Tire

Abstract

To provide a tire 2 capable of achieving weight saving while securing rigidity.SOLUTION: A tire 2 includes: a pair of beads 10; a carcass 12; a pair of cord reinforcement layers 22; a pair of first rubber reinforcement layers 24; and a pair of second rubber reinforcement layers 26. The carcass 12 is composed of one carcass ply 34. The carcass ply 34 comprises a ply body 40 and a pair of folding parts 42. Each of the cord reinforcement layers 22 is positioned on the axial inside of the ply body 40.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to tires, and more particularly to tires mounted on vehicles used in racing. [Background technology]

[0002] Tyres fitted to vehicles driven at their limits, such as in races, need to be lightweight in order to transmit engine power to the road without loss. Methods for reducing the weight of tires include using thin sidewalls, shortening the folded-up portion of the carcass ply, etc. However, there are concerns that these methods may degrade the running performance of the tire, such as steering stability and durability. Studies are being conducted on reducing the weight of tires while taking into consideration the impact on driving performance (for example, Patent Document 1 listed below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-172104 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can achieve weight reduction while ensuring rigidity. [Means for solving the problem]

[0005] The tire according to the present invention includes a pair of beads each including a core and an apex located radially outward of the core, a carcass spanning between a first bead and a second bead, which are the pair of beads, a pair of cord reinforcing layers each including a number of parallel filler cords, a pair of first rubber reinforcing layers each located axially inward of each of the cord reinforcing layers, and a pair of second rubber reinforcing layers each located further axially inward of each of the first rubber reinforcing layers. The carcass is formed of a single carcass ply including a number of parallel carcass cords. The carcass ply includes a ply body spanning between the core of the first bead and the core of the second bead, and a pair of turn-up portions turned up at each of the cores. Each of the cord reinforcing layers is located axially inward of the ply body. Effect of the Invention

[0006] The present invention can provide a tire that can achieve weight reduction while maintaining rigidity. Although the tire of the present invention has a carcass composed of a single carcass ply, it can stably maintain the contact shape even when the vehicle is running at its limit, such as in a race. Moreover, since the portion including the tread (hereinafter, the tread portion) can be made thin, heat generated during running is less likely to accumulate in the tread portion. Since the temperature rise in the tread portion is suppressed, this tire can maintain the grip performance exhibited by the tread for a longer period of time than conventional tires. This tire can continue to exhibit good grip performance stably, and can reduce the frequency of tire replacement during a race. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a part of FIG. [Diagram 3] FIG. 2 is a schematic diagram illustrating the configuration of a carcass and a cord reinforcing layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The tire of the present invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire mounted on the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire mounted on the rim.

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is called a standard state. In the case where the subject of the present invention is a tire that cannot be driven on public roads, for example a tire used in races, the normal state of the tire is when the tire is mounted on a rim having a rim size of 18 x 13.0J, the internal pressure of the tire is adjusted to 180 kPa, and no load is applied to the tire.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in the meridian section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads is the same as the distance between the beads of the tire mounted on a regular rim. The tire configuration that cannot be confirmed when the tire is mounted on a regular rim is confirmed on the aforementioned cut surface.

[0011] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0012] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] In the present invention, the hardness of an element made of crosslinked rubber among elements constituting a tire is measured using a type A durometer under a temperature condition of 23° C. in accordance with the provisions of JIS K6253. In the present invention, the hardness is represented by the hardness at 23° C.

[0015] In the present invention, the Young's modulus of cords made of organic fibers used for cords such as carcass cords and filler cords is expressed as the apparent Young's modulus obtained using the initial tensile resistance specified in JIS L1017, section 8.8. The Young's modulus of metal cords such as steel cords is calculated from the slope of the straight line portion of a load-elongation curve that is plotted by conducting a test similar to that for obtaining the breaking load and total elongation at break specified in JIS G3510, section 6.4. The unit of Young's modulus is N / mm 2 It is.

[0016] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions. The center of the tread is also called the crown. The edges of the tread are also called the shoulders. The portion consisting of the bead portion and the sidewall portion is also called a side portion.

[0017] [Foundations underlying the present invention] The tire includes a carcass that spans between a pair of beads, that is, a first bead and a second bead. The carcass includes at least one carcass ply, and the carcass ply includes a number of carcass cords arranged in parallel. In a tire, the carcass ply is usually turned up at the bead. The carcass ply includes a ply body that spans between the first bead and the second bead, and a pair of turn-up portions that are continuous with the ply body and turned up at the bead.

[0018] In order to ensure the rigidity of the tire, the carcass is usually composed of two carcass plies. In the carcass composed of two carcass plies, when one is a first carcass ply and the other located radially outside the first carcass ply on the radially inside of the tread is a second carcass ply, the carcass may have a structure in which the first carcass ply and the second carcass ply are folded back from the inside to the outside in the axial direction at the bead (hereinafter, referred to as a 2-0 structure), or a structure in which the first carcass ply is folded back from the inside to the outside in the axial direction at the bead, and the second carcass ply is not folded back at the bead, and the end of the second carcass ply is disposed outside the folded back first carcass ply (hereinafter, referred to as a 1-1 structure). When focusing on the second carcass ply of both structures, the second carcass ply of the 2-0 structure has a ply body and a pair of turned-up portions, while the second carcass ply of the 1-1 structure is entirely the ply body. When focusing on the carcass structure in the bead portion of the tire, the second carcass ply of the 1-1 structure is disposed at a position closer to the outer surface of the tire than the ply body of the second carcass ply of the 2-0 structure.

