GB2163709A

GB2163709A - Pneumatic radial tyre breaker belts

Info

Publication number: GB2163709A
Application number: GB08516038A
Authority: GB
Inventors: Tuneo Morikawa; Kazuyki Kabe; Shuichi Tsukada
Original assignee: Yokohama Rubber Co Ltd
Current assignee: Yokohama Rubber Co Ltd
Priority date: 1984-06-29
Filing date: 1985-06-25
Publication date: 1986-03-05
Also published as: JPS6112409A; GB8516038D0; DE3522767C2; DE3522767A1; KR930000317B1; GB2163709B; KR860000165A; JPH0443804B2

Abstract

In a pneumatic radial tyre, a breaker belt has a layer of aromatic polyamide fiber cords, which is folded at both edge portions and in which the cords have an angle theta of final twist within a range of 31.3 to 39.3 DEG measured with respect to the axes of the cords. <IMAGE>

Description

SPECIFICATION Pneumatic radial tyre for passenger vehicles This invention relates to a pneumatic radial tyre for passenger vehicles, and more particularly, to a pneumatic radial tyre for passenger vehicles, having a belt layer structure consisting of a plurality of laminated layers which include a layer folded back at its both end portions under a tread and composed of aromatic polyamide fiber cords, which are improved so as to prevent separation from occurring at the folded portions of this layer and thereby improve the durability of the tyre to a great extent.

In general, pneumatic radial tyres for passenger vehicles have on the portion of their carcass layer which is under their tread, a belt layer structure consisting of a plurality of laminated layers of reinforcement cords composed of steel cords. Owing to such a belt structure of steel cords provided on the carcass layer, the durability, the high-speed stability and the steering stability of pneumatic radial tyres can be improved as compared with those of bias tyres.

However, a radial tyre having a belt layer structure consisting of a plurality of laminated layers of reinforcement cords composed of steel cords as mentioned above does not provide a comfortable ride.

To solve this problem, a pneumatic radial tyre for passenger vehicles, using as one of a plurality of laminated layers of a belt layer structure provided on the portion of a carcass layer which is under the tread a layer of aromatic polyamide fiber cords, which layer having at it both ends folded portions extending under the tread, has recently been studied, and a radial tyre meeting the purpose has been proposed.

When a layer of aromatic polyamide fiber cords is used as one of the layers in the belt layer structure as mentioned above, the degree of comfort during the ride is improved as compared with the case where a layer of reinforcement cords consisting of steel cords is used as one of a plurality of laminated layers in a belt layer structure in a pneumatic radial tyre for passenger vehicles. Aromatic polyamide fiber cords, however, do not readily adhere to a coat rubber due to the molecular structure thereof. Hence, separation occurs, that is, the cords constituting the layer of aromatic polyamide fiber cords and the coat rubber are separated from each other, especially, at the folded portions of the belt layer structure mentioned above. This shortens the useful life of the tyre.

To solve these problems, the present inventors made experiments and discussed the results thereof to discover the following. In a layer of aromatic polyamide fiber cords, which has folded portions as described above and which is used as one of a plurality of laminated layers in a belt layer structure, there is a close correlation between the angle of the final twist of these cords and the adhesive characteristic of the coat rubber.In more detail, if the cords for the layer of aromatic polyamide fiber cords are made having an angle of the final twist within a range of 31.3 to 39.3 measured of the acute angle with respect to the axes of the cords, by this it is feasible to greatly improve the strength of adhesion between these cords and the coat rubber and effectively prevent from occurring the abovementioned separation in the folded-over portions of the aromatic polyamide cord layer, whereby the durability of the tyre can be greatly enhanced.

The present invention has been developed on the basis of the above-mentioned discoveries, and it is an object of the present invention to provide a pneumatic radial tyre for passenger vehicles, which is capable of preventing separation from occurring at the folded portions of a layer of aromatic polyamide fiber cords, which is used as a member of a belt layer structure, and thereby greatly improving the durability of the tyre.

To this end, the present invention provides a pneumatic radial tyre for passenger vehicles, having left and right bead portions, left and right side wall portions continuous with the bead portions, a tread positioned between the side wall portions, a carcass layer provided between the left and right bead portions, and a belt layer structure consisting of a plurality of layers and laid on the portion of the carcass layer which is under the tread, characterized in that the belt layer structure includes a layer of aromatic polyamide fiber cords, which is folded at both end portions thereof under the tread and in which the cords have an angle of the final twist within a range of 31.3 to 39.3" measured of the acute angle with respect to the axes of the cords.

