JPH04215503A - Radial tire - Google Patents

Abstract

PURPOSE:To prevent a shoulder section from uneven wear and early wear in a radial tire of a passenger car by setting the relationship between the factor of belt tire width and belt end camber amount in filling up regular internal pressure to satisfy a specified formula. CONSTITUTION:A factor K of belt tire width is obtained from a ratio BW/TW of effective belt width BW between the outer end points A, A of an effective belt region BE to tire section width TW in filling up regular internal pressure. The factor K and radial distance of tire (belt end camber amount) CH between the inside point B biased inward by 0.2 times effective belt width BW from the outer end point A and the outer point A are set to satisfy the formula I. Also, the radius of an arc passing through a point C on the equatorial surface of tire of the center line in the thickness of a belt layer 7 and an inside point B in the effective region of belt is set larger than 1.4 times the tire section width TW.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire that can effectively suppress uneven wear in the shoulder portion of the tire.

0002

2. Description of the Related Art Pneumatic tires inevitably wear out as they run. Particularly in radial tires, which have been widely used in recent years, a belt layer made of high-tensile cords such as steel cords is placed on the outside of the carcass arranged in the radial direction, giving a large hoop effect, which allows the tread surface to contact the ground. Pressure distribution tends to be uneven, and uneven wear occurs in which the shoulder portion of the tire wears out earlier than the crown portion. Examples of such uneven wear include so-called heel-and-toe wear, in which the front and rear parts of the tread sandwiching the lateral grooves wear out quickly in radial tires for passenger cars, and only the shoulder part seen in tires for heavy vehicles such as trucks and buses. There is such a thing as shoulder drop wear that wears out early.

[0003] Such uneven wear at the shoulder portion occurs because the tread surface has a substantially arc-shaped cross section that includes the tire axis, so the circumferential length of the crown portion is less than the circumferential length of the shoulder portion. Therefore, when the tread surface makes contact with the ground, the crown part forms the trailing side, the shoulder part forms the trailing side, and on the stepping side of the tire, especially the kicking-off side, there is a gap between the tire and the road surface during the kick-off. It is thought that the uneven wear is accelerated by the sliding friction generated in the above.

Conventionally, in order to prevent such uneven wear, the radius of curvature of the tread surface was increased or the blocks in the shoulder portion were increased in size to increase its rigidity, and furthermore, the rigidity of the belt layer was increased, especially in the shoulder portion. Suggestions are being made to strengthen it.

[0005]

[Problems to be Solved by the Invention] However, even with these proposals, the above-mentioned uneven wear has not been sufficiently solved, and when the rigidity of the shoulder block, belt layer, etc. is increased excessively, tire noise , tend to impede ride comfort and performance.

[0006] In the present invention, various experiments were conducted in order to prevent uneven wear of tires, particularly in the shoulder portions. As a result, we focused on the degree of curvature at the end portion of the belt layer, which is a basic component of a radial tire, that is, the amount of belt end camber CH, and determined the belt end camber in relation to the curvature, effective belt width BW, and tire cross-sectional width TW. By setting the amount CH within a predetermined range, they have found a radial tire that can equalize the ground pressure distribution, effectively suppress uneven wear, and that does not impair other tire performance.

[0007] Accordingly, an object of the present invention is to provide a radial tire that can uniformize the distribution of ground pressure and can effectively suppress uneven wear in the shoulder portion. Moreover, this radial tire can be used as a tire for various purposes such as tires for buses and trucks in addition to tires for passenger cars.

[0008]

[Means for Solving the Problems] The present invention provides a carcass with a radial or semi-radial arrangement that goes from the tread part to the sidewall part and folds back at the bead core of the bead part, and a carcass that is arranged radially outside the carcass and inside the tread part. and a belt layer consisting of at least two belt plies using a belt cord, and in a standard state in which the rim is assembled to a regular rim and filled with a regular internal pressure, at least two belt plies overlap. Ratio BW/TW of the effective belt width BW between the outer end points A and A in the tire axial direction of the belt effective area BE, which is the area of the overlapping area extending to the outermost side in the tire axial direction of the overlapping area, and the tire cross-sectional width TW The belt/tire width coefficient K defined as
The outer end point A of the belt effective area on the thickness median line connecting the points equidistant in the tire radial direction from the centers of the belt cords of the two belt plies forming E, and the effective belt width BW from the outer end point A. For the belt end camber amount CH, which is the distance in the tire radial direction between the inner point B on the thickness median line that separates 0.2 times (0.2BW) inward in the tire axial direction, the following equation 1 is calculated. It is a radial tire that satisfies the following relationship.

