JPH10193918A - Motorcycle tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motorcycle tire that can increase lateral force and side grip at the time of turning. SOLUTION: In the standard state of a tire assembled to a service rim and charged with working internal pressure, the outer surface of a tread part 2 is curved in protruding shape, and tread width TW that is the distance in the axial direction of the tire between the outer ends E, E of the tread part 2 is the maximum width of the tire. In such a motorcycle tire, the tread part outer surface between the outer ends E, E of the tread part 2 in tire meridian cross section including a tire axis in the standard state is so formed that each of tread part outer surface half-width parts 2L, 2R from the tire equator C to the respective tread part outer ends E, E is formed by connecting three or more kinds of circular arcs with different radii of curvature and that the radii of curvature of the respective circular arcs are gradually larger toward the outer end E side of the tread part 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire for a motorcycle capable of improving lateral force and side grip performance at the time of turning with a camber angle given to the tire.

[0002]

2. Description of the Related Art Among motorcycle tires, a racing slick tire, which has a high coefficient of friction on a road surface, such as a racing slick tire developed exclusively for running on a dry circuit road surface, has a higher performance than when traveling straight. In addition, the most severe performance is required during a turn in which the motorcycle is banked and traveling, and particularly, it is required to generate a lateral force enough to overcome a large centrifugal force.

[0003] Conventional motorcycle tires have a bias structure that is convenient for generating camber thrust. However, recently, high-speed motorcycle tires such as racing slick tires have been used. In tires, in order to secure a greater lateral force, it is important to generate a cornering force in addition to the camber thrust, and the use of a radial structure is increasing.

However, even in the conventional radial tire for a motorcycle, in order to exhibit grip performance, it is extremely difficult to consider the profile of the tread portion in spite of the difference in characteristics between straight running and turning. There are few at present.

In order to increase the lateral force and side grip during turning, the inventors of the present invention consider the shape of the ground contact surface to be important. In particular, it is very important to increase the contact width relative to the contact length. Focusing on the importance of this, the following study was conducted.

First, FIG. 8 shows a front view of a motorcycle tire in contact with the ground. The contact width W of the tire is approximately determined by the radius of curvature R of the outer surface of the tread portion of the tire and the amount of vertical deflection Δh of the tire. And can be represented by the following formula (1). Tire contact width W = 2√ (R ^2- (R- △ h) ² ) = 2√ (2R △ h- △ h ² ) ≒ 2√ (2R △ h) (1) Here, the outer surface of the tread portion With respect to the curvature radius R, the amount of vertical deflection Δh is regarded as minute, and the term of Δh ² is omitted.

From the equation (1), the contact width W of the tire is
It can be understood that it is proportional to the square root of the radius of curvature R of the outer surface of the tread portion. Therefore, it is understood that as the camber angle of the tire increases, the contact width W can be increased by increasing the radius of curvature R of the outer surface of the tread from the center of the tread to the outer end of the tread. it can.

[0008] The inventors of the present invention have proposed that the lateral force and the side grip during turning of a motorcycle are basically based on increasing the radius of curvature R of the outer surface of the tread portion from the center of the tread portion toward the outer end of the tread portion. They found that the performance could be improved and completed the present invention.

Japanese Patent Application Laid-Open No. 6-297912 discloses a technique for improving the turning performance of a pneumatic tire for a motorcycle.
The tread portion is divided into a center portion composed of an arc having a radius of curvature R1 and １ ／ of both sides of a center portion composed of a radius of curvature R2.
Portion, and is further divided into a shoulder portion composed of an arc having a radius of curvature R3, and the magnitude of each radius of curvature is R2 <R1.
<R3, which is fundamentally different from the present invention.

JP-A-8-25906 discloses a pneumatic tire in which the radius of curvature of the tread surface gradually changes outward in the tire axial direction.
This change is such that the radius of curvature of the outer surface of the tread portion decreases outward in the tire axial direction, which is the reverse of the present invention.

As described above, an object of the present invention is to provide a motorcycle tire capable of improving lateral force and side grip performance at the time of turning given a camber angle.

