JP5082468B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that improves handling stability while maintaining the advantages of fitability and weight reduction.

  Conventionally, two carcass layers in which organic fiber cords extending in the tire radial direction between the left and right bead portions are arranged at predetermined intervals in the tire circumferential direction are extended, and the two carcass layers are formed in the bead portions. An inner carcass layer with an end folded back from the inner side to the outer side in the tire axial direction around the embedded bead core, and an outer end of the inner carcass layer, and the end along the inner carcass layer to the inner side in the tire axial direction of the bead core A pneumatic tire configured from an extended outer carcass layer is known (see, for example, Patent Document 1).

In this way, the end of the outer carcass layer is not folded back around the bead core together with the end of the inner carcass layer, but is stopped on the inner side in the tire axial direction of the bead core, thereby reducing the rubber thickness of the bead portion on the outer side in the tire axial direction of the bead core. Since it can be made thin, it has the advantage of reducing the fitting pressure when assembling the rim and reducing the weight of the tire, but it does not fold around the bead core, so the locking force against the bead core is reduced, and steering stability There was a problem of getting worse.
JP 7-285305 A

  The objective of this invention is providing the pneumatic tire which can improve steering stability, maintaining the advantage of fitting property and weight reduction.

In the pneumatic tire of the present invention that achieves the above object, at least two carcass layers in which organic fiber cords extending in the tire radial direction are arranged at predetermined intervals in the tire circumferential direction are extended between the left and right bead portions. The two carcass layers are arranged around a bead core embedded in the bead portion, an inner carcass layer whose end portion is folded back from the inner side to the outer side in the tire axial direction, and the end portion is disposed outside the inner carcass layer. In a pneumatic tire constituted by an outer carcass layer extending along the inner carcass layer to the inner side in the tire axial direction of the bead core, the shrinkage S under dry heat of the organic fiber cord of the outer carcass layer, and the organic tire the sum S + E and elongation E when loaded with tension of 2.0 cN / dtex in the fiber cords while below 7.5%, wherein in the tire axial direction outer side of the bead region of the bead core The rubber thickness t from the folded portion of the folded ends of the side carcass layer to the bead outer surface, characterized in that the 2.5 to 5.0 mm.

  According to the present invention described above, the sum S + E of the shrinkage ratio S and the elongation E of the organic fiber cord of the outer carcass layer whose end portion is not folded around the bead core is defined as described above, and is lower than the conventional one. Moreover, the heat shrinkage of the organic fiber cord of the outer carcass layer at the time of tire vulcanization molding can be suppressed. Therefore, it is possible to suppress a decrease in rigidity (elastic modulus) of the organic fiber cord of the outer carcass layer, and it is also possible to suppress a decrease in the length of the end portion of the outer carcass layer sandwiched between the bead core and the inner carcass layer. Steering stability can be improved.

  Since only the physical properties of the organic fiber cord of the outer carcass layer are changed and no other members need to be added, the end of the outer carcass layer is not folded back around the bead core, and the bead core is formed along the inner carcass layer. The advantages of fitting and weight reduction, which are advantages in a pneumatic tire configured to extend to the inside in the tire axial direction, are not impaired.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a tire meridian half sectional view of an embodiment of a pneumatic tire of the present invention, wherein 1 is a tread portion, 2 is a sidewall portion, 3 is a bead portion, and CL is a tire equatorial plane. Since the structure is symmetrical with respect to the tire equatorial plane CL, the left portion is omitted.

  Between the left and right bead portions 3 inside the tire, organic fiber cords f (see FIG. 2) such as polyester and rayon extending in the tire radial direction are arranged at predetermined intervals in the tire circumferential direction and embedded in the rubber layer r. The two carcass layers 4 are extended. On the inner side of the carcass layer 4, an inner liner layer 6 that faces the cavity 5 and functions as an air permeation preventive layer is provided.

