JP7463712B2 - Heavy-duty tubeless tire and manufacturing method - Google Patents

Description

The present invention relates to a tubeless tire for heavy loads and a manufacturing method.

Heavy load tubeless tires that are fitted to vehicles such as trucks and buses are subjected to heavy loads. The rigidity of these tires is adjusted so that they can withstand heavy loads. Tires with high rigidity are difficult to assemble onto rims. Studies have been conducted to improve the ease of assembling tires onto rims, i.e., rim assembly, while still maintaining the necessary rigidity (for example, see Patent Document 1 below).

JP 2007-45375 A

Setting the mold clip width narrower than the rim width can improve rim assembly. However, when this tire is mounted on a rim and air is filled inside the tire, the bead portion (hereafter referred to as the bead portion) tends to collapse significantly. In this case, the tread radius in the shoulder portion of the tire is reduced, raising concerns about uneven wear.

For example, increasing the size of the cushion between the end of the belt and the carcass can improve resistance to uneven wear. However, in this case, the flexible zone between the cushion and the bead is narrowed, which may impair rim assembly. Using a larger cushion may also increase rolling resistance.

The present invention was made in consideration of these circumstances, and aims to provide a tubeless tire for heavy loads that achieves reduced rolling resistance and improved rim assembly while minimizing the impact on uneven wear resistance.

A heavy-duty tubeless tire according to one embodiment of the present invention has an aspect ratio of 60% or more and 80% or less. The tire includes a pair of beads, a carcass that spans between one bead and the other bead, a belt that is located radially outside the carcass, and a pair of cushions that are located between the end of the belt and the carcass. The carcass includes a large number of carcass cords arranged in parallel, and the outer diameter of each carcass cord is 0.6 mm or more and 1.0 mm or less. When the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and the tire is in a regular state in which no load is applied, the contour of the carcass includes a buttress arc that represents the contour of the portion overlapping with the cushion, and a lower arc that represents the contour of the portion from the maximum width position of the carcass to the end of the bead. The ratio of the radius of the buttress arc to the radius of the lower arc is 1.00 or more and 1.10 or less.

Preferably, in this heavy-duty tubeless tire, the ratio of the radius of the lower arc to the radial distance from the bead baseline to the end of the bead is 0.85 or more and 0.95 or less.

Preferably, in this heavy-duty tubeless tire, the ratio of the radial distance from the end of the bead to the longitudinal end of the cushion to the radial distance from the bead base line to the top of the belt is 0.25 or more and 0.45 or less.

Preferably, in this heavy-duty tubeless tire, the ratio of the toe spacing, which is expressed as the axial distance from one toe to the other toe, measured in a state where no load other than the tire's own weight is acting, to the rim width of the regular rim is 0.80 or more and 0.88 or less.

Preferably, in this heavy-duty tubeless tire, the ratio of the tire's cross-sectional width to the toe spacing is 1.60 or greater and 1.90 or less.

A method for manufacturing a tubeless tire for heavy loads according to one aspect of the present invention includes the steps of:
The method includes (1) preparing a green tire for a tire, the green tire including a pair of beads, a carcass spanning between the beads, a belt positioned radially outward of the carcass, and a pair of cushions positioned between the ends of the belt and the carcass, and (2) pressurizing and heating the green tire in a mold, the ratio of a clip width of the mold to a rim width of a regular rim on which the tire is assembled being 1.15 or more and 1.22 or less.

The heavy-duty tubeless tire of the present invention achieves reduced rolling resistance and improved rim assembly while minimizing the impact on uneven wear resistance.

FIG. 1 is a cross-sectional view showing a portion of a tubeless tire for heavy loads according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the equatorial plane of the tire shown in FIG. FIG. 3 is a cross-sectional view showing the contour of the carcass of the tire shown in FIG. FIG. 4 is a diagram for explaining a method for measuring the toe distance of a tire. FIG. 5 is a diagram illustrating a method for manufacturing the tire of FIG.

The present invention will now be described in detail based on a preferred embodiment, with reference to the drawings as appropriate.

In the present 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. In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state.

A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are genuine rims.

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

Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

Figure 1 shows a portion of a heavy-duty tubeless tire 2 (hereinafter, sometimes simply referred to as "tire 2") according to one embodiment of the present invention. This tire 2 is a tire for trucks and buses.

Figure 1 shows a portion of a cross section of tire 2 along a plane including the axis of rotation 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 Figure 1 is the circumferential direction of tire 2. In Figure 1, dashed dotted line EL represents the equatorial plane of tire 2. In Figure 1, tire 2 is mounted on rim R (regular rim). Tire 2 shown in Figure 1 is in a regular state.

In FIG. 1, the solid line BBL extending in the axial direction is the bead baseline. This bead baseline is the line that defines the rim diameter of the rim R (see JATMA, etc.).

In FIG. 1, the solid line RBL extending in the radial direction is the rim baseline. The double-headed arrow RW represents the axial distance from one rim baseline to the other. This distance RW is the rim width (see JATMA, etc.) of the rim R on which this tire 2 is mounted. The rim baseline is the line that defines the rim width RW.

In FIG. 1, the symbol PW is the axial outer end of the tire 2. This outer end PW is determined based on a virtual outer surface obtained by assuming that the outer surface of the tire 2 has no decoration such as patterns or letters. The double-headed arrow MW is the axial distance from one outer end PW to the other outer end PW. This distance MW is the cross-sectional width of the tire 2 (see JATMA, etc.).

