JP3524394B2 - transmission - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention rotatably supports a rotary structure of a rear portion of a transmission, for example, a rotary shaft of an intermediate gear interposed between a counter gear and a drive gear of a toroidal type continuously variable automatic transmission. Bearing lubrication structure.

[0002]

2. Description of the Related Art As a conventional lubricating structure of this type, for example, one disclosed in Japanese Patent Laid-Open No. 7-301300 is known. In this lubrication structure, as shown in FIG. 6, an idler gear (third gear) c arranged between a counter gear (first gear) a and a drive gear (second gear) b, one of which is a transmission case d. The other is integrally formed with an idler shaft g supported by the extension case e via bearings f and f. Lubrication of the bearing f on one side is performed via an oil passage h in the extension case e, a central lubrication hole i in the idler shaft g, and an oblique oil hole j branched from the central lubrication hole i.

[0003]

Since both ends of an idler shaft g formed integrally with the idler gear c are supported by separate members d and e, it is difficult to center the shaft g, and the meshing portion of the idler gear c. There was a risk that gear noise would occur. Furthermore, since the diagonal oil passage j for lubrication of the bearing f on one side does not require a large amount of lubricating oil, a small-diameter oil hole may be used. It was very difficult to provide.

Further, the rigidity of the casing that supports the idler bearing is performed through the joint surface of the extension case, so that the case rigidity cannot be obtained, and moreover,
Since the bearing support points are close to each other, the idler gear tends to sag.

The present invention has been made in order to eliminate such inconvenience, and a bearing for rotatably supporting a rotating shaft of a second gear interposed between a first gear and a third gear of a transmission. An object of the present invention is to provide a transmission that can reliably supply lubricating oil with a structure that is easy to process.

[0006]

In order to achieve such an object, a transmission according to a first aspect of the invention transmits the power from a speed change mechanism arranged on one side in mesh with each other and transmits the power in an axial direction. First gear and second gear arranged in a vertical plane
The gear and the third gear, and a pair of first bearing for rotatably supporting the first gear, and the front Symbol pair of second bearing rotatably supporting the rotary shaft of the second gear, the third A third bearing that rotatably supports the rotating shaft of the gear, a bearing on the other side of the first bearing pair, a bearing on the other side of the second bearing pair, and the third bearing are individually housed. In a transmission including a case, the rotation shaft of the second gear is formed in a tubular shape integral with the second gear, and the fixed shaft supported by the case via a seal member has the second bearing pair. And a spacer is externally inserted to the fixed shaft between the case-side bearing of the second bearing pair and the case inner surface, and the end surface of the inner ring of the bearing is brought into contact with the spacer. A gap is provided between the spacer and the inner surface of the case in the circumferential direction so that lubricating oil can enter. Further, a tubular member is externally fitted and fixed to the fixed shaft between the second pair of bearings, and oil passages communicating with the tubular member and the fixed shaft are provided respectively, and the oil of the tubular member is further provided. The passage is a notch formed on at least one of the end faces of the tubular member, and the oil passage is made to face between the second bearing pair, and the oil passage of the fixed shaft communicates with the gap. It is characterized by having done.

A transmission according to a second aspect is characterized in that, in the first aspect, an oil passage for the fixed shaft is formed by forming a concave flat surface on an outer peripheral portion of the fixed shaft.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An example of an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an explanatory cross-sectional view for explaining a lubricating structure of a toroidal type continuously variable automatic transmission, which is an example of an embodiment of the present invention, FIG. 2 is a partially enlarged view of FIG. 1, and FIG. 3 is an internal structure of a case. 4 is an explanatory plan view for explaining FIG. 4, FIG. 4 is a sectional view taken along line IV-IV of FIG. 3, and FIG. 5 is an enlarged perspective view of a tubular member.

As shown in FIGS. 1 and 2, an input shaft 2 connected to a rotary drive source and a rotary shaft 3 concentrically connected to the right side of the input shaft 2 are arranged in the transmission case 1. On the input shaft 2 side, an oil pump 5 is attached to the end of the transmission case 1 via a bolt 4, and an advancing clutch 6 and a reverse clutch 7 are provided adjacent to the oil pump 5 on the right side of the oil pump 5. The first and second toroidal transmission mechanisms 10 via the planetary gear mechanism 8;
A forward / reverse switching mechanism 9 for switching forward / backward with respect to 11 is provided, and first and second toroidal transmission mechanisms 10 and 11 are provided axially separated from each other on the rotating shaft 3 side. .

