JPH0725203A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire which provides the excellent separation resistance of a tread part strengthening member and the drastically improved uneven abrasion resistance on the tread surface. CONSTITUTION:A pneumatic radial tire has a radial carcass 5, belt 6 consisting of at least two layers of steel cord crossing layers, and at least one layer of hoop 7 which consists of the substantially nonextensive cord layers having the width narrower than the width of the belt 6 and resists with the pneumatic pressure acting on the carcass 5 with the arrangement set along the carcass 5 directly under the belt 6. The belt 6 provides an archery shaped section which is concaved in the center region of the width and has the shape in which the distance from the hoop 7 is gradually increased toward the width end of the hoop 7, and a tread part 3 has the tread surface having the radius of curvature larger than than on the center side, on the edge side in comparison with the normal line which is lowered to the width end of the hoop 7 from the tread surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pneumatic radial tires for heavy loads, especially heavy-duty trucks, wheel cranes, vehicles used mainly on non-paved roads such as civil engineering / construction sites, mining sites, and forestry workshops (hereinafter referred to as heavy vehicles). Say)
For pneumatic radial tires used for, particularly, to significantly improve the separation resistance (including heat separation resistance) of the reinforcing member mainly for the belt of the tread part, which is particularly disadvantageous in the use of these heavy vehicles The present invention proposes a long-lived pneumatic radial tire capable of solving uneven wear of the tread surface of the tread portion at the same time.

[0002]

2. Description of the Related Art Conventionally, a belt separation failure and a bead failure have been taken up as two particularly serious failures for large-sized pneumatic radial tires used in heavy vehicles. In particular, the former has a large amount of heat generation due to the thick tread rubber, and since the heat tends to accumulate, there is an unavoidable disadvantage that the belt becomes high temperature.
In addition, it is a failure that occurs as a result of large strain due to heavy load of the tire acting on the belt end, and therefore, in order to improve the separation failure of the belt, significant strain reduction and temperature reduction must be achieved at the same time. Was holding.

Various means have been proposed to solve the above-mentioned problems, but among them, the application of a cap / base tread rubber which is customary for reducing heat generation does not lead to a drastic solution to the above separation problem. Regarding distortion reduction, for example, Japanese Patent Laid-Open Nos. 54-126306 and 5
Japanese Laid-Open Patent Publication No. 4-126307 discloses that a two-layer cord crossing layer named a limiter block is provided in a tire equatorial zone width in which a carcass and a breaker (hereinafter, referred to as a belt in accordance with a radial tire convention) are parallel to each other. There is.

If the limiter block functions so as to sufficiently suppress the carcass swelling when the tire is filled with the internal pressure and to significantly reduce the tension load on the belt, the strain at the end of the belt is reduced and the strain is reduced. The belt separation based on it can be effectively suppressed.

[0005]

It has been clarified that the measures according to the above-mentioned conventional technique for reducing the circumferential tension by the belt in order to avoid the separation of the end portion of the belt are accompanied by an increase in uneven wear on the tread surface of the tread portion. Was done. The cause of this uneven wear is described below as one of the results of the investigation conducted by the inventors.

That is, the tension-resisting member (limiter block) that transfers the load of the circumferential tension from the belt has a tensile rigidity along the circumference (expressed in kgf / mm, for example).
First, it is indispensable to raise the tire pressure to a high level in advance before filling the inner pressure of the tire.Therefore, it is necessary for the cords in each layer of the member to have high strength and low elongation properties and to set the cord intersection angle between the layers to be extremely small. And As a result, by sufficiently tightening the carcass under an extremely high tension load after the tire is filled with the internal pressure, it becomes possible to significantly reduce the tension load on the belt.

However, the central portion of the tread surface (equatorial zone) that matches the installation width range of the tension member has a significantly higher rigidity than the both side portions, and as a result, the footprint of the tread surface of the tread portion under load ( The ground contact shape shows a so-called butterfly shape (see FIGS. 6A and 6B) in which the ground contact length of the tread central portion is significantly shorter than that of both side portions.