In FIG. 1, the symbol PT is the radially inner end of the tire 2. This inner end PT is also called the toe. The toe PT is the boundary between the outer surface and the inner surface of the tire 2.

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of beads 8, a pair of chafers 10, a carcass 12, a belt 14, a pair of cushions 16, an inner liner 18, an insulation 20, a pair of reinforcing layers 22, a pair of interlayer strips 24, and a pair of edge strips 26.

The tread 4 comes into contact with the road surface at its outer surface 4s (i.e., the tread surface 4s). The symbol PE is the intersection point between the tread surface 4s and the equatorial plane. The intersection point PE is the equator of the tire 2. The equator PE of the tire 2 is also the radially outer end of the tire 2.

In FIG. 1, the double-headed arrow HE indicates the radial distance from the bead baseline to the equator PE. This distance HE is the cross-sectional height of the tire 2 (see JATMA, etc.).

The tread 4 comprises a base portion 28 and a cap portion 30 located radially outward of 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 that takes into consideration wear resistance and grip performance.

The tread 4 is formed with grooves 32 (i.e., circumferential grooves 32) that extend continuously in the circumferential direction. As a result, the tread 4 is formed with a plurality of land portions 34 that are arranged in parallel in the axial direction. The tread 4 has a plurality of land portions 34 that are partitioned by the circumferential grooves 32.

In this tire 2, four circumferential grooves 32 are cut into the tread 4, forming five land portions 34. Of the four circumferential grooves 32, the circumferential groove 32 located on the outer side in the axial direction is the shoulder circumferential groove 32s, and the circumferential groove 32 located on the inner side of the shoulder circumferential groove 32s is the middle circumferential groove 32m. Of the five land portions 34, the land portion 34 located on the outer side in the axial direction and including the end TE of the tread surface 4s is the shoulder land portion 34s. The land portion 34 located on the inner side in the axial direction and including the equator PE is the center land portion 34c. The land portion 34 located between the shoulder land portion 34s and the center land portion 34c is the middle land portion 34m.

In this tire 2, from the viewpoint of contributing to drainage and traction performance, the width of the circumferential groove 32 is preferably 1% to 10% of the width of the tread surface 4s. The depth of the circumferential groove 32 is preferably 10 mm to 25 mm. The width of the tread surface 4s is represented by the length from one end TE of the tread surface 4s to the other end TE. This length is measured along the tread surface 4s.

Each sidewall 6 is continuous with an end of the tread 4. The sidewalls 6 extend radially inward from the end of the tread 4 along the carcass 12. The sidewalls 6 are made of crosslinked rubber.

Each bead 8 is located radially inward from the sidewall 6. The bead 8 includes a core 36 and an apex 38.

The core 36 extends in the circumferential direction. Although not shown, the core 36 includes a wound steel wire. The apex 38 is located radially outside the core 36. The apex 38 extends radially outward from the core 36. The symbol PA is the radially outer end of the apex 38. This outer end PA is also the end of the bead 8.

In FIG. 1, the double-headed arrow HA is the radial distance from the bead baseline to the end PA of the bead 8. This distance HA is also called the height of the bead 8. In this tire 2, the height HA of the bead 8 is adjusted so that the ratio (HA/HE) of the height HA of the bead 8 to the cross-sectional height HE is 0.30 or more and 0.40 or less. This ratio (HA/HE) is preferably 0.33 or more and 0.37 or less.

The apex 38 comprises an inner apex 38u and an outer apex 38s. The outer apex 38s is located radially outward of the inner apex 38u. The inner apex 38u and the outer apex 38s are made of crosslinked rubber. The outer apex 38s is softer than the inner apex 38u.

Each chafer 10 is located axially outward of the bead 8. The chafers 10 are located radially inward of the sidewall 6. The chafers 10 contact the rim R. The chafers 10 are made of crosslinked rubber.

The carcass 12 is located inside the tread 4, the sidewall 6, and the chafer 10. The carcass 12 spans between one bead 8 and the other bead 8. This carcass 12 has a radial structure. The carcass 12 has at least one carcass ply 40. The carcass 12 of this tire 2 consists of one carcass ply 40.

In this tire 2, the carcass ply 40 is folded back from the inside to the outside in the axial direction around the core 36 of each bead 8. This carcass ply 40 has a ply body 40a extending from one core 36 to the other core 36, and a pair of folded back portions 40b connected to this ply body 40a and folded back from the inside to the outside in the axial direction around each core 36. In this tire 2, the ends of the folded back portions 40b are positioned in the same positions as in conventional tires.

Figure 2 shows a cross section of the tire 2 along the equatorial plane. In Figure 2, the left-right direction is the circumferential direction of the tire 2, and the up-down direction is the radial direction of the tire 2.

As shown in FIG. 2, the carcass ply 40 that constitutes the carcass 12 includes a number of carcass cords 42 arranged in parallel. These carcass cords 42 are covered with a topping rubber 44. In this tire 2, the material of the carcass cords 42 is steel. The carcass cords 42 are steel cords.

In FIG. 2, the double arrow CD indicates the outer diameter of the carcass cord 42. In this tire 2, the outer diameter CD of the carcass cord 42 is 0.6 mm or more and 1.0 mm or less.

