JPS6245082B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic tire for a vehicle, and in particular to a radial tire made of polyester carcass ply, the durability of the tire is improved by interposing a nylon cord reinforcing layer between the main part of the carcass ply and the folded part of the carcass ply. This relates to pneumatic tires for vehicles that have significantly improved performance and handling stability. Fiber cords such as nylon, rayon, and polyester are generally used for carcass ply cords. However, nylon fiber cords have the problem of flat spots, meaning that if the tire heats up while running and is cooled down under a load, when the tire starts running again, it will deform during cooling until it reaches a certain level of heat generation. Its use is limited because it has the problem of remaining and generating abnormal vibrations. Additionally, rayon fiber cords are being reduced in the industry due to supply issues. Therefore, polyester fiber cords have come to dominate the carcass ply cords used in recent tires. Conventionally, the carcass ply made of polyester fiber cord is made by folding the carcass ply P around the bead core 2 from the inside of the tire to the outside at the bead part 1 of the tire to form a folded part 4, as shown in FIG. On the other hand, the folded portion 4 is configured to maintain a constant distance from the carcass ply main body portion 3 by a bead filler 5. However, this structure has the drawback that stress is concentrated on the end portion 6 of the carcass folded portion 4, and the durability of the tire is significantly reduced. As a measure to eliminate these drawbacks,
The following proposal is made in Publication No. 52-131305. That is, as shown in FIG. 2, the end of the carcass ply P made of polyester fiber cord is folded around the bead core 2 from the inside to the outside, and the inner surface of the folded portion 4 is attached to the outer surface of the carcass ply main body 3. By bringing them into close contact, stress concentration on the end portion 6 of the folded portion 4 is alleviated. However, even if the folded part 4 is brought into close contact with the carcass ply body 3 in this way, when the tire is used under conditions that are much harsher than usual, such as low pressure and high load, the following Separation occurred in the terminal portion 6 due to the combination of these factors, and there was still a problem with durability. That is, in the configuration shown in FIG. 2, the carcass ply P is composed of two pieces in the area _l0 where the folded part 4 is in direct contact with the main body part 3, whereas it is composed of one piece in the area l above the terminal part 6. Therefore, a step is created between the two areas, and the bending load during running causes the end portion 6 to
Stress is concentrated on the parts, making bending fatigue more likely to occur. Furthermore, not only the above-mentioned bending load but also a tensile load is applied to the carcass ply P, causing relative movement between the main body part 3 and the folded part 4, which causes the thin adhesive rubber layer between them to Interlaminar shear stress is generated. According to the teachings of composite materials engineering, this interlayer shear stress is extremely concentrated at the end of the fiber-reinforced layer (i.e., the end of the folded part) [end effect (end effect)].
The magnitude of the maximum shear stress generated by this terminal effect increases as the Young's modulus of the fiber-reinforced layer increases. When the carcass ply is a polyester fiber cord, its Young's modulus is approximately 3 to 6 times greater than that of a nylon fiber cord, so that the maximum shear stress due to the above-mentioned end effect is further increased. In addition, when tires are used under harsh conditions and the inside of the tire becomes hot due to rubber hysteresis loss, polyester fiber cords have a characteristic that their heat generation is higher than that of nylon fiber cords, so they adhere well to thermal deterioration. The adhesion of the rubber layer also tends to deteriorate. Therefore, in the tire shown in Fig. 2, in addition to the stress concentration on the end portion due to the bending load, the maximum value of the interlayer shear stress concentration that occurs in the adhesive rubber layer due to the tensile load is increased, and the adhesion due to heat generation is increased. Sexual deterioration also occurs. Therefore, due to the combination of these conditions, under severe running conditions such as low pressure and high load, separation will occur at the terminal part even if the folded part 4 is in close contact with the main body part 3. They will come to do so. The present invention was made in view of the above-mentioned current situation, and
It is an object of the present invention to provide a pneumatic tire for a vehicle that solves the above-mentioned problems. A pneumatic tire for a vehicle according to the present invention that achieves the above object has the following features:
The inner surface of this folded portion is brought into close contact with the outer surface of the carcass ply main body over the bead filler disposed on the upper surface of the bead core, with a nylon cord reinforcing layer interposed therebetween, and the reinforcing layer is attached to the carcass ply. Extending at least from the side surface of the bead core beyond the end portion of the folded portion to tightly contact the outer surface of the main body portion of the carcass ply, without using any other reinforcing layer such as a metal cord layer having greater rigidity than the ply. Furthermore, a hard rubber stock having a tongue-shaped cross section is disposed on the outside of the folded portion, and is in close contact with the bead core from the outside over the upper end of the reinforcing layer. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the pneumatic tire for vehicles of the present invention will be explained by way of examples with reference to the drawings. 3 and 4 each show an embodiment of the present invention, and the pneumatic tire _E1 for vehicles shown in FIG. While folding both ends of the carcass ply P around the bead core 2 from the inside of the tire to the outside,
This folded portion 4 extends beyond the bead filler 10 disposed on the outer peripheral side of the bead core 2 and approaches the main body portion 3 of the carcass ply P. In addition, the blind-shaped nylon cord reinforcing layer 8 is
