Tire, tire mold, and tire manufacturing method

Abstract

To provide a tire 2 which achieves improvement of a brake performance and reduction of rolling resistance while securing required steering stability.SOLUTION: A tire 2 includes a tread 4, a pair of side walls 6, a pair of beads 10, and a carcass 12. The bead 10 includes a core 38, and an apex 40. In the tire 2 set in a normal state, a ratio (HA / HS) of a radial distance HA to an outer end PA of the apex 40 from a bead base line to a tire cross sectional height HS is 20% or more and 30% or less, and an angle θt of a line segment connecting a center PM of an axial width of a contact face with the core 38 and the outer end PA of the apex 40 with respect to the bead base line is 45° or more and 55° or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, a mold for a tire, and a method for manufacturing a tire. [Background technology]

[0002] In consideration of the environment, there is a demand for tires with reduced rolling resistance (for example, Patent Document 1 below).

[0003] In order to reduce rolling resistance, for example, the use of low heat generation rubber in the cap layer of the tread has been considered. If low heat generation rubber is used in the cap layer, there is a risk that the gripping force will decrease and the braking performance of the tire will decrease. Therefore, the cap layer has been improved in composition by focusing on the loss tangent at 30°C and the structure of the tire has been simplified to ensure braking performance and reduce rolling resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-2008 A Summary of the Invention [Problem to be solved by the invention]

[0005] Demands for reduced rolling resistance are increasing, and structural simplification alone is no longer enough to meet these demands.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a tire that can improve braking performance and reduce rolling resistance while ensuring the necessary handling stability, as well as a tire mold for obtaining the tire and a tire manufacturing method. [Means for solving the problem]

[0007] As a result of further investigations focusing on tire deflection, the inventors discovered that by redesigning the structure and controlling the deflection, it is possible to improve braking performance and reduce rolling resistance while ensuring the necessary handling stability, and thus completed the present invention.

[0008] A tire according to one embodiment of the present invention has a speed symbol of W or more. The tire includes a tread that comes into contact with a road surface, a pair of sidewalls that are continuous with the ends of the tread and located radially inward of the tread, a pair of beads that are located radially inward of the sidewalls, and a carcass that bridges between one bead and the other bead on the inside of the tread and the pair of sidewalls. The bead includes a core and an apex that is located radially outward of the core. In a normal state in which the tire is mounted on a normal rim, the internal pressure of the tire is adjusted to a normal internal pressure, and no load is applied to the tire, the ratio of the radial distance from the bead base line to the outer end of the apex to the tire cross-sectional height is 20% or more and 30% or less, and the angle that a line segment connecting the center of the axial width of the contact surface of the apex with the core and the outer end of the apex forms with the bead base line is 45° or more and 55° or less.

[0009] Preferably, in this tire, the carcass includes a first carcass ply and a second carcass ply. The first carcass ply includes a first ply body spanning between one core and the other core, and a pair of first turn-up portions connected to the first ply body and turned back around the core from the inside to the outside in the axial direction. An end of the first turn-up portion is located radially outward from the maximum tire width position. The second carcass ply includes a second ply body spanning between one core and the other core, and a pair of second turn-up portions connected to the second ply body and turned back around the core from the inside to the outside in the axial direction. An end of the second turn-up portion is located radially between a contact surface of the apex with the core and an outer end of the apex.

[0010] Preferably, in the tire, the sidewall has a thickness of 4.0 mm or less at the tire maximum width position.

[0011] Preferably, in this tire, when a load represented by a load index is applied as a vertical load to the tire set in the normal state, the amount of vertical deflection is B100 and the contact area is A100, and when a load that is 73% of the load represented by the load index is applied as a vertical load, the amount of vertical deflection is B73 and the contact area is A73, the amount of vertical deflection B100 and the amount of vertical deflection A100, as well as the amount of vertical deflection B73 and the contact area A73, satisfy the following formula (1). 1.03≦(B100 / B73) / (A100 / A73)≦1.06 Formula (1)

[0012] A tire mold according to one aspect of the present invention is a mold for molding the tire described above. The mold includes a cavity surface that shapes the outer surface of a raw tire for the tire. The cavity surface includes a reference surface that defines a clip width of the mold. In the contour of the cavity surface, the reference surface is represented by a straight line extending in the radial direction, and the maximum width position is specified by three contour lines that connect the maximum width position and the reference surface and are formed of arcs. The three contour lines are an outer contour line that is continuous with the maximum width position, an inner contour line that is continuous with the reference surface, and an intermediate contour line that is located between the outer contour line and the inner contour line. The center of the arc that represents the outer contour line is located on a straight line that passes through the maximum width position and extends in the axial direction, inside the cavity surface. The center of the arc that represents the inner contour line is located on a straight line that passes through the outer end of the reference surface and extends in the axial direction, outside the cavity surface. The center of the arc representing the intermediate contour line is located inside the cavity surface. The intermediate contour line is tangent to each of the outer contour line and the inner contour line. The arc representing the outer contour line is tangent to a diagonal line that passes through an outer end of the reference surface and is inclined with respect to the axial direction, and the angle that the diagonal line makes with respect to the axial direction is 50° or more and 60° or less.

[0013] Preferably, in the tire mold, a ratio of a radius of the arc representing the intermediate contour line to a radius of the arc representing the outer contour line is equal to or greater than 0.48 and is equal to or less than 0.75.

