JPH04260805A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve the durability of a bead part for a radial tire having a low high L at a folded part of a carcass layer folded about a bead. CONSTITUTION:A distance M from a tire outer surface F to a radial outer end 46 of a folded part 22 is set to be 0.6 times or more a distance N from the tire outer surface F to a main body part 21, so at least the radial outer end 46 is positioned in a tensile stress zone so as to improve the rigidity of the folded part 22. When the value M/N exceeds 0.9, a shear distortion between the folded part 22 and the main body part 21 becomes too large, so it is set to be 0.9 or less. A distance between the folded part 22 and the main body part 21 is gradually reduced to the radial outer side for preventing increase of a thickness of a bead part 13 or the like.

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 repeatedly concentrate on the outer end portion in the radial direction of the folded portion and separation may occur.

[0003] For this reason, in the past, as described in, for example, Japanese Unexamined Patent Publication No. 52-131305, the folded part is formed in the main body part of the carcass layer (the carcass layer located axially inward from the bead). The parts are brought into close contact with each other, particularly in the position corresponding to the rim flange that is greatly affected when the folding occurs, thereby increasing the locking effect of the folding and suppressing stress concentration at the radially outer end of the folded part. is proposed.

0004

[Problems to be Solved by the Invention] However, in such conventional pneumatic radial tires, since the rubber gauge between the folded part of the carcass layer and the main body is extremely thin, the folded part cannot be easily formed during load rolling. There is a problem in that the shear strain between the folded portion and the main body portion becomes significantly large, and as a result, there is a risk that separation may occur between the folded portion and the main body portion when the vehicle is driven for a long period of time.

[0005] The present invention provides a pneumatic radial tire that can effectively suppress both the radial outer end of the folded portion and the separation between the folded portion and the main body, thereby improving the durability of the bead portion. The purpose is to

[0006]

[Means for Solving the Problems] Therefore, in order to explore the cause of the low rigidity of the bead portion mentioned above, the inventors of the present invention conducted extensive research and found that the reason for the low rigidity of the bead portion is due to the collapse of the bead portion. It turned out that this is because the internal stress in the extending direction of the carcass layer becomes compressive at the folded part, and the cord in this folded part is an organic fiber that has extremely low rigidity when subjected to compressive stress. did. From this, it has been found that the rigidity of the bead portion can be increased by arranging at least a portion of the folded portion in a region where the internal stress is on the tensile side. For this reason, we analyzed the stress distribution at the bead using the finite element method, and as shown in Figure 3, the distance from the tire outer surface to the main body is 0.
．． It has been found that the internal stress is on the tensile side between the main body and a position 6 times farther away from the tire outer surface. For this reason, the distance from the tire outer surface to the folded portion (at least the radial outer end of the folded portion) is set to be at least 0.6 times the distance from the tire outer surface to the main body. Here, the reason why the boundary of internal stress, that is, the position where it changes from the tension side to the compression side, is 0.6 times the distance from the outer surface of the tire to the tire body, rather than 0.5, is because the body has organic matter inside. This is because although the fibers are embedded, the tire has high rigidity, but the space between the main body and the outer surface of the tire is only rubber and has low rigidity, and as a result, the boundary is closer to the main body. In addition,
In FIG. 3, 0 is the outer surface of the tire, and 1 is the center of the main body in the thickness direction. Next, the shear strain between the folded parts and the main body was analyzed using the finite element method when the distance between the folded parts and the main body changed. The results are shown in Fig. 4. As is clear from Fig. 4, when the distance from the tire outer surface to the folded part exceeds 0.9 times the distance from the tire outer surface to the main body, the shear strain suddenly increases. It increases to . For this reason, the folded part is
It must be placed closer to the outer surface of the tire than the 0.9x position. In addition, in Figure 4, the outer surface of the tire is 0, the center of the main body in the thickness direction is 1, and the shear when the folded part is placed at a position 0.99 times the distance from the outer surface of the tire to the main body. The distortion is set to 1. Here, if the folded part is made to extend almost parallel to the main body (in this case, the distance between the folded part and the main body is almost constant at any position), the tire When the distance from the outer surface of the tire to the folded portion is approximately 0.6 times the distance from the outer surface of the tire to the main body, the thickness of the bead portion becomes extremely thick. In order to prevent this situation, it is conceivable to bend the folded portion abruptly toward the main body part halfway, but if this is done, a large stress will be concentrated on the folded portion. Therefore, in the present invention, the folded portion is arranged so that the distance from the main body portion gradually decreases toward the outside in the radial direction.

