JP7534624B2 - tire - Google Patents

Description

This invention relates to tires.

Increasing the tan δ of the tread rubber and increasing the contact area improves braking performance on dry roads. However, increasing tan δ and the contact area is counterproductive to improving braking performance on dry roads. When sand is kicked up on the contact area and splashes inside the tire housing, it increases noise inside the vehicle, affecting quietness.

Therefore, for example, in the pneumatic tire of Patent Document 1, when the land portion on the outer side in the tire width direction of the outermost main groove in the tire width direction is defined as the shoulder region, and the land portion defined by the main groove on the inner side in the tire width direction of the outermost main groove in the tire width direction is defined as the center region, the ground contact area ratio of the land portion in the center region is made larger than the ground contact area ratio of the land portion in the shoulder region, and the tan δ (20°C) of the cap rubber of the land portion in the shoulder region is made larger than the tan δ (20°C) of the cap rubber of the land portion in the center region.

JP 2019-188853 A

In the above-mentioned pneumatic tire of Patent Document 1, the tan δ (20°C) of the cap rubber of the land portion is made larger than the tan δ (20°C) of the cap rubber of the land portion in the center region in the shoulder region, which contributes greatly to improving the braking performance on dry road surfaces, thereby ensuring the braking performance on dry road surfaces. On the other hand, in the center region, the tan δ (20°C) of the cap rubber of the land portion is made smaller than the tan δ (20°C) of the cap rubber of the land portion in the shoulder region, thereby reducing the amount of sand adsorbed to the ground surface and improving the quietness performance. In addition, in the shoulder region, the ground contact area ratio of the land portion is made smaller than the ground contact area ratio of the land portion in the center region, thereby reducing the amount of sand adsorbed to the ground surface and improving the quietness performance. On the other hand, in the center region, the ground contact area ratio of the land portion is made larger than the ground contact area ratio of the land portion in the shoulder region, thereby ensuring the braking performance on dry road surfaces. As a result, the pneumatic tire of Patent Document 1 can improve the quietness performance without impairing the braking performance on dry road surfaces.

With the recent improvements in vehicle performance, there is a demand for greater improvements in the braking performance of individual tires. At the same time, there is also a demand for improvements in quietness, which is a contradictory issue, in order to suppress sand splashes.

The objective of this invention is to provide a tire that can improve braking performance and quietness.

In order to achieve the above object, a tire according to one aspect of the present invention has a specified orientation of inside and outside the vehicle when mounted on a vehicle, and has at least two land portions in the tread portion defined by at least one main groove that extends along the tire circumferential direction and is closest to the tire equatorial plane, and when the land portion on the vehicle outer side of the main groove is defined as a vehicle outer region and the land portion on the vehicle inner side of the main groove is defined as a vehicle inner region, the ground contact area ratio Gout of the land portion in the vehicle outer region and the ground contact area ratio Gin of the land portion in the vehicle inner region satisfy the relationship Gin < Gout, and the land portion in the vehicle outer region Tout20, which is the tan δ (20°C) of the cap rubber of the land portion of the vehicle inner region, and Tin20, which is the tan δ (20°C) of the cap rubber of the land portion of the vehicle inner region, satisfy the relationship Tout20<Tin20, Tout60, which is the tan δ (60°C) of the cap rubber of the land portion of the vehicle outer region, and Tin60, which is the tan δ (60°C) of the cap rubber of the land portion of the vehicle inner region, satisfy the relationship Tout60<Tin60, and X20, which is Tin20/Tout20, and X60, which is Tin60/Tout60, satisfy the relationship X60<X20.

It is preferable that Yout, which is Tout60/Tout20, and Yin, which is Tin60/Tin20, satisfy the relationship Yin<Yout.

It is preferable that the ground contact area ratio Gout' of the land portion in the vehicle outer region and the ground contact area ratio Gin' of the land portion in the vehicle inner region satisfy the relationship 10%≦Gout'-Gin'≦50%.

It is preferable that X20 and X60 are in the range of 1.01 or more and 2.0 or less.

It is preferable that the Tout60 and the Tout20 satisfy the relationship 0.2≦Tout60/Tout20≦0.5.

It is preferable that the Tin60 and the Tin20 satisfy the relationship 0.3≦Tin60/Tin20≦0.6.

It is preferable that the product Pout60 of the actual ground contact area Aout of the land portion in the vehicle outer region and the Tout60, and the product Pin60 of the actual ground contact area Ain of the land portion in the vehicle inner region and the Tin60, are in the range of 10 to 50.

It is preferable that the product Pout20 of the actual ground contact area Aout of the land portion in the vehicle outer region and the Tout20, and the product Pin20 of the actual ground contact area Ain of the land portion in the vehicle inner region and the Tin20, are in the range of 30 to 90.

It is preferable that the product Pout60 of the Gout and the Tout60 and the product Pin60 of the Gin and the Tin60 satisfy the relationship 0.90≦Pout60/Pin60≦1.10, and the product Pout20 of the Gout and the Tout20 and the product Pin20 of the Gin and the Tin20 satisfy the relationship 0.90≦Pout20/Pin20≦1.10.

