JPH0723044B2 - Radial tires for motorcycles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motorcycle tire, and more particularly to a motorcycle radial tire having excellent durability at high speeds.

[Prior art]

Recently, with the improvement of road network and pavement, speeding up of vehicles has been promoted, and radial radial tires for motorcycles are also required to have high speed durability.

As a conventionally proposed radial tire for motorcycles, the maximum width of the tread has a cross-sectional profile that makes the maximum width of the tire, and the carcass is made of more than one layer of a carcass ply with a radial structure made of organic fiber cords, and both ends are The breaker has a toroidal shape folded around a pair of left and right bead cores, and is arranged outside of the carcass in the radial direction, and has a breaker composed of a plurality of plies arranged at a shallow cord angle with respect to the tire circumferential direction. Discloses that the radially outer ply is narrower than the inner ply. (For example, JP-A-58-22704 and JP-A-58-20503).

[Problems to be solved]

However, since a motorcycle tire is required to have a special motion characteristic of turning at a large camber angle, the cross-sectional profile of the tread portion has an arched shape with a small radius of curvature. The fact that the tread has a profile that allows it to contact the ground even when it is greatly inclined is a point greatly different from the tread profile of a tire for a four-wheeled vehicle or the like. However, due to this profile, the deformation strain at the ends of the breaker during running becomes severe, and as a result, the adhesive strength at the ends of the breaker is originally inferior, resulting in peeling from the carcass or damage between the breaker plies. . In particular, as disclosed in the above publication, the conventional breaker ply having a radial structure has a structure in which a wide first ply is arranged adjacent to a carcass and a narrow second ply is arranged radially outside thereof. Therefore, the strain is concentrated on both ends of the second ply, and peeling occurs between the second ply and the peripheral rubber. An object of the present invention is to solve such a problem and to provide a radial tire for a motorcycle having excellent durability while maintaining the original properties of the radial tire, that is, wear resistance, ground contact property and high-speed running performance.

[Means for solving problems]

The present invention is directed to a tread portion having an arch-shaped cross-sectional profile extending to both sides in the meridian direction from a tire center equatorial plane, side wall portions extending inward in a radial direction from both sides, and a radial inner end of the side wall portion. A toroidal carcass, which has a bead portion located in a portion and a cord extending substantially parallel to the radial direction of the tire, and whose both ends are folded back around a bead core, and the tread portion is substantially the same as the tread portion on the outer side in the radial direction of the carcass. In a radial tire for a motorcycle having a width and a breaker made of an aromatic polyamide fiber cord, the breaker has two cords with cords arranged at a shallow angle of 10 ° to 45 ° with respect to the tire circumferential direction, and It is wider than the inner ply on the outside and the steps on both ends are 3-10 mm each. It is a radial tire for a motorcycle according to claim.

Further, on the outer side in the radial direction of the carcass ply, from one bead part to the other bead part, both ends thereof are not folded around the bead core and end at a position overlapping with the folded part (5T) of the carcass ply. The turning performance can be further enhanced by disposing one or more reinforcing layers (8) made of fiber cords. An embodiment of a radial tire for a motorcycle according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a partial sectional view of a radial tire for a motorcycle according to the present invention. In the figure, a tire 1 of the present invention has a tread portion 2, a side wall portion 3 extending inward in the radial direction from both ends thereof, and a bead portion 4 located at an inner end portion in the radial direction of the side wall portion. There is. Here, the tread portion 2 extends on the crown of the carcass cord from the center of the crown almost in parallel to the contour of the carcass cord, and the linear width Wt of the tread portion 2 is usually configured to have a cross-sectional shape exceeding the maximum width Ws of the sidewall portion. The camber thrust when tilted is maintained.

Next, the carcass 5 of the tire of the present invention is composed of two plies, and both ends thereof are folded back around the bead core 6 from the inner side to the outer side and terminate in the bead portion 4 or the side wall portion 3. Here, the folded-back end 5a located outside the bead portion extends to a position higher than the folded-back end 5b located inside the bead portion, completely covering the inner folded-back end, and relieving stress concentration at the end portion. Is desirable. Further, in order to reinforce the side wall portion, the respective heights Hb and Ha of the inner folded portion 5b and the outer folded portion 5a from the bead base portion are 55 of the height H from the bead base portion at the maximum width position of the side wall portion. ~ 65% and 70 ~ 100
It is desirable to set in the range of%. Next, the cords of the carcass are arranged parallel or substantially parallel to the radial direction of the tire. Here, substantially parallel means that the cord is inclined at an angle of 10 ° or less in the radial direction.
If a structure exceeding ° is adopted, the excellent high-speed running characteristics characteristic of radial tires cannot be obtained. As the fiber used for the carcass cord, organic fiber such as nylon, polyester, rayon or aromatic polyamide fiber is used. In the present invention, one or more plies of the carcass are used, but the structure for folding back around the bead core 6 may be a structure for folding back from the inside as shown in the figure, a structure for folding back from the outside to the inside, or a combination of both. However, the figure shows a structure in which the inside is folded back from the outside as an optimum example.

