tire

Abstract

To provide a tire 2 capable of improving riding comfort while maintaining favorable silence property.SOLUTION: A tire 2 includes a pair of beads 10, a carcass 12, and a pair of strip apexes 20. An inner end 48 of each of the strip apexes 20 is located between a ply body 38a and an apex 32. An outer end 46 of each of the strip apexes 20 is located in the radially outside of an end of a folding part 36b of a first ply 36. The inner end 48 of each of the strip apexes 20 is located in the radially outside of an end of a folding part 38b of a second ply 38.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire, and more particularly to a tire mounted on a passenger vehicle. [Background technology]

[0002] Run-flat tires are known as tires that can be driven for a certain distance even when punctured. These tires have a reinforcing layer with a crescent-shaped cross section provided on the sidewall. The reinforcing layer increases the rigidity of the sidewalls. However, this tire has a lower ride comfort than a tire without a reinforcing layer on the sidewalls (a normal tire). Studies are being conducted to improve the ride comfort (for example, see Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-26158 Summary of the Invention [Problem to be solved by the invention]

[0004] The adoption of run-flat tires eliminates the need for a spare tire. However, because run-flat tires have a reinforcement layer on the sidewall, the improvement in ride comfort is minimal. Increasingly, vehicles are replacing their standard tires with run-flat tires and carrying puncture repair kits instead of spare tires.

[0005] Replacing run-flat tires with standard tires improves ride comfort. However, the rigidity of the sidewalls of standard tires is lower than that of run-flat tires. As a result, with standard tires, the resonance frequency of the front-to-rear torsional mode shifts to the lower frequency side, which can overlap with the frequency band of the vehicle's resonance. In this case, a muffled sound in the 40 Hz range is generated. If run-flat tires are replaced with normal tires to improve ride comfort, there is a risk that quietness will be compromised.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a tire that can achieve an improvement in ride comfort while maintaining good quietness. [Means for solving the problem]

[0007] A tire according to one aspect of the present invention includes a carcass having a pair of beads each having a core and an apex, a first ply and a second ply stacked together, each of the first ply and the second ply spanning one core and the other core, and a pair of turnup portions connected to the ply body and turned up around the core, and a pair of strip apexes located axially outward of the ply body. The inner ends of each strip apex are located between the ply body and the apex. The outer ends of the strip apexes are located radially outward of the ends of the turnup portions of the first ply. The inner ends of the strip apexes are located radially outward of the ends of the turnup portions of the second ply.

[0008] Preferably, in the tire, a carcass line representing an outline of the carcass in a meridian cross section includes a first inner portion connecting a maximum width position and a position corresponding to the inner end of the strip apex, and a second inner portion connecting the position corresponding to the inner end of the strip apex and a position corresponding to the boundary between the core and the apex. The first inner portion has an outwardly convex shape, and the second inner portion has an inwardly convex shape. The curvature of the first inner portion is represented by a first inner circular arc that has a center on a straight line that passes through the maximum width position and extends in the axial direction, and that passes through the maximum width position and the position corresponding to the inner end of the strip apex, and the radius of the first inner circular arc is 35 mm or more and 55 mm or less.

[0009] Preferably, in this tire, the curved state of the second inner portion is represented by a second inner arc that has a center on the bead base line and passes through a position corresponding to the inner end of the strip apex and a position corresponding to the boundary between the core and the apex, and the radius of the second inner arc is smaller than the radius of the first inner arc.

[0010] Preferably, in the tire, the axial distance from a position corresponding to the boundary between the core and the apex to the maximum width position is greater than half the radial distance from the position corresponding to the boundary between the core and the apex to the maximum width position.

[0011] Preferably, in the tire, a ratio of a radial distance from a bead base line to an inner end of the strip apex to a tire section height is equal to or greater than 0.14 and is equal to or less than 0.20.

[0012] Preferably, in the tire, a ratio of a radial distance from an inner end to an outer end of the strip apex to a tire section height is equal to or greater than 0.32 and is equal to or less than 0.56.

[0013] Preferably, in the tire, the strip apex has a complex modulus of elasticity at 70° C. of 50 MPa or greater and 100 MPa or less. [Effects of the Invention]

[0014] According to the present invention, a tire can be obtained that can achieve an improvement in ride comfort while maintaining good quietness. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a part of a carcass line. [Figure 3] FIG. 3 is a cross-sectional view showing a part of the carcass line of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0017] 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.

