Abstract:
A drive system with an 8-gear gearbox for a motor vehicle with a driving machine  11 , more particularly an internal combustion engine, comprising a distribution gearbox  12  which is drivingly connected to the driving machine  11  and comprises three members, as well as two 2-gear partial gearboxes  17, 18 , wherein a first member of the distribution gearbox  12  is drivingly connected to the internal combustion engine  11  and the two other members of the distribution gearbox  12  are each connected to an input shaft  20, 28  of one of the two 2-gear partial gear-boxes  17, 18  and wherein, between two members of the distribution gearbox  12 , there is provided a switchable bridging coupling  19  and wherein one output element of each of the two 2-gear partial gearboxes  17, 18  is permanently drivingly connected to a driven gear  38, 39  or to a driven shaft  40.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national phase of PCT/EP2008/000069 filed Jan. 8, 2008, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a drive system with an 8-gear gearbox for a motor vehicle with a driving machine, more particularly an internal combustion engine. 
       BACKGROUND OF THE INVENTION 
       [0003]    Gearboxes with an increasing number of gear stages are required on the one hand as a result of an increase in maximum speeds of vehicles and on the other hand as a result of the demand for advantageous consumption figures, which make it necessary to operate the internal combustion engine at all driving speeds at consumption-advantageous numbers of revolution and loads. 
         [0004]    In addition to the above-mentioned requirements, there exists the desire for a higher degree of driving comfort which can be achieved with gear-changing procedures without interrupting the traction force; typically, this can be achieved by using double-coupling gearboxes. 
         [0005]    It is therefore the object of the invention to provide a gearbox with eight gears which is characterised by a simple and compact design and a limited number of gear shifting elements. 
       SUMMARY OF THE INVENTION 
       [0006]    The objective is achieved by proving a drive system with an 8-gear gearbox for a motor vehicle with a driving machine, more particularly an internal combustion engine, comprising a distribution gearbox which is drivingly connected to the driving machine and comprises three members, as well as two 2-gear partial gearboxes, wherein a member of the distribution gearbox is drivingly connected to the internal combustion engine and the two other members of the distribution gearbox are each connected to an input shaft of one of the two 2-gear partial gearboxes and wherein, between two members of the distribution gearbox, there is provided a switchable bridging coupling and wherein one output element of each of the two 2-gear partial gearboxes is permanently drivingly connected to a driven gear or to a driven shaft. 
         [0007]    With a view to achieving a short and simple design, it is proposed more particularly that the distribution gearbox is a planetary gearbox which, in the form of rotating members coupled to one another, comprises a sun gear, a planetary carrier with at least one planetary gear and a hollow gear. In a typical application the switchable bridging and lock-up coupling is arranged between the sun gear and the planetary carrier. If the bridging and lock-up coupling is closed, the distribution gearbox acts as rigid through-drive, whereas, if the bridging and lock-up coupling is open, a differential movement takes place in the distribution gearbox. This can be regarded as a gear stage if one of the members of the differential gearbox is fixed. 
         [0008]    For designing the two partial gearboxes, there will be made two proposals which are both characterised by a simple and short design. 
         [0009]    According to a first proposal, it is proposed that the two-gear partial gearboxes each constitute shift gearboxes with switchable gears with an input shaft and with an output shaft extending parallel to the input shaft and with two gears each firmly connected to one of the shafts and with two gears which are individually switchably connected to the other one of the shafts. Gearboxes of said type can, in the usual way, constitute two gearbox stages. In addition, it is possible to move a switchable element for the switchable gears into a neutral position in order to interrupt the torque flow between the input shaft and the output shaft. 
         [0010]    This makes it possible to change gears in all gear stages without interrupting the traction force, with the switchable bridging coupling being engaged. Furthermore, when switching into some of the higher gears, a limited support for the traction force is ensured by some released mass moments of inertia. 
