JP2908461B2 - Pneumatic radial tire for heavy loads - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heavy-duty pneumatic radial tire having a lug pattern, and more particularly, to a so-called tread rubber generated on tread rubber due to rough road running. This greatly reduces belt edge cracks.

(Prior Art) FIG. 3 shows a conventional tire of this type having a lug pattern, for example. In the drawing, the upper half shows a part of the tread pattern, and the lower half shows a part of the cross section in the width direction.

In this tire, the bending point a of the lug groove 31 that is bent and extended at the shoulder portion, that is, the bending point b, c of each of the lug groove walls 31a, 31b, is half the distance in the tire width direction. , A point on the center line of the lug groove is located within a range of 8 to 15% of the tread width TW from the tread edge, and a separation distance in the tire width direction of each bending point b, c is set to 0 to 5 mm. Further, the width of the portion of the lug groove 31 located outside the bending point a in the tire width direction is set to 140% or less of the width of the portion located inside the bending point a, while the lug groove 31 is positioned at 1
Belt consisting of two or more belt layers formed of steel cords intersecting at an angle of 0 to 30 °, wherein at least one belt layer has a steel cord extending in a direction intersecting with another belt layer steel cord. 32, the belt layers 32b to 32d located on the outer peripheral side of the innermost peripheral belt layer 32a, and the extending direction of the steel cord is different from that of the innermost peripheral belt layer. The side edge f of the inner peripheral side is arranged at a position substantially corresponding to the lug groove bending point a.

(Problems to be Solved by the Invention) By the way, in such a conventional tire, particularly when traveling on a rough road, when stepping on a stone near the bending point of the lug groove 31, the structure of the lug groove is limited. As shown by the imaginary line in the figure, the lug groove walls 31a and 31b are easy to pinch the stone strongly at three places, and there is almost no possibility that the stone once pinched will fall out of the stone naturally. There is a problem that the groove bottom of 31 is easily cut by a stone, and when such a cut occurs, the side edge f of the belt layer 32c is
Due to the presence of the lug groove 31 at a position substantially corresponding to the bending point a, a crack that has grown from the cut is located at the belt layer side edge f where there is a high possibility of belt separation occurring structurally. There is a problem that the tread portion may reach and damage the tread portion significantly.

That is, only the side edge f of the belt layer 32c is a problem here because the belt generally exhibits a reinforcing strength with a laminated structure of belt layers having different extending directions of steel cords. Such a belt causes a particularly large shear strain due to the so-called pantograph movement of the steel cord between belt layers having different extending directions of the steel cord due to filling of the tire with internal pressure, rolling of the tire, and the like. However, since the distortion is larger at the side end portions where the restraining force between the belt layers is small, as shown in the figure, the side end portions of the belt layer 32c are slightly jumped outward in the radial direction, and By increasing the rubber volume between the inner peripheral side belt layer 32b and the inner peripheral side belt layer 32b, the amount of distortion in the region adjacent to the side end portion of the belt layer 32c is reduced.
Since the side edge f of c causes much greater distortion than the respective side edges of the other belt layers 32a, 32b, 32d,
When the side edge f of the belt layer 32c is positioned substantially corresponding to the bending point a of the lug groove 31, the input from the stone caught in the lug groove 31 causes the side edge f at the side edge f. Further increases the belt separation more easily,
In addition, the cut generated at the bottom of the lug groove by the stone,
This is due to the fact that it is particularly easy to grow toward a portion having a large distortion.

On the other hand, between the belt layers 32a and 32b and the belt layer 32
Between c and 32d, even when the tire is subjected to internal pressure filling, load rolling of the tire, or the like, a large shear strain as in the above-described case does not occur, thereby, the belt layers 32a, 32b
Also, the strain at each side edge of 32d and 32d is also much less than that at said side edge f, so if any of the side edges of those belt layers 32a, 32b, 32d Even if it is located corresponding to the bending point a of the lug groove 31,
There is almost no risk of belt separation occurring at the side edge, and even if a cut due to stone formation occurs at the groove bottom of the lug groove, the cut may grow toward the side edge. Absent.

The present invention advantageously solves such a problem of the conventional tire, and when a stone is bitten in the lug groove, the stone easily falls off, and the groove bottom of the lug groove is temporarily cut. Even in this case, it is an object of the present invention to provide a heavy-load pneumatic radial tire that can effectively prevent the progress of cracks from the cut portion to the belt layer side edge.

