JP2005075186A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire having improved bead durability by suppressing settling from occurring in a rubber member contacting with a rim following travel. <P>SOLUTION: The pneumatic tire has a bead core 14A having hexagonal cross section. Bead base width Wa, width Wb of a bead core side wall 14N nearest to the bead base 17, and bead core maximum width Wc satisfy 4Wa/7 ≤ Wb ≤ Wc. Thus, even when a rubber gage section 15 is not thickened, the durability of the rubber gage section 15 can be improved remarkably comparing with the conventional art. Bead inner diameter BID (mm) and rim diameter RD (mm) satisfy RD-5 ≤ BID ≤ RD. This prevents troubles where the lower end of the bead core 14A contacts with the rim 19 to decrease the durability during travel or a bead toe section 13F lifts up in mounting the rim to extremely increase the grounding pressure of a bead heel section 13H. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that is particularly suitable for heavy-duty vehicles such as trucks.

  As shown in FIG. 7, the conventional pneumatic tire is generally bent so that the end portion of the carcass 82 covers the bead core 84 inside. A rim 82 is provided on the inner diameter end side (the lower end side in FIG. 7) of the bead core 84 via a rubber gauge portion 85 (a rubber member having a width equal to that of the lower end portion of the bead core and interposed between the bead core and the rim). (For example, refer to Patent Document 1).

  By the way, in the conventional bead structure, so-called sag (retreat) has occurred in the rubber gauge portion 85 as the rim is pushed up during traveling. When this sag becomes large, there is a problem that the carcass and the tuffer disposed around the bead core are damaged, and further, the durability of the bead portion 83 is lowered.

  As a countermeasure, it is conceivable to increase the thickness d of the rubber gauge portion 85. However, when the rim 82 is assembled in the tire manufacturing process, the bead toe portion 83F is easily lifted, and as a result, the contact pressure of the bead heel portion 83H is high. Therefore, there is a problem that the rubber gauge portion in contact with the bead heel portion 83H has a sag.

  In general, pneumatic radial tires for heavy loads, especially flat radial tires for small light trucks, have improved car durability compared to normal passenger car pneumatic tires in order to improve tire durability and wandering performance. 82 and the bead reinforcement layer 88 have a large number of layers, and the bead width (tire thickness at the center of the bead core) Wd and the bead base width Wa are wide (see, for example, Patent Documents 2 and 3).

  Here, when the bead base width Wa is increased, the bead expansion force correlated with the bead fit pressure is increased. In particular, when the inner circumference of the rim 82 used is in the vicinity of the lower limit of the standard, a bead fitting failure occurs in which the bead does not rise unless the internal pressure is increased to 600 kPa or more. May cause a burst accident.

  As a measure for preventing the occurrence of this bead fit failure, it is effective to reduce the bead expansion force. This measure has been conventionally performed, but there is a problem that other bead functions are impaired.

More specifically, (1) If the number of carcass is reduced and the bead portion reinforcing layer is removed in order to reduce the bead expansion force, the bead durability and the wandering performance deteriorate. (2) When the bead base diameter is increased in order to reduce the bead expansion force, air leakage occurs with the rim incorporated. (3) When the inner diameter of the bead core is increased in order to reduce the bead expansion force, the bead portion 83 has a defective shape due to insufficient volume of the bead portion 83 when a pneumatic tire is manufactured.
JP 2003-136922 A Japanese Patent Laid-Open No. 5-139127 JP 2000-62040 A

  In view of the above fact, the present invention has an object to provide a pneumatic tire with improved bead durability by suppressing sag generated in a rubber member that is in contact with a rim during traveling. To do. It is another object of the present invention to provide a pneumatic tire that does not impair bead functions such as bead durability even if the bead width or bead base width is increased.

  As shown in FIG. 7, the present inventor has examined the cause of the rubber gauge portion 85 sagging due to running. And it discovered that it originated in supporting most of the pressure from the rim | limb 82 with the rubber gauge part 85 whose width | variety is equivalent to bead core lower end width Wb. That is, since the pressure Pb received by the rubber gauge portion 85 located on the inner diameter side of the bead core 84 is larger than the pressure Ps received by the rubber surrounding portion 87 continuous around the rubber gauge portion 85, the rubber surrounding portion 87 is accompanied with traveling. It has been found that this is due to the large amount of sag generated in the rubber gauge portion 85. And it examined about making the structure which reduces the pressure Pb, without making the rubber gauge part 85 thick, and repeated the experiment.

