Patent Publication Number: US-2019186311-A1

Title: Actuator of link mechanism for internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to an actuator of a link mechanism for an internal combustion engine. 
     BACKGROUND ART 
     As this kind of technique, there is disclosed a technique discussed in the following patent literature, PTL 1. PTL 1 discloses a variable compression ratio mechanism that makes a compression ratio of an internal combustion engine variable by changing a stroke characteristic of a piston with use of a multi-link piston-crank mechanism. 
     Further, an actuator includes a control link configured to vary an operating characteristic of the link mechanism for the internal combustion engine, an arm link relatively rotatably connected to the control link via a connection pin, a control shaft inserted and fixed in a fixing hole provided at the arm link, a housing including a receiving portion in which a connection portion between the other end portion of the control link and the arm link is received, and rotatably supporting the control shaft in a support hole formed within the housing, and a strain wave gearing speed reduction device configured to reduce a rotation speed of a driving motor and transmit the reduced rotation to the control shaft. A wave generator of the strain wave gearing speed reduction device is held by a ball bearing. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent Application Public Disclosure No. 2015-145647 
     SUMMARY OF INVENTION 
     Technical Problem 
     The receiving chamber of the actuator discussed in PTL 1 is filled with lubricant oil so as to lubricate the ball bearing. However, the technique discussed in PTL 1 may lead to a tilt of an oil level in the receiving chamber and thus a drop of a height of the oil level when the actuator tilts on, for example, an uphill road. In this case, the supply of the lubricant oil to the ball bearing may fall shaft. This raises such a drawback that an increase in an output torque also leads to an increase in a load imposed on the actuator especially on the uphill road, and the insufficiency of the lubricant oil results in a reduction in durability of the ball bearing. 
     An object of the present invention is to provide an actuator of a link mechanism for an internal combustion engine capable of ensuring lubricity regardless of the tilt. 
     Solution to Problem 
     According to one aspect of the present invention, an actuator of a link mechanism for an internal combustion engine includes a roller bearing having an inner race held by a wave generator of a strain wave gearing speed reducer and an outer race held by a housing, and a holding mechanism capable of holding lubricant oil on a radially inner side with respect to the outer race of this roller bearing. 
     Therefore, according to the one aspect of the present invention, the actuator can secure the lubricant oil to the roller bearing, thereby improving a wear-resistant performance of the roller bearing holding the wave generator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates an internal combustion engine including an actuator of a link mechanism for the internal combustion engine according to the present invention. 
         FIG. 2  is an exploded perspective view of the actuator of the link mechanism for the internal combustion engine according to a first embodiment. 
         FIG. 3  is a perspective view of the actuator of the link mechanism for the internal combustion engine according to the first embodiment. 
         FIG. 4  is a left side view of the actuator of the link mechanism for the internal combustion engine according to the first embodiment. 
         FIG. 5  is a cross-sectional view taken along a line A-A that illustrates the actuator of the link mechanism for the internal combustion engine in  FIG. 4 . 
         FIG. 6  is an exploded perspective view of a strain wave gearing speed reducer according to the first embodiment. 
         FIG. 7  is a cross-sectional view of main portions near the strain wave gearing speed reducer according to the first embodiment. 
         FIG. 8  schematically illustrates a change in a height of an oil level between running on a flatland and running on an uphill road according to the first embodiment. 
         FIG. 9  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to a second embodiment. 
         FIG. 10  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to a third embodiment. 
         FIG. 11  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  schematically illustrates an internal combustion engine including an actuator of a link mechanism for the internal combustion engine according to the present invention. This internal combustion engine has a basic configuration similar to the configuration illustrated in FIG. 1 of Japanese Patent Application Public Disclosure No. 2011-169152, and therefore will be described briefly herein. 
     An upper end of an upper link  3  is rotatably coupled with a piston  1  via a piston pin  2 . The piston  1  reciprocates in a cylinder of a cylinder block of the internal combustion engine. A lower link  5  is rotatably coupled with a lower end of the upper link  3  via a coupling pin  6 . A crankshaft  4  is rotatably coupled with the lower link  5  via a crank pin  4   a . Further, an upper end portion of a first control link  7  is rotatably coupled with the lower link  5  via a coupling pin  8 . A lower end portion of the first control link  7  is coupled with a coupling mechanism  9 , which includes a plurality of link members. The coupling mechanism  9  includes a first control shaft  10 , a second control shaft  11 , and a second control link  12  that couples the first control shaft  10  and the second control shaft  11  with each other. 
     The first control shaft  10  extends in parallel with the crankshaft  4  extending in a direction of a cylinder bank inside the internal combustion engine. The first control shaft  10  includes a first journal portion  10   a , a control eccentric shaft portion  10   b , and an eccentric shaft portion  10   c . The first journal portion  10   a  is rotatably supported on a main body of the internal combustion engine. The lower end portion of the first control link  7  is rotatably coupled with the control eccentric shaft portion  10   b . One end portion  12   a  of the second control link  12  is rotatably coupled with the eccentric shaft portion  10   c.    
     A first arm portion  10   d  has one end coupled with the first journal portion  10   a  and the other end coupled with the lower end portion of the first control link  7 . The control eccentric shaft portion  10   b  is provided at a position eccentric with respect to the first journal portion  10   a  by a predetermined amount. A second arm portion  10   e  has one end coupled with the first journal portion  10   a  and the other end coupled with the one end portion  12   a  of the second control link  12 . 
     The eccentric shaft portion  10   c  is provided at a position eccentric with respect to the first journal portion  10   a  by a predetermined amount. One end of the arm link  13  is rotatably coupled with the other end portion  12   b  of the second control link  12 . The second control shaft  11  is coupled with the other end of the arm link  13 . The arm link  13  and the second control shaft  11  are not movable relative to each other. The second control shaft  11  is rotatably supported in a housing  20 , which will be described below, via a plurality of journal portions. 
     The second control link  12  is prepared in the form of a lever, and the one end portion  12   a  coupled with the eccentric shaft portion  10   c  is generally linearly formed. On the other hand, the other end portion  12   b  with the arm link  13  coupled therewith is formed in a curved manner. An insertion hole  12   c  is formed through a distal end portion of the one end portion  12   a  in a penetrating manner (refer to  FIG. 3 ). The eccentric shaft portion  10   c  is rotatably inserted through the insertion hole  12   c . The other end portion  12   b  includes distal end portions  12   d  formed into a fork-like shape as illustrated in a cross-sectional view of the actuator illustrated in  FIG. 5 . A coupling hole  12   e  is formed at each of the distal end portions  12   d . Further, a coupling hole  13   c  is formed through a protrusion portion  13   b  of the arm link  13  in a penetrating manner. The coupling hole  13   c  is generally equal in diameter to the coupling hole  12   e . The protrusion portion  13   b  of the arm link  13  is inserted through between each of the distal end portions  12   d  formed into the fork-like shape, and a coupling pin  14  is fixedly press-fitted by penetrating through the coupling holes  12   e  and  13   c  in this state. 
