JP4984637B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire in which an annular bead core formed by continuously winding one or a plurality of steel wires is embedded in a bead portion. More particularly, the fitting property to a rim is favorably maintained. However, the present invention relates to a pneumatic tire that can reduce the weight of the bead core.

  An annular bead core formed by continuously winding a steel wire is embedded in the bead portion of the pneumatic tire. The rigidity of the bead core greatly affects the bead unseating resistance value (see, for example, Patent Document 1).

In other words, if the amount of steel wire that constitutes the bead core is increased, the bead unseating resistance value increases, and conversely, if the amount of steel wire that constitutes the bead core is decreased, the bead unseating resistance value decreases. become. Therefore, it is difficult to reduce the weight of the bead core based on the reduction in the amount of steel wire used while maintaining good fitting characteristics to the rim represented by the bead unseating resistance value.
Japanese Patent Laid-Open No. 2001-233023

  An object of the present invention is to provide a pneumatic tire that can reduce the weight of the bead core while maintaining good fitting characteristics with respect to the rim.

In order to achieve the above object, a pneumatic tire according to the present invention is a pneumatic tire in which an annular bead core formed by continuously winding one or a plurality of steel wires is embedded in a bead portion.
The steel wire circumferential portions are arranged in the tire axial direction to form one layer, and a plurality of layers comprising the steel wire circumferential portions are stacked in the tire radial direction to form the bead core into a multilayer structure, and the steel The wire is continuously brazed with a radius of curvature R ′ of 0.60R to 1.10R with respect to the inner diameter 2R of the bead core,
When the bead core is taken from the tire and the expansion force and strain when the single bead core is expanded are measured, the bead core stiffness coefficient K calculated by the following equation (1) is K ≧ 250 (N / 1%) It is characterized by satisfying the relationship of strain / mm ² ).
K = [(H _0.4 -H _0.2 ) / (0.4% -0.2%)] / S (1)
However, H _0.2 : Expansion force at 0.2% strain (N)
H _0.4 : Expansion force at 0.4% strain (N)
S: Total cross-sectional area of the bead core steel wire (mm ² )

  The present inventor collected bead cores from various pneumatic tires, and when these bead cores were expanded, the expansion force (fitting force) and the amount of change in diameter (strain) were measured. Even under the conditions, it was found that the increase rate of the fitting force with respect to the increase in strain differs for each bead core.

  Therefore, the present inventor formed a bead core under various conditions of the bead core stiffness coefficient K calculated in the above (1), and examined the bead unseating resistance value of the pneumatic tire provided with the bead core. By increasing the bead core rigidity coefficient K defined as described above, it is possible to reduce the weight of the bead core while increasing the bead unseating resistance value, that is, maintaining good fitting characteristics with respect to the rim. As a result, the present invention has been achieved.

In the present invention, the bead core rigidity coefficient K needs to satisfy the relationship of K ≧ 250 (N / 1% strain / mm ² ), but 500 (N / 1% strain / mm ² ) ≧ K ≧ 250 ( N / 1% strain / mm ² ) is preferably satisfied. By defining the upper limit value of the bead core stiffness coefficient K, eccentric fitting becomes difficult to occur, and deterioration of uniformity after rim assembly can be avoided.

  Further, the storage elastic modulus E ′ at 20 ° C. of the insulation rubber covering the steel wire of the bead core is preferably E ′ ≧ 8.0 MPa, preferably 35.0 MPa ≧ E ′ ≧ 8.0 MPa. Adopting the insulation rubber having such physical properties is advantageous in optimizing the bead core rigidity coefficient K. The storage elastic modulus E ′ was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Co., Ltd. under conditions of a temperature of 20 ° C., a frequency of 20 Hz, an initial strain of 10%, and a dynamic strain of ± 2%.

Furthermore, in the present invention, the steel wire constituting the bead core has a continuous radius of curvature R ′ of 0.60R to 1.10R, preferably 0.88R to 0.98R with respect to the inner diameter 2R of the bead core. Make sure to give a proper brazing. By brazing the steel wire with a curvature radius R ′, the bead core stiffness coefficient K can be increased. The radius of curvature R ′ of the brazing of the steel wire in the tire is specified by the following method. That is, after a bead core having an inner diameter of 2R is cut out so that the steel wire is not damaged from inside the tire, the steel wire corresponding to two rounds is not newly wrinkled from the end of the steel wire arranged on the outer side in the tire radial direction. Cut out carefully. Then, the cut steel wire is allowed to stand on a smooth floor, and the inner diameter of the annular material formed by the steel wire in a natural state is measured at eight locations that are evenly spaced on the circumference. The curvature radius is R ′.

