Abstract:
A hybrid drive manual transmission, for a motor vehicle, having two input shafts (GE 1 , GE 2 ) and one common output shaft. The first shaft (GE 1 ) can connect with a combustion engine drive shaft and can drive the output shaft via a first group of gearwheel sets. The second shaft (GE 2 ) can connect with an electric machine and, via a second group of gearwheel sets, the output shaft. The input shafts (GE 1 , GE 2 ) can connect with one another via a coupling device. For inexpensive production, the transmission is derived from a double clutch transmission having a hollow input shaft (GE 2 ) and a coaxial inner input shaft (GE 1 ) and a coupling device of which comprises a gear step and/or a shiftable clutch, which replaces that gearset and associated gear clutch. The gearset of the underlying double clutch transmission is allocated to first input shaft (GE 1 ) and adjacent the gear-side end of shaft (GE 2 ).

Description:
This application is a National Stage completion of PCT/EP2012/051629 filed Feb. 1, 2012, which claims priority from German patent application serial no. 10 2011 005 561.4 filed Mar. 15, 2011. 
     FIELD OF THE INVENTION 
     The invention relates to a manual transmission of a hybrid drive for a motor vehicle having two input shafts and a common output shaft, wherein the first input shaft can be connected with the drive shaft of an internal combustion engine and can be drivingly connected with the output shaft by means of a first group of selectively shiftable gearwheel sets, wherein the second input shaft is drivingly connected with the rotor of an electric machine that can be operated as a motor and as a generator and can be drivingly connected with the output shaft by means of a second group of selectively shiftable gearwheel sets, and wherein both input shafts can be drivingly connected with one another by means of a shiftable coupling device. 
     BACKGROUND OF THE INVENTION 
     A manual transmission of this kind comprises an internal combustion power transmission branch and an electromotive power transmission branch, which are brought together at the output shaft. The internal combustion power transmission branch comprises the first input shaft, the gear sets of the first group as well as the output shaft and allows the transmission of torque between the internal combustion engine, and the drive wheels of the motor vehicle drivingly connected with the output shaft. The electromotive power transmission branch comprises the second input shaft, the gear sets of the second group as well as the output shaft and allows the transmission of torque between the electric machine and the drive wheels of the motor vehicle. When the coupling device is disengaged, a purely internal combustion drive operation is thereby possible by means of a engaged gear set of the first group, a purely electromotive drive operation is possible by means of an engaged gear set of the second group, and a combined drive operation of both aggregates (internal combustion engine and electric machine) with operation of the electric machine as a motor or generator and with a fixed transmission ratio is possible by means of an engaged gear set of the first and second group respectively. 
     When the motor vehicle is at a standstill, the internal combustion engine can be started by means of the electric machine by engaging the coupling device. In addition, the gear sets of the second group are made available for the internal combustion drive operation and the gear sets of the first group are made available for the electromotive drive operation by engaging the coupling device. With an appropriate transmission ratio and allocation of the gear sets, fewer gear sets are needed overall and accordingly, the manual transmission can have a simpler and more compact design. 
     DE 199 60 621 B4 describes a manual transmission of this kind in three alternative designs. In all embodiments, the internal combustion power transmission branch has a first countershaft, which can be drivingly connected with the drive shaft of an internal combustion engine on the input side by means of a input constant, a first input shaft and a friction clutch, and can be drivingly connected on the output side with an output shaft by means of a first group of selectively shiftable gearwheel sets. In the first embodiment according to  FIG. 1  there, a second input shaft is designed as a second countershaft, which can be connected in a rotationally fixed manner with the rotor of an electric machine and drivingly connected with the output shaft by means of a second group of selectively shiftable gearwheel sets. In this case, the coupling device comprises a drive stage disposed between the input shaft and the second countershaft as well as a shiftable clutch, which is disposed between the driving wheel of the drive stage on the countershaft side and the second countershaft. 