     The arm link  13  is formed as a different member from the second control shaft  11  as illustrated in an exploded perspective view of the actuator illustrated in  FIG. 2 . The arm link  13  is a thick member made from a ferrous metallic material, and includes an annular portion and the protrusion portion  13   b . A press-fitting hole  13   a  is formed through an approximately central position of the annular portion in a penetrating manner. The protrusion portion  13   b  protrudes toward an outer periphery. A fixation portion  23   b , which is formed between each of the journal portions of the second control shaft  11 , is press-fitted in the press-fitting hole  13   a , and the second control shaft  11  and the arm link  13  are fixed by this press-fitting. The coupling hole  13   c  is formed through the protrusion portion  13   b . The coupling pin  14  is rotatably supported in the coupling hole  13   c . A central axis of this coupling hole  13   c  (a shaft center of the coupling pin  14 ) is positioned radially eccentrically with respect to a shaft center of the second control shaft  11  by a predetermined amount. 
     A rotational position of the second control shaft  11  is changed by a torque transmitted from a driving motor  22  via a strain wave gearing speed reducer  21 , which is a part of the actuator of the link mechanism for the internal combustion engine. The change in the rotational position of the second control shaft  11  causes a change in an orientation of the second control link  12  and thus a rotation of the first control shaft  10 , thereby causing a change in a position of the lower end portion of the first control link  7 . This results in a change in an orientation of the lower link  5  and thus a change in a stroke position and a stroke amount of the piston  1  in the cylinder, thereby leading to a change in an engine compression ratio according thereto. 
     [Configuration of Actuator of Link Mechanism for Internal Combustion Engine] 
       FIG. 2  is the exploded perspective view of the actuator of the link mechanism for the internal combustion engine according to the first embodiment.  FIG. 3  is a perspective view of the actuator of the link mechanism for the internal combustion engine according to the first embodiment.  FIG. 4  is a left side view of the actuator of the link mechanism for the internal combustion engine according to the first embodiment.  FIG. 5  is a cross-sectional view taken along a line A-A in  FIG. 4 . As illustrated in  FIGS. 2 to 5 , the actuator of the link mechanism for the internal combustion engine includes the driving motor  22 , the strain wave gearing speed reducer  21 , the housing  20 , and the second control shaft  11 . The strain wave gearing speed reducer  21  is attached to a distal end side of the driving motor  22 . The housing  20  contains the strain wave gearing speed reducer  21  therein. The second control shaft  11  is rotatably supported on the housing  20 . 
     (Configuration of Driving Motor) 
     The driving motor  22  is a brushless motor, and includes a bottomed cylindrical motor casing  45 , a cylindrical coil  46 , a rotor  47 , a motor driving shaft  48 , and a resolver  55 . The coil  46  is fixed to an inner peripheral surface of the motor casing  45 . The rotor  47  is rotatably provided inside the coil  46 . The motor driving shaft  48  include one end portion  48   a  fixed to a center of the rotor  47 . The resolver  55  detects a rotational angle of the motor driving shaft  48 . 
     The motor driving shaft  48  is rotatably supported by a ball bearing  52  provided at a bottom portion of the motor casing  45 . The motor casing  45  includes four boss portions  45   a  on an outer periphery of a front end thereof. A bolt insertion hole  45   b  is formed through each of the boss portions  45   a  in a penetrating manner. A bolt  49  is inserted through the bolt insertion hole  45   b.    
     The resolver  55  includes a resolver rotor  55   a  and a sensor portion  55   b . An outer periphery of the motor driving shaft  48  is fixedly press-fitted in the resolver rotor  55   a . The sensor portion  55   b  detects a multi-toothed target formed on an outer peripheral surface of the resolver rotor  55   a . The resolver  55  is provided at a position protruding from an opening of the motor casing  45 . The sensor portion  55   b  is fixed inside a cover  28  with use of two screws, and also outputs a detection signal to a not-illustrated control unit. When the motor casing  45  is attached to the cover  28 , the bolts  49  are inserted through the boss portions  45   a  while an O-ring  51  is interposed between an end surface of the resolver  55  and the cover  28 , and the bolts  49  are fastened to male screw portions formed on the driving motor  22  side of the cover  28 . By this attachment, the motor casing  45  is fixed to the cover  28 . A motor containing chamber, which contains the driving motor  22  by the motor casing  45  and the cover  28 , is formed as a drying chamber to which lubricant oil or the like is not supplied. 
     (Configuration of Second Control Shaft) 
     The second control shaft  11  includes a shaft portion main body  23  and a fixation flange  24 . The shaft portion main body  23  axially extends. The fixation flange  24  has a diameter that increases from the shaft portion main body  23 . The second control shaft  11  includes the shaft portion  23  and the fixation flange  24  that are integrally formed from a ferrous metallic material. The shaft main body  23  includes a sensor shaft portion  231  and a retainer shaft portion  232  (refer to  FIG. 5 ). An axially stepped shape is formed on the sensor shaft portion  231 , and the sensor shaft portion  231  is positioned on an inner periphery of an angle sensor  32 . The retainer shaft portion  232  is larger in diameter than the sensor shaft portion  231 , and is fixedly press-fitted in a retainer  350 . The retainer  350  is a restriction member that restricts a movement of the second control shaft  11  toward the strain wave gearing speed reducer side in the axial direction. The second control shaft  11  includes a rotor  32   b  on an outer periphery of the sensor shaft portion  231  (refer to  FIG. 5 ). The rotor  32   b  functions as a component of the angle sensor  32 . Further, the second control shaft  11  includes a small-diameter first journal portion  23   a  on a distal end portion side, an intermediate-diameter fixation portion  23   b , and a large-diameter second journal portion  23   c  on the fixation flange  24  side on the strain wave gearing speed reducer side with respect to the retainer shaft portion  232 . The fixation portion  23   b  is press-fitted into the press-fitting hole  13   a  of the arm link  13  from the first journal portion  23   a  side. Further, a first stepped portion  23   d  is formed between the fixation portion  23   b  and the second journal portion  23   c . Further, a second stepped portion  23   e  is formed between the first journal portion  23   a  and the fixation portion  23   b . Further, a third stepped portion  23   f  is formed between the first journal portion  23   a  and the retainer shaft portion  232 . This third stepped portion  23   f  serves as a stopper when the retainer shaft portion  232  is press-fitted into the retainer  350 , and therefore can facilitate the press-fitting. 
