JP5207723B2 - Torque transmission mechanism for automatic transmission - Google Patents

Description

  The present invention relates to a wet friction material that obtains a rotational torque by applying a high pressure to the opposing surface in a state immersed in oil, and a rotational torque obtained by pressure bonding to a surface to which the friction material base material of the wet friction material is bonded. The present invention relates to a torque transmission mechanism for an automatic transmission that includes a separator plate that transmits the frictional force, and an automatic transmission case that alternately accommodates a plurality of wet friction materials and separator plates.

  In recent years, as a wet friction material, a friction material cut into segment pieces along a flat plate ring shape on a flat plate ring-shaped core plate with the aim of reducing costs by improving material yield and reducing fuel consumption in vehicles by reducing drag torque A segment type friction material has been developed, in which the base material is sequentially aligned with an adhesive at intervals to become oil grooves and bonded over the entire circumference, and the friction material base material cut into segment pieces is also bonded to the back surface. ing. Such a segment type friction material is a friction material engagement provided with a plurality or a single friction plate used in an automatic transmission (hereinafter abbreviated as “AT”) such as an automobile or a transmission such as a motorcycle. It can be used for devices.

  As an example, wet hydraulic clutches are used in automatic transmissions for automobiles, etc., and multiple segment type friction materials and multiple separator plates are alternately stacked, and torque is transmitted by pressure-contacting both plates with hydraulic pressure. In order to absorb frictional heat generated when shifting from the non-fastened state to the fastened state and to prevent wear of the friction material, lubricating oil (Automatic Transmission Fluid) Lubricating oil, hereinafter also referred to as “ATF”). (“ATF” is a registered trademark of Idemitsu Kosan Co., Ltd.)

  However, in order to increase the response of the hydraulic clutch, the distance between the segment type friction material and the separator plate which is the counterpart material is set small, and in order to sufficiently secure the torque transmission capacity when the hydraulic clutch is engaged, The total area of the oil passage on the segment type friction material is limited. As a result, the ATF remaining between the segment type friction material and the separator plate is difficult to be discharged when the hydraulic clutch is not engaged, and there is a problem that drag torque due to ATF is generated by the relative rotation of both plates.

  Therefore, in the invention described in Patent Document 1, since the two sides of the segment piece with the opposite direction R to the core plate are bonded so as to be the inner periphery and the outer periphery, the oil groove direction is formed on the inner periphery. And the width of the outer peripheral opening of the gap serving as the oil groove is larger than the width of the inner peripheral opening, thereby greatly improving the ATF discharge performance due to the idling of the segment type friction material, The drag torque by ATF is said to be greatly reduced.

  Further, in the invention described in Patent Document 2, the segment type friction material rotates in a non-fastened state when incorporated into the AT by cutting off the inner peripheral side angle of the segment piece at a predetermined angle in the segment type friction material. When the ATF supplied from the inner peripheral side comes into contact with the cut-off portion of the segment piece, the ATF is positively supplied to the friction surface of the friction material base, and the contact between the separator plate and the friction surface The drag torque caused by ATF is greatly reduced.

Furthermore, in Patent Document 3, in the segment type friction material, the outer periphery of the segment piece is separated from the outer periphery of the core plate to increase the pull-in amount of the segment piece, thereby widening the distance from the inner peripheral portion of the automatic transmission case. By doing so, there is a portion where the gap between the segment piece and the separator plate is widened when not fastened, and the drag torque due to ATF can be reduced.
Japanese Patent Laying-Open No. 2005-06941 JP 2005-282648 A JP 2006-132581 A

  However, in the techniques described in Patent Document 1 to Patent Document 3, since the size of the separator plate is the same as the conventional size, dragging occurs when an oil pool is generated on the outer periphery and the stirring torque increases in the actual machine. The effect of reducing torque is still small, and it has been difficult to achieve a significant reduction in fuel consumption in vehicles.

  Therefore, the present invention can surely obtain a larger drag torque reduction effect even when an oil pool is generated on the outer periphery of the wet friction material and the stirring torque is increased, and further improvement in fuel consumption can be realized. An object of the present invention is to provide a torque transmission mechanism for an automatic transmission.

