JP2013063738A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wear resistance and steering stability of a center area.SOLUTION: The pnuematic tire includes a steel-reinforced layer 9 which is provided between a belt layer 7 and a carcass layer 6, and in which steel cords oriented at substantially 90 degrees relative to a tire circumference direction are arranged side by side in the tire circumference direction. The steel-reinforced layer 9 is formed within a range of 5-25% of an effective belt width of the belt layer from a tire equatorial plane CL, and in a total width of 10-50% of the effective belt width. When an intersection point between respective extended lines of a shoulder side arc 21b and a side part arc 21d is defined as a reference point P, an angle θ between a straight line A connecting the reference point and a center crown CC and a straight line B in the tire width direction passing through the center crown with respect to a tire profile β satisfies a relation of 0.025×β+1.0≤θ≤0.045×β+2.5. A curvature radius Rc of a center part arc 21a and a curvature radius Rs of the shoulder side arc satisfy a relation of 12≤Rc/Rs≤30. A reference developed width L from the tire equatorial plane CL to an inner side end part in the tire width direction of the shoulder side arc and a tread developed width TDW satisfy a relation of 0.2≤L/(TDW/2)≤0.7.

Description

  The present invention relates to a pneumatic tire, and in particular, when the use air pressure is increased in order to reduce rolling resistance for the purpose of reducing fuel consumption, wear of the center region due to an increase in contact pressure accompanying an increase in diameter growth of the center region and The present invention relates to a pneumatic tire with improved steering stability deterioration.

  Conventionally, a pneumatic tire is known in which the curvature of a profile along a tire width direction of a tread surface is made close to a straight line (see, for example, Patent Document 1). In this pneumatic tire, the tread surface is formed of an arc having a plurality of different radii of curvature including at least a central arc positioned at the center in the tire width direction and a shoulder-side arc positioned at the outermost position in the tire width direction. In a pneumatic tire, it is incorporated in a normal rim and filled with 5% of the normal internal pressure, and the cross-sectional view in the tire meridian direction from the outermost position in the tire width direction of the belt layer to the outer side in the tire radial direction The intersection of the imaginary line parallel to the tire radial direction and the profile of the tread surface is the reference point, the intersection of the tire equator surface and the tread surface profile is the center crown, and the line connecting the reference point and the center crown Is the angle formed by the line parallel to the tire width direction, θ, the radius of curvature of the central arc is Rc, the radius of curvature of the shoulder side arc is Rs, and from the tire equatorial plane When the reference developed width that is the arc length to the inner end position in the tire width direction of the shoulder side arc is L and the tread deployed width that is the arc length of the tread surface in the tire width direction is TDW, the tread surface is 1 [°] <θ <4.5 [°], 5 <Rc / Rs <10, and 0.4 <L / (TDW / 2) <0.7.

JP 2008-307948 A

  In recent years, in order to reduce the fuel consumption of a vehicle equipped with a pneumatic tire, in order to reduce the rolling resistance of the pneumatic tire, it has been studied to increase the working air pressure. However, when the air pressure used is increased, the diameter growth of the center region, which is the center in the tire width direction, is increased, and if the contact pressure of the center region is increased accordingly, the center region of the tread surface is easily worn. In addition, the amount of deflection is reduced by increasing the air pressure used, and accordingly, the contact length is shortened and the steering stability is likely to deteriorate.

  In the pneumatic tire described in Patent Document 1 described above, the wear of the center region of the tread surface tends to be improved by bringing the curvature of the profile along the tire width direction of the tread surface close to a straight line. However, when the pneumatic tire described in Patent Document 1 is at a high pressure, it is difficult to sufficiently suppress the uneven wear of the pneumatic tire, and it is difficult to improve the steering stability.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can improve the abrasion resistance of the center area | region of a tread surface, and can improve steering stability.

  In order to solve the above-described problems and achieve the object, a pneumatic tire according to the present invention includes a carcass layer and a belt layer disposed on the outer side in the tire radial direction of the carcass layer. A steel reinforcing layer in which steel cords of substantially 90 degrees with respect to the tire circumferential direction are juxtaposed in the tire circumferential direction is further provided between the innermost belt in the tire radial direction and the carcass layer, and the steel reinforcement The layers are provided in the range of 5% to 25% of the effective belt width of the belt layer on both sides in the tire width direction from the tire equatorial plane, and the total width is 10% of the effective belt width. It is a pneumatic tire formed in the range of 50% or less, and the tread surface of the tread portion has a central arc located at the center in the tire width direction and the outer side in the tire width direction of the central arc. Is formed with a plurality of arcs with different curvature radii including at least a shoulder-side arc, and is embedded in a normal rim and filled with 5% of the normal internal pressure, in a cross-sectional view in the tire meridian direction, The intersection of the virtual extension line of the shoulder side arc and the virtual extension line of the outermost side arc of the tire width direction in the tread portion is used as a reference point, and the intersection point of the tire equator plane and the profile of the tread surface is the center. An angle formed by a straight line connecting the reference point and the center crown and a straight line passing through the center crown and parallel to the tire width direction is defined as θ, and a radius of curvature of the central arc is defined as Rc. Rs is the radius of curvature of the shoulder-side arc, and the reference development is the arc length from the tire equatorial plane to the inner edge position of the shoulder-side arc in the tire width direction. Is defined as L, and the tread developed width which is the arc length in the tire width direction between the points passing through the reference point and parallel to the tire equator plane intersects the tread surface is TDW, and the flatness is β The tread surface is 0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5, 12 ≦ Rc / Rs ≦ 30, and 0.2 ≦ L / (TDW / 2) ≦ 0. .7 and is formed.

