JP6672892B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire.

  The tire has a pair of beads. Each bead has a core and an apex. The apex extends radially outward from the core. Apex is made of a high-hardness crosslinked rubber.

  The carcass of a tire is formed by folding a carcass ply around a core. Thus, the carcass ply has a main portion extending from the equatorial plane toward the core, and a folded portion extending radially outward from the core along the apex.

  In the tire, the bead portion is fitted on the rim. In the running state, a large load is applied to this bead portion. For this reason, the durability of the bead portion is important. Various studies have been made on the configuration of the bead portion. Examples of this study are disclosed in JP-A-2012-025280 and JP-T-2013-545671.

  In the tire described in Japanese Patent Application Laid-Open No. 2012-025280, in addition to the apex (hereinafter, first apex) extending radially outward from the core, another apex (hereinafter, first apex) is provided at the carcass folded portion in the axial direction. , Second apex). In this tire, by adjusting the configuration of the bead portion in this way, the durability is improved and the weight is reduced.

  Also in the tire disclosed in JP-T-2013-545671, the bead is provided with a bead filler (corresponding to a first apex) and an outer strip (corresponding to a second apex). The height of the bead filler is less than 20% of the cross-sectional height of the tire. By adjusting the shape of the bead, rolling resistance is reduced while maintaining durability.

JP 2012-025280 A JP-T-2013-545671

  Further improvement in durability is desired. In the running state of the tire, the bead portion repeats deformation and restoration. At this time, the strain tends to concentrate particularly near the tip of the first apex. This concentration of distortion hinders improvement in durability. In conventional tires, the suppression of the concentration of the strain has not been sufficiently studied. As a result, the durability may not be sufficiently improved.

  In order to improve durability, a method of increasing the first apex may be employed as long as the steering stability is not impaired. The main part of the carcass ply is located axially inside the first apex. A turn-back portion of the carcass ply is located outside the first apex in the axial direction. When the bead portion is deformed, a pulling force is applied radially outward to the main portion, and a compressive force is applied radially inward to the folded portion. With a large first apex, the first apex also receives a large pulling force from the main portion and a large compressive force from the turn-back portion. Thereby, bending deformation may occur in the first apex. When the vehicle stops for a long time, the deformation of the first apex becomes difficult to recover. As a result, a “flat spot” that is not restored while the tire is deformed may occur. A large first apex can lead to a flat spot.

  Further, the size of a bead has often been defined in the past in relation to the sectional height of the tire. However, the section height of the tire includes parameters that are not directly related to the durability of the bead portion, such as the thickness of the tread. When the size of the bead is determined according to this definition, the expected effect of improving the durability may not be obtained.

  An object of the present invention is to provide a pneumatic tire having improved durability and reduced flat spots.

  A pneumatic tire according to the present invention includes a pair of beads and a carcass bridged between the beads. Each bead has a core and a first apex extending radially outward from the core. When the tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and a load of 120% of the regular load is applied to the tire, the tire has a profile on an outer surface thereof. The position where the width of the tire becomes maximum is defined as a reference position Pm, a straight line extending in the axial direction passing through the reference position Pm is defined as a reference line M, and the height from the reference position Pm to the outer end of the tread in the radial direction is defined as a height. When the position on the profile of the outer surface of the tire, which is a distance 0.2 times the height Ht radially outward from the reference position Pm, is Pl, the reference line A radius of curvature Rm of an arc Cm having a center Zm on M and passing through the reference position Pm and the position Pl is smaller than a distance Lm between the center Zm and the tip of the first apex.

  Preferably, a ratio (Rm / Lm) of the radius of curvature Rm to the distance Lm is 0.75 or more and 0.95 or less.

  Preferably, in the above state, the intersection between the reference line M and the outer surface of the carcass is Pp, and a straight line extending in the axial direction passing through the position Pl is a reference line L, and the reference line L and the carcass Is defined as Pq, the radius of curvature Rp of an arc Cp having a center Zp on the reference line M and passing through the intersection Pp and the intersection Pq is represented by the center Zp and the first apex. Is smaller than the distance Lp with respect to the tip.

  Preferably, a ratio (Rp / Lp) of the radius of curvature Rp to the distance Lp is 0.70 or more and 0.90 or less.

  Preferably, the bead further includes a second apex located axially outside the first apex. The carcass has a carcass ply. The carcass ply is folded around the core from the inside to the outside in the axial direction, and a main portion and a folded portion are formed in the carcass ply by the folding. The folded portion is located between the first apex and the second apex. The tire is mounted on a regular rim, filled with air so that the tire has a regular internal pressure, and in a state where a load is not applied to the tire, a radial direction from a bead base line to an outer end of the second apex is set. The ratio (H2 / Hc) of the height H2 to the radial height Hc from the bead base line to the outer end of the folded portion of the carcass splice is 1.05 or more.

  The bead further includes a second apex positioned axially outside the first apex, the carcass includes a carcass ply, and the carcass ply is axially inward around the core. The carcass ply is folded back to form a main portion and a folded portion, and the folded portion is located between the first apex and the second apex. When the tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and no load is applied to the tire, the outer end of the folded portion of the carcass splice from the bead base line is provided. To the radial height H2 from this bead baseline to the outer end of the second apex. (Hc / H2) may be 1.05 or more.

  The inventors have studied in detail the structure of a bead for improving durability. As a result, it has been found that the relationship between the tire profile when bent by the load and the structure of the bead greatly affects durability. By determining the structure of the bead in relation to the profile of the tire when a load is applied, the durability can be effectively improved as compared with the conventional method in which the structure is determined in relation to the sectional height. That is, by appropriately adjusting the relationship between the profile of the outer surface of the tire when flexed by the load and the position of the tip of the first apex, distortion near the tip of the first apex can be effectively reduced. . Thereby, even if the first apex is reduced, good durability can be realized.

