JP2007045333A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing the rigidity and the durability of a bead part. <P>SOLUTION: A carcass 6 consists of two folding plies 6A and one wind-down ply 6B. The height hci, hco of a folding part 6b is 0.1 to 0.7 time the tire sectional height H. An inner apex 8 having JISA hardness of 75-95°, an outer apex 9 more flexible than that, and a clinch rubber 10 having JISA hardness of 60-80° are provided on a bead part 4. The folding part 6b of at least one folding ply 6A extends in contact with a body part 6a through a space between the inner apex 8 and the outer apex 9. The height Hai of the inner apex 8 is 0.1-0.3 time the tire sectional height H, the height Hao of the outer apex 9 is 0.3-0.5 time the tire sectional height H, and the ratio (to/tk) of the thickness to of the outer apex 9 to the thickness tk of the clinch rubber 10 is 0.5-1.0 at the inner end position of a side wall rubber 3G. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that can improve the rigidity and durability of a bead portion in a well-balanced manner.

  For example, pneumatic tires used in commercial vehicles such as light trucks and vans are subjected to a larger load than passenger car tires. For this reason, it is important to sufficiently increase the rigidity of the bead portion to ensure steering stability. Conventionally, as shown in FIG. 3, the bead apex b made of hard rubber provided between the main body portion a1 and the folded portion a2 of the carcass ply a is enlarged, more specifically, the height and width thereof. It was done to enlarge.

  However, when the bead apex b is enlarged, the distance X from the bending neutral line N when the bead portion is bent and deformed to the folded portion a2 of the carcass ply a tends to increase. As a result, there is a problem that a large compressive stress periodically acts on the folded portion a2 when the tire travels, and damage such as breakage or looseness of the carcass cord occurs at the folded portion a2.

  The present applicant has proposed the following Patent Document 1 in order to solve the above problems, but there is room for further improvement in the hardness distribution of the carcass structure and the bead apex.

JP 2004-182021 A

  The present invention has been devised in view of the above-described problems. The bead apex is divided into an inner side and an outer side, and a folded portion and a lowering ply of a so-called 2-1 structure carcass ply are provided between them. It is an object of the present invention to provide a pneumatic tire capable of improving durability while further increasing the rigidity of the bead portion.

  The invention according to claim 1 of the present invention includes a carcass extending in a toroidal shape across a bead core embedded in each of a pair of bead parts, a belt layer disposed outside the carcass in the tire radial direction and inside the tread part, The carcass is folded around the bead core from the inner side in the tire axial direction to the outer side in a toroidal main body part extending from the tread part through the sidewall part to the bead core of the bead part. It is composed of two folded plies in which folded portions are continuously provided, and a single lowering ply that is arranged outside the folded ply and is composed only of the toroidal main body portion, and a bead of each folded portion. The heights hci and hco from the baseline are greater than 0.1 times and less than 0.7 times the tire cross-section height H, and the bead portion An inner bead apex made of rubber having a taper shape extending outward from the bead core in the radial direction of the tire and having a JISA hardness of 75 to 95 degrees between the body portion and the folded portion, and the folded portion and the lowering ply An outer bead apex that is attached to the inner bead apex and extends from the vicinity of the bead core to the outer side in the tire radial direction and made of rubber that is softer than the inner bead apex; and an outer rim of the outer bead apex in the tire axial direction and a rim; A clinch rubber having a JISA hardness of 60 to 80 degrees, which is disposed in a contact area, and a folded portion of at least one folded ply passes between the inner bead apex and the outer bead apex, and the main body The tire extends substantially outward in the tire radial direction Further, the height Hai of the inner bead apex from the bead base line is larger than 0.1 times and smaller than 0.3 times the tire cross-sectional height H, and the height from the bead base line of the outer bead apex is smaller than 0.3 times. The height Hao is greater than 0.3 times and less than 0.5 times the tire cross-section height H, and is disposed on the sidewall portion and has an inner end connected to the clinch rubber. The ratio (to / tk) of the thickness to of the outer bead apex at the normal position of the outer surface of the tire passing through the inner end and the thickness tk of the clinch rubber is 0.5 to 1.0. It is a pneumatic tire.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the outer bead apex is made of rubber having a JISA hardness of 45 to 65 degrees and a JISA hardness or less of the clinch rubber.