This invention can improve braking performance and quietness.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment. FIG. 2 is a plan view of the pneumatic tire according to the embodiment. FIG. 3 is a diagram showing a viscoelasticity curve of rubber. FIG. 4 is a table showing the results of a performance test of the pneumatic tire according to the embodiment.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the components of this embodiment include those that are easily replaceable by a person skilled in the art, or those that are substantially the same. Furthermore, the multiple modified examples described in this embodiment can be arbitrarily combined within the scope of what is obvious to a person skilled in the art.

The pneumatic tire according to this embodiment will be described. Figure 1 is a meridian cross-sectional view of the pneumatic tire according to this embodiment. Figure 2 is a plan view of the pneumatic tire according to this embodiment.

In the following description, the tire radial direction refers to a direction perpendicular to the rotation axis (not shown) of the pneumatic tire 1, the tire radial inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radial outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotation axis as the central axis. The tire width direction refers to a direction parallel to the rotation axis, the tire width inner side refers to the side toward the tire equatorial plane (tire equatorial line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire width is the width in the tire width direction between the parts located on the outer sides in the tire width direction, that is, the distance between the parts farthest from the tire equatorial plane CL in the tire width direction. The tire equatorial line refers to a line that is on the tire equatorial plane CL and runs along the tire circumferential direction of the pneumatic tire 1. In this embodiment, the tire equator line is given the same symbol "CL" as the tire equatorial plane.

As shown in Figures 1 and 2, the pneumatic tire 1 of this embodiment has a tread portion 2, shoulder portions 3 on both sides of the tread portion 2, and sidewall portions 4 and bead portions 5 that are successively continuous with each shoulder portion 3. The pneumatic tire 1 also has a carcass layer 6 and a belt layer 7.

The tread portion 2 is made of a rubber material (tread rubber) and is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and its surface forms the outline of the pneumatic tire 1. A tread surface 21 is formed on the outer peripheral surface of the tread portion 2, that is, the tread surface that comes into contact with the road surface during running. The tread surface 21 is provided with a plurality of main grooves 22 (three in this embodiment) that extend along the tire circumferential direction and are aligned in the tire width direction. The tread surface 21 is formed with a plurality of rib-shaped land portions 23 (four in this embodiment) that extend along the tire circumferential direction and are parallel to the tire equator line CL by these plurality of main grooves 22. The main grooves 22 have a groove width of 3 mm or more, a groove depth of 5 mm or more, and are required to display a wear indicator as stipulated by JATMA.

The shoulder portions 3 are the portions of the tread portion 2 on both outer sides in the tire width direction. The sidewall portions 4 are the outermost exposed portions in the tire width direction of the pneumatic tire 1. The bead portions 5 have a bead core 51 and a bead filler 52. The bead core 51 is formed by winding a bead wire, which is a steel wire, into a ring shape. The bead filler 52 is a rubber material that is placed in a space formed by folding back the tire width direction end portion of the carcass layer 6 at the position of the bead core 51.

The carcass layer 6 has each end in the tire width direction folded back from the inner side in the tire width direction to the outer side in the tire width direction by a pair of bead cores 51, and is wound around the tire circumferential direction in a toroidal shape to form the tire framework. This carcass layer 6 is made of multiple carcass cords (not shown) arranged side by side at an angle to the tire circumferential direction along the tire meridian direction and covered with coating rubber. The carcass cords are made of organic fibers (polyester, rayon, nylon, etc.). This carcass layer 6 is provided in at least one layer.

The belt layer 7 has a multi-layer structure of at least two layers of belts 7A and 7B, and is disposed on the outer periphery of the carcass layer 6 in the tread portion 2 in the radial direction of the tire, covering the carcass layer 6 in the circumferential direction of the tire. The belts 7A and 7B are made of multiple cords (not shown) arranged side by side at a predetermined angle (e.g., 20 degrees to 30 degrees) to the circumferential direction of the tire, covered with a coating rubber. The cords are made of steel or organic fibers (such as polyester, rayon, or nylon). The overlapping belts 7A and 7B are disposed so that the cords cross each other.

Although not shown in the figure, a belt reinforcing layer may be provided on the outer side of the belt layer 7 in the tire radial direction. The belt reinforcing layer covers the belt layer 7 in the tire circumferential direction. The belt reinforcing layer is a rubber-coated cord (not shown) arranged in parallel in the tire width direction, approximately parallel (±5 degrees) to the tire circumferential direction. The cord is made of steel or organic fiber (polyester, rayon, nylon, etc.). The belt reinforcing layer is provided by wrapping a strip material (e.g., 10 mm wide) in the tire circumferential direction. For example, the belt reinforcing layer is arranged to cover only the tire width direction end of the belt layer 7, or to cover the entire belt layer 7, or to have two reinforcing layers, with the reinforcing layer on the inner side in the tire radial direction being larger in the tire width direction than the belt layer 7 and arranged to cover the entire belt layer 7, and the reinforcing layer on the outer side in the tire radial direction being arranged to cover only the tire width direction end of the belt layer 7, or to have two reinforcing layers, with each reinforcing layer arranged to cover only the tire width direction end of the belt layer 7.

