JP2003267002A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire less prone to cause an air under tread in a manufacturing process. <P>SOLUTION: A carcass part of the pneumatic tire includes a carcass ply 23 having a bias structure. The carcass ply 23 comprises many parallel cords 29 and topping rubber 31. The parallel cords 29 are buried under the topping rubber 31. Assuming diameter of the cords 29 is A and thickness of the carcass ply 23 is B, the ratio (B/A) exceeds 1.15 and is less than 2.50. Assuming the distance from the center of the cords 29 to the radial outer surface of the carcass ply 23 is α and the distance from the center of the cords 29 to the radial inner surface of the carcass ply 23 is β, the ratio (β/α) exceeds 1.20 and is less than 2.00. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pneumatic tire, and more particularly to improvement of a carcass ply of a pneumatic bias tire.

[0002]

2. Description of the Related Art Pneumatic tires are roughly classified into bias tires and radial tires depending on the structure of a carcass ply. In a bias tire, the cord of the carcass ply extends obliquely with respect to the tire circumferential direction. In this bias tire, local deformation can easily occur due to the low continuity of the carcass portion. In other words,
Bias tires have excellent characteristics (enveloping characteristics) that wrap around road surface protrusions. Therefore, the bias tire is excellent in riding comfort and is also excellent in following the road surface when traveling on rough terrain.
This bias tire is suitable for a vehicle running in a wasteland (for example, an off-road motorcycle or ATV).

[0003] In the manufacture of tires, a preform (called a "green cover") made of carcass ply, bead core, tread rubber and the like is put into a mold and heated and pressed. Upon heating, the rubber causes a crosslinking reaction to obtain a tire. This process is called a vulcanization process. A concave-convex pattern is formed on the inner peripheral surface of the mold, and a tread pattern having a shape in which the concave-convex pattern is reversed is formed in the tread portion by the vulcanization process. In other words, the uneven pattern of the mold has a shape in which the tread pattern is inverted.

[0004]

In the vulcanization process, the tread rubber flows into the recess of the mold. Due to this inflow, the rubber composition may be deficient, and a void may be generated between the tread portion and the carcass portion. This phenomenon is due to AUT (Air
Under / Tread).

Bias tires and ATs for off-road motorcycles
In V bias tires, a tread pattern called a block pattern is often formed in the tread portion. In the block pattern, the tread surface is divided into a large number of blocks by the grooves carved in the tread portion. The recesses of the molding die correspond to the individual blocks, and the volume of each recess is relatively large. Therefore, a large amount of tread rubber flows into the recess, which promotes the generation of AUT. In the manufacture of bias tires, reduction of AUT has become a major issue.

The present invention has been made in view of the above problems, and an object thereof is to provide a pneumatic tire in which AUT is unlikely to occur in the manufacturing process thereof.

[0007]

SUMMARY OF THE INVENTION The invention made to achieve the above object is to provide a tread portion having an outer surface serving as a tread surface, and a pair of sidewalls extending inward in a substantially radial direction from both ends of the tread portion. Section, a pair of bead portions extending further inward in the radial direction from the sidewall portion, and a carcass portion bridged between the bead portions, and the carcass portion includes a carcass ply having a bias structure. The diameter of the cord included in the carcass ply is A, the thickness of the carcass ply is B, and the distance from the center of the cord to the radially outer surface of the carcass ply is α. , The distance from the center of the cord to the inner surface of the carcass ply in the radial direction is β
And the ratio (B / A) exceeds 1.15, 2.5
Is less than 0, and the ratio (β / α) exceeds 1.20 and is 2.0.
It is a pneumatic tire characterized by being less than 0.

In this pneumatic tire, since the ratio (B / A) and the ratio (β / α) are set within the predetermined ranges, AU
T is suppressed.

The AUT suppressing effect is particularly remarkable in the pneumatic tire in which the land ratio L of the tread surface is 10% or more and 50% or less.

