JP2021075221A - Pneumatic tire - Google Patents

Abstract

To secure the steering stability while improving the noise performance and rolling resistance.SOLUTION: In a pneumatic tire 1, an average gauge Ga_ce of an under-tread rubber 152 on an inner center land part 33 on a tire equator surface CL or closest to the tire equator surface CL, an average gauge Ga_c of the under-tread rubber 152 on at least one outer center land part 32, 34 and average gauges Ga_s1, Ga_s2 of the under-tread rubber 152 of respective shoulder land parts 31, 35 have the relation of Ga_s1<Ga_ce, Ga_s2<Ga_ce, Ga_c<Ga_ce. Also in the pneumatic tire 1, a groove area ratio S_ce of a tread surface 15a on the inner center land part 33 and a groove area ratio S_c of the tread surface 15a on at least one outer center land part 32, 34 have the relation of S_c<S_ce.SELECTED DRAWING: Figure 3

Description

The present invention relates to pneumatic tires.

For example, Patent Document 1 discloses a pneumatic tire having a structure in which a tread portion is composed of an undertread rubber and a cap rubber having different rubber hardness.

Japanese Patent No. 3822324

In the structure of the tread portion, if the rubber volume of the tread portion is increased in order to improve the noise performance for reducing the road noise, there is a concern that the rolling resistance leading to low fuel consumption may be deteriorated. Further, in the structure of the tread portion, in order to improve the noise performance for reducing the road noise, if the rubber hardness of the tread portion is lowered, there is a concern that the steering stability performance may be deteriorated.

An object of the present invention is to provide a pneumatic tire capable of ensuring steering stability performance while improving noise performance and rolling resistance.

In order to achieve the above object, the pneumatic tire according to one aspect of the present invention is obtained by laminating a carcass layer, a pair of cross belts arranged radially outside the carcass layer, and a cap tread rubber and an under tread rubber. At least one center main groove between the tread rubber arranged on the radial outer side of the cross belt, the pair of shoulder main grooves formed on the outermost side of the tread surface in the tire width direction, and the shoulder main groove. A pneumatic tire including a pair of shoulder treads partitioned on the outer side of the shoulder main groove in the tire width direction, and at least two center treads partitioned on the shoulder main groove and the center main groove. The average gauge Ga_ce of the under tread rubber on the tire equatorial plane or the inner center land portion closest to the tire equatorial plane, and the average gauge Ga_c of the under tread rubber on the other at least one outer center land portion, respectively. The average gauges Ga_s1 and Ga_s2 of the under tread rubber in the shoulder land portion have a relationship of Ga_s1 <Ga_ce, Ga_s2 <Ga_ce, Ga_c <Ga_ce, and the groove area ratio S_ce of the tread surface in the inner center land portion The groove area ratio S_c of the tread surface in at least one land portion of the outer center has a relationship of S_c <S_ce.

According to the present invention, in this pneumatic tire, the average gauge Ga_ce of the inner center land portion is made thicker than the average gauge Ga_s1 and Ga_s2 of each shoulder land portion for the under tread rubber, so that each shoulder land portion and the inner center The rubber volume of the under tread rubber 152 is different from that of the land part. Further, this pneumatic tire has at least one outer center land part and inner center by increasing the average gauge Ga_ce of the inner center land part with respect to at least one outer center land part average gauge Ga_c for the under tread rubber. The rubber volume of the under tread rubber 152 is different from that of the land part. Moreover, this pneumatic tire has at least one outer center land by reducing the groove area ratio S_ce of the tread surface of the inner center land portion with respect to the groove area ratio S_c of the tread surface of at least one outer center land portion. The rubber rigidity of the part and the inner center land part are different. Therefore, this pneumatic tire has a relatively large rubber volume of the under tread rubber in the inner center land area, lowers the vibration coefficient, reduces road noise, contributes to improvement of noise performance, and reduces rolling resistance that leads to low fuel consumption. Contribute to. Further, in this pneumatic tire, the rubber volume of the under tread rubber is relatively small in the shoulder land portion and at least one outer center land portion, and the deterioration of durability performance is suppressed. Moreover, this pneumatic tire reduces the input from the road surface by increasing the rubber volume to increase the rubber rigidity and increasing the groove area ratio of the tread surface in the under tread rubber in the inner center land area. By doing so, deterioration of steering stability performance is suppressed. As a result, the pneumatic tire can secure steering stability performance while improving noise performance and rolling resistance.

FIG. 1 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a plan view showing the tread surface of the pneumatic tire shown in FIG. FIG. 3 is an enlarged view showing a tread portion of the pneumatic tire shown in FIG. FIG. 4 is an enlarged view showing a tread portion of the pneumatic tire shown in FIG. FIG. 5 is an enlarged view showing a tread portion of the pneumatic tire shown in FIG. FIG. 6 is a schematic view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. FIG. 7 is a schematic view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. FIG. 8 is a schematic view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. FIG. 9 is a schematic view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. FIG. 10 is a schematic view showing a tread portion of a pneumatic tire according to an embodiment of the present invention. FIG. 11 is a chart showing the results of a performance test of a pneumatic tire according to an embodiment of the present invention.

Hereinafter, embodiments of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, the components of this embodiment include those that are replaceable and self-explanatory while maintaining the identity of the invention. Further, the plurality of modifications described in this embodiment can be arbitrarily combined within a range self-evident by those skilled in the art.

[Pneumatic tires]
FIG. 1 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to the present embodiment. The figure shows a cross-sectional view of one side region in the tire radial direction. Further, the figure shows a radial tire for a passenger car as an example of a pneumatic tire.

The cross section in the tire meridian direction is defined as the cross section when the tire is cut on a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the measurement point of the tire cross-sectional width defined by JATTA and is perpendicular to the tire rotation axis. The tire width direction is defined as the direction parallel to the tire rotation axis. The inside in the tire width direction refers to the side toward the tire equatorial plane CL in the tire width direction, and the outside in the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction. The tire radial direction is defined as the direction perpendicular to the tire rotation axis. The inner side in the tire radial direction means the side facing the tire rotation axis in the tire radial direction, and the outer side in the tire radial direction means the side away from the tire rotation axis in the tire radial direction. Further, the point T is a tire ground contact end.

The pneumatic tire 1 has an annular structure centered on the tire rotation axis, and as shown in FIG. 1, a pair of bead cores 11 and 11, a pair of bead fillers 12 and 12, a carcass layer 13 and a belt layer. It includes 14, a tread rubber 15, a pair of sidewall rubbers 16 and 16, and a pair of rim cushion rubbers 17 and 17.

The pair of bead cores 11 and 11 are formed by winding one or a plurality of bead wires made of steel in an annular shape and in a plurality of manners, and are embedded in the bead portions to form cores of the left and right bead portions. The pair of bead fillers 12 and 12 are respectively arranged along the tire circumferential direction on the outer side of the pair of bead cores 11 and 11 in the tire radial direction to reinforce the bead portion.