The pneumatic tire 1 of this embodiment has its orientation specified as being inside or outside the vehicle when mounted on the vehicle, for example, by indicators provided on the sidewall portion 4 indicating the orientation. Note that the designation of the inside and outside of the vehicle is not limited to when mounted on a vehicle. For example, when mounted on a rim, the orientation of the rim relative to the inside and outside of the vehicle in the tire width direction is fixed. Therefore, when mounted on a rim, the orientation of the pneumatic tire 1 relative to the inside and outside of the vehicle in the tire width direction is specified.

In the pneumatic tire 1 of this embodiment, as shown in Figs. 1 and 2, one main groove 22 is arranged on the tire equatorial plane CL in the tread portion 2. This main groove 22 on the tire equatorial plane CL is called the center main groove 22A. The main groove 22 is arranged on the tire equatorial plane CL, meaning that the range of the opening of the main groove 22 to the tread surface 21 overlaps with the tire equatorial plane CL. In this embodiment, the center main groove 22A is arranged on the tire equatorial plane CL, but the center main groove 22A may be the main groove 22 closest to the tire equatorial plane CL. When there are two main grooves 22 closest to the tire equatorial plane CL, one of them is appropriately selected. In addition, each main groove 22 (two in the figure) on the outer side in the tire width direction other than the center main groove 22A is called the shoulder side main groove 22B. Furthermore, the area defined on the vehicle outer side of the center main groove 22A is referred to as the vehicle outer area, and the land portion 23 in this vehicle outer area is referred to as the vehicle outer land portion 23A. In this embodiment, the vehicle outer land portion 23A includes the land portion 23 defined by the center main groove 22A and the shoulder side main groove 22B adjacent to the vehicle outer side of the center main groove 22A, and the land portion 23 defined on the vehicle outer side of the shoulder side main groove 22B. In addition, the area defined on the vehicle inner side of the center main groove 22A is referred to as the vehicle inner area, and the land portion 23 in this vehicle inner area is referred to as the vehicle inner land portion 23B. In this embodiment, the vehicle inner land portion 23B includes the land portion 23 defined by the center main groove 22A and the shoulder side main groove 22B adjacent to the vehicle inner side of the center main groove 22A, and the land portion 23 defined on the vehicle inner side of the shoulder side main groove 22B.

In the pneumatic tire 1 of this embodiment, as shown in FIG. 1, the tread rubber of the tread portion 2 has a cap rubber 24 that forms a contact surface that contacts the road surface on the tread surface 21. The tread rubber of the tread portion 2 has a base rubber 25 on the tire radial inside of the cap rubber 24. The cap rubber 24 is composed of a vehicle-outer cap rubber 24A on the vehicle outer side of the center main groove 22A and a vehicle-inner cap rubber 24B on the vehicle inner side of the center main groove 22A, with the groove bottom of the center main groove 22A on the tire equatorial plane CL (closest to the tire equatorial plane CL) as the boundary. That is, the vehicle-outer land portion 23A is formed by the vehicle-outer cap rubber 24A, and the vehicle-inner land portion 23B is formed by the vehicle-inner cap rubber 24B.

The outer cap rubber 24A has a tan δ (20°C) in the range of 0.2 to 0.48, while the inner cap rubber 24B has a tan δ (20°C) in the range of 0.5 to 0.7, and the viscoelasticity of the two rubbers is different. Note that tan δ (20°C) is the value measured in accordance with JIS K6394:2007 using a viscoelasticity spectrometer (e.g., manufactured by Toyo Seiki Seisakusho Co., Ltd.) under conditions of an elongation deformation strain rate of 10% ± 2%, a vibration frequency of 20 Hz, and a temperature of 20°C.

The outer cap rubber 24A has a tan δ (60°C) in the range of 0.1 to 0.28, while the inner cap rubber 24B has a tan δ (60°C) in the range of 0.25 to 0.35, and the viscoelasticity of the two is different. Note that tan δ (60°C) is the value measured in accordance with JIS K6394:2007 using a viscoelasticity spectrometer (e.g., manufactured by Toyo Seiki Seisakusho Co., Ltd.) under conditions of an elongation deformation strain rate of 10% ± 2%, a vibration frequency of 20 Hz, and a temperature of 60°C.

