BACKGROUND OF THE INVENTION 
   The invention concerns a load torque lock for automatically locking load-side torques. 
   Load torque locks belong to the species of automatically locking locks and are used in terms of their functioning with self-switching free-wheel mechanisms. They are installed as locking elements in a drive train and automatically block the torques initiated by the output mechanism in one or both directions of rotation when the driving mechanism is at an standstill, while the torques initiated by the drive side are transmitted in the one or the other direction of rotation. As a result, torques acting on the load side in a drive train can be supported and locked with the aid of the load torque lock against a stationary frame or housing. It forms a safety element, which prevents impermissible movement of the load side from outside forces or torques in the case of a decrease or cessation of the driving mechanism. Such load torque locks are suited especially for use in drive trains with alternating directions of rotation. Using them permits braking systems or self-locking transmissions that would otherwise be required to be dispensed with. 
   Different types of physical effects are already currently being utilized for load torque locks. Thus, in accordance with DE 30 30 767 C2, a coil spring lock is used for manually driven lifting apparatuses, which utilize a frictionally engaged catch band effect. Moreover, the utilization of a frictional clamping effect is known in accordance with G 89 10 857, according to which clamping rollers cooperate with a profiled output shaft. 
   These systems are based on frictionally engaged principles of action and require a certain pretension of the clamping or locking elements for continual locking readiness in order to cooperate quickly and reliably with components fixed to a frame with the occurrence of load torques. As a result of this pretension of the clamping or locking elements, which is not completely suspended even in the case of a drive-side drive-through, they remain in continual frictional contact with the components fixed to a frame. However, this results in high frictional losses and poor efficiency, which leads to greater warming when high rpms are to be transmitted. The range of application of the load torque locks functioning according to the known frictionally engaged principles of action is therefore restricted to driving mechanisms with low rpms. 
   Another design of the load torque locks is known from DE 197 53 106 C2, which is based on the tilting and swiveling effect. The clamping or locking bodies used there are carried along by rotating the drive shaft with driving elements on an orbit, which has a relatively large radial distance to the axis of rotation of the load torque lock. Because of this off-center arrangement of the clamping or locking bodies, centrifugal forces develop in the case of a drive-side drive-though, which can for their part cause undesired tilting of the clamping or locking bodies. In fact the patent specification mentions in reference to  FIG. 9  that in order to avoid frictional contact of the clamping or locking bodies with the clamping or locking ring unit that is fixed to a frame from developing centrifugal forces, these centrifugal forces can be supported by a certain embodiment via the add-on parts of the output shaft. However, this is only the case at a certain operating point dependent upon the driving mechanism&#39;s rpms and the torque. 
   The attainment at hand attempts to embody a load torque lock in such a way that an impermissible response of the load torque lock to centrifugal forces is reliably avoided over the entire rpm range. 
   SUMMARY OF THE INVENTION 
   The load torque lock, in accordance with the invention, has the advantage that the occurrence of centrifugal forces on the clamping bodies is avoided for the most part by displacing the mass center of gravity of the clamping bodies to the area of the axis of rotation, which in turn results in reliable avoidance over the entire rpm range of centrifugal-force-induced swiveling of the locking bodies and locking of the drive load that is thereby triggered. This results in a further advantage that this type of load torque lock can also be used preferably for high speed driving mechanisms such as electric motors that drive adjusters or components that move back and forth. 
   Advantageous further developments and improvements exist. 
   Thus, the locking body is designed in a simple-to-manufacture and space-saving manner as a locking disk, which is arranged perpendicular to the axis of rotation in the housing and is preferably embodied to be circular or annular. 
   A quick and effective clamping or releasing of the locking disk on the locking ring fixed to the housing is achieved by slightly swiveling the locking disk so that the locking disk features at least two locking means on different radii and offset from one another around an angle in the circumferential direction, of which the one locking means cooperates with the outside of at least one locking ring fixed to the housing and the other locking means cooperates with its inside. 
   In order to counteract any inclination of the locking disk when the load torque lock is responding and to avoid an initial axial springiness of the locking disk, it is proposed that on both front sides of the locking disk two aligned locking means are each arranged laterally reversed, each of which cooperate with one of two locking rings arranged fixed to the housing on both sides of the locking disk. The locking means in this connection are embodied in a simple and reliable manner as clamping bolts projecting from the front side of the locking disk on both sides parallel to the axis of rotation. 
