JP2007253875A - Tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of suppressing stone bite in a circumferential sub-groove without sacrificing the durability of a die projecting bar for forming the circumferential sub-groove arranged on the outer side of an outermost circumferential main groove of a tread part. <P>SOLUTION: A circumferential sub-groove 3 is arranged on the outer side in the tire width direction of a circumferential groove. The circumferential sub-groove 3 comprises a longitudinal groove part 5 extending straight from an opening part to a tire center in the tire meridian section, and a transverse groove part 6 which is bent from a terminating end of a straight-shaped part and directed toward a tire equator. A plurality of branch parts 7 communicated with the longitudinal groove part 5 of the circumferential sub-groove 3 and extending in the tire width direction are arranged with a spacing in the circumferential direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a longitudinal groove portion that is disposed on the outer side in the tire width direction of a circumferential main groove provided in a tread portion and linearly extends from an opening portion toward a tire central axis, and is bent from an end of the longitudinal groove portion. In particular, the present invention relates to a pneumatic tire provided with a circumferential sub-groove having a lateral groove portion facing the tire equatorial plane, and more particularly to a tire capable of improving the stone biting performance.

  In order to suppress uneven wear of the shoulder portion of the tire, in the tread portion having the circumferential main groove, a circumferential sub groove is arranged outside the outermost main groove in the width direction, and the sub groove is arranged from the opening to the center of the tire. A pneumatic tire composed of a longitudinal groove portion extending linearly toward the shaft and a lateral groove portion bent from the end of the linear shape portion and facing the tire equator surface is known. For uneven wear that starts from the vicinity of the edge of the tread surface of the part, the outside of the secondary groove called the defense side groove is abandoned as a partial wear sacrifice part, and the uneven wear of the tread rubber inside the tire width direction from the secondary groove is suppressed. Can do. (For example, refer to Patent Document 1).

FIG. 1 is a meridian cross-sectional view showing such a tire. A plurality of circumferential main grooves 92 are provided in the tread portion 91, and the outer circumferential grooves 92 are arranged on the outer sides of the outermost grooves 92. Direction sub-grooves 93 are disposed, and the circumferential sub-grooves 93 are longitudinal grooves 95 extending linearly from the opening 94 toward the tire central axis, and bent from the ends of the vertical groove sections 95 to be on the tire equatorial plane. And a transverse groove 96 that faces. By arranging the circumferential sub-grooves 93, the uneven wear that has progressed from the outer side in the tire width direction is blocked, and the tread rubber 97 on the outer side in the tire width direction of the sub-grooves 93 is subjected to the uneven wear sacrificial portion. Thus, uneven wear of the tread rubber 98 on the inner side in the tire width direction from the auxiliary groove 93 can be suppressed. In FIG. 1, 99 indicates a bead core.
JP 2001-206015 A

  However, as shown in FIG. 2, the circumferential sub-groove 93 of such a tire generally has a narrow vertical groove portion 95 with respect to the horizontal groove portion 96, and once passes through the vertical groove portion 95 to the horizontal groove portion 96. The so-called stone bite that is hardly discharged is generated, and if it continues running with the stone bitten, it will be damaged in the circumferential sub-groove 93, and that scratch will be the starting point and the tread on the outer side in the tire width direction There is a problem that a tire failure such as a tear in which the rubber 97 is missing occurs, or a biting stone is pushed into the inside of the tire to damage the belt.

