligible speed even when they are completely deflated, without this giving rise to contact. between the internal surface of the sidewall and the internal surface of the tread, this condition being the characteristic of tires which support the operation called "running flat". The present invention is particularly applicable to radial tires, that is to say tires whose carcass cords (cords) extend from one bead to the other and lie in planes inclined at an angle of 90 ° or slightly different from 90th with respect to the equatorial plane of the tire.

Tires of the indicated type are well known to technicians. These tires have a carcass structure comprising a profile made of elastomeric material having a significant thickness and a high hardness, inserted into the sidewalls of the tire; this profile can be indifferently placed outside the carcass fabrics (plies) or between the fabrics or even inside the tire with respect to the carcass fabrics.

The purpose of the aforementioned profile, normally of lenticular section tapered towards the extended ends respectively in the direction of the heels and the tread, consists in exerting an action of effective support of the load weighing on the wheel whereas, as a result of deflation, the support action normally exerted by the air contained inside the tire is lacking, even partially.

'' These tires have the disadvantage that during use in the deflated state the lenticular rubber profile, strongly stressed by cyclic compressions due to the weight of the vehicle which presses * on the sidewalls of the tire, absorbs a quantity con - 2 siderrable energy which therefore releases a large amount of heat which is difficult to get rid of and which causes a progressive degradation of the resistance characteristics of the entire structure of the tire and, in particular, of the resistance of the rubberized fabric or of the cords of the carcass fabrics, and of the profile itself.

This progressive degradation of the characteristics of the constituent elements of the tire and, consequently, of the general structure of the tire imposes limits on the distance which can be traveled and on the speed of use of the tire in the inflated state. In addition, in general, after a period of operation in the above conditions the tire is badly damaged and is no longer recoverable.

The Applicant has now found that it is possible to raise these limits of use of the tire appreciably, so that the subject of the present patent consists of a tire of the self-supporting type provided with a new structure which functions in a a new way in which the tire can be used under load, in the deflated state, over long distances and at high speeds, and this repeatedly during the period of use.

The object of this patent 'therefore consists of a tire for vehicle wheels provided with a textile carcass comprising two fabrics or groups of fabrics, a tread placed in a crown on said carcass, an annular reinforcing structure circumferentially inextensible cir-inserted between the carcass and the tread, sidewalls and beads for fixing the tire to a corresponding mounting rim, these beads comprising an annular circumferentially inextensible reinforcing core and a stuffing in material elastomer, of substantially triangular cross-section, superimposed radially on said core 1 ----------------------------- 3 returned from the inside towards the outside around the annular reinforcing core, the sides comprising an annular profile of elastomeric material, of substantially lenticular cross section, extending between the heels and the crown zone and having its maximum thickness in the line radially external median side, characterized in that said lenticular profile is inserted between the fabrics or group of carcass fabrics and has an ISO hardness not greater than 47 and thermal stability - defined as the time of destruction of a sample of said material elastomer on the GOODRICH flexometer - not less than 20 minutes.

The elastomeric material of this lenticular profile also preferably has a mechanical tg S value not greater than 0.0750 and a dynamic elasticity modulus not greater than 4 megapascals (MPa).

According to a preferred embodiment of the invention, the radially external end of the aforementioned lenticular section extends axially towards the interior of the tire, in a position of reciprocal superposition with the annular reinforcement structure, on a non-superior axial development section. at 15% of. the total width of the abovementioned annular structure, while the radially internal end is superimposed on the stuffing, beyond the fabric or the group of fabrics axially external, on a development section not greater than 20% of the section height tire. As for the stuffing, it is very expedient for it to develop radially outwards over a height not less than 15% of the section height of the tire.

According to another suitable embodiment of the aforementioned tire, the radially internal end of the lenticular section is superimposed, beyond the stuffing, on a reinforcing textile edge arranged in i ............. .....— 4 of the carcass fabrics and extended radially from the annular core to a height not greater than 40% of the section height of the tire. In addition, the carcass fabrics are reinforced with cords of textile material, natural and / or artificial, resistant to the action of heat, preferably in rayon or in an aromatic polyamide.

In any case, the present invention will be better understood below with the aid of the description given and of the appended figure, which constitutes a non-limiting example and which represents - in cross section - a preferred embodiment of the tire. the invention

As can be seen in this figure, the tire comprises a two-ply carcass, of textile type, radial, constituted by two fabrics (plies) of rayon 1 and 2 folded at their ends, from the inside to the outside, around an annular core 3 which reinforces the heels, these cores being well known per se and being called hereinafter the "rod1".

Alternatively, the number of carcass fabrics could also be greater than two, but they will always be divided into two groups separated from each other.

