Patent Publication Number: US-2019176530-A1

Title: Pneumatic tire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Application No. 2017-238872 (filed on Dec. 13, 2017) and claims priority from Japanese Patent Application No. 2017-238872. The present disclosure incorporates entire contents of Japanese Patent Application No. 2017-238872. 
     TECHNICAL FIELD 
     The present disclosure relates to a pneumatic tire. 
     BACKGROUND ART 
     A surface of a new pneumatic tire is a mirror surface, and a release agent applied to a mold used for molding penetrates into the surface of the new pneumatic tire. Therefore, in some cases, the new pneumatic tire may not be able to exhibit sufficient traveling performance. Attempts have been made to provide shallow grooves on a surface of a tread of a pneumatic tire, and to secure traveling performance for the new pneumatic tire by an edge effect of the shallow grooves. 
     Patent Document 1 discloses providing a uniform shallow groove over an entire surface of a tread. Patent Document 2 discloses directing an extending direction of a shallow groove which becomes shallower gradually toward a grounding end side (an outer side of a tire width direction) to the tire width direction. Patent Document 3 discloses, in a narrow range in a tread width direction, directing a direction of shallow groove to a circumferential direction of a tire more than other grooves in other locations. Patent Document 4 and Patent Document 5 disclose an annular shallow groove. 
     Patent Document 1: Japanese Patent No. 3702958 
     Patent Document 2: Japanese Patent No. 4735137 
     Patent Document 3: Japanese Patent No. 4519141 
     Patent Document 4: Chinese Patent Application Publication No. 1789024 
     Patent Document 5: Europe Patent Application Publication No. 1580034 
     DISCLOSURE OF THE INVENTION 
     Problem that the Invention is to Solve 
     By the way, the shallow groove exerts an edge effect in a direction orthogonal to an extending direction thereof. Therefore, when the uniform shallow groove is provided over the entire surface of the tread as in Patent Document 1, balance of a direction of the edge effect is poor. Further, when the extending direction of the shallow groove which becomes shallower gradually toward the grounding end side as in Patent Document 2, balance of a direction of the edge effect is poor in a center portion in the tire width direction and in both sides in the tire width direction. Further, since the edge effect of the shallow groove is small, when the extending direction of the shallow groove is changed only in the narrow range in the tread width direction as in Patent Document 3, the effect by changing the extending direction is small. 
     Therefore, the present disclosure is to provide a pneumatic tire with good directional balance of an edge effect of a shallow groove. 
     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; a shoulder land portion between the shoulder main groove and the grounding end portion; and shallow grooves on a surface of each of the land portions, in which the shallow grooves in the center land portion and the shoulder land portion have many components in a circumferential direction of the tire, and the shallow grooves in the mediate land portion have more components in a tire width direction than the shallow grooves in the center land portion and the shoulder land portion. 
     Advantage of the Invention 
     The pneumatic tire of the embodiment has excellent directional balance of an edge effect of the shallow grooves because of the above features. 
    
    
     
       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 (shallow grooves are omitted in the drawing) of the pneumatic tire of the embodiment. 
         FIG. 3  A tread pattern (shallow grooves are illustrated in the drawing) of the pneumatic tire of the embodiment. 
         FIG. 4  A cross-sectional view in a width direction of a shallow groove. 
     
    
    