  As the groove width of the longitudinal groove portion 95 is narrowed, stone biting is less likely to occur, but there is a problem that the durability of the vulcanization mold for vulcanizing and molding the tire is reduced in this way. . FIG. 3 is a perspective view showing such a vulcanization mold, and the tread forming surface 81 corresponding to the tread portion 91 of the vulcanization mold 80 has a mold circumferential direction corresponding to the circumferential sub-groove 93. The ridge 83 is formed in a straight line-shaped portion 85 having a linear cross section extending perpendicularly from the tread forming surface 81, and is bent in the lateral direction from the tip of the line-shaped portion 85. And a bent portion 86 connected to each other. The linear shape portion 85 corresponds to the vertical groove portion 95 of the circumferential sub-groove 93, and the bent portion 86 corresponds to the lateral groove portion 96 of the circumferential sub-groove 93. When the vulcanized tire is taken out from the vulcanization mold 80, the tread rubber 98 on the inner side in the tire width direction from the auxiliary groove 93 interferes with the bent portion 86, and the interference force at this time causes the linear shape portion 85 to move. The tread forming surface 81 acts to be bent outward in the width direction.

  Under such circumstances, if the groove width of the longitudinal groove portion 95 of the circumferential sub-groove 93 is to be reduced, the width of the linear portion 85 of the ridge 83 must naturally be reduced, and the interference force As a result, the straight-shaped portion 85 is easily bent, so that it is difficult to narrow the groove width of the longitudinal groove portion 95, and it is not possible to suppress stone biting.

  The present invention has been made in view of such a problem, and stone biting in the circumferential sub-groove is performed without sacrificing the durability of the mold ridge for forming the circumferential sub-groove. An object of the present invention is to provide a pneumatic tire that can be suppressed.

<1> has a circumferential sub-groove disposed on the outer side in the tire width direction of the circumferential main groove provided in the tread portion, and the circumferential sub-groove is arranged from the opening to the tire central axis in the tire meridian cross section. In a pneumatic tire formed by a longitudinal groove portion that linearly extends toward and a lateral groove portion that is bent from the end of the linear shape portion and faces the tire equatorial plane,
It is a pneumatic tire in which a plurality of branch portions that communicate with the longitudinal groove portion and extend in the tire width direction are arranged at intervals in the circumferential direction.

  <2> is a pneumatic tire according to <1>, wherein a groove width of the vertical groove portion is 1.0 mm or less.

  <3> is a pneumatic tire according to <1> or <2>, wherein a length in the tire width direction of the branch portion is 1/3 to 1 times a groove width of the lateral groove portion.

  <4> is a pneumatic tire according to any one of <1> to <3>, wherein a width in the tire circumferential direction of the branch portion is equal to or less than a length in the tire width direction of the branch portion.

<5> is any one of <1> to <4>, wherein c1 is a tire circumferential interval of the branch portion, w2 is a groove width of the lateral groove portion, and w3 is a tire width of the branch portion. A pneumatic tire satisfying the formula (1), where h1 is a radial direction distance from the tire equatorial plane tread surface at the opening of the circumferential sub-groove to the groove bottom of the circumferential sub-groove, is there.

2x (w3 / w2) xh1 ≧ c1 (1)

According to <1>, in the circumferential sub-groove, a plurality of branch portions communicating with the longitudinal groove portion are arranged at intervals in the circumferential direction. Even if the groove width of the longitudinal groove portion of the circumferential sub-groove is reduced by narrowing the width of the linear shape portion, the linear shape is obtained. The portion is not bent, and stone biting can be greatly reduced while ensuring the durability of the mold.

According to <2>, since the groove width of the vertical groove portion is 1.0 mm or less, the stone biting can be further reduced as will be described in detail later.

<3> According to <3>, the length in the tire width direction of the branch portion is 1/3 to 1 times the groove width of the lateral groove portion. In the mold for forming this tire, when the ratio of the length in the tire width direction of the branch portion to the groove width of the lateral groove portion is less than 1/3, as will be described in detail later, When the length of the mold part corresponding to the branch portion that functions as a reinforcing rib becomes insufficient and the durability of the mold cannot be sufficiently satisfied, on the other hand, when this ratio exceeds 1 The branch portion extends longer in the tire width direction than the lateral groove portion, and the effect of suppressing uneven wear is reduced.

