JPH06115307A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To greatly reduce the heat and rolling resistance of a belt by using coating rubber containing short-fibered material in the belt. CONSTITUTION:Coating rubber 8, 8' for covering the organic fiber belt cord 7, 7' of a belt contains a predetermined amount of short-fibered material (f). The coating rubber 8, 8' is reinforced thereby and its modulus of elasticity is increased, so the difference in modulus of elasticity between the rubber 8, 8'and the organic fiber belt cord 7, 7' is reduced to prevent separation; further, the cut resistance or fatigue resistance and the like of the belt is enhanced. The short-fibered material (f) blended in the coating rubber 8, 8' is oriented within a predetermined range along the belt cord 7, 7' so that the coating rubber 8, 8' becomes anisotropic. Therefore, the difference in modulus of elasticity between the rubber 8, 8' and the belt cord 7, 7' can be further reduced and the heat of the end portions or shoulder portions 6 of the belt can be reduced.

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, and more particularly to a fuel-efficient pneumatic radial tire having reduced heat generation and rolling resistance.

[0002]

2. Description of the Related Art In a conventional pneumatic radial tire, a steel cord or an organic fiber cord covered with a coating rubber is used as a belt composed of a plurality of layers arranged between a carcass ply and a tread. As the carcass cord, a cord having a substantially circular cross section is used.

[0003]

With the increasing performance of automobiles, the emergence of high-performance tires with excellent durability, steering stability, riding comfort, etc. is desired, while conserving resources and reducing pollution. Due to problems, the advent of low fuel consumption tires is desired.

However, durability performance, steering stability performance,
Ride comfort and low fuel consumption tend to be so-called trade-offs.For example, if steel cords are used as belt cords to improve tire durability, the weight of the tires will increase and fuel consumption will deteriorate. Become.

Further, in order to reduce the weight of the tire, it is known to use an organic fiber cord such as nylon or polyester as a belt cord. However, since the organic fiber itself generates a large amount of heat due to hysteresis loss, rolling resistance is high. Is large, and it will go against fuel efficiency.

Here, a conventional pneumatic radial tire will be described with reference to FIG.

The pneumatic radial tire 1 is composed of a bead portion 2, a carcass ply 3, a belt 4 and a tread 5. The belt 4 is arranged between the carcass ply 3 and the tread 5 as shown in FIG. 1, and acts as a so-called hoop that suppresses expansion of the carcass ply 3 in the radial direction. . Further, 6 is a shoulder portion.

The belt 4 is usually composed of a plurality of layers, for example, 2 to 4 layers (in FIG. 1 and FIG. 2 showing the tire radial section, the case of two layers is shown. .), As shown in FIG. 2, each of the belt layers 4 ', 4 "forming the belt 4 is made of steel or organic fiber having a substantially circular cross section and arranged at a predetermined angle with respect to the equator of the tire 1. Cord 7, 7'Coating rubber 8, 8 '
It is covered with.

By the way, the pneumatic radial tire 1 is
When the vehicle is running, it receives an impact due to unevenness of the road surface or cornering. Such an impact is caused by the deformation strain of the belt layers 4'and 4 ", the cords 7 and 7 ', the coating rubbers 8 and 8', and the shear strain between the belt layers. Has been relaxed.

However, the cords 7, 7'of the belt layers 4 ', 4 "and the coating rubbers 8, 8'or the belt 4
Since there is a large difference in elastic modulus, fatigue characteristics, strain, etc. between the shoulder portion 6 and the shoulder portion 6, so-called separation occurs particularly at the cord end portion where stress is concentrated, which is a major problem for tire safety. There is. Further, even if the separation does not occur, there is a problem that at the cord end portion, since the shear strain between the belt layers is large, the heat generation becomes large and the rolling resistance of the tire becomes large.

Recently, steel cords having high elastic modulus and high strength are used as belt cords.
As mentioned above, steel cords are heavier than organic fiber cords, which is not preferable for improving the fuel efficiency of tires, and the rigidity of tires in the circumferential direction is large, and the riding effect is poor due to the small envelope effect. There is.

Further, when the steel cord is used as the belt cord, the difference in elastic modulus and the like from the coating rubber is extremely large as compared with the organic fiber cord, so that the possibility of separation is increased.