[0018] In this disclosure, 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 a meridian cross section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured by cutting the tire along a plane including the rotation axis, and the distance between the left and right beads in the cross section is measured so that it matches the distance between the beads when the tire is mounted on a regular rim.

[0019] A genuine rim is a rim 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 all genuine rims.

[0020] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0021] 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 the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0022] In this disclosure, a crosslinked rubber is a molded article of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0023] Examples of base rubbers include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Examples of chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of base rubber and chemicals, the content of the selected chemicals, etc. are determined appropriately depending on the specifications of each element to which the rubber composition is applied, such as the tread and sidewall.

[0024] In the present disclosure, the complex modulus of an element made of crosslinked rubber, among elements constituting a tire, at a temperature of 70°C 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 strain = 10% Dynamic strain = 2% Frequency = 10 Hz Deformation mode = tension In this measurement, test specimens are sampled from tires. If it is not possible to sample test specimens from tires, test specimens are sampled from a sheet of 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.

[0025] In this disclosure, 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 side 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 side portions.

[0026] 1 shows a portion of a tire 2 according to one embodiment of the present invention. The tire 2 is a pneumatic tire for passenger cars. FIG. 1 shows a portion of a cross section (hereinafter referred to as a meridian cross section) of the tire 2 taken along a plane including the rotation axis 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. The dashed-dotted line CL represents the equatorial plane of the tire 2.

[0027] 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 mounted on the rim R is also called a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on this rim R.

[0028] In Figure 1, the position indicated by the symbol AE is the axially outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the outer end AE is identified based on a virtual outer surface obtained assuming that there is no decoration. The axial distance from the first outer end AE to the second outer end AE obtained in a normal state is the cross-sectional width of the tire 2 (see JATMA, etc.).

[0029] In Fig. 1, the solid line BBL extending in the axial direction is the bead base line, which defines the rim diameter of the rim R (see JATMA, etc.).

[0030] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of chafers 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a band 16 , an inner liner 18 , and a pair of strip apexes 20 . No reinforcing layer that would allow the tire to be driven in a punctured state is provided on the side of the tire 2. The tire 2 is a normal tire, not a side-reinforced run-flat tire.

[0031] The outer surface of the tread 4 comes into contact with the road surface. This outer surface is a tread surface 22. Grooves 24 are cut into the tread 4. This forms a tread pattern. The tread 4 includes a base portion 26 and a cap portion 28 located radially outward of the base portion 26. The base portion 26 is made of a low-heat-generating cross-linked rubber. The cap portion 28 is made of a cross-linked rubber that takes into consideration wear resistance and grip performance.

[0032] 1, the symbol PC denotes the intersection of the tread surface 22 and the equatorial plane. The intersection PC is the equator of the tire 2. The equator PC is the outer edge of the tire 2 in the radial direction. In Figure 1, the length indicated by the symbol HS is the tire section height (see JATMA, etc.). The tire section height HS is the radial distance from the bead base line to the equator PC.

[0033] Each sidewall 6 is continuous with the edge of the tread 4. The sidewalls 6 are located radially inward of the tread 4. The sidewalls 6 extend from the edge of the tread 4 toward the chafer 8 along the carcass 12. The sidewalls 6 are made of crosslinked rubber in consideration of cut resistance.

[0034] Each chafer 8 is located radially inside the sidewall 6. The chafers 8 come into contact with the rim R. The chafers 8 are made of crosslinked rubber in consideration of wear resistance.

[0035] Each bead 10 is located axially inward of the chafer 8. The beads 10 are located radially inward of the sidewall 6. The bead 10 has a core 30 and an apex 32. Although not shown, the core 30 includes a steel wire. The apex 32 is located radially outward of the core 30. The apex 32 tapers outward. The apex 32 is made of crosslinked rubber having high rigidity.

[0036] 1, the length indicated by the symbol HA is the apex height, which is the radial distance from the bead base line to the outer end of the apex 32. In the tire 2, the ratio (HA / HS) of the apex height HA to the tire cross-sectional height HS is set in the range of 0.2 or more and 0.4 or less.

[0037] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of chafers 8. The carcass 12 bridges between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0038] The carcass 12 has two laminated carcass plies 34. In the tire 2, the carcass ply 34 located radially inward on the inside of the tread 4 is a first ply 36, and the carcass ply 34 located outward of the first ply 36 is a second ply 38. The carcass 12 may be made up of three or more carcass plies 34. From the viewpoint of weight reduction, it is preferable that the carcass 12 be made up of two carcass plies 34.

