JP4473608B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run-flat tire with improved ride comfort while exhibiting excellent run-flat performance.

A side-reinforcing rubber with a roughly crescent-shaped cross-section that supports the load load during puncture inside the sidewall as a run-flat tire that can travel relatively long distances even when the air in the tire escapes due to puncture etc. there is a so-called side-reinforced type in which a layer. As one of the side-reinforced tires, for example, as shown in FIG. 3, the ply turn-up portion a1 of the carcass a extends to the lower side of the belt layer b, and the side reinforcing rubber layer b is formed of the carcass a. A structure in which the inner layer b1 inside the ply body part a2 and the outer layer b2 between the ply body part a2 and the folded part a1 are divided has been proposed (see, for example, Patent Document 1).

JP 2001-322410 A

  This split structure has a high reinforcing effect because the outer layer b2 is sandwiched between the ply main body a2 and the folded portion a1. Therefore, the rubber thickness and rubber volume of the side reinforcing rubber layer b as a whole can be reduced, and there is an advantage that the riding comfort is excellent as compared with the side reinforcing rubber layer b constituted only by the inner layer b1. However, with the recent high performance of vehicles, further improvement in ride comfort is desired even for run flat tires.

  Here, in the function of the side reinforcing rubber layer, it is important that the rubber hardness is high (high hardness) for supporting the load at the time of puncture, and the elongation at the time of cutting is large (high elongation) for durability. ) And low tangent loss (low heat generation). In general, however, a hard, hard rubber is incompatible with high hardness and high extensibility and low heat generation, such as being hard to stretch and having a large exothermic property. Development is extremely difficult. Conventionally, the run-flat performance is secured under the balance of the three rubber properties.

Therefore, the inventor paid attention to the divided structure of the side reinforcing rubber layer b, and proposed that the physical properties of the inner layer b1 and the outer layer b2 are different, and conducted an experiment. As a result, a high-strength and low-heat generation rubber that dares to sacrifice the rubber hardness is used for the outer layer b2 having a high reinforcing effect, and a high-hardness rubber that sacrifices the elongation and the low heat-generation property to the inner layer b1. It has been clarified that the physical properties of each rubber can be more effectively exhibited when using, and the side rigidity can be reduced and the ride comfort can be improved while ensuring excellent run-flat performance.

  Further, as a result of further research, the pneumatic tire is provided with a bead apex rubber c having a triangular cross section in order to increase the bead rigidity. The bead apex rubber c generates heat as compared with the side reinforcing rubber layer b. Due to its large properties and rubber hardness, it has a great disadvantage in ride comfort and durability. Therefore, even when the high-hardness rubber is used for both the inner and outer layers b1 and b2, when the same rubber as the outer layer b2 is adopted for the bead apex rubber c, the above-mentioned inner layers are used. -It has been found that the ride quality can be improved as in the case where the outer layer b1, b2 has different rubber properties.

  Accordingly, the present invention provides a run-flat tire having a split structure of side reinforcing rubber layers, and uses a high elongation and low heat generation rubber for the outer layer and a high hardness rubber for the inner layer, or the inner and outer layers. The purpose is to provide a run-flat tire that can improve ride comfort while exhibiting excellent run-flat performance, based on the use of high-hardness rubber and integrating bead apex rubber with the outer layer. Yes.

The invention of claim 1 includes a carcass extending from a tread portion through a sidewall portion to a bead core of the bead portion, a belt layer disposed inside the tread portion and radially outside the carcass, and the bead core to the tire. A run flat tire comprising a bead apex rubber extending in a radially outward direction and a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed on the sidewall portion,
The carcass includes a ply body part straddling between the bead cores, a ply folded part that is continuous with the ply body part and folded around the bead core from the inner side to the outer side in the tire axial direction and between the ply body part and the belt layer. And at least one carcass ply having
The side reinforcing rubber layer includes an inner layer disposed on the inner side in the tire axial direction of the ply main body portion, and an outer layer disposed between the ply main body portion and the ply folded portion and continuing to the bead apex rubber. As it is formed,
The inner layer is made of high hardness rubber having a rubber hardness of 70 ° or more, an elongation at break of less than 200%, and a tangent loss tan δ of 0.045 or more, and the outer layer has a rubber hardness of less than 70 °. It is characterized in that it is made of a rubber having a high elongation and low heat generation with an elongation at cutting of 200% or more and a tangent loss tan δ of less than 0.045.

  According to a second aspect of the present invention, the bead apex rubber is made of the same rubber as the outer layer.

In the invention of claim 3, the high hardness rubber has a rubber hardness of 80 ° or less, an elongation at break of 150% or more, a tangent loss tan δ of 0.1 or less, and the high hardness rubber. The run flat tire according to claim 1 or 2, wherein a difference Hb-Ha between a hardness Hb and a rubber hardness Ha of the high elongation and low heat generation rubber is 5 ° or more and 10 ° or less.

