JP2000185517A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a belt, which is provided in a prescribed arrangement on an inner periphery of a tread portion, to exhibit good cut resistance, improve breakage resistance of a cord, and at the same time enhance ease of recapping involved in peeling off a cord layer by forming three layers of cord in the belt and specifying an arrangement angle of the cord in each layer. SOLUTION: In a belt 6 provided in a prescribed arrangement to reinforce a tread portion 3 on an outer periphery of a tire carcass 5, three layers of rubber-coated cord layers 7 to 9 are provided. The innermost cord layer 7 and the middle cord layer 8 of all of these three layers are formed so that the cord crosses each other in such a way that the cord has a slant angle in the range between 10 and 25 degrees with respect to the equator plane of the tire is formed in. The outermost cord layer 9 is placed so that its cord is slant 45 to 115 degrees with respect to the equator plane as measured in the same direction as that used to measure the slant angle of the middle cord layer 8. The cord layer line drawn by connecting the center in thickness of the outermost cord layer 9 and the middle cord layer 8 on a tire cross-section is formed by either a curved line or a combined curve consisting of curved and straight lines.

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 heavy loads, and more particularly to a tire for use in heavy vehicles such as trucks and buses. The belt durability and cornering performance are maintained at a level equal to or higher than that of a conventional tire having a belt with a four-layer cord layer structure, and the cut resistance of the belt and the recap workability are also improved. And a heavy-duty pneumatic radial tire for heavy duty.

[0002]

2. Description of the Related Art A heavy-duty pneumatic radial tire used for heavy vehicles such as trucks and buses generally has a belt 20 of a tread portion 19 having four layers of rubber as shown in FIG. The cord of the first cord layer 21 which is constituted by the covering cord layers 21 to 24 and is located closest to the carcass 5 is relatively formed with respect to a plane including the circumference of the tread portion 19 (a plane parallel to the tire equatorial plane E). The cords of the second cord layer 22 and the third cord 23 are arranged at a large inclination angle, and the cords of the second cord layer 22 and the third cord 23 intersect with the plane interposed therebetween. Nominally, the cords of the cross layer 25 are arranged at a smaller inclination angle with respect to the plane, and the cords of the fourth code layer 21 are arranged in the same direction as the cords of the third code layer 23, and the inclination angle is also set. Substantially the same city as the code of the third cord layer 23, although a more narrow. Note that a steel cord is applied to the cords of the cord layers 21 to 24 of the belt 20, and the same applies hereinafter.

When a tire provided with the belt 20 rolls under a load on a road surface on which foreign matters such as pebbles and metal pieces are scattered, a tread portion 19 which happens to be stepped on a sharp corner edge of the pebbles and metal pieces and the like. May often receive cuts that reach the belt 20. For this reason, the fourth cord layer 2 is arranged so that the damage of the belt 20 by the cut is stopped by the fourth cord layer 24 of the outermost cord layer, with the aim of preventing the belt 20 from being fatally damaged by the cut.
A configuration in which the main role of No. 4 is a protective layer has been proposed.

[0004] On the other hand, as with pneumatic radial tires for passenger cars, demands for weight reduction of pneumatic radial tires for heavy loads have increased, so that the belt 20 occupying a large proportion of the tire weight has a four-layer cord. 3 from layer
It has been proposed to be a layer code layer. The three-layer cord layer belt 20A (see the dashed line in FIG. 6) arranges the cords of the first cord layer 21 closest to the carcass at a relatively large inclination angle with respect to the plane described above, and forms the second cord layer. The code cross layer 22 and the third code layer 23 (see the broken line in FIG. 6) are the above-mentioned code cross layers, and the codes of the respective code cross layers are arranged at a relatively small inclination angle with respect to the above-mentioned plane.

[0005] With respect to a tire having the structure of this type of three-layer belt 20A, for example, in the tire disclosed in Japanese Patent Application Laid-Open No. Hei 7-186613, the belt 20A is constituted by three breakers (referring to the above-mentioned cord layer). And, based on the finding that the third breaker, which is counted from the carcass, has the least strength, the third breaker has a higher power per unit width than the first and second breakers. It is. It says that when the tread of the tire rides on foreign matter such as crushed stone or small rock, it can stop at most the break of the cord of the third breaker, and can effectively prevent catastrophic failure such as burst at low cost. .

