JP2009269504A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of a flat spot without using an additional configuration. <P>SOLUTION: A carcass cord 61 in at least one layer of carcass includes: a high cord section 611S with relatively high carcass rigidity; and a low cord section 612S with relatively low carcass rigidity. Further, grooves 9 which continue along a tire peripheral direction and have different tire meridian cross-sectional shapes according to the carcass rigidity of each cord section are provided at a tire outer shell in a range of a sidewall section. That is, owing to the low cord section 612S and the grooves 9, the number of ends of the carcass cord 61 is reduced so as to obtain a flexible region. Thus, deformation of a tread section 2 and a shoulder section is suppressed, and generation of the flat spot is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire having flat spot resistance.

  The pneumatic tire includes a tread portion that forms a tread surface, shoulder portions on both sides of the tread portion, and a sidewall portion and a bead portion that are sequentially continuous from the shoulder portions. In addition, a carcass is bridged over each bead portion. The carcass is arranged in a toroidal shape in the tire circumferential direction to form a tire skeleton. A belt layer is disposed on the outer side in the tire radial direction of the carcass, and a belt reinforcing layer is disposed on the outer side in the tire radial direction of the belt layer.

  For example, such a pneumatic tire generates heat when a vehicle equipped with the pneumatic tire travels at a high speed. And when a vehicle stops in the state which generate | occur | produced heat | fever and a pneumatic tire has touched the road surface for a long time as it is, a flat spot may generate | occur | produce. That is, when the pneumatic tire is in contact with the road surface for a long time at a high temperature, the tread surface of the tread portion that contacts the road surface is deformed by the influence of a vertical load such as the weight of the vehicle. Thereafter, when the temperature of the pneumatic tire decreases, residual strain is generated while the rubber and organic fibers constituting the pneumatic tire remain deformed. A flat spot is a flat part formed by this residual strain. When a flat spot is generated, the vehicle starts running and the deformation is maintained for a while. Therefore, the toroid shape becomes uneven with respect to the circumferential direction of the pneumatic tire, and vibration is generated to deteriorate the riding comfort. In addition, the steering stability may be reduced.

  Conventionally, for example, a pneumatic tire described in Patent Document 1 has a reinforcing layer composed of a composite cord composed of low-rigidity fibers and high-rigidity fibers. The reinforcing layer is provided adjacent to the carcass so that the composite cord is parallel to the carcass cord. The composite cord of the reinforcing layer has a low elastic region extending from the origin to the inflection point and a high elastic region exceeding the inflection point in the stress-elongation curve, and the elongation at the inflection point is 0.5. It is set in the range of [%] to 5.0 [%]. In addition, the stiffness index of the low elasticity region in the composite cord with respect to the stiffness index of the carcass is set to 50 [%] or less, and the stiffness index of the high elasticity region is set to 100 [%] or more.

JP 2006-298162 A

  According to the conventional pneumatic tire described above, the reinforcing layer is disposed adjacent to the carcass so that the composite cord is parallel to the carcass cord, so that the stress acting on the carcass from the inside of the tire can be reliably ensured by the reinforcing layer. Receiving and ensuring sufficient tire rigidity. In addition, when the tire is at a low air pressure, the occurrence of a flat spot is surely suppressed by the rigidity of the high elastic range of the composite cord, while in the normal running state, the deterioration of the riding comfort is prevented by the rigidity of the low elastic area.

  As described above, in the conventional pneumatic tire, it is possible to prevent the deterioration of the riding comfort while suppressing the occurrence of the flat spot by the reinforcing layer including the element for increasing the rigidity and the element for decreasing the rigidity. However, in a conventional pneumatic tire, the weight of the pneumatic tire increases due to the addition of a configuration such as a reinforcing layer.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can suppress generation | occurrence | production of a flat spot, without using an additional structure.

  In order to achieve the above object, in the pneumatic tire according to the present invention, a bead filler is provided inside each end of the pair of annular bead portions, and the toroidal arrangement is provided in the tire circumferential direction. And at least one layer of carcass having a plurality of carcass cords arranged side by side in the tire circumferential direction along the tire meridian direction, and a belt layer having at least two belts arranged on the outer side in the tire radial direction of the carcass The carcass cord of at least one layer of the carcass includes at least two types of cord portions having different carcass rigidity per predetermined unit in the tire circumferential direction, and a tire outer shell in a range of a sidewall portion In the tire meridian cross section, the cord portions are arranged along the circumferential direction of the tire according to the carcass rigidity of each cord portion. Wherein the different grooves are provided.

  According to this pneumatic tire, the number of ends of the carcass cord is substantially reduced in the range of the sidewall portion by the cord portion and the groove portion having low carcass rigidity, and a region having flexibility can be obtained. Accordingly, the rigidity of the carcass is reduced in the range of the sidewall portion, and the amount of deflection in the range is increased, so that the stiffness in the tire radial direction is reduced, and bending deformation of the tread portion and the shoulder portion is suppressed. For this reason, deterioration of the rigidity in the tire width direction and the tire circumferential direction is suppressed, and the tire durability is improved. As a result, the vertical load such as the weight of the vehicle is absorbed in the range of the sidewall portion, and the deformation of the tread portion and the shoulder portion that are in contact with the road surface is suppressed, so that the occurrence of a flat spot can be suppressed. In addition, since the configuration of the carcass cord is changed, no additional configuration is used as before.