  Since the present invention is configured as described above, ride comfort can be improved while exhibiting excellent run-flat performance.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, a pneumatic tire 1 is disposed on a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, inside the tread portion 2, and radially outside the carcass 6. Belt layer 7 and a side reinforcing rubber layer 11 disposed on the sidewall portion 3 and responsible for a load supporting function when the tire escapes from the air.

  The carcass 6 includes at least one carcass cord in which the carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire circumferential direction, and in this example, one carcass ply 6A. As the carcass cord, nylon, polyester, rayon, An organic fiber cord such as aromatic polyamide is preferably used. The carcass ply 6A includes a series of ply turn-up portions 6b that are turned back from the inside in the tire axial direction around the bead core 5 on both sides of the ply body portion 6a straddling the bead cores 5 and 5. A bead apex rubber 8 for reinforcing a bead extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b.

  In addition, the carcass ply 6A has a high turn-up structure in which the ply turn-up portion 6b passes between the sidewall portions 3 and is then sandwiched between the ply body portion 6a and the belt layer 7 and terminates. As a result, the bending rigidity from the bead portion 4 to the sidewall portion 3 is increased, and the outer end of the ply turn-up portion 6b does not appear in the sidewall portion 3 that is greatly bent during puncture travel. Damage can be suppressed. Note that if the overlap width Wj in the tire axial direction between the ply turn-up portion 6b and the belt layer 7 is excessively small, the above-described effect cannot be exhibited. On the other hand, excessively large overlap causes unnecessary weight increase and is disadvantageous for fuel efficiency. . Accordingly, the overlap width Wj is preferably in the range of 5 to 25 mm.

  The belt layer 7 is formed by two or more belt plies 7A and 7B in which high-strength belt cords such as steel cords are arranged at, for example, about 10 to 35 ° with respect to the tire circumferential direction. The belt cords cross each other between the plies to increase the belt rigidity, and substantially reinforce the substantially entire width of the tread portion 2 with a tagging effect. A band layer 9 in which band cords of organic fibers such as nylon are arranged at an angle of 5 degrees or less with respect to the circumferential direction is provided on the outer side in the radial direction of the belt layer 7 mainly for the purpose of improving high-speed durability. be able to. As the band layer 9, a pair of left and right edge band plies that covers only the outer end portion in the tire axial direction of the belt layer 7 and a full band ply that covers substantially the entire width of the belt layer 7 can be used as appropriate. The case where it forms with an edge band ply and a full band ply is illustrated.

  Next, the side reinforcing rubber layer 11 includes an inner layer 12 disposed on the inner side in the tire axial direction of the ply main body portion 6a, and an outer layer 13 disposed between the ply main body portion 6a and the ply folded portion 6b. It is divided into two parts.

  The inner and outer layers 12 and 13 each have a substantially crescent shape in cross section with the thickness gradually decreased from the central portion having the maximum thickness inward and outward in the radial direction. The radially inner ends of the inner and outer layers 12 and 13 terminate radially outside the bead core 5 and radially inward from the tip of the bead apex rubber 8, and bead bases at the inner ends. The heights h2 and h3 in the radial direction from the line BL are different from each other. In particular, in this example, the inner end portion of the outer layer 13 is preferably joined to the bead apex rubber 8 on the outer side surface in the tire axial direction, and the height h3 is regulated to be smaller than the height of the rim flange. The case is illustrated.

  Further, the radially outer ends of the inner and outer layers 12 and 13 are terminated under the belt layer 7 with overlapping widths W2 and W3 with the belt layer 7 being different from each other. In particular, in this example, the overlapping width W2 of the inner layer 12 is made larger than the overlapping width Wj of the ply folding portion 6b, while the overlapping width W3 of the outer layer 13 is made smaller than the overlapping width Wj. Is completely wrapped between the ply body portion 6a and the folded portion 6b. Thereby, it can reinforce smoothly from the bead part 4 to the tread part 2 without causing a big rigidity level | step difference. In addition, by completely wrapping the outer layer 13 with the ply main body portion 6a and the folded portion 6b, the movement of the outer layer 13 can be more strongly restrained, and the reinforcing effect can be greatly enhanced.

In the run flat tire of this embodiment , the inner layer 12 and the outer layer 13 are formed of rubbers having different physical properties.

  Here, in the side reinforcing rubber layer, in general, it is important that the rubber hardness is high, the elongation at cutting is large, and the tangent loss is low and the heat generation is low, and the higher the physical properties, the better the run flat performance. It is as described above. However, high-hardness rubber tends to be inferior in extensibility and low exothermic properties, such as being hard and difficult to stretch, and having high exothermic properties. This technology is extremely difficult.