[0006]

However, as a result of actually verifying the tire disclosed in the above-mentioned publication, the belt 20A of this tire has a second cord layer 22 and a third cord layer 23.
Is a crossed cord layer, and the crossing angle between the cords of these layers 22 and 23 is relatively small, so that when the tire is filled with a predetermined internal pressure, the cords of the layers 22 and 23 of the second and third cord layers are formed. A large tension acts on the third cord layer 23, and even if the cord strength per unit width of the third cord layer 23 (specifically, tensile strength, the same applies hereinafter) is increased, the cord may be cut by foreign matter such as pebbles or metal fragments. It turned out that it cannot fully suppress. The reason for this is that a cord under a large tension has a significantly reduced remaining force against the cut input.

FIG. 6 is a schematic view showing a part of the front of a tire rolling under a load (the belt is shown by three cord layers 21 to 23). When the belt 20A rides on a projecting foreign matter 31 such as a stone or a piece of metal present on the road surface 30 to some extent, the bending force in the direction of the arrow 32 acts on the belt 20A, so that the cord of the outermost cord layer 23 is locally localized. The buckling phenomenon is apt to occur, and if this buckling occurs repeatedly, the cord will be fatigued and the cord will be broken. If the tire continues running in this state, the other cord layer 2 of the belt 20A will be damaged.
2, 21 will be damaged, eventually leading to a separation failure of the belt 20A, making the tire unusable.

On the other hand, especially for heavy duty pneumatic radial tires used for heavy vehicles such as trucks and buses, repeated recaps are required to be implemented in order to reduce the cost of users and respond to demands for resource saving. In general, tires suitable for recapping include belts 20, 20.
It is required that A has no fatal cuts or cord breakage, and that there is no large separation failure around the belts 20 and 20A.

Further, in the conventional tire shown in FIG. 5, the first cord layer having cords having a relatively large inclination angle arrangement is the innermost cord layer, and each of the cord cross layers 25 and the fourth cord layer. 21. Since the inclination angle of each cord with respect to the equatorial plane E is small, when the vulcanization molding is performed on the unvulcanized tire, when the rib tip of the mold bites into the unvulcanized tread rubber of the tread portion of the unvulcanized tire. The bending stiffness of the unvulcanized cord layer laminate is small, and the bending resistance of the laminate is not sufficient with respect to the entry of the die rib tip. As a result, when a product tire is obtained, as shown in FIG. The portion of the belt 20 immediately below the circumferential groove 26 has a concave shape on the outside of the tire. The concave-shaped cord layers 24 and 23 have a problem that they are difficult to peel off at the time of recapping, and significantly impair the recapping workability.

In particular, the belt 2 having a three-layer code layer structure
In the case of 0A, since the number of belt layers is one less than the belt 20 of the conventional tire shown in FIG. 5, the bending resistance (rigidity) as a laminate is smaller than that of the conventional tire.
The degree of the concave shape of No. 3 is larger than that of the conventional tire. As a result, the number of belt layers is small, the number of belt layers is small, the cut is as small as possible, the cord is hardly broken, and the separation at the end of the belt 20A is within a slight crack. That
Further, improvement of the recap workability is required. However, at present, the tires provided with the belt 20A having the three-layer cord layer do not satisfy these requirements.

Therefore, according to the invention described in claims 1 to 3, the belt is composed of three cord layers to maintain the weight reduction and to improve various properties such as separation resistance and cornering performance of the belt by four. With a level equal to or higher than that of the conventional tire having the belt of the cord layer of the layer, the tread portion has the same or higher cut resistance as the conventional tire of the four-layer belt, and has the resistance of the outermost cord layer cord of the belt. A lightweight heavy-duty pneumatic radial tire with improved fatigue resistance, improved breakage resistance of cords, improved recapping workability for peeling off the cord layer, long life, and excellent recapping workability. The purpose is to provide.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, a pair of sidewall portions and a tread portion are formed between bead cores embedded in a pair of bead portions. A carcass that becomes one or more plies of rubber-coated radial array cords to be reinforced; and a belt that strengthens the tread portion around the perimeter of the carcass. The belt has three rubber-coated cord layers. The inner cord layer and the intermediate cord layer form a cord crossing layer, and the tread portion has at least two circumferential grooves at least in a central region. Each of the cords has an inclination angle in the range of 10 to 25 ° with respect to a plane including the tread portion circumference, and the cord of the outermost cord layer has a middle angle. The cord layer cord has an inclination angle in the range of 45 to 115 ° with respect to the plane measured in the same direction as the direction in which the inclination angle of the cord from the plane is measured. The code layer line connecting each thickness center is composed of at least one of a curve and a composite curve of a curve and a straight line for at least the outermost code layer, and the pair of bead portion outer widths is adjusted to the applicable rim width. In the tire cross section, the maximum distance between an extension of a line bisecting the groove width of each of the circumferential grooves adjacent to each other, a line connecting two intersections with the code layer line, and the code layer line is 1 It is a pneumatic radial tire for heavy loads characterized by being not more than 0.0 mm.

