JP4436166B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that can improve the durability of a bead portion.

  FIG. 4 shows a general structure of a bead portion a of a conventional pneumatic tire. The bead portion a is provided with one or more carcass plies b1 and b2 that are folded and locked around the bead core c, and a bead apex d that extends in a tire radial direction from the outer surface of the bead core c. ing. During the load running, the bead portion a comes into contact with the rim flange f and undergoes a large bending deformation, so that the bead apex d and the carcass plies b1 and b2 are likely to be peeled off.

  As a countermeasure, it has been proposed to use a harder rubber material for the bead apex d. However, such measures are accompanied by drawbacks such as deterioration in ride comfort and increase in road noise. Further, although the bead apex d having a high hardness is useful for reducing the bending deformation of the bead portion 4, the difference in rigidity between the bead apex d and the side wall rubber e is increased, and the outer end portion dt of the bead apex d is increased. Stress is concentrated in the vicinity of the surface and damage is likely to occur. Further, as schematically shown in FIG. 5, it is described in FIG. 4 of the following Patent Document 1 that the bead apex d is composed of a hard rubber di on the inner side in the tire radial direction and a flexible rubber do arranged on the outer side. However, there is room for further improvement in this structure. That is, even if the bead apex of FIG. 5 can improve riding comfort and node noise by the flexible rubber do on the outer side in the tire radial direction, the above effect is not sufficient because the rubber di abutting on the bead core c is hard.

JP 2003-291613 A

  The present invention has been devised in view of the above-described circumstances, and the bead apex is composed of an inner rubber portion located on the inner side in the tire radial direction, an outer rubber portion located on the outer side in the tire radial direction, and a gap between them. The outer rubber portion and the inner rubber portion are arranged without being in contact with each other, and the JISA hardness of the intermediate rubber portion is larger than those of the outer rubber portion and the inner rubber portion. Basically, the object is to provide a pneumatic tire capable of improving the durability, ride comfort and driving stability in a well-balanced manner.

  According to the first aspect of the present invention, at least one sheet having a main body part extending from the tread part through the sidewall part to the bead core of the bead part and a folded part connected to the main body part and folded around the bead core. A pneumatic tire comprising a carcass made of a carcass ply, and a bead apex that is disposed between the main body portion and the turned-up portion and extends outwardly in the tire radial direction from the outer surface of the bead core in the tire radial direction, The bead apex includes an inner rubber portion located on the inner side in the tire radial direction, an outer rubber portion located on the outer side in the tire radial direction, and an intermediate rubber portion therebetween, and the outer rubber portion and the inner rubber portion. And the intermediate rubber part is more JIS than the outer rubber part and the inner rubber part. It is characterized in hardness is large.

  The invention according to claim 2 is the tire meridian section in a loaded state in which a normal rim is assembled with a rim and filled with a normal internal pressure and a normal load is applied, and the intermediate rubber portion includes a rim flange and a bead portion of the normal rim. The pneumatic system according to claim 1, wherein the air is disposed at a position intersecting with a normal line standing on a main body portion of the carcass ply from a rim separation point which is a point radially outermost in contact with an outer surface of the carcass ply. Tire.

  The invention according to claim 3 is the pneumatic tire according to claim 2, wherein the outer rubber part and the inner rubber part are arranged at positions not intersecting with the normal line.

  The invention according to claim 4 is characterized in that the intermediate rubber portion has a JISA hardness of 90 to 99 °, and the outer rubber portion and the inner rubber portion have a JISA hardness of 75 to 88 °. The pneumatic tire according to any one of claims 1 to 3.

  According to a fifth aspect of the present invention, in the intermediate rubber portion, the height to the outer end in the tire radial direction is 40 to 70% of the height of the bead apex. The pneumatic tire according to any one of the above.

  In the invention according to claim 6, the intermediate rubber portion has an inner surface in the tire axial direction contacting the main body portion and an outer surface in the tire axial direction contacting the folded portion, and the inner surface and the main body portion. The pneumatic tire according to any one of claims 1 to 5, wherein a length in a tire radial direction of a contact portion with the tire is 3 to 10 mm.

