JP2021187192A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire 2 capable of improving straight line stability and uneven wear resistance performance while securing steering stability and high speed durability.SOLUTION: In a tire 2, an inner ply 34 of a belt 18 comprises a plurality of inner ply pieces 56 in parallel with an axial direction, and a boundary 60 between one inner ply piece 56a and the other inner ply piece 56b is inclined toward a circumferential direction. An inclined direction of belt cords 48 included in the one inner ply piece 56a is a direction opposite to the inclined direction of the belt cords 48 included in the other inner ply piece 56b. An outer ply 36 of the belt 18 comprises a plurality of outer ply pieces 58 in parallel with the axial direction, and a boundary 60 between one outer ply piece 58a and the other outer ply piece 58b is inclined toward the circumferential direction. An inclined direction of the belt cords 48 included in the one outer ply piece 58a is a direction opposite to the inclined direction of the belt cords 48 included in the other outer ply piece 58b.SELECTED DRAWING: Figure 3

Description

The present invention relates to a pneumatic tire.

A belt is provided between the tread of the tire and the carcass. The belt contains a large number of parallel belt cords. The rigidity of the tread portion is controlled by adjusting the material of the cord used for the belt cord, the arrangement of the belt cord, and the like (for example, Patent Document 1).

A steel cord is usually used for the belt cord. A belt using a steel cord as a belt cord contributes to ensuring the rigidity of the tread portion. This tire is expected to improve durability, steering stability and dimensional stability.

Japanese Unexamined Patent Publication No. 8-104103

When the driver releases his hand from the steering wheel while driving straight, the vehicle tries to move to the left or right. In order to maintain straight running, the driver needs to hold the steering wheel with some force.

The cornering force at the slip angle where the self-aligning torque becomes zero is also called the residual cornering force. The residual cornering force is affected by the tread pattern and the tilt angle of the belt cord. If the residual cornering force is large, there is a concern that straight-line stability will decrease and uneven wear will occur.

The belt is composed of at least two plies laminated in the radial direction. In order to improve straight-line stability and uneven wear resistance, the ply is divided into two ply pieces arranged in parallel in the axial direction, and the direction of inclination of the belt cord contained in one ply piece is included in the other ply piece. Attempts have been made to reduce residual cornering force by configuring plies so that they are oriented in the opposite direction of the belt cord.

When the ply is divided into two ply pieces so that the boundary between one ply piece and the other ply piece extends in the circumferential direction, the direction of the boundary coincides with the rotation direction of the tire. Therefore, strain tends to concentrate on the boundary extending in the circumferential direction. In competitions such as races, since the load acting on the tire is large, there is a concern that the ply piece may peel off at this boundary.

The present invention has been made in view of such an actual situation, and provides a pneumatic tire capable of improving straight-line stability and uneven wear resistance while ensuring steering stability and high-speed durability. The purpose is to do.

The pneumatic tire according to one aspect of the present invention includes a pair of beads, a carcass extending between one bead and the other bead, a belt located outside the carcass in the radial direction, and the above-mentioned in the radial direction. It is located on the outside of the belt and has a tread that constitutes a tread surface that comes into contact with the road surface. The belt includes a large number of belt cords in parallel, and the large number of the belt cords are inclined with respect to the circumferential direction. The belt comprises an inner ply and an outer ply located outside the inner ply in the radial direction. The inner ply consists of a plurality of inner ply pieces arranged in parallel in the axial direction, and the boundary between one inner ply piece and another inner ply piece located next to the one inner ply piece is inclined with respect to the circumferential direction. .. The direction of inclination of the belt cord included in the one inner ply piece is opposite to the direction of inclination of the belt cord included in the other inner ply piece. The outer ply consists of a plurality of outer ply pieces arranged in parallel in the axial direction, and the boundary between one outer ply piece and the other outer ply piece located next to the one outer ply piece is inclined with respect to the circumferential direction. .. The direction of inclination of the belt cord included in the one outer ply piece is opposite to the direction of inclination of the belt cord included in the other outer ply piece. When the inner ply piece and the outer ply piece located on one end side of the belt are the first inner ply piece and the first outer ply piece, respectively, the direction of inclination of the belt cord included in the first inner ply piece. Is the direction opposite to the direction of inclination of the belt cord included in the first outer ply piece.

