JP5944700B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire.

  Some tires have a fold ply on the inner belt layer of the tread. In this field ply, the outer edge in the axial direction is folded back inward in the axial direction. The folded portion increases the rigidity of the shoulder region of the tread. This tire is excellent in straight running stability and turning performance during high speed running. A tire including a belt layer including the fold ply is disclosed in Japanese Patent Application Laid-Open No. 2008-238878.

  In this tire, the rigidity of the shoulder region of the tread is larger than that of the center region. The center area of the tread is more easily deformed than the shoulder area. For this reason, a difference in the amount of wear tends to occur between the shoulder region and the center region. In this tire, uneven wear tends to occur.

  Japanese Unexamined Patent Application Publication No. 2009-298236 discloses a tire that includes a fold ply and includes a reinforcing sheet on a tire lumen surface. This reinforcing sheet is located in a region between the edges of the folded portion of the fold ply in the axial direction. By providing the tire with this reinforcing sheet, uneven wear can be suppressed without impairing high-speed running performance.

JP 2008-238878 A JP 2009-298236 A

  The reinforcing sheet described in the above Japanese Patent Application Laid-Open No. 2009-298236 is attached to the tire cavity surface. It is difficult to accurately position the folded portion of the fold ply between one end edge and the other end edge. When the reinforcing sheet extends in the axial direction beyond the edge of the folded portion, the reinforcing sheet and the folded portion overlap in the radial direction. The rigidity is increased at the overlapping portion. If an axial gap is formed between the edge of the folded portion and the axial end of the reinforcing sheet, the tread is easily deformed at the gap. In this tire, there is a possibility that sufficient uneven wear cannot be suppressed depending on the position where the reinforcing sheet is attached.

  An object of the present invention is to provide a pneumatic tire that can suppress uneven wear with a simple configuration without impairing high-speed running performance.

  The pneumatic tire according to the present invention has 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 each positioned radially inward of the sidewalls. A pair of beads, a carcass spanned between one bead and the other bead along the inside of the tread and the sidewall, and a belt laminated with the carcass on the radially inner side of the tread ing. The tread includes a base layer located on the radially inner side and a cap layer located on the radially outer side of the base layer. This belt includes a fold ply. The fold ply includes a main portion located at the center in the axial direction and a pair of folded portions located on the outer side in the axial direction and folded back from the inner side in the radial direction. The axially inner ends of the pair of folded portions of the fold ply are separated from each other. A base layer is laminated between the axially inner end of one folded portion of the fold ply and the axially inner end of the other folded portion. The hardness of the crosslinked rubber of the base layer is greater than the hardness of the crosslinked rubber of the cap layer.

  Preferably, the rubber hardness of the crosslinked rubber of the base layer is 50 or more and 60 or less. Preferably, the hardness of the crosslinked rubber of the cap layer is 35 or more and 45 or less.

  Preferably, a ratio (Wa / Wt) between a distance Wa between the axially inner end of the one folded portion and the axially inner end of the other folded portion and a distance Wt from one axial end to the other end of the tread. ) Is 0.83 or more and 0.89 or less.

  Preferably, a ratio (Wb / Wt) between the axial width Wb of the inner layer and the distance Wt from one end to the other end in the axial direction of the tread is 0.94 or more and 0.97 or less.

  In the pneumatic tire according to the present invention, the rigidity of the center region and the shoulder region of the tread is made uniform with a simple configuration. Thereby, uneven wear of the tread is suppressed.

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

  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 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2. The shape of the tire 2 is symmetric with respect to the equator plane. In FIG. 1, a solid line BBL represents a bead base line. The bead base line is a line that defines a rim diameter (see JATMA) of a rim (not shown) on which the tire 2 is mounted.

  The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a belt 12, a band 14, an inner liner 16, and a chafer 18. The tire 2 is a tubeless type. The tire 2 is attached to a four-wheeled vehicle for racing.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 20 that contacts the road surface. The tread surface 20 has no groove. Grooves may be cut into the tread surface 20 to form a tread pattern.

  The tread 4 includes a base layer 22 and a cap layer 24. The cap layer 24 is located on the outer side in the radial direction of the base layer 22. The cap layer 24 is laminated on the base layer 22. The base layer 22 is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber of the base layer 22 is natural rubber. The cap layer 24 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties.

