JP2015024758A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire in which a sipe formed at a tread portion is improved in a stone non-biting property.SOLUTION: The pneumatic radial tire has, at a grounding area W of an annularly formed tread portion 10, a land portion 3 partitioned by at least three main grooves 1 extending continuously in a tire circumference direction. When main grooves outside in a tire width direction are specified as shoulder main grooves 1a, a main groove further inside in the tire width direction than the shoulder main grooves 1a is specified as a center main groove 1b, a land portion formed further outside in the tire width direction than the shoulder main grooves 1a is specified as a shoulder land portion 3a, and a land portion formed further inside in the tire width direction than the shoulder land portion 3a is specified as a center land portion 3b, a circumferential sipe 4 extended in the tire circumference direction and an inclined sipe 5 extended inclining toward the tire circumference direction are formed in the shoulder land portion 3a and the center land portion 3b, where a width Wa of the circumferential sipe 4 and a width Wb of the inclined sipe 5 satisfy a relation represented by formula: Wa<Wb and the circumferential sipe is shallower than the inclined sipe 5.

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic radial tire with improved stone biting resistance of a sipe provided in a tread portion.

  In general, a tread pattern is formed on a tread portion of a pneumatic radial tire for the purpose of improving so-called wet performance such as drainage and steering stability when the vehicle travels on a wet road surface. As a technique for improving the wet performance, there are a plurality of main grooves extending in the tire circumferential direction in the tread portion of the tire, and a plurality of lug grooves and sipes extending in the tire width direction in the land portion defined by the main grooves. It is generally performed. Here, the main groove means a wide groove in the tread portion, and has a tread wear indicator that is a protrusion that can visually distinguish the degree of wear of the tread.

  In a tire having such a main groove in the tire circumferential direction, a lug groove in the tire width direction, a sipe, and the like, stones may be caught in these grooves and sipe (stone engagement). When stone biting occurs, so-called stone drilling may occur in which the stone bottom cracks as the stone bites and wear progresses. If the groove bottom of the main groove is cut by stone drilling, the belt layer may be damaged, leading to separation between the tread portion and the belt layer. For this reason, conventionally, a protrusion called a stone rejector is provided on the groove bottom to prevent the stone from biting into the groove (for example, Patent Document 1).

Japanese Patent Laid-Open No. 3-67706

  Conventionally, in light truck tires and the like based on rib patterns, wet performance, stone biting resistance, etc. are utilized by utilizing tread grooves, sipes extending in the tire circumferential direction, sipes extending in the tire width direction, etc. Improvements have been made. However, the current situation is that the study on the stone biting resistance of the sipe provided in the tread portion has not been sufficiently performed.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire in which the stone biting resistance of a sipe provided in a tread portion is improved.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor assumes that the relationship between the circumferential sipe provided in the contact area of the tread portion and the inclined sipe that is inclined with respect to the tire circumferential direction is predetermined. Thus, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the pneumatic radial tire of the present invention is a pneumatic radial tire having a land portion defined by at least three main grooves continuously extending in the tire circumferential direction in a contact area of a tread portion formed in an annular shape. ,
A main groove on both outer sides in the tire width direction is a shoulder main groove, a main groove on the inner side in the tire width direction from the shoulder main groove is a center main groove, and a land portion formed on the outer side in the tire width direction from the shoulder main groove Shoulder land portion, when the land portion formed on the inner side in the tire width direction than the shoulder land portion is a center land portion, a circumferential sipe extending in the tire circumferential direction on the shoulder land portion and the center land portion, and a tire An inclined sipe extending obliquely with respect to the circumferential direction, and a width Wa of the circumferential sipe and a width Wb of the inclined sipe are expressed by the following formula (1),
Wa <Wb (1)
And the circumferential sipe is shallower than the inclined sipe.

Here, the ground contact area means that the tire is mounted on a standard rim specified in JATMA YEAR BOOK (2008 edition, Japan Automobile Tire Association Standard), and the maximum load capacity (internal pressure) in the applicable size / ply rating in JATMA YEAR BOOK. -The tire contact surface when an internal pressure of 100% of the air pressure (maximum air pressure) corresponding to the load capacity correspondence table (bold load) is filled and 80% of the maximum load capacity is loaded.

