Pneumatic tire and manufacturing method therefor

Abstract

The present invention provides a pneumatic tire capable of improving steering stability while maintaining good appearance and rim assembly properties of the tire, and a manufacturing method therefor. Provided is a pneumatic tire including: a tread part 1 extending in the tire circumferential direction and forming an annular shape; a pair of side wall parts 2 arranged on both sides of the tread part 1; a pair of bead parts 3 arranged on the inner sides of the side wall parts 2 in the tire radial direction; and a plurality of belt layers 7 embedded in the tread part 1, wherein the flatness ratio is in the range of 55% or more and less than 75% and the tire cross-sectional height SH is set to 120 mm or more. In the pneumatic tire, the tread development width TDW of the tread part 1 is set to 80% or more of the tire nominal width, and the bead base width TBW between the bead parts 3 is set to 107% or more of the tread development width TDW of the tread part 1.

Description

Pneumatic tire and manufacturing method thereof

[0001] The present invention relates to a pneumatic tire and a manufacturing method thereof, and more particularly to a pneumatic tire and a manufacturing method thereof that can improve steering stability while maintaining good tire appearance and rim assembly properties.

[0002] In order to improve the steering stability of pneumatic tires, it has been proposed to increase the tread width, which is the length along the tread profile (see, for example, Patent Document 1). However, increasing the tread width has problems such as poor rim assembly and poor appearance due to collapse of the side profile. These problems are particularly pronounced in pneumatic tires with a large cross-sectional height (high section height size pneumatic tires).

[0003] Japanese Patent No. 5541416

[0004] An object of the present invention is to provide a pneumatic tire that can improve steering stability while maintaining good tire appearance and rim assembly properties, and a method for manufacturing the same.

[0005] In order to achieve the above object, the pneumatic tire of the present invention comprises a tread portion extending circumferentially of the tire to form a ring, a pair of sidewall portions arranged on both sides of the tread portion, a pair of bead portions arranged radially inward of the sidewall portions, and a plurality of belt layers embedded in the tread portion, wherein the pneumatic tire has an aspect ratio in the range of 55% or more but less than 75%, and a tire cross-sectional height SH set to 120 mm or more, and wherein the tread developed width TDW of the tread portion is set to 80% or more of the nominal tire width, and the bead base width TBW of the bead portions is set to 107% or more of the tread developed width TDW of the tread portion.

[0006] Furthermore, in order to achieve the above-mentioned object, the present invention provides a method for manufacturing a pneumatic tire comprising a tread portion extending circumferentially in a ring-like shape in the tire circumferential direction, a pair of sidewall portions arranged on both sides of the tread portion, a pair of bead portions arranged radially inward of the sidewall portions, and a plurality of belt layers embedded in the tread portion, wherein the aspect ratio is in the range of 55% or more and less than 75%, and the tire cross-sectional height SH is set to 120 mm or more, the method being characterized in that a mold is used that is formed so that the tread developed width TDW of the tread portion is 80% or more of the nominal tire width and the bead base width TBW of the bead portions is 107% or more of the tread developed width TDW of the tread portion, and the pneumatic tire is vulcanized in this mold.

[0007] In this invention, a pneumatic tire has an aspect ratio of 55% or more but less than 75%, a tire section height SH of 120 mm or more, and a tread developed width TDW of the tread of 80% or more of the nominal tire width. This allows for a wide contact width, which is the maximum width of the contact area in the tire width direction, ensuring sufficient cornering power and contributing to improved steering stability on dry roads. Furthermore, by setting the bead base width TBW of the bead of 107% or more of the tread developed width TDW of the tread, the spacing between the bead portions is optimized before the tire is inflated, effectively preventing deterioration of rim assembly and collapse of the sidewalls, even when the tread developed width TDW is widened. In this way, steering stability can be improved while maintaining good tire appearance and rim assembly performance.

[0008] In the present invention, the bead base width TBW and the developed tread width TDW are both dimensions in a mold. Therefore, when manufacturing a pneumatic tire having an aspect ratio of 55% or greater and less than 75% and a tire section height SH of 120 mm or greater as described above, a mold is used that is formed so that the developed tread width TDW of the tread portion is 80% or greater of the nominal tire width and the bead base width TBW of the bead portion is 107% or greater of the developed tread width TDW of the tread portion, and the pneumatic tire is vulcanized in this mold.

