Patent Publication Number: US-2023141361-A1

Title: Gear Shift Drum

Description:
This application claims priority from the German patent application 10 2021 128 917.3 filed Nov. 5, 2021, the content of which is incorporated herein in the entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to a device for axially moving a gearbox element according to the preamble of the valid claim  1 . 
     BACKGROUND 
     DE 89 12 348 U1, U.S. Pat. No. 4 782 782 A and DE 689 10 468 T2 each disclose a device according to the preamble of the current claim  1 . A device of this type is also known from U.S. Pat. No. 6 370 976 B1. 
     It is object of the invention to improve the known device. 
     The task is fulfilled by the characteristics of the independent claims. Preferred embodiments are the subject matter of the dependent claims. 
     SUMMARY 
     According to one aspect of the invention, a device for axially moving a gearbox element comprises a gear shift drum mounted rotatably about an axis of rotation and having a shifting groove formed circumferentially about the axis of rotation in its outer casing, which shifting groove is axially inclined at least in certain areas, a cage holding the gear shift drum and having a cage wall delimiting an inner cage space from an outer cage space and a wall slot extending axially through the cage wall, which opens the inner cage space to the outer cage space, a carriage held between the gear shift drum and the cage wall in the area of the wall slot so as to be axially movable, and a shift fork with two fork legs between which the gearbox element can be received in a form-fitting manner for axial movement in the axial direction, and a guidance pin connected to the fork legs which is inserted into the shifting groove guided by the wall slot and the carriage. According to the invention, the shifting groove is moulded into the gear shift drum with a closed curve. 
     The device is based on the consideration that the shift fork should move as free of play as possible in directions other than the axial direction. For this purpose, the shift forks in the aforementioned device are mounted on shafts via guiding sleeves, which are designed to take up installation space in the axial direction. 
     The specified device takes a different approach and does not mount the shift fork on its own shaft but guides it between the gear shift drum itself and a cage in which the gear shift drum is held. In this way, the specified device can be designed to be very space-saving, even if the gear shift drum guides a larger number of shift forks of, for example, three or four. 
     In an embodiment of the specified device, the shifting groove is elliptically formed in the gear shift drum. In this way, an endless loop is created for the shifting groove, via which all shifting states of the specified device can be set by endless rotation of the gear shift drum. 
     In another embodiment of the specified device, the axial ends of the gear shift drum are guided through the cage to the outer cage space, wherein a drive shaft for rotating the gear shift drum can be introduced into at least one of the axial ends in a form-fitting manner in the circumferential direction about the axis of rotation. In this way, means for rotating the gear shift drum can be connected by simply plugging on axle elements. 
     In a particular embodiment of the specified device, the gear shift drum is held in the cage in the area of its axial ends in and against the axial direction in a form-fitting manner. In this way, an axial play of the gear shift drum is minimised so that the shifting states of the device can be precisely defined. 
     In yet another embodiment of the specified device, the cage is constructed from at least a first cage part and a second cage part which are separable in the axial direction. In this way, the cage can be constructed in a simple manner as a modular system, for example in the field of model making. 
     In an additional embodiment of the specified device, the two cage parts are connected to each other by means of a cage form fit acting in the axial direction. In this way, the cage parts can be disassembled and reused, for example, in the field of model making for alternative models. 
     In a preferred embodiment of the specified device, the cage form fit comprises catch hooks. In this way, the aforementioned disassembly is achieved on the one hand, but also a secure cohesion of the two cage parts on the other hand. 
     In a further embodiment of the specified device, the carriage is guided in the slot in the axial direction with a carriage form fit acting in the circumferential direction about the axis of rotation. The purpose of this slot is to further increase the axial guiding effect, i.e. the guiding in the axial direction, and to prevent other degrees of freedom. 
     In a still further embodiment of the specified device, the carriage has, on its side facing the gear shift drum, a recess which is circular-segmented in cross-section and into which the gear shift drum is inserted. This circular-segmented recess prevents movements of the carriage transverse to the axial direction to be guided and further increases the axial guiding effect. 
     In a particularly preferred embodiment of the specified device, the carriage is held guided in the axial direction in the cage at its left and right ends as seen in the axial direction. In this way, the axial guiding effect is increased even further. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer in connection with the following description of the embodiments, which are explained in more detail in connection with the drawing, in which: 
         FIG.  1    is a perspective view of a device engaged with four gearbox elements, 
         FIG.  2    is a perspective view of the device of  FIG.  1    engaged with one gearbox element, 
         FIG.  3    is a partial perspective exploded view of the device of  FIG.  1   , and 
         FIG.  4    is a full perspective exploded view of the device of  FIG.  1   . 
       