  In the pneumatic tire according to the present invention, when the tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and the tire is loaded with 120% of a regular load, The position where the width of the tire is maximum on the profile of the outer surface of the tire is defined as a reference position Pm, a straight line extending in the axial direction passing through the reference position Pm is defined as a reference line M, and the reference line P is defined in the radial direction from the reference position Pm. The height up to the outer end of the tread is defined as Ht, and a position on the profile of the outer surface of the tire, which is radially outward from the reference position Pm and separated by a distance of 0.2 times the height Ht, When Pl is set, the radius of curvature Rm of the arc Cm having the center Zm on the reference line M and passing through the reference position Pm and the position Pl is determined by the distance Lm between the center Zm and the tip of the first apex. Small. In other words, the tip of the first apex is located outside the virtual circle including the arc Cm. Thereby, distortion near the tip of the first apex when the tire is bent is effectively reduced. This tire has excellent durability.

  Furthermore, in this tire, since distortion near the tip of the first apex is reduced, good durability can be realized even if the first apex itself is reduced. The first apex can be made smaller than the conventional first apex. The bending deformation of the first apex is small. In this tire, a flat spot is prevented.

FIG. 1 is a sectional view showing a part of a pneumatic tire according to one embodiment of the present invention. FIG. 2 is an enlarged sectional view showing a part of the tire of FIG. FIG. 3 is a sectional view showing a part of a pneumatic tire according to another embodiment of the present invention.

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

  FIG. 1 shows a pneumatic tire 2. In this figure, the up-down direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents an equatorial plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equatorial plane except for the tread pattern.

  The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, an inner liner 18, and a pair of chafers 20. The tire 2 is a tubeless type. The tire 2 is mounted on a small truck.

  The tread 4 has a shape convex outward in the radial direction. The tread 4 forms a tread surface 22 that contacts the road surface. A groove 24 is formed in the tread 4. The grooves 24 form a tread pattern. The tread 4 has a base layer 26 and a cap layer 28. The cap layer 28 is located radially outside the base layer 26. The cap layer 28 is laminated on the base layer 26. The base layer 26 is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber of the base layer 26 is a natural rubber. The cap layer 28 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties.

  Each sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. A radially inner end of the sidewall 6 is joined to the clinch 8. The sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 6 prevents the carcass 12 from being damaged.

  Each clinch 8 is located substantially inside the sidewall 6 in the radial direction. The clinch 8 extends from the end of the sidewall 6 substantially inward in the radial direction. The clinch 8 is located outside the bead 10 and the carcass 12 in the axial direction. The clinch 8 is made of a crosslinked rubber having excellent wear resistance. The clinch 8 abuts the flange of the rim.

  Each bead 10 is located axially inward of the clinch 8. The bead 10 includes a core 30 and a first apex 32. The core 30 is ring-shaped and includes a wound non-stretchable wire. A typical material of the wire is steel. The first apex 32 extends radially outward from the core 30. The first apex 32 tapers radially outward. The first apex 32 is made of a high-hardness crosslinked rubber.

  The carcass 12 has a carcass ply. In this embodiment, the carcass 12 comprises two carcass plies, a first ply 34 and a second ply. The first ply 34 and the second ply are bridged between the beads 10 on both sides, and are along the tread 4 and the sidewall 6.

  The first ply 34 is folded around the core 30 from the inside to the outside in the axial direction. By this folding, the main portion 34a and the folded portion 34b are formed in the first ply 34. The main portion 34a passes through the inside of the first apex 32 in the axial direction. The folded portion 34b extends radially outward through the outside of the first apex 32 in the axial direction.

  The second ply 36 is folded around the core 30 from the inside to the outside in the axial direction. By this folding, the main portion 36a and the folded portion 36b are formed in the second ply 36. The main portion 36a passes through the inside of the first apex 32 in the axial direction. The folded portion 36b extends radially outward through the outside of the first apex 32 in the axial direction. In this embodiment, the end of the folded portion 36b of the second ply 36 is located outside the end of the folded portion 34b of the first ply 34 in the radial direction. As described above, when the carcass 12 includes a plurality of carcass plies, the end of the folded portion located on the outermost side in the radial direction is referred to as the outer end of the folded portion of the carcass ply. In this embodiment, the end of the folded portion 34b of the first ply 34 is the outer end of the folded portion of the carcass ply.

  Although not shown, the first ply 34 and the second ply 36 are composed of a number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equatorial plane CL is 75 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is made of organic fibers. Preferred organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers. The carcass 12 may be formed from a single ply.

  The belt 14 is located inside the tread 4 in the radial direction. The belt 14 is laminated on the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner layer 14a and an outer layer 14b. As is clear from FIG. 1, the width of the inner layer 14a is slightly larger than the width of the outer layer 14b in the axial direction. Although not shown, each of the inner layer 14a and the outer layer 14b is composed of a number of parallel cords and topping rubber. Each code is inclined with respect to the equatorial plane. A typical absolute value of the tilt angle is 10 ° or more and 35 ° or less. The direction of inclination of the cord of the inner layer 14a with respect to the equatorial plane is opposite to the direction of inclination of the cord of the outer layer 14b with respect to the equatorial plane. The preferred material of the cord is steel. Organic fibers may be used for the cord. The axial width of the belt 14 is preferably 0.7 times or more the maximum width of the tire 2. The belt 14 may include three or more layers.

  The band 16 is located radially outside the belt 14. In the axial direction, the width of the band 16 is larger than the width of the belt 14. Although not shown, the band 16 is made of a cord and a topping rubber. The cord is spirally wound. This band 16 has a so-called jointless structure. The cord extends substantially circumferentially. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 14 is restrained by this cord, lifting of the belt 14 is suppressed. The cord is made of organic fibers. Preferred organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

  The inner liner 18 is located inside the carcass 12. The inner liner 18 is joined to the inner surface of the carcass 12. The inner liner 18 is made of a crosslinked rubber having excellent air shielding properties. A typical base rubber for the inner liner 18 is butyl rubber or halogenated butyl rubber. The inner liner 18 holds the internal pressure of the tire 2.