  In the tire according to the present invention, a plurality of lug grooves extending from the center main groove in an inclined direction with respect to the tire circumferential direction are provided, and the lug groove is substantially centered in the tire width direction of the center land portion. The circumferential sipe and the inclined sipe provided in a portion, and the depth of the lug groove in the communicating portion between the lug groove and the circumferential sipe, and the communicating portion between the inclined sipe, It is preferable that the depth of the circumferential sipe and the inclined sipe is shallower. Moreover, in the tire of this invention, it is preferable that the depth of the circumferential sipe provided in the said center land part is deepest in the approximate center between the said lug grooves. Further, in the tire of the present invention, the depth at the deepest portion of the circumferential sipe provided in the center land portion is the same as the depth at the deepest portion of the circumferential sipe provided in the shoulder land portion. Preferably there is. Furthermore, in the tire of the present invention, it is preferable that a circumferential sipe provided on the shoulder land portion extends continuously in the tire circumferential direction.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire which improved the stone biting property of the sipe provided in the tread part can be provided.

It is a development top view of the grounding surface of the tread part of the pneumatic radial tire concerning one suitable embodiment of the present invention. 1 is a tire width direction sectional view of a pneumatic radial tire according to a preferred embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a developed plan view of a tread portion of a pneumatic radial tire according to a preferred embodiment of the present invention. The illustrated tire has at least three (three in the illustrated example) main grooves 1 continuously extending in the tire circumferential direction in the contact area W of the annularly formed tread portion 10 and the tire circumferential direction. And a lug groove 2 extending in an inclined manner. In the illustrated example, the main groove 1 has a zigzag shape extending in the circumferential direction. However, in the tire of the present invention, it may have a wave shape or a linear shape.

In the tire of the present invention, of at least three main grooves 1 in the ground contact region W of the tread portion 10, the main grooves 1 on both outer sides in the tire width direction are the shoulder main grooves 1a and the tire main grooves 1a in the tire width direction. The main groove 1 on the inner side is the center main groove 1b, and the land portion 3 formed on the outer side in the tire width direction from the shoulder main groove 1a is formed on the shoulder land portion 3a and on the inner side in the tire width direction from the shoulder land portion 3a. When the land portion 3 is the center land portion 3b, the shoulder land portion 3a and the center land portion 3b are inclined with respect to the circumferential direction sipe 4 (4a, 4b in the illustrated example) extending in the tire circumferential direction and the tire circumferential direction. And an inclined sipe 5 (in the illustrated example, 5a, 5b, 5c). In the tire of the present invention, the width Wa of the circumferential sipes 4a and 4b and the width Wb of the inclined sipes 5a, 5b and 5c are expressed by the following formula (1),
Wa <Wb (1)
The circumferential sipe 4 is shallower than the inclined sipe 5.

  As for the stone biting in the sipe provided in the ground contact area W of the tread portion 10, the sipe opens and closes with the deformation of the stepping and kicking-out during the rolling of the tire in the inclined sipe 5 that inclines in the tire circumferential direction. Even if a stone is caught, it is easy to be discharged and it does not become a big problem. However, since the sipe 4 that extends in the circumferential direction does not open and close when the tire rolls, the stones sandwiched between the circumferential sipe 4 are not easily discharged. Therefore, in the tire of the present invention, the circumferential sipe 4 is designed to be thinner and shallower than the inclined sipe 5 so that stones are not easily caught in the circumferential sipe 4 and the rigidity of the land portion 3 is increased. Reduced to prevent wear. Preferably, Wa is 0.5 to 0.75 times Wb, and the depth of the circumferential sipe 4 is 0.7 to 0.9 times the depth of the inclined sipe 5.

