JP3124608B2 - Pneumatic radial tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a radial tire having improved durability by improving a belt for reinforcing a tread thereof.

[0002]

2. Description of the Related Art A belt for a radial tire is generally used as a rubberized layer in which cords or monofilament reinforcing elements which are obliquely arranged in parallel to the equatorial plane of the tire are usually embedded at equal intervals.

[0003]

In the conventional belt in which the parallel arrangement of the reinforcing elements is arranged at regular intervals, the rubber facing the end of each reinforcing element at the width end of the belt layer is connected to the ground of the tire. Since it is poked every time it is deformed, a fine crack is generated.
That is, there is no plating layer on the end face of each reinforcing element at the width end of the belt layer, and since this end face and rubber are not bonded, the terminal of the reinforcing element pecks the rubber facing it due to the ground deformation at the time of rolling the tire. This is where the rubber peels and subsequently grows into fine cracks. The cracks eventually grow between adjacent reinforcing elements, and then spread between the stacks of belts. This crack propagation proceeds rapidly with the help of shear strain generated between the belt layers during rolling of the tire under load, and the rate of crack propagation leading to so-called belt separation increases significantly, which increases the durability of the radial tire. Determine.

Here, it is important to suppress the growth of cracks described above. For this purpose, it is naturally advantageous to increase the distance between adjacent reinforcing elements, but it is necessary in addition to the strong demand for reducing the weight of tires. To simplify the code
Since it is desired to reduce the wire diameter of the reinforcing elements, as a result, in order to maintain the same tire strength, there is no other way than to increase the number of driving of the reinforcing elements, and the spacing between the reinforcing elements is rather narrowed and cracks are reduced. This is incompatible with growth control.

[0005] Also, from the standpoint of resource saving, the tires have been rehabilitated and used many times, and the improvement of tread compounds has progressed. As a result, the total life of the tires has been remarkably increased. However, improving belt durability is an urgent matter.

[0006] Therefore, an effective and appropriate solution to the deterioration of belt durability due to the subsequent growth and development of fine cracks generated in the rubber at the width end of the belt layer and facing the end of the reinforcing element. It is an object of the present invention to provide a radial tire with an improved belt layer which can be advantageously adapted to this problem.

[0007]

SUMMARY OF THE INVENTION The present invention is a pneumatic radial tire having a belt layer used for reinforcing a tread of a tire as a rubberized layer of a reinforcing element which is obliquely arranged in parallel to an equatorial plane of the tire. At least one of the belt layers divides the individual reinforcing elements occupying the layer into individual bundles of several or less, and widens the dispersion interval between the bundle and the reinforcing element adjacent thereto. The elements are arranged side by side, and the ratio d / l of the width d of the bundle in the direction orthogonal to the reinforcing element and the distance l between the bundle and the reinforcing element adjacent thereto is in the range of not less than 1/2 and not more than 2. A pneumatic radial tire characterized by the following.

[0008] Here, the bundle is made of the same number of reinforcing elements, the bundle is made of a different number of reinforcing elements, and at least some of the reinforcing elements adjacent to each other in the bundle are arranged in contact with each other. Each case in which the spacing between adjacent reinforcing elements in the bundle is smaller than the dispersion interval of the bundle is included.

[0009] Here, a surplus in the division of the bundle may occur depending on the total number of reinforcement elements required for reinforcing the tire with the belt. It is possible to adopt a dispersive arrangement so as to be substantially uniform over the circumference.

In order to prepare a rubberized layer of a reinforcing element such as a steel cord as a belt used in the present invention,
In particular, the belt treat is first made by a calendering roll with an improved comb tooth roll. This comb-toothed roll thereby serves to combine the reinforcing elements with the rubber sheet by means of a calendering roll with juxtaposed arrangements of several reinforcing elements, for example every two bundles.

The comb-shaped roll has a plurality of circumferential grooves for the above-mentioned arrangement of the reinforcing elements, the circumferential grooves being delimited by collar-shaped comb teeth for extending between adjacent ones of the section bundles. Has a groove width corresponding to a section bundle of two independent reinforcing elements which are in contact with each other without restriction in the above example.

When the belt treat thus produced is used for reinforcing the belt, the treat width is cut obliquely in accordance with the required inclination of the reinforcing element with respect to the equatorial plane of the tire, and then the ears at the width ends of the treat are separated from each other. Is re-joined, wound around a raw coil together with a liner, and then subjected to a tire building process.

