JPH0592701A - Radial tire for heavy load vehicle - Google Patents

Abstract

PURPOSE:To obtain steel cord terminal end arrangement to efficiently improve the belt separation durability of a radial tire for a heavy load vehicle. CONSTITUTION:The cord end contour (A) of inside cord arrangement unit Ui of a main belt layer is arranged within a range where the cord end of Uo adjacent to the outside of Ui out of the Uo cord ends which are adjacent to Uo through Ui holding Uo coincides with the projection of the contour (B), by defining the range as an external limit, where Uo adjacent to the outside of Ui interposed between the arrangement units Uo of the outside cord does not overlap the projection of the cord end contour (B) relative to the tire equator plane but is brought into contact with the projection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel radial tire for heavy-duty vehicles, especially for construction vehicles, without using any special additional member, and further maintaining the wear life and the low heat build-up characteristic of the steel radial tire. It is an object of the present invention to provide a steel radial tire for heavy-duty vehicles, which is being improved, or an economical tire that efficiently enhances the separation resistance of a belt for which there is a strong demand for improvement.

[0002]

2. Description of the Related Art Recently, radial tires for heavy-duty vehicles, particularly large construction vehicles, have been extended in recent years due to the expansion of mines and the number of curves, and the speed and loading of vehicles due to demands for improved productivity. Due to the increase in the amount, the load input to the belt is increasing, and as a result, the separation of the belt has tended to increase compared to before. This separation failure is a serious problem for both the user and the supplier, and various proposals have been made in the past to improve the separation durability of the belt adapted to the severe usage conditions.

For example, in JP-A-61-37501, the value corresponding to Do / Dc of the belt layer (reinforcing layer) is 0.9.
A tire having a belt layer of 5 or less, more preferably 0.90 or less, in which the number of cords to be driven in at least one end portion of the belt layer is reduced as compared with that of the crown center, is proposed. This is because in a tire with a large belt layer curvature, the usual belt has an extremely large number of cords driven in the vicinity of the layer end, and the excessive shear strain resulting from this is measured. This is a proposal to suppress belt separation. At the same time, although the effect of the tire having the extremely small Do / Dc is recognized as described above, if it is not applied to the tire for heavy-duty vehicles, especially the tire for construction vehicles, the following problems occur.

That is, in the tire for heavy-duty vehicles according to the present invention, in particular, the tire for construction vehicles, if the curvature of the belt layer is large, the curvature of the crown of the tread must be set large in accordance with the belt layer. Not get
As a result of extremely large interlaminar shear strain / stress at the layer ends of the laminated belt subjected to forced deformation in accordance with the ground contact surface under heavy load, separation of the belt ends occurs early. Further, the ground contact pressure at the central portion of the crown, which is most likely to be cut and damaged by rocks or the like when running on a wasteland, is increased, and cut damage is promoted. In addition, tread center wear is caused and wear life is greatly shortened. On the other hand, if the curvature of the crown is made small (the crown radius is large) while keeping the curvature of the belt layer large, the strain and stress described above are suppressed, but the tread gauge near the end of the belt layer is inevitably large. Therefore, an excessive temperature rise, which is fatal for a heavy-duty vehicle tire, is caused at this portion, which causes a problem of early heat separation.

In addition, if the curvature of the belt layer is increased and the shear strain of the belt layer is reduced, as described in the embodiments of the above publications, the number of cords to be driven in the narrow region of the belt width end is set. It is not enough to reduce the number of times, and it is necessary to take a wide enough area to reduce the number of code inputs. With such a configuration, the effective width of the belt layer as a single body is inevitably narrowed, so-called the hoop effect is reduced, and the reduction in the wear life, which is the most strongly required as a basic characteristic of the heavy-duty vehicle tire, is further reduced. This is also not preferable because it also causes a reduction in heat separation resistance.

Further, in Japanese Patent Publication No. 3-23361,
A narrow tread reinforcement different from the main belt is inserted between the carcass and the main belt centering on the equatorial plane of the tire to reduce the tension load on the main belt when inflating air and to reduce the tension of the main belt. This is a proposal to measure the stress reduction and prevent the separation of the main belt. However, although the effect can be recognized depending on the usage conditions, the steel cord in the tread reinforcement has a small inclination angle with respect to the tire equatorial plane. However, there is a problem that separation is likely to occur between the tread reinforcement itself or between the reinforcement and the main belt. In addition to the increase in the manufacturing cost due to the addition of the tread reinforcement, the increase in the tread gauge is unavoidable, which causes a rise in the temperature of the main belt, which causes a problem of heat separation.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a major part of the tension of a main belt of a steel radial tire used in heavy-duty vehicles, especially construction vehicles, that is to say, when it is filled with a predetermined air pressure as a reinforcing layer of a tread. In the main belt that bears, even under use conditions in which excessive strain input is frequently added, without efficiently using the special additional member as described above, while efficiently and effectively suppressing the separation of the main belt, On the other hand, we are trying to extend the wear life of the tread and ensure cut resistance, and to extend the durable life of the tire comprehensively.

