JPH05319016A - Pneumatic radial tire for construction vehicle - Google Patents

Abstract

PURPOSE:To propose a pneumatic radial tire for a construction vehicle which is made to improve separation resistance of a belt by arranging a desired rubber strip on a belt end. CONSTITUTION:Between both ends of two belt plies 5a, 5b having respectively steel cords which cross each other in such a state of inclining in the opposite directions to the tread cicumferencial direction, a rubber strip 6 whose modulus in 100% expansion is smaller than the value of a coated rubber constituting a belt ply and whose cross section in the width direction is an approximately half-moon or trapezoidal shape formed from a bottom part, a top part, and inside and outside inclined parts by which the top part is sandwiched, is so arranged that the side end of one belt ply is located on the surface of the outside inclined part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for a construction vehicle such as a dump truck, a scraper, and a loader / dozer which mainly travels in a wasteland, and particularly to a long-life pneumatic tire having a markedly improved belt separation resistance. The present invention relates to a radial tire with a filler.

[0002]

2. Description of the Related Art Heretofore, many techniques have been known for improving the separation resistance of a belt in a pneumatic radial tire for heavy loads. For example, JP-A-62-1
244702 is a belt in which the end portion of the belt layer indicated by the line in the same figure is reinforced by a rubber composition including short fibers and having anisotropy of modulus, which is indicated by the hatched portion in FIG. Is a technology to improve the separation resistance of the.

In Japanese Patent Laid-Open No. 63-103705, an end portion of a belt layer is covered with a rubber layer shown by hatched portions in FIGS. This is a technique for improving the separation resistance of the belt by forming a separated portion between the respective end portions, thereby alleviating the strain generated at the end portions of the adjacent belts.

[0004]

However, the conventional techniques including the above disclosed technique, in which a rubber layer or a rubber composition layer is provided at the end portion of the belt layer in order to improve the separation resistance of the belt, mainly run on a paved road. Moreover, since it is intended for pneumatic radial tires for automobiles such as passenger cars, trucks and buses, which are significantly lighter in weight than construction vehicles, it is expected that these conventional technologies will be used for pneumatic radial tires for construction vehicles. There is a problem that the effect of improving the separation resistance cannot be obtained. The reason for this will be described below.

Pneumatic radial tires for construction vehicles are: (i) The absolute value of the load carried by the tire is extremely large;
For example, the load per tire is about 3100 kg for truck / bus tires, while about 10000 kg to 6 kg for large to super large construction vehicle tires.
(Ii) The vehicle mainly runs on a wasteland with unevenness on the road surface, and because the position of the center of gravity of the vehicle is high, the vehicle constantly repeats large pitching and rolling, which causes vertical acceleration far exceeding 1 G (gravitational acceleration). Is frequently input to the belt; (iii) There are many opportunities to ride on a convex foreign substance or road surface projection, and there is a lot of opportunity to apply excessive local input to the belt; Compared to pneumatic radial tire belts for automobiles, the situation is extremely severe.

When the above-mentioned severe input is applied to the belt, among the layers constituting the belt, the respective belt layers laminated so that the respective steel cords are inclined and intersect with each other in the directions opposite to the circumferential direction of the tread. The steel cord is forced to have a significantly large inclination angle with respect to the circumferential direction of the tread. It is important to note that the displacement of the steel cord of the belt layer in the pneumatic radial tire for construction vehicles is a constant displacement that depends only on the input applied to the belt layer. At that time, the displacement amount of each steel cord in a direction substantially parallel to the circumferential direction of the tread becomes substantially proportional to the distance from the tire equatorial plane, and becomes maximum at the edge of each belt layer. As a result, each end including the edge of each belt layer is subjected to extremely large shear strain.

In addition to the above, the maximum tread width for truck / bus tires of 12.00R20 is about 205 mm.
To 260 mm, the tread width of pneumatic radial tires for construction vehicles is relatively small.
About 400 mm to 450 mm at 8.00R25, about 800 mm to 850 m at super large size 36.00R51
Considering the fact that the maximum belt width is almost proportional to the tread width, the belt end of pneumatic radial tires for construction vehicles is subject to significantly greater shear strain than truck / bus tires. become.

