Abstract:
A rear-wheel drive for a bicycle or a trailer bike comprises an output sprocket of a chain drive, a rear-wheel shaft, and a driving mechanism being supported outside to the bicycle frame. The rear-wheel shaft is supported only on one side of the driving in a supporting manner relative to the bicycle frame. The driving mechanism on the side facing the bicycle frame is not, as commonly known, supported relative to the rear wheel shaft but relative to the bicycle frame. That creates the required space for arranging a freewheel clutch, that fulfills the strength requirements for transmitting the occurring torques even when using sprockets with only a few teeth. Thus, short distances between the rear wheel and the bottom bracket and single-arm suspensions in the bicycle frame can be implemented together with the implementation of suitable developments of the chain drive for small running wheels.

Description:
TECHNICAL FIELD 
     The disclosure relates to a rear-wheel drive for a bicycle or a trailer bike, in particular for use with small running wheels. 
     BACKGROUND 
     Bicycles are preferably driven by means of a chain drive. Commonly the drive chain wheel connected to the crank arm lies predominantly outside the bicycle frame, while the output sprocket that is mounted on the rear-wheel axle is predominantly arranged inside the bicycle frame between the bicycle frame and the rear wheel. 
     Bicycles having smaller running wheels are preferably used so as to achieve small packing dimensions and weights, often designed as folding bicycles. Bicycles having 14 inch running wheels and less require a gear ratio of at least 1:5 between pedaling frequency and running-wheel frequency to be usable. 
     Trailer bikes are attached to the rear of a bicycle and, in contrast to those bicycles to which they are attached, mostly exhibit much smaller running wheels. Up till now, mostly transmissions having similar gear ratios are used for these running wheels as for the bicycles themselves. Thus the person riding the trailer bike has to ride at much higher pedaling frequencies than the person on the bicycle to which the trailer bike is attached. Even trailer bikes having small running wheels require the gear ratios mentioned above between the pedaling frequency and the running-wheel frequency. 
     So that the gear ratios that have been mentioned can be achieved with a single-stage chain drive, an output sprocket having as few teeth as possible has to be used. All tooth counts that have been mentioned below in this document, of the output sprockets and drive chain wheels refer to the chain pitch of 12.7 mm that is conventional for bicycle chains. 
     In the following solutions, output sprockets having low tooth counts are used: 
     a. In most cases the output sprocket is arranged between the bicycle frame and the rear wheel, the output sprocket being supported on a rear-wheel axle that is firmly connected to the bicycle frame. This solution has the disadvantage that on account of the strength requirements on the rear-wheel axle resulting from the bending loads, this axle must exhibit across its entire length a minimum diameter, on which the output sprocket is mounted, as a result of which the tooth count of the output sprocket amounts to at least nine teeth. This solution also has the disadvantage that the required freewheel has to be arranged in the rear-wheel hub or on the bottom bracket. JP 2003-054 479 A discloses a chain drive with an output sprocket having only eight teeth. Here it is a disadvantage that, on account of the system, no freewheel clutch is provided on the rear wheel. It would then have to be disposed between the crank arm and the drive chain wheel, seen in the power flow. 
     b. JP 11-321 768 A discloses a chain drive that uses an output sprocket that is arranged outside the bicycle frame and exhibits only seven teeth. A disadvantage of this solution is that the output sprocket exhibits an outer thread that is screwed directly to the rear-wheel shaft and that a freewheel clutch is arranged between the bottom bracket and the drive chain wheel, as a result of which no commercially available drive chain wheel directly connected to a crank arm can be used and as a result of which the output sprocket, the drive chain wheel, and the chain co-rotate in the freewheel case. 
     c. DE 101 27 614 A1 discloses a chain drive having an output sprocket of fewer than eleven teeth respectively having seven teeth. It is a disadvantage that the rear wheel is rotationally engaged with the chain and no freewheel clutch is provided. 
     d. JP 2005-289 283 A discloses a one-armed rear-wheel suspension on the bicycle frame, the output sprockets of the chain drive being mounted on both sides in the bicycle frame that has been designed as the gear case, and the rear wheel being arranged outside the gear case on one side of the bicycle frame. A freewheel clutch is arranged between the output sprockets and the rear-wheel shaft. So that a chain line distance that is conventional for bicycles is achieved for the bicycle drive, seen axially, the bicycle frame is designed between the output sprockets and the rear wheel as a thin-walled gear case. The consequence is that, seen axially, the rear-wheel shaft and the bottom-bracket shaft have to be mounted on both sides of the output sprocket respectively of the drive chain wheel relative to the gear case, in order to achieve the required stiffness between the rear-wheel shaft and the gear case respectively between the bottom-bracket shaft and the gear case. It is a disadvantage that in the process the rear-wheel shaft has to absorb, in the area of the freewheel clutch, the bending moments that are introduced from the rear wheel and are caused by the weight, and has to exhibit a minimum diameter that complies with the strength requirements and that in the process the smallest output sprocket of the sprocket assembly exhibits at least 13 teeth. It is further a disadvantage that on account of the fact that the rear-wheel shaft and the drive chain wheel are mounted in a supporting gear case on both sides, no commercially available drive chain wheel that is directly connected to a crank arm, can be used. 