  The invention according to claim 3 is the pneumatic tire according to claim 1, wherein the outer bead apex rubber is made of a rubber having a JISA hardness of 70 to 90 degrees and a JISA hardness or more of the clinch rubber.

  In the invention according to claim 4, in the two folded plies, the height of one of the folded portions is larger than 0.1 times and smaller than 0.2 times the tire cross-sectional height H, The pneumatic tire according to any one of claims 1 to 3, wherein the other height of the folded portion is greater than 0.4 times and less than 0.7 times the tire cross-section height H.

  In the present specification, the height and the thickness are values measured in a normal state in which a tire is assembled on a normal rim, filled with a normal internal pressure, and is unloaded unless otherwise specified.

  The “regular rim” is a rim defined by the standard in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. If there is, “Measuring Rim”.

  The “regular internal pressure” is the air pressure defined by each standard for each tire. The maximum air pressure described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum air pressure for JATMA and TRA for TRA. If the value is ETRTO, it is “INFLATION PRESSURE”, but if the tire is for a passenger car, it is uniformly 180 (kPa).

  Further, each height is a height from a bead base line passing through a rim diameter position of a normal rim defined by each standard.

  In addition, the JISA hardness is a durometer type A hardness (durometer A hardness) based on JIS-K6253.

  The pneumatic tire according to the present invention allows the folded portion of the folded ply and the lowering ply to pass between the inner and outer bead apex, thereby ensuring sufficient rigidity of the bead portion and compressive stress acting on these during running. Can be eased. Accordingly, the durability of the pneumatic tire of the present invention can be greatly improved while exhibiting excellent steering stability.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a right-half cross-sectional view in a normal state of a light truck tire having a flatness ratio of 60 to 75% as the pneumatic tire 1 of the present embodiment. FIG. 2 shows a partially enlarged view thereof.

  In the figure, a pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 provided at an inner end of each sidewall portion 3. It has a toroidal shape. The pneumatic tire 1 includes a toroidal carcass 6 extending over bead cores 5 embedded in a pair of bead parts 4, and a belt disposed outside the carcass 6 in the tire radial direction and inside the tread part 2. Layer 7 is provided.

  The belt layer 7 is composed of a plurality of belt plies using steel cords. The belt layer 7 of the present embodiment includes, for example, the first innermost belt ply 7A in the radial direction in which the steel cord is arranged at an angle of 45 to 75 ° with respect to the tire equator C, and the tire equator C, for example. An embodiment comprising second to third belt plies 7B and 7C arranged at an angle of 10 to 35 ° is shown. Each belt ply 7B and 7C is preferably overlaid so that the steel cord intersects between the plies. As a result, the belt layer 7 can increase the rigidity in the tire circumferential direction and can reinforce the tread portion 2 firmly.

  If necessary, the belt layer 7 may have an increased or decreased number of belt plies, and the belt layer 7 has a band ply formed by a band ply in which cords extending substantially in the tire circumferential direction are arranged in parallel. A layer (not shown) is provided.

  The carcass 6 includes two folded plies 6A and a single lowering ply 6B disposed on the outside thereof. The so-called 2-1 structure carcass 6 can sufficiently increase the rigidity from the bead part 4 to the sidewall part 3 as well as the basic rigidity of the tire, so that a small truck with a large load is applied. It is particularly suitable as a structure for use.

  Each of the plies 6A and 6B has a radial structure in which the carcass cord is inclined at 75 to 90 ° with respect to the tire equator C. Although not particularly limited, the carcass cord is preferably an organic fiber cord that is lightweight and excellent in adhesion to rubber. As the organic fiber, for example, nylon, rayon, aromatic polyamide, polyethylene terephthalate or polyethylene 2,6 naphthalate is suitable.