[0019] In order to establish a technology that can achieve weight reduction while maintaining the rigidity of a tire, the inventors focused on the tension generated in the ply body of the carcass ply and calculated the change in tension of the ply body when a lateral force is applied to the tire by a simulation using the finite element method (FEM). As a result, the inventors confirmed that in the 2-0 structure, even when a lateral force is applied to the tire, there was almost no change in the tension of each of the ply bodies of the first carcass ply and the second carcass ply, whereas in the 1-1 structure, there was almost no change in the tension of the ply body of the first carcass ply, but the tension of the second carcass ply as the ply body increased, leading to the completion of the invention described below.

[0020] [Overview of the embodiment of the present invention] [Configuration 1] A tire according to one embodiment of the present invention comprises a pair of beads having a core and an apex located radially outward of the core, a carcass spanning between a first bead and a second bead of the pair of beads, a pair of cord reinforcement layers including a large number of filler cords arranged in parallel, a pair of first rubber reinforcement layers located axially inward of each of the cord reinforcement layers, and a pair of second rubber reinforcement layers located further axially inward of each of the first rubber reinforcement layers, wherein the carcass is constituted by a single carcass ply including a large number of carcass cords arranged in parallel, and the carcass ply comprises a ply body spanning between the core of the first bead and the core of the second bead, and a pair of turn-up portions folded back at each core, and each of the cord reinforcement layers is located axially inward of the ply body.

[0021] By arranging the tire in this manner, the tire can be made lighter while maintaining its rigidity.

[0022] [Configuration 2] Preferably, in the tire according to the above-mentioned [Configuration 1], the Young's modulus of the carcass cords is lower than the Young's modulus of the filler cords.

[0023] [Configuration 3] Preferably, in the tire according to the above-mentioned [Configuration 1] or [Configuration 2], the second rubber reinforcing layer is folded back on the core.

[0024] [Configuration 4] Preferably, in the tire according to any one of the above-mentioned [Configuration 1] to [Configuration 3], an intersection between the following reference line and the ply body is located radially inward of an inner end of the cord reinforcement layer. Reference line: A straight line extending radially from the axial outside of the core, circumscribing the core.

[0025] [Configuration 5] Preferably, in the tire according to any one of the above-mentioned [Configuration 1] to [Configuration 4], an outer end of the first rubber reinforcing layer is located radially outward of a maximum width position of the tire.

[0026] [Configuration 6] Preferably, in the tire described in the above-mentioned [Configuration 5], an outer end of the cord reinforcing layer is located radially outward of an outer end of the first rubber reinforcing layer, and an outer end of the second rubber reinforcing layer is located radially outward of an outer end of the cord reinforcing layer.

[0027] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0028] 1 shows a portion of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on a racing vehicle that runs on a circuit. This tire 2 is a pneumatic tire for racing.

[0029] FIG. 1 shows a portion of a cross section of a tire 2 taken along a plane including the rotation axis (not shown) of the tire 2. The cross section shown in FIG. 1 is also called a meridian cross section. The direction indicated by the double arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double arrow RD is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, a dashed dotted line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0030] In FIG. 1, a tire 2 is mounted on a rim R. The rim R is a regular rim. A solid line BBL extending in the axial direction is a bead base line. The bead base line is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0031] 1 is the intersection point between the outer surface of the tire 2 and the equatorial plane. The intersection point PC is also called the equator of the tire 2. When a groove is located on the equatorial plane, the equator PC is determined based on a virtual outer surface obtained by assuming that there is no groove. The equator PC is also the radially outer end of the tire 2. 1, the length indicated by the double arrow HS is the radial distance from the bead base line to the equator PC. The radial distance HS obtained in a normal tire 2 is the cross-sectional height of the tire 2 (see JATMA, etc.).

[0032] 1, the position indicated by the symbol PW is the axial outer end of the tire 2. This outer end PW is also referred to as the maximum width position of the tire 2 (hereinafter, the maximum tire width position). The maximum tire width position PW is determined for a tire 2 in a normal state. If there is decoration such as a pattern or lettering on the outer surface of the tire 2, the maximum tire width position PW is determined based on a virtual outer surface obtained by assuming that there is no decoration. 1, the length indicated by the double-headed arrow HW is the radial distance from the bead base line to the maximum tire width position PW. The radial distance HW is also called the maximum tire width height. In tire 2, a ratio (HW / HS) of tire maximum width height HW to section height HS is equal to or greater than 0.40 and is equal to or less than 0.60.

[0033] The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, an inner liner 18, a pair of chafers 20, a pair of cord reinforcing layers 22, a pair of first rubber reinforcing layers 24, and a pair of second rubber reinforcing layers 26.

[0034] Fig. 2 shows a part of the tire 2 shown in Fig. 1. Fig. 3 shows the configuration of the carcass 12 and the cord reinforcing layer 22 at the tire maximum width position PW when the side surface of the tire 2 is viewed from the axially outer side. Each element constituting the tire 2, such as a tread 4, will be described with reference to FIGS. 1-3.