     In the second and third embodiment according to the  FIGS. 2 and 3  there, the second input shaft is formed as a hollow rotor shaft, which is disposed coaxially over the input shaft and connected in a rotationally fixed manner with the rotor of an electric machine disposed coaxially over the first input shaft. The rotor shaft is drivingly connected with the second countershaft by means of a second input constant, which can be drivingly connected with the output shaft by means of the second group of selectively shiftable gearwheel sets. In this case, the coupling device comprises a shiftable clutch, which is disposed between the first input shaft and the rotor shaft. 
     In a further manual transmission of this kind according to WO 2008/138 387 A1, both input shafts are formed as countershafts. The first input or countershaft of the internal combustion power transmission branch can be connected with the drive shaft of an internal combustion engine on the input side by means of a controllable separator clutch and can be drivingly connected with an output shaft on the output side by means of a first group of selectively shiftable gearwheel sets. The second input or countershaft of the electromotive power transmission branch is connected with the rotor of an electric machine on the input side in a rotationally fixed manner and can be drivingly connected on the output side with the output shaft by means of a second group of selectively shiftable gearwheel sets. The gear sets of both groups are disposed in common radial planes and each use a common power take-off gear disposed on the output shaft. In this case, the coupling device is designed in such a way that the idler gears and the allocated gear clutches of two axially adjacent gear sets of the second group on the output shaft, which are combined into a shift set, are disposed on the output shaft, whereby it is possible to couple both input shafts independently of the shifting of one of the respective gear sets. 
     The known manual transmissions that are designed specifically for use in a hybrid drive of a motor vehicle are therefore relatively complex and expensive to manufacture. The market success of hybrid-powered vehicles, however, depends largely on favorable manufacturing costs of the components of the hybrid power train, and in particular of the manual transmission. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is therefore to provide a manual transmission of a hybrid drive of said kind, which can be manufactured in an especially cost-effective way without substantial functional limitations. 
     A first solution for this objective is achieved with a manual transmission which is derived from a double clutch transmission having two coaxial input shafts, the first input shaft of which is disposed centrally, the second input shaft of which is formed as a hollow shaft as well as disposed coaxially above the first input shaft, and the coupling device of which comprises a gear step and/or a shiftable clutch, which is provided instead of that gear set and the allocated gear clutch thereof, wherein that gear set is allocated to the first input shaft in the underlying double clutch transmission and is disposed axially adjacent to the gear-side end of the second input shaft. 
     The invention is thus based on a known manual transmission of a hybrid drive for a motor vehicle, which has two input shafts GE 1 , GE 2  and a common output shaft GA. In this manual transmission, the first input shaft GE 1  can be connected with the drive shaft of an internal combustion engine VM and can be drivingly connected with the output shaft GA by means of a first group of selectively shiftable gearwheel sets (G 1 , G 3 , G 5 ; G 2 , G 4 , G 6 ). The second input shaft GE 2  is drivingly connected with the rotor of an electric machine that can be operated as a motor and as a generator EM and can be drivingly connected with the output shaft GA by means of a second group of selectively shiftable gearwheel sets (G 2 , G 4 ; G 1 , G 3 , G 5 , G 7 ). Both input shafts GE 1 , GE 2  can be drivingly connected with one another by means of a shiftable coupling device. 
     According to the invention it is provided that this manual transmission is derived from a double clutch transmission having two coaxial input shafts GE 1 , GE 2  in the aforementioned arrangement for the cost-effective manufacture of a manual transmission of this kind. The coupling device thereby comprises a gear step and/or a shiftable clutch, which is provided instead of that gear set and the allocated gear clutch thereof, wherein that gear set is allocated to the first input shaft GE 1  in the underlying double clutch transmission and is disposed axially adjacent to the gear-side end of the second input shaft GE 2 . This means that the respective gear set available in the underlying double clutch transmission and the gear clutch allocated to this transmission are omitted in the manual transmission according to the invention and replaced by the gear step and/or the shifting clutch of the coupling device in a manner that requires no additional installation space in order to connect the two input shafts GE 1 , GE 2 . In this way, a manual transmission of a hybrid drive is created that is largely identical to the underlying double clutch transmission, i.e. it has a large number of parts that are identical thereto, and therefore can be manufactured in a cost-effective manner, for example on the same production line as the double clutch transmission. 