  Further, the ratio Sg / Sw of the volume of use of the steel wire constituting the bead core to the volume of use of the insulation rubber covering the steel wire in the bead core is 0.40 or more and 1.00 or less, preferably 0.40. It is preferable to set it to 0.75 or less. Thereby, bead core rigidity coefficient K can be raised.

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. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the 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 inside to the outside of the tire. On the outer peripheral side of the carcass layer 4 in the tread portion 1, a belt layer 6 is disposed over the entire tire circumference. These belt layers 6 include reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged such that the reinforcing cords cross each other between the layers.

  FIG. 2 is an enlarged view of the bead core of the pneumatic tire of FIG. As shown in FIG. 2, the bead core 5 includes a steel wire W and an insulation rubber G that covers the steel wire W. The bead core 5 is formed by continuously winding one or a plurality of steel wires W, and has a multilayer structure laminated in the tire radial direction. When the bead core 5 is formed from one steel wire W, one steel wire W is continuously wound while shifting the position in the tire axial direction to form one layer, and the formation of such a layer is repeated. As a result, a bead core 5 having a multilayer structure is obtained. On the other hand, when the bead core 5 is formed from a plurality of steel wires W, the bead core 5 having a multilayer structure can be obtained by continuously winding the plurality of steel wires W arranged in the tire axial direction.

In the pneumatic tire, when the bead core 5 is cut out from the tire and the expansion force and strain when the single bead core 5 is expanded are measured, the bead core stiffness coefficient K calculated by the following equation (1) is K. ≧ 250 (N / 1% strain / mm ² ), preferably 500 (N / 1% strain / mm ² ) ≧ K ≧ 250 (N / 1% strain / mm ² ) is satisfied.
K = [(H _0.4 -H _0.2 ) / (0.4% -0.2%)] / S (1)
However, H _0.2 : Expansion force at 0.2% strain (N)
H _0.4 : Expansion force at 0.4% strain (N)
S: Total cross-sectional area of the bead core steel wire (mm ² )

  Here, a method for measuring the expansion force and strain of the bead core will be described. In the present invention, a bead core expansion force tester manufactured by Hoffman is used for measuring the expansion force and strain of the bead core. This bead part expansion force tester is usually used to measure the expansion force and distortion of a bead part which is a part of a tire. Here, the means for measuring the expansion force and distortion of a single bead core cut out from a tire is used. Use as This is because the original rigidity of the bead core is obtained in a state where the influence due to the difference in the thickness of the rubber layer interposed between the bead core and the bead base is eliminated.

  3-5 shows the principal part of a bead part expansion force tester. As shown in FIG. 3 to FIG. 5, the bead portion expansion force testing machine arranges rim blocks 11 divided into eight parts on the circumference, and the expansion force when expanding these rim blocks 11 radially outward. It is configured to measure distortion. Each rim block 11 includes a step portion 11a for installing the bead core 5 on the outer peripheral side thereof. Further, a rubber sheet 12 is disposed between the step portion 11a of the rim block 11 and the bead core 5 in order to avoid mutual contact therebetween. The rubber sheet 12 preferably has a thickness of 3 mm and a modulus at 100% elongation of 3.0 MPa. As the rubber sheet 12, for example, a rubber composition having the composition shown in Table 1 below vulcanized at 160 ° C. for 20 minutes can be used.

  When measuring the expansion force and strain of the bead core using the bead portion expansion force tester, the bead core 5 from which the surrounding rubber has been scraped is placed on the step portion 11a of the rim block 11 with the rubber sheet 12 interposed therebetween, The rim block 11 is simultaneously spread outward in the radial direction at an expansion speed of 6.4 mm / min, and the expansion force and strain (diameter change) at that time are measured. In calculating the strain, the inner diameter of the bead core at an expansion force of 50 N is used as a reference. For example, the inner peripheral length of the bead core at an expansion force of 50 N is measured with a steel strip-shaped measure, and a value obtained by dividing it by π may be used as a reference for the bead core inner diameter. A value obtained by dividing the expansion force of the bead core obtained by using this bead portion expansion force tester by the total cross-sectional area of the steel wire of the bead core is a tensile strength (fitting force) per unit cross-sectional area of the steel wire.

FIG. 6 shows the relationship between the expansion force (N / mm ² ) per unit cross-sectional area of the bead core and strain (%). FIG. 6 shows that the expansion force per steel wire cross-sectional area of various bead cores 5A to 5E has an inherent inclination with respect to strain.