2.50K-1.25<CH<13.3K-4.65
■

0010

[Operation] In the radial tire of the present invention, the shape of the belt layer is set in a standard state in which the radial tire is assembled on a regular rim and filled with a regular internal pressure. Here, the official rims refer to the JATMA rims published by the Japan Automobile Tire Association.
This is the underlined rim among the applicable rims specified in "YEAR BOOK", and the regular internal pressure is the rim specified in the same JA
Defined as the maximum air pressure for each tire in the TMA air pressure-load correspondence table. In addition to tires for passenger cars, radial tires can also be used as tires for trucks, buses, small trucks, etc.

Furthermore, in the radial tire of the present invention, the belt/tire width coefficient K, defined as the ratio BW/TW between the effective belt width BW and the tire cross-sectional width TW, is determined by the following equation for the belt end camber amount CH: It satisfies the relationship of Eq. 2.50K-12.5<CH<13.3K-4.65
■

In the case of a radial tire, in order to exhibit performance such as handling stability, rolling characteristics, and wear resistance, it is preferable to arrange a belt layer in the ground contact area where the tire contacts the ground under normal load conditions. Furthermore, it is desirable to arrange a belt effective area BE in the ground contact area, which is an overlapping area in which at least two belt plies overlap and can exhibit a sufficient hoop effect due to the intersecting belt cords. Moreover, this belt effective area BE is the area of the overlapping area with the maximum width that extends to the outermost side in the tire axial direction among the overlapping areas, and excessively widening the belt layer in the tire axial direction may deteriorate ride comfort. lower.

On the other hand, in the shoulder portion of the tread portion, the belt layer curves toward the sidewall portion of the tire, thereby forming a curved surface with a smaller radius of curvature than that in the crown portion.

The present inventors conducted various experiments in order to prevent uneven wear in the shoulder portion. As a result, it was found that the radius of curvature of the belt layer at the shoulder portion is related to the uneven wear of the shoulder portion, and
The following findings were obtained.

The first is that uneven wear in the shoulder portion correlates with the radius of curvature of the belt layer in the shoulder portion, and especially in the belt effective area BE, which is the outermost overlapping area in the axial direction of the tire where two belt plies overlap. is relevant. Here, the belt effective area BE is an area of the overlapping area extending to the outermost side in the tire axial direction among the overlapping areas where at least two belt plies overlap. Therefore, when consisting of two belt plies, the width of the narrow belt ply is the effective belt width BW, and when consisting of three or more belt plies, the width of the second widest belt ply is the belt effective area. Becomes BE.

Second, in the belt effective area BE,
The area that affects uneven wear and early wear is the outer end point A of the belt effective area BE in the tire axial direction, and the inner side that is separated from this outer end point A by 0.2 times the effective belt width BW in the tire axial direction. The region between point B and uneven wear and early wear are affected by the degree of curvature of the region. In addition, the effective belt width BW refers to the belt effective area B.
It is defined as the length in the tire axial direction between the tire axial outer end points A and A of E.

The degree of curvature is determined by a thickness center line L connecting points equidistant in the tire radial direction from the respective centers of the belt cords of the two belt plies forming the belt effective area BE.
It is given by the belt end camber amount CH, which is the distance in the tire radial direction between the outer end point A and the inner point B at the top.

Thirdly, in order to prevent uneven wear and early wear, the belt end camber amount CH is defined as the ratio BW/TW of the effective belt width BW and the tire cross-sectional width TW. It is to be set within the range of the equation (2) which is linearly correlated with the coefficient K.

[0019] CH<13.3K-4.65 ■

This is based on the results shown in FIG. 6, which were measured on tires having various belt end camber amounts CH and belt/tire width coefficients K while changing the number of belt plies, aspect ratio, and tire type.