Preferably, the ratio (B / A) and the land ratio L
And satisfy the relationship of the following mathematical expression (I). (B / A) ≧ −0.0025 × L + 1.325 −− (I) In this pneumatic tire, the generation of AUT is further suppressed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, with reference to the drawings,
The present invention will be explained in detail based on the preferred embodiments.

FIG. 1 is a sectional view showing a part of a pneumatic tire 1 (hereinafter also simply referred to as “tire”) according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction of the tire 1, and the horizontal direction is the axial direction of the tire 1. The tire 1 has a substantially symmetrical shape centered on the one-dot chain line in FIG. The tire 1 includes a tread portion 3, a sidewall portion 5, a bead portion 7, a carcass portion 9 and an inner liner 11.

The tread portion 3 is made of a crosslinked rubber and has a circular arc shape which is convex outward in the radial direction. The outer surface of the tread portion 3 is
A tread surface 13 that contacts the road surface is formed. The tread surface 13 has a block pattern divided into a large number of blocks 17 by the grooves 15. This block pattern is suitable for running on rough terrain such as a rocky place, rubble, and weak knowledge.

The sidewall portions 5 extend radially inward from both ends of the tread portion 3. This sidewall portion 5 is also made of crosslinked rubber. The sidewall portion 5 is
The flexure absorbs the impact from the road surface. Further, the sidewall portion 5 prevents the carcass portion 9 from being damaged.

The bead portion 7 comprises a bead core 19 and a bead apex 21 extending outward from the bead core 19 in the radial direction. The bead core 19 is annular,
It consists of multiple non-stretchable wires (typically steel wires). The bead apex 21 has a tapered shape that tapers outward in the radial direction and is made of a crosslinked rubber.

The carcass portion 9 is bridged between the bead portions 7 on both sides along the inner peripheral surfaces of the tread portion 3, the sidewall portion 5 and the bead portion 7. Carcass part 9
Is the first carcass ply 23, the second carcass ply 25
And a third carcass ply 27. The first carcass ply 23 and the second carcass ply 25 are the bead core 1
Around 9 is wound from the inner side to the outer side in the axial direction. The third carcass ply 27 is a bead apex 2
It ends inside 1.

The inner liner 11 is joined to the inner peripheral surface of the carcass portion 9. The inner liner 11 is also made of crosslinked rubber. The inner liner 11 is made of rubber having low air permeability. Inner liner 11
Plays a role of maintaining the internal pressure of the tire 1.

FIG. 2 is an enlarged sectional view showing a part of the first carcass ply 23 of the tire 1 shown in FIG. In this figure, the upper side is the outer side in the radial direction of the tire 1, and the lower side is the inner side in the radial direction of the tire 1. Although not shown, the second carcass ply 25 and the third carcass ply 27 are also
It has the same structure and dimensions as the first carcass ply 23. The first carcass ply 23 includes a large number of cords 29 arranged in parallel and a topping rubber 31.
The cord 29 is embedded in the topping rubber 31.
All cords 29 have approximately the same diameter.

The first carcass ply 23 has a bias structure, and the cord 29 extends obliquely with respect to the circumferential direction of the tire 1 (the direction perpendicular to the plane of FIG. 2). The inclination angle of the cord 29 with respect to the circumferential direction is usually 24 ° or more and 45 ° or less.

In FIG. 2, what is indicated by a double-headed arrow A is the diameter (mm) of the cord 29. The double-headed arrow B indicates the thickness of the first carcass ply 23 (m
m). The code 29 is indicated by the double-headed arrow α.
Is the distance (mm) from the center to the radially outer surface of the first carcass ply 23. The double-headed arrow β indicates the distance (mm) from the center of the cord 29 to the radially inner surface of the first carcass ply 23.

In the first carcass ply 23, the ratio (B
/ A) exceeds 1.15 and is less than 2.50,
The diameter A and the thickness B are set. When the ratio (B / A) exceeds 1.15, even if the tread rubber flows into the concave portion of the mold in the vulcanization step, the topping rubber 31 compensates for this and the occurrence of AUT is suppressed. From this viewpoint, the ratio (B / A) is more preferably 1.40 or more.
50 or more is particularly preferable. By setting the ratio (B / A) to be less than 2.50, it is possible to prevent the mass of the tire 1 from increasing. From this viewpoint, the ratio (B / A) is 2.
10 or less are more preferable, and 1.80 or less are especially preferable.