[0009] In the present invention, the contour line of the sidewall portion is composed of an upper circular arc and a lower circular arc, with the maximum tire width position as the boundary, and the radius of curvature SUR of the upper circular arc is preferably in the range of 90% to 110% of the radius of curvature SLR of the lower circular arc. This ensures an appropriate carcass line in the sidewall portion and suppresses a decrease in the rigidity of the sidewall portion, thereby ensuring steering stability and improving the tire's appearance. When manufacturing such a pneumatic tire, it is sufficient that the mold is formed so that the radius of curvature SUR of the upper circular arc is in the range of 90% to 110% of the radius of curvature SLR of the lower circular arc.

[0010] The bead base width TBW is preferably in the range of 120% or more and less than 130% of the rim width RW of the standard rim. This effectively improves rim assembly. When manufacturing such a pneumatic tire, it is sufficient that the mold is formed so that the bead base width TBW is in the range of 120% or more and less than 130% of the rim width RW of the standard rim.

[0011] Of the multiple belt layers, the width of the belt layer located at the outermost position in the tire radial direction is preferably in the range of 94% to 99% of the tread developed width TDW of the tread portion. This increases the rigidity of the belt layer in the tire contact patch and increases cornering power, thereby effectively improving steering stability. When manufacturing such a pneumatic tire, it is sufficient that the mold is formed so that the width of the belt layer located at the outermost position in the tire radial direction is in the range of 94% to 99% of the tread developed width TDW.

[0012] The minimum rubber thickness in the flexure region of the sidewall portion, including the tire's maximum width position, is preferably set in the range of 2.5 mm to 4.5 mm, and the height of the bead filler embedded in the bead portion is preferably 25% or more of the tire's cross-sectional height SH. This allows for a well-balanced improvement in tire appearance, rim mounting ease, and handling stability, even when the sidewall portion is thinned. Note that the flexure region of the sidewall portion, including the tire's maximum width position, refers to an area that is 20% of the tire's cross-sectional height SH and is centered on the tire's maximum width position.

[0013] Fig. 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. Fig. 2 is a meridian cross-sectional view showing a standard rim to which a pneumatic tire according to an embodiment of the present invention is mounted. Fig. 3 is a meridian cross-sectional view showing a mold used during vulcanization of a pneumatic tire according to an embodiment of the present invention.

[0014] The present invention will now be described in detail with reference to the accompanying drawings, in which: Fig. 1 shows a pneumatic tire according to an embodiment of the present invention; and Fig. 2 shows a standard rim on which the pneumatic tire is mounted.

[0015] As shown in FIG. 1 , the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed radially inward of the sidewall portions 2.

[0016] At least one carcass layer 4 (one layer in FIG. 1 ) made of a plurality of carcass cords arranged in the radial direction is mounted between a pair of bead portions 3. The carcass layer 4 is folded back from the inside to the outside of the tire around a bead core 5 arranged in each bead portion 3. Organic fiber cords such as nylon or polyester are preferably used as the carcass cords that make up the carcass layer 4. A bead filler 6 made of a rubber composition and having a triangular cross section is arranged on the outer periphery of the bead core 5. An inner liner layer 9 is arranged on the inner surface of the tire along the carcass layer 4.

[0017] Meanwhile, multiple belt layers 7 (two layers in FIG. 1 ) are embedded on the tire outer circumferential side of the carcass layer 4 in the tread portion 1. The belt layer 7 includes multiple reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. The two belt layers 7 include an inner belt layer 7A located on the inner side in the tire radial direction and an outer belt layer 7B located on the outer side of the inner belt layer 7A, and the width of the inner belt layer 7A is wider than the width of the outer belt layer 7B. In the belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers 7.

[0018] At least one belt cover layer 8 (two layers in Fig. 1 ) is disposed on the tire outer circumferential side of the belt layer 7, with the aim of improving high-speed durability. The belt cover layer 8 has reinforcing cords arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction. In Fig. 1 , the belt cover layer 8 located on the inner side in the tire radial direction constitutes a full cover that covers the entire width of the belt layer 7, while the belt cover layer 8 located on the outer side in the tire radial direction constitutes an edge cover layer that covers only the ends of the belt layer 7. As the reinforcing cords of the belt cover layer 8, organic fiber cords such as nylon and aramid are preferably used.