         [0011]    According to a further proposal, the two-gear partial gearboxes constitute switchable planetary gearboxes with the following members: a sun gear, a planetary carrier with at least one planetary gear and hollow gear, wherein one of the members is connected to an input shaft, one of the members to an output shaft and the third member to a brake disc/brake carrier which can be fixed relative to a stationary part, and wherein, between the two members of the planetary gearbox, there is provided a switchable bridging coupling. If the bridging and lock-up coupling is opened and the brake closed, the planetary gearbox constitutes a gear stage between the input shaft and the output shaft. If the bridging or lock-up coupling is closed and the brake opened, there is obtained a rigid through-drive from the input shaft to the output shaft. If both of said components are opened, i.e. the bridging or lock-up coupling and the brake, the connection between the input shaft and the output shaft is uncoupled in the torque flow. 
         [0012]    As only load switch couplings are used, with a maximum of two gear changing elements being engaged in each gear, switching without interrupting the traction force is also possible. 
         [0013]    For both the above-mentioned proposals it is advantageous if one of the input shafts in an inner shaft and the other input shaft is a hollow shaft extending coaxially relative thereto. 
         [0014]    According to the first proposal (gearbox with switchable gears), the output shafts can form different planes with the input shafts. According to the second proposal (planetary gearbox) the output shafts both extend coaxially relative to the input shafts. 
         [0015]    According to an advantageous further development, the drive system of the above-described type can be supplemented to form a hybrid drive system with an secondary driving machine. Said secondary driving machine, more particularly, can be coupled to one of the members of the distribution gearbox or to one of the input shafts of the partial gearbox. 
         [0016]    In a distribution gearbox provided in the form of a planetary gearbox, the secondary driving machine can be an annular electric motor which is connected to the hollow gear. In such a hybrid drive system, there is no need for a separating coupling between the internal combustion engine and the input shaft for the distribution gearbox. 
         [0017]    By converting the inventive drive system into a hybrid drive system, there are achieved the known options for operating the vehicle equipped with such a hybrid drive system such as starting and driving entirely electrically, energy recuperation (converting kinematic vehicle energy into electric energy), pre-synchronisation of the drive-shafts prior to gear changing, traction-force-free gear changing, starting the internal combustion engine with the secondary driving machine while the vehicle is stationary or during electric driving. 
         [0018]    Further advantageous embodiments are described in the sub-claims to the contents of which reference is hereby made. 
         [0019]    The different operating conditions of the drive system are more easily understood with reference to the following description of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Two preferred embodiments of the invention are illustrated in the drawings and will be described below. 
           [0021]      FIG. 1  is the gearbox diagram of an inventive hybrid drive system in a first embodiment in the neutral position. 
           [0022]      FIG. 2  is the gearbox diagram according to  FIG. 1  in the r t  gear. 
           [0023]      FIG. 3  is the gearbox diagram according to  FIG. 1  in the 2 nd  gear. 
           [0024]      FIG. 4  is the gearbox diagram according to  FIG. 1  in the 3 rd  gear. 
           [0025]      FIG. 5  is the gearbox diagram according to  FIG. 1  in the 4 th  gear. 
           [0026]      FIG. 6  is the gearbox diagram according to  FIG. 1  in the 5 th  gear. 
           [0027]      FIG. 7  is the gearbox diagram according to  FIG. 1  in the 6 th  gear. 
           [0028]      FIG. 8  is the gearbox diagram according to  FIG. 1  in the 7 th  gear. 
           [0029]      FIG. 9  is the gearbox diagram according to  FIG. 1  in the reverse gear. 
           [0030]      FIG. 10  is the gearbox diagram of an inventive hybrid drive system in a second embodiment in the neutral position. 
           [0031]      FIG. 11  is the gearbox diagram according to  FIG. 10  in the r t  gear. 
           [0032]      FIG. 12  is the gearbox diagram according to  FIG. 10  in the 2 nd  gear. 
           [0033]      FIG. 13  is the gearbox diagram according to  FIG. 10  in the 3 rd  gear. 