Preferably, in this pneumatic tire, the angle formed by the belt cord with respect to the circumferential direction is 15 ° or more and 30 ° or less.

Preferably, in this pneumatic tire, the angle formed by the belt cord included in the outer ply with respect to the circumferential direction is smaller than the angle formed by the belt cord included in the inner ply with respect to the circumferential direction.

Preferably, in this pneumatic tire, the ratio of the angle formed by the belt cord included in the outer ply to the circumferential direction is 70% or more with respect to the angle formed by the belt cord included in the inner ply with respect to the circumferential direction. It is 90% or less.

Preferably, in this pneumatic tire, the inner ply consists of two inner ply pieces juxtaposed in the axial direction and the outer ply consists of two outer ply pieces juxtaposed in the axial direction.

According to the present invention, it is possible to obtain a pneumatic tire capable of improving straight-line stability and uneven wear resistance while ensuring steering stability and high-speed durability.

FIG. 1 is a cross-sectional view showing a part of a tire according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a ply sheet used for manufacturing a belt. FIG. 3 is a schematic diagram illustrating the configuration of the belt.

Hereinafter, the present invention will be described in detail based on a preferred embodiment with reference to the drawings as appropriate.

In the present disclosure, a state in which a tire is assembled on a regular rim, the internal pressure of the tire is adjusted to the normal internal pressure, and no load is applied to the tire is referred to as a normal state. In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in normal condition.

Regular rim means the rim defined in the standard on which the tire relies. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

The normal internal pressure means the internal pressure defined in the standard on which the tire relies. The "maximum air pressure" in the JATTA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures. In the case of passenger car tires, the normal internal pressure is 180 kPa unless otherwise specified.

Normal load means the load specified in the standard on which the tire relies. The "maximum load capacity" in the JATTA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads. In the case of passenger car tires, unless otherwise specified, the normal load is a load corresponding to 88% of the above load.

In the present disclosure, the tread portion of a tire is a portion of the tire that comes into contact with the road surface. The bead portion is a part of the tire that is fitted to the rim. The side part is a part of the tire that bridges between the tread part and the bead part. The tire includes a tread portion, a pair of bead portions, and a pair of side portions as portions.

In the present disclosure, the hardness of an element made of crosslinked rubber among the elements constituting the tire is measured by using a type A durometer under a temperature condition of 23 ° C. according to the provisions of JIS K6253.

In the present disclosure, the crosslinked rubber is a molded product obtained by crosslinking a rubber composition. The crosslinked rubber is obtained, for example, by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and a chemical in a kneader such as a Banbury mixer. The crosslinked rubber is also referred to as vulcanized rubber, and the rubber composition is also referred to as unvulcanized rubber.

The base rubber includes natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). And butyl rubber (IIR) are exemplified. Chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, antiaging agents, processing aids, sulfur and A vulcanization accelerator is exemplified. Although not described in detail, the selection of the base rubber and the chemicals, the content of the selected chemicals, and the like are appropriately determined according to the specifications of the elements to which the rubber composition is applied.

In the present disclosure, the number of cords contained in an element 5 cm wide including parallel cords is expressed as the density of cords (unit: ends / 5 cm).

FIG. 1 shows an example of a pneumatic tire 2 (hereinafter, may be simply referred to as “tire 2”) according to an embodiment of the present disclosure. The tire 2 is mounted on a four-wheeled vehicle for racing. This tire 2 is a racing tire. The tire 2 may be mounted on a four-wheeled vehicle other than a racing vehicle, for example, a passenger car.

In FIG. 1, the tire 2 is assembled on the rim R (regular rim). The tire 2 assembled on the rim R is also referred to as a tire-rim complex. The tire-rim complex comprises a rim R and a tire 2 assembled on the rim R.

FIG. 1 shows a part of a cross section of a tire 2 along a plane including a rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the vertical direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, the alternate long and short dash line CL represents the equatorial plane of the tire 2.

The tire 2 includes tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a pair of chafers 14, an inner liner 16 and a belt 18 as elements.

The tread 4 comes into contact with the road surface on its outer surface, that is, the tread surface 20. The tread 4 constitutes a tread surface 20 that comes into contact with the road surface. The tread 4 is located on the outside of the belt 18 in the radial direction. The tread 4 is made of crosslinked rubber.

