JP5399778B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire with improved bead durability.

  A pneumatic tire for a construction vehicle is composed of a carcass main body made of a ply coated with a plurality of cords straddling a toroidal shape between a pair of bead cores, and from the carcass main body around each bead core from the inside to the outside of the tire. And a carcass folded portion made of the ply that extends back to the tire radial direction. This type of tire has many opportunities to run on rough rough terrain such as protrusions or rocks under heavy load, so that the durability of the bead part can withstand its use even in harsh environments. It is known to improve the performance.

  However, when a large load is applied and the tire bends, compressive strain is generated in the carcass folded portion that contributes to improving the durability of the bead portion, and fatigue occurs when this compressive strain is repeatedly generated in the carcass folded portion in a particularly severe environment. Breaking will occur. Such fatigue rupture of the carcass folded portion significantly reduces the life of the tire. Therefore, suppressing the fatigue rupture of the carcass folded portion is one of the problems required for this type of tire. .

  The occurrence of compressive strain that causes fatigue fracture of the carcass folded portion is caused by the carcass folded portion being on the compression side in bending deformation with the carcass main body as the neutral axis that occurs when the bead portion collapses. ing. Thus, in order to suppress the compressive strain of the carcass folded portion, it is generally known as a typical technique that can reduce the compressive strain to bring the carcass folded portion as close as possible to the carcass main body portion. Furthermore, this technique also has the effect of suppressing the shear strain of rubber between the outer surface of the bead part and the carcass folded part, which is caused by the deformation of the carcass folded part at the contact part between the rim flange and the bead part of the applied rim. Yes, it is also effective in suppressing the separation of rubber generated along the carcass folding portion.

  However, just bringing the carcass folded part and the carcass main body part closer will promote the shearing strain of the rubber existing between the carcass folded part and the carcass main body part, and between the carcass folded part and the carcass main body part. Rubber separation will occur early in the tire usage period. Furthermore, even if the carcass folded part and the carcass main body part are brought close to each other to suppress the compressive strain, the carcass folded part is brought closer to the carcass main body part in the portion on the outer side in the tire radial direction from the place where the compressive strain is suppressed, On the contrary, the bending rigidity of the carcass folded portion is reduced.

  That is, in order to suppress the compressive strain of the carcass folding portion, it is known as an effective measure to bring the carcass folding portion closer to the carcass main body portion. On the other hand, the rubber between the carcass folding portion and the carcass main body portion is known. It is a problem that the bending rigidity of the carcass folded portion is reduced by promoting the shear strain.

  Therefore, in Patent Document 1, the distance between the cords between the carcass main body portion and the carcass folding portion is gradually decreased from the bead core toward the outside in the tire radial direction to once become a minimum value, and then gradually increased to once become a maximum value. When the tire is mounted on the applicable rim, the minimum and maximum carcass body parts from the rim baseline of the applicable rim are further reduced and further reduced to the minimum value at the end of the carcass folding portion. By adjusting the height to the point and the height of the rim flange, the shear strain of the rubber between the carcass folded part and the carcass folded part is suppressed, and the decrease in the bending rigidity of the carcass folded part is suppressed, A technique for reducing the compressive strain of the carcass folded portion has been proposed.