Further, in addition to the above, the diameter and tensile strength of the steel cord of the belt layer in which belt separation occurs in a pneumatic radial tire for construction vehicles are significantly larger than those of automobile tires. For example, in diameter, the latter is about 0.5 mm to 1.2 mm, while the former is about 1.5 mm to 4.5 mm. The tensile strength of the latter is about 30 kgf / piece to 200 kgf / piece, while the former is about 300 kgf / piece to 2200 kg.
f / book.

The large difference in diameter and tensile strength of the steel cords described above is
Compared to pneumatic radial tire belts for construction vehicles, (a) the steel cord has a large cut surface at the edge of the belt layer, and this cut surface has not been treated with adhesive rubber. Excessive shear stress acts on the surrounding rubber, resulting in earlier crack initiation and its faster propagation; (b) Buckling over the entire length of the steel cord for excessive input. More resistant to static deformation, which forces the steel cords at the ends of the belt layers to undergo circumferential displacement of the tread in response to input, resulting in greater shear strain between the ends of the laminated belt layers; Pneumatic radial tires for construction vehicles are also subject to far more severe conditions for steel cord than belt / bus tires in terms of belt separation resistance. It is.

Under the above-mentioned circumstances, if the above-mentioned conventional technique is used for the belt of a pneumatic radial tire for construction vehicles, first, in JP-A-62-244702, the height is extremely high in the direction along the side edge of the belt layer. Providing a rubber composition having a 100% modulus between the end portions of the layers causes excessive shear stress at the end portions of each belt layer, and there is a problem that separation occurs at the end portions in a short time and develops. ..

Japanese Unexamined Patent Publication (Kokai) No. 63-103705 does not disclose the modulus or hardness of the rubber layer wrapping the end portions of the belt layer, but the thickness of the rubber layer between the end portions of the belt layers is substantially uniform. Yes, this uniform thickness rubber layer is able to cope with the aforementioned severe input conditions, relatively low 100%
There is a problem in that it is impossible in production to secure a rubber layer having an extension modulus and a sufficient thickness.
These are due to the fact that the rubber has increased fluidity during vulcanization molding of the tire and that a large pressure for pushing the rubber layer outward in the width direction is applied. This is disclosed in JP-A-62-244702.
The same applies when the rubber composition of (1) is used as a rubber alone.

On the other hand, if a rubber layer having a low 100% modulus sufficient to relieve shear stress is used between the end portions of the belt layer, the required thickness of the rubber layer can be ensured. On the other hand, this means that the use of rubbers with a significantly higher 100% elongation modulus, which is undesirable in terms of shear stress relaxation, is sought in order to ensure the required rubber layer thickness. Therefore, there is no conventional technique for easily improving the separation resistance of the belt end portion of the pneumatic radial tire for construction vehicles by using the rubber layer to the extent that it does not pose a problem in practical use.

Therefore, an object of the present invention is to produce a steel cord having a desired large diameter and tensile strength, which can be easily produced by using a rubber layer without requiring a special material or a particularly difficult work. It is used as a layer, and has a high degree of separation resistance that suppresses the occurrence and separation of separation that begins at the belt layer end even when running under a very high load in a wasteland with severe irregularities and large protruding foreign matter scattered around. The purpose is to propose a pneumatic radial tire for construction vehicles.

[0014]

In order to achieve the above object, a pneumatic radial tire for a construction vehicle according to the present invention comprises a carcass having steel cords in a radial arrangement and a tread arranged on the outer peripheral side of the carcass. At least two steel cords between the steel cords that are inclined in opposite directions to the tread circumferential direction and intersect each other.
In a radial tire in which a belt composed of a belt layer is provided, and rubber strips are provided between the belt layers at both end portions of the belt layer, the rubber strip is made of 100% of the coated rubber constituting the belt layer. It is made of rubber having a 100% elongation modulus smaller than the value of% elongation modulus, and the cross-sectional profile in the width direction thereof is a substantially half-moon shape or a substantially half-moon shape having a bottom portion and a top portion and inner and outer inclined portions sandwiching the top portion. It is characterized in that it has a trapezoidal shape, and the rubber strip is arranged so that the side edge of one of the belt layers is located on the surface of the outer inclined portion.

In a preferred embodiment of the present invention, when the maximum diameter of the steel cord of each belt layer in contact with the rubber strip is d, the height of the cross-sectional contour of the rubber strip with respect to the bottom is the maximum height of its top. 2.0 × in the position
It can be D or more and 4.0 × D or less and 0.5 × D or more and 3.0 × D or less at the side edge position of the one belt layer.

