JPH08169211A - Pneumatic tire for two-wheeler - Google Patents

Abstract

PURPOSE: To ease transverse tensile distortion in a tread part and deter groove-bottom cracks occurring, by composing a belt layer of a spiral belt, by forming asymmetric circumferential main grooves which have a specified inclination angle and a specified length measured in the circumferential direction, and by making the curvature radius of a groove bottom corner at the tread center greater than that of side zones. CONSTITUTION: A spiral belt composed of cords configurated substantially in the circumferential direction is arranged in a tread part in contiguity with a carcass layer. Transverse main grooves 2 extending tendingly transversely are configurated in the center zone of the tread part, while circumference main grooves 4 extending tendingly in the circumferential direction are configurated in side zones thereof which do not contact the ground at the time of straight traveling. An inclination angle θ of the circumference main grooves 4 relative to the circumferential direction falls within a range from 0 to 30 degrees, a length L measured in the circumferential direction falls in a range from 10 to 60% of a pattern pitch length P, and a cross section shape thereof is made asymmetric. Further, the curvature radius of a groove bottom corner at the tread center is made greater than that of the side zones. Thereby traveling performance such as high-speed durability and control stability is promoted, wet performance is improved, and groove-bottom cracks is deterred from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire for a motorcycle suitable for high speed running having a directional pattern having excellent lateral slip resistance on wet road surfaces and groove bottom crack resistance, and more particularly to a belt layer. Relates to a pneumatic radial tire for a high speed two-wheeled vehicle formed by a spiral belt.

[0002]

2. Description of the Related Art Pneumatic radial tires for motorcycles are mainly composed of spiral belts in order to meet the demands for high speed durability and improved steering stability. Here, the belt having the spiral structure is a belt having a structure in which the cords are substantially arranged in the tire circumferential direction between the tread portion, that is, the carcass layer and the tread rubber, and is generally composed of one or a plurality of cords. It is called a spiral belt because it is formed by winding a belt-like body around the outside of the carcass ply in a spiral shape. This spiral belt exerts a strong binding force in the circumferential direction, so it has high-speed durability and steering stability. Increase.

[0003]

The tread surface of a pneumatic tire for a motorcycle during straight running is divided into a central area that contacts the road surface and both side areas that do not contact the ground surface. A tensile strain occurs in the width direction. In pneumatic tires for passenger cars, such a tensile strain does not occur because the entire tread tread area becomes the ground contact area,
This is a phenomenon unique to pneumatic tires for motorcycles.

In a pneumatic radial tire for a motorcycle, in which only a belt having a spiral structure is adopted as a belt layer,
Since the restraining force in the width direction is lower than that of a pneumatic radial tire for a motorcycle having a cross belt, the tensile strain is considerably large. Further, if grooves are provided in such both side areas, they will be exposed to the tensile strain in the width direction, and especially when a high-angle peripheral main groove inclined at a low angle with respect to the peripheral direction is greatly affected. It has been found that stress concentration occurs in the corners of the groove bottom, which causes cracks in the groove bottom to occur early.

[0005]

In order to achieve the above-mentioned object, the invention according to claim 1 is provided with a large number of lateral main grooves which are provided in the central region and tend to extend in the lateral direction and which are provided in both side regions. In a pneumatic radial tire for a motorcycle having a tread tread portion in which a pattern made up of a plurality of circumferential main grooves extending in the circumferential direction is provided, a belt layer that reinforces the tread portion is a spiral consisting of a cord extending substantially in the circumferential direction. It is made of a belt, the inclination angle of the circumferential main groove with respect to the circumferential direction is 0 to 30 degrees, the circumferential length L of the circumferential main groove is 0.1 to 0.6 of the pattern pitch length P, and the circumferential main groove is The cross-sectional shape is asymmetric, and the radius of curvature Rc of the groove bottom corner on the tread center side is made larger than the radius of curvature Rs of the groove bottom corner on the tread lateral side.

According to a second aspect of the present invention, the lateral main groove is
It is characterized in that it has a directivity extending in a direction in which it gradually expands from a lower side to an upper side with a pattern center as a boundary in a front view of a mounting posture on a vehicle.

According to a third aspect of the present invention, the radius of curvature R is
c is 0.2 to 0.5 of the groove width W of the circumferential main groove.

