JP2004042907A - Radial tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radial tire for a heavy load furnished with a belt capable of improving a cut separation proofing property without spoiling a cut through proofing property of a tread part. <P>SOLUTION: A belt is furnished with four layers of main crossing layers in which chords cross with each other between the adjoining layers, these layers are sequentially specified as a first layer to a fourth layer toward the outside in the tire radial direction from the belt layer nearest a carcass, the second layer has width within a range of 70 to 85% of tread width at the tread part which is the largest width of the main crossing layer, and the fourth layer is made into a narrow rigidity reinforced layer where the width is within a range of 50 to 60% of the maximum width of the main crossing layer and the chord is arranged inclined within a range of 5 to 15% against a tire equatorial surface. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a heavy-duty radial tire with improved durability related to a belt, and in particular, advantageously achieves compatibility between cut separation resistance and cut penetration resistance in a tread portion among durability mainly related to a belt. Heavy-duty radial tires.

Tires used for heavy-duty vehicles that run on rough terrain, rough roads, or roads scattered with protruding foreign matter, although they are partial, will not often have deep cuts on the outer part of the tread, that is, the tread rubber. Even if this is not obtained, there is a strong tendency not to stop at this cut damage but also to a failure called cut separation. The cut separation failure referred to here means that, when deep cut damage such as reaching the belt in the central area of the tread area occurs, separation along the outer circumferential surface of the belt from the cut damage site as the tire progresses. Refers to failures that progress to

This separation is caused by the deformation behavior in which the belt is bent in the tread circumferential direction (hereinafter abbreviated as circumferential direction) at the tread portion and the kick-out portion of the tread during rolling of the tire. It is derived from the effect of shear strain generated between the tread rubber and the tread rubber. Since such cut separation occurs between the tread rubber and the outer peripheral surface of the belt, the tire is removed at that point when the separation area is conspicuously expanded or sometimes the tread rubber in the separation portion is peeled off. This is a serious problem.

Therefore, conventionally, it has been attempted to increase the circumferential bending stiffness of the belt as much as possible in order to suppress the above-mentioned shear strain, and in practice, to minimize the inclination arrangement angle of the cord in the belt layer, in this case, mainly the steel cord in the circumferential direction. I have been.

However, the above-mentioned trial did not show a remarkable improvement effect on the cut separation property. This is because the smaller the angle of inclination of the cord, the more likely it is that another separation will occur at the end of the belt.Considering this point, the angle of inclination of the cord is reduced and the belt is bent in the circumferential direction. This is because the means for improving the rigidity is naturally limited, and as a result, the desired excellent cut separation resistance is not achieved.

Furthermore, if the bending rigidity of the entire belt is increased by reducing the cord inclination arrangement angle, the envelope (EP) property when the tread portion rides on a protrusion such as rock, that is, the wrapping property of the protrusion is deteriorated. In addition to increasing the chance of the tread receiving cuts, the cuts become deeper, which leads to a so-called cut-through failure, which sometimes penetrates the entire tread, which is a fatal failure.

Accordingly, an object of the present invention is to provide a heavy-duty radial tire having both excellent cut separation resistance and sufficient cut penetration resistance while maintaining sufficient separation resistance at the end of the belt. To provide.

To achieve the above object, a radial tire for heavy load according to the present invention includes a radial carcass for reinforcing a sidewall portion and a tread portion between bead cores embedded in a pair of bead portions, and a tread portion reinforced at an outer periphery of the carcass. A heavy duty radial tire having a belt made of a steel cord crossing layer, wherein the belt has four main crossing layers where the cords cross each other between adjacent layers, and the belt extends radially outward from the cord layer closest to the carcass. As a first layer to a fourth layer, the second layer has a width within a range of 70 to 85% of a tread width in a tread portion that is a maximum width of the main cross layer, and the fourth layer has An array whose width is within the range of 50 to 60% of the maximum width of the main intersection layer, and the cord is inclined within a range of 5 to 15 ° with respect to the tire equatorial plane. Characterized in that it is a narrow rigid reinforcing layer composed. Further, it is preferable that another narrow width enhancement layer is provided as the first layer.

The present invention will be described in detail below with reference to FIGS.
FIG. 1 to FIG. 3 are cross-sectional views schematically illustrating main parts of a left half cross section of the tire. Each cross section is symmetrical. In each figure, 1 is a sidewall portion, 2 is a tread portion, 3 is a tread rubber, 4 is a carcass, and 5 is a belt. The carcass 4 comprises a rubberized ply of radially arranged cords, reinforces the sidewall portion 1 and the tread portion 2 between the bead cores embedded in a pair of bead portions (not shown), and the belt 5 comprises a plurality of steel cord layers. Layer.

