AIRLESS TIRE

[Technical Field]

The present invention relates to an airless tire that allows both good drainage performance and good durability to be achieved and allows uneven wear resistance to be improved.

[Technical Background]

In recent years, various airless tires have been proposed. An airless tire, without using high pressure air, can support a load by a structural member of its own. Therefore, the airless tire has an advantage that it does not go flat.

For example, an airless tire that includes a cylindrical tread ring is described in the following Patent Document 1. Multiple through holes and a reinforcing body are provided in the tread ring, the multiple through holes penetrating the tread ring in a thickness direction of the tread ring. The through holes allow drainage performance of the airless tire to be improved, and the reinforcing body allows durability of the airless tire to be improved.

[Related Art]

[Patent Document]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2008-044445.

[Summary of the Invention]

[Problems to Be Solved by the Invention]

In Patent Document 1, in order to prevent the reinforcing body from being corroded by water penetrating from the through holes, the annular reinforcing body is arranged so as to be spaced apart from the through holes in a tire width direction. Therefore, the tread ring of Patent Document 1 does not have uniform rigidity in the tire width direction, and such non-uniform rigidity causes uneven wear to occur.

The present invention is accomplished in view of the above-described situation and is intended to provide an airless tire that, on a basis of including multiple first reinforcing bodies that extend in regions between through holes, allows both good drainage performance and good durability to be achieved and allows uneven wear resistance to be improved.

[Means for Solving the Problems]

An airless tire according to the present invention includes a cylindrical tread ring that has a ground contact surface. Multiple through holes and a reinforcing body are provided in the tread ring, the multiple through holes penetrating the tread ring in a thickness direction of the tread ring. The multiple through holes are arranged at intervals along a tire circumferential direction. The reinforcing body includes a first reinforcing body that extends in the tire circumferential direction in regions between adjacent through holes. Both ends of the first reinforcing body in the tire circumferential direction terminate without being exposed from inner peripheral surfaces of the through holes.

It is desirable that, in the airless tire according to the present invention, the reinforcing body further include an annular second reinforcing body that continuously extends in the tire circumferential direction, and the second reinforcing body extend in a region where the through holes are not formed.

It is desirable that, in the airless tire according to the present invention, the second reinforcing body be a ply that includes multiple reinforcing cords.

It is desirable that, in the airless tire according to the present invention, the ply of the second reinforcing body be a jointless ply that is formed by spirally winding the reinforcing cords at an angle of five degrees or less with respect to the tire circumferential direction.

It is desirable that, in the airless tire according to the present invention, in a transverse cross section of the tread ring, the first reinforcing body be positioned at the same position in the tire radial direction as the second reinforcing body.

It is desirable that, in the airless tire according to the present invention, the first reinforcing body be a ply of the same material as the ply of the second reinforcing body.

It is desirable that, in the airless tire according to the present invention, the first reinforcing body be a ply that includes multiple reinforcing cords.

It is desirable that, in the airless tire according to the present invention, the first reinforcing body be a ply that includes a metal plate.

It is desirable that, in the airless tire according to the present invention, the multiple through holes be provided on a tire equator.

It is desirable that, in the airless tire according to the present invention, the multiple through holes include multiple first through holes that are arranged on a first tire circumferential direction line and multiple second through holes that are arranged on a second tire circumferential direction line.

It is desirable that, in the airless tire according to the present invention, the first reinforcing body include an outer-side first reinforcing body and an inner-side first reinforcing body that is arranged on a tire radial direction inner side of the outer-side first reinforcing body, and a shear layer formed of elastomer be arranged between the outer-side first reinforcing body and the inner-side first reinforcing body.

[Effect of the Invention]

In the airless tire of the present invention, the multiple through holes and the reinforcing body are provided in the tread ring, the multiple through holes penetrating the tread ring in the thickness direction of the tread ring. Such through holes allow drainage performance of the airless tire to be improved. Further, the reinforcing body allows rigidity of the tread ring to be improved, and as a result, allows steering stability of the airless tire to be improved.

