JP5094103B2 - Pneumatic tire - Google Patents

Description

  The present invention comprises a carcass extending in a toroidal shape and at least two belt layers positioned on the outer side in the tire radial direction of the carcass and coated with rubber, and the cords constituting these belt layers are tire equator surfaces. And a tread portion located on the outer side in the tire radial direction of the belt, and the tread portion from both tread ends toward the tire equatorial plane. The present invention relates to a pneumatic tire formed by arranging a plurality of pairs of one-end opening grooves extending in the same inclination direction and terminating in the land portion in the tire circumferential direction, particularly a radial tire for heavy loads, and particularly the belt durability of such a tire. Improve.

  Pneumatic radial tires, especially pneumatic radial tires mounted on heavy-duty vehicles, are the angle formed by a large inclined belt layer made of rubber-coated cord with a relatively large angle with the tire equator and the tire equator. It is common to have a cross belt in which a cord with a relatively small cord is combined with a small inclined belt layer formed by rubber coating, and the cords of each belt layer are arranged so that they cross each other across the tire equatorial plane between adjacent layers (For example, see Patent Document 1). In such a tire, a large inclined belt layer ensures rigidity against deformation along the belt surface (hereinafter referred to as “in-plane bending rigidity”) to maintain motion performance, while a small inclined belt layer provides a tire circumferential direction. Thus, the tire's load capacity is secured by suppressing the tire diameter growth and preventing the crown shape from changing during running. However, when the tire rolls under load, shear strain is inevitably applied to the end region of the belt, so that separation between the cord and the coated rubber occurs particularly at the end of the small inclined belt layer where the inclination angle of the cord is small. However, this may cause a tire failure.

  In order to prevent such separation from occurring at the end of the belt, for example, Patent Document 2 discloses that at least three belt layers formed by rubber-covering the cord, and the cord constituting the belt layer has a tire equator surface. A belt is formed by forming a cross belt layer that intersects with each other, and two belt layers arranged on the carcass side of these belt layers are 0.25 to 0.50 times as wide as the tread width. The ratio W2 / W1 between the width W1 of the small inclined belt layer disposed on the carcass side and the width W2 of the other small inclined belt layer is set in a range of 1.1 to 1.3 times. A radial tire is described. In such a tire, the separation generated at the end of the small inclined belt layer is suppressed by optimizing the width of the small inclined belt layer.

  In Patent Document 3, a belt is composed of at least one narrow small inclined belt layer and at least two wide large inclined belt layers, and the outer surface at the center of the width of the widest large inclined belt layer. There is described a heavy-duty pneumatic radial tire in which the tire radial distance from the tread part tread is equal to or less than the tire radial direction distance from the outer surface at the width end position of the large inclined belt layer to the tread tread. In such a tire, a normal crown shape is obtained at the time of internal pressure filling, and the diameter growth of the width center portion of the tread portion at the time of tire load rolling is suppressed, so that durability of the carcass and the belt is improved.

  In particular, for heavy-duty pneumatic tires, from the viewpoint of achieving both drainage and traction properties, the tread portion extends from the tread ends toward the tire equatorial plane in the same inclination direction and terminates in the land portion. In general, a so-called non-directional tread pattern in which a plurality of pairs of one-end opening grooves are arranged in the tire circumferential direction is employed. However, in such a tire, when a large lateral force repeatedly acts on the tire, the cord constituting the outermost belt layer that is the outermost belt layer in the tire radial direction is broken near the position near the lug groove, and this cord Separation may occur starting from the fractured end of the belt. Even if the belt structures described in Patent Documents 2 and 3 above are employed, separation from the end of the small inclined belt layer can be prevented, but the outermost It is difficult to effectively prevent separation from the end of the belt layer, and there is still a problem that the belt durability is poor.

JP 54-126306 A JP 2002-362109 A JP 2003-136911 A

  Accordingly, an object of the present invention is to provide a pneumatic tire having a non-directional lug groove pattern in which the belt durability is improved by optimizing the arrangement of the cords constituting the belt.

