JPH11227414A - Pneumatic radial tire for construction vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire improved in resistance to edge separation of belt layers without causing center wear or chipping of a tread. SOLUTION: In this radial tire, spiral belt reinforcing layers 6, each of which is formed into a flattened cylindrical shape by spirally and continuously wrapping reinforcing cords at cord-angles of 10 to 30 degrees to the circumferential direction of the tire, are arranged on both end arears of belt layers 5 of bias structure consisting of at least three layers which intersect each other between layers at cord-angles of 20 to 30 degrees to the tire-circumferential direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for a construction vehicle that travels in rough terrain under severe conditions, and more particularly, to reduce the center wear and chipping of a tread while reducing the edge resistance of a belt layer. The present invention relates to a pneumatic radial tire for construction vehicles that improves separation.

[0002]

2. Description of the Related Art A pneumatic radial tire has a structure in which a belt layer having high rigidity is arranged between a tread and a carcass, and the arrangement of the belt layer exerts excellent wear resistance and low rolling resistance. It has the following features. However, in the case of a pneumatic radial tire for a construction vehicle that travels at high speed on a rough terrain under a high load, the deformation due to the high load and the uneven deformation of the rough terrain surface are repeated during the rolling of the tire. There is a problem that stress is concentrated on both ends and edge separation easily occurs. This tendency of edge separation was particularly noticeable in tires for flat large construction vehicles having a flatness of 85% or less.

Conventionally, as a countermeasure against such a problem, JP-A-61-157403 and JP-A-2-28002 disclose a steel cord arranged on the outer periphery of a carcass 23 as shown in FIG. As the belt layer 24, the form before the tire is filled with air pressure is concave outward in the tire radial direction, and the strain at the end of the belt layer is reduced by reducing the tension at the end of the belt layer when air pressure is applied. In addition, there has been proposed a device having improved edge separation resistance.

[0004] However, in the tire in which the belt layer before the pneumatic charging is formed concave in the tire radially outward direction, the contact pressure in the center region of the crown when the tire is driven with the pneumatic pressure becomes high, so that the tread There has been a problem that center wear and tread chipping and cutting are likely to occur.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic radial tire for a construction vehicle which improves edge separation of a belt layer without causing center wear or chipping of a tread.

[0006]

The pneumatic radial tire for a construction vehicle according to the present invention, which achieves the above object, has a cord angle between the carcass layer and the tread of 15 to 30 degrees with respect to the tire circumferential direction, and At least three belt layers having a bias structure intersecting each other between the layers are arranged, and reinforcing cords are continuously spirally provided at both end regions of the belt layers at cord angles of 10 ° to 30 ° with respect to the tire circumferential direction. And a spiral belt reinforcing layer having a flat cylindrical cross section formed by winding the spiral belt reinforcing layer.

[0007] As described above, the spiral belt reinforcing layer is disposed so as to overlap the both end regions of the belt layer, and the spiral belt reinforcing layer bears the tension in both shoulder regions. And edge separation can be reduced. In addition, the spiral belt reinforcing layer itself has a configuration in which the reinforcing cord is folded back at the end and has no cut end, and therefore does not cause edge separation unlike the belt layer.

Further, since the above-mentioned edge separation is not obtained by making the belt layer concave like the conventional tire, the contact pressure at the center of the tread is not extremely increased, and the center wear of the tread and chipping / cutting are prevented. And so on. Further, the spiral belt reinforcing layers are arranged at both left and right ends, and the center area is hollowed out to reduce rigidity, so that the envelope property can be improved and the tread cut property can be improved.

[0009]

FIG. 1 is a longitudinal sectional view of a pneumatic radial tire for a construction vehicle according to an embodiment of the present invention.
Inside the tire, from the tread part 1 to the left and right bead parts 2, 2
The carcass layer 3 is provided so as to extend respectively, and both end portions thereof are turned around the bead cores 4 and 4 from the inside to the outside of the tire. As the carcass cords (reinforcement cords) of the carcass layer 3, high-strength and high-modulus cords such as steel cords and aromatic polyamide cords are used, and are arranged at approximately 90 ° with respect to the tire circumferential direction.