Here, the above-mentioned cord crossing layer refers to a laminated structure in which two adjacent cords are arranged in different directions (rightward and leftward) with respect to the tire equatorial plane. The central region of the tread portion refers to a region where the tread width of the tread portion is divided into four equal parts, and a quarter of the width is distributed to both sides of the tire equatorial plane. 1/4 on both sides of central area
The area of the tread width is called a both-side area.

According to the above definition, "providing at least two circumferential grooves in at least the central region" according to claim 1 means that the central region has at least two circumferential grooves, This includes both the case where at least one circumferential groove is provided in each of both side regions.

[0015] The application rim described in claim 1 is a standard rim (or "Approved Rim", "Recommended Rim") in an application size described in the following standard. The standard is determined by an industrial standard effective in an area where the tire is manufactured or used. For example,
In the United States, "The Tire and Rim Association In
c. "Year Book" and in Europe, "The European Tire
and Rim TechnicalOrganization "Standards Manua
l "in Japan and the Japan Automobile Tire Association's" JATMA Yea
r Book ".

[0016] In the tire according to the first aspect of the present invention, the code layer line has a center of curvature inside the tire radial direction over the entire width of the outermost code layer. . When the code layer line is a composite curve, it is represented by the center of curvature of the curve.

The constituent element described in claim 1 that "the maximum distance between a line segment connecting two intersections and the code layer line is 1.0 mm or less" and the "code layer line described in claim 2" Has a center of curvature inside the tire radial direction "can be realized by the configuration of the inclination angle of the cord of each cord layer of the belt. Furthermore, when manufacturing an unvulcanized tire, applying an unvulcanized tread rubber in which a groove is formed in advance at a position where a mold rib for forming a circumferential groove is applied by vulcanization molding, The value of the ratio of the outer circumference of the belt member to the outer circumference of the vulcanized tire is as close to 1 as possible, and the number of cords of each cord layer of the vulcanized tire is 18/50 m.
When the number is m or more, the above configuration becomes more reliable.

In order to improve the buckling fatigue resistance of the outermost cord layer cord, the cord covering rubber of the outermost cord layer has a compression elastic modulus of 200 kgf / cm ² or more. It is suitable to have.

Here, a value calculated according to the method described below is used as the above-mentioned compression modulus. That is, as shown in FIG. 7, the diameter d is 14 mm, and the height h is 28 mm.
A rubber test piece 34 is filled in the hollow portion of a jig 33 made of metal, for example, steel having a cylindrical hollow portion without any gap,
As shown in FIG. 8, this jig 33 is set on a compression tester 35, and the speed of the rubber test piece 34 is set to 0.6 m with respect to the upper and lower surfaces thereof.
A load w is applied at m / min.
Is measured by the laser displacement meter 36, and the compression elastic modulus is calculated from the relationship between the load w and the displacement.

As the ply cord of the carcass and the cord of each layer of the belt, a steel cord is suitable.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view of a heavy-load pneumatic radial tire according to the present invention, taken along a plane including a rotation axis. FIG. 2 is a developed view of a belt obtained by cutting a tread rubber of the tire shown in FIG. 1 and performing a step-down cut. FIG. 3 is an enlarged cross-sectional view of a main portion of a tread central portion of the tire shown in FIG. 1, and FIG. 4 is a main portion of a tread central portion of the tire shown in FIG. It is an expanded sectional view.

Referring to FIG. 1, a heavy-duty pneumatic radial tire (hereinafter referred to as a tire) has a pair of bead portions 1 and a pair of sidewall portions 2, and a tread portion 3 connected to both sidewall portions 2. The tire 1 has one or more plies for reinforcing the pair of bead portions 1, the pair of sidewall portions 2 and the tread portion 3 between the bead cores 4 embedded in the pair of bead portions 1. A carcass 5 of a radially arranged steel cord (hereinafter referred to as a cord) and a tread portion 3 around the outer periphery of the carcass 5
And a belt 6 for strengthening.

