A drive unit for a vertical Venetian blind includes a shared driving element ( 15 ) for the displacing motion and the rotating motion of vertical slats. A differential gear ( 13 ) is provided with a driving element coupled to the shared driving element ( 15 ), a first driven element ( 17 ) coupled to the first drive means ( 21 ) for the rotating motion of the vertical slats, and a second driven element ( 16 ) coupled to second drive means for the displacing motion of the vertical slats. Displacing motions and rotating motions of the vertical slats can be driven by the shared driving element ( 15 ). A complete closing of the vertical slats is made possible in both directions of rotation and, at the same time, a hooking up of the vertical slats by means of displacing same in an unsuitable rotating position is prevented.

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2006 023 789.7 filed May 16, 2006, and German Patent Application DE 20 2007 000 605.5 filed Jan. 10, 2007, the entire contents of each German Patent Application is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention pertains to a drive unit for a vertical Venetian blind with a shared driving element for the displacing motion and the rotating motion of vertical slats, with a differential gear, whose first driving element is coupled to the shared driving element, whose first driven element is coupled to first drive means for the rotating motion of the vertical slats, and whose second driven element is coupled to second drive means for the displacing motion of the vertical slats.  
       BACKGROUND OF THE INVENTION  
       [0003]     In drive units of this type, both the displacing motion and the rotating motion of the vertical slats are driven by means of the shared driving element. In the meaning of this patent application differential gear is defined here such that a driving element with two driven elements is coupled using gears, so that either both driven elements or, with one driven element fixed, the other driven element are or is driven by means of the driving element. Moreover, by means of a differential gear of this type, it is possible, like in a differential, by fixing one driven element, to achieve a reversal of direction of the other driven element. In drive units of the above-mentioned type, a driving gear for the displacing of the vertical slats is driven, for example, by means of a planet gear as a differential gear. In this case, moreover, a spline shaft for the rotation of the slats is driven via an outer ring on the pinion cage of the planet gear. Since the necessary forces for the rotation of the slats are lower than for the displacing of the slats, when the driving element is actuated, first the necessary rotating motion of the vertical slats is carried out and then the displacing of the vertical slats. In particular, in case of an open vertical Venetian blind, at first the vertical slats are rotated into their closed orientation and then extended in this closed, rotated position for closing the vertical Venetian blind. To open the vertical Venetian blind, the shared driving element is actuated in the opposite direction. Here, the vertical slats again rotate at first into their opposite rotated position because of the lower force that is needed for this. When this opposite rotated position is reached, a stop limits a first rotation, such that the rotating motion and the related first driven element are blocked. With another actuation of the shared driving element, a displacement of the vertical slats takes place by means of the second driven element for the complete opening of the vertical Venetian blind. So that the vertical slats do not now get hooked up in their opposite rotated position with the opening of the vertical Venetian blind, this opposite rotated position is aligned in such a way that complete shading in this opposite rotated position is not possible. However, with different angles of incidence, it would be desirable for the vertical slats to be able to be closed completely in both directions of rotation. Up to now, however, this possibility requires either a separate driving element for the rotating motion or a gear with switching possibilities between rotating motion and displacing motion. A separate driving element for the rotating motion is uncomfortable, since in this case, for example, two ball chains have to be operated and, according to experience, the wrong ball chain is usually actuated. Thus, instead of performing a turning of the vertical slats, a displacing of the slats may be actuated in this case, which, in the closed rotated state, may lead to hooking up of the vertical slats. A switchable gear is in turn complicated and prone to difficulties. Moreover, the actuation of such a switchable gear is possible only with difficulty at unfavorable pulling angles.  
       SUMMARY OF THE INVENTION  
       [0004]     The basic object of the present invention is thus to provide a drive unit for a vertical Venetian blind, with which displacing motion and rotating motion of the vertical slats can be driven by means of a shared driving element, whereby a complete closing of the vertical slats is made possible in both directions of rotation and, at the same time, a hooking up of the vertical slats by means of moving same in an unsuitable rotated position shall be prevented as much as possible.  
         [0005]     The object is accomplished in that in a drive unit of the type mentioned above another differential gear is inserted between the first driven element and the first drive means for the rotating motion.  
