JP7448781B2 - pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that can reduce the rolling resistance of the tire when running in a low-temperature atmosphere while suppressing fluctuations in tire fuel efficiency caused by changes in ambient temperature. .

Focusing on the fact that in conventional pneumatic tires, the tire temperature when running at room temperature is approximately 60 [℃], the tan δ value (loss tangent) of the tread rubber at 60 [℃] is set low. This reduces the rolling resistance of the tire. At the same time, the wet performance of the tire is ensured by setting a high tan δ value of the tread rubber (particularly the cap rubber constituting the tire contact surface) at 0[° C.].

However, the above configuration has a problem in that the rolling resistance of the tire deteriorates when running in a low-temperature atmosphere. As a conventional pneumatic tire related to such a problem, a technique described in Patent Document 1 is known.

Patent No. 5998310

On the other hand, when the ambient temperature during driving changes due to seasonal changes, the rolling resistance of the tire also changes. Therefore, there is a problem that the fuel efficiency of the tire fluctuates due to changes in the ambient temperature.

Therefore, the present invention has been made in view of the above, and is capable of reducing the rolling resistance of tires when running in low-temperature atmospheres while suppressing fluctuations in tire fuel efficiency caused by changes in ambient temperature. The purpose is to provide pneumatic tires.

In order to achieve the above object, a pneumatic tire according to the present invention includes a pair of bead cores, a pair of bead fillers arranged radially outside of the bead cores, a carcass layer spanning the bead cores, and a carcass layer extending over the bead cores. a belt layer disposed radially outward of the layers; a tread rubber composed of a cap tread and an undertread disposed radially outward of the belt layer; and a pair of tread rubber disposed radially outward of the carcass layer. A pneumatic tire comprising a sidewall rubber and a pair of rim cushion rubbers arranged radially inside the pair of bead cores, wherein the tan δ value T20_rc of the rim cushion rubber at 20 [°C] and 60 [°C] It is characterized in that the tan δ value T60_rc in satisfies the conditions of 0.70≦T20_rc/T60_rc≦1.30 and T20_rc≦0.22.

In the pneumatic tire according to the present invention, (1) the ratio T20/T60 of the tan δ value T20 at 20 [°C] and the tan δ value T60 at 60 [° C] of the rim cushion rubber is optimized; The difference between resistance and rolling resistance at room temperature can be reduced. Furthermore, (2) since the tan δ value T20 at 20 [° C.] of the rim cushion rubber is within the above range, rolling resistance in a low temperature atmosphere is reduced. This has the advantage of reducing the rolling resistance of the tire when running in a low-temperature atmosphere while suppressing fluctuations in the fuel efficiency of the tire due to changes in ambient temperature.

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 an enlarged view showing a bead portion of the pneumatic tire shown in FIG. 1. FIG. FIG. 3 is an enlarged view showing the tread portion of the pneumatic tire shown in FIG. 1. FIG. FIG. 4 is a chart showing the results of a performance test of the pneumatic tire according to the embodiment of the present invention.

Hereinafter, this invention will be explained in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Further, the constituent elements of this embodiment include elements that can be replaced while maintaining the identity of the invention and are obvious to be replaced. Further, the plurality of modifications described in this embodiment can be arbitrarily combined within the range obvious to 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 an embodiment of the present invention. This 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.

In the figure, a cross section in the tire meridian direction is defined as a cross section when the tire is cut along a plane that includes the tire rotation axis (not shown). Further, the tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire cross-sectional width measurement points specified by JATMA and is perpendicular to the tire rotation axis. Further, the tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis. Further, point P is the tire maximum width position.

The pneumatic tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, and a tread rubber 15. , a pair of sidewall rubbers 16, 16, a pair of rim cushion rubbers 17, 17, and an inner liner 18 (see FIG. 1).

The pair of bead cores 11, 11 are formed by winding one or more bead wires made of steel in an annular manner and multiple times, and are embedded in the bead portions to constitute the cores of the left and right bead portions. The pair of bead fillers 12, 12 are arranged on the outer peripheries of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

The carcass layer 13 has a single layer structure consisting of one carcass ply or a multilayer structure consisting of a plurality of carcass plies laminated, and is stretched in a toroidal shape between the left and right bead cores 11, 11, and is the frame of the tire. Configure. Further, both ends of the carcass layer 13 are wound back and locked outward in the tire width direction so as to wrap around the bead core 11 and bead filler 12. Further, the carcass ply of the carcass layer 13 is constructed by rolling a plurality of carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with coated rubber, and has an 80 [deg. The cord angle (defined as the inclination angle of the carcass cord in the longitudinal direction with respect to the tire circumferential direction) is greater than or equal to 100 [deg] or less.

In addition, in the structure of FIG. 1, the carcass layer 13 has a single layer structure consisting of a single carcass ply. However, the present invention is not limited to this, and the carcass layer 13 may have a multilayer structure formed by laminating two or more carcass plies (not shown).

Moreover, in the configuration of FIG. 1, the carcass layer 13 has a continuous structure in the tire width direction, and extends across the tire equatorial plane CL to the left and right regions of the tire. However, the present invention is not limited to this, and the carcass layer 13 may have a structure (so-called carcass split structure) consisting of a pair of left and right carcass plies, which have a dividing part in the tread part and are separated in the tire width direction. omission).

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

The pair of crossed belts 141 and 142 are constructed by rolling a plurality of belt cords made of steel or organic fibers coated with rubber, and have a cord angle of 15 [deg] or more and 55 [deg] or less in absolute value. have Further, the pair of crossing belts 141 and 142 have cord angles of opposite signs (defined as an inclination angle in the longitudinal direction of the belt cords with respect to the tire circumferential direction), and the longitudinal direction of the belt cords crosses each other. (so-called cross-ply structure). Further, the pair of crossing belts 141 and 142 are stacked and arranged on the outside of the carcass layer 13 in the tire radial direction.

The belt cover 143 and the belt edge cover 144 are constructed by covering 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. The belt cover 143 and the belt edge cover 144 are, for example, strip materials made by covering one or more belt cover cords with coated rubber, and these strip materials are applied to the outer peripheral surfaces of the crossed belts 141 and 142. It is constructed by spirally wrapping the tire multiple times in the circumferential direction of the tire. Further, a belt cover 143 is arranged to cover the entire area of the crossing belts 141, 142, and a pair of belt edge covers 144, 144 are arranged to cover the left and right edge portions of the crossing belts 141, 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 constitute a tread portion of the tire. Further, the tread rubber 15 includes a cap tread 151 and an undertread 152. The cap tread 151 is made of a rubber material with excellent ground contact characteristics and weather resistance, and is exposed on the tread surface over the entire tire contact surface, and constitutes the outer surface of the tread portion. The undertread 152 is made of a rubber material that has better heat resistance than the cap tread 151, is sandwiched between the cap tread 151 and the belt layer 14, and forms a base portion of the tread rubber 15.

