JP2018083475A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire with appropriate mass as well as with excellent durability and wear resistance.SOLUTION: A tire 2 comprises an overlapping portion continuously outward from a contact point Pz in a substantially radial direction on a part of a bead 10 and a flange when a cross-section of a part of the bead 10 based on a cavity surface of a mold and a cross-section of a rim R are made overlapped such that the contact point Pz between a heel surface 64 and a side surface 62 coincides with a reference point Pr of a nominal rim width in a cross-section vertical to a circumferential direction. When an arc configuring an inner contour 58 of the flange at an outside section of the reference point Pr in a radial direction is referred to as Cr and a curvature radius of the arc Cr is referred to as Rr, a ratio (x/Rr) of a maximum thickness x of the overlapping portion to the curvature radius Rr is 2.5% or more and 13% or less. An angle θ of a straight line connecting an outer side end of the overlapping portion in the radial direction and a center Or of the arc Cr with respect to an axial direction is 45° or more and 90°or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire.

  In the tire, the bead portion is fitted to the rim. In the traveling state, a large load is applied to the bead portion. As the tire travels, the tire repeats deformation and restoration. At this time, the distortion increases particularly in the bead portion. When the tire is used for a long period of time, this distortion can cause damage to the bead portion. High durability is required for the bead portion. Further, wear tends to proceed at the bead portion fitted to the rim. The bead portion is also required to have high wear resistance.

  The durability can be improved by increasing the size of the bead portion or adding a reinforcing layer to the bead portion. However, these cause an increase in tire mass. This can be a factor that impairs the fuel efficiency of the tire.

  The shape of the bead portion affects the amount of distortion of the bead portion. The shape of the bead portion affects the durability of the bead portion. The shape of the bead portion affects the wear resistance of the bead portion. By optimizing the shape of the bead portion, durability and wear resistance can be improved while suppressing an increase in mass. Examination of the shape of the bead portion is disclosed in Japanese Unexamined Patent Application Publication Nos. 2014-189178 and 2015-174526.

JP 2014-189178 A JP-A-2015-174526

  There is a demand for a tire in which the durability and wear resistance of the bead portion are further improved while suppressing an increase in tire mass.

  An object of the present invention is to provide a tire in which good durability and wear resistance are realized while an increase in mass is suppressed.

  The pneumatic tire according to the present invention includes a pair of beads. For each bead, the outer surface of the bead portion includes a bottom surface that contacts the seat surface of the rim when the tire is mounted on a regular rim, a side surface that contacts the flange of the rim, and a bottom surface and the side surface. And a heel surface located between the two. The contact point between the heel surface and the side surface is Pz, the nominal reference point of the rim width located on the inner surface of the flange is Pr, and the cross section perpendicular to the circumferential direction is based on the cavity surface of the mold. When the cross-section of the bead portion and the cross-section of the rim are overlapped so that the contact point Pz and the reference point Pr coincide with each other, the bead portion and the flange are substantially radially outward from the contact point Pz. It has a continuous overlap part. When an arc constituting the contour of the inner surface of the flange is defined as Cr in the radially outer portion of the reference point Pr, and the curvature radius of the arc Cr is defined as Rr, the maximum thickness x of the overlapping portion with respect to the curvature radius Rr The ratio (x / Rr) is not less than 2.5% and not more than 13%. An angle θ formed by a straight line connecting the radially outer end of the overlapping portion and the center Or of the arc Cr with the axial direction is not less than 45 ° and not more than 90 °.

  Preferably, in this tire, the bead includes a core and an apex extending radially outward from the core. The tire is mounted on the rim, and the tire is filled with air so as to have a normal internal pressure. In a state where a load of 120% of the normal load is applied to the tire, the tip of the apex and the arc Cr The angle α formed by the straight line connecting the center Or and the axial direction is 90 ° or less.

  Preferably, the tire further includes a carcass and a pair of clinch apex. The carcass includes a carcass ply. The carcass ply includes a main portion that extends from one bead to the other bead, and a folded portion that is located on the outer side in the axial direction of each bead. Each clinch apex is located on the outer side in the axial direction of the folded portion. The tire is mounted on the rim, and the tire is filled with air so as to have a normal internal pressure. In a state where a load of 120% of the normal load is applied to the tire, the center Or of the arc Cr is applied to the bead. When the straight line with an angle of 45 ° drawn to the axial direction is the reference line M, the thickness Tb of the bead portion of the clinch apex thickness Tc measured along the reference line M. The ratio to (Tc / Tb) is 5% or more and 25% or less.

