JPH05131805A - Radial tire - Google Patents

Abstract

PURPOSE:To enhance high-speed steering stability, comfortability, and highspeed durability by properly setting the relative relationship among the rigidity of belts, the rigidity of side walls, and the crown R (not shown) of the tread. CONSTITUTION:A radial tire is provided with one-layer cap ply 8 for covering the central part and both end parts of two-layer scale belts 3, 4, and with one- layer edge plies 9 for covering both end parts thereof. Denoting by CPW the width of the cap ply 8, and by EPW the width of the edge ply 9, the ratio EPW/-CPW is set to satisfy the relationship 0.2<EPW/CPW<0.4. And the sectional width W of the tire measured in no-load condition and in such a condition that the tire had been assembled in a prescribed standard rim and filled with a prescribed compressed air is set to be less than the nominal width. Further, denoting by CW the ground-contacting width of the tire at the time a prescribed load has been loaded, and by h the displacement in the radial direction of the ground-contacting end part P measured between the no-load condition and the loaded condition, the ratio h/CW is set to satisfy the relationship 0.035<-h/Cw<0.045. Thus, various characteristics at the initial stage can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire capable of improving comfortability, high-speed steering stability and high-speed durability.

[0002]

2. Description of the Related Art In recent years, flattening of tires has progressed as the performance of vehicles has improved, and dynamic performance has been improved by using radial tires having a flatness rate of 55% or less.

The high-speed steering stability and high-speed durability of a vehicle equipped with such a radial tire having a low flatness ratio largely depend on the change of the tire ground contact surface due to centrifugal force. That is, the ground contact area decreases due to centrifugal force during high-speed running,
Since the restraint force of the belt on the tread shoulder is smaller than that on the center, the tread shoulder rises radially outward. For this reason, the ground contact surface shape shown by the solid line A in FIG. 2 when the vehicle is stopped changes as shown by the broken line B in the figure during high-speed traveling, and the ground contact length at the center of the tread becomes shorter than that at the shoulder portion. In this way, when the contact length in the center of the tread becomes shorter,
The self-aligning torque is reduced to reduce high-speed steering stability, and heat generation in the shoulder portion is increased to reduce high-speed durability.

Therefore, the crown R is reduced or the belt is covered with a reinforcing ply to increase the rigidity of the belt, thereby increasing the belt tension of the shoulder portion of the tread and suppressing the growth of the shoulder portion of the tread to operate at high speed. It is intended to improve stability and high-speed durability.

[0005]

However, if the belt tension at the shoulder portion is increased by reducing the crown R or covering the belt with a reinforcing ply, the enveloping property for wrapping the unevenness of the road surface is deteriorated and the comfortability is deteriorated. Become. Further, since the belt tension at the center portion of the tread becomes small, a buckling phenomenon occurs in which the center portion of the tread floats up from the road surface, and steering stability deteriorates. Furthermore, the center part of the tread grows radially outward due to centrifugal force, and the ground contact area easily changes due to changes in the load applied due to road surface irregularities and side winds, increasing the load dependency of the change in the ground contact surface. High-speed steering stability is reduced,
The heat generated in the center part increases and the high-speed durability deteriorates.

An object of the present invention is to provide a radial tire which can solve the above-mentioned problems of the prior art.

[0007]

A feature of the present invention is that one layer of cap ply covers the center and both ends of a two-layer steel belt, and one layer covers each end of the cap ply. Edge ply is provided, the width of the cap ply is CPW, the width of the edge ply is EPW, 0.2 <EPW / CPW <0.4, and a predetermined air pressure is obtained by assembling to a predetermined standard rim. The tire cross-section width W measured in a loaded and unloaded state is smaller than the nominal width of the tire, and the ground contact width under load when a predetermined load is applied is CW. The point is that 0.035 <h / CW <0.045, where h is the radial displacement.

[0008]

The present invention is intended to improve high-speed maneuvering stability, comfort and high-speed durability by optimizing the relative relationship among belt rigidity, sidewall rigidity, and tread crown R. .