     US 2006/0 108 858 A1, US 2006/0 108 859 A1 and BE 558 090 A reveal rear-wheel drives where a bearing supports a rear-wheel shaft relative to the frame and, seen in the power flow, a freewheel is arranged between a driving mechanism and the rear-wheel shaft, the freewheel being installed as a complete unit on the rear-wheel shaft. The freewheel comprises a freewheel clutch and bearing that supports the driving mechanism on the rear-wheel shaft. 
     A disadvantage of these embodiments is the fact that the bearings of the freewheel support the driving mechanism in each case relative to the rear-wheel shaft and, seen radially, are thus arranged between the driving mechanism and the rear-wheel shaft. On account of the design, the freewheel mechanism arranged between these bearings can thus again, seen radially, be implemented only between the sprockets of the driving mechanism and the rear-wheel shaft. In addition, the complete freewheel unit is connected to the rear-wheel shaft using a shaft-hub-connection. The radial installation space required for these elements in the area of the bearings, of the freewheel clutch and of the shaft-hub-connection probably does not permit an implementation of a driving mechanism having an output sprocket of fewer than 11 teeth in this area on account of the strength that is required for bicycles. It is in particular the bearing, which supports the driving mechanism, that is responsible for these disadvantages that, seen axially, is arranged between the freewheel mechanism and the bearing that supports the rear-wheel shaft relative to the frame. This bearing prevents an output sprocket having a lower tooth count and an acceptable chain line distance being implemented on the driving mechanism. 
     SUMMARY 
     The present disclosure provides an improved rear-wheel drive for bicycles or for trailer bikes, having at least one output sprocket that is driven by a chain drive, the output sprocket comprising a freewheel clutch arranged between a driving mechanism and a rear-wheel shaft and the output sprocket still having the lowest possible tooth counts and the rear-wheel drive making it possible to use a commercially available drive chain wheel that is directly connected to a crank arm. In combination with the drive chain wheel it shall be possible that the ratio of the tooth counts of output sprockets and drive chain wheel amounts to 1:5 or less so that a low total gear ratio can be achieved that is suitable for small running wheels. 
     Since, as a result of the arrangement of the output sprocket on the side of the bicycle frame opposite the rear wheel, the rear-wheel shaft only has to transmit torque and no loads in the area of the freewheel clutch due to weight, the rear-wheel shaft can exhibit markedly reduced diameters in the area of the output sprocket, as a result of which, seen in the power flow, a freewheel clutch can be realized between the output sprocket and the rear-wheel shaft and the output sprocket can exhibit very low tooth counts of less than 13 teeth down to 6 teeth. 
     Further advantages of the present disclosure are: 
     a. Rear-wheel drive variants for one-armed suspension in the bicycle frame and also variants for the suspension, provided on both sides of the rear wheel, can be implemented in the bicycle frame. 
     b. The rear-wheel drive can be used in particular for bicycles having small running-wheel sizes of 8 up to 14 inch on account of gear ratios of the chain drive that can be achieved, and in the process very short axle distances can be realized between the bottom-bracket axle and the rear-wheel shaft, so as to achieve small folding dimensions for example for folding bicycles. 
     c. A freewheel clutch does not have to be provided, neither inside the running wheel nor on the crank arm, on account of the freewheel clutch arranged between the driving mechanism and the rear-wheel shaft, as a result of which different shapes of running wheels can be used and can be firmly connected to the rear-wheel drive and as a result of which the same rear-wheel drive can be adapted to different running wheel sizes with the same achievable development, in exchanging the drive chain wheel of the chain drive. 
     d. Ergonomically favorable chainline distances can be achieved that can amount to less than 40 mm on account of the transmission components that have been implemented in a particularly space-saving manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the sectional view of a first embodiment of a rear-wheel drive in a one-armed suspension in the bicycle frame having a driving mechanism that comprises two output sprockets with 8 respectively 9 teeth, a pawl-freewheel clutch and a two-part rear-wheel shaft. 
         FIG. 2  shows the sectional view I-I through the driving mechanism and the freewheel clutch of  FIG. 1  and the output sprocket having 8 teeth. 
         FIG. 3  shows a partial sectional view of the drive shaft of the rear-wheel shaft, of the driving mechanism comprising the output sprockets, and of the freewheel clutch as in  FIG. 1 . 
         FIG. 4  shows the sectional view of a second embodiment of a rear-wheel drive in a one-armed suspension in the bicycle frame having a driving mechanism that exhibits an output sprocket having seven teeth, of an end-tooth freewheel clutch and a two-part rear-wheel shaft. 
         FIG. 5  shows a partial sectional view II-II of the freewheel clutch as in  FIG. 4  showing the components pressure element, pressure spring, pressure sleeve, and guide bushing. 
         FIG. 6  represents the corresponding side view of the rear-wheel drive as in  FIG. 4 . 
         FIG. 7  shows a third embodiment of a rear-wheel drive having a driving mechanism that exhibits an output sprocket having six teeth, of an end-tooth freewheel clutch, of an undivided rear-wheel shaft on which a solid 10 inch plastic running wheel is fastened. 
         FIG. 8  shows a view of the rear-wheel drive as in  FIG. 7  having the output sprocket that exhibits six teeth. 
         FIG. 9  shows in the side view a forth embodiment of a rear-wheel drive having a pawl freewheel clutch, the output sprocket exhibiting only seven teeth. 
         FIG. 10  to  FIG. 12  show further embodiments of the end toothing of clutch member and driving mechanism for the embodiments as in  FIG. 4  and  FIG. 7 . 
