PNEUMATIC TIRE

To obtain a uniform ground contact pressure distribution in a pneumatic tire including a zigzag-shaped sipe. In a pneumatic tire according to an embodiment, a land portion formed in a tread portion is provided with a zigzag-shaped sipe extending in a tire circumferential direction. The zigzag-shaped sipe is formed in a zigzag shape by a plurality of lateral sipe portions arranged at intervals in the tire circumferential direction and a plurality of longitudinal sipe portions alternately connecting the end portions thereof. Each longitudinal sipe portion includes an extension portion in which one end portion (for example, an end portion on a rear side in a rotation direction) of both end portions in the tire circumferential direction extends to the one side beyond a connection portion with the lateral sipe portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2017-238876, filed on Dec. 13, 2017; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

An embodiment of the present invention relates to a pneumatic tire.

2. Description of the Related Art

Conventionally, a pneumatic tire in which a plurality of sipes are provided in a land portion formed in a tread portion is known for the purpose of improving performance of the pneumatic tire on icy and snowy roads.

For example, JP-A-2007-030686 discloses a structure with a zigzag-shaped sipe extending in a tire circumferential direction using a tire width direction as an amplitude direction as a structure easily obtaining moderate deflection for improving performance on ice. The zigzag-shaped sipe is formed in a zigzag shape by a plurality of lateral sipe portions arranged at intervals in the tire circumferential direction and a plurality of longitudinal sipe portions alternately connecting end portions of the lateral sipe portions. For that reason, there is a large difference in rigidity between a bag-shaped portion connected by the longitudinal sipe portion and an opening portion (a portion facing the bag-shaped portion in the tire width direction) not connected by the longitudinal sipe portion. Accordingly, since a ground contact pressure distribution becomes non-uniform, it is difficult to sufficiently exhibit performance such as traction performance, uneven wear resistance, and performance on ice.

SUMMARY

An object of an embodiment of the invention is to obtain a uniform ground contact pressure distribution in a pneumatic tire including a zigzag-shaped sipe.

A pneumatic tire according to an embodiment of the invention is a pneumatic tire in which a land portion formed in a tread portion is provided with a zigzag-shaped sipe extending in a tire circumferential direction, in which the zigzag-shaped sipe is formed in a zigzag shape by a plurality of lateral sipe portions arranged at intervals in the tire circumferential direction and a plurality of longitudinal sipe portions alternately connecting end portions of the lateral sipe portions, and each longitudinal sipe portion includes an extension portion in which one end portion out of both end portions in the tire circumferential direction of each longitudinal sipe portion extends to the one side beyond a connection portion with the lateral sipe portion.

According to the embodiment, it is possible to obtain a uniform ground contact pressure distribution in a tire including a zigzag-shaped sipe.

DETAILED DESCRIPTION

Although not illustrated in the drawings, a pneumatic tire according to an embodiment includes a pair of right and left bead portions, a pair of right and left sidewall portions, and a tread portion provided between both sidewall portions to connect outer end portions of the right and left sidewall portions in the radial direction and a general tire structure can be used for a structure other than a tread pattern.

As illustrated inFIG. 1, a tread rubber surface of a tread portion10is provided with a plurality of main grooves12extending in a tire circumferential direction CD and in this example, four main grooves are formed at intervals in a tire width direction WD. That is, a pair of center main grooves12A and12A provided at both sides of a tire equator CL and a pair of shoulder main grooves12B and12B respectively disposed at the outside thereof are provided. Four main grooves12are zigzag-shaped grooves which extend in the tire circumferential direction CD while being bent with an amplitude in the tire width direction WD. Furthermore, inFIG. 1, Reference Sign E indicates a ground contact end.

The pneumatic tire is a tire having a specified rotation direction and in the drawings, the rotation direction is indicated by Reference Sign R. The pneumatic tire is attached to a vehicle so that the tire rotates in a direction indicated by the arrow R when the vehicle runs forward. As a mark for this purpose, a display for designating the rotation direction is provided on, for example, the sidewall portion or the like of the pneumatic tire.

In the tread portion10, a plurality of land portions are divided by the main groove12in the tire width direction WD. Specifically, a center land portion14interposed between the pair of center main grooves12A and12A, a pair of right and left intermediate land portions16and16interposed between the center main groove12A and the shoulder main groove12B, and a pair of right and left shoulder land portions18and18located at the outside of the shoulder main groove12B in the tire width direction are provided. The intermediate land portion16and the shoulder land portion18are formed as a block row in which a plurality of blocks are arranged in the tire circumferential direction CD in such a manner that a plurality of lateral grooves20are provided at intervals in the tire circumferential direction CD. Meanwhile, the center land portion14is not divided by the lateral groove and is formed as a rib which is continuous in the entire circumference of the tire circumferential direction CD.

The embodiment has a characteristic in the configuration of the center land portion14and the configuration of the center land portion14will be described in detail below with reference toFIGS. 1 and 2.