[0012]

According to the first aspect of the present invention, in a standard state in which a tire is mounted on a rim and a used internal pressure is filled, the outer surface of the tread portion is convexly curved and the outer surface of the tread portion is bent. A motorcycle tire in which a tread width, which is a tire axial distance between ends E and E, forms a tire maximum width, and in a tire meridional section including a tire shaft in the standard state, the tread outer ends E and E
The tread portion outer surface between the tread portion outer surface half width portion from the tire equator C to the one tread portion outer end E is formed by connecting three or more types of arcs having different radii of curvature. The radius of curvature of each arc is gradually increased toward the outer end E of the tread portion.

According to a second aspect of the present invention, the outer surface of the tread portion between the outer ends E of the tread portions is substantially equal to the outer surface of the tread portion by a division number N of 5 or more along the outer surface. When the divided areas are formed, the radius of curvature R _i of the i-th divided area from the tire equator C and the radius of curvature R of the (i + 1) -th divided area are defined assuming that the divided area including the tire equator C is 1.
_{i + 1} and the ratio of _{(R i + 1 / R i} ) includes: the division number N, in relation to a numerical value TL of the outer surface length along this outer surface of the tread portion outer surface (mm), EXP (2 × 10 ⁻³ × TL / N) ≦ R _{i + 1} / R _i ≦ EXP (5 ×
10 ⁻³ × TL / N).

According to a third aspect of the present invention, the half width portion of the outer surface of the tread portion has a radius of curvature R1 of an arc at the position of the tire equator C and a length along the outer surface of the tread portion starting from the tire equator C ( mm) and the radius of curvature R (S) of the arc at the position of this length, R (S) = R1 × EXP (α × S) (where 2 × 10 ⁻³ ≦ α ≦ 5 × ^10-3 ).

[0015]

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the motorcycle tire of the present embodiment has a symmetrical structure in which the outer surface of the tread portion 2 is convexly curved in a standard state where the tire is rim-assembled into a rim and a used internal pressure is filled. With
The tread width TW, which is the distance between the outer ends E of the tread portion 2 and the tire axial direction E, forms the maximum tire width.

The rim used is JIS, JATM
It is preferable to use a standard applicable rim such as A, but if there is no standard such as a racing tire, the rim used is 70 to 90% of the maximum width of the tire in a standard state, and furthermore 75 to 8%.
Preferably, a 5% rim width is used.

In order to enable the motorcycle to turn while giving a bank angle, the tread height TH, which is the height in the tire radial direction from the tire equator C to the outer end E of the tread portion, is determined by the tire sectional height TH. 0.4 times or more of H and 0.7
The ratio is less than twice.

The motorcycle tire has a tread portion 2
And a carcass 6 that turns around the bead core 5 of the bead portion 4 through the side wall portion 3 and a belt layer 7 disposed outside the carcass 6 in the tire radial direction.

The carcass 6 is composed of, for example, one or more plies having a radial structure, and in this embodiment, is composed of one ply in which nylon cords are arranged at an angle of 90 ° with respect to the tire equator C. Further, as the carcass cord, other various organic fiber cords such as polyester, rayon, and the like can be appropriately adopted.

The belt layer 7 comprises two inner and outer belt plies in which an aromatic polyamide cord is arranged at a small angle of 40 ° or less with respect to the tire equator C, in this embodiment, at an angle of 20 °. A so-called cross belt constituted by superposing 7A and 7B in the direction in which the cords cross is illustrated.

In this embodiment, the belt ply 7A on the inner side in the tire radial direction is formed to have a smaller width than the outer belt ply 7B, and the step amount at both ends is set to 5 mm. As a result, it is possible to prevent distortion from being concentrated at both ends of the belt layer 7,
Can be improved in durability. The step amount is desirably, for example, 3 mm or more, and preferably 10 mm or less.

Further, as the belt layer 7, a so-called jointless belt formed by spirally winding a small-width strip-shaped strip having a cord covered with topping rubber may be used. According to this, since the seam of the ply can be eliminated in the tread portion 2, the tire uniformity can be further improved.

In the tire meridional section including the tire shaft in the standard state, the tread outer ends E, E
The outer surface of the tread portion between the tread portion outer surface half width portions 2 between the tire equator C and one of the tread portion outer ends E is 2
L and 2R are formed by connecting three or more types of arcs each having a different radius of curvature, and the radius of curvature R of each arc is gradually increased as approaching the outer end E side of the tread portion 2. Features.

In the present embodiment, as an example of gradually increasing the radius of curvature R, an example in which the radius of curvature is continuously increased at a constant rate of change is exemplified. Can be realized.

