JP7714280B2 - pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

Some pneumatic tires have shoulder lateral grooves extending in a direction that intersects with the circumferential direction of the tire in the shoulder land portion formed between the circumferentially extending shoulder main groove and the ground contact edge.

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 makes it easy for the belt end to lift outward in the tire radial direction, a phenomenon known as belt lift, when the tire rolls. For this reason, pneumatic tires are known that have raised portions in the shoulder lateral grooves at positions corresponding to the belt ends (see, for example, Patent Document 1 below).

International Publication No. 2012/026546

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.

The present invention was made in consideration of these circumstances, and aims to provide a pneumatic tire that can suppress the occurrence of belt lift while also suppressing the occurrence of cracks at the base of the bottom-raised portion.

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 the 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 a reinforcing rubber made of rubber having a higher rubber hardness than the cap rubber layer is disposed between the raised bottom portions and the belt layer. a rubber layer is provided, the bottom-raised portion includes 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, the belt layer includes a maximum width belt that is longest in the tire width direction, and an outer belt that is provided overlapping the maximum width belt on the tire radially outer side, the belt end of the outer belt overlapping the flat portion in the tire radial direction and the belt end of the maximum width belt is provided on the tire width outer side of the flat portion of the bottom-raised portion, the reinforcing rubber layer overlaps the tire radial direction with the root portion on the inner side of the bottom-raised portion in the tire width direction, and is provided overlapping the outer belt from the belt end of the outer belt on the outer side in the tire width direction so that the outer end of the reinforcing rubber layer in the tire width direction coincides with the outer belt end.

The above-mentioned pneumatic tire can suppress the occurrence of belt lift while also suppressing the occurrence of cracks at the base of the raised bottom portion.

FIG. 1 is a half cross-sectional view of a pneumatic tire according to a first embodiment of the present invention; FIG. 2 is a development view of the tread portion and buttress portion of the pneumatic tire of FIG. 1. Enlarged cross-sectional view of the main part of Figure 1

One embodiment of the present invention will now be described with reference to the drawings. Figure 1 is a tire meridian cross-section of a pneumatic tire T, and Figure 2 is a developed view of the pneumatic tire T. Only the right half is shown in Figure 1.

In the figure, the symbol CL indicates the tire equatorial plane, which corresponds to the tire widthwise center. In this example, the pneumatic tire T is symmetrical with respect to the tire equatorial plane CL.

Here, the tire width direction is the direction parallel to the tire rotational axis, and is indicated by the symbol WD in the diagram. 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 rotational axis, and is indicated by the symbol RD in the diagram. The inner side of the tire radial direction RD is the direction approaching the tire rotational axis, and the outer side of the tire radial direction RD is the direction away from the tire rotational axis. The tire circumferential direction CD is the circumferential direction centered on the tire rotational axis.

Unless otherwise specified, the dimensions of each part of a pneumatic tire in this specification refer to the tire being mounted on a standard rim, inflated to the standard internal pressure, and in a standard, unloaded state.

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

A normal rim is a rim specified for each tire by the standard system, including the standard on which the tire is based. For example, in the case of JATMA, it is a standard rim, in the case of TRA, it is a "Design Rim," and in the case of ETRTO, it is a "Measuring Rim." Normal internal pressure is the air pressure specified for each tire by the standard system, including the standard on which the tire is based. In the case of JATMA, it is the maximum air pressure, in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and in the case of ETRTO, it is "INFLATION PRESSURE."

Furthermore, the normal load is the load specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the maximum load capacity, for TRA, it is the maximum value listed in the table above, and for ETRTO, it is "LOAD CAPACITY."

This pneumatic tire T comprises 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 sidewall 2, and a pair of left and right buttresses 14 positioned radially inward of the tread 3. The buttresses 14 are the boundary region between the sidewalls 2 and tread 3, and are provided to connect the sidewalls 2 and tread 3.

The bead 1 has an annular bead core 1a and a bead filler 1b. A toroidal carcass 4 is provided between the pair of beads 1.

