Abstract:
A hybrid drive of a motor vehicle comprising a combustion engine having a drive shaft, at least one electric machine, a manual transmission having input shafts (GE 1 , GE 2 ) and an output shaft. Shaft (GE 1 ) couples the combustion engine drive shaft and the electric machine can drive shaft (GE 2 ). For efficient driving with the combustion engine and/or electric machine optionally decoupled or coupled, and for a reduction of size, shafts (GE 1 , GE 2 ) are coaxially located one after the other, the output shaft coaxially surrounds one of the shafts (GE 1 , GE 2 ) and planetary gearsets are disposed coaxially behind one another, each having an input and output element. The combustion engine can be coupled alternately to shaft (GE 2 ), via a first shift element or to the input element of the first planetary gearset, via a second shift element. The output elements of the planetary gearsets are connected to the output shaft.

Description:
This application is a National Stage completion of PCT/EP2012/051631 filed Feb. 1, 2012, which claims priority from German patent application serial no. 10 2011 005 531.2 filed Mar. 15, 2011. 
     FIELD OF THE INVENTION 
     The invention relates to a hybrid drive of a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Hybrid drives with internal combustion engine and electric motor drive sources contribute to the reduction of fuel consumption and polluting emissions in automobile traffic. In order to obtain the most effective and efficient operation of a hybrid drive, drive strategies are used that can flexibly utilize the electric machine of the hybrid drive depending on the situation. The electric machine is to be used as the sole drive source in the case of startup for example, in city short-haul traffic, or in stop-and-go operation, as an additional drive source in the case of increased power demands in a boost operation, as a starter generator for fast starts of the internal combustion engine and as a generator for generating electrical current, or for energy recovery in a recuperation operation. In contrast, the internal combustion engine is to be operated at least predominantly at operating points that are favorable for consumption, torque and speed with high efficiency. 
     In vehicle drive trains, hybrid drive arrangements are frequently combined with automated vehicle transmissions for forming drive transmission ratios. In doing so, hybrid drives, with which the electric drive and the internal combustion engine can be coupled to the drive train independently of each other, at least for individual transmission ratio steps, have advantages due to more flexible control thereof in comparison to arrangements with which the electric drive is permanently connected to the drive at the transmission input or at the transmission drive, that is, in the power flow of the drive train. With such hybrid drives, during shift procedures with the internal combustion engine, that is, gear changes while the internal combustion engine serves a drive source of the vehicle, the tractive force can be largely maintained with the aid of the electric drive. Conversely, during gear changes of the electric drive, the tractive force can be maintained with the aid of the internal combustion engine, insofar as the internal combustion engine is not currently switched off. 
     The shift procedures can be synchronized using the internal combustion engine and a friction engaged clutch acting between the internal combustion engine and the transmission input, and/or using the electric drive, so that synchronization devices can be replaced, at least to some extent, by more cost effective claw clutches. The shifting points with electric shifts, thus shifts occurring during the electric motor drive, can be basically very variably selectable due to the typically greater speed range available, with good efficiency compared to the internal combustion engine. Additionally, the attainable shifting times allow the use of a relatively inexpensive shift actuating system. Because an electric machine can basically be operated in both directions of rotation, by using a controllable reversal of the direction of rotation, it is possible to eliminate a separate reverse gear set. Additionally, the step changes of the internal combustion engine gears in such a hybrid drive system can be selected to be relatively large, whereby a relatively small number of gears can be used for implementing a specified overall gear ratio spread. 
     Such drive concepts have already been proposed for vehicles with which the electric drive is designed so that the electric drive alone has sufficient driving performance at least for a short-haul operation, in city traffic for example. These are so-called plug-in hybrid vehicles or range extender electric vehicles, with which an electric energy store is additionally externally chargeable and/or the internal combustion engine serves mainly for increasing the range and for generating energy for the electric drive. 
     Such hybrid drives with a manual transmission, which has two input shafts and a common output shaft, are known, wherein the output shaft is disposed in countershaft design and axis parallel to the input shafts. The one input shaft can be driven via an internal combustion engine, and the other input shaft can be driven via an electric machine. Both input shafts can be shifted, via gear sets coupled to the output shaft, and can be combined in a drive connection. 
