JPH0310903A - Radial tire - Google Patents

Abstract

PURPOSE:To suppress change in a carcass profile following its running by dividing the carcass profile into respective upper and lower spheres while respectively specifying such as ratio in respective radii of curvature in the respective upper and lower spheres and ratio between respective radii of curvature at the time of difference in inside pressures in the upper sphere. CONSTITUTION:The carcass profile 15 of a carcass 9 is divided into an upper sphere C1 expanded outward between a belt outer periphery point (a) and a carcass maximum width point (b) and a lower sphere C2 expanded outward from the carcass maximum width point (b) to an inflection point (c). Ratio in respective radii of curvature R1, R2 in respective upper and lower spheres C1, C2 is set into a range of 0.95-1.08. Moreover, ratio of respective radii of curvature R1 of each upper sphere C1 in an inside pressure charged up state in 5% of regular inside pressure and a regular inside pressure charged up state is set up into a range of 0.70-0.95. Still more, ratio of radius of curvature TR1 of the surface of the tread part 4 to the tire maximum width SW in the regular inside pressure charged up state is set up into a range of 1.28-1.95.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to a radial tire that can be suitably used for heavy vehicles such as trucks, buses, and light trucks.

[Conventional technology]

Radial tires, especially radial tires used for heavy vehicles such as large and small trucks and buses, that is, radial tires for heavy loads, are required to reduce the so-called total cost, which is related to tire maintainability, overall life, etc. There is.

Regarding maintainability, it is necessary to reduce tire replacement, that is, tire rotation, on each vehicle by improving tire wear resistance and, in particular, increasing uneven wear resistance.

Furthermore, in order to increase the overall lifespan, it is required to increase the number of times a tire is retreaded using a base tire including a carcass, a belt layer, etc. by improving the wear life and durability of the tire.

On the other hand, in order to improve various performances of such heavy-duty radial tires, adjusting the carcass profile of the tire has been proposed, for example, in Japanese Patent Laid-Open No. 60-61305.

This proposal is intended to reduce rolling resistance while maintaining wet performance by intentionally deviating the carcass profile from its natural equilibrium shape.

Furthermore, regarding tire retreading performance, in order to improve tire durability, we have made proposals regarding the materials and structures of carcass cords, breaker cords, and reinforcement structures for bead parts, etc.
Various proposals regarding carcass profiles have been made.

[Problem to be solved by the invention]

However, none of the other conventional proposals regarding carcass profiles, including the above-mentioned Japanese Patent Application Laid-open No. 60-61305, are concerned with improving the prevention of uneven wear of tires, and furthermore, they are not related to improvements in preventing uneven wear of tires. This article relates to a carcass profile or a change in the shape of a carcass profile due to internal pressure filling in a new tire, and does not focus on changes in the carcass profile in a new tire and in a state after driving.

The present inventor has made various developments in order to improve tire maintainability, such as reducing tire rotation by increasing wear resistance and preventing uneven wear. the result,
The carcass profile also greatly contributes to uneven wear resistance, especially the difference between the carcass profile in a new tire and the carcass profile after running, that is, even when the tire is running for a long time without wear. , the carcass profile changes due to long-term loads associated with running, as if the constituent members of each part such as the carcass, belt layer, tread section, etc. undergo permanent deformation. This comes from the discovery that by minimizing changes in the carcass profile, uneven wear can be prevented and the performance of the tire can be maintained close to that of a new tire for a long time.

Moreover, it has been found that the change in carcass profile can be reduced by setting the ratio of the radius of curvature of the upper region and the lower region in the sidewall portion to a predetermined range.

In addition, the present applicant has proposed, in accordance with Japanese Patent Application Laid-Open No. 61-200004, that the radius of curvature of the carcass in a part of the shoulder is reduced by filling the carcass profile with the normal internal pressure from 5% of the normal internal pressure. As such, we are proposing a tire that can improve the cut resistance, abrasion resistance, high-speed durability, fuel efficiency, longitudinal stability, etc. of the tread in a well-balanced manner without degrading ride comfort. Although this proposed tire exhibits excellent functions and effects in terms of the various performances described above, uneven wear resistance has not been sufficiently improved.

