JPH1029408A - Flat pneumatic radial tire for small truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the track-road traveling performance while high cornering force is maintained, in a pneumatic tire for use in small trucks, the oblateness of which is less than 85%. SOLUTION: The sectional shape of groove walls 8A, 8B in the tire meridian section of a circumferential groove 8 on a tread face 1A in the outside area X located on the outer side of a wheel with respect to a tire center CL when a tire is loaded to the wheel, are formed so as to be asymmetrical with the right and left direction, and the sectional shape of the groove wall 8A located on the outer side with respect to the wheel, is formed so that it has a curved part 8a which is directed from the tread face 1A toward the groove bottom side and tangentially tangent to the tread face 1A. Further, out of the ground pressure at the edge parts 9a, 9b of ribs 9 on both sides of the circumferential groove 8, the ground pressure at the edge 9b of the circumferential groove 8, which is located on the inner side of the wheel, is formed to be higher.

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 having a flatness of 85% or less for use in a small truck, and more particularly to improving a rutted road running performance while securing a high cornering force. The present invention relates to a flat pneumatic radial tire for light trucks.

[0002]

2. Description of the Related Art In recent years, flat tires having a flatness of 85% or less have been widely used as pneumatic radial tires for small trunks. Adopting this flat tire has the advantage that the cornering force can be increased and the section height can be reduced, so that the truck bed can be lowered.

The flat tire has a structure in which the rigidity of the belt portion is higher than that of a general pneumatic radial tire for a small truck in order to secure a high cornering force. Therefore, when the tire falls into a rut formed by the traveling of a heavy load vehicle (such as a large truck), there is a problem that it is difficult to get out of the rut, and the rut road surface traveling performance when traveling on the rut surface is poor. For example, in the case of a small truck, unlike a passenger car, the load is heavy, so even if you try to climb on a slope of a rut diagonally, the component force of the load is larger than the camber thrust acting in the opposite direction and the inside of the tire Therefore, a phenomenon that it is hard to get out of the rut occurs.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve running performance on a rutted road while maintaining a high cornering force in a pneumatic radial tire having a flatness of 85% or less used in a small truck. It is an object of the present invention to provide a flat pneumatic radial tire for a light truck.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a small truck having a plurality of circumferential grooves formed on a tread surface along a circumferential direction of a tire and ribs formed on both sides of the circumferential grooves. In a pneumatic radial tire having a flatness of 85% or less, at least a tire wall cross-sectional shape of a circumferential meridian cross section of the circumferential groove on a tread surface in an outer region outside the vehicle from the tire center when the vehicle is mounted is formed to be asymmetric. In addition, the cross-sectional shape of the groove wall on the outside of the vehicle is formed so as to have a curved portion tangentially tangent to the tread surface from the tread surface toward the groove bottom, and the edges of the rib on both sides of the circumferential groove. The configuration is such that the contact pressure in the portion is higher at the edge portion located inside the vehicle in each circumferential groove.

[0006] By forming the cross-sectional shape of the circumferential groove in the region outside the vehicle from the tire center asymmetrically in the left-right direction, the contact pressure distribution on the tread contact surface in the region outside the vehicle that is greatly affected when the vehicle escapes from the rut. Can be gradually increased from the outside of the vehicle toward the tire center as compared with a conventional tire having a symmetrical groove structure.
As a result, a lateral force greater than before can be applied to the outside of the vehicle, so that the component force of the load acting toward the inside of the vehicle can be offset by the lateral force, and the vehicle escapes from the rut. Can be facilitated.

Further, since the cross-sectional shape of the circumferential groove is devised and the structure of the belt relating to a high cornering force is not changed at all, a high cornering force can be maintained as in the prior art.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an example of a flat pneumatic radial tire for a light truck according to the present invention, wherein 1 is a tread portion, 2 is a bead portion, and 3 is a sidewall portion. Left and right side wall portions 3 are connected to the right and left bead portions 2 and extend on the tire outer diameter side, and a tread portion 1 extending in the tire circumferential direction is provided between the left and right side wall portions 3. The carcass 4 is disposed inside the tire, and both end portions 4a of the carcass 4 are folded from the tire inside to the outside around the bead cores 5 embedded in the right and left bead portions 2, respectively, and are disposed on the outer periphery of the bead core 5. The bead filler 6 extends so as to exceed the outer peripheral end. A plurality of belts 7 are buried in the tread portion 1 on the outer peripheral side of the carcass 4, and the flatness of the tire is 85.
% Or less.

In the tread surface 1A of the tread portion 1, a plurality of circumferential grooves 8 composed of four in this embodiment are straightened along the circumferential direction of the tire so that the width of the grooves 8 gradually decreases toward the groove bottom. The ribs 9 are formed on both sides of the circumferential groove 8. The groove bottom 8C of the circumferential groove 8 is formed in an arc portion 8c in contact with the groove walls 8A and 8B.
On both sides. CL is a tire center, and the right side of the tire center CL is an outer region X that is outside the vehicle when the tire is mounted on the vehicle,
The left side is an inside area Y inside the vehicle.