A pair of sidewall rubbers 16, 16 are arranged on the outside of the carcass layer 13 in the tire width direction, respectively, and constitute left and right sidewall portions. For example, in the configuration shown in FIG. 1, the outer end of the sidewall rubber 16 in the tire radial direction is disposed below the tread rubber 15 and sandwiched between the belt layer 14 and the carcass layer 13. However, the present invention is not limited thereto, and the outer end of the sidewall rubber 16 in the tire radial direction may be disposed on the outer layer of the tread rubber 15 and exposed to the buttress portion of the tire (not shown).

A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the rolled-up portion of the left and right bead cores 11, 11 and the carcass layer 13, and constitute a rim fitting surface of the bead portion. For example, in the configuration shown in FIG. 1, the outer end of the rim cushion rubber 17 in the tire radial direction is inserted into the lower layer of the sidewall rubber 16 and placed between the sidewall rubber 16 and the carcass layer 13. ing.

The inner liner 18 is an air permeation prevention layer disposed on the inner cavity surface of the tire to cover the carcass layer 13, and suppresses oxidation due to exposure of the carcass layer 13, and also prevents air filled in the tire from leaking. The inner liner 18 is made of, for example, a rubber composition containing butyl rubber as a main component, a thermoplastic resin, a thermoplastic elastomer composition obtained by blending an elastomer component into the thermoplastic resin, or the like.

[Characteristics of tire rubber components]
In this pneumatic tire 1, each rubber member constituting the tire casing has the following configuration in order to reduce rolling resistance in a room temperature atmosphere and a low temperature atmosphere while ensuring wet performance of the tire.

First, the tan δ value T0_ct at 0 [°C] and the tan δ value T60_ct at 60 [°C] of the cap tread 151 have a relationship of 2.00≦T0_ct/T60_ct≦4.38, and 3.00≦T0_ct/T60_ct≦ It is preferable to have a relationship of 4.35, and more preferably a relationship of 3.10≦T0_ct/T60_ct≦4.31. This makes it possible to improve the tire's wet performance while reducing the temperature dependence of the tire's fuel efficiency.

Loss tangent tan δ is measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under the conditions of predetermined temperature, shear strain 10 [%], amplitude ±0.5 [%], and frequency 20 [Hz]. be done.

The tan δ value at 0 [° C.] is an index related to tire performance when driving on a wet road surface. In addition, the tan δ value at 20 [°C] is an index assuming the tire temperature when running at an ambient temperature of approximately 10 [°C], and the tan δ value at 60 [°C] is an index assuming an ambient temperature of approximately 25 [°C]. This index assumes the tire temperature when driving at Further, the ratio of these tan δ values is an index of the temperature dependence of the rubber member.

Further, the tan δ value T20_ct at 20 [°C] and the tan δ value T60_ct at 60 [° C.] of the cap tread 151 have a relationship of 1.60≦T20_ct/T60_ct≦1.90, and 1.70≦T20_ct/T60_ct≦ It is preferable to have a relationship of 1.80. As a result, the difference between the rolling resistance in a low-temperature atmosphere and the rolling resistance in a normal-temperature atmosphere is reduced, and the temperature dependence of the tire's fuel efficiency is reduced.

Further, the tan δ value T0_ct of the cap tread 151 at 0 [° C.] is in the range of T0_ct≦0.75. Further, the tan δ value T20_ct of the cap tread at 20 [° C.] is in the range of T20_ct≦0.48. Further, the tan δ value T60_ct of the cap tread at 60 [° C.] is in the range of T60_ct≦0.38. This improves the wet performance of the tire while reducing rolling resistance in low-temperature and high-temperature atmospheres. Note that the lower limits of T0_ct, T20_ct, and T60_ct are not particularly limited and are preferably as close to 0 as possible, but are restricted by the above ratio conditions.

Further, the rubber hardness Hs_ct of the cap tread 151 at 20 [° C.] is in the range of 50≦Hs_ct≦75. Further, the modulus of the cap tread 151 at 100 [%] elongation is in the range of 1.0 [MPa]≦E'_ct≦3.5 [MPa].

Rubber hardness is measured in accordance with JIS K6253.

The modulus is measured by a tensile test at a temperature of 20 [° C.] using a dumbbell-shaped test piece in accordance with JIS K6251 (using a No. 3 dumbbell).

Further, the tan δ value T20 at 20 [°C] and the tan δ value T60 at 60 [° C] of rubber members other than the cap tread 151 constituting the tire casing have a relationship of 0.50≦T20/T60≦2.00. , 0.65≦T20/T60≦1.55, and more preferably 0.80≦T20/T60≦1.50.

Specifically, as the above-mentioned rubber member, at least one of the bead filler 12, the undertread 152 of the tread rubber 15, the sidewall rubber 16, and the rim cushion rubber 17 satisfies the above conditions. Detailed conditions regarding these rubber members will be described later. Further, for example, the coating rubber of the bead wire of the bead core 11, the coating rubber of the carcass cord of the carcass layer 13, and the coating rubber of the belt cord of the belt layer 14 may satisfy the above conditions.

In the above configuration, the ratio T20/T60 of the tan δ value T20 at 20 [°C] and the tan δ value T60 at 60 [° C] of the rubber member is optimized, so the rolling resistance in a low temperature atmosphere and the rolling resistance in a normal temperature atmosphere are optimized. It is possible to reduce the difference between This makes it possible to suppress fluctuations in tire fuel efficiency caused by changes in ambient temperature (for example, seasonal changes).

Further, the tan δ value T20 of the rubber member at 20 [° C.] is in the range of T20≦0.22, and preferably in the range of T20≦0.15. Further, the tan δ value T60 of the rubber member at 60 [° C.] is in the range of T60≦0.17. The lower limits of T20 and T60 are not particularly limited and are preferably as close to 0 as possible; however, they are restricted by the above ratio conditions. This reduces rolling resistance in a low-temperature atmosphere.

[Characteristics of bead filler]
Furthermore, the tan δ value T20_bf at 20 [°C] and the tan δ value T60_bf at 60 [°C] of the bead filler 12 have a relationship of 0.90≦T20_bf/T60_bf≦1.05, and 0.91≦T20_bf/T60_bf≦ It is preferable to have a relationship of 1.04, and more preferably a relationship of 0.92≦T20_bf/T60_bf≦1.03. This makes it possible to reduce the difference between the rolling resistance under a low temperature atmosphere and the rolling resistance under a normal temperature atmosphere.

Further, the tan δ value T20_bf of the bead filler 12 at 20 [°C] is in the range of T20_bf≦0.18, preferably in the range of T20_bf≦0.17, and preferably in the range of T20_bf≦0.16. More preferred. Further, the tan δ value T60_bf of the bead filler 12 at 60 [° C.] is in the range of T60_bf≦0.20. This reduces rolling resistance under low-temperature and high-temperature atmospheres. Note that the lower limits of T20_bf and T60_bf are not particularly limited and are preferably as close to 0 as possible; however, they are restricted by the above ratio conditions.

