JP2012091735A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rolling resistance and improve center wear resistance and dry braking performance.SOLUTION: When an intersection between lines extended from a shoulder-side arc 21b and a side-part arc 21d is a reference point P, the following conditions are satisfied: 0.025×β+1.0≤θ≤0.045×β+2.5, wherein θ is an angle between a straight line A connecting the reference point and a center crown CC and a straight line B passing the center crown in a tire width direction, with respect to an aspect ratio β; 10≤Rc/Rs≤50, wherein Rc is a curvature radius Rc of a center-part arc 21a, and Rs is a curvature radius of the shoulder-side arc; 0.2≤L/(TDW/2)≤0.7, wherein L is a reference expansion width from a tire equatorial plane CL to an inner end of the shoulder-side arc in a tire width direction, and TDW is a tread expansion width; 12 [%]≤GR≤25 [%], wherein GR is a groove area ratio in a grounding region of a tread face; and GCR<GSR, wherein GCR is a groove area ratio in a center region of the tread face and GSR is a groove area ratio in a shoulder region of the tread face.

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 dry braking performance.

  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. Moreover, when the ground contact pressure in the center region increases, the friction coefficient between the shoulder portion of the tread surface and the road surface decreases, and the dry braking performance on the dry road surface tends 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, simply making the curvature of the profile along the tire width direction of the tread surface close to a straight line does not sufficiently increase the coefficient of friction between the shoulder portion of the tread surface and the road surface, and can improve dry braking performance on a dry road surface. difficult.

  The present invention has been made in view of the above, and provides a pneumatic tire capable of reducing rolling resistance, improving wear resistance of a center region of a tread surface, and improving dry braking performance. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the pneumatic tire of the present invention includes a central arc in which the tread surface of the tread portion is located at the center in the tire width direction, and the tire width direction of the central arc. In a pneumatic tire formed of a plurality of arcs of different radii of curvature including at least a shoulder-side arc that is continuous to the outside, the tire meridian direction in a state where it is incorporated in a normal rim and is filled with 5% of the normal internal pressure. In the cross-sectional view, the intersection of the virtual extension line of the shoulder side arc and the virtual extension line of the outermost side arc in the tire width direction in the tread portion is a reference point, and the tire equator plane and the tread surface The intersection with the profile is a center crown, 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. The angle between the center arc and the radius of curvature of the central arc is Rc, the radius of curvature of the shoulder arc is Rs, and the arc from the tire equatorial plane to the inner edge position in the tire width direction of the shoulder arc. TDW is a tread deployment width which is an arc length in the tire width direction between points where a reference line parallel to the tire equator plane and a reference line parallel to the tire equator plane intersects the tread surface. When the flatness ratio is β, the tread surface is 0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5, 10 ≦ Rc / Rs ≦ 50, and 0.2 ≦ L / ( TDW / 2) ≦ 0.7, and the groove area ratio in the contact area in the tread surface is GR, and 45 [TDW / 2] from the tire equatorial plane in the contact area to the outside in the tire width direction. %] And the groove area ratio in the center region is GCR, and is within the range from the tire equator plane to the 90% position of TDW / 2 outward in the tire width direction in the ground contact region. When the range from the outer end in the tire width direction of the center region to the outer side in the tire width direction is a shoulder region, and the groove area ratio in the shoulder region is GSR, the ground contact region is 12 [%] ≦ GR ≦ 25 [ %] And GCR <GSR.

  According to this pneumatic tire, an angle θ 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 0.025 × β + 1.0 ≦ θ ≦ 0. By setting the range to 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 10 ≦ Rc / Rs ≦ 50, 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 radial growth of the central arc is suppressed, wear of the center region of the tread surface can be improved. Moreover, according to this pneumatic tire, the groove area ratio GR in the contact area of the tread surface is set to 12 [%] or more and 25 [%] or less, and is set to be relatively low with respect to a general pneumatic tire, and the shoulder By setting the groove area ratio GSR of the region to be larger than the groove area ratio GCR of the center region, it becomes possible to improve dry braking performance, which is braking performance on a dry road surface.

