GB1589578A

GB1589578A - Tyre casing

Info

Publication number: GB1589578A
Application number: GB4335677A
Authority: GB
Original assignee: Euteco SpA
Current assignee: Euteco SpA
Priority date: 1976-10-19
Filing date: 1977-10-18
Publication date: 1981-05-13
Also published as: IT1073356B; FR2368377A1; FR2368377B1

Description

(54) TYRE CASING (71) We, EUTECO S.p.A., an Italian Joint Stock Company, of 11, Via Galiani, Milan, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in tyre casings, particularly with regard to their structure and the construction of their strengthening reinforcement.

As known, at present two main types of casings of different structure are manufactured, specially. those with a cross-ply carcass and those with a radial ply carcass.

Cross ply carcasses are essentially formed of two or more plies in which the direction of the cords is alternately crossed when passing tion or form small angles with these planes.

follows it. The fundamental characteristic of radial ply carcasses lies in the fact that they contain at least one ply in which the cords lie in planes passing through the axis of rotation of form small angles with these planes.

Casings with cross-ply carcasses are produced by a more simple and economical process and require a lower degree of accuracy than those with radial ply carcasses. Furthermore cross-ply casings do not have wall weaknesses and possess better absorption characteristics with respect to the shocks to which the tyre is continuously subjected when running on the road surface.

On the other hand, the radial carcass type tread offers a much higher resistance to wear. In fact, this tyre is provided, in the area beneath the tread, with a crown reinforcement, formed of plies of fabric the cords of which form small angles with the longitudinal direction, that is to say, with the median plane which intersects perpendicularly the axis of rotation. These plies, two or more in number, are usually formed of cords, which because of their characteristics and because of the fact that they are embedded in a mass of elastomer of high rigidity and hardness, form a ring which is resistant to tension and compression and this ring prevents longitudinal contractions of the tread which are a negative characteristic of cross-ply casings. The action of the incompressible ring placed under the tread is assisted by the fact that the ring rests on a radial ply carcass, that is, on an assembly of cords which do not offer resistance to the longitudinal movements.

For a better understanding of the phenomenon under discussion it is necessary to bear in mind that the ring of the crown reinforcement changes its circular arc shape into a segment corresponding to the cord of the arc, in that portion of the tread which is squashed against the ground. In radial ply tyres the difference in length between the arc and cord is recovered upstream and downstream of the position in which the tyre is flattened against the ground, because of the fact that the underlying radial ply carcass does not oppose these movements.

In other words, one avoids those longitudinal contractions which have been previously referred to. In every case, the absence, or at least the very great reduction of such contractions, endows the radial ply tyre with a much longer life.

In an attempt to combine in the same tyre the desirable characteristics of ease of production and lateral stability, characteristic of the cross-ply tyre, and those features relating to the greater duration of the tread, characteristic of radial ply tyres the socalled "bias belted" solution has been proposed, which provides for the adoption of a cross-ply carcass formed of an even number of continuous plies, all anchored to the bead cores, on which is superimposed an intermediate element composed of plies of fabric the cords of which are more rigid to tensile stress and compression than those of the carcass and are disposed at an angle equal to, or slightly different from, the angle assumed by the cords of the carcass in correspondence to the equatorial median plane.

Obviously, the efficiency of this intermediate element is much reduced for reasons previously illustrated and in every case one only partly achieves the object of reducing the wear on the tread.

Other proposed solutions provide for the adoption of a carcass formed of continuous plies anchored to the bead cores, and the disposition of the cords of which is at first almost longitudinal in the area beneath the tread, and then radial or almost radial, in a side wall area of reduced width and finally crossed in the area between the area of greater width of the tyre and the bead cores.

Other known solutions provide for the adoption of a carcass formed of a ply anchored to the bead cores and of two part plies which extend from the area of the bead cores up to a point under the lateral ends of the intermediate element, thus leaving free a restricted central area in which the cords of the continuous ply assume a sinuous path.

