JP2004075056A - Off-the-road tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the wear resistance at positions of circumferential grooves and the wear resistance as an entire tread by providing a pair of circumferential grooves continuous in the circumferential direction of the tread. <P>SOLUTION: The depth Gh of each circumferential groove 2 is set to be 60-130 mm. An innermost belt layer is a steeply inclined belt layer (a) with the belt cord intersecting angle with respect to the equatorial plane EP of a tire in a range of 3-12°. The overlapping width Bw of the steeply inclined belt layer (a) and a belt layer (b) adjacent to an outer circumferential side thereof with the belt cords across each other between the layers is set to be 0.25-0.50 time the tread width Tw, and further equal to or more than the center-to-center distance Gw of the circumferential grooves. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to off-the-road tires used in construction vehicles and other vehicles, and in particular, proposes a technique for improving the wear resistance of a tread.

Off-the-road tires used for construction vehicles and the like are required to have significantly higher load capacity and traction performance than tires for the same heavy load, for example, truck and bus tires. The tread pattern has ribs at the center of the tread that allow for excellent wear resistance even under high loads, and lugs on both sides of the tread for excellent traction performance. Was generally formed.

However, if the width of the linear or zigzag rib formation area between the imaginary line connecting the tips of the lug grooves in the central part of the tread is made wider than necessary, the traction performance at the time of climbing a slope becomes insufficient, and In the first place, this tread pattern has a drawback that, since there is no circumferential groove, side slip tends to occur at the time of steering.Therefore, today, a row of blocks that provides an edge effect in the tread width direction is provided at the center of the tread. The so-called rug block mix pattern thus formed has been used frequently.

On the other hand, with the improvement of vehicle performance in recent years, there has been a strong demand for further improvement in wear resistance in addition to further improvement in tire load capacity, traction, and skid resistance.
In order to realize a tire that can withstand large traction and exhibit excellent skid resistance while leaving a continuous land row considering wear resistance in the center of the tread, However, it has been proposed to provide a pair of circumferential grooves that are continuous in the circumferential direction. In this case, the circumferential grooves contribute to a decrease in wear resistance, and in particular, the tread width from the tire equator line. However, there is a problem that large abrasion occurs near the position of about 1/4.

An object of the present invention is to solve such problems of the prior art, and a main object of the present invention is to provide a tread with a circumferential groove that is continuous in a circumferential direction of the tread. It is an object of the present invention to provide an off-the-road tire in which the wear resistance of the tread as a whole is advantageously improved not only in the vicinity of the circumferential groove, but also in addition to the above, in addition to the above, cracks to the groove bottom of the circumferential groove. An object of the present invention is to provide an off-the-road tire in which the generation is effectively prevented.

The off-the-road tire according to the present invention is provided with a pair of circumferential grooves extending continuously in the circumferential direction of the tread, defining a land portion row of the tread center, and a belt including three or more belt layers for reinforcing the tread. The depth (Gh) of each circumferential groove is set to 60 to 130 mm, and the innermost belt layer is a steeply inclined belt having a belt cord intersection angle (Ba) with respect to the tire equatorial plane in the range of 3 to 12 °. The overlap width (Bw) of this steeply inclined belt layer, in which the belt cords intersect each other between the layers, and the belt layer adjacent to the outer peripheral side of the steeply inclined belt layer is set to a tread width (Tw) of 0.25 to 0. 50 times and equal to or more than the center line distance (Gw) of the circumferential groove.

Here, the tread width refers to the distance in the tire axis direction between the tread grounding ends, and the tread grounding end refers to JATMA, TRA, and the like effective in the area where the tire is manufactured, sold, and used. A tire is assembled to an applicable rim or a design rim specified in ETRTO or other standards, industrial standards, or the like, and the tire has a 100% internal pressure based on the air-load capacity table specified in the standards, industrial standards, and the like. , And a tread contact side edge when a mass corresponding to a load capacity corresponding to the internal pressure is applied in the vertical direction.

A study was conducted on the cause of wear (hereinafter referred to as "1/4 point wear"), which is particularly large in the vicinity of a position approximately 1/4 of the tread width from the tire equator due to the formation of the circumferential groove in the tread. When the crossover width (Bw) of the steeply sloping belt layer having a large circumferential tensile strength is narrower than the interval between the pair of circumferential grooves, the tire rolls immediately before contact with the load when rolling on the tire. At the position, for example, as shown in the cross-sectional view in the tread width direction in FIG. 8A, the tread side region tends to protrude outward in the radial direction, so that the portion is in contact with the ground, and the tread tread is not drawn. When the tire is crushed and deformed into a flat shape as shown in FIG. 8 (b), a portion near a circumferential groove extending from the tire equator line to a portion substantially equal to １ ／ of the tread width often has a tread width relative to the road surface. Relative to the inside of the Displacement brings about a local increase in the wear amount of work it was found to be due to the fact that the wear distribution uneven.