           [0034]      FIG. 14  is the gearbox diagram according to  FIG. 10  in the 4 th  gear. 
           [0035]      FIG. 15  is the gearbox diagram according to  FIG. 10  in the 5 th  gear. 
           [0036]      FIG. 16  is the gearbox diagram according to  FIG. 10  in the 6 th  gear. 
           [0037]      FIG. 17  is the gearbox diagram according to  FIG. 10  in the 7 th  gear. 
           [0038]      FIG. 18  is the gearbox diagram according to  FIG. 10  in the 8 th  gear. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  shows the gearbox diagram of an inventive drive system in the form of a hybrid drive system in a first embodiment. The following description of  FIG. 1 , in principle, also applies to  FIGS. 2 to 9  which show different gear change conditions of the gearbox diagram according to  FIG. 1 . 
         [0040]    The drive system comprises a main driving machine  11 , in this case in the form of an internal combustion engine, a distribution gearbox  12  in the form of a lockable planetary gearbox, as well as two 2-gear partial gearboxes  17 ,  18 , each in the form of a 2-gear stepped manual gearbox. The planetary gearbox  12  comprises the following members: a sun gear  13  which is connected to the crankshaft of the driving machine  11  in a rotationally fast way, a planetary carrier  14  with planetary gears  15 , as well as a hollow gear  16 . The hollow gear  16  is connected to an input shaft  20  of the first partial gearbox  17  in rotationally fast way, which input shaft  20  is provided in the form of a hollow shaft. The planetary carrier  14  is connected in a rotationally fast way to an input shaft  28  of the second partial gearbox  18 , which input shaft  28  is provided in the form of an inner shaft arranged coaxially relative to the input shaft  20 . 
         [0041]    The planetary gearbox  12  can be replaced by any other distribution gearbox or differential gearbox. In accordance with the invention, the distribution gearbox contains a lock-up coupling  19  which is able to couple the sun gear  13  to the planetary carrier  14 . i.e. the crankshaft of the internal combustion engine  11  to the input shaft  28  of the second partial gearbox. The hollow gear  16 , as the third member of the distribution gearbox  12 , is coupled to a secondary driving machine  41  which, in this case, is provided in the form of an annular electric machine. 
         [0042]    Apart from the input shaft  20  which carries two fixed gears  22 ,  23 , the first partial gearbox  17  comprises an output shaft  21  which carries two switchable gears  24 ,  25  (loose gears) which, optionally, can be coupled by a switching unit  26  to the output shaft  21 . The switching unit can comprise a fixed gear connected to the output shaft and a switching muff by means of which the loose gears are optionally connected to said fixed gear. Furthermore, on the output shaft  21  there is arranged an output gear  35  which engages a driven gear  39  on the driven shaft  40 . In addition to the input shaft  28  which carries two fixed gears  30 ,  31 , the second partial gearbox  18  comprises two fixed gears  30 ,  31 , an output shaft  29  on which there are arranged two switchable gears  32 ,  33  (loose gears) which by means of a switching unit  34  can optionally be coupled to the output shaft  29 . The switching unit can comprise a fixed gear connected to the output shaft  29  and a switching muff by means of which the loose gears can optionally coupled to said fixed gear. Furthermore, the output shaft  29  of the second partial gearbox  18  carries an output gear  36  which also engages the driven gear  39  of the driven shaft  40 . 
         [0043]    The following illustrations show eight different gear shift conditions of which four are illustrated by opening the lock-up coupling  19  and four by closing the lock-up coupling. In the former case the distribution gearbox retains its distribution function, whereas in the latter case it forms a rigid bridge from the input end to the blocked parts of the output end (planetary carrier and hollow gear). In all gear shift conditions, there is shown the boost function of the hybrid drive system, i.e. the secondary driving machine  41  additionally transmits torque to the driveshaft  40  (driven shaft). 
