Pneumatic tires

Abstract

To suppress occurrence of belt lift while suppressing increase in a rubber amount and reduction in drainage performance.SOLUTION: A pneumatic tire T in the present invention includes a shoulder lateral groove 26 that is provided on a shoulder land part 23 and extends in a direction crossing a tire circumferential direction CD. A belt layer 6 includes a maximum width belt 8 longest in a tire width direction, and an outside belt 9 provided so as to overlap outside in a tire radial direction, and the shoulder lateral groove 26 has a bottom-up part 30 raised from a groove bottom so that a groove depth becomes shallow. The bottom-up part 30 has a flat part 31 having a constant groove depth. A flat part 31 is provided so as to be positioned inside in the tire width direction of the maximum width belt end 8a and outside in a direction vertical to a contour line of a tread surface of an outside belt end 9a.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Some pneumatic tires are provided with shoulder lateral grooves extending in a direction intersecting the circumferential direction of the tire in a shoulder land portion formed between a shoulder main groove extending in the circumferential direction of the tire and a ground contact edge.

[0003] In such pneumatic tires, the rubber thickness is thin at the position where the width direction end (belt end) of the belt layer and the shoulder lateral groove overlap in the tire radial direction. Therefore, a movement called belt lift, in which the belt end rises outward in the tire radial direction when the tire rolls, is likely to occur. For this reason, a pneumatic tire is known in which the shoulder lateral groove has a bottom-raised portion at a position corresponding to the belt end (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2012 / 026546 Summary of the Invention [Problem to be solved by the invention]

[0005] However, providing a raised bottom portion at the groove bottom of the shoulder lateral groove increases the amount of rubber, thereby increasing the tire weight, and reduces the groove volume of the shoulder lateral groove, thereby reducing the drainage performance. Therefore, when providing a raised bottom portion, it is preferable to limit the amount of protrusion from the groove bottom.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a pneumatic tire that can suppress the occurrence of belt lift while suppressing an increase in the amount of rubber and a decrease in drainage performance. [Means for solving the problem]

[0007] The pneumatic tire of the present invention is a pneumatic tire comprising a tread rubber provided on a tread, and a belt layer consisting of a plurality of belts provided on the tire radially inner side of the tread rubber, the tread rubber comprising a main groove extending in the tire circumferential direction formed on the outer side in the tire width direction, a shoulder land portion formed between the main groove and a ground contact edge, and a lateral groove provided in the shoulder land portion and extending in a direction intersecting the tire circumferential direction, the belt layer comprising a maximum width belt that is the longest in the tire width direction, and an outer belt provided overlapping the maximum width belt on the tire radially outer side, The lateral groove includes a bottom-raised portion that rises from a groove bottom so as to reduce a groove depth, and the bottom-raised portion includes a flat portion having a constant groove depth and a root portion that connects the flat portion and the groove bottom of the lateral groove, and the flat portion is provided so as to be located inside in the tire width direction from an end of the maximum width belt in the tire width direction and outside in a direction perpendicular to a contour line of the tread surface of the end of the outer belt in the tire width direction, and the lateral groove includes a first lateral groove portion on the main groove side, a second lateral groove portion that is provided wider than the first lateral groove portion on the outer side of the first lateral groove portion in the tire width direction, and a second lateral groove portion that connects the first lateral groove portion and the second lateral groove portion and connects the first lateral groove portion and the second lateral groove portion. beside a connecting portion whose groove width gradually increases toward the groove portion, the flat portion is provided in the second lateral groove portion, and the root portion is provided on the inner side in the tire width direction in the connecting portion. Effect of the Invention

[0008] In the above pneumatic tire, the occurrence of belt lift can be suppressed while suppressing an increase in the amount of rubber and a decrease in drainage performance. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a half cross-sectional view of a pneumatic tire according to a first embodiment of the present invention. [Diagram 2] An exploded view of the tread and buttress of the pneumatic tire of FIG. [Diagram 3] Enlarged cross-sectional view of the main part of Figure 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a tire meridian cross-sectional view of a pneumatic tire T, and Fig. 2 is a development view of the pneumatic tire T. Fig. 1 shows only the right half.

