Pneumatic tire

A pneumatic tire includes a center land portion, intermediate land portions, and shoulder land portions each with sipes arranged at intervals in a circumferential direction. Center land sipes have a widened portion with a wide groove width at one end. Shoulder land sipes extend from the outer side of a ground contact end in a lateral direction toward an outer main groove. The orientation of the center and shoulder land sipes with respect to the circumferential direction is opposite to the orientation of intermediate land sipes. Respective inclination angles θCE, θMD, θSH of the center, intermediate and shoulder land sipes satisfy θCE<θMD<θSH<90°, an end of the intermediate land sipe on the side of the inner main groove is between ends of the center land sipes, and at any position on the entire circumference at least one center or intermediate land sipe is present on a meridian.

TECHNICAL FIELD

The present technology relates to a pneumatic tire suitable as an all-season tire and particularly relates to a pneumatic tire that can improve snow performance while suppressing the occurrence of pattern noise.

BACKGROUND ART

In all-season tires, there is a demand to exhibit excellent snow performance during snowfall. In the known all-season tire, land portions defined by a plurality of main grooves each are provided with a plurality of sipes, thereby increasing edge components to improve snow performance (for example, see Japan Unexamined Patent Publication No. 2014-205410). However, depending on the arrangement of the sipes provided in the tread portion, there is a problem that variations in the area of grooves at the ground contact leading edge are large, to easily generate pattern noise is easily generated.

SUMMARY

The present technology provides a pneumatic tire that can improve snow performance while suppressing pattern noise.

A pneumatic tire according to an embodiment of the present technology for achieving the above-described object includes: an annular tread portion extending in a tire circumferential direction; a pair of sidewall portions disposed on both sides of the tread portion; and a pair of bead portions disposed inward of the sidewall portions in a tire radial direction, the tread portion being provided with four main grooves including a pair of outer main grooves and a pair of inner main grooves that extend in the tire circumferential direction, the main grooves defining a center land portion, a pair of intermediate land portions located outward of the center land portion, and a pair of shoulder land portions located outward of the intermediate land portions, wherein the center land portion, the intermediate land portions, and the shoulder land portions each are provided with a plurality of sipes arranged at intervals in the tire circumferential direction, the sipes in the center land portion each have a widened portion formed with a wide groove width at one end, the sipes in the shoulder land portions each extend from an outer side of a ground contact end in a tire lateral direction toward the outer main groove, orientation of the sipes in the center land portion and the shoulder land portions with respect to the tire circumferential direction is opposite to orientation of the sipes in the intermediate land portions, an inclination angle θCEof the sipes in the center land portion with respect to the tire circumferential direction, an inclination angle θMDof the sipes in the intermediate land portions with respect to the tire circumferential direction, and an inclination angle θSHof the sipes in the shoulder land portion with respect to the tire circumferential direction satisfy a relationship θCE<θMD<θSH<90°, an end of the sipe in the intermediate land portion on the side of the inner main groove is disposed between ends of the adjacent sipes in the center land portion in the tire circumferential direction, and at any position on the entire circumference of the tire, at least one of the sipe in the center land portion and the sipe in the intermediate land portion is present on a tire meridian.

According to the present technology, the center land portion, the intermediate land portions, and the shoulder land portions each are provided with the plurality of sipes arranged at intervals in a tire circumferential direction, the sipes of the center land portion each have the widened portion formed with a wide groove width at one end thereof, and the sipes of the shoulder land portion each extend from the outer side of the ground contact end in a tire lateral direction toward outer main groove. Therefore, snow performance (particularly steering stability performance on snow-covered road surfaces) can be improved while efficiently increasing edge components. Additionally, since the orientation of the sipes in the center land portion and the shoulder land portions with respect to the tire circumferential direction is opposite to the orientation of the sipes in the intermediate land portions, the sipes in the land portions appropriately acts on the ground contact leading edge, and since the inclination angle θCEof the sipes, the inclination angle θMDof the sipes, and the inclination angle θSHof the sipe satisfy the relationship θCE<θMD<θSH<90°, the generation of pattern noise can be suppressed while improving snow performance. Further, since the end of the sipe in the intermediate land portion on the side of the inner main groove is disposed between ends of the adjacent sipes in the center land portion in the tire circumferential direction, and at any position on the entire circumference of the tire, at least one of the sipe in the center land portion and/or the sipe in the intermediate land portion is present on the tire meridian, variations in the area of the grooves at the ground contact leading edge can be suppressed, reducing the occurrence of pattern noise.

