JP7172215B2 - Heavy duty pneumatic tire - Google Patents

Description

The present invention relates to heavy duty pneumatic tires.

Heavy loads act on tires mounted on vehicles such as trucks and buses (including small trucks and small buses), that is, heavy duty pneumatic tires. Therefore, from the viewpoint of securing rigidity, a carcass ply having steel cords as carcass cords, that is, a steel ply is generally used for the carcass of this tire.

Ends of members such as carcass plies are present in the bead portion of the tire. Movement of the bead portion concentrates strain on this edge and can cause damage. In this tire, from the viewpoint of improving durability, it is being studied to reinforce the bead portion to suppress its movement (for example, Patent Documents 1 and 2).

Patent Literature 1, for example, discusses a technique for controlling the sidewall at the turn-up end of the carcass ply to have a predetermined thickness.

In Patent Document 2, for example, the height of the folded portion is set to a predetermined height, and a stiffener (also called an apex) at the end of the folded portion and a buffer placed outside the stiffener Techniques for controlling the thickness of the rubber are being studied.

JP-A-06-219111 JP-A-2002-120521

Constructing the carcass with the aforementioned steel plies may result in creases in the chafer. In order to prevent this crease chafer from occurring, it is necessary to secure the height of the folded portion and the height of the apex of the bead. Adopting a tall apex can suppress the movement of the bead, which is expected to improve durability.

A region extending from the inner end of the cushion layer provided between the end of the belt and the carcass to the outer end of the apex in the radial direction of the tire is also called a flexible zone. This flexible zone is soft and contributes to the deflection of the tire.

A tire having an aspect ratio of 75% or less has a short side portion. Therefore, if an apex having a height is adopted, the flexible zone becomes narrow. In this case, since the side portion has high rigidity, there is a concern that the easiness of mounting the tire to the rim, that is, the ease of assembling the tire to the rim will be deteriorated. Cracks may occur at places where the strain amplitude is locally large (near the buttress).

Due to the introduction of environmental regulations and labeling systems, tires are required to be lighter. Adopting an apex with a low height is expected to reduce weight. However, as mentioned above, from the viewpoint of durability and prevention of crease chafer, it is necessary to ensure the height of the apex, and it is not possible to sufficiently reduce the mass of the tire.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heavy-duty pneumatic tire that achieves weight reduction while ensuring rim assembly performance and durability.

A preferred heavy-duty pneumatic tire according to the present invention is
A heavy-duty pneumatic tire having an aspect ratio of 75% or less,
a carcass extending from one bead to the other on the inside of the tread and a pair of sidewalls extending radially inward from the ends of the tread;
a belt positioned between the tread and the carcass;
A pair of cushioning layers positioned between the ends of the belt and the carcass.
The carcass comprises at least one carcass ply, the carcass ply comprising a number of juxtaposed carcass cords, each carcass cord being made of aramid fiber.
The bead includes a core and an apex located radially outward of the core.
In the radial direction, a zone from the inner end of the cushion layer to the outer end of the apex is a flexible zone,
A ratio of the radial length of the flexible zone to the sectional height of the belt is 0.32 or more and 0.45 or less.

Preferably, in this heavy-duty pneumatic tire, the ratio of the radial distance from the tire maximum width position to the outer end of the apex to the sectional height of the belt is 0.13 or more and 0.20 or less.

Preferably, in this heavy-duty pneumatic tire, the carcass ply includes a body portion that bridges one core and the other core, and a body portion that extends from the body portion and extends from the axially inner side to the outer side around the core. and a pair of folded portions that are folded back. A radial distance from the bead baseline to the end of the folded portion is 24 mm or more and 30 mm or less.

Preferably, the heavy duty pneumatic tire comprises a pair of steel reinforcement layers located radially inward of said beads. The steel reinforcing layer is folded back around the core from the axially inner side to the outer side along the carcass ply, and the diameter from the bead base line to the outer end of the steel reinforcing layer located axially outwardly is The directional distance is 14 mm or more and 20 mm or less.

Preferably, in this heavy-duty pneumatic tire, the outer ends of the steel reinforcing layers are located radially inwardly of the ends of the folded portions. The radial distance from the outer edge of the steel reinforcing layer to the edge of the folded portion is greater than or equal to 10 mm.

Preferably, in this heavy duty pneumatic tire, the thickness of the apex at the end of the folded portion is 7.5 mm or more and 9.0 mm or less.

In the heavy-duty pneumatic tire of the present invention, cords made of aramid fibers (hereinafter referred to as aramid cords) are used as carcass cords. The inventors conducted extensive research and found that if aramid cords are used for the carcass cords, the same degree of rigidity as that of steel plies can be ensured, and even if the apex height is set to a lower height than before, This is due to the finding that chafer creases can be suppressed. With this tire, setting the outer edge position of the apex does not have the restrictions of conventional tires that employ steel plies.

