Pneumatic tire having bead core with stretchable portion

A pneumatic tire 22 includes a pair of beads 30 and a carcass 32 extending on and between both beads 30. Each bead 30 includes a core 48. The core 48 includes: a main body 56 including a cord 60 extending in a circumferential direction; and a stretchable portion 58 formed from a crosslinked rubber. The stretchable portion 58 is located inward of the main body 56 in an axial direction. The stretchable portion 58 has a size with which at least one cross-section of the cord 60 can be included therein in a cross-section of the bead 30. Preferably, in the tire 22, the main body 56 includes a hard unit and a soft unit. The soft unit is located outward of the hard unit in a radial direction. A hard cord of the hard unit stretches more easily than a soft cord of the soft unit.

TECHNICAL FIELD

The present invention relates to pneumatic tires.

BACKGROUND ART

FIG. 14shows a conventional pneumatic tire2. The tire2includes a pair of beads4and a carcass6. Each bead4includes a ring-shaped core8and an apex10extending from the core8outward in a radial direction. The carcass6extends on and between one of the beads4and the other bead4.

FIG. 15shows a cross-section of the core8of the bead4. The core8includes a cord12extending in a circumferential direction. In the bead4, the core8is formed by winding the cord12in the circumferential direction a plurality of times.

The tire2is fitted onto a rim. When the tire2is fitted onto the rim, each bead4portion comes into contact with a flange of the rim. As described above, the core8is formed by winding the cord12in the circumferential direction a plurality of times. The core8tightens the rim. Thus, the tire2is prevented from being displaced or coming off from the rim.

FIG. 16shows a state where the tire2is fitted onto a rim14. As shown in the drawing, one bead4aportion is brought into contact with one flange16aof the rim14. The other bead4bportion is dropped into a drop18of the rim14. Air is injected into the space surrounded by the inner surface of the tire2and the rim14, whereby the other bead4bportion comes into contact with the other flange16b. Accordingly, fitting the tire2onto the rim14is completed. The pressure of the air injected during fitting is referred to as fitting pressure. The fitting pressure influences ease of fitting the tire2onto the rim14. Various examinations have been made in order to reduce the fitting pressure. One example of the examinations is disclosed in JP2002-36830.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

FIG. 17shows movement of the bead4portion of the tire2during fitting. As shown in the drawing, when air is injected into the interior of the tire2, the bead4portion moves along the rim14outward in an axial direction. The bead4portion passes over a hump20and comes into contact with the flange16bof the rim14.

As is obvious from the drawing, when the bead4portion passes over the hump20, the core8is stretched most. At this time, the tension of the core8becomes maximum. In particular, great tension is applied to a cord12aat a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core8shown inFIG. 15.

Normally, an element wire formed from steel is used for the cord12of the core8. The cord12is difficult to stretch, that is, non-stretchable. The non-stretchable cord12influences deformation of the core8.

There is a need for reducing flattening of a tire. A tire with low flattening is easily displaced or comes off from a rim. For preventing the tire from being displaced or coming off from the rim, it is effective to enhance a tightening force generated by a core. However, a core having an enhanced tightening force is difficult to deform. With the core that is difficult to deform, a bead portion is difficult to pass over a hump. For fitting the tire onto the rim, a high fitting pressure is required. An excessively high fitting pressure influences the workability.

From the standpoint that running can continue at a high speed for a certain distance even during puncture, a run flat tire having a reinforced rubber layer provided at each sidewall portion may be adopted. In the run flat tire, each sidewall portion has high stiffness, and thus the run flat tire is easily displaced or comes off from a rim. For preventing the run flat tire from being displaced or coming off from the rim, it is effective to enhance a tightening force generated by a core, similarly to the above-described tire with low flattening. However, a core having an enhanced tightening force is difficult to deform. With the core that is difficult to deform, a bead portion is difficult to pass over a hump. For fitting the tire onto the rim, a high fitting pressure is required. An excessively high fitting pressure influences the workability.

An object of the present invention is to provide a pneumatic tire that allows a low fitting pressure to be achieved without impairing a tightening force.

Solution to the Problems

A pneumatic tire according to the present invention includes a pair of ring-shaped beads and a carcass extending on and between one of the beads and the other bead. Each bead includes a core and an apex extending from the core outward in a radial direction. The core includes: a main body including a cord extending in a circumferential direction; and a stretchable portion formed from a crosslinked rubber. The stretchable portion is located inward of the main body in an axial direction. The stretchable portion has a size with which at least one cross-section of the cord can be included therein in a cross-section of the bead.

Preferably, in the pneumatic tire, the main body includes a hard unit and a soft unit. The soft unit is located outward of the hard unit in the radial direction. The hard unit includes a hard cord extending in the circumferential direction. The soft unit includes a soft cord extending in the circumferential direction. The soft cord stretches more easily than the hard cord. The stretchable portion has a size with which at least one cross-section of the hard cord can be included therein in the cross-section of the bead.

Preferably, in the pneumatic tire, the main body further includes a middle unit. The middle unit is located outward of the hard unit in the radial direction and located outward of the soft unit in the axial direction. The middle unit includes a middle cord extending in the circumferential direction. The middle cord stretches more easily than the hard cord. The soft cord stretches more easily than the middle cord. In a cross-section of the main body, one cross-section of the middle cord is located outward of one cross-section of the hard cord in the radial direction and inward of the one cross-section of the hard cord in the axial direction. One cross-section of the soft cord is located outward of the one cross-section of the middle cord in the radial direction and inward of the one cross-section of the middle cord in the axial direction.

Another pneumatic tire according to the present invention includes a pair of ring-shaped beads and a carcass extending on and between one of the beads and the other bead. Each bead includes a core and an apex extending from the core outward in a radial direction. The core includes a hard unit and a soft unit. The hard unit includes a hard cord extending in a circumferential direction. The soft unit includes a soft cord extending in the circumferential direction. The soft cord stretches more easily than the hard cord. One cross-section of the hard cord is located at a portion, at an outer side in an axial direction and at an inner side in the radial direction, of a cross-section of the core. One cross-section of the soft cord is located at a portion, at an inner side in the axial direction and at an outer side in the radial direction, of the cross-section of the core.

Preferably, in the pneumatic tire, the core further includes a middle unit. The middle unit is located between the hard unit and the soft unit. The middle unit includes a middle cord extending in the circumferential direction. The middle cord stretches more easily than the hard cord. The soft cord stretches more easily than the middle cord. In the cross-section of the core, one cross-section of the middle cord is located outward of the one cross-section of the hard cord in the radial direction and inward of the one cross-section of the hard cord in the axial direction. The one cross-section of the soft cord is located outward of the one cross-section of the middle cord in the radial direction and inward of the one cross-section of the middle cord in the axial direction.

Advantageous Effects of the Invention

In the pneumatic tire according to the present invention, the configuration of each bead is adjusted such that a portion to which great tension is applied when the pneumatic tire is fitted onto a rim easily stretches. With the tire, a low fitting pressure is achieved without impairing a tightening force.

DESCRIPTION OF EMBODIMENTS

The following will describe in detail the present invention based on preferred embodiments with appropriate reference to the drawings.

FIG. 1shows a pneumatic tire22. InFIG. 1, the up-down direction is the radial direction of the tire22, the right-left direction is the axial direction of the tire22, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire22. InFIG. 1, an alternate long and short dash line CL represents the equator plane of the tire22. The shape of the tire22is symmetrical about the equator plane except for a tread pattern.FIG. 1shows a cross-section of the tire22along the radial direction.

The tire22includes a tread24, sidewalls26, clinches28, beads30, a carcass32, a belt34, a band36, an inner liner38, wings40, and cushion layers42. The tire22is of a tubeless type. The tire22is mounted on a passenger car.

The tread24has a shape projecting outward in the radial direction. The tread24forms a tread surface44that is brought into contact with a road surface. Grooves46are formed on the tread surface44. The tread pattern is formed by the grooves46. The tread24includes a base layer and a cap layer, which are not shown. The cap layer is located outward of the base layer in the radial direction. The cap layer is laminated on the base layer. The base layer is formed from a crosslinked rubber that is excellent in adhesiveness. A typical base rubber of the base layer is a natural rubber. The cap layer is formed from a crosslinked rubber that is excellent in wear resistance, heat resistance, and grip performance.

The sidewalls26extend from the edges of the tread24substantially inward in the radial direction. The outer edges, in the radial direction, of the sidewalls26are joined to the tread24. The inner edges, in the radial direction, of the sidewalls26are joined to the clinches28. The sidewalls26are formed from a crosslinked rubber that is excellent in cut resistance and weather resistance. The sidewalls26prevent the carcass32from being damaged.

The clinches28are located substantially inward of the sidewalls26in the radial direction. The clinches28are located outward of the beads30and the carcass32in the axial direction. The clinches28are formed from a crosslinked rubber that is excellent in wear resistance. The clinches28come into contact with flanges of a rim.

The beads30are located inward of the clinches28in the axial direction. Each bead30has a ring shape. Each bead30includes a core48and an apex50. The apex50extends from the core48outward in the radial direction. The apex50is tapered outward in the radial direction. The apex50is formed from a highly hard crosslinked rubber.

The carcass32is formed of a carcass ply52. The carcass ply52extends on and between the beads30at both sides and along the tread24and the sidewalls26. The carcass ply52is turned up around each core48from the inner side to the outer side in the axial direction. Due to this turning-up, a main portion52aand turned-up portions52bare formed in the carcass ply52.

The carcass ply52includes a large number of cords aligned with each other, and a topping rubber. The absolute value of the angle of each cord relative to the equator plane is 75° to 90°. In other words, the carcass32has a radial structure. The cords are formed from an organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass32may be formed of two or more carcass plies52.

The belt34is located inward of the tread24in the radial direction. The belt34is laminated on the carcass32. The belt34reinforces the carcass32. The belt34includes an inner layer54aand an outer layer54b. As is obvious fromFIG. 1, the width of the inner layer54ais slightly larger than the width of the outer layer54bin the axial direction. Each of the inner layer54aand the outer layer54bincludes a large number of cords aligned with each other, and a topping rubber, which are not shown. Each cord is tilted relative to the equator plane. The absolute value of the tilt angle is generally equal to or greater than 10° and equal to or less than 35°. The direction in which each cord of the inner layer54ais tilted relative to the equator plane is opposite to the direction in which each cord of the outer layer54bis tilted relative to the equator plane. The material of the cords is preferably steel. An organic fiber may be used for the cords. The width of the belt34in the axial direction is preferably equal to or greater than 0.7 times of the maximum width of the tire22. The belt34may include three or more layers54.

The band36is located outward of the belt34in the radial direction. The width of the band36is equal to the width of the belt34in the axial direction. The band36includes a cord and a topping rubber, which are not shown. The cord is helically wound. The band36has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord relative to the circumferential direction is equal to or less than 5° and further equal to or less than 2°. The belt34is held by the cord, so that lifting of the belt34is suppressed. The cord is formed from an organic fiber. Examples of preferable organic fibers include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

The belt34and the band36form a reinforcing layer. A reinforcing layer may be composed of only the belt34. A reinforcing layer may be composed of only the band36.

The inner liner38is located inward of the carcass32. The inner liner38is joined to the inner surface of the carcass32. The inner liner38is formed from a crosslinked rubber. A rubber that is excellent in air blocking property is used for the inner liner38. A typical base rubber of the inner liner38is an isobutylene-isoprene-rubber or halogenated isobutylene-isoprene-rubber. The inner liner38maintains the internal pressure of the tire22.

Each wing40is located between the tread24and the sidewall26. Each wing40is joined to each of the tread24and the sidewall26. Each wing40is formed from a crosslinked rubber that is excellent in adhesiveness.

The cushion layers42are laminated on the carcass32near the edges of the belt34. The cushion layers42are formed from a flexible crosslinked rubber. The cushion layers42absorb stress on the edges of the belt34. The cushion layers42suppress lifting of the belt34.

As described above, each bead30of the tire22includes the core48and the apex50.FIG. 2shows a cross-section of the core48that forms a portion of the bead30. InFIG. 2, the up-down direction is the radial direction of the tire22, the right-left direction is the axial direction of the tire22, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire22. InFIG. 2, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.FIG. 2shows a portion of a cross-section of the tire22along the radial direction.