In the first carcass ply 23, the ratio (β
/ Α) is more than 1.20 and less than 2.00,
The distance α and the distance β are set. When the ratio (β / α) exceeds 1.20, the topping rubber 31 is sucked up, the generation of AUT is suppressed, and the open threat is also suppressed. From this viewpoint, the ratio (β / α) is 1.4
0 or more is more preferable, and 1.60 or more is particularly preferable.
By setting the ratio (β / α) to be less than 2.00,
Variations in the distance α and the distance β are suppressed. From this viewpoint, the ratio (β / α) is more preferably 1.80 or less.
70 or less is particularly preferable.

The diameter A and the thickness B are the ratio (B /
It is arbitrarily selected within the range in which A) is achieved. Normally, the diameter A is 0.45 mm or more and 0.8 mm or less, and the thickness B is
Is 0.63 mm or more and 1.68 mm or less. Distance α
And the distance β are arbitrarily selected within the range where the ratio (β / α) in the above range is achieved. Normally, the distance α is 0.3 mm or more and 0.7 mm or less, and the distance β is 0.42 mm or more and 1.26 mm or less. The distance α and the distance β are larger than the diameter A. In other words, the cord 29 is not exposed on the surface of the first carcass ply 23.

The diameter A, the thickness B, the distance α and the distance β are measured at the cut surface of the completed tire 1 cut. If the dimensions are not uniform, randomly selected 2
The diameter A, the thickness B, the distance α and the distance β are measured at 0 points, and the average value of each is calculated. When the cross-sectional shape of the cord 29 is not a circle, the smallest circle among the circles including this cross-sectional shape inside is assumed, and the diameter of this assumed circle is set to the diameter A. Further, the distance α and the distance β are measured with the assumed center of the circle as a reference.

The material of the cord 29 is not particularly limited, and polyamide fiber, rayon fiber, polyester fiber, polyethylene naphthalate fiber, aramid fiber and the like can be preferably used. The fiber thickness is not particularly limited and is usually 94.
Items from 0 to 2100 denier are prized.
Normally, the density of cords 29 (the number per 5 cm) is 30.
It is set to more than 55 ends. The cord 29 may be formed by twisting two or more fibers. In this case, 1
The number of twists per 0 cm is 30 times or more and 55 times or less.

By setting the ratio (B / A) and the ratio (β / α) within the above ranges, AUT is suppressed even in the tire 1 in which the tread portion 3 has a block pattern. In the block pattern, the land ratio L tends to be smaller than in other tread patterns. The land ratio L of the normal block pattern is 10% or more and 50% or less. In the present specification, the land ratio means the ratio of the area of the tread surface 13 excluding the groove 15 to the area of the tread surface 13 when it is assumed that the groove 15 is absent.

FIG. 3 is a graph showing the relationship between the ratio (B / A) and the land ratio L. In this figure, reference numeral S1
Is a straight line represented by the following formula (II). The symbol S2 indicates the following mathematical formula (III)
It is a straight line represented by. What is indicated by reference numeral S3 is
It is a straight line represented by the following mathematical formula (IV). (B / A) =-0.0025 * L + 1.325 --- (II) L = 10 --- (III) L = 50 --- (IV)

The region between the straight line S2 and the straight line S3 and above the straight line S1 (the hatched region in FIG. 3) is particularly A in the block pattern tire 1.
This is a region where UT is unlikely to occur. In this region, the land ratio L is 10% or more and 50% or less, and the ratio (B / A)
And the land ratio L are areas that satisfy the following mathematical expression (I). (B / A) ≧ −0.0025 × L + 1.325 −−− (I)

This tire 1 has three carcass plies 2
Although 3, 25 and 27 are provided, the number of carcass plies is not particularly limited. In a tire including a plurality of carcass plies, it is not necessary for all carcass plies to have the same structure and dimensions. In at least one carcass ply of a tire including a plurality of carcass plies, the ratio (B / A) and the ratio (β / α) are set within the above ranges, whereby the occurrence of AUT is suppressed.