  The pneumatic tire of the present invention secures the main bending rigidity of the bead apex by the intermediate rubber portion having a large JISA hardness, and suppresses excessive bending deformation due to contact with the rim flange. This helps to improve steering stability and durability. In addition, the flexible inner rubber part and the outer rubber part that are arranged inside and outside the tire in the radial direction of the intermediate rubber part alleviate the difference in rigidity of the surrounding area to further enhance durability and improve ride comfort and road noise. obtain.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a right half sectional view of the pneumatic tire 1 of the present embodiment in a normal state, and FIG. 2 is a partially enlarged view of the bead portion 4. Here, the “normal state” uniquely defines the posture of the tire, and is defined as a no-load state in which the rim is assembled to the normal rim J and filled with the normal internal pressure. The dimensions and the like are values measured in this normal state.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, and ETRTO If there is, “Measuring Rim”. Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA and the table “TIRE LOAD LIMITS AT” is TRA. Maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars.

  The pneumatic tire 1 of the present embodiment includes a radial carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the carcass 6 on the outer side in the tire radial direction and inside the tread portion 2. Examples of the tubeless type include the arranged belt layer 7 and a bead apex 8 that tapers outward from the outer surface of the bead core 5 in the tire radial direction to the tire radial direction. Moreover, the pneumatic tire 1 of this embodiment is a tire for passenger cars, for example, and a tire that is used for a 4WD vehicle or the like, among others, is subjected to a relatively large load.

  The carcass 6 includes at least one main body portion 6a that extends from the tread portion 2 through the sidewall portion 3 to the bead core of the bead portion 4 and a folded portion 6b that is connected to the main body portion 6a and is folded around the bead core 5. In this example, a configuration including a plurality (two) of carcass plies 6A and 6B is illustrated. The turned-up portions 6b of the carcass plies 6A and 6B are turned up to, for example, a position that exceeds the maximum width position M that is the maximum tire width outward in the tire radial direction.

  Each of the carcass plies 6A and 6B is formed by covering carcass cords arranged in parallel with a topping rubber, and organic fibers such as nylon, polyester, rayon, and aromatic polyamide are suitably used for the carcass cord. In the present embodiment, the carcass cord has a radial structure that is arranged at an angle of 80 to 90 degrees, more preferably 85 to 90 degrees with respect to the tire equator C.

  The belt layer 7 is composed of two belt plies 7A and 7B in which a belt cord made of steel is inclined with respect to the tire equator C at, for example, about 10 to 35 ° in this example. The belt plies 7A and 7B are overlapped so that the belt cords cross each other. As a result, the belt layer 7 strongly tightens the carcass 6 to increase the rigidity of the tread portion 2 and exhibits the advantages of a radial tire. In addition to the steel material, a highly elastic organic fiber cord such as aramid or rayon can be used as necessary for the belt cord.

  The bead apex 8 is disposed between the main body portion 6a and the folded portion 6b of the carcass plies 6A and 6B. The bead apex height ha, which is the height in the tire radial direction from the bead base line BL to the outer end 8T of the bead apex 8, is not particularly limited, but if it is too small, the basic bending rigidity of the bead portion 4 is obtained. On the contrary, even if it is too large, the outer end 8T of the bead apex 8 tends to approach the maximum width position M where the distortion during running is large. From such a viewpoint, the height ha of the bead apex is preferably 10% or more, more preferably 20% or more of the tire cross-section height H, and the upper limit is preferably 70% or less, more preferably 60% or less.

  The bead apex 8 includes an inner rubber portion 9 located on the inner side in the tire radial direction, an outer rubber portion 11 located on the outer side in the tire radial direction, and an intermediate rubber portion 10 located therebetween.

  As shown in FIG. 2, the inner rubber portion 9 of the present embodiment is arranged such that the inner surface 9 i in the tire radial direction is in contact with the substantially entire area of the outer surface 5 o of the bead core 5. Further, the inner rubber portion 9 has the largest thickness on the inner surface 9i, and is formed in a tapered shape in which the thickness gradually decreases from there toward the outer side in the tire radial direction. The inner surface of the inner rubber portion 9 in the tire axial direction extends in contact with and along the main body portion 6a of the carcass ply 6B. Further, the outer surface in the tire axial direction of the inner rubber portion 9 forms a slope inclined inward in the tire radial direction toward the outer side in the tire axial direction, and an intermediate rubber portion 10 is connected thereto.

  The outer rubber portion 11 constitutes an outer end 8T of the bead apex 8 and terminates in an inner surface 11i that is inclined outward in the tire radial direction toward the outer side in the tire axial direction in the present embodiment. The intermediate rubber portion 10 is connected to the inner surface 11i. Further, the inner surface 11a of the outer rubber portion 11 in the tire axial direction is in contact with the main body portion 6a of the carcass ply 6B, and the outer surface 11b is in contact with the turned-up portion 6b.