along the inner surface of the folded part 4 from the outer surface of the bead core 2, and the terminal part 6 of this folded part 4.
It is brought into close contact with the outer surface of the main body part 3 of the carcass ply P by crossing over. Further, a hard rubber stock 7 having a tongue-shaped cross section is arranged on the outside of the folded portion 4 of the carcass ply P, starting from the outside of the bead core 2 and extending beyond the upper end 9 of the nylon cord reinforcing layer 8 to near the maximum width of the tire. That's what I do. As described above, the reinforcing layer 8 is attached to the bead core 2 as shown in the figure in the region where the outer surface of the carcass ply main body portion 3 and the inner surface of the folded portion 4 are in close contact with each other.
from a region substantially corresponding to the upper end of the rim flange beyond the bead filler 10 disposed on the upper part of the nylon cord reinforcing layer 8 extending beyond the upper end of the reversible portion 4 to the upper end 9 of the nylon cord reinforcing layer 8. , is in close contact with the outer surface of the carcass ply main body part 3. The rubber stock 7 and bead filler 10 are preferably made of hard rubber having a shore A hardness of 90 or more. In the present invention, the cord used for the reinforcing layer 8 must be a nylon fiber cord. In addition to nylon fiber cords, polyester fiber cords, steel cords, rayon fiber cords, etc. are also used as cords used for such reinforcing layers, but polyester fiber cords and steel cords are more durable than nylon fiber cords. Since the Young's modulus is extremely large, the maximum shear stress due to the above-mentioned terminal effect becomes large, and there is a problem in that adhesive peeling is likely to occur. In addition, rayon fiber cords have a disadvantageous weight-to-strength ratio compared to nylon fiber cords, and therefore have problems such as a thicker gauge at the rim cushioning part and being weak against bending fatigue. FIG. 4 shows a tire according to another embodiment of the present invention.
Showing E ₂ . In this embodiment, the nylon cord reinforcing layer 8 is connected to the bead core 2 and bead filler 1.
0 so as to surround it, and the rest of the structure is the same as the embodiment shown in FIG. 3 described above. Hereinafter, the effects exhibited by the tire of the present invention will be explained. In the tire of the present invention, when the folded part 4 of the carcass ply P made of polyester fiber cord is brought into close contact with the main body part 3, the interdigital nylon cord reinforcing layer 8 having a low Young's modulus is inserted between the carcass plies P such as a metal cord layer. The reinforcing layer 8 is also inserted without using a reinforcing layer with high rigidity, and the reinforcing layer 8 is arranged beyond the end portion 6 of the folded portion 4 from at least the side surface of the bead core 2. Therefore, the change in rigidity from the tire side part to the bead part, which has the highest rigidity, gradually increases, and there is no part in the middle where the rigidity suddenly changes. Therefore, when a bending load (bending load) is applied to the carcass ply P, stress concentration generated at the end portion 6 of the folded portion 4 is reduced. On the other hand, in the tire of the present invention, at the end portion 6, the thin adhesive rubber layer is formed by the carcass ply P.
The reinforcing layer 8 is interposed between the polyester fiber cord and the nylon fiber cord of the reinforcing layer 8, and is not between the polyester fiber cords as in the conventional case. That is,
Since a nylon fiber cord, which has a Young's modulus approximately 1/3 to 1/6 smaller than that of the polyester fiber cord, is adhered to one side of the adhesive rubber layer, the above-mentioned terminal effect of interlayer shear stress is alleviated. Furthermore, by interposing the nylon cord reinforcing layer 8, it is possible to reduce the decrease in adhesion caused by thermal deterioration of the polyester fiber cord due to heat generation. In this way, in the tire of the present invention, the stress concentration at the end portion 6 is alleviated in response to both the bending load and the tensile load applied to the carcass ply P, and the decrease in adhesion due to heat generation of the polyester fiber cord is also alleviated. Therefore, by synergistically, the occurrence of separation at the folded end portion can be reduced even under severe running conditions of low pressure and high load. Furthermore, the effects of the present invention will be explained with reference to FIGS. 5 to 11. Figure 5 shows the conventional structure shown in Figure 2.
The symbol is shown in a separate figure to make it easier to understand. Similarly, Figure 6 shows
This is the one shown in Figure 3. In Fig. 5, l ₁ is a part where carcass ply P is made up of one piece, and l ₂ is a part where two carcass plies P are made up of carcass folding part 4 and carcass main part 3. Figures 7 and 8 are models of these. Similarly, in Figure 6, L ₁ is the carcass ply.
_L2 is a two-layer part consisting of carcass ply P and reinforcing layer 8, and _L3 is a three-layer part consisting of two carcass plies P and reinforcing layer 8. FIG. 11. When a vehicle is traveling straight or cornering, tires are subjected to various external forces due to reaction forces from the road surface. At this time, bending moments M ₁ and M ₂ and tensile forces P ₁ and P ₂ are generally applied to the carcass plies, and interlaminar shear stress occurs in the adhesive rubber layer between the plies. _M1
The bending stiffness M ₁₁ resisting this M ₁ is calculated for each location such as l ₁ , l ₂ in the conventional tire in FIG. 5 and L ₁ , L ₂ , L ₃ in the inventive tire in FIG. 6. , respectively, are calculated based on composite material theory regarding unidirectional fiber-reinforced laminates in composite materials engineering, and the results are as shown in the following table. A computer is used for this calculation, and various data such as Young's modulus, Poisson's ratio, shear modulus, and fiber content in the rubber of the polyester fiber cord and nylon fiber cord placed in the carcass ply and reinforcing layer are used. .