[0014] A tire manufacturing method according to one aspect of the present invention is a method for manufacturing the tire described above. The tire manufacturing method includes a step of pressurizing and heating a raw tire for the tire in a mold. The mold has a cavity surface that shapes the outer surface of the raw tire. The cavity surface includes a reference surface that defines a clip width of the mold. In the contour of the cavity surface, the reference surface is represented by a straight line extending in a radial direction, and the maximum width position is specified by three contour lines that connect the maximum width position and the reference surface and are formed of arcs. The three contour lines are an outer contour line that is continuous with the maximum width position, an inner contour line that is continuous with the reference surface, and an intermediate contour line that is located between the outer contour line and the inner contour line. The center of the arc representing the outer contour line is located on a straight line that passes through the maximum width position and extends in the axial direction, inside the cavity surface. The center of the arc representing the inner contour line is located on a straight line that passes through the outer end of the reference surface and extends in the axial direction, outside the cavity surface. The center of the arc representing the intermediate contour line is located inside the cavity surface. The intermediate contour line is tangent to each of the outer contour line and the inner contour line. The arc representing the outer contour line is tangent to a diagonal line that passes through an outer end of the reference surface and is inclined with respect to the axial direction, and the angle that the diagonal line makes with respect to the axial direction is 50° or more and 60° or less. Effect of the Invention

[0015] According to the present invention, a tire can be obtained that is capable of improving braking performance and reducing rolling resistance while ensuring the necessary driving stability. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Diagram 2]FIG. 2 is a cross-sectional view of a portion of the tire shown in FIG. [Diagram 3] FIG. 3 is a schematic diagram illustrating the amount of vertical deflection of a tire. [Figure 4] FIG. 4 is a schematic diagram showing an example of the shape of a contact patch of a tire. [Diagram 5] FIG. 5 is a cross-sectional view showing a portion of a tire mold according to one embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of a portion of the mold shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0018] In this disclosure, 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 referred to as a standard state. In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured with the tire set in the standard state.

[0019] Genuine rims are rims that are specified in the standards on which the tires are based. "Standard rims" in the JATMA standard, "Design Rim" in the TRA standard, and "Measuring Rim" in the ETRTO standard are genuine rims.

[0020] Normal internal 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 internal pressures. If the tire is for passenger cars, the normal internal pressure is 180kPa unless otherwise specified.

[0021] The normal load means 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. If the tire is for passenger cars, the normal load is a load equivalent to 88% of the above load, unless otherwise specified.

[0022] In this disclosure, the load index (LI) is an index that is defined, for example, in the JATMA standard and indicates the maximum mass that can be loaded onto a tire under specified conditions, that is, the maximum load capacity.

[0023] In the present disclosure, the loss tangent (also referred to as tan δ) at a temperature of 30°C of an element made of crosslinked rubber among the elements constituting a tire is measured in accordance with the provisions of JIS K6394 using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions. Initial distortion = 10% Dynamic strain = 2% Frequency = 10Hz Deformation mode = tension In this measurement, the test specimen is sampled from a tire. If it is not possible to sample the test specimen from a tire, the test specimen is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes.

[0024] In the present disclosure, the hardness of an element made of crosslinked rubber among the 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.

[0025] FIG. 1 shows a part of a tire 2 according to one embodiment of the present invention. This tire 2 is a tire for passenger cars. In FIG. 1, the tire 2 is mounted on a rim R. The rim R is a regular rim. Air is filled inside the tire 2, and the internal pressure of the tire 2 is adjusted. The tire 2 shown in FIG. 1 is set in a regular state.

[0026] The tire 2 mounted on the rim R is also referred to as a tire-rim complex. The tire-rim complex includes the rim R and the tire 2 mounted on the rim R.

[0027] 1 shows a part of a cross section of the tire 2 taken along a plane including a rotation axis (not shown) of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction 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 represents the equatorial plane of the tire 2.

[0028] In Fig. 1, the solid line BBL extending in the axial direction is the bead base line. This bead base line is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0029] 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 , a pair of cushion layers 18 , a pair of chafers 20 , and an inner liner 22 .

[0030] The tread 4 comes into contact with the road surface at its outer surface, i.e., a tread surface 24. The tread 4 is located radially outward of the band 16. Grooves 26 are formed in the tread 4 of the tire 2. The grooves 26 shown in Fig. 1 are circumferential grooves 26p that extend continuously in the circumferential direction. In the tire 2, the groove depth of the circumferential grooves 26p is 8 mm or less.

[0031] In Fig. 1, the symbol PC is the equator of the tire 2. The equator PC is represented by the intersection of the tread surface 24 and the equatorial plane CL. In Fig. 1, the length represented by the double-headed arrow HS is the tire section height (see JATMA, etc.). The tire section height HS is represented by the radial distance from the bead base line BBL to the equator PC.

[0032] The tread 4 has a base layer 28 and a cap layer 30. The base layer 28 covers the entire band 16. The base layer 28 is made of a crosslinked rubber having low heat buildup. In the tire 2, the loss tangent of the base layer 28 at 30° C. is 0.10 or less.

[0033] The cap layer 30 is located radially outside the base layer 28. The cap layer 30 covers the entire base layer 28. The outer surface of the cap layer 30 is the above-mentioned tread surface 24. The cap layer 30 is made of a crosslinked rubber in consideration of wear resistance and grip performance. In the tire 2, the loss tangent of the cap layer 30 at 30° C. is 0.20 or more and 0.25 or less.

[0034] 1, the double-headed arrow TB indicates the thickness of the base layer 28. The double-headed arrow TC indicates the thickness of the cap layer 30. In the tire 2, the thickness TB of the base layer 28 and the thickness TC of the cap layer 30 are obtained by measuring along the equatorial plane CL in a cross section of the tire 2 obtained by cutting the tire 2 along a plane including the rotation axis.

[0035] In the tire 2, from the viewpoint of grip performance, the tread 4 is configured so that the thickness TC of the cap layer 30 is thicker than the thickness TB of the base layer 28. Specifically, the ratio (TC / TB) of the thickness TC of the cap layer 30 to the thickness TB of the base layer 28 is preferably 70 / 30 or more and 90 / 10 or less.

[0036] The tread 4 includes, in addition to the base layer 28 and the cap layer 30, wings 32 located between the tread body consisting of the base layer 28 and the cap layer 30 and the sidewalls 6. The wings 32 join the tread body and the sidewalls 6. The wings 32 are made of crosslinked rubber with adhesive properties taken into consideration.

