Abstract:
A shiftable toothed-belt drive, containing an engagement and disengagement device, in order alternately to mesh radially and demesh radially a toothed belt, which is guided around at least two gearwheels, with and from at least one of the two gearwheels. A disengager in the form of two externally profiled pulleys is urged axially along the shaft of one of the gearwheels supporting the toothed belt for radially raising the belt and demeshing the belt from the gearwheel. An engager engages the outside of the belt for tensioning the belt sufficiently to counter the effect of the disengager, move the pulleys apart and mesh the belt with the one gearwheel.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a shiftable toothed-belt drive using a plurality of gearwheels and particularly to meshing and demeshing the belt and gearwheels. 
   The invention accordingly relates to a shiftable toothed-belt drive containing at least one drive set which has at least two gearwheels arranged axially parallel and at a distance from one another and a toothed belt which extends around these gear wheels. The teeth of the belt can mesh into the teeth of the gearwheels. 
   The shiftable toothed-belt drive according to the invention is suitable for driving any desired machines, but, in particular, also as a travel drive for motor vehicles, such as passenger cars, motor trucks and motor cycles, and also for motorboats and motor ships. 
   SUMMARY OF THE INVENTION 
   The invention is to achieve the object of providing a shiftable toothed-belt drive which runs quietly, can be shifted easily and quickly, is operationally reliable and has a long useful life. 
   This object is achieved, according to the invention, by a shiftable toothed-belt drive, containing an engagement and disengagement device, in order alternately to mesh radially and demesh radially a toothed belt, which is guided around at least two gearwheels, with and from at least one of the two gearwheels. A disengager in the form of two externally profiled pulleys is urged axially along the shaft of one of the gearwheels supporting the toothed belt for radially raising the belt and demeshing the belt from the gearwheel. An engager engages the outside of the belt for tensioning the belt sufficiently to counter the effect of the engager, move the pulleys apart and mesh the belt with the one gearwheel. 
   Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below by means of preferred exemplary embodiments, with reference to the drawings in which: 
       FIG. 1  shows diagrammatically, and not true to scale, a side view of a shiftable toothed-belt drive according to the invention, as seen in the cross section I of  FIG. 2 , 
       FIG. 2  shows an axial section through part of  FIG. 1 , 
       FIG. 3  shows the shiftable toothed-belt drive of  FIG. 1 , with the toothed belt in meshed position with both gearwheels, corresponding to the upper half of  FIG. 2 , 
       FIG. 4  shows diagrammatically, and not true to scale, a side view of a further embodiment of a shiftable toothed-belt drive according to the invention, the toothed belt being demeshed from a lower gearwheel according to the unbroken lines of  FIG. 4  and according to  FIG. 5 , but also being capable of being meshed according to the broken lines of  FIG. 4  and according to  FIG. 6 , while the toothed belt is constantly meshed with the other gearwheel. 
       FIG. 5  shows the one gearwheel of  FIG. 4 , together with a disengager of an engagement and disengagement device in a disengagement position, the toothed belt, in its demeshed position, being spaced radially apart from the gearwheel, 
       FIG. 6  shows the one gearwheel of  FIG. 4 , together with the disengager of the engagement and disengagement device in an engagement position, the toothed belt being in the meshed position with the gearwheel, and 
       FIG. 7  shows a shiftable toothed-belt drive according to the invention with a plurality of drive sets according to  FIGS. 1 to 3  (or  FIGS. 4 to 6 ). 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The shiftable toothed-belt drive according to the invention, shown in  FIGS. 1 to 3 , contains at least one drive set which has at least two gearwheels  2  and  4  which are arranged axially parallel and at a distance from one another, and a toothed belt  6  which extends around these gearwheels  2 ,  4 . The teeth of the belt can mesh into the spaces  2 - 1  and  4 - 1  between the teeth  2 - 2  and  4 - 2  of the gearwheels  2  and  4 . The gearwheels  2  and  4  are arranged rotatably about respective axes of rotation  10  and  12 . 
   An engagement and disengagement device  14 ,  16  is provided, in order alternately to mesh and demesh the toothed belt  6  with and from at least one of the two gearwheels, in the present case with and from the gearwheel  2 . 