In addition, in the pneumatic tire 1 of this embodiment, a ground contact area ratio is set between the vehicle outer land portion 23A and the vehicle inner land portion 23B. The ground contact area ratio is calculated by ground contact area/(groove area+ground contact area) for each land portion 23 in the entire tire circumferential direction, excluding the main groove 22. The groove area is the opening area of all grooves except the main groove 22 (for example, lug grooves 26 intersecting in the tire circumferential direction and narrow grooves and sipes 27 having a narrower groove width than the main groove 22). In the vehicle outer land portion 23A, the land portion 23 on the inner side of the shoulder side main groove 22B in the tire width direction has the center main groove 22A and the adjacent opening end of the shoulder side main groove 22B adjacent thereto as the tire width direction ends, and the land portion 23 on the outer side of the shoulder side main groove 22B in the tire width direction has the tire width direction outer opening end and ground contact end T of the shoulder side main groove 22B as the tire width direction ends. The vehicle outer land portion 23A has a ground contact area ratio in the range of 0.8 to 1.0, and the vehicle inner land portion 23B has a ground contact area ratio in the range of 0.5 to 0.7, so the ground contact area ratios are different.

Here, the ground contact ends T refer to the outermost ends in the tire width direction in the area where the tread surface 21 of the tread portion 2 of the pneumatic tire 1 comes into contact with the road surface (horizontal surface) when the pneumatic tire 1 is mounted on a regular rim, inflated with regular internal pressure, and 70% of the regular load is applied, and are continuous in the tire circumferential direction. The tire width dimension between each ground contact end T is called the ground contact width TW. Similarly, the ground contact area and groove area are obtained from the area excluding the main groove 22 where the tread surface 21 of the tread portion 2 of the pneumatic tire 1 comes into contact with the road surface (horizontal surface) when the pneumatic tire 1 is mounted on a regular rim, inflated with regular internal pressure, and 70% of the regular load is applied. A regular rim is a "standard rim" specified by JATMA, a "design rim" specified by TRA, or a "measuring rim" specified by ETRTO. In addition, the normal internal pressure is the "maximum air pressure" specified by JATMA, the maximum value specified in the "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Inflation Pressures" specified by ETRTO. In addition, the normal load is the "maximum load capacity" specified by JATMA, the maximum value specified in the "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Load Capacity" specified by ETRTO.

In the pneumatic tire 1 of this embodiment, the ground contact area ratio Gout of the outer land portion 23A in the outer region of the vehicle and the ground contact area ratio Gin of the inner land portion 23B in the inner region of the vehicle satisfy the relationship Gin < Gout. This relationship Gin < Gout can be achieved by forming more narrow grooves and sipes 27 with narrower groove widths than the lug grooves 26 and main grooves 22 that intersect in the tire circumferential direction in the inner land portion 23B than in the outer land portion 23A. In addition, in the pneumatic tire 1 of this embodiment, the relationship Tout20, which is the tan δ (20°C) of the outer cap rubber 24A of the outer land portion 23A in the outer region of the vehicle, and Tin20, which is the tan δ (20°C) of the inner cap rubber 24B of the inner land portion 23B in the inner region of the vehicle, satisfy the relationship Tout20 < Tin20. In addition, in the pneumatic tire 1 of this embodiment, Tout60, which is the tan δ (60°C) of the vehicle outer cap rubber 24A of the vehicle outer land portion 23A in the vehicle outer region, and Tin60, which is the tan δ (60°C) of the vehicle inner cap rubber 24B of the vehicle inner land portion 23B in the vehicle inner region, satisfy the relationship Tout60 < Tin60. In addition, in the pneumatic tire 1 of this embodiment, X20, which is Tin20/Tout20, and X60, which is Tin60/Tout60, satisfy the relationship X60 < X20.

According to the pneumatic tire 1 of this embodiment, the amount of sand splashing can be reduced by relatively reducing the tan δ (20°C) and tan δ (60°C) of the vehicle outer cap rubber 24A in the vehicle outer land portion 23A in the vehicle outer region where the ground contact area ratio is relatively large. On the other hand, according to the pneumatic tire 1 of this embodiment, the braking performance on a dry road surface can be ensured by relatively increasing the tan δ (20°C) and tan δ (60°C) of the vehicle inner cap rubber 24B in the vehicle inner land portion 23B in the vehicle inner region where the ground contact area ratio is relatively small. In addition, according to the pneumatic tire 1 of this embodiment, by defining the ratio X20 of the tan δ (20°C) of the vehicle outer cap rubber 24A to the vehicle inner cap rubber 24B to be larger than the ratio X60 of the tan δ (60°C) of the vehicle outer cap rubber 24A to the vehicle inner cap rubber 24B, it is possible to contribute to improving the braking performance during high-speed driving and improving the quietness performance by suppressing sand splashing.

