Patent Publication Number: US-2019176533-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. 2017-238877, 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, for example, JP-A-2007-030686 discloses a technique in which a zigzag-shaped sipe continuously extending in a tire circumferential direction using a tire width direction as an amplitude direction is provided in order to improve performance of a pneumatic tire on icy and snowy roads. 
     Meanwhile, in order to reduce pitch noise as tire noise, there is known a technique in which a plurality of pitch patterns having different pitch lengths are arranged in a tire circumferential direction to form a tread portion so that a tread pattern has a pitch variation (see JP-A-2014-221573). 
     SUMMARY 
     In a case in which the tread pattern has a pitch variation when the sipe continuous in the tire circumferential direction is provided in the tread portion, a problem arises in that an interrupted portion is formed in the sipe at a boundary between the pitch patterns. 
     For example, as in a comparative example illustrated in  FIG. 4 , a case in which a rib  100  extending in a tire circumferential direction CD is provided with a zigzag-shaped sipe  102  extending in the tire circumferential direction CD is considered. The pitch length is set as three types of Pl, Pm, and Ps in order from the large pitch length and the pitch patterns are set as  104 ,  106 , and  108 . The sipe  102  extends in the tire circumferential direction while alternately swinging to the right and left sides in the tire width direction and a sipe component  110  as a repeating unit is repeated in the tire circumferential direction. 
     The length of the sipe component  110  in the tire circumferential direction is generally uniform and the pitch lengths Pl, Pm, and Ps are adjusted by changing the number of times of repeating the sipe component  110  of each of the pitch patterns  104 ,  106 , and  108 . 
     However, since it is difficult to adjust each of the pitch lengths P 1 , Pm, and Ps just by changing the number of times of repeating the sipe component  110 , an interrupted portion  114  is formed in the sipe  102  at each boundary  112  of the pitch patterns  104 ,  106 , and  108  as illustrated in  FIG. 4 . When such an interrupted portion  114  is formed, the rigidity of the portion increases so that the ground contact pressure distribution becomes non-uniform and uneven wear occurs. 
     In view of the above-described circumstances, an object of an embodiment of the invention is to prevent an interrupted portion in a sipe in a case in which a pneumatic tire with a sipe continuous in a tire circumferential direction has a pitch variation. 
     A pneumatic tire according to an embodiment of the invention is a pneumatic tire including: a tread portion in which a plurality of pitch patterns having different pitch lengths are arranged in a tire circumferential direction, in which a rib formed in the tread portion and extending in the tire circumferential direction is provided with a sipe continuous in the tire circumferential direction, in which the sipe is formed by repeating a sipe component in the tire circumferential direction, each pitch pattern includes a plurality of the sipe components, and a position in the sipe component at each boundary between the pitch patterns is set to the same position, and in which a length of the sipe component in the tire circumferential direction is set according to the pitch length of the pitch pattern. 
     According to the embodiment, since it is possible to prevent an interrupted portion in a sipe in a case in which a pneumatic tire with a sipe continuous in a tire circumferential direction has a pitch variation, it is possible to obtain a uniform ground contact pressure distribution and to prevent uneven wear. 
    
    
     
       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 a plan view illustrating a center land portion of the tread pattern. 
         FIG. 3  is an enlarged plan view of the center land portion. 
         FIG. 4  is a plan view illustrating a center land portion of a tread pattern according to a comparative example. 
     
    
    
     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. 
     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. 
     In the tread portion  10 , a plurality of lateral grooves  20  extending in the tire width direction WD are provided at intervals in the tire circumferential direction CD. As the lateral groove  20 , a first lateral groove  20 A which opens to a ground contact end, obliquely extends in a curved shape from the ground contact end toward a tire equator CL, and is terminated inside an intermediate land portion  16  and a second lateral groove  20 B which opens to a ground contact end, obliquely extends in a curved shape from the ground contact end toward the tire equator CL, and is terminated inside the center land portion  14  are provided. The first lateral groove  20 A and the second lateral groove  20 B are alternately provided in the tire circumferential direction CD. Further, the first lateral grooves  20 A are provided with the phases shifted from each other on the right and left sides of the tire equator CL and the second lateral grooves  20 B are also provided with the phases shifted from each other on the right and left sides of the tire equator CL. 
