JP7629301B2 - Run-flat tires - Google Patents

Description

The present invention relates to a run-flat tire.

Conventionally, side-reinforced run-flat tires with a reinforcing rubber layer on the sidewall are known (for example, Patent Document 1, etc.). In such run-flat tires, when the internal pressure of the tire drops, the reinforcing rubber layer prevents the tire from becoming completely flat, making it possible to run-flat for a certain distance (driving with the internal pressure of the tire reduced).

JP 2016-203671 A

In run-flat tires, it is desirable to suppress a phenomenon called buckling, in which the tread in contact with the road surface during run-flat driving, dents inward in the radial direction of the tire, and to minimize a reduction in the contact area with the road surface.
However, in a tire in which the outermost main groove in the tire width direction is disposed near the shoulder portion where the tread transitions from the tread to the sidewall, as in the tire shown in Patent Document 1, the tread is likely to bend radially inward from the main groove, resulting in a large degree of buckling. If the degree of buckling becomes large, the tire contact area during run-flat driving will be significantly reduced, and the increased ground pressure may reduce run-flat durability, so a solution to this problem was desired.

The present invention was made in consideration of the above problems, and its purpose is to provide a run-flat tire that can sufficiently suppress buckling that occurs during run-flat driving, thereby suppressing the reduction of the tire's contact area and improving run-flat durability.

The run-flat tire of the present invention comprises a pair of beads, a pair of sidewalls extending radially outward from each of the pair of beads, a tread disposed between the pair of sidewalls and having a ground contact surface, a carcass ply stretched between the pair of beads, and a reinforcing rubber layer disposed on the sidewalls, and in the ground contact surface of the tread, a first region extends from a position 25 mm outward from the center position in the tire width direction to the outer side in the tire width direction, and the first region is a main groove non-positioned region in which no main grooves extending continuously along the tire circumferential direction are positioned.

The present invention provides a run-flat tire that can adequately suppress buckling that occurs during run-flat driving, thereby preventing a reduction in the tire's contact area and improving run-flat durability.

1 is a view showing a half cross section in the tire width direction of a run-flat tire according to a first embodiment of the present invention. 1 is a schematic diagram showing a circumferential portion of a contact surface of a tread of a run-flat tire according to a first embodiment, developed into a planar shape; 1 is a partial cross-sectional view showing a state of a run-flat tire of a first embodiment during run-flat driving. FIG. 1 is a partial cross-sectional view showing a state of a conventional run-flat tire as a reference example during run-flat driving. FIG. 5 is a schematic diagram showing a circumferential portion of a contact surface of a tread of a run-flat tire according to a second embodiment of the present invention, developed into a planar shape. FIG. 11 is a view showing a half cross section in the tire width direction of a run-flat tire according to a third embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view in the tire width direction showing a main groove of a run-flat tire according to a third embodiment. FIG. 8 is a view taken in the direction of an arrow VIII in FIG. 7, and is a plan view of a tread showing a main groove of a run-flat tire according to a third embodiment. FIG. 11 is a plan view of a tread showing a modified example of a main groove of a run-flat tire according to a third embodiment.

The following describes an embodiment of the present invention with reference to the drawings.

First Embodiment
FIG. 1 is a diagram showing a half cross section in the tire width direction of a tire 1 which is a run-flat tire according to a first embodiment.

The basic structure of tire 1 is symmetrical in cross section in the tire width direction, so FIG. 1 shows a cross section of the right half. In FIG. 1, the symbol S1 indicates the tire equatorial plane. The tire equatorial plane S1 is a plane that is perpendicular to the tire rotation axis (tire meridian) and is located at the center in the tire width direction. The tire equatorial plane S1 is, in other words, the center position in the tire width direction.

The cross-sectional view in Figure 1 is a cross-sectional view in the tire width direction (cross-sectional view at the tire meridian) of a tire mounted on a specified rim and inflated to the specified internal pressure in an unloaded state. The specified rim refers to the standard rim determined by JATMA for the tire size. The specified internal pressure is, for example, 180 kPa when the tire is for a passenger car.