[0039] The first ply 36 includes a first ply body 36a that spans between the first core 30 and the second core 30 (not shown), and a pair of first folded portions 36b that are connected to the first ply body 36a and folded back from the inside to the outside in the axial direction around each core 30.

[0040] The second ply 38 includes a second ply body 38a that spans between the first core 30 and the second core 30, and a pair of second folded portions 38b that are connected to the second ply body 38a and folded back from the inside to the outside in the axial direction around each core 30.

[0041] Although not shown, the carcass ply 34 includes a number of parallel carcass cords. Each carcass cord intersects the equator plane. The carcass cords are cords made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0042] In this tire 2, the end of the first turned-up portion 36b is located radially outward from the outer end of the apex 32. The end of the second turned-up portion 38b is located radially inward from the outer end of the apex 32. The end of the second turned-up portion 38b is located radially inward from the end of the first turned-up portion 36b. The second turned-up portion 38b is located axially inward from the first turned-up portion 36b. The end of the second turned-up portion 38b is located between the apex 32 and the first turned-up portion 36b. The end of the first turned-up portion 36b is located between the sidewall 6 and the strip apex 20, which will be described later.

[0043] 1, the length indicated by the symbol H1 is the radial height of the first turned-up portion 36b. This radial height H1 is the radial distance from the bead baseline to the end of the first turned-up portion 36b. The length indicated by the symbol H2 is the radial height of the second turned-up portion 38b. This radial height H2 is the radial distance from the bead baseline to the end of the second turned-up portion 38b.

[0044] In this tire 2, from the viewpoint of providing appropriate rigidity to the side portions, the ratio (H1 / HS) of the radial height H1 of the first folded portion 36b to the tire cross-sectional height HS is preferably 0.40 or greater and 0.60 or less. The ratio (H2 / HS) of the radial height H2 of the second folded portion 38b to the tire cross-sectional height HS is preferably 0.12 or greater and 0.18 or less.

[0045] The belt 14 is located radially inside the tread 4. The belt 14 is layered on the carcass 12 from the outside in the radial direction. The belt 14 is made up of at least two layers 40 laminated in the radial direction. The belt 14 of this tire 2 is made up of two layers 40 laminated in the radial direction. Of the two layers 40, the layer 40 located on the inner side is an inner layer 42, and the layer 40 located on the outer side is an outer layer 44.

[0046] Although not shown, each of the inner layer 42 and the outer layer 44 includes a number of parallel belt cords, each of which is inclined relative to the equator plane. The belt cords are made of steel.

[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 inside of the tread 4. The band 16 has a jointless structure. The band 16 of this tire 2 is a full band whose two ends face each other across the equatorial plane. The band 16 covers the entire belt 14.

[0048] Although not shown, the band 16 includes a spirally wound band cord. 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. In the tire 2, a cord made of organic fiber is used as the band cord. Examples of organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0049] The inner liner 18 is located 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 a low gas permeability coefficient. The inner liner 18 maintains the internal pressure of the tire 2.

[0050] Each strip apex 20 is made of crosslinked rubber. The strip apex 20 is located axially inward of the sidewall 6 and axially outward of the second ply body 38a of the carcass 12. An outer end 46 of the strip apex 20 is located radially outward from the axially outer end AE of the tire 2. An inner end 48 of the strip apex 20 is located radially inward from the end of the apex 32. An inner end 48 of the strip apex 20 is located between the second ply body 38a and the apex 32. The entire inner surface of the strip apex 20 contacts the outer surface of the second ply body 38a. In the meridian cross section of the tire 2 shown in FIG. 1 , the strip apex 20 extends from the outer end 46 toward the inner end 48 along the second ply body 38a.

[0051] As described above, no reinforcing layer that allows running in a punctured state is provided in the side portion of this tire 2. This tire 2 provides better ride comfort than a run-flat tire. This tire 2 improves ride comfort. This tire 2 has a lower vertical spring constant than a run-flat tire. With this tire 2, there is a concern that the resonance frequency of the longitudinal torsional mode will shift to the lower frequency side and overlap with the frequency band of the vehicle resonance. In this case, muffled noise in the 40 Hz range will be generated. With this tire 2, there is a risk that quietness will be impaired.