Next, the breaker 7 in the tire of the present invention is arranged so as to have a width extending over substantially the entire width of the tread portion to enhance the hoop effect of the tread portion. Here, the breaker 7 is located on the outer side in the radial direction of the first ply 7a and the first ply arranged adjacent to the carcass.
A second ply 7b, which is wider than the first ply 7a, is arranged. The second ply 7b is arranged with a width across the entire width of the tread belt portion, and the first ply 7a is configured to have a step (S) of 3 to 10 mm narrower than that of the second ply 7b. That is, the first ply is 6 to 20 mm narrower than the second ply.

If the step width exceeds 10 mm, the width of the first ply becomes too narrow, and the reinforcing effect on the tread part, especially the shoulder part, is not sufficient, while if it is less than 3 mm, the step difference in rigidity at the breaker end becomes severe. The ply is easily separated from the carcass. As described above, according to the present invention, the breaker ply cut end, which is likely to concentrate the repeated deformation strain transmitted from the tread portion during traveling and is originally inferior in adhesion to rubber, is provided.
Since the width of the first ply is narrowed so that it is located on the inner side in the radial direction of the ply, and the entertainment is covered with the second ply with high rigidity, the strain is effectively concentrated on the cut end of the first ply. The ply separation can be prevented.

The breaker ply cords are arranged at an angle of 10 ° to 45 ° with respect to the tire circumferential direction. If the code angle is too small, the tread rigidity will be increased and the impact on stones or irregularities on the road surface will be great, which will impair running safety and riding comfort, while if the code angle is too large, steering stability at high speeds Inhibit. The breaker 7 is usually composed of two plies, but at least the width of the second ply is the tread width Wt.
Are formed with substantially the same width as.

Conventionally, the fiber cord used for the breaker, rayon, polyester, nylon, and steel cords and the like materials are used, in the present invention is an aromatic polyamide fiber cord, strength 7 g / d or more, initial modulus 200 g / d or more The twist coefficient (NT) expressed by the following formula is 0.36 to 0.60, preferably
The range of 0.44 to 0.55 is preferable.

NT: Twisting factor N: Number of twists / 10 cm D: 1/2 of total denier of cord ρ: Specific gravity of the cord The above breaker cord has a 300% modulus of 100 to 100
It is preferable to bury the rubber parallel to 240 kg / cm ^{2 with} a density of 30 to 65 pieces / 5 cm.

Next, in the present invention, as shown in FIG. 2, the carcass ply 5 is folded back to the outside in the radial direction of the carcass from one bead portion to the other bead portion, and both ends thereof are not folded back around the bead core. A reinforcing layer 8 made of a fiber cord that ends at a position overlapping the portion 5T can be arranged. The reinforcing layer 8 crosses the carcass cord at a constant angle and has a reinforcing function of the side wall portion. However, in order to improve the camber thrust without impairing the riding comfort, the vertical spring constant of the side wall portion is set. It is necessary to increase the lateral spring constant without increasing it, so the cord hardness is 45 ° to 85 °, preferably 60 ° to the circumferential direction.
Must be arranged at 80 °. When the cord hardness is 45 ° or less, both the horizontal spring constant and the vertical spring constant become hard, and when the cord hardness is 85 ° or more, both the horizontal spring constant and the vertical spring constant become small, which is not preferable. Further, the cord of the reinforcing layer is arranged continuously from one bead portion to the other bead portion, and both ends thereof are configured to overlap each other at the bead portion with the folded back 5T of the carcass to relieve stress concentration in the region. It is desirable to do.

