JP3455693B2 - Pneumatic tire - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 vehicle safety equipment has been remarkable.
For example, equipment such as ABS, airbag system, and shock absorbing body tends to be installed as standard equipment even in low-priced vehicles, and safety is now the most important issue in the field of the automobile industry. This kind of safety is not an exception for tires as well, and it is desired to develop not only basic performance such as running, bending, and stopping, but also running capacity after puncture. In other words, even if the tires are flat while driving, you can drive to the nearest gas station or repair shop without having to change tires on the highway, at midnight, or in bad weather. The demand for tires is increasing.

The inventors have examined the damage process of the tire after puncture, and found that it is roughly as follows. First of all, when air is leaked out due to puncture, the vertical deflection of the tire becomes large, and stress is concentrated especially on a part of the inner surface of the tire, and the part having large strain is heated. Such heat generation causes rubber peeling and abrasion at an early stage to expose the carcass that forms the skeleton of the tire, and the carcass and the road surface or the carcass rub against each other, leading to breakage and fatal damage, making traveling impossible. Become.

[0004] As a countermeasure for this, normally, the rigidity of the entire tire is 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 rubber is increased. Also, these methods have been embodied almost empirically, which has led to a significant increase in tire weight.

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

[0006]

The invention according to claim 1 of the present invention is 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 being a regular rim. In a tire meridional section in a normal state in which the rim is assembled to the rim, a normal internal pressure is filled, and no load is applied, a 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. And a first point A that intersects on the tread portion side, a second point B that the tire radial direction line Y intersects the tire intermediate line on the bead portion side, and a first point A and a second point B of these. The radius of curvature Ra of a first arc having a center Oa on the tire axial direction line X passing through the middle and on the tire bore side and contacting the tire intermediate line at the first point A, the tire axial direction line X Above and on the tire bore side It has a heart Ob, and the second point B
And the radius of curvature R of the second arc tangent to the tire middle line
b, an angle φa formed by the tire axial direction line X and a straight line Oa-A connecting the center Oa and the first point A, the tire axial direction line X, the center Ob and the second point B. The following equations (1) to (5) are satisfied at the angle φb formed by the straight line Ob-B connecting the two and the outer diameter D of the tire in the normal state. 0.01 ≤ Ra / D ≤ 0.075 ... 0.01 ≤ Rb / D ≤ 0.075 ... 0 <φa ≤ 50 ° ... 0 <φb ≤ 50 ° ...

In the pneumatic tire of the invention according to claim 1, the tire constant T defined by the following equation is 1.6.
It is × 10 ⁻³ or less . T = {(Ra / D) / Z} × {1-cos (φa / 2)} + {(Rb / D) / Z} × {1-cos (φb / 2)}
However, Z = h2 / 6 h = thickness of the sidewall portion on the tire axial direction line X

Further, the pneumatic tie of the invention according to claim 1
Ya, the thickness h of the sidewall portion on said tire axial direction line X is 0.008 to 0.022 times the outer diameter D of the tire.

The pneumatic tire of the invention according to claim 2 has a tire curvature constant V defined by the following equation of 1
It is preferably 0 × 10 ⁻³ or less. V = (Ra / D) × {1-cos (φa / 2)} + (Rb / D) × {1-cos (φb / 2)} ...

In the present specification, the "regular rim" means
In a standard system including a standard on which a tire is based, the standard is a rim defined for each tire.
Standard rim for A, "Design Rim" for TRA,
Or for ETRTO, use "Measuring Rim".
In addition, the "normal internal pressure" is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. In the case of JATMA, the maximum air pressure, TRA
Then the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLA
If the maximum value stated in "TION PRESSURES" is ETRTO
"INFLATION PRESSURE", but 180kPa if the tire is for passenger cars.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a tire meridian cross section of a pneumatic tire 1 of the present embodiment. A carcass 6 extending from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3 and a carcass 6 on the outer side in the tire radial direction. The radial tire for a passenger car (205 / 55R15) of a tubeless type having a belt layer 7 arranged therein and having an inner liner rubber on the inner surface i of the tire is illustrated. Note that FIG. 1 shows an assembly of the tire and the rim in an unloaded normal state in which the tire is assembled to the regular rim J and is filled with the regular internal pressure (180 kPa). The tire sectional width SW is 223.0 mm and the tire sectional height H is 112.0 mm.

