JP2000264013A - Pneumatic tire for motor cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the transverse rigidity of a tire including the tire having a large camber angle by setting the ratio of the compressive rigidity in the axial direction of at least one layer cord of a belt comprising a rubber coated layer to the tensile rigidity to be a specific range to ensure the sufficient tread rigidity. SOLUTION: A tire for a motor cycle is considerably small in radius of curvature of a tread surface 3t of a tread portion, and thus, large in compressive strain in the direction of the tread portion 3 of a belt 6 on a ground contact surface, in particular, large in compressive strain of a cord 6-1c embedded in a cord layer 6-1 of the belt 6 in order to provide a large camber angle. The ratio of the compressive rigidity in the axial direction of the cord 6-1c of the cord layer 6-1 in the tire to the tensile rigidity is set to be in a range of 1/2 to 1/5. The transverse rigidity of the tire having a large camber angle can be sufficiently increased, and the steering stability by the turn can be improved.

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 two-wheeled vehicle, and more particularly to a radial ply tire, and more particularly to a pneumatic tire for a two-wheeled vehicle having improved steering stability.

[0002]

2. Description of the Related Art A pneumatic tire for a two-wheeled vehicle has a significantly smaller radius of curvature of a tread portion in a tire cross section than that of a pneumatic tire for a four-wheeled vehicle (particularly a passenger car), and therefore has a higher degree of height. Steering stability performance is required. The superiority of this steering stability performance is, of course, not only when traveling straight,
Appears when turning with a relatively large camber angle on the vehicle.

[0003] Among pneumatic tires for motorcycles, radial ply tires have a belt similar to other types of radial ply tires. Generally, the belt of a pneumatic radial tire for a two-wheeled vehicle is a rubber-coated organic fiber cord layer, and the cord has a circular cross-sectional shape. This belt has insufficient lateral force due to the tread portion having a small radius of curvature.

[0004]

As will be apparent from the above, the belt of the pneumatic tire for a two-wheeled vehicle has a smaller compression along the circumference of the tread portion than the belt of another type of tire having a cord cross layer. The stiffness is less in the tread and tends to buckle in the tread. In this regard, the belt that acts as the dominant element of the steering stability performance depends on the rigidity at the tread contact surface, especially when a large-angle camber is attached, the compression stiffness of the tread portion within the contact surface. The shortage results in a shortage of camber thrust and significantly impairs steering stability.

In order to improve the steering stability, Japanese Patent Application Laid-Open No. 6-55906 discloses a method in which a spirally wound layer of a belt is applied with a cord in which a plurality of strands of 840 to 1890D aromatic polyamide fibers are twisted. A pneumatic tire for a two-wheeled vehicle has been proposed in which the cross section of a cord is flattened in the tire axial direction and the cord has a low twist of 29 or less per 10 cm.

[0006] However, it has been found that even with the tires proposed in the above publication, sufficient steering stability cannot be obtained. Therefore, the invention described in claims 1 to 8 of the present invention secures sufficient tread portion rigidity, thereby increasing the lateral rigidity of the tire even when a large camber angle is applied, and particularly, the vehicle turning behavior An object of the present invention is to propose a pneumatic tire for a two-wheeled vehicle in which the steering stability performance at the time is sufficiently improved.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a pair of sidewall portions and a tread portion are formed between bead cores embedded in a pair of bead portions. In a pneumatic tire for a two-wheeled vehicle including one or more ply of radial carcass to be reinforced and a belt made of one or more rubber-coated cord layers for reinforcing the tread portion at the outer periphery of the carcass, at least one layer of the belt has a cord of at least one layer. , The ratio Rc / Rt of the compression stiffness Rc to the tensile stiffness Rt in the cord axis direction
Is in the range of 1/2 to 1/5.

[0008] Two types of belt layers of cords satisfying the above range of the ratio Rc / Rt are suitable, one of which is the above-mentioned ratio Rc / Rt.
The belt layer of the cord having the ratio Rc / Rt is a spirally wound cord layer. Is a wound code layer.