Specifically, according to the pneumatic tire 1 of this embodiment, in the vehicle inner region, which contributes greatly to improving the braking performance on dry road surfaces, the tan δ (20°C) Tin20 and tan δ (60°C) Tin60 of the vehicle inner cap rubber 24B of the vehicle inner land portion 23B are made larger than the tan δ (20°C) Tout20 and tan δ (60°C) Tout60 of the vehicle outer cap rubber 24A of the vehicle outer land portion 23A in the vehicle outer region, thereby ensuring the braking performance on dry road surfaces. On the other hand, in the vehicle inner region, the ground contact area ratio Gin of the vehicle inner land portion 23B is made smaller than the ground contact area ratio Gout of the vehicle outer land portion 23A in the vehicle outer region, thereby reducing the amount of sand adsorbed to the ground contact surface and improving the quietness performance. Moreover, according to the pneumatic tire 1 of the present embodiment, in the vehicle inner region, the ground contact area ratio Gin of the vehicle inner land portion 23B is smaller than the ground contact area ratio Gout of the vehicle outer land portion 23A in the vehicle outer region, so that uneven wear of the vehicle inner land portion 23B can be suppressed. In the vehicle outer region, the tan δ (20°C) Tout20 and tan δ (60°C) Tout60 of the vehicle outer cap rubber 24A of the vehicle outer land portion 23A are smaller than the tan δ (20°C) Tin20 and tan δ (60°C) Tin60 of the vehicle inner cap rubber 24B of the vehicle inner land portion 23B in the vehicle inner region, so that the amount of sand adsorbed to the ground contact surface can be reduced and the quietness performance can be improved. On the other hand, in the vehicle outer region, the ground contact area ratio Gout of the vehicle outer land portion 23A is larger than the ground contact area ratio Gin of the vehicle inner land portion 23B in the vehicle inner region, so that the braking performance on a dry road surface can be ensured. Here, during high-speed driving, the tire temperature rises, making it difficult for sand to splash. Therefore, according to the pneumatic tire 1 of this embodiment, during low-speed driving, the braking performance and quietness are improved by the relationship between tan δ (20°C) and the ground contact area ratio, as defined by X20, which has a relatively low temperature, while during high-speed driving, the ratio of tan δ (60°C) between the vehicle outer cap rubber 24A and the vehicle inner cap rubber 24B is reduced due to the difference between X60, which has a relatively high temperature, and X20, which increases the grip force and improves the braking performance on a stable dry road surface. As a result, the pneumatic tire 1 of this embodiment can further improve the quietness and braking performance. In this embodiment, low-speed driving is assumed to be in the speed range of 40 km/h to 60 km/h when driving in urban areas, and high-speed driving is assumed to be in the speed range of 80 km/h to 100 km/h when driving on a highway.

Here, FIG. 3 is a diagram showing the viscoelastic curve of the cap rubber 24. As shown in FIG. 3, one of the two curves shown by solid lines represents an example of the viscoelastic curve of the vehicle outer cap rubber 24A, and the other represents an example of the viscoelastic curve of the vehicle inner cap rubber 24B. As shown in FIG. 3, in the pneumatic tire 1 of this embodiment, Tout20, which is the tan δ (20°C) of the vehicle outer cap rubber 24A, and Tin20, which is the tan δ (20°C) of the vehicle inner cap rubber 24B, satisfy the relationship Tout20<Tin20. In addition, in the pneumatic tire 1 of this embodiment, Tout60, which is the tan δ (60°C) of the vehicle outer cap rubber 24A, and Tin60, which is the tan δ (60°C) of the vehicle inner cap rubber 24B, satisfy the relationship Tout60<Tin60. In addition, in the pneumatic tire 1 of this embodiment, X20, which is Tin20/Tout20, and X60, which is Tin60/Tout60, satisfy the relationship X60<X20. Note that in FIG. 3, the curves shown by the dashed lines and the curves shown by the dashed lines show examples of viscoelasticity curves of other examples of rubber, and by appropriately selecting rubbers with various viscoelasticity curves, performance can be improved according to the season and speed range.

In addition, in the pneumatic tire 1 of this embodiment, the relationship Tout60/Tout20 between tan δ (60°C) and tan δ (20°C) of the vehicle outer cap rubber 24A in the vehicle outer land portion 23A in the vehicle outer region is defined as Yout, and the relationship Tin60/Tin20 between tan δ (60°C) and tan δ (20°C) of the vehicle inner cap rubber 24B in the vehicle inner land portion 23B in the vehicle inner region is defined as Yin, and it is preferable that Yout and Yin satisfy the relationship Yin<Yout.

Yout represents the slope of tan δ (viscoelastic curve) in FIG. 3, which is the temperature dependence of tan δ (60°C) and tan δ (20°C) of the vehicle outer cap rubber 24A, and Yin represents the slope of tan δ in FIG. 3, which is the temperature dependence of tan δ (60°C) and tan δ (20°C) of the vehicle inner cap rubber 24B. As described above, with this pneumatic tire 1, the tire temperature rises during high-speed driving, making it difficult for sand splashes to occur. Therefore, by using the vehicle outer cap rubber 24A with a small slope between tan δ (60°C) and tan δ (20°C) (i.e., high tan δ (60°C)) in the vehicle outer land portion 23A in the vehicle outer region, it is possible to improve braking performance on more stable dry road surfaces.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that the ground contact area ratio Gout' of the outer land portion 23A in the outer region of the vehicle and the ground contact area ratio Gin' of the inner land portion 23B in the inner region of the vehicle satisfy the relationship of 10%≦Gout'-Gin'≦50%. The ground contact area ratio is calculated as the percentage of ground contact area/(groove area+ground contact area) in the entire tire circumferential direction in each land portion 23, excluding the main groove 22. The above Gout'-Gin' relationship can be achieved by forming more fine grooves and sipes 27 with narrower groove widths than the lug grooves 26 and main grooves 22 that intersect in the tire circumferential direction in the inner land portion 23B than in the outer land portion 23A.