In another embodiment of the present invention, the width of the bottom portion of the rubber strip may be 5% or more and 20% or less of the distance from the side edge of the one belt layer to the tire equatorial plane.

In still another embodiment of the present invention, the rubber of the rubber strip has a 100% elongation modulus of 30 kgf / cm ² or more and 80 kgf / cm ² or less in the coating rubber constituting each belt layer in contact with the rubber strip. The 100% elongation modulus of the above can be 30% or more and 90% or less of the 100% modulus of the coated rubber.

The present invention will be described more specifically below with reference to the embodiments shown in the drawings. FIG. 1 is a diagram showing a left half from a tire equatorial plane E of a widthwise cross section of a pneumatic radial tire for a construction vehicle according to an embodiment of the present invention shown by 1. Reference numeral 2 denotes a carcass formed by coating steel cords in a radial arrangement with rubber. The carcass 2 straddles a pair of bead cores 3 (only one is shown) in a toroidal shape, and these bead cores 3 are surrounded by a tire inside. Has a folded-back portion that is folded back from the outside.

A tread indicated by 4 is arranged on the outer peripheral side of the carcass 2, and a belt indicated by 5 is arranged between the tread 4 and the outer peripheral side of the carcass 2. The belt 5 is composed of a belt layer 5a on the tread side and a belt layer 5b on the carcass side in this embodiment.

Each of the belt layers 5a and 5b is composed of a reinforcing steel cord and a rubber coating the steel cord. Further, these steel cords extend obliquely with respect to the tread circumferential direction, and
The steel cords of a and 5b intersect each other with the directions of the inclination being opposite to each other. Reference numeral 6 is a rubber strip provided between the two belt layers at both end portions (only one side is shown) of the belt layers 5a and 5b. The rubber strip 6 is arranged over the entire circumference in the tread circumferential direction.

In the embodiment of FIG. 1, the width from the side edge of the belt layer 5a to the tire equatorial plane E is indicated by W, and the similar width of the belt layer 5b is wider than the width W of the belt layer 5a. Wg shown in the figure indicates the maximum width of the bottom portion of the rubber strip 6 which will be described later. The cross section of the right half omitted in FIG. 1 is symmetrical to the cross section of the left half with respect to the tire equatorial plane E.

The rubber strip 6 is made of a rubber having a 100% elongation modulus value which is smaller than the 100% elongation modulus value of the covering rubber of the belt layers 5a and 5b in contact therewith. In the preferred embodiment, the belt layer 5
The modulus values of a and 5b are 30 kgf / cm ²
It is desirable to set the pressure to 80 kgf / cm ² or more.
The value of the modulus of the rubber of the rubber strip 6 is 30% or more of the value of the modulus of the belt layers 5a and 5b.
% Or less is desirable.

2A and 2B are partially enlarged views of the rubber strip 6 shown in FIG. FIG. 2A shows an arrangement state of the rubber strip 6 having a substantially half-moon-shaped cross-sectional contour shape in the width direction, and FIG. 2B shows a substantially trapezoidal cross-sectional contour shape in the width direction. The arrangement | positioning state of the rubber strip 6 which has is shown.

2A and 2B, the contour shape of the rubber strip 6 is composed of a bottom portion indicated by B, a top portion indicated by T and an inclined portion indicated by Ci and Co. Ci indicates the inclined portion on the inner side in the width direction, and Co indicates the inclined portion on the outer side in the width direction. The bottom portion B is in contact with the belt layer 5b, and the top portion T and the inclined portions Ci and Co are in contact with the belt layer 5a. Wg shown
Is the width of this bottom and Ht is the maximum height of the top T relative to the bottom B. Ea shown in the figure is a side edge of the belt layer 5a, and this side edge Ea is located on the surface of the outer inclined portion Co of the rubber strip 6. The illustrated He is the height of the rubber strip 6 at the position where the side edge Ea contacts the surface of the inclined portion Co. Incidentally, Sa and Sb shown in the figure are steel cords of the belt layers 5a and 5b, respectively.

In the preferred embodiment, the width Wg of the bottom portion of the rubber strip 6 is preferably 5% or more and 20% or less of the width W from the side edge Ea of the belt layer 5a to the tire equatorial plane E.

