JPH0885308A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To restrain the generation of uneven wear by reducing tread radius, and forming dimples at ribs in regions other than shoulder region. CONSTITUTION: In a tread surface 5, two or more main grooves 10 extending in the peripheral direction EE' of a tire are formed, and ribs 11 are partitioned. In the surfaces of the ribs 11 within the regions other than shoulder regions M up to the outer end part in the tire width direction of a main groove on the outermost side outwards from the ground end in the width direction of the tire, namely within a center region L, a plurality of dimples 12 are provided. Since the force of rib being deformed by grounding of a tire can be released to the dimples, the dimples 12 are crushed, and the tire circumferential length of an inner rib in a foot print becomes practically same as the tire circumferential length of the tire inside edge part of a shoulder rib, so that a ground front edge part is roughly straight in a center region L, and a position of different ground contact surface pressure is practically eliminated, thus eliminating generation of uneven wear.

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 based on a rib pattern which suppresses the occurrence of uneven wear such as cupping and chunking without impairing rut wandering resistance due to a smaller tread radius. Relates to a heavy duty pneumatic radial tire.

[0002]

2. Description of the Related Art Rutler wandering means that when a tire (mainly for a heavy load) mounted on a vehicle is running along a rut, when the tire attempts to escape from the rut, the tire faces inward from the rut edge. A phenomenon in which a vehicle is swayed by being pushed back into the rut by receiving the reaction force of. Cupping means that the tread surface is worn in a saw tooth shape in the tire rotation direction. Chunking means that a cut or a crack is generated on the tread surface during traveling and grows, and a part of the rib is chipped in a block shape.

Conventionally, in order to improve the rut-proof wandering property, the tread radius of a pneumatic tire has been reduced. This is to increase the canvas last when the rut is to be escaped by reducing the diameter, and to facilitate the escape (Japanese Patent Laid-Open No. 5-178005). However, when the diameter is reduced in this way, the diameter difference between the center region and the shoulder region of the tread surface becomes large, and therefore when a tire is attached to the front wheels of a rear-wheel drive vehicle, drag wear (shoulder wear) occurs in the shoulder region. When the tire is mounted on the rear wheel, the ground pressure of the drive wheel in the center region is larger than that in the shoulder region, which causes uneven wear (center wear) in the center region.

Therefore, in order to avoid such problems associated with the reduction in diameter, kerfs (fine grooves) are arranged on the tread surface to optimize the shape of the ground contact surface. However, in this case, since the tread rigidity is lowered due to the arrangement of the kerf, there is a drawback that another uneven wear such as cupping and chunking occurs.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to prevent rut wandering resistance from being impaired by reducing the tread radius and to prevent uneven wear such as shoulder wear, center wear, cupping and chunking. It is to provide a pneumatic tire that can be suppressed.

[0006]

According to the present invention, there is provided a tread having a tread radius reduced, and air having a rib pattern formed by providing two or more main grooves continuous in the tire circumferential direction on the tread surface. In a radial tire with a core, a large number of dimples are arranged on inner ribs existing inside the shoulder ribs except for the left and right shoulder ribs forming the rib pattern, and a standard design load is applied to the radial tire under standard air pressure. The tire circumferential length of the inner rib in the footprint at that time is substantially the same as the tire circumferential length of the tire inner edge portion of the shoulder rib.

As described above, the tread radius is reduced so as not to impair rut wandering resistance, and dimples (concave holes) are provided in the ribs in the area other than the shoulder area, that is, the center area. When a tire under a standard design load under air pressure comes into contact with the ground and the ribs deform, the deformation force can be released to the dimples (the dimples are crushed). Can be made substantially equal (that is, there is substantially no difference in diameter on the ground contact surface for each rib), so there is virtually no point where the contact pressure is different, so uneven wear can be suppressed. it can.