[0013]

As described above, the process of breaking the rubber at the width end of the belt of the radial tire does not involve the initial stage in which a fine crack generated at the end of the reinforcing element progresses along the surface of the reinforcing element. When the reinforcing elements are arranged in parallel at equal intervals according to the above, there is a disadvantage that as soon as they start to grow between adjacent reinforcing elements, they are immediately connected between the laminations of the belt and suddenly expanded, thereby progressing to belt separation. . On the other hand, according to the present invention, when the bundle and the bundle or the reinforcing element which does not belong to the bundle are mixed, the dispersion interval 1 between the reinforcing element and the bundle is much wider than that in the case of the conventional equispaced arrangement. Therefore, the crack growth between the reinforcing elements adjacent to each other with the dispersion interval l after the initial stage is delayed according to the dispersion interval, and thereafter, the cracks between the laminations of the belts which rapidly progress to the belt separation. Expansion is effectively suppressed. On the other hand, in order to increase the time of the initial stage, that is, the stage in which the cracks in the bundle grow along the surface of the reinforcing element, it is necessary to increase the width d of the bundle in the direction perpendicular to the reinforcing element (hereinafter referred to as the bundle width). It is valid. That is, as d increases, the surface area of the bundle increases, resulting in an increase in the area in which the crack must propagate, and a reduction in the crack growth rate.

As described above, in order to reduce the crack growth rate within the bundle and between the bundles, it is preferable to increase the bundle width d and the dispersion interval l, respectively. In consideration of the distortion concentrated between the bundles and the rubber around the bundle, it is necessary to regulate the relationship between the bundle width d and the dispersion interval l. That is, in a tire under rolling load, especially in the tread shoulder portion, the contact pressure increases, and the belt undergoes compression strain in the tire radial direction, and the rubber in the belt is an incompressible material. , Tensile strain occurs in the tire axial direction. In the case of a crack along the bundle, the tensile strain is carried by the rubber between the bundle and the reinforcing element adjacent thereto, so that if the bundle width d is too large with respect to the dispersion distance l, the per unit area of the rubber The strain increases, and excessive strain is applied to the tip of the crack in the bundle, and the crack rapidly propagates from the inside of the bundle to the rubber side. On the other hand, if the bundle width d is reduced with respect to the dispersion interval l, the strain concentrated on the rubber is reduced, but if the bundle width d is too small with respect to the dispersion interval l, the strain load in the bundle increases, and Is unfavorable because the crack growth is accelerated. Therefore, it is important to regulate the ratio d / l between the dispersion interval l and the bundle width d. In order to avoid the above disadvantage, d / l
1 is in the range of not less than 1/2 and not more than 2.

The dispersion interval l and the bundle width d do not need to be constant in the circumferential direction of the tread as long as the ratio d / l is within the above range, as long as the basic performance of the belt is not impaired. d may change in the circumferential direction.

Here, only a part of the reinforcing elements among the total number of reinforcing elements between the rubberized layers is bundled, and even if the distributed arrangement is made so as to be substantially even over the entire circumference of the tire, the bundle and the adjacent Since the spacing between the reinforcing elements and the reinforcing elements to be formed is wider than the spacing between the reinforcing elements in a case where the reinforcing elements are arranged at regular intervals according to the related art, the propagation of cracks between the stacked layers of the belt, which rapidly progresses to the belt separation, is suppressed. However, the effect may not be remarkable in some cases, so that the bundle is divided into at least half or more of the reinforcing elements around the entire circumference, and the effect is remarkable.

Further, the reason why the number of reinforcing elements in the bundle is set to several or less is that as the number of reinforcing elements increases, the dispersion interval can be widened, and it is advantageous. However, it is necessary to use at most several bundles because of the disadvantage of crack propagation in the bundle.

[0018]

EXAMPLE 1 Various arrangements of reinforcing elements when the belt treat described above in relation to the present invention is used as the tread reinforcing belt 2 of the radial tire 1 for a passenger car of size 165 SR13 whose cross section is shown in FIG. FIGS. 2 to 7 illustrate cross sections orthogonal to the arrangement direction of the reinforcing elements of the tread reinforcing belt 2,
3 is a reinforcing element and 4 is a bundle thereof.

As shown in each figure, the tread reinforcing belt 2 is formed as a divided bundle 4 of several reinforcing elements 3 in the rubberized layer. Are arranged. In addition, the spacing between the reinforcing elements in the bundle was shown as being in contact with and slightly apart from each other.

