JPH03235701A - Pneumatic tire for heavy load - Google Patents

Abstract

PURPOSE:To restrain partical abrasion or prevent gravel biting by specifying the displacement of the width and the surface of a stepped land part demarcated with a pair of slender grooves and the groove depth of the slender grooves respectively, and also appendantly providing projections having specific width and height on the groove bottom parts of the slender grooves. CONSTITUTION:Peripheral direction main grooves 34 and slender grooves 36 are ar ranged on the tread part 32 of a tire 30, and stepped land parts 38 are demarcated with the pair of the slender grooves 36. In this case, the width W2 of the stepped land parts 38 is set to 50 - 150% of the groove width W1 of the peripheral direction main grooves 34. Also the surfaces of the stepped land parts 38 are deviated by 1 - 5% of the groove depth D1 of the peripheral direction main grooves 34 from the surface of the tread part 32 to an inner part in a tire radius direction. Moreover in the slender grooves 36, their groove depth D3 is set to 85 - 120% of the groove depth D1 of the peripheral direction main grooves 34 and the groove width W3 is set to 10 - 90% of the groove width W1 of the peripheral direction main grooves 34 respectively. Projections 42, having a height of 10 - 70% of the groove depth D3 of the slender grooves 36 and a width W4 of 20 - 40% of the groove width W3 of the slender grooves 36, are appendantly provided on the groove bottom part of the slender grooves 36.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heavy-duty pneumatic tire with improved rock-biting resistance without impairing uneven wear resistance.

(Prior Art) A carcass consisting of a carcass ply of cords uniformly arranged at an angle of 75° to 90° with respect to the tire equatorial plane and a carcass with a shallow angle, for example 20°
Due to the so-called "hoop effect" of the belt, radial tires have a belt consisting of braids of cords arranged obliquely in a certain direction within the following angular range. Due to the small movement of the tread rubber in the ground, excellent maneuverability, wear resistance, and high-speed running performance, it has become popular for vehicles such as trucks and buses as expressway networks have become more complete and developed in recent years. It is used.

Tires used for vehicles such as trucks and buses that often travel on expressways have a plurality of circumferential grooves extending in the circumferential direction of the tire and ribs partitioned by the circumferential grooves. A tread pattern called a "rib pattern" is widely used because it has low skidding and rolling resistance, and low tire noise.

On the other hand, in tires with a rib pattern,
When used for a long period of time, there is a drawback in that uneven wear, or so-called "river wear", tends to occur at the edges of the ribs defined by the circumferential grooves.

In order to deal with this problem, as shown in the tire 10 shown in FIG. Narrow grooves 14.14 are provided to partition the step land portion 16 extending in the tire circumferential direction, and the surface of the step land portion 16 is partitioned by circumferential main grooves 18 extending in the tire circumferential direction. A tire has been proposed in which the rib 20 is located on the inside in the tire radial direction from the surface thereof. Note that the tire 10 is
Since it has a nearly symmetrical structure with respect to the equatorial plane, only half of it is shown in Figure 3 for simplicity.

According to this tire, when the tire 10 rolls under the action of a load, the ribs 20 and the stepped land portion 16 that form the tire tread come into contact with the road surface, but the stepped land portion 1
Since the pressure acting on the ribs 6 is smaller than the pressure acting on the ribs 20, the stepped land portion is dragged against the road surface.

However, when the tire is transferred, the sum of the shear force in the tire rotation direction and the shear force in the opposing direction that is generated in the tread portion 12 including the stepped land portion 16 can be considered to be approximately constant. Therefore, the larger the proportion of the shearing force generated in the stepped land portion 16 that opposes the tire rotational direction, the smaller the proportion of the shearing force generated in the rib 20 that opposes the tire rotational direction.

On the other hand, uneven wear of a tire is greatly affected by shearing force that opposes the direction of rotation, so this conventional tire effectively suppresses the occurrence and progression of uneven wear at the ribs 20, especially at the edges. be able to.

(Problems to be Solved by the Invention) Although this conventional tire having a stepped land portion can suppress uneven wear, it is easy for stones to get caught in the narrow grooves that partition the stepped land portion. New problems have arisen, such as chipped stones in the ribs.

Moreover, when a stone is inserted, the stepped land portion and the rib are connected via the stone and move as one.
The ribs facing the stepped land portion, especially the edges thereof, are dragged against the road surface, causing uneven wear.