Therefore, in order to prevent the occurrence of such 1/4 point wear, here, as shown in a schematic cross-sectional view of the tread portion in FIG. By making the center line distance Gw equal to or more than the center line distance Gw, it is possible to advantageously restrain the tread side area from being deformed when the tire is rolling.

On the other hand, in order to ensure sufficient durability of the entire belt including the steeply inclined belt layer a, the overlap width Bw is set to be in a range of 0.25 to 0.50 times the tread width Tw, and Suppress the occurrence of rubber cracks at the ends.
Further, here, by setting the angle of intersection of the belt cord of the steeply inclined belt layer a with the tire equatorial plane EP in the range of 3 to 12 °, the circumferential tension resistance is secured and the crown shape changes during running. Belt distortion can be reduced.

The depth Gh of each circumferential groove is in the range of 60 to 130 mm in order to secure the total wear life.
The mutual overlapping width Bw of the belt layers a and b is set in a range of 0.25 to 0.50 times the tread width Tw and equal to or more than the center line distance (Gw) of the circumferential groove.

In the tire as described above, preferably, the belt layer b contributing to the specification of the overlap width Bw adjacent to the outer peripheral side of the innermost layer of the steeply inclined belt layer a is defined as a belt cord of the steeply inclined belt layer a. And a steeply inclined belt layer made of a belt cord extending in the opposite direction to the tire equatorial plane EP. According to this, the circumferential tensile strength can be further increased under the cooperation of the two steeply inclined belt layers.

Preferably, the circumferential groove 2 has a groove width at which the groove walls are in contact with each other in the ground plane, and more preferably, the groove width is 8 to 20 mm.
According to this, at the time of load rolling of the tire, as a result of the contact between the respective circumferential groove walls, the rigidity in the width direction of the tread land portion is greatly increased, so that the cornering power (Cp) can be improved. This leads to an improvement in the wear resistance of the front wheel tires, particularly the steered wheels.

By the way, when the groove bottom radius in the cross section of the circumferential groove 2 is set to be larger than that of the tread side portion and the tread center side as shown in the enlarged sectional view of FIG. Occasionally, a so-called wiping deformation occurs in which the land portion on the tread side portion is deformed in a direction approaching the land portion on the center side within the ground contact surface, whereby the groove wall ow of the circumferential groove 2 on the tread side portion is generated. , Even if it is displaced close to the groove wall iw on the tread center side, the concentration of stress on the base of the side groove wall ow can be reduced, and the generation of cracks on the groove bottom base can be effectively prevented. .
This is particularly noticeable when the ratio (Rs / Rc) of the groove bottom radius Rs on the tread side to the groove bottom radius Rc on the tread center side is 1.0 or more and 2.7 or less.

According to the present invention, in particular, by covering the extension area of the circumferential groove with the overlapping width of the steeply inclined belt layer, it is possible to greatly improve the wear resistance of the tread under excellent belt durability, Further, by selecting the radius of curvature of the groove bottom of the peripheral groove, it is possible to effectively suppress the occurrence of cracks at the groove bottom.

Hereinafter, an embodiment of a tire according to the present invention will be described with reference to the drawings.
FIG. 3 is a development view of a tread pattern showing one embodiment. Here, a pair of circumferential grooves 2 forming a pair with a tire equator line ec interposed therebetween are formed in a tread 1 in a zigzag shape in a circumferential direction thereof. The center land portion row 3 is defined between the circumferential grooves 2 and 2, and in each side area of the center land portion row 3, from each tread end to each circumferential groove 2. By providing a lug groove 4 that reaches and bends in a substantially U-shape, the lugs 5 are separated at predetermined intervals in the circumferential direction.

Also, here, a lateral groove 6 is provided which extends linearly between the two circumferential grooves 2 and 2 and communicates the circumferential grooves 2 with each other at a corner portion into the center land portion row. 3 is divided into a plurality of blocks 7.
Here, the depth of each circumferential groove 2 is in the range of 60 to 130 mm, and the depth of each of the lug groove 4 and the lateral groove 6 is preferably in the range of 60 to 120 mm.

Incidentally, the groove bottom of the circumferential groove 2 has a groove bottom radius Rs on the tread side portion equal to or greater than the groove bottom radius Rc on the tread center side as shown in an enlarged cross-sectional view of FIG. Preferably, the ratio Rs / Rc of the two radii is selected in the range of 1.0 or more and 2.7 or less.

