Patent Application
20080017290
The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.
A pneumatic tire 22 for a motorcycle shown in
The tread 24 is formed by a crosslinked rubber and takes the shape of an outward convex in the radial direction. An external surface of the tread 24 forms a tread surface 38 to come in contact with a road surface. A groove 40 is provided on the tread surface 38. By the groove 40, a tread pattern is formed.
The sidewall 26 is extended almost inward in the radial direction from an end of the tread 24. The sidewall 26 is formed by a crosslinked rubber. The sidewall 26 absorbs a shock from the road surface. Furthermore, the sidewall 26 prevents the external damage of the carcass 30.
The bead 28 is extended almost inward in the radial direction from the sidewall 26. The bead 28 includes a core 42 and an apex 44 extended outward in the radial direction from the core 42. The core 42 is ring-shaped and includes a plurality of non-extensible wires (typically wires formed of steel). The apex 44 is outward tapered in the radial direction and is formed by a crosslinked rubber having a high hardness.
The carcass 30 is formed by a carcass ply 46. The carcass ply 46 is laid between the beads 28 on both sides along the insides of the tread 24 and the sidewall 26. The carcass ply 46 is turned up around the core 42 from the inside toward the outside in the axial direction.
The carcass ply 46 is constituted by a carcass cord and a topping rubber, which is not shown. An absolute value of an angle formed by the carcass cord with respect to the equator plane is equal to or greater than 60 degrees and is equal to or smaller than 90 degrees. In other words, the tire 22 is a radial tire. The carcass cord is usually constituted by an organic fiber. Examples of a preferable organic fiber include a polyester fiber, a nylon fiber, a rayon fiber, a polyethylene naphthalate fiber and an aramid fiber.
The inner liner 34 is bonded to the inner surface of the carcass 30. The inner liner 34 is formed by a crosslinked rubber. A rubber having a low air permeability is used for the inner liner 34. The inner liner 34 plays a part in holding the internal pressure of the tire 22.
The chafer 36 is positioned in the vicinity of the bead 28. When the tire 22 is fitted to a rim, the chafer 36 abuts on the rim. By the abutment, the vicinity of the bead 28 is protected. The chafer 36 is usually constituted by a cloth and a rubber impregnated into the cloth. It is also possible to use a chafer formed only by a rubber.
The belt 32 is positioned on an outside in the radial direction of the carcass 30. The belt 32 is provided on the carcass 30. The belt 32 reinforces the carcass 30. In the tire 22, the belt 32 is constituted by a first belt ply 48 and a second belt ply 50. The first belt ply 48 is provided on the outside in the radial direction of the carcass ply 46. The second belt ply 50 is provided on the outside in the radial direction of the first belt ply 48. The second belt ply 50 is close to the tread 24. The second belt ply 50 includes a center portion 52 and a pair of side portions 54 positioned on the outside in the axial direction of the center portion 52. As shown, a part of the carcass ply 46 turned up around the core 42 is positioned on the inside of the first belt ply 48. A turned-up end 56 of the carcass ply 46 is positioned on the outside in the radial direction from an outer end 58 of the first belt ply 48. An outer end 60 of the second belt ply 50 is positioned on the outside in the radial direction of the outer end 58 of the first belt ply 48. The turned-up end 56 may be disposed on the inside in the radial direction from the outer end 58 of the first belt ply 48. The outer end 60 of the second belt ply 50 may be disposed on the inside in the radial direction from the outer end 58 of the first belt ply 48.
The first belt ply 48 is constituted by a first cord and a topping rubber, which is not shown. The first cord is inclined to the circumferential direction. An absolute value of an angle formed by the first cord with respect to the circumferential direction is equal to or greater than 60 degrees and is equal to or smaller than 80 degrees. The first cord is usually constituted by an organic fiber. Examples of a preferable organic fiber include a polyester fiber, a nylon fiber, a rayon fiber, a polyethylene naphthalate fiber and an aramid fiber. The first belt ply 48 is referred to as a cut ply.
As described above, the second belt ply 50 is positioned on the outside in the radial direction of the first belt ply 48 positioned on the outside in the radial direction of the carcass ply 46. The tread 24 is disposed on the outside in the radial direction of the second belt ply 50. In the tire 22, the center cord 62 and the side cord 66 in the second belt ply 50 are spirally wound in the substantially circumferential direction. Consequently, the first belt ply 48 and the carcass ply 46 are restrained. The tire 22 is excellent in a stability.