         FIG. 13  shows a sectional view and a view of the driving mechanism and of the freewheel clutch of a further embodiment, the output sprocket being co-rotatingly connected with, but releasably to the driving mechanism and exhibiting only seven teeth. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first embodiment of a rear-wheel drive in a one-armed suspension in the bicycle frame. 
     A driving mechanism  2  is driven by a chain  1  and comprises two output sprockets  2   a  and  2   b  of an endless chain drive. Driving mechanism  2  is mounted on its one side inside via a first drive mechanism bearing  5  on a rear-wheel shaft, that in this embodiment is designed as a two-part rear-wheel shaft comprising a drive shaft  3  and an output shaft  4 , and on its other side outside via a second drive mechanism bearing  6  in a bearing bushing  7 . 
     The bearing bushing  7  is connected firmly or releasably to a bicycle frame  8 . The bearing bushing  7  receives a two-row rear-wheel shaft bearing  9 , preferably an angular contact ball bearing, that in turn, supports the output shaft  4  of the rear-wheel shaft on the inside. The angular contact ball bearing is fixed axially in the bearing bushing  7  by a retaining ring  10 . A rear wheel  11  is fastened on the output shaft  4 . The drive shaft  3  of the rear-wheel shaft is operatively co-rotatingly connected with the output shaft  4  of the rear-wheel shaft by a splined shaft  3   a . A threaded connection or similar can likewise be implemented. 
     An arrangement is likewise possible of two adjacent bearings for supporting the rear-wheel shaft in the bicycle frame that is connected to the bearing bushing  7 , or also a support of the rear-wheel shaft that takes place on both sides of the rear wheel  11 . So that the drive shaft  3  of the rear-wheel shaft is not exposed to any bending moments that are caused by impact and no bending moments that are essentially caused by weight, the rear-wheel shaft is supported, seen axially, only on one side of the driving mechanism in a supporting manner to the bicycle frame  8 . This enables the implementation of a freewheel clutch that is particularly space saving and seen in the power flow is arranged between the driving mechanism  2  and the rear-wheel shaft, as a result of which particularly small output sprockets  2   a  and  2   b  can be realized on the driving mechanism  2 . 
     Between the driving mechanism  2  and the drive shaft  3  of the rear-wheel shaft a pawl freewheel consisting at least of one pawl  12  and a spring ring  13  may be arranged. As illustrated in  FIG. 1  the first drive mechanism bearing  5  exhibits a smaller inner diameter than the inner diameter of the recesses, provided on the drive shaft  3  of the rear-wheel shaft, for the pawls  12 , as a result of which these recesses can be milled on the end face. 
     The axial definition of the drive mechanism bearing  5  and  6  is carried out using a screw  14  that is screwed into the drive shaft  3  of the rear-wheel shaft and braces the first drive mechanism bearing  5  against the driving mechanism  2  and the latter against the second drive mechanism bearing  6  and the latter against the retaining ring  10 . It is also possible to use a nut instead of the screw  14 . In this case, the drive shaft  3  of the rear-wheel shaft would have to exhibit a corresponding outer thread. These and further possible embodiments (for example having retaining rings) of the axial definition of the drive mechanism bearings  5  and  6  can be imagined. 
     It is also possible to dispense with the retaining ring  10 , the screw  14  then bracing the second drive mechanism bearing  6  directly against the angular contact ball bearing  9  via the first drive mechanism bearing  5  and the driving mechanism  2 . 
     A nut  15  locks the output shaft  4  of the rear-wheel shaft against the drive shaft  3 . In this exemplary embodiment, the output shaft  4  of the rear-wheel shaft is designed as a rear-wheel flange and exhibits at least three, preferably four or five nut threads on the circumference, to which the rear wheel  11  can be screwed using the screws  16 . 
     The rear-wheel drive and the freewheel clutch are sealed against the outside by the sealed bearings  5 ,  6  and  9 . Further dynamic seals are not required. 
     To center radially the drive shaft  3  and the output shaft  4  of the rear-wheel shaft, the drive shaft  3  exhibits a centering face. The output shaft  4  likewise exhibits a centering face for the rear wheel  11 . 
     The outside diameters of the drive shaft  3  and of the output shaft  4  of the rear-wheel shaft can be greater at the outside lying, not interconnected ends than, seen axially, at the level of the angular contact ball bearing  9 . 
     In this way, for receiving the rear wheel  11  and for transmitting the weight forces and torques from the output shaft  4  of the rear-wheel shaft to the rear wheel  11  and in the opposite direction, many embodiments that are already known for one-sided running-wheel fastening mechanisms can be provided for the output shaft  4  in addition to the embodiment that has been shown. 
     Likewise it is possible to use a variety of shapes of rear wheels that are either screwed directly to the output shaft  4  of the rear-wheel shaft or can be connected to the output shaft  4  of the rear-wheel shaft by means of additional elements of the rear wheel  11 . 
     In the exemplary embodiment of  FIG. 1 , screws  17  serve for fastening the bearing bushing  7  on the bicycle frame  8 . Here again, a multiplicity of positive or releasable connections are possible between the bearing bushing  7  and the bicycle frame  8 . 
       FIG. 2  shows the sectional view I-I through the driving mechanism  2  and the freewheel clutch as in  FIG. 1 . 
