Patent Publication Number: US-11642256-B2

Title: Auxiliary drive device for a wheelchair

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from German patent application No. DE 10 2018 122 366.8 filed on Sep. 13, 2018, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The technology relates to an auxiliary drive device for a wheelchair. 
     Wheelchairs basically can be grouped into two categories, namely on the one hand wheelchairs which primarily are designed for manual drive, that is a drive provided by either the person sitting in the wheelchair, this being done by hand, for instance via pushrims, which are mounted at the large rear wheels of the wheelchair, or by an assisting person pushing the wheelchair, and, on the other hand, such wheelchairs which already from their original concept are designed for electric drive. 
     Manually driven wheelchairs in general are characterized by a considerably lower weight as compared with those wheelchairs where an electric drive unit is permanently installed. Furthermore, manually driven wheelchairs often are designed as so-called folding wheelchairs which, not only due to their lower weight, but also due to the fact that they can be folded and therefore have smaller dimensions, can be easily transported, for instance in the trunk of a passenger car. 
     Manually driven wheelchairs have, if the propulsion is effected by the person sitting in the wheelchair, a therapeutic effect because providing the driving power constitutes a valuable physical exercise. On the other hand, when manually driving a wheelchair, wheelchair drivers doing so sometimes soon reach the limits of their physical capacities, especially when slopes are to be negotiated, when the wheelchair has to be maneuvered on difficult terrain or when long distances are to be covered. Furthermore, use of a manually driven wheelchair over a long time may lead to injuries because of repeated high strain and to premature signs of wear in muscles, tendons and joints. For this reason, auxiliary drive devices for wheelchairs have been developed which, when later being attached to a wheelchair, support the user in moving the wheelchair. 
     Such an auxiliary drive device for a wheelchair can for instance be provided by replacing the two original large rear wheels of the wheelchair by such rear wheels in which a hub motor is integrated. Such an auxiliary drive device for a wheelchair is for instance disclosed in DE 197 48 201 C1. 
     US 2014/0262575 A1 discloses a different kind of auxiliary drive device for a wheelchair, namely a device which comprises an additional drive wheel which can be driven electrically, that is a drive wheel which is not exchanged with an original wheel of the wheelchair but which is part of a separate device, which, in addition, comprises a coupling mechanism for coupling the auxiliary drive device to the wheelchair. 
     Obviously, wheelchairs must be able to drive through a curve having a narrow radius. In case of manually driven wheelchairs, this is done usually such that the two large rear wheels are rotated with different rotational speeds. Accordingly, an auxiliary drive device for a wheelchair must make sure that negotiating curves is possible. 
     In case of an auxiliary drive device for a wheelchair according to DE 197 48 201 C1, i.e. an auxiliary drive device where a hub motor is integrated in each of the two large rear wheels of the wheelchair, steering is provided, just as in case of a manually driven wheelchair, by respective differences in the rotational speeds of the two rear wheels. 
     If, however, the auxiliary drive device is designed in accordance with that one disclosed in US 2014/0262575 A1, as far as the basic technical conception is concerned, which means that a separate electrically driven drive wheel which is not a wheel of the wheelchair is provided, it has to be made sure that such an auxiliary drive device, when coupled to a wheelchair, allows negotiating a curve and, preferably, does not impede it. This technical problem is solved in accordance with the disclosure of US 2014/0262575 A1 such that lateral rollers are provided along the circumference of the drive wheel which lateral rollers allow lateral movement of the electrically driven drive wheel, namely in a direction which does not correspond to the rotational direction of the drive wheel which provides the drive. 
     The lateral rollers of this known auxiliary drive device for a wheelchair allow lateral rolling of the drive wheel. However, they also provide the disadvantage that they cause increased tire/road noise emissions and vibrations, caused by the lateral rollers, that the design of the tire surface of the drive wheel is complex and expensive, both with respect to manufacturing, service and maintenance, since tires naturally are subject to wear and the lateral rollers lead to increased wear, and that the lateral rollers also lead to an increased need of force to initiate a turning maneuver and maintaining the radius of the curve when negotiating the curve. 
     SUMMARY 
     It is desirable to provide an auxiliary drive device for a wheelchair which is capable to allow negotiating a curve when coupled to a wheelchair such that disadvantages, specifically the disadvantages as explained above, are avoided. 
     An aspect of the technology provides an auxiliary drive device for a wheelchair which has at least one electrically driven drive wheel and a coupling mechanism for coupling the auxiliary drive device to the wheelchair. The electrically driven drive wheel is supported at a steering shaft and freely pivotable with respect to the auxiliary drive device. The steering shaft is arranged such that, when the auxiliary drive device is coupled at a wheelchair ready to be operated, a castor is provided for the electrically driven drive wheel. 
     The auxiliary drive device for a wheelchair has an electrically driven drive wheel which is not, as in case of the prior art according to US 2014/0262575 A1, rigidly supported in a housing, that means in a way that it can only rotate in the direction of drive, but is supported at a steering shaft in a freely pivotable manner. The steering shaft is arranged such that when the auxiliary drive device is coupled to a wheelchair ready to be operated, a castor is provided for the electrically driven drive wheel. 
     The freely pivotable drive shaft makes it possible that the electrically driven drive wheel is always aligned exactly in a position corresponding to the movement of the wheelchair including situations when the wheelchair is negotiating a curve. The curve and its radius for instance can be defined by respective handling of pushrims mounted at large rear wheels of the wheelchair. Other than in case of a drive wheel which is fixedly arranged in the direction of straight forward movement of the wheelchair, the present technology provides superior maneuverability. Moreover, initiating the negotiation of a curve is simple and possible with only little effort concerning the required force. Even turning on the spot is possible and provides superior drivability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of the specification. The drawings illustrate exemplary embodiments and, together with the specification, serve to explain principles and details of the disclosed technology. 
         FIG.  1    is a perspective view of a first embodiment of an auxiliary drive device for a wheelchair which is coupled to the axis of a wheelchair. 
         FIG.  2    is a side view of the auxiliary drive device according to  FIG.  1    wherein parts of the wheelchair are omitted in the depiction. 
         FIG.  3 A  is a perspective, partially cut-away view of a further embodiment of an auxiliary drive device for a wheelchair wherein the drive wheel of the auxiliary drive device is in a position for driving straight forward. 
         FIG.  3 B  is a further perspective, partly cut-away view of the auxiliary drive device according to  FIG.  3 A  wherein the drive wheel of the auxiliary drive device is in a position for driving a curve in a state of forward driving. 
         FIG.  4    is a back view of the auxiliary drive device according to  FIGS.  3 A,  3 B . 
         FIG.  5    is a partially cut-away side view of the auxiliary drive device according to  FIG.  3    wherein the drive wheel of the auxiliary drive device is in a position for driving straight forward. 
         FIG.  6    is a view according to  FIG.  5    with a coupled wheelchair being depicted only schematically wherein the drive wheel of the auxiliary drive device is in a position for driving straight forward. 
         FIG.  7    is a schematic view according to  FIG.  6    wherein the drive wheel of the auxiliary drive device is in a position for driving straight backwards. 
         FIG.  8    is a view of the auxiliary drive device according to  FIG.  3    taken from below wherein the drive wheel of the auxiliary drive device is in a position for driving a curve in a backwards direction. 
         FIG.  9    is a top view of the auxiliary drive device according to  FIG.  3    wherein lateral elements of the frame of the wheelchair coupled to it are shown only schematically and the drive wheel of the auxiliary drive device is in a position for driving a curve in the forward direction. 
         FIG.  10    is a partially cut-away perspective view of a further embodiment of an auxiliary drive device for a wheelchair. 
         FIG.  11    is a view of a detail of an embodiment of an auxiliary drive device for a wheelchair where the drive wheel is in a first stop position. 
         FIG.  12    is a view of a detail of the embodiment of the auxiliary drive device according to  FIG.  11    where the drive wheel is in a second stop position. 
         FIG.  13    is a perspective front view of an embodiment of an operating satellite. 
         FIG.  14    is a perspective rear view of the operating satellite according to  FIG.  13   . 