Further, in Patent Document 2, a carcass main body portion made of a ply in which a plurality of cords straddling a toroidal shape between a pair of bead cores is covered with rubber, and the carcass main body portion is wound around each bead core from the inside to the outside of the tire. A pneumatic tire having a carcass skeleton having a carcass folded portion made of the ply extending outward in the tire radial direction, and a distance between cords between the carcass main body portion and the carcass folded portion is a tire diameter from the bead core. It gradually decreases toward the outside in the direction, once reaches a minimum value, then gradually increases to a maximum value, and when the tire is mounted on the application rim, the minimum value and the maximum value are obtained from the baseline of the application rim. the height _{H a} and _{H B,} measured to the point of the carcass main body portion, the flange height _{H f} of application rim, 1.26 × H _{≦ H A ≦ 2.14 × H f} , 2.43 × H f ≦ H B ≦ 3.75 × satisfied _{H f,} and the ratio of the maximum value b of the minimum value a and the inter-cord distance code distance b A pneumatic tire characterized by / a exceeding 1.00 is disclosed. By adopting such a configuration and providing the maximum value and the minimum value of the above-described inter-cord distance, fatigue fracture at the carcass folded portion due to reduction of the compression input to the carcass folded portion is suppressed. Further, by providing the maximum value of the distance between the cords, the distance between the carcass folding portion and the carcass main body portion is widened, so that the shear strain of the rubber existing between them is alleviated, and the rubber carcass of which the strain is alleviated is reduced. The separation from is suppressed. Furthermore, by providing the minimum value of the distance between cords, the gap between the carcass folded portion and the outer surface is widened, so that the shear strain of the rubber existing between the two is relieved, and the rubber with the relaxed strain is reduced. Separation is suppressed. Due to the effects as described above, the durability of the bead portion is improved.

Japanese Patent Laid-Open No. 4-185510 Japanese Patent Application No. 2007-291026

  However, in recent years, tires for construction vehicles are expected to further suppress fatigue fracture as tires become larger and heavier, and to achieve tires with high durability that can withstand use in harsh environments. It is rare.

  Then, this invention aims at providing the pneumatic tire which improved the endurance of a bead part by suppressing further the compressive distortion of a carcass folding part, especially suppressing the fatigue fracture of a carcass folding part. To do.

  The inventor has left room for suppression in the region where the minimum value of the inter-cord distance exists, due to the shear strain of the rubber existing between the carcass folded portion and the carcass main body portion, and the market usage conditions exceed the current conditions. When assumed, it was discovered that the suppression of the shear strain of the rubber is essential. Therefore, by adopting the configuration shown below, in the region where the minimum value of the distance between cords exists, the shear strain of rubber existing between the carcass folded portion and the carcass main body portion is effectively suppressed, and the durability of the bead portion is increased. It has been found that it can be improved.

That is, the gist of the present invention is as follows.
(1) A carcass main body portion made of a ply in which a plurality of cords straddling a toroidal shape across a pair of bead cores is covered with rubber, and the carcass main body portion is wound around each bead core from the inner side to the outer side of the tire, and the tire radial direction A hard stiffener comprising a carcass having a carcass folded portion made of the ply extending outward and having a rubber hardness higher than that of the rubber constituting the sidewall on the outer side in the tire radial direction of the bead core, the hard stiffener A pneumatic tire having a soft stiffener made of rubber having a rubber hardness smaller than that of the rubber constituting the hard stiffener on the outer side in the tire radial direction,
The distance between the cords between the carcass main body portion and the carcass folded portion is gradually reduced from the bead core toward the outer side in the tire radial direction, once formed to a minimum value, and then gradually increased to a maximum value.
When the tire is mounted on the application rim, the height measured from the base line of the application rim to the maximum carcass body point is HB, and the tire radial direction of the hard stiffener from the base line of the application rim When the height measured to the outer edge position is HS and the flange height of the applicable rim is Hf,
A tire radial outer end position HS of the hard stiffener is larger than Hf;
The HS is on the inner side in the tire radial direction than HB, and
At least a part of the soft stiffener is included in an inter-code region where the inter-code distance is a minimum value ,
When the tire is mounted on the applicable rim, the height measured from the base line of the applicable rim to the point of the carcass main body that is the minimum value is HA, and the tire height measured from the baseline of the applicable rim is HT. When HT ≧ 8.00Hf,
1.26 × Hf ≦ HA ≦ 2.14 × Hf,
2.43 × Hf ≦ HB ≦ 3.75 × Hf,
1.00 × Hf ≦ HS ≦ 2.25 × Hf,
Satisfied,
The ratio b / a of the minimum value a of the inter-code distance and the maximum value b of the inter-code distance exceeds 1.00,
A pneumatic tire characterized by that.

( 2 ) The pneumatic tire according to (1) , wherein the ratio b / a is 1.40 or more and 4.00 or less.