No groove is carved on this tread 4. This tire 2 is a slick type. A groove may be carved in the tread 4 to form a tread pattern.

In FIG. 1, the position represented by the reference numeral PC is the equator of the tire 2. The equatorial PC is represented by the intersection of the tread surface 20 and the equatorial surface. Although not shown, if the groove is located on the equatorial plane, the equatorial PC is identified based on the contour of the virtual tread plane obtained assuming no groove.

In FIG. 1, the position represented by the reference numeral TE is the end of the tread surface 20. The end TE of the tread surface 20 is represented by the axial outer end of the ground contact surface obtained by applying a normal load to the tire 2 in a normal state, setting the camber angle to 0 °, and bringing the tread 4 into contact with a flat surface.

In FIG. 1, the length represented by the double-headed arrow TW is the width of the tread surface 20. The width TW of the tread surface 20 is the axis from one end TE1 (hereinafter, also referred to as the first end TE1) of the tread surface 20 to the other end TE2 (hereinafter, also referred to as the second end TE2). Expressed by tread.

Each sidewall 6 runs on the edge of the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the edge of the tread 4 towards the clinch 8. The sidewall 6 is made of crosslinked rubber.

Each clinch 8 is located radially inside the sidewall 6. The clinch 8 comes into contact with the flange F of the rim R. The clinch 8 is made of crosslinked rubber.

Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 22 and an apex 24. Although not shown, the core 22 includes a steel wire. The apex 24 is located radially outside the core 22. Apex 24 is made of crosslinked rubber.

The carcass 12 is located inside the tread 4, the pair of sidewalls 6 and the pair of clinches 8. The carcass 12 bridges between one bead 10 and the other bead 10. The carcass 12 has a radial structure. The carcass 12 is composed of at least one carcass ply 26.

The carcass 12 of the tire 2 is composed of one carcass ply 26. The carcass ply 26 is a pair of a ply body 28 that bridges between one core 22 and the other core 22, and a pair that is connected to the ply body 28 and is folded back from the inside to the outside in the axial direction around each core 22. It has a folded-back portion 30 of.

Although not shown, the carcass ply 26 includes a number of parallel carcass cords. These carcass cords are covered with carcasting rubber made of crosslinked rubber. Each carcass code intersects the equatorial plane. In this tire 2, a cord made of organic fibers is used as a carcass cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber and aramid fiber.

Each chafer 14 is located radially inside the bead 10. The chafer 14 comes into contact with the seat S of the rim R. The chafer 14 of the tire 2 is composed of a cloth and rubber impregnated in the cloth.

The inner liner 16 is located inside the carcass 12. The inner liner 16 constitutes the inner surface of the tire 2. The inner liner 16 holds the internal pressure of the tire 2. The inner liner 16 is made of crosslinked rubber.

The belt 18 is located outside the carcass 12 in the radial direction. The belt 18 is covered with the tread 4. In the tire 2, a band including a cord spirally wound in the circumferential direction may be provided between the belt 18 and the tread 4.

In FIG. 1, the length represented by the double-headed arrow BW is the width of the belt 18. The width BW of the belt 18 is represented by the axial distance from the end of one belt 18 to the end of the other belt 18. In this tire 2, the ratio (BW / TW) of the width BW of the belt 18 to the width TW of the tread surface 20 is 80% or more and 110% or less. Preferably, this ratio (BW / TW) is 85% or more and less than 100%.

The belt 18 includes a large number of parallel belt cords. These belt cords are tilted with respect to the circumferential direction. The belt cord is covered with a belt topping rubber made of crosslinked rubber.

The material of the belt cord is steel. In other words, the belt cord is a steel cord. The belt 18 is also referred to as a steel belt (or steel breaker).

The belt 18 includes at least two plies 32 laminated in the radial direction. The belt 18 of the tire 2 is composed of two plies 32 laminated in the radial direction. In the radial direction, the inner ply 32 is the inner ply 34 and the outer ply 32 is the outer ply 36. The belt 18 includes an inner ply 34 and an outer ply 36.

The inner ply 34 is located outside the carcass 12 in the radial direction. In this tire 2, the inner ply 34 is laminated on the carcass 12. The outer ply 36 is located outside the inner ply 34 in the radial direction. In this tire 2, the outer ply 36 is laminated on the inner ply 34.

