tire

Abstract

To provide a tire 2 which can improve both of durability and weight saving.SOLUTION: A tire 2 comprises: a pair of beads 8; a carcass 10; a pair of protective rubber layers 6; and a pair of reinforcement rubber layers 22. A carcass ply 42a of the carcass 10 includes: a ply body 48a; and a pair of folding parts 50a. The reinforcement rubber layer 22 is positioned between the folding part 50a and the protective rubber layer 6. An outer end PA of an apex 40 of the bead 8 is positioned between an outer end PRS of the reinforcement rubber layer 22 and an inner end PRU thereof in a radial direction. Thickness of the protective rubber layer 6 in a zone from a rim contact end PF to an outer end PRS of the reinforcement rubber layer 22 is thin at a center part in the radial direction of the reinforcement rubber layer 22, and thick at the other parts.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] A bead of a tire is composed of a core and an apex. In order to improve durability, for example, as disclosed in the following Patent Document 1, studies have been made on reducing the size of the apex, and providing a reinforcing rubber layer on the axially outer side of the apex with a folded portion of a carcass ply interposed therebetween. In this case, the reinforcing rubber layer is formed of a hard crosslinked rubber to ensure the rigidity of the bead portion. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2020-026171 Summary of the Invention Problem to be Solved by the Invention

[0004] A tire is assembled to a rim, and the inside thereof is filled with air. This causes the tire to expand. Therefore, strain occurs on the outer surface of the tire whose internal pressure has been adjusted.

[0005] The tire includes a protective rubber layer as a component that constitutes a side surface of the tire. The protective rubber layer includes a clinch that contacts the rim, and a side wall located radially outward of the clinch. The aforementioned reinforcing rubber layer is covered by the protective rubber layer. If the thickness of the protective rubber layer is set according to the same conventional concept, the mass of the tire will increase.

[0006] The reinforcing rubber layer is harder than the protective rubber layer. Therefore, if the thickness of the protective rubber layer is set using the same approach as before, the rigidity of the rubber layer located on the outside of the carcass will increase in the area including the reinforcing rubber layer. As a result, there is a concern that the difference between areas with large and small surface strain will be larger compared to tires without a reinforcing rubber layer. It is anticipated that strain will concentrate in the radially outer part of the reinforcing rubber layer from its center, which may reduce durability.

[0007] This invention has been made in view of these circumstances. The object of this invention is to provide a tire that can improve the degree to which durability and weight reduction can be achieved. [Means for solving the problem]

[0008] The tire according to the present invention comprises a pair of beads, a carcass spanning between the pair of beads, a pair of protective rubber layers located axially outward of the carcass and constituting the side surface of the tire, and a pair of reinforcing rubber layers located axially outward of the beads. The carcass comprises carcass plies including carcass cords, the carcass plies comprising a ply body spanning between the pair of beads and a pair of folded portions connected to the ply body and folded back by the beads. The reinforcing rubber layers are located between the folded portions and the protective rubber layers. The beads comprise a core and an apex located radially outward of the core. The outer end of the apex is located radially between the outer and inner ends of the reinforcing rubber layers. The thickness of the protective rubber layer in the zone from the rim contact end to the outer end of the reinforcing rubber layer is thinner in the radially central portion of the reinforcing rubber layer and thicker in other portions. [Effects of the Invention]

[0009] According to the present invention, a tire can be obtained that can improve the balance between durability and weight reduction. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing a part of a tire relating to one embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the bead portion of a tire. [Figure 3] This is a cross-sectional view showing the bead portion of a tire. [Figure 4] This is a cross-sectional view showing part of the contour of the outer surface of the tire. [Modes for carrying out the invention]

[0011] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0012] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0013] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state. When a tire is mounted on a standard rim, its internal pressure is adjusted to 30 kPa, and no load is applied to the tire, this is referred to as the standard condition.

[0014] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured in the cross-section of the tire obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim.

[0015] A genuine rim refers to a rim defined in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are all considered genuine rims.

[0016] The term "normal internal pressure" means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" set forth in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures.

[0017] The term "normal load" means the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" set forth in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0018] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that is fitted onto a rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire includes, as portions thereof, a tread portion, a pair of bead portions and a pair of sidewall portions.

[0019] In the present invention, among the elements constituting the tire, the complex modulus of elasticity of an element formed of crosslinked rubber is measured in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial strain = 10% Dynamic strain = ±1% Frequency = 10Hz Mode = elongation mode Temperature = 70°C In this measurement, a test piece (40 mm length × 4 mm width × 1 mm thickness) is sampled from the tire. The length direction of the test piece is aligned with the circumferential direction of the tire. If it is not possible to sample a test piece from the tire, a test piece is sampled from a sheet-shaped crosslinked rubber obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the complex elastic modulus is represented by the complex elastic modulus at 70°C.

[0020] [Summary of Embodiments of the Invention] [Configuration 1] A tire according to one aspect of the present invention comprises: a pair of beads; a carcass spanning between the pair of beads; a pair of protective rubber layers located axially outward of the carcass and constituting side surfaces of the tire; and a pair of reinforcing rubber layers located axially outward of the beads. The carcass comprises a carcass ply including carcass cords, the carcass ply comprises a ply main body spanning between the pair of beads, and a pair of folded portions connected to the ply main body and folded back at the beads. The reinforcing rubber layers are located between the folded portions and the protective rubber layers. The bead comprises a core and an apex located radially outward of the core, an outer end of the apex is located between an outer end and an inner end of the reinforcing rubber layer in the radial direction, and a thickness of the protective rubber layer in a zone from a rim contact end to the outer end of the reinforcing rubber layer is thinner at a radial center portion of the reinforcing rubber layer and thicker at other portions.