Therefore, in this embodiment ,
(1) Instead of sacrificing rubber hardness, high elongation and low exothermic rubber Ga with enhanced extensibility and low exothermic property, specifically, rubber hardness Ha of less than 70 ° and elongation at break Ea of 200% The rubber having a tangent loss tanδa of less than 0.045 is used for the outer layer 13 having a high reinforcing effect, and
(2) High hardness rubber Gb with increased rubber hardness instead of sacrificing extensibility and low exothermic property, specifically, rubber hardness Hb is 70 ° or more, elongation at break Eb is less than 200%, and Rubber having a tangent loss tan δb of 0.045 or more is used for the inner layer 12 that is easily dissipated by being located on the tire lumen side.

  Thus, by classifying rubber hardness, extensibility and low heat build-up, each rubber physical property can be set higher, and the rubber is matched to the functions of the inner layer 12 and the outer layer 13. Are used properly. Therefore, it is possible to improve ride comfort while ensuring excellent run-flat performance.

  Here, in the high hardness rubber Gb, when the rubber hardness Hb is less than 70 °, although it is advantageous for the ride comfort, the load supporting ability at the time of puncture is reduced and the tire deformation is increased. The mileage on the flat decreases. In the case of rubber Ga with high elongation and low heat generation, if the elongation Ea during cutting is less than 200% and the tangent loss tan δa is greater than 0.045, the durability of the rubber is insufficient, and the rubber breaks even with relatively small tire deformation. In such cases, it becomes impossible to exhibit excellent run-flat performance, and the rubber hardness Ha is inevitably increased, so that ride comfort is hindered. To do.

  However, if the rubber hardness Hb of the high-hardness rubber Gb is too high, it is difficult to improve the ride comfort and the rigidity balance is impaired even when the rubber hardness Ha of the high-elongation and low-heat generation rubber Ga is sufficiently low. This is disadvantageous for durability and handling stability. Therefore, the upper limit value of the rubber hardness Hb in the high hardness rubber Gb is preferably 80 ° or less, and more preferably 75 ° or less.

Also in order to sufficiently exhibit effects of the present application, the rubber hardness Hb and the rubber hardness Ha and difference Hb-Ha of 5 ° or more, and it is more preferable to secure 8 ° or more. However, if the rubber hardness difference Hb−Ha exceeds 10 °, the tire stiffness balance is impaired, which is disadvantageous for durability and steering stability. Accordingly, the lower limit value of the rubber hardness Ha of the high elongation and low heat generation rubber Ga is limited by the upper limit value (10 °) of the difference Hb−Ha. It is also preferable for the rubber hardness sum Hb + Ha to be 160 ° or less in order to improve riding comfort.

  Further, when the elongation Eb at the time of cutting is too small or the tangent loss tan δb is too large in the high-hardness rubber Gb, the durability in run-flat running and normal running at normal internal pressure tends to be impaired. Therefore, the lower limit value of the elongation Eb at the time of cutting of the high-hardness rubber Gb is preferably 150% or more, and the upper limit value of the tangent loss tan δb is preferably 0.1 or less. In the high elongation and low heat generation rubber Ga, the upper limit value of the elongation at break Ea and the lower limit value of the tangent loss tan δa are not particularly restricted, and are limited by the upper limit value (10 °) of the difference Hb−Ha. Technically possible values can be employed within the range of the lower limit value of the rubber hardness Ha.

  The “rubber hardness” is a hardness by durometer type A measured according to “Hardness test method of vulcanized rubber and thermoplastic rubber” of JIS-K6253, and “elongation at cutting” is JIS- The elongation at break measured in accordance with K6251 “Tensile test method for vulcanized rubber” at a pulling speed of 500 mm / min, and the tangent loss tan δ is the motion of vulcanized rubber and thermoplastic rubber according to JIS-K6394. It is a tangent loss measured under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain rate of 2% using a viscoelastic spectrometer in accordance with the “Test Method for Mechanical Properties”.

  Conventionally, the bead apex rubber 8 has a rubber hardness of 80 to 95 ° and a tangent loss of 0.1 to 0.2 for the purpose of ensuring bead rigidity, and is harder than the side reinforcing rubber layer 11. It is made of rubber with high exothermic properties. However, as a result of experiments by the present inventor, in the side reinforcing type run flat tire, the side reinforcing rubber layer 11 sufficiently secures the rigidity from the bead portion 4 to the sidewall portion 4. It has been found that there is no need to use hard rubber as in the prior art, but rather the use of hard rubber causes a decrease in ride comfort and durability. Therefore, in this example, the bead apex rubber 8 is formed of the same high elongation and low heat generation rubber Ga as that of the outer layer 13, thereby further improving ride comfort and durability. At this time, the bead apex rubber 8 can be formed in advance by a single rubber member integrated with the outer layer 13, and in such a case, the bead apex rubber pasting step at the time of raw tire formation may be eliminated. This also helps improve productivity.

