JP2013248970A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for a heavy load with improved durability of a bead part.SOLUTION: A pneumatic radial tire for a heavy load includes a carcass rubber that is arranged along the outer side of a returning part of at least a single layer steel radial carcass and is formed of a plurality of layers extending in a radial direction. The carcass rubber includes: a first carcass rubber layer that is the closest to the returning part; and a second carcass rubber layer that is arranged on the outer side of the first carcass rubber layer.

Description

  The present invention relates to a heavy-duty pneumatic radial tire, and more particularly to a heavy-duty pneumatic radial tire with improved durability of a bead portion.

  Heavy load pneumatic radial tires (hereinafter referred to as tires) used for trucks, buses, construction vehicles, and the like have improved wear resistance due to an increase in tread volume. However, increasing tread volume resulted in increased input of shear and compression strains. In addition, as a result of extending the service life due to improved wear resistance, the repeated input of shear strain and compression strain experienced before the tire becomes a waste product further increases.

  When the tire rolls under load, the tire collapses toward the outside in the tire width direction and repeats deformation. As a result, shear strain and compression strain were repeatedly input to the bead portion, and many failures such as separation on the outside of the carcass folded portion, carcass-covered rubber breakage, and carcass cord cutting were observed.

  Thus, a heavy-duty pneumatic radial tire that improves the durability of the bead portion by optimizing the carcass line around the bead portion is known as the prior art. This is a region where the shear strain is maximum in the bead portion, and by adjusting the arrangement of the folded portion of the carcass, the collapse deformation is suppressed and the shear strain is reduced.

  Further, a heavy-duty pneumatic radial tire in which carcass protective rubber is disposed along the outer side of the carcass folded portion and the durability of the bead portion is improved is known as the prior art.

JP 2008-143291 A JP 2009-62014 A

  However, when the protective rubber is arranged along the outer side of the carcass folding portion, the rigidity is improved, but it is necessary to apply cement in order to bond the protective rubber to the covering rubber of the carcass cord. The cement applied in the tire molding process remains as a foreign matter between rubbers even after becoming a product through the tire vulcanization process. Since the location where the cement is applied is located in the vicinity of the carcass cord where the strain is large when the tire receives a load, there is a problem that cracks are likely to occur.

In order to solve the above problems, the present invention has the following features. The first feature of the present invention is that a main body part (main carcass part 4a) straddling a pair of bead cores (bead cores 3a) and a main body part are continuous to the outer side from the tire inner side along the bead cores. A carcass rubber formed of at least one steel radial carcass (carcass 4) having a folded portion (folded portion 4b) wound in the radial direction, and a plurality of layers arranged along the outside of the folded portion and extending in the radial direction. (Carcass rubber 5), a heavy-duty pneumatic radial tire, wherein the carcass rubber is a first carcass rubber layer (first carcass rubber layer 5a) closest to the folded portion, and the first carcass rubber layer. A second carcass rubber layer (second carcass rubber layer 5b) disposed outside the rim, and a standard rim (standard rim 2). In the state in which the tire is incorporated into the tire and the internal pressure is 50 kPa, the rim diameter of the standard rim is R, the rim flange height is Hf, and the radial position from the tire center axis is (R / 2 + 1.18 × Hf) on the tire outer surface. P1 is the position of the maximum tire width, O is the position of the maximum width of the tire, and P2 is the point closest to P1 among the points obtained by dividing O and P1 along the tire outer surface into three equal parts. The intersections between the normals drawn toward the main body and the boundaries of the first and second carcass layers are M1 and M2, respectively, and the intersections with the folded portion are T1 and T2, respectively. Is W1, the distance from M1 to T1 is W1 ′, the distance from P2 to T2 is W2, and the distance from M2 to T2 is W2 ′.
0.25 ≦ W1 ′ / W1 ≦ 0.42
0.20 ≦ W2 ′ / W2 ≦ 0.36
The gist is to satisfy.

  According to this feature, the carcass rubber disposed along the outside of the folded portion of the carcass is formed from a plurality of layers extending in the radial direction. Here, the first carcass rubber layer closest to the folded portion is sufficiently thin with respect to the entire thickness of the carcass rubber, and can be bonded to the carcass folded portion without applying cement. Therefore, it is possible to reduce the possibility that the cement does not remain on the outer side of the carcass folded portion having the largest shear strain and cracks occur.

