JPH08118918A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To prevent such uneven wear as heel and toe wear and improve an antiuneven wear property without degrading the original property of a block pattern and impairing an antiwear durability. CONSTITUTION: In a pneumatic radial tire having block patterns formed by disposing circumferentially a plurality of blocks defined by a plurality of peripheral main grooves and lateral grooves on the tread surface part, a plurality of holes 5 having approximately same depth as that h of the main groove 2 from the block surface and the cross sectional area enlarged toward the bottom are provided in the block 4a of at least shoulder part near the central part of the respective blocks 4a. A rubber amount moved to the block end by a vertical load is absorved by a plurality of the holes in the central part to reduce a shearing force produced on the block surface.

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 mainly for heavy loads, which is excellent in uneven wear resistance.

[0002]

2. Description of the Related Art Generally, a tread pattern for a heavy-duty tire has a plurality of main grooves in the tire circumferential direction and lateral grooves intersecting with the main grooves, and the outermost main groove is formed on the shoulder portion of the tread. Many block patterns have blocks defined by lateral grooves extending outwardly from.

In the case of such a block pattern, uneven wear caused by running of the tire is called heel and toe wear which causes a difference in wear mainly at both circumferential ends of the block. That is, looking at the wear state of the block, due to the relationship between the motion of the block during running and the deformation due to the load, the wear is more severe on the one end side in the running direction and less on the other end, and as shown in FIG. Wear that is inclined like a blade occurs, and the wear of this block in a tilted state is called heel and toe wear.

When such wear occurs, the habitability of the vehicle is deteriorated due to the occurrence of vibration, which causes a decrease in steering stability along with the occurrence of noise, and this heel-and-toe wear causes other uneven wear. It is also the basis of the occurrence of.

Many attempts have been made to suppress such wear from hitherto, and among them, a method of making a part of the lateral groove defining the block shallow, that is, a method of providing a bridge in the lateral groove is generally used. However, in this case, the greater the effect, the shallower the lateral groove becomes, which results in deterioration of the original meaning of the block pattern, drainage, and traction. Was there.

[0006]

One of the main causes of the above heel-and-toe wear is the shearing force generated on the surface of the block when a vertical load is applied to the block, especially in the circumferential direction. The component is involved, and as shown in FIG. 7, the shearing force (fr) of this circumferential component becomes greater toward both ends of the block in the tire circumferential direction, and the direction is opposite.

In addition to the above shearing force (fr), the tire tread portion, that is, the block surface, has a driving force, a braking force, a force due to rolling resistance, and a circumferential difference (center portion and shoulder portion) based on the crown radius of the tread portion. A circumferential force due to a force (caused by the difference in diameter of the portion), that is, a shearing force (fc) acts.

These forces may act individually, simultaneously, or only individually, but the drive shaft on which the drive force is applied and the braking shaft (steering wheel or idle). The direction of the shearing force (fc) is constant in the tire circumferential direction except that the direction of the force between the wheel and the wheel is opposite. At one end, F = fc + fr and the shearing force increases, and at the other end, F = fc-fr, and the absolute value of the shearing force becomes small.

If this total shearing force (F) is different at both ends in the circumferential direction of one block, one end side easily slips over the frictional force between the block surface and the road surface, and the other end side. Is less than frictional force, and there is little slippage between the block and the road surface. Friction energy is generated by this slip, so wear is large on the addition side,
The wear is small on the subtraction side, and generally changes gradually in the region between them. Therefore, in order to prevent heel and toe wear, it is necessary to reduce the shearing force (fr).

As a method therefor, a rubber volume (deflection × block tread surface area) corresponding to bending of the block caused by vertical force resists the frictional force of the surface when it escapes to the free surface on the side of the block, and Since the amount of rubber movement is integrated toward the end of the block and a large shearing force acts, it is necessary to reduce the amount of rubber movement.

That is, if the amount of rubber moving to the end of the block is partially absorbed by the central portion of the block, the shearing force (fr) can be effectively reduced.
For this absorption, it is sufficient to provide a relief area for the rubber, and as a means for this, a plurality of holes (spaces) may be provided near the center of the block.