In FIG. 6, mark shapes such as circles and squares indicate the tire sizes shown in the figure, and black marks indicate cases where uneven wear or early wear has occurred. As is clear from FIG. 6, regardless of the above-mentioned aspect ratio, number of belt plies, and tire type, uneven wear and early wear occur in relation to the belt/tire width coefficient K and the belt end camber amount CH. The area in which this does not occur is given by the equation (2) above.

By setting the belt end camber amount CH to a value less than or equal to the value obtained from the equation (2), the degree of curvature of the belt layer at the shoulder portion is reduced. , as the belt layer deformation line X after ground contact is shown by the dashed dotted line, the belt layer deforms smoothly and continuously in the tire radial direction from the crown part to the shoulder part upon contact with the ground, and further deforms between the crown part and the shoulder part at the time of contact with the ground. By reducing the difference in the amount of deformation of the belt layer in the tire radial direction and suppressing the amount of deformation at the end of the belt layer, the ground pressure is made uniform and the amount of slip between the shoulder portion and the road surface is reduced. It is thought that wear and early wear can be reduced.

A more preferable range for the belt end camber amount CH is the formula (2).

CH<10.0K-3.0 ■ Fourthly, when the belt end camber amount CH is excessively small, the ground pressure at the shoulder portion increases,
Particularly when turning, this shoulder portion suffers a great deal of wear. Therefore, the belt end camber amount CH is set to be larger than the value given by the equation (2). A more preferable range is the formula (2).

CH>2.50K-12.5 CH>6.67
K-3.33 (2) Therefore, from the equations (2) and (2), the preferable range of the belt end camber amount CH is determined by the equation (2) above. 2.50K-1.25<CH<13.3K-4.65
(2) Deformation of the belt layer due to contact with the ground can be measured using a CT scanner.

[0026] Regarding the formula (■), the belt effective area BE
However, when the width is set to be approximately the same as the tire contact patch, the belt/tire width coefficient K, which is the ratio between the effective belt width BW and the tire cross-sectional width TW, tends to increase as the tire oblateness decreases. Therefore, it can be qualitatively reasoned that a tire with a small aspect ratio has a relatively large effective belt width BW, and therefore a relatively large belt end camber amount CH can be adopted.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a standard state in which the radial tire 1 is mounted on a regular rim R and filled with a regular internal pressure. Here, the regular rim means JATM as mentioned above.
This is the underlined rim among the applicable rims specified in the AYEAR BOOK, and the normal internal pressure is defined as the maximum air pressure of each tire in the air pressure-load correspondence table in the above regulations. In the figure, a radial tire 1 has a tread part 2, sidewall parts 3 extending radially inward from both ends of the tread part 2, and bead parts 4 provided at both ends of the tread part 2. It includes a carcass 6 that is folded back from the inside to the outside and is locked, and a belt layer 7 that is arranged on the outside of the carcass 6 in the radial direction. Further, in this embodiment, a band layer 9 is provided which is disposed on the radially outer side of the belt layer 7.

The carcass 6 includes an inner layer 6A surrounding the bead core 2, and an outer layer 6B disposed along the outer surface of the inner layer 6A.
The folded end 6A1 of the inner layer 6A is discontinued above the bead core 5, and the folded end 6B1 of the outer layer 6B is discontinued near the maximum width position of the tire. Note that the carcass 6 may have another structure, and may also include a reinforcing layer to prevent friction between the inner layer 6A and the bead core 5, which moves due to deformation caused by the tire's contact with the ground, etc., and to increase the rigidity of the bead portion, and to prevent rim slippage. A chafer (both not shown) or the like may also be provided. Note that the band layer 9 may also be omitted. Further, the bead portion 4 is provided with a bead apex 10 made of a rubber material that tapers outward in the radial direction from the bead core 5 to improve lateral rigidity. The carcass 3 has a radial or semi-radial structure in which the carcass cord is arranged at an angle of 60 to 90 degrees with respect to the tire equatorial plane CO, and the carcass cord is made of organic fibers such as nylon, rayon, polyester, etc. in addition to steel cord. Code can be used.

In this example, the belt layer 7 is composed of a stacked body of two inner and outer belt plies 7A and 7B, and the width W7A of the inner belt ply 7A on the carcass 6 side is the width of the outer belt ply 7B. It is approximately 1.01 to 1.20 times wider than W7B, and the outer belt ply 7B is set to have a width approximately equal to the ground plane. By using wide and narrow plies in this way, it is possible to prevent a concentration of a difference in rigidity between the belt plies 7A and 7B and the surrounding rubber due to the outer edges of the belt plies 7A and 7B coinciding in the tire axial direction. ing.