This is because the load radius of a tire of this kind is practically dominated by the central portion of the tread, and on a tread exhibiting a butterfly-shaped footprint, especially under load rolling due to heavy load on the tire, Both tread parts with long contact length lead to the other and step on the ground to receive a large impact force from the road surface, which causes self-excited wear as a result of the tread rubber of that part exhibiting a self-excited vibration phenomenon. It is considered that uneven wear, which is so-called step-down wear, is caused and the wear life of the tire is significantly impaired.

In addition, since the tension load on the belt is significantly reduced, the rigidity difference between the belt and the tension member, which exhibits low rigidity, is significant, but the cross cord of each belt layer is a pantograph in the contact area. While exhibiting a deformation behavior called movement, such behavior hardly occurs in the tension member,
This causes a large shear strain at the end contacting the belt,
Separation may occur in this part and it may be a problem.

Further, the interposition of the above-mentioned tension member is accompanied by an increase in the gauge of the tread portion. Therefore, it is inevitable that the temperature near the end portion of the belt is further increased, which is also disadvantageous in terms of heat separation. Here, the more severe changes in the operating conditions in recent years, that is, the product of the average load (W) and the average speed (S) of the tire W × S
It depends on the improvement in heat resistance of the tread part that it is necessary to further increase the load velocity product represented by the tire failure.
In order to sufficiently enhance the separation resistance of the belt, it is necessary to consider the avoidance of heat separation.

In view of the above-mentioned problems, the present invention mainly relates to belt separation in a large-sized or heavy-load pneumatic radial tire mainly used for heavy vehicles, including heat separation, and other tread surface uneven wear and the like. It is an object of the present invention to propose a pneumatic radial tire which is remarkably reduced without a disadvantage and has a long life.

[0012]

To achieve the above object, a pneumatic radial tire of the present invention comprises a pair of bead portions, sidewall portions and a tread portion, and the bead cores are embedded between the respective bead portions. A radial carcass consisting of a ply that reinforces the belt, a belt composed of at least two layers of steel cord crossing layers that reinforce the tread portion on the outer periphery of the carcass, and a substantially inextensible cord that is narrower than the width of the belt. A pneumatic radial tire having at least one layer of hoops, which comprises at least one layer of hoops, which is arranged immediately below the belt and along the carcass, and which opposes the air pressure acting on the carcass, in which the belt is concave in the central region of its width. It also has a shape of a cross section and gradually increases the distance from the hoop toward the width end of the hoop. , Tread portion, at the edge side than the normal line drawn from the tread in the width ends of the hoop, also compared to the curvature at the center side, it has a tread surface with a larger curvature, and wherein.

In carrying out the present invention, the hoop is
It consists of two layers of steel cords, and the cords in each layer intersect each other and are 1 with respect to the plane including the center line of the tread.
The slanted arrangement is 0 ° or less, or the hoop is a lateral arrangement of a plurality of rings formed by winding a steel cord in several cross windings side by side along the width direction, and the tread portion is When there is at least one orbiting main groove in the central region near the centerline of the tread, the arrangement of the orbiting main groove has a groove wall separated from the normal of the tread passing through the width end of the hoop. Should be.

The present invention will be described in more detail below with reference to FIG. FIG. 1 shows a left half cross section by a plane including a rotation axis of a pneumatic radial tire according to the present invention. In the figure, 1 is a pair of bead portions, 2 is a pair of sidewall portions, and only one side is shown, 3 is a tread portion, 3-1 is a tread surface thereof, and 3-2 is a tread portion rubber. 4 is a bead core embedded in the bead portion 1 and 5 is a ply (in the illustrated example, 1
A radial carcass composed of a ply), and this carcass 5 has a pair of bead portions 1 extending across the bead cores 4 from each other.
Also, the sidewall portion 2 and the tread portion 3 are reinforced.