[0037] Each sidewall 6 is continuous with an edge of the tread 4. The sidewalls 6 are located radially inward of the tread 4. The sidewalls 6 extend along the carcass 12 from the edge of the tread 4 toward the clinch 8. The sidewalls 6 are made of crosslinked rubber in consideration of cut resistance. The outer surface of the sidewalls 6 and the outer surface of the clinch 8 described below constitute a side surface 34 that forms part of the outer surface of the tire 2. The side surface 34 is continuous with the tread surface 24.

[0038] Each clinch 8 is located radially inside the sidewall 6. The clinch 8 contacts the rim R. The clinch 8 is made of crosslinked rubber in consideration of wear resistance.

[0039] In this tire 2, a rim protector 36 is configured at the boundary between the sidewall 6 and the clinch 8. In Fig. 1, a two-dot chain line LS represents a virtual outer surface of the tire 2 obtained assuming that there are no irregularities such as the rim protector 36, patterns, letters, etc. The rim protector 36 protrudes outward from this virtual outer surface LS. The rim protector 36 extends in the circumferential direction. This rim protector 36 prevents damage to the sidewall 6 and the rim R when a vehicle equipped with this tire 2 is pulled over to the shoulder of the road.

[0040] In Fig. 1, the symbol PW indicates the tire maximum width position. As described above, the tire 2 is provided with a rim protector 36 that protrudes from the imaginary outer surface LS. The tire maximum width position PW is specified based on the contour of the imaginary outer surface LS. The axial distance from one tire maximum width position PW to the other tire maximum width position PW is the tire section width (see JATMA, etc.).

[0041] Each bead 10 is located axially inward of the clinch 8. Each bead 10 is located radially inward of the sidewall 6. Each bead 10 includes a core 38 and an apex 40.

[0042] Although not shown, the core 38 includes a steel wire. The core 38 is formed by winding the wire in the circumferential direction. The cross section of the core 38 includes a plurality of cross sections of the wire. In the tire 2, the number of cross sections of the wire included in the cross section of the core 38 is preferably 20 or more and 25 or less.

[0043] The apex 40 is located radially outward of the core 38. The apex 40 is made of crosslinked rubber having high rigidity. The hardness of the apex 40 is 85 or more and 95 or less. The apex 40 tapers outward. In FIG. 1, the symbol PA denotes the outer end of the apex 40.

[0044] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between one bead 10 and the other bead 10.

[0045] The carcass 12 includes at least one carcass ply 42. The carcass 12 of the tire 2 is made up of two carcass plies 42. The carcass ply 42 located radially inward on the inner side of the tread 4 is a first carcass ply 44, and the carcass ply 42 located outward of the first carcass ply 44 is a second carcass ply 46. The carcass 12 includes the first carcass ply 44 and the second carcass ply 46.

[0046] The first carcass ply 44 includes a first ply body 44a that spans between one core 38 and the other core 38, and a pair of first turned-up portions 44b that are continuous with the first ply body 44a and turned up around each core 38 from the inside to the outside in the axial direction. In the tire 2, an end of the first turned-up portion 44b is located outside the tire maximum width position PW in the radial direction. An end of the first turned-up portion 44b is located inside the end of the belt 14 in the radial direction.

[0047] The second carcass ply 46 includes a second ply body 46a that spans between one core 38 and the other core 38, and a pair of second turned-up portions 46b that are continuous with the second ply body 46a and are turned up from the inside to the outside in the axial direction around each core 38. In the tire 2, an end of the second turned-up portion 46b is located between a contact surface of the apex 40 with the core 38 and an outer end PA of the apex 40 in the radial direction. An end of the second turned-up portion 46b is located between the apex 40 and the first turned-up portion 44b in the axial direction.

[0048] Although not shown, the carcass ply 42 includes a number of carcass cords arranged in parallel. These carcass cords are covered with a topping rubber. The carcass cords are cords made of organic fibers. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0049] The carcass cords intersect with the equatorial plane. The carcass 12 of the tire 2 has a radial structure. Each of the carcass cords included in the carcass 12 spans between one end and the other end of the carcass ply 42.

[0050] The belt 14 is located radially inside the tread 4. The belt 14 is located between the carcass 12 and the band 16. The belt 14 is laminated on the carcass 12. The width of the belt 14 of the tire 2 is 70% or more and 85% or less of the tire cross-sectional width.

[0051] The belt 14 is composed of at least two layers 48 laminated in the radial direction. The belt 14 of the tire 2 is composed of two layers 48 laminated in the radial direction. Of the two layers 48, the layer 48 located on the inner side is an inner layer 50, and the layer 48 located on the outer side is an outer layer 52. As shown in FIG. 1, the inner layer 50 has a width wider than that of the outer layer 52. In the axial direction, an end of the inner layer 50 is located outside an end of the outer layer 52. The distance from the end of the outer layer 52 to the end of the inner layer 50 is 3 mm or more and 10 mm or less.

[0052] Although not shown, each of the inner layer 50 and the outer layer 52 includes a number of belt cords arranged in parallel. These belt cords are covered with a topping rubber. Each belt cord is inclined with respect to the equator plane. The material of the belt cord is steel.

[0053] 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. In the axial direction, an end of the band 16 is located outward from an end of the belt 14. The distance from the end of the belt 14 to the end of the band 16 is 3 mm or more and 7 mm or less.

[0054] Although not shown, the band 16 includes a band cord wound in a spiral shape. The band cord extends substantially in the circumferential direction. Specifically, the angle that the band cord forms with the circumferential direction is 5° or less. The band 16 has a jointless structure. In the tire 2, a cord made of an organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0055] The band 16 of the tire 2 includes a full band 54 having both ends facing each other across the equatorial plane, and a pair of edge bands 56 that are spaced apart in the axial direction and that restrain the ends of the belt 14 and the full band 54. The band 16 may be composed of the full band 54. The band 16 may be composed of a pair of edge bands 56.