The carcass layer 13 has a single-layer structure composed of one carcass ply or a multi-layer structure formed by laminating a plurality of carcass plies, and is bridged between the left and right bead cores 11 and 11 in a toroidal shape to form a tire skeleton. To configure. Further, both ends of the carcass layer 13 are wound and locked outward in the tire width direction so as to wrap the bead core 11 and the bead filler 12. The carcass ply of the carcass layer 13 is formed by coating a plurality of carcass cords made of steel or an organic fiber material (for example, aramid, nylon, polyester, rayon, etc.) with coated rubber and rolling them, and is formed by rolling 80 deg or more and 100 deg or less. Has a cord angle (defined as the longitudinal inclination angle of the carcass cord with respect to the tire circumferential direction).

For example, in the configuration of FIG. 1, the carcass layer 13 has a single layer structure composed of a single carcass ply, and the rewinding portion 132 thereof extends along the outer peripheral surface of the main body portion 131 with respect to the belt layer 14. It overlaps in the tire width direction. Further, the end portion of the rewinding portion 132 of the carcass layer 13 is located outside the shoulder main grooves 21 and 24 described later in the tire width direction.

The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is arranged so as to be hung around the outer circumference of the carcass layer 13. The belt plies 141 to 144 include a pair of intersecting belts 141 and 142, and a belt cover 143 and a belt edge cover 144.

The pair of crossing belts 141 and 142 are formed by coating a plurality of belt cords made of steel or an organic fiber material with coated rubber and rolling them, and have a cord angle of 15 deg or more and 55 deg or less in absolute value. Further, the pair of crossing belts 141 and 142 have cord angles having different signs (defined as inclination angles in the longitudinal direction of the belt cord with respect to the tire circumferential direction), and the longitudinal directions of the belt cords intersect each other. (So-called cross-ply structure). Further, the pair of crossing belts 141 and 142 are laminated and arranged on the outer side of the carcass layer 13 in the tire radial direction.

The belt cover 143 and the belt edge cover 144 are formed by coating a belt cover cord made of steel or an organic fiber material with a coated rubber, and have a cord angle of 0 deg or more and 10 deg or less in absolute value. Further, the belt cover 143 and the belt edge cover 144 are strip materials formed by coating one or a plurality of belt cover cords with coated rubber, and the strip materials are applied to the outer peripheral surfaces of the cross belts 141 and 142. It is configured by winding it in a spiral shape multiple times in the tire circumferential direction. Further, the belt covers 143 are arranged so as to cover the entire area of the cross belts 141 and 142, and a pair of belt edge covers 144 and 144 are arranged so as to cover the left and right edge portions of the cross belts 141 and 142 from the outside in the tire radial direction.

The tread rubber 15 is arranged on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the tire. Further, the tread rubber 15 includes a cap tread rubber 151 and an under tread rubber 152. Details of the tread rubber 15 will be described later.

The pair of sidewall rubbers 16 and 16 are arranged on the outer sides of the carcass layer 13 in the tire width direction, respectively, to form the left and right sidewall portions. For example, in the configuration of FIG. 1, the outer end portion of the sidewall rubber 16 in the tire radial direction is arranged under the tread rubber 15 and sandwiched between the belt layer 14 and the carcass layer 13. Not limited to this, the outer end portion of the sidewall rubber 16 in the tire radial direction may be arranged on the outer layer of the tread rubber 15 and exposed to the buttress portion (not shown).

The pair of rim cushion rubbers 17 and 17 extend in the tire radial direction on the outer side of the rewinding portion of the left and right bead cores 11 and 11 and the carcass layer 13 in the tire width direction to form a rim fitting surface of the bead portion.

The inner liner 18 is an air permeation prevention layer that is arranged on the inner surface of the tire and covers the carcass layer 13, suppresses oxidation due to exposure of the carcass layer 13, and prevents leakage of air filled in the tire. Further, the inner liner 18 is composed of, for example, a rubber composition containing butyl rubber as a main component, a thermoplastic resin, a thermoplastic elastomer composition in which an elastomer component is blended in the thermoplastic resin, and the like.

[Tread pattern]
FIG. 2 is a plan view showing the tread surface of the pneumatic tire shown in FIG. The figure shows the tread surface 15a of the summer tire. The tread surface 15a is an outer peripheral surface of the tread portion, that is, a surface forming a tread tread surface (tire contact patch) that comes into contact with the road surface during traveling.

In the figure, the tire circumferential direction is defined as a circumferential direction centered on the tire rotation axis. Further, reference numeral T is a tire ground contact end. The tire ground contact end T is a contact surface between the tire and the flat plate when the tire is mounted on the specified rim to apply a specified internal pressure and the tire is placed perpendicular to the flat plate in a stationary state and a load corresponding to the specified load is applied. It is defined as the maximum width position in the tire axial direction in.

The specified rim means a "standard rim" specified by JATMA, a "Design Rim" specified by TRA, or a "Measuring Rim" specified by ETRTO. The specified internal pressure means the "maximum air pressure" specified in JATTA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or "INFLATION PRESSURES" specified in ETRTO. The specified load means the "maximum load capacity" specified in JATTA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or the "LOAD CAPACITY" specified in ETRTO. However, in JATMA, in the case of passenger car tires, the specified internal pressure is an air pressure of 230 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

As shown in FIG. 2, the pneumatic tire 1 includes a plurality of circumferential main grooves (main grooves) 21 to 24 extending in the tire circumferential direction, and a plurality of circumferential main grooves 21 to 24. The land portions 31 to 35 are provided on the tread surface 15a.

The main groove is a groove that is obliged to display a wear indicator specified in JATTA, and has a groove width of 4.0 mm or more and a groove depth of 6.5 mm or more.

The groove width is measured as the distance between the opposing groove walls at the groove opening in a no-load state in which the tire is mounted on the specified rim and the specified internal pressure is filled. In the configuration in which the notch or chamfer is provided in the groove opening, the groove is set at the intersection of the extension line of the tread surface 15a and the extension line of the groove wall in the cross-sectional view parallel to the groove width direction and the groove depth direction. The width is measured.

The groove depth is measured as the distance from the tread tread to the maximum groove depth position in a no-load state in which the tire is mounted on the specified rim and the specified internal pressure is filled. Further, in the configuration having a partially uneven portion or a sipe at the groove bottom, the groove depth is measured by excluding these.

For example, in the configuration of FIG. 2, the pneumatic tire 1 has a left-right asymmetric tread pattern with the tire equatorial plane CL as a boundary. However, the present invention is not limited to this, and the pneumatic tire 1 may have, for example, a left-right axisymmetric tread pattern centered on the tire equatorial plane CL, or a point symmetry having a center point on the tire equatorial plane CL. Tread pattern may be provided (not shown).

Further, the tread pattern having the configuration shown in FIGS. 1 and 2 has two circumferential main grooves 21 and 22 in the left region with the tire equatorial plane CL as the boundary, and the right region with the tire equatorial plane CL as the boundary. It has two circumferential main grooves 23 and 24, respectively. In the tread pattern, five rows of land portions 31 to 35 are partitioned by these circumferential main grooves 21 to 24. In the tread pattern, one of the land portions 33 to 35 is arranged on the tire equatorial plane CL.

The tread pattern is not limited to the above configuration. For example, in the tread pattern, three or five or more circumferential main grooves may be arranged (not shown). Further, in the tread pattern, the main grooves in the circumferential direction may be arranged symmetrically or asymmetrically with respect to the tire equatorial plane CL (not shown). Further, in the tread pattern, one circumferential main groove may be arranged on the tire equatorial plane CL (not shown).