A sun gear 13, which is rotatably supported by the input shaft 2 via a needle bearing 12 and constitutes a planetary gear mechanism 8 of a forward / reverse switching mechanism 9, is provided between the two shafts 2 and 3. The loading cam 14 that is engaged with the claw portion 13a and is rotatably supported by the rotating shaft 3.
And an input disk 17 connected to the loading cam 14 via an engagement roller 15 and supported on the rotary shaft 3 via a ball spline 16. The rotational force from the input shaft 2 is transmitted from the claw portion 13a of the sun gear 13 to the loading cam 14, the engagement roller 15 and the input disk 17 via the forward / reverse switching mechanism 9, and half the rotational force drives the power roller 70. The other half is transmitted to the rotary shaft 3 for driving the power roller 170 through the input disk 19 at the rear through the ball spline 16 in sequence.

Loading cam 14 and input disk 1
Wave-shaped cam surfaces with which the engagement roller 15 engages are formed on the opposing surfaces of 7, respectively, and a thrust force proportional to the torque due to the lead of the cam surface by the engagement roller 15 is generated.

For convenience of explanation, the first and second toroidal speed change mechanisms 10 and 11 will be described first. In the first toroidal speed change mechanism 10, a toroidal surface 17a is formed on the surface of the first toroidal speed change mechanism 10 away from the engagement roller 15. Input disk 1 described above
7 and the toroid surface 18 on the opposite surface of the input disk 17.
a and the output disc 18 rotatably supported by the rotary shaft 3 and the toroid surface 17 of both discs 17, 18.
In the toroidal groove formed by a and 18a, there is a friction roller (not shown) in contact with both disks 17 and 18 so as to be tiltable.

The friction roller is supported by a roller support mechanism (not shown) so as to be tiltable, and the drive roller (not shown) operates the roller support mechanism to input and output the friction roller input disk 17 and output disk. By changing the radial contact position with respect to 18, it is possible to continuously change the rotation speed ratio between the input disk 17 and the output disk 18, that is, the gear ratio.

The second toroidal speed change mechanism 11 has an input disk 19, an output disk 20, a friction roller, a roller support mechanism and a drive mechanism like the first toroidal speed change mechanism 10, but a rotary shaft 3 is provided with a ball spline 21. The externally fitted input disk 19 is arranged on the side far from the first toroidal transmission mechanism 10, and the output disk 20 is arranged on the side close to the first toroidal transmission mechanism 10.

Cylindrical shaft portions 18b and 20b are provided on the back surfaces of the output disks 18 and 20 facing each other, and an output gear 22 is integrally coupled to the cylindrical shaft portions 18b and 20b. The output gear 22 is supported via a bearing 24 in a gear housing 23 fixed to the inner peripheral wall of the transmission case 1. The output gear 22 meshes with the first counter gear 25, and the first counter gear 25
A counter shaft 27 is spline-coupled at one end to a central portion of the shaft and rotates integrally with the first counter gear 25.

The boss portion 25a of the first counter gear 25
Is rotatably supported by a cylindrical roller bearing 26 mounted on the gear housing 23 between the output disks 18 and 20, whereby the end portion of the counter shaft 27 on the first counter gear 25 side has the boss portion 25a. It is rotatably supported by the cylindrical roller bearing 26.

A second counter gear (first gear) 60 that rotates integrally with the counter shaft 27 is provided at a position of the counter shaft 27 that is spaced apart from the first counter gear 25 in the axial right direction. The end portion of the counter shaft 27 on the second counter gear 60 side is a pair of tapered roller bearings (first bearing pair) 28a, 28b arranged on both axial ends of the second counter gear 60.
It is rotatably supported by. Of the pair of tapered roller bearings 28a and 28b, the tapered roller bearing 28a arranged on the first counter gear 25 side with the second counter gear 60 as a boundary is attached to the transmission case 1 and is attached to the first counter gear 25. The tapered roller bearing 28 b arranged on the side spaced apart from is attached to the rear case 1 a attached to the rear end of the transmission case 1.