In addition, in order to improve other characteristics of the tire, such as wear resistance, uneven wear resistance such as shoulder drop wear resistance, and cut resistance, it is necessary to improve the carcass profile as well as the radius-gravity ratio of the radius of curvature of the tread surface to the tire width. We have also learned that it is good to keep the value within a predetermined range.

The present invention is based on the tire proposed in Japanese Patent Application Laid-open No. 61-200004, and is capable of maintaining its various performances even after running by reducing changes in the carcass profile caused by running. To provide a radial tire that can improve the maintainability of the tire and the durability of retreaded tires by improving the abrasion resistance, uneven wear resistance, etc. of tires, thereby increasing the overall lifespan and reducing total costs. It is an object.

(Means for Solving Problems a'a) The present invention provides one or more layers of carcass cords that extend from the tread portion through the sidewall portion, are folded back at the bead core of the bead portion, and are arranged substantially in the radial direction. A carcass consisting of a carcass ply, and a belt layer including a belt bridle of 2N or more using belt cords disposed inside the tread portion and outside the carcass in the radial direction at an angle inclined to the circumferential direction of the tire. At the same time, when the rim is assembled to a regular rim and is filled with a regular internal pressure, the carcass profile of the carcass is the tire axis of the narrowest belt braai within three layers from the carcass side of the plurality of belt braais. A belt outer edge point a, which is a point where a radial line extending in the tire radial direction from the outer edge e intersects the carcass, and a maximum width point of the carcass, which is a point at the maximum tire middle Wr on the inside in the radial direction from the belt outer edge point a. and an inflection point C that is a carcass position at a height of 160% of the rim flange height of the rim radially inward from the maximum width point C1.
It includes a lower region C2 of outward bulge leading to
1 is formed by a curved surface where arcs with a single radius of curvature R1 overlap in a range of 90% or more, and the lower region C2 is
Ii where the arc with a single radius of curvature R2 is 90% or more! The radius ratio R1/R2, which is the ratio of the radius of curvature R1 of the upper region CI to the radius of curvature R2 of the lower region C2, is 0.95 or more and 1.08 or less, and Rim assembled to regular rim and 5% of regular internal pressure
Belt outer edge point a (0°5%) and maximum width point b (0°5%) of the carcass profile at 5% internal pressure filled with
The radius of curvature R1 (0.5%) of the curved surface forming the upper region C1 (0.5%) between the radius of curvature R1 and the radius of curvature R1 (0.5%) is 0.70 or more and 0.9
5 or less, and the radius-gravity ratio TRI/SW of the radius of curvature TRI of the surface of the tread portion and the tire maximum width SW, which is the length between the tire maximum width position f in the normal internal pressure state, is 1.28. This is a radial tire with a diameter of at least 1.95 and at most 1.95.

[Effect]

For example, 10, which is the representative size of radial tires for heavy loads.
．． What about 00R2014PH truck and bus tires?
, is installed on the regular rim of 50VX20. The tread width of this tire is approximately 180 to 200 mm, and the surface of the tread portion has an arcuate curved surface.

The tread surface of such a heavy-duty radial tire changes due to running, as shown in Figure 4, where the tread surface TI of a new tire is shown by a solid line and the tread surface T2 after running is shown by a broken line. There is a so-called rounding phenomenon in which TR2 becomes smaller than the radius of curvature TRI of a new tire, and finally, as shown in Figure 5, the tread surface becomes flat due to running, and the radius of curvature TR2
There is a so-called flattening phenomenon in which the tread surface T2 becomes larger than the radius of curvature TRI and the tread surface T2 becomes flat.

Due to this phenomenon, the height difference in the tire radial direction between the equatorial point The amount of camber z2 on the tread surface after driving changes with respect to the amount of camber xi of the tire.
For example, in the case of the rounding phenomenon shown in Figure 4,
The camber amount z2 increases compared to the camber amount z1 when new, and in the flattening phenomenon shown in FIG.
The camber amount z2 is smaller than the camber amount zl for the new tire.

Ideally, the tread surface should be as shown in Figure 3.
The camber amount z2 of the tread surface T2 after running is approximately equal to the camber amount z1 of the tread surface of the new tire.