  Preferably, the tire further includes a carcass and a pair of strip apex. The carcass includes a carcass ply. The carcass ply includes a main portion that extends from one bead to the other bead, and a folded portion that is located on the outer side in the axial direction of each bead. Each strip apex extends from the inner side in the axial direction of the bead to between the main portion and the folded portion. The tire is mounted on the rim, and the tire is filled with air so as to have a normal internal pressure. In a state where a load of 120% of the normal load is applied to the tire, the center Or of the arc Cr is applied to the bead. When a straight line with an angle of 45 ° drawn with respect to the axial direction is the reference line M, the thickness Tb of the bead portion of the strip apex thickness Ts measured along the reference line M. The ratio to (Ts / Tb) is 5% or more and 15% or less.

  The inventors examined the cause of damage to the bead portion. As a result, in addition to the contact pressure between the bead portion and the rim being excessive, the difference in the contact pressure between no load and load load increases the distortion of the bead portion. It has been found. In particular, the distortion of the bead portion on a line (referred to as the reference line M) that is drawn from the center of the arc that forms the contour of the inner surface of the flange toward the bead portion and has an angle of 45 ° with the axial direction. Turned out to be large. The inventors have found that this distortion can be reduced by adjusting the shape of the bead portion. It has been found that durability is improved by adjusting the shape of the bead portion on the side surface that has been conventionally matched to the shape of the flange.

  In the pneumatic tire according to the present invention, in the cross section perpendicular to the circumferential direction, the cross section of the bead portion based on the cavity surface of the mold and the cross section of the rim are referred to as the contact point Pz between the heel surface and the side surface and the rim width. When superposed so as to coincide with the reference point Pr, the bead portion and the flange have an overlapping portion that is continuous outward from the contact point Pz in a substantially radial direction. The ratio (x / Rr) of the maximum thickness x of the overlapping portion to the curvature radius Rr of the arc Cr constituting the contour of the inner surface of the flange is 2.5% or more and 13% or less. In this tire, the angle θ formed by the straight line Lo connecting the outer end of the overlapping portion and the center Or of the arc Cr with the axial direction is 45 ° or more and 90 ° or less. That is, in this tire, the overlapping portion extends from the contact point Pz to the reference line M or beyond the reference line M. By making the shape of the bead portion in this way, when the tire is mounted on the rim, the contact pressure difference between the no load and the load load is effectively reduced while the contact pressure is properly maintained. By making the shape of the bead portion in this way, the distortion of the bead portion on the reference line M is effectively reduced. The tire bead portion is hardly damaged. This tire is excellent in durability.

  As described above, the contact pressure is appropriately maintained in this tire. This suppresses wear of the bead portion. This tire is excellent in wear resistance.

  In this tire, the effect of providing this overlapping portion on the tire mass is small. In this tire, the increase in the tire mass is suppressed, and the durability of the bead portion is improved.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a schematic view showing a part of the contour of the bead portion of the tire and a part of the contour of the rim of FIG. 1. FIG. 3 is an enlarged cross-sectional view showing a part of the tire of FIG. 1 in a state where a load is applied.

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

  FIG. 1 shows a pneumatic tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal 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 the equator plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern. The tire 2 is incorporated in the rim R. This rim R is a regular rim.

  The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinch 8, a pair of beads 10, a carcass 12, a belt 14, a pair of edge bands 16, a band 18, an inner liner 20, a pair of chafers 22, and a pair. The clinch apex 24 and a pair of strip apex 26 are provided. The tire 2 is a tubeless type. The tire 2 is mounted on a small truck. The tire 2 corresponds to a small truck tire 2 which is a target of Chapter B of the JATMA standard.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 28 that contacts the road surface. A groove 30 is carved in the tread 4. The groove 30 forms a tread pattern. The tread 4 has a cap layer 32 and a base layer 34. The cap layer 32 is located on the radially outer side of the base layer. The cap layer 32 is laminated on the base layer. The cap layer 32 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties. The base layer is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber for the base layer is natural rubber.

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

  Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is located on the outer side in the axial direction of the bead 10 and the carcass 12. The clinches 8 are tapered outward in the radial direction. The clinch 8 is made of a crosslinked rubber having excellent wear resistance. The clinch 8 contacts the flange of the rim R.

  Each bead 10 is located inside the clinch 8 in the axial direction. The bead 10 is located radially inward of the sidewall 6. The bead 10 includes a core 36 and an apex 38 that extends radially outward from the core 36. The core 36 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 38 is tapered outward in the radial direction. The apex 38 is made of a crosslinked rubber. The apex 38 is smaller than the conventional apex 38. This apex 38 is a small apex 38.