   In  FIG. 1 , a toothed belt is shown demeshed from one of the gearwheels, but capable of being meshed according to broken lines, while the toothed belt is constantly meshed with another gearwheel, and shows the toothed belt  6  in the demeshed position from one gearwheel  2  and in the meshed position with the other gearwheel  4 . 
     FIG. 2  shows an engagement and disengagement device. In the lower half of  FIG. 2 , the device is in a disengagement position, in which the toothed belt is shown in the demeshed position in relation to the gearwheel, while in the upper half of  FIG. 2 , the engagement and disengagement device is in the engagement position and consequently the toothed belt is in the meshed position with the gearwheel. 
     FIG. 3  shows the toothed belt  6  in its meshed position with both gearwheels  2  and  4 . 
   In the case of the gearwheel  2  shown in  FIG. 2 , where the toothed belt  6  is to be meshed and demeshed, the engagement and disengagement device  14 ,  16  comprises a split belt pulley with two axially spaced pulleys  20 ,  22  which are arranged on both sides of the gearwheel  2  and are arranged to be axially displaceable in relation to the gearwheel  2  and to be freely rotatable about the axis of rotation  10  of the wheel. The two pulleys  20  and  22  have a circular belt running surface  24  and  26  on each of their sides facing one another. The belt running surfaces descend in the axial direction toward one another and descend obliquely to the axis of rotation  10 , so that they form between them a V-groove for receiving the toothed belt  6 . The belt running surfaces  24  and  26  roll on lateral edges of the toothed belt  6 . 
   The engagement and disengagement device  14 ,  16  contains a disengager  16 , which can exert an axial force on the two pulleys  20  and  22  to urge them axially in the direction toward one another. As a result, the two pulleys  20  and  22  can be moved axially toward one another to an extent such that they lift the toothed belt  6  radially off the gearwheel  2  arranged between them and consequently bring the toothed belt radially from the meshed position shown in  FIG. 3  into the demeshed position shown in  FIG. 1 . In this case, the toothed belt  6  runs on the belt running surfaces  24 ,  26  of the pulleys  20 ,  22  from a smaller to a larger pulley diameter. 
   Moreover, the engagement and disengagement device  14 ,  16  includes an engager  14 , which can exert on the toothed belt  6 , particularly on its outside, and transversely to the axes of rotation  10 ,  12  of the gearwheels  2 ,  4 , an engagement force which tensions the toothed belt  6  to an extent such that the belt can press the two pulleys  20 ,  22  axially away from one another to an extent such that the belt moves in relation to the gearwheel  2  from the demeshed position of  FIG. 1  into the meshed position of  FIG. 3 . In this case, the toothed belt  6  runs on the belt running surfaces  24 ,  26  of the pulleys  20 ,  22  from a larger to a smaller pulley diameter. 
   In the embodiment according to  FIGS. 1 to 3 , the disengager  16  includes disengagement spring means  30 ,  31 ,  32  and  33  for generating the disengagement force, which prestress the two pulleys  20  and  22  resiliently elastically in the axial direction toward one another. This prestress forms a disengagement force, by means of which the two pulleys  20  and  22  can be pressed axially more closely together, for lifting the toothed belt  6  radially off the gearwheel  2  and consequently bringing the belt from the meshed position of  FIG. 3  into the demeshed position of  FIG. 1 . 
   The engager  14  has an actuating drive for generating the engagement force in a direction which is illustrated by arrow  38  in  FIG. 1 . The force is such that it can overcome the resiliently elastic disengagement force of the disengager  16 . The two pulleys  20 ,  22  are capable of being pressed axially away from one another, counter to the force of the disengagement spring means  30 ,  31 ,  32 ,  33 , by the tensile stress in the toothed belt  6 , so that the toothed belt  6  can be meshed radially with the gearwheel  2  after the radial movement of the toothed belt from the demeshed position of  FIG. 1  into the meshed position of  FIG. 3 . 
   The disengagement spring means  30 ,  31 ,  32  and  33  exert their disengagement force constantly, whereas the servomotor  36  of the engager  14  exerts its engagement force only as required. 