[0011] In the drawing, the symbol CL indicates a tire equatorial plane corresponding to the center in the tire width direction. In this example, the pneumatic tire T is symmetrical with respect to the tire equatorial plane CL.

[0012] Here, the tire width direction is the direction parallel to the tire rotation axis, and is indicated by the symbol WD in the drawings. The inner side of the tire width direction WD is the direction approaching the tire equatorial plane CL, and the outer side of the tire width direction WD is the direction away from the tire equatorial plane CL. The tire radial direction is the direction perpendicular to the tire rotation axis, and is indicated by the symbol RD in the drawings. The inner side of the tire radial direction RD is the direction approaching the tire rotation axis, and the outer side of the tire radial direction RD is the direction away from the tire rotation axis. The tire circumferential direction CD is the circumferential direction centered on the tire rotation axis.

[0013] In this specification, unless otherwise specified, the dimensions of each part of a pneumatic tire are those of the pneumatic tire mounted on a standard rim, inflated to a standard internal pressure, and in a standard, unloaded state.

[0014] In addition, in Figs. 1 and 2, the symbol E indicates the contact end when a pneumatic tire is mounted on a standard rim, inflated to a standard internal pressure, placed vertically on a flat road surface, and subjected to a standard load.

[0015] A regular rim is a rim that is determined for each tire by the standard system that includes the standard on which the tire is based, for example, the standard rim for JATMA, "Design Rim" for TRA, and "Measuring Rim" for ETRTO. Regular internal pressure is the air pressure that is determined for each tire by each standard in the standard system that includes the standard on which the tire is based, for example, the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO.

[0016] In addition, the normal load is the load that each standard specifies for each tire in the standard system, including the standard on which the tire is based. In the case of JATMA, it is the maximum load capacity, in the case of TRA, it is the maximum value listed in the table above, and in the case of ETRTO, it is "LOAD CAPACITY."

[0017] This pneumatic tire T includes a pair of left and right beads 1, a pair of left and right sidewalls 2 extending radially outward from the beads 1, a tread 3 continuing to the radially outer ends of each of the sidewalls 2, and a pair of left and right buttresses 14 disposed radially inward of the tread 3. The buttresses 14 are boundary regions between the sidewalls 2 and the tread 3, and are provided so as to connect the sidewalls 2 and the tread 3 together.

[0018] An annular bead core 1a and a bead filler 1b are provided in the bead 1. A toroidal carcass 4 is provided between the pair of beads 1.

[0019] The carcass 4 runs from the tread 3 through the buttresses 14 and sidewalls 2 to the beads 1 and is anchored by the bead cores 1a, reinforcing the beads 1, the sidewalls 2, the buttresses 14 and the tread 3. In this example, the carcass 4 is anchored by folding back both ends around the bead cores 1a from the inner side to the outer side in the tire width direction. An inner liner is disposed inside the carcass 4 to retain air pressure.

[0020] The carcass 4 has at least one ply in which organic fiber or steel cords are arranged at a predetermined angle (e.g., 70° to 90°) with respect to the tire circumferential direction CD and covered with a topping rubber. In this example, it is configured with two plies. As the organic fiber cords that make up the carcass 4, for example, polyester fiber, rayon fiber, aramid fiber, nylon fiber, etc. are preferably used.

[0021] In the sidewall 2, a sidewall rubber 5 is provided on the outer side of the carcass 4 (that is, on the outer surface side of the tire).

[0022] In the tread 3, a belt layer 6 is provided on the outer side of the carcass 4 in the tire radial direction RD, and a tread rubber 7 is laminated on the outer side of the belt layer 6 in the tire radial direction RD.