First, the rigidity of the belt is made appropriate by the regulation of the width ratio EPW / CPW of the width of the cap ply which is the reinforcing material of the belt and the edge ply.

That is, by setting 0.2 <EPW / CPW, it is possible to prevent the deterioration of the envelope property due to the excessive belt tension of the shoulder portion of the tread and to improve the comfortability. Further, the change in shape of the ground contact surface is reduced, the decrease of the self-aligning torque is prevented, the heat generation of the shoulder portion is reduced, and the high speed steering stability and high speed durability are improved.

By setting EPW / CPW <0.4,
The tension of the center part of the tread does not become too small, the occurrence of buckling is prevented, the load dependency of the contact surface change is reduced, and the high-speed steering stability is improved.
Further, heat generation in the center portion of the tread is reduced, and high speed durability is improved.

By making the tire cross-section width W smaller than the nominal width of the tire, the cord path of the carcass ply in the sidewall of the tire is shortened, and the rigidity of the sidewall is increased. As a result, the growth of the shoulder portion of the tread due to centrifugal force is suppressed, the change in shape of the ground contact surface is reduced, the decrease in self-aligning torque is prevented, and high-speed steering stability can be improved. By preventing heat generation, high speed durability can be improved.

The crown R is optimized by defining the ratio between the load contact width CW and the tire radial displacement h of the load contact end P from no load.

That is, by setting h / CW <0.045, the crown R of the tire is made relatively large. As a result, the deterioration of the envelope property due to the excessive belt tension of the shoulder portion of the tread is prevented, and the comfortability is improved. In addition, the belt tension at the center of the tread does not become too low, preventing the occurrence of buckling and reducing the load dependency of changes in the contact surface to improve high-speed steering stability. The heat generation of the part is reduced and the high speed durability is improved.

By setting 0.035 <h / CW, the belt tension at the shoulder portion of the tread does not become too small, the shape change of the ground contact surface becomes small, and the decrease of the self-aligning torque is prevented. Heat generation in the shoulder is reduced, and high-speed steering stability and high-speed durability are improved.

The reason why the two-layer steel belt is used as the belt is that the belt rigidity is too small for one layer and too large for three or more layers.

The nominal width of the tire is ISO, JIS,
It is standardized by the standards established by Japan Automobile Tire Manufacturers Association (JATMA). The width of the cap ply and the edge ply is the actual length. In addition, a predetermined standard rim,
The predetermined air pressure and the predetermined load are those specified by the standard defined by JATMA (JATMA YEAR).
BOOK, 1990 edition, see Chapter A). This is because when the rim width, the air pressure, and the applied load are different, the sectional width of the tire and the ground contact width at the time of loading are different. Therefore, the JATMA standard is used as a standard for numerically limiting the sectional width of the tire and the like. In this JATMA standard, a standard rim is defined according to a tire size, and a design regular load is defined as a predetermined load corresponding to a case where a predetermined air pressure is filled.

Since a tire having a large flatness has a small ground contact area, steering stability is greatly reduced when the shoulder portion of the tread grows at high speed. Therefore, in a tire having a large flatness, it is necessary to reduce the crown R to suppress the growth of the shoulder portion.
It is difficult to make W smaller than 0.045. Therefore, the present invention is preferably applied to radial tires having a small flatness, particularly those having a flatness of 55% or less.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross section of a radial tire according to an embodiment of the present invention which is orthogonal to the equatorial plane and includes a rotation axis. 1 is a tread, 2 is a carcass ply, 3 and 4 are two-layer steel. Belt 5 is a bead core, 6 is a bead filler, 7 is a sidewall, 8 is a single layer of cap ply covering the central portions and both ends of the belts 3 and 4, and 9 is a single layer covering each end of the cap ply 8. Shows the edge ply of.
The cord angle of each of the steel belts 3 and 4 with respect to the tire circumferential direction is in the range of about 15 ° to about 30 °. The cap ply 8 and the edge ply 9 are nylon cords rubberized, and the cord angle with respect to the tire circumferential direction is approximately 0 °.