Further, in the circumferential main grooves 21 and 22 arranged in one region with the tire equatorial plane CL as a boundary, the outermost circumferential main groove 21 in the tire width direction is defined as the shoulder main groove, and the other circumference is defined as the shoulder main groove. The directional main groove 22 is defined as the center main groove. Further, in the circumferential main grooves 23 and 24 arranged in the other region with the tire equatorial plane CL as the boundary, the outermost circumferential main groove 24 in the tire width direction is defined as the shoulder main groove, and the other circumference is defined as the shoulder main groove. The directional main groove 23 is defined as the center main groove. When there are three circumferential main grooves, the two outermost circumferential main grooves in the tire width direction are defined as shoulder main grooves, and the other one circumferential main groove is defined as the center main groove (). Not shown).

Further, the land portions 31 and 35 on the outer side in the tire width direction divided into the shoulder main grooves 21 and 24 are defined as the shoulder land portions. The shoulder land portions 31 and 35 are the outermost land portions in the tire width direction and are located on the tire ground contact end T. The other land areas 32 to 35 are defined as the center land areas.

In the configuration including the four circumferential main grooves 21 to 24 as shown in FIG. 2, a pair of shoulder land portions 31 and 35 and three rows of center land portions 32 to 34 are defined. Then, in the configuration including the four circumferential main grooves 21 to 24 as shown in FIG. 2, among the three rows of center land portions 32 to 34, the circumferential main groove 21 which is the shoulder main groove and the circumferential main groove 21 The center land portion 32 partitioned between the groove 21 and the circumferential main groove 22 which is the center main groove adjacent to each other in the tire width direction is defined as the outer center land portion. Further, in the configuration including the four circumferential main grooves 21 to 24 as shown in FIG. 2, among the three rows of center land portions 32 to 34, the circumferential main groove 24 which is the shoulder main groove and the circumferential main groove 24 The center land portion 34 partitioned between the groove 24 and the circumferential main groove 23, which is the center main groove adjacent to each other in the tire width direction, is defined as the outer center land portion. Further, in the configuration including the four circumferential main grooves 21 to 24 as shown in FIG. 2, among the three rows of center land portions 32 to 34, the partition is divided between the circumferential main grooves 22 and 23 which are the center main grooves. The center land portion 33 to be formed is defined as the inner center land portion.

In the configuration including three main grooves in the circumferential direction, a pair of shoulder land portions and two rows of center land portions are defined. In this case, the two rows of center land areas are defined as the inner center land area on the tire equatorial plane or the center land area closest to the tire equatorial plane, and the other center land areas as the outer center land area. When the two rows of center land areas are equidistant from the tire equatorial plane, one center land area is defined as the inner center land area and the other center land area is defined as the outer center land area.

In the configuration including five main grooves in the circumferential direction, a pair of shoulder land portions and four rows of center land portions are defined. Then, in a configuration including five circumferential main grooves, the shoulder main groove and each center main groove adjacent to the shoulder main groove in the tire width direction are partitioned among the four rows of center land portions. The center land area is defined as the outer center land area. Further, in a configuration having five main grooves in the circumferential direction, of the four rows of center land portions, two rows of center land portions partitioned between the adjacent center main grooves in the tire width direction are on the tire equatorial plane. Alternatively, the center land area closest to the tire equatorial plane is defined as the inner center land area. If the two rows of center land areas that are partitioned between the adjacent center main grooves in the tire width direction are equidistant from the tire equatorial plane, one of the center land areas is inside. It is defined as the center land area and the other center land area is defined as the outer center land area.

The shoulder land portion 31 includes a lug groove 311 and a sipe 312. The lug groove 311 opens to the tire ground contact end T at one end and opens to the circumferential main groove 21 which is a shoulder main groove at the other end. A plurality of lug grooves 311 are provided in the tire circumferential direction. The sipe 312 opens at one end to the tire ground contact end T and at the other end to the circumferential main groove 21, which is the shoulder main groove. One sipe 312 is provided between the lug grooves 311 adjacent to each other in the tire circumferential direction, and a plurality of sipes 312 are provided in the tire circumferential direction.

Here, the lug groove has a groove width in the range of 1.5 mm or more and 4.5 mm or less, and a groove depth in the range of 0.55 times or more and 0.80 times or less with respect to the groove depth of the main groove. It is in. Further, the sipe has a sipe width of 1.8 mm or less and a sipe depth of 3.0 mm or more and 7.0 mm or less. The sipe is a notch formed in the tread surface 15a, and is distinguished from the lug groove in that it is closed when the tire touches the ground by having the sipe width and the sipe depth described above.

Further, the shoulder land portion 31 has a groove area ratio S_s1 of the tread surface 15a of 13 ± 5%. Here, the groove area ratio is defined by the percentage of groove area / (groove area + ground contact area). The groove area means the opening area of the groove on the ground plane. Further, the groove means a circumferential narrow groove and a lug groove of the tread portion, and does not include a sipe, a calf, a notch and the like. The ground contact area is measured as the contact area between the tire and the road surface. In addition, the groove area and ground contact area are the tires when the tire is mounted on the specified rim and the specified internal pressure is applied, and when the tire is placed perpendicular to the flat plate in a stationary state and a load corresponding to the specified load is applied. It is measured on the contact surface between the flat plate and the flat plate.

The center land portion 32, which is the outer center land portion, includes a lug groove 321 and a sipe 322. The lug groove 321 opens at one end to the circumferential main groove 21 which is the shoulder main groove and at the other end to the circumferential main groove 22 which is the center main groove. One end of the lug groove 321 faces the other end of the lug groove 311 via the circumferential main groove 21. A plurality of lug grooves 321 are provided in the tire circumferential direction. The sipe 322 opens in the circumferential main groove 21 which is the shoulder main groove at one end and opens in the circumferential main groove 22 which is the center main groove at the other end. One end of the sipe 322 faces the other end of the sipe 312 via a circumferential main groove 21. One sipe 322 is provided between the lug grooves 321 adjacent to each other in the tire circumferential direction, and a plurality of sipes 322 are provided in the tire circumferential direction. Further, in the center land portion 32, the groove area ratio S_c (S_c1) of the tread surface 15a is set to 13 ± 5%.

The center land portion 33, which is the inner center land portion, includes one circumferential groove 25. The circumferential groove 25 extends in the tire circumferential direction and divides the center land portion 33 into two in the tire width direction. Here, the circumferential narrow groove has a narrower groove width than the main groove and a shallower groove depth than the main groove. Further, the center land portion 33 includes a lug groove 331 and a sipe 332. The lug groove 331 opens in the circumferential main groove 22 which is the center main groove at one end, and opens in the circumferential fine groove 25 at the other end. One end of the lug groove 331 faces the other end of the lug groove 321 via a circumferential main groove 22. A plurality of lug grooves 331 are provided in the tire circumferential direction. The sipe 332 opens in the circumferential main groove 22 which is the center main groove at one end and ends in the center land 33 without intersecting the circumferential narrow groove 25 at the other end. One end of the sipe 332 faces the other end of the sipe 322 via a circumferential main groove 22. One sipe 332 is provided between the lug grooves 331 adjacent to each other in the tire circumferential direction, and a plurality of sipe 332s are provided in the tire circumferential direction. In the center land portion 33, no groove is provided between the circumferential narrow groove 25 and the circumferential main groove 23. Further, the center land portion 33 has a groove area ratio S_ce of the tread surface 15a of 16 ± 5%.