In this tire 2, the outer ply 36 is narrower than the inner ply 34. The outer ply 36 may be wider than the inner ply 34 and the outer ply 36 may have the same width as the inner ply 34. When the width of the outer ply 36 is different from the width of the inner ply 34, the distance from the end of the inner ply 34 to the end of the outer ply 36 (also referred to as a step amount) is set in the range of 3 mm or more and 7 mm or less. Will be done.

In the tire 2, the ply 32 constituting the belt 18 is manufactured by using the ply sheet. The belt 18 includes a ply 32 made by using a ply sheet. In the tire 2, the inner ply 34 is manufactured by using the inner ply sheet, and the outer ply 36 is manufactured by using the outer ply sheet.

FIG. 2 shows a ply sheet 38 prepared for making the ply 32. FIG. 2A shows the inner ply sheet 40 for the inner ply 34, and FIG. 2B shows the outer ply sheet 42 for the outer ply 36. In FIG. 2, the vertical direction is the length direction of the ply sheet 38. The length direction of the ply sheet 38 corresponds to the circumferential direction of the tire 2. The left-right direction is the width direction of the ply sheet 38. The width direction of the ply sheet 38 corresponds to the axial direction of the tire 2. The left side of the paper in FIG. 2 corresponds to the left side of the paper in FIG. In FIG. 2, the alternate long and short dash line WL is the center line in the width direction of the ply sheet.

The ply sheet 38 has a rectangular shape. Specifically, the ply sheet 38 has a parallel quadrilateral shape. The ply sheet 38 may have a rectangular shape.

The ply sheet 38 is composed of a plurality of ply piece sheets 44 arranged in parallel in the axial direction. The boundary 46 between one ply piece sheet 44a and another ply piece sheet 44b located next to this one ply piece sheet 44a is inclined with respect to the length direction. The ply sheet 38 shown in FIG. 2 is composed of the ply piece sheet 44 of 2. The boundary 46 between the ply piece sheets 44 in the ply sheet 38 extends along the long diagonal of the two diagonal lines of the ply sheet shape.

As shown in FIG. 2, each ply piece sheet 44 contains a large number of belt cords 48 in parallel. These belt cords 48 are inclined with respect to the length direction. In one ply sheet 38, the direction of inclination of the belt cord 48 included in one ply piece sheet 44a is the inclination of the belt cord 48 included in the other ply piece sheet 44b located next to the one ply piece sheet 44a. The direction is opposite to that of. The belt cord 48 included in the ply piece sheet 44 is covered with the belt topping rubber 50, but in FIG. 2, the belt cord 48 is represented by a solid line for convenience of explanation. The belt topping rubber 50 in the ply piece sheet 44 is in an uncrosslinked state.

In the inner ply sheet 40, the ply piece sheet 44a located on one side in the width direction, that is, on the left side of the paper surface is referred to as the first inner ply piece sheet 52a, and in the outer ply sheet 42, on one side in the width direction, that is, on the left side of the paper surface. When the positioned ply piece sheet 44a is the first outer ply piece sheet 54a, the direction of the belt cord 48 included in the first inner ply piece sheet 52a is the direction of the belt cord 48 included in the first outer ply piece sheet 54a. And the opposite direction.

Although not described in detail, the method for manufacturing the tire 2 includes a step of preparing a raw tire and a step of pressurizing and heating the raw tire in a mold. In the preparatory step, an unvulcanized tire 2 (hereinafter, also referred to as a raw tire) is prepared by combining elements such as an unvulcanized tread 4 and a sidewall 6. By pressurizing and heating the raw tire in the pressurizing and heating step, that is, the vulcanization step, the tire 2 which is a crosslinked body of the raw tire can be obtained.

In the manufacture of the tire 2, the above-mentioned inner ply sheet 40 and the outer ply sheet 42 are prepared in the preparation step. The inner ply sheet 40 is wound around a drum of a molding machine (not shown). By joining one end of the inner ply sheet 40 in the length direction to the other end, the inner ply sheet 40 is processed into a cylindrical shape. The outer ply sheet 42 is further wound around the tubular inner ply sheet 40. By joining one end of the outer ply sheet 42 in the length direction to the other end, the outer ply sheet 42 is processed into a cylindrical shape. As a result, the unvulcanized belt 18 is obtained. In the vulcanization step, the unvulcanized belt 18 is pressurized and heated to obtain the belt 18.