In a cornering operation, a rider inclines the motorcycle inward. Consequently, a contact surface of the tire 22 is changed from a center region 72 of the tread 24 to a shoulder region 74 thereof. As described above, in the tire 22, the center cord 62 of the center portion 52 is formed of steel and the side cord 66 of the side portion 54 positioned on the outside in the axial direction of the center portion 52 is formed by an aramid fiber. In the tire 22, a stiffness of the side portion 54 is lower than that of the center portion 52. As will be described below, in the tire 22, a ratio of a perimeter of the center portion 52 to that of the side portion 54 is regulated into a proper range. The tire 22 sufficiently comes in contact with the road surface in the cornering operation, thereby transmitting a driving force and a braking force to the road surface reliably. The tire 22 is excellent in a cornering performance. Even if a disturbance such as a side wind or an irregular road surface is caused in the tire 22 so that the running condition of the vehicle is changed suddenly, a driver can easily correct the running condition into a proper condition. The tire 22 is excellent in a handling property. The tire 22 has the handling property and the stability which are compatible with each other. The tire 22 has a smaller tire weight than that of a tire in which the cord of the second belt ply 50 is constituted by only the steel. As compared with a tire in which the cord of the second belt ply 50 is constituted by only the aramid fiber, the tire 22 has a lower cost. In the tire 22, the tire weight and the cost can be prevented from being increased.
In
In the tire 22, a ratio of the half perimeter LA of the center portion 52 to the perimeter LB of the side portion 54 is equal to or higher than 10% and is equal to or lower than 50%. By setting the ratio to be equal to or higher than 10%, it is possible to effectively restrain the carcass ply and the first belt ply. The tire 22 is excellent in a stability. The amount of the aramid fiber used in the second belt ply 50 is decreased. Therefore, the cost of the tire 22 is reduced. From this viewpoint, the ratio is preferably equal to or higher than 12% and is more preferably equal to or higher than 25%. By setting the ratio to be equal to or lower than 50%, the tire 22 sufficiently comes in contact with the road surface also in the cornering operation, thereby transmitting the driving force and the braking force to the road surface reliably. The tire 22 is excellent in the handling property. The amount of the steel used in the second belt ply 50 is decreased. Therefore, the weight of the tire 22 is reduced. From this viewpoint, the ratio is preferably equal to or lower than 45% and is more preferably equal to or lower than 30%.
In the tire 22, it is preferable that a density of the center cord 62 in the center portion 52 (the number of the center cords 62 per 5 cm width) should be equal to or greater than 30 ends and be equal to or smaller than 60 ends. It is preferable that a sectional area of the center cord 62 should be equal to or greater than 0.10 mm2 and be equal to or smaller than 1.6 mm2. In the tire 22, it is preferable that a density of the side cord 66 in the side portion 54 (the number of the side cords 66 per 5 cm width) should be equal to or greater than 30 ends and be equal to or smaller than 60 ends. It is preferable that a sectional area of the side cord 66 should be equal to or greater than 0.10 mm2 and be equal to or smaller than 1.6 mm2.
When measuring dimensions and angles of the tire 22, the tire 22 is fitted into a normal rim and filled with air to have a normal internal pressure. Under the measurement, a load is not put on the tire 22. In the present specification, the normal rim means a rim provided by a standard system including standards of the tire 22. A “standard rim” in JATMA standards, a “Design Rim” in TRA standards and a “Measuring Rim” in ETRTO standards are included in the normal rim. In the present specification, a normal internal pressure means an internal pressure provided by a standard system including standards of the tire 22. A “maximum air pressure” in the JATMA standards, a “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE” in the TRA standards, and “INFLATION PRESSURE” in the ETRTO standards are included in the normal internal pressure.
A pneumatic tire for a motorcycle according to an example 1 which has the basic structure shown in
A tire was obtained in the same manner as in the example 1 except that the ratio (LA/LB×100) is set as shown in the following Table 1. In a comparative example 1, the cord (the center cord and the side cords) of the second belt ply is constituted by only an aramid fiber. In a comparative example 4, the cord (the center cord and the side cords) of the second belt ply is constituted by only steel.
In a comparative example 5, there is shown a conventional pneumatic tire for a motorcycle which is put on the market.
A trial tire was attached to a rear wheel of a motorcycle (four cycles) having a displacement of 1000 cm3 and put on the market. A rim was set to have a size of MT 6.00×17 and the tire was set to have an air internal pressure of 290 kPa. A conventional tire put on the market is attached to a front wheel. A tire size of the front wheel is 120/70ZR17. A rim has a size of MT 3.50×17 and the tire has an air internal pressure of 250 kPa. In a circuit course constituted by a dry asphalted road, cornering at a speed of 100 km/h to 150 km/h and straight running at a speed of 250 km/h to a maximum speed of a vehicle (approximately 280 km/h) were executed and a rider carried out a functional evaluation having a full point set to be 5.0. It is indicated that the function is more excellent if the numeric value is greater. Items for the evaluation include a straight running stability, a cornering stability, an absorption, a ride comfort, a cornering force and a grip force. The result is shown in the following Table 1.
As shown in the Table 1, it was confirmed that the tire according to each of the examples is excellent in the straight running stability, the cornering stability, the cornering force and the grip force with the absorption and the ride comfort maintained. The tire has a handling property and a stability which are compatible with each other. From the result of the evaluation, the advantages of the present invention are apparent.
The above description is only illustrative and various changes can be made without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-141761 | May 2006 | JP | national |