In the present invention, the reinforcing body includes multiple first reinforcing bodies that extend in the tire circumferential direction in regions between adjacent through holes. Such first reinforcing bodies can effectively reinforce regions between the through holes where rigidity is decreased due to the through holes. Further, by adjusting rigidity of the first reinforcing bodies, the first reinforcing bodies allow the rigidity of the tread ring in the tire width direction to be substantially uniform and thus allow uneven wear resistance of the airless tire to be improved.

Further, in the present invention, both ends of each of the first reinforcing bodies in the tire circumferential direction terminate without being exposed from the inner peripheral surfaces of the through holes. Such first reinforcing bodies do not come into contact with water penetrating from the through holes. Therefore, the first reinforcing bodies are not corroded at an early stage and thus allow durability of the airless tire to be improved.

[Brief Description of the Drawings]

• Fig. 1 is an overall perspective view illustrating an embodiment of an airless tire of the present invention.
• Fig. 2 is a perspective view (partially cut-away view) of a tread ring of Fig. 1.
• Fig. 3 is a partial perspective view of a reinforcing body of Fig. 2.
• Fig. 4 is a cross-sectional view along an A-A line of the tread ring of Fig. 1.
• Fig. 5 is a partial perspective view of a reinforcing body of another embodiment.
• Fig. 6 is a perspective view (partially cut-away view) of a tread ring of yet another embodiment.
• Fig. 7 is an overall perspective view of an airless tire of yet another embodiment.

[Mode for Carrying Out the Invention]

In the following, an embodiment of the present invention is described in detail with reference to the drawings.

As illustrated in Fig. 1, an airless tire 1 of the present embodiment includes a cylindrical tread ring 2, a hub part 3 that is arranged on a tire radial direction inner side of the tread ring 2, and multiple spokes 4 that connect the tread ring 2 and the hub part 3.

The hub part 3 includes a disc part (3a) that is fixed to an axle, and a cylindrical part (3b) that is formed on an outer periphery of the disc part (3a) and extends in a circumferential direction. Similar to a conventional tire wheel, the hub part 3 can be formed, for example, of a metal material such as steel, aluminum alloy or magnesium alloy.

The spokes 4 each have a plate-like shape. The multiple spokes 4 are provided along the tire circumferential direction. Although not particularly limited, the spokes 4 are formed by a cast-molded body of a polymer material such as polyurethane. For example, the tread ring 2 and the hub part 3 are arranged in advance in a mold, and the polymer material is filled in the mold so as to connect the tread ring 2 and the hub part 3. By curing the polymer material, the spokes 4 that connect the tread ring 2 and the hub part 3 are formed. Regarding the shape of the spokes 4, various embodiments can be adopted in addition to that illustrated in the drawings.

The tread ring 2 of the present embodiment has a ground contact surface 5 that is in contact with a road surface, and has an inward surface 6 that is on an opposite side of the ground contact surface 5 and faces the hub part 3 side. As a preferred embodiment, at least one groove is provided in the ground contact surface 5. In the present embodiment, two grooves 7 are provided in the ground contact surface 5. When running on a wet road surface, such grooves 7 allow water on the road surface to be removed and thus allow drainage performance of the airless tire 1 to be improved.

Multiple through holes 8 that penetrate the tread ring 2 from the ground contact surface 5 to the inward surface 6 in a thickness direction of the tread ring 2 are provided in the tread ring 2. A cross-sectional shape of each of the through holes 8 can be selected from arbitrary shapes including, for example, a circular shape, an elliptical shape, a polygonal shape and the like. When running on a wet road surface, the through holes 8 allow water on the road surface to be efficiently removed and thus allow the drainage performance of the airless tire 1 to be further improved.

The through holes 8 of the present embodiment, for example, are provided on the grooves 7. It is desirable that portions of the grooves 7 where the through holes 8 are respectively provided be locally enlarged portions as widened portions 9 that have a larger groove width than other portions. When running on a wet road surface, the widened portions 9 allow water on the road surface to be removed and thus allow the drainage performance of the airless tire 1 to be further improved.

