JPH04252705A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To prevent edge separation of a belt layer under the super severe condition by interposing belt edge cushion rubber between edges of adjoining two layers, and, at the same time, coating the edge parts with a rubber sheet of specified thickness. CONSTITUTION:Belt layers 5a, 5b, 5c, 5d made of four layers of steel cords whose width in the tire widthwise direction are different are provided between an under tread rubber layer 3 and a carcass layer 4. First belt layer 5a and second belt layer 5b are so arranged that their belt cords tilt in the same direction with respect to the tire circumferential direction, and third belt layer 5c and fourth belt layer 5d are so arranged that their belt cords cross each other substantially at the same cord angle with respect to the tire circumferential direction and reversely tilted with respect to first belt layer 5a and second belt layer 5b. Belt edge cushon rubber 6 is interposed between the edges of second belt layer 5b, and a rubber sheet 8 is inserted between second belt layer 5b and third belt layer 5c.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic radial tire with improved belt separation resistance.

0002

2. Description of the Related Art In general, heavy-duty pneumatic radial tires for buses, trucks, etc., as shown in FIG. , 5c, and 5d are arranged. Among these belt layers, the belt cords of the first belt layer 5a and the second belt layer (hereinafter referred to as the second belt layer) 5b counting from the carcass layer side are in the same direction, but the belt cord of the third belt layer is in the same direction. The belt cords of the layer (hereinafter referred to as the third belt layer) 5c and the fourth belt layer 5d are both in the same direction, and the belt cords of the first belt layer 5a and the second belt layer 5b are intersected with each other. .

However, in such a belt structure, shearing force acts between the second belt layer 5b and the third belt layer 5c, where the belt cords intersect with each other, so that the rubber is damaged especially at the belt edges where stress tends to concentrate. The problem was that separation easily occurred between the two. However, this problem was solved by inserting a belt edge cushion rubber 6 with the same hardness as the belt coat rubber between the edges of the second belt layer 5b and the third belt layer 5c, and the durability was dramatically improved. had improved.

However, for heavy-load radial tires used on dump trucks, refrigerated vehicles, etc., or tires used on vehicles such as trailers and carrier cars where torsional force is applied to the tires while driving, it is difficult to load Because the belt edge cushion rubber 6 is sometimes used under severe conditions where the load is as much as 300% to 400% of the normal load, it is not possible to simply insert the belt edge cushion rubber 6.
It was not possible to prevent peeling between the edges of the belt layer 5c and the third belt layer 5c. Furthermore, since a strong impact force acts on the outermost No. 4 belt layer 5d from the road surface, there is a problem that the undertread rubber layer 3 is likely to peel off, and in the worst case, cracks may form around the edge. In some cases, the rubber layer grows above or in the lateral direction, causing the tread to be missing, or grows between the second belt layer 5b and the third belt layer 3c, causing peeling.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty pneumatic radial tire that prevents edge separation of the belt layer even under extremely severe conditions and has significantly improved durability.

[0006]

[Means for Solving the Problems] An object of the present invention is to provide a radial tire in which a belt layer consisting of at least four steel cords is disposed on a carcass layer in a tread portion, in which the belt cord is one of the belt layers. Belt edge cushion rubber is interposed between the edges of two adjacent belt layers so as to intersect with each other, and at least the edge portion is covered with a rubber sheet having a gauge thickness of 1.0 to 3.0 mm. rubber sheet 5
This can be achieved by making the 0% modulus less than the coat rubber of the belt layer and greater than the undertread.

In this way, the belt edge cushion rubber is interposed between the edges of the two belt layers in which the belt cords intersect with each other, and the edge portion is covered with a rubber sheet having a specific gauge thickness and modulus. By doing so, stress concentrated on these edges is alleviated and separation is prevented from occurring. It also prevents these separations from growing from the edges to the center of the tread.

The heavy-duty radial tire of the present invention will be explained in detail below with reference to the drawings. FIG. 1 shows an embodiment of the belt structure of the tire of the present invention. As shown in FIG. 1, the tread portion 1 consists of a cap tread rubber layer 2 and an undertread rubber layer 3, and between the undertread rubber layer 3 and the carcass layer 4, there is a tread layer 4 having different widths in the tire width direction. belt layers 5a, 5 consisting of layers of steel cord;
b, 5c, and 5d are arranged. The first belt layer 5a and the second belt layer 5b from the carcass layer 4 have belt cords inclined in the same direction with respect to the tire circumferential direction, while the third belt layer 5c and the fourth belt layer 5d have belt cords inclined in the same direction with respect to the tire circumferential direction. The belt cords intersect with each other at substantially the same cord angle with respect to the tire circumferential direction, with opposite inclinations to the first belt layer 5a and the second belt layer 5b. Further, the belt width of these belt layers is the largest in the second belt layer 5b.

In the belt structure as described above, a belt edge cushion rubber 6 is interposed between the edges of the second belt layer 5b and the third belt layer 5c where the belt cords intersect with each other, and furthermore, the outer side of this edge is Rubber sheet (
(hereinafter referred to as edge cover rubber sheet) 7. Further, a rubber sheet 8 is inserted between the second belt layer 5b and the third belt layer 5c over the central region of the tread sandwiched between the left and right edge cushion rubbers 6.

