JP2000219011A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire wherein wear resistance is improved without giving influence on running performance and good uniformity is maintained if pitch variation is adopted. SOLUTION: Five main grooves 2 extending to the peripheral direction of a tire are provided on a tread 1 to form six-line split lands. Each land is split into block lines 4, 5, 6 consisting of a plurality of blocks 4a, 5a, 6a, respectively, with a plurality of subsidiary grooves 2 extending to the cross direction of the tire. In a region between both ends (e), (e) of the widest belt layer embedded in the tread 1, the area ratio of the blocks 4a, 5a, 6a has a relationship of 1:0.9-1.1:1.8-2.2 ranging from the block line 4 on the shoulder side to the block line 6 on the center side. Plural types of pitches are set in the block lines 4, 5, 6 with the lengths being different in the peripheral direction of the tire and the variation of a groove area ratio for every pitch in one round of a tire is 5-point or less.

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 having a block pattern, and more particularly, to a uniform pneumatic radial tire having improved wear resistance without substantially affecting running performance and uniformity even when a pitch variation is adopted. TECHNICAL FIELD The present invention relates to a pneumatic radial tire capable of maintaining good quality.

[0002]

2. Description of the Related Art In general, in a pneumatic radial tire, a center wear or a one-sided wear occurs on a tread, and a wear life is reached when at least a part of the wear reaches a required minimum groove depth. Therefore, various methods have been proposed for improving the wear resistance by increasing the tread deployment width or reducing the groove area.

However, for example, if the width of the tread is expanded, the weight and the cost are increased, and the tires are more likely to be caught by the rut, so that the so-called rut wandering property is deteriorated. There is a problem that the running performance on the road surface is reduced. Therefore, it has been extremely difficult to improve the wear resistance without substantially affecting the running performance of the tire.

In a pneumatic radial tire having a block pattern, a pitch variation is generally adopted to reduce noise. However, the adverse effect on uniformity due to the pitch variation is problematic.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve abrasion resistance without substantially affecting running performance, and to maintain good uniformity even when pitch variations are adopted. It is an object of the present invention to provide a pneumatic radial tire.

[0006]

In order to achieve the above object, a pneumatic radial tire according to the present invention is provided with five main grooves extending in the tire circumferential direction in a tread, and dividing and forming six rows of land portions. Each land portion is divided into a block row composed of a plurality of blocks by a plurality of sub-grooves extending in the tire width direction. From the block row on the side to the block row on the center side, 1: 0.9 to 1.1: 1.
In addition to the relationship of 8 to 2.2, a plurality of types of pitches having different lengths in the tire circumferential direction are set in each block row, and the variation of the groove area ratio for each pitch in one circumference of the tire is 5
It is characterized by the following points.

As described above, the area ratio of each block is changed from the block row on the shoulder side to the block row on the center side:
1: 2 (variation within ± 10% is possible) improves wear resistance even when the ratio of groove area is increased to ensure tire performance such as traction performance can do. In order to ensure tire performance such as traction performance, the ratio of the groove area to the total area of the tread is preferably in a range of 25 ± 10%.

[0008] Even if a pitch variation consisting of a plurality of types of pitches is adopted to reduce noise, vulcanization can be achieved by restricting the amount of variation in the groove area ratio of each pitch to one point or less in one round of the tire. Since the tread rubber is prevented from flowing unevenly at the time of molding and the fluctuation of the gauge under the groove of the tread is suppressed, the uniformity can be favorably maintained. In order to reduce the variation of the groove area ratio for each pitch while adopting the pitch variation, the width of the sub-groove may be changed so as to be proportional to the pitch of the adjacent block. Even if the variation of the groove area ratio for each pitch is set in the above range, the improved wear resistance and low noise as described above are not impaired.

In the present invention, the area of each block, the total area of the tread, and the groove area of the tread are measured in a region between both ends of a belt layer having a maximum width embedded in the tread. The region between both ends of the maximum width belt layer substantially coincides with the contact region when the tire is used.

In the present invention, each land portion is divided into a plurality of blocks mainly using a plurality of sub-grooves. However, even if these plurality of sub-grooves and sipes on the extension of the sub-grooves are used in combination. good. As described above, since the sipes on the extension of the sub-groove behave with the sub-groove, they contribute to the separation of adjacent blocks.
Further, a sipe that is not on an extension of the groove, for example, a sipe that intersects with the groove or an independent sipe without communicating with the groove may be appropriately provided in the block. Such sipes are narrowly spaced and behave independently of the grooves, so they have no effect of breaking the block into further smaller blocks.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 illustrates a tread pattern of a pneumatic radial tire according to an embodiment of the present invention. In the figure, the tread 1 has a JIS-A hardness of 50 to 75 in order to obtain excellent wear resistance.
It consists of a cap compound. The tread 1 is provided with five main grooves 2 extending in the tire circumferential direction, and these main grooves 2 divide and form six rows of land portions. The main groove 2 may be straight or zigzag.