Further, in FIG. 1, reference numeral 6 denotes a belt composed of at least two layers (two layers in the illustrated example) of steel cord intersecting layers, which participate in strengthening the tread portion 3 on the outer periphery of the carcass 5. Further, 7 is a hoop composed of at least one layer (two layers in the illustrated example) of substantially non-stretchable cords, and the hoop 7 is narrower than the width of the belt 6 and directly below the belt 6. It is arranged along the carcass 5, and plays a role of suppressing the expansion of the carcass 5 by competing with the air pressure acting on the carcass 5 by filling the inner pressure of the tire. The term "substantially non-extensible cord" as used herein means that the breaking elongation thereof is about 0.5 to 3.
Refers to those within the range of 5%. Incidentally, 8 is a relatively soft cushion rubber.

As shown in FIG. 1, the belt 6 has an archery-shaped cross section that is concave in the central region of its width, and has a shape in which the distance from the hoop 7 gradually increases toward the width end of the hoop 7. is necessary. Here, the central region of the belt 6 refers to a region in which two regions near the center are combined among regions formed by dividing the width of the belt 6 into four equal parts in the width direction. Further, both sides of the central region may have a convex shape as shown in the figure, a concave shape similar to the central area, or a shape having no curvature in the width direction.

Further, it is desirable that the closest position between the belt 6 and the hoop 7 is on or near the plane E including the central circumferential line of the tread 3-1. It is desirable that the steel cords in each of the layers of the belt 6 be arranged in an inclined arrangement within the range of 15 to 70 ° with respect to the plane E, and the belt 6 made of a layer of steel cords having a large arrangement inclination angle is particularly tread surface. 3-1 Suitable for pneumatic radial tires for heavy vehicles that run in rough places where there are many opportunities for cut damage.

The line segment indicated by L in FIG. 1 is a normal line drawn from the tread surface 3-1 of the tread portion 3 to the width end of the hoop 7, and the tread portion 3 is closer to the edge side than the normal line L. It has a tread 3-1 having a curvature larger than that on the center side of the normal line L. In other words, as shown in the figure, the tread portion 3 has the intersection V of the normal line L and the tread 3-1.
With the radius of curvature Rc on the center side and the radius of curvature R on the edge side
has a tread 3-1 formed by smoothly connecting s and Rc> R
s. Here, it is desirable that Rc / Rs be in the range of 2 to 8, and the radii of curvature Rs on both sides of the tread 3-1 can be the same or different values. Select in consideration of the camber angle etc. attached at times.

2 (a) and 2 (b), the main part in the cross section is mainly shown as a diagram as in FIG.
In (a) and (b), the belt 6 is composed of four steel cord layers 6-1 to 6-4, among which the layers 6-1 and 6-2 indicated by solid lines are the belt 6 shown in FIG. The layers 6-3 and 6-4 indicated by broken lines are so-called high elongation (hereinafter abbreviated as HE) steel cord layers. This HE steel cord has a cutting elongation of 4 to
It has a twisted structure of 10% and is easy to stretch with respect to the steel cords (cutting elongation 0.5 to 3.5%) used for the layers 6-1 and 6-2, and also functions as a cushioning member against a cut input. .

A hoop 7 shown as an example in FIG. 2 (a) is composed of two layers 7-1 and 7-2 made of steel cords as in FIG. 1, and the cords in the respective layers 7-1 and 7-2 intersect each other. 10 ° with respect to the plane E including the central circumference of the tread 3-1
It becomes the following inclined array. The hoop 7 illustrated in this figure
Is a laminated body in which the respective widths of the two layers 7-1 and 7-2 are aligned with the respective end edges, but is a stepped laminated body in which the widths of the other layers are different or an offset laminated body in which the widths of the respective layers are aligned. be able to. It is suitable that the hoop 7 having a small inclination angle of the cord is a layer formed by winding the cord, and the hoop 7 having a large angle is a layer having a cut-off end of the cord at its edge.