     Accordingly, the shoulder land portion  18  is divided by the first lateral groove  20 A and the second lateral groove  20 B to be formed as a block row in which a plurality of shoulder blocks  21  are arranged in the tire circumferential direction CD. Further, the intermediate land portion  16  is divided by the second lateral groove  20 B to be formed as a block row in which an intermediate block  22  that is twice the length of the shoulder block  21  is disposed in the tire circumferential direction CD. 
     Meanwhile, the center land portion  14  which is located on the tire equator CL is not divided by the lateral groove  20  and extends in the tire circumferential direction CD. That is, the center land portion  14  is formed as a rib which is continuous in the entire circumference of the tire circumferential direction CD. In the center land portion  14 , the right and left side walls  24  and  24  are formed in a zigzag shape by both zigzag-shaped center main grooves  12 A and  12 A. Further, the center land portion  14  is provided with the leading end portions of the second lateral grooves  20 B which are alternately formed at the right and left sides at intervals in the tire circumferential direction CD. 
     As illustrated in  FIG. 1 , the tread portion  10  is formed by arranging a plurality of pitch patterns having different pitch lengths in the tire circumferential direction CD. In this example, the pitch length is set to three types and is set as PL, PM, and PS in order of the large pitch length. Thus, a pitch pattern  25 L of the pitch length PL, a pitch pattern  25 M of the pitch length PM, and a pitch pattern  25 S of the pitch length PS are provided. Here, the pitch pattern indicates the minimum unit of the component of the thread pattern repeated in the tire circumferential direction (the minimum component unit in the tire circumferential direction). In this example, the pitch lengths PL, PM, and PS are defined by the lengths corresponding to two of the shoulder block  21  of the shoulder land portion  18 . This is the same as the length corresponding to one of the intermediate block  22  in the intermediate land portion  16  and is the same as the length corresponding to a gap between the second lateral grooves  20 B and  20 B of one side wall  24  of the center land portion  14 . 
     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. The zigzag-shaped sipe  26  is a sipe which does not open to the main groove  12  and is a wavy sipe of which an amplitude direction is substantially the same as the tire width direction WD. The zigzag-shaped sipe  26  extends in the entire circumference of the tire circumferential direction CD while swinging in the tire width direction WI) with a predetermined amplitude. 
     As illustrated in  FIG. 2 , the zigzag-shaped sipe  26  is formed by repeating a sipe component  28  as a repeating unit in the tire circumferential direction CD. The sipe component  28  is a sipe portion for one wavelength of the zigzag-shaped sipe  26  forming a wave shape. In  FIG. 2 , the sipe component  28  is illustrated as a sipe portion in a range indicated by Reference Sign DS and the position corresponding to the start point of the repeating unit is not particularly limited as long as a length for one wavelength is provided. 
     Each of the pitch patterns  25 L,  25 M, and  25 S includes the plurality of sipe components  28  and the sipe is formed in a zigzag shape by the repetition of the sipe component  28  in each of the pitch patterns  25 L,  25 M, and  25 S. 
     As illustrated in  FIG. 2 , a position in the sipe component  28  at each of the boundaries  30  between the pitch patterns  25 L,  25 M, and  25 S is set to the same position. That is, the zigzag-shaped sipe  26  is set to straddle a boundary  30  at the same position (the same phase) of the sipe component  28  in any boundary  30  when straddling the boundary  30  of the adjacent pitch patterns  25 L,  25 M, and  25 S and the phase of the sipe  26  at each straddling portion is the same. 