In a crown on this structure is a tread 4 made of elastomeric material on which is carved, by stamping, the useful surface sculpture of the tire.

Between this tread and the carcass is inserted an annular reinforcement structure, circumferentially inextensible, of the usual type, usually known by the name of "belt structure". In the tire of the invention, for example, this structure is adequately formed by two cords. ches 5 and 6 of metallic cords, parallel to each other in each layer, crossed over one another B in the adjacent layers, and oriented symmetrically 5 with respect to the circumference of the tire, and by a layer 7 of cords made of material textile, suitably made of nylon, disposed in a radially external position relative to the above-mentioned layers of metal cords and sufficiently wide to cover the ends of these layers.

The total width L of this structure (in the figure only the part L / 2 has been shown) corresponds to the distance between the two circumferential lines situated at the center line of each gap between the widest metal strip and the narrowest strip.

In the radially external position relative to the rod is an annular packing 8, in a mixture of high hardness, extending radially outward. The bead is then suitably reinforced further by means of a textile border 9, that is to say constituted by a strip of fabric with textile cords, preferably nylon, inclined relative to the circumferential direction of the tire at an angle. 22 °, anyway between 20 ° and 45 °.

The aforementioned reinforcement is disposed in an axially external position relative to said stuffing and to the folds of carcass fabrics and extends radially outwards from the rod to a height "g" which does not exceed 40% of the height tire cross section indicated by H in the figure.

Between the carcass fabrics, in the sidewall of the tire, is inserted a profile 10 of elastomeric material, of lenticular section, which has its maximum thickness in the radially external midline of the sidewall and tapers towards the ends which develop radially towards the tread and towards the heel.

The elastomeric material which constitutes the aforementioned lenticular profile is a very soft material which is not suitable, per se, for exerting a load-bearing action acting on the wheels when the tire is deflated. It is advantageous that the hardness of the material, measured according to standard ASTM 1415-81, does not exceed 47. Likewise, also, the dynamic elastic modulus must not exceed 6 megapascals, and preferably must not exceed 4 megapascals .

The main characteristic of this material must reside in the fact that it can withstand a very high number of working cycles while the sidewall of the tire flexes under load during use in deflation conditions, without absorbing quantities excessive energy nor give off a large amount of heat, keeping its characteristics constant over time, even at high temperatures and despite repeated use.

These characteristics are ensured as soon as the elastomeric material has a thermal stability (defined by the time necessary to destroy a sample of the aforementioned elastomeric material, under determined conditions, on the GOODRICH flexometer and according to standard ASTM 623-78) not less than 20 minutes and a mechanical tg <£ value of not more than 0.075. The thermal stability of a material is precisely the capacity of this material to resist for long periods of severe dynamic stresses, that is to say to maintain substantially constant its physical and chemical characteristics despite prolonged dynamic fatigue and 1 ' consecutive increase of the temperature which tends to destroy the bonds of the chemical network of vulcanization, which causes a degradation of the structure and, consequently, qualities of behavior.

It follows that the mixture per se must have characteristics which minimize the temperature increases due to dynamic stresses, that is to say that it must have the low values of the dynamic modulus and of the mechanical tg & which represents H "hysteresis loss". This known parameter is proportional to the quantity of energy dispersed with respect to the maximum elastic energy imposed.

To determine which mixtures meet the requirements of the invention with regard to thermal stability, the Applicant has found it expedient to use the GOODRICH flexometer according to the ASTM standard mentioned above.

In short, the GOODRICH flexometer consists of a bar placed in equilibrium on a knife blade so as to achieve a balance.

Two weights of 24 Kg each are applied to the two arms of the balance in order to greatly increase the moment of inertia of the system to dampen the oscillations.

The sample to be tested is placed between the bar (on the side opposite the weights and at a point very close to the fulcrum) and the head of a piston capable of urging the sample, axially in compression, by a sinusoidal, shape and frequency value imposed.

A test load is placed on the end of the bar on the side opposite the sample relative to the fulcrum.

A micrometric screw allows the sample support base to be moved in both directions perpendicular to the bar, towards the piston head, so that by. the choice of this distance and of the weight of the test load it is possible to subject the sample to an initial preloading while maintaining the direction of the stress strictly axial.

The test is carried out by subjecting the sample to continuous cyclic compression until the sample is brought to rupture (blow-out). The temperatures of the sample are also measured at the start and end of the test.

The time required to bring the sample to rupture, as well as the increase in temperature observed, adequately define the characteristic of thermal stability of the elastomeric material examined.

The Applicant has found that the most significant test conditions consist in a sinusoidal oscillation frequency of the piston equal to 30 Hz with an imposed deformation, between two adjacent peaks of the sine wave, equal to 6.35 mm, with a static load on the bar equal to 48.46 pounds (weight) corresponding to a preload on the sample of 489 newtons and an initial temperature of the sample of 100 ° C.