     The unpublished document DE 10 2010 030 567 A1 describes such a hybrid drive with which two input shafts are disposed coaxially and axially adjacent to each other, and a common output shaft is disposed axis parallel to the input shafts. One of the two input shafts is separated into an axially outer and an axially inner shaft section. The outer shaft section is drive connected, or can be, drive connected to an associated internal combustion engine or to an associated electric machine. The inner shaft section supports gear sets assigned to the drive gears. Additionally, a superposition transmission is preferably provided as a planetary gear set having a sun gear and a ring gear as an input elements and a planet carrier as an output element. The input elements are each connected in a rotationally fixed manner to one of the two shaft sections. The output element is connected, or can be connected, in a rotationally fixed manner to the drive gear of an assigned startup gear set. A lock-up clutch, by means of which the superposition transmission can be locked, is disposed between the planet carrier and the ring gear. 
     This hybrid drive, in the case of an active superposition transmission, with an internal combustion engine drive that is running and connected to the respective input shaft, with the input shafts coupled together and an engaged start-up gear wheel set under the control of the electric machine from generator operation into motor operation, allows a wear-free startup with high tractive force, whereby a conventional friction clutch is not necessary as a start-up element. This function corresponds to the start-up function of comparable known electro-dynamic start-up elements, as described for example in the document DE 199 34 696 A1. This document shows one such wear-free electro-dynamic start-up element, with which a planetary gear set is disposed between the internal combustion engine and the transmission input, wherein a planet carrier is connected to a manual transmission, a ring gear is connected to the internal combustion engine, and a sun gear is connected to an electric machine. On the other hand, a hybrid drive according to the document DE 10 2010 030 567 A1 can be operated with an engaged lock-up clutch such as a hybrid drive with two input shafts and one common output shaft without a superposition transmission. A suitable basic hybrid drive with a three speed manual transmission with spur gears in countershaft design, with which two pure electric motor drive gears and three internal combustion engine drive gears and a boost operation, a recuperation operation and a charge operation can be selected, is also described in this unpublished document. 
     The document DE 10 2010 030 573 A1, also unpublished, also shows a comparable basic hybrid drive. Two input shafts are disposed coaxially over one another in sections, wherein the one input shaft assigned to the internal combustion engine is the inner shaft, and the shaft assigned to the electric machine is the outer shaft. A common output shaft is disposed axis parallel to the input shafts. A second electric machine is disposed on the input shaft assigned to the internal combustion engine. A friction clutch, by means of which the drive shaft of the internal combustion engine which could be connected, switchable to the respective transmission input shaft, is eliminated. 
     SUMMARY OF THE INVENTION 
     Based on this background, the problem addressed by the invention is to provide a hybrid drive of the initially named type, which allows efficient driving operation with the internal combustion engine selectively coupled or decoupled, or with the electric machine selectively coupled or decoupled, and which has a compact design, particularly with respect to the radial dimensions. 
     The problem is solved by the shift logic and functionality of a typical range extender transmission designed in spur gear design, or the like, for a hybrid drive train that can also be implemented in planetary design saving construction space. 
     Accordingly the invention is based on a hybrid drive of a motor vehicle that has an internal combustion engine having a drive shaft, at least one electric machine having a rotor and a manual transmission having two input shafts and a common output shaft, wherein the first input shaft is or can be connected to the drive shaft of the internal combustion engine, and the second input shaft can be directly or indirectly driven by the rotor of the electric machine. 
     For solving the problem, the invention provides that the two input shafts are disposed coaxially behind one another, that the output shaft is disposed coaxially above one of the two input shafts, and that at least two planetary gear sets, each having at least one input element and one output element, are disposed coaxially behind one another, wherein the internal combustion engine can be alternately coupled, via a first shift element, to the second input shaft, or, via a second shift element, to the input element of the first planetary gear set, and wherein the output elements of the two planetary gear sets are connected to the output shaft. 
     This hybrid drive train in planetary design with two planetary gear sets has the same functionality as the initially described hybrid drive. However a more compact radial design is attained by eliminating the gear set in the spur gear design. This is particularly advantageous for vehicles in which the drive assemblies are installed front-transverse to the vehicle longitudinal axis. 