[0056] Each cushion layer 18 is located at an end of the belt 14 between the belt 14 and the carcass 12. The cushion layer 18 is made of a soft crosslinked rubber.

[0057] Each chafer 20 is located radially inside the bead 10. 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.

[0058] The inner liner 22 is positioned inside the carcass 12. The inner liner 22 constitutes the inner surface of the tire 2. The inner liner 22 is made of a crosslinked rubber having a low gas permeability coefficient. The inner liner 22 maintains the internal pressure of the tire 2.

[0059] Fig. 2 shows a part of the tire 2 shown in Fig. 1, specifically, a part of the bead 10. In Fig. 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 2 is the circumferential direction of the tire 2.

[0060] In FIG. 2, the symbol PM denotes the center of the axial width of the contact surface of the apex 40 with the core 38. The center PM of the axial width of the contact surface is also referred to as the width center. A solid line TL is a straight line passing through the width center PM and the outer end PA of the apex 40. Angle θt is an angle that the solid line TL forms with the bead baseline BBL. In this tire 2, this angle θt is an angle that a line segment connecting the center PM of the axial width of the contact surface of the apex 40 with the core 38 and the outer end PA of the apex 40 forms with the bead baseline BBL. This angle θt is also referred to as the apex angle. In FIG. 2, a double-headed arrow HA denotes the radial distance from the bead baseline BBL to the outer end PA of the apex 40. This radial distance HA is also referred to as the apex height.

[0061] A low apex height HA increases the amount of deflection of the tire 2. An increase in the amount of deflection contributes to an increase in the contact area, and is therefore expected to improve braking performance. However, a low apex height HA reduces the lateral rigidity of the tire 2, and there is concern that the steering stability may decrease. However, the inventors have discovered that even if the apex height HA is set to a height lower than that of a conventional tire, by setting the apex angle θt to an angle smaller than that of a conventional tire, the tension distribution of the carcass cords included in the ply bodies 44a, 46a changes, increasing the in-plane torsional rigidity, and as a result, it is possible to ensure lateral rigidity, which has led to the completion of the present invention.

[0062] In the tire 2 set in a normal state, the ratio (HA / HS) of the apex height HA to the tire cross-sectional height HS is equal to or greater than 20% and equal to or less than 30%.

[0063] Since the ratio (HA / HS) is 30% or less, the amount of deflection of the tire 2 is ensured. In this tire 2, the contact area is increased. In particular, when a large load acts on the tire 2, such as when braking a vehicle, a sufficient contact area is obtained. In this tire 2, good braking performance is obtained. An increase in the contact area (more specifically, an increase in the contact width) distributes the load acting on the tread 4. In this tire 2, distortion at the edge portions of the tread 4, which contribute greatly to rolling resistance, is reduced. In this tire 2, rolling resistance is reduced. From the viewpoints of ensuring good braking performance and reducing rolling resistance, the ratio (HA / HS) is preferably 27% or less.

[0064] Since the ratio (HA / HS) is equal to or greater than 20%, the amount of deflection is prevented from becoming too large. In the tire 2, necessary rigidity is ensured in the portion of the bead 10. From this viewpoint, the ratio (HA / HS) is preferably equal to or greater than 23%.

[0065] In this tire 2, the ratio (HA / HS) is set to 30% or less in order to ensure the amount of deflection necessary to improve braking performance. Therefore, compared to conventional tires with a ratio (HA / HS) exceeding 30%, there is a concern that the lateral rigidity will decrease and the handling stability will decrease. However, as described above, in this tire 2, the apex angle θt is set to a smaller angle than that of conventional tires. Specifically, the apex angle θt is 55° or less.

[0066] Since the apex angle θt is 55° or less, the in-plane torsional rigidity of the tire 2 is increased and the necessary lateral rigidity is ensured. In this tire 2, good driving stability is maintained. The small apex angle θt contributes to a low apex height HA. This tire 2 can improve braking performance and reduce rolling resistance while ensuring the necessary driving stability.

[0067] In this tire 2, the apex angle θt is equal to or greater than 45°. Since the amount of deflection is prevented from becoming too large, necessary rigidity is ensured. In this tire 2, good steering stability is maintained. From this viewpoint, the apex angle θt is preferably equal to or greater than 50°.

[0068] In this tire 2, in a normal state, the ratio (HA / HS) of the apex height HA to the tire cross-sectional height HS is 20% or more and 30% or less, and the apex angle θt is 45° or more and 55° or less. This tire 2 can increase the amount of deflection while ensuring lateral rigidity. This tire 2 can improve braking performance and reduce rolling resistance while ensuring necessary steering stability.

[0069] 2, the double-headed arrow E indicates the thickness of the sidewall 6 measured along a straight line that passes through the tire maximum width position PW and extends in the axial direction. In this tire 2, the thickness E is the thickness of the sidewall 6 at the tire maximum width position PW.

[0070] In the tire 2, the thickness E of the sidewall 6 at the tire maximum width position PW is preferably 4.0 mm or less. From the viewpoint of enabling the sidewall 6 to contribute to an increase in the amount of deflection of the tire 2, the thickness E is more preferably 3.5 mm or less. From the viewpoint of ensuring necessary rigidity, the thickness E is preferably 2.5 mm or more, and more preferably 3.0 mm or more.