  In the pneumatic tire according to the present invention, when the carcass rigidity per unit of the cord part having the highest carcass rigidity is RA and the carcass rigidity per unit of the cord part having the lowest carcass rigidity is RB, The carcass rigidity RB is set in a range of 0.4 ≦ RB / RA ≦ 0.9 with respect to the rigidity RA.

  According to this pneumatic tire, when the ratio of the carcass rigidity RB to the carcass rigidity RA is less than 0.4, the difference in carcass rigidity between the cord portion having the highest carcass rigidity and the cord portion having the lowest carcass rigidity is large. The uniformity (UF: uniformity) of the pneumatic tire that causes the vibration of the steering wheel and the vehicle and the vehicle interior noise is deteriorated. On the other hand, when the ratio of the carcass rigidity RB to the carcass rigidity RA exceeds 0.9, the difference in the carcass rigidity between the cord portion having the highest carcass rigidity and the cord portion having the lowest carcass rigidity is small, and the rigidity of the carcass cannot be reduced. For this reason, it is preferable that the carcass rigidity RB is set in a range of 0.4 ≦ RB / RA ≦ 0.9 with respect to the carcass rigidity RA.

  In the pneumatic tire according to the present invention, the total number n of the cord portions is set in a range of 20 ≦ n ≦ 200.

  According to this pneumatic tire, when the total number n of the cord portions is less than 20, the strength is insufficient due to a local decrease in the rigidity of the carcass, and the tire durability is deteriorated. On the other hand, when the total number n of cord portions exceeds 200, the effect on deformation is small, and it is difficult to obtain the effect of suppressing deformation (flat spots) of the tread portion and the shoulder portion. For this reason, it is preferable that the total number n of code portions is set in a range of 20 ≦ n ≦ 200.

  In the pneumatic tire according to the present invention, the depth d of the groove is set in a range of 1 [mm] ≦ d ≦ 4 [mm].

  According to this pneumatic tire, when the depth d of the groove portion is less than 1 [mm], it is difficult to promote the deformation of the sidewall portion. On the other hand, when the depth d of the groove exceeds 4 [mm], the strength is insufficient due to a local decrease in the rigidity of the carcass, and the tire durability is deteriorated. For this reason, it is preferable that the depth d of the groove is set in a range of 1 [mm] ≦ d ≦ 4 [mm].

  Further, in the pneumatic tire according to the present invention, the groove portion has the belt layer tire width direction outermost end from the position of the normal line of the carcass passing through the tire radial direction outer end of the bead filler in the tire meridional section. The range in which the cord portion having the lowest carcass rigidity is located with respect to the cross-sectional area SA in the range where the cord portion having the highest carcass rigidity is provided, which is provided in the range up to the normal line of the carcass passing therethrough. The sectional area SB is set in a range of 1.01 ≦ SB / SA.

  According to this pneumatic tire, when the ratio of the cross-sectional area SB where the cord portion with the lowest carcass rigidity is located to the cross-sectional area SA where the cord portion with the highest carcass stiffness is located is less than 1.01, the groove portion Therefore, the difference in the carcass rigidity of each cord portion is small, and the rigidity of the carcass cannot be reduced. For this reason, it is preferable that the ratio of the cross-sectional area SB to the cross-sectional area SA is set in a range of 1.01 ≦ SB / SA.

  Further, in the pneumatic tire according to the present invention, the groove portion continues in the tire circumferential direction on a reference line parallel to the tire width direction while passing through the maximum width position of the carcass in the tire width direction when the specified internal pressure is filled. It is provided.

  According to this pneumatic tire, a region having flexibility can be obtained within the range in which the amount of deformation can be increased with the maximum width of the sidewall portion in the tire width direction. For this reason, it is possible to further suppress the occurrence of flat spots by further absorbing the vertical load such as the weight of the vehicle and further suppressing the deformation of the tread portion and the shoulder portion that are in contact with the road surface.

  Further, in the pneumatic tire according to the present invention, the tread surface of the tread portion includes a plurality of different curvatures including at least a central arc positioned at the center in the tire width direction and a shoulder side arc positioned at the outermost side in the tire width direction. It is formed by a circular arc of a radius, and is seen from a tire meridian cross-sectional view in a state where it is incorporated in a normal rim and filled with 5% of the normal internal pressure, from the outermost end in the tire width direction of the belt layer to the outer side in the tire radial direction. An intersection of an imaginary line parallel to the tire radial direction and the profile of the tread surface is a reference point, an intersection of the tire equator surface and the profile of the tread surface is a center crown, and the reference point and the center crown The angle between the line connecting the two and the line parallel to the tire width direction is θ, the radius of curvature of the central arc is R1, and the curvature of the shoulder arc is half R2 and L as the reference development width that is the arc length from the tire equator plane to the inner edge position of the shoulder-side arc in the tire width direction, and the tread deployment width that is the arc length of the tread surface in the tire width direction. In the case of TDW, the tread surface satisfies 1 [degree] <θ <3 [degree], 5 <R1 / R2 <10, and 0.4 <L / (TDW / 2) <0.7. It is formed.

