JP2006176012A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire, suppressing the occurrence of distortion in a belt edge part and improving belt durability. <P>SOLUTION: The size of each organic fiber cord constituting at least one carcass layer 4A is 5,000 to 14,000 dtex, and an interval of the cords in a ply at a tread center position of the carcass layer 4A is 0.4 to 4.0 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire provided with a carcass layer made of an organic fiber cord. More specifically, the present invention relates to a pneumatic radial tire that suppresses the occurrence of distortion at a belt edge portion and improves belt durability. About.

In a pneumatic radial tire, an organic fiber cord is sometimes used for a carcass material for reasons such as manufacturing simplicity and weight reduction (for example, see Patent Document 1). However, for example, a pneumatic radial tire for a small truck has a maximum use air pressure of about 350 to 650 kPa, and similarly has a higher internal pressure than a pneumatic radial tire for a passenger car that uses an organic fiber cord carcass material. Since the casing strength (tensile strength) that can be tolerated is necessary, it is required to increase the number of carcass materials and increase the driving density of the organic fiber cord. As a result, in this type of pneumatic radial tire, the bending rigidity of the sidewall portion is high, the sidewall portion does not bend sufficiently when a load is applied to the tire, the strain concentrates on the belt edge portion, and belt durability There is a problem that gets worse.
JP-A-6-24206

  An object of the present invention is to provide a pneumatic radial tire that can suppress the occurrence of distortion at a belt edge portion and improve belt durability.

  In order to achieve the above object, the pneumatic radial tire of the present invention has an organic fiber cord constituting at least one carcass layer having a thickness of 5,000 to 14000 dtex, and an in-ply cord interval at a tread center position of the carcass layer. Is 0.4 to 4.0 mm.

  The present inventor pays attention to the deformation of the sidewall portion when a load is applied to the tire, and adopts a carcass structure that easily causes eccentric deformation while securing tensile strength, thereby generating distortion at the belt edge portion. This is to suppress the belt durability.

  That is, in the present invention, by adopting a thick organic fiber cord for the carcass layer, while ensuring the tensile strength that can withstand high internal pressure, the in-plane shear rigidity of the carcass layer is increased by increasing the inter-ply cord interval of the carcass layer. Is reduced. As a result, the sidewall portion is likely to bend with eccentric deformation, so that the occurrence of distortion at the belt edge portion can be suppressed and the belt durability can be improved.

  In the present invention, in the case of a pneumatic radial tire including at least two carcass layers made of organic fiber cords, the inner-ply cord interval at the tread center position of the innermost carcass layer is set to 0.3 to 1.5 mm. The thickness of the organic fiber cord constituting the at least one carcass layer excluding the innermost carcass layer is 5000 to 14000 dtex, and the in-ply cord interval at the tread center position of the at least one carcass layer is 0.00. The thickness is preferably 4 to 4.0 mm.

  In other words, when the inner liner layer is directly bonded to the carcass layer in which thick organic fiber cords are arranged at a low driving density, the inner liner layer is pushed between the cords of the carcass layer by the internal pressure during vulcanization, and air pressure retention May decrease. Therefore, by providing a carcass layer having a relatively high driving density of organic fiber cords on the innermost side, it is possible to maintain good air pressure retention while enjoying the effect of improving belt durability. The thickness of the organic fiber cord of the innermost carcass layer is preferably 1880 to 5520 dtex.

  Furthermore, in the present invention, in order to reduce the bending rigidity of the sidewall portion, it is also effective to regulate the winding height TUH of the carcass layer and the height BFH of the bead filler. That is, at least one carcass layer is wound up so as to wrap the bead core and the bead filler, the carcass layer winding end is disposed at a position higher than the apex of the bead filler, and the carcass layer winding height TUH is set to the tire. A relation of 0.3 × SH ≦ TUH ≦ 0.7 × SH is preferable with respect to the cross-sectional height SH. Alternatively, at least one carcass layer is wound up so as to wrap the bead core and the bead filler, the apex of the bead filler is arranged at a position higher than the winding end of the carcass layer, and the height BFH of the bead filler is set to the tire cross section. A relation of 0.25 × SH ≦ BFH ≦ 0.6 × SH may be made with respect to the height SH.