The tire can employ an apex that has a lower height than conventional apexes. The end of the folded portion formed by folding the carcass ply around the core can also be set at a position lower than the position of the end of the conventional folded portion. Moreover, aramid cords are lighter than steel cords. Since aramid cords do not rust like steel cords, the inner liner and insulation provided inside the carcass can be made thinner. With this tire, sufficient weight reduction and reduction in rolling resistance can be achieved.

In this tire, the radial length of the flexible zone is set in the range of 0.32 to 0.45 times the sectional height of the belt. Although this tire has an aspect ratio of 75% or less, a sufficient flexible zone is ensured in the side portion. The flexing sides make this tire easy to assemble on the rim. In addition, cracks are less likely to occur because the side portion, specifically, the strain around the buttress is suppressed. Furthermore, since the end of the folded portion can be arranged further inside in the axial direction, concentration of strain on the end of the folded portion can be suppressed. In this tire, damage originating from the end of the folded portion is less likely to occur. This tire ensures the necessary rim assembly properties and durability.

According to the present invention, it is possible to obtain a heavy-duty pneumatic tire that achieves weight reduction while ensuring rim assemblability and durability.

FIG. 1 is a cross-sectional view showing a portion of a heavy-duty pneumatic tire according to one embodiment of the present invention. 2 is a cross-sectional view showing a side portion of the tire of FIG. 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

FIG. 1 shows part of a heavy-duty pneumatic tire 2 (hereinafter sometimes simply referred to as "tire 2") according to one embodiment of the present invention. The tire 2 is mounted, for example, on heavy-duty vehicles such as trucks and buses (including small trucks and small buses).

FIG. 1 shows part of a cross-section of this tire 2 along a plane containing the axis of rotation of the tire 2 . In FIG. 1 , the horizontal 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 this FIG. 1 , the dashed-dotted line CL represents the equatorial plane of the tire 2 .

In FIG. 1, the tire 2 is mounted on the rim R. This rim R is a regular rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted to a normal internal pressure. No load is applied to this tire 2 .

In the present invention, a state in which the tire 2 is mounted on a rim R (normal rim), the internal pressure of the tire 2 is adjusted to the normal internal pressure, and no load is applied to the tire 2 is called a normal state. In the present invention, the tire 2 and the dimensions and angles of each portion of the tire 2 are measured under normal conditions unless otherwise specified.

In the present specification, a regular rim means a rim defined in the standard on which the tire 2 relies. A "standard rim" in the JATMA standard, a "design rim" in the TRA standard, and a "measuring rim" in the ETRTO standard are regular rims.

In this specification, the normal internal pressure means the internal pressure defined in the standard on which the tire 2 relies. The "maximum air pressure" in JATMA standards, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standards, and the "INFLATION PRESSURE" in ETRTO standards are regular internal pressures.

In this specification, the normal load means the load defined in the standard on which the tire 2 relies. "Maximum load capacity" in the JATMA standard, "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

In FIG. 1, the axially extending solid line BBL is the bead baseline. This bead baseline is a line that defines the rim diameter (see JATMA, etc.) of the rim R (regular rim).

The tire 2 comprises a tread 4 , a pair of sidewalls 6 , a pair of beads 8 , a pair of chafers 10 , a carcass 12 , a belt 14 , a pair of cushion layers 16 , an innerliner 18 and a pair of steel reinforcing layers 20 .

The tread 4 contacts the road surface on its outer surface 22 . The outer surface 22 of the tread 4 is the tread surface. In this tire 2 , the tread 4 includes a base portion 24 and a cap portion 26 located radially outside the base portion 24 . The base portion 24 is made of crosslinked rubber in consideration of adhesiveness. The cap portion 26 is made of crosslinked rubber in consideration of abrasion resistance and grip performance.

In this tire 2 , at least three circumferential grooves 28 are cut into the tread 4 . Four circumferential grooves 28 are cut into the tread 4 in the tire 2 shown in FIG. Thus, the tread 4 has five land portions 30 . These circumferential grooves 28 are arranged in parallel in the axial direction and extend continuously in the circumferential direction. Among these circumferential grooves 28, the circumferential groove 28c located near the equatorial plane is the center circumferential groove 28c. 28 s of circumferential grooves located on the outer side in the axial direction are shoulder circumferential grooves 28s.

In this tire 2, the width of the center circumferential groove 28c and the shoulder circumferential groove 28s is the length from one end 32 to the other end 32 of the tread surface 22 from the viewpoint of contribution to drainage performance and traction performance. About 1.5 to 5% of the expressed tread width is preferred. The depth of the center circumferential groove 28c and the shoulder circumferential groove 28s is preferably 10 to 20 mm.

