JPH03248902A - Radial tire - Google Patents

Abstract

PURPOSE:To make smooth tension of a belt by adopting a belt of a rigidity distribution wherein the sizes of a crown and side edge part of a tread increased while the size of central part of the trea reduce, and thereby increasing the tension of belt at the aforesaid respective parts. CONSTITUTION:In a radial tire, at least two sheets of belts 20, 30 are arranged on a carcass 10 while the aspect ratio is set at 65% or less. In this case, when a cut plane passing through the center of tire while being vertical to the equatorial plane of tire is assumed, and provided that the virtual cross point between the extension curves 60, 61 of a main parts of both sides as well as a tread in point P, the difference in height between the center of the grounding face of tread and the point P is set at 5% or less of the distance between both points P, that is, the width of tread. The belt 20 is provided with a sheet cord while the belt 30 with a cord having a lower young rate than the former. Both ends of the belt 30 is bent back with the width set in a range of 15-30% of tread width TW.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a radial tire having an aspect ratio of 65% or less and having at least two belts disposed on the carcass.

[Prior Art and Problems to be Solved by the Invention] A radial tire is known that has a tread portion in which two steel belts are arranged on the carcass.

In this tire, the tread side edges, where the belt circumferential restraining force is lower than the tread center, rise significantly due to centrifugal force during high-speed running, and the radius of curvature of the tread, that is, the crown R, tends to increase. At this time, the contact surface becomes cocoon-shaped and the contact length at the center of the tread is particularly reduced.

This decrease in ground contact length becomes more severe as the running speed increases, leading to a decrease in self-lining torque and deteriorating straight-line stability. Furthermore, when cornering, when the camber angle or slip angle becomes large, this tire receives lateral force and the contact patch becomes approximately triangular. At this time, the cornering force may decrease as the total ground contact area decreases, and a buckling phenomenon may occur in spots on the ground contact surface on the tread side edge OUT side due to belt compression force.

Conventionally, this problem has been addressed by increasing the belt's rigidity by widening the belt width, reducing the cord angle of the belt, or covering the entire belt with nylon reinforcing material. However, if the rigidity of the entire belt is increased, the belt tension at the tread side edges increases, but the belt tension at the tread center decreases. Therefore, while the change in the contact surface shape due to centrifugal force and cornering lateral force can be reduced,
Not only is there a risk of buckling occurring in the center of the tread, but in tires with an aspect ratio of 65% or less, there is a problem of deterioration of envelope properties due to increased belt tension at the tread side edges. Here, the property of enveloping the tires of a running car or protrusions on the road surface is called enveloping property, and if this property deteriorates, the ride comfort of the car, that is, the livability of the car will deteriorate.

On the other hand, if the crown radius at the same internal pressure is set large, the belt tension at the center of the tread increases and buckling can be prevented, but the belt tension at the side edges of the tread decreases and the shape of the contact patch changes significantly. turn into.

Now, as a result of carrying out dynamic simulation of tires using three-dimensional FEM (finite element method), the inventors of the present application found that
The following findings were obtained.

(1) An increase in heald tension does not always reduce the envelope property, but the problem is an increase in belt tension at the tread side edges.

(2) In other words, by increasing the belt tension at the center of the tread, which causes buckling, and at the same time not increasing the belt tension at the side edges of the tread more than necessary, it is possible to balance the stability of the contact patch shape and the enveloping property. This leads to things.

The present invention has been made in view of the above points, and the aspect ratio of at least two belts arranged on the carcass is 6.
The purpose is to stabilize the contact patch shape, including prevention of buckling, and to ensure good envelope properties in radial tires with a diameter of 5% or less.

[Means for Solving the Problems] The radial tire according to the present invention considers a cutting plane that is perpendicular to the tire equatorial plane and passes through the tire center, and a virtual intersection between the tread main part extension curve and both side main part extension curves. When each point is defined as P point, the height difference (h) between the center of the tread surface and P point is the distance between both P points, that is, the tread width (TW
), the first belt on the carcass has a steel cord, the second belt on this belt has a cord with a lower Young's modulus than the steel cord, and both ends of the second belt have a tire The second belt is folded back toward the equatorial plane, and each fold width (FW) of this second belt is the tread width (TW).
It is characterized by being 15% or more and 35% or less of.

[Function] Compared to a conventional radial tire in which the height difference (h) between the center of the tread surface and the point P was about 6% of the tread width (TW), the radial tire according to the present invention has By setting this ratio to 5% or less, a large crown radius is achieved. Furthermore, in the radial tire according to the present invention, both ends of the second belt are folded back by 15 to 35%, thereby increasing the belt rigidity at the tread side edges compared to the tread center.

If only the crown R is increased, the belt tension at the center of the tread increases as described above, but the belt tension at the side edges of the tread decreases.

On the other hand, if a belt stiffness distribution is adopted in which the belt stiffness is large at the tread side edges and small at the tread center, belt tension tends to increase at both the tread center and the tread side edges. Therefore, at the same time as making the crown R thicker, the tread side edges are made larger.
In the radial tire according to the present invention, which adopts a small belt stiffness distribution in the center of the tread, it is possible to increase the belt tension in the center of the tread while maintaining the belt tension in the side edges of the tread at the same level as before. Tension leveling, smoothing is realized.

In other words, even when running at high speed, the folded portion of the second belt or the side edge of the tread is prevented from sagging, which reduces the change in the contact surface shape and maintains the contact length at the center of the tread. Therefore, straight-line stability during high-speed driving is ensured.

Additionally, the reduction in the total ground contact area due to changes in camber angle and slip angle during cornering can be suppressed, ensuring a large cornering force. Moreover, since the belt tension is high at the center of the tread, it is necessary to avoid the risk of huckling occurring at this position, which improves ground contact during cornering.