The center land portion 34, which is the outer center land portion, includes one circumferential groove 26. The circumferential groove 26 extends in the tire circumferential direction and divides the center land portion 34 into two in the tire width direction. Further, the center land portion 34 includes a lug groove 341 and a sipe 342. The lug groove 341 does not intersect the circumferential narrow groove 26 at one end, ends in the center land portion 34, and opens at the other end to the circumferential main groove 24 which is a shoulder main groove. A plurality of lug grooves 341 are provided in the tire circumferential direction. The sipe 342 opens in the circumferential narrow groove 26 at one end and terminates in the center land portion 34 at the other end without reaching the circumferential main groove 26. One sipe 342 is provided between the lug grooves 341 adjacent to each other in the tire circumferential direction, and a plurality of sipe 342s are provided in the tire circumferential direction. In the center land portion 34, no groove is provided between the circumferential narrow groove 26 and the circumferential main groove 23. Further, in the center land portion 34, the groove area ratio S_c (S_c2) of the tread surface 15a is set to 13 ± 5%.

The shoulder land portion 35 includes a lug groove 351 and a sipe 352. The lug groove 351 opens at one end to the circumferential main groove 24, which is the shoulder main groove, and at the other end to the tire ground contact end T. A plurality of lug grooves 351 are provided in the tire circumferential direction. One end of the lug groove 351 faces the other end of the lug groove 341 via the circumferential main groove 24. The sipe 352 opens to the circumferential main groove 24, which is the shoulder main groove, at one end and opens to the tire ground contact end T at the other end. One sipe 352 is provided between the lug grooves 351 adjacent to each other in the tire circumferential direction, and a plurality of sipes 352 are provided in the tire circumferential direction. Further, the shoulder land portion 35 has a groove area ratio S_s2 of the tread surface 15a of 13 ± 5%.

[Tread rubber]
3 to 5 are enlarged views showing a tread portion of the pneumatic tire shown in FIG. 1. FIG. 3 is an enlarged view of the entire tread portion. FIG. 4 is an enlarged view of a part of the tread portion, showing the shoulder land portion 31 and the center land portion 32. FIG. 5 mainly shows the center land areas 32 to 34.

The tread rubber 15 includes a cap tread rubber 151 and an under tread rubber 152.

The cap tread rubber 151 is made of a rubber material having excellent ground contact characteristics and weather resistance, and is exposed to the tread surface 15a over the entire area of the tire ground contact surface to form the outer surface of the tread portion. The cap tread rubber 151 preferably has a loss tangent (tan δ) Tac in the range of 0.10 or more and 0.30 or less. Further, the cap tread rubber 151 preferably has a rubber hardness Hsc in the range of 60 or more and 70 or less.

Here, the loss tangent (tan δ) is based on JIS-K6394, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), frequency 20 Hz, initial strain 10%, dynamic strain ± 2%, temperature 60 ° C. It is measured under the conditions of. The rubber hardness is JIS-A hardness, which is a durometer hardness measured under the condition of a temperature of 20 ° C. using an A type durometer in accordance with JIS K-6253.

Here, the thickness of the cap tread rubber 151, the under tread rubber 152, and the tread rubber 15 is also referred to as a gauge. The gauges of the cap tread rubber 151, the under tread rubber 152, and the tread rubber 15 are measured on a virtual line (normal line) perpendicular to the tangent line of the tread surface 15a in the cross section in the tire meridional direction.

The cap tread rubber 151 and the under tread rubber 152 are also provided at the maximum groove depth positions of the groove bottoms of the main grooves 21 to 24 in the circumferential direction. The gauges of the cap tread rubber 151 and the under tread rubber 152 provided at the maximum groove depth position of the groove bottoms of the main grooves 21 to 24 in the circumferential direction are called groove bottom gauges. The groove bottom gauges of the circumferential main grooves 21 to 24 are measured in a no-load state in which the tire is mounted on the specified rim and the specified internal pressure is filled. At this time, for example, the following measurement method is used. First, a single tire is applied to the virtual line of the tire profile measured by the laser profiler and fixed with tape or the like. Then, the gauge to be measured is measured with a caliper or the like. The laser profiler used here is a tire profile measuring device (manufactured by Matsuo Co., Ltd.).

The cap tread rubber 151 preferably has a minimum gauge Gac_m of 0.6 mm or more in the groove bottom gauge. Further, the cap tread rubber 151 is preferably 40% or more of the total groove bottom gauge Gat_m of the tread rubber 15 which is the total thickness of the cap tread rubber 151 and the under tread rubber 152 at the minimum gauge Gac_m position (see FIG. 5). ).

The under tread rubber 152 is made of a rubber material having lower hardness and excellent heat resistance than the cap tread rubber 151, and is arranged so as to be sandwiched between the cap tread rubber 151 and the belt layer 14 to form a base portion of the tread rubber 15. Configure. The undertread rubber 152 preferably has a loss tangent Tau of less than 0.10. Further, the under tread rubber 152 preferably has a rubber hardness Hsu in the range of 50 or more and 60 or less.

It is preferable that the loss tangent Tau of the under tread rubber 152 is smaller than the loss tangent Tac of the cap tread rubber 151 (Tac> Tau). The difference between the loss tangent Tac of the cap tread rubber 151 and the loss tangent Tau of the under tread rubber 152 is preferably 0.02 or more.

Further, it is preferable that the rubber hardness Hsu of the under tread rubber 152 is smaller than the rubber hardness Hsc of the cap tread rubber 151 (Hsc> Hsu). The difference between the rubber hardness Hsc of the cap tread rubber 151 and the Hsu of the under tread rubber 152 is preferably 4 or more.

The under tread rubber 152 preferably has a minimum gauge Gau_m in the groove bottom gauge in the range of 0.2 mm or more and 1.0 mm or less. Further, the under tread rubber 152 is preferably 8% or more and 60% or less of the total groove bottom gauge Gat_m of the tread rubber 15 which is the total thickness of the cap tread rubber 151 and the under tread rubber 152 at the minimum gauge Gau_m position ( (See FIG. 5).

Further, in the under tread rubber 152, the average gauge Ga_c (Ga_c1, Ga_c2) in the outer center land portions 32 and 34 of the center land portions 32 to 34 is in the range of 1.5 mm or more and 4.0 mm or less (see FIG. 3). ). Further, the under tread rubber 152 has an average gauge Ga_ce of 1.5 mm or more and 4.0 mm or less in the inner center land portion 33 of the center land portions 32 to 34. Here, the average gauges Ga_c (Ga_c1, Ga_c2) and Ga_ce of the undertread rubber 152 of the center land portion 32 to 34 are 70% of the center in the tire width direction with respect to the tire width direction dimension CW of the center land portion 32 to 34, respectively. In the range CWa, the gauges at the three tire radial positions at both ends a and b in the tire width direction and the center c are averaged (see FIG. 4). The total average gauges Gat_c (Gat_c1, Gat_c2) and Gat_ce of the tread rubber 15 which is the total thickness of the cap tread rubber 151 and the under tread rubber 152 of the center land portion 32 to 34 are also tires of the center land portion 32 to 34, respectively. In the range CWa of 70% of the tire width direction center with respect to the width direction dimension CW, the gauges at the three tire radial positions of both ends a and b and the center c in the tire width direction are averaged and obtained (see FIG. 4). The total average gauges Gat_c (Gat_c1, Gat_c2) and Gat_ce of the tread rubber 15 are the sum of the thicknesses of the cap tread rubber 151 and the under tread rubber 152 from the tread surface 15a, and are not related to the lug grooves 321 to 341 (Fig.). 3). The under tread rubber 152 has a maximum gauge position at the center land portions 32 to 34 (mainly the outer center land portions 32 and 34) of 1.6 mm from the groove bottoms of the main grooves 21 to 24 in the circumferential direction to the outside in the tire radial direction. It is located inside the tire radial direction through the point and parallel to the virtual line Lw parallel to the profile line of the tread surface 15a (see FIG. 5).