On the outer peripheral side of the carcass layer 3 in the tread portion 1, a belt layer 5 having at least three bias structures is provided.
A pair of left and right spiral belt reinforcing layers 6 each having a configuration described later, and a single auxiliary belt reinforcing layer 7 that covers the entire outermost side of the belt layer 5 are arranged in both end regions. The spiral belt reinforcing layer 6 is arranged so as to be sandwiched between the belt layer 5 and the carcass layer 3, and is arranged so that the central region is hollow. The auxiliary belt reinforcing layer 7 is wider than the belt layer 5 having the maximum width, and both ends of the auxiliary belt reinforcing layer 7 extend outside the ends of the belt layer 5.

The belt layer 5 having the above-mentioned bias structure has a structure in which high elastic modulus cords such as steel cords and aromatic polyamide fiber cords are arranged obliquely with respect to the tire circumferential direction, and cross each other between layers. I have.
Since these belt layers 5 are formed by cutting both ends, they have a structure having cut ends of the reinforcing cords at both ends.

The reinforcing cord of the belt layer 5 has a cord angle α with respect to the tire circumferential direction of 15 ° to 30 °, preferably in the range of 22 ° to 25 °. Cord angle α
Is smaller than 15 °, the lateral rigidity of the tread portion is reduced, and it is difficult to obtain stable steering stability. On the other hand, if it is larger than 25 °, the hoop effect in the tire circumferential direction is insufficient, and the durability is reduced.

The spiral belt reinforcing layer 6 is formed by forming a high elasticity cord such as a steel cord or an aromatic polyamide fiber cord at a cord angle β of 10 ° to 30 ° with respect to the tire circumferential direction.
And is formed into a cylindrical shape by continuously turning spirally, and the cylindrical shape is formed so as to be crushed flat. Therefore, the spiral belt reinforcing layer 6 has a substantially two-layer structure, and the reinforcing cords intersect each other between the upper and lower layers, and both ends are folded so that no cut ends are formed. .

The auxiliary belt reinforcing layer 7 is made of a steel cord having a higher elongation than the reinforcing cord used for the belt layer 5 and the spiral belt reinforcing layer 6, so that the rigidity in the tire circumferential direction is reduced. . Such high elongation can be easily obtained by adjusting the number of twists to be greater than that of the steel cord used for the belt layer 5 and the spiral belt reinforcing layer 6. It is preferable that the cord angle γ of the reinforcing cord of the auxiliary belt reinforcing layer 7 with respect to the tire circumferential direction is set in a range of 15 ° to 30 °.

As described above, the auxiliary belt reinforcing layer 7 disposed on the outermost side of the belt layer 5 is not necessarily required in the present invention. However, when the auxiliary belt reinforcing layer 7 is disposed, local damage to the tread due to rocks or the like is reduced. Thus, tread cut, damage to the belt layer, and the like can be reduced. In the pneumatic radial tire for a construction vehicle according to the present invention having the above-described configuration, the spiral belt reinforcing layer 6 is disposed at both ends of the belt layer 5, so that the tension in the shoulder region is shared, and the belt layer 5 acts to relatively reduce the tension at both end regions. By reducing the tension at the end of the belt layer as described above, the concentration of stress on both ends of the belt layer 5 is reduced, so that edge separation can be reduced. On the other hand, since the spiral belt reinforcing layer 6 itself does not have a cutting end at an end portion, stress concentration does not occur even if it is arranged in the shoulder region.

In order to reduce the stress concentration at both end regions of the belt layer 5 by sharing the tension of the spiral belt reinforcing layer 6, the shape of the belt layer 5 in the meridional cross section is curved outwardly convex like a normal tire. Anything should do.
Therefore, unlike the conventional tire in which the cross-sectional shape of the belt layer 5 when the air pressure is not filled is made concave outward, the contact pressure in the center region of the tread does not increase, and tread center wear, chipping, and cutting are prevented. Etc. do not occur.