Here, the tire width direction is a direction parallel to the tire rotation axis, and corresponds to the left-right direction on the paper surface in the cross-sectional view of Fig. 1. In Fig. 1, this direction is illustrated as tire width direction X.
The inner side in the tire width direction is a direction approaching the tire equatorial plane S1, which is the left side in Fig. 1. The outer side in the tire width direction is a direction away from the tire equatorial plane S1, which is the right side in Fig. 1.
The tire radial direction is a direction perpendicular to the tire rotation axis, and is the up-down direction on the paper surface in Fig. 1. In Fig. 1, this direction is illustrated as tire radial direction Y.
The outer side in the tire radial direction is a direction away from the tire rotation axis, and is the lower side on the paper in Fig. 1. The inner side in the tire radial direction is a direction approaching the tire rotation axis, and is the upper side on the paper in Fig. 1.
The same applies to Figs. 3, 4 and 6.

The tire 1 is, for example, a run-flat tire for passenger cars. As shown in FIG. 1, the tire 1 includes a pair of beads 10 provided on both sides in the tire width direction, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, a carcass ply 40 disposed between the pair of beads 10, and an inner liner 50 disposed on the tire cavity side of the carcass ply 40.

The bead 10 has a bead core 11, a bead filler 12 extending radially outward from the bead core 11, a chafer 13, and a rim protector 15.

The bead core 11 is an annular component formed by winding a rubber-coated metal bead wire multiple times, and serves to secure the tire 1 filled with air to the rim.
The bead filler 12 is a rubber member that tapers toward the outside in the tire radial direction. The bead filler 12 is a member provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of rubber that is harder than the surrounding rubber members, for example.

The chafer 13 is provided on the inner side in the tire radial direction of the carcass ply 40 provided around the bead core 11 .
The rim protector 15 includes a rim strip rubber 14. The rim strip rubber 14 is disposed on the outer side of the chafer 13 and the carcass ply 40 in the tire width direction. An apex 14a along the tire circumferential direction is formed on the outer surface of the rim strip rubber 14. The rim strip rubber 14 comes into contact with the rim on which the tire 1 is mounted. The rim protector 15 is continuous in an annular shape in the tire circumferential direction. The rim protector 15 has the function of protecting the rim (not shown) from external damage.

The sidewall 20 includes a sidewall rubber 21 arranged on the outer side of the carcass ply 40 in the tire width direction, and a reinforcing rubber layer 60 .
The sidewall rubber 21 constitutes the outer wall surface of the tire 1. The sidewall rubber 21 is the portion that bends the most when the tire 1 performs a cushioning function, and typically, flexible rubber having fatigue resistance is used for the sidewall rubber 21.
The reinforcing rubber layer 60 will be described later.

The tread 30 comprises an endless belt 31, a cap ply 32, and a tread rubber 33.

The belt 31 is disposed on the outer side in the tire radial direction of the carcass ply 40. The cap ply 32 is disposed on the outer side in the tire radial direction of the belt 31.
The belt 31 is a member that reinforces the tread 30. The belt 31 in this embodiment has a two-layer structure including an inner belt 311 and an outer belt 312. Both the inner belt 311 and the outer belt 312 have a structure in which a plurality of cords, such as steel cords, are covered with rubber.

In the two-layer belt 31 of this embodiment, the inner belt 311 is wider than the outer belt 312, and therefore the outer end 31A in the tire width direction of the belt 31 is formed by the outer end in the tire width direction of the inner belt 311. By providing the belt 31, the rigidity of the tire 1 is ensured and the contact of the tread 30 with the road surface is improved.
The belt 31 is not limited to a two-layer structure, but may have a one-layer structure or a three-layer or more structure.

The cap ply 32 is a member that reinforces the tread 30 together with the belt 31. The cap ply 32 has a structure in which a plurality of insulating organic fiber cords, such as polyamide fiber cords, are covered with rubber.
In this embodiment, an outer end 32A in the tire width direction of the cap ply 32 is disposed at approximately the same position as an outer end 31A in the tire width direction of the belt 31. By providing the cap ply 32, it is possible to improve durability and reduce road noise during driving.

