JP3227401B2 - Motorcycle tires - Google Patents

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 grip performance when turning with a camber angle given to the tire.

[0002]

2. Description of the Related Art Since a motorcycle performs a turning operation while tilting the vehicle, it is more likely to fall down than a four-wheeled vehicle and has a low coefficient of friction of a road surface, such as a wet road surface. When turning around, wheel spin (idling) is likely to occur at the time of rising at the corner exit.

As described above, in the tire for a motorcycle, in order to prevent the vehicle from overturning and to generate a lateral force enough to overcome the centrifugal force, the improvement of the grip performance during cornering is more than that in straight traveling. This is an important issue.

However, in the conventional motorcycle tires, there are very few tires that take into account the profile of the tread portion in order to exhibit grip performance, despite the fact that the characteristics differ between straight running and turning. Is the current situation.

[0005] The present inventors have paid attention to the fact that the ground contact surface is a very important factor for improving the grip performance when turning, from the viewpoint that the grip performance is generated by the contact between the tire and the road surface. The following study was conducted.

First, FIG. 8 shows a side view and a front view of a motorcycle tire in contact with the ground. The contact area A of the tire is approximately equal to the contact length L of the tire as shown in the following equation (1).
And the contact width W. Tire contact area A∝L × W (1)

On the other hand, the contact length L and the contact width W can be expressed by the following equations (2) and (3) using the tire radius r and the radius of curvature R of the tread surface, respectively. In addition,
Δh is the amount of vertical deflection of the tire. L = 2√ (r ² − (r− △ h) ² ) = 2√ (2r △ h− △ h ² ) (2) W = 2√ (R ² − (R− △ h) ² ) = 2 √ (2R △ h- △ h ² ) (3)

Here, with respect to the tire radius r and the radius of curvature R of the outer surface of the tread portion, the amount of vertical deflection Δh is regarded as minute and the term of Δh ² is omitted. W can be expressed as in the following equations (4) and (5), respectively. L = 2√ (2r △ h) (4) W = 2√ (2R △ h) (5)

By substituting the above equations (4) and (5) into the above equation (1) indicating the contact area A of the tire, the following equation (6) can be obtained. Tire contact area A∝L × W = 2√ (2r △ h) ・ 2√ (2R △ h) = 8 △△ h√ (r ・ R) (6) Further, the equation (6) is changed to △ h. When deformed, the following equation (7) is obtained. Δh∝A / (8√ (r · R)) (7)

The equation (7) is expressed by the following equation:
And the shape of the tire. And
Normally, the contact area A of the tire, if the tire pressure is determined,
Since it has a substantially constant value, it can be understood that Δh is inversely proportional to the square root of the radius of curvature R of the outer surface of the tread portion.

The above equation (7) shows that when the radius of curvature R of the outer surface of the tread portion of the tire is reduced, the amount of vertical deflection Δh of the tire is increased, which reduces the vertical spring of the tire. Means you can. Further, reducing the vertical spring of the tire means that when the load on the tire increases, the degree of increase in the contact area A increases, which is advantageous in securing grip force. In particular, in the case of motorcycle rear tires, when the driving force acts, the load on the rear tire increases, but if the degree of increase in the contact area at that time increases, the grip force also increases, so that falling and wheel spin are less likely to occur. It can be understood.

The inventors of the present invention have found that motorcycle tires include:
It is necessary to increase the degree of increase in the contact area when the load is increased and to increase the grip when turning, in which the camber angle is given to the tire, rather than when traveling straight, so that the radius of curvature R of the outer surface of the tread portion is changed to the center of the tread portion. The present invention was found to improve the grip performance during turning of the motorcycle on the basis of decreasing the distance from the portion to the outer end side of the tread portion, 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 the 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.

Japanese Patent Application Laid-Open No. Hei 8-25906 discloses that in a pneumatic tire, the radius of curvature of the tread surface gradually decreases outward in the tire axial direction. However, this tire does not suggest anything about turning at a given camber angle during turning, and the tread width, which is the axial distance between the outer ends of the tread portion, is not the tire maximum width. . Therefore, it does not provide any motivation for the technical idea of the present invention, which aims to improve the grip performance when turning when given a camber angle.