As described above, in the tire 2, the inner ply 34 is manufactured by using the inner ply sheet 40, and the outer ply 36 is manufactured by using the outer ply sheet 42. The inner ply 34 includes an inner ply piece 56 made of an inner ply piece sheet 52, and the outer ply 36 includes an outer ply piece 58 made of an outer ply piece sheet 54. In this tire 2, the number of inner ply pieces 56 included in the inner ply 34 is represented by the number of inner ply piece sheets 52 constituting the inner ply sheet 40, and the number of outer ply pieces 58 included in the outer ply 36 is , It is represented by the number of outer ply piece sheets 54 constituting the outer ply sheet 42. In this tire 2, the boundary 60 between the inner ply pieces 56 in the inner ply 34 corresponds to the boundary 46 between the inner ply piece sheets 52 in the inner ply sheet 40 and between the outer ply pieces 58 in the outer ply 36, which will be described later. The boundary 60 corresponds to the boundary 46 between the outer ply piece sheets 54 in the outer ply sheet 42.

FIG. 3 shows the configuration of the belt 18 of the tire 2. In FIG. 3, the left-right direction is the axial direction of the tire 2, and the vertical direction is the circumferential direction of the tire 2. Also in FIG. 3, for convenience of explanation, the belt cord 48 covered with the belt topping rubber 50 is represented by a solid line.

In the tire 2, the inner ply 34 is composed of a plurality of inner ply pieces 56 arranged in parallel in the axial direction. The boundary 60 between one inner ply piece 56a and the other inner ply piece 56b located next to the one inner ply piece 56a is inclined with respect to the circumferential direction. The outer ply 36 is also composed of a plurality of outer ply pieces 58 arranged in parallel in the axial direction. The boundary 60 between one outer ply piece 58a and the other outer ply piece 58b located next to this one outer ply piece 58a is also inclined with respect to the circumferential direction.

In this tire 2, the inner ply 34 is composed of two inner ply pieces 56 arranged in parallel in the axial direction. In the inner ply 34, the inner ply piece 56a located on one side of the inner ply 34 in the axial direction is also referred to as the first inner ply piece 56h, and the inner ply piece 56b located on the other side of the inner ply 34 is It is also called the second inner ply piece 56m. The outer ply 36 is composed of two outer ply pieces 58 arranged in parallel in the axial direction. In the outer ply 36, the outer ply piece 58a located on one side of the outer ply 36 in the axial direction is also referred to as the first outer ply piece 58h, and the outer ply piece 58b located on the other side of the outer ply 36 is It is also called the second outer ply piece 58m.

In the tire 2, the ply 32 is composed of a plurality of ply pieces 62 arranged in parallel in the axial direction, and the boundary 60 between one ply piece 62a and the other ply piece 62b located next to the one ply piece 62a is in the circumferential direction. Instead of extending to, it tilts with respect to the circumferential direction. Since the boundary 60 included in the belt 18 intersects the rotation direction of the tire 2, the strain acting on the boundary 60 is dispersed in the axial direction. In this tire 2, since the ply piece 62 is difficult to peel off at the boundary 60, the occurrence of damage due to this peeling can be suppressed. The tire 2 ensures the required high-speed durability.

Further, in the tire 2, in the inner ply 34, the direction of inclination of the belt cord 48 included in one inner ply piece 56a is included in the other inner ply piece 56b located next to the one inner ply piece 56a. The direction of inclination of the belt cord 48 is opposite to that of the inclination. In the outer ply 36, the direction of inclination of the belt cord 48 included in one outer ply piece 58a is the inclination of the belt cord 48 included in the other outer ply piece 58b located next to the one outer ply piece 58a. The direction is opposite to the direction.

In the tire 2, in each of the plurality of plies 32 constituting the belt 18, the direction of inclination of the belt cord 48 included in one ply piece 62a arranged across the boundary 60 is included in the other ply piece 62b. The direction of inclination of the belt cord 48 is opposite to that of the inclination. In this tire 2, the force along the belt cord 48 of the ply piece 62 is canceled out, so that the generation of residual cornering force is suppressed. In this tire 2, straight running stability and uneven wear resistance are improved.

