JP2000177318A - Pneumatic tire for two wheeler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reconcile improved straight running stability resulting from shimmy prevention and steering performance. SOLUTION: The crown portion of a carcass 16 is reinforced by a peripheral belt layer 22 as a spiral belt for improving high-speed durability. A tread 28 is formed in a cap-base structure consisting of a high-hardness cap rubber layer 24 and a base rubber layer 26 and the structural flexibility of the spiral belt is reinforced by the high-hardness cap rubber layer 24, so that the shearing rigidity of the tread 28 is maintained in the condition that the tread is so relatively thick as new, high-speed stability, smooth handling and high responsibility are so obtained as new and the occurrence of shimmy is prevented. Since the hardness of the base rubber layer 26 is lower than that of the cap rubber layer 24, the increasing rate of the shearing rigidity of the tread 28, increasing more as worn, is restricted and the change of the shearing rigidity in a period from a new one to a badly worn one, namely, the change of handling performance can be kept to a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire for a motorcycle, and more particularly to a pneumatic tire suitable for a front wheel of a motorcycle, which can improve straight running stability by preventing shimming.

[0002]

2. Description of the Related Art A front tire of a motorcycle has a spiral structure belt layer which is inferior in bending rigidity to a tread surface in a tire width direction in comparison with a conventional cross structure belt layer because steering characteristics such as handling are emphasized. However, at least it was not actively proposed as a belt structure for front tires.

[0003]

In recent years, the weight of vehicles has been reduced,
As the performance has been improved, minute vibration of the steering wheel, a so-called shimmy problem, has become apparent. In particular, measures against shimmy in a high frequency region have been strongly desired. Also, it has become more important to ensure stability at ultra-high speeds and high speeds.

[0004] With the conventional cross-structure belt layer, it is difficult to flexibly absorb thrust of the tread surface caused by minute unevenness of the road surface and minute vibration of the steering wheel resulting therefrom. As the speed increases, the protruding amount of the crown center becomes large, and it becomes difficult to solve the shortage of the contact property in the high-speed region caused by a large change in the contact shape. However, it is necessary to study the application of a spiral structure belt layer to a front tire, which has a disadvantage of low width (in the width direction) but has a small change in the contact shape at high speed and is excellent in high-speed durability.

However, simply replacing the belt layer of the conventional tire structure with the spiral structure belt layer as it is, the handling responsiveness due to its flexible structure,
It was not possible to compensate for the decrease in maneuvering performance such as low road grip force.

The present invention has been made in consideration of the above-described circumstances, and in particular, has been made to provide a pneumatic tire for a two-wheeled vehicle, which is particularly suitable for a front wheel and can achieve both improvement in straight running stability by preventing shimming and steering performance. Is the purpose.

[0007]

According to a first aspect of the present invention, there is provided a bead core embedded in a pair of left and right bead portions, and an end portion that straddles from one bead portion to the other bead portion in a toroidal shape. A carcass layer wound around the bead core and locked, a belt layer disposed radially outside the crown portion of the carcass layer, and a tread portion disposed radially outside the belt layer in the tire radial direction. The carcass layer has at least one carcass ply in which organic fiber cords extending in a direction of 60 ° to 90 ° with respect to the tire equatorial plane are arranged, and the belt layer is A long rubber-coated cord in which one cord is covered with rubber or a belt-like ply in which a plurality of cords are covered with rubber are spirally wound so that the cord direction is substantially different. A spiral belt layer extending in the ear circumferential direction, wherein the tread portion has at least a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer on the tread bottom surface side at least in a central region in the tire width direction. It is characterized by:

Next, the operation of the pneumatic tire for a motorcycle according to the first aspect will be described.

In the pneumatic tire for a motorcycle according to the present invention, a long rubber-covered cord in which one cord is covered with rubber or a belt-like ply in which a plurality of cords are covered with rubber are provided on the crown portion of the carcass. By providing a circumferential belt layer that is formed by spirally winding and the cord direction is substantially the tire circumferential direction, that is, a so-called circumferential spiral belt, the high-speed durability is improved compared to the conventional cross belt. In addition, the protrusion of the crown center at the time of high-speed running can be suppressed, so that the shortage of the contact property in a high-speed region caused by a large change in the contact shape can be solved.

The spiral belt has a structurally low rigidity in the tire width direction. However, in this pneumatic tire for a motorcycle, at least a central region in the tire width direction of the tread has at least a two-layer structure of a cap rubber layer and a base rubber layer. Since the so-called cap-base structure is used, the hardness of the rubber forming the cap rubber layer and the hardness of the rubber forming the base rubber layer can be made different, and the high flexibility rubber can compensate for the structural flexibility of the spiral belt. .