Here, the compression stiffness and the tensile stiffness described in claim 1 are determined by compressing the cord taken out from the tire in the axial direction of the cord with respect to a test piece in which the cord is taken out of rubber as in the invention described in claim 4. The initial compression resistance when the force is applied is defined as the compression rigidity Rc of the cord, and the initial tensile resistance when the tensile force is applied to the cord taken out of the same tire is defined as the tensile rigidity Rt of the cord.

The initial compression resistance and the initial tensile resistance described in claim 4 are determined as follows. First, the initial compression resistance will be described with reference to FIGS. That is, a sample piece in which a cord C taken out of a tire is embedded in an unvulcanized rubber is subjected to vulcanization molding, and a cylindrical rubber G having a diameter d (at a maximum of 18 mm) and a height h (at a maximum of 48 mm) is attached to its shaft. A cylindrical test piece S (shown as a perspective view in FIG. 5) was prepared by adhering a cord C having an axis aligned with that of the test piece S. The test piece S was compressed in the axial direction, and the load (gf) was increased as shown in FIG. -Draw a displacement (mm) curve. Next, the maximum point A of the load change with respect to the compression change near the origin T of the curve in FIG. 6 is obtained, the point from point T to point A is set as the initial characteristic, and the initial compression resistance (gf / D), (gf
/ mm ² ). The number of tests is two, and the average value is calculated to one decimal place. Initial compression resistance (gf / D), (gf
/ mm ² ) = P / {(L / L ₀ ) × D}, where (gf / d) is an organic fiber cord, (gf / mm ² ) is a steel cord, and P: load at point A (gf) L ₀ : Original length of test piece (mm) L: Compressive displacement from point T to point H (mm) (Point H is point A
D: Organic fiber cord is total denier, steel cord is total cross-sectional area of strand (mm ² )

Next, the initial tensile resistance will be described with reference to FIG. The cords taken out from the tires are JIS L 1017 (1983) for organic fiber cords and JIS G 3510 (1986) for steel cords.
Then, a tensile test is performed based on each. Using an Instron tensile tester, a load-elongation curve (shown in FIG. 7) of each test cord is drawn. Next, the maximum point A of the load change with respect to the change in elongation near the origin T of the curve in FIG. 7 is determined, the point from point T to point A is set as the initial characteristic, and the initial tensile resistance (gf /
D) and (kgf / mm ² ). The number of tests is 10 times,
The average value is calculated to one decimal place. Initial tensile resistance (gf / D), (kgf / mm ² ) = P / {(L / L ₀ ) × D}, where (gf / D) is organic fiber cord and (kgf / mm ² ) is steel Code: P: Load at point A (gf for organic fiber cord, kgf for steel cord) L ₀ : Original length of test piece (mm) L: Compressive displacement from point T to point H (mm) (Point H Is point A
D: Organic fiber cord is total denier, steel cord is total cross-sectional area of wire (mm ² )

Preferably, the cord having the above-mentioned ratio Rc / Rt is preferably a steel cord. Further, as in the invention described in claim 6, the steel cord having the above ratio Rc / Rt has a flat cross section in the tire rotation axis direction.
This leads to an increase in lateral force when turning.

[0013] In relation to the invention described in claim 6, in practice, as in the invention described in claim 7, the ratio Rc /
The steel cord having Rt has a rectangular cross-sectional shape, or the steel cord having the above-mentioned ratio Rc / Rt has any one of an elliptical cross section and an elliptical cross section. It is advantageous to have a one-way shape.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a left half sectional view of a pneumatic tire for a two-wheeled vehicle according to the present invention.
3 is a perspective view of a part of a cord layer of the belt shown in FIG. 1, and FIG. 3 is a perspective view of a part of a cord layer different from the cord layer shown in FIG.

Referring to FIG. 1, a pneumatic tire for a two-wheeled vehicle (hereinafter referred to as a tire) has a pair of bead portions 1 (only one side is shown), a pair of sidewall portions 2 (only one side is shown), and both sidewall portions 2. A carcass 5 having a tread portion 3 extending between the bead cores 4 embedded in the bead portion 1 and reinforcing the above portions 1, 2, and 3; and a belt 6 reinforcing the tread portion 3 around the outer periphery of the carcass 5. Is provided.