  In the pneumatic tire of the present invention, the relationship between the groove area ratio GCR in the center region and the groove area ratio GSR in the shoulder region satisfies 1.2 ≦ GSR / GCR ≦ 1.8. It is characterized by being.

  If GSR / GCR is 1.2 or more, sufficient shear rigidity of the tread portion can be secured in the center region, and if GSR / GCR is 1.8 or less, shear strength of the tread portion in the shoulder region can be secured. The decrease can be suppressed. Therefore, according to this pneumatic tire, the rolling resistance can be reduced, the wear resistance of the center region of the tread surface can be improved, and the dry braking performance can be significantly improved.

  The pneumatic tire according to the present invention is formed such that the sub-groove gauge GD at the maximum depth position in the groove formed on the tread surface satisfies 0.5 [mm] ≦ GD ≦ 3.0 [mm]. It is characterized by.

  If the sub-groove gauge GD is 0.5 [mm] or more, cracks (groove cracks) at the groove bottom can be suppressed, and if the sub-groove gauge GD is 3.0 [mm] or less, the shear rigidity of the tread portion. Can be secured. Therefore, according to this pneumatic tire, the rolling resistance can be reduced, the wear resistance of the center region of the tread surface can be improved, and the dry braking performance can be significantly improved.

  In the pneumatic tire of the present invention, the tread portion has an under tread rubber, and the JIS-A hardness H of the under tread rubber satisfies 68 [degree] ≦ H ≦ 80 [degree]. It is characterized by.

  If the JIS-A hardness H of the undertread rubber is a high hardness of 68 [degrees] or more, the shear rigidity of the tread portion can be sufficiently secured, and if it is 80 [degrees] or less, the durability is maintained. be able to. As described above, according to this pneumatic tire, by increasing the hardness H of the undertread rubber, the shear rigidity of the tread portion is improved, so that the rolling resistance is reduced and the resistance of the center region of the tread surface is reduced. The effect of improving the wear resistance and the dry braking performance can be remarkably obtained.

  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 rolling resistance in order to reduce fuel consumption, it is preferable to increase the operating air pressure. Thus, according to this pneumatic tire, by applying it to a pneumatic tire for passenger cars with a high internal pressure, the rolling resistance is reduced, the wear resistance of the center region of the tread surface is improved, and the dry braking performance is also improved. The effect which improves can be acquired notably.

  The pneumatic tire according to the present invention can provide a pneumatic tire that can reduce rolling resistance, improve wear resistance in the center region of the tread surface, and improve dry braking performance.

FIG. 1 is a partially cut meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a plan view of a part of the tread surface in the pneumatic tire according to the embodiment of the present invention. FIG. 3 is a partially enlarged view of the pneumatic tire shown in FIG. FIG. 4-1 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-2 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-3 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-4 is a table showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-5 is a table showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-6 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-7 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-8 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 4-9 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention. FIG. 5 is a chart showing the composition of the under tread in 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 partially cut meridian sectional view of a pneumatic tire according to the present embodiment, and FIG. 2 is a plan view of a part of a tread surface in the pneumatic tire according to the embodiment of the present invention.

  In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, the tire radial direction outer side. 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 rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. 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 CL in the tire width direction. The tire equator line is a line along the circumferential direction of the pneumatic tire 1 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. In addition, since the pneumatic tire 1 described below is configured to be substantially symmetric about the tire equator plane CL, the pneumatic tire 1 is cut along a plane passing through the rotation axis of the pneumatic tire 1. In the meridional sectional view (FIG. 1), only one side (right side in FIG. 1) centered on the tire equatorial plane CL is illustrated and only one side is described, and the other side (left side in FIG. 1). Description of is omitted.