Next, FIG. 2 illustrates a comparative example of a run flat tire. In this example , both the inner layer 12 and the outer layer 13 are made of the high-hardness rubber Gb having a rubber hardness Hb of 70 ° or more, an elongation at break Eb of less than 200%, and a tangent loss tan δb of 0.045 or more. In addition, the bead apex rubber 8 is formed of the same high hardness rubber Gb as the outer layer 13.

  This high hardness rubber Gb is also smaller than that of the conventional bead apex rubber, such as the upper limit value of the rubber hardness Hb is 80 ° or less and the upper limit value of the tangent loss tan δb is 0.1 or less. is there. Accordingly, even in such a case, the bead apex rubber 8 is formed of the same rubber Gb as that of the outer layer 13, whereby the side rigidity can be lowered, and the ride comfort can be improved while ensuring the run-flat performance. it can. In addition, when the bead apex rubber 8 and the outer layer 13 are previously formed as a single rubber member, the step of attaching the bead apex rubber can be eliminated and productivity can be improved.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A run-flat tire (tire size 225 / 60R17) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 was prototyped, and the run-flat performance, general durability, side rigidity, ride comfort, and productivity of the sample tire were evaluated. . Specifications other than those listed in Table 1 are substantially the same.

(1) Run-flat performance:
The test tire is run on the drum tester under the conditions of speed (90 km / h) and longitudinal load (5.16 kN) with the internal pressure being 0 with the rim assembled on the rim from which the valve core has been removed until the tire breaks. The travel distance was measured and evaluated by an index with Comparative Example 1 taken as 100. The larger the value, the better.

(2) General durability:
A test tire was run on a drum test machine under the conditions of internal pressure (190 kPa), speed (80 km / h), and longitudinal load (8.49 kN), and the running distance until the tire broke was measured. Was evaluated with an index of 100. The larger the value, the better.

(3) Side rigidity:
The test tire is filled with internal pressure (230 kPa), the reference longitudinal load is 6.0 kN, and longitudinal deflections d1 and d2 at the load of 1.0 kN before and after (5.0 kN, 7.0 kN) are measured. The longitudinal spring obtained by the equation (1) was converted into an index with Comparative Example 1 as 100 and evaluated. The smaller the value, the smaller the side rigidity and the better the ride comfort.
(7.0-5.0) / (d2-d1) --- (1)

(4) Ride comfort:
A comparative example of the ride comfort when a test tire is mounted on a vehicle (3000 cc, 1 Box vehicle) under conditions of internal pressure (240 kPa) and travels on a tire test course (dry pavement) by sensory evaluation of the driver It is displayed in a 10-point method with 6. A larger index is better.

(5) Productivity:
The reciprocal of the process time when producing a raw tire is displayed as an index with the comparative example being 100. The larger the value, the better the productivity.

It is sectional drawing which shows the run flat tire of embodiment of this invention. It is sectional drawing which shows the run flat tire of a comparative example . It is sectional drawing explaining a prior art.

Explanation of symbols

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 6A Carcass ply 6a Ply main body portion 6b Ply folded portion 7 Belt layer 8 Bead apex rubber 11 Side reinforcing rubber layer 12 Inner layer 13 Outer layer

Claims (3)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a belt layer disposed inward of the tread portion and radially outward of the carcass, and extends in a tapered manner from the bead core outward in the tire radial direction. A run flat tire comprising a bead apex rubber and a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed on the sidewall portion,
The carcass includes a ply body part straddling between the bead cores, a ply folded part that is continuous with the ply body part and folded around the bead core from the inner side to the outer side in the tire axial direction and between the ply body part and the belt layer. And at least one carcass ply having
The side reinforcing rubber layer includes an inner layer disposed on the inner side in the tire axial direction of the ply main body portion, and an outer layer disposed between the ply main body portion and the ply folded portion and continuing to the bead apex rubber. As it is formed,
The inner layer is made of high hardness rubber having a rubber hardness of 70 ° or more, an elongation at break of less than 200%, and a tangent loss tan δ of 0.045 or more, and the outer layer has a rubber hardness of less than 70 °. A run-flat tire comprising a high-elongation, low-heat-generating rubber having an elongation at break of 200% or more and a tangent loss tan δ of less than 0.045.   The run-flat tire according to claim 1, wherein the bead apex rubber is made of the same rubber as the outer layer. The high hardness rubber has a rubber hardness of 80 ° or less, an elongation at break of 150% or more, a tangent loss tan δ of 0.1 or less, and
The run flat tire according to claim 1 or 2, wherein a difference Hb-Ha between a rubber hardness Hb of the high hardness rubber and a rubber hardness Ha of the high elongation and low heat generation rubber is 5 ° or more and 10 ° or less .

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