PNEUMATIC TIRE

This application claims priority of Japanese Patent Application No. 2018-125051 filed on Jun. 29, 2018, the content of which is incorporated herein by reference.

The present invention relates to a pneumatic tire.

The pneumatic tire disclosed in Japanese Patent No. 6104215 includes a shoulder block on which a sipe extending in the tire width direction is formed.

The sipe formed on the shoulder block improves the traction performance on the snowy road surface and contributes to the improvement of the traveling performance on the snowy road surface. However, conventional pneumatic tires having a shoulder block on which a sipe is formed, including those disclosed in Japanese Patent No. 6104215, still have room for improvement in terms of improving braking performance on the dry road surface and wear-resistant performance while ensuring traveling performance on the snowy road surface.

An object of the present invention is to provide a pneumatic tire that achieves improvement in braking performance on the dry road surface and improvement in wear-resistant performance while ensuring traveling performance on the snowy road surface.

One aspect of the present invention provides a pneumatic tire including: a shoulder main groove formed on a tread portion so as to extend in a tire circumferential direction on a grounding end side; a plurality of lateral grooves formed on the tread portion so as to extend in a direction intersecting with the tire circumferential direction; a shoulder block defined by the shoulder main groove and the lateral grooves; a first shoulder sipe that is formed on the shoulder block, extends from the grounding end toward the shoulder main groove, and has an end portion that terminates in the shoulder block; and a second shoulder sipe that is formed in the shoulder block at an interval in the tire circumferential direction with respect to the first shoulder sipe, extends from the grounding end toward the shoulder main groove, and has an end portion that terminates in the shoulder block, wherein the end portion of the first shoulder sipe and the end portion of the second shoulder sipe are different in position of a tire width direction.

Specifically, the difference between the distance from the end portion of the first shoulder sipe to the shoulder main groove and the distance from the end portion of the second shoulder sipe to the shoulder main groove is 2 mm or more and 15 mm or less.

Providing the first and second shoulder sipes on the shoulder block improves the traction performance on the snowy road surface and ensures the traveling performance on the snowy road surface. In addition, since the end portions terminating in the shoulder blocks included in the first and second shoulder sipes are different in position of the tire width direction, it is possible to avoid the ground contact pressure in the shoulder block from concentrating in one position in the tire width direction, that is, in one straight line extending in the tire circumferential direction. As a result, braking performance on the dry road surface can be improved. The end portions of the first and second shoulder sipes terminate in the shoulder block. That is, both the first and second shoulder sipes are not in communication with the shoulder main groove. Therefore, the rigidity of the shoulder block can be ensured, and the wear-resistant performance can be improved.

Each of the first and second shoulder sipes may have a first portion that includes the end portion and extends in a first direction and a second portion that is continuous to the first portion and extends at an angle different from the first direction.

By having the first portion and the second portion that extend at different angles, it is possible to avoid matching between the first and second shoulder sipes with the grounding shape, and it is possible to reduce impact noise when traveling on the dry road surface in particular. That is, such the constitution can improve noise performance.

Specifically, the angle formed between the first portion and the tire width direction may be 10 degrees or more and 40 degrees or less.

The angle formed between the second portion and the tire width direction may be 0 degrees or more and 30 degrees or less.

The length of the first portion may be 5% or more and 30% or less of the length of the second portion.

The pneumatic tire may include a recess formed in a portion facing the shoulder main groove of the shoulder block.

This constitution can further improve traction performance on the snowy road surface.

The recess may be provided at a position corresponding to a region between the end portion of the first shoulder sipe and the end portion of the second shoulder sipe in the tire circumferential direction.

Providing the recess portion at such the position homogenizes the distribution of the edge component included in the shoulder block. That is, uneven distribution of the edge component in the shoulder block can be avoided. As a result, a better traction performance is obtained on the snowy road surface.

The pneumatic tire according to the present invention can realize improvement in braking performance on the dry road surface and improvement in wear-resistant performance while ensuring traveling performance on the snowy road surface.

An embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, FIG. 1 and FIG. 2 will be mainly referred to. For the other drawings, the drawings to be referred to are mentioned in the individual descriptions.

