Patent Application
20100243117
The present invention relates to a pneumatic tire having a carcass layer having a single-ply structure and wound-up sections each extended up to a region below a belt layer so as to overlap with an end section of the belt layer, and more specifically relates to a pneumatic tire in which the performance change of driving stability due to continuous driving can be suppressed.
In recent years, requirements for weight reduction have been becoming stricter for pneumatic tires mounted to vehicles such as sports cars which are made to be driven at high speeds. In addition to satisfying such requirements for weight reduction, ensuring driving stability equivalent to or greater than those of conventional pneumatic tires is required.
In this regard, a pneumatic tire has been proposed in which a single-ply structured carcass layer is laid between a pair of bead sections. A belt layer is arranged on the outer peripheral side of the carcass layer in a tread section of the tire. The carcass layer is wound up, from the inner side to the outer side of the tire, around each of bead cores arranged respectively in the bead sections. Bead fillers arranged respectively on the bead cores are each sandwiched by a body section and a wound-up section of the carcass layer, and each wound-up section of the carcass layer extended up to a region below the belt layer so as to overlap with an end section of the belt layer (for example, see Patent Documents 1 to 3).
The pneumatic tire having the carcass layer having the single-ply structure and the wound-up sections each extended up to the region below the belt layer so as to overlap with the end section of the belt layer, can exhibit excellent driving stability by causing the body section and each wound-up section of the carcass layer to overlap with each other in each side wall section, while obtaining an effect of weight reduction by providing a single ply for the carcass layer.
However, the pneumatic tire having the structure described above has a problem that the driving stability decreases along with the tire being heated when a continuous driving in a circuit is performed, for example. Therefore, there is a demand for suppressing the performance change of driving stability due to continuous driving in the pneumatic tire in which weight reduction and driving stability are both achieved based on the structure described above.
An object of the present invention is to provide a pneumatic tire in which the performance change of driving stability due to continuous driving can be suppressed even with a carcass layer having a single-ply structure and wound-up sections each extended up to a region below a belt layer so as to overlap with an end section of the belt layer.
In order to achieve the object described above, a pneumatic tire according to the present invention is one in which a single-ply structured carcass layer having a cord angle in a range of 75° to 90° to a tire circumferential direction is laid between a pair of bead sections, a belt layer is arranged on an outer peripheral side of the carcass layer in a tread section, bead cores around each of which the carcass layer is wound up from an inner side to an outer side of a tire are arranged respectively in the bead sections, bead fillers are arranged respectively on the bead cores and are each sandwiched by a body section and a wound-up section of the carcass layer, and each wound-up section of the carcass layer is extended up to a region below the belt layer so as to overlap with an end section of the belt layer. The pneumatic tire is characterized in that a height of the bead filler from a bead heel is not more than 25 mm, a sectional area of the bead filler is not more than 65 mm2, and tan δ at 60° C. of a rubber composition constituting the bead filler is not more than 0.20.
In the present invention, the carcass layer, which has the single-ply structure and the wound-up section extended up to the region below the belt layer so as to overlap with the end section of the belt layer, is provided in order to achieve both weight reduction and driving stability. By further lowering the bead filler, which repeatedly deforms at the time of the rolling motion of the tire, to reduce the sectional area thereof and reducing the tan δ at 60° C. of the rubber composition constituting the bead filler, the heat of the tire due to continuous driving in a circuit is suppressed to suppress the performance change of the driving stability. Accordingly, the initial driving stability can be maintained for a long period of time in the continuous driving.
In the present invention, in the case of the pneumatic tire having a mounting direction specified with respect to a front and back of the tire at a time of mounting the tire to a vehicle, it is preferable that at least two types of cap tread rubber layers having different rubber compositions are arranged in the tread section to be adjacent to each other in a tire width direction, and tan δ at 60° C. of the rubber composition constituting the cap tread rubber layer on an outer side of the vehicle be larger than tan δ at 60° C. of the rubber composition constituting the cap tread rubber layer on an inner side of the vehicle
Generally speaking, increasing the tan δ at 60° C. of the rubber composition constituting the cap tread rubber layer improves the driving stability, but causes the performance change of the driving stability due to heat to easily occur. On the other hand, by relatively increasing the tan δ on the outer side of the vehicle and relatively decreasing the tan δ on the inner side of the vehicle as described above, it becomes possible to suppress the performance change of the driving stability due to continuous driving while improving the driving stability.
It is preferable that the ratio (tan δ H/tan δ L) of a maximum value tan δ H to a minimum value tan δ L of the tan δ at 60° C. of the rubber compositions constituting the at least two types of cap tread rubber layers be in a range of 1.05 to 1.80. Accordingly, the effect of suppressing the performance change of driving stability due to continuous driving while improving the driving stability can be obtained sufficiently.