The belt 5 shown in FIG. 1 includes four main cross layers 1B to 4B and one protective layer Bp, and the belt 5 illustrated in FIG. 2 includes four main cross layers 1B to 4B and is illustrated in FIG. The belt 5 includes four main cross layers 1B to 4B and one protective layer Bp. In each of the drawings, the main crossing layer is denoted by B with reference numerals 1 to 4 indicating the first to fourth layers in order from the cord layer closest to the carcass 4 toward the tire radially outward (narrow width). The rigidity enhancement layer is as follows). The codes of the respective layers of the main intersection layers 1B to 4B are arranged so as to cross each other between adjacent layers, that is, between 1B and 2B, between 2B and 3B, and between 3B and 4B. The tread width of the tread portion 2 is denoted by Wt, and the maximum width of the main cross layer is denoted by Wb, where the maximum width Wb is within a range of 70 to 85% of the tread width Wt.

The narrow rigidity enhancement layer is represented by a particularly thick solid line in each drawing, and the suffix r is added to B and is indicated by Br. The narrow rigidity enhancement layer of the present invention is applied to the fourth layer, and is indicated by 4Br in each drawing. Further, in the example shown in FIG. 3, the present invention is also applied to the first layer 1Br closest to the carcass 4.

The width of the narrow rigidity reinforcing layer Br is indicated by w in each figure, and the width w of the reinforcing layer Br is set to be within a range of 50% to 60% of the maximum width Wb. Are arranged at an angle of 5 to 15 degrees with respect to the tire equatorial plane E. It is desirable that the inclination angle of each of the other layers B be 18 to 35 degrees. Due to the distribution of the inclination angles, the cord of the rigidity strengthening layer Br bears a considerably large tension when filling the tire with the internal pressure, so that the steel having a larger diameter, that is, a higher tensile strength than the cords of the other layers B. It is desirable to apply the code.

Further, since the protection layer Bp is provided for the purpose of protecting the main cross layer from being cut, the protection layer Bp is disposed on the outer peripheral side of the main cross layer as a rubberized layer of a so-called high elongation steel cord. Is appropriate.

結果 As a result of intensive research, it was first clarified that the cut separation failure evolved from a cut injured in the tread portion 2, particularly in the central region. Therefore, it has been clarified that the occurrence of cut separation failure can be effectively suppressed by reducing the above-described shear strain in the central region, that is, by increasing the circumferential bending rigidity of the belt 5 in the central region.

Next, the magnitude of the circumferential bending stiffness of the belt 5 depends not only on the laminating effect of the cord layers constituting the belt 5 but also significantly depending on the magnitude of the circumferential tension generated on the belt 5 when the tire is filled with the internal pressure. From the fact, it has been found that the bending rigidity in the central region of the tread portion 2 can be increased by increasing the tension at the time of filling the belt 5 with the internal pressure.

As a result of further research, the value of the shear strain generated in the central region of the tread portion 2 is determined by the value of the circumferential tension acting on the central region of the main cross layer corresponding to 50 to 60% of the maximum width Wb of the main cross layer of the belt 5. It has been found that the value is governed by the value, that is, the value of the former can be reduced by increasing the value of the circumferential tension of the latter.

As shown in FIG. 5, the circumferential tension distribution acting on the belt 5 when the tire is filled with the internal pressure is a parabolic curve having a maximum value at the width center position E ′ of the belt 5 (substantially the same position as the tire equatorial plane E). In the figure, a solid line shows a distribution diagram of a conventional tire, and a broken line shows a distribution diagram of a tire according to an embodiment of the present invention. Here, as a result of examining the sum of the circumferential tensions (the areas A and A 'surrounded by the horizontal axis and the curve), even if the cord layer structure of the belt 5 is changed, for example, the inclination angle of the cord with respect to the tire equatorial plane E is changed. Even if it is changed, the sum of the circumferential tensions is almost constant (for example, the area A ≒ A ′), and even if the inclination angle of the cord of each layer of the belt is reduced, no significant change is observed in the circumferential tension distribution curve. It turns out.

However, the width w of the main crossing layers 1B to 4B is 50 to 60% of the maximum width Wb of 70 to 85% of the tread width Wt, and the cord is 5 to the tire equatorial plane E. By providing, as the fourth layer 4Br, one narrow width rigidity strengthening layer Br having a steep inclination arrangement within the range of 〜15 °, the circumferential tension of the belt 5 is increased at the center as shown by the broken line in FIG. It is possible to transform the distribution into a significantly prominent distribution. This is because the circumferential tension load on the reinforcement layer Br portion is more remarkably increased than the circumferential tension load on the main cross layer B composed of the gentle inclined arrangement cord layers excluding the reinforcement layer Br.