The belt 6 is composed of three rubber-coated steel cord layers (hereinafter referred to as cord layers) 7, 8, and 9, and the innermost cord layer 7 and the intermediate cord layer 8 form a cord crossing layer 10. The tire has a tread rubber 11 on the tread portion 3 on the outer peripheral side of the outermost cord layer 9, and the tread portion 3 forms at least two pairs extending in the circumferential direction of the tread portion 3.
The tread portion 3 in the illustrated example has two circumferential grooves at least in the tread rubber 11 in the central region Rc.
One circumferential groove 15 (hereinafter referred to as a circumferential central groove 15) is provided in the central region Rc, and one circumferential groove 16 (hereinafter referred to as a circumferential shoulder groove 16) is provided in each region of the both side regions Rs.

The central region Rc is the tread surface 3t of the tread portion 3.
幅 of the width W, ie, (１ ／) × W (hereinafter 1 / W)
4W) are distributed to both sides of the tire equatorial plane E, and the both side regions Rs are each a 1/4 W width region. In the case where the end of the tread portion 3 is a round shoulder, the distance between the intersections of the extension line of the tread surface 3t and the extension line of the buttress is defined as the width W as shown in the figure. In the illustrated example, the circumferential central groove 15 and the circumferential shoulder groove 16 are straight grooves, see-through straight grooves with ingress and egress, and have a large radius of curvature, and the center of the radius alternates in and out of the tread surface 3t width direction with the groove interposed therebetween. A curved groove having arcs at both edges of the groove and a zigzag groove having a relatively small swing width are suitable.

In FIG. 2, the code 7a of the innermost code layer 7 closest to the carcass 5 and the code 8a of the intermediate code layer 8
“a” is a plane including the circumference of the tread portion 3, and in FIGS. The inclination angles α and β between the code 7a of the innermost code layer 7 and the code 8a of the intermediate code layer 8 with respect to the equatorial plane E are in the range of 10 to 25 °, preferably in the range of 15 to 22 °. The measurement direction of the inclination angle α of the code 7a with respect to the equatorial plane E is indicated by an arrow, and the measurement direction of the inclination angle β of the code 8a with respect to the equatorial plane E is indicated by an arrow. The measurement direction of the inclination angle α and the measurement direction of β are opposite to each other with respect to the equatorial plane E.

As shown in FIG. 2, the code 9a of the outermost code layer 9 has the same direction as the direction in which the inclination angle β of the code 8a of the intermediate code layer 8 from the equatorial plane E is measured (the direction of the arrow in the figure) ( (The direction of the arrow in the figure)
It has an inclination angle γ in the range of 15 °, preferably in the range of 50 to 100 °.

In FIGS. 3 and 4, at least the outermost code layer 9 (only the innermost code layer 9) of the intermediate code layer 8 and the innermost code layer 9 is located at the center of the thickness of the outermost code layer 9. cord layer line C ₉ to contiguous with shall consist composite curve of curve and curves and straight lines. Figures 3 and 4
Cord layer line C ₉ shown in is an example of a curve, this curve is a circular arc having a radius of curvature R _9. The cord layer line C ₉ has a center O of a radius of curvature inside the tire over the entire width of the outermost cord layer 9.

The intermediate code layer 8 may have the same code layer line C ₈ (not shown) as described above. Further, although not shown, in the case of a code layer line C ₉ (including a line C ₈ ) composed of a composite curve of a curve and a straight line,
The straight part is the circumferential central groove 15 and the circumferential shoulder groove 16
It is located directly below.

Here, as shown in FIG. 1, a tire section in which the outer width M of the bead portion 1 of the tire is adjusted to the width of the applicable rim (according to the above description) of the tire is shown in FIG.
Lines Vc ₁ and Vc that bisect the groove width of circumferential center groove 15
_2, a line segment L ₁₂ connecting the two intersection points P _1, P ₂ of the cord layer line C ₉ is present in the tire inside the cord layer line C ₉ or matches, a line segment L _12, cord layer Line C
The maximum distance d ₁₂ between ₉ 1.0 mm or less, preferably is 0.7mm or less. Straight F indicating the maximum distance d ₁₂
Position substantially coincides with an intermediate position between the pair of circumferential central grooves 15.