According to <4>, since the tire circumferential width of the branch portion is equal to or less than the tire width direction length of the branch portion, stone biting can be further suppressed, and the tire circumferential width of the branch portion is This is because when the length of the branch portion exceeds the tire width direction length, the width of the branch portion in the tire circumferential direction becomes too large, and the frequency of stone biting increases rapidly.

According to <5>, c1 is a tire circumferential interval of the branch portion, w2 is a groove width of the lateral groove portion, w3 is a tire width direction length of the branch portion, and h1 is a sub-groove length. When the distance in the tire radial direction from the tire equatorial plane tread surface to the groove bottom of the opening is set to satisfy the above-described formula (1), as described in detail later, Durability can be further improved.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a perspective view showing the circumferential sub-groove of the tire according to the first embodiment of the present invention. FIG. 4 (a) shows the circumferential sub-groove as a space, and FIG. 4 (b) shows the circumferential sub-groove. FIG. 5 is an enlarged view showing a cross section of the circumferential sub-groove in FIG. 4A, and the circumferential sub-groove 3 is provided in the tread portion 1. Of the circumferential main grooves, the longitudinal grooves 5 are disposed further outside the outermost groove in the tire width direction and extend linearly from the opening toward the tire central axis in the tire meridian cross section. And a lateral groove portion 6 that is bent from the end and faces toward the tire equatorial plane.

  Since this tire is configured as described above, the tread rubber 17 outside the circumferential sub-groove 3 is abandoned as a partial wear sacrificial part against the uneven wear starting from the vicinity of the tread edge of the tread portion 1. Thus, uneven wear of the tread rubber 18 on the inner side in the tire width direction than the auxiliary groove 3 can be suppressed.

  The tire according to the present invention is characterized in that a plurality of branch portions 7 communicating with the longitudinal groove portion 5 are arranged in the circumferential sub-groove 3 at intervals in the circumferential direction.

  FIG. 6 is a perspective view showing a portion corresponding to the circumferential sub-groove 3 of the mold for vulcanizing and molding the tire of the present invention, and the tread forming the surface of the tread portion 1 of the vulcanizing mold 20. On the forming surface 21, a ridge 23 extending in the mold circumferential direction is formed corresponding to the circumferential sub-groove 3, and the ridge 23 is linear in cross section extending perpendicularly from the tread forming surface 21. And a bent portion 26 that is bent and connected in a lateral direction from the tip of the linear shape portion 25 is provided. The linear shape portion 25 corresponds to the longitudinal groove portion 5 of the circumferential sub-groove 3, and the bent portion 26 corresponds to the lateral groove portion 6 of the circumferential sub-groove 3. When the vulcanized tire is taken out from the vulcanization mold 20, the tread rubber 18 located on the inner side in the tire width direction from the auxiliary groove 3 interferes with the bent portion 26, and this interference force causes the linear shape portion 25 to Although it acts so that it bends with respect to the tread formation surface 21, since the reinforcement rib 27 corresponding to the branch part 7 is formed in this metal mold | die 20, even if the thickness of the linear shape part 25 is thin, the said It can withstand interference forces and can prevent bending.

  As described above, in the tire according to the present embodiment, since the branch portions 7 are arranged in the circumferential direction sub-groove 3 at intervals in the tire circumferential direction, the groove width of the vertical groove portion 5 is reduced in order to suppress stone biting. Accordingly, even if the thickness of the linear shape portion 25 corresponding to the longitudinal groove portion 5 is reduced, the linear shape portion 25 of the mold 20 can be prevented from being bent.

  Figure 7 investigates the relationship between the number of stones biting into the circumferential sub-groove and the width w1 (mm) of the longitudinal groove after running 80000 km with tires of size 295 / 75R22.5 mounted on the actual vehicle. FIG. 7 is a graph showing the number of stones biting in the circumferential sub-groove on the vertical axis and the width w1 (mm) of the vertical groove on the horizontal axis. According to this investigation, as shown in FIG. It can be seen that when the groove width w1 exceeds 1 mm, the number of stone bites increases rapidly. As described above, in order to significantly suppress stone biting, it is preferable that the groove width w1 of the longitudinal groove portion is 1 mm or less.