( 3 ) The pneumatic tire according to (2) , wherein the ratio b / a is 2.00 or more and 3.00 or less.

( 4 ) In the pneumatic tire, when the height measured from the base line of the applied rim to the point of the carcass main body portion having the minimum value when the tire is mounted on the applied rim, HS <HA The pneumatic tire according to any one of (1) to (3) , wherein

  According to the present invention, by arranging an appropriate stiffener in a region where the minimum value of the distance between cords exists, in a region where the minimum value of the distance between cords exists, shearing of rubber existing between the carcass folded portion and the carcass main body portion is achieved. Strain is effectively suppressed and the durability of the bead portion is improved.

The width direction half sectional view of the pneumatic radial tire according to the present invention is shown. The width direction half sectional view of the other pneumatic radial tire according to the present invention is shown.

  Hereinafter, the present invention will be specifically described. FIG. 1 shows a widthwise half sectional view of a pneumatic tire (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 shows a widthwise half sectional view of another tire according to the present invention.

  In FIG. 1, 1 is a bead core, 2 is a carcass main body made of a ply coated with a plurality of cords straddling a toroidal shape between a pair of bead cores, and 3 is a ply from the carcass main body 2 around each bead core. Each is a carcass turn-up portion that rewinds from the inside to the outside of the tire and extends outward in the tire radial direction. The carcass includes a carcass main body 2 and a carcass folding portion 3. A belt 6 is disposed outside the carcass body 2 in the radial direction, and a tread portion 7 is provided further outside in the radial direction of the belt 6 to constitute a tire 8. Reference numeral 4 denotes an applied rim, 5 denotes a rim flange, and L denotes a base line (hereinafter referred to as a rim base line) of the applied rim that extends through the equator of the tire and is parallel to the rotation axis of the tire. Also. The distance between the cords between the carcass main body 2 and the carcass folding part 3 gradually decreases from the vicinity of the bead core 1 toward the outer side in the tire radial direction, temporarily reaches a minimum value, and then gradually increases toward the outer side in the tire radial direction. It becomes the form which becomes the maximum value.

  That is, by gradually reducing the distance between cords between the carcass folding portion 3 and the carcass main body portion 2 to a minimum value, the compressive strain acting on the carcass folding portion 3 is reduced. This is because by bringing the carcass folding part 3 closer to the carcass main body part 2, the carcass folding part 3 approaches the neutral axis of bending, and the compression action of the carcass folding part 3 in that region is reduced. As a result, the compressive strain of the carcass folded portion 3 can be suppressed and fatigue fracture can be suppressed.

  Further, by gradually reducing the distance between the cords between the carcass folding part 3 and the carcass body part 2, the distance between the carcass folding part 3 and the outer surface is increased, and the carcass folding part 3 and the outer surface in this region Is reduced because the shear strain generated during the relaxation is relaxed. As a result, separation between the carcass folded portion 3 and the rubber can be suppressed.

  Further, the cord distance between the carcass folded portion 3 and the carcass main body portion 2 is gradually increased from the minimum value to the radially outer side to obtain the maximum value, whereby the carcass folded portion in that region is separated from the neutral axis of bending. Further, since the tensile force becomes stronger, the tensile strain increases. Therefore, the action of the compression force is reduced by the increase. As a result, since the compressive strain acting on the carcass folded portion 3 can be reduced, the fatigue fracture of the carcass can be suppressed.

  Here, the center point of the cord of the carcass body 2 at the minimum value is A, the center point of the cord of the carcass body 2 at the maximum value is B, and the normal line lowered from A to the carcass folding portion 3 and the carcass folding portion 3 Is the center point of the cord where the carcass folding part 3 intersects with the normal point of the cord where the carcass folding part 3 intersects with B ′. The distance between cords B to B ′ is b.