The carcass 5 has one or more plies, a rubber-coated plies having a radial arrangement code of one ply in the illustrated example, and this cord is made of an organic fiber cord such as a nylon cord. The belt 6 is composed of one or more rubber-coated cord layers in the illustrated example. At least one of the cord layers constituting the belt 6 is a spirally wound layer 6-1 type of a cord 6-1c as shown in FIG. Wound code layer 6 wound around
One type of code layer is compatible with the present invention. The wound cord layer 6-1 has a configuration in which the cord arrangement is parallel to the equatorial plane E, and has a configuration in which the cord arrangement is parallel to the equator plane E. Either is acceptable. Here, the case where the wound code layer 6-1 is the inclined code layer 6-1 will be described.

As shown in FIGS. 2 and 3, the spirally wound layer 6-1 has one to five (three in the illustrated example) cords 6-1.
c is a layer of cord 6-1c that is spirally wound with a predetermined interval in the width direction of the tread portion 3 continuously in the circumferential direction of the tread portion 3. Therefore, the cord 6-1c of the spirally wound layer 6-1
Has an array of minute intersection angles that cannot be said to be inclined with respect to a plane parallel to the tire equatorial plane E.
It is an almost parallel array.

On the other hand, as the inclined cord layer 6-1, an unvulcanized cord layer member obtained by cutting an unvulcanized rubber coated cord for a wide belt member obliquely at a predetermined width in a tire molding stage is applied. Things. Therefore, the inclined cord layer 6-1 in the product tire has cut sections of the cord 6-1c at both width ends, and is also referred to as a separated cord layer 6-1 in comparison with the spirally wound layer 6-1. Code 6 of inclined code layer 6-1
-1c is 10 to 50 with respect to the tire equatorial plane E.
Within the range of ° is suitable. Hereinafter, the spirally wound layer 6-1 and the inclined code layer 6-1 are collectively referred to as a code layer 6-1 unless it is necessary to distinguish them.

Here, the cord layer 6-1 in the tire
The ratio Rc / Rt of the compression stiffness Rc to the tensile stiffness Rt in the axial direction of the cord 6-1c needs to be in the range of 1/2 to 1/5. The reason is as follows.

That is, the rigidity ratio Rc / Rt of the cord is 1
7 types of tires in which seven types of cords having the same cord tensile strength are applied to the spirally wound layer so as to be / 30, 1/10, 1/6 to 1/2, but with the same number of cords. And the lateral stiffness of these tires is adjusted to a camber angle of 45 °.
FIG. 4 shows a plot of the experimental results measured under the following conditions. The belt had only one layer. FIG. 4 shows the cord rigidity ratio R
It is indicated by an index with the lateral stiffness of the tire at c / Rt = 1/2 being 100. As is clear from FIG. 4, the rigidity ratio Rc / Rt
Decreases, the tire lateral rigidity decreases.

In a tire for a passenger car (radial ply), since a radius of curvature of a tread portion tread surface in a cross section is relatively large,
While the circumferential compression strain of the belt on the tread is small, the two-wheeled vehicle tire has a large camber angle as shown in FIG. 1, so that the radius of curvature of the tread portion 3 tread surface 3 t is extremely small. , The compressive strain in the circumferential direction of the tread portion 3 of the belt 6 is large. Also, the compression strain of the cord 6-1c embedded in the cord layer 6-1 of the belt 6 is large.

In the first place, the cord in rubber exhibits rigidity under the action of tension, and has a characteristic of exhibiting a minimum rigidity under the action of only compressive force, with the rigidity decreasing as the tension decreases. The tire lateral rigidity shows a larger value as the rigidity of the belt 6 increases. Tire lateral stiffness is a very important characteristic for a two-wheeled vehicle tire. This is because when a large camber angle is applied to a tire, a tire having a large lateral rigidity generates a large lateral force and exhibits excellent steering stability performance. Conversely, the smaller the tire has lateral rigidity, the lower the steering stability performance.

When the steering stability performance of the seven types of tires on a real vehicle was tested, when the rigidity ratio became smaller than Rc / Rt = 1/5 (transverse rigidity index 98), the cord rigidity ratio Rc / R
It was found that t was sharply decreased and the steering stability performance was below the permissible level with this. Also,
When the rigidity ratio Rc / Rt = 1/2 to 1/3, the tire lateral rigidity shows a saturating tendency, and the rigidity ratio Rc / Rt = 1 /
A code exceeding 2 is out of the range because it is extremely difficult to manufacture.