[0071] As described above, in the tire 2, by increasing the deflection amount and ground contact area of ​​the tire 2 while ensuring lateral rigidity, it is possible to improve braking performance and reduce rolling resistance while ensuring necessary steering stability. In the tire 2, from the viewpoint of further improving braking performance and further reducing rolling resistance, when the load represented by the load index is applied as a vertical load to the tire 2 set in a normal state, the vertical deflection amount B100 and the ground contact area A100 are set as vertical deflection B73 and the ground contact area A73 are set as vertical deflection B73 and ground contact area A73, preferably, the vertical deflection amount B100 and the ground contact area A100, as well as the vertical deflection amount B73 and the ground contact area A73 satisfy the following formula (1). 1.03≦(B100 / B73) / (A100 / A73)≦1.06 Formula (1)

[0072] Here, the vertical deflection amount B100 when the load represented by the load index is applied as a vertical load to the tire 2 set in the normal state is measured, for example, as follows. As shown in Fig. 3, the tire 2 set in the normal state is set relative to a flat road surface G so that its rotation axis is parallel to the road surface G, and then the road surface G is raised. The displacement amount of the road surface G until the vertical load acting on the tire 2 reaches the load represented by the load index (the length indicated by the double arrow B in Fig. 3) is measured. This displacement amount B is the vertical deflection amount B100 when the load represented by the load index is applied as a vertical load to the tire 2. The vertical deflection amount B73 when a load that is 73% of the load represented by the load index is applied as a vertical load to the tire 2 is measured in the same manner.

[0073] In measuring the amount of longitudinal deflection of the tire 2, a contact patch image as shown in Fig. 4 is obtained. For this tire 2, based on this contact patch image, a contact area A100 when a load represented by the load index is applied as a longitudinal load to the tire 2, and a contact area A73 when a load that is 73% of the load represented by the load index is applied as a longitudinal load to the tire 2 are obtained. This contact area also includes the area of ​​the portion corresponding to the groove 26 (for example, the portion corresponding to the main direction groove 26p represented by the symbol GR in Fig. 4).

[0074] In this tire 2, when the longitudinal deflection B100 and the contact area A100, and the longitudinal deflection B73 and the contact area A73 satisfy the above-mentioned formula (1), the ratio (B100 / B73) of the longitudinal deflection B100 to the longitudinal deflection B73 is preferably 1.38 or more from the viewpoint of sufficiently reducing the rolling resistance. From the viewpoint of sufficiently improving the braking performance, the ratio (A100 / A73) of the contact area A100 to the contact area A73 is preferably 1.34 or more.

[0075] The tire 2 described above is manufactured as follows. Although not described in detail, in the manufacture of this tire 2, the elements that constitute the tire 2, such as the tread 4, the sidewalls 6, the beads 10, etc., are combined in a molding machine (not shown) to prepare the tire 2 in an unvulcanized state (hereinafter also referred to as a raw tire).

[0076] In manufacturing the tire 2, a green tire is placed in a mold of a vulcanizer (not shown). The green tire is pressurized and heated in the mold to obtain the tire 2. The tire 2 is a vulcanized product of the green tire.

[0077] The manufacturing method of this tire 2 includes a step of preparing a raw tire for the tire 2, and a step of pressurizing and heating the raw tire in a mold. Although not described in detail, in the manufacturing of this tire 2, there are no particular limitations on the vulcanization conditions such as temperature, pressure, and time, and general vulcanization conditions are adopted.

[0078] FIG. 5 shows an example of a mold 62 used in manufacturing a tire 2. FIG. 5 shows a part of a cross section of the mold 62 along a plane including a central axis (not shown) corresponding to the rotation axis of the tire 2. In FIG. 5, the up-down direction corresponds to the axial direction of the tire 2. The left-right direction corresponds to the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 5 corresponds to the circumferential direction of the tire 2. For ease of explanation, the dimensions of this mold 62 are represented by the dimensions of the tire 2. In FIG. 5, a dashed dotted line ML is the center line of this mold 62. This center line ML corresponds to the equatorial plane CL of the tire 2.

[0079] The mold 62 includes a tread ring 64, a pair of side plates 66, and a pair of bead rings 68. In Fig. 5, the mold 62 is in a state in which the tread ring 64, the pair of side plates 66, and the pair of bead rings 68 are assembled together, i.e., in a closed state. The mold 62 is a split mold.

[0080] The tread ring 64 constitutes the radially outer portion of the mold 62. The tread ring 64 has a tread forming surface 70 on its inner surface. The tread forming surface 70 forms the tread surface 24 of the tire 2. The tread ring 64 of the mold 62 is composed of a number of segments 72. These segments 72 are arranged in a ring shape.

[0081] Each side plate 66 is located radially inward of the tread ring 64. The side plates 66 are continuous with the ends of the tread ring 64. The side plates 66 are provided with a sidewall forming surface 74 on their inner surfaces. The sidewall forming surfaces 74 form the side surfaces 34 of the tire 2.

[0082] Each bead ring 68 is located radially inward of the side plate 66. The bead ring 68 is continuous with the end of the side plate 66. The bead ring 68 has a bead forming surface 76 on its inner surface. The bead forming surface 76 forms a portion of the bead 10 of the tire 2, specifically, a portion that fits onto the rim R.

[0083] In this mold 62, a number of segments 72, a pair of side plates 66, and a pair of bead rings 68 are combined to form a cavity surface 78 that shapes the outer surface of the tire 2 on the outer surface of the raw tire 2r. This mold 62 has a cavity surface 78. The cavity surface 78 is composed of a tread forming surface 70, a pair of sidewall forming surfaces 74, and a pair of bead forming surfaces 76.

[0084] In the pressurizing and heating process, the green tire 2r is pressed against the cavity surface 78 of the mold 62 by the inflated bladder 80. This causes the outer surface of the tire 2 to be shaped onto the outer surface of the green tire 2r. In this pressurizing and heating process, a rigid core (not shown) may be used instead of the inflated bladder 80.

[0085] Fig. 6 shows a part of the mold 62 shown in Fig. 5. Fig. 6 shows a part of the sidewall forming surface 74 and the bead forming surface 76, i.e., a part of the cavity surface 78. In Fig. 6, the up-down direction is the radial direction of the tire 2. The left-right direction is the axial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 6 is the circumferential direction of the tire 2.