By setting the outer diameter CD to 0.6 mm or more, the carcass cord 42 itself has a suitable rigidity. In the carcass ply 40 including this carcass cord 42, damage involving cutting of the carcass cord 42 is unlikely to occur. From this viewpoint, the outer diameter CD is preferably 0.7 mm or more. By setting the outer diameter CD to 1.0 mm or less, the effect of the carcass cord 42 on the rigidity of the carcass ply 40 is suppressed. In this tire 2, good rim assembly properties are maintained. The thin carcass cord 42 contributes to reducing the weight of the tire 2. From this viewpoint, the outer diameter CD is more preferably 0.9 mm or less.

In this tire 2, the number of ends of the carcass cords 42 included in the carcass ply 40 is preferably 20 or more, and preferably 40 or less. The number of ends of the carcass cords 42 is represented by the number of carcass cords 42 included per 50 mm width of the carcass ply 40.

By setting the number of ends of the carcass cords 42 to 20 or more, the carcass ply 40 has appropriate rigidity. Since excessive deformation is suppressed, the carcass ply 40 is less susceptible to damage involving the cutting of the carcass cords 42. From this perspective, it is more preferable that the number of ends of the carcass cords 42 is 25 or more. By setting the number of ends of the carcass cords 42 to 40 or less, the rigidity of the carcass ply 40 is appropriately maintained. With this tire 2, good rim assembly properties are maintained.

In this tire 2, from the viewpoint of effectively suppressing the occurrence of damage involving breakage of the carcass cord 42, it is preferable that the outer diameter CD of the carcass cord 42 is 0.6 mm or more and that the number of ends of the carcass cord 42 is 20 or more. From the viewpoint of maintaining good rim assembly properties, it is preferable that the outer diameter CD of the carcass cord 42 is 1.0 mm or less and that the number of ends of the carcass cord 42 is 40 or less.

As shown in FIG. 1, the belt 14 is located radially inside the tread 4. The belt 14 is located radially outside the carcass 12.

The belt 14 is composed of multiple layers 46 stacked in the radial direction. In this tire 2, the belt 14 is composed of three layers 46. In this tire 2, there is no particular limit to the number of layers 46 that make up the belt 14. The configuration of the belt 14 is determined appropriately, taking into account the specifications of the tire 2.

Although not shown, each layer 46 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The material of the belt cords is steel.

In this tire 2, of the three layers 46, the second layer 46B located between the first layer 46A and the third layer 46C has the largest axial width. The first layer 46A located radially innermost has the smallest axial width.

Each cushion 16 is located radially between the end of the belt 14 and the carcass 12. The cushions 16 are made of crosslinked rubber.

As shown in FIG. 1, in this tire 2, the cushion 16 has a maximum thickness at the end 48 of the belt 14 (specifically, the end 48 of the second layer 46B). The cushion 16 tapers axially inward from the portion having the maximum thickness. The cushion 16 tapers radially inward from the portion having the maximum thickness.

As shown in FIG. 1, the end 50 of the cushion 16 located on the equatorial plane side (hereinafter, the lateral end 50) is located axially outside the shoulder circumferential groove. The end 52 of the cushion 16 layer located on the bead 8 side (hereinafter, the longitudinal end 52) is located radially outside the axially outer end PW of the tire 2.

The inner liner 18 is located inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber with excellent air barrier properties.

The insulation 20 is located between the carcass 12 and the inner liner 18. The insulation 20 is bonded to the carcass 12 and to the inner liner 18. In other words, the inner liner 18 is bonded to the carcass 12 via the insulation 20. The insulation 20 is made of cross-linked rubber with good adhesive properties.

Each reinforcing layer 22 is located in the bead 8. The reinforcing layer 22 is folded axially from the inside to the outside around the core 36 along the carcass ply 40. In this tire 2, the carcass ply 40 is located between the reinforcing layer 22 and the bead 8.

Although not shown, the reinforcing layer 22 includes a number of filler cords arranged in parallel. In the reinforcing layer 22, the filler cords are covered with topping rubber. The material of the filler cords is steel.

In this tire 2, one end (hereinafter, the inner end) of the reinforcing layer 22 is located between the outer end of the inner apex 38u and the core 36 in the radial direction. The other end (hereinafter, the outer end) of the reinforcing layer 22 is located between the end of the folded-back portion 40b and the core 36 in the radial direction. As shown in FIG. 1, in this tire 2, the outer end of the reinforcing layer 22 is located inside the inner end in the radial direction.

Each interlayer strip 24 is located between the outer apex 38s of the bead 8 and the chafer 10. The interlayer strip 24 covers the end of the folded portion 40b and the outer end of the reinforcing layer 22. The interlayer strip 24 is made of crosslinked rubber.

Each edge strip 26 is located between the outer apex 38s of the bead 8 and the interlayer strip 24. The end portion of the folded-up portion 40b abuts against the edge strip 26. In this tire 2, the end of the folded-up portion 40b is sandwiched between the edge strip 26 and the interlayer strip 24. The edge strip 26 is made of crosslinked rubber. In this tire 2, the edge strip 26 is made of the same material as the interlayer strip 24.

Figure 3 shows a portion of the tire 2 shown in Figure 1. Figure 3 shows the contour CL of the carcass 12 included in the tire 2. This contour CL of the carcass 12 is the contour of the ply body 40a specified in the tire 2 in a normal state. In Figure 3, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Figure 3 is the circumferential direction of the tire 2.