  The torque transmission mechanism for an automatic transmission according to the first aspect of the present invention includes a flat plate ring-shaped core plate as a wet friction material and a friction material base material cut into segment pieces along the flat ring shape. A segment type friction material in which a plurality of oil grooves are formed in the radial direction by gaps between adjacent segment pieces bonded to one side of the entire circumference, or both sides or one side of a flat plate ring-shaped core plate as a wet friction material A ring-type friction material in which a ring-shaped friction material base material is bonded and pressed or cut to leave an island-like portion to form a plurality of oil grooves in the radial direction, and the friction of the wet friction material A plurality of spline engaging protrusions are provided on the outer periphery that transmits the rotational torque of the wet friction material by being pressure-bonded to the surface to which the material base material is bonded. Separator plates and a plurality of spline grooves that engage with the plurality of spline engaging protrusions of the separator plates are provided along the axial direction on the inner periphery, and a plurality of the wet friction materials and the separator plates are alternately arranged. A torque transmission mechanism for an automatic transmission comprising a housed automatic transmission case, wherein a radius of an outer periphery of a portion of the separator plate other than the plurality of spline engagement protrusions is an inner periphery of the automatic transmission case These are set smaller in the range of 0.6 mm to 5.0 mm than the portions other than the plurality of spline grooves.

Further, in the portions other than the plurality of spline engaging protrusions of the separator plate, the plurality of spline grooves on the inner periphery of the automatic transmission case within a range of 5 mm to 15 mm at substantially equal intervals at three or more locations. The outer periphery protrusion part whose outer periphery radius is only 0.2 mm-0.5 mm smaller than other parts is provided.

  The torque transmission mechanism for an automatic transmission according to the first aspect of the present invention includes a flat plate ring-shaped core plate as a wet friction material and a friction material base material cut into segment pieces along the flat plate ring shape. A segment type friction material in which a plurality of oil grooves are formed in the radial direction by gaps between adjacent segment pieces that are bonded to a circumferential single surface, or a ring on both sides or one side of a flat plate ring-shaped core plate as a wet friction material A ring-type friction material in which a plurality of oil grooves are formed in a radial direction by pressing or cutting with a shape friction material base material bonded and leaving an island-shaped portion, and a friction material base material of a wet friction material Separator plate provided with a plurality of spline engaging protrusions on the outer periphery that transmits the rotational torque of the wet friction material by being crimped to the bonded surface And an automatic transmission case in which a plurality of spline grooves engaging with a plurality of spline engaging protrusions of the separator plate are provided along the axial direction on the inner periphery, and a plurality of wet friction materials and separator plates are alternately accommodated. A torque transmission mechanism for an automatic transmission comprising: a radius of an outer periphery of the separator plate other than the plurality of spline engaging protrusions is larger than a portion of the inner periphery of the automatic transmission case other than the plurality of spline grooves. It is set small in the range of 0.6 mm to 5.0 mm.

  With such a configuration, a wide gap is secured between the outer periphery of the separator plate and the inner periphery of the automatic transmission case, and there is more space for the lubricating oil to flow on the outer periphery of the wet friction material. When the friction material idles in either direction, it is possible to reliably prevent a situation where an oil reservoir is generated on the outer periphery and drag torque is increased. Furthermore, since the separator plate is reduced in weight by reducing the outer periphery of the separator plate, it can contribute to further improvement in fuel consumption.

Further, the portions other than the plurality of spline engaging protrusions of the separator plate are located at three or more locations within a range of 5 mm to 15 mm at substantially equal intervals from portions other than the plurality of spline grooves on the inner periphery of the automatic transmission case. Also, an outer peripheral protrusion having an outer peripheral radius of 0.2 mm to 0.5 mm is provided.

These outer peripheral protrusions are only 0.2 mm to 0.5 mm smaller in outer peripheral radius than the inner peripheral radius of the automatic transmission case, and since the gap with the inner diameter of the automatic transmission case is small, these outer peripheral protrusions Due to the presence of the portion, the separator plate can be easily attached, and an effect of facilitating assembly of the automatic transmission torque transmission mechanism can be obtained.

  It should be noted that the outer peripheral protrusions may be provided in any number of places as long as there are three or more. However, in order to ensure as wide a gap as possible between the outer periphery of the separator plate and the inner periphery of the automatic transmission case, it is the minimum necessary. It is desirable to limit it to the limit, and it is preferable to provide it at three or four locations. For the same reason, the width of the outer peripheral protrusion may be in the range of 5 mm to 15 mm, but it is desirable that the width is narrow, and it is more preferable if it is in the range of 5 mm to 8 mm.