  According to this pneumatic tire, the profile variable factors of the angle θ, the radius of curvature R1 of the central arc, the radius of curvature R2 of the shoulder side arc, and the reference development width L are appropriately set, so that the tire width direction of the tread surface is increased. Since the curvature of the profile along the line approaches a straight line, it is possible to optimize both the steering stability performance and the flat spot resistance performance.

  In the pneumatic tire according to the present invention, the flatness is 55 [%] or less.

  According to this pneumatic tire, when applied to tires having a relatively long flatness ratio of 55 [%] or less in the tire width direction, the effect of improving flat spot resistance is more remarkably exhibited.

  The pneumatic tire according to the present invention can suppress the occurrence of flat spots without using an additional configuration.

  Embodiments of a pneumatic tire according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  In the following description, the tire radial direction means a direction orthogonal to the rotational axis of the pneumatic tire, the tire radial inner side is the side toward the rotational axis in the tire radial direction, and the tire radial outer side is in the tire radial direction. The side away from the rotation axis. Further, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction is the side facing the tire equator plane in the tire width direction, and the outer side in the tire width direction is separated from the tire equator plane in the tire width direction. Say the side.

  The pneumatic tire described below is configured to be substantially symmetric with respect to the tire equatorial plane. The tire equator plane is a plane that is orthogonal to the rotational axis of the pneumatic tire and passes through the center of the tire width of the pneumatic tire. The tire width is the width in the tire width direction between the portions located outside in the tire width direction, that is, the distance between the portions farthest from the tire equatorial plane in the tire width direction. The tire equator line is a line on the tire equator surface along the circumferential direction of the pneumatic tire. Since the pneumatic tire described below is configured to be substantially symmetrical about the tire equatorial plane, the meridian when the pneumatic tire is cut on a plane passing through the rotation axis of the pneumatic tire is used. In the cross-sectional view, only one side centered on the tire equator plane is illustrated and only the one side is described, and description on the other side is omitted.

  FIG. 1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention, FIG. 2 is a schematic side view showing a carcass cord and a groove of a carcass in the pneumatic tire shown in FIG. 1, and FIGS. 1 is a schematic meridional sectional view showing a groove in the pneumatic tire shown in FIG. 1, FIG. 5 and FIG. 6 are schematic side views of a pneumatic tire according to another embodiment of the present invention, and FIG. 7 and FIG. FIG. 9 is a schematic sectional view showing the depth of the groove, and FIG. 10 shows the results of the performance test of the pneumatic tire according to the embodiment of the present invention. It is a chart.

  As shown in FIG. 1, the pneumatic tire 1 according to the present embodiment includes a tread portion 2, shoulder portions 3 on both sides of the tread portion 2, and sidewall portions 4 and bead portions 5 successively from the shoulder portions 3. Have. The pneumatic tire 1 includes a carcass 6, a belt layer 7, and a belt reinforcing layer 8.

  The tread portion 2 is exposed to the outside of the pneumatic tire 1, and the surface thereof is the contour of the pneumatic tire 1. A tread surface 21 is formed on the outer peripheral surface of the tread portion 2, that is, on the tread surface that contacts the road surface during traveling. The tread surface 21 includes a plurality of (four in the present embodiment) circumferential main grooves 22 that extend in the tire circumferential direction, and a plurality of land that is defined by the circumferential main grooves 22. The rib 23 which makes a part is provided.

  The shoulder portion 3 is a portion on both outer sides in the tire width direction of the tread portion 2. Further, the sidewall portion 4 is exposed at the outermost side in the tire width direction of the pneumatic tire 1. The bead unit 5 includes a bead core 51 and a bead filler 52. The bead core 51 is formed by winding a bead wire, which is a steel wire, in a ring shape. The bead filler 52 is disposed in a space formed by folding the end of the carcass 6 outward in the tire width direction at the position of the bead core 51.

  The carcass 6 is configured such that each tire width direction end portion is folded with respect to the pair of bead portions 5 and is wound around in a toroidal shape in the tire circumferential direction to constitute a tire skeleton. The carcass 6 is a carcass cord 61 (see FIG. 2) such as organic fiber (nylon, polyester, etc.) or steel covered with a rubber material. A plurality of carcass cords 61 are arranged in the tire circumferential direction while being along the tire meridian direction perpendicular to the tire equator line of the pneumatic tire 1. The carcass 6 shown in FIG. 1 is composed of one layer, but may have a multilayer structure in order to improve rigidity. That is, the carcass 6 in the present embodiment is provided with at least one layer according to the desired rigidity. Further, the carcass cord 61 is orthogonal to the tire equator line, but the angle with respect to the tire equator line (tire circumferential direction) is substantially 90 degrees, and is −5 with reference to 90 degrees with respect to the tire equator line. Includes angles in the range of [degrees] to +5 [degrees].

  The belt layer 7 has a multilayer structure in which at least two belts 71 and 72 are laminated, and is disposed outside the carcass 6 in the tire radial direction so as to cover the carcass 6 in the tire circumferential direction. The belts 71 and 72 are made of a cord made of organic fibers (nylon, polyester, etc.) or steel covered with a rubber material, and the cords have a predetermined angle with respect to the tire circumferential direction, that is, the tire equator line. Has been placed. The belts 71 and 72 are arranged with their cords inclined in opposite directions with respect to the tire equator line.