In order to achieve the above object, the present invention comprises a carcass extending in a toroidal shape, and at least two belt layers positioned on the outer side in the tire radial direction of the carcass and coated with rubber, and these belt layers. And a tread portion located on the outer side in the tire radial direction of the belt, and the tread ends of the tread portions thereof. In the pneumatic tire formed by arranging a plurality of pairs of one end opening grooves extending in the same inclination direction toward the tire equator surface and terminating in the land portion in the tire circumferential direction, the pneumatic tires are located on the outermost side in the tire radial direction. The cord constituting the outermost belt layer which is a belt layer and the groove width center line of the one-end opening groove extend in the same inclination direction, and the cord and the groove width center Ranges angle of 30 to 70 ° with the outermost belt layer, the value of center-to-center distance between adjacent code divided by the cord diameter was constituting the outermost belt layer is larger than 1.15 1. It is a pneumatic tire characterized by being smaller than 35 .

  Here, “extending in the same inclination direction” means extending in the same quadrant in a two-dimensional coordinate system in which the tire width direction is the x axis and the tire equatorial plane is the y axis. When a cord extends over the second and fourth quadrants in the coordinate system, it means that the other cords also extend over the second and fourth quadrants. In addition, “the groove width center line of the one-end opening groove” means a line connecting the groove width center position in each part of the one-end opening groove, and “the angle formed with the groove width center line” means the tire width of the belt If the groove width center line is a straight line at the position corresponding to the outer edge in the direction, the angle made with this is the angle formed with the tangent line of the groove width center line when the groove width center line is a curve. And

  Further, at least one belt reinforcement comprising a cord rubber coating layer having a width of 25 to 60% of the tread width between the belt and the carcass and having a cord inclined at a range of 3 to 15 ° with respect to the tire equator plane. It is preferred to further dispose a layer.

  Further, at least one belt protective layer having a width larger than that of the outermost belt layer and covered with an extensible cord is further disposed between the belt and the tread portion. Is preferred. Here, the “extensible cord” refers to a cord having an elongation at break in the range of 4 to 7%. For example, a steel cord or the like in which filaments are loosely twisted can be used.

  In addition, when the cord constituting the outermost belt layer has a twisted layer structure, the value obtained by raising the cord diameter to the fourth power is less than 30 times the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. In the case where the cord constituting the outermost belt layer has a double twist structure, the value obtained by raising the cord diameter to the fourth power is the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. It is preferably less than 400 times.

  According to the present invention, it is possible to improve the belt durability of a pneumatic tire having a non-directional lug groove pattern by optimizing the arrangement of the cords constituting the belt.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a left half sectional view in the tire width direction of a main part of a typical pneumatic tire (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 shows a part of the tread portion of the tire of FIG. It is an expanded view shown with an internal structure. A tire 1 shown in FIG. 1 includes a carcass 2 extending in a toroid shape, and at least two belt layers formed by rubber-covering a cord, which are located on the outer side of the carcass 2 in the tire radial direction, and in FIG. 1, two belt layers 3a. 3b, and a tread portion 5 positioned on the outer side of the belt 4 in the tire radial direction. As shown in FIG. 2, the belt layers 3a and 3b are arranged so that the cords constituting them intersect each other across the tire equatorial plane E, thereby forming an intersecting belt layer. The tread portion 5 includes a plurality of pairs of one end opening grooves 7a and 7b extending in the same inclination direction from the tread ends 6a and 6b toward the tire equatorial plane E and terminating in the land portion in the tire circumferential direction. They are arranged side by side.

  The main feature of the configuration of the present invention is that the extension direction of the cord 8 constituting the outermost belt layer 3a that is the outermost belt layer positioned in the tire radial direction is optimized. Specifically, the cord 8 constituting the outermost belt layer 3a and the groove width center line G of the one end opening grooves 7a and 7b extend in the same inclination direction, that is, FIG. Then, the cord 8 and the groove width center line G extend in the second quadrant and the fourth quadrant, respectively, and the angle α formed by the cord 8 and the groove width center line G is in the range of 30 to 70 °. There is.

