JP2000289410A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve run-flat performance which is the continuous running performance after a puncture by setting the tire profile constant for a unit peripheral length defined by a specific equation of the radius of curvature of a first circular arc, the radius of curvature of a second circular arc and the distance in the tire radial direction to a specific value or below. SOLUTION: An intersection between a tire radial line passing through the inner face position of a rim flange and a tire intermediate line on the tread side is made a first point, and an intersection on the bead section side is made a second point. The radius of curvature of a first circular arc tangent to the tire intermediate line at the first point is Ra, the radius of curvature of a second circular arc tangent to the tire intermediate line at the second point is Rb, and the distance from the first point to the second point in the tire radial direction is H. The tire profile constant J for a unit peripheral length defined by the equation is 0.8 or below, where Z=h2/6, and (h) indicates the thickness of a side wall section on the tire axial line. The run-flat performance of this tire can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire capable of improving run flat performance while suppressing an increase in tire weight.

[0002]

2. Description of the Related Art In recent years, the enhancement of safety equipment for vehicles has been remarkable.
For example, equipment such as ABS, airbag systems, and shock-absorbing bodies tend to be installed as standard even on low-cost vehicles, and safety is now a top priority in the automotive industry. For tires, such safety is no exception, and development of basic running performance such as running, turning, and stopping, as well as running performance after puncturing is desired. In other words, even if the tires are punctured while driving, you can drive to the nearest gas station or repair shop by yourself, eliminating the need to change tires on the roadside at highways, midnight, bad weather, etc. Demand for tires is growing.

[0003] The inventors of the present invention have studied the damage process of a tire after puncturing and found that the process is generally as follows. First, if air leaks out due to puncturing, the longitudinal deflection of the tire increases, stress is concentrated on a part of the tire cavity surface, and a part having a large distortion generates heat. Such heat generates rubber peeling and abrasion at an early stage, exposing the carcass forming the skeleton of the tire, causing the carcass and the road surface or the carcass to rub against each other, resulting in breakage, resulting in fatal damage and inability to run. Become.

[0004] As a countermeasure, the rigidity of the entire tire is usually improved in order to improve the durability. Specifically, for example, the number of plies of the carcass forming the skeleton of the tire is increased, or the thickness of the rubber is increased. Also, these methods have been embodied almost empirically, and have resulted in a significant increase in tire weight.

The present invention has been devised in view of such a situation, and considering a tire stress analysis model, it is possible to reduce the maximum stress acting on the tire while minimizing the increase in tire weight. It is an object of the present invention to provide a pneumatic tire capable of improving a run flat performance, which is a continuous running performance after a puncture, based on improving an optimum cross-sectional shape.

[0006]

According to the present invention, there is provided a pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, the tire having a regular rim. In the normal tire meridian section where the rim is assembled and filled with the normal internal pressure and no load is applied, the tire radial line Y passing through the rim width position of the normal rim is a tire middle line passing through the middle of the tire thickness. A, a first point A intersecting at the tread portion side, a second point B at which the tire radial direction line Y intersects the tire middle line at the bead portion side, and a first point A and a second point B A radius of curvature Ra of a first circular arc having a center Oa on the tire axial line X passing through the middle and on the tire lumen side and contacting the tire middle line at the first point A, the tire axial line X Above and on the tire lumen side It has a heart Ob, and the second point B
The radius of curvature R of the second circular arc in contact with the tire middle line
b, and at a distance H in the tire radial direction from the first point A to the second point, a tire section constant J per unit circumferential length defined by the following equation is 0.8 or less. It is characterized by.

(Equation 3)

The thickness h of the sidewall portion on the tire axial line X is the outer diameter D of the tire in the normal state.
It is preferably 0.01 to 0.022 times of the above.

It is desirable that the arc coefficient C of the tire defined by the following equation is not more than 5.0.

(Equation 4)

Further, it is preferable that the distance H in the tire radial direction is not more than 0.085 times the outer diameter D of the tire in the normal state.

[0010] In this specification, the "regular rim"
In the standard system including the standard on which the tire is based, the rim is defined by the standard for each tire.
A for standard rim, TRA for "Design Rim",
Or "Eeasto Rim" for ETRTO.
The “normal internal pressure” is the air pressure that is defined for each tire in the standard system including the standard on which the tire is based.
Then the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLA
TION PRESSURES ", ETRTO
"INFLATION PRESSURE", but if the tire is for a passenger car, the pressure is 180 kPa.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a tire meridian section of the pneumatic tire 1 of the present embodiment. The carcass 6 extends from the tread portion 2 to the bead core 5 of the bead portion 4 through the sidewall portion 3 and the carcass 6 extends radially outward of the carcass 6. A tubeless radial tire (205 / 55R15) of a tubeless type having a belt layer 7 disposed thereon and having an inner liner rubber on a tire inner surface i is illustrated. FIG. 1 shows an assembly of the tire and the rim in a normal state in which the tire is mounted on a normal rim j and filled with a normal internal pressure (180 kPa) under no load. The tire section width SW is 223.0 mm and the tire section height F is 112.0 mm.

