JPH06320914A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire for heavy load which can be prevented from the occurrence of a crack resulting from biting a stone into a thin groove even in case where a shoulder rib is provided with the thin groove extending in the peripheral direction of the tire. CONSTITUTION:In a pneumatic radial tire for heavy load having a tread pattern based on a rib-shape in a tread section 1, a shoulder rib 6 is provided with a thin groove 7 extending in the peripheral direction of the tire, and the width of the thin groove 7 is narrowed by stages in the direction of depth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic radial tire having a rib-based pattern on a tread. More specifically, even when a shoulder groove is provided with a narrow groove extending in the tire circumferential direction, The present invention relates to a heavy-duty pneumatic radial tire designed to prevent the occurrence of cracks due to stone trapping.

[0002]

2. Description of the Related Art Pneumatic radial tires having a rib-based pattern that are used for heavy loads such as trucks and buses are prone to uneven wear on shoulder ribs, especially on the steering shaft side. There is a drawback that the ring phenomenon is likely to occur. As a countermeasure against this, it has been proposed to provide the shoulder rib with a thin groove extending in the tire circumferential direction to reduce the rigidity of the shoulder end portion and prevent the uneven wear and the wandering phenomenon from occurring.

However, the fine groove provided in the shoulder rib is easy to bite stones, and when the bitten stone further digs into the groove bottom, the groove bottom is damaged and cracks are generated. In some cases, the shoulder rib is bordered by the fine groove. There was a problem that was lost. Therefore, in order to prevent the occurrence of cracks due to stone trapping as described above, it is conceivable to narrow the width of the narrow groove or to make the depth of the narrow groove shallow. However, it was not a fundamental measure because it decreased.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of cracks due to stone trapping in the narrow grooves even when the shoulder ribs are provided with the narrow grooves extending in the tire circumferential direction. It is to provide a pneumatic radial tire for heavy loads.

[0005]

A heavy-duty pneumatic radial tire of the present invention for achieving the above object is a heavy-duty pneumatic radial tire having a rib-based tread pattern on a tread. It is characterized in that a narrow groove extending in the direction is provided and the width of the narrow groove is narrowed stepwise in the depth direction.

By providing the shoulder rib with the narrow groove extending in the tire circumferential direction as described above, it is possible to prevent uneven wear and wandering from occurring in a heavy-duty pneumatic radial tire having a rib-based pattern. By gradually narrowing the width of the narrow groove in the depth direction, the stone caught in the narrow groove will be locked by the step, and it will not go further into the groove bottom side, so cracks at the groove bottom due to stone trapping Can be prevented.

The structure of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a pneumatic radial tire for heavy load according to an embodiment of the present invention.
In the figure, 1 is a tread portion, 2 is a belt layer arranged inside the tread portion 1 in the tire circumferential direction, and 3 is a carcass layer. The carcass layer 3 is composed of at least one layer of reinforcing cords substantially 90 ° in the tire circumferential direction. As the reinforcing cords, metal cords such as steel and organic fiber cords such as nylon, polyester and polyaramid are preferably used. To be done. The belt layer 2 is composed of at least two layers made of a metal cord such as steel, and is designed to enhance the rigidity of the tread portion 1. More preferably, this belt layer is composed of at least two tensile strength layers and one reinforcing layer, and the reinforcing cords of the tensile strength layers are 15 ° to 30 ° with respect to the tire circumferential direction.
And the reinforcing cords of the reinforcing layer are arranged at 40 ° to 75 ° with respect to the tire circumferential direction such that the reinforcing cords of the reinforcing layer intersect with each other with the tire circumferential direction sandwiched between the adjacent layers. Be good.

In the tread portion 1, the cross-sectional shape of the tread surface forms a main grounding area M having a developed width TDW by an arc having a curvature radius TR, and both shoulder portions have an auxiliary arc having a curvature radius Ra. The ground area S is formed. The main ground contact area M is a ground contact surface mainly when traveling straight ahead, and the auxiliary ground contact area S is used as a ground contact surface when cornering or over a rut. The arc forming the main ground area M and the arc forming the auxiliary ground area S intersect with each other, and a clear edge boundary E is formed by this intersection. The presence of the edge-like boundary E reduces the relative slippage of the shoulder region with respect to the central region of the tread surface and suppresses shoulder drop wear, which is one of the uneven wear.
In addition, the radius of curvature Ra forming the arc of the auxiliary ground area S
Is larger than the depth of 4 of the main groove described later and smaller than 5 times the depth of 4 of the main groove.