     With one embodiment, the two planetary gear sets and the output shaft are disposed above the second input shaft, wherein the first planetary gear set comprises a ring gear as an input element, a fixed sun gear, and a planet carrier, having a plurality of planet gears meshing between the sun gear and the ring gear, as an output element, wherein the second planetary gear set comprises a sun gear as an input element, a ring gear that can be fixed via a third shift element, and a planet carrier, having a plurality of planet gears meshing between the sun gear and the ring gear, as an output element, and with which the second planetary gear set can be locked by means of a fourth shift element. 
     This arrangement represents a three speed manual transmission which, due to variable control and coupling of the two drive assemblies, via the planetary gear sets, to the output shaft and the two input shaft among themselves, enables the use of two drive gears that are driven solely by the electric motor, wherein the internal combustion engine is decoupled from the drive train, three internal combustion engine drive gears are facilitated, wherein the electric machine is coupled to the drive train, and facilitates a drive gear driven solely by the internal combustion engine, wherein the electric machine is decoupled from the drive train. 
     The shift logic of the transmission according to the invention corresponds to the shift logic of a comparable transmission in spur gear design having at least three gear set planes. The shifts of the internal combustion engine drive gears can occur with the tractive force bridged by the electric motor. It is also fundamentally possible to bridge the tractive force of the shifts of the electric motor drive gears using the internal combustion engine. Additionally, a charge operation for charging an electric energy store is possible using the electric motor in a neutral position of the transmission. A reverse gear, driven by the electric motor, can be implemented by reversing the direction of rotation of the electric drive in a startup gear so that transmission components for a separate reverse gear can be eliminated. 
     It can be further provided that the two planetary gear sets have the same transmission ratio. With the use of the two planetary gear sets having the same transmission ratio, additional cost savings can be attained by using the same components. 
     The output shaft can be in drive connection, via an output gear set, with an axle differential of a vehicle axle, which is positioned axially between the two planetary gear sets, or axially in front of, or behind, the planetary gear set. Due to the variable arrangement of the output gear set, the drive can be adapted relatively easily to the installation space conditions of a vehicle. 
     The output gear set can be designed as a simple spur gear pair, or as a two-stage output with a drive gear that is connected to the output shaft in a rotationally fixed manner, with an output gear that is in drive connection with the axle differential, and with an intermediate gear, mounted on an intermediate shaft, which is in gear engagement with the drive gear and the output gear. Thereby, a change in the direction of rotation can be implemented for the output in order to obtain the usual direction of rotation, particularly with a front-transverse installation. Thus, rotation of the drive is not necessary. In order to save as much space as possible with the installation of the intermediate shaft, it can be positioned in a free space axially between the two planetary gear sets. It is also possible to design the intermediate gear as a double gear having two gears of different sizes connected together in a rotationally fixed manner, wherein one of the gears is in engagement with the drive gear and the other is in engagement with the output gear, in order to keep the radial extension of the output gear set with the reversal of the change of direction as low as possible. 
     For further savings of component costs, installation space and weight, it can be provided that the first and second shift elements and the third and fourth shifts elements are each combined as shift packets that can be actuated on both sides. The shift packets can be designed as inexpensive claw clutches, because synchronizing the gears with shift procedures can be performed by regulating the speed of the electric drive, or the internal combustion engine. 
     Additionally, it can be provided, as an alternative to a direct connection of the rotor to the electric machine at the respective input shaft, that the rotor is in drive connection, via an input gear set, with the second input shaft. The input gear set can be designed as a simple spur gear pair which results in a constant input transmission ratio of the electric drive. Thereby the rotational speed level of the electric machine can be increased or decreased in the electric drive gears. For example, with a higher level of rotational speed an electric machine can be used that is less expensive and has comparatively weaker torque. 
     Using the input gear set, the electric machine can be attached laterally at the drive train. Such a lateral attachment of the electric machine, above the planetary gear set, allows a reduction in the axial construction length of the drive train, if appropriate construction space is available for the electric machine in the radial extension. 