In the present description, the term “groove” means a notch having a certain width of, for example, about 2.5 mm or more, and the term “sipe” means a notch thinner than “groove” and having a width of, for example, 0.8 mm or more and 1.5 mm or less.

A pneumatic tire 1 (hereinafter simply referred to as a tire) according to the embodiment of the present invention is an all-weather, all-season tire that is suitable for traveling on a dry road surface but can also travel on a snowy road surface. In the figure, a reference symbol CD indicates a tire circumferential direction, and a reference symbol WD indicates a tire width direction. In the figure, a reference symbol CE indicates a center line in the tire width direction of a tread portion of the tire 1. Reference symbols GEa and GEb indicate grounding ends of a tread portion 2. A reference symbol CF indicates a grounding shape. The grounding ends GEa and GEb and the grounding shape CF are under the condition of 220 kPa/490 kgf.

The tread portion 2 is formed with four main grooves 3A, 3B, 4A, and 4B each extending in the tire circumferential direction. In the present embodiment, each of the main grooves 3A, 3B, 4A, and 4B is a linear groove having a certain groove width. The main grooves 3A, 3B, 4A, and 4B may have distribution in the groove width in the tire circumferential direction, or may be meandering or zigzag grooves.

The center main grooves 3A and 3B are arranged adjacent to each other across the center line CE. The shoulder main grooves 4A and 4B are arranged on the grounding end GEa and GEb sides. The shoulder main groove 4A is arranged on an outer side in the tire width direction with respect to the center main groove 3A, that is, adjacent to the grounding end GEa side. The shoulder main groove 4B is arranged on an outer side in the tire width direction with respect to the center main groove 3B, that is, adjacent to the grounding end GEb side.

The tread portion 2 is provided with five types of lateral grooves (lag grooves) 5, 6A, 6B, 7A, and 7B each extending generally in the tire width direction.

A plurality of the center lateral grooves 5 are provided at regular intervals in the tire circumferential direction. Both end portions of each of the center lateral grooves 5 are in communication with the center main grooves 3A and 3B. Each of the center lateral grooves 5 is linear as a whole, and is inclined with respect to the tire width direction so as to be downward-sloping in the figure. Each of the center lateral grooves 5 includes a first portion 5a communicating with the center main groove 3A, a second portion 5b communicating with the center main groove 3B, and a third portion 5c between the first portion and the second portion. The groove depth of the third portion 5c is shallower than the first and second portions 5a and 5b.

A plurality of the mediate lateral grooves 6A are provided at regular intervals in the tire circumferential direction. Each of the mediate lateral grooves 6A includes a first portion 6a communicating with the center main groove 3A and a second portion 6b communicating with the shoulder main groove 4A. The first portion 6a is inclined with respect to the tire width direction so as to be downward-sloping in the figure. The second portion 6b is inclined with respect to the tire width direction so as to be upward-sloping in the figure. That is, each of the mediate lateral grooves 6A has a bent shape bent at a bent portion 6c. The first portion 6a is sufficiently shorter in length than the second portion 6b. The first portion 6a is shallower in groove depth than the second portion 6b. A tapered portion 6d is provided on a groove wall at a connecting portion of the second portion 6b with the shoulder main groove 4A.

A plurality of the shoulder lateral grooves 7A are provided at regular intervals in the tire circumferential direction. Each of the shoulder lateral grooves 7A includes a first portion 7a communicating with the shoulder main groove 4A and a second portion 7b extending outward in the tire width direction beyond the grounding end GEa. The first and second portions 7a and 7b are both inclined with respect to the tire width direction so as to be upward-sloping in the figure. That is, each of the shoulder lateral grooves 7A has a bent shape slightly bent at a bent portion 7c. The inclination angle of the first portion 7a with respect to the tire width direction is larger than that of the second portion 7b. The first portion 7a is shallower in groove depth than the second portion 7b.

One center block 11 is defined by the center main grooves 3A and 3B and the two center lateral grooves 5 adjacent in the tire circumferential direction. A plurality of the center blocks 11 are aligned in the tire circumferential direction. Each of the center blocks has a parallelogram shape that is elongated in the tire circumferential direction as viewed in a tire radial direction.