The outer half width portion 2L, 2R of the tread portion
As shown in FIG. 2, the radius of curvature R1 (mm) of the arc at the position of the tire equator C, the numerical value S of the length (mm) along the outer surface of the tread starting from the tire equator C, and the length R (S) = R1 × EXP (α × S) (2) (provided that 2 × 10 ⁻³ ≦ α ≦ 5 × 10 ^{−) 3} ) An example that satisfies the relationship of is shown. Further, each required curvature radius R (S) is always perpendicular to the outer surface of the tread portion.

The exponential function represented by the above equation (2) is the radius of curvature of the arc at the position on the outer surface of the tread portion 2 that is separated from the tire equator C by a numerical value S of length (mm) along the outer surface of the tread portion. R (S) is determined, and at the same time, the rate of change of the increasing radius of curvature is always constant.

Here, the radius of curvature of the arc at each position separating the numerical values S and S + △ S of the length from the tire equator C can be expressed by the following equations (3) and (4). R (S + △ S) = R1 × EXP (α × (S + △ S)) (3) R (S) = R1 × EXP (α × S) (4)

The rate of change of the radius of curvature is R (S + △
Since S) / R (S), it can be expressed as in the following equation (5). R (S + △ S) / R (S) = EXP (α × △ S) (5) As is apparent from the above equation (5), the rate of change of the radius of curvature is independent of the numerical value S of the length. It can be seen that it becomes constant at an arbitrary position.

Next, the relationship between the contact width and the camber angle of the tire whose curvature radius gradually increases toward the outer end E of the tread portion will be examined.

First, when the camber angle is given to the tire, the curvature radius R of the arc where the outer surface of the tread portion contacts the ground is
Each is obtained from the above equation (2), and is substituted into the above equation (1) to calculate the theoretical value of the contact width. Further, FIG.
Is plotted with a broken line.

Further, using the above formula (2) and R1 = 9
2 / mm, α = 3 × 10 ^-3 Tire size 190 /
Prototype of a motorcycle tire of 55R17 (rim size: 6.25 × 17), load 110kgf, air pressure 2.1kg
The actual tire contact width W was measured under the condition of f / mm ² . This measured value is also plotted by the solid line in FIG. FIG. 4 shows the footprint of the ground contact surface with each camber angle given.

From FIG. 3, it can be seen that the theoretical value and the measured value of the contact width are almost the same, and that the radius of curvature of the outer surface of the tread is gradually increased toward the outer end E of the tread. It can be confirmed that, with the tire of No. 5, the contact width index monotonically increases as the camber angle increases.

Therefore, the tire for a motorcycle of the present invention can gradually change the contact width of the tire as the camber angle is given to the tire to turn the motorcycle, and thus the lateral force and the side grip performance can be improved. Can be improved. In this example, since the increase in the contact width changes monotonously, the lateral force and the side grip force can be continuously changed according to the steering even when the camber angle is gradually increased. This is preferable in that controllability in the inside can also be made easy.

Next, α in the above equation (2) represents the rate of increase of the exponential function, and this value is set based on experimental results of lateral force and side grip performance in an actual vehicle. In this experiment, a tire having an outer surface of a tread portion having a single arc with α = 0 in the equation (2) was used, and α = 6 × 10
^The test was performed on motorcycle tires having an increase rate of up to ^-3 .

As for the performance, the side grip performance and the control performance during turning on a dry road surface were evaluated according to the rider's sensuality by a five-point method. Three or more points are good levels.

FIG. 5 shows the results of the test. The increase rate α
However, good results were obtained in the range of 2 × 10 ^{−3 to} 5 × 10 ⁻³ . If the increase rate α is smaller than 2 × 10 ⁻³ , there is no change in performance in comparison with a tire using a single arc, and if it exceeds 5 × 10 ⁻³ , the shoulder side with respect to the center of the tread portion. It has been confirmed that when the radius of curvature of the circular arc becomes too large and the camber angle is given to the tire, monotonous behavior is not exhibited and the sensory score is lowered.

Next, R1 in the equation (2) is the tire equator C
Is the radius of curvature (mm) of the circular arc at the position of. The specific radius of curvature at the position on the outer surface of each tread portion can be set by setting this R1. This R1 is, for example, 35% to 60% of the tread width TW, more preferably 40% to
It is desirable to set it to 55%.