The second counter gear 60 meshes with a drive gear (third gear) 65 arranged above the second counter gear 60 via an intermediate gear (second gear) 66. The rotary shaft 65a of the drive gear 65 is rotatably supported by a tapered roller bearing (third bearing) 67 attached to the rear case 1a.

The outputs that have a predetermined gear ratio due to the tilting operation of the friction roller are combined by the output gear 22, and the first counter gear 25, the counter shaft 27, the second counter gear 60, and the intermediate gear 66. And is sequentially transmitted to the output shaft via the drive gear 65.

Referring to FIG. 4, the rotary shaft 66a of the intermediate gear 66 has a cylindrical shape integral with the intermediate gear 66, and a seal ring (sealing member) 68 is provided on the rear case 1a.
A pair of tapered roller bearings (second bearing pair) 69 axially spaced from each other on a fixed shaft 68 supported via a.
It is rotatably extrapolated via a and 69b. Of the pair of tapered roller bearings 69a and 69b, the tapered roller bearing 69b on the rear case 1a side is housed in the rear case 1a via a spacer 70. Tapered roller bearings 69a, 6
9b has a back face combination, and the shaft support span is longer than the bearing distance.

The spacer 70 is externally fitted to the fixed shaft 68 between the tapered roller bearing 69b and the inner surface of the rear case 1a, and the inner ring end surface of the tapered roller bearing 69b is in contact with the spacer 70 in the fitted state. . About 2/3 of the surface of the spacer 70 facing the rear case 1a side is in contact with the inner surface of the rear case 1a, and the remaining about 1/3 of the surface is formed by the step portion 1b provided on the inner surface of the rear case 1a. A non-contact type is provided with a gap 72 therebetween. The gap 72 is arranged on the side facing the drive gear 65, as shown in FIG. 3, in order to facilitate the entry of the lubricating oil.

Further, the tapered roller bearing 69 of the fixed shaft 68
The tapered roller bearing 6 is provided in the portion located between the pair of a and 69b.
A tubular member 74 having substantially the same diameter as the inner rings of 9a and 69b is externally fitted and fixed, and a spacer 75 is interposed between the tubular member 74 and the tapered roller bearing 69b to form a tapered roller bearing 69.
The inner ring of a, the tubular member 74, the spacer 75, and the inner ring of the tapered roller bearing 69b are continuously arranged in the axial direction. The spacer 75 determines the preload of the tapered roller bearings 69a and 69b. Notches 76 (see FIG. 5) forming oil passages penetrating from the outer peripheral surface to the inner peripheral surface are provided on both end surfaces of the cylindrical member 74, and are separated from each other by 180 ° in the circumferential direction. The passage 76 communicates with an oil passage 77 provided on the fixed shaft 68, and at the same time, the tapered roller bearings 69a, 69a.
It is arranged so as to face the space between the pair of 9b.

On the outer peripheral portion of the fixed shaft 68, concave flat surfaces 73 extending in the axial direction from the step portion 1b of the rear case 1a to a position slightly beyond the tubular member 74 are arranged in the circumferential direction.
The two concave flat surfaces 73 and the inner ring of the tapered roller bearing 69a, the tubular member 74, the spacer 75, the inner ring of the tapered roller bearing 69b, and the inner peripheral surfaces of the spacer 70 are provided at two locations spaced apart by 80 °. The oil passage 77 of the fixed shaft 68 described above is formed between and. As shown in FIG. 3, the two oil passages 77 are arranged so as to communicate with the gap 72, whereby the gap 72, the oil passage 77 of the fixed shaft 68, and the oil passage 76 of the tubular member 74 are mutually connected. It is designed to communicate. The fixed shaft 68 has a detent washer 100 fitted in a detent groove 101, and is raised by a nut 102. Anti-rotation washer 100 is the rear case 1a
It is fitted in the detent groove 103 provided on the.