An endless rubber pad 35 is arranged between both ends of the inner belt 311 and the outer belt 312 on the outer side in the tire width direction and both ends of the cap ply 32 on the outer side in the tire width direction.

The tread rubber 33 is disposed radially outward of the cap ply 32. The tread rubber 33 is a component that constitutes the contact surface 331 that comes into contact with the road surface during driving.

Figure 2 is a schematic diagram showing a part of the contact surface 331 of the tread 30 developed into a planar shape. In Figure 2, arrow X indicates the tire width direction, and arrow Z indicates the tire circumferential direction.

1 and 2, a tread pattern 34 consisting of a plurality of grooves is provided on the ground contact surface 331. The tread pattern 34 has a plurality of main grooves 341 and a plurality of sub grooves 345.
In this embodiment, two main grooves 341 are provided. Each of the two main grooves 341 extends along the tire circumferential direction. The two main grooves 341 are arranged in a main groove arrangement region 72, which serves as a second region, as described below.
2, the sub grooves 345 extend in a direction intersecting the tire circumferential direction. The sub grooves 345 of this embodiment are arranged in main groove non-arrangement regions 71 (first regions) described below on both sides in the tire width direction of the ground contact surface 331. The sub grooves 345 of this embodiment are arranged at a predetermined inclination angle with respect to the tire circumferential direction.

The carcass ply 40 constitutes a ply that serves as the framework of the tire 1. The carcass ply 40 is embedded in the tire 1 in a manner that passes between a pair of beads 10, a pair of sidewalls 20, and the tread 30.
The carcass ply 40 includes a plurality of carcass cords that form the framework of the tire 1. The plurality of carcass cords extend, for example, in the tire radial direction and are arranged side by side in the tire circumferential direction. The carcass cords are made of insulating organic fiber cords such as polyester or polyamide. The carcass ply 40 is formed by covering the plurality of carcass cords with rubber.

The carcass ply 40 has a ply body 401 that extends from one bead core 11 to the other bead core 11 and extends between the tread 30 and the bead 10, a pair of bends 402 that are folded back from the ply body 401 at the bead core 11, and a pair of turn-up portions 403 that extend radially outward from each of the bends 402. The ply body 401, the bends 402, and the turn-up portions 403 are continuous.

The ply body portion 401 is disposed on the inner side in the tire radial direction, on the inner side in the tire width direction of the bead core 11 and the bead filler 12. The folded-up portion 403 is disposed on the outer side in the tire width direction of the bead core 11 and the bead filler 12 on the inner side in the tire radial direction. In the portion other than the bead core 11 and the bead filler 12, the folded-up portion 403 is overlapped with the ply body portion 401. The bent portion 402 constitutes the innermost portion in the tire radial direction of the carcass ply 40.

In this embodiment, the carcass ply 40 is composed of two carcass plies, the first carcass ply 410 and the second carcass ply 420, but the carcass ply 40 may be composed of one layer or three or more layers.

As in this embodiment, it is preferable that a carcass ply 40 consisting of at least two plies is sandwiched between the bead filler 12 and the reinforcing rubber layer 60 described below. This more effectively prevents local deformation near the rim mounting portion, further improving run-flat durability.

The chafer 13 of the bead 10 described above is arranged to surround the radially inner end of the carcass ply 40 including the bend 402. The rim strip rubber 14 is arranged on the outer side in the tire width direction of the chafer 13 and the folded-back portion 403 of the carcass ply 40. The radially outer end of the rim strip rubber 14 is covered with the sidewall rubber 21 described above.

The inner liner 50 covers the tire inner surface between the pair of beads 10 and constitutes the inner wall surface of the tire 1. The inner liner 50 covers the inner surface of the ply body portion 401 of the carcass ply 40 in the tread 30, covers the inner surface of the reinforcing rubber layer 60 in the region extending from the tread 30 to the pair of sidewalls 20, and covers the inner surfaces of the reinforcing rubber layer 60 and the chafer 13 in the region extending from the pair of sidewalls 20 to the pair of beads 10.
The inner liner 50 is made of air-resistant rubber and prevents air within the tire cavity from leaking to the outside.

