JP5200690B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having a so-called half radial structure, and more particularly to a pneumatic tire that can improve flat spot resistance while maintaining good high-speed durability.

  In recent years, with the improvement in performance of passenger cars, high exercise performance is also required for pneumatic tires. In order to satisfy these requirements, a pneumatic angle having a so-called half radial structure in which the cord angle of the carcass layer with respect to the tire circumferential direction is made smaller than 90 ° and the reinforcing cords of the carcass layer are arranged so as to cross each other. Tires have been proposed. In a pneumatic tire having a half radial structure, a 66 nylon fiber cord is generally used as a reinforcing cord for a carcass layer, but a low elastic fiber made of a high twist fiber yarn made of an aliphatic polyketone and 66 nylon. It has also been proposed to use a composite cord in which a yarn is twisted together with a yarn (see, for example, Patent Document 1).

  By the way, if a vehicle is parked for a long time after running at high speed, a flat spot may be formed on the tire. In other words, a tire that has generated heat due to high-speed traveling is cooled in a deformed state while the vehicle is stopped, thereby causing a creep set (a phenomenon in which deformation is fixed) to the tire constituent member. In particular, when a material having a low glass transition point is used for the tire constituent member, a flat spot is easily formed. When such a flat spot is formed, the uniformity of the tire is deteriorated, and road noise and vibration are increased.

Since the pneumatic tire having the half radial structure described above uses a 66 nylon fiber cord having a low glass transition point or a composite cord containing 66 nylon fiber as a reinforcing cord for the carcass layer, there is a problem that flat spot resistance is poor. It has been pointed out. In particular, when a flat spot is formed in a pneumatic tire having a half radial structure, adverse effects due to the flat spot tend to be noticeable.
JP 2006-88719 A

  An object of the present invention is to provide a pneumatic tire that can improve flat spot resistance while maintaining good high-speed durability.

In order to achieve the above object, a pneumatic tire according to the present invention is constructed by mounting at least two carcass layers having a cord angle in a range of 70 ° to 88 ° with respect to the tire circumferential direction between a pair of bead portions. In the pneumatic tire in which the reinforcing cords of the layers are arranged so as to cross each other and the belt layer is arranged on the outer peripheral side of the carcass layer in the tread portion, the elastic cord has a modulus of elasticity of 10,000 MPa or more as the reinforcing cord of the single carcass layer. A composite cord obtained by twisting a low-elastic fiber yarn made of 46 nylon and a low-elastic fiber yarn made of 46 nylon by twisting them in the opposite direction to the lower twist is used as a reinforcing cord of another carcass layer. A nylon fiber cord is used .

  In the present invention, in a pneumatic tire having a half radial structure, a composite cord is used in which a low-elastic fiber yarn of a composite cord is twisted into 66 nylon using a composite cord in which a low-elastic fiber yarn and a low-elastic fiber yarn are twisted together. Comparing with 46 nylon having a higher glass transition point, flat spot resistance can be improved while maintaining high speed durability.

In the half radial structure according to the present invention, at least two carcass layers having a cord angle with respect to the tire circumferential direction in a range of 70 ° to 88 ° are mounted between a pair of bead portions, and the reinforcing cords of these carcass layers are interposed between the layers. It is a structure arranged so as to cross each other. In this structure, even when the above-mentioned composite cord is used as a reinforcing cord for one carcass layer and a 46 nylon fiber cord is used as a reinforcing cord for another carcass layer, the high-speed durability is maintained well. The effect of improving flat spot resistance can be obtained.

  In the present invention, the cord angle of the carcass layer with respect to the tire circumferential direction is preferably in the range of 82 ° to 88 °. Increasing the cord angle of the carcass layer is advantageous in terms of high-speed durability.

  The tan δ at 60 ° C. of the coat rubber of the carcass layer is preferably 0.15 or less. Thereby, the temperature rise at the time of driving | running | working can be suppressed and high-speed durability and flat spot resistance can further be improved.

  The composite cord preferably has a three-strand structure in which one low twist yarn of a low elastic fiber yarn and two low twist yarns of a high elastic fiber yarn are twisted together. Thereby, since the rigidity of a composite cord becomes high, high-speed durability and flat spot resistance can be further improved.

