JP2017121848A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire achieving both low rolling resistance and high abrasion resistance.SOLUTION: A pneumatic tire 2 comprises a pair of side walls 6 respectively extending substantially inward in a radial direction from an end of a tread 4 and a pair of clinches 8 respectively positioned closer to substantially inside in the radial direction than the side walls 6. The clinches 8 comprise an inner layer 8a and an outer layer 8b positioned outside in a shaft direction of the inner layer 8a. The maximum thickness Tmax of the outer layer 8b is 2.0 mm or less and the minimum thickness Tmin thereof is 1.0 mm or more. A complex elastic modulus E2of the inner layer is lower than a composite elastic modulus E1of the outer layer 8b. A loss tangent LT2 of the inner layer 8a is lower than a loss tangent LT1 of the outer layer 8b.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire. In particular, the present invention relates to improved tire clinching.

  In recent years, the demand for lower fuel consumption of vehicles has become particularly strong due to environmental considerations. Since tires affect the fuel efficiency of a vehicle, the development of “low fuel consumption tires” that contribute to the reduction of fuel consumption is underway. In order to achieve low fuel consumption by using a tire, it is important to reduce the rolling resistance of the tire. The main cause of tire rolling resistance is energy loss due to hysteresis loss caused by deformation when the tire rolls. It is also required to reduce this loss in tire clinching. This is particularly important in a low flat tire having a rim protector. This is because, in this tire, the amount of rubber constituting the clinch increases, so that energy loss in the clinch increases.

  In order to reduce energy loss in the clinch, there is a method in which the clinch is made of a low heat generation rubber. However, generally, when the clinches are made of rubber with low heat generation, the abrasion resistance of the clinches is lowered. The clinch is in contact with the rim flange. A large load is applied to the clinch from the flange. Decreasing the abrasion resistance of the clinch can lead to tire damage. Furthermore, the use of a low heat-generating rubber for the clinches can lead to a decrease in tire conductivity.

  Japanese Unexamined Patent Application Publication No. 2011-73464 discloses a tire that reduces an increase in rolling resistance and suppresses a decrease in wear resistance. In this tire, the rim protector includes an insert made of soft rubber. This insert is covered with a clinch made of hard rubber. With this insert, rolling resistance is reduced and riding comfort is improved. The insert is covered with clinches, so that a reduction in wear resistance is suppressed.

JP 2011-73464 A

  Due to the increasing demand for lower fuel consumption of vehicles, further reduction in rolling resistance is required. Clinch is required to further reduce energy loss. In addition, clinch is required to have high abrasion resistance.

  An object of the present invention is to provide a pneumatic tire that achieves low rolling resistance and high wear resistance.

The pneumatic tire according to the present invention has a tread whose outer surface forms a tread surface, a pair of sidewalls that extend substantially inward in the radial direction from the end of the tread, and each of which is substantially radially inward of the sidewalls. A pair of clinch positioned. The clinch includes an inner layer and an outer layer located outside the inner layer in the axial direction. The maximum thickness Tmax of the outer layer is 2.0 mm or less, and the minimum thickness Tmin thereof is 1.0 mm or more. The complex elastic modulus E2 ^* of the inner layer is lower than the complex elastic modulus E1 ^{* of the} outer layer. The loss tangent LT2 of the inner layer is lower than the loss tangent LT1 of the outer layer.

Preferably, the complex elastic modulus E2 ^* is higher than the complex elastic modulus E3 ^{* of the} sidewall.

Preferably, the ratio (E2 ^* / E1 ^* ) of the complex elastic modulus E2 ^{* to} the complex elastic modulus E1 ^* is 0.6 or more and 0.8 or less.

Preferably, the complex elastic modulus E2 ^* is 6 MPa or more and 8 MPa or less.

  Preferably, the loss tangent LT2 is not less than 0.05 and not more than 0.10.