The multiple through holes 8 of the present embodiment include multiple first through holes (8a) that are arranged on a first tire circumferential direction line (La) and multiple second through holes (8b) that are arranged on a second tire circumferential direction line (Lb). It is desirable that the multiple through holes 8 including multiple first through holes (8a) and the multiple second through holes (8b) be respectively arranged at intervals in the tire circumferential direction.

Fig. 2 illustrates a perspective view (partially cut-away view) of the tread ring 2 alone. As illustrated in Fig. 2, the tread ring 2 of the present embodiment includes a tread rubber part 10 that forms the ground contact surface 5 and the inward surface 6. Since the tread rubber part 10 forms the ground contact surface 5, a sulfur vulcanized rubber composition that is excellent in frictional force and wear resistance against the road surface can be preferably adopted.

A reinforcing body 11 that is arranged inside the tread rubber part 10 is provided in the tread ring 2 of the present embodiment. The reinforcing body 11 includes, for example, a first reinforcing body 12 that discontinuously extends in the tire circumferential direction in regions between through holes 8 that adjacent to each other in the tire circumferential direction, and an annular second reinforcing body 13 that continuously extends in the tire circumferential direction in a region where the through holes 8 are not formed. Such a reinforcing body 11 allows the rigidity of the tread ring 2 to be improved, and as a result, allows steering stability of the airless tire 1 to be improved.

Fig. 3 illustrates a partial perspective view of the reinforcing body 11. As illustrated in Fig. 3, it is desirable that the second reinforcing body 13 be a ply (13P) that includes multiple reinforcing cords 14. As the reinforcing cords 14, for example, steel cords are preferably adopted. The ply (13P) of the second reinforcing body 13, for example, is a jointless ply that is formed by spirally winding the reinforcing cords 14 at an angle of five degrees or less with respect to the tire circumferential direction. Such a second reinforcing body 13 allows both reduction in weigh and enhancement in strength to be achieved.

It is desirable that the first reinforcing body 12 be a ply (12P) that includes multiple reinforcing cords 14. The ply (12P) of the first reinforcing body 12, for example, is a ply that is formed of the same material as the ply (13P) of the second reinforcing body 13, and is a jointless ply that is formed by winding the reinforcing cords 14 at an angle of five degrees or less with respect to the tire circumferential direction. Such a first reinforcing body 12 has rigidity that is substantially equal to that of the second reinforcing body 13 and allows rigidity of the tread ring 2 in the tire width direction to be substantially uniform. Therefore, uneven wear resistance of the airless tire 1 can be improved.

Both ends (12e) of the first reinforcing body 12 in the tire circumferential direction terminate without being exposed from inner peripheral surfaces of the through holes 8. For example, the rubber composition of the tread rubber part 10 (illustrated in Fig. 2) during vulcanization flows into between the ends (12e) of the first reinforcing body 12 and the inner peripheral surfaces of the through holes 8 and prevents the ends (12e) of the first reinforcing body 12 from being exposed from the inner peripheral surfaces of the through holes 8. The ends (12e) of the first reinforcing body 12 are not exposed from the inner peripheral surface of the through holes 8, and thus do not come into contact with water penetrating from the through holes 8. Therefore, even when the reinforcing cords 14 of the first reinforcing body 12 are steel cords, the first reinforcing body 12 is not corroded at an early stage and thus the durability of the airless tire 1 can be improved.

As illustrated in Fig. 2, the first reinforcing body 12 includes, for example, an outer-side first reinforcing body 15, and an inner-side first reinforcing body 17 that is arranged on a tire radial direction inner side of the outer-side first reinforcing body 15. Similarly, the second reinforcing body 13 also includes, for example, an outer-side second reinforcing body 16, and an inner-side second reinforcing body 18 that arranged on a tire radial direction inner side of the outer-side second reinforcing body 16.

