CA1171348A

CA1171348A - Tyres

Info

Publication number: CA1171348A
Application number: CA000410603A
Authority: CA
Inventors: Jean E.P. Moracchini
Original assignee: Dunlop Ltd
Current assignee: BTR Industries Ltd
Priority date: 1981-09-14
Filing date: 1982-09-01
Publication date: 1984-07-24
Also published as: ZA826390B; AU549706B2; GB2106457B; GB2106457A; JPS58156403A; FR2512748B1; IT1152531B; FR2512748A1; JPH0417805B2; IT8223126A0; BR8205279A; DE3233879A1; AU8835382A

Abstract

ABSTRACT
IMPROVEMENTS IN OR RELATING TO TYRES
A tyre casing comprising a carcass 30 an end portion of which is folded around a bead core 42 and a rubber apex strip 44. The apex strip 44 is disposed `
between the carcass 30, its folded end portion 40 and the bead core 42. A shaped element 46 made of rubber having a higher modulus than the rubber of the apex strip 44 is placed on the outside of and in direct contact with the fold 40 and at least part of the apex strip 44.

Description

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IMPROVEMENTS IN OR RELATING TO TYRES
This invention concerns improvements in or relating to tyres.
More specifically, the invention relates to tyre casings, in par-ticular tyre casings having a radial carcass and especially those reinforced with at least one metal ply.
The lower part of each side of the tyre casing, called the "bead", includes -the end part of the carcass which is folded towards the outside around a bead core. In general, a shaped element made of rubber in one or two parts, called the "apex" is disposed on the bead core, along the side, between the casing fabric and its fold. The apex extends along the side to a certain height, its thickness gradually tapering off Such tyre casings are used in particular for heavy goods vehicles.
In the known casings, one or~two steel cord reinforcing plies inclined in relation to the bead core, provide reinforcement and increase the rigidity in this area. In addition, the bead has a shaped element made of relatively soft rubber joined to the or each reinforcing ply ac-ting as a shock absorber and then a hard rubber cover layer which withstands -the friction between the bead and a wheel rim on which the tyre is mounted in use.
Figure 1 of the accompanying drawings shows in partial cross-section an example of such a known tyre casing, specifically showing its bead;
Figure 2 is a diagrammatic cross-section of part of a tyre casing in accordance with one embodiment of the invention; and Figure 3 is a cross-section similar to that of Figure 2, in accordance with a second embodiment of the invention.
This casing has a radial carcass 109 the top of which has folded breaker layers 12 on the side nearest the tread 14. At the wheel rim, marked with reference 15 on the drawing, the casing ends in a bead 16. More specifically, this bead is formed by the end portion of the carcass which, ~q~

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as indicated by re~erences 18 and 20, is folded around a bead core 22 and extends upwards towards the outside forming fold 100 An apex 24 of a relatively hard rubber is disposed between the carcass 10, the bead core 22 and -the fold 20, and tapers off at ~ ~ `
1~7~3-~8 its external radial part.
In accordance with -the known state of the art, reinforcing plies 26 (only one shown in Figure 1) are placed on the outside of fold 20 in order to strengthen and stiffen this a.rea~ More specifically, the. plies are usually reinforced by metal o.r -textile cords which are parallel with one ano-ther and inclined at a slight angle to the longitudina] direction, thus forming a rigid ne-twork with fold 20 of the carcass which they cross. ..
Figure 1 shows that the bead 16 also has a shaped element 28 made of a relatively soft rubber.at the edge of -the s-trip, and a hard rubber cover layer 30 which extends around the entire bead and withstands the ~ear caused by friction between the bead and the wheel rim in which the tyre is mounted in use.
Tyre casings of the type indicated above have the disadvantage of need:i.ng many precautions and a high level of precision during manu~acture. In fact, the reinforcing plies have to be precisely cut, tran~ported and ~it-ted, using expensive tooling. The int~rnal mo~ement which inevitably occurs during ~ulcanisation : can lead to displacement of these plies so that the tyre cas.ings produced a.re somet:imes completely unsui~able ~or use. For this reason, systematic in-depth monito~ing techniques have -to be used so tha-t these de~ecti~e -tyre casings~can be eliminated.
The elimination of reinforcing.plies from this type of tyre casing has already been proposed~ ~Thus, 30 French Patent No 1 343 402 described -the production of a tyre casing ha~ing a bead with an apex o~ very hard rubber, tapering off at~i.ts external radial:par-t into : the side, and able to extend towards the internal radial :~ part of the bead, thus forming the rim rubber. These tyres have a certain number o~ disadvantages. First of all, the assembly of the section on the fold of the carcass, before vulcanisation, causes problems and the union between the edge of -the fabric and the rubber is . . - ~

