JPH04306108A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent separation in the axial outer side (the side of tire outer surface) of a radial outer end part of a folded part 22 of a radial tire 11, in which a height D of the folded part 22 of a carcass layer 17 folded around a bead 12 is low. CONSTITUTION:When a tire 11 is filled with inner pressure and is loaded and rotated, a folded part 22 is attracted to the side of a bead 12, and stress is concentrated on a coating rubber 19 between a radial outside end part of the folded part 22 and a chafer 34. A cushion rubber layer 50, the modulus of which is lower than that of the coating rubber 19 is arranged on the part where such a large stress is generated, and the stress is dispersed thereby, and separation is thus prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a pneumatic radial tire having a carcass layer with a low folding height.

0002

[Prior Art] In general, pneumatic radial tires with a low folding height, for example, where the distance from the rim diameter line to the radial outer end of the folding part of the carcass layer is 0.33 times the carcass height or less, Since the rigidity of the folded portion is low, the bead portion may fall significantly outward in the axial direction due to load rolling, and as a result, stress may be repeatedly concentrated on the outer end of the folded portion in the radial direction and separation may occur.

In order to prevent such a situation, a pneumatic radial tire has been proposed in which a filler or chafer made of hard rubber is placed axially inside or axially outside the folded part to increase the rigidity of the bead part. However, in such a tire, the folded part is drawn toward the bead side by filling the tire with internal pressure and rolling under load, so that the radial outer end of the folded part and the filler,
There is a problem in that a large stress is generated between the chafer and the chafer, which may cause separation from the chafer. Here, among such separations, the separation that occurs between the folded part and the chafer develops toward the outer surface of the tire, so
If the separation extends to the outer surface of the tire, the water and air that enter through the separation deteriorate the internal rubber and cord, reducing tire durability. For this reason, separation between the folded portion and the chafer must be prevented.

[0004] In order to prevent such separation,
Conventionally, as described in Japanese Patent Application Laid-open No. 57-70707, for example, side treads with relatively low rubber hardness are extended radially inward to create a space between the radially outer end of the folded portion and the chafer. It is known that the stress is absorbed by the side tread and the separation is prevented.

[0005]

[Problems to be Solved by the Invention] However, although such conventional tires can prevent separation to some extent, when running for a long period of time under heavy loads, the radial outer end of the folded portion and the chafer There is still a problem that separation occurs between the two.

[0006] This invention allows the axially outer (
An object of the present invention is to provide a pneumatic radial tire that can reliably prevent separation on the tire outer surface side.

[0007]

[Means for Solving the Problems] Therefore, as a result of extensive research to find out why the prior art cannot sufficiently prevent separation as described above, the inventors have found that the stress Small cracks are concentrated in the coating rubber, and these cracks develop to form separations. Also, the modulus of the side tread is considerably larger than that of the coating rubber, so it is difficult to sufficiently absorb the stress concentration mentioned above. I discovered that it cannot be restricted.

The present invention has been made based on the above-mentioned knowledge, and by folding both widthwise end portions around the bead from the axially inner side to the axially outer side, the main body portion is axially inner than the bead. a loidal carcass layer comprising a folded portion axially outward from the bead and in which organic fiber cords extending in the radial direction are embedded; a belt layer disposed radially outwardly of the carcass layer;
A pneumatic radial tire comprising: a tread disposed on the radially outer side of the belt layer; and a distance D from the rim diameter line to the radially outer end of the folded portion is 0.33 times or less the carcass height K. , a buffer rubber layer in contact with the folded part is disposed on the axially outer side of the radially outer end of the folded part, and the total thickness T of the buffer rubber layer and the coating rubber of the folded part is defined as the diameter of the organic fiber cord. This is a pneumatic radial tire in which the 50% modulus of the buffer rubber layer is 5 kg/cm2 or more and the 50% modulus of the coating rubber of the folded portion is 50% or less.

[0009]

