JP2005238995A - Pneumatic radial tire for construction vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for a construction vehicle capable of improving the envelope characteristic without degrading the strength of a belt layer and a carcass layer. <P>SOLUTION: In the pneumatic radial tire for the construction vehicle in which at least one carcass layer 15 with a plurality of steel cords S arranged in the tire radial direction between a pair of right-to-left bead parts is mounted, and at least two belt layers 1B-7B with cords intersected with each other between the layers are arranged on the outer circumferential side of the carcass layer 15 at a crown part, the steel cords S of the carcass layer 15 are curved in a wavy shape at the crown part, and the amplitude (Ac, As) of the steel cords S are gradually reduced from the crown center side to the shoulder side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire for a construction vehicle suitable for traveling on rough terrain such as a civil engineering construction site. More specifically, the present invention provides an envelope characteristic without reducing the strength of a belt layer or a carcass layer in a crown portion. The present invention relates to a pneumatic radial tire for construction vehicles that can be improved.

  In the pneumatic radial tire for construction vehicles, at least one steel cord carcass layer is mounted between a pair of left and right bead portions, and at least two steel cord belt layers are disposed on the outer peripheral side of the carcass layer in the crown portion. It is configured (see, for example, Patent Document 1).

  Such pneumatic radial tires for construction vehicles are superior in puncture resistance performance compared to conventional pneumatic tires having a bias structure, but the bending rigidity of the crown portion is increased, so that the envelope on uneven terrain is increased. There is a problem that characteristics deteriorate. In particular, in the case of a pneumatic radial tire used for a large construction vehicle such as a dump truck having a maximum loading capacity of 50 tons or more, the deterioration of the envelope characteristics is remarkable. When the envelope characteristics are deteriorated, the proportion of the impact received from the road surface by the tread rubber itself is higher than that of the bias tire. Therefore, even if a tread rubber excellent in cut resistance is employed, sufficient cut resistance cannot be exhibited, and the tread rubber is likely to break (cut) or chip (chipping) after the middle stage of wear.

On the other hand, if the strength of the belt layer (the product of the number of cords driven per unit width and cord breaking strength) is reduced in order to improve the envelope characteristics, the durability of the belt layer may be reduced due to the reduced tagging effect, The reinforcement effect by a layer will fall. In addition, when the strength of the carcass layer is reduced in order to improve the envelope characteristics, durability and pressure resistance at the tire side portion are reduced, and steering stability is reduced. Therefore, it is not practical to improve the envelope characteristics based on the change in strength of the belt layer or the carcass layer.
JP-A-11-227414

  An object of the present invention is to provide a pneumatic radial tire for a construction vehicle that can improve the envelope characteristics without reducing the strength of the belt layer and the carcass layer.

  In order to achieve the above object, a pneumatic radial tire for construction vehicles according to the present invention has at least one carcass layer formed by arranging a plurality of steel cords in the tire radial direction between a pair of left and right bead portions. In addition, in the pneumatic radial tire for a construction vehicle in which at least two belt layers in which the cords cross each other are arranged on the outer peripheral side of the carcass layer in the crown portion, the steel cord of the carcass layer is waved in the crown portion. The carcass layer is bent and the amplitude of the steel cord is gradually reduced from the crown center side toward the shoulder side.

  In the present invention, the steel cord of the carcass layer is curved in a wave shape at the crown portion, thereby reducing the contribution of the carcass layer to the bending stiffness in the tire meridian cross-sectional direction, thereby reducing the bending stiffness of the crown portion in the tire meridian cross-sectional direction. Let Therefore, the envelope characteristics can be improved without reducing the strength of the belt layer or the carcass layer. Further, by improving the envelope characteristics, it becomes possible to achieve both puncture resistance and cut / chipping resistance in a pneumatic radial tire for construction vehicles.

  Further, when the carcass cord is linearly arranged in the tire radial direction at the crown portion as in the prior art, the tension of the carcass cord locally increases when the protrusion rides, and the carcass cord may break. Then, since the carcass cord curved in a wavy shape relaxes the tension, it is possible to avoid the carcass cord from being broken at the time of riding on the protrusion.

  Furthermore, in the present invention, since the bending rigidity of the crown portion in the tire meridian cross-sectional direction is adjusted by curving the carcass cord in a wave shape, the degree of freedom in designing the belt structure is increased. That is, in the conventional pneumatic radial tire, the steel cord of the carcass layer is arranged linearly at an angle of approximately 90 ° with respect to the tire circumferential direction in the crown portion, while the cord angle of the belt layer, the width, the laminated structure, Although the rigidity of the crown portion is optimized by adjusting the belt structure such as strength, in the present invention, the rigidity of the crown portion is adjusted based on the carcass structure, so the belt structure design condition is eased.

  In the present invention, it is necessary to gradually reduce the amplitude of the steel cord of the carcass layer from the crown center side toward the shoulder side. That is, if the amplitude of the steel cord of the carcass layer is increased as much as possible, the effect of improving the envelope characteristics is also increased. On the other hand, when the amplitude on the shoulder side is increased, the rise of the shoulder due to the internal pressure is increased, The durability of the belt layer is reduced. Therefore, the amplitude of the steel cord is gradually reduced from the crown center side toward the shoulder side.