     In order that the gear set that is omitted, as compared with the underlying double clutch transmission, does not lead to functional limitations in the manual transmission or in the respective hybrid drive, the respective gear set disposed in the underlying double clutch transmission, axially adjacent to the gear-side end of the second input shaft GE 2 , should preferably be designed as a reverse gear set R and allocated to the reverse gear. It is possible to omit the gear set of the reverse gear in the manual transmission of the hybrid drive without a problem, since a reverse start or reverse maneuvering is possible by means of a gear set of a forward gear in conjunction with a reverse of rotation by means of the electric machine. If this suitable arrangement of the reverse gear set R is not provided in the underlying double clutch transmission, that arrangement can be created if necessary by a corresponding modification of the axial arrangement of the gear sets allocated to the input shaft, if the spatial conditions allow for this. 
     In the underlying double clutch transmission (as shown in  FIG. 10 ), when the gear sets (G 1 -G 5 , R) are each disposed immediately between one of the two input shafts GE 1 , GE 2  and the output shaft GA, and at least the idler gear as well as the allocated gear clutch C of the gear set R allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end of the second input shaft GE 2 , are disposed on the first input shaft GE 1 , the coupling device can comprise only one shifting clutch S for directly coupling the first input shaft GE 1  with the gear-side end of the second input shaft GE 2 . 
     In the underlying double clutch transmission (as shown in  FIG. 10 ), when the idler gear and the allocated gear clutch D of the axially adjacent gear set G 1  allocated to the first input shaft GE 1  are also disposed on the first input shaft GE 1 , the shifting clutch S of the coupling device is integrated with the gear clutch D of this remaining gear set G 1  in a common shift set S 2   a  in order to simplify the control mechanism, by means of which common shift set S 2   a  the first input shaft GE 1  is connected with the second input shaft GE 2  in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the idler gear of the remaining gear set G 1  in a rotationally fixed manner in a second shift position. 
     In the underlying double clutch transmission (as shown in  FIG. 11 ), when the gear sets (G 1 -G 5 , R) are each disposed immediately between one of the two input shafts GE 1 , GE 2  and the output shaft GA, and at least the idler gears and the allocated gear clutches C, D of the gear sets R, G 1 , both allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end of the second input shaft GE 2 , are disposed on the output shaft GA, the coupling device comprises a gear step GK, which comprises an idler gear rotatably mounted on the output shaft GA and a fixed gear disposed on the gear-side end of the second input shaft GE 2  in a rotationally fixed manner, that coupling device also comprising a shifting clutch T for coupling the idler gear of the remaining gear set G 1  of the two gear sets R, G 1  with the idler gear of the gear step GK. 
     The transmission ratio i GK  of the gear step GK preferably corresponds to the transmission ratio i G1  of the gear set (G 1 ) that can be coupled by means of the shifting clutch T of the coupling device (i GK =i G1 ), since the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is then equal to one (i K =i G1 /i GK =1) when the shifting clutch T is engaged. 
     If, in addition to the aforementioned features, the idler gear and the gear clutch B of the transmission-internal gear set G 4  allocated to the second input shaft GE 2  and disposed on the gear-side end of the second input shaft GE 2  are also disposed on the output shaft GA in the underlying double clutch transmission (as shown in  FIG. 11 ), the coupling device can also alternatively comprise the transmission-internal gear set G 4  and a shifting clutch U for coupling the idler gear of the remaining gear set (G 1 ) of the two gear sets R, G 1  with the idler gear of the transmission-internal gear set G 4 . In this case, the advantage of saving a separate gear step GK counteracts the possible disadvantage of a clutch transmission ratio i K  between the two input shafts GE 1 , GE 2  that is not equal to one (i K ≠1). 