[Operation] Let us now assume that the tire of the present invention is rolling while receiving a load after being filled with internal pressure. At this time, the folded part of the carcass layer is pulled toward the bead, so stress is generated around the radially outer end of the folded part, but this stress tends to concentrate on the coating rubber because the modulus of the coating rubber is small. shall be. However, in the present invention, a buffer rubber layer is disposed on the axially outer side of the radially outer end of the folded part in contact with the folded part and whose 50% modulus is less than 50% modulus of the coating rubber of the folded part. Therefore, the stress is dispersed in both the coating rubber and the buffer rubber (if the modulus of the buffer rubber is less than the modulus of the coating rubber, a larger stress is generated in the buffer rubber), which causes shear in the coating rubber. This reduces strain and prevents cracks and separation on the outer surface of the tire. Here, if the 50% modulus of the buffer rubber layer is less than 5 kg/cm2, the buffer rubber layer becomes too soft and stress concentrates only on this buffer rubber layer, causing separation in the buffer rubber layer. Therefore, the buffer rubber layer has a 50% modulus of 5 kg.
/cm2 or more. Note that if the total thickness T of the buffer rubber layer and the coating rubber is less than 0.5 times the diameter d of the organic fiber cord, the thickness of these rubbers is too thin. Stress is concentrated and it cannot be used.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, reference numeral 11 indicates a pneumatic radial tire to be mounted on a passenger car. The tread includes a pair of sidewall portions 14 extending toward the vehicle, and a substantially cylindrical tread portion 15 that connects the outer ends of the sidewall portions 14 in the radial direction. The tire 11 is reinforced by a carcass layer 17 having a toroidal shape extending from one bead part 13 to the other bead part 13, and this carcass layer 17 is made of a large number of organic fibers extending in the radial direction (meridian direction). At least one piece of cord 18 covered with coating rubber 19, here one
It is composed of two carcass plies 20. and,
Both ends of the carcass layer 17 in the width direction are folded back around the bead 12 from the axially inner side to the axially outer side, so that the carcass layer 17 connects to the main body part 21 axially inner than the bead 12. Outer folded part 2
It will be composed of 2. A radially inner end portion of a filler 23 having a triangular cross section and whose radially inner end is crimped to the bead 12 is arranged between the main body portion 21 and the folded portion 22, and these fillers 23 have a rubber hardness. It is made of hard rubber with a angle of 75 degrees or more. Also,
A belt layer 25 is arranged radially outside the carcass layer 17, and this belt layer 25 is composed of at least one belt ply 26, here two belt plies 26. A large number of reinforcing cords inclined with respect to the tire equatorial plane 27 are embedded in these belt plies 26, and these reinforcing cords intersect in at least two belt plies 26. A top tread 30 as a top tread is arranged on the radially outer side of the belt layer 25, and a wide groove 31, for example, a main groove and a lateral groove, are formed on the outer peripheral surface of the top tread 30. Further, a side tread 33 is disposed on the axially outer side of the carcass layer 17, and chafers 34 are disposed on the axially outer side and the radially inner side of the folded portion 22, and these chafers 34 have more rubber than the filler 23. Constructed from hard rubber with low hardness.

Reference numeral 40 denotes a rim, and the rim 40 includes a pair of bead seat portions 41 on which the bead portions 13 of the tire 11 are seated, and a rim extending approximately radially outward from the axial outer ends of the bead seat portions 41. It has a flange portion 42.

In this tire 11, the folding height D of the folding portion 22, that is, the rim diameter line 45
The radial distance D from the center to the radial outer end 46 of the folded portion 22 is 0.33 of the carcass height K (radial distance from the rim diameter line 45 to the intersection of the tire equatorial plane 27 and the carcass layer 17). Low, less than double. In addition, the value of this D/K is usually in the range of 0.16 to 0.31 in the tire 11 with a low folding height D. When such a tire 11 is filled with internal pressure and then rolled under a load, the folded portion 22 is drawn toward the bead 12 with a large force because the folded height D is low as described above. At this time, the coating rubber 19 located at the outer end in the radial direction of the folded portion 22 is sandwiched between the chafer 34, which has high rubber hardness and is difficult to deform, and the organic fiber cord 18, which has high rigidity. Since the rubber 19 is made of rubber with a small modulus, stress tends to concentrate on the coating rubber 19.

In order to suppress such stress concentration, in this embodiment, a buffer rubber layer 50 whose 50% modulus is less than the 50% modulus of the coating rubber 19 of the folded part 22 is provided at the outer end in the radial direction of the folded part 22. The coating rubber 19 is placed on the axially outer side of the coating rubber 19.
, that is, between the coating rubber 19 at the radially outer end of the folded portion 22 and the chafer 34 . As a result, the stress is dispersed in both the coating rubber 19 and the buffer rubber layer 50 (if the modulus of the buffer rubber 50 is less than the modulus of the coating rubber 19, a larger stress is generated in the buffer rubber 50). According to
The shear strain in the coating rubber 19 is reduced, preventing cracks on the outer surface of the tire and preventing separation. Note that this buffer rubber layer 50 may extend radially outward from the radially outer end 46 as necessary, as in this embodiment, or may extend radially inwardly to the bead heel. . Here, if the 50% modulus of the buffer rubber layer 50 is less than 5 kg/cm2, the buffer rubber layer 50
0 becomes too soft and stress concentrates only on this buffer rubber layer 50, and the separation is caused by this buffer rubber layer 5.
Since there is a risk of this occurring, the buffer rubber layer 50 should be
% modulus must be 5 kg/cm2 or more. Here, the thickness of this buffer rubber layer 50 and the folded portion 2
The total thickness T of the coating rubber 19 of No. 2 is 0.5 of the diameter d of the organic fiber cord 18 in the folded portion 22.
It must be more than double. The reason for this is that when the total thickness T is less than 0.5 times the diameter d, stress rapidly concentrates on the thin and easily deformed buffer rubber layer 50 and coating rubber 19, as shown in FIG. This is because it is more likely to occur. Note that FIG. 3 is a graph showing the results of analyzing the stress in the low modulus rubber placed between the organic fiber cord 18 and the chafer 34 using the finite element method, and the vertical axis is the organic fiber cord. 18 and chafer 34
There is no low modulus rubber between the organic fiber cord 1
The stress when the chafer 34 is in direct contact with 8 is defined as 1. In addition, this total thickness T is preferably set to four times or less of the diameter d so as not to reduce the effect of improving the rigidity of the bead portion 13 by the chafer 34. and,
Such arrangement of the buffer rubber layer 50 may be performed by attaching a rubber sheet that will become the buffer rubber layer 50 to the carcass ply 20 attached to the tire molding drum, or,
A rubber sheet serving as the buffer rubber layer 50 may be attached to the chafer 34 in advance, and the chafer 34 may be supplied to the carcass ply 20 on the tire building drum. In this way, the arrangement of the buffer rubber layer 50 can be performed very easily and is advantageous in terms of cost.