[0021] By configuring the tire in this manner, an increase in rigidity of the rubber layer located outside the carcass at the portion including the reinforcing rubber layer is suppressed. Since strain generated on the side surfaces of the tire is effectively dispersed, concentration of strain in a specific portion is suppressed. This tire can have improved durability. Since the volume of the protective rubber layers is reduced, the tire can have reduced mass. This tire can improve the compatibility between durability and weight reduction.

[0022] [Configuration 2] Preferably, in the tire described in [Configuration 1] above, the protective rubber layer has a reference thickness T0 at the maximum width position, an outer edge thickness T1 at the outer edge of the reinforcing rubber layer, a minimum thickness T2 at the radial center portion of the reinforcing rubber layer, and a contact thickness T3 at the rim contact end. The reinforcing rubber layer has a contact thickness TB at the rim contact end, the minimum thickness T2 is thinner than the outer edge thickness T1, the outer edge thickness T1 is the same as the reference thickness T0, and the sum of the contact thickness T3 and the contact thickness TB, T3B, is thicker than the reference thickness T0. By shaping the tire in this way, the rigidity of the rubber layer located on the outside of the carcass is effectively suppressed, preventing it from increasing in areas including the reinforcing rubber layer. The strain generated on the tire's sidewall is effectively distributed, preventing strain from concentrating in specific areas. This improves the tire's durability. The volume of the protective rubber layer is reduced, thus reducing the tire's mass.

[0023] [Configuration 3] Preferably, in the tire described in [Configuration 1] or [Configuration 2] above, the ratio of the minimum thickness T2 to the outer edge thickness T1 (T2 / T1) is 0.5 or more, and the ratio of the total thickness T3B to the reference thickness T0 (T3B / T0) is 3.0 or more and 5.0 or less. By adjusting the tires in this way, it is possible to reduce their mass while further improving their durability.

[0024] [Structure 4] Preferably, in the tire described in any of the above-described configurations [1] to [3], the reinforcing rubber layer has an intermediate thickness TA at the position where the protective rubber layer shows the minimum thickness T2, and the ratio (T2A / T1) of the total thickness T2A of the minimum thickness T2 and the intermediate thickness TA to the outer edge thickness T1 is 0.5 or more and 2.0 or less. By adjusting the tires in this way, it is possible to reduce their mass while further improving their durability.

[0025] [Composition 5] Preferably, in the tire described in any of the above-described configurations [1] to [4], in a reference state in which the tire is mounted on a regular rim and the internal pressure of the tire is adjusted to 30 kPa, the contour line of the side surface includes a first curved portion located radially outside the maximum width position and bulging outward, a second curved portion located radially inside the maximum width position and bulging outward, and an inverted curved portion located radially inside the second curved portion and recessing inward, wherein the first curved portion, the second curved portion, and the inverted curved portion are each represented by an arc, the radius Rr of the arc representing the inverted curved portion is smaller than the radius Rj of the arc representing the first curved portion, and the ratio (Rr / Rj) of the radius Rr of the arc representing the inverted curved portion to the radius Rj of the arc representing the first curved portion is 0.50 or more. By shaping the tire in this way, the rigidity of the rubber layer located on the outside of the carcass is effectively suppressed, preventing it from increasing in areas including the reinforcing rubber layer. The strain generated on the sidewall of the tire is effectively distributed, preventing strain from concentrating in specific areas. This improves the durability of the tire. The volume of the protective rubber layer is reduced, thus reducing the mass of the tire. Surface strain generated in reverse curved areas is prevented from becoming excessively large, thus maintaining good durability.

[0026] [Details of the Embodiments of the Invention] Figure 1 shows a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on a vehicle such as a small truck. This tire 2 is also called a small truck tire.

[0027] Figure 1 shows a portion of the cross-section of tire 2 (hereinafter referred to as the meridian cross-section) along the plane containing the rotation axis of tire 2. In Figure 1, the left-right direction is the axial direction of tire 2, and the up-down direction is the radial direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the circumferential direction of tire 2. Figure 2 shows a portion of the cross-section shown in Figure 1. Figure 2 shows the bead portion of tire 2. In Figures 1 and 2, tire 2 is mounted on rim R (regular rim).

[0028] In Figure 1, the dashed line CL extending radially represents the equatorial plane of tire 2. Figure 1 shows In this diagram, the solid line BBL extending axially is the bead baseline. The bead baseline is the line that defines the rim diameter (see JATMA, etc.) of the rim radius.

[0029] The surface SF of this tire 2 comprises an inner surface USF and an outer surface SSF. Although not described in detail, the inner surface USF is formed by a bladder (or rigid core). The outer surface SSF is formed by a mold. The boundary between the inner surface USF and the outer surface SSF is the toe PT.

[0030] This tire 2 comprises a tread 4, a pair of protective rubber layers 6, a pair of beads 8, a carcass 10, a belt 12, a band 14, a pair of chafers 16, a pair of insulation 18, an inner liner 20, and a pair of reinforcing rubber layers 22.