     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 of 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 (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. 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 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 , the first groove portion  16  is inclined such that a portion to be grounded later heads toward the tire grounding end E side. 
     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 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 . 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 . Such first lateral grooves  20  and second lateral grooves  25  are alternately arranged in the circumferential direction of the tire. The second groove portion  17  of the shoulder main groove  15  overlaps with the first lateral groove  20  and the second lateral groove  25 . 
     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. 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. 
     Annular sipes  80  are provided in the mediate block  36 . An 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 where the opening end to the grounding surface is closed in the loaded state. The small sipe  81  extends in a circumferential direction of the annular sipe  80 . Further, the small sipe  81  is bent toward an inner side of the annular sipe  80 . 
     A dimple  84  is provided along the small sipe  81  on the inner side of the bent portion of the small sipe  81 . The dimple  84  is a recessed portion with respect to a grounding surface. 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 sipe  45  extending in the circumferential direction of the tire is provided 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 heads toward the tire grounding end E side. 
     Further, the center land portion  30 , the mediate block  36 , and the shoulder block  41  are provided with a plurality of tire width direction sipes  32 ,  37 , and  42  extending in the tire width direction, respectively. 
     As illustrated in  FIG. 3 , shallow grooves  33 ,  38 , and  43  are provided in the center land portion  30 , the mediate block  36 , and the shoulder block  41 , respectively.  FIG. 4  illustrates a cross-sectional view of the shallow grooves  33 ,  38 , and  43 . A depth of these shallow grooves  33 ,  38 , and  43  is, for example, 0.2 to 0.4 mm (including 0.2 mm and 0.4 mm). Further, a width of these shallow grooves  33 ,  38 , and  43  is, for example, 0.4 to 0.6 mm (including 0.4 mm and 0.6 mm). 
     The shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41  have many components in the circumferential direction of the tire. In other words, the shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41  extend toward the circumferential direction of the tire rather than the tire width direction. Meanwhile, the shallow grooves  38  in the mediate block  36  have more components in a tire width direction than the shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41 . 
     Taking a look into the shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41 , these shallow grooves  33  and  43  are inclined such that a portion that is grounded later during rolling of the tire heads toward the tire grounding end E side. Further, the shallow grooves  33  in the center land portion  30  are straight, whereas the shallow grooves  43  in the shoulder block  41  have a zigzag shape. Further, the shallow grooves  43  in the shoulder block  41  are arranged more densely than the shallow grooves  33  in the center land portion  30 . The density of the shallow grooves is calculated by dividing the total area of the shallow grooves in the land portion or in the block in a plan view (that is, when viewed from the tire outer radial side) by the area of the land portion or the area of the block. 
     Further, the shallow grooves  38  in the mediate block  36  illustrated are annular (closed loop) in a plan view. Therefore, it is not able to define whether the shallow grooves  38  extend in the circumferential direction of the tire or in the tire width direction. Therefore, as compared with the shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41 , the shallow grooves  38  may be defined to have many components in the tire width direction. As illustrated in  FIG. 3 , one annular sipe  80  is surrounded by a plurality of shallow grooves  38  having different sizes of closed loops. The shallow grooves  38  in the mediate block  36  is a pentagon in a plan view, but may be another polygon or circle in a plan view. A portion that is interrupted at the end portion of the mediate block  36  may be regarded as a part of the annular shallow grooves  38 . 
     As illustrated in drawings, these shallow grooves  33 ,  38 , and  43  may intersect with the tire width direction sipes  32 ,  37 , and  42 . Of course, the shallow grooves  33 ,  38 , and  43  are shallower than the tire width direction sipes  32 ,  37 , and  42 . 
     As described above, in the pneumatic tire  1  of the embodiment, the shallow grooves  33  in the center land portion  30  and the shallow grooves  43  in the shoulder block  41  have many components in the circumferential direction of the tire, and the shallow grooves  38  in the mediate block  36  have more components in the tire width direction than the shallow grooves  33  and  43 . Therefore, taking a look into the whole tread, the directional balance of the edge effect of the shallow grooves  33 ,  38 , and  43  are excellent. 
     Further, although the shoulder land portion  40  has a shorter grounding length in the circumferential direction of the tire than the center land portion  30 , the shallow grooves  43  in the shoulder block  41  are arranged more densely than the shallow grooves  33  in the center land portion  30 . Therefore, the edge effect occurs sufficiently in the region of the shoulder block  41 . 
     Further, since the shallow grooves  43  in the shoulder block  41  has a zigzag shape, as compared with a case of being straight, the shallow grooves  43  are long, and thus, the length of the edge thereof is long. Therefore, the edge effect occurs sufficiently even in the region of the shoulder block  41  having a short grounding length. 
     Further, since the shallow grooves  38  in the mediate block  36  are annular, the directional balance of the edge effect in the mediate block  36  is particularly excellent. Further, since the shallow grooves  38  in the mediate block  36  are annular and arranged so as to surround the annular sipe  80 , the new pneumatic tire  1  is excellent in design. 
     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. For example, instead of the annular shallow grooves, shallow grooves extending in the tire width direction may be provided in the mediate block  36 . 
     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,  25  . . . second lateral groove,  30  . . . center land portion,  32  . . . tire width direction sipe,  33  . . . shallow groove,  35  . . . mediate land portion,  36  . . . mediate block,  37  . . . tire width direction sipe,  38  . . . shallow groove,  40  . . . shoulder land portion,  41  . . . shoulder block,  42  . . . tire width direction sipe,  43  . . . shallow sipe  43 ,  45  . . . sipe,  80  . . . annular sipe,  81  . . . small sipe,  84  . . . dimple