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

The carcass 6 has a body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a folded portion 6b extending from the body portion 6a and folded around the bead core 5. And a bead apex 10 made of hard rubber extending from the bead core 5 to the outer side in the tire radial direction is arranged between the main body portion 6a and the folded-back portion 6b. It is reinforced. In addition, in this example, a tire including a rim protector 4a that protrudes on the bead portion 4 so as to cover the outside of the rim flange JF in the tire radial direction is illustrated.

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

FIG. 2 shows a contour line of the tire meridian section (right half) of the pneumatic tire 1 in a normal state.
Further, in the drawing, a tire middle line CL passing through the middle of the thickness of this tire is shown by a one-dot chain line. Here, the "intermediate line of the tire" does not include a pattern on the outer surface of the tire or a protrusion such as the rim protector 4a provided on the bead portion 4, and therefore, in this example, the bead portion 4 excluding the rim protector 4a is included. It is specified based on the contour line (shown by a dotted line).

In FIG. 2, 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 with the tire middle line CL on the side of the tread portion 2 at A, and This tire radial direction line Y is the bead portion 4
Let B be the second point on the side that intersects the tire midline. Further, on the tire axial direction line X passing through the middle of the first point A and the second point B, and having a center Oa on the tire bore side,
Also, the radius of curvature of the first arc Ca that contacts the tire intermediate line CL at the first point A is Ra, and the center Ob is on the tire axial direction X and on the tire bore side, and at the second point B. The radius of curvature of the second arc Cb in contact with the tire intermediate line CL is Rb.

The intersection point P between the tire intermediate line CL and the tire axial direction line X is, in this example, on the tire axial direction line X outside the arcs Ca, Cb in the tire axial direction. Is illustrated.

Further, an angle formed by the tire axial direction line X and a straight line Oa-A connecting the center Oa and the first point A is φa (deg), the tire axial direction line X and the center O.
The angle formed by the straight line Ob-B connecting b and the second point B is φ
b (deg). The outer diameter of the tire in the normal state is D
In that case, the pneumatic tire 1 is characterized by satisfying the following formulas (1) to (4). 0.01 ≤ Ra / D ≤ 0.075 ... 0.01 ≤ Rb / D ≤ 0.075 ... 0 <φa ≤ 50 ° ... 0 <φb ≤ 50 ° ...

The inventors have found that the curved beam 1 as shown in FIG.
Attempts were made to apply the stress analysis of No. 2 to tires. First,
In the curved beam 12 having a radius of curvature R as shown in FIG.
When compressive load W is applied, maximum stress σ in cross section ZZ
m is approximately represented by a formula. .sigma.m = WR.multidot. {1-cos (.phi. / 2)} / Z ', where Z' = bh2 / 6. In addition, Z in FIG.
As shown in FIG . 6B which is a −Z cross section, h is a cross section Z−.
It is the thickness of Z and b is its width.

From this equation, it is understood that in order to reduce the maximum stress σm without increasing the thickness h of the beam, it is preferable to reduce the radius of curvature R of the curved beam and its central angle φ. If this is applied to a tire, the radius of curvature R and the central angle φ of the curved beam correspond to the radius of curvature and the central angle of the sidewall portion of the tire, respectively. Therefore, the maximum stress can be reduced without increasing the rubber thickness of the tire, for example, by restricting the radius of curvature of the sidewall portion of the tire to be small and the central angle to be small (the height of the cross section is small). As a result, the durability is improved and the continuous traveling distance after the flat tire can be increased.

The inventors have variously changed the contour shape of the sidewall portion of the tire to obtain the above-described radius of curvature R.
When a number of tires with different a, Rb and central angles φa and φb were made on a trial basis and the continuous running distance after the puncture was examined,
It has been found that, regardless of the tire size or the like, it is particularly preferable to limit the shape of the tire so as to satisfy the above formula or to improve durability.

Incidentally, in the conventional general pneumatic tire, Ra / D (or Rb / D) is set to be larger than about 0.08, and in the present invention, the ratio Ra / D thereof is set.
The value of (or Rb / D) is set smaller than the conventional value.
The radius of curvature Ra of the first circular arc and the radius of curvature Rb of the second circular arc may be the same or different. Similarly, φa and φb may be the same or different.