Neither of the latter described solutions have produced entirely satisfactory results as regards the lateral stability characteristics of the tyre or as regards the life of the tread.

According to the invention there is provided a tyre casing comprising a carcass, and an intermediate element between the carcass and the tread having a width substantially equal to that of the tread wherein the carcass comprises at least one continuous ply which extends between and is anchored to the bead cores and, in each side wall, at least one part ply extending from the bead to its end which is positioned between a first line connecting the points of maximum width across the tyre and a second line parallel thereto which is at a distance from the first line equal to two thirds of the distance of the first line from the centre point of the continuous ply or plies, the measurements being made in the radial direction, the continuous and part plies each comprising parallel cords and the cords of the part plies having a modulus of elasticity less than that of the cords of the continuous ply or plies; the carcass comprising three zones; a central zone wider than the tread which contains only cords of the continuous ply or plies which cords form an angle of 75" to 90" with the equatorial plane. and two lateral zones which comprise the bead cores and those parts of side walls containing cords of the continuous ply or plies and the part ply or plies, the cords of the continuous ply or plies being crossed relative to the cords of the part ply or plies and the cords of each ply making an angle of 4() to 750 with the circumferential direction between the respective bead and position of maximum width of the tyre; and the intermediate element comprises at least two plies, the cords of adjacent plies being crossed with respect to each other and forming angles of 16 to 40 with the equatorial plane.

This tyre casing possesses good optimum lateral stability, high running softness and has a length of life similar to that of radial ply tyres.

When the carcass comprises more than one continuous ply and more than one part ply in each side wall, all the continuous plies and all the part plies have cords oriented as defined.

The preferred embodiment comprises a single continuous ply and a single part ply for each side wall and an intermediate element comprising two plies and we shall refer to this ebodiment in the following description.

Furthermore, the part plies located in the two side walls may reach different heights in each wall and the cords of the intermediate element, placed between the carcass and the tread, can form different angles for the different plies, thus giving rise to an asymmetric configuration. Although the angles are always within the range of values of 16 to 40".

The ply formed of continuous cords extends between the two bead cores to which they are anchored, and is cut on the bias with an angle of the same order as or smaller than that of ordinary cross-ply carcasses, the latter angle typically varying within a range of 4() to 60".

The part plies may or may not be anchored to the bead core and in the second case the preferable configurations are those described in the United States Patent Specification No. 4162698 which provides for toward the bead the part plies to be folded back upon themselves with consequent formation of a fold which, according to the preferred embodiments, is positioned between that part of the continuous ply extending between the bead cores and a part of the continuous ply turned back around the bead core or at substantially the same level as the bead core and being outside a part of the continuous ply turned back around the bead core.

The angle at which the part plies are cut is suitably equal to that of the continuous ply, but of opposite inclination. The material of these part plies is selected from materials having a modulus of elasticity lower than that of the continuous ply. Thus for example if the continuous ply is of rayon. the half-plies are suitably made of aliphatic polyamide (for example "nylon"); furthermore, if the continuous ply is made of an aromatic polyamide (for example "Kevlar") the part plies can be made of "rayon" or "nylon". (Kevlar" is a registered Trade Mark.

The intermediate element located between the carcass and the tread is formed of two or more plies of cord fabric suitably of high rigidity to tension and/or compression, disposed at angles of 16 to 4() with respect to the equatorial plane of summetry of the tyre.

Furthermore, the course followed by the cords, and their angles in the moulded and vulcanized casing is as follows: - from the bead up to the position of maximum width of the tyre there are, for each side wall, two directions of the cords with those of the continuous ply being crossed relative to those of the part ply and forming angles of 4() to 75" and preferably of 45" to 600 with the circumferential direction; - from the position of maximum width to the extreme end of the part plies one also has two crossed directions with gradually increasing angles with respect to the circumferential direction: - from the terminal position of the part plies and up to the line symmetry of the tyre, only the cords of the carcass ply acquire rapidly, after a short connection zone, a path close to a radial one, the cords being disposed in such a manner as to form angles of not less than 75" with the equatorial plane of symmetry of the casing.

