JP4056161B2 - Pneumatic radial tire - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic radial tire having a block pattern. More specifically, the present invention improves wear resistance with little influence on running performance and maintains good uniformity even when pitch variations are adopted. The present invention relates to a pneumatic radial tire.
[0002]
[Prior art]
In general, in a pneumatic radial tire, center wear or side wear is caused on a tread, and the wear life is reached when at least a part of the wear reaches a necessary minimum groove depth. Therefore, various methods for improving the wear resistance by increasing the tread development width or reducing the groove area have been proposed.
[0003]
However, for example, widening the tread deployment width causes an increase in weight and cost, and the tire is likely to be caught by the soot, so-called soot wandering performance is deteriorated, and if the groove area is reduced, the traction performance and wet road surface are reduced. There was a problem that the running performance deteriorated. For this reason, it has been extremely difficult to improve the wear resistance without substantially affecting the running performance of the tire.
[0004]
Further, pneumatic radial tires having a block pattern generally employ pitch variations in order to reduce noise, but there is a problem of adverse effects on uniformity caused by the pitch variations.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a pneumatic radial tire that has improved wear resistance with little influence on running performance and that can maintain good uniformity even when pitch variations are adopted. It is in.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the pneumatic radial tire of the present invention is provided with five main grooves extending in the tire circumferential direction on the tread to divide and form six rows of land portions, and each land portion extends in the tire width direction. A plurality of sub-grooves are divided into block rows made up of a plurality of blocks, the ratio of the groove area to the total area of the tread is in the range of 25 ± 10%, and between the ends of the maximum width belt layer embedded in the tread. In the region, the area ratio of each block is set to a relationship of 1: 0.9 to 1.1: 1.8 to 2.2 from the shoulder side block row to the center side block row, and each block row has a tire circumference. A plurality of types of pitches having different lengths in the direction are set, and the amount of fluctuation in the tire circumference of the groove area ratio for each pitch is set to 5 points or less.
[0007]
In this way, the ratio of the area of each block is made 1: 1: 2 from the block block on the shoulder side to the block block on the center side (variation within ± 10% is possible), thereby increasing the ratio of the groove area. Thus, even when tire performance such as traction performance is secured, wear resistance can be improved. To ensure the tire performance such as traction performance, the ratio of groove area to the total area of the tread in the range of 25 ± 10%.
[0008]
Also, even if pitch variations consisting of multiple types of pitches are used to reduce noise, the amount of variation in the groove area ratio for each pitch on the tire circumference is restricted to 5 points or less, so that treads can be made during vulcanization molding. Since the rubber is prevented from flowing unevenly and the variation of the sub-groove gauge of the tread is suppressed, the uniformity can be maintained satisfactorily. In order to reduce the fluctuation amount of the groove area ratio for each pitch while adopting the pitch variation in this way, the width of the sub-groove may be changed in proportion to the pitch size of the adjacent block. Even if the variation amount of the groove area ratio for each pitch is set within the above range, the improved wear resistance and low noise performance as described above are not impaired.
[0009]
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 the belt layer having the maximum width embedded in the tread. A region between both ends of the maximum width belt layer substantially coincides with a ground contact region when the tire is used.
[0010]
In the present invention, each land portion is mainly divided into a plurality of blocks using a plurality of sub-grooves, but these sub-grooves and sipes on the extension lines of the sub-grooves may be used in combination. Thus, the sipe on the extension line of the sub-groove behaves together with the sub-groove and contributes to the division of adjacent blocks. The block may be appropriately provided with a sipe that is not on the extension line of the groove, for example, a sipe that intersects the groove or an independent sipe without communicating with the groove. Such a sipe has a narrow interval and behaves independently of the groove, and therefore has no effect of dividing the block into further small blocks.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described 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 is composed of a cap compound having a JIS-A hardness of 50 to 75 in order to obtain excellent wear resistance. The tread 1 is provided with five main grooves 2 extending in the tire circumferential direction, and six rows of land portions are divided and formed by the main grooves 2. The main groove 2 may be straight or zigzag.