The core48of the tire22includes a main body56and a stretchable portion58. The core48is composed of the main body56and the stretchable portion58.

The main body56is located outward of the stretchable portion58in the axial direction. The main body56includes a cord60extending in the circumferential direction. When the tire22is fitted on a rim, the main body56serves to tighten the tire22on the rim.FIG. 3shows a cross-section of the cord60for the main body56. The cord60is formed of an element wire.

In the tire22, the main body56is formed by winding the cord60in the circumferential direction a plurality of times. Accordingly, the main body56is obtained in which cross-sections of the cord60are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the cord60included in a cross-section of the main body56is 11. The main body56of the tire22is formed by helically winding the cord60in the circumferential direction 11 times. The main body56may be formed by winding, in the circumferential direction, a bundle composed of a plurality of cords60.

In the tire22, the material of the cord60is preferably steel. The cord60is difficult to stretch as compared to one formed from an organic fiber. The cord60of which the material is steel can contribute to tightening the tire22on the rim.

In the tire22, as the cord60, one formed of a single element wire as shown inFIG. 3is preferable. The cord60is difficult to stretch as compared to one formed of a plurality of element wires. The cord60can contribute to tightening the tire22on the rim.

In the tire22, preferably, the material of the cord60is steel, and the cord60is formed of an element wire. The stretch of the cord60is small. In other words, the cord60is non-stretchable. The non-stretchable cord60can effectively contribute to tightening the tire22on the rim. The main body56composed of the non-stretchable cord60can firmly tighten the tire22on the rim.

In the tire22, one cross-section (reference character H inFIG. 2) of the hard cord60is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the main body56of the core48. As described above, the cord60is non-stretchable. The core48configured such that the non-stretchable cord60is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire22on the rim.

In the present invention, the stretchability of the cord60is determined on the basis of an elongation at specific load (hereinafter, the elongation at specific load is sometimes referred to merely as “elongation”). More specifically, in the present invention, one having an elongation of less than 1% at a load of 44 N is determined as being non-stretchable. One having an elongation of 1% or greater at a load of 44 N is determined as being stretchable. One that breaks at a load less than 44 N is not used as the cord60for tightening the tire22on the rim. In the case where the cord60is formed from an organic fiber, an elongation at specific load is obtained according to JIS-L1017 “Testing methods for chemical fiber tire cords”. In the case where the material of the cord60is steel, an elongation at specific load is obtained according to JIS-G3510 “Testing methods for steel tire cords”. In the case where the cord60is formed from a glass fiber, an elongation at specific load is obtained according to JIS-R3420 “Testing methods for textile glass products”. In the case where the cord60is formed from a carbon fiber, an elongation at specific load is obtained according to JIS-R7606 “Carbon fibre—Determination of the tensile properties of the single-filament specimens”.

In the tire22, the cord60for the main body56only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. As long as the cord60is non-stretchable, one formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the cord60of the main body56, or one formed from a plurality of element wires (a stranded wire) may be used as the cord60of the main body56. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

The stretchable portion58is located inward of the main body56in the axial direction. The stretchable portion58is located outward of the main portion52aof the carcass ply52in the axial direction. The stretchable portion58is located between the main body56and the main portion52ain the axial direction.

The stretchable portion58of the tire22is composed of a portion of the apex50. Therefore, the stretchable portion58is formed from a crosslinked rubber. The stretchable portion58can stretch. As described above, the cord60that forms the main body56of the core48is non-stretchable. The stretchable portion58stretches more easily than the cord60of the main body56.

As described above, the stretchable portion58of the tire22is composed of the portion of the apex50. Therefore, the stretchable portion58is formed from a rubber composition that is the same as a rubber composition that forms the apex50. The stretchable portion58may be formed from a rubber composition that is different from the rubber composition that forms the apex50.

In the tire22, a portion, at the inner side in the axial direction and at outer side in the radial direction, of the cross-section of the core48is composed of the stretchable portion58. This portion corresponds to the portion in the core8of the conventional tire2in which portion the cord12is present and to which portion great tension is applied when the tire2is fitted onto the rim. As described above, the stretchable portion58stretches more easily than the cord60of the main body56. Deformation of the core48is easy. When the tire22is fitted onto the rim, a bead30portion of the tire22easily passes over a hump of the rim. The fitting pressure of the tire22is low. Fitting the tire22onto the rim is easy. In addition, the main body56of the core48contributes to a tightening force. Thus, with the tire22, a low fitting pressure is achieved without impairing the tightening force.

InFIG. 2, the size of a circle indicated by an alternate long and two short dashes line C is equal to the size of the cross-section of the cord60of the main body56. As shown in the drawing, the stretchable portion58of the tire22has a size with which at least one cross-section of the cord60can be included therein in a cross-section of the bead30. In the tire22, a portion at which the cord12is wound in the conventional tire2is replaced with the stretchable portion58that is formed from the crosslinked rubber. This replacement can contribute to weight reduction of the tire22. In addition, the stretchable portion58can contribute to reduction of the fitting pressure, and the main body56can contribute to the tightening force. With the tire22, while the weight of the tire.22is reduced, a low fitting pressure can be achieved without impairing the tightening force. In the tire22, in light of reduction of the weight and achievement of a low fitting pressure, the stretchable portion58may have a size with which two or more cross-sections of the cord60can be included therein in the cross-section of the bead30.

In the tire22, the width (a double-headed arrow W inFIG. 2) of the core48in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 2) of the core48in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 2) of the core48in the axial direction to the inner edge (reference character P2inFIG. 2) of the core48in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3) of the core48in the radial direction to the outer edge (reference character P4inFIG. 2) of the core48in the radial direction.

In the tire22, the ratio of the total sum HA of the areas of the cross-sections of the cord60included in the cross-section of the main body56of the core48, relative to the area BA of the cross-section of the core48, is preferably equal to or greater than 20% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 20%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, the stretchable portion58is sufficiently ensured, and thus weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core48is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction. In addition, in the case where the cord60is formed of a plurality of element wires, the areas of the cross-sections of the cord60are represented by the area of a virtual cross-section obtained on the basis of an outer diameter represented by the diameter of the circumcircle of these element wires.

InFIG. 3, a double-headed arrow dh indicates the outer diameter of the cord60for the main body56of the core48. In light of tightening force, the outer diameter dh is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh is preferably equal to or less than 10 mm.

In the present invention, the dimensions and angles of each component of the tire22are measured in a state where the tire22is mounted on a normal rim and inflated to a normal internal pressure. During the measurement, no load is applied to the tire22. In the present specification, the normal rim means a rim specified in a standard on which the tire22is based. The “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, and the “Measuring Rim” in the ETRTO standard are normal rims. In the present specification, the normal internal pressure means an internal pressure specified in the standard on which the tire22is based. The “highest air pressure” in the JATMA standard, the “maximum value” recited in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and the “INFLATION PRESSURE” in the ETRTO standard are normal internal pressures. It should be noted that in the case of a tire22for a passenger car, the dimensions and angles are measured in a state where the internal pressure is 180 kPa. The same also applies to tires described later.

FIG. 4shows a portion of a pneumatic tire62according to another embodiment of the present invention.FIG. 4shows a bead64portion of the tire62. InFIG. 4, the up-down direction is the radial direction of the tire62, the right-left direction is the axial direction of the tire62, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire62.FIG. 4shows a portion of a cross-section of the tire62along the radial direction. InFIG. 4, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire62, the configuration except for the beads64is the same as that of the tire22shown inFIG. 1. The tire62includes, in addition to the beads64, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

In the tire62, each bead64has a ring shape. Each bead64includes a core66and an apex68. The apex68extends from the core66outward in the radial direction. The apex68is tapered outward in the radial direction, which is not shown. The apex68is formed from a highly hard crosslinked rubber.

The core66of the tire62includes a main body70and a stretchable portion72. The core66is composed of the main body70and the stretchable portion72. The main body70includes a hard unit74.

The hard unit74is located outward of the stretchable portion72in the axial direction. The hard unit74includes a hard cord76extending in the circumferential direction. When the tire62is fitted on a rim, the hard unit74serves to tighten the tire62on the rim.

In the tire62, the hard unit74is formed by winding the hard cord76in the circumferential direction a plurality of times. Accordingly, the hard unit74is obtained in which cross-sections of the hard cord76are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord76included in a cross-section of the hard unit74is nine. The hard unit74of the tire62is formed by helically winding the hard cord76in the circumferential direction nine times. The hard unit74may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords76.

In the tire62, the material of the hard cord76is preferably steel. The hard cord76is difficult to stretch as compared to one formed from an organic fiber. The hard cord76can contribute to tightening the tire62on the rim.

In the tire62, as the hard cord76, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord76is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord76can contribute to tightening the tire62on the rim.

In the tire62, preferably, the material of the hard cord76is steel, and the hard cord76is formed of an element wire. The stretch of the hard cord76is small. In other words, the hard cord76is non-stretchable. The non-stretchable hard cord76can effectively contribute to tightening the tire62on the rim. The hard unit74composed of the non-stretchable hard cord76can firmly tighten the tire62on the rim.

In the tire62, one cross-section (reference character H inFIG. 4) of the hard cord76is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the main body70that forms a portion of the core66. As described above, the hard cord76is non-stretchable. The core66configured such that the hard cord76is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire62on the rim.

In the tire62, the hard cord76only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord76, or one formed from a plurality of element wires may be used as the hard cord76, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire62, in light of tightening force, the outer diameter dh of the hard cord76is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord76is preferably equal to or less than 10 mm.

The stretchable portion72is located inward of the main body70in the axial direction. The stretchable portion72is located outward, in the axial direction, of a main portion80aof a carcass ply80that forms a carcass78. The stretchable portion72is located between the main body70and the main portion80ain the axial direction.

The stretchable portion72of the tire62is composed of a portion of the apex68. Therefore, the stretchable portion72is formed from a crosslinked rubber. The stretchable portion72can stretch. As described above, the hard cord76that forms a portion of the main body70of the core66, is non-stretchable. The stretchable portion72stretches more easily than the hard cord76.

As described above, the stretchable portion72of the tire62is composed of the portion of the apex68. Therefore, the stretchable portion72is formed from a rubber composition that is the same as a rubber composition that forms the apex68. The stretchable portion72may be formed from a rubber composition that is different from the rubber composition that forms the apex68.

In the tire62, a portion, at the inner side in the axial direction and at the outer side in the radial direction, of a cross-section of the core66is composed of the stretchable portion72. In the tire62, the stretchable portion72is located at the portion in the core8of the conventional tire2in which portion the cord12is present and to which portion great tension is applied when the tire2is fitted onto the rim. As described above, the stretchable portion72stretches more easily than the hard cord76. Deformation of the core66is easy. When the tire62is fitted onto the rim, the bead64portion of the tire62easily passes over a hump of the rim. The fitting pressure of the tire62is low. Fitting the tire62onto the rim is easy. In addition, the main body70of the core66contributes to a tightening force. Thus, with the tire62, a low fitting pressure is achieved without impairing the tightening force.

InFIG. 4, the size of a circle indicated by an alternate long and two short dashes line C is equal to the size of each cross-section of the hard cord76. As shown in the drawing, the stretchable portion72of the tire62has a size with which at least three cross-sections of the hard cord76can be included therein in a cross-section of the bead64. In the tire62, the portion at which the cord12is wound in the conventional tire2is replaced with the stretchable portion72that is formed from the crosslinked rubber. This replacement can contribute to weight reduction of the tire62. In addition, the stretchable portion72can contribute to reduction of the fitting pressure, and the main body70can contribute to the tightening force. With the tire62, while the weight of the tire62is reduced, a low fitting pressure can be achieved without impairing the tightening force.

In the tire62, in addition to the hard unit74, the main body70further includes a soft unit82. That is, the main body70includes the hard unit74and the soft unit82. The soft unit82is located outward of the hard unit74in the radial direction. The soft unit82includes a soft cord84extending in the circumferential direction. When the tire62is fitted on the rim, the soft unit82serves to tighten the tire62on the rim.