It is desirable that a shear layer 19 formed of elastomer be arranged between the outer-side first reinforcing body 15 and second reinforcing body 16 and the inner-side first reinforcing body 17 and second reinforcing body 18. In the present specification, the term "elastomer" is a general term for all polymeric materials that exhibit rubber elasticity at normal temperatures, and is a concept that includes vulcanized rubber and resin as typical examples. Such a shear layer 19 allows rolling resistance to be reduced while allowing steering stability of the airless tire 1 to be maintained.

Fig. 4 illustrates a cross-sectional view along an A-A in Fig. 1. As illustrated in Fig. 4, it is desirable that, in a transverse cross section of the tread ring 2, the outer-side first reinforcing body 15 be positioned at the same position in the tire radial direction as the outer-side second reinforcing body 16. Further, it is desirable that the inner-side first reinforcing body 17 be positioned at the same position in the tire radial direction as the inner-side second reinforcing body 18. Such first reinforcing bodies 15, 17 and second reinforcing bodies 16, 18 allow the tread ring 2 to easily have substantially uniform rigidity in the tire width direction, and thus allow uneven wear resistance of the airless tire 1 to be improved.

As illustrated in Figs. 2 and 4, the outer-side first reinforcing body 15 of the present embodiment includes a first outer-side first reinforcing body (15a) that is arranged along the first tire circumferential direction line (La) (illustrated in Fig. 1) and a second outer-side first reinforcing body (15b) that is arranged the second tire circumferential direction line (Lb) (illustrated in Fig. 1). Similarly, the inner-side first reinforcing body 17 of the present embodiment includes a first inner-side first reinforcing body (17a) that arranged along the first tire circumferential direction line (La) and a second inner-side first reinforcing body (17b) that is arranged along the second tire circumferential direction line (Lb).

The outer-side second reinforcing body 16 of the present embodiment includes a first outer-side second reinforcing body (16a) that is arranged on a tire width direction outer side of the first outer-side first reinforcing body (15a) and a second outer-side second reinforcing body (16b) that is arranged on a tire width direction outer side of the second outer-side first reinforcing body (15b). The outer-side second reinforcing body 16 further includes a third outer-side second reinforcing body (16c) that is arranged between the first outer-side first reinforcing body (15a) and the second outer-side first reinforcing body (15b).

Similarly, the inner-side second reinforcing body 18 of the present embodiment includes a first inner-side second reinforcing body (18a) that is arranged on a tire width direction outer side of the first inner-side first reinforcing body (17a) and a second inner-side second reinforcing body (18b) that is arranged on a tire width direction outer side of the second inner-side first reinforcing body (17b). The inner-side second reinforcing body 18 further includes a third inner-side second reinforcing body (18c) that is arranged between the first inner-side first reinforcing body (17a) and the second inner-side first reinforcing body (17b).

It is desirable that the above-described first reinforcing bodies (15a, 15b, 17a, 17b) and second reinforcing bodies (16a, 16b, 16c, 18a, 18b, 18c) be respectively formed using separate plies and be arranged inside the tread rubber part 10. Since the plies are separated formed in such a reinforcing body 11, even when some of the plies are damaged, other plies are not affected by the damage.

In the above, a particularly preferred embodiment of the present invention is described in detail. However, the present invention is not limited to the above-described embodiment and can be embodied in various modified forms.

For example, the through holes 8 of the above-described embodiment penetrate the tread ring 2 along the tire radial direction. However, without being limited to this embodiment, it is sufficient that the through holes 8 penetrate the tread ring 2 from the ground contact surface 5 to the inward surface 6 in a thickness direction of the tread ring 2. Therefore, the through holes 8, for example, may be inclined with respect to the tire radial direction, and further may be bent or curved in the tread ring 2.