  In the tire of the present invention, it is preferable that the lug groove 2 is provided in the land portion 3 as illustrated. For example, in the illustrated example, a plurality of lug grooves 2a extending from the center main groove 1b in an inclined manner with respect to the tire circumferential direction are provided at equal intervals. In this case, the lug grooves 2a are formed on the center land portion 3b. It is preferable to terminate at approximately the center in the tire width direction. When the lug groove 2a is provided in the center land portion 3b, the rigidity of the center land portion 3b is lowered, so that stones caught in the groove are easily discharged, and the effect of improving the stone biting resistance is obtained. At the same time, an edge effect is generated by the lug groove 2a, and the traction performance is also improved. In the illustrated example, the lug grooves 2a are provided at substantially equal intervals. However, in the present invention, the lug grooves 2a are not limited to this, and the intervals between the lug grooves 2a may be arbitrary.

  In general, in a light track, a circumferential shear force acts on the center land portion 3b of the tread portion 10 in the traveling direction (driving direction), and the center land portion 3b is worn (center wear). By providing the lug groove 2a in 3b, it is possible to prevent the center wear by changing the circumferential shear force in the direction opposite to the traveling direction (braking direction) due to the deformation of the rubber in the center land portion.

  On the other hand, in the light track, the contact pressure tends to be released in the vicinity of the shoulder main groove 1a of the tread portion 10, so that a force in the braking direction works and the opening end of the shoulder main groove 1a wears preferentially. Riverware is likely to occur. Therefore, by terminating the lug groove 2a at the approximate center in the tire width direction of the center land portion 3b, the center wear and the river wear are suppressed at the same time without lowering the rigidity of the center land portion 3b more than necessary. This improves the wear appearance. In the tire of the present invention, the width of the lug groove 2a may be appropriately designed according to the use of the tire, and may be, for example, 3 mm to 6 mm. Here, the approximate center in the tire width direction of the center land portion 3b refers to a region of 20% of the entire width in the width direction of the center land portion 3b with the center in the tire width direction of the center land portion 3b as the center.

  In the tire of the present invention, the lug groove 2a communicates with the circumferential sipe 4a and the inclined sipe 5a at the approximate center of the center land portion 3a, and in the communicating portion 6a between the lag groove 2a and the circumferential sipe 4a. The depth of the lug groove 2a and the depth of the lug groove 2a in the communication part 6b between the lug groove 2a and the inclined sipe 5a are shallower than the depths of the circumferential sipe 4a and the inclined sipe 5a in the communication parts 6a and 6b. preferable. By reducing the depth of the lug groove 2a in the communication portions 6a and 6b, rigidity in the communication portions 6a and 6b can be ensured, and good wear resistance can be ensured. Further, by making the lug groove 2a shallow, the stone biting resistance of the lug groove 2a can be improved in the vicinity of the communicating portions 6a and 6b.

  Moreover, in the tire of this invention, it is preferable that the depth of the circumferential sipe 4a provided in the center land part 3b is deepest in the approximate center between the lug grooves 2a. By making the circumferential sipe 4a the deepest at the approximate center of the distance L between the lug grooves 2a, the edge effect can be obtained while maintaining the rigidity of the center land portion 3b, and the wear resistance and the wet road surface can be improved. Steering stability can be improved. Here, the approximate center between the lug grooves 2a refers to a region in the circumferential direction 20% of the distance L between the lug grooves 2a, with the center of the distance L between the lug grooves 2a as the center.

  Furthermore, in the tire of the present invention, the depth at the deepest portion of the circumferential sipe 4a provided in the center land portion 3b and the depth at the deepest portion of the circumferential sipe 4b provided in the shoulder land portion 3a are: Preferably they are the same. Thereby, traction balance can be maintained until the end of wear.

  Furthermore, in the tire of the present invention, it is preferable that the circumferential sipe 4b provided in the shoulder land portion 3a is a circumferential sipe extending continuously in the tire circumferential direction. When the tire of the present invention is used for a front tire such as a light truck, generally, the shoulder land portion 3a of the tread portion 10 is likely to be worn. Therefore, in the tire of the present invention, the circumferential sipe provided on the shoulder land portion 3a is a circumferential sipe 4b that extends continuously in the circumferential direction, so that the wear that progresses from the shoulder progresses to the center region. It is preventing.

