JPH03178807A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To make a radial tire lightweight and improve the cornering performance thereof by so changing the cord angle of a steel cord as to satisfy an equation specified with a ratio of the function of axial stress to the function of the in-plane bending rigidity of a belt layer, and keeping the minimum value of the cord angle within a specific range. CONSTITUTION:The cord angle theta of a steel cord 6 constituting a belt layer 5 with a tire circumferential direction CL is made to change so as to satisfy the equation I (where X: value of x to make f(x) maximum, alpha: minimum value of cord angle theta to make g(theta) maximum) specified with a ratio of the function of f(x) of axial stress acting on the steel cord 6 as expressed by the equation II (where b: 1/2 of belt effective width, A: constant term for making the maximum value of f(x) equal to 1) to the function g(theta) of the in-plane bending rigidity of a belt layer expressed by the equation III, corresponding to a radial direction (x) from a tread center CL. In addition, the minimum value alpha of the cord angle thetain the equation I is kept within 16 to 23 degrees with an allowance of + or -2 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pneumatic radial tire that improves cornering performance while reducing the weight of the belt layer.

[Prior art]

Conventionally, many materials have been proposed for reinforcing cords in the belt layer of pneumatic radial tires. Of these,
Steel cord has the advantage of being more stable in quality than other materials, and having significantly higher strength and elastic modulus, so it can significantly improve the cornering performance of tires.

However, a disadvantage of such steel cords compared to other materials is that they are heavy. This is because such a large weight deteriorates the fuel consumption rate of the vehicle. Therefore, one of the technical challenges when using steel cord for the belt layer is how to minimize the disadvantage of increased weight while making the most of the features of steel cord.

[Problem to be solved by the invention]

An object of the present invention is to provide a pneumatic radial tire that improves cornering performance while reducing weight when steel cord is used in the belt layer as described above.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a radial tire in which a belt layer of steel cords is arranged in the trend part, and the cord angle θ of the steel cord with respect to the tire circumferential direction is adjusted to the center of the trend part. Corresponding to the distance X in the radial direction from The cord angle θ is changed so as to satisfy the following formula (1) specified by the ratio with the function g(θ) of the internal bending stiffness, and the minimum value α of the cord angle θ in the formula (1) is 16° to 23°. It is characterized by being within a range that allows variation of ±2°.

f(x)=-(A(b2-x"))"'
-(2)g(θ) = 1-cot"θ+cot'θ
−・−・・−(3) [However, in each of the above equations, X: Value of X that maximizes f(x) α: Minimum value of cord angle θ that maximizes g(θ) b: Belt layer 1/2 of the effective width A; constant term that makes the maximum value of f(x) equal to 1] The above equation (1) means the relationship between stress/rigidity and strain in material mechanics. In other words, in this (+)2, keeping the right-hand side corresponding to the distortion constant means keeping the distortion in the belt layer constant when the tire corners, and the right-hand side can be made as shown in equation (1). By specifying this, it is possible to improve cornering performance while removing excess rigidity of the belt portion, thereby reducing the weight of the belt layer.

Furthermore, by making the strain distribution of the belt layer uniform during cornering, lifting of the belt layer is suppressed and ground contact is improved, further improving the cornering performance of the tire.

In the present invention, the above-mentioned equation (2) represents the function of the axial stress applied to the steel cord during cornering, which was obtained by analyzing the stress in the belt layer from the results of tire cornering experiments. It is something.

In other words, from the stress analysis in the belt layer, the axial stress y applied to the steel cord with the internal pressure and deflection state of the belt layer as the origin is expressed by the following equation (4) for the distance χ in the radial direction from the tread center. It was discovered that it can be approximated by a function.

b′ In this (4)2, l y l = f(x) (
Equation (2) can be obtained by setting 0≦X≦b).

Figure 3 (A') shows the axial stress y based on (2) 2 above.
This is a graph showing the relationship between X and the distance from the tread center CL.
The corresponding marks are shown.

This graph shows an air pressure of 1.7 kgf/cTIN and a load of 3.
The origin is the value when 00 kg is added, and the maximum value when 150 kgf is added to this is expressed as 1. Also, corresponding to this Figure 3 (A),
The belt layer 5 is illustrated in FIG. 3(B).

As is clear from this graph, the axial stress y of the steel cord gradually increases toward one end of the shoulder, and reaches its maximum (maximum) at the position of x=X, slightly inside from one end of the shoulder. Since this X is the X value at which y = fCx ) is the maximum value, df(x)/dx = O
It is found as the solution of

On the other hand, in contrast to the above equation (2), equation (3) is a function of the in-plane bending rigidity of the belt layer, and was derived as follows.

According to research by Takashi Akasaka and colleagues at Chuo University, it is known that the in-plane bending stiffness of a two-ply bias plate is expressed by the following equation (5). For details, see "Japan Rubber Association Journal" νof, 51/1978. 152nd~
Page 167 (Refer to the bottom paragraph of the left column of page 161 of the special edition)
As stated in

2 [where h is the wire diameter and Ey is the modulus of the coated rubber] In this formula (5), if the tire is determined, Et.

Since h and b are constants, the function g(θ) of the in-plane bending stiffness of the belt layer with respect to the cord angle θ can be simplified as in the above-mentioned equation (3).

Now, as mentioned above, f(x) in equation (2) is a function of stress, and g(θ) in equation (3) is a function of stiffness, so stress/stiffness and strain in material mechanics are related. From the relationship, if the belt layer is configured such that the ratio f(x)/g(θ) of both openings is constant, the distortion of the belt layer when the tire corners is constant ζ,':.

can do.

In the present invention, when the ratio of both openings corresponding to the strain in the belt layer is made constant, the constant value and 12. Therefore, it is defined as the right side of equation (1). That is, the maximum value f(
X) and the maximum value g(α) of the in-plane bending rigidity g(θ) of the belt layer with the cord angle θ set to the minimum value α.