  In the tire 2, a portion fitted with the rim R in the vicinity of the bead 10 is referred to as a bead 10 portion. The tire 2 includes a pair of beads 10.

  The carcass 12 includes a first ply 40 and a second ply 42. The first ply 40 and the second ply 42 are bridged between the beads 10 on both sides. The first ply 40 and the second ply 42 are folded around the core 36. The first ply 40 includes a first main portion 44 that extends from one bead 10 to the other bead 10, and a first folded portion 46 that is positioned on the axially outer side of the bead 10. The first main portion 44 extends along the inside of the second ply 42. The first main portion 44 is laminated on the outer side of the inner liner 20. The first folded portion 46 extends substantially in the radial direction along the inside of the clinch apex 24. The second ply 42 includes a second main portion 48 that extends from one bead 10 to the other bead 10, and a second folded portion 50 that is positioned on the outer side in the axial direction of the bead 10. The second main portion 48 extends along the inside of the tread 4 and the sidewall 6. The second main portion 48 is stacked outside the first main portion 44. The second folded portion 50 extends in the substantially radial direction along the outside of the bead 10. The second folded portion 50 is located between the bead 10 and the first folded portion 46.

  As shown in FIG. 1, the end of the second folded portion 50 is located near the maximum width position. The carcass 12 of the tire 2 has a “high turn-up (HTU)” structure. The carcass 12 may be configured such that the end of the first folded portion 46 and the end of the second folded portion 50 are positioned near the bead 10. In this case, the structure of the carcass 12 is referred to as a “low turn-up (LTU)” structure.

  Although not shown, each of the first ply 40 and the second ply 42 includes a plurality of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, aramid fibers, and polyketone fibers.

  The carcass 12 may be composed of a single carcass ply. At this time, the carcass 12 includes only the first ply 40 or the second ply 42 described above.

  The belt 14 is located on the inner side in the radial direction of the tread 4. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner layer 52 and an outer layer 54. As apparent from FIG. 1, the width of the inner layer 52 is slightly larger than the width of the outer layer 54 in the axial direction. Although not shown, each of the inner layer 52 and the outer layer 54 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The general absolute value of the tilt angle is 10 ° or more and 35 ° or less. The inclination direction of the cord of the inner layer 52 with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 54 with respect to the equator plane. A preferred material for the cord is steel. An organic fiber 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.

  Each edge band 16 is located radially outside the belt 14 and in the vicinity of the end of the belt 14. The edge band 16 is located between the belt 14 and the band 18. The edge band 16 may be located outside the band 18 in the radial direction. Although not shown, the edge band 16 is made of a cord and a topping rubber. The cord is wound in a spiral. The edge band 16 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the end of the belt 14 is restrained by this cord, the lifting of the belt 14 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The band 18 is located on the radially outer side of the belt 14. In the axial direction, the width of the band 18 is larger than the width of the belt 14. Although not shown, the band 18 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. 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 fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The inner liner 20 is located inside the carcass 12. The inner liner 20 is joined to the inner surface of the carcass 12. The inner liner 20 is made of a crosslinked rubber having excellent air shielding properties. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 2.

  Each chafer 22 is located in the vicinity of the bead 10. The chafer 22 contacts the rim R. By this contact, the vicinity of the bead 10 is protected. In this embodiment, the chafer 22 is integral with the clinch 8. In this embodiment, the material of the chafer 22 is the same as that of the clinch 8. The chafer 22 may be made of a cloth and a rubber impregnated in the cloth.

  Each clinch apex 24 is located between the carcass 12 and the clinch 8 in the axial direction. The clinch apex 24 is located outside the second folded portion 50 in the axial direction. The clinch apex 24 extends from the vicinity of the core 36 substantially outward in the radial direction. In this embodiment, the outer end of the clinch apex 24 is located inside the outer end of the clinch 8 in the radial direction. The position of the outer end of the clinch apex 24 may coincide with the position of the outer end of the clinch 8 in the radial direction. The clinch apex 24 is made of a crosslinked rubber.

  Each strip apex 26 extends in a substantially radial direction along the axially inner side of the bead 10. The strip apex 26 extends between the second main portion 48 and the second folded portion 50. The strip apex 26 is made of a crosslinked rubber.

  The tire 2 may not include the clinch apex 24. The tire 2 may not include the strip apex 26.