On the other hand, when the organic cords are used as the belt cords, the elastic modulus is smaller than that of the steel cords and the belts are soft, so that the riding comfort performance is improved and the fuel efficiency is improved because the tires are lightweight. Since the rigidity in the lateral direction is small, the response performance to cornering is poor, and thus the steering stability performance is deteriorated. Further, although not as great as the steel cord, there is still a large difference in elastic modulus and the like from the coating rubber, so that there is a possibility that separation may occur.

Further, when the organic fiber is used as the belt cord, there is a problem that the rolling resistance is larger than that of the steel cord because the tension variation of the organic fiber is larger than that of the steel cord and the heat generated by the organic fiber itself is large.

The present invention solves the above-mentioned problems in the case of using a light organic fiber as a belt cord in order to improve the fuel economy performance of a tire, and improves the fuel economy performance and steering stability performance of a tire. It is an object of the present invention to provide a pneumatic radial tire having well-balanced performance.

[0016]

In order to achieve the above object, a pneumatic radial tire of the present invention uses a rubber containing a short fibrous substance oriented in a predetermined direction as a coating rubber of a belt. By using an organic monofilament having a flat cross section as a carcass cord, the problems with the conventional pneumatic radial tire described above are solved.

First, organic fibers are used as the belt cords 7 and 7 ', and the organic fiber belt cords 7 and 7'are used.
The belt 4 covered with the coating rubbers 8 and 8'containing the short fibrous substance f oriented in the predetermined direction will be described.

In the present invention, the organic fiber belt cords 7 and 7'used for the belt 4 are, for example,
Twisted cords such as aromatic polyamide fibers, aliphatic polyamide fibers, polyester fibers and polyvinyl alcohol fibers are used, and aromatic polyamide fibers are particularly suitable.

Organic fiber belt cords 7, 7'of belt 4
When a predetermined amount of a short fibrous substance is contained in the coating rubbers 8 and 8 ′ for coating the coating rubbers 8 and 8 ′, the coating rubbers 8 and 8 ′ are reinforced and the elastic modulus is increased. The difference is reduced, the occurrence of separation is prevented, and the cut resistance or fatigue resistance is greatly improved as compared with the coating rubber containing no short fibrous substance.

Then, as schematically shown by a short line in FIG. 3, the short fibrous substance f mixed in the coating rubbers 8 and 8'within a predetermined range with respect to the belt cords 7 and 7'directions. By making the coating rubbers 8 and 8'anisotropic, the difference in elastic modulus between the belt cords 7 and 7'can be further reduced, and heat generation at the belt end portion or the shoulder portion 6 can be reduced. You can reduce more.

Further, the bending rigidity of the belt 4 can be enhanced by orienting the short fibrous substance f mixed in the coating rubbers 8 and 8'within a predetermined range with respect to the belt cords 7 and 7'directions. Because it can be done, compared with the conventional ones that simply use organic fiber cords as belt cords,
The cornering power is increased and therefore the steering stability performance is improved.

For example, when the angle θ formed by the orientation direction of the short fibrous substance f and the direction of the belt cords 7 and 7 ′ is θ ≦ 30 °, the above-described action and effect can be effectively exhibited. To be

The anisotropy of the above coating rubbers 8 and 8'is preferably configured as follows. (1) Physical properties of coating rubber in the orientation direction of short fibrous substances Modulus at 50% elongation ... 30 kg / cm ² or more Dynamic elastic modulus E '... 4 × 10 ⁷ dyn /
cm ² or more Dynamic loss tan δ ... 0.25 or less (2) Physical properties of the coating rubber in the direction perpendicular to the orientation direction of the short fibrous material Modulus at 50% elongation ... 10 kg / Cm ² or more Dynamic elastic modulus E '... 2 × 10 ⁷ dyn /
cm ² or more Dynamic loss tan δ ... 0.15 or less (3) Relationship between the cord direction and the modulus in the direction perpendicular to the cord direction The modulus at 50% elongation in the cord direction is in the cord direction On the other hand, it should be 1.5 times or more, and preferably 2.0 times or more, the modulus at 50% elongation in the right angle direction.