   In order to achieve a reliable clamping of the clamping bolts on the locking rings, they are embodied in a structurally rugged and simple-to-manufacture manner as a locking ring wall projecting from each front side of the housing towards the inside until in front of the locking disk and concentric to the axis of rotation, on whose outside and inside circumferential surfaces a clamping bolt of the locking disk is each able to engage. Locking means known in the state of the art can also be used as an alternative to the clamping bolts, whereby then the outside and inside circumferential surfaces of the locking ring wall must feature a corresponding locking gear design. Alternatively, in the case of load torque locks whose possible load torques are relatively small, a locking ring wall arranged on both sides of the locking disk can be dispensed with by arranging it only on the front side of the locking disk. This allows the axial width of the housing to be reduced. 
   For the lowest possible swiveling of the locking disk in order to achieve a quick response and release of the load torque lock, the locking means are expediently arranged in a radial external area of the locking disk, whereby the driving elements and the locking elements of the drive shaft and the output shaft engage on its radial interior area to swivel the locking disk. 
   It is important for the arrangement of the driving and locking elements that these cooperate as effectively as possible with the locking disk in order to swivel the locking disk for locking and releasing the load torque lock when turning the drive shaft or the output shaft. For this purpose, a first plane is mentally stretched over the axis of rotation, which runs through the locking means (clamping bolts) and, related to this first plane, the at least one driving element is arranged on the one side and the at least one locking element is arranged on the other side of this plane, whereby these elements engage at the locking disk in such a way that they swivel the locking disk to release or lock the locking means (clamping bolts) perpendicular to this first plane in the one direction or the other opposing direction. 
   In order to permit a load torque lock to become effective for both directions of rotation, one driving element and one locking element are each provided for each direction of rotation, which engage on the locking disk. Since to lock or release the load torque lock, the locking disk may be swiveled independently of the direction of rotation of the drive shaft and the output shaft only in the one direction or only in the other opposing direction, the driving and locking elements must consequently be arranged for each direction of rotation. For this purpose, a second plane is stretched over the axis of rotation, which runs perpendicular to the first plane and, related to the this second plane, a driving element and a locking element are each arranged to engage on the one side and a driving element and a locking element are each arranged to engage on the other side of this second plane at the locking disk. 
   In order to guarantee the most defined contact points possible between the driving elements or the locking elements and the locking disk, the driving elements are embodied in a simple and rugged manner as driving bolts projecting from a flange-like end of the drive shaft parallel to the axis of rotation, each of which engages in a larger recess of the locking disk. In addition, the locking elements are embodied in a corresponding manner as locking bolts projecting from a flange-like end of the output shaft parallel to the axis of rotation, each of which engages preferably together with a spring element in a larger recess of the locking disk. 
   It is particularly expedient with respect to the lines of application of the force originating from the driving and locking elements to swivel the locking disk if, when the locking disk is in a position of rest, at least one driving element forms a contact point with the locking disk on its side facing the first plane and if, moreover, the at least one locking element features a small distance to a contact point with the locking disk on its side facing the first plane. In this connection, the previously mentioned distance is bridged in an advantageous manner by the spring element, which is arranged on the locking bolts serving as the locking element. 
   For a compact and rugged embodiment of the load torque lock, it is further proposed that the flange-like ends of the drive shaft and the output shaft be positioned on the opposing front sides of the housing. In this connection, the locking disk is arranged in a structurally simple and safe manner between the spaced-apart, flange-like ends of the drive shaft and output shaft. Since, due to the position of the contact points of the driving and locking elements with the corresponding recesses of the locking disk, the forces that become effective when locking or opening the load torque lock for slight swiveling of the locking disk run almost perpendicular to the first plane, an opened lock in normal operation simultaneously achieves that no significant frictional force occurs between the locking ring fixed with the housing and the locking means (clamping bolts) so that it is possible to dispense with additional measures for contact free revolution on the locking ring. 
   For the most stable possible positioning of the drive shaft and output shaft it is further proposed that the locking disk be provided with a centric opening, through which a bearing neck of the output shaft projects, which is accommodated in a bearing inserted in a front-side bearing bore hole of the drive shaft. Alternatively, this can also takes place in a reverse manner via a bearing neck of the drive shaft positioned on the output shaft. 