         [0044]      FIG. 2  shows the gear shift condition in the first gear in which the lock-up coupling is open. In the first partial gearbox  17 , the switching muff of the switching unit  26  is displaced to the right for the purpose of coupling the switching gear  25  to the output shaft  21 . In the second partial gearbox  18 , the switching muff of the switching unit  34  is displaced to the left for the purpose of coupling the switching gear  32  to the output shaft  29 . Via the sun gear  13  and the planetary carrier  14  torque is transmitted from the internal combustion engine  11  via the input shaft  28  and the pair of gears  30 ,  32  to the output shaft  29 . Via the hollow gear  16 , torque is transmitted from the secondary driving machine  41  and the input shaft  20  and the gears  23 ,  25  to the output shaft  21 . Both output shafts  20 ,  28  thus transmit torque into the driven shaft  40 . The differential movement of the distribution gearbox  12  is determined by the speed ratio between the gears  23 ,  30  because the output gears  35 ,  36 , while being of identical size, rotate at the same speed. 
         [0045]      FIG. 3  shows the gear shift condition in the second gear wherein the lock-up coupling  19  is open. In the first partial gearbox  17 , the switching muff of the switching unit  26  is displaced towards the right, so that the switching gear  25  is connected to the output shaft  21  of the first partial gearbox  17 , and the switching muff of the switching unit  34  in the second partial gearbox  18  is displaced towards the right, so that, in deviation from the first gear, the switchable gear  33 , in the second gear, is connected to the output shaft  29  of the second partial gearbox  18 . Torque is thus transmitted from the driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  and via the pair of gears  31 ,  33  to the output shaft  29  of the second partial gearbox  18 , whereas the input shaft  20  is torque-loaded by the secondary driving machine  41  with the hollow gear  16 , and the output shaft  21  of the first partial gearbox  17  is torque-loaded via the pair of gears  23 ,  25 . The differential movement of the differential gearbox is determined by the speed ration between the gears  23  and  31 . 
         [0046]      FIG. 4  shows the gear shift condition of the third gear wherein the lock-up coupling  19  is closed. As now no differential movements can take place at the distribution gearbox  12 , only one of the partial gearboxes, i.e. the first partial gearbox  17 , can be used, whereas the second partial gearbox  18  is disconnected by displacing the switching muff of the switching unit  34  into the neutral position. Torque is thus transmitted entirely via the distribution gearbox  12 , which has to be regarded as a rigid unit, into the input shaft  20 , with both the main driving machine  11  and the secondary driving machine  41  being able to transmit torque. The switching muff of the switching unit  26  of the first partial gearbox has been displaced towards the right, so that the pair of gears  23 ,  25  of the partial gearbox  17  is effective. 
         [0047]      FIG. 5  shows the gear shift condition of the fourth gear wherein the lock-up coupling  19  is closed. As now no differential movements can take place at the distribution gearbox  12 , only one of the partial gearboxes, i.e. the second partial gearbox  18 , can be used, whereas the first partial gearbox  17  is disconnected by displacing the switching muff of the switching unit  26  into the neutral position. Torque is thus transmitted entirely via the distribution gearbox  12 , which has to be regarded as a rigid unit, into the input shaft  28 , with both the main driving machine  11  and the secondary driving machine  41  being able to transmit torque. The switching muff of the switching unit  34  has been displaced towards the right, so that the pair of gears  31 ,  33  of the partial gearbox  18  is effective. 
         [0048]      FIG. 6  shows the gear shift condition of the fifth gear wherein the lock-up coupling  19  is closed. As, in consequence, no differential movements can take place at the distribution gearbox  12 , only one of the partial gearboxes, i.e. the second partial gearbox  18 , can be used, whereas the first partial gearbox  17  is disconnected by displacing the switching muff of the switching unit  26  into the neutral position. Torque is thus transmitted entirely via the distribution gearbox  12 , which has to be regarded as a rigid unit, into the input shaft  28 , with both the main driving machine  11  and the secondary driving machine  41  being able to transmit torque. The switching muff of the switching unit  34  has been displaced towards the left, so that the pair of gears  30 ,  32  of the partial gearbox  18  is effective. 