In FIG. 2B, a hoop 7 of another example different from the above.
The hoop 7 is a horizontal array of a plurality of rings 7r formed by a bundle of steel cords that are wound by cross winding several times along the width direction of the hoop 7. This ring 7r
Is one or more steel cords cut into a predetermined length and wound several times with a predetermined diameter, for example, 2 to 4 times, and from the second winding onwards, entangle each time the cord is wound. It will be wound. In addition, the winding start end and the winding end end are
Whether to be joined to each other to be endless or to be left as a separated end can be selected based on the type of tire and difficulty in manufacturing.

Each layer of the hoop 7 illustrated in FIG. 2 is an integral layer in the width direction, but it is also possible to form a plurality of horizontally arranged layers in which at least one layer is divided in the width direction.

2A and 2B, the mutual spacing between the cord of the layer 7-1 or 7 of the hoop 7 and the cord of the innermost layer 6-1 of the belt 6 adjacent to this layer is defined as It is preferable that Sc is shown on the plane E or in the vicinity thereof, Se is shown at a position along the normal line L, and Se / Sc is within a range of 2 to 10.

Next, application of the rib lug pattern shown in FIGS. 3 and 4 will be described. FIG. 3 shows the tread portion 3
4 is an exploded view of the main part of the tread 3-1 of FIG.
A cross section along the X-ray is shown. Hoop 7 shown in Figure 4 here
Illustrated common four types of hoops 7 whose width ends are located at A, B, C and D in the figure.

As shown in FIG. 3, the tread portion 3 of the tire, which needs to secure skid resistance, is near the center circumferential line of the tread 3-1 (shown as a plane E including this circumferential line in the figure). It is desirable to have at least one (two in the illustrated example) circular main groove Gc in the central region, and the circular main groove G
The arrangement of c is the normal line L of the tread 3-1 passing through the width end of the hoop 7.
On the other hand, it should have a groove wall separated from it. Here, the groove wall is composed of a groove bottom wall and a groove side wall.

Therefore, the orbiting main groove Gc shown in FIG. 4 has the normals Lc and L of the tread 3-1 passing through the width ends C and D of the hoop 7.
While it is suitable for d, it is not suitable for normals La and Lb passing through the width ends A and B of the hoop 7 because they pass through the groove wall. It should be noted that the orbiting main groove Gc is preferably a zigzag groove having a groove swing angle of 30 ° or less with respect to the central peripheral line (E) or a groove extending along the circumference.

The lug pattern shown in FIG. 5 in which the essential parts are developed is also applicable, and the tread portion 3 having only the lug groove indicated by G1 in the drawing or a lateral groove similar thereto is referred to as the normal line L. The relationship of is excluded from consideration.

[0028]

First, the belt 6 has an archery-shaped cross section that is concave in the central region of the width thereof, and has a shape in which the distance from the hoop 7 gradually increases toward the width end of the hoop 7. The distance between the cords in the layer 7-1 (or 7) and each layer of the layer 6-1 of the belt 6 adjacent to the layer 7-1 is set to be large through the soft cushion rubber 8 having a sufficient thickness at the end of the hoop 7. As a result, the shear strain (stress) generated between the edge of the layer 7-1 (or 7) and the layer 6-1 can be significantly increased without increasing the thickness of the central portion of the tread portion 3. It becomes possible to relax.

As a result, it is possible to sufficiently suppress the separation at the end of the hoop 7, which has been apt to occur in the past, without the disadvantage of lowering the heat separation resistance of the belt 6 at the center of the tread portion 3.

In addition, it is possible to sufficiently increase the tensile rigidity of the hoop 7 to a desired value before the tire is filled with the internal pressure without being concerned about the occurrence of separation at the end of the hoop 7, and the tension load of the belt 6 is thereby increased. As compared with the conventional case, the distortion is further remarkably reduced, and as a result, the distortion generated at the belt end portion is remarkably reduced, and the occurrence of the separation due to the distortion is further remarkably suppressed as compared with the conventional case.

