JPH03128706A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent eccentric wear and facilitate molding of a heavy duty pneumatic radial tire for bus, etc., by providing a thin cut in a rib or a block formed at the tread, wherein the cut is stretching in the direction across the width and has a specific depth and bottom radius. CONSTITUTION:A thin cut 5 stretching in the direction across the tire width is formed in a rid 3 partitioned by the main groove of the tread surface. This thin cut 5 has a bottom in the form of an arc of circle, and the max. groove depth t shall be related to the main groove depth h so that 1/4h<=t<=3/4h. The radius R of the bottom shall be related to the rid 3 width W in the direction across the tire width so that 1<=R/W<=4. This provides uniform rigidity for the rid and decreases eccentric wear without impairing the driving and braking characteristics. Further, the molding process will be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pneumatic radial tire having good braking performance and driving performance and improved resistance to uneven wear, particularly a pneumatic radial tire for heavy loads.

[Conventional technology]

Pneumatic radial tires, especially heavy-duty pneumatic radial tires for trucks, buses, etc. (hereinafter referred to as heavy-duty tires), have a rib pattern or a block pattern on the tread surface. A large number of thin cuts are formed substantially parallel to the tire to improve the braking and driving performance of the tire.

In the past, the thin cuts formed in the ribs or blocks of tires generally had a constant (uniform) depth from the surface of the rib or block, resulting in insufficient rigidity of the ribs or blocks, resulting in a decrease in steering stability. There was a drawback to that.

To solve this problem, as shown in Fig. 4, the bottom of the thin cut 5 formed in the rib or block 3 is made to protrude in a convex shape, or as shown in Fig. 5, it is made to have a concave shape. Something has been proposed. However, since the depth of these thin cuts 5 varies greatly at the inflection point 10, the rigidity of the rib or block 3 changes significantly, and uneven wear is likely to occur. Furthermore, such a thin cut has a problem in that the bottom plate has a complicated shape, and it is difficult to process it by placing it in a mold.

[Problem to be solved by the invention]

An object of the present invention is to provide a pneumatic tire in which thin cuts are made in the ribs or blocks, so that the rigidity of the ribs or blocks is made uniform to prevent uneven wear, without impairing the inherent driving and braking performance of the tire. It is an object of the present invention to provide a pneumatic radial tire, especially a tire for heavy loads, which is easy to mold and process.

(Means for Solving the Problems) The tire of the present invention provides a rib defined by a plurality of main grooves in the circumferential direction of the tire, or a block defined by the main groove and a plurality of sub-grooves intersecting the main groove. It is characterized in that a thin notch is provided across the width direction, the bottom of this thin notch is shaped like an arc, and the relationships of the following formulas (I) and (II) are satisfied.

1/4h≦t≦3/4h...---1------...
・−・−(I) 1≦R/W≦4・−−−−−−−−
・・・・−・−・・・・・−(II) (However, h is the depth of the main groove (mu), t is the maximum depth from the surface of the rib or block of the thin cut (mu), R is the radius of the bottom of the thin cut (mm), and W is the width of the rib or block in the tire width direction (mi). , a rib pattern is formed in which a plurality of main grooves 1 are provided in the tire circumferential direction on the tread surface, ribs 3 are partitioned by the main grooves 1, and lugs 46 are provided in parts of both shoulders. The ribs 3 are provided with thin notches 5 at intervals in the circumferential direction of the tire, which penetrate in the direction of the tire's rotational axis.
is provided. This thin cut 5 is A in Fig. 3.
As shown in the cross-sectional view of FIG. 1 corresponding to the -A line, it has an arc-shaped bottom with a radius R that is convex with respect to its surface.

This thin cut may have an arcuate bottom with a concave radius R relative to the surface of the rib 3, as shown in FIG.

By forming the bottom of the thin notch 5 into an arcuate shape in this way, there is no sudden change in depth like at the point of inflection, and the stiffness of the rib changes gradually, resulting in uniform stiffness of the rib. can be ensured and uneven wear can be prevented.

Furthermore, the thin incisions formed in the ribs of the tire of the present invention are
It is necessary to satisfy the relationship between formula (I) and formula (II) described above.

That is, if the maximum depth t (m) of the thin cut 5 from the surface of the rib 3 is less than 1/4 of the depth h (m) of the main groove,
Braking performance and drive performance become insufficient. On the other hand, if the depth is deeper than 3/4, the rigidity of the rib 3 decreases, and the steering stability decreases.