The tread 1 is provided with a plurality of sub-grooves 3 extending in the tire width direction. The sub-grooves 3 divide the land portion closest to the shoulder into a block row 4 including a plurality of blocks 4a. The land portion inside is divided into a block row 5 composed of a plurality of blocks 5a, and the land section closest to the center is divided into a block row 6 composed of a plurality of blocks 6a. At substantially the same position in the tire circumferential direction of each of the block rows 4, 5, and 6, the pitch of the sub-grooves 3 is substantially the same.

The blocks 4a, 5a and 6a can be provided with sipes narrower than the sub-grooves 3 and having a width of 2.0 mm or less, if necessary. For example, a plurality of independent sipes 4s are provided in the shoulder side block 4a in parallel with the sub-groove 3 without communicating with the groove. Further, in the shoulder-side block row 4, some of the blocks 4 a, 4 a that are adjacent in the tire circumferential direction are separated by sipes 3 s that are on the extension of the sub-groove 3. In the block 6a on the center side, a sipe 6s crossing in the diagonal direction of the block is provided so as to intersect the sub groove 3 and the main groove 2.

A plurality of belt layers (not shown) are embedded in the tread 1, and both belt ends e and e of the belt layer having the maximum width are located at the left and right shoulders. The area sandwiched between these belt ends e, e is a substantial ground contact area.

In the region between the belt ends e, e of the pneumatic radial tire, the ratio of the total groove area including the main groove 2 and the sub groove 3 to the tread area is 25 ± 10%.
Is set in the range. If the groove area ratio is less than 15%, traction performance and running performance on a wet road surface decrease, and if it exceeds 35%, abrasion resistance decreases.

In the region sandwiched between the belt ends e, e, the area ratio of the blocks 4a, 5a, 6a is 1: 1: 2 (± 10) from the shoulder side block row 4 to the center side block row 6. % Is possible), and the block area ratio of the entire tread is 1: 1: 2: 2: 1: 1 (fluctuations within ± 10% are possible).
Is in a relationship. Thus, the blocks 4a, 5a,
6a area ratio from shoulder side to center side 1: 1:
By making the relationship 2, it is possible to suppress the occurrence of uneven wear such as center wear and one-sided wear, and to extend the wear life. However, if the area ratio of the blocks 4a, 5a, 6a deviates from the above relationship by more than 10%, the effect of improving the wear resistance cannot be obtained.

As described above, when the pitch of the sub-grooves 3 is substantially the same at substantially the same position in the tire circumferential direction of each of the block rows 4, 5, and 6, the length of each of the blocks 4a, 5a, and 6a in the tire width direction. The ratios are generally in a 1: 1: 2 relationship. That is, the main groove 2 is provided at a position where the maximum width belt layer is equally divided into four in the tire width direction, the ratio of the block area of the center part to the shoulder part is set to 1: 1, and the blocks of the right and left shoulder parts are further divided. By providing the main grooves 2 at positions equally divided into two in the tire width direction, the area ratio of the blocks 4a, 5a, and 6a can be set to a relationship of 1: 1: 2.

In each of the block rows 4, 5, 6, the blocks 4a, 5a, 6a are arranged in the tire circumferential direction based on a plurality of types of pitches having different lengths in the tire circumferential direction. That is, a pitch variation is adopted in this block pattern to reduce noise. on the other hand,
The groove width of the sub groove 3 changes in proportion to the pitch length of the adjacent block. For this reason, in this block pattern, the variation amount of the groove area ratio for each pitch in one circumference of the tire is restricted to 5 points or less, although a pitch variation is adopted.

For example, as shown in FIG. 2, the blocks 6a on the center side are arranged in the tire circumferential direction based on the pitches P _{1 to} P ₃ . At this time, the pattern regions A ₁ to A ₃ which are partitioned by the pitch P ₁ to P ₃ are assumed if the width of the minor groove 3 are the same, inversely the groove area ratio to the length of the pitch P ₁ to P ₃ And become smaller. Therefore, by changing the width of the sub-groove 3 in proportion to the length of the pitches P _{1 to} P ₃ , it becomes possible to reduce the variation of the groove area ratio of the pattern regions A _{1 to} A ₃ .

As described above, the variation of the groove area ratio for each pitch in one round of the tire is restricted to 5 points or less, thereby preventing the tread rubber from flowing unevenly during vulcanization molding and allowing the tread rubber to flow under the groove of the tread. Since the fluctuation of the gauge is suppressed, the uniformity can be favorably maintained.

[0021]

[Example] Tire size is 175R14 8PR LT
In the pneumatic radial tire having the tread pattern shown in FIG. 1, the ratio of the groove area to the tread area is set to 25%, and the area ratio of each block is changed from the block row on the shoulder side to the block row on the center side: 1: X, test tires having various X values were manufactured. However, a pitch variation was adopted as the block pattern, and the variation of the groove area ratio for each pitch in one round of the tire was set to 5 points.