[0012]
The tread 1 is provided with a plurality of sub-grooves 3 extending in the tire width direction. The sub-grooves 3 divide the most shoulder side land portion into block rows 4 composed of a plurality of blocks 4a. The land portion is divided into block rows 5 composed of a plurality of blocks 5a, and the land portion closest to the center is divided into block rows 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, 6, the pitch of the sub grooves 3 is substantially the same.
[0013]
The blocks 4a, 5a, 6a can be provided with sipes narrower than the sub-groove 3 and having a width of 2.0 mm or less as required. For example, the shoulder-side block 4 a is provided with a plurality of independent sipes 4 s in parallel with the sub-groove 3 without communicating with the groove. Further, in the shoulder-side block row 4, a part of the blocks 4 a and 4 a adjacent to each other in the tire circumferential direction is divided by a sipe 3 s on the extension line of the sub-groove 3. A sipe 6s crossing the block diagonal direction is provided in the block 6a on the center side so as to intersect the sub-groove 3 and the main groove 2.
[0014]
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 shoulder portions. A region sandwiched between the belt ends e and e is a substantial ground contact region.
[0015]
In the region sandwiched between the belt ends e and 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 set in a range of 25 ± 10%. If the groove area ratio is less than 15%, the traction performance and the running performance on a wet road surface deteriorate, and conversely if it exceeds 35%, the wear resistance decreases.
[0016]
In the area between the belt ends e and e, the area ratio of the blocks 4a, 5a and 6a is 1: 1: 2 (within ± 10%) from the shoulder side block row 4 to the center side block row 6. The relationship between the block areas is 1: 1: 2: 2: 1: 1 (variation within ± 10% is possible) for the entire tread. Thus, by making the area ratio of the blocks 4a, 5a, 6a 1: 1: 1 from the shoulder side to the center side, the occurrence of uneven wear such as center wear and side wear is suppressed and the wear life is increased. Can be extended. However, if the area ratio of the blocks 4a, 5a, and 6a exceeds 10% from the above relationship, the effect of improving the wear resistance cannot be obtained.
[0017]
As described above, when the pitch of the sub-groove 3 is made substantially the same at substantially the same position in the tire circumferential direction of each of the block rows 4, 5, 6, the length ratio of the blocks 4a, 5a, 6a in the tire width direction is approximately The relationship is 1: 1: 2. 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 portion and the shoulder portion is 1: 1, and the shoulder blocks on both the left and right sides 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, 6a can be set to a 1: 1: 2 relationship.
[0018]
In each of the block rows 4, 5, and 6, the blocks 4a, 5a, and 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, pitch variation is adopted for this block pattern in order to reduce noise. On the other hand, the groove width of the auxiliary groove 3 changes in proportion to the length of the pitch between adjacent blocks. Therefore, although the block pattern adopts a pitch variation, the variation amount of the groove area ratio for each pitch in the tire circumference is regulated to 5 points or less.
[0019]
For example, as shown in FIG. 2, the center side block 6a is 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 get smaller. Therefore, by changing the width of the sub-groove 3 in proportion to the lengths of the pitches P _{1 to} P ₃ , the amount of variation in the groove area ratio of the pattern areas A _{1 to} A ₃ can be reduced.
[0020]
As described above, by restricting the fluctuation amount of the groove area ratio for each pitch in the tire circumference to 5 points or less, it is possible to prevent the tread rubber from flowing unevenly at the time of vulcanization molding, and the fluctuation of the sub-groove gauge of the tread. Therefore, the uniformity can be maintained satisfactorily.
[0021]
【Example】
In the pneumatic radial tire having the tread pattern shown in FIG. 1 with a tire size of 175R14 8PR LT, 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 center side. Test tires having different X values were prepared at 1: 1: X to the block rows. However, pitch variation was adopted for the block pattern, and the amount of change in the tire circumference of the groove area ratio for each pitch was set to 5 points.