According to the present technology, it is preferred that the sipes in the shoulder land portions do not communicate with the outer main groove. This can suppress reduction in the block rigidity of the shoulder land portions, thereby suppressing the occurrence of pattern noise.

According to the present technology, it is preferred that a width W1of the center land portion, a width W2of the intermediate land portion, and a width W3of the shoulder land portion in a ground contact region satisfy a relationship W1<W2<W3. As a result, edge components that contribute to the improvement of snow braking and snow traction can be increased, effectively improving snow performance.

According to the present technology, it is preferred that a plurality of lug grooves extending in the tire circumferential direction while intersecting with the sipe in the intermediate land portion are provided in the intermediate land portions, and one end of the lug groove opens to the outer main groove, and an other end terminates within the intermediate land portion. Since the plurality of lug grooves extending in the tire circumferential direction while intersecting with the sipe in the intermediate land portion are provided, snow performance can be improved and variations in the area of the grooves at the ground contact leading edge can be reduced. Additionally, since one end of the lug groove opens to the outer main groove, and the other end terminates within the intermediate land portion, the occurrence of pattern noise can be suppressed.

According to the present technology, the lug grooves of the intermediate land portions each preferably have an acute bent portion. As a result, edge components can be increased, thereby effectively improving snow performance.

According to the present technology, the sipes are grooves having a groove width of 1.5 mm or less. The ground contact end is an outermost position of the ground contact region in the tire lateral direction. The “ground contact region” refers to a region in the tire lateral direction corresponding to the maximum linear distance in the tire lateral direction of a ground contact surface formed on a flat plate when a tire is inflated to an air pressure, which corresponds to the maximum load capacity defined by the standards (JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.), TRA (The Tire and Rim Association, Inc.), ETRTO (The European Tyre and Rim Technical Organisation), and the like), and is placed vertically on the flat plate in a stationary state, and loaded with a load equivalent to 80% of the maximum load capacity.

DETAILED DESCRIPTION

Configurations of embodiments of the present technology will be described in detail below with reference to the accompanying drawings.FIGS.1to3illustrate a pneumatic tire according to an embodiment of the present technology. InFIGS.2and3, Tc indicates the tire circumferential direction and Tw indicates the tire lateral direction.

As illustrated inFIG.1, a pneumatic tire according to an embodiment of the present technology includes an annular tread portion1extending in the tire circumferential direction, a pair of sidewall portions2,2disposed on both sides of the tread portion1, and a pair of bead portions3,3disposed inward of the sidewall portions2in the tire radial direction.

A carcass layer4is mounted between the pair of bead portions3,3. The carcass layer4includes a plurality of reinforcing cords extending in the tire radial direction and is folded back around bead cores5disposed in each of the bead portions3from a tire inner side to a tire outer side. A bead filler6having a triangular cross-sectional shape formed from rubber composition is disposed on the outer circumference of the bead core5.

A plurality of belt layers7are embedded on the outer circumferential side of the carcass layer4in the tread portion1. The belt layers7each include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, the reinforcing cords being disposed between layers in a criss-cross manner. In the belt layers7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction falls within a range from 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers7. To improve high-speed durability, at least one belt cover layer8, formed by arranging reinforcing cords at an angle of, for example, not greater than 5° with respect to the tire circumferential direction, is disposed on an outer circumferential side of the belt layers7. Nylon, aramid, or similar organic fiber cords are preferably used as the reinforcing cords of the belt cover layer8.

Note that the tire internal structure described above represents a typical example for a pneumatic tire, and the pneumatic tire is not limited thereto.

As illustrated inFIG.2, four main grooves9extending in the tire circumferential direction are formed in the tread portion1. The main grooves9includes a pair of inner main grooves9A,9A located on both sides of the tire center line CL and a pair of outer main grooves9B,9B located on the outermost side in the tire lateral direction. The tread portion1is divided into land portions10in by the four main grooves9. The land portions10include a center land portion10A located on the tire center line CL, a pair of intermediate land portions10B,10B located outward of the center land portion10A in the tire lateral direction, and a pair of shoulder land portions10C,10C located outward of the intermediate land portions10B,10B in the tire lateral direction.