     When the fixation portion  23   b  is press-fitted into the press-fitting hole  13   a  of the arm link  13  from the first journal portion  23   a  side, an end portion of the press-fitting hole  13   a  on one side on the second journal portion  23   c  side abuts against the first stepped portion  23   d  from the axial direction. By this abutment, the first stepped portion  23   d  restricts a movement of the arm link  13  to the second journal portion  23   c  side. On the other hand, the second stepped portion  23   e  restricts a movement of the second control shaft  11  in the axial direction and to an opposite side from the strain wave gearing speed reducer  21  side by abutting against a stepped hole edge portion  30   c  of a support hole  30  and a bearing  301  when the shaft portion main body  23  is inserted through an internal race  701  press-fitted in the support hole  30  formed in the housing  20 . The shaft portion main body  23  is supported rotatably and slightly axially movably in a first bearing hole  301   a  of the bearing  301  and a second bearing hole  304   a  of a bearing  304 . In other words, slight spaces are generated between an inner periphery of the first bearing hole  301   a  and the shaft portion main body  23  and between an inner periphery of the second bearing hole  304   a  and the shaft portion main body  23 . The fixation flange  24  includes six bolt insertion holes  24   a  formed at even intervals in a circumferential direction of an outer peripheral portion thereof. The second control shaft  11  is coupled with a strain wave gear output shaft member  27 , which is internal teeth of the strain wave gearing speed reducer  21 , via a thrust plate  26 , with six bolts  25  inserted through these bolt insertion holes  24   a.    
     The second control shaft  11  includes an introduction portion, which introduces the lubricant oil press-fed from a not-illustrated oil pump, in a shaft of the second control shaft  11 . The introduction portion includes a conical oil chamber  64   a  and a bottomed axial oil passage  64   b . The oil chamber  64   a  is formed at a center of the fixation flange  24 , and the lubricant oil is supplied from the axial oil passage  64   b , which will be described below, to the oil chamber  64   a . The axial oil passage  64   b  is formed from the oil chamber  64   a  along a shaft center direction of the second control shaft. A narrow hole member  400  is press-fitted in an end portion of the axial oil passage  64   b  on the oil chamber  64   a  side. A narrow hole  401  penetrating along the shaft center is formed through the narrow hole member  400 . The narrow hole member  400  includes the narrow hole  401  formed so as to penetrate along the shaft center. The narrow hole  401  has a smaller area in cross section in a direction perpendicular to the shaft than an area of the axial oil passage  64   b  in cross section in the direction perpendicular to the shaft, thereby functioning as an orifice. By this configuration, even with the large-diameter axial oil passage  64   b  formed by being bored from the oil chamber  64   a  side, an orifice effect can be exerted due to the narrow hole  401  provided near a lubricant oil discharge port on the oil chamber  64   a  side, and the lubricant oil can be spread in the oil chamber  64   a . The lubrication oil supplied to the oil chamber  64   a  is supplied to the strain wave gearing speed reducer  21 , which will be described below. Further, the second control shaft  11  includes a plurality of radial oil passages  65   a  and  65   b , which is in communication with the axial oil passage  64   b , in the shaft of the second control shaft  11 . 
     The bearing  301  includes a bearing portion lubricant oil supply oil passage  302  in a radial direction thereof. The bearing portion lubricant oil supply oil passage  302  is in communication with a second lubricant oil supply oil passage  202 , which will be described below, and is opened at a position facing the radial oil passage  65   a  of the second control shaft  11 . A radially outer side of the radial oil passage  65   a  is opened to a clearance between an outer peripheral surface of the first journal portion  23   a  and the first bearing hole  301   a , and supplies the lubricant oil to the first journal portion  23   a . Further, a groove that is a groove approximately equal in width to a diameter of the radial oil passage  65   a  is formed on an outer periphery at an axial position where the radial oil passage  65   a  is formed, and the lubricant oil supplied to the outer periphery of the first journal portion  23   a  is guided from an entire circumference to flow into the radial oil passage  65   a , thereby being supplied to the axial oil passage  64   b . The radial oil passage  65   b  is in communication with an oil hole  65   c  formed inside the arm link  13 , and supplies the lubricant oil to between an inner peripheral surface of the coupling hole  13   c  and an outer peripheral surface of the coupling pin  14  via the oil hole  65   c.    
     (Configuration of Housing) 
     The housing  20  is formed into a generally cubic shape with use of an aluminum allow material. A large-diameter annular opening groove portion  20   a  is formed at a rear end side of the housing  20 . This opening groove portion  20   a  is closed by the cover  28  via the O-ring  51 . The cover  28  includes a motor shaft penetration hole  28   a  and four boss portions  28   b . The motor shaft through-hole  28   a  penetrates through a central position of the cover  28 . The boss portions  28   b  have diameters that increase toward a radially outer peripheral side. The cover  28  and the housing  20  are fixedly fastened to each other with bolts  43  inserted through bolt insertion holes formed through the boss portions  28   b  in a penetrating manner. 
     An opening for the second control link  12  coupled with the arm link  13  is formed on a side surface perpendicular to an opening direction of the opening groove portion  20   a . A containing chamber  29  is formed inside the housing  20  with this opening formed therein. The containing chamber  29  serves as a working area of the arm link  13  and the second control link  12 . A speed reducer-side through-hole  30   b  is formed between the opening groove portion  20   a  and the containing chamber  29 . The second journal portion  23   c  of the second control shaft  11  penetrates through the speed reducer-side through-hole  30   b . The support hole  30  is formed on an axial side surface of the containing chamber  29 . The first journal portion  23   a  of the second control shaft  11  penetrates through the support hole  30 . The bearing  301  is disposed between the support hole  30  and the first journal portion  23   a , and the bearing  304  is disposed between the support hole  30   b  and the second journal portion  23   c.    