The elastic modulus of the highly elastic fiber yarn is obtained by breaking a cord taken out from a tire into yarn units and performing a tensile test according to JIS L1017 “Test method for chemical fiber tire cord”. More specifically, when the elongation of the yarn at a load of 44 N is e ₁ (%) and the elongation of the yarn at a load of 149 N is e ₂ (%), the elastic modulus E is obtained by the following equation.
E = [105 / (e ₂ −e ₁ ) × 100] / S
Here, S is the cross-sectional area (mm ² ) of the yarn, and is calculated from the following equation.
S = D / 10000ρ
Where D is the nominal fineness (dtex) of the yarn and ρ is the nominal specific gravity of the fiber.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a pneumatic tire according to an embodiment of the present invention, wherein 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A plurality of carcass layers 4 are mounted between the pair of left and right bead portions 3 and 3, and end portions of the respective carcass layers 4 are folded around the bead core 5 from the inner side to the outer side of the tire. These carcass layers 4 are set such that the cord angle with respect to the tire circumferential direction is in a range of 70 ° to 88 °, and the reinforcing cords cross each other between the layers. That is, the reinforcing cord of one carcass layer 4 is inclined to one side with respect to the tire radial direction, and the reinforcing cord of the other carcass layer 4 is inclined to the other side with respect to the tire radial direction.

  A plurality of belt layers 6 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 6 are disposed such that the steel cords are inclined with respect to the tire circumferential direction and the steel cords cross each other between the layers. Furthermore, a belt reinforcing layer 7 formed by winding an organic fiber cord in the tire circumferential direction is disposed on the outer peripheral side of the belt layer 6. This belt reinforcing layer 7 has a jointless structure in which at least one organic fiber cord is aligned and rubber-coated strip material is continuously wound substantially at 0 ° with respect to the tire circumferential direction. Yes.

  In the pneumatic tire described above, as a reinforcing cord constituting at least one carcass layer 4, a low elastic fiber yarn made of a low twist fiber of high elastic fiber yarn having an elastic modulus of 10,000 MPa or more and 46 nylon (polytetramethylene adipamide) is used. A composite cord is used in which a lower twisted yarn is twisted by giving an upper twist in a direction opposite to that of the lower twist.

The composite cord has an upper twist coefficient K represented by the following formula of 1600 to 2300, more preferably 1800 to 2100.
K = T × D ^1/2
However, T is the number of upper twists (times / 10 cm), and D is the total fineness (dtex) of the composite cord.

  In the pneumatic tire having a half radial structure as described above, a composite cord in which a low-elastic fiber yarn and a low-elastic fiber yarn are twisted together is used, and the low-elastic fiber yarn of the composite cord is made of 46 nylon. By doing so, it is possible to improve the flat spot resistance while maintaining good high-speed durability. In other words, the low elastic fiber yarn of the composite cord is made of 46 nylon (glass transition temperature: about 78 ° C.) having a glass transition point higher than that of 66 nylon (glass transition temperature: about 50 ° C.). Even if it is parked for a long time after running, it is difficult to generate a flat spot. Further, since the low twist fiber yarn is combined with the low elastic fiber yarn, the high speed durability can be improved based on the physical properties of the high elastic fiber yarn.

  The material of the highly elastic fiber yarn is not particularly limited, and for example, aramid fiber, polyparaphenylene benzoxazole fiber (PBO), or polyolefin ketone fiber (POK) can be used.

In the embodiment described above, it is conceivable to use the composite cord as a reinforcing cord for all the carcass layers 4. However, the composite cord is used as a reinforcing cord for one carcass layer 4 and used as a reinforcing cord for another carcass layer 4. so that use of the 46 nylon fiber cord. As described above, even when the composite cord is used for only one of the plurality of carcass layers 4, the effect of improving the flat spot resistance can be obtained while maintaining high-speed durability favorably. .