  The use of the pneumatic radial tire of the present invention is not particularly limited, but it is suitable for small trucks. In particular, a remarkable effect is obtained in a pneumatic radial tire for a small truck having a flatness ratio of 50 to 75% and an air pressure corresponding to the maximum load capacity in a range of 350 to 650 kPa. The flatness ratio is the ratio of the tire cross-section height to the tire cross-section width, and is a value expressed in the tire size. The air pressure corresponding to the maximum load capacity is the air pressure corresponding to the maximum load capacity specified by the standard, for example, the air pressure specified in the air pressure-load capacity correspondence table of the JATMA Yearbook (2004 edition). .

  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 a small truck according to an embodiment of the present invention. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. Two carcass layers 4 </ b> A and 4 </ b> B are mounted between the pair of bead portions 3 and 3. Each of these carcass layers 4A and 4B is composed of a plurality of organic fiber cords oriented in the tire radial direction. As the organic fiber cord, nylon cord, polyester cord, or the like can be used. The organic fiber cord may be either a multifilament or a monofilament, but a multifilament twist cord is more preferable. The innermost carcass layer 4 </ b> A is wound up from the inside of the tire to the outside so as to wrap the bead core 5 and the bead filler 6 embedded in the bead portion 3. In addition, the carcass layer 4B located outside the carcass layer 4A is disposed so as to extend to the lower side of the bead core 5 through the outside of the winding portion of the carcass layer 4A.

  On the other hand, on the outer peripheral side of the carcass layers 4A and 4B in the tread portion 1, a plurality of belt layers 7 are embedded over the entire circumference of the tire. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. Further, a belt cover layer 8 formed by winding a reinforcing cord in the tire circumferential direction is provided at the end of the belt layer 7 in the tire width direction.

  In the pneumatic radial tire, an organic fiber cord having a thickness (total fineness) in the range of 5000 to 14000 dtex is used for the carcass layer 4B, and the inter-ply cord interval at the tread center position of the carcass layer 4B is 0.00. It is set to 4 to 4.0 mm. On the other hand, an organic fiber cord having a thickness (total fineness) in the range of 1880 to 5520 dtex is used for the innermost carcass layer 4A, and the inter-ply cord interval at the tread center position of the carcass layer 4A is 0.3 to It is set to 1.5 mm. The inter-ply cord interval is a mutual interval T of cords C measured along the surface direction of the carcass layers 4A and 4B, in other words, the rubber thickness between cords, as shown in FIG.

  By adopting a thick organic fiber cord for the carcass layer 4B as described above, a tensile strength that can withstand high internal pressure is secured, and by increasing the inter-ply cord distance of the carcass layer 4B, The shear rigidity can be lowered to easily cause eccentric deformation of the tire.

  Here, the eccentric deformation of the tire will be described with reference to FIG. In FIG. 3, T1 indicates a tire in a state where the rim is assembled and is grounded with no load, T2 indicates a tire in a state in which normal deformation is generated, and T3 indicates a tire in a state in which eccentric deformation is generated. Is. However, the tires T2 and T3 are in a state where the rim is assembled and the same load (for example, 200% of the maximum load specified by JATMA) is applied. Since the tires T2 and T3 are under the same load condition, the movement distance (vertical direction) at the rim center is A, but the movement distance B at the virtual tire center is greater than the movement distance A due to eccentric deformation of the tire T3. Is also small. That is, in the tire T3, the rim moves downward as much as the tire T2 that causes normal bending deformation, but the amount of downward movement of the tire itself is small. This also appears in the contact length relationship (L1> L2) with the same load applied. When such eccentric deformation occurs, the amount of deformation of the belt portion having a correlation with the contact length is reduced, so that stress is less likely to be concentrated on a portion that affects the durability of the tire, and the durability is improved. .

  In order to cause the eccentric deformation, the cord C constituting the carcass layer in the tire T3 needs to be displaced as illustrated. In order to allow the displacement of the cord C, it is desirable that the rubber between the cords C is easily sheared. On the other hand, when the mutual space | interval of the code | cord | chord C is enlarged, it will become easy to produce the side wall part to bend with eccentric deformation. As a result, deformation does not concentrate on the belt edge portion or the like, and the occurrence of distortion can be suppressed, and the belt durability can be improved.