  The inventors have studied in detail the structure of clinch for the purpose of achieving both reduction in rolling resistance and wear resistance. As a result, the clinch comprises an inner layer and an outer layer located axially outside of the inner layer, the thickness of the outer layer is appropriate, and the complex modulus and loss of the inner and outer layers. It has been found that by adjusting the tangent, both reduction in rolling resistance and high wear resistance can be achieved.

  In the tire according to the present invention, the clinch includes an inner layer and an outer layer. The loss tangent of the inner layer is lower than the loss tangent of the outer layer. When the tire rolls, there is little energy loss in this inner layer. Furthermore, the maximum thickness of the outer layer is 2.0 mm or less. In this clinch, the volume of the outer layer having a large loss tangent is smaller than the volume of the inner layer having a small loss tangent. In the tire having the clinch, the rolling resistance is reduced. In this tire, the complex elastic modulus of the outer layer is smaller than the complex elastic modulus of the inner layer. The minimum value of the outer layer thickness is 1.0 mm or more. The clinch provided with this outer layer is excellent in abrasion resistance. In this tire, low rolling resistance and high wear resistance are achieved.

FIG. 1 is a cross-sectional view showing a part of a tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 shows a pneumatic tire. In FIG. 1, the vertical direction is the radial direction of the tire, the horizontal direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire. The shape of the tire is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 2 includes a tread 4, a sidewall 6, a clinch 8, a bead 10, a carcass 12, a belt 14, a band 16, an edge band 18, an inner liner 20, and a chafer 22. The tire 2 is a tubeless type. The tire 2 is mounted on a passenger car.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 24 that contacts the road surface. A groove 26 is carved in the tread surface 24. The groove 26 forms a tread pattern. The tread 4 has a base layer 28 and a cap layer 30. The cap layer 30 is located on the radially outer side of the base layer 28. The cap layer 30 is laminated on the base layer 28. The base layer 28 is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber of the base layer 28 is natural rubber.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. This sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. This sidewall 6 prevents the carcass 12 from being damaged.

  The clinch 8 is located substantially inside the sidewall 6 in the radial direction. The clinch 8 is located outside the beads 10 and the carcass 12 in the axial direction. The clinch 8 contacts the flange of the rim.

  The bead 10 is located inside the clinch 8 in the axial direction. The bead 10 includes a core 32 and an apex 34 that extends radially outward from the core 32. The core 32 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 34 is tapered outward in the radial direction. The apex 34 is made of a highly hard crosslinked rubber.

  The carcass 12 includes a first ply 12a and a second ply 12b. The first ply 12 a and the second ply 12 b are bridged between the beads 10 on both sides, and extend along the tread 4 and the sidewall 6. The first ply 12 a is folded around the core 32 from the inner side toward the outer side in the axial direction. By this folding, a main portion 36 and a folding portion 38 are formed in the first ply 12a. The second ply 12b is folded around the core 32 from the inner side to the outer side in the axial direction. By this folding, a main portion 40 and a folding portion 42 are formed in the second ply 12b. The end of the folded portion of the first ply 12a is located outside the end of the folded portion of the second ply 12b in the radial direction.

  Although not shown, each of the first ply 12a and the second ply 12b includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 12 may be formed from a single ply.

  The belt 14 is located on the inner side in the radial direction of the tread 4. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes a first layer 14a and a second layer 14b. Although not shown, each of the first layer 14a and the second layer 14b is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the first layer 14a with respect to the equator plane is opposite to the inclination direction of the cord of the second layer 14b with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The belt 14 may include three or more layers.

  The band 16 is located on the inner side in the radial direction of the tread 4. The band 16 is located on the radially outer side of the belt 14. The band 16 is laminated on the belt 14. The band 16 is made of a cord and a topping rubber. The cord is wound in a spiral. The band 16 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. The band 16 can contribute to the radial rigidity of the tire 2. The band 16 can suppress the influence of centrifugal force that acts during traveling. The tire 2 is excellent in high speed stability. A preferred material for the cord is steel. An organic fiber may be used for the cord. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 14 and the band 16 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 14. A reinforcing layer may be formed only from the band 16.

