JP2733438B2 - Radial tires for trucks and buses - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire for a truck or a bus, which can reduce the carcass cord while maintaining the strength of the carcass and can reduce the weight of the tire.

[0002]

2. Description of the Related Art Since a large load acts on a tire for trucks and buses compared to the size of the tire, the carcass and belt layers are reinforced with steel cords to further increase the rigidity of the tire. There are many.

[0003] However, it is not easy to calculate the tension applied to the carcass cord when the tire is filled with the internal pressure. Conventionally, it is simple to calculate the balance of the force from the geometrical shape of the tire. Was calculated by a simple formula. Also, the validity of this formula has not been confirmed.

[0004]

On the other hand, the appearance of vehicles with low fuel consumption has been demanded from the viewpoint of energy saving and the preservation of the global environment, and the weight of tires has been strongly demanded. For this reason, it is necessary to accurately grasp the tension acting on the cord of the carcass and to establish a proper configuration and arrangement of the carcass cord.

[0005] The inventors have repeated research on the above request,
By analyzing the tension acting on the carcass cord using the finite element method, the tension of the carcass cord at the time of filling the internal pressure of the tire can be calculated in advance from these calculation results, and by forming the carcass based on the calculation formula, It has been found that a carcass having a reduced carcass cord can be formed without reducing the strength of the carcass, and the weight of the tire can be reduced.

An object of the present invention is to provide a tire for a truck or a bus, which can reduce the weight of a carcass while maintaining the strength of the carcass, thereby reducing the weight of the tire.

[0007]

SUMMARY OF THE INVENTION The present invention provides a carcass comprising a carcass ply having a carcass ply in which steel carcass cords are radially arranged while turning around a bead core of a bead portion from a tread portion through a sidewall portion, and a tread portion. A radial tire for trucks and buses comprising a belt layer having a belt ply having a belt ply in which a steel belt cord is arranged inside and radially outside of the carcass, which is rim-assembled to a regular rim and 8 kgf / cm. ^Two
Flattening rate of carcass when the internal pressure is filled (%)
Is As, the internal volume (liter) enclosed by the carcass and the regular rim is Av, the number of carcass cords driven per 5 cm in the tire circumferential direction at the outer peripheral edge of the bead core of the carcass ply is N, and the actual filling internal pressure (kgf / cm ^2). ) Is P, the ratio S (= Fs / Fc) between the applied load Fc per carcass cord determined by the following equation (1) and the actual breaking strength Fs per carcass cord is obtained. 2 or more and 5.7
A radial tire for trucks and buses characterized by the following. Fc = (P / 8) x (32 / N) x (0.358 x As + 0.125 x Av-21.2) ... (1)

Preferably, the ratio S (= Fs / Fc) is not less than 4.2 and not more than 5.7.

Here, the carcass flattening rate means that the reference dimension of the carcass is the carcass center line passing through the center in the thickness direction of the carcass, and the maximum width of the carcass is W and the maximum height from the bead base line 1 as shown in FIG. When the height H is set, the ratio H / W × 100 between the two is defined as the carcass flatness (%).

[0010]

The tension per carcass cord changes from the equatorial plane of the tire to the bead as shown in the graph of FIG. That is, in the tread portion, the tension gradually increases from the tire equatorial plane toward the tread shoulder region,
The value is substantially constant in the side wall portion and the bead portion. As shown in the graph of FIG. 5, this tendency is substantially the same even if the tire size and the flatness are different.

The tension acting on the carcass cord was determined for a plurality of test tires having different tire types and tire sizes. Table 1 shows the specifications and the tension per carcass cord. Here, the measured internal pressure is 8.0 kg / c.
m ² and the number of carcass cords to be driven per 5 cm were 32 and the same conditions were used.

[0012]

[Table 1]

From the measurement results of these test tires,
Assuming that the internal pressure and the number of carcass cords driven are constant, the tension per wire can be determined by the following empirical formula regardless of the tire type and tire size.

F ₀ = 0.358 × As + 0.125 × Av-21.2 (2) where F ₀ = tension applied to one carcass cord (kgf) As = carcass flatness ratio (%) Av = carcass And the normal volume of the rim.

The calculation of the flatness ratio (%) As of the carcass is performed according to the following criteria. Fig. 4
In the tire meridional section, as shown in the figure, the maximum width W between the center lines L in the tire axial direction of the carcass on the center line L in the thickness direction of the main body and the nominal rim diameter of the regular rim with which each tire fits The ratio H / W × 100 to the height H in the radial direction from the peripheral surface to the center line L is defined as the flatness As of the carcass expressed in%.

The inner volume Av surrounded by the carcass is a center that smoothly extends from the center line L of the carcass to the normal rim from the outer peripheral surface 1 of the nominal rim diameter of the normal rim and the center line L of the carcass. It is defined that the volume surrounded by the extension line L is expressed in liters.