In the present invention, in the flat pneumatic radial tire for a light truck having the above-described structure, the cross-sectional shape of each circumferential groove 8 at the tire meridian cross section is shown in FIG.
As shown in detail, the cross-sectional shape of the groove wall 8A that is formed asymmetrically on the left and right and that is on the outside of the vehicle is tangent to the tread surface 1 from the tread surface 1A toward the groove bottom without having a bending point. Groove wall 8 formed so as to have a curved portion 8a tangent to the shape, and located on the vehicle inner side facing the groove wall 8A.
The cross-sectional shape of B is formed so as to have a straight portion 8b from the tread surface 1 toward the groove bottom, and the ground pressure at the edge portions 9a and 9b of the rib 9 on both sides of the circumferential groove 8 is
The edge portion 9a of each circumferential groove 8 located inside the vehicle is higher.

As a result, the contact pressure distribution on the tread surface 1A when the tire is in contact with the ground is shown by a solid line in FIG. 3 as compared with a tire using a left-right symmetrical circumferential groove having a configuration having both straight portions 8b. As described above, the height can be gradually increased from the outside to the inside of the vehicle as compared with the conventional case (dotted line). Therefore, a lateral force L larger than before can be applied to the outside of the vehicle as shown in FIG. 3, whereby the tire acts toward the inside of the vehicle when traveling on a rutted slope when getting out of the rut. Since the component components of the load can be offset, it is possible to easily escape from the inside of the rut and improve the running performance on the rut road surface.

Further, since there is no need to change the configuration of the belt 7 for increasing the cornering force, it is possible to maintain the same high cornering force as before.
The curved portion 8a of the groove wall 8A is formed of an arc having a radius of curvature R of 3 mm or more, and the lower end of the arc is preferably set to be within 80% of the groove depth D of the circumferential groove 8. If the radius of curvature R is less than 3 mm, the rigidity of the edge portion 9a cannot be sufficiently increased, and it becomes difficult to improve rutted road surface running performance. The lower end of the curved portion 8a consisting of an arc is the groove depth D
If it is 80% or more, the apparent groove width becomes too wide, and the wear becomes worse.

It is preferable that the straight portion 8b of the groove wall 8B is substantially in a normal direction to the tread surface 1A where the straight portion 8b intersects. FIG. 4 shows another example of the flat pneumatic radial tire for a light truck according to the present invention. In this embodiment, the cross-sectional shape of the circumferential groove 8 in the tread surface 1A of the inner region Y is made to be opposite to the above-described embodiment.

That is, the cross-sectional shape of the groove wall 8B on the vehicle inner side of the circumferential groove 8 in the inner region Y has a curved portion 8a tangent to the tread surface 1A from the tread surface 1A to the groove bottom side. The groove wall 8A facing the groove wall 8B is formed so that the cross-sectional shape of the groove wall 8A facing the groove wall 8B has a linear portion 8b from the tread surface 1 toward the groove bottom side. The ground pressure at the edges 9a and 9b of the rib 9 on both sides of the directional groove 8 is higher at the edge 9b of each circumferential groove 8 located inside the vehicle, and the circumferential pressure is higher than the tire center CL. The direction groove 8 is symmetrical.

In this case, the contact pressure distribution on the tread surface 1A when the tire is in contact with the ground, as shown by the solid line in FIG. Of the tire (dotted line in Fig. 5)
Rather than higher. Therefore, lateral forces L1 and L2 of the same magnitude are applied in both directions. However, when traveling on a rutted slope, the influence of the tread surface on the slope side more than the tire center CL acts. Therefore, when the vehicle escapes from the rut, the lateral force L2 in the outer region X is applied to facilitate the escape from the rut.

Naturally, in this embodiment as well, since the structure of the belt 7 is not changed at all, it is needless to say that a high level of cornering force as in the prior art can be maintained. Further, in this embodiment, since the circumferential groove 8 has a symmetrical structure, the mounting direction is not limited as in the above-described embodiment, and the tire may be mounted from any side, The tire mounting can be facilitated while improving the running performance on the rutted road surface.

In the present invention, in the embodiment of FIG. 1 described above, the outer circumferential area 8 and the inner circumferential area Y are each provided with the circumferential groove 8 having the same sectional shape. At least because the tread surface acts greatly,
The groove wall cross-sectional shape of the circumferential groove 8 formed on the tread surface 1A of the outer region X may be constituted by the above-mentioned left-right asymmetric groove. In addition, the small truck in the present invention means a truck having a size of 4t or less.

[0018]

[Example] Flatness is 85%, tire size is 195/8
5R16, tire tires 1 and 2 of the present invention having the configuration shown in FIGS.
And a conventional tire having the configuration shown in FIG. 6 in which the cross-sectional shape of the circumferential groove 8 is symmetrical. In each test tire, the groove depth of the circumferential groove is 12 mm, and the radius of curvature of the curved portion of the groove wall in the tire of the present invention is 6 mm.