  The edge band 18 is located radially outside the belt 14 and in the vicinity of the end of the belt 14. Although not shown, the edge band 18 is made of a cord and a topping rubber. The cord is wound in a spiral. The edge band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the end of the belt 14 is restrained by this cord, the lifting of the belt 14 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The inner liner 20 is located inside the carcass 12. The inner liner 20 is joined to the inner surface of the carcass 12. The inner liner 20 is made of a crosslinked rubber. The inner liner 20 is made of rubber having excellent air shielding properties. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 2.

  The chafer 22 is located in the vicinity of the bead 10. When the tire 2 is incorporated into the rim, the chafer 22 comes into contact with the rim. By this contact, the vicinity of the bead 10 is protected. The chafer 22 is made of cloth and rubber impregnated in the cloth. The chafer 22 may be configured integrally with the clinch 8.

  FIG. 2 is an enlarged cross-sectional view of the tire 2 of FIG. 1 in which a portion of the bead 10 is shown. In FIG. 2, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. As shown in the figure, the sidewall 6 and the clinch 8 (which are collectively referred to as a side portion) protrude in a tapered shape toward the outside in the axial direction in the vicinity of the boundary between them. By this protrusion, a rim protector 44 is formed on the side portion. Although not shown, when the tire 2 is mounted on the rim, the end surface of the rim protector 44 is positioned outside the end of the rim flange in the axial direction. The rim protector 44 protrudes from the end of the flange in the axial direction.

  When the driver turns the vehicle handle and the vehicle is brought close to the shoulder, the rim protector 44 contacts the curb. This contact causes a reaction force on the handle. With this reaction force, the driver detects contact between the curb and the tire 2. When the driver turns the handle in the opposite direction, contact between the rim flange and the curb is avoided. The rim protector 44 prevents damage to the flange.

  When the tire 2 is greatly deformed over the cat's eye, a rim protector 44 is interposed between the cat's eye and the flange. The rim protector 44 prevents the flange and the cat's eye from colliding with each other. The rim protector 44 prevents damage to the flange.

  As shown in FIG. 2, the clinch 8 includes an inner layer 8a and an outer layer 8b. The clinch 8 includes an inner layer 8a and an outer layer 8b. The inner layer 8 a is located outside the carcass 12 in the axial direction. The inner layer 8 a is in contact with the carcass 12. The inner layer 8 a is located on the radially inner side of the sidewall 6. The inner layer 8 a is in contact with the sidewall 6. The inner layer 8a is located on the inner side in the axial direction of the outer layer 8b. The inner layer 8a is in contact with the outer layer 8b. Since the inner layer 8a is covered with the outer layer 8b and the sidewall 6, the inner layer 8a is not exposed to the outer surface.

  The outer layer 8b is located on the outer side in the axial direction of the inner layer 8a. In the outer layer 8 b, the outer surface in the axial direction forms a part of the outer surface of the tire 2. When the tire 2 is incorporated in the rim, the outer layer 8b contacts the rim.

  As shown in the figure, the outer layer 8b is in contact with the sidewall 6 only at the radially outer end. Most of the contact surfaces between the sidewalls 6 and the clinch 8 are contact surfaces between the sidewalls 6 and the inner layer 8a. The inner layer 8 a is mainly in contact with the sidewall 6. The area of the contact surface between the sidewall 6 and the outer layer 8b is 1/8 or less, and further 1/10 or less, of the area of the contact surface between the sidewall 6 and the inner layer 8a.