The carcass 4 runs from the tread 3 through the buttress 14 and sidewall 2 to the bead 1, where it is anchored by the bead core 1a, reinforcing the bead 1, sidewall 2, buttress 14, and tread 3. In this example, the carcass 4 is anchored by folding both ends around the bead core 1a from the inside to the outside in the tire width direction. An inner liner is arranged inside the carcass 4 to maintain air pressure.

The carcass 4 has at least one ply made of organic fiber or steel cords arranged at a predetermined angle (e.g., 70° to 90°) relative to the tire circumferential direction CD and covered with topping rubber. In this example, it is made up of two plies. Preferred organic fiber cords that make up the carcass 4 include polyester fiber, rayon fiber, aramid fiber, and nylon fiber.

A sidewall rubber 5 is provided on the sidewall 2 on the outside of the carcass 4 (i.e., on the outer surface of the tire).

The tread 3 has a belt layer 6 provided on the outer side of the carcass 4 in the tire radial direction RD, and tread rubber 7 laminated on the outer side of the belt layer 6 in the tire radial direction RD.

The belt layer 6 is composed of multiple belts 8, 9 arranged on the inner side of the tread rubber 7 in the tire radial direction RD. The belts 8, 9 are made of belt cords such as steel cords arranged at an angle of, for example, 10° to 35° relative to the tire circumferential direction CD and covered with rubber. In this example, the belt layer 6 has a two-layer structure with two belts, a first belt 8 and a second belt 9, arranged from the inner side in the tire radial direction RD. Note that the number of belt layers 6 is not limited to two, and may be three or more.

The first belt 8 is the innermost belt arranged on the innermost side in the tire radial direction RD. Of the two belts, the first belt 8 is the widest belt (hereinafter, the first belt 8 may be referred to as the "widest belt 8"), having the largest width (belt width, i.e., the dimension of the belt in the tire width direction WD). The second belt 9 is the outermost belt arranged on the outermost side in the tire radial direction RD (hereinafter, the second belt 9 may be referred to as the "outer belt 9").

Between the widest belt 8 and the carcass 4, an underbelt rubber layer 10 is provided, which does not contain cord reinforcing materials such as organic fibers or steel cords, and which gradually becomes more spaced apart from the carcass 4 as it approaches the tire width direction end of the widest belt 8 (hereinafter sometimes referred to as the "widest belt end 8a").

The outer belt 9 is overlapped on the tire radially outer side 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 outer side of the maximum width belt 8.

The tread rubber 7 has a two-layer structure consisting of a cap rubber layer 12 that provides the tread surface that comes into contact with the road surface, and a base rubber layer 13 that is arranged on the inside of the cap rubber layer 12 in the tire radial direction (RD). The tread rubber 7 covers the outer edge of the sidewall rubber 5 in the tire radial direction.

The outer end of the cap rubber layer 12 in the tire width direction covers the outer end of the base rubber layer 13 in the tire width direction, and terminates further inward in the tire radial direction RD than the outer end of the base rubber layer 13 in the tire width direction. In other words, the outer end of the cap rubber layer 12 in the tire width direction is located further outward in the tire width direction WD and further inward in the tire radial direction RD than the outer end of the base rubber layer 13 in the tire width direction. 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 tire surface.

The cap rubber layer 12 is formed with multiple main grooves 20A, 20A, 20B, 20B extending along the tire circumferential direction CD and spaced apart in the tire width direction WD. In this example, there are 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 located on the outside of them. The four main grooves 20A, 20A, 20B, 20B are zigzag grooves that extend in the tire circumferential direction CD while bending with amplitude in the tire width direction WD.

The cap rubber layer 12 is divided into multiple land portions in the tire width direction WD by the main grooves 20A, 20A, 20B, 20B. Specifically, there is 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 tread edge E.

The center land portion 21 is provided with a plurality of center lateral grooves 24 spaced apart in the tire circumferential direction CD, each extending intersecting the center main groove 20A. The center lateral grooves 24 are arranged across the center land portion 21, forming a block row in the center land portion 21, with multiple blocks arranged in the tire circumferential direction CD.

The intermediate land portion 22 is provided with a plurality of intermediate lateral grooves 25 spaced apart in the tire circumferential direction CD, which extend intersecting 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, forming a block row in the intermediate land portion 22, with multiple blocks arranged in the tire circumferential direction CD.