A rib 1d is provided on the lower surface side of the space 1c in which the parking gear 65b of the rotary shaft 65a of the rear case 1a is housed, and the rib 1d is provided in front of the rib 1d on the side of the intermediate gear 66. And an oil sump 1e is provided. The oil sump 1e communicates with a step portion 1b provided on the inner surface of the case 1a. Then, when the oil pump 5 is driven, the lubricating oil discharged from the rotating shaft 65a for lubricating the parking gear 65b and the bearing 67 and the case 1 are discharged.
The lubricating oil scraped up and scattered from the lower surface side 1f of the space accommodating the intermediate gear 66 of a flows into the gap 72 via the rib 1d and the oil sump 1e or directly. The lubricating oil that has flowed into the gap 72 passes through the oil passage 77 of the fixed shaft 68 and the notch portion 76 that is the oil passage of the tubular member 74, and then the tapered roller bearings 69 a and 69 b of the intermediate gear 66.
Is supplied to.

On the other hand, when the oil pump 5 is not driven, the counter gear 60 at the bottom is pulled.
The lubricating oil raised by the gear goes through the meshing and the intermediate gear 6
6, the lubricant oil is scraped up and scattered by the intermediate gear 66 and passed through the rib 1d and the oil sump 1e, or scraped up and directly flows into the gap 72. Intermediate gear 6 through path 76
It is supplied to the six tapered roller bearings 69a and 69b.

Next, the forward / reverse switching mechanism 9 will be described with reference to FIG. 1. The forward / backward switching mechanism 9 switches between the first and second toroidal transmission mechanisms 10 and 11 and, in turn, the drive shaft. And includes a forward clutch 6, a reverse clutch 7 and a planetary gear mechanism 8.

The forward clutch 7 includes a clutch drum 29 which is located between the oil pump 5 and the sun gear 13 and which is fitted onto the input shaft 2. The clutch drum 29 is the input shaft 2
And the sun gear 13 of the planetary gear mechanism 8 are arranged radially inward of the clutch drum 29.
A clutch hub 30 supported by is disposed. The clutch drums 29 and the clutch hubs 30 support clutch discs 31 that are alternately arranged.

The inside of the base end of the clutch drum 29 (the end on the oil pump 5 side) is a cylinder chamber 32, and a piston 33 is housed in the cylinder chamber 32. A hydraulic chamber 34 is formed between the piston 33 and the cylinder chamber 32. By controlling the supply of hydraulic oil to the hydraulic chamber 34 to move the piston 33 back and forth, the clutch disc 31 is pressed or The forward clutch 6 is engaged / disengaged by releasing the pressing force. In the figure, reference numeral 35 is a return spring that returns the piston 33 to its original position when the clutch disc 31 is released.

A ring gear 36 is attached to the inner peripheral portion of the clutch drum 29 on the front end side, and the ring gear 36 is meshed with the sun gear 13 via a pinion 37.

The reverse clutch 7 includes a clutch drum 42 arranged radially outward of the clutch drum 29.
The clutch drum 42 is integrated with the case 1.
A clutch hub 43 is arranged between the clutch drum 42 and the clutch drum 29 of the forward clutch 6, and the clutch hub 43 is supported by a carrier plate 38 on the side of the first toroidal transmission mechanism 10 of the carrier. The clutch drum 42 and the clutch hub 43 support clutch discs 44 arranged alternately.

In FIG. 1, reference numeral 44a is a support wall attached to the inner peripheral wall of the clutch drum 42 closer to the toroidal transmission mechanism than the reverse clutch 7 via a snap ring or the like. The support wall 44a is arranged so as to face the carrier plate 38 so as to receive the thrust force from the carrier generated on the side of the forward / reverse switching mechanism 9, whereby the thrust force is applied to the first and second toroidal transmission mechanisms 10. , 11 side is not transmitted.

On the right side portion of the oil pump 5 located radially inward of the clutch drum 42, two circumferential wall portions 45a, 45b extending along the entire circumference are formed separately from each other in the radial direction. A cylinder chamber 46 is formed between the peripheral wall portions 45a and 45b. A piston 47 is housed in the cylinder chamber 46, and a hydraulic chamber 48 is formed between the piston 47 and the cylinder chamber 46. Hydraulic chamber 4
By controlling the supply of hydraulic oil to the piston 8 and moving the piston 47 back and forth, the clutch disc 44 is pressed or released, and the reverse clutch 7 is engaged / disengaged. In FIG. 1, reference numeral 49 is a return spring that returns the piston 47 to its original position when the pressing of the clutch disc 44 is released.