   The servomotor  36  may be a linear actuating drive or a spindle drive. Preferably, it has an axially extendable tappet  40 . This tappet  40  preferably does not press directly onto the toothed belt  6 , since that would cause frictional contact between them, but, instead, presses via a roller  42  which is mounted rotatably on the tappet  40  and which is in rolling contact with the belt outside of the toothed belt  6 , the belt outside facing away from the toothing  8 .  FIG. 1  shows the roller  42  in the disengagement position by unbroken lines and in an engagement position  42 - 2  by broken lines, with a portion  6 - 2  of the toothed belt  6  also being depicted in the engagement position by broken lines.  FIG. 3  shows the engager  14  in its engagement position by unbroken lines and consequently shows the toothed belt  6  in the meshed position with both gearwheels  2  and  4 . 
   The engager  14 , in particular its roller  42 , may, in the disengagement position, bear against the toothed belt  6  according to  FIG. 1  or be spaced apart from the toothed belt  6 , in order to avoid energy losses. If the engager  14 , in particular its roller  42 , bears against the toothed belt  6  in the engagement position of  FIG. 1 , it may be expedient to provide a prestressing spring which presses the roller  42  resiliently elastically onto the toothed belt  6 , in order to prevent the roller  42  from hopping on the toothed belt  6 . However, such a prestressing spring has only a low spring force such that it cannot overcome the disengagement spring force of the disengagement spring means  30 ,  31 ,  32  and  33  of the disengager  16 . 
   The upper half of  FIG. 2  shows the disengager  16  in the engaged position, in which the toothed belt  6  is meshed with the gearwheel  2  according to  FIG. 3  and the lower half of  FIG. 2  shows the disengager in the disengagement position, in which the toothed belt  6  is not meshed with the gearwheel  2 , but is in its demeshed position according to  FIG. 1 . 
   The disengagement spring means  30 ,  31 ,  32  and  33  may comprise two compression springs  30  and  32  or, according to  FIG. 2 , also two pairs  30 ,  31  and  32 ,  33  of compression springs, which are clamped axially with prestress between the respective outer end faces, facing away from one another, of the pulleys  20  and  22  and the inner end faces, axially opposite these, of respective counterpressure elements  46  and  48 . The counterpressure elements  46  and  48  are held at a defined and invariable axial distance both from one another and from the gearwheel  2  which is located between the pulleys  20  and  22 . This is illustrated diagrammatically in  FIG. 2  by a connecting yoke  50  which connects the two counterpressure elements  46  and  48 . Instead of such a connecting yoke or connecting body, the counterpressure elements  46  and  48  could also be fixed axially on a shaft  52 , to which the gearwheel  2  is connected for rotation, for example, according to  FIG. 2 , and with which the latter is formed in one piece. For axially fixing the counterpressure elements  46  and  48 , for example, a spring ring may be fastened to the shaft  52  in a shaft groove. 
   In the embodiments shown in  FIGS. 1 ,  2  and  3 , the disengager is the passive part which constantly generates the disengagement force, and the engager is the active part which is activated only when the toothed belt  6  is to be moved from the demeshed position of  FIG. 1  into the meshed position of  FIG. 3 . The engager  14  overcomes the disengagement force of the disengager  16 . After the engager  14  has been switched off, the disengagement spring means  30 ,  31 ,  32  and  33  of the disengager  16  again urges the toothed belt  6  from the meshed position of  FIG. 3  into the demeshed position of  FIG. 1 . 
   The embodiment of  FIGS. 4 ,  5  and  6 , like  FIGS. 1 ,  2  and  3 , has two gearwheels  2  and  4  and a toothed belt  6  which can be alternately meshed with and demeshed from one gearwheel  2  and is constantly meshed with the other gearwheel  4 . An engager  114  has, again, a tappet  40  with a roller  44 . Furthermore, once again a belt pulley is provided, having the two pulleys  20  and  22  which are arranged on both sides of the one gearwheel  2  and are adjustable, for example displaceable or screwable, rotatably and axially in relation to this gearwheel  2 . Moreover, a disengagement device  116  is provided, by means of which the two pulleys  20  and  22  can be moved, for example displaced, axially toward one another from a disengagement position of  FIG. 5  into an engagement position of  FIG. 6  to an extent such that the toothed belt  6  can be moved radially away from its meshed position, shown in  FIG. 6 , with the gearwheel  2  into the demeshed position, shown by unbroken lines in  FIGS. 4 and 5 , from the gearwheel  2 .  FIG. 4  also shows the meshed position of the toothed belt  6  by broken lines. 
