JP2008143240A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing the uniformity in the tire employing the pitch variation. <P>SOLUTION: In the tire employing the pitch variation as a tread pattern, the groove area ratios in pitches 3a, 3b, 3c are reduced more for the pitch as the pitch length is larger. The difference between the groove area ratio in the longest pitch 3a and the groove area ratio in the shortest pitch 3c is set to be ≤0.5% or ≥2.0% and ≤10.0%. A bottom raised part 7 is formed in a groove bottom of a longitudinal groove 1 at the longest pitch 3a if the difference in the groove area ratio is ≤0.5%, and in a groove bottom of the longitudinal groove 1 at the shortest pitch 3c if the difference in the groove area ratio is ≥2.0% and ≤10.0%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that improves uniformity by eliminating a circumferential rigidity difference in a tire that employs pitch variation to suppress pattern noise.

  Generally, in a pneumatic tire, if the tire pattern divided by the lateral grooves has a constant pitch length, the sound pressure concentrates at a constant frequency and generates a large noise. In order to reduce this noise, a plurality of pitches having different pitch lengths are arranged in an appropriate combination in the circumferential direction to disperse the pitch noise over a wide frequency and improve the noise characteristics of the tire. Yes. However, when a plurality of pitches having different pitch lengths are arranged in the circumferential direction in this way, a difference in block rigidity occurs between a pitch having a large pitch length and a pitch having a small pitch length. Cause it to occur.

  That is, in a tire in which a plurality of pitches having different pitch lengths are arranged in the circumferential direction, the groove area ratio for each pitch is usually set to be equal. Since the volume also increases, as shown in FIG. 6, as the pitch length increases, the tread rubber G is pushed more into the groove lower side by the mold M, and the gauge thickness of the groove rubber becomes thicker. Cause a difference in rigidity.

  In order to solve this problem, the groove area ratio in each pitch is reduced as the pitch length increases, and the amount of tread rubber pushed by the mold is kept even regardless of the pitch length. There is a proposal to eliminate the difference in rigidity (see, for example, Patent Document 1).

  However, in this proposal, when the difference between the groove area ratio in the pitch having the largest pitch length and the groove area ratio in the pitch having the smallest pitch length is in the range of more than 0.5% and less than 2.0%. Although the rigidity difference between the pitches can be eliminated, if the difference is 0.5% or less or 2.0% or more, the rigidity difference between the pitches can be eliminated. It turned out to be difficult.

  That is, when the above-described difference in groove area ratio is 0.5% or less, as shown in FIG. 7, the gauge thickness of the tread rubber G pushed by the mold M is below the horizontal groove at a pitch having a large pitch length. Since it is still larger than the gauge thickness of the tread rubber G under the lateral groove at a pitch with a small pitch length, the RFV waveform at a pitch with a large pitch length becomes convex, the RFV waveform at a pitch with a small pitch length becomes concave, and a uniform It was found that Mitie's improvement effect was insufficient.

  On the other hand, when the above-described difference in the groove area ratio is 2.0% or more, as shown in FIG. 8, the volume of the horizontal groove at each pitch is substantially equal, but the horizontal groove according to the size of the pitch length. Therefore, the amount of rubber of the tread rubber G pushed by the mold M is smaller than the amount of rubber of the tread rubber G under the lateral groove in the pitch with a small pitch length. Thus, it was found that the RFV waveform at a pitch with a large pitch length becomes concave, and the RFV waveform at a pitch with a small pitch length becomes convex, so that the effect of improving uniformity is insufficient.

From such a background, when the difference in the groove area ratio described above is set to 0.5% or more or 2.0% or less, the rubber gauge thickness and the rubber amount under the groove of each pitch are uniformly maintained. It came to know that new measures are necessary.
JP 2004-210133 A

  An object of the present invention is to solve the above-described conventional problems, and to provide a pneumatic tire that further improves uniformity in a tire adopting pitch variation.

  The present invention for achieving the above object comprises two inventions, and the pneumatic tire of the invention according to claim 1 (hereinafter referred to as the first invention) intersects with the longitudinal grooves extending in the tire circumferential direction and the longitudinal grooves. A block row is formed by lateral grooves extending in the tire width direction, and a plurality of pitches having different pitch lengths are periodically arranged in the tire circumferential direction, and the groove area ratio in each pitch is reduced as the pitch length increases. The difference between the groove area ratio in the longest pitch with the largest pitch length and the groove area ratio in the shortest pitch with the smallest pitch length is 0.5% or less, and the grooves of the longitudinal grooves in the longest pitch. A bottom raised portion is formed at the bottom.

