JP4671319B2 - Run flat tire - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a run flat tire having a tread portion and a sidewall portion reinforced with a reinforcing rubber.
[0002]
[Prior art]
A run-flat tire is a tire that can continuously maintain running performance even when the tire is in a state where air is removed due to puncture or the like. As such a run-flat tire, there is a tire disclosed in Japanese Patent Laid-Open No. 11-310019, and its configuration is shown in FIG.
[0003]
In FIG. 4, the tire 1 includes a tread portion 2 that is in contact with a road surface, a sidewall portion 3 that is positioned on a side surface, and a rim stop portion 4. Moreover, it has a pair of bead part 5 in a tire axial direction, and has the carcass layer 6 so that it may span between a pair of bead part 5. The carcass layer 6 includes a first carcass ply 6a and a second carcass ply 6b, and each carcass ply 6a, 6b is constituted by a carcass cord wound around the tire equator line C at a predetermined angle.
[0004]
The carcass layer 6 has a belt layer 7 immediately outside in the tire radial direction, and the first belt ply 7a on the inner side in the radial direction and the second belt ply 7a disposed on the outer side of the first belt ply 7a. Belt ply 7b.
[0005]
Further, the side wall 3 is provided with a reinforced rubber layer 8 having a substantially crescent-shaped cross section, and even when the tire 1 is deflated (when the tire internal pressure is zero), the side wall 3 is bent. The amount of deformation is suppressed. This is intended to maintain the run-flat performance.
[0006]
[Problems to be solved by the invention]
However, the reinforcing effect cannot be sufficiently obtained only by the reinforcing rubber layer 8 of the sidewall portion 3. That is, when air escape occurs in the tire, even if the bending deformation of the sidewall portion 3 can be suppressed, a buckling phenomenon occurs as shown in FIG. Buckling refers to a phenomenon in which the central portion in the width direction of the tread portion 2 is lifted, and the occurrence of buckling increases the amount of bending deformation of the tire and causes the run-flat performance to deteriorate. Therefore, in order to improve the run-flat performance, it is necessary to suppress not only the deformation of the sidewall portion but also the deformation of the tread portion.
[0007]
In the tire disclosed in the prior art, the tread portion 2 is formed of a tread inner layer rubber and a tread outer layer rubber, the outer layer rubber has a hardness of 60 according to JIS A, and the inner layer rubber has a hardness of 30 to 60. Are disclosed as examples. In order to suppress the buckling, it is considered that there is room for improvement regarding the hardness of the rubber constituting the tread portion.
[0008]
This invention is made | formed in view of the said situation, The subject is providing the run flat tire which can suppress a buckling by selecting the rubber | gum which comprises a tread part appropriately. .
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a run flat tire according to the present invention is:
The tread part,
A run flat tire having a sidewall portion reinforced with a reinforced rubber,
The tread portion has a base rubber layer located on the inner side in the tire radial direction and a cap rubber layer located on the outer side in the tire radial direction, and the hardness of the rubber constituting the base rubber layer constitutes the cap rubber layer. It is higher than the hardness of rubber, and is 78 to 95 according to JIS A.
[0010]
According to this configuration, the tread portion has a base rubber layer and a cap rubber layer, and the hardness of the rubber constituting the base rubber layer is 78 to 95 according to JIS A. That is, high hardness rubber is used as the base rubber layer. As a result, even if the tires lose air and the internal pressure becomes zero, deformation of the tread portion can be suppressed. As a result, a run flat tire capable of suppressing buckling can be provided. The hardness is based on a type A durometer of JIS K6253 durometer hardness test.
[0011]
When the hardness of the rubber is less than 78, there is no effect of suppressing buckling, and when the hardness exceeds 95, the fracture characteristics are deteriorated and become impractical.
[0012]
As a preferred embodiment of the present invention, a base rubber layer having a thickness of 0.5 mm to 5 mm can be mentioned.
[0013]
By selecting a thickness within such a range, buckling can be effectively suppressed. If the thickness of the base rubber layer is thinner than 0.5 mm, the effect of suppressing buckling is almost lost. When the thickness of the base rubber layer exceeds 5 mm, riding comfort deteriorates.
[0014]
As another preferred embodiment of the present invention, one in which the width dimension of the base rubber layer along the tire axial direction is 40% to 100% of the width dimension of the tread portion.