  Each folded ply 6A includes a toroid-shaped main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and connected to the main body portion 6a and around the bead core 5 in the tire axial direction. And a folded portion 6b folded from the inside to the outside. Further, the folded ply 6A includes an inner folded ply 6Ai disposed inward in the tire radial direction at the position of the tire equator C, and an outer folded ply 6Ao disposed outside thereof.

  In this specification, when it is desired to specify that the main body portion 6a and the folded portion 6b are of the inner folded ply 6Ai, the reference numerals 6ai and 6bi may be used respectively. Similarly, when it is desired to specify that the main body portion 6a and the folded portion 6b are of the outer folded ply 6Ao, the symbols 6ao and 6bo may be used respectively. Moreover, when it is not necessary to distinguish these in particular, the code | symbol 6a and 6b are used for a main-body part and a folding | returning part, respectively.

  Further, in the folded ply 6A, the respective heights hci and hco from the bead base line BL of the folded portions 6bi and 6bo are greater than 0.1 times and 0.7 times the tire cross-section height H. Set to small. When each of the heights hci or hco is not more than 0.1 times the tire cross-section height H, the rigidity reinforcing effect of the bead portion 4 by the folded portion 6b cannot be sufficiently obtained. On the other hand, when each of the heights hci or hco is 0.7 times or more of the tire cross-section height H, the outer ends of the turned-up portions 6bi and 6bo are likely to be positioned at the buttress portion where the distortion during load running is large. Damage tends to occur starting from the outer end of the folded portion 6b.

  In one embodiment, the difference between the heights hci and hco of each of the folded portions is preferably 5 mm or more, more preferably 10 mm or more. If the difference in height is less than 5 mm, the outer ends of the two folded portions 6bi and 6bo come close to each other, so that a large rigidity step is generated in that portion, and as a result, strain is concentrated on the portion, which tends to be a starting point of damage. .

  Further, as a preferred mode, one height of the folded portion 6b is suppressed to be lower than 0.1 times and smaller than 0.2 times the tire cross-section height H, while the other height of the folded portion 6b is suppressed. Is preferably higher than 0.4 times and lower than 0.7 times the tire cross-section height H.

  In the present embodiment, the height hci of the folded portion 6bi of the inner folded ply 6Ai is suppressed to be lower than 0.1 times and smaller than 0.2 times the tire cross-section height H, while the outer folded ply The height hco of the folded portion 6bo of 6Ao is formed to be higher than 0.4 times the tire cross-section height H and smaller than 0.7 times. As a result, the outer ends of the folded portions 6bi and 6bo can be sufficiently separated in the tire radial direction to prevent the formation of a rigid step and ensure durability, and the side portions are formed by the folded portion 6bo having a large height. Can be fully reinforced.

  Further, in the pneumatic tire 1, the range from the bead base line BL to 0.1 times the tire cross-sectional height H and smaller than 0.2 times is substantially the separation point P from the rim J (see FIG. 1). It is a region outside (shown). By positioning the folded portions 6i and 6bo in this region, the bending rigidity of the bead portion 4 can be effectively increased.

  Further, in the pneumatic tire 1, a region larger than 0.4 times and smaller than 0.7 times the tire cross-section height H is a region having a large bending strain including the tire maximum width position M. And the bending rigidity of the side part of a tire can be effectively improved from the bead part 4 to the sidewall part 3 by providing the other folding | turning part 6bo in this area | region. In addition, the outer ends of the folded portions 6bi and 6bo are separated by at least 0.2 times the tire cross-section height H in the tire radial direction, thereby reducing the rigidity step and improving the durability. To help.

  In the above-described embodiment, the height hci of the folded portion 6bi of the inner folded ply 6Ai is low and the height hco of the folded portion 6bo of the outer folded ply 6Ao is large. But it goes without saying.

  The lowering ply 6B is composed of only a toroidal main body portion 6c extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and an end portion 6ct thereof reaches the bead core 5 and terminates. The lowering ply 6B is excellent in durability because the end portion 6ct is disposed in a region where the distortion during traveling is small. Moreover, the lowering ply 6B is unwound along the outside so as to cover both the main body portion 6a and the folded portion 6b of the folded ply 6A.