In FIG. 3, the symbol PL denotes the intersection of a straight line that passes through the lateral end 50 of the cushion 16 and extends in the radial direction with the contour CL of the carcass 12. The symbol PV denotes the intersection of a straight line that passes through the longitudinal end 52 of the cushion 16 and extends in the axial direction with the contour CL of the carcass 12. In this tire 2, the portion of the contour CL of the carcass 12 from the intersection PL to the intersection PV is the contour of the portion that overlaps with the cushion 16.

In this tire 2, the outline of the portion overlapping with the cushion 16 is represented by a circular arc, and this circular arc is called a buttress arc. In FIG. 3, the symbol CB is the center of this buttress arc. In this tire 2, the center CB of the buttress arc is identified as follows.

The perpendicular bisector (hereinafter, the first perpendicular bisector L1) of the line segment connecting the intersection points PL and PV is drawn. The intersection point P1 between the first perpendicular bisector L1 and the contour CL of the carcass 12 is determined. The perpendicular bisector (hereinafter, the second perpendicular bisector L2) of the line segment connecting the intersection points P1 and PL is drawn. The intersection point (hereinafter, also referred to as the first intersection point) of the second perpendicular bisector L2 and the first perpendicular bisector L1 is the center CB of the buttress arc. Although not shown, the perpendicular bisector (hereinafter, the third perpendicular bisector L3) of the line segment connecting the intersection points P1 and PV may be drawn, and the center CB of the buttress arc may be represented by the intersection point (hereinafter, also referred to as the second intersection point) of this third perpendicular bisector L3 and the first perpendicular bisector L1.

3, the arrow Rb is the radius of the buttress arc. In this tire 2, the average value of the length from the center CB to the contour CL of the carcass 12 measured along the first perpendicular bisector L1 and the length from the center CB to the contour CL of the carcass 12 measured along the second perpendicular bisector L2 is expressed as the radius Rb of this buttress arc. When the center CB of the buttress arc is expressed by the intersection point between the third perpendicular bisector L3 and the first perpendicular bisector L1, i.e., the second intersection point, the average value of the length from the second intersection point measured along the first perpendicular bisector L1 to the contour CL of the carcass 12 and the length from the second intersection point measured along the third perpendicular bisector L3 to the contour CL of the carcass 12 is expressed as the radius Rb of this buttress arc. When the intersection of the second perpendicular bisector L2 and the first perpendicular bisector L1, i.e., the first intersection and the second intersection, coincide with each other, the average value of the length from the first intersection to the contour CL of the carcass 12 measured along the first perpendicular bisector L1 and the length from the first intersection to the contour CL of the carcass 12 measured along the second perpendicular bisector L2, as well as the length from the second intersection to the contour CL of the carcass 12 measured along the first perpendicular bisector L1 and the length from the second intersection to the contour CL of the carcass 12 measured along the third perpendicular bisector L3, is expressed as the radius Rb of this buttress arc. Note that in this tire 2, when the distance between the first intersection and the second intersection is within 3 mm, this is the case where the first intersection and the second intersection coincide with each other.

In FIG. 3, the symbol PM is the axially outer end of the contour CL of the carcass 12. The carcass 12 has its maximum width at the position of this outer end PM. The position indicated by the symbol PM is the position on the contour CL of the carcass 12 that corresponds to the maximum width position of the carcass 12. In this tire 2, this axially outer end PM is located on a straight line that passes through the aforementioned axially outer end PW and extends in the axial direction. The symbol PN is the intersection point between the contour CL of the carcass 12 and a straight line that passes through the end PA of the bead 8 and extends in the axial direction. In this tire 2, the portion of the contour CL of the carcass 12 from the axially outer end PM to the intersection point PN is the contour of the portion from the maximum width position of the carcass 12 to the end PA of the bead 8.

In this tire 2, the contour of the portion from the maximum width position of the carcass 12 to the end PA of the bead 8 is represented by an arc, and this arc is called the lower arc. In FIG. 3, the symbol CS is the center of this lower arc. In this tire 2, the center CS of the lower arc is identified as follows.

A perpendicular bisector (hereinafter, the fourth perpendicular bisector L4) of the line segment connecting the axial outer end PM and the intersection point PN is drawn. The intersection point P4 between the fourth perpendicular bisector L4 and the contour CL of the carcass 12 is determined. A perpendicular bisector (hereinafter, the fifth perpendicular bisector L5) of the line segment connecting the intersection point P4 and the intersection point PN is drawn. The intersection point (hereinafter, also referred to as the third intersection point) between the fifth perpendicular bisector L5 and the fourth perpendicular bisector L4 is the center CS of the lower arc. Although not shown, a perpendicular bisector (hereinafter, the sixth perpendicular bisector L6) of the line segment connecting the intersection point P4 and the axial outer end PM may be drawn, and the center CS of the lower arc may be represented by the intersection point (hereinafter, also referred to as the fourth intersection point) between the sixth perpendicular bisector L6 and the fourth perpendicular bisector L4. In this tire 2, the center CS of the lower arc is preferably located on a straight line that passes through the axially outer end PM and extends in the axial direction.