In the tire62, the soft unit82is formed by winding the soft cord84in the circumferential direction a plurality of times. Accordingly, the soft unit82is obtained in which cross-sections of the soft cord84are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord84included in a cross-section of the soft unit82is three. The soft unit82of the tire62is formed by helically winding the soft cord84in the circumferential direction three times. The soft unit82may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords84.

The soft cord84stretches more easily than the above-described hard cord76. The elongation of the soft cord84is greater than the elongation of the hard cord76. Thus, when the tire62is fitted onto the rim, the soft unit82composed of the soft cord84does not inhibit deformation of the core66. Since the core66easily deforms, the bead64portion of the tire62easily passes over the hump of the rim. According to the present invention, the tire62can be fitted onto the rim at a low fitting pressure. Fitting the tire62onto the rim is easy. In addition, due to a synergistic effect of the hard unit74and the soft unit82, the core66can more firmly tighten the tire62on the rim. With the tire62, a low fitting pressure is achieved without impairing the tightening force.

Diagram (a) ofFIG. 5shows an example of the soft cord84. The soft cord84is formed by twisting together three element wires86a. As described above, the hard cord76is formed of a single element wire. The soft cord84stretches more easily than the hard cord76. Thus, when the tire62is fitted onto the rim, the soft unit82composed of the soft cord84does not inhibit deformation of the core66. Since the core66easily deforms, the bead64portion of the tire62easily passes over the hump of the rim. According to the present invention, the tire62can be fitted onto the rim at a low fitting pressure. Fitting the tire62onto the rim is easy. Furthermore, in addition to the hard unit74, the soft unit82synergistically contributes to the tightening force. Thus, a sufficient tightening force is obtained. With the tire62, a low fitting pressure is achieved without impairing the tightening force.

In (a) ofFIG. 5, an alternate long and two short dashes line DMa indicates the circumcircle of the soft cord84. The outer diameter (a double-headed arrow ds in (a) ofFIG. 5) of the soft cord84is represented by the diameter of the circumcircle DMa. In light of tightening force, the outer diameter ds is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds is preferably equal to or less than 10 mm.

Diagram (b) ofFIG. 5shows another example of the soft cord84. The soft cord84is formed by twisting together three element wires86bthat are reformed in a wavy shape. As described above, the hard cord76is formed of a single element wire. The soft cord84stretches more easily than the hard cord76. Thus, when the tire62is fitted onto the rim, the soft unit82composed of the soft cord84does not inhibit deformation of the core66. Since the core66easily deforms, the bead64portion of the tire62easily passes over the hump of the rim. According to the present invention, the tire62can be fitted onto the rim at a low fitting pressure. Fitting the tire62onto the rim is easy. Furthermore, in addition to the hard unit74, the soft unit82synergistically contributes to the tightening force. Thus, a sufficient tightening force is obtained. With the tire62, a low fitting pressure is achieved without impairing the tightening force.

In (b) ofFIG. 5, an alternate long and two short dashes line DMb indicates the circumcircle of the soft cord84. The outer diameter (a double-headed arrow ds in (b) ofFIG. 5) of the soft cord84is represented by the diameter of the circumcircle DMb. In light of tightening force, the outer diameter ds is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds is preferably equal to or less than 10 mm. An alternate long and two short dashes line DSb indicates the circumcircle of the element wire86bthat is reformed in a wavy shape. Each element wire86bis reformed in a wavy shape, for example, by using a device (not shown). The device includes two disc-shaped rollers. Each roller has a plurality of projections arranged on the circumferential surface thereof so as to be spaced apart from each other. A recess is formed between the two projections that are adjacent to each other. When both rollers rotate, the projection of one of the rollers is fitted into the recess of the other roller, and the projection of the other roller is fitted into the recess of the one roller. By passing the element wire86bbetween both rollers, the element wire86bhaving a straight shape is processed into a zigzag shape. Accordingly, the element wire86bthat is reformed in a wavy shape is obtained.

Diagram (c) ofFIG. 5shows still another example of the soft cord84. The soft cord84is formed by twisting together four element wires86c. As described above, the hard cord76is formed of a single element wire. The soft cord84stretches more easily than the hard cord76. Thus, when the tire62is fitted onto the rim, the soft unit82composed of the soft cord84does not inhibit deformation of the core66. Since the core66easily deforms, the bead64portion of the tire62easily passes over the hump of the rim. According to the present invention, the tire62can be fitted onto the rim at a low fitting pressure. Fitting the tire62onto the rim is easy. Furthermore, in addition to the hard unit74, the soft unit82synergistically contributes to the tightening force. Thus, a sufficient tightening force is obtained. With the tire62, a low fitting pressure is achieved without impairing the tightening force.

In (c) ofFIG. 5, an alternate long and two short dashes line DMc indicates the circumcircle of the soft cord84. The outer diameter (a double-headed arrow ds in (c) ofFIG. 5) of the soft cord84is represented by the diameter of the circumcircle DMc. In light of tightening force, the outer diameter ds is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds is preferably equal to or less than 30 mm.

Diagram (d) ofFIG. 5shows still another example of the soft cord84. The soft cord84is formed by twisting together four element wires86dthat are reformed in a wavy shape. As described above, in the tire62, the hard cord76is formed of a single element wire. The soft cord84stretches more easily than the hard cord76. Thus, when the tire62is fitted onto the rim, the soft unit82composed of the soft cord84does not inhibit deformation of the core66. Since the core66easily deforms, the bead64portion of the tire62easily passes over the hump of the rim. According to the present invention, the tire62can be fitted onto the rim at a low fitting pressure. Fitting the tire62onto the rim is easy. Furthermore, in addition to the hard unit74, the soft unit82synergistically contributes to the tightening force. Thus, a sufficient tightening force is obtained. With the tire62, a low fitting pressure is achieved without impairing the tightening force.

In (d) ofFIG. 5, an alternate long and two short dashes line DMd indicates the circumcircle of the soft cord84. The outer diameter (a double-headed arrow ds in (d) ofFIG. 5) of the soft cord84is represented by the diameter of the circumcircle DMd. In light of tightening force, the outer diameter ds is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds is preferably equal to or less than 30 mm. In the drawing, an alternate long and two short dashes line DSd indicates the circumcircle of the element wire86dthat is reformed in a wavy shape.

In the tire62, the soft cord84only needs to have an elongation greater than the elongation of the hard cord76, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord84, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord84, as long as it stretches more easily than the hard cord76. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

An elongation EH at specific load (hereinafter, elongation EH) of the hard cord76and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord84influence the tightening force and the fitting pressure. In the tire62, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire62, the width (a double-headed arrow w inFIG. 4) of the core66in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 4) of the core66in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 4) of the core66in the axial direction to the inner edge (reference character P2inFIG. 4) of the core66in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 4) of the core66, in the radial direction to the outer edge (reference character P4inFIG. 4) of the core66in the radial direction.

In the tire62, the ratio of the sum (HA+SA) of the total sum HA of the areas of the cross-sections of the hard cord76included in the cross-section of the hard unit74of the core66and the total sum SA of the areas of the cross-sections of the soft cord84included in the cross-section of the soft unit82of the core66, relative to the area BA of the cross-section of the core66, is preferably equal to or greater than 15% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 15%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, the stretchable portion72is sufficiently ensured, and thus weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core66is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire62, the ratio of the total sum HA of the areas of the cross-sections of the hard cord76included in the cross-section of the hard unit74, relative to the area BA of the cross-section of the core66, is preferably equal to or greater than 10% and equal to or less than 90%. When this ratio is set so as to be equal to or greater than 10%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 90%, weight reduction and a low fitting pressure are achieved.

In the tire62, the ratio of the total sum SA of the areas of the cross-sections of the soft cord84included in the cross-section of the soft unit82, relative to the area BA of the cross-section of the core66, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

FIG. 6shows a portion of a pneumatic tire88according to sill another embodiment of the present invention.FIG. 6shows a bead90portion of the tire88. InFIG. 6, the up-down direction is the radial direction of the tire88, the right-left direction is the axial direction of the tire88, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire88.FIG. 6shows a portion of a cross-section of the tire88along the radial direction. InFIG. 6, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire88, the configuration except for the beads90is the same as that of the tire22shown inFIG. 1. The tire88includes, in addition to the beads90, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

In the tire88, each bead90has a ring shape. Each bead90includes a core92and an apex94. The apex94extends from the core92outward in the radial direction. The apex94is tapered outward in the radial direction, which is not shown. The apex94is formed from a highly hard crosslinked rubber.

The core92of the tire88includes a main body96and a stretchable portion98. The core92is composed of the main body96and the stretchable portion98. The main body96includes a hard unit100.

The hard unit100is located outward of the stretchable portion98in the axial direction. The hard unit100includes a hard cord102extending in the circumferential direction. When the tire88is fitted on a rim, the hard unit100serves to tighten the tire88on the rim.

In the tire88, the hard unit100is formed by winding the hard cord102in the circumferential direction a plurality of times. Accordingly, the hard unit100is obtained in which cross-sections of the hard cord102are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord102included in a cross-section of the hard unit100is eight. The hard unit100of the tire88is formed by helically winding the hard cord102in the circumferential direction eight times. The hard unit100may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords102.

In the tire88, the material of the hard cord102is preferably steel. The hard cord102is difficult to stretch as compared to one formed from an organic fiber. The hard cord102can contribute to tightening the tire88on the rim.

In the tire88, as the hard cord102, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord102is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord102can contribute to tightening the tire88on the rim.

In the tire88, preferably, the material of the hard cord102is steel, and the hard cord102is formed of an element wire. The stretch of the hard cord102is small. In other words, the hard cord102is non-stretchable. The non-stretchable hard cord102can effectively contribute to tightening the tire88on the rim. The hard unit100composed of the non-stretchable hard cord102can firmly tighten the tire88on the rim.

In the tire88, one cross-section (reference character H inFIG. 6) of the hard cord102is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the main body96of the core92. As described above, the hard cord102is non-stretchable. The core92configured such that the hard cord102is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire88on the rim.

In the tire88, the hard cord102only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord102, or one formed from a plurality of element wires may be used as the hard cord102, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire88, in light of tightening force, the outer diameter dh of the hard cord102is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord102is preferably equal to or less than 10 mm.

The stretchable portion98is located inward of the main body96in the axial direction. The stretchable portion98is located outward, in the axial direction, of a main portion106aof a carcass ply106that forms a carcass104. The stretchable portion98is located between the main body96and the main portion106ain the axial direction.

The stretchable portion98of the tire88is composed of a portion of the apex94. Therefore, the stretchable portion98is formed from a crosslinked rubber. The stretchable portion98can stretch. As described above, the hard cord102that forms a portion of the main body96of the core92, is non-stretchable. The stretchable portion98stretches more easily than the hard cord102.

As described above, the stretchable portion98of the tire88is composed of the portion of the apex94. Therefore, the stretchable portion98is formed from a rubber composition that is the same as a rubber composition that forms the apex94. The stretchable portion98may be formed from a rubber composition that is different from the rubber composition that forms the apex94.

In the tire88, a portion, at the inner side in the axial direction and at the outer side in the radial direction, of a cross-section of the core92is composed of the stretchable portion98. In the tire88, the stretchable portion98is located at the portion in the core8of the conventional tire2in which portion the cord12is present and to which portion great tension is applied when the tire2is fitted onto the rim. As described above, the stretchable portion98stretches more easily than the hard cord102. Deformation of the core92is easy. When the tire88is fitted onto the rim, the bead90portion of the tire88easily passes over a hump of the rim. The fitting pressure of the tire88is low. Fitting the tire88onto the rim is easy. In addition, the main body96of the core92contributes to a tightening force. Thus, with the tire88, a low fitting pressure is achieved without impairing the tightening force.

In the tire88, the stretchable portion98has a size with which at least one cross-section of the hard cord102can be included therein in a cross-section of the bead90. In the tire88, the portion at which the cord12is wound in the conventional tire2is replaced with the stretchable portion98that is formed from the crosslinked rubber. This replacement can contribute to weight reduction of the tire88. In addition, the stretchable portion98can contribute to reduction of the fitting pressure, and the main body96can contribute to the tightening force. With the tire88, while the weight of the tire88is reduced, a low fitting pressure can be achieved without impairing the tightening force.