  Further, the inventor of the present invention pays attention to the fact that in a pneumatic radial tire for heavy loads, a plurality of carcass and bead reinforcement layers are conventionally provided in order to improve the durability and wrinkleability of the tire bead portion. did. The tire thickness Wd in a direction parallel to the tire axial direction passing through the center of gravity 84C in the tire radial direction cross section of the bead core 84 was examined. The distance Wh between the plane S passing through the tire outer end of the tire thickness Wd and the bead toe end 83T is in the range of 18.5 to 22 mm. In such a conventional pneumatic tire, the bead fit pressure is about 600 kPa. It was also noted that the bead expansion force correlated with the bead fit pressure was 10 to 12 kPa. As a result of repeated experiments, the inventors found that there is a possibility that the bead fit pressure and the bead expansion force can be reduced by reducing the distance Wh with respect to the tire thickness Wd, and further studies were made.

  The present inventor has repeated the above experiments and examinations, and further thoughts, and has completed the present invention.

  The invention according to claim 1 is a pneumatic tire having a bead core having a polygonal cross-sectional shape in the tire radial direction, wherein the bead base width Wa and the width of the side wall surface of the bead core closest to the bead base. The width component Wb in the same direction as the width direction of the bead base and the width component Wc in the same direction as the bead base among the maximum widths of the bead core satisfy the relationship of 4 Wa / 7 ≦ Wb ≦ Wc, and the inner diameter of the bead core BID (mm) and rim diameter RD (mm) satisfy the relationship of 0.99 × RD ≦ BID ≦ RD.

  If Wb is smaller than 4/7, the rubber gauge portion (a rubber member having a width equal to that of the lower end portion of the bead core and interposed between the bead core and the rim) is not preferable. On the other hand, if Wc is smaller than Wb, the ply restraining force when the internal pressure is applied is weak, and the distortion generated at the end of the ply increases depending on the use conditions such as high internal pressure, resulting in poor bead durability.

  Further, if the BID is smaller than 0.99 × RD, the thickness of the rubber gauge portion, that is, the distance between the bead core and the rim becomes too small, and if a minute sag occurs, the rim and the bead core come into contact with each other and the bead core is damaged. . Therefore, the durability of the bead core is lowered, which is not preferable. Also, if BID is larger than RD, the bead toe part is likely to float when the rim is mounted, and as a result, the contact pressure of the bead heel part becomes too high, and the rubber gauge part in contact with the bead heel part is caused to sag. It is not preferable.

  The width of the rubber gauge portion having the same value as Wb, that is, the contact width between the rubber gauge portion and the bead core, by satisfying the relationship of 4Wa / 7 ≦ Wb ≦ Wc as in the invention described in claim 1, This is a sufficient value for the base width Wa. Accordingly, the pressure Pb applied to the rubber gauge portion during traveling can be sufficiently reduced compared to the conventional case, and the durability of the rubber gauge portion can be significantly improved compared to the conventional case without increasing the thickness of the rubber gauge portion. .

  In addition, by satisfying the relationship of 0.99 × RD ≦ BID ≦ RD, the thickness of the rubber gauge portion is too thin so that the bead core and the rim do not come into contact with each other during running and the durability is not deteriorated. When the rim is installed, the bead toe does not rise and the contact pressure of the bead heel does not become too high.

  Wa is inevitably larger than Wc. In addition, if the bead inner diameter BID and the rim diameter RD satisfy the relationship of RD-10 ≦ BID, the rim and the bead core come into contact with each other even if a minute sag occurs in the rubber gauge portion, and the bead core is damaged. Is easy to prevent.

  The invention according to claim 2 includes the tire thickness Wd in a direction parallel to the tire axial direction through the center of gravity in the tire radial cross section of the bead core, and the tire axial direction including the tire outer end that defines the tire thickness Wd. The distance Wh from the plane orthogonal to the bead toe end satisfies the relationship of 1.05 ≦ Wh / Wd ≦ 1.15, and the distance Wh is in the range of 16 mm ≦ Wh ≦ 18 mm. It is characterized by that.

  When Wh / Wd is smaller than 1.05, it is not preferable from the viewpoint of the shape of the bead portion and the durability of the bead portion, and when Wh / Wd is larger than 1.15, the shape of the bead portion and the bead fit property are poor. Easy to be.

