JP2001287510A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for preventing early abrasion of a rib end part and improving maneuvering stability and rolling resistance in DRY/ WET. SOLUTION: Circular arcs 14A and 14B contacting with a crown outer contour shape 16 by passing through the respective grounding ends P1 and P2 having a radius of curvature smaller than a radius of curvature of the crown outer contour shape 16 are added to both end parts of a rib 14. The relationship between respective chamfer widths L1 and L2 and chamfer heights H1 and H2 of the circular arcs 14A and 14B is set so as to become L1.H1>L2.H2 in the case of F1>=F2 and L1.H1<L2.H2 in the case of F1<F2, where the grounding lengths at points P1 and P2 in an initial tire are respectively F1 and F2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a circumferential groove, and more particularly, to a cross-sectional shape of a tire rib which influences a wear characteristic and a rolling resistance value of a rib end related to a steering performance of the tire.

[0002]

2. Description of the Related Art Conventionally, in a pneumatic tire having at least one continuous groove extending in a circumferential direction, when the tire comes into contact with a road surface and rolls while supporting a load, the tire is separated by the circumferential groove. It is known that in a land portion of a tread (hereinafter, referred to as a rib), a greater shear strain is generated at a rib end, which is a corner portion on the surface side of the rib, than at a center portion. This concentration of distortion leads to deterioration of rolling resistance, and also causes so-called abnormal wear, in which the rib ends are worn early. In order to solve this, conventionally, a method of trimming a rib end to form a rounded shape has been adopted.

[0003]

However, according to this conventional method, since the cross-sectional shape of the rib is determined based on past experience, if the method of determining the shape is erroneously determined, the early wear of the rib end portion is adversely affected. There was a problem. When the phenomenon of early wear was examined in detail, the uneven wear that occurred when the rib end was rounded was found to be small because the ground length at the rib end was shorter than the ground length in the nearby ground area. It has been found that a diameter difference occurs between the region and the end of the rib, and that the shear force and slip in the circumferential direction increase sharply.

The present invention has been made in view of the conventional problems, and the shape of a rib end is changed to the shape of the other end in the same rib, or the end of the rib facing the rib with a groove interposed therebetween. It is an object of the present invention to provide a pneumatic tire having improved wear characteristics, steering stability in DRY / WET, and rolling resistance by determining the shape in relation to the shape of the tire and the contact shape of the end of each rib.

[0005]

A pneumatic tire according to a first aspect of the present invention is a tire in which both ends of a rib are trimmed, and a rib contact portion having a longer contact length at a portion contacting a road surface. Is trimmed more than the trimming amount of the shorter contact length.

A pneumatic tire according to a second aspect of the present invention is a tire obtained by trimming two rib ends facing each other across a groove, wherein the rib end having a longer contact length at a portion contacting a road surface is provided. The present invention is characterized in that the trimming amount is larger than the shorter trimming amount.

According to a third aspect of the present invention, there is provided the pneumatic tire according to the first aspect, wherein both ends of the cross section of the tire pass through respective grounding ends P1 and P2 and contact points Q1 and Q2.
2, arcs (14A, 14B) having a radius of curvature smaller than the radius of curvature of the crown outer contour shape (16) are provided in contact with the crown outer contour shape (16).
The distance parallel to the tire rotation axis between 1 and Q1 is L1, and the distance parallel to the tire rotation axis between P2 and Q2 is L2, P1, P2.
The distances parallel to the tire equatorial plane between the tire and the crown outer contour shape (16) are H1, H2, respectively, and the arcs (14A, 14A)
Assuming that the lengths of the ground contact lengths in the circumferential direction at P1 and P2 in the case where the curvature of B) matches the curvature of the crown outer contour shape (16) are F1 and F2, the above H1, H2, L1, L
2 is configured to satisfy the following relationship (see FIG. 1). When F1 ≧ F2, L1 · H1 ≧ L2 · H2 When F1 <F2, L1 · H1 <L2 · H2 Strictly speaking, the above-mentioned rib grounding end is strictly described in the air pressure-load load table of the JATMA earbook. The above air pressure is the air pressure at the maximum load capacity in the applicable size and ply rating in the case of a single wheel specified in the 1999 JATMA standard, and the load is the maximum load at the applied size and ply rating specified in the same standard. This is the load corresponding to the ability.