In the tire88, in addition to the hard unit100, the main body96further includes a soft unit108. That is, the main body96includes the hard unit100and the soft unit108. The soft unit108is located outward of the hard unit100in the radial direction. The soft unit108is located between the hard unit100and the stretchable portion98in the axial direction.

The soft unit108includes a soft cord110extending in the circumferential direction. When the tire88is fitted on the rim, the soft unit108serves to tighten the tire88on the rim.

In the tire88, the soft unit108is formed by winding the soft cord110in the circumferential direction a plurality of times. Accordingly, the soft unit108is obtained in which cross-sections of the soft cord110are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord110included in a cross-section of the soft unit108is four. The soft unit108of the tire88is formed by helically winding the soft cord110in the circumferential direction four times. The soft unit108may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords110.

The soft cord110stretches more easily than the above-described hard cord102. The elongation of the soft cord110is greater than the elongation of the hard cord102. Thus, when the tire88is fitted onto the rim, the soft unit108composed of the soft cord110does not inhibit deformation of the core92. Since the core92easily deforms, the bead90portion of the tire88easily passes over the hump of the rim. According to the present invention, the tire88can be fitted onto the rim at a low fitting pressure. Fitting the tire88onto the rim is easy. In addition, due to a synergistic effect of the hard unit100and the soft unit108, the core92can more firmly tighten the tire88on the rim. With the tire88, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord110in the tire88include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord110only needs to have an elongation greater than the elongation of the hard cord102, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord110, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord110, as long as it stretches more easily than the hard cord102. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire88, in light of tightening force, the outer diameter ds of the soft cord110is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord110is preferably equal to or less than 30 mm.

An elongation EH at specific load (hereinafter, elongation EH) of the hard cord102and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord110influence the tightening force and the fitting pressure. In the tire88, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire88, the width (a double-headed arrow w inFIG. 6) of the core92in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 6) of the core92in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 6) of the core92in the axial direction to the inner edge (reference character P2inFIG. 6) of the core92in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 6) of the core92in the radial direction to the outer edge (reference character P4inFIG. 6) of the core92in the radial direction.

In the tire88, the ratio of the sum (HA+SA) of the total sum HA of the areas of the cross-sections of the hard cord102included in the cross-section of the hard unit100of the core92and the total sum SA of the areas of the cross-sections of the soft cord110included in the cross-section of the soft unit108of the core92, relative to the area BA of the cross-section of the core92, is preferably equal to or greater than 15% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 15%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, the stretchable portion98is sufficiently ensured, and thus weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core92is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire88, the ratio of the total sum HA of the areas of the cross-sections of the hard cord102included in the cross-section of the hard unit100, relative to the area BA of the cross-section of the core92, is preferably equal to or greater than 10% and equal to or less than 90%. When this ratio is set so as to be equal to or greater than 10%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 90%, weight reduction and a low fitting pressure are achieved.

In the tire88, the ratio of the total sum SA of the areas of the cross-sections of the soft cord110included in the cross-section of the soft unit108, relative to the area BA of the cross-section of the core92, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

FIG. 7shows a portion of a pneumatic tire112according to sill another embodiment of the present invention.FIG. 7shows a bead114portion of the tire112. InFIG. 7, the up-down direction is the radial direction of the tire112, the right-left direction is the axial direction of the tire112, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire112.FIG. 7shows a portion of a cross-section of the tire112along the radial direction. InFIG. 7, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire112, the configuration except for the beads114is the same as that of the tire22shown inFIG. 1. The tire112includes, in addition to the beads114, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

In the tire112, each bead114has a ring shape. Each bead114includes a core116and an apex118. The apex118extends from the core116outward in the radial direction. The apex118is tapered outward in the radial direction, which is not shown. The apex118is formed from a highly hard crosslinked rubber.

The core116of the tire112includes a main body120and a stretchable portion122. The core116is composed of the main body120and the stretchable portion122. The main body120includes a hard unit124, a middle unit126, and a soft unit128.

The hard unit124forms an inner portion of the main body120of the core116in the radial direction. The hard unit124includes a hard cord130extending in the circumferential direction. When the tire112is fitted on a rim, the hard unit124serves to tighten the tire112on the rim.

In the tire112, the hard unit124is formed by winding the hard cord130in the circumferential direction a plurality of times. Accordingly, the hard unit124is obtained in which cross-sections of the hard cord130are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord130included in a cross-section of the hard unit124is four. The hard unit124of the tire112is formed by helically winding the hard cord130in the circumferential direction four times. The hard unit124may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords130.

In the tire112, the material of the hard cord130is preferably steel. The hard cord130is difficult to stretch as compared to one formed from an organic fiber. The hard cord130can contribute to tightening the tire112on the rim.

In the tire112, as the hard cord130, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord130is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord130can contribute to tightening the tire112on the rim.

In the tire112, preferably, the material of the hard cord130is steel, and the hard cord130is formed of an element wire. The stretch of the hard cord130is small. In other words, the hard cord130is non-stretchable. The non-stretchable hard cord130can effectively contribute to tightening the tire112on the rim. The hard unit124composed of the non-stretchable hard cord130can firmly tighten the tire112on the rim.

In the tire112, one cross-section (reference character H inFIG. 7) of the hard cord130is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the main body120of the core116. As described above, the hard cord130is non-stretchable. The core116configured such that the hard cord130is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire112on the rim.

In the tire112, the hard cord130only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord130, or one formed from a plurality of element wires may be used as the hard cord130, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire112, in light of tightening force, the outer diameter dh of the hard cord130is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord130is preferably equal to or less than 10 mm.

The middle unit126is located outward of the hard unit124in the radial direction. The middle unit126is located outward of the soft unit128in the axial direction. The middle unit126is located between the soft unit128and a turned-up portion134bof a carcass ply134that forms a carcass132, in the axial direction.

The middle unit126includes a middle cord136extending in the circumferential direction. When the tire112is fitted on the rim, the middle unit126serves to tighten the tire112on the rim.

In the tire112, the middle unit126is formed by winding the middle cord136in the circumferential direction a plurality of times. Accordingly, the middle unit126is obtained in which cross-sections of the middle cord136are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the middle cord136included in a cross-section of the middle unit126is four. The middle unit126of the tire112is formed by helically winding the middle cord136in the circumferential direction four times. The middle unit126may be formed by winding, in the circumferential direction, a bundle composed of a plurality of middle cords136.

The middle cord136stretches more easily than the above-described hard cord130. The elongation of the middle cord136is greater than the elongation of the hard cord130. Thus, when the tire112is fitted onto the rim, the middle unit126composed of the middle cord136does not inhibit deformation of the core116. Since the core116easily deforms, the bead114portion of the tire112easily passes over a hump of the rim. According to the present invention, the tire112can be fitted onto the rim at a low fitting pressure. Fitting the tire112onto the rim is easy. In addition, due to a synergistic effect of the hard unit124and the middle unit126, the core116can more firmly tighten the tire112on the rim. With the tire112, a low fitting pressure is achieved without impairing the tightening force.

Examples of the middle cord136in the tire112include those having the configurations shown in (a) to (d) ofFIG. 5described above. The middle cord136only needs to have an elongation greater than the elongation of the hard cord130, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the middle cord136, or one formed by twisting together a plurality of the raw yarns may be used as the middle cord136, as long as it stretches more easily than the hard cord130. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire112, in light of tightening force, the outer diameter dm of the middle cord136is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dm of the middle cord136is preferably equal to or less than 30 mm.

The soft unit128is located outward of the hard unit124in the radial direction. The soft unit128is located inward of the middle unit126in the axial direction. The soft unit128is located between the middle unit126and the stretchable portion122in the axial direction.

The soft unit128includes a soft cord138extending in the circumferential direction. When the tire112is fitted on the rim, the soft unit128serves to tighten the tire112on the rim.

In the tire112, the soft unit128is formed by winding the soft cord138in the circumferential direction a plurality of times. Accordingly, the soft unit128is obtained in which cross-sections of the soft cord138are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord138included in a cross-section of the soft unit128is three. The soft unit128of the tire112is formed by helically winding the soft cord138in the circumferential direction three times. The soft unit128may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords138.

The soft cord138stretches more easily than the above-described hard cord130. The elongation of the soft cord138is greater than the elongation of the hard cord130. The soft cord138stretches more easily than the above-described middle cord136. The elongation of the soft cord138is greater than the elongation of the middle cord136. Thus, when the tire112is fitted onto the rim, the soft unit128composed of the soft cord138does not inhibit deformation of the core116. Since the core116easily deforms, the bead114portion of the tire112easily passes over the hump of the rim. According to the present invention, the tire112can be fitted onto the rim at a low fitting pressure. Fitting the tire112onto the rim is easy. In addition, due to a synergistic effect of the hard unit124, the middle unit126, and the soft unit128, the core116can more firmly tighten the tire112on the rim. With the tire112, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord138in the tire112include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord138only needs to have an elongation greater than the elongation of the middle cord136, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord138, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord138, as long as it stretches more easily than the middle cord136. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire112, in light of tightening force, the outer diameter ds of the soft cord138is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord138is preferably equal to or less than 30 mm.

In the tire112, in the cross-section of the main body120of the core116, one cross-section (reference character M inFIG. 7) of the middle cord136is located outward of the one cross-section H of the hard cord130in the radial direction and inward of the one cross-section H of the hard cord130in the axial direction, and one cross-section (reference character S inFIG. 7) of the soft cord138is located outward of the one cross-section M of the middle cord136in the radial direction and inward of the one cross-section M of the middle cord136in the axial direction. The main body120is configured such that the elongation of a cord140that forms the main body120gradually increases from a portion of the cross-section thereof at the outer side in the axial direction and at the inner side in the radial direction toward a portion of the cross-section thereof at the inner side in the axial direction and at the outer side in the radial direction. The main body120can effectively contribute to achievement of a low fitting pressure without impairing the tightening force.

An elongation EH at specific load (hereinafter, elongation EH) of the hard cord130, an elongation EM at specific load (hereinafter, elongation EM) of the middle cord136, and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord138influence the tightening force and the fitting pressure.

In the tire112, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, further preferably equal to or greater than 104%, and particularly preferably equal to or greater than 108%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire112, in light of reduction of the fitting pressure, the ratio of the elongation EM relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire112, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EM is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

The stretchable portion122is located inward of the main body120in the axial direction. The stretchable portion122is located outward, in the axial direction, of a main portion134aof the carcass ply134that forms the carcass132. The stretchable portion122is located between the main body120and the main portion134ain the axial direction.

The stretchable portion122of the tire112is composed of a portion of the apex118. Therefore, the stretchable portion122is formed from a crosslinked rubber. The stretchable portion122can stretch. As described above, the hard cord130that forms a portion of the main body120of the core116, is non-stretchable. The stretchable portion122stretches more easily than the hard cord130.

As described above, the stretchable portion122of the tire112is composed of the portion of the apex118. Therefore, the stretchable portion122is formed from a rubber composition that is the same as a rubber composition that forms the apex118. The stretchable portion122may be formed from a rubber composition that is different from the rubber composition that forms the apex118.

In the tire112, a portion, at the inner side in the axial direction and at the outer side in the radial direction, of a cross-section of the core116is composed of the stretchable portion122. In the tire112, the stretchable portion122is located at the portion in the core8of the conventional tire2in which portion the cord12is present and to which portion great tension is applied when the tire2is fitted onto the rim. As described above, the stretchable portion122stretches more easily than the hard cord130. Thus, deformation of the core116is easy as compared to the conventional core8that does not include the stretchable portion122. When the tire112is fitted onto the rim, the bead114portion of the tire112easily passes over the hump of the rim. The fitting pressure of the tire112is low. Fitting the tire112onto the rim is easy. In addition, the main body120of the core116contributes to a tightening force. Thus, with the tire112, a low fitting pressure is achieved without impairing the tightening force.