         FIG.  15    is a partial view of the operating satellite according to  FIG.  13    in a first rotational position. 
         FIG.  16    is a partial view of the operating satellite according to  FIG.  13    in a second rotational position. 
         FIG.  17    is a partial rear view of the operating satellite according to  FIG.  13    where a cover element has been removed. 
         FIG.  18    is an exploded view of the operating satellite according to  FIG.  13    having an operating satellite-wheelchair mounting element and an operating satellite locking element. 
         FIG.  19    is a view of an operating satellite mounting surface of the operating satellite locking element according to  FIG.  18   . 
         FIG.  20    is a combined depiction of the operating satellite according to  FIG.  13    having the operating satellite wheelchair mounting element and the operating satellite locking element. 
         FIG.  21    is an exploded view of a reversing mechanism of an operating satellite mounting tilting element. 
         FIG.  22    is a schematic view of a released position of latches of an operating satellite mounting tilting element. 
         FIG.  23    is a schematic view of a latch position of latches of an operating satellite mounting tilting element. 
         FIG.  24    is a side view of a coupling mechanism of an embodiment of an auxiliary drive device for a wheelchair together with a wheelchair coupling element in a ready to be coupled position. 
         FIG.  25    is a side view of the coupling mechanism according to  FIG.  24    in a locked position. 
         FIG.  26    is a side view of the coupling mechanism according to  FIGS.  24  and  25    in a release position. 
         FIG.  27    is an exploded perspective view of the coupling mechanism according to  FIGS.  24  to  26   . 
         FIG.  28    is a rear view of the coupling mechanism according to  FIGS.  24  to  27   . 
         FIG.  29    is a depiction of a display of a smartphone arranged for adjusting the sensitivity of a rotational control ring. 
         FIG.  30    is a depiction of a display of a smartphone arranged for setting an automatic adaption of the travelling speed when negotiating a curve in dependence of the steering angle of the drive wheel. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, some embodiments of the technology are described with reference to the accompanying drawings. Note that the following description is directed to illustrative examples of the technology and not to be construed as limiting the technology. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting the technology. Further, elements in the following example embodiments which are not recited in most generic independent claims of the technology are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification of the drawings, elements having substantially the same function and configuration are denoted with the same numerals to avoid any redundant description. 
       FIG.  1    shows a perspective view of an embodiment of an auxiliary drive device  100  for a wheelchair which is coupled to an axis  501  of a wheelchair  500 . In the embodiment as depicted, the axis  501  is the axis connecting the two large rear wheels  502 , i.e. the left rear wheel  502 L, as seen in the forward driving direction, and the right rear wheel  502 R, as seen in the forward driving direction. As common in case of manually driven wheelchairs, pushrims  504  are mounted at both large rear wheels  502 L,  502 R. Via said pushrims  504 , the wheelchair can be manually propelled and steered. Furthermore, the wheelchair  500  has two small and freely pivotable front wheels  505 .  FIG.  2    shows the embodiment of the auxiliary drive device  100  according to  FIG.  1    in a side view wherein parts of the wheelchair  500 , especially the right rear wheel  502 R, are omitted in this depiction. 
     The auxiliary drive device  100  serves to be used as an auxiliary drive device for a wheelchair  500  which basically is intended to be manually driven. Details regarding the function of the auxiliary drive device  100  as well as the coupling to the wheelchair  500  and the structure of the respective coupling mechanism  300  are explained in detail further below. 
     General Structure of the Auxiliary Drive Device  100   
       FIG.  3 A  is a perspective view of the auxiliary drive device  100  wherein the drive wheel  110  of the auxiliary drive device  100  is in a position for driving straight forward.  FIG.  3 B  shows the auxiliary drive device  100  according to  FIG.  3    in an operational condition in which the drive wheel  110  is in a position for driving a curve in a forward direction.  FIG.  4    is a rear view of the auxiliary drive device  100  and  FIG.  5    is a partially cut-away side view of the auxiliary drive device  100 . 
     Main components of the auxiliary drive device  100  are inter alia a drive wheel  110 , an auxiliary drive device main body  120  and a coupling mechanism  300 . An operating satellite  200  is provided for controlling the auxiliary drive device  100  and its functions by a user. 
     The drive motor of the drive wheel  110  is an electric hub motor  111 , for example a brushless DC motor with or without a gearing mechanism, which is integrated in the drive wheel  110 . The tire surface  112  of the drive wheel  110  naturally is subject to wear. It is therefore an advantage if the tire can be replaced easily. In case of the embodiment as shown in the figures, the tire surface is split in the center, connected to the rotating part of the drive motor in a positive-locking manner and fixed from the side via tire surface bolts  113 . It is noted that there are several other technical options for different kinds of connections, for example force-fitting connections like adhesion, which a person skilled in the art is aware of. 
     The electric hub motor  111  is connected via an electric conductor to a main power storage in the form of a rechargeable main battery  121  located in the auxiliary drive device main body  120 . Further elements not shown in the figures are also located in the auxiliary drive device main body  120 , for instance elements of a battery management system for managing the state of charge, particularly the charging and discharging of the main battery  121 , elements of a power and control unit, i.e. an electronic control device for controlling the functions of the auxiliary drive device  100 , particularly the electric hub motor  111 , as well as further electric components of the auxiliary drive device  100 , for example a rear light  122 , which for instance can be provided in the form of a band of LED lighting elements glued to said band, which can be supplied with power from the rechargeable main battery  121 . At a suitable position of the auxiliary drive device main body  120 , there can also be provided a main switch  123  for switching the auxiliary drive device  100  to an OFF-state and a ready-to-operate state as well as a main body charging socket  124 , for example in the form of a USB socket, which is connected in particular to the rechargeable main battery  121 . 
     The power and electronic control unit is also connected to the operating satellite  200  which, as well as its functions and the sensors used therefore, will be explained in more detail further below. 
       FIGS.  1  and  2    show the coupling of the auxiliary drive device  100  at the axis  501  of the wheelchair  500  which allows a pivotional movement of the auxiliary drive device  100  in a plane which is vertical to the axis  501  but not a pivotional movement in a plane in which the axis  501  lies, i.e. which the axis  501  is part of. Accordingly, the drive wheel  110  has to allow a steering operation if lateral slip of the drive wheel  110  is to be avoided when the wheelchair negotiates a curve. In case of an auxiliary drive device as disclosed in US 2014/0262575 A1, such drivability of the drive wheel which is arranged in a rigid manner with respect to the wheelchair is provided by lateral rollers arranged along the circumference of the drive wheel. 
     In case of the embodiment of an auxiliary drive device  100  according to the present technology as shown in the figures and as described here, a completely different technical solution is chosen. The drive wheel  110  of the auxiliary drive device  100  is freely pivotable, which means, that its running direction with respect to the wheelchair  500  is self-adjusting when the auxiliary drive device  100  is coupled to the wheelchair  500 . In order to provide this function, a steering shaft  130  is provided to which the drive wheel  110  is connected. In one embodiment, the drive wheel  110  is supported in a steering fork  131  which is fixedly attached to the steering shaft  130 . It has to be noted that a person skilled in the art is aware of various different technical means to connect the drive wheel  110  to the steering shaft  130 . 
     The steering shaft  130  is rotatably supported in the auxiliary drive device main body  120  and specifically in such a manner that it can be rotated without hindrance over a wide range of rotation. In an advantageous embodiment, the steering shaft  130  can be rotated without any hindrance over a range of rotation of at least 360°, in a specific embodiment over a range of rotation of for instance 380°. In other words, the steering fork  131  and, together with it, the drive wheel  110  supported therein, can be freely pivoted with respect to the auxiliary drive device main body  120  and, when the auxiliary drive device  100  is coupled to a wheelchair  500 , also with respect to the wheelchair  500 . 
     In one embodiment, the auxiliary drive device main body  120  is coupled to the wheelchair  500  for operation of the auxiliary drive device  100  such that the steering shaft  130  and the drive wheel  110 , when the latter is in a position for driving straight forward, lie in a plane which is in the center between the two rear wheels  502 R,  502 L. 
