Patent Application
20210094358
The present invention relates to a tire.
In recent years, as a means for improving the fuel economy performance of tires and further vehicles, attention has been paid to reduction of the air resistance of tires during running in addition to reduction of rolling resistance. A tire in which a turbulent flow prevention region is formed in each buttress portion so as to be connected to a tread portion without having a step, in order to reduce air resistance, has been proposed (see, for example, Japanese Patent No. 4295455).
Meanwhile, the shape of each buttress portion of a tire has been known to affect the ride comfort of the tire. However, in the tire disclosed in Japanese Patent No. 4295455, ride comfort is not sufficiently considered, leaving room for improvement.
The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a tire capable of reducing air resistance without sacrificing ride comfort.
The present invention is directed to a tire including a tread portion and sidewall portions extending from both ends of the tread portion through buttress regions and maximum width positions to bead portions, wherein a projection portion extending in a tire circumferential direction and a recess portion extending in the tire circumferential direction are formed in each of the buttress regions, the projection portion has a projection height of 0.1 to 0.3 mm from a reference surface of the buttress region toward an outer side in a tire radial direction, and the recess portion has a recess depth of 0.1 to 0.3 mm from the reference surface toward an inner side in the tire radial direction.
In the tire according to the present invention, the projection portion is preferably continuous in the tire circumferential direction.
In the tire according to the present invention, the recess portion is preferably continuous in the tire circumferential direction.
In the tire according to the present invention, the projection portion preferably has an external corner portion that is continuous in the tire circumferential direction.
In the tire according to the present invention, a line is preferably formed at the external corner portion by a parting line between a tread mold for molding the tread portion and a side mold for molding the sidewall portion.
In the tire according to the present invention, preferably, the projection portion has a plurality of external corner portions that are continuous in the tire circumferential direction, and the line is formed at an external corner portion located at an outermost side in the tire radial direction, of the plurality of external corner portions.
In the tire according to the present invention, preferably, the projection portion includes a first projection portion and a second projection portion located inward of the first projection portion in the tire radial direction, and the recess portion is provided between the first projection portion and the second projection portion.
Preferably, the tire according to the present invention further includes: a carcass extending from the tread portion through the sidewall portions to the bead portions; and sidewall rubbers disposed outward of the carcass, and a thickness of the sidewall rubber in each buttress region is not greater than 2.5 mm.
In the tire according to the present invention, the thickness of the sidewall rubber in each buttress region is preferably not greater than 40% of a thickness of the sidewall rubber at the maximum width position.
In the tire according to the present invention, in each of the buttress regions, the projection portion and the recess portion extending in the tire circumferential direction are formed. The projection portion has the projection height of 0.1 to 0.3 mm from the reference surface of the buttress region toward the outer side in the tire radial direction, and the recess portion has the recess depth of 0.1 to 0.3 mm from the reference surface toward the inner side in the tire radial direction. Owing to the projection portion and the recess portion described above, the air resistance of the tire during running is reduced, and the fuel economy performance of the tire is improved. In addition, the recess portion serves as a bending point when the tire is bent due to application of a load to the tire, and ensures flexibility of the sidewall portion. Accordingly, the vertical spring constant of the tire is decreased, and the ride comfort of the tire is improved.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the tire 1 according to the present embodiment, a carcass 6 extends on and between the bead portions 4, 4, and a belt layer 7 is disposed within the tread portion 2 outward of the carcass 6.
The carcass 6 is composed of one or more carcass plies, one carcass ply 6A in this example, in which carcass cords are arranged, for example, at an angle of 75° to 90° relative to the tire circumferential direction. The carcass ply 6A has a main body portion 6a extending between the bead portions 4, 4, and turned-up portions 6b turned up around bead cores 5 of the bead portions 4 from the inner side to the outer side to be engaged at both ends of the main body portion 6a. A bead apex rubber 8 for reinforcing a bead portion is disposed between the main body portion 6a and each turned-up portion 6b so as to extend from the bead core 5 outwardly in the tire radial direction in a tapered shape.
The belt layer 7 is composed of two or more belt plies, two belt plies 7A and 7B in this example, in which belt cords are arranged, for example, at an angle of 15° to 45° relative to the tire circumferential direction. The cords of the respective plies intersect each other, thereby reinforcing the tread portion 2 with high stiffness. For the purpose of improving high-speed durability and steering stability, a band layer composed of a band ply obtained by spirally winding a band cord in the circumferential direction can be provided outward of the belt layer 7.