  If the steel reinforcement layer is formed on both sides of the tire equator from the tire equatorial plane to the effective belt width of 25% of the belt layer and the total width exceeds 50% of the effective belt width, Since the compression rigidity of the tread surface becomes too high and the self-aligning torque is reduced, it is not possible to improve the handling stability. In addition, if a steel reinforcing layer is formed on both sides of the tire equatorial plane from the tire equatorial plane, with the total belt width being less than 5% of the effective belt width and the total width being less than 10% of the effective belt width, It is not possible to keep it suitable, and the improvement of the handling stability cannot be expected. In this regard, according to the pneumatic tire of the present invention, by arranging the steel reinforcing layer within a specified range, the compression deformation rigidity of the tread portion can be improved and the ground contact state can be suitably maintained, and the steering stability can be improved. Can be improved. Moreover, according to this pneumatic tire, the angle θ formed by the straight line connecting the reference point and the center crown and the straight line passing through the center crown and parallel to the tire width direction is 0.025 × β + 1.0 ≦ θ. By setting it as the range of ≦ 0.045 × β + 2.5, the amount of sagging inward in the tire radial direction from the central arc to the shoulder side arc becomes smaller. Further, the relation between the radius of curvature Rc of the central arc and the radius of curvature Rs of the shoulder side arc is 12 ≦ Rc / Rs ≦ 30, and the central portion from the tire equatorial plane to the inner edge position in the tire width direction of the shoulder side arc By setting the relation between the reference developed width L, which is the arc length of the arc, and the tread developed width TDW to 0.2 ≦ L / (TDW / 2) ≦ 0.7, the tread extends from the central arc to the shoulder side arc. The arc of the surface is closer to the straight line. For this reason, since the radial growth of the central arc is suppressed, the wear of the shoulder region and the wear of the center region of the tread surface can be improved. More specifically, the wear of the center region can be improved while suppressing the deterioration of the wear of the shoulder region.

  Further, in the pneumatic tire of the present invention, the curvature radius SHR of the shoulder portion arc in which one end portion is in contact with the shoulder side arc and the other end portion is in contact with the outermost side arc in the tire width direction of the tread portion is set. 32 ≦ SHR ≦ 40.

  By setting the curvature radius SHR to 32 or more, shoulder wear can be more suitably suppressed, and by setting it to 40 or less, center wear can be preferably suppressed.

In the pneumatic tire of the present invention, the steel reinforcing layer has a product of one cross-sectional area of the steel cord and the number of driven portions per 50 [mm] of 1.0 [mm ² ] or more and 8.0 [ mm ² ] or less and the strength is 3200 [MPa].

If the product of the cross-sectional area of one steel cord and the number of driven wires per 50 [mm] is less than 1.0 [mm ² ], the compression rigidity of the steel reinforcing layer tends to be difficult to ensure, and the degree of increase in cornering power Decreases. On the other hand, when the product of the cross-sectional area of one steel cord and the number of driven wires per 50 [mm] exceeds 8.0 [mm ² ], the compression rigidity of the steel reinforcing layer tends to be too high, and the cornering power increases. As the degree decreases, the tire mass increases and the steering stability improvement effect decreases. In this regard, according to the pneumatic tire of the present invention, the product of one cross-sectional area of the steel cord and the number of driven portions per 50 [mm] is 1.0 [mm ² ] or more and 8.0 [mm ² ] or less. In addition, by setting the strength to 3200 [MPa], the compression rigidity of the steel reinforcing layer is ensured and the cornering power is increased, so that the effect of improving the steering stability can be remarkably obtained.

  In the pneumatic tire of the present invention, the steel reinforcing layer is characterized in that the number of driven steel cords per 50 [mm] is 10 or more and 50 or less.

  When the number of driven steel cords per 50 [mm] is less than 10, the compression rigidity of the steel reinforcing layer tends to be difficult to ensure, and the cornering power increases. On the other hand, when the number of driven steel cords per 50 [mm] exceeds 50, the compression rigidity of the steel reinforcing layer tends to be too high, the cornering power is increased, the tire mass is increased, and the steering stability is increased. The effect of improving the property is reduced. In this regard, according to the pneumatic tire of the present invention, by setting the number of steel cords driven per 50 [mm] to 10 or more and 50 or less, the compression rigidity of the steel reinforcing layer is ensured and the cornering power is increased. In addition, since it is easy to follow the unevenness of the road surface, the effect of improving the steering stability can be obtained remarkably.

  In the pneumatic tire of the present invention, the steel cord of the steel reinforcing layer is a non-twisted monofilament having a diameter of 0.20 [mm] or more and 0.45 [mm] or less.

  The steel reinforcing layer improves the compression deformation rigidity of the tread portion, but it is preferable to employ a monofilament in order not to increase the tire mass.

  In the pneumatic tire according to the present invention, the steel reinforcing layer is divided, and an end portion on the inner side in the tire width direction is at a position of 2 [%] or more and 8 [%] or less of the effective belt width from the tire equator plane. It is provided.

  When the steel reinforcing layer is divided, in order to ensure compression rigidity, it is preferable that the inner end portion in the tire width direction is not greatly separated from the tire equatorial plane. It is preferable that the end portion is provided at a position of 2% to 8% of the effective belt width from the tire equator plane.

  In the pneumatic tire of the present invention, the steel reinforcement layer is formed continuously in the tire width direction.

  In order to ensure the compression rigidity of the steel reinforcing layer, it is preferable that the steel reinforcing layer is not separated at the position of the tire equatorial plane, and therefore, it is preferable that the steel reinforcing layer is continuously formed in the tire width direction.

  In the pneumatic tire of the present invention, the carcass cord forming the carcass layer is an organic fiber.

  Since the compression rigidity is ensured by the steel reinforcing layer, when the carcass cord of the carcass layer is a metal cord, the compression rigidity is too high. For this reason, it is preferable that the carcass cord forming the carcass layer is an organic fiber in order to appropriately secure the compression rigidity.

  The pneumatic tire of the present invention is characterized by being applied to a pneumatic tire for passenger cars having a high internal pressure.

  In order to reduce the fuel consumption of passenger vehicles equipped with pneumatic tires, it is effective to increase the operating air pressure in order to reduce the rolling resistance of pneumatic tires. In order to increase the input, the diameter growth in the center region, which is the center in the tire width direction, increases, and if the contact pressure in the center region increases accordingly, the center region of the tread surface is easily worn, and the air pressure used is high. As a result, the amount of deflection is reduced, and as a result, the contact length is shortened, and the steering stability is likely to deteriorate. According to this pneumatic tire, in such a pneumatic tire for passenger cars with a high internal pressure, the effects of improving the wear resistance of the center region of the tread surface and improving the steering stability can be obtained.

  The pneumatic tire according to the present invention can improve the wear resistance of the center region of the tread surface and improve the handling stability.

