JP5104050B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire suitable for trucks and buses. More specifically, even when used under severe load conditions, the carcass layer separation failure at the bead portion is prevented and durability is improved. The present invention relates to a pneumatic tire that can be used.

  In a pneumatic tire, the carcass layer is folded around the bead core from the inside of the tire to the outside, and a bead filler extending so as to taper from the bead core toward the tread side is disposed between the main body portion and the folded portion of the carcass layer. Is common. The bead filler is composed of a rubber composition having a relatively high hardness, and mainly contributes to improvement in handling stability.

  By the way, when a load is applied to the pneumatic tire, the sidewall portion is normally bent, but when used under severe load conditions, not only the sidewall portion bends but also the bead portion including a bead filler has a rim flange. It will fall to the outside of the tire as a fulcrum. Therefore, under severe load conditions, there is a problem that very large compressive strain and compressive stress act on the bead portion, resulting in separation failure of the carcass layer.

  Conventionally, in order to prevent separation failure of the carcass layer in the bead portion, for example, the coat rubber of the carcass layer is thickened in a region adjacent to the bead filler in the main body portion of the carcass layer (see, for example, Patent Document 1), or It has been proposed that a stress relaxation rubber layer that is softer than the coat rubber of the carcass layer is interposed between the main body portion of the carcass layer and the bead filler (see, for example, Patent Document 2).

However, in these methods, when a pneumatic tire is used under severe load conditions, the carcass layer separation failure in the bead portion cannot be prevented at present.
JP-A-8-2219 JP-A-10-76820

  An object of the present invention is to provide a pneumatic tire capable of improving durability by preventing a carcass layer separation failure in a bead portion even when used under severe load conditions. is there.

In order to achieve the above object, the pneumatic tire according to the present invention folds the carcass layer around the bead core from the inside to the outside of the tire, and extends from the bead core to the tread side between the main body portion and the folded portion of the carcass layer. In the pneumatic tire for trucks and buses, a bead filler extending so as to be tapered is disposed , and a plurality of belt layers including a plurality of steel cords are embedded on an outer peripheral side of the carcass layer in a tread portion. A strain reducing rubber layer is disposed between the body portion of the layer and the bead filler; the strain reducing rubber layer has a JIS hardness of 70 to 80 and is higher than the JIS hardness of the coat rubber of the carcass layer; the hardest part is intended lower than JIS hardness of the thickness of the strain reducing rubber layer 0.5mm~5.0mm of Yes, the width of the strain-reducing rubber layer is 0.1H to 0.6H with respect to the height H of the bead filler in the tire radial direction from the bead core, and the tire radial direction of the bead filler from the bead core is The strain-reducing rubber layer is arranged in a range of 0.2H to 0.8H with respect to a height H of .

  In the present invention, since a strain reducing rubber layer that is harder than the coat rubber of the carcass layer but softer than the hardest part of the bead filler is interposed between the body portion of the carcass layer and the bead filler, the pneumatic tire is severe. Even when the load is used under various load conditions, the strain that the carcass layer is subjected to at the bead portion can be reduced, the separation failure of the carcass layer can be prevented, and the durability can be improved.

In the present invention, in order to obtain the effect of preventing separation failure without deteriorating riding comfort, the JIS hardness of the strain reducing rubber layer needs to be 70-80. The thickness of the strain reducing rubber layer is required to be 0.5 mm to 5.0 mm. Furthermore, the width | variety of a distortion reduction rubber layer needs to be 0.1H-0.6H with respect to the height H of the tire radial direction from the bead core of a bead filler.

It is necessary to dispose the strain reducing rubber layer in the range of 0.2H to 0.8H with respect to the height H in the tire radial direction from the bead core of the bead filler. In particular, when the bead filler is composed of the lower bead filler having a relatively high hardness located on the bead core side and the upper bead filler having a relatively low hardness located on the tread side, the strain reducing rubber layer is located on the lower side. It is preferable to arrange the bead filler at a position adjacent to the end portion on the outer side in the tire radial direction. Moreover, when it is set as the bead structure which wrapped the main-body part and winding-up part of the carcass layer with the steel cord reinforcement layer, it is preferable to arrange | position a distortion reduction rubber layer in the position adjacent to the edge part inside a tire of a steel cord reinforcement layer.

  The JIS hardness in the present invention is measured using a type A durometer in accordance with a durometer hardness test specified in JIS K6253.

  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, and FIG. 2 shows an enlarged view of the bead portion. 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 the carcass layer 4 is folded around the bead core 5 from the inside to the outside of the tire. A bead filler 6 extending from the bead core 5 toward the tread side is disposed between the main body portion 4A and the folded portion 4B of the carcass layer 4.