  In addition, since the first carcass rubber layer can be bonded to the carcass folded portion without applying cement, in the tire molding process, before winding the both ends of the carcass cord along the bead core to form the folded portion, The first carcass rubber layer can be bonded in advance to both ends of the carcass.

  The first carcass rubber layer has a certain thickness that satisfies the above formula. Therefore, the boundary between the first and second carcass rubber layers is located away from the outside of the carcass folded portion having the largest shear strain and is located in a relatively small strain region. That is, even when the first and second carcass rubber layers are bonded by cement application, since the cement remains in a relatively small strain region, the possibility of occurrence of cracks can be reduced.

  The second feature of the present invention relates to the first feature of the present invention, and is summarized in that a loss tangent tan δ of the first carcass rubber layer is 0.07 or less.

  A third feature of the present invention is related to the first feature of the present invention, and is summarized in that the first carcass rubber layer is disposed outside the folded portion without interposing an adhesive substance.

  A fourth feature of the present invention relates to the third feature of the present invention, and is summarized in that the first carcass rubber layer and the second carcass rubber layer are bonded together by cement application.

  The present invention has the effect of improving the durability of the bead portion in a heavy-duty pneumatic radial tire.

FIG. 1 is a cross-sectional view in the width direction of a tire according to an embodiment of the present invention. FIG. 2 is a detailed view of a bead portion in the tire shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and ratios of dimensions are different from actual ones. Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  FIG. 1 is a cross-sectional view in the width direction of a tire according to an embodiment of the present invention. The heavy-duty pneumatic radial tire 1 is mounted on a standard rim 2 having a rim diameter R. The tire 1 is in a deflated state filled with an internal pressure of 50 kPa, the tire section height is SH, and the rim flange height is Hf. In the present embodiment, the flatness of the tire 1 is 90% or more.

  Here, the standard rim is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. Means "Measuring Rim".

  FIG. 2 is a detailed view of the bead portion 3 in the tire 1 shown in FIG. The tire 1 is fixed to the rim 2 at a pair of bead portions 3, and the bead portion 3 includes a bead core 3a formed by bundling high carbon steel. The tire 1 includes at least one steel radial carcass 4, and the skeleton of the tire 1 is formed by the carcass 4. The carcass 4 includes a main carcass portion 4a straddling a pair of bead cores 3a in a toroidal shape, and a folded portion 4b that is continuous with the main carcass portion 4a and wound up in the radial direction from the tire inner side to the outer side along the bead core 3a. . In the present specification, “inside” and “outside” mean the inside in the width direction and the outside in the width direction unless otherwise specified.

  The tire 1 further includes a carcass rubber 5 arranged along the outer side of the folded portion 4b for holding the carcass line. The carcass rubber 5 is formed from a plurality of layers extending in the radial direction. The carcass rubber 5 shown in FIG. 1 includes a first carcass rubber layer 5a that is located on the innermost side and is closest to the folded portion 4b of the carcass 4, and a second carcass rubber layer 5b that is bonded to the outside. The second carcass rubber layer 5b can be bonded to the first carcass rubber layer 5a by cement application. The radial length of the first carcass rubber layer 5a may be longer or shorter than the second carcass rubber layer 5b. The carcass rubber 5 can also be formed from three or more layers.

Here, on the tire outer surface, the position where the radial position from the tire central axis is (R / 2 + 1.18 × Hf) is P1, the tire maximum width position is O, and O and P1 are along the tire outer surface. Of the points obtained by dividing the connected distance into three equal parts, the point closest to P1 is P2, normal lines drawn from P1 and P2 toward the main carcass part 4a, and the first and second carcass layers 5a and 5b. M1 and M2 are the intersections with the boundary, and T1 and T2 are the intersections with the folded portion 4b, respectively. The distance from P1 to T1 is W1, the distance from M1 to T1 is W1 ′, and the distance from P2 to T2 Is W2, and the distance from M2 to T2 is W2 ′,
0.25 ≦ W1 ′ / W1 ≦ 0.42 (1)
0.20 ≦ W2 ′ / W2 ≦ 0.36 (2)
Meet.