It was noticed that the amount of change in camber is correlated with the carcass profile, and the results of searching for a carcass profile that could reduce the change in the amount of camber 2 are shown in FIG.

Note that the horizontal axis in FIG. 2 represents the radius of curvature R1 in the upper region C1 of the sidewall portion and the radius of curvature R in the lower region C2.
2 and the radius ratio R1/R2 is taken, and the vertical axis shows the change in camber amount 2 from the new tire after driving z2
-t1 is taken.

Fig. 2 shows the change in camber amount after the vehicle was loaded with a normal load (2700 kg) at a normal internal pressure filled with air pressure of 7.25 kyx/cm' and ran for 10,000 km without any wear. This camber change amount refers to the tread l1iiTT2 after the running.
The difference (z2-zl) between the camber amount z2 of the new tire and the camber amount z1 of the tread surface T1 of the new tire, (0) on the vertical axis indicates that there was no change in the camber fz, and (+ ) means that the camber amount z2 increases due to running and the tread surface T2 becomes rounded, and (-) means that the tread surface T2 becomes flat due to running.

In FIG. 2, in the range where the radius ratio R1/R2 is 0.95 or more and l,08 or less, the camber change amount z
It can be seen that 2-zl can be reduced to almost zero.

From this point of view, in the present invention, the radius ratio R1/R2 is set within the range.

Note that the lower region C1 refers to one of the plurality of belt plies.
A radius line K extending in the tire radial direction from the tire axial direction outer edge e of the narrowest belt ply within three layers from the carcass side
The region between the belt outer edge point a, which is the point where e intersects the carcass, and the maximum width point of the carcass, which is the point of the carcass at the tire maximum width position f, and the lower region C2 is:
It means the area from the maximum width point to the inflection point C, which is the carcass position at a height H2 which is 160% of the rim flange height Hl.

Furthermore, the radius of curvature R1 is a radius of curvature that overlaps the curved surface of the upper region C1 when mounted on a regular rim and filled with a regular internal pressure, and the radius of curvature R2
means a radius of curvature that overlaps with the curved surface of the lower region C2 by 90% or more.

Moreover, the present invention provides the lower area C1 in the normal internal pressure state.
The radius of curvature R1 and 5% filled with 5% of the normal internal pressure.
Upper region C1 of the carcass profile in the internal pressure state (
Radius ratio R1 of curvature radius R1 (0.5%) of
/R1 (0.5%) is set to be 0.70 or more and 0.95 or less. Accordingly, the radius of curvature R1 of the upper region C1 is reduced while filling the normal internal pressure. This pushes down the shoulder side portion of the tread portion and increases the radius of curvature of the tread surface. As a result, compressive strain is applied to the crown portion of the tread portion. This compressive strain results in an increase in the apparent in-plane rigidity of the tread portion, and can improve the cut resistance, wear resistance, and fuel efficiency of the tread portion.

This relatively large in-plane stiffness also stems from structural requirements,
Therefore, the tires can be maintained for a relatively long period of time, so the steering stability of the car will not be compromised. Furthermore, wet grip and trough properties can be improved, and by making the rubber gauge thinner, the weight of the tires can be reduced. can also be realized.

Preferably, the radius width ratio TRI/SW of the curvature radius TRI of the tread portion surface, that is, the tread surface, and the tire maximum width SW in the normal internal pressure state of the new tire is 1.2.
8 or more and 1.95 or less. This is to maintain wear resistance, uneven wear resistance such as shoulder drop wear, and cut resistance, and the radius width ratio TRI/SW is 1.28.
If it is smaller than this, the tread surface becomes excessively arcuate, promoting wear at the crown portion, resulting in poor uneven wear characteristics, as well as an increase in the ground pressure at the crown portion, resulting in a decrease in load bearing capacity.

Furthermore, when it is greater than 1.95, the ground pressure at the shoulder portion increases, heat generation on the inner surface of the tread at the shoulder side portion increases, and durability decreases.

Therefore, in order to optimize the pressure distribution on the ground contact surface and further improve wear resistance, uneven wear resistance, cut resistance, and carcass durability, it is preferable that the radius width ratio TRI/SW of a new tire be within the above range.