A long rubber-coated cord in which one cord is covered with rubber or a belt-like ply in which a plurality of cords are covered with rubber are spirally wound around a crown portion of a carcass, and the cord direction is substantially formed. A circumferential belt layer which is generally in the tire circumferential direction, a so-called circumferential spiral belt, has structural flexibility as compared with a cross belt, and therefore has a disadvantage in handling performance that is frequently used in running on a general road.

However, at least the center region in the tire width direction (here, the portion of the tread that is grounded when straight running and cornering is performed) has a cap-base structure, so that the cap rubber layer and the base rubber layer are separated from each other. The hardness of the cap rubber layer and the hardness of the base rubber layer are made different by using different rubbers, and the rubber having high hardness is used for one of them, so that the structural flexibility of the spiral belt can be supplemented.

For example, when the steering wheel is turned while the tire is in contact with the road surface, when the tread contacts the ground,
The tread rubber between the tread and the belt layer will be subjected to shear forces in a direction along the plane of the tread.

Here, when the tread is thick, as in the case of a new product, the deviation between the angle at which the handle is turned and the angle at which the tread moves is large, and from the handle to the tread (or vice versa). In addition, the transmission of the force is delayed, and in addition to the low bending rigidity of the tread surface due to the spiral belt, handling lightness and responsiveness deteriorate.

On the other hand, when the thickness of the tread is thin, the deviation between the angle at which the handle is turned and the angle at which the tread moves is small, and the delay in the transmission of force from the handle to the tread (or vice versa). Becomes smaller.

Therefore, compared with the case where the entire tread is made of low-hardness rubber, if the tread has a cap-base structure and a high-hardness rubber is used for one of the rubber layers, shearing when the new tread is thick is performed. Rigidity (when stress in the direction along the tread is applied) can be secured, and the structural flexibility of the spiral belt can be supplemented, and high-speed stability, handling agility and responsiveness can be improved. Becomes

Furthermore, if the entire tread is made of low-hardness rubber, a large amplitude shimmy is generated when disturbance is input due to insufficient rigidity, and the stability is deteriorated. By adopting, the rigidity of the tread can be ensured, and the occurrence of shimmy can be prevented.

If the angle of the cord of the carcass layer with respect to the equatorial plane of the tire is less than 60 °, the cord tends to be deformed by a lateral force, and the merit of the radial structure of the tire is lost.

According to a second aspect of the present invention, in the motorcycle pneumatic tire according to the first aspect, the hardness of the cap rubber layer is higher than the hardness of the base rubber layer.

Next, the operation of the pneumatic tire for a motorcycle according to the second aspect will be described.

The tread has a low shear stiffness when it is thick and new, and tends to have a high shear stiffness as it wears and becomes thin, that is, the tread tends to have a small shear deformation.

3. The pneumatic tire for a motorcycle according to claim 2, wherein the hardness of the cap rubber layer is set to be higher than the hardness of the base rubber layer as a cap and base structure. Compared to
In the pneumatic tire for a motorcycle according to claim 2,
It is possible to suppress the rate of increase in the shear rigidity that increases with wear, suppress changes in the shear rigidity due to tread wear, and keep changes in handling performance small.

According to a third aspect of the invention, in the pneumatic tire for a motorcycle according to the first aspect, the hardness of the cap rubber layer is in a range of 55 ° to 75 °.

Next, the operation of the pneumatic tire for a motorcycle according to the third aspect will be described.

By setting the hardness of the cap rubber layer in the range of 55 ° to 75 °, it is possible to reliably and sufficiently improve high-speed stability, handling lightness, and responsiveness when new.

When the hardness of the cap rubber layer is less than 55 °, the shear rigidity of the tread required at the time of new product and
Since the reinforcing effect of the structural flexibility of the spiral belt cannot be obtained, it is not possible to reliably obtain high-speed stability, handling lightness, and responsiveness when new.

On the other hand, if the hardness of the cap rubber layer exceeds 75 °, the cap rubber layer becomes too hard, the road surface gap absorbency is extremely poor, and the grip force with the road surface cannot be sufficiently obtained.

According to a fourth aspect of the present invention, in the pneumatic tire for a motorcycle according to any one of the first to third aspects, the difference between the hardness of the cap rubber layer and the hardness of the base rubber layer is provided. Is 2 ° or more.

Next, the operation of the pneumatic tire for a motorcycle according to the fourth aspect will be described.

If the difference between the hardness of the cap rubber layer and the hardness of the base rubber layer is not more than 2 °, there is no point in dividing the tread into the cap rubber layer and the base rubber layer.

Further, in the combination with the second aspect, it becomes impossible to keep the change in handling performance due to wear small.