  In a tire having a one-end opening groove in the tread portion, when the tread portion contacts the ground, stress is inevitably closed in the direction that closes the one-end opening groove, that is, in a direction perpendicular to the groove width center line. A large compressive force is likely to be applied to the portion located immediately below the one-end opening groove. In the conventional tire, since the relationship between the extending direction of the one-end opening groove and the extending direction of the cord constituting the outermost belt layer is not defined, when these extending directions are reversed, the outermost belt layer is In some cases, a large compressive force is applied to the constituting cord, and the cord breaks or the separation from the broken end of the cord occurs. Therefore, the inventor reduces the concentration of compressive stress on the cord 8 by extending the cord 8 constituting the outermost belt layer 3a in the same inclination direction as the groove width center line G of the one end opening grooves 7a and 7b. I got the idea that I could do it.

  However, the cord breakage cannot be effectively prevented simply by simply extending the cord 8 and the groove width center line G in the same inclination direction. Accordingly, the inventor paid attention to the angle α formed by the cord 8 and the groove width center line G, and conducted earnest research on the relationship between the cord 8 and the compressive stress applied to the cord 8, and as a result, a graph as shown in FIG. Got. In the figure, the compressive stress index is the finite element method used to analyze a tire with a normal load specified by TRA and a lateral force equivalent to 0.15G, and analyze the outermost tire below one end opening groove. This refers to an index of the maximum stress generated in the belt layer. In the case of steel cords that are generally used as tire cords, a situation in which separation due to cord breakage has occurred (user usage conditions) )), It is clear that no failure has occurred in the situation where the average lateral force is less than 0.1G. Therefore, if this index is 60 or less, it may be difficult to break. I know it. Therefore, if the angle α is in the range where the compressive stress index is 60 or less, that is, in the range of 30 to 70 °, the concentration of compressive stress on the cord can be avoided, so that the cord is prevented from breaking and consequently the durability of the belt is improved. Can be realized.

  The belt 4 and the carcass 2 have at least one cord rubber coating layer having a width of 25 to 60% of the tread width W and in which the cord is inclined with respect to the tire equator plane E in the range of 3 to 15 °. It is preferable to further dispose two belt reinforcing layers 9a and 9b in FIGS. In heavy-duty tires to which high internal pressure and high load are applied, especially in the vicinity of the tire equatorial plane E, the diameter growth (protrusion) of the tread portion 5 increases, and as a result, sufficient durability of the belt and the carcass can be obtained. There may not be. In order to suppress such diameter growth, it is useful to dispose a belt reinforcing layer in which the cord is inclined at a relatively small angle of 3 to 15 ° with respect to the tire equatorial plane E, thereby improving the so-called brazing effect. . However, when the tire rolls under load, shear strain inevitably occurs at the end portion of the belt reinforcing layer, and there is a possibility that a separation failure may occur starting from the end of the cord that is not bonded to the covering rubber. Since the shear strain is known to increase as the width of the belt reinforcing layer increases, the width of the belt reinforcing layers 9a and 9b is within a range in which both the improvement of the tightening effect and the suppression of the shear strain can be achieved. Specifically, it is preferably 25 to 60% of the tread width W.

  Further, at least one belt protective layer having a width w2 larger than the width w1 of the outermost belt layer 3a between the belt 4 and the tread portion 5 and made of rubber covered with an extensible cord, FIG. 1 and 2, it is preferable to further dispose a single belt protective layer 10. In this way, if the entire width of the outermost belt layer 3a is covered with the belt protective layer 10 formed of an extensible cord, the outermost belt layer 3a is protected from the outside by the belt protective layer 10, and has cut resistance and penetration resistance. As a result, the durability of the belt 4 is further improved. In this case, stress is applied to the portion of the belt protective layer 10 located immediately below the one-end opening grooves 7a and 7b in a direction perpendicular to the groove width center line G, similarly to the outermost belt layer 3a. However, since the belt protective layer 10 is formed of an extensible cord, the cord extends following the tensile deformation, so that no great tension is applied to the cord and the cord is less likely to break.