  In the pneumatic radial tire described above, if the thickness of the organic fiber cord constituting the carcass layer 4B is less than 5000 dtex, the tensile strength against the internal pressure becomes insufficient, or the number of carcass needs to be increased to compensate for it. Conversely, if it exceeds 14000 dtex, the carcass layer 4B becomes thicker than necessary, leading to an increase in weight. A more preferable range of the thickness of the organic fiber cord constituting the carcass layer 4B is 6700 to 11000 dtex. Further, if the inter-ply cord distance at the tread center position of the carcass layer 4B is less than 0.4 mm, the tire is less likely to be eccentrically deformed, and conversely if it exceeds 4.0 mm, the internal pressure holding ability is reduced. A more preferable range of the inter-ply cord interval at the tread center position of the carcass layer 4B is 0.8 to 4.0 mm.

  On the other hand, when the inner-ply cord distance at the tread center position of the innermost carcass layer 4A is set to 0.3 to 1.5 mm, the inner liner layer disposed on the inner surface of the tire is subjected to the carcass layer 4A by the internal pressure during vulcanization. Can be prevented from being pushed in between the cords, and good air pressure retention can be maintained. That is, it is possible to prevent a failure such as a spread code at the time of a new product, and further prevent a blow-by failure during traveling. If the cord distance in the ply of the innermost carcass layer 4A is less than 0.3 mm, the stress relaxation effect due to rubber cannot be obtained, so that peeling between cords is likely to occur and durability is reduced. Reduces air pressure retention. The thickness of the organic fiber cord constituting the innermost carcass layer 4A may be set in a range applicable to a normal carcass layer, that is, in a range of 1880 to 5520 dtex. For example, organic fiber cords of 940 dtex / 2, 1650 dtex / 2, and 1840 dtex / 3 can be used.

  Furthermore, in the pneumatic radial tire, it is preferable to optimize the winding height TUH of the carcass layer and the height BFH of the bead filler in order to reduce the bending rigidity of the sidewall portion 2.

  That is, in FIG. 1, the carcass layer 4 </ b> A is wound up so as to wrap the bead core 5 and the bead filler 6, and the winding terminal of the carcass layer 4 </ b> A is disposed at a position higher than the apex of the bead filler 6, and The winding height TUH is in a relationship of 0.3 × SH ≦ TUH ≦ 0.7 × SH with respect to the tire cross-section height SH. The winding height TUH of the carcass layer 4A is a height measured in the tire radial direction from the bead heel position. If the winding height TUH of the carcass layer 4A is less than 0.3 times the tire cross-section height SH, the steering stability deteriorates. Conversely, if the carcass layer 4A is more than 0.7 times the tire cross-section height SH, the side wall portion Since the bending rigidity of No. 2 does not decrease, the effect of improving the belt durability becomes insufficient.

  As another means, the carcass layer 4A is wound up so as to wrap the bead core 5 and the bead filler 6, the apex of the bead filler 6 is arranged at a position higher than the winding terminal of the carcass layer 4A, and the height of the bead filler 6 is increased. BFH may be in a relationship of 0.25 × SH ≦ BFH ≦ 0.6 × SH with respect to the tire cross-section height SH. The height BFH of the bead filler 6 is a height measured in the tire radial direction from the bead heel position. If the height BFH of the bead filler 6 is less than 0.25 times the tire cross-section height SH, the steering stability deteriorates. Conversely, if the height BFH exceeds 0.6 times the tire cross-section height SH, the sidewall portion 2 Since the bending rigidity of the belt does not decrease, the effect of improving the belt durability becomes insufficient.

  In the embodiment described above, the case of a pneumatic radial tire provided with two carcass layers made of organic fiber cords has been described. However, the present invention is applied to a pneumatic radial tire provided with at least one carcass layer. Can do. As the innermost carcass layer, it is preferable to arrange a carcass layer having a narrower inter-cord distance than the other carcass layers, but a carcass layer having a narrow inter-cord distance is not necessarily provided. Further, in the pneumatic radial tire provided with at least two carcass layers, when winding at least one carcass layer around the bead core, the carcass layer to be rolled up is not particularly limited.

  Various pneumatic radial tires for small trucks with tire size 205 / 60R17.5 111 / 109L (air pressure corresponding to the maximum load capacity: 600 kPa) and two carcass layers made of organic fiber cords. Different tires of Conventional Examples 1-2, Examples 1-3, and Comparative Examples 1-3 were produced. In the test tire, the ratio TUH / SH of the winding height TUH of the carcass layer to the tire cross-section height SH is 0.5, and the ratio BFH / SH of the bead filler height BFH to the tire cross-section height SH is 0.4. did.

