JPH05294108A - Pneumatic radial tire for construction vehicle - Google Patents

Abstract

PURPOSE:To prevent separation and break of steel cords by setting a protective belt layer reinforced with steel cords which lie at right angles to the circumference of a tread, and whose outside edge is arranged inner from the outside edge of the inside belt layer, between a carcass and an inside belt layer nearest to the carcass. CONSTITUTION:A protective belt layer 5 is set between a carcass 2 and an inside belt layer 4i nearest to the carcass 2. This protective belt layer 5 is reinforced with steel cords which lie at almost right angles to the circumference of a tread. The widthwise most outside edge of the protective belt layer 5 is positioned to be nearer to the equatorial plane E of a tire than the widthwise outside edge of the inside belt layer 4i. Consequently, separation failure and break of the steel cords of the carcass can be prevented and longer life can be provided.

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 having improved carcass durability of tires used for construction vehicles and the like, and particularly to a crown portion which is seen in a large flat tire having a nominal flatness of 85% or less. The present invention relates to a pneumatic radial tire for a construction vehicle, which is improved in breakage failure of the steel cord of the carcass and separation failure of the carcass in the section.

[0002]

2. Description of the Related Art Conventionally, a failure of a crown portion of a radial tire has been referred to as a separation failure of a belt layer or a cut-through failure, and an individual failure of a radial carcass in a crown portion has not been caused. Therefore, there is no direct countermeasure technology against this failure,
There has been a strong demand from users for improvement for this failure.

[0003]

In recent years, however, the occurrence of failures in the radial carcass has been increasing. This new failure mode is due to the fact that changes in the tire itself and changes in its usage conditions are strongly related to each other. That is, construction vehicles that mainly run in a wasteland, such as articulated dump trucks, loader / dozers or scrapers, have preferentially used flatter tires for the following reasons. (I) Since the internal pressure can be reduced and the tire diameter can be reduced with the same load capacity, the position of the center of gravity of the vehicle can be lowered and the running stability can be improved. (Ii) It is possible to enhance the traction performance that is strongly required for construction vehicles.

However, in order to easily improve the traction of these tires or to easily take measures against cut penetration, the number of cases where the tire internal pressure is lower than the standard internal pressure has been increasing.

The flat radial tire which runs at such a low internal pressure and under a large lateral load or an unbalanced load is (a) inevitably subject to the tension applied to the steel cord of the carcass as compared with when the standard internal pressure is used. Will be reduced,
(B) Due to the flat tire, the tread width is wide and the tread central portion is easily buckled. (C) The pantograph motion of the steel cord of the belt layer at the tread ground contact portion becomes vigorous. (D) The belt is subject to a large lateral load or unbalanced load. With the phenomenon that excessive input is applied to one end of the layer and more vigorous pantograph movement is forced, these phenomena are caused by the breakdown of the carcass in the crown portion from the rubber surrounding the steel cord or It has been clarified that it triggers a failure of the steel cord itself.

Therefore, the object of the present invention is to provide the following phenomena (a) to (d) due to the use of low internal pressure:
We proposed a flat radial tire for super heavy loads that fulfills the wear life of the tread without causing a failure of the radial carcass in the crown part to separate from the rubber surrounding the steel cord or a failure of the steel cord itself to break, and meet the user's requirements. To respond. Here, the flat tire means a ratio of the sectional width S to the sectional height H of the tire H / S ×
A tire having a nominal value of 100 (%) of 85 or less.

[0007]

In order to achieve the above object, a radial tire for a construction vehicle according to the present invention comprises a carcass of one ply or more reinforced by a steel cord in a radial arrangement, straddling a pair of bead cores in a toroidal shape, A tire provided with two or more belt layers arranged on the outer peripheral side of this carcass and reinforced by steel cords, and a tread arranged on the outer peripheral side of these belt layers,
One or more protective belt layers are provided between the carcass and the inner belt layer closest to the carcass, and the protective belt layer is reinforced by steel cords substantially orthogonal to the circumferential direction of the tread. The outermost edge in the width direction is located closer to the tire equatorial plane than the outer edge in the width direction of the inner belt layer.