  In the present invention, in the relationship between the tensile strength and strain of the bead core obtained as shown in FIG. 6, the expansion per unit cross-sectional area of the steel wire in the strain range of 0.2% to 0.4% is obtained from the above equation (1). Find the slope of the force. Such a deformation in the range of 0.2% to 0.4% greatly affects the bead unseating resistance value.

In the pneumatic tire described above, the bead core stiffness coefficient K is in a relationship of K ≧ 250 (N / 1% strain / mm ² ), so that the bead core can be reduced in weight while increasing the bead unseating resistance value. it can. Furthermore, by satisfying the condition of 500 (N / 1% strain / mm ² ) ≧ K, eccentric fitting becomes difficult to occur, and deterioration of uniformity after rim assembly can be avoided.

  Further, the storage elastic modulus E ′ at 20 ° C. of the insulation rubber G covering the steel wire W of the bead core 5 is set to E ′ ≧ 8.0 MPa, preferably 35.0 MPa ≧ E ′ ≧ 8.0 MPa. preferable. If the storage elastic modulus E ′ is less than 8.0 MPa, the bead core is likely to be deformed. Conversely, if it exceeds 35.0 MPa, the heat generation of the bead core is increased, and permanent deformation due to compression is likely to occur.

  FIG. 7 schematically shows an annular object made of steel wire cut out from the bead core of FIG. As shown in FIG. 3, the steel wire W has a radius of curvature of 0.60R to 1.10R, more preferably 0.88R to 0.98R with respect to the inner diameter 2R (R: radius) of the bead core 5. Continuous brazing with R '.

  When continuous brazing having a radius of curvature R ′ is applied to the steel wire W in this way, the steel wire W constituting the bead core 5 is disturbed because a force to tighten the steel wire itself acts in the tire forming process. It becomes difficult to cause meandering and meandering, and the material properties of the steel wire W can be maximized. Thereby, even if it is a case where the usage-amount of the steel wire W is reduced and weight reduction of the bead core 5 is aimed at, a bead unseating resistance value can be increased. However, when the radius of curvature R ′ is less than 0.60R, eccentric fitting tends to occur, and conversely, when it exceeds 1.10R, the bead unseating resistance value decreases.

  In the pneumatic tire described above, the ratio Sg / Sw of the volume of use of the steel wire W constituting the bead core 5 to the volume of use of the insulation rubber G in the bead core 5 is 0.40 or more and 1.00 or less. Preferably, it is set to 0.40 or more and 0.75 or less. Thus, by reducing the use volume Sg of the insulation rubber G, the bead unseating resistance value can be increased. However, if the ratio Sg / Sw is out of the above range, the effect of increasing the bead unseating resistance value decreases.

  The tire size is 205 / 50R16 (rim size 16 × 6 1 / 2JJ), and the bead core is configured in a pneumatic tire in which an annular bead core formed by continuously winding a plurality of steel wires is embedded in the bead portion. The tires of Comparative Examples 1-2 and Examples 1-4 in which the amount of steel wire used, the bead core stiffness coefficient K, and the storage elastic modulus E ′ of the bead core insulation rubber at 20 ° C. were set as shown in Table 2, respectively. Produced. However, the amount of steel wire used is indicated by an index with Comparative Example 1 as 100. In Comparative Example 2 and Examples 1 to 4, the amount of steel wire constituting the bead core is reduced as compared with Comparative Example 1.

  For these test tires, the bead unseating resistance value and the radial force variation (RFV) after assembling the rim were measured, and the results are also shown in Table 2. The bead unseating resistance value was determined in accordance with the bead unseating test of JIS D4230 6.2. For RFV, the test tire is assembled to a wheel with a rim size of 16 × 6 1/2 JJ, the air pressure is set to 200 kPa, and the drum is equipped with a rotating drum having a diameter of 1707 mm, in accordance with the JASO C607-87 standard. The value (PP value) from the maximum peak to the minimum peak of RFV was measured. And the said RFV measurement was performed 5 each about each test tire, and the average value was calculated | required.

  As can be seen from Table 2, the tires of Examples 1 to 4 have a bead core that is lighter than Comparative Example 1, but have a sufficiently large bead unseat resistance. However, in the tire of Example 4, the deterioration of RFV after the rim assembly was observed. On the other hand, since the tire of Comparative Example 2 has a bead core stiffness coefficient K that is too small, the bead unseating resistance value has also decreased with the weight reduction of the bead core.