[0031] The tread 4 is located radially outward of the carcass 10. The tread 4 makes contact with the road surface at the tread surface 24. Grooves 26 are cut into the tread 4. The tread surface 24 is the outer surface of the tire 2. SSF It constitutes a part of something. The tread 4 comprises a base portion 28 and a cap portion 30 located radially outward from the base portion 28. The base portion 28 is made of low-heat-generating cross-linked rubber. The cap portion 30 is made of cross-linked rubber with consideration for wear resistance and grip performance. The cap portion 30 includes the tread surface 24.

[0032] In Figure 1, the symbol TE indicates the edge of the tread surface 24. The tread surface 24 forms part of the outer surface SSF. Of the outer surface SSF, the portion between the edge TE of the tread surface 24 and the toe PT is the side surface 32. The outer surface SSF comprises the tread surface 24 and a pair of side surfaces 32.

[0033] Each protective rubber layer 6 is located on the axially outer side of the carcass 10. The protective rubber layer 6 forms part of the side surface 32. In this invention, the thickness of the protective rubber layer 6 is measured along the normal to the side surface 32. If there is decoration such as a pattern or letters on the side surface 32, the thickness of the protective rubber layer 6 is measured along the normal to a hypothetical side surface obtained by assuming that there is no decoration.

[0034] The position indicated by the symbol PW is the axial outer end of tire 2 (hereinafter referred to as outer end PW). If there are decorations such as patterns or letters on the side surface 32, the outer end PW is determined based on the aforementioned hypothetical side surface. Tire 2 exhibits its maximum width at its outer edge PW. The outer edge PW is also called the maximum width position. The axial distance from the first maximum width position PW to the second maximum width position PW in tire 2 under normal conditions is the cross-sectional width of tire 2 (see JATMA, etc.). The length indicated by the symbol HW is the radial distance from the bead baseline to the maximum width position PW. The radial distance HW is also called the radial height at the maximum width position PW.

[0035] The protective rubber layer 6 comprises a sidewall 34 and a clinch 36. The sidewall 34 is connected to the edge of the tread 4. The sidewall 34 is located radially inward of the tread 4. The sidewall 34 is made of cross-linked rubber with cut resistance in mind. The sidewall 34 includes the aforementioned maximum width position PW. The complex modulus of elasticity of the sidewall 34 is between 2.0 MPa and 6.0 MPa. The clinch 36 is located radially inward of the sidewall 34. The clinch 36 contacts the flange of the rim R. The clinch 36 is made of cross-linked rubber with wear resistance considered. The clinch 36 is harder than the sidewall 34. The complex modulus of elasticity of the clinch 36 is between 10 MPa and 15 MPa.

[0036] Each bead 8 is located axially inward of the clinch 36. The bead 8 is ring-shaped. The bead 8 comprises a core 38 and an apex 40.

[0037] Core 38 extends circumferentially. Core 38 contains a steel wire wound circumferentially. Apex 40 is located radially outward from Core 38. Apex 40 extends radially outward from Core 38. Apex 40 tapers outward. Apex 40 is composed of rigid cross-linked rubber. The complex modulus of elasticity of Apex 40 is between 60 MPa and 90 MPa.

[0038] The length denoted by the symbol HA is the radial distance from the bead baseline to the outer edge PA of the apex 40. The radial distance HA is also called the radial height of the apex 40. The ratio (HA / HW) of the radial height HA of Apex 40 to the radial height HW at the maximum width position PW is between 0.25 and 0.40.

[0039] The carcass 10 is located inside the tread 4 and a pair of protective rubber layers 6. The carcass 10 spans between a pair of beads 8, i.e., between the first bead 8 and the second bead 8 (not shown). The carcass 10 of this tire 2 has a radial structure.

[0040] The carcass 10 comprises at least one carcass ply 42. The carcass 10 of this tire 2 consists of two carcass plies 42. The first carcass ply 42a and the second carcass ply 42b are folded over at their respective bead 8.

[0041] The first carcass ply 42a comprises a ply body 48a and a pair of folded portions 50a. The ply body 48a spans between a pair of beads 8. Each folded portion 50a is connected to the ply body 48a and is folded over by the bead 8 from the axial inner side outward. The second carcass ply 42b comprises a ply body 48b and a pair of folded portions 50b. The ply body 48b spans between a pair of beads 8. Each folded portion 50b is connected to the ply body 48b and is folded over by the bead 8 from the axial inner side outward.

[0042] Tire shown in Figure 12 Then, the end of the folded portion 50b of the second carcass ply 42b is covered by the folded portion 50a of the first carcass ply 42a. The end of the folded portion 50b is located radially inward of the maximum width position PW, and the end of the folded portion 50a is located radially outward of the maximum width position PW.

[0043] Although not shown in the diagram, the carcass ply 42 contains numerous parallel carcass cords. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane. The carcass cords are made of polyester fibers (polyester cords). Compared to cords made of nylon or rayon fibers, polyester cords have higher rigidity. The carcass 10 effectively increases the rigidity of the tire 2.

[0044] The belt 12 comprises three belt plies 44. The belt 12 may also be composed of two belt plies 44 or four belt plies 44. The three belt plies 44 are the first belt ply 44A, the second belt ply 44B, and the third belt ply 44C. These belt plies 44 are arranged radially. Of the three belt plies 44, the first belt ply 44A is located furthest inward in the radial direction, the second belt ply 44B has the widest width, and the third belt ply 44C has the narrowest width.