Further, the tan δ value T20_bf of the bead filler 12 at 20 [°C] has the relationship T20_ct×T20_bf≦0.040 with respect to the tan δ value T20_ct of the cap tread 151 at 20 [° C.], and T20_ct×T20_bf≦0. It is preferable to have a relationship of 039. Thereby, rolling resistance in a low-temperature atmosphere can be appropriately reduced.

Further, the tan δ value T60_bf of the bead filler 12 at 60 [°C] has a relationship with the tan δ value T60_ct of the cap tread 151 at 60 [° C.] as T60_ct×T60_bf≦0.030, and T60_ct×T60_bf≦0. It is preferable to have a relationship of 0.028, and more preferably a relationship of T60_ct×T60_bf≦0.026. This optimizes the rolling resistance at room temperature.

Furthermore, the ratio T20_bf/T60_bf of the tan δ value T20_bf at 20 [°C] of the bead filler 12 and the tan δ value T60_bf at 60 [°C] is the same as the tan δ value T20_ct of the cap tread 151 at 20 [°C] and the tan δ value T20_bf at 60 [°C]. The ratio T20_ct/T60_ct with the value T60_ct has a relationship of 0.40≦(T20_bf/T60_bf)/(T20_ct/T60_ct)≦0.60, and 0.45≦(T20_bf/T60_bf)/(T20_ct/T60_ct )≦0.55. In this configuration, the tan δ ratio of the rubber member located on the tire contact surface side is set smaller than that of the rubber member located on the rim fitting surface side, so that the deformation and vibration of the rubber member when the tire rolls is reduced to the tire contact surface. It is efficiently damped from the rim toward the rim fitting surface. As a result, the energy consumption of the tire as a whole is reduced, and the rolling resistance of the tire is reduced, regardless of the ambient temperature during running.

Further, the rubber hardness Hs_bf of the bead filler 12 at 20[° C.] is in the range of 70≦Hs_bf≦97. Further, the modulus of the bead filler 12 when expanded by 100% is in the range of 1.0 [MPa]≦E'_bf≦13.0 [MPa].

Furthermore, the rubber hardness Hs_bf of the bead filler 12 at 20 [°C] has a relationship of 25≦Hs_bf−Hs_ct≦30 with respect to the rubber hardness Hs_ct of the cap tread 151 at 20 [°C]. With this configuration, the relationship between the rubber hardness of the bead filler 12 and the cap tread 151 is optimized, and the transmission efficiency and responsiveness of steering force from the bead portion to the tire contact surface are improved. This improves the steering stability performance of the tire.

FIG. 2 is an enlarged view showing the bead portion of the pneumatic tire 1 shown in FIG. In the figure, an area A1 from the top surface of the bead core 11 to a distance of the cross-sectional height H1 of the bead core 11 is defined.

At this time, the maximum gauge Ga_bf of the bead filler 12 in the area A1 and the tan δ value T20_bf of the bead filler 12 at 20 [°C] have a relationship of Ga_bf×T20_bf≦0.90, and Ga_bf×T20_bf≦0.80. It is preferable to have the following relationship. Further, the maximum gauge Ga_bf of the bead filler 12 has a relationship of 0.90≦Ga_bf/W1≦1.10 with respect to the maximum width W1 of the bead core 11. Thereby, the energy consumption of the bead filler 12 during tire rolling is reduced, and rolling resistance in a low-temperature atmosphere can be reduced.

The maximum gauge Ga_bf of the bead filler 12 is measured as the maximum thickness in the tire width direction when the tire is mounted on a specified rim, a specified internal pressure is applied, and the tire is in an unloaded state.

The standard rim refers to a "standard rim" defined by JATMA, a "Design Rim" defined by TRA, or a "Measuring Rim" defined by ETRTO. In addition, the specified internal pressure refers to the "maximum air pressure" specified in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or "INFLATION PRESSURES" specified in ETRTO. In addition, the specified load refers to the "maximum load capacity" specified in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified in TRA, or "LOAD CAPACITY" specified in ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 [kPa], and the specified load is 88 [%] of the maximum load capacity at the specified internal pressure.

Further, in FIG. 1, the height H2 of the bead filler 12 has a relationship with the tire cross-sectional height SH of 0.15≦H2/SH≦0.21, and 0.18≦H2/SH≦0. It is more preferable to have a relationship of 20. Further, at this time, it is preferable that the rolled-up height H3 of the carcass layer 13 has a relationship of 0.15≦H3/SH with respect to the tire cross-sectional height SH, and a relationship of 0.17≦H3/SH. is more preferable, and it is even more preferable to have a relationship of 0.19≦H3/SH.

The height H2 of the bead filler 12 is measured as the extension length of the bead filler 12 in the tire radial direction.

The rolled-up height H3 of the carcass layer 13 is measured as the distance in the tire radial direction from the radially innermost point of the bead core 11 to the radially outermost point of the rolled up portion of the carcass layer 13.

[Undertread characteristics]
Furthermore, the tan δ value T20_ut at 20 [°C] and the tan δ value T60_ut at 60 [°C] of the undertread 152 have a relationship of 0.50≦T20_ut/T60_ut≦1.55, and 0.75≦T20_ut/T60_ut≦ It is preferable to have a relationship of 1.50, and more preferably a relationship of 0.80≦T20_ut/T60_ut≦1.45. This makes it possible to reduce the difference between the rolling resistance under a low temperature atmosphere and the rolling resistance under a normal temperature atmosphere.

Further, the tan δ value T20_ut of the undertread 152 at 20 [° C.] is preferably in the range of T20_ut≦0.15, and preferably in the range of T20_ut≦0.07. Further, the tan δ value T60_ut of the undertread 152 at 60[° C.] is preferably in the range of T60_ut≦0.30, and preferably in the range of T60_ut≦0.15. This reduces rolling resistance under low-temperature and high-temperature atmospheres. Note that the lower limits of T20_ut and T60_ut are not particularly limited and are preferably as close to 0 as possible, but they are restricted by the above ratio conditions.

Further, the tan δ value T20_ut of the under tread 152 at 20 [°C] has a relationship with the tan δ value T0_ct of the cap tread 151 at 0 [° C.] of T0_ct×T20_ut≦0.050, and T0_ct×T20_ut≦0. It is preferable to have a relationship of 050. Thereby, rolling resistance in a low-temperature atmosphere can be appropriately reduced.

Regarding the product of the tan δ values, according to the temperature distribution inside the tire when the tire is rolling, the temperature of the cap tread 151 that contacts the road surface tends to be lower than the temperature of the undertread 152. Therefore, by using a tan δ value at a relatively low temperature for the cap tread 151, it is possible to appropriately evaluate the influence of the tan δ value on rolling resistance in a low temperature atmosphere.

Further, the tan δ value T60_ut of the under tread 152 at 60 [°C] has the relationship T40_ct×T60_ut≦0.024 with respect to the tan δ value T40_ct of the cap tread 151 at 40 [° C.], and T40_ct×T60_ut≦0. 020, and more preferably T40_ct×T60_ut≦0.015. Thereby, rolling resistance in a high temperature atmosphere can be appropriately reduced.