     In one embodiment, the steering shaft  130  is, when the auxiliary drive device  100  is coupled to the wheelchair  500  in a state ready to be operated, in a position which ideally is perpendicular to the ground surface on which the wheelchair  500  stands. In other words, when the wheelchair  500  stands on a flat and horizontal surface, the steering shaft  130  stands perpendicular to this flat and horizontal surface, i.e. vertically (see  FIG.  6   ), when the auxiliary drive device  100  is coupled to the wheelchair  500  ready to be operated. 
     Preferably, the deviation from this ideal case concerning the vertical position should not be larger than 5°, in a specifically preferred embodiment it should not be larger than 3°. 
     A further geometric feature of the embodiment according to  FIG.  6    is that an imaginary line extending through the axis of rotation of the drive wheel  110  and the axial center of the steering shaft  130  is inclined with respect to the steering shaft  130 , i.e. the center axis of the steering shaft  130  in an angle of about 25°, and that in a preferred embodiment this angle is not deviated from by more than 5°, in a specifically preferred embodiment not more than 3°, and that a castor is provided, which means that the distance from a vertical line extending through the axis of rotation of the drive wheel  110  to the horizontal contact surface of the wheelchair  500  to the steering shaft  130 , i.e. the center line of the steering shaft  130 , is for example 60 millimeter and that in a preferred embodiment the deviation from this value is not more than 20 millimeter, in a specifically preferred embodiment not more than 10 millimeter. Furthermore, in the embodiment as described here, the contact point of the drive wheel  110  with the ground surface is, in each rotational position of the steering shaft  130 , behind the contact point of the rear wheels  502 R,  502 L, if seen in a forward driving direction of the wheelchair  500 . 
     Although the drive wheel  110  is freely pivotable due to the freely pivotable steering shaft  130 , in operation, that is when the auxiliary drive device  100 , powered by the electric hub motor  111 , propels the wheelchair  500  to which the auxiliary drive device  100  is connected, said drive wheel  110 , in a self-acting manner, takes a position which allows a steering of the wheelchair by the user via the pushrims  504  without any problems. The drive wheel  110  automatically aligns itself in the direction of the curve which is defined by respective manual action via the pushrims  504  of the two rear wheels  502 R,  502 L. This includes driving on a straight both in forward and backward direction, driving curves of any radius and even turning the wheelchair on the spot. 
     It is to be noted that auxiliary drive devices of the present kinds have to be suited to be mounted to a variety of wheelchairs. On the other hand, wheelchairs are designed in accordance with the physical dimensions of the user. This leads to the fact that inter alia the seating height of the wheelchairs and particularly the diameter of the rear wheels  502 R,  502 L vary. Accordingly, also the height of an axle bar connecting the rear wheels  502 R,  502 L varies. Typical wheelchairs commercially available have usually rear wheels with a diameter of for instance 22″, 24″, 25″ or 26″. In accordance with this customary increments, various variants of the steering fork  131  can be provided for adapting the auxiliary drive device  100  to the dimensions of a given wheelchair, specifically with respect to the geometrical aspects as explained above. Since in many cases medical aids are used in a plurality of applications and auxiliary drive devices of the present kind during their life cycle may be mounted to various wheelchairs, easy replacement of respective components to be adapted constitute an important economic factor. 
     Steering Motion and Power Supply 
     As explained above, it is advantageous if the drive wheel  110  can assume any pivotable position which means that the steering shaft  130  can freely rotate, preferably over 360°. However, this basically includes the possibility that the steering shaft  130  rotates several subsequent times in the same direction of rotation. 
     As also explained above, the electric hub motor  111  is connected via an electrical conductor to the rechargeable main battery  121  which is arranged in the auxiliary drive device main body  120 . If this electrical conductor is provided by a cable, care has to be taken that a plurality of rotations of the steering shaft  130  in the same direction does not lead to a winding of the cable which finally would hinder the rotatability of the steering shaft and, accordingly, would interfere with the operability of the auxiliary drive device  100 . 
     In one embodiment, power transmission can be provided via a slip ring  118  in a position where a rotating component and a fixed component have to be bridged. Such an embodiment is shown in  FIG.  10   . 
     Another embodiment includes a stop for the rotation of the steering shaft  130  which allows preferably more than a rotation over 360°, however prevents a plurality of sequential full rotations in one and the same direction. Such an embodiment is shown in  FIGS.  11  and  12   . A stop gliding element—guiding element  132  which is fixedly connected to the steering shaft  130  has a crescent-shaped elongated hole  133  in which a stop gliding element  134  is movably guided. When the steering shaft  130  is rotated in a first direction of rotation (see  FIG.  11   ), the stop gliding element  134  gets in abutment of a first side  135 A of a stop element  135  which is fixedly arranged with respect to the auxiliary drive device main body  120 , wherein it rests against a first end of the elongated hole  133 . When the steering shaft  130  is rotated in a direction opposite to the first direction of rotation (see  FIG.  12   ), the stop gliding element  134  gets in contact with a second side  135 B of the stop element  135 , wherein it rests against a second end of the elongated hole  133 . 
     Due to the movability of the stop gliding element  134  in the elongated hole  133 , with appropriate choice of the dimensions of the respective components, it can be achieved that the steering shaft  130  can be rotated over a range of for instance 380° before it gets in abutment. 
     This makes it possible that the drive wheel  110  can be pivoted by more than 360° and, therefore, can assume all directions which preferably are desired for a driving operation and, on the other hand, it is still avoided that the steering shaft  130  rotates several times subsequently in the same direction so that winding of a power cable which connects the drive motor  111  to the rechargeable main battery  121  in the auxiliary drive device main body  120  is prevented. 
     Motion-Based System and Operating Satellite 
     In one embodiment, the auxiliary drive device  100  can be operated as a purely motion-based system, i.e. a system in which a motion, specifically of the drive wheel  110 , is detected and this motion then is supported or amplified, respectively, by the electric motor. If, for instance, the wheelchair  500  to which the auxiliary drive device  100  is coupled to, is manually propelled by the user via the pushrims  504  at the rear wheels  502 R,  502 L in a direction for driving forward, the power and the electronic control unit for controlling the functions of the auxiliary drive device  100  detects this motion via respective sensors, which include, without limitation, one or more of the following sensors, namely a rotational speed sensor, which detects the rotational speed and the direction of rotation of the drive wheel  110 , and/or one or more acceleration sensors which detect acceleration in various spatial directions, a gyro sensor and further optical, capacitive or inductive sensors, as the case shall be also a steering shaft rotational angle sensor  105  (see  FIG.  3 B ) which detects the position of the steering shaft  130 , and controls the hub motor  111  in order to provide electromotive rotation in the detected direction. 
     In another embodiment, operation is effected via an operating satellite  200  to be operated by the user. It is to be noted that this embodiment also can have one or more of the sensors as listed above which can be used in addition or alternatively also for other functions. The structure of this embodiment is explained in the following. A description of the operating functions and the drive follows subsequently. 
     An embodiment of the operating satellite  200  is shown in  FIGS.  13  to  20   . One of various positions where the operating satellite  200  can be attached to a wheelchair  500 , preferably in a removable manner, as shown in  FIG.  2   . 
       FIGS.  13  and  14    show, each in a perspective view, a front view and a rear view of an embodiment of an operating satellite  200 . The operating satellite  200  serves for controlling the auxiliary drive device  100  and has, specifically inside of it, the electric and electronic components necessary for this purpose (not shown in the figures) which for the further description of this embodiment in the following are summarized under the term operating satellite control unit. Bidirectional communication between the operating satellite control unit of the operating satellite and the electronic control unit for controlling the functions of the auxiliary drive device  100  can, for instance, be provided via wires and cables, not shown in the figures, or wireless, for instance by a Bluetooth coupling. 
     The operating satellite  200  has an operating satellite control portion  202  and an operating satellite mounting element  210 . 