  Here, the tire width direction length w3 including the vertical groove portion 5 of the branch groove 7 (hereinafter simply referred to as the tire width direction length of the branch portion) is 1/3 to 1 times the groove width w2 of the lateral groove portion 6. When this value is less than 1/3, the length of the reinforcing rib 27 corresponding to the branching portion 7 in the mold 20 becomes insufficient, and the durability of the mold is sufficiently satisfied. On the other hand, when this value exceeds 1, the branch portion 7 extends longer in the tire width direction than the lateral groove portion 6, and the effect of suppressing uneven wear is reduced. .

  FIG. 8 shows the occurrence frequency of bending failure of the linear portion 25 of the mold 20 when the length w3 of the branch groove 7 in the tire width direction and the tire circumferential interval c1 are changed. The value obtained by dividing the length w3 by the width in the tire width direction of the lateral groove portion 6 of the sub-groove 3 by w2, that is, w3 / w2, takes the defect of the mold, that is, the bending failure of the linear portion 25 on the vertical axis. FIG. 5 is a graph showing the occurrence frequency, and as is apparent with reference to this graph, in the above, a preferable range of the ratio w3 / w2 of the tire width direction length w3 of the branch portion 7 to the groove width w2 of the lateral groove portion 6 When the tire circumferential interval c1 satisfies the above-described expression (1) with respect to 1/3 to 1 as described above, since the frequency of occurrence of bending problems in the linear portion 25 is zero, the expression ( 1) can be a preferable range of the tire circumferential direction interval c1.

  Note that the vertical axis in FIG. 8 is an index with the frequency of mold defects occurring as c1 = 5xh1 and w3 / w2 = 0.3, where the frequency is 1, and h1 is The distance in the tire radial direction from the tire equatorial plane side tread surface 18 of the opening 4 to the groove bottom is represented. Here, the width w4 in the tire circumferential direction of the branch portion 7 is preferably equal to or less than the length w3 in the tire width direction of the branch portion 7, because the stone biting frequency can be further reduced.

  FIGS. 9-12 is a perspective view which shows the circumferential direction secondary groove of the tire of 2nd-5th embodiment which concerns on this invention, and FIGS. 9-12 (a) is the circumferential direction of embodiment corresponding to this order, respectively. The sub-groove is represented as a space, and FIGS. 9 to 12 (b) represent the circumferential sub-groove as an actual state. Of the main grooves, the longitudinal grooves 5 are disposed further outside the outermost groove in the tire width direction and extend linearly from the opening 4 toward the tire central axis in the tire meridian cross section, and the end of the longitudinal grooves 5 A plurality of branch portions 7A, 7B, 7C, 7D communicating with the longitudinal groove portion 5 in the sub-grooves 3A, 3B, 3C, 3D. Is the same as in the first embodiment, with respect to the points arranged at intervals. The shape of the branch portions 7A, 7B, 7C, and 7D is different from that of the first embodiment, and the branch portion 7 in the first embodiment extends from the longitudinal groove portion 5 toward both sides in the tire width direction and has a substantially circular cross section. In contrast, the branch portions 7A, 7B, 7C and 7D of the second to fifth embodiments extend from the longitudinal groove portion 5 only toward the tire equatorial plane, and the branch portion 7A of the second embodiment is The side extending in the tire width direction has a rectangular cross section longer than the side extending in the tire circumferential direction, and the branch portion 7B of the third embodiment has a side extending in the tire width direction extending in the tire circumferential direction. An example in which the cross-sectional rectangular shape is shorter than the existing side, the branch portion 7C of the fourth embodiment has a triangular cross-section shape, and the branch portion 7D of the fifth embodiment has a semi-circular cross-sectional shape, respectively. Show.