The present invention has been made in view of the above, and does not deteriorate the original characteristics of the block pattern, the drainage performance required for all-season performance, the traction performance on a shallow snow road, and the wear durability. The purpose of the present invention is to prevent uneven wear such as heel and toe wear and to improve uneven wear resistance without impairing the wear resistance.

[0013]

DISCLOSURE OF THE INVENTION The present invention is a pneumatic tread having a block pattern in which a plurality of blocks defined by a plurality of circumferential main grooves and a plurality of lateral grooves are circumferentially arranged on a tread surface. In the radial tire, in order to solve the above-mentioned problems, at least the block of the shoulder portion has a plurality of holes having a depth substantially equal to the depth of the main groove from the block surface, and a larger cross-sectional area as the depth increases,
It is provided near the center of each block.

In the above, the plurality of holes in each block are
It is particularly preferable that the block is distributed so that it approaches the side portion at a portion close to the midpoint of each side portion forming the main portion of the outer peripheral contour of the block and moves away at both end portions thereof.

Further, it is desirable that the total area of all the holes in one block on the block surface is 4 to 8% of the block surface area. That is, the larger the total area of the plurality of holes in one block is, the better the uneven wear resistance is. On the other hand, the area receiving friction energy is small, and therefore the wear is accelerated. Therefore, it is preferable to set the total area of a plurality of holes as described above. If it is 4% or less, effective uneven wear resistance cannot be obtained, and if it exceeds 8%, the wear durability is significantly deteriorated. , Not preferable. Further, the deflection of the tread rubber due to the load, that is, the amount of movement of the rubber is generally 7/10%, and therefore 8% covers most of the rubber, so there is no need for any further increase.

Further, it is particularly preferable that the plurality of holes have a circular cross section and the diameter of the opening is 2.5 to 5.0 mm.

When the hole has a circular cross-sectional shape, the cost for processing the mold for molding the tire is the lowest, and when the diameter of the hole is less than 2.5 mm at the opening, the tire molding metal is used. The strength of the pin for hole formation attached to the inner surface of the mold is
The tire could not withstand the force to remove it from the mold, causing breakage,
This is because it is virtually impossible to machine the hole. That is, for example, a truck bus tire generally has a deep groove of 12 to 24 mm as compared with a passenger car tire, and therefore, it is difficult to set the depth to 2.5 mm or less for a hole having a depth equivalent to the depth of the groove. . If the diameter of the opening exceeds 5 mm, pebbles will easily enter this hole during traveling, and the function of the hole will deteriorate. Therefore, as described above, 2.5-
It is good to set it to 5.0 mm.

[0018]

[Operation] According to the invention of the present application described above, at least the block of the shoulder portion has a plurality of holes having a depth substantially equal to the depth of the main groove in the circumferential direction from the block surface and having a larger cross-sectional area at a deeper portion. Since the blocks are provided near the center of each block, when a vertical load is applied to the block, the amount of rubber that moves to the end of the block due to the vertical load can be absorbed by the plurality of holes in the center of the block.

That is, when a vertical force acts on the block to cause the rubber to move and the rubber moves, a part of the rubber escapes into a plurality of holes (to make the holes smaller), thereby reducing the movement to the end of the block. As a result, the shearing force of the circumferential component of the shearing force generated on the block surface due to the vertical load is reduced.

In particular, since almost the same shearing force is generated on the surface and the base of the block when loaded, if the depth of the hole is shallow, only the rigidity of the surface side becomes low, and the rubber movement is likely to concentrate on the surface side, which is the opposite. Although it is also effective, as in the present invention, the depth of the hole is made equal to the depth of the main groove, and the cross-sectional area is increased toward the bottom side to increase the rubber movement on the base side of the block. The shearing force of the circumferential component due to the vertical load can be reduced more effectively. Further, as described above, if the hole has a shape that expands toward the bottom side, stone trapping due to the hole is reduced.