FIG. 1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a partially cut meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 3A is a schematic diagram illustrating the presence and arrangement of a steel reinforcing layer. FIG. 3-2 is a schematic diagram illustrating the presence and arrangement of a steel reinforcing layer. FIG. 3-3 is a schematic diagram showing the presence and arrangement of a steel reinforcing layer. FIG. 3-4 is a schematic diagram showing the presence and arrangement of a steel reinforcing layer. FIG. 3-5 is a schematic view showing the presence and arrangement of a steel reinforcing layer. FIG. 4-1 is a diagram illustrating cornering power at the time of normal internal pressure in the form of the steel reinforcing layer of FIGS. 3-1 to 3-5. FIG. 4-2 is a diagram showing cornering power at the time of high internal pressure in the form of the steel reinforcing layer of FIGS. 3-1, 3-4, and 3-5. FIG. 5-1 is a diagram showing a self-aligning torque at the time of normal internal pressure in the form of the steel reinforcing layer of FIGS. 3-1 to 3-5. FIG. 5-2 is a diagram showing a self-aligning torque at the time of high internal pressure in the form of the steel reinforcing layer of FIGS. 3-1, 3-4, and 3-5. FIG. 6-1 is a chart showing results of performance tests of pneumatic tires according to examples of the present invention. FIG. 6-2 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 6-3 is a table showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 6-4 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 6-5 is a table showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 6-6 is a table showing the results of the performance test of the pneumatic tire according to the example of the present invention.

  Embodiments of 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.

  FIG. 1 is a meridional sectional view of a pneumatic tire according to the present embodiment, and FIG. 2 is a partially cut meridional sectional view of the pneumatic tire according to the present embodiment. In the following description, the tire radial direction refers to a direction orthogonal to the rotational axis (not shown) of the pneumatic tire, and the tire radial inner side refers to the side toward the rotational axis in the tire radial direction, the tire radial outer side, and Means the side away from the rotation axis in the tire radial direction. 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 means the side toward the tire equator plane (tire equator line) CL in the tire width direction, and the outer side in the tire width direction means the tire width direction. Is the side away from the tire equatorial plane CL. The tire equatorial plane CL 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 SW 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 CL in the tire width direction. The tire equator line is a line along the tire circumferential direction of the pneumatic tire on the tire equator plane CL. In the present embodiment, the same sign “CL” as that of the tire equator plane is attached to the tire equator line.

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

  The tread portion 2 is made of a rubber material (tread rubber), and is exposed at the outermost side in the tire radial direction of the pneumatic tire, and the surface thereof is the contour of the pneumatic tire. 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 is provided with a plurality of (four in this embodiment) main grooves 22 that are straight main grooves extending along the tire circumferential direction and parallel to the tire equator line CL. The tread surface 21 extends along the tire circumferential direction by the plurality of main grooves 22, and a plurality of rib-like land portions 23 parallel to the tire equator line CL are formed. Although not shown in the figure, the tread surface 21 is provided with a lug groove that intersects the main groove 22 in each land portion 23. The land portion 23 is divided into a plurality of portions in the tire circumferential direction by lug grooves. Further, the lug groove is formed to open to the outer side in the tire width direction on the outermost side in the tire width direction of the tread portion 2. Note that the lug groove may have either a form communicating with the main groove 22 or a form not communicating with the main groove 22.

  The shoulder portion 3 is a portion on both outer sides in the tire width direction of the tread portion 2. The sidewall portion 4 is exposed at the outermost side in the tire width direction of the pneumatic tire. 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 a rubber material disposed in a space formed by folding the end portion in the tire width direction of the carcass layer 6 at the position of the bead core 51.

  The carcass layer 6 is configured such that each tire width direction end portion is folded back from the tire width direction inner side to the tire width direction outer side by a pair of bead cores 51 and is wound around in a toroidal shape in the tire circumferential direction. It is. This carcass layer 6 has a 90 ° (± 5 °) angle with respect to the tire circumferential direction, and a plurality of carcass cords (not shown) arranged in the tire circumferential direction along the tire meridian direction and covered with a coat rubber. It is. The carcass cord is made of organic fibers (polyester, rayon, nylon, etc.). The carcass layer 6 is provided as at least one layer.

  The belt layer 7 has a multilayer structure in which at least two belts 71 and 72 are laminated, and is disposed on the outer side in the tire radial direction which is the outer periphery of the carcass layer 6 in the tread portion 2 and covers the carcass layer 6 in the tire circumferential direction. It is. The belts 71 and 72 are made by coating a plurality of cords (not shown) arranged in parallel at a predetermined angle (for example, 20 degrees to 30 degrees) with a coat rubber with respect to the tire circumferential direction. The cord is made of steel or organic fiber (polyester, rayon, nylon, etc.). Further, the overlapping belts 71 and 72 are arranged so that the cords intersect each other.

  The belt reinforcing layer 8 is disposed on the outer side in the tire radial direction which is the outer periphery of the belt layer 7 and covers the belt layer 7 in the tire circumferential direction. The belt reinforcing layer 8 has reinforcing layers 81 and 82 arranged in at least two layers so as to cover the outer periphery of the belt layer 7. The reinforcing layers 81 and 82 are made by coating a plurality of cords (not shown) arranged in parallel in the tire width direction (± 5 degrees) in the tire circumferential direction with a coat rubber. The cord is made of steel or organic fiber (polyester, rayon, nylon, etc.). The belt reinforcing layer 8 shown in FIG. 1 is disposed so that the reinforcing layer 81 and the reinforcing layer 82 cover only the end portion of the belt layer 7 in the tire width direction. The configuration of the belt reinforcing layer 8 is not limited to the above, and is not clearly shown in the drawing, but the reinforcing layers 81 and 82 are both formed larger in the tire width direction than the belt layer 7 and are arranged so as to cover the entire belt layer 7. The reinforcing layer 81 on the belt layer 7 side is formed to be larger in the tire width direction than the belt layer 7 so as to cover the entire belt layer 7, and the reinforcing layer 82 on the outer side in the tire radial direction of the reinforcing layer 81. May be disposed only at the end portion of the reinforcing layer 81 in the tire width direction so as to cover the end portion of the belt layer 7 in the tire width direction. That is, the belt reinforcing layer 8 overlaps at least the end portion in the tire width direction of the belt layer 7. Further, the belt reinforcing layer 8 may be configured by any one of the reinforcing layers 81 and 82. The belt reinforcing layer 8 (reinforcing layers 81 and 82) is provided by winding a strip-like strip material (for example, a width of 10 [mm]) in the tire circumferential direction.