     The operating satellite mounting element  210  serves for mounting the operating satellite  200  to a wheelchair  500 . For this purpose, a quick release unit can be latched with an operating satellite mounting pivot element  220  by hooking an undercut  201  of the operating satellite mounting element  210  in a fixing hook  222  of the operating satellite mounting pivot element  220 . Then, the operating satellite mounting element  210  is brought in abutment with the operating satellite mounting pivot element  220  so that a locking hook  211  provided at the operating satellite mounting element  210  snaps into place with spring-loaded latches  221  at the operating satellite mounting pivot element  220  (see, also with respect to respective start up slopes,  FIGS.  18  to  20   ). Releasing the operating satellite mounting element  210  from the operating satellite mounting pivot element  220  is done in a reverse sequence wherein the spring-loaded latches  221  of the operating satellite mounting pivot element  220  can be retracted (i.e. lowered down), by means of a release button  223  which is also spring-loaded and which is connected to the spring-loaded latches  221  of the operating satellite mounting pivot element  220  via a reverse mechanism. 
     As shown in  FIGS.  21  to  23   , the two latches  221  at the upper ends of respective latch bars  221 A are pushed each via a respective pressure spring  225  in the latch position as shown in  FIG.  23    and are connected via reverse levers  226  to a push rod  224  which in turn is connected to a release button  223 . If, starting out from the latch position as shown in  FIG.  23   , the release button  223  is pushed against the spring force of the pressure springs  225  in the direction towards the housing of the operating satellite mounting pivot element  220 , the latch bars  221 A are shifted due to the reverse levers  226  in the opposite direction of the push rod  224  and cause a lowering of the latches  221  so that the operating satellite mounting pivot element  220  is released. This condition of a release position of the latches  221  is shown in  FIG.  22   . If the release button  223  is released, the latches  221  return, due to the pressure force of the pressure springs  225 , back into their latch positions according to  FIG.  23   . 
     The operating satellite mounting pivot element  220  can be connected to a wheelchair mounting element  230  in a rotational position which can be freely determined and can be fixed by a mounting bolt  231  in this freely determinable position. Due to the structure as described above and shown in the figures, there is a great variety of possible positions for attaching the operating satellite  200  to a wheelchair  500  and for choosing appropriate positions for such attachment. In particular, it is possible to select either the right side or the left side of the wheelchair for such attachment which allows easy operation for left-handed persons and right-handed persons, respectively. 
     The operating satellite control portion  202  has control and switching elements by which via respective actuation processes the control and drive of the auxiliary drive device  100  can be effected. Specifically, these processes can be effected via a rotational control ring  203  which is arranged at the outer circumference of the operating satellite control portion  202  and provided with grip links  208  and a push control knob  204  within the outer circumference of the operating satellite control portion  202  and, thus, also within the outer circumference of the rotational control ring  203 . The push control knob  204  can be pushed in the direction of the axis of rotation of the rotational control ring  203  and is designed having a considerable surface and is attached upon mounting at the wheelchair with the face surface of the operating satellite control portion  202  facing to the outside of the wheelchair (not facing to the center of the wheelchair) and therefore also at the outer part of the push control knob  204 . 
     The rotational control ring  203  can be rotated in both directions of the circumference, that is clockwise and counter clockwise, with no limit. No respective abutment is provided. However, the rotational control ring  203  is provided with a clearly sensible ratchet which provides the user upon rotating this element with a tactile and/or audible operation feedback, thus providing distinctive increments of rotation. In other words, the rotational control ring  203  can be rotated arbitrarily far, over as many full rotations as desired, and in each direction. However, the angle range of 360° of a full rotation is divided in a certain number of sub-ranges, namely the above-mentioned increments provided by the ratchets, so that each time when such a sub range is exceeded, a respective ratchet is sensible and/or audible. 
     Exceeding such a sub range or increment triggers a signal of the operating satellite control unit which signal can be defined in a program with respect to its characteristics and is transmitted to the electronic control unit for controlling the functions of the auxiliary drive device  100 , wherein also the direction of rotation of the operation influences the content of the signal. 
     Details concerning the control functions which are transmitted to the electronic control unit for controlling the functions of the auxiliary drive device  100  by operating the operating satellite  200  are explained further below. 
     The push control knob  204  can be operated by pressing it in an inward direction against pressure force of a spring. Its operation also triggers a signal of the operating satellite control unit which is transmitted to the electronic control unit for controlling functions of the auxiliary drive device  100  wherein also the duration of the operation has influence on the content of the signals. 
     On the outer side of the operating satellite  200 , in case of the shown embodiment on the outer circumference of the operating satellite control portion  202 , there is provided a display device  205 , for instance in the form of LED displays. This display device  205  displays information regarding operational conditions of the drive device or the auxiliary drive device  100 , respectively, and informs, for example, in the shown embodiment regarding the state of charge of the main battery  121  in the auxiliary drive device main body  120 , for instance by providing a strip of several white LED elements  205 A wherein the number of luminous or lighted elements corresponds to the state of charge, and also concerning the state of charge of a rechargeable operating satellite battery (not shown) which is integrated in the operating satellite, for instance by a single RGB LED element  205 B which communicates the state of charge by changing the color. 
     The display device  205  is designed such that its arrangement on the operating satellite can be adjusted, that is, it can be altered. This makes it possible to adjust the position of the display device  205  with respect to its visibility for a person sitting in the wheelchair  500  in connection with a respective place of attachment of the operating satellite  200  at the wheelchair  500 . In the embodiment as shown in the figures, this is for instance achieved by the structure as described below. 
     A cover element  206  is provided at a face side of the operating satellite control portion  202  which, when mounted at a wheelchair  500 , faces to the center of the wheelchair  500 . This cover element  206  can be removed and also be fixed back in place by operating a spring-loaded unlocking element  209  (see  FIG.  14    and  FIG.  17   ). Removing the cover element  206  allows access to three fixing screws  207 , to an adaptor charging socket  218  arranged at the operating satellite  200 , for instance in the form of a USB socket, and to a pairing button  219 . 
     Untightening the three fixing screws  207  allows rotating the outer circumference of the operating satellite control portion element  202  in a circumferential direction (see  FIG.  15    and  FIG.  16   ). The subsequent tightening of the three fixing screws  207  fixes the outer circumference of the operating satellite control portion  202  in the newly selected position with respect to the operating satellite mounting element  210 . Hereby it can be ensured that, regardless at which part of the wheelchair  500  and in which position with respect to the wheelchair  500  the operating satellite  200  is attached, the display device  205  is always within sight of the user. 
     The adaptor charging socket  218  can be used for charging the operating satellite battery of the operating satellite  200  also upon operation, that is when the wheelchair travels supported by the auxiliary drive device  100 , wherein the energy for this purpose can either be provided by a separate power source or by connection with the main body charging socket  124  provided at the auxiliary drive device main body  120 . 
     The pairing button  219  serves to establish a Bluetooth connection with the electronic control unit in the auxiliary drive device main body  120  for controlling the functions of the auxiliary drive device  100 . 
     Operating Function and Travel 
     In the following, as an example, operation of the auxiliary drive device  100  and the drive or travel of a wheelchair  500  connected to such an auxiliary drive device  100  are explained. It is understood that a plurality of amendments from this exemplary embodiment can be provided by a person skilled in the art. 
     Starting out from a nonoperating state, in which the auxiliary drive device  100  is switched OFF, the auxiliary drive device  100  is put into a ready to operate state by operating the main switch  123  at the auxiliary device main body  120 . In the ready to operate state, the electronic control unit in the auxiliary device main body  120  for controlling the functions of the auxiliary drive device  100  receives signals from the operating satellite control unit provided in the operating satellite  200 . 