When the width of the cap ply 8 is CPW and the width of the edge ply 9 is EPW, 0.2 <EPW /
CPW <0.4. In addition, the tire cross-section width W measured in an unloaded state after being assembled in a standard rim defined according to the tire size in the JATMA standard and filled with the specified air pressure is made smaller than the nominal width of the tire. Further, when the design ground load corresponding to the air pressure specified in the JATMA standard is loaded, the ground width under load is CW, and the radial displacement of the ground contact end portion P under load from no load is h. 0.035 <h / CW <0.045.

Table 1 below shows the data of Examples and Comparative Examples.

[Table 1]

The radial tire size used to determine the data in Table 1 above was 225 / 50ZR16,
The high-speed driving stability and the riding comfort are based on the feeling test, and the result of the conventional example is set to 100,
The larger the index, the better. In addition, high-speed durability is based on Regulation No. 30
orm Provisions Cncerning the Approval of Pneumatic
Tires for Motor Vehicl and Their Trairers), which is based on the tests conducted in accordance with the conditions for tires with speed code V defined as the load / speed performance test procedure in Annex 7 to the specified speed and time. Under the conditions, no failure was observed and the test passed, but the speed was changed to 10 every 10 minutes.
Incrementing by km / h, drum running is continued until a failure occurs, the result of the conventional example is set to 100, and the larger the index, the better.

From Table 1 above, it is recognized that the examples are superior to the conventional examples in high-speed steering stability, riding comfort, and high-speed durability. Further, in Comparative Example 1 in which the cross-sectional width is larger than the nominal width, high-speed steering stability and high-speed durability are deteriorated. This is because the shoulder portion of the tread grows due to the centrifugal force due to the decrease in the rigidity of the sidewall, the ground contact surface shape changes, the self-aligning torque decreases, and the heat generation of the shoulder portion increases. In Comparative Example 2 in which h / CW is decreased and crown R is increased, high-speed steering stability and high-speed durability are deteriorated. This is because the shoulder portion of the tread grows due to the centrifugal force due to the reduction of the belt tension, the shape of the contact surface changes, the self-aligning torque decreases, and the heat generation of the shoulder portion increases. In Comparative Example 3 in which h / CW is increased and crown R is decreased, high-speed steering stability, riding comfort and high-speed durability are deteriorated. Backlinks tend to occur due to a decrease in the belt tension at the center of the tread,
This is because the growth of the center portion increases the load dependency of the ground contact surface change and the heat generation of the center portion, and the increase in the belt tension of the shoulder portion reduces the envelope property. E
In Comparative Example 4 in which PW / CPW is reduced to reduce belt rigidity, high-speed steering stability, riding comfort, and high-speed durability are deteriorated. This is because the belt tension of the shoulder portion of the tread becomes excessive and the envelope property deteriorates, the shoulder portion grows due to centrifugal force, the self-aligning torque decreases, and the heat generation of the shoulder portion increases. In Comparative Example 5 in which the EPW / CPW is increased to increase the belt rigidity, the high-speed steering stability is reduced. This is because a back link is likely to occur due to a decrease in the belt tension in the center portion of the tread, and the growth of the center portion increases the load dependency of the change in the ground contact surface.

[0025]

According to the radial tire of the present invention,
With a new structure that has never existed before, high-speed steering stability, comfort and high-speed durability can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a sectional structure of a radial tire according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a change in a tire contact surface

[Explanation of symbols]

 3, 4 Belt 8 Cap ply 9 Edge ply

Claims (1)

[Claims] 1. A one-layer cap ply covering a central portion and both end portions of a two-layer steel belt, and one layer of edge ply covering each end portion of the cap ply, and the width of the cap ply. Is CPW, and the width of the edge ply is EPW, 0.2 <EPW / CPW <0.4, and the tire cross-section width W measured in an unloaded state after being assembled in a predetermined standard rim and filled with a predetermined air pressure. Is smaller than the nominal width of the tire, the ground contact width under load when a predetermined load is applied is CW, and the radial displacement of the ground contact end portion P under load from no load is 0.035 <h / A radial tire having CW <0.045.