Pneumatic tires

Abstract

To suppress occurrence of cracking in a root part of a bottom-up part while suppressing occurrence of belt lift.SOLUTION: A pneumatic tire T in the present invention includes a tread rubber 7 provided on a tread 3, and a belt layer 6 provided inside in a tire radial direction of the tread rubber 7. The tread rubber 7 includes a cap rubber layer 12 having a tread surface in contact with a road surface, and a base rubber layer 13 arranged inside in the tire radial direction of the cap rubber layer 12. A shoulder lateral groove 26 provided on the cap rubber layer 12 has a bottom-up part 30 raised from a groove bottom 26a so that a groove depth becomes shallow, and a reinforcement rubber layer 50 made of rubber having higher rubber hardness than that of the cap rubber layer 12 is provided between the bottom-up part 30 and the belt layer 6 so as to overlap a root part 32a inside in a tire width direction of the bottom-up part 30 and a tire radial direction RD.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] 2. Description of the Related Art Some pneumatic tires have shoulder lateral grooves extending in a direction intersecting the tire circumferential direction in a shoulder land portion formed between a shoulder main groove extending in the tire circumferential direction and a ground contact edge.

[0003] In such pneumatic tires, the rubber thickness is thin where the widthwise end of the belt layer (belt end) and the shoulder lateral groove overlap in the tire radial direction. This causes a movement called belt lift, in which the belt end rises outward in the tire radial direction when the tire rolls. Therefore, pneumatic tires are known that have raised groove bottoms in the shoulder lateral grooves at positions corresponding to the belt ends (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, if a raised portion is provided at the groove bottom of the shoulder lateral groove, cracks are likely to occur from the portion rising from the groove bottom of the shoulder lateral groove (the base of the raised portion) due to strain generated at the belt end when the tire rolls.

[0006] The present invention has been made in consideration of the above-described circumstances, and aims to provide a pneumatic tire that can suppress the occurrence of belt lift while suppressing the occurrence of cracks at the base of the bottom-raised portion. [Means for solving the problem]

[0007] The pneumatic tire of the present invention is a pneumatic tire comprising a tread rubber provided in a tread and a belt layer provided on the radially inner side of the tread rubber, wherein the tread rubber comprises a cap rubber layer having a tread surface that comes into contact with a road surface, and a base rubber layer disposed on the radially inner side of the cap rubber layer, the cap rubber layer comprising main grooves formed on the outer side in the tire width direction and extending in the tire circumferential direction, shoulder land portions formed between the main grooves and the ground contact edge, and lateral grooves provided in the shoulder land portions and extending in a direction intersecting the tire circumferential direction, the lateral grooves comprising raised bottom portions that protrude from the groove bottoms so as to reduce the groove depth, and the raised bottom portions and Between the belt layers, a reinforcing rubber layer made of rubber having a higher rubber hardness than the cap rubber layer is provided, and the bottom-up portion has a flat portion provided parallel to the contour line of the tread and a root portion connecting the flat portion and the groove bottom of the lateral groove, and the belt layer has a maximum width belt that is the longest in the tire width direction, and an outer belt that is provided overlapping the maximum width belt on the outer side in the tire radial direction, and a belt end of the outer belt overlaps the flat portion in the tire radial direction, and a belt end of the maximum width belt is provided on the outer side in the tire width direction than the flat portion of the bottom-up portion, and the reinforcing rubber layer overlaps the root portion on the inner side in the tire width direction of the bottom-up portion in the tire radial direction. and the outer end of the reinforcing rubber layer in the tire width direction coincides with the outer belt end The outer belt is provided so as to overlap the outer belt from the belt end of the outer belt to the inner side in the tire width direction. Effect of the Invention

[0008] In the above pneumatic tire, it is possible to suppress the occurrence of belt lift and also to suppress the occurrence of cracks at the base of the bottom-raised portion. [Brief description of the drawings]

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[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 developed view of the pneumatic tire T. Only the right half is shown in FIG. 1.

[0011] In the figure, the symbol CL indicates the tire equatorial plane corresponding to the center in the tire width direction. In this example, the pneumatic tire T is symmetric about the tire equatorial plane CL.

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

[0013] In this specification, unless otherwise specified, the dimensions and the like of each part of the pneumatic tire are those in the normal state without load when the pneumatic tire is mounted on a normal rim and filled with the normal internal pressure.

[0014] Also, in FIGS. 1 and 2, the symbol E indicates the grounding end in a state where the pneumatic tire is mounted on a normal rim, filled with the normal internal pressure, placed perpendicular to a flat road surface, and a normal load is applied.