In this tire 2, when the inner ply piece 56a and the outer ply piece 58a located on one end side of the belt 18 are the first inner ply piece 56h and the first outer ply piece 58h, respectively, the first inner ply piece The direction of inclination of the belt cord 48 included in 56h is opposite to the direction of inclination of the belt cord 48 included in the first outer ply piece 58h.

In the tire 2, the belt 18 is configured so that one ply 32a and another ply 32b laminated on the one ply 32a are restrained from each other. In the tire 2, the belt 18 contributes to ensuring the rigidity of the tread portion T. The tire 2 ensures the required steering stability.

The tire 2 can improve straight-line stability and uneven wear resistance while ensuring steering stability and high-speed durability.

In FIG. 3, the angle α is an angle formed by the belt cord 48 included in the inner ply 34 with respect to the circumferential direction (hereinafter, the inclination angle of the belt cord 48). The angle β is an inclination angle of the belt cord 48 included in the outer ply 36. As described above, in this tire 2, the ply 32 is composed of a plurality of ply pieces 62 arranged in parallel in the axial direction. In this tire 2, in one ply 32, the inclination angle of the belt cord 48 included in one ply piece 62a is set to be the same as the inclination angle of the belt cord 48 included in the other ply piece 62b. In this tire 2, the difference between the inclination angle of the belt cord 48 included in one ply piece 62a and the inclination angle of the belt cord 48 included in the other ply piece 62b is -1 ° or more and 1 ° or less. In this case, it is determined that the inclination angle of the belt cord 48 included in one ply piece 62a and the inclination angle of the belt cord 48 included in the other ply piece 62b are the same angle.

In the tire 2, the inclination angle α of the belt cord 48 included in the inner ply 34 is preferably 15 ° or more, and preferably 30 ° or less. The inclination angle β of the belt cord 48 included in the outer ply 36 is preferably 15 ° or more, and preferably 30 ° or less. That is, the inclination angle of the belt cord 48 included in the belt 18 is preferably 15 ° or more, and preferably 30 ° or less.

By setting the inclination angle of the belt cord 48 to 15 ° or more, the belt 18 contributes to ensuring the rigidity of the tread portion T. With this tire 2, good steering stability can be obtained. From this viewpoint, the inclination angle of the belt cord 48 is more preferably 16 ° or more, further preferably 18 ° or more.

By setting the inclination angle of the belt cord 48 to 30 ° or less, the belt 18 contributes to the reduction of the residual cornering force. With this tire 2, good straight running stability and uneven wear resistance can be obtained. From this point of view, the inclination angle of the belt cord 48 is more preferably 27 ° or less, further preferably 25 ° or less.

The residual cornering force is affected by the ply 32 near the tread surface 20. Therefore, by setting the inclination angle β of the belt cord 48 included in the outer ply 36 closer to the tread surface 20 than the inner ply 34 to be smaller than the inclination angle α of the belt cord 48 included in the inner ply 34, residual cornering is performed. A belt 18 that can contribute to ensuring the rigidity of the tread portion T while reducing the force is configured. In this tire 2, the inclination angle β of the belt cord 48 included in the outer ply 36 is included in the inner ply 34 from the viewpoint of improving straight-line stability and uneven wear resistance while ensuring steering stability. It is preferably smaller than the inclination angle α of the belt cord 48.

In this tire 2, the ratio (β / α) of the inclination angle β of the belt cord 48 included in the outer ply 36 to the inclination angle α of the belt cord 48 included in the inner ply 34 is preferably 70% or more, preferably 90% or less. Is preferable.

By setting the ratio (β / α) to 90% or less, the outer ply 36 effectively contributes to the reduction of the residual cornering force. In this tire 2, straight running stability and uneven wear resistance are improved. From this point of view, this ratio (β / α) is more preferably 88% or less, still more preferably 85% or less.

By setting the ratio (β / α) to 70% or more, the outer ply 36 effectively contributes to ensuring the rigidity of the tread portion T. With this tire 2, good steering stability can be obtained. From this point of view, this ratio (β / α) is more preferably 72% or more, further preferably 75% or more.

