GB2096949A

GB2096949A - Pneumatic radial tire

Info

Publication number: GB2096949A
Application number: GB8209930A
Authority: GB
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1981-04-03
Filing date: 1982-04-02
Publication date: 1982-10-27
Also published as: GB2096949B; JPS57159806U

Abstract

A heavy duty pneumatic tire (1) comprises a carcass (4) composed of one or more rubberized plies each containing cords arranged in radial planes, an inner liner rubber (6), a belt (8), and a rubber strip (11) having a modulus at 20% elongation higher than that of the inner liner rubber, as measured in the circumferential direction of the tire, arranged between the carcass and the inner liner rubber at each side of the tire within a region extending from the mid position (M-M) of the sidewall to the adjacent end (8a) of the belt. The strips (11) may be reinforced with textile fibres, have a modulus at 20% elongation of at least 10 kg/cm<2>, and a thickness of 0.5-3 mm. <IMAGE>

Description

SPECIFICATION Pneumatic radial tire This invention relates to a pneumatic radial tire and in particular to a heavy duty pneumatic radial tire to be used under a high internal pressure.

Heavy duty pneumatic radial tires to be used under high internal pressure have been known to have such a structure that the rigidity of the tire is strengthened by a carcass consisting of one rubberized ply layer containing steel cords embedded in planes parallel to a radial plane containing the rotational axis of the tire and a belt superimposed about the crown portion of the carcass and having substantially the same width as the tread width, and the whole inner peipheral surface of the carcass being lined with an inner liner rubber having a thinner gauge.

On the other hand, as is well-known, the manufacture of radial tires comprises a laminating process consisting of a first stage of forming a green case by successively winding an inner liner rubber of uniform thickness and a cord layer for the carcass, the cords of which are substantially in planes parallel with the rotational axis of a drum, around the outer peripheral surface of a flat cylindrical drum having an outer diameter slightly larger than the diameter of a bead core, and a second stage of forming a green tire by moving the resulting cylindrical green case from the drum to another device to deform the carcass into a toroidal shape and successively superimposing a belt and a tread rubber layer about the crown portion of the toroidal carcass,and carrying out a vulcanization process of the resuling green tire.

In the above second stage, the expansion of the diameter is not caused at both ends on the rotational axis of the cylindrical green case because a bead core for engaging both end portions of the carcass cord layer is disposed at each axial end of the green case, but the degree of expansion of the diameter of the green case gradually increases from the position of both the bead cores toward the inside of the green case along the rotational axis. Therefore, both the cord interval in the carcass and the gauge of the inner liner are substantially the same in any portion of the green case immediately after formation at the first stage in the laminating process.However, as regards the green tire after the toroidal deformation at the second stage, the cord interval changes in proportion to a different expanded diameter amount at each portion of the carcass cord layer, and the gauge of the inner liner changes in inverse proportion to the expanded diameter amount, so that the distance between cords is increased from the position of the bead core to the crown centre of the carcass, while the gauge of the inner liner become correspondingly thinner. Since the green tire is vulcanized as its shape is substantially maintained, the interval difference between cords and the thinned inner liner remain as they are in the finished tire.

This relation may be examined by actually taking a tire of 10.00--20 size (cord diameter: 1.21 mm, gauge of inner liner: 2 mm). As a result, the cord interval at the position of the bead core is 1 mm, while the cord interval at the upper end portion of the sidewall is extended to 2 mm, and at that portion where the cord interval is doubled the inner liner rubber is absorbed between the extended cords and the gauge is reduced by half or more.

There is applied to heavy duty pneumatic tires such as truck and bus tires an internal pressure as high as not less than 7 kg/cm2, so that the internal pressure may reach 10 kg/cm2 or more by heat generation of the tire during running. In a tire of this type, a belt consisting of a plurality of rubberized ply layers each containing cords arranged at an angle substantially perpendicular to the cord angle of the carcass is disposed on the crown portion of the carcass, so that the interval difference between cords of the carcass hardly becomes a problem. However, the upper portion of the sidewall extending from both end portions of the belt has no cord layer other than the carcass, so that if this upper portion is exposed to the high internal pressure for a long time, a crack or its growth is produced between the cords, resulting in air leakage.This is because the upper portion of the sidewall is a portion strongly subjected to a large repetitive bending deformation produced during running and producing large heat generation, so that if the high internal pressure is applied to the upper portion under such conditions for a long time, the inner liner rubber is deteriorated and penetrates between the opened cords from the inside to produce a crack, which may result in air leakage or burst.

The present invention provides a pneumatic radial tire comprising a pair of bead cores, a pair of sidewalls, a tread extending between the sidewalls, a toroidal carcass composed of one or more rubberized ply layers each containing cords arranged in planes substantially parallel to a radial plane containing the rotational axis of the tire, an inner liner rubber at the inner peripheral surface of the carcass, and a belt superimposed about the crown portion of the carcass, wherein between the carcass and the inner liner rubber is arranged a rubber sheet extending within a region from substantially the middle position of the sidewall to the end portion of the belt, the rubber sheet having a modulus at 20% elongation which is higher than that of the inner liner rubber in the circumferential direction of the tire.

The invention will be further described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a schematical radial half section of one embodiment of a pneumatic radial tire according to the invention; and Figure 2 is a partial plan view of an embodiment of the rubber sheet to be used in the tire of the invention.

In Figure 1 is schematically shown an embodiment of a heavy duty pneumatic radial tire according to the invention in radial half section, wherein a tire 1 comprises a sidewall 2, a tread 3, a toroidal carcass 4 and a bead core 5. In this case, the tread and both sidewalls are totally reinforced with the toroidal carcass extending between both the bead cores. In Figure 1, the right half section of the tire is omitted, but it is a matter of course that both sides of the tire are symmetrical about the equatorial line E-E.