[0022]
These test tires were mounted on a small truck, traveled at an air pressure of 450 kPa, and the travel distance until reaching the wear life (including removal due to center wear or side wear) was measured, and the results are shown in FIG. The evaluation results are shown as an index with the tire of X = 1 being 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 improvement of the wear life was noticeable in the range where the block area ratio was 1: 1: 1.8 to 2.2.
[0023]
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 shoulder side block row to the center side block row, and this Y value is Different test tires were produced. However, pitch variation was adopted for the block pattern, and the amount of change in the tire circumference of the groove area ratio for each pitch was set to 5 points.
[0024]
These test tires were mounted on a small truck and traveled at an air pressure of 450 kPa. The travel distance until reaching the wear life (including removal due to center wear or side wear) was measured, and the results are shown in FIG. The evaluation results are shown as an index with the tire of Y = 1 being 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.
[0025]
Next, in the pneumatic radial tire having the tread pattern shown in FIG. 1 with a tire size of 175R14 8PR LT, the ratio of the groove area to the tread area is set to 25%, and the area ratio of each block is set to a block row on the shoulder side. The test tires were manufactured by varying the amount of variation in the groove circumference ratio for each pitch from one to the other by varying the pitch ratio of 1: 1: 2 from the center to the block row on the center side.
[0026]
The pitch variation sets the ratio of the three types of pitches A, B, C to A: B: C = 6: 5: 4, sets the ratio of the maximum pitch to the minimum pitch to 1.5, and sets the total number of pitches. No. 67 and configured in the following order.
[0027]
BBCCC CCBBA AABBBB BCCCC CBBAB BBBBC
CCCCB ABBBC CCCBB BAAAAA BBBCC BBBBB
AAAB CC
[0028]
The difference in the groove area ratio between pitch A and pitch C was changed by appropriately changing the width of the sub-groove with the groove area ratio of pitch C as a reference (25%). 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%. .
[0029]
These test tires were measured for radial force variation (RFV) based on the uniformity test method described in JASO C607, and the results are shown in FIG. The evaluation results are indicated by an index using the reciprocal of the measured value and the reciprocal of the RFV level of a tire not adopting the pitch variation (single 67 pitch) as 100. The larger the index value, the smaller the RFV level and the better the uniformity. As can be seen from FIG. 5, good uniformity was obtained when the amount of change in the groove area ratio for each pitch was 5 points or less.
[0030]
【The invention's effect】
As described above, according to the present invention, the tread is provided with five main grooves extending in the tire circumferential direction to divide and form six rows of land portions, and each of the land portions extends in the tire width direction. Are divided into block rows consisting of a plurality of blocks, the ratio of the groove area to the total area of the tread is in the range of 25 ± 10% , and each block in the region between both ends of the maximum width belt layer embedded in the tread. The area ratio of the shoulder side block row to the center side block row is 1: 0.9 to 1.1: 1.8 to 2.2, and each block row has a tire circumferential length. By setting different types of pitches, and by changing the amount of change in the groove area ratio for each pitch in the tire circumference to 5 points or less, the wear resistance is improved almost without affecting the running performance. Barrier The uniformity be employed ® emissions can be maintained.
[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 areas 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 the relationship between the block area ratio (1: Y: 2) and the wear life (index).
FIG. 5 is a graph showing the relationship between the fluctuation amount of the groove area ratio for each pitch and the RFV level (index).
[Explanation of symbols]
1 tread 2 main groove 3 sub groove 3s sipe 4-6 block row 4a-6a block

Claims (1)

The 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 divided into a plurality of blocks by a plurality of sub grooves extending in the tire width direction. The ratio of the groove area to the total area of the tread is in the range of 25 ± 10%. A plurality of types of pitches having different lengths in the tire circumferential direction are set in each block row, and the pitch is set to the block row on the side, and the pitch is set to 1: 0.9 to 1.1: 1.8 to 2.2. A pneumatic radial tire in which the amount of change in the circumference of the tire for each groove area ratio is 5 points or less.

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