  The pneumatic tire 1 of the present embodiment has a tread portion 2 as shown in FIG. The tread portion 2 is made of a rubber material (tread rubber), is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and the surface thereof is the contour of the pneumatic tire 1. The surface of the tread portion 2 is formed as a tread surface 21 that is a surface that comes into contact with the road surface when a vehicle (not shown) on which the pneumatic tire 1 is mounted travels.

  The tread surface 21 has a land portion formed by a plurality of grooves. As an example, in the pneumatic tire 1 of the present embodiment, the tread surface 21 is provided with a plurality of vertical grooves 22 extending along the tire circumferential direction, as shown in FIGS. 1 and 2. The longitudinal groove 22 in the present embodiment includes four circumferential main grooves 22 a provided on the tread surface 21 and two circumferential narrow grooves 22 b provided on the tread surface 21. The tread surface 21 extends along the tire circumferential direction by a plurality of circumferential main grooves 22a, and a plurality of rib-like land portions 23 parallel to the tire equator line CL are formed. In the present embodiment, five land portions 23 are provided on the tread surface 21 with the circumferential main groove 22a as a boundary, and the first land portion 23a disposed on the tire equator line CL, and the first land portion 23a. A second land portion 23b disposed on the outer side in the tire width direction; and a third land portion 23c disposed on the outermost side in the tire width direction of the tread surface 21 on the outer side in the tire width direction of the second land portion 23b. ing. The second land portion 23b is provided with a circumferential narrow groove 22b.

  Moreover, the tread surface 21 is provided with a lateral groove 24 that intersects the longitudinal groove 22 for each land portion 23 (23a, 23b, 23c). The lateral groove 24 provided in the first land portion 23a is formed as a protruding groove 24a having one end opened in the circumferential main groove 22a and the other end closed, and inclined with respect to the tire width direction and the tire circumferential direction. Yes. The protrusion groove 24a is formed so that the inclination direction from the circumferential main groove 22a is opposite to the tire equator line CL.

  Further, the lateral groove 24 provided in the second land portion 23b has one end opened in the circumferential main groove 22a on the outer side in the tire width direction, the other end opened in the circumferential narrow groove 22b, and the tire width direction and the tire circumference. It is formed as an inclined groove 24b that is inclined while being inclined with respect to the direction. The inclined groove 24b is formed so that the inclined direction from the circumferential main groove 22a is opposite to the tire equator line CL.

  Further, the lateral groove 24 provided in the third land portion 23c is curvedly extended from the outermost end in the tire width direction of the tread surface 21 to the inner side in the tire width direction, and the extended end opens into the circumferential main groove 22a. It is formed as an arc groove 24c. The arc groove 24c is formed so that the curve direction is opposite to the tire equator line CL.

  Moreover, the tread surface 21 is provided with sipes 24d and 24e that intersect the tire circumferential direction as the lateral grooves 24 with respect to the second land portion 23b and the third land portion 23c. The sipe 24d provided in the second land portion 23b is curved while being inclined with respect to the tire width direction and the tire circumferential direction, with one end opening in the circumferential main groove 22a on the outer side in the tire width direction and the other end closed. Is formed. The sipe 24d is formed so that the inclination direction from the circumferential main groove 22a is opposite to the tire equator line CL. The sipe 24e provided in the third land portion 23c has one end opened in the circumferential main groove 22a on the outer side in the tire width direction and the other end closed, and is inclined with respect to the tire width direction and the tire circumferential direction. While being curved, it is formed. The sipe 24e is formed so that the inclination direction from the circumferential main groove 22a is opposite to the tire equator line CL.

  Here, the circumferential main groove 22a is a groove extending in the tire circumferential direction with a groove width of 4 mm or more. Moreover, the circumferential direction narrow groove 22b shows the groove | channel extended in the tire circumferential direction whose groove width is less than 4 [mm]. Sipes 24d and 24e indicate grooves that cross the tire circumferential direction with a groove width of 1 mm or less. The protruding grooves 24a, the inclined grooves 24b, and the circular arc grooves 24c are collectively referred to as lug grooves, and indicate grooves that cross the tire circumferential direction with a groove width exceeding 1 [mm] except for the sipes 24d and 24e. In addition, the structure of a groove | channel or a land part is not limited to the example mentioned above, There exist various structures by arrangement | positioning of the vertical groove 22 or the horizontal groove 24. FIG. Although not clearly shown in the figure, the tread surface 21 may have a configuration in which only the lateral groove 24 that is bent or curved in the tire width direction is provided without the longitudinal groove 22.