[0035] The tread 4 is located radially outside the carcass 12. The tread 4 extends in the circumferential direction. The tire 2 comes into contact with the road surface at the tread 4. The outer peripheral surface of the tread 4 includes a tread surface 28 that comes into contact with the road surface. The tread surface 28 includes the above-mentioned equator PC. The tread 4 is made of crosslinked rubber. Although not described in detail, a portion including a tread surface 28 of the tread 4 is made of crosslinked rubber in consideration of grip performance.

[0036] The tread 4 shown in Fig. 1 has no grooves. The tire 2 is a slick type. The tread 4 may have grooves to form a tread pattern.

[0037] Each sidewall 6 is continuous with the tread 4. The sidewalls 6 are located axially outward of the carcass 12. The sidewalls 6 form the outer surface of the tire 2 (more specifically, the side surface of the tire 2). The sidewalls 6 are made of crosslinked rubber. The sidewalls 6 protect the carcass 12.

[0038] Each clinch 8 is located radially inward of the maximum width position PW. The clinches 8 are located axially outward of the carcass 12. The clinches 8 are located between the carcass 12 and the rim R. The clinches 8 are made of crosslinked rubber. The clinches 8 have higher rigidity than the sidewalls 6. The clinches 8 of this tire 2 are covered by the sidewalls 6.

[0039] Each bead 10 is located axially inward of the clinch 8. The beads 10 are located radially inward of the clinch 8. The bead 10 includes a core 30 and an apex 32 . The core 30 is a cable bead having a circular cross-sectional shape. Although not shown, the core 30 is formed by winding a plurality of sheath wires in a spiral shape around a core wire. The position indicated by the symbol CG in FIG. 2 is the radially outer end of the core 30. The apex 32 is located radially outward of the core 30. The apex 32 is tapered. The apex 32 is made of a crosslinked rubber having high hardness. Specifically, the hardness of the apex 32 is 80 or more and 95 or less.

[0040] The carcass 12 is located on the inside of the tread 4 and the pair of sidewalls 6. The carcass 12 bridges between a first bead 10 (not shown) and a second bead 10, which are a pair of beads 10. The carcass 12 of the tire 2 is composed of one carcass ply 34.

[0041] 3, the carcass ply 34 includes a number of parallel carcass cords 36. For ease of explanation, the carcass cords 36 are represented by solid lines, but in the carcass ply 34, the carcass cords 36 are covered with a topping rubber 38. Although not shown, the carcass cord 36 intersects with the equatorial plane. The angle that the carcass cord 36 makes with the equatorial plane (hereinafter, the intersection angle) is equal to or greater than 70 degrees and equal to or less than 90 degrees. The carcass 12 of this tire 2 has a radial structure. In the carcass 12 of the tire 2, the crossing angle of the carcass cords 36 is 90 degrees. The carcass cords 36 shown in Fig. 3 extend in the radial direction.

[0042] The carcass cord 36 is a cord (organic fiber cord) made of organic fibers. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0043] The carcass ply 34 is turned up at each bead 10. The carcass ply 34 of the tire 2 is turned up at each bead 10 from the inside toward the outside in the axial direction. The carcass ply 34 includes a ply body 40 and a pair of turn-up portions 42. The ply body 40 spans between the core 30 of the first bead 10 and the core 30 of the second bead 10. Each turn-up portion 42 is continuous with the ply body 40 and is turned up around the core 30. 2, an end 42e of the turned-up portion 42 of the tire 2 is located radially inward of the tire maximum width position PW. The end 42e of the turned-up portion 42 is joined to the ply body 40 radially outward of the outer end 32e of the apex 32. The bead 10 of the tire 2 is entirely covered with the carcass ply 34.

[0044] 1 is the axially outer end of the ply body 40. This axially outer end PM is also called the ply maximum width position. The ply maximum width position PM is represented by the axially outer end of the ply body 40 of the carcass ply 34 including the turn-up portion 42 in the tire 2 in a normal state. This turn-up portion 42 is formed by turning up the carcass ply 34 at the core 30 from the axially inner side to the axially outer side.

[0045] The ply maximum width position PM is located near the tire maximum width position PW. The ply maximum width position PM of the tire 2 coincides with the tire maximum width position PW in the radial direction. The ply maximum width position PM may be located radially outward of the tire maximum width position PW. In this case, the radial distance from the ply maximum width position PM to the tire maximum width position PW is preferably 3 mm or less.

[0046] The belt 14 is located between the tread 4 and the carcass 12 in the radial direction. The belt 14 is laminated on the carcass 12 on the radially inner side of the tread 4. The belt 14 is composed of two belt plies 44 laminated in the radial direction. The belt ply 44 located on the inner side (hereinafter, inner belt ply 44u) has an axial width larger than the axial width of the belt ply 44 located on the outer side (hereinafter, outer belt ply 44s). Although not shown, each of the inner belt ply 44u and the outer belt ply 44s includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. In the tire 2, the belt cords are steel cords.

[0047] The band 16 is located between the tread 4 and the belt 14 in the radial direction. The band 16 is laminated on the belt 14 on the radially inner side of the tread 4. Although not shown, the band 16 includes a band cord wound in a spiral shape. The band cord extends substantially in the circumferential direction. The angle that the band cord makes with the circumferential direction is 5 degrees or less. The band 16 has a jointless structure. The band cord is an organic fiber cord. Examples of organic fibers include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0048] The band 16 covers the entire belt 14. This band 16 is a full band. This band 16 may be composed of a pair of edge bands that cover each end of the belt 14. This band 16 may be composed of a full band and a pair of edge bands.