   In the embodiment of  FIGS. 4 ,  5  and  6 , the engager  114  is the passive part which, by engagement spring means  136 , for example comprised of one or more compression springs, constantly generates an engagement spring force, by means of which the tappet  40  together with the roller  44  can be moved from its disengagement position, shown by unbroken lines in  FIG. 4 , into the engagement position, shown by broken lines in  FIG. 4 , as long as the disengager  116  is not activated (switched on). When the disengager  116  is activated, it generates a disengagement force which overcomes the engagement force of the engagement spring means  136  of the engager  114  and thereby moves the pulleys  20  and  22  more closely together in relation to one another and in relation to the gearwheel  2  arranged between them, from the meshed position of  FIG. 6  into the demeshed position of  FIG. 5 , so that the pulleys  20  and  22  lift off the toothed belt  6  radially from the gearwheel  2 . 
   For this purpose, the disengager  116  has an actuating drive  130 / 132 . The actuating drive  130 / 132  may be designed in various ways. It may have threaded spindles, for axially displacing the pulleys  20  and  22 , in a threaded nut, one part of which is rotatable and the other part is nonrotatable.  FIGS. 5 and 6  show an actuating drive  130 / 132  with linear servomotors  130  and  132  which act on the two pulleys  20 ,  22  and which can be jointly actuated in each case, for example electrically, pneumatically or hydraulically.  FIGS. 5 and 6  show a pneumatic embodiment, in which an axially acting pressure chamber  131  and  133  for compressed air is formed in each case between the two pulleys  20  and  22  and two counterpressure elements  146  and  148 . The two counterpressure elements  146  and  148  are arranged axially at a fixed location in relation to one another and in relation to the gearwheel  2  which is arranged between the pulleys  20  and  22 . When the pressure chambers  131  and  133  are acted upon by compressed air, the pulleys  20  and  22  are pushed axially more closely together, counter to the engagement force of the engager  114 , from the meshed position of the toothed belt  6  with the gearwheel  2  of  FIG. 6  into the demeshed position of the toothed belt  6  from the gearwheel  2  of  FIG. 5 . 
   After the pressure has been cut back or vented in the pressure chambers  131  and  133 , the two pulleys  20  and  22  are moved axially apart from one another by the engagement force of the engagement spring means  136  of the engager  114 , as a result of the tensile stress generated in the toothed belt  6  by the engagement spring means  136 . In this case, the toothed belt  6  urges the pulleys  20  and  22  axially apart from one another until the toothed belt  6  is meshed with the gearwheel  2  again. 
   In  FIGS. 4 ,  5  and  6 , parts corresponding to  FIGS. 1 ,  2  and  3  are given the same reference numerals. In both embodiments, the toothed belt  6  runs on the conical or otherwise obliquely designed belt running surfaces  24  and  26  up and down between a smaller running surface diameter, in the toothed-belt meshing position in the upper half of  FIG. 2  and in  FIG. 6 , and the relatively larger running surface diameter, at which the toothed belt  6  is in its demeshed position which is shown in the lower half of  FIG. 2  and in  FIG. 5 . Although the axial distance between the counterpressure elements  46  and  48  is set at a fixed value, this distance value may be variably adjustable to any desired fixed values. 
   A shiftable toothed-belt drive according to the invention may consist in each case of one, of two or of a plurality of drive sets which are designed in each case according to the drive set of  FIGS. 1 to 3  or to the drive set of  FIGS. 4 to 6 . 