[0023] The belt layer 6 is composed of a plurality of belts 8, 9 provided on the inner side of the tread rubber 7 in the tire radial direction RD. The belts 8, 9 are formed by arranging belt cords such as steel cords at an inclined angle of, for example, 10° to 35° with respect to the tire circumferential direction CD and covering them with rubber. In this example, the belt layer 6 has a two-layer structure having two belts, a first belt 8 and a second belt 9, in that order from the inner side in the tire radial direction RD. The belt layer 6 is not limited to two layers, and may be three or more layers.

[0024] The first belt 8 is an innermost belt disposed on the innermost side in the tire radial direction RD. The first belt 8 is the widest belt (hereinafter, the first belt 8 may be referred to as the "widest belt 8") that has the largest width (belt width, i.e., the dimension of the belt in the tire width direction WD) among the two belts. The second belt 9 is an outermost belt disposed on the outermost side in the tire radial direction RD (hereinafter, the second belt 9 may be referred to as the "outer belt 9").

[0025] Between the maximum width belt 8 and the carcass 4, a belt under rubber layer 10 that does not contain cord reinforcing materials such as organic fibers or steel cords is provided so as to gradually move away from the carcass 4 toward the tire width direction end of the maximum width belt 8 (hereinafter sometimes referred to as the "maximum width belt end 8a").

[0026] The outer belt 9 is overlapped on the tire radially outside of the maximum width belt 8 over the entire tire width direction WD, and the tire width direction end 9a of the outer belt 9 (hereinafter sometimes referred to as the "outer belt end 9a") is also overlapped on the tire radially outside of the maximum width belt 8.

[0027] The tread rubber 7 has a two-layer structure consisting of a cap rubber layer 12 having a tread surface that comes into contact with the road surface, and a base rubber layer 13 arranged on the inner side in the tire radial direction RD of the cap rubber layer 12. The tread rubber 7 covers the outer end portion of the sidewall rubber 5 in the tire radial direction.

[0028] The cap rubber layer 12 has an outer end in the tire width direction covering an outer end in the tire width direction of the base rubber layer 13, and terminates on the inner side in the tire radial direction RD than the outer end in the tire width direction of the base rubber layer 13. In other words, the outer end in the tire width direction of the cap rubber layer 12 is located on the outer side in the tire width direction WD and on the inner side in the tire radial direction RD than the outer end in the tire width direction of the base rubber layer 13. As a result, the entire width of the base rubber layer 13 is covered by the cap rubber layer 12, and is not exposed to the tire outer surface.

[0029] In the cap rubber layer 12, a plurality of main grooves 20A, 20A, 20B, 20B extending along the tire circumferential direction CD are formed at intervals in the tire width direction WD. In this example, a pair of center main grooves 20A, 20A are provided on both sides of the tire equatorial plane CL, and a pair of shoulder main grooves 20B, 20B are provided on the outside of the center main grooves 20A, 20A. The four main grooves 20A, 20A, 20B, 20B are zigzag grooves extending in the tire circumferential direction CD while bending with amplitude in the tire width direction WD.

[0030] A plurality of land portions are defined in the tire width direction WD by the main grooves 20A, 20A, 20B, 20B in the cap rubber layer 12. In detail, a center land portion 21 is sandwiched between the pair of center main grooves 20A, 20A, a pair of left and right intermediate land portions 22 are sandwiched between the center main groove 20A and the shoulder main groove 20B, and a pair of left and right shoulder land portions 23 are formed between the shoulder main groove 20B and the ground contact edge E.

[0031] The center land portion 21 is provided with a plurality of center lateral grooves 24 that extend crossing the center main groove 20A and are spaced apart in the tire circumferential direction CD. The center lateral grooves 24 are provided so as to cross the center land portion 21, and form a block row in the center land portion 21, with a plurality of blocks arranged in the tire circumferential direction CD.