  When a load is applied to the tire, the shear strain input to the bead portion is maximized near the outside of the folded portion 4 b of the carcass 4. In addition, when the tire is subjected to a collapse due to a load, the collapse to the rim flange is maximized near T1, and the input of the shear strain is also maximized. In the tire 1, when W1 ′ / W1 and W2 ′ / W2 satisfy the above formulas (1) and (2), the boundary between the first and second carcass rubber layers 5a and 5b is set in a region having a large shear strain. Among them, it can be arranged in a region having relatively small shear. Here, the maximum tire width means the maximum width of a tire when mounted on an applicable rim in an applicable size defined in the 2008 YEAR BOOK issued by JATMA and filled with an internal pressure of 50 kPa.

  When the values of W1 '/ W1 and W2' / W2 are small, the thickness of the first carcass rubber layer 5a is relatively small with respect to the entire thickness of the carcass rubber 5. In general, in a tire molding process, carcass rubber is cemented to the covered rubber of the folded portion after winding both ends of the carcass cord covered with rubber to form the folded portion. However, when the first carcass rubber layer 5a is thin, the first carcass rubber layer 5a and the covering rubber at both ends of the carcass cord can be bonded without applying cement. Thereafter, the first carcass rubber layer 5a can be wound together with both ends of the carcass cord to form a folded portion. As a result, in the vicinity of the outside of the folded portion 4b having a large shear strain, no cement remains between the rubbers, so that the possibility of cracking is reduced. Further, when the first carcass rubber layer 5a is thin, there is little unevenness in the thickness even after the first carcass rubber layer 5a is wound up, and variations in product quality are prevented. However, when the value of W1 ′ / W1 is less than 0.25 and the value of W2 ′ / W2 is less than 0.20, the boundary between the first and second carcass rubber layers 5a and 5b approaches the folded portion 4b, Enter the region with large shear strain. Therefore, separation may occur at the boundary between the first and second carcass rubber layers 5a and 5b.

  When the values of W1 '/ W1 and W2' / W2 are large, the thickness of the first carcass rubber layer 5a is relatively larger than the thickness of the entire carcass rubber 5. When the first carcass rubber layer 5a is thick, the boundary between the first and second carcass rubber layers 5a and 5b is away from the outside of the folded portion 4b having a large shear strain. For this reason, the possibility of occurrence of separation at the boundary between the first and second carcass rubber layers 5a and 5b decreases. That is, even when the first and second carcass rubber layers 5a and 5b are cemented, the residual cement is unlikely to cause cracks. However, if the value of W1 ′ / W1 exceeds 0.42 and the value of W2 ′ / W2 exceeds 0.36, the thickness of the first carcass rubber layer 5a becomes excessive, and the carcass is not applied without applying cement. It becomes difficult to bond the cord with the covering rubber. For this reason, the first carcass rubber layer 5a must be cemented to the outside of the folded portion 4b after the folded portion 4b is formed. This is because, when the thickness of the first carcass rubber layer 5a that has been bonded in advance to both ends of the carcass cord is excessive, variation in thickness occurs due to winding, which may lead to a decrease in yield.

  Therefore, when W1 ′ / W1 and W2 ′ / W2 satisfy the above formulas (1) and (2), the first carcass rubber layer 5a is attached to the carcass cord before winding up both ends of the carcass cord in the tire molding step. Can be glued to both ends. At that time, since it is not necessary to apply cement, it is possible to reduce the possibility of cracks in the vicinity of the outside of the folded portion 4b of the carcass 4 having a large shear strain. Further, the boundary between the first and second carcass rubber layers 5a and 5b can be disposed in a region having a relatively small shear strain. Thereby, even when the first and second carcass rubber layers 5a and 5b are cemented, the possibility of cracking in the remaining cement is low. As described above, the durability of the bead portion can be improved.

  The first carcass rubber layer 5a is preferably formed of a low heat-generating rubber having a small loss tangent (tan δ). Thereby, the temperature rise in the outer side of the folding | turning part 4b can be suppressed, and generation | occurrence | production of the separation in the boundary of the 1st and 2nd carcass rubber layers 5a and 5b can be suppressed. Preferably, the loss tangent tan δ of the first carcass rubber layer 5a is 0.07 or less. Tan δ was measured using a spectrometer manufactured by Toyo Seiki Co., Ltd., with a test piece having a width of 5 mm, a thickness of 2 mm, and a length of 20 mm at an initial load of 150 g, a frequency of 50 Hz, a dynamic strain of 1%, and a temperature of 30 ° C.