FIG. 6 shows the correlation between the calculated value according to the above equation (2) and the tension per carcass cord obtained by the finite element method. The calculated value according to the above equation (2) is substantially equal to the actual value. Can be considered equal.

Taking into account the internal pressure factor and the factor of the number of hits N per 5 cm in the tire circumferential direction at the outer peripheral edge of the bead core of the carcass cord, the acting force per carcass cord at the actually used internal pressure P is added to the above equation (2). Fc can be obtained by the following equation (1). Fc = (P / 8) x (32 / N) x (0.358 x AS + 0.125 x Av-21.2) ... (1)

The ratio of the applied load per carcass cord determined by the formula (1) to the ratio S (= Fs / Fc) of the actual breaking strength Fs per carcass cord is regulated. It is. The actual internal pressure P is JATM
It refers to the maximum internal pressure specified in A, TRA, or ETRTO.

Table 2 shows the result of calculating the above equation (1) for a plurality of and actual tires. Also, the ratio S (= Fs / F
FIG. 7 is a graph showing the value of c).

[0021]

[Table 2]

As can be understood from Table 2 and FIG. 7, the value of the ratio S tends to increase in a tire having a small aspect ratio.
Such a tendency is a problem that cannot be grasped by a conventional calculation formula derived from a geometric shape.

In the present invention, the ratio S (= Fs / F)
c) is set to 2 or more and 5.7 or less. When the ratio S is less than 2, the strength of the cord is insufficient and the rigidity of the tire is reduced. On the other hand, when the ratio exceeds 5.7, the cord diameter is excessively large or the number of hits increases and the weight of the carcass increases, and the weight of the tire is reduced. I can't achieve it. It is more preferable that the ratio S be 4.2 or more and 5.7 or less.

As described above, the strength S is calculated by using the above equation (1) and the ratio S to the actual breaking strength of the carcass cord is regulated within a certain range in consideration of the factor of the flatness of the carcass. It is possible to form a carcass having a small carcass cord while holding the tire, and to reduce the weight of the tire.

[0025]

An embodiment of the present invention will be described below with reference to the drawings. 1 to 3, a radial tire 1 for trucks and buses has a tread portion 2, a pair of sidewall portions 3 extending radially inward from both sides of the tread portion 2, and beads extending inward of the sidewall portion 3. A part 4.

The radial tire 1 for trucks and buses
From the tread section 2 to the side wall section 3 to the bead section 4
A carcass 6 integrally including a folded portion 6b that turns around the bead core 5 from the inside to the outside in the tire axial direction on a main body portion 6a extending to the main body portion 6a, and a belt disposed outside the carcass 6 and inside the tread portion. Comprising a layer 7, and in this embodiment,
A bead apex 8 made of rubber having a triangular cross-section and arranged between the main body 6a and the folded back portion 6b of the carcass 6.
Is provided.

The carcass 6 is composed of one or a plurality of carcass plies, in this example, one carcass ply 6A. The carcass ply 6A is formed by forming the carcass cord 11 made of steel at an angle of 75 to 90 ° with respect to the tire equator C. And is formed as a radial or semi-radial array arranged at an angle. Also, by covering these carcass cords 11 with topping rubber, a sheet-like carcass ply is formed.

In the present embodiment, the carcass cord 11 is formed, as shown in FIG.
7 × 3 / 0.175 as shown in FIG.
0.20 + 7 / 0.23 , or 3 / 0.17 + 7/0.
It consists of a steel cord twisted into the configuration of No. 20. Note that a core 13 made of an organic fiber cord can be provided at the center as shown by a dashed line in FIG.

In this embodiment, the belt layer 7 is formed by superposing and arranging four belt plies in which belt cords made of steel are arranged at an angle to the circumferential direction of the tire so as to increase the rigidity of the tread portion by exerting a tag effect. ing.

In the radial tire for trucks and buses having the above-described configuration, the applied load Fc (kgf) per cord acting on the carcass cord 11 can be calculated by the following equation (1). Fc = (P / 8) x (32 / N) x (0.358 x AS + 0.125 x Av-21.2) ... (1)

Here, As: Carcass flattening rate (%) when the internal pressure of 8 kgf / cm ² is charged, Av: Inner volume (liter) surrounded by the carcass and the regular rim N: Tire at the bead core outer peripheral edge SU of the carcass ply Number of carcass cords per 5 cm in the circumferential direction P: Internal pressure actually charged (kgf / cm ² )

Here, the ratio S (= Fs / Fc) of the applied load Fc (kgf) per carcass cord to the actual breaking strength Fs per carcass cord is 2 or more and 5.7. Below, preferably 4.2 or more and 5.7 or less.