  The tire of the present invention relates to the improvement of the tread portion, and there is no particular limitation other than that as long as the circumferential sipe 4 and the inclined sipe 5 of the tread portion 10 satisfy the above relationship. In the tire of the present invention, as shown in the figure, a sipe 5c that is inclined with respect to the tire circumferential direction is provided from the center main groove 1b, and stones sandwiched at the intersection of the center main groove 1b and the lug groove 2a are discharged. It may be easy to do. Moreover, the effect which raises an edge effect is acquired by providing the sipes 5b and 5c. Further, in the tire of the present invention, the shoulder main groove 1a may be provided with a lug groove 2b having an inclination with respect to the tire circumferential direction. This lug groove 2b can also enhance the edge effect in the circumferential direction. Furthermore, as shown in the drawing, the inclined sipe 5b provided in the shoulder land portion 3a may be a sipe extending substantially outward in the tire width direction from the tip of the lug groove 2b. Further, as shown in the figure, the shoulder land portion 3a may be appropriately provided with a groove 2c and an inclined sipe 5d depending on the purpose.

  In the tire of the present invention, the negative rate, which is the ratio of the total groove area to the entire surface of the tread portion 10, may be about 20 to 30%, and the total area of the main groove 1 occupying the negative rate. The ratio may be about 60 to 70%. In the tire of the present invention, the structure other than the tread portion 10 is not particularly limited, and a known member or a known material can be used.

  FIG. 2 is a tire width direction cross-sectional view of a pneumatic radial tire according to one preferred embodiment of the present invention. The illustrated tire 20 has a pair of left and right bead portions 12 and a pair of sidewall portions 13 in which the bead cores 11 are embedded, and a tread portion 10 connected to both sidewall portions 13, and spans between the pair of left and right bead cores 11. The carcass ply 14 extends in a toroidal shape and reinforces each part. In the illustrated example, on the outer side in the tire radial direction of the crown portion of the carcass ply 14, three belt layers 15 a, 15 b, 15 c composed of rubberized layers of reinforcing cords arranged to be inclined with respect to the tire circumferential direction. Is arranged.

  In the example shown in FIG. 2, the number of carcass plies 14 is one, but in the tire 20 of the present invention, the number of carcass plies 14 is not limited to this, and may be two or more. Further, the structure is not particularly limited. The locking structure of the carcass ply 14 in the bead portion 12 is not limited to the structure in which the carcass ply 14 is wound around and locked around the bead core 11 as shown in the drawing, and may be a structure in which the end portion of the carcass ply is sandwiched between two layers of bead cores ( Not shown).

  Further, the belt layers 15a, 15b, and 15c are made of a rubberized layer of a cord, preferably a rubberized layer of a steel cord, which extends with an inclination of ± 15 to 40 ° with respect to the tire circumferential direction, for example. In the illustrated example, the belt layers 15a, 15b, and 15c of the three layers are laminated so that the cords constituting each belt layer intersect with each other across the tire equatorial plane, thereby forming a crossing layer. It is not restricted to the example to do.

  Further, in the tire of the present invention, although not shown, an inner liner is usually disposed in the innermost layer of the tire 20. Furthermore, in the pneumatic tire of the present invention, as the gas filled in the tire 20, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Examples 1 and 2 and conventional example>
A tread pattern tire having three zigzag main grooves as shown in FIG. 1 was produced with a tire size of 195 / 70R15. The width of the center main groove was 7 mm, and the width of the shoulder main groove was 7 mm. The center main groove 1b was disposed on the tire equator, and the shoulder main groove 1a was disposed at a position of 47% of the full width in the tire width direction centered on the center of the tread portion 10. Width Wa (mm) of circumferential sipes 4a and 4b, width Wb (mm) of inclined sipes 5a and 5b, depth (mm) of circumferential sipes 4a and 4b, depth (mm) of inclined sipes 5a and 5b, The depth (mm) of the lug groove 2a is as shown in Table 1. The depth of the main groove was 9.5 mm, the depth of the lug groove was 7 mm, and the end position of the lug groove was the center of the center land portion in the tire width direction. Moreover, the deepest part of the circumferential sipe 4a was provided in the approximate center between lug grooves.