  In this way, even when an oil pool is generated on the outer periphery of the wet friction material and the stirring torque increases, it is possible to surely obtain a large drag torque reduction effect, and the assembly is easy and the weight is reduced. Combined with the effect, it becomes a torque transmission mechanism for an automatic transmission that can realize further improvement in fuel consumption.

  Hereinafter, a torque transmission mechanism for an automatic transmission according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a partial cross-sectional view showing a part of a cross section of a torque transmission mechanism for an automatic transmission according to Example 1 of an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing a part of a cross section of the automatic transmission torque transmission mechanism according to Example 2 of the embodiment of the present invention. FIG. 3 is a line graph showing the magnitude of drag torque with respect to the number of revolutions in the automatic transmission torque transmission mechanism according to the embodiment of the present invention (Examples 1 and 2).

  FIG. 4 is a bar graph showing the reduction rate of drag torque in the automatic transmission torque transmission mechanism (Example 1 and Example 2) according to the embodiment of the present invention. FIG. 5 is a line graph showing the magnitude of drag torque with respect to the magnitude of D3 in the automatic transmission torque transmission mechanism according to the embodiment of the present invention. FIG. 6 is a partial cross-sectional view showing a part of a cross section of the torque transmission mechanism for an automatic transmission according to the first modification of the embodiment of the present invention. FIG. 7 is a partial cross-sectional view showing a part of a cross section of the torque transmission mechanism for an automatic transmission according to the second modification of the embodiment of the present invention.

  As shown in FIG. 1, in the torque transmission mechanism 41 for an automatic transmission according to Example 1 of the embodiment of the present invention, the segment type friction material 22 as the wet friction material is made of a flat plate ring-shaped steel plate. A plurality of segment pieces 24A and 24B obtained by cutting out a normal friction material base material for a wet friction material on the core plate 23 are separated from the oil grooves 25A and 25B by using an adhesive (thermosetting resin). They are attached side by side, and are similarly attached to the back surface of the core plate 23 with an adhesive. Here, since the left inner peripheral corner portion of the segment piece 24A and the right inner peripheral corner portion of the segment piece 24B are cut off, the oil groove 25A has a shape in which the inner peripheral side is expanded, and the oil groove 25B is substantially linear. It has a shape.

  In the torque transmission mechanism 41 for an automatic transmission, a separator plate 27 made of a flat plate ring-shaped steel plate is incorporated alternately with the segment type friction material 22. A plurality of spline engaging protrusions 27A are provided on the outer periphery of the separator plate 27, and these spline engaging protrusions 27A are formed in a plurality of spline grooves 8A provided on the inner periphery of the automatic transmission case 8. Each is engaged. Further, the outer peripheral protrusions 26 having a width of 8 mm are provided at substantially equal intervals (that is, about every 90 degrees) at four locations on the outer periphery of the separator plate 27.

  As shown in FIG. 1, in the automatic transmission torque transmission mechanism 41 according to the first embodiment, the radius of the portion other than the outer peripheral projection 26 on the outer periphery of the separator plate 27 is the inner radius of the automatic transmission case 8. It is set smaller by 1.45 mm than the circumference radius. On the other hand, as shown in FIG. 1, the radius of the outer peripheral protrusion 26 is set to be slightly smaller by 0.2 mm than the radius of the inner periphery of the automatic transmission case 8.

  As a result, a wide gap is secured between the outer periphery of the separator plate 27 and the inner periphery of the automatic transmission case 8, and there is sufficient space for the lubricating oil to flow on the outer periphery of the wet friction material 22. When the wet friction material 22 idles in either direction, it is possible to reliably prevent a situation where an oil reservoir is generated on the outer periphery and drag torque is increased. Furthermore, since the separator plate 27 is reduced in weight by reducing the outer periphery of the separator plate 27, it can contribute to further improvement in fuel consumption.

  Further, by providing an outer peripheral protrusion 26 having a width of 8 mm that is set to be slightly smaller than the inner peripheral radius of the automatic transmission case 8, the separator plate 27 with respect to the automatic transmission case 8 is provided. As a result, it is easy to mount and the automatic transmission torque transmission mechanism 41 can be easily assembled.