         
           
             
                 
               
                 
                     
                 
                 
                   List of reference signs 
                 
                 
                     
                 
               
              
                 
                     
                 
              
             
             
                 
                 
              
                 
                   2 
                   Longitudinal direction 
                 
                 
                   4 
                   Transverse direction 
                 
                 
                   6 
                   Vertical direction 
                 
                 
                   8 
                   Axis of rotation 
                 
                 
                   10 
                   Device 
                 
                 
                   12 
                   Gearbox element 
                 
                 
                   14 
                   Gear drive 
                 
                 
                   16 
                   Gearwheel 
                 
                 
                   17 
                   Circumferential direction 
                 
                 
                   18 
                   Shaft 
                 
                 
                   20 
                   Form-fit element 
                 
                 
                   22 
                   Ring 
                 
                 
                   24 
                   Slot 
                 
                 
                   26 
                   Coupling element 
                 
                 
                   28 
                   Wall 
                 
                 
                   30 
                   Cage 
                 
                 
                   32 
                   Top surface 
                 
                 
                   34 
                   Casing 
                 
                 
                   36 
                   Cage part 
                 
                 
                   38 
                   Cage part 
                 
                 
                   40 
                   Slot 
                 
                 
                   42 
                   Carriage 
                 
                 
                   44 
                   Insertion opening 
                 
                 
                   46 
                   Shift fork 
                 
                 
                   48 
                   Inner cage space 
                 
                 
                   50 
                   Gear shift drum 
                 
                 
                   51 
                   Shift drum opening 
                 
                 
                   52 
                   Insertion opening 
                 
                 
                   54 
                   Linear direction of movement 
                 
                 
                   56 
                   Direction of insertion 
                 
                 
                   58 
                   Shift drum body 
                 
                 
                   60 
                   Shift drum pin 
                 
                 
                   61 
                   Shift drum shoulder 
                 
                 
                   62 
                   Shifting groove 
                 
                 
                   64 
                   Angle of inclination 
                 
                 
                   66 
                   Supporting surface 
                 
                 
                   68 
                   Carriage form fit element 
                 
                 
                   70 
                   Carriage guiding element 
                 
                 
                   72 
                   Protrusion 
                 
                 
                   74 
                   Support shoulder 
                 
                 
                   76 
                   Support element 
                 
                 
                   78 
                   Guidance pin 
                 
                 
                   80 
                   Fork leg 
                 
                 
                   82 
                   Catch hook 
                 
                 
                   84 
                   Chamfer 
                 
                 
                     
                 
              
             
           
         
       
     
    