   In order to compensate for any imbalance caused by the locking means of the locking disk, it is expediently proposed to arrange a material accumulation on the circumferential area of the locking disk that is diametrically opposed to the locking means in such a way that the mass center of gravity of the locking disk lies as precisely as possible on the axis of rotation. As an alternative to this material accumulation, it is also possible to carry out a material reduction for the same purpose in the area of the locking means (clamping means), e.g., by bore holes in the locking disk arranged in the circumferential direction on both sides next to the locking means (clamping bolts). 
   A compact load torque lock can be achieved in an advantageous manner by the housing being embodied cylindrically inside, whereby a ring air gap sufficient for the swivel movement of the locking disk to release or lock the locking means (clamping bolts) lies between the locking disk and the inside wall of the housing. In the case of this embodiment, the locking means of the locking disk engaging on the inside circumference of the locking ring can also be arranged alternatively on the outside circumference of the locking disk and engage there by swiveling the locking disk on the inside wall of the housing. 
   Instead of driving and locking bolts fastened on the flange-like ends of the drive shaft and output shaft and engaging in the recesses of the locking disk, they can be fastened alternatively in an reverse manner also on the locking disk and engage in corresponding recesses of the flange-like ends of the drive shaft and the output shaft. 
   For a particularly advantageous use of the load torque lock, it is proposed that it be combined with an electric motor into a drive unit, in which the output shaft of the electric motor simultaneously forms the drive shaft of the load torque lock. In addition, the load torque lock can also be used in a preferred manner in cases where till now self-locking transmission with an efficiency of &lt;50% are being used. For this purpose it is proposed that the load torque lock be used between the output shaft of an electric motor and the drive shaft of a non-self-locking transmission unit. Such a system has the advantage that the overall degree of efficiency of the system is clearly increased above 50% by the use of an easy-running transmission. In addition, the functional and/or manufacturing-related swing angle clearances connected with a load torque lock are transmitted to the transmission output only to a degree that corresponds to the transmission ratio. In addition, rotational movements initiated on the drive side in both directions of rotation are blocked while maintaining the drive-side possibility of power transmission. Due to the improved efficiency of such a system, an electric motor with a smaller structural shape and the same drive power can consequently be used with the advantages of cost savings, smaller construction space, a lower mass and inertia of masses, better dynamic behavior, lower consumption of energy and better installation conditions. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional details of the invention are explained in more detail in the exemplary embodiment described in the following on the basis of the associated drawings. The drawings show: 
       FIG. 1  shows a cross-section of a load torque lock in accordance with the invention according to Line I—I from  FIG. 2 . 
       FIG. 2  shows the same load torque lock in a longitudinal section of the housing. 
       FIG. 3  shows a schematic block diagram of drive unit made up of an electric motor and a load torque lock. 
       FIG. 4  shows a schematic block diagram of drive system made up of an electric motor, load torque lock and transmission unit. 
   


   DETAILED DESCRIPTION 
     FIGS. 1 and 2  show a cross-section or longitudinal section of load torque lock  10  in accordance with the invention. It has a stationary housing  11  fixed to a frame with an external cylindrically embodied housing wall  12  and flange-like front sides  11   a  and  11   b , on which a drive shaft  14  with a flange-like end  14   a  is pivoted on the one side  11   a  and an output shaft  15  with a flange-like end  15   a  is pivoted on the other side  11   b . The drive shaft and output shaft  14 ,  15  lie on a common axis of rotation  16 . Arranged between their spaced-apart, flange-like ends  14   a ,  15   a  is a locking body in the form of a locking disk  17  in a housing  11 , which cooperates via locking means with locking rings fixed with the housing. The locking rings are embodied in the exemplary embodiment as a locking ring walls  18  projecting from the two front sides  11   a ,  11   b  of the housing  11  towards the inside until in front of the locking disk  17  and concentric to the axis of rotation  16 . Serving as locking elements are two clamping bolts  19  and  20  that are solidly inserted in the locking disk  17  parallel to the axis of rotation  16 , which project from the locking disk  17  laterally reversed on both sides. Thus, on both sides of the locking disk  17 , the clamping bolts  19  and  20  each form two aligned locking means, which each cooperate with one of the locking ring walls  18  fixed to the housing on both sides of the locking disk  17 . The two clamping bolts  19  and  20  are arranged on radii of varying sizes in the external circumferential area of the locking disk  17 , whereby the clamping bolt  19  cooperates with the larger radius to the axis of rotation  16  with the outside  21  and the clamping bolt  20  cooperates with the smaller radius to the axis of rotation  16  with the inside  22  of the two locking ring walls  18 . In order to be able to clamp or release the clamping bolts  19  and  20  to the locking ring walls  18  by a slight swiveling on both sides transverse to the axis of rotation  16 , the two clamping bolts  19  and  20  are offset from one another in the circumferential direction by an angle α, which is approx. 5° in the case of the example given. The outside and inside  21 ,  22  of the locking ring walls  18  thus form working surfaces for the clamping bolts  19  and  20  to fix the locking disk  17 . 