  In the pneumatic tire 1 of the present invention, the bead portion 4 includes an inner bead apex 8, an outer bead apex 9 disposed on the outer side in the tire axial direction, and a clinch rubber 10 disposed on the outer side in the tire axial direction. Provided.

  The inner bead apex 8 is disposed between the body portion 6a and the folded portion 6b of the folded ply 6A, and extends from the bead core 5 to the outside in the tire radial direction with a small height and a tapered shape. The inner bead apex 8 is formed of a hard rubber having a JISA hardness of 75 to 95 degrees. Thereby, the bending rigidity of the bead part 4 is improved and steering stability is ensured. In order to prevent the formation of a rigid step, it is preferable that the inner bead apex 8 has a substantially triangular shape in cross section with a gradually decreasing width in the tire axial direction as in this embodiment.

  Further, the height Hai of the inner bead apex 8 from the bead base line BL is set to be larger than 0.1 times and smaller than 0.3 times the tire cross-sectional height H. When the height hai is not more than 0.1 times the tire cross-section height H, the effect of reinforcing the bead portion 4 by the inner bead apex 8 cannot be sufficiently obtained. On the other hand, when the height hai is 0.3 times or more of the tire cross-section height H, the bead apex is enlarged as in the conventional case, and a large compressive stress is likely to be generated in the carcass cord of the folded portion 6b. Decreases. From this viewpoint, the height hai is particularly preferably 0.15 times or more of the tire cross-section height H, and the upper limit is particularly preferably 0.25 or less the tire cross-section height H. Is desirable.

  The height bei of the inner bead apex 8 is larger than one height (lower height hci) of the folded portions 6bi and 6bo and higher than the other height (higher height hco). Small is desirable. Thereby, the outer end 8t of the inner bead apex 8 can be arranged without overlapping each outer end of the two folded portions 6b. Therefore, it is possible to prevent the formation of a significant rigidity step from the bead portion 4 to the sidewall portion 3. In particular, the difference between the outer end 8t of the inner bead apex 8 and the height of the folded portion 6b is preferably 5 mm or more, more preferably 10 mm or more.

  The outer bead apex 9 is attached to the inner bead apex 8 via the folded portion 6b and the lowering ply 6B. In the present embodiment, the outer bead apex 9 has an inner end 9i in the tire radial direction in the vicinity of the bead core 5 and extends from the outer end 9o to the outer side in the tire radial direction. The inner end 9i is preferably terminated on the outer surface of the bead core 5 in the tire radial direction or on the inner side in the tire radial direction. Thereby, damage starting from the inner end 9i of the outer bead apex 9 is effectively prevented. In the present embodiment, the outer bead apex rubber 9 has a cross-sectional shape in which the thickness gradually decreases from the thick central portion toward the inner end 9i and the outer end 9o.

  The folded-back portion 6b and the lowering ply 6B pass between the outer bead apex 9 and the inner bead apex 8 and are formed from the vicinity of the outer end 8t of the inner bead apex 8 provided at a relatively low position. It can extend substantially close to the main body 6a. This enables the folded portion 6b and the lowering ply 6B to approach a bending neutral line when the tire is bent and deformed from a relatively inner position in the tire radial direction. Accordingly, the compressive stress acting on the carcass cords of the folded portion 6b and the lowering ply 6B can be greatly relaxed, and the durability of the bead portion 4 can be improved by suppressing the occurrence of breakage and cord looseness.

  Further, the lowering ply 6B extends from the tread portion 2 to the bead core 5 so as to cover the main body portion 6a and the folded portion 6b of the folded ply 6A. Accordingly, the step formed by the outer end of the folded portion 6b is covered and relaxed by the lowering ply 6B. Accordingly, the inner side surface 9P in the tire axial direction of the outer bead apex 9 is smoothly formed along the lowering ply 6B. If the lowering ply 6B is not provided, a step corresponding to the outer end of the turned-up portion 6b is formed on the inner surface in the tire axial direction of the outer bead apex 9, and stress is concentrated there during the compression deformation and cracks occur. Damage is likely to occur. The pneumatic tire of the present invention is preferable in that the inner side surface 9P of the outer bead apex 9 can be smoothly formed, and as a result, such damage can be effectively prevented.