In practice, the direction of the cords is determined case by case, depending upon the initial angle of crossing of the continuous ply relatively to the part plies, the types of fabrics and the rubberization mixtures, the degree of the extension of the part plies and other factors.

In practice, when producing the casing one must establish an adequate distance between the bead cores on the drum in such a manner that the length of the cords of the ply on this drum is equal to that required for the final desired tyre shape.

The application of the intermediate element to the carcass takes place, preferably after the latter has been changed from a cylindrical to a toric shape, when the cords of the continuous ply assume a configuration very close to a radial one, that is to say, they form an angle of 75" to 9()0 with the equatorial plane of the casing where there are no plies crossed relatively to one another.

It has been found that the vibrations transmitted by the tread through the carcass to the beads and the rim, as well as the relative properties of lateral stability. are unexpectedly improved when the part plies remain adhered to the continuous ply over as large a part as possible of their length and when the part plies are formed of cords having a modulus of elasticity less than that of the cords forming the continuous ply.

This last fact probably has a determining influence on the properties of high resistance to wear of the tread.

In fact the greater extensibility of the cords forming the part plies in the zones of the carcass where one passes from the configuration having a ply with parallel cords to one with several plies having crossed cords, offers a better possibility for the carcass itself to follow the recoverv of the difference of length that must be effected by the crown reinforcement or the intermediate element to avoid the dragging effects of the tread against the ground.

Several practical constructions and arrangements are illustrated by way of example in the accompanying drawings, wherein: Figure 1 is a partial cross-section of one embodiment of a tyre casing according to the present invention; Figure 2 is a schematical perspective view of a tyre casing according to the invention after removal of the rubber from the side wall and from the thread; Figure 3 shows in a developed plan schematic view the arrangement of paths of the cords of the continuous ply and of the part plies with respect to the other elements of the tyre casing; Figure 4 is a partial schematic crosssection of another embodiment of a tyre casing according to the invention; Figure 5 is a partial schematic crosssection of a further embodiment of a tyre casing according to the invention Figure 6 is a plan view showing the process diagram of manufacturing the carcass of the tyre casing according to the Figure 4; Figures 7 and 8 are schematic crosssections showing two consecutive steps of manufacturing of the carcass of the tyre casing according to Figure 4.

Figure 1 shows in section part of a casing, symmetrical to the plane XX', in an embodiment according to the present invention.

In Figure 1 XX' indicates the symmetry plane of the tyre casing and CC' indicates the keying line (or line of support of the bases of the beads on the mounting rim), LL' indicates the line connecting the points of maximum width of the inflated tyre, radially spaced from the line CC' by a distance H. K indicates the distance to LL' from the highest point reached on the centreline by the ply of the carcass.

This carcass is formed by a continuous ply 1 which folds around the bead core 5 with its limb 1R and by two part plies 2 symmetrical in the two side walls, which in the case under discussion fold around the bead core with the limbs 2R.

The ends 2E of the part plies reach a distance Y, radially external with respect to LL', which is about half the distance K.

3 and 3' indicate the two plies of the intermediate element which have a width very close to that of the tread, indicated by B.

In the case under discussion the ply 1 is formed of rayon cords, the part plies 2 of "nylon" and in section the part plies 2 run parallel to and close to the ply 1.

Further in Figure 1, 4 indicates the rubberized side wall and 6 the tread.

Figure 2 shows the course followed by the cords of the carcass according to the invention and for reasons of convenience and greater clarity only some of the cords of the carcass are indicated.

In the Figure, 1 indicates a cord of the continuous ply which is folded around the bead core 5 to form the limb 1R; 2 indicates a cord of the part ply belonging to the side wall, in the embodiment in which this cord is folded around the bead 5 to form the limb 2R which ends at a level lower than the end of the limb IR.

All the elements illustrated correspond to those indicated in the tyre section of Figure 1. Thus LL' still shows the line joining the points of maximum width and TT' the ideal line which is reached by the ends 2B of the half-plies.