A tread rubber 20 is disposed outward of the belt layer 7. In addition, in each sidewall portion 3, a sidewall rubber 30 is disposed outward of the carcass 6.
The projection height of the projection portion 33 and the recess depth of the recess portion 34 are optimized as described later. Accordingly, turbulence of airflow, that is, separation of airflow, around the buttress region 31 is inhibited. Therefore, the air resistance of the tire 1 during running is reduced, and the fuel economy performance of the tire 1 is improved.
In the present embodiment, the recess portion 34 having low stiffness is formed adjacent to the projection portion 33 having high bending stiffness. Such a recess portion 34 serves as a bending point when the tire 1 is bent due to application of a load to the tire 1, and ensures flexibility of the sidewall portion 3. Accordingly, the vertical spring constant of the tire 1 is reduced, and the ride comfort of the tire 1 is improved.
The projection portion 33 is continuously formed in the tire circumferential direction. The recess portion 34 is also continuously formed in the tire circumferential direction. Owing to such a projection portion 33 and such a recess portion 34, the air resistance of the tire 1 during running is continuously reduced, and the ride comfort of the tire 1 is continuously improved.
The mold 10 includes a tread mold 11 for vulcanizing and molding the tread portion 2, and side molds 12 for vulcanizing and molding the sidewall portions 3. The tread mold 11 is divided into a plurality of segments 14 in the circumferential direction. Each side mold 12 is movable in the tire axial direction, and each segment 14 is movable in the tire radial direction.
The tread mold 11 and each side mold 12 abut at the buttress region 31 to cause mold closing. Therefore, on the tire molded surface of the buttress region 31, a line 36 is continuously formed in the tire circumferential direction by a parting line 15 between the tread mold 11 and the side mold 12. The line 36 is a trace of the sidewall rubber 30 protruding at the parting line 15 during vulcanization and molding.
The projection portion 33 has an external corner portion 37 (see
When the projection height H of the projection portion 33 is not less than 0.1 mm, protrusion of the sidewall rubber 30 from the parting line 15 between the tread mold 11 and the side mold 12 is inhibited. On the other hand, when the projection height H of the projection portion 33 is not greater than 0.3 mm, turbulence of airflow around the buttress region 31 is inhibited, and the air resistance of the tire 1 during running is reduced.
The recess portion 34 has a recess depth D of 0.1 to 0.3 mm from the reference surface 35 toward the inner side in the tire radial direction.
When the recess depth D of the recess portion 34 is not less than 0.1 mm, favorable bending is achieved at the recess portion 34, and the ride comfort is improved. On the other hand, when the recess depth D of the recess portion 34 is not greater than 0.3 mm, in cooperation with the projection portion 33 having the projection height H, turbulence of airflow around the buttress region 31 is inhibited, and the air resistance of the tire 1 during running is reduced.
In the tire 1, a plurality of (two in the present embodiment) projection portions 33 are provided in the buttress region 31. That is, in the buttress region 31, a first projection portion 33a and a second projection portion 33b located inward of the first projection portion 33a in the tire radial direction are formed.
The projection height H of the first projection portion 33a and the projection height H of the second projection portion 33b may be equal or may be different from each other. In addition, the projection height H of each projection portion and the recess depth D of the recess portion 34 may be equal or may be different from each other.
In the tire 1 according to the present embodiment, the first projection portion 33a has external corner portions at the outer side and the inner side thereof in the tire radial direction. Similarly, the second projection portion 33b has external corner portions at the outer side and the inner side thereof in the tire radial direction.
The parting line 15 between the tread mold 11 and the side mold 12 is formed at the external corner portion 37 located at the outermost side in the tire radial direction, of a plurality of external corner portions (in
The recess portion 34 of the present embodiment is provided between the first projection portion 33a and the second projection portion 33b. Owing to such arrangement, the difference between high stiffness and low stiffness in the stiffness distribution in the buttress region 31 becomes large, so that the recess portion 34 can easily serve as a starting point of bending. Accordingly, good ride comfort is easily achieved.
