JPH06143919A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a light and low rolling resistant pneumatic radial tire which maintains equal steering stability to that of a steel belt radial tire by employing a polyamide fiber monofilament for a fiber cord of a radial carcass and employing a twisted cord layer of alamide fiber for a fiber cord of a belt. CONSTITUTION:A monofilament cord consisting of polyamide fiber or polyester fiber is used for a fiber cord of a carcass 1, and at least two layers in a belt 2 employ a twisted cord layer consisting of at least one fiber selected from alamide fiber and polyvinylalcohol fiber for each of their cords. Then, at least one layer among the twisted cord layers is used as a separation layer, and the ratio alpha/beta is in the range of 0.80-1.15, when an average inclination against the tire meridian cross section direction for a cord inside the same layer of the separation layer is represented by alpha deg. in the center area while represented by beta deg. in both of the end part, areas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for an automobile which meets the social demand for environmental protection and is economical and capable of safe driving, and more particularly, a steel cord is used for each layer of a belt. In comparison with so-called steel belt radial tires, the carcass and the cords of each layer in the belt are used as fiber cords to realize a significant weight reduction, while at the same time reducing rolling resistance and exhibiting equivalent steering stability. And a pneumatic radial tire suitable for buses.

The relationship between tires and the social environment and social needs will be described below. In recent years, the problem of global warming due to the increase of atmospheric CO ₂ and the health problem caused by the increase of atmospheric COx and NOx in the urban space to the human body have been taken up seriously by society as serious problems. It became so. Furthermore, in preparation for future depletion of fossil fuels, there has been a strong demand for energy saving of fuels.

Under the above-mentioned social environment, there is an increasing public opinion that automobiles are required to improve fuel consumption efficiency and reduce exhaust gases such as COx and NOx.
In relation to this demand, regarding tires, there has been a strong demand for further reduction of tire weight and further reduction of rolling resistance, which contributes to reduction of running resistance of automobiles. In addition, in connection with the reduction of fossil fuel consumption, the ease of reuse of used tires is strongly required.

[0004]

BACKGROUND OF THE INVENTION Almost all tires for passenger cars are pneumatic radial tires at the present time, and these tires are steel belt radial tires exhibiting excellent steering stability. This excellent performance is achieved by using steel cords with high tensile rigidity and compression rigidity in comparison with fiber cords for the belt, and by laminating multiple layers of this belt so that the steel cords cross each other, the belt has high bending rigidity. It comes from having.

In the passenger car tire, one organic fiber such as nylon or polyester is extremely thin, for example, a large number of filaments of 1 denier to 10 denier per filament are bundled and twisted. Fiber cord is used for carcass plies.
This steel belt radial tire is used not only in passenger cars but also in light trucks and light trucks.
For medium or large truck and bus tires,
Due to the above excellent performance, the usage ratio of so-called steel radial tires using steel cords for both the carcass and the belt is extremely high.

[0006]

However, although the steel belt radial tire and the steel radial tire described above certainly exhibit excellent steering stability, they cannot meet the above-mentioned changes in social environment and social demands. was there. First, there is a problem in that the weight reduction of the tire is limited by using the steel cord, and it becomes impossible to achieve the required weight reduction without sacrificing durability and excellent performance. At the same time, there is a problem that the rolling resistance is limited due to the heavy weight of the tire.

Secondly, at the end of wear of the tread rubber layer, there are many opportunities to receive deep cut scratches reaching the belt. Therefore, when the used tire is regenerated, the corrosion of the steel cord of the belt due to the cut scratches is promoted. Or, there is a problem that recap is impossible due to separation occurring near the cut scratch. Further, when reused as fuel, there is a problem that cutting and handling of the tire is difficult due to the steel cord having high strength.
The above-mentioned problems relating to reuse develop into problems that prompt the disposal of used tires.