According to a fourth aspect of the present invention, there is provided the pneumatic tire according to the second aspect, wherein the groove (1) in the cross section of the tire rib is provided.
1) at the ends of the ribs (13, 14) opposed to each other with the contact points Q0, Q1 passing through the respective grounding ends P0, P1, and contacting the crown outer contour shape (16). ), Arcs (13A, 14A) having a smaller radius of curvature than P0 and Q
The distance parallel to the tire rotation axis at 0 is L0, the distance parallel to the tire rotation axis between P1 and Q1 is L1, the distance parallel to the tire equatorial plane between P0, P1 and the crown outer contour shape (16) is H0, H1, and the ground contact length in the circumferential direction at P0, P1 when the curvature of the arc (13A, 14A) matches the curvature of the crown outer contour shape (16) is F
Assuming that 0, F1, the above H0, H1, L0, L1 are:
It is configured to satisfy the following relationship (see FIG. 5). When F0 ≧ F1, L0 · H0 ≧ L1 · H1 When F0 <F1, L0 · H0 <L1 · H1

According to a fifth aspect of the present invention, there is provided the pneumatic tire according to the third aspect, wherein the rib (14) having the grounded ends P1 and P2 is provided between the rib (14) having the grounded ends and the grounded end P1 or the grounded end P2. The rib having the opposite ground end P0 has, on the ground end P0 side, a curvature radius smaller than the radius of curvature of the crown outer contour shape (16) passing through P0 and contacting the crown outer contour shape (16) at the contact point Q0. Arc (13A)
L0 is the distance parallel to the tire rotation axis between P0 and Q0, H0 is the distance parallel to the tire equatorial plane between P0 and the crown outer contour (16), and the arc (13A)
Is H0, H1, L0, L1 or H0, H2, where F0 is the length of the circumferential contact length in the above-mentioned P0 when the curvature of the outer ring coincides with the curvature of the crown outer contour shape (16).
L0 and L2 are configured to satisfy the following relationship (see FIG. 6). When F0 ≧ F1, L0 · H0 ≧ L1 · H1 When F0 <F1, L0 · H0 <L1 · H1 or when F0 ≧ F2, L0 · H0 ≧ L2 · H2 When F0 <F2, L0 · H0 < L2 ・ H2

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a diagram showing the shape of a tread portion of a pneumatic tire according to Embodiment 1; FIG. 1 (a) is a diagram showing the shape of a ground contact surface of the tire; FIG. It is a figure showing a shape. The pneumatic tire according to the first embodiment has a tread 1
0, four circumferentially continuous grooves 11, 1 symmetrical left and right
2 and five left and right symmetrical ribs 13 to 15 separated by these grooves 11 and 12. Where 11
Denotes a groove on the center side, 12 denotes a groove on the side, and 13 denotes a first rib located in the tire equatorial plane, that is, at the center.
4 is a second rib facing the first rib 13 with the groove 11 interposed therebetween.
Of the second rib 14 are located on the side.
And a third rib opposed to the second rib 14 with the groove 12 interposed therebetween. At both ends of the second rib 14, the crown outer contour 16 is in contact with the crown outer contour 16 through the respective ground ends P1 and P2. Arcs 14A and 14B having a radius of curvature smaller than the radius of curvature are added. Second rib 14
The shape of the arc 14A added to one end of the tire is the distance parallel to the tire equatorial plane between the P1 and the crown outer contour 16 when the contact point between the arc 14A and the crown outer contour 16 is Q1. It is determined by two values: (dropping width) L1 and the distance (falling height) H1 between the contact point Q1 and the ground end P1 which is the arc end on the groove bottom side of the arc 14A. The shape of the other arc 14B is also the distance L2 parallel to the tire equatorial plane between the grounding end P2, which is the arc end on the groove bottom side, and the crown outer contour shape 16, the arc end P2, the arc 14B, and the outside of the crown. It is determined by the distance H2 between the contour Q16 and the contact Q2.

In the present invention, two distances L (L1, L2 and L0 described later), H (H
The value of L · H, which is the product of 1, H2 and H0 described below,
It is used as a scale indicating the magnitude of shape change from a tire (initial tire) whose rib cross-sectional shape matches the crown outer contour shape 16. When the curvatures of the arcs 14A and 14B (or the arc 13A to be described later) are large, the value of L · H is substantially proportional to the amount of trimming of the rib ends, that is, the amount of rubber removed from both ends of the initial tire. Therefore, as the value of L · H is larger, the rubber in the portion that receives a larger strain is removed, and the concentration of the strain at the end of the rib can be reduced.

