AU671653B2

AU671653B2 - Anchoring carcass cords in the bead of a pneumatic tyre

Info

Publication number: AU671653B2
Application number: AU44412/93A
Authority: AU
Inventors: Yves Herbelleau; Jean-Jacques Pradelle
Original assignee: Sedepro SA
Current assignee: Manufacture Francaise des Pneumatiques Michelin SAS
Priority date: 1992-08-05
Filing date: 1993-08-04
Publication date: 1996-09-05
Anticipated expiration: 2013-08-04
Also published as: KR100286626B1; PL299919A1; EP0582196B1; RU2111867C1; EP0582196A1; DE69301789D1; DE69301789T2; CN1040736C; CA2101970A1; CN1084461A; AU4441293A; BR9303244A; FR2694521A1; JP3202428B2; CZ284222B6; CZ158793A3; TW279832B; JPH06171306A; CA2101970C; PL172137B1

Abstract

The carcass of the tyre is made up from a single wire 3 passing to and fro from one bead to the other. The anchoring of the carcass in the bead 2 is produced by arranging, on each side (in the axial direction) of the carcass wires 3, at least one pile of wires 61, 62 pointing circumferentially, with interposition of a layer 5 of a mixture of rubber having a Shore hardness A of greater than 70. <IMAGE>

Description

F-/UU/U1 1 2815V91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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cc e Application Number: Lodged: Invention Title: ANCHORING CARCASS CORDS IN THE BEAD OF A PNEUMATIC TYRE The following statement is a full description of this invention, including the best method oi performing it known to :-US C 00:367 5 040893 -1- The present invention relates to tires. More particularly, it concerns the arrangement of the reinforcement cords in the sidewalls and the beads; it also concerns the anchoring of the carcass cords in the bead.

The carcass reinforcement of tires consists at present of one or more plies, generally radial, which are turned up around one or more bead wires arranged in the beads. The beads constitute the means which make it possible to fasten the tire on the rim. The rigidity of the bead which is constituted in this manner is very great.

It is desirable to assure a progressive evolution of the rigidity of the bead upon moving radially upward in the direction of the sidewall. In the present technique, it is rather difficult to assure such a progressive evolution of rigidity between the sidewall, which must have substantial flexibility, and the bead, which, on the other hand, must have substantial rigidity. In fact, the reinforcements which r o are arranged in this part of the tire inevitably always present a discontinuity: At the radially upper end of the carcass turn-up one passes without transition into a region which does not have this carcass turn-up, which region is therefore inevitably less rigid. By way of reminder, o "radially upward" or "radially upper" means towards the largest radii, and conversely.

rrr*@ ou The state of the art already knows other principles of design of a radial carcass which make it possible to avoid the turn-ups around a bead wire. By way of example, mention may be made of U.S. Patent 3,815,652 in which it is proposed that the carcass reinforcement be formed of a single cord extending on a special trajectory from one bead of the tire to the other so that the same cord partially and progressively forms a reinforcement which replaces the conventional bead wire. In the known structure, the carcass f 2cord forms within the sidewalls the lower part of said being located in the bead, concentrically to the tire.

The lower part of the U's extends over a certain length of arc in the bead. U's are provided as many times as necessary, shifting them from each other until they cover the entire sidewall of the tire. This results in a structuie in which, within the beads, the reinforcement cord, viewed radially, forms steps; the lower part of a U is not aligned precisely along a circle included within a plane perpendicular to the axis of the tire. This reinforcement structure is prejudicial to a precise positioning of the cords and it is not of such a nature as to confer very good uniformity upon the tire. Now, at the present time, the quality level demanded of tires is increasingly higher.

The object of the present invention is to propose a new manner of laying the carcass reinforcement cord in order to

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be able to assure as progressive an evolution as possible of oae the flexural rigidi"3y of the sidewall of the tire in the r direction towards the bead.

Another object of the invention is to propose a tire reinforcement structure which is as homogeneous as possible S" in the circumferential direction.