         [0006]     When the vertical slats are rotated into their position necessary for opening the vertical Venetian blind, a reversal of direction can be brought about by means of this other differential gear to the extent that the vertical slats are at first completely rotated in the opposite direction for closing and with further actuation of the shared driving element in the same direction of actuation by means of the other differential gear, the vertical slats are at first again slightly opened, before moving of the vertical slats for opening starts.  
         [0007]     One variant of the present invention is characterized in that the other differential gear has another driving element, another first driven element and another second driven element, that the other driving element is coupled to the first driven element, and that the other first driven element is coupled to the first drive means for the rotating motion. In this way, the drive means for the rotating motion can be driven with the other differential gear in a simple and reliable manner. Thus, it is possible for limiting means to be assigned to the other second driving element for limiting the motion of the other second driving element. The limiting means may have, for example, a spiral at the other second driven element and a worm gear assigned to same, which together form a stop for limiting the motion of the other second driven element. Moreover, it is advantageous if the limiting means are embodied such that the rotation range of the vertical slats is limited to 180°. In this way, a complete closing of the vertical slats in both directions of rotation can be achieved by means of actuating the shared driving element.  
         [0008]     Another variant of the present invention is characterized in that other limiting means are assigned to the other driving element, which limit the relative motion between the other driving element and the other second driven element. If the motion of the other second driven element is thus hindered in this case by means of the limiting means, it can be guaranteed by means of the other limiting means that the other driving element can still be moved a little bit against the other second driven element. For example, the other limiting means may have another stop each at the other driving element and at the other second driving element. It is then possible that the relative motion between the other driving element and the other second driven element is limited to one revolution by means of the other stops. This embodiment offers the possibility to use the other stops for two discrete stopping positions. In this mode of operation, it is possible that when the shared driving element is actuated, a rotating motion is carried out to the extent that the limiting means prevent another rotation of the vertical slats, whereby, at the same time, the other stops completely block the other differential gear in this position. With another actuation of the shared driving element, a displacing motion of the vertical slats for closing then starts by means of the differential gear. If the shared driving element now in the closed state is actuated in the opposite direction, then the vertical slats are at first rotated in their opposite, closed rotated position by means of the other differential gear, whereby the limiting means in this opposite, closed, rotated position limit another motion of the other second driven element. If the shared driving element is now further actuated in the same direction, then a reversal of direction of the other first driven element takes place because of the blocked other second driven element. By means of the other stops, because of the reversal of direction of the other first driven element, the vertical slats can again be opened to the extent that the other differential gear is blocked by means of the other stops after one revolution between the other driving element and the other second driven element and thus a displacing motion via the differential gear is initiated. The other driving element may be connected to the other second driven element, for example, in a spring-mounted manner. No rigid stopping action occurs in this case. Rather, already with a sufficiently large opening angle of the vertical slats, such that the spring force corresponds approximately to the force needed for displacing, a displacing of the vertical slats can be started. The other driving element may be connected to the other second driven element, for example, by means of an especially pretensioned leg spring.  
         [0009]     However, such a spring-mounted connection of the other driving element to the other second driven element may also be considered to be a drawback. On the one hand, malfunction may occur in case of defective coordination of the spring rate or wear or contamination of the mechanism, in which a displacing of the vertical slats already starts, before the springs are already deflected and the vertical slots have thus been rotated into a displaced position. Another advantageous variant arises hereby in that the other driving element is detachably connected to the other second driven element by means of a snap-in coupling. In this case, a spring force does not have to be overcome, but rather it is sufficient to release the snap-in coupling. This can be accomplished, for example, by the snap-in coupling having a radially pretensioned spring section at the other first driven element, which can be released from a coupling position with a release element assigned to the other second driven element. This spring section acts here as a carrier and is pretensioned in its coupling position in such a way that a snap-in connection is reliably produced in the coupling position by means of the spring force, while this snap-in connection is released with the release element when the spring section is released. Furthermore, it is advantageous if the spring section in the coupling position actively meshes with a mount assigned to the other second driven element. By means of this active meshing, for example, a torque can be transmitted from the spring section onto the mount and thus onto the other second driven element. An advantageous embodiment of the release element arises in that a section connected at the spiral can be driven by means of the worm gear when the stop for actuating the release element is reached. In this case, when the stop is reached, the section is actuated in such a way, for example, pressed radially inwards against a spring force, that the spring section is released from the mount, so that the result is an uncoupled position.  