Also, in the preferred embodiment, the maximum height Ht at the top T of the rubber strip 6 is the belt layer 5
a and 5b of steel cords Sa and Sb, whichever has the larger diameter D (m
It is desirable to set it to 2.0 times or more and 4.0 times or less of m).
The height He of the rubber strip 6 at the position where the side edge Ea of the belt layer 5a contacts the surface of the inclined portion Co is 0.5 times or more and 3.0 times or less the diameter D (mm) of the steel cord. Is desirable.

3 (a), 3 (b) and 3 (c) respectively show another embodiment of the present invention different from the embodiment shown in FIG. Incidentally, these three examples are illustrated for the entire belt width. FIG. 3 (a) uses belt layers having substantially the same width at the stage of the members and different in the inclination direction of the steel cord from each other. As shown in the drawing, the belt 15 is formed by the belt layers 15a and 15b. This is an example in which a tire has a step difference in the width direction. In this belt structure, each rubber strip 6 is attached to the top T of the rubber strip on one side thereof.
Is located on the tread side, and the top T of the rubber strip on the other side is located on the carcass side. The illustrated W is the same as the W in FIG.

FIG. 3B shows an embodiment in which the belt 25 is composed of belt layers 25a and 25b having substantially the same width in the tire. In this embodiment, the belt layer 25
A half width of b is indicated by Wb, and Wb is substantially equal to the value of W. The rubber strips 6 shown in the figure are arranged such that their tops T are on the tread side, but in some cases, the tops T of both rubber strips are both on the carcass side as shown on the right side of FIG. May be In addition, W shown in (a) of FIG. 3 and W and Wb shown in (b) have the same sign on the left and right with the tire equatorial plane E sandwiched therebetween. However, when W and / or Wb have different values on the left and right sides. Including.

FIG. 3 (c) is basically similar to the belt and rubber strip shown in FIG. 1, but with the belt layer 35a.
Is a modified example in which a single belt layer 35c is added between the rubber strips 35 and 35b in a non-contact state with the rubber strip 6. In this configuration, the steel cords of the belt layers 35a and 35b are inclined and intersect in the opposite directions as described above, but the steel cords of the belt layer 35c are inclined in the steel cords of one of the belt layers contacting this layer. It is the same as the inclination direction of the cord, but it is not always necessary that the inclination angle with respect to the tread circumferential direction is the same.

When the belt 5 is composed of three or more belt layers, at least one of the belt layers suitable for disposing the rubber strip 6 has the maximum width on one side when viewed from the tire equatorial plane E. It is preferable that the rubber strip is disposed so that the bottom portion B of the rubber strip 6 is adjacent to the belt layer having the maximum width on one side. Further, another belt layer suitable for disposing the rubber strip 6 is not limited to the belt layer having the maximum width on one side, but a belt layer reinforced by a steel cord having the maximum diameter.

The inclination angle of the steel cord in each belt layer in contact with the rubber strip 6 with respect to the circumferential direction of the tread is preferably 10 ° or more and 30 ° or less.

In order to realize the present invention in a simple, reliable and accurate manner, when molding an unvulcanized tire, first, a width of the rubber strip 6 that is higher than the desired height Ht at the top and narrower than the desired width Wg at the bottom is used. It is preferable to dispose the unvulcanized rubber strip 6u that is provided at a predetermined position between the ends of the unvulcanized belt layers 5au and 5bu. During the vulcanization molding, especially when the Mooney viscosity of the unvulcanized rubber strip 6u is remarkably reduced, the unvulcanized belt layer 5a
It is preferable to bond the side edge Eau of u so as to be closer to the surface of the unvulcanized belt layer 5bu. The drawings showing the arrangement of the respective members in the unvulcanized state are generally the same as those shown in FIGS. 2A and 2B, and are omitted. The same applies below.

Next, it is preferable to add consideration to the tread. That is, when an unvulcanized tread rubber having a predetermined cross-sectional contour is extruded by an extruder and a tire is stretch-molded using this, the cross-sectional contour of the belt layer portion in contact with the top side of the unvulcanized rubber strip 6u is obtained. It is preferable to provide a concave portion having a substantially cross-sectional profile on the surface of the tread rubber that comes into contact with the belt layer portion. Also, for example, about 1.0m
It is more preferable to form the tread by winding a thin unvulcanized rubber sheet having a thickness of from m to about 2.0 mm many times without the above consideration.