A plurality of main grooves 4 extending in the tire circumferential direction are provided on the tread surface of the main ground contact area M, and a plurality of ribs 5 are formed in the central portion of the tread by these main grooves 4 in a divided manner. Shoulder ribs 6 are separately formed on the shoulder portions. Further, the shoulder rib 6 is provided with a narrow groove 7 near the end thereof so as to be narrower than the main groove 4 so as to extend in the tire circumferential direction. And an outer thin rib 6b.

In the present invention, the width of the narrow groove 7 is gradually narrowed in the depth direction, the groove portion 7a remains on the tread surface side, and the narrow sipe portion 7b is formed on the groove bottom side. Is configured to be. The narrow groove 7 may be linear or wavy in a plan view. For example, in FIG.
As shown in FIG. 3A, the groove portion 7a and the sipe portion 7b are both linear, or as shown in FIG. 3B, the groove portion 7a is linear, while the sipe portion 7b is corrugated. As shown in FIG. 3D, the sipe portion 7b is linear while the groove portion 7a is wavy.
Can be wavy together.

As described above, by providing the shoulder rib 6 with the thin groove 7 extending in the tire circumferential direction, it is possible to prevent uneven wear and wandering from occurring in the heavy-duty pneumatic radial tire having a rib-based pattern. it can. Moreover, the width of the narrow groove 7 is gradually narrowed in the depth direction,
By forming the groove portion 7a on the tread surface side and the sipe portion 7b on the groove bottom side, the stone caught in the narrow groove 7 is locked by the step between the groove portion 7a and the sipe portion 7b, and the groove bottom side is further extended. Since it does not dig into it, it is possible to prevent the occurrence of cracks at the groove bottom due to stone trapping. Further, the stones locked in such a state will come off due to centrifugal force during traveling. Since the narrow groove 7 is not narrowed over the entire depth, even if the sipe portion 7b having a narrow width is formed, it is possible to secure uneven wear resistance equivalent to that in the conventional case.

In the present invention, the width W of the groove portion 7a of the narrow groove 7
₁ is preferably set in the range of 0.5 to 2.5% of the tread development width TDW. If the width W _{1 of the} groove portion 7a is less than 0.5% of the tread development width TDW, the substantial effect of providing the fine groove 7 is lost, and the uneven wear resistance is reduced. If it exceeds, stone trapping is likely to occur and cracks are likely to occur at the groove bottom.

On the other hand, the width W ₂ of the sipe portion 7b of the narrow groove 7 is
Tread development width TDW 0.2-0.6%, and W
It is preferable to set so as to satisfy the relationship of ₂ / W ₁ ≦ 0.5. The width W ₂ of the sipe portion 7b is the tread development width T
If it is less than 0.2% of DW, the molding bone arranged in the tire mold for molding this sipe portion 7b will be easily bent, and its molding will be difficult. If it exceeds, stones will easily enter the sipe portion 7b. Further, by satisfying the relationship of W ₂ / W ₁ ≦ 0.5, a sufficient step is formed between the groove portion 7a and the sipe portion 7b, and the stone can be effectively locked.

The width W ₂ of the thin rib 6b on the tread surface is
It is preferable to set it to 0.5 to 3% of the tread development width TDW. The width W ₂ of the thin rib 6b is the tread development width TDW
If it is less than 0.5%, the thin ribs 6b are likely to be broken, and conversely, if it exceeds 3%, the shear rigidity of the thin ribs 6b is increased, and the uneven wear resistance is reduced. The formation position of the thin groove 7 is defined by the width W ₂ of the thin rib 6b.

The narrow groove 7 satisfies the above-mentioned groove width and position, and is further inclined in the depth direction toward the inside of the tire with respect to the perpendicular to the tire rotation axis, and the angle α with respect to the perpendicular is 2 It is preferable to set the angle to 12 °. This is because when the depth direction of the narrow groove 7 is directed to the outside of the tire with respect to the perpendicular, stress concentrates on the groove bottom of the narrow groove 7 and a crack extending in the lateral direction is generated. This is because the thin rib 6b is missing. However, if the angle α exceeds the upper limit of 12 °, the rigidity of the thin ribs 6b increases, and the uneven wear resistance decreases.