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often far from adequate. In addition, during utilisation it has been noticed that tyres with this type of bead do not have the qualities required.
Tyre casings are also known where the outside of the bead is protected with a hard rubber section. This section is placed on the outside of the fold but the bead has no apex. Such a bead is not sufficiently rigid.
According to one aspect of the present invention, a tyre casing comprises a carcass extending between a pair of beads wherein at least one bead includes a bead core and a rubber apex strip around which a respective one end portion of said carcass is folded and a rubber element positioned in direct contact with the folded end portion of said carcass and at least part of said apex strip, said element rubber having a modulus which is greater than that of said apex rubber, said rubber element having a radial dimension between 20% and 60% of the radial dimension of the tyre and extending radially outwards from its respective bead heel.
Preferably, the modulus of the element rubber is at least double that of the apex rubber. More specifically, it is advantageous for the stabilised modulus at 20% of the element rubber to be at least equal to 1.5 MPa, the Shore A hardness of the rubber being at least equal to 75, whilst the stabilised modulus at 20% of the apex rubber is only of the order of 0.65 MPa, its Shore A hardness being of the order of 65.
In one particular embodiment, the element is extended around part of the bead core and forms the cover layer which contacts the rim on which a tyre incorporating the tyre casing is mounted in use.
It is advantageous for the radial dimension of the element, measured in a plane perpendicular to the axis of rotation of the casing, to be ~etween 20 and 60% of the radial dimension of the casing, also measured in a plane perpendicular to the axis of-rotation. It is advantageous for the thickness of the element to be between 5 and 30%
of its radial dimension.
The design indicated above has several advantages.
First of all, the fatigue life of the shaped casings ~13~
is very high. Then, the manufacture of the tyre casings does not pose any particular problems because the in-ternal movements of the elements during vulcanisation are smaller -than those of reinforcing plies and in any event have fewer disadvantages. Thus the production accuracy can be increased. Furthermore when -the shaped element also forms the cover layer, -the number of elements incorporated in the tyre casing is reduced so -that the cost of the latter can be decreased.
Preferably the carcass is of radial construction comprising one or more plies each comprising a plurality ~
of parallel reinforcement members e.g. cords of flexible material such as nylon,Kevlar,lor no~-textile material such as steel wire. Preferably the rein~orcement members have a high modulus, for example a modulus greater than 2500 Kg/cm2.
The bead core may be of any known cons-t~uction e.g. cable, creel or close-packed wires and have any desired cross-section e.g. circular, hexagonal~
rectangular. Preferably the bead core is subsia~ltially inextensible.
The invention will now be described in more detail , b~ way of example only, with reference to Figures

2 and 3 of the accompanying drawings,(Figure 1 already having been described)"~ hiehl-Figure 2 is a diagrammatic cross-section of part of a tyre casing in accordance with one embodiment of the~invention; and Figure 3 is a cross-section similar to that of Figure 2, in accordance with a second embodiment of the invention.
Referring to Figure 2 -the casing shown comprises a radial carcass 30 comprising one or more reinforcement plies the end portion of which, indicated by reference numerals 39 and 40, is ~olded towards the outside around a bead comprising a bead core 42 and an apex strip 44 of rubber. The apex strip 44 is tapered tawards its

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radially outer extremity and pro~ec~s beyond the end of the carcass fold 40. An element 46 of rubber having a higher modulus than the apex rubber is positioned nex~
axially outwards of and in direc-t contact with the carcass fold 40 and part of the apex strip 44. Element 46 extends from the bead heel to a point below the radially outer extremity of -the apex s-trip 44, A
cover layer 50 of hard rubber is positioned next axially ou-twards of -the element 46 and extends below the bead base and around the bead toe. Layer 50 contacts the bead seat of a rim 35 on which the -tyre is mounted in use.
Assuming'the radial dimension of the casing, measured in a plane perpendicular to the axis of rotation, is H as shown in Figure 1, the element 46 has a radial dimension h which, advantageously, is between Z0 and 600/o of the total radial dimension H, depending on the particular dimensions and the aspect ratio of the casing. It is advantageous for -the thickness of the element 46 to be between 5 and 30% of its radial dimension h.
In the particular example shown, which is that of a tyre casing of standard dimensions 8.5-17.5, the element 46 is made of a rubber, or rather of a mixture of rubbers, where the stabilised modulus at 2Q% is greater than or equal to 1~5 MPa 3 i-ts Shore A hardness being at leas-t equal to 75, As a comparison, the apex 44 is made of a rubber or rather a mixture o~
rubbers where the s-tabilised modulus at 20% is of the ordér o~ 0.65 ~Pa, its Shore A hardness being of the order of 65.
I~e modulus indicated above is measured a-t just Z0% extension. In fac-t, this extension is ver~
representative of the conditions of use o~ the rubber in the apex and in the shaped element. This modulus is called "stabilised" because each value is measured several times in succession and it is noted ~that the measurements s-tabillse, generally after the fifth one.

