Patent Publication Number: US-2019176535-A1

Title: Pneumatic tire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Application No. 2017-238855 (filed on Dec. 13, 2017) and claims priority from Japanese Patent Application No. 2017-238855. The present disclosure incorporates entire contents of Japanese Patent Application No. 2017-238855. 
     TECHNICAL FIELD 
     The present disclosure relates to a pneumatic tire. 
     BACKGROUND ART 
     For example, as disclosed in Patent Documents 1 to 3, it has been known to provide a narrow groove called a sipe in a tread of a pneumatic tire. Since an edge effect occurs in a direction orthogonal to an extending direction of the sipe, a pneumatic tire having a sipe is suitable for traveling on snow. 
     Patent Document 1: JP-A-2015-166243 
     Patent Document 2: JP-A-2014-172600 
     Patent Document 3: Japanese Patent No. 5814985 
     DISCLOSURE OF THE INVENTION 
     Problem that the Invention is to Solve 
     However, in a sipe in the related art, there is a problem that an edge effect does not occur in an extending direction of the sipe. 
     Therefore, the present disclosure is to provide a pneumatic tire having a sipe that causes an edge effect in all directions. 
     Means for Solving the Problem 
     In a pneumatic tire of an embodiment, an annular sipe is provided in a land portion, and the annular sipe is constituted by a plurality of independent small sipes extending in a circumferential direction of the annular sipe. 
     Advantage of the Invention 
     In the pneumatic tire of the embodiment, an edge effect occurs in all directions by the annular sipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A cross-sectional view in the width direction of a pneumatic tire of an embodiment. 
         FIG. 2  A tread pattern of the pneumatic tire of the embodiment. 
         FIG. 3  A tread pattern of the pneumatic tire of a modification. 
         FIG. 4  An enlarged view of an annular sipe. 
         FIG. 5  A cross-sectional view in a width direction of a small sipe. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     As illustrated in  FIG. 1 , a bead portion  2  is provided on both sides in a tire width direction of a pneumatic tire  1 . The bead portion  2  is constituted by a bead core  2   a  made of a steel wire wound in a circular shape and a bead filler  2   b  made of rubber and provided on a radial outer side of the bead core  2   a.  A carcass ply  5  is laid across the bead portion  2  on both sides in the tire width direction. The carcass ply  5  is a sheet type member in which a plurality of ply cords arranged in a direction orthogonal to a circumferential direction of the tire are covered with rubber. The carcass ply  5  forms a frame shape of the pneumatic tire  1  between the bead portions  2  on both sides of the tire width direction, and surrounds the bead portions  2  by folding back from inside to outside in the tire width direction around the bead portions  2 . A sheet type inner liner  6  made of rubber having low air permeability is adhered to the inside of the carcass ply  5 . 
     One or a plurality of belts  7  are provided on the tire radial outer side of the carcass ply  5 . The belt  7  is a member made by covering a plurality of steel-based cords with rubber. A tread rubber  3  having a grounding surface with a road surface (hereinafter, referred to as a “grounding surface”) is provided on the tire radial outer side of the belt  7 . Further, a side wall rubber  4  is provided on both sides in the tire width direction of the carcass ply  5 . In addition to these members, according to functional requirements of the pneumatic tire  1 , members, for example, a belt lower pad or a chafer are provided. 
     A tread pattern illustrated in  FIG. 2  is formed on a surface of the tread rubber  3 . In  FIG. 2 , the vertical direction is the circumferential direction of the tire, and the lateral direction is the tire width direction. Further, in  FIG. 2 , a lower side is grounded first during rolling of the tire (that is, when the vehicle is traveling). 
     In this tread pattern, as a main groove that extends in the circumferential direction of the tire and has a wide width, a total of four main grooves, that is, two center main grooves  10  on a tire equator C side (center side in the tire width direction) and two shoulder main grooves  15  on a tire grounding end E side (an outer side in the tire width direction) are formed. Then, a center land portion  30  between the two center main grooves  10 , a mediate land portion  35  between the center main groove  10  and the shoulder main groove  15 , and a shoulder land portion  40  between the shoulder main groove  15  and the tire grounding end E are provided. 
     Here, the land portion is a portion formed by being partitioned by grooves. Further, the tire grounding end E is an end portion of the grounding surface in the tire width direction in a loaded state. The loaded state is a state where the pneumatic tire is rim-assembled into a normal rim to be a normal inner pressure and loaded by a normal load. Here, the normal rim is a standard rim defined by standards such as JATMA, TRA, and ETRTO. Further, the normal load is a maximum load defined in the above standards. Further, the normal inner pressure is an inner pressure corresponding to the maximum load. 
