Pneumatic tire

A pneumatic tire includes a land portion having a circumferential direction sipe extending in a direction inclined with respect to the tire circumferential direction, a partial land portion positioned on at least one of the land portion partitioned with the circumferential direction sipe, and a plurality of cross sipes extending in a direction intersecting with the circumferential direction sipe in the partial land portion. The partial land portion includes a wide end portion and a narrow end portion. The plurality of cross sipes include a wide portion sipe located closest to a wide end of the partial land portion, and a narrow portion sipe located closest to a narrow end of the partial land portion. The wide portion sipe has a distal end positioned in a sipe projection portion, and the narrow portion sipe has a distal end positioned in a non-sipe projection portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Japanese Patent Application No.: 2017-88811 filed on Apr. 27 2017, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a pneumatic tire.

Related Art

It is known that in a pneumatic tire including land portions (for example, ribs) partitioned with plurality of main grooves extending in a tire circumferential direction, forming circumferential direction sipes extending in a direction slanting toward the tire circumferential direction in the land portions increases the groove volume to improve drainage performance (for example, see Japanese Unexamined Patent Application Publication No. 2014-162295).

SUMMARY

However, when the circumferential direction sipes are slanted toward the tire circumferential direction, partial land portions partitioned in the tire width direction with the circumferential direction sipes have different widths in the tire circumferential direction. That is, when the circumferential direction sipe extends in a direction slanting toward one side in the tire width direction as the circumferential direction sipe goes to one side in the tire circumferential direction, the partial land portions partitioned on the other side in the tire width direction of the circumferential direction sipe have widths in the tire width direction increasing toward one side in the tire circumferential direction.

In this case, since the partial land portion has the configuration in which an end portion on one side in the tire circumferential direction is relatively wide, whereas an end portion on the other side in the tire circumferential direction is relatively narrow, the rigidity of the end portion on one side becomes relatively high and the rigidity of the end portion on the other side becomes relatively low. As a result, the rigidity difference between both end portions of the partial land portion in the tire circumferential direction is increased, and uneven wear in the tire circumferential direction is increased.

It is an object of the present invention to provide a pneumatic tire having improved drainage performance due to the formation of a circumferential direction sipe extending in a direction slanting toward the tire circumferential direction in the land portion, the pneumatic tire being capable of suppressing uneven wear in the tire circumferential direction.

The present invention provides a pneumatic tire including a main groove extending in a tire circumferential direction; a lateral groove extending in a tire width direction; and a land portion defined by the main groove and the lateral groove. The land portion includes a circumferential direction sipe extending in a direction inclined with respect to the tire circumferential direction and partitioning the land portion, a partial land portion positioned on at least one side in a tire width direction of the land portion with respect to the circumferential direction sipe, and a plurality of cross sipes extending in a direction intersecting with the circumferential direction sipe in the partial land portion. The partial land portion includes a wide end portion relatively wide on one side and a narrow end portion relatively narrow on the other side in the tire circumferential direction. The plurality of cross sipes include a wide portion sipe located closest to a wide end of the partial land portion in the tire circumferential direction and a narrow portion sipe located closest to a narrow end of the partial land portion in a tire circumferential direction. The wide portion sipe has a distal end, positioned closer to the circumferential direction sipe, which is positioned in a sipe projection portion defined by a projection of the circumferential direction sipe in the tire circumferential direction. The narrow portion has a distal end, positioned closer to the circumferential direction sipe, which is positioned in a non-sipe projection portion which is a portion other than the sipe projection portion of the partial land portion.

According to the present invention, in the wide end portion being wider in width of the partial land portion, the wide portion sipe bites into the sipe projection portion, and in the narrow end portion being narrower in width of the partial land portion, the narrow portion sipe does not bite into the sipe projection portion and terminates in the non-sipe projection portion. As a result, while the rigidity of the wide end portion, which is likely to have relatively high rigidity, is effectively lowered, reduction in the rigidity of the narrow end portion, which is likely to have relatively low rigidity, is suppressed.

That is, since the rigidity difference between the end portions in the tire circumferential direction of the partial land portion defined by the circumferential direction sipe is reduced while the circumferential direction sipe extending slantingly toward the tire circumferential direction is formed in the land portion, uneven wear in the tire circumferential direction can be suppressed.

Preferably, the distal end of the wide portion sipe is positioned in a range of one third of the sipe projection portion which is located closer to the circumferential direction sipe in the tire width direction.