     A retainer containing hole  31  is formed at an end portion of the support hole  30  on the angle sensor  32  side. The retainer containing hole  31  is larger in diameter than an opening of the support hole  30 . The housing  20  includes a stepped surface  31   a  between the opening of the support hole  30  on the angle sensor  32  side and the retainer containing hole  31 . The stepped surface  31   a  is formed in a direction generally perpendicular to the second control shaft  11 . The retainer  350  restricts the movement of the second control shaft  11  to the strain wave gearing speed reducer side in the axial direction by abutting against the stepped surface  31   a . The housing  20  includes a first lubricant oil supply oil passage  201  and a second lubricant oil supply oil passage  202  in the housing  20 . The first and second lubricant oil supply oil passages  201  and  202  introduce the lubricant oil pressure-fed from the not-illustrated oil pump. The first lubricant oil supply oil passage  201  extends in the direction generally perpendicular to the second control shaft  11 . The second lubricant oil supply oil passage  202  connects the first lubricant oil supply oil passage  201  and the support hole  30  to each other. The housing  20  includes a lubricant oil return flow oil passage  203 . The lubricant oil return flow oil passage  203  is in communication with the retainer containing hole  31 , and also returns the lubricant oil to the containing chamber  29  side. 
     (Configuration of Angle Sensor) 
     The angle sensor  32  includes a sensor holder  32   a  attached so as to close the retainer containing hole  31  from outside the housing  20 . The sensor holder  32   a  includes a through-hole  32   a   1  and a flange portion  32   a   2 . A detection coil  32   a   2  is disposed on an inner peripheral portion of the through-hole  32   a   1 . The flange portion  32   a   2  is used to fix the sensor holder  32   a  to the housing  20  by a bolt. A seal ring  33  is provided between the sensor holder  32   a  and the housing  20 , and ensures liquid tightness between the retainer containing hole  31  and the outside. Further, the angle sensor  32  includes a sensor cover  32   c  on an outer peripheral side of the sensor holder  32   a . The sensor cover  32   c  closes the through-hole  32   a   1 . A seal ring  323  is provided between the sensor cover  32   c  and the sensor holder  32   a , and ensures liquid tightness between the retainer containing hole  31  and the through-hole  32   a   1  and the outside. 
     The sensor shaft portion  231  is inserted in the through-hole  32   a   1 . The rotor  32   b  is attached to the outer periphery of the sensor shaft portion  231 . The rotor  32   b  is a generally elliptic component. The angle sensor  32  detects a change in a distance set between an inner periphery of the through-hole  32   a   1  and the rotor  32   b  due to a rotation of the rotor  32   b  based on a change in inductance of the detection coil. By this detection, the angle sensor  32  detects a rotation position of the rotor  32   b , i.e., a rotational angle of the second control shaft  11 . The angle sensor  32  is a so-called resolver sensor as described above, and outputs rotational angle information to the not-illustrated control unit that detects an engine operation state. 
     (Configuration of Strain Wave Gearing Speed Reducer) 
       FIG. 6  is an exploded perspective view of the strain wave gearing speed reducer according to the first embodiment. The strain wave gearing speed reducer  21  is a harmonic drive (registered trademark) speed reducer, and each component thereof is contained in the opening groove portion  20   a  of the housing  20  that is closed by the cover  28 . The strain wave gearing speed reducer  21  includes an annular first strain wave gear output shaft member  27 , a flexible external gear  36 , a wave generator  37 , and a second strain wave gear fixation shaft member  38 . The first strain wave gear output shaft member  27  is fixed to the fixation flange  24  of the second control shaft  11  with use of a bolt, and includes a plurality of internal teeth  27   a  formed on an inner periphery thereof. The flexible external gear  36  is disposed on a radially inner side of the first strain wave gear output shaft member  27 , is deflectably deformable, and includes external teeth  36   a  meshed with the internal teeth  27   a  on an outer peripheral surface thereof. The wave generator  37  is elliptically formed, and an outer peripheral surface thereof is slidably moved along an inner peripheral surface of the flexible external gear  36 . This occurs because, since the flexible external gear  36  is provided deflectably deformably, the flexible external gear  36  is deformed as if being twisted due to an input from the wave generator or a reverse input from the engine side to the strain wave gear output shaft member  27  that is applied to the arm link  13 , and the external teeth  36   a  of the flexible external gear  36  is deformed obliquely with respect to the axial direction due to this twist, whereby the second control shaft  11  coupled with the strain wave gear output shaft member  27  fitted thereto is moved in a thrust direction. The second strain wave gear fixation shaft member  38  is disposed on a radially outer side of the flexible external gear  36 , and includes internal teeth  38   a  meshed with the external teeth  36   a  on an inner peripheral surface thereof. 
     Male screw holes  27   b , which serve as respective nut portions of the bolts  25 , are formed at positions at even intervals in the circumferential direction on an outer peripheral side of the first strain wave gear output shaft member  27 . The flexible external gear  36  is made from a metallic material, and is a deflectably deformable thin cylindrical member. The number of teeth of the external teeth  36   a  of the flexible external gear  36  is equal to the number of teeth of the internal teeth  27   a  of the first strain wave gear output shaft member  27 . 
     The wave generator  37  includes an elliptic main body portion  371  and a ball bearing  372 . The ball bearing  372  permits a relative rotation between an outer periphery of the main body portion  371  and an inner periphery of the flexible external gear  36 . A through-hole  37   a  is formed at a center of the main body portion  371 . A serration is formed on an inner periphery of the through-hole  37   a , and is coupled with a serration formed on an outer periphery of the other end portion  48   b  of the motor driving shaft  48  by serration coupling. This coupling may be achieved by coupling using a keyway or spline coupling, and is not especially limited. The wave generator  37  includes a cylindrical portion  371   b  on a driving motor-side side surface  371   a  of the main body portion  371 . The cylindrical portion  371   b  is provided to extend to the driving motor side so as to surround an outer periphery of the through-hole  37   a . This cylindrical portion  371   b  has a perfect circular shape in cross section, and an outer periphery of the cylindrical portion  371   b  is set to a smaller diameter than a minor axis of the main body portion  371 . 
     A flange  38   b  is formed on an outer periphery of the second strain wave gear fixation shaft member  38 . The flange portion  38   b  is used for fastening the second strain wave gear fixation shaft member  38  to the cover  28 . Six bolt through-holes  38   c  are formed through the flange  38   b  in a penetrating manner. The second strain wave gear fixation shaft member  38  and a second thrust plate  42  are fixedly fastened to the cover  28  by placing the second thrust plate  42  between the second strain wave gear fixation shaft member  38  and the cover  28  and inserting bolts  41  through the bolt insertion holes  38   c . The second thrust plate  42  is made from a ferrous metallic material as wear-resistant as or more wear-resistant than the flexible external gear  36 . Due to this configuration, the actuator prevents the cover  28  from being worn due to a thrust force generated on the flexible external gear  36 , and also regulates an axial position of a ball bearing  700 , which will be described below. Further, the second thrust plate  42  is an annular disk-like member, and is formed in such a manner that an inner peripheral-side edge portion  42   a  thereof is located on the shaft center side with respect to an inner periphery of an outer race  702  of the ball bearing  700 , which will be described below. Details thereof will be described below. The number of teeth of the internal teeth  38   a  of the second strain wave gear fixation shaft member  38  is greater than the number of teeth of the external teeth  36   a  of the flexible external gear  36  by two. Therefore, the number of teeth of the internal teeth  38   a  of the second strain wave gear fixation shaft member  38  is greater than the number of teeth of the internal teeth  27   a  of the first strain wave gear output shaft member  27  by two. The speed reduction ratio of the strain wave gearing speed reduction mechanism is determined according to this difference between the numbers of teeth, and therefore a significantly high speed reduction ratio can be acquired. 