In addition to the above-mentioned steel belt tires, tires using twisted cords of organic fiber or inorganic fiber in each cord layer of the belt are well known. However, this type of tire has a problem that it is not possible to obtain excellent or nearly equivalent excellent steering stability in comparison with a steel belt tire. This deterioration in performance is due to the problem that both the bending rigidity and the compression rigidity of the tread portion are largely insufficient as compared with the tread portion of the steel belt tire.

In order to avoid the above-mentioned deterioration in performance, there is known a tire provided with a belt composed of multiple layers of fiber cords. However, this tire has a problem that it goes against the demand for weight reduction and the demand for reduction of rolling resistance, and there is a problem that performance improvement corresponding to cost increase due to weight increase and productivity decrease cannot be achieved.

Although the above description has been made on a steel belt tire, a steel tire using a steel cord for the carcass together with the belt has the same problem.

Therefore, an object of the present invention is to further reduce the weight in comparison with steel belt tires and steel tires, and at the same time, to have excellent steering stability equivalent to that of the comparison tire, and to reduce rolling resistance more than the comparison tire. Another object of the present invention is to propose a pneumatic radial tire that further enhances the reusability of used tires.

[0012]

In order to achieve the above object, a pneumatic radial tire of the present invention is a radial carcass of one or more plies consisting of fiber cords, which spans in a toroidal shape between a pair of bead cores, and a radial carcass thereof. In a pneumatic tire comprising a belt composed of a plurality of fiber cord layers arranged on the outer periphery of the belt, and a tread rubber layer arranged further on the outer periphery of the belt, the fiber cord of the radial carcass is polyamide fiber or polyester. A monofilament cord of fibers, at least two layers of the belt, each fiber cord is a twisted cord layer of at least one fiber of aramid fibers or polyvinyl alcohol fibers and at least one of these layers is a cut layer, Code in the same layer of the cut-off layer Assuming that the average inclination angle with respect to the meridional section direction of the tire is (α) degrees in the central region of the layer and (β) degrees in both side end regions of the layer, the ratio of (β) to (α) (β / α ) Is within the range of 0.80 to 1.15.

In an embodiment of the present invention, the radial carcass has two or more plies, and the plies adjacent to each other are laminated so as to intersect each other at an angle of the fiber cord with respect to the tire equatorial plane of 70 ° or more and less than 90 °. Pneumatic radial tires are desirable.

In another embodiment of the present invention, a pneumatic radial tire in which the fiber cord of at least one ply of the radial carcass has an angle of 90 ° with respect to the tire equatorial plane can be provided.

Hereinafter, the present invention will be described more specifically with reference to the drawings. FIG. 1 shows a cross section in the width direction of the pneumatic radial tire of the present invention with respect to the left half of the tire equatorial plane E. 1 is one or more plies (1 ply in the example of the figure) consisting of a fiber cord extending between a pair of bead cores 3 (only one side is shown in the figure). Radial carcass 2 is a plurality of fiber cord layers arranged on the outer periphery of the radial carcass 1. It is a belt composed of layers (two layers in the example shown). The belt 2 shown in the figure comprises a fiber cord layer 2a on the inner side in the tire radial direction and a fiber cord layer 2b on the outer side thereof. A tread rubber layer 4 is arranged further on the outer periphery of the belt 2, and sidewalls 5 are continuous with both sides of the tread rubber layer 4 and extend to the bead portion.

The fiber cord of the radial carcass 1 is a monofilament cord of polyamide fiber or a monofilament cord of polyester fiber. The monofilament cord is different from ordinary fiber cords for tires, and is made of one filament cord, and its denier number is preferably 1,000 or more and 10,000 or less. More preferably, this denier number is 2
000 or more and 6000 or less.

FIG. 2 shows three examples of the cross-sectional shape of the monofilament cord taken along a plane perpendicular to the central axis of the length direction. In FIG. 2A, the major axis is L ₁ and the minor axis is L _2.
2B shows a monofilament cord having a substantially elliptical cross section, and in FIG. 2B, an oblong shape in which both sides of a rectangular major axis L ₁ are substantially arcuate and substantially parallel portions are provided on the minor axis L ₂ side. A monofilament cord having a cross section is shown. Further, FIG. 2 (c) shows a monofilament cord having a substantially circular cross section in which L ₁ and L ₂ are equal to each other and L is the same. Where the value of L ₁ / L ₂ is preferably set to 1.0 to 5.0, more preferably L ₁
The value of / L ₂ is 2.0 or more and 5.0 or less.