[0052] In the tire 2, the end of the first folded-back portion 36b is located at the outer end in the axial direction of the tire 2. AE Specifically, the end of the first folded portion 36b is located near the axially outer end of the tire 2. AE The outer end 46 of the strip apex 20 of the tire 2 is located radially outside the end of the first folded-up portion 36b. The end of the second turned-up portion 38b is located radially near the outer end of the flange of the rim R. The inner end 48 of the strip apex 20 of the tire 2 is located radially outward from the end of the second turned-up portion 38b. The strip apex 20 does not have a crescent-shaped cross section like the reinforcing layer of a run-flat tire, but has a sheet-like cross section with a uniform thickness. In the tire 2, the strip apex 20, the first folded portion 36b, and the second folded portion 38b effectively increase the rigidity of the side portion. In this tire 2, the resonance frequency of the longitudinal torsion mode is prevented from shifting to the lower frequency side. Since the generation of muffled noise is suppressed, this tire 2 maintains excellent quietness. The tire 2 can achieve an improvement in ride comfort while maintaining good quietness.

[0053] Fig. 2 shows a carcass line 50 representing the outline of the carcass 12 in a meridian cross section of the tire 2 shown in Fig. 1. In this tire 2, the carcass line 50 is represented by the outline of the outer surface of the second ply body 38a that constitutes the carcass 12. If the outline of this outer surface cannot be obtained, the carcass line 50 is represented by the center line of a carcass cord (not shown) included in the second ply body 38a. If the carcass 12 is composed of three or more carcass plies 34, the carcass line 50 is identified by the ply body that is located outermost.

[0054] 2, the position indicated by the symbol CE is the intersection of the equatorial plane and the carcass line 50. This intersection CE is the equator of the carcass line 50. The position indicated by the symbol CW is the axially outer end of the carcass line 50. In the tire 2, the axially outer end CW is the maximum width position of the carcass line 50. The line indicated by the symbol LW passes through the maximum width position CW and extends in the axial direction. This line LW is the axial reference line and is parallel to the bead baseline. The position indicated by the symbol SG is a position on the carcass line 50 corresponding to the outer end 46 of the strip apex 20. The position SG is a position equivalent to the outer end of the strip apex 20. This outer end equivalent position SG is represented by the intersection of the carcass line 50 and a normal to the carcass line 50 that passes through the outer end 46 of the strip apex 20. The position indicated by the symbol CA is a position on the carcass line 50 that corresponds to the boundary between the core 30 and the apex 32. Position CA is a position equivalent to the boundary between the core 30 and the apex 32. This boundary-equivalent position CA is represented by the intersection of the carcass line 50 and a straight line that passes through the radially outer end of the core 30 and extends in the axial direction.

[0055] The carcass line 50 is formed by smoothly connecting a plurality of arcs and straight lines. The carcass line 50 includes a center portion 52 formed of an arc passing through the equator CE. In Fig. 2, the position indicated by the symbol Ca is a position on the carcass line 50 that is 20 mm away from the equator CE. Although not shown, the arc that constitutes the center portion 52 (hereinafter referred to as the center arc) has a center on the equatorial plane and is represented by an arc that passes through the equator CE and a pair of positions Ca located on either side of the equator CE. The arrow indicated by the symbol Rc indicates the radius of the center arc. In the tire 2, the radius Rc of the center arc is set in the range of 800 mm or more and 1200 mm or less.

[0056] The carcass line 50 includes an outer portion 54 formed of an arc passing through the maximum width position CW. The arc constituting the outer portion 54 (hereinafter referred to as the outer arc) has its center on the axial reference line LW and is represented by an arc passing through the maximum width position CW and a position SG corresponding to the outer end of the strip apex 20. The arrow indicated by the symbol Rj indicates the radius of the outer arc. In this tire 2, the radius Rj of the outer circular arc is set in the range of 30 mm to 70 mm. The radius Rj of the outer circular arc is measured by matching the distance between the left and right beads 10 in a cross section of the tire 2 obtained by cutting the tire 2 along a plane including the rotation axis to the distance between the beads 10 in the tire 2 mounted on a regular rim.

[0057] In this tire 2, the zone of the carcass line 50 from the maximum width position CW to the position CA corresponding to the boundary between the core 30 and the apex 32 includes a first inner portion 56 connecting the maximum width position CW and the position SU corresponding to the inner end of the strip apex 20, and a second inner portion 58 connecting the position SU corresponding to the inner end of the strip apex 20 and the position CA corresponding to the boundary between the core 30 and the apex 32.

[0058] The first inner portion 56 has an outwardly convex shape. In a meridian cross section of the tire 2, the first inner portion 56 has a rounded shape. The first inner portion 56 may be formed of a single arc, may be formed by smoothly connecting multiple arcs, or may be formed by smoothly connecting multiple arcs and straight lines.