Finally, still another object of the invention is to propose a reinforcement structure for tires which easily lends itself to mechanized manufacture.

o ~The radial tire of the present invention, wherein the radial carcass is anchored on each side in a bead the base of which is intended to be mounted on a rim seat, each bead is extended by a sidewall and the sidewalls join the tread, the carcass is formed from a carcass cord which extends radially back and forth and the bead is reinforced by circumferentially oriented cords, is characterized by the fact that the anchoring of the carcass in the bead is assured in the following manner: 2J; 3 the backward and forward paths of the carcass cord are arranged adjacent to each other, without overlap, and are aligned circumferentially, with a loop connecting in each case a forward path to a return path; the forward and return paths of radial cords form one or more circumferential alignments in the bead; each circumferential alignment of radial cords is bordered, on each side in axial direction, by at least one pile of circumferentially oriented cords, with the interpositioning of a layer of a rubber mix having a Shore A hardness of more than In the present specification, the expression "cord" designates very generally both monofilaments and multifilaments, or assemblages such as cables or twists or else any other type of equivalent assemblage, and this whatever the material and the treatment of these cords, for instance, surface treatment or coating or pre-sizing to favor the adherence on the rubber. The carcass reinforcement is ol ~arranged in sandwich fashion between two piles of circumferentially oriented cords with the interposition of rubber. A carcass is said to be radial when its cords are arranged at 900 but also, in accordance with usage, at an angle close to 900.

It is known that in the present technique, the carcass ply or plies are turned up around a bead wire. The bead wire therefore serves for the anchoring of the carcass, that is to say it takes up the tension which is developed in the carcass cords under the effect of the inflation pressure. The arrangement claimed here shows this carcass anchoring function.

It is also known in the present state of the i t for the bead wire itself also to assure a function of pressing the bead on its rim. The arrangement claimed here is also capable ofi i- .1 4 assuring sufficient pressing.

All the details of development are given in the following description, read with reference to the drawing, in which: Fig. 1 is a radial section showing essentially a sidewall and a bead of a tire in accordance with the invention; Fig. 2 is a perspective view, showing only the arrangement of the reinforcement cords; Fig. 3 is a radial section showing a second embodiment i of the invention; Fig. 4 is a perspective view showing a part of the reinforcement cords arranged in a manner which S. corresponds to the second embodiment; Fig. 5 shows a third embodiment of the invention in radial section showing the sidewall and the bead of the tire.

Figs. 1 and 2 illustrate the simplest embodiment. There are shown therein the different well-known parts of a tire which are more specifically involved in the present invention, namely the sidewall 1 and the bead 2. The carcass reinforcement is formed by portions of cord 3 which are here oriented radially in the sidewalls i. The cord 3 forms juxtaposed loops 30 located within the bead 2. The loops r* are adjacent each other and do not overlap.

By arranging the cord in loops, one avoids all cut edges, which constitute discontinuities. In actual fact, the reinforcement cord is generally a cable; the cable ends show, at the place of the cut, flarings in which all the monofilaments are apart from each other. This constitutes incipient points of rupture within the tire. When the cords consist of textile, they are sized in order to assure very iij s I 'i -l I;.

good adherence to the rubber. Unfortunately, there is no presizing on each cable end after it has been cut, with the result that there also the rubber does not adhere at the place of the cut, and therefore the risk of incipient ruptures within the bead. With the arrangement described here, this type of drawback need not be feared.

By the presence of loops between forward and return paths, it is seen that the carcass is of the "single cord" type. Of course, the carcass might be produced otherwise than continuously from a single cord. In accordance with the present invention, however, it is advisable to use only a i small number of cords and to arrange the starting and ending points of the cord below the tread rather than in the beads.

In order to assure a perfect anchoring of a carcass, a stratified composite bead is produced. Within the bead 2, a pile of circumferentirlly oriented cords (piles 61 and 62) eeo are arranged on both sides of the forward and return paths of S the carcass cord 3, with the interposition of a layer 5 of a rubber mix of a Shore A hardness of more than 70. In each pile 61, 62, the cords are substantially concentric and superposed. One can, for instance, wind several turns of brass-coated metal wire.