In the tire112, the stretchable portion122has a size with which at least one cross-section of the hard cord130can be included therein in a cross-section of the bead114. In the tire112, the portion at which the cord12is wound in the conventional tire2is replaced with the stretchable portion122that is formed from the crosslinked rubber. This replacement can contribute to weight reduction of the tire112. In addition, the stretchable portion122can contribute to reduction of the fitting pressure, and the main body120can contribute to the tightening force. With the tire112, while the weight of the tire112is reduced, a low fitting pressure can be achieved without impairing the tightening force.

In the tire112, the width (a double-headed arrow w inFIG. 7) of the core116in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 7) of the core116in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 7) of the core116in the axial direction to the inner edge (reference character P2inFIG. 7) of the core116in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 7) of the core116in the radial direction to the outer edge (reference character P4inFIG. 7) of the core116in the radial direction.

In the tire112, the ratio of the sum (HA+MA+SA) of the total sum HA of the areas of the cross-sections of the hard cord130included in the cross-section of the hard unit124of the core116, the total sum MA of the areas of the cross-sections of the middle cord136included in the cross-section of the middle unit126of the core116, and the total sum SA of the areas of the cross-sections of the soft cord138included in the cross-section of the soft unit128of the core116, relative to the area BA of the cross-section of the core116, is preferably equal to or greater than 15% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 15%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, the stretchable portion122is sufficiently ensured, and thus weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core116is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire112, the ratio of the total sum HA of the areas of the cross-sections of the hard cord130included in the cross-section of the hard unit124, relative to the area BA of the cross-section of the core116, is preferably equal to or greater than 7% and equal to or less than 87%. When this ratio is set so as to be equal to or greater than 7%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 87%, weight reduction and a low fitting pressure are achieved.

In the tire112, the ratio of the total sum MA of the areas of the cross-sections of the middle cord136included in the cross-section of the middle unit126, relative to the area BA of the cross-section of the core116, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

In the tire112, the ratio of the total sum SA of the areas of the cross-sections of the soft cord138included in the cross-section of the soft unit128, relative to the area BA of the cross-section of the core116, is preferably equal to or greater than 3% and equal to or less than 70%. When this ratio is set so as to be equal to or greater than 3%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 70%, weight reduction and a low fitting pressure are achieved.

FIG. 8shows a pneumatic tire142according to sill another embodiment of the present invention. InFIG. 8, the up-down direction is the radial direction of the tire142, the right-left direction is the axial direction of the tire142, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire142. InFIG. 8, an alternate long and short dash line CL represents the equator plane of the tire142. The shape of the tire142is symmetrical about the equator plane except for a tread pattern.FIG. 8shows a cross-section of the tire142along the radial direction.

The tire142includes a tread144, sidewalls146, clinches148, beads150, a carcass152, a belt154, a band156, an inner liner158, wings160, and cushion layers162. The tire142is of a tubeless type. The tire142is mounted on a passenger car. The tire142has the same configuration as that of the tire22shown inFIG. 1, except for the beads150of the tire142.

The beads150are located inward of the clinches148in the axial direction. Each bead150has a ring shape. Each bead150includes a core164and an apex166. The apex166extends from the core164outward in the radial direction. The apex166is tapered outward in the radial direction. The apex166is formed from a highly hard crosslinked rubber. In the drawing, reference character KP indicates a carcass ply that forms the carcass152. The carcass ply KP is turned up around the core164from the inner side to the outer side in the axial direction.

FIG. 9shows a cross-section of the core164that forms a portion of the bead150. InFIG. 9, the up-down direction is the radial direction of the tire142, the right-left direction is the axial direction of the tire142, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire142. InFIG. 9, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.FIG. 9shows a cross-section of the tire142along the radial direction.

The core164includes a hard unit168and a soft unit170. The core164of the tire142is composed of the hard unit168and the soft unit170.

The hard unit168forms an inner portion of the core164in the radial direction. The hard unit168includes a hard cord172extending in the circumferential direction. When the tire142is fitted on a rim, the hard unit168serves to tighten the tire142on the rim.

In the tire142, the hard unit168is formed by winding the hard cord172in the circumferential direction a plurality of times. Accordingly, the hard unit168is obtained in which cross-sections of the hard cord172are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord172included in a cross-section of the hard unit168is four. The hard unit168of the tire142is formed by helically winding the hard cord172in the circumferential direction four times. The hard unit168may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords172.

In the tire142, the material of the hard cord172is preferably steel. The hard cord172is difficult to stretch as compared to one formed from an organic fiber. The hard cord172can contribute to tightening the tire142on the rim.

In the tire142, as the hard cord172, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord172is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord172can contribute to tightening the tire142on the rim.

In the tire142, preferably, the material of the hard cord172is steel, and the hard cord172is formed of an element wire. The stretch of the hard cord172is small. In other words, the hard cord172is non-stretchable. The non-stretchable hard cord172can effectively contribute to tightening the tire142on the rim. The hard unit168composed of the non-stretchable hard cord172can firmly tighten the tire142on the rim.

In the tire142, one cross-section (reference character H inFIG. 9) of the hard cord172is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the core164. As described above, the hard cord172is non-stretchable. The core164configured such that the hard cord172is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire142on the rim.

In the tire142, the hard cord172only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord172, or one formed from a plurality of element wires may be used as the hard cord172, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire142, in light of tightening force, the outer diameter dh of the hard cord172is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord172is preferably equal to or less than 10 mm.

The soft unit170is located outward of the hard unit168in the radial direction. The soft unit170includes a soft cord174extending in the circumferential direction. When the tire142is fitted on the rim, the soft unit170serves to tighten the tire142on the rim.

In the tire142, the soft unit170is formed by winding the soft cord174in the circumferential direction a plurality of times. Accordingly, the soft unit170is obtained in which cross-sections of the soft cord174are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord174included in a cross-section of the soft unit170is 20. The soft unit170of the tire142is formed by helically winding the soft cord174in the circumferential direction 20 times. The soft unit170may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords174.

The soft cord174stretches more easily than the above-described hard cord172. The elongation of the soft cord174is greater than the elongation of the hard cord172. Thus, when the tire142is fitted onto the rim, the soft unit170composed of the soft cord174does not inhibit deformation of the core164. Since the core164easily deforms, a bead150portion of the tire142easily passes over a hump of the rim. According to the present invention, the tire142can be fitted onto the rim at a low fitting pressure. Fitting the tire142onto the rim is easy.

In the tire142, one cross-section (reference character S inFIG. 9) of the soft cord174is located at a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core164. This portion corresponds to the portion in the core8of the conventional tire2to which portion great tension is applied when the tire2is fitted onto the rim. Since the soft cord174stretches more easily than the hard cord172, the soft cord174located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core164can effectively contribute to deformation of the core164. Since the bead150portion of the tire142easily passes over the hump of the rim, the tire142can be fitted onto the rim at a low fitting pressure. In addition, due to a synergistic effect of the hard unit168and the soft unit170, the core164can more firmly tighten the tire142on the rim. With the tire142, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord174in the tire142include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord174only needs to have an elongation greater than the elongation of the hard cord172, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord174, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord174, as long as it stretches more easily than the hard cord172. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire142, the soft cord174is preferably one formed from an organic fiber.

In the tire142, in light of tightening force, the outer diameter ds of the soft cord174is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord174is preferably equal to or less than 30 mm.

In the tire142, particularly, the one cross-section H of the hard cord172is located at the portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the core164, and the one cross-section S of the soft cord174is located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core164. The core164in which the hard cord172and the soft cord174are located as described above can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure. As described later, in the tire142, an elongation EH at specific load (hereinafter, elongation EH) of the hard cord172and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord174are appropriately adjusted. Therefore, with the tire142, a low fitting pressure can be achieved without impairing the tightening force.

The elongation EH of the hard cord172and the elongation ES of the soft cord174influence the tightening force and the fitting pressure. In the tire142, in light of reduction of the fitting pressure, the ratio of the elongation. ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire142, the width (a double-headed arrow w inFIG. 9) of the core164in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 9) of the core164in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 9) of the core164in the axial direction to the inner edge (reference character P2inFIG. 9) of the core164in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 9) of the core164in the radial direction to the outer edge (reference character P4inFIG. 9) of the core164in the radial direction.

In the tire142, the ratio of the total sum HA of the areas of the cross-sections of the hard cord172included in the cross-section of the hard unit168of the core164, relative to the area BA of the cross-section of the core164, is preferably equal to or greater than 10% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 10%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 90%, weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core164is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire142, the ratio of the total sum SA of the areas of the cross-sections of the soft cord174included in the cross-section of the soft unit170, relative to the area BA of the cross-section of the core164, is preferably equal to or greater than 5% and equal to or less than 90%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 90%, weight reduction and a low fitting pressure are achieved.

FIG. 10shows a portion of a pneumatic tire176according to sill another embodiment of the present invention.FIG. 10shows a bead178portion of the tire176. InFIG. 10, the up-down direction is the radial direction of the tire176, the right-left direction is the axial direction of the tire176, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire176.FIG. 10shows a portion of a cross-section of the tire176along the radial direction. InFIG. 10, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire176, the configuration except for the beads178is the same as that of the tire142shown inFIG. 8. The configuration except for the beads178is also the same as that of the tire22shown inFIG. 1. The tire176includes, in addition to the beads178, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

Each bead178has a ring shape. Each bead178includes a core180and an apex182. The apex182extends from the core180outward in the radial direction. The apex182is tapered outward in the radial direction. The apex182is formed from a highly hard crosslinked rubber. In the drawing, reference character K indicates the carcass, and reference character KP indicates a carcass ply that forms the carcass K. The carcass ply KP is turned up around the core180from the inner side to the outer side in the axial direction.

The core180includes a hard unit184and a soft unit186. The core180of the tire176is composed of the hard unit184and the soft unit186.

The hard unit184forms an inner portion of the core180in the radial direction. The hard unit184includes a hard cord188extending in the circumferential direction. When the tire176is fitted on a rim, the hard unit184serves to tighten the tire176on the rim.

In the tire176, the hard unit184is formed by winding the hard cord188in the circumferential direction a plurality of times. Accordingly, the hard unit184is obtained in which cross-sections of the hard cord188are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord188included in a cross-section of the hard unit184is eight. The hard unit184of the tire176is formed by helically winding the hard cord188in the circumferential direction eight times. The hard unit184may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords188.

In the tire176, the material of the hard cord188is preferably steel. The hard cord188is difficult to stretch as compared to one formed from an organic fiber. The hard cord188can contribute to tightening the tire176on the rim.

In the tire176, as the hard cord188, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord188is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord188can contribute to tightening the tire176on the rim.

In the tire176, preferably, the material of the hard cord188is steel, and the hard cord188is formed of an element wire. The stretch of the hard cord188is small. In other words, the hard cord188is non-stretchable. The non-stretchable hard cord188can effectively contribute to tightening the tire176on the rim. The hard unit184composed of the non-stretchable hard cord188can firmly tighten the tire176on the rim.

In the tire176, one cross-section (reference character H inFIG. 10) of the hard cord188is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the core180. As described above, the hard cord188is non-stretchable. The core180configured such that the hard cord188is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire176on the rim.

In the tire176, the hard cord188only needs to have non-stretchability, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord188, or one formed from a plurality of element wires may be used as the hard cord188, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire176, in light of tightening force, the outer diameter dh of the hard cord188is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord188is preferably equal to or less than 10 mm.

The soft unit186is located outward of the hard unit184in the radial direction. The soft unit186includes a soft cord190extending in the circumferential direction. When the tire176is fitted on the rim, the soft unit186serves to tighten the tire176on the rim.

In the tire176, the soft unit186is formed by winding the soft cord190in the circumferential direction a plurality of times. Accordingly, the soft unit186is obtained in which cross-sections of the soft cord190are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord190included in a cross-section of the soft unit186is 10. The soft unit186of the tire176is formed by helically winding the soft cord190in the circumferential direction 10 times. The soft unit186may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords190.