  At this time, the inter-cord distance minimum value a is preferably 0.18 to 0.33 times the cross-sectional maximum diameter L of the bead core. That is, if it is less than 0.18 times the maximum cross-sectional diameter L of the bead core, the bending rigidity of the bead portion is insufficient, and the bead portion falls greatly. Therefore, an increase in the shear strain of rubber existing between the carcass folded portion and the carcass main body portion is caused. On the other hand, if it exceeds 0.33 times the maximum cross-sectional diameter L of the bead core, the carcass folded portion 3 is too far from the carcass main body portion 2, and the compressive strain generated in the carcass folded portion 3 is significantly increased. Further, when the carcass folded portion 3 is too close to the outer surface of the bead portion, the shear strain of rubber between the outer surface of the bead portion and the carcass folded portion 3 is increased, and the durability of the bead portion is improved. It becomes impossible.

Further, the tire shown in FIG. 1 includes a hard stiffener 8 made of rubber having a rubber hardness larger than that of the rubber constituting the sidewall on the outer side in the tire radial direction of the bead core 1, and the hard stiffener 8 is hardened on the outer side in the tire radial direction. A soft stiffener 9 made of rubber having a lower hardness than the rubber constituting the stiffener 8 is provided. Further, when the tire is mounted on the application rim, the height measured from the base line of the application rim to the point of the carcass main body that is the maximum value is H _B , and the height of the hard stiffener is measured from the base line of the application rim. When the height measured up to the tire radial direction outer end position is H _S and the flange height of the applied rim is H _f , the tire radial outer end position H _{S of the} hard stiffener is larger than H _f . Further, H _S is on the inner side in the tire radial direction than H _B , and at least a part of the soft stiffener 9 is included in the inter-cord region where the inter-cord distance is the minimum value.

That is, by adopting the above configuration, the hard stiffener 8 is disposed on the outer side in the tire radial direction of the bead core 1, and the soft stiffener 9 is further disposed on the outer side in the tire radial direction, so that distortion is effectively concentrated on the soft stiffener 9 side. However, the hard stiffener 8 effectively suppresses the falling deformation of the bead portion, and the durability of the bead portion is improved. In addition, since at least a part of the soft stiffener 9 is included in the inter-cord region where the inter-cord distance is the minimum value, the soft stiffener 9 functions as a cushioning material when the soft stiffener 9 falls down and deforms. Compared to the case where only the hard stiffener is arranged in the inter-cord region where the inter-cord distance is the minimum value, the rubber breakage is suppressed in the inter-cord region where the inter-cord distance is the minimum value, and the durability of the bead part is reduced. Will be improved. Further, since the outer radial end position H _{S of} the hard stiffener is larger than H _f and the H _S is on the inner side in the tire radial direction of H _B , the hard stiffener collapses and effectively suppresses deformation. It will be.

Now, the height from the rim base line L to the point A of the carcass main body 2 that is the minimum value is HA, the height from the rim base line L to the point B of the carcass main body 2 that is the maximum value is HB, the rim base When the height of the rim flange 5 from the line L is Hf and HT ≧ 8.00Hf ,
1.26 × Hf ≦ HA ≦ 2.14 × Hf,
2.43 × Hf ≦ HB ≦ 3.75 × Hf,
1.00 × Hf ≦ HS ≦ 2.25 × Hf,
It is important to satisfy

That is, if H _A is less than 1.26 × H _f, the change of the minimum value of the inter-cord distance from the bead core 1 is increased on the outermost end, to a convex shape carcass turnup portion 3 to the carcass main body 2 Since a rapid change in curvature is required, tire manufacture becomes difficult. Further, since the bending rigidity of the bead portion in the vicinity of the lower end of the rim flange 5 is reduced and the amount of the bead portion falls down, the increase in shear strain acting on the rubber between the carcass folded portion 3 and the carcass main body portion 2 is remarkable. become. In addition to this, the increase in the shear strain of the rubber along the carcass turn-up portion 3 is remarkably increased, resulting in separation of the carcass turn-up portion 3 from the rubber on the carcass main body side and the rim flange side. Will fall.