Furthermore, in the structure mentioned above, it is preferable to comprise as described in the following (1)-(3).
(1) The bottom raised portion is formed on the groove bottom of each vertical groove except for the shortest pitch, and the volume of the bottom raised portion is formed so as to gradually decrease as the pitch length decreases.
(2) The height of the bottom raised portion is set to 1.6 mm or less.
(3) The length of the bottom raised portion in the tire circumferential direction is set to 1 mm or more and the pitch length or less.

  The pneumatic tire of the invention according to claim 3 (hereinafter referred to as the second invention) forms a block row by a longitudinal groove extending in the tire circumferential direction and a transverse groove extending in the tire width direction intersecting the longitudinal groove. In a pneumatic tire in which a plurality of pitches having different pitch lengths are periodically arranged in the tire circumferential direction and the groove area ratio in each pitch is reduced as the pitch length is increased, the groove at the longest pitch length is the largest. The difference between the area ratio and the groove area ratio at the shortest pitch with the smallest pitch length is 2.0% or more and 10.0% or less, and a bottom raised portion is formed at the groove bottom of the vertical groove at the shortest pitch. It is characterized by.

Furthermore, in the structure mentioned above, it is preferable to comprise as described in the following (4)-(6).
(4) The bottom raised portion is formed on the groove bottom of each vertical groove except for the longest pitch, and the volume of the bottom raised portion is formed so as to gradually decrease as the pitch length increases.
(5) The height of the bottom raised portion is set to 1.6 mm or less.
(6) The length of the bottom raised portion in the tire circumferential direction is set to 1 mm or more and the pitch length or less.

  According to the first invention, when the difference in the groove area ratio between the longest pitch and the shortest pitch is set to 0.5% or less, the problem is that the larger the pitch length, the thicker the groove under the rubber gauge is maintained. Since the bottom raised portion is formed at the bottom of the vertical groove at the longest pitch, the amount of rubber pushed in by the mold is reduced, and the thickness of the sub-groove rubber gauge at each pitch is made substantially uniform over the entire circumference of the tire. The difference in block rigidity due to the difference is eliminated, and the uniformity can be improved.

  Further, according to the second invention, when the difference in groove area ratio between the longest pitch and the shortest pitch is set to 2.0% or more and 10.0% or less, the smaller the pitch length, the lower the rubber amount under the groove By increasing the bottom of the vertical groove at the shortest pitch, the amount of rubber that can be pushed in by the mold is reduced, and the amount of rubber under the groove at each pitch is substantially uniform over the entire circumference of the tire. Therefore, the difference in block rigidity due to the difference in pitch length is eliminated, and the uniformity can be improved.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a partial plan view showing a tread surface of a pneumatic tire according to an embodiment of the first invention, and FIG. 2 is a sectional view taken along line XX of FIG.

  In FIG. 1, a tread surface of a pneumatic tire forms block rows 4 and 4 by a longitudinal groove 1 extending in the tire circumferential direction and a lateral groove 2 intersecting the longitudinal groove 1 and extending in the tire width direction. Pitches 3a, 3b, 3c consisting of a plurality (3 in the figure) of different pitch lengths P1, P2, P3 (P1> P2> P3) are periodically arranged in the direction, and the groove area at each pitch 3a, 3b, 3c The ratio is made smaller as the pitch length is larger than the pitch length is smaller. In the figure, 6 indicates a rib.

  In the pneumatic tire of the first invention shown in FIG. 1, the difference between the groove area ratio in the longest pitch 3a with the largest pitch length and the groove area ratio in the shortest pitch 3c with the smallest pitch length is 0.5% or less. The raised portion 7 is formed at the groove bottom of the longitudinal groove 1 at the longest pitch 3a.

  As a result, the problem that the under-groove rubber gauge is kept thicker as the pitch becomes larger is the amount of rubber that is pushed in by the mold by forming the bottom raised portion 7 at the groove bottom of the longitudinal groove 1 at the longest pitch 3a. And the thickness of the in-groove rubber gauge at each pitch 3a, 3b, 3c is made substantially uniform over the entire circumference of the tire, so that the difference in block rigidity due to the difference in pitch length is eliminated and the uniformity can be improved.

  In the first invention described above, the bottom raised portion 7 may be formed also on the groove bottom of the vertical groove 1 at each pitch (pitch 3b in the drawing) except the shortest pitch 3c. In this case, the volume of the bottom raised portion 7 may be formed so as to gradually decrease as the pitch length decreases. Thereby, the block rigidity in each pitch 3a, 3b, 3c can be more easily suppressed, and the uniformity can be further improved.