     FIG. 7  shows a shiftable toothed-belt drive according to the invention with, for example, three drive connections  201 ,  202  and  203  between an input shaft  206  and an output shaft  208 . Each of these drive connections  201 ,  202  and  203  contains at least one drive set according to  FIGS. 1 to 3  or  4  to  6 . In the embodiment of  FIG. 7 , the two drive connections  201  and  202  each contain one drive set according to  FIGS. 1 to 3  (or according to  FIGS. 4 to 6 ). The third drive connection  203  contains two drive sets, of which both or only one may be designed according to  FIGS. 1 to 3  (or  FIGS. 4 to 6 ), while the other drive set has only one toothed belt  6  on two gearwheels  2  and  4 , but no engagement and disengagement device. 
   In  FIG. 7 , as an example, only the gearwheel  2  which is connected fixedly in terms of rotation to the output shaft  208  is provided with pulleys  20 ,  22  and with an engagement and disengagement device  14 / 16 . 
   In  FIG. 7 , the gearwheels  2  which are provided with pulleys  20 ,  22  and with a disengager  16  are connected fixedly in terms of rotation to the output shaft  208  (or, in another embodiment, are connected fixedly in terms of rotation to the input shaft  208 ). The gearwheels  4  are connected fixedly in terms of rotation to the input shaft  206  (or, in the other embodiment, to the output shaft  208 ). Moreover, in the third drive connection  203 , a gearwheel  2  and a gearwheel  4  are axially connected to one another fixedly in terms of rotation at the connection between the two drive sets. 
   The input shaft  206  can be coupled via a shiftable clutch  208  to an intermediate shaft  210  to which a gearwheel  212  is connected fixedly in terms of rotation. The intermediate shaft  210  can be coupled to an internal combustion engine  216  via a further shiftable clutch  214 . A gearwheel  218 , which is drive-connected to an electric machine  220 , is meshed with the gearwheel  212  of the intermediate shaft  210 . The electric machine  220  can thereby serve as a starter motor for starting the internal combustion engine  216  when one clutch  208  is opened and the other clutch  214  is closed. Furthermore, the electric machine  220  may be operated as an electric motor, in order, with one clutch  208  closed, to drive the driveshaft  206  and by the latter, via one of the drive connections  201 ,  202  or  203 , the output shaft  208 , either alone or together with the internal combustion engine  206 . Preferably, the electric machine  220  can be driven as an electric motor alternately in one direction of rotation or the other, so that it not only can deliver drive energy for the forward drive of a vehicle, but can also serve as a drive motor for the reverse travel of the motor vehicle. Furthermore, it is advantageous if the electric machine  220  can also be operated as a generator for current generation, in which case it can be driven either by the internal combustion engine  206  or by the output shaft  208  via one of the drive connections  201 ,  202  or  203 . 
   Shiftable toothed-belt drives according to the invention are suitable for the drive of any desired machine, but, in particular for the drive of motor vehicles, such as, in particular, cars, motorcycles and motor trucks, but also motorboats and motor ships. The shiftable toothed-belt drive with the drive connections  201 ,  202  and  203  and, if appropriate, with further or other drive connections may be a manually shiftable or an automatically shiftable gear-change transmission or, together with a torque converter, form an automatic transmission. The individual gear steps are formed in that, in the various drive connections  201 ,  202 ,  203 , various transmission ratios are formed by means of different diameters of the gearwheels  2  and  4  and/or by means of one or more intermediate steps corresponding to the third drive connection  203  of  FIG. 7 . 
   For the shifting of gears, in each case at least one of the toothed belts  6  is demeshed from one of its gearwheels, for example the gearwheel  2 , and then another toothed belt  6  is meshed with all its gearwheels  2 ,  4 . For such a gear change, one of the clutches  208  or  214  is opened and, after the gear change, is closed again. In this case, there is also the possibility of operating the respective clutch  208  or  214 , during a predetermined phase of the gear change, in the slipping mode (with sliding friction) as a function of predetermined criteria. As a result, shifts can be executed, for example, without any interruption in the traction of the drive trains. The clutches  208  and  214  are preferably multiple-disk clutches. The control of the gear-shifting operations, including the control of the clutch, is carried out by means of a control device  300 . 
   Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.