In the above example, the radius of curvature of the arc on the outer surface of the tread portion is continuously changed using an exponential function, and the change rate is constant. However, the technical idea of the present invention is that The outer surface of the part 2 is substantially equally divided into 5 or more, preferably 7 or more, and more preferably 9 or more as a finite number of regions, and a connected body of arcs in which each region corresponds to an arc having a single radius of curvature. It can also be realized by configuring as

FIG. 6 shows the contour of the outer surface of the tread portion 2. In this example, the outer surface has a bilaterally symmetrical structure substantially equally divided into five along the contour, so that the tire equator C
Is formed, and a second region T2 and a third region T3 successively formed on both sides of the first region T1 are formed. In this way, when the outer surface of the tread portion is divided into a finite number and a single arc is assigned to each region, it is preferable in that a mold can be manufactured at a low cost.

The ratio (R2 / R1) of the radius of curvature R1 of the arc of the first region T1 to the radius of curvature R2 of the arc of the second region T2, and the radius of curvature R2 of the arc of the second region T2 In this example, the rate of change of the radius of curvature, which is the ratio (R3 / R2) between the radius of curvature of the arc of the third region T3 and R3 / R2, is constant at 1.16.

Here, the outer surface of the tread portion between the outer ends E of the tread portion is a divided area obtained by substantially equally dividing the outer surface of the tread portion by a division number N of 5 or more along the outer surface. When formed, the radius of curvature R _i of the i-th sub-region from the tire equator C is defined as 1 for the sub-region including the tire equator C,
The ratio (R _{i +} ) to the radius of curvature R _{i + 1} of the (i + 1) -th divided area
_The rate of change of ₁ 1 / R _i ) can be easily set using the increase rate α of the exponential function shown in the above equation (2).

When the above exponential function is used, the rate of change of the radius of curvature can be expressed by the following equation (5). R (S + △ S) / R (S) = EXP (α × △ S) (5)

Therefore, the value (dimensionless value) obtained by dividing ΔS in the above equation (5) by the numerical value TL of the outer surface length (mm) of the outer surface of the tread portion along the outer surface of the tread portion by the number of divisions N ( TL
/ N), it can be expressed as the following equation (6). (R _{i + 1} / R _i ) = EXP (α × TL / N) (6)

Then, the range of the increase rate α (2 × 10
Substituting ⁻³ ≦ α ≦ 5 × 10 ⁻³ ) into the equation (6), the rate of change of the radius of curvature can be defined as satisfying the following equation (7). EXP (2 × 10 ⁻³ × TL / N) ≦ R _{i + 1} / Ri ≦ EXP (5 × 10 ⁻³ × TL / N) (7)

Here, the tire size 190 / 55R17
For example, if the tire is divided into five parts, TL = 23
6, N = 5 and TL / N = 47.2, so R _{i + 1} /
It is preferable that Ri can be selected and set from the range of 1.09 to 1.27.

When the outer surface of the tread portion 2 of the tire has a symmetrical structure with respect to the tire equator C, the division number N
Is odd, the number n of types of different radii of curvature is (N +
1) / 2, and when the number of divisions N is an even number, the number n of types of different radii of curvature is N / 2, and substantially the tire equator C
May be arcs having the same radius of curvature.

FIG. 7 shows the contour of the outer surface of the tread portion 2. In this example, the outer surface is substantially equally divided into nine parts and is symmetrical, so that the first area T1 including the tire equator C is obtained. And second, third, fourth, and fifth regions T2 to T5 successively formed on both sides thereof are illustrated. In this example, there are five types of curvature radii. Further, the rate of change of the radius of curvature can be set preferably in the range of 1.05 to 1.14 for the same size by using the above equation (7). ing.

As described above, the motorcycle is turned by gradually increasing the curvature radii R1, R2,... Ri of the respective arcs forming the outer surface of the tread portion toward the outer end E of the tread portion. As the camber angle is given to the tire, the contact width of the tire can be increased, and thus the lateral force and the side grip performance can be improved.