  The intermediate rubber portion 10 includes an inner surface 10a in the tire axial direction in contact with the main body portion 6a of the carcass ply 6B, an outer surface 10b in the tire axial direction in contact with the turned-up portion 6b of the carcass ply 6B, and the tire shaft of the inner rubber portion 9. An inner surface 10c in the tire radial direction connected to the outer surface in the direction, and an outer surface 10d connected to the inner surface 11i of the outer rubber portion 11. Thereby, the outer rubber part 11 and the inner rubber part 9 are arranged without the intermediate rubber part 10 interposed therebetween and in contact with each other. The intermediate rubber portion 10 has an inner end 10 i in the tire radial direction that is tapered and extends to the bead core 5.

  The intermediate rubber portion 10 is made of a rubber composition having a JIS hardness greater than that of the outer rubber portion 11 and the inner rubber portion 9. As shown in FIG. 3, the bead portion 4 undergoes a large bending deformation with the rim flange Jf serving as a fulcrum during the load application. However, in the pneumatic tire 1 of the present embodiment, the intermediate rubber having a large JISA hardness is used. The portion 10 effectively increases the bending rigidity of this portion and suppresses the amount of bending deformation. Thereby, the heat generation of the bead part 4 at the time of load running is suppressed, and the durability can be improved by preventing rubber peeling and carcass cord breakage. Further, since the lateral rigidity of the bead portion 4 is improved, the steering stability is improved.

  Further, the outer rubber portion 11 constituting the outer end 8T of the bead apex 8 or the vicinity thereof, and the inner rubber portion 9 in contact with the bead core 5 over a wide area have a rubber composition having a JISA hardness smaller than that of the intermediate rubber portion 10. Consists of. For this reason, the outer rubber part 11 can reduce the difference in rigidity with the flexible sidewall rubber 3G disposed around the outer rubber part 11, and effectively prevents stress or strain from concentrating on the part. In addition, the inner rubber portion 9 effectively reduces and absorbs vibration or impact during traveling input from the tread portion 2 in front of the bead core 5 and helps to prevent vibration transmission to the rim J. This is particularly effective for improving riding comfort and reducing road noise.

  In order to exhibit the above-mentioned action more effectively, for example, as shown in FIG. 3, in the tire meridian cross section in a load state in which a normal load is applied from the normal state and the tire 1 is grounded on a plane, the intermediate rubber portion It is particularly desirable that 10 is arranged at a position that intersects the normal line N raised from the rim separation point P to the main body portions 6a of the carcass plies 6A and 6B. Here, the “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” if it is ETRTO, but if the tire is for a passenger car, the value is 0.88 times that value. The “rim separation point” is a point on the outermost side in the tire radial direction where the rim flange Jf of the rim J and the outer surface of the bead portion 4 are in contact with each other, and this position is usually obtained in the vicinity of the ground contact surface.

  When the tire is loaded, the bead portion 4 is bent around the normal line N. By placing the intermediate rubber portion 10 having a large JISA hardness at a position intersecting with the normal line N, the bending strength is further increased. It can be increased more effectively. In other words, it is desirable that the outer rubber portion 11 and the inner rubber portion 9 are arranged at positions that do not intersect the normal line N.

  As a particularly preferable aspect, in the tire meridian cross section including the rim separation point P in the load state shown in FIG. 3, the inner side of the intermediate rubber portion 10 divided in the tire radial direction and outside by the normal N in the tire radial direction. It is desirable that the area Ai and the outer area Ao be formed at a ratio of 30:70 to 70:30, more preferably 40:60 to 60:40. Thereby, the intermediate rubber part 10 can suppress the bending deformation of the bead part 4 when traveling with a better balance, and the durability and the handling stability can be improved.

  Further, the JISA hardness Hc of the intermediate rubber portion 10 is preferably 90 ° or more, more preferably 92 ° or more, and the upper limit is preferably 99 ° or less, more preferably 97 ° or less. . That is, if the JISA hardness Hc of the intermediate rubber portion 10 is less than 90 °, the effect of improving the bending rigidity of the bead portion 4 cannot be sufficiently obtained, and the steering stability and durability tend to be lowered. On the contrary, when the JISA hardness Hc exceeds 99 °, the rigidity of the bead portion 4 is remarkably increased, and the ride comfort tends to be deteriorated.