[0034]

When the tire is vulcanized and molded, each unvulcanized rubber strip 6u tends to move outward in the width direction due to a decrease in Mooney viscosity and an increase in its fluidity. However, in the present invention, (i) the end portion including the side edge of the unvulcanized belt layer 5au is positioned on the surface of the outer inclined portion of the unvulcanized rubber strip 6u, and (ii) and in FIG. Height Heu in the unvulcanized state corresponding to He shown in a) and (b)
(Iii) the pressure applied to the unvulcanized tread rubber in contact with the end portion of the belt layer 5au presses this end portion against the side of the unvulcanized rubber strip 6u. To obtain a desired end portion disposition form of the rubber strip 6 and the belt layer 5a which can suppress the outward movement in the width direction and have both a desired low 100% elongation modulus value and a desired contour shape. Is possible.

The cut surface of the steel cord at the side edge of the belt layer 5a and the covering rubber are not adhered to each other, and the steel cord in the vicinity of the cut surface of the belt layer 5b is violently displaced due to the above-mentioned severe displacement in the tread circumferential direction. Since it is repeatedly subjected to an extremely large shear strain with the steel cord, early cracking occurs in the coating rubber around the steel cord in the vicinity of the side edge of the belt layer 5a.

According to the present invention, however, the belt layer 5a
Since a rubber strip having a low value of 100% elongation modulus and a thickness (height) of He is interposed between the side edge Ea and the belt layer 5b of the side edge Ea and the belt layer 5b. Even if the shear strain with 5b is extremely large, the shear stress acting on the side edge Ea can be relaxed and reduced, and the timing of the above-described crack generation can be delayed first.

Next, according to the present invention, the thickness of the rubber strip 6 is increased at the side edge portion of the belt layer 5a as the side edge Ea is directed inward in the width direction. It becomes possible to further enhance the effect of mitigating and reducing the shear stress, and it is possible to suppress the tendency of the cracks to propagate inward in the width direction and develop into the separation between the belt layers 5a and 5b, and to prevent the cracks from occurring. The separation resistance of the belt 5 can be remarkably improved with the delay of time.

It is preferable that the respective coated rubbers of the steel cords of the belt layers 5a and 5b have a 100% elongation modulus as high as possible in order to obtain various rigidity required for the belt 5. Therefore, in the present invention, in order to enhance the effect of relaxing / reducing the shear stress of the rubber strip 6 as much as possible, the rubber strip 6 10
The value of 0% elongation modulus is set to be less than that of the coating rubber of each belt layer.

For the above reason, the value of 100% elongation modulus of the coated rubber of each of the belt layers 5a and 5b is set to 30 k.
If it is less than gf / cm ^{2, the} belt 5 having desired rigidity cannot be obtained, and the abrasion resistance and heat generation characteristics of the tread are hindered. If this value exceeds 80 kgf / cm ² , the belt 5 is covered. The elongation at break of the rubber is remarkably reduced, which causes a problem in the durability of the belt.

It is rational to set the value of the 100% elongation modulus of the rubber of the rubber strip 6 in relation to the value of the similar modulus of the coated rubber of the belt layers 5a and 5b. If the value of the 100% elongation modulus of the rubber of the rubber strip 6 is less than 30% of the same value as that of the coated rubber, the degree of movement of the rubber during vulcanization molding becomes large, and it becomes difficult to obtain the desired contour shape. There is a problem, and if this value exceeds 90%, the desired effect of relaxing / reducing the above-mentioned shear stress decreases, and the object of the present invention may not be achieved.

The width Wg of the bottom portion B of the rubber strip 6 is 5% or more of the width W from the belt layer 5a and the side edge Ea to the equatorial plane E of the tire because the rubber strip required after vulcanization molding of the tire is formed. This is in order to secure the maximum height Ht of the top T of 6 and below this value, the rubber strip 6 during vulcanization molding
The movement of the rubber becomes even easier, and it becomes difficult to secure the height Ht. Further, if this value exceeds 20%, the above-mentioned separation resistance reaches a ceiling and is meaningless.

Maximum height Ht of the top T of the rubber strip 6
For that purpose, the diameters Da (mm) and Db (m) of the steel cords Sa and Sb of the belt layers 5a and 5b are
It is rational to set it in relation to m), and when these diameters are different, the larger diameter D (m
It is rational to use m) as a standard.

If the maximum height Ht is less than twice the diameter D (mm), the effect of relaxing and reducing the shear stress is too small to achieve the desired object of the present invention. When the maximum height Ht exceeds 4 times, the outer inclined portion C of the rubber strip 6 is related to He described below.
The gradient of o becomes too large, and the side end portion of the belt layer 5a cannot be along the surface of the outer inclined portion Co due to the impact resilience of the steel cord at the side end portion of the belt layer 5a.