Here, the ratio (Ra / D) or (Rb /
When D) exceeds 0.08, the maximum stress acting on the sidewall portion 3 cannot be reduced, and the durability of the pneumatic tire cannot be sufficiently improved. Similarly, angles φa and φb
However, even if it exceeds 50 °, the maximum stress acting on the sidewall portion 3 cannot be reduced, and improvement in durability cannot be expected sufficiently. On the other hand, if the ratio (Ra / D) or (Rb / D) is too small, the riding comfort tends to deteriorate. Preferably, the ratio (Ra / D) or (Rb / D) is 0 to
0.075, more preferably 0.01 to 0.07, still more preferably 0.03 to 0.065, and 0.01 to 0.075 in the present invention.
It The angle φa or φb is 0 to 45 °, more preferably 10 to 40 °, and further preferably 20 to 35 °.
Is desirable.

When the above equation is applied to a tire, it can be expressed as the equation. σm = WRa · {1-cos (φa / 2)} / Z + WRb · {1-cos (φb / 2)} / Z ... This expression shows the maximum stress for a certain load W. The expression divided by the load W and divided by the outer diameter D of the tire in order to eliminate the influence of the tire size is represented by the parameter "tire constant T" per unit circumferential direction in the present specification. Defined by Then, it has been found that it is preferable to set the tire constant T to 1.6 × 10 −3 or less. T = {(Ra / D) / Z} × (1-cos (φa / 2)) + {(Rb / D) / Z} × (1-cos (φb / 2))
However, Z = h2 / 6 h = thickness of the sidewall portion on the tire axial direction line X

FIG. 3 is a graph showing the results of examining the run-flat performance of each of the tires with various tire constants T being changed. Run-flat performance is tire size 215/45 ZR17 and 205
/ 55R15 was performed, and a punctured tire with a rim assembled at a domestic passenger car with an internal pressure of 0 kPa was mounted on the right side of the front, and the test course was run, and the continuous running distance until this punctured tire became unable to run was examined and indexed It is a thing. Further, the test course includes a straight line portion and a turning portion, and the running speed of the straight line portion was 50 km / H and the running speed of the turning portion was 40 km / H under the same conditions. The thickness h of the sidewall portion on the tire axial direction line X is 1
The test was conducted by unifying it to 3 mm.

As is clear from FIG. 3, the runflat performance tends to decrease as the tire constant T increases.
However, by setting the tire constant T to 1.6 × 10 ⁻³ or less, more preferably 1.0 × 10 ⁻³ or less, and further preferably 0.6 × 10 ⁻³ or less, the run flat performance is maintained high. I understand that it will be done.

FIG. 4 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 this sidewall portion is too small, the absolute rigidity of the sidewall portion 3 tends to decrease, so this thickness h
Is preferably 5 mm or more, and more preferably 8 mm or more in the above size. Further, if the thickness h of the side wall portion is too large, the tire weight tends to remarkably increase, so that it is desirable to set it to 13 mm or less, for example. When such a specific thickness is expressed as a ratio with the outer diameter D of the tire, the ratio (h / D) is set to 0.008 to 0.022.

Further, in the present embodiment, the above equation is multiplied by Z to remove the factor of the thickness h of the sidewall portion of the tire, and the curvature constant V of the tire is investigated in order to investigate the influence of the sectional shape of the sidewall portion 3. Is defined by the following equation. It was found that it is preferable to set the curvature constant V of this tire to 10 × 10 ⁻³ or less. V = (Ra / D) × {1-cos (φa / 2)} + (Rb / D) × {1-cos (φb / 2)} ...

FIG. 5 shows the results of examining the run-flat performance by variously changing the curvature constant V of this tire. The run-flat performance is the same as the above test. As is clear from FIG. 5, the runflat performance tends to decrease as the curvature constant V of the tire increases. However, this curvature constant V is 10.0 × 1
By setting it to 0 ⁻³ or less, more preferably 9.0 × 10 ⁻³ or less, and further preferably 8.0 × 10 ⁻³ or less,
The run-flat performance can be maintained high.

Table 1 shows the values Ra, Rb, φa and φ.
An example of b, h, T, and V is shown.

[0031]

[Table 1]

In Table 1, the thickness h of the sidewall portion
Comparing the tires A, B, the tires C, D, and the tires E, F with different values, it can be seen from FIG. 3 that the tire constant T decreases due to the increase in h, and the run-flat performance improves. Further, when tires A and C having the same sidewall thickness h are compared, the tire constant can be reduced as Ra and Rb are smaller.
Further, comparing tires A and E having the same thickness h of the sidewall portion, the tire constant can be reduced as φa and φb are smaller.