Furthermore, setting the radius ratio R1/R2 to a value within the above range improves performance based on the increase in rigidity of the tread portion due to the deformation of the carcass profile between the 5% internal pressure state and the normal internal pressure state. , the improvement in radius width ratio TR/SW becomes a condition that can be maintained even after driving, suppressing dimensional changes in various parts, especially changes in the road surface shape (footprint) of the tread, and improving the performance of retreaded tires from new tires. To reduce changes in carcass profile over the life of a tire. Therefore, the various performances of the tire can be maintained in conditions close to those of new tires.

Such improvements also help increase tire retreading frequency, increase overall lifespan, and lower total cost by increasing high-speed durability and reducing heat generation.

〔Example〕

An embodiment of the present invention will be described below with a tire size of 10°00R2.
Taking as an example the case of a 014PH heavy-duty radial tire, description will be made based on the drawings.

What size is the new radial tire 1? , mounted on a regular rim of 50VX20, with a regular internal pressure of 7.25 k
The solid line represents the normal internal pressure state when the internal pressure is filled to 5% of the normal internal pressure and other conditions are the same as the normal internal pressure state. Accordingly, in FIG. 1 shown in the left half of the cross section including the tire axis, the radial tire 1 includes a carcass 9 which passes from the tread portion 4 through the sidewall portion 5 and is folded back at the bead core 7 of the bead portion 6, and the tread portion. A tapered hard rubber belt or hard rubber belt extending from the bead core 7 is provided between the main body part 9a and the folded part 9b of the carcass 9. A bead X 12 is provided which is made of a double material of a rubber and a soft rubber.Furthermore, the bead portion 6 includes a reinforcing M13 made of a metal cord, a reinforcing layer made of an organic fiber cord, a chafer for preventing rim slippage, etc. (not shown). By providing various known reinforcing structures, the bead portion 6 is reinforced and its rigidity is increased.

The carcass 9 is made of a non-stretchable or low-stretchable carcass cord such as a steel cord, with respect to the tire equator.
At least one layer of carcass plies arranged at an angle of 70 to 90 degrees is used. In this example, carcass 9 is carcass code ? It consists of an IFJ carcass ply consisting of a steel cord of x410.175m embedded in rubber, and in Fig. 1, under normal internal pressure,
The carcass profile 15 passing through the mid-thickness position of the carcass 9 is represented by a solid line as the carcass 9, and the carcass profile 15 (0.5%) in the above-mentioned 5% internal pressure state is -
Indicated by a dotted chain line.

The belt JillO has a plurality of layers, for example, four layers of first to fourth belt plies 10a to 10a arranged from the carcass 9 side.
Consists of lods. Moreover, each belt ply 10a to 10d is
In both cases, non-stretchable steel cords and low-stretchable cords such as aramid cords are used.In this example, 1+3
10.20+IX6/0.38 wa steel cord is used.

Also, the belt [maximum of 10, i.e. belt ply lOa~1
The width of the widest belt ply in 0d should be 80 to 95% of the width TW of the tread section 4, and it is preferable to reinforce it over a wide range of the tread section.
a NI O (the smaller of 1 (both 2 layers, in this example, 3WII belt braces 10b to 10d) have their belt cords at a relatively small angle of 10 to 25 degrees with respect to the tire circumferential direction, 16 degrees in this example. angle, and each belt ply 1
The direction of each stone is selected according to 0a to 10d, and a hoop effect is imparted to the tread portion 4.

For example, by tilting the belt cord of one belt ply, in this example the innermost belt ply 10a, at an angle range of 40 to 70 degrees, for example, at an angle of 67 degrees, each belt ply 10a to 10d can be tilted together with the carcass cord. A strong triangular structure can be formed, and the in-plane and out-of-plane bending stiffness of the tread portion 4 is improved.

The carcass profile 15 in the normal internal pressure state is defined as the belt area CO below the bell fan 10, the upper area C1 which is connected to the belt area CO and forms the upper part of the sidewall part 5, the lower area C2 below the belt area CO, and the bead part 6. The bead MC3 located in the section 2 and MC3 will be considered separately. The belt area CO
is an area where there is almost no deformation due to internal pressure filling due to the hoop effect due to the belt [10] and the triangle structure that provides large rigidity.