A narrow groove 7 having a groove portion 7a and a sipe portion 7b.
The total depth D ₁ of the main groove 4 is preferably 50
˜120%, more preferably 70 to 10 of the depth of the main groove 4.
Set to 0%. If the total depth D ₁ of the fine groove 7 is less than 50% of the depth of the main groove 4, the uneven wear resistance becomes insufficient, and if it exceeds 120%, cracks occur at the groove bottom due to stone trapping. It tends to occur.

The depth D ₂ of the groove portion 7a is preferably 25 to 80% of the total depth D ₁ of the narrow groove 7, and more preferably 35 to 70% of the total depth D ₁ . Groove 7a
Depth D ₂ of less than 25% of total depth D ₁ ,
The uneven wear resistance becomes insufficient because most of the fine grooves 7 are composed of the sipe portion 7b. Conversely, when it exceeds 80%,
Since the step between the groove portion 7a and the sipe portion 7b comes close to the groove bottom, cracks are likely to occur due to stone trapping.

In the present invention, the cross-sectional shape of the narrow groove 7 is not limited to that shown in FIG. 1, but various modes as shown in FIGS. That is, in FIG. 1, the groove 7
a is formed so as to cut out both the rib main body 6a of the shoulder rib 6 and the thin rib 6b around the sipe portion 7b, but the groove portion 7a is arranged so as to be biased toward the thin rib 6b side as shown in FIG. Alternatively, as shown in FIG. 5, the groove 7a may be formed in the rib body 6a.
It can be arranged to be biased to the side. Further, if the bottom portion of the sipe portion 7b is rounded as shown in FIG. 6, it is possible to avoid stress concentration at the bottom portion, and thus it is possible to effectively prevent the occurrence of cracks. Further, the step provided in the narrow groove 7 is not particularly limited as long as it is one step or more,
The number of steps can be two or more as shown in FIG. 7, and the steps of the left and right groove walls may be offset from each other as shown in FIG.

[0019]

[Examples] In a heavy-duty pneumatic radial tire having a tire size of 11R22.5 14PR, a tread having a rib pattern, and a tread development width of 220 mm, the width, depth, and cross-sectional shape of the narrow groove provided in the shoulder rib Comparative tires 1 to 1 in which the following are variously changed
5 and tires 1 to 12 of the present invention were manufactured. Comparative tires 1 to 6 The comparative tire 1 has no fine groove as shown in FIG. 9, and the others have fine grooves of uniform width in the depth direction as shown in FIG. 10, and the fine groove depth is the main groove depth. The ratio (%) of the narrow groove width to the tread development width was varied. Comparative tires 7 to 13 Fine grooves having a uniform width are provided in the depth direction as shown in FIG. 10, the fine groove width is 2.5 mm, and only the ratio (%) of the fine groove depth to the main groove depth is different. Let Inventive Tires 1 to 5 and Comparative Tires 14 and 15 As shown in FIG. 1, fine grooves each having a groove portion on the tread surface side and a sipe portion on the groove bottom side are provided, and the total depth of the fine grooves is defined as the main groove depth. Along with 100%, the width of the groove is 2.5 mm,
The width of the sipe portion was set to 0.6 mm, and only the ratio (%) of the groove depth to the total depth of the fine grooves was varied. The comparative tire 14 had a groove depth of 100%, and the comparative tire 15 had a groove depth of 0%. Tires 6 to 12 of the present invention As shown in FIG. 1, a fine groove including a groove portion on the tread surface side and a sipe portion on the groove bottom side is provided, and the width of the groove portion is 2.5 mm and the width of the sipe portion is 0.6 mm. At the same time, the groove depth and the sipe depth were made equal to each other, and only the ratio (%) of the total depth of the fine grooves to the main groove depth was varied.

The comparative tires 1 to 15 and the tires 1 to 12 of the present invention were assembled on a wheel having a rim size of 22.5 × 8.25, mounted on the front axle of a large vehicle (2-D4), and the air pressure was 7.0 kg. / Cm ² , after running 20,000 km on a paved road including a part of the gravel road surface, the shoulder drop wear amount, the number of stone traps and the crack length were measured, and the results are shown in Tables 1 to 4.