[0030]

The effects of the present invention will be clarified by the following examples, but the present invention should not be construed in a limited way based on the description of the examples.

Example 1 A motorcycle tire having the structure shown in FIG. 1 was manufactured. The size of this tire is 110 / 90-19. The tread surface has a block pattern, and the land ratio L is 25.1%.
Is. The three carcass plies have the same structure. The carcass ply is provided with a cord made of polyester fiber and having a fiber degree of 1100 dtex / 2.
The density of the cord is 48 ends. The cord has a diameter A of 0.51 mm and a carcass ply thickness B of 0.8.
16 mm, the distance α is 0.363 mm, and the distance β is 0.453 mm. Therefore, the ratio (B / A) of this tire is 1.60, and the ratio (β / α) is 1.25.
Is.

[Examples 2 to 8 and Comparative Examples 1 to 3] The same as Example 1 except that a carcass ply having a diameter A, a thickness B, a distance α and a distance β shown in Table 1 below was used. The tires of Examples 2 to 8 and Comparative Examples 1 to 3 were obtained.

[Investigation of AUT Occurrence Rate] 100 tires were manufactured for each example and each comparative example, and the crown portion was cut in the circumferential direction to confirm the presence or absence of AUT. The ratio of tires with AUT is shown in Table 1 below.

[Measurement of Mass] The mass of the above 100 tires was measured. The average values are shown in Table 1 below.

[0035]

[Table 1]

In Table 1, the tire of Comparative Example 1 having a ratio (B / A) of 1.15 or less, and a ratio (β / α) of 1.2.
In the tire of Comparative Example 2 which is 0 or less, the occurrence rate of AUT is high. The tire of Comparative Example 3 having a ratio (B / A) of 2.50 or more has a large mass. On the other hand, the tires of the respective examples have a low AUT generation rate and the mass thereof is not so large. From these evaluation results, the superiority of the present invention is clear.

[0037]

As described above, the pneumatic tire of the present invention is unlikely to cause AUT in its manufacturing process.
This tire is excellent in quality and productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of a first carcass ply of the tire shown in FIG.

FIG. 3 is a graph showing a relationship between a ratio (B / A) and a land ratio L.

[Explanation of symbols]

1 ... Pneumatic tire 3 ... Tread part 5 ... Sidewall part 7 ... Bead part 9 ... Carcass part 11 ... Inner liner 13 ... Tread surface 15 ... groove 17 ... Block 19 ... Bead core 21 ... Bead Apex 23 ... First Carcass Ply 25: Second carcass ply 27 ... Third carcass ply 29 ... Code 31 ... Topping rubber

Claims (3)

[Claims] 1. A tread portion whose outer surface forms a tread surface, a pair of sidewall portions extending inward in a substantially radial direction from both ends of the tread portion, and a pair extending further inward in a substantially radial direction from the sidewall portion. Bead part of
A carcass part provided between the bead parts, the carcass part including a carcass ply having a bias structure, and a diameter of a cord included in the carcass ply is A. When the thickness of the carcass ply is B, the distance from the center of the cord to the radially outer surface of the carcass ply is α, and the distance from the center of the cord to the radially inner surface of the carcass ply is β, Ratio (B / A) is 1.15
And less than 2.50, and the ratio (β / α) is 1.20.
Pneumatic tire characterized by being above and below 2.00. 2. The land ratio L of the tread surface is 10%.
The pneumatic tire according to claim 1, which is 50% or more and 50% or less. 3. The pneumatic tire according to claim 2, wherein the ratio (B / A) and the land ratio L satisfy the relationship of the following formula (I). (B / A) ≧ −0.0025 × L + 1.325 −−− (I)