  Further, the JISA hardness Ho of the outer rubber portion 11 and the JISA hardness Hi of the inner rubber portion 9.0 are desirably 75 ° or more, more preferably 80 ° or more, and the upper limit is preferably 88 ° or less. The angle is preferably 86 ° or less. When the JISA hardness Ho and Hi are less than 75 °, the difference in rigidity from the intermediate rubber portion 10 increases, and strain tends to be concentrated at the rubber interface, and the durability tends to decrease. Exceeding this tends to deteriorate the ride comfort and increases the difference in rigidity with the side wall rubber 3G in the vicinity of the outer end portion of the outer rubber portion 11, and this portion is likely to be damaged. In the present embodiment, the inner rubber portion 9 and the outer rubber portion 11 are made of rubber having the same JIS hardness, but may be different. Preferably, the JISA hardness Ho of the outer rubber portion 11 is preferably smaller than the JISA hardness Hi of the inner rubber portion 9. Since the outer rubber portion 11 greatly contributes to noise performance and riding comfort performance during traveling, it is desirable to improve the riding comfort by reducing its hardness Ho. On the other hand, since the inner rubber portion 9 is in contact with the bead core 5, it is desirable to improve steering stability by making it smaller than the intermediate rubber portion 10 and larger than the outer rubber portion 11.

  Further, the difference (Hc−Ho) between the JISA hardness Hc of the intermediate rubber portion 10 and the JISA hardness Ho of the outer rubber portion 11, or the JISA hardness Hc of the intermediate rubber portion 10 and the JISA hardness Hi of the inner rubber portion 9. The difference (Hc-Hi) is not particularly limited, but if it is too small, either the steering stability or the ride comfort tends to decrease, and conversely if too large, the interface of the joints of each rubber part Distortion tends to concentrate in From such a viewpoint, the difference in the JISA hardness (Hc-Ho) or (Hc-Hi) is preferably 2 to 24 °, more preferably 7 to 22 °.

  Moreover, as a preferable aspect, it is desirable to determine the height of each rubber part 9, 10 and 11 of the bead apex 8 as follows. First, the height h1 in the tire radial direction from the bead base line BL to the outer end 9T of the inner rubber portion 9 is preferably 20 to 80%, more preferably 25 to 75% of the height ha of the bead apex. . If the height h1 is less than 20% of the height ha of the bead apex, the rubber volume of the inner rubber portion 9 cannot be sufficiently secured, and the ride comfort and road noise performance are likely to deteriorate, conversely 80% If it exceeds, the steering stability tends to decrease.

  Further, the height h2 from the bead base line BL to the outer end 10T in the tire radial direction of the intermediate rubber portion 10 is larger than the height h1, and particularly preferably 40 to 70% of the height ha of the bead apex. More preferably, it is 50 to 60%. If the height h2 is less than 40%, the rubber volume of the intermediate rubber part 10 tends to decrease, and the steering stability and ride comfort tend to deteriorate. Conversely, if it exceeds 70%, the rubber of the outer rubber part 11 The volume is lowered, the strain relaxation ability in the vicinity of the outer end 8T of the bead apex 8 is lowered, and damage is likely to occur.

  Further, the length Li in the tire radial direction of the contact portion between the inner surface 10a in the tire axial direction of the intermediate rubber portion 10 and the main body portion 6a of the carcass ply is not particularly limited. As can be seen, the carcass cord of the main body 6a tends to be bent locally with the inner surface 10a of the intermediate rubber portion 10 as a fulcrum during load running, resulting in breakage of the carcass cord and separation from surrounding rubber. It becomes easy. From such a viewpoint, the length Li is preferably 3 mm or more, more preferably 5 mm or more, and the upper limit is preferably 10 mm or less.

  Further, as in this embodiment, the intermediate rubber portion 10 may have a length Lo in the tire radial direction of the outer surface 10b in the tire axial direction larger than a length Li in the tire radial direction of the inner surface 10a in the tire axial direction. desirable. The intermediate rubber portion 10 has a substantially crescent-shaped cross section due to the slopes of the inner surface 10c and the outer surface 10d in the tire radial direction, and can exhibit effective strength against bending deformation during load running.

  In the above-described embodiment, the example in which the carcass 6 is configured by the two carcass plies 6A and 6B has been described. However, the carcass ply may be configured by one carcass ply. Moreover, although the said embodiment demonstrated and demonstrated the tire for passenger cars as an example, it is not limited to this, It can implement with a various form.