   While the clamping bolts  19  and  20  are arranged in a radial external area of the locking disk  17 , driving and locking elements of the drive shaft and the output shaft  14 ,  15  engage in a radial interior area to swivel the locking disk  17 . In this connection, the driving elements are formed by driving bolts  23 ,  24  projecting from the flange-like end  14   a  of the drive shaft  14  parallel to the axis of rotation  16 , each of which engages in a larger recess  25 ,  26  in the form of a bore hole of the locking disk  17 . The locking elements in this case are formed by two locking bolts  27 ,  28  projecting from the flange-like end  15   a  of the output shaft  15  parallel to the axis of rotation  16 , which each engage with a fitted spring element in the form of a ring  29  made of elastic material in a larger recess  30 ,  31  in the form of a bore hole of the locking disk  17 . By rotating the drive shaft or output shaft  14 ,  15  in the one or the other direction of rotation, the locking disk  17  can be swiveled somewhat to one or the other side by a driving bolt  23 ,  24  or locking bolt  27 ,  28  around a non-fixed, anisotrophic swiveling axis  32  running between the two clamping bolts  19 ,  20 . 
   In the exemplary embodiment according to  FIG. 1 , the locking disk must be swiveled somewhat to the right to clamp the clamping bolts  19  and  20  on the locking ring walls  18 , while it must be swiveled somewhat to the left to release the clamping bolts  19 ,  20  from the locking ring walls  18 . In order to guarantee that this happens, the driving bolts and locking bolts  23 ,  24  and  27 ,  28  must correspondingly engage on the locking disk  17 . For this purpose, a first plane  33  is stretched over the axis of rotation  16  running though the clamping bolts  19 ,  20 . Related to this plane  33 , the driving bolts  23 ,  24  of the drive shaft  14  are now arranged on the right and the locking bolts  27 ,  28  of the output shaft  15  are arranged on the other, left side of this plane  33  engaging at the locking disk  17 . In addition, a physical mathematical requirement for clamping or releasing the locking disk is that to achieve a position of equilibrium via the so-called tilting, an outside force on the tilted body must run through the sectional area of the angle of friction on the contact locations. The angles of friction running downward and occurring on the contact points between the clamping bolts  19 ,  20  and the locking ring walls  18  are depicted in  FIG. 1 . A first angle of friction  34  runs from contact point  35  of the upper clamping bolt  19  with the outside of the locking ring wall  18  radially inward and a second angle of friction  36  runs from the contact point  37  of the inner clamping bolt  20  with the inside  22  of the locking ring wall  18  radially inward. The two angles of friction  34  and  36  are shown opposed and shaded. They form a sectional area  38  with crosshatching, through which the aforementioned first plane  33  runs. The driving bolts and locking bolts  23 ,  24  and  27 ,  28  are now arranged in such a way in the recesses  25 ,  26  and  30 ,  31  of the locking disk  17  that, when the locking disk  17  is in a position of rest in accordance with  FIG. 1 , the driving bolts  23 ,  24  of the drive shaft  14  each form a contact point  42 ,  43  with the locking disk  17  on their sides facing the first plane  33 , on the one hand. On the other hand, the locking bolts  27 ,  28  each have a small distance  41  to a contact point  39 ,  40  with the locking disk  17  on their side facing the first plane  33 , whereby the elastic ring  29  bridges this distance  41  as a spring element of the locking bolts  27 ,  28 . Because of this arrangement, the driving bolts and locking bolts  23 ,  24  and  27 ,  28  engage on the locking disk  17  in such a way that it can swivel somewhat in the one or the other opposing direction to release or lock the clamping bolts  19 ,  20  perpendicular to the first plane  33 . 