  Each tire obtained was assembled into a rim (rim width: 6J), filled with an internal pressure of 450 kPa, mounted on the vehicle, and applied with a load of 6.00 kPa. Evaluation was performed according to the following procedure.

<Stone chewing resistance>
The vehicle equipped with each tire was repeatedly run 10 times at 60 km / h on a 20 m gravel road covered with pebbles with a diameter of about 1 to 10 mm, and the number of stones caught in the sipe was counted. The obtained results were expressed as an index with the result of the conventional example as 100. The obtained results are also shown in Table 1. In addition, the smaller the value, the smaller the number of stones caught in the groove, and the better the result.

<Wet performance>
An actual vehicle was run on a vehicle equipped with each tire, and the braking performance on a wet road surface was evaluated. The obtained results were expressed as an index with the result of the conventional example as 100. The results are also shown in Table 1. The larger this value, the better the result.

<Abrasion resistance>
The remaining groove was measured, and the travel distance required to wear the center region of the tread portion by 1 mm was measured. The obtained results were expressed as an index with the result of the conventional example as 100. The results are also shown in Table 1. The larger this value, the better the result.

※：主溝１ｂとラグ溝２ａとの連通部６ａにおける深さが７ｍｍであり、センター陸部３ｂの略中央で深さが２ｍｍとなるように徐々にラグ溝２ａの深さが浅くなる。

*: The depth of the lug groove 2a gradually decreases so that the depth at the communication portion 6a between the main groove 1b and the lug groove 2a is 7 mm, and the depth is 2 mm at the approximate center of the center land portion 3b.

  From Table 1, it can be seen that the pneumatic radial tire of the present invention has improved stone biting resistance of the sipe provided in the tread portion.

DESCRIPTION OF SYMBOLS 1 Main groove 2 Lug groove 3 Land part 4 Circumferential sipe 5 Inclined sipe 6 Communication part 10 Tread part 11 Bead core 12 Bead part 13 Side wall part 14 Carcass ply 15 Belt layer

Claims (5)

In a pneumatic radial tire having a land portion partitioned by at least three main grooves continuously extending in the tire circumferential direction in a ground contact region of a tread portion formed in an annular shape,
A main groove on both outer sides in the tire width direction is a shoulder main groove, a main groove on the inner side in the tire width direction from the shoulder main groove is a center main groove, and a land portion formed on the outer side in the tire width direction from the shoulder main groove Shoulder land portion, when the land portion formed on the inner side in the tire width direction than the shoulder land portion is a center land portion, a circumferential sipe extending in the tire circumferential direction on the shoulder land portion and the center land portion, and a tire An inclined sipe extending obliquely with respect to the circumferential direction, and a width Wa of the circumferential sipe and a width Wb of the inclined sipe are expressed by the following formula (1),
Wa <Wb (1)
And a radial radial tire characterized in that the circumferential sipe is shallower than the inclined sipe.   A plurality of lug grooves extending obliquely with respect to the tire circumferential direction from the center main groove are provided, and the lug groove is provided in the center land portion at a substantially center of the center land portion in the tire width direction. The sipe is in communication with the sipe and the inclined sipe, and the depth of the lag groove in the communication portion between the lag groove and the circumferential sipe and the communication portion with the inclined sipe is the circumferential sipe and the inclined sipe. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is shallower than a sipe depth.   The pneumatic radial tire according to claim 1 or 2, wherein a depth of a circumferential sipe provided in the center land portion is deepest at a substantially center between the lug grooves.   The depth in the deepest part of the circumferential sipe provided in the said center land part and the depth in the deepest part of the circumferential sipe provided in the said shoulder land part are the same among Claims 1-3 A pneumatic radial tire according to claim 1.   The pneumatic radial tire according to any one of claims 1 to 4, wherein a circumferential sipe provided in the shoulder land portion extends continuously in a tire circumferential direction.

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