Next, in order to further clarify the effects of the present invention, (1) a bead portion heat test and (2) a bead portion durability test were performed using tires according to examples, conventional examples, and comparative examples. Table 1 shows various conditions of each tire. In addition, this invention is not limited at all by these examples.

(1) Bead part heat test After each tire (tire for a construction vehicle having a tire size of 46 / 90R57; the same applies below) is incorporated into a standard rim, under a regular internal pressure determined by TRA, a speed of 8 km / h, and a drum diameter of 5 m, The temperature of the bead portion was measured at 100% of the normal load determined by TRA, and the temperature reduction effect was evaluated.

  Here, the normal internal pressure is the air pressure determined for each tire by the standard system including the standards on which the tire is based. If it is ETRTO, it is “INFLATION PRESSURE”. The regular load is the load specified by the above-mentioned standard for each tire. If it is JATMA, the maximum load capacity, if it is TRA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", ETRTO If so, it is "LOAD CAPACITY".

(2) Bead endurance test After each tire is incorporated into the standard rim, a durability test is conducted at 170% of the normal load determined by TRA under the normal internal pressure, speed 8 km / h and drum diameter 5 m determined by TRA. did. The vehicle was run until a failure occurred in the bead, and the durability was evaluated based on the running time. These test results are also shown in Table 1.

  As can be seen from Table 1, it was found that the tire according to the example had a longer running time and improved the durability of the bead portion than the tire according to the conventional example and the comparative example. In Example 2 where the loss tangent (tan δ) was small, the temperature of the bead portion was lower than in other examples. On the other hand, in other examples having the same loss tangent, the temperature of the bead portion was similar. In other words, even if the carcass rubber formed of the same material is used and the calorific value of the bead portion is approximately the same, the carcass rubber is formed of a plurality of layers extending in the radial direction, and W1 ′ / W1 and W2 ′ / W2 In Examples 1 and 2 whose values are in the ranges of the above formulas (1) and (2), it was found that the durability of the bead portion was improved.

  As described above, the present invention can be used to improve the durability of the bead portion in the heavy-duty pneumatic radial tire.

1 Heavy-duty pneumatic radial tire 2 Standard rim 3 Bead part 3a Bead core 4 Carcass 4a Main carcass part 4b Turned part 5 Carcass rubber 5a First carcass rubber layer 5b Second carcass rubber layer R Rim diameter Hf Rim flange height

Claims (4)

At least one steel radial carcass having a main body portion straddling a pair of bead cores, and a folded portion that is continuous with the main body portion and wound up in the radial direction from the tire inner side along the bead core;
A heavy-duty pneumatic radial tire comprising a carcass rubber formed from a plurality of layers extending along the radial direction and disposed along the outer side of the folded portion;
The carcass rubber includes a first carcass rubber layer that is closest to the folded portion, and a second carcass rubber layer that is disposed outside the first carcass rubber layer,
In a state where the tire is incorporated into the standard rim and the internal pressure is 50 kPa, the rim diameter of the standard rim is R, the height of the rim flange is Hf,
On the tire outer surface, the position where the radial position from the tire central axis is (R / 2 + 1.18 × Hf) is P1, the tire maximum width position is O, and the distance connecting O and P1 along the tire outer surface P2 is the point closest to P1 among the points divided into three equal parts.
The intersections between the normals drawn from P1 and P2 toward the main body and the boundaries of the first and second carcass rubber layers are M1 and M2, respectively, and the intersections with the folded portion are T1 and T2, respectively. ,
If the distance from P1 to T1 is W1, the distance from M1 to T1 is W1 ′, the distance from P2 to T2 is W2, and the distance from M2 to T2 is W2 ′,
0.25 ≦ W1 ′ / W1 ≦ 0.42
0.20 ≦ W2 ′ / W2 ≦ 0.36
Satisfy the tire.   The tire according to claim 1, wherein a loss tangent tan δ of the first carcass rubber layer is 0.07 or less.   The tire according to claim 1, wherein the first carcass rubber layer is disposed outside the folded portion without interposing an adhesive substance.   The tire according to claim 3, wherein the first carcass rubber layer and the second carcass rubber layer are bonded together by cement application.

Images