According to this pneumatic tire 1, the difference between the ground contact area ratio Gout' of the outer land portion 23A in the outer region of the vehicle and the ground contact area ratio Gin' of the inner land portion 23B in the inner region of the vehicle is set to 10% or more, thereby reducing the amount of sand adsorbed to the ground surface in the inner region of the vehicle. On the other hand, the effect of reducing the amount of sand adsorbed to the ground surface in the inner region of the vehicle can be ensured by setting the difference between the ground contact area ratio Gout' of the outer land portion 23A in the outer region of the vehicle and the ground contact area ratio Gin' of the inner land portion 23B in the inner region of the vehicle to 50% or less. For example, when the grip force of the inner cap rubber 24B in the inner region of the vehicle is high and the amount of sand adsorbed is large, the quietness performance tends to decrease. However, by defining the difference between the ground contact area ratio Gout' of the outer land portion 23A and the ground contact area ratio Gin' of the inner land portion 23B, the effect of reducing the amount of sand adsorbed to the ground surface in the inner region of the vehicle can be improved.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that X20, which is the ratio of tan δ (20°C) between the vehicle outer cap rubber 24A and the vehicle inner cap rubber 24B, satisfies the range of 1.01≦X20≦2.0, and that X60, which is the ratio of tan δ (60°C) between the vehicle outer cap rubber 24A and the vehicle inner cap rubber 24B, satisfies the range of 1.01≦X60≦2.0.

In this pneumatic tire 1, by setting X20 and X60 to 1.01 or more, the tan δ of the vehicle inner cap rubber 24B is large, and braking performance on dry road surfaces can be improved. On the other hand, by setting X20 and X60 to 2.0 or less, excessive tan δ is suppressed, and the effect of suppressing sand splashing can be ensured.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that the ratio Yout of tan δ (60°C) to tan δ (20°C) of the vehicle outer cap rubber 24A in the vehicle outer land portion 23A in the vehicle outer region, Tout60/Tout20, satisfies the range of 0.2≦Tout60/Tout20≦0.5.

In this pneumatic tire 1, the range of the slope of tan δ (viscoelastic curve) in FIG. 3 is set for the vehicle-outside cap rubber 24A in the vehicle-outside land portion 23A in the vehicle-outside region. In this pneumatic tire 1, the range of the slope of the viscoelastic curve is set for the vehicle-outside cap rubber 24A, making it possible to achieve both the contradictory braking performance on dry road surfaces and the quietness performance that suppresses sand splashing.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that the ratio Yin of tan δ (60°C) to tan δ (20°C) of the vehicle inner cap rubber 24B in the vehicle inner land portion 23B in the vehicle inner region, Tin60/Tin20, satisfies the relationship 0.3≦Tin60/Tin20≦0.6.

In this pneumatic tire 1, the range of the slope of tan δ (viscoelastic curve) in FIG. 3 is set for the vehicle-inside cap rubber 24B in the vehicle-inside land portion 23B in the vehicle-inside region. In this pneumatic tire 1, the range of the slope of the viscoelastic curve is set for the vehicle-inside cap rubber 24B, making it possible to achieve both the contradictory braking performance on dry road surfaces and the quietness performance that suppresses sand splashing.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that the product Pout60 of the actual contact area Aout of the outer land portion 23A in the outer region of the vehicle and the tan δ (60°C) Tout60 of the outer cap rubber 24A of the outer land portion 23A, and the product Pin60 of the actual contact area Ain of the inner land portion 23B in the inner region of the vehicle and the tan δ (60°C) Tin60 of the inner cap rubber 24B of the inner land portion 23B in the inner region of the vehicle, satisfy the range of 10 to 50.

The actual contact areas Aout and Ain are the areas excluding the groove areas of all grooves, including the main grooves 22, in the contact area G where the tread surface 21 of the tread portion 2 comes into contact with the road surface (horizontal surface), as surrounded by the two-dot chain line in Figure 2, when the pneumatic tire 1 is mounted on a standard rim, inflated to the standard internal pressure, and subjected to 70% of the standard load.

According to this pneumatic tire 1, if Pout60 in the vehicle outer land portion 23A and Pin60 in the vehicle inner land portion 23B are 10 or more, the ground contact area ratio Gout can be increased in the vehicle outer region and tan δ (60°C) Tout60 can be increased in the vehicle inner region, so that braking performance on dry road surfaces can be ensured in the vehicle outer region and the vehicle inner region. On the other hand, if Pout60 in the vehicle outer land portion 23A and Pin60 in the vehicle inner land portion 23B are 50 or less, tan δ (60°C) Tout60 can be suppressed in the vehicle outer region and the ground contact area ratio Gin can be suppressed in the vehicle inner region, so that the amount of sand adsorbed to the ground contact surface in the vehicle outer region and the vehicle inner region can be reduced, and quietness performance can be improved.