In one embodiment of the present invention, the protective belt layer may be arranged as a layer continuous in the width direction or as a discontinuous layer divided in the tire equatorial plane region in the width direction. desirable.

In another embodiment of the present invention, it is desirable that the strength of the steel cord of the protective belt layer is equal to or lower than the strength of the steel cord of the carcass and equal to or higher than 100 kgf / strand.

In another embodiment of the present invention, the strength per unit length in the tread circumferential direction of the protective belt layer is 35 times the strength per unit length in the tread circumferential direction of the carcass.
It is desirable to set the ratio to be not less than% and not more than 85%.

In still another embodiment of the present invention, a stress relieving rubber layer is provided between the protective belt layer and the carcass and / or between the protective belt layer and the inner belt layer. Is desirable.

In another embodiment of the present invention, it is desirable to dispose the stress relaxation rubber layer between each layer of the laminated protective belt layers.

In still another embodiment of the present invention, the 100% elongation modulus of the rubber of the stress relaxation rubber layer is 30 k.
It is desirable that the gf / cm ^{2 is} 55 kgf / cm ² or less.

In another embodiment of the present invention, when the thickness of the stress relaxation rubber layer is h and the diameter of the steel cord of the carcass is d, the following equation is obtained.

## EQU2 ## It is desirable to satisfy 0.7 × d ≦ h ≦ 2.0 × d.

The present invention will be described below more specifically with reference to the illustrated embodiments. FIG. 1 is a diagram showing a cross section in the width direction of a heavy-duty pneumatic radial tire 1 according to an embodiment of the present invention in a left half from a tire equatorial plane E. 2 shown
Is a carcass of one ply or more (one ply in the illustrated example) reinforced by a radial arrangement of steel cords in a toroidal shape across a pair of bead cores 3 (only one side is shown).

Reference numeral 4 denotes a belt layer of two or more layers (two layers in the example shown) arranged on the outer peripheral side of the carcass 2. These belt layers are reinforced by steel cords and at least two belt layers are provided. The steel cords of the layers intersect at different angles with respect to the circumferential direction of the tread. Inclination angle of steel cord of belt layer with respect to tread circumferential direction is 10 °
The angle is preferably 40 ° or less. Reference numeral 6 is a tread arranged on the outer peripheral side of the belt layer 4, and reference numeral 7 is a sidewall which is continuous with the tread 6 and extends to the bead portion.

Reference numeral R shown in FIG. 1 denotes a standard rim of the tire 1, and S and H shown in the drawing denote a sectional width and a sectional height when the tire is assembled to the standard rim and inflated at a standard internal pressure. The tire according to the present invention is a flat tire whose H / S × 100 value is 85 or less as a nominal value according to JATMA or other standards.

Reference numeral 5 shown in FIG. 1 denotes a protective belt layer disposed between the carcass 2 and the innermost belt layer 4i closest to the carcass, that is, the innermost belt layer in the tire radial direction. is there. The protective belt layer is reinforced by steel cords, and these steel cords extend substantially orthogonal to the circumferential direction of the tread. Furthermore, it is preferable that the angle of intersection of these steel cords with the circumferential direction of the tread is in the range of 90 ° to 85 °. Here, the tread circumferential direction refers to the direction of the line of each member that intersects with the tire equatorial plane E, or the direction of the line parallel to this line, which is represented by the tread circumferential direction. The embodiment shown in FIG. 1 shows one protective belt layer 5 continuous in the width direction.

TW shown in FIG. 1 is the tread width, BW is the width of the inner belt layer 4i, and PW is the width of the protective belt layer 5. The relationship between these widths is

## EQU3 ## It is preferable that 0.50 × TW ≦ PW ≦ 0.74 × TW and 0.60 × BW ≦ PW ≦ 0.90 × BW.

Further, the width of the protective belt layer 5 is preferably arranged at least in a region where the inner belt layer 4i is substantially parallel to the carcass 2. Although not shown, the width of the parallel regions is preferably 50% or more and 70% or less of the tread width TW in terms of tire performance and heat separation resistance of the belt layer 4.