  A double arrow t <b> 1 in FIG. 1 indicates the thickness of the tread 4. The thickness t1 indicates the combined thickness of the base layer 22 and the cap layer 24. In a racing tire, the thickness t1 is smaller than a general passenger car tire. In the tire 2 in which the thickness of the tread 4 is small, the heat generation of the tread 4 is suppressed. Thereby, this tire 2 is excellent in high-speed durability. From this viewpoint, particularly in a racing tire, the thickness t1 is 5.5 mm or less, more preferably 4.5 mm or less. On the other hand, from the viewpoint of wear resistance of the tire 2, the thickness t1 is preferably 2.0 mm or more, and more preferably 3.0 mm or more.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. A portion of the sidewall 6 on the outer side in the radial direction is joined to the tread 4. The radially inner end of the sidewall 6 is located on the outer side in the axial direction of the bead 8. The sidewall 6 is made of a crosslinked rubber. The side wall 6 prevents the carcass 10 from being damaged.

  The bead 8 is located inside the sidewall 6 in the radial direction. The bead 8 includes a core 26 and an apex 28 extending outward from the core 26 in the radial direction. The core 26 has a ring shape. The core 26 includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 28 is tapered outward in the radial direction. The apex 28 is made of a highly hard crosslinked rubber.

  The carcass 10 includes a first carcass ply 30 and a second carcass ply 32. The first carcass ply 30 and the second carcass ply 32 are bridged between the beads 8 on both sides, and extend along the tread 4 and the sidewall 6. The first carcass ply 30 is folded around the core 26 from the inner side to the outer side in the axial direction. By this folding, the main carcass ply 30 is formed with a main portion 30a and a folding portion 30b. The second carcass ply 32 is folded around the core 26 from the inner side to the outer side in the axial direction. By this folding, the main part 32a and the folding part 32b are formed in the second carcass ply 32. The end of the folded portion 30b of the first carcass ply 30 is located outside the end of the folded portion 32b of the second carcass ply 32 in the radial direction.

  Each of the carcass plies 30 and 32 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 45 ° to 90 °, and further 75 ° to 90 °. In other words, the carcass 10 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 10 may be formed from a single carcass ply.

  The belt 12 is located on the radially outer side of the carcass 10. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10. The belt 12 includes an inner layer 34 and an outer layer 36.

  The inner layer 34 is folded back from the inner side in the radial direction at the end 14 a of the band 14. By this folding, the inner layer 34 includes a main portion 34 a located on the inner side in the radial direction of the band 14 and a folded portion 34 b located on the outer side in the radial direction of the band 14. An outer layer 36 is laminated on the outer side in the radial direction of the main portion 34a. The band 14 covers the radially outer side of the outer layer 36. The end 36 a of the outer layer 36 and the end 14 a of the band 14 are encased in the inner layer 34. This inner layer 34 is a fold ply. In the tire 2, the belt 12 and the band 14 are effectively restrained in the shoulder region.

  Although not shown, each of the inner layer 34 and the outer layer 36 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 inner layer 34 with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 36 with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The axial width of the belt 12 is preferably 0.7 times or more the maximum width of the tire 2. The belt 12 may include three or more layers.

  The band 14 is located radially outside the main portion 34 a of the inner layer 34 and the outer layer 36. The band 14 of the tire 2 has a width substantially equal to the width of the belt 12 in the axial direction. Although not shown, the band 14 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 14 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, further 2 ° or less. Since the belt 12 is restrained by this cord, lifting of the belt 12 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 belt 12 and the band 14 constitute a reinforcing layer 38. The reinforcing layer 38 may be formed only from the belt 12.

  The inner liner 16 is located inside the carcass 10. The inner liner 16 covers the inner peripheral surface of the carcass 10. The inner liner 16 is made of a crosslinked rubber. For the inner liner 16, rubber having excellent air shielding properties is used. A typical base rubber of the inner liner 16 is butyl rubber or halogenated butyl rubber. The inner liner 16 holds the internal pressure of the tire 2.

  The chafer 18 is located in the vicinity of the bead 8. When the tire 2 is incorporated into the rim, the chafer 18 comes into contact with the rim. By this contact, the vicinity of the bead 8 is protected. The chafer 18 is made of cloth and rubber impregnated in the cloth.

  A point Pt in FIG. 1 indicates the axial end of the tread 4. A double-headed arrow Wt indicates a distance from one end Pt to the other end Pt (not shown). This distance Wt is the tread width. A double-headed arrow Wa indicates the distance between the axially inner end 34c of one folded portion 34b and the axially inner end 34c of the other folded portion 34b (not shown). A double-headed arrow Wb indicates the width of the inner layer 34 in the axial direction. A double-headed arrow Wc indicates the width of the base layer 22 in the axial direction. This width Wt is measured along the tread surface 20. The width Wa, the width Wb, and Wc are measured along the radial outer peripheral surface of the folded portion 34b of the inner layer 34 in the cross section of FIG.