     The spring ring  13  of the freewheel clutch, that is arranged in a recess of the pawl  12  in the center of the pawl  12 , biases the pawl  12  outward, whereby it is pressed with its rounding  12   a  that faces the driving mechanism  2 , into the recess  2   c  of the driving mechanism  2 . The pawl  12  exhibits at its end arranged toward the rear-wheel shaft, curves  12   b  that enable the required rotatability of the pawl  12  on the rear-wheel shaft. In addition, the pawl  12  exhibits an edge  12   c  that is pressed, in the coupling case, radially inward by the spring ring  13  or that presses the spring ring  13  radially outward in the freewheel case. This principle realizes the freewheel clutch: The spring ring  13  that is tensioned in the freewheel case, exerts a radially inwardly directed force on the edge  12   c  of the pawl  12 . The pawl  12  rotates radially outward as soon as the driving mechanism that overtakes the rear-wheel shaft releases the corresponding radial space with its recess, whereby finally the curve  12   a  of the pawl is pressed into the recess  2   c  of the driving mechanism  2 . When the rear-wheel shaft in the freewheel case overtakes the driving mechanism  2 , the pawl  12  is again pressed radially inward by the driving mechanism  2 , whereby the spring ring  13  is tensioned again. These principles are well known and are not detailed here any further. 
     As  FIG. 2  shows, the output sprocket  2   a  only exhibits  8  teeth, while the output sprocket  2   b  exhibits  9  teeth, as  FIG. 3  shows. 
       FIG. 3  shows a partial sectional view of the drive shaft  3  of the rear-wheel shaft, of the driving mechanism  2  that comprises the output sprockets  2   a  and  2   b , and of the freewheel clutch in the freewheel as shown in  FIG. 1 . 
     As  FIG. 3  shows only two half-round recesses  3   b  and  3   c  that can be milled by facing the end face are to be provided in the drive shaft  3  so as to accommodate the pawl  12  inside the diameter, that exists there, of the drive shaft  3  of the rear-wheel shaft in the freewheel case. 
     The driving mechanism  2  comprises on its hub side a rectangular recess  2   d  that is normal for parallel keys, the driving mechanism  2  in addition exhibiting on that side of the recess that is in contact with the pawl  12 , the half-round millable recess  2   c  into which the rounding  12   a  of the pawl engages for force transmission. 
     Since the drive shaft  3  of the rear-wheel shaft and the driving mechanism  2  in each case exhibit half-round recesses  2   c  respectively  3   c  for guiding the pawls  12 , the requirements in terms of the absolute positioning accuracy of these recesses  2   c  and  3   c  relative to the drive shaft  3  can be selected so as to be low, as long as a relatively high positional accuracy in terms of the recesses  2   c  and  3   c  exists between a plurality of similar half-round recesses  2   c  respectively  3   c.    
       FIG. 4  shows a second embodiment of the rear-wheel drive. 
     For reasons of clarity, the parts of the rear-wheel drive in  FIG. 4 , that are described for  FIG. 1  and are represented in  FIG. 4  with a corresponding function, have been designated with a numeral that is increased by 100 in comparison to  FIG. 1 . The description of the parts in  FIG. 1  is to be transferred for the corresponding parts in  FIG. 4  to the extent that nothing to the contrary is described below. 
     In comparison to  FIG. 1 , the following features are modified: 
     a. As a freewheel clutch, an end-tooth connection is implemented between the driving mechanism  2  and a clutch member  118  that can slide axially, pushed by a pressure spring  121  and a pressure element  119 , and an involute gearing is implemented between the clutch member  118  and the rear-wheel shaft. 
     b. The pressure mechanism for the clutch member  118  of the freewheel clutch enables the pressure spring  121  to be arranged on the side of the pressure element  119  facing the driving mechanism  102 . 
     c. Seen radially, the driving mechanism  102  is supported on the rear-wheel shaft in the interior by means of a needle bearing  105 . The bearing  126  lying on the outside only serves for fixing the driving mechanism  102  axially. 
     d. The driving mechanism  102  exhibits an output sprocket  102   a  having only seven teeth. 
     Re a. From the driving mechanism  102  that exhibits an output sprocket  102   a  having seven teeth, the torque is transmitted to the drive shaft  103  using a clutch member  118  that can be shifted axially and that is operatively co-rotatingly connected with the drive shaft  103  of the rear-wheel shaft. For this purpose, end teeth  118   a  are arranged on an end face of the clutch member  118  uniformly distributed on the circumference and can engage into corresponding recesses, in  FIG. 4  into corresponding end teeth  102   b , of the driving mechanism  102 . It is likewise possible that only one clutch partner exhibits end teeth and the other clutch partner exhibits claws on its end face into which the end teeth of the one clutch partner can engage. 
     The end teeth  118   a  of the clutch member  118  are pressed axially into the end teeth  102   b  of the driving mechanism  102  by a pressure element  119  that penetrates the drive shaft  103  of the rear-wheel shaft at right angles to its axle and is arranged in corresponding radial opening of the drive shaft  103  of the rear-wheel shaft. 
     Seen radially, in involute gearing  118   b  is provided inside the clutch member  118 , that transmits the torque from the clutch member  118  to the drive shaft  103 . 
     An involute gearing  118   b  having the module 0.8 with 16 teeth according to DIN 5480 may be used for transmitting torque from the clutch member  118  to the drive shaft  103 , as a result of which the tooth count can be divided by four and the base circle diameter is slightly larger than 12 mm and the head circle diameter is slightly smaller than 14 mm. In contrast, eight end teeth  118   a , and thus again a tooth count that can be divided by four, is provided for the end gearing of the clutch member  118 . This symmetry that is achieved using the tooth counts that can be divided by four permits simple manufacture of the clutch member  118  and of the driving mechanism  102 . 
     The clutch member  118  of the freewheel clutch exhibits the following design that is particularly space-saving: At an end face, the clutch member  118  exhibits an end toothing having the end teeth  118 , and the clutch member  118  exhibits no recesses for receiving and guiding the pressure element  119 . The pressure element  119  can be designed as a rectangle and without further recesses. Apart from a pressure element, also round pressure rods or flattened pressure rods can be used. A disk  120  that keeps the pressure element  119  in position is arranged axially between the retaining ring  110  and the bearing  106  that supports, seen radially, the driving mechanism  102  on the inside. 