The structure of the present invention will be described in detail below. FIG. 1 is a half sectional view in the meridian direction of an example of a pneumatic radial tire of the present invention. In FIG. 1, a carcass layer 2 is mounted on a pair of left and right bead cores 1. The carcass layer 2 is made of a steel cord, and the cord angle is about 90 ° with respect to the tire circumferential direction. In the tread 3, three belt layers, a first belt layer 4d, a second belt layer 4m, and a third belt layer 4u, are arranged in the tire circumferential direction on the outer side of the carcass layer 2 in the direction from the carcass layer 2 to the tread surface 5. The tires are arranged in an annular shape over the circumference of the tire. These belt layers are made of steel cords. The cord angle of the first belt layer 4d is 50 ° to 75 ° with respect to the tire circumferential direction, and the cord angle of the second belt layer 4m is 15 ° with respect to the tire circumferential direction. The cord angle of the third belt layer 4u of 30 ° is −15 ° to −30 ° with respect to the tire circumferential direction. Also,
The cord inclination direction of these belt layers is such that, when viewed from above the tire when the tire touches the ground, the first belt layer 4d descends to the right, the second belt layer 4m descends to the right, and the third belt layer 4
At u, it is going down left.

The tread radius R constituting the tread profile of the meridional section of FIG. 1 is the maximum width W of the tire section.
On the other hand, 1.20W <R <1.50W. In the conventional tire, the tread radius R is relative to the maximum width W of the tire section.
Since it is about 2.50 times, the tread radius R in the present invention with the upper limit of 1.50 W is very small. Figure 2
Shows an example of a rib pattern provided on the tread surface 5.

In FIG. 2, the tread surface 5 is provided with two or more main grooves 10 extending in the tire circumferential direction EE ', and ribs 11 are defined. A plurality of dimples 12 are provided on the surface of the rib 11 in a region other than the shoulder region M from the ground contact end in the tire width direction to the inner end in the tire width direction of the outermost main groove, that is, the center region L. There is. The depth of the dimples 12 is 1/2 or more, preferably 0.5 to 1.0 times the depth of the deepest main groove 10. If it is less than 1/2, it is too shallow to be deformed when the rib is deformed, and the deformation force of the rib cannot escape to the dimple.

FIG. 3 is an enlarged view of portion G in FIG.
The tire width direction diameter D2 of the dimple 12 is equal to that of the dimple 1
1/3 or less of the rib width of the rib 11 to which 2 belongs, preferably 1/10
It should be in the range of 3/10. Tire circumferential diameter D1
Is preferably not more than the diameter D2 in the tire width direction. In the present invention, the tire circumference of the inner rib in the footprint when a standard design load is applied under standard air pressure is 100% to 103% of the tire circumference of the tire inner edge portion of the shoulder rib.
The dimples are arranged to have the size of.

Except for the left and right shoulder ribs (ribs in the shoulder region M) forming the rib pattern in this way, a large number of dimples are provided on the inner ribs (ribs in the center region L) existing inside the shoulder ribs. Due to the arrangement, when the tire is grounded and the ribs 11 are deformed, as in the tread contact surface (footprint) shown in FIG. 4 when a standard design load is applied to the tire under standard air pressure, the deformation force thereof is Since the dimples 12 can be released to the dimples 12, the tire peripheral length of the inner rib in the footprint is crushed to be substantially the same as the tire peripheral length of the tire inner edge portion of the shoulder rib, and the ground contact leading edge line 13 Is substantially linear in the center region L, so that there is substantially no portion where the contact surface pressure is different, so that the occurrence of uneven wear can be suppressed. Kill.

On the other hand, the conventional rib pattern shown in FIG. 5, that is, except for the absence of dimples, is shown in FIG.
In a tire having a rib pattern similar to the above, at the time of contact with the ground, as shown in FIG. 6, the contact length of each rib in the circumferential direction of the tire is different, and the contact front edge line 13 becomes a convex curve. For this reason, a portion having a different contact surface pressure is generated, which causes uneven wear.

[0014]

EXAMPLES For pneumatic tires having the tire sizes of the following sizes shown in FIG. 1 and having the specifications shown in Table 1 (Examples 1 to 4, Comparative Examples 1 to 5, conventional examples), rut resistance wandering The properties, wear degree, cupping and chunking were evaluated. The evaluation vehicle was forward 4t, constant volume, and air pressure 700KPa. Table 1 shows the results.