The carcass 6 has at least one carcass cord having a radial structure in which carcass cords are arranged at an angle of 75 ° to 90 ° with respect to the tire equator C, in this embodiment, one carcass ply 6.
A. As the carcass cord, an organic fiber cord such as nylon, rayon, or polyester is used in this example.

The carcass 6 has a main body 6a extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the sidewall portion 3, and a folded portion 6b extending from the main body portion 6a and being turned around the bead core 5. A bead apex 10 that extends from the bead core 5 in the tire radial direction and is made of hard rubber is disposed between the main body 6a and the folded portion 6b. Reinforced. In this example, a tire provided with a rim protector 4a protruding from the bead portion 4 so as to cover the rim flange if outside in the tire radial direction is illustrated.

The belt layer 7 has at least two belt plies, in which cords are arranged at a small angle of, for example, 15 to 40 ° with respect to the tire equator, and in this example, two inner and outer belt plies 7.
A and 7B are configured so as to overlap in a direction where the cords cross each other. Although the belt cord employs a steel cord in the present embodiment, a highly elastic organic fiber cord such as aramid or rayon may be used if necessary. A band layer including cords arranged at an angle of 5 ° or less with respect to the tire equator C may be provided outside the belt layer 7 in the tire radial direction. In the present embodiment, a rubber reinforcing layer having a substantially crescent-shaped cross section is not provided on the inner surface of the sidewall portion 3, but the sidewall portion 3 may be formed by adding this.

FIG. 2 shows a contour of a tire meridional section (right half) of the pneumatic tire 1 in a normal state.
In the drawing, a tire middle line CL passing through the middle of the thickness of the tire is shown by a one-dot chain line. Here, the “intermediate line of the tire” does not include the pattern on the outer surface of the tire or the protrusion of the rim protector 4a or the like provided on the bead portion 4. Therefore, in this example, the bead portion 4 excluding the rim protector 4a is used. It is specified based on the contour (shown by the dotted line).

In FIG. 2, A is a first point at which the tire radial direction line Y passing through the rim width position of the regular rim j (the inner surface position of the rim flange jf) intersects the tire middle line CL on the tread portion 2 side, and This tire radial direction line Y is the bead portion 4
A second point that intersects the tire middle line CL on the side is B. In addition, the tire has a center Oa on the tire axial direction line X passing through the middle between the first point A and the second point B and on the tire lumen side. First contact
Is the radius of curvature of the arc Ca, and the radius of curvature of the second arc Cb having the center Ob on the tire axial line X and on the tire lumen side and in contact with the tire middle line CL at the second point B. Rb. Further, the distance in the tire radial direction from the first point A to the second point B is represented by H.

At this time, the pneumatic tire 1 has a tire sectional constant J per unit circumferential length defined by the following equation.
Is 0.8 or less.

(Equation 5)

The inventors have proposed a bent beam 1 as shown in FIG.
2 was applied to tires. First,
A curved beam 12 having a radius of curvature R as shown in FIG.
When a compressive load W is applied, the maximum stress σ in the cross section ZZ
m is approximately represented by an equation. σm = WR · {1-cos (φ / 2)} / Z '... However, Z' is a = bh ^2/6. 9 (A).
As shown in FIG. 9B which is a −Z cross section, h is a cross section Z−
Z is the thickness and b is its width. In addition, load W, W
Let H 'be the distance between the action points of H. The H' can be represented by the following equation. H '= 2R · sin (φ / 2) ...

When the equations are rearranged into the equations of H ′ and R using this equation, the maximum stress σm at the cross section ZZ can be expressed by the following equation.

(Equation 6)

When this equation is applied to a tire as shown in FIG. 2, the maximum stress σm can be obtained as the sum of the maximum stresses σmb and σma inside and outside the tire axial line X. The radius of curvature R of the curved beam can be approximately applied to the radii of curvature Ra and Rb, respectively. Further, H ′ of the bent beam is 1/2 of the distance H in the tire radial direction between the first point A and the second point B on the sidewall portion of the tire.
It can be applied as Therefore, the equation can be applied to the pneumatic tire in a manner similar to the following equation. However, Z is a section modulus of the side wall portion of the unit circumferential length "h ^2/6", h is the thickness of the sidewall portion on the tire axial direction line X.

