JP2008254619A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for rally superior in driveability and cut-resistance. <P>SOLUTION: This tire 2 comprises a pair of beads 10, a carcass 12 stretched between both the beads 10, and side walls 6. The side wall 6 comprises an inner layer 50 and an outer layer 52. The inner layer 50 is positioned outside the carcass 12 in the axial direction. The outer layer 52 is positioned outside the inner layer 50 in the axial direction. The ratio of thickness of the inner layer 40 to thickness of the side wall 6 is set to 30%-80%. The ratio of complex modulus of the outer layer 52 to the complex modulus of the inner layer 50 is set to 70%-90%. The ratio of loss factor of the outer layer 50 to loss factor of the inner layer 50 is set to 105%-135%. Preferably, thickness of the side wall 6 in this tire 2 is set to 4 mm -12 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire. More specifically, the present invention relates to a pneumatic tire mainly mounted on a rally vehicle.

In the rally, the vehicle runs on rough terrain. In order for the vehicle to travel stably on the rough terrain at a high speed, a tire having excellent steering stability is required. In this rally, crushed stones and the like collide with the tires while traveling. This collision may cause a cut in the tire sidewall. This cut can be the starting point for puncture. Therefore, tires with excellent cut resistance are required for rally vehicles. An example of a tire excellent in handling stability and cut resistance for a passenger car is disclosed in Japanese Patent Application Laid-Open No. 2006-21671.
JP 2006-21671 A

  The sidewall of the tire is made of a crosslinked rubber. This sidewall is usually made of a single crosslinked rubber. In order to obtain a tire having excellent cut resistance, a tire may be provided with a sidewall made of a crosslinked rubber having a high hardness and having a large thickness. In this tire, the flexibility of the sidewall is insufficient. Since this tire does not sufficiently contact the ground, the steering stability is inferior. The sidewall having a large thickness affects the tire mass. In this tire, since the surface of the sidewall has a high tension, a crack may be formed on the surface when the tire travels a long distance.

  An object of the present invention is to provide a pneumatic tire for rally that is excellent in handling stability and cut resistance.

  The pneumatic tire for rally according to the present invention includes a pair of beads, a carcass spanned between both beads, and a sidewall. The sidewall includes an inner layer and an outer layer. The inner layer is located outside the carcass in the axial direction. The outer layer is located further outside the inner layer in the axial direction. The ratio of the thickness of the inner layer to the thickness of the sidewall is 20% or more and 80% or less. The ratio of the complex elastic modulus of the outer layer to the complex elastic modulus of the inner layer is 70% or more and 90% or less. The ratio of the loss factor of the outer layer to the loss factor of the inner layer is 105% or more and 135% or less.

  Preferably, in this tire, the complex elastic modulus of the inner layer is 4 MPa or more and 5 MPa or less. The inner layer has a loss coefficient of 0.12 to 0.15.

  Preferably, in this tire, the sidewall has a thickness of 4 mm or more and 12 mm or less.

  Preferably, in the tire, the outer layer includes a protector rib at a position where the tire has the maximum width.

  In this tire, the outer layer has a complex elastic modulus smaller than that of the inner layer. For this reason, when a crushed stone collides with this outer layer, this outer layer can be easily deformed by the external force at the time of the collision. The outer layer has a loss factor that is greater than the loss factor of the inner layer. The outer layer can convert the elastic energy stored as work performed by the external force into heat energy. The outer layer is less likely to be cut due to the impact of crushed stone or the like. This tire is excellent in cut resistance. Since this outer layer is excellent in elasticity, even if this tire is used for long-distance running, the surface does not crack. This tire is excellent in durability. In this tire, the inner layer having a large complex elastic modulus is positioned on the inner side in the axial direction of the outer layer which is easily deformed. This inner layer can prevent excessive deformation of the sidewall. This inner layer can effectively prevent the occurrence of cuts due to this excessive deformation. This tire is excellent in cut resistance. In this tire, the ratio of the inner layer thickness to the sidewall thickness is appropriately adjusted. For this reason, this side wall can maintain flexibility appropriately. Since this tire has sufficient ground contact properties, it has excellent steering stability.