As described above, the inner ply 34 is composed of a plurality of inner ply pieces 56 parallel in the axial direction, and the outer ply 36 is composed of a plurality of outer ply pieces 58 parallel in the axial direction. The inner ply 34 includes a boundary 60 between one inner ply piece 56a and the other inner ply piece 56b. The outer ply 36 includes a boundary 60 between one outer ply piece 58a and the other outer ply piece 58b. Since the boundary 60 includes the end of the belt cord 48, there is concern that the boundary 60 will be the starting point of damage. From the viewpoint of suppressing the occurrence of damage starting from the boundary 60 and improving high-speed durability, it is preferable that the number of boundaries 60 included in the inner ply 34 and the number of boundaries 60 included in the outer ply 36 are small. Specifically, the number of inner ply pieces 56 constituting the inner ply 34 is preferably 3 or less, and the number of outer ply pieces 58 constituting the outer ply 36 is preferably 3 or less. From the viewpoint of improving straight-line stability and uneven wear resistance while ensuring high-speed durability, the inner ply 34 is composed of two inner ply pieces 56 parallel in the axial direction, and the outer ply 36 is parallel in the axial direction. It is more preferably composed of 2 outer ply pieces 58.

In this tire 2, the inner ply 34 is composed of two inner ply pieces 56 in parallel in the axial direction, that is, the first inner ply piece 56h and the second inner ply piece 56m, and the outer ply 36 is in parallel in the axial direction. In the case of the outer ply piece 58, that is, the first outer ply piece 58h and the second outer ply piece 58m, straight-line stability and uneven wear resistance are improved while ensuring steering stability and high-speed durability. From the viewpoint, the end of the boundary 60 between the first inner ply piece 56h and the second inner ply piece 56m included in the inner ply 34 is located at the end 64 of the inner ply 34, and is included in the outer ply 36. It is more preferable that the end of the boundary 60 between the outer ply piece 58h and the second outer ply piece 58m is located at the end 66 of the outer ply 36. In this case, the length of the boundary 60 of the inner ply 34 is longer than the circumferential length of the inner ply 34, and the length of the boundary 60 of the outer ply 36 is longer than the circumferential length of the outer ply 36. More preferred.

As described above, according to the present invention, it is possible to obtain a pneumatic tire 2 capable of improving straight-line stability and uneven wear resistance while ensuring steering stability and high-speed durability.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to such Examples.

[Example 1]
Pneumatic tires for passenger cars (tire size = 255 / 40R18) having the basic configurations shown in FIGS. 1 and 3 and having the specifications shown in Table 1 below were obtained.

The belt of the first embodiment consists of an inner ply and an outer ply. The number of outer ply pieces constituting the outer ply is 2, and the number of inner ply pieces constituting the inner ply is 2. This is indicated by "2" in the "number of ply pieces" column of Table 1 below.

In the first embodiment, the boundary between one outer ply piece and the other outer ply piece included in the outer ply is inclined with respect to the circumferential direction, and one inner ply piece and the other inner ply piece included in the inner ply are included. The boundary with the ply piece is inclined with respect to the circumferential direction. This is indicated by "inclination" in the "boundary orientation" column of Table 1.

In Example 1, the inclination angle β of the belt cord included in the outer ply was 20 °, and the inclination angle α of the belt cord included in the inner ply was 25 °. Therefore, the ratio (β / α) of the tilt angle β to the tilt angle α was 80%.

[Comparative Example 1]
The tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the number of outer ply pieces constituting the outer ply was 1, the number of inner ply pieces constituting the inner ply was 1, and no boundary was provided. rice field. This Comparative Example 1 is a conventional tire.

[Comparative Example 2]
An outer ply was formed by two outer ply pieces arranged across the equator surface, and an inner ply was formed by two inner ply pieces arranged across the equator surface. Obtained the tire of Example 2. This Comparative Example 2 is a conventional tire. In Comparative Example 2, the boundary included in each of the outer ply and the inner ply extends in the circumferential direction. This is represented by "circumference" in the "boundary orientation" column of Table 1.

[Example 2-5]
The tires of Example 2-5 were obtained in the same manner as in Example 1 except that the inclination angle β was changed and the ratio (β / α) was set as shown in Tables 1 and 2 below.

[Example 6]
The tire of Example 6 is used in the same manner as in Example 1 except that the number of outer ply pieces constituting the outer ply and the number of inner ply pieces constituting the inner ply are as shown in Table 2 below. Obtained.