Hoop 7 having desired high tensile rigidity
Is the two layers 7-1 and 7 as shown in FIGS.
It can be easily and effectively realized by applying the hoop 7 formed of the -2 code crossing layer or the hoop 7 in which the plurality of rings 7a are arranged side by side. Especially the latter hoop 7
Has the feature that extremely high tensile rigidity can be easily obtained. The inclination angle of the cords of the layers 7-1 and 7-2 is 1
If the angle exceeds 0 °, the tension load on the hoop 7 becomes insufficient, which is not desirable.

Further, due to the load rolling of the tire under the use condition in which the value of load velocity product W × S is extremely high, the conventional belt end portion becomes remarkably high in temperature and heat separation is apt to occur, but it is likely to occur in an archery state. The end portion of the belt 6 having a cross section is located closer to the tread surface 3-1 as compared with that of the conventional belt, and therefore the tread rubber 3 on the lower temperature side is provided.
-2, so that heat separation based on high temperature can be effectively prevented.

As described above, the belt 6 and the hoop 7 have their respective synergistic effects remarkably reducing the strain at each end, and at the same time the temperature of the belt 6 can be lowered. The separation resistance can be remarkably improved.

Next, having the belt 6 and the hoop 7,
The tread portion 3 having the tread surface 3-1 having a larger curvature than the curvature on the center side on the edge side of the normal line L lowered from the tread surface 3-1 to the width end of the hoop 7 is 100 The footprint of the tread 3-1 at the time of% load is shown in FIG. 6 in comparison with the conventional butterfly shape shown in FIGS. 6 (a) and 6 (b).
It can be a barrel shape having a middle bulge shown in (c). Note that FIG. 6 shows only the outer contour of the footprint excluding the groove portion and the like, and E ′ in the figure corresponds to the center circumferential line of the tread 3-1.
Reference numeral 1'denotes a ground contact portion of the tread 3-1.

The tread rubber 3-2 having the barrel-shaped footprint does not exhibit the above-mentioned self-excited vibration phenomenon at any part of the tread surface 3-1 and therefore there is no possibility of causing self-excited wear. Therefore, uneven wear such as step-down wear can be avoided. Note that FIG. 6 (d) is a footprint in which the crown curvature radius Rs on both sides of the tread 3-1 shown in FIG. 1 is smaller on the left side than on the right side of FIG. The tread 3-1 showing a footprint having the center within the range can prevent the uneven wear from occurring.

Further, in contrast to the tire with a lug pattern which emphasizes traction, a tire having at least one orbiting main groove Gc in the central region of the tread portion 3 is particularly resistant to skid when running on a wet road surface on an unpaved road. Can be advantageously exhibited. At the same time, the heat dissipation of the tread rubber 3-2 in the central region is enhanced, and the temperature of the belt 6 is further lowered.

However, it was found that cracks often occur in the groove bottom wall of the orbiting main groove Gc during the use of the tire, and therefore the effect of the hoop 7 on this groove bottom wall crack is as follows.
Using an ultra-large pneumatic radial tire having a size of 36.00R51, the width end of the hoop 7 with respect to the circumferential main groove Gc was tested at the positions A, B, C and D shown in FIG. 4, and the following results were obtained. Here, the groove depth of the main groove Gc is 8
The value was 0 mm, and the other specifications were the values shown in FIG.

That is, the normals La and L from the tread 3-1 passing through the width ends A, B, C and D of the hoop 7 from the tread 3-1.
The groove bottom width direction strain (width direction strain% of the tread 3-1) of the orbiting main groove Gc at each normal line position of b, Lc, and Ld was measured, and the result is shown in the line graph of FIG. 7. The normal line Lb passes through the side wall of the groove whose depth is about ½ of the groove depth and the groove width is about 30 mm in FIG. 4, and the normal line Lc is separated from it by about 30 mm.

Further, after performing a long run test with the drum of the tire under the conditions of a load of 100%, a speed of 10 km / h and an additional torque of 7.5 ton-meter, the bottom wall of the orbiting main groove Gc was observed. , It was found that a very long and deep crack was generated in the groove bottom wall at the normal line La position, and a crack that was lighter than this was also generated in the groove bottom wall at the normal line Lb position. No sign of cracking was found at the Ld position.