     In the underlying double clutch transmission (as shown in  FIG. 12 ), when the gear sets (G 1 -G 7 , R) are each disposed between one of the two input shafts GE 1 , GE 2  and one of two countershafts VG 1 , VG 2 , each drivingly connected with the output shaft GA by means of an output constant AK 1 , AK 2 , and at least the idler gears and the allocated gear clutches C, D of the gear sets R, G 6 , both allocated to the first input shaft GE 1  and a countershaft (VG 2 ) of both countershafts VG 1 , VG 2  as well as disposed axially adjacent to the gear-side end of the second input shaft GE 2 , are disposed on the respective countershaft VG 2 , the coupling device preferably comprises a gear step GK′, which comprises an idler gear rotatably mounted on the respective countershaft VG 2  and a fixed gear disposed on the gear-side end of the second input shaft GE 2  in a rotationally fixed manner, that coupling device also comprising a shifting clutch V for coupling the idler gear of the remaining gear set (G 6 ) of the two gear sets R, G 6  with the idler gear of the gear step GK′. 
     In this case as well, the transmission ratio i GK ′ of the gear step GK′ preferably corresponds to the transmission ratio i G6  of the gear set (G 6 ) that can be coupled by means of the shifting clutch V of the coupling device (i GK ′=i G6 ), so that the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is equal to one (i K =i G6 /i GK ′=1) when the shifting clutch V is engaged. 
     If, in addition to the aforementioned features, the idler gear and the allocated gear clutch B of the transmission-internal gear set G 7 , allocated to the second input shaft GE 2  and disposed on the gear-side end of the second input shaft GE 2 , are also disposed on the respective countershaft VG 2  in the underlying double clutch transmission (as shown in  FIG. 12 ), the coupling device can alternatively also comprise the transmission-internal gear set G 7  and a shifting clutch W for coupling the idler gear of the remaining gear set (G 6 ) of the two gear sets R, G 6  with the idler gear of the transmission-internal gear set G 7 . In this case as well, the advantage of saving a separate gear step GK′ counteracts the possible disadvantage of a clutch transmission ratio i K  between the two input shafts GE 1 , GE 2  that is not equal to one (i K ≠1). 
     In the aforementioned embodiments of the manual transmission (according to  FIGS. 4 to 7 ), in order to simplify the control mechanism, it is preferably provided that the shifting clutch (T, U; V, W) of the respective coupling device be integrated with the gear clutch D of the remaining gear set (G 1 ; G 6 ) of the two gear sets (R, G 1 ; R, G 6 ) in a common shift set (S 2   b , S 2   c ; S 2   d , S 2   e ), by means of which the idler gear of the remaining gear set (G 1 ; G 6 ) of the two gear sets (R, G 1 ; R, G 6 ) is coupled with the idler gear of the gear step (GK; GK′) or the transmission-internal gear set (G 4 ; G 7 ) in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and coupled with the output shaft GA or with the respective countershaft VG 2  in a rotationally fixed manner in a second shift position. 
     A second solution to the stated objective according to the invention is achieved a manual transmission which is derived from a double clutch transmission having two coaxial input shafts, the first input of which shaft is centrally disposed, the second input shaft of which is formed as a hollow shaft and is disposed coaxially above the first input shaft, and the coupling device comprises a gear step and/or a shiftable clutch, which is provided instead of that gear set and the allocated gear clutch thereof, wherein that gear set is allocated to the second input shaft in the underlying double clutch transmission and is disposed axially adjacent to the gear-side end of the second input shaft. 
     Accordingly, the invention according to the second solution to the stated objective relates to a manual transmission of a hybrid drive for a motor vehicle having two input shafts and a common output shaft, wherein the first input shaft can be connected with the drive shaft of an internal combustion engine and can be drivingly connected with the output shaft by means of a first group of selectively shiftable gearwheel sets, wherein the second input shaft is drivingly connected with the rotor of an electric machine that can be operated as a motor and as a generator and can be drivingly connected with the output shaft by means of a second group of selectively shiftable gearwheel sets, and wherein both input shafts can be drivingly connected with one another by means of a shiftable coupling device. 
     Analogous to the first solution to the stated objective, in order to achieve the inexpensive manufacture of a manual transmission of this kind, it is provided that the manual transmission is derived from a double clutch transmission having two coaxial input shafts, the first input shaft of which is centrally disposed, the second input shaft of which is formed as a hollow shaft and is disposed coaxially above the first input shaft, and the coupling device of which comprises a gear step and/or a shiftable clutch, which is provided instead of that gear set and the allocated gear clutch thereof, wherein that gear set is allocated to the second input shaft in the underlying double clutch transmission and is disposed axially adjacent to the gear-side end of the second input shaft. 