     As a result of the arrangement of the elements of the rear-wheel drive, the required fixed fits can be provided between the angular contact ball bearing  109  and the output shaft  104  of the rear-wheel shaft and also between the angular contact ball bearing  109  and the bearing bushing  107 . 
     Re b. Since an end toothing is used as clutch between the driving mechanism  102  and the clutch member  118 , the clutch member  118  has to be moved axially against the driving mechanism  102 . This takes place by means of the pressure element  119  via a pressure spring  121  arranged inside the rear-wheel shaft, according to the mechanism described below: 
     Since, as in  FIG. 1 , a two-part rear-wheel shaft is used that consists of the drive shaft  103  and the output shaft  104  that are interconnected, no sufficient radial installation space exists inside the rear-wheel shaft for the pressure spring  121  of the freewheel clutch in  FIG. 4 , seen axially, between the pressure element  119  and the angular contact ball bearing  109 . The pressure spring  121  having the arrangement described below is arranged on the side of the pressure element  119  facing the driving mechanism  102 . In  FIG. 5 , the elements described below of the freewheel clutch are illustrated in the part-sectional view II-II of  FIG. 4 . A pressure sleeve  122  having two legs, that is supported in the drive shaft  103 , is kept at a distance from the pressure element  119  by a washer  123 . The pressure spring  121  is supported on the washer  123  and it again exerts an axial force on a guide bushing  124 . The guide bushing  124  exhibits a continuous recess, preferably a bore, in which the pressure element  119  is accommodated. The guide bushing  124  guides the pressure force of the pressure spring  121 , seen radially, inside the pressure spring  121  and inside the pressure sleeve  122  again onto the axially seen other side of the pressure element  119 . Via the bore of the guide bushing  124 , the pressure element  119  is finally pressed against the clutch member  118 . In the freewheel case, the end teeth  102   b  of the driving mechanism  102  press the end teeth  118  of the clutch member  118  out of the end-tooth connection. In this case, the pressure spring  121  is pressed by the guide bushing  124  against the washer  123  that is supported on the pressure sleeve  122  and on the drive shaft  103 . The design of the freewheel clutch having the features described above enables a freewheel clutch that is particularly space-saving, that can transmit high torque values. Instead of a contact shoulder, that is present on the drive shaft side, for the angular contact ball bearing, a washer  125  serves as contact shoulder for the angular contact ball bearing  109 . The bearing bushing  107  exhibits a bore  107   a  that can be closed using a plug, a screw or the like, that makes it possible to install and remove the pressure element  119  and thus the entire freewheel clutch without having to separate the bicycle frame, the bearing bushing  107 , the angular contact ball bearing  109 , the drive shaft  103  and the output shaft  104  from each other. In this way, the drive shaft  103  can also be positively connected to the output shaft  104 , for example by soldering. 
     c. Seen radially, the driving mechanism  102  is supported on the inside by a needle bearing  105  on the drive shaft  103  of the rear-wheel shaft. The needle bearing  105  absorbs the loads of the cyclist due to the weight that act, when the rear wheel  111  is blocked, via the pedals onto the drive chain wheel, the chain and finally onto the output sprocket  102   a  and the driving mechanism  102 . A bearing  126  lying outside now only serves for axially fixing the driving mechanism  102  and can therefore be designed with a particularly small outside diameter. Seen radially on the inside, the bearing  126  is supported on a fixing screw  114  that is screwed into the drive shaft  103 . The radial positioning of the bearing  126  should take place with clearance between the fixing screw  114  and the drive shaft  103 . Seen radially, it is likewise possible to provide additional seal elements between the fixing screw  114  and the bearing  126  and/or between the bearing  126  and the driving mechanism  102 . 
     d. Due to the use of the needle bearing  105  for supporting the driving mechanism  102  and due to the small outside diameter of the bearing  126 , the output sprocket exhibits only seven teeth. 
       FIG. 5  shows the partial sectional view II-II of the freewheel clutch as in  FIG. 4  having the pressure element  119 , the pressure spring  121  arranged inside the drive shaft  103 , the pressure sleeve  122 , and the guide bushing  124 . 
       FIG. 6  represents the corresponding side view of the rear-wheel drive as in  FIG. 4  having the driving mechanism  102  that exhibits the output sprocket  102   a  having seven teeth. 
       FIG. 7  shows a third exemplary embodiment of a rear-wheel drive. 
     For reasons of clarity the parts of the rear-wheel drive that are described with reference to  FIG. 4  and are represented in  FIG. 7  with a corresponding function, have been designated with a numeral that is increased by 100 in comparison to  FIG. 4 . The description of the parts in  FIG. 1  respectively  FIG. 4  is to be transferred for the corresponding parts in  FIG. 7  to the extent that nothing to the contrary is described below. 
     In comparison to  FIG. 4 , the following features are modified: 
     a. The rear-wheel shaft  203  is designed such that it is undivided. The inside diameter of the angular contact ball bearing  209  is at least as large as the seat of the rear wheel  211  on the rear-wheel shaft  203 , so that the angular contact ball bearing  209  can be installed and removed. 