The soft cord190stretches more easily than the above-described hard cord188. The elongation of the soft cord190is greater than the elongation of the hard cord188. Thus, when the tire176is fitted onto the rim, the soft unit186composed of the soft cord190does not inhibit deformation of the core180. Since the core180easily deforms, the bead178portion of the tire176easily passes over a hump of the rim. According to the present invention, the tire176can be fitted onto the rim at a low fitting pressure. Fitting the tire176onto the rim is easy.

In the tire176, one cross-section (reference character S inFIG. 10) of the soft cord190is located at a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core180. This portion corresponds to the portion in the core8of the conventional tire2to which portion great tension is applied when the tire2is fitted onto the rim. Since the soft cord190stretches more easily than the hard cord188, the soft cord190located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core180can effectively contribute to deformation of the core180. Since the bead178portion of the tire176easily passes over the hump of the rim, the tire176can be fitted onto the rim at a low fitting pressure. In addition, due to a synergistic effect of the hard unit184and the soft unit186, the core180can more firmly tighten the tire176on the rim. With the tire176, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord190in the tire176include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord190only needs to have an elongation greater than the elongation of the hard cord188, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord190, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord190, as long as it stretches more easily than the hard cord188. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire176, the soft cord190is preferably one formed from an organic fiber.

In the tire176, in light of tightening force, the outer diameter ds of the soft cord190is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord190is preferably equal to or less than 30 mm.

In the tire176, particularly, the one cross-section H of the hard cord188is located at the portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the core180, and the one cross-section S of the soft cord190is located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core180. The core180in which the hard cord188and the soft cord190are located as described above can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure. As described later, in the tire176, an elongation EH at specific load (hereinafter, elongation EH) of the hard cord188and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord190are appropriately adjusted. Therefore, with the tire176, a low fitting pressure can be achieved without impairing the tightening force.

The elongation EH of the hard cord188and the elongation ES of the soft cord190influence the tightening force and the fitting pressure. In the tire176, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire176, the width (a double-headed arrow w inFIG. 10) of the core180in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 10) of the core180in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 10) of the core180in the axial direction to the inner edge (reference character P2inFIG. 10) of the core180in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 10) of the core180in the radial direction to the outer edge (reference character P4in FIG.10) of the core180in the radial direction.

In the tire176, the ratio of the total sum HA of the areas of the cross-sections of the hard cord188included in the cross-section of the hard unit184of the core180, relative to the area BA of the cross-section of the core180, is preferably equal to or greater than 20% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 20%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core180is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire176, the ratio of the total sum SA of the areas of the cross-sections of the soft cord190included in the cross-section of the soft unit186, relative to the area BA of the cross-section of the core180, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

FIG. 11shows a portion of a pneumatic tire192according to sill another embodiment of the present invention.FIG. 11shows a bead194portion of the tire192. InFIG. 11, the up-down direction is the radial direction of the tire192, the right-left direction is the axial direction of the tire192, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire192.FIG. 11shows a portion of a cross-section of the tire192along the radial direction. InFIG. 11, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire192, the configuration except for the beads194is the same as that of the tire142shown inFIG. 8. The configuration except for the beads194is also the same as that of the tire22shown inFIG. 1. The tire192includes, in addition to the beads194, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

Each bead194has a ring shape. Each bead194includes a core196and an apex198. The apex198extends from the core196outward in the radial direction. The apex198is tapered outward in the radial direction. The apex198is formed from a highly hard crosslinked rubber. In the drawing, reference character K indicates the carcass, and reference character KP indicates a carcass ply that forms the carcass K. The carcass ply KP is turned up around the core196from the inner side to the outer side in the axial direction.

The core196includes a hard unit200and a soft unit202. The core196of the tire192is composed of the hard unit200and the soft unit202.

The hard unit200forms an inner portion of the core196in the radial direction. The hard unit200includes a hard cord204extending in the circumferential direction. When the tire192is fitted on a rim, the hard unit200serves to tighten the tire192on the rim.

In the tire192, the hard unit200is formed by winding the hard cord204in the circumferential direction a plurality of times. Accordingly, the hard unit200is obtained in which cross-sections of the hard cord204are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord204included in a cross-section of the hard unit200is 10. The hard unit200of the tire192is formed by helically winding the hard cord204in the circumferential direction 10 times. The hard unit200may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords204.

In the tire192, the material of the hard cord204is preferably steel. The hard cord204is difficult to stretch as compared to one formed from an organic fiber. The hard cord204can contribute to tightening the tire192on the rim.

In the tire192, as the hard cord204, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord204is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord204can contribute to tightening the tire192on the rim.

In the tire192, preferably, the material of the hard cord204is steel, and the hard cord204is formed of an element wire. The stretch of the hard cord204is small. In other words, the hard cord204is non-stretchable. The non-stretchable hard cord204can effectively contribute to tightening the tire192on the rim. The hard unit200composed of the non-stretchable hard cord204can firmly tighten the tire192on the rim.

In the tire192, one cross-section (reference character H inFIG. 11) of the hard cord204is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the core196. As described above, the hard cord204is non-stretchable. The core196configured such that the hard cord204is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire192on the rim.

In the tire192, the hard cord204only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord204, or one formed from a plurality of element wires may be used as the hard cord204, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire192, in light of tightening force, the outer diameter dh of the hard cord204is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord204is preferably equal to or less than 10 mm.

The soft unit202is located outward of the hard unit200in the radial direction. The soft unit202includes a soft cord206extending in the circumferential direction. When the tire192is fitted on the rim, the soft unit202serves to tighten the tire192on the rim.

In the tire192, the soft unit202is formed by winding the soft cord206in the circumferential direction a plurality of times. Accordingly, the soft unit202is obtained in which cross-sections of the soft cord206are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord206included in a cross-section of the soft unit202is two. The soft unit202of the tire192is formed by helically winding the soft cord206in the circumferential direction twice. The soft unit202may be formed by winding, in the circumferential direction, a bundle composed of two soft cords206.

The soft cord206stretches more easily than the above-described hard cord204. The elongation of the soft cord206is greater than the elongation of the hard cord204. Thus, when the tire192is fitted onto the rim, the soft unit202composed of the soft cord206does not inhibit deformation of the core196. Since the core196easily deforms, the bead194portion of the tire192easily passes over a hump of the rim. According to the present invention, the tire192can be fitted onto the rim at a low fitting pressure. Fitting the tire192onto the rim is easy.

In the tire192, one cross-section (reference character S inFIG. 11) of the soft cord206is located at a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core196. This portion corresponds to the portion in the core8of the conventional tire2to which portion great tension is applied when the tire2is fitted onto the rim. Since the soft cord206stretches more easily than the hard cord204, the soft cord206located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core196can effectively contribute to deformation of the core196. Since the bead194portion of the tire192easily passes over the hump of the rim, the tire192can be fitted onto the rim at a low fitting pressure. In addition, due to a synergistic effect of the hard unit200and the soft unit202, the core196can more firmly tighten the tire192on the rim. With the tire192, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord206in the tire192include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord206only needs to have an elongation greater than the elongation of the hard cord204, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord206, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord206, as long as it stretches more easily than the hard cord204. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire192, the soft cord206is preferably one formed from an organic fiber.

In the tire192, in light of tightening force, the outer diameter ds of the soft cord206is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord206is preferably equal to or less than 30 mm.

In the tire192, particularly, the one cross-section H of the hard cord204is located at the portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the core196, and the one cross-section S of the soft cord206is located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core196. The core196in which the hard cord204and the soft cord206are located as described above can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure. As described later, in the tire192, an elongation EH at specific load (hereinafter, elongation EH) of the hard cord204and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord206are appropriately adjusted. Therefore, with the tire192, a low fitting pressure can be achieved without impairing the tightening force.

The elongation EH of the hard cord204and the elongation ES of the soft cord206influence the tightening force and the fitting pressure. In the tire192, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire192, the width (a double-headed arrow w inFIG. 11) of the core196in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 11) of the core196in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 11) of the core196in the axial direction to the inner edge (reference character P2inFIG. 11) of the core196in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 11) of the core196in the radial direction to the outer edge (reference character P4inFIG. 11) of the core196in the radial direction.

In the tire192, the ratio of the total sum HA of the areas of the cross-sections of the hard cord204included in the cross-section of the hard unit200of the core196, relative to the area BA of the cross-section of the core196, is preferably equal to or greater than 20% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 20%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core196is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire192, the ratio of the total sum SA of the areas of the cross-sections of the soft cord206included in the cross-section of the soft unit202, relative to the area BA of the cross-section of the core196, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

FIG. 12shows a portion of a pneumatic tire208according to sill another embodiment of the present invention.FIG. 12shows a bead210portion of the tire208. InFIG. 12, the up-down direction is the radial direction of the tire208, the right-left direction is the axial direction of the tire208, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire208.FIG. 12shows a portion of a cross-section of the tire208along the radial direction. InFIG. 12, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire208, the configuration except for the beads210is the same as that of the tire142shown inFIG. 8. The configuration except for the beads210is also the same as that of the tire22shown inFIG. 1. The tire208includes, in addition to the beads210, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

Each bead210has a ring shape. Each bead210includes a core212and an apex214. The apex214extends from the core212outward in the radial direction. The apex214is tapered outward in the radial direction. The apex214is formed from a highly hard crosslinked rubber. In the drawing, reference character K indicates the carcass, and reference character KP indicates a carcass ply that forms the carcass K. The carcass ply KP is turned up around the core212from the inner side to the outer side in the axial direction.

The core212includes a hard unit216and a soft unit218. The core212of the tire208is composed of the hard unit216and the soft unit218.

The hard unit216forms an outer portion of the core212in the axial direction. The hard unit216includes a hard cord220extending in the circumferential direction. When the tire208is fitted on a rim, the hard unit216serves to tighten the tire208on the rim.

In the tire208, the hard unit216is formed by winding the hard cord220in the circumferential direction a plurality of times. Accordingly, the hard unit216is obtained in which cross-sections of the hard cord220are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord220included in a cross-section of the hard unit216is three. The hard unit216of the tire208is formed by helically winding the hard cord220in the circumferential direction three times. The hard unit216may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords220.

In the tire208, the material of the hard cord220is preferably steel. The hard cord220is difficult to stretch as compared to one formed from an organic fiber. The hard cord220can contribute to tightening the tire208on the rim.

In the tire208, as the hard cord220, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord220is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord220can contribute to tightening the tire208on the rim.

In the tire208, preferably, the material of the hard cord220is steel, and the hard cord220is formed of an element wire. The stretch of the hard cord220is small. In other words, the hard cord220is non-stretchable. The non-stretchable hard cord220can effectively contribute to tightening the tire208on the rim. The hard unit216composed of the non-stretchable hard cord220can firmly tighten the tire208on the rim.

In the tire208, one cross-section (reference character H inFIG. 12) of the hard cord220is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the core212. As described above, the hard cord220is non-stretchable. The core212configured such that the hard cord220is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire208on the rim.

In the tire208, the hard cord220only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord220, or one formed from a plurality of element wires may be used as the hard cord220, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire208, in light of tightening force, the outer diameter dh of the hard cord220is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord220is preferably equal to or less than 10 mm.

The soft unit218is located inward of the hard unit216in the axial direction. The soft unit218includes a soft cord222extending in the circumferential direction. When the tire208is fitted on the rim, the soft unit218serves to tighten the tire208on the rim.

In the tire208, the soft unit218is formed by winding the soft cord222in the circumferential direction a plurality of times. Accordingly, the soft unit218is obtained in which cross-sections of the soft cord222are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the soft cord222included in a cross-section of the soft unit218is 20. The soft unit218of the tire208is formed by helically winding the soft cord222in the circumferential direction 20 times. The soft unit218may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords222.

The soft cord222stretches more easily than the above-described hard cord220. The elongation of the soft cord222is greater than the elongation of the hard cord220. Thus, when the tire208is fitted onto the rim, the soft unit218composed of the soft cord222does not inhibit deformation of the core212. Since the core212easily deforms, the bead210portion of the tire208easily passes over a hump of the rim. According to the present invention, the tire208can be fitted onto the rim at a low fitting pressure. Fitting the tire208onto the rim is easy.