The reinforcing rubber layer 60 that constitutes the sidewall 20 is sandwiched between the carcass ply 40 and the inner liner 50.

The reinforcing rubber layer 60 is a side reinforcing rubber that has a generally crescent shape in a cross section in the tire width direction (cross section at the tire meridian). The reinforcing rubber layer 60 is provided in an annular shape around the entire circumference of the tire 1. The reinforcing rubber layer 60 has the function of preventing the tire 1 from becoming completely flattened even if the internal pressure of the tire 1 drops.

As shown in FIG. 1, on the tire outer surface side of the carcass ply 40 in the transition region between the tread 30 and the sidewall 20, the sidewall rubber 21 extends toward the tread 30, and the tread rubber 33 extends toward the sidewall 20, and the outer surface side of the sidewall rubber 21 is covered by the tread rubber 33.

In addition, on the tire outer surface side of the carcass ply 40 in the transition region between the bead 10 and the sidewall 20, the sidewall rubber 21 extends toward the bead 10, the rim strip rubber 14 extends toward the sidewall 20, and the sidewall rubber 21 covers the outer surface side of the rim strip rubber 14.

Furthermore, on the tire inner cavity side of the carcass ply 40 of the bead 10 , the tire radially inner end of the reinforcing rubber layer 60 is covered by the tire radially outer end of the chafer 13 .
An inner liner 50 further covers the tire cavity side of these rubber members.

Here, the rubber used for the bead filler 12 and the reinforcing rubber layer 60 has a hardness at least higher than that of the sidewall rubber 21 and the inner liner 50 .
The hardness of rubber is a value (durometer hardness) measured in an atmosphere of 23° C. using a type A durometer in accordance with JIS K6253.

For example, when the hardness of the sidewall rubber 21 is used as a standard, it is more preferable that the hardness of the bead filler 12 be made of rubber having a hardness of about 1.2 to 2.3 times the hardness of the sidewall rubber 21. It is also more preferable that the hardness of the reinforcing rubber layer 60 be made of rubber having a hardness of about 1.1 to 1.9 times the hardness of the sidewall rubber 21.
Furthermore, it is more preferable that the hardness of the rim strip rubber 14 be approximately 1 to 1.6 times that of the sidewall rubber 21 .
By setting the hardness within this range, it is possible to maintain a balance between the flexibility of the tire and the rigidity in the vicinity of the bead 10, and also to ensure run-flat durability.

As shown in Figures 1 and 2, in the ground contact surface 331 of the tread 30 of the tire 1 of the first embodiment, a main groove boundary 70 is virtually provided at a position 25 mm outward in the tire width direction from the tire width direction center position indicated by S1. In the ground contact surface 331, the area outward in the tire width direction from the main groove boundary 70 is defined as a main groove non-arrangement area (first area) 71. The main groove non-arrangement area 71 as the first area is provided on both sides of the ground contact surface 331 in the tire width direction. No main groove 341 is provided in the main groove non-arrangement area 71.

As shown in Figures 1 and 2, the tire widthwise inner side of the main groove boundary 70 on the contact surface 331 of the tread 30 is the main groove arrangement region (second region) 72. In this second region, the main groove arrangement region 72, a plurality of main grooves 341 that extend continuously along the tire circumferential direction are arranged. In this embodiment, a total of two main grooves 341 are arranged, one on each side, at symmetrical positions with the tire widthwise central position as the symmetrical center.

The main groove 341 is a so-called vertical groove that extends continuously along the tire circumferential direction, and is the widest and deepest groove among the grooves formed in the ground contact surface 331, and is a groove that greatly contributes to drainage. As shown in FIG. 1, the main groove 341 is formed surrounded by a bottom surface 36 formed in the tread rubber 33 and a first groove wall 37 and a second groove wall 38 that face each other in the tire width direction. The first groove wall 37 is disposed on the inner side in the tire width direction, and the second groove wall 38 is disposed on the outer side in the tire width direction. The main groove 341 has a cross-sectional shape in which the groove width increases from the bottom toward the opening to the ground contact surface 331. The width of the main groove 341 is, for example, 5 mm or more and 23 mm or less, and the depth of the main groove 341 is, for example, 5 mm or more and 11 mm or less.