[0019] Furthermore, a tread rubber layer 11 is disposed on the outside of the belt cover layer 8 in the tread portion 1, a sidewall rubber layer 12 is disposed on the outside of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outside of the carcass layer 4 in the bead portion 3. The above-described tire internal structure shows a typical example of a pneumatic tire, but is not limited to this.

[0020] In the pneumatic tire, the aspect ratio is set to a range of 55% or more and less than 75%. Furthermore, the tire section height SH is set to 120 mm or more. The tire section height SH is preferably set to 130 mm or more, and the upper limit is preferably 160 mm or less.

[0021] The tread developed width TDW of the tread portion 1 is set to 80% or more of the tire nominal width. The tread developed width TDW is the distance from the tread edge E1 to the tread edge E2 measured along the outline of the tread surface of the tread portion 1, when the tread edges E1 and E2 are defined as the intersections of an extension of an arc defining the outline of each shoulder region of the tread portion 1 and an extension of an arc defining the outline of each buttress region of the tread portion 1 outside the contact patch, respectively, in a tire meridian cross section. Furthermore, the bead base width TBW of the bead portions 3 is set to 107% or more of the tread developed width TDW of the tread portion 1. The bead base width TBW is the width of the bead base between a pair of bead portions 3 measured based on the surface of each bead portion 3 that abuts against the rim flange.

[0022] In the pneumatic tire described above, while a high section height is set, by setting the tread developed width TDW of the tread portion 1 to 80% or more of the nominal tire width, the contact width can be widened, ensuring sufficient cornering power and contributing to improved steering stability on dry roads. Furthermore, by setting the bead base width TBW of the bead portion 3 to 107% or more of the tread developed width TDW of the tread portion 1, the spacing between the bead portions is optimized before the tire is inflated, effectively preventing deterioration of rim assembly and crushing of the sidewall portion 2 even when the tread developed width TDW is widened. In this way, steering stability can be improved while maintaining good tire appearance and rim assembly performance.

[0023] If the ratio of the tread developed width TDW to the tire nominal width (TDW / nominal width x 100%) is less than 80%, the effect of improving steering stability on dry roads cannot be sufficiently obtained.Also, if the ratio of the bead base width TBW to the tread developed width TDW (TBW / TDW x 100%) is less than 107%, the effect of suppressing side profile collapse and deterioration of rim assemblyability cannot be sufficiently obtained, making it impossible to maintain good tire appearance and rim assemblyability.

[0024] In the above pneumatic tire, the bead base width TBW is preferably set in the range of 120% or more and less than 130% of the rim width RW of the standard rim R (see FIG. 2). By appropriately setting the ratio of the bead base width TBW to the rim width RW (TBW / RW x 100%) in this way, rim assembly performance can be effectively improved. Here, when the ratio TBW / RW is 120% or more, rim assembly performance tends to improve, while when the ratio TBW / RW is less than 130%, the radius of curvature of the arc constituting the contour line of the sidewall portion 2 becomes large, improving the rigidity of the sidewall portion 2 and therefore tending to improve steering stability.

[0025] Furthermore, the width BW (see FIG. 1) of the outer belt layer 7B measured in the tire width direction is preferably in the range of 94% to 99% of the developed tread width TDW of the tread portion 1. In this case, the tensile modulus of the cord of the belt cover layer 8 covering the belt layer 7 is preferably set in the range of 2.0 GPa to 20 GPa. By appropriately setting the ratio BW / TDW×100% in this way, the rigidity of the belt layer 7 within the tire's contact patch can be increased, and cornering power can be increased, thereby effectively improving steering stability. Here, if the ratio BW / TDW is 99% or less, tire durability and resistance to uneven wear can be maintained without deterioration.

[0026] Furthermore, the minimum rubber thickness in the flexure region X of the sidewall portion 2, which includes the tire's maximum width position Pmax, is preferably set in the range of 2.5 mm to 4.5 mm, and more preferably in the range of 3.0 mm to 4.0 mm. The flexure region X of the sidewall portion 2, which includes the tire's maximum width position Pmax, is a region that is 20% of the tire's cross-sectional height SH and is centered at the tire's maximum width position Pmax. The minimum rubber thickness is the minimum value when the thickness of the sidewall portion 2, including the carcass layer 4, inner liner layer 9, and sidewall rubber layer 12, is measured in the flexure region X along the normal direction to the tire's outer surface. Furthermore, the height Fh of the bead filler 6 (see FIG. 1) is preferably 25% or more, and more preferably 28% or more, of the tire's cross-sectional height SH. The height Fh of the bead filler 6 is the height measured in the tire radial direction from the bead heel to the radially outer end of the bead filler 6.