[0015] The regular rim is the rim defined for each tire in a standard system that includes the standards on which the tire is based. For example, in JATMA, it is the standard rim; in TRA, it is the "Design Rim"; and in ETRTO, it is the "Measuring Rim". The regular internal pressure is the air pressure defined for each tire in a standard system that includes the standards on which the tire is based. In JATMA, it is the maximum air pressure; in TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and in ETRTO, it is the "INFLATION PRESSURE".

[0016] Also, the regular load is the load defined for each tire in a standard system that includes the standards on which the tire is based. In JATMA, it is the maximum load capacity; in TRA, it is the maximum value described in the above table; and in ETRTO, it is the "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 in the tire diameter direction, a tread 3 connected to each radially outer end of the sidewalls 2 in the tire diameter direction, and a pair of left and right buttresses 14 disposed radially inward of the tread 3 in the tire diameter direction. The buttress 14 is a boundary region between the sidewall 2 and the tread 3 and is provided so as to connect between the sidewall 2 and the tread 3.

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

[0019] The carcass 4 is locked by the bead core 1a at the bead 1 through the beltless 14 and the sidewall 2 from the tread 3, and reinforces the bead 1, the sidewall 2, the beltless 14, and the tread 3. In this example, the carcass 4 is locked by folding both ends around the bead core 1a from the inner side to the outer side in the tire width direction. An inner liner for maintaining air pressure is disposed inside the carcass 4.

[0020] The carcass 4 has at least one ply formed by arranging organic fiber or steel cords at a predetermined angle (for example, 70° to 90°) with respect to the tire circumferential direction CD and covering them with topping rubber. In this example, it is composed of two plies. As the organic fiber cords constituting the carcass 4, for example, polyester fibers, rayon fibers, aramid fibers, nylon fibers, etc. are preferably used.

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

[0022] A belt layer 6 is provided on the outer side of the carcass 4 in the tire radial direction RD of the tread 3, 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 and 9 provided on the inner side of the tread rubber 7 in the tire radial direction RD. The belts 8 and 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 with two belts, the first belt 8 and the second belt 9, in order from the inner side in the tire radial direction RD. Note that the belt layer 6 is not limited to two sheets and may be three sheets or more.

[0024] The first belt 8 is the innermost belt arranged most inwardly in the tire radial direction RD. Among the two belts, the first belt 8 is the belt with the largest width (belt width, i.e., the dimension in the tire width direction WD of the belt), and is sometimes referred to as the "maximum-width belt 8" hereinafter. The second belt 9 is the outermost belt arranged most outwardly in the tire radial direction RD (hereinafter, the second belt 9 is sometimes 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 a cord reinforcing material such as organic fiber or steel cord is provided so as to gradually separate from the carcass 4 as it goes towards 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 outside in the tire radial direction 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 outside in the tire radial direction of the maximum-width belt 8.

[0027] The tread rubber 7 has a two-layer structure composed of a cap rubber layer 12 having a tread surface in contact with the road surface and a base rubber layer 13 arranged inside the cap rubber layer 12 in the tire radial direction RD. The tread rubber 7 covers the outer end in the tire radial direction of the sidewall rubber 5.

[0028] The outer end in the tire width direction of the cap rubber layer 12 covers the outer end in the tire width direction of the base rubber layer 13 and terminates inside the tire radial direction RD from the outer end in the tire width direction of the base rubber layer 13. That is, the outer end in the tire width direction of the cap rubber layer 12 is located outside the tire width direction WD and inside the tire radial direction RD from 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 on the outer surface of the tire.

[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 provided on both sides of the tire equatorial plane CL and a pair of shoulder main grooves 20B, 20B respectively arranged outside thereof. The four main grooves 20A, 20A, 20B, 20B are zigzag grooves extending in the tire circumferential direction CD while bending with an amplitude in the tire width direction WD.

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

[0031] In the center land portion 21, a plurality of center cross grooves 24 extending intersecting with the center main groove 20A are provided at intervals in the tire circumferential direction CD. The center cross grooves 24 are provided so as to cross the center land portion 21, and a block row in which a plurality of blocks are arranged in the tire circumferential direction CD is formed in the center land portion 21.

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

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

[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 of the first lateral groove portion 27 in the tire width direction and with a wider groove width 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 inward 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 grooves 26 are provided with bottom-raised portions 30 that rise from the groove bottoms to connect the lateral sides 23a, 23a of the shoulder land portions 23 that form the shoulder lateral grooves 26 and reduce the groove depth.

[0036] Specifically, as shown in Figure 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 as to reduce the groove depth, a root portion 32a that connects the groove bottom 26a (here, the groove bottom of the first lateral groove portion 27) at the tire widthwise inner end of the lateral groove 26 and the flat portion 31, and a root portion 32a that connects the groove bottom 26a (here, the groove bottom of the second lateral groove portion 28) at the tire widthwise outer end of the lateral groove 26 and the flat portion 31.