  Further, if Wh is shorter than 16 mm, the durability of the bead portion deteriorates, which is not preferable. If Wh is longer than 18 mm, the bead fit property deteriorates, which is not preferable.

  According to the second aspect of the present invention, it is possible to realize a pneumatic tire with a good bead fit by raising the bead without deteriorating the bead function and without increasing the internal pressure in a state where the rim is incorporated. That is, it is possible to realize a pneumatic tire that suppresses the sag generated in the rubber member that is in contact with the rim during traveling and improves the bead durability and the wandering performance.

  The invention according to claim 3 is characterized in that, among the tire thickness Wd, the thickness t of the rubber layer provided on the outer side in the tire width direction than the bead reinforcement layer outside the carcass wound around the bead core, and the The distance Wh satisfies a relationship of 0.075 ≦ t / Wh ≦ 0.15.

  If t / B is smaller than 0.075, further measures need to be taken from the viewpoint of the strength and durability of the rubber layer. On the other hand, when t / B is larger than 0.15, the rigidity of the rubber layer becomes high, and it becomes difficult to easily obtain good bead fit.

  According to the third aspect of the present invention, it is easy to make the bead fit good without impairing the bead function.

  Since the present invention has the above configuration, the following effects can be obtained.

  According to the first aspect of the present invention, the pressure Pb applied to the rubber gauge portion during traveling can be sufficiently reduced as compared with the conventional case, and the durability of the rubber gauge portion can be improved without increasing the thickness of the rubber gauge portion. Compared to this, it can be improved significantly. In addition, the rubber gauge part is too thin and the lower end of the bead core and the rim come into contact with each other during running, resulting in poor durability, or the bead toe part rises when the rim is attached and the ground pressure of the bead heel part becomes too high. There is nothing.

  According to the second aspect of the present invention, without sacrificing the bead function, sag generated in the rubber member that is in contact with the rim during traveling is suppressed, and the bead durability and the wandering performance are improved. A pneumatic tire can be realized.

  According to invention of Claim 3, it is easy to make it the state which made the bead fit favorable, without impairing a bead function.

  Hereinafter, pneumatic tires for heavy-duty vehicles will be cited as embodiments, and embodiments of the present invention will be described.

[First Embodiment]
First, a 1st form is demonstrated. As shown in FIG. 1, a pneumatic tire 10 according to the present embodiment includes a carcass 12 for maintaining an internal pressure due to filled air. The carcass 12 is constituted by a carcass ply in which carcass cords (not shown) formed of steel cords are arranged radially around the tire rotation axis R and covered with a rubber layer. A belt layer 16 is formed in a plurality of layers on the outer side in the tire radial direction of the carcass 12.

  The carcass 12 is wound around the bead cores 14A and 14B embedded in the bead portions 13A and 13B and formed in a ring shape around the tire rotation axis R from the inner side to the outer side in the tire width direction. Is folded.

  A plurality of belt layers 16 are formed on the outer side of the carcass 12 in the tire radial direction, and a bead reinforcing layer 18 (see FIG. 2) is provided on the inner side of the carcass 12 in the tire radial direction.

  In this embodiment, since the configuration and operation of the bead portions 13A and 14A are exactly the same, the bead portion 13A will be described in detail below, and the description of the bead portion 13B will be omitted.

  As shown in FIG. 2, a plate-like rubber gauge portion 15 is interposed between the bead core 14A and the rim 19, and the bead core 14A has a hexagonal cross section.

A bead core side wall surface 14N (hereinafter simply referred to as a side wall surface 14N) closest to the bead base 17 is parallel to the bead base 17. And the bead base width Wa, the width Wb of the side wall surface 14N, and the width component Wc in the same direction as the bead base 17 among the maximum width of the bead core 14A,
4Wa / 7 ≦ Wb ≦ Wc Formula (1)
Meet the relationship.

  On the other hand, the width of the rubber gauge portion (rubber member interposed between the bead core 14A and the rim 19) 15 is the same as the width Wb of the side wall surface 14N.

  Accordingly, the contact width Wb between the rubber gauge portion 15 and the rim 19 with respect to the bead base width Wa is a sufficient value. Thereby, the pressure Pb applied to the rubber gauge part 15 at the time of driving | running | working can fully be reduced compared with the past, and durability of the rubber gauge part 15 can be improved significantly compared with the past.

Further, the bead inner diameter BID and the rim diameter RD are:
RD-5 ≦ BID ≦ RD Formula (2)
Meet the relationship.