  As shown in FIG. 2, small protrusions 46 are present on the radially outer surface of the outer layer 8b. The outer surface of the outer layer 8b obtained on the assumption that there is no small protrusion 46 is referred to as a virtual outer surface of the outer layer 8b. In FIG. 2, point P is a point on the virtual outer surface of the outer layer 8b. A double-headed arrow T is the thickness of the outer layer 8b at the point P. Specifically, the thickness T is a distance between the virtual outer surface and the inner surface of the outer layer 8b measured along the normal drawn from the point P. The thickness of the outer layer 8b at the point where the thickness of the outer layer 8b is maximum is referred to as the maximum thickness Tmax. The thickness of the outer layer 8b at the point where the thickness of the outer layer 8b is minimized is referred to as the minimum thickness Tmin.

  In the tire 2, the maximum thickness Tmax is 2.0 mm or less. The minimum thickness Tmin is 1.0 mm or more. In the example of FIG. 1, the thickness of the outer layer 8b is substantially constant. That is, the maximum thickness Tmax and the minimum thickness Tmin are the same. In this case, as shown in FIG. 2, the thickness of the outer layer 8 b is simply represented by “thickness T” instead of “maximum thickness Tmax” and “minimum thickness Tmin”. The thickness of the outer layer 8b may not be constant.

In the tire 2, the complex elastic modulus E2 ^* of the inner layer 8a is set lower than the complex elastic modulus E1 ^* of the outer layer 8b. In other words, the outer layer 8b is less likely to be deformed when the tire 2 rolls than the inner layer 8a. The outer layer 8b is hard. The loss tangent LT2 of the inner layer 8a is set lower than the loss tangent LT1 of the outer layer 8b. The inner layer 8a generates less heat than the outer layer 8b.

In the present invention, the complex elastic modulus E1 ^* , E2 ^*, the complex elastic modulus E3 ^* , which will be described later, and the loss tangent LT1 and LT2 are viscoelastic spectrometers (manufactured by Iwamoto Seisakusho Co., Ltd.) in accordance with the provisions of “JIS K 6394”. “VESF-3”) and measured under the conditions shown below.
Initial strain: 10%
Amplitude: ± 2.0%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  Below, the effect of this invention is demonstrated.

  Due to the increasing demand for low fuel consumption of vehicles, tires are required to further reduce rolling resistance. In clinch, it is required to reduce energy loss. In particular, in a low flat tire having a rim protector, it is effective to reduce the rolling resistance to reduce the energy loss in the clinch. This is because, in this tire, the amount of rubber in the clinch is large, so that energy loss in the clinch is also large. In addition, clinch is required to have high abrasion resistance. In order to reduce energy loss in the clinch, there is a method in which the clinch is made of a low heat generation rubber. However, generally, when the clinches are made of rubber with low heat generation, the abrasion resistance of the clinches is lowered.

  In the tire 2 according to the present invention, the clinch 8 includes an inner layer 8a and an outer layer 8b in contact with the flange of the rim. In the tire 2, the loss tangent LT2 of the inner layer 8a is lower than the loss tangent LT1 of the outer layer 8b. When the tire 2 rolls, there is little energy loss in the inner layer 8a. This contributes to reduction of rolling resistance. Further, in the tire 2, the maximum thickness Tmax of the outer layer 8b is 2.0 mm or less. In this clinch 8, the volume of the outer layer 8b having a large loss tangent is smaller than the volume of the inner layer 8a having a small loss tangent. The energy loss in the clinches 8 is less than that of the conventional clinches in which the whole is composed of rubber having high wear resistance. The tire 2 having the clinch 8 has reduced rolling resistance.

In the tire 2, the complex elastic modulus E1 ^* of the outer layer 8b is higher than the complex elastic modulus E2 ^* of the inner layer 8a. This outer layer 8b is hard. Further, the minimum thickness Tmin of the outer layer 8b is 1.0 mm or more. The outer layer 8b is prevented from being worn even when a large load is applied from the flange. The clinch 8 provided with the outer layer 8b has sufficient abrasion resistance against the load from the flange. The clinch 8 maintains high wear resistance.

