Abstract:
An electromagnetic shift arrangement for a transmission ( 2 ) with gear wheels ( 4, 6 ) arranged on a gear shift ( 12 ) rotatable about an axis ( 20 ) which can be non-rotatably connected with the gear shaft ( 12 ) to form a ratio step via an axial movement of a shift dog ( 18 ) along the axis ( 20 ). An electromagnetic device ( 24, 26, 40 ) is provided which is adequate for axial movement of the shift dog ( 18 ) along the axis ( 20 ). The electromagnetic device ( 24, 26, 40 ) is disposed in the area of the shift dog ( 18 ) and acts upon the shift dog ( 18 ) directly without shift fork.

Description:
FIELD OF THE INVENTION 
   The invention relates to a shift arrangement for a vehicle transmission. 
   BACKGROUND OF THE INVENTION 
   An electromagnetically activated shift arrangement for a transmission has been disclosed in U.S. Pat. No. 5,460,060. For each ratio pair to be shifted between which one shift arrangement is located there is provided here a shift fork situated upon a rod and meshing in a shift dog. A gear shaft upon which are rotatably situated the gear wheels of the relevant ratio can be connected each time with one of the gear wheels by the axial movement of the shift dog. Upon the rod is located the shift fork by means of which a respective laterally placed spring is forced to a middle position out of which it can be axially moved after activation of one magnet. The shift fork here moves axially opposite to the direction of the activated magnet. The ratio is switched off after termination of the activation of the magnet by the respective spring. The shift arrangement has the disadvantage of being structurally designed with a high mass to be moved. The shift arrangement is switched off only by the tension of the springs provided. 
   The problem on which the invention is based is to overcome the disadvantages of the prior art and show a shift arrangement in which the masses to be moved during the shift are as small as possible. 
   SUMMARY OF THE INVENTION 
   According to the invention an electromagnetic shift arrangement is proposed for a transmission having gear wheels rotatably disposed upon a gear shaft around an axis. To form a ratio step, the gear wheels are non-rotatably connectable with the gear shaft by an axial movement of a shift dog along the axis of rotation of the gear shaft. The shift arrangement also has an electromagnetic device suitable for axial movement of the shift dog along the axis. The electromagnetic device is situated directly in the area of the shift dog and acts upon the shift dog directly without assistance and intercalation of a shift fork. The electromagnetic device thus acts directly upon the shift dog and makes possible for a significant reduction of the masses to be moved during the shift operation. Experience has shown that relatively strong shift forces are needed, especially for switching off a ratio step. The disconnecting forces needed depend on the masses to be shifted and on the shifting speed that can be achieved. The smaller the masses to be shifted and the higher the shift speed achievable are, the smaller the shift force can be. In suitably dimensioned electromagnetic devices, it is thus possible to implement extremely short shift times which can be accomplished specially in case of gear shifts in uneven roads. In one development, by adequate control of the electromagnetic device, it is possible to adjust different load reduction times which ensure a long load reduction time, for example, in the course of an even road and shorter load reduction times in an inclination of the road without which control a disadvantageous speed decrease of the vehicle and in the most unfavorable case a rolling back of the vehicle could be associated. In one advantageous development, an electromagnetic device is provided for each axial direction of movement along the axis of the gear shaft which has the gear wheels to be shifted. An advantageous embodiment of the invention shows that the magnetic field to be generated in the electromagnetic device is reversible in its action. It is thus possible, to implement a control of the magnetic fields in different operational directions in order to produce movements of the shift dog in both directions along the axis. This results in that in an advantageous development that only one electromagnetic device is provided for both directions of movement along the axis. In one development, by the control of the magnetic fields, a reversal of the magnetic field can be produced to form a damping device against an impact of the shift dog and in another advantageous development, the shift dog is kept in neutral position by the electromagnetic device. In one embodiment, the shift dog is kept in neutral position by spring tension. One embodiment finally shows that the electromagnetic devices are mounted fixed to the housing and electric feed lines are provided in or on the housing of the transmission. The electromagnetic devices are magnetically insulated in relation to parts of the transmission not to be shifted. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be described, by way of example, with reference to the accompanying drawing in which: 
       FIG. 1  shows two electromagnetic devices for two ratio steps; and 
       FIG. 2  shows one electromagnetic device for two ratio steps. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a section from a transmission  2 . A first gear wheel  4  and a second gear wheel  6  are rotatably supported by bearings  8 ,  19  upon a gear shaft  12 . The gear wheels  4 ,  6  have one internal toothing  14 ,  16 , respectively. A shift dog  18  is non-rotatable, but axially displaceable along an axis  20  of the gear shaft  12 . A disc  22  meshes in the shift dog  18  or is designed integral therewith. Upon each side of the disc  22  is situated one electromagnetic device  24 ,  26 , respectively, which is stationarily fixed to the housing of the transmission in a manner not show here. The electromagnetic devices  24 ,  26  are connected with a control device  28 . Between the electromagnetic devices  24 ,  26  and the relevant gear wheels  4 ,  6  one electromagnetic insulating disc  30  and  32  is provided. 
   For non-rotatable connection of the gear wheel  4  with the gear shaft  12  and for the formation produced thereby of a ratio step of the transmission  2 , the shift dog  18  is axially displaceable to the left along the axis of the plane of the drawing. This occurs by control of the electromagnetic device  24  by the control device  28 . The electromagnetic device generates a magnetic field by which the disc  22  is drawn in direction to the gear wheel  4 . An external toothing  34  on the shift dog  18  then meshes in the internal toothing  14  of the gear wheel  4 . Thereby the gear wheel  4  is non-rotatably connected with the gear shaft  12 . To assist the movement of the shift dog  18  in direction to the gear wheel  4 , the electromagnetic device  26  can also be controlled. In the electromagnetic device  26  is likewise generated a magnetic field which is oriented so that it ejects the disc  22  in direction to the gear wheel  4 . Thereby the electromagnetic devices can be developed accordingly small or the shift force be accordingly increased. 