  The pneumatic tire includes a steel reinforcing layer 9. The steel reinforcing layer 9 is disposed between the innermost belt 71 in the tire radial direction of the belt layer 7 and the carcass layer 6. The steel reinforcing layer 9 has a steel cord (not shown) arranged in parallel in the tire circumferential direction at an angle of 90 degrees (including an error of ± 5 degrees) with respect to the tire circumferential direction, and is coated with a coat rubber. Yes. The steel cord (metal cord) of the steel reinforcing layer 9 is made of, for example, steel or carbon steel. The steel reinforcing layer 9 is provided on both sides in the tire width direction from the tire equatorial plane CL so that the tire width direction dimension W2 is in the range of 5% to 25% of the effective belt width W of the belt layer 7, and The total width, which is the tire width direction dimension W1, is formed in the range of 10% to 50% of the effective belt width W. Specifically, as shown in FIG. 1, the steel reinforcing layer 9 is continuously provided in the tire width direction, and is disposed on the tire equatorial plane CL that is the center position in the tire width direction of the pneumatic tire. The total width of the tire width direction dimension W2 is provided in the range of 5% to 25% of the effective belt width W of the belt layer 7 from the surface CL to both sides in the tire width direction, and is the tire width direction dimension W1. Is formed in the range of 10 [%] to 50 [%] of the effective belt width W. Further, although not shown in the drawing, the steel reinforcing layer 9 is divided into two in the tire width direction with the tire equatorial plane CL as a boundary, and the tire width direction dimension W2 is on each side of the tire width direction from the tire equatorial plane CL. The layer 7 is provided in the range of 5% to 25% of the effective belt width W, and the total width is in the range of 10% to 50% of the effective belt width W. Also good. The effective belt width W of the belt layer 7 indicates the tire width direction dimension of the belt (the belt 72 in the present embodiment) having the shortest tire width direction dimension in the belt layer 7.

  In the pneumatic tire of the present embodiment, the profile of the tread surface 21 that is the surface of the tread portion 2 is formed by a plurality of arcs having different curvature radii that are convex outward in the tire radial direction. Specifically, as shown in FIG. 2, the tread surface 21 includes a central arc 21a, a shoulder-side arc 21b, a shoulder arc 21c, and a side arc 21d.

  The central arc 21a is located in the center of the tread surface 21 in the tire width direction, includes the tire equator plane CL, and is formed on both sides in the tire width direction with the tire equator plane CL as the center. The central arc 21a is formed with the largest diameter in the tire radial direction of the portion including the tire equatorial plane CL. The shoulder-side arc 21b is formed continuously outside the central arc 21a in the tire width direction. The shoulder arc 21c is formed continuously outside the shoulder arc 21b in the tire width direction. The side portion arc 21d is formed continuously outside the shoulder portion arc 21c in the tire width direction and is located on the outermost side in the tire width direction of the tread portion 2.

  A hypothetical extension of the shoulder-side arc 21b in a cross-sectional view in the tire meridian direction shown in FIG. 1 in a no-load state in which a pneumatic tire is incorporated in a normal rim and filled with 5% of the normal internal pressure. And the intersection of the imaginary extension line of the side portion arc 21d is defined as a reference point P. The intersection of the tire equatorial plane CL and the profile of the tread surface 21 is a center crown CC, a straight line A connecting the reference point P and the center crown CC, and a straight line passing through the center crown CC and parallel to the tire width direction. The angle formed by B is θ. Further, the radius of curvature of the central arc 21a is Rc. The radius of curvature of the shoulder-side arc 21b is Rs. Further, let L be a reference developed width that is the arc length from the tire equatorial plane CL to the inner end position in the tire width direction of the shoulder-side arc 21b. Further, a tread developed width which is an arc length in the tire width direction between points where a reference line passing through the reference point P and parallel to the tire equatorial plane CL intersects the tread surface 21 is defined as TDW. Also, let the flatness be β.

In this case, the tread surface 21 of the pneumatic tire of the present embodiment is formed so as to satisfy the following formulas (1) to (3).
0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5 (1)
12 ≦ Rc / Rs ≦ 30 (2)
0.2 ≦ L / (TDW / 2) ≦ 0.7 (3)

  Here, the regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. The normal internal pressure is “maximum air pressure” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The flatness is the ratio of the cross-sectional height to the cross-sectional width of the tire. The cross-sectional width is a width excluding patterns and characters on the side surface of the tire in a no-load state in which the tire is assembled on a regular rim and filled with a regular internal pressure. The cross-sectional height is ½ of the difference between the outer diameter and the rim diameter of the unloaded tire in which the tire is assembled on the normal rim and filled with the normal internal pressure.

  Thus, in the pneumatic tire according to the present embodiment, a steel cord of substantially 90 degrees with respect to the tire circumferential direction is provided between the carcass layer 6 and the innermost belt 71 in the tire radial direction of the belt layer 7. A steel reinforcing layer 9 is provided in parallel in the tire circumferential direction. The steel reinforcing layer 9 is provided in the range of 5% to 25% of the effective belt width of the belt layer 7 on both sides in the tire width direction from the tire equatorial plane CL, and the total width is the effective belt width. 10 [%] to 50 [%]. Further, when the intersection point of each extension line of the shoulder side arc 21b and the side portion arc 21d is defined as the reference point P, the straight line A connecting the reference point and the center crown CC with respect to the flatness β passes through the center crown CC. The angle θ with the straight line B in the tire width direction is 0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5, and the curvature radius Rc of the central arc 21a and the curvature radius Rs of the shoulder-side arc 21b are 12 ≦ Rc / Rs ≦ 30, and the reference deployment width L and the tread deployment width TDW from the tire equatorial plane CL to the inner end of the shoulder-side arc 21b in the tire width direction are 0.2 ≦ L / (TDW / 2). ≦ 0.7.