At least two layers of the belt 2, and in the example shown in FIG. 1, two layers of the cord layers 2a and 2b have a fiber cord of these layers as a twist cord layer of at least one fiber of aramid fiber or polyvinyl alcohol fiber. In this case, the cords of the cord layers 2a and 2b may be twisted cords of one of the above fibers or twisted cords of different fibers.

The twisted cord of each of the aramid fiber and the polyvinyl alcohol fiber has a dynamic elastic modulus E'value of 0.7 × 10 ¹¹ dyn / cm ² or more and 5.0 ×.
10 ¹¹ dyn / cm ² or less is preferable, and
The denier number is preferably 400 or more and 10,000 or less. The dynamic elastic modulus E'is a value measured at 100 ° C and 30 Hz using a viscoelastic spectrometer.

At least one of the cord layers 2a and 2b is a cut cord layer having cord terminals at both ends thereof. Further, the cord layers 2a and 2b are preferably laminated so that the cords intersect the tire equatorial plane E with their inclination directions different from each other.

In the cut-off cord layer, the average inclination angle of the cords in the same layer with respect to the meridional section direction of the tire is (α) degrees in the central region of the cut-off cord layer and (β) degrees in both side end regions of the layer. And when this (β)
The value of the ratio (β / α) to (α) of 0.80 to 1.1
It is within the range of 5. The value of this ratio is 0.90
It is more preferable to set it to 1.10.

The above-mentioned (α) and (β) will be described in more detail with reference to the drawings. In FIG. 1, Ca and Cb represent the widths of the central regions of the code layers 2a and 2b, respectively, and S
a and Sb represent the widths of the end regions of the respective layers. W
a and Wb represent the widths of the code layers 2a and 2b, and the end regions Sa and Sb have portions that overlap each other.

FIG. 3 is an expanded view of the code layer 2a shown in FIG. The XX line is a line of intersection between the tire equatorial plane E and the cord layer 2a. The ZZ line is a line orthogonal to the XX line and coincides with the tire meridional section direction.

As shown in FIG. 3, in the central region Ca, 1/6 of the width Wa of the cord layer 2a is Z− from the tire equatorial plane E.
The areas are divided in the direction along the Z line. Therefore, the central area Ca has a width of 1/3 of the code layer 2a.
The end region Sa has a width 1/6 of the width Wa of the code layer 2a. The central region Cb and the end region S of the code layer 2b
The same applies to b.

In FIG. 3, the code of the code layer 2a is represented by a single code K. K shown by a solid line is an actual cord arrangement of the cord layer 2a in the belt 2 of the tire, and a two-dot chain line portion shows an extension line of the cord K in the central region Ca.

In FIG. 3, the central region C of the code layer 2a.
The average value of the inclination angle (angle of the tangent line) of the code K included in a with respect to the ZZ line is indicated by (α). Similarly, the average value of the inclination angle (angle of tangent line) of the code K included in the both side end regions Sa with respect to the ZZ line is (β). Although the code layer 2a is shown in FIG. 3, the same applies to the code layer 2b.

The above (α) in the code layers 2a and 2b
Is preferably 60 ° to 80 °, and 65 ° to 75 °
Is more preferable.

Next, the tendency of the inclination angle of the cord of each belt layer in the conventional pneumatic radial tire will be described with reference to FIGS. 7 and 8. FIG. 7 shows a part of a widthwise cross section of a pneumatic radial tire, and FIG. 8 shows a belt 2 of this tire.
Two code layers are developed and the code K is represented by one. As shown in FIG. 7, the crown portion of the tread rubber layer 4 has a crown radius R centered on the inside of the tire according to a convention in order to equalize the ground contact pressure. The thickness of the tread rubber layer is substantially uniform in the width direction, or is increased at both end portions of the tread rubber layer. Therefore, the diameter Dc of the belt 22 on the tire equatorial plane E and the belt 22
The relationship with the diameter Df at the side edge of is Dc> Df.