[0008]

SUMMARY OF THE INVENTION The present invention provides a radial carcass that provides at least one layer of steel cord reinforcement and a substantially inextensible steel cord that is substantially parallel within the layers radially outward of the carcass and intersects between the layers. A main belt having two or more layers and a tread rubber layer arranged radially outside the main belt, and the cord layers forming the main belt are adjacent to each other in the layers of the cord layers at the side edges of the main belt. The radial tires are arranged in a staggered arrangement in which the end positions of the cords each including at least one cord are alternately staggered, and the outer cord arranging units Uo terminating at the width end of the main belt are connected to each other. The inner cord arranging unit Ui interposed between them is the inner cord arranging unit Ui among the terminals of the outer cord arranging unit Uo which is imaginary on the plane including the central circumferential line of the tread. The outer cord arrangement adjacent to the outer cord arrangement unit Uo is not coincident with the projection of the contour B of the outer adjacent cord terminal, but is adjacent to the outer cord arrangement unit Uo via the inner cord arrangement unit Ui sandwiching the outer cord arrangement unit Uo. Unit Uo
Of the innermost code arrangement unit Ui, the end of the innermost code arrangement unit Ui where the contour A of the code terminal of the innermost code arrangement unit Ui is located until it coincides with the projection of the similar contour B. A radial tire for a heavy-duty vehicle having excellent separation durability at the side edge of the belt, which is arranged in a staggered manner.

Further, in the present invention, the outer cord arranging unit Uo and the inner cord arranging unit Ui, which are arranged in a staggered arrangement on the main belt, are each composed of two or more and four or less steel cords. The cord terminals of the inner cord arrangement unit Ui in the zigzag arrangement are arranged side by side substantially parallel to the belt width, or the cord terminals of the inner cord arrangement unit Ui in the zigzag arrangement of the main belt are , The cord terminals of the inner cord arranging unit Ui, which are arranged vertically in a direction substantially orthogonal to the belt width or in a zigzag arrangement of the main belt, are arranged so as to be separated from each other in a direction substantially orthogonal to the belt width. It is preferable that the above configuration is included or any of the configurations is included.

Further, in the present invention, the ratio of the inner diameters Do and Dc of the cord ends of the cord arrangement units Uo on the outer side in the zigzag arrangement of the main belt and the center of the belt width of the cord arrangement units Uo is 0. Value greater than or equal to .97,
It is desirable that the cord end of the outer cord arrangement unit Uo in the zigzag arrangement of the main belt occupies the maximum width of the main belt, and in addition, the inner cord arrangement unit Ui of the main belt in the zigzag arrangement of the main belt. The arithmetic mean of the distances from the tire equatorial plane of each cord terminal and the cord arrangement unit U on the outside
It is particularly desirable that the effective half width of the cord layer of the main belt defined by the average value of the distance from the cord end of the cord belt at 0 is at least 70% of the tread half width. Furthermore,
It is preferable that the main belts in the zigzag arrangement and the other main belts adjacent to each other are laminated so that the width ends of the cord layers are located further inside from the innermost end of the inner cord arranging unit Ui.

Now, FIG. 1 shows a cross section of the construction of the radial tire 1 according to the present invention for the left half of the tire equatorial plane XX. In the figure, 2 is a bead core, 3 is a radial carcass (one layer in the figure) for reinforcing one or more steel cords in a toroidal shape over the bead core 1 and 4
Are belts for reinforcing steel cords arranged on the radial outside of the radial carcass, each of which has a main belt 4M and a protective belt 4N (both shown in FIG. 1) that bear most of the tension when the tire 1 is filled with air pressure. 2 shows an example of two layers), 5 is a tread rubber layer arranged on the outer side in the radial direction of the belt, and 6 is a side rubber layer continuous with the tread rubber layer and extending radially inward to the vicinity of the bead core. Reference numeral 7 is a standard rim on which the tire 1 is mounted. In FIG. 1, the belt 4 has a first belt layer and a second belt layer (the same applies hereinafter) from the radial carcass 3 toward the radially outer side, and the main belt in the staggered arrangement according to the present invention is the second belt layer. ..

Then, the second belt layer in a virtual staggered arrangement on the plane including the central circumferential line of the tread intersecting with the equatorial plane XX of the tire according to the present invention shown in FIG. 1, that is, in practice, the tread rubber. FIG. 2 shows a partial schematic view of the arrangement of steel cords at the side end portion of the second main belt layer in which the layer 5 and the protective belt 4N are removed and horizontally developed. In FIG. 2, S is a steel cord constituting the second belt layer, and Uo and Ui
Indicates an outer cord arranging unit and an inner cord arranging unit in which one steel cord S adjacent to each other is arranged as a arranging unit in the second belt layer, and the cord end of Ui always exists inside of that of Uo. B is the outline of the cord terminal adjacent to the outside of the inner cord arrangement unit Ui, and A ₁
Is the contour of the code terminal at the outermost position of the Ui code terminal, and A ₁ 'is the contour of the code terminal at the innermost position of the terminal. Here, the contour of the cord terminal refers to the outer contour of the end surface of the cut end of the steel cord, and the outer side refers to a state in which it is more distant from the inner side with respect to the tire equatorial plane, and the like below.