In addition, in the pneumatic tire 1 of this embodiment, it is preferable that the product Pout20 of the actual contact area Aout of the outer land portion 23A in the outer region of the vehicle and the tan δ (20°C) Tout20 of the outer cap rubber 24A of the outer land portion 23A, and the product Pin20 of the actual contact area Ain of the inner land portion 23B in the inner region of the vehicle and the tan δ (20°C) Tin20 of the inner cap rubber 24B of the inner land portion 23B in the inner region of the vehicle, satisfy the range of 30 or more and 90 or less.

According to this pneumatic tire 1, if Pout20 in the vehicle outer land portion 23A and Pin20 in the vehicle inner land portion 23B are 30 or more, the ground contact area ratio Gout can be increased in the vehicle outer region and tan δ (20°C) Tout20 can be increased in the vehicle inner region, so that braking performance on dry road surfaces can be ensured in the vehicle outer region and the vehicle inner region. On the other hand, if Pout20 in the vehicle outer land portion 23A and Pin20 in the vehicle inner land portion 23B are 90 or less, tan δ (20°C) Tout20 can be suppressed in the vehicle outer region and the ground contact area ratio Gin can be suppressed in the vehicle inner region, so that the amount of sand adsorbed to the ground contact surface in the vehicle outer region and the vehicle inner region can be reduced, thereby improving quietness.

In addition, in the pneumatic tire 1 of this embodiment, the ratio of the product of the ground contact area ratio Gout of the outer land portion 23A in the outer region of the vehicle and the tan δ (60°C) Tout60 of the outer cap rubber 24A of the outer land portion 23A to the product of the ground contact area ratio Gin of the inner land portion 23B in the inner region of the vehicle and the tan δ (60°C) Tin60 of the inner cap rubber 24B of the inner land portion 23B in the inner region of the vehicle is in the range of 0.90≦(Gout×Tout60)/(Gin×Tin60)≦1.10. It is preferable that the ratio of the product of the ground contact area ratio Gout of the outer land portion 23A in the outer region of the vehicle and the tan δ (20°C) Tout20 of the outer cap rubber 24A of the outer land portion 23A of the vehicle to the product of the ground contact area ratio Gin of the inner land portion 23B in the inner region of the vehicle and the tan δ (20°C) Tin20 of the inner cap rubber 24B of the inner land portion 23B of the inner region of the vehicle satisfies the range of 0.90≦(Gout×Tout20)/(Gin×Tin20)≦1.10.

With this pneumatic tire 1, the ratio of the product of the ground contact area ratio Gout and tan δ (60°C) Tout60 in the vehicle outer region to the product of the ground contact area ratio Gin and tan δ (60°C) Tin60 in the vehicle inner region is uniformed within a range of 0.90 to 1.10, and the ratio of the product of the ground contact area ratio Gout and tan δ (20°C) Tout20 in the vehicle outer region to the product of the ground contact area ratio Gin and tan δ (20°C) Tin20 in the vehicle inner region is uniformed within a range of 0.90 to 1.10, thereby suppressing the deviation in quietness and braking performance due to the difference between the two, ensuring braking performance, reducing sand splashing noise (sound pressure level on the high frequency side), and further suppressing uneven wear of the tread portion 2.

In this embodiment, as described above, a pneumatic tire has been described as an example of a tire. However, the present invention is not limited to this, and the configuration described in this embodiment can be arbitrarily applied to other tires within the scope of what is obvious to a person skilled in the art. Examples of other tires include airless tires.

In this example, performance tests were conducted on several types of pneumatic tires under different conditions with respect to quietness (resistance to sand splashing noise) and braking performance on dry road surfaces (see Figure 4).

In the performance evaluation test, a pneumatic tire (test tire) with a tire size of 215/45R18 was mounted on a standard rim of 18x7.0J, inflated to a standard internal pressure of 250kPa, and mounted on a vehicle (test vehicle) with an engine displacement of 1500cc class.

In the performance test for quietness, the above test vehicle is run-in for 100km on a dry road surface from the time it is new, and then driven on a 50m long and 3m wide dry road surface that has been air-blowed, sand spread and evenly smoothed with a broom, and then driven on a circular test course, where a panelist performs a sensory evaluation of the noise inside the vehicle. The sensory evaluation is performed after two laps around the circular test course, one lap around the circular test course, and one lap around the circular test course again, and the average of the three laps is calculated. This evaluation is performed using an index evaluation with the conventional example as the standard (100), and the higher the value, the quieter the sand splashing noise and the better the quietness performance.