     The first input shaft can be connected to the drive shaft of the internal combustion engine in a conventional manner, shiftable via a controllable friction engaged clutch. The friction engaged clutch can be used as a separation and start-up clutch and as a synchronization means with shift procedures. If, in contrast, the electric machine is used as a start-up element, the friction engaged clutch can, in principle, be omitted and the internal combustion engine can respectively be coupled to the drive train, or decoupled from the drive train, via one or more of the provided shift elements. 
     It is also possible that a second electric machine is provided, the rotor of which is, or can be, in drive connection with the drive shaft of the internal combustion engine. The second electric machine can be operated as a motor and generator, as well as being implemented as a crankshaft starter generator of the internal combustion engine. Thus, the second electric machine is implemented so that, as a generator, it can generate a required mean electrical power for supplying the first electric machine as a traction machine for maintaining extended stop-and-go operation. A series hybrid operation of the drive train results that is available in a load speed range and is particularly favorable with respect to emissions. 
     An alternative to an embodiment with a friction engaged clutch as a startup and separation clutch, and possibly a second electric machine drive connected to the internal combustion engine, it can be provided that a third planetary gear set is disposed between the second planetary gear set and the electric machine, and comprises a sun gear as an input element, a ring gear, and a planet carrier having a plurality of planet gears meshing between the sun gear and the ring gear as an output element, wherein the second input shaft has an axially inner shaft section and an axially outer shaft section, wherein the input element of the third planetary gear set is drive connected, via the outer shaft section of the second input shaft, to the rotor of the electric machine, wherein the ring gear is connected in a rotationally fixed manner to the inner shaft section of the second input shaft, and wherein the output element is connected in a rotationally fixed manner, via a hollow shaft, to the input element of the second planetary gear set, and in that the third planetary gear set can be blocked via a fifth shift element. 
     Due to the arrangement of the additional planetary gear set, wear-free startup control can be implemented without a clutch, as is known for example as an electrodynamic start-up element from the initially cited document DE 199 34 696 A1. Thereby, particularly even in the case of an empty electrical energy store and without a friction engaged clutch, a comfortable startup can be ensured in a start-up gear, in that the internal combustion engine and the electric machine are used in a speed-superposition operation with the electric machine initially running as a generator. 
     With the arrangement having an additional third planetary gear set, additionally a separate starter device can be provided for the internal combustion engine, in order to start the internal combustion engine in an easy and speed-favorable manner without additional rotating masses of this planetary gear set. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For illustrating the invention, the description is accompanied by drawings with exemplary embodiments. They show: 
         FIG. 1  a first embodiment of the hybrid drive according to the invention in a schematic representation, 
         FIG. 1   a  a shift pattern with operating modes and example transmission ratio of the hybrid drive according to  FIG. 1  in a tabular representation, 
         FIG. 2  a second embodiment of the hybrid drive according to the invention in a schematic representation, 
         FIG. 3  a third embodiment of the hybrid drive according to the invention in a schematic representation, 
         FIG. 4  a fourth embodiment of the hybrid drive according to the invention in a schematic representation, and 
         FIG. 5  a fifth embodiment of the hybrid drive according to the invention in a schematic representation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Accordingly, a hybrid drive  1   a  of a motor vehicle, preferably designed as a range extender drive, comprises an internal combustion engine VM having a drive shaft  2 , an electric machine EM that can be operated as a motor and generator having a rotor  3   a  and a stator  3   b , and an optional second electric machine EM 2 , and a manual transmission  4  having two planetary gear sets PG 1 , PG 2 . The manual transmission  4  has two input shafts GE 1 , GE 2  disposed coaxially one behind the other, and a common output shaft GA designed as a hollow shaft, wherein the latter is disposed coaxially about the longer, second input shaft GE 2 . The second electric machine EM 2  is in drive connection with the drive shaft  2  of the internal combustion engine VM. The first input shaft GE 1  can be connected radially, via an optional controllable friction clutch K 1  and the second electric machine EM 2 , to the drive shaft  2  of the internal combustion engine VM. The second input shaft GE 2  is connected in a rotationally fixed manner to the rotor  3   a  of the electric machine EM. 