Specifically, the amplitude Ac of the corrugated portion located closest to the crown center of the carcass layer is set to 15 mm or more, and the relationship between the quarter wavelength λc of the corrugated portion having the amplitude Ac and the amplitude Ac is tan ^−1. While (Ac / λc) ≧ 30 °, the amplitude As of the waveform portion located on the most shoulder side of the carcass layer is set to 10 mm or less, and the quarter wavelength λs of the waveform portion having the amplitude As and the amplitude As And tan ⁻¹ (As / λs) ≦ 10 ° is preferable.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a pneumatic radial tire for construction vehicles according to an embodiment of the present invention, FIG. 2 shows an extracted portion of the carcass layer and belt layer in the tire circumferential direction, and FIG. 3 shows the steel of the carcass layer. Indicates a code. In FIG. 1, 11 is a crown portion, 12 is a shoulder portion, 13 is a sidewall portion, 14 is a bead portion, and CL is a tire center line. A carcass layer 15 in which a plurality of steel cords are arranged in the tire radial direction is mounted between the pair of left and right bead portions 14, 14, and the end portion in the tire width direction of the carcass layer 15 is around the bead core 16. The tire is wound up from the inside to the outside.

  On the outer peripheral side of the carcass layer 15 in the crown portion 11, seven belt layers 1 </ b> B to 7 </ b> B each including a plurality of steel cords are provided. The belt layers 1B to 7B are arranged such that the cords are inclined with respect to the tire circumferential direction and the cords cross each other between the layers. Among these belt layers 1B to 7B, the cord angle with respect to the tire circumferential direction of the narrow belt layers 1B and 2B is set in a range of 15 ° to 22 °, and the cord angle with respect to the tire circumferential direction of the other belt layers 3B to 7B. Is set in the range of 20 ° to 35 °.

  In the pneumatic radial tire, as shown in FIG. 2, the steel cord S of the carcass layer 15 is arranged linearly at an angle of substantially 90 ° with respect to the tire circumferential direction from the bead portion to the shoulder portion. However, the crown portion from one shoulder portion to the other shoulder portion is curved in a wave shape.

  Thus, when the steel cord S of the carcass layer 15 is bent in a wave shape at the crown portion, the strength of the belt layers 1B to 7B and the carcass layer 15 (the product of the number of cords driven per unit width and the cord breaking strength) is changed. Even without this, it is possible to improve the envelope characteristics by reducing the bending rigidity of the crown portion in the tire meridian cross-sectional direction. As a result, the pneumatic radial tire for construction vehicles can exhibit excellent puncture resistance performance based on the radial structure, while exhibiting cut / chipping resistance performance based on the improved envelope characteristics.

The amplitude of the steel cord S of the carcass layer 15 is gradually reduced from the crown center side toward the shoulder side. More specifically, as shown in FIG. 3, the amplitude Ac of the corrugated portion located closest to the crown center of the carcass layer 15 is 15 mm or more, preferably 15 to 35 mm, and 4 of the corrugated portion having the amplitude Ac. The fractional wavelength λc and the amplitude Ac satisfy the relationship of tan ⁻¹ (Ac / λc) ≧ 30 °, preferably 30 ° ≦ tan ⁻¹ (Ac / λc) ≦ 62 °. By setting the amplitude Ac and the wavelength λc as described above, the bending rigidity of the carcass layer 15 in the tire meridian cross-sectional direction can be effectively reduced, and the effect of improving the envelope characteristics can be sufficiently obtained. Here, if Ac <15 mm or tan ⁻¹ (Ac / λc) <30 °, the effect of improving the envelope characteristics becomes insufficient.

When the above numerical range defined by the amplitude Ac and the wavelength λc is applied to the vicinity of the belt edge, the shoulder rises due to the internal pressure, and the durability of the belt layer decreases. Therefore, the amplitude As of the waveform portion located on the most shoulder side of the carcass layer 15 is 10 mm or less, and the quarter wavelength λs of the waveform portion having the amplitude As and the amplitude As are tan ⁻¹ (As / λs). The relationship of ≦ 10 ° is satisfied. By setting the amplitude As and the wavelength λs as described above, it is possible to avoid a decrease in durability of the belt layer.

  When the structure of the carcass layer 15 is defined as described above, not only the envelope characteristics are improved, but also the carcass cord can be prevented from being broken when the protrusion is run. In addition, since the bending rigidity in the tire meridian cross-sectional direction can be adjusted based on the structure of the carcass layer 15, the design freedom of the belt layers 1B to 7B is increased.

  In the above embodiment, a pneumatic radial tire for construction vehicles having one carcass layer and seven belt layers has been described. However, the present invention is a construction having at least one carcass layer and at least two belt layers. It can be applied to pneumatic radial tires for vehicles.