FIGS. 2 (a) and 2 (b) are explanatory views schematically showing a cross section in the width direction of a part of the protective belt layer, the belt layer and the carcass in another embodiment. FIG. 2A shows an example in which two protective belt layers 5a and 5b continuous in the width direction are stacked. PW, TW and BW
And preferably satisfy the above relationship.

In FIG. 2B, the protective belt layer is formed by Z
In the area of the tire equatorial plane E shown in FIG.
It is arranged on both sides of. The illustrated example shows this protective belt layer at 15a. Although not shown in the figure, the protective belt layer 15b is provided at a symmetrical position on the equatorial plane E of the tire. When the protective belt layer is arranged in the width direction as a discontinuous layer, the width Z of the discontinuous area is tread width T.
It is preferable to set it to 15% or more and 26% or less of W. In this case, it is preferable that the PW be the width of each outer edge of the discontinuous protective belt layers 15a and 15b in the width direction, and that the PW and TW and BW satisfy the above relationship. Also, FIG. 2B
In the above example, each of the protective belt layers 15a and 15b has one layer, but it can have two or more layers.

The strength of the steel cords of the protective belt layers 5 and 15a, 15b is preferably equal to or lower than the strength of the steel cord of the carcass and 100 kgf / strand or more. Here, the strength of the steel cord of the carcass is 150 kgf / piece or more. This is because the size of the tire for construction vehicles according to the present invention is, for example, 15.5R25 (the nominal flatness of 83% on a wide base) to 40.5 / 75R3.
This is because it covers an extremely wide range up to 9.

Further, the strength per unit length in the circumferential direction of the tread of each protective belt layer, for example, per 5 cm,
It is desirable to set the strength per unit length of the carcass 2 in the tread circumferential direction to 35% or more and 85% or less. These strengths are values obtained by totaling the strengths per steel cord included in the above unit length.

3 (a) and 3 (b) are schematic views of cross sections in the width direction according to still another embodiment. In these examples, a rubber layer for relieving stress is added to the example shown in FIG.
This is an example of arrangement. 3A shows an example in which a stress relaxation rubber layer G is arranged between the protective belt layer 5 and the carcass 2, and FIG. 3B shows the protective belt layer 5 and the inner belt layer 4i. This is an example in which a stress relaxation rubber layer G is provided between the and.
The width of the rubber layer G preferably covers at least a region where the inner belt layer 4i and the carcass 2 are substantially parallel to each other.

FIGS. 4A and 4B are schematic views of cross sections in the width direction according to still another embodiment. These examples are examples in which a stress relaxation rubber layer is added and arranged to the example shown in FIG. FIG. 4A shows an example in which the stress relaxation rubber layer G is disposed between the two protective belt layers 5a and 5b shown in FIG. The width of the rubber layer G is preferably the same as the above.

FIG. 4B shows between the protective belt layers 15a and 15b (not shown) discontinuous in the width direction shown in FIG. 2B and the carcass 2 and between the inner belt layer 4i. ,
An example is shown in which the stress relaxation rubber layers Ga and Gb are provided between them. The width of each of the rubber layers Ga and Gb is preferably the same as that of the rubber layer G.

One of the stress relaxation rubber layers G, Ga and Gb
00% elongation modulus Md is 30 kgf / cm ² or more 5
It is desirable that the pressure is 5 kgf / cm ² . Also, this Md
The value of is 1 for the rubber that covers the steel cord of the belt layer.
85% to 140% of the 00% elongation modulus is preferable, and further, 65% to 125 of the 100% elongation modulus of the rubber coating the steel cord of the carcass.
% Or less is preferable.

The thickness h in the tire radial direction of each of the stress relaxation rubber layers G, Ga and Gb shown in FIGS. 3 and 4.
Is 0.7 for the diameter d of the steel cord of the carcass
It is desirable to satisfy the relationship of xd ≦ h ≦ 2.0 × d.