It is not necessary to add a rubber mix which is specific for assuring the impregnation of the carcass cord 3 or the cord windings forming the piles 61 or 62, but it is necessary to avoid that the circumferentially oriented cords are in direct ou contact with the radially oriented cords. The same type of mix assures the functions of calendering and connection between the portions of cord of one and the same pile and between the different piles of cord, by impregnation upon the molding.

Experiments have shown very interesting results as to life by using for the interposed rubber layers 5 a mix containing an SBR synthetic elastomer used by itself or blended with I-

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-6polybutadiene, the said SBR having a glass transition temperature (Tg) of between -700C and -30 0 C and the said polybutadiene having a Tg of -40 0 C and -10 0 C, the said synthetic elastomer or elastomers being used in a total proportion of at least 40% of the tLtal weight of elastomer, the balance being formed of natural rubber. The Tg's in question are measured by differential thermal analysis. An SBR solution is preferably used. For instance, a mix is used containing 50% SBR solution having a Tg of -48 0 C, 50% natural rubber with addition of reinforcing fillers and resin in order to obtain the Shore A hardness desired. The layer can be obtained in the vulcanized tire since the carcass cord 3 and/or the cords of the windings 61, 62 have been laid sufficiently coated with rubber so that, after molding, the layers 5 which have just been described here appear.

i e' Instead of rubber base mixes such as indicated above, one l could also use thermoplastic resins (aliphatic polyamide, It's 0t. polyphenylene oxide) or thermosetting resins (phenol formaldehyde resins) which make it possible to obtain suitable rigidity and adherence.

In order to obtain good adherence of a layer 5 of rubber to both the brass-plated metal wires of the piles 61, 62 and the textile cords 3 of the carcass, and in order to assure a long life of this adherence at high temperature, the said layer of rubber contains a large amount of sulfur and adhesion-promoting additives are employed (for instance, metal salts of cobalt or nickel) in well-adjusted proportions. For example, an amount of sulfur of between and 8 of the total weight of elastomer and an amount of cobalt of 0.2 of the total weight of elastomer are used.

In order to assure an excellent taking up of the tension appearing in the carcass cords under the effect of the inflation pressure, it is desirable for said loops to be arranged radially at a level below the lowest part of the 1 A r 1 c 7 adjacent circumferentially oriented piles of cords.

The carcass cord 3 preferably forms forward and return paths from one bead 2 of the tire to the other passing below the tread; the cord is therefore continuous from one bead to the other. The different reinforcement means of the structure of the tire below the tread do not form part of the present invention. It is sufficient to point out that they may be formed, for instance, by any suitable method of reinforcement such as, for instance, cords arranged in such a manner as to assure a triangulated belting. Furthermore, one can, to be sure, arrange within the bead a very stiff rubber mix of the type used for the filler on a bead wire in conventional tires. This filler rubber is arranged on one side or on both sides of the carcass reinforcement.

When the tire mounted on the rim for which it is designed is o orr subjected to alternating deformations, the region of contact with the rim, that is to say the part of the bead located below the rim flange, suffers practically no deformation. The upper part of the sidewall, that is to say, as a general rule, the portion between the equator and the shoulder of the tire, flexes rather strongly in order to impart the necessary flexibility to the tire. The equator is the widest part of the sidewall, corresponding to the maximum size of the tire mounted on its rim.

In order to assure as progressive as possible a transition between the region of contact with the rim and the equator, abovii the region of contact with the rim and below the equator, the rubber components located on both sides of the carcass satisfy the following equation: Z E e (outside) 3 E E e (inside) in which E is the modulus in the rda direction, e the in whichE is the modulus in the rdia± directin, e~ the 8thickness of each component of rubber on the outside and the inside 71 of the carcass cord respectively. When there are several carcass alignments in said portion of the tire, only the components on the outside of the outermost cord and on the inside of the innermost cord respectively will be considered.

When the modulus of all the components employed is comparable, this means that it is advisable to have the carcass pass as much as possible on the inner side of the sidewall. One can also use softer rubbers (that is to say, of lower modulus) on the inner side of the sidewall. This assures a good compromise between the life of the tire and the comfort which it produces.