In FIG. 1, symbol PE is the equator of this tire 2 . This equator is the intersection of the tread plane 22 and the equatorial plane. The double arrow HS is the radial distance from the bead baseline to this equator PE. This radial distance HS is the cross-sectional height of this tire 2 (see JATMA, etc.).

Each sidewall 6 continues to the edge of the tread 4 . Sidewalls 6 extend radially inward from the ends of tread 4 . The outer surface 34 of the sidewall 6 forms part of the side surface of the tire 2 . The sidewall 6 is made of crosslinked rubber.

In FIG. 1, the symbol PW is the outer end of the tire 2 in the axial direction. The outer edge PW is specified based on a virtual side surface obtained by assuming that the side surface 34 of the tire 2 has no decoration such as a pattern or letters. In FIG. 1, the axial distance from one outer end PW to the other outer end PW indicated by a double arrow WS is the maximum width of the tire 2, that is, the cross-sectional width (see JATMA, etc.). The outer end PW is the position where the tire 2 exhibits the maximum width.

Each bead 8 is located radially inside the sidewall 6 . Bead 8 comprises core 36 and apex 38 . The core 36 extends circumferentially. Core 36 includes steel wire. In this tire 2, the core 36 has a substantially hexagonal cross-sectional shape. The core 36 may be configured to have a substantially rectangular cross-sectional shape. Apex 38 is located radially outward of core 36 . Apex 38 extends radially outward from core 36 . In FIG. 1, the symbol PA is the outer edge of the apex 38. In FIG.

The apex 38 includes an inner apex 38u and an outer apex 38s. The inner apex 38u is located radially outside the core 36 . The outer apex 38s is located radially outside the inner apex 38u.

Inner apex 38u extends radially outward from core 36 . In the cross-section of the tire 2 shown in FIG. 1, the inner apex 38u tapers radially outward.

The inner apex 38u is made of crosslinked rubber. The inner apex 38u is stiffer than the outer apex 38s. The inner apex 38u contributes to the rigidity of the portion BD of the bead 8 (bead portion BD hereinafter).

Outer apex 38s extends radially outward from inner apex 38u. In this tire 2, the outer apex 38s has a greater thickness in its central portion. In the cross-section of the tire 2 shown in FIG. 1, the outer apex 38s tapers radially inwardly from the central portion and tapers radially outwardly from this central portion.

The outer apex 38s is made of crosslinked rubber. Outer apex 38s is softer than inner apex 38u. This outer apex 38s contributes to smooth deformation of the bead portion BD.

Each chafer 10 is positioned axially outside the bead 8 . The chafer 10 is located radially inside the sidewall 6 . The chafer 10 contacts the seat S and the flange F of the rim R. The chafer 10 is made of crosslinked rubber in consideration of abrasion resistance.

The carcass 12 extends from one bead 8 toward the other bead 8 inside the tread 4 , the pair of sidewalls 6 and the pair of chafers 10 . Carcass 12 comprises at least one carcass ply 40 . The carcass 12 of this tire 2 consists of one carcass ply 40 .

Although not shown, the carcass ply 40 includes a large number of parallel carcass cords. These carcass cords are covered with a topping rubber. Each carcass cord intersects the equatorial plane. In this tire 2, the angle formed by the carcass cords with respect to the equatorial plane is 70° or more and 90° or less. The carcass 12 of this tire 2 has a radial structure.

In this tire 2, the carcass cords are made of aramid fibers. In the tire 2, the carcass 12 is composed of a carcass ply 40 having a carcass cord made of aramid fiber (hereinafter also referred to as an aramid cord).

In this tire 2, the carcass ply 40 is folded back around each core 36 from the axial inner side to the outer side. The carcass ply 40 includes a main body portion 42 that bridges one core 36 and the other core 36, and a pair of main body portions 42 that are connected to the main body portion 42 and folded back around the respective cores 36 from the inner side to the outer side in the axial direction. A folded portion 44 is provided. In this tire 2 , the end 44 a of the folded portion 44 is arranged inside the outer end PA of the apex 38 in the radial direction in order to suppress concentration of strain on the end 44 a of the folded portion 44 . Further, the end 44a of the folded portion 44 is sandwiched between the intermediate layer 46 and the strip 48. As shown in FIG.

A belt 14 is positioned between the tread 4 and the carcass 12 . A belt 14 is laminated to the carcass 12 . A tread 4 covers this belt 14 .

In this tire 2 , the belt 14 is made up of three belt plies 50 . In this tire 2, the number of belt plies 50 forming the belt 14 is not particularly limited. The configuration of the belt 14 is appropriately determined in consideration of the specifications of the tire 2 .