  The pneumatic tire 1 according to the present embodiment includes a carcass layer 6, a belt layer 7, and a belt reinforcing layer 8.

  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 (not shown), and is wound around in a toroidal shape in the tire circumferential direction. It constitutes. 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.). As shown in FIG. 1, the carcass layer 6 is provided in two layers in the present embodiment, but may be provided in 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 reinforcement layer 8 shown in FIG. 1 is arranged so that the reinforcement layer 81 on the belt layer 7 side is formed larger in the tire width direction than the belt layer 7 so as to cover the entire belt layer 7. The outer reinforcing layer 82 is disposed only at the end portion in the tire width direction of the reinforcing layer 81 so as to cover the end portion in the tire width direction of the belt layer 7. 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. Alternatively, the reinforcing layers 81 and 82 may be arranged so as to cover only the end portion of the belt layer 7 in the tire width direction. That is, the belt reinforcing layer 8 only needs to overlap at least the end portion in the tire width direction of the belt layer 7. 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.

  In the pneumatic tire 1 configured as described above, the profile of the tread surface 21 which is the surface of the tread portion 2 is formed by a plurality of arcs having different curvature radii convex outward in the tire radial direction. Specifically, as shown in FIG. 1, 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.

  The virtual extension of the shoulder-side arc 21b in the tire meridian cross-sectional view shown in FIG. 1 in a no-load state in which the pneumatic tire 1 is incorporated in a normal rim and filled with 5% of the normal internal pressure. The intersection point between the line and the virtual extension line of the side 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 1 of the present embodiment is formed to satisfy the following formulas (1) to (3).
0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5 (1)
10 ≦ Rc / Rs ≦ 50 (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.

  Furthermore, as shown in FIG. 2, the groove area ratio in the ground contact region G on the tread surface 21 is defined as GR. Further, a range from the tire equatorial plane CL in the ground contact region G to a position of 45 [%] of TDW / 2 on the outer side in the tire width direction is defined as a center region GC, and a groove area ratio in the center region GC is defined as GCR. Further, in the range from the tire equatorial plane CL in the ground contact region G to the position of 90 [%] of TDW / 2 outward in the tire width direction, the range from the outer end in the tire width direction of the center region GC to the outer side in the tire width direction Is the shoulder region GS, and the groove area ratio in the shoulder region GS is GSR.

In this case, the ground contact region G of the pneumatic tire 1 of the present embodiment is formed so as to satisfy the following expressions (4) and (5).
12 [%] ≦ GR ≦ 25 [%] (4)
GCR <GSR (5)

  Here, the contact area G means that the tread surface 21 contacts the road surface when the pneumatic tire 1 is assembled to a normal rim, is filled with a normal internal pressure (230 kPa), and 70% of the normal load is applied. This is a region in the tire circumferential direction. In FIG. 2, the maximum width in the tire width direction of the ground contact region G is indicated as a ground contact width TW, and both outermost ends of the ground contact region G in the tire width direction are indicated as ground contact ends T. In FIG. 2, the maximum width in the tire width direction of the center region GC is indicated as a contact width CW, and the maximum width in the tire width direction of the shoulder region GS is indicated as a contact width SW. 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. The groove area ratio GR is a ratio (Y1 / X1 × 100) between the total groove area Y1 of the grooves 22 and 24 opened in the grounding region G and the area (grounding area) X1 of the grounding region G. The groove area ratio GCR is a ratio (Y2 / X2 × 100) between the total groove area Y2 of the grooves 22 and 24 opened in the center region GC and the area (grounding area) X2 of the center region GC. The groove area ratio GSR is a ratio (Y3 / X3 × 100) between the total groove area Y3 of the grooves 22 and 24 opened in the shoulder region GS and the area (grounding area) X3 of the shoulder region GS.

