JP4899776B2 - Pneumatic tire for run flat - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a run-flat pneumatic tire with improved run-flat durability and resistance to rim displacement without reducing rim assembly performance and productivity.

  Conventionally, a so-called side-reinforced run-flat tire has been known in which a reinforcing rubber with a crescent-shaped cross section made of hard rubber is arranged on the side wall so that it can safely travel a predetermined distance even when the tire is punctured. It has been. In such a side-reinforcing run-flat tire, as shown in FIG. 3, by providing a rim protect bar 10 outside the sidewall portion 7, the rim flange 9 comes into contact with an obstacle such as a curb stone and is damaged. There is something to prevent this.

  However, this run-flat tire generates a large distortion when the tire is punctured and run-flat, because the rim protect bar 10 is strongly pressed against the rim flange upper portion 9a due to the bending deformation of the sidewall portion 7. As a result, the rim protect bar 10 falls down with the rim flange upper portion 9a as the bending point, and the bead portion 2 moves to the inside of the tire and the fitting with the rim 11 is deteriorated. For this reason, there are problems that run-flat durability is lowered and rim displacement occurs and the bead portion 2 is easily damaged.

As a countermeasure for solving such a problem, Patent Document 1 proposes that a bead core or bead filler different from the bead core of the bead portion is inserted into the rim protect bar. However, inserting a bead core or a bead filler having a different configuration in this way has a problem in that the production process is increased and the productivity is lowered, and the rim assembly performance is lowered.
JP 2006-44611 A

  An object of the present invention is to provide a run-flat pneumatic tire with improved run-flat durability and resistance to rim displacement without reducing rim assembly performance and productivity.

  In the run-flat tire of the present invention for achieving the above object, a carcass layer is mounted between a pair of left and right bead portions, and bead fillers made of hard rubber are disposed on the outer peripheral side of the bead core of the bead portions. In the run-flat pneumatic tire in which a reinforcing rubber made of hard rubber having a crescent-shaped cross section is disposed on the sidewall portion and a rim protection bar is formed on the outer side of the sidewall portion, the cross-sectional shape of the bead filler is the rim protect. It is characterized by being formed wide so as to bulge into the rim protection bar at a location corresponding to the bar.

  The bead filler preferably has a thickness of 5 to 14 mm at the apex of the portion bulged in the rim protect bar.

  The rubber hardness of type A conforming to JIS K6253 of the bead filler is desirably 80 or more.

  Also, at least two types of rubber compositions in which the bead filler has a rubber hardness different from each other between a main body portion extending in the radial direction in contact with the outer peripheral side of the bead core and a bulging portion bulging into the rim protect bar. The rubber hardness of the main body may be 5 to 15 lower than the rubber hardness of the bulging portion in the type A rubber hardness according to JIS K6253.

Furthermore, the terminal of the both ends of the said carcass layer can be extended in a tire radial direction.
Here, “type A rubber hardness in accordance with JIS K6253” refers to a value measured at a temperature of 25 ° C. with a JIS K6253 type A durometer.

  According to the run-flat pneumatic tire of the present invention, in the side-reinforced run-flat pneumatic tire in which the rim protect bar is formed on the outer side of the sidewall portion, the cross-sectional shape of the bead filler is a portion corresponding to the rim protect bar. The rim protection bar is wide so that it swells into the rim protection bar, so the rim protection bar's rigidity is improved, which prevents the rim protection bar from being distorted during run-flat run-flat running, and has run-flat durability and rim resistance. Shiftability can be improved. Moreover, since only the cross-sectional shape of the bead filler is changed, the conventional tire productivity is not changed, and the rim assembly performance is not significantly reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an example of a run-flat pneumatic radial tire according to an embodiment of the present invention.

  This run-flat pneumatic tire (hereinafter simply referred to as “tire”) has a carcass layer 3 mounted on the inner side of the tire from a tread portion 1 to a pair of left and right bead portions 2, and both end portions of the carcass layer 3. Are folded around the bead core 4 so as to sandwich the bead filler 5 from the inside to the outside of the tire. On the outer peripheral side of the carcass layer 3 in the tread portion 1, a plurality of belt layers 6 made of steel cords are arranged so that the cords cross each other.

  A reinforcing rubber 8 having a crescent-shaped cross section made of hard rubber is disposed inside the tire of the sidewall portion 7. The rubber strength of the reinforcing rubber 8 is preferably 80 to 90 in terms of type A rubber hardness (hereinafter simply referred to as “rubber hardness”) in accordance with JIS K6253. The reinforcing rubber 8 prevents the tire from being flattened during the run-flat running and enables safe running. A rim protect bar 10 is formed outside the sidewall portion 7. The rim protect bar 10 is formed so as to protrude to the tire outer side than the rim flange 9, thereby preventing the rim flange 9 from being damaged due to contact with an obstacle such as a curb stone.

  The bead filler 5 is formed wide so that its cross-sectional shape bulges into the rim protect bar 10 at a location corresponding to the rim protect bar 10. This increases the rigidity of the rim protect bar 10 and suppresses distortion when the bottom portion 10a of the rim protect bar 10 is pressed against the rim flange upper portion 9a during run-flat travel. By holding, rim displacement can be prevented. In addition, since breakage due to generation of strain is reduced, run-flat durability can be improved.