As described above, an object of the present invention is to provide a motorcycle tire capable of improving the grip performance when turning with a given camber angle.

[0016]

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 characteristic is that the radius of curvature of each arc is gradually reduced toward the outer end E of the tread portion.

The invention according to claim 2 is characterized in that the tread
The outer surface of the tread portion between the outer ends E, E is the outer surface of the tread portion.
Is substantially equal to the number of divisions N of 5 or more along the outer surface.
When the divided area is formed, the tire includes the equator C
The tune of the i-th division from tire equator C with the division being 1
Rate radius R_iAnd the radius of curvature R of the (i + 1) th divided area
_{i + 1}And the ratio (R_{i + 1}/ R_i) Indicates the number of divisions N and the
Numerical value of outer surface length (mm) along this outer surface of tread outer surface
In relation to TL, EXP (−7 × 10^-3× TL / N) ≦ R_{i + 1}/ R_i≤ EXP (−
2 × 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 starting from the tire equator C ( mm) and the radius of curvature R (S) of the arc at this length position, R (S) = R1 × EXP (β × S) (where −7 × 10 ⁻³ ≦ β ≦ − 2 × 10 ⁻³ ).

[0019]

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 the outer surface of the tread portion 2 convexly curved and the tread portion 2 The tread width TW, which is the distance between the outer ends E and E in the tire axial direction, 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.

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 set so that the motorcycle can be turned with a puncture angle given to the motorcycle. It is constituted by a ratio of 0.4 times or more and 0.7 times or less of H.

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. In this embodiment, the carcass 6 is composed of one ply in which nylon cords are arranged at an angle of 90 ° with respect to the tire equator C. May be appropriately selected from various other organic fiber cords such as polyester and rayon.

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

Further, in the present embodiment, the belt ply 7A on the inner side in the tire radial direction is formed to be narrower 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.

The belt layer 7 may be a so-called jointless belt formed by spirally winding a small-width strip having a cord covered with topping rubber. 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 reduced as approaching the outer end E side of the tread portion 2. Features.

In the present embodiment, an example in which the radius of curvature R is gradually reduced is shown as an example in which the radius of curvature is reduced continuously and at a constant rate. Can be realized.

The tread outer surface half width portion 2L, 2R
As shown in FIG. 2, the radius of curvature R1 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 position of this length R (S) = R1 × EXP (β × S) (8) (provided that -7 × 10 ⁻³ ≦ β ≦ −2 × 10 ⁻³ ) Meet. Also, each required curvature radius R (S)
Is always perpendicular to the outer surface of the tread.

The exponential function expressed by the above equation (8) is the curvature of the arc at the position on the outer surface of the tread portion 2 which is separated from the tire equator C by a numerical value S of a length (mm) along the outer surface of the tread portion. At the same time that the radius R (S) is determined, the rate of change of the decreasing radius of curvature is always constant.

Here, the radius of curvature of the arc at each position separating S and S + △ S as a numerical value of the length (mm) from the tire equator C to the outer surface of the tread portion is as follows (9), (10)
It can be represented by an equation. R (S + △ S) = R1 × EXP (β × (S + △ S)) (9) R (S) = R1 × EXP (β × S) (10)

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 (11). R (S + △ S) / R (S) = EXP (β × △ S) (11) As is apparent from the above equation (11), the rate of change of the radius of curvature is expressed by the numerical value S of the length (mm). Irrelevant, and it is seen that it becomes constant at an arbitrary position.