    
     DETAILED DESCRIPTION 
     In the figures, the same technical elements are provided with the same reference signs, and are only described once. The figures are purely schematic and, in particular, do not reflect the actual geometric proportions. The description is given in a space spanned by a longitudinal direction  2 , a transverse direction  4  transverse to the longitudinal direction  2  and a height direction  6  transverse to the longitudinal direction  2  and transverse to the transverse direction  4 . 
     Reference is made to  FIG.  1   , which shows a perspective view of a device  10  aligned parallel to an axis of rotation  8 . The axis of rotation  8  runs parallel to the longitudinal direction  2 . 
     In  FIG.  1   , the device  10  is in engagement with four gearbox elements  12  of a superordinate gearbox in the form of a gear drive  14 , only parts of which are shown. 
     The task of a gearbox, and thus also of the gear drive  14 , is to change movement variables. In the present embodiment, the movement variables are changed by means of gearwheels  16  which are held on shafts  18  so as to be rotatable in a circumferential direction  17  about the axis of rotation  8 . The shafts  18  have form-fit elements  20  acting in the circumferential direction  17  which, for the sake of clarity, are not provided with their own reference sign on all shafts  18  in  FIG.  1   . In contrast to the gearwheels  16 , the gearbox elements  12  are held positively on these form-fit elements  20 , so that the gearbox elements  12  can move in the longitudinal direction  2  and thus in the direction of the axis of rotation  8 , but cannot rotate in the circumferential direction  17 . 
     Each gearbox element  12  is constructed from two rings  22  arranged parallel to the axis of rotation  8  and held axially spaced apart from each other and concentric with the respective shaft  18 , so that an axial slot  24  is formed between the rings  22 . The rings  22  of each gearbox element  12  are supported on coupling elements  26 , which are arranged concentrically within the rings  22  and are secured to the rings  22  via walls  28 . In each gearbox element  12 , the respective coupling elements  26  are positively connected to the form-fit elements  20  of the respective shaft  18  so that the coupling elements  26  rotate with the rotation of the respective shaft  18 . If the gearbox elements  12  are moved back and forth on the respective shafts  18  in the longitudinal direction  2 , they can be positively engaged in the gearwheels in the circumferential direction  17 , so that by rotating the respective shaft  18  not only the gearbox element  12  but also the engaged gearwheel is rotated. 
     The structure and the mode of operation of the gearbox elements  12  are basically known from WO 2019/137 993 A1 and shall therefore not be further elaborated. 
     For further explanation of the device  10 , reference is made to  FIG.  2   , which shows the device  10  in a perspective view with a single gearbox element in engagement. 
     The device  10  comprises a cage  30  of cylindrical construction with substantially square shaped top surfaces  32  and a casing  34  connecting the top surfaces. The top surfaces  32  are arranged perpendicular to the axis of rotation  8 , the axis of rotation  8  passing centrally through the axis of rotation  8 . The cage  30  is made of a first cage part  36  and a second cage part  38 , the second cage part  38  being placed as a cover on the first cage part  36 . The connection between the two cage parts  36 ,  38  will be discussed in more detail later. 
     Four slots  40  are formed through the casing  34 , running parallel to the axis of rotation  8  and spaced 90° apart from each other as seen in the circumferential direction  17 . In the perspective of  FIG.  2   , only two of the four slots  40  are visible. Each slot  40  holds a carriage  42  which is adapted to the shape of the respective slot  40  so that it is guided in the longitudinal direction  2 . Each carriage  42  has a slot-shaped insertion opening  44  directed towards the axis of rotation  8 , into which a shift fork  46  can be inserted. In the perspective and configuration of  FIG.  1   , only one of each of the slot-shaped insertion openings  44  and the insertable shift forks  46  can be seen. 
     The top surfaces  32  and the casing  34  of the cage  30  enclose an inner cage space  48  referenced later in  FIG.  4   , in which a gear shift drum  50  rotatable about the axis of rotation  8  is accommodated. The gear shift drum  50  is guided out of the inner cage space  48  through shift drum openings  51  in the top surfaces  32  of the cage  30 , which can be seen in  FIG.  4   , and has a cross-shaped insertion opening  52  at each end, into each of which a shaft  18  can be inserted, as already described above. In the perspective of  FIG.  2   , only one of the cross-shaped insertion openings  52  can be seen, and only one of the cross-shaped insertion openings  52  has a shaft  18  inserted into it. Further construction details of the gear shift drum  50  will be discussed in detail later. 
     The gear shift drum  50  can be rotated in and against the circumferential direction  17  via the shafts  18  which can be inserted into the cross-shaped insertion openings  52 . The task of the gear shift drum is to convert this rotary movement into a linear movement  54  of the carriages  42 , which move the shift forks  46  with the linear movement  54 . The shift forks  46 , in turn, are positively inserted into the axial slots  24  of the gearbox elements  12  in the longitudinal direction  2  and can thus transmit the linear movement  54  to the gearbox elements  12 . In this way, the gear drive  14  can be shifted in the manner explained further above. 
     The device  10  makes it possible to construct the gear drive  14  in a modular manner with any number of gearwheels  16  between one and eight. This will be illustrated by  FIG.  3   , which shows a partial perspective exploded view of the device  10  of  FIG.  1   . 
     A shift fork  46  can be received in each slot-shaped insertion opening  44  in a corresponding insertion direction  56  directed towards the axis of rotation  8 , so that the device  10  guides up to four shift forks  46 . Each received shift fork  46  can then in turn engage a gearbox element  12  previously described in connection with  FIG.  2   , and thus shift either one gearwheel  16  or two gearwheels  16 , depending on how many gearwheels  16  are arranged on the respective shaft  18 . Thus, between one and eight shift stages can be constructed in any manner using the device  10 . 