[0032] In the intermediate land portion 22, a plurality of intermediate lateral grooves 25 are provided at intervals in the tire circumferential direction CD, the intermediate lateral grooves 25 extending crossing the center main groove 20A and the shoulder main grooves 20B. The intermediate lateral grooves 25 are provided so as to cross the intermediate land portion 22, and form a block row in the intermediate land portion 22, in which a plurality of blocks are arranged in the tire circumferential direction CD.

[0033] A plurality of shoulder lateral grooves 26 are provided at intervals in the tire circumferential direction CD in the shoulder land portion 23, the shoulder lateral grooves 26 extending intersecting the shoulder main groove 20B. The shoulder lateral grooves 26 open at the ground contact edge E on the outer side in the tire width direction, and terminate within the shoulder land portion 23 on the inner side in the tire width direction without opening into the shoulder main groove 20B.

[0034] The shoulder lateral groove 26 includes a first lateral groove portion 27 on the shoulder main groove 20B side (inner side in the tire width direction), a second lateral groove portion 28 provided on the outer side in the tire width direction of the first lateral groove portion 27 and having a groove width wider than the first lateral groove portion 27, and a connecting portion 29 connecting the first lateral groove portion 27 and the second lateral groove portion 28. The second lateral groove portion 28 extends to the inner side in the tire width direction from the outer belt end 9a so as to overlap with the maximum width belt end 8a and the outer belt end 9a in the tire radial direction RD.

[0035] The shoulder lateral groove 26 is provided with a bottom-raised portion 30 that rises from the groove bottom so as to connect the lateral sides 23a, 23a of the shoulder land portion 23 that forms the shoulder lateral groove 26 and to make the groove depth shallower.

[0036] Specifically, as shown in FIG. 3 , the bottom-raised portion 30 includes a flat portion 31 that rises from the groove bottom 26a of the shoulder lateral groove 26 so that the groove depth is shallow, a base portion 32a that connects the groove bottom 26a (here, the groove bottom of the first lateral groove portion 27) at the inner end of the lateral groove 26 in the tire width direction to the flat portion 31, and a base portion 32a that connects the groove bottom 26a (here, the groove bottom of the second lateral groove portion 28) at the outer end of the lateral groove 26 in the tire width direction to the flat portion 31.

[0037] The flat portion 31 is provided parallel to the contour line (profile line) of the tread surface, and the groove depth H in the flat portion 31 is constant. The groove depth H in the flat portion 31 is shallower than the groove depth H1 at the groove bottom of the first lateral groove portion 27 and the groove depth H2 at the groove bottom of the second lateral groove portion 28, and is preferably 20% to 70% of the groove depth H1 at the inner end portion in the tire width direction of the shoulder lateral groove 26. By making the groove depth H0 in the flat portion 31 20% or more, a sufficient groove volume can be secured and a decrease in drainage can be suppressed. In addition, by making it 70% or less, a rubber thickness can be secured in the vicinity of the outer belt end 9a, and the effect of suppressing belt lift can be enhanced.

[0038] The bottom-raised portion 30 is provided at the groove bottom 26a of the shoulder lateral groove 26 so that the flat portion 31 is located inside the maximum width belt end 8a in the tire width direction and outside the outer belt end 9a in the direction perpendicular to the contour line of the tread surface. In other words, the bottom-raised portion 30 is provided in the shoulder lateral groove 26 so that the flat portion 31 does not exist outside the maximum width belt end 8a in the tire radial direction, but exists outside from the outer belt end 9a in the direction perpendicular to the contour line of the tread surface.

[0039] As shown in Figures 2 and 3, it is preferable that such a bottom-raised portion 30 is provided at the groove bottom of the second lateral groove portion 28 in the shoulder land portion 23, in which the spacing between the lateral sides 23a, 23a is large, and connects the lateral sides 23a, 23a that define the second lateral groove portion 28.

[0040] In such a pneumatic tire T, a reinforcing rubber layer 50 is preferably provided between the bottom raised portion 30 and the belt layer 6.

