JP5183997B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire with improved tire rim assemblability and tire uniformity after assembly (assembly uniformity).

  A pneumatic tire is formed by arranging a plurality of rubber-coated wires in parallel and winding them in a ring shape and then laminating them, so-called strand beads or a single wire is covered with rubber, and a plurality of spiral wires are formed. In general, a so-called monostrand bead, which is wound and laminated, is embedded in a bead portion as a bead core, and a tire is attached to the rim through the bead portion for use.

  In recent years, tires tend to have a larger diameter than before, and it is not uncommon to install tires having a rim diameter of 17 inches or more on a new vehicle. As the tire diameter increases, it is necessary to improve the strength of the bead core in order to prevent the rim from coming off, and measures such as increasing the number of cores of the bead core have been taken.

  However, improving the strength of the bead core leads to an increase in the bead expansion force when the tire is mounted on the rim, and the strengthening of the bead core, on the other hand, deteriorates the rim assemblability. Here, the bead expansion force is a value measured using a bead expansion tester manufactured by Hoffman.

  That is, if the bead expansion force is too high, the tire rim assembly is hindered, and it is difficult to properly attach the tire to the rim. As a result, the uniformity of the tire after assembling the rim may deteriorate. Therefore, it is necessary to reduce the bead expansion force while maintaining the strength of the bead core.

Therefore, in Patent Document 1, a rubber layer having an adjusted thickness is disposed within the width range of the bead core in the tire width direction and on the inner side in the tire radial direction of the bead core without increasing the width of the bead portion. There has been proposed a method for reducing the bead expansion force by increasing the inner periphery of the bead.
JP 2006-159985 A

  However, depending on the volume of the rubber layer disposed inside the bead core, the bead expansion force may not be sufficiently reduced as described below.

  Here, the bead expansion force was investigated using a pneumatic tire of size 215 / 55R17. That is, when one side bead portion of a pneumatic tire to be measured is arranged on an eight-part rim block of a Hoffman bead expansion force testing machine, the bead portion of the tire is expanded outward in the radial direction. FIG. 1 shows the result of recording the amount of change (usually in the range of −3.5 mm to 2.5 mm of the standard rim diameter) on the horizontal axis and the generated force on the vertical axis. This bead expansion test is the first recording. This is because the second and third measurements are not preferable because the rubber has changed, and it is preferable to use the first measured value.

  In the measurement profile shown in FIG. 1, the gradually inclined range (in FIG. 1, the influence region of the rubber compression of the rubber layer disposed on the radially inner side of the bead core) is the compression (rubber compression) of the rubber layer disposed on the radially inner side of the bead core ) And the range in which the inclination is constant (the influence range of the bead expansion rigidity in FIG. 1) is influenced by the bead expansion rigidity, and the bead expansion force increases.

In particular, the rubber compression (P) correlates with the rubber volume (s) of the rubber layer 2 disposed on the radially inner side of the bead core 1 shown in FIG. 2, and the rubber compression (P) and the rubber volume (s) The relationship is as shown in the following formula (1). The rubber volume (s) can be calculated by the following formula (2) when the tire is assembled with a rim. K (coefficient) represents the Young's modulus of rubber.
Record
P = k × s (1)
Where k: coefficient (Young's modulus of rubber)

s = A ′ × X (2)
However, A ′: Area of the bottom surface of the rubber layer (≈ Area A of the bottom surface of the bead core)
X: Displacement amount of the rubber layer before and after assembling the rim

  Further, since the rubber layer 2 arranged on the inner side in the radial direction of the bead core 1 only needs to be arranged in a range in contact with the bottom surface of the bead core in order to receive the rubber compression, the width of the bead core 1 in the tire axial direction is sufficient. (Hereinafter simply referred to as width). Accordingly, if the width of the bead core 1 is increased in order to improve the bead rigidity, the width of the rubber layer 2 is also increased and the rubber volume is increased.

  That is, when the rubber volume increases, as shown in the above formula (1), the rubber compression increases and the bead expansion force also increases. As a result, the rim assembly property when the tire is mounted on the rim is deteriorated, and the assembly uniformity of the pneumatic tire after the rim assembly is also deteriorated.

  Here, in order to reduce the rubber compression and reduce the bead expansion force, for example, as shown by a dotted line in FIG. 3, the width of the bead core 1 is reduced without changing the number of cores of the bead core 1. Although it is conceivable to narrow the width, there is a possibility that the bead core 1 becomes longer toward the outer side in the tire radial direction and the bead collapse occurs.