In the first embodiment, the relationship between the shapes of the left and right rib ends of the second rib 14 is defined as follows. In the second rib 14, the point P in the initial tire
1, P2, that is, the arcs 14A, 14B
Are respectively F1 and F2 at the points P1 and P2 when the respective curvatures coincide with the curvature of the crown outer contour shape 16. When F1 ≧ F2,
When L1 · H1 ≧ L2 · H2 and F1 <F2, L1
L1, H1, L2, so that H1 <L2 · H2
Set the value of H2. This is because if the rib end on the short contact length is rounded more than the rib end on the long contact length, the difference in the contact length in the rib becomes larger, and This is because the rib ends are worn out early. Then, one end of the second rib 14 (point P1
The relationship between the product L1 · H1 of the drop width L1 and the drop height H1 on the other side and the product L2 · H2 of the drop width L2 and the drop height H2 on the other end (point P2 side) is shown in FIG. Length F1 and F
By setting the shape of the both ends of the rib 14 so as to be the same as the magnitude relationship with 2, it is possible to prevent the difference in grounding length within the rib from increasing. Therefore, it is possible to obtain a pneumatic tire with improved wear characteristics, DRY / WET steering stability and rolling resistance, while suppressing uneven wear that occurs when the rib ends are rounded.

[0013]

First Embodiment Here, an example in which the technology of the first embodiment is applied to two types of tires having four circumferentially continuous left and right symmetric grooves in a tread portion will be described below. In the experiment, 315 / 70R22.5 size truck tires (conventional tire 1) and 11R22.5 size truck tires (conventional tire 2) whose rib outer contour matches the crown outer contour were used. Example tires 1 to 4 and comparative tires 1 to 4 in which the shapes of rib end portions of conventional tires 1 and 2 were changed were used. Table 1 shows the specifications of the two types of tires.

[Table 1] FIG. 2 and FIG. 3 are diagrams showing the grounding shapes of the conventional tires 1 and 2. Here, as shown in FIG. 4, the grounding length at the rib end of the first rib 13 is F0, and the second rib 14
F0, F0, when the contact length at the rib end is F1 and F2 in the order closer to the tire equatorial plane (from the rib 13 side)
The values of F1 and F2 are shown in Table 2 below.

[Table 2]

Next, the working tires 1 to 4 and the comparative tire 1
4 to 4 will be described. Implementation tires 1 and 2 are F
1> For 315 / 70R22.5 size tire which is F2,
As shown in FIG. 1, arcs 14A and 14B are added to both ends of the second rib 14, respectively. At this time, in the working tires 1 and 2, the relationship of L1 · H1> L2 · H2 is satisfied. , L1, H1, L2, and H2 are set. On the other hand, the comparative tires 1 and 2 replace the values of (L1, H1) and (L2, H2) of the working tires 1 and 2, respectively, so that L1 · H1 <L2 · H2. It is. The actual tires 3 and 4 have F1 <F
L1 · H1 for 11R 22.5 size tires
<L1, H1, L such that the relationship of L2 · H2 is satisfied
2 and H2, and the comparative tires 3 and 4 replace the values of (L1, H1) and (L2, H2) of the working tires 3 and 4 with L1 · H1> L2 · H2. It is to become. Specific values of L1, H1, L2, and H2 in the example tires 1 to 4 and the comparative tires 1 to 4 are as shown in Tables 3 and 4 below. As in the case of the conventional tires 1 and 2, no arcs are added to the end portions of the first rib 13 and the third rib 15 of the working tires 1 to 4 and the comparative tires 1 to 4.

[Table 3]

[Table 4]

The results of the rolling resistance test, uneven wear drum test, and WET lateral force test performed on these tires are shown in Tables 5 and 6 below.