[0059] The second inner portion 58 has an inwardly convex shape. In a meridian cross section of the tire 2, the second inner portion 58 has a rounded shape. The second inner portion 58 may be formed by a single arc, may be formed by smoothly connecting multiple arcs, or may be formed by smoothly connecting multiple arcs and straight lines.

[0060] In this tire 2, the curved state of the first inner portion 56 is represented by an arc (hereinafter referred to as the first inner arc) that has its center on the axial reference line LW and passes through the maximum width position CW and a position SU corresponding to the inner end of the strip apex 20. The arrow indicated by the symbol V1 in Fig. 3 indicates the radius of the first inner arc. The radius V1 of the first inner arc is measured by matching the distance between the left and right beads 10 in a cross section of the tire 2 obtained by cutting the tire 2 along a plane including the rotation axis to the distance between the beads 10 in the tire 2 mounted on a regular rim.

[0061] In this tire 2, the zone from the maximum width position CW to the boundary-equivalent position CA is represented by an S-shaped line. Because the first inner circular arc, which represents the curvature of the first inner portion 56, has a small radius V1, the outer end of the apex 32 in this tire 2 can be positioned axially outward compared to conventional tires. In other words, the apex 32 in this tire 2 can be positioned laterally. This tire 2 can further improve ride comfort. From this viewpoint, the radius V1 of the first inner circular arc is preferably 55 mm or less, and more preferably 50 mm or less. From the viewpoint of appropriately maintaining the rigidity of the side portion and suppressing the generation of muffled noise, the radius V1 of the first inner circular arc is preferably 35 mm or more, and more preferably 40 mm or more.

[0062] It is preferable that the first inner portion 56 can be represented by a single arc, but if the first inner portion 56 cannot be represented by a single arc, the first inner arc will deviate from the first inner portion 56, as shown in FIG. 3, for example. 3, the position indicated by the symbol P1 is the position where the length from the first inner circular arc to the first inner portion 56, measured along the normal to the first inner circular arc, is at its maximum. The double-headed arrow X1 indicates the length of the line segment connecting the center of the first inner circular arc and the position P1. In the present disclosure, the ratio (V1 / X1) of the radius V1 of the first inner circular arc to the length X1 is an index for understanding the degree to which the first inner circular arc deviates from the first inner portion 56. The closer this ratio (V1 / X1) is to 1, the smaller the deviation of the first inner circular arc from the first inner portion 56; in other words, the more the first inner circular arc coincides with the first inner portion 56.

[0063] In the tire 2, the closer the first inner circular arc coincides with the first inner portion 56, the more effectively the first inner portion 56 can contribute to improving ride comfort and suppressing the generation of muffled noise. From this viewpoint, the ratio (V1 / X1) is preferably equal to or greater than 0.95 and equal to or less than 1.05, more preferably equal to or greater than 0.97 and equal to or less than 1.03, and still more preferably equal to or greater than 0.99 and equal to or less than 1.01.

[0064] In the tire 2, the radius V1 of the first inner circular arc is preferably smaller than the radius Rj of the outer circular arc. This achieves a good balance between quietness and ride comfort. From this viewpoint, the ratio (V1 / Rj) of the radius V1 to the radius Rj is more preferably equal to or less than 0.95, and further preferably equal to or less than 0.90. From the viewpoint of forming a carcass line 50 with an appropriate shape, the ratio (V1 / Rj) is preferably equal to or greater than 0.70, more preferably equal to or greater than 0.75, and further preferably equal to or greater than 0.80.

[0065] In this tire 2, the curved state of the second inner portion 58 is represented by an arc (hereinafter referred to as the second inner arc) that has its center on the bead baseline and passes through a position SU corresponding to the inner end of the strip apex 20 and a position CA corresponding to the boundary. The arrow indicated by the symbol V2 in Fig. 3 indicates the radius of the second inner arc. The radius V2 of the second inner arc is measured by matching the distance between the left and right beads 10 in a cross section of the tire 2 obtained by cutting the tire 2 along a plane including the rotation axis to the distance between the beads 10 in the tire 2 mounted on a regular rim.