Therefore, the present invention has a toroidal carcass layer whose widthwise ends are folded back around the bead from the axially inner side to the axially outer side, and 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, and the distance from the rim diameter line to the radially outer end of the folded portion of the carcass layer is the carcass layer. In a pneumatic radial tire whose height is 0.33 times or less, the distance between the main body of the carcass layer located axially inward from the bead and the folded part of the carcass layer is gradually decreased as it goes radially outward. In addition, the distance from the tire outer surface to the radial outer end of the folded part on the normal line to the main body passing through the radial outer end of the folded part is 0 of the distance from the tire outer surface to the main body part on the normal line. .6 times to 0.9
This is a pneumatic radial tire that is within the double range.

[0008]

[Operation] Let us now assume that the tire of this invention is rolling while receiving a load. At this time, the bead portion on the grounding side collapses outward in the axial direction due to the load, and internal stresses on the tension side and compression side are generated in the bead portion. Here, as mentioned above, the distance from the outer surface of the tire to the radial outer end of the folded part was set to be at least 0.6 times the distance from the tire outer surface to the main body, so at least the radial outer end of the folded part The bead portion is located in the region of tension-side internal stress, and the rigidity of the bead portion increases. As a result, the amount by which the bead portion falls axially outward during load rolling is reduced, stress concentration at the radially outer end of the folded portion is alleviated, and separation is suppressed. In addition, the distance from the tire outer surface to the radial outer end of the folded portion is 0.9 of the distance from the tire outer surface to the main body, as described above.
Since it is less than double, the shear strain that occurs between the folded part and the main body part during load rolling can be suppressed to a small value.
Separation between them can be suppressed. Furthermore, since the distance between the main body and the folded part is gradually reduced toward the outside in the radial direction, there is no possibility that the bead part becomes abnormally thick or stress concentration occurs in a part of the folded part. do not have.

[0009]

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 toroidal carcass layer 17 extending from one bead part 13 to the other bead part 13, and this carcass layer 17 has a large number of organic fibers extending in the radial direction (meridian direction) inside. It consists of at least one carcass ply 18, in this embodiment one carcass ply 18, in which a cord is embedded. And this carcass layer 17
Both widthwise end portions of the carcass layer 17 are folded back around the bead 12 from the axially inner side to the axially outer side, so that the carcass layer 17 has a body portion 21 on the axially inner side than the bead 12 and a folded portion on the axially outer side. It will be composed of 22. Then, these main body portion 21 and folded portion 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 interposed between the fillers 2 and 2, and these fillers 23 are made of hard rubber. A belt layer 2 is provided on the radially outer side of the carcass layer 17.
5 is arranged, 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 tread is disposed outside the belt layer 25 in the radial direction.
Wide grooves 31, for example, main grooves and lateral grooves, are formed on the outer circumferential surface of 0. Further, a side tread 33 is arranged on the axially outer side of the carcass layer 17, and a chafer 34 made of hard rubber is arranged on the axially outer side and the radially inner side of the folded portion 22.

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 extends substantially radially outward from the axial outer ends of the bead seat portions 41. It has a rim flange portion 42.

In this tire 11, the folding height L of the folding portion 22, that is, the rim diameter line 45
The radial distance L from the center to the radial outer end 46 of the folded portion 22 is 0.33 of the carcass height H (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 L/H is usually in the range of 0.16 to 0.31 in the tire 11 with a low folding height L. When such a tire 11 is run, the bead portion 13 on the grounding side receives a load and falls axially outward, but as described above, the L
If the folding height L is low, such as when the value of /H is 0.33 or less, the reinforcing effect on the bead portion 13 is small;
If the amount of the folding becomes large and the folded part 22 is arranged in a region of compressive stress generated in the bead part 13 due to the folded part, the rigidity of the organic fiber cord embedded in the folded part 22 will be significantly reduced. Since it becomes smaller, the amount of fall of the bead portion 13 becomes even larger.