Although not shown, each belt ply 50 includes a large number of belt cords arranged side by side. These belt cords are covered with a topping rubber. Each belt cord is inclined with respect to the equatorial plane. In the tire 2, the belt ply 50A located on the innermost side in the radial direction has an angle formed by the belt cord with respect to the equatorial plane within a range of 50° or more and 70° or less. In the belt ply 50B and the belt ply 50C positioned radially outside the belt ply 50A, the angle formed by the belt cords with respect to the equatorial plane is set within the range of 15° or more and 35° or less.

In this tire 2, of the three belt plies 50, the belt ply 50B positioned between the belt ply 50A and the belt ply 50C has the largest axial width. The radially innermost belt ply 50A has the smallest axial width. In this tire 2, the material of the belt cord is steel. A cord made of organic fibers may be used as the belt cord.

In FIG. 1, the symbol PV is the position where the radial distance from the bead baseline to the outer surface of the belt 14 is maximized. This position PV is the radially outer end of the belt 14 . In this tire 2, this position PV is located on the equatorial plane. In FIG. 1, the double arrow V is the radial distance from the bead baseline to the position PV. In the present invention, this radial distance V is the cross-sectional height of the belt 14 .

Each cushioning layer 16 lies between the belt 14 and the carcass 12 at the ends 52 of the belt 14 . In other words, this cushioning layer 16 is located between the edge 52 of the belt 14 and the carcass 12 . The cushion layer 16 is made of crosslinked rubber.

As shown in FIG. 1, in this tire 2, the cushion layer 16 has the greatest thickness at the ends 52 of the belt 14, specifically the ends 52 of the belt plies 50B. The cushion layer 16 tapers axially inwardly from its point of greatest thickness. The cushion layer 16 tapers radially inward from its portion of maximum thickness.

An inner liner 18 is positioned inside the carcass 12 . In this tire 2 , the inner liner 18 is joined to the carcass 12 by an insulation 54 . The inner liner 18 constitutes the inner surface of the tire 2 . This inner liner 18 is made of a crosslinked rubber having excellent air shielding properties. The inner liner 18 retains the internal pressure of the tire 2 .

Each steel reinforcement layer 20 is located at the bead portion BD. The steel reinforcement layer 20 is located radially inside the bead 8 . The steel reinforcement layer 20 is folded axially inwardly outwardly around the core 36 along the carcass plies 40 . At least part of the steel reinforcement layer 20 contacts the carcass ply 40 . A carcass ply 40 is located between the steel reinforcing layer 20 and the bead 8 .

The end 56 of the steel reinforcing layer 20 positioned axially inward (hereinafter also referred to as the inner end 56 of the steel reinforcing layer 20) is positioned radially near the end 44a of the turnup portion 44 of the carcass ply 40. . 1, the position of the inner end 56 of the steel reinforcing layer 20 coincides with the position of the end 44a of the folded portion 44 in the radial direction. The end 58 of the steel reinforcing layer 20 located on the outer side in the axial direction (hereinafter also referred to as the outer end 58 of the steel reinforcing layer 20) is radially inside the end 44a of the folded portion 44 of the carcass ply 40. To position.

Although not shown, the steel reinforcement layer 20 includes multiple steel cords in parallel. These steel cords are covered with a topping rubber. The steel reinforcing layer 20 contributes to improving the bending rigidity of the bead portion BD.

In FIG. 1, the symbol PK is the radially inner end of the cushion layer 16. As shown in FIG. In this tire 2, the zone from the inner end PK of the cushion layer 16 to the outer end PA of the apex 38 in the radial direction is a flexible zone. Double arrow F is the radial length of this flexible zone.

As shown in FIG. 1, the flexible zone is free of the cushioning layer 16 and apex 38 . The stiffness of this flexible zone is lower than that of its radially outer portion. The stiffness of this flexible zone is lower than that of its radially inner portion.

The aspect ratio of the tire 2 is represented by the ratio of the cross-sectional height HS to the cross-sectional width WS of the tire 2 under normal conditions. This tire 2 has an aspect ratio of 75% or less. In this tire 2, the length of the portion from the sidewall 6 to the chafer 10, that is, the side portion SD is limited compared to a tire having an aspect ratio of more than 75%. In the tire 2 having an aspect ratio of 75% or less, the size of the flexible zone affects the rigidity of the side portion SD.

In this tire 2, the ratio of the radial length F of the flexible zone to the sectional height V of the belt 14 is 0.32 or more and 0.45 or less. By setting this ratio to 0.32 or more, the flexible zone imparts moderate flexibility to the side portion SD. By setting this ratio to 0.45 or less, each member constituting the tire 2 can be formed in an appropriate shape, and the side portion SD can be prevented from becoming excessively soft. In this tire 2, the rigidity of the side portion SD is appropriately maintained.