[0027] In this way, by reducing the minimum rubber thickness in the flexure region X that includes the tire maximum width position Pmax of the sidewall portion 2 and by appropriately setting the ratio of the height Fh of the bead filler 6 to the tire cross-sectional height SH (Fh / SH x 100%), it is possible to achieve a balanced improvement in the tire's appearance, rim assembly performance, and handling stability, even when the sidewall portion 2 is thinned.

[0028] Figure 3 shows a mold used when vulcanizing a pneumatic tire according to an embodiment of the present invention. In Figure 3, CL is the tire centerline, and T is the tire. As shown in Figure 3, the mold 20 includes a sector mold 21 for molding the tread portion 1 of the tire T, a side plate 22 for molding the sidewall portion 2 of the tire T, and a bead ring 23 for molding the bead portion 3 of the tire T. During vulcanization, a rubber bladder is inserted inside the tire T, and the tire T is pressed against the inner surface of the mold 20 by the expansion of the bladder.

[0029] The mold 20 configured in this manner is processed so that the tread developed width TDW of the tire T is 80% or more of the tire nominal width, and the bead base width TBW of the tire T is 107% or more of the tread developed width TDW.

[0030] Then, a mold 20 is used that is formed so that the tread developed width TDW is a predetermined ratio to the tire nominal width and the bead base width TBW is a predetermined ratio to the tread developed width TDW, and the tire T is vulcanized in the mold 20, thereby making it possible to manufacture a pneumatic tire such as that shown in FIG. 1.

[0031] In the above mold, the contour line of the sidewall portion 2 of the tire T is formed by an upper circular arc C1 and a lower circular arc C2, with the tire maximum width position Pmax as the boundary, as shown in FIG. The radially outer end of the upper circular arc C1 corresponds to the separation position between the sector mold 21 and the side plate 22, while the radially inner end of the lower circular arc C2 corresponds to the separation position between the side plate 22 and the bead ring 23. The radius of curvature SUR of the upper circular arc C1 is preferably in the range of 90% to 110% of the radius of curvature SLR of the lower circular arc C2. By appropriately setting the ratio of the radius of curvature SUR of the upper circular arc C1 to the radius of curvature SLR of the lower circular arc C2 (SUR / SLR × 100%) in this way, the carcass line of the sidewall portion 2 is optimized, and a decrease in the rigidity of the sidewall portion 2 is suppressed, thereby ensuring steering stability and improving the tire's appearance.

[0032] For a pneumatic tire with a tire size of 235 / 60R18 (i.e., an aspect ratio of 60%), the tire section height SH, the tread developed width TDW, the ratio of the tread developed width TDW to the tire nominal width (TDW / nominal width x 100%), the bead base width TBW, the ratio of the bead base width TBW to the tread developed width TDW (TBW / TDW x 100%), the radius of curvature of the upper circular arc SUR, the radius of curvature of the lower circular arc SLR, and the radius of curvature of the upper circular arc SUR relative to the radius of curvature of the lower circular arc SLR. The ratio of the bead base width TBW to the standard rim width RW (SUR / SLR x 100%), the rim width RW of the standard rim, the ratio of the bead base width TBW to the standard rim width RW (TBW / RW x 100%), the width BW of the outer belt layer, the ratio of the width BW of the outer belt layer to the tread developed width TDW (BW / TDW x 100%), the minimum rubber thickness in the flexure region, and the ratio of the bead filler height Fh to the tire cross-sectional height SH (Fh / SH x 100%) were set as shown in Table 1 to produce tires of the conventional example, comparative example, and examples 1 to 12.

[0033] These test tires were evaluated for appearance, rim assembly properties, and steering stability on dry roads by the following test methods. The results are shown in Table 1.

[0034] Tire appearance: After each test tire was vulcanized and left to stand for one hour, the spacing between the bead portions was measured at four points on the tire circumference, and the average value was calculated. The evaluation results were expressed as an index, with the conventional example being set at 100. The larger the index value, the wider the spacing between the bead portions and the better the tire appearance.