     This manual transmission of a hybrid drive is also largely identical to the underlying double clutch transmission, has a large number of parts that are identical thereto, and therefore can be manufactured in a cost-effective manner, for example on the same production line as the double clutch transmission. 
     In order to avoid functional limitations in the manual transmission or in the respective hybrid drive, the gear set disposed in the underlying double clutch transmission on the gear-side end of the second input shaft and replaced in the manual transmission of the hybrid drive by the coupling device should also preferably be designed as a reverse gear set and allocated to the reverse gear, since it is possible to omit a reverse gear in the manual transmission of the hybrid drive without a problem due to the reversible rotational direction of the electric machine. 
     In accordance with the second solution of the stated objective with the underlying double clutch transmission (as shown in  FIG. 13 ), when the gear sets (G 1 -G 5 , R) are each disposed immediately between one of the two input shafts GE 1 , GE 2  and the output shaft GA, and at least the idler gear and the allocated gear clutch C of the gear set R allocated to the second input shaft GE 2  and disposed on the gear-side end of the second input shaft GE 2  are disposed on the second input shaft GE 2 , the coupling device can comprise only a shifting clutch S for directly coupling the gear-side end of the second input shaft GE 2  with the first input shaft GE 1 . 
     In the underlying double clutch transmission (as shown in  FIG. 13 ), when the idler gear and the allocated gear clutch D of the gear set G 1 , allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end of the second input shaft GE 2 , are disposed on the first input shaft GE 1 , the shifting clutch S of the coupling device is preferably integrated with the gear clutch D of this gear set G 1  in a common shift set S 2   a  in order to simplify the control mechanism, by means of which common shift set S 2   a  the first input shaft GE 1  is coupled with the second input shaft GE 2  in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the idler gear or the respective gear set G 1  in a rotationally fixed manner in a second shift position. 
     In the underlying double clutch transmission (as shown in  FIG. 14 ), when the gear sets (G 1 -G 5 , R) are each disposed immediately between one of the two input shafts GE 1 , GE 2  and the output shaft GA, and at least the idler gears and the allocated gear clutches C, D of the transmission-internal gear set G 1  allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end of the second input shaft GE 2  as well as the gear set R allocated to the second input shaft GE 2  and disposed on the gear-side end of the second input shaft GE 2 , are disposed on the output shaft GA, the coupling device comprises a gear step GK, which comprises an idler gear rotatably mounted on the output shaft GA and a fixed gear disposed on the gear-side end of the second output shaft GE 2  in a rotationally fixed manner, that coupling device also comprising a shifting clutch T for coupling the idler gear of the transmission-internal gear set G 1  with the idler gear of the gear step GK. 
     The transmission ratio i GK  of the gear step GK preferably corresponds to the transmission ratio i G1  of the gear set G 1  that can be coupled by means of the shifting clutch T of the coupling device GK =i G1 ) since the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is then equal to one (i K =i G1 /i GK =1) when the shifting clutch T is engaged. 
     In the underlying double clutch transmission (as shown in  FIG. 14 ), when, in addition to the aforementioned features, the idler gear and the gear clutch B of the gear set G 4  allocated to the second input shaft GE 2  and disposed axially adjacent to the outer-most gear set R on the gear-side end of the second input shaft GE 2  are also disposed on the output shaft GA, the coupling device can alternatively also comprise the remaining gear set (G 4 ) of the gear sets G 4 , R, both allocated to the second input shaft GE 2  and a shifting clutch U for coupling the idler gear of the transmission-internal gear set G 1  with the idler gear of the remaining gear set G 4 . In this case, the advantage of saving a separate gear step GK counteracts the possible disadvantage of a clutch transmission ratio i K  between the two input shafts GE 1 , GE 2  that is not equal to one (i K ≠1). 