As described above, in this tire 2, aramid cords are used as the carcass cords. This is because the inventors conducted intensive studies and found that the aramid cord can suppress the occurrence of chafer creases even when the height of the apex 38 is set lower than in the conventional case. In this tire 2, the setting of the position of the outer end PA of the apex 38 is not restricted like a conventional tire using steel plies.

This tire 2 can employ an apex 38 having a lower height than a conventional apex. The end 44a of the folded portion 44 formed by folding the carcass ply 40 around the core 36 can also be set at a position lower than the end position of the conventional folded portion. Moreover, aramid cords are lighter than steel cords. Since aramid cords do not rust like steel cords, the inner liner 18 and the insulation 54 provided inside the carcass 12 can be made thinner. With this tire 2, sufficient weight reduction and reduction in rolling resistance can be achieved.

In this tire 2 , the radial length F of the flexible zone is set within the range of 0.32 to 0.45 times the sectional height V of the belt 14 . In this tire 2, although the aspect ratio is 75% or less, the flexible zone is sufficiently secured in the side portion SD. The tire 2 can be easily mounted on the rim R because the side portion SD is flexibly bent. Moreover, since the side portion SD, specifically, the strain near the buttress 60 is suppressed, cracks are less likely to occur. Furthermore, since the end 44a of the folded portion 44 can be arranged further inside in the axial direction, concentration of strain on the end 44a of the folded portion 44 can be suppressed. In this tire 2, damage starting from the end 44a of the folded portion 44 is less likely to occur. In this tire 2, necessary rim assembly properties and durability are ensured.

With this tire 2, it is possible to reduce the weight while ensuring the rim assemblability and durability.

In FIG. 1 , the double arrow H indicates the radial distance from the maximum width position PW of the tire 2 to the outer end PA of the apex 38 . The double arrow HW is the radial distance from the bead baseline to the maximum width position PW.

In this tire 2, the ratio of the radial distance H from the maximum width position PW of the tire 2 to the outer end PA of the apex 38 to the sectional height V of the belt 14 is preferably 0.13 or more, and 0.20 or less. preferable. By setting this ratio to 0.13 or more, the height of the apex 38 is appropriately maintained. Since the flexible zone is sufficiently secured in the side portion SD, the tire 2 can be easily incorporated into the rim R. By setting this ratio to 0.20 or less, the apex 38 contributes to the rigidity of the bead portion BD. This tire 2 maintains good bead durability.

In this tire 2, the flexible zone is arranged so as to straddle the maximum width position PW in the radial direction. In this tire 2 , the radial distance HW from the bead base line to the maximum width position PW is set in the range of 0.5 to 0.6 times the sectional height V of the belt 14 . In this tire 2, the deflection in the radially outer portion of the maximum width position PW and the deflection in the radially inner portion of the maximum width position PW are balanced. Since the flexible zone effectively contributes to the flexible bending of the side portion SD, this tire 2 can be easily incorporated into the rim R. Since strain around the buttress 60 is suppressed, cracks are less likely to occur. In this tire 2, necessary rim assembly properties and durability are ensured. From this point of view, in the tire 2, the ratio of the radial distance HW from the bead base line to the maximum width position PW to the sectional height V of the belt 14 is preferably 0.5 or more and 0.6 or less.

FIG. 2 shows the bead portion BD of the tire 2 of FIG. In FIG. 2 , the horizontal 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 plane of FIG. 2 is the circumferential direction of the tire 2 .

In FIG. 2, the double arrow C is the radial distance from the bead baseline to the end 44a of the turnup portion 44. As shown in FIG. Double arrow E is the radial distance from the bead baseline to the outer edge 58 of the steel reinforcement layer 20 .

In this tire 2, the radial distance C from the bead base line to the end 44a of the folded portion 44 is preferably 24 mm or more, and preferably 30 mm or less. By setting the distance C to 24 mm or more, the length of the folded portion 44 is sufficiently secured. The folded portion 44 is prevented from being pulled out due to the tension generated in the body portion 42 . In this tire 2, damage to the bead portion BD is effectively prevented. As described above, in the tire 2, the ends 44a of the turned-up portions 44 are arranged radially inwardly of the outer ends PA of the apex 38 in order to suppress concentration of strain on the ends 44a of the turned-up portions 44. placed in Therefore, by setting the distance C to 30 mm or less, the outer end PA of the apex 38 is arranged at an appropriate position in consideration of securing the flexible zone. This tire 2 can improve durability while ensuring necessary rim assembly properties.