A ₁ and A ₁ ′ will be described in more detail with reference to FIG. 2. A ₁ is a pair of adjacent outer cord discharge units Uo (in particular, Uo ₁ and Uo ₂ are additionally shown. The same applies hereinafter. Inner cord arrangement unit Ui (U
i ₁₎ it does not overlap the outline B of the code terminal code Hairetsu units Uo adjoining the outside (Uo ₂₎ and the projection to the tire equatorial plane, the contour of the code terminals Ui having substantially the same contour in contact with the projection On the other hand, A ₁ ′ is a cord arrangement unit Ui (Ui ₁ , U that sandwiches the outer cord arrangement unit Uo (Uo ₂ ).
Uo adjacent to the outside of one Ui (Ui ₂ ) of i ₂ )
The above-mentioned projection of the contour B at the code end of (Uo ₃ ) is once Ui (U
It is the contour of the code terminal of the inner code row unit that matches the other Ui (Ui ₁ ) via i ₂ ). Therefore, it is preferable that the contour A of the cord terminal of the inner cord arranging unit Ui in the zigzag arrangement of the main belt according to the present invention is located between the above A ₁ and A ₁ ′. At this time, the shape of the contour A at the code end may be the same as or different from that of the contour B. Further, in the present invention, the shape of the contours A and B shown in FIG. 2 is not a limitation, and for example, the contour shape as shown in FIG. 3 may be used. , B
Of course, it is also possible to mix.

Next, FIG. 4 shows the inner and outer sleeves according to the present invention.
Each code arrangement unit is two steel cords each
The cord layer of the constructed main belt is shown in FIG.
1 shows a code layer composed of a Cheer code. Both figures
Inside of each steel cord terminal of the cord arrangement unit Ui
The outermost position is A₁Innermost, matching the projection of
The same position is A₁Matches the projection of ′. That is, the figure
A in 4₂Is A₁Of A₂′ Is A₁′ Each projection
And A in FIG.₂, A₃Is A₁Of A₂′, A ₃′ Is A
₁′ Corresponds to each projection. Inner code here
The outline A of each code terminal of the unit Ui of arrangement is indicated by a bell in FIG.
The width of the belt is almost parallel to the belt width in FIG.
The following is an example of arrangement.

In FIG. 1, the inner diameter of the cord end of the cord arrangement unit outside the second belt layer according to the present invention is Do, the inner diameter of the belt layer at the equatorial plane XX is Dc, and Do / Dc is 0. It is set to 0.97 or more and 1.01 or less. Further, the width w of the cord terminal of the cord arrangement unit outside the second belt layer occupies the maximum width in the main belt, and the width w is 0.7XTW to 1.0XT in relation to the tread width TW.
Allowed to be within the range of W. In addition, the staggered cord layers according to the present invention are not limited to the belt layers occupying the maximum width of the entire main belt, and naturally, the cord layers of other main belts can be applied. With the configuration, the effect of the present invention is further amplified.

Further, in FIG. 2, W is the contour A and the contour B of the cord terminals of the respective discharge units Ui and Uo from the central circumferential line ZZ where the equatorial plane of the tire intersects the second belt layer. Distance to the outermost edge (L in Fig. 2, 1 / in Fig. 1
2 × w), which is the average value of the sum, and W is the effective half width of the single code layer of the belt. In the present invention, this W is preferably 70% or more of the half width of the tread width TW, and more preferably 75% or more. In the examples of FIGS. 4 and 5, the plurality of contours A from ZZ to Ui are used.
The effective half width W is defined as the average value of the sum of the distances to the outermost ends of the above and the average value of the sum of the distances to the outermost ends of the contour B. This will be explained with reference to FIG. 4. The maximum distances from ZZ to the contour A located inside and outside the cord terminal of the row unit Ui are L ₁ and L ₂ , respectively (L ₁ + L ₂ ).
1/2 is La, the maximum distance to the contour B of the cord terminal of the row arrangement unit Uo is Lo, and the average value W of (La + Lo) is the effective half width of the belt layer. Here, Lo × 2 matches w.

1, FIG. 2, FIG. 3, FIG. 4 and FIG. 5, of the cord layer (the first belt layer in FIG. 1) of the other main belt adjacent to the second belt layer in the staggered arrangement according to the present invention. The steel cord terminal can be placed further inside the contour A of the cord terminal of FIGS. 2 and 3 and the innermost contour A of the plurality of cord terminals of FIGS. 4 and 5. Furthermore, in the present invention, the belt layers arranged in a staggered arrangement and the cord layers of the other main belts adjacent to the belt layers are not limited to one layer, and include a configuration of two layers. It is preferable that the inclination direction of at least one steel cord with respect to the tire equatorial plane is different from the inclination direction of the steel cords of the belt layer in the zigzag arrangement, and the steel cords intersect each other.
Further, it is needless to say that the position of the steel cord terminal is preferably the same as the above even for the adjacent main belts having the same inclination direction.

Here, an example of arrangement in which the inner and outer cord arrangement units shown in FIG. 2A are each made of one steel cord, and in FIGS. 6 and 7, the entire arrangement of several steel cords over the entire belt width is made into a central circle. It is shown schematically along with the circumference line ZZ. FIG. 6 shows an example in which the lengths of steel cords in the belt are alternately arranged with different lengths, and FIG. 7 shows an example in which steel cords having substantially the same length are alternately arranged. still,
FIG. 2 is an enlarged detailed view of a portion indicated by a dotted line in both drawings.