     The first planetary gear set PG 1  comprises a central sun gear  8   a , which is disposed radially about the output shaft GA and is fixed or firmly braked at a machine part, a radially outer ring gear  8   b , which is disposed rotatably on the second input shaft GE 2 , and a planet carrier  8   c , which is connected in a rotationally fixed manner to the output shaft GA. The planet carrier  8   c  supports a plurality of planet gears  8   d , which are in engagement with the sun gear  8   a  and the ring gear  8   b . The planet carrier  8   c  serves an output element or output drive element of the planetary gear set PG 1 . The ring gear  8   b  serves as an input element, or drive gear. It can be connected in a rotationally fixed manner, via a second shift element B, to the first input shaft GE 1 . The two input shafts GE 1  and GE 2  can be combined together via a first shift element A, wherein the two shift elements A and B are designed as claw clutches, which can be engaged and disengaged, and are combined in a shift packet S 1 . 
     The second planetary gear set PG 2  comprises a central sun gear  9   a , which is connected in a rotationally fixed manner to the second input shaft GE 2  and serves as an input element, or drive gear, an outer ring gear  9   b , and a planet carrier  9   c , which is connected in a rotationally fixed manner to the output shaft GA and serves as an output element, or output driven element. The planet carrier  9   c  supports a plurality of planetary gears  9   d , which are in engagement with the sun gear  9   a  and the ring gear  9   b . The planet carrier  9   c  and the ring gear  9   b  are connected, via hollow shaft sections, to a second shift packet S 2 , which has a third shift element C and a fourth shift element D, which are designed as claw clutches that can be engaged and disengaged. The ring gear  9   b  can be fixed, or braked, to a machine part, via the third shift element C. The ring gear  9   b  can be coupled to the planet carrier  9   c , via the fourth shift element D, whereby the planetary gear set PG 2  can be bridged, or locked. 
     The common output shaft GA is in drive connection with the axle differential  5 , via an output gear set Z 1 . The output gear set Z 1  comprises a drive gear z 11  that is connected in a rotationally fixed manner to the output shaft GA and that is in engagement with an output gear z 21 , which interacts with the axle differential  5 . Two axle shafts  7   a ,  7   b  of a vehicle axle  7 , which are each connected to a vehicle wheel  6   a ,  6   b , are driven via the axle differential  5 . 
     According to the table in  FIG. 1   a , for the purely electric driving operation, the hybrid drive has two forward gears G1 and G3; for the internal combustion engine driving operation with optional boost operation and recuperation operation, it has three forward gears G1, G2 and G3; and for the purely internal combustion engine driving operation, it has one forward gear G2. In the table, as an example, a transmission ratio of i0_PG 1 , 2=−1.6 is assumed for both the first planetary gear set PG 1  as well as for the second planetary gear set PG 2 . The given drive transmission ratios i_EM or i_VM result depending on the mode of operation. The output transmission ratio of the output gear set Z 1  is not taken into consideration in the table. The engaged shift elements A, B, C, D of the shift packets S 1 , S 2  or the neutral position thereof, are specified for the represented modes of operation. 
     If both shift packets S 1 , S 2  are in neutral N, thus both the internal combustion engine VM and also the electric machine EM are decoupled, then the vehicle axle  7  is completely separated from the drive. In the case of the engaged shift element A, the two input shafts GE 1 , GE 2  are coupled together. This can be used as a neutral charging operation when the second shift packet S 2  is in the neutral position. In this charging operation, an electric energy store connected to the electric machine EM can be charged, with vehicle standstill, by the running internal combustion engine VM, in the generator operation of the electric machine EM. As an alternative to this, when only the shift position A is engaged, the internal combustion engine VM is started using the electric machine EM. 
     The second planetary gear set PG 2 , with the engaged shift element C, generates the first gear G1, via the sun gear  9   a  as a drive and the planetary carrier  9   c  as output. The electric machine EM can use this drive gear as a first pure electric motor drive gear. In the shift position D, that is, with the engaged shift element D, the second planetary gear set PG 2  is bridged. As a result, a third gear G3 can be used with a direct drive transmission ratio. The electric machine EM can use this gear G3 as a second purely electric motor drive gear. In the case of the two electric motor drive gears, the internal combustion engine VM can be decoupled from the drive. By operating the electric machine EM in the reverse direction of rotation, the first gear G1 can be used as a reverse gear. 
