TECHNICAL FIELD

The present technology relates to a pneumatic tire.

BACKGROUND ART

In a technical field relating to a pneumatic tire, development has been promoted to reduce the weight and rolling resistance of the pneumatic tire, in order to improve the fuel efficiency of a vehicle. Japanese Unexamined Patent Application Publication No. 2012-091731 discloses a technology that is designed to reduce the weight and rolling resistance of the pneumatic tire by extending a carcass folded back portion up to a point between a belt and a carcass main body portion, and consequently reducing the size of a rubber gage in a side portion.

SUMMARY

Due to the weight reduction of the pneumatic tire, there is a possibility that rigidity and cut resistance of the pneumatic tire may deteriorate. Thus, there is a demand for development of a pneumatic tire that achieves the weight reduction while suppressing the deterioration in the rigidity and the cut resistance.

The present technology provides a pneumatic tire that achieves weight reduction while suppressing deterioration of rigidity and cut resistance of the pneumatic tire.

According to the present technology, a pneumatic tire rotatable about a rotation axis is provided. Such a pneumatic tire includes a tread portion; side portions disposed on both sides of the tread portion in a tire width direction; a carcass including a carcass main body portion and a carcass folded back portion formed as a result of the carcass being folded back at a bead core; a side rubber connected to a carcass outer surface of the carcass main body portion and including a side surface on which a tire maximum width position is positioned; and a plurality of protrusion portions connected to the side surface, the protrusion portions protruding from the side surface and being disposed in a tire circumferential direction. At least one of the plurality of protrusion portions is connected to the side surface so as to include the tire maximum width position. Each of the plurality of protrusion portions includes a first end portion and a second end portion that is disposed on an outer side of the first end portion in a tire radial direction. A distance between the first end portion and the second end portion is larger than a short-direction maximum width of the protrusion portion in a plane orthogonal to the rotation axis. In a case that a tire center in the tire width direction is denoted as CL, an intersection point of a parallel line LP with the carcass outer surface is denoted as P1, the parallel line LP extending parallel with the rotation axis and passing through the tire maximum width position, an intersection point of the parallel line LP with the side surface is denoted as P2, an intersection point of the parallel line LP with a protrusion portion outer surface of the protrusion portion is denoted as P3which is disposed in the outermost position in the tire width direction, a distance between the tire center CL and the intersection point P1in a direction parallel with the rotation axis is denoted as W1, a distance between the tire center CL and the intersection point P2in the direction parallel with the rotation axis is denoted as W2, a distance between the tire center CL and the intersection point P3in the direction parallel with the rotation axis is denoted as W3, a distance between the intersection point P1and the intersection point P2is denoted as G1, and a distance between the intersection point P2and the intersection point P3is denoted as G2, the conditions of
0.80≤W1/W3≤0.95  (1) and
0.1≤G1/G2≤1  (2) are satisfied.

According to the present technology, as a result of the protrusion portions being provided on the side surface of the side rubber, even when a weight reduction is achieved by causing the distance G1, which indicates the thickness of the side rubber, to be smaller, a deterioration in rigidity and cut resistance is suppressed. Since the protrusion portions, each of which has a longitudinal shape, are connected to the side surface so as to include the tire maximum width position, and the plurality of the protrusion portions are provided in the tire circumferential direction, bending of the side portion is suppressed, and the side rubber is protected by the protrusion portions. As a result, the deteriorations in the rigidity and cut resistance of the pneumatic tire are suppressed. Further, as a result of the bending of the side portion being suppressed and the side rubber being protected, the carcass is sufficiently protected, and a deterioration of the carcass is thus suppressed.

Further, it is suitable that the carcass folded back portion do not extend as far as the tire maximum width position. Even when the carcass folded back portion does not extend as far as the tire maximum width position, the deteriorations in the rigidity and cut resistance of the pneumatic tire are suppressed by the protrusion portions. Further, by not extending the carcass folded back portion as far as the tire maximum width position, an increase in the weight of the pneumatic tire due to the carcass is suppressed.