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

  FIG. 1 is a cross-sectional view showing a part of a pneumatic tire 2 according to an embodiment of the present invention. FIG. 2 is a partially enlarged cross-sectional view showing a part of the tire 2 of FIG. 1 and 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. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 2. The tire 2 is mounted on a rally vehicle. 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, a first strip 18, a second strip 20, an inner liner 22, and a chafer 24. The tire 2 is a tubeless type.

  The tread 4 includes a main body 26 and a pair of wings 28. The main body 26 is made of a crosslinked rubber having excellent wear resistance. The main body 26 has a shape protruding outward in the radial direction. The main body 26 forms a tread surface 30 that contacts the road surface. A groove 32 is carved in the tread surface 30. The groove 32 forms a tread pattern. The wing 28 is located outside the main body 26 in the axial direction. The wing 28 is made of a crosslinked rubber. This crosslinked rubber is different from the crosslinked rubber constituting the main body 26.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is located between the tread 4 and a clinch 8 described later in the radial direction. The sidewall 6 absorbs an impact from the road surface by bending. Further, the sidewall 6 prevents the carcass 12 from being damaged.

  The bead 10 is located substantially inward of the sidewall 6 in the radial direction. The bead 10 includes a core 34 and an apex 36 that extends radially outward from the core 34. The core 34 has a ring shape. The core 34 includes a plurality of non-stretchable wires (typically steel wires). The apex 36 is tapered outward in the radial direction. The apex 36 is made of a highly hard crosslinked rubber.

  The clinch 8 is located inside the sidewall 6 in the radial direction. The clinch 8 is located outside the bead 10 in the axial direction. The clinch 8 is made of a crosslinked rubber.

  The carcass 12 includes a first carcass ply 38 and a second carcass ply 40. The first carcass ply 38 and the second carcass ply 40 are bridged between the beads 10 on both sides, and are along the inside of the tread 4 and the sidewall 6. The first carcass ply 38 and the second carcass ply 40 are folded around the core 34 from the inner side to the outer side in the axial direction. The carcass 12 may be composed of three carcass plies.

  Although not shown, the first carcass ply 38 and the second carcass ply 40 are composed of 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 usually 70 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is usually made of organic fibers. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. A carcass 12 having a bias structure may be employed.

  The belt 14 is located on the radially outer side of the carcass 12. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner ply 42 and an outer ply 44. Although not shown, each of the inner ply 42 and the outer ply 44 includes a plurality 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 not less than 10 ° and not more than 35 °. The cord inclination direction of the inner ply 42 is opposite to the cord inclination direction of the outer ply 44. A preferred material for the cord is steel. An organic fiber may be used for the cord.

  The band 16 is located on the radially outer side of the belt 14. The band 16 covers the belt 14. The band 16 includes an inner band ply 46 and an outer band ply 48. Although not shown, the inner band ply 46 and the outer band ply 48 are made of a cord and a topping rubber. The cord extends substantially in the circumferential direction and is wound spirally. The band 16 has a so-called jointless structure. Since the belt 14 is restrained by this cord, lifting of the belt 14 is suppressed. The cord is usually made of organic fibers. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  In the tire 2, the sidewall 6 includes an inner layer 50 and an outer layer 52. The inner layer 50 is located outside the carcass 12 in the axial direction. The inner layer 50 is made of a crosslinked rubber. The outer layer 52 is located further outside the inner layer 50 in the axial direction. The outer layer 52 is made of a crosslinked rubber. The outer layer 52 includes a plurality of protector ribs 54. In FIG. 2, the point P1 represents the position where the tire has the maximum width. Therefore, these protector ribs 54 include protector ribs 54a that are present at positions corresponding to the maximum tire width. In other words, the outer layer 52 includes the protector rib 54a at the position where the tire has the maximum width.

  In the tire 2, the boundary 56 between the inner layer 50 and the outer layer 52 extends in the radial direction. One end 58 of the boundary 56 is located on the boundary 60 between the tread 4 and the sidewall 6. The other end 62 of the boundary 56 is located on the boundary 64 between the sidewall 6 and the clinch 8. In the tire 2, the inner layer 50 and the outer layer 52 overlap in the axial direction.