  In FIG. 2, a solid line is the outline 56 of the outer surface of the bead 10 portion of the tire 2 in FIG. 1 in a cross section perpendicular to the circumferential direction. The contour 56 is determined based on the shape of the cavity surface of the mold. This is the outline 56 of the portion of the bead 10 when the tire 2 is not attached to the rim R. In FIG. 2, dotted lines are contours 58 of the inner surface of the seat surface and the inner surface of the flange of the regular rim R to which the tire 2 is mounted in a cross section perpendicular to the circumferential direction. In the figure, the up and down direction is the radial direction of the tire 2, the left and 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.

  As shown in FIG. 2, when the tire 2 is mounted on the rim R, the outer surface of the bead 10 is in contact with the bottom surface 60 that contacts the seat surface of the rim R and the flange of the rim R. A side surface 62 and a heel surface 64 positioned between the bottom surface 60 and the side surface 62 are provided. In a cross section cut by a plane perpendicular to the circumferential direction, the bottom surface 60 extends substantially in the axial direction. The angle formed by the bottom surface 60 and the axial direction is 0 ° to 20 °. The side surface 62 extends generally in the radial direction. The contour 56 of the side surface 62 is provided with an inwardly convex arc at the radially inner portion thereof. The contour 56 of the heel surface 64 is an outwardly convex arc. The heel surface 64 is in contact with the bottom surface 60. The heel surface 64 is in contact with the side surface 62. In FIG. 2, a point Pz is a contact point between the heel surface 64 and the side surface 62.

  In FIG. 2, a point Pr is a reference point for calling the rim width. The reference point Pr is located on the inner surface of the flange of the rim R. In this figure, the reference point Pr overlaps the contact point Pz. As shown in the figure, the contour 58 of the inner surface of the flange includes an arc Cr that protrudes inwardly on the radially outer side of the reference point Pr. In the figure, the symbol Or is the center of the arc Cr. Reference sign Rr is the radius of curvature of the arc Cr.

  In FIG. 2, the contour 56 of the outer surface of the portion of the bead 10 based on the cavity surface of the mold and the contour 58 of the inner surface of the rim R are overlapped so that the contact point Pz and the reference point Pr coincide with each other. These are superposed so that the respective axial directions coincide. As is apparent from the figure, the contour 56 of the side surface 62 and the contour 58 of the inner surface of the flange intersect at the contact point Pz and the point Po. Between the contact point Pz and the point Po, the contour 58 of the inner surface of the flange enters the inside of the bead 10 portion. That is, in the tire 2, when the cross-section of the bead 10 and the cross-section of the rim R are overlapped so that the contact point Pz and the reference point Pr coincide with each other, the bead 10 and the flange have an overlapping portion. doing. This overlapping portion extends substantially radially outward from the contact point Pz. This overlapping portion exists continuously from the contact point Pz. Point Po is the outer edge of this overlap.

  In FIG. 2, the double-headed arrow x is the maximum thickness of the overlapping portion. Here, the thickness of the overlapping portion is measured along the normal line of the arc Cr. The maximum thickness x is the maximum value of the distance between the arc C and the contour 56 of the side surface 62 at the overlapping portion, measured along the normal line of the arc C. In the tire 2, the ratio (x / Rr) of the maximum thickness x to the curvature radius Rr is 2.5% or more and 13% or less as a percentage. In the tire 2, the contour 56 of the side surface 62 is determined so that the ratio (x / Rr) is 2.5% or more and 13% or less.

  In FIG. 2, a solid line Li is a reference line extending in the axial direction through the center Or. The reference line Li passes through the reference point Pr. A solid line M is a reference line passing through the center Or and having an angle of 45 ° with the reference line Li. The reference line M extends toward the bead 10 portion. The reference line M intersects the bead 10 portion. The reference line M intersects the arc Cr. In the drawing, a solid line Lo is a straight line connecting the center Or and the outer end Po of the overlapping portion. The symbol θ is an angle formed by the reference line Li and the straight line Lo. In the tire 2, the angle θ is not less than 45 ° and not more than 90 °. That is, this overlapping portion extends from the contact point Pz to the reference line M or beyond the reference line M.

  Below, the effect of this invention is demonstrated.

  The inventors examined the cause of damage to the bead portion. As a result, in addition to the contact pressure between the bead portion and the rim being excessive, the difference in the contact pressure between no load and load load increases the distortion of the bead portion. It has been found. In particular, it has been found that the distortion of the bead portion increases on the reference line M. The inventors have found that this distortion can be reduced by adjusting the shape of the bead portion. It has been found that durability is improved by adjusting the shape of the bead portion on the side surface that has been conventionally matched to the shape of the flange.