[0049] The inner liner 18 is positioned inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber with excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0050] Each chafer 20 is located radially inward of the bead 10. A portion of the chafer 20 contacts the rim R. The chafer 20 of the tire 2 is made of a cloth and rubber impregnated into the cloth.

[0051] Each cord reinforcement layer 22 is located between the carcass 12 and the inner liner 18 in the axial direction. The entire cord reinforcement layer 22 is laminated on the ply body 40. An outer end 22g of the cord reinforcement layer 22 is located radially outward from the tire maximum width position PW. An inner end 22n of the cord reinforcement layer 22 is located radially inward from an end 42e of the turned-up portion 42. The inner end 22n of the cord reinforcement layer 22 is located radially inward from an outer end 32e of the apex 32.

[0052] As shown in Fig. 3, the cord reinforcement layer 22 includes a large number of parallel filler cords 46. For ease of explanation, Fig. 3 shows a part of the cord reinforcement layer 22 located on the inner side of the carcass ply 34, and indicates the filler cords 46 covered with a topping rubber 48 by solid lines.

[0053] The filler cord 46 is a steel cord or an organic fiber cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber. The cord reinforcing layer 22 reinforces the bead portion. From this viewpoint, the filler cord 46 is preferably a cord made of aramid fiber or a steel cord. As shown in Fig. 3, the filler cord 46 is inclined with respect to the carcass cord 36. The angle indicated by the symbol θ in Fig. 3 is the angle that the filler cord 46 makes with respect to the carcass cord 36 at the maximum width position PW (hereinafter, referred to as the inclination angle of the filler cord 46). The inclination angle θ of the filler cord 46 of the tire 2 is equal to or greater than 70 degrees and equal to or less than 80 degrees.

[0054] Each of the first rubber reinforcing layers 24 is located axially inside the cord reinforcing layer 22. The first rubber reinforcing layers 24 are located radially outside the apex 32. A ply body 40 is located radially inside the inner end 22n of the cord reinforcing layer 22 between the first rubber reinforcing layer 24 and the apex 32. The first rubber reinforcing layers 24 are made of hard crosslinked rubber.

[0055] 2, the first rubber reinforcing layer 24 is thick at its center, tapers inward from the center, and tapers outward. The first rubber reinforcing layer 24 includes a body 50, an inner tapered portion 52 located radially inside the body 50, and an outer tapered portion 54 located radially outside the body 50. The inner tapered portion 52 includes an inner end 24n of the first rubber reinforcing layer 24, and tapers from the body 50 toward the inner end 24n. The outer tapered portion 54 includes an outer end 24g of the first rubber reinforcing layer 24, and tapers from the body 50 toward the outer end 24g.

[0056] An inner end 24n of the first rubber reinforcing layer 24 is located radially inside of an inner end 22n of the cord reinforcing layer 22. The inner end 24n of the first rubber reinforcing layer 24 of the tire 2 is located radially inside of an outer end CG of the core 30. An outer end 24g of the first rubber reinforcing layer 24 is located radially inside of an outer end 22g of the cord reinforcing layer 22.

[0057] 1 is the radial height of the first rubber reinforcing layer 24. The radial height HP is the radial distance from the bead base line to the outer end 24g of the first rubber reinforcing layer 24. An outer end 24g of the first rubber reinforcing layer 24 is located radially outward of the tire maximum width position PW. Specifically, the ratio (HP / HW) of the radial height HP of the first rubber reinforcing layer 24 to the tire maximum width height HW is 1.05 or greater and 1.10 or less.

[0058] Each of the second rubber reinforcing layers 26 is located axially further inward from the first rubber reinforcing layers 24. The second rubber reinforcing layers 26 are made of a hard crosslinked rubber. The outer end 26g of the second rubber reinforcing layer 26 of the tire 2 is located radially outside the outer end 22g of the cord reinforcing layer 22. In the radially inner portion of the outer end 24g of the first rubber reinforcing layer 24, the second rubber reinforcing layer 26 is sheet-shaped. In the radially inner portion of the inner end 24n of the first rubber reinforcing layer 24, the second rubber reinforcing layer 26 is folded back at the core 30 along the carcass ply 34. The inner end 26n of the second rubber reinforcing layer 26 of the tire 2 is located axially outside the folded-back portion 42. It is located between the outer end CG of the core 30 and the outer end 32e of the apex 32 in the radial direction. The inner end 26n of the second rubber reinforcing layer 26 is located radially between the outer end CG of the core 30 and the outer end 32e of the apex 32.

[0059] 2, the first rubber reinforcing layer 24 and the cord reinforcing layer 22 are located in a space surrounded by the second rubber reinforcing layer 26 and the ply body 40. The first rubber reinforcing layer 24 and the cord reinforcing layer 22 fill the space surrounded by the second rubber reinforcing layer 26 and the ply body 40. The second rubber reinforcing layer 26, the first rubber reinforcing layer 24, and the cord reinforcing layer 22 are located between the inner liner 18 and the ply body 40.