Therefore, by stipulating a constant value in this way,
In areas other than position X where the steel cord stress is maximum, the in-plane bending stiffness must be reduced in proportion to the reduction in stress, and the cord angle θ is increased to reduce the stiffness. This is how it changes.

In this way, at a position where the cord angle θ is large, the number of cords (density) per unit width in the radial direction is smaller than at a position where the cord angle θ is small, so the weight of the belt layer is reduced by that amount. become.

In the present invention, the minimum value α of the code angle θ is 16
It is necessary to select within the range of @ to 23°.

If the minimum value α is smaller than 16″, it becomes difficult to obtain the effect of weight reduction due to the difference in the density of the steel cord, and if it is larger than 23″, it becomes difficult to obtain a sufficient reinforcing effect. Further, in the present invention, when the minimum value α is set within the above range of 16° to 23°, there is no problem in having variations within the range of ±2° from the set value.

FIG. 1 shows the belt layer 5 according to the present invention developed in a plane when the minimum value α of the cord angle θ is 23°. As is clear from FIG. 1, the steel cords 6 are arranged in a curved line with the cord angle θ sequentially changing with respect to the radial direction (X direction) of the belt layer 5.

That is, the cord angle θ is maximum at the tread center CL portion, becomes smaller toward one end of the shoulder, and reaches the minimum value α of 23° just before the one end of the shoulder. The arrangement direction of the steel cords 6 when this minimum value α is varied is as shown in FIG.

FIG. 4 illustrates, in meridian section, a radial tire according to the invention having a belt layer as described above. The tire has a tread part 1 in the center, sidewall parts 2.2 on the left and right sides thereof, and beet parts 3.3 connected to their ends to form a tire outer shell. The inner side of this tire outer shell is reinforced by a carcass layer 4, and the tread portion 1 is further reinforced by two belt layers 5.5 arranged so that their cord directions intersect with each other.

The belt layer 5 uses steel cord 6 as a reinforcing cord,
The reinforcing cord of the carcass layer 4 may be an organic fiber cord such as polyester, polyamide, or rayon, or may be an inorganic fiber cord such as steel.

Examples will be described below.

(Example) As the tire of the present invention (tire I), the tire size is 16
5 A tire having a radial structure as shown in FIG. 4 was manufactured using SR13 using a polyester cord for the carcass layer and a steel cord for the belt layer. The belt layer has the minimum value α of the steel cord cord angle θ equal to 2
The cord angle θ was set to 3°, and an arrangement was made in which the cord angle θ was changed according to equation (1).

On the other hand, as a conventional tire (tire ■), a tire was produced that differed from the tire ■ described above only in the arrangement of the steel cords in the belt layer. The cord angle of the steel cord of this belt layer was set to 23°±2°, which is approximately the same angle throughout the width direction.

The weight, cornering power, and dry circular turning performance of the two types of tires I and II were measured using the following measurement methods, and the results shown in the table were obtained.

(Cornering power) JATMA design air pressure for normal load is 1°9kgf
The cornering force at a slip angle of 1° was measured using an indoor flat plate tester with a load of 300 kg and a slip angle of 1°. The measured values were expressed as index values, with the measured value of the conventional tire H being 100.

(Dry turning performance) The tire was installed in an evaluation vehicle at an air pressure of 1.9 kgf/cffl, and the value of the maximum lateral acceleration G when turning in a circle with a radius of 15 m was measured. The measured value is the measured value of the conventional tire ■ by 100
It is expressed as an index value.

(Margins below this page) From the table, it can be seen that the tires of the present invention are lighter than conventional tires and yet have excellent cornering performance.

[Effects of the Invention] As described above, the radial tire of the present invention improves tire cornering by changing the cord angle θ of the steel cord of the belt layer so as to satisfy equation (1) at each position in the radial direction. Since the strain within the belt layer is made constant during the rotation, the excess rigidity of the belt portion is removed, thereby making it possible to reduce the weight of the belt layer and improve cornering performance. Furthermore, the uniform 4° strain distribution of the belt layer during cornering suppresses lifting of the belt layer and improves ground contact. Therefore, the cornering performance of the tire can be further improved.

[Brief explanation of drawings]

FIG. 1 is a plan development view showing an example of the belt layer arranged in the radial tire of the present invention, and FIG. 2 is a minimum value α of the cord angle.
Figures 3(A) and 3(B) are diagrams illustrating the difference in steel cord when changing y = f(x), respectively.
FIG. 4 is a cross-sectional view of the same radial tire. DESCRIPTION OF SYMBOLS 1... Tread part, 4... Carcass layer, 5... Belt layer, 6... Steel cord.

Claims (1)

[Claims] In a radial tire in which a belt layer of steel cords is disposed in the tread portion, the cord angle θ of the steel cords with respect to the tire circumferential direction is determined by the following ( 2) Specified by the ratio of the function f(x) of the axial stress applied to the steel cord expressed by the formula and the function g(θ) of the in-plane bending stiffness of the belt layer expressed by the following formula (3) The minimum value α of the chord angle θ in the equation (1) is set to be within a range of 16° to 23°, and within a range that allows a variation of ±2°. pneumatic radial tire. f(x)/g(θ)=f(X)/g(α)...
...(1) f(x) = (x/b) [A(b^2-x^
2)]＾1＾/＾4...(2) g(θ)=1-cot
^2θ+cot^4θ・・・・・・(3) [However, in each of the above formulas, X: Value of x that maximizes f(x) α: Minimum value of code angle θ that maximizes g(θ) b: 1/2 of the effective width of the belt layer A: constant term that makes the maximum value of f(x) equal to 1]