Patent Publication Number: US-2007111845-A1

Title: Driving mechanism and door closing apparatus for vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2005-333259, 2005-333260, 2005-333261 and 2005-333262, all of which were filed on Nov. 17, 2005, the entire content of which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a driving mechanism and a door closing apparatus for vehicle.  
     BACKGROUND  
      It has been conventionally known a door closing apparatus for a vehicle, for example disclosed in JP2002-250165A (FIGS. 1-3, U.S. 2002-119861A1). According to a driving mechanism, which is provided in the door closing apparatus, rotational torque of an electric motor is inputted into a sun gear of a planetary gear mechanism, and each planetary gear rotates and revolutes relative to a ring gear fixed against rotation by an engagement cancel block of a connection interrupting mechanism. In response to rotation of a planetary carrier associated with rotation of each planetary gear, an output shaft rotates so as to output operation force for shifting a latch mechanism from a half-latched state to a fully latched state. As a result, a closing operation is implemented for operating a door from a half-closed state to a fully closed state. The ring gear is fixed against rotation with external teeth engaged with teeth of the engagement cancel block.  
      Meanwhile, when a door handle is operated to open a door, this operation force is inputted into the engagement cancel block. The engagement cancel block retracts backward and the ring gear is allowed to rotate, wherein torque transmission between the electric motor and the output shaft is discontinued. At the same time, when the door handle is operated to open the door, operation force for releasing the latch mechanism from a latched state is outputted, wherein the door can open.  
      According to the door closing apparatus disclosed above, the sun gear exhibits a substantially cylindrical shape with a bottom so as not to interfere with the planetary gears. A worm is firmly attached to a rotational shaft of the electric motor. The sun gear is formed with a worm wheel portion, which is engaged with the worm, such that the sun gear of the planetary gear mechanism is operatively connected to the worm. Meanwhile, the ring gear exhibits a substantially cylindrical shape with a bottom so as to house the planetary gears therein. The ring gear is formed with external teeth, which are engaged with the teeth of the engagement cancel block, at an outer peripheral surface. For the purpose of avoiding mutual interference between the worm wheel portion and the ring gear, the worm wheel portion and the ring gear are arranged on a different plane in the axial direction and are cumulated in the axial direction.  
      Therefore, the central engagement portion of the worm and the worm wheel portion is shifted in the axial direction relative to the central engagement portion of the ring gear, the sun gear and the planetary gears. Further, the electric motor is positioned on the basis of a rotation shaft (rotational axis) defining the central engagement portion of the worm and the worm wheel portion. Accordingly, the electric motor is positioned at one side of an axis of the planetary gear mechanism, which may increase the thickness and size of an entire structure of the driving mechanism. Especially, in a situation in which this driving mechanism is housed in a door for a vehicle, the freedoms or possibilities for positioning the driving mechanism are reduced because of this upsizing.  
      It has been conventionally known a door closing apparatus for a vehicle, in which driving force of a driving mechanism is transmitted to a latch mechanism via drive cable and a vehicle door at the half-closed state is shifted to a fully closed state. JP09-42265A (FIG. 3) discloses a structure for assembling a drive cable on a door closing apparatus for a vehicle. An outer tube of the drive cable is inserted into a bore of an attachment wall standing up at a base member. The drive cable is prevented from dropping out and fixed by fastening the end of the drive cable by nuts from both sides of the attachment wall.  
      In this case, in order to fix the end of the drive cable, it was necessary to first insert the outer tube into the first nut and insert into the bore and the second nut. Therefore, a fixing performance was low. Especially, in order to stabilize the behavior of the drive cable, it is general to arrange the end of the drive cable in the vicinity of a member to be linked. This may force a fastening of nuts in a limited space with a deteriorated workability.  
      Meanwhile, in order to avoid complexity for inserting the drive cable (outer tube) in the axial direction as described above, it is possible to open the attachment wall in a U-shaped structure and to press-fit the outer tube into this opening in a radial direction, wherein the drive cable is prevented from dropping and is fixed stably. However, because the drive cable is required to have tension at a level sufficient for transmitting force between the driving mechanism and the latch mechanism, the drive cable is designed to have large rigidity. This may require a large force to press-fit the drive cable, force that is not achieved by general jigs.  
      The present invention has been made in view of the above circumstances, and provides a driving mechanism and a door closing apparatus for a vehicle, both of which have a reduced size, and the door closing apparatus in which a fixedly assembling performance of an end of a drive cable for transmitting driving power of the driving mechanism to the latch mechanism is enhanced.  
     SUMMARY OF THE INVENTION  
      According to an aspect of the present invention, a driving mechanism includes: a drive gear fixed at a rotational shaft of a motor; a sun gear rotatably provided and having a gear portion engaged with the drive gear; a ring gear arranged coaxially with the sun gear, the ring gear being locked not to rotate relative to the sun gear and being allowed to rotate relative to the sun gear; a planetary gear engaged with the sun gear and the ring gear; and a planetary carrier arranged coaxially with the sun gear and connected to the planetary gear. The planetary carrier outputs rotational force in response to rotation and revolution of the planetary gear operatively associated with rotation of the sun gear and relative to the ring gear locked not to rotate. A central engaged portion of the driving gear and the gear portion and a central engaged portion of the sun gear, the ring gear and the planetary gear are arranged on the same plane.  
      According to another aspect of the present invention, a door closing apparatus for a vehicle includes a planetary gear mechanism having a sun gear, a ring gear, a planetary gear and a planetary carrier. An input shaft is selected from among the sun gear, the ring gear, the planetary gear and is rotatably driven by an electric motor. A fixed shaft is selected from among the sun gear, the ring gear and the planetary gear and is different from the input shaft. An output shaft is selected from among the sun gear, the ring gear, the planetary gear and is different from the input shaft and the fixed shaft. The door closing apparatus for the vehicle further includes: a first engagement portion formed at the fixed shaft of the planetary gear mechanism; a latch mechanism holding a door of the vehicle at a half-closed state and a fully closed state; a locking member having a second engagement portion. The locking member locks the fixed shaft not to rotate with the second engagement portion engaged with the first engagement portion of the fixed shaft and unlocks the fixed shaft to rotate with the second engagement portion disengaged from the first engagement portion of the fixed shaft. The door closing apparatus still further includes power transmitting means for transmitting force outputted by the output shaft to the latch mechanism so that the latch mechanism is operated to shift the door from the half-closed state to the fully closed state in a state where the locking member is engaged with the ring gear; and switching means for switching an engagement or disengagement between the first engagement portion and the second engagement portion. The switching means releases an engagement between the first engagement portion and the second engagement portion by transmitting an operation force to the locking member and engages the first engagement portion and the second engagement portion by discontinuing transmission of the operation force to the locking member, regardless of the force transmission by the power transmitting means. The first engagement portion and the second engagement portion are formed in a serrated manner so that the first engagement portion and the second engagement portion are engaged smoothly in a rotational direction of the fixed shaft.  
      According to still another aspect of the present invention, a door closing apparatus for a vehicle includes: a planetary gear mechanism having a sun gear, a ring gear, a planetary gear and a planetary carrier. An input shaft is selected from among the sun gear, the ring gear, the planetary gear and is rotatably driven by an electric motor. A fixed shaft is selected from among the sun gear, the ring gear and the planetary gear and is different from the input shaft. The fixed shaft is locked not to rotate by being engaged with a locking member and is unlocked to rotate by being disengaged from the locking member. An output shaft is selected from among the sun gear, the ring gear, the planetary gear and is different from the input shaft and the fixed shaft. The door closing apparatus further includes: a latch mechanism holding a door of the vehicle at a half-closed state and a fully closed state; power transmitting means for transmitting force outputted by the output shaft to the latch mechanism so that the latch mechanism is operated to shift the door from the half-closed state to the fully closed state in a state where the locking member is engaged with the ring gear; and switching means for switching an engagement or disengagement between the locking member and the fixed shaft. The switching means releases an engagement between the locking member and the fixed shaft by transmitting an operation force to the locking member and engages the locking member and the fixed shaft by discontinuing transmission of the operation force to the locking member, regardless of the force transmission by the power transmitting means. The door closing apparatus further includes an elastic body provided at an axial portion of at least one of the sun gear, the ring gear and the planetary gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein:  
       FIG. 1  is a front view illustrating a door for a vehicle according to an embodiment of the present invention;  
       FIG. 2  is an aerial view illustrating the door for the vehicle;  
       FIG. 3  is a front view illustrating a door latch apparatus;  
       FIG. 4  is a side view illustrating the door latch apparatus;  
       FIG. 5  is another front view illustrating the door latch apparatus;  
       FIG. 6  is another front view illustrating the door latch apparatus;  
       FIG. 7  is a front view illustrating an actuator;  
       FIG. 8A  is a side view illustrating the actuator;  
       FIG. 8B  is another side view illustrating the actuator;  
       FIG. 9  is a cross sectional view taken along line IX-IX in  FIG. 8 ;  
       FIG. 10A  is an enlarged view illustrating the actuator;  
       FIG. 10B  is another enlarged view illustrating the actuator;  
       FIG. 11A  is a cross sectional view taken along line XIA-XIA in  FIG. 7 ; and  
       FIG. 11B  is a cross sectional view taken along line XIB-XIB in  FIG. 7 . 
    
    
     DETAILED DESCRIPTION  
      An embodiment of the present invention will be described below with reference to the attached drawing figures.  
       FIG. 1  is a front view illustrating a door  1  for a vehicle according to the embodiment of the present invention.  FIG. 2  is an aerial view illustrating the door  1 . The door  1  for a vehicle is hinged to a body  2  and opens and closes an opening of the body  2 , i.e., the door  1  is a swing-type door. A door latch unit  10  is mounted at a vehicle rearward end in the door  1 . The door latch unit  10  is engaged with or disengaged from a U-shaped or C-shaped striker  3  fixed to the body  2  so as to hold the door  1  at a half-closed state or a fully closed state. The door latch unit  10  is connected to an outside door handle  4  and an inside door handle  5 , each of which is provided at an outside and inside of the door  1 . When the door latch unit  10  is transmitted with operation force from either the outside door handle  4  or the inside door handle  5 , the door latch unit  10  is disengaged from the striker  3  and the door  1  is allowed to open.  