  In the tire 2, the pair of folded portions 34 b improves the rigidity of the shoulder region of the tread 4. Since the rigidity of the shoulder region is improved, the tire 2 is excellent in straight running stability and turning performance during high speed running. From this viewpoint, the ratio (Wb / Wt) of the width Wb to the width Wt is preferably 0.94 or more, and more preferably 0.95 or more. On the other hand, if the ratio (Wb / Wt) is too large, the tread rubber is thinned in the axial direction outside the inner layer 34 in the axial direction. If this ratio (Wb / Wt) is too large, the durability of the tread at high speeds is lowered. From this viewpoint, the ratio (Wb / Wt) is preferably 0.97 or less, and more preferably 0.96 or less.

  In the tire 2, the ratio of the width Wa to the width Wt (Wa / Wt) is preferably 0.89 or less, and more preferably 0.87 or less, from the viewpoint of straight running stability and turning performance during high speed running. It is. On the other hand, the tire 2 having a large width of the folded portion 34b has a large mass. From this viewpoint, the ratio (Wa / Wt) is preferably 0.83 or more, and more preferably 0.85 or more.

  The hardness of the crosslinked rubber of the base layer 22 of the tread 4 is made larger than the hardness of the crosslinked rubber of the cap layer 24. In the tire 2, the base layer 22 is laminated between the inner end 34c of one folded portion 34b and the inner end 34c of the other folded portion 34b. In the tire 2, the ratio of the width Wc to the width Wa (Wc / Wa) is set to 1.0. The rigidity of the tread 4 is improved between the one folded portion 34b and the other folded portion 34b. Thereby, the difference in rigidity between the shoulder region and the center region of the tread 4 is reduced. A difference in wear amount between the shoulder region and the center region of the tread 4 is reduced. In the tire 2, uneven wear of the tread 4 is suppressed.

  From the viewpoint of suppressing uneven wear of the tread 4, the hardness of the crosslinked rubber of the base layer 22 is preferably 50 or more. The hardness of the crosslinked rubber of the base layer 22 is more preferably 52 or more, and particularly preferably 54 or more.

  On the other hand, the tire 2 having a low hardness of the crosslinked rubber of the base layer 22 suppresses a decrease in grip performance of the tread 4. In particular, in the race tire, since the thickness t1 of the tread 4 is small, the hardness of the crosslinked rubber of the base layer 22 greatly affects the grip performance. From this viewpoint, the hardness of the crosslinked rubber of the base layer 22 is preferably 60 or less, more preferably 58 or less, and particularly preferably 56 or less.

  Since the cap layer 24 is located on the outer side in the radial direction between the pair of folded portions 34b and the base layer 22, rubber having excellent grip performance can be used. The hardness of the crosslinked rubber of the cap layer 24 is preferably 45 or less. The hardness of the crosslinked rubber of the cap layer 24 is more preferably 43 or less, and particularly preferably 41 or less.

  On the other hand, the tire 2 in which the hardness of the cross-linked rubber of the cap layer 24 is excellent in wear resistance. From this viewpoint, the hardness of the crosslinked rubber of the cap layer 24 is preferably 35 or more. The hardness of the crosslinked rubber of the cap layer 24 is more preferably 37 or more, and particularly preferably 39 or more.

  Like the tire 2, in the racing tire, the thickness t <b> 1 is small, so the hardness of the crosslinked rubber of the base layer 22 greatly contributes to the rigidity of the tread 4. The tire 2 can exhibit the effect of uniforming the rigidity of the tread 4 in a racing tire. In addition, the configuration in which the base layer 22 is stacked between the inner ends 34c of the pair of folded portions can suppress the thickness t1 of the tread 4 to be small. The tire 2 in which the base layer 22 is laminated between the inner ends 34c of the pair of folded portions is particularly suitable for a racing tire. The tire 2 including the base layer 22 is suitable for a tire having a thickness t1 of the tread 4 of 5.0 mm or less, and further a tire having a thickness t1 of 4.0 mm or less.

  In the present invention, the rubber has a JIS-A hardness. This hardness is measured with a type A durometer in an environment of 23 ° C. in accordance with the provisions of “JIS-K6253”. More specifically, the hardness of the crosslinked rubber of the base layer 22 and the hardness of the crosslinked rubber of the cap layer 24 are measured by pressing a type A durometer against the cross section shown in FIG.

  In the present invention, unless otherwise specified, the dimension and angle of each member of the tire 2 are such that the tire 2 is incorporated in a normal rim and air is supplied to the tire 2 so as to have a normal internal pressure unless otherwise measured. Measured in the filled state. 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 pneumatic tire of Example 1 having the basic configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The tire size was “330 / 710R17”.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that a base layer was not provided and a tread composed of a single crosslinked rubber was provided.