The center land portion14is a rib which extends on the tire equator CL in the tire circumferential direction CD and a pair of right and left side walls22of the center land portion14is formed in a zigzag shape by the zigzag-shaped center main grooves12A and12A at both sides. Further, in the center land portion14, lateral grooves24not penetrating the center land portion14are alternately provided on the right and left sides at intervals in the tire circumferential direction CD. The lateral groove24is formed as a leading end portion of the lateral groove20on the extension line of the lateral groove20crossing the intermediate land portion16and the shoulder land portion18.

The center portion of the center land portion14is provided with a zigzag-shaped sipe26which continuously extends in the tire circumferential direction CD. In this example, the zigzag-shaped sipe26extends in the entire circumference of the tire circumferential direction CD on the tire equator CL at the center portion of the center land portion14in the width direction. The zigzag-shaped sipe26is a sipe which does not open the main groove12and is a wavy sipe in which the tire width direction WD substantially matches the amplitude direction. The sipe extends in the tire circumferential direction CD while swinging in the tire width direction WD with a predetermined amplitude. Furthermore, a width W (corresponding to double the amplitude) of the zigzag-shaped sipe26is not particularly limited and may be, for example, 8 to 20 mm.

As illustrated inFIG. 2, the zigzag-shaped sipe26is formed in a zigzag (that is, winding) cross-sectional shape by a plurality of lateral sipe portions28which are arranged at intervals in the tire circumferential direction CD and a plurality of longitudinal sipe portions30which alternately connect the end portions of the lateral sipe portions28at the right and left sides.

The lateral sipe portion28is a sipe which extends in the tire width direction WD and in this example, the lateral sipe portion has a straight cross-sectional shape and is inclined with respect to the tire width direction WD. The inclination angle with respect to the tire width direction WD is not particularly limited and may be, for example, 30° or less or 20° or less. In this example, the lateral sipe portions28and28which are adjacent to each other in the tire circumferential direction CD are not parallel to each other and are inclined in the opposite directions with respect to the tire width direction WD. A gap between the adjacent lateral sipe portions28and28is not particularly limited and may be, for example, 4 to 10 mm in the interval S at the amplitude center.

The longitudinal sipe portion30is a sipe which extends in the tire circumferential direction CD. In this example, the longitudinal sipe portion30has a straight cross-sectional shape and is inclined with respect to the tire circumferential direction CD. The inclination angle with respect to the tire circumferential direction CD is not particularly limited and may be, for example, 30° or less or 20° or less. The longitudinal sipe portion30is a sipe which alternately connects the facing end portions of the lateral sipe portions28and28adjacent to each other in the tire circumferential direction CD on the right and left sides in the tire circumferential direction CD and connects the end portions having a short distance therebetween in the adjacent lateral sipe portions28in both end portions of the lateral sipe portion28.

Each longitudinal sipe portion30includes an extension portion34which is formed by extending only one end portion out of both end portions in the tire circumferential direction CD of each longitudinal sipe portion30to one side beyond a connection portion32with the lateral sipe portion28. That is, the extension portion34is an extended portion of one end portion out of both end portions of the longitudinal sipe portion30to the one side beyond a connection portion32. In this example, each longitudinal sipe portion30is provided with the extension portion34in which only the end portion on the rear side RR in the rotation direction out of both end portions of each longitudinal sipe portion30goes beyond the connection portion32with the lateral sipe portion28, extends to the rear side RR, and is terminated. Here, the rear side RR in the rotation direction indicates an opposite direction with respect to the rotation direction R. In this way, each of the longitudinal sipe portions30alternately disposed at the right and left sides is formed so that the end portion on the rear side RR in the rotation direction protrudes to the rear side RR and the protruding portion is formed as the extension portion34.

In a land portion36between the pair of adjacent lateral sipe portions28and28, one end side of the tire width direction WD is connected by the longitudinal sipe portion30and is formed in a bag-shaped (that is, closed) portion38and the other end side thereof is formed in an opening portion40opening to the outside WO in the width direction of the zigzag-shaped sipe26. The extension portion34is provided so that an opening width of the opening portion40on the stepping side of the land portion36(the front side R in the rotation direction) decreases and is not provided on the kicking side of the land portion36(the rear side RR in the rotation direction). That is, the kicking side is not provided with the extension portion protruding toward the opening portion40from a bent portion42obtained by connecting the lateral sipe portion28and the longitudinal sipe portion30and the opening portion40is formed between the kicking side bent portion42and the stepping side extension portion34to open to the outside WO in the width direction. Here, the outside WO in the width direction indicates a direction moving away from the center (amplitude center) of the zigzag-shaped sipe26in the width direction and is the same as the outside of the tire width direction WD in this example.

The longitudinal sipe portion30is inclined to the outside WO in the width direction from the other end portion of the tire circumferential direction CD (the end portion opposite to the one end portion) toward the front end of the extension portion34. In this example, the longitudinal sipe portion30is provided to be inclined to the outside WO in the width direction toward the rear side RR in the rotation direction. That is, the longitudinal sipe portion is formed in a shape opening outward.