In this example, an overlapping area is formed in which the belt plies 7A and 7B overlap in the width of the outer belt ply 7B, and in this example consisting of two belt plies 7A and 7B, this overlapping area is Configure the belt effective area BE.

The belt plies 7A, 7B are made of steel cords, and the steel cords are inclined at an angle of about 10 to 30 degrees with respect to the tire equator, and intersect with each other by the inner and outer belt plies 7A, 7B. By arranging the tires in such a way as to improve the uniformity of the tires. In addition, Figure 3
, for example, three belt plies 7A, 7 as shown in FIG.
B, 7C can also be used, and the outer belt ply 7B
can be made wider than the inner belt ply 7A.

Furthermore, the inner belt ply 7A may be separated from the carcass 6 at the outer side in the tire axial direction, and in this case, a breaker cushion rubber (not shown) is provided at the separated part.
It is better to arrange

[0034] The band layer 9 also has an inner belt ply 7.
It covers the outer surface end of the outer belt ply 7B starting from the outer end of A, and its width W9 is equal to the width W of the belt ply 7A.
It is set at 15-40% of 7A. Further, the band layer 9 is made of a band ply using band cords, and the band cords are made of relatively extensible organic fibers such as nylon, polyester, and rayon. Thereby, it is possible to follow the expansion and contraction of the belt layer 7 when the tire is deformed, and separation between the belt layer 7 and the belt layer 7 can be prevented. The band cords are arranged substantially parallel to the tire equatorial plane CO, that is, in a range of 0° to 10°, preferably 0° to 5°, with respect to the tire equator C. be placed approximately parallel to. This band layer 9 can reduce the difference in rigidity between the ends of the belt layer 7, make the ground pressure distribution uniform, improve the steering stability at high speeds, and even out wear. In addition to tires for passenger cars, radial tires can also be used as tires for trucks, buses, light trucks, etc.

Furthermore, the radial tire 1 of the present invention has a ratio BW/TW of the effective belt width BW and the tire cross-sectional width TW.
The belt/tire width coefficient K defined as follows satisfies the relationship (■) with respect to the belt end camber amount CH.

2.50K-1.25<CH<13.3K-4.65
■

The effective belt width BW is defined as the length in the tire axial direction between the outer end points A and A of the belt effective area BE. The belt effective area BE is an area of the overlapping area where at least two belt plies overlap, which extends to the outermost side in the tire axial direction. Therefore, as in this embodiment, two belt plies 7A
, 7B, the width of the narrow belt ply 7B becomes the effective belt width BW, as described above. Moreover, as shown in FIGS. 3 and 4, three or more belt plies 7A, 7B,
7C, the width of the second widest belt ply becomes the belt effective area BE.

Furthermore, the tire cross-sectional width TW refers to the JAT
As stipulated in MA YEAR BOOK, it is the maximum width of a tire excluding the pattern, letters, etc. on the side of the tire from the total width of the tire. Also, the belt end camber amount CH
means the outer end point A of the belt effective area BE, and the distance from the outer end point A to 0.2 times the effective belt width BW (0.2BW
) is the distance in the tire radial direction of the outer area OP between the inner point B that separates the inner point B in the axial direction of the tire, and the outer end point A,
The inner point B is located within the belt effective area BE, as shown in FIG.
Belt cord D of two belt plies 7A and 7B forming a
1 and D2 at equal distances a and a in the tire radial direction from the centers D1C and D2C, that is, on the thickness center line L, which is a curve connecting the equidistant points. As described above, the equation (2) is based on the results shown in FIG. 6, which were measured using various types of tires while changing the belt end camber amount CH and the belt/tire width coefficient K. In FIG. 6, black marks indicate cases where uneven wear or early wear occurs. As is clear from FIG. 6, in relation to the belt/tire width coefficient K and the belt end camber amount CH, there is a linear correlation in the area where uneven wear does not occur.
Belt end camber amount CH that does not cause uneven wear or early wear
is expressed by the following formula.