[Comparative Example 2-3]
A tire of Comparative Example 2-3 was obtained in the same manner as in Example 1 except that the ratio between the width Wc of the base layer and the separation width Wa was as shown in Table 1 below.

[Comparative Example 4]
A tire of Comparative Example 4 was obtained in the same manner as in Example 1 except that the rubber hardness of the base layer and the cap layer was as shown in Table 1.

[Example 2-9]
A tire of Example 2-9 was obtained in the same manner as Example 1 except that the rubber hardness of the base layer was as shown in Table 2.

[Example 10-17]
Tires of Examples 10-17 were obtained in the same manner as Example 1 except that the rubber hardness of the cap layer was as shown in Table 3.

[Lap time, steering stability and turning performance]
The tire was assembled in a standard rim, and this tire was filled with air so that the internal pressure was 160 kPa. This tire was mounted on a racing four-wheeled vehicle having a displacement of 3400 cc. I let the driver drive this car on the racing circuit. The lap time of 4.5 km per lap was measured 10 times, and the average lap time was measured. In addition, the driver was given a sensory evaluation of steering stability and turning performance. This result is an index based on 100 and is shown in Tables 1 to 3 below. This index is a relative evaluation based on Comparative Example 1 as 100, and the larger the value, the better.

[Uneven wear]
The tire was assembled in a standard rim, and this tire was filled with air so that the internal pressure was 160 kPa. This tire was mounted on a racing four-wheeled vehicle having a displacement of 3400 cc. I drove the racing circuit at high speed. The maximum wear amount and the minimum wear amount of the tread rubber were measured in the cross section cut out from the tire after traveling a distance of 150 km. The uneven wear amount was determined as the difference between the maximum wear amount and the minimum wear amount. The result is an index based on 100 and is shown in Tables 1 to 3 below. This index is a relative evaluation based on Comparative Example 1 as 100, and the larger the value, the better.

[Comprehensive evaluation]
For each, a comprehensive evaluation was performed in five stages from A to E. This comprehensive evaluation uses Comparative Example 1 as a reference comprehensive evaluation C, and uses this comprehensive evaluation C as a reference. This evaluation means that A is the best and E is the worst.

  As shown in Tables 1 to 3, the tires of the examples have higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The pneumatic tire described above can be applied to various tires.

2 ... tyre 4 ... tread 6 ... side wall 8 ... bead 10 ... carcass 12 ... belt 14 ... band 16 ... inner liner 18 ... chafer 20 ... .. tread surface 22 ... base layer 24 ... cap layer 26 ... core 28 ... apex 30 ... first carcass ply 32 ... second carcass ply 34 ... inner layer 36 ... Outer layer 38 ... Reinforcing layer

Claims (7)

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, a pair of beads each positioned radially inward of the sidewalls, the tread and the above It has a carcass stretched between one bead and the other bead along the inside of the sidewall, and a belt located radially inward of the tread ,
The tread includes a base layer located on the radially inner side and a cap layer located on the radially outer side of the base layer,
The belt includes a fold ply and an outer layer . The fold ply includes a main portion located in the center in the axial direction, and a pair of folded portions that are located on the outer side in the axial direction and are folded back from the inner side in the radial direction. And
The axially inner ends of the pair of folded portions of the fold ply are separated from each other,
This outer layer is laminated radially outward of the main part of the fold ply, the axial end of this outer layer is wrapped in the fold ply,
The base layer is located in a separation section from the axially inner end of the one folded part to the axially inner end of the other folded part,
A pneumatic tire in which the hardness of the crosslinked rubber of the base layer is greater than the hardness of the crosslinked rubber of the cap layer.   The pneumatic tire according to claim 1, wherein the hardness of the crosslinked rubber of the base layer is 50 or more and 60 or less.   The pneumatic tire according to claim 1 or 2, wherein the hardness of the crosslinked rubber of the cap layer is 35 or more and 45 or less.   The ratio (Wa / Wt) between the distance Wa between the axially inner end of the one folded part and the axially inner end of the other folded part and the distance Wt from one end to the other end of the tread in the axial direction, The pneumatic tire according to any one of claims 1 to 3, which is 0.83 or more and 0.89 or less. The ratio (Wb / Wt) between the axial width Wb of the fold ply and the distance Wt from one end to the other end in the axial direction of the tread is 0.94 or more and 0.97 or less. The pneumatic tire according to Crab. With a band,
  This band has a cord and topping rubber, and this cord is spirally wound in the circumferential direction.
The pneumatic according to any one of claims 1 to 5, wherein the band is located radially outside the main part of the fold ply and the outer layer, and an axial end of the band is encased in the fold ply. tire. The pneumatic tire according to any one of claims 1 to 6, wherein the base layer is not located radially outside the folded portion.

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