Further, in the under tread rubber 152, the average gauges Ga_s1 and Ga_s2 on the shoulder land portions 31 and 35 are in the range of 0.5 mm or more and 3.0 mm or less (see FIG. 3). Here, the average gauges Ga_s1 and Ga_s2 of the undertread rubber 152 of the shoulder land portions 31 and 35 are from the opening end d of the circumferential main grooves 21 and 24, which are the shoulder main grooves, to the tire ground contact end, respectively. Two tire radial directions, the opening end d of the main grooves 21 and 24 in the circumferential direction and the end e of the SWa in a range of 20% from the opening end d to the tire ground contact end T side with respect to the tire width direction dimension SW up to T. Calculate by averaging the gauges at the positions (see FIG. 4). The total average gauges Gat_s1 and Gat_s2 of the tread rubber 15 which is the total thickness of the cap tread rubber 151 and the under tread rubber 152 of the shoulder land portions 31 and 35 are also in the circumferential direction which is the shoulder main groove in the shoulder land portions 31 and 35. 20% of the tire width direction dimension SW from the opening end d of the main grooves 21 and 24 to the tire ground contact end T from the opening end d of the circumferential main grooves 21 and 24 and the opening end d to the tire ground contact end T side. The gauges at the two tire radial positions with the end e of the range WSa are averaged (see FIG. 4). The total average gauges Gat_s1 and Gat_s2 of the tread rubber 15 are the sum of the thicknesses of the cap tread rubber 151 and the under tread rubber 152 from the tread surface 15a, and are not related to the lug grooves 311, 351 (see FIG. 3). In the under tread rubber 152, the maximum gauge position on the shoulder land portions 31 and 35 passes through a point 1.6 mm outward from the groove bottom of each circumferential main groove 21 to 24 in the tire radial direction to the profile line of the tread surface 15a. It is located inside the tire radial direction with respect to the parallel virtual line Lw (see FIG. 5).

[Features and effects]
As described above, the pneumatic tire 1 of the present embodiment includes a carcass layer 13, a pair of crossing belts 141 and 142 arranged radially outside the carcass layer 13, a cap tread rubber 151, and an under tread rubber 152. A pair of shoulder main grooves 21, 24 and shoulder main grooves 21, which are laminated and arranged on the outer side in the radial direction of the cross belts 141 and 142, and the outermost side in the tire width direction of the tread surface 15a, At least one center main groove 22, 23 between 24, a pair of shoulder treads 31, 35 partitioned on the outer side of the shoulder main groove 21, 24 in the tire width direction, and the shoulder main groove 21, 24 and the center main. It includes at least two center treads (inner center tread 33, outer center treads 32, 34) partitioned by grooves 22 and 23.

That is, the pneumatic tire 1 of the present embodiment has, for example, four circumferential main grooves (shoulder main grooves 21, 24, center main grooves 22, 23) as shown in FIGS. 6 to 8. A configuration in which five rows of land (shoulder land 31, 35, outer center land 32, 34, inner center land 33) are partitioned, or three circumferences, for example, as shown in FIGS. 9 and 10. It has four rows of land (shoulder land 31, 35, inner center land 33, outer center land 32 (34)) with directional main grooves (shoulder main grooves 21, 24, center main groove 22 (23)). ) Is partitioned, and for example, although not clearly shown in the figure, it includes a configuration in which six rows of land parts are partitioned with five circumferential main grooves.

Then, as shown in FIG. 3, the pneumatic tire 1 of the present embodiment has an average gauge Ga_ce of the under tread rubber 152 on the tire equatorial plane CL or the inner center land portion 33 closest to the tire equatorial plane CL, and other tires. The average gauge Ga_c (Ga_c1, Ga_c2) of the under tread rubber 152 in at least one outer center land portion 32, 34 and the average gauge Ga_s1, Ga_s2 of the under tread rubber 152 in each shoulder land portion 31, 35 are Ga_s1 <Ga_ce. , Ga_s2 <Ga_ce, Ga_c <Ga_ce. Further, in the pneumatic tire 1 of the present embodiment, the groove area ratio S_ce of the tread surface 15a in the inner center land portion 33 and the groove area ratio S_c of the tread surface 15a in at least one outer center land portion 32, 34 are set. It has a relationship of S_c <S_ce.

Therefore, in this pneumatic tire 1, the average gauge Ga_ce of the inner center land portion 33 is made thicker than the average gauge Ga_s1 and Ga_s2 of each shoulder land portion 31.35 for the under tread rubber 152, so that each shoulder land portion 31 The rubber volumes of the under tread rubber 152 are different between .35 and the inner center land 33. Further, the pneumatic tire 1 has at least one outer side by increasing the average gauge Ga_ce of the inner center land portion 33 with respect to the average gauge Ga_c of at least one outer center land portion 32, 34 for the under tread rubber 152. The rubber volumes of the under tread rubber 152 are different between the center land portion 32.34 and the inner center land portion 33. Moreover, in this pneumatic tire 1, the groove area ratio S_ce of the tread surface 15a of the inner center land portion 33 is made smaller than the groove area ratio S_c of the tread surface 15a of at least one outer center land portion 32, 34. , At least one outer center land portion 32, 34 and the inner center land portion 33 have different rubber rigidity. Therefore, in the pneumatic tire 1, the rubber volume of the under tread rubber 152 is relatively large in the inner center land portion 33, the vibration coefficient is lowered, the road noise is reduced, the noise performance is improved, and the rolling leads to low fuel consumption. Contributes to reduction of resistance. Further, in the pneumatic tire 1, the rubber volume of the under tread rubber 152 is relatively small in the shoulder land portions 31, 35 and at least one outer center land portion 32, and the deterioration of durability performance is suppressed. Moreover, in the pneumatic tire 1, the rubber volume of the under tread rubber 152 at the inner center land portion 33 is relatively increased to increase the rubber rigidity, and the groove area ratio of the tread surface 15a is increased to increase the groove area ratio from the road surface. By reducing the input of, the deterioration of steering stability performance is suppressed. As a result, the pneumatic tire 1 can secure steering stability performance while improving noise performance and rolling resistance.

Further, in the pneumatic tire 1 of the present embodiment, the average gauge Ga_c of the under tread rubber 152 in at least one outer center land portion 32, 34 and the average gauge Ga_s1 of the under tread rubber 152 in each shoulder land portion 31.35. It is preferable that Ga_s2 has a relationship of Ga_s1 <Ga_c and Ga_s2 <Ga_c.