Further, in the above-described embodiment, the ply (12P) of the first reinforcing body 12 and the ply (13P) of the second reinforcing body 13 are formed as separate plies. However, for example, the ply (12P) and the ply (13P) may also be formed as a single ply. In this case, it is desirable that large-diameter holes that are concentric to the through holes 8 and have a diameter larger than a maximum diameter of the through holes 8 are provided in the single ply. Even for the reinforcing body 11 that includes such a single ply, since end surfaces of the large-diameter holes are not exposed from the inner peripheral surfaces of the through holes 8, the reinforcing body 11 is not corroded at an early stage and thus the durability of the airless tire 1 can be improved.

Fig. 5 illustrates a partial perspective view of a reinforcing body (11A) of another embodiment. As illustrated in Fig. 5, a first reinforcing body (12A) of the reinforcing body (11A) of the present embodiment includes a metal plate (12AP). By adjusting a plate thickness of such a metal plate (12AP), the rigidity of the first reinforcing body (12A) can be adjusted. Therefore, the metal plate (12AP) allows the reinforcing body (11A) to easily have substantially uniform rigidity in the tire width direction, and thus allows uneven wear resistance of the airless tire that includes the reinforcing body (11A) to be improved.

Even for such a first reinforcing body (12A), both ends (12e) in the tire circumferential direction terminate without being exposed from the inner peripheral surfaces of the through holes 8. Therefore, the first reinforcing body (12A) is prevented from being corroded at an early stage.

Fig. 6 illustrates a perspective view (partially cut-away view) of a tread ring (2B) of yet another embodiment. As illustrated in Fig. 6, in the tread ring (2B) of the present embodiment, multiple through holes (8b) are formed on the tire equator (C). In the tread ring (2B), for example, a groove is not provided on a ground contact surface (5B). In this way, depending on a size and arrangement of the through holes (8b) and further depending on an intended use of an airless tire that includes the tread ring (2B), whether or not to provide a groove in the tread ring (2B) can be selected.

In the tread ring (2B) of the present embodiment, an outermost-side first reinforcing body (20B) is arranged on a tire radial direction outer side of the outer-side first reinforcing body (15b). Similarly, in the tread ring (2B), an outermost-side second reinforcing body (21B) is arranged on a tire radial direction outer side of the outer-side second reinforcing body (16b). In this way, a reinforcing body on a tire radial direction outer side of a shear layer (19B) has a two-layer structure, and thereby, rigidity of the tread ring (2B) can be further improved.

The first reinforcing bodies (15b, 20B) and the second reinforcing bodies (16b, 21B), for example, are each a ply that includes multiple reinforcing cords. It is desirable that the reinforcing cords of the outer-side first reinforcing body (15b) and the reinforcing cords of the outermost-side first reinforcing body (20B) be arranged at the same inclination angle (for example, 15 - 65 degrees) with respect to the tire circumferential direction but in mutually opposite inclination directions. Similarly, it is desirable that the reinforcing cords of the outer-side second reinforcing body (16b) and the reinforcing cords of the outermost-side second reinforcing body (21B) be arranged at the same inclination angle (for example, 15 - 65 degrees) with respect to the tire circumferential direction but in mutually opposite inclination directions.

Such first reinforcing bodies (15b, 20B) and second reinforcing bodies (16b, 21B) can enhance tire circumferential direction rigidity, tire axial direction rigidity and torsional rigidity of the tread ring (2B) in a well-balanced manner, and thus can effectively reinforce the tread ring (2B).

In the tread ring (2B) of the present embodiment, an inner-side first reinforcing body (17b) and an inner-side second reinforcing body (18b) are further arranged on a tire radial direction inner side of the shear layer (19B). It is desirable that the inner-side first reinforcing body (17b) and the inner-side second reinforcing body (18b) also be each a ply that includes multiple reinforcing cords. It is preferable that the plies of the inner-side first reinforcing body (17b) and the inner-side second reinforcing body (18b) be each a jointless ply that is formed by spirally winding the reinforcing cords at an angle of five degrees or less with respect to the tire circumferential direction.