In this embodiment, the carcass 4 is constructed by turning a single rubberized ply layer containing steel cords arranged in planes parallel to the radial plane containing the rotational axis of the tire, that is in a direction perpendicular to the equatorial line E-E, around the bead core 5 and lining the inner peripheral surface of the carcass with an inner liner rubber 6.

Between the carcass 4 and the tread 3 in the crown portion 7 of the tire is arranged a belt 8 composed of a plurality of rubberized ply layers each containing cords inclined at an angle of 100--250 with respect to the equatorial plane E-E in a conventional manner, the cords of the belt ply layers being crossed with each other, up to the tread width. In the illustrated embodiment, the belt 8 is composed of three layers each containing steel cords. The tire has an outer reinforcing rubber 9.

In Figure 1, between the carcass 4 and the inner liner rubber 6 in an upper portion 10 of the sidewall extending from a line M-M dividing the sidewall into two in the radial direction of the tire to an end portion 8e of the belt 8 is arranged a rubber sheet 11, preferably reinforced with fibrous filaments 12 embedded therein.

Figure 2 shows in detail the rubber sheet 11 reinforced with the embedded fibrous filaments 12. In this case, the filaments 1 2 are preferably selected from nylon fibre, rayon fibre, polyester fibre, cotton filaments and wool filaments. The rubber sheet is formed by coating a layer of filaments 12 entangled with each other with rubber, or by cutting filaments into short lengths and kneading them into rubber with orientation or non-orientation of the filaments. The gauge of the rubber sheet 11 depends upon the applicable tire size, but is preferably 0.5-3 mm, more preferably 1-2 mm.The rubber sheet 11 is not necessarily arranged over the whole region extending from the line M-M to the end portion 8e of the belt 8, but can be arranged from the end portion 8e of the belt 8 towards the line M-M within the range of about 3/4, particularly 1/2, of the above region as shown in Figure 1. The modulus of the rubber sheet 11 must be higher than the modulus of the inner liner 6 as measured in the circumferential direction of the tire (or direction perpendicular to the plane of the drawing) in the arrangement shown in Figure 1 regardless of the reinforcement with the filaments, or otherwise the abovedescribed deterioration of the inner liner rubber cannot be avoided.Since the inner liner rubber usually has a modulus at 20% elongation of about 6 kg/cm2, the rubber sheet 11 preferably has a modulus at 20% elongation of 10 kg/cm2 or more.

In the case of manufacturing the tire according to the invention, the inner liner, rubber sheet and carcass ply can be successively placed on a cylindrical drum in order at the first stage, so that even if the green case is toroidally deformed at the second stage, the rubber sheet does not prevent the opening between cords of the carcass ply, that is toroidal deformation in the unvulcanized state.

After the vulcanization of the tire, the rubber sheet is strengthened and can effectively prevent the penetration of the inner liner rubber or tube between cords of the carcass induced by a high internal pressure when embedding the reinforcing filaments in the rubber sheet.

As described above, by means of the tire according to the invention, it is possible to simply and advantageously overcome weakening of carcass reinforcement in the region outside the edge of the belt, which occurs in the manufacture of heavy duty pneumatic radial tires.

Claims

1. A pneumatic radial tire comprising a pair of bead cores, a pair of sidewalls, a tread extending between the sidewalls, a toroidal carcass composed of one or more rubberized ply layers each containing cords arranged in planes substantially parallel to a radial plane containing the rotational axis of the tire, an inner liner rubber at the inner peripheral surface of the carcass, and a belt superimposed about the crown portion of the carcass, wherein between the carcass and the inner liner rubber is arranged a rubber sheet extending within a region from substantially the middle position of the sidewall to the end portion of the belt, the rubber sheet having a modulus at 20% elongation which is higher than that of the inner liner rubber in the circumferential direction of the tire.

2. A tire as claimed in Claim 1, wherein the rubber sheet has a modulus at 20% elongation of at least 10 kg/cm2.

3. A tire as claimed in Claim 1, wherein the rubber sheet is arranged within a range of about 3/4 of the region extending from the middle portion of the sidewall to the end portion of the belt.

4. A tire as claimed in any of Claims 1 to 3, wherein the rubber sheet is reinforced with fibrous filaments embedded therein.

5. A tire as claimed in Claim 4, wherein the fibrous filaments are selected from nylon fibre, rayon fibre, polyester fibre, cotton filaments and wool filaments.

6. A tire as claimed in any of Claims 1 to 5, wherein the rubber sheet has a gauge of 0.5 to 3 mm.

7. A tire as claimed in Claim 6, wherein the rubber sheet has a gauge of 1 to 2 mm.

8. A pneumatic radial tire according to Claim 1, substantially as herein described with reference to and as shown in, the accompanying drawings.

9. In a heavy duty pneumatic radial tire comprising a pair of bead cores, a pair of sidewalls, a tread extending between both sidewalls, a toroidal carcass composed of one or few rubberized ply layers each containing cords arranged substantially in parallel to a radial plane including the rotary axis of the tire, an inner liner rubber covering the inner peripheral surface of the carcass, and a belt superimposed about a crown portion of the carcass, the improvement wherein between the carcass extending from substantially the middle position of the sidewall to the end portion of the belt, and the inner liner rubber is arranged a rubber sheet having a modulus at 20% elongation in one direction, which is at least higher than that of the inner liner rubber by aligning the direction having the above modulus value in parallel to the equatorial line of the tire.