It is preferable that boundary of the at least two types of cap tread rubber layers be arranged below a main groove extending in the tire circumferential direction in the tread section. Accordingly, the occurrence of uneven wear due to the difference of the rubber compositions can be suppressed.
In the case of the pneumatic tire having the mounting direction specified with respect to the front and back of the tire at the time of mounting the tire to the vehicle, it is preferable that at least one main groove extending in the tire circumferential direction be provided in the tread section, and an asymmetric tread pattern be formed in which a groove area ratio GAo in a ground contact region on the outer side of the vehicle with respect to the tread center is smaller than a groove area ratio GAi in a ground contact region on the inner side of the vehicle with respect to the tread center.
In the asymmetric tread pattern, it is preferable that a groove area ratio GA in an entire ground contact region be in a range of 20% to 40%, and a difference (GAi−GAo) between the groove area ratio GAo in the ground contact region on the outer side of the vehicle and the groove area ratio GAi in the ground contact region on the inner side of the vehicle be in a range of 1% to 15%. Accordingly, the effect of suppressing the performance change of driving stability due to continuous driving while improving the driving stability can be obtained sufficiently.
In the present invention, the height of the bead filler from the bead heel is a height measured under measurement conditions of the tire dimension defined by a specification with which the tire complies, and is a dimension from the bead heel corresponding to the reference position of the rim diameter to the peak of the bead filler in the radial direction of the tire. The tan δ at 60° C. is measured using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of a 60° C. temperature, a 20 Hz frequency, a 10% initial strain, and a ±2% dynamic strain. The groove area ratio is a ratio (%) of a groove area in a ground contact region with respect to the whole area of the ground contact region measured under measurement conditions of a static loaded radius of the tire defined by the specification with which the tire complies.
Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
In the bead section 3, a bead filler 6 formed of a high-hardness rubber composition is arranged on the outer periphery of the bead core 5, and the bead filler 6 is sandwiched by the body section 4a and the wound-up section 4b of the carcass layer 4. In the bead section 3, an organic fiber reinforcement layer 7 which includes organic fiber cords each tilted to the tire circumferential direction is buried to enwrap the bead core 5 and the bead filler 6. An end section of the organic fiber reinforcement layer 7 on the inner surface side of the tire is arranged on the outer side in the radial direction of the tire with respect to the peak of the bead filler 6, and an end section of the organic fiber reinforcement layer 7 on the outer surface side of the tire is arranged on the outer side in the radial direction of the tire with respect to the end section of the organic fiber reinforcement layer 7 on the inner surface side of the tire.
Meanwhile, a belt layer 8 formed of layers including a reinforcement cord tilted to the tire circumferential direction is arranged on the outer peripheral side of the carcass layer 4 in the tread section 1. Further, a belt cover layer 9 including a reinforcement cord aligned in the tire circumferential direction is arranged on the outer periphery side of the belt layer 8. The wound-up section 4b of the carcass layer 4 described above extends up to a region below the belt layer 8 to overlap with an end section of the belt layer 8 in the tire width direction.
In the pneumatic tire described above, the carcass layer 4, which has a single-ply structure and the wound-up section 4b extended up to the region below the belt layer 8 to overlap with the end section of the belt layer 8, is provided in order to achieve both weight reduction and driving stability. On the basis of such structure, a height H of the bead filler 6 from a bead heel is not more than 25 mm, the sectional area of the bead filler 6 in a meridian section of the tire is not more than 65 mm2, and tan δ at 60° C. of the rubber composition constituting the bead filler 6 is not more than 0.20.
In the pneumatic tire, deformation of the bead filler 6 is repeated at the time of rolling motion, whereby the performance change of the driving stability becomes apparent when the heating value due to the bead filler 6 correspondingly increases. Thus, by lowering the bead filler 6 to reduce the sectional area thereof and reducing the tan δ at 60° C. of the rubber composition constituting the bead filler 6, it is possible to suppress heat of the tire due to continuous driving at a circuit and suppress the performance change of the driving stability. As a result, the initial driving stability can be maintained over a long period of time in the continuous driving.
When the height H of the bead filler 6 exceeds 25 mm, the effect of suppressing the performance change of the driving stability becomes insufficient. The lower limit value of the height H of the bead filler 6 is preferably 10 mm.
In the same manner, when the sectional area of the bead filler 6 exceeds 65 mm2, the effect of suppressing the performance change of the driving stability becomes insufficient. The lower limit value of the sectional area of the bead filler 6 is preferably 15 mm2.