[0033]

EXAMPLES Pneumatic tires having a tire size of 215 / 45R16 and shown in Table 2 were prototyped (Examples 1 to 4), and the run-flat performance, tire weight, rolling resistance, etc. were measured. For comparison, tires not included in the present invention were also prototyped and tested. Comparative Examples 1 and 2 have the same size as above, and Comparative Example 3 and Conventional Example have tire sizes of 2
05 / 55R15.

The contents of the test were the above-mentioned run-flat performance (the larger the numerical value in the index display with the conventional example being 100, the better), and the tire weight and rolling resistance were measured. For tire weight, measure the weight per tire,
This is displayed as an index with the conventional example being 100, and the smaller the value, the better. The rolling resistance was 275 per tire by mounting the test tire on a regular rim and applying an internal pressure of 180 kPa to the tire using a drum type tire rolling resistance tester with a drum diameter of 1707.6 mm.
The tire was run at a speed of 80 km / H under a load of kg, and the rolling resistance value was measured. Evaluation is based on the conventional example 1
The index is set to 00, and the smaller the value, the less rolling resistance. Table 2 shows the test results.

[0035]

[Table 2]

As a result of the test, it can be confirmed that the tires of the examples have improved run-flat performance without a significant increase in tire weight.

[0037]

As described above, the pneumatic tire of the present invention is based on the fact that the contour shape of the sidewall portion in a normal state is restricted to a certain range, and the maximum stress acting on the sidewall portion is higher than that of the conventional tire. The run-flat performance can be improved while suppressing an increase in tire weight.

[Brief description of drawings]

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

FIG. 2 is a right half sectional view showing its contour.

FIG. 3 is a graph showing the relationship between tire constant T and runflat performance.

FIG. 4 is a graph showing the relationship between tire weight and sidewall thickness.

FIG. 5 is a graph showing a relationship between a tire curvature constant V and run-flat performance.

6A and 6B are conceptual diagrams illustrating a curved beam.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-2-147427 (JP, A) JP-A-4-15111 (JP, A) JP-A-11-334315 (JP, A) JP-A-9- 164822 (JP, A) JP 7-215023 (JP, A) JP 10-297226 (JP, A) JP 10-297224 (JP, A) JP 5-178006 (JP, A) JP-A-5-104904 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 17/00 B60C 17/04 B60C 13/00 B60C 9/08 B60C 3/04 WPI (DIALOG )

Claims (2)

(57) [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, the tire being assembled on a regular rim, the regular internal pressure being filled, and no load being applied. A tire radial direction line Y passing through the rim width position of the regular rim in the tire meridian section in the state
Is a first point A that intersects the tire intermediate line passing through the middle of the tire thickness on the tread portion side, a second point B that the tire radial line Y intersects the tire intermediate line on the bead portion side, A first axis having a center Oa on the tire axial direction line X passing through the middle of the first point A and the second point B and on the tire bore side and contacting the tire middle line at the first point A A radius of curvature Ra of an arc of a second arc having a center Ob on the tire axial direction X and on the tire bore side and contacting the tire midline at the second point B, An angle φa formed by the tire axial direction line X and a straight line Oa-A connecting the center Oa and the first point A, a straight line connecting the tire axial direction line X, the center Ob and the second point B The angle φb formed by Ob-B and the outer diameter D of the tire in the normal state are as follows: As well as fulfillment, tire constants defined by 0.01 ≦ Ra / D ≦ 0.075 ... 0.01 ≦ Rb / D ≦ 0.075 ... 0 <φa ≦ 50 ° ... 0 <.phi.b ≦ 50 ° ... formula T is 1.6 × 1
0-3 or less, T = {(Ra / D) / Z} × {1-cos (φa / 2)} + {(Rb / D) / Z} × {1-cos (φb / 2)}
... However, Z = h2 / 6 h = the sidewall portion on the thickness moreover the tire axial direction line X of the sidewall portion on the tire axial direction line X
The thickness h is 0.008 to 0.022 times the outer diameter D of the tire
Pneumatic tire characterized by being . 2. A tire curvature constant defined by the following equation :
V is 10 × 10 ⁻³ or less.
The pneumatic tire according to 1. V = (Ra / D) × {1-cos (φa / 2)} + (Rb / D) × {1-cos (φb / 2)} ...