  As a result, the thickness d of the rubber gauge portion 15 is too thin and the bead core 14A and the rim 19 come into contact with each other during traveling, or the bead toe portion 13F rises when the rim is mounted and the contact pressure of the bead heel portion 13H becomes too high. Nor.

[Experimental Example 1]
In this experimental example, Wb and BID are changed as parameters, and the two types of pneumatic tires according to the first embodiment have different dimensions and satisfy both the expressions (1) and (2). (See Example 1 and Example 2 in Table 1). A tire size of 12R22.5 and a rim size of 9.00 × 22.5 were applied.

  And the maximum value M (refer FIG. 3) of the amount of sag of said rubber gauge part 15 of this pneumatic tire was measured by experiment in relation to the travel distance. The measurement results are shown in Table 1.

また、比較例として、Ｗｂ、Ｗｃ、及び、ＢＩＤをパラメータとして変更して、式（１）及び式（２）の何れか一方の条件を満たしている４種類の空気入りタイヤを製造し（表１の比較例１〜４を参照）、上記のゴムゲージ部のへたり量の最大値Ｍを、走行距離との関係で同様に実験により測定した。測定結果を表１に併せて示す。

Moreover, as a comparative example, Wb, Wc, and BID are changed as parameters, and four types of pneumatic tires that satisfy any one of the expressions (1) and (2) are manufactured (Table 1 (see Comparative Examples 1 to 4), and the maximum value M of the amount of sag of the rubber gauge portion was measured by experiment in the same manner in relation to the travel distance. The measurement results are also shown in Table 1.

  Further, with respect to the conventional pneumatic tire that does not satisfy any of the conditions of the formula (1) and the formula (2), the maximum value M of the sag amount of the rubber gauge portion is similarly tested in relation to the travel distance. It was measured by. The measurement results are also shown in Table 1.

  As can be seen from Table 1, in the pneumatic tire according to the first embodiment (Example 1 and Example 2 in Table 1) that satisfies both the expressions (1) and (2), the expressions (1) and (1) Compared to the conventional pneumatic tire that does not satisfy any of the conditions of the formula (2), the amount of sag relative to each travel distance was greatly reduced. Further, in the pneumatic tires (Comparative Examples 1 to 4 in Table 1) that satisfy one of the conditions of the formula (1) and the formula (2), the amount of sag is less than that of the conventional pneumatic tire. Although it was reduced to about 2/3, it was not reduced as much as Examples 1 and 2.

[Second Embodiment]
Next, a second embodiment will be described. As shown in FIG. 4, the pneumatic tire according to the present embodiment has a heavy structure in which the number of carcass 22 and bead reinforcement layers 26 is large for use in heavy-duty vehicles, and the bead base width and bead core. The tire thickness of 24 is wider than that of ordinary passenger cars.

In the pneumatic tire according to the present embodiment, the tire thickness Wd in a direction parallel to the tire axial direction through the center of gravity 24C in the tire radial cross section of the bead core 24 and the tire outer end that defines the tire thickness Wd are provided. The distance Wh between the plane S perpendicular to the tire axial direction and the bead toe end 23T,
1.05 ≦ Wh / Wd ≦ 1.15
Meet the relationship.

In addition, the above Wh (mm) is
16mm ≤ Wh ≤ 18mm
Has been in the range.

  Thus, without impairing the bead function, the pneumatic tire 20 in which the bead is raised and the bead fit is improved without increasing the internal pressure in a state where the rim is incorporated, that is, in contact with the rim as the vehicle runs. Accordingly, it is possible to realize the pneumatic tire 20 that suppresses the sag generated in the rubber member and improves the bead durability and the wandering performance. Further, it is not necessary to increase the rubber gauge thickness d determined by the difference between the bead base diameter BBD and the bead core inner diameter BID.

In the present embodiment, the ratio of the thickness t of the rubber layer 28 provided on the outer side in the tire width direction from the bead reinforcement layer 26 to the distance Wh in the tire thickness Wd is as follows.
0.075 ≦ t / Wh ≦ 0.15
Meet the relationship.

  Therefore, it is easy to avoid that the bead function is impaired because the thickness t of the rubber layer 28 is too thin, and that the bead fit is deteriorated because the rigidity is too high because the rubber layer 28 is too thick.