In the present invention, the steel cord of the cord layer of the main belt is preferably inclined at an angle of 5 ° to 25 ° with respect to the equatorial plane, and the inclination angle is 15 ° to 22 °.
It is more preferable if the angle is °. The diameter of the steel cord used in the staggered code layer of the present invention is preferably 1.4 mm or more, and when it is 2.5 mm or more, the remarkable effect of the present invention is further obtained. can get. Especially when a steel cord having a small diameter is used, it is particularly convenient in terms of production if there are two or more cord discharge units.

[0020]

The inventors of the present invention have obtained the following findings as a result of investigating why the tire according to the prior art cannot exhibit sufficient durability of the belt under the use condition in which the strain input is severe. That is, the strain and stress reduction of the belt layer end portion according to the conventional technique, especially the reduction of the shear strain / stress between the belt layers is sufficiently effective when the strain input to the tire is not relatively large, but once the strain input When used under excessive use conditions, the effect is limited only by reducing the shear strain / stress between layers, especially when the width of the main belt is wide to obtain the performance peculiar to radial tires. I found that the problem was serious. In the present invention, the strict use condition of strain input means that the absolute value of the ground contact pressure is high over the entire tread surface, and the ground contact pressure of the tread surface near the cord layer end of the belt is near the tire equatorial plane. It is a condition that is always or frequently higher than that.

Further conclusions reached by the inventors of the present invention will be described below. That is, in the tire running under the above-mentioned severe usage conditions, the inventors of the present invention, before the separation occurs at the cord layer end portion of the laminated belt, first of all, the steel cord at the wider belt end. An initial minute crack is generated in the rubber near the cut end face, and this minute crack propagates along the edge of the steel cord of the belt with the passage of running time, and at the same time when the cracks are connected to each other, this crack is the steel cord. It also expanded to the inside along with and found that narrow separation occurred along the belt width edge.

Next, although the inventors of the present invention have narrowed the width of the belt, the separation of the cord layers of the laminated belts approached each other when the separations extending inward over substantially the entire circumference of the belts progressed inward. It has been clarified that the shear stress acting between the cord layers of the cord promotes the rapid expansion of the initial separation, leading to a total belt separation failure. Therefore, it was found that the core of the failure, which is the main cause of the failure due to the severe use condition, is a crack generated in the rubber in the vicinity of the cut end surface of the steel cord, and the present invention has been completed. Figure 9
Figure 1 summarizes the explanatory diagram of the development process from the initial crack (the upper part of the figure) of this separation failure to the narrow separation state in the middle period (the lower part of the figure). The crack is indicated by K, and the separation portion is indicated by a shaded portion.

Next, the mechanism of crack initiation was clarified as follows based on the results of the experiment. That is, as shown in the tire cross section at the ground contact portion in FIG. 8A, the tread rubber is compressed on the tire ground contact surface and extends from the buttress position shown by the two-dot chain line in the figure to the position indicated by the solid line. At this time, each part of the tread rubber is displaced in the buttress direction substantially perpendicular to the tire equatorial plane, which is the non-restrained area, as shown by the arrow in the figure. In FIG. 8B, the distribution state of the tread rubber displacement amount between the belt layer and the tread contact surface is schematically represented by the same arrows.
As is clear from this, when a large load is applied to the tread, the belt layer reinforced by the non-stretchable steel cord is in contact with the belt layer because the displacement in the above direction can be neglected as compared with the tread rubber. Displacement of the tread rubber is constrained to almost zero as shown by point P in Fig. 8 (b), but on the contrary, since the end face of the steel cord cut end in the belt layer has not been treated with adhesive, The rubber in contact with the displacement relatively easily follows the displacement as shown at point Q in the figure. For this reason, a cavity is formed in the vicinity of the end face, and as a result, a large tensile stress is applied to the cut edge of the steel cord firmly bonded to the surrounding rubber. As a result of the tensile stress being repeatedly applied during the running of the tire, the rubber near the cut edge causes fatigue fracture and leads to cracking.

Once the microcracks are generated, the cracks grow in a relatively short time due to stress concentration. If the running progresses further, the cracks will be connected to each other and the entire circumference of the tire will be cracked.However, at almost the same time, since shear stress acts between the cord layer and the tread rubber, the cracks run along the cord layer. Also propagates inside, and narrow separations as shown in FIG. 9 occur. Since the above rubber displacement amount is almost proportional to the ground contact pressure of the tread, the heavy load vehicle, in particular, the super heavy load, also frequently runs on the unevenness of the wasteland and the curve with a large curvature, and the frequent unbalanced load acts on the tread. In the construction vehicle tire, the cracks are likely to be generated and propagated, and the separation problem of the belt layer is likely to be caused.

Based on the above findings, the reason why the outermost arrangement of the contour A of the cord terminal at the inner cord discharge end Ui is set to A ₁ will be described in more detail with reference to FIG.
As described above, in the tread ground contact portion, the layer end portion of the belt for reinforcing the steel cord receives a force in the arrow direction shown in the upper part of the figure as the tread rubber is displaced. (The arrow is stopped only in the necessary portion.) At that time, the projection of the contour B of the cord terminal of the outer cord arranging portion Uo (Uo ₂ ) and the portion where the cord end overlaps (triangular portion in the figure) are Since a part or almost all of the filaments forming the steel cord are lacking in the direction, the property of resisting the force is weaker than other parts that do not overlap with the projection, and it is easy to follow the tread rubber displacement. Therefore, the inner cord arrangement unit Ui (U
If the contour A of the cord end of i ₁ ) is arranged at a position overlapping with the projection, a relatively large tensile stress acts on the end edge of this end, and a rubber crack near the end face of the Uo (Uo ₂ ) cord end is generated. Then, after a short running time, a crack similarly occurs in the cord terminal of Ui (Ui ₁ ).