         [0010]     Another embodiment of the present invention is characterized in that the first drive means for the rotating motion of the vertical slats have a spline shaft, which is connected to the other first driving element in a manner adapted to rotate in unison. By means of such a spline shaft, a rotating gear in the traveling carriage of the vertical slats can be actuated in the known manner. At the same time, this spline shaft offers the possibility of also being used as a bearing for, for example, a toothed wheel as the other driving element.  
         [0011]     Another variant of the present invention is characterized in that the other differential gear is a differential gear. The differential gear here may be a spur planet gear or a bevel planet gear. By means of a differential gear of this type, a reversal of direction can be achieved by fixing the gear housing as the other second driven element.  
         [0012]     In another variant of the present invention, the shared driving element actively meshes with a lengthwise extended, endless pulling element. The shared driving element here may be a chain wheel and the pulling element may be a ball chain. In this way, the chain wheel can be actuated as the shared driving element with the ball chain in a reliable and largely slip-free manner.  
         [0013]     An advantageous embodiment of the present invention is characterized in that the differential gear is a planet gear, whose central wheel is connected to the shared driving element in a manner adapted to rotate in unison. Consequently, the result is an especially compact design. The planet gear may have an outer ring as the first driven element, which meshes with the other driving element. The outer ring may be arranged, for example, at a planet carrier. In this case, a good gearing can be achieved, so that at first a rotation of the vertical slats takes place when the shared driving element is actuated.  
         [0014]     Moreover, it is possible for the second driven element to be actively connected to a driving gear for a pull cord, especially a ball chain, for displacing the vertical slats. If this pull cord is connected, for example, to the first carriage for the vertical slats, a reliable displacement with low exertion of force can thus be guaranteed in a simple manner and with little space requirement.  
         [0015]     Another variant of the present invention pertains to a vertical Venetian blind with a drive unit having the features of the present invention. With such a vertical Venetian blind, shading can be brought about at any angles of incidence in a simple manner and without the risk of error on the part of the operator.  
         [0016]     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the drawings:  
         [0018]      FIG. 1  is an exploded a schematic view of a drive unit having the features of the present invention with open housing;  
         [0019]      FIG. 2  is a perspective top view of the drive unit of  FIG. 1  with removed upper housing part;  
         [0020]      FIG. 3  is a view similar to  FIG. 2  with partly disassembled other differential gear;  
         [0021]      FIG. 4  is a schematic view of the other differential gear in a lateral view for illustrating the stopping function;  
         [0022]      FIG. 5  is a view similar to  FIG. 4  in a state for achieving another completely closed, rotated position of the vertical slats;  
         [0023]      FIG. 6  is a view similar to  FIGS. 4 and 5  of a state for again achieving a partly open rotated position for displacing the vertical slats;  
         [0024]      FIG. 7  is a schematic view of a drive unit with removed upper housing part as another exemplary embodiment of the present invention;  
         [0025]      FIG. 8  is a schematic view of another embodiment of another differential gear;  
         [0026]      FIG. 9  is an enlarged partial view of a front surface of the other differential gear;  
         [0027]      FIG. 10  is a schematic rear view of the other differential gear of  FIG. 8 ;  
         [0028]      FIG. 11  is a top view of the drive unit of  FIG. 7 ; and  
         [0029]      FIG. 12  is a view similar to  FIG. 11  in a released state of the snap-in coupling. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Referring to the drawings in particular,  FIG. 1  shows a schematic view of a drive unit  10  with the features of the present invention. The drive unit is used for driving a vertical Venetian blind not shown in  FIG. 1 . The drive unit  10  has an upper housing part  11  and a lower housing part  12 , wherein in  FIG. 1  the upper housing part  11  is shown removed from the lower housing part  12 .  
         [0031]     As can be inferred from  FIG. 1 , a differential gear  13  and another differential gear  14  are mounted at the lower housing part  12 . In particular, the differential gear is a planet gear  13  and the other differential gear is a differential gear  14 . The planet gear  13  and the differential gear  14  have a shared actuating element  15 , namely a chain wheel  15 . In the exemplary embodiment shown, the chain wheel  15  is connected to a central wheel (not shown in  FIG. 1 ) of the planet gear  13  in a manner adapted to rotate in unison.  
         [0032]     The planet gear  13  has a first driven element  17  and a second driven element  16 . The first driven element  17  in this embodiment is an outer ring  17  on the outer circumference of the planet gear  13 , namely on the planet carrier, and the second driven element  16  is a bevel gear  16 .  