3, the arrow Rs is the radius of the lower arc. In this tire 2, the average value of the length from the center CS to the contour CL of the carcass 12 measured along the fourth perpendicular bisector L4 and the length from the center CB to the contour CL of the carcass 12 measured along the fifth perpendicular bisector L5 is expressed as the radius Rs of this lower arc. When the center CS of the lower arc is expressed by the intersection point between the sixth perpendicular bisector L6 and the fourth perpendicular bisector L4, i.e., the fourth intersection point, the average value of the length from the fourth intersection point measured along the fourth perpendicular bisector L4 to the contour CL of the carcass 12 and the length from the fourth intersection point measured along the sixth perpendicular bisector L6 to the contour CL of the carcass 12 is expressed as the radius Rs of this lower arc. When the intersection of the fifth perpendicular bisector L5 and the fourth perpendicular bisector L4, i.e., the third intersection and the fourth intersection, coincide with each other, the average value of the length from the third intersection to the contour CL of the carcass 12 measured along the fourth perpendicular bisector L4 and the length from the third intersection to the contour CL of the carcass 12 measured along the fifth perpendicular bisector L5, as well as the length from the fourth intersection to the contour CL of the carcass 12 measured along the fourth perpendicular bisector L4 and the length from the fourth intersection to the contour CL of the carcass 12 measured along the sixth perpendicular bisector L6 is expressed as the radius Rs of this lower arc. In this tire 2, the third intersection and the fourth intersection coincide with each other when the distance between the third intersection and the fourth intersection is within 3 mm.

In this tire 2, in a normal state where the tire is mounted on the rim R, i.e., a normal rim, the internal pressure is adjusted to the normal internal pressure, and no load is applied, the contour CL of the carcass 12 includes a buttress arc as an arc representing the contour of the portion overlapping with the cushion 16, and a lower arc as an arc representing the contour of the portion from the maximum width position of the carcass 12 to the end PA of the bead 8. The ratio (Rb/Rs) of the radius Rb of the buttress arc to the radius Rs of the lower arc is 1.00 or more and 1.10 or less.

In this tire 2, in the contour CL of the carcass 12 in the normal state, the difference between the radius Rb of the buttress arc and the radius Rs of the lower arc is suppressed to within 10% of the radius Rs of the lower arc. In this tire 2, a buttress arc with a large radius Rb is set by setting a lower arc with a larger radius Rs than in conventional tires. In this tire 2, the collapse of the bead portion during inflation is suppressed, and the reduction in the tread radius in the shoulder portion is suppressed, so that it is not necessary to increase the size of the cushion 16 to improve the uneven wear resistance, as in conventional tires. A small cushion 16 can be adopted, and this tire 2 can reduce the rolling resistance. Furthermore, this tire 2 can expand the distance between the vertical end 52 of the cushion 16 and the end PA of the bead 8, i.e., the flexible zone, and therefore can improve the rim assembly performance.

In this tire 2, the aspect ratio, which is expressed as the ratio of the cross-sectional height HE to the cross-sectional width MW, is 60% or more and 80% or less. In other words, this tire 2 has an aspect ratio of 60% or more and 80% or less. In this tire 2, compared to a tire with an aspect ratio exceeding 80%, the side portion that bridges the tread 4 portion (hereinafter, the tread portion) and the bead portion is short, making it difficult to ensure a flexible zone that affects rim assembly.

However, as mentioned above, by setting the difference between the radius Rb of the buttress arc and the radius Rs of the lower arc to within 10% of the radius Rs of the lower arc, tire 2 improves uneven wear resistance even when a small cushion 16 is used. In tire 2, despite the limitation on the length of the side portion, a sufficient flexible zone is ensured. The small cushion 16 contributes to reducing rolling resistance. In tire 2, reduced rolling resistance and improved rim assembly are achieved while minimizing the impact on uneven wear resistance.

Furthermore, in this tire 2, the difference between the radius Rb of the buttress arc and the radius Rs of the lower arc is small, so distortion is less likely to concentrate on the carcass 12 having this contour CL. Since the force acting on the carcass 12 is dispersed, the durability of this tire 2 is also improved.

In this tire 2, the ratio (Rs/HA) of the radius Rs of the lower arc to the radial distance HA from the bead base line to the end PA of the bead 8 is preferably 0.85 or more and 0.95 or less.

By setting the ratio (Rs/HA) to 0.85 or more, collapse of the bead portion during inflation is effectively suppressed. In this tire 2, a small cushion 16 can be used, and a sufficient flexible zone is ensured. In this tire 2, the rolling resistance is reduced and rim assembly is improved while minimizing the impact on uneven wear resistance. From this perspective, it is more preferable that the ratio (Rs/HA) is 0.87 or more.

By setting the ratio (Rs/HA) to 0.95 or less, the contour CL of the carcass 12 is properly maintained, so that distortion is less likely to concentrate on the carcass 12. The force acting on the carcass 12 is dispersed, so that the durability of the tire 2 is improved. In particular, the concentration of distortion at the end PA of the bead is effectively suppressed, so that bead durability is improved. From this perspective, it is more preferable that the ratio (Rs/HA) is 0.93 or less.

In FIG. 1, the symbol PB is the apex of the belt 14. This apex PB is represented by the radially outer end of the belt 14. The double-headed arrow HB is the radial distance from the bead baseline to the apex PB of the belt 14. The double-headed arrow HF is the radial distance from the end PA of the bead 8 to the vertical end 52 of the cushion 16. This distance HF is the radial length of the flexible zone in this tire 2. In this tire 2, the aforementioned axially outer end PW is located radially outboard of the position half the radial length HF of the flexible zone.

In this tire 2, the ratio (HF/HB) of the radial distance HF from the end PA of the bead 8 to the vertical end 52 of the cushion 16 to the radial distance HB from the bead base line to the top PB of the belt 14 is preferably 0.25 or more and 0.45 or less.