[0035] Rim assembly performance: The work time required to assemble each test tire onto a standard rim was measured. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional example being set at 100. The higher the index value, the better the rim assembly performance.

[0036] Steering stability on dry roads: Each test tire was mounted on a wheel with a rim size of 18x7.5J, mounted on a front-wheel drive test vehicle with an engine displacement of 2500cc, and the air pressure was adjusted to 230kPa. A sensory evaluation was conducted by a test driver. The evaluation results were expressed as an index, with the conventional example being set at 100. The higher the index value, the better the steering stability on dry roads.

[0037]

[0038] As can be seen from Table 1, the pneumatic tires of Examples 1 to 12 were able to improve the tire appearance, rim assembly properties, and steering stability on dry roads compared to the conventional tire.

[0039] In the comparative example pneumatic tire, the ratio of the bead base width TBW to the developed tread width TDW was set lower than the value specified in the present invention, and therefore the appearance and rim assembly properties of the tire were deteriorated.

[0040] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer 9 inner liner layer 20 mold T tire

Claims

1. A pneumatic tire comprising a circumferentially extending annular tread portion, a pair of sidewall portions disposed on both sides of the tread portion, a pair of bead portions disposed radially inward of the sidewall portions, and multiple belt layers embedded in the tread portion, with an aspect ratio of 55% or greater but less than 75% and a tire cross-sectional height SH of 120 mm or greater, wherein the tread developed width TDW of the tread portion is 80% or greater of the nominal tire width, and the bead base width TBW of the bead portions is 107% or greater of the tread developed width TDW of the tread portion.

2. The pneumatic tire according to claim 1, characterized in that the contour line of the sidewall portion is composed of an upper arc and a lower arc, with the boundary at the maximum tire width position, and the radius of curvature SUR of the upper arc is in the range of 90% to 110% of the radius of curvature SLR of the lower arc.

3. A pneumatic tire according to claim 1 or 2, characterized in that the bead base width TBW is in the range of 120% or more and less than 130% of the rim width RW of a standard rim.

4. A pneumatic tire according to any one of claims 1 to 3, characterized in that the width of the belt layer located at the outermost position in the tire radial direction among the plurality of belt layers is in the range of 94% to 99% of the tread developed width TDW of the tread portion.

5. A pneumatic tire as described in any one of claims 1 to 4, characterized in that the minimum rubber thickness in the flexure region including the maximum tire width position of the sidewall portion is set in the range of 2.5 mm to 4.5 mm, and the height of the bead filler embedded in the bead portion is 25% or more of the tire cross-sectional height SH.

6. A method for manufacturing a pneumatic tire having a circumferentially extending annular tread portion, a pair of sidewall portions disposed on both sides of the tread portion, a pair of bead portions disposed radially inward of the sidewall portions, and multiple belt layers embedded in the tread portion, wherein the aspect ratio is between 55% and 75% and the tire cross-sectional height SH is set to 120 mm or greater, wherein a mold is used that is formed so that the tread developed width TDW of the tread portion is 80% or greater of the nominal tire width and the bead base width TBW of the bead portions is 107% or greater of the tread developed width TDW of the tread portion, and the pneumatic tire is vulcanized within this mold.

7. A method for manufacturing a pneumatic tire as described in claim 6, characterized in that the contour line of the sidewall portion is composed of an upper arc and a lower arc, with the maximum tire width position as the boundary, and the mold is formed so that the radius of curvature SUR of the upper arc is in the range of 90% to 110% of the radius of curvature SLR of the lower arc.

8. A method for manufacturing a pneumatic tire according to claim 6 or 7, characterized in that the mold is formed so that the bead base width TBW is in the range of 120% or more and less than 130% of the rim width RW of a standard rim.

9. A method for manufacturing a pneumatic tire according to any one of claims 6 to 8, characterized in that the mold is formed so that the width of the belt layer located at the outermost position in the tire radial direction among the plurality of belt layers is in the range of 94% to 99% of the tread developed width TDW of the tread portion.

10. A method for manufacturing a pneumatic tire as set forth in any one of claims 6 to 9, characterized in that the minimum rubber thickness in the flexure region of the sidewall portion, including the maximum tire width position, is set in the range of 2.5 mm to 4.5 mm, and the height of the bead filler embedded in the bead portion is 25% or more of the tire cross-sectional height SH.

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