  In any of the embodiments, the groove width of the vertical groove portion is preferably 1.0 mm or less, and the length in the tire width direction of the branch portions 7A, 7B, 7C, 7D with respect to the tire width direction length w2 of the horizontal groove portion 6 is increased. The ratio w3 / w2 of w3 is preferably 1/3 to 1, and the circumferential distance c1 between the branch portions 7A, 7B, 7C and 7D preferably satisfies the above-mentioned formula (1). These are the same as described for the first embodiment.

  As shown in FIG. 9B according to the second embodiment, the cross section perpendicular to the tire radial direction of the branch portion may not be constant, and in the case of the second embodiment, this cross section approaches the tire central axis. Configured to increase according to

  The present invention can be suitably used for tires of various types and applications.

It is meridian sectional drawing which shows the conventional tire. It is sectional drawing which shows the circumferential direction secondary groove of the conventional tire in the state which bited the stone. It is a perspective view which shows the vulcanization mold part which forms the circumferential direction secondary groove of the conventional tire. It is a perspective view which shows the circumferential direction secondary groove of the tire of 1st embodiment. It is sectional drawing which shows the circumferential direction secondary groove of the tire of 1st embodiment. It is a perspective view which shows the vulcanization mold part which forms the circumferential direction secondary groove of the tire of 1st embodiment. 4 is a graph showing the relationship between the number of stones biting into the circumferential sub-groove and the width of the longitudinal groove in the tire after running on a real vehicle. It is a graph which shows the bending malfunction occurrence frequency of the linear shape part of a metal mold | die when changing the tire width direction length of a branch groove, and a tire circumferential direction space | interval. It is a perspective view which shows the circumferential direction secondary groove of the tire of 2nd embodiment. It is a perspective view which shows the circumferential direction secondary groove of the tire of 3rd embodiment. It is a perspective view which shows the circumferential direction secondary groove of the tire of 4th embodiment. It is a perspective view which shows the circumferential direction secondary groove of the tire of 5th embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 3, 3A, 3B, 3C, 3D Circumferential subgroove 4 Opening part 5 Vertical groove part 6 Lateral groove part 7, 7A, 7B, 7C, 7D Branch groove 17 Tread part 18 on the outer side in the tire width direction from the circumferential subgroove 18 Tread portion on the inner side in the tire width direction from the circumferential auxiliary groove 20 Mold 21 Tread forming surface 23 Convex ridge 25 Linear shape portion 26 Bending portion

Claims (5)

It has a circumferential sub-groove arranged on the outer side in the tire width direction of the circumferential main groove provided in the tread portion, and the circumferential sub-groove is linear in the tire meridian section from the opening toward the tire central axis. In a pneumatic tire formed by a longitudinal groove extending to the side and a lateral groove bent toward the tire equator plane from the end of the linear shape portion,
A pneumatic tire in which a plurality of branch portions communicating with the longitudinal groove portion and extending in the tire width direction are arranged at intervals in the circumferential direction.   The pneumatic tire according to claim 1, wherein a groove width of the vertical groove portion is 1.0 mm or less.   The pneumatic tire according to claim 1 or 2, wherein a length of the branch portion in the tire width direction is set to 1/3 to 1 times a groove width of the lateral groove portion.   The pneumatic tire according to any one of claims 1 to 3, wherein a width in the tire circumferential direction of the branch portion is equal to or less than a length in the tire width direction of the branch portion. c1 is the tire circumferential interval of the branch portion, w2 is the groove width of the lateral groove portion, w3 is the tire width direction length of the branch portion, and h1 is the opening of the circumferential sub-groove. The pneumatic tire according to any one of claims 1 to 4, wherein when the tire radial direction distance from the surface of the tread portion on the tire equatorial plane side to the groove bottom is satisfied, the formula (1) is satisfied.

2x (w3 / w2) xh1 ≧ c1 (1)

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