By setting the ratio (HF/HB) to 0.25 or more, a sufficient flexible zone is ensured. The flexible zone imparts appropriate flexibility to the side portion, which improves the rim assembly properties of this tire 2. From this perspective, it is more preferable that the ratio (HF/HB) is 0.27 or more.

By setting the ratio (HF/HB) to 0.45 or less, the size of the flexible zone is appropriately maintained. In this tire 2, the rigidity of the side portion is ensured, so good durability is maintained. In particular, the concentration of strain at the end PA of the bead 8 is effectively suppressed, improving bead durability. From this perspective, it is more preferable that the ratio (HF/HB) is 0.40 or less.

In this tire 2, the toe spacing, which is the axial distance from one toe PT to the other toe PT, is also taken into consideration. The method for measuring this toe spacing will be described with reference to FIG. 4.

In the method of measuring the toe spacing, as shown in FIG. 4(a), the tire 2 is placed on a flat road surface without being mounted on a rim R. The height of the tire 2, represented by the double arrow HT, is measured. The position of half of the measured height HT, represented by the dashed dotted line HL, is identified. As shown in FIG. 4(b), the axial distance TW from one toe PT to the other toe PT at this position HL is measured. For this tire 2, this distance TW is the toe spacing TW measured when no load other than its own weight is acting on it.

In this tire 2, the ratio (TW/RW) of the toe distance TW, which is expressed as the axial distance from one toe PT to the other toe PT, to the rim width RW of the rim R, measured in a state where no load other than the tire's own weight is acting on the tire, is preferably 0.80 or more and 0.88 or less.

By setting the ratio (TW/RW) to 0.80 or more, collapse of the bead portion during inflation is effectively suppressed. In this tire 2, a small cushion 16 can be used, and a sufficient flexible zone is ensured. In this tire 2, the rolling resistance is reduced and rim assembly is improved while minimizing the impact on uneven wear resistance. From this perspective, the ratio (TW/RW) is preferably 0.82 or more.

By setting the ratio (TW/RW) to 0.88 or less, the contour CL of the carcass 12 is properly maintained, so that distortion is less likely to concentrate on the carcass 12. The force acting on the carcass 12 is dispersed, so that the durability of the tire 2 is improved. In particular, the concentration of distortion on the end PA of the bead portion is effectively suppressed, so that bead durability is improved. From this perspective, it is more preferable that the ratio (TW/RW) is 0.86 or less.

In this tire 2, the ratio of the cross-sectional width MW to the toe distance TW (MW/TW) is preferably 1.60 or more and 1.90 or less.

By setting the ratio (MW/TW) to 1.60 or greater, the contour CL of the carcass 12 is properly maintained, so that distortion is less likely to concentrate on the carcass 12. The force acting on the carcass 12 is dispersed, so that the durability of the tire 2 is improved. In particular, the concentration of distortion at the end PA of the bead portion is effectively suppressed, so that bead durability is improved. From this perspective, the ratio (MW/TW) is more preferably 1.62 or greater, and even more preferably 1.68 or greater.

By setting the ratio (MW/TW) to 1.90 or less, collapse of the bead portion during inflation is effectively suppressed. In this tire 2, a small cushion 16 can be used, and a sufficient flexible zone is ensured. In this tire 2, the rolling resistance is reduced and rim assembly is improved while minimizing the impact on uneven wear resistance. From this perspective, the ratio (MW/TW) is more preferably 1.82 or less.

In this tire 2, from the viewpoint of reducing rolling resistance and improving rim assembly and bead durability while suppressing the effect on uneven wear resistance, it is preferable that the ratio (TW/RW) of the toe spacing TW, which is expressed as the axial distance from one toe PT to the other toe PT measured in a state where no load other than the tire's own weight is acting, to the rim width RW of the rim R is 0.80 or more and 0.88 or less, and the ratio (MW/TW) of the cross-sectional width MW to this toe spacing TW is 1.60 or more and 1.90 or less.

In FIG. 1, the double-headed arrow D1 indicates the thickness of the tire 2 at the equatorial plane. This thickness D1 is represented as the distance from the inner surface to the outer surface of the tire 2 measured along the equatorial plane. The double-headed arrow TC indicates the thickness of the cushion 16. This thickness TC is represented as the maximum thickness of the cushion 16 measured along the surface of the cushion 16 facing the carcass 12, i.e., the normal to the inner surface.

As described above, the tire 2 employs a smaller cushion 16 than conventional tires. The smaller cushion 16 contributes to reducing rolling resistance. From this viewpoint, the ratio (TC/D1) of the thickness TC of the cushion 16 to the thickness D1 of the tire 2 is preferably 0.35 or less, and more preferably 0.30 or less. From the viewpoint that the cushion 16 can effectively reduce the load acting on the end of the belt 14, the ratio (TC/D1) is preferably 0.20 or more, and more preferably 0.25 or more.

In FIG. 1, the double-headed arrow C1 indicates the thickness from the axially outer end PW of the tire 2 to the outer surface of the carcass 12. This thickness C1 is the thickness of the outer portion of the carcass 12 at the axially outer end PW.