[0008]

According to the pneumatic radial tire for a motorcycle of claim 1, in order to enhance high speed running performance such as high speed durability and steering stability, the tread portion is reinforced by forming the belt with a spiral belt. In the central area of the tread surface, horizontal main grooves that tend to extend in the lateral direction are provided in order to obtain slip resistance during straight running and lateral slip resistance during the transition between straight running and turning. Circumferential main grooves that tend to extend in the circumferential direction in order to obtain lateral slip resistance during turning are provided in both side areas that do not touch the ground during traveling, and the inclination angle of the circumferential main groove with respect to the circumferential direction is 30 degrees. If it exceeds the range, drainage performance and skid resistance at the time of turning on a wet road surface at a large camber angle cannot be sufficiently obtained, so the inclination angle of the lateral main groove with respect to the circumferential direction is 0 to
A high angle within the range of 30 degrees is obtained, while lateral length resistance L of the circumferential main groove is less than 0.1 of the pattern pitch length P, lateral slip resistance cannot be obtained and exceeds 0.6. The bending rigidity becomes too weak, and when the vehicle travels at a large camber angle, the rigidity becomes discontinuous. Therefore, the circumferential length L is set in the range of 0.1 to 0.6 of the pitch length P and the width direction is set. Radius of curvature Rc of the groove bottom corner on the tread center side where the tensile strain of
By making it larger, it is possible to prevent the early occurrence of groove bottom cracks, despite the high-angle arrangement.

According to a second aspect of the present invention, in a front view of a mounting posture on a vehicle, a pattern structure in which a large number of directional inclined grooves extending in a direction in which the pattern center is used as a boundary and which is gradually expanded upward from below is arranged. As a result, water can be discharged in the direction along the slope of the inclined groove when running on wet roads, improving drainage.

According to a third aspect of the invention, the radius of curvature R is
If c is less than 0.2 of the groove width W of the circumferential main groove, the effect of suppressing the generation of groove bottom cracks cannot be obtained, and if it exceeds 0.5, the groove width becomes narrow after wear, especially after the middle period, and the drainage performance and Since the skidability cannot be obtained, the radius of curvature Rc is set in the range of 0.2 to 0.5 of the groove width W of the peripheral main groove.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, the carcass layer 3 is wound around the bead core 5 from the inside to the outside,
The carcass layer 3 is composed of two layers of nylon cords arranged substantially in the radial direction. A bead filler 9 between the carcass body and the folded portion of the carcass.
Is arranged. In the tread portion 1, a spiral belt 7 made of cords arranged substantially in the circumferential direction is arranged adjacent to the carcass layer 3, and the spiral belt 7 is composed of two layers made of nylon cords. .

A belt 7 is formed by winding a belt-shaped member having a nylon cord covered with rubber and arranged in the longitudinal direction and having a width of about 5 mm on the spirally outer side of the carcass layer 3 in the radial direction, and the winding pitch is approximately the width of the belt-shaped member. As a half, a band-like member is formed by overlapping the width of almost half of the band-shaped member. As a result, the rigidity difference of the belt is eliminated and the rigidity distribution is made uniform.

In the central region of the tread surface, lateral main grooves 2 are arranged so as to extend in the lateral direction. When driving straight ahead, circumferential main grooves 4 tend to extend in the circumferential direction and are arranged in both areas not touching the ground. The horizontal main groove 2 has a directionality that extends in a direction in which the horizontal main groove 2 gradually expands from the lower side to the upper side with the pattern center C as a boundary in a front view of the mounting posture on the vehicle. The continuous circumferential main groove 4 forms a directional groove 6 as a whole. In the figure, P is the pattern pitch of the directional grooves 6, and D is the tire rotation direction.

Θ is an inclination angle of the lateral main groove 2 with respect to the circumferential direction, and is 63 degrees in this example. If the inclination angle is less than 35 degrees, uneven wear is likely to occur, and if it exceeds 85 degrees, the wet performance deteriorates. Therefore, the inclination angle is preferably in the range of 35 to 85 degrees.

L is the circumferential length of the circumferential main groove 4, and especially in a pneumatic radial tire for a motorcycle in which the tread portion is reinforced only by the spiral belt, cracks occur at the groove bottom of the circumferential main groove 4. Because it is easy, it cannot be made too long. The angle of the circumferential main groove 4 with respect to the circumferential direction is 0 degree in this example, but is selected in the range of 0 to 30 degrees.

As shown in FIGS. 3a and 3b, the cross-sectional shape of the circumferential main groove 4 is asymmetric, and the radius of curvature of the groove bottom corner on the center side of the tread is Rc and the radius of curvature of the groove bottom corner on the side of the tread is Rc. Is Rs, Rc> Rs. W is the groove width of the circumferential main groove, and Rc is 0.2 W to 0.
It is selected in the range of 5W. The groove bottom of the circumferential main groove 4 may be formed smoothly and continuously by Rc and Rs as shown in FIG. 3a, and as shown in FIG.
A flat portion 14A may be formed between c and RS.