         [0033]     As can be further inferred from  FIG. 1 , a toothed wheel  18  meshes with the outer ring  17 . The toothed wheel  18  is used as the other driving element for the differential gear  14 . For this purpose, the toothed wheel  18  is connected to a bevel gear (not shown in the figure) of the differential gear  14  in a manner adapted to rotate in unison. Moreover, the toothed wheel  18  is connected by means of a leg spring  19  to a bushing  20  of the differential gear  14 , as is explained in detail below. The bushing  20  is used as the housing of the differential gear  14 . A spline shaft  21  extends through the differential gear  14  and the toothed wheel  18  and is connected to a bevel gear (not shown  FIG. 1 ) of the differential gear  14  as the other first driven element. The bushing  20  has a spiral  22  on its outer circumference as the other second driven element of the differential gear  14 .  
         [0034]     Meshing with the spiral  22 , a stop element  24  is pivotably arranged about an axle  23 . The stop element  24  has a toothed ring section  25 .  
         [0035]      FIG. 2  shows a view of the drive unit  10  with the upper housing part removed. As can be clearly inferred from  FIG. 2 , the toothed ring section  25  has six teeth, so that six revolutions of the bushing  20  are possible. In the respective end positions, a front surface of the spiral  22  in each case stops at the stop element  24  in the known manner.  
         [0036]      FIG. 3  shows a view similar to  FIG. 2 , whereby the bushing  20  is removed from the differential gear  14 . As can be inferred from  FIG. 3 , the leg spring  19  has a leg  26 , which meshes with the bushing  20  in the mounted state. Moreover, it can be recognized in  FIG. 3  that the toothed wheel  18  is connected by means of a sleeve  27  to a bevel gear  28  of the differential gear  14  in a manner adapted to rotate in unison. The leg spring  19  is arranged on the sleeve  27 , and a leg of the leg spring turned away from the leg  26  is connected to the toothed wheel  18  in a manner adapted to rotate in unison.  
         [0037]     As can be further inferred from  FIG. 3 , the differential gear has, besides the bevel gear  28 , two other bevel gears  29 ,  30 , which are each mounted rotatably at the bushing  20  by means of axles  31 . Each of the bevel gears  29 ,  30  meshes on one side with the bevel gear  28  and at the end turned away from same with another bevel gear  32 , which forms the other first driven element of the differential gear  14 . The bevel gear  32  is connected to the spline shaft  21  in a manner adapted to rotate in unison.  
         [0038]      FIG. 4  shows the differential gear  14  in a lateral view, as viewed from the toothed wheel  18 . As can be inferred from  FIG. 4 , the sleeve  27  has a mount  33  for a leg at the end of the leg spring  19  turned away from the leg  26 . Another mount  34  is arranged at the bushing  20  and meshes with the leg  26 . The bushing  20  has, moreover, a stop  35 , which, in the exemplary embodiment shown, is a thickened section with rectangular cross section, in the middle of which the mount  34  is formed as a blind hole. Moreover, as can be inferred from  FIG. 4 , a stop  36  is arranged at the bevel gear  28 , which interacts with the stop  35 . In the exemplary embodiment shown, the leg spring  19  is pretensioned in such a way that the stops  35 ,  36  are held against one another in the position shown.  
         [0039]      FIG. 5  and  FIG. 6  each show a view similar to  FIG. 4 , wherein a leg  37  of the leg spring  19  arranged in the mount  33  is shown, moreover, in  FIG. 6 .  
         [0040]     The mode of operation of the drive unit  10  is explained in detail below on the basis of  FIGS. 1 through 6 . For closing a completely open vertical Venetian blind, the chain wheel  15  is actuated by means of a ball chain not shown in the figures. In the completely open state of the vertical Venetian blind, the differential gear  14  is in the state shown in  FIG. 6 , in which the stop element  24  stops at a front end of the spiral  22  and the stop  36  in  FIG. 6  comes into contact with the stop  35  from above. Here the leg spring  19  is tensioned by one revolution. Since the displacing motion of the vertical slats is tighter than the rotation motion thereof, the toothed wheel  18  is now first driven via the outer ring  17  when the chain wheel  15  is actuated. At first the stop  36  is brought into the position under the stop  35  shown in  FIG. 5 , while the leg spring  19  is released. The vertical slats are then brought into a closed position by means of driving the spline shaft  21  via the bevel gears  28 ,  29 ,  30 ,  32  from an approximately 30° open position with stationary bushing  20 . With further actuation of the chain wheel  15 , the bushing  20  is rotated over the stop  36  and the stop  35  to the extent that the stop element  24  is located in its opposite stop positions compared to  FIGS. 5 and 6  and the spiral  22  stops at its other front end at the stop element  24 . The vertical slats are then rotated into their closed, final position. With another actuation of the chain wheel  15 , the bevel gear  16  is driven because of the now blocked toothed wheel  18  and thus also because of the blocked toothed wheel  17 . The bevel gear  16  meshes with a driving gear for a pull cord for displacing the vertical slats. With a further actuation of the chain wheel  15 , the vertical slats are then displaced into their completely closed, final position.  