Furthermore, the ratio T20_ut/T60_ut of the tan δ value T20_ut at 20 [°C] of the undertread 152 and the tan δ value T60_ut at 60 [°C] is the same as the tan δ value T20_ct of the cap tread 151 at 20 [°C] and the tan δ value T20_ut at 60 [°C]. The ratio T20_ct/T60_ct with the value T60_ct has a relationship of 0.75≦(T20_ut/T60_ut)/(T20_ct/T60_ct)≦1.00, and 0.78≦(T20_ut/T60_ut)/(T20_ct/T60_ct )≦0.95.

In the above configuration, the tan δ ratio of the rubber member located on the tire contact surface side is set smaller than that of the rubber member located on the rim fitting surface side, so deformation and vibration of the rubber member during tire rolling are reduced. Effectively damps from the ground toward the rim fitting surface. As a result, the energy consumption of the tire as a whole is reduced, and the rolling resistance of the tire is reduced, regardless of the ambient temperature during running.

Further, the rubber hardness Hs_ut of the undertread 152 at 20 [° C.] is in the range of 55≦Hs_ut≦65. Further, the modulus of the undertread 152 at 100 [%] elongation is in the range of 1.5 [MPa]≦E'_ut≦3.0 [MPa].

Furthermore, the rubber hardness Hs_ut of the undertread 152 at 20 [° C.] has a relationship of 1≦Hs_ct−Hs_ut≦10 with respect to the rubber hardness Hs_ct of the cap tread 151, and a relationship of 3≦Hs_ct−Hs_ut≦8. It is preferable to have a relationship of 4≦Hs_ct−Hs_ut≦7. In this configuration, since the cap tread 151 is harder than the undertread 152, the steering stability of the tire is improved, and the road surface followability of the undertread 152 is improved, so that the wet performance of the tire is improved.

In addition, in FIG. 1, the cross-sectional area S_ct of the cap tread 151 and the cross-sectional area S_ut of the undertread 152 in a cross-sectional view in the tire meridian direction have a relationship of 0.11≦S_ut/(S_ct+S_ut)≦0.50, and 0. It is preferable to have a relationship of .13≦S_ut/(S_ct+S_ut)≦0.45, and it is preferable to have a relationship of 0.15≦S_ut/(S_ct+S_ut)≦0.40. With the above lower limit, the volume of the undertread 152 having a relatively small tan δ value is ensured, and the above-described rolling resistance reduction effect is ensured. This has the advantage of ensuring a reduction in tire rolling resistance. With the above upper limit, the volume of the hard cap tread 151 is ensured, and the effect of improving the steering stability performance of the tire described above is ensured.

The cross-sectional area S_ct of the cap tread 151 and the cross-sectional area S_ut of the undertread 152 are calculated as average values over the entire circumference of the tire.

Further, in FIG. 1, the maximum width Wb2 of the widest cross belt 141 among the cross belts 141 and 142 constituting the belt layer 14, the maximum width Wct of the cap tread 151, and the maximum width Wut of the undertread 152 are 15 mm. ]≦Wct−Wb2≦30 [mm] and Wb2<Wut<Wct are satisfied. With the above upper limit, the maximum width Wb2 of the crossing belt 142 is ensured, and the rolling resistance of the tire is reduced. Furthermore, the above-mentioned size relationship Wb2<Wut<Wct ensures the durability of the tire.

The maximum width Wb2 of the cross belt 142, the maximum width Wct of the cap tread 151, and the maximum width Wut of the under tread 152 are measured with the tire mounted on a specified rim, a specified internal pressure applied, and an unloaded state.

FIG. 3 is an enlarged view showing the tread portion of the pneumatic tire 1 shown in FIG. In the figure, an imaginary line L1 is defined that passes through the end of the widest cross belt 141 among the cross belts 141 and 142 constituting the belt layer 14 and is perpendicular to the carcass layer 13.

At this time, the gauge Ga_ct of the cap tread 151 and the gauge Ga_ut of the undertread 152 on the virtual line L1 have a relationship of 0.20≦Ga_ut/Ga_ct≦0.40. With the above lower limit, the volume of the undertread 152 having a relatively small tan δ value is ensured, and the above-described rolling resistance reduction effect is ensured. With the above upper limit, the volume of the hard cap tread 151 is ensured, and the effect of improving the steering stability performance of the tire described above is ensured.

Further, the cross-sectional area S_ct of the cap tread 151 and the cross-sectional area S_ut of the undertread 152 in a cross-sectional view in the tire meridian direction, and the tan δ value T0_ct of the cap tread 151 at 0 [° C.] are 0.20≦{S_ct/(S_ct+S_ut )}×T0_ct≦0.60, and preferably 0.30≦{S_ct/(S_ct+S_ut)}×T0_ct≦0.58. With the above lower limit, the volume of the cap tread 151 is ensured, and the above-described effect of improving the steering stability performance of the tire is ensured. The above upper limit suppresses deterioration in rolling resistance caused by excessive volume or tan δ value of the cap tread 151.

Further, the cross-sectional area S_ct of the cap tread 151 and the cross-sectional area S_ut of the undertread 152 in a cross-sectional view in the tire meridian direction, and the tan δ value T20_ut of the undertread at 20 [° C.] are 0.01≦{S_ut/(S_ct+S_ut) }×T20_ut≦0.60 and preferably 0.01≦{S_ut/(S_ct+S_ut)}×T20_ut≦0.05. The above upper limit ensures the road surface followability of the undertread 152, thereby ensuring the above-mentioned effect of improving the wet performance of the tire. Deterioration of stability performance is suppressed.

[Characteristics of sidewall rubber]
Further, the tan δ value T20_sw at 20 [°C] and the tan δ value T60_sw at 60 [°C] of the sidewall rubber 16 have a relationship of 0.50≦T20_sw/T60_sw≦1.50, and 0.75≦T20_sw/T60_sw It is preferable to have a relationship of ≦1.45, and more preferably a relationship of 0.80≦T20_sw/T60_sw≦1.40. This makes it possible to reduce the difference between the rolling resistance under a low temperature atmosphere and the rolling resistance under a normal temperature atmosphere.

Further, the tan δ value T20_sw of the sidewall rubber 16 at 20 [° C.] is in the range of T20_sw≦0.11, and preferably in the range of T20_sw≦0.10. Further, the tan δ value T60_sw of the sidewall rubber 16 at 60[° C.] is in the range of T60_sw≦0.22. This reduces rolling resistance under low-temperature and high-temperature atmospheres. Note that the lower limits of T20_sw and T60_sw are not particularly limited and are preferably as close to 0 as possible, but they are restricted by the above ratio conditions.

Further, the tan δ value T20_sw of the sidewall rubber 16 at 20 [°C] has a relationship of T0_ct×T20_sw≦0.070 with respect to the tan δ value T0_ct of the cap tread 151 at 0 [°C], and T0_ct×T20_sw≦0. It is preferable to have a relationship of .65, and more preferably to have a relationship of T0_ct×T20_sw≦0.60. Thereby, rolling resistance in a low-temperature atmosphere can be appropriately reduced.