In the tire208, one cross-section (reference character S inFIG. 12) of the soft cord222is located at a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core212. This portion corresponds to the portion in the core8of the conventional tire2to which portion great tension is applied when the tire2is fitted onto the rim. Since the soft cord222stretches more easily than the hard cord220, the soft cord222located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core212can effectively contribute to deformation of the core212. Since the bead210portion of the tire208easily passes over the hump of the rim, the tire208can be fitted onto the rim at a low fitting pressure. In addition, due to a synergistic effect of the hard unit216and the soft unit218, the core212can more firmly tighten the tire208on the rim. With the tire208, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord222in the tire208include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord222only needs to have an elongation greater than the elongation of the hard cord220, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord222, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord222, as long as it stretches more easily than the hard cord220. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire208, the soft cord222is preferably one formed from an organic fiber.

In the tire208, in light of tightening force, the outer diameter ds of the soft cord222is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord222is preferably equal to or less than 30 mm.

In the tire208, particularly, the one cross-section H of the hard cord220is located at the portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the core212, and the one cross-section S of the soft cord222is located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core212. The core212in which the hard cord220and the soft cord222are located as described above can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure. As described later, in the tire208, an elongation EH at specific load (hereinafter, elongation EH) of the hard cord220and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord222are appropriately adjusted. Therefore, with the tire208, a low fitting pressure can be achieved without impairing the tightening force.

The elongation EH of the hard cord220and the elongation ES of the soft cord222influence the tightening force and the fitting pressure. In the tire208, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire208, the width (a double-headed arrow w inFIG. 12) of the core212in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 12) of the core212in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 12) of the core212in the axial direction to the inner edge (reference character P2inFIG. 12) of the core212in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 12) of the core212in the radial direction to the outer edge (reference character P4inFIG. 12) of the core212in the radial direction.

In the tire208, the ratio of the total sum HA of the areas of the cross-sections of the hard cord220included in the cross-section of the hard unit216of the core212, relative to the area BA of the cross-section of the core212, is preferably equal to or greater than 20% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 20%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core212is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire208, the ratio of the total sum SA of the areas of the cross-sections of the soft cord222included in the cross-section of the soft unit218, relative to the area BA of the cross-section of the core212, is preferably equal to or greater than 5% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 5%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

FIG. 13shows a portion of a pneumatic tire224according to sill another embodiment of the present invention.FIG. 13shows a bead226portion of the tire224. InFIG. 13, the up-down direction is the radial direction of the tire224, the right-left direction is the axial direction of the tire224, and the direction perpendicular to the surface of the sheet is the circumferential direction of the tire224.FIG. 13shows a portion of a cross-section of the tire224along the radial direction. InFIG. 13, the right side of the surface of the sheet is the inner side in the axial direction, and the left side of the surface of the sheet is the outer side in the axial direction.

In the tire224, the configuration except for the beads226is the same as that of the tire142shown inFIG. 8. The configuration except for the beads226is also the same as that of the tire22shown inFIG. 1. The tire224includes, in addition to the beads226, a tread, sidewalls, clinches, a carcass, a belt, a band, an inner liner, wings, and cushion layers.

Each bead226has a ring shape. Each bead226includes a core228and an apex230. The apex230extends from the core228outward in the radial direction. The apex230is tapered outward in the radial direction. The apex230is formed from a highly hard crosslinked rubber. In the drawing, reference character K indicates the carcass, and reference character KP indicates a carcass ply that forms the carcass K. The carcass ply KP is turned up around the core228from the inner side to the outer side in the axial direction.

The core228includes a hard unit232, a first middle unit234, a second middle unit236, and a soft unit238. The core228of the tire224is composed of the hard unit232, the first middle unit234, the second middle unit236, and the soft unit238.

The hard unit232forms an inner portion of the core228in the radial direction and an outer portion of the core228in the axial direction. The hard unit232includes a hard cord240extending in the circumferential direction. When the tire224is fitted on a rim, the hard unit232serves to tighten the tire224on the rim.

In the tire224, the hard unit232is formed by winding the hard cord240in the circumferential direction a plurality of times. Accordingly, the hard unit232is obtained in which cross-sections of the hard cord240are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the hard cord240included in a cross-section of the hard unit232is seven. The hard unit232of the tire224is formed by helically winding the hard cord240in the circumferential direction seven times. The hard unit232may be formed by winding, in the circumferential direction, a bundle composed of a plurality of hard cords240.

In the tire224, the material of the hard cord240is preferably steel. The hard cord240is difficult to stretch as compared to one formed from an organic fiber. The hard cord240can contribute to tightening the tire224on the rim.

In the tire224, as the hard cord240, one formed of the single element wire as shown inFIG. 3is preferable. The hard cord240is difficult to stretch as compared to one formed of a plurality of element wires. The hard cord240can contribute to tightening the tire224on the rim.

In the tire224, preferably, the material of the hard cord240is steel, and the hard cord240is formed of an element wire. The stretch of the hard cord240is small. In other words, the hard cord240is non-stretchable. The non-stretchable hard cord240can effectively contribute to tightening the tire224on the rim. The hard unit232composed of the non-stretchable hard cord240can firmly tighten the tire224on the rim.

In the tire224, one cross-section (reference character H inFIG. 13) of the hard cord240is located at a portion, at the outer side in the axial direction and at the inner side in the radial direction, of a cross-section of the core228. As described above, the hard cord240is non-stretchable. The core228configured such that the hard cord240is located at the portion at the outer side in the axial direction and at the inner side in the radial direction can more firmly tighten the tire224on the rim.

In the tire224, the hard cord240only needs to be non-stretchable, and is not limited to the element wire of which the material is steel. One formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the hard cord240, or one formed from a plurality of element wires may be used as the hard cord240, as long as it is non-stretchable. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

In the tire224, in light of tightening force, the outer diameter dh of the hard cord240is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dh of the hard cord240is preferably equal to or less than 10 mm.

The first middle unit234is located outward of the hard unit232in the radial direction. The first middle unit234is located inward of the hard unit232in the axial direction. The first middle unit234is located between the hard unit232and the second middle unit236. The first middle unit234includes a first middle cord242extending in the circumferential direction. When the tire224is fitted on the rim, the first middle unit234serves to tighten the tire224on the rim.

In the tire224, the first middle unit234is formed by winding the first middle cord242in the circumferential direction a plurality of times. Accordingly, the first middle unit234is obtained in which cross-sections of the first middle cord242are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the first middle cord242included in a cross-section of the first middle unit234is five. The first middle unit234of the tire224is formed by helically winding the first middle cord242in the circumferential direction five times. The first middle unit234may be formed by winding, in the circumferential direction, a bundle composed of a plurality of first middle cords242.

The first middle cord242stretches more easily than the above-described hard cord240. The elongation of the first middle cord242is greater than the elongation of the hard cord240. Thus, when the tire224is fitted onto the rim, the first middle unit234composed of the first middle cord242does not inhibit deformation of the core228. Since the core228easily deforms, the bead226portion of the tire224easily passes over a hump of the rim. According to the present invention, the tire224can be fitted onto the rim at a low fitting pressure. Fitting the tire224onto the rim is easy.

Examples of the first middle cord242in the tire224include those having the configurations shown in (a) to (d) ofFIG. 5described above. The first middle cord242only needs to have an elongation greater than the elongation of the hard cord240, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the first middle cord242, or one formed by twisting together a plurality of the raw yarns may be used as the first middle cord242, as long as it stretches more easily than the hard cord240. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire224, the first middle cord242is preferably one formed from an organic fiber.

In the tire224, in light of tightening force, the outer diameter dm1of the first middle cord242is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dm1of the first middle cord242is preferably equal to or less than 30 mm.

The second middle unit236is located outward of the first middle unit234in the radial direction. The second middle unit236is located inward of the first middle unit234in the axial direction. The second middle unit236is located between the first middle unit234and the soft unit238. The second middle unit236includes a second middle cord244extending in the circumferential direction. When the tire224is fitted on the rim, the second middle unit236serves to tighten the tire224on the rim.

In the tire224, the second middle unit236is formed by winding the second middle cord244in the circumferential direction a plurality of times. Accordingly, the second middle unit236is obtained in which cross-sections of the second middle cord244are arranged in the axial direction and the radial direction. As shown in the drawing, the number of the cross-sections of the second middle cord244included in a cross-section of the second middle unit236is three. The second middle unit236of the tire224is formed by helically winding the second middle cord244in the circumferential direction three times. The second middle unit236may be formed by winding, in the circumferential direction, a bundle composed of three second middle cords244.

The second middle cord244stretches more easily than the above-described first middle cord242. The elongation of the second middle cord244is greater than the elongation of the first middle cord242. Thus, when the tire224is fitted onto the rim, the second middle unit236composed of the second middle cord244does not inhibit deformation of the core228. Since the core228easily deforms, the bead226portion of the tire224easily passes over the hump of the rim. According to the present invention, the tire224can be fitted onto the rim at a low fitting pressure. Fitting the tire224onto the rim is easy.

Examples of the second middle cord244in the tire224include those having the configurations shown in (a) to (d) ofFIG. 5described above. The second middle cord244only needs to have an elongation greater than the elongation of the first middle cord242, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the second middle cord244, or one formed by twisting together a plurality of the raw yarns may be used as the second middle cord244, as long as it stretches more easily than the first middle cord242. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire224, the second middle cord244is preferably one formed from an organic fiber.

In the tire224, in light of tightening force, the outer diameter dm2of the second middle cord244is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter dm2of the second middle cord244is preferably equal to or less than 30 mm.

The soft unit238is located outward of the second middle unit236in the radial direction. The soft unit238is located inward of the second middle unit236in the axial direction. The soft unit238forms a portion, at the outer side in the radial direction and at the inner side in the axial direction, of the core228. The soft unit238includes a soft cord246extending in the circumferential direction. When the tire224is fitted on the rim, the soft unit238serves to tighten the tire224on the rim.

As shown in the drawing, the number of cross-sections of the soft cord246included in a cross-section of the soft unit238is one. In the tire224, the soft unit238is formed by winding the soft cord246in the circumferential direction once. The soft unit238may be formed by winding the soft cord246in the circumferential direction a plurality of times. The soft unit238may be formed by winding, in the circumferential direction, a bundle composed of a plurality of soft cords246.

The soft cord246stretches more easily than the above-described second middle cord244. The elongation of the soft cord246is greater than the elongation of the second middle cord244. Thus, when the tire224is fitted onto the rim, the soft unit238composed of the soft cord246does not inhibit deformation of the core228. Since the core228easily deforms, the bead226portion of the tire224easily passes over the hump of the rim. According to the present invention, the tire224can be fitted onto the rim at a low fitting pressure. Fitting the tire224onto the rim is easy.

In the tire224, one cross-section (reference character S inFIG. 13) of the soft cord246is located at a portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core228. This portion corresponds to the portion in the core8of the conventional tire2to which portion great tension is applied when the tire2is fitted onto the rim. As described above, the soft cord246stretches more easily than the second middle cord244. The second middle cord244stretches more easily than the first middle cord242. The first middle cord242stretches more easily than the hard cord240. Therefore, the soft cord246stretches more easily than the hard cord240. Accordingly, the soft cord246located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core228can effectively contribute to deformation of the core228. Since the bead226portion of the tire224easily passes over the hump of the rim, the tire224can be fitted onto the rim at a low fitting pressure. In addition, due to a synergistic effect of the hard unit232, the first middle unit234, the second middle unit236, and the soft unit238, the core228can more firmly tighten the tire224on the rim. With the tire224, a low fitting pressure is achieved without impairing the tightening force.

Examples of the soft cord246in the tire224include those having the configurations shown in (a) to (d) ofFIG. 5described above. The soft cord246only needs to have an elongation greater than the elongation of the second middle cord244, and is not limited to one formed by twisting together a plurality of element wires of each of which the material is steel. A raw yarn formed from an organic fiber, a glass fiber, or a carbon fiber may be used as the soft cord246, or one formed by twisting together a plurality of the raw yarns may be used as the soft cord246, as long as it stretches more easily than the second middle cord244. Examples of the organic fiber include nylon fibers, polyethylene terephthalate fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. In light of weight reduction of the tire224, the soft cord246is preferably one formed from an organic fiber.