  The bead filler 6 has a triangular cross-section and is composed of a rubber composition having high hardness. More specifically, as shown in FIG. 2, the bead filler 6 is located on the bead core side and has a relatively high hardness, the lower bead filler 6A, and the tread side is located on the tread side and has a relatively low hardness. 6B. The JIS hardness of the lower bead filler 6A is selected from the range of 80 to 90, and the JIS hardness of the upper bead filler 6B is selected from the range of 55 to 65. When the bead filler 6 is composed of a single type of rubber composition, the JIS hardness may be selected from the range of 55 to 90.

  Further, the main body portion 4 </ b> A and the winding portion 4 </ b> B of the carcass layer 4 are wrapped by a steel cord reinforcing layer 7 that is folded around the bead core 5. The steel cord reinforcing layer 7 includes a plurality of steel cords inclined with respect to the tire circumferential direction. Furthermore, two layers of organic fiber cord reinforcement layers 8 are disposed on the outer side in the tire width direction than the bead filler 6, the rolled-up portion 4 </ b> B of the carcass layer 4, and the steel cord reinforcement layer 7. These organic fiber cord reinforcing layers 8 include a plurality of organic fiber cords inclined with respect to the tire circumferential direction.

  On the other hand, a plurality of belt layers 9 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 9 include a plurality of steel cords inclined with respect to the tire circumferential direction, and are disposed so that the steel cords cross each other between the layers.

  In the pneumatic tire, a strain reducing rubber layer 10 is disposed between the main body portion 4 </ b> A of the carcass layer 4 and the bead filler 6. The JIS hardness of the strain reducing rubber layer 10 is set higher than the JIS hardness of the coat rubber of the carcass layer 4 and lower than the JIS hardness of the hardest part of the bead filler 6, that is, the lower bead filler 6A. .

  Thus, when the strain reducing rubber layer 10 that is harder than the coat rubber of the carcass layer 4 but softer than the hardest part of the bead filler 6 is interposed between the main body portion 4A of the carcass layer 4 and the bead filler 6, Even when the entering tire is used under severe load conditions, the strain that the carcass layer 4 receives in the bead portion 3 can be reduced. That is, under severe load conditions, when the bead portion 3 including the bead filler 6 falls to the outside of the tire with the rim flange as a fulcrum, the strain reducing rubber layer 10 relaxes the compressive strain acting on the carcass layer 4. Thereby, the separation failure of the carcass layer 4 in the bead part 3 can be prevented and durability can be improved.

  In the pneumatic tire, the JIS hardness of the strain reducing rubber layer 10 is set in a range of 70 to 80, preferably in a range of 72 to 78. If the JIS hardness of the strain reducing rubber layer 10 is less than 70, the strain reducing effect will be insufficient. Conversely, if it exceeds 80, the stiffness will be too high locally and the strain will concentrate near the end of the strain reducing rubber layer. In addition to this, riding comfort is reduced.

  The thickness of the strain reducing rubber layer 10 is set in the range of 0.5 mm to 5.0 mm. If the thickness of the strain-reducing rubber layer 10 is less than 0.5 mm, the effect of reducing the strain becomes insufficient. Conversely, if the thickness exceeds 5.0 mm, the rigidity becomes excessively high and the vicinity of the end of the strain-reducing rubber layer. In addition to the concentration of distortion, the riding comfort is reduced.

  The width W of the strain reducing rubber layer 10 is set in the range of 0.1H to 0.6H with respect to the height H in the tire radial direction from the bead core 5 of the bead filler 6. If the width W of the strain reducing rubber layer 10 is less than 0.1H, the strain reducing effect will be insufficient. Conversely, if the width W exceeds 0.6H, the stiffness will become too high locally and near the end of the strain reducing rubber layer. In addition to the concentration of distortion, the riding comfort is reduced.

  The distortion reducing rubber layer 10 is disposed in the range of 0.2H to 0.8H with respect to the height H in the tire radial direction from the bead core 5 of the bead filler 6. When the position of the strain reducing rubber layer 10 is out of the above range, the strain reducing effect becomes insufficient.

  In particular, when the bead filler 6 is composed of a lower bead filler 6A having a relatively high hardness positioned on the bead core side and an upper bead filler 6B having a relatively low hardness positioned on the tread side, the strain reducing rubber layer 10 is arrange | positioned in the position adjacent to the edge part E1 of the tire radial direction outer side of 6 A of lower side bead fillers. That is, under severe load conditions, separation failure of the carcass layer 6 tends to occur in the vicinity of the end E1 on the outer side in the tire radial direction of the lower bead filler 6A. Therefore, the strain reducing rubber layer 10 along the end E1. It becomes possible to prevent the separation failure of the carcass layer 6 more effectively.