  The maximum thickness Tmax is preferably 1.8 mm or less. In the tire 2 including the outer layer 8b having the maximum thickness Tmax of 1.8 mm or less, the rolling resistance is more effectively reduced. In this respect, the maximum thickness Tmax is more preferably 1.6 mm or less. The maximum thickness Tmin is preferably 1.2 mm or more. In the clinch 8 including the outer layer 8b having the maximum thickness Tmin of 1.2 mm or more, higher wear resistance is realized. In this respect, the maximum thickness Tmin is more preferably equal to or greater than 1.4 mm.

The complex elastic modulus E1 ^* is preferably 8 MPa or more. The clinch 8 having the outer layer 8b having a complex elastic modulus E1 ^* of 8 MPa or more is excellent in abrasion resistance. From this viewpoint, the complex elastic modulus E1 ^* is more preferably 9 MPa or more. The complex elastic modulus E1 ^* is preferably 12 MPa or less. In the tire 2 having the outer layer 8b having the complex elastic modulus E1 ^* of 12 MPa or less, the rigidity of the side portion can be adjusted appropriately. The tire 2 is excellent in ride comfort and handling stability. In this respect, the complex elastic modulus E1 ^* is more preferably 11 MPa or less.

  As described above, the clinch has a complex elastic modulus sufficient to withstand the load from the flange. On the other hand, when the complex elastic modulus of the sidewall is increased, the rigidity of the side portion of the tire is increased. Excessive rigidity of the side portion causes steering stability and ride quality deterioration. Accordingly, the complex elastic modulus of the side wall is usually smaller than the complex elastic modulus of clinch. Typically, the complex elastic modulus of the sidewall is 5 MPa.

  The clinch is in contact with the sidewall. Due to the difference between the complex elastic modulus of the sidewall and the complex elastic modulus of the clinch, when a load is applied from the outside, distortion occurs at the contact portion between the sidewall and the clinch. This strain increases as the difference between the complex elastic modulus of the sidewall and the complex elastic modulus of the clinch increases. This distortion can also cause damage at the boundary between the clinch and the sidewall. This distortion can reduce the durability of the tire.

The complex elastic modulus E2 ^* of the inner layer 8a is preferably higher than the complex elastic modulus E3 ^{* of the} sidewall 6. At this time, the complex elastic modulus E2 ^* of the inner layer 8a is a height between the complex elastic modulus E1 ^* of the outer layer 8b and the complex elastic modulus E3 ^* of the sidewall 6. As described above, in the tire 2, the inner layer 8a is mainly in contact with the sidewall 6 and the outer layer 8b. By setting the complex elastic modulus E2 ^* to a height between the complex elastic modulus E1 ^* and the complex elastic modulus E3 ^* , the difference between the complex elastic modulus of the clinch and the complex elastic modulus of the sidewall in the conventional tire is compared. Thus, the difference between the complex elastic modulus E1 ^* and the complex elastic modulus E2 ^* of the tire 2 can be reduced. The difference between the complex elastic modulus E2 ^* and the complex elastic modulus E3 ^* can be made smaller than the difference between the complex elastic modulus of the clinch and the complex elastic modulus of the sidewall in the conventional tire. In the tire 2, the distortion caused by the difference between these complex elastic moduli is small. The tire 2 has high durability.

Complex elastic modulus E2 ^* the ratio of the complex elastic modulus ^{E1 * (E2 * / E1 *} ) is preferably 0.6 or more. In specific ^{(E2 *} / E1 *) 0.6 or more clinch 8, the difference between the complex elastic modulus E1 ^* of the complex elastic modulus E2 ^* and the outer layer 8b of the inner layer 8a can be reduced. In the tire 2, when a load is applied to the tire 2, distortion at the boundary between the inner layer 8a and the outer layer 8b can be reduced. In this respect, the ratio (E2 ^* / E1 ^* ) is more preferably equal to or greater than 0.65. The ratio (E2 ^* / E1 ^* ) is preferably 0.8 or less. In the clinch 8 having a ratio (E2 ^* / E1 ^* ) of 0.8 or less, the difference between the complex elastic modulus E2 ^* of the inner layer 8a and the complex elastic modulus E3 ^* of the sidewall 6 can be reduced. In the tire 2, when a load is applied to the tire 2, distortion at the boundary between the inner layer 8 a and the sidewall 6 can be reduced. The tire 2 has high durability. In this respect, the ratio (E2 ^* / E1 ^* ) is more preferably equal to or less than 0.74.