     In the two aforementioned embodiments of the manual transmission (according to  FIGS. 6 and 7 ), in order to simplify the control mechanism, it is preferably provided that the shifting clutch (T, U) of the respective coupling device be integrated with the gear clutch D of the transmission-internal gear set G 1  in a common shift set (S 2   b , S 2   c ), by means of which the idler gear of the transmission-internal gear set G 1  is coupled with the idler gear of the gear step GK or of the remaining gear set (G 4 ) of the gear sets G 4 , R, both allocated to the second input shaft GE 2  in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the output shaft GA in a rotationally fixed manner in a second shift position. 
     In the underlying double clutch transmission (as shown in  FIG. 15 ), when the gear sets (G 1 -G 7 , R) are each disposed between one of the two input shafts GE 1 , GE 2  and one of two countershafts VG 1 , VG 2 , each drivingly connected with the output shaft GA by means of an output constant AK 1 , AK 2 , and at least the idler gears and the allocated gear clutches C, D of the gear sets R, G 6 , both allocated to the second input shaft GE 2  and a countershaft (VG 2 ) of both countershafts VG 1 , VG 2  and disposed on the gear-side end of the second input shaft GE 2 , are disposed on the respective countershaft VG 2 , the coupling device preferably comprises a gear step GK*, which comprises an idler gear rotatably mounted on the respective countershaft VG 2  and a fixed gear disposed on the first input shaft GE 1  in a rotationally fixed manner, that coupling device also comprising a shifting clutch X for coupling the idler gear of the remaining gear set (G 6 ) of the gear sets R, G 6  both allocated to the second input shaft GE 2  with the idler gear of the gear step GK*. 
     In this case as well, the transmission ratio i GK * of the gear step GK* preferably corresponds to the transmission ratio i G6  of the gear set G 6  that can be coupled by means of the shifting clutch X of the coupling device (i GK *=i G6 ), so that the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is equal to one (i K =i G6 /i GK *=1) when the shifting clutch X is engaged. 
     In the underlying double clutch transmission (as shown in  FIG. 15 ), when in addition to the aforementioned features, the idler gear and the allocated gear clutch B of the transmission-internal gear set G 7  allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end of the second input shaft GE 2  are also disposed on the respective countershaft VG 2 , the coupling device can alternatively also comprise the transmission-internal gear set G 7  and a shifting clutch Y for coupling the idler gear of the remaining gear set (G 6 ) of the two gear sets R, G 6  with the idler gear of the transmission-internal gear set G 7 . In this case as well, the advantage of saving a separate gear step GK* counteracts the possible disadvantage of a clutch transmission ratio i K  between the two input shafts GE 1 , GE 2  that is not equal to one (i K ≠1). 
     In the two aforementioned embodiments of the manual transmission (according to  FIGS. 8 and 9 ), in order to simplify the control mechanism, it is preferably provided that the shifting clutch (X, Y) of the respective coupling device be integrated with the gear clutch D of the remaining gear set (G 6 ) of the gear sets R, G 6  both allocated to the second input shaft GE 2  in a common shift set (S 2   f , S 2   g ), by means of which the idler gear of the respective gear set G 6  is coupled with the idler gear of the gear step GK* or of the transmission-internal gear set G 7  allocated to the first input shaft GE 1  in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the respective countershaft VG 2  in a rotationally fixed manner in a second shift position. 
     In the aforementioned embodiments of the hybrid drive, the first input shaft can be connected in each case with the drive shaft of the internal combustion engine by means of a friction clutch K 1 . 
     It is also possible, however, that the first input shaft can be connected in each case with the drive shaft of the internal combustion engine by mans of a more robust and more cost-effective dog clutch, since that dog clutch can be synchronized by means of an electric machine when the shifting clutch is engaged. 
     However the first input shaft can also be directly connected with the drive shaft of the internal combustion engine in a rotationally fixed manner and thus the respective separator clutch can be eliminated. Although the gear sets (G 1 , G 3 , G 5 ; G 2 , G 4 , G 6 ) allocated to the first input shaft are hereby unavailable for purely electric vehicle operation, that is, for actuation using only the electric machine, this does not present a substantial functional limitation due to the larger usable speed range of an electric machine as compared to an internal combustion engine. 