Similarly, in FIG. 4, the tread portion 3
Also in the case of a tire having a pair of circumferential central grooves 15 and a circumferential shoulder groove 16, the intersection P of the line Vc ₃ bisecting the groove width of the circumferential shoulder groove 16 and the code layer line C ₉ is also used.
_3, the line segment L ₁₃ code layer line C ₉ connecting the intersection point P ₁
The line segment L exists or coincides with the inner side of the tire.
₁₃ and the code layer line C ₉ have a maximum distance d ₁₃ of 1.
0 mm or less, desirably 0.7 mm or less. Position of the straight line F showing this maximum distance d ₁₃ coincides substantially intermediate position between the circumferential center grooves 15 and the circumferential shoulder groove 16.

If the maximum distance d exceeds 1.0 mm, especially if it exceeds 0.7 mm, the workability of peeling off the innermost cord layer 9 at the time of recapping is deteriorated, which is not possible. The lower limit of the maximum distance d is zero. Although the radius of curvature R ₉ code layer line C ₉ is shown only one, there may be a plurality not always one. The same applies to the intermediate code layer 8 described above.

The inclination angles α and β of the cord 7a of the innermost code layer 7 and the cord 8a of the intermediate code layer 8 with respect to the equatorial plane E are within the range of 10 to 25 °, preferably 15 to 2 °.
On the other hand, the code 9a of the outermost code layer 9 is measured in the same direction as the direction in which the inclination angle β of the code 8a of the intermediate code layer 8 from the equatorial plane E is measured.
In the range of 45 to 115 °, preferably 50 to
By setting the inclination angle γ within the range of 0 °, as shown in FIG. 2, the circumferential tension Fx of the tread portion 3 generated on the belt 6 when the tire is filled with the internal pressure becomes the inclination angle with respect to the equatorial plane E. Form the small code cross layer 10, the codes 7a and 8a of the innermost code layer 7 and the intermediate code layer 8
Mainly bear, and the tension to be borne by the outermost cord layer 9 can be greatly reduced.

Thus, when the tread portion 3 of the tire rolling under a load is riding on a foreign matter such as a pebble or a metal piece having a sharp corner, the corner of the foreign matter penetrates the tread rubber 11. And reach belt 6,
Since the outermost cord layer 9 has a small tension load on the cord 9a and therefore has a sufficient spare force against cutting,
The cord 9a is hard to be cut, and as a result, the ability to stop the entry of the corner of the foreign matter by the outermost cord layer 9 is significantly increased, and the cord 8a of the intermediate cord layer 8 hardly breaks, and the tire relating to cut resistance is hardly cut. Durability is improved.

Referring to FIG. 2, the belt 6 has a tendency to project outward in the radial direction of the tire due to the tension Fx generated on the belt 6 when the tire is filled with the internal pressure. The cords 7a, 8a, and 9 of the layers 7, 8, and 9 of the belt 6 contract inward in the width direction indicated by the arrows.
a tends to change in a direction in which the inclination angles α, β, and γ decrease. However, under the configuration of the belt 6, the cord 9a of the outermost cord layer 9 has the inclination angle γ of the cords 7a, 8 of the innermost cord layer 7 and the intermediate cord layer 8, respectively.
Since the inclination angle a is extremely large as compared with the inclination angle a, the degree of decrease in the inclination angle is extremely small as compared with the cords 7a and 8a. As a result, the outermost cord layer 9 tends to hardly shrink in the width direction.

This does not mean that the outermost code layer 9 acts to suppress the contraction of the code cross layer 10 in the width direction, because the code 9a of the outermost code layer 9 is This is because it has an effect like a stick. The cord crossing layer 10 in which the shrinkage in the width direction is suppressed has increased circumferential rigidity of the tread portion 2, and as a result, the cornering power (hereinafter referred to as CP) is improved even in a tire with the belt 6 having the three-layer structure. Of 4
Cornering performance equal to or higher than that of a tire including a belt having a layer configuration can be exhibited. Further code cross layer 1
The increase in the circumferential rigidity of 0 suppresses the radial growth of the tire when the tire is filled with the internal pressure, and this suppression greatly contributes to improving the separation resistance of the end of the belt 6, particularly the end of the cord crossing layer 10.