  Further, as in the relationship between the bead core 1 and the rubber layer 2 indicated by the solid line in FIG. 3, if only the width of the rubber layer 2 is narrowed while the width of the bead core 1 is left as it is, the rubber layer 2 radially inward of the bead core 1 This leads to a manufacturing failure of bead portions such as so-called heel bears and base bears.

  Accordingly, an object of the present invention is to provide a pneumatic tire that has an excellent assembly uniformity as a result of reducing the bead expansion force and improving the rim assembly property when the tire is mounted on the rim. To do.

  As a result of earnestly examining the measures to reduce the bead expansion force, the inventor can reduce the number of cores constituting the radially innermost row of the bead cores, and can narrow the width of the rubber layer while maintaining the strength of the bead part. It has been found that the bead expansion force can be reduced, and the present invention has been completed.

That is, the gist configuration of the present invention is as follows.
(1) A pneumatic tire having a bead core formed by winding a bead wire in which one or a plurality of wires are covered with rubber in a ring shape, in each of the pair of bead parts, The bead core has a laminated structure in which a plurality of rows of cores formed of the wires are stacked in a plurality of stages, and the number of cores constituting the innermost radial stage of the bead core is smaller than the number of cores constituting the other stages. A rubber layer having a 100% elongation modulus of 1.0 to 5.0 MPa is arranged in contact with the bottom surface of the bead core on the radially inner side of the bead core, and the width of the rubber layer is the innermost radial direction of the bead core. A pneumatic tire characterized by being equal to the width of the step .

(2) The pneumatic tire according to (1), wherein the rubber layer has a thickness of 0.5 to 2.0 mm.

(3) The pneumatic tire according to (1) or (2), wherein the bead core and the rubber layer are wound and integrated with a wrapping tape.

  According to the present invention, when the rubber layer having a 100% elongation modulus in a predetermined range is arranged on the radially inner side of the bead core, the core of the step constituting the radially innermost side of the bead core among the steps constituting the bead core. By minimizing the number, the width of the rubber layer can be reduced, and the bead expansion force can be reduced while maintaining the strength of the bead core. As a result, the rim assembly property when the tire is mounted on the rim is improved. Therefore, it is possible to provide a pneumatic tire excellent in assembly uniformity.

Hereinafter, the pneumatic tire of the present invention will be described in detail with reference to the drawings.
First, FIG. 4 shows a cross-sectional view of a pneumatic tire according to the present invention.
The illustrated tire has a carcass 4 extending in a toroidal shape across a pair of bead cores 3 and has a two-layer belt 5 on the outer side in the tire radial direction of the carcass. The tread 6 is arranged. In addition, the pneumatic tire of this invention is not restricted to this, For example, a belt structure can also be made into 3 layers or 4 layers.

  As shown in FIG. 5, the bead core 3 is formed by winding a steel wire 7 in which one wire is covered with rubber in a ring shape. And this bead core 3 has the laminated structure which piled up the row | line | column with which the core with the steel wire 7 was located in multiple steps in the cross section of the width direction of a tire. Further, the rubber layer 2 is disposed inside the bead core 3 in the radial direction.

  Here, it is important that the number of cores constituting the radially innermost row of the bead cores 3 is smaller than the number of cores constituting the other rows. That is, the number of cores constituting the radially innermost row of the bead cores 3 is the smallest among all the rows constituting the bead cores 3, so that the rubber layer 2 disposed on the radially innermost side of the bead cores 3 The width can be reduced. This is because the width of the rubber layer 2 is in contact with the radially innermost row constituting the bead core, so that the width of the rubber layer 2 can be reduced according to the width of this row. If the width of the rubber layer 2 is reduced, the rubber volume is reduced and the rubber compression is also reduced, so that the bead expansion force can be reduced.

The bead core 3 is not limited to the stacked structure shown in FIG. 5, and the number of cores and the number of stacked layers in each row can be adjusted as long as the configuration of the present invention is satisfied. For example, as shown in FIG. 6A, the uppermost layer has 5 cores, the middle (upper) has 5 cores, the middle (middle) has 5 cores, the middle (lower) has 5 cores, and the lowermost has 4 cores. As shown in FIG. 6B, the uppermost row is 8 cores, the middle row (upper) is 7 wires, the middle row (middle) is 5 wires, the middle row (lower) is 3 wires, and the lowermost row is 1 core. A laminated structure with a core may be used. The advantageous effect of the present invention can be obtained even with a strand bead in which a plurality of wires are arranged in parallel and a rubber-coated plate-like ply wire is wound in a ring shape a plurality of times and laminated.