The present invention has been made in view of these problems, and an object of the present invention is to provide a new heavy-duty pneumatic tire that suppresses the occurrence of uneven wear and also solves problems such as stone chewing. .

(Means for Achieving the Object) In order to achieve this object, the present invention includes at least two circumferential main grooves extending in the circumferential direction of the tread portion of the tire and spaced apart from each other. at least one pair of narrow grooves extending in the circumferential direction of the tire, or at least one narrow groove that cooperates with the circumferential main groove to partition a stepped land portion extending in the circumferential direction of the tire; In a heavy-duty pneumatic tire with
150%, and the surface is 1 to 5% of the groove depth of the circumferential main groove from the tread surface inward in the tire radial direction.
On the other hand, the groove depth of the narrow grooves is set to 85 to 120% of the groove depth of the circumferential main groove, and the groove width is set to 10 to 90% of the groove width of the circumferential main groove. The groove bottom has a height of 10 to 70% of the groove depth of the narrow groove, and a height of 20 to 4% of the groove width.
Protrusions having a width of 0% are arranged.

(Function) According to this tire, when the tire is transferred, the stepped land portion divided by the narrow grooves extending in the circumferential direction of the tire, or by the narrow grooves and the circumferential main groove, does not pull against the road surface. As a result, the shearing force generated in the ribs formed on the tread portion, which opposes the direction of rotation of the tire, is reduced, and the development of uneven wear at the edges can be effectively suppressed.

On the other hand, the protrusions arranged in the narrow grooves prevent stones from entering the narrow grooves, and also facilitate the ejection of stones stuck in the narrow grooves. Stone fire caused by chewing does not cause any problems.

(Example) The invention will now be described with reference to preferred embodiments.

FIG. 1 is a cross-sectional view of a tire according to the present invention. In this example, since the cross-sectional shape of the tire is approximately symmetrical with respect to the tire equatorial plane P, for the sake of simplicity, the cross-sectional shape of the tire is In addition, since its internal structure is equivalent to that of a known radial structure tire, its explanation will be omitted here.

The tire 30 shown in this embodiment has a circumferential main groove 34 extending in the tire circumferential direction formed in the center side portion of the tire in each half of its tread portion 32, and a circumferential main groove 34 extending in the tire circumferential direction formed in the center side portion of the tire, and a circumferential main groove 34 and a tread portion. A pair of narrow grooves 36 are formed between both ends of the tire 32 and extend in the circumferential direction of the tire.

In each half of the tread portion 32, the narrow grooves 36 that are paired with each other are spaced apart from each other in the tire width direction, and partition step land portions 38 extending in the tire circumferential direction into each half of the tread portion 32. do. The width w2 of these stepped land portions 38 is selected from within the range of 5θ to 150% of the groove width W of the circumferential main groove 34.

This means that the width w2 of the stepped land portion is the groove width W of the circumferential main groove 34.
If the shear force is smaller than 50% of 1, the shear force generated in the stepped land portion in the direction of tire rotation becomes smaller, and as a result, the ratio of the shear force to the rib 40 increases, so the rib 40, especially its This is because uneven wear at the edges becomes unavoidable.

On the other hand, the width w2 of the stepped land portion 38 is
If the groove width W is larger than 150%, the width of the rib 40 relative to the tire tread width, or the effective width of the rib 40, decreases, resulting in a decrease in uneven wear resistance and wear life.

On the other hand, a stepped land portion 38 defined by a pair of narrow grooves 36
The surface of the rib 40 that is defined by the circumferential main groove 34 and the narrow grooves and forms the tire tread section is shifted inward in the radial direction of the tire, and the amount of the shift is as follows: The groove depth of the circumferential main groove is within the range of 1 to 5%.

This means that if the deviation of the surface of the stepped land portion 38 from the surface of the rib 40 is smaller than 1% of the groove depth of the circumferential main groove,
The shear force generated in the tire rotation direction is transferred to the stepped land portion 38.
This is because it becomes difficult to concentrate on the surface of the rib 40, and there is virtually no difference from the surface of the rib 40. On the other hand, if the amount of deviation exceeds 5% of the groove depth Dl of the circumferential main groove, the stepped land portion Since the pressure on the road surface becomes too small and it becomes impossible to substantially generate a shearing force opposing the tire rotation direction on the stepped land portion, the amount of deviation of the surface of the stepped land portion 38 with respect to the rib 40 is Groove depth of circumferential main groove.