[0037] The flat portions 31 are arranged parallel to the profile line of the tread surface, and have a constant groove depth H in the flat portions 31. The groove depth H in the flat portions 31 is shallower than the groove depth H1 at the groove bottom of the first lateral groove portions 27 and the groove depth H2 at the groove bottom of the second lateral groove portions 28, and is preferably between % and 70% of the groove depth H1 at the inner end of the shoulder lateral groove 26 in the tire width direction. By making the groove depth H0 in the flat portions 31 % or more, sufficient groove volume can be secured and a decrease in drainage performance can be suppressed. Furthermore, by making it 70% or less, a sufficient rubber thickness can be secured near the outer belt end 9a, thereby enhancing the belt lift suppression effect.

[0038] The raised portion 30 is provided at the groove bottom 26a of the shoulder lateral groove 26 such that the flat portion 31 is located inside the tire width direction from the maximum width belt end 8a and overlaps with the outer belt end 9a of the outer belt 9 in the tire radial direction RD. In other words, the raised portion 30 is provided in the shoulder lateral groove 26 such that the flat portion 31 does not exist outside the tire radial direction of the maximum width belt end 8a and the flat portion 31 exists outside the tire radial direction of the outer belt end 9a.

[0039] As shown in FIGS. 2 and 3, such a raised portion 30 is provided at the groove bottom of the second lateral groove portion 28 where the interval between the lateral surfaces 23a, 23a in the shoulder land portion 23 is large, and it is preferable to connect the lateral surfaces 23a, 23a partitioning the second lateral groove portion 28.

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

[0041] Specifically, as shown in FIG. 3, the reinforcing rubber layer 50 is a narrow strip-shaped member extending along the tire circumferential direction CD. The reinforcing rubber layer 50 is provided so as to overlap the outer side in the radial direction of the outer belt 9 so as to overlap with the attachment root portion 32a inside the tire width direction of the raised 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 so as to overlap the outer belt 9 such that the outer end 50a in the tire width direction of the reinforcing rubber layer 50 coincides with the outer belt end 9a.

[0043] Here, for the reinforcing rubber layer 50, rubber having a higher rubber hardness than the cap rubber layer 12 is used. Also, for the reinforcing rubber layer 50, rubber having a higher rubber hardness than the base rubber layer 13 may be used, or rubber having a higher rubber hardness than the under-belt rubber layer 10 may be used. Further, for the base rubber layer 13, rubber having a higher rubber hardness than the under-belt rubber layer may be used.

[0044] For example, for the reinforcing rubber layer 50, rubber with a rubber hardness in the range of 75 to 85 may be used, and for the cap rubber layer 12, rubber with a rubber hardness in the range of 50 to 74 may be used. Also, for the base rubber layer 13, rubber with a rubber hardness in the range of 50 to 70 may be used, and for the under-belt rubber layer 10, rubber with a rubber hardness in the range of 40 to 55 may be used.

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

[0046] Also, the thickness of the reinforcing rubber layer 50 is preferably thinner than the thickness of the tread rubber 7 on the outer side in the tire radial direction of the reinforcing rubber layer 50 (that is, the combined thickness of the base rubber layer 13 and the cap rubber layer 12). For example, the thickness of the reinforcing rubber layer 50 may be provided within the range of 0.2 to 1.2 mm, and the thickness of the tread rubber 7 may be provided within the range of 1.0 to 5.0 mm.

[0047] In the pneumatic tire T of the present embodiment as described above, since the flat portion 31 of the bottom raising portion 30 that rises from the groove bottom of the shoulder land portion 23 is provided on the outer side in the tire radial direction of the outer belt end 9a, it is possible to secure the rubber thickness in the vicinity of the outer belt end 9a where distortion is likely to occur during tire rolling, and belt lift can be suppressed.

[0048] Also, in the pneumatic tire T, since the flat portion 31 of the bottom raising portion 30 ends on the inner side in the tire width direction from the maximum width belt end 8a, it is possible to suppress an increase in the amount of rubber and a decrease in the drainage performance of the shoulder lateral groove 26. Moreover, in the vicinity of the maximum width belt end 8a, the inner side (carcass 4 side) of the belt layer 6 is curved significantly inward in the tire radial direction compared to the outer side (tread rubber side), and since it is easy to secure the thickness of the tread rubber 7 in the vicinity of the maximum width belt end 8a, belt lift can be suppressed even without the flat portion 31 on the outer side in the tire radial direction of the maximum width belt end 8a.