  Further, when the bead structure in which the main body portion 4 </ b> A and the winding portion 4 </ b> B of the carcass layer 4 are wrapped with the steel cord reinforcing layer 7, the strain reducing rubber layer 10 is positioned adjacent to the tire inner end E <b> 2 of the steel cord reinforcing layer 7. Placed in. That is, under severe load conditions, separation failure of the carcass layer 6 is likely to occur in the vicinity of the end E2 inside the tire of the steel cord reinforcing layer 7, and the strain reducing rubber layer 10 is disposed along the end E2. By doing so, it becomes possible to prevent the separation failure of the carcass layer 6 more effectively.

  Air with tire size 1100R20 in which the carcass layer is folded from the inside to the outside of the tire around the bead core, and bead filler extending from the bead core toward the tread side is disposed between the main body portion and the folded portion of the carcass layer. In the entering tire, between the main body portion of the carcass layer and the bead filler, a strain reducing rubber layer having a width of 0.4 H is arranged with respect to the height H in the tire radial direction from the bead core of the bead filler, Tires of Examples 1 to 5 and Comparative Examples 1 to 2 in which the JIS hardness and thickness of the strain reducing rubber layer were set as shown in Table 1 were manufactured. For comparison, a conventional tire without a strain reducing rubber layer was prepared. In the tires of these conventional examples, Examples 1 to 5 and Comparative Examples 1 and 2, the bead filler was composed of a lower bead filler having a JIS hardness of 83 and an upper bead filler having a JIS hardness of 59. The JIS hardness of the carcass layer coat rubber was 68.

  These test tires were evaluated for load durability and riding comfort by the following methods, and the results are also shown in Table 1.

Load durability:
For the test tire, a drum endurance test was conducted under the conditions of an air pressure of 700 kPa (standard air pressure of 830 kPa), a rim size of 20 × 8.00 V, a load of 82.18 kN (250% of the single wheel specified load), and a speed of 20 km / h. The mileage until failure was measured. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the load durability.

Ride comfort:
The test tire was assembled on a wheel having a rim size of 20 × 8.00V and mounted on a truck having a GVW (total vehicle weight) of 25 tons, the air pressure was set to 830 kPa, and the feeling of riding comfort was evaluated by a test driver on a paved road. The evaluation results are shown as an index with the conventional example being 100. It means that riding comfort is excellent, so that this index value is large.

  As apparent from Table 1, the tires of Examples 1 to 5 were able to improve the load durability while maintaining the riding comfort as compared with the conventional example. On the other hand, in the tire of Comparative Example 1, the effect of improving the load durability was not obtained because the JIS hardness of the strain reducing rubber layer was too low. In the tire of Comparative Example 2, since the JIS hardness of the strain reducing rubber layer was too high, the effect of improving the load durability was small, and the ride comfort was remarkably deteriorated.

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 part of the pneumatic tire of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4A Main part 4B Folding part 5 Bead core 6 Bead filler 6A Lower bead filler 6B Upper bead filler 7 Steel cord reinforcement layer 8 Organic fiber cord reinforcement layer 9 Belt layer 10 Strain reduction Rubber layer

Claims (4)

The carcass layer is folded around the bead core from the inside to the outside of the tire, and a bead filler extending so as to taper from the bead core toward the tread side is disposed between the main body portion and the folded portion of the carcass layer, and the tread portion. In a pneumatic tire for trucks and buses, in which a plurality of belt layers including a plurality of steel cords are embedded on the outer peripheral side of the carcass layer, a strain-reducing rubber is provided between the body portion of the carcass layer and the bead filler. The strain reducing rubber layer has a JIS hardness of 70 to 80, which is higher than the JIS hardness of the coat rubber of the carcass layer and lower than the JIS hardness of the hardest part of the bead filler , The strain-reducing rubber layer has a thickness of 0.5 mm to 5.0 mm, and the bead filler has a thickness from the bead core. The width of the strain-reducing rubber layer is 0.1H to 0.6H with respect to the height H in the radial direction, and the strain with respect to the height H in the tire radial direction from the bead core of the bead filler. A pneumatic tire , wherein the reduced rubber layer is disposed in a range of 0.2H to 0.8H . The bead filler is composed of a lower bead filler having a relatively high hardness positioned on the bead core side and an upper bead filler positioned on the tread side having a relatively low hardness, and the strain reducing rubber layer is formed on the lower bead. The pneumatic tire according to claim 1 , wherein the pneumatic tire is disposed at a position adjacent to an end portion of the filler on the outer side in the tire radial direction. The carcass layer has a bead structure in which a main body portion and a winding portion are wrapped with a steel cord reinforcing layer, and the strain-reducing rubber layer is disposed at a position adjacent to an end portion on the tire inner side of the steel cord reinforcing layer. The pneumatic tire according to claim 1 or 2 . An organic fiber cord layer is disposed outside the bead filler, the carcass layer winding portion and the steel cord reinforcing layer in the tire width direction, and the carcass layer winding portion is disposed between the bead filler and the organic fiber cord layer. The pneumatic tire according to claim 3, wherein the steel cord reinforcing layer is interposed.

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