Next, a test example will be explained. In this test, we used a conventional tire 1 in which a cushioning rubber layer was not provided between the folded part and the chafer, and a tire 1 in which the side tread 33 was extended radially inward as shown in FIG. A conventional tire 2 is interposed between the outer end and the chafer 34, and a buffer rubber layer 50 is arranged between the radially outer end of the folded portion 22 and the chafer 34 as shown in FIGS. and a test tire 2 in which the cushioning rubber layer 51 is arranged on the axially outer side and the radially inner side of the folded portion 22 as shown in FIG. A comparative tire was prepared in which a rubber layer made of rubber with a small modulus was arranged in place of the rubber layer 50. Here, the side tread 33 of the conventional tire 2 extends from the rim diameter line 45 to a position 0.08 times the carcass height K, and the thickness of the side tread 33 and the thickness of the coating rubber 19 are different. The total thickness is 3.0 times the diameter d, and the buffer rubber layer 5 of the test tire 1
0 is 0.08 of carcass height K from rim diameter line 45
It extends from a position 0.26 times the carcass height K to a position 0.26 times the carcass height K, and the total thickness T is the diameter d.
Furthermore, the buffer rubber layer 51 of the test tire 2 is 0.2 times the carcass height K from the rim diameter line 45.
It extends from a distance of 6 times to the radial inside of the bead 12 and has a total thickness T of 1.5 times the diameter d. In addition, the 50% modulus of the filler 23, chafer 34, coating rubber 19, side tread 33, buffer rubber layers 50 and 51 of test tires 1 and 2, and rubber layer of the comparative tire are 50 kg/cm2 and 25, respectively.
kg/cm2, 10kg/cm2, 12kg/cm2,
6 kg/cm2 and 4.5 kg/cm2. Further, the size of each tire is 165SR13,
The value of D/K was 0.17. Next, after mounting each tire on a regular rim with a rim diameter of 4 1/2J, the weight of 1.9 kg
It was filled with a normal internal pressure of /cm2. After that, a load of 850 kgf (twice the normal load) is applied to each such tire.
The vehicle was run for 40,000 km at 80 km/h on the drum while being operated. The result was 15,000 km with conventional tire 1.
At the time of running, separation occurred between the radially outer end of the folded portion 22 and the chafer 34 with the conventional tire 2 after running 25,000 km, and with the comparative tire after running 25,000 km. At this point, separation occurred in the additional rubber layer with a small modulus, but test tire 1
, 2, there was no separation at any point at the time of completion.

[0015]

[Effects of the Invention] As explained above, according to the present invention, even when running for a long period of time under heavy load, separation on the axially outer side (tire outer surface side) of the radially outer end of the folded portion can be prevented. It can definitely be prevented.

[Brief explanation of the drawing]

FIG. 1 is a meridian cross-sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the vicinity of the bead portion.

FIG. 3 is a graph showing the relationship between internal stress in the vicinity of an organic fiber cord and distance from the surface of the organic fiber cord.

FIG. 4 is a meridian cross-sectional view near the bead of the conventional tire 2 used in the test.

FIG. 5 is a meridian cross-sectional view near the bead of the test tire 2 used in the test.

[Explanation of symbols]

Claims (1)

[Claims] Claim 1: Both ends in the width direction are folded back around the bead from the axially inner side to the axially outer side, so that the main body part is axially inner than the bead and the folded part is axially outer than the bead. , a toroidal carcass layer in which organic fiber cords extending in the radial direction are embedded, a belt layer disposed radially outward of the carcass layer, and a tread disposed radially outward of the belt layer;
In a pneumatic radial tire, in which the distance D from the rim diameter line to the radial outer end of the folded portion is 0.33 times or less the carcass height K, the axial direction of the radially outer edge of the folded portion is A buffer rubber layer is disposed on the outside in contact with the folded part, and the total thickness T of the buffer rubber layer and the coating rubber of the folded part is 0.5 times or more the diameter d of the organic fiber cord, and the buffer rubber layer is 50 layers
A pneumatic radial tire characterized by having a % modulus of 5 kg/cm2 or more and a 50% modulus or less of the coating rubber of the folded portion.