  When the steel reinforcing layer 9 is formed on the both sides in the tire width direction from the tire equatorial plane CL to exceed 25 [%] of the effective belt width W of the belt layer 7 and the total width exceeds 50 [%] of the effective belt width W. In addition, the compression rigidity of the tread surface 21 at the time of ground deformation becomes too high, and the self-aligning torque is reduced, so that it is not possible to improve the steering stability. Further, the steel reinforcing layer 9 is formed on both sides in the tire width direction from the tire equatorial plane CL so that the belt width 7 is less than 5% of the effective belt width W and the total width is less than 10% of the effective belt width W. As a result, the grounding state cannot be suitably maintained, and the improvement in handling stability cannot be expected. In this regard, according to the pneumatic tire of the present embodiment, since the steel reinforcing layer 9 is disposed within a specified range, the compression deformation rigidity of the tread portion 2 can be improved and the ground contact state can be suitably maintained. It becomes possible to improve the handling stability.

  Here, the effect | action of the steel reinforcement layer 9 is demonstrated concretely. FIGS. 3-1 to 3-5 are schematic views showing the presence and arrangement of a steel reinforcing layer, and FIG. 4-1 is a diagram showing the steel reinforcing layer in FIGS. 3-1 to 3-5 at normal internal pressure. FIG. 4B is a diagram showing the cornering power at (for example, 230 [kPa]), and FIG. 4B is a diagram at the time of high internal pressure in the form of the steel reinforcing layer in FIGS. Is the cornering power at 230 [kPa], and the configuration of FIGS. 3-4 and 3-5 is 300 [kPa]), FIG. 5-1 is the steel of FIGS. It is a figure which shows the self-aligning torque at the time of normal internal pressure (for example, 230 [kPa]) in the form of a reinforcement layer, FIG. 5-2 is high in the form of the steel reinforcement layer of FIGS. 3-1 and FIGS. 3-4. At internal pressure (for example, the configuration in FIG. 3-1 is 230 kPa, FIG. Form of beauty Figure 3-5 is a diagram showing a self-aligning torque at 300 [kPa]).

  3 to 3-5, the carcass layer 6 is not shown, but the belt layer 7 (belts 71 and 72) and the belt reinforcing layer 8 (one reinforcing layer) are shown. And FIG. 3-1 is a form which does not have the steel reinforcement layer 9. FIG. 3-2 has the steel reinforcing layer 9, but the tire width direction dimension is 90 [%] of the effective belt width W of the belt layer 7. FIG. FIG. 3C has the steel reinforcing layer 9 and the total width in the tire width direction is 45 [%] of the effective belt width W of the belt layer 7, but is divided on both sides in the tire width direction. In this embodiment, the belt is provided in the range of 90% of the effective belt width W of the belt layer 7 on both sides in the tire width direction from the equator plane CL. 3-4 includes the steel reinforcing layer 9, the tire width direction dimension is 45% of the effective belt width W of the belt layer 7, and continuously in the tire width direction at the center position in the tire width direction. By being arranged, it is provided in the range of 22.5 [%] of the effective belt width W of the belt layer 7 on both sides in the tire width direction from the tire equatorial plane CL. 3-5 has the steel reinforcing layer 9, the tire width direction dimension is 45 [%] of the effective belt width W of the belt layer 7, and is divided into both sides in the tire width direction, and the tire equatorial plane CL is used as the tire. Provided on both sides in the width direction within a range of 50 [%] of the effective belt width W of the belt layer 7 and the inner end in the tire width direction is at a position of 5 [%] of the effective belt width W from the tire equatorial plane CL It is the form provided. Further, in FIGS. 4-1 and 5-1, the form of FIG. 3-1 is a thick broken line, the form of FIG. 3-2 is a dashed line, the form of FIG. 3-3 is a thin solid line, and the form of FIG. The thick solid line and the form of FIG. 3-5 are shown by a thin broken line, and in FIGS. 4-2 and 5-2, the form of FIG. 3-1 is shown by a thick broken line, and the form of FIG.

  As shown in FIG. 4-1, at normal internal pressure, the cornering power is relatively high at a low load (1 [kN] to 3 [kN]) and the cornering power at a high load (3 [kN] or more). Is not too high in order to improve steering stability. In this regard, the forms shown in FIGS. 3-1, 3-4, and 3-5 do not have excessive cornering power at high loads. On the other hand, the form shown in FIG. 3-3 has a relatively high cornering power at a high load (3 [kN] or more), and the form shown in FIG. 3-2 has a too high cornering power at a high load.

  Further, as shown in FIG. 4B, at high internal pressure, it is preferable that the cornering power does not decrease at low load in order to improve the steering stability. In this respect, the form shown in FIG. 3-4 does not show a decrease in cornering power as the form shown in FIG. 3-1. In the configuration shown in FIG. 3-4, the cornering power does not decrease even at a high load.

  Further, as shown in FIG. 5A, at the normal internal pressure, it is preferable that the self-aligning torque is relatively high in order to improve the steering stability. In this regard, the forms shown in FIGS. 3-4 and 3-5 have a relatively high self-aligning torque. On the other hand, the forms shown in FIGS. 3-1 and 3-3 have a relatively low self-aligning torque, and the form shown in FIG. 3-2 has a significantly low self-aligning torque.

  Further, as shown in FIG. 5B, at the time of high pressure, the form shown in FIG. 3-4 does not show a decrease in self-aligning torque as the form shown in FIG.

  Moreover, according to the pneumatic tire of the present embodiment, the angle θ formed by the straight line A connecting the reference point P and the center crown CC and the straight line B passing through the center crown CC and parallel to the tire width direction is By setting the range of 0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5, the amount of sagging inward in the tire radial direction from the central arc 21a to the shoulder arc 21b becomes smaller. Further, the relationship between the radius of curvature Rc of the central arc 21a and the radius of curvature Rs of the shoulder-side arc 21b is 12 ≦ Rc / Rs ≦ 30, and the position in the tire width direction inner end of the shoulder-side arc 21b from the tire equatorial plane CL is set. The relationship between the reference developed width L that is the arc length of the central arc 21a and the tread developed width TDW is 0.2 ≦ L / (TDW / 2) ≦ 0.7. The shoulder side arc 21b is reached and the arc of the tread surface 21 is closer to a straight line. For this reason, since the radial growth of the central arc 21a is suppressed, it is possible to improve the wear of the shoulder region GS of the tread surface 21 and the wear of the center region GC of the tread surface 21. More specifically, it is possible to improve the wear of the center region GC while suppressing the deterioration of the wear of the shoulder region GS.