Further, according to the present invention, by arranging the bead apex 9 made of hard rubber extending gradually from the bead core 6 in the side wall direction at the portion surrounded by the carcass and the folded-back end portion or the cord reinforcing layer, the bead apex 9 can be removed from the bead portion. Lateral rigidity can be enhanced up to the shoulder portion direction. The bead apex 9 preferably extends to the vicinity where the upper end overlaps the breaker end, and its JIS hardness is in the range of 65 ° to 85 °.

Example 1 An example of the present invention and a comparative example were experimentally manufactured with a tire size 120 / 90R18 for a rear wheel. Detailed materials for trial tires No. 1
The results are shown in Table 2 and Table 2.

The method of each test is shown below.

(1) Durability Each tire is run at an internal pressure of 2.25 kg / cm ² , a speed of 65 km / h, and a load of 290 kg until the breaker is damaged on the drum, and the running distance is displayed as an index.

(2) Camber thrust Under the internal pressure of 2.25 kg / cm ² , the speed of 65 km / h, and the load of 290 kg, the average values of the camber thrust at the camber angles of 10 °, 20 °, 30 ° and 40 ° were used for comparison.

(3) Vibration generation speed and disturbance convergence performance On a highway, the feeling of a trained test rider gave a disturbance during actual vehicle running at a speed at which body vibration naturally occurs, and this convergence was evaluated by the feeling.

The results of the check are shown in Tables 1 and 2. Table 1 and 2
The table shows that the tire of the present invention has excellent durability. The vehicle used in the actual vehicle test is the Yamaha XL750.
So, 100290V19 cross-ply tires were used for the front, and test tires of Tables 1 and 2 were used for the rear.

Example 2 As an example of the present invention, a tire for a rear wheel having a tire size of 120 / 90R18 was experimentally manufactured using the structure shown in FIG. 2 with the ply structure of the breaker partially changed according to the specifications of Table 3. On the other hand, as a comparative example, a step S having a width of 10 mm and a width of the first ply wider than that of the second ply was used.

After running each tire on the drum for 15000 km at an internal pressure of 2.25 kg / cm ² , a speed of 65 kg / h, and a load of 290 kg, the tire was disassembled and the distribution of the ply cord strength of the breaker was measured. Examples of the present invention are shown in FIGS. 3 (a) to 3 (c), and comparative examples are shown in FIGS. 4 (a) to 4 (c). In FIG. 4 of the comparative example, the cord strength of the first ply at both end positions of the FIG. 2 ply is significantly reduced, but FIG.
From FIG. 3 (b), it is recognized that the cords of the first ply and the second ply maintain the same strength in the tread width direction.

[Effect] Therefore, in the radial tire for a motorcycle of the present invention, the first ply and the second ply constituting the breaker are arranged as described above, and the first ply and the second ply which are located in the region where the deformation and distortion from the tread portion are the largest. By removing the 2-ply terminal from this area, narrowing the width of the first ply, and positioning this terminal in the area with less strain, and covering both terminals with the second ply, the original characteristics of the radial tire are maintained. While high speed durability can be improved.

[Brief description of drawings]

1 and 2 are partial cross-sectional views of a radial tire for a motorcycle of the present invention, FIGS. 3 (a) to 3 (c), and FIGS. 4 (a) to 4 (c). It is a graph and a figure which show the intensity | strength of the code | cord in each position of the 1st ply and the 2nd ply of the breaker of this invention, and the breaker of a comparative example, respectively.

Claims (2)

[Claims] 1. A tread portion having an arch-shaped cross-sectional profile extending from the tire central equatorial plane to both sides in the meridian direction,
It consists of a side wall portion extending inward in the radial direction from both sides thereof, a bead portion located at an inner end portion in the radial direction of the side wall portion, and a cord extending substantially parallel to the radial direction of the tire. A toroidal carcass that is folded back around the bead core, and a radial tire for a motorcycle provided with a breaker made of an aromatic polyamide fiber cord having substantially the same width as the tread portion on the outer side in the radial direction of the carcass, the breaker is a cord. The two plies arranged at a shallow angle of 10 ° to 45 ° with respect to the tire circumferential direction, the outer ply is wider than the inner ply, and the steps at both ends are 3 to 10 mm, respectively. Radial tires for motorcycles characterized by 2. The carcass ply extends radially outward from one bead portion to the other bead portion, and both ends thereof are not folded around the bead core but are terminated at positions overlapping the folded portion of the carcass ply. The radial tire for a motorcycle according to claim 1, wherein one or more reinforcing layers (8) made of the organic fiber cord are arranged.