The center land portion10A, the intermediate land portions10B, and the shoulder land portions10C each are provided with a plurality of sipes11,12, and13, respectively, at intervals in the tire circumferential direction. Further, the intermediate land portions10B and the shoulder land portions10C each are provided with a plurality of lug grooves21,24inclined in the tire circumferential direction, respectively, at intervals in the tire circumferential direction.

Both ends of the sipes11in the center land portion10A communicate with the pair of inner main grooves9A,9A. That is, the sipe11is an open sipe. The sipe11has a single widened portion14formed with a wide groove width to increase edge components. The widened portion14is disposed on one side of the sipe11, and the sipe11communicates with the inner main groove9A via the widened portion14. Such sipes11are alternately disposed in the tire circumferential direction.

One end of the sipe12of the intermediate land portion10B communicates with the inner main groove9A, and the other end communicates with the outer main groove9B. That is, the sipe12is an open sipe. The sipe12has a structure divided into a plurality of sections by the lug grooves21, but the divided portions of the same sipe12are disposed on the same straight line.

Both ends of the sipe13in the shoulder land portion10C terminate within the shoulder land portion10C. That is, the sipe13is a closed sipe. The sipes13extend from the outer side of the ground contact end E in the tire lateral direction toward the outer main groove9B, improving snow performance.

The sipes11in the center land portion10A, the sipes12in the intermediate land portions10B, and the sipes13in the shoulder land portions10C are all inclined with respect to the tire circumferential direction. These sipes11to13are not inclined in the same direction with respect to the tire circumferential direction. In other words, the orientation of the sipes11in the center land portion10A with respect to the tire circumferential direction is the same as the orientation of the sipes13in the shoulder land portions10C, while the orientation of the sipes12in the intermediate land portions10B with respect to the tire circumferential direction is opposite to the orientation of the sipes11,13.

An inclination angle of the sipes11to13with respect to the tire circumferential direction is defined as θ. At this time, an inclination angle θCEof the sipes11in the center land portion10A, an inclination angle θMDof the sipes12in the intermediate land portions10B, and an inclination angle θSHof the sipes13in the shoulder land portion10C satisfy a relationship θCE<θMD<θSH<90°. The sipes13in the shoulder land portions10C are set to be substantially perpendicular to the tire circumferential direction. In particular, it is preferred that the inclination angle θCEranges from 60° to 75°, the inclination angle θMDranges from 70° to 85°, and the inclination angle θSHranges from 83° to 88°. Alternatively, it is preferred that a ratio of the inclination angle θCEto the inclination angle θMDranges from 85% to 95%, and a ratio of the inclination angle θMDto the inclination angle θSHranges from 80% to 95%. Note that the inclination angle θ is an inclination angle on the acute angle side of the sipe with respect to the tire circumferential direction.

As illustrated inFIG.3, an end12aof each sipe12in the intermediate land portion10B on the side of the inner main groove9A is disposed between ends11aof the adjacent sipes11in the center land portion10A on the side of the inner main groove9A in the tire circumferential direction. That is, the end12aof each sipe12is disposed in a section S in the tire circumferential direction that faces the inner main groove9A. Additionally, at any position on the entire circumference of the tire, at least one of the sipe11in the center land portion10A and/or the sipe12in the intermediate land portion10B is present on the tire meridian. In other words, when the tread portion1is cut along the tire lateral direction, the sipes11in the center land portion10A and the sipes12in the intermediate land portion10B are disposed so as to overlap each other in the tire circumferential direction.

In the pneumatic tire described above, the center land portion10A, the intermediate land portions10B, and the shoulder land portions10C each are provided with the plurality of sipes11to13, respectively, arranged at intervals in a tire circumferential direction, the sipes11in the center land portion10A each have the widened portion14formed with a wide groove width at one end thereof, and the sipes13in the shoulder land portions10C each extend from the outer side of the ground contact end E in the tire lateral direction toward outer main groove9B. Therefore, snow performance (particularly steering stability performance on snow-covered road surfaces) can be improved while efficiently increasing edge components. Since the orientation of the sipes11,13in the center land portion10A and the shoulder land portions10C with respect to the tire circumferential direction is opposite to the orientation of the sipes12in the intermediate land portions10B, the sipes11to13in the land portions10A to10C appropriately act on the ground contact leading edge, and since the inclination angle θCEof the sipes11, the inclination angle θMDof the sipes12, and the inclination angle θSHof the sipe13satisfy the relationship θCE<θMD<θSH<90°, the generation of pattern noise can be suppressed while improving snow performance. Additionally, since the end12aof the sipe12in the intermediate land portion10B is disposed between ends11aof the adjacent sipes11in the center land portion10A in the tire circumferential direction, and at any position on the entire circumference of the tire, at least one of the sipe11in the center land portion10A and/or the sipe12in the intermediate land portion10B is present on the tire meridian, variations in the area of the grooves at the ground contact leading edge can be suppressed, thereby reducing the occurrence of pattern noise.