According to the present configuration, since the wide portion sipe is configured to be sufficiently long, the rigidity of the wide end portion can be sufficiently reduced with the wide portion sipe.

In addition, preferably, the distal end of the narrow portion sipe is positioned in a range of one third of the non-sipe projection portion which is located closer to the sipe projection portion in the tire width direction.

According to the present configuration, since the narrow portion sipe is configured to be appropriately long, the rigidity of the narrow end portion can be appropriately reduced with the narrow portion sipe.

In addition, preferably, the plurality of cross sipes are formed in each of a pair of the partial land portions positioned adjacent to each other in a tire circumferential direction across the lateral groove. A difference in distances from the lateral groove to a respective pair of the cross sipes positioned closest to the lateral groove in each of the pair of partial land portions in the tire circumferential direction, is not larger than 10% of a longer distance of the distances. Furthermore, each of distances in a tire circumferential direction from the lateral groove to each of the pair of cross sipes positioned adjacent to each other in a tire circumferential direction across the lateral groove may be is not smaller than 7% and not larger than 35% of a length in a tire circumferential direction of the partial land portion in which each of the pair of cross sipes is formed.

According to the present configuration, since the rigidity between the partial land portions adjacent in the tire circumferential direction across the lateral groove is substantially equalized, uneven wear in the tire circumferential direction can be further suppressed.

In addition, preferably, the lateral groove extends in a direction crossing at a crossing angle θ1to a tire circumferential direction. The pair of cross sipes positioned adjacent to each other in a tire circumferential direction across the lateral groove extend at crossing angles θ2and θ3to a tire circumferential direction. Each of differences in angle from the crossing angle θ1to crossing angle θ2and θ3is not larger than 10% of the crossing angle θ1.

According to the present configuration, since a pair of cross sipes positioned closest to both sides in the tire circumferential direction across the lateral groove extend substantially parallel to the lateral groove, the rigidity of the end portion of the partial land portion in the tire circumferential direction is easily reduced substantially uniformly over the tire width direction. Thus, since increase or decrease in local rigidity in the tire width direction is suppressed, uneven wear in the tire width direction can also be suppressed while uneven wear in the tire circumferential direction is suppressed.

In addition, the plurality of cross sipes are formed on at least one of the partial land portions partitioned in a tire width direction with the circumferential direction sipe. Preferably, the plurality of cross sipes are formed in at least the partial land portions partitioned on an outer side in a tire width direction with the circumferential direction sipe.

According to the present configuration, forming a plurality of cross sipes in the tire width direction outer side portion of land portions susceptible to deformation in the tire width direction and the tire circumferential direction particularly in a grounded state allows the uneven wear caused by the deformation to be suppressed even more effectively.

In addition, preferably, the distal end of the wide portion sipe communicates with the circumferential direction sipe.

In addition, preferably, the circumferential direction sipe slants toward a tire circumferential direction at a slanting angle of 10° or less.

According to the present invention, uneven wear in the tire circumferential direction can be suppressed in a pneumatic tire having improved drainage performance due to the formation of a circumferential direction sipe extending in a direction slanting toward the tire circumferential direction in the land portion.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, an embodiment according to the present invention will be described with reference to the accompanying drawings. It should be noted that the following description is, fundamentally, merely illustrative and is not intended to limit the present invention, products to which the present invention is applied, or applications of the present invention. In addition, the drawings are schematic, and the ratio and the like of each dimension are different from actual ones.

FIG. 1is a plan view showing a developed tread pattern of a tread portion2of a pneumatic tire1according to an embodiment of the present invention. It should be noted that for convenience of explanation, the direction toward the right side in the drawing in the tire circumferential direction is referred to as F side, and the direction toward the left side in the drawing is referred to as R side.

As shown inFIG. 1, four main grooves11to14extending in the tire circumferential direction are formed in the tread portion2. Specifically, two central main grooves11and12are formed in a substantially central portion in the tire width direction, and two outer main grooves13and14are respectively formed on the outside of these two central main grooves11and12in the tire width direction. The central main grooves11and12are positioned on both sides across a tire equator line CL.

A center land portion3is partitioned between the central main grooves11and12. A mediate land portion4is partitioned between the central main groove11and the outer main groove13, and a mediate land portion5is partitioned between the central main groove12and the outer main groove14. Furthermore, shoulder land portions6and7are respectively partitioned outside the outer main grooves13and14in the tire width direction.

That is, the tread portion2is configured as a rib pattern including the five land portions3to7extending in the tire circumferential direction with the four main grooves11to14extending in the tire circumferential direction.