Also preferably, the groove width of each peripheral groove 2, more preferably the groove width of the lateral groove 6, should also be such that the groove walls are in contact with each other in the ground contact surface when the tire is rolling. Their groove width is in the range of 8 to 20 mm.

On the other hand, on the inner layer side of the tread 1, a belt 8 consisting of three or more layers contributing to the reinforcement of the tread 1 and, as shown in FIG. Of these, the belt layer a located at the innermost layer, preferably the belt layer b adjacent to the outer peripheral side thereof, is also a steeply inclined belt having a belt intersection angle (Ba) with respect to the tire equatorial plane EP in the range of 3 to 12 °. The belt cords extend between and cross the tire equatorial plane EP in a direction opposite to each other between the two belt layers a and b.
Then, the mutual overlapping width Bw of the belt layers a and b is set in a range of 0.25 to 0.50 times the tread width Tw and equal to or more than the center line distance (Gw) of the circumferential groove. .

For example, in FIG. 1, the distance Gw between the center lines of the circumferential grooves is defined as the distance Gw / 2 between the center line c of the circumferential groove 2 and the portion farthest from the tire equator line ec from the tire equator line ec. It is preferable that the center line distance Gw is 0.15 to 0.50 times the tread width Tw.

FIG. 4 is an exploded view of a tread pattern showing another embodiment. In particular, the pair of circumferential grooves 2 extend linearly, and the lug grooves 4 are terminated at a position before the circumferential groove 2. The lateral groove 6 is formed as a bent groove which is bent in a stepped manner at the center, and the other configuration is the same as that described above.

When a tire having a size of 4000R57 is mounted on a rim having a rim diameter of 29 inches and a flange height of 6 inches, the air pressure charged to the tire is 700 kPa, and the load mass is 100% (60 t) of the TRA standard. The abrasion resistance (average abrasion index) of the tread and the belt durability (crack growth inhibition index) when the load mass was 150% of the TRA standard were measured, and the results shown in Table 1 were obtained.
In the table, the dimensions of each tire are also shown. Here, the comparative tires 1-1 to 1-3 and the example tires 1-1 to 1-3 are shown in FIG. The example tires 2-1 and 2-2 have the respective tread patterns shown in FIG. 4, and the conventional tire has the tread pattern shown in FIG.

In addition, the abrasion resistance here is as follows. The tires are attached to the front wheels of a 240t dump truck, and the tires run at a constant speed of 10 km / h off-road, and after running for 1000 hours, the tread is moved in the width direction. By the remaining groove measurement at each position divided into eight, the average value of the tread rubber thickness spent on running is calculated as the wear amount, and the value obtained by dividing the running time by the wear amount is evaluated by an index as a wear resistance value,
The belt durability was measured by measuring the length of a crack generated at a side edge position of a steeply inclined belt layer after running for 3800 km while constantly generating a 0.1 G side force on a drum. Was calculated by exponential evaluation of the crack growth rate divided by the running distance.

FIG. 5 is a graph showing the belt durability shown in Table 1 with Bw / Tw as a parameter. According to this graph, when the ratio is less than 0.25, the overlapping width of the steeply inclined belt layer is reduced. Because the belt layer is too narrow and lacks rigidity, the deformation of the belt layer with respect to the side force is large, and the distortion of the side edge of the belt layer increases. As a result, the crack easily develops, but the value exceeds 0.50. In addition, the overlapping width of the steeply inclined belt layer becomes too large, and the side edge of the belt layer is stretched in the circumferential direction when a load is applied to the tire, so that shear deformation is easily generated between the steeply inclined belt layers, and the strain accompanying this is increased. It can be understood that an increase in the amount facilitates crack propagation.

FIG. 6 is a graph showing the wear resistance shown in Table 1 using Bw / Gw as a parameter. According to this graph, when the ratio is 1.0 or more, 1/4 point wear is effective. As a result, the average wear resistance index increases rapidly.

When the length of a crack generated at the bottom of the circumferential groove was measured under the same tire use conditions as in Example 1, the results shown in Table 2 were obtained.
Note that the example tires 3-1 to 3-5 in the table have the tread pattern shown in FIG. 4, and the crack length in Table 2 indicates that the tires were respectively attached to the front wheels of a 240 t dump truck. The average value of the length of cracks generated on the circumference after traveling for 1000 hours at almost constant speed at a speed of 10 km / h on off road is shown as a quantified value.