Fig. 7 illustrates an overall perspective view of an airless tire (1C) of yet another embodiment. As illustrated in Fig. 7, the airless tire (1 C) of the present embodiment includes the hub part 3 and the multiple spokes 4 that are common to the above-described airless tire 1, the hub part 3 including the disc part (3a) and the cylindrical part (3b). The airless tire (1C) further includes a tread ring (2C) that has a ground contact surface (5C) and an inward surface (6C).

Three grooves (7C) and multiple through holes (8C) are provided in the ground contact surface (5C) of the tread ring (2C). The multiple through holes (8C) of the present embodiment include multiple first through holes (8Ca) that are arranged on the first tire circumferential direction line (La), multiple second through holes (8Cb) that are arranged on the second tire circumferential direction line (Lb), and multiple third through holes (8Cc) that are arranged on the tire equator (C).

Although not illustrated in the drawings, also in the present embodiment, a first reinforcing body is provided in the tread ring (2C), the first reinforcing body extending along the tire circumferential direction in regions between adjacent first through holes (8Ca), between adjacent second through holes (8Cb) and between adjacent third through holes (8Cc). Both ends of the first reinforcing body also terminate, of course, without being exposed from inner peripheral surfaces of the through holes (8Ca, 8Cb, 8Cc).

[Examples]

Airless tires (tires corresponding to a tire size of 125/80R13) that each form the basic structure of Figs. 1 - 4 were prototyped based on specifications of Table 1, and drainage performance, durability and uneven wear resistance were tested. The spokes were integrally molded with the tread ring and the hub part using cast molding method using a urethane resin (thermosetting resin). A test method is as follows.

<Drainage Performance>

Each of the prototyped tires was mounted to a compact passenger car, which was run by a test driver on a test course of a paved road surface in a wet state. Running characteristics related to drainage performance in this case were evaluated based on a sensory evaluation by the test driver. The result is an index number with a result of a comparative example 1 as 100. A larger index number indicates a better drainage performance.

<Durability>

A drum testing machine was used. Durability test for each of the prototyped tires in a humid and hot condition was performed under the following conditions. After the test, each of the prototyped tires was cut, and whether or not rust had occurred in the ply of the first reinforcing body was confirmed by visual inspection. The result is expressed as "Yes" indicating that rust had occurred or "No" indicating that rust had not occurred. That rust had not occurred indicates that corrosion had not occurred to the first reinforcing body and the durability is excellent.

• Load: 1.5 kN
• Speed: 60 km/h

<Uneven Wear Resistance>

An uneven wear testing machine was used. Each of the prototyped tires was run under the following conditions, and an average of uneven wear amounts under the running conditions was calculated. The result is an index number with a result of the comparative example 1 as 100. A larger index number indicates a better uneven wear resistance.

• Load: 1.5 kN
• Running Condition: Braking Condition, Driving Condition, Free-Rolling Condition, Turning Condition

The test results are illustrated in Table 1.

Comparative example 1

Comparative example 2

Comparative example 3

Example 1

Example 2

Example 3

Example 4

Through holes in tread ring

No

Yes

Yes

Yes

Yes

Yes

Yes

Groove on ground contact surface

Yes

Yes

Yes

Yes

Yes

Yes

No

First reinforcing body

No

No

Yes

Yes

Yes

Yes

Yes

Exposure of first reinforcing body in through holes

-

-

Yes

No

No

No

No

Material of first reinforcing body

-

-

Ply

Ply

Ply

Metal plate

Ply

Diameter difference between first reinforcing body and second reinforcing body (mm)

-

-

0

0

3

0

0

Drainage performance (index number)

100

130

130

130

130

130

110

Durability (rust occurred to first reinforcing body)

-

-

Yes

No

No

No

No

Uneven wear resistance (index number)

100

70

100

100

80

100

100

As is apparent from Table 1, it is confirmed that the airless tires of the examples allow drainage performance, durability and uneven wear resistance to be improved in a well-balanced manner as compared to the comparative examples.

[Description of Reference Numerals]

1:

airless tire

2:

tread ring

5:

ground contact surface

8:

through holes

11:

reinforcing body

12:

first reinforcing body