     The center main groove  10  includes long first groove portions  11  that extend obliquely with respect to the circumferential direction of the tire, and short second groove portions  12  that are inclined with respect to the circumferential direction of the tire and extend in a direction different from that of the first groove portion  11 . Then, the first groove portion  11  and the second groove portion  12  are arranged alternately, and thus, the center main groove  10  is formed in a zigzag shape. 
     The shoulder main groove  15  includes long first groove portions  16  that extend obliquely with respect to the circumferential direction of the tire, and short second groove portions  17  that are inclined with respect to the circumferential direction of the tire and extend in a direction different from that of the first groove portion  16 . Then, the first groove portion  16  and the second groove portion  17  are arranged alternately, and thus, the shoulder main groove  15  has a zigzag shape. 
     Further, as lateral grooves that extend in the tire width direction, first lateral grooves  20  and second lateral grooves  25  are formed. The first lateral grooves  20  and second lateral grooves  25  are alternately formed in the circumferential direction of the tire. The first lateral groove  20  and the second lateral groove  25  extend obliquely such that the tire grounding end E side is grounded later during rolling of the tire. 
     The first lateral groove  20  traverses the shoulder land portion  40  and the mediate land portion  35 , and extends to the center land portion  30  and is closed in the center land portion  30 . Therefore, a notch  21  that is a part of the first lateral grooves  20  is formed in the center land portion  30 . 
     Further, the second lateral groove  25  traverses the shoulder land portion  40 , and extends to the mediate land portion  35  and is closed in the mediate land portion  35 . Therefore, a notch  26  that is a part of the second lateral grooves  25  is formed in the mediate land portion  35 . 
     The second groove portion  17  of the shoulder main groove  15  overlaps with the first lateral groove  20  and the second lateral groove  25 . 
     As a modification, as illustrated in  FIG. 3 , a second lateral groove  125  which is a substitute for the second lateral groove  25  may traverse the shoulder land portion  40  and the mediate land portion  35 , and then end in the center main groove  10  while being opened. The tread pattern in  FIG. 2  is used for, for example, a high-performance tire, and a tread pattern in  FIG. 3  is used for, for example, a tire for a sports utility vehicle (SUV). Hereinafter, the tread pattern in  FIG. 2  will be described as an example. 
     With the configuration of the groove as described above, the center land portion  30  between the two center main grooves  10  is configured as a rib extending in the circumferential direction of the tire without being divided by lateral grooves. Further, the mediate land portion  35  is divided by the first lateral groove  20 , and thus, is a row of a plurality of mediate blocks  36  arranged in the circumferential direction of the tire. In the mediate block  36 , a portion to be grounded prior to the notch  26  is referred to as “a stepped side block portion  37 ,” and a portion to be grounded later than the notch  26  is referred to as “a kick-out side block portion  38 .” Further, the shoulder land portion  40  is divided by the first lateral groove  20  and the second lateral groove  25 , and thus, is a row of a plurality of shoulder blocks  41  arranged in the circumferential direction of the tire. 
     An annular sipe  80  is formed one by one on each of the stepped side block portion  37  and the kick-out side block portion  38  of the mediate block  36 . The annular sipe  80  on the stepped side block portion  37  is closer to the tire equator C than the annular sipe  80  on the kick-out side block portion  38 . Then, since the annular sipe  80  is formed on the stepped side block portion  37  and the kick-out side block portion  38  of each of the mediate blocks  36  arranged in the circumferential direction of the tire, the annular sipes  80  are arranged in a zigzag manner in the circumferential direction of the tire. 
     As illustrated in  FIG. 4 , the annular sipe  80  is formed by annularly arranging a plurality of (e.g., five as illustrated in the drawing) independent small sipes  81 . A small sipe  81  is a narrow groove having a narrow width of, for example, 0.4 to 0.6 mm, which is so small as to be occluded in the loaded state when a dimple  84  to be described later disappears due to wear. The small sipe  81  extends in a circumferential direction of the annular sipe  80 . Further, the small sipe  81  is bent toward the inner side of the annular sipe  80  (in other words, so as to extend along a circumference of the annular sipe  80 ). Further, one end of the small sipe  81  is closer to a center of the annular sipe  80  than the other end thereof. The end portion of the small sipe  81  which is closer to the center of the annular sipe  80  is referred to as a “center side end portion  82 ”, and the end portion on the other side is referred to as an “outer side end portion  82 .” A relationship between a length from the bent portion of the small sipe  81  to the center side end portion  82  and a length from the bent portion to the outer side end portion  83  is not limited, but in the case of the illustrated embodiment, the length from the bent portion to the center side end portion  82  is longer. 