  These test tires were evaluated for durability and air pressure retention by the following test methods, and the results are shown in Table 1.

durability:
After performing the durability test specified in JIS D-4230 using a drum testing machine with a drum diameter of 1707 mm, the load is increased by 8% of the maximum specified load every 6 hours and the speed is increased by 5 km / h. The travel distance until the failure occurred in the belt edge portion was measured. The evaluation results are shown as an index with Conventional Example 1 as 100. The larger the index value, the better the durability.

Air pressure retention:
The initial pressure of the test tire was set to 600 kPa, and the test tire was left to stand for 6 months at room temperature of 25 ° C. under no load condition, and the pressure drop rate (% / month) was obtained. The evaluation result is indicated by “◎” when the pressure drop rate is less than 2.5%, “◯” when the pressure drop rate is 2.5% or more and less than 5%, and when the pressure drop rate is 5% or more and less than 7.5%. The case of “Δ” is shown, and the case of 7.5% or more is shown by “x”.

  As can be seen from Table 1, the tires of Examples 1 to 3 were excellent in both durability and air pressure retention in comparison with Conventional Example 1. On the other hand, in the conventional example 2 and the comparative example 2, the durability improvement effect was not acquired. In Comparative Examples 2 and 3, although the effect of improving durability was obtained, the air pressure retention was insufficient.

Next, for the tire of Example 2, tires of Examples 4 to 7 having various ratios TUH / SH of the carcass layer winding height TUH to the tire cross-section height SH were prepared, and the durability was the same as described above. Evaluated. The results are shown in Table 2.

  From Table 2, it can be seen that the best durability is exhibited when the ratio TUH / SH is 0.3 to 0.7.

Next, for the tire of Example 2, tires of Examples 8 to 11 having different ratios BFH / SH of the height BFH of the bead filler to the tire cross-section height SH are prepared, and the durability is the same as described above. evaluated. The results are shown in Table 3.

  From Table 3, it can be seen that the best durability is exhibited when the ratio BFH / SH is 0.25 to 0.6.

1 is a meridian half sectional view showing a pneumatic radial tire for a small truck according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a carcass layer in the pneumatic radial tire of FIG. 1. It is explanatory drawing for demonstrating eccentric deformation of a tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4A, 4B Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer

Claims (7)

A pneumatic radial tire in which the thickness of an organic fiber cord constituting at least one carcass layer is 5000 to 14000 dtex, and the inter-ply cord interval at the tread center position of the carcass layer is 0.4 to 4.0 mm. In a pneumatic radial tire having at least two carcass layers made of organic fiber cords, the innermost ply cord distance at the tread center position of the innermost carcass layer is 0.3 to 1.5 mm, and the innermost The thickness of the organic fiber cord constituting the at least one carcass layer excluding the carcass layer is 5000 to 14000 dtex, and the in-ply cord interval at the tread center position of the at least one carcass layer is 0.4 to 4. Pneumatic radial tire with 0mm. The pneumatic radial tire according to claim 2, wherein the thickness of the organic fiber cord constituting the innermost carcass layer is 1880 to 5520 dtex. A structure in which at least one carcass layer is wound up so as to wrap a bead core and a bead filler, the winding terminal of the carcass layer is disposed at a position higher than the apex of the bead filler, and a winding height TUH of the carcass layer is set. The pneumatic radial tire according to claim 1, wherein a relation of 0.3 × SH ≦ TUH ≦ 0.7 × SH is satisfied with respect to a tire cross-section height SH. A structure in which at least one carcass layer is wound up so as to wrap a bead core and a bead filler, the apex of the bead filler is disposed at a position higher than the winding terminal of the carcass layer, and the height BFH of the bead filler is set to a tire. The pneumatic radial tire according to any one of claims 1 to 3, wherein a relationship of 0.25 x SH ≤ BFH ≤ 0.6 x SH is set with respect to the cross-section height SH. The pneumatic radial tire according to any one of claims 1 to 5, wherein the flatness ratio is 50 to 75%. The pneumatic radial tire according to any one of claims 1 to 6, wherein an air pressure corresponding to a maximum load capacity is 350 to 650 kPa.

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