(Equation 7)

This equation approximately shows the maximum stress σm acting on the ZZ cross section of the side wall portion for a certain load W, and a value obtained by dividing the maximum stress σm by the load W is herein referred to as a unit. It is represented by a parameter called tire section constant J per circumferential length, and is defined by the above equation. Then, the inventors varied the profile of the sidewall portion of the tire in various ways, produced a considerable number of tires having different radiuses of curvature Ra and Rb and the above-described distance H in the tire radial direction, and continued production after puncturing. When the running distance was examined, it was found that it is particularly preferable to restrict the tire cross-sectional constant J defined by the above equation to 0.8 or less irrespective of the tire size and the like for improving the durability of the tire.

FIG. 3 is a graph showing the results of trial production of tires in which the tire section constant J was changed variously and the run-flat performance of each tire. Run flat performance is for tire sizes 215 / 45ZR17 and 2
For two types of 05 / 55R15, a puncture tire with a rim assembled to a domestic passenger car with an internal pressure of 0 kPa is mounted on the front right side, running on a test course, and the continuous mileage until the puncture tire becomes unable to run is indexed. (Very good). The test course includes a straight section and a turning section, and the running speed of the straight section is 50 km.
/ H, and the running speed of the turning section was 40 km / H, and the same conditions were set. The test was performed by unifying the thickness h of the sidewall portion on the tire axial line X to 13 mm.

As is apparent from FIG. 3, the run flat performance tends to decrease as the tire section constant J increases. However, by setting the tire section constant J to 0.8 or less, preferably 0.7 or less, more preferably 0.5 or less, and more preferably 0.1 to 0.5, the run flat performance is maintained high. You can see that.

In the case of a conventional general passenger car pneumatic tire, the tire section constant J is generally larger than 0.8.
In particular, many are set to 1.0 or more. As described above, in the present invention, for example, the thickness of the sidewall portion is increased based on the setting of the curvature radii Ra, Rb and the distance H so that the tire sectional constant J can be reduced as compared with the related art. Without this, the maximum stress acting on the side wall portion 3 can be reduced as compared with the conventional case. Thereby, the durability of the tire can be improved, and the continuous running distance after puncturing can be increased.

If the tire section constant J exceeds 0.8, the maximum stress acting on the sidewall portion 3 cannot be reduced to the same level as the conventional tire, and the durability of the pneumatic tire can be improved. Cannot be expected.

In this embodiment, the above equation is multiplied by “Z” to calculate the thickness h of the sidewall portion of the tire.
The effect of the cross-sectional shape of the sidewall portion 3 was examined using a parameter called the arc coefficient C (defined by the above equation) of the tire from which the above element was removed. And it turned out that it is preferable to set the arc coefficient C of this tire to 5.0 or less.

(Equation 8)

FIG. 4 shows the results of examining the run-flat performance by changing the arc coefficient C of the tire in various ways. The run flat performance is performed with the same contents as the above test. As is clear from FIG. 4, the run flat performance tends to decrease as the arc coefficient C of the tire increases. However, when this arc coefficient C is 5.0 or less,
More preferably 4.0 or less, even more preferably 2.5 to
It was found that by setting the value to 4.0, the run flat performance could be kept high.

FIG. 5 shows the circular arc coefficient C on the vertical axis.
The abscissa plots the tire section constant J, and the graph plots the run flat performance (index) of each test tire and the thickness h of the sidewall portion on the tire axial line X on this graph. ing. In FIG. 5, J ≦ 0.8,
It can be seen that a tire satisfying both C ≦ 5.0 shows very good run flat performance.

From the formula, the formula and the formula, σm = W
Since the relationship of J = CW / Z holds, the following equation holds between the tire section constant J and the arc coefficients C and Z. J = C / Z ...

This equation shows that the tire section constant J and the arc coefficient C have a linear relationship when the thickness h of the sidewall portion is constant. Further, J = 0.8 and Z = h ^2/6 of the side wall portion is substituted into the equation thickness h = 6.13 (mm) is obtained. Therefore, the thickness h of the sidewall portion is, in the above tire size,
It is desirable that the thickness be 6.13 mm or more.

FIG. 6 shows the relationship between the thickness h of the sidewall portion 3 on the tire axial line X and the tire weight (index) per tire. If the thickness h of the side wall portion is too large, the weight of the tire tends to increase remarkably. Therefore, in order to make the weight increase 110% or less, it is desirable to set the thickness to 13 mm or less, for example. Therefore, in the present embodiment, the thickness h of the sidewall portion
Is preferably 6.13 to 13 mm.
When such a specific thickness is represented by a ratio to the outer diameter D of the tire, the ratio (h / D) is set to about 0.01 to 0.022.

FIG. 7 shows a model of a long column receiving a load in the axial direction. The buckling load Pk of this long column is
It can be expressed by the following equation from Euler's theoretical equation. Pk = nπ ² EA / (L / k) ² where n: end condition of column E: modulus of longitudinal elasticity of material A: sectional area of column L: length of column k: secondary radius of section It is.