Even if there is some time delay, once cracks occur on both end faces, the shear stress component applied to the Uo cord ends concentrates at the cracks, and both cracks are connected early. , Ui from the code terminal to the inside, resulting in partial separation in a short time, which is not preferable. FIG. 10 schematically illustrates the state of this progressing process on the upper side and the lower side of the figure.

On the other hand, if the contour A is stopped at the position A ₁ which is in contact with the projection of the contour B as shown in FIG. 2, the above-mentioned almost simultaneous cracks on both end faces do not occur, and a crack is generated at the Uo cord terminal, which causes A crack is caused at the end face of the terminal only after reaching the Ui cord terminal by advancing inward along the cord, and further, the crack propagates along the outer side of the Uo cord through the end surface of the Ui cord terminal. Until the cracks are connected to each other, at least only the Uo cord portion is separated, and the Ui cord portion is not separated. During this period, the separation life of the tire according to the present invention can be significantly extended as compared with the conventional tire. FIG. 11 shows a position A where the contour A of the Ui code terminal is in contact with the projection of the contour B of the Uo code terminal.
The process of cracking and separation development of the belt layer, which was set as ₁ , is summarized from the upper side to the lower side of the figure.

Next, referring to FIG. 2 again, the reason why the innermost arrangement of the contour A of the Ui code terminal is A ₁ ′ will be described below. That is, if the contour A of the code terminal of Ui (Ui ₁ ) shown in FIG. 2 is inside the position of the contour A ₁ ′ that coincides with the projection of the contour B of the code terminal of Uo (Uo ₃ ), the projection and the The rubber part partitioned between Uo (Uo ₁ and Uo ₂ ) which sandwiches the cord of Ui increases, and the displacement of the tread rubber above this rubber part (indicated by the arrow below in the figure)
Promotes an increase in the rubber displacement of the cord end of the contour B of the original (Uo ₃ ) of the projection via Uo (Uo ₂ ) adjacent to the outside of the Ui, resulting in an increase in the tensile stress of the edge. This has the effect of causing a problem of accelerating the occurrence of cracks in the rubber near this terminal. For the above reason, it is preferable that the innermost part of the contour A of the Ui code terminal is the contour A ₁ ′.

At first glance, it is best to set the contour A of the Ui cord terminal to the innermost A ₁ ′ in terms of extending the running time until the separation failure, but on the other hand,
It is necessary to consider that the effective width becomes narrower and the width of the main belt layer adjacent to this becomes narrower, and as a result, the effective width of the entire main belt becomes narrower. The arrangement is not the best, and it is possible to set the arrangement position of the contour A of the Ui code terminal between A ₁ and A ₁ ′ according to the required performance.

Although the case where each of the inner and outer code sequence units is composed of one line has been described above, the same applies to the case where it is composed of two to four. However, even when the present invention is applied with an extremely large strain input, as described above, the steel cord terminal of the belt layer cannot be escaped from crack generation and bonding, but as illustrated in FIG. 11, the present invention, Even if the rubber near the contour B of the Uo cord terminal may crack, the crack A near the contour B of the Ui cord terminal does not cause a crack due to tensile stress. And a crack is formed in the vicinity of the contour A only when it reaches the vicinity of the contour A.
It has one major feature in that the durability life up to separation is greatly extended, and in addition, the effective width of the main belt required to maintain or improve other performances can be sufficiently secured. Has the major characteristics of.

Next, the outer and inner cord arranging units are set to be 2 or more and 4 or less because the steel cords having a small diameter, for example, 1.4 mm to 2.0 mm in diameter are arranged in a zigzag in the belt layer of the present invention. When used for, not only is it convenient for production, but regardless of the code diameter, crack development from the outer cord terminal to the inside, it takes a lot of time for connection,
This is because it is preferable in terms of improving the separation durability life. Further, if a plurality of terminals of Ui are arranged side by side substantially parallel to the belt width, it is convenient in that the distance to the connection of the cracks becomes long and it becomes difficult to connect the cracks entirely.
It is convenient to arrange the plurality of terminals vertically so as to be substantially orthogonal to the belt width, and it is convenient in that the effective width of the cord layer of the belt can be set wide.
It is preferable in that the degree of freedom for adjusting the distance Lo to the cord terminal can be increased. Further, if the plurality of terminals are arranged so as to be separated from each other in the direction substantially orthogonal to the belt width, the distance between the Ui cords and the plurality of terminals can be increased, and at the same time, the effective width of the belt layer alone can be widened. Good results with advantages are obtained.

Next, Do / Dc in FIG. 1 is set to 0.9.
As described in the above-mentioned prior art, the value of 7 or more is 0.
If it is less than 97, in order to prevent heat separation, the crown radius of the tread must inevitably be set to a small value in accordance with this value. In this way, the interlayer shear strain / stress at the end of the laminated cord layer of the main belt becomes excessive, This is because the separation between the layers occurs at an early stage before the crack progresses and the object of the present invention cannot be achieved.