  FIG. 3 is a partial plan view showing a tread surface of a pneumatic tire according to an embodiment of the second invention, and FIG. 4 is a cross-sectional view taken along line YY of FIG. 3 and 4, the same constituent elements as those of the first invention will be described below using the same reference numerals.

  In FIG. 3, the tread surface of the pneumatic tire forms block rows 4 and 4 by vertical grooves 1 extending in the tire circumferential direction and horizontal grooves 2 intersecting the vertical grooves 1 and extending in the tire width direction. Pitches 3a, 3b, 3c consisting of a plurality (3 in the figure) of different pitch lengths P1, P2, P3 (P1> P2> P3) are periodically arranged in the direction, and the groove area at each pitch 3a, 3b, 3c The ratio is made smaller as the pitch length is larger than the pitch length is smaller.

  In the pneumatic tire of the second invention shown in FIG. 3, the difference between the groove area ratio in the longest pitch 3a having the largest pitch length and the groove area ratio in the shortest pitch 3c having the smallest pitch length is 2.0% or more. The bottom raised portion 7 is formed at the groove bottom of the vertical groove 1 at the shortest pitch 3c.

  This reduces the amount of rubber that can be pushed in by the mold by forming the bottom raised portion 7 at the groove bottom of the vertical groove 1 at the shortest pitch 3c. Thus, since the amount of rubber under the groove at each pitch 3a, 3b, 3c is made substantially uniform over the entire circumference of the tire, the difference in block rigidity due to the difference in pitch length is eliminated, and the uniformity can be improved.

  In the second invention described above, the bottom raised portion 7 may be formed also on the groove bottom of the vertical groove 1 at each pitch (pitch 3b in the figure) excluding the longest pitch 3a. In this case, the volume of the bottom raised portion 7 may be formed so as to gradually decrease as the pitch length increases. Thereby, the block rigidity in each pitch 3a, 3b, 3c can be more easily suppressed, and the uniformity can be further improved.

  In the first and second inventions described above, the height of the bottom raised portion 7 may be set to 1.6 mm or less. If the height h of the raised bottom portion 7 exceeds 1.6 mm, it is impossible to distinguish the wear indicator having a height of 1.6 mm formed on the bottom of the longitudinal groove 1 to indicate the wear limit. It becomes an obstacle to know.

  The length of the raised portion 7 in the tire circumferential direction may be set to 1 mm or more and the pitch length or less. If the length of the bottom raised portion 7 in the tire circumferential direction is less than 1 mm, it is difficult to equalize block rigidity at each of the pitches 3a, 3b, and 3c.

  In the present invention, the width of the bottom raised portion 7 is usually formed over the entire width of the vertical groove 1, but depending on the configuration of the tread pattern, the bottom raised portion 7 and the groove wall of the vertical groove 1 may be secured from the viewpoint of ensuring drainage. It may be necessary to form an interval between them.

  In the present invention, the vertical groove 1 refers to a main groove extending in the tire circumferential direction having a width of about 3 to 25 mm that intersects the horizontal groove 2 to form a block row, and is described above at the groove bottom of the vertical groove 1. Although the bottom raised portion 7 is formed, depending on the type and size of the tire or the configuration of the tread pattern, a vertical groove (for example, the vertical groove 5 shown in FIGS. 1 and 3) that does not intersect the above-described bottom raised portion 7 with the horizontal groove 2. It may also be formed on the groove bottom. In this way, by forming the raised portion 7 at the groove bottom of the vertical groove 5, the block rigidity at each pitch 3a, 3b, 3c may be more easily equalized.

  The pitch lengths P1, P2, and P3 in the present invention refer to unit lengths when the pattern arrangement on the tire circumference is repeated with different unit lengths in the tire circumferential direction, as shown in FIG. 1 and FIG. In addition, the pitch lengths P1, P2, and P3 at each pitch are determined by the distance between the lateral grooves 2 and 2 that divide the unit length.

  In the embodiment described above, the case where the tread surface has an asymmetric pattern in which the ribs 6 are arranged in the center region of the tread and the block rows 4 and 4 are arranged on both shoulder sides is shown. The tread pattern is not limited to this, and the entire tread surface may be configured by a block pattern as illustrated in FIG. Furthermore, the vertical groove 1 formed on the tread surface may be formed in a wave shape or a zigzag shape.