[0045] Although not shown in the diagram, each belt ply 44 contains numerous parallel belt cords. Each belt cord is inclined with respect to the equatorial plane. The belt cords are made of steel cord.

[0046] The band 14 is located radially between the tread 4 and the belt 12. The band 14 is laminated on the belt 12. Although not shown, band 14 includes a helically wound band cord. The band cord is covered with topping rubber. The band cord extends substantially circumferentially. In detail, the angle that the band cord makes with respect to the circumferential direction is 5° or less. Band 14 has a jointless structure. A cord made of organic fibers is used as the band cord. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0047] The band 14 of this tire 2 comprises two full bands 46. The two full bands 46 cover the entire belt 12 from the radially outer side. Although not shown, band 14 may consist of a single full band 46. Band 14 may consist of a pair of edge bands spaced apart axially on either side of the equatorial plane. Band 14 may consist of a full band 46 and a pair of edge bands.

[0048] Each chafer 16 is located radially inward of the bead 8. The chafer 16 contacts the seat of the rim R. The chafer 16 is made of cross-linked rubber with wear resistance in mind.

[0049] Each insulation 18 is located axially inward of the sidewall 34. The insulation 18 is laminated onto the ply body 48b. The outer end of the insulation 18 is located axially inward of the end of the belt 12 and between the ply body 48b and the first belt ply 44A (i.e., between the carcass 10 and the belt 12). The inner end of the insulation 18 is located radially inward of the outer end PA of the apex 40 and between the ply body 48b and the apex 40. The insulation 18 is made of cross-linked rubber.

[0050] The inner liner 20 is located inside the carcass 10. The inner liner 20 is bonded to the inner surface of the carcass 10 via an insulation (not shown) made of cross-linked rubber. The inner liner 20 constitutes the inner surface USF of the tire 2. The inner liner 20 is made of cross-linked rubber with excellent air-shielding properties. The inner liner 20 plays a role in maintaining the internal pressure of the tire 2.

[0051] Each reinforcing rubber layer 22 is located axially outward from the bead 8. The reinforcing rubber layer 22 is located between the folded portion 50a of the first carcass ply 42a and the protective rubber layer 6. The reinforcing rubber layer 22 is in contact with the folded portion 50a on its inner surface. The reinforcing rubber layer 22 is in contact with the protective rubber layer 6 on its outer surface. The outer end PA of the aforementioned apex 40 is located radially between the outer end PRS and the inner end PRU of the reinforcing rubber layer 22. The outer end PRS of the reinforcing rubber layer 22 is located radially inward of the end of the folded portion 50b of the second carcass ply 42b. In Figure 1, the position indicated by the symbol PF is a position on the side surface 32 that corresponds to the radially outer end of the contact surface between the rim R and the side surface 32. In this invention, this position PF is the rim contact end. The inner end PRU of the reinforcing rubber layer 22 is located radially inward from the rim contact end PF.

[0052] The length indicated by the symbol HR is the radial distance from the bead baseline to the outer edge PRS of the reinforcing rubber layer 22. The radial distance HR is also called the radial height of the reinforcing rubber layer 22. The ratio (HR / HW) of the radial height HR of the reinforcing rubber layer 22 to the radial height HW at the maximum width position PW is between 0.55 and 0.70.

[0053] The reinforcing rubber layer 22 is composed of hard cross-linked rubber. The complex modulus of elasticity of the reinforcing rubber layer 22 is between 60 MPa and 90 MPa. The reinforcing rubber layer 22 of the tire 2 shown in Figure 1 is composed of the same cross-linked rubber as the cross-linked rubber that makes up the apex 40.

[0054] There are no particular restrictions on the cross-sectional shape of the reinforcing rubber layer 22 in the meridian section. The cross-sectional shape may be arranged to have a uniform thickness overall, or it may be arranged so that it is thicker in the center and gradually thins outwards from the center. From the viewpoint of easy thickness control, it is preferable that the reinforcing rubber layer 22 is constructed using a sheet-shaped rubber sheet 52. The reinforcing rubber layer 22 shown in Figure 1 is composed of two rubber sheets 52, but there is no particular limit to the number of rubber sheets 52 that make up the reinforcing rubber layer 22. The reinforcing rubber layer 22 may be composed of one rubber sheet 52, or it may be composed of three or more rubber sheets 52. When the reinforcing rubber layer 22 is made of a single rubber sheet 52, it is preferable that the ends of the rubber sheet 52 corresponding to the outer end PRS and inner end PRU of the reinforcing rubber layer 22 have a tapered shape, from the viewpoint of suppressing the concentration of strain. When the reinforcing rubber layer 22 is made of two or more rubber sheets 52, it is preferable to construct the reinforcing rubber layer 22 by laminating a narrow rubber sheet 52n on the outside of a wide rubber sheet 52w, as shown in Figure 1. In this case, it is more preferable that the narrow rubber sheet 52n is laminated on the wide rubber sheet 52w such that the outer end of the narrow rubber sheet 52n is located radially inward of the outer end of the wide rubber sheet 52w, and the inner end of the narrow rubber sheet 52n is located radially outward of the inner end of the wide rubber sheet 52w.