  The two carcass layers 4 are composed of an inner carcass layer 4A adjacent to the inner liner layer 6 and an outer carcass layer 4B disposed outside the inner carcass layer 4A. Both end portions 4A1 of the inner carcass layer 4A are folded back from the inner side in the tire axial direction so as to sandwich the bead filler 8 around the bead core 7 embedded in the bead portion 3 and further extend to the sidewall portion 2. . Both end portions 4B1 of the outer carcass layer 4B are extended to the inner side in the tire axial direction of the bead core 7 along the tire axial direction inner side surface 8a of the bead filler 8 disposed on the outer peripheral side of the inner carcass layer 4A and the bead core 7. There is no wrap around. The portion of the end 4B1 adjacent to the bead core 7 is configured to be sandwiched between the inner carcass layer 4A and the bead core 7.

  On the outer peripheral side of the carcass layer 4 of the tread portion 1, two belt layers 9 in which reinforcing cords arranged to be inclined with respect to the tire circumferential direction are arranged so as to intersect with each other with the inclination direction with respect to the tire circumferential direction reversed. Is arranged. On the outer peripheral side of the belt layer 9, a belt full cover layer 10 and a belt edge cover layer 11 in which rubber-coated organic fiber cords such as nylon are spirally wound at an angle close to 0 ° with respect to the tire circumferential direction are respectively provided. One layer is provided.

  In the bead portion region 3X on the outer side in the tire axial direction of the bead core 7, the rubber thickness t in the tire axial direction from the folded side portion 4A1 ′ of the folded end portion 4A1 of the inner carcass layer 4A to the outer surface 3a of the bead portion 3 is The end portion 4B1 of the outer carcass layer 4B is thin as it does not extend, and is in the range of 2.5 to 5.0 mm. If the rubber thickness t is less than 2.5 mm, there will be a problem in strength. Conversely, if the rubber thickness t exceeds 5.0 mm, the path over the hump will be longer when assembling the rim, so that fitting with a low fitting pressure is possible. You will not be able to take advantage of sex.

  The outer carcass layer 4B has a shrinkage rate S (%) of the organic fiber cord f under dry heat and an elongation E (%) when a tension of 2.0 cN / dtex is applied to the organic fiber cord f. The sum S + E is 7.5% or less, which is smaller than before. In addition, the shrinkage | contraction rate S said here is measured (150 degreeC x 30 minutes) according to the method (B method) of JISL1017-2002 8.10. The elongation E is also measured by a tensile test described in JIS L1017-2002 8.5 a).

  Thus, in order to obtain an organic fiber cord f having a sum S + E of 7.5% or less, a low shrinkage yarn (for example, a highly oriented unoriented yarn (POY (partial oriented yarn)) is used, Obtained by reducing the number of twists, the ratio of S and E can be adjusted by adjusting the dip treatment temperature and tension conditions of the above-mentioned twisted yarn cord.

  In the cord satisfying the sum S + E in the organic fiber cord taken out from the tire as described above, the dry heat shrinkage ratio S0 (measurement method is the same as the shrinkage ratio S) of the raw material cord before application to the tire is less than 3.5%. Is preferred. Thereby, the suppression effect of the heat shrink of the organic fiber cord at the time of tire vulcanization molding is improved.

  Such a cord uses a low-shrinkage yarn as described above, and when dipping a twisted cord with a reduced number of twists, the cord is sufficiently relaxed by reducing the tension in the normalizing process. Can be obtained.

  The present inventor is concerned with the decrease in steering stability in a pneumatic tire configured to extend to the inner side in the tire axial direction of the bead core along the inner carcass layer without folding the end portion of the outer carcass layer around the bead core. As a result of the research, the following was found.