  With a tire size of 2400R35, a single carcass layer in which a plurality of steel cords are arranged in the tire radial direction is mounted between a pair of left and right bead portions, and a cord is provided between the outer peripheral sides of the carcass layer in the crown portion. In the pneumatic radial tire for type 1 construction vehicles in which seven belt layers intersecting each other are arranged, the tires of the conventional examples, the comparative examples 1 and 2 and the examples in which only the structure of the carcass layer is varied are manufactured. .

The structure of the belt layer of each tire is shown in Table 1. However, the first belt layer and the second belt layer located on the inner side in the tire radial direction are arranged only in the crown center region.

  On the other hand, for the carcass layer, the number of driven steel cords (7 × 7 × 0.23) per unit width was 12.5 / 50 mm. In the conventional tire, as shown in FIG. 4, the steel cords of the carcass layer are arranged linearly in the crown portion. In the tires of Comparative Examples 1 and 2, as shown in FIG. 5, the steel cord of the carcass layer was curved in a wave shape at the crown portion, and the amplitude and wavelength were made constant from the crown center side to the shoulder side. In the tire of the example, as shown in FIG. 2, the steel cord of the carcass layer was curved in a wave shape at the crown portion, and the amplitude and wavelength were gradually decreased from the crown center side toward the shoulder side. Further, the carcass layer is folded around the bead core from the inside to the outside of the tire, and the folded height is 55% of the tire cross-sectional height.

  For these test tires, the durability and envelope characteristics of the belt layer were evaluated by the following test methods, and the results are shown in Table 2.

Durability of belt layer:
Each test tire is mounted on a test rim having a rim size of 17.00 × 33 (3.5) OR, filled with a specified internal pressure (700 kPa), and a rotating drum under the conditions of a load rate of 120% (218 kN) and a speed of 8 km / h. After running for 240 hours with a testing machine, the outer diameter growth amount (Δs) of the tire shoulder portion was measured with reference to the tire mold. In a tire in which the outer diameter growth amount Δs exceeds 18 mm, a separation failure between the belt layers tends to easily occur due to a large initial strain of the belt layer.

Envelope characteristics:
Each test tire was mounted on a test rim having a rim size of 17.00 × 33 (3.5) OR and filled with a specified internal pressure (700 kPa). Then, as shown in FIG. 6, when the load is increased in a state where the square member W having a width of 100 mm × the height of 100 mm is sandwiched between the tires T at the position where it becomes the tread grounding center, and the tire T is grounded across the square members The applied load was measured. It means that the smaller the load, the better the envelope characteristics.

  As can be seen from Table 2, the tires of the examples had better envelope characteristics than the conventional examples, and the durability of the belt layer was not lowered. On the other hand, in the tire of Comparative Example 1, although the effect of improving the envelope characteristics was recognized, the durability of the belt layer was insufficient. In the tire of Comparative Example 2, although the durability of the belt layer was ensured, the effect of improving the envelope characteristics was not recognized.

It is a meridian half sectional view showing a pneumatic radial tire for construction vehicles according to an embodiment of the present invention. FIG. 2 is a development view showing a portion of the carcass layer and the belt layer in the tire circumferential direction extracted from the pneumatic radial tire of FIG. 1. FIG. 2 is a plan view showing a steel cord of a carcass layer in the pneumatic radial tire of FIG. 1. FIG. 6 is a development view showing a part of the circumferential direction of a carcass layer and a belt layer in a pneumatic radial tire for construction vehicles according to a conventional example. FIG. 5 is a development view showing a part of the carcass layer and the belt layer in the tire circumferential direction in a pneumatic radial tire for construction vehicles according to a comparative example. It is explanatory drawing which shows the test method of an envelope characteristic.

Explanation of symbols

1B-7B Belt layer 11 Tread portion 12 Shoulder portion 13 Side wall portion 14 Bead portion 15 Carcass layer 16 Bead core S Steel cord Ac Amplitude of corrugated portion on the crown center side As Amplitude of corrugated portion on the shoulder side λc Corrugated portion on the crown center side 1/4 wavelength of λs 1/4 wavelength of the waveform part on the shoulder side

Claims (2)

At least one carcass layer in which a plurality of steel cords are arranged in the tire radial direction is mounted between a pair of left and right bead portions, and the cords cross each other on the outer peripheral side of the carcass layer in the crown portion. In a pneumatic radial tire for construction vehicles in which at least two belt layers are arranged, the steel cord of the carcass layer is curved in a wave shape at the crown portion, and the amplitude of the steel cord of the carcass layer is changed from the crown center side to the shoulder side. Pneumatic radial tire for construction vehicles that gradually decreases toward the front. The amplitude Ac of the waveform portion located closest to the crown center of the carcass layer is set to 15 mm or more, and the relationship between the quarter wavelength λc of the waveform portion having the amplitude Ac and the amplitude Ac is expressed as tan ⁻¹ (Ac / λc). ) While ≧ 30 °, the amplitude As of the waveform portion located on the most shoulder side of the carcass layer is 10 mm or less, and the relationship between the quarter wavelength λs of the waveform portion having the amplitude As and the amplitude As The pneumatic radial tire for construction vehicles according to claim 1, wherein tan ⁻¹ (As / λs) ≦ 10 °.

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