The value shall be within the range of 1 to 5%.

By the way, the groove depth D3 of each set of narrow grooves 36 that respectively partition the stepped land portion 40 is 8 times the groove depth Dl of the circumferential main groove 34.
5 to 120%, and the groove width W is set to a value within the range of 10 to 90% of the groove width W+ of the circumferential main groove.

This is because if the groove depth D3 of the narrow groove 36 is smaller than 85% of the groove depth of the circumferential main groove 34, the narrow groove will disappear even though the main groove remains at the end of wear. This is because it becomes difficult to concentrate the shear force on the stepped land portion, and the effect of suppressing uneven wear becomes insufficient.
If the groove depth is larger than 120% of 4, the skid base, which is usually arranged to protect the belt even if the tire wears out, cannot be removed sufficiently at the bottom of the narrow groove.
This is because there is a concern about FM scratches (on the bell at the end of wear).

On the other hand, the groove width w3 of the narrow groove 36 is the groove width W of the circumferential main groove.
If it is smaller than 10% of 1, like when driving on a curve,
Under conditions where a strong side force acts, the vicinity of the opening of the narrow groove will come into contact with the step land portion 38 and move integrally, so that the end of the rib 40 closer to the narrow groove will not touch the road surface. This is because the groove width W3 of the narrow groove is larger than 90% of the groove width W of the circumferential main groove, the proportion of the groove in the tread surface increases. This is because the volume of rubber that contributes to wear resistance decreases, resulting in a problem of shortened wear life.

Furthermore, in the tire of the present invention, the groove bottoms of the narrow grooves 36 have a width of 20 to 40% of the groove width W3 of the narrow grooves, and a height of 10 to 70% of the groove depth of the narrow grooves. By continuously providing the protrusions 42 having a radius in the circumferential direction of the tire along the narrow grooves, it is possible to prevent roughness between the narrow grooves.

Here, the width W4 of the protrusion 42 is set to 20 times the width W3 of the narrow groove 36.
The reason why the value is within ~40% is that if the width W4 of the protrusion 42 is smaller than 20% of the groove width W3 of the narrow groove 36, the compression rigidity of the protrusion decreases as the groove width (of the narrow groove) becomes smaller. However, there is a problem that the effect of suppressing stone build-up is reduced by tR, and if it is larger than 40% of the groove width W3 of the narrow groove 36, the width of the groove bottom of the narrow groove becomes relatively narrow, and the groove bottom radius is This is because there is a concern that cracks at the bottom of the groove may occur if sufficient amount is not removed.

In this embodiment, the protrusions 42 are provided continuously in the circumferential direction of the tire along the narrow grooves 36, but the present invention is not limited to this embodiment. It can also be placed separately.

Next, another embodiment of the present invention is shown in FIG. The tire of this example also has a normal radial structure, and its cross-sectional shape is symmetrical with respect to the tire equatorial plane P, so only half of it is shown.

The tire 50 shown in this embodiment has a tread portion 32 that includes:
There are four circumferential main grooves extending in the tire circumferential direction, therefore, in FIG. A set of narrow grooves 56 are provided spaced apart from each other and extend in the tire circumferential direction and are spaced apart from each other in the tire width direction with respect to the circumferential main groove 55 located on the end side of the tread portion 52. are provided, and the stepped land portions 58 extending in the tire circumferential direction are respectively partitioned by the circumferential main groove 55 and the narrow groove 56 adjacent thereto, and
A protrusion 62 is formed continuously in the tire circumferential direction at the bottom of the narrow groove 56.

In this embodiment as well, the width W2 of the stepped land portion 58 and the amount of deviation of the surface of the stepped land portion 58 from the rib 40 inward in the tire radial direction are as follows:
While the groove depth Dl of the circumferential main groove is within the range of 1 to 5%, the groove depth D3 of the narrow groove 56 is 85 to 120% of the groove depth Dl of the circumferential main groove 55. At the same time, the groove width W3 is selected from a value within the range of 10 to 90% of the groove width W of the circumferential main groove, and the height D2 and width W4 of the protrusion 62 are selected to be 10% of the groove depth of the narrow groove. ~70%, and 20 to 4 of the groove width W3 of the narrow groove
Of course, it should be 0%.