According to a fifth aspect of the present invention, in the motorcycle pneumatic tire according to any one of the first to fourth aspects, the thickness of the cap rubber layer is A, and the thickness of the base rubber layer is B. B / (A + B) is 0.2 to 0.5
Is within the range.

Next, the operation of the pneumatic tire for a motorcycle according to the fifth aspect will be described.

When B / (A + B) is less than 0.2, the thickness of the base rubber layer becomes too thin, so that even if the hardness of the base rubber layer is low, the change in handling performance cannot be kept small.

On the other hand, when B / (A + B) exceeds 0.5, the thickness of the cap rubber layer becomes thin, so that even when the hardness of the cap rubber layer is high, the required shear rigidity of the tread when it is new is secured. This makes it impossible to reliably and sufficiently improve high-speed stability, handling agility, and responsiveness when new.

[0036]

[First Embodiment] Next, a first embodiment of a pneumatic tire for a motorcycle according to the present invention will be described with reference to FIG.

As shown in FIG. 1, the pneumatic tire 10 for a motorcycle according to the present embodiment has a first carcass ply 12 and a second carcass ply 12 in which a cord extending in a direction intersecting the tire equatorial plane CL is embedded. The carcass 16 includes a ply 14.

Each of the first carcass ply 12 and the second carcass ply 14 is wound up from the inside to the outside of the tire around a bead core 20 embedded in a bead portion 18 at both ends.

The first carcass ply 12 and the second carcass ply 12
The carcass ply 14 is formed by arranging a plurality of organic fiber cords (for example, nylon cords) in parallel and rubber coating the cords.
Extend in the direction of 60 ° to 90 °. The cords of the first carcass ply 12 and the cords of the second carcass ply 14 intersect each other, and are inclined in directions opposite to each other with respect to the tire equatorial plane CL.

Outside the carcass 16 in the tire radial direction,
A circumferential belt layer 22 is provided.

The circumferential belt layer 22 is a long rubber-coated cord (not shown) in which one cord is covered with rubber.
Alternatively, it is a so-called spiral belt formed by spirally winding a band-like ply (not shown) in which a plurality of cords are covered with rubber, and in which the cord direction is substantially the tire circumferential direction.

The cord is preferably made of high-strength, high-tensile aramid fiber (for example, Kevlar trade name).

A tread 28 is disposed outside the circumferential belt layer 22 in the tire radial direction. The tread 28 of this embodiment has a so-called cap-base structure, and the entire width direction is divided into two layers, a cap rubber layer 24 on the tread surface side and a base rubber layer 26 on the tread bottom surface side.

The hardness of the rubber forming the cap rubber layer 24 is preferably set higher than the hardness of the rubber forming the base rubber layer 26, and the difference in hardness is preferably set to 2 ° or more.

When the thickness of the cap rubber layer 24 is A and the thickness of the base rubber layer 26 is B, B / (A +
B) is preferably set in the range of 0.2 to 0.5.

Next, the operation of the pneumatic tire 10 for a motorcycle according to the present embodiment will be described.

The pneumatic tire 10 for a motorcycle according to the present embodiment.
Since the tire crown portion of the carcass 16 is reinforced by a so-called spiral belt, the tire has excellent high-speed durability as compared with a tire reinforced by a cross belt.

The structural flexibility of the circumferential belt layer 22, which is a spiral belt, is reinforced by the relatively high hardness cap rubber layer 24, and the relatively high hardness cap rubber layer 2
4 ensures the shear rigidity of the tread 28 when the tread is relatively thick when new, so that high-speed stability, handling lightness and high responsiveness can be obtained when new.

The pneumatic tire 10 for motorcycles
Increases the hardness of the cap rubber layer 24 of the tread 28,
Since the hardness of the base rubber layer 26 is set low, it is possible to suppress the rate of increase in the shear rigidity of the tread 28, which rises as it wears, and to change the shear rigidity from the time of brand-new to the end of wear, that is, the handling performance. The change can be kept small.

If the entire tread of the tire is made of low-hardness rubber, a large amplitude shimmy occurs at the time of disturbance input due to insufficient rigidity, and the stability is reduced. However, as in this embodiment, the tread 28 is capped with a cap. By setting the hardness of the cap rubber layer 24 to be high, the rigidity of the tread 28 can be secured, and the occurrence of shimming can be prevented.

If the angle of the cord of the carcass 16 with respect to the tire equatorial plane is less than 60 °, the pneumatic tire 10 for a motorcycle is easily deformed by a lateral force, and the merit of making the tire a radial structure is lost.