Particularly in the case of tires for construction vehicles, there are many occasions of traveling on a wasteland where rocks or the like are scattered or buried due to their use, and wear is promoted when traveling on general roads. in addition,
In combination with the fact that the tire size is extremely large, securing the wear life is the most important issue.
It is customary to use a large groove depth value like Putred. In this case, it is a matter of course that the total amount of the tread rubber is large and the heat generation increases due to the increase in the amount of heat generation, and the end portion of the belt has a high degree of risk in combination with the interlaminar shear stress. Here, the ratio of Do / Dc is 0.9.
If the crown radius is made large, that is, if the tread gauge of the shoulder portion is made larger than that near the equatorial plane of the tire while keeping 7 or less, the heat generation temperature at the belt end portion near the shoulder portion becomes higher and the risk of heat separation increases. ..

According to experiments by the inventors, the above Do / Dc
Of construction vehicle tires with belts according to the invention having values of 0.96 and 0.97 of sizes 18.00R25 and 37.
00R57 was prepared, the crown radii were made uniform for each size, running under constant conditions for each size, and the temperature of the belt end was compared. The maximum temperature of the tire with Do / Dc of 0.96 is the former tire size. It was about 15 ° C higher, and the latter tire size was 19 ° C higher. Therefore, in the present invention, in order to avoid the risk of this heat separation, the ratio of the gauge near the tire equatorial plane to the tread gauge at the upper end of the main belt having the maximum width is made substantially equal to or slightly smaller. Things are preferred. For example, it is desirable that this ratio be 0.98 or more and 1.01 or less. Thus, if Do / Dc is less than 0.97, the crown radius of the tread is unavoidably small, and in addition to the above problems, the ground pressure near the equatorial plane of the tread, which is the most vulnerable to cutting during rough land travel, To increase the chances of cut damage and promote tread center wear and significantly shorten the wear life.

The outermost cord arranging unit Uo in the zigzag arrangement of the main belt occupies the maximum width of the main belt because the rough road surface or the frequency of the rough land is high and the frequency is high. When the vehicle is subjected to an unbalanced load due to rolling or cornering of a vehicle when traveling on a curve with a large curvature, the tread ground contact pressure of the outer portion of the tread width TW is significantly higher than 70% of the center, particularly 75%. This is because it is meaningless to dispose the cord layer end portion of the main belt other than the present invention in this portion where cracking is most likely to occur and where cracking is likely to occur. Further, the effective width w of the cord layer in the zigzag arrangement of the main belt is set to 70% of the half width of the tread width TW.
% Or more, and preferably 75% or more, if less than 70%, the effective width of the entire cord layer constituting the main belt according to the present invention is insufficient, that is, the function of the tread reinforcing layer is deteriorated due to insufficient rigidity of the main belt. This is because as a result, other performance deteriorations such as reduction of wear life, promotion of heat separation due to increase of heat generation amount, and increase of chances of cut penetration are caused.

The inclination angle of the steel cord of each layer of the main belt with respect to the equatorial plane is 5 ° to 25 °
If it is less than 25 °, the circumferential rigidity of the main belt becomes too high, which causes a problem of being susceptible to cutting due to deterioration of the envelope property. If it exceeds 25 °, the circumferential rigidity of the main belt becomes too low, resulting in diameter growth. Becomes large, the tensile strain of the tread rubber layer becomes large, and similarly it is easy to receive a cut,
In addition, this is also a problem in that the wear life is also reduced.

Furthermore, the diameter of the steel cord used in the cord layer of the main belt of the present invention is 1.4 mm or more. If the diameter is less than 1.4 mm, cracks at the cord end are less likely to occur, which is why the cords are arranged in a staggered arrangement. This is because it is difficult to obtain the effect, and the rigidity of the main belt becomes insufficient, resulting in a decrease in the reinforcing function of the tread rubber layer.

[0038]

【Example】

Example 1 A construction vehicle tire having a size of 18.00 R25 E4 and a basic configuration according to FIG. 1 and a tread width TW of 432.
mm, carcass is a one-ply radial arrangement with steel cord reinforcement (breaking load 400 kgf), the Do / Dc value of the cord layer of the second belt is 0.9745, and the tread gauge at the cord layer end of the second belt The ratio of the tread gauge on the tire equatorial plane of the cord layer to 0.99 is 0.99, and the steel cord used for the main belt 4M has an elongation at break of 2.0% to 5.0% (2.5% in this embodiment). %), And the steel cord used for the protective belt 4N has a breaking elongation of 6.0% to 9.0%.
% (7.5% in this embodiment) is a high elongation steel cord. Further, the tires of the examples of the present invention and the comparative tire each have one steel cord as the cord arranging unit for each of the inner side and the outer side, and the conventional tire is the same as the tire of the present invention except for the constitution of the cord layer end portion of the second belt. Further, belt specifications other than the above are collectively shown in Tables 1 and 2 for the tire of the present invention, the comparative tire, and the conventional tire. Further, a schematic view of the arrangement of the end portions of the cord layers of these second belts is shown in FIG. In the figure, the steel cord terminals 21 to 25 are tires of the present invention, and 26 and 27.
Is a comparative tire and 28 is a conventional tire.