[Straight running stability and steering stability]
The prototype tire was assembled on the regular rim and filled with air to adjust the internal pressure of the tire to the regular internal pressure. Tires were attached to a test vehicle (displacement 2000 cc, rear-wheel drive vehicle), and the test vehicle was run on a test course on a dry asphalt road surface. The driver was made to evaluate the straight running stability and the steering stability (sensory evaluation). The results are shown exponentially in Table 1-2 below. The larger the value, the better the straight running stability and the steering stability of the tire. An index of up to 90 is acceptable as tire performance.

[High-speed durability]
The prototype tire was assembled on the regular rim, filled with air, and the internal pressure of the tire was adjusted to 340 kPa. This tire was mounted on a drum type running tester, and a vertical load of 4.8 kN was applied to the tire. This tire was run at a speed of 240 km / h on a drum having a drum diameter of 1.7 m. The mileage until the tire broke was measured. The results are shown exponentially in Table 1-2 below. The larger the value, the better the high-speed durability. An index of up to 90 is acceptable as tire performance.

[Uneven wear resistance]
The uneven wear condition of each prototype tire after running on the above-mentioned test course was confirmed, and the amount of wear was measured. The results are shown exponentially in Table 1-2 below. The larger the value, the better the uneven wear resistance of the tire. An index of up to 90 is acceptable as tire performance.

As shown in Table 1-2, in the examples, it has been confirmed that improvement in straight-line stability and uneven wear resistance is achieved while ensuring steering stability and high-speed durability. From this evaluation result, the superiority of the present invention is clear.

The technique described above that can improve straight-line stability and uneven wear resistance while ensuring steering stability and high-speed durability can be applied to various tires.

2 ... Tire 4 ... Tread 10 ... Bead 12 ... Carcass 18 ... Belt 20 ... Tread surface 26 ... Carcass ply 32, 32a, 32b, 34, 36 ... Ply 38, 40, 42 ... Ply sheet 44, 44a, 44b, 52, 52a, 54, 54a ... Ply piece sheet 46, 60 ... Boundary 48 ... Belt code 56, 56a, 56b, 56h, 56m, 58, 58a, 58b, 58h, 58m, 62, 62a, 62b ... Ply piece

Claims (5)

A pair of beads and
The carcass that bridges between one bead and the other,
A belt located on the outside of the carcass in the radial direction,
It is provided with a tread that is located on the outside of the belt in the radial direction and constitutes a tread surface that comes into contact with the road surface.
The belts include a large number of belt cords in parallel, and the large number of the belt cords are tilted with respect to the circumferential direction.
The belt comprises an inner ply and an outer ply located outside the inner ply in the radial direction.
The inner ply consists of a plurality of inner ply pieces arranged in parallel in the axial direction.
The boundary between one inner ply piece and the other inner ply piece located next to the one inner ply piece is inclined with respect to the circumferential direction.
The direction of inclination of the belt cord included in the one inner ply piece is opposite to the direction of inclination of the belt cord included in the other inner ply piece.
The outer ply consists of a plurality of outer ply pieces arranged in parallel in the axial direction.
The boundary between one outer ply piece and the other outer ply piece located next to the one outer ply piece is inclined with respect to the circumferential direction.
The direction of inclination of the belt cord included in the one outer ply piece is opposite to the direction of inclination of the belt cord included in the other outer ply piece.
When the inner ply piece and the outer ply piece located on one end side of the belt are the first inner ply piece and the first outer ply piece, respectively.
A pneumatic tire in which the direction of inclination of the belt cord included in the first inner ply piece is opposite to the direction of inclination of the belt cord included in the first outer ply piece. The pneumatic tire according to claim 1, wherein the angle formed by the belt cord with respect to the circumferential direction is 15 ° or more and 30 ° or less. The pneumatic tire according to claim 1 or 2, wherein the angle formed by the belt cord included in the outer ply with respect to the circumferential direction is smaller than the angle formed by the belt cord included in the inner ply with respect to the circumferential direction. 3. The ratio of the angle formed by the belt cord included in the outer ply with respect to the circumferential direction to the angle formed by the belt cord included in the inner ply with respect to the circumferential direction is 70% or more and 90% or less. Pneumatic tires listed in. The inner ply consists of two inner ply pieces arranged in parallel in the axial direction.
The pneumatic tire according to any one of claims 1 to 4, wherein the outer plies are composed of two outer ply pieces arranged in parallel in the axial direction.

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