     (Regarding Support Structure of Rotational Member) 
     The cover  28  includes female screw portions  28   c , a plate containing portion  281   a , a bearing containing portion  281   b , and a cylindrical seal containing portion  281   d . The bolts  41  are threadably engaged with the female screw portions  28   c . The plate containing portion  281   a  has a depth approximately equal to a thickness of the second thrust plate  42 , and houses the second thrust plate  42  therein. The bearing containing portion  281   b  is a bottomed cylindrical stepped portion formed by being bent from the plate containing portion  281   a  to the driving motor  22  side. The seal containing portion  281   d  stands on the wave generator side in the axial direction at a radially inner position of a bottom surface  281   c  of the bearing containing portion  281   b . The above-described motor shaft through-hole  28   a  is formed on a more radially inner side than the seal containing portion  281   d . In other words, the bearing containing portion  281   b  is an annular recessed portion recessed from the end surface  281  of the cover  28  on the strain wave gearing speed reducer  21  side to one end side in a direction of a rotational axis of the wave generator  37 . 
     The open-type ball bearing  700  is contained in the bearing containing portion  281   b . The ball bearing  700  is a four-point contact roller bearing that can receive a load in the thrust direction. The ball bearing  700  includes an inner race  701 , balls  703 , and the outer race  702 . The inner race  701  supports a cylindrical portion  371   b , which will be described below. The balls  703  are rolling members. The outer race  702  is held by the housing  20 . An axial thickness of the ball bearing  700  is approximately equal to an axial depth of the bearing containing portion  281   b . Further, an outer diameter of the ball bearing  700  is set to a larger diameter than an outer diameter of the ball bearing  52 , and therefore a sufficient bearing capacity is ensured. The outer race  702  is contained in the bearing containing portion  281   b . An end surface of the outer race  702  on the strain wave gearing speed reducer  21  side is in abutment with or slightly spaced apart from the second thrust plate  42 , and an end surface of the outer race  702  on the driving motor  22  side is in abutment with the bottom surface  281   c . Due to this configuration, the support structure regulates a position of the outer race  702  in an axial direction of the ball bearing  700  and in both directions on the strain wave gearing speed reducer  21  side and the driving motor  22  side. Further, the bearing containing portion  281   b  is provided on the driving motor  22  side of the wave generator  37 . In other words, the support structure supports the ball bearing  700  at a position further close to the driving motor  22 , thereby preventing or reducing a deformation of the motor driving shaft  48  and preventing or cutting down an increase in an axial dimension thereof toward the second control shaft  11  side. 
     The outer diameter of the outer race  702  is set to a larger diameter than inner diameters of the first and second strain wave gear fixation shaft members  27  and  38 . Further, an inner diameter of the outer race  702  is set to a smaller diameter than an inner diameter of the flexible external gear  36 . An outer peripheral side of the cylindrical portion  371   b  provided so as to extend from the main body portion  371  of the wave generator  37  is fixed (press-fitted) to an inner periphery of the inner race of the ball bearing  700 . Being fixed here is not limited to being press-fitted, and also includes, for example, being axially positionally regulated with use of a step or a snap ring. Due to this configuration, the motor driving shaft  48  is supported by the ball bearing  52  provided between the motor driving shaft  48  and the motor casing  45 , and is also supported by the ball bearing  700  via the main body portion  371  and the cylindrical portion  371   b.    
     The second control shaft  11  is supported at the first journal portion  23   a  and the second journal portion  23   c  rotatably relative to the housing  20 . An alternate load is input from a primary motion system of the internal combustion engine to this second control shaft  11 . Therefore, the speed should be slowed down by the strain wave gearing speed reducer  21  to allow the second control shaft  11  to rotate against this alternate load. However, an axial load is generated on this strain wave gearing speed reducer  21  when the speed is slowed down, and therefore is also applied to the second control shaft  11 . Further, an axial load due to a tilt of the arm link  13  is applied. This occurs because, since the flexible external gear  36  is provided deflectably deformably, the flexible external gear  36  is deformed as if being twisted due to an input from the wave generator  37  or a reverse input from the engine side to the strain wave gear output shaft member  27  that is applied to the arm link  13 , and the external teeth  36   a  of the flexible external gear  36  is deformed obliquely with respect to the axial direction due to this twist, whereby the second control shaft  11  coupled with the strain wave gear output shaft member  27  fitted thereto is moved in the thrust direction. If the second control shaft  11  is excessively axially moved at this time, this movement may cause an unnecessary load to be applied to the strain wave gearing speed reducer  21 , thereby leading to a reduction in durability. Therefore, the second control shaft  11  is provided with the retainer  350  including the restriction surface  501  oriented to the strain wave gearing speed reducer side in the axial direction, and the housing  20  side is provided with the stepped surface  31   a  that abuts against the restriction surface  501 . Due to this provision, the present configuration is allowed to function as a restriction mechanism that restricts the excessive movement of the second control shaft  11  toward the strain wave gearing speed reducer side. 
     (Configuration of Seal Portion) 
     The support structure includes the seal containing portion  281   d  on the radially inner side of the cylindrical portion  371   b . The seal containing portion  281   d  is smaller in diameter than an inner peripheral surface of the cylindrical portion  371   b . A seal member  310  is provided between an inner periphery of the seal containing portion  281   d  and the outer periphery of the motor driving shaft  48 . The seal member  310  liquid-tightly seals between the opening groove portion  20   a  containing the strain wave gearing speed reducer  21  and the driving motor  22 . The seal containing portion  281   d  is erected on the radially inner side of the cylindrical portion  371   b . In other words, the seal containing portion  281   d  is formed so as to overlap the cylindrical portion  371   b  and the ball bearing  700  as viewed from the radial direction. 