[0055] The reinforcing rubber layer 22 is harder than the sidewall 34 and clinch 36 that make up the protective rubber layer 6. Therefore, if the thickness of the protective rubber layer 6 is set to the same level as a conventional tire without the reinforcing rubber layer 22, the rigidity of the rubber layer located on the outside of the carcass 10 will increase in the portion including the reinforcing rubber layer 22. As a result, there is a concern that the difference between the portion with large surface strain and the portion with small surface strain will be larger than in a conventional tire. It is anticipated that strain will concentrate in the radially outer portion of the reinforcing rubber layer 22 from its center position RC, which may reduce durability. Here, the rubber layer located on the outside of the carcass 10 refers to the element made of cross-linked rubber located on the outside of the carcass 10 in the sidewall portion. In the tire 2 shown in Figure 1, the element made up of the protective rubber layer 6 and the reinforcing rubber layer 22 is the rubber layer located on the outside of the carcass 10.

[0056] However, in this tire 2, the thickness of the protective rubber layer 6 in the zone from the rim contact edge PF to the outer edge PRS of the reinforcing rubber layer 22 is thinner in the radial center portion of the reinforcing rubber layer 22 and thicker in other portions. In other words, the protective rubber layer 6 in this zone exhibits its minimum thickness in the radial center portion of the reinforcing rubber layer 22. Therefore, the rigidity of the rubber layer located on the outside of the carcass 10 is suppressed from increasing in the portion including the reinforcing rubber layer 22. Since the strain generated on the side surface 32 of the tire 2 is effectively distributed, the concentration of strain in a particular area is suppressed. This tire 2 can have improved durability. Since the volume of the protective rubber layer 6 is reduced, this tire 2 can have reduced mass. This tire 2 can improve the balance between durability and weight reduction.

[0057] In Figure 2, the length indicated by the symbol MR is the radial distance from the inner end PRU to the outer end PRS of the reinforcing rubber layer 22. The distance MR is the radial length of the reinforcing rubber layer 22. The solid line LM extending in the axial direction is a straight line indicating the center of the radial length MR of the reinforcing rubber layer 22. The position indicated by the symbol RC is the intersection of the straight line LM and the outer surface of the reinforcing rubber layer 22. In this invention, the intersection point RC is the radial center position of the reinforcing rubber layer 22. The straight line indicated by the symbol LC is the normal to the side surface 32 passing through the radial center position RC of the reinforcing rubber layer 22. The normal line LC is also called the reference line.

[0058] The length indicated by symbol M1 is the radial distance from the position on the outer surface of the reinforcing rubber layer 22 indicated by symbol R1 to the inner end PRU of the reinforcing rubber layer 22. In this invention, the ratio of the radial distance M1 to the radial length MR of the reinforcing rubber layer 22 is 40%. The dotted line L1 is a straight line passing through position R1 and parallel to the normal LC. The dotted line L1 is also called the first boundary line. The first boundary line L1 is a straight line passing through the position on the outer surface of the reinforcing rubber layer 22 where the radial distance M1 from the inner end PRU of the reinforcing rubber layer 22 is 40% of the radial length MR of the reinforcing rubber layer 22, and is parallel to the reference line LC.

[0059] The length indicated by the symbol M2 is the radial distance from the position on the outer surface of the reinforcing rubber layer 22 indicated by the symbol R2 to the inner end PRU of the reinforcing rubber layer 22. In this invention, the ratio of the radial distance M2 to the radial length MR of the reinforcing rubber layer 22 is 45%. The dotted line L2 is a straight line passing through position R2 and parallel to the normal LC. The dotted line L2 is also called the second boundary line. The second boundary line L2 is a straight line passing through the position on the outer surface of the reinforcing rubber layer 22 where the radial distance M2 from the inner end PRU of the reinforcing rubber layer 22 is 45% of the radial length MR of the reinforcing rubber layer 22, and is parallel to the reference line LC.

[0060] The length indicated by symbol M3 is the radial distance from the position on the outer surface of the reinforcing rubber layer 22 indicated by symbol R3 to the inner end PRU of the reinforcing rubber layer 22. In this invention, the ratio of the radial distance M3 to the radial length MR of the reinforcing rubber layer 22 is 55%. The dotted line L3 is a straight line passing through position R3 and parallel to the normal LC. The dotted line L3 is also called the third boundary line. The third boundary line L3 is a straight line passing through the position on the outer surface of the reinforcing rubber layer 22 where the radial distance M3 from the inner end PRU of the reinforcing rubber layer 22 is 55% of the radial length MR of the reinforcing rubber layer 22, and is parallel to the reference line LC.

[0061] The length indicated by the symbol M4 is the radial distance from the position on the outer surface of the reinforcing rubber layer 22 indicated by the symbol R4 to the inner end PRU of the reinforcing rubber layer 22. In this invention, the ratio of the radial distance M4 to the radial length MR of the reinforcing rubber layer 22 is 60%. The dotted line L4 is a straight line passing through position R4 and parallel to the normal LC. The dotted line L4 is also called the fourth boundary line. The fourth boundary line L4 is a straight line passing through the position on the outer surface of the reinforcing rubber layer 22 where the radial distance M4 from the inner end PRU of the reinforcing rubber layer 22 is 60% of the radial length MR of the reinforcing rubber layer 22, and is parallel to the reference line LC.

[0062] In this invention, the zone between the first boundary line L1 and the fourth boundary line L4 is also called the standard zone ZN. The zone between the second boundary line L2 and the third boundary line L3 is the special zone. ZS It is also called [another name].