Therefore, the pneumatic tire 1 reduces road noise and has noise performance by increasing the rubber volume of the under tread rubber 152 at at least one outer center land portion 32, 34 with respect to the shoulder land portions 31, 35. It also contributes to the improvement of rolling resistance, which leads to low fuel consumption.

Further, in the pneumatic tire 1 of the present embodiment, the groove area ratio S_ce of the tread surface 15a in the inner center land portion 33 and the groove area ratio S_c of the tread surface 15a in at least one outer center land portion 32, 34 are obtained. It is preferable that the groove area ratios S_s1 and S_s2 of the tread surface 15a on the shoulder land portions 31 and 35 have a relationship of S_s1 <S_ce, S_s2 <S_ce, S_s1 <S_c, S_s2 <S_c.

Therefore, the pneumatic tire 1 has a groove area of the tread surface 15a on the outer center land portion 32, 34 with respect to a groove area ratio of the tread surface 15a on the inner center land portion 33 and at least one outer center land portion 32, 34. By reducing the ratio, the rubber rigidity of the outer center land areas 32 and 34 is increased, and steering stability performance is ensured.

Further, in the pneumatic tire 1 of the present embodiment, the total average gauge Ga_ce of the tread rubber 15 in the inner center land portion 33 and the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 33 are Ga_ce / Gat_ce = 0. It has a relationship of .30 ± 0.05 (0.25 ≤ Ga_ce / Gat_ce ≤ 0.35), and the total average gauge Gat_c of the tread rubber 15 in at least one outer center land portion 32, 34 and the outer center land. It is preferable that the average gauge Ga_c of the under tread rubber 152 in portions 32 and 34 has a relationship of Ga_c / Gat_c = 0.23 ± 0.05 (0.18 ≦ Ga_c / Gat_c ≦ 0.28). Further, in the pneumatic tire 1 of the present embodiment, the total average gauge Ga_s1 of the tread rubber 15 on one shoulder land portion 31 and the average gauge Ga_s1 of the under tread rubber 152 on one shoulder land portion 31 are Ga_s1 / Gat_s1. It has a relationship of ≤0.20, and the total average gauge Ga_s2 of the tread rubber 15 on the other shoulder land portion 35 and the average gauge Ga_s2 of the under tread rubber 152 on the other shoulder land portion 35 are Ga_s2 / Gat_s2 ≤0. It is preferable to have a relationship of .20.

Therefore, in the pneumatic tire 1, the under tread rubber 152 in the inner center land portion 33 is defined to be relatively thicker than the other land portions, thereby reducing road noise and improving noise performance. It also contributes to the reduction of rolling resistance that leads to low fuel consumption.

Further, in the pneumatic tire 1 of the present embodiment, the average gauge Ga_ca of the under tread rubber 152 in the inner center land portion 33 and the average gauge Ga_c of the under tread rubber 152 in at least one outer center land portion 32, 34 are 1. The maximum gauge of each under tread rubber 152 in each center land portion 32, 33, 34 in the range of .5 mm or more and 4.0 mm or less is the outer side in the tire radial direction from the groove bottom of each main groove 21, 22, 23, 24. It is preferable that the tire is located inside the tire radial direction with respect to the virtual line Lw which passes through the point 1.6 mm and is parallel to the profile line of the tread surface.

Therefore, the pneumatic tire 1 can prevent the under tread rubber 152 of each center land portion 32, 33, 34 from being exposed to the tread tread even when the tread portion reaches the wear life (end of wear).

Further, in the pneumatic tire 1 of the present embodiment, the cap tread rubber 151 preferably has a minimum gauge Gac_m of 0.6 mm or more in the groove bottom gauge. Moreover, in the pneumatic tire 1 of the present embodiment, the cap tread rubber 151 is 40% of the total groove bottom gauge Gat_m of the tread rubber 15 which is the total thickness of the cap tread rubber 151 and the under tread rubber 152 at the minimum gauge Gac_m position. The above is preferable.

Therefore, in the pneumatic tire 1, by securing the groove bottom gauge of the cap tread rubber 151, it is possible to suppress the occurrence of cracks in the groove bottoms of the main grooves 21, 22, 23, 24 due to repeated strain. The minimum gauge Gac_m in the groove bottom gauge of the cap tread rubber 151 is preferably 0.7 mm or more, and the occurrence of cracks in the groove bottoms of the main grooves 21, 22, 23, 24 can be further suppressed.

Further, in the pneumatic tire 1 of the present embodiment, the average gauges Ga_s1 and Ga_s2 of the under tread rubber 152 in the shoulder land portions 31 and 35 have a relationship of 0.98 ≦ Ga_s1 / Ga_s2 ≦ 1.02, respectively. It is preferable that the groove area ratios S_s1 and S_s2 of the tread surfaces 15a on the shoulder land portions 31 and 35 have a relationship of 0.97 ≦ S_s1 / S_s2 ≦ 1.03.

Therefore, the pneumatic tire 1 has the same rubber volume and rigidity of the tread rubber 152 by making the average gauge and groove area ratio of the under tread rubber 152 in the shoulder land portions 31 and 35 the same, and has the same steering stability performance. To secure more.

Further, in the pneumatic tire 1 of the present embodiment, the loss tangent Tac of the cap tread rubber 151 at 60 ° C. and the loss tangent Tau of the under tread rubber 152 at 60 ° C. are 1.20 ≦ Tac / Tau ≦ 13.0. It is preferable to have the relationship of.

That is, in this pneumatic tire 1, the loss tangent at 60 ° C. is smaller in the under tread rubber 152 than in the cap tread rubber 151. Therefore, this pneumatic tire 1 can reduce road noise and contribute to the improvement of noise performance by defining the average gauge of the undertread rubber 152 having a small loss tangent at 60 ° C., and the rolling resistance that leads to low fuel consumption. It can contribute by reduction. In the pneumatic tire 1 of the present embodiment, the cap tread rubber 151 has a loss tangent Tac of 0.10 or more at 60 ° C., and the undertread rubber 152 has a loss tangent Tau of less than 0.10 at 60 ° C. Is preferable.

Further, in the pneumatic tire 1 of the present embodiment, it is preferable that the rubber hardness Hsc of the cap tread rubber 151 and the rubber hardness Hsu of the under tread rubber 152 have a relationship of HSc> HSu.

Therefore, the pneumatic tire 1 can reduce road noise and contribute to the improvement of noise performance by defining the average gauge of the undertread rubber 152 having a small rubber hardness, and by reducing the rolling resistance leading to low fuel consumption. Can contribute. In the pneumatic tire 1 of the present embodiment, the rubber hardness Hsc of the cap tread rubber 151 and the rubber hardness Hsu of the under tread rubber 152 have a relationship of 1.10 ≦ HSc / HSu ≦ 1.80. Is preferable. Further, in the pneumatic tire 1 of the present embodiment, the rubber hardness Hsc of the cap tread rubber 151 is in the range of 60 or more and 70 or less, and the rubber hardness Hsu of the under tread rubber 152 is in the range of 50 or more and 60 or less. Is preferable.