One mediate block 12A is defined by the center main groove 3A, the shoulder main groove 4A, and the two mediate lateral grooves 6A adjacent in the tire circumferential direction. A plurality of the mediate blocks 12A are aligned in the tire circumferential direction. As described above, since the mediate lateral groove 6A has a bent shape, the individual mediate blocks 12A also have a bent shape as viewed in the tire radial direction. That is, each of the mediate blocks 12A has, on the center main groove 3A side, a first portion 12a that is inclined with respect to the tire width direction so as to be downward-sloping in the figure and is relatively short in length. Each of the mediate blocks 12A has, on the shoulder main groove 4A side, a second portion 12b that is inclined with respect to the tire width direction so as to be upward-sloping in the figure and is relatively long in length. Each of the mediate blocks 12A has a shape elongated in the tire width direction overall.

One shoulder block 13A is defined by the shoulder main groove 4A and the two shoulder lateral grooves 7A adjacent in the tire circumferential direction. A plurality of the shoulder blocks 13A are aligned in the tire circumferential direction. As described above, since the shoulder lateral grooves 7A have a slightly bent shape, each of the shoulder blocks 13A also has a first portion 13a that is relatively steep upward-sloping and is short in length and a second portion 13b that is relatively gentle upward-sloping and is long in length, as viewed in the tire radial direction. Each of the shoulder blocks 13A has a shape elongated in the tire width direction overall. The second portion 13b of the shoulder block 13A extends outward in the tire width direction beyond the grounding end GEa.

The mediate block 12A and the shoulder block 13A are provided at the identical pitch in the tire circumferential direction. On the other hand, the center block 11 is provided in the tire circumferential direction at a pitch twice the pitch of the mediate block 12A and the shoulder block 13A. That is, the one center block 11 is provided for the two mediate blocks 12A and the two shoulder blocks 13A. Therefore, as described above, the mediate block 12A and the shoulder block 13A have a shape elongated in the tire width direction, whereas the center block 11 has a shape elongated in the tire circumferential direction.

The pattern of the tread portion 2 of the present embodiment has a symmetry with respect to the center line CE. That is, the shape and structure of the mediate lateral groove 6B, the shoulder lateral groove 7B, the mediate block 12B, and the shoulder block 13B on the right side (grounding end GEb side) with respect to the center line CE in the figure are identical to those of the mediate lateral groove 6A, the shoulder lateral groove 7A, the mediate block 12A, and the shoulder block 13A, except being reversed upside down in the figure. In the figure, the elements included in the mediate lateral groove 6B and the like are given similar or identical reference symbols as the elements included in the mediate lateral groove 6A and the like. In the following description, unless otherwise necessary, the mediate lateral groove 6A, the shoulder lateral groove 7A, the mediate block 12A, and the shoulder block 13A on the left side (grounding end GEa side) with respect to the center line CE in the figure will be described.

One center sipe 21 is formed in each of the center blocks 11. The center sipe 21 extends from one side portion to the other side portion of the center block 11 in the tire width direction and crosses the center block 11 in the tire width direction. The center sipe 21 has a reverse S-shape extending in the tire circumferential direction as a whole, and is provided, in a continuous manner, with a first widthwise protrusion portion 21a projecting to the right side (grounding end GEb side) in the figure, and a second widthwise protrusion portion 21b projecting in the opposite direction to the first widthwise protrusion portion 21a, i.e., the left side (grounding end GEa side) in the figure. In other words, the center sipe 21 has an amplitude in the tire width direction. The other structure of the center block 11 will be described later.

One mediate sipe 22A is formed in each of the mediate blocks 12A. The mediate sipe 22A includes a first portion 22a, a second portion 22b, and a third portion 22d, each of which is linear. The first portion 22a includes an end portion terminating in the mediate block 12A, and is inclined with respect to the tire width direction so as to be downward-sloping in the figure. The end portion of the first portion 22a is positioned near the center main groove 3A. The second portion 22b is connected to the first portion 22a via a bent portion 22c, and is inclined with respect to the tire width direction so as to be upward-sloping in the figure. The third portion 22d is connected to the second portion 22b via a bent portion 22e, and is inclined with respect to the tire width direction at a gentler angle than the second portion 22b so as to be upward-sloping in the figure. The end portion of the third portion 22d opposite to the bent portion 22e is in communication with the shoulder main groove 4A. The other structure of the mediate block 12A will be described later.