  The belt reinforcing layer 8 is disposed outside the belt layer 7 in the tire radial direction and covers the belt layer 7 in the tire circumferential direction. The belt reinforcing layer 8 is made of an organic fiber (nylon, polyester, etc.) or a steel cord covered with a rubber material, and the cord is substantially 0 degrees (tire) with respect to the tire circumferential direction, that is, the tire equator line. It arrange | positions so that the angle with respect to the circumferential direction may become an angle of 10 degrees or less.

  As shown in FIG. 2, the carcass cord 61 in the at least one layer of the carcass 6 has at least two types of cord portions 611S and 612S having different carcass rigidity per predetermined unit in the tire circumferential direction. I am doing.

  The cord portion 611S is a high cord portion that has a relatively high carcass rigidity. As shown in FIG. 2, the high cord portion 611 </ b> S of the carcass cords 61 that are configured to have the same rigidity in the carcass 6 has a close distance in the tire circumferential direction and a predetermined dimension in the tire circumferential direction. The number of carcass cords 61 (number of ends) is relatively large. On the other hand, the cord portion 612S is a low cord portion having a relatively low carcass rigidity. As shown in FIG. 2, the low cord portion 612 </ b> S of the carcass 6 configured to have the same rigidity in the carcass 6 has a sparse adjacent distance in the tire circumferential direction and a predetermined dimension in the tire circumferential direction. The number of carcass cords 61 (number of ends) is relatively small.

  The rigidity of one of the carcass cords 61 is defined by the force at the time of 2 [%] extension. In addition, although not shown in the figure, the high cord portion 611S and the low cord portion 612S can change the cord material such as aramid fiber, rayon fiber, polyester fiber, or the cord diameter in addition to the above-described number of ends. The carcass rigidity can be adjusted by changing the initial tension or changing the number of turns. As described above, when the carcass rigidity is adjusted by the cord material, the cord diameter, the bending, the initial tension, and the number of twists, the cord portions 611S and 612S can be configured by a single carcass cord 61.

  Further, a groove portion 9 is provided in the tire outer shell in the range of the sidewall portion 4. As shown in FIGS. 1 and 2, the groove portion 9 is within the range of the sidewall portion 4 and from the position of the normal line A (see FIG. 1) of the carcass 6 that passes through the tire radial direction outer end of the bead filler 52. In the tire circumferential direction of the tire outer shell in the range up to the position of the normal B (see FIG. 1) of the carcass 6 passing through the outermost end in the tire width direction of the belt layer 7 (the belt 71 having the maximum width in the tire width direction). Are continuously formed in a band shape.

  The groove portion 9 is formed with a different shape in the tire meridian section according to the carcass rigidity of each cord portion 611S, 612S. Specifically, the groove portion 9 has a cross-sectional shape that adjusts the rigidity of the sidewall portion 4 in a range where the high cord portion 611S having high carcass rigidity is arranged, or arranges the low cord portion 612S having low carcass rigidity. The rigidity of the sidewall portion 4 within the range is adjusted to be low or high. That is, when the carcass rigidity cannot be further increased by the high cord portion 611S, the groove portion 9 increases the rigidity of the sidewall portion 4 in the range in which the high cord portion 611S is disposed by the cross-sectional shape, or by the high cord portion 611S. When the carcass rigidity is too high, the rigidity of the sidewall portion 4 in the range where the high cord portion 611S is disposed is lowered due to the cross-sectional shape thereof. Further, when the carcass rigidity cannot be further reduced by the low cord portion 612S, the groove portion 9 lowers the rigidity of the sidewall portion 4 in the range where the low cord portion 612S is disposed due to its cross-sectional shape, or by the low cord portion 612S. When the carcass rigidity is too low, the rigidity of the sidewall portion 4 in the range where the low cord portion 612S is disposed is increased due to the cross-sectional shape thereof.

  The groove 9 shown in FIG. 2 has a uniform groove depth in the tire circumferential direction, and has a groove opening in the tire radial direction so that the rigidity of the sidewall portion 4 is relatively high according to the high cord portion 611S. Is narrowly formed (see FIG. 3), and the groove opening is formed wide in the tire radial direction so as to make the rigidity of the sidewall portion 4 relatively low in accordance with the low cord portion 612S (see FIG. 4). In addition, the groove part 9 shown in FIG. 2 is formed so that the groove opening may change gradually until it reaches the part corresponding to the high code part 611S and the low code part 612S.

  In addition, the groove 9 shown in FIG. 5 has a uniform groove depth in the tire circumferential direction, and in the tire radial direction so as to make the rigidity of the sidewall portion 4 relatively low according to the high cord portion 611S. The groove opening is formed wide (see FIG. 4), and the groove opening is formed narrow in the tire radial direction so as to make the rigidity of the sidewall portion 4 relatively high according to the low cord portion 612S (see FIG. 3). ). In addition, the groove part 9 shown in FIG. 5 is formed in the groove | channel opening in the tire radial direction in the site | part corresponding to the high cord part 611S and the low cord part 612S, respectively, and is formed in the high cord part 611S and the low cord part 612S. Between corresponding parts, the groove opening is formed so as to change abruptly.

