JPH10119514A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particularly studless type pneumatic radial tire for a 4-WD vehicle keeping the on-snow performance and improving the on-ice performance. SOLUTION: In a tire/rim assembly filled with a low inner pressure, the central region spread on both sides from the equatorial plane E respectively by the distance corresponding to the range of 30-45% of the width from the tire equatorial plane E to the tread end edge Q is formed into a circular arc on a tread 2t appearing on the cross section of the assembly in the self-supporting attitude of a tire. The remaining both side regions are formed into contour shapes serving as tangential lines at the circular arc ends, and the radius of curvature R of the circular arc at the central region is set within the range of 2.5-4.5 times the tread width.

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 pneumatic radial tire having a tread portion capable of obtaining a large contact area and a uniform contact pressure when a load is applied. However, the present invention relates to a studless pneumatic radial tire that exhibits remarkably excellent braking performance on an icy road when used in a four-wheel drive vehicle (hereinafter referred to as a 4WD vehicle).

[0002]

2. Description of the Related Art A studless type tire used for a 4WD vehicle among passenger cars particularly emphasizes the running performance on a deep snowy road in winter, and the tread pattern (especially groove edge component amount) and the negative ratio ( The ratio of the surface area of the groove to the total surface area of the tread), and the same tread rubber material, the tire having the longest possible contact length of the tread portion of the tread under the load is advantageous. Generalized. As a means for increasing the contact length as much as possible, a tread portion 2A in a left half section of a main part of a plane including the rotation axis of the conventional tire 1A shown in FIG.
The tread 2At contour is formed by a radius of curvature R ₁ centered on the tire equatorial plane E.

However, increasing the contact length of the tread 2At does not necessarily increase the contact length at the center of the tread width (tire equatorial plane E). The tread contact shape is a circular shape, which will be described in detail later, or an elliptical shape close to a circle.
The portion near the t-end Q (shoulder) is hardly grounded. This eventually resulted in a decrease in the contact area of the tread on the icy road surface, and as a result, the braking performance on the icy road surface deteriorated, and it was found that the user's requirements were not satisfied in this regard.

[0004] Further, the contact shape of a circle or an ellipse close to a circle is not limited to the shortage of the contact area, and the contact pressure distribution also has a steep peak at the center in the contact width direction and sharply decreases on both sides. A tire having a steep chevron shape and having a contact pressure distribution having such a steep chevron shape cannot avoid a decrease in braking performance on an icy road surface.

[0005]

SUMMARY OF THE INVENTION Accordingly, the inventions described in claims 1 to 3 of the present invention are of a studless type capable of remarkably improving braking performance on an icy road surface while maintaining sufficient snow performance. In particular, it is an object of the present invention to provide a pneumatic radial tire for 4WD.

[0006]

In order to achieve the above-mentioned object, the invention described in claim 1 of the present invention comprises a pair of bead portions, a pair of sidewall portions, and a tread portion, and these respective portions are reinforced. In a pneumatic radial tire having one or more plies of a radial carcass and a belt for reinforcing the tread portion at the outer periphery of the carcass, a tread appearing in a cross section of the tire in a vulcanization mold by a plane including a rotation axis of the tire. The center area where each tread is distributed on both sides from the equatorial plane by a distance corresponding to a range of 30 to 45% of the width from the tire equatorial plane to the tread edge is an arc, and the remaining both side areas are arc ends. Characterized in that the radius of curvature of the arc in the central region is in the range of 2.5 to 4.5 times the tread width, the pneumatic radial radiator having It is an arrow.

The tire in the vulcanization mold is, of course, a tire after vulcanization molding, and the cross-sectional shape of the tire in the mold is generally called an in-mold shape. A tire and a rim assembly in which the tire is mounted on the applicable rim are filled with an extremely low internal pressure corresponding to 3 to 7% of the internal pressure corresponding to the maximum load of the tire, and the tire cross-sectional shape is substantially equivalent to that of the tire in a self-standing position. .

[0008] The radial tire having the above-described tread surface contour shape adjusts the tensile stiffness and bending stiffness in a direction along the circumference of the belt (hereinafter referred to as a circumferential direction) to thereby achieve internal pressure filling corresponding to actual use conditions. Under the load, the shoulder portion indicated by a broken line is also grounded with a sufficient length in the circumferential direction as illustrated in FIG. FIG. 2 shows that the size of the pneumatic radial tire for a passenger car is 265 / 70R15,
FIG. 4 is a footprint of a flat plate under the conditions of an internal pressure of 2.0 kgf / cm ² and a load of 500 kg, and reference symbol E corresponds to the tire equatorial plane.