Next, the belt endurance test conditions of these tires and the results will be shown. A tire filled with air pressure of 7 kgf / cm ² was pressed against a drum with a diameter of 5 m rotating at a speed of 16 km / h with a camber angle of 2 ° so that an unbalanced load was applied, so-called step spread condition, that is, 100 at the beginning.
Run for 24 hours at% load (9250kgf), then
48 hours with 120% load, 1 load every 48 hours thereafter
It was increased by 0%, and the belt was run until a failure occurred.
The evaluation was performed by the total running time until separation occurred at the end of the main belt. The results are shown in the right column of Table 2 as an index with the conventional tire being 100. The larger the value, the better the market demand level was 110% or more compared to the conventional tire. From Table 2, all the tires according to the present invention show a remarkable improvement effect on the separation durability of the main belt. On the other hand, the comparative tires show some improvement, but the degree of the effect is low. It did not meet the market demand.

[0040]

[Table 1]

[0041]

[Table 2]

Example 2 The elongation at break of the steel cord of the main belt was 2.4%. Except for the belt specifications shown in Table 1 and Table 2 of Example 1 and the cord layer end portion configuration of the second belt The same size and the same tire as in Example 1 are shown in Table 3 and Table 4 together with the tire of the present invention and the conventional tire, and the code layer specifications of the second belt are shown. 13, FIG.
And FIG. 15 respectively. FIG. 13 shows two types of examples and the end portion arrangement of the conventional tire in an overlapping manner.
In FIG. 15, the illustration of the end portion of the conventional tire is omitted. In this embodiment, as is clear from the drawings, the cord discharge end positions are each constituted by two steel cords, and the steel cord terminals 31 to 34 are tires according to the present invention, 35
Is a conventional tire.

The belt endurance test of these tires and the results thereof are shown in the right column of Table 4. The test conditions and the evaluation of the results are shown in Example 1.
Is the same as. From this result, it can be seen that even if the steel cord has a small diameter, a remarkable effect can be obtained if the present invention is applied with two cords as one discharge end position.

[0044]

[Table 3]

[0045]

[Table 4]

Example 3 A tire for a construction vehicle having a size of 37.00R57 E4 and having a basic structure in which the main belt 4M of FIG. 1 has four layers, and the second belt has a zigzag arrangement of the present invention. Is. Steel cord with a tread width TW of 845 mm and a carcass with a one-ply radial arrangement (breaking load 113
0 kgf), the value of Do / D _c of the second belt layer is 0.9828, and the ratio of the tread gauge at the tire equatorial plane of the cord layer to the tread gauge at the cord layer end of the second belt is 1.0. Yes, the steel cord used for the main belt 4M has an elongation at break of 2.0% to 5.5%.
(In the present embodiment, the first and second belts are 3.0%, the third and fourth belts are 4.5%), which is virtually non-stretchable, and the steel cord used for the protective belt 4N has a breaking elongation. 6.0%
To 9.0% (7.1% in this embodiment) of high elongation steel cord. Further, the tires of the examples of the present invention and the comparative tire each have one steel cord as the cord arranging unit for each of the inner side and the outer side, and the conventional tire is the same as the tire of the present invention except for the constitution of the cord layer end portion of the second belt. The belt specifications other than the above are collectively shown in Tables 5 and 6 for the tire of the present invention, the comparative tire, and the conventional tire. A schematic view of the arrangement of the cord layer end portions of these second belts is shown in FIG. In the figure, steel cord terminals 41 to 43 are tires of the present invention, 44 is a comparative tire, and 45 is a conventional tire.

Next, the belt endurance test conditions of these tires and the results will be shown. A tire filled with air pressure of 7 kgf / cm ² was pressed against a drum with a diameter of 5 m rotating at a speed of 8 km / h with a camber angle of 2 ° so as to apply an unbalanced load, so-called step spread condition, that is, 100 at the beginning.
The belt was allowed to run for 24 hours under a% load (51500 kgf), then for 120 hours under a 120% load, and the load was increased by 10% every 48 hours until the belt failed. The evaluation was performed by the total running time until separation occurred at the end of the main belt. The results are shown in the right column of Table 6 as an index with the conventional tire being 100. The larger the value, the better. From Table 6, all the tires according to the present invention showed a significant improvement effect on the separation durability of the main belt, while the comparative tires did not show any improvement.

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

As described above, according to the present invention, it is possible to prevent a severe overload or an unbalanced load without adding a special member and further without impairing the wear life, the cut resistance of the tread and the heat generation characteristics. It is possible to significantly improve the separation resistance performance of the belt of a heavy-duty vehicle to be added, especially a tire for a construction vehicle.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a left half including a tire rotation axis showing a configuration of a tire according to the present invention.

FIG. 2 is a schematic diagram showing contour positions of steel cord ends of cord arrangement units on the inside and outside of the main belt according to the present invention.

FIG. 3 is a schematic diagram according to the present invention showing a cord terminal having a different contour inclination than the cord terminal of FIG.

FIG. 4 is a schematic diagram showing a contour position of a cord terminal in which each of the cord discharge units on the inner side and the outer side of the main belt according to the present invention is composed of two steel cords.