  In the tire 2, the complex elastic modulus of the outer layer 52 of the sidewall 6 is smaller than the complex elastic modulus of the inner layer 50. The loss factor of the outer layer 52 is larger than the loss factor of the inner layer 50 of the sidewall 6. In other words, the sidewall 6 includes an outer layer 52 having a small complex elastic modulus and a large loss coefficient, and an inner layer 50 having a large complex elastic modulus and a small loss coefficient.

  In the tire 2, the outer layer 52 has a small complex elastic modulus. For this reason, when a crushed stone collides with this outer layer 52, this outer layer 52 deform | transforms easily with the external force at the time of this collision. The outer layer 52 has a large loss factor. The outer layer 52 can convert elastic energy stored as work performed by the external force into heat energy. The outer layer 52 is less likely to be cut by a collision of crushed stones or the like. The tire 2 is excellent in cut resistance. Since the outer layer 52 is excellent in stretchability, no cracks are generated on the surface of the tire 2 even when the tire 2 is used for long distance running. The tire 2 is excellent in durability.

  In the tire 2, the inner layer 50 having a large complex elastic modulus is positioned on the inner side in the axial direction of the outer layer 52 that is easily deformed. The inner layer 50 can prevent excessive deformation of the sidewall 6. This inner layer 50 can effectively prevent the occurrence of cuts due to this excessive deformation. The tire 2 is excellent in cut resistance.

  As will be described later, in the tire 2, the ratio of the thickness of the inner layer 50 to the thickness of the sidewall 6 is appropriately adjusted. For this reason, this sidewall 6 can maintain the flexibility appropriately. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability.

  In the tire 2, it is preferable that the complex elastic modulus (E *) of the inner layer 50 measured under the condition that the temperature is 70 ° C. and the amplitude is 2% is 4 MPa or more and 5 MPa or less. By setting the complex elastic modulus to 4 MPa or more, the inner layer 50 can prevent excessive deformation of the sidewall 6. The tire 2 is excellent in cut resistance. In this respect, the complex elastic modulus is more preferably equal to or greater than 4.1 MPa, and particularly preferably equal to or greater than 4.2 MPa. By setting the complex elastic modulus to 5 MPa or less, excessive rigidity of the sidewall 6 can be prevented. In the tire 2, the flexibility of the sidewall 6 can be maintained. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability. From this viewpoint, the complex elastic modulus is more preferably 4.9 MPa or less, and particularly preferably 4.8 MPa or less.

  In the tire 2, it is preferable that the loss factor (tan δ) of the inner layer 50 measured under the condition that the temperature is 70 ° C. and the amplitude is 2% is 0.12 or more and 0.15 or less. The inner layer 50 whose loss coefficient is set to 0.12 or more can effectively absorb the impact received by the tire 2. The tire 2 is excellent in ride comfort. From this viewpoint, the loss factor is more preferably 0.13 or more. By setting the loss factor to 0.15 or less, heat generation of the inner layer 50 due to deformation of the tire 2 can be suppressed. In this respect, the loss factor is more preferably 0.14 or less.

In the present invention, the complex elastic modulus and loss coefficient of the inner layer 50 and the complex elastic modulus and loss coefficient of the outer layer 52 to be described later are viscoelastic under the conditions shown below in accordance with the provisions of “JIS-K 6394”. It is measured by a spectrometer (“VES • F-3” manufactured by Iwamoto Seisakusho).
Initial strain: 10%
Amplitude: 2%
Frequency: 10Hz
Deformation mode: Tensile
Starting temperature: -100 ° C
End temperature: 100 ° C
Temperature rising temperature: 3 ° C / min
Measurement temperature: 70 ° C

  The test piece used for the measurement by a viscoelastic spectrometer is plate shape, the length is 45 mm, the width is 4 mm, and the thickness is 2 mm. Measurement is performed by chucking both ends of the test piece. The length of the displacement part of the test piece is 30 mm. This test piece is cut out from the tire 2. When it is difficult to cut out, this test piece is punched out from a slab obtained by holding the rubber composition constituting the inner layer 50 or the outer layer 52 in a mold having a temperature of 160 ° C. for 10 minutes.