[0066] As described above, in the tire 2, the zone from the maximum width position CW to the boundary-equivalent position CA is represented by an S-shaped line. The second inner arc representing the curved state of the second inner portion 58 has a radius V2 smaller than the radius V1 of the first inner arc representing the curved state of the first inner portion 56, allowing the apex 32 of the tire 2 to be positioned in a reclined position. The tire 2 can further improve ride comfort. From this viewpoint, it is preferable that the radius V2 of the second inner arc be smaller than the radius V1 of the first inner arc. Specifically, the ratio (V2 / V1) of the radius V2 of the second inner arc to the radius V1 of the first inner arc is preferably 0.85 or less, more preferably 0.80 or less, and even more preferably 0.78 or less. From the viewpoint of appropriately maintaining the rigidity of the side portion and effectively suppressing the generation of muffled noise, the ratio (V2 / V1) is preferably 0.60 or more, more preferably 0.65 or more, and still more preferably 0.70 or more.

[0067] Like the first inner portion 56, it is preferable that the second inner portion 58 can be represented by a single arc, but if the second inner portion 58 cannot be represented by a single arc, the second inner arc will deviate from the second inner portion 58, as shown in FIG. 3. 3, the position indicated by the symbol P2 is the position where the length measured along the normal to the second inner circular arc from the second inner circular arc to the second inner portion 58 is at its maximum. The double-headed arrow X2 indicates the length of the line segment connecting the center of the second inner circular arc and the position P2. In the present disclosure, the ratio (V2 / X2) of the radius V2 of the second inner circular arc to the length X2 is an index for understanding the degree to which the second inner circular arc deviates from the second inner portion 58. The closer this ratio (V2 / X2) is to 1, the smaller the deviation of the second inner circular arc from the second inner portion 58; in other words, the more the second inner circular arc coincides with the second inner portion 58.

[0068] In the tire 2, the closer the second inner circular arc coincides with the second inner portion 58, the more effectively the second inner portion 58 can contribute to improving ride comfort and suppressing the generation of muffled noise. From this viewpoint, the ratio (V2 / X2) is preferably equal to or greater than 0.95 and equal to or less than 1.05, more preferably equal to or greater than 0.97 and equal to or less than 1.03, and still more preferably equal to or greater than 0.99 and equal to or less than 1.01.

[0069] 2, the length indicated by the symbol AW is the axial distance from a position CA corresponding to the boundary between the core 30 and the apex 32 to the maximum width position CW. The length indicated by the symbol HW is the radial distance from the position CA corresponding to the boundary to the maximum width position CW.

[0070] In this tire 2, the axial distance AW is preferably greater than half the radial distance HW. In other words, the ratio (AW / HW) of the axial distance AW to the radial distance HW is preferably greater than 0.5. The carcass line 50 of this tire 2 is configured to run outward compared to the carcass lines of conventional tires. The carcass line 50 is configured with a small curve in the side portion. This carcass line 50 contributes to improving ride comfort. From this viewpoint, the ratio (AW / HW) is more preferably 0.55 or greater. From the viewpoint of appropriately maintaining the rigidity of the side portion and effectively suppressing the generation of muffled noise, the ratio (AW / HW) is preferably 0.70 or less, and more preferably 0.65 or less.

[0071] 1, the length indicated by the symbol HU is the radial distance from the bead base line to the inner end 48 of the strip apex 20. The length indicated by the symbol HX is the radial distance from the inner end 48 to the outer end 46 of the strip apex 20.

[0072] In the tire 2, the ratio (HU / HS) of the radial distance HU from the bead base line to the inner end 48 of the strip apex 20 to the tire cross-sectional height HS is preferably 0.14 or greater and 0.20 or less. By setting the ratio (HU / HS) to 0.20 or less, the strip apex 20 effectively increases the rigidity of the side portion. The generation of muffled noise is effectively suppressed. The strip apex 20 contributes to improving quietness. From this viewpoint, the ratio (HU / HS) is more preferably 0.18 or less. By setting the ratio (HU / HS) to 0.14 or greater, the inner end 48 of the strip apex 20 is positioned at an appropriate position. In manufacturing the tire 2, the strip apex 20 is prevented from entering the radially inner side of the core 30, thereby preventing a deterioration in force variation. The tire 2 has good uniformity. From this viewpoint, the ratio (HU / HS) is more preferably 0.16 or greater.

[0073] In the tire 2, the ratio (HX / HS) of the radial distance HX from the inner end 48 to the outer end 46 of the strip apex 20 to the tire cross-sectional height HS is preferably 0.32 or greater and 0.56 or less. By setting the ratio (HX / HS) to 0.32 or more, the strip apex 20 increases the rigidity of the side portion. This effectively suppresses the generation of muffled noise. The strip apex 20 can contribute to improving quietness. From this perspective, it is more preferable that the ratio (HX / HS) be 0.40 or more. By setting the ratio (HX / HS) to be equal to or less than 0.56, the rigidity of the side portion is appropriately maintained. The tire 2 has a good ride comfort. From this viewpoint, the ratio (HX / HS) is more preferably equal to or less than 0.48.