  In addition, the groove portion 9 shown in FIG. 6 has a uniform groove opening in the tire circumferential direction, so that the rigidity of the sidewall portion 4 is relatively high according to the high cord portion 611S. The groove depth is formed shallowly (see FIG. 7), and the groove depth is formed deep in the tire radial direction so that the rigidity of the sidewall portion 4 is relatively lowered according to the low cord portion 612S (see FIG. 7). (See FIG. 8). Alternatively, the groove portion 9 shown in FIG. 6 is formed with a deep groove depth (see FIG. 8) so that the rigidity of the sidewall portion 4 is relatively low in accordance with the high cord portion 611S, and the low cord portion 612S Accordingly, the groove depth is shallow so that the rigidity of the sidewall portion 4 is relatively high (see FIG. 7).

  Thus, in the pneumatic tire 1 including the carcass 6 having the high cord portion 611S and the low cord portion 612S, the end number of the carcass cord 61 is substantially reduced in the range of the sidewall portion 4 due to the low cord portion 612S. A reduced and flexible area is obtained. As a result, the rigidity of the carcass 6 is reduced in the range of the sidewall portion 4 and the amount of deflection in the range is increased, so that the rigidity in the tire radial direction is reduced, and bending deformation of the tread portion 2 and the shoulder portion 3 is suppressed. Is done. For this reason, deterioration of the rigidity in the tire width direction and the tire circumferential direction is suppressed, and the tire durability is improved. As a result, the vertical load such as the weight of the vehicle is absorbed in the range of the sidewall portion 4, and the deformation of the tread portion 2 and the shoulder portion 3 that are in contact with the road surface is suppressed, so that the occurrence of a flat spot can be suppressed. . In addition, since the configuration of the carcass cord 61 is changed, no additional configuration is used as before. Further, the combination of the high cord portion 611S and the low cord portion 612S and the groove portion 9 facilitates or adjusts the deformation of the sidewall portion 4, and thus further suppresses or adjusts the bending deformation of the tread portion 2 and the shoulder portion 3, The occurrence of flat spots can be further suppressed.

  Further, in the pneumatic tire 1 according to the present embodiment, the carcass stiffness per unit of the high cord portion 611S having the highest carcass stiffness is RA, and the carcass stiffness per unit of the low cord portion 612S having the lowest carcass stiffness is RB. In this case, the carcass rigidity RB is set in a range of 0.4 ≦ RB / RA ≦ 0.9 with respect to the carcass rigidity RA. That is, the ratio of the carcass rigidity RB per unit of the low cord portion 612S to the carcass rigidity RA per unit of the high cord portion 611S is set in a range of 40 [%] to 90 [%].

  If the ratio of the carcass rigidity RB to the carcass rigidity RA is less than 40 [%], the difference in the carcass rigidity between the high cord portion 611S and the low cord portion 612S is large, causing the vibration of the steering wheel and the vehicle and the occurrence of the vehicle interior noise. The uniformity (UF: uniformity) of the pneumatic tire becomes worse. On the other hand, if the ratio of the carcass rigidity RB to the carcass rigidity RA exceeds 90 [%], the difference in carcass rigidity between the high cord portion 611S and the low cord portion 612S is small, and the rigidity of the carcass 6 cannot be reduced. For this reason, it is preferable that the ratio of the carcass rigidity RB to the carcass rigidity RA is set in a range of 40 [%] to 90 [%]. Further, when the ratio of the carcass rigidity RB to the carcass rigidity RA is set in the range of 50 [%] to 80 [%] (0.5 ≦ RB / RA ≦ 0.8), the uniformity is deteriorated. Since it can prevent and the rigidity of the carcass 6 can be reduced, it is more preferable.

  In the pneumatic tire 1 according to the present embodiment, the total number n of the high cord portion 611S and the low cord portion 612S is set in a range of 20 ≦ n ≦ 200.

  When the total number n of the cord portions 611S and 612S is less than 20, the strength is insufficient due to a local decrease in the rigidity of the carcass 6 and tire durability is deteriorated. On the other hand, when the total number n of the cord portions 611S and 612S exceeds 200, the effect on the deformation is small, and it is difficult to obtain the effect of suppressing the deformation (flat spot) of the tread portion 2 and the shoulder portion 3. For this reason, it is preferable that the total number n of the code portions 611S and 612S is set in a range of 20 ≦ n ≦ 200. In order to obtain an effect of suppressing deformation (flat spot) of the tread portion 2 and the shoulder portion 3, the maximum dimension Smax in the tire circumferential direction in each cord portion 611S, 612S is 10 [mm] ≦ Smax ≦ It is preferably set in the range of 100 [mm].

  In the pneumatic tire 1 according to the present embodiment, the depth d of the groove 9 is set in a range of 1 [mm] ≦ d ≦ 4 [mm]. As shown in FIG. 9, the depth d of the groove 9 is defined by a straight line connecting each inflection point Q that forms an opening of the groove 9 that deforms from the tire outer shell to the groove 9, and the bottom of the groove 9. It is defined as the distance from a certain maximum depression position.

  When the depth d of the groove 9 is less than 1 [mm], it is difficult to promote the deformation of the sidewall 4. On the other hand, when the depth d of the groove 9 exceeds 4 [mm], the strength is insufficient due to a local decrease in the rigidity of the carcass 6 and tire durability deteriorates. For this reason, it is preferable that the depth d of the groove 9 is set in a range of 1 [mm] ≦ d ≦ 4 [mm].