When subjected to these test conditions, the mixtures according to the invention withstand a test duration of not less than 20 minutes and also exhibit, at the end of the test, a temperature increase which does not exceed 25 °. vs.

'With regard to the dynamic elastic modulus and the mechanical tg S, the above characteristics were determined by the Applicant in support. bringing the sample of elastomeric material to be examined (cylindrical, height 26 mm, diameter 29 mm, pre-compression 20%) to a sinusoidal cyclic deformation, of amplitude equal to 6% of the height of the non-deformed sample, generated by a servohydraulic device controlled by a computer which measures the area W of the hysteresis cycle (expressed in joules / m3), the peak force s (in pascal) and the peak deformation d, then calculating the mechanical tg% = tg arcsin W / 7T.sd and the dynamic elasticity module E '= s / <T.cos <T.

By way of example only, the Applicant gives below a mixture recipe which has proved suitable for use in the structure of the tire of the invention in order to illustrate the most important physical characteristics thereof noted on the vulcanized mixture.

9.

Recipe Parts by weight x 100 of SMR 10 rubber (standard Malaysian rubber) 100.00

Zinc oxide 5.00

Stearic acid 2.50

Flectol M (from MONSANTO) 1.00

Isopropyl-phenyl-para-phenylenediamine 1.50

Microcrystalline wax 1.50

Polyplastol-6 (from Β0ΖΖΕΤΤ0) 3.00

Carbon black N-326 20.00 N-oxydiethylene-benzothiazol-2-sulfenamide 1.50

Diphenyl dimethyl thiuram disulfide 0.375

Sulfasan-R (from MONSANTO) 2.00

Characteristics

Thermal stability 26 min.

Dynamic elastic modulus 3.175 MPa tg <f mechanical 0.072

Temperature increase in

end of test 18 ° C

According to the preferred embodiment illustrated in the appended figure, the profile of lenticular section, made of elastomeric material having the characteristics indicated above, has its radially external end which extends axially inwards below the structure of belt to a point whose distance b from the end of said belt structure is equal to 12.5% of the total width of the belt structure and, in any case, less than 15% of said width.

The aforementioned belt structure and lenticular profile therefore have a reciprocal superposition zone of axial development comprised within the abovementioned limits.

Likewise, in the lower zone of the flank and the heels, the lenticular profile has a section of i "10 superimposed with the stuffing and with the possible textile reinforcement in order to create a progressive stiffening of this zone which is necessary to give good qualities. tire behavior on the road. Thus, the lenticular profile is superimposed on the stuffing, beyond the fabric or the most or most external bundle of fabrics 2 on a section c whose amplitude is not greater than 20% of the section height of the pneumatic.

The zone in which this superposition occurs can vary within certain limits inside the sidewall of the tire. In any case, the radial height f of the abovementioned stuffing 8 must not be less than 15% of the section height of the tire.

Likewise, with regard to the possible textile reinforcement border at the bead, it is preferable that the radial height g of this reinforcement does not exceed 40% of the section height of the tire. In addition, the above-mentioned lenticular section section has its maximum thickness in the radially outermost part of the sidewall. This thickness is preferably between 3% and 6% of the maximum tire width (cord).

It has been found that the tire according to the invention makes it possible to appreciably increase the distances which can be covered and the speeds which can be used under conditions of complete deflation, as well as significantly increase the life of the tire. These advantages were obtained because the Applicant abandoned the old concept which consisted in making bear the load weighing on the deflated tire by the mixture inserted in the sidewalls of the tire, in favor of the new and inventive concept consisting mainly in making work the carcass fabrics and not the interposed mixture.

It must be taken into account that, substantially, an elastomeric material is a volumetrically incompressible material, so that when this material is deformed by compression in a certain direction it extends in the other directions by the even because of its substantial incompressibility. It follows that when a mixture, as in the tire of the invention, is enclosed between the carcass fabrics, that is to say in a substantially closed receptacle, in the tire in operation, it is subjected a state of triaxial compression thanks to which it gives the whole structure a rigidity - particularly in flexion - considerably higher than that which is inherent in the mixture in question.

It can also be noted that when the tire is subjected to a load under deflation conditions, the mixture inserted between the carcass fabrics is strongly compressed in the radial direction due to the effect of the bending of the sidewall of the tire, so that because of its substantial incompressibility, it must be able to extend in the other directions.

However, the mixture cannot extend in the circumferential direction because the tire does not allow dimensional variations in this direction.

Consequently, there remains the transverse, or better axial direction, but in this direction any expansion of the mixture towards the outside is prevented by the axially external carcass fabrics which are subjected to a high tension and which are, therefore, undeformable _ in that direction.