[0033]

【Concrete example】

A. Experiment 1 A conventional tire (conventional example) having a tire size of 10.00R20 and having a configuration shown in FIG.
And tires reduced in weight according to the regulations of the present application (Example)
Were compared as shown in Table 3.

[0034]

[Table 3]

In the case of the embodiment, the actual load acting on one carcass cord is grasped by using the above formula (1) and the carcass ply is disposed on the carcass ply. It was confirmed that the actual breaking force Fs per wire can be made smaller, that is, the cord diameter can be made smaller than that of the conventional one, and that the tire weight can be greatly reduced in conjunction with the thinner carcass ply. .

Further, an actual vehicle test was performed on the above-described Examples and Comparative Examples, and the presence or absence of carcass damage and the durability were compared. The results of the test are shown in the graph of FIG.

Here, the wear rate means that the depth of the remaining groove of the main groove 15 in the tread portion 2 is 0.
When it reaches 7 times, it is defined as a wear rate of 100%.

As a result of the test, the strength of the carcass cord was
In the embodiment, the carcass damage was recognized even when the wear rate of the tread surface was 100% although the ratio S and the low value were used, although the value slightly decreased with the increase in the amount of wear due to the increase in the traveling distance. Did not.

B. Experiment 2 The experiment 1 was further advanced, and the tire size was 11R2.
Table 4 shows the actual breaking strength of the carcass cords and the number of the cords to be set to the ratio S of 4.2 for the tire of No. 2B in Table 2 and the sample number 2B in Table 2 so as to set the ratio S to 4.2. As shown in FIG. 9, durability was compared by actual vehicle tests as shown in FIG.

[0040]

[Table 4]

Similarly, tire size 295 / 80R2
For the 2.5 tire, an improved tire was prototyped as shown in Table 5 and the durability was compared as shown in the graph of FIG. For tires having a tire size of 365 / 70R22.5, the durability shown in the graph of FIG. 11 was compared based on the specifications shown in Table 6.

[0042]

[Table 5]

[0043]

[Table 6]

As a result of the test, the ratio S (= Fs / Fc)
Was reduced to 4.2 or less, no occurrence of carcass damage and no decrease in durability was observed.

[0045]

As described above, the radial tire for trucks and buses according to the present invention having the above-mentioned structure enables the working load acting on one carcass cord to be accurately grasped with the internal pressure applied. Thus, a carcass having a small carcass cord can be formed while maintaining the strength of the carcass, and the weight of the tire can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a perspective view showing the arrangement of the carcass and the belt layer.

FIG. 3 is a sectional view showing a configuration of a carcass cord.

FIG. 4 is a sectional view defining a flattening rate and an internal volume of a carcass.

FIG. 5 is a graph showing a distribution of a load acting on a carcass cord.

FIG. 6 is a graph showing a correlation between a measured value and a calculated value of an applied load.

FIG. 7 is a graph showing the ratio S in Table 2.

FIG. 8 is a graph showing a relationship between a tire wear rate and an actual breaking strength of a carcass cord due to the wear.

FIG. 9 is a graph showing a relationship between a wear rate of a tire and an actual breaking strength of a carcass cord due to the wear.

FIG. 10 is a graph showing a relationship between a wear rate of a tire and an actual breaking strength of a carcass cord due to the wear.

FIG. 11 is a graph showing a relationship between a tire wear rate and an actual breaking strength of a carcass cord due to the wear.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 7 Belt layer 11 Carcass cord J Regular rim

Claims (2)

(57) [Claims] 1. A carcass comprising a carcass ply in which a carcass cord made of steel is radially arranged while turning around a bead core of a bead portion from a tread portion through a sidewall portion, and a carcass ply inside a tread portion and a radial outside of the carcass. Radial tires for trucks and buses comprising a belt layer having a belt ply in which steel belt cords are arranged in a regular rim and filled with an internal pressure of 8 kgf / cm ² . The flattening rate (%) of the carcass is As, the internal volume (liter) surrounded by the carcass and the normal rim is Av,
Assuming that the number of carcass cords per 5 cm in the tire circumferential direction at the outer peripheral edge of the bead core of the carcass ply is N and the actual filling internal pressure (kgf / cm ² ) is P, one carcass cord obtained by the following equation (1) And the applied load Fc,
Ratio S to actual breaking strength Fs per carcass cord
A radial tire for trucks and buses, wherein (= Fs / Fc) is 2 or more and 5.7 or less. Fc = (P / 8) x (32 / N) x (0.358 x As + 0.125 x Av-21.2) ... (1) 2. The radial tire for trucks and buses according to claim 1, wherein said ratio S (= Fs / Fc) is not less than 4.2 and not more than 5.7.