  A pneumatic tire has a process of applying heat to vulcanize in a manufacturing process. On the other hand, an organic fiber cord is used as a reinforcing cord for the carcass layer. Therefore, in the vulcanization process, the organic fiber cord of the carcass layer undergoes heat shrinkage. In the case of the inner carcass layer with the end folded around the bead core, the organic fiber cord is locked to the bead core, so heat shrinkage is suppressed, but the outer carcass layer does not have the end folded around the bead core. Then, heat shrinkage occurs in the organic fiber cord. As a result, the rigidity (elastic modulus) of the organic fiber cord of the outer carcass layer is reduced, while the outer carcass layer contracts in the tire radial direction due to the thermal contraction, thereby the end portion of the outer carcass layer disposed adjacent to the bead core is Since it moves to the outer side in the tire radial direction, the length of the end portion sandwiched between the bead core and the inner carcass layer is reduced, or the end portion is sandwiched between the bead core by moving from the bead core to the outer side in the tire radial direction. No state. As a result, there has been a problem that the tire circumferential rigidity and the lateral rigidity are lowered and the steering stability is deteriorated.

  Therefore, in the present invention, as described above, the sum S + E of the shrinkage ratio S and the elongation E of the organic fiber cord f of the outer carcass layer 4B is 7.5% or less, which is lower than the conventional one, and the heat during tire vulcanization molding The contraction was suppressed. Thereby, while the rigidity (elastic modulus) fall of the organic fiber cord f of the outer carcass layer 4B can be suppressed, the length of the end portion 4B1 of the outer carcass layer 4B sandwiched between the bead core 7 and the inner carcass layer 4A. Can be reduced. As a result, a decrease in tire circumferential rigidity and lateral rigidity is suppressed, and steering stability can be improved.

  On the other hand, since it is not necessary to add any other member, the end 4B1 of the outer carcass layer 4B is not folded back around the bead core 7 but extends to the inner side in the tire axial direction of the bead core 7 along the inner carcass layer 4A. The advantages of the pneumatic tire thus configured, that is, the advantages of fitability and weight reduction can be maintained.

  If the sum S + E exceeds 7.5%, it is not possible to suppress a decrease in rigidity of the organic fiber cord f of the outer carcass layer 4B, and the end 4B1 of the outer carcass layer 4B sandwiched between the bead core 7 and the inner carcass layer 4A. Since it becomes difficult to suppress the reduction in the length of the portion, the steering stability cannot be improved. The lower limit of the sum S + E is not particularly limited, but is preferably 4% or more from the viewpoint of both ride comfort and workability.

In the present invention, as the organic fiber cord f of the outer carcass layer 4B, it is preferable to use one having a twist coefficient K represented by the following formula of 1900 or less.
K = T × D ^1/2
D: Total fineness of organic fiber cord (dtex)
T: Number of twists of organic fiber cord (times / 10cm)

  When the tire is deformed when it comes in contact with the road surface, only the force in the pulling direction acts on the outer carcass layer 4B that is not folded back around the bead core 7, without the force in the compressing direction. Twisted cords are subject to fatigue failure when force in the compression direction is applied, so it is necessary to increase the number of twists. However, when only the force in the tensile direction acts in this way, fatigue is reduced even if the number of twists is reduced. Destruction is unlikely to occur. Therefore, an organic fiber cord having a lower twisting coefficient than the conventional one can be used for the organic fiber cord f of the outer carcass layer 4B that is not folded around the bead core 7. Since the carcass layer folded around the bead core is subjected to a compressive force on the folded side, if an organic fiber cord having a low twist coefficient is used for the carcass layer folded around the bead core, fatigue failure on the folded side may occur. Although the durability deteriorates, such a problem does not exist in the outer carcass layer 4B.

  By using the one having a low twist coefficient K of 1900 or less as the organic fiber cord f of the outer carcass layer 4B that is not folded around the bead core 7, the rigidity of the organic fiber cord f of the outer carcass layer 4B is reduced. While the (elastic modulus) can be increased and the steering stability can be further improved, the number of twists is reduced, so that there is an advantage that the productivity of the organic fiber cord is increased and the production cost can be reduced. The lower limit value of the twist coefficient K is preferably 1400 or more from the viewpoint of fatigue resistance. The total fineness D of the organic fiber cord can be 2000 to 5000 dtex.