This belt area CO extends from the outer edge e in the tire axial direction of the narrowest one of the three belt plies 10a to 10c counted sequentially from the carcass side, in this example, the third belt ply lOc from the inside. It is defined as a region including the tire equatorial plane C3 between the belt outer edge points A and a, which is the point where the radial line Ke extending in the radial direction intersects with the carcass profile 15.

As mentioned above, there is a small amount of ti between the belt outer edge points a and a.
(In both cases, three belt plies lOa to 10c are present, providing great rigidity.

Further, the bead area C3 is a 9W area between a point d where the main body part 9a of the carcass 9 contacts the bead core 7 and an inflection point C, and the inflection point C is the rim sea of the lino, 2).
Radial height Hl from 2a to rim flange 2b
A point on the carcass profile 15 at a height H2 of 160%. This bead region C3 is also a region to which large rigidity is imparted by the bead reinforcements such as the above-mentioned BEAD
It has an indented curved surface. Note that at or near the inflection point C, there is an inflection position that smoothly continues with the curved surface of the outward bulge of the lower region C2 above the inflection point C.

The upper region C1 is a region between the belt outer edge point a and the maximum width point A, which is a point of the carcass profile 15 at the maximum middle fff of the tire, and the lower region C2 is a region between the maximum width point In the region between the inflection point C, the carcass profile 15 has a curved surface with an outward bulge in both the regions C1 and C2.

Furthermore, in the carcass profile at 5% internal pressure, a half-a line K e extending from the outer edge C (0°5%) of the belt ply 10c (approximately equal to the outer edge e of the normal internal pressure)
(0,5%) carcass profile 15 (0,5%
) and the carcass profile 15 (0.5%) at the tire maximum width position f.
) includes the lower region C1 (0.5%) in the 5% internal pressure state between the maximum width point b (0.5%), and the upper region C1 (0.5%) includes the outer bulge. As the internal pressure is filled, the carcass profile 15 changes to the normal internal pressure shown by the solid line.

Further, the upper region CL and the lower region C2 have relatively low rigidity and low resistance to deformation, and therefore deform due to internal pressure and load. In addition, the shape and stiffness of the bell 1 ICO and the bead area C3, the carcass length which is the length of the carcass profile 15 in the tire axial cross section between the contact point dSd with the bead core 7, the rubber thickness of each part, and the mold. By adjusting the inter-bead dimension (clip ring width), shape, etc., the curved shapes of the lower regions C1 and C2 can be adjusted relatively freely.

At the time of the above change, the upper region C1 (0
．． The radius ratio R1/ of the lower area C1 of the normal internal pressure to the radius of curvature R1 (0.5%) of the radius of curvature R1 (0.5%)
R1 (0.5 extension) is set to be 0.70 or more and 0.95 or less. As a result, the radius of curvature R1 of the upper region CL at the normal internal pressure decreases as the internal pressure is filled.

Radius of curvature R1 of the curved surface forming the upper region C1 (0.5%)
(0.5%) means a radius that "overlaps within 90% or more" of the curved surface.

"The radius of curvature overlaps with the curved surface by r90% or more" means, as mentioned above, in addition to the case where the curved surface is formed by a single correct radius of curvature in the range exceeding 909A, It is defined as an area within a range of %, including cases where it overlaps with the curved surface.

As mentioned above (by filling with the normal internal pressure, the carcass profile 15 is deformed so as to reduce the radius of curvature R1 of the upper region C1, thereby pushing up the shield part of the tread part 4. Furthermore, the deformation is 5% In the curvature of the tread surface T (0.5%) of the tire shaft cross section under the internal pressure state, the radius of curvature TR of the tread surface T under the normal internal pressure state is increased compared to the radius TR (0.5%), and the tread surface T can be flattened. This causes compressive strain to be applied to the tread portion 4, increasing the apparent in-plane rigidity.