It is rational to set the height He of the rubber strip 6 at the side edge Ea of the belt layer 5a in consideration of both the effect of relaxing / reducing the shear stress and the movement of the rubber strip 6. Further, it is rational that both of them are based on the large diameter D (mm) of the steel cords Sa and Sb. This height He is the diameter D (m
If m) is less than 0.5, the shear stress in the vicinity of the cut surface of the steel cord Sa at the side edge Ea becomes too large, and the above-mentioned rubber crack occurs at an early stage. If this is 3 times or more of D (mm), In addition, there is a problem that the desired contour shape of the rubber strip 6 cannot be obtained because the moving amount of the rubber strip 6u becomes large during the vulcanization molding.

[0045]

[Example] A pneumatic radial tire for a construction vehicle having a size of 36.00R51 was selected. Although the basic structure of this embodiment is in accordance with (a) of FIGS. 1 and 2, the belt 5 is composed of six belt layers. The carcass 2 was a 1-ply rubber covered steel cord having a radial arrangement. 6 layers of belts, 1B and 2B3 respectively from the carcass side
B, 4B, 5B and 6B, the width of each of these belt layers is L (mm), the 100% elongation modulus of the coated rubber is Md ₁₀₀ (kgf / cm ² ), the JIS hardness is Hd (degrees), and the steel is The angle of inclination of the cord with respect to the tread circumferential direction is α (degrees), and the diameter of the steel cord is D
(Mm), and these values are shown in Table 1. The symbols R and L added before the inclination angle α (degrees) represent the inclination directions of the arrangement of the steel cords in each belt layer, where R indicates upward rising and L indicates upward rising.

[0046]

[Table 1]

As shown in FIG. 2 (a), a rubber strip 6 having a substantially half-moon-shaped cross section was disposed between the both side ends of each of the belt layers 2B and 3B. The 100% elongation modulus of this rubber product was 29 kgf / cm ² and its hardness was 60 °. The belt layer 5b shown in FIG. 2 (a) is the above-mentioned 2B, and the same 5a is the above-mentioned 3B.
Equivalent to B.

Tires of the following two examples were manufactured with the above-mentioned common structure. [Example 1] The width of the unvulcanized rubber strip in the cross-sectional profile in the width direction is 50 mm, the maximum height is 15 mm, and the height of the rubber strip at the edge Ea of the belt layer 3B in the unvulcanized state is 6 mm. And [Example 2] The width of the unvulcanized rubber strip in the cross-sectional profile in the width direction was 30 mm, the maximum height was 10 mm, and the height of the rubber strip at the edge Ea of the belt layer 3B in the unvulcanized state was 4 mm. And

A comparison between the following two examples in which the outer shape including the tire size and the structure of the belt excluding the rubber strip are the same as those in the embodiment, and a rubber sheet having a substantially uniform thickness is arranged at substantially the same position as the embodiment. The example tire was manufactured. [Comparative Example 1] The above-mentioned rubber sheet is No. 10 in the product.
A rubber material having the same 0% elongation modulus and hardness as in the example was used, and the thickness in the unvulcanized state was 6 mm. [Comparative Example 2] The above-mentioned rubber sheet uses a rubber material different from that of the example having a 100% elongation modulus of the rubber in the product of 45 kgf / cm ² and a hardness of 70 °, and its thickness in the unvulcanized state is 10 mm. did.

[Prior art example] The outer shape including the tire size and the structure of the belt excluding the rubber strip 6 are the same as those of the embodiment, and a rubber sheet having a substantially uniform thickness is arranged at substantially the same position as the embodiment. A conventional tire was prepared. The material of the rubber sheet was the same as in Comparative Example 2, and the thickness in the unvulcanized state was 6 mm.

In order to verify the effect of each tire of the example,
An evaluation test was carried out using each of the above tires as a test tire according to the following test conditions. First, it was confirmed by an anatomical test whether or not the desired contour shape of the rubber strip and the thickness of the rubber sheet were obtained. The results are shown in Table 2.