FIG. 4 shows the footprint of a conventional tire having the same size as that of the above-mentioned tire with the same internal pressure and load conditions and the same scale, and it is clear from comparison between the two contact shapes shown in FIGS. As described above, the tire according to claim 1 of the present invention has a slightly shorter ground contact length on the equatorial plane E of the conventional tire, but has a significantly longer ground contact length of the shoulder portion, and as a result, the groove portion has The total contact area including the contact area greatly increases, and the contact pressure in the contact width direction (direction orthogonal to the equatorial plane E) also increases as can be fully estimated from the figure.
The distribution gradually decreases from both sides.

Further, in order to realize a sufficient increase in the contact length of the shoulder portion and the entire contact area, and to realize various characteristics such as a preferable contact pressure distribution, the invention as described in claim 2 can be adopted.
Combining the angle of inclination of the tangent with a straight line perpendicular to the tire equatorial plane within the range of 2 to 10 degrees is further ensured by combining the invention with the first aspect.

According to the third aspect of the present invention, the braking performance on the icy and snowy road surface is substantially improved by the wide ground contact area and the leveled ground pressure distribution, and the essential improvement is realized in actual running. As described above, the negative ratio of the tread portion tread is set in the range of 35 to 45%. Thereby, the groove edge (edge) component can be increased, and the edge effect at the time of braking can be enhanced. In particular, the snow braking and traction performance based on a long contact length on the equatorial plane E required for a 4WD vehicle is improved by adding an edge component due to an increase in the contact area to an edge component due to a negative ratio of 35 to 45%. The edge component can be retained by increasing significantly.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic cross-sectional view (shape diagram of a mold) of a left half of a pneumatic radial tire (hereinafter referred to as a tire) in a vulcanization mold (not shown) surrounding the outside of the tire. Tire 1
Consists of a pair of bead portions (not shown), a pair of sidewall portions (not shown), and a tread portion 2 in accordance with a customary manner, and the radial carcass 3 of one ply or more has a bead core embedded in a bead portion (not shown). The belt 4 disposed on the outer periphery of the carcass 3 reinforces the tread portion 2 while reinforcing these portions over the space. The illustration of the groove provided in the tread portion is omitted.

The contour of the tread 2t of the tread portion 2 is formed by the following means. That is, first, referring to FIG. 1, the points P to which the distance C corresponding to the range of 30 to 45% of the width W from the tire equatorial plane E to the edge Q of the tread surface 2t is distributed to both sides of the equatorial plane E. The area sandwiched by the points P is defined as the central area of the tread 2t, and the outline of this central area is formed with a radius of curvature R centered on the tire equatorial plane E. The radius of curvature R is in the range of 2.5 to 4.5 times the width 2 × W of the tread 2t.

Next, it is assumed that the contour of the remaining area excluding the central area of the tread 2t is formed by a tangent at a point P in FIG. This tangent line is, of course, a straight line, but strictly speaking, includes an arc having an extremely large radius of curvature so as to be regarded as a straight line, in other words, a straight contour line. This is because the mold used for vulcanizing the tire according to the present invention is shown in FIG.
It is necessary that the inner peripheral surface of the mold that forms the tread surface from the point P to the point Q forms the side surface of the truncated cone, and the tread surface in the self-standing position of the tire defined above generally matches the inner peripheral surface. Or almost similar in shape. In any case, the portion between the points P and Q forms a conical surface or a conical surface viewed as the tread surface 2t of the entire tire.

Although it has been described above that the radius of curvature R needs to be determined to be 2.5 to 4.5 times the width 2 × W of the tread 2t, the tire equatorial plane E passing through the point P in FIG. It is even more effective that the inclination angle θ of the line segment PQ with respect to the normal L is within the range of 2 to 10 ° and that the above magnification is applied. Preferably, the negative ratio of the tread of the tread portion is set in the range of 35 to 45%.

The tire 1 provided with the tread 2t having the above-described structure on the tread portion 2 is shown in FIG.
It is possible to obtain the footprint shown in the above, and it is possible to exhibit excellent braking performance on icy road surfaces by the linked operation of a wide contact area and a uniform contact pressure distribution where the total value of the edge length is longer it can. Further, the on-snow performance can be sufficiently secured by further increasing the edge component caused by the negative ratio and the wider contact area. The tire according to the present invention is particularly advantageous when mounted on a 4WD vehicle as a studless tire based on a block pattern having a large number of groove edge components on the tread surface 2t.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pneumatic radial tire for a passenger car having a size of 265 / 70R15 and a radial carcass 3 according to FIG.
The belt 4 is made of plies, and the two-layer structure is composed of 1 × 3 steel cord cross layers. The half width W of the tread 2t is 107
mm, and the distance C from the equatorial plane E to the point P is 48.5.
mm. The radius of curvature R in the central area of the tread 2t is 750
mm and about 3.5 times the width of the tread 2t. The inclination angle θ of the line segment PQ with respect to the straight line L is about 5 °.