The shoulder land portion 23 is provided with multiple shoulder lateral grooves 26 spaced apart in the tire circumferential direction CD, extending intersecting the shoulder main grooves 20B. The shoulder lateral grooves 26 open at the 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 grooves 20B.

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 on the outer side of the first lateral groove portion 27 in the tire width direction and 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 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.

The shoulder lateral grooves 26 are provided with raised bottom portions 30 that rise from the groove bottom to shallow the groove depth and connect the lateral sides 23a, 23a of the shoulder land portions 23 that form the shoulder lateral grooves 26.

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 as to reduce the groove depth, a root portion 32a that connects the groove bottom 26a at the inner end of the lateral groove 26 in the tire width direction (here, the groove bottom of the first lateral groove portion 27) to the flat portion 31, and a root portion 32a that connects the groove bottom 26a at the outer end of the lateral groove 26 in the tire width direction (here, the groove bottom of the second lateral groove portion 28) to the flat portion 31.

The flat portions 31 are arranged parallel to the profile line of the tread surface, and the groove depth H in the flat portions 31 is constant. 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 0.05% and 70% of the groove depth H1 at the inner end of the shoulder lateral groove 26 in the tire width direction. By having the groove depth H0 in the flat portions 31 be 0.05% or more, sufficient groove volume can be ensured and a decrease in drainage performance can be suppressed. Furthermore, by having it be 70% or less, sufficient rubber thickness can be ensured near the outer belt end 9a, thereby improving the belt lift suppression effect.

The raised bottom portion 30 is provided at the groove bottom 26a of the shoulder lateral groove 26 so that the flat portion 31 is located inward in the tire width direction from the widest 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 bottom portion 30 is provided in the shoulder lateral groove 26 so that the flat portion 31 does not exist on the tire radially outer side of the widest belt end 8a, but does exist on the tire radially outer side of the outer belt end 9a.

As shown in Figures 2 and 3, such bottom-raised portions 30 are preferably provided at the groove bottoms of the second lateral groove portions 28 in the shoulder land portion 23, where the spacing between the lateral sides 23a, 23a is large, and connect the lateral sides 23a, 23a that define the second lateral groove portions 28.

In addition, in such a pneumatic tire T, a reinforcing rubber layer 50 is provided between the bottom raised portion 30 and the belt layer 6.

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 on the radially outer side of the outer belt 9 so as to overlap the tire radial direction with the tire widthwise inner root portion 32a of the bottom-raised portion 30, and is embedded in the base rubber layer 13 of the tread rubber 7.

In this example, the reinforcing rubber layer 50 is superimposed on the outer belt 9 so that the tire width direction outer end 50a of the reinforcing rubber layer 50 coincides with the outer belt end 9a.

Here, the reinforcing rubber layer 50 is made of rubber with a higher hardness than the cap rubber layer 12. The reinforcing rubber layer 50 may also be made of rubber with a higher hardness than the base rubber layer 13, or may also be made of rubber with a higher hardness than the under-belt rubber layer 10. The base rubber layer 13 may also be made of rubber with a higher hardness than the under-belt rubber layer.

For example, the reinforcing rubber layer 50 may be made of rubber with a hardness range of 75 to 85, and the cap rubber layer 12 may be made of rubber with a hardness range of 50 to 74. Furthermore, the base rubber layer 13 may be made of rubber with a hardness range of 50 to 70, and the underbelt rubber layer 10 may be made of rubber with a hardness range of 40 to 55.

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

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

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 located radially outward of the outer belt end 9a, ensuring sufficient rubber thickness near the outer belt end 9a, where distortion is likely to occur when the tire rolls, and suppressing belt lift.

In addition, in the pneumatic tire T, the flat portion 31 of the bottom-raised portion 30 terminates inward in the tire width direction from the maximum-width belt end 8a, which prevents an increase in the amount of rubber and a decrease in the drainage performance of the shoulder lateral grooves 26. Furthermore, near the maximum-width belt end 8a, the tire inner side (carcass 4 side) of the belt layer 6 curves more toward the tire radially inward than the outer side (tread rubber side). This makes it easier to ensure the thickness of the tread rubber 7 near the maximum-width belt end 8a, so belt lift can be suppressed even without the flat portion 31 on the tire radially outer side of the maximum-width belt end 8a.