[0041] 3, the reinforcing rubber layer 50 is a narrow band-like member extending along the tire circumferential direction CD. The reinforcing rubber layer 50 is provided on the radially outer side of the outer belt 9 so as to overlap with the tire widthwise inner root portion 32a of the bottom raising portion 30 in the tire radial direction, and is embedded in the base rubber layer 13 of the tread rubber 7.

[0042] In this example, the reinforcing rubber layer 50 is provided overlapping the outer belt 9 so that an outer end 50a in the tire width direction of the reinforcing rubber layer 50 coincides with an outer belt end 9a.

[0043] Here, the reinforcing rubber layer 50 is made of rubber having a higher hardness than the cap rubber layer 12. The reinforcing rubber layer 50 may be made of rubber having a higher hardness than the base rubber layer 13, or may be made of rubber having a higher hardness than the underbelt rubber layer 10.

[0044] For example, the reinforcing rubber layer 50 may be made of rubber having a rubber hardness in the range of 75 to 85, and the cap rubber layer 12 may be made of rubber having a rubber hardness in the range of 50 to 74. The base rubber layer 36 may be made of rubber having a rubber hardness in the range of 50 to 70, and the underbelt rubber layer 10 may be made of rubber having a rubber hardness in the range of 40 to 55.

[0045] In this specification, the rubber hardness is JIS K6253-1-2012 3.2 durometer hardness, and is measured in an atmosphere of 23°C using a type A durometer for general rubber (medium hardness).

[0046] Moreover, the thickness of the reinforcing rubber layer 50 is preferably thinner than the thickness of the tread rubber 7 (i.e., the combined thickness of the base rubber layer 13 and the cap rubber layer 12) on the radially outer side of the reinforcing rubber layer 50. For example, the thickness of the reinforcing rubber layer 50 may be set within a range of 0.2 to 1.2 mm, and the thickness of the tread rubber 7 may be set within a range of 1.0 to 5.0 mm.

[0047] In the pneumatic tire T of this embodiment as described above, the flat portion 31 of the bottom-raised portion 30 that protrudes from the groove bottom of the shoulder land portion 23 is provided on the tire radial outside of the outer belt end 9a, so that the rubber thickness can be ensured in the vicinity of the outer belt end 9a, which is prone to distortion when the tire rolls, and belt lift can be suppressed.

[0048] In addition, in the pneumatic tire T, the flat portion 31 of the bottom raised portion 30 terminates on the inner side in the tire width direction than the maximum width belt end 8a, which makes it possible to suppress an increase in the amount of rubber and a decrease in the drainage performance of the shoulder lateral grooves 26. Moreover, in the vicinity of the maximum width belt end 8a, the tire inner surface side (carcass 4 side) of the belt layer 6 is curved more toward the tire radial direction inner side than the outer surface side (tread rubber side), and it is easy to ensure the thickness of the tread rubber 7 in the vicinity of the maximum width belt end 8a, so that belt lift can be suppressed even if there is no flat portion 31 on the tire radial direction outer side of the maximum width belt end 8a.

[0049] Furthermore, in the pneumatic tire T, a shoulder land portion 23, 23 is provided which includes a first lateral groove portion 27 and a second lateral groove portion 28 which is wider than the first lateral groove portion 27, and a bottom-raised portion 30 is provided at the groove bottom of the second lateral groove portion 28 so as to connect the lateral sides 23a, 23a which define the second lateral groove portion 28. Therefore, the groove volume of the shoulder land portion 23 is secured and drainage performance is improved, while the bottom-raised portion 30 prevents a decrease in the rigidity of the land portion near the second lateral groove portion 28.

[0050] In addition, in the pneumatic tire T, a belt under rubber layer 10 is disposed between the widthwise end of the maximum-width belt 8 and the carcass 4, and the maximum-width belt end 8a does not come into direct contact with the carcass 4, which contains organic fibers, steel cords, etc., so that distortion occurring near the maximum-width belt end 8a during tire rolling can be alleviated and belt lift can be suppressed.