The test tires were mounted on a small truck and run at an air pressure of 450 kPa, and the running distance until the wear life (including removal due to center wear or one-sided wear) was measured. The results are shown in FIG. Indicated. The evaluation results were indicated by an index with the tire at X = 1 being taken as 100. The larger the index value, the longer the wear life and the better the wear resistance. As can be seen from FIG. 3, the wear life was remarkably improved in the range where the block area ratio was 1: 1: 1.8 to 2.2.

Next, in the tire, the ratio of the groove area to the tread area is set to 25%, and the area ratio of each block is set to 1: Y: 2 from the block row on the shoulder side to the block row on the center side. Test tires having various Y values were manufactured. However, a pitch variation was adopted as the block pattern, and the variation of the groove area ratio for each pitch in one round of the tire was set to 5 points.

These test tires were mounted on a small truck and run at an air pressure of 450 kPa. The running distance until the wear life (including removal due to center wear or one-sided wear) was measured, and the results are shown in FIG. Indicated. The evaluation results were indicated by an index with the tire of Y = 1 as 100. The larger the index value, the longer the wear life and the better the wear resistance. As can be seen from FIG. 4, the wear life was excellent in the range where the block area ratio was 1: 0.9 to 1.1: 2.

Next, when the tire size is 175R148P
In the pneumatic radial tire having the tread pattern shown in FIG. 1, the ratio of the groove area to the tread area is set to 25%, and the area ratio of each block is changed from the shoulder-side block row to the center-side block row. 1: 1: 2, and the following pitch variations were used for the block pattern, and test tires were manufactured in which the amount of variation in the groove area ratio for each pitch in one round of the tire was varied.

The pitch variation is such that the ratio of the three types of pitches A, B, and C is set to A: B: C = 6: 5: 4, the ratio of the maximum pitch to the minimum pitch is 1.5, and the total The number of pitches was set to 67, and they were configured in the following order.

BBCCC CCBBA AABBB BCCCC CBBAB BBBBC CCCCB ABBBC CCCBB BAAAAA BBBCC BBBBBB AAABB CC

Then, based on the groove area ratio of the pitch C (2
5%), and the difference in the groove area ratio between the pitch A and the pitch C was changed by appropriately changing the width of the sub-groove. The pitch B is an intermediate value between the pitch A and the pitch C.
For example, when the variation amount of the groove area ratio is 5 points,
The groove area ratio of the pitch A is 20%, the groove area ratio of the pitch B is 22.5%, and the groove area ratio of the pitch C is 25%.
And

Radial force variations (RFV) of these test tires were measured based on the uniformity test method described in JASO C607, and the results are shown in FIG. The evaluation result was represented by an index using the reciprocal of the measured value and the reciprocal of the RFV level of a tire (single 67 pitch) not adopting the pitch variation as 100. The larger the index value, the smaller the RFV level and the better the uniformity. As can be seen from FIG.
When the amount of change in the groove area ratio for each pitch was 5 points or less, good uniformity could be obtained.

[0030]

As described above, according to the present invention, the tread is provided with five main grooves extending in the circumferential direction of the tire to form six rows of land portions, and each land portion extends in the tire width direction. Divided into a block row composed of a plurality of blocks by a plurality of sub-grooves, and in the region between both ends of the maximum width belt layer embedded in the tread, the area ratio of each block is changed from the shoulder side block row to the center side block. To row 1: 0.9 ~
1.1: A relationship of 1.8 to 2.2 is set, and a plurality of types of pitches having different lengths in the tire circumferential direction are set in each block row, and a groove area ratio for each pitch varies in one circumference of the tire. By setting the amount to 5 points or less, the wear resistance can be improved without substantially affecting the running performance, and the uniformity can be maintained well even if a pitch variation is adopted.

[Brief description of the drawings]

FIG. 1 is a development view illustrating a tread pattern of a pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is a plan view showing the tread pattern of FIG. 1 divided into pattern regions based on pitch.

FIG. 3 is a graph showing a relationship between a block area ratio (1: 1: X) and a wear life (index).

FIG. 4 is a graph showing a relationship between a block area ratio (1: Y: 2) and a wear life (index).

FIG. 5 is a graph showing a relationship between a variation amount of a groove area ratio for each pitch and an RFV level (index).

[Explanation of symbols]

 Reference Signs List 1 tread 2 main groove 3 sub groove 3s sipes 4-6 block row 4a-6a block

Claims (2)

[Claims] 1. A tread is provided with five main grooves extending in the tire circumferential direction to divide and form six rows of land portions, and each land portion is formed of a plurality of blocks by a plurality of sub-grooves extending in the tire width direction. In the region between both ends of the maximum width belt layer embedded in the tread, the area ratio of each block is changed from the shoulder-side block row to the center-side block row in a range of 1: 0.9 to 1.1. In addition to the relationship of 1.8 to 2.2, a plurality of types of pitches having different lengths in the tire circumferential direction are set for each block row, and the variation of the groove area ratio for each pitch in one circumference of the tire is 5 Pneumatic radial tires below the point. 2. The pneumatic radial tire according to claim 1, wherein a ratio of a groove area to a total area of the tread is in a range of 25 ± 10%.