As shown in FIG. 2, in each of the main groove non-placement areas 71 set on both sides of the contact surface 331 in the tire width direction, multiple secondary grooves 345 extending in a direction intersecting the tire circumferential direction are arranged in parallel in the tire circumferential direction.

The sub grooves 345 of this embodiment are linear grooves that are narrower than the main grooves 341 and are arranged at a predetermined inclination angle with respect to the tire circumferential direction. The sub grooves 345 are arranged in pairs, and multiple pairs are arranged in parallel with a gap in the tire circumferential direction. The multiple sub grooves 345 are arranged in the main groove non-aligned regions 71 on both sides in the tire width direction, with the directions of inclination with respect to the tire circumferential direction being opposite to each other.
In addition, the sub groove 345 of this embodiment extends from the tread 30 toward the sidewall 20 and extends to a region also called a shoulder portion, which is a portion where the tread 30 transitions to the sidewall 20 .

Figure 3 shows tire 1 during run-flat running when the internal pressure of tire 1 of a vehicle running on road surface H is approximately equal to atmospheric pressure. Meanwhile, Figure 4 shows, as a reference example, a situation in which tire 2, which has the same configuration as in the first embodiment except that main groove 349 is arranged in main groove non-arrangement region 71, which is the first region in the first embodiment, is running in a run-flat state.

As shown in FIG. 3, when the tire 1 of this embodiment is running run-flat, buckling may occur in which the tread 30 dents radially inward from the main groove 341 arranged in the main groove arrangement region 72. When buckling occurs, as shown in FIG. 3, the outer end of the contact surface 331 of the tread 30 in the tire width direction becomes the tire contact surface 331A and contacts the road surface H. Since the main groove 341 is not arranged in the non-main groove arrangement region 71, the rigidity is high, and bending that starts from buckling is unlikely to occur in the non-main groove arrangement region 71.

On the other hand, FIG. 4 shows a case where buckling occurs in the tire 2 during run-flat driving. In this case, buckling occurs in which the tread 30 is recessed radially inward from the main groove 349 located in the non-main-groove region 71. In this case, the tire contact surface 331B at the outer end in the tire width direction of the contact surface 331 of the tread 30 is in contact with the road surface H.

Comparing Figures 3 and 4, in the tire 2 shown in Figure 4, the main groove 349 arranged in the main groove non-placement region 71 is located closer to the sidewall 20, so the distance in the tire width direction from the main groove 349, which is the starting point of buckling, to the tire contact surface 331B is short, and the contact surface 331 in that region is inclined at a relatively steep angle with respect to the road surface H.
In contrast, in the tire 1 of this embodiment shown in Figure 3, the distance in the tire width direction from the main groove 341, which is the starting point of buckling, to the tire contact surface 331A is long, and the contact surface 331 from the main groove 341 to the tire contact surface 331A is gently inclined with respect to the road surface H.

Therefore, during run-flat driving, the tire contact surface 331A of tire 1 of this embodiment is longer in the tire width direction than the tire contact surface 331B of tire 2, and when comparing the contact areas, tire 1 of this embodiment is larger than tire 2. For this reason, tire 1 of this embodiment has less buckling than tire 2, thereby suppressing the reduction in the tire contact area. When the reduction in the tire contact area is suppressed and the tire contact area increases, this leads to a reduction in tire contact pressure, which results in a reduction in the burden on tire 1 and improved run-flat durability.

The tire 1 according to the first embodiment described above provides the following advantages:

(1) The tire 1 according to the first embodiment includes a pair of beads 10, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20 and having a ground contact surface, a carcass ply 40 spanning between the pair of beads 10, and a reinforcing rubber layer 60 disposed on the sidewall 20. In the ground contact surface 331 of the tread 30, a first region extends from a position 25 mm outward from the center position in the tire width direction to the outer side in the tire width direction, and this first region is a main groove non-positioned region 71 in which no main groove is positioned and which extends continuously along the tire circumferential direction.