Further, in the case of the present invention, since a large number of holes are formed in the central portion of the block as described above, a strong braking force or driving is applied to the block surface, and the ground surface pressure is applied to one end in the circumferential direction. Even if it is biased to the side, since the block rigidity is kept large at the end portion, it is possible to suppress the increase in bending, and it is possible to reduce the rubber movement to the block end and keep the shearing force small as described above. .

If this hole is provided near both ends of the block, the pressure of the ground surface applied to the surface of the block will be reduced by the action of the shearing force in the circumferential direction due to factors other than the vertical force such as driving and braking forces. When it is biased to one end side in the tire circumferential direction,
The rigidity of the end portion becomes too small, the footing is not effective, the deflection becomes large and complicated, and uneven wear (including other than heel and toe wear) is increased.

Further, in each side portion forming the block, the movement of the rubber is maximized in the vicinity of the center of the side portion, so that a plurality of holes formed in the block are formed in the side portion. By forming the portions close to the midpoint so as to be close to the side portions and distributed, it is possible to increase the places where the rubber movement escapes in the central portions of the side portions, and to further effectively suppress the rubber movement outward.

[0024]

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

FIG. 1 is a partially developed view showing a block pattern of a tread portion of one embodiment of a tire of the present invention, and FIG. 2 is a schematic sectional view of the same.

The reinforcing structure such as the carcass structure and the belt structure inside the tire is the same as that of a general radial tire, and therefore the description thereof is omitted.

As a pattern of the tire tread portion (1), a plurality of main grooves (2) in the tire circumferential direction are provided on the tread surface, and lateral grooves (3) extending from the main groove (2) in the crossing direction are formed. A large number of blocks (4a) and (4b) defined by are arranged in the tire circumferential direction to form a so-called block pattern. (4a) shows a shoulder block and (4b) shows a center block.

As shown in the figure, at least in the shoulder block (4a), the depth (h) of the main groove (2) adjacent to the block (4a) from the block surface is approximately equal to the depth (h), and A plurality of inversely tapered holes (5) having a larger cross-sectional area in the deeper part are provided in a dense state near the central part of each block.

The plurality of holes (5) in each of the blocks (4a) are located near the midpoint of each side forming the main part of the outer peripheral contour of the block (4a) as shown in the figure. Are formed so as to be close to and away from both end portions, that is, corner portions, for example, distributed in a rhombus as shown in the figure. This makes it possible to effectively prevent the rubber from moving outward.

The total area on the block surface of the plurality of holes (5) in one block (4a) is set within the range of 4 to 8% of the block surface area. This allows
Effective uneven wear resistance can be obtained without impairing wear durability.

The cross-sectional shape of the hole (planar shape of the opening) is not limited to the circular shape as shown in FIG. 1, but as shown in FIG. 4, it may be oval, substantially triangular or cruciform, and various other shapes. Can be implemented by In practice, a circular hole is easy to form and is particularly preferable. The diameter of the opening of the hole (5) in the case of a circular shape is set in the range of 2.5 to 5.0 mm. The plurality of holes (5) may be a combination of holes having different diameters.

As a way of expanding the cross-sectional area of the hole,
The ratio of the cross-sectional area between the opening (5a) and the bottom (5b) of the hole (5) is about 1.6 to 2.5 times, and the diameter ratio of the circular shape is about 1.2 to 1.6 times. The position is particularly good because of the reduction of the area during wear progress (increased wear rate), the occurrence of cracks at the bottom of the hole during traveling, the ease of removal from the mold during tire vulcanization molding, etc. .

In the illustrated embodiment described above, a plurality of holes (5) are formed only in the shoulder block (4a), but the same hole is formed in the center block (4b). be able to.

According to the tire of the present invention having the block pattern having the above-mentioned structure, when the vertical load is applied to the block and the block (4a) is flexed, the rubber corresponding to that amount moves in the outer peripheral direction of the block. , Part of which escapes to a plurality of holes (5) in the central part, the movement to the block end is reduced, and the shear force (fr) of the circumferential component of the shear force generated on the block surface by the vertical load. Becomes smaller. Particularly, since the hole (5) has the same depth as the main groove (2) and the cross-sectional area is larger toward the bottom side, rubber movement increases on the base side of the block, and the shearing force decreases. Is made more effective. Moreover, since the hole is located at the center of the block, even if the ground contact surface pressure is biased toward one end side in the tire circumferential direction, the rigidity is largely maintained at the end portion, so that it is possible to suppress the increase in bending.