The complex elastic modulus E2 ^* is preferably 6 MPa or more. Complex elastic modulus E2 ^* are more inner layers 8a 6 MPa, the difference between the complex elastic modulus E1 ^* of the complex elastic modulus E2 ^* and the outer layer 8b of the inner layer 8a it can be reduced. In the tire 2, when a load is applied to the tire 2, distortion at the boundary between the inner layer 8a and the outer layer 8b can be reduced. From this viewpoint, the complex elastic modulus E2 ^* is more preferably 6.5 MPa or more. The complex elastic modulus E2 ^* is preferably 8 MPa or less. In the following inner layer 8a complex elastic modulus E2 ^* are 8 MPa, the difference between the complex elastic modulus E3 ^* of the complex elastic modulus E2 ^* and the sidewall 6 of the inner layer 8a can be reduced. In the tire 2, when a load is applied to the tire 2, distortion at the boundary between the inner layer 8 a and the sidewall 6 can be reduced. In this respect, the complex elastic modulus E2 ^* is preferably 7.4 MPa or less.

  The loss tangent LT1 is preferably 0.17 or less. In the tire 2 including the outer layer 8b having the loss tangent LT1 of 0.17 or less, the energy loss in the clinch 8 can be reduced. In the tire 2, a low rolling resistance can be realized. In this respect, the loss tangent LT1 is more preferably equal to or less than 0.16. The loss tangent LT1 is preferably 0.13 or more. The outer layer 8b having a loss tangent LT1 of 0.13 or more has excellent wear resistance. In this respect, the loss tangent LT1 is more preferably equal to or greater than 0.14.

  Loss tangent LT2 is preferably 0.10 or less. The inner layer 8a having the loss tangent LT2 of 0.10 or less can reduce the energy loss in the clinch 8. In the tire 2, a low rolling resistance can be realized. In this respect, the loss tangent LT2 is more preferably equal to or less than 0.09. The loss tangent LT2 is preferably 0.05 or more. In the tire 2 including the inner layer 8a having the loss tangent LT2 of 0.05 or more, the rigidity of the side portion can be made appropriate. The tire 2 is excellent in ride comfort and handling stability. In this respect, the loss tangent LT2 is more preferably 0.06 or more.

  In the present invention, the dimensions and angles of the tire 2 and each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures. In the case of the passenger car tire 2, the dimensions and angles are measured in a state where the internal pressure is 180 kPa.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A tire of Example 1 having the structure shown in FIG. 1 was obtained. The tire size was 245 / 45R18. Table 1 shows the specifications of the tire. The complex elastic modulus E3 ^* of the sidewall of this tire is 5 MPa. In this tire, the thickness of the outer layer is uniform. Accordingly, the thickness of the outer layer is expressed as “thickness T”.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the entire clinch was made of the same rubber as the outer layer. Comparative Example 1 is a conventional tire.

[Comparative Example 2]
A tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the entire clinch was made of the same rubber as the inner layer.

[Example 2-5 and Comparative Example 3-4]
Tires of Example 2-5 and Comparative Example 3-4 were obtained in the same manner as Example 1 except that the thickness T was changed to the value shown in Table 2.

[Examples 6-12 and Comparative Example 5]
Tires of Examples 6-12 and Comparative Example 5 were obtained in the same manner as Example 1 except that the complex elastic modulus E2 ^* was changed to the values shown in Tables 3 and 4. Since the complex elastic modulus E2 ^* is changed, the ratio (E2 ^* / E1 ^* ) is also changed.