  Each chafer 20 is located near the bead 10. When the tire 2 is mounted on the rim, the chafer 20 comes into contact with the rim. By this contact, the vicinity of the bead 10 is protected. In this embodiment, the chafer 20 is made of a cloth and a rubber impregnated in the cloth. The chafer 20 may be integral with the clinch 8. In this case, the material of the chafer 20 is the same as the material of the clinch 8.

  FIG. 2 shows a part of the tire 2 shown in FIG. The tire 2 is mounted on a regular rim 40, is filled with air so as to have a regular internal pressure, and is in a state where a load of 120% of the regular load is applied from the outside to the inside in the radial direction. In FIG. 2, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the vertical direction to the paper surface is the circumferential direction of the tire 2.

  In this specification, the regular rim 40 means a rim defined in a standard on which the tire 2 depends. The “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, and the “Measuring Rim” in the ETRTO standard are regular rims. In this specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 depends. The “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the JATMA standard, “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “INFLATION PRESSURE” in the ETRTO standard are normal internal pressures. In the present specification, the normal load means a load determined in a standard on which the tire 2 depends. “Maximum load capacity” in the JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “LOAD CAPACITY” in the ETRTO standard are normal loads.

  In the present invention, the contour of the outer surface of the tire 2 is referred to as a profile 38. When the groove 24 or the protrusion is provided on the outer surface, the profile 38 is represented by using a virtual outer surface obtained assuming that the groove 24 or the protrusion is not provided. FIG. 2 shows a partial profile 38 of the tire 2 shown in FIG. This figure further shows the outline of the core 30, the first apex 32, and the second ply.

  In FIG. 2, the symbol Pm is a position on the profile 38 on the outer surface. At this position, the width of the tire 2 is maximized. This position Pm is called a reference position. The straight line M is a reference line that passes through the reference position Pm and extends in the axial direction. The double-headed arrow Ht indicates a height from the reference position Pm to a radially outer end of the tread 4. The symbol Pl is a position on the profile 38 on the outer surface. The position Pl is a position located radially outward of the reference position Pm at a distance of 0.2 times the height Ht. That is, the height from the reference position Pm to the position Pl is 0.2 times the height Ht. The straight line L is a reference line that passes through the position P1 and extends in the axial direction.

  In FIG. 2, reference numeral Cm is an arc having a center Zm on a straight line M. The arc Cm follows the profile 38 of the tire 2 from the reference position Pm toward the outside in the radial direction. Specifically, the arc Cm is an arc having the center Zm on the straight line M and passing through the reference position Pm and the position Pl. In FIG. 2, the arc Cm is extended to the vicinity of the first apex 32.

  In FIG. 2, a double arrow Lm is a distance between the tip 41 of the first apex 32 and the center Zm. In the tire 2, the radius of curvature Rm of the arc Cm is smaller than the distance Lm. In other words, the tip 41 of the first apex 32 is located outside the circle including the arc Cm.

  Hereinafter, the operation and effect of the present invention will be described.

  In the running state of the tire, the bead portion repeats deformation and restoration. At this time, the strain tends to concentrate particularly near the tip of the first apex. This concentration of distortion hinders improvement in durability. In conventional tires, the suppression of the concentration of the strain has not been sufficiently studied. In order to improve durability, a method of increasing the first apex may be employed as long as the steering stability is not impaired. The main part of the carcass ply is located axially inside the first apex. A turn-back portion of the carcass ply is located outside the first apex in the axial direction. When the bead portion is deformed, a pulling force is applied radially outward to the main portion, and a compressive force is applied radially inward to the folded portion. As the first apex increases, the pulling force received by the first apex from the main portion and the compressive force received from the folded portion increase. Thereby, bending deformation may occur in the first apex. When the vehicle stops for a long time, the deformation of the first apex becomes difficult to recover. As a result, a “flat spot” that is not restored while the tire is deformed may occur. A large first apex can lead to a flat spot.

  The inventors have studied in detail the structure of a bead for improving durability. As a result, it has been found that the relationship between the tire profile when bent by the load and the structure of the bead greatly affects durability. By determining the structure of the bead in relation to the profile of the tire when a load is applied, the durability can be effectively improved as compared with the conventional method in which the structure is determined in relation to the sectional height. Specifically, in the conventional tire, the tip of the first apex enters the orbit of the circular arc of the profile of the sidewall when flexed by a load, so that the concentration of strain and the generation of heat near this tip are caused. It turned out that concentration was occurring. The concentration of distortion and the concentration of heat can cause looseness between tire components. By appropriately adjusting the relationship between the profile of the outer surface of the tire when flexed by the load and the position of the tip of the first apex, distortion near the tip of the first apex can be effectively reduced. Thereby, even if the first apex is reduced, good durability can be realized.

  In the pneumatic tire 2 according to the present invention, when an arc having the center Zm on the above-mentioned reference line M and passing through the reference position Pm and the position Pl is defined as Cm, the radius of curvature Rm of the arc Cm is the first Apec. It is smaller than the distance Lm between the tip 41 of the thread 32 and the center Zm. In other words, the tip 41 of the first apex 32 is located outside the virtual circle including the arc Cm. Thereby, the concentration of distortion and the concentration of heat near the tip 41 of the first apex 32 when the tire 2 is bent are effectively reduced. This tire 2 has excellent durability.

  Further, in the tire 2, the distortion near the tip 41 of the first apex 32 is reduced, so that the first apex 32 can be made smaller than the conventional first apex 32. The bending deformation of the first apex 32 is small. In the tire 2, a flat spot is prevented.