FIG. 2 shows a pneumatic tire according to another embodiment (reference example) of the present invention. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. As shown in FIG. 2, a single carcass layer 4 is mounted between a pair of left and right bead portions 3, 3, and an end portion of the carcass layer 4 is folded around the bead core 5 from the tire inner side to the outer side. Yes. In the carcass layer 4, the cord angle with respect to the tire circumferential direction is set in a range of 70 ° to 88 °.

  A plurality of belt layers 6 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Furthermore, a belt reinforcing layer 7 formed by winding an organic fiber cord in the tire circumferential direction is disposed on the outer peripheral side of the belt layer 6. Then, the rolled-up portion of the carcass layer 4 extends to a position overlapping the belt layer 6. Thus, a laminated portion is formed in the carcass layer 4 in the sidewall portion 2, and the reinforcing cords of the carcass layer 4 are arranged so as to cross each other between the layers of the laminated portion. That is, the reinforcing cord is inclined to one side with respect to the tire radial direction in the main body portion of the carcass layer 4, and the reinforcing cord is inclined to the other side with respect to the tire radial direction in the rolled-up portion of the carcass layer 4.

  In the pneumatic tire, as a reinforcing cord constituting the carcass layer 4, a low twist fiber yarn made of 46 nylon (polytetramethylene adipamide) and a low elastic fiber yarn yarn made of 46 nylon (polytetramethylene adipamide) are used. A composite cord is used which is twisted by giving an upper twist in a direction opposite to the lower twist.

  In the pneumatic tire having a half radial structure as described above, a composite cord in which a low-elastic fiber yarn and a low-elastic fiber yarn are twisted together is used, and the low-elastic fiber yarn of the composite cord is made of 46 nylon. By doing so, it is possible to improve the flat spot resistance while maintaining good high-speed durability. In the embodiment of FIG. 2, the half radial structure is formed using the single carcass layer 4, so that the weight can be reduced as compared with the embodiment of FIG. 1.

  In each of the embodiments described above, the cord angle of the carcass layer 4 with respect to the tire circumferential direction needs to be set in a range of 70 ° to 88 °. If the cord angle is less than 70 °, the high-speed durability becomes insufficient, and if it exceeds 88 °, the motion performance represented by the steering stability becomes insufficient. In particular, when high-speed durability is important, the cord angle of the carcass layer 4 is preferably set in the range of 82 ° to 88 °.

  The tan δ at 60 ° C. of the coated rubber of the carcass layer 4 is preferably 0.15 or less. Thereby, since heat_generation | fever of the coat rubber of the carcass layer 4 at the time of driving | running | working is suppressed and the temperature rise is suppressed, high-speed durability and flat spot resistance can further be improved. The tan δ of the coated rubber at 60 ° C. was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz.

  3 and 4 each illustrate a composite cord used for the carcass layer of the pneumatic tire of the present invention. In FIG. 3, the composite cord 14 has a two-strand structure in which one low-elastic fiber yarn under-twist 14L and one high-elastic fiber yarn under-twist 14H are twisted together. In FIG. 4, the composite cord 14 has a three-strand structure in which a single low-elastic fiber yarn and a two high-elastic fiber yarns are twisted together. As shown in FIG. 4, when the composite cord 14 has a triple twist structure in which the low twist fiber 14L of one low elastic fiber yarn and the low twist yarn 14H of two high elastic fiber yarns are twisted together, the rigidity of the composite cord 14 Therefore, high-speed durability and flat spot resistance can be further improved.

For pneumatic tires with tire size 235 / 45R17 and half radial structure, the ply structure and cord angle of the carcass layer, the twist structure of the carcass cord used for the carcass layer, the driving density, the number of upper twists and the upper twist coefficient, and the carcass cord The material of the high elastic yarn constituting, the fineness and the number of lower twists, the material of the low elastic yarn constituting the carcass cord, the fineness and the number of lower twists, and the 100% modulus (according to JIS K6251) and tan δ of the coat rubber of the carcass layer The pneumatic tires of Conventional Examples 1 to 3 , Reference Examples 1 to 8 and Example 1 set as shown in Table 1 and Table 2 were manufactured.