  Next, as shown in FIG. 2, in the torque transmission mechanism 51 for an automatic transmission according to Example 2 of the embodiment of the present invention, the segment type friction material 22 as the wet friction material is the Example 1 described above. In the same manner, a plurality of segment pieces 24A and 24B obtained by cutting out a normal friction material base material for a wet friction material on a core plate 23 made of a flat plate ring-shaped steel plate using an adhesive (thermosetting resin). Then, the oil grooves 25A and 25B are arranged side by side with a gap therebetween, and are similarly attached to the back surface of the core plate 23 with an adhesive. Here, since the left inner peripheral corner portion of the segment piece 24A and the right inner peripheral corner portion of the segment piece 24B are cut off, the oil groove 25A has a shape in which the inner peripheral side is expanded, and the oil groove 25B is substantially linear. It has a shape.

  In the automatic transmission torque transmission mechanism 51, a separator plate 37 made of a flat plate ring-shaped steel plate is incorporated alternately with the segment type friction material 22. A plurality of spline engaging protrusions 37A are provided on the outer periphery of the separator plate 37, and these spline engaging protrusions 37A are formed in a plurality of spline grooves 8A provided on the inner periphery of the automatic transmission case 8. Each is engaged. In addition, the outer peripheral protrusions 36 having a width of 8 mm are provided at four positions on the outer periphery of the separator plate 37 at substantially equal intervals (that is, every approximately 90 degrees).

  As shown in FIG. 2, in the automatic transmission torque transmission mechanism 51 according to the second embodiment, the radius of the portion other than the outer peripheral protrusion 36 on the outer periphery of the separator plate 37 is the inner radius of the automatic transmission case 8. It is set smaller by 2.45 mm than the circumference radius. On the other hand, as shown in FIG. 2, the radius of the outer peripheral protrusion 36 is set to be slightly smaller than the inner peripheral radius of the automatic transmission case 8 by 0.2 mm.

  As a result, a wide gap is secured between the outer periphery of the separator plate 37 and the inner periphery of the automatic transmission case 8, and there is sufficient space for the lubricating oil to flow on the outer periphery of the wet friction material 22. When the friction material 22 idles in either direction, it is possible to reliably prevent a situation where an oil pool is generated on the outer periphery and drag torque is increased. Furthermore, since the separator plate 37 is reduced in weight by reducing the outer periphery of the separator plate 37, the fuel consumption can be further improved.

  Further, by providing an outer peripheral protrusion 36 having a width of 8 mm, which is set to be slightly smaller than the inner peripheral radius of the automatic transmission case 8, the separator plate 37 with respect to the automatic transmission case 8 is provided. As a result, it is easy to mount and the automatic transmission torque transmission mechanism 51 can be easily assembled.

  These automatic transmission torque transmission mechanisms 41 (Embodiment 1) and 51 (Embodiment 2) are actually compared with conventional automatic transmission torque transmission mechanisms, and drag torque measurement experiments are actually performed. The relationship between the rotational speed and drag torque was verified by testing.

  The test conditions were as follows: the number of segment pieces 24A, 24B was 40 on one side (80 on both sides), the width of oil grooves 25A, 25B = 2 mm, the disc size was outer circumference φ1 = 184 mm, inner circumference φ2 = 164 mm, The number of discs was 3 (therefore, 4 separator plates 27 and 37 were used as mating members), and the pack clearance was 0.25 mm / sheet. And it carried out with relative rotation speed = 500-6000 rpm, ATF oil temperature = 80 degreeC, and ATF oil amount = 2400mL / min. The test results are shown in FIG.

  As shown in FIG. 3, there is almost no difference between the first and second embodiments and the conventional example when the relative rotational speed is 500 rpm, but when the relative rotational speed is 1000 rpm, the second embodiment and the conventional example are different from each other. There is already a clear difference between the two, and at the time when the relative rotational speed is 2000 rpm, there is also a clear difference between Example 1 and the conventional example. The transmission torque transmission mechanisms 41 and 51 have a smaller drag torque than the conventional automatic transmission torque transmission mechanism. This difference is further increased as the relative rotational speed is increased to 3000 rpm, 4000 rpm, and 4500 rpm.