On the other hand, when the H _A exceeds 2.14 × H _f, the position of the minimum value for a region that acts compressive strain in the carcass turnup portion 3 will be too close to the radially outward, radially inward (bead core side) The compression distortion of will increase. Further, since the carcass folded portion 3 in the vicinity of the rim flange 5 has a shape protruding in the opposite direction to the carcass main body portion 2, the shear strain acting on the rubber between the outer surface of the bead portion and the carcass folded portion 3 is increased. And it becomes difficult to suppress generation | occurrence | production of the separation of the carcass folding | turning part 3 and rubber | gum.

In addition, since the height _HA can further exhibit the advantageous effects of the present invention by setting the height _HA in a region where the compressive strain generated in the carcass folded portion 3 starts to increase significantly, 1.4 × H _f it is preferable to _{≦ H a ≦ 1.9 × H f} .

Next, reduce the H _B is less than 2.43 × H _f, compressive strain acting on the carcass turnup portion 3 at the position where the maximum value becomes strong, the compressive strain by the action of tensile strain to the carcass turnup portion 3 This reduces the effect of suppressing the fatigue rupture of the carcass folded portion 3.

On the other hand, if H _B exceeds 3.75 × H _f , the maximum value is too far from the region where the compressive force is applied, so the effect of reducing the compressive strain by applying tensile strain to the carcass folded portion 3 is reduced. As a result, the fatigue fracture of the carcass folded portion 3 cannot be suppressed.
Further, in the side wall portion region near the end of the carcass folding portion 3, the tension applied to the carcass folding portion 3 is increased, and this tension acts in the direction in which the end of the carcass folding portion is pulled out from the bead core 1. As a result, the shear strain of the rubber near the end of the carcass folded portion 3 increases, and a crack occurs at the end of the carcass folded portion 3.

Note that the height H _B can exert the advantageous effects of the present invention further by setting the region where the compressive strain is significantly reduced by causing the tensile force to act strongly and reducing the compressive force. It is preferable that 2.8 × H _f ≦ H _B ≦ 3.4 × H _f .

Next, when the height H _S is less than 1.00 × H _f , the hard stiffener 8 is not sufficiently arranged, so that the falling deformation at the time of tire load rolling is not effectively suppressed, and the bead The durability of the part may not be improved effectively. On the other hand, if the height H _S exceeds 2.25 × H _f is too wide area hard stiffener 8 is arranged, since the function as a cushioning material for soft stiffener 9 is not effectively exhibited As described above, there is a possibility that the effect obtained by arranging the two types of stiffeners cannot be sufficiently obtained.

  Further, it is important that the ratio b / a between the minimum inter-code distance value a and the maximum inter-code distance value b exceeds 1.00. That is, when the ratio b / a is 1.00 or less, it becomes impossible to reduce the compression distortion. This is because in the shape where the ratio b / a is 1.00 or less, the tensile force is not increased in the region T where tensile deformation occurs, and thus the effect of sufficiently reducing the compressive strain is lost. As a result, the fatigue fracture of the carcass folded portion 3 cannot be suppressed.

  Here, the thickness of the entire bead portion is increased, and in particular, the separation is caused by the increase in heat generation and heat storage in the rubber between the carcass folding portion 3 and the carcass main body portion 2 from the increase in thickness near the maximum value. In order to eliminate the avoidance, it is preferable to set the value between 1.40 and 4.00. Furthermore, in order to suppress fatigue rupture of the carcass folded portion 3 under heavy load environment or low internal pressure environment and rubber heat generation between the carcass folded portion 3 and the carcass main body portion 2 and an increase in heat storage, 2.00 or more. It is preferable to set it to 3.00 or less.

  Further, from the viewpoint of effectively suppressing the falling deformation of the bead portion, the hardness of the rubber constituting the hard stiffener 8 is preferably in the range of 75 ° to 85 °, and the hardness of the rubber constituting the soft stiffener 9 is The hardness of the rubber constituting the soft stiffener 9 is preferably 15 to 25 ° larger than the hardness of the rubber constituting the soft stiffener 9.

  The above description is only a part of the embodiment of the present invention, and these configurations can be alternately combined or various changes can be made without departing from the gist of the present invention. . For example, as shown in FIG. 2, it is possible to adopt a configuration in which the hard stiffener 8 is disposed on the inner side in the tire radial direction from the inter-cord region where the inter-cord distance is the minimum value.