　表２の溝底亀裂長さを、Ｒｓ／Ｒｃをパラメータとして示す図７のグラフによれば、いわゆるワイピング変形によって、測部側陸部がセンタ側陸部に向けて変形されることに起因する、側部側周溝壁の基部への亀裂の発生は、上記比を１．０以上とすることによって急激に改善され、その比の値が１．６〜２．１の範囲では、亀裂の発生を完全に防止できることが明らかである。
　この一方で、２．１を越えるとセンタ側の周溝底の曲率半径が小さくなるため、そのセンタ側の溝壁基部に亀裂が生じはじめ、その比が２．７を越えると、センタ側の溝壁基部に、比を１．０としたときよりも長い溝底亀裂が発生することが解る。
　従って、Ｒｓ／Ｒｃを１．０〜２．７の範囲とすることで、いずれの溝底基部に発生する亀裂も十分小さく押さえることができる。

According to the graph of FIG. 7 showing the groove bottom crack length in Table 2 using Rs / Rc as a parameter, the measurement section side land portion is deformed toward the center side land portion by so-called wiping deformation. The generation of cracks at the base of the side circumferential groove wall is sharply improved by setting the above ratio to 1.0 or more, and when the value of the ratio is in the range of 1.6 to 2.1, cracks are not generated. It is clear that the occurrence can be completely prevented.
On the other hand, if the ratio exceeds 2.1, the radius of curvature of the bottom of the circumferential groove on the center side becomes small, so that cracks begin to be formed in the base of the groove wall on the center side, and if the ratio exceeds 2.7, the ratio on the center side decreases. It can be seen that a groove bottom crack is generated at the groove wall base longer than when the ratio is set to 1.0.
Therefore, by setting Rs / Rc in the range of 1.0 to 2.7, cracks generated at any groove bottom base can be suppressed to a sufficiently small value.

The off-the-road tires used here are applicable to dump trucks, towing vehicles as off-road vehicles, motor graders used on rough terrain, irregular terrain, construction vehicles such as scrapers, etc. Can be brought.

FIG. 3 is a cross-sectional view in a width direction of a part of a main portion including a tread portion of the off-the-road tire according to the present invention. FIG. 2 is a cross-sectional view in the width direction of a circumferential groove shown in FIG. It is a development view of a tread pattern showing an embodiment. It is a development view of a tread pattern showing other embodiments. It is the figure which showed the relationship between a crack growth suppression index and Bw / Tw. It is a figure showing relation between average abrasion resistance index and Bw / Gw. It is the figure which showed the relationship between groove bottom crack length and Rs / Rc. It is a figure for explaining a problem of a tire whose crossing overlap width of a steeply inclined belt layer is narrower than the center line distance of a peripheral groove, (a) is a tire shape just before contact with the ground, (b) is This is the tire shape when touching down. It is a development view of the tread pattern of the conventional tire.

Explanation of reference numerals

Reference Signs List 1 tread 2 circumferential groove 3 center land row 4 lug groove 5 lug 6 lateral groove 7 block 8 belt ec tire equatorial line EP tire equatorial plane Gh circumferential groove depth Bw overlapping width Gw centerline distance Tw tread width a steeply inclined belt layer b Belt layer Rs, Re Groove bottom radius iw, ow Groove wall

Claims (6)

A pair of circumferential grooves extending continuously in the circumferential direction of the tread and defining a tread center land row are provided, and a belt comprising three or more belt layers for reinforcing the tread is provided, and the depth of each circumferential groove is provided. (Gh) in the range of 60 to 130 mm,
The innermost belt layer is a steeply inclined belt layer having a belt cord crossing angle (Ba) with respect to the tire equatorial plane in the range of 3 to 12 °. An off-the-air device in which the overlap width (Bw) with the belt layer adjacent to the outer peripheral side is 0.25 to 0.50 times the tread width (Tw) and equal to or more than the center line distance (Gw) of the circumferential groove. Road tire. A belt layer adjacent to the outer peripheral side of the innermost steeply inclined belt layer, wherein the steeply inclined belt layer is a steeply inclined belt layer made of a belt cord extending in a direction opposite to the tire equatorial plane. 2. The off-the-road tire according to 1. The off-the-road tire according to claim 1 or 2, wherein the circumferential groove has a groove width in which the groove walls contact each other in the ground contact surface. The off-the-road tire according to claim 3, wherein a groove width of the circumferential groove is in a range of 8 to 20 mm. The off-the-road tire according to any one of claims 1 to 4, wherein the groove bottom radius in the cross section of the circumferential groove is greater than the tread center side on the tread side. The off-the-road road according to claim 5, wherein a ratio (Rs / Rc) of the groove bottom radius (Rs) on the tread side portion to the groove bottom radius (Rc) on the tread center side is 1.0 or more and 2.7 or less. tire.

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