Patent Publication Number: US-2019176532-A1

Title: Pneumatic tire

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a developed view illustrating a tread pattern of a pneumatic tire according to an embodiment. 
         FIG. 2  is an enlarged view of a main part of the tread pattern. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment will be described with reference to the drawings. 
     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 in  FIG. 1 , a tread rubber surface of a tread portion  10  is provided with a plurality of main grooves  12  extending 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 grooves  12 A and  12 A provided at both sides of a tire equator CL and a pair of shoulder main grooves  12 B and  12 B respectively disposed at the outside thereof are provided. Four main grooves  12  are zigzag-shaped grooves which extend in the tire circumferential direction CD while being bent with an amplitude in the tire width direction WD. Furthermore, in  FIG. 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 portion  10 , a plurality of land portions are divided by the main groove  12  in the tire width direction WD. Specifically, a center land portion  14  interposed between the pair of center main grooves  12 A and  12 A, a pair of right and left intermediate land portions  16  and  16  interposed between the center main groove  12 A and the shoulder main groove  12 B, and a pair of right and left shoulder land portions  18  and  18  located at the outside of the shoulder main groove  12 B in the tire width direction are provided. The intermediate land portion  16  and the shoulder land portion  18  are 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 grooves  20  are provided at intervals in the tire circumferential direction CD. Meanwhile, the center land portion  14  is 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 portion  14  and the configuration of the center land portion  14  will be described in detail below with reference to  FIGS. 1 and 2 . 
     The center land portion  14  is a rib which extends on the tire equator CL in the tire circumferential direction CD and a pair of right and left side walls  22  of the center land portion  14  is formed in a zigzag shape by the zigzag-shaped center main grooves  12 A and  12 A at both sides. Further, in the center land portion  14 , lateral grooves  24  not penetrating the center land portion  14  are alternately provided on the right and left sides at intervals in the tire circumferential direction CD. The lateral groove  24  is formed as a leading end portion of the lateral groove  20  on the extension line of the lateral groove  20  crossing the intermediate land portion  16  and the shoulder land portion  18 . 
     The center portion of the center land portion  14  is provided with a zigzag-shaped sipe  26  which continuously extends in the tire circumferential direction CD. In this example, the zigzag-shaped sipe  26  extends in the entire circumference of the tire circumferential direction CD on the tire equator CL at the center portion of the center land portion  14  in the width direction. The zigzag-shaped sipe  26  is a sipe which does not open the main groove  12  and 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 sipe  26  is not particularly limited and may be, for example, 8 to 20 mm. 
     As illustrated in  FIG. 2 , the zigzag-shaped sipe  26  is formed in a zigzag (that is, winding) cross-sectional shape by a plurality of lateral sipe portions  28  which are arranged at intervals in the tire circumferential direction CD and a plurality of longitudinal sipe portions  30  which alternately connect the end portions of the lateral sipe portions  28  at the right and left sides. 
     The lateral sipe portion  28  is 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 portions  28  and  28  which 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 portions  28  and  28  is not particularly limited and may be, for example, 4 to 10 mm in the interval S at the amplitude center. 
     The longitudinal sipe portion  30  is a sipe which extends in the tire circumferential direction CD. In this example, the longitudinal sipe portion  30  has 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 portion  30  is a sipe which alternately connects the facing end portions of the lateral sipe portions  28  and  28  adjacent 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 portions  28  in both end portions of the lateral sipe portion  28 . 
     Each longitudinal sipe portion  30  includes an extension portion  34  which is formed by extending only one end portion out of both end portions in the tire circumferential direction CD of each longitudinal sipe portion  30  to one side beyond a connection portion  32  with the lateral sipe portion  28 . That is, the extension portion  34  is an extended portion of one end portion out of both end portions of the longitudinal sipe portion  30  to the one side beyond a connection portion  32 . In this example, each longitudinal sipe portion  30  is provided with the extension portion  34  in which only the end portion on the rear side RR in the rotation direction out of both end portions of each longitudinal sipe portion  30  goes beyond the connection portion  32  with the lateral sipe portion  28 , 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 portions  30  alternately 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 portion  34 . 