[Table 5]

[Table 6] In Tables 5 and 6, the smaller the rolling resistance value is, the smaller the loss during rolling is, which is advantageous for fuel saving.
The uneven wear ratio indicates the ratio of the wear amount of the rib edge to the wear amount of the rib at the rib center (the larger one), and the closer the value is to 1, the more uniform the wear amount in the rib is. . The WET lateral force indicates the magnitude of the grip force during cornering on a wet road surface.
In addition, the value of the rolling resistance and the value of the WET lateral force were indicated by an index with the value of the conventional tire 1 or the conventional tire 2 being 100.

As shown in the above Tables 5 and 6, the working tires 1 to 4 have rolling resistance,
The uneven wear ratio and WET lateral force are all improved.
On the other hand, in the comparative tires 1 to 4, the rolling resistance and the WET lateral force are improved, but the uneven wear ratio is further deteriorated as compared with the conventional tires 1 and 2. Thus, when the rib end is rounded, its shape is determined in consideration of the grounding length ratio of both ends of the rib, so that the wear characteristics and DRY / WE are obtained.
It has been demonstrated that the steering stability at T and the rolling resistance can be improved. In addition, it has also been proved that if the shape is incorrect, the early wear of the rib end portion is worsened.

Second Embodiment In the first embodiment, the shape of both ends of one rib is determined in consideration of the grounding length ratio of both ends. Is determined in consideration of the contact length ratio of each rib end, it is possible to suppress uneven wear of each rib end due to a difference in contact length between ribs. In the second embodiment, as shown in FIG.
The drop width of the arc 13A added to the end of the rib 13 is L
0, the falling height is H0, and the length of the ground contact length in the initial tire is F0, the rib end shape of the first rib 13 is opposed to the rib end of the rib 14 with the groove 11 therebetween. The relationship with the side rib end shape is defined as follows.
When F0 ≧ F1, L0 · H0 ≧ L1 · H1, and
When F0 <F1, L0 · H0 <L1 · H1. This is because if the end of the rib with the short contact length is rounded more than the end of the rib with the long contact length, the difference in the contact length between the ribs 13 and 14 becomes larger, and the contact between the rib 13 and the rib 14 becomes larger. This is because the rib ends on the short side are worn away early. Therefore, the magnitude relationship between the product L0 · H0 of the drop width L0 and the drop height H0 of the rib 13 and the product L1 · H1 of the drop width L1 and the drop height H1 of the end of the rib 14 facing the rib 13 is described. The rib end shape on the side facing the rib end of the rib 13 and the rib end of the rib 14 across the groove 11 is set so that the magnitude relationship between the ground contact lengths F0 and F1 is the same. Accordingly, it is possible to prevent the difference in grounding length between the ribs 13 and 14 from increasing. Therefore, uneven wear that occurs when the rib ends are rounded can be suppressed, and a pneumatic tire with improved wear characteristics, steering stability in DRY / WET, and rolling resistance can be obtained.

[0018]

[Embodiment 2] In this experimental example 2, the same rib outer contour shape as the above-described first embodiment matches the crown outer contour shape.
70R22.5 size truck tire (conventional tire 1) and 11R22.5 size truck tire (conventional tire 2)
The technology of the second embodiment is applied, and the specifications of the two types of tires and the value of the contact length of the rib end are the same as those in Tables 1 and 2.

Next, the practical tires 5 to 8 and the comparative tire 5
The shapes No. to No. 8 will be described. The execution tires 5 and 6 are F
For 315 / 70R22.5 size tires where 0> F1,
As shown in FIG. 5, arcs 13A are added to both ends (only one end is shown) of the first rib 13, and arcs 14A are added to the ends of the second ribs 14 facing the ribs 13.
At that time, in the execution tires 5 and 6,
In order to satisfy the relationship of L0 · H0> L1 · H1, the above L
Set the values of 0, H0, L1, H1. On the contrary,
Comparative tires 5 and 6 are (L0,
H0) and (L1, H1), respectively,
0 · H0 <L1 · H1. Further, the implementation tires 7 and 8 set the values of L0, H0, L1, and H1 so as to satisfy the relationship of L0 · H0 <L1 · H1 with respect to the 11R 22.5 size tire where F0 <F1. The comparative tires 7 and 8 are (L) of the working tires 7 and 8 described above.
(0, H0) and (L1, H1) are interchanged, so that L0.H0> L1.H1. Specific values of L0, H0, L1, and H1 in the execution tires 5 to 8 and the comparison tires 5 to 8 are as shown in Tables 7 and 8 below. In addition, in the execution tires 5 to 8 and the comparison tires 5 to 8, the other rib end of the second rib 14 and the rib end of the third rib 15 are formed with arcs, similarly to the conventional tires 1 and 2. Not added.