  The ratio (Rm / Lm) of the radius of curvature Rm to the distance Lm is preferably 0.95 or less. By setting the ratio (Rm / Lm) to 0.95 or less, in the tire 2, the concentration of strain and the concentration of heat in the vicinity of the tip 41 of the first apex 32 are more effectively reduced. This tire 2 has excellent durability. In this respect, the ratio (Rm / Lm) is more preferably equal to or less than 0.90. The ratio (Rm / Lm) is preferably 0.75 or more. By setting the ratio (Rm / Lm) to 0.75 or more, the rigidity of the bead 10 is appropriately maintained. In the tire 2, a decrease in durability due to a decrease in rigidity is suppressed. This tire 2 has excellent durability. Further, in the tire 2, since the rigidity of the bead 10 is appropriately maintained, good steering stability is maintained. From these viewpoints, the ratio (Rm / Lm) is more preferably equal to or greater than 0.78.

  As shown in FIG. 2, in this embodiment, the entire first apex 32 is located outside the virtual circle including the arc Cm. By positioning the entire first apex 32 outside the virtual circle including the arc Cm, the concentration of distortion and the concentration of heat in the first apex 32 are effectively reduced. This tire 2 has excellent durability.

  As shown in FIG. 2, in this embodiment, the profile 38 and the arc Cm match between the reference position Pm and the position Pl. Thus, it is preferable that the profile 38 and the arc Cm match between them. When the profile 38 matches the arc Cm, the side portion of the tire 2 flexes flexibly. In the tire 2, better durability and riding comfort can be realized. Here, “the profile 38 and the arc Cm match” indicates that the maximum value of the distance between the profile 38 and the arc Cm is equal to or less than a certain value. Specifically, when the maximum value of the distance between the profile 38 measured along the normal line of the circular arc Cm and the circular arc Cm is Δm, the ratio (Δm / Rm) of the maximum value Δm to the radius of curvature Rm is: , 0.03 or less.

  Although not shown, the position Pn is a position on the profile 38 on the outer surface, and is a position radially inward from the reference position Pm and separated by a distance of 0.2 times the height Ht. It is preferable that the profile 38 and the arc Cm match between the reference position Pm and the position Pn. When the profile 38 matches the arc Cm, the side portion of the tire 2 flexes flexibly. Better durability and ride comfort can be realized. In the tire 2, it is more preferable that the profile 38 and the arc Cm match between the position Pl and the position Pn. By matching the profile 38 and the arc Cm between the position Pl and the position Pn, the side portion of the tire 2 flexes flexibly in a wide range. As a result, better durability and riding comfort can be realized.

  In FIG. 2, a point Pp is an intersection of the reference line M and the outer surface of the carcass 12. In this embodiment, the point Pp is the intersection of the reference line M and the outer surface of the main portion 36a of the second ply 36. The point Pq is the intersection of the reference line L and the outer surface of the carcass 12. In this embodiment, the point Pq is the intersection of the reference line L and the outer surface of the main portion 36a of the second ply 36.

  In FIG. 2, reference numeral Cp is an arc having a center Zp on the reference line M. The arc Cp follows the contour of the carcass 12 from the intersection Pp toward the outside in the radial direction. Specifically, the arc Cp is an arc having a center on the straight line M and passing through the intersection Pp and the intersection Pq. In FIG. 2, the arc Cp is extended to the vicinity of the first apex 32.

  In FIG. 2, reference symbol Lp is the distance between the tip 41 of the first apex 32 and the center Zp. In the tire 2, the radius of curvature Rp of the arc Cp is preferably smaller than the distance Lp. At this time, the tip 41 of the first apex 32 is located outside the virtual circle including the arc Cp. This effectively reduces the concentration of distortion and the concentration of heat generated near the tip 41 of the first apex 32 when the tire 2 is bent. This tire 2 has excellent durability.

  The ratio (Rp / Lp) of the radius of curvature Rp to the distance Lp is preferably 0.90 or less. By setting the ratio (Rp / Lp) to 0.90 or less, in the tire 2, the concentration of distortion and the concentration of heat near the tip 41 of the first apex 32 are more effectively reduced. This tire 2 has excellent durability. In this respect, the ratio (Rp / Lp) is more preferably equal to or less than 0.85. The ratio (Rp / Lp) is preferably 0.70 or more. By setting the ratio (Rp / Lp) to 0.70 or more, the rigidity of the bead 10 is appropriately maintained. In the tire 2, a decrease in durability due to a decrease in rigidity is suppressed. This tire 2 has excellent durability. Further, in the tire 2, good steering stability is maintained. In this respect, the ratio (Rp / Lp) is more preferably equal to or greater than 0.73.

  As shown in FIG. 2, in this embodiment, the entire first apex 32 is located outside the virtual circle including the arc Cp. By locating the entire first apex 32 outside the virtual circle including the arc Cp, the concentration of distortion and the concentration of heat on the first apex 32 are effectively reduced. This tire 2 has excellent durability.

  As shown in FIG. 2, in this embodiment, between the intersection Pp and the intersection Pq, the contour of the carcass 12 matches the arc Cp. Thus, between these, it is preferable that the contour of the carcass 12 and the arc Cp match. Since the contour of the carcass 12 matches the arc Cp, the side portion of the tire 2 flexes flexibly. In the tire 2, better durability and riding comfort can be realized. Here, "the contour and the arc Cp match" indicates that the maximum value of the distance between the contour and the arc Cp is equal to or less than a certain value. Specifically, when the maximum value of the distance between the contour measured along the normal line of the circular arc Cp and the circular arc Cp is Δp, the ratio (Δp / Rp) of the maximum value Δp to the radius of curvature Rp is: 0.03 or less.