The inclination angles α and β of the cords 7a and 8a of the innermost code layer 7 and the intermediate code layer 8 with respect to the equatorial plane E are substantially equal to each other.
This is preferable in that the tension is evenly distributed. Code 7
The reason why the inclination angles α and β of the a and 8a are in the range of 10 to 25 ° is that when the inclination angles α and β are less than 10 °, the interlayer shear generated at the end between the innermost cord layer 7 and the intermediate cord layer 8 is formed. When the strain becomes too large and a separation failure is likely to occur at this end, when the inclination angles α and β exceed 25 °, the width of the outermost cord layer 9 due to the tension Fx acting on the belt 6 in the tire filled with the internal pressure. This is because the effect of suppressing the directional shrinkage cannot be sufficiently exerted, and the circumferential rigidity of the cord cross layer 10 is remarkably reduced, resulting in deterioration of CP characteristics, increase in tire diameter growth, and reduction in separation resistance. .

Regarding the above-mentioned CP characteristics, FIG.
And a conventional four-layer cord layer 21 shown in FIG.
As shown in the comparison diagram of the CP (index) with the tire including the belt 20 having the configuration
When the inclination angle γ of the code 9a is variously changed, the CP equal to or higher than the index indicated by an index with the CP of the conventional tire being 100
It can be seen that the inclination angle γ indicating the index is within an appropriate range, and the appropriate inclination angle γ is within the range of 45 to 115 °.
If the inclination angle γ is less than 45 ° or more than 115 °, the CP characteristic is lower than that of the conventional tire, so that it is impossible. From this, the code 9a of the outermost code layer 9 is
It plays the role of a sticking rod in the width direction contraction of 0, thereby enhancing the circumferential rigidity of the cord cross layer 10.

The code layer line C of the outermost code layer 9
₉ (see FIGS. 3 and 4), including the case of cord layer line C ₈ of the intermediate cord layer 8, either one city composite curve of curve and the curve and the straight line, this curve or compound curve, the outermost cord layer 9, the center O of the radius of curvature inside the tire
By setting at least the cross-sectional shape of the outermost cord layer 9 so that the outermost cord layer 9 is cut and damaged, it is extremely easy to peel off the outermost cord layer 9 that has been cut and damaged during the recapping operation after using the tire. Significantly improved.

The configuration of the above-described code layer lines C ₉ and C ₈ is such that the inclination angle γ of the code 9a of the outermost code layer 9 is 45 to 45.
This can be achieved by being within the range of 115 °. This is because, in the vulcanization molding of the unvulcanized tire, under the action of the high-pressure gas filled inside the unvulcanized tire, the rib tips of the molds forming the circumferential grooves 15 and 16 form the unvulcanized tire. When biting into the unvulcanized tread rubber in the tread,
The unvulcanized cord layer 9u to be the outermost cord layer 9 (not shown)
This is because the cord inclination angle is an angle close to the range of 45 to 115 °, so that the bending rigidity in the width direction increases, and the bending resistance of the laminate to the entry of the die rib tip increases. is there.

Further, at the time of manufacturing an unvulcanized tire, a groove is previously formed at a position where a mold rib for forming the circumferential central groove 15 and the circumferential shoulder groove 16 is formed by vulcanization molding. By applying the vulcanized tread rubber to the unvulcanized tire and reducing the pressing force of the mold ribs on the unvulcanized cord layers 7u, 8u, 9u serving as the belt 6, the same applies to the production of the unvulcanized tire. The value of the ratio of the outer periphery (outer diameter) of the unvulcanized cord layer 9u of the unvulcanized tire to the outer periphery (outer diameter) of the outermost cord layer 9 of the vulcanized tire is as close as possible to 1, and the vulcanization molding is performed. By minimizing the change in the circumferential length of the unvulcanized cord layer 9u in the above, the configuration of the cord layer lines C ₉ and C ₈ can be made even more sufficient. In addition, the number of cords inserted into each cord layer of the belt 6 is 18/50 mm.
As described above, the dense arrangement of the codes in each layer also contributes.

It is suitable that the covering rubber 9b of the cord 9a of the outermost cord layer 9 has a compression modulus of 200 kgf / cm ² or more. This compression modulus is a value obtained according to the test method described above. The effect of the compression modulus of 200 kgf / cm ² or more will be described below.