Furthermore, the pneumatic tire T has shoulder land portions 23, 23 each comprising a first lateral groove portion 27 and a second lateral groove portion 28 that 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 to connect the lateral sides 23a, 23a that define the second lateral groove portion 28.This ensures the groove volume of the shoulder land portion 23 and improves drainage performance, while the bottom-raised portion 30 prevents a decrease in land portion rigidity near the second lateral groove portion 28.

In addition, in the pneumatic tire T, an underbelt rubber layer 10 is disposed between the widthwise end of the maximum width belt 8 and the carcass 4. This prevents the maximum width belt end 8a from coming into direct contact with the carcass 4, which contains organic fibers, steel cords, etc., and therefore reduces distortion that occurs near the maximum width belt end 8a when the tire rolls, thereby suppressing belt lift.

In addition, in the pneumatic tire T, a reinforcing rubber layer 50 with a higher rubber hardness than the cap rubber layer 12 is provided at a position that overlaps with the root portion 32a of the bottom raised portion 30 on the inner side in the tire width direction in the tire radial direction RD. This suppresses distortion that occurs near the root portion 32 of the bottom raised portion 30 when the tire rolls, and suppresses cracks that occur at the root portion 32 of the bottom raised portion 30.

Furthermore, in the pneumatic tire T, the reinforcing rubber layer 50 is overlapped on the outer belt 9 from the outer belt end 9a toward the inside in the tire width direction. Therefore, when manufacturing a green tire, the reinforcing rubber layer 50 can be positioned and attached to the outer belt 9 in advance at a predetermined position before winding the outer belt 9 around the building drum. This allows the reinforcing rubber layer 50 to be attached with high positional accuracy and allows for efficient manufacturing of green tires.

Furthermore, in the pneumatic tire T, the reinforcing rubber layer 50 is thinner than the tread rubber 7 provided radially outward of the reinforcing rubber layer 50, so that the thickness of the tread rubber 7 can be ensured at the groove bottoms of the shoulder lateral grooves 26 where the thickness of the tread rubber 7 tends to be thin, and the occurrence of cracks can be suppressed in the region from the groove bottoms of the shoulder lateral grooves 26 to the base 32 of the bottom-raised portion 30.

The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be embodied in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention.

T...Tire, 1...Bead, 2...Sidewall, 3...Tread, 4...Carcass, 5...Sidewall rubber, 6...Belt layer, 7...Tread rubber, 8...Widest belt, 8a...Widest belt edge, 9...Outer belt, 9a...Outer belt edge, 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-up portion, 31...Flat portion, 32a...Root portion, 32b...Root portion, 50...Reinforcing rubber layer

Claims (2)

A pneumatic tire having a tread rubber provided in a tread and a belt layer provided on the tire radially inner side of the tread rubber,
The tread rubber includes a cap rubber layer having a tread surface that comes into contact with a road surface, and a base rubber layer disposed radially inward of the cap rubber layer,
the cap rubber layer 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 lateral grooves each include a bottom-raised portion that rises from the bottom of the groove so as to reduce the groove depth,
a reinforcing rubber layer made of rubber having a higher rubber hardness than the cap rubber layer is provided between the bottom raised portion and the belt layer;
The bottom-raised portion includes a flat portion provided parallel to a contour line of the tread, and a root portion connecting the flat portion and a 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 that is overlapped on the tire radially outer side of the maximum width belt, a belt end of the outer belt overlaps the flat portion in the tire radial direction, and the belt end of the maximum width belt is provided on the tire width outer side of the flat portion of the bottom-up portion,
the reinforcing rubber layer overlaps in the tire radial direction with the root portion of the bottom-raised portion on the inner side in the tire width direction, and is provided overlapping 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 of the reinforcing rubber layer in the tire width direction coincides with the outer belt end. The pneumatic tire according to claim 1, wherein the reinforcing rubber layer is thinner than the tread rubber provided radially outward of the reinforcing rubber layer.