  A pneumatic tire for a 4WD vehicle having a size of 265 / 65R17 was prototyped according to the specifications shown in Table 1, and tested for bead durability, handling stability, and riding comfort for each tire, and the performance was compared. The test method is as follows.

<Bead durability>
Each test tire is mounted on a rim (17 × 8.0) and filled with an internal pressure of 190 kPa. A longitudinal load of 12.7 kN, a speed of 70 km / H, and a drum with a diameter of 1.7 m are run for 30,000 km. The distance traveled until identifiable damage occurred was measured. The results were expressed as an index with Comparative Example 1 as 100. The larger the value, the better.

<Steering stability>
A four-wheel drive vehicle made in Japan with a displacement of 2400 cc is fitted with four test tires, filled with internal pressure kPa and driven on a dry asphalt road test course with one driver, handling response, rigidity, grip The characteristic regarding etc. was evaluated by the sensory evaluation of the driver. The results were evaluated by a 10-point method with Comparative Example 1 as 6.0. The larger the value, the better.

<Ride comfort>
Using a test vehicle similar to the above, sensory evaluation was performed on bumpy feeling, push-up and dumping on stepped roads on dry asphalt roads, Berjaso roads (cobblestone roads), Bitzmann roads (roads covered with pebbles), etc. Evaluation was performed by a 10-point method in which 1 was 6.0. The larger the value, the better.

<Road noise>
The test vehicle was run on a smooth road surface at a speed of 50 km / h, and the noise level (dB) of the 1/3 octave 250 Hz band was measured at the driver seat left ear permitting position. The evaluation is indicated by an increase / decrease value based on Comparative Example 1.
Tables 1 and 2 show the test results.

  From the test results, it can be confirmed that the bead durability of the tire of the example is improved as compared with the comparative example. At the same time, it was confirmed that the steering stability, ride comfort and road noise exceeded the comparative example.

1 is a right half sectional view of a pneumatic tire in a normal state showing an embodiment of the present invention. It is the elements on larger scale of the bead part. It is a fragmentary sectional view of the load state. It is a fragmentary sectional view which shows the structure of the conventional bead part. It is a fragmentary sectional view which shows the structure of the conventional bead part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 8 Bead apex 9 Inner rubber part 10 Intermediate rubber part 11 Outer rubber part

Claims (6)

A carcass composed of at least one carcass ply having a main body part extending from the tread part through the sidewall part to the bead core of the bead part and a folded part connected to the main body part and folded around the bead core;
And a pneumatic tire comprising a bead apex arranged between the main body portion and the folded portion and extending in a tire radial direction outside from the outer surface of the bead core in the tire radial direction,
The bead apex is composed of an inner rubber portion located on the inner side in the tire radial direction, an outer rubber portion located on the outer side in the tire radial direction, and an intermediate rubber portion therebetween.
The outer rubber portion and the inner rubber portion are arranged without being in contact with each other, and the intermediate rubber portion has a JISA hardness higher than that of the outer rubber portion and the inner rubber portion. . In the tire meridian cross section in the loaded state where the rim is assembled to the regular rim and filled with the regular internal pressure and the regular load is loaded,
The intermediate rubber portion is arranged at a position intersecting with a normal line standing on the main body portion of the carcass ply from a rim separation point that is a point on the outermost side in the tire radial direction at which the rim flange of the regular rim contacts the outer surface of the bead portion. The pneumatic tire according to claim 1, wherein the pneumatic tire is provided.   The pneumatic tire according to claim 2, wherein the outer rubber portion and the inner rubber portion are arranged at positions that do not intersect with the normal line.   4. The intermediate rubber portion according to claim 1, wherein the intermediate rubber portion has a JISA hardness of 90 to 99 °, and the outer rubber portion and the inner rubber portion have a JISA hardness of 75 to 88 °. Pneumatic tire described in 2.   The pneumatic tire according to any one of claims 1 to 4, wherein the intermediate rubber portion has a height to an outer end in a tire radial direction of 40 to 70% of a height of the bead apex.   The intermediate rubber portion has an inner surface in the tire axial direction in contact with the main body portion and an outer surface in the tire axial direction in contact with the folded portion, and a length in a tire radial direction of a contact portion between the inner surface and the main body portion. The pneumatic tire according to any one of claims 1 to 5, wherein the tire has a length of 3 to 10 mm.

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