     In a land portion  36  between the pair of adjacent lateral sipe portions  28  and  28 , one end side of the tire width direction WD is connected by the longitudinal sipe portion  30  and is formed in a bag-shaped (that is, closed) portion  38  and the other end side thereof is formed in an opening portion  40  opening to the outside WO in the width direction of the zigzag-shaped sipe  26 . The extension portion  34  is provided so that an opening width of the opening portion  40  on the stepping side of the land portion  36  (the front side R in the rotation direction) decreases and is not provided on the kicking side of the land portion  36  (the rear side RR in the rotation direction). That is, the kicking side is not provided with the extension portion protruding toward the opening portion  40  from a bent portion  42  obtained by connecting the lateral sipe portion  28  and the longitudinal sipe portion  30  and the opening portion  40  is formed between the kicking side bent portion  42  and the stepping side extension portion  34  to 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 sipe  26  in the width direction and is the same as the outside of the tire width direction WD in this example. 
     The longitudinal sipe portion  30  is 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 portion  34 . In this example, the longitudinal sipe portion  30  is 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 sipe  26  is provided with a wide portion  46  having a groove width wider than that of a narrow portion  44  which is the other portion. In this example, the wide portion  46  is provided in a part of the lateral sipe portion  28  (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 portion  30  is formed as the narrow portion  44 . 
     The groove width of the narrow portion  44  is 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 portion  46  is not particularly limited as long as the groove width is wider than the groove width of the narrow portion  44  and 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 sipe  26  is not particularly limited and may be, for example, 30 to 80% of the main groove depth. 
     The center land portion  14  is further provided with a triangular notch portion  48  provided at each of both side walls  22  and  22  and the notch portion  48  is provided at a plurality of positions at intervals in the tire circumferential direction CD. The center land portion  14  is further provided with a wavy sipe  50  extending in the tire width direction WD and having a wavy cross-sectional shape and a straight sipe  52  extending in the tire width direction WD and having a straight cross-sectional shape. The wavy sipe  50  and the straight sipe  52  are basically formed to open to the side wall  22  of the center land portion  14  and are terminated so as not to intersect the zigzag-shaped sipe  26 . The wavy sipe  50  and the straight sipe  52  are 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 sipe  26  is 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 portion  28  and to exhibit the edge effect in the lateral direction (the tire width direction WD) by the longitudinal sipe portion  30 . Accordingly, it is possible to improve the running performance such as performance on ice. Further, since the extension portion  34  is provided in each longitudinal sipe portion  30 , 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 portion  40  by the extension portion  34  in the land portion  36  formed between the pair of lateral sipe portions  28  and  28 , it is possible to decrease a difference in rigidity between the bag-shaped portion  38  and the opening portion  40  and 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 portion  34  is provided on the stepping side of the land portion  36  and the extension portion  34  is not provided on the kicking side thereof, it is possible to ensure the rigidity of the kicking side bent portion  42  and to improve the braking performance. 
     Further, since the longitudinal sipe portion  30  is provided to be inclined to the outside WO in the width direction toward the front end of the extension portion  34 , it is possible to ensure a distance between the front end of the stepping side extension portion  34  and the kicking side bent portion  42  and to further ensure the rigidity of the portion. 
     Further, since the zigzag-shaped sipe  26  is provided with the wide portion  46  along with the narrow portion  44 , it is possible to maintain an edge effect or a water removal effect in the wide portion  46  even when the narrow portion  44  is closed at the time of braking the tire. 
     Furthermore, in the above-described embodiment, an example in which the zigzag-shaped sipe  26  is provided in the center land portion  14  extending 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 portion  16  or the shoulder land portion  18  is not limited to one illustrated in  FIG. 1  and various configurations can be employed. 
     Further, in the above-described embodiment, the lateral sipe portion  28  and the longitudinal sipe portion  30  are 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 sipe  26  is 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 sipe  26  is provided with the wide portion  46 , but the wide portion  46  is 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.