Further, when a vehicle on which the pneumatic tires are mounted travels, air resistance at the tire maximum width position tends to become large. As a result of the longitudinal-shape protrusion portions being provided so as to include the tire maximum width position, an air distribution promotion effect and an air streamlining effect are obtained. As a result, air resistance is reduced, and fuel efficiency of the vehicle is thus improved.

The distance W1corresponds to a carcass cross-sectional width S1, the distance W2corresponds to a tire cross-sectional width S2, and the distance W3corresponds to a total tire width S3. The carcass cross-sectional width S1is equivalent to two times the distance W1, the tire cross-sectional width S2is equivalent to two times the distance W2, and the total tire width S3is equivalent to two times the distance W3. The distance G1is a difference between the distance W2and the distance W1, and the distance G2is a difference between the distance W3and the distance W2.

As a result of the distance W3being defined, a pneumatic tire, which has a total tire width suitable for the vehicle on which the tire is mounted, is manufactured. As a result of the distance W3being specified, the distance W1is unequivocally determined by the condition (1). When W1/W3is larger than 0.95, a distance between the carcass outer surface and the protrusion portion outer surface becomes too short, and the carcass2is not sufficiently protected. When W1/W3is smaller than 0.80, the distance between the carcass outer surface and the protrusion portion outer surface becomes too large, and the weight reduction of the pneumatic tire becomes difficult. By satisfying the condition (1), the weight reduction is achieved while sufficiently protecting the carcass.

As a result of the distance W1and the distance W3being determined, the distance W2is unequivocally determined by the condition (2). The distance G1indicates the thickness of the side rubber, and the distance G2indicates the height of the protrusion portion. When G1/G2is smaller than 0.1, the thickness of the side rubber becomes too thin, and the carcass is not sufficiently protected. When G1/G2is larger than 1, the thickness of the side rubber becomes larger than the height of the protrusion portion, and the weight reduction of the pneumatic tire becomes difficult. By satisfying the condition (2) as well as the condition (1), the weight reduction of the pneumatic tire is achieved while suppressing the deterioration in the rigidity and cut resistance of the pneumatic tire.

According to the present technology, a pneumatic tire rotatable about a rotation axis is provided. Such a pneumatic tire includes a tread portion; side portions disposed on both sides of the tread portion in a tire width direction; a carcass including a carcass main body portion and a carcass folded back portion formed as a result of the carcass being folded back at a bead core; a side rubber connected to a carcass outer surface of the carcass main body portion and including a side surface on which a tire maximum width position is positioned; and a plurality of protrusion portions connected to the side surface, the protrusion portions protruding from the side surface and being disposed in a tire circumferential direction. At least one of the plurality of protrusion portions is connected to the side surface so as to include the tire maximum width position. Each of the plurality of protrusion portions includes a first end portion and a second end portion that is disposed on an outer side of the first end portion in a tire radial direction. A distance between the first end portion and the second end portion is larger than a short-direction maximum width of the protrusion portion in a plane orthogonal to the rotation axis. In a case that a tire center in the tire width direction is denoted as CL, an intersection point of a parallel line LP with the carcass outer surface is denoted as P1, the parallel line LP extending parallel with the rotation axis and passing through the tire maximum width position, an intersection point of the parallel line LP with the side surface is denoted as P2, an intersection point of the parallel line LP with a protrusion portion outer surface of the protrusion portion is denoted as P3which is disposed in the outermost position in the tire width direction, a distance between the tire center CL and the intersection point P1in a direction parallel with the rotation axis is denoted as W1, a distance between the tire center CL and the intersection point P2in the direction parallel with the rotation axis is denoted as W2, a distance between the tire center CL and the intersection point P3in the direction parallel with the rotation axis is denoted as W3, a distance between the intersection point P1and the intersection point P2is denoted as G1, and a distance between the intersection point P2and the intersection point P3is denoted as G2, the conditions of
0.80≤W1/W3≤0.95  (3) and
1.0 mm≤G1≤2.5 mm  (4) are satisfied.