   Moreover, the arrangement of the driving bolts and the locking bolts  23 ,  24  and  27 ,  28  shall be selected in such a way that both a drive-through of the drive shaft  14  as well as a triggering of the torque lock  10  is possible in both directions of rotation by rotating the output shaft  15  when there is a lacking driving mechanism. For this purpose, a driving bolt  23 ,  24  and a locking bolt  27 ,  28  for each of the two directions of rotation each engage at the locking disk  17 . For a corresponding arrangement of the driving bolts and locking bolts, a second plane  44  is now stretched over the axis of rotation  16  perpendicular to the first plane  33 . Related to this second plane  44 , a driving bolt and a locking bolt  23  and  27  are each arranged on lower side and a driving bolt and locking bolt  24  and  28  are each arranged on the upper side of this second plane  44  in order to engage there with the locking disk  17 . 
   A feature of the load torque lock  10  that is essential for the invention is the embodiment of the locking disk  17  in such a way that its mass center of gravity M lies in the area of the axis of rotation  16  of the aligned drive shaft and output shaft  14 ,  15 . Since the arrangement of the clamping bolts  19  and  20  in the outer circumferential area of the locking disk  17  would now cause an imbalance, a kidney-shaped material accumulation  45  is arranged on the circumferential area of the locking disk  17  that is diametrically opposed to the clamping bolts  19 ,  20  on both sides of the locking disk  17  in such a way that the mass center of gravity M of the locking disk  17  lies as precisely as possible on the axis of rotation  16 . In addition, the locking disk  17  is arranged inside the housing  11  in such a way that a ring air gap  46  sufficient for the swivel movement of the locking disk  17  to release or lock the clamping bolts  19 ,  20  lies between it and the inside wall  12   a  of the outer housing wall  12 . Moreover, the locking disk  17  is provided with a centric bore hole  47  though which a bearing neck  48  on the flange-like end  15   a  of the output shaft  15  projects. The bearing neck  48  is accommodated in a bearing  49 , which is inserted in a front-side bearing bore hole  50  of the drive shaft  14 . 
   The operation of the load torque lock  10  in accordance with  FIGS. 1 and 2  is such that, in the position of rest depicted, the locking disk  17  is accepted by the driving bolts and locking bolts  23 ,  24  and  27 ,  28  between the drive shaft and output shaft  14 ,  15 , whereby clamping bolts  19 ,  20  are pressed by the elastic rings  29  of the locking bolts  27 ,  28  with low force against the locking ring walls  18 . The load torque lock is therefore pre-tensioned in a defined manner. 
   If the shaft  14  is now driven by a driving mechanism (not shown) in the one or the other direction of rotation, then the driving bolts  23  and  24  are also consequently rotated to the right or left. In order to transmit this rotation also to the output shaft  15  via the locking disk  17 , the locking disk  17  must rotate along. This takes place as follows with respect to  FIG. 1 . 
   In the case of a right-hand rotation, a force in the direction of line of application A occurs at contact point  42  of the driving bolt  23  with the locking disk  17 . This force runs through the sectional area  38  of the two angles of friction  34 ,  36  originating from the clamping bolts  19 ,  20  with the consequence that, as a result, the locking disk  17  swivels around the assumed swiveling axis  32  so far and thereby compresses the elastic ring  29  until this force is absorbed by it at contact point  39  of the locking disk  17  with the locking bolt  27 . As a result, the contacts of the two clamping bolts  19 ,  20  at the locking ring walls  18  are practically lifted and the locking ring  17  rotates frictionlessly with the drive shaft  15 . Since the locking disk  17  also carries along the locking bolt  27  via the contact point  39 , the output shaft  15  also rotates along accordingly, whereby, on the one hand, the upper locking bolt  28  with the ring  29  prevents the locking disk  17  from another lateral swivel and, on the other hand, a practically frictionless drive-through takes place. Since no centrifugal forces occur in the area of the rotational axis  16  even with high rpms on the locking disk  17  due to its center of gravity M the drive-through is also kept stable over the entire rpm range. 