  According to the pneumatic tire 1 of the present embodiment configured as described above, a straight line A connecting the reference point P and the center crown CC, and a straight line B passing through the center crown CC and parallel to the tire width direction. Is set to a range of 0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5, and the amount of sagging inward in the tire radial direction from the central arc 21a to the shoulder-side arc 21b is general. Compared to a new pneumatic tire. 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 10 ≦ Rc / Rs ≦ 50, and the tire width direction inner end position of the shoulder-side arc 21b from the tire equatorial plane CL. 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. It reaches the shoulder-side arc 21b and the arc of the tread surface 21 is closer to a straight line than a general pneumatic tire. For this reason, since the diameter growth of the central arc 21a is suppressed, it is possible to improve the wear (center wear) of the center region GC of the tread surface 21.

  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 It is possible to remarkably obtain the effect of improving center wear without causing wear.

  Further, when Rc / Rs is less than 10, the diameter growth of the central arc 21a cannot be sufficiently suppressed, and the contact pressure in the center region increases to improve the wear (center wear) of the center region GC of the tread surface 21. It becomes difficult. On the other hand, when Rc / Rs exceeds 50, 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 12 <= Rc / Rs <= 30, the diameter growth of the center part circular arc 21a is fully suppressed, and the effect which improves the abrasion (center abrasion) of the center area | region GC of the tread surface 21 is acquired notably. It is possible.

  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 increases and the center region GC of the tread surface 21 is worn. It becomes difficult to improve (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 wear of the center area | region GC of the tread surface 21 (center wear) It is possible to obtain a remarkable effect of improving.

  Moreover, according to the pneumatic tire 1 of the present embodiment, the groove area ratio GR in the ground contact region G of the tread surface 21 is set to 12 [%] or more and 25 [%] or less and compared with a general pneumatic tire. By setting the groove area ratio GSR of the shoulder region GS larger than the groove area ratio GCR of the center region GC, it is possible to improve the dry braking performance, which is the braking performance on the dry road surface. . The range of 16 [%] ≦ GR ≦ 20 [%] is more preferable because both dry braking performance and wet braking performance, which is braking performance on a wet road surface, can be achieved.

  As a result, according to the pneumatic tire 1 of the present embodiment, the rolling resistance is reduced, the wear resistance (center wear resistance) of the center region GC of the tread surface 21 is improved, and the dry braking performance is improved. Is possible.

  In the pneumatic tire 1 of the present embodiment, the relationship between the groove area ratio GCR in the center region GC and the groove area ratio GSR in the shoulder region GS satisfies 1.2 ≦ GSR / GCR ≦ 1.8. It is preferable to be formed.

  If GSR / GCR is 1.2 or more, sufficient shear rigidity of the tread portion 2 can be secured in the center region GC, and if GSR / GCR is 1.8 or less, the tread portion 2 in the shoulder region GS. Therefore, the rolling resistance can be reduced, the wear resistance of the center region GC of the tread surface 21 can be improved, and the dry braking performance can be significantly improved. is there. In addition, since it can ensure the shear rigidity of the tread part 2 more by setting it as the range of 1.4 <= GSR / GCR <= 1.6, while reducing rolling resistance, the abrasion resistance of center area | region GC of the tread surface 21 It is possible to obtain the effect of improving the dry braking performance more significantly.

  Further, the pneumatic tire 1 of the present embodiment has a groove depth GD at the maximum depth position in the grooves 22 and 24 formed on the tread surface 21, that is, from the groove bottom of the groove with the maximum depth in the tire radial direction. It is preferable that the dimension up to the cord immediately below satisfies 0.5 [mm] ≦ GD ≦ 3.0 [mm].