[0060] As described above, the carcass ply 34 is turned up from the inside to the outside in the axial direction at each bead 10. This forms the carcass ply 34 with a ply body 40 and a pair of turned-up portions 42. Since the carcass 12 of this tire 2 has a radial structure, the carcass cord 36 included in the ply body 40 spans between the core 30 of the first bead 10 and the core 30 of the second bead 10. The side portion of the tire 2 is bent by the load acting on the tire 2. This increases the tension of the carcass cords 36 included in the ply body 40. This increase in tension increases the rigidity of the tire 2.

[0061] When the side of the tire 2 is deflected, the inner portion of the side is compressed and the outer portion is stretched. On the axially inner side of the ply body 40, from the sidewall 6 side toward the inner liner 18 side, the cord reinforcing layer 22, the first rubber reinforcing layer 24, and the second rubber reinforcing layer 26 are located. Compared to the ply body of a conventional tire that does not have the cord reinforcing layer 22, the first rubber reinforcing layer 24, and the second rubber reinforcing layer 26, the ply body 40 of this tire 2 is located at a position closer to the outer surface of the tire 2. A force in the tensile direction acts more effectively on the ply body 40 of this tire 2 than on the ply body of a conventional tire. The tension generated in the ply body 40 of this tire 2 is higher than the tension generated in the ply body of a conventional tire.

[0062] In this tire 2, not only is the ply body 40 disposed closer to the outer surface of the tire 2 than in conventional tires, but the cord reinforcing layer 22 is located axially inside the ply body 40. Since the cord reinforcing layer 22 acts to resist a force acting in a tensile direction inside the ply body 40, the force in the tensile direction acts effectively on the ply body 40. In the ply body 40 of this tire 2, tension is effectively increased.

[0063] Furthermore, the cord reinforcing layer 22 is located axially inside the ply body 40, the first rubber reinforcing layer 24 is located axially inside the cord reinforcing layer 22, and the second rubber reinforcing layer 26 is located axially inside the first rubber reinforcing layer 24. In other words, of the cord reinforcing layer 22, the first rubber reinforcing layer 24, and the second rubber reinforcing layer 26, which are located axially inside the ply body 40, the cord reinforcing layer 22 is located at a position closest to the ply body 40. This arrangement of the cord reinforcing layer 22 can contribute to increasing the tension generated in the ply body 40.

[0064] A higher tension is generated in the ply body 40 of this tire 2 compared to that of conventional tires. The higher tension increases the rigidity of the tire 2. This tire 2 can stably maintain the contact shape even when the vehicle is traveling at its limit, such as in a race. The tread 4 of this tire 2 can fully demonstrate its function. This tire 2 can improve grip performance. Moreover, as described above, the carcass 12 of the tire 2 is composed of one carcass ply 34. Although the carcass 12 of the tire 2 is composed of one carcass ply 34, the tire 2 can stably maintain a contact shape even when the vehicle is running at its limit, such as in a race. Since the carcass 12 is made up of one carcass ply 34, the carcass 12 is lighter than a conventional carcass made up of two carcass plies. The tire 2 can achieve a reduced weight while maintaining rigidity.

[0065] Furthermore, in this tire 2, the carcass 12 is composed of a single carcass ply 34, so the tread portion can be made thin. Heat generated during driving is less likely to accumulate in the tread portion. Because the temperature rise in the tread portion is suppressed, this tire 2 can maintain the grip performance exhibited by the tread 4 for a longer period of time than conventional tires. This tire 2 can continue to stably exhibit good grip performance, and can reduce the frequency of tire 2 replacement during a race.

[0066] When the side portion bends, a compressive force acts on the inner portion. The first rubber reinforcing layer 24 and the second rubber reinforcing layer 26, which are located axially inside the cord reinforcing layer 22, are made of hard crosslinked rubber, similar to the apex 32. The side portion bends flexibly. The tension in the ply body 40 changes in conjunction with the bending. The tension generated in the ply body 40 can effectively contribute to the grip performance of the tire 2. From this viewpoint, it is preferable that the first rubber reinforcing layer 24 and the second rubber reinforcing layer 26 have a hardness similar to that of the apex 32. Specifically, it is preferable that the difference between the hardness of the first rubber reinforcing layer 24 and the apex 32 is -5 or more and 5 or less, and the difference between the hardness of the second rubber reinforcing layer 26 and the apex 32 is -5 or more and 5 or less. The difference in hardness between the first rubber reinforcing layer 24 and the apex 32 is preferably −3 or more and 3 or less, and the difference in hardness between the second rubber reinforcing layer 26 and the apex 32 is more preferably −3 or more and 3 or less.

[0067] In this tire 2, it is preferable that the Young's modulus Yc of the carcass cords 36 is lower than the Young's modulus Yf of the filler cords 46. Since the cord reinforcing layer 22 located on the inner side of the ply body 40 has high rigidity, the ply body 40, which has a lower rigidity than the cord reinforcing layer 22, is effectively stretched. Since the force in the tensile direction acts effectively on the ply body 40, the tension generated in the ply body 40 is effectively increased. Since the tension generated in the ply body 40 is effectively increased, the tire 2 can improve the grip performance. From this viewpoint, it is more preferable that the ratio (Yc / Yf) of the Young's modulus Yc of the carcass cords 36 to the Young's modulus Yf of the filler cords 46 is 0.8 or less. From the viewpoint of ensuring the rigidity of the ply body, it is more preferable that the ratio (Yc / Yf) is 0.6 or more.