For this reason, at the equatorial points x and x (0,5%) where the tread surface T in the normal internal pressure state and the tread surface T (0.5%) in the 5% internal pressure state intersect with the tire equatorial plane C3, respectively, Radius Rx% from the tire axis of the equatorial point X, X (0.5%)
Rx(0,5%) is their radius ratio Rx/Rx(0,
5%) shall be greater than or equal to 1 and less than or equal to 1°05. It is preferable that this suppresses excessive expansion at the equatorial point X and promotes flattening of the tire.

More preferably, the degree of expansion is within 0.3%, so that the radius ratio Rx/Rx (0.5%) is 1.
o o a or less.

To explain in more detail, the trend planes T, T (0°5%)
End point y, which is the outer edge of the tire in the axial direction, y (0.5%)
radius Ry, , radius ratio Ry/Ry (of Ry (0,5%))
0.5%) is the equatorial point x, and the radius ratio of x(0.5%) Rχ/
It is set to be larger than Rx (0.5%).

When they are the same, no effective compressive strain can be applied to the tread portion 4, and when the radius ratios are opposite, tensile strain is applied due to the large expansion of the equatorial point It happens.

Therefore, it is preferable that the radius ratio Rx/Rx (0.5%) is smaller than the radius ratio Ry/Ry (0.5%).

Furthermore, the end point y (0°5%) in a 5% internal pressure state
to the intersection point p where the radius line Ky (0,5%) parallel to the tire equator C8 intersects with the carcass profile 15 (0,5%)
(0,5%) is the intersection p where 7 intersects the carcass profile 15 on the radius line extending from the end point y in the normal internal pressure state.
It is preferable to locate the tire center side in both the radial direction and the tire axial direction.

, - to arrange the upper region CI (0° 5%) of the carcass profile 15 (0.5%) in the 5% internal pressure state below the carcass profile in the normal internal pressure state in the radial direction. , the center point x (0,5%
) and the end point y (0.5%), the camber amount 21 (0.5%) in the 5% internal pressure state is expressed as the radial height between the equatorial point X and the end point y in the normal internal pressure state. It is preferable that the height in the radial direction is larger than the camber tzl in the normal internal pressure state.
This makes it possible to position the carcass profile 15 (0.5%) below the carcass profile 15 without increasing the thickness in a portion of the cylinder.

Note that when the rubber thickness of a part of the shigolder is increased to suppress the carcass profile to the lower side, the tire heat generation due to internal energy loss of the rubber increases, reducing high-speed durability.

In addition, in a tire in which the radius ratio R1/R1 (0.5%) is within the range, when the carcass profile moves upward at the cylinder part due to filling with the normal internal pressure and becomes carcass profile 15, as shown in FIG. First, the outer surface shape of the tire is deformed from the buff tress portion corresponding to 60% or more of the tire cross-sectional height H to the tread portion. The dashed line is 5%
The solid line indicates the normal internal pressure state, and the conventional tire is deformed throughout the tire, as shown by the dashed line in the figure. Note that this tire shape was molded using plaster.

Such deformation is caused by increasing the tension in the carcass 9 from above the sidewall portion 5, where the amount of deformation is large, to the buttress portion and the tread portion 4, in the tension distribution of the carcass 9.
Increases apparent stiffness.

In addition, in such a tire, as described above, the deformation amount at the end point y is larger than the amount of deformation at the tire equator point X, so compressive strain acts on the tread contact surface as described above,
Increase lateral stiffness by improving in-plane stiffness.

This improvement prevents part of the shield from lifting due to torsional deformation, enables high cornering power to be exerted, and improves steering stability. Furthermore, since the movement of the rubber associated with tire transfer is reduced and energy consumption is reduced, rolling resistance can be improved without impairing wet grip performance or high-speed durability. Furthermore, wear resistance and cut resistance can also be improved.

Further, the radius of curvature TR of the new tread surface under the normal internal pressure condition and the tire maximum width SW, which is the length between the maximum width points ", f," and the radius intermediate pressure TR1, "sw are 1.28
or more and 1.95 or less.

This is to further improve abrasion resistance, uneven wear resistance such as shoulder drop wear, cut resistance, and durability. wiI
When the marked value is smaller than 1.28, the tread surface becomes excessively arcuate, which increases the ground contact pressure at the crown part and accelerates center wear, resulting in poor wear life and the durability of this part. Cutting performance deteriorates.