     b. The rear wheel is connected to the rear-wheel shaft  203  by means of a threaded sleeve  227  that is designed as a rear-wheel hub. Seen axially between the angular contact ball bearing  209  and the involute gearing of the rear-wheel shaft  203 , the washer  225  that can also be designed as a retaining ring serves as the contact shoulder on the shaft side for the angular contact ball bearing  209 . The rear wheel  211  that seen radially exhibits a threaded sleeve  227  on the inside, is screwed onto the rear-wheel shaft  203  and presses the angular contact ball bearing  209  on the rear-wheel shaft  203  against the washer  225  for the purpose of axially fixing the angular contact ball bearing  209 . By suitably choosing the fit, a fit section  227   a  of the threaded sleeve  227  is firmly connected to the rear-wheel shaft  203  by means of a fixed fit and carries the loads that are caused by the weight and the road surface. The torque is transmitted between the rear-wheel shaft  203  and the rear wheel  211  essentially by means of the threaded section  227   b  of the threaded sleeve  227 . The threaded sleeve  227  that supports the rear wheel  211  is locked by means of a screw  215  and a washer  228 . 
     c. The pressure spring  221  that shifts the clutch member  218  toward the driving mechanism  202  is arranged on the side of the pressure element  219  facing the rear wheel  211 . On account of the single-part design of the rear-wheel shaft  203 , there is created inside the rear-wheel shaft  203  space for arranging the pressure spring  221  on the side of the pressure element  219  facing the angular contact ball bearing  209 . The pressure spring  221  presses the guide bushing  224  against the pressure element  219  and the latter against the clutch member  218  and the driving mechanism  202 . The pressure spring  221  is supported on the screw  215  via the washer  223  and a guide tube  229 . 
     d. The driving mechanism  202  exhibits an output sprocket  202   a  having only six teeth. In comparison to the exemplary embodiment from  FIG. 4 , in the exemplary embodiment illustrated in  FIG. 7  another smaller needle bearing  205  having an inside diameter of 8 mm and having an outside diameter of 11 mm is designed for supporting the driving mechanism  202  on the rear-wheel shaft  203 . In a similar manner, the bearing  226  is designed to be smaller, to be precise having an inside diameter of 6 mm and an outside diameter of 13 mm. This exemplary embodiment thereby enables the implementation of a driving mechanism  202  that exhibits an output sprocket  202   a  having only six teeth. 
     e. On account of the small gear ratio of the chain drive, that can be achieved using an output sprocket  202   a  having six teeth, it is even a solid plastic running wheel having a size of only 10 inch that is used. It would even be possible to use a running wheel having a size of 8 inch in the case of a sufficiently large drive chain wheel. 
       FIG. 8  shows a view of the rear-wheel drive from  FIG. 7  having the output sprocket  202   a  that exhibits six teeth. 
     In a side view,  FIG. 9  shows a fourth embodiment of the rear-wheel drive having a pawl freewheel clutch, the output sprocket  302   a  exhibiting only seven teeth. To comply with increased strength requirements, the width of the pawl  312  in this case corresponds to the entire length of the rear-wheel shaft  303  that is available between the two bearings that support the driving mechanism  302 . On top of this,  FIG. 9  shows a further embodiment of the pawls  312  for the pawl freewheel. The pawl  312  exhibits a flattened, rectangular tip  312   a  that engages into a hub-side rectangular recess  302   b  of the driving mechanism  302 . The choice of the diameter makes it possible, even for this embodiment, to use an output sprocket  302   a  having only seven teeth. 
       FIG. 10  to  FIG. 12  show further possible embodiments of the end toothing of the clutch member  118  and the driving mechanism  102  for the exemplary embodiments from  FIG. 4  and  FIG. 7  in the exploded view, the designations referring to  FIG. 4 . 
       FIG. 10  shows an embodiment where the clutch member  118  and the driving mechanism  102  in each case exhibit an eight-teeth millable end gearing. 
     In  FIG. 11  it is only one clutch partner, in this case the clutch member  118 , that exhibits the eight millable end teeth  118 , while the other clutch partner, in this case the driving mechanism  102 , exhibits millable claws  102   c  into which the end teeth  118   a  of the clutch member  118  engage. 
     In  FIG. 12 , both clutch partners, clutch member  118  and driving mechanism  102 , exhibit a modified end toothing having end teeth  118   c  and  102   d  that are uniformly arranged next to each other on the circumference and mesh. 
       FIG. 13  shows a sectional view and a view of a driving member  402  on which co-rotatingly connected with, but releasably, an output sprocket  430  having only seven teeth  430   a  can be fastened. For axially fixing the driving mechanism  402 , an angular ball bearing  426  having an outside diameter of 13 mm can be used. The radial loads are taken up by a needle bearing  405  having an outside diameter of 11 mm. Seen axially relative to the bicycle frame, the output sprocket  430  is defined against a contact shoulder of the driving mechanism  402 , while axial fixation takes place from the outside by means of a distance sleeve  431  through a retaining ring  432 . As is sufficiently known for output sprockets, the torque is transmitted from the output sprocket  430  via a round recess  402   a  to the driving mechanism  402 . Other embodiments of the releasable connection between the output sprocket  430  and the driving mechanism  402  can be imagined, but are not detailed here separately. Finally this exemplary embodiment, too, reveals that the smallest possible output sprockets  2   a ,  2   b ,  102   a ,  202   a ,  302   a ,  430  can be implemented for the chain drive of the bicycle. 
     In all exemplary embodiments described above it is likewise possible to implement output sprockets having more teeth than mentioned in the respective exemplary embodiment. 
     Using the embodiments mentioned above, the gear ratios described in more detail in an exemplary manner below can be implemented. 
     Since the resulting gear ratios produce very small numbers, the illustration of the gear ratios has been selected to be in the format of a prefixed ratio “1:”. The respective row for the gear ratio that has been shown of the respective chain drive then lists the divisor of the gear ratio of 1:. For example a gear ratio of 0.125 is for example illustrated as =1:8. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE A 
               