[0049] Further, in the pneumatic tire T, shoulder land portions 23, 23 are provided which include a first lateral groove portion 27 and a second lateral groove portion 28 provided wider than the first lateral groove portion 27, and a bottom raising portion 30 is provided at the groove bottom of the second lateral groove portion 28 so as to connect lateral side surfaces 23a, 23a partitioning the second lateral groove portion 28. Therefore, while securing the groove volume of the shoulder land portion 23 and improving the drainage performance, it is possible to suppress a decrease in the land rigidity in the vicinity of the second lateral groove portion 28 by the bottom raising portion 30.

[0050] Further, in the pneumatic tire T, a belt under rubber layer 10 is disposed between the widthwise end portion 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 including cords of organic fibers, steel, etc. Therefore, it is possible to relieve the strain generated in the vicinity of the maximum width belt end 8a during tire rolling and suppress belt lift.

[0051] Further, in the pneumatic tire T, a reinforcing rubber layer 50 having a higher rubber hardness than the cap rubber layer 12 is provided at a position overlapping with the attachment root portion 32a on the inner side in the tire width direction of the bottom raising portion 30 in the tire radial direction RD. Therefore, it is possible to suppress the strain generated in the vicinity of the attachment root portion 32 of the bottom raising portion 30 during tire rolling and suppress cracks generated at the attachment root portion 32 of the bottom raising portion 30.

[0052] Further, in the pneumatic tire T, since the outer belt 9 is provided so as to overlap the outer belt 9 from the outer belt end 9a toward the inner side in the tire width direction, before winding the outer belt 9 around the molding drum during the manufacture of the green tire, the reinforcing rubber layer 50 can be positioned and attached in advance at a predetermined position of the outer belt 9. The reinforcing rubber layer 50 can be attached with high positional accuracy, and the green tire can be manufactured efficiently.

[0053] Further, in the pneumatic tire T, since the reinforcing rubber layer 50 is thinner than the tread rubber 7 provided on the outer side in the tire radial direction of the reinforcing rubber layer 50, the thickness of the tread rubber 7 tends to be reduced. It is possible to ensure the thickness of the tread rubber 7 at the groove bottom portion of the shoulder transverse groove 26, and it is possible to suppress the occurrence of cracks in the region from the groove bottom of the shoulder transverse groove 26 to the attachment root portion 32 of the bottom raising portion 30.

[0054] The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention.

Explanation of Reference Numerals

[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... Under Belt Rubber Layer, 12... Cap Rubber Layer, 13... Base Rubber Layer, 14... Buttress, 20A... Center Main Groove, 20B... Shoulder Main Groove, 21... Center Land, 22... Intermediate Land, 23... Shoulder Land, 24... Center Transverse Groove, 25... Intermediate Transverse Groove, 26... Shoulder Transverse Groove, 27... First Transverse Groove Portion, 28... Second Transverse Groove Portion, 29... Connecting Portion, 30... Bottom Raising Portion, 31... Flat Portion, 32a... Attachment Root Portion, 32b... Attachment Root Portion, 50... Reinforcing Rubber Layer

Claims

1. In a pneumatic tire comprising tread rubber provided on a tread and a belt layer provided on the inner side in the tire radial direction of the tread rubber, the tread rubber includes a cap rubber layer having a tread surface that contacts the road surface, and a base rubber layer disposed on the inner side in the tire radial direction of the cap rubber layer, the cap rubber layer includes 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 the ground contact end, and a lateral groove provided on the shoulder land portion and extending in a direction intersecting the tire circumferential direction, the lateral groove includes a bottom raising portion that bulges from the groove bottom so that the groove depth becomes shallower, a reinforcing rubber layer made of rubber having a higher rubber hardness than the cap rubber layer is provided between the bottom raising portion and the belt layer, the bottom raising portion includes a flat portion provided parallel to the contour line of the tread, and an attachment root portion connecting the flat portion and the groove bottom of the lateral groove, the belt layer includes a maximum width belt that is the longest in the tire width direction, and an outer belt provided overlapping on the outer side in the tire radial direction of the maximum width belt. The belt end of the outer belt overlaps with the flat portion in the tire radial direction, and the belt end of the maximum width belt is provided on the outer side in the tire width direction than the flat portion of the bottom raising portion, the reinforcing rubber layer overlaps with the attachment root portion on the inner side in the tire width direction of the bottom raising portion in the tire radial direction, and is provided overlapping on the outer belt from the belt end of the outer belt to the inner side in the tire width direction so that the outer end in the tire width direction of the reinforcing rubber layer coincides with the outer belt end. A pneumatic tire.

2. The pneumatic tire according to claim 1, wherein the reinforcing rubber layer is thinner than the tread rubber provided on the outer side in the tire radial direction of the reinforcing rubber layer.

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