In this tire 2, the radial distance E from the bead base line to the outer end 58 of the steel reinforcing layer 20 is preferably 14 mm or more and preferably 20 mm or less. By setting the distance E to 14 mm or more, the steel reinforcing layer 20 can contribute to improving the rigidity of the bead portion BD. This tire 2 maintains good bead durability. By setting the distance E to 20 mm or less, the influence of the steel reinforcing layer 20 on the mass is suppressed. Also in this case, good bead durability is maintained because strain concentration on the outer end 58 of the steel reinforcing layer 20 is suppressed.

As described above, in this tire 2 , the outer end 58 of the steel reinforcing layer 20 is located radially inside the end 44 a of the folded portion 44 of the carcass ply 40 . In this tire 2 , the outer edge 58 of the steel reinforcement layer 20 is spaced from the edge 44 a of the turnup 44 . In this tire 2, strain occurring in the bead portion BD is effectively dispersed. From this point of view, in this tire 2 , the outer end 58 of the steel reinforcing layer 20 is positioned radially inwardly of the end 44 a of the turn-up portion 44 of the carcass ply 40 , and the outer end 58 of the steel reinforcing layer 20 extends from the turn-up portion. The radial distance to the end 44a of 44 is preferably 10 mm or more. From the viewpoint of strain dispersion, the larger the radial distance, the better. However, due to structural restrictions of the tire 2, the upper limit of the radial distance is 20 mm. The radial distance from the outer end 58 of the steel reinforcing layer 20 to the end 44a of the folded portion 44 is represented by the difference (CE) between the radial distance C and the radial distance E described above.

In FIG. 2, a double arrow ta indicates the thickness of the apex 38 at the end 44a of the folded portion 44. As shown in FIG. This thickness ta is represented by the length from the end 44 a of the folded portion 44 to the main body portion 42 . In this tire 2 , this thickness ta also includes the thickness of the strip 48 . This thickness ta is measured along the normal line of the main body portion 42 .

In this tire 2, the thickness ta of the apex 38 at the end 44a of the folded portion 44 is preferably 7.5 mm or more, and preferably 9.0 mm or less. By setting the thickness ta to 7.5 mm or more, the apex 38 contributes to improving the rigidity of the bead portion BD. Good bead durability is obtained in this tire 2 . By setting the thickness ta to 9.0 mm or less, the end 44a of the folded portion 44 is arranged further inside in the axial direction. In this tire 2, since the concentration of strain on the end 44a of the folded portion 44 is suppressed, the occurrence of damage originating from the end 44a of the folded portion 44 is prevented. Even in this case, the tire 2 can be improved in bead durability. Since the volume of the apex 38 is reduced, the tire 2 can achieve weight reduction and reduction in rolling resistance.

In FIG. 2, the double arrow ts is the thickness of the outer apex 38s. This thickness ts is measured along the normal for the measurement of the thickness ta described above. This thickness ts is the thickness of the outer apex 38 s at the end 44 a of the folded portion 44 .

In this tire 2, most of the apex 38 at the end 44a of the folded portion 44 is composed of the outer apex 38s that is softer than the inner apex 38u. In this tire 2 , the apex 38 effectively suppresses strain concentration on the end 44 a of the folded portion 44 . In this tire 2, the occurrence of damage originating from the end 44a of the folded portion 44 is prevented. From this point of view, the ratio of the thickness ts of the outer apex 38s to the thickness ta of the apex 38 at the end 44a of the folded portion 44 is preferably 0.6 or more, more preferably 0.7 or more. From the viewpoint of ensuring the rigidity of the apex 38, this ratio is preferably 0.9 or less.

In FIG. 2, the double arrow tc indicates the thickness of the portion outside the folded portion 44 at the end 44a of the folded portion 44. As shown in FIG. This thickness tc is represented by the length from the end 44a of the folded portion 44 to the side surface. This thickness tc is measured along the normal to side 34 .

In this tire 2, the folded portion 44 is arranged such that the space between the main body portion 42 and the folded portion 44 narrows toward the radially outer side. Therefore, in this tire 2 , the apex 38 at the end 44 a of the folded portion 44 is thinner than the outer portion from the folded portion 44 . In this tire 2, since the end 44a of the folded portion 44 is arranged further inside in the axial direction, concentration of strain on the end 44a of the folded portion 44 is suppressed. Since the occurrence of damage originating from the end 44a of the folded portion 44 is prevented, the tire 2 can improve the bead durability. From this point of view, the ratio of the thickness ta of the apex 38 to the thickness tc of the outer portion from the folded portion 44 is preferably 0.5 or more, more preferably 0.6 or more. This ratio is preferably 0.8 or less, more preferably 0.7 or less.