         [0041]     If now the vertical slats shall be rotated out of the extended position for the complete closing in the opposite direction because of an unfavorable angle of incidence, then the chain wheel  15  is actuated in the opposite direction. The vertical slats are rotated here in the opposite direction by the sleeve  20  being rotated by means of actuating the toothed wheel  18  via the outer ring  17  by means of the spring force of the leg spring  19  to the extent that the stop element  24  has been rotated from the position shown in  FIG. 4  into the position shown in  FIG. 5 .  
         [0042]     For opening the vertical Venetian blind, the chain wheel  15  can be further actuated in the same direction. Because the spiral  22  stops at the stop element  24  and thus prevents a further rotation of the bushing  20 , the bevel gear  28  can be rotated one revolution further against the bushing  20  while tensioning the leg spring  19  until the stop  36  comes to lie at the stop  35  as shown in  FIG. 6  from above. Because the bevel gear  28  meshes with the bevel gears  29 ,  30 , the rotary motion of the bevel gear  28  is converted via the bevel gears  29 ,  30  to the bevel gear  32  into a rotary motion of same in the opposite direction. The vertical slats are rotated by means of the spline shaft  21  for an opening into an approximately 30° opened position. A further actuation of the chain wheel  15  then leads to a displacing of the vertical slats via the bevel gear  16  for opening the vertical Venetian blind because of the differential gear  14 , which is now blocked in this position. Because of the approximately 30° opened position of the vertical slats, they cannot get hooked up when brought together into a pack.  
         [0043]      FIG. 7  shows a schematic view of a drive unit  38  as another exemplary embodiment of the present invention. The drive unit  38  essentially corresponds to the drive unit  10 . Identical elements have the same reference numbers. Unlike the drive unit  10 , the drive unit  38  has another differential gear  39 . In the differential gear shown, the other differential gear is likewise a differential gear  39 . The other differential gear  39  essentially corresponds to the other differential gear  14 . However, the other differential gear  39  does not have a leg spring  19 .  
         [0044]     For better overall view,  FIG. 7  does not show the housing of the other differential gear  39 . As can be inferred from  FIG. 7 , the other differential gear  39  has a bevel gear  40  instead of the bevel gear  32 . Unlike the bevel gear  32 , a part of the outer circumference of the bevel gear  40  is embodied as a spring section  41 . The spring section  41  protrudes a little bit over the outer circumference of the remaining circumference of the bevel gear  40 . In particular, the spring section  41  is pretensioned radially in the outward direction. In  FIG. 7 , the spring section  41  has a front surface  42  at the lower end.  
         [0045]      FIG. 8  shows a perspective view of the differential gear  39 . The differential gear  39  has a bushing  43 , similar to the bushing  20 , as a housing. The bushing  43  likewise has a spiral  44  similar to the spiral  22  as the other second driven element. Unlike in the spiral  22 , the spiral  44  has, however, more than one turn. In particular, a second turn section  45 , which is arranged on a spring section  46 , is connected to the first turn of the spiral  44 . In the normal state, the spring section  46  is embodied as a continuation of the circumference of the bushing  43  in the area of the spiral  44 . On its side turned away from the second turn section  45 , the spring section  46  has a web  47 .  
         [0046]      FIG. 9  shows an enlarged partial view of the front side of the bushing  43 . As can be inferred from  FIG. 9 , a mount, which is turned towards the web  47  and is assigned to the spiral  44 , for the front surface  42  of the spring section  41 , is arranged at the bushing  43 . In the state shown, the front surface  42  actively meshes with the mount  48 , so that a coupled state of the snap-in coupling is produced. In particular, the bevel gear  40  and the bushing  43  and thus the spiral  44  are connected by means of the front surface  42  and the mount  48  to one another in a manner adapted to rotate in unison.  