This effectively suppresses buckling that occurs during run-flat driving, prevents a reduction in the tire's contact area, and improves run-flat durability.

(2) In the tire 1 according to the first embodiment, in the contact surface 331 of the tread 30, the inner side in the tire width direction of the main groove non-placement region 71 as the first region is the main groove placement region 72 as the second region, and the main groove 341 extending continuously along the tire circumferential direction is placed in this main groove placement region 72.

As a result, even if buckling occurs starting from the main groove 341 arranged in the main groove arrangement region 72, the degree of buckling is kept small, preventing a reduction in the tire's contact area and improving run-flat durability. In addition, the main groove 341 ensures drainage, improving hydroplaning resistance.

(3) In the tire 1 according to the first embodiment, at least in the main groove non-positioned region 71 as the first region, a plurality of secondary grooves 345 extending in a direction intersecting the tire circumferential direction are arranged in parallel in the tire circumferential direction.

As a result, even in the main groove non-placement area 71 where no main groove is placed, the multiple secondary grooves 345 provide drainage, improving hydroplaning resistance.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to FIG.
In the tire 1 of the second embodiment, the form of the grooves provided in the ground contact surface 331 of the tread 30 is different from that of the first embodiment, but the other configurations are the same as those of the first embodiment. Therefore, the differences will be described below.
In FIG. 5, arrow X indicates the tire width direction, and arrow Z indicates the tire circumferential direction.
In the second embodiment, the region referred to as the non-main groove region 71 in the first embodiment is referred to as a first region 71, and the region referred to as the main groove region 72 in the first embodiment is referred to as a second region 72.

Figure 5 is a schematic diagram showing a circumferential portion of the ground contact surface 331 of the tread 30, developed into a flat surface. In the second embodiment, a plurality of V-shaped grooves 346 are arranged at intervals in the circumferential direction of the tire as grooves of the present invention over the entire ground contact surface 331. The V-shaped grooves 346 are arranged in a V shape with the center of symmetry in the tire width direction of the ground contact surface 331 (S1 in Figure 5). In the second embodiment, neither the first region 71 nor the second region 72 has a main groove extending in the circumferential direction of the tire, such as the main groove 341 of the first embodiment.

The V-shaped groove 346 includes an inclined groove 346a on one side of the tire width direction center and an inclined groove 346b on the other side. The inclination angles of the inclined grooves 346a and 346b with respect to the tire circumferential direction are the same and inclined in opposite directions. Each of the inclined grooves 346a and 346b extends in a direction that inclines and intersects with the tire circumferential direction from the second region 72 on the tire width direction inner side of the main groove arrangement boundary 70 to the first region 71 on the tire width direction outer side of the second region 72. The inclined grooves 346a and 346b of this embodiment extend from the tread 30 toward the sidewall 20, and extend to a region called a shoulder portion, which is a portion where the tread 30 transitions to the sidewall 20.

(4) In the tire 1 according to the second embodiment, multiple V-shaped grooves 346 extending in a direction intersecting the tire circumferential direction from the second region 72 to the first region 71 are arranged in parallel in the tire circumferential direction.

In the second embodiment, the contact surface 331 of the tread 30 does not have a main groove extending in the tire circumferential direction, but has a V-shaped groove 346 extending in a direction intersecting the tire circumferential direction. Because the main groove is not arranged in the first region 71, buckling originating from the main groove is unlikely to occur during run-flat driving. Therefore, buckling during run-flat driving can be sufficiently suppressed, and reduction in the tire contact area is suppressed, improving run-flat durability.

Third Embodiment
Next, a third embodiment of the present invention will be described with reference to FIGS.
The third embodiment has almost the same configuration as the first embodiment described above, and differs only in the configuration of the main groove 341. Therefore, in the following description of the third embodiment, the description of the same configuration as the first embodiment will be omitted or simplified, and only the main differences will be described.