The above and other objects as well as advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

Fig. 1 is a partially cutaway view, in perspective of an example of the pneumatic radial tyre for passenger vehicles according to the present invention; Fig. 2 is a graph showing the relation between the angle of the final twist of the cord in a layer, which has folded portions, of aromatic polyamide fiber cords and the durability of the tyre; Fig. 3 is an enlarged view of a part of the layer of aromatic polyamide fiber cords; and Figs. 4(a), 4(b) and 4(c) show the condition of the shearing deformation of a cord in the layer, which has folded portions, of aromatic polyamide fiber cords occurring when a force F is exerted on the cord in the direction which is at right angles to the axis of the cord.

Referring to Fig. 1, the reference letter E denotes a pneumatic tyre embodying the present invention, which consists of left and right bead portions 1 and 1, left and right side wall portions 2 and 2, a tread 3 positioned between the side wall portions 2 and 2, a carcass layer 4 provided between the bead portions 1 and 1 and having an angle of cord with respect to the circumferential direction of the tyre of substantially 90 , and a belt layer structure V, which is laid on the portion of the carcass layer 4 which is under the tread 3, and which is composed of a plurality of layers crossing one another with an angle of cords therein with respect to the circumferential direction of the tyre of 10 to 35".

According to the present invention, the belt layer structure V consists of a belt layer (layer of steel cords) Vs using steel cords S as reinforcement cords, and a belt layer (layer of aromatic polyamide fiber cords) Va folded at its both end portions under the tread 3 to form folded portions A and using aromatic polyamide fiber cords 10 as reinforcement cords.

Each cord 10 in the belt layer Va has an acute or a smaller angle of the final twist with respect to the axis thereof, which is set to be within a range of 31.3 to 39.3 .

Taking into consideration the results of experiments later to be described, the abovementioned angle of the final twist is set in the above range for reasons as follows: Namely, when the angle 0 (Fig. 3) of the final twist of the aromatic polyamide fiber cord 10, which is measured of the smaller angle of the final twist with respect to the axis of the cord, is less than 31.3 , the adhesion characteristic between the cords 10 and the coat rubber 20 decrease, and separation occurs at the foldedover portions A of the belt layer Va, thereby reducing the durability of the tyre.When the angle 0 of the final twist of the cords 10 exceeds 39.3 , the adhesive characteristic between the cords 10 and the coat rubber 20 also decrease, and separation occurs at the folded portions A of the belt layer Va to reduce the durability of the tyre. Also, it becomes difficult to carry out the step of twisting the cords 10 of aromatic poiyamide fiber cords, and the cords 10 are easily damaged.

Consequently, the physical characteristics of the cords are so degraded as to adversely affect the durability of the tyre.

In this embodiment, each cord 10 of aromatic polyamide fiber is formed by twisting yarn of such fiber as having a tensile strength of not less than 150 kg/mm2 and a tensile modulus of not less than 3000 kg/mm2, in such a manner that the angle 0 of the final twist of each cord 10 with respect to the axis thereof is in the range of 31.3 to 39.3 ; and thereafter applying an adhesive agent to the surface of the cord.

In this embodiment, each cord 10 consists of a 1000 d/2 cord. These cords are arranged at an angle of inclination of 20 with respect to the circumferential direction of the tyre, and the number of the cords 10 embedded in the coat rubber 20 in a width of 50 mm taken in the direction at right angles to the axes of the cords 10 is 60 (arranged in parallel with one another).

The number of the cords 10 embedded in the coat rubber 20 per 50 mm width taken in the direction at right angles to the axes of the same cords 10 is preferably 40 to 70 (arranged in parallel with one another) for the following reasons: When the number of the cords 10 in reference is less than 40, the strength of the belt layer is reduced to an unacceptable degree. Then, if the number exceeds 70, the intervals between adjacent cords 10 becomes too short, so that the coat rubber 20 does not flow between the cords 10 during the tyre-manufacturing process.

Consequently, the adhesive strength between the cords 10 and coat rubber 20 decrease, so that the durability of the tyre is decreased.

Also, the number of cords 10 is then so great as to disadvantageously raise the tyre manufacturing cost.

It is preferable, for the above reasons, to set the number of the cords 10 embedded in the coat rubber per width of 50 mm to 45 to 65.

The 100% modulus of the coat rubber 20 is preferably set to 30 to 70 kg/cm2 for the following reasons: When the modulus of the coat rubber 20 is less than 30 kg/cm2, the adhesion characteristic between the cords 10 and coat rubber 20 cannot be improved; the modulus of the aromatic polyamide fiber cords is too high. Consequently, the durability of the tyre cannot be improved. When the 100% modulus of the coat rubber exceeds 70 kg/cm2, the coat rubber 20 becomes so hard as to unacceptably reduce production rate of the tyres, with a consequent increase in the cost of manufacture.