[Table] As is clear here, in the structure of the present invention
The bending stiffness difference between L ₁ , L ₂ , and L ₃ is smaller than the bending stiffness difference between l ₁ and l ₂ of the conventional structure, and the stiffness changes more continuously. In general, when pulling a single layer bias ply, the cord angle is calculated from the following formula in the circumferential direction.
It is known that setting the angle to 54.7° minimizes the interlayer shear stress of the adhesive rubber layer at the end, but as is clear from Figure 13, in terms of tire lateral stiffness, if the angle with respect to the circumferential direction is 30° or more, effective. angle=cos ^-1 √3=54.7゜ Using a nylon cord as a reinforcing layer,
In addition, by adopting the above angle, the degree of stress concentration can be significantly alleviated. As shown in the table below, the adhesion of coated polyester cords due to thermal deterioration decreases to 85% at 60 minutes and 65% at 180 minutes, when 148℃ x 30 minutes is 100. The decrease in adhesion of nylon cord due to heat deterioration is 98% in 60 minutes, assuming 148℃ x 30 minutes as 100.
At 180 minutes, the adhesion was 98%, with almost no decrease in adhesion.

[Table] Furthermore, as shown in Figure 12, polyester and nylon were molded into a tube shape, and the tube was rotated at a predetermined angle to compare heat generation. The surface temperature of the tube is significantly higher than that of nylon (indicated by the dotted line). In other words, when the load on the tires increases extremely or when cornering is repeated,
The heat generated by the sidewall of a tire is significantly higher than that of nylon, and the heat generated promotes the deterioration of the rubber and decreases its adhesive strength, resulting in a decrease in durability. In the structure of the present invention, the cross-shaped nylon cord reinforcing layer 8 with low heat generation is located between the polyester carcass plies P, which alleviates heat generation and has high rigidity, so that bending that causes heat generation is also alleviated, resulting in The durability is improved. In order to confirm the durability effect of the bead part structure of the present invention as described above, a drum durability test was conducted in comparison with the conventional structure, and it was found that the durability was improved by about 25%.