     The dimple  84  is formed along the small sipe  81  on the inner side of the bent portion of the small sipe  81 . As illustrated in  FIG. 5 , the dimple  84  is a recessed portion with respect to a grounding surface  87 . A depth of the dimple  84  is shallower than that of the adjacent small sipe  81 , and for example, is 40% or less of a depth of the small sipe  81 . 
     Further, a width of the dimple  84  (that is, a length of a direction orthogonal to the extending direction of the small sipe  81 ) is narrow on the center side end portion  82  of the small sipe  81  and is widened toward the outer side end portion  83  of the small sipe  81 . Therefore, the width of the dimple  84  is narrow on the inner side of the annular sipe  80  and is widened toward the outer side. 
     Sipes other than the annular sipe  80  are formed in the mediate block  36 . For example, a center sipe  85  independent from the small sipe  81  that constitutes the annular sipe  80  is provided on the inner side of the annular sipe  80 . The center sipe  85  is, for example, wavy in a plan view. Further, for example, on the outer radial side of the annular sipe  80 , a plurality of width direction sipes  86  extending in the tire width direction are formed. 
     Since the annular sipe  80  is formed in the embodiment as described above, an edge effect occurs in all directions. Here, since the annular sipe  80  is constituted by the plurality of independent small sipes  81 , as compared with a case where one circular sipe is formed, the rigidity in the vicinity of the annular sipe  80  hardly decreases. 
     Further, since the center sipe  85  is provided on the inner side of the annular sipe  80 , the rigidity on the inner side of the annular sipe  80  decreases and the rigidity of the entire vicinity of the annular sipe  80  becomes uniform. 
     Further, since dimple  84  is formed along the small sipe  81 , rubber in the vicinity of the small sipe  81  is easy to move, and further a contour of the recessed portion (that is, an edge) obtained by adding the small sipe  81  and the dimple  84  is long. Therefore, the edge effect is exerted more remarkably. 
     Further, since the small sipe  81  is bent toward the inner side of the annular sipe  80 , as compared with a case where it is not bent, the size of the annular sipe  80  is not changed and the small sipe  81  is long. Therefore, the edge effect is exerted more remarkably. 
     Here, the rigidity of the inner side of the bent portion may be decreased when simply the small sipe  81  is bent, but, since the dimple  84  is formed on the inner side of the bent portion, a portion with a low rigidity is removed. Therefore, the rigidity of the entire vicinity of the annular sipe  80  becomes uniform. 
     Further, since the width of the dimple  84  is widened from the center side end portion  82  of the small sipe  81  toward the outer side end portion  83  thereof, snow or water that has entered into the annular sipe  80  is likely discharged to the outer radial side of the annular sipe  80 . 
     Further, since the annular sipes  80  are arranged in a zigzag manner, the edge effect is exerted over a wide range in the tire width direction. 
     The above embodiments are examples, and the scope of the present disclosure is not limited thereto. Various modifications may be made to the above embodiments within the scope without escaping from the purpose of the present disclosure. 
     In the above embodiment, the annular sipe  80  is formed in the mediate land portion  35 , but the annular sipe  80  may be formed in at least one of the center land portion  30  or the shoulder land portion  40 , instead of the mediate land portion  35 , or with the mediate land portion  35 . Further, the tread pattern is not limited to those having the center land portion  30 , the mediate land portion  35 , and the shoulder land portion  40 . 
     Description of Reference Numerals and Signs 
     
         
         C . . . tire equator, E . . . tire grounding end,  1  . . . pneumatic tire,  2  . . . bead portion,  2   a  . . . bead core,  2   b  . . . bead filler,  3  . . . tread rubber,  4  . . . side wall rubber,  5  . . . carcass ply,  6  . . . inner liner,  7  . . . belt,  10  . . . center main groove,  11  . . . first groove portion,  12  . . . second groove portion,  15  . . . shoulder main groove,  16  . . . first groove portion,  17  . . . second groove portion,  20  . . . first lateral groove,  21  . . . notch,  25  . . . second lateral groove,  26  . . . notch,  30  . . . center land portion,  35  . . . mediate land portion,  36  . . . mediate block,  37  . . . stepped side block portion,  38  . . . kick-out side block portion,  40  . . . shoulder land portion,  41  . . . shoulder block,  80  . . . annular sipe,  81  . . . small sipe,  82  . . . center side end portion,  83  . . . outer side end portion,  84  . . . dimple,  85  . . . center sipe,  86  . . . width direction sipe,  87  . . . grounding surface,  125  . . . second lateral groove