[0063] As described above, the protective rubber layer 6 exhibits its minimum thickness at the radial center portion of the reinforcing rubber layer 22. From the viewpoint of effectively improving the balance between durability and weight reduction, it is preferable that the protective rubber layer 6 exhibits its minimum thickness in the standard zone ZN, and more preferably in the special zone ZS. It is even more preferable that the protective rubber layer 6 exhibits its minimum thickness at the radial center position RC of the reinforcing rubber layer 22.

[0064] Figure 3 shows the bead portion of Figure 1. In Figure 3, the position indicated by the symbol RT is a position on the outer surface of the reinforcing rubber layer 22. The straight line indicated by the symbol LT is the normal to the side surface 32 passing through position RT. The length indicated by the symbol T2 is the thickness of the protective rubber layer 6 measured along the normal LT. The protective rubber layer 6 of the tire 2 shown in Figure 3 has a minimum thickness T2 at position RT. Position RT is the position where the protective rubber layer 6 exhibits a minimum thickness T2. When the protective rubber layer 6 exhibits a minimum thickness T2 at the radial center position RC of the reinforcing rubber layer 22, the position RT where the protective rubber layer 6 exhibits a minimum thickness T2 coincides with the radial center position RC of the reinforcing rubber layer 22, and the normal LT coincides with the normal LC.

[0065] In Figure 3, the length indicated by the symbol T0 is the thickness of the protective rubber layer 6 measured along the normal LW of the side surface 32 passing through the maximum width position PW. The length indicated by the symbol T1 is the thickness of the protective rubber layer 6 measured along the normal LS of the side surface 32 passing through the outer end PRS of the reinforcing rubber layer 22. The length indicated by the symbol TA is the thickness of the reinforcing rubber layer 22 measured along the normal LT. The length indicated by the symbol T3 is the thickness of the protective rubber layer 6 measured along the normal LF of the side surface 32 at the rim contact end PF. The length indicated by the symbol TB is the thickness of the reinforcing rubber layer 22 measured along the normal LF. The protective rubber layer 6 has a thickness T0 (hereinafter, reference thickness T0) at the maximum width position PW, a thickness T1 (hereinafter, outer end thickness T1) at the outer end PRS of the reinforcing rubber layer 22, a minimum thickness T2 at the radial center portion of the reinforcing rubber layer 22, and a thickness T3 (hereinafter, contact thickness T3) at the rim contact end PF. The reinforcing rubber layer 22 has a thickness TA (hereinafter referred to as intermediate thickness TA) at position RT where the protective rubber layer 6 has a minimum thickness T2, and a thickness TB (hereinafter referred to as contact thickness TB) at the rim contact end PF.

[0066] In this tire 2, it is preferable that the minimum thickness T2 of the protective rubber layer 6 is thinner than the outer edge thickness T1, the outer edge thickness T1 is equivalent to the reference thickness T0, and the sum of the contact thickness T3 and the contact thickness TB, T3B, is thicker than the reference thickness T0. This effectively suppresses the increase in rigidity of the rubber layer located on the outside of the carcass 10 in the portion including the reinforcing rubber layer 22. Since the strain generated on the side surface 32 of the tire 2 is effectively distributed, the concentration of strain in a particular area is suppressed. This tire 2 can have improved durability. Since the volume of the protective rubber layer 6 is reduced, this tire 2 can have reduced mass.

[0067] In the present invention, the outer edge thickness T1 being equivalent to the reference thickness T0 means that the ratio of the outer edge thickness T1 to the reference thickness T0 (T1 / T0) is in the range of 0.95 or more and 1.05 or less.

[0068] In this tire 2, the ratio (T2 / T1) of the minimum thickness T2 to the outer edge thickness T1 is preferably 0.5 or greater. This ensures that the thickness of the protective rubber layer 6 in the radial center portion of the reinforcing rubber layer 22 is appropriately maintained. The effect on rigidity due to the thinness of the protective rubber layer 6 in the radial center portion of the reinforcing rubber layer 22 is effectively suppressed. The entire protective rubber layer 6 has the rigidity necessary to maintain the shape of the tire 2. This tire 2 can have improved durability. From this viewpoint, a ratio (T2 / T1) of 0.6 or greater is more preferable, and 0.7 or greater is even more preferable. From the viewpoint of effectively reducing the mass of the tire 2 and effectively distributing the strain generated on the side surface 32 of the tire 2, a ratio (T2 / T1) of 0.9 or less is more preferable, and 0.8 or less is even more preferable.

[0069] In this tire 2, the ratio of the total thickness T3B to the standard thickness T0 (T3B / T0) is preferably between 3.0 and 5.0. By setting the ratio (T3B / T0) to 3.0 or higher, the rim contact end PF The reinforcing rubber layer 22 and protective rubber layer 6 contribute to increasing the rigidity of the bead portion. This further enhances the durability of the tire 2. From this perspective, a ratio (T3B / T0) of 3.3 or higher is more preferable. By setting the ratio (T3B / T0) to 5.0 or less, the volume of the rubber layer located on the outside of the carcass 10 is appropriately maintained. The influence of this rubber layer on the mass is suppressed. From this viewpoint, a ratio (T3B / T0) of 4.5 or less is more preferable, and 4.0 or less is even more preferable.

[0070] From the viewpoint of achieving further improvements in durability while reducing mass, it is more preferable that the ratio of the minimum thickness T2 to the outer edge thickness T1 (T2 / T1) is 0.5 or more, and the ratio of the total thickness T3B to the standard thickness T0 (T3B / T0) is 3.0 or more and 5.0 or less.