During forward movement, the clutch disk 31 of the forward clutch 6 is pressed by the piston 33 to bring the forward clutch 6 into the engaged state, and the clutch disk 44 of the reverse clutch 7 is released from the pressing by the piston 47. The reverse clutch 7 is in the disengaged state. In such a state, the input shaft 2, the clutch drum 29, the ring gear 36, the carrier 38, and the sun gear 13 integrally rotate in the same direction, whereby the rotational force is engaged with the claw portion 13a of the sun gear 13. Cam 14
And is transmitted to the first toroidal transmission mechanism 10.

On the other hand, when the vehicle is moving backward, the clutch disc 31 of the forward clutch 6 is released from the pressing force of the piston 33, and the forward clutch 6 is disengaged.
The clutch disc 44 is pressed by the piston 47 to bring the reverse clutch 7 into the engaged state, and the revolution of the pinion 37 is blocked via the clutch hub 43 and the carrier 38. In such a state, the integrated rotational force of the input shaft 2 and the clutch drum 29 is transmitted from the ring gear 36 to the sun gear 13 via the pinion 37, but the revolution of the pinion 38 is blocked as described above, The sun gear 13 rotates in the opposite direction with respect to the input shaft 2, and the first toroidal transmission mechanism 10 passes through the loading cam 14 whose rotational force engages the claw portion 13 a of the sun gear 13.
Be transmitted to.

As is apparent from the above description, in the toroidal type continuously variable automatic transmission having such a structure, the rigidity of the case does not support the intermediate gear 66, but the fixed shaft 68 is lifted up by the nut 102 to form the tapered roller. Bearing 69
The supporting rigidity of a and 69b can be obtained, and the bearing span can be widened by combining the tapered roller bearings 69a and 69b with the back surface.

A gap 72 is provided between the spacer 70 and the inner surface of the rear case 74, and a cutout portion 76, which is an oil passage, is provided on the end face of the tubular member 74.
Since the oil passage 77 that connects the notch portion 76 to the fixed shaft is provided in the fixed shaft 78, it is not necessary to provide a small-diameter diagonal oil hole in the shaft member, and lubricating oil can be provided to the bearing member of the intermediate gear 66 with a simple structure. It can be reliably supplied.

Further, since the fixed shaft 68 is supported by the rear case 1a via the seal member 68a for sealing the oil passage 77, the centering of the intermediate gear 66 supported by another member becomes easy, and the fixed shaft 68 is there. Since the nut is tightened with the nut 102, the shaft end contacts the rear case 1a at right angles through the washer 100 while ensuring the rigidity of the fixed shaft 68, and the rigidity of the tapered roller bearings 69a and 69b is increased. However, the position of the rear case 1a may be determined according to the hole accuracy and the case hole accuracy without rattling the seal member 68a.
Hole position accuracy is prioritized over hitting the rear case 1a at a right angle via. In this case, if the hole position accuracy is poor, the tapered roller bearings 69a and 69b will be slightly offset, but this error can be absorbed by the seal member 68a, and gear noise can be reduced.

Even when the vehicle is being towed by the oil pump 5, the lubricating oil accumulated in the gap 72 is passed through the oil passage 77 of the fixed shaft 68 and the oil passage 76 of the tubular member 74 to form the intermediate gear 66. The tapered roller bearings 69a, 69b can be supplied to the tapered roller bearings 69a, 69b.
The lubricating oil can be reliably supplied to b.

Further, since the oil passage 77 on the fixed shaft 68 side is formed by forming the concave flat surface on the outer peripheral portion of the fixed shaft 68, the oil passage 77 can be formed more easily. it can.

In the above embodiment, the fixed shaft 68 is formed by forming a concave flat surface on the outer peripheral portion of the fixed shaft 68.
Although the case where the oil passage 77 on the side is formed is taken as an example, the invention is not limited to this. For example, the oil passage of the fixed shaft 68 is formed inside the fixed shaft to form the oil passage in the gap 72 and the tubular member 74. Oil passage 76
Or the opening of the center hole 69a of the fixed shaft 68 is closed by a plug to form an oil passage for the fixed shaft 68, and the oil passage is used for the gap 72 and the oil passage 76 for the tubular member 74.
The lubricating oil introduced into the center hole 69a through the gap 72 may be discharged from the oil passage 76 of the tubular member 74 by thermal expansion.