Each of the test tires shown in the following Table 1, which were produced using reinforcing elements of different cord types in accordance with the above, was subjected to a drum tester under the conditions of an internal pressure of 1.9 kmf / cm ² and a load of 425 kg. After running 60,000 km at a speed of 80 km / h, dissect and measure the length of the crack generated near the width end of the belt 2, and the ratio to the crack length in the case of a conventional tire with reinforcing elements arranged at equal intervals Are also shown in Table 1 and are shown in FIG. 8 corresponding to the ratio d / l.

[0021]

[Table 1]

In this example, two belts 2 are laminated.
The reinforcing elements of each layer cross each other at 24 ° to the tire equatorial plane, and the width of the tread side layer is slightly smaller than that of the carcass side layer. The cracks generated near the width end of the belt are generated only in the tread-side layer, and the measurement results are obtained only for the tread-side layer. Based on this fact, it is of course possible to apply the rubberized layer of the present invention only to the belt on the tread side.

Example 2 Similarly, a tread reinforcing belt 2 of a radial tire for a passenger car of size P215 / 75 SR15 whose cross section is shown in FIG. 1 was prototyped using reinforcing elements having different cord types shown in Table 2. Each test tire shown in the following Table 2 was run on a drum tester at a speed of 80 km / h for 60,000 km under an internal pressure of 2.45 kgf / cm ² and a load of 790 kg, and then dissected. The length of the crack generated near the width end was measured, and the ratio to the crack length in the case of the conventional tire in which the reinforcing elements were arranged at regular intervals is also shown in Table 2, and FIG. 9 corresponding to the ratio d / l is shown in FIG. Show.

[0024]

[Table 2]

In this example, two belts 2 are laminated.
The reinforcing elements of each layer cross each other at 24 ° to the tire equatorial plane, and the width of the tread side layer is slightly smaller than that of the carcass side layer. The cracks generated near the width end of the belt described above are generated only in the tread side layer, and the measurement results are also obtained only for the tread side layer.

[0026]

According to the present invention, cracks in the vicinity of the end of the reinforcing element used for the reinforcing element of the belt, which is the cause of separation at the width end of the belt, which has been regarded as a weak point of reinforcing the tread of the pneumatic radial tire, are considered. Growth can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a test tire for a passenger car.

FIG. 2 is a schematic view showing an arrangement of reinforcing elements.

FIG. 3 is a schematic view showing an arrangement of reinforcing elements.

FIG. 4 is a schematic view showing an arrangement of reinforcing elements.

FIG. 5 is a schematic view showing an arrangement of reinforcing elements.

FIG. 6 is a schematic view showing an arrangement of reinforcing elements.

FIG. 7 is a schematic view showing an arrangement of reinforcing elements.

FIG. 8 is a graph showing a relationship between a ratio d / l and a crack length.

FIG. 9 is a graph showing a relationship between a ratio d / l and a crack length.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 tire 2 belt for reinforcing tread 3 reinforcing element 4 bundle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-240402 (JP, A) JP-A-51-47702 (JP, A) JP-A-62-149929 (JP, A) 29405 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 9/00 B60C 9/18-9/20

Claims (5)

(57) [Claims] 1. A pneumatic radial tire having a belt layer used for reinforcing a tread of a tire as a rubberized layer of a reinforcing element arranged obliquely parallel to an equatorial plane of the tire, wherein at least one of the belt layers is provided. Is separated into the individual reinforcing elements occupying the layer in each bundle of several or less, and becomes a juxtaposed array of reinforcing elements in which the dispersion interval between the bundle and the reinforcing element adjacent thereto is widened, A pneumatic radial, wherein a ratio d / l of a width d of the bundle in a direction orthogonal to the reinforcing element and a distance l between the bundle and the reinforcing element adjacent thereto is in a range of not less than 1/2 and not more than 2. tire. 2. The radial tire according to claim 1, wherein the bundle comprises the same number of reinforcing elements. 3. The radial tire according to claim 1, wherein the bundle is composed of different numbers of reinforcing elements. 4. The radial tire according to claim 1, wherein at least some of the reinforcing elements adjacent to each other in the bundle are arranged in contact with each other. 5. The radial tire according to claim 4, wherein the spacing between adjacent reinforcing elements in the bundle is smaller than the dispersion of the bundle.