From this equation, it can be seen that in order to reduce the buckling load Pk, the shorter the column length L, the more difficult it is to buckle.
This is applied to the sidewall portion of the tire to reduce the radial distance H between the first point A and the second point B in the tire radial direction, for example, to increase the thickness h of the sidewall portion. The maximum stress acting on the sidewall portion 3 can be reduced without the need.

FIG. 8 shows the results obtained by examining the run flat performance while changing the distance H variously. Note that the horizontal axis represents a ratio (H / D) obtained by dividing the distance H by the outer diameter D of the tire in a normal state in order to eliminate the influence of the tire size. The run flat performance is the same as the above test, and the thickness h of the sidewall portion is
It was unified to 13mm. From FIG. 8, it can be seen that the run flat performance tends to decrease as the distance H of the tire increases. However, this ratio (H / D) is 0.8
It is understood that the run flat performance can be maintained high by setting the value to 5 or less, more preferably 0.8 or less.

[0035]

EXAMPLES Pneumatic tires having a tire size of 215 / 45R16 and shown in Table 1 were produced as prototypes (Examples 1 to 4), and run-flat performance, tire weight, rolling resistance and the like were measured. For comparison, a tire other than the present invention was prototyped and tested. Comparative Examples 1 and 2 have the same size as above, and Comparative Example 3 and the conventional example have a tire size of 2
05 / 55R15.

The content of the test was measured for tire weight and rolling resistance in addition to the above-mentioned run flat performance (the larger the numerical value is expressed by an index with the conventional example being 100). For tire weight, measure the weight per tire,
This is indicated by an index with the conventional example being 100, and the smaller the numerical value, the better. The rolling resistance was measured by mounting the test tire on the regular rim j and applying an internal pressure of 180 kPa, and using a drum type tire rolling resistance tester having a drum diameter of 1707.6 mm for a tire of 275 per tire.
The tire was run at a speed of 80 km / H under a load of kg, and its rolling resistance was measured. Evaluation is 1 for the conventional example
The index is set to 00, and the smaller the numerical value, the lower the rolling resistance. Table 1 shows the test results and the like.

[0037]

[Table 1]

As a result of the test, it can be confirmed that the tire of the example has improved run flat performance without a significant increase in tire weight.

[0039]

As described above, in the pneumatic tire of the present invention, the maximum stress acting on the sidewall portion is conventionally controlled on the basis of regulating the contour shape and the like of the sidewall portion in a normal state to a certain range. Thus, for example, it is possible to improve the run flat performance while suppressing an increase in tire weight.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a pneumatic tire showing one embodiment of the present invention.

FIG. 2 is a right half sectional view showing the outline.

FIG. 3 is a graph showing a relationship between a tire section constant J and run flat performance.

FIG. 4 is a graph showing a relationship between an arc coefficient C of a tire and run flat performance.

FIG. 5 is a graph showing a relationship between a tire section constant J and an arc coefficient C of the tire.

FIG. 6 is a graph showing a relationship between a tire weight and a thickness of a sidewall portion.

FIG. 7 is a diagram illustrating a buckling model of a long column.

FIG. 8 is a graph showing a relationship between a ratio (H / D) and run flat performance.

FIGS. 9A and 9B are conceptual diagrams illustrating a curved beam.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer A First point B Second point CL Tire middle line j Regular rim X Tire radial line Y Tire axial line

Claims (4)

[Claims] 1. A pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the tire is assembled to a regular rim, filled with a regular internal pressure, and has no load. In the tire meridian section in the state, the tire radial direction line Y passing through the rim width position of the regular rim
A first point A at the tread portion side that intersects a tire middle line passing through the middle of the tire thickness, a second point B at which the tire radial direction line Y intersects the tire middle line at the bead portion side, A first point A having a center Oa on the tire axial line X passing through the middle between the first point A and the second point B and on the tire lumen side, and contacting the tire middle line at the first point A; The radius of curvature Ra of the arc of curvature, the radius of curvature Rb of the second arc having the center Ob on the tire axial line X and on the tire lumen side, and contacting the tire middle line at the second point B; At a distance H in the tire radial direction from the first point A to the second point, a tire sectional constant J per unit circumferential length defined by the following equation is 0.8 or less. Pneumatic tires. (Equation 1) 2. The air according to claim 1, wherein the thickness h of the sidewall portion on the tire axial line X is 0.01 to 0.022 times the outer diameter D of the tire in the normal state. Containing tires. 3. The pneumatic tire according to claim 1, wherein an arc coefficient C of the tire defined by the following equation is not more than 5.0. (Equation 2) 4. The pneumatic tire according to claim 1, wherein the distance H in the tire radial direction is equal to or less than 0.085 times the outer diameter D of the tire in the normal state.