(Means for Solving the Problems) The present invention relates to a carcass comprising one or more steel cord layers and a belt layer formed of a steel cord which intersects the tire equator at an angle of 10 to 30 °. Consisting of the above, the steel cord of at least one belt layer,
In a heavy-duty pneumatic radial tire including a belt extending in a direction intersecting the steel cords of the other belt layers and a tread portion having a lug groove bent and extended at a shoulder portion, the folding of the lug groove is performed. The bending point is located within the range of 15 to 25% of the tread width from the tread end, and the separation distance in the tire width direction at each bending point position of the lug groove groove wall is set to 6 to 15 mm. The width of the portion located outside the bending point in the tire width direction is set to 150 to 170% of the width of the portion located inside the bending point, and is located on the outer peripheral side of the innermost peripheral belt layer. A belt layer,
The extending direction of the steel cord, of the belt layer different from that of the innermost peripheral belt layer, the side edge of the innermost peripheral layer is located between the bending point of the lug groove and the tread end, The side edge position and the lug groove bending point position are separated by 10% or more of the tread width in the tread width direction.

(Operation) In this radial tire, since the bending point of the lug groove is within the range of 15 to 25% of the tread width from the tread edge, the side edge of the belt layer specified earlier is the tire width. It is located outside this bending point with respect to the direction, and therefore, even if the lug groove is stoned, the side edge portion can directly receive input such as impact. Absent. Further, the separation distance in the tire width direction at each bending point position of the lug groove wall is 6 mm or more, and,
By setting the width of the part of the lug groove located outside the bending point in the tire width direction to be 150% or more of the width of the part located inside the bending point, stones can be caught in the lug groove. Is likely to occur between the two opposing wall surfaces of the narrow portion, and the pinching force of the stone by the two wall surfaces is considerably smaller than that of the conventional tire, and furthermore, it is bitten into the lug groove. The falling stones are smoothly and easily dropped from the stones, and the possibility that the stones cut the bottoms of the lug grooves is effectively removed.

In addition, here, of each bending point position of the lug groove groove wall,
If the distance in the tire width direction and the width of the portion of the lug groove located outside in the tire width direction from the bending point position are too large, the rigidity of the shoulder block is reduced, which may cause the block to be broken or other problems. Therefore, here, the upper limits are set to 15 mm and 170%, respectively.

Further, here, the belt layer is located on the outer peripheral side from the innermost peripheral belt layer, and the extending direction of the steel cord is located on the innermost peripheral side among the belt layers different from that of the innermost peripheral belt layer. The side edge of the object is located between the lug groove bending point and the tread edge, and the side edge position and the lug groove bending point position are separated by 10% or more of the tread width in the tread width direction. By doing so, even if the bottom of the groove is cut by a stone caught in the lug groove, the progress of the crack from the cut position to the edge of the belt layer is extremely effectively prevented. Will be done.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an embodiment of the present invention. The upper half of the figure shows a part of a tread pattern, and the lower half shows a part of a cross section in the width direction.

In the figure, reference numeral 1 denotes a carcass comprising one or more steel cord layers, 2 denotes a belt disposed on the outer peripheral side of the carcass 1, and the belt 2 is located at a distance of 10 mm from the tire equator line.
Two or more belt layers formed of steel cords intersecting at an angle of ~ 30 °, here, four belt layers 2a, 2b, 2
c, 2d, at least one of the belt layers, for example, the steel cords of the belt layers 2c, 2d, and the other belt layers 2a, 2b
Extend in the direction crossing the steel cord.

Further, in the figure, reference numeral 3 denotes a tread portion of the tire, and the tread portion 3 has a lug groove 4 which is bent and extended at a shoulder portion.
Having.

Here, the bending point a of the lug groove 4, in other words,
The distance k in the tire width direction from the tread to the point located at a position half the tire width direction distance l of each of the bending points b and c of the lug groove walls 4a and 4b is 15 to 25% of the tread width TW. In this case, the side edge f of the belt layer 2c is located considerably outside of the bending point in the tire width direction, and the propagation of external force to the side edge f at the time of rocking is performed. Is greatly reduced.

In the lug groove 4, the lug groove walls 4a, 4b
The distance between each of the bending points b and c in the tire width direction is set to 6 to 15 mm, and the width d of the portion located outside the bending point a of the lug groove 4 in the tire width direction is calculated from the bending point. It is set to 150 to 170% of the width e of the portion located inside. According to this, the biting of the stone into the lug groove 4 is mainly performed between the two opposing wall surfaces of the narrow portion of the lug groove 4 as shown by the imaginary line in the figure. The pinching of the stone at the two locations of the lug groove walls 4a and 4b will be performed with a considerably smaller force than the conventional tire, and the stone caught in the lug groove 4 is From there, the possibility of falling off naturally increases significantly, and the risk that the lug groove bottom will be cut by the stone will be greatly reduced.