As a result of considering the above-mentioned two kinds of experimental results together, by separating the groove wall of the circumferential main groove Gc from the normal line L of the tread 3-1 passing through the width end of the hoop 7, the groove bottom wall crack It is also possible to provide a pneumatic radial tire capable of exhibiting excellent separation resistance and skid resistance in line with requirements while avoiding the occurrence of the above.

[0041]

EXAMPLE A size of a rear dump truck mainly used on an unpaved road is 36.00R51, a carcass 5 is a single ply having a radial arrangement of steel cords, and a belt 6 is shown in FIG. According to b), layer 6-
1, 6-2 have an inclination arrangement angle of 25 ° with respect to the plane E.
Cutting strength is 600 kgf / piece, cutting elongation is 2.5
% Steel cord, layer 6-1 has a half width of 320
mm, and the half width of the layer 6-2 was 280 mm. Layer 6-
For 3 and 6-4, the cutting strength with the above angle of 20 ° is 300.
It was made of HE steel cord having a kgf / piece and a breaking elongation of 6.5%, and the half width of the layer 6-3 was 400 mm and the half width of the layer 6-4 was 300 mm.

The degree of concavity of the belt 6 with respect to the hoop 7 is set such that the cord spacing Sc in the vicinity of the plane E is 2 mm, and the cord spacing S along the normal L is S.
e was defined as 8 mm.

With respect to the hoop 7, which is common to the above, the first, second, third and fourth embodiments are the same as the fifth and sixth embodiments according to FIG.
2 (b), and Example 7 has two layers of the hoop 7 of FIG. 2 (b). Here, the configuration of the hoop 7 and the crown curvature radii Rc and R of the tread 3-1 are described for each of Examples 1 to 7.
s, the tread pattern applied is described below.

Hoop 7; (i) Examples 1, 2, 3 and 4; (a) Steel cord in each layer; Cutting strength 600 k
gf / piece, cutting elongation 2.5 (%), (a) Examples 1 and 2; winding of steel cord, number of driven pieces 12 / 5c
m, Examples 3 and 4; Steel cord 7 relative to plane E
It becomes an inclined arrangement of °, and the number of driving is 15 pieces / 5 cm, (ii) Examples 5 and 6; (a) Steel cord; Cutting strength 1000 kgf / piece,
Cutting elongation 2.5 (%), (a) Number of times of cross winding of the ring 7r is two, driving number is 10 pieces / 5 cm, (iii) Example 7; (a) Steel cord in each layer; Cutting strength 800 k
gf / piece, cutting elongation 2.0 (%), (a) number of cross windings of ring 7r 3 times, number of driving 12 pieces / 5 cm. Hoop 7
The half width of was set to 150 mm in each example.

Regarding the radius of curvature of the crown; (i) Examples 1, 2, 3 and 5, 6, 7; center side Rc is 3000 mm, both edge side Rs is 1000 mm, (ii) Example 4; center side Rc is 3000 mm, One edge Rs
Is 1000 mm and the other edge Rs is 1500 mm.

Applicable tread patterns: (i) Examples 1, 3, 4, 5 and 7; rib rug patterns shown in FIG. 3, (ii) Examples 2 and 6; rug patterns shown in FIG. In FIG. 3, w represents the width direction length from the groove edge closest to the center among the groove edges of the circular zigzag main groove Gc to the central peripheral line (E) of the tread 3-1 and this length w is 1
It was set to 60 mm.

For each of the above-described embodiments, an annular belt according to conventional practice is provided, and a single crown radius of curvature 3
Examples 1, 3 and 5 except having a tread of 000 mm
The tires of Comparative Examples 1, 2 and 3 in accordance with the above were prepared, and the tires of each Example were subjected to a comparative evaluation test for the separation resistance of the belt 6 and the hoop 7 and the uneven wear resistance of the tread 3-1. .