SIn Figs. 3, 4 and 5 it is seen that in each sidewall 1 the carcass cord 3 forms a single circumferential alignment of juxtaposed radial portions of cord and that, starting from a sidewall in the direction of the bead 2, the carcass is divided into two circumferential alignments of radial cords rlt 31, 32 which progressively move axially away from each other.

Each circumferential alignment of radial cords 3 is bordered, as explained above, on each side by a pile of circumferentially oriented cords with the interpositioning of a layer of rubber having the constitution described above.

~The alignment 31 is bordered by the piles 61 and 62 and the alignment 32 is bordered by the piles 62 and 63. All the .r ~piles of circumferentially oriented cords are produced here by spiral winding. It is advantageous that the median pile 62 rises radially further upward than the side piles 61 and 63.

This leads to a staggered arrangement which is clearly evident in the perspective view of Fig. 4, where it is clearly seen that the different alignments are separated by a stack of circumferentially oriented cords.

There could, of course, be more than two circumferential i L -9alignments of radial cords extending progressively axially away from each other. In such case, each alignment is formed from a single carcass cord which forms radial forward and return passes. The cord portions of the different alignments are disposed in such a manner that, in the sidewalls, two adjacent carcass cord portions come from different alignments in the bead 2. Stated differently, there is an interlacing of the cords of each alignment in the sidewall but not in the bead, so that, there also, the loops 30 of each alignment do not overlap.

This second variant is of very particular interest since, at the level of the sidewall 1 of the tire, there is a single circumferential alignment of radial cord portions (in a single layer). This is of such a nature as to permit very great flexibility of the sidewalls; the flexural rigidity of i the sidewall to the crushing of a tire provided with such a S reinforcement structure remains small, smaller than when there are two carcass plies, as in the tires currently employed.

As the bead 2 is approached, the carcass cords 3 distribute themselves in two circumferential alignments which move apart progressively from each other, and one can, of course, adjust the height at which this separation into several alignments is organized by interposing rubber over a selected height.

In this way, the flexural rigidity is increased very progressively. Furthermore, the number of radial portions of cord in an alignment within the bead is divided by two as compared with the number of radial portions in the alignment itself of the sidewall, which is very advisable since, as the radius is smallest at the height of the bead, there is less i room to place the aligned cords than in the sidewall. This distribution of the cords favors the perfect positioning of them with good impregnation with rubber.

Fig. 5 shows a third embodiment of the invention. Within the

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bead 2, the circumferential cord windings 64 and 65 have been added. Only thin layers of rubber remain between the cords, that is to say layers which are not thicker than the diameter of the cords of the windings or the alignments.

In the same figure it is seen that there are circumferentially oriented portions of cord 66 rising radially upward in the portion of the sidewall located below the equator. This makes it possible to impart shapes different from the natural equilibrium shapes of an inflated radial carcass. One can also excellently control the shape of the tire when it is inflated on the wheel. One can, of i course, use cords of different kind in the sidewalls and in the bead, or on the inside of them.

The density of the circumferentially oriented cords is I (4t S preferably less in the sidewall 1 than in the beads 2. it is desirable that the variation in density be progressive, so as to assure as progressive as possible a transition between the bead and the sidewall of the tire.

It is seen that the radial carcass reinforcement structure proposed permits a progressive development of the rigidities t

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between -he sidewall and the bead. This structure offers the Sdesigner of the tire very great latitude for adjustment of this rigidity and its evolution by simply acting on the a ~density of the circumferentially oriented cords and possibly on the number of circumferential alignments of radial cords :41 in the beads, and on the nature of the cords.

The structure thus proposed does not present any discontinuity of reinforcement, which is very favorable for the life of the tire and also leads unexpectedly to greater comfort of the tire.

In order to position the reinforcement cords as precisely as possible, it is very advantageous to build the tire on a rigid core which establishes the shape of its inner cavity.

-rq V r rr4. ii -11- Onto this core there are applied, in the order required by the final architecture, all the components of the tire, which are put directly in their final place, without undergoing i shaping at any time during the building of the tire. In this case, the tire can be molded and vulcanized in the manner explained in the U.S. Patent 4,895,692.

