Patent Publication Number: US-2019176529-A1

Title: Pneumatic tire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Application No. 2017-238846 (filed on Dec. 13, 2017) and claims priority from Japanese Patent Application No. 2017-238846. The present disclosure incorporates entire contents of Japanese Patent Application No. 2017-238846. 
     TECHNICAL FIELD 
     The present disclosure relates to a pneumatic tire. 
     BACKGROUND ART 
     As disclosed in Patent Document 1 or Patent Document 2, a pneumatic tire having a main groove that extends in a zigzag manner in a circumferential direction of a tire is known. Since the main groove has a zigzag shape, such pneumatic tire is excellent in traction performance, but drainage performance is not sufficient. 
     Further, as disclosed in Patent Document 1 or Patent Document 3, there has been known a pneumatic tire including a center land portion at the center of a tire width direction, a shoulder land portion at both sides in the tire width direction, and a mediate land portion between the center land portion and the shoulder land portion, in which lateral grooves traverses the shoulder land portion and the mediate land portion. In such a pneumatic tire, drainage performance is good since water can pass through the inside of the lateral grooves. 
     Patent Document 1: JP-A-2010-274695 
     Patent Document 2: JP-A-2014-240204 
     Patent Document 3: JP-A-2002-002229 
     DISCLOSURE OF THE INVENTION 
     Problem that the Invention is to Solve 
     In a pneumatic tire having a center land portion, a mediate land portion, and a shoulder land portion, the applicant has considered to form a main groove at both sides of the center land portion in a zigzag shape and to provide a bulging portion in a tire width direction in the center land portion. In this case, it is expected that drainage performance and traction performance are not sufficiently exhibited in the vicinity of the bulging portion of the tire width direction of the center land portion. 
     Therefore, the present disclosure is to provide a pneumatic tire with good drainage performance and traction performance. 
     Means for Solving the Problem 
     A pneumatic tire of an embodiment includes: two center main grooves on a tire equator side and two shoulder main grooves on a grounding end side of the tire as main grooves extending in a circumferential direction of the tire; a center land portion between the two center main grooves; a mediate land portion between the center main groove and the shoulder main groove; and a shoulder land portion between the shoulder main groove and the grounding end portion. The center main groove extends in a zigzag manner by alternately arranging a long first groove portion and a short second groove portion that are inclined with respect to the circumferential direction of the tire, respectively, and a bulging portion in a tire width direction is formed in the center land portion, a first groove portion of the center main groove is inclined such that a portion to be grounded later during rolling heads toward the grounding end side, and first lateral grooves each extending in the tire width direction traverses the mediate land portion and the shoulder land portion and forms a notch in the bulging portion in the center land portion. 
     Advantage of the Invention 
     The pneumatic tire has good drainage performance and traction performance, in particular, by the above configuration of the center main groove and the first lateral groove. 
    
    
     
       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  Another tread pattern of the pneumatic tire of the embodiment. 
     
    
    