[0051] Furthermore, in the pneumatic tire T, a reinforcing rubber layer 50 having a rubber hardness higher than that of the cap rubber layer 12 is provided at a position overlapping with the root portion 32a on the inner side in the tire width direction of the raised bottom portion 30 in the tire radial direction RD, so that distortion occurring near the root portion 32 of the raised bottom portion 30 when the tire rolls can be suppressed and cracks occurring at the root portion 32 of the raised bottom portion 30 can be suppressed.

[0052] Furthermore, in the pneumatic tire T, the outer belt end 9a is overlapped on the outer belt 9 on the inside in the tire width direction. Therefore, when manufacturing a green tire, the reinforcing rubber layer 50 can be positioned and attached to a predetermined position on the outer belt 9 before the outer belt 9 is wound around the building drum. This allows the reinforcing rubber layer 50 to be attached with high positional accuracy and allows the green tire to be manufactured efficiently.

[0053] In addition, in the pneumatic tire T, the reinforcing rubber layer 50 is thinner than the tread rubber 7 provided on the outer side of the reinforcing rubber layer 50 in the tire radial direction, so that the thickness of the tread rubber 7 tends to be thin. The thickness of the tread rubber 7 can be ensured at the groove bottom portion of the shoulder lateral groove 26, and the occurrence of cracks can be suppressed in the region from the groove bottom of the shoulder lateral groove 26 to the root portion 32 of the bottom-up portion 30.

[0054] The above-described embodiment is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0055] T... tire, 1... bead, 2... sidewall, 3... tread, 4... carcass, 5... sidewall rubber, 6... belt layer, 7... tread rubber, 8... maximum width belt, 8a... maximum width belt end, 9... outer belt, 9a... outer belt end, 10... underbelt rubber layer, 12... cap rubber layer, 13... base rubber layer, 14... buttress, 20A... center main groove, 20B... shoulder main groove, 21... center land portion, 22... intermediate land portion, 23... shoulder land portion, 24... center lateral groove, 25... intermediate lateral groove, 26... shoulder lateral groove, 27... first lateral groove portion, 28... second lateral groove portion, 29... connecting portion, 30... bottom raised portion, 31... flat portion, 32a... root portion, 32b... root portion, 50... reinforcement rubber layer

Claims

1. A pneumatic tire having a tread rubber provided on a tread and a belt layer consisting of a plurality of belts provided on the radially inner side of the tread rubber, The tread rubber includes a main groove formed on an outer side in the tire width direction and extending in the tire circumferential direction, a shoulder land portion formed between the main groove and a ground contact edge, and a lateral groove provided in the shoulder land portion and extending in a direction intersecting the tire circumferential direction, The belt layer includes a maximum width belt that is the longest in the tire width direction, and an outer belt that is overlapped on the outer side of the maximum width belt in the tire radial direction, The lateral groove has a bottom-raised portion that rises from the bottom of the groove so that the groove depth is shallower, The bottom-raised portion includes a flat portion having a constant groove depth and a root portion connecting the flat portion and a groove bottom of the lateral groove, The flat portion is provided so as to be located on the inner side in the tire width direction from the width direction end of the maximum width belt and on the outer side in a direction perpendicular to a contour line of the tread surface of the width direction end of the outer belt, a connecting portion that connects the first lateral groove portion and the second lateral groove portion and that has a groove width that gradually increases toward the second lateral groove portion, the flat portion being provided in the second lateral groove portion, and the root portion being provided on the inner side in the tire width direction.

2. The pneumatic tire according to claim 1 , further comprising a rubber layer disposed between the end portion in the width direction of the maximum width belt and the carcass.

3. 3. The pneumatic tire according to claim 1, wherein the groove depth of the bottom raised portion is 70% or less of the groove depth of the lateral groove at an inner end portion in the tire width direction.

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