  In the above embodiment, an example in which two carcass layers 4 are provided has been described. However, more than that may be provided, and the pneumatic tire of the present invention has a pneumatic tire having at least two carcass layers. If it is.

  Although this invention can be preferably used especially for the pneumatic tire used for a passenger car, it is not limited to it, The pneumatic tire of other uses may be sufficient.

  The tire size is the same for 205 / 65R15, sum S + E, dry heat shrinkage S0, rubber thickness t in the bead area, twist coefficient Kin of the organic fiber cord (polyester cord [1670dtex / 2]) of the inner carcass layer and the outer side The tires 1 and 2 (Examples 1 and 2) of the present invention having the structure shown in FIG. 1 in which the twist coefficient Kout of the organic fiber cord (polyester cord [1670 dtex / 2]) of the carcass layer is as shown in Table 1 and the conventional tire 2 ( Conventional Example 2) and Conventional Tire 1 (Conventional Example 1) in which both ends of the inner and outer carcass layers in the conventional tire 2 were turned back from the inner side in the tire axial direction around the bead core were produced.

  Each of these test tires was assembled to a rim having a rim size of 15 × 6 JJ, the air pressure was set to 230 kPa, and the vehicle was mounted on a passenger car with a displacement of 2500 cc. A steering stability evaluation test was performed according to the following test method. The result was obtained. Table 1 also shows the measured fitting pressure at the time of rim assembly, tire circumferential rigidity and lateral rigidity (index display with the conventional tire 1 as 100).

Steering stability In the dry road test course, a sensory evaluation test was conducted by a test driver, and the evaluation result was shown by a five-point method. The larger this value, the better the steering stability.

  As shown in Table 1, the present invention has a low fitting pressure as in the case of the conventional tire 2 in which the end portion of the outer carcass layer is not folded back around the bead core and is stopped on the inner side in the tire axial direction of the bead core. It can be seen that the steering stability can be improved as compared with the conventional tire 2, and the steering stability can be improved while maintaining the advantage of fitting.

It is a tire meridian half section view showing one embodiment of a pneumatic tire of the present invention. It is a partial expanded sectional view of a two-layer carcass layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 3X area | region 4 Carcass layer 4A Inner carcass layer 4A1 End part 4A1 'part 4B Outer carcass layer 4B1 End part 7 Bead core f Organic fiber cord t Rubber thickness

Claims (3)

At least two carcass layers in which organic fiber cords extending in the tire radial direction are arranged at predetermined intervals in the tire circumferential direction are extended between the left and right bead portions, and the two carcass layers are embedded in the bead portions. An inner carcass layer having an end folded back from the inner side to the outer side in the tire axial direction around the bead core, and an inner side in the tire axial direction of the bead core disposed along the inner carcass layer. In a pneumatic tire composed of an outer carcass layer extending to
The sum S + E of the shrinkage S under dry heat of the organic fiber cord of the outer carcass layer and the elongation E when a tension of 2.0 cN / dtex is applied to the organic fiber cord is 7.5% or less . In addition, in the bead core region on the outer side in the tire axial direction of the bead core, air having a rubber thickness t from the folded side portion of the folded back end portion of the inner carcass layer to the outer surface of the bead portion is 2.5 to 5.0 mm. Enter tire. The pneumatic tire according to claim 1 , wherein a dry heat shrinkage rate of the organic fiber cord of the outer carcass layer is less than 3.5% before tire vulcanization molding. The pneumatic tire according to claim 1 or 2 , wherein the twist coefficient K of the organic fiber cord of the outer carcass layer represented by the following formula is 1900 or less.
K = T × D ^1/2
D: Total fineness of organic fiber cord (dtex)
T: Number of twists of organic fiber cord (times / 10cm)

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