Further, in the above embodiment, the case where the present invention is applied to the toroidal type continuously variable automatic transmission is taken as an example, but the present invention is not limited to this and, for example, the output gear and the final gear of the FF automatic transmission are used. The structure of the present invention may be applied to the intermediate gear arranged between the two.

[0042]

As is apparent from the above description, according to the invention of claim 1, it is not necessary to provide a small-diameter oblique oil hole in the shaft member, and the lubricating oil can be provided to the bearing of the second gear with a simple structure. The effect that it can be reliably supplied is obtained.

Even when the vehicle is towed by the oil pump, the lubricating oil accumulated in the gap is supplied to the bearing of the second gear through the oil passage of the fixed shaft and the oil passage of the tubular member. Therefore, it is possible to reliably supply the lubricating oil to the bearing.

According to the invention of claim 2, in addition to claim 1, the oil passage on the fixed shaft side is formed by forming a concave flat surface on the outer peripheral portion of the fixed shaft. It is possible to obtain the effect that the formation can be made simpler.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view for explaining a lubricating structure of a toroidal type continuously variable automatic transmission that is an example of an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is an explanatory plan view for explaining the internal structure of the case.

4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is an enlarged perspective view of a tubular member.

FIG. 6 is an explanatory cross-sectional view for explaining a conventional lubrication structure for a transmission.

[Explanation of symbols]

1a ... rear case 10 ... 1st toroidal transmission mechanism 11 ... Second toroidal speed change mechanism 22 ... Output gear 25 ... 1st counter gear 27 ... Counter shaft 28a, 28b ... Tapered roller bearing (first bearing pair) 60 ... Second counter gear (first gear) 65 ... Drive gear (third gear) 65a ... rotating shaft of drive gear 66 ... Intermediate gear (second gear) 66a ... Rotating shaft of intermediate gear 67 ... Tapered roller bearing (third bearing) 68 ... Fixed shaft 68a ... Seal ring (seal member) 69a, 69b ... Tapered roller bearing (second bearing pair) 70 ... Spacer 72 ... Gap 73 ... concave flat surface 74 ... Cylindrical member 76 ... Notch forming oil passage of tubular member 77 ... Fixed shaft oil passage

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-86348 (JP, A) JP-A-7-301300 (JP, A) Actually opened 61-126147 (JP, U) Actually opened 60- 172050 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F16H 57/00-57/12

Claims (2)

(57) [Claims] 1. A first gear, a second gear, and a third gear which are arranged to be aligned with each other in a plane perpendicular to an axial direction, by transmitting power from a speed change mechanism arranged on one side to each other and transmitting the power. gear and a pair of first bearing for rotatably supporting the first gear, and the front Symbol pair of second bearing rotatably supporting the rotary shaft of the second gear, the rotation shaft of the third gear A rotatably supporting a third bearing, a bearing on the other side of the first bearing pair, a bearing on the other side of the second bearing pair, and a case for individually housing the third bearing. In the transmission,
The rotating shaft of the second gear is formed in a tubular shape integral with the second gear, and is externally inserted via a second bearing pair to a fixed shaft supported by the case via a seal member. Between the bearing on the case side of the pair of bearings and the inner surface of the case, a spacer is externally inserted to the fixed shaft to bring the end surface of the inner ring of the bearing into contact with the spacer, and between the spacer and the inner surface of the case. Is provided with a gap into which a lubricating oil can enter, and a tubular member is externally fitted and fixed to the fixed shaft between the second bearing pair, and the tubular member and the fixed shaft are fixed to each other. Oil passages that communicate with each other are provided, and the oil passage of the tubular member is a cutout portion formed on at least one of the end faces of the tubular member. And the oil passage of the fixed shaft communicates with the gap. Machine. 2. The transmission according to claim 1, wherein an oil passage of the fixed shaft is formed by forming a concave flat surface on an outer peripheral portion of the fixed shaft.