In Figure 2 it will be noted that a cord of the ply I leaves the bead core forming an angle a of 5() , intersects the line joining the points of greatest width at an angle of 45 , then starts a connection curve in the most peripheral area of the superimposition with the part ply (the cords of which follow a crossed and symmetrical course relatively to those of the continuous ply) until they assume a direction which forms an angle of 75" to 900 with the equatorial plane of symmetry.

In Figure 3 the path of a cord of the continuous ply 1, is shown by a full line. and those of the part-plies 2 by dashed lines. In connection with this Figure, it will be noted that the cord of the continuous ply, which departs from the bead core 5 slanted at an angle a of 50. intersects the median line at an angle greater than 75".

The central part of the Figure 3 shows, partly in section. the peripheral strips the cords of which form angles t) of opposite direction, generally equal relative to one another, having a value of 16 to 4() (210 in the case in question).

Furthermore in Figure 3 the various elements are indicated bv numerals corresponding to those used in Figure 2 and the part plies anchored to the bead core are indicated by dashed lines.

In the Figure 4. showing in section one half of a casing, symmetrical to the plane XX', similar to that of Figure 1, the tread and the side wall are not shown, and shown in section is the path of the carcass ply in a preferred embodiment of the present invention. More particularly l indicates the continuous ply and 2 the part ply folded over at its lower end in accordance with what has been described in United States Patent Specification No. 4162698. The part ply 2 is not anchored to the bead core but forms the fold Z by being folded back upon itself, this fold being contained in the space between the continuous ply 1 itself and its relative folded up limb portion 1R. This latter folding is effected in the anchorage of the ply 1 to the bead core 5.

The part ply ends in 2E at a level radially distant by a distance Y from the line LL', Y being half the value of K and this in the same manner as described with reference to Figure 1.

In Figure 5 the part ply 2 is not anchored to the bead core, it is folded over on itself as its lower end and the lower end is located externally to the folded up limb portion 1R of the continuous ply 1. The fold Z formed by the folded portion of the part ply 2 is at a level practically the same as that of the bead core.

Referring now to Figure 6 the process of producing the carcass of Figure 4 will now be described. In particular. the continuous ply of which a core I is shown in the Figure 6, has a width W and is placed on a cylindrical drum. This ply is cut at an angle 6 of 5() with respect to the centreline of the drum XX'.

At a distance P. symmetrical with respect to the centreline, the bead cores 5 are placed.

The total width W of the ply is equal to the sum of the segment P (emplacement of the bead cores) plus twice IR, this latter being the height of the folded-up portions of the ply l around the bead core 5.

Thereafter one places in position the part plies 2 already folded over, with the fold Z close to the bead core and the ends 1R of the continuous ply are folded over.

Figures 7 and 8 show in cross-section the steps which have been described in relaton to Figure 6. In these Figures RR' constitutes the axis of rotation of the drum F.

Referring once again to Figure 6, the determination of the emplacement P or distance of the bead cores is very important.

This value is determined experimentally and must be such that the length AA' of a cord of the continuous ply, corresponds to the length AA' of the cord which follows the course and forms the required angles on the casing as illustrated in Figure 3.

Obviously during the operation for changing the carcass from a cylindrical to a toric shape the bead cores must be moved through a predetermined angle. This angle, expressed in degrees may be given by the formula: M -N ao = R x 57.29 - M is the length of the arc of the bead core comprised between two radial planes which pass through the points A and A', the ends of a cord of the continuous ply placed on the cylindrical forming drum (see Figure 6); - N is the length. as above, between two radial planes which pass through the points AA', the ends of the cord of the continuous ply on the inflated casing; - R is the radius of the bead core.