[0030]

The number of driving steel cords of the radial carcass shows the maximum value in the vicinity of the bead portion and the minimum value in the crown region from the vicinity of the equatorial plane of the tire to the shoulder regardless of the molding method. Therefore, although tension is applied to these steel cords by filling with the internal pressure, the total tension of the carcass per unit length in the tread circumferential direction in the crown region is not always sufficient, and if the internal pressure is low, Furthermore, this total tension decreases.

When a conventional flat tire travels diagonally across a rough road surface with deep ruts under low internal pressure and large traction, the steel cord at the end of the belt layer is inclined with respect to the circumferential direction of the tread. Intense pantograph movement that greatly reduces the angle. This movement alternates at both ends of the belt layer. As a result, the carcass portion in contact with the belt layer is subjected to large shear strain in the vicinity of the end portion of this layer, and the steel cord of the carcass is repeatedly subjected to buckling deformation along the surface of the carcass. This buckling deformation is sometimes near the equatorial plane of the tire and sometimes near the edge of the belt layer.However, since it is local deformation in all cases, the steel cord at this local deformation position does not suffer from buckling fatigue fracture. Will be awakened.

In a conventional tire, when a high speed turning is performed under a relatively low internal pressure and a large traction, a large unbalanced load is applied to the tread shoulder portion, and moreover, a surface for generating a cornering force is generated in this portion. A twist is added. For this reason, the steel cord of the belt layer in this portion is forced to perform a severe pantograph movement, which promotes the above failure. When deeper rut crossing is added to these running methods, this movement becomes more vigorous and further promotes buckling fatigue failure of steel cord.

Even when the steel cord is not broken as described above, the rubber near the bonding interface of the steel cord causes shear fatigue fracture and develops into separation. still,
The above pantograph movement refers to a movement in which cords intersecting each other between a plurality of belt layers change their inclination angles with respect to the tread circumferential direction. The amount of this movement is generally proportional to the distance from the equatorial plane of the tire regardless of whether the vehicle is straight, turning, or traversing over a rut, and usually becomes maximum at the end of the belt layer.

According to the embodiment shown in FIG. 1 of the present invention, at least the region where the belt layer 4 and the carcass 2 are in parallel relationship is covered between the inner belt layer 4i and the carcass,
By disposing the protective belt layer 5 continuous in the width direction and extending the steel cords of the layer 5 in substantially the same direction as the arranging direction of the steel cords of the carcass, the steel of the carcass in each part of the above crown portion is formed. While increasing the resistance to buckling deformation of the cord, low internal pressure,
Protective belt layer 5 absorbs excessive shear strain that occurs repeatedly due to frequent crossing over ruts and sudden turns under large traction, and the degree of buckling compression fatigue of steel cord in each part of the crown carcass is remarkable. Reduced to
It is possible to prevent cord breakage or separation.

The embodiment shown in FIG. 2 (a) further enhances the above function of the embodiment of FIG. 1 by disposing two protective belt layers 5a and 5b. Incidentally, the outer edges of the protective belt layers 5, 5a and 5b are held in rubber so that the steel cords of these layers are prevented from buckling deformation or separation.

In the embodiment shown in FIG. 2B, the protective belt layers 15a and 15b are formed as a discontinuous layer having a width Z in the width direction.
By disposing on both sides of the carcass in the crown portion, these layers absorb at least the excessive shear strain generated near the both end portions of the belt layer, and the carcass in the entire crown portion including the vicinity of the tire equatorial plane. It efficiently prevents compression fracture or separation of the steel cord. This embodiment is particularly suitable for use conditions in which the above-mentioned failures are likely to occur in the carcass steel cord near the shoulder.