     When in this ready to operate state of the auxiliary drive device  100  the push control knob  204  at the operating satellite control portion  202  of the operating satellite  200  is pushed for longer than a respective threshold value, which for instance can be 3 seconds, the auxiliary drive device  100  is put into a ready to drive state. If in this ready to drive state the rotational control ring  203  at the operating satellite control portion  202  of the operating satellite  200  is rotated in a first direction, for instance in, as seen from a user sitting in the wheelchair, a forward direction, the electronic control unit for controlling the functions of the auxiliary drive device  100  receives corresponding signals from the operating satellite control unit and drives the motor  111  such that a torque is delivered for rotating the drive wheel  110 . 
     Turning of this control element, namely of the rotational control ring  203 , is a direction sensitive operational process which causes, depending on the operational direction, an activation of the auxiliary drive device  100  corresponding to this operational direction wherein the correlation between the operational direction of the rotational control ring  203  and the activation of the auxiliary drive device  100  caused by this rotation can be changed. 
     For instance, the rotational direction of the rotational control ring  203  which initiates start of a drive can be changed, for instance by respective programming. This means that regardless of whether the operating satellite  200  is mounted on the left side or on the right side of the wheelchair  500 , which for instance can be chosen depending on whether the user is left-handed or right-handed, the start of a drive always can be initiated by rotation in a forward direction which allows an intuitive operation. Such programming, just as also other options for programming which can be made by a user, can be done with the aid of an end terminal like for instance a PC or a smartphone where a respective software designed to run on a mobile device, in the following referred to as app, has been downloaded on, i.e. a respective user program which is provided to the user. 
     The level of the torque is set such that a respective travelling speed is achieved. The level of the travelling speed depends on how many ratchets (increments) have been exceeded when the rotational control ring  203  is rotated. 
     In other words, after switching ON into the ready to operate state by pushing the main switch  123  and switching ON to the ready to drive state by continued pushing of the push control knob  204 , the user can start driving with electric power of the auxiliary drive device  100  by rotating the rotational control ring  203  in a forward direction. The speed of the drive is set by the user such that a certain number of ratchets (increments) are exceeded upon rotating the rotational control ring  203 . In other words, if for instance, starting out from a stand still condition, the rotational control ring  203  is rotated such that five ratchets are exceeded, a predetermined speed will be reached. If in the same rotational direction another ratchet is exceeded, the speed will be increased by a predetermined amount. On the other hand, if the rotational control ring  203  will be rotated in an opposite direction, each time a ratchet is exceeded, the speed will be lowered to a lower by a predetermined amount. 
     The correlation between ratchet and speed is freely programmable wherein only an upper speed limit can be provided which cannot be changed by the user. The correlation between ratchet and speed is expressed in how many ratchets have to be exceeded in order to obtain a specific speed, namely an increase of the speed or a reduction of the speed. This adjustability makes it possible to change the response or sensitivity, respectively, of the rotational control ring  203  and thus adapt it to specific needs of various user groups and their level of handicap. This is a particular advantage for those users who have limited coordination ability because the adjustment movement then, as the case may be, can be executed more heavy-handed, that is in a kind of gross motor manner. 
     In one exemplary embodiment, the setting can be such that the upper speed limit is set to 12 km/h and the correlation between ratchet and speed is set such that exceeding one ratchet means a speed increase of 1 km/h. If, under such a condition, a user, starting from a standing still condition, rotates the rotational control ring  203  by one ratchet in a forward direction, the wheelchair  500  starts moving due to the electric drive power of the auxiliary drive device  100  with a driving speed of 1 km/h. Each further rotation of the rotational control ring  203  in a forward direction exceeding one further ratchet increases the drive speed by 1 km/h. In another exemplary embodiment, the setting for instance could be that each time a ratchet is exceeded the change in speed is only 0.5 km/h. If the set top speed is reached, which means that in the first example given above 12 ratchets are exceeded and in the second example 24 ratchets are exceeded, further rotation of the rotational control ring  203  in the forward direction is possible as far as the mechanics are concerned. However, it has no effect as far as control of the auxiliary drive device is concerned. 
     Turning the rotational control ring  203  in a backward direction decreases the speed in a corresponding manner, namely with a set speed increment each time a ratchet is exceeded. Turning the rotational control ring  203  in a backward direction therefore leads to a reduction in speed and, after a respective number of ratchets have been exceeded, it leads to complete stopping, that is to termination of the production of drive torque. Also in this case it is possible to further rotate the rotational control ring  203  in a backward direction as far as the mechanics are concerned, however without any effect concerning control functions. 
     A complete stop is also possible by pushing the push control knob  204  during the drive. In this case, a short push is sufficient. This pushing of the push control knob  204 , even if it is only for a short period of time, makes it possible to immediately terminate the production of drive torque. 
     If in the ready to drive condition of the auxiliary drive device  100  the push control knob  204  at the operating satellite control portion  202  of the operating satellite  200  is pushed for a longer duration than a respective threshold value, which threshold value for instance can be 3 seconds, the auxiliary drive device  100  is set back into the ready to operate state. 
     The above describes basic aspects of the operation of the auxiliary drive device  100  by means of respective electric and electronic components like switches, control elements and programming. In the following, operation and drive with a wheelchair  500  at which an embodiment of the auxiliary drive device  100  is coupled to is described. 
     As explained above, the drive wheel  110  is supported via the steering shaft  130  and can be freely pivoted with respect to the auxiliary drive device main body  120 . Force is developed by the auxiliary drive device  100  basically only with respect to propulsion, i.e. with respect to the rotation of the drive wheel  110  by the hub motor  111 . Steering is effected via the pushrims  504  at the rear wheels  502 R,  502 L such that when driving a curve is intended, by decelerating the inner rear wheel, i.e. the inside rear wheel of the intended curve. The freely pivotable drive wheel  110  then behaves with respect to its pivoting, in spite of the applied drive power, like a freely pivotable castor and aligns itself automatically corresponding to the curve. 
     The freely pivotable drive wheel  110  provides, especially as compared with a drive wheel which is rigidly installed with respect to the driving direction, superior maneuverability and allows simple initiation of driving a curve without the need of substantial force. Since the drive wheel  110  always by itself takes the position of the vector of this curve which is initiated manually via the pushrims  504  by one-sided deceleration, negotiating the curve is initiated easily also when power is provided from the auxiliary drive device  100 . If one rear wheel of the wheelchair is completely stopped, this leads to turning on the spot. Furthermore, driving in a backward direction is possible in a position of the drive wheel which is opposite to the one for driving in a forward direction. The physical conditions which specifically include the freely pivotable drive wheel and the castor and, preferably, the coupling in the center, and the application of the power of the drive wheel  110  rearwards of the contact point of the large wheelchair wheels  502 R,  502 L provide responsive and agile handling and driving performance with little effort as far as manual forces are concerned. 
     Due to the fact that steering is effected via the pushrims  504  at the rear wheels  502 R,  502 L, attachment of the operating satellite is preferably done at a position which the hand of a user lying at the pushrim  504  can reach quickly and intuitively. 
     For all settings which can be done by a user it is possible, as explained above, to provide the option of a computer program installed on an end terminal, for instance a smartphone app or a PC service application. This does not only relate to the functional steps described above like the operation sensitivity of the rotational control ring  203 . Also switching ON and switching OFF can be done by a user by means of a smartphone and a respective user application. If, for instance during traveling on public roads, it should be getting dark and switching ON of the rear light  122  should become necessary and a switch for switching ON the rear light  122  at the auxiliary drive device main body  120  should be difficult to be reached by a user or could not be reached at all, the user can switch ON the rear light easily while sitting in the wheelchair  500  by means a respective smartphone app. Carrying along a separate battery light for such cases is therefore not necessary. 