[Experiment 2]
In this experimental example, a pneumatic tire according to the second embodiment was manufactured using “LT 225 / 85R16 121L rib”. The dimensions and the like are shown in Table 2 (see the tire of the second embodiment in Table 2). Further, the bead expansion force and the bead fit pressure necessary for obtaining a good bead fit are also shown in Table 2, FIG. 5 and FIG. 6 (indicated by x in FIGS. 5 and 6).

また、Ｗｈが互いに異なる従来の空気入りタイヤについて、寸法等を表２に併せて示す（表２の従来タイヤＡ、Ｂを参照）。また、良好なビードフィットを得るために必要であったビード拡張力及びビードフィット圧を、表２及び図５、図６に併せて示す（図５、図６では、黒丸で示す）。なお、図５、図６では、表２に示さなかった、Ｗｈが２２ｍｍの従来の空気入りタイヤについてのデータも示す。

Moreover, about the conventional pneumatic tire from which Wh mutually differs, a dimension etc. are combined with Table 2 (refer the conventional tires A and B of Table 2). Further, the bead expansion force and the bead fit pressure necessary for obtaining a good bead fit are shown in Table 2, FIG. 5 and FIG. 6 (indicated by black circles in FIG. 5 and FIG. 6). In addition, in FIG. 5, FIG. 6, the data about the conventional pneumatic tire whose Wh is 22 mm which is not shown in Table 2 are also shown.

  As can be seen from Table 2, FIG. 5, and FIG. 6, in the conventional pneumatic tire, both the bead expansion force and the bead fit pressure were high.

  On the other hand, in the pneumatic tire according to the second embodiment, both the bead expansion force and the bead fit pressure can be kept low. Therefore, according to the second embodiment, it has been found that a pneumatic tire in which the bead is raised and the bead fit is improved without impairing the bead function and without increasing the internal pressure in a state where the rim is incorporated.

  The embodiments of the present invention have been described above with reference to the embodiments. However, these embodiments are merely examples, and various modifications can be made without departing from the scope of the invention. Needless to say, the scope of rights of the present invention is not limited to the above embodiment.

It is a tire width direction sectional view of the pneumatic tire concerning a 1st embodiment. It is a tire width direction sectional view of a bead part of a pneumatic tire concerning a 1st embodiment. FIG. 3 is a cross-sectional view in the tire width direction of a bead portion showing a maximum amount of sag generated in a rubber gauge portion of the bead portion in Experimental Example 1. It is a tire width direction sectional view of a bead part of a pneumatic tire concerning a 2nd embodiment. In Experimental example 2, it is a graph which shows the relationship between Wh and bead fit pressure. In Experimental Example 2, it is a graph which shows the relationship between Wh and bead expansion force. It is tire width direction sectional drawing of the bead part of the conventional pneumatic tire.

Explanation of symbols

10 Pneumatic tire 12 Carcass 14A, B Bead core 18 Bead reinforcement layer 22 Carcass 23T Bead toe end 24 Bead core 24C Center of gravity 26 Bead reinforcement layer 28 Rubber layer 82 Carcass 83T Bead toe end 84 Bead core 84C Center of gravity 88 Bead reinforcement layer

Claims (3)

A pneumatic tire having a bead core having a polygonal cross-sectional shape in the tire radial direction,
The bead base width Wa, the width component Wb in the same direction as the width direction of the bead base in the width of the side wall surface of the bead core closest to the bead base, and the width in the same direction as the bead base in the maximum width of the bead core Component Wc,
4Wa / 7 ≦ Wb ≦ Wc
Satisfy the relationship
The inner diameter BID (mm) of the bead core and the rim diameter RD (mm)
0.99 x RD ≤ BID ≤ RD
Pneumatic tire characterized by satisfying the relationship A tire thickness Wd in a direction parallel to the tire axial direction through the center of gravity in the tire radial cross section of the bead core;
The distance Wh from the plane perpendicular to the tire axial direction including the tire outer end that defines the tire thickness Wd to the bead toe end,
1.05 ≦ Wh / Wd ≦ 1.15
Satisfy the relationship
And the distance Wh is
16mm ≤ Wh ≤ 18mm
A pneumatic tire characterized by being within the range of Of the tire thickness Wd, the thickness t of the rubber layer provided on the outer side in the tire width direction than the bead reinforcement layer outside the carcass wound around the bead core and the distance Wh,
0.075 ≦ t / Wh ≦ 0.15
The pneumatic tire according to claim 2, wherein the relationship is satisfied.

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