     In the embodiment, a length DS (a length for one wavelength) of the sipe component  28  in the tire circumferential direction CD is set according to the pitch lengths PL, PM, and PS of the pitch patterns  25 L,  25 M, and  25 S. Specifically, the number of the sipe components  28  provided in each of the pitch patterns  25 L,  25 M, and  25 S is set so that the length DS of the sipe component  28  is substantially the same in all of the pitch patterns  25 L,  25 M, and  25 S. Then, the sipe components  28  are arranged at the same intervals in each of the pitch patterns  25 L,  25 M, and  25 S with the position of the sipe component  28  at the boundary  30  as a base point. That is, the length DS of the sipe component  28  is set to be uniform in each of the pitch patterns  25 L,  25 M, and  25 S. Meanwhile, since the length DS of the sipe component  28  for each of the pitch patterns  25 L,  25 M, and  25 S is set by the pitch lengths PL, PM, and PS and the number of the sipe components  28 , the lengths are generally set to different values. That is, the length DS of the sipe component  28  is generally differently for each of the pitch lengths PL, PM, and PS. 
     The length DS of the sipe component  28  is preferably set to within ±10% of a range with reference to a median value of the length DS of the sipe component  28  (that is, 90 to 110% of the median value) in the plurality of pitch patterns  25 L,  25 M, and  25 S having different pitch lengths PL, PM, and PS. For example, in the example illustrated in  FIG. 2 , the number of the sipe components  28  is seven in the pitch pattern  25 L having a long pitch length PL, six in the reference pitch pattern  25 M having an intermediate pitch length PM, and five in the pitch pattern  25 S having a short pitch length PS and the length DS of the sipe component  28  is 10.54 mm, 10.98 mm, and 11.72 mm, respectively. Thus the length DS of each of the pitch patterns  25 L and  25 S is within ±10% of a range with reference to a median value of the length DS (=10.98 mm) of the pitch pattern  25 M. 
     As illustrated in  FIG. 3 , the zigzag-shaped sipe  26  has a zigzag-shaped (that is, winding-shaped) cross-section by alternately arranging a first L-shaped sipe  32  and a second L-shaped sipe  34  in the tire circumferential direction CD. The first L-shaped sipe  32  has an L-shaped cross-section by a lateral sipe portion  32 A extending in the tire width direction WD and a longitudinal sipe portion  32 B extending in the tire circumferential direction CD from one end portion  32 AE of the lateral sipe portion  32 A in the tire width direction WD. The second L-shaped sipe  34  has a L-shaped cross-section by a lateral sipe portion  34 A extending in the tire width direction WD and a longitudinal sipe portion  34 B extending in the tire circumferential direction CD from the other end portion  34 AE of the lateral sipe portion  34 A in the tire width direction WD (that is, an end portion opposite to one side of the end portion  32 AE). 
     In the first L-shaped sipe  32  and the second L-shaped sipe  34 , a common member is used as a sipe forming piece for forming the first and second L-shaped sipes and the first and second L-shaped sipes have the same shape when the first and second L-shaped sipes are rotated about the rotation axis along the tire equator line by 180°. 
     The zigzag-shaped sipe  26  is formed by connecting the front end of the lateral sipe portion  34 A of the second L-shaped sipe  34  to the side surface of the longitudinal sipe portion  32 B of the first L-shaped sipe  32  in an abutting state and connecting the front end of the lateral sipe portion  32 A of the first L-shaped sipe  32  to the side surface of the longitudinal sipe portion  34 B of the second L-shaped sipe  34  in an abutting state. The connection positions of the lateral sipe portions  32 A and  34 A and the longitudinal sipe portions  32 B and  34 B between the first L-shaped sipe  32  and the second L-shaped sipe  34  are different, and thereby the length DS of the sipe component  28  is set to a different value. Specifically, when the lateral sipe portions  32 A and  34 A abut at a position close to the front ends of the longitudinal sipe portions  32 B and  34 B, the length DS of the sipe component  28  increases. In contrast, when the lateral sipe portions  32 A and  34 A abut at a position away from the front ends of the longitudinal sipe portions  32 B and  34 B, the length DS of the sipe component  28  decreases. 