In the center land portion3, a lug groove21and a width direction sipe40(cross sipe) extending in the tire width direction and a circumferential direction sipe23extending in the tire circumferential direction are formed.

Herein, terms such as a circumferential direction sipe and a width direction sipe may be used, and these sipes mean those formed with a plate-shaped sipe blade in a tire vulcanization mold. In other words, the sipe means a groove in which the groove width is about 1.5 mm or less and the groove wall surfaces facing each other are in contact with each other in a grounded state.

In the following, the center land portion3will be described with reference toFIG. 2.

FIG. 2is an enlarged view of a portion A inFIG. 1. As shown inFIG. 2, a plurality of lug grooves21are formed at intervals in the tire circumferential direction, each lug groove21extends slantingly toward the F side in the tire circumferential direction from one end portion communicating with the central main groove11toward the central main groove12, and the other end communicates with the central main groove12. That is, the center land portion3is partitioned in the tire circumferential direction into a plurality of blocks30with the lug grooves21.

The circumferential direction sipe23extends in the tire circumferential direction between a pair of the lug grooves21and21positioned adjacent in the tire circumferential direction, and extends in a direction slanting toward the central main groove11from the lug groove21positioned on the F side in the tire circumferential direction toward the R side in the tire circumferential direction to reach the lug groove21positioned on the R side in the tire circumferential direction. A crossing angle θ0of the circumferential direction sipe23to the tire circumferential direction is set to 10° or less. That is, each of the blocks30is partitioned in the tire width direction with the circumferential direction sipe23into a pair of a first block31positioned on the side of the central main groove12and a second block32positioned on the side of the central main groove11.

It should be noted that since the crossing angle θ0to the tire circumferential direction is set to 10° or less in the circumferential direction sipe23, the circumferential direction sipe23is configured to be longer in length, and as a result, the groove volume effectively increases, and the drainage effect by the circumferential direction sipe23can be effectively exerted.

In the first block31, an end portion positioned on the R side in the tire circumferential direction is configured as a wide end portion31W having a relatively wide width, and an end portion positioned on the F side in the tire circumferential direction is configured as a narrow end portion31S having a relatively narrow width. In other words, the first block31is configured to be wider toward the R side in the tire circumferential direction.

In the second block32, an end portion positioned on the F side in the tire circumferential direction is configured as a wide end portion32W having a relatively wide width, and an end portion positioned on the R side in the tire circumferential direction is configured as a narrow end portion32S having a relatively narrow width. In other words, the second block32is configured to be narrower toward the R side in the tire circumferential direction.

A plurality of the width direction sipes40are formed in each of the first block31and the second block32. In the following, the width direction sipes40formed in the first block31will be described as an example.

The width direction sipes40include a wide portion sipe41formed closest to a wide end of the first block31, a narrow portion sipe42formed closest to a narrow end of the first block31, and an intermediate portion sipe43formed between the wide portion sipe41and the narrow portion sipe42in the tire circumferential direction.

Of the blocks30, the portion where the circumferential direction sipe23is projected in the tire circumferential direction is referred to as a sipe projection portion X0, the other portion is referred to as a non-sipe projection portion Y0, and the wide portion sipe41and the narrow portion sipe42are formed as follows in relation to the sipe projection portion X0and the non-sipe projection portion Y0.

The wide portion sipe41extends in the tire width direction from distal end41aon the side of the circumferential direction sipe23to the other end41bcommunicating with the central main groove12. Specifically, the distal end41aof the wide portion sipe41is positioned in the sipe projection portion X0, and more specifically, is positioned in a range X1(indicated by hatching inFIG. 2) of one third of the sipe projection portion X0which is located closer to the circumferential direction sipe23in the tire width direction. In other words, the wide portion sipe41bites into the sipe projection portion X0at least in a range of two third in the tire width direction and extends over the entire area of the non-sipe projection portion Y0.

The narrow portion sipe42extends in the tire width direction from distal end42aon the side of the circumferential direction sipe23to the other end42bcommunicating with the central main groove12. Specifically, the distal end42aof the narrow portion sipe42is positioned in the non-sipe projection portion Y0, and more specifically, is positioned in a range Y1(indicated by hatching inFIG. 2) of one third of the non-sipe projection portion Y0which is located closer to the circumferential direction sipe23in the tire width direction. In other words, the narrow portion sipe42extends in a range of at least two third to the non-sipe projection portion Y0in the tire width direction, and does not extend to the sipe projection portion X0.