[0052]

[Table 2]

Next, an indoor drum test was conducted. Each test tire was installed in a standard rim of 26.00 x 51, filled with standard internal pressure, and a load condition was standard load 4 so that a large load was applied to the belt end under a speed of 15 km / h.
A so-called step load system was used in which the vehicle was started from 120% load of 5000 kg, and after running for a predetermined time, 20% load was sequentially added until a failure occurred and 200% load was the final condition. The results of this drum test are shown in the lower part of Table 2. Table 2 is a value in which the total running time until a separation failure occurs in the belt portion is represented by an index with the conventional example being 100, and the larger the value, the better.

As is clear from Table 2, the tires of the respective examples according to the present invention provided a rubber strip having a desired contour shape, and provided the belt at the desired position on the surface of the outer inclined portion of the rubber strip. Positioning the layer edges could be achieved.

Further, since the tires of the respective examples are provided with the above-mentioned rubber strip form, not only the tires of the conventional examples but also the tires of the comparative examples are subjected to the separation failure due to the above test conditions. It can be seen that the effect of greatly suppressing the occurrence of the belt is obtained and the separation resistance of the belt is remarkably improved.

[0056]

According to the present invention, a rubber layer having an intended cross-sectional profile in the width direction and a 100% elongation modulus can be provided at a desired belt layer end portion without requiring a special material or a particularly difficult work. Steel cord having a desired large diameter and tensile strength can be used for the wide belt layer, and it is possible to apply extremely high load load to the wasteland where there are severe irregularities and large protruding foreign matters are scattered. It is possible to provide a pneumatic radial tire for a construction vehicle, which has a high degree of separation resistance that suppresses the occurrence and progress of the separation that starts at the end of the belt layer even when traveling underneath.

[Brief description of drawings]

FIG. 1 is a view showing a left half from a tire equatorial plane of a widthwise cross section of a pneumatic radial tire for a construction vehicle according to an embodiment of the present invention.

2 (a) and 2 (b) are enlarged explanatory views of an end portion of the belt in FIG.

3 (a), (b) and (c) of FIG. 3 are explanatory views showing a structure of a belt according to another embodiment of the present invention.

FIG. 4 is an enlarged explanatory view of a belt end portion according to a conventional technique.

[Explanation of symbols] 2 Radial carcass 4 Tread 5 Belt 6 Rubber strip B Bottom of rubber strip T Top of rubber strip Co Outer slope of rubber strip Ci Inner slope of rubber strip Ea Side edge of belt layer

[Procedure amendment]

[Submission date] May 14, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

In a preferred embodiment of the present invention, when the maximum diameter of the steel cord of each belt layer in contact with the rubber strip is D, the height of the cross-sectional contour of the rubber strip with respect to the bottom is the maximum height of its top. 2.0 × in the position
It can be D or more and 4.0 × D or less and 0.5 × D or more and 3.0 × D or less at the side edge position of the one belt layer.

Claims (4)

[Claims] 1. A steel cord having a radial arrangement of steel cords, and a tread disposed on the outer peripheral side of the carcass, each having steel cords that intersect with each other in a direction opposite to the circumferential direction of the tread. A radial tire in which a belt composed of at least two belt layers is provided, and rubber strips are provided between the belt layers at both end portions of the belt layer, wherein the rubber strip is a coated rubber forming the belt layer. Value less than 100% elongation modulus of 100
One of the belts is made of rubber having a% elongation modulus and has a cross-sectional profile in the width direction which is a substantially half-moon shape or a trapezoidal shape having a bottom portion and a top portion and inner and outer inclined portions sandwiching the top portion. A pneumatic radial tire for a construction vehicle, wherein a rubber strip is arranged such that a side edge of the layer is located on a surface of the outer inclined portion. 2. When the maximum diameter of the steel cord of each belt layer in contact with the rubber strip is d, the height of the cross-sectional contour of the rubber strip with respect to the bottom is 2.0 × D at the maximum height position of the top thereof. And more than 4.0 × D and less than 0.5 × D and more than 3.0 × at the side edge position of the one belt layer.
The radial tire according to claim 1, which is D or less. 3. The width of the bottom portion of the rubber strip is set to 5% or more and 20% or less of the distance from the side edge of the one belt layer to the equatorial plane of the tire. Radial tire described. 4. The value of 100% elongation modulus of the coated rubber constituting each belt layer in contact with the rubber strip is 3
Any of claims 1 to 3, wherein the value is 0 kgf / cm ² or more and 80 kgf / cm ² or less, and the 100% elongation modulus of the rubber of the rubber strip is 30% or more and 90% or less of the 100% modulus value of the coated rubber. The radial tire according to item 1.