The belt layer structure V in this embodiment consists, as shown in Fig. 1, of a total of three layers including two belt layers Vs, which are laid on the carcass layer 4 with reinforcement cords composed of steel cords S, and a belt layer Va, which is laminated on the side of the two belt layers Vs which is under the tread, and which has folded portions A.

This belt layer structure V formed as in this embodiment may, of course, be modified by laying the belt layer Va, which has the folded portions A, directly on the carcass layer 4, and not on such a side of the two belt layers Vs, which use steel cords S as reinforcement cords, that is under the tread 3; and laminating at least one belt layer Vs on such a side of the belt layer Va which is under the tread 3 so that both end portions of the belt layer Vs are covered with the folded-over portions A of the belt layer Va.

Referring to Fig. 1, the reference numeral 5 denotes a bead wire, and 6 a bead filler.

As described above, the present invention provides a pneumatic radial tyre for passenger vehicles, which uses as one of a plurality of laminated layers constituting a belt layer structure a layer of aromatic polyamide fiber cords, which layer is folded at its both end portions so as to form folded-over portions and in which each cord has an angle of the final twist, measured of the acute or smaller angle with respect to the axis of the cord, within a range of 31.3 to 39.3 . Accordingly, shearing deformation of the cords in the layer of aromatic polyamide fiber cords can be prevented, and separation does not occur in the interface between the cords and the coat rubber while the tyre is run.

Since separation can be prevented from occurring in the folded portions of the belt layer of the mentioned fiber cords, the durability of the tyre can be greatly improved.

Advantages and/or effects of the present invention will now be described concretely with reference to an experimental example.

Experimental Example: The specification of the pneumatic radial tires for passenger vehicles used in the experiments and test conditions employed are as follows.

(1) Specification of tyre: Tire size: 195/70HR14 (Carcass layer) (a) The angle of each cord with respect to the circumferential direction of the tyre is substantially 90 . Two layers are provided.

(b) The carcass cords consist of 1000d/2 polyester cords.

(Belt layer structure) The belt layer structure consists, as shown in Fig. 1, of a total of three layers, i.e. two belt layers Vs laid on the carcass layer 4 with steel cords S as reinforcement cords, and a belt layer Va laminated on the side of the two belt layers Vs which is under the tread 3, and having folded portions A.

Belt layers Vs: (a) Two layers are arranged so that the cords in one layer cross those in another with the cords in both of these layers inclined at 20 with respect to the circumferential direction of the tyre.

(b) The cord S consists of a steel cord 1 X 5 (0.22).

(c) The number of the cords embedded in the coat rubber in a width of 50 mm in the direction at right angles to the axes of the cords is 40.

(d) The 100% modulus of the coat rubber is 55 kg/cm2.

Belt layer Va: (a) One layer is provided so that the cords therein are inclined at 20 with respect to the circumferential direction of the tyre with the cords in the folded portions crossing those in the non-folded portion.

(b) The cord 10 consists of a 1000d/2 cords of aromatic polyamide fiber.

(c) The number of the cords embedded in the coat rubber in a width of 50 mm in the direction at right angles to the axes of the cords is 60.

(d) The 100% modulus of the coat rubber is 55 kg/cm2.

(e) Each cord of aromatic polyamide fiber is obtained from yarn of such fiber having a tensile strength of not less than 150 kg/mm2 and a tensile modulus of not less than 3000 kg/mm2.

Pneumatic radial tyres for passenger vehicles, having the above specification were prepared with the angle 0 of the final twist of the cords 10 in the belt layers Va, which have folded portions A, set variously to 23.3 , 27.3 , 31.3 , 35.3 , 39.3 and 43.3 .

(2) Test conditions: Rim . . . .. 52JJX14 Air pressure ... . - 1.9 kg/cm2 Diameter of drum . ........ 1707 mm Speed . . ............. .. 80 km/hr Tests were conducted with an initial load of 525 kg which was increased every two hours by 50 kg, to measure the travelling distances of these tyres between the test-starting time and the time at which the tyres were no longer serviceable (the measurement results were shown by indexes with a base travelling distance of a conventional tyre set to 100). The results of these tests are shown in Fig. 2.

Fig. 2 is a graph showing the relation between angles 8 of the final twist of the cord in the belt layer Va, which has folded portions A, and the durability of tyres. The vertical axis of this graph represents the travelling distance of the tires between the starting time of the tests and the time at which the tyres were no longer serviceable, i.e. the durability of the tyres expressed by indexes, and the lateral axis thereof, the angles 0 of the final twist of the cords.

It is understood from Fig. 2 that the pneumatic radial tyre for passenger vehicles according to the present invention, which uses cords 10 of aromatic polyamide fiber as the reinforcement cords in the belt layer Va having folded portions A, which cords are twisted at an angle 0 of 31.3 to 39.3 , is capable of greatly improving the durability of the tyre as compared with the conventional tyre in which the angle 0 of the final twist of the cords 10 is set to 27.3 .