In addition, regarding the pair of first blocks31partitioned on both sides in the tire circumferential direction across the lug groove21, the width direction sipes40formed in the first blocks31are formed to have the following relationship.

That is, a pair of the wide portion sipe41and the narrow portion sipe42positioned closest to the lug groove21in each of the pair of first blocks31are set so that the respective distances L1and L2from the lug groove21in the tire circumferential direction are substantially equal to each other. Specifically, in the pair of the wide portion sipe41and the narrow portion sipe42across the lug groove21, the difference between the distances L1and L2is not larger than 10% of the longer one of the distances L1and L2.

The distances L1and L2from the lug groove21are measured on a cross section taken along the tire circumferential direction in any tire width direction position, and are the distances from the edge portion in the tire circumferential direction of each of the blocks30partitioned by the lug groove21to the center position in the tire circumferential direction of the target width direction sipe40. It should be noted that inFIG. 2, as an example, the distances L1and L2at the edge portion of the first block31on the side of the central main groove12are shown. It should be noted that it is desirable that the distances L1and L2be set to be not less than 7% and not larger than 35%, preferably not less than 15% and not larger than 30% of the length L0in the tire circumferential direction of the first block31in order to reduce the rigidity of the wide end portion31W and the narrow end portion31S.

In addition, a crossing angle θ2of the wide portion sipe41to the tire circumferential direction and a crossing angle θ3of the narrow portion sipe42to the tire circumferential direction each are set to have an angle difference of 10% or less to the crossing angle θ1of the lug groove21to the tire circumferential direction.

FIG. 3is a cross-sectional view taken along line III-III inFIG. 2, and is a cross-sectional view taken along the width direction sipe40positioned on the R side in the tire circumferential direction of each of the blocks30as viewed in the tire circumferential direction. In the cross section shown inFIG. 3, the wide end portion31W of the first block31is shown on the right side in the drawing, and the narrow end portion32S of the second block32is shown on the left side in the drawing. That is, the wide portion sipe41is shown on the right side across the circumferential direction sipe23in the drawing, and the narrow portion sipe42is shown on the left side in the drawing.

As shown inFIG. 3, partition wall portions24are formed between each of the wide portion sipe41and the narrow portion sipe42and the circumferential direction sipe23. Although in each of the partition wall portions24, the inner portion in the tire radial direction is formed wider than the surface side, instead of this, as indicated with a two-dot chain line, each of the partition wall portions24may be configured to extend in the tire radial direction to have a constant width in the tire width direction.

In addition, the wide portion sipe41may be formed to communicate with the circumferential direction sipe23, and in this case, the partition wall portions24are not formed in the wide end portion31W of the first block31.

According to the pneumatic tire1described above, the following effects are obtained. It should be noted that in the following description, the first block31will be described as an example, but the same effects are also obtained in the second block32.

(1) In the wide end portion31W of the first block31, the wide portion sipe41bites into the sipe projection portion X0, and in the narrow end portion31S of the first block31, the narrow portion sipe42does not bite into the sipe projection portion X0and terminates in the non-sipe projection portion Y0. As a result, while the rigidity of the wide end portion31W, which is likely to have relatively high rigidity, is effectively lowered, excessive reduction in the rigidity of the narrow end portion31S, which is likely to have relatively low rigidity, is suppressed.

That is, since the rigidity difference between the wide end portion31W and the narrow end portion31S positioned at both ends in the tire circumferential direction of the first block31defined by the circumferential direction sipe23is reduced while the circumferential direction sipe23extending slantingly toward the tire circumferential direction is formed in each of the blocks30, uneven wear in the tire circumferential direction can be suppressed.

(2) Since the distal end41aof the wide portion sipe41on the side of the circumferential direction sipe23is positioned in the range X1of one third of the sipe projection portion X0which is located closer to the circumferential direction sipe23in the tire width direction, the wide portion sipe41is configured to be sufficiently long, so that the rigidity of the wide end portion31W can be sufficiently lowered with the wide portion sipe41.

(3) Since the distal end42aof the narrow portion sipe42on the side of the circumferential direction sipe23is positioned in the range Y1of one third of the non-sipe projection portion Y0which is located closer to the sipe projection portion X0in the tire width direction, the narrow portion sipe42is configured to be appropriately long, so that the rigidity of the narrow end portion31S can be appropriately lowered with the narrow portion sipe42.