Therefore, the cord of each layer of the belt 22 having a substantially uniform inclination angle at the member stage does not have a uniform inclination angle in the product tire, and as shown in K of FIG. Is the inclination angle (α) degree and (αo) degree at the central portion and both end portions in the width direction with respect to the line ZZ.
> Αo, and the difference between these angles is large.

The relationship between the α degree and the β degree in the present invention can be easily obtained by processing the member before forming the cord layers 2a and 2b by the means illustrated in FIG. 4, for example. FIG. 4 shows a member 1 which becomes the code layer 2a or 2b.
2 is an expanded view of K, and K represents a single code as a representative as in the above. The xx line is a line corresponding to the XX line of the cord layer in the tire. F
Is a strip-shaped pressing tool, and Rs and Rt are rotating bodies.

The width of the pressing tool F is the code layer 2a or 2b.
It is preferable that the width is substantially equal to the width of the central region Ca.
The portions where the rotating bodies Rs and Rt overlap with the code layer member 12 are preferably substantially equal to or less than the end region Sa. The support (not shown) of the cord layer member 12 is made of a hard material at the portion where the pressing tool F contacts the cord layer member 12, and the rotating bodies Rs and Rt are the cord layer member 12.
It is preferable that the portion that comes into contact with is made of a flexible material that is easily deformable. The support 12 is a flat or cylindrical drum.

The code layer member 12 is placed or wound around the support, the code layer member 12 is pressed and fixed by the pressing tool F, and the rotating body Rs on the right side of FIG. 4 is fixed to the code layer member 12.
A predetermined pressure is applied to and brought into contact with, and moved while rotating upward in FIG. 4 (direction of arrow). Due to the tangential force in the direction of the arrow between the rotating body Rs and the cord layer member 12 and the flexible material of the support body that is easily deformed, the cords at both end portions of the cord layer member 12 are, as shown in the drawing, two points before processing Plastic deformation is performed from the position of Ko shown by the chain line to the position of K shown by the solid line. See also FIG.
The same result as described above can be obtained by rotating the rotating body Rt on the left side of FIG.

The above-mentioned processing of the cord layer can be achieved by rotating the drum and the cord layer member 12 in the forward and reverse directions when a drum or the like is used as the support. In this case, one layer of the belt 2 is processed, which is suitable for production of many kinds.

When the same processing is performed on a large number of code layers, the support may be a flat surface and the long code layer member may be continuously processed. In either case, the rotating body R
The rotation and movement of s and Rt have a relative relationship with the code layer member 12. That is, the rotating bodies Rs and Rt may be rotated and moved, or the code layer member 12 may be rotated or moved. Further, when the support body is flat, instead of the rotating body, both end portions of the cord layer member 12 are clamped along the length direction thereof, and these clamp tools are attached to the xx section.
The above-mentioned processing may be performed by moving in opposite directions parallel to the line.

In the embodiment of the present invention, the radial carcass 1 can be composed of two or more plies. In this case, the inclination angle of the cord of each ply with respect to the tire equatorial plane E is set to 70 ° or more and less than 90 °, and the cords of adjacent plies intersect with the tire equatorial plane E in different inclination directions. It is desirable to stack plies.

In another embodiment of the present invention, the fiber cord of at least one ply of the radial carcass 1 may have an inclination angle of 90 ° with respect to the tire equatorial plane E.

Another example of the belt of the present invention is shown in FIGS. FIG. 5 shows a main part of a widthwise cross section of a pneumatic radial tire according to another embodiment. In FIG. 5, reference numeral 12 is a belt, and the belt 12 is composed of a cord layer 12a on the side close to the carcass and a cord layer 12b on the outside of this layer. The cord layer 12a is a cut-off belt layer having cord ends at both ends thereof, and the cord layer 12b is a so-called fold type cord layer having end portions on both sides thereof folded back inward. The width Gb of the folded back portion is preferably in the range of 5% to 50% of the width Wb of the code layer 12b. More preferably, it is set to 5% or more and 30% or less.