Each of these test tires was rim size 5.5K.
An evaluation test of running performance on a rutted road surface was carried out under the following measurement conditions under the following conditions: Running performance on rutted road surface Feeling test A feeling test was carried out on a 2t light truck (all four wheels) and running on an ordinary national road with the vehicle empty.
Named by a test driver. The results are shown as index values with the conventional tire being 100. The larger this value, the better the running performance on the rutted road. 2. Substitution characteristic test The camber stiffness (CS) value used as a substitute for the rutted road running performance was measured by a flat belt type cornering test device, and the result was evaluated by an index value with the conventional tire being 100. The term “CS” as used herein means that the lateral force (= camber thrust) generated when a tire is run at a camber angle is proportional to the camber angle, and this proportional constant is called CS. The larger this value, the better the running performance on the rutted road.

[0020]

[Table 1] As is clear from Table 1, it can be understood that the tire of the present invention can improve the running performance on the rutted road surface.

[0021]

As described above, the present invention provides a flat truck with a flatness of 8 having a plurality of circumferential grooves on the tread surface along the tire circumferential direction and ribs formed on both sides of the circumferential grooves.
In a pneumatic radial tire of 5% or less, at least a tire wall meridional section of the circumferential groove on the tread surface of an outer region outside the vehicle from the tire center when the vehicle is mounted is formed to be asymmetrical in the left and right directions,
The cross-sectional shape of the groove wall on the outside of the vehicle is formed so as to have a curved portion tangentially tangent to the tread surface from the tread surface toward the groove bottom, and at the edge portions of the rib on both sides of the circumferential groove. Since the contact pressure is made higher at the edge of each circumferential groove located inside the vehicle, it is possible to improve the rutted road running performance while maintaining a high cornering force.

[Brief description of the drawings]

FIG. 1 is a tire meridian sectional view showing an example of a flat pneumatic radial tire for a light truck according to the present invention.

FIG. 2 is an enlarged sectional view of a circumferential groove of FIG. 1;

FIG. 3 is an explanatory graph showing a contact pressure distribution when a tread surface contacts the ground.

FIG. 4 is a tire meridian sectional view showing another example of the flat pneumatic radial tire for a light truck according to the present invention.

FIG. 5 is a graph explanatory diagram showing a contact pressure distribution when a tread surface contacts the tire in FIG. 4;

FIG. 6 is a tire meridian sectional view showing an example of a conventional flat pneumatic radial tire for a small truck.

[Explanation of symbols]

Reference Signs List 1 tread portion 1A tread surface 2 bead portion 3 sidewall portion 8 circumferential groove 8A, 8B groove wall 8a curved portion 8b straight portion 9 rib 9a, 9b edge portion R radius of curvature X outer region Y inner region CL tire center

Claims (6)

[Claims] 1. A pneumatic radial tire having a flatness of 85% or less for a small truck, wherein a plurality of circumferential grooves are provided on a tread surface along a tire circumferential direction, and ribs are formed on both sides of the circumferential grooves. Along with forming the groove wall cross-sectional shape of the tire meridian cross section of the circumferential groove in the tread surface of the outer region outside the vehicle from the tire center when the vehicle is mounted on the vehicle, the cross-sectional shape of the groove wall on the vehicle outside is From the tread surface toward the groove bottom side, it is formed so as to have a curved portion tangentially tangent to the tread surface, and the ground pressure at the edge of the rib on both sides of the circumferential groove is applied to the vehicle inside of each circumferential groove. A flat pneumatic radial tire for small trucks, in which the located edge is higher. 2. The flat pneumatic radial tire for a light truck according to claim 1, wherein said circumferential groove is also provided on a tread surface in an inner region inside the vehicle from a tire center when the vehicle is mounted on the vehicle. 3. A groove wall cross-sectional shape of a tire meridian section of the circumferential groove on a tread surface of an inner region that is on the inner side of the vehicle from the tire center when the vehicle is mounted on the tire center is formed asymmetrically, and the groove wall on the vehicle inner side is formed. The cross-sectional shape is formed so as to have a curved portion tangentially tangent to the tread surface from the tread surface to the groove bottom side, and the ground pressure at the edge portion of the rib on both sides of the circumferential groove is set in each circumferential groove. 2. The flat pneumatic radial tire for a light truck according to claim 1, wherein an edge portion located inside the vehicle is higher. 4. A sectional wall shape of the circumferential groove,
The cross-sectional shape of the groove wall facing the groove wall having the curved portion,
The flat pneumatic radial tire for a small truck according to claim 1, 2 or 3, wherein the flat tire has a straight portion from the tread surface toward the groove bottom. 5. The groove according to claim 1, wherein the curved portion of the groove wall cross-sectional shape is an arc having a radius of curvature of 3 mm or more, and the lower end of the arc is within 80% of the groove depth. The flat pneumatic radial tire for light trucks as described. 6. The flat pneumatic radial tire for a small truck according to claim 4, wherein the straight portion having the groove wall cross section has a direction substantially normal to an intersecting tread surface.