     When the electric machine EM is used as a start-up element, the friction clutch K 1  can be eliminated and the coupling and decoupling of the internal combustion engine VM occurs using the shift elements A or B of the first shift packet S 1 . 
     During electric driving with the electric machine EM via the second planetary gear set PG 2  and the first or third gear G1 or G3, the first planetary gear set PG 1  can be shifted load-free in the background. The synchronization of the first planetary gear set PG 1  can occur using an active speed regulation with the internal combustion engine VM, or with existing friction engaged clutch K 1  alternatively, with disengaged friction engaged clutch K 1  by means of synchronized shift elements A, B of a first shift packet S 1  implemented as a synchronizing device. 
     The internal combustion engine VM can be coupled, via a first shift element A, to the sun gear or input element  9   a  of the second planetary gear set PG 2 . The internal combustion engine VM, in the case of the engaged shift element C, can use the first gear G1, and in the case of a bridged planetary gear set PG 2  in the shift position D, can use the third gear G3 as an internal combustion engine drive gear. The internal combustion engine VM is simultaneously in operative engagement with the electric machine EM. Here, the electric machine EM can be operated in boost operation, recuperation operation, or with no-load. 
     The internal combustion engine VM can be coupled to the ring gear or the input element  8   b  of the first planetary gear set PG 1  by engaging the second shift element B. A second gear G2, lying between the first gear G1 and the third gear G3, for the internal combustion engine VM, results. Here, the planet carrier  8   c  acts as an output, the sun gear  8   a  is firmly braked. The second gear G2 can be used in three variants for the internal combustion engine VM. In the first variant, the shift element C is engaged. This gear is shifted via only the internal combustion engine VM. In the second variant, the second shift packet S 2  is in neutral. The electric machine EM is completely decoupled from the drive. The first planetary gear set PG 1  generates a second gear G2 for the internal combustion engine VM that is independent of the second planetary gear set PG 2 . In the third variant, the shift element D is engaged. 
     While the driving using the internal combustion engine VM via the first planetary gear set PG 1  in the second gear G2, the second planetary gear set PG 2  can be shifted, load-free, in the background. The second planetary gear set PG 2  can be synchronized by an active rotational speed regulation using the electric machine EM. 
     The optional second electric machine EM 2  can be used as a starter for the internal combustion engine VM, and as a generator driven by the internal combustion engine VM for supplying the first electric machine EM for a serial driving operation in the low speed range below the first gear G1. 
       FIG. 2  shows a hybrid drive  1   b  with which the electric machine EM is connected laterally to the drive train via an input gear set Z 2  designed as a spur gear pair. The input gear set Z 2  consists of a drive gear z 12 , driven by the electric machine EM, that is in engagement with an output gear z 22  which is disposed rotationally fixed on the second input shaft GE 2 . The input gear set Z 2  provides a constant input transmission ratio to the electric machine EM. Apart from that, the hybrid drive  1   b  has an design and function equivalent to that of the hybrid drive  1   a  shown in  FIG. 1 . 
       FIG. 3  shows a hybrid drive  1   c , with which the output gear set Z 1  is disposed laterally displaced in the direction toward the electric machine EM, whereby the output gear shaft GA is extended rearward via the planet gear carrier  9   c  of the second planetary gear set PG 2 . The two planetary gear sets PG 1 , PG 2  are therefore moved axially closer together. 