[0071] From the viewpoint of ensuring rigidity at the rim contact edge PF, it is preferable that the ratio of the contact thickness T3 of the protective rubber layer 6 to the outer edge thickness T1 (T3 / T1) be 2.0 or greater. From the viewpoint of minimizing the influence of the protective rubber layer 6 on mass, it is preferable that the ratio (T3 / T1) be 2.5 or less.

[0072] In this tire 2, the ratio (T2A / T1) of the total thickness T2A (minimum thickness T2 and intermediate thickness TA) to the outer edge thickness T1 is preferably 0.5 or more and 2.0 or less. By setting the ratio (T2A / T1) to 0.5 or higher, the thinning of the rubber layer located outside the carcass 10 in the radial center portion of the reinforcing rubber layer 22 is suppressed. This rubber layer has the rigidity necessary to maintain its shape. Good durability is maintained in this tire 2. From this viewpoint, a ratio (T2A / T1) of 1.0 or higher is more preferable, and 1.5 or higher is even more preferable. By setting the ratio (T2A / T1) to 2.0 or less, the mass of tire 2 is effectively reduced, and the strain generated on the side surface 32 of tire 2 is effectively distributed. From this viewpoint, it is more preferable that the ratio (T2A / T1) be 1.8 or less.

[0073] Figure 4 shows a portion of the contour line of the side surface 32 of tire 2 in a meridional cross-section. The contour line of the side surface 32 shown in Figure 4 is obtained by measuring the outer surface shape of the tire 2 using, for example, a displacement sensor, in the reference state. If there is any decoration on the side surface 32, this contour line is represented assuming that the decoration is absent. The position indicated by the symbol PWp is the position of the maximum width of the tire 2 in the reference state.

[0074] The contour lines of the side surface 32 are formed by combining multiple arcs, connecting them with straight lines where necessary. As shown in Figure 4, the contour of this side surface 32 has a shape that bulges outward near the maximum width position PWp and a shape that curves inward near the rim R. More specifically, this contour line includes a first curved portion 54 located radially outside the maximum width position PWp and bulging outward, a second curved portion 56 located radially inside the maximum width position PWp and bulging outward, and an inverted curved portion 58 located radially inside the second curved portion 56 and recessing inward. The inverted curved portion 58 is located between the rim R and the second curved portion 56.

[0075] In this invention, "bulging outward" means a shape that curves from the inner surface to the outer surface of the tire, and "concave inward" means a shape that curves from the outer surface to the inner surface of the tire.

[0076] The first curved section 54, the second curved section 56, and the reverse curved section 58 are each represented by a circular arc. In Figure 4, the arrow denoted by Rj represents the radius of the arc of the first curved section 54. Although not shown, this arc has its center on a straight line that passes through the maximum width position PWp and extends axially. The arrow denoted by the symbol Rk represents the radius of the arc of the second curved section 56. Although not shown in the figure, this arc has its center on a straight line that passes through the maximum width position PWp and extends axially. The arc of the first curved section 54 and the arc of the second curved section 56 are tangent at the position of maximum width PWp. The arrow denoted by the symbol Rr represents the radius of the arc of the inverted curve 58. Although not shown in the figure, the center of this arc is located outside the side surface 32. The position indicated by the symbol Pb is the boundary between the reverse curved section 58 and the second curved section 56. In this tire 2, the arc of the reverse curved section 58 and the arc of the second curved section 56 are tangent at boundary Pb. The arc of the reverse curved section 58 and the arc of the second curved section 56 may be connected by a straight line, or by one or more outwardly bulging arcs. When the arc of the reverse curved section 58 and the arc of the second curved section 56 are connected by a straight line or an arc, boundary Pb is represented by the end of the arc of the reverse curved section 58.

[0077] In this tire 2, preferably, the radius Rr of the arc representing the reverse curve 58 is smaller than the radius Rj of the arc representing the first curve 54. In other words, it is preferable that the ratio (Rr / Rj) of the radius Rr of the arc representing the reverse curve 58 to the radius Rj of the arc representing the first curve 54 is less than 1.00. This configures the protective rubber layer 6 in the zone from the rim contact end PF to the outer end PRS of the reinforcing rubber layer 22 to have a thickness that is thinner in the radial center portion of the reinforcing rubber layer 22 and thicker in other portions. Since the stiffness of the rubber layer located on the outside of the carcass 10 is suppressed to increase in the portion including the reinforcing rubber layer 22, the strain generated on the side surface 32 of the tire 2 is effectively distributed. Since the concentration of strain in a particular area is suppressed, the tire 2 can have improved durability. Since the volume of the protective rubber layer 6 is reduced, the tire 2 can have reduced mass. From this perspective, the ratio (Rr / Rj) is more preferably 0.90 or less, and even more preferably 0.80 or less.

[0078] In this tire 2, it is preferable that the ratio (Rr / Rj) is 0.50 or higher. This suppresses excessive surface distortion in the reverse-curved portion 58 when air is filled into the tire 2 and the internal pressure is adjusted to the specified internal pressure. In this tire 2, good durability is maintained. From this viewpoint, it is more preferable that the ratio (Rr / Rj) is 0.56 or higher.

[0079] In Figure 4, the length indicated by the symbol HWp is the radial distance from the bead baseline to the maximum width position PWp. The radial distance HWp is also called the radial height at the maximum width position PWp. The length indicated by the symbol Hb is the radial distance from the bead baseline to the boundary Pb.