As a result, the mixture extends axially inwards where the carcass fabrics, as a result of the bending of the sidewall, are subjected to a state of compression and, consequently, to a reduction in development which allows such expansion. Due to the effect of this axial expansion of the lenticular rubber profile inserted between the carcass fabrics, the fabrics or the group of fabrics axially internal are also, by

L

'- 12 Consequently, put or put in a state of traction and thus contribute effectively to support the load which weighs on the tire in the absence of inflation pressure.

In other words, in the tire of the invention, the lenticular mixing profile inserted between the carcass fabrics has not so much the aim of directly supporting the load but mainly that of maintaining the geometry of the structure of the tire. It follows, among other things, that it is obvious that this profile must necessarily be inserted between the carcass fabrics and that no other alternative arrangement can be accepted, externally or internally with respect to said fabrics.

It is also easy to understand why the mixture of the lenticular profile must have the lowest possible power absorption and the highest possible thermal stability. From this point of view, the values indicated by the Applicant have been found to be critical values to guarantee the proper functioning of the tire.

It is clear, in fact, that if these values vary - that is to say if the hysteresis of the mixing of the lenticular profile increases - the heat generated by this profile in operation in the deflated tire also increases. In addition, this heat is very difficult to dissipate precisely because of the thickness of the lenticular profile contained between two layers of carcass fabrics which reduces the conduction of heat towards the outside and, consequently, the cooling of the side of the pneumatic in service.

Thus, due to the increase in temperature in the lenticular profile, in a short time not only would the characteristics of the mixture of said profile be compromised, but also the resistance characteristics of the entire structure of the tire and, in particular, those of carcass fabrics. Precisely

J

, 13 ψ for this reason, it is preferable that the reinforcing cords of the carcass fabrics in the tire - of the invention are made of a material which resists the action of heat. According to the invention, they will very conveniently consist of natural and / or artificial textile materials such as, for example, rayon or an aromatic polyamide, in particular that known under the brand "KEVLAR" from Du Pont.

It is obvious that the present description has been given by way of non-limiting example and that, for this reason, it must be considered that the scope of the invention also includes all the modifications and variants which are not have not been described here but that any technician in the industry can easily deduce from r

Claims (10)

1. A tire for vehicle wheels provided with a textile carcass comprising two fabrics or groups of fabrics, a tread placed in a crown on said carcass, an annular structure of circumferentially inextensible reinforcement inserted between the carcass and the band of treads, sidewalls and beads for fixing the tire to a corresponding mounting rim, these beads comprising a circumferentially annular annular reinforcing core and a filling of elastomeric material, of substantially triangular cross section, radially superimposed on said annular core of reinforcement, the carcass fabrics being turned from the inside towards the outside around the annular reinforcement core, the sides comprising an annular profile of elastomeric material, of substantially lenticular cross section, extending between the heels and the crown zone and having its maximum thickness in the radially out center line sidewall, characterized in that said lenticular profile is inserted between the fabrics or groups of carcass fabrics and in that the elastomeric material of this profile has an ISO hardness not greater than 47 and a thermal stability - defined as time, destruction of a sample of said elastomeric material! on the GOODRICH flexometer - not less than 20 minutes! your. * ‘” "2“ A tire according to claim 1, characterized in that said elastomeric material has a value of tg <^ mechanical not greater than 0.0750. 3. A tire according to claim 1 characterized in that said elastomeric material has a dynamic elasticity modulus not greater than 6 megapascals. '' 4. A tire according to claim 1 characterized in that the radially outer end of the pro-. lenticular yarn extends axially inwards at i 15 in a position of reciprocal superposition with the annular reinforcement structure, on an axial development section not greater than 15% of the total width of said annular structure. 5. A tire according to claim 1 characterized in that the radially interned end of the lenticular section is superimposed on the stuffing, beyond the fabric or the group of fabrics axially external, on a development section greater than 20% of the height of tire section. 6. A tire according to claim 5 characterized in that the stuffing develops radially outward to a height not less than 15% of the section height of the tire. 7. A tire according to claim 1 characterized in that the radially internal end of the lenticular profile is superimposed, beyond the stuffing, on a reinforcing textile edge disposed in an axially external position relative to the drawdown of the carcass fabrics and extended radially from the canceling core to a height of not more than 40% of the section height of the tire. 8. A tire according to claim 1 characterized in that the carcass fabrics are reinforced by rayon cords. '' 9. A tire according to claim 1 characterized in that the carcass fabrics are reinforced by cords of aromatic polyamide. - 10. The tire as claimed in claim 1, characterized in that the maximum thickness of the lenticular section is between 3% and 6% of the maximum width (cord) of the tire. fj ______