As described above, since the circumferential tension acting on the belt 5 can be intensively borne at the central portion of the belt 5, bending deformation in the central region of the tread portion 2 is largely suppressed, and as a result, the tread portion 2 is stepped on. The shear strain between the tread rubber 3 and the belt 5 generated at the portion and the kick-out portion is significantly reduced, so that even if a deep cut reaching the belt 5 in the central area of the tread portion 2 is received. In addition, it is possible to effectively prevent the progress of separation from the cut scratch, and to improve cut separation resistance.

The one narrow width rigidity strengthening layer Br needs to be arranged as a fourth layer 4Br, and when the tread portion 2 rides on the protrusion having the blunt tip, the cord layer close to the carcass 4 at the climbing point is required. This is because the larger the tension, the greater the tension applied to B, and there is the joy of cutting the cord. Therefore, even if the layer Br is arranged as the fourth layer 4Br, in consideration of the high cord tension at the time of filling the internal pressure, the cord of the layer Br is maintained in order to maintain high resistance to cutting the cord when riding on the protrusion. It is desirable that the diameter be larger than the cord diameter of the inner layer B than the layer Br.

Further, by providing another narrow width stiffening layer as the first layer 1Br, the circumferential tension in the central region of the belt 5 indicated by the broken line in FIG. 5 is further increased, so that the cut separation resistance is further improved.

At this time, the increase in the cord tension in the narrow width rigidity enhancement layer 1Br when the protrusions are climbed is achieved by disposing the layers 1Br and 4Br as a pair so that the cords of both the layers 1Br and 4Br disperse the burden of the tension increase. , So that it is possible to eliminate the joy of the code disconnection failure of the layer 1Br.

By arranging the narrow width stiffening layer Br having high bending stiffness in the central region of the belt 5, the rigidity in both side regions of the central region is significantly reduced as compared with the rigidity of the conventional belt 5 '(see FIG. 4). Therefore, when the tread portion 2 rides on the protrusion, the tread portion 2 including the belt 5 including the narrow rigidity enhancement layer Br is more easily deformed in the tread width direction than the tread portion 2 including the conventional belt 5 '. It shows easy behavior. This does not result in a significant improvement in the EP property, and thus the cut resistance and the cut penetration resistance are significantly improved. If a high elongation steel cord layer is provided as a protective layer Bp outside the main intersection layer, the performance of these characteristics is further improved.

Here, when the inclination angle of the cord of the narrow rigidity enhancement layer Br with respect to the tire equatorial plane E exceeds 15 °, the circumferential tension in the central region of the belt 5 is insufficiently improved. Even if they are not stacked adjacently, separation failure is likely to occur at the end of the reinforcing layer Br, so neither is possible. In addition, the reason why the width w of the narrow rigidity reinforcing layer Br is set to 50 to 60% of the maximum width Wb of the main cross layer of the belt 5 is that the shear strain leading to the cut separation failure is caused by the main cross layer maximum width Wb. This is because it corresponds to the circumferential tension distribution in the 50 to 60% region.

In addition, regarding the general separation resistance not derived from the cut of the belt 5, since this separation occurs at the end of the wide cord layer, the disadvantage of providing the narrow rigidity enhancement layer Br is completely avoided, and the above separation resistance is reduced. We can secure enough.

(A) radial ply tires (TBR) for trucks and buses;
The size is 275 / 80R22.5, and the main configuration thereof is in accordance with FIG. 2 (Example 1). The tread width Wt is 210 mm, the carcass 4 is made of a rubberized ply of a one-ply radially arranged steel cord, and the steel cord applied to each cord layer of the belt 5 has a structure of (3 + 9 + 15) × 0.23 mm and a cord diameter. Is 1.4 mm. In addition, tires of Conventional Example 1 and Comparative Example 1 were prepared in accordance with the embodiment, except that a belt 5 'having a different configuration was provided, including all types of steel cords. FIG. 4 (a) shows the main part of the left half section of these tires. Table 1 shows the specifications of each layer of the belts 5 and 5 'as 4B to 1B (a portion surrounded by a thick frame in the table is a narrow rigidity strengthening layer Br). The width / angle described in Table 1 is the code layer width (mm) / cord inclination angle (degree, angle with respect to the tire equatorial plane E). Indicates an ascending sequence of codes. The number of hits is the number of cords hit per 25 mm.