Regarding the twisted structures of Tables 1 and 2, “2L” means a two-stranded structure in which two low-elastic fiber yarns are twisted together, and “H + L” is a single low-elastic fiber yarn. Means a two-twist structure in which a high-strength fiber yarn is twisted together, and “H + 2L” means two low-elastic fiber yarns and a single high-elastic fiber yarn. “2H + L” means a three-strand structure in which one low-elastic fiber yarn and two high-elastic fiber yarns are twisted together. However, in Example 1 , the composite cord described in Table 2 is used for one carcass layer, and 46 nylon fiber cords (fineness: 1400 dtex / 2, number of twists: 37 times) are used for the other carcass layers. / 10 cm, the number of twists: 37 times / 10 cm, and the driving density is 33/50 mm). Further, in Conventional Examples 1 to 3 and Reference Examples 1 to 7, cords made of the same material were used for the two carcass layers.

  These test tires were evaluated for weight, high-speed durability and flat spot resistance by the following methods, and the results are also shown in Tables 1 and 2.

weight:
The weight of each test tire was measured and indicated by an index with Conventional Example 2 being 100. A smaller index value means a lighter weight.

High speed durability:
About a test tire inflated with a rim size of 17 × 7.5JJ and a test internal pressure of 180 kPa, using a drum tester having a drum surface of smooth steel and a drum diameter of 1707 mm, controlling the ambient temperature to 38 ± 3 ° C. , Running for 2 hours at a speed of 120 km / h while giving a load of 120% of the maximum load specified by JATMA, then running for 15 minutes at a speed of 150 km / h with the same load. The speed was stepped up by 10 km / h every minute, and the running distance until the tire broke was measured. The evaluation results are shown as an index with Conventional Example 2 as 100. It means that high speed durability is excellent, so that this index value is large.

Flat spot resistance:
The radial force variation (RFV) of each test tire was measured in accordance with JASO C607 “Testing method for uniformity of automobile tires”, then pre-run for 30 minutes at a speed of 150 km / h, and then loaded. The drum was stopped for 1 hour. Thereafter, the RFV was measured again, the difference between the RFV before and after the preliminary running was obtained, and this was used as an evaluation index. The evaluation results are shown as an index with Conventional Example 2 as 100. The smaller the index value, the better the flat spot resistance, that is, it is difficult to form a flat spot.

These Tables 1 and Table 2, the tires of Example 1 was able to improve the flat spot resistance while maintaining good high-speed durability as compared with conventional examples 1 to 3.

It is a meridian half section view showing a pneumatic tire according to an embodiment of the present invention. FIG. 6 is a meridian half-sectional view showing a pneumatic tire according to another embodiment (reference example) of the present invention. It is sectional drawing which shows an example of the composite cord used for the carcass layer of the pneumatic tire of this invention. FIG. 6 is a cross-sectional view showing another example of the composite cord used for the carcass layer of the pneumatic tire of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Belt layer 7 Belt reinforcement layer 14 Composite cord 14L Low elastic fiber yarn 14H High elastic fiber yarn

Claims (4)

At least two carcass layers having a cord angle with respect to the tire circumferential direction in the range of 70 ° to 88 ° are mounted between the pair of bead portions, and the reinforcing cords of the carcass layers are arranged so as to intersect each other between the layers. In a pneumatic tire in which a belt layer is disposed on the outer peripheral side of the carcass layer in the tread portion, a low elastic fiber made of a high twist fiber yarn having a modulus of elasticity of 10,000 MPa or more and 46 nylon as a reinforcing cord for one carcass layer A pneumatic tire characterized by using a composite cord obtained by twisting a yarn with a yarn twisted in the opposite direction of the yarn and using a 46 nylon fiber cord as a reinforcing cord for another carcass layer . The pneumatic tire according to claim 1 , wherein a cord angle of the carcass layer with respect to a tire circumferential direction is in a range of 82 ° to 88 °. The pneumatic tire according to any one of claims 1 to 2, tanδ at 60 ° C. of the coating rubber of the carcass layer is equal to or more than 0.15. To any one of claims 1 to 3 in which the composite code is characterized by having three twisted structure twisted and twisted yarn 2 of the high elastic fiber yarn and the lower yarn one of the low-elastic fiber yarn The described pneumatic tire.

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