  In the tire 2, the complex elastic modulus (E *) measured under the condition that the temperature of the outer layer 52 is 70 ° C. and the amplitude is 2% is preferably 2.8 MPa or more and 4.5 MPa or less. . By setting the complex elastic modulus to be 2.8 MPa or more, it is possible to prevent the outer layer 52 from being excessively rigid. In the tire 2, the rigidity of the sidewall 6 can be appropriately maintained. The tire 2 is excellent in handling stability. From this viewpoint, the complex elastic modulus is more preferably 3.0 MPa or more, and particularly preferably 3.2 MPa or more. By setting the complex elastic modulus to 4.5 MPa or less, excessive rigidity of the sidewall 6 can be prevented. In the tire 2, the flexibility of the sidewall 6 can be maintained. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability. In this respect, the complex elastic modulus is more preferably 4.3 MPa or less, and particularly preferably 4.1 MPa or less.

  In the tire 2, it is preferable that the loss coefficient (tan δ) of the outer layer 52 measured under the condition that the temperature is 70 ° C. and the amplitude is 2% is 0.13 or more and 0.20 or less. By setting the loss factor to be 0.13 or more, when crushed stone collides with the outer layer 52, the outer layer 52 converts the elastic energy stored as work performed by the external force at the time of collision into thermal energy. It can be converted effectively. In the tire 2, a cut due to a collision with crushed stones is difficult to occur. The tire 2 is excellent in cut resistance. From this viewpoint, the loss factor is more preferably 0.15 or more. By setting the loss factor to 0.20 or less, excessive heat generation of the outer layer 52 due to deformation of the tire 2 can be suppressed. The tire 2 is excellent in durability. From this viewpoint, the loss factor is more preferably 0.18 or less.

  In the tire 2, the ratio of the complex elastic modulus of the outer layer 52 to the complex elastic modulus of the inner layer 50 is 70% or more and 90% or less. By setting this ratio to 70% or more, the rigidity of the outer layer 52 is prevented from being excessively low. In the tire 2, the rigidity of the sidewall 6 can be appropriately maintained. The tire 2 is excellent in handling stability. In this respect, the ratio is more preferably equal to or greater than 75%, and particularly preferably equal to or greater than 78%. By setting this ratio to 90% or less, the outer layer 52 can be easily deformed when crushed stones or the like collide with the outer layer 52. The tire 2 is excellent in cut resistance. Since the outer layer 52 has sufficient elasticity, even if the tire 2 is used for long-distance running, no cracks are generated on the surface thereof. The tire 2 is excellent in durability. In this respect, the ratio is more preferably equal to or less than 85%, and particularly preferably equal to or less than 83%.

  In the tire 2, the ratio of the loss coefficient of the outer layer 52 to the loss coefficient of the inner layer 50 is 105% or more and 135% or less. When this ratio is set to 105% or more, when crushed stone collides with the outer layer 52, the outer layer 52 is effective for heat energy, and the outer layer 52 is effective for heat energy. Can be converted to In the tire 2, a cut due to a collision with crushed stones is difficult to occur. The tire 2 is excellent in cut resistance. In this respect, the ratio is more preferably equal to or greater than 105%, and particularly preferably equal to or greater than 110%. By setting this ratio to 135% or less, excessive heat generation of the outer layer 52 can be suppressed. The tire 2 is excellent in durability. In this respect, the ratio is more preferably equal to or less than 130%, and particularly preferably equal to or less than 125%.

  In FIG. 2, a solid line L1 is a straight line passing through the point P1 and extending in the axial direction. A double arrow line TA represents the thickness of the sidewall 6 in the straight line L1. In the present invention, this thickness TA is used as the total thickness of the sidewall 6. A double arrow line TB represents the thickness of the inner layer 50 in the straight line L1. In the present invention, this thickness TB is used as the thickness of the inner layer 50.

  In the tire 2, the thickness TA is preferably 4 mm or more and 12 mm or less. By setting the thickness TA to 4 mm or more, the occurrence of puncture starting from the cut generated in the sidewall 6 can be reliably prevented. The tire 2 provided with the sidewall 6 is excellent in puncture resistance. From this viewpoint, the thickness TA is more preferably 5 mm or more, and particularly preferably 6 mm or more. By setting the thickness TA to 12 mm or less, the flexibility of the sidewall 6 can be maintained. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability. In this respect, the thickness TA is more preferably 10 mm or less, and particularly preferably 9 mm or less.