A thickness G1 of the sidewall rubber 30 in the buttress region 31 is preferably not greater than 2.5 mm. When the thickness G1 is not greater than 2.5 mm, the recess portion 34 easily serves as a starting point of bending, and good ride comfort is achieved.
The thickness G1 is preferably not less than 1.5 mm. When the thickness G1 is not less than 1.5 mm, sufficient lateral stiffness of the sidewall portion 3 is ensured, and good steering stability is achieved.
The recess portion 34 forms a thinnest region of the sidewall portion 3. The thickness G1 of the sidewall rubber 30 in the buttress region 31 is preferably not greater than 40% of a thickness G2 of the sidewall rubber 30 at the maximum width position 32. When the thickness G1 is not greater than 40% of the thickness G2, the recess portion 34 easily serves as a starting point of bending, and good ride comfort is achieved.
The thickness G1 is preferably not less than 25% of the thickness G2. When the thickness G1 is not less than 25% of the thickness G2, sufficient lateral stiffness of the sidewall portion 3 is ensured, and good steering stability is achieved.
As shown in
A turned-up height h2 of each turned-up portion 6b from a bead base line is preferably 17 to 115 mm. When the turned-up height h2 is not less than 17 mm, sufficient lateral stiffness of the sidewall portion 3 is ensured, and good steering stability is achieved. When the turned-up height h2 is not greater than 115 mm, good ride comfort is achieved.
As shown in
A width W2 of the recess portion 34 is preferably 3 to 5 mm. When the width W2 is not less than 3 mm, small turbulent flow occurs around the recess portion 34, and the air resistance of the tire 1 as a whole is reduced. When the width W2 is not greater than 5 mm, the recess portion 34 easily serves as a bending point, and the ride comfort is improved.
Here, at each sidewall portion 3, the rotation speed is faster at the outer side in the tire radial direction, and the air is easily separated. However, in the tire 1, since the projection portion 33 and the recess portion 34 are provided in the buttress region 31 located at the outer side in the tire radial direction, separation of the air can be delayed, and the separation position can be moved to the rear side. Therefore, an effect of causing the air to flow around to the tread surface 2a side is enhanced, and the pressure at the tire rear portion C is increased, so that it is possible to more effectively reduce the air resistance.
Although the tire 1 according to the present invention has been described in detail above, the present invention is not limited to the above specific embodiment, and various modifications can be made to implement the present invention.
Pneumatic tires having the basic structure in
<Amount of Burrs Generated>
The amount of rubber protruding to the gap between a tread mold and a sidewall mold in each buttress region was visually confirmed. A lower value indicates that the generated burrs are smaller and the appearance is better.
<Air Resistance>
Each tire fitted to a rim having a size of 15×6.0 J and inflated to an internal pressure of 230 kPa was rotated on a drum tester at a rotation speed equivalent to a running speed of 100 km/h, and wind corresponding to the running speed was sent to the front of the tire. In addition, the air resistance acting on the tire at this time was measured. The air resistance was calculated by subtracting the rolling resistance from the resistance acting on the tire. The result is an index with the value of Comparative Example 2 being regarded as 100. A lower value indicates that the air resistance is lower and the fuel economy performance is better.
<Vertical Spring Constant>
Each of the above tires was fitted to the above rim and brought into contact with a flat surface under conditions of an internal pressure of 230 kPa and a load of 4.82 kN, and the amount of vertical bending of the tire was measured. Then, a vertical spring constant was approximately obtained by dividing the load of 4.82 kN by the amount of vertical bending. The result is indicated as an index with the value of Comparative Example 2 being regarded as 100. A lower value indicates that the vertical spring is lower, which is more advantageous for ride comfort.
<Ride Comfort>
Each of the above tires was fitted to the above rim, inflated to an internal pressure of 230 kPa, and mounted to each wheel of a front wheel drive vehicle produced in Japan. A driver drove the vehicle on a test course, and made overall evaluation of lumpy feeling, push-up, and damping through sensory evaluation. The result is indicated as a score with the score of Comparative Example 2 being regarded as 6.0. A higher value indicates a better result.
The results of the tests are shown in Table 1.
As is obvious from Table 1, it was confirmed that the tire of each Example has a significantly small amount of burrs generated as compared to that in each Comparative Example and thus can reduce air resistance without sacrificing ride comfort.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-180273 | Sep 2019 | JP | national |