In accordance with the basic structure of the tire shown in FIG. 1, pneumatic radial tires for construction vehicles of size 59 / 80R63 were manufactured under various specifications shown in Tables 1 and 2. The resulting tire, width 1117.6Mm, flange height _{H f} is incorporated into a rim of 127 mm, by adjusting the internal pressure to 600 kPa, a durability test was carried out of the bead portion. The results are shown in Tables 1 and 2.

  The durability of the bead portion is determined by a step load method with a drum endurance tester having a drum diameter of 7 m, a drum speed of 8 km / h, and a drum load of 150% to 180% of a normal load of 996.4 kN. Evaluation was made by the test to be given. In the step load method, when a drum load for 12 hours is applied to a pneumatic radial tire to be measured, the starting load is set to 150% of the normal load, and after that, 10% of the normal load is added and finally the normal load is applied. The load is 180% of the load. The results were indexed with the conventional example as 100.

  Moreover, about the failure location, it investigated by cutting and dissecting the pneumatic radial tire after a test the pneumatic radial tire after a test.

  Comparing the results shown in Tables 1 and 2, in the pneumatic radial tire of the invention example, when the durability test described above was performed and the durability of the bead part was measured, the pneumatic radial tire of the invention example was more durable in the bead part. It turns out that it is excellent in property.

  According to the present invention, it is possible to provide a tire in which the shear strain of rubber existing between the carcass folded portion and the carcass main body portion is effectively suppressed and the durability of the bead portion is improved.

DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass main-body part 3 Carcass folding | turning part 4 Applicable rim 5 Rim flange 6 Belt 7 Tread part 8 Hard stiffener 9 Soft stiffener

Claims (4)

A carcass main body made of a ply coated with a plurality of cords straddling a toroidal shape across a pair of bead cores, and extends from the carcass main body around each bead core from the inside to the outside of the tire and extends outward in the tire radial direction. A carcass having a carcass folded portion made of the ply as a skeleton, and having a hard stiffener made of rubber having a rubber hardness larger than that of the rubber constituting the sidewall on the outer side in the tire radial direction of the bead core, the tire diameter of the hard stiffener A pneumatic tire comprising a soft stiffener made of rubber having a lower rubber hardness than the rubber constituting the hard stiffener on the outside in the direction,
The distance between the cords between the carcass main body portion and the carcass folded portion is gradually decreased from the bead core toward the outer side in the tire radial direction, once formed to a minimum value, and then gradually increased to a maximum value.
When the tire is mounted on the application rim, the height measured from the base line of the application rim to the maximum carcass body point is HB, and the tire radial direction of the hard stiffener from the base line of the application rim When the height measured to the outer edge position is HS and the flange height of the applicable rim is Hf,
A tire radial outer end position HS of the hard stiffener is larger than Hf;
The HS is on the inner side in the tire radial direction than HB, and
At least a part of the soft stiffener is included in an inter-code region where the inter-code distance is a minimum value ,
When the tire is mounted on the applicable rim, the height measured from the base line of the applicable rim to the point of the carcass main body that is the minimum value is HA, and the tire height measured from the baseline of the applicable rim is HT. When HT ≧ 8.00Hf,
1.26 × Hf ≦ HA ≦ 2.14 × Hf,
2.43 × Hf ≦ HB ≦ 3.75 × Hf,
1.00 × Hf ≦ HS ≦ 2.25 × Hf,
Satisfied,
The ratio b / a of the minimum value a of the inter-code distance and the maximum value b of the inter-code distance exceeds 1.00,
A pneumatic tire characterized by that. The pneumatic tire according to claim 1 , wherein the ratio b / a is 1.40 or more and 4.00 or less. The pneumatic tire according to claim 2 , wherein the ratio b / a is 2.00 or more and 3.00 or less. In the pneumatic tire, when the tire is mounted on the application rim, when the height measured from the base line of the application rim to the point of the carcass main body having the minimum value is HA, HS <HA is satisfied. The pneumatic tire according to any one of claims 1 to 3 .

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