  In the pneumatic tire 2 according to the present invention, in the cross section perpendicular to the circumferential direction, the aforementioned contact point Pz and the reference point Pr match the cross section of the bead 10 portion based on the cavity surface of the mold and the cross section of the rim R. Thus, when it overlap | superposes, the part of the bead 10 and a flange have the overlapping part which continued toward the radial direction outer side from the contact Pz. As described above, the ratio (x / Rr) of the maximum thickness x of the overlapping portion to the radius of curvature Rr of the arc Cr constituting the contour 58 of the inner surface of the flange is 2.5% or more and 13% or less. By setting the ratio (x / Rr) to 2.5% or more, when the tire 2 is mounted on the rim R, the contact pressure difference between no load and load is effectively reduced. By setting the ratio (x / Rr) to 13% or less, the contact pressure is properly maintained. By making the shape of the portion of the bead 10 in this way, the contact pressure difference between the no load and the load load is effectively reduced while the contact pressure is properly maintained. The distortion of the bead 10 portion of the tire 2 is small. The bead 10 portion of the tire 2 is hardly damaged. This tire 2 is excellent in durability.

  In the tire 2, the angle θ formed by the straight line Lo connecting the outer end Po of the overlapping portion and the center Or of the arc Cr with the axial direction is 45 ° or more and 90 ° or less. By setting the angle θ to 45 ° or more, in the tire 2, the overlapping portion extends from the contact point Pz to the reference line M or beyond the reference line M. This effectively reduces the distortion of the portion of the bead 10 on the reference line M. By setting the angle θ to 90 ° or less, the contact pressure difference between no load and load is effectively reduced. Furthermore, the contact pressure is properly maintained by setting the angle θ to 90 ° or less. By making the shape of the bead 10 portion in this way, the distortion of the bead 10 portion is effectively reduced. The bead 10 portion of the tire 2 is hardly damaged. This tire 2 is excellent in durability.

  As described above, in the tire 2, the contact pressure is properly maintained. This suppresses wear of the bead 10 portion. The tire 2 is excellent in wear resistance.

  In the tire 2, the effect of providing the overlapping portion on the mass of the tire 2 is small. In the tire 2, an increase in mass is suppressed. In the tire 2, the durability and wear resistance of the bead 10 are improved while suppressing an increase in mass.

  The ratio (x / Rr) is more preferably 3.0% or more. By setting the ratio (x / Rr) to 3.0% or more, the difference in contact pressure between no load and load can be more effectively reduced. In the tire 2, the distortion of the bead 10 portion is more effectively reduced. In this respect, the ratio (x / Rr) is more preferably 4.0% or more. The ratio (x / Rr) is more preferably 12.0% or less. When the ratio (x / Rr) is 12.0% or less, the contact pressure is more appropriately maintained. Thereby, distortion of the part of bead 10 by excessive contact pressure is controlled. The bead 10 portion of the tire 2 is hardly damaged. Furthermore, by setting the ratio (x / Rr) to 12.0% or less, wear of the bead 10 portion can be effectively suppressed. The tire 2 is excellent in durability and wear resistance. From these viewpoints, the ratio (x / Rr) is more preferably 10% or less.

  The angle θ is more preferably 50 ° or more. By setting the angle θ to 50 ° or more, the distortion of the portion of the bead 10 on the reference line M is more effectively reduced. In this respect, the angle θ is more preferably 55 ° or more. The angle θ is more preferably 85 ° or less. By setting the angle θ to 85 ° or less, the difference in contact pressure between no load and load can be more effectively reduced. By setting the angle θ to 85 ° or less, the contact pressure is properly maintained. In the tire 2, the distortion of the bead 10 portion is more effectively reduced. The bead 10 portion of the tire 2 is hardly damaged. Further, by setting the angle θ to 85 ° or less, wear of the bead 10 portion can be suppressed. The tire 2 is excellent in durability and wear resistance. From these viewpoints, the angle θ is more preferably 80 ° or less.