The evaluation method for braking performance on dry roads involves low-speed and high-speed driving. For the evaluation method for low-speed driving, the test vehicle is driven on a dry road surface, and the braking distance is measured from a driving speed of 50 km/h to 0 km/h. For the evaluation method for high-speed driving, the test vehicle is driven on a dry road surface, and the braking distance is measured from a driving speed of 100 km/h to 0 km/h. Then, based on these measurement results, an index evaluation is performed with the conventional example as the standard (100). In this evaluation, the higher the numerical value, the shorter the braking distance and the better the braking performance.

In FIG. 4, the pneumatic tires of the conventional example, Comparative Example 1 to Comparative Example 3, and Example 1 to Example 4 have four land areas defined by three main grooves in the tread portion as shown in FIG. 1 and FIG. 2. Tan δ (20°C) and tan δ (60°C) are shown as indexes with the land area in the vehicle outer region of the conventional example as the reference (100). The ground contact area ratio is also shown as an index with the land area in the vehicle outer region of the conventional example as the reference (100). The pneumatic tires of the conventional example and Comparative Example 1 to Comparative Example 3 are outside the range of the relationship between the ground contact area ratio Gout and the ground contact area ratio Gin, the relationship between tan δ (20°C) Tin20 and tan δ (20°C) Tout20, the relationship between tan δ (60°C) Tin60 and tan δ (60°C) Tout60, and the relationship between X20 and X60. On the other hand, for the pneumatic tires of Examples 1 to 4, the relationship between the ground contact area ratio Gout and the ground contact area ratio Gin, the relationship between tan δ (20°C) Tin20 and tan δ (20°C) Tout20, the relationship between tan δ (60°C) Tin60 and tan δ (60°C) Tout60, and the relationship between X20 and X60 are within the specified ranges.

As shown in the test results in Figure 4, the pneumatic tires of Examples 1 to 4 ensure quietness and have improved braking performance when driving at low speeds and high speeds on dry road surfaces.

Reference Signs List 1 Pneumatic tire 22 Main groove 22A Center main groove 23 Land portion 23A Vehicle outer land portion 23B Vehicle inner land portion 24 Cap rubber 24A Vehicle outer cap rubber 24B Vehicle inner cap rubber

Claims (9)

The tire has a specified orientation in the inside and outside of the vehicle when mounted on the vehicle, and has at least two land portions defined by at least one main groove extending in the circumferential direction of the tire in the tread portion and closest to the tire equatorial plane,
When the land portion on the vehicle outer side of the main groove is defined as a vehicle outer region and the land portion on the vehicle inner side of the main groove is defined as a vehicle inner region,
a ground contact area ratio Gout of the land portion in the vehicle outer region and a ground contact area ratio Gin of the land portion in the vehicle inner region satisfy a relationship of Gin<Gout,
Tout20, which is the tan δ (20° C.) of the cap rubber of the land portion in the vehicle outer region, and Tin20, which is the tan δ (20° C.) of the cap rubber of the land portion in the vehicle inner region, satisfy the relationship Tout20<Tin20,
Tout60, which is the tan δ (60° C.) of the cap rubber of the land portion in the vehicle outer region, and Tin60, which is the tan δ (60° C.) of the cap rubber of the land portion in the vehicle inner region, satisfy the relationship Tout60<Tin60,
A tire in which X20, which is Tin20/Tout20, and X60, which is Tin60/Tout60, satisfy the relationship X60<X20. The tire according to claim 1, in which Yout, which is Tout60/Tout20, and Yin, which is Tin60/Tin20, satisfy the relationship Yin<Yout. The tire according to claim 1 or 2, wherein the ground contact area ratio Gout' of the land portion in the vehicle outer region and the ground contact area ratio Gin' of the land portion in the vehicle inner region satisfy the relationship 10%≦Gout'-Gin'≦50%. The tire according to any one of claims 1 to 3, wherein X20 and X60 are in the range of 1.01 or more and 2.0 or less. The tire according to any one of claims 1 to 4, wherein the Tout60 and the Tout20 satisfy the relationship 0.2≦Tout60/Tout20≦0.5. The tire according to any one of claims 1 to 5, wherein the Tin 60 and the Tin 20 satisfy the relationship 0.3≦Tin 60/Tin 20≦0.6. The tire according to any one of claims 1 to 6, wherein the product Pout60 of the actual contact area Aout of the land portion in the vehicle outer region and the Tout60, and the product Pin60 of the actual contact area Ain of the land portion in the vehicle inner region and the Tin60, are in the range of 10 to 50. The tire according to any one of claims 1 to 7, wherein the product Pout20 of the actual contact area Aout of the land portion in the vehicle outer region and the Tout20, and the product Pin20 of the actual contact area Ain of the land portion in the vehicle inner region and the Tin20, are in the range of 30 to 90. The tire according to any one of claims 1 to 8, wherein the product Pout60 of the Gout and the Tout60 and the product Pin60 of the Gin and the Tin60 satisfy the relationship of 0.90≦Pout60/Pin60≦1.10, and the product Pout20 of the Gout and the Tout20 and the product Pin20 of the Gin and the Tin20 satisfy the relationship of 0.90≦Pout20/Pin20≦1.10.

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