  Although not shown, the intersection Pr is an intersection between the reference line extending in the axial direction from the position Pn and the outer surface of the carcass 12. It is preferable that the contour of the carcass 12 and the arc Cp coincide between the intersection Pp and the intersection Pr. Since the contour of the carcass 12 matches the arc Cp, the side portion of the tire 2 flexes flexibly. Better durability and ride comfort can be realized. More preferably, between the intersection Pq and the intersection Pr, the contour of the carcass 12 matches the arc Cp. Since the contour of the carcass 12 and the arc Cp match between the intersection Pq and the intersection Pr, the side portion of the tire 2 flexes flexibly in a wide range. As a result, better durability and riding comfort can be realized.

  In FIG. 1, the double arrow L1 is the length of the first apex 32. This length L1 is represented by the length from the axial center of the bottom surface of the first apex 32 to its tip. The length L1 is measured in a state where the tire 2 is incorporated into the regular rim 40, the tire 2 is filled with air so as to have a regular internal pressure, and no load is applied to the tire 2. The same applies to the height Hc, the height H2, and the distance Ha described later.

  In the tire 2, the length L1 is preferably 5 mm or more. By setting the length L1 to 5 mm or more, the first apex 32 can effectively contribute to the rigidity of the bead 10 portion. This tire 2 has excellent durability. The tire 2 has excellent steering stability. The length L1 is preferably 15 mm or less. By setting the length L1 to 15 mm or less, the bending deformation of the first apex 32 is small. In the first apex 32, it is prevented that the deformation hardly returns even after parking for a long time. In the tire 2, a flat spot is prevented.

  In the tire 2, the complex elastic modulus E1 of the first apex 32 is preferably 60 MPa or more. When the elastic modulus E1 is set to 60 MPa or more, the first apex 32 contributes to supporting the tire 2. The tire 2 has excellent steering stability. The complex elastic modulus E1 is preferably 70 MPa or less. By setting the elastic modulus E1 to 70 MPa or less, the influence of the first apex 32 on the rigidity is suppressed. In the tire 2, good riding comfort is maintained.

In the present invention, the complex elastic modulus E1 of the first apex 32 and the complex elastic modulus E2 of the second apex described later are measured according to the provisions of “JIS K 6394”. The measurement conditions are as follows.
Viscoelastic spectrometer: "VESF-3" of Iwamoto Seisakusho
Initial distortion: 10%
Dynamic distortion: ± 1%
Frequency: 10Hz
Deformation mode: tensile Measurement temperature: 70 ° C

  FIG. 3 shows a pneumatic tire 42 according to another embodiment of the present invention. In this figure, the up-down direction is the radial direction of the tire 42, the left-right direction is the axial direction of the tire 42, and the direction perpendicular to the paper is the circumferential direction of the tire 42. In FIG. 3, an alternate long and short dash line CL represents an equatorial plane of the tire 42. The shape of the tire 42 is symmetrical with respect to the equatorial plane except for the tread pattern.

  The tire 42 includes a tread 44, a pair of sidewalls 46, a pair of clinches 48, a pair of beads 50, a carcass 52, a belt 54, a band 56, an inner liner 58, and a pair of chafers 60. The tire 42 is of a tubeless type. The tire 42 is mounted on a small truck. The tire 42 is the same as the tire 2 of FIG. 1 except for a clinch 48, a bead 50, and a carcass 52. Hereinafter, the clinch 48, the bead 50, and the carcass 52 will be described.

  Each clinch 48 is located substantially inside the sidewall 46 in the radial direction. The clinch 48 extends from the end of the sidewall 46 substantially inward in the radial direction. The clinch 48 is located outside the bead 50 and the carcass 52 in the axial direction. The clinch 48 is in contact with the second apex of the bead 50. The clinch 48 is made of a crosslinked rubber having excellent wear resistance. Clinch 48 abuts the flange of the rim.

  Each bead 50 is located axially inward of the clinch 48. The bead 50 includes a core 62, a first apex 64, and a second apex 66. The core 62 is ring-shaped and includes a wound non-stretchable wire. A typical material of the wire is steel. The first apex 64 extends radially outward from the core 62. The first apex 64 tapers radially outward. The second apex 66 is located outside the first apex 64 in the axial direction. The second apex 66 is located between the clinch 48 and the carcass 52 in the axial direction. In the tire 42, the outer end 68 of the second apex 66 is located outside the tip 70 of the first apex 64 in the radial direction. The first apex 64 and the second apex 66 are made of a high-hardness crosslinked rubber.

  The carcass 52 has a carcass ply. In this embodiment, the carcass 52 includes two carcass plies, a first ply 72 and a second ply 74. The first ply 72 and the second ply 74 are bridged between the beads 50 on both sides, and are along the tread 44 and the sidewall 46.

  The first ply 72 is folded around the core 62 from the inside in the axial direction to the outside. By this folding, the main part 72a and the folded part 72b are formed in the first ply 72. The main portion 72a passes through the inside of the first apex 64 in the axial direction. The folded portion 72b extends radially outward through the first apex 64 in the axial direction and through the second apex 66 in the axial direction. The folded portion 72b passes between the first apex 64 and the second apex 66. In this embodiment, the end 76 of the folded portion 72b is located between the inner end of the second apex 66 and the outer end 68 thereof in the radial direction.

  The second ply 74 is folded around the core 62 from the inside in the axial direction to the outside. By this folding, the main part 74a and the folded part 74b are formed in the second ply 74. The main portion 74a passes through the inside of the first apex 64 in the axial direction. The folded portion 74b extends radially outward through the first apex 64 in the axial direction and through the second apex 66 in the axial direction. The folded portion 74b passes between the first apex 64 and the second apex 66. In this embodiment, the end 78 of the folded portion 74b is located between the inner end of the second apex 66 and the outer end 68 thereof in the radial direction. In this embodiment, the end 78 of the folded portion 74b of the second ply 74 is located inside the end 76 of the folded portion 72b of the first ply 72 in the radial direction. When the carcass 52 includes a plurality of carcass plies in this manner, the end of the folded portion located on the outermost side in the radial direction is referred to as the outer end 80 of the folded portion of the carcass ply. In this embodiment, the end 76 of the folded portion 72b of the first ply 72 is the outer end 80 of the folded portion of the carcass ply.