Regarding the product of the above tan δ values, according to the temperature distribution inside the tire when the tire is rolling, the temperature of the cap tread 151 in contact with the road surface tends to be lower than the temperature of the sidewall rubber 16. Therefore, by using a tan δ value at a relatively low temperature for the cap tread 151, it is possible to appropriately evaluate the influence of the tan δ value on rolling resistance in a low temperature atmosphere.

Further, the tan δ value T60_sw of the sidewall rubber 16 at 60 [°C] has a relationship with the tan δ value T40_ct of the cap tread 151 at 40 [° C.] as T40_ct×T60_sw≦0.024, and T40_ct×T60_sw≦0 It is preferable to have a relationship of .21, and more preferably a relationship of T40_ct×T60_sw≦0.18. Thereby, rolling resistance in a high temperature atmosphere can be appropriately reduced.

In addition, the ratio T20_sw/T60_sw of the tan δ value T20_sw at 20 [°C] of the sidewall rubber 16 and the tan δ value T60_sw at 60 [°C] is the same as the tan δ value T20_ct of the cap tread 151 at 20 [°C] and the tan δ value T20_ct at 60 [°C]. The ratio T20_ct/T60_ct with the tan δ value T60_ct has a relationship of 0.70≦(T20_sw/T60_sw)/(T20_ct/T60_ct)≦0.90, and 0.75≦(T20_sw/T60_sw)/(T20_ct/ It is preferable to have a relationship of T60_ct)≦0.85. In this configuration, the tan δ ratio of the rubber member located on the tire contact surface side is set smaller than that of the rubber member located on the rim fitting surface side, so that the deformation and vibration of the rubber member when the tire rolls is reduced to the tire contact surface. It is efficiently damped from the rim toward the rim fitting surface. As a result, the energy consumption of the tire as a whole is reduced, and the rolling resistance of the tire is reduced, regardless of the ambient temperature during running.

Also, the ratio T20_sw/T60_sw of the tan δ value T20_sw at 20 [°C] of the sidewall rubber 16 and the tan δ value T60_sw at 60 [°C] is the same as the tan δ value T20_bf of the bead filler 12 at 20 [°C] and the tan δ value T20_bf at 60 [°C]. The ratio T20_bf/T60_bf with the tan δ value T60_bf has a relationship of 0.62≦(T20_bf/T60_bf)/(T20_sw/T60_sw)≦0.72, and 1.40≦(T20_sw/T60_sw)/(T20_bf/ It is preferable to have a relationship of T60_bf)≦1.60. This reduces the rolling resistance of the tire.

Furthermore, the ratio T20_sw/T60_sw of the tan δ value T20_sw at 20 [°C] of the sidewall rubber 16 and the tan δ value T60_sw at 60 [°C] is the same as the tan δ value T20_ut of the undertread 152 at 20 [°C] and the tan δ value T20_ut at 60 [°C]. The ratio T20_ut/T60_ut with the tan δ value T60_ut has a relationship of 0.90≦(T20_sw/T60_sw)/(T20_ut/T60_ut)≦1.10, and 0.95≦(T20_sw/T60_sw)/(T20_ut/ It is preferable to have a relationship of T60_ut)≦1.05. This reduces the rolling resistance of the tire.

Further, the rubber hardness Hs_sw of the sidewall rubber 16 at 20 [° C.] is in the range of 50≦Hs_sw≦60. Further, the modulus of the sidewall rubber 16 when stretched by 100% is in the range of 1.0 [MPa]≦E'_sw≦2.5 [MPa].

Further, the rubber hardness Hs_sw of the sidewall rubber 16 at 20 [°C] has a relationship of 1≦Hs_ct−Hs_sw≦10 with respect to the rubber hardness Hs_ct of the cap tread 151 at 20 [°C], and 3≦Hs_ct -Hs_sw≦8, and more preferably 4≦Hs_ct-Hs_sw≦7. With this configuration, the relationship between the rubber hardness of the sidewall rubber 16 and the cap tread 151 is optimized, and the transmission efficiency and responsiveness of steering force from the rim fitting surface to the tire contact surface are improved. This improves the steering stability performance of the tire.

Further, the rubber hardness Hs_sw of the sidewall rubber 16 at 20 [°C] has a relationship of 35≦Hs_bf−Hs_sw≦40 with respect to the rubber hardness Hs_bf of the bead filler 12 at 20 [°C], and 36≦Hs_bf -Hs_sw≦39. This improves the steering stability performance of the tire.

Further, in FIG. 1, an area A2 of 50% of the tire cross-sectional height centered on the tire maximum width position P is defined.

At this time, the minimum thickness Ga_sw (see FIG. 2) of the sidewall rubber 16 in the region A2 and the tan δ value T20_sw at 20 [°C] of the sidewall rubber 16 have a relationship of Ga_sw×T20_sw≦0.25. , Ga_sw×T20_sw≦0.23, and more preferably Ga_sw×T20_sw≦0.21. Thereby, the energy consumption of the sidewall rubber 16 during tire rolling is reduced, and rolling resistance in a low-temperature atmosphere can be reduced. Further, the minimum thickness Ga_sw of the sidewall rubber 16 is in the range of 1.5 [mm]≦Ga_sw≦3.5 [mm].

Further, the overlap amount La between the tread rubber 15 (specifically, at least one of the cap tread 151 and the undertread 152) and the sidewall rubber 16 is in the range of 30 [mm]≦La≦60 [mm]. be. The above lower limit suppresses separation of the tread rubber, and the above upper limit suppresses an increase in rolling resistance due to excessive distortion of the shoulder portion during tire rolling.

The overlap amount La is measured as a length along the inner peripheral surface of the tire.

[Characteristics of rim cushion rubber]
Further, the tan δ value T20_rc at 20 [°C] and the tan δ value T60_rc at 60 [°C] of the rim cushion rubber 17 have a relationship of 0.70≦T20_rc/T60_rc≦1.30, and 0.80≦T20_rc/T60_rc It is preferable to have a relationship of ≦1.25, and more preferably a relationship of 0.90≦T20_rc/T60_rc≦1.20. This makes it possible to reduce the difference between the rolling resistance under a low temperature atmosphere and the rolling resistance under a normal temperature atmosphere.

Further, the tan δ value T20_rc of the rim cushion rubber 17 at 20 [° C.] is in the range of T20_rc≦0.22, preferably in the range of T20_rc≦21, and more preferably in the range of T20_rc≦21. Further, the tan δ value T60_rc of the rim cushion rubber 17 at 60[° C.] is in the range of T60_rc≦0.31. This reduces rolling resistance under low-temperature and high-temperature atmospheres. Note that the lower limits of T20_rc and T60_rc are not particularly limited and are preferably as close to 0 as possible, but they are restricted by the above ratio conditions.