[0039] CH<13.3K-4.65 ■

By setting the belt end camber amount CH to a value less than or equal to the value obtained by the equation (2) using the belt tire width number K, the belt layer deformation line X shown by the dashed line in FIG. , as the broken line indicates the belt layer before ground contact, the belt layer smoothly continues in the radial direction of the tire from the crown part to the shoulder part upon contact with the ground, and the belt layer in the tire radial direction between the crown part and the shoulder part during contact with the ground. The uneven wear and early wear can be reduced by reducing the difference in the amount of deformation at the end of the belt layer and by suppressing the amount of deformation at the end of the belt layer, thereby equalizing the ground pressure and reducing the amount of slippage between the shoulder portion and the road surface. it is conceivable that. $Also belt end camber amount C
A more preferable range of H is the formula (■).

[0041] CH<10.0K-3.0 ■

On the other hand, if the belt end camber amount CH is too small, the ground pressure at the shoulder portion increases when the belt touches the ground, and wear at the shoulder portion becomes large, especially when turning. Therefore, the belt end camber amount CH is set to be larger than the value given by the equation (2). A more preferable range is the formula (2). Therefore, based on the above, the preferable range of the belt end camber amount CH is expressed by the formula (2).

[0043] CH>2.50K-1.25 ■

[0044] CH>6.67-3.33 ■

[Specific Example] Tires having the structure shown in FIG. 1 (however, without using a band layer) and having a tire size of Z15/60R15 90H were prototyped as Examples 1 to 3 according to the specifications shown in Table 1. In addition, the products shown in Comparative Examples 1 to 3 in Table 2 were also prototyped and compared with the Example products in terms of uniformity of wear, durability against cornering wear, and handling performance.

Durability was determined by a step speed test using ECE30, and the results are shown in Tables 1 and 2. In addition, each tire was attached to a 3000cc rear-wheel drive passenger car, and the handling performance was measured by a feeling test and the results were evaluated. This test was performed on a flat road at a speed of 80km/h.
Measurements were taken while driving around a curve at m/h.

[0047] The wear condition was also tested by an actual vehicle test. All tires were evaluated after running the tires under rated load for 3000 km. Also, cornering wear is at a radius of 50m.
The vehicle was evaluated by making 500 turns on the circumference of the vehicle at a speed of 40 km/h and measuring the amount of wear on the shoulder portion. All evaluations were made using an index with Comparative Example 1 as 100, and are shown in Tables 1 and 2. In both cases, the larger the value, the better.

[0048]

[Table 1]

[0049]

[Table 2]

[0050] All of the Example products had no uneven wear compared to the Comparative Example products, and were worn uniformly.

[0051]

As described above, the ground pressure distribution of the radial tire of the present invention is made uniform, and uneven wear of the shoulder portion is prevented. It can also effectively prevent wear on the shoulder part during turning.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a thickness center line.

FIG. 3 is a sectional view showing another example of the belt ply.

FIG. 4 is a sectional view showing another example of the belt ply.

FIG. 5 is a cross-sectional view illustrating tire deformation.

FIG. 6 is a graph illustrating test results.

[Explanation of symbols]

2 Tread part 3 Sidewall section 4 Bead part 5 Bead core 6 Carcass 7 Belt layer

Claims (1)

[Claims] Claim 1: A carcass with a radial or semi-radial arrangement that goes from the tread part to the sidewall part and folds back at the bead core of the bead part, and a belt cord arranged radially outside the carcass and inside the tread part. in the axial direction of the tire within the overlapping area where at least two belt plies overlap in the standard state in which the rim is assembled on a regular rim and filled with the regular internal pressure. The effective belt width BW between the outer end points A and A in the tire axial direction of the belt effective area BE, which is the overlapping area extending to the outermost side, and the tire cross-sectional width TW
The belt/tire width coefficient K, defined as the ratio BW/TW, is on the thickness median line connecting points equidistant in the tire radial direction from each center of the belt cord of the two belt plies forming the belt effective area BE. an outer end point A of the belt effective area;
From the outer end point A to 0.2 times the effective belt width BW (0
．． A radial tire that satisfies the following relationship (2) with respect to the belt end camber amount CH, which is the distance in the tire radial direction between the inner point B on the thickness median line that separates the radial tire (2BW) inward in the tire axial direction. 2.50K-1.25<CH<13.3K-4.65
■