In this tire 2, the ratio (2·C1/MW) of the thickness C1 of the outer portion of the carcass 12 at the axially outer end PW to half the cross-sectional width MW is preferably 0.05 or less. This allows the carcass 12 to be positioned further outward in the tire 2. In this tire 2, a carcass 12 having a long cord path is obtained, specifically, a carcass 12 having a contour CL including a lower arc having a large radius Rs and a buttress arc having a large radius Rb. In this tire 2, the rolling resistance is reduced and the rim assembly property and bead durability are improved while suppressing the effect on uneven wear resistance. From this viewpoint, the ratio (2·C1/MW) is more preferably 0.04 or less. From the viewpoint of sufficiently protecting the carcass 12 and suppressing the occurrence of damage to the carcass 12, the ratio (2·C1/MW) is preferably 0.02 or more, and more preferably 0.03 or more.

Next, a method for manufacturing the tire 2 will be described. In manufacturing the tire 2, the tread 4, sidewall 6, and other components are combined in a molding machine (not shown) to prepare an uncrosslinked tire 2 for the tire 2 shown in FIG. 1, i.e., a raw tire 2r. The raw tire 2r is pressurized and heated in a mold 56 of a vulcanizer 54, which will be described later, to obtain the tire 2. The manufacturing method for the tire 2 includes a process for preparing the raw tire 2r and a process for pressurizing and heating the raw tire 2r in the mold 56.

Figure 5 shows a part of a vulcanizer 54 used in the manufacturing method of this tire 2. In Figure 5, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Figure 5 is the circumferential direction of the tire 2. In this vulcanizer 54, the raw tire 2r is vulcanized. This vulcanizer 54 is equipped with a mold 56 and a bladder 58.

The mold 56 has a cavity surface 60 on its inner surface. This cavity surface 60 abuts against the outer surface of the raw tire 2r and shapes the outer surface of the tire 2. Although not described in detail, this mold 56 is a split mold.

The bladder 58 is located inside the mold 56. The bladder 58 is made of crosslinked rubber. A heating medium such as steam is filled inside the bladder 58. This causes the bladder 58 to expand. The bladder 58 shown in FIG. 5 is in an expanded state filled with a heating medium. The bladder 58 abuts against the inner surface of the raw tire 2r and shapes the inner surface of the tire 2. In the manufacture of the tire 2, a metal rigid core (not shown) may be used instead of the bladder 58. The rigid core has a toroidal outer surface. The shape of this outer surface is approximated to the shape of the inner surface of the tire 2 when it is filled with air and the internal pressure is maintained at 5% of the normal internal pressure.

In the manufacture of this tire 2, the raw tire 2r is placed into a mold 56 set at a predetermined temperature. After placement, the mold 56 is closed. A bladder 58 expands by filling it with a heating medium, and presses the raw tire 2r from the inside against a cavity surface 60. The raw tire 2r is pressurized and heated for a predetermined time in the mold 56. This crosslinks the rubber composition of the raw tire 2r, and the tire 2 is obtained.

In FIG. 5, the solid line MBL is a reference line corresponding to the bead baseline mentioned above. This reference line is also called the mold baseline. The symbol PC is the intersection point between the mold baseline and the cavity surface 60. This intersection point PC is also called the clip width reference point. The double arrow CW is the axial distance from one clip width reference point PC to the other clip width reference point PC. This distance CW is the clip width of this mold 56.

In this manufacturing method, the clip width CW of the mold 56 is wider than the rim width RW of the rim R on which the tire 2 manufactured using this mold 56 is assembled. Specifically, the ratio (CW/RW) of the clip width CW of the mold 56 to the rim width RW of the rim R on which the tire 2 is assembled is 1.15 or more and 1.22 or less.

Since the ratio (CW/RW) is 1.15 or more, in the tire 2 manufactured by this mold 56, the difference between the radius Rb of the buttress arc and the radius Rs of the lower arc is small, and the contour CL of the carcass 12 is configured so that the lower arc has a large radius Rs. In this tire 2, the collapse of the bead portion during inflation is effectively suppressed. In this tire 2, a small cushion 16 can be used, and a flexible zone is sufficiently secured. In this tire 2, the rolling resistance is reduced and the rim assembly is improved while suppressing the impact on uneven wear resistance. In other words, according to this manufacturing method, a tire 2 is obtained that achieves the reduction of rolling resistance and the improvement of rim assembly while suppressing the impact on uneven wear resistance. From this viewpoint, the ratio (CW/RW) is preferably 1.16 or more.

Since the ratio (CW/RW) is 1.22 or less, the contour CL of the carcass 12 is properly maintained in the tire 2 manufactured with this mold 56. Distortion is less likely to concentrate on the carcass 12 of this tire 2. Since the force acting on the carcass 12 is dispersed, the durability of this tire 2 is improved. In particular, the concentration of distortion at the end PA of the bead 8 is effectively suppressed, improving bead durability. In other words, this manufacturing method results in a tire 2 that achieves improved bead durability. From this perspective, it is more preferable that the ratio (CW/RW) is 1.21 or less.

As is clear from the above explanation, the heavy-duty tubeless tire 2 of the present invention achieves reduced rolling resistance and improved rim assembly while minimizing the impact on uneven wear resistance. The present invention is particularly effective in tires 2 with an aspect ratio of 60% to 80%, where it is difficult to ensure a flexible zone, and further in tires 2 with an aspect ratio of 60% to 80% and an outer diameter of 850 mm or less (see JATMA, etc.).

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

[Example 1]
A heavy-duty tubeless tire (size=215/75R17.5) was obtained having the configuration shown in Fig. 1 and the specifications shown in Table 1. The outer diameter of this tire was 770 mm.