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Claims

12- 12 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A radial tire comprising a carcass anchored on each side of the tire in a bead the base (20) of which is intended to be mounted on a rim seat, each bead being extended by a sidewall the sidewalls joining the tread, the carcass being formed from a carcass cord forming forward and return paths, the bead being reinforced by circumferentially oriented cords (61, 62), characterized by the fact that the anchoring of the carcass in the bead is assured in the following manner: the forward and return paths of the carcass cord are arranged adjacent to each other and are aligned circumferentially, with a loop (30) connecting in each case a forward path to a return path; the r l forward and return paths of cord form one or more circumferential alignments (31, 32) in the bead each circumferential alignment of radia cords is bordered, on each side in axial direction, by at least one S c pile of circumferentially oriented cords, with the St interpositioning of a layer of a rubber mix having a Shore A hardness of more than 2. A tire according to Claim 1, characterized by the fact that the carcass cord forms forward and return paths from one bead to the other pacsing balow- -h i. e 3. A tire according to either of Claims 1 and 2, characterized by the fact that the carcass cord is oriented radially within the sidewalls. 4. A tire according to any of Claims 1 to 3, characterized by the fact that the said loops are arranged radially at a level lower than the lowest part of the adjacent piles of cords. A tire according to any of Claims 1 to 4, characterized by i 0 Ii. Up Shore A hardness of more than 13 the fact that, within the portion of the sidewall located just above the region of contact with the rim and below the equator, the rubber eemp~~nnte located on both sides of the carcass satisfy the equation SiEei (outside) Z E e (inside) i lI in which E is the modulus in radial direction, e the thickness of each component in rubber on the inside and the outside respectively of the carcass cord. 6. A tire according to any of Claims 1 to 5, characterized by the fact that the layer of interposed rubber mix is a mix containing an SBR synthetic elastomer the Tg of which is between -70 0 C and -30 0 C, in a proportion of at least 40% of the total weight of elastomer. 7. A tire according to Claim 6, characterized by the fact that the SBR is used blended with PB the Tg of which is between -40 0 C and -10 0 C, the total proportion of synthetic Cf elastomer being equal to at least 40% of the total weight of elastomer. 8. A tire according to Claim 6 or 7, characterized by the fact that the SBR used is of solution type. 9. A tire according to any of Claims 6 to 8, characterized by the fact that the amount of sulfur in the mix of said layer is between 5 and 8 of the total weight of elastomer. A tire according to any of Claims 1 to 5, characterized by the fact that the layer is formed essentially of a resin selected from the group consisting cf aliphatic polyamide, polyphenylene oxide and phenol formaldehyde resins. 11. A tire according to any of Claims 1 to 10, characterized JI. '4'4- 1 I a

14- by the fact that the bead comprises circumferentially oriented cords arranged in several piles over its entire width. 12. A tire according to any of Claims 1 to 11, characterized by the fact that, in each sidewall, the carcass cord form a single circumferential alignment of radial forward and return paths and, passing from a sidewall in the direction of the base of a bead, the said alignment is divided into at least two alignments (31, 32) moving progressively axially away from each other. 13. A tire according to Claim 12, characterized by the fact that each alignment arranged in the bead is formed from a single carcass cord forming forward and return paths, and by the fact that, at the level of the sidewalls two adjacent portions of carcass cord come from different alignments of the bead. 14. A tire according to any of claims 1 to 13, characterized by the fact that it comprises a pile of circumferentially oriented cords in the portion of the sidewall located below the equator. that the density of circumferentially oriented cords is less in the sidewall than in the bead DATED this 3rd day of August 1993. SEDEPRO WATERMARK PATENT TRADEMARK ATTORNEYS "THE ATRIUM" 290 BURWOOD ROAD HAWTHORN. VIC. 3122. i L i ABSTRACT OF THE DISCLOSURE The carcass of the tire is formed from a single cord 3 which extends backward and forward from one bead to the other. The anchoring of the carcass in the bead 2 is effected by at I least one pile of circumferentially directed cords 61, 62 on each side (in axial direction) of the carcass cords 3, with the interposition of a layer 5 of a rubber mix having a Shore A hardness of more than it 4 I e i I •a t 4 s *i l IU 'I ^1 1 H 1 1