Therefore, in this embodiment, the folded portion 2
When the normal line that passes through the radial outer end 46 of No. 2 and is orthogonal to the main body portion 21 is S, the distance from the tire outer surface F to the radial outer end 46 of the folded portion 22 on the normal S M is set to be 0.6 times or more the distance N from the tire outer surface F to the main body 21 on the normal line S. In this way, if distance M is set to 0.6 times or more of distance N,
At least the outer end in the radial direction of the folded portion 22 is placed in the region of tension-side internal stress, thereby increasing the rigidity of the folded portion 22 and, by extension, the bead portion 13, and reducing the amount of collapse of the bead portion 13. As a result,
Stress concentration at the radially outer end 46 of the folded portion 22 is alleviated, and separation is effectively suppressed. As the value of M/N approaches 1, the length of the folded portion 22 located in the region of tension-side internal stress increases, and the rigidity of the bead portion 13 improves. However, M
When the value of /N exceeds 0.9, the shear strain between the folded portion 22 and the main body portion 21 when the tire 11 rolls under load becomes significantly large, and as a result, when the tire 11 runs for a long period of time, the folded portion 22 and There is a possibility that separation may occur between the main body portion 21 and the main body portion 21 . Therefore, the value of M/N is 0
．． Must be 9 or less. In addition, it is preferable that the value of M/N is in the range of 0.6 to 0.8 in order to reliably prevent the separation. Further, in this embodiment, the distance P between the main body portion 21 and the folded portion 22 is gradually decreased toward the outside in the radial direction. When gradually decreasing the distance P in this way, the folded portion 2
2 may extend linearly, may be bent convexly outward in the axial direction, or may be bent concavely inwardly in the axial direction. If the distance P is gradually decreased toward the outside in the radial direction as described above, the bead portion will not become abnormally thick or stress concentration will occur in a portion of the folded portion. Note that the values of H, L, M, and N are for carcass layer 1.
7 is composed of one carcass ply 18, the value measured at the center of the carcass ply 18 in the thickness direction, and when the carcass layer 17 is composed of a plurality of carcass plies 18, , the value measured at the center of all carcass plies 18 in the thickness direction.

Next, a test example will be explained. In this test, comparative tire 1 with an M/N value of 0.3,
Comparison Tire 2 has an M/N value of 0.5, Comparative Tire 3 has an M/N value of 0.95, and Comparative Tire 3 has an M/N value of 0.
．． A test tire of No. 7 was prepared. Here, each tire has a size of 165SR13 and an L/H value of 0.2.
1, and the 50% modulus is 50 kg/cm2
25 kg of hard rubber filler and 50% modulus
/cm2 hard rubber chafer. next,
After each of these tires was mounted on a regular rim with a rim diameter of 4 1/2 J, the tire was filled with a regular internal pressure of 1.9 kg/cm2. Next, a load of 850 kgf (
8 on the drum while applying a load (twice the normal load)
I drove it for 40,000km at 0km/h. The results showed that in comparison tire 1, separation occurred at the radially outer end of the folded part after traveling 15,000 km, and in comparison tire 2
In this case, separation occurred at the radially outer end of the folded part after traveling 25,000 km, and in comparison tire 3, separation occurred at the radially outer end of the folded part.
Separation occurred between the folded part and the main body after traveling for 5,000 km, but no separation occurred at any part of the test tire at the time of completion.

[0014]

[Effects of the Invention] As explained above, according to the present invention, the durability of the bead portion is improved by effectively suppressing the separation between the radially outer end of the folded portion and between the folded portion and the main body portion. be able to.

[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 section A in FIG. 1;

FIG. 3 is a graph showing the relationship between internal stress in a bead portion and distance from the tire outer surface.

FIG. 4 is a graph showing the relationship between the shear stress between the main body portion and the folded portion and the distance from the tire outer surface to the folded portion.

[Explanation of symbols]

Claims (1)

[Claims] Claims: 1. A toroidal carcass layer whose widthwise ends are folded back around a bead from the axially inner side to the axially outer side, and in which organic fiber cords extending in the radial direction are embedded; A belt layer disposed radially outwardly, and a tread disposed radially outwardly of the belt layer, the distance from the rim diameter line to the radially outer end of the folded portion of the carcass layer being 0 of the carcass height. ．．
In a pneumatic radial tire that is 33 times or less, the distance between the main body of the carcass layer located axially inward from the bead and the folded part of the carcass layer is gradually decreased toward the outside in the radial direction, and the folded part The distance from the outer surface of the tire to the outer radial end of the folded portion on the normal line to the main body passing through the outer radial end of the tire is 0.6 times the distance from the outer surface of the tire to the main body on the normal line. A pneumatic radial tire characterized by being within the range of .9 times.