[Table] The conventional structure tested was a pneumatic radial tire with the structure shown in FIG. 2, in which the distance from the bead portion 1 to the terminal portion 6 of the folded portion 4 was 30 mm, and the distance to the upper end of the bead filler 5 was 70 mm. The tested structure according to the present invention is different from the above-mentioned conventional structure in that the upper end 9 of the reinforcing layer 8 is separated from the bead portion 1 by 50 mm.
This is a tire in which a nylon cord reinforcing layer 8 is inserted. On the other hand, the rigidity of the sides has a large effect on steering stability. In order to improve handling stability, it is necessary to appropriately balance the rigidity of the tread and side parts. Regarding the rigidity distribution of radial tires, since a highly rigid belt is placed in the tread portion, the side portions generally tend to lack rigidity. Therefore,
Rigidity is supplemented by a hard bead filler 10 or a rubber stock 7. However, the basic rigid members in the bead portion 1 are the carcass ply main body portion 3 and the carcass folded portion 4, and as described in the explanation of the prior art, the carcass ply P between the pair of bead cores 2 provides stable handling. This basically determines the material of the carcass ply main body part 3, and the folded part 4 is formed of the same material as the carcass ply main body part 3. It is difficult to balance the rigidity of the side and tread sections under these restrictive conditions.
By using another part that is not subject to these restrictions, that is, the interdigital nylon cord reinforcing layer 8 of the present invention, it becomes possible to easily set the balance. In addition, to improve durability, stress concentration is avoided, and the structure gradually increases rigidity from the side to the bead core, which also improves transient response such as sudden turns and improves steering stability. Connect. Furthermore, the material properties of the nylon cord reinforcing layer 8, such as the number of filaments, number of twists, thickness, and material, can be adjusted by selecting the number of ends and arrangement angle (cord angle) when arranging the cords in layers. Since the lateral spring constant (rigidity) can be set arbitrarily, it is possible to improve steering stability while minimizing the reduction in ride comfort. The lateral spring constant, which represents the stiffness effect of the side part and the effect of steering stability, was also measured using the same test tire as described above, and as shown in the table below, it was improved by about 10%.

[Table] Furthermore, when the steering stability was measured in an actual vehicle condition, as shown below, the tires of the present invention had larger yaw angular velocity and lateral acceleration relative to the steering angle, and clearly improved responsiveness.

[Table] Input pulse
On the other hand, as for the longitudinal spring constant which affects riding comfort, only an increase of 0.6% was observed as shown below, and the structure of the present invention keeps the deterioration of riding comfort to a minor extent.