         [0049]      FIG. 7  shows the gear shift condition of the sixth gear wherein the lock-up coupling  19  is closed. As, again, no differential movements can take place at the distribution gearbox  12 , only one of the partial gearboxes, i.e. the first partial gearbox  17 , can be used, whereas the second partial gearbox  18  is disconnected by displacing the switching muff of the switching unit  34  into the neutral position. Torque is thus transmitted entirely via the distribution gearbox  12 , which has to be regarded as a rigid unit, into the input shaft  20 , with both the main driving machine  11  and the secondary driving machine  41  being able to transmit torque. The switching muff of the switching unit  26  has been displaced towards the left, so that the pair of gears  22 ,  24  of the partial gearbox  17  is effective. 
         [0050]      FIG. 8  shows the gear shift condition of the seventh gear, with the lock-up coupling  19  being open. The switching muff of the switching unit  26  has been displaced towards the left, so that the switchable gear  24  is connected to the output shaft  21  of the first partial drive  17 , and the switching muff of the switching unit  34  is displaced towards the left, so that the switchable gear  32  is connected to the output shaft  29  of the second partial gearbox. Torque is thus transmitted by the driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  and via the pair of gears  30 ,  32  to the output shaft  29  of the second partial gearbox  18 , whereas the input shaft  20  is torque-loaded by the secondary driving machine  41  with the hollow gear  16  and the output shaft  21  of the first partial gearbox is torque-loaded via the pair of gears  22 ,  24 . The differential movement of the differential gearbox  12  is determined by the speed ratio between the gears  11  and  30 . 
         [0051]      FIG. 9  shows the gear shift condition of a reverse gear, wherein the lock-up coupling  19  is open. The switching muff of the switching unit  26  is displaced towards the left, so that the switchable gear  24  is connected to the output  21  of the first partial gearbox  17 , and the switching muff of the switching unit  34  is displaced towards the right, so that the switchable gear  33  is connected to the output shaft  29  of the second partial gearbox  18 . Torque is transmitted by the driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28 , and via the pair of gears  31 ,  33  to the output shaft  29  of the second partial drive  18 , whereas the input shaft  20  is torque-loaded by the secondary driving machine  41  with the hollow gear  16 , and via the pair of gears  22 ,  24 , the output shaft  21  of the first partial gearbox  17  is torque-loaded. The differential movement of the differential gearbox in this case, is determined on the basis of the speed ratio between the teeth of the fixed gears  22  and  31 . In this embodiment, the direction of rotation of the secondary driving machine  41  (electric machine) has to be reversed, and the speed ratio between the secondary driving machine and the main driving machine  11  (internal combustion engine) has to be selected to be such that, with an unchanged direction of rotation of the internal combustion engine, the direction of rotation of the main driving machine, too, has to be reversed. By maintaining the direction of rotation of the secondary driving machine, it is possible to create an eighth gear. 
         [0052]      FIG. 10  shows the gearbox diagram of an inventive drive system in the form of a hybrid drive system in a second embodiment. The following description of  FIG. 10 , in principle, also applies to  FIGS. 11 to 18  which show different gear shift conditions of the gearbox diagram according to  FIG. 10 . The drive system comprises a main driving machine  11 , in this case in the form of an internal combustion engine, a distribution gearbox  12  in the form of a lockable planetary gearbox, as well as two 2-gear partial gearboxes  17 , 18 , here in the form of special planetary gearboxes. The planetary gearbox  12  comprises the following members: a sun gear  13  which is connected to the crankshaft of the driving machine  11  in a rotationally fast way, a planetary carrier  14  with planetary gears  15 , as well as a hollow gear  16 . The hollow gear  16  is connected to an input shaft  20  of the first partial gearbox  17  in rotationally fast way, which input shaft  20  is provided in the form of a hollow shaft. The planetary carrier  14  is connected in a rotationally fast way to an input shaft  28  of the second partial gearbox  18 , which input shaft  28  is provided in the form of an inner shaft arranged coaxially relative to the input shaft  20 . 