     Cornering Speed Limitation 
     In one embodiment of an auxiliary drive device propelling a wheelchair by electric power in the way described above, it is possible to reduce the cornering speed when a curve is negotiated. 
     Reducing the drive power especially in narrow curves can improve the controllability of the wheelchair, especially for wheelchair drivers having a higher spinal paralysis and limited function of the hand and fingers so that controlling the wheelchair under demanding drive conditions can be difficult. Particularly for such user groups, limiting the cornering speed or providing automatic reduction of the cornering speed can be a contribution to enhanced safety. 
     Appropriate reduction of the drive power, i.e. the driving torque of the motor  111  of the drive wheel  110 , also can be useful during drive in narrow environments like indoors where hitting furniture and other objects must be avoided or in heavily frequented pedestrian zones. Generally, in narrow curves an appropriate reduction of the cornering speed can be an additional safety feature. 
     For realizing such cornering speed limitation, at least one sensor is provided which serves to detect cornering and/or the cornering speed. In one embodiment, the electronic control unit for controlling the functions of the auxiliary drive device  100  uses a plurality of respective sensors including, but not limited thereto, a steering shaft rotational angle sensor  105  (see  FIG.  3 B ) which detects the position of the steering shaft  130 , a rotational speed sensor detecting the rotational speed and the direction of rotation of the drive wheel  110 , several acceleration sensors detecting accelerations in various spatial directions, a gyro sensor as well as optical, capacitive and/or inductive sensors, based on signals from one or more of these sensors, the hub motor  111  is driven such that electro motor drive torque is produced only in a manner which is suitable for the present driving situation. 
     A drive torque leading to a constant drive straight ahead for instance can be reduced depending on the detected radius of the curve wherein the reduction increases when the radius of the curve becomes smaller and/or the cornering speed increases. 
     Respective values can be stored in maps and the values can be determined in respective experiments. A control program stored in the electronic control unit for controlling the functions of the auxiliary drive device  100  then can, based on current sensor signals, refer to such map when conducting respective calculations. Alternatively, the control program can execute real-time calculation on the basis of respective signals from the sensors. 
     If for instance the steering shaft rotational angle sensor  105  which detects the position of the steering shaft  130  is, in addition to monitoring the driving speed, used as one of the main input values for the function of the cornering speed limitation, this sensor can permanently monitor the steering angle of the drive wheel  110 . 
     Furthermore, settings can be made via a computer program or an external interface defining by which amount the drive power or the drive torque, respectively, shall be reduced depending on the radius of the curve or the steering angle. Moreover, in cases where the radius of the curve increases again and/or transition is made to driving straight ahead, the drive power or drive torque, respectively, can be increased automatically. 
     Coupling Mechanism (Structure) 
     The coupling of the auxiliary drive device  100  to the wheelchair  500  has to be safe and secure. Furthermore, coupling and uncoupling should be easy to be accomplished and the coupling should be preferably such that in order to negotiate obstacles like a curb, so-called tipping or tilting of the wheelchair for clearing this obstacle, that is a lifting of the front wheels, should be possible. One embodiment having a coupling mechanism  300  described below with reference to  FIGS.  24  to  28   , fulfils all these requirements. 
     The coupling mechanism  300  according to  FIGS.  24  to  28    is shown as a structural unit having a coupling mechanism main body  320  in which coupling grooves  321  are formed, which coupling mechanism main body  320  serves for supporting functional elements of the coupling mechanism  300 , specifically a handle  310  and a rocker  311  connected thereto, and which coupling mechanism main body  320  can be mounted to the front end of the auxiliary drive device main body  120 . 
     It is to be noted that in a further embodiment the functions of the coupling mechanism main body  320  can be realized by respective elements formed in the same manner which elements according to this embodiment are part of the auxiliary drive device main body  120 . In other words, it is possible to design the coupling mechanism main body  320  and the auxiliary drive device main body  120  as an integrated unit. 
     The coupling grooves  321  are formed basically V-shaped in order to facilitate insertion of a coupling pin  381  which is preferably formed cylindrical. The coupling pin  381  is an embodiment of an element to be held in a positive-locking manner in order to effect the coupling. It is understood that such an element to be kept in a positive-locking manner in order to effect the coupling can also have different shapes and can be formed in a different way. The coupling pin  381  described in connection with the present embodiment can be formed in two parts and can be attached at both sides of a coupling clamp  380  which can be attached removably at an axis  501  of a wheelchair  500  (see  FIG.  1    and  FIG.  2   ). In case a wheelchair does not have such an axis, a corresponding component (not shown) which fulfils the supporting function of the axis for such coupling clamp  380  can also be provided as a separate component and attached to the wheelchair, for instance by respective bolts. 
     The rocker  311  is firmly and rigidly connected to the handle  310  and supported via a rocker support pin  312  in the coupling mechanism main body  320  such that it can be rotated over a certain angular range around the center axis of the rocker support pin  312  and in particular can assume positions between a locked operational position shown in  FIG.  25    and a release position shown in  FIG.  26    with a ready to be coupled position in between and shown in  FIG.  24   . 
     Bores  313  are formed in both sides of the rocker  311  which each hold an operating pin  314  which, when the coupling mechanism  300  is in a condition mounted ready to be operated, extend through a gate window  331  of a locking element  330  which is supported via a locking element support pin  332  in the coupling mechanism main body  320  and biased by a leg spring  338  in a clockwise direction, the term clockwise being based on the plane of depiction of  FIGS.  24  to  26   . 
     The locking element  330  is moveably supported in the coupling mechanism main body  320 . In a locked position it allows locking in a positive-locking manner in which the auxiliary drive device  100  is coupled to the wheelchair  500  and the locking element  330  can be brought in a release position by operating the handle  310  in which release position uncoupling of the auxiliary drive device  100  from the wheelchair  500  is possible. The locking element  330  is formed such that it can, in a spring loaded manner, in the embodiment as shown via the leg spring  338 , close the coupling groove  321  completely or at least partially. In other words, in the locked position the locking element prevents that a coupling pin  381  inserted into the coupling groove  321  can move out of the coupling groove  321 . 
       FIG.  28   , in connection with  FIG.  27   , shows the symmetrical structure of the coupling mechanism  300  having two locking elements  330  and, correspondingly, two leg springs  338 . Basically, provision of one locking element  330  and one leg spring  338  is sufficient. The redundant embodiment having two locking elements  330  and two corresponding leg springs  338  shown in the figures provides single fault safety. 
     Coupling Mechanism (Coupling and Uncoupling) 
     The functions and the interaction as well as details of the design of respective elements of an embodiment of the coupling mechanism  300  are explained in the following in connection with the process of coupling and uncoupling of an embodiment of an auxiliary drive device  100  to and from a wheelchair  500 . 
     First, a coupling clamp  380  is attached at an axis  501  of a wheelchair  500 , preferably in the center between both rear wheels, or, if the wheelchair  500  does not have such an axis  501 , for instance because it is a so-called folding wheelchair having a lateral folding mechanism having cross struts, at a corresponding accessory axis (not shown) which is provided for this purpose and can be mounted to the wheelchair. The mounting of the coupling clamp  380  can be achieved for instance by a clamp mechanism. 
     The height of the coupling pin or, in case of a redundant design having two coupling pins  381 , of the coupling pins which these pins have above the road or the ground, that is the vertical distance of the pin or the pins with respect to the plane on which the wheels of the wheelchair  500  stand, is of particular relevance. This height has an impact on the driving geometry of the auxiliary drive device  100  and, accordingly, on the drivability, especially concerning the position of the steering shaft  130  which in an ideal case should be vertical with respect to the surface on which the wheelchair stands. A particular influence concerning this height has the diameter of the rear wheels  502 R,  502 L of the wheelchair which in trade typically is for instance 24″ or 25″ and which, specifically depending on the chosen tires, leads to an effective diameter of the wheel from 595 mm to 620 mm or 620 mm to 645 mm, respectively. A further major factor in this respect is the position at which the accessory axis (not shown) is attached to the wheelchair. 