The preferable range of the anisotropy is set as described above because the rigidity of the belt is not sufficient outside the above range or the effect of reducing the hysteresis loss is not sufficiently large, and the tire This is because the rolling resistance cannot be significantly reduced.

Next, a structure using an organic monofilament having a flat cross section as a carcass cord will be described. As shown in FIG. 4, in a preferred embodiment of the present invention, the carcass cord 9 is composed of an organic monofilament cord 9 having a flat cross section, unlike a conventional cord having a substantially circular cross section. Further, the long diameter of the flat cross section is arranged so as to face the circumferential direction of the tire 1.

The flat shape of the cross section is, for example, a substantially elliptical shape or a rectangular shape such that the bending rigidity in the long width direction of the cross section is larger than the bending rigidity in the short width direction. Alternatively, it is not limited to the rectangular shape. The ratio of the shorter width to the longer width of the cross section is preferably about 1/5 to about 1/2.

As described above, since the organic monofilament having a flat cross section is arranged in the carcass ply 3 such that the major axis of the flat cross section is oriented in the circumferential direction of the tire 1, the rigidity of the tire 1 in the radial direction is low, and therefore The increase in the vertical rigidity of the tire due to the inclusion of the short fibrous substance f in the coating rubbers 8 and 8'of the belt 4 described above can be alleviated, and the riding comfort performance can be significantly improved.

Further, since the long diameter of the flat cross section is arranged so as to be oriented in the circumferential direction of the tire 1, the carcass ply 3 can be made thin and the tire 1 can be made light in weight. It is possible to improve fuel efficiency.

As the organic monofilament cord 9 having a flat cross section, HYTEN (trademark) manufactured by Dyupon Co. is widely known.
It is preferable.

In the present invention, in addition to the fact that the coating rubber 8, 8'covering the organic fiber belt cord 7, 7'contains a predetermined amount of the short fibrous substance f to form the belt 4, the carcass cord has a cross section. By constructing the organic monofilament cord 9 formed in a flat shape and arranging the long diameter of the flat shape in the cross section to face the circumferential direction of the tire 1, the tensile rigidity in the circumferential direction of the belt 4 is improved by the synergistic effect. It is possible to significantly reduce the heat generation and to significantly reduce the rolling resistance, and to significantly improve the riding comfort performance. Furthermore, due to the reduction in rolling resistance and weight reduction, the fuel consumption can be significantly reduced. .

[0031]

EXAMPLES Examples of the present invention will be described below.
The size of the tire used is 165SR13 and the pattern is a smooth tire. The measuring method and conditions are as follows.

Rolling resistance index Internal pressure of 2.00 kg / c was set on a drum having an outer diameter of 1708 mm.
The test tire adjusted to m ² was installed, the tire was preliminarily run at 80 km / hr for 30 minutes, and the air pressure was readjusted to 200 km.
After increasing the drum rotation speed to a speed of / hr, the drum was coasted and calculated from the moment of inertia until the drum rotation speed decreased from 185 km / hr to 20 km / hr.

Rolling resistance of tire = ds / dt (Id /
Rd ² + It / Rt ² ) −Resistance of drum alone, where 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 rolling resistance value at 50 km / hr obtained by the above equation was obtained as a representative value. The environment is 24 ± 0.
The measurement was carried out in a room controlled at 5 ° C. The indexing was represented by rolling resistance index = (representative value of test tire / representative value of control tire) × 100, rounded to the nearest whole number. As a result, the smaller the rolling resistance index, the better the fuel consumption.

The load when measuring the rolling resistance index is 250 k
gf, and the rolling resistance index is measured by the uniaxial coasting method.

Belt end temperature measurement conditions : The belt end temperature was measured after running for 15 minutes starting from a tire at room temperature (25 ° C) on a drum under a load of 200 kgf and 50 km / hr.

Elastic modulus at 50% elongation At room temperature, JIS No. 3 dumbbell was pulled at 300 mm / min to measure stress.