  Further, in the pneumatic tire 1 according to the present embodiment, the groove portion 9 is the tire of the belt layer 7 from the position of the normal line A of the carcass 6 that passes through the tire radial outer end of the bead filler 52 in the tire meridional section. It is provided in a range up to the position of the normal B of the carcass 6 passing through the outermost end in the width direction. Further, in this range, the cross-sectional area SB where the low cord portion 612S with the lowest carcass rigidity is located is 1.01 ≦ SB / SA with respect to the cross-sectional area SA where the high cord portion 611S with the highest carcass rigidity is located. Is set to That is, the ratio of the cross-sectional area SB where the low cord portion 612S with the lowest carcass rigidity 612S to the cross-sectional area SA where the high cord portion 611S with the highest carcass rigidity is located is set in a range of 1 [%] or more. Yes.

  If the ratio of the cross-sectional area SB where the low cord portion 612S with the lowest carcass rigidity is located to less than 1% with respect to the cross-sectional area SA where the high cord portion 611S with the highest carcass rigidity is located, the depth of the groove 9 Since the groove opening is not sufficient, the difference in the carcass rigidity between the high cord portion 611S and the low cord portion 612S is small, and the rigidity of the carcass 6 cannot be reduced. For this reason, it is preferable that the ratio of the cross-sectional area SB to the cross-sectional area SA is set in a range of 1 [%] or more (1.01 ≦ SB / SA).

  Further, in the pneumatic tire 1 according to the present embodiment, as shown in FIG. 1, the groove portion 9 is parallel to the tire width direction while passing through the maximum width position in the tire width direction of the carcass 6 when the specified internal pressure is filled. On the reference line J, it is provided continuously in the tire circumferential direction. According to such a configuration, a region having flexibility can be obtained within a range in which the deformation amount can be increased with the maximum width of the sidewall portion 4 in the tire width direction. For this reason, it is possible to further suppress the occurrence of flat spots by further absorbing the vertical load such as the weight of the vehicle and further suppressing the deformation of the tread portion 2 and the shoulder portion 3 that contact the road surface.

  Further, in the pneumatic tire 1 according to the present embodiment, as shown in FIG. 1, the tread surface 21 of the tread portion 2 is at least a central arc 21a located at the center in the tire width direction and the outermost side in the tire width direction. Are formed by a plurality of arcs having different radii of curvature, including the shoulder-side arc 21b located at the same position. And it is formed as follows in the cross-sectional view in the tire meridian direction in a state where it is incorporated in the normal rim and filled with 5% of the normal internal pressure. The regular rim here refers to an “applied rim” defined in JATMA, a “Design Rim” defined in TRA, or a “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The normal load means “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO.

  First, an imaginary line C that is virtually parallel to the tire radial direction is set from the outermost end in the tire width direction of the first belt 71 of the belt layer 7 to the outer side in the tire radial direction. An intersection of the virtual line C and the profile (contour) of the tread surface 21 is defined as a reference point D, and a line connecting the reference point D and the center crown CL is defined as a shoulder fall line E. The shoulder fall line E is parallel to the tire width direction and has a tire cross-section height Ht ((outer diameter in the tire radial direction−rim diameter) / 2), and the inner circumference in the tire radial direction of the bead portion 5. An angle formed by a parallel line F that is a side end (that is, the height in the tire radial direction from the center crown CL that is the intersection of the tire equator surface S and the tread surface 21) from the side end portion (that is, the position of the rim base 53) To do. The angle θ is an acute angle formed by the shoulder fall line E and the parallel line F. Further, the radius of curvature of the central arc 21a is R1, the radius of curvature of the shoulder-side arc 21b is R1, and the tire width direction inner end position G of the shoulder-side arc 21b from the tire equatorial plane S (the central arc 21a and the shoulder arc). The reference developed width which is the arc length up to the position where the side arc 21b continues) is L, and the tread developed width which is the arc length of the tread surface 21 in the tire width direction is TDW.

  The angle θ corresponds to the amount of sagging of the shoulder portion 3 continuous with both ends of the tread portion 2 with respect to the center crown CL. The tread development width TDW is defined as TDW = (L1 + L2) where L1 is the arc length in the tire width direction of the central arc 21a with the radius of curvature R1 and L2 is the arc length in the tire width direction of the shoulder side arc 21b with the radius of curvature R2. ) × 2. In the present embodiment, since the arcs having different radii of curvature are not set between the central arc 21a and the shoulder-side arc 21b on the tread surface 21, the tire width in the central arc 21a having the curvature radius R1 is set. The arc length L1 in the direction corresponds to the reference development width L. In the case where an arc having a different radius of curvature is set between the central arc 21a and the shoulder-side arc 21b on the tread surface 21, the reference development width L is the tire width direction of the shoulder-side arc 21b from the tire equatorial plane S. This is the sum of the arc lengths of arcs between the inner end position G. In other words, L = TDW / 2−L2.

  When each part of the pneumatic tire 1 is defined as described above, the tread surface 21 is set such that the angle θ is in the range of 1 [degree] <θ <3 [degree], and the curvature radius R1 and the curvature radius R2 The relationship is obtained by the following equation (1), and F1 (tread surface curvature radius ratio) obtained by the equation (1) is set in a range of 5 <F1 <10. Further, the relationship between the reference development width L and the tread development width TDW is obtained by the following equation (2), and F2 (expansion width ratio) obtained by this equation (2) is 0.4 <F2 <0.7. It is formed so as to be set within the range.