     For further explanation of the device  10 , reference is made to  FIG.  4   , which shows a full perspective exploded view of the device  10 . 
     The gear shift drum  50  is the core of the device  10 . It has a shift drum body  58  laid rotationally symmetrically about the axis of rotation  8 , to the end faces of which are connected shift drum pins  60  laid rotationally symmetrically about the axis of rotation  8 . The insertion openings  52 , which are not visible in the perspective of  FIG.  4   , are moulded into the axial end faces of these shift drum pins  60 , which are opposite the shift drum body  58 . Seen from the axis of rotation  8 , the shift drum pins  60  have a smaller radius than the shift drum body  58 , so that a shift drum shoulder  61  is formed at each of the axial ends of the shift drum body  58 . The shift drum shoulders  61  can abut the shift drum openings  51  of the cage  30  for an axial form fit. 
     The shift drum body  58  has a casing, not further referenced, in which a shifting groove  62  is moulded. In order to be able to move a shift fork  46  axially by rotating the gear shift drum  50  about the axis of rotation  8 , the shifting groove  62  must be laid in the area of the fork to be shifted so as to extend circumferentially about the axis of rotation  8  and be designed so as to extend with an angle of inclination  64  of greater than 0° and less than 90°. Individual shifting grooves  62  can be formed in the shift drum body  58  for moving each shift fork  46  individually. The common shifting groove  62  shown in  FIG.  4    is merely a preferred example of an embodiment. Furthermore, the shifting groove  62  may be open in a manner not shown, with a beginning not shown and an end not shown formed into the shift drum body  58 , for example in a spiral shape. The closed design of the shifting groove  62  shown in  FIG.  4    with a basically elliptical course is merely a preferred example of an embodiment. However, this has the decisive advantage that the shifting groove can be produced without undercuts and can be separated into an upper shifting groove part and a lower shifting groove part at a dividing line in the form of supporting surfaces  66  indicated in  FIG.  4   , where two injection moulds can be brought together. 
     The cage  30  constructed from the two cage parts  36 ,  38  holds the gear shift drum  50  on the shift drum pins  60  in the shift drum openings  51  in the inner cage space  48 , which has already been explained in connection with  FIGS.  1  and  2   . In this way, a guide space not further referenced is created between the gear shift drum and the casing surface  34  of the cage  30 , in which the carriages  42  can be guided axially in and against the longitudinal direction  2 . For this purpose, each carriage  42  has on its underside, viewed from the axis of rotation  8 , a supporting surface  66  which is formed in a circular-segmented shape in a cross-section extending at right angles to the axis of rotation  8  through the respective carriage  42 . The circular segment has a radius equal to the radius of the shift drum body  58 . In this way, the carriage is guided on the shift drum body  58  with as little tolerance as possible. 
     Furthermore, each carriage  42  optionally has on each of its sides viewed in the circumferential direction  17  a carriage form fit element  68 , which in the embodiment of  FIG.  4    is designed as a semicircular rod and is held on the carriage base body, which is not further referenced. For guiding the carriage form fit elements  68 , the cage  30  has corresponding carriage guiding elements  70  into which the carriage form fit elements  68  can be inserted so that the carriage can be guided back and forth in the longitudinal direction  2 . Not all of these carriage guiding elements  70  existing in the cage  30  can be seen in the perspective of  FIG.  4   . 
     To further improve the guidance of the carriages  42  in and against the longitudinal direction, protrusions  72  can be formed on the carriages  42  which can be inserted in a positive-locking manner into the slots  40  in and against the circumferential direction  17 . The protrusions  72  should be circular or elliptical in shape, at least in the area of contact with the walls of their respective slot  40 , to minimise contact friction. 
     The slot-shaped insertion openings  44  through the carriages  42  change in their cross-section and thus have support shoulders  74 , of which only two can be seen in the perspective of  FIG.  4   . Support elements  76  held on the shift forks  46  can be placed on these support shoulders  74 , between which a guidance pin  78  is held in each shift fork  46 . Two fork legs  80  are connected to each guidance pin  78 . 
     For assembling the cage  30 , the two cage parts  36 ,  38  each have four catch hooks  82 , each with a hook form fit surface not further referenced, facing the top surface  32  of the respective cage part  36 ,  38 . In this respect, on the second cage part  38 , the catch hooks  82  are each held in a chamfer  84  which extends in the longitudinal direction  2  over the entire length of the second cage part  38 . The chamfers  84  open the hook form fit surfaces of the catch hooks  82  on the second cage part  38  in the longitudinal direction, so that the second cage part  38  together with the catch hooks  82  can be manufactured without slides using a primary moulding process such as injection moulding. 
     To assemble the device  10  from the individual parts shown in  FIG.  4   , the carriages  42  are first inserted with their carriage form fit elements  68  into the carriage guiding elements  70  on the second cage part  38 . Subsequently, the shift drum body  58  is inserted into the passage formed by the supporting surfaces  66  of the carriages  42  with one of the shift drum pins  60  in front, whereby the inserted shift drum pin  60  is guided outwards through the shift drum opening  51  on the second cage part  38 . Finally, the first cage part  36  is placed on the second cage part  38  in the longitudinal direction  2  and the catch hooks  82  are hooked together. Now the shift forks  46  can be inserted with their guidance pins  78  into the slot-shaped insertion openings  44 . Care must be taken that each inserted guidance pin  78  ends in the shifting groove  62  in order to ensure the abovementioned shifting function.