When the tan δ at 60° C. of the rubber composition constituting the bead filler 6 exceeds 0.20, the effect of suppressing the performance change of the driving stability becomes insufficient. The lower limit value of the tan δ at 60° C. of the rubber composition constituting the bead filler 6 is preferably 0.03.
The pneumatic tire described above is a tire whose mounting direction is specified with respect to the front and back of the tire at the time of mounting the tire to a vehicle. In
As shown in
The ratio (tan δ H/tan δ L) of a tan δ H at 60° C. of the rubber composition constituting the cap tread rubber layer 1A to a tan δ L at 60° C. of the rubber composition constituting the cap tread rubber layer 1B is set in a range of 1.05 to 1.08, and preferably in a range of 1.10 to 1.50. When the ratio (tan δ H/tan δ L) is too small, the effect of suppressing the performance change of the driving stability decreases. On the other hand, when it is too large, the grip force normally required cannot be obtained. Note that it is preferable to arrange the boundary of the cap tread rubber layers 1A and 1B below a main groove 60 extending in the tire circumferential direction in the tread section 1. Accordingly, the occurrence of uneven wear due to the difference of the rubber compositions can be suppressed.
In this embodiment, two types of the cap tread rubber layers 1A and 1B having different rubber compositions are arranged in the tread section 1. However, two or more types of the cap tread rubber layers may be arranged so as to be adjacent to each other in the tire width direction.
In the pneumatic tire described above, at least one main groove 60 extending in the tire circumferential direction is formed in the tread section 1, and has an asymmetric tread pattern, in which a groove area ratio GAo in a ground contact region on the outer side of the vehicle with respect to the tread center CL is smaller than a groove area ratio GAi in a ground contact region on the inner side of the vehicle with respect to the tread center CL, over the entire ground contact region specified by a ground contact width TCW. Accordingly, the effect of suppressing the performance change of the driving stability due to continuous driving while improving the driving stability can be sufficiently obtained.
The groove area ratio GA in the entire ground contact region is in a range of 20% to 40%, and the difference (GAi−GAo) between the groove area ratio GAo in the ground contact region on the outer side of the vehicle with respect to the tread center CL and the groove area ratio GAi in the ground contact region on the inner side of the vehicle with respect to the tread center CL is in a range of 1% to 15%, and more preferably in a range of 2% to 13%. When the difference (GAi−GAo) is too small, the effect of suppressing the performance change of the driving stability decreases. When it is too large, the driving stability decreases due to insufficiency in block rigidity normally required.
The preferred embodiment of the present invention has been described above in detail. However, it should be understood that various modifications, alterations, and substitutions maybe made without departing from the spirit and the scope of the present invention defined by the accompanying scope of claims.
Pneumatic tires of Comparative Examples 1 to 3 and Examples 1 to 5 were prepared in the following manner. Each of these pneumatic tires had a tire size of 235/40R18, and a single-ply structured carcass layer having a cord angle of 85° to the tire circumferential direction was laid between a pair of bead sections. A belt layer was arranged on the outer peripheral side of the carcass layer in a tread section of the tire. The carcass layer was wound up, from the inner side to the outer side of the tire, around each of bead cores arranged respectively in the bead sections. Bead fillers arranged respectively on the bead cores were each sandwiched by a body section and a wound-up section of the carcass layer, and each wound-up section of the carcass layer extended up to a region below the belt layer so as to overlap with an end section of the belt layer. Moreover, for each of these pneumatic tires of Comparative Examples 1 to 3 and Examples 1 to 5, the height of each bead filler from bead heels, the sectional area of each bead filler, tan δ at 60° C. of the rubber composition constituting the bead fillers, tan δ at 60° C. of the rubber composition constituting a cap tread rubber layer on the outer side of a vehicle and the inner side of the vehicle, and groove area ratios on the outer side of the vehicle and the inner side of the vehicle were set as shown in Table 1.
The performance changes of the driving stability of these test tires were evaluated by use of the following test method, and the results are also shown in Table 1.
Each test tire was fitted onto a wheel having a rim size of 18×8J, and the wheel with the test tire was mounted on a vehicle having a displacement of approximately 4000 cc, whereby a continuous driving for the distance of 200 km was performed by a test driver under a condition of a 250 kPa pneumatic pressure to perform a sensory evaluation of the change between the driving stability at the beginning of driving and the driving stability at the end of driving. The evaluation result is shown by use of an index with 100 as an acceptable level. A larger index value indicates a smaller performance change.
As shown in Table 1, the tires of Examples 1 to 5 all showed small performance change of the driving stability due to the continuous driving. On the other hand, the performance changes of the driving stability were evaluated to be below the acceptable level in Comparative Examples 1 to 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-206931 | Aug 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/058480 | 5/7/2008 | WO | 00 | 11/21/2008 |