[Table 7]

[Table 8]

The results of the rolling resistance test, uneven wear drum test, and WET lateral force test performed on these tires are shown in Tables 9 and 10 below.

[Table 9]

[Table 10]

As shown in Tables 9 and 10, the working tires 5 to 8 have improved rolling resistance, uneven wear ratio and WET lateral force as compared with the conventional tires 1 and 2. On the other hand, in Comparative Tires 5 to 8, rolling resistance and WET
Although the lateral force is improved, the uneven wear ratio is worse than the conventional tires 1 and 2. Thus, when the rib ends are rounded, the shape of the two rib ends facing each other across the groove is determined in consideration of the grounding length ratio,
It has been demonstrated that the abrasion characteristics, the steering stability in DRY / WET, and the rolling resistance can be improved. In addition, it has also been proved that if the shape is incorrect, the early wear of the rib end portion is worsened.

In the first and second embodiments, the rib 1
Although the method of determining the shape of both ends of the second rib 4 or the shape of the rib end facing each other across the groove has been described, for example, as shown in FIG.
A and 14B are added, and even if an arc 13A is added to the rib end of the first rib 13 that faces the second rib 14 with the groove 11 interposed therebetween, each arc 13A
By determining the shapes of A, 14A, and 14B in consideration of the contact lengths F0, F1, and F2 of the respective ends, it is possible to further suppress early wear of the rib ends. That is, in the rib 14, when F1 ≧ F2, L1 · H1 ≧ L2 · H2 When F1 <F2, L1 · H1 <L2 · H2 ‥‥‥‥ (1) When F0 ≧ F1, L0 · H0 ≧ L1 · H1 When F0 <F1, L0 · H0 <L1 · H1 ‥‥‥‥ (2) By defining the shape, early wear of the rib end can be more effectively suppressed, and wear characteristics, steering stability in DRY / WET, and rolling resistance can be significantly improved.

As shown in FIG. 7, when an arc 15A is further added to a rib end of a third rib 15 which faces the second rib 14 with the groove 12 therebetween, the arc 15
When the drop width of A is L3, the drop height is H3, and the length of the contact length of the rib 15 at the end of the rib is F3,
In addition to the above equations (1) and (2), between the ribs 14 and 15, when F2 ≧ F3, L2 · H2 ≧ L3 · H3 When F2 <F3, L2 · H2 <L3 · H3 ‥ By defining the rib end shapes of the ribs 13, 14 and 15 so that と (3), early wear of the rib ends can be further suppressed.

In the first and second embodiments, the tread portion 10 has four circumferentially continuous grooves 1 symmetrical left and right.
Although a tire having 1, 12 has been described, it goes without saying that even in a tire having a different number of grooves, it is possible to suppress early wear of the rib end portion by applying the present invention. Further, in the above example, the relationship between the product L · H of the drop width (L) and the drop height (H) of the rib end and the ground contact length is specified, but the drop width L and the arc added to the rib end are defined. The shape of the rib end may be determined by defining the relationship between the curvature radius ρ or the drop height H, the value of the curvature radius ρ, and the ground contact length. In addition, although the shape of the rib end is an arc, another curve may be used. Alternatively, the shape may be a combination of an arc and a straight line such that a straight line portion comes to the groove side.
However, at this time, the above-mentioned curve is made to touch the outer contour shape of the crown at the outer peripheral portion of the rib, and the radius of curvature at the contact point is smaller than the radius of curvature of the outer contour shape of the crown, so that the rib shape changes smoothly. It is desirable to set so that.

[0025]

As described above, according to the present invention, 1
2 opposing each other with the shape or groove at both ends of two ribs
By determining the shape of the two rib ends in consideration of the contact length of each rib end, it is possible to suppress early wear of the rib ends, and to attain wear characteristics, DRY / WET steering stability and rolling resistance. And a good tire having an improved tire can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional shape of a rib according to the first embodiment.

FIG. 2 is a diagram showing a contact shape of a conventional tire.

FIG. 3 is a diagram showing a contact shape of a conventional tire.