[0068] From the viewpoint of obtaining a filler cord 46 having a high Young's modulus Yf and a carcass cord 36 having a low Young's modulus Yc, it is preferable that the filler cord 46 is a steel cord or a cord made of aramid fiber, and when the filler cord 46 is a steel cord, the carcass cord 36 is a cord made of nylon fiber, rayon fiber, polyester fiber, or aramid fiber, and when the filler cord 46 is a cord made of aramid fiber, the carcass cord 36 is a cord made of nylon fiber, rayon fiber, or polyester fiber. It is more preferable that the filler cord 46 is a steel cord, and the carcass cord 36 is a cord made of polyester fiber.

[0069] From the viewpoint of effectively improving the grip performance of the tire 2, the Young's modulus Yc of the carcass cord 36 is set to 1400 N / mm 2 It is preferable that the strength is equal to or more than 1600N / mm 2 More preferably, it is 1600N / mm 2 From the viewpoint of ensuring the flexure of the side portion, the Young's modulus Yc of the carcass cord 36 is preferably 2800 N / mm 2 It is preferable that:

[0070] 1, the length indicated by the double-headed arrow HP is the radial height of the first rubber reinforcing layer 24. The radial height HP is the radial distance from the bead baseline to the outer end 24g of the first rubber reinforcing layer 24. The length indicated by the double-headed arrow HQ is the radial height of the cord reinforcing layer 22. The radial height HQ is the radial distance from the bead baseline to the outer end 22g of the cord reinforcing layer 22. The length indicated by the double-headed arrow HR is the radial height of the second rubber reinforcing layer 26. The radial height HR is the radial distance from the bead baseline to the outer end 26g of the second rubber reinforcing layer 26.

[0071] The outer end 22g of the cord reinforcing layer 22 is located radially outside the outer end 24g of the first rubber reinforcing layer 24. In other words, the outer end 22g of the cord reinforcing layer 22 is located away from the outer end 24g of the first rubber reinforcing layer 24. This suppresses concentration of strain on the outer end 22g of the cord reinforcing layer 22 or the outer end 24g of the first rubber reinforcing layer 24. The tire 2 can maintain good durability. The tire 2 can stably exhibit the effect of arranging the ply body 40 in a position close to the outer surface of the tire 2. From this viewpoint, it is preferable that the outer end 22g of the cord reinforcing layer 22 is located radially outside the outer end 24g of the first rubber reinforcing layer 24. Specifically, the ratio (HQ / HP) of the radial height HQ of the cord reinforcing layer 22 to the radial height HP of the first rubber reinforcing layer 24 is preferably 1.10 or more, and more preferably 1.15 or more. In order to maintain a good ride comfort, the ratio (HQ / HP) is preferably equal to or less than 1.30, and more preferably equal to or less than 1.25.

[0072] The outer end 26g of the second rubber reinforcing layer 26 is located radially outward of the outer end 22g of the cord reinforcing layer 22. In other words, the outer end 26g of the second rubber reinforcing layer 26 is located away from the outer end 22g of the cord reinforcing layer 22. This suppresses concentration of strain on the outer end 26g of the second rubber reinforcing layer 26 or the outer end 22g of the cord reinforcing layer 22. The tire 2 can maintain good durability. The tire 2 can stably exhibit the effect of arranging the ply body 40 in a position close to the outer surface of the tire 2. From this viewpoint, it is preferable that the outer end 26g of the second rubber reinforcing layer 26 is located radially outward of the outer end 22g of the cord reinforcing layer 22. Specifically, the ratio (HR / HQ) of the radial height HR of the second rubber reinforcing layer 26 to the radial height HQ of the cord reinforcing layer 22 is preferably 1.15 or more, and more preferably 1.20 or more. In order to maintain a good ride comfort, the ratio (HR / HQ) is preferably equal to or less than 1.35, and more preferably equal to or less than 1.30.

[0073] From the viewpoint of enabling the tire 2 to maintain good durability and stably exerting the effect of disposing the ply body 40 at a position close to the outer surface of the tire 2, it is more preferable that the outer end 22g of the cord reinforcing layer 22 is located radially outside the outer end 24g of the first rubber reinforcing layer 24, and the outer end 26g of the second rubber reinforcing layer 26 is located radially outside the outer end 22g of the cord reinforcing layer 22. Specifically, it is more preferable that the ratio (HQ / HP) of the radial height HQ of the cord reinforcing layer 22 to the radial height HP of the first rubber reinforcing layer 24 is 1.10 or more and 1.30 or less, and the ratio (HR / HQ) of the radial height HR of the second rubber reinforcing layer 26 to the radial height HQ of the cord reinforcing layer 22 is 1.15 or more and 1.35 or less.

[0074] As described above, in the tire 2, in the radially inner portion of the inner end 24n of the first rubber reinforcing layer 24, the second rubber reinforcing layer 26 is folded back at the core 30 along the carcass ply 34. The second rubber reinforcing layer 26 effectively increases the rigidity around the bead 10. Since the core 30 is stably held, a force in the tensile direction acts effectively on the ply body 40. The tire 2 can effectively increase the tension generated in the ply body 40. The tire 2 can exhibit good grip performance. From this viewpoint, it is preferable that the second rubber reinforcing layer 26 is folded back at the core 30.