The cord layer 6 of the tire belt 6 shown in FIG.
Among the cords of -1, the cord having a rigidity ratio Rc / Rt = 1/30 (transverse stiffness index 89) is the Kevlar cord having the highest rigidity among the organic fiber cords, and is a cord having a circular cross section. The cord having a rigidity ratio Rc / Rt = 1/10 (lateral stiffness index 91) is a Kevlar cord having an elliptical cross section.

Further, the same experiment as described above was carried out for a tire in which two layers of the inclined cord layer having a cord inclination angle of 22 ° with respect to the tire equatorial plane E were applied to the belt, and the same result as above was obtained. I'm sure that.

As is apparent from the above, even if the Kevlar cord has the maximum tensile strength and the maximum rigidity, as long as the organic fiber cord is used, the tire using the cord layer 6-1 at present has the following problems. Regardless of how the structure and cross-sectional shape of the cord are devised, insufficient lateral rigidity is inevitable. Therefore, a steel cord that easily secures rigidity even under a compressing action is applied to the cord 6-1c of the cord layer 6-1.

The steel cord to be applied to the cord 6-1c has a conventional circular cross-section (the shape of a smooth line in contact with the outer surface of the outermost strand constituting the cord, the same applies hereinafter).
However, the steel cord having a flat sectional shape having a large second moment of area along the arrangement direction of the cords 6-1c of the cord layer 6-1 actually leads to an improvement in lateral rigidity and is large. A lateral force can be generated.

This kind of flat-section steel cord has n
Both a conventional steel cord in which (n = 3 to 10) strands are twisted and a single strand type are compatible. When the tensile strengths are matched, a single strand is advantageous for improving the lateral rigidity and improving the steering stability, and which type is selected depends on the level of the steering stability required for the tire.

Steel cord 6-1c having a flat cross section
As shown in FIG. 2, an elliptical cross section or an elliptical cross section (an example of twisting n strands) and a rectangular cross section (single strand) as shown in FIG. All of the examples) are suitable. FIGS. 2 and 3 show a part of the inclined cord layer 6-1 and the unit of spiral winding of the spirally wound cord layer 6-1. In the illustrated example, three steel cords 6-1c are combined. It is assumed to be a unit of spiral winding of a set. Code 6
-1 g is a cord-coated rubber.

In this case, if the steel cord 6-1c has an elliptical cross section or an elliptical cross section, the major axis of the ellipse or ellipse is arranged in the belt 6 as a direction orthogonal to the direction in which the cord 6-1c extends. Also in the case of a rectangular cross section, the long side is arranged as a direction orthogonal to the direction in which the cord 6-1c extends. In the case of an ellipse or an ellipse, the value of the ratio of the major axis to the minor axis is in the range of 1.5 to 5.0. It is desirably within the range of -5.0.

Here, it is difficult to accurately measure the compression stiffness Rc and the tensile stiffness Rt of the cord 6-1c in a state where the cord 6-1c is buried in the tire. Resistance = P / ｛(L / L ₀ ) ×
D｝ (gf / D) and (gf / mm ² ) are applied, and the initial tensile resistance = P / 初期 (L / L ₀ ) × D｝ (gf / D)
, (Kgf / mm ² ). The cylindrical test piece S (FIG. 5) used for measuring the initial compression resistance had a diameter d = 18.
mm and a height h = 48 mm are in line with the actual situation.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire 70 series for a two-wheeled vehicle is for road use, has a size of 120 / 70R17, has a configuration according to FIG.
In the tire of Example 1, the steel cord 6-1c (1) shown in FIG.
× 4 structure, a major axis of 0.8 mm, and a minor axis of 0.5 mm).
The single strand shown in FIG. 3 (long side 1.0 mm, short side 0.5
mm) of the steel cord 6-1c, and the tire of the third embodiment is formed on the inclined cord layer 6-1 of the belt 6 according to the second embodiment.
The same steel cord 6-1c as that of the tire was applied.