FIG. 6 shows a half cross section in the tire width direction of a tire 1 according to a third embodiment.
Fig. 7 is a cross-sectional view showing details of a main groove 341 provided in the tire 1. In Fig. 7, the tire width direction is indicated by an arrow X, and the tire radial direction is indicated by an arrow Y. As shown in Fig. 7, the cross-sectional shape of the main groove 341 in the tire width direction has a bilaterally symmetrical shape when the tire width direction is taken as the left-right direction.
Fig. 8 is a view seen in the direction of arrow VIII in Fig. 7. In Fig. 8, arrow X indicates the tire width direction, and arrow Z indicates the tire circumferential direction.

As shown in FIG. 6, the main groove 341 of the tire 1 according to the third embodiment is surrounded by a bottom surface 36 and a first groove wall 37 and a second groove wall 38 that face each other in the tire width direction.

As shown in FIG. 7, the main groove 341 has an opening 81 on the ground contact surface 331 side. Between the first groove wall 37 and the second groove wall 38, the main groove 341 includes a groove bottom 82 formed on the bottom surface 36 side, and a narrow portion 83 formed on the opening 81 side and having a narrower groove width than the groove bottom 82.

The first groove wall 37 includes a first protruding portion 37A formed on the opening 81 side so as to protrude toward the second groove wall 38 side. The second groove wall 38 includes a second protruding portion 38A formed on the opening 81 side so as to protrude toward the first groove wall 37 side.
The narrow portion 83 is formed between the first protruding portion 37A and the second protruding portion 38A. The first protruding portion 37A and the second protruding portion 38A have cross-sectional shapes that are symmetrical in Fig. 7. An opposing surface 37a of the first protruding portion 37A facing the second protruding portion 38A and an opposing surface 38a of the second protruding portion 38A facing the first protruding portion 37A are parallel to each other and extend along the tire radial direction.

The first protrusion 37A is connected to the ground surface 331 and has a first ground surface 37b that is flush with the ground surface 331. Similarly, the second protrusion 38A is connected to the ground surface 331 and has a second ground surface 38b that is flush with the ground surface 331.
The main groove 341 ensures drainage, and the first ground contact surface 37b and the second ground contact surface 38b are in contact with the ground despite the presence of the main groove 341, thereby improving ground contact.

Each of the first protruding portion 37A and the second protruding portion 38A is made of a rubber material different from that of the tread rubber 33. The rubber material of the first protruding portion 37A and the second protruding portion 38A is preferably harder than that of the tread rubber 33. The first protruding portion 37A and the second protruding portion 38A, which are made of a rubber material different from that of the tread rubber 33, are integrally joined to the tread rubber 33, thereby forming the main groove 341 of the third embodiment.
As shown in FIG. 8, the first protruding portion 37A and the second protruding portion 38A of this embodiment are both provided endlessly and continuously in the tire circumferential direction.

As shown in FIG. 7, when the depth of the main groove 341 from the ground contact surface 331 to the bottom surface 36 is L, and the groove width of the groove bottom 82 at a depth position of 80%, i.e., 4/5L, is D, and the groove width of the narrow portion 83 is d, it is preferable that the ratio of the groove width d of the narrow portion 83 to the groove width D of the groove bottom 82 is approximately 20% or more and 50% or less.

According to the third embodiment, as shown in FIG. 3 in the first embodiment described above, when buckling occurs starting from the main groove 341 during run-flat driving, the first protrusion 37A and the second protrusion 38A approach each other, and the opposing surfaces 37a and 38a of both come into contact. This prevents the main groove 341 from narrowing any further, reduces the degree of buckling, and more effectively suppresses buckling.

(5) In the tire 1 of the third embodiment, the main groove 341 arranged in the main groove arrangement region 72, which is the second region, is formed by being surrounded by the bottom surface 36 and the first groove wall 37 and the second groove wall 38 that face each other in the tire width direction, and includes a groove bottom 82 formed on the bottom surface 36 side between the first groove wall 37 and the second groove wall 38, and a narrow portion 83 formed on the opening 81 side toward the ground contact surface 331 side and having a smaller groove width than the groove bottom 82, and the narrow portion 83 is formed between at least the first protruding portion 37A that protrudes from the first groove wall 37 toward the second groove wall 38 side, and the second groove wall 38.