The viscoelastic dynamic elastic modulus E'and the dynamic loss tan δ are values obtained by measurement under the following conditions. That is, the length is 20m
A viscoelasticity measuring device (Toyo Seiki Co., Ltd. L-IR)
The initial tension of 1.7 kg on the rubber test piece
f / cm ² was applied, and in this state, the rubber test piece had a frequency of 5
Vibration is applied at 0 Hz and an amplitude distortion of 5%, and the measurement is performed at room temperature.

The compositions and physical properties of the coating rubbers used in the examples and comparative examples detailed below are shown in Tables 1 and 2. In Tables 3 and 4, the carcass cords used in Examples and Comparative Examples (the flattened cross-section monofilament is HYTEN (trademark) manufactured by Dyupon Co., Ltd.) and the coating rubber composition (Tables) The coating rubber compositions A, B, C and D of No. 1), and the measurement results of the belt end temperature and the rolling resistance index are shown.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

In Comparative Example 1 shown in Table 3, the carcass cord has a circular cross section, the belt coating rubber does not contain a short fibrous substance, and the temperature at the belt end is high.
Moreover, the rolling resistance index is large.

Comparative Example 2 is different from Comparative Example 1 in that the belt coating rubber contains a short fibrous substance.
Although the temperature at the belt edge has dropped, the rolling resistance index is still high.

In Comparative Example 3, a flat monofilament having a cross section was used as the carcass cord, but the belt coating rubber did not contain a short fibrous substance.
The temperature at the belt edge is high and the rolling resistance index is high.

Comparative Examples 4 and 5 shown in Table 4
The belt coating rubber contains a short fibrous substance, but the carcass cord has a circular cross section, the temperature at the belt end is high, and the rolling resistance index is large.

Compared with the above-mentioned Comparative Examples 1 to 5, the examples of the present invention shown in Tables 3 and 4 have belt end temperatures of 33 ° C., 38 ° C. and 36 ° C. Low,
Moreover, the rolling resistance index is also very small.

As described above, according to the present invention, the belt cord made of the organic fiber is coated with the coating rubber containing the short fibrous substance, and the organic monofilament having a flat cross section is used as the carcass cord. As shown in (1), since the temperature at the belt end is low and the rolling resistance index is also small, the fuel efficiency is remarkably improved as compared with the comparative example.

[0050]

Since the pneumatic radial tire of the present invention is constructed as described above, it has the following effects.

By using a coating rubber containing a short fibrous substance for the belt, and in particular, by giving the coating rubber anisotropy by the orientation of the short fibrous substance, heat generation and rolling resistance of the belt are greatly increased. Can be reduced to

Further, since the coating rubber contains a short fibrous substance for strengthening the belt, the belt can be made thinner, so that the pneumatic radial tire can be made lighter and therefore the fuel consumption can be remarkably improved.

Furthermore, since the organic monofilament having a flat cross section is arranged on the carcass ply so that the major axis of the flat cross section is oriented in the circumferential direction of the tire, the vertical rigidity of the tire in the radial direction is reduced, and therefore the longitudinal length of the tire is reduced. Even when a directional load is applied, it is possible to flexibly cope with the function of the belt as a hoop, so that the riding comfort performance is significantly improved.

Furthermore, since the long diameter of the carcass cord having a flat cross section is arranged in the tire circumferential direction,
The thickness of the carcass ply can be reduced, the weight of the tire can be reduced, and thus the fuel consumption can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional pneumatic radial tire.

FIG. 2 is a radial cross-sectional view of a belt layer of the present invention.

FIG. 3 is a plan view showing a belt cord direction and an orientation direction of a short fibrous substance according to the present invention.

FIG. 4 is a circumferential sectional view of the carcass ply of the present invention.

[Explanation of symbols]

 3 Carcass ply 4 Belt 6 Shoulder part 7, 7'Belt cord 8, 8 'Coating rubber 9 Organic monofilament carcass cord f Short fibrous substance

Claims (2)

[Claims] 1. A belt in which a belt cord made of an organic fiber is coated with a coating rubber containing a short fibrous substance, and a carcass cord made of an organic monofilament having a flat cross section is arranged so that the major axis of the flat is oriented in the tire circumferential direction. Pneumatic radial tire having a carcass ply. 2. The pneumatic radial tire according to claim 1, wherein the coating rubber containing a short fibrous substance has anisotropy.