[Examples 13-18 and Comparative Example 6]
Tires of Examples 13-18 and Comparative Example 6 were obtained in the same manner as in Example 1 except that the loss tangent LT2 was changed to the values shown in Tables 5 and 6.

[Rolling resistance]
Using a rolling resistance tester, rolling resistance was measured under the following measurement conditions.
Rim used: 18 x 8.0
Internal pressure: 210 kPa
Load: 5.57kN
Speed: 80km / h
The results are shown in Tables 1 to 6 below as index values with Comparative Example 1 taken as 100. The smaller the value, the smaller the rolling resistance and the better the fuel efficiency. A smaller numerical value is preferable.

[Abrasion resistance]
The tire was assembled in a standard rim (18 × 8.0), and the tire was filled with air to adjust the internal pressure to 210 kPa. This tire was mounted on the front wheel of a commercial passenger car, and a longitudinal load (5.57 kN) corresponding to 80% of the ETRTO maximum load load was applied to the tire. The road surface was an asphalt test course, and the vehicle was turned in a figure 8 with a radius of curvature of 7m and a lateral acceleration of 0.7G. This figure 8 turn was repeated 500 times. The amount of clinch wear was measured for the right front wheel tire. The reciprocal of this value is an index value with Comparative Example 1 as 100, and is shown in Table 1-6 below. Larger numbers are preferable.

[durability]
The prototype tire was assembled into a regular rim (18 × 8.0), and the tire was filled with air to adjust the internal pressure to 210 kPa. This tire was mounted on a drum-type running test machine, and a longitudinal load (5.57 kN) corresponding to 80% of the ETRTO maximum load load was applied to the tire. This tire was run on a drum having a radius of 1.7 m at a speed of 80 km / h. The distance traveled until the side portion of the tire was damaged was measured. The results are shown in Tables 1 to 6 below as index values with Comparative Example 1 taken as 100. Larger numbers are preferable.

  As shown in Table 1-6, in the tire according to the present invention, rolling resistance is reduced while maintaining good wear resistance. From this evaluation result, the superiority of the present invention is clear.

  The tire according to the present invention can be mounted on various vehicles.

DESCRIPTION OF SYMBOLS 2 ... Tire 4 ... Tread 6 ... Side wall 8 ... Clinch 8a ... Inner layer 8b ... Outer layer 10 ... Bead 12 ... Carcass 12a ... First ply 12b ... second ply 14 ... belt 14a ... first layer 14b ... second layer 16 ... band 18 ... edge band 20 ... inner liner 22 ... chafer 24 ... Tread surface 26 ... Groove 28 ... Base layer 30 ... Cap layer 32 ... Core 34 ... Apex 36, 40 ... Main part 38, 42 ... Folded part 44 ... Rim protector 46 ... Small protrusion

Claims (5)

A tread whose outer surface forms a tread surface, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and a pair of clinch each positioned substantially radially inward of the sidewalls And
The clinch includes an inner layer and an outer layer located outside the inner layer in the axial direction,
The maximum thickness Tmax of the outer layer is 2.0 mm or less, and the minimum thickness Tmin thereof is 1.0 mm or more;
The complex elastic modulus E2 ^* of the inner layer is lower than the complex elastic modulus E1 ^{* of the} outer layer,
A pneumatic tire in which the loss tangent LT2 of the inner layer is lower than the loss tangent LT1 of the outer layer. The tire according to claim 1, wherein the complex elastic modulus E2 ^* is higher than the complex elastic modulus E3 ^{* of the} sidewall. The tire according to claim 1 or 2, wherein a ratio (E2 ^* / E1 ^* ) of the complex elastic modulus E2 ^{* to} the complex elastic modulus E1 ^* is 0.6 or more and 0.8 or less. The tire according to any one of claims 1 to 3, wherein the complex elastic modulus E2 ^* is 6 MPa or more and 8 MPa or less.   The tire according to any one of claims 1 to 4, wherein the loss tangent LT2 is 0.05 or more and 0.10 or less.

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