In the evaluation test, the condition is set to tire load 100.
%, Speed 10 km / h, additional torque 7.5 ton meter Long run by drum. At the same time, in order to compare with uneven wear, the tire was pressed against a flat plate at 100% load and a footprint was sampled. Note that the experimental results described above were applied to the groove bottom wall crack of the orbiting main groove Gc.

The test results are shown in Table 1. In addition, B. SEP is belt separation,
H. SEP is a separation at the end of the hoop 7, R. D is the distance traveled before the separation occurred, I.D. W is uneven wear, and F.I. P represents a footprint. B. in the table. SE
P. H. The tires in which SEP has occurred are marked with a circle for each item, and R. D is shown as an index with Comparative Example 1 being 100. In addition, I. Regarding W, whether or not it occurred ◎, ○, ×
Marked with ⊚, marked uneven wear, ◯ indicates slight uneven wear, and × means no occurrence. In the item of P, FIG.
The shape of the footprint shown in (d) is described as a to d in correspondence with the reference numerals in parentheses.

[0050]

[Table 1]

All the tires from Table 1 to Examples 1 to 7 have markedly superior separation resistance to the tires of Comparative Examples 1, 2 and 3 equipped with conventional belts, and each Example It was found that the uneven wear of the tread surface 3-1 was suppressed in each of the tires, and thus the running life of the pneumatic radial tire can be significantly extended without using any special additional member. Is obvious. The slight uneven wear of Example 4 shown in Table 1 is a result of a drum test without a camber angle, and does not occur when used in a vehicle with a large camber angle.

[0052]

According to the present invention, the excellent separation resistance of the belt can be sufficiently exerted without the separation failure of the other reinforcing members in the tread portion, and the tread surface of the tread portion can be obtained. It is possible to provide a long-lived pneumatic radial tire for heavy vehicles, which can eliminate disadvantages such as uneven wear that were won.

[Brief description of drawings]

FIG. 1 is a left half sectional view of a pneumatic tire of the present invention.

FIG. 2 is a left half cross-sectional diagram of the main part of the pneumatic tire of the present invention.

FIG. 3 is a partial development view of a tread pattern used for the pneumatic tire of the present invention.

FIG. 4 is a partial development view of a tread pattern used for the pneumatic tire of the present invention.

FIG. 5 is a left half partial sectional view showing a relationship between a hoop end and a circulating main groove.

FIG. 6 is a diagram showing a shape of a footprint on a tread.

FIG. 7 is a line graph showing the relationship between strain in the groove bottom width direction and normal position.

[Explanation of symbols]

 3 Tread part 3-1 Tread 5 Carcass 6 Belt 7 Hoop L Normal

Claims (4)

[Claims] 1. A radial carcass consisting of a pair of beads, a sidewall and a tread, and a ply that reinforces these parts across bead cores embedded in the bead, and a tread part reinforced at the outer periphery of the carcass. A belt consisting of at least two steel cord crossing layers and a layer of substantially inextensible cord narrower than the width of the belt, which acts on the carcass in an arrangement along the carcass directly below the belt. In a pneumatic radial tire including at least one layer of hoops that opposes air pressure, the belt has an archery-shaped cross section that is concave in the central region of the width, and the hoop is separated from the hoop toward the width end. It has a gradually increasing shape, and the tread portion is closer to the edge than the normal line of the tread from the tread to the width end of the hoop. Te, also compared to the curvature at the center side, a pneumatic radial tire that is characterized with a tread surface having a larger curvature. 2. The hoop is composed of two layers of steel cords, and the cords in each layer intersect each other to form an inclined arrangement of 10 ° or less with respect to a plane including the center circumferential line of the tread. The pneumatic radial tire described in. 3. The air according to claim 1, wherein the hoop is a side-by-side arrangement in the width direction of a plurality of rings each made up of a bundle of steel cords wound several times in a cross winding manner. Radial tires with. 4. The tread portion has at least one orbiting main groove in a central region near the centerline of the tread, and the orbiting main groove is separated from a tread normal passing through the width end of the hoop. The pneumatic radial tire according to claim 1, 2 or 3, wherein the pneumatic radial tire has a wall.