[0086] In FIG. 6, a single arrow CW represents the clip width of the mold 62. The cavity surface 78 includes a reference surface 82 that defines the clip width CW. This reference surface 82 is a surface that forms a contact surface with the flange F of the rim R among the contact surfaces between the tire 2 and the rim R. In the contour of the cavity surface 78 shown in FIG. 6, the reference surface 82 is represented by a straight line extending in the radial direction. The clip width CW is represented by the axial distance from one reference surface 82 to the other reference surface 82 (not shown). In FIG. 6, the symbol PB is the outer end of the reference surface 82.

[0087] In Fig. 6, the symbol PV represents the maximum width position of the cavity surface 78. As shown in Fig. 6, a recess 84 for forming the rim protector 36 is provided in the cavity surface 78. The two-dot chain line SL in Fig. 6 is an imaginary cavity surface obtained assuming that there are no irregularities such as the recess 84. In this disclosure, this imaginary cavity surface is also referred to as the reference line of the cavity surface 78. In this mold 62, the maximum width position PV of the cavity surface 78 is specified on this reference line SL.

[0088] In this mold 62, in the contour of the cavity surface 78, the maximum width position PV is specified by three contour lines connecting between the maximum width position PW and the outer end PB of the reference surface 82. In other words, the reference line of this cavity surface 78 includes three contour lines connecting between the maximum width position PW and the outer end PB of the reference surface 82. Each of the three contour lines is represented by a circular arc.

[0089] In this mold 62, the three contour lines are an outer contour line connected to the maximum width position PV, an inner contour line connected to the reference plane 82, and an intermediate contour line located between the outer contour line and the inner contour line. In Fig. 6, the symbol SM is the boundary between the outer contour line and the intermediate contour line. The symbol MU is the boundary between the intermediate contour line and the inner contour line.

[0090] An arrow Rs in Fig. 6 indicates the radius of the arc representing the outer contour. Although not shown, the center of the arc representing the outer contour is located on a straight line (solid line AL in Fig. 6) that passes through the maximum width position PV inside the cavity surface 78 and extends in the axial direction.

[0091] An arrow Ru indicates the radius of the arc representing the inner contour. Although not shown, the center of the arc representing this inner contour is located on a straight line (solid line BL in FIG. 6) that passes through the outer end PB of the reference surface 82 and extends in the axial direction outside the cavity surface 78. The radius Ru of the arc representing this inner contour is set in the range of 9 mm to 12 mm.

[0092] Arrow Rm indicates the radius of the arc representing the intermediate contour line. Although not shown, the center of the arc representing the intermediate contour line is located inside the cavity surface 78. The intermediate contour line is tangent to the outer contour line at boundary SM. The intermediate contour line is tangent to the inner contour line at boundary MU. The intermediate contour line is tangent to both the outer contour line and the inner contour line.

[0093] In Fig. 6, the solid line LT is a diagonal line that passes through the outer end PB of the reference surface 82 and is inclined with respect to the axial direction. The diagonal line LT is inclined with respect to the axial direction so that the distance between the diagonal line LT and the center line ML of the mold 62 expands outward in the radial direction. In Fig. 6, the angle θm is the angle that the diagonal line LT makes with respect to the axial direction.

[0094] 6, the arc indicated by the dotted line EL is an extension of the outer contour. This arc EL represents the outer contour.

[0095] In the contour of the cavity surface 78, the portion between the boundary SM and the boundary MU affects the degree of inclination of the apex 40 in the tire 2, specifically, the apex angle θt.

[0096] In the conventional mold, the maximum width position PV and the boundary MU are connected by one arc, whereas in the mold 62, the maximum width position PV and the boundary MU are connected by two arcs, one representing the outer contour line and the other representing the intermediate contour line. The mold 62 can lay down the portion between the boundary SM and the boundary MU, which stands in the approximately radial direction in the conventional mold. The mold 62 can set the apex angle θt at a smaller angle than the apex angle set in the conventional mold. Moreover, in the mold 62, the arc representing the outer contour line is tangent to the oblique line LT at the position TS, and the angle θm that the oblique line LT makes with respect to the axial direction is 50° or more and 60° or less.

[0097] With this mold 62, the tire 2 shown in Fig. 1 can be obtained in which, in a normal state, the ratio (HA / HS) of the apex height HA to the tire cross-sectional height HS is 30% or less, and the apex angle θt is 55° or less. As described above, this tire 2 can increase the amount of deflection while ensuring lateral rigidity. With this mold 62 and the manufacturing method using this mold 62, the tire 2 can be obtained in which the braking performance is improved and the rolling resistance is reduced while ensuring the necessary steering stability.

[0098] From the viewpoint of enabling the mold 62 to contribute to the manufacture of a tire 2 that can increase the amount of deflection while ensuring lateral rigidity, the angle θm that the oblique line LT forms with respect to the axial direction is preferably equal to or greater than 52°, and more preferably equal to or greater than 54°. The angle θm is preferably equal to or less than 58°, and more preferably equal to or less than 56°.

[0099] In this mold 62, from the viewpoint of contributing to the manufacture of a tire 2 capable of increasing the amount of deflection while ensuring lateral rigidity, it is preferable that the arc representing the intermediate contour has a radius Rm smaller than the radius Rs of the arc representing the outer contour. Specifically, the ratio (Rm / Rs) of the radius Rm of the arc representing the intermediate contour to the radius Rs of the arc representing the outer contour is more preferably 0.48 or more, and even more preferably 0.50 or more. This ratio (Rm / Rs) is more preferably 0.76 or less, and even more preferably 0.74 or less.

[0100] In this mold 62, the reference line of the cavity surface 78 includes an upper contour line that is continuous with the outer contour line at the maximum width position PV. In Fig. 6, an arrow Rg indicates the radius of the arc that represents the upper contour line. Although not shown, the center of the arc that represents the upper contour line is located on a straight line AL that passes through the maximum width position PV and extends in the axial direction inside the cavity surface 78. This upper contour line is tangent to the outer contour line at the maximum width position PV.

