Patent Publication Number: US-2010107502-A1

Title: Opening-and-closing drive device for opening-and-closing member 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 2008-284596, filed on Nov. 5, 2008, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure generally relates to an opening-and-closing drive device for an opening-and-closing member for a vehicle. 
     BACKGROUND DISCUSSION 
     Disclosed in JP2002-242532A is an opening-and-closing drive device for an opening-and-closing member for a vehicle (which will be hereinafter referred to as an opening-and-closing drive device), that drives an opening-and-closing member, such as a trunk lid, a back door, a slide door and the like mounted at a vehicle such as an automobile, to be opened and closed by means of an electrical driving source. The opening-and-closing drive device includes an output arm, which is rotatably driven by the electrical driving source (an electric motor) provided at a vehicle body, and a hinge arm, which connects the opening-and-closing member with the vehicle body so as to be opened and closed. The output arm and the hinge arm are connected to each other. A driving force generated by the electrical driving source is transmitted to the opening-and-closing member via the output arm and the like. Accordingly, the opening-and-closing member is actuated so as to be opened and closed. 
     Furthermore, the opening-and-closing drive device disclosed in JP2002-242532A further includes an electromagnetic clutch for establishing and interrupting a power transmission between the electrical driving source and the opening-and-closing member, so that the opening-and-closing member is manually opened and closed. 
     However, because the opening-and-closing drive device disclosed in JP2002-242532A uses the electromagnetic clutch, which establishes the power transmission by displacing a disk by means of a magnetic force, a magnetic material such as iron, which conducts the magnetic force therethrough, needs to be used for the electromagnetic clutch, which may result in increasing a mass of the electromagnetic clutch. Furthermore, because a relatively large coil, which generates the magnetic force, is used, the electromagnetic clutch is also enlarged. Additionally, a control circuit for electrifying the coil, interrupting power supply to the coil and controlling power supply to the coil needs to be provided at the opening-and-closing drive device. As a result, an entire configuration of the opening-and-closing drive device disclosed in JP2002-242532A may become complicated and manufacturing costs of the opening-and-closing drive device may be increased. Additionally, a battery load may be increased because electricity is consumed when the coil is electrified. 
     Additionally, the opening-and-closing drive device disclosed in JP2002-242532A increases an output (a motor output) of the electrical driving source by means of a speed reducing gear mechanism in order to obtain a necessary output. Therefore, for example, in a case where a force is applied to the opening-and-closing member in a direction opposite to an actuating direction while the opening-and-closing member is being actuated, a significant shock load may be generated at the opening-and-closing member and the like. In this case, because the opening-and-closing drive device disclosed in JP2002-242532A does not include a portion for absorbing the shock load, a sufficient strength needs to be ensured at each of the opening-and-closing member, the hinge arm, the output arm, a gear, the electrical driving source and the like in order to endure the shock load, so that a deformation and a damage do not occur at the opening-and-closing member, the hinge arm, the output arm, the gear, the electrical driving source and the like. As a result, each of the opening-and-closing member, the hinge arm, the output arm, the gear, the electrical driving source and the like may need to be increased in size, thickness and weight. 
     A need thus exists to provide an opening-and-closing drive device for an opening-and-closing member for a vehicle which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     According to an aspect of this disclosure, an opening-and-closing drive device for an opening-and-closing member for a vehicle includes an electric driving source serving as a power source for opening and closing the opening-and-closing member, which is supported by a vehicle body so as to be opened and closed, an output portion connected to the electric driving source and transmitting a driving force generated by the electric driving source to the opening-and-closing member in order to open and close the opening-and-closing member via a connecting member; and a clutch mechanism provided on a power transmission path between the electric driving source and the output portion and including a viscous fluid for transmitting a power between the electric driving source and the output portion by viscosity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a side view illustrating an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a first embodiment; 
         FIG. 2  is an exterior view illustrating a driving unit; 
         FIG. 3  is a cross-sectional view illustrating the driving unit taken along line III-III; 
         FIG. 4  is a graph illustrating a relationship between a relative rotational speed and a torque; 
         FIG. 5  is a graph illustrating a relationship between a motor torque and a motor rotational speed; 
         FIG. 6  is a time chart illustrating a transition of the motor torque in a case where a pinch (trap) occurs; 
         FIG. 7  is a graph illustrating a relationship between the relative rotational speed and the torque; 
         FIG. 8  is a side view illustrating an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a second embodiment; 
         FIG. 9  is a plane view illustrating the opening-and-closing drive device for the opening-and-closing member for the vehicle according to the second embodiment; 
         FIG. 10  is a cross-sectional view illustrating a driving unit; 
         FIG. 11  is a cross-sectional view illustrating a driving unit according to a third embodiment; 
         FIG. 12  is a partial cross-sectional view illustrating a driving unit according to a fourth embodiment; 
         FIG. 13  is a cross-sectional view illustrating a driving unit according to a fifth embodiment; 
         FIG. 14  is a cross-sectional view illustrating a driving unit according to a sixth embodiment; 
         FIG. 15  is a graph illustrating a relationship between the relative rotational speed and the torque; 
         FIG. 16  is a time chart illustrating a transition of a motor torque in the case where a pinch occurs; 
         FIG. 17  is a cross-sectional view illustrating a driving unit according to a seventh embodiment; 
         FIG. 18  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a modified example; 
         FIG. 19  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to another modified example; 
         FIG. 20  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; 
         FIG. 21  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; 
         FIG. 22  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; 
         FIG. 23  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; 
         FIG. 24  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; 
         FIG. 25  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example; and 
         FIG. 26  is an opening-and-closing drive device for an opening-and-closing member for a vehicle according to a further modified example. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment  
     A first embodiment of an opening-and-closing drive device for an opening-and-closing member for a vehicle (which will be hereinafter referred to simply as an opening-and-closing drive device), which is adapted as an opening-and-closing drive device for a luggage panel, will be described below with reference to the attached drawings. 
     Illustrated in  FIG. 1  is a side view of a rear end portion of a vehicle, such as an automobile, to which the opening-and-closing drive device is adapted. As illustrated in  FIG. 1 , a vehicle body  10 , which defines a main body of the vehicle, includes an opening-and-closing mechanism  20 . More specifically, a pair of opening-and-closing mechanisms  20  is provided at the vehicle body  10  at both end portions thereof in a vehicle width direction (i.e. in a direction orthogonal to a sheet of paper on which  FIG. 1  is illustrated), respectively. 
     As illustrated in  FIG. 1 , each of the pair of the opening-and-closing mechanisms  20  includes a hinge arm  21 , which is obtained by bending a bar material (i.e. a column-shaped material whose cross section is formed in a quadrangle) in a U-shape, and a torsion bar link  23 . Furthermore, one of the pairs of the opening-and-closing mechanisms  20 , which is provided at the left portion of the vehicle when being viewed from a back of the vehicle towards a front portion thereof, includes an attachment member  22 , a driving unit  24 , a first link  25  and a second link  26 . The first link  25  and the second link  26  serve as an arm. 
     The hinge arms  21  are provided at the vehicle body  10  so as to freely rotatable about a rotating axis O 1 , which extends in the vehicle width direction. Furthermore, a luggage panel  11 , which serves as an opening-and-closing member, is supported at end portions of the respective hinge arms  21 . The luggage panel  11  is opened and closed in response to a rotation of the hinge arms  21  relative to the rotating axis O 1 . 
     The attachment member  22  is made of a metal plate, which is formed in a L-shape. For example, the attachment member  22  is fixed at the hinge arm  21  by welding. An end portion of the torsion bar link  23  is connected to the vehicle body  10  so as to be freely rotatable. The other end portion of the torsion bar link  23  is connected to the hinge arm  21  so as to be freely rotatable. The torsion bar link  23  biases the hinge arm  21  in a counterclockwise rotating direction in  FIG. 1  in order to assist an opening operation of the luggage panel  11 . In other words, the torsion bar link  23  generates an assisting force for opening the luggage panel  11 . 
     The driving unit  24  is fixed at the vehicle body  10 . Furthermore, the driving unit  24  rotates an output shaft  30 , which serves as an output portion, in a clockwise rotating direction in  FIG. 1  or in the counterclockwise rotating direction when the driving unit  24  is electrified. An end portion of the first link  25  is connected to the output shaft  30  so as to be rotated with the output shaft  30  as one unit. The other end portion of the first link  25  is connected to one end portion of the second link  26  so as to be freely rotatable. The other end portion of the second link  26  is connected to the attachment member  22  so as to be freely rotatable. 
     The hinge arm  21 , which is fixed at the attachment member  22 , the first link member  25  and the second link member  26  configure a quadric crank chain together with the vehicle body  10 . Accordingly, the quadric crank chain, which is actuated when the driving unit  24  (i.e. the output shaft  30 ) is rotatably driven, allows the hinge arms  21  to be pushed and pulled via the first link  25 , the second link  26  and the attachment member  22 , thereby opening and closing the luggage panel  11 , which is provided at the hinge arms  21 . Additionally, the first link  25  and the like, which relates to a power transmission between the output shaft  30  and the hinge arms  21  (the luggage panel  11 ), configures a connecting member. 