  In the tire 2, the ratio of the thickness TB to the thickness TA is 20% or more and 80% or less. By setting this ratio to 20% or more, the inner layer 50 can contribute to prevention of occurrence of puncture starting from a cut generated in the sidewall 6. The tire 2 is excellent in puncture resistance. In this respect, the ratio is more preferably equal to or greater than 25%, and particularly preferably equal to or greater than 30%. By setting this ratio to 80% or less, the flexibility of the sidewall 6 can be maintained. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability. In this respect, the ratio is more preferably equal to or less than 75%, and particularly preferably equal to or less than 70%.

  In the tire 2, the inner layer 50 is formed by crosslinking a rubber composition containing a base rubber and carbon black as a filler. This rubber composition contains chemicals such as a crosslinking agent, a vulcanization accelerator and an anti-aging agent in addition to the base rubber and carbon black. In consideration of the workability and performance of the tire 2, an optimal chemical is blended in the rubber composition in an optimal amount. This carbon black is “N550” manufactured by Cabot Japan. In the tire 2, the blending amount of the softening agent contained in the rubber composition constituting the inner layer 50 is small. This rubber composition may not contain a softener. Specifically, the blending amount of the softening agent contained in the rubber composition constituting the inner layer 50 is preferably 5 parts by mass or less with respect to 100 parts by mass of the base rubber.

  In the tire 2, as the base rubber of the inner layer 50, natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene copolymer, polychloroprene, acrylonitrile-butadiene copolymer, and isobutylene- An isoprene copolymer is exemplified. The base rubber of the inner layer 50 is preferably constituted by blending natural rubber and polybutadiene. The mass ratio ((natural rubber) / (polybutadiene)) of this blend is preferably 20/80 or more and 60/40 or less. In the tire 2, the natural rubber is “RSS # 3”. This polybutadiene is “BR01” manufactured by JSR Corporation.

  In the tire 2, the outer layer 52 is formed by crosslinking a rubber composition containing a base rubber and carbon black as a filler. In the tire 2, unlike the rubber composition of the inner layer 50 described above, the rubber composition of the outer layer 52 further includes a softening agent. Therefore, the crosslinked rubber constituting the outer layer 52 is different from the crosslinked rubber constituting the inner layer 50. The rubber composition of the outer layer 52 contains chemicals such as a crosslinking agent, a vulcanization accelerator, and an anti-aging agent in addition to the base rubber, carbon black, and softening agent. In consideration of the workability and performance of the tire 2, an optimal chemical is blended in the rubber composition in an optimal amount. In the tire 2, the carbon black is “N550” manufactured by Cabot Japan. The softening agent for the inner layer 50 is “X140” manufactured by Japan Energy Co., Ltd.

  In the tire 2, as the base rubber of the outer layer 52, natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene copolymer, polychloroprene, acrylonitrile-butadiene copolymer, and isobutylene- An isoprene copolymer is exemplified. The base rubber of the inner layer 50 is preferably constituted by blending natural rubber and polybutadiene. The mass ratio ((natural rubber) / (polybutadiene)) of this blend is preferably 25/75 or more and 65/35 or less. In the tire 2, the base rubber of the outer layer 52 is different from the base rubber of the inner layer 50. In the tire 2, the natural rubber is “RSS # 3”. This polybutadiene is “BR01” manufactured by JSR Corporation.

  In the tire 2, the complex elastic modulus and loss factor of the inner layer 50 are adjusted by optimizing the amount of carbon black. The complex elastic modulus and the outer layer 52 are adjusted by optimizing the amounts of carbon black and softening agent.

  In the tire 2, the amount of carbon black contained in the rubber composition constituting the inner layer 50 is preferably 35 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 35 parts by mass or more, the inner layer 50 can prevent excessive deformation of the sidewall 6. The tire 2 is excellent in cut resistance. In this respect, the amount is more preferably equal to or greater than 40 parts by weight. By setting the blending amount to 50 parts by mass or less, excessive rigidity of the sidewall 6 can be prevented. In the tire 2, the flexibility of the sidewall 6 can be maintained. Since the tire 2 has a sufficient ground contact property, it is excellent in handling stability. In this respect, the amount to be blended is more preferably equal to or less than 45 parts by weight. In the tire 2, the amount of carbon black contained in the rubber composition constituting the inner layer 50 is 42 parts by mass with respect to 100 parts by mass of the base rubber.