(4) The pair of the wide portion sipe41and the narrow portion sipe42positioned on both sides in the tire circumferential direction across the lug groove21are set so that the distances L1and L2in the tire circumferential direction from the lug groove21interposed between the wide portion sipe41and the narrow portion sipe42are substantially equal to each other, and more specifically, the difference between the distances L1and L2is not larger than 10% of the longer one of the distances L1and L2. Since this substantially equalizes the rigidity between the first blocks31adjacent in the tire circumferential direction across the lug groove21, uneven wear in the tire circumferential direction can be further suppressed.

(5) Each of the crossing angle θ2of the wide portion sipe41to the tire circumferential direction and the crossing angle θ3of the narrow portion sipe42to the tire circumferential direction is set to have an angle difference of ±10% or less to the crossing angle θ1of the lug groove21to the tire circumferential direction. Since this causes the wide portion sipe41and the narrow portion sipe42to extend substantially parallel to the lug groove21, the rigidity of the end portion of the first block31in the tire circumferential direction is easily reduced substantially uniformly in the tire width direction. Thus, since increase or decrease in local rigidity in the tire width direction is suppressed, uneven wear in the tire width direction can also be suppressed while uneven wear in the tire circumferential direction is suppressed.

In the above embodiment, since the circumferential direction sipe23is formed so as to slant toward one side in the tire width direction, the wide end portion31W and the narrow end portion31S are aligned in the tire circumferential direction between the first blocks31(or the second blocks32) adjacent in the tire circumferential direction across the lug groove21. However, as shown inFIG. 4, the direction of slanting the circumferential direction sipe23toward the tire width direction may be changed for each of the plurality of blocks30formed in the tire circumferential direction.

In this case, between the first blocks31adjacent in the tire circumferential direction, the wide end portions31W are adjacent to each other across the lug groove21, or the narrow end portions31S are adjacent to each other across the lug groove21.

In addition, in the above embodiment, the width direction sipe40is configured as a notch continuously extending in the tire width direction from the central main groove12, but the width direction sipe40is not limited to this, and as shown inFIG. 5A, the width direction sipe40may be configured to intermittently extend in the tire width direction, or as shown inFIG. 5B, the width direction sipe40may be configured as a plurality of hole portions drilled at intervals in the tire width direction, and although illustration is omitted, they may be combined to be configured. In any case, the width direction sipe40may be configured to reduce the rigidity of the blocks30.

In addition, in the above embodiment, a case where the plurality of width direction sipes40are formed in each of the first block31and the second block32partitioned in the tire width direction with the circumferential direction sipe23of each of the blocks30has been described as an example, but the present invention is not limited to this, and the plurality of width direction sipes40may be formed only on any one side of the first block31and the second block32.

For example, inFIG. 6, a case where the circumferential direction sipe23and the width direction sipe40are formed in the mediate land portions4and5are exemplified, and in this case, the plurality of width direction sipes40may be formed only in the first block31positioned on the outer side in the tire width direction of the first block31and the second block32partitioned in the tire width direction with the circumferential direction sipe23. In particular, applying the plurality of width direction sipes40to the first block31positioned on the outer side in the tire width direction, the first block31susceptible to deformation input in the tire width direction and the tire circumferential direction during grounding, further suppresses uneven wear, and the present invention can be performed more favorably.

In addition, in the above embodiment, a case where the center land portion3is partitioned into the plurality of blocks30with the lug groove21has been described as an example, but the present invention is not limited to this. As shown inFIG. 7, the present invention is also applied to a rib pattern configured to cause the lug groove21to extend in the tire width direction from one end portion communicating with the central main groove11to terminate in the middle of the center land portion3in the tire width direction without communicating with the central main groove12.

Also in this case, the circumferential direction sipe23only has to be formed in a portion formed between the pair of lug grooves21adjacent to each other in the tire circumferential direction, and the plurality of width direction sipes40only have to be formed in the partial land portion partitioned on the side of the central main groove11.

In addition, in the above embodiment, the width direction sipe40has been described as an example of a sipe extending in the tire width direction, however, the present invention is not limited to the above embodiment. That is, the sipe may be configured as a cross sipe extending in a direction crossing the extending direction of the circumferential direction sipe23.

In addition, in the above embodiment, the intermediate portion sipe43is formed between the wide portion sipe41and the narrow portion sipe42, but the intermediate portion sipe43may not be formed. In addition, even when the intermediate portion sipe43is formed, there is no particular limitation, and a plurality of intermediate portion sipes43may be formed, in addition, the intermediate portion sipe43may be formed so as to terminate in the sipe projection portion X0or the non-sipe projection portion Y0, further, the intermediate portion sipe43may communicate with the circumferential direction sipe23.