  Although not shown, the reference position Pm refers to a state where the tire 42 is mounted on a normal rim, the tire 42 is filled with air so as to have a normal internal pressure, and a load of 120% of the normal load is applied to the tire 42. This is the position on the profile of the outer surface where the width of the tire 42 is maximum. Although not shown, the straight line M is a reference line extending in the axial direction passing through the reference position Pm. The height Ht is a height from the reference position Pm to a radially outer end of the tread 44. The position Pl is a position on the profile of the outer surface. The position Pl is a position located radially outward of the reference position Pm at a distance of 0.2 times the height Ht. That is, the height from the reference position Pm to the position Pl is 0.2 times the height Ht. The straight line L is a reference line that passes through the position P1 and extends in the axial direction.

  Although not shown, the arc Cm has a center Zm on the straight line M. The arc Cm conforms to the profile of the tire 42 from the reference position Pm toward the outside in the radial direction. Specifically, the arc Cm is an arc having the center Zm on the straight line M and passing through the reference position Pm and the position Pl.

  Although not shown, the distance Lm is the distance between the tip 70 of the first apex 64 and the center Zm. In the tire 42, the radius of curvature Rm of the arc Cm is smaller than the distance Lm. In other words, the tip 70 of the first apex 64 is located outside the circle including the arc Cm. In this embodiment, the entire first apex 64 is located outside the circle including the arc Cm.

  In the pneumatic tire 42 according to the present invention, when an arc conforming to the profile having the center Zm on the above-mentioned reference line M and conforming to the profile at the reference position Pm is Cm, the radius of curvature Rm of the arc Cm is the first Apex. The distance is smaller than the distance Lm between the tip 70 of the center 64 and the center Zm. In other words, the tip 70 of the first apex 64 is located outside the virtual circle including the arc Cm. Thereby, the concentration of distortion and the concentration of heat near the tip 70 of the first apex 64 when the tire 42 is bent are effectively reduced. The tire 42 has excellent durability.

  Further, in the tire 42, the distortion near the tip 70 of the first apex 64 is reduced, so that the first apex 64 can be made smaller than the conventional first apex 64. The bending deformation of the first apex 64 is small. In the tire 42, a flat spot is prevented.

  In FIG. 3, a solid line BBL is a bead baseline. The bead base line BBL is a line that defines the rim diameter of the rim R (see JATMA). The double arrow Hc is the height from the bead base line BBL to the outer end 80 of the folded portion of the carcass ply. In this embodiment, the height Hc is the height from the bead base line BBL to the end 76 of the folded portion 72b of the first ply 72. The double arrow H2 is the height from the bead base line BBL to the outer end 68 of the second apex 66.

  As shown in FIG. 3, in this embodiment, the height H2 is greater than the height Hc. In other words, the second apex 66 covers the end 76 of the folded portion 72b of the first ply 72. Since the end 76 of the folded portion 72b is covered with the second apex 66, the step due to the end 76 is prevented from affecting the outer surface of the tire 42. In the tire 42, generation of basil and dent on the outer surface is suppressed. The tire 42 has an excellent appearance.

  The ratio (H2 / Hc) of the height H2 to the height Hc is preferably 1.05 or more. When the outer end 80 of the folded portion of the carcass ply and the outer end 68 of the second apex 66 are located close to each other, concentration of strain occurs near the outer end. This can cause looseness near the outer edge 80 of the turnup. By setting the ratio (H2 / Hc) to 1.05 or more, the concentration of distortion near the outer end can be suppressed. In the tire 42, looseness in the vicinity of the outer end 80 of the folded portion is suppressed. The tire 42 has excellent durability. The ratio (H2 / Hc) is preferably 1.8 or less. By setting the ratio (H2 / Hc) to 1.8 or less, the rigidity of the bead 50 is appropriately maintained. With the tire 42, good riding comfort is realized.

  In FIG. 3, a double-headed arrow Ha indicates a radial distance between the outer end 80 of the folded portion of the carcass ply and the outer end 68 of the second apex 66. The distance Ha is preferably 2.0 mm or more. By setting the distance Ha to be equal to or greater than 2.0 mm, the concentration of distortion near the outer end 80 of the folded portion of the carcass ply can be suppressed. In the tire 42, looseness near the outer end 80 of the folded portion of the carcass ply is suppressed. The tire 42 has excellent durability. Further, by setting the distance Ha at 2.0 mm or more, the second apex 66 effectively contributes to the rigidity of the bead 50 portion. In the tire 42, excellent steering stability is realized. The distance Ha is preferably equal to or less than 50 mm. By setting the distance Ha to 50 mm or less, the rigidity of the bead 50 is properly maintained. With the tire 42, good riding comfort is realized.