  Here, the center region GC of the tread surface 21 is a range from the tire equator surface CL to the outer side in the tire width direction to a position of 45 [%] of TDW / 2 in the ground contact region G of the tread surface 21. Further, the shoulder region GS of the tread surface 21 is within the range from the tire equator surface CL to the position 90% of TDW / 2 on the outer side in the tire width direction in the ground contact region G, and in the tire width direction of the center region GC. The range is from the outer edge to the outer side in the tire width direction. The ground contact area G refers to the tire width direction in which the tread surface 21 contacts the road surface when a pneumatic tire is assembled on a normal rim, filled with a normal internal pressure and 70% of the normal load is applied. This is a region in the tire circumferential direction. The normal load is “maximum load capacity” defined by JATMA, a maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO.

  When the angle θ is less than “0.025 × β + 1.0”, the amount of sagging from the central arc 21a to the shoulder-side arc 21b is too small, and wear of the shoulder region GS (shoulder wear) is likely to occur. On the other hand, when the angle θ exceeds “0.045 × β + 2.5”, the amount of sagging from the central arc 21a to the shoulder-side arc 21b is large, and wear of the center region GC of the tread surface 21 (center wear) is improved. It becomes difficult. In addition, since the amount of sagging from the central arc 21a to the shoulder-side arc 21b is optimized by setting the angle θ to a range of 0.03 × β + 1.2 ≦ θ ≦ 0.04 × β + 2.3, the shoulder An effect of improving center wear without causing wear, that is, while suppressing deterioration of wear of the shoulder region GS of the tread surface 21 (or improving deterioration of wear of the shoulder region GS of the tread surface 21). It is possible to obtain significantly.

  Further, when Rc / Rs is less than 12, the diameter growth of the central arc 21a cannot be sufficiently suppressed, and the contact pressure of the center region GC is increased to improve the wear (center wear) of the center region GC of the tread surface 21. Difficult to do. On the other hand, when Rc / Rs exceeds 30, the effect of suppressing the radial growth of the central arc 21a cannot be sufficiently obtained, and the effect of improving the wear (center wear) of the center region GC of the tread surface 21 cannot be expected. In addition, by setting it as the range of 15 <= Rc / Rs <= 25, diameter growth of the center part circular arc 21a is fully suppressed, and the deterioration of wear of the shoulder region GS of the tread surface 21 is suppressed (or the tread surface 21). It is possible to remarkably obtain the effect of improving the wear (center wear) of the center region GC of the tread surface 21 (while improving the deterioration of the wear of the shoulder region GS).

  Further, even when L / (TDW / 2) is less than 0.2, the diameter growth of the central arc 21a cannot be sufficiently suppressed, and the contact pressure of the center region GC increases and the center region GC of the tread surface 21 increases. It becomes difficult to improve wear (center wear). On the other hand, even when L / (TDW / 2) exceeds 0.7, the effect of suppressing the radial growth of the central arc 21a cannot be sufficiently obtained, and the wear (center wear) of the center region GC of the tread surface 21 is improved. The effect to do is not expected. In addition, by setting it as the range of 0.4 <= L / (TDW / 2) <= 0.5, the diameter growth of the center part circular arc 21a is fully suppressed, and the deterioration of wear of the shoulder region GS of the tread surface 21 is suppressed. However, it is possible to significantly obtain the effect of improving the wear (center wear) of the center region GC of the tread surface 21 while improving the deterioration of the wear of the shoulder region GS of the tread surface 21.

  As a result, according to the pneumatic tire of the present embodiment, the steering stability is improved, the wear resistance (center wear resistance) of the center region GC of the tread surface 21 is improved, and the shoulder region GS is improved. It is possible to improve the wear resistance (shoulder wear resistance). Or while improving steering stability, suppressing the fall of the abrasion resistance (shoulder abrasion resistance) of shoulder region GS, the abrasion resistance (center abrasion resistance) of center region GC of tread surface 21 is improved. It is possible.

  In the pneumatic tire according to the present embodiment, one end is in contact with the shoulder-side arc 21b (arc having a radius of curvature Rs), and the other end is the outermost side portion of the tread portion 2 in the tire width direction. It is preferable that the curvature radius SHR of the shoulder portion arc 21c in contact with the arc 21d (arc having an curvature radius of SCR) satisfies 32 ≦ SHR ≦ 40.

  By setting the curvature radius SHR to 32 or more, shoulder wear can be more suitably suppressed, and by setting it to 40 or less, center wear can be preferably suppressed. The curvature radius SHR is more preferably 35 ≦ SHR ≦ 37. By setting the curvature radius SHR to 35 ≦ SHR ≦ 37, the above effect can be further improved. When the pneumatic tire is applied to a pneumatic tire for passenger cars with a high internal pressure, a particularly preferable effect is obtained by setting the curvature radius SHR to a range of 32 ≦ SHR ≦ 40 (preferably 35 ≦ SHR ≦ 37). It is possible.

In the pneumatic tire of the present embodiment, the steel reinforcing layer 9 has a product of one cross-sectional area of the steel cord and the number of driven portions per 50 [mm] of 1.0 [mm ² ] or more and 8.0. [Mm ² ] or less and the strength is preferably 3200 [MPa].

When the product of the cross-sectional area of one steel cord and the number of driven wires per 50 [mm] is less than 1.0 [mm ² ], the compression rigidity of the steel reinforcing layer 9 tends to be difficult to ensure, and the cornering power increases. The degree decreases. On the other hand, when the product of the cross-sectional area of one steel cord and the number of driven wires per 50 [mm] exceeds 8.0 [mm ² ], the compression rigidity of the steel reinforcing layer 9 tends to be too high, and the cornering power As the degree of increase decreases, the tire mass increases and the steering stability improvement effect decreases. In this regard, according to the pneumatic tire of the present embodiment, the product of the cross-sectional area of one steel cord and the number of driven portions per 50 [mm] is 1.0 [mm ² ] or more and 8.0 [mm ² ]. ], And by setting the strength to 3200 [MPa], the compression rigidity of the steel reinforcing layer 9 is ensured and the cornering power is increased, so that the effect of improving the steering stability can be remarkably obtained. . In addition, the steel reinforcing layer 9 is obtained by setting the product of the cross-sectional area of one steel cord and the number of driven wires per 50 [mm] within a range of 1.5 [mm ² ] to 5.0 [mm ² ]. The compression rigidity is appropriately secured, the cornering power is further increased, and the effect of improving the steering stability can be obtained more remarkably.