         [0047]      FIG. 10  shows a perspective rear view of the differential gear  39  similar to the view of  FIG. 4 .  FIG. 11  shows a top view of the drive unit  38  in a coupled state and  FIG. 12  shows a top view of the drive unit  38  in a released state of the coupling.  
         [0048]     The mode of operation of the drive unit  38  is explained in detail below on the basis of  FIGS. 7 through 12 . The mode of operation essentially corresponds to that of the drive unit  10 . A different mode of operation arises when turning the vertical slats for complete closing in the opposite direction in the extended position. In the completely closed position reached during the extension, the spring section  41  actively meshes with the mount  48 , as shown in  FIG. 9 . At the same time, the stop  36 , as shown in  FIG. 10 , stops at the stop  35  from below, and a front end of the spiral  44  abuts against the stop element  24 , as shown in  FIG. 11 . If because of an unfavorable angle of incidence the vertical slat shall now be turned in a position extended in the opposite direction for the complete closing, then the chain wheel  15  is actuated in the opposite direction. Here, the vertical slats are rotated in the opposite direction by the sleeve  43  being rotated by means of actuating the toothed wheel  18  via the outer ring  17  by the active meshing of the spring section  41  and of the mount  48  to the extent that the stop element  24  has been rotated from the position shown in  FIG. 11  into the position shown in  FIG. 12 . In this state, the vertical slats are completely closed in the opposite direction. For opening the vertical Venetian blind, the chain wheel  15  can now be further actuated in the same direction as for rotating. Because the stop  24  now presses the spring section  46  in  FIG. 9  radially in the inward direction via the second turn section  45 , the spring section  41  is pressed via the web  47  radially inwardly to the extent that the front surface  42  no longer meshes with the mount  48 . With a further actuation of the chain wheel  15 , the bushing  43  cannot be further rotated counterclockwise in  FIGS. 8 and 9  because of the stopping of the spiral  44  at the stop element  24 . However, because the spring section  41  no longer meshes with the mount  48  in this state, the toothed wheel  18  can be further rotated by one revolution until it lies on the stop  35  from above in  FIG. 10  after one clockwise rotation of the stop  36 . However, because the bevel gear  28  meshes with the bevel gears  29  and  30 , the rotary motion of the bevel gear  28  in  FIG. 7  in the counterclockwise direction is converted into a clockwise rotary motion of the bevel gear  40 . In this case, the spring section  41  slides along on the inner circumference surface of the bushing  43  under the spiral  44 . With this clockwise rotation of the bevel gear  40  in  FIGS. 7 and 8 , the vertical slats are rotated by means of the spline shaft  21  for opening into an approximately 30° opened position. Because of the differential gear  39  being blocked in this position, a further actuation of the chain wheel  15  then leads to a displacing of the vertical slats by means of the bevel gear  16  for opening the vertical Venetian blind. Because of the approximately 30° opened position of the vertical slats, they cannot get hooked up when being brought together into a pack. The mode of operation of the drive unit  38  is thus similar to that of the drive unit  10 , and the opening by approximately 30° before bringing together into a pack does not take place against the spring  19 , but rather essentially without additional forces after the front surface is no longer meshing with the mount  48 .  
         [0049]     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.  
       Appendix  
     List of Reference Numbers  
       [0000]    
       
           10  Drive unit  
           11  Upper housing part  
           12  Lower housing part  
           13  Planet gear  
           14  Differential gear  
           15  Chain wheel  
           16  Bevel gear  
           17  Outer ring  
           18  Toothed wheel  
           19  Leg spring  
           20  Bushing  
           21  Spline shaft  
           22  Spiral  
           23  Axle  
           24  Stop element  
           25  Toothed ring section  
           26  Leg  
           27  Sleeve  
           28  Bevel gear  
           29  Bevel gear  
           30  Bevel gear  
           31  Axle  
           32  Bevel gear  
           33  Mount  
           34  Mount  
           35  Stop  
           36  Stop  
           37  Leg  
           38  Drive unit  
           39  Differential gear  
           40  Bevel gear  
           41  Spring section  
           42  Front surface  
           43  Bushing  
           44  Spiral  
           45  Second spiral section  
           46  Spring section  
           47  Web  
           48  Mount