  Next, in the pneumatic tire in which the tire size is 205 / 50R16 (rim size 16 × 6 1 / 2JJ), and an annular bead core formed by continuously winding a plurality of steel wires is embedded in the bead portion, Tires of Examples 5 to 9 in which the amount of steel wire constituting the bead core, the bead core stiffness coefficient K, and the storage elastic modulus E ′ of the bead core insulation rubber at 20 ° C. were set as shown in Table 3 were produced. However, the amount of steel wire used is indicated by an index with Comparative Example 1 as 100. In each of Examples 5 to 9, the amount of steel wire constituting the bead core was reduced as compared with Comparative Example 1.

  For these test tires, the bead unseating resistance value was measured when new and after dry heat deterioration, and the results are also shown in Table 3. Regarding the bead unseating resistance value after dry heat deterioration, the test tire was assembled on the rim and held at an internal pressure of 350 kPa in an atmosphere of 80 ° C. for 4 weeks, and then the bead unseating resistance value was measured.

  As can be seen from Table 3, in the tires of Examples 5 to 9, the bead core was reduced in weight as compared with Comparative Example 1, but the bead unseating resistance value at the time of a new article was sufficiently large. In particular, when the storage elastic modulus E ′ at 20 ° C. of the insulation rubber of the bead core is in the range of 8.0 MPa to 35.0 MPa, a good bead unseating resistance value was maintained even after dry heat deterioration. . On the other hand, if the storage elastic modulus E ′ at 20 ° C. of the insulation rubber of the bead core is less than 8.0 MPa, the initial bead unseating resistance value is relatively low, and therefore the bead unseating resistance value after dry heat deterioration. When the storage elastic modulus E ′ at 20 ° C. of the bead core insulation rubber exceeds 35.0 MPa, the compression set generated in the heated bead core insulation rubber is large, and the bead unseating after dry heat deterioration The resistance value was insufficient.

It is a meridian half section view showing a pneumatic tire according to an embodiment of the present invention. It is sectional drawing which expands and shows the bead core of the pneumatic tire of FIG. It is a top view which shows the principal part of a bead part expansion force tester. It is a top view which shows the state which installed the single bead core cut out from the tire in the bead part expansion force test machine of FIG. It is AA arrow sectional drawing of FIG. It is a graph which shows the relationship between the expansion force per steel wire cross-sectional area of a bead core (N / mm < ² >), and distortion (%). It is a top view which shows the steel wire cut out from the bead core of FIG.

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 W Steel wire G Insulation rubber

Claims (7)

In a pneumatic tire in which an annular bead core formed by continuously winding one or a plurality of steel wires is embedded in a bead portion,
The steel wire circumferential portions are arranged in the tire axial direction to form one layer, and a plurality of layers comprising the steel wire circumferential portions are stacked in the tire radial direction to form the bead core into a multilayer structure, and the steel The wire is continuously brazed with a radius of curvature R ′ of 0.60R to 1.10R with respect to the inner diameter 2R of the bead core,
When the bead core is taken from the tire and the expansion force and strain when the single bead core is expanded are measured, the bead core stiffness coefficient K calculated by the following equation (1) is K ≧ 250 (N / 1%) A pneumatic tire characterized by satisfying a relationship of strain / mm ² ).
K = [(H _0.4 -H _0.2 ) / (0.4% -0.2%)] / S (1)
However, H _0.2 : Expansion force at 0.2% strain (N)
H _0.4 : Expansion force at 0.4% strain (N)
S: Total cross-sectional area of the bead core steel wire (mm ² ) ^2. The pneumatic tire according to claim 1, wherein the bead core stiffness coefficient K satisfies a relationship of 500 (N / 1% strain / mm ² ) ≧ K ≧ 250 (N / 1% strain / mm ² ). .   3. The pneumatic tire according to claim 1, wherein a storage elastic modulus E ′ at 20 ° C. of the insulation rubber covering the steel wire is E ′ ≧ 8.0 MPa. 4.   The pneumatic tire according to claim 3, wherein the storage elastic modulus E ′ is 35.0 MPa ≧ E ′ ≧ 8.0 MPa. The pneumatic tire according to any one of claims 1 to 4, wherein a radius of curvature R 'of the steel wire brazing is 0.88R or more and 0.98R or less. The ratio Sg / Sw of the used volume Sw of the steel wire constituting the bead core to the used volume Sg of the insulation rubber covering the steel wire in the bead core is 0.40 or more and 1.00 or less. The pneumatic tire according to any one of Items 1 to 5 . The pneumatic tire according to claim 6 , wherein the ratio Sg / Sw is 0.40 or more and 0.75 or less.

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