  In addition, as a mechanism for the failure occurrence of the outermost belt layer, if there is a broken portion in the cord constituting the belt, the rigidity of the broken portion decreases and the deformation of the belt increases. It is known that the material breaks, further lowers the rigidity and deforms the belt, and as a result, the broken portions expand in a chain, and the separation progresses rapidly, leading to a burst failure. Therefore, from the viewpoint of preventing the chain of cord breaks, it is advantageous that the cord constituting the outermost belt layer is made of a thick filament. In addition, when a compressive force is applied to the cord, the filament has a buckling deformation in the cord having the layer twist structure, and the strand has a buckling deformation in the cord having the double twist structure, which causes the buckling deformation. It is advantageous to increase the bending rigidity of the cord which is difficult. Specifically, when the cord constituting the outermost belt layer 3a has a layer twist structure, the value obtained by raising the cord diameter to the fourth power is the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. When the cord constituting the outermost belt layer 3a has a double twist structure, the value obtained by raising the cord diameter to the fourth power is the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. Advantageously, it is less than 400 times.

  FIG. 4 is a cross-sectional view of the outermost belt layer 3a taken along a plane perpendicular to the cord 8 constituting the outermost belt layer 3a. The outermost belt layer 3a preferably has a value obtained by dividing the distance d between the centers of the cords 8 constituting the outermost belt layer 3a by the cord diameter D and is larger than 1.15 and smaller than 1.35. By reducing the distance d between the centers of the cords 8 to less than 1.35 times the cord diameter D and arranging the cords 8 closely, the burden of compressive force per cord is reduced and cord breakage is suppressed. Because you can. On the other hand, when the distance d between the cords 8 center is 1.15 or less of the cord diameter D, the amount of the covering rubber existing between the adjacent cords becomes too small, and cracks from the end portions of the belt layer 3a are likely to occur. Because.

  The extension angle of the cord constituting the belt is not particularly limited. However, when the belt reinforcing layer is provided, the angle formed by the cord constituting the belt and the tire equatorial plane is set to 15 to 45 °. It is preferable to share the improvement of in-plane bending rigidity with the belt reinforcing layers 9a and 9b, respectively, to prevent diameter expansion. Further, in this case, from the viewpoint of preventing the shear strain from concentrating on the widthwise ends of the belt reinforcing layers 9a and 9b, the belt 4 is made wider than the belt reinforcing layers 9a and 9b, and the belt reinforcing layers 9a, 9b, It is preferable to cover the end of 9b. Further, from the viewpoint of balancing drainage and traction in a balanced manner, it is preferable that the angle formed by the one-end opening grooves 7a and 7b and the tire equatorial plane E is in the range of 50 to 85 °. Furthermore, from the viewpoint of further effectively suppressing the diameter growth, the belt constituting the belt reinforcing layer, the belt, and the belt reinforcing layer are arranged so that the cords constituting each cross each other across the tire equatorial plane between all adjacent layers. It is preferable to arrange in.

  In addition, the place mentioned above only showed a part of embodiment of this invention, and can add a various change in a claim.

  Next, tires according to the present invention were prototyped and performance evaluations were performed, which will be described below.

  The tires of Examples 1 to 3 are radial tires for construction vehicles having a tire size of 40.00R57. As shown in FIG. 5, two layers of belt reinforcing layers, two layers of belts, and two layers of belt protection It has a layer, the tread width is 980 mm, and has the specifications shown in Table 1.

  For comparison, although the tire size and the tread width are the same as those of Examples 1 to 3, a tire of a conventional example having the tire structure shown in FIG.

  In addition, the inclination direction of the cord in Table 1 is represented as positive when extending in the second quadrant and negative when extending in the first quadrant. Further, “inner side” and “outer side” indicate members positioned on the inner side and the outer side in the tire radial direction, respectively.