     (Regarding Supply of Lubricant Oil) 
     The lubricant oil supplied from the first lubricant oil supply oil passage  201  flows into the axial oil passage  64   b  via the second lubricant oil supply oil passage  202 , the bearing portion lubricant oil supply oil passage  302 , and the radial oil passage  65   a . The lubricant oil delivered to the axial oil passage  64   b  is effectively spread in the oil chamber  64   a  due to the orifice effect because passing through the narrow hole  401  of the narrow hole member  400 . At this time, the lubricant oil is also supplied to the space between the first journal portion  23   a  of the second control shaft  11  and the inner periphery of the bearing  301  when flowing from the bearing portion lubricant oil supply oil passage  302  to the radial oil passage  65   a . The lubricant oil supplied to this space flows to the arm link  13  side, and also flows to the angle sensor  32  side. The lubricant oil supplied to between the side surface of the retainer  350  and the stepped surface  31   a  is returned from the lubricant oil return flow oil passage  203  provided at a lower side in  FIG. 5  to the containing chamber  29  side. 
     (Regarding Retention of Lubricant Oil) 
     Next, retention of the lubricant oil will be descried.  FIG. 7  is a cross-sectional view of main portions near the strain wave gearing speed reducer according to the first embodiment. The strain wave gearing speed reducer  21  is contained and a strain wave gearing speed reducer containing chamber  500  is also defined in the opening groove  20   a  formed in the housing  20 . An opening of the strain wave gearing speed reducer containing chamber  500  is closed by the cover  28 . The lubricant oil is stored in this strain wave gearing speed reducer containing chamber  500  so as to keep a predetermined oil level height h 1  when the vehicle is running on a flatland. A height of h 1  in a direction of gravitational force is located at a higher position than a lower end portion of the flexible external gear  36  of the strain wave gearing speed reducer  21  and a lower end portion of the inner periphery of the outer race  702  of the ball bearing  700  in the direction of gravitational force when the vehicle is running on the flatland. Due to this configuration, the actuator achieves the supply of the lubricant oil to the strain wave gearing speed reducer  21  and the ball bearing  700 , and thus improvement of the durability. 
     A drain hole  600  is formed at the housing  20  to maintain this predetermined oil level height h 1 . Even when the lubricant oil is excessively supplied, the actuator allows the lubricant oil to be discharged from the drain hole  600 , thereby preventing or cutting down an increase in friction due to excessive lubrication. Now, L 1  and L 3  are defined to represent a length in the direction of gravitational force from the shaft center on the flatland to a lower end of the drain hole  600 , and a length in the direction of gravitational force from the shaft center to a lower end  702   a  of a rolling surface near a contact surface where the outer race  702  of the ball bearing  700  and the balls  703  are in contact with each other, respectively. The outer race  702  and the balls  703  are in contact with each other at two portions, and these contact positions are regarded as approximately the same position as the lower end  702   a  of the rolling surface although being located on a slightly upper side with respect to the lower end  702   a  of the rolling surface in the direction of gravitational force. The drain hole  600  is formed at such a position that L 1  is shorter than L 3 . 
       FIG. 8  schematically illustrates a change in the oil level height between running on the flatland and running on an uphill road according to the first embodiment when the actuator is mounted on the vehicle. When the running is switched from the running on the flatland to the running on the uphill road, the position of the drain hole  600  is also changed according to a slope of the uphill road. Then, the length from the shaft center to the lower end of the drain hole  600  in the direction of gravitational force increases such that L 1 ′ is longer than L 1 , and an oil level height h 2  is located on a lower side with respect to the lower end  702   a  of the rolling surface in the direction of gravitational force. At this time, exceeding L 1 ′ over L 3  makes it impossible to sufficiently supply the lubricant oil to the lower end  702   a  of the rolling surface. This leads to such a problem that the insufficiency of the supply of the lubricant oil to the ball bearing  700  especially with a large engine output generated, like on the uphill road, results in a reduction in the durability of the ball bearing  700 . 
     With the aim of solving this problem, in the first embodiment, the second thrust plate  42  is formed in such a manner that L 2  is shorter than L 3  and L 2  is longer than L 1 , when L 2  is defined to represent a length from the shaft center to the inner peripheral-side edge portion  42   a  of the second thrust plate  42 . Due to this configuration, when the vehicle is running on the flatland, the predetermined oil level height h 1  is located on an upper side with respect to the inner peripheral-side edge portion  42   a , and therefore the lubricant oil can be supplied to a region surrounded by the bearing containing portion  281   b  and the second thrust plate  42 . On the other hand, when the vehicle is running on the uphill road, even with the oil level height being h 2  and being located on a lower side with respect to the inner peripheral-side edge portion  42   a , the inner peripheral-side edge portion  42   a  is kept at a higher position than the lower end  702   a  of the rolling surface, and therefore the ball bearing  700  can be lubricated by the stored lubricant oil. 
     Advantageous Effects 
     (1) The first embodiment is the actuator configured to be used for the link mechanism for the internal combustion engine and configured to rotate the second control shaft  11  (a control shaft) for changing the orientation of the link mechanism for the internal combustion engine. The actuator includes the strain wave gearing speed reducer  21  configured to decrease the rotational speed of the driving motor  22  (an electric motor) and transmit the rotation thereof to the second control shaft  11 , the housing  20  including the strain wave gearing speed reducer containing chamber  500  (a containing chamber) in which the driving motor  22  is fixed and the strain wave gearing speed reducer  21  is also contained, and the axial oil passage  64   b  (a communication passage) provided at the housing  20  or the second control shaft  11  and establishing the communication between the strain wave gearing speed reducer containing chamber  500  and the lubricant oil passage of the internal combustion engine. The strain wave gearing speed reducer  21  includes the wave generator  37  having the elliptic outline coupled with the motor driving shaft  48  (an output shaft) of the driving motor  22 , the flexible external gear  36  including the external teeth  36   a  on the outer periphery thereof and the cylindrical portion inserted through the outer peripheral side of the wave generator  37  and configured to transmit the rotation of the cylindrical portion to the second control shaft  11 , and the first strain wave gear output member  27  and the second strain wave gear fixation shaft member  38  (an internal gear) fixed to the housing  20  and including the internal teeth  27   a  meshed with the flexible external gear  36 . The actuator includes the ball bearing  700  (a roller bearing) provided on the radially inner side with respect to the flexible external gear  36 . The ball bearing  700  includes the inner race  701  held by one of the housing  20  and the wave generator  37 , the outer race  702  held by the other of the housing  20  and the wave generator  37 , and the balls  703  that are a rolling member between the inner race  701  and the outer race  702 . The actuator further includes the second thrust plate  42  and the bearing containing portion  281   b  (a holding mechanism) provided at the housing  20  and capable of holding the lubricant oil on the radially inner side with respect to the outer race  702 . 