The value of the inclination angle (α) of the cord in the central region Cb of the cord layer 12b is the cord layer 2b.
The value is in the same range as, and the processing for obtaining the value of β is not necessarily required. The cords of the cut-off cord layer 12a satisfy the above relationships (α) and (β).

FIG. 6 shows an essential part of a cross section in the width direction of a pneumatic radial tire according to still another embodiment. The belt of this embodiment is the belt 2 shown in FIG. 1, the cap belt 13 on the outer peripheral side of the belt 2, and the cap belt 13 further.
And a so-called layer 14 disposed on both side ends of the belt on the outer peripheral side. Cap belt 13 and layer 1
No. 4 has a configuration in which the organic fiber cords whose respective reinforcing cords are relatively easily stretched extend substantially along the tire equatorial plane E. It is preferable that the width Wm of the cap belt 13 has a margin and is equal to or larger than the maximum width of the belt 2, that is, the width Wa of the cord layer 2a in the example of FIG. The layer 14 is a narrow layer that covers both end portions of the maximum width end of the belt 2, and the width Wn of the layer is Wn.
It is desirable to be 5% or more and 20% or less of a.

[0040]

First, the cord of the radial carcass 1 is a monofilament cord having the cross-sections illustrated in FIGS. 2 (a), (b) and (c), so that the tension in the radial carcass can be reduced in comparison with the conventional twisted cord. rigidity,
It is possible to significantly increase the compression rigidity and the bending rigidity at the same time.

Next, the cords of the cord layers 2a and 2b provided on the outer circumference of the radial carcass are attached to the tire equatorial plane E at 1
A cord which forms a number of rhombuses by intersecting each other at an inclination angle of 0 ° to 30 °, or 15 ° to 25 °, a monofilament cord of a radial carcass having high rigidity crosses in the width direction, Since a strong truss structure having high rigidity is formed, the steering stability of the tire can be highly enhanced. In this case, the monofilament cord of the radial carcass mainly acts as a tension member.

If the radial carcass is 2 plies or more, the above various rigidity can be further enhanced, and the inclination angle of the cords of these plies with respect to the tire equatorial plane E is 70 ° or more and less than 90 °, and the ply of the adjacent plies is not increased. By crossing the cords with each other, it is possible to increase various rigidity not only in the crown portion but also in the sidewall 5, and further improve the steering stability.

Furthermore, by using a twisted cord of aramid fiber or polyvinyl alcohol fiber having a high dynamic elastic modulus E'for the cords of the cord layers 2a and 2b, the tensile rigidity, compression rigidity and bending rigidity of the truss structure can be improved. It is possible to raise it further. By providing this strong truss structure on the belt 2, it becomes possible to impart rigidity to the crown portion of the tread rubber layer 4 that is comparable to the various rigidity of the pneumatic radial tire using a steel belt.

Thus, the steering stability obtained based on the rigidity of the crown portion can be made equal to that of the steel belt radial tire, and at the same time, the weight can be further reduced in comparison with the steel belt tire.

Furthermore, as described with reference to FIG. 8, the conventional tire has a cord inclination angle α in the end region of each belt layer.
Since o becomes a remarkably smaller angle than the inclination angle α of the central region, the various rigidity in this end region is reduced, which leads to a reduction in steering stability.However, in the present invention, The value of the ratio (β / α) of the average inclination angle (β) in the end region of the cord K of the cut-off cord layer 2a to that angle (α) in the central region is 0.8 to 1.15.
By so doing, it is possible to maintain the various rigidity of the end region of the belt 2 at a high level, which contributes to obtaining higher steering stability.