In the tire of this embodiment, the groove width W1 of the circumferential main groove 55 is sufficiently larger than that of the narrow groove 56, and there is virtually no problem of stone entrainment. Groove 5
There is no need to provide a protrusion at the bottom of the groove as in No. 6.

In order to investigate the uneven wear resistance and rock-biting resistance of such tires, a comparative test was conducted using the tire of the present invention and a conventionally constructed tire, and the results are shown in the following table.

Note that the size of the tires used in the comparative test was 11R22,514PR for all ties.

◎ Test tire/invention tire 1: A tire having the structure shown in Fig. 1, with a groove width W1 of the circumferential main groove of 13.5 mm and a groove depth of 14.7 m.
m, the width W2 of the stepped land portion is 2.0 m + n, the deviation amount of the surface of the stepped land portion with respect to the rib is 3.0 mm, the groove width W3 of the narrow groove is 3 mm, and the groove depth D3 is 14.7 mm, protrusion. Width W4
is 25 mm, and the height D2 of the protrusion is 6 mm.

- Invention Tire 2: A tire having the structure shown in FIG. 2, in which the groove width W of the circumferential main groove is 13.5 m+n, and the groove depth is 14.5 m+n.
7 mm, the width W2 of the stepped land portion is 2.5 + nm, the deviation of the surface of the stepped land portion from the rib is 2.5 m, the groove width W of the narrow groove.
3 is 6M, its groove depth D3 is 16.7mm, and the protrusion width W
Tire with 4 as 2nd threshold and protrusion height D2 as 7th generation.

・Conventional tire: A tire having the structure shown in Figure 3, with a circumferential main groove width of 12 mm, a groove depth of 14.5 mm, a step land portion width of 3M, and a narrow groove width. A tire with a diameter of 3mm.

◎Test method The invention tire 1.2 and the conventional tire were tested with a width of 8.25×22.
They were attached to the rims of No. 5 and applied the regular internal pressure, and were alternately attached to an actual vehicle loaded with the regular load to measure the width and depth of uneven wear after 100,000 miles, while also checking the number of stones caught in each. Ta.

◎Test results: The test results are shown in the table below.

Incidentally, "unmeasurable depth and width of uneven wear" means that the depth and width could not be measured by visual observation, and "number of stones caught" means the number of stones per tire.

As is clear from this table, uneven wear due to stone build-up is unavoidable in conventionally constructed tires.
It can be seen that in the tire of the present invention, almost no stone entrapment occurs.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be applied to, for example, a tire in which a narrow groove dividing a stepped land portion is disposed on one side of the trend portion. Various modifications are possible within the range.

(Effects of the Invention) Thus, according to the present invention, while maintaining the effect of suppressing the occurrence of uneven wear along the edges of the ribs defined by the circumferential main grooves, the stepped land portions are also It is possible to provide a heavy-duty pneumatic tire that is free from stone chipping on ribs or stepped land portions and uneven wear caused by stones getting into the grooves.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a half of a heavy-duty pneumatic tire according to the present invention with respect to the tire equatorial plane. FIG. 2 is a cross-sectional view of a half of another embodiment of a tire according to the present invention. FIG. 3 is a perspective view of a half part of a tire having a conventional structure. 10, 30.50-one tire 12.32.52'-
) Red 14.36.56 -- Thin groove 16.38.
5 total - Step land portion 18.34.54 ~... Circumferential main groove

Claims (1)

[Scope of Claims] 1. At least two circumferential main grooves extending in the circumferential direction of the tread portion of the tire, and at least one of a pair of two circumferential main grooves extending in the tire circumferential direction spaced apart from each other. In a heavy-duty pneumatic tire comprising a set of narrow grooves or at least one narrow groove that cooperates with the circumferential main groove to partition a stepped land area extending in the circumferential direction of the tire, the width of the stepped land area is 50 to 150% of the groove width of the circumferential main groove, and the surface thereof is shifted 1 to 5% of the groove depth of the circumferential main groove from the tread surface inward in the tire radial direction. , the groove depth of the narrow groove is 85 to 1 of the groove depth of the circumferential main groove.
20%, and the groove width is 10 to 10% of the groove width of the circumferential main groove.
90%, and 1 of the groove depth of the narrow grooves is placed at the bottom of the narrow grooves.
A pneumatic tire for heavy loads, characterized in that a protrusion having a height of 0 to 70% and a width of 20 to 40% of the width of a narrow groove is provided.