As a result, if buckling occurs starting from the main groove 341 during run-flat driving, the first protrusion 37A abuts against the second groove wall 38, preventing the main groove 341 from narrowing any further, reducing the degree of buckling and more effectively suppressing buckling.

(6) In the third embodiment of the tire 1, the second groove wall 38 includes a second protruding portion 38A that protrudes toward the first protruding portion 37A, and includes a configuration in which a narrow portion 83 is formed between the first protruding portion 37A and the second protruding portion 38A.

As a result, if buckling occurs starting from the main groove 341 during run-flat driving, the first protrusion 37A and the second protrusion 38A will abut against each other, preventing the main groove 341 from narrowing any further, reducing the degree of buckling and more effectively suppressing buckling.
In addition, each of the first protruding portion 37A and the second protruding portion 38A may be made of the same rubber material as the tread rubber 33, and in that case, they may be molded integrally with the tread 30.

As shown in FIG. 8, the first protrusion 37A and the second protrusion 38A are both provided in an endless manner in the tire circumferential direction, but as shown in FIG. 9, a plurality of first protrusions 37A and second protrusions 38A facing each other in the tire width direction may be provided in a state in which they are each divided at appropriate intervals in the tire circumferential direction.

The tire of the present invention can be used as a tire for various vehicles such as passenger cars, light trucks, trucks, and buses.

The present invention is not limited to the above-described embodiments, and any modifications or improvements that can achieve the object of the present invention are included within the scope of the present invention.
For example, the main grooves are arranged in the main groove arrangement region 72, but the number of main grooves is arbitrary, and one main groove may be arranged in the center of the main groove arrangement region 72 in the tire width direction, or one main groove may be arranged in a position shifted from the center in the tire width direction to either side in the tire width direction.
As long as the sub-grooves arranged in the main groove non-allocated region 71 are arranged so as to intersect with the tire width direction, the intersecting angle may be arbitrary, and may be, for example, parallel to the tire width direction.
The sub-grooves may be located in the main groove region 72 or may extend from the main groove region 72 to the non-main groove region 71 .

1. Tires (run-flat tires)
REFERENCE SIGNS LIST 10 Bead 20 Sidewall 30 Tread 36 Bottom surface 37 First groove wall 37A First protruding portion 38 Second groove wall 38A Second protruding portion 40 Carcass ply 60 Reinforcing rubber layer 70 Main groove arrangement boundary 71 Main groove non-arrangement region (first region)
72 Main groove arrangement area (second area)
82 Groove bottom 83 Narrow part 331 Ground surface 341 Main groove 345 Minor groove 346 V-shaped groove (groove)

Claims (3)

A pair of beads;
a pair of sidewalls extending radially outward from each of the pair of beads;
a tread disposed between the pair of sidewalls and having a ground contact surface;
a carcass ply disposed between the pair of beads;
A reinforcing rubber layer disposed on the sidewall,
In the contact surface of the tread, a first region is defined as a region extending from a position 25 mm outward in the tire width direction from a center position in the tire width direction to an outer side in the tire width direction, and the first region is defined as a main groove non-arrangement region in which a main groove continuously extending along a tire circumferential direction is not arranged ,
In the contact surface of the tread, a second region is formed on an inner side in a tire width direction of the first region,
A main groove is disposed in the second region and extends continuously along the tire circumferential direction,
A plurality of sub-grooves extending in a direction intersecting the tire circumferential direction are arranged in parallel in the tire circumferential direction at least in the first region,
The secondary groove is narrower than the primary groove . The main groove disposed in the second region is
the groove is surrounded by a bottom surface and a first groove wall and a second groove wall opposed to each other in the tire width direction, and includes a groove bottom portion formed on the bottom surface side between the first groove wall and the second groove wall, and a narrow portion formed on an opening side toward the ground contact surface side and having a groove width smaller than that of the groove bottom portion,
2. The run-flat tire according to claim 1 , wherein the narrow portion is formed at least between a first protruding portion formed to protrude from the first groove wall toward the second groove wall and the second groove wall. 3. The run-flat tire according to claim 2, wherein the second groove wall includes a second protruding portion protruding toward the first protruding portion, and the narrow portion is formed between the first protruding portion and the second protruding portion.

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