     Therefore, the first embodiment can secure the lubricant oil to the ball bearing  700 , thereby improving a wear-resistant performance of the ball bearing  700  holding the wave generator  37 . 
     (2) The housing  20  includes the drain hole  600  (a discharge oil passage) capable of discharging the lubricant oil from the strain wave gearing speed reducer containing chamber  500 . The lower end portion of the opening portion of the drain hole  600  to the strain wave gearing speed reducer containing chamber  500  in the direction of gravitational force on the flatland road is positioned at the upper side in the direction of gravitational force with respect to the inner peripheral-side edge portion  42   a  of the second thrust plate  42 . 
     Therefore, when the vehicle is running on the flatland, the first embodiment can allow the oil level to be located on the upper surface with respect to the inner peripheral-side edge portion  42   a  of the second thrust plate  42 , thereby storing the lubricant oil on the ball bearing  700  side of the second thrust plate  42 . 
     (3) The lower end portion of the opening portion of the drain hole  600  to the strain wave gearing speed reducer containing chamber  500  in the direction of gravitational force on the flatland road is positioned at the upper side in the direction of gravitational force with respect to the lower end portion of the flexible external gear  36  in the direction of gravitational force. Therefore, when the vehicle is running on the flatland, the first embodiment can allow the lubricant oil to be constantly supplied to the flexible external gear  36 , thereby improving the durability of the flexible external gear  36 .
 
(4) The second thrust plate  42  includes the bottom surface  281   c  of the bearing containing portion  281   b . The bottom surface  281   c  is the extension portion provided at the housing  20 . The extension portion faces one side of the ball bearing  700  in the rotational axis direction, and extends radially inward beyond the inner diameter of the outer race  702  with respect to the outer race  702 . The second thrust plate  42  further includes the inner peripheral-side edge portion  42   a  (a plate member) facing the other side of the ball bearing  700  in the rotational axis direction and extending radially inward beyond the inner diameter of the outer race  702  with respect to the outer race  702 .
 
     Therefore, the first embodiment can hold the lubricant oil in the portion where the ball bearing  700  is contained. 
     (5) The ball bearing  700  is the open-type roller bearing. In other words, the first embodiment ensures a lubrication performance, and therefore allows an inexpensive bearing to be employed instead of an expensive bearing such as a bearing sealingly containing lubricant oil.
 
(6) The second thrust plate  42  is provided abuttably in the axial direction of the flexible external gear  36 .
 
     Due to this configuration, the first embodiment can prevent the cover  28  from being worn due to the thrust force generated on the flexible external gear  36 , and also regulate the axial position of the ball bearing  700  and store the lubricant oil. 
     (7) The second thrust plate  42  is formed into the disk-like shape. Therefore, even when the vehicle rolls, the first embodiment can maintain the height of the inner peripheral-side edge portion  42   a , thereby stably storing the lubricant oil.
 
(8) The second thrust plate  42  is fixedly fastened to the housing  20  together with the strain wave gear fixation shaft member  38 .
 
     Therefore, the first embodiment can allow these components to be mounted by one process, thereby ensuring facilitation of assembling. 
     Second Embodiment 
     Next, a second embodiment will be described. The second embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing on only differences therefrom.  FIG. 9  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to the second embodiment. In the first embodiment, the second thrust plate  42  is formed as the flat-plate annular member. On the other hand, the second embodiment is different from the first embodiment in terms of the second thrust plate  42  including a step on the inner peripheral side thereof. The second thrust plate  42  according to the second embodiment includes a first disk portion  42   a   1  and a second disk portion  42   a   2 . The first disk portion  42   a   1  is fastened to the housing  20  together with the second strain wave gear fixation shaft member  38 . The second disk portion  42   a   2  is formed into a stepped shape from around the inner periphery of the outer race  702  on an inner peripheral side of the first disk portion  42   a . The second disk portion  42   a   2  is set in a direction away from the inner race  701  in the axial direction. Due to this configuration, the actuator can avoid a contact of the inner race  701  with the second thrust plate  42 , thereby eliminating or reducing resistance against the rotation. Further, the second disk portion  42   a   2  is set in the direction away from the inner race  701  in the axial direction, whereby the actuator can increase a volume capable of storing the lubricant oil therein. 
     Third Embodiment 
     Next, a third embodiment will be described. The third embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing on only differences therefrom.  FIG. 10  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to a third embodiment. In the first embodiment, the lubricant oil is stored in the space defined by the housing  20  and the second thrust plate  42 . On the other hand, the third embodiment is different from the first embodiment in terms of provision of an extension portion  7021  extending toward the inner race at an end portion of the outer race  702  of the ball bearing  700  on the strain wave gearing speed reducer  21  side and storage of the lubricant oil in the ball bearing  700 . The actuator can store the lubricant oil in the ball bearing  700  regardless of the position of the inner peripheral-side end portion  42   a  of the second thrust plate  42 . 
     Fourth Embodiment 
     Next, a fourth embodiment will be described. The fourth embodiment has a basic configuration similar to the first embodiment, and therefore will be described focusing on only differences therefrom.  FIG. 11  is a cross-sectional view of main portions near a strain wave gearing speed reducer according to a fourth embodiment. In the first embodiment, the lubricant oil is stored with use of the second thrust plate  42 . On the other hand, the third embodiment is different from the first embodiment in terms of provision of seal members  705  at both axial end portions of the outer race  702  of the ball bearing  700  on the inner peripheral side thereof. These seal members  705  have a space between the seal members  705  and the inner race  701  on inner peripheral sides thereof, and allow the lubricant oil to flow into the ball bearing  700 . The actuator can store the lubricant oil in the ball bearing  700  regardless of the position of the inner peripheral-side end portion  42   a  of the second thrust plate  42 . 
     OTHER EMBODIMENTS 
     Having described the present invention based on the first to fourth embodiments thereof, the specific configuration of each invention is not limited to the first to fourth embodiments, and the present invention also includes a design modification and the like thereof made within a range that does not depart from the spirit of the present invention if any. 
     For example, in the embodiments, the present actuator of the link mechanism for the internal combustion engine is employed for the mechanism that makes the compression ratio of the internal combustion engine variable, but the present actuator may be employed for a link mechanism of a variable valve actuating mechanism of an internal combustion engine that makes variable an operating characteristic of an intake valve or a discharge valve like, for example, Japanese Patent Application Public Disclosure No. 2009-150244. 