  FIG. 3 is an enlarged cross-sectional view of a portion of the bead 10 of the tire 2 of FIG. In this figure, the tire 2 is incorporated in a regular rim R, and the tire 2 is filled with air so as to have a regular internal pressure. In this figure, the tire 2 is loaded with a load of 120% of the normal load. For this reason, the portion of the bead 10 is deformed as compared with the case of no load. Below, the dimension and angle of each member of the tire 2 are measured in this state. In the figure, the up and down direction is the radial direction of the tire 2, the left and 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. 3, a solid line La is a straight line connecting the center Or of the arc Cr and the tip 66 of the apex 38. In the figure, symbol α is an angle formed by the reference line Li and the straight line La. In the tire 2, the angle α is preferably 90 ° or less. In the tire 2, the tip 66 of the apex 38 is located on the inner side in the axial direction from the center Or of the arc Cr even when a load of 120% of the normal load is applied. As a result, the concentration of distortion on the apex 38 is effectively suppressed. This tire 2 is excellent in durability. In this respect, the angle α is more preferably 80 ° or less. The angle α is preferably 30 ° or more. By setting the angle α to 30 ° or more, the apex 38 contributes to the rigidity of the bead 10 portion. The portion of the bead 10 is excellent in durability. In this respect, the angle α is more preferably 40 ° or more.

  As shown in FIG. 3, the tire 2 preferably includes a clinch apex 24 on the outer side in the axial direction of the carcass 12. Thereby, the first folded portion 46 and the second folded portion 50 are arranged at positions close to the inner surface of the tire 2. In the tire 2, a force in the compression direction is prevented from acting on the first folded portion 46 and the second folded portion 50. The carcass 12 of the tire 2 is hardly damaged. Moreover, sufficient tension is applied to the carcass 12. This carcass 12 contributes to rigidity. Even when 120% of the normal load is applied to the tire 2, the deformation of the bead 10 is small. The distortion of the portion of the bead 10 is suppressed. The bead 10 portion of the tire 2 is hardly damaged. The tire 2 is excellent in durability.

  In FIG. 3, the double-headed arrow Tb is the thickness of the bead 10 portion measured along the reference line M. The double-headed arrow Tc is the thickness of the clinch apex 24 measured along the reference line M. The ratio of the thickness Tc to the thickness Tb (Tc / Tb) is preferably 5% or more as a percentage. By setting the ratio (Tc / Tb) to 5% or more, the first folded portion 46 and the second folded portion 50 are arranged at a position closer to the inner surface of the tire 2. In the tire 2, a force in the compression direction is effectively prevented from acting on the first folded portion 46 and the second folded portion 50. The deformation of the bead 10 is small. Further, the clinch apex 24 effectively reduces the distortion of the bead 10 portion on the reference line M. The bead 10 portion of the tire 2 is hardly damaged. The tire 2 is excellent in durability. In this respect, the ratio (Tc / Tb) is more preferably 7% or more. The ratio (Tc / Tb) is preferably 15% or less. By setting the ratio (Tc / Tb) to 15% or less, the rigidity of the bead 10 is properly maintained. In the tire 2, a good riding comfort is maintained. In this respect, the ratio (Tc / Tb) is more preferably equal to or less than 13%.

  As shown in FIG. 3, the tire 2 preferably includes a strip apex 26 extending from the inner side in the axial direction of the bead 10 to between the second main portion 48 and the second folded portion 50. The strip apex 26 contributes to the rigidity of the bead 10 portion. Even when 120% of the normal load is applied to the tire 2, the deformation of the bead 10 is small. Distortion at the bead 10 portion is suppressed. The bead 10 portion of the tire 2 is hardly damaged. The tire 2 is excellent in durability.

  In FIG. 3, the double arrow Ts is the thickness of the strip apex 26 measured along the reference line M. The ratio (Ts / Tb) of the thickness Ts to the thickness Tb is preferably 5% or more as a percentage. By setting the ratio (Ts / Tb) to 5% or more, the strip apex 26 effectively contributes to the rigidity of the bead 10 portion. The strip apex 26 effectively reduces the distortion of the bead 10 portion on the reference line M. The bead 10 portion of the tire 2 is hardly damaged. The tire 2 is excellent in durability. The ratio (Ts / Tb) is preferably 15% or less. By setting the ratio (Ts / Tb) to 15% or less, heat generation at the strip apex 26 can be suppressed. The tire 2 is excellent in durability. From this viewpoint, the ratio (Ts / Tb) is more preferably 12% or less.

  The complex elastic modulus Ea of the apex 38 is preferably 20 MPa or more. By setting the complex elastic modulus Ea to 20 MPa or more, the apex 38 contributes to rigidity. Even when 120% of the normal load is applied to the tire 2, the deformation of the bead 10 is small. Distortion at the bead 10 portion is suppressed. The tire 2 is excellent in durability. The complex elastic modulus Ea is preferably 70 MPa or less. By setting the complex elastic modulus Ea to 70 MPa or less, the rigidity of the portion of the bead 10 is properly maintained. The tire 2 is excellent in ride comfort.