Furthermore, when it is larger than 1.95, the ground pressure at a portion of the shoulder increases, and the internal heat generation of the rubber at the shoulder portion becomes excessively large, and the durability decreases due to the temperature rise.

Therefore, in order to optimize the pressure distribution on the ground contact surface and improve wear resistance, uneven wear resistance, cut resistance, and durability, the medium radius pressure TRI/SW of a new tire is set within the above range.

In order to maintain this kind of performance even after driving,
curvature radius R1 of the curved surface of the lower region C1, lower region C2
The radius ratio R1/R2 of the curved surface with the radius of curvature R2 is set to 0.
95 or more and 1.08 or less. This allows the second
By reducing the change Wkz2-zl of the camber tz shown in the figure when it is new and after driving, it is possible to suppress the change in the shape of the tread surface in the cross section of the tire axis, and the change in the shape of the tread surface and the deformation of the carcass profile are extremely small. They discovered that the tire maintains the same performance as a new tire even after driving.

Here, the radii of curvature R1 and R2 refer to the curved surface of the lower region C1 and lower region C2 of the carcass profile 15, that is, the shape curve passing through the thickness intermediate position of the carcass 9, respectively, and r9.
This means a radius of curvature that overlaps within a range of 0% or more.

By setting the radius ratio R1/R2t to the above range, as shown in FIGS. 2 and 3 (change in camber amount 2 11z2
-Zl can be reduced.

The amount of change in camber 5it is the camber when new, which is the height in the radial direction between the center point x1 of the tread surface T1 and the end point y1, which is the tread edge, in a new tire.
It means the difference (z2-zl) between the amount z1 and the camber amount t2 after running, which is the height in the radial direction between the center point X2 of the tread surface T2 and the tread edge y2 after running. Note that the amount of change is "+", as shown in Fig. 4, the radius of curvature TR2 of the tread surface after running is reduced from the radius of curvature TRI of the tread surface T1 when new, and the tread surface becomes rounded. It means that. Furthermore, the second rf! " on the vertical axis of l
-'' means that the tread surface becomes flat.

The range of the radius ratio R1/R2 is as shown in FIG.
This is the range in which the change M (xi to z2) of the camber 31z becomes substantially zero.

In this way, the present invention focuses on the fact that the performance of a tire before and after running is correlated with the carcass profile,
Moreover, this is based on the fact that the carcass profile can be optimized using the radius ratio R1/R2 and the change in shape can be minimized even after driving, and that the optimum value range has been discovered through development.

〔Concrete example〕

A tire with a tire size of 10.00 R20 shown in Fig. 1 was prototyped along with an example product according to the specifications shown in Table 1, and a comparative example product was tested for high-speed durability, cut resistance,
W4 drop wear resistance, heat generation resistance, abrasion resistance, and retreading durability were tested, and the results are shown in Table 1.

For each tire, the carcass is 90° relative to the tire equator.
Steel cord (7x410°L75ra)
A single layer carcass ply is used.

Also, as a belt layer, steel cord (1+310.20
+1x610.38m), and the belt cord of the innermost layer 10a is 67 degrees,
The belt cords of the other braais 10b to 10d are connected at an angle of 16 degrees to the tire equator, and in the same direction as the plies 10a and 10b, and in the same direction as the plies 10c and 10d, and in the same direction as the ply 10a.

10b. Also, the tire was installed on the regular rim (7,50Vx20), and the weight was 7゜25kg.
/cm”, each radius of curvature R1, R2, T
Measuring RI. The radius of curvature TR2 of the tread surface after running is 2700)c! , at a speed equivalent to 50-mph, 1.6 mfl! I by the diameter drum running test machine
Measured after running QOOOb.

Each test result is expressed in an index format with Comparative Example 1 as 100, and the larger the number, the better the result. Also, each test item in the left column of Table 1 is The passing criteria, which are the standard values for passing the test, are also listed in parentheses.

Here, high-speed durability was measured using an indoor drum running test machine under the durability test conditions of 140% of the JIS standard load and 100% normal internal pressure. The distance traveled is measured.