       FIG. 4  shows a further hybrid drive  1   d , with which a third planetary gear set PG 3 , which acts as an electrodynamic startup element, is disposed far from the internal combustion engine VM. It comprises a sun gear  10   a , which is connected in a rotationally fixed manner to an outer shaft section GE 2   a  of the second input shaft, a ring gear  10   b , which is connected in a rotationally fixed manner to an inner shaft section GE 2   b  of the second input shaft, and a planet carrier  10   c , which is connected in a rotationally fixed manner to the input element, or sun gear  9   a , of the second planetary gear set PG 2 , via a hollow shaft  11 , and a plurality of planet gears  10   d , guided by the planet carrier  10   c , and in engagement with the sun gear  10   a  and the ring gear  10   b . A fifth shift element E is also disposed on the axially outer shaft section GE 2   a  of the second input shaft, and by means of this shift element the planet carrier  10   c  can be coupled to the outer shaft section GE 2   a , and thus with the sun gear  10   a , whereby the planetary gear set PG 3  can be blocked or bridged. 
     With the shift element E engaged, the planetary gear set PG 3  is bridged, and thus not functioning. In contrast, with the shift element E disengaged, the transmission ratio of the third planetary gear set PG 3  is effective, for example i0_PG 2 =−2. This transmission ratio can be used by a superpositioned operation of the internal combustion engine VM and the electric machine EM, wherein the electric machine EM operates, at least initially, as a generator, for wear-free start-up in the first gear G1, wherein the appropriate shift elements A and C are engaged. This function corresponds to an electric start-up element, as described in the initially cited document DE 199 34 696 A1. The friction engaged clutch K 1  and the second electric machine EM 2  are omitted with the hybrid drive  1   d  as seen according to  FIG. 4 . 
     Finally,  FIG. 5  shows a hybrid drive  1   e , with which a two-stage output gear set Z 1   a  is provided. The output gear set Z 1   a  additionally has an intermediate shaft ZW, on which an intermediate gear z 31   a /z 31   b  is disposed. The intermediate gear z 31   a /z 31   b  is implemented as a double gear. It comprises a first gear z 31   a , which is in engagement with the drive gear z 11 , and a second gear z 31   b , which is in engagement with the output gear z 21 . A reversal of the direction of rotation of the drive train to the output can be implemented by means of the intermediate gear z 31 . 
     REFERENCE LIST 
     
         
           1   a  hybrid drive 
           1   b  hybrid drive 
           1   c  hybrid drive 
           1   d  hybrid drive 
           1   e  hybrid drive 
           2  drive shaft of the internal combustion engine 
           3   a  rotor of the electric machine 
           3   b  stator of the electric machine 
           4  manual transmission 
           5  axle differential 
           6   a ,  6   b  vehicle wheel 
           7  vehicle axle 
           7   a ,  7   b  axle shaft 
           8   a  sun gear of the first planetary gear set 
           8   b  input element, ring gear of the first planetary gear set 
           8   c  output element, planet carrier of the first planetary gear set 
           8   d  planet gear of the first planetary gear set 
           9   a  input element, sun gear of the second planetary gear set 
           9   b  ring gear of the second planetary gear set 
           9   c  output element, planet carrier of the second planetary gear set 
           9   d  planet gear of the second planetary gear set 
           10   a  input element, sun gear of the third planetary gear set 
           10   b  ring gear of the third planetary gear set 
           10   c  output element, planet carrier of the third planetary gear set 
           10   d  planet gear of the third planetary gear set 
           11  hollow shaft 
         A first shift element 
         B second shift element 
         C third shift element 
         D fourth shift element 
         E fifth shift element 
         EM electric machine 
         EM 2  second electric machine 
         GA output shaft 
         GE 1  first input shaft 
         GE 2  second input shaft 
         GE 2   a  outer shaft section of the second input shaft 
         GE 2   b  inner shaft section of the second input shaft 
         K 1  friction engaged clutch 
         PG 1  first planetary gear set 
         PG 2  second planetary gear set 
         PG 3  third planetary gear set 
         S 1  shift packet 
         S 2  shift packet 
         VM internal combustion engine 
         Z 1 , Z 1   a  output gear set 
         Z 2  input gear set 
         ZW intermediate shaft 
         i_VM drive transmission ratio of the internal combustion engine 
         i_EM drive transmission ratio of the electric machine 
         z 11  drive gear of Z 1   
         z 21  output gear of Z 1   
         z 31   a  first intermediate gear of Z 1   a    
         z 31   b  second intermediate gear of Z 1   a    
         z 12  drive gear of Z 2   
         z 22  output gear of Z 2