The mediate sipe 12A overall has a bent shape projecting upward in the tire circumferential direction in the figure. On the other hand, the mediate sipe 22B formed in the mediate block 12B has a bent shape projecting in the opposite direction to the mediate sipe 12A, i.e., downward in the tire circumferential direction in the figure.

Two shoulder sipes 23A and 24A are formed in each of the shoulder blocks 13A.

The shoulder sipe 23A overall extends from the grounding end GEa toward the shoulder main groove 3A. The shoulder sipe 23A includes a first portion 23a and a second portion 23b. The first portion 23a is generally straight, includes an end portion terminating in the shoulder sipe 23A, and is inclined with respect to the tire width direction so as to be upward-sloping in the figure. The end portion of the first portion 23a is positioned near the shoulder main groove 4A. The second portion 23b is generally straight, is connected to the first portion 23a via a bent portion 23c, and is inclined with respect to the tire width direction at a gentler angle than the first portion 23a so as to be upward-sloping in the figure. The second portion 23b extends outward in the tire width direction beyond the grounding end GEa.

The shoulder sipe 24A overall extends from the grounding end GEa toward the shoulder main groove 3A. The shoulder sipe 24A includes a first portion 24a and a second portion 24b. The first portion 24a is generally straight, includes an end portion terminating in the shoulder block 13A, and is inclined with respect to the tire width direction so as to be upward-sloping in the figure. The end portion of the first portion 24a is positioned near the shoulder main groove 4A. The second portion 24b is generally straight, is connected to the first portion 24a via a bent portion 24c, and is inclined with respect to the tire width direction at a gentler angle than the first portion 24a so as to be upward-sloping in the figure. The second portion 24b extends outward in the tire width direction beyond the grounding end GEa.

The other structure of the shoulder block 13A will be described later.

Next, the center block 11 will be further described with reference to FIG. 3.

As described above, one center block 11 is provided with the two mediate blocks 12A and the two shoulder blocks 13A, and has a shape elongated in the tire circumferential direction. Specifically, a length (dimension in the tire circumferential direction) BL1 of the center block 11 is set to be not less than twice and not more than 5 times a width (dimension in the tire width direction) BW1 of the center block 11.

As described above, the center sipe 21 formed in the center block 11 includes the first widthwise protrusion portion 21a projecting toward the right side (grounding end GEb side) in the figure and the second widthwise protrusion portion 21b projecting in the opposite direction, and the first and second widthwise protrusion portions 21a and 21b are continuously provided in the tire circumferential direction. The center sipe 21 includes a first linear portion 21c having one end connected to the first widthwise protrusion portion 21a and the other end communicating with the center main groove 3A. The first linear portion 21c is inclined with respect to the tire width direction so as to be downward-sloping in the figure. The center sipe 21 includes a second linear portion 21d having one end connected to the second widthwise protrusion portion 21b and the other end communicating with the center main groove 3B. The second linear portion 21d is inclined with respect to the tire width direction so as to be downward-sloping in the figure. The first and second widthwise protrusion portions 21a and 21b have flat portions 21e at their top portions.

The center sipe 21 has four bent portions 21f, 21g, 21h, and 21i, which are bent gently and smoothly. That is, the center sipe 21 does not have a sharply bent portion, that is, a bent portion.

In the figure, a distance DC1 from the upper end of the center block 11 to the end portion of the first linear portion 21c communicating with the center main groove 3A is set in a range of 5% or more and 25% or less of the length BL1 of the center block 11. In the figure, a distance DC2 from the lower end of the enter block 11 to the end portion of the second linear portion 21d communicating with the center main groove 3B is set in a range of 5% or more and 25% or less of the length BL1 of the center block 11. That is, both end portions of the center sipe 21 are positioned in a range of 55% or more and 85% or less of the length BL1 of the center block 11 from both end portions of the center block 11 in the tire circumferential direction.