  The ratio (Ec / Ea) of the complex elastic modulus Ec of the clinch apex 24 to the complex elastic modulus Ea is preferably 0.4 or more. By setting the ratio (Ec / Ea) to 0.4 or more, the clinch apex 24 contributes to rigidity. Even when 120% of the normal load is applied to the tire 2, the deformation of the bead 10 is small. Distortion at the bead 10 portion is suppressed. The tire 2 is excellent in durability. The ratio (Ec / Ea) is preferably 1.3 or less. By setting the ratio (Ec / Ea) to 1.3 or less, the rigidity of the portion of the bead 10 is properly maintained. The tire 2 is excellent in ride comfort.

  The ratio (Es / Ea) of the complex elastic modulus Es to the complex elastic modulus Ea of the strip apex 26 is preferably 0.7 or more. By setting the ratio (Es / Ea) to 0.7 or more, the strip apex 26 contributes to rigidity. Even when 120% of the normal load is applied to the tire 2, the deformation of the bead 10 is small. Distortion at the bead 10 portion is suppressed. The tire 2 is excellent in durability. The ratio (Es / Ea) is preferably 3.0 or less. By setting the ratio (Es / Ea) to 3.0 or less, the rigidity of the portion of the bead 10 is properly maintained. The tire 2 is excellent in ride comfort.

In the present invention, the complex elastic modulus Ea, Ec, and Es are viscoelastic spectrometers (trade name “VESF-3” manufactured by Iwamoto Seisakusho Co., Ltd.) according to the following measurement conditions in accordance with the provisions of “JIS K 6394”. It is measured using. In this measurement, a plate-shaped test piece (length = 45 mm, width = 4 mm, thickness = 2 mm) is formed from the rubber composition for each of the apex 38, the clinch apex 24, and the strip apex 26. This test piece is used for measurement.
Initial strain: 10%
Amplitude: ± 2.0%
Frequency: 10Hz
Deformation mode: Tensile
Measurement temperature: 70 ° C

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

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
The tire shown in FIG. 1-3 was manufactured. The size of this tire is LT265 / 75R16. Table 1 shows the specifications of the tire. In this tire, a carcass having an “HTU” structure was adopted. The standard rim to which this tire is attached is 7.5J. The curvature radius Rr of the arc Cr constituting the inner surface of the flange of the rim is 9.5 mm. Based on this, the shape of the bead portion of the tire is determined. The complex elastic modulus Ea of the apex was 20 MPa, the complex elastic modulus Ec of the clinch apex was 20 MPa, and the complex elastic modulus Es of the strip apex was 60 MPa.

[Comparative Example 1-2, Example 2-4]
Tires of Comparative Example 1-2 and Example 2-4 were obtained in the same manner as in Example 1 except that the maximum thickness x of the overlapping portion was changed and the ratio (x / Rr) was changed as shown in Table 1.

[Comparative Example 3-4, Example 5-6]
Tires of Comparative Example 3-4 and Example 5-6 were obtained in the same manner as in Example 1 except that the position of the outer end of the overlapping portion was changed and the angle θ was changed as shown in Table 2.

[Example 7-9]
Tires of Examples 7-9 were obtained in the same manner as Example 1 except that the apex tip position was changed and the angle α was changed as shown in Table 2.

[Example 10-11]
Tires of Example 10-11 were obtained in the same manner as Example 1 except that the thickness of the clinch apex was changed and the ratio (Tc / Tb) was changed as shown in Table 3.

[Examples 12-14]
Tires of Examples 12-14 were obtained in the same manner as Example 1 except that the thickness of the strip apex was changed and the ratio (Ts / Tb) was changed as shown in Table 3.

[durability]
The tire was incorporated into a regular rim (size = 7.5 J), and the tire was filled with air to adjust the internal pressure to 550 kPa. This tire was mounted on a drum type running test machine, and a 20 kN longitudinal load was applied to the tire. This tire was run on a drum having a radius of 1.7 m at a speed of 100 km / h. The distance traveled until the tire was damaged was measured. However, when damage did not occur when the travel distance reached 4500 km, the test was terminated. The results are shown in Tables 1 to 3 below as indices. A larger numerical value is preferable. The damage mode of the damaged tire was all carcass damage in the bead portion.

[Abrasion resistance evaluation]
The tire was incorporated into a regular rim (size = 7.5 J), and the tire was filled with air to adjust the internal pressure to 550 kPa. This tire was mounted on a drum type running test machine, and a 20 kN longitudinal load was applied to the tire. This tire was run on a drum having a radius of 1.7 m at a speed of 100 km / h until the running distance reached 150 km. The wear depth of the portion of the tire in contact with the rim flange was measured. From this result, the wear resistance was evaluated in three stages of A, B and C. A, B, and C are preferable in this order. A and B are acceptable.