WHAT WE CLAIM IS: 1. A tyre casing comprising a carcass, and an intermediate element between the carcass and the tread having a width substantially equal to that of the tread wherein the carcass comprises at least one continuous ply which extends between and is anchored to the bead cores and. in each side wall, at least one part ply extending from the bead to its end which is positioned between a first line connecting the points of maximum width across the tyre and a second line parallel thereto which is at a distance from the first line equal to two thirds of the distance of the first line from the centre point of the continuous ply or plies, the measurements being made in the radial direction. the continuous and part plies each comprising parallel cords and the cords of the part plies having a modulus of elasticity less than that of the cords of the continuous ply or plies: the carcass comprising three zones: a central zone wider than the tread which contains only cords of the continuous ply or plies which cords form an angle of 75" to 9 with the equatorial plane, and two lateral zones which comprise the bead cores and those parts of side walls containing cords of the continuous ply or plies and the part ply or plies. the cords of the continuous ply or plies being crossed relative to the cords of the part ply or plies and the cords of each ply making an angle of 4() to 75" with the circumferential direction between the respective bead and position of maximum width of the tyre; and the intermediate element comprises at least two plies. the cords of adjacent plies being crossed with respect to each other and forming angles of 16" to 4() with the equatorial plane.

2. A casing according to claim l wherein, in the lateral zones. the cords of each ply make an angle of 45" to 6() with the circumferential direction. between the respective bead and position of maximum width of the tyre.

3. A casing according to claim 1 or 2 which contains more than one continuous ply and more than one part ply in each side wall.

4. A casing according to any one of the preceding claims wherein the part plies are not anchored to the bead cores but toward the bead are folded back upon themselves to orm a fold, the fold being positioned between that part of the continuous ply extending between the bead cores and a part of the continuous ply turned back around the bead core.

5. A casing according to any one of claims 1 to 3 wherein the part plies are not anchored to the bead cores but toward the bead core fold back upon themselves to form a fold, the fold being positioned at substantially the same level as the bead core and being outside a part of the continuous ply turned back around the bead core.

6. A casing according to any one of the preceding claims wherein the end of the part ply in one side wall is at a different level from that in the other side wall.

7. A casing according to any one of the preceding claims wherein the intermediate element comprises two plies. the cords of which are crossed with respect to each other and form angles of from 16 to 40" with the equatorial plane but the angles being different for the different plies to give an asymmetrical configuration.

8. A tyre casing constructed and arranged substantially as herein described.

with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. through a predetermined angle. This angle, expressed in degrees may be given by the formula: M -N ao = R x 57.29 - M is the length of the arc of the bead core comprised between two radial planes which pass through the points A and A', the ends of a cord of the continuous ply placed on the cylindrical forming drum (see Figure 6); - N is the length. as above, between two radial planes which pass through the points AA', the ends of the cord of the continuous ply on the inflated casing; - R is the radius of the bead core. WHAT WE CLAIM IS:

1. A tyre casing comprising a carcass, and an intermediate element between the carcass and the tread having a width substantially equal to that of the tread wherein the carcass comprises at least one continuous ply which extends between and is anchored to the bead cores and. in each side wall, at least one part ply extending from the bead to its end which is positioned between a first line connecting the points of maximum width across the tyre and a second line parallel thereto which is at a distance from the first line equal to two thirds of the distance of the first line from the centre point of the continuous ply or plies, the measurements being made in the radial direction. the continuous and part plies each comprising parallel cords and the cords of the part plies having a modulus of elasticity less than that of the cords of the continuous ply or plies: the carcass comprising three zones: a central zone wider than the tread which contains only cords of the continuous ply or plies which cords form an angle of 75" to 9ü with the equatorial plane, and two lateral zones which comprise the bead cores and those parts of side walls containing cords of the continuous ply or plies and the part ply or plies. the cords of the continuous ply or plies being crossed relative to the cords of the part ply or plies and the cords of each ply making an angle of 4() to 75" with the circumferential direction between the respective bead and position of maximum width of the tyre; and the intermediate element comprises at least two plies. the cords of adjacent plies being crossed with respect to each other and forming angles of 16" to 4() with the equatorial plane.

8. A tyre casing constructed and arranged substantially as herein described.

with reference to and as illustrated in the accompanying drawings.