   On the other hand, in the case of a left-rotating driving mechanism, a force engages in the contact point  43  of the driving bolt  24  with the locking disk  17 , which cuts the sectional area  38  of the two angles of friction  34 ,  36  in the line of application B starting from contact point  43 . The consequence of this is that with a left-hand rotation, the locking disk  17  swivels from the driving bolt  24  around the swiveling axis  32  so far to the left until this force is absorbed by it at contact point  40  of the locking disk  17  with the locking bolt  28  after the compression of the elastic ring  29 . In this case as well, the friction between the clamping bolts  19 ,  20  and the locking ring walls  18  is lifted so that the locking disk  17  can now also rotate along in the other direction of rotation. The rotating locking disk  17  carries along the locking bolt  28  in this process so that the output shaft  15  is also thereby rotated along. Again in this case a transmission of torques thus takes place in drive-through from the drive shaft  14  via the locking disk  17  to the output shaft  15 , whereby the clamping bolts  19 ,  20  also rotate along practically frictionlessly on the locking ring walls  18 . In this case as well, another lateral swivel of the locking disk  17  is prevented because it is supported on the lower locking bolt  27  at the contact point  39  with the elastic ring  29 . 
   In the case of a decrease or cessation of the load-side torque by switching off or shutting down the driving mechanism (not shown), the load torque lock is supposed to reliably prevent a rotation of the drive shaft by a load coupled. This takes place by swiveling the locking disk  17  to the right as follows: 
   In the case of the occurrence of a left-rotating (with respect to  FIG. 1 ) load torque on the output shaft  15 , when the spring element  29  is compressed in the contact point  39  of the lower locking bolt  27  with the locking disk  17 , a force occurs in the line of application C running through this contact point  39 , which goes through the sectional area  38  of the two angles of friction  34 ,  36 . With this force the locking disk  17  is now swiveled somewhat to the right around its swiveling axis  32 , whereby the two clamping bolts  19 ,  20  automatically clamp at their contact points  35 ,  37  with the locking ring walls  18  via a so-called tilting effect. The locking disk  17  is thereby fixed so that transmission of the torque to the drive shaft  14  cannot occur. 
   In the case of a load torque occurring on the output side for a rotation of the output shaft  15  to the right, the lock is triggered by the upper locking bolt  28  and, in this case, with the compression of the spring element  29  in the contact point  40  of the upper locking bolt  28  with the locking disk  17 , a force occurs in the line of application D, which also cuts the sectional area  38  of the two angles of friction  34 ,  36 , and which consequently effects a swiveling of the locking disk  17  around the swiveling axis  32  to the right to trigger an automatic clamping of the clamping bolts  19  and  20  on the locking ring walls  18 . In the process, the output torque is also absorbed by the locking disk  17  and the associated housing  11  locked on the locking ring walls  18  and is not transmitted to the drive shaft  14 . 
     FIG. 3  shows a schematic representation of the application of a load torque lock  10  in accordance with  FIGS. 1 and 2  in a drive unit  60  in which it is combined with an electric motor  61  of such a type that the output shaft  62  of the electric motor  61  simultaneously forms the drive shaft of the load torque lock  10 . Such an application is advantageous for example in motor vehicles for the driving mechanisms of windshield wipers, window lifters, seat adjusters, clutch adjusters and the like since it permits the possibility of precisely maintaining the achieved intermediate and end positions of the unit, something which is urgently required, e.g., in the case of adjuster driving mechanisms. 
     FIG. 4  depicts another application of the load torque lock  10  from  FIGS. 1 and 2  namely a load torque lock in a drive train with a transmission. Since, e.g., in the domain of electrical tools or, e.g., in the case of cable winches, high-speed electric motorized driving mechanisms with a self-locking transmission are required, an overall efficiency of clearly under 50% is produced due to the friction losses of these types of transmissions. According to  FIG. 4 , it is now planned that the load torque lock  10  be used between the output shaft  65  of an electric motor  66  and a drive shaft  67  of a transmission unit  68  without a self-locking device, whereby the overall efficiency can be improved to clearly over 50%.
The invention concerns a load torque lock for automatically locking load-side torques in the case of a decrease or cessation of a drive-side torque having a housing ( 11) fixed to a frame, a locking ring ( 17) permanently connected to it and a locking body ( 17) cooperating with it and revolving on the drive side, with locking devices which, on the one hand, clamp on the locking ring ( 17) with the occurrence of a load torque by swiveling the locking body ( 17) by means of locking elements ( 27, 28) of the output shaft ( 15) and, on the other hand, release from the locking ring ( 17) by swiveling the locking body ( 17) back by means of driving elements ( 23, 24) of the drive shaft ( 14). To avoid undesired friction or defective jamming of the locking devices on the locking ring ( 18) by the centrifugal forces of the locking body ( 17) it is embodied in such a way that its mass center of gravity (M) lies in the area of the rotational axis of the drive shaft and the output shaft that are aligned with one another.