  If the sub-groove gauge GD is 0.5 [mm] or more, cracks (groove cracks) at the groove bottom can be suppressed, and if the sub-groove gauge GD is 3.0 [mm] or less, the shear of the tread portion 2 is achieved. Since the rigidity can be ensured, it is possible to significantly reduce the rolling resistance, improve the wear resistance of the center region GC of the tread surface 21, and improve the dry braking performance. In addition, by setting it as the range of 1.5 [mm] <= GD <= 2.5 [mm], since the shear rigidity of the tread part 2 can be ensured more, while reducing rolling resistance, center area | region GC of the tread surface 21 The effect of improving the wear resistance and improving the dry braking performance can be obtained more remarkably.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 3, the tread rubber constituting the tread portion 2 includes a cap tread rubber 2a that forms a tread surface 21, and a tire diameter of the cap tread rubber 2a. It is the inner side in the direction and is composed of an under tread rubber 2b provided between the cap tread rubber 2a and the belt reinforcing layer 8. In the pneumatic tire 1 of the present embodiment, it is preferable that the JIS-A hardness H of the undertread rubber 2b satisfies 68 [degrees] ≦ H ≦ 80 [degrees].

  If the JIS-A hardness H of the undertread rubber 2b is a high hardness of 68 [degrees] or more, the shear rigidity of the tread portion 2 can be sufficiently secured, and if it is 80 [degrees] or less, the durability is improved. Can be maintained. In this way, by making the hardness H of the undertread rubber 2b relatively high, the shear rigidity of the tread portion 2 is improved, so that the rolling resistance is reduced and the wear resistance of the center region GC of the tread surface 21 is improved. In addition, the effect of improving the dry braking performance can be remarkably obtained. In addition, since the shear rigidity of the tread portion 2 can be further ensured by setting the range of 72 [degrees] ≦ H ≦ 76 [degrees], the rolling resistance is reduced and the wear resistance of the center region GC of the tread surface 21 is reduced. It is possible to obtain the effect of improving the dry braking performance more significantly.

  Moreover, it is preferable that the pneumatic tire 1 of this Embodiment is applied to the pneumatic tire for passenger cars with a high internal pressure.

  In order to reduce the rolling resistance in order to reduce fuel consumption, it is preferable to increase the operating air pressure. In the present embodiment, the high internal pressure is 280 [kPa] or more and 350 [kPa] or less in the passenger car pneumatic tire. Thus, by applying to a pneumatic tire for passenger cars with a high internal pressure, the effect of reducing the rolling resistance, improving the wear resistance of the center region GC of the tread surface 21, and improving the dry braking performance is remarkable. It is possible to get to.

  In this example, performance tests on tire performance (center wear, dry braking performance, wet braking performance, rolling resistance) were performed on a plurality of types of pneumatic tires having different conditions (FIGS. 4-1 to 4-9). reference).

  In this performance test, a pneumatic tire with a tire size of 215 / 55R17 was assembled on a rim of a 17 × 7J aluminum wheel, filled with air pressure applied to each example, and mounted on a test vehicle (3 liter FR sedan). In the conventional examples 3 and 4, Example 13 to Example 16, and Comparative Examples 7 and 8 shown in FIG. 4-4, a pneumatic tire having a tire size of 245 / 35ZR19 is replaced with a 19 × 81 / 2J aluminum wheel. The air pressure applied to each example was filled and mounted on a test vehicle (3 liter FR sedan).

  In the center wear evaluation method, the remaining groove amount (groove depth) at the maximum groove depth position in the center region when traveling on a dry road surface of 10,000 [km] is measured. Then, based on the measurement result, index evaluation with the conventional example 2 as a reference (100) is performed. In this index evaluation, the larger the numerical value, the better the center wear resistance performance.

  In the dry braking performance evaluation method, the distance to stop when braking from 100 [km / h] on a dry road surface is measured. Then, based on the measurement result, index evaluation with the conventional example 2 as a reference (100) is performed. In this index evaluation, the larger the numerical value, the better the dry braking performance.