[Contact pressure difference]
The tire was incorporated into a regular rim (size = 7.5 J), and the tire was filled with air to adjust the internal pressure to 550 kPa. Using a pressure distribution measuring device (I-SCAN), the contact pressure between the bead portion and the flange when no load was applied and when a longitudinal load of 20 kN was applied was measured. In each case, the average contact pressure in the portion radially outside the reference line Li was calculated. The difference between these average contact pressures is shown as an index in Tables 1 to 3 below. The smaller the value, the better.

  As shown in Tables 1 to 3, the tires of the examples have a higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The tire described above can be applied to various vehicles.

2 ... tyre 4 ... tread 6 ... side wall 8 ... clinch 10 ... bead 12 ... carcass 14 ... belt 16 ... edge band 18 ... band 20 ... -Inner liner 22 ... Chafer 24 ... Clinch apex 26 ... Strip apex 28 ... Tread surface 30 ... Groove 32 ... Cap layer 34 ... Base layer 36 ... Core 38 ... Apex 40 ... First ply 42 ... Second ply 44 ... First main part 46 ... First turn-up part 48 ... Second main part 50 ... First Folded portion 52 ... Inner layer 54 ... Outer layer 56 ... Contour of bead portion 58 ... Contour of rim 60 ... Bottom surface 62 ... Side surface 64 ... Heel surface 66・ ・ Apex Tip

Claims (4)

With a pair of beads,
For each bead, the outer surface of the bead portion is in contact with the seat surface of the rim when the tire is mounted on a regular rim, the side surface in contact with the flange of the rim, the bottom surface and the side surface. And a heel surface located between
The contact point between the heel surface and the side surface is Pz, the reference point of the nominal rim width located on the inner surface of the flange is Pr,
In a cross section perpendicular to the circumferential direction, when the cross section of the bead portion based on the cavity surface of the mold and the cross section of the rim are overlapped so that the contact point Pz and the reference point Pr coincide, And the flange has an overlapping portion that is continuous from the contact point Pz toward the outside in the radial direction,
When the arc that forms the contour of the inner surface of the flange at the radially outer portion of the reference point Pr is Cr, and the curvature radius of the arc Cr is Rr,
The ratio (x / Rr) of the maximum thickness x of the overlapping portion to the radius of curvature Rr is 2.5% or more and 13% or less,
A pneumatic tire in which an angle θ formed by a straight line connecting the radially outer end of the overlapping portion and the center Or of the arc Cr with the axial direction is 45 ° or more and 90 ° or less. The bead includes a core and an apex extending radially outward from the core;
The tire is mounted on the rim, and the tire is filled with air so as to have a normal internal pressure. In a state where a load of 120% of the normal load is applied to the tire, the tip of the apex and the arc Cr The pneumatic tire according to claim 1, wherein an angle α formed by a straight line connecting the center Or and the axial direction is 90 ° or less. It further includes a carcass and a pair of clinch apex,
The carcass has a carcass ply,
The carcass ply includes a main portion extending from one bead to the other bead, and a turn-back portion positioned on the outer side in the axial direction of each bead,
Each clinch apex is located outside in the axial direction of the folded portion,
When this tire is mounted on the rim and filled with air so that the tire has a normal internal pressure, a load of 120% of the normal load is applied to the tire.
When a straight line having an angle of 45 ° with the axial direction drawn from the center Or of the arc Cr toward the bead is the reference line M, the clinch apex measured along the reference line M is used. The pneumatic tire according to claim 1 or 2, wherein a ratio (Tc / Tb) of the thickness Tc to the thickness Tb of the bead portion is 5% or more and 15% or less. It further includes a carcass and a pair of strip apex,
The carcass has a carcass ply,
The carcass ply includes a main portion extending from one bead to the other bead, and a turn-back portion positioned on the outer side in the axial direction of each bead,
Each strip apex extends from the inside in the axial direction of the bead to between the main portion and the folded portion,
When this tire is mounted on the rim and filled with air so that the tire has a normal internal pressure, a load of 120% of the normal load is applied to the tire.
When a straight line drawn from the center Or of the arc Cr toward the bead and having an angle of 45 ° with the axial direction is the reference line M, the strip apex measured along the reference line M is measured. The pneumatic tire according to any one of claims 1 to 3, wherein a ratio (Ts / Tb) of the thickness Ts to the thickness Tb of the bead portion is 5% or more and 15% or less.

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