According to the present technology, as a result of the distance W3being determined, the distance W1is unequivocally determined by the condition (3). By satisfying the condition (3), the weight reduction of the pneumatic tire is achieved while suppressing the deterioration in the rigidity and cut resistance of the pneumatic tire. The distance G1indicates the thickness of the side rubber. A side rubber gage of a tire in the related art is thicker than 2.5 mm. As a result of making the distance G1to be 2.5 mm or less, which is smaller than the side rubber gage of the tire in the related art, the weight reduction of the pneumatic tire is achieved. When the distance G1is smaller than 1.0 mm, the thickness of the side rubber8becomes too thin. Thus, the carcass2is not sufficiently protected. By satisfying the condition (4) as well as the condition (3), the weight reduction is achieved while sufficiently protecting the carcass.

In the present technology, it is suitable that all of the plurality of protrusion portions be connected to the side surface so as to include the tire maximum width position.

As a result of all of the plurality of protrusion portions being provided so as to include the tire maximum width position, bending of the side portion is sufficiently suppressed at the tire maximum width position, and the side rubber and the carcass are sufficiently protected. Further, the air resistance is reduced, and consequently, the fuel efficiency of the vehicle is improved.

In the present technology, when a tire cross-sectional height, which indicates a distance between an innermost end portion and an outermost end portion in the tire radial direction, is denoted as SH, it is suitable that the protrusion portions be provided within a range of from 0.1×SH to 0.4×SH in the tire radial direction.

In a range in which the tire cross-sectional height is larger than 0.4×SH, the protrusion portions reach outer regions of the side portions. Consequently, the weight of the pneumatic tire simply increases, while no significant improvement in functions of the protrusion portions (namely, a rigidity reduction suppression function, a cut resistance reduction suppression function, and a carcass protection function) is expected. In a range in which the tire cross-sectional height is smaller than 0.1×SH, the carcass protection function is not sufficiently used. As a result of the protrusion portions being provided in the range of from 0.1×SH to 0.4×SH, the functions of the protrusion portions are fully used while achieving the weight reduction of the pneumatic tire.

In the present technology, the number of the protrusion portions disposed on the side surface in the tire circumferential direction is suitably in a range of from 10 to 50.

When the number of protrusions is less than 10, the air distribution promotion effect and the air streamlining effect are not sufficiently obtained. When the number of protrusion portions is more than 50, the protrusion portions themselves become a source of air resistance, and the air distribution promotion effects and the air streamlining effects are not sufficiently obtained. Further, when the number of protrusion portions is too large, the weight of the pneumatic tire increases. As a result of setting the number of protrusion portions to be in the range of from 10 to 50, the air resistance and the fuel efficiency of the vehicle is improved while suppressing the increase in the weight of the pneumatic tire.

In the present technology, it is suitable that the short-direction maximum width of the protrusion portion be in a range of from 0.5 mm to 5.0 mm.

When the short-direction maximum width of the protrusion portion is less than 0.5 mm, the protrusion portion easily deforms and becomes difficult to obtain the air distribution promotion effect and the air streamlining effect. When the short-direction maximum width of the protrusion portion is greater than 5.0 mm, the protrusion portion itself becomes a source of air resistance, and the air distribution promotion effect and the air streamlining effect are not sufficiently obtained. Further, when the protrusion portion is too thick, the weight of the pneumatic tire increases. As a result of the short-direction maximum width of the protrusion portion being set to be in a range of from 0.5 mm to 5.0 mm or less, the air resistance and the fuel efficiency of the vehicle is improved while suppressing the increase in the weight of the pneumatic tire.

In the present technology, it is suitable that a plurality of recessed portions be provided, in the side surface, between the protrusion portions that are adjacent to each other.

As a result, the air resistance of the vehicle is further reduced, and the fuel efficiency of the vehicle is thus improved. As a result of the recessed portions being provided in addition to the protrusion portions, the air flowing from the front side to the rear side of the vehicle becomes turbulent. As a result, a turbulent flow boundary layer is generated in the periphery of the pneumatic tire, and an expansion of the air is suppressed. As a result of the expansion of the air passing the vehicle being suppressed, the air resistance of the vehicle is reduced, and the fuel efficiency of the vehicle is thus improved.

According to an aspect of the present technology, provided is a pneumatic tire that achieves weight reduction while suppressing deterioration in rigidity and cut resistance of the pneumatic tire.