  In the wet braking performance evaluation method, the distance to stop when braking is performed from 100 [km / h] on a road surface with a water depth of 3 [mm] is measured. Then, based on the measurement result, index evaluation with the conventional example 2 as a reference (100) is performed. In this index evaluation, the larger the value, the better the wet braking performance.

  In the rolling resistance evaluation method, the above test tire to which a load (4.2 [kN]) was applied was rolled at a speed of 80 [km / h] using a drum type rolling resistance tester having a drum diameter of 1707 [mm]. Resistance is measured. Then, based on the measurement result, index evaluation with the conventional example 2 as a reference (100) is performed. In this index evaluation, the larger the value, the lower the rolling resistance and the better.

  4-1 to 4-9, the pneumatic tires of Conventional Example 1 to Conventional Example 4 are the pneumatic tires of Patent Document 1 (Japanese Patent Application No. 2008-307948). Conventional Example 1 and Conventional Example The pneumatic tire No. 3 had an internal pressure of 230 [kPa], and the pneumatic tires of Conventional Example 2 and Conventional Example 4 had an internal pressure of 300 [kPa].

  4A, in Examples 1 to 4, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, in Comparative Example 1 and Comparative Example 2, L / (TDW / 2) in the profile of the tread surface was excluded from the specified range with respect to Examples 1 to 4.

  4B, in Examples 5 to 8, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, in Comparative Example 3 and Comparative Example 4, Rc / Rs in the profile of the tread surface was excluded from the specified range with respect to Examples 5 to 8.

  4-3, in Examples 9 to 12, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, in Comparative Example 5 and Comparative Example 6, with respect to Examples 9 to 12, θ in the profile of the tread surface was excluded from the specified range.

  4-4, in Example 13 to Example 16, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, the comparative example 7 and the comparative example 8 remove | deviated (theta) from the profile of the tread surface with respect to Example 13-16.

  4-5, in Example 17 to Example 20, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, Comparative Example 9 and Comparative Example 10 excluded the groove area ratio GR of the tread pattern from the specified range with respect to Examples 17 to 20.

  4-6, in Examples 21 to 24, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were set within a specified range. On the other hand, in Comparative Example 11, the groove area ratio GR of the tread pattern was excluded from the specified range and from the specified range as GCR> GSR with respect to Examples 21 to 24.

  4-7, in Example 25 to Example 28, the internal pressure was set to 300 [kPa], and the profile and tread pattern of the tread surface were within a specified range. On the other hand, the comparative example 12 and the comparative example 13 remove | excluded the groove area ratio GR and GSR / GSR of the tread pattern from the regulation range with respect to Example 25-28. Further, in Example 29, the groove area ratio GR of the tread pattern is within a specified range with respect to Examples 25 to 28, but GSR / GSR is excluded from the specified range. For example, in the pneumatic tires of the conventional example 1 and the conventional example 2, the circumferential width of the circumferential main groove 22a and the lug grooves 24a, 24b, and 24c in FIG. A sipe is further provided on the outer side in the tire width direction between the groove communicating between the lug grooves 24c and the arc groove (lug groove) 24c. On the other hand, the pneumatic tire of Example 25 has the tread pattern shown in FIG. Further, in the pneumatic tire of Example 28, the groove width of the circumferential main groove 22a in the center region is formed small in the tread pattern of the pneumatic tires of Conventional Example 1 and Conventional Example 2.

  4-8, in Example 30 to Example 33, the internal pressure was set to 300 [kPa], the tread surface profile and the tread pattern were set to a specified range, and the sub-groove gauge GD was set to a specified range. On the other hand, Example 34 and Example 35 removed the sub-groove gauge GD from the specified range with respect to Example 30 to Example 33.

  4-9, in Examples 36 to 39, the internal pressure is set to 300 [kPa], the tread surface profile and the tread pattern are set to a specified range, and the sub-groove gauge GD and the undertread rubber hardness are set to a specified range. It was. On the other hand, Example 40 and Example 41 remove | excluded the undertread rubber hardness from the regulation range with respect to Example 36-Example 39. Here, FIG. 5 shows a blending example of the under tread rubber having the hardness in Example 34 and Example 40.