[0101] In this mold 62, from the viewpoint of contributing to the manufacture of a tire 2 that can increase the amount of deflection and ensure a large contact area while ensuring lateral rigidity, it is preferable that the arc representing the upper contour line has a radius Rg smaller than the radius Rs of the arc representing the outer contour line. Specifically, the ratio (Rg / Rs) of the radius Rg of the arc representing the upper virtual line to the radius Rs of the arc representing the outer contour line is more preferably 0.85 or more, and even more preferably 0.88 or more. This ratio (Rg / Rs) is more preferably 0.97 or less, and even more preferably 0.94 or less.

[0102] As described above, the present invention provides a tire 2 that can improve braking performance and reduce rolling resistance while ensuring necessary steering stability, and a mold 62 and manufacturing method for obtaining the tire 2. The present invention is particularly effective for a tire 2 having a speed rating of W or higher. EXAMPLES

[0103] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0104] [Example 1] A pneumatic tire for passenger cars (tire size=225 / 45R19 92W) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

[0105] In this Example 1, the apex angle θt was set to 55°. The ratio (HA / HS) of the radial distance HA from the bead base line to the outer end PA of the apex to the tire cross-sectional height HS was set to 25%. The sidewall thickness E at the tire maximum width position PW was set to 4.0 mm.

[0106] In this Example 1, the vertical deflection ratio (B100 / B73) was 1.38, which is the ratio of the vertical deflection amount B100 when the load represented by the load index was applied as a vertical load to the vertical deflection amount B73 when a load of 73% of the load represented by the load index was applied as a vertical load. The ground contact area ratio (A100 / A73) was 1.34, which is the ratio of the contact area A100 when the load represented by the load index was applied as a vertical load to the contact area A73 when a load of 73% of the load represented by the load index was applied as a vertical load. The coefficient α, which is the ratio of the vertical deflection ratio (B100 / B73) to the contact area ratio (A100 / A73), was 1.03.

[0107] In measuring the amount of vertical deflection and the contact area, the tire was mounted on a rim (size = 19 x 7.5) and filled with air to adjust the internal pressure of the tire to 240 kPa.

[0108] [Comparative Example 1-2] A tire of Comparative Example 1-2 was obtained in the same manner as Example 1, except that the apex angle θt was set as shown in the following Table 1. The longitudinal deflection ratio, contact area ratio, and coefficient α of Comparative Examples 1 and 2 were as shown in Table 1.

[0109] [Example 2-3] Tires of Examples 2-3 were obtained in the same manner as in Example 1, except that the thickness E was set as shown in the following Table 1. The longitudinal deflection ratio, ground contact area ratio, and coefficient α of Examples 2 and 3 were as shown in Table 1.

[0110] [Example 4] A tire of Example 4 was obtained in the same manner as Example 1, except that the angle θ and the ratio (HA / HS) were as shown in the following Table 2. The longitudinal deflection ratio, the contact area ratio, and the coefficient α of this Example 4 were as shown in this Table 2.

[0111] [Example 5 and Comparative Example 3] Tires of Example 5 and Comparative Example 3 were obtained in the same manner as Example 1, except that the ratio (HA / HS) was set as shown in the following Table 2. The longitudinal deflection ratio, ground contact area ratio, and coefficient α of Example 5 and Comparative Example 3 were as shown in Table 2.

[0112] [Braking performance] The prototype tire was mounted on a rim (size = 19 x 7.5) and filled with air to adjust the internal pressure of the tire to 240 kPa. The tire was mounted on a test vehicle (passenger car) and the test vehicle was driven on a test course for evaluating braking performance. The braking distance from a speed of 64 km / h was measured. The results are shown as indices in Tables 1 and 2 below. The higher the value, the higher the tire's friction force on dry roads and the better its braking performance.

[0113] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) of the prototype tires was measured when they were running on a drum at a speed of 80km / h under the following conditions. The results are shown as indices in Tables 1 and 2 below. The higher the value, the lower the rolling resistance of the tire. Rim: 19×7.5 Internal pressure: 240kPa Vertical load: 4.75kN

[0114] [Handling stability] The prototype tire was mounted on a rim (size = 19 x 7.5) and filled with air to adjust the internal tire pressure to 240 kPa. The tire was mounted on a test vehicle (passenger car) and the test vehicle was driven on a test course with a dry asphalt road surface. The driver was asked to evaluate the driving stability (sensory evaluation). The results are shown in the indices in Tables 1 and 2 below. The higher the value, the better the driving stability of the tire. In this evaluation, an index of 95 or more is considered to have ensured the necessary driving stability and is therefore acceptable.

[0115] [Table 1]

[0116] [Table 2]

[0117] As shown in Tables 1 and 2, in the examples, the braking performance was improved and the rolling resistance was reduced while maintaining the necessary steering stability. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0118] The technology described above that can achieve improved braking performance and reduced rolling resistance while ensuring the necessary driving stability can be applied to various tires. [Explanation of symbols]

[0119] 2. Tires 2r: Raw tires 4. Tread 6. Sidewall 8. Clinch 10...Bead 12. Carcass 24 Tread surface 26, 26p...Groove 28...Base layer 30 Cap layer 34. Side 36 Rim protector 38 Core 40. Apex 42, 44, 46...Carcass ply 62 Mold 64 Tread ring 66 Side plate 68···Bead ring 78 Cavity surface 80...Bladder 82...Reference plane 84. Depression