FIG. 5 is a schematic diagram showing a contour position of a cord terminal in which the cord arranging units on the inner side and the outer side of the main belt according to the present invention are each constituted by three steel cords.

FIG. 6 is a schematic view showing an example of steel cord arrangement of the main belt according to the present invention.

FIG. 7 is a schematic view showing another example of steel cord arrangement of the main belt according to the present invention.

8A and 8B are explanatory views of the tread rubber displacement in the tire ground contact portion.

FIG. 9 is an explanatory diagram of a process from crack initiation of a cord end of a conventional tire to partial separation.

FIG. 10 is an explanatory diagram of a process from generation of a crack in a cord terminal beyond the scope of the present invention to partial separation.

FIG. 11 is an explanatory diagram of a process from crack initiation to partial separation in the outermost contour arrangement of the inner cord terminal according to the present invention.

FIG. 12 is a schematic diagram showing the arrangement of cord terminals at the end portions of the belt layers in Example 1, Comparative Example and Conventional Example.

FIG. 13 is a schematic diagram showing the arrangement of cord terminals at the end portions of the belt layers of Example 2 and the conventional example.

FIG. 14 is a schematic diagram showing the arrangement of cord terminals at the belt layer end portion of another example of the second embodiment.

FIG. 15 is a schematic diagram showing the arrangement of cord terminals at the end portions of the belt layer in still another example of the second embodiment.

FIG. 16 is a schematic diagram showing the arrangement of cord terminals at the end portions of the belt layers of Example 3, Comparative Example, and Conventional Example.

[Explanation of symbols]

 1 Radial tire 2 Bead core 3 Radial carcass 4 Belt 5 Tread rubber layer 6 Side rubber layer TW Tread width W Belt layer effective half width w Belt layer maximum width Dc Belt layer tire equatorial plane inner diameter Do Belt layer cord end inner diameter S Steel Code Ui Inner cord arrangement unit Uo Outer cord arrangement unit A Inner cord arrangement unit Code terminal contour B Outer cord arrangement unit Code terminal contour K Code terminal crack

Claims (9)

[Claims] 1. A radial carcass that reinforces at least one steel cord, and two or more main belts made of virtually inextensible steel cords that are substantially parallel to each other in the layers radially outside the carcass and intersect between the layers. A tread rubber layer disposed on the outer side in the radial direction of the main belt, wherein the cord layers forming the main belt are made of at least one cord that is adjacent to each other in the cord layer at the side edge of the main belt. The radial tires are arranged in a staggered arrangement in which the end positions of the respective discharge units are alternately staggered, and the outer cords that occupy the width end of the main belt and terminate at the inner cords that intervene between the outer cord discharge units Uo Alignment unit Ui
Is not coincident with the projection of the outline B of the cord terminal adjacent to the outside of the inner cord arrangement unit Ui among the terminals of the outer cord arrangement unit Uo, which is hypothesized on the plane including the central circumferential line of the tread. , Adjacent to the outside of the inner cord arrangement unit Ui of the terminals of the outer cord arrangement unit Uo that are adjacent to the outer cord arrangement unit Uo via the inner cord arrangement unit Ui that sandwiches the outer cord arrangement unit Uo. In the side edge of the belt, which has a termination in which the contour A of the code terminal of the inner code array unit Ui is located until it coincides with the projection of the similar contour B in the cord terminal. A radial tire for heavy duty vehicles with excellent separation durability. 2. The radial tire according to claim 1, wherein the outer cord arranging unit Uo and the inner cord arranging unit Ui, which are arranged in a staggered arrangement on the main belt, are each composed of two or more and four or less steel cords. 3. The radial tire according to claim 2, wherein the cord ends of the cord arrangement units Ui on the inner side in the zigzag arrangement of the main belt are arranged side by side substantially parallel to the belt width. 4. The radial tire according to claim 2, wherein the cord ends of the cord arrangement units Ui on the inner side in the zigzag arrangement of the main belt are vertically arranged substantially orthogonal to the belt width. 5. The radial tire according to claim 2, wherein the cord ends of the cord arrangement units Ui on the inner side in the zigzag arrangement of the main belt are arranged so as to be separated from each other in a direction substantially orthogonal to the belt width. 6. The main belt is a cord terminal of the cord arrangement unit Uo on the outside in the zigzag arrangement, and inner diameters Do and Dc of the cord arrangement unit Uo at the center of the belt width.
The radial tire according to claim 1, wherein the ratio is 0.97 or more. 7. The radial tire according to claim 1, wherein the cord ends of the cord arrangement units Uo on the outer side in the zigzag arrangement of the main belt occupy the maximum width of the main belt. 8. The arithmetic mean of the distances from the tire equatorial planes of the cord terminals of the inner cord arrangement units Ui that are arranged in a staggered arrangement of the main belt and the cord terminals of the outer cord arrangement units Uo from the equatorial plane. The radial tire according to any one of claims 1 to 7, wherein the effective half width of the cord layer of the main belt defined by the average value of the distance is at least 70% of the tread half width. 9. The cord arrangement unit U on the inner side is the width end of the cord layer of another main belt adjacent to the main belt in the zigzag arrangement.
The radial tire according to any one of claims 1 to 8, which is located further from the innermost side of the end of i.