  Furthermore, it is important that the rubber layer 2 disposed on the radially inner side of the bead core is a rubber layer having a 100% elongation modulus of 1.0 to 5.0 MPa. Here, the 100% elongation modulus means an amount obtained by dividing the tension by the cross-sectional area before deformation when the rubber test piece is pulled to 100% elongation.

  That is, when the 100% elongation modulus in the rubber layer 2 is less than 1.0 MPa, the rubber is too soft and the effect of suppressing deformation of the bead portion is poor, and a phenomenon such as rim slip is likely to occur. On the other hand, if it exceeds 5 MPa, the bead expansion rate becomes too high, and there is a risk that the rim assembly and rim fit properties will be deteriorated and rim deformation due to excessive air pressure will occur.

  Further, the thickness of the rubber layer is preferably 0.5 to 2.0 mm. That is, when the thickness of the rubber layer is less than 0.5 mm, the expansion allowance of the inner peripheral diameter inside the bead core is reduced, and it is difficult to improve the rim assembly property. On the other hand, if it exceeds 2.0 mm, the inner peripheral diameter of the rubber layer inside the bead core becomes too large, and there is a concern that the rim may come off due to looseness during running.

  And by providing the above-mentioned bead core and rubber layer in the bead part of the pneumatic tire, the expansion force of the bead part can be reduced as expected, so such a tire is under an appropriate rim assembly. It becomes possible to attach to the rim. As a result, a pneumatic tire excellent in assembly uniformity can be provided.

  Next, as shown in FIG. 7, the bead core 3 and the rubber layer 2 are preferably wound and integrated with a wrapping tape 8. Here, the wrapping tape 8 is preferably a cloth-like tape having a coarse mesh. That is, if the wrapping tape has a coarse mesh, the rubber separated by the tape can be bonded through the mesh and integrated with each other during vulcanization molding.

  The bead core 3 and the rubber layer 2 are wound with the wrapping tape 8 so that the bead core 3 and the rubber layer 2 are integrated, and the rubber layer 2 can be accurately placed at a desired position. During the vulcanization molding, fluidization of rubber can be suppressed. Furthermore, it is possible to prevent the rubber layer 2 from protruding on both sides of the bead core 3 in the tire width direction.

  Under various specifications shown in Table 1, a pneumatic tire in which a bead core having each laminated structure was embedded in a bead portion was prototyped, and bead expansion force, tire uniformity, and rim assembly were measured. The results are shown in Table 1.

  A bead expansion force shows the value measured using the above-mentioned bead part expansion force tester by Hoffman.

The uniformity of pneumatic tires investigated the lateral force variation (LFV) of pneumatic tires and evaluated the results. In addition, LFV was investigated using the Bridgestone Cycle Industry Co., Ltd. uniformity measuring machine. In the table, AVE represents an average value of the total number of tires measured. Σ represents the standard deviation of the total number of tires measured.

It is the figure which showed the measurement result of the expansion force test of a bead part. It is the figure which showed the width | variety and rubber volume of the bead core. It is the figure shown in order to demonstrate the relationship between the width | variety of a bead core and the width | variety of a rubber layer. It is the figure which showed the suitable pneumatic tire according to this invention. It is the figure which showed the bead core and rubber layer of this invention. It is the figure which showed the bead core and rubber layer of this invention. FIG. 3 is a view showing a bead core and a rubber layer of the present invention integrated with a wrapping tape. It is the figure which showed the bead core and rubber layer of the prior art example and this invention. It is the figure which showed the bead core and rubber layer of the prior art example and this invention.

Explanation of symbols

1 Bead core 2 Rubber layer 3 Bead core 4 Carcass 5 Belt 6 Tread 7 Steel wire 8 Wrapping tape

Claims (3)

A pneumatic tire having a bead core formed by winding a bead wire in which one or a plurality of wires are covered with rubber in a ring shape, in each of the pair of bead portions, And having a laminated structure in which a plurality of rows of cores made of wires are stacked in a plurality of stages, and the number of cores constituting the innermost stage in the radial direction of the bead core is less than the number of cores constituting the other stages, A rubber layer having a 100% elongation modulus of 1.0 to 5.0 MPa is arranged in contact with the bottom surface of the bead core , and the width of the rubber layer is the diameter of the innermost step in the radial direction of the bead core. A pneumatic tire characterized by being equal in width .   The pneumatic tire according to claim 1, wherein the rubber layer has a thickness of 0.5 to 2.0 mm.   The pneumatic tire according to claim 1 or 2, wherein the bead core and the rubber layer are integrated by being wound with a wrapping tape.

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