     Naturally, a person skilled in the art has several options for providing such adjustment. In one exemplary embodiment, adjustment can be provided by means of various steering forks  131  in different length. However, in order to reduce the number of different versions, in one embodiment a fork can be provided with two or more bores or a slotted fork can be provided, i.e. a fork having an elongated hole in which a so called flip-chip can be inserted which allows two or more different attachment heights. Furthermore, different versions of the coupling clamp  380  can be provided in order to address varying heights of the attachment and the proper height of the coupling pin  381  can be set and checked by using a caliber or gauge. 
     When a coupling clamp  380  is attached at the wheelchair  500  and the coupling pin  381  or the coupling pins  381  are adjusted in the proper height, the wheelchair  500  is ready for coupling of the auxiliary drive device  100 . Firstly, the coupling mechanism of the auxiliary drive device  100  is in the coupling ready position as shown in  FIG.  24   . In this coupling ready position, the locking element  330 , biased by the force of the leg spring  338  and limited by the abutment of the operating pin  314  in an angle of the gate window  331  correspondingly formed for this purpose, takes an end position with respect to pivoting around the center axis of the locking element support pin  332  in a clockwise direction, based on the drawing plane in the depictions according to  FIGS.  24  to  26   , which plane is also the indication of direction for the following description. 
     In this coupling ready position, no further rotation or pivotal movement of the locking element  330  can be effected by operation of the handle  310 . Accordingly, the handle  310  in so far assumes a firm position with respect to the auxiliary drive device main body  120  which allows that the auxiliary drive device  100  can be lifted and carried by using the handle  310  in order to place it over the coupling pin  381  so that, when the auxiliary drive device  100  is lowered, the coupling pin  381  enters into the coupling groove  321  and rotates the locking element  330  by contact at a first locking element contact surface  333  against the spring force of the leg spring  338  in a counter clockwise direction around the center axis of the locking element support pin  332 . This rotation is made possible by a corresponding design of the gate window  331 . 
     When the coupling pin  381  has completely entered into the coupling groove  321 , the coupling pin  381  has come into contact with a correspondingly formed button of the coupling groove  321  and hereby partly releases the locking element  330  so that the locking element  330 , due to the spring force of the leg spring  338 , is rotated in a clockwise direction around the center axis of the locking element support pin  332  to an extent that a second locking element contact surface  334  gets in contact with the coupling pin  381 . This rotation is made possible by a corresponding design of the gate window  331 . Due to this, the coupling pin  381  is held in the coupling groove  321  in a positive-locking manner and the auxiliary drive device  100  is ready to be operated and safely coupled to the wheelchair  500  in the locked operation position of the coupling mechanism  300  as shown in  FIG.  25    while tilting or tipping of the wheelchair  500  is still possible. 
     The locking element  330  is designed such that during the coupling process, namely when this process is successfully terminated, it strikes, in a spring-biased manner, an element which is to be held in a positive-locking manner for effecting the coupling. In one embodiment, the element to be held in a positive-locking manner for effecting the coupling is the coupling pin  381 . This strike produces a metallic sound. 
     In the embodiment as described here, this principle striking is realized in that after release of the locking element  330 , when the coupling pin  381  has passed the first locking element contact surface  333 , the locking element  330  flips back under the effect of the leg spring  338  until it strikes on the second locking element contact surface  334  of the coupling pin  381  whereby a metallic sound is produced in the form of a click or clack in a simple way, specifically without providing additional structural elements. This metallic sound is an acoustic feedback for the full, complete and safe coupling process. This is of particular advantage in cases where the coupling process is executed by a person sitting in the wheelchair who, from this position, can conduct an optical check regarding the coupling only with great difficulty or not at all. 
     The interaction of the leg spring  338 , the locking element  330  and its geometric design, specifically with respect to the point of rotation around the center axis of the locking element support pin  332 , the gate window  331  and the two locking element contact surfaces  333  and  334  as well as the coupling groove  321  allow a safe, secure and backlash-free three point support of the coupling pins  381  which also is able to compensate tolerances and wear. Particularly in connection with a drive system having a freely pivotable drive wheel  110 , a backlash-free connection of the auxiliary drive device  100  and the wheelchair  500  is of particular importance. 
     A tendency of the coupling pin  381  to move downwards, that is in the direction to the aperture of the V-shaped coupling groove  321  due to the specific geometric design, specifically the shape and orientation of the second locking element contact surface  334  with respect to the shape of a coupling groove  321  and the position of the point of rotation of the locking element  330  around the center axis of the locking element support pin  332 , has the effect that the torque of the locking element  330  around the center axis of the locking element support pin  332  in a clockwise direction is increased and the clamping force is also further increased. This further enhances safety against unintended uncoupling. 
     An intended uncoupling of the auxiliary drive device  100  from the wheelchair  500  conducted by an operating person is effected in that the handle  310  of the coupling mechanism  300  is pulled upward and, by doing so, it is rotated in a clockwise direction, together with the rocker  311 , around the center axis of the rocker support pin  312 . This has the effect that the operating pin  314 , due to respective engagement in the correspondingly designed gate window  331  of the locking element  330 , rotates the locking element  330  around the center axis of the locking elements support pin  332  in an anti-clockwise direction so that the coupling groove  321  is unblocked. 
     In the release position shown in  FIG.  26   , the auxiliary drive device can be lifted by means of the handle  310  and uncoupled from the wheelchair  500 . The direction in which power has to be exerted for unlocking the lock and lifting the auxiliary drive device  100  for uncoupling it from the wheelchair  500  by means of the handle  310  are practically identical so that the unlocking and uncoupling process can be easily and smoothly effected by one simple move of the hand. In other words, the operation of the handle  310  which moves the locking element  330  in the unlocking position has the same direction of force as carrying the auxiliary drive device  100  by means of the handle  310 . 
     Upon releasing the handle  310 , this and the locking element  330 , due to the force of the leg spring  338 , return to the coupling ready position according to  FIG.  24   . 
     Adaption and Adjustment of the Operating Satellite 
     In connection with the explanation of the structure and the functions of the operating satellite  200 , specific features including the adjustable ratchet sensitivity have already been addressed. Further explanation is given in the following. 
     The ratchet upon rotating the rotational control ring  203  provides an audible ratchet sound and a tactile feedback via the hand of the operating person by means of a correspondingly selected encoder like, for example, an encoder type E33, provided by the company ELMA. 
     As far as software is concerned, the sensitivity of the ratchet distance of the rotation control ring  203 , i.e. the interrelation between one increment of turning and the effect on the speed, can be individually set via an end terminal like a smart phone or a PC, namely by a smartphone app or a PC service application. This makes it possible to address the needs of various user groups as well as their level of handicap. For instance, it can be desirable to provide only a very small change in speed in spite of a considerably large distance of the movement of operation. This is of considerable advantage for users having limited coordination ability of their arms and hands since the movements then can be executed in a gross motor manner. 
     On the other hand, in case of good fine motor skills and for well-trained users, it can be of advantage if already a movement over a small distance leads to a comparatively great change of the speed. This is particularly useful when driving outdoors where it may be intended to obtain the top speed quickly. 
     Exemplary values for a the effect of “ratchet” (or a click), i.e. a distinct increment of rotation, can be taken from table  1  below. 
     