  Although not shown, the height Hc may be larger than the height H2. That is, the end 76 of the folded portion 72b of the first ply 72 may be located outside the end 68 of the second apex 66. By doing so, the torsional rigidity of the side portion of the tire changes smoothly from near the maximum width position of the tire 42 to the bead 50 portion. That is, in a region (outside side region) outside the end 76 of the folded portion 72b of the first ply 72, the main portion 72a of the first ply 72 and the main portion 74a of the second ply 74 are located inside the side portion. I do. In a region (intermediate side region) between the end 68 of the second apex 66 and the end 76 of the folded portion 72b of the first ply 72, in addition to the two main portions 72a and 74a, the first ply 72 Is located inside the side portion. The torsional rigidity of the intermediate side region is greater than the torsional rigidity of the outer side region. In a region inside the end 68 of the second apex 66 (inner side region), the second apex 66 is further located in addition to these. The torsional rigidity of the inner side region is greater than the torsional rigidity of the intermediate side region. In this tire, the torsional rigidity increases from the outer side region toward the inner side region. Further, the torsional rigidity of the second apex 66 is greater than the first ply 72 and the second ply 74. Since the second apex 66 having large torsional rigidity is located inside the end 76 of the folded portion 72b of the first ply 72, a rapid change in torsional rigidity is suppressed. The torsional rigidity of the side part changes smoothly. This contributes to the riding comfort of the tire 42. The tire 42 has excellent ride comfort.

  The ratio (Hc / H2) of the height Hc to the height H2 is preferably 1.05 or more. When the outer end 80 of the folded portion of the carcass ply and the outer end 68 of the second apex 66 are located close to each other, concentration of strain occurs near the outer end. This can cause looseness near the outer edge 80 of the turnup. By setting the ratio (Hc / H2) to 1.05 or more, concentration of distortion near the outer end can be suppressed. In the tire 42, looseness in the vicinity of the outer end 80 of the folded portion is suppressed. The tire 42 has excellent durability. The ratio (Hc / H2) is preferably 1.8 or less. By setting the ratio (Hc / H2) to 1.8 or less, the second apex 66 effectively contributes to the rigidity of the bead 50 portion. In the tire 42, excellent steering stability is realized.

  Although not shown, even when the height H2 is smaller than the height Hc, the distance Ha is defined as the radial distance between the outer end 80 of the folded portion of the carcass ply and the outer end 68 of the second apex 66. In this case, the distance Ha is preferably 2.0 mm or more. By setting the distance Ha to be equal to or greater than 2.0 mm, the concentration of distortion near the outer end 80 of the folded portion of the carcass ply is suppressed. In the tire 42, looseness near the outer end 80 of the folded portion of the carcass ply is suppressed. The tire 42 has excellent durability. The distance Ha is preferably equal to or less than 50 mm. By setting the distance Ha to 50 mm or less, the second apex 66 effectively contributes to the rigidity of the bead 50 portion. In the tire 42, excellent steering stability is realized.

  In the tire 42, the second apex 66 is located between the clinch 48 and the folded portion 72 b of the first ply 72 and the folded portion 74 b of the second ply 74. In the tire 42, the folded portion 72b of the first ply 72 and the folded portion 74b of the second ply 74 are disposed axially inside the folded portion of the conventional tire. This arrangement can suppress the concentration of distortion on the folded portion. Since the generation of looseness is suppressed, the tire 42 has excellent durability.

  In the tire 42, the complex elastic modulus E1 of the first apex 64 is preferably 60 MPa or more. When the elastic modulus E1 is set to 60 MPa or more, the first apex 64 contributes to supporting the tire 42. The tire 42 has excellent steering stability. The complex elastic modulus E1 is preferably 70 MPa or less. By setting the elastic modulus E1 to 70 MPa or less, the influence of the first apex 64 on the rigidity is suppressed. In the tire 42, good riding comfort is maintained.

  In the tire 42, the complex elastic modulus E2 of the second apex 66 is preferably 60 MPa or more. By setting the elastic modulus E2 to 60 MPa or more, the second apex 66 contributes to the rigidity. The tire 42 has excellent steering stability. The complex elastic modulus E2 is preferably 70 MPa or less. By setting the elastic modulus E2 to 70 MPa or less, the influence of the second apex 66 on the rigidity is suppressed. In the tire 42, good riding comfort is maintained.

  Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed as being limited based on the description of the examples.

[Experiment 1]
[Example 1]
A pneumatic tire of Example 1 having the configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The size of this tire was "LT265 / 75R16 123 / 120Q". In this tire, the radius of curvature Rm was 50 mm, the distance Lm was 55 mm, the radius of curvature Rp was 45 mm, and the distance Lp was 53 mm. The length L1 of the first apex is 10 mm.

[Comparative Example 1]
The tire of Comparative Example 1 having the configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. This tire is a conventional tire.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the profile of the sidewall was changed and the ratio (Rm / Lm) was as shown in Table 1.

[Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the contour of the carcass was changed and the ratio (Rp / Lp) was as shown in Table 1.

[Example 3-5]
Except that the height of the first apex, the profile of the sidewall and the contour of the carcass were changed and the ratio (Rm / Lm) and the ratio (Rp / Lp) were as shown in Table 2, The tire of Example 3-5 was obtained.

[durability]
The tire was mounted on a regular rim (size: 7.5 J), and the tire was filled with air to adjust the internal pressure to 550 kPa. The tire was mounted on a drum type running test machine, and a vertical load of 20 kN was applied to the tire. The tire was run on a drum having a radius of 1.7 m at a speed of 100 km / h. The running distance until the tire was found to be damaged was measured. However, at the time when the vehicle traveled 35,000 km, if there was no damage, the test was terminated. The results are shown in Table 1-2 below as indices with the case where the vehicle travels 35,000 km taken as 100. The larger the value, the better. In the failure mode column of the table, “A” indicates that looseness occurred near the tip of the first apex.

[Flat spot resistance]
The tire was mounted on a regular rim (size: 7.5 J), and the radial force variation (RFV) of the tire was measured in accordance with JASO C607. This measured value is the initial RFV (F0) of the tire. Next, the tire was run at a speed of 60 km / h for an additional hour using a drum tester. The air pressure of the tire during this running is 550 kPa, and the load is 18.75 kN. Next, the tire was allowed to stand still for 16 hours. The air pressure of the tire when left unattended is 550 kPa, and the load is 18.75 kN. The RFV of this tire was measured according to JASO C607. This measured value is RFV (F1) at the time of flat spot generation. The difference between F1 and F0 was calculated. The results are shown in Table 1-2 as index values with the result of Comparative Example 1 being 100. The larger the value, the better. The larger the value, the better the flat spot resistance.