Further, the tan δ value T20_rc of the rim cushion rubber 17 at 20 [°C] has a relationship with the tan δ value T20_ct of the cap tread 151 at 20 [° C.] of T20_ct×T20_rc≦0.070, and T20_ct×T20_rc≦0. It is preferable to have a relationship of .060. The above product is an index of rolling resistance in a low temperature atmosphere.

Further, the tan δ value T20_rc of the rim cushion rubber 17 at 20 [°C] has a relationship with the tan δ value T20_bf of the bead filler 12 at 20 [° C.] of T20_bf×T20_rc≦0.050, and T20_bf×T20_rc≦0. It is preferable to have a relationship of .040. Thereby, rolling resistance in a low-temperature atmosphere can be appropriately reduced.

Further, the tan δ value T20_rc of the rim cushion rubber 17 at 20 [°C] has the relationship T20_ct×T20_sw≦0.06 with respect to the tan δ value T20_sw of the sidewall rubber 16 at 60 [°C], and T20_ct×T20_sw≦ It is preferable to have a relationship of 0.05. The above product is an index of rolling resistance in a low temperature atmosphere.

Further, the tan δ value T60_rc of the rim cushion rubber 17 at 60 [°C] has a relationship of T60_ct×T60_rc≦0.030 with respect to the tan δ value T60_ct of the cap tread 151 at 60 [°C], and T60_ct×T60_rc≦0. It is preferable to have a relationship of .27, and it is more preferable to have a relationship of T60_ct×T60_rc≦0.25. Thereby, rolling resistance in a high temperature atmosphere can be appropriately reduced.

Further, the tan δ value T60_rc of the rim cushion rubber 17 at 60 [°C] has a relationship with the tan δ value T60_bf of the bead filler 12 at 60 [° C.] of T60_bf×T60_rc≦0.040, and T60_bf×T60_rc≦0 It is preferable to have a relationship of .030. Thereby, rolling resistance in a high temperature atmosphere can be appropriately reduced.

Further, the tan δ value T60_rc of the rim cushion rubber 17 at 60 [°C] has the relationship T60_sw×T60_rc≦0.030 with respect to the tan δ value T60_sw of the sidewall rubber 16 at 60 [°C], and T60_sw×T60_rc≦ It is preferable to have a relationship of 0.020. The above product is an index of rolling resistance in a low temperature atmosphere.

In addition, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 and the tan δ value T60_rc at 60 [°C] is the same as the tan δ value T20_ct of the cap tread 151 at 20 [°C] and the tan δ value T20_ct at 60 [°C]. The ratio T20_ct/T60_ct with the tan δ value T60_ct has a relationship of 0.55≦(T20_rc/T60_rc)/(T20_ct/T60_ct)≦0.85, and 0.65≦(T20_rc/T60_rc)/(T20_ct/ It is preferable to have a relationship of T60_ct)≦0.75.

In the above configuration, the tan δ ratio of the rubber member located on the tire contact surface side is set smaller than that of the rubber member located on the rim fitting surface side, so deformation and vibration of the rubber member during tire rolling are reduced. Effectively damps from the ground toward the rim fitting surface. As a result, the energy consumption of the tire as a whole is reduced, and the rolling resistance of the tire is reduced, regardless of the ambient temperature during running.

Furthermore, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 and the tan δ value T60_rc at 60 [°C] is the same as the tan δ value T20_bf of the bead filler 12 at 20 [°C] and the tan δ value T20_bf at 60 [°C]. The ratio T20_bf/T60_bf with the tan δ value T60_bf has a relationship of 1.00≦(T20_rc/T60_rc)/(T20_bf/T60_bf)≦1.40, and 1.02≦(T20_rc/T60_rc)/(T20_bf/ It is preferable to have a relationship of T60_bf)≦1.38, and more preferably a relationship of 1.04≦(T20_rc/T60_rc)/(T20_bf/T60_bf)≦1.36.

In the above configuration, since the rubber members that make up the tire side part to the bead part have the same temperature dependence, the deformation and vibration of the rubber members when the tire is rolling is directed from the tire contact surface to the rim fitting surface. attenuates efficiently. As a result, the energy consumption of the tire as a whole is reduced, and the rolling resistance of the tire is reduced, regardless of the ambient temperature during running.

Also, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 and the tan δ value T60_rc at 60 [°C] is the same as the tan δ value T20_sw of the sidewall rubber 16 at 20 [°C] and 60 [°C]. has a relationship of 0.85≦(T20_rc/T60_rc)/(T20_sw/T60_sw)≦1.15 with respect to the ratio T20_sw/T60_sw with the tan δ value T60_sw, and 0.85≦(T20_rc/T60_rc)/(T20_sw /T60_sw)≦1.00. This reduces the rolling resistance of the tire.

Further, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [° C.] is in the range of 65≦Hs_rc≦75. Further, the modulus of the rim cushion rubber 17 when stretched by 100% is in the range of 3.5 [MPa]≦E'_rc≦6.0 [MPa].

Further, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] has a relationship of 7≦Hs_rc-Hs_ct≦11 with respect to the rubber hardness Hs_ct of the cap tread 151 at 20 [°C], and 8≦Hs_rc -Hs_ct≦10. In this configuration, the relationship between the rubber hardness of the rim cushion rubber 17 and the cap tread 151 is optimized, and the efficiency and responsiveness of steering force transmission from the rim fitting surface to the tire contact surface are improved. This improves the steering stability performance of the tire.

Further, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] has a relationship of 18≦Hs_bf-Hs_rc≦21 with respect to the rubber hardness Hs_bf of the bead filler 12 at 20 [°C], and 19≦Hs_bf -Hs_rc≦21. In this configuration, the relationship between the rubber hardnesses of the bead filler 12 and the rim cushion rubber 17 that are adjacent to each other in the tire width direction is optimized, and the deformation of the bead portion in the tire width direction becomes continuous when the vehicle turns. This improves the steering stability performance of the tire.

Further, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] has a relationship of 17≦Hs_rc−Hs_sw≦20 with respect to the rubber hardness Hs_sw of the sidewall rubber 16 at 20 [°C], and 18≦ It is preferable to have a relationship of Hs_rc−Hs_sw≦19. In this configuration, the relationship between the rubber hardness of the sidewall rubber 16 and the rim cushion rubber 17 that constitute the tire side portion from the bead portion is optimized, and the tire side portion is continuously deformed in the tire width direction when the vehicle turns. become a target. This improves the steering stability performance of the tire.

Further, in FIG. 2, a virtual line L2 parallel to the tire rotation axis is defined at a distance from the top surface of the bead core 11 to the cross-sectional height H1 of the bead core 11.

At this time, the gauge Ga_rc of the rim cushion rubber 17 on the virtual line L2 and the tan δ value T20_rc of the rim cushion rubber 17 at 20 [°C] have a relationship of Ga_rc×T20_rc≦0.80, and Ga_rc×T20_rc≦ It is preferable to have a relationship of 0.70. Further, the gauge Ga_rc of the rim cushion rubber 17 is in the range of 3.5 [mm]≦Ga_rc≦4.5 [mm]. Thereby, the energy consumption of the rim cushion rubber 17 during tire rolling is reduced, and rolling resistance in a low temperature atmosphere can be reduced.