       
         
           
               
               
             
               
                   
               
               
                 Change of speed per ratchet 
                 Set sensitivity: 
               
               
                   
               
             
            
               
                 0.1 km/h 
                 low 
               
               
                 0.2 km/h 
               
               
                 0.3 km/h 
               
               
                 0.4 km/h 
               
               
                 0.5 km/h 
               
               
                 0.6 km/h 
               
               
                 0.7 km/h 
               
               
                 0.8 km/h 
               
               
                 0.9 km/h 
               
               
                 1.0 km/h 
                 high 
               
               
                   
               
            
           
         
       
     
       FIG.  29    shows a display of a smartphone arranged for setting and adjusting the sensitivity of the rotational control ring  203  of the operating satellite  200 . The sensitivity can be set between low and high by means of an electronic sliding controller. 
     Setting of the Automatic Adaption of the Cornering Speed 
     As already explained in connection with the description of the structure of an embodiment of an auxiliary drive device  100 , a sensor can be adapted at the steering shaft  130  of the auxiliary drive device  100  which sensor permanently monitors the steering angle of the drive wheel  110 . 
     In such case, a setting can be made as from which angle on the drive power shall be reduced or increased. In one embodiment, this can be done for instance via a computer program or a smartphone app. By reducing the drive power in tight curves, controllability and ultimately the safety will be increased because the cornering speed will be automatically reduced. Specifically those wheelchair drivers having a higher spinal paralysis and limited function of the hands and fingers therefore gain additional control concerning the drive. 
     In a narrow environment like for instance indoors, where for instance furniture or other objects must be avoided, or while driving in heavily frequented pedestrian zones as well as generally in narrow curves, monitoring the steering angle is an additional safety feature because the drive power is appropriately reduced. When the steering angle becomes smaller again and finally becomes zero, i.e. a straight drive, the drive power is increased correspondingly. 
     In a further embodiment, as a specific safety feature, the drive may be completely switched off as soon as a critical steering angle is reached, for instance in case a steering angle is larger than 55° to the left side or the right side which gives, in this example, a total rotational range of 110°. 
     In order to effect such a programming concerning the drive characteristics, the auxiliary drive device  100  is coupled with a respective end terminal, for instance a personal computer or smartphone, by use of a Bluetooth module. On this computer or smartphone, a respective software application for this additional drive features has been installed. In one embodiment, a computer can be connected with the auxiliary drive device  100  via a cable, for instance a USB cable, and programming can be effected via cable connection. 
       FIG.  30    shows, in an exemplary depiction, a display of a smartphone arranged for setting the automatic adaption of the cornering speed depending on a steering angle of the drive wheel  110 . Monitoring of the angle can be completely switched off or can be set up to a maximum value of for instance 110° by use of an electronic slide controller. 
     It is understood that also other settings and switching on or off operations can be effected by such an external device, for instance switching ON and OFF of the rear light  122 . Furthermore, such an app can display operational parameters like for instance the state of charge of the main battery  121  or of the operating satellite battery on the smartphone. 
     The control functions of the described embodiments make use of electronic control elements, wherein respective components are arranged in particular in the operating satellite  200 , in the auxiliary drive device main body  120  and in the drive wheel  110 . 
     The control functions can be implemented by circuitry including at least one semiconductor integrated circuit such as at least one processor (e.g., a central processing unit (CPU)), at least one application specific integrated circuit (ASIC), and/or at least one field programmable gate array (FPGA). At least one processor is configurable, by reading instructions from at least one machine readable non-transitory tangible medium, to perform all or a part of the control functions. Such a medium may take many forms, including, but not limited to, any type of magnetic medium such as a hard disk, any type of optical medium such as a CD and a DVD, any type of semiconductor memory (i.e., semiconductor circuit) such as a volatile memory and a non-volatile memory. The volatile memory may include a DRAM and a SRAM, and the nonvolatile memory may include a ROM and a NVRAM. The ASIC is an integrated circuit (IC) customized to perform, and the FPGA is an integrated circuit designed to be configured after manufacturing in order to perform, all or a part of the control functions. 
     Although some example embodiments of the technology are described hereinabove, the foregoing example embodiments are mere examples and are not intended to limit the scope of the technology. It should be appreciated that modifications and alterations of the foregoing example embodiments may be made. It should be also appreciated that various omissions, replacements, and modifications may be made in the foregoing example embodiments described herein, without departing from the scope of the spirit of the technology. The technology is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof. 
     LIST OF REFERENCE SIGNS 
     
         
           100  auxiliary drive device 
           105  steering shaft rotational angle sensor 
           110  drive wheel 
           111  motor 
           112  tire surface 
           113  tire surface bolts 
           118  slip ring 
           120  auxiliary drive device main body 
           121  main battery 
           122  rear light 
           123  main switch 
           124  main body charging socket 
           130  steering shaft 
           131  steering fork 
           132  stop gliding element—guiding element 
           133  elongated hole 
           134  stop gliding element 
           135  stop element 
           135 A first side of stop element  135   
           135 B second side of stop element  135   
           200  operating satellite 
           201  undercut 
           202  operating satellite control portion 
           203  rotational control ring 
           204  push control knob 
           205  display device 
           205 A LED element white 
           205 B LED element RGB 
           206  cover element 
           207  fixing screw 
           208  grip link 
           209  unlocking element 
           210  operating satellite mounting element 
           211  locking hook 
           218  adapter charging socket 
           219  pairing button 
           220  operating satellite mounting pivot element 
           221  latches 
           221 A latch bar 
           222  fixing hook 
           223  release button 
           224  push rod 
           225  pressure spring 
           226  reverse lever 
           230  wheelchair mounting element 
           231  mounting bolt 
           300  coupling mechanism 
           310  handle 
           311  rocker 
           312  rocker support pin 
           313  operating pin receiving bore 
           314  operating pin 
           320  coupling mechanism main body 
           321  coupling groove 
           330  locking element 
           331  gate window 
           332  locking element support pin 
           333  first locking element contact surface 
           334  second locking element contact surface 
           338  leg spring 
           380  coupling clamp 
           381  coupling pin 
           500  wheelchair 
           501  axis 
           502 L left rear wheel 
           502 R right rear wheel 
           504  pushrim 
           505  front wheel