      The door latch unit  10  is further connected to an actuator  40 , which serves as a driving mechanism and is mounted inside the door  1 . When the door latch unit  10  is transmitted with driving force of the actuator  40 , the door latch unit  10  is engaged with the striker  3  in a way that the door  1  is shifted from the half-closed state to the fully closed state. The actuator  40  is connected to each of the outside door handle  4  and the inside door handle  5 , and driving force transmission from the actuator  40  to the door latch unit  10  is discontinued in response to operation force transmitted from either the outside door handle  4  or the inside door handle  5  to the actuator  40 .  
      Described below is a structure of the door latch unit  10  with reference to  FIGS. 3, 4 ,  5  and  6 .  
       FIG. 3  is a front view of the door latch unit  10  and corresponds to a view viewed from a rear side of the vehicle.  FIG. 4  is a side view of the door latch unit  10  and corresponds to a view viewed from an inside of the vehicle in a width direction. As illustrated therein, inside a main body  11 , which forms an outer profile of the door latch unit  10  and houses or supports various components therein, an open lever  12 , which is made of a plate material, is supported to be pivotable about a first rotational shaft O 1 . The open lever  12  is biased by a torsion spring  13 , which is wound around the first rotational shaft O 1 , and is retained at a predetermined pivot position. The open lever  12  is linked, at an end  12   a , to the outside door handle  4  via known mechanical connecting members. When the open lever  12  is transmitted with operation force of the outside door handle  4 , the open lever  12  pivots clockwise in  FIG. 3  against the biasing force of the torsion spring  13 , and the other end  12   b  of the open lever  12  is lifted up (left side in  FIG. 3 ). On the other hand, when the outside door handle  4  is discontinued from being operated, the open lever  12  is biased by the torsion spring  13  and pivots counterclockwise in  FIG. 3  so that the other end  12   b  of the open lever  12  is lifted down. The open lever  12  then returns to the predetermined pivot position.  
      As illustrated in  FIG. 4 , an open link  14 , which is made of a plate, is pivotably supported, at a lower end thereof, by the other end  12   b  of the open lever  12 . The open link  14  is formed with an L-shaped flange  14   a  at an intermediate portion in an up and down direction. The L-shaped flange  14   a  is positioned so as to face from below a distal end  15   a  of a lift lever  15 , which is made of a plate and is rotatably supported by the main body  11 .  
      Further as illustrated in  FIG. 4 , inside the main body  11 , an inside open lever  16 , which is made of a plate, is rotatably supported about a rotational shaft O. The inside open lever  16  includes a distal end  16   a , which extends in a radial outward direction and is arranged so as to face the flange  14   a  from below. The inside open lever  16  is linked to the inside door handle  5  via known mechanical connecting members. When the inside open lever  16  is transmitted with operation force of the inside door handle  5 , the inside open lever  16  rotates counterclockwise in  FIG. 4  and the distal end  16   a  is lifted up. On the other hand, when the inside door handle  5  is discontinued from being operated, the inside open lever  16  rotates clockwise in  FIG. 4  and the distal end  16   a  is lifted down. The inside open lever  16  is biased by the torsion spring  13  up to an initial position of the open link  14  and is biased to an initial position of the inside open lever  16  by the inside door handle  5 . The inside open lever  16  then returns to a predetermined pivot position.  
      As illustrated in  FIG. 3 , inside the main body  11 , a latch  21  is rotatably supported at an upper side of the open lever  12 . The latch  21  includes an engagement recess  21   a  and exhibits a U-shaped structure. The latch  21  includes a first detent  21   b , which is formed at an end of the latch  21  in a clockwise direction in  FIG. 3 , and a second detent  21   c , which is formed at the other end of the latch  21  in a counterclockwise direction in  FIG. 3 . The engagement recess  21   a  is interposed between the first and second detents  21   b  and  21   c . The first detent  21   b  includes a first engagement portion  21   d  facing an opposite side to the engagement recess  21   a . The second detent  21   c  includes a second engagement portion  21   e  facing the engagement recess  21   a  at an end of the second detect  21   c . The latch  21  further includes a driven portion  21   f  extending toward the opposite side to the engagement recess  21   a  relative to the rotational axis. A latch biasing spring  22  is housed in the main body  11 , one end of which is fixed by the main body  11  and the other end of which is fixed at the latch  21 . The latch  21  is then biased towards a clockwise rotation direction. The clockwise rotation of the latch  21  is restrained with a surface of the first detent  21   b  in contact with a latch stopper  23  firmly attached to the main body  11 , wherein the latch  21  is retained at a predetermined pivot position.  
      Further, in the main body  11 , a pole  24  is rotatably supported between the open lever  12  and the latch  21 . This pole  24  is connected to the lift lever  15  so as to rotate integrally therewith. The pole  24  includes an engagement portion  24   a , which extends to one side from a rotational axis (toward the right side in  FIG. 3 ), and an extending portion  24   b , which extends to the other side from the rotational axis (toward the left side in  FIG. 3 ). The pole  24  is biased by a pole biasing spring (not illustrated), one end of which is supported by the main body  11  and the other end of which is supported by the pole  24 . The pole  24  is biased by the pole biasing spring towards a counterclockwise direction, i.e., in a direction for lifting up the engagement portion  24   a . The further counterclockwise rotation of the pole  24  is restrained with a ball stopper  25 , which is provided at the main body  11 , in contact with a surface of the extending portion  24   bm  wherein the pole  24  is retained at a predetermined pivot position. The pole  24  configures a latch mechanism  20  with the latch  21  and so on.  
      Described below is a fundamental operation of the latch mechanism  20 . As illustrated in  FIG. 3 , when the door  1  is open, the latch  21  is being retained at the predetermined pivot position with the latch stopper  23  in contact with the surface of the first detent  21   b . The engagement recess  21   a  is open facing an approach patch of the striker  3  in response to a closing operation of the door  1 . The pole  24  is being retained at the predetermined pivot position with the ball stopper  25  in contact with the surface of the extending portion  24   b . The engagement portion  24   a  is positioned below the second detent  21   c . In this case, the latch mechanism  20  is set at an unlatched state.  
      When the striker  3  enters into the engagement recess  21   a  in response to the closing operation of the door  1 , the striker  3  pushes an inner wall surface of the engagement recess  21   a . The latch  21  then rotates counterclockwise against the biasing force of the latch biasing spring  22 , as illustrated in  FIG. 5 . The second engagement portion  21   e  of the latch  21  comes in contact with the engagement portion  24   a  so that the latch  21  is locked against clockwise rotation. Here, the door  1  is at the half-closed state in which the striker  3  is engaged with the engagement recess  21   a  and is blocked from dropping or moving away. The latch mechanism  20  is at the half-latched state.  
      When the striker  3  further enters into the engagement recess  21   a  as the door  1  is further closed, the striker  3  pushes the inner wall surface of the engagement recess  21   a . As illustrated in  FIG. 6 , the latch  21  further rotates counterclockwise against the biasing force of the latch biasing spring  22 , and the engagement portion  24   a  is engaged with the first engagement portion  21   d . Here, the door  1  is at the fully closed state in which the striker  3  is engaged with the engagement recess  21   a  and is blocked from dropping or moving away. The latch mechanism  20  is at the fully latched state.  
      When the pole  24  rotates clockwise against the biasing force of the pole biasing spring with the latch  21  at the half-latched state or fully latched state, the engagement of the engagement portion  24   a  with the first engagement portion  21   d  or the second engagement portion  21   e  is released. Here, the latch  21  is biased by the latch biasing spring  22  and rotates clockwise while the inner wall surface of the engagement recess  21   a  is pushing the striker  3 . The striker  3  is disengaged from the engagement recess  21   a  and the door  1  is opened.  
      As illustrated in  FIG. 3 , an operation lever  31  is pivotably supported at an upper side of the latch  21  inside the main body  11 . The operation lever  31  is formed with a drive portion  31   a  extending at its one end toward the lower side in  FIG. 3 . A lever biasing spring (not illustrated) is supported, at its one end, by the main body  11 , and the other end thereof is engaged with the operation lever  31 , wherein the operation lever  31  is biased to pivot counterclockwise in  FIG. 3 . The operation lever  31  comes in contact with a lever stopper  32 , which is provided at the main body  11 , and is prohibited from rotating further counterclockwise and is retained at a predetermined pivot position. When the latch mechanism  20  at the half-latched state, the drive portion  31   a  is arranged in a way that the driven portion  21   f  of the latch  21  is positioned on a pivot-movement path of the drive portion  31   a , as illustrated in  FIG. 5 .  
      The operation lever  31  is formed with an arc-shaped guiding surface  31   b  at the upper side of a rotational shaft of the operation lever  31 . The guiding surface  31   b  is interposed between two planar shaped guiding plates  33 .  FIG. 3  illustrates only one guiding plate  33 . Further in the main body  11 , an end  35   a  of an outer tube  35 , which includes a drive cable  34 , is supported at the lower side of the operation lever  31 . The guiding plates  33  supports one end  36   a  of a drive wire  36 , which is pulled out from the end  35   a  of the outer tube  35  and guided by the guiding surface  31   b . Therefore, when the drive wire  36  retracts into the end  35   a  of the outer tube  35 , the operation lever  31 , which is fixed with the guiding plates  33 , rotates clockwise against the biasing force of the lever biasing spring. Mores specifically, the drive wire  36  (drive cable  34 ) is connected to the actuator  40 . When driving force of the actuator  40  is transmitted to the drive wire  36 , the drive wire  36  retracts into the end  35   a  of the outer tube  35  such that the operation lever  31  pivotably rotates clockwise.  
      When the drive wire  36  is retracted towards the outer tube  35  in a situation where the latch mechanism  20  is at the half-latched state, the operation lever  31  rotates clockwise and the drive portion  31   a  of the operation lever  31  pushes the driven portion  21   f  of the latch  21 . As a result, the latch  21  rotates counterclockwise against the biasing force of the latch biasing spring  22 . The striker  3 , which is to be engaged with the engagement recess  21   a  of the latch  21 , is pulled and the latch mechanism  20  is shifted to the fully latched state, as illustrated in  FIG. 6 . Here, a door closing operation is implemented in a way that the door  1  is shifted from the half-closed state to the fully closed state.  
      Described below is a structure of the actuator  40  with reference to  FIGS. 7, 8  and  9 .  
       FIG. 7  is a front view illustrating the actuator  40  and corresponds to a view viewed from a laterally outside of the vehicle.  FIG. 8  is a back view of the actuator  40 .  FIG. 9  is a cross sectional vie taken along line IX-IX in  FIG. 8 . As illustrated in  FIG. 7 , a plate-made and rectangular shaped bracket  41  is fastened, at its one end  41   a , to a plate-made supporting bracket  42  by means of a screw  43 . The other end of the bracket  41  is fastened to main body  11  of the door latch unit  10 , which is not illustrated. A housing  44 , which forms an outer shape of the actuator  40  and houses and supports various components, is fastened to the supporting bracket  42  so that the actuator  40  is fixed to and supported by the door latch unit  10  via the bracket  41 . As illustrated in  FIG. 9 , the housing  44  includes a case  45  of cylindrical shaped with a bottom, in which various components are housed, and a cover  46 , which closes an opening of the case  45 .  
      As illustrated in  FIGS. 7 and 9 , an axis of the case  45  extends, at an end of one side (upper right in  FIG. 7 ) to the one side (lower right in  FIG. 7 ). The case  45  includes a worm housing portion  45   a , which exhibits a cylindrical shape and open partially at the side of the housing portion  45   a  (lower side in  FIG. 9 ), at the upper side in  FIG. 9 . In the worm housing portion  45   a , a worm  48 , which serves as a drive gear and is firmly attached to a rotational shaft  47   a  of an electric motor  47  fastened to the case  45 , is rotatably housed. The electric motor  47  is controlled to actuate by a controller which is not illustrated and rotates the rotational shaft  47   a  (worm  48 ) in a normal or reverse rotational direction.  
      As illustrated in  FIGS. 8 and 9 , the case  45  includes a gear housing portion  45   b , which exhibits an approximately cylindrical-shape with a bottom and is partially notched to form the cylindrical shape of the worm housing portion  45   a . The gear housing portion  45   b  is formed so as to open at a radially one end (the left side in  FIGS. 8A and 8B ). The case  45  includes a housing  45   c  which exhibits a polygonal cylindrical shape and communicates with an opening side (left side in  FIG. 8 ) of the gear housing portion  45   b . That is, the bottom wall of the case  45  exhibits a shape combined with a circle and a polygon.  
      The gear housing portion  45   b  includes a recess  45   d , which has an inner diameter smaller than a diameter of the gear housing portion  45   b  and is recessed in a circular from a bottom wall of the gear housing portion  45   b . The recess  45   d  is formed with a bearing bore  45   e  at a center of its bottom wall (see  FIG. 9 ). The bearing bore  45   e  is fitted with one end of an output shaft  49  so as to freely rotate. An axis of the output shaft  49  extends along an axis of the gear housing portion  45   b . A distal end of the output shaft  49  extends outside of the case  45  (housing  44 ). The other end of the output shaft  49  is supported at a recess  46   a  formed at the cover  46  so as to be rotatable and not to be movable to an axial one side, i.e., to the right side in  FIG. 9 .  
      A sun gear  51  is housed in the gear housing portion  45   b  at the side of the cover  46 . The sun gear  51  is formed with a sun gear portion  52 , a disc-shaped flange  53  and a worm wheel portion  54 . An inner diameter of the cylindrical sun gear portion  52  is substantially identical to an outer diameter of the output shaft  49 . The flange  53  extends radially outwardly at one axial end (right in  FIG. 9 ) of the sun gear portion  52 . The worm wheel portion  54  extends from a periphery of the flange  53  towards the other axial end (left in  FIG. 9 ) and exhibits a cylindrical shape. The worm wheel portion  54  serves as a gear portion engageable with the worm  48 . The sun gear portion  52 , the flange  53  and the worm wheel portion  54  of the sun gear  51  forms a cylindrical box-shaped portion with a bottom, and formed within it is a ring-shaped housing space S. An inner peripheral surface of the sun gear portion  52  serves as a bearing bore  52   a  into which the output shaft  49  is relative-rotatably fitted. The sun gear portion  52  is formed to lie over or overlap the worm wheel portion  54  in the axial direction.  
      The recess  45   d  is formed with a cylindrical projection  45   f , which projects towards the cover  46  and is coaxial with the bearing bore  45   e . The projection  45   f  supports a ring gear  55  to be freely rotatable. The ring gear  55  exhibits a cylindrical shape with a bottom and possesses an outer diameter smaller than the inner diameters of the worm wheel portion  54  and the recess  45   d . The ring gear  55  is formed with a bottom wall portion  56  and a cylindrical ring-shaped gear portion  57 . The bottom wall portion  56  includes a bearing bore  56   a  into which the projection  45   f  is fitted. The cylindrical ring gear portion  57  extends from a periphery of the bottom wall portion  56  towards the axial one end (right in  FIG. 9 ). The ring gear portion  57  is arranged to be at the same position along the axial direction as the sun gear portion  52  in a way that a distal end of the ring gear portion  57  is housed inside the housing space S of the sun gear  51 . The ring gear portion  57  is formed with engagement nails  58  at the base side that is shifted from the axial position of the worm wheel portion  54 . The engagement nails  58  are designed at a predetermined pitch over an entire circumference of the ring gear portion  57  and serve as plural first engagement portions.  
      Multiple planetary gears  59  are arranged at a predetermined angle between the sun gear portion  52  and the ring gear portion  57  and are gear-meshed therewith. According to the first embodiment of the present invention, provided are three planetary gears  59 . Each planetary gear  59  is arranged at the same position along the axial direction as the sun gear portion  52  and the gear portion  57 . That is, the central engaged portion of the worm  48  and the worm wheel portion  54  and the central engaged portion of the sun gear  51  (sun gear portion  52 ), the ring gear  55  (gear portion  57 ) and the planetary gears  59  are arranged on the same imaginary surface P (the same plane P) in  FIG. 9 . The aforementioned central engaged portion is determined at an arbitrary position at an intermediate within a range in which plural gears are mutually gear-meshed and does not represent an accurate center. Further, as described above, the central engaged portions are arranged at the same plane. That is, all the engagement centers are positioned on a predetermined imaginary surface perpendicular with the axis of the sun gear  51  (sun gear portion  52 ) within the axial directional range of the sun gear  51 . Especially, the worm  48 , which is gear-meshed with the worm wheel portion  54 , has the axis positioned on the same imaginary surface P.  
      The output shaft  49  is firmly attached with a planetary carrier  60  at a position in which the planetary carrier  60  slides on a distal end of the sun gear portion  52 . Each planetary gear  59  is interposed in the axial direction between a pair of plates  60   a  and  60   b  configuring the planetary carrier  60 . Supporting shafts  61 , which are supported by the plates  60   a  and  60   b , are inserted along the axis of the planetary gears  59  so that the planetary gears  59  are supported rotatably about the supporting shafts  61 . Therefore, each planetary gear  59  is rotatable about the corresponding supporting shaft  61  and revolutes along the ring gear portion  57  about the output shaft  49  in response to the rotation. At the same time, the planetary carrier  60  rotates integrally with the output shaft  49 .  
      A planetary gear mechanism  50  is configured with the sun gear  51  (sun gear portion  52 ), the ring gear  55  (ring gear portion  57 ), the planetary gears  59 , and the planetary carrier  60 . As is enlarged in  FIG. 9 , each planetary gear  59  is formed to be cylindrical-shaped and includes an inner diameter larger than the outer diameter of the supporting shaft  61 . Each planetary gear  59  includes a gear main body  59   a , which forms an outer shape of the planetary gear  59  and is mostly made of resin material, and an elastic body  59   b , which includes the inner diameter approximately identical to the outer diameter of the supporting shaft  61  and exhibits a ring shape along the inner periphery of the gear main body  59   a . The elastic body  59   b  is made of elastic material. The gear main body  59   a  and the elastic body  59   b  are formed integrally for example by two-color-formation. An inner periphery of the elastic body  59   b , which serves as an axis of the planetary gear  59 , serves as a bearing bore  59   c  into which the supporting shaft  61  is fitted. As described above, the elastic body  59   b  is positioned at an axial portion of the planetary gear  59  such that the elastic body  59   b  absorbs fluctuations between each gear (sun gear  51 , ring gear  55 , planetary gears  59 ), which may occur in the event that the planetary gear mechanism  50  operates at a relatively low load. As illustrated in  FIG. 9 , the gear main body  59   a  is formed with a ring-shaped groove  59   d  at the axial both ends. The axial both ends of the elastic body  59   b  projects radially outwardly so as to fit into the groove  59   d . Therefore, although the gear main body  59   a  and the elastic body  59   b  are made of materials that are not the same, the gear main body  59   a  and the elastic body  59   b  are integrated more firmly. As illustrated in  FIG. 7 , a drive lever  62 , which is made of a plate and exhibits a fan-shaped structure, is firmly attached to the distal end of the output shaft  49  projecting outside of the housing  44 . The drive lever  62  is formed with an arc-shaped guiding surface  62   a  interposed between two planar shaped guiding plates  63 .  FIG. 7  illustrates only one guiding plate  63 . An end  35   b  of the outer tube  35  is supported by the supporting bracket  42  at the one side of the drive lever  62  (left in  FIG. 7 ). The guiding plates  63  support the other end  36   b  of the drive wire  36 , which is pulled out of the end  35   b  of the outer tube  35  and guided to the guiding surface  62   a . Therefore, once the drive lever  62  is rotated in one direction (counterclockwise in  FIG. 7 ) with the output shaft  49 , the drive wire  36  is pulled out of the end  35   b  of the outer tube  35 . In this case, the drive wire  36 , which is supported at the side of the operation lever  31  is retracted into the end  35   a  of the outer tube  35 . That is, a power transmitting means is configured with the drive lever  62 , the drive cable  34 , the operation lever  31  and so on.  
      Described below is a mounting arrangement of the drive cable  34 .  FIGS. 11A and 11B  are cross sectional views taken along lines XIA-XIA and XIB-XIB. As illustrated in FIG.  7 , the bracket  41  is integrally provided with a wall portion  41   b  (supporting plate) formed at the end  41   a  of the bracket  41  and extending towards the electric motor  47 . As illustrated in  FIG. 11A , the wall portion  41   b  includes: a planar shaped fastened portion  41   c ; a U-shaped cross sectional housing portion  41   d ; and an engagement portion  41   e . The planar-shaped fastened portion  41   c  lies on the supporting bracket  42  and is in contact therewith. The housing portion  41   d  is formed continuously at an end of the fastened portion  41   c  and extends away from the supporting bracket  42 . The engagement portion  41   e  is bent from an opening end of the housing portion  41   d  and extends outwardly in parallel with the fastened portion  41   c . The wall portion  41   b  of the bracket  41  is formed in a way that the engagement portion  41   e  projects in an opening direction of the housing portion  41   d  by a thickness of the supporting bracket  42 .  
      Meanwhile, the supporting bracket  42  is formed with a square-shaped engagement hole  42   a  into which the engagement portion  41   e  is inserted. The wall portion  41   b  is fixed to the supporting bracket  42  with the fastened portion  41   c  fastened to the supporting bracket  42  by the screw  43  and with the engagement portion  41   e  inserted into the engagement hole  42   a  and is locked at the back surface of the supporting bracket  42  in a manner that the end  35   b  of the outer tube  35  (drive cable  34 ) lying on the supporting bracket  42  is surrounded by the housing portion  41   d . Therefore, the end  35   b  of the outer tube  35  is surrounded by the inner wall surface of the housing portion  41   d  and a surface of the supporting bracket  42  such that the outer tube  35  is prevented from dropping in a radial direction.  
      As illustrated in  FIG. 11B , the supporting bracket  42  is formed with a U-shaped guiding portion  42   b  to which a circular circumferential groove  35   c  of the end  35   b  of the outer tube  35  is mounted. The end  35   b  of the outer tube  35  is positioned in the axial direction with the circumferential groove  35   c  mounted at the guiding portion  42   b.    
      As illustrated in  FIG. 8A , the housing  45   c  is formed with a guiding groove  45   g , which exhibits a rectangular shape and extends continuously to one side in parallel with a radial direction of the recess  45   d . The housing  45   c  is further provided with a lever-side fan-shaped recess  45   h  continuously formed at an end of the guiding groove  45   g . As illustrated in  FIG. 9 , the lever-side recess  45   h  is formed with a bearing bore  45   i  at the center of the fan-shape. The bearing bore  45   i  is fitted with one end of a lever shaft  66   a  integrally formed at a releasing lever  66  so as to be rotatable. The distal end of the lever shaft  66   a  projects outwardly from the case  45  (housing  44 ). The other end of the lever shaft  66   a  is supported by the recess  46   b  of the cover  46  so as to be freely rotatable and immovable to the axial one side (right in  FIG. 9 ). The releasing lever  66  further includes a lever portion  66   b  and a cam hole  66   c . The lever portion  66   b  exhibits a fan-shaped structure and extends toward the guiding groove  45   g  at the upper side in which the lever portion  66   b  does not interfere with the guiding groove  45   g . The long cam hole  66   c  is formed at a distal end of the lever portion  66   b  and serves as a cam-side engagement portion. The cam hole  66   c  is bent in a way that one end of the cam hole  66   c  in the circumferential direction (the counterclockwise end in  FIGS. 8A and 8B ) is positioned closer to the lever shaft  66   a  rather than the other end thereof (the clockwise end in  FIGS. 8A and 8B ) is.  
      A lever biasing spring  67 , which serves as biasing means, is supported, at its one end, by the inner wall surface at the one side (clockwise side in  FIGS. 8A and 8B ) of the housing  45   c . The lever biasing spring  67  is wound about the lever shaft  66   a  with the other end of the lever biasing spring  67  engaged at the releasing lever  66  such that the releasing lever  66  is biased to pivot counterclockwise in  FIGS. 8A and 8B . When a surface of the lever portion  66   b  comes in contact with a lever stopper  68  of the inner wall surface at the other side (counterclockwise side) of the housing  45   c , the pivot rotation of the releasing lever  66  is restrained and the releasing lever  66  is retained at a predetermined pivot position.  
      Mounted on the guiding groove  45   g  is a canceling gear  69 , which serves as a planar-shaped locking member movable in the radial direction of the recess  45   d  along the guiding groove  45   g . The canceling gear  69  is formed with an engagement pin  69   a  and gear-side engagement nails  69   b . The engagement pin  69   a  (a locking member-side engagement portion) projects toward the one side of the canceling gear  69  (toward the nearside in a perpendicular direction to a sheet of  FIG. 8 ) and is inserted into the cam hole  66   c . The gear-side engagement nails  69   b  are formed at a distal end of the canceling gear  69  at the recess  45   d  side and serves as multiple second engagement portions engageable with the engagement nails  58  facing the guiding groove  45   g . As illustrated in  FIG. 8A , in a state where the releasing lever  66  is retained at the predetermined pivot position with the surface of the lever portion  66   b  in contact with the lever stopper  68 , the engagement pin  69   a  is pushed by the inner wall surface of the cam hole  66   c  and the canceling gear  69  is pushed towards the recess  45   d , wherein the gear-side engagement nails  69   b  of the canceling gear  69  are engaged with the engagement nails  58  of the ring gear  55 . Here, the ring gear  55  is locked to be against rotation. On the other hand, as illustrated in  FIG. 8B , when the releasing lever  66  rotates clockwise against the biasing force of the lever biasing spring  67 , the engagement pin  69   a  is pushed by the inner wall surface of the cam hole  66   c , and the canceling gear  69  is retracted towards the lever shaft  66   a , wherein the gear-side engagement nails  69   b  of the canceling gear  69  are disengaged from the engagement nails  58  of the ring gear  55 . Here, the ring gear  55  is allowed to rotate.  
      As illustrated in  FIG. 7 , a lever  70 , which is made of a plate, is fixed to a distal end of the lever shaft  66   a , which distal end projects outwardly from the housing  44  (case  45 ). At the housing  44 , an end  72   a  of an outer tube  72  of a canceling cable  71  is supported at the upper side of the lever  70 . The lever  70  supports one end  73   a  of a wire  73  pulled out of the end  72   a  of the outer tube  72 . Therefore, when the wire  73  is pulled into the end  72   a  of the outer tube  72 , the lever  70  rotates with the releasing lever  66  counterclockwise in  FIG. 7  (clockwise in  FIGS. 8A and 8B ) against the biasing force of the lever biasing spring  67 . The wire  73  (canceling cable  71 ) is retracted towards the end  72   a  in a manner that the lever  70  rotates counterclockwise in  FIG. 7  when either the outside door handle  4  or the inside door handle  5  is operated.  
      Described below is an operation of the actuator  40 . In a state where the ring gear  55  is locked to be against rotation with the engagement nails  58  being engaged with the gear-side engagement nails  69   b , the electric motor  47  is assumed to be actuated so as to transmit rotational torque to the sun gear  51  (worm wheel portion  54 ), which is in engagement with the worm  48  fixed to the rotation shaft  47   a , for clockwise rotation in  FIG. 8 , the sun gear portion  52  naturally rotate in the same direction, clockwise in  FIG. 8 . Therefore, the planetary gears  59  revolute clockwise in  FIG. 8  while rotating counterclockwise in  FIG. 8  relative to the ring gear  55 . The planetary carrier  60  outputs rotational force to the clockwise direction in  FIG. 8 . That is, the planetary gear mechanism  59  serves a speed reduction mechanism having the sun gear  51 , the ring gear  55  and the planetary carrier  60  as an input shaft, a fixed shaft and an output shaft, respectively. Here, the drive lever  62  rotates counterclockwise in  FIG. 7  in response to rotation of the output shaft  49  so that the drive wire  36  is pulled out of the end  35   b  of the outer tube  35 . The ring gear  55  receives a reaction force of the planetary carrier  60  (output shaft  49 ) and is to rotate counterclockwise in  FIG. 8 . The canceling gear  69  however firmly restrains the ring gear  55  from rotating counterclockwise in  FIG. 8 .  
      On the other hand, in a state where the ring gear  55  is allowed to rotate with the engagement nails  58  in disengagement from the gear-side engagement nails  69   b , the planetary carrier  60  (output shaft  49 ) is discontinued from outputting rotational force. This occurs because a large load is being applied to the side of the output shaft  49 . That is, rotational torque, which is transmitted from the sun gear  51  to each planetary gear  59 , is employed only for rotating the ring gear  55 . As a result, each planetary gear  59  does not revolute thus not allowing the planetary carrier  60  to rotate.  
      According to the embodiment of the present invention, the engagement nails  58  and the gear-side engagement nails  69   b  are each of a serration-type so that the nails  58  and  69   b  are smoothly gear-meshed with each other in a rotating direction of the ring gear  55 . That is, as illustrated in  FIG. 10 , each engagement nail  58  includes a first straight inclined surface  58   a , which slants to a tangential line of the ring gear  55  and defines an acute angle in a circumferential direction of the ring gear  55  (counterclockwise direction in  FIG. 10 ), and a second straight inclined surface  58   b , which slants to the tangential line of the ring gear  55  and defines an acute angle in the other circumferential direction of the ring gear  55  (clockwise direction in  FIG. 10 ). The inclined surface  58   b  is formed continuously at a distal end of the first inclined surface  58   a . An inclined angle θ  1 , which is defined between the first inclined surface  38   a  and the tangential line of an outer periphery of the ring gear  55 , is smaller than an inclined angle θ  2 , which is defined between the second inclined surface  58   b  and the tangential line of the outer periphery of the ring gear  55 . As described above, the ring gear  55  receives reaction force of the rotating planetary carrier  60  (output shaft  49 ) and can rotate counterclockwise in  FIG. 10 . The inclined angles θ  1  and θ  2  are determined corresponding to the rotational direction of the ring gear  55 .  
      In the same manner as described above, each gear-side engagement nail  69   b  includes a first inclined surface  69   c  and a second inclined surface  69   d  so that the gear-side engagement nails  69   b  are engaged with the engagement nails  58 . Therefore, when the ring gear  55  is about to rotate counterclockwise in  FIG. 10 , the ring gear  55  is locked against rotation because of a contact of the second inclined surfaces  58   b  and the second inclined surfaces  69   d , both of which have sharp inclined angles, as illustrated in  FIG. 10A . On the other hand, when the engagement nails  58  are re-engaged with the gear-side engagement nails  69   b  after disengagement, the engagement nails  58  and the gear-side engagement nails  69   b  may be shifted from desired original engagement positions, and each nail may run on a tooth top of a corresponding nail, as illustrated in  FIG. 10B . Here, as the ring gear  55  rotates counterclockwise in  FIG. 10B , the engagement nails  58  and the gear-side engagement nails  69   b  slowly slides on each other along the first inclined surfaces  58   a  and  69   c  and return to the original engagement positions. Therefore, the displacement of the engagement nails  58  and the gear-side engagement nails  69   b  from the original engagement positions is slowly absorbed.  
      As illustrated in  FIG. 3 , a releasing lever  76 , which is made of a plate, is supported by the main body  11  to be pivotably rotatable about a second rotational axis O 2 , which is shifted from a first rotational axis O 1  to the one side (left in  FIG. 3 ). This releasing lever  76  is arranged to be shifted to an axially one side (toward the nearside in a perpendicular direction to a sheet of  FIG. 3 ) relative to the open lever  12  and is formed with a plate-made cam portion  76   a  being bent to the other side (toward the nearside in a perpendicular direction to a sheet of  FIG. 3 ) so as to be arranged on a pivot-movement path of the open lever  12  at the upper side of the other end  12   b  of the open lever  12 . Therefore, as the open lever  12  pivots clockwise in  FIG. 3  about the first rotational axis O 1 , the cam portion  76   a  comes in contact with a surface of the other end  12   b  of the open lever  12  and the releasing lever  76  pivots clockwise about the second rotational axis O 2 . In a state in which the open lever  12  is retained at the predetermined pivot position illustrated in  FIG. 3 , the releasing lever  76  is retained at a predetermined pivot position with the second rotational axis O 2  while the cam portion  76   a  is in engagement with the other end  12   b  of the open lever  12 . The releasing lever  76  is further formed with an attachment portion  76   b  extending to the one side thereof (left in  FIG. 3 ), and the attachment portion  76   b  is lifted up in response to clockwise rotation of the releasing lever  76  about the second rotational axis O 2 .  
      In the main body  11 , an end  72   b  of the outer tube  72  of the canceling cable  71  is supported at the lower side of the releasing lever  76  (attachment portion  76   b ). The attachment portion  76   b  of the releasing lever  76  supports the other end  73   b  of the wire  73  pulled out of the end  72   b . Therefore, as the releasing lever  76  rotates clockwise in  FIG. 3  about the second rotational axis O 2 , the wire  73  is pulled out of the end  72   b  of the outer tube  72 . Here, the wire  73 , which is supported at the side of the lever  70 , is pulled into the end  72   a  of the outer tube  72 . Therefore, the releasing lever  66  rotates against the biasing force of the lever biasing spring  67 . The gear-side engagement nails  69   b  of the canceling gear  69  are disengaged from the engagement nails  58  of the ring gear  55  so that the ring gear  55  is allowed to rotate. That is, when either the outside door handle  4  or the inside door handle  5  is operated for a door opening operation, the attachment portion  76   b  is lifted up via the open lever  12 . Therefore, the ring gear  55  is allowed to rotate and the planetary carrier  60  (output shaft  49 ) is discontinued from outputting rotational force. That is, releasing means is configured with the releasing lever  76 , the releasing lever  66 , the lever  70 , the canceling cable  71  and so on. According to the embodiment of the present invention, the releasing lever  76 , which is operatively associated with engagement or disengagement between the ring gear  55  and the canceling gear  69 , is separated from the open lever  12 . Therefore, even when a return operation of the releasing lever  76 , which responds to releasing of a door handle operation, is implemented insufficiently, the insufficient return operation does not influence on a return operation of the open lever  12 , i.e., a return operation of either the outside door handle  4  or the inside door handle  5 .  
      Described below is an entire operation of the apparatus according to the embodiment of the present invention. First of all, the door  1  is assumed to be at the half-closed state or the fully closed state and the latch mechanism  20  is at the half-latched state or the fully latched state as illustrated in  FIG. 5  or  6 . In such circumstances, as the outside door handle  4  is manipulated for an opening operation of the door  1 , this operation force of the outside door handle  4  is transmitted to the open lever  12 . The open lever  12  then pivotably rotates about the first rotational axis O 1  clockwise in  FIG. 3  and the other end  12   b  of the open lever  12  is lifted up. The open link  14 , which is illustrated in  FIG. 4 , is lifted in response to lifting of the other end  12   b  of the open lever  12  such that the distal end  15   a  of the lift lever  15  is pushed from below by the flange  14   a  of the open link  14 . Therefore, the lift lever  15  rotates and the pole  24 , which rotates integrally with the lift lever  15 , rotates clockwise in  FIG. 5  or  6 , wherein the engagement of the engagement portion  24   a  with the first engagement portion  21   d  or the second engagement portion  21   e  is released. As a result, the latch  21  is biased by the latch biasing spring  22  and rotates clockwise in  FIG. 5  or  6  while the inner wall surface of the engagement recess  21   a  is pushing the striker  3 . The striker  3  is disengaged from the engagement recess  21   a  and the door  1  is allowed to open.  
      Meanwhile, as the inside door handle  5  is manipulated for an opening operation of the door  1 , this operation force of the inside door handle  5  is transmitted to the inside open lever  16 . The inside open lever  16  rotates about the rotational axis O counterclockwise in  FIG. 4  and the distal end  16   a  is lifted up. The flange  14   a  of the open link  14  is pushed from below by the distal end  16   a  of the inside open lever  16 . The open link  14  is lifted such that the pole  24  rotates integrally with the lift lever  15 . Therefore, the striker  3  is disengaged from the engagement recess  21   a  of the latch  21  and the door  1  is allowed to open. Even when the inside open lever  16  rotates, the open lever  12  rotates lifting up the other end  12   b  in response to lifting of the open link  14 .  
      Next, the door  1  is assumed to be at the half-closed state and the latch mechanism  20  is at the half-latched state as illustrated in  FIG. 5 . Besides, neither the inside door handle  4  nor the outside door handle  5  are operated, and the ring gear  55  is locked against rotation with the engagement nails  58  gear-meshed with the gear-side engagement nails  69   b , as illustrated in  FIG. 8A . Here, as the electric motor  47  is actuated and rotational torque is transmitted to the sun gear  51  clockwise in  FIG. 8 , the planetary carrier  60  (output shaft  49 ) outputs rotational power in the same direction, i.e., clockwise in  FIG. 8 . The drive lever  62  then rotates counterclockwise in  FIG. 7  in response to the outputted rotational force. The drive wire  36  is hence pulled out of the end  35   b  of the outer tube  35  and is retracted into the end  35   a  of the outer tube  35  as illustrated in  FIG. 5 . As a result, the operation lever  31  is rotated clockwise in  FIG. 5  and the striker  3  is pulled so as to engage with the engagement recess  21   a  of the latch  21 , wherein the latch mechanism  20  is controlled to the fully latched state. The closing operation of the door  1  is implemented in a manner that the door  1  is shifted from the half-closed state to the fully closed state.  
      After the door  1  has completed at the fully closed state, the electric motor  47  is reverse-driven so as to rotate the drive lever  62 , which rotates integrally with the output shaft  49  (planetary carrier  60 ), clockwise in  FIG. 7 . Here, because the electric motor  47  is driven at a relatively low load, the ring gear  55  is locked against rotation only with a small power of the canceling gear  69 . The operation lever  31  is biased by the lever biasing spring and rotates counterclockwise in  FIG. 6  while pulling the drive wire  36  from the end  35   a  of the outer tube  35   a . The operation lever  31  is retained to the predetermined pivot position (original position) by the lever stopper  32 . In such cases, the planetary gear mechanism  50  operates at a relatively low load. Although fluctuations may occur among each gear of the planetary gear mechanism  50  (sun gear  51 , ring gear  55 , planetary gears  59 ), such fluctuations are absorbed by the elastic body  59   b.    
      Meanwhile, either the inside door handle  4  or the outside door handle  5  is assumed to have been operated for opening the door  1  while the electric motor  47  is activating, i.e., when the door  1  is closing. In such circumstances, the open lever  12  is transmitted with operation force of the door handle and is rotated about the first rotational axis O 1  so as to lift the other end  12   b  of the open lever  12 . The releasing lever  76  is pushed upward with the cam portion  76   a  in contact with the other end  12   b  and rotates about the second rotational axis O 2  clockwise in  FIG. 3 , wherein the attachment portion  76   b  of the releasing lever  76  is lifted up. Accordingly, the wire  73  is pulled out of the end  72   b  and is retracted into the end  72   a . Therefore, the releasing lever  66  is rotated clockwise in  FIG. 8  integrally with the lever  70 , and the gear-side engagement nails  69   b  of the canceling gear  69  are disengaged from the engagement nails  58  of the ring gear  55 , wherein the ring gear  55  is allowed to rotate. The planetary carrier  60  (output shaft  49 ) is discontinued from outputting rotational force. Here, because the planetary gear mechanism  50  operates at a relatively low load, fluctuations may occur among gears of the planetary gear mechanism  50  (sun gear  51 , ring gear  55 , planetary gears  59 ). Such fluctuations are absorbed by the elastic body  59   b . The latch mechanism  20  is shifted to the unlatched state in response to the door opening operation of either the inside door handle  4  or the outside door handle  5 . The operation lever  31 , which is in engagement with the latch  21  for shifting the latch from the half-latched state to the fully latched state, is disconnected from power transmission via the planetary gear mechanism  50 , such that the operation lever  31  allows the latch mechanism  20  to shift to the unlatched state. As a result, the door  1  is allowed to open.  
      Once the inside door handle  4  or the outside door handle  5  is stopped from being operated in the above-described state, the releasing lever  66  is biased by the lever biasing spring  67  and returns to the predetermined pivot position. The canceling gear  69  moves along the guiding groove  45   g  in a way that the gear-side engagement nails  69   b  of the canceling gear  69  are engaged with the engagement nails  58  of the ring gear  55 , wherein the ring gear  55  is locked against rotation. As the lever  70  rotates clockwise in  FIG. 7  in response to rotation of the releasing lever  66 , the wire  73  is pulled out of the end  72   a  of the outer tube  72  and is pulled into the end  72   b . Therefore, when the releasing lever  76  rotate counterclockwise in FIG.  3 , the cam portion  76   a  returns and is retained at the predetermined pivot position at which the cam portion  76   a  is engaged with the other end  12   b  of the open lever  12 .  
      As described above, the following effects are obtained according to the embodiment of the present invention.  
      (1) The central engaged portion of the worm  48  and the worm wheel portion  54  and the central engaged portion of the sun gear  51  (sun gear portion  52 ), the ring gear  55  (gear portion  57 ) and the planetary gears  59  are arranged on the same plane P. The electric motor  47  is positioned on the basis of the rotational shaft  47   a  which defines the central engaged portion of the worm  48  and the worm wheel portion  54  such that the electric motor  47  is positioned so as not to away from the central engaged portion along the axial direction of the planetary gear mechanism  50 . The entire thickness of the actuator  40  is reduced. Further, the assembling performance of the actuator  40  inside the door  1 , in which an assembling space is limited, is enhanced.  
      Further, the central engaged portion of the worm  48  and the worm wheel portion  54  and the central engaged portion of the sun gear  51  (sun gear portion  52 ), the ring gear  55  (gear portion  57 ) and the planetary gears  59  are arranged on the same plane P. Therefore, it is possible to avoid occurrences of fluctuations or rattles of an axis which may occur due to torque generation associated with rotation transmission. This leads to reduction in load loss of rotational force transmission due to such fluctuation or rattles of the axis, and further leads to improvement in load efficiency of each component, which reduces a cost overall.  
      (2) The worm wheel portion  54  is formed at an outer peripheral surface of an enclosed portion, which exhibits a cylindrical shape with a bottom and houses the ring gear  55  therein, with a simple structure. Therefore, without interfering with the ring gear  55 , the worm wheel portion  54  enables to position the central engaged portion of the worm  48  and the worm wheel portion  54  and the central engaged portion of the sun gear  51  (sun gear portion  52 ), the ring gear  55  (gear portion  57 ) and the planetary gears  59  on the same plane P.  
      (3) The door closing apparatus for a vehicle according to the embodiment of the present invention is provided with the actuator  40  that is thinner and downsized, which downsizing the door closing apparatus. Especially, when this type of door closing apparatus is mounted inside the door  1 , a freedom for mounting the actuator  40  is enhanced in the thickness direction of the door  1 .  
      Conventionally, according to JP2002-250165A, when torque transmission is disconnected between an electric motor and an output shaft in response to a door opening operation of a door handle, a canceling gear retracts and the engagement between its toothed portion and an external toothed portion of a ring gear is released. Here, the ring gear keeps rotating by a load-side inertia force and stops rotating with the external toothed portion being shifted from the original engagement position. Therefore, when the first and second engagement portions are re-engaged after releasing the operation of the door handle, each tooth may run on a tooth top of a corresponding tooth. Therefore, when rotational torque of the electric motor is inputted next, a canceling gear is occasionally dropped or depressed towards the ring gear suddenly by an amount at which the tooth have run on a corresponding tooth top, which may cause a noise (slapping sound). The door closing apparatus according to the embodiment of the present invention can restrain such noise occurrences at a time that the electric motor is driven.  
      (4) According to the embodiment of the present invention, the engagement nails  58  and the gear-side engagement nails  69   b  are each formed to have a serrated structure so that the engagement nails  58  and the gear-side engagement nails  69   b  are engaged smoothly in a rotational direction of the ring gear  55 . Therefore, even if the above-described tooth running on each corresponding tooth top occurs, this tooth running, i.e., this shifting is absorbed when the sun gear  51  is rotated. As described above, it is possible to prevent occurrences of noise (e.g., slapping sound) which is created due to the sudden movement of the canceling gear  69  by an amount of such tooth running in the event that the engagement nails  58  and the gear-side engagement nails  69   b  return to the original engagement positions. Further, after the engagement nails  58  and the gear-side engagement nails  69   b  return to the original engagement positions, the ring gear  55  is locked so as not to rotate with the second inclined surfaces  58   b  and  69   d  being engaged.  
      (5) In a state where the ring gear  55  is locked against rotation, the planetary carrier  60  rotates at a slower speed than the rotating speed of the sun gear  51  actuated by the electric motor  47 . Therefore, the planetary carrier  60  outputs higher rotational force. As a result, a power, which is required for shifting the door  1  from the half-closed state to the fully closed state, is obtained by a downsized electric motor  47 .  
      (6) According to the embodiment of the present invention, the ring gear  55  is locked not to rotate with a simple structure. More specifically, the canceling gear  69  is movable to one or the other side along the radial direction of the ring gear  55 , and the gear-side engagement nails  69   b  are engaged with or disengaged from the engagement nails  58 . When the canceling gear  69  is moved to the one side, the gear-side engagement nails  69   b  are engaged with the engagement nails  58 , in which the ring gear  55  is locked not to rotate. On the other hand, when the canceling gear  69  is moved to the other side, the gear-side engagement nails  69   b  are disengaged from the engagement nails  58 , in which the ring gear  55  is allowed to rotate.  
      (7) According to the embodiment of the present invention, the releasing lever  66  is pivotably rotated with the engagement pin  69   a  fitted into or engaged with the cam hole  66   c . A linear movement of the canceling gear  69 , which is associated with the engagement and disengagement of the engagement nails  58  and the gear-side engagement nails  69   b , is achieved with a simple structure by which the pivot rotation of the releasing lever  66  is converted to the linear movement of the canceling gear  69 . When both of the handles  4  and  5  are released from being operated, the releasing lever  66  is biased by the lever biasing spring  67  so as to rotate in one direction, wherein the engagement nails  58  and the gear-side engagement nails  69   b  are engaged with each other and are retained in an engaged manner.  
      (8) According to the embodiment of the present invention, the door closing apparatus includes the wire  73  (canceling cable  71 ) which transmits the operation force of the door handle  4  or  5  to the canceling gear  69 . Therefore, a location of the wire  73  effectively increases a freedom for placement of mechanical linkages between the canceling gear  69  and the door handles  4  and  5 .  
      (9) According to the embodiment of the present invention, the drive wire  46  (drive cable  34 ) is provided, which transmits rotational power outputted from the planetary carrier  60  (output shaft  49 ) to the latch mechanism  20 . Therefore, a location of the drive wire  36  effectively increases a freedom for placement of mechanical linkages between the planetary carrier  60  (planetary gear mechanism  50 ) and the latch mechanism  20 .  
      According to the door closing apparatus disclosed in JP2002-250165A, when torque transmission is disconnected between an electric motor and an output shaft in response to an operation of a door handle for opening the door, a canceling gear retracts and its toothed portion is disengaged from an external toothed portion of a ring gear. Here, a planetary gear mechanism operates at a relatively low load. Likewise, when the output shaft (planetary gear mechanism) returns to the original rotational position, which is set before an electric motor is driven after completely shifting the door from the half-closed state to the fully closed state, the planetary gear mechanism is operated at a relatively low load. In general, a planetary gear mechanism is designed to have a backlash greater than a normal gear unit. Therefore, when the planetary gear mechanism is operated at a relatively low load, fluctuations among gears of the planetary gear mechanism may occur and a noise (gearing noise) may be created. However, according to the embodiment of the present invention, it is possible to restrain noise occurrences in the event that the planetary gear mechanism is operated at a relatively low load.  
      (10) According to the embodiment of the present invention, when the ring gear  55  is locked not to rotate with the canceling gear  69  engaged with the ring gear  55 , the planetary carrier  60  (output shaft  49 ) outputs rotational force in response to a rotation of the sun gear  51 . When this rotational power is transmitted to the latch mechanism  20 , the door  1  is shifted from the half-closed state to the fully closed state. On the other hand, when the canceling gear  69  is transmitted with operation force of either the inside door handle  4  or the outside door handle  5  and the canceling gear  69  is disengaged from the ring gear  55 , the ring gear  55  is allowed to rotate. As a result, the planetary carrier  60  (output shaft  49 ) stops outputting rotational power and the door  1  is discontinued from moving from the half-closed state to the fully closed state. Here, the planetary gear mechanism  50  is operated at a relatively low load, and fluctuations may occur among gears (sun gear  51 , ring gear  55 , planetary gears  59 ) of the planetary gear mechanism  50 . Such fluctuations are absorbed by the elastic body  59   b  and noise (gearing sound) is prevented from occurring.  
      Further, in a situation where the door  1  has shifted from the half-closed state to the fully closed state, even when the planetary carrier  60  (planetary gear mechanism  50 ) is required to return to the original position, which is set before the electric motor is driven, for the purpose of returning the operation lever  31  to the original position, the planetary gear mechanism  50  is operated at a relatively low load. Even in this case, noise (gearing noise) can be prevented from occurring.  
      Still further, when the planetary carrier  60  (output shaft  49 ) outputs rotational force in order to shift the door  1  from the half-closed state to the fully closed state, each gear (sun gear  51 , ring gear  55 , planetary gears  59 ) of the planetary gear mechanism  50  rotates being pushed in one direction. Therefore, such noise may not occur.  
      (11) According to the embodiment of the present invention, the elastic body  59   b  is arranged at an axial portion of the sun gear  51  (sun gear portion  52 ), the ring gear  55  (gear portion  57 ) and the planetary gears  59 . Therefore, it is possible to restrain occurrences of noise (gearing noise).  
      (12) According to the embodiment of the present invention, the wall portion  41   b  of the bracket  41  is fixed to the supporting bracket  42  with the fastened portion  41   c  being inserted into the engagement hole  42   a . The fastened portion  41   c  is fixed to the supporting bracket  42 . Therefore, the end  35   b  is housed in the housing portion  41   d  and is prevented from dropping in a radial direction between the supporting bracket  42  and the housing portion  41   d . As described above, because the end  35   b  is retained only by fixing a single plate (wall portion  41   b ) to the supporting bracket  42 , an assembling performance is enhanced. Further, the wall portion  41   b  is fixed to the supporting bracket  42  only by fastening the fastened portion  41   c  (one side of the wall portion  41   b ) to the supporting bracket  42 , which improves workability.  
      (13) Especially, a direction for fastening the bolt approximately corresponds to a radial direction of the end  35   b  that has less limitation in a space, which improves workability. Further, it requires only a single bolt, which reduces the total number of components.  
      The following modifications are available. According to the embodiment of the present invention, torque transmission between the electric motor  47  and the sun gear  51  is achieved by a speed reduction gear set having the worm  48  and the worm wheel portion  54 . Alternatively, torque transmission between the electric motor  47  and the sun gear  51  can be achieved by engaging helical gears. In this case, rotational speed, which is transmitted from the electric motor  47  to the sun gear  51 , can be reduced, increased or maintained at the same speed level.  
      According to the embodiment of the present invention, the cam hole  66   c  and the engagement pin  68   a , which are associated with an engagement between the releasing lever  66  and the canceling gear  69 , can be formed at the side of the canceling gear  69  and the releasing lever  66 , respectively.  
      According to the embodiment of the present invention, the drive cable  34  is provided, which connects the operation lever  31  of the door latch unit  10  and the drive lever  62  of the actuator  40  and transmit driving force. Alternatively, the operation lever  31  and the drive lever  62  can be gear-connected directly or can be connected via a linking mechanism so as to transmit driving force.  
      According to the embodiment of the present invention, the canceling cable  71  is provided, which connects the releasing lever  76  and the lever  70  of the actuator  40 , which are associated with opening operations of the door handles  4  and  5 . Alternatively, the releasing lever  76  and the lever  70  can be gear-connected directly or connected via a linking mechanism so as to transmit operation force.  
      According to the embodiment of the present invention, the sun gear  51 , the ring gear  55  and the planetary carrier  60  can be any of the input shaft, the fixed shaft and the output shaft which all are different.  
      According to the embodiment of the present invention, the elastic body  59   b , which is arranged at an axial portion of each planetary gear  59 , is secured to the side of each planetary gear  59  (gear main body  59   a ). Alternatively, the elastic body  59   b  can be secured to the side of the supporting shaft  61 . Still alternatively, a bushing, which is made of an elastic material, can be interposed between the supporting shaft  61  and the planetary gear  59  without being secured to either of them.  
      According to the embodiment of the present invention, an elastic body can be arranged at an axial portion of the sun gear  51  (sun gear portion  52 ). In this case, the elastic body can be secured to the side of the sun gear  51  (bearing bore  52   a ) or can be secured to the side of the output shaft  49 . Or, a bushing, which is made of an elastic material, can be interposed therebetween without being secured to either of them.  
      According to the embodiment of the present invention, an elastic body can be arranged at an axial portion of the ring gear  55  (gear portion  57 ). In this case, the elastic body can be secured to the side of the ring gear  55  (bearing bore  56   a ) or can be secured to the side of the housing  44  (projection  45   f ). Or, a bushing, which is made of an elastic material, can be interposed therebetween without being secured to either of them.  
      According to the embodiment of the present invention, an elastic material, which forms an elastic body, can be for example elastomer, natural rubber, synthetic rubber or the like.  
      According to the embodiment of the present invention, the sun gear  51 , the ring gear  55  and the planetary carrier  60  can be any of the input shaft, the fixed shaft and the output shaft which all are different. However, in all cases, in order to perform power transmission reliably, it is preferable that an elastic body is positioned at an axial portion of the output shaft or the fixed shaft not at an axial portion of the input shaft.  
      According to the embodiment of the present invention, the housing portion  41   d  can be formed with a curved or bent portion, which elastically makes a contact with the end  35   b . In this case, it is possible to absorb rattle or looseness of the drive cable  34  in the housing portion  41   d.    
      According to the embodiment of the present invention, the wall portion  41   b , which serves as a supporting plate, is formed integrally with the bracket  41  which secures and supports the actuator  40  at the door latch unit  10 . However, the wall portion  41   b  can be a member separated from the bracket  41 .  
      As described above, a driving mechanism includes: a drive gear fixed at a rotational shaft of a motor; a sun gear rotatably provided and having a gear portion engaged with the drive gear; a ring gear arranged coaxially with the sun gear, the ring gear being locked not to rotate relative to the sun gear and being allowed to rotate relative to the sun gear; a planetary gear engaged with the sun gear and the ring gear; and a planetary carrier arranged coaxially with the sun gear and connected to the planetary gear. The planetary carrier outputs rotational force in response to rotation and revolution of the planetary gear operatively associated with rotation of the sun gear and relative to the ring gear locked not to rotate. A central engaged portion of the driving gear and the gear portion and a central engaged portion of the sun gear, the ring gear and the planetary gear are arranged on the same plane.  
      As described above, the central engaged portion of the drive gear and the gear portion and the central engaged portion of the sun gear, the ring gear and the planetary gear (planetary gear mechanism) are arranged on the same plane. The motor is positioned on the basis of the rotational shaft defining the central engaged portion of the dive gear and the gear portion. Therefore, the motor is positioned not being shifted to one axial side of the planetary gear mechanism, wherein an entire thickness of the driving mechanism becomes thinner.  
      The central engaged portion between gears is an arbitrary position within a range in which the gears are in contact with each other and may not be the accurate center. Further, as described above, when the central engaged portions are arranged on the same plane, all the central engaged portions are positioned on a predetermined imaginary surface perpendicular to an axis within an axial range of the sun gear.  
      It is preferable that the sun gear has a cylindrical box-shaped portion with a bottom, the box-shaped portion housing the ring gear formed at an outer peripheral surface of the box-shaped portion.  
      According to this structure, the gear portion exhibits a simple structure and is formed in a manner that the central engaged portion of the drive gear and the gear portion is arranged on the same plane as the central engaged portion of the sun gear, the ring gear and the planetary gear, while not interfering with the ring gear.  
      It is preferable that a door closing apparatus includes the driving mechanism; a latch mechanism holding a door for a vehicle at a half-closed state and a fully closed state; power transmitting means for transmitting force outputted by the planetary carrier to the latch mechanism in a state where the locking member is engaged with the ring gear so that the latch mechanism is operated to shift the door from the half-closed state to the fully closed state; and releasing means for transmitting an operation force to a locking member and releasing an engagement between the locking member and the ring gear regardless of the force transmission by the power transmitting means.  
      According to the above-described structure, when the ring gear is locked not to rotate with the engagement portion being engaged with the locking member, the planetary gear mechanism is operated. Here, the sun gear is driven to rotate and rotational force is outputted from the planetary gear mechanism. The rotational force is then transmitted to the latch mechanism via the power transmitting means and the door is moved from the half-closed state to the fully closed state. On the other hand, when the operation force is transmitted to the locking member via the releasing means, the locking member is disengaged from the ring gear. The ring gear is hence allowed to rotate and the planetary carrier is discontinued from outputting rotational force, wherein the door closing operation, in which the door is moved from the half-closed state to the fully closed state, is stopped. Such door closing apparatus is provided with a thinner and downsized driving mechanism such that the apparatus itself is downsized. Especially, when such door closing apparatus is mounted inside the vehicle door, it is possible to enhance freedoms for placement in the thickness direction of the door, i.e., in a width direction of a vehicle.  
      Further, a door closing apparatus for a vehicle includes a planetary gear mechanism having a sun gear, a ring gear, a planetary gear and a planetary carrier. An input shaft is selected from among the sun gear, the ring gear, the planetary gear and is rotatably driven by an electric motor. A fixed shaft is selected from among the sun gear, the ring gear and the planetary gear and is different from the input shaft. An output shaft is selected from among the sun gear, the ring gear, the planetary gear and is different from the input shaft and the fixed shaft. The door closing apparatus for the vehicle further includes: a first engagement portion formed at the fixed shaft of the planetary gear mechanism; a latch mechanism holding a door of the vehicle at a half-closed state and a fully closed state; a locking member having a second engagement portion. The locking member locks the fixed shaft not to rotate with the second engagement portion engaged with the first engagement portion of the fixed shaft and unlocks the fixed shaft to rotate with the second engagement portion disengaged from the first engagement portion of the fixed shaft. The door closing apparatus still further includes power transmitting means for transmitting force outputted by the output shaft to the latch mechanism so that the latch mechanism is operated to shift the door from the half-closed state to the fully closed state in a state where the locking member is engaged with the ring gear; and switching means for switching an engagement or disengagement between the first engagement portion and the second engagement portion. The switching means releases an engagement between the first engagement portion and the second engagement portion by transmitting an operation force to the locking member and engages the first engagement portion and the second engagement portion by discontinuing transmission of the operation force to the locking member, regardless of the force transmission by the power transmitting means. The first engagement portion and the second engagement portion are formed in a serrated manner so that the first engagement portion and the second engagement portion are engaged smoothly in a rotational direction of the fixed shaft.  
      As described above, once the fixed shaft is locked not to rotate in response to the engagement between the first engagement portion and the second engagement portion, the planetary gear mechanism is operated. That is, the input shaft is driven to rotate and rotational force is outputted from the output shaft. When the latch mechanism is transmitted with rotational force via the power transmitting means, the door for the vehicle is operated from the half-closed state to the fully closed state. On the other hand, the first engagement portion is disengaged from the second engagement portion when the operation force is transmitted to the locking member via the switching means, wherein the fixed shaft is allowed to rotate. The output shaft then stops outputting rotational force and a door closing operation, in which the door is moved from the half-closed state to the fully closed state, is interrupted. After than, in response to releasing of the operation of the door handle, the first engagement portion and the second engagement portion are re-engaged each other by the switching means. Here, there are cases in which the first and second engagement portions are shifted from the original engagement position and each tooth may run on a corresponding tooth top. However, according to the embodiment of the present invention, the first and second engagement portions are formed in a serrated manner so as to be engaged with each other smoothly in a rotational direction of the fixed shaft. Therefore, such tooth-shifting amount can be absorbed smoothly. As a result, when the first and second engagement portions return to original engagement positions, it is possible to restrain occurrences of noise (slapping sound) which may occur in the invent that the locking member moves suddenly by the tooth-shifting or running amount.  
      It is preferable that the input shaft, the fixed shaft and the output shaft are the sun gear, the ring gear and the planetary carrier, respectively.  
      According to this structure, when the ring gear is locked against rotation, the planetary carrier rotates slowly relative to the sun gear driven to rotate by the electric motor and obtains higher rotational torque. Therefore, power, which is required to move the door from the half-closed state to the fully closed state, is obtained by a downsized electric motor.  
      It is preferable that the locking member is provided to be movable in a radial direction of the fixed shaft, the second engagement portion of the locking member is engaged with the first engagement portion in response to a movement of the locking member to a radial one side of the fixed shaft and is disengaged from the first engagement portion in response to a movement of the locking member to the other radial side of the fixed shaft.  
      According to this structure, the first and second engagement portions are engaged with each other with a simple structure in which the locking member is moved to the radial one side of the fixed shaft, wherein the fixed shaft is locked not to rotate. Meanwhile, the first and second engagement portions are disengaged from each other with a simple structure in which the locking member is moved to the radial other side of the fixed shaft, wherein the fixed shaft is allowed to rotate.  
      It is preferable that the locking member includes a locking member-side engagement portion, the switching means includes a cam-side engagement portion engageable with the locking member-side engagement portion. The door closing apparatus can further includes: a cam member rotated in one direction and moving the locking member to the radial one side of the fixed shaft so that the second engagement portion of the locking member is engaged with the first engagement portion of the fixed shaft and rotated in the other direction on the basis of the operation force and moving the locking member to the radial other side of the fixed shaft so that the second engagement portion of the locking member is disengaged from the first engagement portion of the fixed shaft; and biasing means for biasing the cam member to rotate in the one direction.  
      According to this structure, a linear movement of the locking member, which is associated with the engagement and disengagement of the first and second engagement portions, is achieved with a simple structure by which the pivot rotation of the cam member is converted to the linear movement of the locking member. When the operation force transmission is disconnected, the cam member is biased by the biasing means so as to rotate in one direction, wherein the first and second engagement portions are engaged with each other and are retained in an engaged manner.  
      It is preferable that the operation force is an operation force for operating a door handle in order to open the door, and the switching means has a wire for transmitting the operation force of the door handle to the locking member.  
      According to this structure, the switching means includes a wire for transmitting the operation force of the door handle to the locking member. Therefore, a location of the wire effectively increases a freedom for placement of mechanical linkages between the locking member and the door handle.  
      It is preferable that the power transmitting means includes a drive wire for transmitting the force outputted by the output shaft to the latch mechanism.  
      According to this structure, a location of the drive wire effectively increases a freedom for placement of mechanical linkages between the output shaft (planetary gear mechanism) and the latch mechanism. Especially, when this structure is employed, it is possible to enhance a freedom for placement of the apparatus itself.  
      Still further, a door closing apparatus for a vehicle includes: a planetary gear mechanism having a sun gear, a ring gear, a planetary gear and a planetary carrier. An input shaft is selected from among the sun gear, the ring gear, the planetary gear and is rotatably driven by an electric motor. A fixed shaft is selected from among the sun gear, the ring gear and the planetary gear and is different from the input shaft. The fixed shaft is locked not to rotate by being engaged with a locking member and is unlocked to rotate by being disengaged from the locking member. An output shaft is selected from among the sun gear, the ring gear, the planetary gear and is different from the input shaft and the fixed shaft. The door closing apparatus further includes: a latch mechanism holding a door of the vehicle at a half-closed state and a fully closed state; power transmitting means for transmitting force outputted by the output shaft to the latch mechanism so that the latch mechanism is operated to shift the door from the half-closed state to the fully closed state in a state where the locking member is engaged with the ring gear; and switching means for switching an engagement or disengagement between the locking member and the fixed shaft. The switching means releases an engagement between the locking member and the fixed shaft by transmitting an operation force to the locking member and engages the locking member and the fixed shaft by discontinuing transmission of the operation force to the locking member, regardless of the force transmission by the power transmitting means. The door closing apparatus further includes an elastic body provided at an axial portion of at least one of the sun gear, the ring gear and the planetary gear.  
      As described above, when the fixed shaft is locked against rotation with the engagement between the locking member and the fixed shaft, the planetary gear mechanism is operated. Therefore, the input shaft is driven to rotate and rotational force is outputted from the output shaft. When the rotational force is transmitted to the latch mechanism via the power transmitting means, the vehicle door is moved from the half-closed state to the fully closed state. On the other hand, when the operation force is transmitted to the locking member by the switching means, the engagement between the locking member and the fixed shaft is released. The fixed shaft is allowed to rotate, wherein the output shaft stops outputting rotational force and the door closing operation, in which the door is moved from the half-closed state to the fully closed state, is interrupted. Here, because the planetary gear mechanism operates at a relatively low load, fluctuations or rattles may occur between gears of the planetary gear mechanism (sun gear, ring gear and planetary gears). Such fluctuations or rattles are absorbed by the elastic member and noise (gearing sound) is prevented from occurring.  
      It is preferable that the elastic body is provided at the axial portion of the planetary gear. According to this structure, it is possible to restrain occurrences of noise (gearing sound).  
      It is preferable that the input shaft, the fixed shaft and the output shaft are the sun gear, the ring gear, and the planetary carrier, respectively.  
      According to this structure, in a state where the ring gear is locked not to rotate, the planetary carrier is rotated slower than the sun gear driven to rotate by the electric motor. Therefore, it is possible to obtain higher rotational torque. In such cases, power, which is required to shift the vehicle door from the half-closed state to the fully closed state, is obtained by a downsized electric motor.  
      It is preferable that the locking member is provided to be movable in a radial direction of the fixed shaft, the locking member is engaged with the fixed shaft by moving to a radial one side of the fixed shaft and is disengaged from the fixed shaft by moving to the other radial side of the fixed shaft.  
      According to this structure, the locking member is engaged and the fixed shaft is locked against rotation with a simple structure in which the locking member is moved to the radial one side of the fixed shaft. Meanwhile, the locking member is disengaged and the fixed shaft is unlocked against rotation with a simple structure in which the locking member is moved to the radial other side of the fixed shaft.  
      It is preferable that the locking member includes a locking member-side engagement portion and the switching means includes a cam-side engagement portion engaged with the locking member-side engagement portion. The door closing apparatus can further include: a cam member rotated in one direction and moving the locking member to the radial one side of the fixed shaft so that the second engagement portion of the locking member is engaged with the first engagement portion of the fixed shaft and rotated in the other direction on the basis of an operation force and moving the locking member to the radial other side of the fixed shaft so that the second engagement portion of the locking member is disengaged from the first engagement portion of the fixed shaft; and biasing means for biasing the cam member to rotate in the one direction.  
      According to this structure, a linear movement (movement to the radial one side or the radial other side of the fixed shaft) of the locking member, which is engaged or disengaged with the fixed shaft, is achieved with a simple structure by which the pivot rotation of the cam member is converted to the linear movement of the locking member. When the operation force transmission is stopped, the cam member is biased by the biasing means so as to rotate in one direction, wherein the lock member and the fixed shaft are engaged with each other and are retained in an engaged manner.  
      It is preferable that the operation force is an operation force for operating a door handle in order to open the door, and the switching means includes a wire for transmitting the operation force to the locking member.  
      According to this structure, a location of the wire effectively increases a freedom for placement of mechanical linkages between the locking member and the door handle.  
      It is preferable that the power transmitting means includes a drive wire for transmitting the force outputted by the output shaft to the latch mechanism.  
      According to this structure, a location of the drive wire effectively increases a freedom for placement of mechanical linkages between the output shaft (planetary gear mechanism) and the latch mechanism. Especially, when this structure is employed, it is possible to enhance a freedom for placement of the apparatus itself.  
      It is preferable that the latch mechanism is transmitted with a force via a drive cable so that the door is operated from the half-closed state to the fully closed state. The door closing apparatus can further includes: a base member having an engagement bore; and a supporting plate having: an engagement portion inserted into the engagement bore and engaged at the base member; a fastened portion fastened to the base member; and a housing portion for housing an end of the drive cable and preventing the end from dropping in a radial direction relative to the base member.  
      It is further preferable that the base member is formed with a guiding portion for positioning the end of the drive cable in an axial direction.  
      According to the above-described structure, the supporting plate is secured to the base member with the engagement portion inserted into the engagement bore and fixed to the base member and with the fastened portion fastened to the base member. The housing portion houses, therein, the end of the drive cable connected to the driving mechanism, wherein the end of the drive cable is prevented from dropping or moving away. As described above, the end portion of the drive cable is secured only by fixing a single plate (supporting plate) to the base member, the assembling performance is enhanced. Further, at securely positioning the supporting plate, the one side of the supporting plate is fixed, at one side via the engagement portion, to the base member and only the other side of the supporting plate is needed to be fastened to the base member via the fastened portion. Therefore, a good workability or performance can be obtained.  
      The principles, of the preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention, which is intended to be protected, is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.