As described above, in this tire 2, the carcass cords are made of aramid cords. In this tire 2, the cord diameter of the carcass cord is preferably 0.8 mm or more, and preferably 0.9 mm or less. By setting the cord diameter to 0.8 mm or more, the carcass cord has an appropriate strength, so that cutting of the carcass cord is prevented. This tire 2 ensures necessary durability. By setting the cord diameter to 0.9 mm or less, the rigidity of the carcass 12 is appropriately maintained. In this tire 2, the influence of the carcass 12 on the rim assembly property is suppressed.

In this tire 2, the number of carcass cords included in the 50 mm width of the carcass ply 40 is preferably 20 or more, and preferably 40 or less. By setting this number to 20 or more, the load acting on the carcass cords is appropriately maintained. Since the carcass cords are prevented from being cut, this tire 2 ensures the required durability. By setting this number to 40 or less, the rigidity of the carcass 12 is appropriately maintained. In this tire 2, the influence of the carcass 12 on the rim assembly property is suppressed.

In FIG. 1, double-headed arrow ti is the total thickness of innerliner 18 and insulation 54 at the equatorial plane.

As described above, unlike steel cords, aramid cords do not rust, so in this tire 2 the inner liner 18 and the insulation 54 provided inside the carcass 12 can be made thinner. In the tire 2, the total thickness ti is preferably 2.5 mm or less from the viewpoint of weight reduction and rolling resistance reduction. From the viewpoint of maintaining the internal pressure of the tire 2, the total thickness ti is preferably 1.5 mm or more. In addition, in this tire 2, the ratio of the thickness of the inner liner 18 to the total thickness ti is appropriately set within the range of 0.3 to 0.7 times.

According to the present invention, it is possible to obtain a heavy-duty pneumatic tire 2 that achieves weight reduction while ensuring rim assemblability and durability. In particular, the present invention exhibits a remarkable effect in a tubeless heavy-duty pneumatic tire 2 having an aspect ratio of 75% or less, a cross-sectional width WS of 225 mm or less, and a load index of 129 or less.

The embodiments disclosed this time are illustrative in all respects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configuration described in the claims.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited only to these Examples.

[Example 1]
A heavy duty pneumatic tire (tire size=215/75R17.5) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

The flatness of Example 1 was 75%. A cord made of aramid fiber was used as the carcass cord. This is represented by an "A" in the "Carcass Code" column of the table. The cord diameter of this carcass cord was 0.87 mm. The ratio of the radial length F of the flexible zone to the sectional height V of the belt (F/V) was 0.35.

In Example 1, the ratio (H/V) of the radial distance H from the tire maximum width position PW to the outer end PA of the apex to the cross-sectional height V of the belt was 0.17. The radial distance C from the bead baseline to the end of the turnup was 28 mm. The radial distance E from the bead baseline to the outer edge of the steel reinforcing layer was 18 mm. Therefore, the difference (CE) between the radial distance C and the radial distance E was 10 mm. The total thickness ti of the inner liner and insulation was 2.5 mm. The apex thickness ta at the end of the folded portion was 7.5 mm.

[Comparative Example 1]
In the same manner as in Example 1, except that the cord diameter, ratio (F/V), ratio (H/V), distance C, distance E, thickness ti and thickness ta were set as shown in Table 1 below. , a tire of Comparative Example 1 was obtained. Comparative Example 1 is a conventional tire in which aramid cords (cord diameter=0.76 mm) are used as carcass cords.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1, except that a steel cord (cord diameter=0.85 mm) was used as the carcass cord. The fact that a steel cord was used as the carcass cord is indicated by "S" in the "Carcass cord" column of the table.

[Example 2-6]
Tires of Examples 2-6 were obtained in the same manner as in Example 1, except that the ratio (F/V) and ratio (H/V) were as shown in Tables 1 and 2 below.

[Example 7]
A tire of Example 7 was obtained in the same manner as in Example 1 except that the distance C, distance E, difference (CE), thickness ti and thickness ta were set as shown in Table 2 below.

[Example 8]
A tire of Example 8 was obtained in the same manner as in Example 1 except that the distance E, difference (CE), thickness ti and thickness ta were set as shown in Table 2 below.

[Example 9]
A tire of Example 9 was obtained in the same manner as in Example 1 except that the thickness ti and the thickness ta were set as shown in Table 2 below.

[Example 10]
A tire of Example 10 was obtained in the same manner as in Example 1, except that the thickness ta was set as shown in Table 2 below.

[mass]
The mass of the trial tire was measured. The results are indexed in Tables 1 and 2 below. The smaller the number, the lighter the weight.