[0074] In the tire 2, the complex modulus of elasticity of the strip apex 20 at 70° C. is preferably 50 MPa or more and 100 MPa or less. By setting the complex elastic modulus of the strip apex 20 to 50 MPa or more, the strip apex 20 increases the rigidity of the side portion. This effectively suppresses the generation of muffled noise. The strip apex 20 can contribute to improving quietness. From this viewpoint, the complex elastic modulus is more preferably 60 MPa or more, and even more preferably 65 MPa or more. By setting the complex elastic modulus of the strip apex 20 to 100 MPa or less, the rigidity of the side portion is appropriately maintained. The tire 2 has a good ride comfort. From this viewpoint, the complex elastic modulus of the strip apex 20 is more preferably 90 MPa or less, and further preferably 85 MPa or less.

[0075] In the tire 2, the thickness of the strip apex 20 is preferably 0.8 mm or more and 1.2 mm or less. The thickness of the strip 20 is expressed as the thickness of the strip 20 at the axially outer end AE of the tire 2. By setting the thickness of the strip apex 20 to 0.8 mm or more, the strip apex 20 increases the rigidity of the side portion. The generation of muffled noise is effectively suppressed. The strip apex 20 can contribute to improving quietness. From this viewpoint, the thickness of the strip apex 20 is more preferably 0.9 mm or more. By setting the thickness of the strip apex 20 to 1.2 mm or less, the rigidity of the side portion is appropriately maintained. The tire 2 has a good ride comfort. From this viewpoint, the thickness of the strip apex 20 is more preferably 1.1 mm or less.

[0076] As described above, according to the present invention, a tire can be obtained that can achieve an improvement in ride comfort while maintaining good quietness. [Example]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0078] [Example 1] A pneumatic tire for a passenger car (tire size = 245 / 50R19 101W) having the basic configuration shown in Fig. 1 and the specifications shown in Table 1 below was obtained. The side portions of Example 1 are not provided with a reinforcing layer that is provided on the side portions of a run-flat tire. The complex modulus of elasticity of the strip apex at 70° C. was 75 MPa, and the thickness of the strip apex was 1.0 mm. The radius V1 of the first inner circular arc, which represents the curvature of the first inner portion, was 46 mm. The ratio (V2 / V1) of the radius V2 of the second inner circular arc, which represents the curvature of the second inner portion, to the radius V1 of the first inner circular arc was 0.76. The ratio (V1 / Rj) of the radius V1 of the first inner circular arc to the radius Rj of the outer circular arc was 0.90. The ratio (HU / HS) of the radial distance HU from the bead base line to the inner end of the strip apex to the tire section height HS was 0.17. The ratio (HX / HS) of the radial distance HX from the inner end to the outer end of the strip apex to the tire section height HS was 0.45. The ratio (V1 / X1) of the radius V1 of the first inner circular arc to the length X1 was 0.99. The ratio (V2 / X2) of the radius V2 of the second inner circular arc to the length X2 was 0.99.

[0079] [Comparative Example 1] Comparative Example 1 is a conventional tire. This Comparative Example 1 is a side reinforced type run-flat tire (tire size=245 / 50R19 101W). A reinforcing layer having a crescent-shaped cross section is provided on the side portion of Comparative Example 1. This is indicated by a "Y" in the "Reinforcing Layer" column in Table 1. Comparative Example 1 does not have a strip apex.

[0080] Comparative Example 2 Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that no reinforcing layer was provided on the side portion.

[0081] [Example 2] Example 2 was obtained in the same manner as Example 1, except that the radius V1 and the radius V2 were changed to make the ratio (V2 / V1) and the ratio (AW / HW) as shown in Table 1 below.

[0082] [Muffled noise rating] The prototype tire was mounted on a rim (size = 19 x 8.0J) and air was inflated to adjust the tire's internal pressure to 250 kPa. The tire was then mounted on a test vehicle (a domestic passenger car (engine displacement = 3500 cc)). The test vehicle was driven at 60 km / h on a test course with a dry asphalt surface, and the sound pressure level at 40 Hz was measured at the driver's window ear position. The results are shown in Table 1 below, with Comparative Example 1 indexed as 100. The higher the value, the more muffled noise was suppressed.