         [0053]    The planetary gearbox  12  can be replaced by any other distribution gearbox or differential gearbox. In accordance with the invention, the distribution gearbox contains a lock-up coupling  19  (C 1 ) which is able to couple the sun gear  13  to the planetary carrier  14 , i.e. the crankshaft of the internal combustion engine  11  to the input shaft  28  of the second partial gearbox. The hollow gear  16 , as the third member of the distribution gearbox  12 , is coupled to a secondary driving machine  41  which, in this case, is provided in the form of an annular electric machine (EM). 
         [0054]    The first partial gearbox  17  which is driven by the input shaft  20  provided in the form of a hollow shaft is a planetary gearbox which comprises the following members: a sun gear  43 , a planetary carrier  44  with planetary gears  45  and a hollow gear  46 . Whereas the sun gear  43  is connected to the input shaft  20 , the hollow gear  46  is connected to an output shaft  21  which is also provided in the form of a hollow shaft on which there is arranged an output gear  35  which engages a driven gear  38  on a driven shaft  40  (output). The second partial gearbox  18  is also a planetary gearbox and comprises the following members: a sun gear  48 , a planetary carrier  49  with planetary gears  50  and a hollow gear  51 . The sun gear  48  is connected to the input shaft  28 , the hollow gear  51  to an output shaft  29  provided in the form of a hollow shaft, and carries an output gear  36  which engages a further driven gear  39  on the driven shaft  40 . 
         [0055]    In accordance with the invention, the first partial gearbox  17  is provided with a brake  47  (B 1 ) which is able to brake the planetary carrier  44  relative to a fixed part  53  in order to support same and thus constitute a transmission stage between the sun gear  43  and the hollow gear  46 . Furthermore, in the first partial gearbox  17 , there is provided a coupling  55  (C 2 ) which is able firmly to connect the planetary carrier  44  to the hollow gear  46 , thus blocking the planetary gearbox, so that there takes place a direct transmission from the sun gear  43  to the hollow gear  46 , i.e. from the input shaft  20  to the output shaft  21 . 
         [0056]    In accordance with the invention, the second partial gearbox  18  is provided with a brake  52  (B 1 ) which is able to brake the planetary carrier  49  relative to a fixed part  54  in order to support same and thus constitute a transmission stage between the sun gear  48  and the hollow gear  51 . Furthermore, in the second partial gearbox  18 , there is provided a coupling  56  (C 3 ) which is able firmly to connect the planetary carrier  49  to the hollow gear  51 , thus blocking the planetary gearbox, so that there takes place a direct transmission from the sun gear  48  to the hollow gear  51 , i.e. from the input shaft  28  to the output shaft  29 . 
         [0057]    The following Figures show eight different gear shift conditions of the above-described gearbox; in four cases thereof, the lock-up coupling  19  (C 1 ) is open and the distribution gearbox  12  is thus able to have a differential function. In the four remaining cases, the lock-up coupling  19  of the distribution gearbox  12  is closed, so that the distribution gearbox  12  constitutes a through-drive only. Whereas in the first gear shift position torque can be transmitted via both partial gearboxes  17 ,  18 , it is necessary in the second gear shift position to release one of the partial gearboxes  17 ,  18 . Both partial gearboxes are subject to the condition that they each have to form a transmission stage when the respective lock-up coupling  55 ,  56  is open and when, as a result of the closed brake  47 ,  52 , the planetary carrier  44 ,  49  is supported on the fixed part  53 ,  54 , and that they act as a rigid through-drive when the respective lock-up coupling  55 ,  56  is closed, with the respective brake  47 ,  52  of the planetary carrier  44 ,  49  having to be opened. 