FIG. 4 is a diagram showing a method of measuring a contact length of a rib end;

FIG. 5 is a diagram showing a cross-sectional shape of a rib according to the second embodiment.

FIG. 6 is a view showing a rib cross-sectional shape of the present invention.

FIG. 7 is a view showing a rib cross-sectional shape of the present invention.

[Explanation of symbols]

10 Tread portion, 11 Center side groove, 12 Side side groove, 13 First rib, 13A Arc of first rib, 14 Second rib, 14A, 14B Arc of second rib, 15 Third Rib, 16 crown outer contour shape.

Claims (5)

[Claims] 1. A pneumatic tire having a rib divided by a groove extending in a circumferential direction, and trimming a rib end, which is a corner on the surface side of the rib, to trim both ends of the rib. A pneumatic tire wherein the amount of trimming at the end of the rib having the longer contact length at the portion contacting the road surface is greater than the amount of trimming at the shorter contact length. 2. A pneumatic tire having ribs separated by grooves extending in a circumferential direction and trimming a rib end, which is a corner on the surface side of the rib, to oppose each other with the grooves interposed therebetween. Trimming the two rib ends
A pneumatic tire characterized in that the amount of trimming at the end of the rib with the longer contact length at the portion contacting the road surface is larger than the amount of trimming at the shorter contact length. 3. The radius of curvature of the outer crown shape (16) passing through the respective grounding ends P1 and P2 and contacting the outer crown shape (16) at the contacts Q1 and Q2 at both ends of the cross section of the tire rib. Arcs (14A, 14B) having a small radius of curvature are provided, and a distance parallel to the tire rotation axis between P1 and Q1 is L1, a distance parallel to the tire rotation axis between P2 and Q2 is L2, P1, P2 and a crown. The distances parallel to the tire equatorial plane with the outer contour shape (16) are H1 and H2, respectively, and the curvatures of the arcs (14A, 14B) coincide with the curvature of the crown outer contour shape (16). The length of the ground contact length in the circumferential direction is F1, F
The pneumatic tire according to claim 1, wherein when H is 2, H1, H2, L1, and L2 satisfy the following relationship. When F1 ≧ F2, L1 · H1 ≧ L2 · H2 When F1 <F2, L1 · H1 <L2 · H2 4. The outer contour of the crown (16) at the ends of the ribs (13, 14) facing each other across the groove (11) of the cross section of the tire rib at the contact points Q0, Q1 through the respective grounding ends P0, P1. The outer contour shape of the crown in contact with (16)
Arc (13) having a smaller radius of curvature than the radius of curvature of
A, 14A), the distance parallel to the tire rotation axis between P0 and Q0 is L0, the distance parallel to the tire rotation axis between P1 and Q1 is L1, P0, P1, and the crown outer contour shape (16). The distance parallel to the tire's equatorial plane is H
0, H1, P when the curvature of the arc (13A, 14A) matches the curvature of the crown outer contour shape (16).
3. The pneumatic tire according to claim 2, wherein H0, H1, L0, and L1 satisfy the following relationship, where F0 and F1 are the lengths of the ground contact length in the circumferential direction at 0 and P1. When F0 ≧ F1, L0 · H0 ≧ L1 · H1 When F0 <F1, L0 · H0 <L1 · H1 5. The pneumatic tire according to claim 3, wherein the rib (14) having the ground ends P1 and P2 has a ground end P0 opposed to the ground end P1 or the ground end P2 with the groove interposed therebetween. On the grounding end P0 side of the rib, pass through P0,
An arc (13A) having a radius of curvature smaller than the radius of curvature of the outer crown shape (16), which is in contact with the outer crown shape (16) at the contact point Q0, is provided.
L0 is the distance parallel to the tire rotation axis of the tire and Q0, H0 is the distance parallel to the tire equatorial plane between P0 and the crown outer contour shape (16), and the curvature of the arc (13A) is the crown outer contour shape (16). When the length of the contact length in the circumferential direction at P0 when the curvature coincides with the curvature of F0 is F0, H0, H1,
L0, L1 or H0, H2, L0, L2 satisfy the following relationship. When F0 ≧ F1, L0 · H0 ≧ L1 · H1 When F0 <F1, L0 · H0 <L1 · H1 or when F0 ≧ F2, L0 · H0 ≧ L2 · H2 When F0 <F2, L0 · H0 <L2 / H2