That is, when the tire rolls on a road surface on which a relatively large foreign matter such as a stone or a metal piece exists and rides on the large foreign matter, as described above with reference to FIG. As a result of the outer cord layer 9 being subjected to bending deformation with a large curvature, a large compressive force acts locally,
Where buckling occurs in the cord 9a of the outermost cord layer 9,
The covering rubber 9b of the cord 9a of the outermost cord layer 9 has 200
By applying a rubber having a compression modulus of not less than kgf / cm ^2, the compression resistance of the covering rubber 9b can be increased, and the buckling deformation of the cord 9a of the outermost cord layer 9 can be prevented. As a result, even if the tire often rides on a relatively large foreign matter, it is possible to prevent cord breakage due to buckling fatigue of the cord 9a of the outermost cord layer 9. If the compression modulus is less than 200 kgf / cm ² , this effect is insufficient and the composition is not suitable.

Further, since the unvulcanized rubber having a compression modulus of 200 kgf / cm ² or more has a high minimum Mooney viscosity, when vulcanizing an unvulcanized tire, the belt 6 formed by a mold rib is used. To improve the bending rigidity of the uncured cord layer laminate.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire for trucks and buses having a size of 11R22.5 and having a tread portion 3 having a pair of circumferential central grooves 15 according to the structure shown in FIGS.
, And a pair of circumferential shoulder grooves 16, and the belt 5 includes three innermost cord layers 7, intermediate cord layers 8, and outermost cord layers 9. The code intersection layer 10 is formed.

The codes 7a, 8a of the code layers 7, 8, 9
9a is a steel cord of 1 × 0.34 + 6 × 0.34, and the number of cords is 18.0 / 50 mm. The steel cord covering rubber of the innermost cord layer 7 and the intermediate cord layer 8 is The compression modulus is 170 kgf / cm ² .

The belt 6 in the tires of Examples 1 to 4
Code inclination angles α (°), β of the respective code layers 7, 8, 9
(°), the maximum distance between the gamma (°), shows the compressive modulus of the steel cord coating rubber 9b of the outermost cord layer 9 in Table 1 and the line segment L ₁₂ and code layer line C ₉ d ₁₂ (m
m) and the maximum distance d ₁₃ (mm) between the line segment L ₁₃ and the code layer line C ₉ are measured. In Table 1, the cord inclination angles α (°), β
(°) and γ (°) are denoted by reference numerals 1B,
2B, 3B, and 4B (4B is not present in Examples and Comparative Examples) are shown as the cord inclination angles of the cord layers. A code R preceding the numerical value of the inclination angle indicates an arrangement in which the codes rise to the right, and a code L indicates an arrangement in which the codes rise to the left.

The carcass 5 has one ply, and this one ply is a rubber coating of a (3 + 9 + 15) × 0.175 steel cord in a radial arrangement. At the same time as preparing the tires of Examples 1 to 4 having the above configuration, in order to evaluate the cut resistance, the cord breakage resistance, and the recap workability of these example tires, except for the belt configuration, all other examples were used. The tires of Conventional Examples 1 to 4 shown in FIG. 5 and the tires of Comparative Examples 1 to 3 according to the tires were manufactured together, and the contents of all the tires are described in Table 1.

[0048]

[Table 1]

Using the tires of Examples 1 to 4, the conventional tires and the tires of Comparative Examples 1 to 4 as test tires, each tire was mounted on a truck for each tire type, and the tire was actually run 50,000 km on a rough road. After that, remove each tire and scrape off the remaining tread rubber, expose the outermost cord layer of the belt, peel off the outermost cord layer, first evaluate the stripping workability, then remove the outermost cord The cut flaws of the layer and the broken state of the cord were examined, and the presence or absence of cut flaws on the intermediate cord layer was also observed. In particular, the stripping workability, which is a problem, is evaluated based on the evaluation of the difficulty of stripping and the adverse effect on the intermediate cord layer, and is represented by an index with the conventional tire being 100. Table 1 shows the scoring index. The larger the value, the better.

From the results shown in Table 1, it can be seen that (1) the tires of Examples 1 to 4 show the cut resistance of the belt 6 and the outer cord layer 9 in comparison with the tires of the conventional example and the tires of Comparative Examples 1 and 2. Example 2 that the cord had excellent breakage resistance and cord layer peeling workability, and (2) Example 1 was compared with the tire of Comparative Example 3.
Tires of Nos. 1-4 are excellent in cord breakage resistance and peeling workability. (3) Tires of Examples 1-4 are remarkably excellent in peeling workability in comparison with the tire of Comparative Example 4. You can see that. In summary, the tires of Examples 1 to 4 are tires having not only excellent bad road durability but also excellent recapability including workability.