             
             
               
                   
               
               
                 Exemplary gear ratios for small running wheels 
               
             
          
           
               
                 Running 
                 Tooth Count 
                 Tooth Count 
                   
                 Development in 
               
               
                 Wheel Size 
                 Drive Chain 
                 Output 
                 Gear 
                 m/crank arm 
               
               
                 in Inch 
                 Wheel 
                 Sprocket 
                 Ratio = 1: 
                 revolution 
               
               
                   
               
             
          
           
               
                 8 
                 48 
                 6 
                 8.00 
                 5.3 
               
               
                 8 
                 48 
                 7 
                 6.86 
                 4.6 
               
               
                 10 
                 40 
                 6 
                 6.67 
                 5.3 
               
               
                 10 
                 40 
                 7 
                 5.71 
                 4.6 
               
               
                 12 
                 36 
                 6 
                 6.00 
                 5.4 
               
               
                 12 
                 36 
                 7 
                 5.14 
                 4.6 
               
               
                 10 
                 52 
                 8 
                 6.50 
                 5.2 
               
               
                 10 
                 52 
                 9 
                 5.78 
                 4.6 
               
               
                 12 
                 48 
                 8 
                 6.00 
                 5.4 
               
               
                 12 
                 48 
                 9 
                 5.33 
                 4.8 
               
               
                 14 
                 40 
                 8 
                 5.00 
                 5.4 
               
               
                 14 
                 40 
                 9 
                 4.44 
                 4.8 
               
               
                 16 
                 36 
                 8 
                 4.50 
                 5.4 
               
               
                 16 
                 36 
                 9 
                 4.00 
                 4.8 
               
               
                 10 
                 48 
                 7 
                 6.86 
                 5.5 
               
               
                 12 
                 48 
                 8 
                 6.00 
                 5.4 
               
               
                 14 
                 48 
                 10 
                 4.80 
                 5.1 
               
               
                 16 
                 48 
                 11 
                 4.36 
                 5.2 
               
               
                   
               
             
          
         
       
     