The strength of each steel cord of the various protective belt layers must be carefully selected. That is, if the strength of these steel cords is less than 100 kgf,
Even if the outer edge of the protective belt layer is not constrained, buckling may occur due to insufficient strength and cord breakage may occur. Further, even if the strength of these steel cords exceeds the strength of the steel cords of the carcass, the above effect of the protective belt layer is saturated, resulting in an increase in cost, which is not desirable in terms of cost performance.

Further, it is rational to select the strength per unit length in the tread circumferential direction of each of the various protective belt layers in relation to the strength of the carcass. That is, if the strength of the protective belt layer is less than 35% of the strength of the carcass, the strength of the layer becomes insufficient and the steel cord of the protective belt layer breaks, or the steel cord and the surrounding rubber separate. It is a defect. Further, when this value exceeds 85%, the above-mentioned various effects reach the ceiling and are meaningless in terms of cost.

The stress-releasing rubber layers G, Ga and Gb shown in FIGS. 3 and 4 (a) and (b) are provided because these rubber layers cause excessive shearing from the inner belt layer 4i. This is because the strain input is absorbed and relaxed, the strain is further suppressed from reaching the carcass, and the above-mentioned cord breakage and cord separation are more completely prevented. Therefore, the widthwise outer end of the stress relaxation rubber layer covers at least the width in which the inner belt layer 4i and the carcass 2 are substantially parallel to each other. The structure of the stress relaxation rubber layer is suitable for tires used under the most severe use conditions.

[0040] stress relieve at 100% elongation modulus of the rubber of the rubber layer 30kgf / cm ² or more 55kgf / cm ²
If the amount is below, the above effect is obtained, and if it is less than 30 kgf / cm ² , the strength of the stress relaxation rubber layer is insufficient and it cannot withstand a large repeated shear strain, resulting in damage to the rubber layer itself and lacking practicality. On the other hand, if it exceeds 55 kgf / cm ² , the shear resistance of this rubber layer becomes too high, and the shear strain relaxation effect is weakened and it is meaningless to use.

In order to obtain the desired shear strain relaxation effect, it is necessary to optimize the thickness h of these rubber layers at the same time as selecting the desired modulus of the stress relaxation rubber layers G or Ga and Gb. In the present invention, this thickness h is 0.7 × d ≦ h ≦ with respect to the diameter d of the steel cord of the carcass.
It was confirmed that the effect could be obtained by setting it to 2.0 × d. That is, if h is less than 0.7 × d, the above-mentioned effect is insufficient, and if h exceeds 2.0 × d, the effect reaches a peak and it is not preferable in terms of cost and temperature rise.

The stress-releasing rubber layers G, Ga and Gb are arranged as a continuous layer in the width direction to improve the bending rigidity along the surface of the plate-like body formed by the inner belt layer 4i and the carcass 2. This is for alleviating the shear strain applied to the carcass 2, and for maintaining the linearity of the carcass in the crown region and preventing defects such as air loss during manufacturing.

[0043]

[Example] A tire for a construction vehicle, a pneumatic radial tire with a nominal flatness of 75%, and a size of 40.5 / 75R3
9 2 Star Tread Class E3 was picked up. The cross-sectional height H when assembled in the standard rim 32.00 / 4.5 × 39 and filled with the standard internal pressure of 5.25 kgf / cm ² is 7
The cross sectional width S is 90 mm and the cross sectional width S is 1040 mm. The tread width TW was set to 840 mm. The basic structure of the tire is shown in Fig. 1.
According to the above.

The carcass 2 was a one-ply reinforced with radial-arranged steel cords, and the belt layer 4 had a five-layer structure. The belt layer closest to the carcass is the first belt layer 4
i and the outermost belt layer as the fifth belt layer,
The width BW of the belt layer 4i was 600 mm, and the width PW at which the belt layer 4i was substantially parallel to the carcass was 530 mm. First
And the steel cords of the second belt layers cross each other. The steel cords of the protective belt layer are arranged substantially orthogonal to the circumferential direction of the tread, and are arranged in the same direction as the extending direction of the steel cords of the carcass.