     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 in the tire width direction, and surrounds the bead portions  2  by being folded 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  and  FIG. 3  to be described later, the vertical direction is the circumferential direction of the tire, and the lateral direction is the tire width direction. 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 (outside 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, a first groove portion  11  and a second groove portion  12  are arranged alternately, and thus, the center main groove  10  is formed in a zigzag shape. In  FIG. 2 , a lower side is grounded first during rolling of the tire (that is, when the vehicle is traveling) . As can be seen from the drawing, the first groove portion  11  is inclined such that a portion to be grounded later (in other words, a rear side in the rolling direction) heads toward the tire grounding end E side. The center main groove  10  is shifted in the circumferential direction of the tire on both sides of the tire equator C. That is, the positions of the first groove portion  11  and the second groove portion  12  are shifted in the circumferential direction of the tire on both sides of the tire equator C. 
     Further, 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 portions  16  and the second groove portions  17  are arranged alternately, and thus, the shoulder main groove  15  has a zigzag shape. As can be seen from  FIG. 2 , each of the first groove portions  16  is inclined such that a portion to be grounded later heads toward the tire grounding end E side. The shoulder main groove  15  is shifted in the circumferential direction of the tire on both sides of the tire equator C. That is, the positions of the first groove portion  16  and the second groove portion  17  are shifted in the circumferential direction of the tire on both sides of the tire equator C. 
     The center land portion  30  between the two center main grooves  10  is a rib extending in the circumferential direction of the tire without being divided by lateral grooves. Since the center main groove  10  has a zigzag shape as described above, bulging portions  31  in the tire width direction are formed in the center land portion  30 . The bulging portion  31  is a portion bulging toward the tire grounding end E side from a portion of the center main groove  10  of the zigzag shape which is closest to the tire equator C. In  FIG. 2 , one of the bulging portions  31  is indicated by hatching. Since the center main grooves  10  of the zigzag shape are shifted in the circumferential direction of the tire on both sides of the tire equator C, the bulging portions  31  are also shifted in the circumferential direction of the tire on both sides of the tire equator C. 
     Meanwhile, the mediate land portion  35  and the shoulder land portion  40  are divided by lateral grooves extending in the tire width direction, and thus, are a plurality of rows of blocks arranged in the circumferential direction of the tire. First lateral grooves  20  and second lateral grooves  25  are formed as the lateral grooves. 
     A first lateral groove  20  extends obliquely such that a portion close to the tire grounding end E is grounded later during rolling of the tire. Further, the first lateral groove  20  extends in a curved manner. 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 . A notch is a groove in which one end is opened in the main groove and the other end is closed in the land portion. The notch  21  is formed in the bulging portion  31  in the center land portion  30 . The notch  21  may extend to the tire equator C side from the bulging portion  31  as illustrated in  FIG. 2 . The positions of the first groove portions  20  and the notches  21 , which are a part thereof, are shifted in the circumferential direction of the tire on both sides of the tire equator C. 
     Further, the second lateral groove  25  extends obliquely such that a portion close to the tire grounding end E is grounded later during rolling of the tire. Further, the second lateral groove  25  extends in a curved manner. 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 . The positions of the second groove portions  25  are shifted in the circumferential direction of the tire on both sides of the tire equator C. 
     As a modification, as illustrated in  FIG. 3 , a second lateral groove  125  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). 
     Such first lateral grooves  20  and second lateral grooves  25  are alternately arranged in the circumferential direction of the tire. While the first lateral groove  20  extends to the bulging portion  31  in the center land portion  30 , the second lateral groove  25  extends toward a place between the two bulging portions  31  arranged in the circumferential direction of the tire or toward the vicinity thereof. The second lateral groove  25  does not reach the center land portion  30 , of course. The first lateral groove  20  and the second lateral groove  25  overlap with the second groove portion  17  of the shoulder main groove  15 . 
     Further, a sipe  45  extending in the circumferential direction of the tire is formed in the shoulder land portion  40 . The sipe  45  is a narrow groove having a narrow width where the opening end to the grounding surface is closed in the loaded state. The sipe  45  is inclined such that a portion to be grounded later during rolling of the tire heads toward the tire grounding end E side. 
     The pneumatic tire  1  of the present embodiment is excellent in traction performance in the front-rear direction because of the zigzag shape of the center main groove  10 . In addition, the center main groove  10  is formed by alternately arranging the first groove portions  11  and the second groove portions  12  having different inclination directions. Since the first groove portions  11  which are longer than the second groove portions are inclined such that a portion to be grounded later heads toward the tire grounding end E side during rolling of the tire, it is excellent in drainage performance to the tire grounding end E side by the center main groove  10 . Further, since the first lateral groove  20  traverses the mediate land portion  35  and the shoulder land portion  40 , it is excellent in drainage performance to the tire grounding end E side. 
     Further, since the center main groove  10  has a zigzag shape, the bulging portion  31  in the tire width direction is formed in the center land portion  30 , and a width of the center land portion in the vicinity of the bulging portion  31  is widened. Usually, such a portion of the land portion that has a wide width is difficult to be drained. However, in the present embodiment, the first lateral groove  20  extends to the bulging portion  31  in the center land portion  30  to form the notch  21 , and thus, water around the bulging portion  31  is also drained through the notch  21 . Further, the notch  21  also serves to improve the traction performance. As described above, the pneumatic tire  1  of the present embodiment has good drainage performance and traction performance. 
     Further, since the shoulder main groove  15  has a zigzag shape, it is excellent in the traction performance in the front-rear direction. In addition, since the shoulder main groove  15  is formed by alternately arranging the first groove portions  16  and the second groove portions  17  having different inclination directions, and the first groove portions  16  which are longer portions are inclined such that a portion to be grounded later heads toward the tire grounding end E side during rolling of the tire, it is excellent in drainage performance to the tire grounding end E side by the shoulder main groove  15 . 
     Further, since the second lateral grooves  25  are formed in addition to the first lateral grooves  20 , the traction performance of the pneumatic tire  1  is further improved. Here, the first lateral grooves  20  and the second lateral grooves  25  are alternately arranged in the circumferential direction of the tire and each of the first lateral grooves  20  extends to the bulging portion  31  in the center land portion  30 , whereas each of the second lateral grooves  25  does not extend to the center land portion  30 . Therefore, the width of the center land portion  30  is narrow between the two bulging portions  31  arranged in the circumferential direction of the tire, and the notch is not formed in the narrow width portion. As a result, rigidity of the center land portion  30  is secured. 
     Further, since the positions of the first lateral grooves  20  having an effect of improving grounding performance are shifted in the circumferential direction of the tire on both sides of the tire equator C, when looking at the entire tire width direction, the grounding performance is improved not intermittently, but continuously in the circumferential direction of the tire. Further, since the positions of the first lateral grooves  20  are shifted in the circumferential direction of the tire on both sides of the tire equator C, noise generated during traveling is reduced as compared with a case where the first lateral grooves are not shifted. Further, since the positions of the second groove portions  25  are also shifted in the circumferential direction of the tire on both sides of the tire equator C, the same effect may be obtained. 
     In addition, since the sipe  45  formed in the shoulder land portion  40  that extends in the circumferential direction of the tire is inclined such that a portion to be grounded later heads toward the tire grounding end E side, the sipe  45  also contributes to the improvement of the drainage performance. 
     Further, since the center main grooves  10  and the shoulder main grooves  15  are shifted in the circumferential direction of the tire on both sides of the tire equator C, noise generated during traveling is reduced as compared with a case where the center main grooves and the shoulder main grooves are not shifted. In addition, when the shape of the two center main grooves  10  becomes line symmetric with respect to the tire equator C as an axis of symmetry, difference in the width between the wide portion and the narrow portion of the center land portion  30  becomes large. However, as illustrated in  FIG. 2 or 3 , when the two center main grooves  10  are shifted in the circumferential direction of the tire so as not to be line symmetrical with respect to the tire equator C as the axis of symmetry, the difference in the width between the wide portion and the narrow portion of the center land portion  30  does not become too large. Therefore, the rigidity or grounding pressure at the time of grounding is relatively uniform in the circumferential direction of the tire. 
     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. 
     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,  30  . . . center land portion,  31  . . . bulging portion,  35  . . . mediate land portion,  40  . . . shoulder land portion,  45  . . . sipe,  125  . . . second lateral groove