  In the pneumatic tire of the present embodiment, it is preferable that the steel reinforcing layer 9 has 10 or more and 50 or less driven steel cords per 50 [mm].

  When the number of driven steel cords per 50 [mm] is less than 10, the compression rigidity of the steel reinforcing layer 9 tends to be difficult to ensure, and the degree of increase in cornering power decreases. On the other hand, when the number of driven steel cords per 50 [mm] exceeds 50, the compression rigidity of the steel reinforcing layer 9 tends to be too high, the degree of increase in cornering power is reduced, the tire mass is increased, and the steering is increased. The stability improvement effect is reduced. In this regard, according to the pneumatic tire of the present embodiment, the number of driven steel cords per 50 [mm] is set to 10 or more and 50 or less, so that the compression rigidity of the steel reinforcing layer 9 is secured and the cornering is performed. As the power increases, it is easy to follow the unevenness of the road surface, so that it is possible to obtain a significant improvement in steering stability. By setting the number of steel cords driven per 50 [mm] to 15 or more and 35 or less, the compression rigidity of the steel reinforcing layer 9 is appropriately secured, the cornering power is further increased, and the unevenness of the road surface is followed. As a result, it is possible to more significantly obtain the effect of improving the steering stability.

  In the pneumatic tire of the present embodiment, the steel cord of the steel reinforcing layer 9 is preferably a non-twisted monofilament having a diameter of 0.20 [mm] or more and 0.45 [mm] or less.

  The steel reinforcing layer 9 improves the compression deformation rigidity of the tread portion 2, but it is preferable to employ a monofilament in order not to increase the tire mass. And in order to improve the compression deformation rigidity of the tread part 2 in a monofilament, it is desirable that it is 0.20 [mm] or more and 0.45 [mm] or less in diameter.

  Further, in the pneumatic tire of the present embodiment, the steel reinforcing layer 9 is divided, and the end on the inner side in the tire width direction is 2 [%] or more and 8 [%] or less of the effective belt width W from the tire equatorial plane CL. It may be provided in the position.

  When the steel reinforcing layer 9 is divided, it is preferable that the inner end in the tire width direction is not greatly separated from the tire equatorial plane CL in order to ensure compression rigidity. It is preferable that the end portion on the inner side in the direction is provided at a position from 2 [%] to 8 [%] of the effective belt width W from the tire equatorial plane CL.

  Moreover, in the pneumatic tire of the present embodiment, the steel reinforcing layer 9 is preferably formed continuously in the tire width direction.

  In order to ensure the compression rigidity of the steel reinforcing layer 9, it is preferable that the steel reinforcing layer 9 is not separated at the position of the tire equatorial plane CL, and therefore, it is preferable that the steel reinforcing layer 9 is continuously formed in the tire width direction.

  In the pneumatic tire of the present embodiment, the carcass cord forming the carcass layer 6 is preferably an organic fiber.

  Since the compression rigidity is ensured by the steel reinforcing layer 9, when the carcass cord of the carcass layer 6 is a metal cord, the compression rigidity is too high. For this reason, it is preferable that the carcass cord forming the carcass layer 6 is an organic fiber in order to appropriately secure the compression rigidity.

  Moreover, it is preferable that the pneumatic tire of this Embodiment is applied to the pneumatic tire for passenger cars with a high internal pressure. Here, the high internal pressure indicates an internal pressure in a range of 280 [kPa] to 350 [kPa].

  In order to reduce the fuel consumption of passenger vehicles equipped with pneumatic tires, it is effective to increase the operating air pressure in order to reduce the rolling resistance of pneumatic tires. In order to increase the input, the diameter growth of the center region GC, which is the center in the tire width direction, increases, and when the contact pressure of the center region GC increases, the center region GC of the tread surface 21 is easily worn, By increasing the working air pressure, the amount of deflection is reduced, and as a result, the ground contact length is shortened and steering stability is likely to deteriorate. According to this pneumatic tire, in such a pneumatic tire for passenger cars having a high internal pressure, it is possible to significantly improve the wear resistance of the center region GC of the tread surface 21 and improve the steering stability. It becomes possible.

  In this example, performance tests on tire performance (steering stability, center wear, wear life) were performed on a plurality of types of pneumatic tires having different conditions (see FIGS. 6-1 to 6-6).

  In this performance test, a pneumatic tire having a tire size of 195 / 65R15 was assembled to a rim of a 15 × 6 JJ aluminum wheel and filled with air pressure (230 [kPa] or 300 [kPa]) applied to each example. (1500 [cc] front drive passenger car).

  The steering stability evaluation method is the average of 10-step sensory evaluations by five test drivers regarding the steering performance at the time of lane change and cornering and the stability at the time of straight running on the dry test road with the above test vehicle. Do by value. Based on this sensory evaluation, index evaluation is performed with the conventional pneumatic tire as a reference (100). This index evaluation shows that the larger the value, the better the steering stability.

  In the center abrasion evaluation method, the remaining groove amount (groove depth) at the maximum groove depth position in the center region when the test vehicle travels 10,000 km on the dry test road and the maximum in the shoulder region. The ratio of the groove depth position to the remaining groove amount (groove depth) is measured. Then, based on the measurement result, index evaluation using the conventional example as a reference (100) is performed. This index evaluation indicates that the larger the value, the better the center wear resistance performance.

  In the wear life evaluation method, the remaining groove amount (groove depth) at the maximum groove depth position in the tread portion when the test vehicle travels 10,000 [km] on the dry test road is measured. Then, based on the measurement result, index evaluation using the conventional example as a reference (100) is performed. This index evaluation indicates that the larger the value, the better the wear life.

  In FIG. 6A, the pneumatic tire of the conventional example is the pneumatic tire described in Patent Document 1 (Japanese Patent Application No. 2008-307948), does not have a steel reinforcing layer, and has an internal pressure of 230 [kPa]. It was. In the pneumatic tires of Comparative Example 1 and Comparative Example 2, the profile of the tread surface is within a specified range, but the steel reinforcing layer is not specified. Further, the pneumatic tires of Comparative Examples 3 to 5 have the prescribed steel reinforcing layer, but θ in the profile of the tread surface was out of the prescribed range. On the other hand, the pneumatic tires of Examples 1 to 4 had a prescribed steel reinforcing layer, had a tread surface profile in a prescribed range, and varied θ. The pneumatic tire of this performance test has an aspect ratio of 65, and the specified range of θ is 2.625 to 5.425, preferably 3.15 to 4.9.