[0083] [Driving performance] The prototype tire was mounted on a rim (size = 19 x 8.0J) and air was inflated to adjust the internal pressure of the tire to 250 kPa. The tire was mounted on a test vehicle (a domestic passenger car (engine displacement = 3500 cc)). The test vehicle was run at 100 km / h on a test course with a dry asphalt road surface, and a sensory evaluation was conducted regarding ride comfort and handling stability. The results are shown in Table 1 below, where Comparative Example 1 is indexed to 100. The higher the index, the better the performance.

[0084] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) was measured when the prototype tire ran on a drum at a speed of 80 km / h under the following conditions. The results are shown in Table 1 below as an index, with Comparative Example 1 being set at 100. The higher the value, the lower the rolling resistance of the tire. Rim: 19 x 8.0J Internal pressure: 250kPa Vertical load: 5.67kN

[0085] [Table 1]

[0086] As shown in Table 1, it has been confirmed that the examples can achieve an improvement in ride comfort while maintaining good quietness. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0087] The above-described technology that can achieve an improvement in ride comfort while maintaining good quietness can be applied to various types of tires. [Explanation of symbols]

[0088] 2. Tires 4. Tread 6. Sidewall 10 Bead 12. Carcass 20 Strip Apex 30 cores 32 Apex 36 First Ply 36a First ply body 36b First folded part 38···Second ply 38a Second ply body 38b Second folded part 46···Outer end of strip apex 20 48···Inner end of strip apex 20 50···Carcass line 56 First inner part 58 Second inner part

Claims

1. a pair of beads having a core and an apex; a carcass having a first ply and a second ply stacked together, each of the first ply and the second ply having a ply body spanning between one core and the other core, and a pair of turn-up portions continuous with the ply body and turned up around the core; a pair of strip apexes located axially outward of the ply body; Equipped with an inner end of each strip apex is located between the ply body and the apex; an outer end of the strip apex is located radially outward from an end of the turned-up portion of the first ply, and an inner end of the strip apex is located radially outward from an end of the turned-up portion of the second ply, a carcass line representing an outline of the carcass in a meridian cross section includes a first inner portion connecting a maximum width position and a position corresponding to an inner end of the strip apex, and a second inner portion connecting the position corresponding to the inner end of the strip apex and a position corresponding to a boundary between the core and the apex, The first inner portion has an outwardly convex shape, The second inner portion has an inwardly convex shape, the curved state of the first inner portion is represented by a first inner arc, which is an arc having a center on a straight line passing through the maximum width position and extending in the axial direction, and passing through the maximum width position and a position corresponding to the inner end of the strip apex, The radius of the first inner circular arc is 35 mm or more and 55 mm or less, the curved state of the second inner portion is represented by a second inner arc, which is an arc having a center on the bead baseline and passing through a position corresponding to the inner end of the strip apex and a position corresponding to the boundary between the core and the apex; the radius of the second inner circular arc is smaller than the radius of the first inner circular arc; tire.

2. The ratio of the radius of the second inner circular arc to the radius of the first inner circular arc is 0.60 or more and 0.85 or less.

2. The tire of claim 1.

3. The carcass line further includes an outer portion connecting the maximum width position and a position corresponding to the outer end of the strip apex, the outer portion is represented by an outer arc, which has a center on a straight line passing through the maximum width position and extending in the axial direction, and which passes through the maximum width position and a position corresponding to the outer end of the strip apex, The radius of the first inner circular arc is smaller than the radius of the outer circular arc.

3. The tire according to claim 1 or 2.

4. The ratio of the radius of the first inner circular arc to the radius of the outer circular arc is 0.70 or more and 0.95 or less.

4. The tire of claim 3.

5. a distance in an axial direction from a position corresponding to a boundary between the core and the apex to the maximum width position is greater than half a distance in a radial direction from the position corresponding to a boundary between the core and the apex to the maximum width position; 5. A tire according to any one of claims 1 to 4.

6. a ratio of a radial distance from a bead base line to an inner end of the strip apex to a tire cross section height is 0.14 or more and 0.20 or less; 6. A tire according to any one of claims 1 to 5.

7. a ratio of a radial distance from an inner end to an outer end of the strip apex to a tire section height is 0.32 or more and 0.56 or less; 7. A tire according to any one of claims 1 to 6.

8. The complex elastic modulus of the strip apex at 70 ° C. is 50 MPa or more and 100 MPa or less, 8. A tire according to any one of claims 1 to 7.

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