         [0058]    If a partial gearbox has to be released, i.e. has to remain torque-free, both the lock-up coupling  55 , 56  and the brake  47 , 52  have to be opened. 
         [0059]      FIG. 11  shows the gear shift condition for the first gear, wherein the lock-up coupling  19  of the distribution gearbox  12  is open. Torque is transmitted from the main driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  of the second partial gearbox  18  which, with the lock-up coupling  56  being open and the brake  52  being closed, acts as a transmission stage and drives the output shaft  29  and the output gear  36  at a first speed, whereas torque continues to be transmitted from the secondary driving machine  41  via the hollow gear  16  to the input shaft  20  of the first partial gearbox  17  at which again the lock-up coupling  55  is open and the brake  47  closed, so that the partial gearbox  17 , too, acts as a transmission stage and thus drives the output shaft  21  and thus the output gear  35  at a second speed. The speed ratio of the output gears  35 ,  36  determines the differential movement of the distribution gearbox  12  because the driven gears  38 ,  39  rotate at identical speeds. 
         [0060]      FIG. 12  shows the gear shift position for the second gear. The lock-up coupling  19  of the distribution gearbox  12  is open. Torque is transmitted from the main driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  of the partial gear box  18  and torque is transmitted from the secondary driving machine  41  via the hollow gear  16  to the driveshaft  20  of the partial gearbox  17 . At the second partial gearbox  18 , the brake  52  is open and the lock-up coupling  56  is closed, so that the input shaft  28  is firmly blocked relative to the output shaft  29  which carries the output gear  36 . At the first partial gearbox  17 , the brake  47  is closed and the lock-up coupling is open, so that the output shaft  21  is driven at a transmission ratio relative to the input shaft  20 , and also the output gear  35 . The speed ratio of the output gears  36 ,  35  determines the differential movement in the distribution gearbox  12 . Both output gears  35 ,  36  introduce torque into the driven shaft  40 . 
         [0061]      FIG. 13  shows the gear shift condition of the third gear. The lock-up coupling  19  of the distribution gearbox  12  is closed. The distribution gearbox acts as a rigid through-drive and drives the input shaft  20  and the input shaft  28  at identical speeds. For this reason, the partial gearbox  18  is released by opening the lock-up coupling  56  as well as the brake  52  (open/open). The output gear  36  on the output shaft  29  is thus able to rotate freely. Therefore, torque is transmitted from both the main driving machine  11  and the secondary driving machine  41  entirely via the input shaft  20  to the first partial gearbox  17  at which the lock-up coupling  55  is open and the brake  47  is closed. The partial gearbox  17  thus acts as a reduction stage, so that the output shaft  21  with the output gear  35  is driven at a reduced speed relative to the input shaft  20 . Only the output gear  35  introduces torque into the driven gear  38  of the driven shaft  40 . 
         [0062]      FIG. 14  shows the gear shift condition of the fourth gear. The lock-up coupling  19  of the distribution gearbox  12  is closed. The distribution gearbox acts as a rigid through-drive and drives the input shaft  20  and the input shaft  28  at identical speeds. For this reason, the partial gearbox  17  is released by opening the lock-up coupling  55  as well as the brake  47  (open/open). The output gear  35  on the output shaft  21  is thus able to rotate freely. Therefore, torque is transmitted from both the main driving machine  11  and the secondary driving machine  41  entirely via the input shaft  28  to the second partial gearbox  18  at which the brake  52  is open and the lock-up coupling is closed. The partial gearbox  18  thus acts as a direct through-drive, so that the output shaft  29  with the output gear  36  is driven at the same speed as the input shaft  28 . Only the output gear  36  introduces torque into the driven gear  39  of the driven shaft  40 . 