In order to confirm the effect of the embodiment, the radius of curvature R
₁ was prepared the conventional tire according to Figure 3 of 435 mm. As the tread pattern, the basic block pattern shown in FIG. The negative ratio is slightly different in both cases, and the negative ratio is 40% in the example and 47% in the conventional example.
Using these tires as test tires, tests were performed on the following five items.

(1) Ground contact area: An internal pressure of 2.0 kgf / cm ² was filled by an indoor test, and the empty vehicle weight and two occupants (60
load equivalent to the sum of the weight of 120 kg / kg)
(2) braking performance on ice; braking distance when full braking is applied from a running speed of 20 km / h on an icy road; (3) braking performance on snow; snowy road surface Braking distance when full braking is applied from a running speed of 40 km / h, (4) driving feeling on ice; actual vehicle running on an iced road surface provided on the test course, driving performance, braking performance, handling responsiveness, Comprehensive evaluation of road surface grip performance during steering and controllability after exceeding the slip limit, (5) Snow running feeling; actual vehicle running on a snowy road surface on the test course, similar to the above ice running feeling Comprehensive evaluation of test content. However, (2) ~
In the test of item (5), a 3000cc 4WD (RV) domestic car was used, and each test tire was mounted on four wheels, and the internal pressure and load were adjusted to item (1).

Among the test results of the items (1) to (5), the tests of the items (1) to (3) are represented by an index with the conventional example being 100, and the larger the value, the better. (4), (5)
In the feeling test of the item, the conventional example was used as a control (standard), and the superiority to this standard was scored by + (plus) and-(minus). Of course, the higher the score, the better. Table 1 shows the results.

[0021]

[Table 1]

From the numerical values shown in Table 1, the tires of the embodiment have significantly improved braking performance on ice compared to the conventional tires, and at the same time improved running performance in various running methods on ice, while having improved performance on snow. It is evident that both of these characteristics have been improved rather than maintaining the conventional braking level and running performance, and both characteristics show that the grounding area is increased (the edge length is increased) and the grounding pressure is leveled. It can be seen that the effect is noticeable.

[0023]

According to the invention described in claim 1 or 2 of the present invention, while maintaining or improving the on-snow performance of the conventional tire used particularly for a 4WD passenger car, it has been unsatisfactory for the user. It is possible to provide a pneumatic radial tire capable of significantly improving performance, especially braking performance on ice, which is important for avoiding danger or accident, and in particular, to provide a pneumatic radial tire capable of fully exploiting the performance of a studless tire. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view in the mold of a left main part of a tire according to an embodiment of the present invention.

FIG. 2 is a diagram showing a ground contact shape of a tire tread shown in FIG. 1;

FIG. 3 is a cross-sectional view of the inside of a mold of a left half of a conventional tire.

FIG. 4 is a view showing a ground contact shape of a tire tread shown in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pneumatic radial tire 2 Tread part 2t Tread surface 3 Radial carcass 4 Belt P contact Q Tread surface edge C Central area half width R Central area radius of curvature W Tread half width E Equatorial plane L Normal line to equatorial plane passing through point P θ line Angle of inclination of normal PQ with respect to normal L

Claims (3)

[Claims] 1. A pneumatic pump comprising a pair of bead portions, a pair of sidewall portions, and a tread portion, having one or more plies of a radial carcass for reinforcing these portions, and a belt for reinforcing the tread portion on the outer periphery of the carcass. In the radial tire, the tread surface of the tread portion in the cross-section of the tire in the vulcanization mold by the plane including the rotation axis of the tire is within a range of 30 to 45% of the width from the tire equatorial plane to the tread edge. The central area where the corresponding distance is distributed to both sides from the equatorial plane is a circular arc, and the remaining both side areas have a contour shape that is a tangent to the end of the circular arc, and the radius of curvature of the circular arc in the central area is 2. A pneumatic radial tire characterized by being in the range of 5-4.5 times. 2. The inclination angle of the tangent to a straight line perpendicular to the tire equatorial plane is in the range of 2 to 10 °.
Tire described in. 3. The negative ratio of the tread of the tread portion is 35.
The tire according to claim 1 or 2, which is within the range of ~ 45%.