(B) radial ply tires (ORR) for construction vehicles;
The size is 37.00R57, and the configuration of the main part thereof is as shown in FIG. 1 for the second embodiment and FIG. 3 for the third embodiment. The tread width Wt is 840 mm, the carcass 4 is made of a rubberized ply of one ply radially arranged steel cord, and the steel cord applied to each cord layer of the belt 5 is as follows.
Layers 4B, 3B: twisted structure (3 + 9 + 15) × 7 × 0.175 mm, cord diameter 3.2 mm.
Layers 2B, 1B: twisted structure (3 + 9) × 7 × 0.23 mm, cord diameter 2.8 mm.
Layer Bp: twist structure 3 × 7 × 0.23 mm, cord diameter 1.6 mm.
In addition, tires of Conventional Example 2 and Comparative Example 2 were prepared, all including the steel cord type except for the belt 5 'having a different configuration according to the embodiment. FIG. 4B shows a main part of the left half section of these tires. Table 2 shows the specifications of the respective layers 4B to 1B of the belts 5 and 5 '(a portion surrounded by a thick frame in the table is a narrow rigidity enhancement layer Br). The width / angle and the number of hits described in Table 2 are the same as in the case of the TBR tire.

Using the tires of Examples 1 to 3 and Conventional Examples 1 and 2 and Comparative Examples 1 and 2 as test tires, cut separation resistance and cut penetration resistance were tested by the following evaluation methods.
Cut separation resistance: A tire with a cut wound reaching the belt 5, 5 'in the center of the tread in the width direction is applied to a load equivalent to the maximum load capacity (kg) and the corresponding air pressure (kgf / cm) ² ) After running the drum under the filling and running for a predetermined time, measure the separation length from the cut.
Cut penetration resistance: According to the so-called plunger test. A plunger for TBR tires is 38 mm in diameter, and a plunger for ORR tires is 90 mm in diameter. A steel round bar with a hemispherical tip is fixed vertically, and each test tire is pressed against these hemispherical tips under the above air pressure filling. The plunger is lowered vertically to measure the energy required for the plunger to break the tire (integral value of the force F applied to the plunger and the stroke S to the break).

The results of measurement of the above two characteristics are expressed by the index notation that the TBR tire is Conventional Example 1 and the ORR tire is Conventional Example 2 each being 100, and these index values are shown in the lower part of Tables 1 and 2 above. It shows together. The higher the value, the better. In each table, the cut separation resistance is abbreviated as cut separation resistance.

From Tables 1 and 2, each of the tires of Examples 1, 2 and 3 has both excellent cut-separation resistance and cut-penetration resistance as compared with the corresponding conventional tires 1 and 2, respectively. You can see that it is. On the other hand, the tires of Comparative Examples 1 and 2 all show that the cut penetration resistance is significantly reduced, confirming the unique effects of each of the examples. Although not shown in each table, when the separation resistance at the end portion of the belt 5 was separately evaluated, the tires of the examples showed excellent durability comparable to the conventional example and the comparative example. I have.

ADVANTAGE OF THE INVENTION According to this invention, after maintaining the separation resistance of a belt edge part sufficiently, this performance can be improved rather than accompanied with the deterioration of cut penetration resistance, and the cut separation resistance can be highly enhanced. It is possible to provide a long-life radial tire with a long life that can be used.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which illustrated the principal part of the radial tire for heavy loads of one Example by this invention. It is sectional drawing which illustrated the principal part of the radial tire for heavy loads of another Example by this invention. It is sectional drawing which illustrated the principal part of the radial tire for heavy loads of another Example by this invention. It is sectional drawing which illustrated the principal part of the conventional radial tire for heavy loads. FIG. 3 is a circumferential tension distribution diagram in a main cross layer width direction of the belt.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Side wall part 2 Tread part 3 Tread rubber 4 Carcass 5 Belt 1Br, 2Br, 3Br, 4Br Narrow stiffness enhancement layer 1B, 2B, 3B, 4B Belt cord layer Wt Tread width Wb Maximum width w of main cross layer w Narrow width Rigid reinforcement layer width

Claims (2)

In a heavy-duty radial tire having a radial carcass that reinforces a sidewall portion and a tread portion between bead cores embedded in a pair of bead portions, and a belt made of a steel cord cross layer that reinforces a tread portion at an outer periphery of the carcass. ,
The belt is provided with four main cross layers in which cords cross each other between adjacent layers, and as a first layer to a fourth layer in order from the cord layer closest to the carcass toward the tire radially outward, the second layer has a main cross layer. The fourth layer has a width in the range of 70-85% of the tread width in the tread portion, which is the maximum width of the layer, and the fourth layer has a width in the range of 50-60% of the maximum width of the main cross layer. A radial tire for heavy loads, characterized in that the cord is a narrow width rigidity reinforcing layer arranged in an array inclined within a range of 5 to 15 ° with respect to the tire equatorial plane. (4) The heavy-duty radial tire according to (1), wherein another narrow reinforcing layer is provided as the first layer.

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