Formula (1) ... F1 = Rc / Rs
Formula (2) ... F2 = L / (TDW / 2)

  According to this configuration, the profile of the angle θ, the radius of curvature R1 of the central arc 21a, the radius of curvature R2 of the shoulder-side arc 21b, and the reference development width L (in other words, the arc length L1, the arc length L2, and the tread development width TDW). By setting the variable factors as described above, the curvature of the profile along the tire width direction of the tread surface 21 approaches a straight line, and therefore, optimization for compatibility between steering stability performance and flat spot resistance performance should be performed. Can do.

  That is, by setting the angle θ in the range of 1 [degree] <θ <3 [degree], the angle θ is smaller than 3 [degree]. The angle change in the vicinity of the shoulder portion 3 over 4 is reduced. That is, it is possible to reduce the amount of depression with respect to the center crown CL in the shoulder portion 3 continuous to both end portions of the tread portion 2, and to make the curvature of the tread surface 21 close to flat. On the other hand, since the angle θ is larger than 1 [degree], it is possible to prevent the appropriate shape as the pneumatic tire 1 from collapsing due to the angle θ being too small. Further, F1 obtained by the relational expression (1) between the curvature radius R1 and the curvature radius R2 is set in a range of 5 <F1 = Rc / Rs <10, and the reference development width L and the tread development width TDW are By setting F2 obtained by the relational expression (2) in a range of 0.4 <F2 = L / (TDW / 2) <0.7, the profile of the tread surface 21 is brought closer to a flatter shape, The contact pressure on the tread surface 21 can be made uniform. Thereby, the local deformation | transformation in the tread surface 21, the shoulder part 3, and the bead part 5, especially the belt reinforcement layer 8 arrange | positioned inside the tire radial direction of the tread part 2 in which the tread surface 21 was formed in the surface, and load , The local deformation of the bead filler 52, which has a great influence on the flat spot resistance, is suppressed. Thereby, the residual distortion at the time of thermal cooling of the pneumatic tire 1 can be reduced, and generation | occurrence | production of a flat spot can be suppressed.

  In addition, the pneumatic tire 1 according to the present embodiment is applied to a tire with a relatively long flatness ratio of 55 [%] or less in particular in the tire width direction, so that the flat spot resistance is more remarkably improved. There is an effect. The flatness ratio is a ratio of the tire height Ht to the tire width W, as shown in FIG.

  In the present embodiment, performance tests on side cut resistance, tire durability, uniformity (UF), and flat spot resistance were performed on a plurality of types of pneumatic tires having different conditions (see FIG. 10).

  In this performance test, a pneumatic tire having a tire size of 225 / 45ZR17 was assembled to a regular rim specified by JATMA, filled with the highest air pressure specified by JATMA, and the maximum load specified by JATMA was applied.

  In the performance test of side-cut resistance, the evaluation method is 10 km / h against a steel test curb with a height of 110 mm, which is mounted on a passenger car having a displacement of 2000 cc with a test tire pressure of 200 kPa and a radius of 1 mm. The vehicle was entered with an approach angle of 30 degrees per hour and climbed, and this was increased by 2.5 km / h until air leaks or the tires were destroyed. Based on this result, index evaluation with Comparative Example 1 as a reference (100) is performed. This evaluation is more preferable as the numerical value is larger. In the tire durability performance test, after completion of the JATMA high-speed durability test at a drum diameter of 1707 mm, the test was continued every 30 minutes until the tire broke down at 10 km / h. Based on this result, index evaluation with Comparative Example 1 as a reference (100) is performed. This evaluation is more preferable as the numerical value is larger. Moreover, in the performance test of uniformity, RFV value was measured according to JISD4233. The air pressure at this time is 230 kPa, and the tire load is 5 kPa. Based on this result, index evaluation with Comparative Example 1 as a reference (100) is performed. This evaluation is more preferable as the numerical value is larger. In the performance test of flat spot resistance, the uniformity was measured in the same manner as described above, and after a preliminary run at 150 km / h for 30 minutes, the drum was stopped for 1 hour with a load applied. Thereafter, the tire uniformity is measured again, and the difference ΔRFV before and after the preliminary running of the radial force variation is used as an evaluation index. The smaller this difference ΔRFV, the better the flat spot resistance. Based on this result, index evaluation with Comparative Example 1 as a reference (100) is performed. This evaluation is more preferable as the numerical value is larger.

  The pneumatic tire of the comparative example does not have a high cord portion and a low cord portion, the groove portion depth, the shoulder portion sagging amount θ, the tread surface curvature radius ratio (R1 / R2), and the deployment width ratio (L / (TDW / 2)) is optimized. On the other hand, the pneumatic tires of Examples 1 to 7 have a high cord portion and a low cord portion, a carcass rigidity ratio (RB / RA) of the low cord portion to the high cord portion, and the tire circumference of the cord portion. Maximum dimension in direction, total number of cords, depth of groove, cross-sectional area ratio of low cord to high cord (SB / SA), whether groove includes maximum carcass width position J, shoulder sagging amount θ, tread The surface curvature radius ratio (R1 / R2) and the development width ratio (L / (TDW / 2)) are optimized.