Next, the longitudinal spring of the tire whose curvature radius is gradually reduced toward the outer end E of the tread portion will be examined. The vertical deflection amount Δh of the tire can be approximately expressed by the following expression (12) from the expression (7). Δh = A / (8√ (r · R)) (12)

Here, the tire size 190 / 55R17
For example, a motorcycle tire having a load of 130 kgf, an air pressure of 0.02 kgf / mm ² , and a contact area A = 130 / 0.02
= 6500 mm ² and the tire radius r = 300 mm can be substituted into the above equation (12) to obtain the following equation (13). Δh = 6500 / (8√ (300R)) (13)

Then, the radius of curvature R of the arc where the outer surface of the tread portion touches the ground when the camber angle is given to the tire is obtained from the exponential function, and is substituted for R in the above equation (13). 1 / △ h) is calculated as a theoretical vertical spring characteristic value, and the value when the camber angle is 0 degree is 100.
3 is plotted by a solid line in FIG. In addition, the result of measuring the actual vertical spring of the tire is plotted with a broken line. The reason why the reciprocal of △ h (1 / △ h) is a theoretical vertical spring characteristic value is that 1 / △ h is a characteristic value that is proportional to the vertical spring.

From FIG. 3, it can be seen that the theoretical longitudinal spring characteristic value and the actual longitudinal spring of the tire substantially match, and the radius of curvature of the outer surface of the tread portion gradually increases toward the outer end E of the tread portion. In the tire of the present invention, the longitudinal spring index decreases monotonously as the camber angle increases.

Therefore, the motorcycle tire of the present invention can change the vertical spring of the tire to a small value when a camber angle is given to the tire to turn the motorcycle, and thus the contact area during turning can be increased. It is possible to improve grip performance. Further, since the decrease in the vertical spring index changes monotonously, even if the steering is performed with the camber angle gradually increased, the grip force continuously changes accordingly, so that the controllability during turning of the vehicle can be facilitated. It is preferred in that respect.

Next, β in the above equation (8) represents the rate of decrease of the exponential function, and this value is set based on the experimental result of the grip performance in an actual vehicle. Experiments on grip performance were performed on tires for motorcycles having a reduction rate of β = −10 × 10 ⁻³ , including tires with the outer surface of the tread having a single arc of β = 0. Examined.

The grip performance was evaluated on a slippery wet road surface by side-grip and traction (whether or not there is a wheel spin) during turning and when exiting turning by a 5-point scale according to the rider's sensuality.

FIG. 4 shows the results of the test. The decrease rate β
However, in the range of −7 × 10 ⁻³ to ⁻² × 10 ⁻³ , good results were obtained in the grip performance. If the decrease rate β is smaller than −7 × 10 ^{−3, the} radius of curvature of the arc on the shoulder side with respect to the center of the tread portion becomes too small, and when the camber angle is given to the tire, a monotonous behavior is exhibited. It has been confirmed that it disappears and the grip performance decreases.

Next, R1 in equation (8) is the tire equator C
Is the radius of curvature of the arc at the position of. The specific radius of curvature of the position on the outer surface of each tread portion can be set by setting this R1. This R1 is appropriately set for each tire size, and is 50% to 80% of the tread width TW, more preferably 55% to 75%, and further preferably 60% to
It is desirable to be 70%.

In the above example, the radius of curvature of the circular arc on the outer surface of the tread portion continuously changes 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 follows.

FIG. 5 shows the contour of the outer surface of the tread portion 2. In this example, the outer surface is substantially equally divided into five parts, thereby forming a first region T 1 including the tire equator C and both sides thereof. And a second region T2 and a third region T3 which are successively 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) of the radius of curvature R3 of the arc of the third region T3, is constant at 0.85.

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 rate of decrease β of the exponential function shown in the above equation (8).

When the above-mentioned exponential function is used, the rate of change of the radius of curvature can be expressed by the following equation (11). R (S + △ S) / R (S) = EXP (β × △ S) (11)

Therefore, ΔS in the above equation (11):
Length of the outer surface of the tread portion along the outer surface (mm)
Divided by the number of divisions N (dimensionless value) (T
L / N), it can be expressed as the following equation (14). (R _{i + 1} / R _i ) = EXP (β × TL / N) (14)

Then, the range of the decrease rate β (−7 × 1
By substituting 0 ⁻³ ≦ β ≦ −2 × 10 ⁻³ ) into the equation (14), the rate of change of the radius of curvature can be defined as satisfying the following equation. EXP (−7 × 10 ⁻³ × TL / N) ≦ R _{i + 1} / Ri ≦ EXP (−
2 × 10 ⁻³ × TL / N)

Here, the tire size 190 / 55R17
Taking the example of 5 divisions, TL = 220, N = 5, TL /
Since N = 44, Ri _{+ 1} / Ri is 0.735-0.
916 can be selected and set.