     Further, in the first to fourth embodiments, the number of teeth of the external teeth  36   a  of the flexible external gear  36  is set to the same number as the number of teeth of the internal teeth  27   a  of the first strain wave gear output shaft member  27 , but the speed reduction ratio may be adjusted by making a difference in the number of teeth. In this case, the rotation of the cylindrical portion of the flexible external gear  36  will be transmitted to the second control shaft  11  at a speed reduction ratio due to the difference in the number of teeth between the number of teeth of the external teeth  36   a  and the number of teeth of the internal teeth  27   a.    
     In the following description, technical ideas recognizable from the above-described embodiments will be described. 
     One aspect is an actuator configured to be used for a link mechanism for an internal combustion engine and configured to rotate a control shaft for changing an orientation of the link mechanism for the internal combustion engine. The actuator includes a strain wave gearing speed reducer configured to decrease a rotational speed of an electric motor and transmit a rotation thereof to the control shaft, a housing including a containing chamber in which the electric motor is fixed and the strain wave gearing speed reducer is also contained, and a communication passage provided at the housing or the control shaft and establishing communication between the containing chamber and a lubricant oil passage of the internal combustion engine. The strain wave gearing speed reducer includes a wave generator having an elliptic outline coupled with an output shaft of the electric motor, a flexible external gear including an external tooth on an outer periphery thereof and a cylindrical portion inserted through an outer peripheral side of the wave generator and configured to transmit a rotation of the cylindrical portion to the control shaft, and an internal gear fixed to the housing and including an internal tooth meshed with the flexible external gear. The actuator includes a roller bearing including an inner race held by one of the housing and the wave generator, an outer race held by the other of the housing and the wave generator, and a rolling member between the inner race and the outer race, and a holding mechanism provided at the roller bearing or the housing and capable of holding the lubricant oil in the roller bearing on a radially inner side with respect to the outer race. 
     In another preferable configuration, in the above-described configuration, the housing includes a discharge oil passage capable of discharging the lubricant oil from the containing chamber. A lower end portion of an opening portion of the discharge oil passage to the containing chamber in a direction of gravitational force on a flatland road is positioned at an upper side in the direction of gravitational force with respect to the holding mechanism. 
     In further another preferable configuration, in any of the above-described configurations, the lower end portion of the opening portion of the discharge oil passage to the containing chamber in the direction of gravitational force on the flatland road is positioned at an upper side in the direction of gravitational force with respect to a lower end portion of the flexible external gear in the direction of gravitational force. 
     In further another preferable configuration, the holding mechanism includes an extension portion provided at the housing. The extension portion faces one side of the roller bearing in a rotational axis direction, and extends radially inward beyond an inner diameter of the outer race with respect to the outer race. The holding mechanism further includes a plate member facing the other side of the roller bearing in the rotational axis direction and extending radially inward beyond the inner diameter of the outer race with respect to the outer race. 
     In further another preferable configuration, the roller bearing is an open-type roller bearing. 
     In further another preferable configuration, the plate member is provided abuttably in an axial direction of the flexible external gear. 
     In further another preferable configuration, the plate member includes a portion axially facing the inner race of the roller bearing. This facing portion is formed into a stepped shape in a direction away from the inner race. 
     In further another preferable configuration, the plate member is formed into a disk-like shape. 
     In further another preferable configuration, the plate member is fixedly fastened to the housing together with the internal gear. 
     In further another preferable configuration, the holding mechanism is an extension portion integrally provided at the outer race of the roller bearing and extending from a radially inner side of the outer race toward the inner race of the roller bearing. 
     In further another preferable configuration, the holding mechanism is a seal member attached to the outer race of the roller bearing and forming a space between the seal member and the inner race of the roller bearing. 
     Further, from another aspect, one possible configuration is an actuator configured to be used for a link mechanism for an internal combustion engine and configured to rotate a control shaft for changing an orientation of the link mechanism for the internal combustion engine. The actuator includes a strain wave gearing speed reducer configured to decrease a rotational speed of an electric motor and transmit a rotation thereof to the control shaft, a housing including a containing chamber in which the electric motor is fixed and the strain wave gearing speed reducer is also contained, and a communication passage provided at the housing or the control shaft and establishing communication between the containing chamber and a lubricant oil passage of the internal combustion engine. The strain wave gearing speed reducer includes a wave generator having an elliptic outline coupled with an output shaft of the electric motor, a flexible external gear including an external tooth on an outer periphery thereof and a cylindrical portion inserted through an outer peripheral side of the wave generator and configured to transmit a rotation of the cylindrical portion to the control shaft, an internal gear fixed to the housing and including an internal tooth meshed with the flexible external gear, and a roller bearing including an inner race held by the wave generator, an outer race held by the housing, and a rolling member between the inner race and the outer race. The actuator includes a bearing containing portion formed in the housing. The bearing containing portion is recessed to one end side in a rotational axis direction of the wave generator, and holds the outer race. The actuator further includes a plate member fixed to the roller bearing or the housing. The plate member faces the other end side of the outer race in the rotational axis direction of the wave generator, and extends to a radially inner side with respect to the outer race. 
     Preferably, in the above-described configuration, the housing includes a discharge oil passage capable of discharging the lubricant oil from the containing chamber. A lower end portion of an opening portion of the discharge oil passage to the containing chamber in a direction of gravitational force on a flatland road is positioned at a radially inner side of the control shaft with respect to an inner peripheral surface of the plate member. 
     In a further preferable configuration, the plate member faces in an axial direction of the flexible external gear. 
     Having described merely several embodiments of the present invention, it is apparent to those skilled in the art that the embodiments described as the examples can be modified or improved in various manners without substantially departing from the novel teachings and advantages of the present invention. Therefore, such a modified or improved embodiment is intended to be also contained in the technical scope of the present invention. The above-described embodiments may also be arbitrarily combined. 
     The present application claims priority under the Paris Convention to Japanese Patent Application No. 2016-151934 filed on Aug. 2, 2016. The entire disclosure of Japanese Patent Application No. 2016-151934 filed on Aug. 2, 2016 including the specification, the claims, the drawings, and the abstract is incorporated herein by reference in its entirety. 
     REFERENCE SIGN LIST 
     
         
           11  second control shaft (control shaft) 
           12  second control link 
           13  arm link 
           20  housing 
           21  strain wave gearing speed reducer 
           22  driving motor (electric motor) 
           24  fixation flange 
           27  first strain wave gear output member 
           36  flexible external gear 
           37  wave generator 
           38  second strain wave gear fixation shaft member (internal gear) 
           42  second thrust plate 
           48  motor driving shaft (motor output shaft) 
           64   b  axial oil passage (communication passage) 
           281   b  bearing containing portion 
           500  strain wave gearing speed reducer containing portion 
           700  ball bearing 
           701  inner race 
           702  outer race 
           703  ball 
           600  drain hole (discharge oil passage)