The hardness of the cap rubber layer 24 is 55 °
If it is less than the required value, the reinforcing effect of the shear rigidity of the tread 28 and the structural flexibility of the spiral belt required at the time of a new product cannot be obtained, and high-speed stability, handling lightness, and responsiveness at the time of a new product cannot be obtained. On the other hand, if the hardness of the cap rubber layer 24 exceeds 75 °, the cap rubber layer 2
4 is too hard, the road gap absorbency is extremely poor, and the grip force with the road surface cannot be sufficiently obtained.

If the difference between the hardness of the cap rubber layer 24 and the hardness of the base rubber layer 26 is not more than 2 °, the tread 2
There is no point in dividing 8 into the cap rubber layer 24 and the base rubber layer 26, and it becomes impossible to keep the change in handling performance due to wear small.

If B / (A + B) is less than 0.2, the thickness of the base rubber layer 26 becomes too thin, so that even if the hardness of the base rubber layer 26 is low, the change in handling performance cannot be kept small. . On the other hand, B / (A +
When B) exceeds 0.5, the thickness of the cap rubber layer 24 is reduced, so that even if the cap rubber layer 24 has a high hardness,
It becomes impossible to reliably and sufficiently improve high-speed stability, handling lightness and responsiveness when new.

In the pneumatic tire 10 for a motorcycle according to the first embodiment, the tread 28 has a two-layer structure over the entire width of the tire, but as shown in FIG. May be provided only in the center portion in the tire width direction. (Test Example 1) In order to confirm the effect of the present invention, two types of conventional tires and one type of tire according to the example to which the present invention was applied were prepared, and an actual vehicle (HOND) having test tires mounted on the front was prepared.
A CBR1100XX) was run by a test rider on a test course and evaluated for high-speed straight-running stability, shimminess, lightness / responsiveness, and low-speed steering wheel cut.

The results are as shown in Table 1 below. The results are shown as indices with the conventional tire set to 100. The larger the numerical value, the better the performance.

The tire of the embodiment is a tire having a tread having a cap-base structure shown in FIG. 1, and the conventional tire is a tire whose tread is made of one kind of rubber.

Each of the tires has two layers of carcass plies made of nylon cord on both front and rear sides and one layer of spiral belt made of Kevlar cord. In addition, the hardness and the like of the rubber are as described in Table 1.

In the case of a motorcycle, when the vehicle body is slightly tilted, the steering wheel has a characteristic of cutting inward due to the characteristics of the tire machine, and this characteristic is called "steering wheel cut". In. If the force of this cut is too large, it will be difficult for the rider to operate.

[0060]

[Table 1]

[0061]

As described above, the pneumatic tire for a motorcycle according to the first aspect has the above-described configuration, and therefore has an excellent effect that both straight running stability and steering performance can be achieved. Have.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pneumatic tire for a motorcycle according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a pneumatic tire for a motorcycle according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Pneumatic tire for motorcycle 16 Carcass (carcass layer) 18 Bead portion 20 Bead core 22 Circumferential belt layer 24 Cap rubber layer 26 Base rubber layer 28 Tread (tread portion) 32 Base rubber layer 34 Cap rubber layer

Claims (5)

[Claims] 1. A bead core embedded in a pair of left and right bead portions, and a carcass having a toroidally straddling end portion from one bead portion to the other bead portion wound around the bead core and locked to the bead core. A pneumatic tire for a motorcycle, comprising: a belt layer disposed on a tire radial direction outside of a crown portion of the carcass layer; and a tread portion disposed on a tire radial direction outside of the belt layer. The layer is between 60 ° and 90 ° with respect to the tire equatorial plane.
At least one carcass ply in which organic fiber cords extending in the direction of ° are arranged, and the belt layer covers a long rubber-coated cord in which one cord is covered with rubber or a plurality of cords with rubber. The belt-like ply is a spiral belt layer in which the cord direction is substantially the tire circumferential direction by being spirally wound. A pneumatic tire for a motorcycle, wherein the pneumatic tire has at least a two-layer structure with a base rubber layer on a bottom surface side. 2. The pneumatic tire for a motorcycle according to claim 1, wherein the hardness of the cap rubber layer is higher than the hardness of the base rubber layer. 3. The hardness of the cap rubber layer is 55 ° or more.
The pneumatic tire for a motorcycle according to claim 1, wherein the angle is within a range of 75 °. 4. The air for motorcycles according to claim 1, wherein the difference between the hardness of the cap rubber layer and the hardness of the base rubber layer is 2 ° or more. Containing tires. 5. When the thickness of the cap rubber layer is A and the thickness of the base rubber layer is B, B / (A + B) is 0.2 to 0.2.
The pneumatic tire for a motorcycle according to any one of claims 1 to 4, wherein the value is within a range of 0.5.