The spiral wound layer 6-1 of the belt 6 has 1 × 4 ×
0.23 steel cord (circular cross section, cord diameter 0.
The tire of Comparative Example 1 to which a Kevlar cord of 1670 dtex / 2 (circular cross section, cord diameter 0.63 mm) was applied to the spirally wound layer 6-1 was prepared. The tires of Comparative Examples 1 and 2 were all the same as the tires of Examples except for the belt 6. Also, the cord layers 6 of the tires of Examples 1 to 3 and the tires of Comparative Examples 1 and 2
The tensile strength of cord 6-1c at -1 was matched with the number of cords inserted. Stiffness ratio Rc / Rt of code 6-1c
Is 1 / 3.8 for the tire of Example 1, and Example 2
The tire of No. 3 is 1 / 2.7 and the tires of Comparative Examples 1 and 2 are 1/30.

The tires of Examples 1 to 3 and the tires of Comparative Examples 1 and 2 were mounted on the front of a two-wheeled vehicle, and an experienced rider was used to perform an actual vehicle feeling evaluation test. The test mainly performed slalom running in which the camber angle was 30 to 45 degrees. The rear tires of the tires of Examples 1 to 3 and Comparative Examples 1 and 2 were conventional tires in order to strictly evaluate the steering stability performance of the example tires.

The feeling evaluation result by the actual vehicle test is represented by an index with the tire of Comparative Example 1 being 100, and the tire of Example 1 is 107 and the tire of Example 2 is 1
10, the tire of Example 3 was 116, and the tire of Comparative Example 2 stopped at 100. The larger the index, the better. From this result, it can be seen that the steering stability performance of the example tires 1 to 3 is significantly improved as compared with the comparative example tire.

[0036]

According to the first to eighth aspects of the present invention, in particular, the compression rigidity of the tread portion is advantageously increased, and the lateral rigidity of the tire when a large camber angle is applied is sufficiently increased. Accordingly, it is possible to provide a pneumatic tire for a two-wheeled vehicle, which can significantly improve the steering stability performance accompanying turning.

[Brief description of the drawings]

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

FIG. 2 is a perspective view of a part of a cord layer of a belt of the tire according to the present invention.

FIG. 3 is a perspective view of a part of another cord layer of the belt of the tire of the present invention.

FIG. 4 is a plot diagram showing a relationship between a belt cord rigidity ratio and a tire lateral rigidity.

FIG. 5 is a perspective view of a test piece for measuring compression stiffness.

FIG. 6 is an explanatory diagram for calculating an initial compression resistance.

FIG. 7 is an explanatory diagram for calculating an initial tensile resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 3t Tread surface 4 Bead core 5 Carcass 6 Belt 6-1 Belt cord layer 6-1c Cord of belt cord layer 6-1g Cord covering rubber of cord layer E Tire equatorial plane

Claims (8)

[Claims] At least one ply of radial carcass for reinforcing a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions, and at least one layer for reinforcing a tread portion on an outer periphery of the carcass. In the pneumatic tire for a two-wheeled vehicle provided with a belt comprising a rubber-coated cord layer, the cord of at least one layer of the belt has a ratio (Rc / Rt) of compression stiffness (Rc) to tensile stiffness (Rt) in the cord axis direction. Is in the range of 1/2 to 1/5. 2. The tire according to claim 1, wherein the belt layer of the cord having the ratio (Rc / Rt) is a spirally wound cord layer. 3. The tire according to claim 1, wherein the belt layer of the cord having the ratio (Rc / Rt) is a wound cord layer of the layer. 4. A compression stiffness (Rc) of a cord obtained by applying a compressive force in a cord axial direction to a test piece in which a cord taken out from a tire is embedded in rubber in a cord axis direction.
The initial tensile resistance when a tensile force is applied to the cord taken out of the same tire is defined as the tensile rigidity (R
2. The tire according to claim 1, wherein t). 5. The tire according to claim 1, wherein the cord having the ratio (Rc / Rt) is a steel cord. 6. The tire according to claim 5, wherein the steel cord having the above ratio (Rc / Rt) has a flat cross section in the tire rotation axis direction. 7. The tire according to claim 5, wherein the steel cord having the above ratio (Rc / Rt) has a rectangular cross-sectional shape. 8. The tire according to claim 5, wherein the steel cord having the ratio (Rc / Rt) has one of an elliptical cross section and an elliptical cross section.