[Bead durability]
The prototype tire was mounted on a rim (size=17.5×6.0) and filled with air to adjust the internal pressure of the tire to 700 kPa. This tire was mounted on a drum tester, applied with a load of 200% of the normal load, and run on a drum (drum diameter=1707 mm) at a speed of 20 km/h. The running time was measured until damage occurred in the bead portion. The results are indexed in Tables 1 and 2 below. The higher the value, the longer the running time and the better the bead durability. In this bead durability, an index value of 60 or more was set as an acceptance criterion.

[Rim assembly]
Ease of assembly of the tire to the rim was evaluated when the prototype tire was mechanically assembled to the rim (size = 17.5 x 6.0). The results are indexed in Tables 1 and 2 below. The higher the number, the easier it is to assemble the tire onto the rim.

[Sidewall crack (SW crack)]
The prototype tire was mounted on a rim (size=17.5×6.0) and filled with air to adjust the internal pressure of the tire to 700 kPa. This tire was mounted on a drum tester, applied with a load of 200% of the normal load, and run on a drum (drum diameter=1707 mm) at a speed of 20 km/h for 600 hours. After running, the side surface of the tire was observed to confirm the occurrence of sidewall cracks. The results are indexed in Tables 1 and 2 below. The larger the numerical value, the more suppressed the occurrence of sidewall cracks and the better the durability.

[Rolling resistance count (RRC)]
Using a rolling resistance tester, the rolling resistance coefficient was measured under the following measurement conditions. The results are indexed in Tables 1 and 2 below. The larger the number, the smaller the rolling resistance coefficient.
Rim used: 17.5 x 6.0
Internal pressure: 700kPa
Load: 14.17kN
Running speed: 80km/h

[Crease resistant chafer]
The external appearance of the trial tire and the cross section of the trial tire were observed to confirm the occurrence of crease chafer. The results are indexed in Tables 1 and 2 below. The larger the value, the more the crease chafer is suppressed and the better the crease chafer resistance.

As shown in Tables 1 and 2, it is confirmed that weight reduction is achieved while securing rim assemblability and durability in the examples. Examples are evaluated higher than Comparative Examples. From this evaluation result, the superiority of the present invention is clear.

The technique of securing flexible zones by applying aramid cords as carcass cords as described above can also be applied to various tires.

2 Tire 4 Tread 6 Sidewall 8 Bead 10 Chafer 12 Carcass 14 Belt 16 Cushion layer 18 Inner liner 20 Steel reinforcing layer 22 Tread surface 28 Circumferential groove 30 Land portion 34 Side surface 36 Core 38 Apex 38u Inner apex 38s・Outer apex 40 Carcass ply 42 Body portion 44 Folded portion 44a End of folded portion 44 54 Insulation 58 Outer end of steel reinforcement layer 20 60・・・Buttress

Claims (5)

A heavy-duty pneumatic tire having an aspect ratio of 75% or less,
a carcass extending from one bead to the other on the inside of the tread and a pair of sidewalls extending radially inward from the ends of the tread;
a belt positioned between the tread and the carcass;
a pair of cushioning layers positioned between the ends of the belt and the carcass;
The carcass has at least one carcass ply, the carcass ply includes a large number of parallel carcass cords, each carcass cord made of aramid fiber,
the bead comprises a core and an apex located radially outward of the core;
In the radial direction, a zone from the inner end of the cushion layer to the outer end of the apex is a flexible zone,
the ratio of the radial length of the flexible zone to the cross-sectional height of the belt is 0.32 or more and 0.45 or less;
A pneumatic tire for heavy loads, wherein the ratio of the radial distance from the tire maximum width position to the outer end of the apex to the sectional height of the belt is 0.13 or more and 0.20 or less. The carcass ply comprises a main body part that bridges one core and the other core, and a pair of folded parts connected to the main body part and folded back from the inner side to the outer side in the axial direction around the core,
The heavy-duty pneumatic tire according to claim 1, wherein the radial distance from the bead base line to the end of the folded portion is 24 mm or more and 30 mm or less. a pair of steel reinforcing layers located radially inward of the bead;
said steel reinforcing layers are folded axially inwardly outwardly around said core along said carcass plies;
3. The heavy duty pneumatic tire according to claim 1 or 2, wherein the radial distance from the bead base line to the outer end of the steel reinforcing layer positioned axially outward is 14 mm or more and 20 mm or less. the outer end of the steel reinforcing layer is positioned radially inward from the end of the folded portion;
4. The heavy duty pneumatic tire according to claim 3, wherein the radial distance from the outer edge of the steel reinforcing layer to the edge of the folded portion is 10 mm or more. The heavy duty pneumatic tire according to any one of claims 2 to 4, wherein the thickness of the apex at the end of the folded portion is 7.5 mm or more and 9.0 mm or less.

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