Strength of one steel cord used for the carcass 2, the protective belt layer and the first to fifth belt layers, the number of hammers per 25 mm (the number), the first to fifth belt layers The inclination direction and inclination angle of the steel cord of each layer with respect to the tread circumferential direction were set as follows. These values are shown in the order of multiplication.
Incidentally, among the following symbols, R indicates a steel cord arrangement that goes up to the right in the circumferential direction of the tread, and L indicates a steel cord arrangement that goes up to the left in this direction.

Carcass: 800 kgf × 3 pieces, cord diameter 2.8 mm. Protective belt layer: 300 kgf x 6 pieces. First belt layer: 300 kgf × 7 lines × R23 °, Second belt layer: 500 kgf × 7 lines × L23 °, Third belt layer: 500 kgf × 7 lines × R23 °, Fourth belt layer: 250 kgf × 9 lines × L23 °, 5th belt layer; 250 kgf x 9 strands x R23 °.

Tires of the following seven examples were prepared with the above-mentioned common structure. Example 1 A tire according to FIG. 1 except for the number of belt layers. [Example 2]; except for the number of belt layers, according to FIG.
A tire in which two layers having the specifications of the protective belt layer are laminated. [Example 3]: According to FIG. 2 (b) except for the number of belt layers,
The value of Z is 200 mm, and the protective belt layers 15a and 15 are
Tires each having a width b of 165 mm. [Example 4]: According to (a) of FIG. 3, except for the number of belt layers,
A tire having a modulus of 100% elongation of the rubber of the stress relaxation rubber layer G of 35 kgf / cm ² and a thickness h of 3 mm. Example 5: According to FIG. 3B, except for the number of belt layers,
A tire in which the modulus of 100% elongation of the rubber of the stress relaxation rubber layer G is 35 kgf / cm ² and the thickness h thereof is 3 mm. Example 6; according to FIG. 4A, except for the number of belt layers,
A tire in which the modulus of 100% elongation of the rubber of the stress relaxation rubber layer G is 40 kgf / cm ² and the thickness h thereof is 2.5 mm. Example 7: According to FIG. 4B, except for the number of belt layers,
The stress relaxation rubber layers Ga and Gb have a modulus at 100% elongation of 35 kgf / cm ² and 40 kgf, respectively.
/ Cm ² , the thickness h of Ga was 3 mm, and the thickness h of Gb was 2.5 mm. A tire in which the value of Z is 180 mm and the width of each of the protective belt layers 15a and 15b is 210 mm.

[Conventional Example] A conventional tire was prepared in order to verify the effects of the tires of the above-described examples. This tire has the same outer dimensions including size as those of the example tire, the internal configuration is the same as that of the above example except that the protective belt layer is removed, and the above-mentioned specifications of the steel cord of the fourth belt layer are the third. According to the belt layer (however, the inclination direction is L), the inclination direction of the steel cord of the fifth belt layer was L, and the sixth belt layer was laminated further on the outer peripheral side of this layer. The specifications of the steel cord of the sixth belt layer are the same as those of the fifth belt layer except that the inclination direction is R.

The durability of the carcass was evaluated by testing the tires of the above-mentioned 7 examples and conventional examples under the following conditions.
That is: (a) Each test tire was assembled in a standard rim and filled with a low internal pressure corresponding to 70% of the standard internal pressure of 5.25 kgf / cm ² . (B) The peripheral speed of a rotating drum with a diameter of 5 meters is 10 km.
/ H, apply a slip angle of 5 ° to each drum, and press each test tire. (C) Initially, a standard load of 29000 kgf is applied and 24
After running for an hour, add a load equivalent to 10% of the standard load every 12 hours, and remove it when a failure occurs in the carcass or other parts. (D) The durability of the carcass is evaluated based on the cumulative time that the vehicle has traveled until this failure occurs.

The results of the above-described test evaluations are shown in Table 1 in index notation with the tire of Conventional Example as 100. The larger the value, the better. The test in which the tire has a low internal pressure and a slip angle of 5 ° is applied to the tire is to give an input to the carcass crown portion that approximates the actual operating conditions, and to actively cause a failure in this portion. is there.