It is thought that the improved high-speed durability was achieved by applying uniform ground pressure to the tread surface, enabling well-balanced pressure distribution and deformation, and as a result, improved high-speed durability.

The cut resistance is determined by pressing a wedge piece with a width of 10 am with a tip of 0.5 R and a 25 degree taper against the tire with a constant force, and based on the depth of damage to the tread.

In addition, shoulder-drop abrasion resistance and abrasion resistance were determined by measuring the depth of the longitudinal groove between the crown and shoulder of a tire that was run on a highway and ordinary paved road at a ratio of 70:30. The measured average value of the difference from the depth before running is 1! ! The difference in the amount of wear between the shoulder portion and the crown portion was taken as the amount of shoulder drop wear.

In addition, the heat resistance was tested using an indoor drum tester at a speed of 8 mph.
The results show the results of measuring the temperature rise at the outer edge portion of the belt layer of the tread portion by running the tire under a 100% load according to the 01 GIS JIS standard until the tire temperature became constant. It is judged that, as described above, in the case of the actual product, by maintaining a shape with an even and well-balanced ground pressure distribution, not only the cut resistance but also the heat generation resistance could be reduced.

In addition, retreading durability is measured by running a new tire to its wear limit in an actual vehicle test, then using it as a base tire and retreading it using the retread method using a precure tread, and running it again to its limit. I asked for it.

In either case, the example is superior, and the other example is
Wet grip performance, handling stability performance, ride comfort performance, fuel efficiency, etc. were able to maintain the same or better characteristics than conventional products.

〔Effect of the invention〕

In this way, the radial tire structure of the present invention can maintain tire performance such as handling stability, cut resistance, and wet grip over a long period of time, while also improving wear resistance and preventing uneven wear, thereby improving tire maintainability. At the same time, it increases the number of refurbishments, increases the total lifespan, and helps lower the total cost.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing one embodiment of the present invention, Fig. 2 is a diagram showing the relationship between changes in camber amount and radius ratio R1/R2, and Fig. 3 is a diagram showing changes in tread surface of different products according to implementation. Line diagram shown, 4th
．． Figure 5 is a diagram showing changes in the tread surface of conventional tires;
The figure is a diagram illustrating tire deformation from a 5% internal pressure state to a normal internal pressure state. 2... Rim, 4... Tread section, 5... Sidewall section, 6... Bead section, 7... Bead core 9...
Carcass, 10--belt layer, 15--carcass profile.

Claims (1)

[Claims] 1. A carcass consisting of one or more layers of carcass ply using a carcass cord that is folded back from the tread portion through the sidewall portion, by the bead core of the bead portion, and arranged substantially in the radial direction, and the inside of the tread portion and the carcass. A belt layer including two or more belt plies using belt cords arranged on the radially outer side of the tire and at an angle inclined to the circumferential direction of the tire. In the normal internal pressure state where the carcass is filled with The upper region C1 of the outer bulge between the belt outer edge point a, which is a point that intersects with the carcass, and the maximum width point of the carcass, which is a point at the tire maximum width position f, radially inward from this belt outer edge point a, and the maximum width of the carcass. The upper region C1 comprises a lower region C2 of outward bulge extending from the width point b to an inflection point c, which is the carcass position at a height of 160% of the rim flange height of the rim radially inwardly.
The lower region C2 is formed by a curved surface where arcs with a single radius of curvature R1 overlap in a range of 90% or more, and the lower region C2 is formed by a curved surface where arcs with a single radius of curvature R2 overlap in a range of 90% or more, The radius of curvature R of the upper region C1
1 and the radius of curvature R2 of the lower region C2.
1/R2 is 0.95 or more and 1.08 or less, and the belt outer edge point a (0.5% ) and the maximum width point b (0.5%), the radius of curvature R of the curved surface forming the upper region C1 (0.5%)
1 (0.5%) is the radius ratio R1/of the radius of curvature R1.
A tire in which R1 (0.5%) is 0.70 or more and 0.95 or less, and is the length between the radius of curvature TR1 of the surface of the tread portion and the tire maximum width position f in the normal internal pressure state. Radial width ratio TR1/S to maximum width SW
A radial tire with a W of 1.28 or more and 1.95 or less.