As described above, the motorcycle tire of the present invention may be mounted on either or both of the front and rear wheels of the vehicle.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A slick-type racing motorcycle tire having a tire size of 190 / 55R17 and various shapes of an outer surface of a tread having the basic structure shown in FIG. 1 was prototyped (Examples 1 to 6; In Comparative Example 1), the rider performed a sensory evaluation on the lateral force during turning and the side grip performance to compare the performance. Note that in Examples 1 to 3, the radius of curvature of the arc on the outer surface of the tread portion changes continuously using an exponential function.
For 6, the tread outer surface was 5, 7, 9 respectively.
It shows what is divided and changed stepwise. The details of the tire and the test method are shown below.

Carcass: 1 ply of nylon cord, 90 ° to tire equator Belt layer: 2 ply of aromatic polyamide 20 ° to tire equator (intersecting each other)

Test Method A test tire was mounted on the rear wheel of a motorcycle with a displacement of 750 cc (rim size: 6.25 × 17, internal pressure 2.1 kgf / cm).
² ) Turn around on a dry pavement. The evaluation was made mainly on the critical turning speed during turning and the transient characteristics of the grip force during turning. Table 1 shows the test results.

[0053]

[Table 1]

As a result of the test, it was confirmed that all the tires of the examples had excellent sensory scores. It was also confirmed that Example 5 in which the outer surface of the tread portion was divided into seven or more sections could have the same level of performance as compared with Example 2 in which the outer surface was continuously changed using an exponential function.

[0055]

As described above, the tire for a motorcycle according to the present invention can greatly change the tire contact width as the camber angle is given to the tire for turning the motorcycle. By improving the performance, high-speed turning performance can be enhanced.

In the tire for a motorcycle according to the third aspect, since the radius of curvature can be continuously changed and the rate of change can be kept constant, the contact width of the tire with respect to the tire camber angle is also reduced. Thus, the controllability of the vehicle during turning can be made easier.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tire showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating a radius of curvature R (S) of an arc at a position on an outer surface of a tread portion.

FIG. 3 is a graph showing a relationship between a contact width index and a camber angle.

FIG. 4 is a diagram showing a footprint of a ground plane.

FIG. 5 is a graph showing a relationship between a sensory score of lateral force and side grip performance and an increase rate α.

FIG. 6 is a diagram illustrating a contour of an outer surface of a tread portion according to another embodiment of the present invention.

FIG. 7 is a diagram illustrating a contour of an outer surface of a tread portion according to another embodiment of the present invention.

FIG. 8 is a front view showing a contact state of the tire.

[Explanation of symbols]

 2 Tread portion 2L, 2R Half width portion of outer surface of tread portion N Number of divisions TL Length of outer surface of tread portion TW Tread width E Outer edge of tread portion C Tire equator

Claims (3)

[Claims] In a standard condition in which a tire is assembled on a rim and a used internal pressure is filled, the outer surface of the tread portion is convexly curved and the tread width, which is the axial distance between the outer ends E of the tread portion, E, is equal to the tire width. A motorcycle tire having a maximum width, wherein in a tire meridional section including a tire axis in the standard state, a tread outer surface between the tread outer ends E and E is located outside one of the tread portions from a tire equator C. The outer half width portion of each tread portion up to the end E is formed by connecting three or more types of arcs having different radii of curvature, and the radius of curvature of each of the arcs gradually increases as approaching the tread portion outer end E side. A motorcycle tire characterized by having a larger size. 2. An outer surface of a tread portion between the tread ends E, E forms a divided area substantially equal to the outer surface of the tread with a division number N of 5 or more along the outer surface. , The division area including the tire equator C is defined as 1
Curvature of the i-th divided area from a radius R _i, (i + 1) th divided area ratio of the radius of curvature R _{i + 1} of the _{(R i + 1 / R i} ) includes: the division number N, the tread portion outer surface In relation to the outer surface length (mm) along this outer surface with the numerical value TL, EXP (2 × 10 ⁻³ × TL / N) ≦ R _{i + 1} / R _i ≦ EXP (5 ×
The motorcycle tire according to claim 1, wherein the following relationship is satisfied: ^10-3 x TL / N). 3. The half width portion of the outer surface of the tread portion includes a radius of curvature R1 of an arc at the position of the tire equator C, a numerical value S of a length (mm) along the outer surface of the tread starting from the tire equator C, Radius of curvature R of the arc at this length position
And (S) satisfying the following relationship: R (S) = R1 × EXP (α × S) (where 2 × 10 ⁻³ ≦ α ≦ 5 × 10 ⁻³ ). Motorcycle tires.