[Test Example] In order to confirm the effect of suppressing the generation of groove bottom cracks, a pneumatic radial tire for a motorcycle having a tire size of 160 / 60R17 was used with a nylon cord ply 2
A radial carcass consisting of one sheet and two spiral belts were arranged in the tread portion, and the tire of the present invention and the tire of the comparative example were manufactured based on the specifications of Table 1 based on the example of FIG. In the table, the angle is the angle with respect to the circumferential direction, and the position is the distance from the tread center C. Further, the cross-sectional shape of the circumferential main groove was the type shown in FIG. 3b.

When an actual vehicle running test was carried out, a groove bottom crack was generated in the peripheral main groove at 5000 km for the comparative example tire, whereas it was 15000 km for the tire of the present invention (until complete abrasion).
No occurrence of cracks at the bottom of the circumferential main groove was observed.

[0019]

[Table 1]

[0020]

As described above, according to the present invention, by adopting the spiral belt as described above, high-speed running performance such as high-speed durability and steering stability can be improved, and the lateral main groove is arranged in the central region of the tread tread portion. This has the effect of improving wet performance when traveling straight ahead, and by arranging high-angle peripheral main grooves on both sides of it, it has the effect of improving skid resistance during turning when wet. Effect of suppressing groove bottom cracks that tend to occur early in the main groove by making the radius of curvature Rc of the groove bottom corner on the tread center side of the peripheral main groove larger than the radius of curvature Rs of the groove bottom corner on the side of the tread. Have.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3a is a cross-sectional view of a circumferential main groove of the present invention.

FIG. 3b is a cross-sectional view showing another example of the circumferential main groove of the present invention.

[Explanation of symbols]

 1 tread portion 2 lateral main groove 3 carcass layer 4 circumferential main groove 7 spiral belt C pattern center P pattern pitch L circumferential length of circumferential main groove Rc radius of curvature of groove bottom corner on the tread center side of circumferential main groove Rs circumferential main Curvature radius of the groove bottom corner on the tread side of the groove

[Procedure amendment]

[Submission date] May 12, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

As shown in FIG. 3, the circumferential main groove 4 has an asymmetrical cross-sectional shape, and the radius of curvature of the groove bottom corner on the center side of the tread is Rc and the radius of curvature of the groove bottom corner on the side of the tread is Rs.
In this case, Rc> Rs is set. W is the groove width of the peripheral main groove, and Rc is selected in the range of 0.2W to 0.5W. The groove bottom of the circumferential main groove 4 may be formed smoothly and continuously by Rc and Rs as shown in the left side view of FIG. 3, and as shown in the right side view of FIG. A flat portion 14A may be formed between RS.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is a sectional view of a circumferential main groove of the present invention.

[Explanation of symbols] 1 tread portion 2 lateral main groove 3 carcass layer 4 peripheral main groove 7 spiral belt C pattern center P pattern pitch L circumferential length of the peripheral main groove Rc of groove bottom corner on the tread center side of the peripheral main groove Curvature radius Rs Curvature radius of the groove bottom corner on the tread side of the circumferential main groove

Claims (3)

[Claims] 1. A tread tread portion having a pattern formed by a large number of lateral main grooves that are provided in a central region and tend to extend laterally, and a large number of circumferential main grooves that are provided in both regions and tend to extend circumferentially. In a pneumatic radial tire for a motorcycle having: a belt layer for reinforcing the tread portion is a spiral belt made of a cord extending substantially in the circumferential direction, and the inclination angle of the circumferential main groove with respect to the circumferential direction is 0 to 30.
And the circumferential length L of the circumferential main groove is the pattern pitch length P.
0.1 to 0.6, the cross-sectional shape of the peripheral main groove is made asymmetric, and the radius of curvature Rc of the groove bottom corner on the tread center side is made larger than the radius of curvature Rs of the groove bottom corner on the tread lateral side. A characteristic pneumatic radial tire for motorcycles. 2. The lateral main groove has a directivity extending in a direction in which the lateral main groove gradually expands from a lower side to an upper side with a pattern center as a boundary in a front view of a mounting posture on a vehicle. The tire described in. 3. The tire according to claim 1, wherein the radius of curvature Rc is 0.2 to 0.5 of the groove width W of the peripheral main groove.