     A detailed description of the driving unit  24  will be given below. Illustrated in  FIG. 2  is a front view of the driving unit  24  when being viewed in an axial direction of the output shaft  30 . Illustrated in  FIG. 3  is a cross-sectional view of the driving unit  24  taken along line III-III in  FIG. 2 . As illustrated in  FIGS. 2 and 3 , the driving unit  24  includes a housing  31  and a cover  32 , which define an outer shape of the driving unit  24  and each of which is made of resin. The output shaft  30  is rotatably supported by first and second bearings  33  and  34 , which are supported by the housing  31  and the cover  32  respectively, so as to be concentric with the first and second bearings  33  and  34 . The first link  25  is connected to an end portion of the output shaft  30 , which outwardly protrudes from the housing  31 , so as to be rotated with the output shaft  30  as one unit. Additionally, the output shaft  30  is formed in a column shape having a step. More specifically, the output shaft  30  includes a shaft portion  30   a,  which is formed in a column shape, between the first bearing  33  and the second bearing  34  so that the shaft portion  30   a  is positioned closer to the first bearing  33  when comparing to the second bearing  34 . Furthermore, the output shaft  30  includes a fitting portion  30   b  between the first bearing  33  and the second bearing  23  so that the fitting portion  30   b,  which is formed in a column shape whose cross sectional shape is formed in a quadrangle, is positioned closer to the second bearing  34  when comparing to the first bearing  33 . 
     A speed reduction gear mechanism  36  and a clutch mechanism  40  are accommodated within an accommodating space S 1 , which is defined by the housing  31  and the cover  32 . The speed reduction gear mechanism  36  includes a worm  37  and a worm wheel  38  (a wheel gear). The worm  37  is fixed at a rotating shaft (a motor shaft) of an electric motor  35  (see  FIG. 2 ), which serves as an electric driving source. The worm wheel  38  is engaged with the worm  37  and is supported by the shaft portion  30   a  of the output shaft  30  so as to be freely rotatable. Accordingly, when power is supplied to the electric motor  35  and the electric motor  35  is rotatably driven, a rotation of the worm  37 , which is rotated with the rotating shaft of the electric motor  35  as one unit, is transmitted to the worm wheel  38 . As a result, the worm wheel  38  is rotated about the shaft portion  30   a  of the output shaft  30 . The speed reduction gear mechanism  36  decelerates a rotational speed of the worm  37  in response to a transmission ratio established between the worm  37  and the worm wheel  38 , so that the decelerated rotational speed is transmitted to the worm wheel  38 . 
     The worm wheel  38  includes a protruding wall portion  38   a,  which protrudes towards the clutch mechanism  40  in the axial direction so as to form a cylinder shape and so as to face the clutch mechanism  40 . As illustrated in a schematic exterior view of a portion of the speed reduction gear mechanism  36  in  FIG. 3  when being viewed in the axial direction of the output shaft  30 , the protruding wall portion  38   a  includes plural recessed portions  38   b  (in this embodiment, four recessed portions  38   b ) on a surface of the protruding wall portion  38   a  facing the clutch mechanism  40  while being spaced away therefrom so as to form equal angles between the neighboring recessed portions  38   b.    
     The clutch mechanism  40  includes a rotor  41 , which serves as an output-side member, and a housing  42 , which serves as an input-side member. The rotor  41  includes a cylinder portion  41   a  formed in a cylinder shape and having a fitting bore, which is formed in a quadrangle and into which the fitting portion  30   b  is inserted. Furthermore, the rotor  41  includes a flange portion  41   b,  which outwardly extends in a radial direction of the cylinder portion  41   a  and whose cross sectional view is formed in a chaser-tooth shape. 
     The housing  42  includes a housing main body  43 , a cover  44  and a base  45 . The housing main body  43  includes a cylinder portion  43   a,  which is formed in a cylinder shape and whose inner diameter is set to be equal to an outer diameter of the cylinder portion  41   a.  Furthermore, the housing main body  43  includes a flange portion  43   b,  which outwardly extends from the cylinder portion  43   a  in a radial direction thereof and whose cross sectional view is formed in a chaser-tooth shape. Furthermore, the flange portion  43   b  is formed so that the chaser-tooth shape thereof alternates with the chase-tooth shape of the flange portion  41   b,  so that the flange portion  41   b  and the flange portion  43   b  are engaged with each other while forming a slight clearance therebtween. The cylinder portion  41   a  is fluid-tightly inserted into the cylinder portion  43   a  of the housing main body  43 . Furthermore, the flange portion  41   b  is fitted with the flange portion  43   b,  so that the flange portion  43   b  is connected to the rotor  41  so as to be rotatable relative to the rotor  41 . Additionally, the housing main body  43  includes plural protruding portions  43   c  protruding towards the second bearing  34  in the axial direction. 
     Each of the cover  44  and the base  45  is formed in an annular shape. The cover  44  is positioned closer to the second bearing  34  than the worm wheel  38 . The base  45  is positioned closer to the worm wheel  38  than the second bearing  34 . The cover  44  and the base  45  are arranged so as to face each other in the axial direction and are integrally connected by means of calks  45   a  at outer circumferential portions of the cover  44  and the base  45 . The rotor  41  and the housing main body  43  are fluid-tightly accommodated within an inner space defined by the cover  44  and the base  45 . Additionally, a clearance between the rotor  41  and the housing main body  43  is filled with a viscous fluid F. Accordingly, the housing  42  accommodates therein the rotor  41  together with the viscous fluid F. 
     The cover  44  includes plural fitting bores  44   a,  into which the respective protruding portions  43   c  are inserted, so as to penetrate the cover  44  in the axial direction. The base  45  includes plural protruding portions  45   b,  which are fitted into the respective recessed portions  38   b,  so as to protrude towards the worm wheel  38  in the axial direction. Accordingly, when the worm wheel  38  rotates about the shaft portion  30   a  (i.e. the output shaft  30 ), the housing main body  43  also rotates with the worm wheel  38  as one unit via the cover  44  and the base  45 . Furthermore, the rotation of the housing main body  43  is transmitted to the rotor  41  by a viscosity of the viscous fluid F, although the rotor  41  is connected to the housing main body  43  so as to be rotatable relative to each other. Accordingly, the rotor  41  is rotated with the output shaft  30  as one unit. 
     A sensor rotor  51  is connected to the fitting portion  30   b  so as to be positioned between the rotor  41  and the second bearing  34  in the axial direction and so as to be rotatable with the output shaft  30  as one unit. The sensor rotor  51  is formed in a cylinder shape having a cover portion so as to surround and cover the clutch mechanism  40 . A ring magnet  52  is fixed at a radially outer circumferential surface of the sensor rotor  51 . The ring magnet  52  includes plural N-poles and S-poles in an alternate manner in a circumferential direction of the ring magnet  52 . An electronic control unit  53  (which will be hereinafter referred to as an ECU  53 ) is accommodated within the accommodating space S 1 . Plural hall sensors  54  are arranged at a radially outer position relative to the ring magnet  52  at regular intervals while being spaced away from the ring magnet  52 . Furthermore, the hall sensors  54  are electrically connected with the ECU  53 . The hall sensors  54  detect a rotational position and a rotational speed of the output shaft  30 , which is rotated with the ring magnet  52  as one unit, so that the detection result of the hall sensors  54  is used for detecting opening and closing positions of the luggage panel  11  and opening and closing speeds of the luggage panel  11 . 
     When the electric motor  35  is rotatably driven, the rotation of the worm  37  is transmitted to the worm wheel  38 , so that the worm wheel  38  rotates about the shaft portion  30   a  (the output shaft  30 ). Accordingly, the housing  42  is rotated with the worm wheel  38  as one unit. Furthermore, the rotation of the housing  42  (the housing main body  43 ) is transmitted to the rotor  41  via the viscous fluid F, so that the rotor  41  is rotated with the output shaft  30  as one unit. The rotation of the output shaft  30  is transmitted to the luggage panel  11  via the first link  25  and the like, thereby opening and closing the luggage panel  11 . 
     A characteristic and a function of the clutch mechanism  40  will be described below. The clutch mechanism  40  according to the first embodiment includes the rotor  41 , which serves as a connecting portion to the luggage panel  11 , and the housing  42  (the housing main body  43 ), which serves as a connecting portion to the electric motor  35 , so that the rotor  41  and the housing  42  are connected by means of the viscous fluid F. Therefore, as illustrated in  FIG. 4 , the rotor  41  and the housing  42  start rotating relative to each other when a transmission torque between the rotor  41  and the housing  42  exceeds a predetermined transmission torque X. The transmission torque is increased and decreased in response to an increase and a decrease of a relative speed (a relative rotational speed) at that time. 
     &lt;Transmission Function&gt; 
     In a case where the luggage panel  11  is manually opened and closed, the rotor  41  and the housing  42  of the clutch mechanism  40  are rotated relative to each other in order to open and close the luggage panel  11  because the electric motor  35  does not rotate. Therefore, when decreasing a relative speed a (i.e. an opening-and-closing speed a), a transmission torque A (i.e. a load torque A, a load) also decreases. Accordingly, the luggage panel  11  is manually opened and closed without applying a relatively large force thereto. On the other hand, in a case where the luggage panel  11  is opened and closed by means of a driving force generated by the electric motor  35 , a transmission torque B is increased when increasing a relative speed b (i.e. an opening-and-closing speed b), so that a torque necessary for opening and closing the luggage panel  11  is obtained. Accordingly, although the clutch mechanism  40  of the opening-and-closing drive device has a simple configuration that uses the viscous fluid F, the luggage panel  11  is opened and closed with relatively light operating force when being operated manually, and the torque necessary for opening and closing the luggage panel  11  is obtained when being opened and closed by means of the driving force generated by the electric motor  35 . In other words, the clutch mechanism  40  has the simple configuration, yet, the clutch mechanism  40  has a function similar to a electromagnetic clutch. Furthermore, because resin is used for a portion of the clutch mechanism  40 , a weight and a size of the clutch mechanism  40  may be reduced. Furthermore, a control circuit for the clutch mechanism  40  is not necessary. As a result, manufacturing costs of the clutch mechanism  40  may be reduced. Additionally, because electricity does not need to be supplied to the clutch mechanism  40 , a battery load may be reduced. 
     &lt;Absorption Function&gt; 
     Even in a case where a force is applied to the luggage panel  11  in a direction opposite to an operating direction while the luggage panel  11  is being operated, the force is absorbed by the viscous fluid F as a shearing force because the rotor  41  and the housing  42  of the clutch mechanism  40  rotate relative to each other. As a result, a generation of a shock load (an impact load) may be reduced or avoided. Accordingly, a necessary strength of the luggage panel  11  and the opening-and-closing mechanism  20  (i.e. the hinge arms  21  and the like) may be reduced, which may further result in reducing a size and thickness of each component and reducing the weight of the opening-and-closing drive device as a whole. Alternatively, a portion of the opening-and-closing mechanism  20  may be made of resin. 
     As illustrated in  FIGS. 5 and 6 , in a case where an object is caught at the luggage panel  11  while being operated and in a case where a pinch detecting function is not provided at the luggage panel  11 , a motor torque of the electric motor  35  reaches a lock torque f, by which the rotation of the electric motor  35  is locked, if the clutch mechanism  40  is not provided at the driving unit  24 , which may result in generating an excessive anti-pinch force in response to the lock torque f. However, because the clutch mechanism  40  is provided at the driving unit  24  in this embodiment, even if the motor torque increases towards the lock torque f, the rotation of the rotor  41 , which serves as the connecting portion of the luggage panel  11 , is stopped and the housing  42  and starts rotating relative to the rotor  41 . As a result, an increase of the motor torque is stopped at a point (i.e. a motor rotational speed E, a motor torque e) where the motor torque is balanced against the load torque, which increases in response to the increase of the relative speed. Accordingly, the motor torque does not reach the lock torque f, which may further result in reducing the anti-pinch force. 
     &lt;Absorption Function&gt; 
     On the other hand, in a case where the object is caught at the luggage panel  11  while being operated and in a case where a known pinch detecting function (see e.g. JP2002-194947A) is provided at the luggage panel  11 , the motor torque is increased rapidly towards the lock torque f if the clutch mechanism  40  is not provided at the driving unit  24 . However, according to the first embodiment, because the clutch mechanism  40  is provided at the driving unit  24 , the relative speed is increased while shearing the viscous fluid F. As a result, an increasing speed of the transmission torque may be restricted. Therefore, for example, assuming that a time necessary for detecting a pinch (trap) of the object at the luggage panel  11  (i.e. a time between when the pinch (trap) occurs and when the pinch of the object is detected, in other words, a time between when a luggage panel  11  is stopped and a time when the ECU  53  detects that the luggage panel  11  is stopped) is constant, the motor torque to be generated when the pinch of the object is detected, i.e. the anti-pinch force, may be reduced. 
     &lt;Free Stop Function&gt; 
     Furthermore, in a case where the load torque (the transmission torque X) generated when the relative speed between the rotor  41  and the housing  42  is zero (0) is used as a retaining force for retaining the luggage panel  11  in a stopped state, for example, the luggage panel  11  may be avoided being opened and closed by its own weight while the vehicle is on a inclined road, or the luggage panel  11  may be avoided being opened and closed due to the assisting force generated by the torsion bar link  23  by means of the load torque in conjunction with a stopping torque Y (a cogging torque) of the electric motor  35 . Alternatively, the luggage panel  11  may be stopped at any desired opened and closed position in a case where a torque, which is obtained by adding the load torque (X) to the stopping torque Y, is set to be greater than a torque for opening and closing the luggage panel  11  by means of its own weight or the assisting force generated by the torsion bar link  23 . 
     &lt;Motion Slowing Function&gt; 
     Furthermore, even if the luggage panel  11  is rapidly opened and closed by its own weight on the inclined road soon after a door lock mechanism for retaining the luggage panel  11  to be in a closed state is released on the inclined road in a case where the luggage panel  11  is manually opened and closed while the transmission torque X (the retaining force) is insufficient, or even if the luggage panel  11  is rapidly opened and closed so as to exceed a turn-over point, at which the assisting force of the torsion bar link  23  is rapidly weakened, or even if the luggage panel  11  is rapidly closed when a mass of snow falls on the luggage panel  11 , the electric motor  35  does not rotate, i.e. the electric motor  35  is stopped by its own cogging torque. Accordingly, the rotor  41  and the housing  42  of the clutch mechanism  40  rotate relative to each other, thereby increasing the relative speed. As a result, the load torque increases, which may further result in avoiding the increase of the opening-and-closing speed of the luggage panel  11 . 
     As illustrated in  FIG. 7 , when a user manually applies a force to the luggage panel  11  in the opening-and-closing direction so as to be consistent with the operating direction of the luggage panel  11  in order to increase the opening-and-closing speed of the luggage panel  11  in the case where the luggage panel  11  is opened and closed by means of the driving force generated by the electric motor  35 , the rotational speed of the rotor  41 , which serves as the connecting portion to the luggage panel  11 , is reduced so as to be approximate to the rotational speed of the housing  42  (i.e. the relative speed is reduced), so that the opening-and-closing speed of the luggage panel  11  is increased. Specifically, because the opening-and-closing speed of the luggage panel  11  is increased due to the decrease of the relative speed, i.e. the decrease of the load torque, the operating force necessary for manually opening and closing the luggage panel  11  may be reduced. 
     According to the first embodiment, the following advantages and merits are achievable. The clutch mechanism  40  of the opening-and-closing drive device according to the first embodiment has a simple configuration and is light in weight, yet the clutch mechanism  40  transmits the power between the electric motor  35  and the luggage panel  11  while allowing the luggage panel  11  to be manually opened and closed. Furthermore, the clutch mechanism  40  absorbs the shock load, which is to be generated when the force is applied to the luggage panel  11  in the direction opposite to the operating direction while being operated. Moreover, the clutch mechanism  40  may function as a mechanism for transmitting the power, absorbing the load and generating the load. More specifically, because the clutch mechanism  40  is configured so as to absorb the shock load, each component relating to the power transmission may be made of resin and may be reduced in thickness and weight. Furthermore, the clutch mechanism  40  reduces the anti-pinch force, so that the opening-and-closing drive device is reduced in weight and size and the manufacturing costs of the opening-and-closing drive device may be reduced when comparing to a case where the electromagnetic clutch is adapted instead of the clutch mechanism  40 . Additionally, the free-stop function, the motion slowing function, a manual operation function in the case where the luggage panel  11  is automatically opened and closed, and the like may be added to the opening-and-closing drive device. 
     Second Embodiment  
     A second embodiment of the opening-and-closing drive device, which is adapted as an opening-and-closing drive device of a slide door, will be described below with reference to the attached drawings. 
     Illustrated in  FIG. 8  is a side view of a vehicle, such as an automobile, to which the opening-and-closing drive device is adapted. Illustrated in  FIG. 9  is a plane view of the opening-and-closing drive device. As illustrated in  FIG. 8 , a vehicle body  60  includes an upper rail  61  and a lower rail  62 , which extend in a front-rear direction along an upper edge portion and a lower edge portion, respectively, of a door opening  60   a,  which is formed at a side portion of the vehicle body  60 . A center rail  63  is provided at a quarter panel  60   b,  which is provided at a rear portion of the vehicle door  60  relative to the door opening  60   a,  so as to extend in the front-rear direction. A slide door  70 , which serves as the opening-and-closing member, is supported at the upper rail  61 , the lower rail  62  and the center rail  63  via first, second and third guide roller units  64 ,  65  and  66 , respectively, so as to be movable in the front-rear direction. 
     A driving unit  71  is fixed at the slide door  70 . The driving unit  71  rotates an output drum  72 , which serves as an output portion, in a clockwise direction and a counterclockwise direction in  FIG. 9  when a power is supplied to the driving unit  71 . An end portion of a first wire  73   a  and an end portion of a second wire  73   b  of a cable  73  (a connecting member, a string member) are engaged with the output drum  72 , so that the first and second wires  73   a  and  73   b  are wound around the output drum  72 . The first wire  73   a  is guided to a pulley mechanism  74 , which is provided at the third guide roller unit  66  and is led into the center rail  63 , so that the other end portion of the first wire  73   a  is engaged at a rear end portion of the center rail  63 . The second wire  73   b  is guided to the pulley mechanism  74  and is led into the center rail  63 , so that the other end portion of the second wire  73   b  is engaged at a front end portion of the center rails  63 . Additionally, the cable  73  may be configured with one wire, which is wound around the output drum  72  and whose both end portions are fixed at respective predetermined portions of the vehicle body  60 , instead of the first and second wires  73   a  and  73   b.    
     The pulley mechanism  74  includes a pair of guide pulleys  75  and  76  (i.e. first and second guide pulleys  75  and  76 ), which are supported by the third guide roller unit  66  so as to be freely rotatable. The other end portions of the first and second wires  73   a  and  73   b  are guided to the first and second guide pulleys  75  and  76 , respectively, so as to be crossed between the first and second guide pulleys  75  and  76 , and then, the other end portions of the respective first and second wires  73   a  and  73   b  are led into the center rails  63 . 
     When the driving unit  71  (the output drum  72 ) is rotatably driven in one direction in a case where the slide door  70  is in a closed state as illustrated by a solid line in  FIG. 9 , the first wire  73   a  of the cable  73  is wound around the output drum  72 , and the second wire  73   b  is reeled out from the output drum  72 . In this case, because the other end portion of the first wire  73   a  and the other end portion of the second wire  73   b  are fixed at the vehicle body  60 , the second pulley  76  moves the third guide roller unit  66  towards a rear portion of the vehicle along the center rail  63  so as to slide relative to the center rail  63 . As a result, the slide door  70  is slidably moved in an opening direction (to the right in  FIG. 9 ) as illustrated by a chain double-dashed line in  FIG. 9 . 
     On the other hand, when the driving unit  71  (the output drum  72 ) is rotatably driven in the other direction while the slide door  70  is in an opened state, the second wire  73   b  of the cable  73  is wound around the output drum  72  and the first wire  73   a  is reeled out from the output drum  72 . Accordingly, the first guide pulley  75  moves the third guide roller unit  66  towards a front portion of the vehicle along the center rail  63  so as to slide relative to the center rail  63 . As a result, the slide door  70  is slidably operated in a closing direction (to the left in  FIG. 9 ). 
     As illustrated in  FIG. 10 , the driving unit  71  according to the second embodiment differs from the driving unit  24  of the first embodiment in that the driving unit  71  includes an output shaft  77  for supporting the output drum  72  instead of the first link  25  of the driving unit  24 . The output shaft  77  includes a shaft portion  77   a,  which corresponds to the shaft portion  30   a,  for supporting the worm wheel  38  so as to be rotatable. Furthermore, the output shaft  77  includes a fitting portion  77   b,  which corresponds to the fitting potion  30   b  and to which the rotor  41  and the sensor rotor  51  are connected so as to be rotatable with the fitting portion  77   b  as one unit. The output drum  72  is connected at an end portion of the output shaft  77 , which outwardly protrudes from the housing  31 , so as to be rotated with the output shaft  77  as one unit. 
     A drum cover  78  for accommodating the output drum  72  is connected to the housing  31  together with the cover  32 . A bearing  79  for supporting an end portion of the output shaft  77  penetrating and protruding from the output drum  72  so as to be freely rotatable is retained by the drum cover  78 . 
     When the electric motor  35  (see  FIG. 2 ) is rotatably driven, the rotation of the worm  37  is transmitted to the worm wheel  38 , so that the worm wheel  38  rotates about the shaft portion  77   a  (the output shaft  77 ). Accordingly, the housing  42  is rotated with the worm wheel  38  as one unit. Furthermore, the rotation of the housing  42  (the housing main body  42 ) is transmitted to the rotor  41  via the viscous fluid F, so that the rotor  41  is rotated with the output shaft  77  as one unit. A rotation of the output shaft  77  is transmitted to the vehicle body  60  via the output drum  72  and the like, then the slide door  70 , which is supported at the vehicle body  60 , is opened and closed. 
     According to the second embodiment, advantages and merits similar to the first embodiment are achievable. 
     Third Embodiment  
     A third embodiment of the opening-and-closing drive device, which is adapted as an opening-and-closing drive device for a luggage panel, will be described below with reference to the attached drawing. The opening-and-closing drive device according to the third embodiment differs from the opening-and-closing drive device according to the first embodiment in that a driving unit for driving the luggage panel  11  to be opened and closed is modified. Other configurations of the opening-and-closing drive device according to the third embodiment are similar to the opening-and-closing drive device of the first embodiment. Therefore, only differences between the first and third embodiments will be described below. 
     Illustrated in  FIG. 11  is a cross-sectional view of a driving unit  81  according to the third embodiment. As illustrated in  FIG. 11 , the driving unit  81  is connected to the vehicle body  10  by means of a bracket  82 , which is made of, for example, a metal plate. Furthermore, the driving unit  81  includes a driving portion  83  and a transmitting portion  84 , which are supported by the bracket  82 . 
     The driving portion  83  includes a housing  86  and a cover  87 , which define an outer shape of the driving portion  83  and each of which is made of resin. Furthermore, a first output shaft  89  is rotatably supported at the driving portion  83  by means of a bearing bore  86   a,  which is formed at the housing  86 , and a bearing  88 , which is retained by the cover  87 . The bearing bore  86   a  and the bearing  88  are provided so as to be concentric with each other. 
     A speed reduction gear mechanism  91  is accommodated within an accommodating space S 11 , which is defined by the housing  86  and the cover  87 . The speed reduction gear mechanism  91  includes a worm  92  and a worm wheel  93  (a wheel gear). The worm  92  is fixed at the rotating shaft of the electric motor  35  (see  FIG. 2 ). The worm wheel  93  is engaged with the worm  92  and is connected to the first output shaft  89  so as to be rotatable therewith as one unit. Accordingly, when the power is supplied to the electric motor  35  and the electric motor  35  is rotatably driven, a rotation of the worm  92 , which is rotated with the rotating shaft of the electric motor  35  as one unit, is transmitted to the worm wheel  93 , so that the worm  92  is rotated together with the first output shaft  89 . Then, the speed reduction gear mechanism  91  decelerates a rotational speed of the worm  92  in response to a transmission ratio established between the worm  92  and the worm wheel  93 , so that the decelerated rotational speed is transmitted to the worm wheel  93  (and the first output shaft  89 ). Additionally, a gear  94 , whose diameter is well smaller than a diameter of the worm wheel  93 , is connected at an end portion of the first output shaft  89 , which outwardly protrudes from the housing  86  and the bracket  82 , so as to be rotated with the first output shaft  89  as one unit. 
     The transmitting portion  84  includes a holder  96 , which is arranged at a position opposite from the driving portion  83  relative to the bracket  82  and which is made of, for example, a metal plate. Bearing bores  82   a  and  96   a  are formed at the bracket  82  and the holder  96 , respectively, so as to be concentric with each other. Both end portions of a supporting shaft  97 , which serves as an intermediate shaft and which extends in parallel with the first output shaft  86 , are supported by the bearing bores  82   a  and  96   a,  respectively, while allowing the supporting shaft  97  to be freely rotated. A dual gear  98  is connected to the supporting shaft  97  so as to be rotatable therewith as one unit and so as to be sandwiched between the bracket  82  and the holder  96 . The dual gear  98  integrally includes a first gear portion  98   a  and a second gear portion  98   b.  The first gear portion  98   a  is formed so that a diameter thereof is set to be well greater than the diameter of the gear  94 . Furthermore, the first gear portion  98   a  is engaged with the gear  94 . The second gear portion  98   b  is formed so that a diameter thereof is set to be well smaller than the first gear portion  98   a.  The dual gear  98  is rotated when the rotation of the gear  94  (the first output shaft  89 ) is transmitted thereto. In this case, the dual gear  98  further decelerates a rotational speed of the gear  94  in response to a transmission ratio established between the gear  94  an the first gear portion  98   a.  Additionally, the dual gear  98 , which is engaged with the gear  94  and which decelerates the rotational speed of the gear  94 , configures a first deceleration gear train G 1 . 
     Bearing bores  82   b  and  96   b  are formed at the bracket  82  and the holder  96 , respectively so as to be concentric with each other. Both end portions of a second output shaft  100 , which serves as an output shaft extending in parallel with the first output shaft  89  and the supporting shaft  97 , are supported by the bearing bores  82   b  and  96   b,  respectively, while allowing the second output shaft  100  to be freely rotated. The first link  25  is connected to an end portion of the second output shaft  100 , which outwardly extends from the holder  96 , so as to be rotatable with the output shaft  100  as one unit. 
     The second output shaft  100  is formed in a column shape having a stepped portion. More specifically, the second output shaft  100  includes a shaft portion  100   a,  which is formed in a column shape, between the bracket  82  and the holder  96  so as to be positioned closer to the bearing bore  82   b  when comparing to the bearing bore  96   b.  Furthermore, the second output shaft  100  includes a fitting portion  100   b,  which is formed in a column shape whose cross-sectional shape is formed in a quadrangle, between the bracket  82  and the holder  96  so as to be positioned closer to the bearing bore  96   b  when comparing to the bearing bore  82   b.  A gear  101  is rotatably supported by the shaft portion  100   a.  The gear  101  is formed to have a well greater diameter than the diameter of the second gear portion  98   b  and is engaged with the second gear portion  98   b.  Accordingly, when the rotation of the second gear portion  98   b  (the dual gear  98 ) is transmitted to the gear  101 , the gear  101  rotates about the second output shaft  100 . In this case, the gear  101  further decelerates a rotational speed of the second gear portion  98   b  in response to a transmission ratio established between the second gear portion  98   b  and the gear  101 . In other words, the rotational speed of the first output shaft  89  (the worm wheel  93 ) is decelerated between the gear  94  and the first gear portion  98   a,  and then, the rotational speed of the first output shaft  89  is further decelerated between the second gear portion  98   b  and the gear  101 , so that the gear  101  is rotated by the decelerated rotational speed. Additionally, the gear  101 , which is engaged with the first gear portion  98   a  and which decelerates the rotational speed of the first gear portion  98   a,  configures a second deceleration gear train G 2 . 
     A clutch mechanism  110  is accommodated within a space formed between the holder  96  and the gear  101 . The clutch mechanism  110  includes a housing  111 , a cover  112  and a rotor  113 . The housing  111  is connected to the gear  101 , serves as an input-side member and is formed in a cylinder shape having a bottom cover. The cover  112  closes an opening of the housing  111  in a fluid-tight manner. The rotor  113  serves as an output-side member and is accommodated within an inner space defined by the housing  111  and the cover  112 . 
     As illustrated by an exterior view of the clutch mechanism  110  in  FIG. 11  when being viewed in an axial direction of the second output shaft  100 , a bearing bore  111   a,  which is formed in a circular shape and into which the fitting portion  100   b  is inserted, is formed at the bottom cover of the housing  111 . Furthermore, a partition wall  111   b  is formed on a side wall of the housing  111  within a predetermined angle range. More specifically, the partition wall  111   b  is formed in a sector shape whose inner diameter is set to be greater than an inner diameter of the bearing bore  111   a  and which protrudes towards a center portion of the clutch mechanism  110 . Furthermore, a bearing bore  112   a,  formed in a circular shape similar to the bearing bore  111   a,  is formed at the cover  112 , so that the fitting portion  100   b  is freely inserted into the bearing bore  112   a.    
     The rotor  113  includes a fitting bore  113   a,  which is formed in a quadrangle shape and into which the fitting portion  100   b  is fittedly inserted. Furthermore, the rotor  113  includes a shaft portion  113   b,  which is rotatably supported by the bearing bores  111   a  and  112   a  in a fluid-tight manner. The rotor  113  has an enlarged diameter so that the shaft portion  113   b  thereof slidably contacts an inner circumferential surface of the partition wall  111   b  between the bottom cover of the housing  111  and the cover  112 . Furthermore, the rotor  113  includes a vane portion  113   c,  which radially-outwardly protrudes within a predetermined angle range of the enlarged portion of the rotor  113  so as to slidably contact the inner circumferential surface of the housing  111 . Accordingly, a relative rotational amount between the housing  111  and the rotor  113  (the second output shaft  100 ), which are rotated with the gear  101  as one unit, is set to fall within a range until the vane portion  113   c  contacts an opposing surface of the partition wall  111   b,  i.e. within a range smaller than 360 degrees. 
     An inner space defined by the housing  111  and the cover  112  is divided into two by means of the vane portion  113   c.  More specifically, the rotor  113  includes a first fluid chamber  114   a  extending at one side of the vane portion  113   c  (i.e. so as to extend in a clockwise direction relative to the vane portion  113   c  in  FIG. 11 ) and a second fluid chamber  114   b  extending at the other side of the vane portion  113   c  (i.e. so as to extend in the counterclockwise direction relative to the vane portion  113   c ). The first and second fluid chambers  114   a  and  114   b  are filled with the viscous fluid F, e.g. viscous oil. Furthermore, an orifice  115  is formed at the vane portion  113   c  so as to establish a communication between the first and second fluid chambers  114   a  and  114   b  via the orifice  115 . 
     Accordingly, when the rotor  113  is rotated in a direction indicated by an arrow a in  FIG. 11  or when the housing  111  is rotated in a direction indicated by an arrow b, the viscous fluid F, which is provided within the clutch mechanism  110 , is about to move from the first fluid chamber  114   a  to the second fluid chamber  114   b  via the orifice  115 . However, because a fluid channel (a bore diameter) of the orifice  115  is formed to be small, a sufficient flow of the viscous fluid F is not likely to be ensured. Therefore, the viscous fluid F is compressed within the first fluid chamber  114   a,  thereby generating the transmission torque (the load torque) between the rotor  113  and the housing  111 . 
     On the other hand, even in a case where the rotor  113  is rotated in the direction indicated by the arrow b or in the case where the housing  111  is rotated in the direction indicated by a, the viscous fluid F is compressed within the second fluid chamber  114   b,  thereby generating the transmission torque (the load torque) between the rotor  113  and the housing  111 . 
     Accordingly, as is the case with the clutch mechanism  40 , the clutch mechanism  110  of the third embodiment increases and decreases the transmission torque (the load torque) in response to the increase and decrease of the relative speed (the relative rotational speed) between the rotor  113  and the housing  111  (see  FIG. 4 ). Specifically, the clutch mechanism  110  having the orifice  115  enhanced the above-described characteristic of the transmission torque or the load torque when comparing to the clutch mechanism  40 . Accordingly, the clutch mechanism  110  obtains further advantages and merits relating to the rotational transmission and the like. Additionally, the characteristic of the transmission torque and the load torque may be easily changed by modifying the fluid channel (the bore diameter) of the orifice  115  or by changing a viscosity of the viscous fluid F. 
     According to the third embodiment, when the electric motor  35  is rotatably driven, the rotation of the worm  92  is transmitted to the worm wheel  93 , thereby rotating the worm wheel  93 . Then, the first output shaft  89  and the gear  94  are rotated with the worm wheel  93  as one unit. Furthermore, the rotation of the gear  94  is transmitted to the dual gear  98  (the first gear portion  98   a ), thereby rotating the dual gear  98 . Then, the rotation of the dual gear  98  (the second gear portion  98   b ) is transmitted to the gear  101 , thereby rotating the housing  111  with the gear  101  as one unit. The rotation of the housing  111  is transmitted to the rotor  113  via the viscous fluid F, thereby rotating the output shaft  100  with the rotor  113  as one unit. The rotation of the second output shaft  100  is transmitted to the luggage panel  11  via the first link  25  and the like, thereby opening and closing the luggage panel  11 . 
     According to the third embodiment, the clutch mechanism  110  is provided at the second output shaft  100 , which serves as a final stage of deceleration of the transmitting portion  84 . Furthermore, the relative rotational amount between the housing  111  and the rotor  113  is set to be smaller than 360 degrees. Accordingly, no negative influence is likely to affect the clutch mechanism  110  using the orifice  115 . 
     According to the third embodiment, the opening-and-closing drive device achieves the following advantages and merits in addition to the advantages and merits similar to the first embodiment. According to the third embodiment, the rotation of the electric motor  35  is well decelerated via the first and second deceleration gear trains G 1  and G 2 , so that the decelerated rotation is transmitted to the housing  111 . Furthermore, because the relative rotational amount between the housing  111  and the rotor  113  is set to be smaller than 360 degrees and the clutch mechanism  110  having the orifice  115  is adapted to the opening-and-closing drive device, an increasing and decreasing characteristic of the transmission torque relative to the relative speed may be further enhanced. 
     Fourth Embodiment  
     A fourth embodiment of an opening-and-closing drive device will be described below with reference to the attached drawing. The opening-and-closing drive device according to the fourth embodiment differs from the opening-and-closing drive device according to the first and second embodiments in that the clutch mechanism  40  is provided at the rotating shaft of the electric motor instead of the output shaft  30 . Therefore, only the differences between the first and second embodiments on the one hand and the fourth embodiment on the other will be described below. 
     Illustrated in  FIG. 12  is a cross sectional view of a driving unit  121  according to the fourth embodiment. As illustrated in  FIG. 12 , the driving unit  121  includes a worm  122  and a rotational shaft  123  (a motor shaft) of the electric motor  35  so as to be arranged separately from each other in an axial direction thereof. The worm  122  is engaged with the worm wheel  38 . The worm  122  includes a fitting portion  122   a,  which is formed in a column shape whose cross-sectional shape is formed in a quadrangle, at an end portion of the worm  122  facing the rotating shaft  123 . Furthermore, the rotating shaft  123  includes a fitting portion  123   a,  which is formed in a column shape whose cross-sectional shape is formed in a quadrangle, at an end portion of the rotating shaft  123  facing the worm  122 . 
     The clutch mechanism  40  according to the fourth embodiment is provided between the worm  122  and the rotating shaft  123  in the axial direction. The rotor  41  of the clutch mechanism  40  is fitted to the fitting portion  122   a  of the worm  122 . The housing  42  is fitted to the fitting portion  123   a  of the rotating shaft  123 . Accordingly, when the electric motor  35  is rotatably driven, the housing  42  is rotated with the rotating shaft  123  as one unit. Then, the rotation of the housing  42  is transmitted to the rotor  41  via the viscous fluid F, thereby rotating the rotor  41 . Accordingly, the worm  122  is rotated with the rotor  41  as one unit, and then, the rotation of the worm  122  is transmitted to the worm wheel  38 . The worm wheel  38  according to the fourth embodiment is connected to the output shaft  30  so as to be rotated therewith as one unit. Then, the output shaft  30  rotates in response to the rotation of the worm wheel  38 . The rotation of the output shaft  30  is transmitted to the luggage panel  11  via the first link  25  and the like, thereby opening and closing the luggage panel  11 . 
     The clutch mechanism  40  according to the fourth embodiment has a function relating to the rotational transmission similar to the functions of the clutch mechanism  40  mentioned in the first and second embodiments. Additionally, a lead angle is set for the worm  122  in order to allow the worm  122  to be lightly rotated when a load (an inverse input) is applied (inputted) to the luggage panel  11 . 
     According to the fourth embodiment, the following advantages and merits are achievable in addition to the advantages and merits similar to the first embodiment. According to the fourth embodiment, the clutch mechanism  40  is provided at a position closer to the rotating shaft  123  of the electric motor  35  relative to the worm  122 . More specifically, the clutch mechanism  40  is provided at a former stage of the deceleration mechanism ( 122 ,  38 ). Accordingly, the torque, which is generated by the electric motor  35  and which is not yet increased by the speed reduction gear mechanism, is transmitted to the clutch mechanism  40 . Therefore, a strength necessary for the clutch mechanism  40  (the rotor  41 , the housing  42 ) may be reduced. As a result, each component may be reduced in size and thickness, which may further result in reducing the weight of the clutch mechanism  40  as a whole. 
     Fifth Embodiment  
     A fifth embodiment of an opening-and-closing drive device, which is adapted as an opening-and-closing drive device for a slide door, will be described below with reference to the attached drawings. The opening-and-closing drive device according to the fifth embodiment differs from the opening-and-closing drive device according to the second embodiment in that the clutch mechanism  40  according to the fifth embodiment is modified so that a portion thereof overlaps with the output drum in the axial direction, so that the portion of the clutch mechanism  40  is accommodated within the output drum. Therefore, only the differences between the second embodiment and the fifth embodiment will be described below. 
     Illustrated in  FIG. 13  is a cross-sectional view of a driving unit  130  according to the fifth embodiment. As illustrated in  FIG. 13 , the driving unit  130  includes a housing  131  and a cover  132 , which define an outer shape of the driving unit  130  and each of which is made of resin. The housing  131  and the cover  132  support bearings  133  and  134 , respectively, so that the bearings  133  and  134  are arranged in a concentric manner. The bearings  133  and  134  rotatably support both end portions of an output shaft  135 , respectively, while allowing the output shaft  135  to be freely rotatable. The output shaft  135  is formed in a column shape having a stepped portion. More specifically, the output shaft  135  includes a fitting portion  135   a  between the bearings  133  and  134  so as to be positioned closer to the bearing  133  when comparing to the bearing  134 . Furthermore, the output shaft  135  includes a shaft portion  135   b,  which is formed in a column shape, between the bearings  133  and  134  so as to be positioned closer to the bearing  134  relative to the bearing  133 . 
     A speed reduction gear mechanism  136 , an output drum  139 , which serves as an output portion, and the clutch mechanism  40  are accommodated within an accommodating space S 12  formed by the housing  131  and the cover  132 . The deceleration mechanism  136  includes a worm  137  and a worm wheel  138  (a wheel gear). The worm  137  is fixed at the rotating shaft of the electric motor  35  (see  FIG. 2 ). The worm wheel  138  is engaged with the worm  137  and is rotatably supported by the shaft portion  135   b  of the output shaft  135 . When the power is supplied to the electric motor  35  in order to rotatably drive the electric motor  35 , the worm wheel  138  rotates about the shaft portion  135   b,  as is explained in the first and second embodiments. 
     The worm wheel  138  includes plural recessed portions  138   a  at a surface of the worm wheel  138  facing the clutch mechanism  40  so as to be spaced away therefrom in an axial direction of the output shaft  135 , while forming equal angles between the neighboring recessed portions  138   a.  The rotor  41  of the clutch mechanism  40  is fitted at the fitting portion  135   a,  which is positioned in the vicinity of the worm wheel  138 . The housing  42 , which is rotatably supported by the rotor  41  in a fluid-tight manner, does not include the protruding portion  45   b  at the base  45  unlike in the second embodiment, instead, the protruding portions  43   c  of the housing main body  43  penetrate the cover  44  (the fitting bores  44   a ) and are fitted into the respective recessed portions  138   a.  Accordingly, when the worm wheel  138  rotates about the shaft portion  135   b  (the output shaft  135 ), the housing main body  43  (the housing  42 ) is rotated with the worm wheel  138  as one unit. The rotation of the housing main body  43  is transmitted to the rotor  41  by the viscosity of the viscous fluid F, as is explained above. 
     The output drum  139  is fitted to the fitting portion  135   a  at a position between the bearing  133  and the rotor  41  in the axial direction. The cable  73  is wound around the output drum  139 . The output drum  139  is made of, for example, resin and is formed in a cylinder shape having a bottom cover portion. Furthermore, the output drum  139  includes a circumferential wall  139   a,  which is formed in a cylinder shape, so as to protrude towards the worm wheel  138  in the axial direction. A portion of the clutch mechanism  40  is accommodated within the circumferential wall  139   a.  Accordingly, a thickness of the driving unit  130  in the axial direction is reduced. 
     The rotations of the output shaft  135  and the output drum  139  are transmitted to the slide door  70  via the cable  73  and the like, thereby opening and closing the slide door  70 . A ring magnet  141  is fixed at an opening end surface of the circumferential wall  139   a  in the axial direction. The ring magnet  141  includes plural N-poles and S-poles in a circumferential direction so as to be arranged in an alternating manner. Furthermore, hall sensors  142 , which are supported by the cover  132 , are arranged at an outer position relative to the ring magnet  141  so as to be spaced away from each other in the axial direction while ensuring regular distances between the neighboring hall sensors  142 . The hall sensors  142  detect a rotational position and a rotational speed of the output shaft  135 , which is rotated with the ring magnet  141  as one unit, so that the detection results of the hall sensors  142  are used for detecting the opening and closing position and the opening and closing speed of the slide door  70 . 
     According to the fifth embodiment, the following advantages and merits are achievable in addition to advantages and merits similar to the first embodiments. According to the fifth embodiment, because a portion of the clutch mechanism  40  is accommodated within the output drum  139 , the thickness of the driving unit  130  in the axial direction is reduced. 
     According to the fifth embodiment, the ring magnet  141  is fixed at the output drum  139  so that the output drum  139  and the ring magnet  141  serve as the sensor rotor ( 51 ). As a result, a number of components used for the opening-and-closing drive device are reduced. 
     Sixth Embodiment  
     A sixth embodiment of an opening-and-closing drive device, which is adapted as an opening-and-closing drive device for a luggage panel, will be described below with reference to the attached drawings. The opening-and-closing drive device according to the sixth embodiment differs from the opening-and-closing drive device according to the first embodiment in that the clutch mechanism  40  is filled with a magnetic viscous fluid as the viscous fluid relating to the rotational transmission. Therefore, only the differences between the first embodiment and the sixth embodiment will be described below. 
     Illustrated in  FIG. 14  is a cross-sectional view of the driving unit  24  according to the sixth embodiment. As illustrated in  FIG. 14 , a clearance of the clutch mechanism  40  of the driving unit  24 , into which the rotor  41  and the housing main body  43  are fitted, is filled with a magnetic viscous fluid F 1  instead of the viscous fluid F. An electromagnet  146 , which is formed in a cylinder shape, is provided at an outer circumferential surface of the cover  44  in a state where the electromagnet  146  is surrounded (covered) by the sensor rotor  51 . 
     The clutch mechanism  40 , which is filled with the magnetic viscous fluid F 1 , has the characteristic of increasing and decreasing the transmission torque (the load torque) in response to the increase and decrease of the relative speed (the relative rotational speed) between the rotor  41  and the housing  42 . However, as illustrated in  FIG. 15 , the characteristic of the transmission torque (the load torque) is changed in response to a power supply state of the electromagnet  146 . More specifically, the characteristic of the transmission torque (the load torque) to be obtained when the electromagnet  146  is electrified is enhanced when comparing to the characteristic of the transmission torque (the load torque) to be obtained when the electromagnet  146  is not electrified, because when the electromagnet  146  is electrified, a magnetic field is generated and is applied to the magnetic viscous fluid F 1 , which results in changing the viscosity of the magnetic viscous fluid F 1 . The characteristic of the transmission torque (the load torque) may be continuously enhanced or reduced by controlling a power supply to the electromagnet  146 . Accordingly, the characteristic of the clutch mechanism  40  relating to the transmission torque (the load torque) may be widened when comparing to the case where the clutch mechanism  40  is filled with the viscous fluid F having a constant viscosity. 
     For example, in the case where the luggage panel  11  is opened and closed by using the driving force generated by the electric motor  35 , the transmission torque B may be increased when increasing the relative speed b (i.e. the opening and closing speed). Accordingly, the torque necessary for driving the luggage panel  11  to be opened and closed may be obtained. 
     Furthermore, as illustrated in  FIG. 16 , in the case where the object is caught at the luggage panel  11  while being operated and in a case where a known pinch detecting function is provided at the luggage panel  11 , the viscosity of the magnetic viscous fluid F 1  may be decreased when the power supply to the electromagnet  146  is turned off at the same time when the known pinch detecting function detects the pinch. Accordingly, an increasing speed of the transmission torque may be restricted, which may further result in reducing the motor torque generated after the pinch is detected (i.e. the anti-pinch force). 
     Accordingly to the sixth embodiment, the following advantages and merits are achievable in addition to advantages and merits similar to the first embodiment. According to the sixth embodiment, the viscosity of the magnetic viscous fluid F 1  is changed when the magnetic field is applied to the magnetic viscous fluid F 1  by the electromagnet  146 . Accordingly, the characteristic relating to the transmission torque (the load torque) of the clutch mechanism  40  may be widened. 
     Seventh Embodiment  
     A seventh embodiment of an opening-and-closing drive device, which is adapted as an opening-and-closing drive device for a luggage panel, will be described below with reference to the attached drawing. The opening-and-closing drive device according to the seventh embodiment differs from the opening-and-closing drive device according to the sixth embodiment in that the clutch mechanism  40  according to the seventh embodiment is filled with an electroviscous fluid F 2  as the viscous fluid relating to the rotational transmission. Therefore, only the differences between the sixth embodiment and the seventh embodiment will be described below. 
     Illustrated in  FIG. 17  is a cross-sectional view of the driving unit  24  according to the seventh embodiment. As illustrated in  FIG. 17 , the clearance of the clutch mechanism  40  of the driving unit  24 , into which the rotor  41  and the housing main body  43  is fitted, is filled with an electroviscous fluid F 2  instead of the viscous fluid F. Electrodes  147  and  148  are connected to the flange portion  41   b  of the rotor  41  and the flange portion  43   b  of the housing main body  43 , respectively, so as to face each other and so as to be against a flow of the electroviscous fluid F 2 . 
     The clutch mechanism  40 , which is filled with the electroviscous fluid F 2 , has the characteristic of increasing and decreasing the transmission torque (the load torque) in response to the increase and decrease of the relative speed (the relative rotational speed) between the rotor  41  and the housing  42 . Furthermore, the characteristic of the transmission torque (the load torque) is enhanced because a voltage, which is generated when the electrodes  147  and  148  are electrified, is added to the electroviscous fluid F 2  and the viscosity of the electroviscous fluid F 2  is changed (see  FIG. 15 ) in response to the power supply state of the electrodes  147  and  148 . Accordingly, the range of the characteristic of the transmission torque (the load torque) to be generated at the clutch mechanism  40  may be extended when comparing to the viscous fluid F having the constant viscosity. 
     According to the seventh embodiment, advantages and merits similar to the sixth embodiment may be achieved. Additionally, the opening-and-closing drive device according to the above-described embodiments may be modified as follows. 
     As illustrated in  FIG. 18 , each of the driving units  24 ,  81  and  121  may be adapted to an opening-and-closing drive device for a back door. A back door  151 , which serves as an opening-and-closing member, is attached to a rear portion of a vehicle body  150  via a door hinge  152  so as to be opened and closed. The back door  151  is supported by means of a gas damper  153 . Additionally, the back door  151  is opened in a manner where the back door  151  is upwardly pushed so as to be rotated about the door hinge  152 , which is provided at an upper edge portion of the vehicle body  150 , and the gas damper  153  supports the upward pushing of the back door  151  by a gas reaction force generated by the gas damper  153 . 
     Either one of the driving units  24 ,  81  and  121  is provided at the rear portion of the vehicle body  150 . An elongated arm  154 , which serves as a connecting member, is rotatably connected to the output shaft  30  or the output shaft  100  of either one of the driving units  24 ,  81  and  121 . The arm  154  is rotatably connected to an end portion of a rod  155 , which is formed in a bar shape, at an end portion of the arm  154 . The other end portion of the arm  154  is rotatably connected to the back door  151 . Accordingly, when the electric motor  35  (see  FIG. 2 ) is rotatably driven, the output shaft  30  ( 100 ) is rotated as explained above. Then, the rod  155  is upwardly pushed in response to a rotation of the arm  154  with the output shaft  30  ( 100 ) as one unit, thereby opening and closing the back door  151 , which is supported by the vehicle body  150 . Accordingly, each of the driving units  24 ,  81  and  121  is used as the opening-and-closing drive device for the back door. 
     As illustrated in  FIG. 19 , the worm wheel  38  of the first embodiment may be modified so as not to include the recessed portions  38   b.  Furthermore, the base  45  of the first embodiment may be modified so as not to include the protruding portion  45   b.  Alternatively, the worm wheel  38  may be modified so as to include plural recessed portions  161 , each of which is formed in a round shape, so as to extend in the axial direction at a surface of the worm wheel  38  facing the clutch mechanism  40  so as to be spaced away therefrom and so as to form equal angles between the neighboring recessed portions  161 . Furthermore, the clutch mechanism  40  may be modified so that the housing main body  43  includes plural protruding portions  162 , each of which is formed in a pin-shape and each of which is inserted into each of the recessed portions  161  so as to penetrate through the cover  44 , so that the worm wheel  38  and the housing main body  43  (the housing  42 ) are connected to be rotated with each other as one unit. 
     As illustrated in  FIG. 20 , the worm wheel  38  may be modified so as to include plural protruding portions  163 , each of which is formed in an arc shape and extends in the axial direction, at an outer circumferential portion of the worm wheel  38 , more specifically on a surface thereof facing the clutch mechanism  40  so as to be spaced away therefrom. Furthermore, the clutch mechanism  40  may be modified so that the base  45  includes plural protruding portions  164 , each of which is formed by bending a portion of the base  45  so as to extend in the axial direction to form a nail shape. The worm wheel  38  and the base  45  (the housing  42 ) may be connected so as to rotate with each other as one unit. 
     The magnetic viscous fluid F 1  or the electroviscous fluid F 2  may be used for the clutch mechanism  40  of the second embodiment, as is the case with the sixth and seventh embodiments. Furthermore, as illustrated in  FIG. 21 , the clutch mechanism  110  of the third embodiment may be filled with the magnetic viscous fluid F 1  as the viscous fluid relating to the rotational transmission. In this case, an electromagnet  167 , which is formed in an arc shape, is provided at an outer circumferential surface of the housing  111 . According to the above-described modification, the characteristic of the transmission torque (the load torque) and the like of the clutch mechanism  110  may be used in a wider range when comparing to the case where the viscous fluid F having a constant viscosity is used, in addition to advantages and merits similar to the third embodiment. 
     As illustrated in  FIG. 22 , the clutch mechanism  110  of the third embodiment may be modified so as to be filled with the electroviscous fluid F 2  as the viscous fluid relating to the rotational transmission. In this case, an electrode  168  is provided at an inner circumferential surface of the housing  111 . Furthermore, an electrode  169  is provided at an inner circumferential surface of each of an outer wall of the rotor  113  and the orifice  115 . According to the above-described modification, the characteristic of the transmission torque (the load torque) of the clutch mechanism  110  may be used in a wider range when comparing to the case where the viscous fluid F having the constant viscosity is used, in addition to advantages and merits similar to the third embodiment. 
     As illustrated in  FIG. 23 , the output drum  139  may be modified so as to include a groove portion  171 , which is formed in a circular shape, at an end surface of the output drum  139  facing the housing  131 . Furthermore, a ring magnet  172  may be embedded and fixed within the groove portion  171 . In this case, plural hall sensors  173  are supported by the housing  131  so as to correspond to the ring magnet  172  at an outer position relative to the ring magnet  172  and so as to be spaced away from the ring magnet  172  in the axial direction while maintaining regular intervals between the neighboring hall sensors  173 . According to the above-described modification, advantages and merits similar to the fifth embodiment may be achievable. 
     As illustrated in  FIG. 24 , the driving unit  130  of the fifth embodiment may be modified so as to include a pulley  175 , which serves as an output portion, and a belt  176 , which serves as a connecting member engaged with the pulley  175 , instead of the output drum  139  and the cable  73 , which relate to an opening and closing drive of the slide door  70 . 
     As illustrated in  FIG. 25 , the driving unit  130  of the fifth embodiment may be modified so that the worm wheel  138  is connected to the clutch mechanism  40  so as to be rotated with the rotor  41  of the clutch mechanism  40  as one unit, and further, so as to include an output shaft  177  for rotatably supporting the output drum  139 . In this case, the recessed portions  138   a  and the protruding portions  43   c,  which relate to the rotational transmission between the worm wheel  138  and the housing  42 , are not provided at the worm wheel  138  and the housing  42 , respectively. The housing  42  is supported by the rotor  41  so as to be rotatable relative to the worm wheel  138 . Furthermore, the output drum  139  may be modified so as to include plural recessed portions  178 , each of which is formed in a circular shape, at a surface of the worm wheel  138  facing the clutch mechanism  40  so as to be spaced away therefrom while forming equal angles between the neighboring recessed portions  178 . The clutch mechanism  40  may be modified so that the base  45  includes plural protruding portion  179 , which are formed by bending a portion of the base  45  so as to extend in the axial direction to form a nail shape. Then, the output drum  139  and the base  45  (the housing  42 ) may be connected so as to rotate with each other as one unit. 
     As illustrated in  FIG. 26 , the driving unit  24  of the first embodiment may be modified so as to include an output shaft  181  for rotatably supporting the rotor  41  of the clutch mechanism  40 . In this case, plural protruding portions  182 , each of which is formed in a pin shape, are provided at an intermediate portion of the worm wheel  38 , more specifically on the surface thereof facing the clutch mechanism  40  so as to extend in the axial direction while maintaining equal angles between the neighboring protruding portions  182 . Furthermore, plural recessed portions  183 , each of which is formed in a circular shape and into which the respective protruding portions  182  are inserted, are formed on the rotor  41 . Accordingly, the worm wheel  38  and the rotor  41  are connected so as to be rotated with each other as one unit. Furthermore, plural fitting bores  184 , into which the respective protruding portions  43   c  fitted so as to penetrate the cover  44  (the fitting bores  44   a ) of the housing main body  43 , are formed at the sensor rotor  51 . Accordingly, the sensor rotor  51  (the output shaft  181 ) and the housing main body  43  are connected so as to rotate with each other as one unit. According to the above-described modification, the rotation of the worm wheel  38  may be transmitted to the output shaft  181  via the clutch mechanism  40 . 
     An output gear (a member having toothed portion) may be adapted as an output member, which is provided at the output shaft, in each of the above-described embodiments. In other words, the connection between the output shaft and the opening-and-closing member may be achieved by means of a gear connection. 
     According to the embodiments, the opening-and-closing drive device includes a speed reduction gear mechanism ( 36 ,  91 ,  136 ) connected to the electric motor ( 35 ) and an output shaft ( 30 ,  77 ,  100 ) for supporting the output portion ( 72 ,  139 ,  175 ). The clutch mechanism ( 40 ,  110 ) includes the housing ( 42 ,  111 ) connected to the deceleration mechanism ( 36 ,  91 ,  136 ) and the rotor ( 41 ,  113 ) connected to the output shaft ( 30 ,  77 ,  100 ) and being connectable to the housing ( 42 ,  111 ) via the viscous fluid (F, F 1 , F 2 ). 
     According to the embodiments, the speed reduction gear mechanism ( 91 ) includes the first deceleration gear train (G 1 ), which is connected to the electric motor ( 35 ) and is rotatably supported by the supporting shaft ( 97 ), and the second deceleration gear train (G 2 ), which is connected to the first deceleration gear train (G 1 ) and is rotatably supported by the output shaft ( 100 ). Furthermore, the housing ( 111 ) is connected to the second deceleration gear train (G 2 ). 
     According to the embodiments, the speed reduction gear mechanism ( 36 ,  91 ,  136 ) includes the worm wheel ( 38 ,  93 ,  138 ) supported by the output shaft ( 30 ,  77 ,  100 ) so as to be rotatable relative to the output shaft ( 30 ,  77 ,  100 ). The housing ( 42 ,  111 ) serves as the input-side member, which is fixed at the worm wheel ( 38 ,  93 ,  138 ) so as to be rotated therewith as one unit. Furthermore, and the rotor ( 41 ,  113 ) serves as the output-side member, which is accommodated within the housing ( 42 ,  111 ) together with the viscous fluid (F, F 1 , F 2 ) and is connected to the output shaft ( 30 ,  77 ,  100 ) so as to be rotated therewith as one unit. 
     According to the embodiments, the opening-and-closing drive device includes the speed reduction gear mechanism ( 36 ) connected to the electric motor ( 35 ) and the rotating shaft ( 123 ) supporting the output shaft ( 30 ) so as to be rotatable. The clutch mechanism ( 40 ) includes the housing ( 42 ) connected to the speed reduction gear mechanism ( 36 ) via the rotating shaft ( 123 ) and the rotor ( 41 ), which is connected to the output shaft ( 30 ) and which is connectable to the housing ( 42 ) via the viscous fluid (F). 