[effect]
As explained above, this pneumatic tire 1 includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12 disposed radially outside of the pair of bead cores 11, 11, and A passed carcass layer 13, a belt layer 14 arranged radially outward of the carcass layer 13, and a tread rubber 15 consisting of a cap tread 151 and an undertread 152 and arranged radially outward of the belt layer 14, It includes a pair of sidewall rubbers 16, 16 arranged on the outside of the carcass layer 13 in the tire width direction, and a pair of rim cushion rubbers 17, 17 arranged on the radially inner side of the pair of bead cores 11, 11 (Fig. reference). Furthermore, the tan δ value T20_rc at 20 [° C.] and the tan δ value T60_rc at 60 [° C.] of the rim cushion rubber 17 satisfy the conditions of 0.70≦T20_rc/T60_rc≦1.30 and T20_rc≦0.22.

In the above configuration, (1) the ratio T20/T60 of the tan δ value T20 at 20 [°C] and the tan δ value T60 at 60 [°C] of the rim cushion rubber 17 is optimized, so that the rolling resistance in a low temperature atmosphere and the normal temperature The difference in rolling resistance under atmospheric conditions can be reduced. Furthermore, (2) the tan δ value T20 at 20[° C.] of the rim cushion rubber 17 is within the above range, thereby reducing rolling resistance in a low-temperature atmosphere. This has the advantage of reducing the rolling resistance of the tire when running in a low-temperature atmosphere while suppressing fluctuations in the fuel efficiency of the tire due to changes in ambient temperature.

Further, in this pneumatic tire 1, the tan δ value T20_rc of the rim cushion rubber 17 at 20 [°C] has a relationship with the tan δ value T20_ct of the cap tread 151 at 20 [° C.] of T20_ct×T20_rc≦0.070. . This has the advantage of appropriately reducing rolling resistance in a low-temperature atmosphere.

Furthermore, in this pneumatic tire 1, the tan δ value T60_rc of the rim cushion rubber 17 at 60 [°C] has a relationship of T60_ct×T60_rc≦0.030 with respect to the tan δ value T60_ct of the cap tread 151 at 60 [° C.]. . This has the advantage of appropriately reducing rolling resistance in a high-temperature atmosphere.

Further, in this pneumatic tire 1, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 to the tan δ value T60_rc at 60 [° C] is the tan δ value of the cap tread 151 at 20 [° C]. The ratio T20_ct/T60_ct between T20_ct and tan δ value T60_ct at 60 [° C.] has a relationship of 0.65≦(T20_rc/T60_rc)/(T20_ct/T60_ct)≦0.75. In this configuration, the tan δ ratio of the rubber member located on the tire contact surface side is set smaller than that of the rubber member located on the rim fitting surface side, so that the deformation and vibration of the rubber member when the tire rolls is reduced to the tire contact surface. It is efficiently damped from the rim toward the rim fitting surface. This has the advantage that the energy consumption of the tire as a whole is reduced and the rolling resistance of the tire is reduced regardless of the ambient temperature during running.

In addition, in this pneumatic tire 1, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 and the tan δ value T60_rc at 60 [° C] is the tan δ value of the bead filler 12 at 20 [° C]. The ratio T20_bf/T60_bf between T20_bf and tan δ value T60_bf at 60 [° C.] has a relationship of 1.00≦(T20_rc/T60_rc)/(T20_bf/T60_bf)≦1.40. In this configuration, the tan δ ratio of the rim cushion rubber 17 located on the outside in the tire width direction is set to be larger than the tan δ ratio of the bead filler 12 located on the inside in the tire width direction, so that deformation and vibration of the rubber member when the vehicle turns is reduced. is efficiently attenuated. This has the advantage that the energy consumption of the tire as a whole is reduced and the rolling resistance of the tire is reduced regardless of the ambient temperature during running.

In addition, in this pneumatic tire 1, the ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber 17 to the tan δ value T60_rc at 60 [°C] is equal to the tan δ value T20_rc at 20 [°C] of the sidewall rubber 16. The ratio T20_sw/T60_sw between the value T20_sw and the tan δ value T60_sw at 60 [° C.] has a relationship of 0.85≦(T20_rc/T60_rc)/(T20_sw/T60_sw)≦1.15. In this configuration, the rubber members that form the tire side part to the bead part have the same temperature dependence, so that the deformation and vibration of the rubber members when the tire rolls is directed from the tire contact surface to the rim fitting surface. Attenuate efficiently. This has the advantage of reducing the rolling resistance of the tire.

Furthermore, in this pneumatic tire 1, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] has a relationship of 1≦Hs_rc−Hs_ct≦11 with respect to the rubber hardness Hs_ct of the cap tread 151 at 20 [°C]. has. With this configuration, the relationship between the rubber hardness of the rim cushion rubber 17 and the cap tread 151 is optimized, and the efficiency and responsiveness of steering force transmission from the rim fitting surface to the tire contact surface are improved. This has the advantage of improving the steering stability performance of the tire.

In addition, in this pneumatic tire 1, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] has a relationship of 18≦Hs_bf−Hs_rc≦21 with respect to the rubber hardness Hs_bf of the bead filler 12 at 20 [°C]. has. In this configuration, the relationship between the rubber hardnesses of the bead filler 12 and the rim cushion rubber 17 that are adjacent to each other in the tire width direction is optimized, and the deformation of the bead portion in the tire width direction when the vehicle turns is made continuous. This has the advantage of improving the steering stability performance of the tire.

In addition, in this pneumatic tire 1, the rubber hardness Hs_rc of the rim cushion rubber 17 at 20 [°C] is 17≦Hs_rc−Hs_sw≦20 with respect to the rubber hardness Hs_sw of the sidewall rubber 16 at 20 [°C]. have a relationship In this configuration, the relationship between the rubber hardness of the sidewall rubber 16 and the rim cushion rubber 17 that constitute the tire side portion from the bead portion is optimized, and the tire side portion is continuously deformed in the tire width direction when the vehicle turns. become a target. This has the advantage of improving the steering stability performance of the tire.

In addition, in this pneumatic tire 1, in a cross-sectional view in the tire meridian direction, an imaginary line L2 parallel to the tire rotation axis is defined from the top surface of the bead core 11 at a distance of the cross-sectional height H1 of the bead core 11 (Fig. 2 ), the gauge Ga_rc of the rim cushion rubber 17 on the virtual line L2 and the tan δ value T20_rc of the rim cushion rubber 17 at 20 [° C.] have a relationship of Ga_rc×T20_rc≦0.80 [mm]. This reduces the energy consumption of the rim cushion rubber 17 during tire rolling, which has the advantage of reducing rolling resistance in a low-temperature atmosphere.