     As illustrated in  FIG. 3 , the lateral sipe portions  32 A and  34 A have a straight cross-sectional shape and are inclined with respect to the tire width direction WD. Further, the longitudinal sipe portions  32 B and  34 B have a straight cross-sectional shape and are inclined with respect to the tire circumferential direction CD. However, the lateral sipe portions  32 A and  34 A and the longitudinal sipe portions  32 B and  34 B may be formed in a curved shape, a straight shape, or a combination thereof. 
     The lateral sipe portions  32 A and  34 A which are adjacent to each other in the tire circumferential direction CD are inclined in the opposite directions with respect to the tire width direction WD). The longitudinal sipe portions  32 B and  34 B are inclined to the outside WO in the width direction toward the rear side RR in the rotation direction. That is, the longitudinal sipe portions  32 B and  34 B are formed in an outward opening shape. Here, the rear side RR in the rotation direction is an opposite direction with respect to the rotation direction R. Further, 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 in the tire width direction WD in this example. 
     Further, a triangular notch portion  36  is provided in each of both side walls  24  and  24  of the center land portion  14  and the notch portion  36  is provided at a plurality of positions at intervals in the tire circumferential direction CD. Further, in the center land portion  14 , a wavy sipe  38  and a straight sipe  40  extending in the tire width direction WD are alternately disposed in the tire circumferential direction CD. Basically, the wavy sipe  38  and the straight sipe  40  are provided to open to the side wall  24  of the center land portion  14  and are terminated so as not to intersect the zigzag-shaped sipe  26 . 
     According to the pneumatic tire of the embodiment with the above-described configuration, the zigzag-shaped sipe  26  is continuously formed in the tire circumferential direction CD. Here, the position of the sipe component  28  at the straddling portions of the pitch patterns  25 L,  25 M, and  25 S is set to the same position in any boundary  30  of the pitch patterns  25 L,  25 M, and  25 S and the length DS of the sipe component  28  is set according to the pitch lengths PL, PM, and PS of the pitch patterns  25 L,  25 M, and  25 S. Accordingly, since the zigzag-shaped sipe  26  is not interrupted at the boundary  30  of the pitch patterns  25 L,  25 M, and  25 S, it is possible to obtain a uniform ground contact pressure distribution and to suppress uneven wear. 
     Further, since the length DS of the sipe component  28  is set to a range of ±10%, the length DS is substantially the same in all of the pitch patterns  25 L,  25 M, and  25 S and hence the ground contact pressure distribution becomes further uniform. 
     Further, it is possible to commonly use the sipe forming piece when the zigzag-shaped sipe  26  is formed by the combination of the first L-shaped sipe  32  and the second L-shaped sipe  34 . At the same time, it is possible to easily change the length DS of the sipe component  28  when the connection position between both members is changed. As a result, it is possible to simply set the length DS of the sipe component  28  according to the pitch lengths PL, PM, and PS of the pitch patterns  25 L,  25 M, and  25 S. 
     Furthermore, in the above-described embodiment, the zigzag-shaped sipe is provided as the sipe which is continuous in the tire circumferential direction, but the shape of the sipe is not limited as long as the sipe has a repeated pattern and is continuous in the tire circumferential direction. Further, in the above-described embodiment, an example in which the sipe continuous in the tire circumferential direction is provided in the center land portion has been described, but there is no limitation in the configuration in which the sipe is provided in the center land portion. Further, the pitch pattern may not be formed in the entire tread portion in the width direction and may be formed only by the land portion provided with the sipe continuous in the tire circumferential direction. Further, in the above-described embodiment, the pitch length is set to three types, but the invention is not limited thereto. For example, five types may be provided or five or more types may be provided. 
     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 “MAXMIMUM 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.