[Driving stability]
The tire was mounted on a regular rim (size: 7.5 J), and the tire was filled with air so that the internal pressure became 550 kPa. The tire was mounted on the rear wheel of the vehicle. The driver was allowed to drive the vehicle on a dry road test course to evaluate steering stability. The results are shown in Table 1-2 below in a 5-grade evaluation with Comparative Example 1 being 3. The larger the value, the better.

[Experiment 2]
[Example 6]
A pneumatic tire of Example 6 having the configuration shown in FIG. 3 and having the specifications shown in Table 3 below was obtained. The size of this tire was "LT265 / 75R16 123 / 120Q". In this tire, the radius of curvature Rm was 50 mm, the distance Lm was 55 mm, the radius of curvature Rp was 45 mm, and the distance Lp was 53 mm. The length L1 of the first apex is 10 mm. The radial height H2 from the bead baseline to the outer end of the second apex is 45 mm.

[Example 7]
A tire of Example 7 was obtained in the same manner as Example 6, except that the height of the second apex was changed and the ratio (H2 / Hc) was as shown in Table 3.

[durability]
The durability was evaluated in the same manner as in Experiment 1. The results are shown in Table 3 below. The larger the value, the better. In the failure mode column of the table, “C” indicates that looseness occurred near the outer end of the folded portion of the carcass ply.

[Flat spot resistance]
Flat spot resistance was evaluated in the same manner as in Experiment 1. The results are shown in Table 3 below. The larger the value, the better. The larger the value, the better the flat spot resistance.

[Driving stability]
The steering stability was evaluated in the same manner as in Experiment 1. The results are shown in Table 3 below. The larger the value, the better.

  As shown in Table 1-3, the tire of Example has a higher evaluation than the tire of Comparative Example. From the evaluation results, the superiority of the present invention is clear.

  The pneumatic tire described above can be applied to various vehicles.

2, 42 ... tire 4, 44 ... tread 6, 46 ... sidewall 8, 48 ... clinch 10, 50 ... bead 12, 52 ... carcass 14, 54 ... belt 16, 56 band 18, 58 inner liner 20, 60 chafer 22 tread surface 24 groove 26 base layer 28 cap layer 30, 62 ..Cores 32, 64: first apex 34, 72: first ply 34a, 72a: main portion 34b, 72b of first ply: folded portion 36, 74 of first ply ..Second plies 36a, 74a: Main parts of second plies 36b, 74b: Folded parts of second plies 38: Profiles 40: Rims 41, 70: Of first apex Tip 66 ...・ Second Apex 68 ・ ・ ・ Outer end of second Apex 76 ・ ・ ・ End of folded part of first ply 78 ・ ・ ・ End of folded part of second ply 80 ・ ・ ・ Outer end of folded part

Claims (6)

It has a pair of beads and a carcass bridged between these beads,
Each bead has a core and a first apex extending radially outward from the core,
When the tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and a load of 120% of the regular load is applied to the tire,
The position where the width of the tire becomes maximum on the profile of the outer surface of the tire is defined as a reference position Pm, a straight line extending in the axial direction passing through the reference position Pm is defined as a reference line M, and the reference position Pm is defined in the radial direction. Is the height from the tread to the outer end of the tread, which is a position on the profile of the outer surface of the tire, and a position radially outward from the reference position Pm and separated by a distance of 0.2 times the height Ht. Is set to Pl,
A pneumatic tire having a center Zm on the reference line M and having a radius of curvature Rm of an arc Cm passing through the reference position Pm and the position Pl smaller than a distance Lm between the center Zm and a tip of the first apex. .   The pneumatic tire according to claim 1, wherein a ratio (Rm / Lm) of the radius of curvature Rm to the distance Lm is 0.75 or more and 0.95 or less. In the above situation,
An intersection between the reference line M and the outer surface of the carcass is Pp, a straight line extending in the axial direction passing through the position P1 is a reference line L, and an intersection between the reference line L and the outer surface of the carcass is Pq. When
The radius of curvature Rp of an arc Cp having a center Zp on the reference line M and passing through the intersection Pp and the intersection Pq is smaller than a distance Lp between the center Zp and a tip of the first apex. 3. The tire according to 2.   The pneumatic tire according to claim 3, wherein a ratio (Rp / Lp) of the radius of curvature Rp to the distance Lp is 0.70 or more and 0.90 or less. The bead further comprises a second apex located axially outside the first apex,
The carcass has a carcass ply,
The carcass ply is folded around the core from the inside to the outside in the axial direction, and the carcass ply is formed with a main portion and a folded portion by this folding,
The folded portion is located between the first apex and the second apex,
In a state where this tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and no load is applied to the tire,
The ratio (H2 / Hc) of the radial height H2 from the bead base line to the outer end of the second apex to the radial height Hc from the bead base line to the outer end of the folded portion of the carcass splice is: The pneumatic tire according to any one of claims 1 to 4, which is 1.05 or more. The bead further comprises a second apex located axially outside the first apex,
The carcass has a carcass ply,
The carcass ply is folded around the core from the inside to the outside in the axial direction, and the carcass ply is formed with a main portion and a folded portion by this folding,
The folded portion is located between the first apex and the second apex,
In a state where this tire is mounted on a regular rim, the tire is filled with air so as to have a regular internal pressure, and no load is applied to the tire,
The ratio (Hc / H2) of the radial height Hc from the bead baseline to the outer end of the turn-up portion of the carcass splice to the radial height H2 from the bead baseline to the outer end of the second apex is The pneumatic tire according to any one of claims 1 to 4, which is 1.05 or more.

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