Here, the denier number of the monofilament cord is set to 1000 or more because if it is less than 1000, the function as the tension member of the truss structure becomes insufficient, and if the denier number exceeds 10,000. Since a large stress is applied to the end portion of the monofilament cord at the end edge of the carcass portion in which the carcass 1 is folded back around the bead core 3 from the tire inner side to the outer side, there is a possibility that a failure such as separation may occur at this end portion. Is.

The value of (β / α) is set within the range of 0.80 to 1.15 because the code layer 2 has a value smaller than 0.80.
This is because the rigidity of both side end regions of the cut-off layer such as a is reduced to an undesired degree, and desired high steering stability cannot be obtained. If the value is larger than 1.15, the load of tension in both end regions of the release layer becomes excessive,
As a result, the rigidity of the end portions of the layer is significantly increased, and separation may easily occur.

For a pneumatic radial tire which requires particularly high crown rigidity, it is effective to use an aramid fiber cord or a polyvinyl alcohol fiber cord as the cord of the belt 2. In that case, the value of the dynamic elastic modulus E ′ of these cords is 0.7 × 10 ¹¹ dyn
If it is less than / cm ² , the desired crown rigidity cannot be obtained.

In the pneumatic radial tire shown in FIG. 5, the cord layer 12a on the radial carcass side of the belt 2 is used.
Is in the range of the above value of (β / α), but the code layer 12b does not necessarily have to have the above relationship between α degree and β degree. Instead of this, the code layer 12b has portions in which both side ends are respectively folded back inward. The width Gb of the folded portion is 5% or more and 50% or less, preferably 5% of the width Wb of the code layer 12b.
By setting the ratio to 30% or less, the rigidity of the end region of the belt 12 can be set to a desired value without necessarily providing the region of (β) degrees in the code layer 12b. In this case, if the width Gb is less than 5% of the width Wb, the desired rigidity cannot be obtained.

[0050]

【Example】

[First Example] The size of the pneumatic radial tires of Examples 1 to 5 was 185 / 70R14.
The radial carcass 1 was all 1 ply, and the inclination angles of the fiber cords with respect to the tire equatorial plane E were all about 90 °. The belts of Examples 1 to 4 have a two-layer structure of 2a and 2b shown in FIG. 1, and only the belt of Example 5 has the cut-off cord layer 12a and the fold type cord layer 12b shown in FIG.

The width Wa of the code layers 2a and 2b shown in FIG.
Is 138 mm, Wb is 128 mm, the width Ca of the central region thereof is 46 mm, Cb is 43 mm, and the width Sa of the end regions on both sides thereof is 23 mm and Sb is 21 mm.
And The values of Wa and Ca of the code layer 12a of Example 5 are the same as above, and Cb of the code layer 12b is 43 mm, G
b was 21 mm.

The cords of the radial carcass 1 of Examples 1 to 3 and Example 5 were nylon 66 monofilament cords having a denier number of 4000, which is an elliptical cross section shown in FIG. The ratio L ₁ / L ₂ of the major axis and the minor axis of this cord is 3.0. In Example 4, other specifications were the same as the above except that the cord was polyester.

The cords of the cord layers of the belts of Examples 1 to 3 and Example 5 had a twist number of 32 × 32 of 15 cords.
It was a 00D / 2 aramid fiber cord. The dynamic elastic modulus of this cord was 2.5 × 10 ¹¹ dyn / cm ² . The cord of Example 4 has a twist number of 25 × 25.
And 1500 D / 3 polyvinyl alcohol fiber cord. The dynamic elastic modulus of this cord is 1.2 × 10
^{It was 11} dyn / cm ² .

In order to verify the effect of the first embodiment, tires of Conventional Example 1 and Comparative Examples 1 and 2 were prepared. These tires have a radial carcass of 1 according to the size.
All ply cords have a tilt angle of about 90 °
Was matched with the example. The belt had a two-layer structure of cut-off cord layers, and the values of the above-mentioned specifications shown in FIG.