  Moreover, since the tensile stress acting on the main body portion 6a of the folded ply 6A is also reduced along with the relaxation of the compressive stress, an increase in the resonance frequency of the tire can be suppressed. This results in a reduction in road noise in the low frequency band.

  Further, the outer bead apex 9 is made of a softer rubber than the inner bead apex rubber 8. Therefore, the outer bead apex 9 can be flexibly deformed to relieve the concentration of compressive stress around the folded portion 6b and further improve the durability performance. However, the outer bead apex 9 is made of rubber that is harder than the sidewall rubber 3G that forms the outer skin portion of the sidewall portion 3. Thereby, the rigidity fall of the bead part 4 accompanying the inner bead apex 8 being formed in small height can be prevented.

  The height hao of the outer bead apex 9 from the bead base line is set to be larger than 0.3 times and smaller than 0.5 times the tire cross-section height H. Since the inner bead apex 8 is formed at a small height, if the height hao of the outer bead apex 9 is not more than 0.3 times the tire cross-sectional height H, the bending rigidity of the bead portion tends not to be sufficiently secured. There is. On the contrary, when the height hao is 0.5 times or more of the tire cross-sectional height H, the rigidity of the sidewall portion 3 is excessively increased, and the ride comfort tends to be remarkably deteriorated. From this point of view, the height hao is preferably 0.35 times or more, more preferably 0.4 times or more of the tire cross-section height H, and the upper limit is particularly preferably the tire cross-section height. 0.45 times or less of H is desirable.

  Further, the height hao of the outer bead apex 9 is preferably smaller than the higher one (hco in this embodiment) of the folded portions 6bi and 6bo. Thereby, the outer end 9t of the outer bead apex 9 can be disposed without overlapping the outer end of the folded portion 6b having a large height. Therefore, it is possible to prevent the formation of a significant rigidity step from the bead portion to the sidewall portion. In particular, the difference between the outer end 9o of the outer bead apex 9 and the height of the folded portion 6bo is preferably 5 mm or more, more preferably 10 mm or more.

  The clinch rubber 10 is disposed on the outer side of the outer bead apex 9 in the tire axial direction and is disposed in a region in contact with the rim J. Specifically, it extends across the bead bottom surface and the bead outer surface in the tire axial direction by extending from the bead toe through the bead heel to the outer side in the tire radial direction. The clinching rubber 10 is connected to a side wall rubber 3G disposed on the side wall portion.

  The clinch rubber 10 prevents wear caused by contact with the rim J and supports the outer bead apex 9 from the outside, thereby helping to ensure the bending rigidity of the bead portion. From such a viewpoint, rubber having a JISA hardness of 60 to 80 degrees is used for the clinch rubber 10. When the hardness is less than 60 degrees, the bead durability tends to be lowered, and when it exceeds 80 degrees, the rim assemblability is deteriorated and rubber chipping is likely to occur.

  Further, although not particularly limited, the height hk of the clinch rubber 10 is larger than the height Hai of the inner bead apex 8 and smaller than the height hao of the outer bead apex 9, as shown in FIG. It is desirable that When the height hk is equal to or less than the height hai of the inner bead apex 8, the arrangement area of the clinch rubber 10 is small, and the bead rigidity is likely to decrease. Conversely, when the height bek is equal to or higher than the height hao of the outer bead apex 9. Ride comfort is likely to deteriorate. From such a viewpoint, the height hk of the clinch rubber 10 is preferably about 0.2 to 0.4 times the tire cross-section height H from the bead base line BL.