  As shown in the test results of FIGS. 4-1 to 4-9, the pneumatic tires of Examples 1 to 41 each have reduced rolling resistance, wear resistance in the center region of the tread surface, and dryness. It can be seen that the braking performance is improved. Moreover, it can be seen that the pneumatic tires of Examples 1 to 41 have improved wet braking performance as well as dry braking performance.

  As described above, the pneumatic tire according to the present invention provides a pneumatic tire that can reduce rolling resistance, improve wear resistance in the center region of the tread surface, and improve dry braking performance. Suitable for that.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 2a Cap tread rubber 2b Under tread rubber 21 Tread surface 21a Center part arc 21b Shoulder side arc 21c Shoulder part arc 21d Side part arc 22 Vertical groove 22a Circumferential main groove 22b Circumferential narrow groove 24 Horizontal groove 24a Projection groove (lug groove)
24b Inclined groove (lug groove)
24c Arc groove (lug groove)
24d, 24e Sipe A A straight line connecting the reference point and the center crown B A straight line passing through the center crown and parallel to the tire width direction CC Center crown CL Tire equator plane (tire equator line)
G Ground area GR Groove area ratio of ground area GC Center area GCR Center area groove area ratio GS Shoulder area GSR Shoulder area groove area ratio GD Under groove gauge L Reference development width P Reference point Rc Center radius of curvature Rs Shoulder Radius of curvature of side arc T Grounding edge TW Grounding width of grounding area TDW Tread unfolding width CW Grounding width of center area SW Grounding width of shoulder area β Flatness θ Angle

Claims (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 continuous to the outer side in the tire width direction of the central arc. In pneumatic tires,
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 the virtual extension line of the partial arc 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 crown An angle formed by a straight line passing through and parallel to the tire width direction is θ, a radius of curvature of the central arc is Rc, a radius of curvature of the shoulder-side arc is Rs, and the shoulder-side arc of the shoulder-side arc is from the tire equatorial plane. A reference developed width which is an arc length to the inner end position in the tire width direction is L, and a reference line passing through the reference point and parallel to the tire equatorial plane is the tread. The tread width is the arc length in the tire width direction between crossed point and TDW, the oblateness when the β to the,
The tread surface is
0.025 × β + 1.0 ≦ θ ≦ 0.045 × β + 2.5
10 ≦ Rc / Rs ≦ 50
0.2 ≦ L / (TDW / 2) ≦ 0.7
Formed to meet the
Furthermore, the groove area ratio in the contact area on the tread surface is GR, and the center area is defined as a range from the tire equator surface to the outer side in the tire width direction of 45% of TDW / 2 in the contact area. The groove area ratio at the center region is GCR, and is within the range from the tire equatorial plane in the ground contact region to the position of 90% of TDW / 2 outward in the tire width direction, and from the outer end in the tire width direction of the center region to the tire When the range to the outside in the width direction is a shoulder region and the groove area ratio in the shoulder region is GSR,
The ground area is
12 [%] ≦ GR ≦ 25 [%]
GCR <GSR
A pneumatic tire characterized by being formed to satisfy the above.   The groove area ratio GCR in the center region and the groove area ratio GSR in the shoulder region are formed so as to satisfy 1.2 ≦ GSR / GCR ≦ 1.8. The pneumatic tire according to 1.   The sub-groove gauge GD at the maximum depth position in the groove formed on the tread surface is formed so as to satisfy 0.5 [mm] ≦ GD ≦ 3.0 [mm]. Or the pneumatic tire of 2.   The tread portion has an under tread rubber, and the JIS-A hardness H of the under tread rubber satisfies 68 [degree] ≦ H ≦ 80 [degree]. The pneumatic tire according to any one of the above.   The pneumatic tire according to any one of claims 1 to 4, which is applied to a pneumatic tire for a passenger car having a high internal pressure.

Images