Tire size 225 / 80R17.5, tread radius R = 300mm, W = 223mm, 1st belt layer 4d; width 118mm
, 57 ° cord angle to the tire circumference, descending to the right, 2
No. belt layer 4m; width 133 mm, cord angle of 18 ° to the tire circumferential direction, right descent No. 3 belt layer 4u; width 118 mm, cord angle of -18 ° to tire circumferential direction, descent to the left. In addition,
Examples 1 to 4 and Comparative Examples 1 to 5 have the rib pattern shown in FIG. 2, and the conventional example has the rib pattern shown in FIG. In Table 1, C is the rib width of the ribs in the center region (the rib width of each rib is the same), E is the average depth of the dimples belonging to each rib, and F is the rib to which the dimple belongs. The average depth of the main groove, the wear degree (F) represents the wear degree of the front tire, and the wear degree (R) represents the wear degree of the rear tire.

Rutting wandering resistance : Evaluation by feeling. Five-point standard is used, and the larger the number, the better. Abrasion degree : It is shown by the rate of change of the tread radius R of each of the front and rear wheels after the tire was mounted on an evaluation vehicle and the vehicle was running 20,000 km. 0.9 to 1.1 is good. Shoulder wear is below 0.8 and center wear is above 1.2.

Degree of cupping : The tire is mounted on the evaluation vehicle,
Shows the maximum cupping amount after traveling 20,000 km. Chunking : Tires are mounted on the evaluation vehicle and 10 unpaved roads
Visually determined after running 0km.

[0018]

[Table 1] It can be seen from Table 1 that the tires of the present invention (Examples 1 to 4) are excellent in all of rut wandering resistance, abrasion degree, cupping and chunking.

[0019]

As described above, according to the present invention, a tread having a reduced tread radius is provided, and two or more main grooves continuous in the tire circumferential direction are provided on the tread surface to form a rib pattern. In the formed pneumatic radial tire, except for the left and right shoulder ribs forming the rib pattern, a large number of dimples are arranged on the inner rib existing inside the shoulder rib, and the radial tire has a standard design under standard air pressure. Shoulder wear, center wear, cupping, chunking, etc. because the tire circumference of the inner rib in the footprint when a load is applied is made substantially the same as the tire circumference of the tire inner edge portion of the shoulder rib. It is possible to suppress the occurrence of uneven wear.

[Brief description of drawings]

FIG. 1 is a half sectional view in the meridian direction of an example of a pneumatic radial tire of the present invention.

FIG. 2 is an explanatory plan view showing an example of a rib pattern of the pneumatic radial tire of the present invention.

FIG. 3 is an enlarged view of a G portion in FIG.

FIG. 4 is an explanatory plan view showing an example of a contact surface (footprint) when the pneumatic radial tire of the present invention contacts the road surface.

FIG. 5 is an explanatory plan view showing an example of a rib pattern of a conventional pneumatic radial tire.

FIG. 6 is an explanatory plan view showing an example of a ground contact surface (footprint) when the conventional pneumatic radial tire contacts the road surface.

[Explanation of symbols]

1 bead core 2 carcass layer 3 tread
4u Upper belt layer 4d Lower belt layer 5 Tread surface 10 Main groove
11 rib 12 dimple

Claims (2)

[Claims] 1. A pneumatic radial tire having a tread with a reduced tread radius, wherein two or more main grooves continuous in the tire circumferential direction are provided on the tread surface to form a rib pattern. Except for the left and right shoulder ribs forming the left and right sides, a large number of dimples are arranged on the inner rib existing inside the shoulder rib, and the inside of the footprint when a standard design load is applied to the radial tire under standard air pressure. A pneumatic radial tire in which the tire circumference of the rib is substantially the same as the tire circumference of the tire inner edge portion of the shoulder rib. 2. The tire circumference of the inner rib in the footprint when a standard design load is applied under standard air pressure is 100% to 103% of the tire circumference of the tire inner edge of the shoulder rib. The pneumatic radial tire according to claim 1.