[Table] In the test tire of the present invention, the upper end 9 of the reinforcing layer 8 was connected to the end portion 6 of the folded portion of the carcass ply P and the rubber stock 7 disposed outside the folded portion 4.
50mm was selected as the intermediate height. It is clear that if the upper end 9 of the reinforcing layer 8 coincides with the upper end of the rubber stock 7 or the end portion 6 of the folded portion 4, the durability will be lower than that of the conventional structure in terms of stress concentration. It is most desirable to set it at an intermediate height as in this test tire from the viewpoint of durability, but from the viewpoint of handling stability, it becomes necessary to change the height of the reinforcing layer 8 in order to change the rigidity of the side. . Therefore, taking into account process variations and the fluidity of parts in the vulcanized state, the positions where there is no risk of matching are set at 5 mm or more above the tip of the folded layer and 5 mm or more below the upper end of the rubber stock 7. It is desirable to set the steering stability. Regarding the lower position of the reinforcing layer 8, it is desirable to lock it to the bead core 2 with the least distortion, but for production reasons, even if the lower part is folded back around the bead core 2 as shown in FIG. 4, as shown in FIG. Even if it is not folded back, the effect of the present invention is not affected in any way. In addition, in the method of inserting the reinforcing layer 8, the shape will differ in the vicinity of the bead portion 1 depending on whether it is inserted along the outside of the carcass ply main body portion 3 or the inside of the fold, but this has no effect on the effects of the present invention. do not have. As described above, in the tire of the present invention, when the end portion of the carcass ply made of polyester fiber cord is brought into close contact with the main body portion by folding back the bead core, a nylon cord reinforcing layer is skillfully interposed. be effective. That is, the reinforcing layer of nylon cord inserted between the main body part of the carcass ply and the folded part is extended beyond the upper end of the folded part so as to be in close contact with the main body part, and the hard rubber stock is further covered on the outside thereof. As a result, changes in rigidity gradually and continuously increase from the tire side part to the bead part, thereby preventing sudden changes in rigidity. Therefore, stress concentration at the folded end can be alleviated with respect to the bending load applied to the carcass ply. In addition, the adhesive rubber layer between the plies near the folded ends of the carcass plies is such that a polyester fiber cord with a high Young's modulus is placed on one side, and a nylon fiber cord with a low Young's modulus is placed on the other side. Therefore, the maximum value of interlaminar shear stress concentration that occurs at the folded end portion when subjected to a tensile load can be reduced compared to conventional polyester fiber cords sandwiched between polyester fiber cords.
Further, by inserting the nylon cord reinforcing layer, it is possible to suppress the decrease in adhesiveness due to thermal deterioration due to heat generation of the polyester fiber cord. In this way, both the bending load and the tensile load applied to the carcass ply are relieved by stress concentration at the folded ends, and the decrease in adhesion due to heat generation of the polyester fiber cord is also alleviated, so these effects are synergistic. By doing so, even if the vehicle runs under severe conditions of low pressure and high load, separation that tends to occur at the folded end portion can be reduced. In addition, in the present invention, the number of filaments, number of twists, thickness,
By selecting the material properties such as the material, the number of ends when layering cords, the arrangement angle (cord angle), etc., the horizontal spring constant (rigidity) can be set arbitrarily. This makes it possible to improve steering stability while minimizing the reduction in comfort.

[Brief explanation of the drawing]

FIGS. 1 and 2 are structural diagrams of a conventional tire, FIGS. 3 and 4 are structural diagrams showing an embodiment of the present invention, and FIGS. 5 and 6 are structural diagrams of a conventional tire. Figure 7 a, b, and c are diagrams that model the carcass ply in the l part of Figure ₅ , respectively (a is a cross-sectional plan view, b is a cross-sectional side view). , c shows the front view), Figures 8a, b, and c are modeled versions of the carcass plies in the L ₂ parts of Figure 5, and Figures 9 a, b, and c are the ₁ part L in Figure 6. Figures 10a, b, and c are modeled carcass plies and reinforcing layers in Figure ₆ . Figure 12 is a diagram that models the carcass ply and reinforcing layer in the L ₃ part of the figure, respectively. FIG. 13 is a diagram showing the relationship between the angle of the nylon cord reinforcing layer and the tire lateral stiffness, with the vertical axis representing the tire lateral rigidity and the horizontal axis representing the angle of the nylon cord reinforcing layer with respect to the circumferential direction. DESCRIPTION OF SYMBOLS 1... Bead part, 2... Bead core, 3... Carcass ply main part, 4... Carcass ply folded part, 6... Terminal part of folded part 4, 7... Rubber stock, 8... Nylon cord reinforcement layer, 9... Upper end of nylon cord reinforcing layer, 10... Bead filler.

Claims (1)

[Claims] 1. Both left and right ends of a carcass ply made of rubberized polyester fiber cord are folded back from the inside to the outside around the left and right bead cores, and the inner surface of this folded portion is placed on the top surface of the bead core. A nylon cord reinforcing layer in the form of a blind is placed in close contact with the outer surface of the main body of the carcass ply beyond the bead filler, with a nylon cord reinforcing layer interposed therebetween, and the reinforcing layer is made of other reinforcement such as a metal cord layer having greater rigidity than the carcass ply. Extending at least from the side surface of the bead core beyond the terminal part of the folded part so as to be in close contact with the outer surface of the carcass ply main body without using a layer together, and further extending from the outside of the bead core to the outside of the folded part. A pneumatic tire for a vehicle, characterized in that a hard rubber stock having a tongue-shaped cross section is disposed in close contact with the upper end of the reinforcing layer.