[0015]
When the width dimension of the base rubber layer is less than 40% of the width dimension of the tread portion, it is difficult to suppress buckling because the width is too narrow. Moreover, when it exceeds 100% of the width dimension of a tread part, the crack property of a buttress will deteriorate.
[0016]
As still another preferred embodiment of the present invention, the base rubber layer is reinforced with short fibers.
[0017]
By strengthening with fibers, deformation of the tread portion can be more effectively suppressed even when the internal pressure becomes zero.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of a run flat tire according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a run-flat tire. Since the tire 1 is symmetrical in the tire width direction, the right half of the tire equator line C is illustrated.
[0019]
The tire 1 includes a tread portion 2 that contacts a road surface, a sidewall portion 3 located on a side surface, and a rim stop portion 4. Moreover, it has a pair of bead part 5 in a tire axial direction, and has the carcass layer 6 so that it may span between a pair of bead part 5. The carcass layer 6 includes a first carcass ply 6a and a second carcass ply 6b, and each carcass ply 6a, 6b is constituted by a carcass cord wound around the tire equator line C at a predetermined angle. Organic fiber is mainly used as the material for the carcass cord.
[0020]
The carcass layer 6 is provided so as to be folded back from the inner side toward the outer side in the bead portion 5, and has an inner portion 60 and a folded outer portion 61. The bead apex rubber 10 and the reinforcing rubber layer 8 are provided so as to be sandwiched between the inner portion 60 and the outer portion 61. The reinforced rubber layer 8 has a JIS A hardness of 60 ° to 80 ° and a cross-sectional shape of a substantially crescent shape. The sidewall portion 3 is reinforced by the reinforcing rubber layer 8.
[0021]
When the air in the tire escapes due to tire puncture or the like and the internal pressure becomes zero, the deflection deformation of the tire increases. In order to suppress this deformation, the reinforcing rubber layer 8 is provided on the sidewall portion 3, whereby the deformation of the sidewall portion 3 can be suppressed. Since the reinforcing rubber layer 8 is provided, the tire thickness at the position that is 1/3 above the rim line position of the tire 1 by 1/3 between the same position and the maximum width position is H1, and the tire thickness at the tire maximum width position is H2. Then, H2 is 60% to 140% with respect to H1. The direction in which the thickness is measured is a direction perpendicular to the R shape of the tire inner surface.
[0022]
The carcass layer 6 has a belt layer 7 immediately outside in the tire radial direction, and the first belt ply 7a on the inner side in the radial direction and the second belt ply 7a disposed on the outer side of the first belt ply 7a. Belt ply 7b. Each belt ply 7a, 7b is formed by arranging, for example, steel cords at an angle of 15 ° to 35 ° with respect to the tire equator line C. Note that the cord arrangement in the first belt ply 7a and the cord arrangement in the second belt ply 7b intersect each other.
[0023]
The tread portion 2 includes a base rubber layer 20 located on the inner side in the tire radial direction and a cap rubber layer 21 located on the outer side in the tire radial direction. A predetermined tread pattern is formed on the outer surface of the cap rubber layer 21. The rubber constituting the base rubber layer 20 has a hardness of 78 to 95 according to JIS A, and a rubber having a hardness higher than that of the cap rubber layer 21 is used. Thereby, even if air deflation occurs in the tire 1 due to puncture or the like, buckling (deformation of the tread portion 2) as shown in FIG. 5 can be suppressed. In order to improve the deterioration of ride comfort due to the use of a high-hardness base rubber, the cap tread rubber layer can be made into a plurality of layers, and the inner cap tread rubber layer not in direct contact with the road surface can be softened.
[0024]
<Example>
Comparison results between the examples (1-5) in the case where the base rubber layer 20 made of high hardness rubber is provided and the tires (comparative example) in the case where there is no high hardness rubber layer are shown in Table 2 shown in FIG. Indicates. The type of tire used is 205 / 50R16. The tires shown in the table are all provided with a reinforced rubber layer in the sidewall portion.
[0025]
In the table, the maximum width side portion thickness ratio means the ratio (%) of the thickness (H2) of the sidewall portion at the tire maximum width position to the bead portion thickness (see H1 in FIG. 1) at the upper end of the rim flange. When both thicknesses are equal, it is 100%. When the sidewall portion 3 is reinforced by the reinforcing rubber layer 8 having a crescent-shaped cross section, the thickness of the sidewall portion, that is, the ratio is increased.