  Further, the pneumatic tire 1 of the present invention has the thickness to of the outer bead apex 9 and the thickness of the clinch rubber 10 at the position of the normal F that is perpendicular to the outer surface of the tire passing through the inner end 3Gi of the sidewall rubber 3G. The ratio (to / tk) to the length tk is set to 0.5 to 1.0. As a result of various experiments by the inventors, when the ratio is less than 0.5, the steering stability, the ride comfort and the durability performance cannot be sufficiently improved, and the reduction of the passing noise is insufficient. I found out. Conversely, when the ratio (to / tk) exceeds 1.0, the durability tends to decrease. From this viewpoint, the ratio (to / tk) is preferably 0.6 or more, more preferably 0.7 or more, and the upper limit is preferably 0.9 or less, more preferably 0.8. The following is desirable.

Further, as a preferred embodiment, the outer bead apex 9 can be formed from a rubber having a JISA hardness of 45 to 65 degrees and a JISA hardness of the clinch rubber 10 or less. In this case, in particular, the JISA hardness of the inner bead apex 8 is represented by Hsi, the JISA hardness of the outer bead apex 9 is represented by Hso, and the JISA hardness of the clinch rubber 10 is represented by Hsc (both are in “degrees”). In this case, it is desirable to satisfy the following relationship.
Hsi>Hsc> Hso

  Such a setting of the rubber hardness in the bead portion 4 is such that the outer bead apex 9 located on the bending neutral line N or the compression side thereof exhibits the compressive stress absorption performance in the peripheral region of the folded portion 6 more effectively. To do. Therefore, riding comfort can be improved and passing noise can be significantly reduced. Further, since the soft outer bead apex 9 is disposed on the compression side of the folded portion 6 and the lowering ply 6B, the occurrence of looseness is effectively prevented.

  In addition, when the clinch rubber 10 is made of a rubber harder than the outer bead apex 9 as in this embodiment, the compression deformation of the soft outer bead apex 9 is suppressed by the clinch rubber 10, thereby suppressing a decrease in steering stability. obtain.

  Here, if the difference in rubber hardness (Hsi-Hso) between the inner and outer bead apexes 8 and 9 is too large, a large shearing force is easily generated in the carcass cord extending between the two rubbers, resulting in a decrease in durability. Tend to. Therefore, the difference in hardness (Hsi-Hso) is preferably 40 degrees or less, more preferably 30 degrees or less. On the other hand, if the difference (Hsi-Hso) is too small, it is difficult to sufficiently relieve the compressive stress. Therefore, the difference is preferably 10 degrees or more, more preferably 20 degrees or more.

As another preferred embodiment, the outer bead apex 9 can be formed from a rubber having a JISA hardness of 70 to 90 degrees and a JISA hardness of the clinch rubber 10 or higher. In this case, in particular, the JISA hardness of the inner bead apex 8 is represented by Hsi, the JISA hardness of the outer bead apex 9 is represented by Hso, and the JISA hardness of the clinch rubber 10 is represented by Hsc (both are in “degrees”). In this case, it is desirable to satisfy the following relationship.
Hsi>Hso> Hsc

  Such setting of the rubber hardness in the bead portion 4 can gradually reduce the rubber hardness from the inner side to the outer side in the tire axial direction. As a result, the difference in rigidity between the rubbers 8 to 10 can be kept small, the effect of reducing the compressive stress can be exhibited, and the durability can be greatly improved. In addition, improvement in handling stability can be expected.

  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 into a various aspect. For example, in order to further improve the bead durability, a reinforcement cord layer or the like can be provided on the bead portion 4. The reinforcing cord layer is formed of one or a plurality of cord plies in which the reinforcing cords are arranged at an angle of, for example, 20 to 70 ° with respect to the tire circumferential direction. As the reinforcing cord, a steel cord excellent in bending rigidity is preferable, but an organic fiber cord can also be adopted as necessary.

  A small truck tire (size: 225 / 60R16) having the basic structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1 and evaluated for bead durability, steering stability, riding comfort and road noise. It was conducted.

Each of the test tires has the following common specifications.
<Carcass>
Cord material: Polyester Cord angle: 88 ° to the tire equator
<Belt layer>
Cord material: Steel Ply number: 3
Cord angle: -50 ° / -18 ° / + 18 ° to the tire equator
Moreover, the evaluation method of each performance is as follows.