  As shown in the test results of FIG. 10, in the pneumatic tires of Examples 1 to 7, durability and uniformity are maintained within an allowable range, respectively, and excellent in side cut resistance and flat spot resistance. I understand that.

1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a schematic side view showing a carcass cord and a groove of a carcass in the pneumatic tire shown in FIG. 1. FIG. 2 is a schematic meridional sectional view showing a groove in the pneumatic tire shown in FIG. 1. FIG. 2 is a schematic meridional sectional view showing a groove in the pneumatic tire shown in FIG. 1. It is a schematic side view of a pneumatic tire according to another embodiment of the present invention. It is a schematic side view of a pneumatic tire according to another embodiment of the present invention. FIG. 7 is a schematic meridional sectional view showing a groove in the pneumatic tire shown in FIG. 6. FIG. 7 is a schematic meridional sectional view showing a groove in the pneumatic tire shown in FIG. 6. It is a schematic sectional drawing showing the depth of a groove part. It is a graph which shows the result of the performance test of the pneumatic tire concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 21 Tread surface 21a Central part arc 21b Shoulder side arc 22 Circumferential main groove 23 Rib 3 Shoulder part 4 Side wall part 5 Bead part 51 Bead core 52 Bead filler 53 Rim base 6 Carcass 61 Carcass cord 611S High cord Part 612S Low cord part 7 Belt layer 71, 72 Belt 8 Belt reinforcing layer 9 Groove part RA High cord part carcass rigidity RB Low cord part carcass rigidity SA High cord part sectional area SB Low cord part sectional area Smax Maximum carcass dimension J Carcass maximum width position CL Center crown F1 Tread surface curvature radius ratio F2 Deployment width ratio L Standard deployment width L1 Arc length of arc at the center portion L2 Arc length of shoulder side arc n Total number of high cord portion and low cord portion Q Inflection Point R1 center circle Curvature radius R2 of curvature radius S tire equatorial plane TDW tread width W tire width θ shoulder drop angle of the shoulder-side arc of

Claims (8)

A pair of annular bead portions are provided with a bead filler on the inner side where each end is folded back, arranged in a toroidal shape in the tire circumferential direction, and juxtaposed in the tire circumferential direction along the tire meridian direction. In a pneumatic tire provided with at least one carcass having a plurality of carcass cords and a belt layer having at least two belts arranged on the outer side in the tire radial direction of the carcass,
The carcass cord of at least one layer of the carcass includes at least two types of cord portions having different carcass rigidity per predetermined unit in the tire circumferential direction, and the tire outer shell in the range of the sidewall portion extends along the tire circumferential direction. The pneumatic tire is characterized in that a groove portion having a different shape in the tire meridional section is provided according to the carcass rigidity of each cord portion while being connected to each other. RA is the carcass rigidity per unit of the cord portion having the highest carcass rigidity,
When the carcass rigidity per unit of the cord portion having the lowest carcass rigidity is RB,
2. The pneumatic tire according to claim 1, wherein the carcass rigidity RB is set in a range of 0.4 ≦ RB / RA ≦ 0.9 with respect to the carcass rigidity RA.   3. The pneumatic tire according to claim 1, wherein the total number n of the cord portions is set in a range of 20 ≦ n ≦ 200.   The depth d of the said groove part is set to the range of 1 [mm] <= d <= 4 [mm], The pneumatic tire as described in any one of Claims 1-3 characterized by the above-mentioned. In the tire meridional section, the groove portion extends from the position of the carcass normal passing through the outer end in the tire radial direction of the bead filler to the position of the carcass normal passing through the outermost end in the belt layer tire width direction. In the range,
The cross-sectional area SB in the range where the cord portion having the lowest carcass rigidity is in a range where 1.01 ≦ SB / SA is compared to the cross-sectional area SA in the range where the cord portion having the highest carcass rigidity is located. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is set to.   The groove portion is provided continuously in the tire circumferential direction on a reference line parallel to the tire width direction while passing the maximum width position of the carcass in the tire width direction when the specified internal pressure is filled. The pneumatic tire according to any one of 1 to 5. The tread surface of the tread portion is formed by an arc having a plurality of different radii of curvature including at least a central arc located at the center in the tire width direction and a shoulder side arc located at the outermost side in the tire width direction.
In the meridional section of the tire with 5% of the normal internal pressure filled in the normal rim,
An imaginary line imaginary parallel to the tire radial direction from the outermost end in the tire width direction of the belt layer to the outer side in the tire radial direction, and an intersection of the profile of the tread surface as a reference point,
The intersection of the tire equator and the profile of the tread is the center crown,
An angle formed by a line connecting the reference point and the center crown and a line parallel to the tire width direction is θ,
The radius of curvature of the central arc is R1,
The radius of curvature of the shoulder side arc is R2,
The reference developed width that is the arc length from the tire equatorial plane to the inner end position in the tire width direction of the shoulder side arc is L,
When the tread development width, which is the arc length of the tread surface in the tire width direction, is TDW,
The tread surface is formed to satisfy 1 [degree] <θ <3 [degree], 5 <R1 / R2 <10, and 0.4 <L / (TDW / 2) <0.7. The pneumatic tire according to any one of claims 1 to 6.   The flatness is 55 [%] or less, The pneumatic tire according to any one of claims 1 to 7 characterized by things.

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