As for the amount of shoulder drop wear, the width X and the amount of step Y of the shoulder rib step portion (uneven wear portion) were measured as shown in FIGS. 9 and 10. When the shoulder rib is provided with a thin groove as shown in FIG. 10, the outer thin rib is for absorbing uneven wear, so the width X of the step portion was measured only for the rib body. The number of stones bitten was the total number of stones bitten in the narrow groove in the two tires on the left and right. Also,
The crack length is the ratio of the total length of cracks to the circumferential length (1 round) of the groove bottom measured by measuring the length of all cracks generated at the groove bottom of the narrow groove. (%) Was calculated, and the average was taken for two tires on the left and right.

[0022] As can be seen from Table 1, if the narrow groove width is simply narrowed, uneven wear is likely to occur. On the contrary, if the narrow groove width is simply widened, uneven wear is likely to occur and stone trapping is caused. It was easy for cracks to occur. However, except for the problem of cracks, the uneven wear resistance was good when the ratio of the narrow groove width to the tread spread width was 0.5 to 2.5%.

[0023] As can be seen from Table 2, if the fine groove depth is simply made shallow, uneven wear is likely to occur, and conversely, if the fine groove depth is simply made deep, cracks due to stone trapping are likely to occur. It was However, except for the problem of cracks, the uneven wear resistance was good when the ratio of the fine groove depth to the main groove depth was 50% or more.

[0024] As can be seen from Table 3, in the tires 1 to 5 of the present invention, the narrow groove is composed of the groove portion and the sipe portion, and the width of the narrow groove is gradually reduced, so that the uneven wear resistance and the crack resistance are excellent. Both were excellent. Particularly, good results were obtained when the ratio of the groove depth to the total depth of the fine grooves was 25 to 80%. Further, when the narrow groove is composed of only the groove portion like the comparative tire 14, cracks are easily generated, and when the thin groove is composed of only the sipe portion like the comparative tire 15, the uneven wear resistance is deteriorated. It was

[0025] As can be seen from Table 4, the tires 6 to 12 of the present invention also have the narrow groove width reduced stepwise like the tires 1 to 5 of the present invention, and therefore have excellent uneven wear resistance and crack resistance. It was Particularly, good results were obtained when the ratio of the total depth of the fine grooves to the depth of the main grooves was 50 to 120%.

[0026]

As described above, according to the present invention, in a heavy duty pneumatic radial tire having a rib-based tread pattern on a tread, a shoulder groove is provided with a narrow groove extending in the tire circumferential direction, and the narrow groove is provided. By gradually narrowing the width of the groove in the depth direction, it is possible to prevent uneven wear and wandering, and the stone caught in the narrow groove is locked by the step, and the groove bottom Since it does not dig into the side as well, it is possible to prevent the occurrence of cracks at the groove bottom due to stone trapping.

[Brief description of drawings]

FIG. 1 is a half cross-sectional view showing a main part of a heavy-duty pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a shoulder portion in FIG.

FIG. 3 is a plan view showing various aspects of a narrow groove in the present invention.

FIG. 4 is a half cross-sectional view showing a main part of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 5 is a half cross-sectional view showing a main part of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 6 is a half sectional view showing a main part of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 7 is a half sectional view showing a main part of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 8 is a half cross-sectional view showing a main part of a heavy duty pneumatic radial tire according to another embodiment of the present invention.

FIG. 9 is a half cross-sectional view showing a main part of a heavy-duty pneumatic radial tire having no fine grooves.

FIG. 10 is a half sectional view showing a main part of a conventional pneumatic radial tire for heavy load.

[Explanation of symbols]

 1 Tread part 4 Main groove 5 Rib 6 Shoulder rib 7 Fine groove 7a Groove part 7b Sipe part

Claims (1)

[Claims] 1. A heavy duty pneumatic radial tire having a rib-based tread pattern on a tread, wherein a shoulder rib is provided with a narrow groove extending in a tire circumferential direction, and the width of the narrow groove is gradually narrowed in a depth direction. Pneumatic radial tire for heavy loads.