<Bead durability>
Each sample tire was run on a drum test machine under the following conditions, and the running time until the bead portion broke was measured. The evaluation was expressed as an index with the conventional example being 100. The larger the value, the better. The conventional example is a pneumatic tire having an integrated bead apex as shown in FIG.
Rim size: 6.75 × 16
Internal pressure: 600 kPa
Longitudinal load: 24.5kN
Travel speed: 20km / h

<Steering stability, ride comfort>
Each sample tire was mounted on all wheels of a light truck (2-D, 4ton diesel vehicle) under the above rim and internal pressure conditions, and ran on a dry pavement with front wheel axle load (2200kgf) and rear wheel axle load (4400kgf). . And the driving stability and ride comfort were evaluated by the driver's sensuality. The results were expressed as an index with the conventional example being 100. The larger the value, the better.

<Road noise performance>
Using a vehicle having the same conditions as described above, a smooth road surface was run at a speed of 50 km / h, and the noise level dB (A) was measured at the position of the driver's left ear. The evaluation was expressed as an index with the conventional example being 100. The smaller the number, the better the noise level.
Table 1 shows the test results.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. It is sectional drawing which expands and shows the bead part. It is a diagram explaining a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Folding ply 6Ai Inner folding ply 6Ao Outer folding ply 6B Lowering ply 6a, 6ai, 6ao Main part 6b, 6bi, 6bo Folding part 7 Belt layer 8 Inner bead apex 9 Outer bead apex 10 Clinch rubber

Claims (4)

A pneumatic tire comprising a carcass extending in a toroid shape across a bead core embedded in each of a pair of bead portions, and a belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion,
The carcass has two toroidal main body portions extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a turn-back portion that is turned around the bead core from the inner side to the outer side in the tire axial direction. Folding ply,
The hlying ply is composed of a single lowering ply arranged only on the outer side of the folded ply and made only of the toroidal body, and the heights hci and hco from the bead base line of each folded portion It is larger than 0.1 times and smaller than 0.7 times the height H, and the bead portion is tapered from the bead core outward in the tire radial direction between the main body portion and the folded portion. Inner bead apex made of rubber with a stretch and JISA hardness of 75-95 degrees,
An outer bead apex that is attached to the inner bead apex via the turned-up portion and the lowering ply and that extends from the bead core vicinity to the outer side in the tire radial direction and is made of a softer rubber than the inner bead apex;
A clinching rubber having a JISA hardness of 60 to 80 degrees, which is disposed in an area outside the tire bead apex in the tire axial direction and in contact with the rim;
The folded portion of the at least one folded ply extends between the inner bead apex and the outer bead apex substantially in contact with the main body portion and radially outward.
The height Hai from the bead baseline of the inner bead apex is greater than 0.1 times and less than 0.3 times the tire cross-section height H,
The height Hao of the outer bead apex from the bead base line is larger than 0.3 times and smaller than 0.5 times the tire cross-sectional height H, and is arranged in the sidewall portion and the inner end is the above-mentioned The ratio (to / tk) of the thickness to of the outer bead apex at the normal position of the tire outer surface passing through the inner end of the sidewall rubber connected to the clinch rubber and the thickness tk of the clinch rubber is 0.5 to A pneumatic tire characterized by being 1.0.   2. The pneumatic tire according to claim 1, wherein the outer bead apex is made of rubber having a JISA hardness of 45 to 65 degrees and a JISA hardness of the clinch rubber.   2. The pneumatic tire according to claim 1, wherein the outer bead apex rubber is made of rubber having a JISA hardness of 70 to 90 degrees and a JISA hardness of the clinch rubber.   In the two folded plies, the height of one of the folded portions is greater than 0.1 times and smaller than 0.2 times the tire cross-section height H, and the other height of the folded portion The pneumatic tire according to any one of claims 1 to 3, wherein is greater than 0.4 times and less than 0.7 times the tire cross-section height H.

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