If 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. 6 shows the outline of the outer surface of the tread portion 2. In this example, the outer surface is substantially equally divided into nine parts, so that the first area T1 including the tire equator C and both sides thereof are provided. , Third, fourth, and fifth regions T2 to T5 successively following
Are formed. In this example, there are five types of curvature radii. In addition, the rate of change of the radius of curvature is calculated by the equation (1)
In the same size using 5), preferably 0.843
The value can be set in the range of 0.952 to 0.952. In this example, the value is fixed at 0.91.

As described above, the motorcycle is turned by gradually decreasing the curvature radii R1, R2,... Ri of the respective arcs forming the outer surface of the tread portion as approaching the outer end E side of the tread portion. When the camber angle is given to the tire, the amount of deflection can be increased by reducing the vertical spring of the tire, so that grip performance during turning 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, but is particularly formed as a rear tire whose load increases when a driving force is applied. Is particularly preferred.

[0054]

EXAMPLE A motorcycle tire having a tire size of 190 / 55R17 and having the basic structure shown in FIG. 1 and the outer surface of the tread varied in various forms, and a tread pattern shown in FIG. At the same time (Examples 1 to 6, Comparative Example 1), the grip during turning was subjected to a sensory evaluation by a rider to compare the performance. In Examples 1 to 3, the radius of curvature of the circular arc on the outer surface of the tread portion continuously changes using an exponential function. In Examples 4 to 6, the outer surface of the tread portion was changed by 5 times. , 7, 9 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) Groove depth of tread groove 5 mm

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 grip performance at that time was evaluated focusing on the critical turning speed during turning and the transient characteristics of the grip force during turning. Table 1 shows the test results.

[0057]

[Table 1]

As a result of the test, it was confirmed that all of the tires of the examples had excellent grip performance during turning. Example 5 in which the outer surface of the tread portion was divided into seven or more parts
It was also confirmed that the grip performance could be kept at the same level even when compared with Example 2 in which 指数 was continuously changed using an exponential function.

[0059]

As described above, the motorcycle tire according to the present invention can change the vertical spring of the tire to a small extent as the camber angle is given to the tire so as to turn the motorcycle. Grip performance can be improved by increasing the area.

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 vertical spring of the tire can also be changed with respect to the tire camber angle. 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 vertical spring index and a camber angle.

FIG. 4 is a graph showing a relationship between a sensory score of grip performance and a reduction rate β.

FIG. 5 is a diagram showing a contour of an outer surface of a tread portion according to another embodiment of the present invention.

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 development view of a tread pattern employed in the embodiment.

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Kobayashi No. 6-12-12, Shinkaiji, Hyogo-ku, Kobe-shi, Hyogo Prefecture (56) References JP-A-5-16609 (JP, A) JP-A-59- 179407 (JP, A) JP-A-5-229308 (JP, A) JP-A-6-191223 (JP, A) JP-A 8-337101 (JP, A) JP-A-10-193918 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B60C 3/00 B60C 9/06-9/08 B60C 9 / 18,11 / 00

Claims (3)

(57) [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 in that the tire is made smaller. 2. The tread outer surface between the tread outer 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. when the radius of curvature R _i of the i-th divided area from the tire equator C divided area as one including the tire equator C, (i + 1) -th of the ratio of the radius of curvature R _{i + 1} of the division zone (R i _{+ 1} / R _i ) is expressed as EXP (−7 × 10 ⁻³ × TL / N) ≦ R in the relationship between the number of divisions N and the numerical value TL of the outer surface length (mm) along the outer surface of the tread portion outer surface. _{i + 1} / R _i ≦ EXP (−
2. The motorcycle tire according to claim 1, wherein a relationship of 2 × 10 ⁻³ × TL / N) is satisfied. 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 (β × S) (where -7 × 10 ⁻³ ≦ β ≦ −2 × 10 ⁻³ ). The motorcycle tire as described.