  Thereafter, as the relative rotational speed increases, the drag transmission torque of any automatic transmission torque transmission mechanism increases. However, in the range of the relative rotational speed from 4500 rpm to 6000 rpm, Examples 1 and 2 and the conventional example The difference between them is maintained. That is, the drag transmission torque of the automatic transmission torque transmission mechanisms 41 and 51 according to the first and second embodiments is smaller than that of the conventional automatic transmission torque transmission mechanism. Further, the automatic transmission torque transmission mechanism 51 according to the second embodiment has a smaller drag torque than the automatic transmission torque transmission mechanism 41 according to the first embodiment.

  In addition, as shown in FIG. 4, in both the first and second embodiments, the drag torque reduction rate is higher in the high rotation region where the ATF tends to accumulate on the outer periphery. As shown in FIG. 5, if the difference between the radius of the inner periphery of the automatic transmission case 8 other than the plurality of spline grooves 8A and the radius of the outer periphery of the separator plates 27 and 37 is D3 [mm]. It can be seen that the drag torque decreases as D3 increases.

  In addition to this, as D3 increases, the outer diameter of the separator plate decreases and the separator plate is reduced in weight, which can contribute to further improvement in fuel consumption.

  In this manner, in the automatic transmission torque transmission mechanisms 41 and 51 according to Examples 1 and 2 of the embodiment of the present invention, an oil pool is generated on the outer periphery of the wet friction material 22 and the stirring torque increases. Even in this case, it is possible to surely obtain a greater drag torque reduction effect, and further improve fuel efficiency.

  Next, a torque transmission mechanism for an automatic transmission according to a modification of the embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 6 and 7, the torque transmission mechanisms 141 and 151 for automatic transmissions according to the first and second modifications of the embodiment of the present invention are the examples of the above-described embodiment of the present invention. The only difference from the automatic transmission torque transmission mechanisms 41 and 51 according to 1 and 2 is that the wet friction material 122 used is not a segment type friction material but a ring type friction material.

  That is, in the automatic transmission torque transmission mechanism 141 according to the first modification of the present embodiment shown in FIG. 6, the wet friction material is formed on the same core plate 23 as the first embodiment of the present embodiment described above. The ring-type friction material 122 is used, in which a ring-shaped friction material base material 109 is bonded and pressed to leave the island portions 124A and 124B to form a plurality of oil grooves 125A and 125B in the radial direction. ing.

  In the automatic transmission torque transmission mechanism 151 according to the second modification of the present embodiment shown in FIG. 7, the same core plate 23 as that of the first embodiment of the present embodiment is also used as the wet friction material. In addition, a ring-type friction material 122 is used in which a ring-shaped friction material base material 109 is bonded and pressed to leave the island portions 124A and 124B to form a plurality of oil grooves 125A and 125B in the radial direction. It has been.

  Therefore, in the automatic transmission torque transmission mechanism 141 according to the first modification of the present embodiment shown in FIG. 6, the outer diameter of the separator plate 27 is as small as that of the first embodiment of the present invention described above. The torque transmission mechanism 151 for the automatic transmission according to the second modification of the present embodiment shown in FIG. 7 is the same as the outer diameter of the separator plate 37 as in the second embodiment of the present invention described above. Therefore, the drag torque reduction effect is the same as that of the conventional automatic transmission torque transmission mechanism.

  As shown in FIGS. 6 and 7, in the torque transmission mechanisms 141 and 151 for automatic transmissions according to the first and second modifications of the embodiment of the present invention, the above-described embodiment of the present invention is used. Since the same separator plates 27 and 37 as the automatic transmission torque transmission mechanisms 41 and 51 according to the first and second embodiments of the present invention are used, the weight of the separator plates is reduced, which contributes to further improvement in fuel consumption. can do.

  Thus, in the torque transmission mechanisms 141 and 151 for automatic transmissions according to the first and second modifications of the embodiment of the present invention, an oil pool is generated on the outer periphery of the wet friction material 122 and the stirring torque is increased. Even in this case, it is possible to surely obtain a greater drag torque reduction effect, and further improve fuel efficiency.