         [0063]      FIG. 15  shows the gear shift condition of the fifth gear. The lock-up coupling  19  of the distribution gearbox  12  is closed. The distribution gearbox acts as a rigid through-drive and drives the input shaft  20  and the input shaft  28  at identical speeds. For this reason, the partial gearbox  17  is released by opening the lock-up coupling  55  as well as the brake  47  (open/open). The output gear  35  on the output shaft  21  is thus able to rotate freely. Therefore, torque is transmitted from both the main driving machine  11  and the secondary driving machine  41  entirely via the input shaft  28  to the second partial gearbox  18  at which the lock-up coupling  56  is open and the brake  52  is closed. The partial gearbox  18  thus acts as a reduction stage, so that the output shaft  29  with the output gear  36  is driven at a reduced speed relative to the input shaft  28 . Only the output gear  36  introduces torque into the driven gear  38  of the driven shaft  40 . 
         [0064]      FIG. 16  shows the gear shift condition of the sixth gear. The lock-up coupling  19  of the distribution gearbox  12  is closed. The distribution gearbox acts as a rigid through-drive and drives the input shaft  20  and the input shaft  28  at identical speeds. For this reason, the partial gearbox  18  is released by opening the lock-up coupling  56  as well as the brake  52  (open/open). The output gear  36  on the output shaft  29  is thus able to rotate freely. Therefore, torque is transmitted from both the main driving machine  11  and the secondary driving machine  41  entirely via the input shaft  20  to the first partial gearbox  17  at which the brake  47  is open and the lock-up coupling is closed. The partial gearbox  17  thus acts as a direct through-drive, so that the output shaft  21  with the output gear  35  is driven at the same speed as the input shaft  20 . Only the output gear  35  introduces torque into the driven gear  38  of the driven shaft  40 . 
         [0065]      FIG. 17  shows the gear shift position for the seventh gear. The lock-up coupling  19  of the distribution gearbox  12  is open. Torque is transmitted from the main driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  of the partial gear box  18  and torque is transmitted from the secondary driving machine  41  via the hollow gear  16  to the driveshaft  20  of the partial gearbox  17 . At the first partial gearbox  17 , the brake  47  is open and the lock-up coupling  55  is closed, so that the input shaft  20  is firmly blocked relative to the output shaft  21  which drives the output gear  35 . At the second partial gearbox  18 , the brake  52  is closed and the lock-up coupling  56  is open, so that the output shaft  29  is driven at a transmission ratio relative to the input shaft  28 , and also the output gear  36 . The speed ratio of the output gears  36 ,  35  determines the differential movement in the distribution gearbox  12 . Both output gears  35 ,  36  introduce torque into the driven shaft  40 . 
         [0066]      FIG. 18  shows the gear shift position for the eighth gear. The lock-up coupling  19  of the distribution gearbox  12  is open. Torque is transmitted from the main driving machine  11  via the sun gear  13  and the planetary carrier  14  to the input shaft  28  of the partial gearbox  18 , and torque is transmitted from the secondary driving machine  41  via the hollow gear  16  to the input shaft  20  of the partial gearbox  17 . At the partial gearbox  18 , the brake  52  is open and the lock-up coupling  56  is closed, so that the input shaft  28  is firmly blocked relative to the output shaft  28  which drives the output gear  36 . At the first partial gearbox  17 , the lock-up coupling  55  is closed and the brake  47  is open, so that the output shaft  21  is driven at the same speed as the input shaft  20 , and also the output gear  35 . The speed ratio of the output gears  36 ,  35  determines the differential movement in the distribution gearbox  12 . Both driven gears  35 ,  36  introduce torque into the driven shaft  40 . 
         [0067]    In this case, too, to illustrate the reverse gear, the direction of rotation of the secondary driving machine  41  can be reversed. 
         [0068]    The invention is not restricted to the illustrative examples or embodiments described above. The examples or embodiments are not intended as limitations on the scope of the invention. Methods, processes, apparatus, compositions, and the like described herein are exemplary and not intended as limitations on the scope of the invention. Changes therein and other uses will occur to those skilled in the art. The scope of the invention is defined by the scope of the claims. 
         [0069]    I Claim: