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This application is based on and claims priority under 35 U.S.C. § 119 with respect to Japanese Patent Application No. 2002-122157 filed on Apr. 24, 2002, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention generally relates to an opening and closing device. More particularly, the present invention pertains to an opening and closing device associated with a movable member (e.g., a vehicle door) for moving the movable member (e.g., opening and closing the vehicle door) using a gear actuation. 
     BACKGROUND OF THE INVENTION 
     A known opening and closing device for a movable member (opening and closing body) is disclosed in Japanese Patent Laid-Open Publication No. 2000-335245. The known opening and closing device disclosed in Japanese Patent Laid-Open Publication No. 2000-335245 is applied to a backdoor provided on a rear portion of a vehicle as the opening and closing device of the movable member. 
     The opening and closing device disclosed in Japanese Patent Laid-Open Publication No. 2000-335245 includes a drive mechanism provided on a vehicle body side and an operation transmission mechanism for connecting the drive mechanism and the backdoor. The backdoor is opened and closed by transmitting the drive force of the drive mechanism to the backdoor via the operation transmission mechanism. The output of an electric motor included in the drive mechanism is transmitted to the operation transmission mechanism by the gear connection. 
     The opening and closing of the backdoor is generally assisted by a damper stay. The damper stay corresponds to a gas piston sealed with high pressure gas. The damper stay generates a resultant force in the closing direction added with the weight of the backdoor per se during the first half of the operation for opening the backdoor to prevent the sudden door opening. On the other hand, the damper stay assists to open the door by generating the resultant force in the opening direction added with the weight of the backdoor per se during the last half of the operation for opening the backdoor. 
       FIGS. 9   a ,  9   b  show the dynamic transmission between a drive gear (i.e., a gear on a motor side)  91  and a driven gear (i.e., a gear on a door side)  92  of the drive mechanism.  FIG. 9   a  shows the first half of the door opening operation.  FIG. 9   b  shows the last half of the door opening operation. For explanatory purpose, distances between adjacent gear teeth  91   a  of the drive gear  91  and distances between adjacent gear teeth  92   a  of the driven gear  92  are exaggerated. As shown in  FIG. 9   a , a force is applied to the driven gear  92  tending to urge the driven gear  92  in the counter direction to the rotational direction of the drive gear  91  during the first half of the door opening operation of the backdoor because the backdoor affecting the driven gear  92  applies a force in the closing direction during the first half of the door opening operation. Thus, the driven gear  92  follows the rotation of the drive gear  91  pushing the gear teeth  92   a  of the driven gear  92  with the gear teeth  91   a  thereof. Accordingly, the backdoor is moved in the opening direction via the driven gear  92 . 
     On the other hand, as shown in  FIG. 9   b , during the last half of the door opening operation, when the backdoor is moved to a position exceeding a position balancing the force of the damper stay and the weight of the backdoor per se, the backdoor applies a force in the opening direction to urge the driven gear  92  in the same rotational direction as the drive gear  91 . Because of the fluctuation in the rotational direction of the force applied to the driven gear  92  by virtue of the weight of the backdoor at the damper stay, the driven gear  92  moves within a backlash range relative to the drive gear  91  to suddenly move the backdoor. This deteriorates the smooth swinging movement of the door opening operation. 
     A need thus exists for an opening and closing device of an movable member for performing a relatively smooth opening and closing operation by restraining undesirable sudden swinging movement of the movable member. 
     SUMMARY OF THE INVENTION 
     In light of the foregoing, the present invention provides an opening and closing device for moving a movable member which includes a drive gear connected to a power source, a driven gear geared with the drive gear, an immovable portion supporting the drive gear and the driven gear, and a dynamic transmission mechanism connected to the driven gear so that the driven gear and the dynamic transmission mechanism rotate together as a unit. The dynamic transmission mechanism transmits a drive force of the power source from the driven gear to the movable member. A direction of a rotational force affecting the driven gear via the dynamic transmission mechanism in accordance with a state of the movable member fluctuates. The opening and closing device further includes a friction member located at least at one position between relatively movable facing surfaces of the immovable portion, the drive gear, the driven gear, and the dynamic power transmission mechanism. 
     According to another aspect of the present invention, an opening and closing device for moving a movable member includes a drive gear connected to a power source, a driven gear geared with the drive gear, an immovable portion supporting the drive gear and the driven gear, a dynamic transmission mechanism, connected to the driven gear so that the driven gear and the dynamic transmission mechanism rotate together as a unit, the dynamic transmission mechanism transmitting a drive force of the power source from the driven gear to the movable member, and a shock absorbing member for applying a force to the movable member in accordance with a state of the movable member. A direction of a rotational force affecting the driven gear via the dynamic transmission mechanism in accordance with a resultant force from a weight of the movable member and the shock absorbing member fluctuates. The opening and closing device further includes a friction member applied at least at one position between relatively movable facing surfaces of the immovable portion, the drive gear, the driven gear, and the dynamic power transmission mechanism. 
     According to further aspect of the present invention, an opening and closing device for moving a movable member includes a drive gear connected to a power source, a driven gear geared with the drive gear, a housing supporting the drive gear and the driven gear, and an arm, connected to the driven gear so that the driven gear and the arm rotate together as a unit. The arm transmits a drive force of the power source from the driven gear to the movable member. A direction of a rotational force affecting the driven gear via the arm in accordance with a state of the movable member fluctuates. The opening and closing member further includes a friction member located at least at one position between relatively movable facing surfaces of the housing, the drive gear, the driven gear, and the arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements. 
         FIG. 1  shows a perspective exploded view of an opening and closing device according to a first embodiment of the present invention. 
         FIG. 2  is a partial cross-sectional view of the opening and closing device according to the first embodiment of the present invention. 
         FIG. 3  is a front view of the opening and closing device according to the first embodiment of the present invention. 
         FIG. 4  is an over view of the opening and closing device according to the first embodiment of the present invention. 
         FIG. 5  is a perspective exploded view of an opening and closing device according to a second embodiment of the present invention. 
         FIG. 6  is a cross sectional view of the opening and closing device according to the second embodiment of the present invention. 
         FIG. 7  is a perspective exploded view of an opening and closing device for particularly indicating portions applied with high viscosity grease according to a third embodiment of the present invention. 
         FIG. 8  is a cross sectional view taken on line VIII—VIII of  FIG. 3 . 
         FIG. 9   a  is an explanatory illustration for purpose of explaining the dynamic transmission of the drive gear and the driven gear during the first half of the door opening operation. 
         FIG. 9   b  is an explanatory illustration for purpose of explaining the dynamic transmission of the drive gear and the driven gear during the last half of the door opening operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of an opening and closing device will be explained with respect to the drawing figures of  FIGS. 1–4 . As shown in  FIG. 4 , an electric backdoor system  1  includes a backdoor  3  serving as a movable member connected to a top rear portion of a vehicle body  2  with a hinge, an actuator  4  for electrically opening and closing the backdoor  3 , and a damper stay  5  serving as a shock absorbing member. 
     The actuator  4  includes a drive unit  11  secured to a rear pillar  2   a  of the vehicle body  2 , an arm  12  serving as a dynamic transmission mechanism connected to an output shaft of the drive unit  11  to be unitarily rotated, and a rod  13  for connecting a tip end portion of the arm  12  and a base end portion of the backdoor  3 . The rod  13  is connected to the tip end portion of the arm  12  and the base end portion of the backdoor  3  via a ball joint construction  7  (shown in  FIG. 8 ) respectively so that the displacement is allowed while rotating. 
     Under the closed state of the backdoor  3 , the tip end side of the arm  12  is arranged to be positioned on a first side (i.e., bottom side of  FIG. 4 ). In accordance with this, the rod  13  is folded. On the other hand, under the state that the backdoor  3  is open, the arm  12  is rotated in one direction (i.e., counterclockwise direction of  FIG. 4 ) to position the tip end side of the arm  12  on a second side (i.e., right side of  FIG. 4 ). Accordingly, the rod  13  is pushed to support the backdoor  3  under the open state. By moving the arm  12  between the foregoing two states by driving the drive unit  1 , the backdoor  3  is opened and closed. 
     The damper stay  5  includes a gas piston injected with the high pressure gas. One end and the other end of the damper stay  5  are connected to the rear portion of the vehicle body  2  and the base end portion of the backdoor  3  respectively. The damper stay  5  generated the resultant force in the closing direction added with the weight of the backdoor  3  per se during the first half of the operation for opening the backdoor  3  to prevent the sudden door opening. On the other hand, the damper stay  5  assists to open the door by generating the resultant force in the opening direction along with the weight of the backdoor  3  per se during the last half of the opening operation of the backdoor  3 . In other words, the damper stay  5  adds the force either one of in the closing direction or the opening direction to the backdoor  3  with reference to the position balancing the generated force and the weight of the backdoor  3  per se. By the fluctuation of the force applied to the backdoor  3 , the rotational direction affecting the arm  12  and the drive unit  11  connected to the backdoor  3  via the rod  13  is fluctuated. 
     The configuration of the drive unit  11  and the arm  12  will be explained with reference to  FIGS. 1–3 . As shown in  FIGS. 1–3 , the drive unit  11  includes an electric motor  21  with decelerator serving as a drive source, a lower case  22  and an upper case  23  serving as an improvable portion (or a fixed housing), a motor side gear  24 , a drive gear  25 , a rotational shaft  26 , a driven gear  27 , and a rubber ring serving as a frictional member. 
     The electric motor  21  with the decelerator accommodates the decelerator including a worm and a worm wheel. An output shaft  31  of the electric motor  21  with a decelerator is projected on one side (i.e., top side of  FIG. 1 ). A serration  31   a  is provided on the output shaft  31 . 
     The lower case  22  is configured being approximately stepped plate shape. The lower case  22  is formed with a bore  22   a  to be inserted with the output shaft  31 . The lower case  22  is provided with the shaft potion  22   b  projected to one side (i.e., top side of  FIG. 1 ) corresponding to the drive gear  25 . Further, the lower case  22  is formed with a bearing bore  22   c  formed corresponding to the rotation shaft  26 . The rotational shaft  26  is rotatably supported by the lower case  22  by being inserted into the bearing bore  22   c.    
     The motor side gear  24  is provided with a bore and is fitted on the output shaft  31 , so that the output shaft  31  passes through the bore. The motor side gear  24  is positioned in the inserting bore  22   a  of the lower case  22 . A serration  24   a  is formed on the internal peripheral surface of the bore in the motor side gear  24  and is adopted to engage the serration  31   a  on the output shaft  31 . The motor side gear  24  is thus unitarily rotated with the output shaft  31  by virtue of the engagement of the serration  24   a  with the serration  31   a  of the output shaft  31 . 
     The drive gear  25  is rotataby supported by the lower case  22  via the shaft portion  22   b  of the lower case  22 . The drive gear  25  includes a first gear portion  25   a  having larger diameter than that of the motor side gear  24  and a second gear portion  25   b  having a smaller diameter than that of the first gear portion  25   a . The first gear portion  25   a  of the drive gear  25  is geared with the motor side gear  24  and thus the drive gear  25  is rotatably driven by the electric motor  21  with the decelerator. 
     The rotational shaft  26  is formed in approximately stepped pillar shape. A first shaft portion  26   a  of the base end side (i.e., bottom side of  FIG. 1 ) is inserted into the bearing bore  22   c  of the lower case  22  so that the rotational shaft  26  is rotatably supported by the lower case  22 . The rotation shaft  26  is configured to have steps whose diameters being reduced from the first shaft portion  26   a  to a tip end side. The rotational shaft  26  includes a first serration shaft portion  26   b , a second shaft portion  26   c , a second serration shaft portion  26   d , and a screw portion  26   e . The driven gear  27  is secured to the first serration shaft portion  26   b  and the arm  12  is secured to the second serration shaft portion  26   d.    
     The driven gear  27  has a sector gear construction configured to have a portion of a circumference and is connected to the rotation shaft  26  for unitary rotating with the rotation shaft  26 . The driven gear  27  is formed with the penetration bore penetrated in the axial direction and an internal peripheral surface of the penetration bore is formed with a serration  27   a  corresponding to the serration of the first serration shaft portion  26   b . Accordingly, the driven gear  27  is connected to the rotations shaft  26  to be unitary rotatable by securing the serration  27   a  to the serration of the first serration shaft portion  26   b . The driven gear  27  is geared with the second gear portion  25   b  of the drive gear  25  so that the driven gear  27  is rotated by the drive gear  25  along with the rotation shaft  26 . 
     The rubber ring  28  is configured to be approximately circular shape having an internal diameter larger than the internal diameter of the serration  27   a  of the driven gear  27 . The rubber ring  28  is penetrated to be placed in approximately coaxial to the rotation shaft  26  surrounding the second shaft portion  26   c  of the rotation shaft  26  projected to one side to be connected to the driven gear  27 . The rubber ring  28  is provided between the driven gear  27  and the uppercase  23 . 
     The upper case  23  is formed in the approximately stepped place shape. An inserting bore  23   a  being inserted with the tip end portion of the shaft portion  22   b  penetrating through the driven gear  25  is formed on the upper case  23 . Thus, the drive gear  25  is accommodated between the opposing surfaced between the lower case  22  and the upper case  23  and the movement of the drive gear  25  in the axial direction is restricted. The upper case  23  is provided with a bearing bore  23   b  formed corresponding to a tip end portion of the second shaft portion  26   c  inserted into the rubber ring  28 . The rotation shaft  26  is inserted into the bearing bore  23   b  to be rotatably supported by the upper case  23 . Thus, the rotation shaft  26  is rotatably supported between the lower case  22  and the upper case  23  along with the driven gear  27 . 
     As shown in  FIG. 2 , the arm  12  is fitted through the shaft bore  23   b  of the upper case  23  to be secured to the second serration shaft portion  26   d  of the rotation shaft  26  projected to one side (i.e., top side of  FIG. 2 ) to be unitarily rotated with the rotation shaft  26 . More specifically, a sleeve  12   a  projected in the axial direction corresponding to the rotation shaft  26  (i.e., second serration shaft portion  26   d ) is secured to the base portion of the arm  12  and a serration  12   b  is formed in an internal peripheral surface of the sleeve  12   a  corresponding to the serration of the second serration shaft portion  26   d . By fitting the serration  12   b  to the serration of the rotation shaft  26  (i.e., the second serration shaft portion  26   d ), the arm  12  is configured to be unitarily rotated with the rotation shaft  26 . A nut  32  is screwed on a screw portion  26   e  of the rotation shaft  26  projected to the one side (i.e., top side of  FIG. 2 ) after fitting the arm  12 . 
     With the foregoing construction, when the output shaft  31  is rotated in one direction by supplying the power to the electric motor  21  with the decelerator, the rotation is transmitted to the arm  12  via the motor side gear  24 , the drive gear  25  (i.e., the first gear portion  25   a  and the second gear portion  25   b ), and the driven gear  27 . Thus, the rotation of the arm  12  is transmitted to the backdoor  3  via the rod  13  for moving the backdoor either in the opening direction or in the closing direction depending on the rotational direction of the arm  12  (shown in  FIG. 4 ). 
     Provided that the direction of the rotational force urging the driven gear  27  via the arm  12  and the rod  13  in accordance with the resultant force of the force from the damper stay  5  and the weight of the backdoor  3  per se is fluctuated (shown in  FIGS. 9   a ,  9   b ). In this case, the drastic change of the urged rotational direction is restrained by the sliding resistance by the rubber ring  28 . In addition, because the movement of the driven gear  27  relative to the driven gear  25  within the range of the backlash is restrained, the undesirable sudden swinging movement due to the sudden movement of the backdoor  3  can be restrained. 
     According to the embodiment of the present invention, the rubber ring  28  is provided between the driven gear  27  and the upper case  23 . Thus, even when the direction of the urged rotational force affecting the driven gear  27  via the rod  13  and the arm  12  in accordance with the resultant force of the force of the damper stay  5  and the weight of the backdoor  3  is fluctuated, the sudden change of the urged rotational direction can be restrained by the sliding resistance of the rubber ring  28 . In addition, because the movement of the driven gear  27  relative to the drive gear  25  within the backlash range is restrained, the undesirable sudden swinging movement due to the sudden movement of the backdoor  3  can be restrained. Thus, the opening and closing operation of the backdoor  3  can be performed smoothly. 
     According to the embodiment of the present invention, the rubber ring  28  can be provided by using the existing housing (i.e., upper case  23 ) for accommodating the driven gear  27 . Thus, the burden at design change can be mitigated. 
     According to the embodiment of the present invention, the rubber ring  28  is positioned approximately coaxial to the driven gear  27 . This absorbs the movement of the driven gear  27  in the axial direction. 
     According to the embodiment of the present invention, the movement within the range of the backlash can be swiftly performed during the initial stage by providing the rubber ring  28  for restraining the sudden change of the urged rotational direction in the drive unit  11  on a portion closest to a final deceleration portion of the drive unit  11 , that is, the loaded side (i.e., backdoor  3 ). Embodiment is not limited to the above-explained embodiment and can be varied as follows. 
     With the first embodiment of the present invention, the rubber ring  28  is provided as the friction member. Instead of the rubber ring  28 , a wave washer  41  (serving as spring ring) may be provided as the friction member as shown in  FIGS. 5–6 . Although a plurality of (i.e., three) wave washers  41  are piled as shown in  FIGS. 5–6 , the number of the wave washers  41  is not limited to three as long as generating the favorable sliding resistance by the elastic force. In place of the wave washer  41 , a coned disc spring or a coil spring may be applied. 
     Although the annular shape friction member such as the rubber ring  28  and the wave washer  41  are applied in the foregoing embodiment, the configuration of the friction member is not limited to the annular shape. For example, a rubber plate serving as the friction member can be provided between the upper case  23  and the driven gear  27 . 
     According to the embodiment, the friction member such as the rubber ring  28  and the wave washer  41  is provided between the upper case  23  and the driven gear  27 . However, the friction member may be provided between the upper case  23  and the arm  12 . The rotational shaft  26  may be provided with a flange or the like opposing to the upper case  23  and the friction member may be provided between the flange or the like and the upper case  23 . 
     Although the friction member such as the rubber ring  28  and the wave washer  41  is provide between the upper case  23  and the driven gear  27  in the foregoing embodiment, the friction member may be provided between the lower case  22  and the driven gear  27 . 
     Although the rotation shaft  26  and the driven gear  27  are provided individually and the rotation shaft  26  and the driven gear  27  are connected in the foregoing embodiment, the rotation shaft  26  and the driven gear  27  may be formed as in one unit. By constructing the rotation shaft  26  and the driven gear  27  as one unit, the number of the parts is reduced in addition to obtaining other effects. 
     The position for applying the friction member such as the rubber ring  28  and the wave washer  41  is not limited to one and the optimal effect may be obtained by applying the frictional member at plural positions. 
     According to a third embodiment of the present invention, instead of the rubber ring  28  and the wave washer  41  serving as the friction member, high viscous grease may be applied as the friction member. By selecting high viscous grease with the low worked penetration degree defined in Japanese Industrial Standard (JIS) K2220 is equal to or less than 250 (i.e., the smaller degree number of the worked penetration indicates the higher viscosity), the better effect can be obtained. Because this method is applicable to the product without changing the parts, the manufacturing cost can be reduced. 
     As shown in  FIG. 7 , the high viscous grease may be applied to one of or a plurality of portions indicated as movable portions  27   b ,  25   c ,  22   d ,  31   b.    
     A fourth embodiment of the present invention will be explained as follows. With the foregoing embodiments, the method for providing the friction member in the drive unit  11  or to the drive unit  11  and the arm  12  in order to solve the drawbacks that the swing is generated by the sudden movement of the backdoor at the changing portion of the load affecting deriving from the backlash between gears. Likewise, as explained from the transmission mechanism of the operation force from the drive unit  11  to the backdoor  3 , in case there is a play for the connection at the ball joint mechanism  7  for connecting the arm  12  and the rod  13 , the phenomenon that the backdoor is suddenly moved is generated. In order to solve the drawback, as shown in  FIG. 8 , a clearance  72  for pooling the grease is provided between a bearing portion  13   a  of the ball joint mechanism  7  formed on the end portion of the rod  13  and a ball  71  fixed to the arm side. By sealing the high viscous grease into the clearance  72 , the sudden load change due to the play can be restrained. Further, by providing a shock absorbing member  73  to prevent the noise generated by the interference between the arm  12  and the rod  13  by the rotation of the rod  13  in the direction shown with an arrow a in  FIG. 8 , further favorable effect can be obtained. 
     Although the drive force of the drive unit  11  (i.e., driven gear  27 ) is transmitted to the backdoor  3  via the arm  12  and the rod  13  in the foregoing embodiments, other constructions may be applied. 
     The construction of the electric motor  21  with the decelerator side for transmitting the dynamic to the drive gear  25  of the drive unit  11  is an example and other construction may be applied. 
     Although the embodiments of the present invention is applied to the electric backdoor system  1 , the embodiment of the present invention may be applied to a system for electrically opening and closing a gull wing door which upwardly flips the side doors of the vehicle. 
     Although the embodiment of the present invention is applied to the movable member (i.e., backdoor  3 ) having the damper stay  5 , the damper stay  5  is not always necessary. For example, the direction of the rotation force affecting the driven gear  27  is changed depending on the relationship between the rotation range of the movable member and the gravity direction only by the weight of the movable member per se without the assist of the damper stay  5 . Accordingly, the same effects can be obtained even in this case. 
     Although the spring ring, the rubber ring, and the high viscous grease serving as the friction member are applied separately in the embodiments, any combination of the spring ring, the rubber ring, and the high viscous grease is applicable. 
     According to the embodiment of the present invention, the smooth opening and closing operation can be performed by restraining the swing of the movable member. 
     According to the embodiment of the present invention, the friction member can be applied using the existing hosing. Thus, the load for design change can be mitigated. 
     According to the embodiment of the present invention, by positioning the friction member coaxial to the driven gear, the vibration of the driven gear in the axial direction can be absorbed. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiment described herein is to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.

Summary:
An opening and closing device for moving a movable member which includes a drive gear connected to a power source, a driven gear geared with the drive gear, an immovable portion supporting the drive gear and the driven gear, and a dynamic transmission mechanism connected to the driven gear so that the driven gear and the dynamic transmission mechanism rotate together as a unit. The dynamic transmission mechanism transmits a drive force of the power source from the driven gear to the movable member. A direction of a rotational force affecting the driven gear via the dynamic transmission mechanism in accordance with a state of the movable member fluctuates. The opening and closing device further includes a friction member located at least at one position between relatively movable facing surfaces of the immovable portion, the drive gear, the driven gear, and the dynamic power transmission mechanism.