Here, in the case where the separation distance between the bending points b and c exceeds 15 mm, and the case where the lug groove width d outside the bending point a exceeds 170% of that of the inside portion, the shoulder block is used. In this invention, the rigidity of the steel is greatly reduced, causing problems such as loss of blocks and reduction of traction force. In the present invention, the upper limits are set to 15 mm and 170%, respectively.
And

Further, here, in the belt 2, the innermost peripheral belt layer
The belt layers 2b to 2d located on the outer peripheral side from 2a, and the extending direction of the steel cord is different from that of the innermost peripheral belt layer 2a. The side edge f of the layer 2c is located between the bend point a of the lug groove 4 and the tread end, and the tread width direction between the side edge f and the lug groove bend point a is defined. Distance m, tread width
Length should be 10% or more of TW.

Here, the side edge f is located between the bending point a and the tread end because the width of the belt layer 2c is set to be equal to 70% of the tread width in order to optimize the growth of the tire diameter at the time of filling the internal pressure. % Or more is necessary to maintain a length of 10% or more of the tread width TW from the bend point a of the lug groove, and the side edge f is shifted from the bend point a to the tread width TW. The reason for separating the TW by 10% or more is that the side edge f, which is liable to cause a so-called belt separation problem, and the vicinity thereof are as far as possible from the lug groove portion where the groove bottom cut is liable to occur, and the tread portion is cracked. In order to prevent progress to that part as much as possible.

Although the present invention has been described based on the illustrated example, the groove width of the portion located inward in the tire width direction from the bending point of the lug groove may be gradually narrowed inward or gradually widened. In such a case, the groove width is defined as the maximum width of the portion located inside the bending point.

(Comparative example)

Hereinafter, the occurrence of cuts at the lug groove bending point and the vicinity thereof between the inventive tire shown in FIG. 1 and the conventional tire shown in FIG. 3 and the side of the specific belt layer which is a problem in this application will be described. A comparative test on the occurrence of cracks at the edges will be described.

・ Invented tire 12.00 R24 18PR S530 Tread width (TW) 236mm Lag groove bending point (k) 48mm Distance between bending points of lug groove wall (l) 10mm Side edge position of specific belt layer relative to lug groove bending point (M) 27mm ・ Conventional tire 12.00 R24 18PR L301 Tread width 232mm Lag groove bending point 33.1mm Distance between bending points of lug groove wall 6mm Side edge position of specific belt layer relative to lug groove bending point 9mm ・ Test method After each tire was mounted on the vehicle and the vehicle was driven for 40,000 km, the number of cuts generated at the lug groove bending point and its vicinity, and the cracks generated at the side edge of the specific belt layer and its vicinity Was counted respectively.

 The results are shown graphically in FIG.

According to FIG. 2, it can be seen that the number of cuts of the inventive tire is less than 1/2 of the conventional tire and the number of cracks is less than 1/3 of the conventional tire.

(Effects of the Invention) Thus, according to the present invention, it is possible to significantly reduce the occurrence of cuts at the bottom of the lug groove, and to prevent cracks from the cut portion generated at the bottom of the groove to the side edge of the specific belt layer. Progress can be prevented very effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a graph showing a comparison result of the number of cuts and the number of cracks generated, and FIG. 3 is a diagram showing a conventional example. 1 Carcass 2 Belt 2a-2d Belt layer 3 Tread portion 4 Lug groove 4a, 4b Lug groove wall a Bending point b, c Bending point d, e …… groove width f …… side edge TW …… tread width

Claims (1)

(57) [Claims] 1. A belt comprising at least one belt comprising a carcass comprising one or more steel cord layers and a belt layer comprising steel cords intersecting at an angle of 10 to 30 ° with respect to the tire equator. The steel cord of the layer includes a belt extending in a direction intersecting with the steel cords of the other belt layers, and a tread portion having a lug groove extending by bending at a shoulder portion. From the tread edge, tread width
It is located within the range of 15 to 25%, and the separation distance in the tire width direction at each bending point position of the lug groove wall is 6 to 15 mm, and the lug groove is located outside the bending point in the tire width direction outside. The width of the portion located is 150 to 170% of the width of the portion located inside the bending point, and the belt layer located on the outer peripheral side from the innermost belt layer, wherein the steel cord extends In the belt layer whose direction is different from that of the innermost peripheral belt layer, the side edge of the belt layer located on the innermost side is located between the bending point of the lug groove and the tread end, and the side edge position A heavy duty pneumatic radial tire that is separated from the lug groove bending point by at least 10% of the tread width in the tread width direction.