  In FIG. 6-2, the pneumatic tires of Comparative Examples 6 to 8 have a prescribed steel reinforcing layer, but Rc / Rs in the profile of the tread surface was out of the prescribed range. On the other hand, the pneumatic tires of Examples 5 to 8 had a prescribed steel reinforcing layer, had a tread surface profile within a prescribed range, and varied Rc / Rs.

  6-3, the pneumatic tires of Comparative Examples 9 to 11 have the specified steel reinforcing layer, but L / (TDW / 2) in the profile of the tread surface is out of the specified range. It was. On the other hand, the pneumatic tires of Example 9 to Example 12 had a prescribed steel reinforcing layer, had a tread surface profile within a prescribed range, and varied L / (TDW / 2).

  6-4, the pneumatic tires of Example 13 to Example 18 had a prescribed steel reinforcing layer, had a tread surface profile in a prescribed range, and varied SHR.

  6-5, the pneumatic tires of Examples 19 to 22 have a prescribed steel reinforcing layer and a profile of the tread surface within a prescribed range, and the cross-sectional area and driving of the steel cord in the steel reinforcing layer. The product with the number was changed.

  6-6, the pneumatic tires of Example 23 to Example 26 have a prescribed steel reinforcing layer and the profile of the tread surface is in a prescribed range, and the steel cord 50 [mm] in the steel reinforcing layer. The number of hits per shot was changed.

  6-6, the pneumatic tire of Example 27 has a prescribed steel reinforcing layer, has a tread surface profile in a prescribed range, and a steel cord structure in the steel reinforcing layer is a prescribed monofilament. .

  6-6, the pneumatic tires of Example 28 and Example 29 had a prescribed steel reinforcing layer, had a tread surface profile in a prescribed range, and the steel reinforcing layer had a divided structure.

  6-6, the pneumatic tire of Comparative Example 12 is the pneumatic tire described in Patent Document 1 (Japanese Patent Application No. 2008-307948), does not have a steel reinforcing layer, and has an internal pressure of 300. [KPa]. On the other hand, the pneumatic tire of Example 30 had a prescribed steel reinforcing layer, had a tread surface profile in a prescribed range, and had an internal pressure of 300 [kPa].

  As shown in the test results of FIGS. 6-1 to 6-6, it can be seen that the pneumatic tires of Examples 1 to 30 have improved steering stability, center wear performance, and wear life.

2 Tread portion 21 Tread surface 21a Center portion arc 21b Shoulder side arc 21c Shoulder portion arc 21d Side portion arc 6 Carcass layer 7 Belt layer 9 Steel reinforcing layer A Straight line connecting the reference point and the center crown B Tire passing through the center crown Straight line parallel to the width direction CC Center crown CL Tire equator plane (tire equator line)
G Grounding area GC Center area GS Shoulder area L Reference development width P Reference point Rc Center radius of curvature Rs Shoulder side arc curvature radius SHR Shoulder arc radius of curvature SW Tire width TDW Tread development width W Effective belt width β Flat Rate θ angle

Claims (9)

A carcass layer and a belt layer disposed on the outer side in the tire radial direction of the carcass layer, and between the belt innermost in the tire radial direction of the belt layer and the carcass layer with respect to the tire circumferential direction. The steel reinforcing layer is further provided with steel cords of substantially 90 degrees arranged in the tire circumferential direction, and the steel reinforcing layer has an effective belt width of 5 from the tire equatorial plane on both sides in the tire width direction. A pneumatic tire provided in a range of [%] to 25 [%] and having a total width of 10 [%] to 50 [%] of the effective belt width,
Further, 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 continuous to the outer side in the tire width direction of the central arc. In the state where the normal internal pressure is 5% and the internal pressure is filled, the virtual extension line of the shoulder-side arc and the outermost side in the tire width direction in the tread portion in a sectional view in the tire meridian direction A point of intersection with a virtual extension line of the side arc of the tire as a reference point, a point of intersection of the tire equator plane and the profile of the tread surface as a center crown, a straight line connecting the reference point and the center crown, and the center The angle formed by a straight line passing through the crown and parallel to the tire width direction is θ, the radius of curvature of the central arc is Rc, and the curvature of the shoulder-side arc is Let Rs be the diameter, and let L be the reference development width that is the arc length from the tire equator plane to the inner end position in the tire width direction of the shoulder side arc, and the reference that passes through the reference point and is parallel to the tire equator plane When the tread development width, which is the arc length in the tire width direction between the points where the line intersects the tread surface, is TDW and the flatness is β,
The tread surface is
0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5
12 ≦ Rc / Rs ≦ 30
0.2 ≦ L / (TDW / 2) ≦ 0.7
A pneumatic tire characterized by being formed to satisfy the above.   A curvature radius SHR of a shoulder arc in which one end portion is in contact with the shoulder-side arc and the other end portion is in contact with the outermost side arc in the tire width direction of the tread portion is formed so as to satisfy 32 ≦ SHR ≦ 40 The pneumatic tire according to claim 1, wherein the pneumatic tire is provided. The steel reinforcing layer has a product of one cross-sectional area of the steel cord and the number of driven wires per 50 [mm] of 1.0 [mm ² ] or more and 8.0 [mm ² ] or less, and has a strength. The pneumatic tire according to claim 1, wherein the pneumatic tire is 3200 [MPa].   The pneumatic tire according to any one of claims 1 to 3, wherein the steel reinforcing layer has a number of driven steel cords per 50 [mm] of 10 or more and 50 or less.   The steel cord of the steel reinforcing layer is a non-twisted monofilament having a diameter of 0.20 [mm] or more and 0.45 [mm] or less, according to any one of claims 1 to 4. Pneumatic tire.   The steel reinforcing layer is divided and an end portion on the inner side in the tire width direction is provided at a position of 2% to 8% of the effective belt width from the tire equator plane. The pneumatic tire according to any one of Items 1 to 5.   The pneumatic tire according to any one of claims 1 to 5, wherein the steel reinforcing layer is formed continuously in a tire width direction.   The pneumatic tire according to claim 1, wherein the carcass cord forming the carcass layer is an organic fiber.   The pneumatic tire according to any one of claims 1 to 8, which is applied to a pneumatic tire for a passenger car having a high internal pressure.

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