Claims

1. Has a speed rating of W or higher; A tread that comes into contact with the road surface; A pair of sidewalls connected to the ends of the tread and positioned radially inward of the tread; A pair of beads located radially inside the sidewall; a carcass extending between one bead and the other bead on the inner side of the tread and the pair of sidewalls; Equipped with The bead includes a core and an apex located radially outward of the core, When mounted on a standard rim, with the internal pressure adjusted to the standard, and without any load applied, The ratio of the radial distance from the bead base line to the outer end of the apex to the tire cross-sectional height is 20% or more and 30% or less, an angle formed by a line segment connecting a center of an axial width of a contact surface of the apex with the core and an outer end of the apex with respect to the bead baseline is equal to or greater than 45° and equal to or less than 55°; The thickness of the sidewall at the maximum tire width position is 4.0 mm or less, When a load represented by the load index is applied as a vertical load to the tire set in the normal state, the vertical deflection amount is B100 and the ground contact area is A100. When a load that is 73% of the load represented by the load index is applied as a vertical load, the vertical deflection amount is B73 and the ground contact area is A73. The vertical deflection amount B100 and the ground contact area A100, as well as the vertical deflection amount B73 and the ground contact area A73, satisfy the following formula (1): The ratio (B100 / B73) of the vertical deflection amount B100 to the vertical deflection amount B73 is 1.38 or more. tire. 1.03≦(B100 / B73) / (A100 / A73)≦1.06 Formula (1)

2. the carcass includes a first carcass ply and a second carcass ply; The first carcass ply includes a first ply body that spans between one core and the other core, and a pair of first turn-up portions that are connected to the first ply body and are turned up around the core from the inside to the outside in the axial direction, an end of the first folded-back portion is located radially outward from a maximum width position of the tire, The second carcass ply includes a second ply body that spans between one core and the other core, and a pair of second turn-up portions that are connected to the second ply body and are turned up around the core from the inside to the outside in the axial direction, An end of the second folded portion is located between a contact surface of the apex with the core and an outer end of the apex in a radial direction.

2. The tire of claim 1.

3. The hardness of the apex is 85 or more and 95 or less.

3. A tire according to claim 1 or 2.

4. The ratio (A100 / A73) of the ground contact area A100 to the ground contact area A73 is 1.34 or more. A tire according to any one of claims 1 to 3.

5. Having a speed symbol of W or more, A tread that comes into contact with the road surface; A pair of sidewalls connected to the ends of the tread and positioned radially inward of the tread; A pair of beads located radially inside the sidewall; a carcass extending between one bead and the other bead on the inner side of the tread and the pair of sidewalls; Equipped with The bead includes a core and an apex located radially outward of the core, When mounted on a standard rim, with the internal pressure adjusted to the standard, and without any load applied, The ratio of the radial distance from the bead base line to the outer end of the apex to the tire cross-sectional height is 20% or more and 30% or less, A mold for molding a tire, wherein an angle formed by a line segment connecting a center of an axial width of a contact surface of the apex with the core and an outer end of the apex with respect to the bead baseline is equal to or greater than 45° and equal to or less than 55°, the mold has a cavity surface that shapes the outer surface of a green tire for the tire, the cavity surface includes a reference surface that defines a clip width of the mold; In the contour of the cavity surface, the reference surface is represented by a straight line extending in a radial direction, and the maximum width position is specified by three contour lines consisting of arcs connecting the maximum width position and the reference surface; the three contour lines are an outer contour line connected to the maximum width position, an inner contour line connected to the reference plane, and an intermediate contour line located between the outer contour line and the inner contour line, The center of the arc representing the outer contour is located on a straight line passing through the maximum width position and extending in the axial direction inside the cavity surface, The center of the arc representing the inner contour line is located on a straight line that passes through an outer end of the reference surface and extends in the axial direction, outside the cavity surface, the center of the arc representing the intermediate contour line is located inside the cavity surface; the intermediate contour line is tangent to each of the outer contour line and the inner contour line; The arc representing the outer contour line passes through the outer end of the reference surface and is in contact with a diagonal line inclined with respect to the axial direction; The angle that the oblique line forms with respect to the axial direction is 50° or more and 60° or less. Tire mould.

6. a ratio of a radius of the arc representing the intermediate contour line to a radius of the arc representing the outer contour line is equal to or greater than 0.48 and is equal to or less than 0.75; The tire mold of claim 5.

7. Having a speed symbol of W or more, A tread that comes into contact with the road surface; A pair of sidewalls connected to the ends of the tread and positioned radially inward of the tread; A pair of beads located radially inside the sidewall; a carcass extending between one bead and the other bead on the inner side of the tread and the pair of sidewalls; Equipped with The bead includes a core and an apex located radially outward of the core, When mounted on a standard rim, with the internal pressure adjusted to the standard, and without any load applied, The ratio of the radial distance from the bead base line to the outer end of the apex to the tire cross-sectional height is 20% or more and 30% or less, A method for manufacturing a tire, comprising the steps of: forming an angle between a center of an axial width of a contact surface of the apex with the core and an outer end of the apex and the bead baseline of the line segment that connects the center of an axial width of the contact surface of the apex with the core and the outer end of the apex, the angle being equal to or greater than 45° and equal to or less than 55°; Pressurizing and heating the green tire for said tire in a mold. Including, the mold has a cavity surface that shapes the outer surface of the green tire, the cavity surface includes a reference surface that defines a clip width of the mold; In the contour of the cavity surface, the reference surface is represented by a straight line extending in a radial direction, and the maximum width position is specified by three contour lines consisting of arcs connecting the maximum width position and the reference surface; the three contour lines are an outer contour line connected to the maximum width position, an inner contour line connected to the reference plane, and an intermediate contour line located between the outer contour line and the inner contour line, The center of the arc representing the outer contour is located on a straight line passing through the maximum width position and extending in the axial direction inside the cavity surface, The center of the arc representing the inner contour line is located on a straight line that passes through an outer end of the reference surface and extends in the axial direction, outside the cavity surface, the center of the arc representing the intermediate contour line is located inside the cavity surface; the intermediate contour line is tangent to each of the outer contour line and the inner contour line; The arc representing the outer contour line passes through the outer end of the reference surface and is in contact with a diagonal line inclined with respect to the axial direction; The angle that the oblique line forms with respect to the axial direction is 50° or more and 60° or less. A method for manufacturing tires.

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