Furthermore, if the ratio R/W of the radius R (mu) of the bottom of the thin cut 5 to the width W (ms) of the rib 3 in the tire width direction is less than 1, the bottom of the thin cut 5 will be too curved and the rigidity of the rib or block will be reduced. becomes uneven, resulting in uneven wear.

On the other hand, when the ratio R/W exceeds 4, the bottom of the thin cut 5 becomes flat, and the uneven wear resistance is no different from that of a conventional tire in which the depth of the thin cut is constant.

The above description has been made of tires with a rib pattern, but the same applies to tires with a block pattern, and by providing the above-mentioned thin cuts in the blocks, the tire can be made to have performance comparable to tires with a rib pattern. be able to.

All of the thin cuts provided in such a rib or block may be aligned with either the convex or concave arcuate bottom surface with respect to the surface of the block, or both may be appropriately combined.

However, when the bottom of the thin cut has a convex arc shape, there is an advantage that cracks are less likely to occur from the edges E at both ends, compared to when the bottom of the thin cut has a concave arc shape.

For this reason, it is preferable to use the former type with a convex bottom surface as a thin cut particularly when applied to a tire for heavy loads.

Further, a plurality of these thin cuts can be provided in one rib or block, but as long as the plurality of thin cuts 5 are substantially parallel to the tire rotation axis direction, the third thin cut can be provided in one rib or block.
As shown in the figure, the intervals between the thin cuts 5 in the ribs 3 do not necessarily have to be equal, but may be different. Furthermore, the intervals between the thin cuts in the ribs on both the left and right sides of the center line of the tire may be the same or may be different.

The width of these thin cuts (width in the tire circumferential direction) is 0.
．． It can be selected within the range of 1 to 1.0 mm.

〔Example〕

Two types of tires of the present invention and a conventional tire having the tread pattern and the shape and dimensions of the bottom of the thin cut shown in the table were prepared. The sizes of these tires were all the same, IO and oOR20.

The uneven wear resistance and crack resistance of these tires were evaluated by the following method, and the results shown in the table were obtained.

The present invention was conducted by attaching each of the above tires to all wheels of a large vehicle, and after driving for 15,000 m on a course with frequent braking and driving, measuring and evaluating the amount of heel and toe difference. It is expressed as an index with the amount of heel and toe difference of the tire as 100. The larger this index is, the better the uneven wear resistance is.

Random Tachiko Komizu: After installing each of the above tires on the drive wheels of a large vehicle and driving for 15,000 meters on a course with frequent braking and driving, the number of cranks generated in the notches of the tire tread was determined. It is expressed as an index with the number of cranks of the invention tire as 100. The larger this index is, the better the crack resistance is.

From the table, all of the tires of the present invention are superior in uneven wear resistance compared to conventional tires. Furthermore, the crank resistance of the tire of the present invention and the conventional tire was 100 and 80, respectively, and the tire of the present invention was also superior to the conventional tire in terms of crack resistance.

〔Effect of the invention〕

According to the present invention, the bottom of the thin notch formed across the width direction of the rib or block constituting the tread pattern of the pneumatic radial tire is arcuate, and the maximum depth t from the surface of the rib or block is By specifying the ratio of the radius R of the bottom of the thin cut to the width W of the rib or block in the tire width direction, it is possible to determine the Uneven wear resistance can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view taken along the line A-A in FIG.
2 is a sectional view showing another bottom shape of the thin cut formed in the rib or block of the tire of the present invention; FIG. 3 is a plan view showing an example of the rib pattern in the tire of the present invention; FIG. 4 and 5 are cross-sectional views showing the bottom shape of a thin cut formed in a rib or block of a conventional tire, respectively. 1... Main groove, 3... Rib, 5... Thin cut. Figure 1 Figure 4 Figure Figure Figure Figure

Claims (1)

[Claims] A thin cut across the width in a rib defined by a plurality of main grooves in the circumferential direction of the tire or in a block defined by the main groove and a plurality of sub grooves intersecting the main groove. A pneumatic radial tire, wherein the thin cut has an arc-shaped bottom, and satisfies the relationships of formulas (I) and (II) below. 1/4h≦t≦3/4h...(I) 1≦R/W≦4...(II) (However, h is the depth of the main groove (mm), and t is the thinly cut rib or block. maximum depth from the surface (mm),
R indicates the radius (mm) of the bottom of the thin cut, and W indicates the width (mm) of the rib or block in the tire width direction. )