Further, since the spiral belt reinforcing layer 6 is arranged at both end regions of the belt layer 5 and the central region is hollow, the belt rigidity in the central region where the spiral belt reinforcing layer 6 does not exist is low. Thus, the envelope property of the tire can be improved. In addition, the tread cutting property can be improved by improving the envelope property.

In the present invention, a steel cord or an organic fiber cord such as an aromatic polyamide cord is used as the reinforcing cord used for the spiral belt reinforcing layer 6 which performs the tension sharing function of the shoulder portion as described above. Can be used. When using steel cord, the tensile modulus of elasticity is 3000 kgf / mm ² or more,
Preferably, the wire diameter is 0.05 to 0.25 mm, and when an organic fiber cord is used, the tensile elastic modulus is 3
000kgf / mm ² or more, tensile strength 150kgf
/ Mm ² or more is preferable. As such an organic fiber cord, an aromatic polyamide fiber cord is excellent.

It is desirable that the spiral belt reinforcing layer 6 has a tensile elastic modulus in the tire circumferential direction larger than that of the belt layer 5. Therefore, as described above, the cord angle β of the spiral belt reinforcing layer 6 with respect to the tire circumferential direction is preferably 10 ° to 30 °, and is preferably smaller than the cord angle α of the belt layer 5. If the cord angle β is more than 30 °, the tensile elastic modulus of the spiral belt reinforcing layer 6 may be lower than that of the belt layer 5, and if it is less than 10 °, the lift (green tire It is not preferable because it is difficult to expand the diameter toward the inner surface of the mold.

In the illustrated embodiment, the spiral belt reinforcing layers 6 are arranged in two rows on one side of the belt layer 5. However, the number of rows is not particularly limited, and may be only one row or two or more rows depending on the size of the reinforcing layer width. Further, in the illustrated embodiment, the spiral belt reinforcing layer 6 is arranged between the carcass layer 3 and the belt layer 5, but the position is arranged on the outer peripheral side of the belt layer 5 for the above purpose. Alternatively, it may be arranged between a plurality of belt layers 5.

[0021]

【Example】

Tires 1 and 2 of the present invention and a conventional tire having the same tire size of 23.5R25 and a tread belt structure as follows were manufactured.

Tire 1 of the present invention Tread belt structure: FIG. 1 Spiral belt reinforcement layer (two rows on one side): Steel cord 3 + 9 (0.22) Cord angle 15 ° Belt layer (2 layers): Steel cord 3 + 9 + 15 (0.22) Cord angle Lower layer ( No. 2) 25 °, Upper layer (No. 3) 20 ° Auxiliary belt reinforcing layer (Single layer): Highly extensible steel cord 3 × 6 (0.23) Cord angle 25 °

Tire 2 of the present invention Tread belt structure: FIG. 1 Spiral belt reinforcing layer (two rows on one side): aromatic polyamide cord 1600d × 2 Cord angle 15 ° Belt layer (two layers): Steel cord 3 + 9 + 15 (0.22) Cord angle Lower layer (No. 2) 25 °, Upper layer (No. 3) 20 ° Auxiliary belt reinforcing layer (Single layer): Highly extensible steel cord 3 × 6 (0.23) Cord angle 25 °

Conventional tire tread belt structure: FIG. 2 No. 1 belt layer (innermost layer): Steel cord 3 + 9 + 15 (0.22) Cord angle 34 ° No. 2 belt layer: Steel cord 3 + 9 + 15 (0.2
2) Cord angle 25 ° 3rd belt layer: Steel cord 3 + 9 + 15 (0.2
2) Cord angle 20 ° 4th belt layer (outermost layer): Highly extensible steel cord 3 × 6 (0.23) Cord angle 25 °

With respect to the above three types of pneumatic radial tires for construction vehicles, the belt edge separation resistance and the contact pressure in the central region of the crown were measured by the following test methods, and the results are shown in Table 1.