   To break up the non-rotatable connection, the electromagnetic device  24  is controlled so that the disc  22  is ejected and thus the toothing  34  of the shift dog  18  detaches itself from the toothing  14  of the gear wheel  4 . It is also possible here to provide an adequate assistance by the electromagnetic device  26  by the magnetic field of which the disc  22  is then drawn in direction to the gear wheel  6 . 
   If the shift dog  18  should remain in the neutral position between the two gear wheels  4 ,  6 , this can take place by an adequate control of both electromagnetic devices  24  and  26 . The two magnetic fields then generated can keep the disc  22  either in a drawing or an ejecting manner and thus retain the shift dog  18  in a neutral intermediate position. The intermediate position can also be brought about by two plate springs  36 ,  38  lying between the disc  22  and the respective electromagnetic device  24 ,  26 . If the disc  22  moves in one or the other direction, the plate springs  36 ,  38  are accordingly compressed. 
   A connection of the gear wheel  6  with the gear shaft  12  by switching off the neutral position accordingly occurs in inverse manner. 
     FIG. 2  shows a section from a transmission  2 . A first gear wheel  4  and a second gear wheel  6  are non-rotatably supported upon a gear shaft  12  by the bearings  8 ,  10 . The gear wheels  4 ,  6  have respective internal toothings  14 ,  16 . A shift dog  18  is non-rotatable, but axially displaceable along an axis of rotation  20  of the gear shaft  12 . A disc  22  meshes in the shift dog  18  or is designed integral therewith. Upon one side of the disc  22  is situated an electromagnetic device  40  which is stationarily fastened on the housing of the transmission in a manner not shown here. The electromagnetic device  40  is connected with a control device  28 . An electromagnetic insulating disc  42  is provided between the electromagnetic device  40  and the gear wheel  6 . 
   In the plane of the drawing, the shift dog  18  is axially displaced to the right along the axis  20  for non-rotatable connection of the gear wheel  6  with the gear shaft  12  and for the formation thereby produced of a ratio step of the transmission  2 . This occurs by the control of the electromagnetic device  40  by the control device  28 . The electromagnetic device  40  generates a magnetic field by which the disc  22  is drawn in direction to the gear wheel  6 . An external toothing  44  on the shift dog  18  meshes then in the internal toothing  16  of the gear wheel  6  during synchronous rotational speeds of the shift dog  18  and the gear wheel  6 . The gear wheel  6  is thereby non-rotatably connected with the gear shaft  12 . 
   To dissolve the non-rotatable connection, the electromagnetic device  40  is controlled so that the disc  22  is ejected and thus the toothing  44  of the shift dog  18  detaches itself from the toothing  16  of the gear wheel  6 . A support by a plate spring  46  provided between disc  22  and electromagnetic device  40  can result whereby the disc  22  is ejected in direction toward the gear wheel  4 . 
   If the shift dog  18  must be kept in the neutral position between both gear wheels  4 ,  6 , this can occur by an adequate control of the electromagnetic device  40 . The magnetic field then generated can keep the disc  22  either in a drawing or an ejecting manner and thus the shift dog  18  in a neutral intermediate position. The intermediate position can be produced also by two plate springs  46 , 48 . The plate spring  46  is between the disc  22  and the electromagnetic device  40  and the plate spring  48  lies between the disc  22  and the gear wheel  4 . When the disc  22  moves in one or the other direction, the plate springs  46 ,  48  are accordingly compressed. 
   The gear wheel  4  is connected with the gear shaft  12  by switching off from the neutral position by control of the electromagnetic device  40  by the control device  28  in a manner such that an ejecting magnetic field is generated and the disc  22  and therewith the shift dog  18  is ejected from the electromagnetic device  40  in direction to the gear wheel  4 . The external toothing  34  on the shift dog  18  meshes then in the internal toothing  14  of the gear wheel  4  during synchronous rotational speeds of the shift dog  18  and the gear wheel  4 . Thereby the gear wheel  4  is non-rotatably connected with the gear shaft  12 . 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               Reference numerals 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                2 transmission 
             
             
                 
                4 gear wheel 
             
             
                 
                6 gear wheel 
             
             
                 
                8 bearing 
             
             
                 
               10 bearing 
             
             
                 
               12 gear shaft 
             
             
                 
               14 internal toothing 
             
             
                 
               16 internal toothing 
             
             
                 
               18 shift dog 
             
             
                 
               20 axis 
             
             
                 
               22 disc 
             
             
                 
               24 electromagnetic device 
             
             
                 
               26 electromagnetic device 
             
             
                 
               28 control device 
             
             
                 
               30 insulating disc 
             
             
                 
               32 insulating disc 
             
             
                 
               34 external toothing 
             
             
                 
               36 plate spring 
             
             
                 
               38 plate spring 
             
             
                 
               40 electromagnetic device 
             
             
                 
               42 insulating disc 
             
             
                 
               44 external toothing 
             
             
                 
               46 plate spring 
             
             
                 
               48 plate spring