Historically, Tread-L is second to none, and since the second belt uses a cord with a lower Young's modulus than still coat, it improves envelope performance.

Note that if the ratio of the second belt folding width (FW) to the tread width (TW) exceeds 3586, it will not be different from the case where the rigidity of the bell 1 is increased overall, and no improvement in ground contact can be expected. On the other hand, if this ratio is less than 15%, the rigidity of the tire will be insufficient and the durability of the tire will be insufficient.

[Example] FIG. 1 is a partial cross-sectional view of a radial tire according to an example of the present invention.

Two belts 20 and 30 are arranged on the carcass 10, and the outer peripheral surfaces of both belts are covered with the rubber of the tread portion 40. Further, the tire side portions are covered with rubber forming side portions 50. The flatness ratio is 65%.

Now, in designing the gold WJ used in manufacturing this tire, when considering a cutting plane that is perpendicular to the tire equatorial plane and passes through the tire center, the intersection of the tire tread portion curve and both tire side curves is Each is called a P point. In FIG. 1, point P is the virtual intersection of the tread main part extension curve 6o and the side main part extension curve 61.

In the radial tire shown in the figure, the height difference (h) between the center of the tread surface and point P is 4.4% of the distance between both points P, that is, the tread width (TW). It is necessary that the ratio of h to TW be 5% or less.

The first belt 20 of the carcass 10 has a steel cord at an angle of 15 to 30 degrees with respect to the tire equatorial plane.

Moreover, although this first Peru 2o contacts the tread center or the carcass 10, the end 2
1 is away from carcass 10. Therefore, the thickness of the tread portion 40 is substantially uniform.

The second belt 3o on this first Peruvian belt 20 has an aramid fiber cord having a lower Young's modulus than that of still steel. The angle of this cord with respect to the tire equatorial plane is set in the range of 10 to 30' smaller than that of the first Peru 2o. After the second belt 3o is stretched along the first belt 20,
Both ends of the first belt are folded back toward the tire equatorial plane at a position 31 further outside the end portion 21, and the fold width (FW) is 21.5% of the l·red width (TW). It is necessary that the ratio of FW to TW be 15 to 35%.

Ta ear belt (BW) is preferably equal to or less than TW.

In the conventional cut edge belt without folding the end, it was necessary to make the BW larger than the TW in order to suppress the heat generation of a part of the belt, but in the case of this embodiment in which the second belt 30 is folded, BW can be made equal to or less than TW. In this example, the ratio of BW to TW is 95.6%.

Now, regarding the radial tire according to this example, Table 1 shows the results of feeling evaluation using an actual vehicle, and Figure 2 shows the relationship between running speed and tread center contact length, and shows the overall effect on camber angle changes during cornering. FIG. 3 shows how the ground contact area changes, and FIG. 4 shows the results of determining the axial force 41 when riding over a protrusion for evaluation of envelope properties.

(Leaving space below) The radial tire of Comparative Example 1 in Table 1 and Figures 2 to 4 has two steel belts placed on the carcass, the entire belt is covered with two nylon reinforcing materials, and the tire is capped. It has a conventional belt structure with plies. The tires of Comparative Examples 2 and 3 have the same belt structure as the present example, but the ratio of FW to TW deviates from the range of 15 to 35%.

The radial tire according to this embodiment uses an aramid fiber cord for the second belt 30, so the rigidity of the entire belt is reduced, so the sharpness of the response in the feeling evaluation is slightly inferior. Not only is the smoothness of response significantly improved, but the center contact length of the tread is maintained even when driving at high speeds, the reduction in total contact area due to changes in camber angle during cornering is suppressed, and the envelope Improved performance and ride comfort. Moreover, unlike the case of Comparative Example 2, no decrease in durability was observed. In the case of Comparative Example 3, no improvement in ground contact was observed.

2 [Effects of the Invention] As explained above, the radial tire according to the present invention has a large crown R and a large tread side edge.
Since the belt rigidity distribution is small in the center of the tread, it is possible to increase the belt tension in the center of the tread while maintaining the belt tension in the side edges of the tread, thereby achieving smooth belt tension. Therefore, according to the present invention, it is possible to ensure good envelope properties while suppressing changes in the shape of the ground contact surface during high-speed driving or cornering.

[Brief Description of the Drawings] Fig. 1 is a partial sectional view of a radial tire according to an embodiment of the present invention, Fig. 2 is a graph showing the relationship between running speed and tread center contact length, and Fig. 3 is a graph showing the relationship between running speed and tread center contact length. , a graph showing changes in total ground contact area with respect to changes in camber angle during cornering, 3. Figure 4 is an envelope property evaluation chart showing the results of measuring axial force when going over a protrusion. Explanation of symbols 10...Carcass, 20...First belt, 30...
- Second belt, 40... tread part, 50... side part. Patent No. 8' (Applicant: Toyo Rubber Industries, Ltd. 4)

Claims (1)

[Claims] 1. For radial tires with at least two belts on the carcass and an aspect ratio of 65% or less, consider a cutting plane that is perpendicular to the tire equatorial plane and passes through the tire center, and calculate the tread main part extension curve and both side main parts. When the virtual intersection with the extension curve is defined as point P, the center of the tread surface and P
The height difference (h) between the two P points is 5% or less of the distance between both P points, that is, the tread width (TW), and the first belt on the carcass has a steel cord, and the second belt on this belt has a steel cord. The belt has a cord with a lower Young's modulus than a steel cord,
A radial tire characterized in that both ends of the second belt are folded back toward the tire equatorial plane, and each fold width (FW) of the second belt is 15% or more and 35% or less of the tread width (TW). tire.