  Furthermore, since the arrangement and number of bead cores and bead fillers are not significantly different from those of conventional tires, rim assembly performance and productivity are not deteriorated.

  In the tire of the present invention described above, the thickness d at the apex 10a of the portion bulged in the rim protect bar 10 is 5 to 14 mm, preferably 10 to 14 mm. If the thickness d is less than 5 mm, the rigidity of the rim protect bar 10 is lowered and the bottom 10a bends. Therefore, the run flat durability and the resistance to rim displacement may be deteriorated. This is because the size does not fit within the bar 10.

  The rubber hardness of the rubber composition constituting the bead filler 5 is desirably 80 or more. This is because when the rubber hardness is less than 80, the rigidity of the rim protect bar 10 is lowered and the bottom 10a is bent, so that the run-flat durability and the rim displacement resistance performance are lowered.

  FIG. 2 shows an example of another embodiment of the run-flat pneumatic tire according to the embodiment of the present invention.

  In the present embodiment, the bead filler 5 is composed of two parts: a main body part 5 </ b> A that extends in the radial direction in contact with the outer periphery of the bead core 4, and a bulging part 5 </ b> B that bulges into the rim protect bar 10. . The main body 5A has substantially the same cross-sectional shape as the conventional bead filler shown in FIG. Each portion is composed of at least two types of rubber compositions having different rubber hardnesses, and the rubber hardness of the main body portion 5A is 5 to 15 lower than the rubber hardness of the bulging portion 5B. By lowering the rubber hardness of the main body portion 5A in this way, even when the rim protect bar 10 falls down, the deformation is not easily transmitted to the bead portion 2 and the bead portion 2 is stabilized. The displacement performance can be further improved.

  The rubber composition constituting the main body portion 5A and the bulging portion 5B may be of a plurality of types.

  In the two embodiments described above, the terminal 3a at the end of the carcass layer may be extended so as to be inserted into the end of the belt layer 6 in the tire radial direction. Thereby, the rigidity of the sidewall portion 7 can be further improved, and the steering stability during the run-flat running can be further improved.

  Tires of the present invention in which the tire size is 235 / 50R17 96V and the basic structure of the tire is as shown in FIG. 1, and the three conditions of the bead filler thickness d, rubber hardness, and configuration are different (Examples 1 to 5). Was made.

  Further, a conventional tire (conventional example) having the same tire size of 235 / 50R17 96V and the basic structure of the tire shown in FIG. 3 was manufactured.

  These six types of tires were evaluated for run flat durability and rim displacement resistance performance by the following measurement methods, and the results are shown in Table 1.

[Run-flat durability]
Mount the tires with rims on the front wheels of a large 4WD sedan with zero internal pressure, run the test course at 90 km / h, and check the mileage and running performance until the tires break and become impossible to run did. Evaluation was shown by the index | exponent which sets the measured value of a prior art example to 100. FIG. The larger the index value, the better the run flat durability.

[Rim displacement performance]
Braking from 100 km / h was performed 10 times, and the amount of deviation from the reference position was compared. Evaluation was shown by the index | exponent which sets the measured value of a prior art example to 100. FIG. The larger the index value, the better the rim displacement resistance.

  From the experimental results shown in Table 1, it can be seen that the run-flat pneumatic tires of the present invention (Examples 1 to 5) are all superior in run-flat durability and resistance to rim displacement compared to conventional tires.

1 is a half cross-sectional view showing an example of a run-flat pneumatic tire according to an embodiment of the present invention. It is a half sectional view showing an example of a pneumatic tire for run flats according to another embodiment of the present invention. It is a half sectional view showing the conventional pneumatic tire for run flats.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Bead part 3 Carcass layer 3a End of carcass layer 4 Bead core 5 Bead filler 5a Apex of bulging part of bead filler 6 Belt layer 7 Side wall part 8 Reinforcement rubber 9 Rim flange 9a Rim flange upper part 10 Rim protect Bar 10a Rim protect bar bottom 11 Rim

Claims (5)

A carcass layer is mounted between a pair of left and right bead parts, bead fillers made of hard rubber are arranged on the outer peripheral side of the bead core of the bead parts, and reinforcing rubber made of hard rubber having a crescent-shaped cross section is arranged on the side wall part. In addition, in a run flat pneumatic tire having a rim protect bar formed on the outside of the sidewall portion,
A run-flat pneumatic tire formed so as to have a cross-sectional shape of the bead filler so as to bulge into the rim protect bar at a position corresponding to the rim protect bar.   2. The run-flat pneumatic tire according to claim 1, wherein the bead filler has a thickness of 5 to 14 mm at an apex of a portion where the bead filler bulges into the rim protect bar.   The pneumatic tire for run-flats according to claim 1 or 2, wherein the bead filler has a rubber hardness of type A conforming to JIS K6253 of 80 or more.   The bead filler is composed of at least two types of rubber compositions having different rubber hardnesses between a main body portion extending in a radial direction in contact with the outer peripheral side of the bead core and a bulging portion bulging in the rim protect bar. The run-flat pneumatic tire according to claim 1, 2 or 3, wherein the rubber hardness of the main body is lower by 5 to 15 than the rubber hardness of the bulging portion by the rubber hardness of type A in accordance with JIS K6253. .   The pneumatic tire for run-flats according to claim 1, 2, 3 or 4, wherein ends of both ends of the carcass layer extend in a tire radial direction.

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