[0075] As described above, the second rubber reinforcing layer 26 has a hardness similar to that of the apex 32. The second rubber reinforcing layer 26 having a hardness similar to that of the apex 32 is folded back by the core 30. Since the core 30 is held more stably, the force in the tensile direction acts more effectively on the ply body 40. From this viewpoint, it is more preferable that the second rubber reinforcing layer 26 having a hardness similar to that of the apex 32 is folded back by the core 30.

[0076] 2, a solid line RL is a straight line extending in the radial direction from the axially outer side of the core 30, circumscribing the core 30. In the present invention, this straight line RL is also called a reference line. The position indicated by the symbol PR is the intersection of the reference line RL and the ply body 40. As shown in FIG. 2, the intersection point PR is located radially inward of the inner end 22n of the cord reinforcement layer 22. As a result, the ply body 40 of this tire 2 is located closer to the outer surface of the tire 2 than that of a conventional tire. A tensile force acts more effectively on the ply body 40 of this tire 2 than on the ply body of a conventional tire. The tire 2 can effectively increase the tension generated in the ply body 40. The tire 2 can exhibit good grip performance. From this viewpoint, when a straight line extending radially from the axial outside of the core 30 to circumscribe the core 30 is defined as a reference line RL, it is preferable that the intersection point PR between the reference line RL and the ply body 40 is located radially inward of the inner end 22n of the cord reinforcement layer 22.

[0077] In FIG. 2, the solid line indicated by the symbol WL is a straight line that passes through the tire maximum width position PW and extends in the axial direction. The length indicated by the double-headed arrow TW is the thickness of the tire 2 measured along the straight line WL. This thickness TW is also called the maximum width position thickness. The solid line indicated by the symbol AL is a straight line that passes through the outer end 32e of the apex 32 and extends in the axial direction. The length indicated by the double-headed arrow TA is the thickness of the tire 2 measured along the straight line AL. This thickness TA is also called the apex outer end position thickness. The length indicated by the double-headed arrow TB is the thickness of the outer portion from the outer end 32e of the apex 32. This thickness TB is the distance from the outer end 32e of the apex 32 to the outer surface of the tire 2 measured along the straight line AL.

[0078] The side portion of the tire 2 is configured so that its thickness is maximum near the flange of the rim R and gradually decreases from the position showing the maximum thickness to the vicinity of the outer end 26g of the second rubber reinforcing layer 26. In the tire 2, the apex outer end position thickness TA is thicker than the maximum width position thickness TW. Specifically, the ratio (TA / TW) of the apex outer end position thickness TA to the maximum width position thickness TW is 2.3 or more and 2.9 or less. In this tire 2, the thickness of the inner portion of the ply body 40 is adjusted, and the ply body 40 is disposed at a position close to the outer surface of the tire 2. This allows a force in the tensile direction to be effectively applied to the ply body 40, and effectively increases the tension generated in the ply body 40. From this viewpoint, it is preferable that the thickness TB of the outer portion of the apex 32 from the outer end 32e is equal to or thinner than the thickness of the inner portion of the apex 32 from the outer end 32e. In other words, it is preferable that the thickness TB of the outer portion of the apex 32 from the outer end 32e is equal to or smaller than the thickness TA at the apex outer end. From the viewpoint of more effectively increasing the tension generated in the ply body 40, it is more preferable that the ratio (TB / TA) of the thickness TB of the outer portion from the outer end 32e of the apex 32 to the thickness TA at the outer end of the apex is 0.48 or less. 2, the ply body 40 has an outwardly curved shape at the side portion. From the viewpoint of enabling the ply body 40 to stably maintain the curved shape, the ratio (TB / TA) is preferably 0.40 or more, and more preferably 0.44 or more.

[0079] As is clear from the above description, the present invention provides a tire that can achieve weight reduction while ensuring rigidity. The present invention is particularly effective in tires having a tire size of 300 / 680R18 to 330 / 710R18 and an aspect ratio of 30 to 45%. EXAMPLES

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] [Example 1] A pneumatic tire (tire size=330 / 710R18) having the basic structure shown in FIG. 1-3 and the specifications shown in Table 1 below was obtained.

[0082] The carcass is composed of one carcass ply. The thickness of the carcass ply is set to 1.05 mm. The carcass cord is made of polyester fiber and has a Young's modulus of 1400 N / mm 2 It is. The thickness of the tread portion of this tire 2 is 10.95 mm. The filler cord in the cord reinforcing layer is a steel cord. The first and second rubber reinforcing layers are made of the same cross-linked rubber as Apex (hardness 90). The fact that the cord reinforcement layer is located axially inside the ply body is indicated by "in" in the "Cord Reinforcement Layer" column. The fact that the intersection of the reference line extending radially, circumscribing the core from the axial outside of the core, and the ply body is located radially inside the inner end of the cord reinforcement layer is indicated by "in" in the "Intersection" column.

[0083] [Example 2-3] Tires of Examples 2-3 were obtained in the same manner as in Example 1, except that the thickness of the carcass cord was changed and the Young's modulus, the thickness of the carcass ply, and the thickness of the tread portion were set as shown in Table 1 below.