Further, in the pneumatic tire 1 of the present embodiment, the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 33 and the average gauge Ga_c of the under tread rubber 152 in at least one outer center land portion 32, 34 are one of them. The average gauge Ga_s1 of the under tread rubber 152 on the shoulder land portion 31 and the average gauge Ga_s2 of the under tread rubber 152 on the other shoulder land portion 35 are 1.20 ≦ Ga_ce / Ga_s1 ≦ 2.10, 1.30 ≦. It is preferable to have a relationship of Ga_ce / Ga_c ≦ 2.60 and 0.90 ≦ Ga_s1 / Ga_s2 ≦ 1.10. Further, in the pneumatic tire 1 of the present embodiment, the groove area ratio S_ce of the tread surface 15a in the inner center land portion 33 and the groove area ratio S_c of the tread surface 15a in at least one outer center land portion 32, 34 are obtained. The groove area ratios S_s1 and S_s2 of the tread surface 15a on the shoulder land portions 31 and 35 are 1.10 ≦ S_ce / S_c ≦ 1.50, 0.70 ≦ S_c / S_s1 ≦ 0.90, 0.80 ≦ S_s1 /. It is preferable to have a relationship of S_s2 ≦ 1.20.

Therefore, the pneumatic tire 1 has an average gauge relationship of the under tread rubber 152 between the inner center land portion 33 and one shoulder land portion 31, and the inner center land portion 33 and at least one outer center land portion 32, 34. The relationship between the average gauges of the under tread rubber 152 and the average gauge of the under tread rubber 152 of each shoulder land 31 is specified, and the tread between the inner center land 33 and at least one outer center land 32, 34. Relationship of groove area ratio of surface 15a, relationship of groove area ratio of tread surface 15a between at least one outer center land portion 32, 34 and one shoulder land portion 31, groove area of tread surface 15a of each shoulder land portion 31. By defining the ratio relationship, it is possible to remarkably obtain the effect of ensuring steering stability performance while improving noise performance and rolling resistance. In addition, 1.1 ≦ Ga_ce / Ga_s2 ≦ 1.3, 1.1 ≦ Ga_c1 / Ga_s1 ≦ 1.3, 1.1 ≦ Ga_c2 / Ga_s2 ≦ 1.3, 1.1 ≦ S_ce / S_s1 ≦ 1.4, By having the relationship of 1.1 ≦ S_ce / S_s2 ≦ 1.4, it is possible to obtain a more remarkable effect of ensuring steering stability performance while improving noise performance and rolling resistance.

Further, in the pneumatic tire 1 of the present embodiment, the groove area ratio S_ce of the tread surface 15a in the inner center land portion 33 and the groove area ratio S_c of the tread surface 15a in at least one outer center land portion 32, 34 are one of the two. The groove area ratio S_s1 of the tread surface 15a on the shoulder land portion 31 and the groove area ratio S_s2 of the tread surface 35 on the other shoulder land portion 35 are S_ce = 16 ± 5% (11% ≤ S_c ≤ 21%). S_c (S_c1, S_c2) = 13 ± 5% (8% ≤ S_c ≤ 18%), S_s1 = 13 ± 5% (8% ≤ S_s1 ≤ 18%), S_s2 = 13 ± 5% (8% ≤ S_s2 ≤ 18) %) Is preferable.

Therefore, the pneumatic tire 1 can be steered while improving noise performance and rolling resistance by defining the groove area ratio of the tread surface 15a of each outer center land portion 32, 34 and each shoulder land portion 31, 35. The effect of ensuring stable performance can be remarkably obtained.

In the example shown in FIG. 6, the four main grooves 21, 22, 23, 24 have an undertread rubber in one outer center land portion 32 with respect to the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 33. The average gauge Ga_c of 152 is small, and the average gauges Ga_s1 and Ga_s2 of the under tread rubber 152 at the shoulder land portions 31 and 35 are smaller. Further, in the example shown in FIG. 7, the four main grooves 21, 22, 23, 24 have an undertread rubber in the other outer center land portion 34 with respect to the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 33. The average gauge Ga_c of 152 is small, and the average gauges Ga_s1 and Ga_s2 of the under tread rubber 152 at the shoulder land portions 31 and 35 are smaller. Further, in the example shown in FIG. 8, in the four main grooves 21, 22, 23, 24, the undertread rubber 152 in each outer center land portion 32 with respect to the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 33. The average gauge Ga_c of the above and the average gauges Ga_s1 and Ga_s2 of the under tread rubber 152 at the shoulder land portions 31 and 35 both represent a small form. Further, in the example shown in FIG. 9, the three main grooves 21, 22, (23), and 24 have the outer center land portion 32 (33) with respect to the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 34 (33). ), The average gauge Ga_c of the undertread rubber 152 is small, and the average gauges Ga_s1 and Ga_s2 of the undertread rubber 152 at the shoulder land portions 31 and 35 are smaller. Further, in the example shown in FIG. 10, the three main grooves 21, 22, (23) and 24, have the outer center land portion 32 (33) with respect to the average gauge Ga_ce of the under tread rubber 152 in the inner center land portion 34 (33). ), The average gauge Ga_c of the undertread rubber 152 and the average gauges Ga_s1 and Ga_s2 of the undertread rubber 152 at the shoulder land portions 31 and 35 both represent small forms.

FIG. 11 is a chart showing the results of a performance test of the pneumatic tire according to the present embodiment.

In this performance test, multiple types of test tires were evaluated for rolling resistance performance, noise performance, and steering stability performance. Further, in this performance test, a test tire having a tire size of 195 / 65R15 91H is assembled to a rim having a rim size of 15 × 6J, and JATTA's specified internal pressure (230 kPa) is applied to this test tire.

In the evaluation of rolling resistance performance, a drum tester with a rim diameter of 1707 [mm] was used, and the rolling resistance coefficient of the test tire was calculated under the conditions of a load of 4.8 kN, an air pressure of 230 kPa, and a speed of 80 km / h in accordance with ISO28580. Was done. This evaluation is performed by an index evaluation based on the conventional example (100), and the larger the value, the smaller the rolling resistance, which is preferable.

In the evaluation of noise performance, a test vehicle (domestic sedan type) equipped with test tires on all wheels traveled on a test course on a dry road surface at a speed of 60 km / h, and the microphone installed at the driver's seat ear position in the test vehicle was used to overall The noise level inside the vehicle (road noise) in the (all frequency range) is measured and evaluated. This evaluation is performed by an index evaluation based on the conventional example (100), and the larger the value, the lower the noise level, which is preferable.

In the evaluation of steering stability performance, the test vehicle traveled on a test course on a dry road surface at a speed of 60 km / h to 100 km / h, and the test driver made a sensory evaluation of the steerability at the time of race change and cornering and the stability at the time of straight running. Was done. This evaluation is performed by an index evaluation based on the conventional example (100), and the larger the value is 99 or more, the higher the steering stability is preferable.

The test tires of Examples 1 to 8 have the configurations of FIGS. 1 to 3 and have an average gauge Ga_ce of undertread rubber 152 in the inner center land portion 33 and at least one other outer center land portion 32,34. The relationship between the average gauge Ga_c (Ga_c1, Ga_c2) of the undertread rubber 152 in the above and the average gauges Ga_s1 and Ga_s2 of the undertread rubber 152 in the shoulder land portions 31 and 35 is Ga_s1 <Ga_ce, Ga_s2 <Ga_ce, Ga_c <Ga_ce The groove area ratio S_ce of the tread surface 15a on the inner center land portion 33 and the groove area ratio S_c (S_c1, S_c2) of the tread surface 15a on at least one outer center land portion 32, 34 are S_c <S_ce. Have a relationship of.