l~7 3~8 It is this s-tabilised value which is indica-ted in the present specification.
I-t will be apparent from the foregoing descrip-tion th~-t -the element 46 made o~ hard rubber replaces -the reinforcing plies 26 and the element 28 of` soft rubber in -the casing shown in Figure 1.
Figure 3 shows ano-ther embodiment, intended for a tyre casing of similar dimension -to that shown in Figure 2. Those elements ln Figure 3 which are similar to those in the embodiment in Figure 2 have been given iden-tical re~erence numbers. Thus it will be seen tha~
the only difference between the embodiments in Figures 2 and 3 is that the element 46 of hard rubber and the cover layer 50 in the embodiment in Figure 2 are replaced by a single component 52 made of a rubber having properties corre~s.ponding to those of the rubber indicated for element 4~.
The advan-tage of the embodimen-t in Figure 3 over the one in Figure 2 is that it provides a reduction in the number of elements used to make up -the tyre casing. It therefore allows a certain reduction in the cost of the casing to be made~
In each of the e~bodiments describe~ with reference to Figures 2 and 3 the apex strip 44 and element 46 or 52 o~ high modulus, harder rubber provide a rigidity in the bead wh.ich varies progressively in a -transverse direction enabling the bead to fully play its part as a connection between the rim and a tyre incorpora-ting the cas.ing.
Tests performed on tyre casings in accordance with the invention, compared with tyre casi.ngs of the known type, show the significant advantages of the inventionf First of all, a stud~ of the distrlbution o~
deformation s-tresses in loaded tyre casings shows that the de~ormation stresses are better distributed in casings made in accordance with the in~entionO This better distribu-tion of the deformation stresses allows ~17~3~
an improvement in -the fa-tigue li~e.
More specifically~ the fatigue life of the tyre casings in accordance with the invention is determined during rolling trials on a rolling machine, with -the application o~ very high loads, the maximum loads reaching 200% of the nominal load standardised by the ETRT0 organisa-tion.
More specifically, tyre cas.ings in accordance wlth -the invention, and traditional casings~ of the standard 11 R 22.5 SC type, have been subjected to rolling tests on overload~ The casings of the traditional type all split in the bead region before 25~ hours o~ rolling. Tyres in accordance with the invention withs-tood -this test for a longer period, one Of them reading 518 hours of rolllng under the same conditions.
Moreover, the tests have been carried out on the -tyre casings in accordan oe with the invention under real conditions of use. These tyres o~ standard dimensions, 8.5 R 17,5 SC, were fitted to a vehicle with a total load equal -to 6250 kg. I-t was confirmed that the beads of the casings were intact af-ter an initi.al utilisation until the tread was worn, and also after a second period of utilisation un-til complete wear permitted by retreading the crown.
Therefore, the previous tests show that the inv.e~tion provides tyre casings having a bett~r fatigue life than -traditiona]. tyre casings, and yet allows these casings to be produced at reduced cost, thanks to the new structure used.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A tyre casing comprising a carcass extending between a pair of beads wherein at least one bead includes a bead core and a rubber apex strip around which a respective one end portion of said carcass is folded and a rubber element positioned in direct contact with the folded end portion of said carcass and at least part of said apex strip, said element rubber having a modulus which is greater than that of said apex rubber, said rubber element having a radial dimension between 20% and 60% of the radial dimension of the tyre and extending radially outwards from its respective bead heel.

2. A casing according to claim 1 wherein said element rubber has a modulus at least double that of said apex rubber.

3. A casing according to claim 2 wherein said element rubber has a stabilised modulus at 20% extension at least equal to 1.5 MPa and said apex rubber has a stabilised modulus at 20% extension of the order of 0.65 MPa.

4. A casing according to claim 1 wherein the Shore A hardness of said element rubber exceeds that of said apex rubber.

5. A casing according to claim 4 wherein the Shore A hardness of said element rubber is at least equal to 75° and that of said apex rubber is of the order of 65°.

6. A casing according to claim 1 wherein said element has a radial dimension of between 20 and 60%
the radial dimension of said casing, both measurements being taken in a plane normal to the axis of rotation of said casing.

7. A casing according to claim 6 wherein said element extends radially outwards from the bead heel and said bead further includes a rubber cover layer on at least that part of the bead which contacts a wheel rim on which a tyre incorporating the casing is mounted in use.

8. A casing according to claim 6 wherein said element extends around at least that part of the bead which contacts a wheel rim on which a tyre incorporating the casing is mounted in use.

9. A casing according to claim 6 wherein the thickness of said element is between 5 and 30% of its radial dimension.

10, A casing according to claim 1 wherein said carcass is of radial construction.

11. A casing according to claim 1 wherein said carcass comprises one or more plies.

12. A casing according to claim 11 wherein the or each ply comprises a plurality of parallel reinforcement members.

13. A casing according to claim 12 wherein said reinforcement members comprise metal cord.

14, A casing according to claim 12 wherein said reinforcement members have a high modulus.

15. A casing according to claim 1 wherein said bead core is substantially inextensible.

16. A tyre bead comprising a bead core and a rubber apex strip around which one end of a tyre carcass is folded and a rubber element positioned in direct contact with the folded end portion of said tyre carcass and at least part of the apex strip, said element rubber having a modulus which is greater than that of said apex rubber.