[0084] [Comparative Example 1] The tire size of Comparative Example 1 is the same as that of Example 1. The carcass structure of Comparative Example 1 is a 1-1 structure. The same cords as those of Example 1 are used for the carcass cords of the two carcass plies. The thickness of the tread is 12.00 mm. Comparative Example 1 does not have a first rubber reinforcing layer and a second rubber reinforcing layer. The apex is made of the same material as the apex of Example 1, but the outer end position of the apex is disposed at the same position as the outer end position of the first rubber reinforcing layer of Example 1. Comparative Example 1 employs a cord reinforcement layer having the same specifications as the cord reinforcement layer of Example 1, but it is disposed axially outward of the bead. Therefore, it is disposed axially outward of the ply body of the first ply. This is indicated by "out" in the "Cord Reinforcement Layer" column. The intersection of the reference line extending radially, circumscribing the core from the axially outer side of the core, and the ply body is located radially outward of the inner end of the cord reinforcement layer, and this is indicated by "out" in the "Intersection" column.

[0085] [Comparative Example 2] A tire of Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that the thickness of the carcass cord was changed and the Young's modulus, the thickness of the carcass ply, and the thickness of the tread portion were set as shown in Table 1 below.

[0086] [Comparative Example 3] A tire of Comparative Example 3 was obtained in the same manner as Comparative Example 1, except that the carcass structure was a "1-0" structure and the thickness of the tread portion was 10.95 mm.

[0087] [Horizontal spring] The lateral springiness of the prototype tires was measured using a static testing machine under the following conditions. The results are shown in Table 1 below as an index, with Comparative Example 1 being indexed at 100. The larger the value, the greater the lateral springiness, which is preferable. Rim: 18×13.0J Internal pressure: 180kPa Vertical load: 5.88kN

[0088] [Cornering Force (CF)] The prototype tire was mounted on a rim (size = 18 x 13.0J), and the tire was filled with air to adjust the internal pressure to 180 kPa. The tire was mounted on a flat belt testing machine, and a low load of 1.96 kN and a high load of 7.84 kN were applied, and the cornering force was measured when the tire was run at a speed of 80 km / h with a slip angle of 4 degrees. The results are shown in Table 1 below, with Comparative Example 1 being indexed to 100. The larger the value, the higher the cornering force, which is preferable.

[0089] [Wear resistance] The prototype tire was mounted on a rim (size = 18 x 13.0J) and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a racing vehicle. A driver with professional skills drove the vehicle on a racing circuit. After 30 laps, the tread thickness at the most worn point was measured to obtain the remaining tread ratio. The results are shown in Table 1 below. The higher the value, the more wear is suppressed, which is preferable.

[0090] [Heat dissipation] The prototype tire was mounted on a rim (size = 18 x 13.0J), and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a racing vehicle. A driver with professional skills drove the vehicle on a racing circuit. The temperature of the inner surface of the tread was measured using a non-contact thermometer attached to the valve of the rim to obtain the saturation temperature. The results are shown in Table 1 below, with Comparative Example 1 being indexed at 100. The smaller the value, the more heat dissipation is promoted, which is preferable.

[0091] [Lap time decrease rate] The prototype tire was mounted on a rim (size = 18 x 13.0J) and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a racing vehicle. A driver with professional skills drove the vehicle on a racing circuit. The vehicle was driven for 30 laps, and the lap times were measured. The ratio of the lap time on the 30th lap to the best time (fastest time) was calculated (the rate of decrease in lap time). The results are shown as an index in Table 1 below. The closer the value is to 100.0, the more suppressed the decrease in lap time is, which is preferable.

[0092] [Table 1]

[0093] As shown in Tables 1 and 2, the Examples were rated higher than the Comparative Examples. In particular, the Examples achieved improved high-speed durability while suppressing deterioration in steering stability. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0094] The above-described technology that can achieve weight reduction while maintaining rigidity can be applied to various tires. [Explanation of symbols]

[0095] 2. Tires 4. Tread 6. Sidewall 8. Clinch 10 Bead 12. Carcass 22 Cord reinforcement layer 24... First rubber reinforcing layer 26 Second rubber reinforcing layer 34···Carcass ply 36···Carcass cord 40···Ply body 42... Folded part 46 Filler code

Claims

1. A pair of beads each including a core and an apex located radially outward of the core; a carcass that bridges between the pair of beads, the first bead and the second bead; A pair of cord reinforcing layers including a number of parallel filler cords; A pair of first rubber reinforcing layers located axially inside each of the cord reinforcing layers; A pair of second rubber reinforcing layers located axially further inward of each of the first rubber reinforcing layers; Equipped with The carcass is composed of one carcass ply including a large number of carcass cords arranged in parallel, The carcass ply includes a ply body that spans between a core of the first bead and a core of the second bead, and a pair of turn-up portions that are turned up at the respective cores, Each of the cord reinforcement layers is located axially inside the ply body. tire.

2. The Young's modulus of the carcass cord is lower than the Young's modulus of the filler cord.

2. The tire of claim 1.

3. The second rubber reinforcing layer is folded over the core.

2. The tire of claim 1.

4. The intersection of the following reference line and the ply body is located radially inside the inner end of the cord reinforcement layer:

2. The tire of claim 1. Reference line: A straight line extending radially from the axially outer side of the core to circumscribe the core.

5. an outer end of the first rubber reinforcing layer is located radially outward of a maximum width position of the tire; A tire according to any one of claims 1 to 4.

6. an outer end of the cord reinforcing layer is located radially outside an outer end of the first rubber reinforcing layer, and an outer end of the second rubber reinforcing layer is located radially outside an outer end of the cord reinforcing layer; 6. The tire of claim 5.

Images