The edge cover rubber sheet 7 is made of a rubber having a 50% modulus larger than that of the undertread rubber 3 and smaller than the belt coat rubber, and has a gauge thickness of 1.0 to 1.0.
The range is 3.0 mm. This gauge thickness is 1.0
If the thickness is less than mm, the effect of suppressing edge separation is insufficient. On the other hand, if it exceeds 3.0 mm, it will deteriorate due to heat generation during running and the durability will deteriorate. The 50% modulus of the edge cover rubber sheet 7 is more preferably JIS
It is desirable that the value measured in accordance with the method specified in K-6301 is in the range of 14 to 36 kg/cm2.

Further, the edge cover rubber sheet 7 has a second belt layer 5b having the above-mentioned gauge thickness and maximum width.
It is preferable to cover an area 5 mm or more away from the edge of the area. Further, the 50% modulus of the edge cushion rubber 6 is preferably the same as or smaller than that of the edge cover sheet 7. In the present invention, the edge cover sheet 7 may cover at least the edge portions of the second belt layer 5b and the third belt layer 5c where the belt cords intersect with each other, but it may be made to extend further to the center of the tread. As shown in FIG. 2, by covering the entire tread side surface of the No. 4 belt layer 5d, the impact force applied from the road surface is alleviated and the separation between the No. 4 belt layer 5d and the undertread rubber layer 3 is reduced. It becomes possible to do so. The 50% modulus of the rubber sheet covering the tread side surface of the No. 4 belt layer 5d in the central region of the tire may be the same as that of the rubber sheet 7 covering the edge portion, but is preferably smaller than that of the rubber sheet 7. Things are good.

Furthermore, in the present invention, a rubber sheet (hereinafter referred to as an interlayer rubber sheet) 8 is also provided between the second belt layer 5b and the third belt layer 5c where the belt cords intersect with each other.
By inserting this, separation between belt layers can be effectively reduced. It is desirable that the interlayer rubber sheet 8 has a gauge thickness in the range of 1.0 to 3.0 mm, similar to the edge cover rubber sheet 7, and a 50% modulus slightly lower than that of the edge cover rubber sheet 7. This interlayer rubber sheet 8 may be placed in a region sandwiched between the belt edge cushion rubbers 6 at both ends as shown in FIG. 1, or may be overlapped with the belt edge cushion rubber 6 as shown in FIG. good.

[0013]

[Example] Undertread rubber, belt coat rubber, edge cover rubber sheet (gauge thickness 1.5 mm), and interlayer rubber having the belt part structure shown in Fig. 1 and consisting of a rubber composition having the compounding composition shown in Table 1. Sheet (gauge thickness 1.0m
m), and the tire size is 1000/R2 and the belt edge cushion rubber is the same as the belt coat rubber.
A 0.14PR tire of the present invention was manufactured.

[0014] Also, for comparison, in the tire of the present invention,
A comparative tire having the same belt structure was manufactured except that the edge cover rubber sheet and the interlayer rubber sheet were not provided. These two types of tires were subjected to the following durability test to evaluate their durability. As a result, when expressed as an index with the measured value of the comparative tire as 100, the durability of the tire of the present invention was 143, indicating that the durability was significantly improved. Durability test: Speed 45Km/hour, Air pressure 7.25Kg/
cm2, run for 24 hours with an initial speed load of 2700 kg, then increase the load by 5% and run for 24 hours, then increase the load by 5% every 24 hours and run continuously until the tire breaks. The distance traveled was measured.

[0015]

[Table 1]

[0016]

According to the present invention, a belt edge cushion rubber is interposed between the edges of two belt layers whose belt cords intersect, and at least the edge portion thereof has a specific gauge thickness and modulus. By covering with a rubber sheet, cracks and separations at these edges are suppressed even under extremely severe conditions, and the durability of the belt layer is significantly improved.

[Brief explanation of the drawing]

1 to 3 are half sectional views showing one example of the structure of the belt portion of the tire of the present invention.

FIG. 4 is a half-sectional view showing the structure of a belt portion of a conventional tire.

[Explanation of symbols]

1 Tread portion 2 Cap tread rubber layer 3 Undertread rubber layer 5a No. 1 belt layer 5b No. 2 belt layer 5c No. 3 belt layer 5d No. 4 belt layer 6 Belt edge cushion rubber 7 Edge cover rubber sheet 8 Interlayer rubber sheet

Claims (1)

[Claims] Claim 1: A radial tire in which a belt layer consisting of at least four steel cords is arranged on a carcass layer in a tread portion, in which two adjacent belt layers of the belt layers are arranged such that the belt cords intersect with each other. A belt edge cushion rubber is interposed between the edges, and at least the edge portion is 1.0 to 3.0 m.
A pneumatic radial tire for heavy loads covered with a rubber sheet having a gauge thickness of m, the 50% modulus of the rubber sheet being less than or equal to that of the coated rubber of the belt layer and greater than that of the undertread.