In this Example 1, a steel cord having an outer diameter CD of 0.76 mm was used for the carcass cord. The ratio (TW/RW) of the toe spacing TW to the rim width RW of the rim R was 0.85. The ratio (MW/TW) of the tire section width MW to the toe spacing TW was 1.65. The ratio (Rb/Rs) of the buttress arc radius Rb to the lower arc radius Rs was 1.09. The ratio (Rs/HA) of the lower arc radius Rs to the radial distance HA from the bead baseline to the bead end PA was 0.89. The ratio (HF/HB) of the radial distance HF from the bead end PA to the vertical end of the cushion to the radial distance HB from the bead baseline to the belt top PB was 0.30. The ratio (CW/RW) of the clip width CW of the mold used in manufacturing this tire to the rim width RW of the rim R was 1.21.

[Example 2]
A tire of Example 2 was obtained in the same manner as in Example 1, except that the ratio (HF/HB) was set as shown in Table 1 below.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the outer diameter CD, the ratio (TW/RW), the ratio (MW/TW), the ratio (Rb/Rs), the ratio (Rs/HA), the ratio (HF/HB) and the ratio (CW/RW) were set as shown in the following Table 1. Comparative Example 1 is a conventional tire.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that the outer diameter CD was set as shown in Table 1 below.

[mass]
The mass of the prototype tires was measured. The results are shown in Table 1 below as an index. The smaller the value, the smaller the mass.

[Resistant to uneven wear]
The prototype tire was mounted on a regular rim, filled with air, and the internal pressure was adjusted to 700 kPa. This tire was mounted on all wheels of a test vehicle (a 4-ton truck). The test vehicle was driven on a general road with 50% of the standard load on the entire bed. The distance traveled until the tire reached the point where it needed to be replaced was measured. The results are shown as an index in Table 1 below. The higher the value, the better the resistance to uneven wear.

[Bead durability]
The prototype tire was mounted on a standard rim, filled with air, and the internal pressure was adjusted to the standard internal pressure. This tire was mounted on a drum testing machine. A load of 33.31 kN was applied to the tire, and the tire was run on a drum (radius = 1.7 m) at a speed of 80 km/h. The running time until the bead was damaged was measured. The results are shown as an index in Table 1 below. The higher the value, the better the bead durability.

[Rim assembly]
The ease of assembling the prototype tires onto the rim when mechanically assembling them onto a regular rim was evaluated. The results are shown as an index in Table 1 below. The higher the value, the easier it is to mount the tire onto the rim, and the better the rim assembling performance.

[Rolling resistance]
Using a rolling resistance tester, the rolling resistance coefficient (RRC) of each prototype tire is measured when it runs on a drum at a speed of 80 km/h under the following conditions. The results are shown as an index in Table 1 below. The larger the value, the smaller the rolling resistance.
Rim: 6.0 x 17.5
Internal pressure: 700 kPa
Vertical load: 14.17kN

As shown in Table 1, in the embodiment, the rolling resistance is reduced and the rim assembly is improved while minimizing the impact on uneven wear resistance. The superiority of the present invention is clear from these evaluation results.

The technology described above, which reduces rolling resistance and improves rim assembly while minimizing the impact on uneven wear resistance, can be applied to a variety of tires.

2 tire 4 tread 6 sidewall 8 bead 10 chafer 12 carcass 14 belt 16 cushion 18 inner liner 32, 32s, 32m circumferential groove 34, 34s, 34c, 34m, 34s land portion 40 carcass ply 40a ply body 40b turn-up portion 42 carcass cord 46, 46A, 46B, 46C layer 48 end of belt 14 50 lateral end of cushion 16 52 longitudinal end of cushion 16 54 vulcanizer 56 mold 58 bladder 60 cavity surface

Claims (4)

An aspect ratio of 60% or more and 80% or less,
A pair of beads;
a carcass that bridges between one bead and the other bead;
A belt positioned radially outward from the carcass;
a pair of cushions positioned between the ends of the belt and the carcass;
The carcass includes a large number of carcass cords arranged in parallel, and each carcass cord has an outer diameter of 0.6 mm or more and 1.0 mm or less,
When mounted on a standard rim, with the internal pressure adjusted to the standard, and without any load applied,
a contour of the carcass including a buttress arc as a circular arc representing a contour of a portion overlapping with the cushion, and a lower arc as a circular arc representing a contour of a portion from a maximum width position of the carcass to an end of the bead,
a ratio of a radius of the buttress arc to a radius of the lower arc is greater than or equal to 1.00 and less than or equal to 1.10 ;
A tubeless tire for heavy loads , wherein a ratio of a radius of the lower circular arc to a radial distance from a bead base line to an end of the bead is 0.85 or more and 0.95 or less. The heavy-duty tubeless tire according to claim 1, wherein the ratio of the radial distance from the end of the bead to the longitudinal end of the cushion to the radial distance from the bead base line to the top of the belt is 0.25 or more and 0.45 or less. The heavy-duty tubeless tire according to claim 1 or 2, in which the ratio of the toe spacing, which is expressed as the axial distance from one toe to the other toe, measured in a state in which no load other than the tire's own weight is acting, to the rim width of the regular rim is 0.80 or more and 0.88 or less. The heavy-duty tubeless tire according to claim 3, wherein the ratio of the tire's section width to the toe spacing is 1.60 or more and 1.90 or less.

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