The test tire of the ninth embodiment does not have the outer center land portion 34, has one center main groove 22, and is inside, as shown in FIGS. 9 and 10 in the configurations of FIGS. 1 to 3. The average gauge Ga_ce of the under tread rubber 152 in the center land portion 33, the average gauge Ga_c (Ga_c1) of the under tread rubber 152 in the outer center land portion 32, and the average gauge Ga_s1 of the under tread rubber 152 in each of the shoulder land portions 31 and 35. , Ga_s2 have a relationship of Ga_s1 <Ga_ce, Ga_s2 <Ga_ce, Ga_c <Ga_ce, and the groove area ratio S_ce of the tread surface 15a in the inner center land portion 33 and the groove area of the tread surface 15a in the outer center land portion 32. The ratio S_c (S_c1) has a relationship of S_c <S_ce.

In the test tire of the conventional example 1, in the configurations of FIGS. 1 to 3, the average gauge of the under tread rubber 152 in all the land portions 31 to 35 is the same. Further, the test tire of the conventional example 2 does not have the outer center land portion 34 and has one center main groove 22 as shown in FIGS. 9 and 10 in the configurations of FIGS. 1 to 3. , The average gauge of the undertread rubber 152 in all the land 31, 32, 33, 35 is the same.

The groove area ratio is represented by the relationship of large> medium> small, and in each conventional example, comparative example, and each embodiment, the relationship is large = large, medium = medium, and small = small.

As shown in the test results, it can be seen that the test tires of Examples 1 to 8 can secure steering stability performance while improving noise performance and rolling resistance as compared with Conventional Example 1. As shown in the test results, it can be seen that the test tire of Example 9 can secure steering stability performance while improving noise performance and rolling resistance as compared with Conventional Example 2.

1 Pneumatic tire 13 Carcus layer 141,142 Cross belt 15 Tread rubber 15a Tread surface 151 Cap tread rubber 152 Under tread rubber 21,24 Shoulder main groove 22,23 Center main groove 31,35 Shoulder land 32,34 Outer center land Department 33 Inner Center Land

Claims (9)

A tread layer, a pair of cross belts arranged radially outside the carcass layer, a cap tread rubber and an under tread rubber laminated, and a tread rubber and a tread arranged radially outside the cross belt. A pair of shoulder main grooves formed on the outermost surface in the tire width direction, at least one center main groove between the shoulder main grooves, and a pair of shoulder treads partitioned on the outer side of the shoulder main groove in the tire width direction. A pneumatic tire comprising a portion and at least two center treads partitioned by the shoulder main groove and the center main groove.
The average gauge Ga_ce of the undertread rubber on the tire equatorial plane or the inner center land portion closest to the tire equatorial plane, the average gauge Ga_c of the undertread rubber on the other at least one outer center land portion, and each of the shoulders. The average gauges Ga_s1 and Ga_s2 of the undertread rubber in the land portion have a relationship of Ga_s1 <Ga_ce, Ga_s2 <Ga_ce, Ga_c <Ga_ce.
The groove area ratio S_ce of the tread surface in the inner center land portion and the groove area ratio S_c of the tread surface in at least one outer center land portion have a relationship of S_c <S_ce.
Pneumatic tires. The average gauge Ga_c of the undertread rubber in at least one outer center land portion and the average gauge Ga_s1, Ga_s2 of the undertread rubber in each shoulder land portion have a relationship of Ga_s1 <Ga_c, Ga_s2 <Ga_c.
The pneumatic tire according to claim 1. The groove area ratio S_ce of the tread surface in the inner center land portion, the groove area ratio S_c of the tread surface in at least one outer center land portion, and the groove area ratio S_s1 of the tread surface in each of the shoulder land portions. S_s2 has a relationship of S_s1 <S_ce, S_s2 <S_ce, S_s1 <S_c, S_s2 <S_c.
The pneumatic tire according to claim 1 or 2. The average gauge Gat_ce of the tread rubber in the inner center land portion and the average gauge Ga_ce of the under tread rubber in the inner center land portion have a relationship of Ga_ce / Gat_ce = 0.30 ± 0.05.
The average gauge Gat_c of the tread rubber in at least one outer center land portion and the average gauge Ga_c of the under tread rubber in the outer center land portion have a relationship of Ga_c / Gat_c = 0.23 ± 0.05. And
The average gauge Ga_s1 of the tread rubber on one shoulder land portion and the average gauge Ga_s1 of the under tread rubber on one shoulder land portion have a relationship of Ga_s1 / Gat_s1 ≦ 0.20.
The average gauge Ga_s2 of the tread rubber on the other shoulder land portion and the average gauge Ga_s2 of the under tread rubber on the other shoulder land portion have a relationship of Ga_s2 / Gat_s2 ≦ 0.20.
The pneumatic tire according to any one of claims 1 to 3. The average gauge Ga_ca of the undertread rubber in the inner center land portion and the average gauge Ga_c of the undertread rubber in at least one outer center land portion are in the range of 1.5 mm or more and 4.0 mm or less.
The maximum gauge of each undertread rubber in each of the center land portions is more than a virtual line parallel to the profile line of the tread surface through a point 1.6 mm outward in the tire radial direction from the groove bottom of each main groove. , Located inside the tire radial direction,
The pneumatic tire according to any one of claims 1 to 4. The average gauges Ga_s1 and Ga_s2 of the undertread rubber in each shoulder land portion have a relationship of 0.98 ≦ Ga_s1 / Ga_s2 ≦ 1.02.
The groove area ratios S_s1 and S_s2 of the tread surface in each shoulder land portion have a relationship of 0.97 ≦ S_s1 / S_s2 ≦ 1.03.
The pneumatic tire according to any one of claims 1 to 5. The loss tangent Tac of the cap tread rubber at 60 ° C. and the loss tangent Tau of the under tread rubber at 60 ° C. have a relationship of 1.20 ≦ Tac / Tau ≦ 13.0.
The pneumatic tire according to any one of claims 1 to 6. The rubber hardness Hsc of the cap tread rubber and the rubber hardness Hsu of the under tread rubber have a relationship of HSc> HSu.
The pneumatic tire according to any one of claims 1 to 7. The average gauge Ga_ce of the undertread rubber in the inner center land portion, the average gauge Ga_c of the undertread rubber in at least one outer center land portion, and the average gauge Ga_s1 of the undertread rubber in one of the shoulder land portions. And the average gauge Ga_s2 of the under tread rubber on the other shoulder land portion are 1.20 ≦ Ga_ce / Ga_s1 ≦ 2.10, 1.30 ≦ Ga_ce / Ga_c ≦ 2.60, 0.90 ≦ Ga_s1 /. It has a relationship of Ga_s2 ≤ 1.10 and has a relationship of Ga_s2 ≤ 1.10.
The groove area ratio S_ce of the tread surface in the inner center land portion, the groove area ratio S_c of the tread surface in at least one outer center land portion, and the groove area ratio S_s1 of the tread surface in each of the shoulder land portions. S_s2 has a relationship of 1.10 ≦ S_ce / S_c ≦ 1.50, 0.70 ≦ S_c / S_s1 ≦ 0.90, 0.80 ≦ S_s1 / S_s2 ≦ 1.20.
The pneumatic tire according to any one of claims 1 to 8.

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