  Each of the test tires is mounted on a rim of size 29.00 / 5.0 × 57 to form a tire wheel, and an air pressure of 700 kPa (relative pressure) is applied to the tire wheel, and the tire load is defined by 84t (TRA). It corresponds to a 140% load of a normal load of 60 t.) Under a condition of 10 km / h, a lateral force of 21 t (corresponding to 0.25 G) was applied and the drum tester with a diameter of 5 m was run for 240 hours I let you.

  Each of the test tires that finished running on the drum was disassembled, and among the cords constituting the outermost belt layer, a broken cord and a range where separation occurred were visually confirmed. Then, the number of the broken cords at the position corresponding to the one end opening groove was examined, and the belt durability was evaluated based on these results. The evaluation results are shown in Table 2.

  From the evaluation results shown in Table 2, it can be seen that the tires of Examples 1 to 3 have significantly improved belt durability as compared with the tires of the conventional examples.

  According to the present invention, it is possible to provide a pneumatic tire having a non-directional lug groove pattern in which belt durability is improved by optimizing the arrangement of the cords constituting the belt.

It is a tire width direction left half sectional view of the principal part of the typical pneumatic tire according to this invention. FIG. 2 is a development view showing a part of a tread portion of the tire of FIG. 1 together with an internal structure. It is a graph which shows the relationship between the angle | corner which the code | cord | chord which comprises an outermost belt layer, and the groove-width centerline of one end opening groove | channel make, and a compressive stress index | exponent. It is sectional drawing when an outermost belt layer is cut | disconnected by a surface perpendicular | vertical to the code | cord | chord which comprises it. It is an expanded view which shows a part of tread part of the tire of Examples 1-3 with an internal structure. It is an expanded view which shows a part of tread part of the tire of a prior art example with an internal structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tire 2 Carcass 3a, 3b Belt layer 4 Belt 5 Tread part 6a, 6b Tread end 7a, 7b One end opening groove 8 Cord 9a, 9b Belt reinforcement layer 10 Belt reinforcing layer constituting outermost belt layer

Claims (5)

It consists of a carcass extending in a toroidal shape and at least two belt layers positioned on the outer side in the tire radial direction of the carcass and coated with rubber, and the cords constituting these belt layers are mutually sandwiched across the tire equatorial plane It comprises a belt formed with intersecting belt layers and a tread portion located on the outer side in the tire radial direction of the belt. In a pneumatic tire formed by arranging a plurality of pairs of one end opening grooves extending and terminating in the land portion in the tire circumferential direction,
The cord constituting the outermost belt layer, which is the outermost belt layer in the tire radial direction, and the groove width center line of the one end opening groove extend in the same inclination direction, and the cord and the groove width Ri range near the angle formed 30 to 70 ° with the center line,
The outermost belt layer is a pneumatic tire characterized in that a value obtained by dividing a distance between centers of adjacent cords constituting the outermost belt layer by a cord diameter is larger than 1.15 and smaller than 1.35.   Between the belt and the carcass, at least one belt reinforcing layer comprising a cord rubber covering layer having a width of 25 to 60% of the tread width and a cord inclined in a range of 3 to 15 ° with respect to the tire equatorial plane. The pneumatic tire according to claim 1, further comprising:   The belt protective layer further includes at least one belt protective layer having a width larger than that of the outermost belt layer and covered with an extensible cord between the belt and the tread portion. The pneumatic tire according to 1 or 2.   The cord constituting the outermost belt layer has a layer twist structure, and the value obtained by raising the cord diameter to the fourth power is less than 30 times the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. The pneumatic tire according to any one of Items 1 to 3.   The cord constituting the outermost belt layer has a double twist structure, and the value obtained by raising the cord diameter to the fourth power is less than 400 times the sum of the values obtained by raising the filament diameter constituting one cord to the fourth power. The pneumatic tire according to any one of Items 1 to 3.

Images