[0080] In this tire 2, the reverse curved section 58 is designed to effectively contribute to weight reduction and improved durability, and the ratio of the radial distance Hb to the radial height HWp of the maximum width position PWp (Hb / HWp ) is preferably between 0.30 and 0.45.

[0081] As is clear from the above description, according to the present invention, a tire 2 can be obtained that can improve the degree to which durability and weight reduction are achieved. [Examples]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0083] [Examples 1-2 and Comparative Examples 1-3] We obtained a small truck tire (tire size = 225 / 85R16) with the basic configuration shown in Figure 1 and the specifications shown in Table 1 below. The reference thickness T0, outer edge thickness T1, minimum thickness T2, total thickness T3B (contact thickness T3 and contact thickness TB), and intermediate thickness TA were set as shown in Table 1 below. Regarding the side profile, the radius Rj of the first curved portion was set as shown in Table 1. No reverse curved portions were provided in the profile of Example 1-2 and Comparative Example 1-3.

[0084] [Examples 3-4] Except for providing a reverse curved section in the side contour line, the tire of Example 3-4 was obtained in the same manner as in Example 1. The radius Rr of the arc of the reverse curved section of Example 3-4 is as shown in Table 1 below.

[0085] [Durability] A prototype tire was mounted on a rim (size = 6.0J), and air was added to achieve the normal internal pressure. This tire was then mounted on a drum-type running test machine. A longitudinal load of 19.8kN was applied to the tire, and it was driven on a drum (radius = 1.7m) at a speed of 80km / h. The distance traveled until damage to the tire was observed was measured. The results are shown in Table 1 below, using an index with Comparative Example 1 set to 100. A higher value indicates less damage and superior durability.

[0086] [Lightweighting] The masses of the protective rubber layer and reinforcing rubber layer located on the outside of the carcass were measured. The results are shown in Table 1 below, with Comparative Example 1 set to 100. A higher number indicates a lighter weight.

[0087] [Compatibility] To assess the balance between durability and weight reduction, a combined index of durability and weight reduction was obtained. The results are shown in Table 1 below. A higher value indicates a better balance between durability and weight reduction.

[0088] [Table 1] As shown in Table 1, the embodiments have confirmed that it is possible to improve the balance between durability and weight reduction. The advantages of the present invention are clear from these evaluation results. [Industrial applicability]

[0089] The technologies described above, which can improve the balance between durability and weight reduction, can be applied to various types of tires. [Explanation of symbols]

[0090] 2... Tires 6. Protective rubber layer 8...bead 10.. Carcass 22. Reinforcement rubber layer 32...side view 38 cores 40...Apex 42...Carcass ply 52 ...rubber sheet

Claims

1. A pair of beads, A carcass spanning between the pair of beads, A pair of protective rubber layers located on the axially outer side of the carcass and constituting the side of the tire, A pair of reinforcing rubber layers located on the axially outer side of the bead and Equipped with, The carcass comprises carcass plies including carcass cords, The carcass ply comprises a ply body that spans between the pair of beads, and a pair of folded portions that are connected to the ply body and folded back by the beads. The reinforcing rubber layer is located between the folded portion and the protective rubber layer. The bead comprises a core and an apex located radially outward from the core. The outer end of the apex is located radially between the outer end and the inner end of the reinforcing rubber layer. The thickness of the protective rubber layer in the zone from the rim contact edge to the outer edge of the reinforcing rubber layer is thinner in the radial center portion of the reinforcing rubber layer and thicker in other portions. The protective rubber layer has a reference thickness T0 at the maximum width position, an outer end thickness T1 at the outer end of the reinforcing rubber layer, a minimum thickness T2 at the radial center portion of the reinforcing rubber layer, and a contact thickness T3 at the rim contact end. The reinforcing rubber layer has a contact thickness TB at the rim contact end. The minimum thickness T2 is thinner than the outer end thickness T1. The outer end thickness T1 is equivalent to the reference thickness T0, The sum of the contact thickness T3 and the contact thickness TB, T3B, is greater than the reference thickness T0. The ratio of the minimum thickness T2 to the outer edge thickness T1 (T2 / T1) is 0.5 or more. The ratio of the total thickness T3B to the reference thickness T0 (T3B / T0) is 3.0 or more and 5.0 or less. tire.

2. The reinforcing rubber layer has an intermediate thickness TA at the position where the protective rubber layer exhibits the minimum thickness T2. The ratio (T2A / T1) of the sum of the minimum thickness T2 and the intermediate thickness TA to the outer edge thickness T1 is 0.5 or more and 2.0 or less. The tire according to claim 1.

3. In a standard state where the tire is mounted on a regular rim and the internal pressure of the tire is adjusted to 30 kPa, the contour line of the side surface includes a first curved portion located radially outside the maximum width position and bulging outward, a second curved portion located radially inside the maximum width position and bulging outward, and an inverted curved portion located radially inside the second curved portion and recessing inward. The first curved section, the second curved section, and the reverse curved section are each represented by an arc. The radius Rr of the arc representing the inverse curve is smaller than the radius Rj of the arc representing the first curve. The ratio (Rr / Rj) of the radius Rr of the arc representing the reverse curved portion to the radius Rj of the arc representing the first curved portion is 0.56 or greater. The tire according to claim 1 or 2.

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