The cords of the radial carcass of Conventional Example 1 and Comparative Example 2 are both 1500 with the number of twists being 40 × 40.
A D / 2 polyester fiber cord was used, and in Comparative Example 1, this cord was the same as in Examples 1 to 3 and 5.
Regarding the cord of the belt, Conventional Example 1 was a steel cord having a twist structure of 1 × 5 with the diameter of the strand being 0.23 mm, and Comparative Examples 1 and 2 were the same as Examples 1 to 3 and 5. The tire weight of Conventional Example 1 was 9.08 kg.

[Second Embodiment] The sizes of the pneumatic radial tires of Examples 6 and 7 were 205 / 60R15. The radial carcass 1 has two plies, and the inclination angle of the fiber cord with respect to the tire equatorial plane E is about 90 ° in Example 6 and about 75 ° in Example 7. The carcass ply of Example 7 was a laminated structure in which the cords intersect each other. The belt is the cord layer 2 shown in FIG.
It is composed of two layers a and 2b, one cap belt 13 and one layer 14.

The width Wa of the code layers 2a and 2b shown in FIG.
Is 157 mm and Wb is 147 mm, the width Ca of the central region is 52 mm, Cb is 49 mm according to FIG. 1, and the widths Sa of both end regions are 26 mm and Sb are 25 m.
m.

The cords of the radial carcass 1 of Examples 6 and 7 are the same monofilament cords as in Examples 1 to 3 and Example 5, and the cords of the cord layers 2a and 2b are also Examples 1 to 3 and Example 5. Same as. Each of the cap belt 13 and the layer has 12 cords.
Tire equatorial plane E as 60D / 2 nylon 66 cord
It is arranged to be substantially aligned with. The cap belt width Wm is 162
mm, and the layer width Wn was 45 mm.

Further, in order to verify the effect of the second embodiment, a tire of Conventional Example 2 was prepared. The size of the radial carcass was set to 2 plies, the cord was a 1000D / 2 polyester fiber cord having a twist number of 49 × 49, and the inclination angle with respect to the tire equatorial plane E was about 90 °. The belt of Conventional Example 2 has widths of Examples 6 and 7
Then, the same steel cord as in Conventional Example 1 was used as the cord. Further, the same cap belt and layer as in Examples 6 and 7 were provided. The tire weight of Conventional Example 2 is 9.
It was 88 kg.

For each of the tires of the above-mentioned examples, comparative examples and conventional examples, the number of plies, specifications of carcass cords and belt cords, α (degrees), β (degrees) and β / α values and conventional examples The weight loss (g; grams) from the tire weight is shown in Table 1.

In Table 1, NY66MF shown in the column of carcass cord is nylon 66 monofilament cord, PEMF is polyester monofilament cord,
PE represents a polyester twisted cord, AM in the belt cord column represents an aramid fiber twisted cord, PVA represents a polyvinyl alcohol fiber twisted cord, and ST represents a steel cord. In the comparative example and the conventional example, β indicates the average inclination angle in the same region as the example.

[0062]

[Table 1]

Next, the performance evaluations of the tires of Examples, Conventional Examples and Comparative Examples were carried out on the following items. First, performance evaluation of steering stability and vibration riding comfort was carried out by an actual vehicle feeling test by a professional driver. Each tire was scored by traveling on various road surfaces at various vehicle speeds ranging from about 60 km / h to 200 km / h with various driving methods such as slalom, lane change, and straight ahead. The score is 0 (zero) based on the tire of the conventional example, the larger the + (plus) score, the better, and the larger the- (minus) score, the worse. Here, ± 1 is a difference that can be recognized only by a skilled professional driver, and ± 2 is a difference that can be recognized by a particularly sensitive driver among general drivers. ± 3 is a difference that even ordinary drivers can see. The evaluation results are shown in Table 1.