     According to the embodiments, the clutch mechanism ( 40 ,  110 ) is arranged on the output shaft ( 30 ,  77 ,  100 ) between the speed reduction gear mechanism ( 36 ,  91 ,  136 ) and the output portion ( 30 ,  72 ,  139 ,  175 ) and is accommodated at the output portion ( 30 ,  72 ,  139 ,  175 ). 
     According to the embodiments, the connecting member includes the cable ( 73 ) connected to the opening-and-closing member ( 11 ,  70 ) and the output portion includes the output drum ( 72 ,  139 ) on which the cable ( 73 ) is wound. 
     According to the embodiments, the connecting member includes the toothed portion connected to the opening-and-closing member ( 11 ,  70 ) and the output portion includes the output gear engaged with the toothed portion. 
     According to the embodiments, the connecting member includes the arm ( 25 ,  26 ,  154 ) connected to the opening-and-closing member ( 11 ,  70 ) and the output portion includes the output shaft ( 30 ), which is rotated with the arm ( 25 ,  26 ,  154 ) as one unit. 
     Accordingly, the clutch mechanism ( 40 ,  110 ) having the viscous fluid (F, F 1 , F 2 ) is actuated in a manner where the housing ( 42 ,  111 ) (the input member of the power transmission, a driving member) and rotor ( 41 ,  113 ) (the input member of the power transmission, a driven member), between which the viscous fluid is provided, start rotating relative to each other when the power transmitted between the electric motor  35  and the output member ( 30 ,  72 ,  139 ,  175 ) exceeds a predetermined level. The transmission torque transmitted to the clutch mechanism ( 40 ,  110 ) is increased or decreased in response to the increase and decrease of the relative speed between the housing ( 42 ,  111 ) and the rotor ( 41 ,  113 ). Therefore, in the case where the opening-and-closing member is manually opened and closed, the opening-and-closing member is opened and closed in the manner where the housing ( 42 ,  111 ) and the rotor ( 41 ,  113 ), between which the viscous fluid is provided, are relatively rotated because the electric motor  35  is not actuated. However, when the relative speed (i.e. the opening-and-closing speed) is reduced, the transmission torque (the load torque) as a load is also reduced. As a result, the opening-and-closing member may be lightly opened and closed when being operated manually. On the other hand, in the case where the opening-and-closing member is opened and closed by the driving force generated by the electric motor  35 , the transmission torque is increased when increasing the relative speed, thereby obtaining a torque necessary for driving the opening-and-closing member to be opened and closed. Accordingly, the opening-and-closing drive device, which has a simple structure, allows the opening-and-closing member to be opened and closed by light operating force when being actuated manually and generates a torque necessary to open and close the opening-and-closing member when being operated by the driving force of the electric motor  35 . 
     Accordingly, even in the case where the force is applied to the opening-and-closing member in the direction opposite to the operating direction while the opening-and-closing member is being actuated, the housing ( 42 ,  111 ) and the rotor ( 41 ,  113 ), between which the viscous fluid is provided, of the clutch mechanism ( 40 ,  110 ) relatively rotate, and the reverse force is absorbed by the viscous fluid as the shearing force. As a result, a generation of the shock load may be reduced or avoided. Accordingly, a necessary strength of each of the opening-and-closing member ( 11 ,  70 ), the connecting member ( 30 ,  21 ,  154 ,  176 ), the output member ( 30 ,  72 ,  139 ,  175 ) and the electric motor  35  may be reduced, which may further result in reducing each of the opening-and-closing member, the connecting member, the output member ( 30 ,  72 ,  139 ,  175 ) and the electric motor  35  in size and thickness, so that the weight of the opening-and-closing drive device as a whole may be reduced. 
     Generally, in the case where the object is caught at the opening-and-closing member ( 11 ,  70 ) while being actuated and where the pinch detecting function is not provided at the opening-and-closing drive device, the electric motor  35  increases the driving force (which corresponds to the anti-pinch force) until the operation of the opening-and-closing member is locked. However, according to the embodiments, the operation of the opening-and-closing member is stopped and the housing ( 42 ,  111 ) and the rotor ( 41 ,  113 ), between which the viscous fluid is provided, of the clutch mechanism ( 40 ,  110 ) start rotating relative to each other, so that the driving force generated by the electric motor  35  is increased until the driving force of the electric motor  35  becomes equal to the load torque, which is increased in response to the increase of the relative speed. As a result, the anti-pinch force may be reduced. On the other hand, even in the case where the opening-and-closing drive device has the pinch detecting function, the relative speed is increased while shearing the viscous fluid when the driving force of the electric motor  35  is increased. Therefore, increasing speed of the transmission torque may be restricted. Therefore, for example, when assuming that a time necessary to detect the pinch (trap) of the object is constant, the driving force of the electric motor  35  to be generated when the pinch is detected, i.e. the anti-pinch force, may be reduced. 
     Accordingly, because the load torque to be generated when the relative speed is zero (0) is used as the retaining force for retaining the stopped state of the opening-and-closing member, the opening-and-closing member may be avoided from, for example, being opened and closed by its own weight on the inclined road. Alternatively, the opening-and-closing member may be stopped at any desired opened and closed position by using the retaining force. 
     Accordingly, even in the case where the retaining force is insufficient and the opening-and-closing member is manually opened and closed, the housing ( 111 ,  42 ) and the rotor ( 41 ,  113 ), between which the viscous fluid is provided, of the clutch mechanism ( 40 ,  100 ) rotate relative to each other because the electric motor  35  is not actuated, so that the relative speed is increased. As a result, because the load torque is increased, the increase of the opening-and-closing speed of the opening-and-closing member may be avoided. Accordingly, the opening-and-closing member is avoided from being rapidly opened and closed by its own weight. 
     Accordingly, when the force is manually applied to the opening-and-closing member in the direction corresponding to the opening and closing direction by the user while the opening-and-closing member is opened and closed by the driving force generated by the electric motor  35 , the relative speed is reduced so as to approximate to the rotational speed of the housing ( 42 ,  111 ). As a result, the opening and closing speed of the opening-and-closing member is increased. Specifically, because the opening and closing speed of the opening-and-closing member is increased when reducing the relative speed, i.e. the load torque, an operating force necessary for manually operating the opening-and-closing member may be reduced. 
     Accordingly, the driving force generated by the electric motor  35  is well reduced by the first and second deceleration gear trans G 1  and G 2 , and then, the decelerated driving force is transmitted to the housing  111 . In a case where the relative rotation between the housing  111  and the rotor  113  is set to be smaller than 360 degrees, for example, the inner space to be filled with the viscous fluid may be formed at either one of the housing  111  and the rotor  113 , and the other one of the housing  111  and the rotor  113  may include the vane portion  113   c  for dividing the inner space in the circumferential direction and the orifice  115  for establishing the communication between the divided inner spaces. Accordingly, the clutch mechanism  110  may obtain the greater increasing and decreasing characteristic of the transmission torque relative to the relative speed. 
     According to the embodiments, the viscous fluid includes the magnetic viscous fluid (F 1 ) whose viscosity is changeable. The clutch mechanism ( 40 ,  110 ) includes the electromagnet ( 146 ,  167 ) for applying the magnetic field to the magnetic viscous fluid (F 1 ). 
     Accordingly, the clutch mechanism ( 40 ,  110 ) is arranged at a position closer to the rotating shaft of the electric motor  35  relative to the worm ( 37 ,  92 ,  122 ,  137 ), i.e. at the former stage of the speed reduction gear mechanism ( 36 ,  91 ,  136 ). Therefore, because the driving force, which is generated by the electric motor  35  and which is not yet increased by the speed reduction gear mechanism ( 37 ,  92 ,  122 ,  137 ), is transmitted to the clutch mechanism ( 40 ,  110 ), the necessary strength of the clutch mechanism ( 40 ,  110 ) (the housing ( 42 ,  111 ) and the rotor ( 41 ,  113 )) may be reduced. As a result, the clutch mechanism ( 40 ,  110 ) may be reduced in size and thickness, which may further result in reducing the weight of the clutch mechanism ( 40 ,  110 ) as a whole. 
     According to the embodiments, the viscous fluid includes the magnetic viscous fluid (F 1 ) whose viscosity is changeable, and the clutch mechanism ( 40 ,  110 ) includes the electromagnet ( 146 ,  167 ) for applying the magnetic field to the magnetic viscous fluid (F 1 ). 
     Accordingly, the viscosity of the magnetic viscous fluid F 1  may be changed in response to the application of the magnetic field to the magnetic viscous fluid F 1  by means of the electromagnet ( 146 ,  167 ). As a result, the characteristic of the transmission torque (the load torque) of the clutch mechanism ( 40 ,  110 ) may be used in a wider range. 
     According to the embodiments, the viscous fluid (F) includes the electroviscous fluid (F 2 ) and the clutch mechanism ( 40 ,  100 ) includes the electrode ( 147 ,  148 ,  168 ,  169 ) for applying the voltage to the electroviscous fluid (F 2 ). 
     Accordingly, the viscosity of the electroviscous fluid F 2  may be changed in response to the voltage applied to the electroviscous fluid F 2  by means of the electrodes ( 147 ,  148 ,  168 ,  169 ). As a result, the characteristic of the transmission torque (the load torque) of the clutch mechanism ( 40 ,  110 ) may be used in a wider range. 
     Accordingly, the opening-and-closing drive device of the embodiments, having a simple and light configuration, includes the clutch mechanism ( 40 ,  110 ), which allows the power transmission between the electric motor  35  and the opening-and-closing member while allowing the manual opening and closing operation of the opening-and-closing member, and which absorbs the shock load generated when the force is applied to the opening-and-closing member in the direction opposite to the operating direction while the opening-and-closing member is being actuated. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the present invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments 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 disclosure. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.