[0026]
The high hardness base rubber layer is the base rubber layer 20 described above. The hardness is based on a JIS K6253 durometer hardness test type A durometer. The thickness is indicated by t in FIG. The width index (%) refers to the ratio to the tread width. Here, the tread width is a width dimension W1 at an intersection P (only one place is shown in FIG. 1 but there are two places in the tire width direction) between the outer shape of the tread portion 2 and the outer shape of the sidewall portion 3. Say. If the width dimension along the tire width direction of the base rubber layer 20 is W2, the width index is
It is indicated by W2 / W1 × 100 (%).
[0027]
When the width dimension W2 of the base rubber layer 20 is equal to the tread width W1, the width index is 100. As the width index decreases, the width of the base rubber layer 20 also decreases.
[0028]
Next, the tire deflection index will be described. As shown in FIG. 3, tangent lines L1 and L2 are drawn in accordance with the outer shape of the bead portion. When the vertical load acting on the tire is 0 and the tire internal pressure is 2 kg / cm ² , the height from the intersection of the tangents L1 and L2 to the surface of the tread portion is A, and the vertical load acting on the tire is 440 kg. Let B be the height from the intersection point to the surface of the tread when the tire internal pressure is 0 (during puncture). The deflection in this case is A−B = δ. The ratio when this deflection is compared with the comparative tire is the tire deflection index. If the index is 100, this means that the same amount of deflection as the comparative tire is applied. The smaller the index is, the smaller the deflection and the better the run flat performance.
[0029]
As can be seen from the table, by forming the base rubber layer 20 of the tread portion 2 with high-hardness rubber, it is understood that the tire deflection index is smaller than that of the comparative example, and the run-flat performance is improved. . The hardness of the rubber used for the base rubber layer 20 is preferably 78 to 95 in terms of JIS A hardness. If the hardness of the rubber is lower than 78, the tire deflection index cannot be improved. On the other hand, if the hardness of the rubber exceeds 95, the destructive properties of the rubber deteriorate, making it impractical.
[0030]
Next, attention is paid to the thickness t of the base rubber layer 20. The tires of the examples are 1.5 mm except for Example 5 and 4 mm in Example 5. In addition, the range of preferable thickness is 0.5-5 mm, and if it becomes thinner than 0.5 mm, a reinforcement effect will hardly appear. Further, when the thickness of the high hardness rubber exceeds 5 mm, there is a drawback that riding comfort is deteriorated.
[0031]
Next, attention is focused on the width index of the base rubber layer 20. As for the width index, the tire deflection index becomes smaller as the width becomes wider (for example, comparison between Examples 2 and 3). That is, it can be seen that the larger the width dimension, the more effective the reinforcement. The width dimension (W2) of the preferable base rubber layer is set to be 40 to 100% of the tread width dimension (W1). When the width becomes narrower than 40% of the tread width dimension, the reinforcing effect becomes thin despite the provision of the high hardness rubber layer. Further, if the width is larger than the tread width dimension, the crack property of the buttress portion is deteriorated.
[0032]
<Another embodiment>
Short fibers may be mixed into the base rubber layer to give FRP characteristics. Thereby, a base rubber layer can be strengthened more and run flat performance can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a run-flat tire. FIG. 2 is a table comparing the run-flat performance of a comparative example and an example. FIG. 3 is a diagram illustrating a tire deflection index. Sectional view [Fig. 5] Diagram showing buckling phenomenon [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tire 2 Tread part 3 Side wall part 8 Reinforcement rubber layer 20 Base rubber layer 21 Cap rubber layer

Claims (4)

The tread part,
A run flat tire having a sidewall portion reinforced with a reinforced rubber,
The tread portion has a base rubber layer located on the inner side in the tire radial direction and a cap rubber layer located on the outer side in the tire radial direction, and the hardness of the rubber constituting the base rubber layer constitutes the cap rubber layer. A run flat tire characterized by being higher in hardness than rubber and having a JIS A of 78 to 95.   The run flat tire according to claim 1, wherein the base rubber layer has a thickness of 0.5 mm to 5 mm.   The run flat tire according to claim 1 or 2, wherein a width dimension of the base rubber layer along a tire axial direction is 40% to 100% of a width dimension of the tread portion.   The run-flat tire according to any one of claims 1 to 3, wherein the base rubber layer is reinforced with short fibers.

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