Next, the rolling resistance was evaluated under the following conditions. Each of the test tires of the examples, conventional examples and comparative examples was filled with an internal pressure of 2.5 kgf / cm ² , and each tire was mounted on a drum having a diameter of 1708 mm rotating at a peripheral speed of 80 km / h and having a JIS 100% of that tire. A load was applied and pressed, and preliminary running was performed for about 30 minutes. After that, the internal pressure of the tire was adjusted to the above value again, and the peripheral speed of the drum was once adjusted to 20
The tire was pressed against the drum under the above load by raising it to 0 km / h, and the drum was inertially rotated from this speed.
The rolling resistance value R. R was calculated by the following formula. R. R = (ds / dt) × {(Id / R
d ² ) + (It / Rt ² )}-(rotational resistance of drum unit) where ds / dt is deceleration at each speed, and Id
Is the moment of inertia of the drum, It is the moment of inertia of the tire, Rd is the radius of the drum, and Rt is the radius of the tire. The above formula is the drum peripheral speed 185km / h to 20km
R. up to / h. It is possible to obtain the R value, but Table 1
The value at a peripheral speed of 100 km / h is 1 for the tire of the conventional example.
The index value was set to 00. The smaller the value, the better.

As is clear from Table 1, the pneumatic radial tires of the respective examples have a large level of steering stability and riding comfort while maintaining comparable levels in comparison with conventional steel belt radial tires. It can be seen that the weight can be reduced and at the same time the rolling resistance can be reduced. On the other hand, the tires of the comparative examples are tires lacking in practicality in terms of steering stability, which impairs practical use and cannot reduce the weight. Although not shown in Table 1, since the tires of the respective examples do not use steel wire except for the bead core, it is possible to further improve the reusability.

[0066]

According to the present invention, in comparison with steel belt tires and steel tires, while maintaining the same excellent steering stability and riding comfort, the rolling resistance is further reduced and the weight is further reduced. It is possible to provide a pneumatic radial tire that can realize the above and further improve the reusability of a used tire.

[Brief description of drawings]

FIG. 1 shows a cross section in the width direction of a pneumatic radial tire of the present invention in a left half from a tire equatorial plane.

FIG. 2 shows a cord cross section of the radial carcass of the present invention.

FIG. 3 shows the development of cord layers in the belt of the present invention.

FIG. 4 illustrates an example of a method of processing the code layer shown in FIG.

FIG. 5 shows a cross section in the width direction of a pneumatic radial tire according to another example of the present invention for the left half from the tire equatorial plane.

FIG. 6 shows a cross section in the width direction of a pneumatic radial tire according to still another example of the present invention for the left half from the tire equatorial plane.

FIG. 7 is a cross-sectional view illustrating a difference in belt diameter.

FIG. 8 shows development of a cord layer in a belt of a conventional tire.

[Explanation of symbols]

 1 Radial carcass 2 Belt 2a Belt cord layer 2b Belt cord layer 3 Bead core 4 Tread rubber layer Ca Belt center area width Sa Belt edge area width

Claims (3)

[Claims] 1. A radial carcass of one or more plies made of fiber cords, which extends in a toroidal shape between a pair of bead cores, a belt made of a plurality of fiber cord layers disposed on the outer periphery of the radial carcass, and the belt thereof. A pneumatic tire further comprising a tread rubber layer arranged on the outer periphery of the belt, wherein the fiber cord of the radial carcass is a monofilament cord of polyamide fiber or polyester fiber, and at least two layers of the belt have aramid fiber cords. A twist cord layer of at least one fiber of fibers or polyvinyl alcohol fiber and at least one layer of those layers as a cut layer, the average inclination angle of the cord in the same layer of the cut layer with respect to the tire meridian cross-sectional direction (Α) degree in the central region of the layer When (β) degrees are set in both side end regions of the air, the value of the ratio (β / α) of (β) to (α) is in the range of 0.80 to 1.15. Radial tires with. 2. The radial carcass comprises two or more plies, and adjacent plies are laminated so as to intersect each other with an angle of the fiber cords with respect to the tire equatorial plane of 70 ° or more and less than 90 °. Pneumatic radial tire. 3. The pneumatic radial tire according to claim 1, wherein the fiber cord of at least one ply of the radial carcass has an angle of 90 ° with respect to the tire equatorial plane.