<Conventional Example 1, Example 1>
A conventional tire (conventional example 1) in which the tire size is 195 / 65R15 91S, the tread pattern is FIG. 1, the groove area ratio in each pitch is Table 1, and the bottom portion is not formed on the groove bottom of the main groove at the longest pitch 3a, Twenty tires of the present invention (Example 1) each having a raised portion (length in the tire circumferential direction: 10 mm, height: 1 mm) on the bottom of the main groove at the longest pitch 3a were produced. In each tire, the pitch lengths P1, P2, and P3 of the pitches 3a, 3b, and 3c were P1 = 32 mm, P2 = 28 mm, and P3 = 23 mm, respectively.

  The above two types of tires were measured for uniformity (RFV) in accordance with JIS D4233, and the results are shown in Table 1 using an index with Conventional Example 1 being 100. The larger the value, the better the uniformity.

  From Table 1, it can be seen that the tire of the present invention (Example 1) has improved uniformity compared to the conventional tire (Conventional Example 1).

<Conventional Example 2 and Example 2>
A conventional tire (conventional example 2) in which the tire size is 195 / 65R15 91S, the tread pattern is FIG. 3, the groove area ratio at each pitch is Table 1, and the bottom portion is not formed at the groove bottom of the main groove at the shortest pitch 3c, Twenty tires of the present invention (Example 2) each having a raised portion (10 mm in the tire circumferential direction length and 1 mm in height) formed on the bottom of the main groove at the shortest pitch 3c were produced. Note that the pitch lengths P1, P2, and P3 of the pitches 3a, 3b, and 3c in each tire are the same as those of the tire of FIG.

  The above two types of tires were evaluated in the same manner as described above, and the results are also shown in Table 1 using an index with Conventional Example 2 as 100. The larger the value, the better the uniformity. From Table 1, it can be seen that the tire of the present invention (Example 2) has improved uniformity as compared with the conventional tire (Conventional Example 2).

It is a partial top view which shows the tread surface of the pneumatic tire by embodiment of 1st invention. It is XX arrow sectional drawing of FIG. It is a partial top view which shows the tread surface of the pneumatic tire by embodiment of 2nd invention. It is a YY arrow sectional drawing of FIG. It is a partial top view which shows the tread pattern of the pneumatic tire by other embodiment of this invention. It is sectional drawing for demonstrating the gauge thickness of the rubber under a groove | channel in the conventional general tire. It is sectional drawing for demonstrating the relationship between the gauge thickness of the rubber under a groove | channel, and RFV waveform in the conventional improved tire. It is sectional drawing for demonstrating the relationship between the rubber amount of the rubber under a groove | channel in another conventional improved tire, and RFV waveform.

Explanation of symbols

1, 5 Vertical groove 2 Horizontal groove 3a, 3b, 3c Pitch
4 Block row 6 Rib 7 Bottom raised part P1, P2, P3 Pitch length

Claims (6)

A block row is formed by vertical grooves extending in the tire circumferential direction and transverse grooves extending in the tire width direction intersecting the vertical grooves, and a plurality of pitches having different pitch lengths are periodically arranged in the tire circumferential direction, and each pitch In a pneumatic tire in which the groove area ratio in
The difference between the groove area ratio in the longest pitch with the largest pitch length and the groove area ratio in the shortest pitch with the smallest pitch length is 0.5% or less, and a bottom raised portion is formed on the groove bottom of the vertical groove in the longest pitch. Formed pneumatic tire.   2. The pneumatic tire according to claim 1, wherein the raised bottom portion is formed on a groove bottom of a vertical groove at each pitch excluding the shortest pitch, and the volume of the raised bottom portion is gradually decreased as the pitch length decreases. A block row is formed by vertical grooves extending in the tire circumferential direction and transverse grooves extending in the tire width direction intersecting the vertical grooves, and a plurality of pitches having different pitch lengths are periodically arranged in the tire circumferential direction, and each pitch In a pneumatic tire in which the groove area ratio in
The difference between the groove area ratio in the longest pitch with the largest pitch length and the groove area ratio in the shortest pitch with the smallest pitch length is 2.0% or more and 10.0% or less, and the vertical groove in the shortest pitch. A pneumatic tire with a raised bottom at the groove bottom.   The pneumatic tire according to claim 3, wherein the bottom raised portion is formed at a groove bottom of a vertical groove at each pitch excluding the longest pitch, and the volume of the bottom raised portion is gradually reduced as the pitch length increases.   The pneumatic tire according to claim 1, 2, 3, or 4, wherein the height of the bottom raised portion is 1.6 mm or less.   The pneumatic tire according to claim 1, 2, 3, 4, or 5, wherein a length of the bottom raised portion in a tire circumferential direction is 1 mm or more and a pitch length or less.

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