As described above, the center sipe 21 has an amplitude in the tire width direction that is constituted by the first widthwise protrusion portion 21a and the second widthwise protrusion portion 21b, which project in the directions opposite to each other in the tire width direction. In FIG. 3, a reference symbol A1 indicates an amplitude amount of the center sipe 21. The amplitude amount A1 is a distance in the tire width direction from a center C1 of the center sipe 21 in the tire width direction (which matches the center line of the tread portion 2 in the present embodiment) to the top portions of the first and second widthwise protrusion portions 21a and 2 lb. The amplitude amount A1 is set to 10% or more and 40% or less of the width BW1 of the center block 11.

The center sipe 21 does not have a bent portion. The both end portions of the center sipe 21 are positioned in the range of 55% or more and 85% or less of the length BL1 of the center block 11 from the both end portions of the center block 11 in the tire circumferential direction, and positioned relatively in proximity to the both end portions of the center block 11 in the tire circumferential direction. The center sipe 21 has a large amplitude, that is, an amplitude of an amount of 60% or more and 85% or less of the width BW1 of the center block. The center sipe 21 has a smooth, large S-shape extending generally over the entire surface of the center block 11. Therefore, the ground contact pressure at the center block 11 is dispersed without being concentrated at one position, and hence the braking performance on the dry road surface can be improved. The two portions of the center block 11 divided by the center sipe 21 support each other at the time of braking, thereby suppressing collapse. As a result, braking performance and uneven wear-resistant performance can be improved.

The center block 11 is provided with notches 25A and 25B extending from both side portions in the tire width direction. The notches 25A and 25B have a tapered shape as viewed in the tire radial direction. The tips of the notches 25A and 25B are positioned between the first widthwise protrusion portion 21a and the second widthwise protrusion portion 21b in the tire circumferential direction. By forming the notches 25A and 25B in addition to the center sipe 21, the distribution of the edge component of the center block 11 is homogenized. That is, uneven distribution of the edge component in the center block 11 can be avoided. As a result, a better traction performance is obtained on the snowy road surface.

FIG. 4 shows an alternative of the center block 11. In the center block 11, not the flat portion (see the reference symbol 21e in FIG. 3) but the bent portion 21j is provided at the top portions of the first and second widthwise protrusion portions 21a and 21b.

FIG. 5 shows another alternative of the center block 11. The center block 11 has a structure in which the structure shown in FIG. 3 is reversed right and left. In particular, the direction in which the first and second widthwise protrusion portions 21a and 21b of the center sipe 21 project is opposite to that in the case of FIG. 3. Therefore, the center sipe 21 has an S shape overall.

Next, the mediate block 12A will be further described with reference to FIG. 6.

As described above, the mediate sipe 22A formed in the mediate block 12A includes the first portion 22a, which is downward-sloping straight, the second portion 22b, which is upward-sloping straight, and the third portion 22d, which is upward-sloping straight, and has a bent shape overall. According to such the bent shape, it is possible to avoid matching between the mediate sipe 22A with the grounding shape CF (see FIG. 1), and it is possible to reduce impact noise when traveling on the dry road surface in particular.

In order to avoid matching with the grounding shape CF while ensuring that the edge component functions on the snowy road surface, it is preferable to set the mediate sipe 22A as follows. First, an inclination angle θm1 of the first portion 22a with respect to the tire width direction is set to 30 degrees or more and 55 degrees or less. An inclination angle θm2 of the second portion 22b with respect to the tire width direction is set to 40 degrees or more and 65 degrees or less. An inclination angle θm3 of the third portion 22d with respect to the tire width direction is set to 25 degrees or more and 50 degrees or less. Furthermore, a length Lm1 of the first portion 22a is set to 8% or more and 20% or less of the sum of a length Lm2 of the second portion 22b and a length Lm3 of the third portion 22d.

As mentioned above, the end portion of the first portion 22a of the mediate sipe 22A terminates in the mediate block 12A. That is, the mediate sipe 22A is not in communication with the center main groove 3A. Therefore, it is possible to ensure the rigidity of the mediate block 12A, and possible to suppress the collapse of these blocks. As a result, braking performance and wear-resistant performance can be improved.

Next, the shoulder block 13A will be further described with reference to FIG. 7.