     The table above reveals in the upper part the advantages of the embodiment from  FIG. 1  having a plurality of output sprockets. The output sprocket  2   a ,  2   b  that is used can be selected by a simple change of the position of the chain (e.g. in  FIG. 1  on the output sprocket  2   a  having eight respectively  2   b  having nine teeth), so that the desired development for the bicycle can be set. On top of this, the table above reveals that with an identical achievable development, the same rear-wheel drive can be adapted to all running wheel sizes of 10 inch up to 16 inch, by simply using another commercially available drive chain wheel. In this way, the same rear-wheel drive can be used for a multiplicity of possible embodiments of bicycles (having solid plastic running wheels, having air-filled running wheels and so on). 
     The table above shows in the lower part that the same rear-wheel drive and the same drive chain wheel can be used with the same achievable development for different running-wheel sizes of 10 inch to 16 inch, by simply exchanging the output sprocket that is designed so as to be releasable in the exemplary embodiment of  FIG. 13 . 
     As an example, a possible embodiment is illustrated below as multi-speed derailleur having six gears, the rear-wheel drive exhibiting the two output sprockets shown in  FIG. 1 . The multi-speed derailleur is implemented using a commercially available drive chain wheel having the chain counts 42-32-24 since in this way gradations of similar size can be achieved between the gears. 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE B 
               
             
             
               
                   
               
               
                 Six-speed transmission for a 16 inch wheel 
               
             
          
           
               
                   
                   
                 Tooth 
                   
                   
                   
                   
               
               
                 Running 
                   
                 Count 
                 Tooth 
                   
                 Development 
                   
               
               
                 Wheel 
                   
                 Drive 
                 Count 
                 Gear 
                 in m/crank 
               
               
                 Size in 
                   
                 Chain 
                 Output 
                 Ratio 
                 arm 
               
               
                 Inch 
                 Gear 
                 Wheel 
                 Sprocket 
                 1: 
                 revolution 
                 Gradation 
               
               
                   
               
               
                 16 
                 1 
                 24 
                 9 
                 2.67 
                 3.2 
                   
               
               
                 16 
                 2 
                 24 
                 8 
                 3.00 
                 3.6 
                 12.5% 
               
               
                 16 
                 3 
                 32 
                 9 
                 3.56 
                 4.3 
                 18.5% 
               
               
                 16 
                 4 
                 32 
                 8 
                 4.00 
                 4.8 
                 12.5% 
               
               
                 16 
                 5 
                 42 
                 9 
                 4.67 
                 5.6 
                 16.7% 
               
               
                 16 
                 6 
                 42 
                 8 
                 5.25 
                 6.3 
                 12.5% 
               
               
                   
               
             
          
         
       
     
     In case a technology is available that is able to change gears even in the case of particularly low tooth counts of the output sprockets, there are illustrated below further possible embodiments as multi-speed gear having six gears and a uniform gear gradation for the running wheel sizes 14 inch and 12 inch. Even in this case, the rear-wheel drive exhibits two output sprockets: 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE C 
               
             
             
               
                   
               
               
                 Six-Speed Transmission for 14 inch Wheel and for 12 inch 
               
               
                 Wheel 
               
             
          
           
               
                   
                   
                 Tooth 
                   
                   
                 Develop- 
                   
               
               
                 Running 
                   
                 Count 
                 Tooth 
                   
                 ment 
               
               
                 Wheel 
                   
                 Drive 
                 Count 
                 Gear 
                 in m/crank 
               
               
                 Size 
                   
                 Chain 
                 Output 
                 Ratio = 
                 arm 
               
               
                 in Inch 
                 Gear 
                 Wheel 
                 Sprocket 
                 1: 
                 revolution 
                 Gradation 
               
               
                   
               
               
                 14 
                 1 
                 24 
                 8 
                 3.00 
                 3.2 
                   
               
               
                 14 
                 2 
                 24 
                 7 
                 3.43 
                 3.7 
                 14.3% 
               
               
                 14 
                 3 
                 32 
                 8 
                 4.00 
                 4.3 
                 16.7% 
               
               
                 14 
                 4 
                 32 
                 7 
                 4.57 
                 4.9 
                 14.3% 
               
               
                 14 
                 5 
                 42 
                 8 
                 5.25 
                 5.6 
                 14.8% 
               
               
                 14 
                 6 
                 42 
                 7 
                 6.00 
                 6.4 
                 14.3% 
               
               
                 12 
                 1 
                 24 
                 7 
                 3.43 
                 3.09 
               
               
                 12 
                 2 
                 24 
                 6 
                 4.00 
                 3.60 
                 16.7% 
               
               
                 12 
                 3 
                 32 
                 7 
                 4.57 
                 4.11 
                 14.3% 
               
               
                 12 
                 4 
                 32 
                 6 
                 5.33 
                 4.80 
                 16.7% 
               
               
                 12 
                 5 
                 42 
                 7 
                 6.00 
                 5.40 
                 12.5% 
               
               
                 12 
                 6 
                 42 
                 6 
                 7.00 
                 6.30 
                 16.7% 
               
               
                   
               
             
          
         
       
     
     In addition, using the features that have been described above or the features that are claimed below, a multiplicity of further gear ratios can be realized. 
     All tooth counts, mentioned below in the patent claims, of output sprockets and drive chain wheels refer to the chain pitch of 12.7 mm that is conventional for bicycle chains. For embodiments having chain pitches that deviate therefrom, those tooth counts are claimed in the respective claims that result from the rounded result of the multiplication of the tooth counts respectively listed below by the quotient of 12.7 mm divided by the deviating chain pitch.