InFIG.2, the sipes13in the shoulder land portions10C do not communicate with the outer main groove9B. With the sipe13of such a structure, a decrease in block rigidity in the shoulder land portion10C can be suppressed, thereby effectively suppressing the occurrence of pattern noise. In contrast, when the sipes13in the shoulder land portions10C communicate with the outer main grooves9B, block rigidity decreases, which disadvantageously leads to deterioration of pattern noise.

Additionally, a width W1of the center land portion10A, a width W2of the intermediate land portion10B, and a width W3of the shoulder land portion10C in the ground contact region satisfy a relationship W1<W2<W3. By setting the widths W1to W3of the land portions10A to10C so as to satisfy such relationship, edge components contributing to the improvement of snow braking and snow traction can be increased, effectively improving snow performance. Specifically, the width W3of the shoulder land portion10C in the ground contact region is the width from the end of the shoulder land portion10C on the side of the outer main groove9B to the ground contact end E.

Further, one end21aof the lug groove21in the intermediate land portion10B opens to the outer main groove9B, while the other end21bterminates in the intermediate land portion10B. The lug grooves21each intersect with the sipe12, and are disposed so as not to overlap each other in the tire circumferential direction. In particular, in order to improve snow performance, the lug groove21may preferably intersect with the plurality of sipes12. The lug groove21includes an acute bent portion22formed at a position between the one end21aand the other end21b. On the other hand, the lug grooves24in the shoulder land portions10C do not communicate with the outer main grooves9B. The lug grooves24in the shoulder land portions10C extend from the outer side of the ground contact end E in the tire lateral direction toward the outer main groove9B.

As described above, since the intermediate land portion10B includes the plurality of lug grooves21extending in the tire circumferential direction while intersecting with the sipe12in the intermediate land portion10B, snow performance can be improved, and variations in the area of the grooves at the ground contact leading edge can be reduced. Additionally, the one end21aof the lug groove21opens to the outer main groove9B, while the other end21bterminates in the intermediate land portion10B. Thus, the occurrence of pattern noise can be suppressed. Further, since each of the lug grooves21in the intermediate land portion10B has the acute bent portion22, edge components can be increased to effectively improve snow performance.

In the above-mentioned embodiments ofFIGS.2and3, the sipes11in the center land portion10A and the sipes12in the intermediate land portions10B each are an open sipe with both ends that communicate with the main grooves9and however, may be a semi-closed sipe with one end that does not communicate with the main groove9, or a closed-sipe with both ends that do not communicate with the main groove9.

Although the lug grooves24do not communicate with the outer main grooves9B in the above-mentioned embodiment inFIG.2, the lug grooves24may communicate with the outer main groove9B via another sipe. In this case, another sipe is a sipe extending along the tire lateral direction between an end of the lug groove24on the side of the outer main groove9B and the outer main groove9B.

Example

Tires in Examples 1 to 6 were produced by using a tire of a tire size 225/50R18 that includes: an annular tread portion extending in a tire circumferential direction; a pair of sidewall portions disposed on both sides of the tread portion; and a pair of bead portions disposed inward of the sidewall portions in the tire radial direction, the tread portion being provided with four main grooves including a pair of outer main grooves and a pair of inner main grooves that extend in a tire circumferential direction, the main grooves defining a center land portion, a pair of intermediate land portions located outward of the center land portion, and a pair of shoulder land portions located outward of the intermediate land portions, wherein the center land portion, the intermediate land portions, and the shoulder land portions each are provided with a plurality of sipes arranged at intervals in the tire circumferential direction, the sipes in the center land portion each have a widened portion formed with a wide groove width at one end, the sipes in the shoulder land portions each extend from an outer side of a ground contact end in a tire lateral direction toward the outer main groove, orientation of the sipes in the center land portion and the shoulder land portions with respect to the tire circumferential direction is opposite to orientation of the sipes in the intermediate land portions, an inclination angle θCE, an inclination angle θMD, and an inclination angle θSHof the sipes in the shoulder land portion satisfy a relationship θCE<θMD<θSH<90°, an end of the sipe in the intermediate land portion on the side of the inner main groove is disposed between ends of the adjacent sipes in the center land portion in the tire circumferential direction, and at any position on the entire circumference of the tire, at least one of the sipe in the center land portion and/or the sipe in the intermediate land portion is present on a tire meridian, under different conditions for positional relationship between the ends of the sipes in the center land portion and the intermediate land portion, the inclination direction of the sipes in each of the land portions with respect to the tire circumferential direction, the presence/absence of the non-overlapping locations of the sipes in the center land portion and the intermediate land portions, the configuration of the sipes in the shoulder land portions, the dimensional relationship between the widths W1, W2, W3of the land portions, the presence/absence of lug grooves in the intermediate land portions, the number of sipes intersecting with the lug grooves in the intermediate land portions, and the presence/absence of the bent portions in the lug grooves of the intermediate land portions, as indicated in Table 1.