Further, in this pneumatic tire 1, the tan δ value T0_ct at 0 [° C.] and the tan δ value T60_ct at 60 [° C.] of the cap tread 151 have a relationship of 2.00≦T0_ct/T60_ct≦4.38. This has the advantage of reducing the temperature dependence of the tire's fuel efficiency while improving the tire's wet performance.

Further, in this pneumatic tire 1, the tan δ value T0_ct of the cap tread 151 at 0 [° C.] is in the range of T0_ct≦0.75. This has the advantage of improving the wet performance of the tire.

FIG. 4 is a chart showing the results of a performance test of the pneumatic tire according to the embodiment of the present invention.

In this performance test, multiple types of test tires were evaluated regarding (1) rolling resistance and (2) wet performance. Also, a test tire with a tire size of 195/65R15 is used.

(1) In the evaluation of rolling resistance, a drum testing machine with a drum diameter of 1707 [mm] was used, and an internal pressure of 180 [kPa] and a load of 88 [%] of the maximum load capacity specified by JATMA were applied to the test tire. The rolling resistance coefficient of the test tire was measured at a speed of 80 [km/h]. Further, the room temperature rolling resistance is a value measured at an ambient temperature of 25 [°C], and the low temperature rolling resistance is a value measured at an ambient temperature of 10 [°C]. This evaluation is performed by index evaluation using the conventional example as a standard (100), and the larger the value, the better. Furthermore, if the rolling resistance at normal temperature is rated at 98 or higher, it can be said that the performance is properly ensured.

(2) In the evaluation of wet performance, test tires were installed on the front and rear wheels of a test vehicle with a displacement of 1800 [cc] and front wheel drive, and the test tires had air pressures of 250 [kPa] (front wheels) and 240 [kPa] (front wheels). (rear wheel) is provided. Then, the test vehicle ran on a test course consisting of an asphalt road surface with a water depth of 2 [mm], and the braking distance from a speed of 100 [km/h] was measured. Then, based on the measurement results, an index evaluation is performed using the conventional example as a standard (100). In this evaluation, the larger the value, the better.

The test tires of the conventional example and the example had the configuration shown in FIG. 1, and each rubber member constituting the tire casing had predetermined physical properties.

As the test results show, the rolling resistance of the tire is reduced and the wet performance of the tire is improved in the test tire of the example.

1 Pneumatic tire; 11 Bead core; 12 Bead filler; 13 Carcass layer; 14 Belt layer; 141, 142 Cross belt; 143 Belt cover; 144 Belt edge cover; 15 Tread rubber; 151 Cap tread; 152 Undertread; 16 Sidewall Rubber; 17 Rim cushion rubber; 18 Inner liner

Claims (12)

a pair of bead cores, a pair of bead fillers disposed radially outwardly of the bead cores, a carcass layer spanning the bead cores, a belt layer disposed radially outwardly of the carcass layer, a cap tread; A tread rubber comprising an undertread and disposed on the radially outer side of the belt layer, a pair of sidewall rubbers disposed on the tire widthwise outer side of the carcass layer, and a tread rubber disposed on the radially inner side of the pair of bead cores. A pneumatic tire comprising a pair of rim cushion rubber,
The tan δ value T20_rc at 20 [°C] and the tan δ value T60_rc at 60 [° C.] of the rim cushion rubber satisfy the following conditions: 0.70≦T20_rc/T60_rc≦1.30 and T20_rc≦0.22. pneumatic tires. The pneumatic tire according to claim 1, wherein a tan δ value T20_rc of the rim cushion rubber at 20 [°C] has a relationship of T20_ct×T20_rc≦0.070 with respect to a tan δ value T20_ct of the cap tread at 20 [° C.]. . The air according to claim 1 or 2, wherein the tan δ value T60_rc of the rim cushion rubber at 60 [°C] has a relationship of T60_ct×T60_rc≦0.030 with respect to the tan δ value T60_ct of the cap tread at 60 [° C.]. Included tires. The ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] and the tan δ value T60_rc at 60 [°C] of the rim cushion rubber is the tan δ value T20_ct at 20 [°C] and the tan δ value at 60 [°C] of the cap tread. The pneumatic tire according to any one of claims 1 to 3, which has a relationship of 0.65≦(T20_rc/T60_rc)/(T20_ct/T60_ct)≦0.75 with respect to the ratio T20_ct/T60_ct. The ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber and the tan δ value T60_rc at 60 [°C] is the tan δ value T20_bf of the bead filler at 20 [°C] and the tan δ value at 60 [° C] The pneumatic tire according to any one of claims 1 to 4, which has a relationship of 1.00≦(T20_rc/T60_rc)/(T20_bf/T60_bf)≦1.40 with respect to the ratio T20_bf/T60_bf. The ratio T20_rc/T60_rc of the tan δ value T20_rc at 20 [°C] of the rim cushion rubber and the tan δ value T60_rc at 60 [°C] is the tan δ value T20_sw of the sidewall rubber at 20 [°C] and the tan δ value at 60 [°C]. The pneumatic tire according to any one of claims 1 to 5, which has a relationship of 0.85≦(T20_rc/T60_rc)/(T20_sw/T60_sw)≦1.15 with respect to the ratio T20_sw/T60_sw with respect to the value T60_sw. . Any one of claims 1 to 6, wherein the rubber hardness Hs_rc of the rim cushion rubber at 20 [°C] has a relationship of 1≦Hs_rc−Hs_ct≦11 with respect to the rubber hardness Hs_ct of the cap tread at 20 [°C]. Pneumatic tires listed in one of the above. Any one of claims 1 to 7, wherein the rubber hardness Hs_rc of the rim cushion rubber at 20 [°C] has a relationship of 18≦Hs_bf−Hs_rc≦21 with respect to the rubber hardness Hs_bf of the bead filler at 20 [°C]. Pneumatic tires listed in one of the above. The rubber hardness Hs_rc of the rim cushion rubber at 20 [°C] has a relationship of 17≦Hs_rc−Hs_sw≦20 with respect to the rubber hardness Hs_sw of the sidewall rubber at 20 [°C]. Pneumatic tires listed in any one of the above. Defining a virtual line L2 parallel to the tire rotation axis at a distance of a cross-sectional height H1 of the bead core from the top surface of the bead core toward the outside in the tire radial direction in a cross-sectional view in the tire meridian direction,
The gauge Ga_rc of the rim cushion rubber on the virtual line L2 and the tan δ value T20_rc of the rim cushion rubber at 20 [° C.] have a relationship of Ga_rc×T20_rc≦0.80 [mm]. Pneumatic tires listed in any one of the above. The tan δ value T0_ct at 0 [°C] and the tan δ value T60_ct at 60 [° C.] of the cap tread have a relationship of 2.00≦T0_ct/T60_ct≦4.38, according to any one of claims 1 to 10. pneumatic tires. The pneumatic tire according to any one of claims 1 to 11, wherein a tan δ value T0_ct of the cap tread at 0 [° C.] is in a range of T0_ct≦0.75.

Images