  In the tire 2, the amount of carbon black contained in the rubber composition constituting the outer layer 52 is preferably 40 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 40 parts by mass or more, the rigidity of the outer layer 52 is prevented from being excessively low. In the tire 2, the rigidity of the sidewall 6 can be appropriately maintained. The tire 2 is excellent in handling stability. In this respect, the amount is more preferably equal to or greater than 45 parts by weight. By setting the blending amount to 55 parts by mass or less, the outer layer 52 can be easily deformed when crushed stone or the like collides with the outer layer 52. The tire 2 is excellent in cut resistance. Since the stretchability of the outer layer 52 can be maintained, even when the tire 2 is used for long distance running, no cracks are generated on the surface thereof. The tire 2 is excellent in durability. In this respect, the amount is more preferably equal to or less than 55 parts by weight. In the tire 2, the compounding amount of carbon black contained in the rubber composition constituting the outer layer 52 is 50 parts by mass with respect to 100 parts by mass of the base rubber.

  In the tire 2, the blending amount of the softening agent contained in the rubber composition constituting the outer layer 52 is preferably 5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 5 parts by mass or more, the outer layer 52 can be easily deformed when crushed stones or the like collide with the outer layer 52. The tire 2 is excellent in cut resistance. Since the stretchability of the outer layer 52 can be maintained, even when the tire 2 is used for long distance running, no cracks are generated on the surface thereof. The tire 2 is excellent in durability. In the production of the rubber composition, good processability can be maintained. In this respect, the amount is more preferably equal to or greater than 8 parts by weight. By setting the blending amount to 15 parts by mass or less, the rigidity of the outer layer 52 is prevented from being excessively low. In the tire 2, the rigidity of the sidewall 6 can be appropriately maintained. The tire 2 is excellent in handling stability. In this respect, the amount is more preferably equal to or less than 12 parts by mass. In the tire 2, the blending amount of the softener contained in the rubber composition constituting the outer layer 52 is 10 parts by weight with respect to 100 parts by weight of the base rubber.

  In the present invention, the size and angle of 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. For convenience, the internal pressure of the passenger car tire 2 is set to 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.

[Adjustment of rubber composition D]
45 parts by mass of natural rubber, 55 parts by mass of polybutadiene, 50 parts by mass of carbon black, and 10 parts by mass of a softening agent were kneaded in a closed kneader to obtain rubber composition D. Natural rubber is “RSS # 3”. The polybutadiene is “BR01” manufactured by JSR Corporation. This carbon black is “N550” manufactured by Cabot Japan. This softener is “X140” manufactured by Japan Energy Corporation. The complex elastic modulus and loss factor of the crosslinked rubber obtained by crosslinking this rubber composition D were measured under the condition that the temperature was 70 ° C. and the amplitude was 2%. The measurement results are shown in Table 1 below.

[Adjustment of rubber compositions B, C, E and F]
Rubber compositions B, C, E, and F were obtained in the same manner as the rubber composition D, except that the blending amount of carbon black was as shown in Table 1 below.

[Adjustment of rubber composition A]
Rubber composition A was obtained in the same manner as rubber composition D, except that the blending amounts of natural rubber, polybutadiene, carbon black and softener were as shown in Table 1 below.

[Example 1]
A pneumatic tire for a rally according to Example 1 having the basic configuration shown in FIG. 1 and having the specifications shown in Table 2 below was obtained. The tire size is 205 / 65R15. The inner layer is formed by crosslinking the rubber composition A. The outer layer is formed by crosslinking the rubber composition D. The total thickness of the sidewall is 8 mm. The thickness of the inner layer is 4 mm. The thickness of the outer layer is 4 mm. The ratio of the thickness of the inner layer to the total thickness is 50%. In Table 2, this ratio is displayed as a thickness ratio. The inner layer has a complex elastic modulus of 4.3 MPa. The complex elastic modulus of this outer layer is 3.4 MPa. Therefore, the ratio of the complex elastic modulus of the outer layer to the complex elastic modulus of the inner layer is 79%. In Table 2, this ratio is displayed as a ratio of complex elastic modulus. The loss factor of this inner layer is 0.13. The loss factor of this outer layer is 0.16. Therefore, the ratio of the loss factor of the outer layer to the loss factor of the inner layer is 123%. In Table 2, this ratio is displayed as the ratio of the loss factor.