As described above, the shoulder sipes 23A and 24A are provided in the shoulder block 13A. The end portion of the shoulder sipe 23A on the shoulder main groove 4A side, i.e., the end portion of the first portion 23a terminating in the shoulder block 13A, and the end portion of the shoulder sipe 24A on the shoulder main groove 4A side, i.e., the end portion of the first portion 24a similarly terminating in the shoulder block 13A are different in position of the tire width direction. Specifically, a distance Ds1 between the end portion of the first portion 23a of the shoulder sipe 23A and the shoulder main groove 4A is shorter than a distance Ds2 between the end portion of the first portion 24a of the shoulder sipe 24A and the shoulder main groove 4A. The difference between the distance Ds1 and the distance Ds2 is set in a range of, for example, 2 mm or more and 15 mm or less.

Providing the shoulder sipes 23A and 24A on the shoulder block 13A improves the traction performance on the snowy road surface and ensures the traveling performance on the snowy road surface. Since the end portion of the first portion 23a of the shoulder sipe 23A and the end portion of the first portion 24a of the shoulder sipe 24A are different in position of the tire width direction, it is possible to avoid the ground contact pressure in the shoulder block 13A from concentrating in one position in the tire width direction, that is, in one straight line extending in the tire circumferential direction. As a result, braking performance on the dry road surface can be improved. Furthermore, the first portion 23a of the shoulder sipe 23A and the first portion 24a of the shoulder sipe 24A terminate in the shoulder block 13A. That is, each of the shoulder sipes 23A and 24A is not in communication with the shoulder main groove 4A. Therefore, the rigidity of the shoulder block 13A can be ensured, and the wear-resistant performance can be improved.

The first portion 23a and the second portion 23b of the shoulder sipe 23A are different in angle formed with respect to the tire width direction. Similarly, the first portion 24a and the second portion 24b of the shoulder sipe 24A are different in angle formed with respect to the tire width direction. By having the first portions 23a and 24a and the second portions 23b and 24b that extend at different angles, it is possible to avoid matching between the shoulder sipes 23A and 24A with the grounding shape CF (see FIG. 1), and it is possible to reduce impact noise when traveling on the dry road surface in particular. That is, such the constitution can improve noise performance.

In order to avoid matching with the grounding shape CF while ensuring that the edge component functions on the snowy road surface, it is preferable to set the shoulder sipes 23A and 24A as follows. First, an inclination angle θs1 of the first portions 23a and 24a with respect to the tire width direction is set to 10 degrees or more and 40 degrees or less. An inclination angle θs2 of the second portions 23b and 24b with respect to the tire width direction is set to 0 degrees or more and 30 degrees or less. Furthermore, a length Ls1 of the first portions 23a and 24a is set to 5% or more and 30% or less of a length Ls2 of the second portions 23b and 24b.

The shoulder block 13A is provided with a recess portion 26 in a portion facing the shoulder main groove 4A, i.e., a portion where the top wall and the side wall of the shoulder block 13A merge. A depth Dp of the recess portion 26 is set to, for example, 3 mm or more and 10 mm or less. With reference also to FIG. 8, the recess portion 26 of the present embodiment is constituted of a tapered surface 26a and a pair of side surfaces 26b opposed in the tire circumferential direction. Providing the recess portion 26 can further improve the traction performance on the snowy road surface.

The recess portion 26 is provided at a position corresponding to the region between the end portion of the first portion 23a of the shoulder sipe 23A and the end portion of the first portion 24a of the shoulder sipe 24A in the tire circumferential direction. Providing the recess portion 26 at such the position homogenizes the distribution of the edge component included in the shoulder block 13A. That is, uneven distribution of the edge component in the shoulder block 13A can be avoided. As a result, a better traction performance is obtained on the snowy road surface.

An alternative shoulder block 13A shown in FIG. 9 is provided with an additional shoulder sipe 27 of a similar shape between the shoulder sipes 23A and 24A.

In another alternative shoulder block 13A shown in FIG. 10, the first portions 23a and 24a of the shoulder sipes 23A and 24A have bent portions 23d and 24d.

In yet another alternative shoulder block 13A shown in FIG. 11, the first portions 23a and 24a and the second portions 23b and 24b of the shoulder sipes 23A and 24A are arc-shaped.