[0051]

According to the invention described in claims 1 to 3 of the present invention, various properties such as separation resistance, cornering performance and cut resistance of the belt are equal to or higher than those of a conventional tire having a four-layered cord layer. , And the belt is composed of three cord layers to meet the demand for weight reduction.
It is possible to provide a pneumatic radial tire for heavy loads having recap workability significantly superior to conventional tires.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a pneumatic radial tire for heavy loads according to the present invention.

FIG. 2 is a development view of a belt subjected to a step-down cut with the tire shown in FIG.

FIG. 3 is an enlarged sectional view of a main part of a central region of a tread portion of the tire shown in FIG. 1;

FIG. 4 is an enlarged sectional view of a main part of a central region of a tread portion and one of both side regions of the tire shown in FIG. 1;

FIG. 5 is a left half sectional view of a main part of a conventional tire.

FIG. 6 is an explanatory diagram of a tire belt deformed state when riding on a large foreign object.

FIG. 7 is a perspective view of a jig for measuring compression elastic modulus of rubber according to the present invention.

FIG. 8 is a front view of a compression tester equipped with the jig shown in FIG.

FIG. 9 is a diagram showing a relationship between a code inclination angle of an outermost code layer and CP according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 3t Tread part tread surface 4 Bead core 5 Carcass 6 Belt 7 Inner code layer 7a Code of inner code layer 8 Intermediate code layer 8a Code of intermediate code layer 9 Outer code layer 9a Outer Cord of cord layer 9b Cord covering rubber of outermost cord layer 10 Cord crossing layer 11 Tread rubber 15 Circumferential center groove 16 Circumferential shoulder groove E Tire equatorial plane W Tread width M Applicable rim width Rc Tread central area Rs Tread Side area α, β Inclination angle of cord crossing layer cord γ Cord inclination angle of outermost cord layer C ₉ Thickness center line of outermost cord layer Vc ₁ , Vc ₂ Circumferential center groove width bisecting line Vc ₃ Circumferential shoulder groove bisecting Intersection point between line P ₁ , P ₂ bisector Vc ₁ , Vc ₂ and center line C ₉ P ₃ Intersection point between bisector Vc ₁ and center line C ₉ L ₁₂ intersection Maximum distance d ₁₃ line L ₁₃ and the thickness center of the P ₁ and the intersection P ₂ and line segment d ₁₂ line L ₁₂ and the thickness center line C ₉ connecting the line segment L ₁₃ intersection P ₁ and the intersection P ₃ connecting Maximum distance from line C ₉ Fx tension

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B60C 11/04 B60C 11/06 A

Claims (3)

[Claims] 1. A carcass having one or more plies of a rubber-coated radial array cord for reinforcing a pair of sidewall portions and a tread portion between bead cores respectively embedded in a pair of bead portions, and a tread portion at an outer periphery of the carcass. A belt to be reinforced, the belt having three rubber-coated cord layers, of which the innermost cord layer and the intermediate cord layer form a cord crossing layer, and the tread portion has at least two cord layers. In a heavy-duty pneumatic radial tire having at least the central groove in the central region, the cords of the innermost cord layer and the intermediate cord layer have an inclination in a range of 10 to 25 ° with respect to a plane including the tread portion circumference. The cord of the outermost code layer is measured in the same direction as the direction in which the angle of inclination of the intermediate code layer cord from the plane is measured, and the above-mentioned flat code layer is used. In the tire cross section, the code layer line connecting the thickness center of each of the outermost code layer and the intermediate code layer has a curve and a curve for at least the outermost code layer. The extension of the line that bisects the groove width of each adjacent circumferential groove in the tire cross-section with the pair of bead part outer widths adjusted to the applicable rim width A pneumatic radial tire for heavy loads, wherein a maximum distance between a line connecting a line and two intersections of the code layer line and the code layer line is 1.0 mm or less. 2. The tire according to claim 1, wherein the cord layer line has a center of curvature inside the tire radial direction over the entire width of the outermost cord layer. 3. The cord covering rubber of the outermost cord layer is 20
^{3. The} tire according to claim 1, having a compression modulus of 0 kgf / cm ² or more.