[Comparative Examples 2 and 3 and Examples 4 to 7]
Tires were obtained in the same manner as in Example 1 except that the thickness ratios were as shown in Tables 2 and 3 below.

[Comparative Examples 4 and 5]
A tire was obtained in the same manner as in Example 1 except that the sidewall was made of a crosslinked rubber composed only of the rubber composition A and the total thickness was as shown in Table 3 below. Comparative Examples 4 and 5 are commercially available conventional tires.

[Comparative Examples 1 and 6 and Examples 3 and 8]
Tires were obtained in the same manner as in Example 1 except that the rubber composition of the outer layer was as shown in Tables 2 and 3 below, and the ratio of the complex elastic modulus and the ratio of the loss coefficient were changed.

[Examples 2 and 9]
Tires were obtained in the same manner as in Example 1 except that the total thickness of the sidewalls was as shown in Tables 2 and 3 below.

[Cut resistance evaluation]
Using a pendulum impact tester, a cut was formed on the side wall of the prototype tire. The energy up to this cut was calculated by a predetermined method. The results are shown in Tables 2 and 3 below as index values with Comparative Example 1 taken as 100. A large index value indicates excellent cut resistance.

[Real car evaluation]
The prototype tire was mounted on a rally vehicle having a displacement of 2000 cm3 and four-wheel drive. The internal pressure of the tire was 220 kPa. This vehicle was run on a dirt course with one lap of 1.5 km. A sensory evaluation by the driver was performed on the driving stability during driving. The evaluation results are shown in Tables 2 and 3 below as index values with 5 points being perfect. Larger values indicate better results.

[Durability evaluation]
The prototype tire was mounted on a rim of a drum durability tester and ran at a speed of 80 km / h under a maximum load load. After traveling 30,000 km, the tire was visually observed to check for cracks in the sidewall. The results are shown in Tables 2 and 3 below as A when the occurrence of cracks was not confirmed and as B when the occurrence was confirmed.

  As shown in Tables 2 and 3, the tires of the examples are excellent in cut resistance, steering stability and durability. From this evaluation result, the superiority of the present invention is clear.

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

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

Explanation of symbols

2 ... Tire 4 ... Tread 6 ... Sidewall 8 ... Clinch 10 ... Bead 12 ... Carcass 14 ... Belt 16 ... Band 18 ... First strip 20 .... Second strip 22 ... Inner liner 24 ... Chafer 26 ... Main body 28 ... Wing 30 ... Tread surface 32 ... Groove 34 ... Core 36 ... Apex 38 ... First carcass ply 40 ... Second carcass ply 42 ... Inner ply 44 ... Outer ply 46 ... Inner band ply 48 ... Outer band ply 50 ... Inner layer 52 ... Outer layer 54, 54a ... Protector rib 56, 60, 64 ... Border 58, 62 ... End

Claims (4)

It has a pair of beads, a carcass spanned between both beads, and a sidewall.
This sidewall has an inner layer and an outer layer,
This inner layer is located outside the carcass in the axial direction,
This outer layer is located further outside this inner layer in the axial direction,
The ratio of the thickness of the inner layer to the thickness of the sidewall is 20% or more and 80% or less,
The ratio of the complex elastic modulus of the outer layer to the complex elastic modulus of the inner layer is 70% or more and 90% or less,
A pneumatic tire for a rally, wherein the ratio of the loss factor of the outer layer to the loss factor of the inner layer is 105% or more and 135% or less. The complex elastic modulus of the inner layer is 4 MPa or more and 5 MPa or less,
The tire according to claim 1, wherein the inner layer has a loss coefficient of 0.12 to 0.15.   The tire according to claim 1 or 2, wherein the sidewall has a thickness of 4 mm or more and 12 mm or less.   The tire according to any one of claims 1 to 3, wherein the outer layer includes a protector rib at a position where the tire has a maximum width.

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