In the tire224, in light of tightening force, the outer diameter ds of the soft cord246is preferably equal to or greater than 0.5 mm. In light of weight reduction, the outer diameter ds of the soft cord246is preferably equal to or less than 30 mm.

In the tire224, particularly, the one cross-section H of the hard cord240is located at the portion, at the outer side in the axial direction and at the inner side in the radial direction, of the cross-section of the core228, and the one cross-section S of the soft cord246is located at the portion, at the inner side in the axial direction and at the outer side in the radial direction, of the cross-section of the core228. The core228in which the hard cord240and the soft cord246are located as described above can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure.

In the tire224, furthermore, in the cross-section of the core228, one cross-section (reference character M1inFIG. 13) of the first middle cord242is located outward of the one cross-section H of the hard cord240in the radial direction and inward of the one cross-section H of the hard cord240in the axial direction. One cross-section (reference character M2inFIG. 13) of the second middle cord244is located outward of the one cross-section M1of the first middle cord242in the radial direction and inward of the one cross-section M1of the first middle cord242in the axial direction. The one cross-section S of the soft cord246is located outward of the one cross-section M2of the second middle cord244in the radial direction and inward of the one cross-section M2of the second middle cord244in the axial direction. The core228of the tire224is configured such that the elongation of a cord248that forms the core228gradually increases from a portion at the outer side in the axial direction and at the inner side in the radial direction toward a portion at the inner side in the axial direction and at the outer side in the radial direction. The core228can effectively contribute to maintenance of the tightening force and reduction of the fitting pressure. With the tire224, a low fitting pressure can be achieved without impairing the tightening force.

An elongation EH at specific load (hereinafter, elongation EH) of the hard cord240, an elongation EM1at specific load (hereinafter, elongation EM1) of the first middle cord242, an elongation EM2at specific load (hereinafter, elongation EM2) of the second middle cord244, and an elongation ES at specific load (hereinafter, elongation ES) of the soft cord246influence the tightening force and the fitting pressure.

In the tire224, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 103%, further preferably equal to or greater than 106%, and particularly preferably equal to or greater than 112%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire224, in light of reduction of the fitting pressure, the ratio of the elongation EM1relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire224, in light of reduction of the fitting pressure, the ratio of the elongation EM2relative to the elongation EH is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire224, in light of reduction of the fitting pressure, the ratio of the elongation EM2relative to the elongation EM1is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire224, in light of reduction of the fitting pressure, the ratio of the elongation ES relative to the elongation EM2is preferably equal to or greater than 101%, more preferably equal to or greater than 102%, and particularly preferably equal to or greater than 104%. In light of maintenance of the tightening force, the ratio is preferably equal to or less than 200%.

In the tire224, the width (a double-headed arrow w inFIG. 13) of the core228in the axial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The height (a double-headed arrow h inFIG. 13) of the core228in the radial direction is equal to or greater than 1 mm and equal to or less than 50 mm. The width w is represented by the length in the axial direction from the outer edge (reference character P1inFIG. 13) of the core228in the axial direction to the inner edge (reference character P2inFIG. 13) of the core228in the axial direction. The height h is represented by the length in the radial direction from the inner edge (reference character P3inFIG. 13) of the core228in the radial direction to the outer edge (reference character P4inFIG. 13) of the core228in the radial direction.

In the tire224, the ratio of the total sum HA of the areas of the cross-sections of the hard cord240included in the cross-section of the hard unit232of the core228, relative to the area BA of the cross-section of the core228, is preferably equal to or greater than 10% and equal to or less than 95%. When this ratio is set so as to be equal to or greater than 10%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 95%, weight reduction and a low fitting pressure are achieved. The area BA of the cross-section of the core228is represented by the product of the above-described width w in the axial direction and the above-described height h in the radial direction.

In the tire224, the ratio of the total sum SM1of the areas of the cross-sections of the first middle cord242included in the cross-section of the first middle unit234, relative to the area BA of the cross-section of the core228, is preferably equal to or greater than 2% and equal to or less than 80%. When this ratio is set so as to be equal to or greater than 2%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 80%, weight reduction and a low fitting pressure are achieved.

In the tire224, the ratio of the total sum SM2of the areas of the cross-sections of the second middle cord244included in the cross-section of the second middle unit236, relative to the area BA of the cross-section of the core228, is preferably equal to or greater than 2% and equal to or less than 70%. When this ratio is set so as to be equal to or greater than 2%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 70%, weight reduction and a low fitting pressure are achieved.

In the tire224, the ratio of the total sum SA of the areas of the cross-sections of the soft cord246included in the cross-section of the soft unit238, relative to the area BA of the cross-section of the core228, is preferably equal to or greater than 1% and equal to or less than 60%. When this ratio is set so as to be equal to or greater than 1%, an appropriate tightening force is obtained. When this ratio is set so as to be equal to or less than 60%, weight reduction and a low fitting pressure are achieved.

EXAMPLES

The following will show effects of the present invention by means of examples, but the present invention should not be construed in a limited manner based on the description of these examples.

A pneumatic tire (size=195/65R15) of Example 1 having the fundamental structure shown inFIG. 1and having specifications shown in Table 1 below was obtained. The configuration of the core of each bead of Example 1 is as shown inFIG. 2. In Example 1, a stretchable portion composed of a portion of each apex was provided. In Example 1, a cord of the type shown inFIG. 3was used for forming the main body of the core. The material of the cord was steel. The outer diameter dh of the cord was set to 1.2 mm. In Example 1, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 5 mm.

Examples 2 to 4

Pneumatic tires of Examples 2 to 4 were obtained in the same manner as Example 1, except the configuration of each bead was as shown in Table 1 below. In Examples 2 to 4, a cord that is the same as the cord used in Example 1 was used for forming the hard unit.

In Example 2, a soft cord of the type shown in (d) ofFIG. 5was used for forming the soft unit. The material of the soft cord was steel. The outer diameter ds of the soft cord was set to 1.6 mm. The soft cord is one formed by twisting together four element wires (wire diameter=0.6 mm). Each element wire is reformed in a wavy shape in which a height represented by the amplitude from a crest of the element wire to a trough of the element wire is 1 mm and a pitch represented by the length from one crest to another crest adjacent to this crest is 10 mm. In Example 2, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 8 mm.

In Example 3, a soft cord of the type shown in (a) ofFIG. 5was used for forming the soft unit. The soft cord is formed from an aramid fiber. The outer diameter ds of the soft cord was set to 1 mm. The soft cord is one formed by twisting together three raw yarns (configuration=1670 dtex/2). In Example 3, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 8 mm.

In Example 4, a middle cord of the type shown in (c) ofFIG. 5was used for forming the middle unit. The material of the middle cord was steel. The outer diameter dm of the middle cord was set to 1 mm. The middle cord is one formed by twisting together four element wires (wire diameter=0.5 mm). Each element wire is not reformed in a wavy shape. A soft cord of the type shown in (b) ofFIG. 5was used for forming the soft unit. The material of the soft cord was steel. The outer diameter ds of the soft cord was set to 1 mm. The soft cord is one formed by twisting together three element wires (wire diameter=0.5 mm). Each element wire is reformed in a wavy shape in which a height represented by the amplitude from a crest of the element wire to a trough of the element wire is 1 mm and a pitch represented by the length from one crest to another crest adjacent to this crest is 10 mm. In Example 4, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set o 8 mm.

A pneumatic tire (size=195/65R15) of Example 5 having the fundamental structure shown inFIG. 8and having specifications shown in Table 2 below was obtained. The configuration of the core of each bead of Example 5 is as shown inFIG. 9. In Example 5, no stretchable portion is provided. In Example 5, a cord that is the same as the hard cord used in Example 1 was used as the hard cord for forming the hard unit. A soft cord of the type shown in (a) ofFIG. 5was used for forming the soft unit. The soft cord is formed from an aramid fiber. The outer diameter DMa of the soft cord was set to 3 mm. The soft cord is one formed by twisting together three raw yarns (configuration=1500 dtex/2). In Example 5, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 14 mm.

Examples 6 to 9

Pneumatic tires of Examples 6 to 9 were obtained in the same manner as Example 5, except the configuration of each bead was as shown in Table 2 below. In Examples 6 to 9, a cord that is the same as the cord used in Example 5 was used as the hard cord for forming the hard unit.

In Example 6, a cord that is the same as the soft cord used in Example 5 was used as the soft cord for forming the soft unit. In Example 6, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 10 mm.

In Example 7, a soft cord of the type shown in (c) ofFIG. 5was used for forming the soft unit. The soft cord is formed from an aramid fiber. The outer diameter ds of the soft cord was set to 4 mm. The soft cord is one formed by twisting together four raw yarns (configuration=1500 dtex/2). In Example 7, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 8 mm.

In Example 8, a cord that is the same as the soft cord used in Example 2 was used as the soft cord for forming the soft unit. In Example 8, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 8 mm.

In Example 9, a cord that is the same as the middle cord used in Example 4 was used as the first middle cord for forming the first middle unit. A second middle cord of the type shown in (a) ofFIG. 5was used for forming the second middle unit. The material of the second middle cord was steel. The outer diameter dm2of the second middle cord was set to 1.1 mm. The second middle cord is one formed by twisting together three element wires (wire diameter=0.3 mm). Each element wire is not reformed in a wavy shape. A cord that is the same as the soft cord used in Example 4 was used as the soft cord for forming the soft unit. In Example 9, the width w of the core in the axial direction was set to 8 mm, and the height h of the core in the radial direction was set to 8 mm.

Comparative Example 1

A pneumatic tire (size=195/65R15) of Comparative Example 1 having the fundamental structure shown inFIG. 14and having specifications shown in Table 1 below was obtained. The configuration of the core of each bead of Comparative Example 1 is as shown inFIG. 15. In Comparative Example 1, no stretchable portion is provided. Comparative Example 1 is a conventional tire. In Comparative Example 1, a cord of the type shown inFIG. 3was used for forming the core. The material of the cord was steel. The outer diameter of the cord was set to 1.2 mm. The cord is the same as the cord in Example 1.

For the cord used for forming the core, an elongation at specific load was measured. The results are shown, in Tables 1 and 2 below, as indexes with the elongation of the cord of Comparative Example 1 defined as 100. It is represented that the higher the value is, the more easily the cord stretches. When the core includes a plurality of types of cords, since the cord that is the same as the cord in Comparative Example 1 is used as the hard cord, the values indicated as the elongation of the middle cord, and the soft cord, etc. are also ratios relative to the elongation of the hard cord.

In Examples 1 to 4, the weight of the main body of the core was measured. In Examples 5 to 9 and Comparative Example 1, the weight of the core was measured. The results are shown, in Tables 1 and 2 below, as indexes with the weight of Comparative Example 1 defined as 100. The lower the value is, the better the result is.

Each tire was mounted onto a rim (size=15×6J) and inflated with air, and a pressure (fitting pressure) was measured when the bead portion of the tire passed over a hump of the rim. The results are shown in Tables 1 and 2 below. The lower the value is, the better the result is. In the measurement of the fitting pressure, the supply pressure of air was adjusted to 500 KPa. A portion of the rim onto which portion the tire was fitted was cleaned to remove dirt. A lubricant (trade name “Mounting Paste” manufactured by TIPTOP JAPAN K.K., or trade name “Tire Cream” manufactured by Japan Seal Rite Co. Ltd.) was applied to the entirety of each bead portion of the tire by using a brush or a sponge. Immediately after the application of the lubricant, the tire was mounted onto the rim and inflated with air, and a fitting pressure was measured. After the measurement, the air is discharged, and the tire was removed from the rim.

As shown in Tables 1 and 2, the evaluation is higher in the tires of the examples than in the tire of the comparative example. From the results of evaluation, advantages of the present invention are clear.

INDUSTRIAL APPLICABILITY

The method described above is applicable to various pneumatic tires.

DESCRIPTION OF THE REFERENCE CHARACTERS