[0051]

[Table 1]

As is clear from Table 1, the tire of the conventional example was reproduced by reproducing the carcass failure that occurred in the actual use condition, but each tire of the example of the present invention has a carcass portion until the end of its life. No failure occurred, and the carcass durability was remarkably excellent.

This means that the steel cord is often buckled along the surface of the carcass to cause a breakage failure or a separation failure by frequently traversing a deeply uneven rutted road surface or repeating sharp turns, especially when a low internal pressure is used. It is shown that the tires of the examples according to the present invention have a remarkably excellent mitigation effect against the above input, and guarantee a long life. That is, the tires of the respective examples ended the test life by the separation between the belt layers or the separation between the protective belt layer and the adjacent belt layer, but this life level guarantees no failure until the complete wear life of the tread. To do.

[0054]

EFFECTS OF THE INVENTION According to the present invention, the use of low internal pressure, frequent deep rutted diagonal crossing, frequent sharp turns, etc. are suppressed by using the same cost as conventional tires without using special materials. Under the conditions, it is possible to sufficiently prevent the separation failure and the breakage failure of the steel cord of the carcass that have conventionally occurred in the tire, and it is possible to provide a long-life pneumatic radial tire for a construction vehicle that can meet user needs.

[Brief description of drawings]

FIG. 1 is a diagram showing a left half of a cross section in a width direction according to an embodiment of the present invention.

2A and 2B are explanatory views showing a left half of a width direction cross section according to another embodiment of the present invention.

3 (a) and 3 (b) are explanatory views showing a left half of a width direction cross section according to still another embodiment of the present invention.

4 (a) and 4 (b) are explanatory views showing the left half of the cross section in the width direction according to another embodiment of the present invention.

[Explanation of symbols]

 2 Radial carcass 3 Bead core 4 Belt layer 4i Innermost belt layer 5 Protective belt layer G Stress relaxation rubber layer PW Maximum width of protective belt layer BW Innermost belt layer width

Claims (8)

[Claims] 1. A toroidal straddle over a pair of bead cores,
One or more ply carcass reinforced by radial arrangement steel cords, two or more belt layers arranged on the outer peripheral side of this carcass and reinforced by steel cords, and a tread arranged further on the outer peripheral side of these belt layers. In the tire including the above, one or more protective belt layers are provided between the carcass and the inner belt layer closest to the carcass, and the protective belt layers are formed by steel cords substantially orthogonal to the tread circumferential direction. A pneumatic radial tire for a construction vehicle, which is reinforced, and an outermost edge of this layer in the width direction is located closer to the tire equatorial side than an outer edge of the inner belt layer in the width direction. 2. The protective belt layer is arranged as a layer continuous in the width direction or as a discontinuous layer divided in the tire equatorial plane region in the width direction.
Radial tire described. 3. The strength of the steel cord of the protective belt layer is equal to or lower than the strength of the steel cord of the carcass, and
The radial tire according to claim 1, wherein the radial tire is 100 kgf / piece or more. 4. The strength per unit length in the tread circumferential direction of the protective belt layer is set to 35% or more and 85% or less of the strength per unit length in the tread circumferential direction of the carcass. The radial tire according to any one of items. 5. Between the protective belt layer and the carcass, and / or between the protective belt layer and the inner belt layer,
The radial tire according to claim 1, further comprising a rubber layer that relieves stress. 6. The radial tire according to any one of claims 1 to 5, wherein the stress relaxation rubber layer is provided between the laminated layers of the protective belt layer. 7. The 100% elongation modulus of the rubber of the stress relaxation rubber layer is 30 kgf / cm ² or more and 55 kgf / c.
The radial tire according to any one of claims 1 to 6, which has a m ² or less. 8. When the thickness of the stress relieving rubber layer is h and the diameter of the steel cord of the carcass is d, the following expression: 0.7 × d ≦ h ≦ 2.0 × d The radial tire according to any one of claims 1 to 7, which satisfies.