Especially, the pneumatic radial tyre for passenger vehicles according to the present invention, in which the angle 6 of the final twist of the cords in the layer Va is set to 35.3 , is capable of improving the durability of the tyre by as much as 10% as compared with the conventional tyre in which the angle 6 of the final twist of the corresponding cords is set to 27.3 .

Such excellent effects of the present invention are ascribed to the following: When the angle 6 of the final twist shown in Fig. 3 of the cord 10 is in the range of 31.3 to 39.3 , shearing deformation rarely occurs in the cord 10 as a whole even if a force F is exerted thereon as shown in Fig. 3, i.e., in directions which are at right angles to the axis of the cord 10.

This fact can be proved on the basis of the fundamental theory of the deformation characteristics of FRR (fiber-reinforced rubber) in the dynamics of compound materials. If the angle 6 of the final twist of the cord 10 is less than 31.3 and when force F is exerted thereon in directions at right angles to the axis thereof, the cord 10 becomes rhomboidal inclined toward right as shown by two-dot-chain lines in Fig. 4(c). That is, shearing deformation occurs in the cord 10. As a result, the adhesive characteristic between the cords 10 and the coat rubber 20 deteriorates during operation and a separation occurs in the folded portions A of the belt layer Va, thereby decreasing the durability of the tyre.

If the angle 6 of the final twist of the cord 10 exceeds 39.3 and when force F is exerted thereon in the directions at right angles to the axis thereof, the cord 10 becomes rhomboidal inclined toward left as shown by two-dotchain lines in Fig. 4(a). That is, a shearing deformation occurs in the cord 10. As a result, the adhesive characteristic of the cords 10 and the coat rubber 20 deteriorates during operation and separation occurs in the folded portions A of the belt layer Va to decrease the durability of the tyre.

Moreover, in this case, it becomes difficult to carry out the step of twisting the cords of aromatic polyamide fiber, so that the cords are readily damaged. Accordingly, the desired physical properties of the cords decrease, and the durability of the tyre cannot be improved.

If the angle 6 of the final twist of the cord 10 is in the range of 31.3 to 39.3 as in the present invention, even when the force F is exerted thereon in directions at right angles to the axis of the cord 10, the cord 10 is deformed as shown by two-dot-chain lines in Fig. 4(b). Namely, the cord 10 hardly undergoes a shearing deformation. Accordingly, separation does not occur in the interface between the cords 10 and the coat rubber 20 while the tyre is run. Namely, no separation occurs in the folded portions A of the belt layer Va. This enables the durability of the tyre to be improved to a great extent.

The present invention is not limited to the above embodiment, and it may be modified in various ways within the scope of the appended claims.

Claims

1. A pneumatic radial tyre for passenger vehicles, having left and right bead portions, left and right side wall portions continuous with said bead portions, a tread positioned between said side wall portions, a carcass layer provided between said left and right bead portions, and a belt layer structure consisting of a plurality of layers and laid on the portion of said carcass layer which is under said tread, characterized in that said belt layer structure includes a layer of aromatic polyamide fiber cords, which is folded at both end portions thereof under the tread and in which the cords have an angle of the final twist within a range of 31.3 to 39.3 measured of the acute or smaller angle with respect to the axes of the cords.

2. A pneumatic radial tyre for passenger vehicles according to claim 1, wherein said belt layer structure consists of a layer of steel cords and a layer of aromatic polyamide fiber cords folded at its both end portions under said tread to form folded-over portions.

3. A pneumatic radial tyre for passenger vehicles according to claim 1 or 2, wherein said layer of aromatic polyamide fiber cords is formed by embedding in parallel with one another 40 to 70 cords of said fiber in coat rubber in a width of 50 mm in directions at right angles to the axial direction of said cords.

4. A pneumatic radial tyre for passenger vehicles according to claim 1 or 2, wherein each cord in said layer of aromatic polyamide fiber cords is formed by using yarn having a tensile strength of not less than 150 kg/mm2 and a tensile modulus of not less than 3000 kg/mm2.

5. A pneumatic radial tyre for passenger vehicles according to claim 3, wherein each cord in said layer of aromatic polyamide fiber cords is formed by using yarn having a tensile strength of not less than 150 kg/mm2 and a tensile modulus of not less than 3000 kg/mm2.

6. A pneumatic radial tyre for passenger vehicles according to claim 3, wherein the 100% modulus of said coat rubber is in the range of 30 to 70 kg/cm2.

7. A pneumatic radial tyre for passenger vehicles, substantially as hereinbefore described with reference to, and as shown in, the drawings.