For comparison, there was prepared a tire in Conventional Example having the same configuration as the tire in Example 1 except that the end of each sipe in the intermediate land portions on the side of the inner main groove is disposed opposed to the end of each sipe in the center land portions on the side of the inner main groove, the orientation of the center land portion, the intermediate land portions, and the shoulder land portions with respect to the tire circumferential direction is uniform, and at any position on the entire circumference of the tire, both of the sipe in the center land portion and the sipe in the intermediate land portions were not present on the tire meridian. Additionally, there were prepared a tire in Comparative Example 1 having the same configuration as the tire in Example 1 except that the orientation of the center land portion, the intermediate land portions, and the shoulder land portions with respect to the tire circumferential direction is uniform, and at any position on the entire circumference of the tire, both of the sipe in the center land portion and the sipe in the intermediate land portions were not present on the tire meridian, and a tire in Comparative Example 2 having the same configuration as the tire in Example 1 except that at any position on the entire circumference of the tire, both of the sipe in the center land portion and the sipe in the intermediate land portions were not present on the tire meridian.

Note that regarding “positional relationship between ends of sipes in the center land portion and the intermediate land portion” in Table 1, “uniform” means that the end of each sipe in the intermediate land portions on the side of the inner main groove is disposed opposed to the end of each sipe in the center land portions on the side of the inner main groove, and “non-uniform” means that the end of each sipe in the intermediate land portions on the side of the inner main groove is disposed between the ends of the adjacent sipes in the center land portion in the tire circumferential direction. Also, regarding “presence or absence of non-overlapping locations of sipes in center land portion and intermediate land portion” in Table 1, “Yes” means that at any position on the entire circumference of the tire, both of the sipe in the center land portion and the sipe in the intermediate land portions were not present on the tire meridian, and “No” means that at any position on the entire circumference of the tire, at least one of the sipe in the center land portion and the sipe in the intermediate land portions were not present on the tire meridian.

These test tires underwent a sensory evaluation by a test driver for steering stability performance on snow-covered road surfaces and pattern noise. The results thereof are shown in Table 1.

The sensory evaluation for steering stability performance on snow-covered road surfaces was performed with the test tires on a wheel with a rim size of 18×7 J mounted on a front-wheel drive vehicle. The evaluation results were shown as 10 grade evaluation values. Larger index values indicate superior steering stability performance on snow-covered road surfaces.

The sensory evaluation for pattern noise was performed with the test tires on a wheel with a rim size of 18×7 J mounted on a front-wheel drive vehicle. The evaluation results were shown as 10 grade evaluation values. Larger index values indicate superior suppressing effect on the occurrence of pattern noise.

As can be seen from Table 1, the tires in Examples 1 to 6 had improved steering stability performance on snow-covered road surfaces and pattern noise in a well-balanced manner as compared to the tire in Conventional Example.

In the tire of Comparative Example 1, the sipes in the center land portions, the intermediate land portions, and the shoulder land portions had the same orientation with respect to the tire circumferential direction, and at any position on the entire circumference of the tire, both of the sipes in the center land portion and the sipes in the intermediate land portion were not present on the tire meridian. Thus, sufficient improvement in steering stability performance on snow-covered road surfaces and pattern noise could not be achieved. In the tire in Comparative Example 2, since both of the sipes in the center land portion and the sipes in the intermediate land portion were not present on the tire meridian at any position on the entire circumference of the tire, sufficient improvement in pattern noise could not be achieved.