Table 1 below shows the stone tires, wear durability and uneven wear resistance of the example tires of the present invention (examples 1 to 3) and the comparative example tires (comparative examples 1 to 4) in the actual vehicle running test. Shows the comparison.

The tires of Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to actual vehicle tests under the following conditions as the following tires based on the tread pattern of FIG.

Tire size: 11R24.5 14PR pattern tread width: 210 mm Depth of main groove h: 22 mm Depth of lateral groove: 22 mm Number of lateral groove pitch: 60 Horizontal groove pitch length: 58.3 mm 1 block area: 1950 mm ² load / Air pressure: 650kpa / 25kN Tire installation: Drive shaft

The sectional shapes and distributions of the holes formed in the shoulder blocks of Examples 1 to 3 and Comparative Examples 2 to 4 are as shown in FIGS. 5 (a) to 5 (f).
Examples 1 to 3 have the shapes and distributions of the holes in FIGS. 5A to 5C, and Comparative Examples 2 to 4 have the shapes and distributions of the holes in FIGS. 5D to 5F.

[0039]

[Table 1]

As is clear from the above, in any of Examples 1 to 3, compared with Comparative Example 1 having no hole, the uneven wear resistance can be greatly improved with almost no loss in wear durability. ,
In addition, stone trapping hardly occurred or could be suppressed to a relatively small range.

On the other hand, Comparative Example 2 in which the hole of the block is shallow
Nos. 4 and 4 had almost no effect of improving uneven wear resistance, and those having an extremely large hole diameter deteriorated wear durability and had the problem of stone trapping in the hole.

[0042]

As described above, according to the present invention, a plurality of holes having the same depth as the main groove and a larger cross-sectional area toward the bottom side are provided at least in the center of the shoulder block. The original characteristics of the block pattern can be maintained as they are, without uneven drainage or traction, without impairing wear durability, and preventing uneven wear such as heel and toe wear, and greatly improving uneven wear resistance. You can

[Brief description of drawings]

FIG. 1 is a partial development view showing a block pattern of a tread portion of an embodiment of a tire of the present invention.

FIG. 2 is a schematic sectional view of the tread portion of the above.

FIG. 3 is an enlarged cross-sectional view taken along the line AA of FIG.

FIG. 4 is a schematic plan view showing another example of the shape of the opening of the hole formed in the block.

FIG. 5 is a schematic view showing cross-sectional shapes and distribution states of holes in Examples and Comparative Examples.

FIG. 6 is a cross-sectional explanatory view of heel and toe wear.

FIG. 7 is an explanatory diagram of a state where a block is bent and a shearing force is generated due to a load.

[Explanation of symbols]

 (1) Tread (2) Main groove (3) Lateral groove (4a) Shoulder block (4b) Center block (5) Hole

Claims (4)

[Claims] 1. A pneumatic radial tire having a block pattern in which a plurality of blocks defined by a plurality of main grooves in the circumferential direction and a plurality of lateral grooves are arrayed in the circumferential direction on a tread surface of a tread. The block is provided with a plurality of holes having a depth substantially equal to the depth of the main groove from the surface of the block and having a larger cross-sectional area in the deeper portion near the central portion of each block. Radial tires. 2. A plurality of holes of each block are distributed such that they approach a side portion at a portion near a midpoint of each side portion forming a main portion of the outer peripheral contour shape of the block and move away at both end portions thereof. The pneumatic radial tire according to claim 1, wherein: 3. The total area on the block surface of all holes in one block is 4 to 8% of the block surface area.
The pneumatic radial tire according to claim 1 or 2. 4. The pneumatic radial tire according to claim 1, wherein the plurality of holes have a circular cross section and a diameter of 2.5 to 5.0 mm.