  In the present embodiment, only the segment type friction material and the ring type friction material press type friction material are described among the wet friction materials, but the ring type cutting type friction material in which similar oil grooves are formed by cutting. In this case, the drag torque reduction effect equivalent to that of the ring type (press type) friction material 122 can be obtained.

  In the present embodiment, the case where the segment piece or the ring-shaped friction material base material is attached to both surfaces of the core plate 23 as the wet friction material has been described. However, depending on the specification, only one surface of the core plate 23 may be used. Alternatively, a segment piece or a ring-shaped friction material base material may be attached.

  Further, in the present embodiment, as the wet friction material, when 40 segment pieces are pasted on one side of the core plate 23, and a ring-shaped friction material base material is pasted to form 40 oil grooves. However, the number of segment pieces per one side of the core plate 23 is not limited to 40, and the number of oil grooves is not limited to 40. It can be set freely.

  In carrying out the present invention, the configuration, shape, quantity, material, size, connection of other parts of the torque transmission mechanism for automatic transmissions including wet friction materials (segment type friction material and ring type friction material) The relationship, manufacturing method, and the like are not limited to the present embodiment.

  In addition, since the numerical value quoted in the embodiment of the present invention does not indicate a critical value but indicates a preferable value suitable for implementation, even if the numerical value is slightly changed, the implementation is denied. is not.

FIG. 1 is a partial cross-sectional view showing a part of a cross section of a torque transmission mechanism for an automatic transmission according to Example 1 of an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing a part of a cross section of the automatic transmission torque transmission mechanism according to Example 2 of the embodiment of the present invention. FIG. 3 is a line graph showing the magnitude of drag torque with respect to the number of revolutions in the automatic transmission torque transmission mechanism according to the embodiment of the present invention (Examples 1 and 2). FIG. 4 is a bar graph showing the reduction rate of drag torque in the automatic transmission torque transmission mechanism (Example 1 and Example 2) according to the embodiment of the present invention. FIG. 5 is a line graph showing the magnitude of drag torque with respect to the magnitude of D3 in the automatic transmission torque transmission mechanism according to the embodiment of the present invention. FIG. 6 is a partial cross-sectional view showing a part of a cross section of the torque transmission mechanism for an automatic transmission according to the first modification of the embodiment of the present invention. FIG. 7 is a partial cross-sectional view showing a part of a cross section of the torque transmission mechanism for an automatic transmission according to the second modification of the embodiment of the present invention.

Explanation of symbols

8 Automatic transmission case 8A Spline grooves 22, 122 Wet friction material 23 Core plates 26, 36 Outer protrusions 27, 37 Separator plates 27A, 37A Spline engagement protrusions 41, 51, 141, 151 Torque transmission mechanism for automatic transmission

Claims (1)

A friction material base material cut into segment pieces along the flat plate ring shape on a flat plate ring-shaped core plate as a wet friction material is bonded to both sides of the whole circumference or one side of the whole circumference, and the gap between the adjacent segment pieces A segment type friction material in which a plurality of oil grooves are formed in the radial direction, or a ring-shaped friction material base material is bonded to both sides or one side of a flat plate ring-shaped core plate as a wet friction material to form island-shaped portions. A ring type friction material formed by pressing or cutting and forming a plurality of oil grooves in the radial direction;
A separator plate provided with a plurality of spline engagement protrusions on the outer periphery that transmits the rotational torque of the wet friction material by being pressure-bonded to the surface of the wet friction material to which the friction material base material is bonded;
An automatic transmission in which a plurality of spline grooves that engage with the plurality of spline engagement protrusions of the separator plate are provided along the axial direction on the inner periphery, and the wet friction material and a plurality of the separator plates are alternately accommodated. Case and
A torque transmission mechanism for an automatic transmission comprising:
The outer peripheral radius of the separator plate other than the plurality of spline engagement protrusions is in the range of 0.6 mm to 5.0 mm than the inner peripheral portion of the automatic transmission case other than the plurality of spline grooves. The portion of the separator plate other than the plurality of spline engaging protrusions is set to be small and the inner periphery of the automatic transmission case has a width of 5 mm to 15 mm at substantially equal intervals at three or more locations. A torque transmission mechanism for an automatic transmission, characterized in that an outer peripheral protruding portion whose outer peripheral radius is smaller by 0.2 mm to 0.5 mm than a portion other than the plurality of spline grooves is provided .

Images