As is clear from Table 1, both the tires 1 and 2 of the present invention exhibit excellent belt edge separation, almost the same durability as the conventional tire, and have a low contact pressure in the central region of the crown, so that the tread is low. It can be seen that the center wear has an effect superior to that of the conventional tire.

(Test method) (a) Using a drum tester for belt edge resistance, the internal pressure of the test tire was set to 500 kp.
a, a traveling speed of 6 km / h, an initial load of 1250 kgf, a preliminary run with a load of 80% of the initial load, a run for 24 hours with the above initial load, and then a step-up of the load by 10% every 24 hours thereafter; Belt-resistant separation was evaluated based on the total running time when the vehicle traveled until a failure occurred in the belt edge.

The evaluation is performed using an index with the measured value of the conventional tire being 100. A larger index means that the belt edge separation is more excellent. (b) Ground pressure in the central region of the crown The ground pressure was measured by a ground pressure gauge equipped with a load cell at every 50 mm square, when a standard load was applied and attached to a 100-ton arm slur. .

The evaluation was performed using an index with the measured value (contact pressure) of the conventional tire being 100. The smaller the index value, the smaller the contact pressure in the central region of the crown, and thus the smaller the center wear.

[0031]

[Table 1]

[0032]

As described above, in the pneumatic radial tire for a construction vehicle according to the present invention, the spiral belt reinforcing layer is disposed at both end regions of the belt layer, and the spiral belt reinforcing layer bears the tension in both shoulder regions. By doing so, the tension at both ends of the belt layer is reduced, so that edge separation can be reduced. Further, since the reinforcing cord is folded back at the end of the spiral belt reinforcing layer itself, there is no occurrence of edge separation unlike the belt layer.

Further, since the edge separation is improved by the spiral belt reinforcing layer without making the belt layer concave to the outside unlike the conventional tire, the contact pressure at the center of the tread is not extremely increased, and the tread of the tread is not increased. Does not cause center wear or chipping / cutting.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a pneumatic radial tire for construction vehicles of the present invention.

FIG. 2 is a longitudinal sectional view showing a tread portion of a conventional pneumatic radial tire for construction vehicles.

[Explanation of symbols]

 Reference Signs List 1 tread 3 carcass layer 5 belt layer 6 spiral belt reinforcement layer 7 auxiliary belt reinforcement layer

Claims (6)

[Claims] 1. A belt layer having at least three bias layers having a cord angle of 15 ° to 30 ° with respect to a tire circumferential direction and intersecting with each other between layers is disposed between a carcass layer and a tread. A construction vehicle having spiral belt reinforcing layers formed into a flat tubular cross section by continuously winding a reinforcing cord spirally at a cord angle of 10 ° to 30 ° with respect to the tire circumferential direction in both end regions of the tire. Pneumatic radial tires. 2. The pneumatic radial tire for a construction vehicle according to claim 1, wherein the spiral belt reinforcing layer is disposed between the carcass layer and the belt layer. 3. The tensile elastic modulus of the spiral belt reinforcing layer in the tire circumferential direction is larger than the tensile elastic modulus of the belt layer in the tire circumferential direction.
The pneumatic radial tire for construction vehicles according to claim 1. 4. An auxiliary belt reinforcing layer made of at least one highly extensible steel cord is provided on the outermost side of the belt group of the belt layer and the spiral belt reinforcing layer from an outer end of the spiral belt reinforcing layer. The pneumatic radial tire for a construction vehicle according to any one of claims 1 to 3, wherein the tire is also arranged to extend to the outside. 5. The pneumatic radial tire for a construction vehicle according to claim 1, wherein the reinforcing cord of the belt layer is a steel cord. 6. The reinforcing cord of the spiral belt reinforcing layer is a steel cord having a tensile modulus of 3000 kgf / mm ² or more, a wire diameter of 0.05 mm to 0.25 mm, or a tensile modulus of 3000 kgf or more and a tensile strength of 15 kg / m ^2.
2. An organic fiber cord of 0 kgf / mm ² or more.
The pneumatic radial tire for construction vehicles according to any one of claims 1 to 5.