The zigzag-shaped sipe26is provided with a wide portion46having a groove width wider than that of a narrow portion44which is the other portion. In this example, the wide portion46is provided in a part of the lateral sipe portion28(specifically, about half the length) and is alternately disposed at the right and left sides in the tire circumferential direction CD. Meanwhile, all of the longitudinal sipe portion30is formed as the narrow portion44.

The groove width of the narrow portion44is not particularly limited and may be, for example, 0.1 to 0.6 mm or 0.2 to 0.5 mm. The groove width of the wide portion46is not particularly limited as long as the groove width is wider than the groove width of the narrow portion44and may be, for example, 0.3 to 1.0 mm or 0.5 to 0.8 mm. Furthermore, the groove depth of the zigzag-shaped sipe26is not particularly limited and may be, for example, 30 to 80% of the main groove depth.

The center land portion14is further provided with a triangular notch portion48provided at each of both side walls22and22and the notch portion48is provided at a plurality of positions at intervals in the tire circumferential direction CD. The center land portion14is further provided with a wavy sipe50extending in the tire width direction WD and having a wavy cross-sectional shape and a straight sipe52extending in the tire width direction WD and having a straight cross-sectional shape. The wavy sipe50and the straight sipe52are basically formed to open to the side wall22of the center land portion14and are terminated so as not to intersect the zigzag-shaped sipe26. The wavy sipe50and the straight sipe52are alternately disposed in the tire circumferential direction CD.

According to the pneumatic tire of the embodiment with the above-described configuration, since the zigzag-shaped sipe26is provided, it is possible to improve the traction performance or the braking performance in the longitudinal direction (the tire circumferential direction CD) by the lateral sipe portion28and to exhibit the edge effect in the lateral direction (the tire width direction WD) by the longitudinal sipe portion30. Accordingly, it is possible to improve the running performance such as performance on ice. Further, since the extension portion34is provided in each longitudinal sipe portion30, it is possible to improve the edge performance particularly in the lateral direction. At the same time, since it is possible to decrease the rigidity of the opening portion40by the extension portion34in the land portion36formed between the pair of lateral sipe portions28and28, it is possible to decrease a difference in rigidity between the bag-shaped portion38and the opening portion40and to obtain a uniform ground contact pressure distribution. For that reason, it is easy to exhibit the traction performance, the uneven wear resistance, or the performance on ice.

Further, since the extension portion34is provided on the stepping side of the land portion36and the extension portion34is not provided on the kicking side thereof, it is possible to ensure the rigidity of the kicking side bent portion42and to improve the braking performance.

Further, since the longitudinal sipe portion30is provided to be inclined to the outside WO in the width direction toward the front end of the extension portion34, it is possible to ensure a distance between the front end of the stepping side extension portion34and the kicking side bent portion42and to further ensure the rigidity of the portion.

Further, since the zigzag-shaped sipe26is provided with the wide portion46along with the narrow portion44, it is possible to maintain an edge effect or a water removal effect in the wide portion46even when the narrow portion44is closed at the time of braking the tire.

Furthermore, in the above-described embodiment, an example in which the zigzag-shaped sipe26is provided in the center land portion14extending on the tire equator CL has been described, but the zigzag-shaped sipe may be provided in the land portion not existing on the tire equator. Further, the number of the zigzag-shaped sipes is not particularly limited and may be plural. Further, the configuration of the intermediate land portion16or the shoulder land portion18is not limited to one illustrated inFIG. 1and various configurations can be employed.

Further, in the above-described embodiment, the lateral sipe portion28and the longitudinal sipe portion30are formed in a straight cross-sectional shape, but may be formed in a curved cross-sectional shape or a combination of the straight shape and the curved shape. Further, in the above-described embodiment, an example in which the zigzag-shaped sipe26is continuous in the tire circumferential direction CD without any interruption has been described, but the zigzag-shaped sipe may include one or plural divided portions. Further, in the above-described embodiment, the zigzag-shaped sipe26is provided with the wide portion46, but the wide portion46is not essential.

Furthermore, the dimensions in the specification are those in a normal state without any load in a state in which a pneumatic tire is mounted on a regular rim and is filled with a normal internal pressure. The regular rim is “Standard Rim” in the JATMA standard, “Design Rim” in the TRA standard, or “Measuring Rim” in the ETRTO standard. The normal internal pressure is “MAXIMUM AIR PRESSURE” in the JATMA standard, the “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, or “INFLATION PRESSURE” in the ETRTO standard.

As the pneumatic tire according to the embodiment, tires for various vehicles such as a tire for a passenger car and a heavy duty tire for a truck, a bus, or a light truck (for example, a SUV car and a pickup truck) can be exemplified. Further, the application of the pneumatic tire is not particularly limited and the pneumatic tire may be used as all season tires and winter tires.

Although several embodiments have been described above, these embodiments have been suggested as an example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms and can be implemented while being omitted, replaced, or changed in various ways without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention as well as in the scope of the invention described in the claims and their equivalents.