     In the aforementioned embodiments of the hybrid drive, the electric machine can be disposed, in each case, coaxially over the first input shaft, and the rotor of the electric machine can be directly connected in a rotationally fixed manner with the second input shaft. 
     In order to be able to use a less powerful and correspondingly more compact and lighter electric machine, it can also be provided that the electric machine is disposed adjacent to the first input shaft and parallel to the axis, and the rotor of the electric machine is drivingly connected with the second input shaft by means of an input transmission stage KE having a transmission ratio i KE  greater than 1 (i KE &gt;1.0). 
     Alternatively, for the same purpose, it may be provided that the electric machine is disposed coaxially over the first input shaft, and the rotor of the electric machine can be drivingly connected with the second input shaft GE 2  by means of an input transmission stage KE′ designed as a planetary gear assembly having a transmission ratio i KE ′ greater than one (i KE ′&gt;1.0). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To illustrate the invention, a drawing having example embodiments follows the description. Shown are: 
         FIG. 1  a hybrid drive of a motor vehicle having a manual transmission, which is derived from a double clutch transmission according to  FIG. 10  or  FIG. 13 , 
         FIG. 2  a first refinement of the hybrid drive according to  FIG. 1 , 
         FIG. 3  a second refinement of the hybrid drive according to  FIG. 1 , 
         FIG. 4  a hybrid drive of a motor vehicle having a first embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 11  or  FIG. 14 , 
         FIG. 5  a hybrid drive of a motor vehicle having a second embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 11  or  FIG. 14 , 
         FIG. 6  a hybrid drive of a motor vehicle having a first embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 12 , 
         FIG. 7  a hybrid drive of a motor vehicle having a second embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 12 , 
         FIG. 8  a hybrid drive of a motor vehicle having a first embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 15 , 
         FIG. 9  a hybrid drive of a motor vehicle having a second embodiment of a manual transmission, which is derived from a double clutch transmission according to  FIG. 15 , 
         FIG. 10  a first double clutch transmission, 
         FIG. 11  a second double clutch transmission, 
         FIG. 12  a third double clutch transmission, 
         FIG. 13  a fourth double clutch transmission, 
         FIG. 14  a fifth double clutch transmission, and 
         FIG. 15  a sixth double clutch transmission. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 10  is a diagram of a known double clutch transmission  1 . 0 , from which a manual transmission  1 . 1  of a hybrid drive  6 . 1 , described below, is derived. The double clutch transmission  1 . 0  has two coaxial input shafts GE 1 , GE 2  and a common output shaft GA. The first input shaft GE 1  is centrally disposed within the second input shaft GE 2 , which is designed as a hollow shaft. Both input shafts GE 1 , GE 2  can be connected on the input side with the drive shaft  4  of an internal combustion engine VM, in each case by means of an allocated friction clutch K 1 , K 2 . On the output side, both input shafts GE 1 , GE 2  can each be drivingly connected with the output shaft GA by means of multiple selectively shiftable gear sets R, G 1 , G 3 , G 5  or G 2 , G 4  respectively. 
     In the present case, the reverse gear set R of the reverse gear and the gear sets G 1 , G 3 , G 5  of the odd forward gears are allocated to the first input shaft GE 1 . The gear sets G 2 , G 4  of the even forward gears are allocated to the second input shaft GE 2 . The idler gears and the gear clutches A, B, C, D, E and F of the gear sets R, G 1 , G 3 , G 5  or G 2 , G 4  respectively are each disposed on the allocated input shaft GE 1 , GE 2 , while the respective fixed gears are each disposed in a rotationally fixed manner on the output shaft GA. The gear clutches A to F are each combined in pairs in a common shift set S 1 , S 2 , S 3 . Thus, the gear clutches A and B of the gear sets G 2 , G 4  of the second and of the fourth forward gear are disposed in a first shift set S 1 , the gear clutches C and D of the reverse gear set R of the reverse gear and of the gear set G 1  of the first forward gear are disposed in a second shift set S 2 , and the gear clutches E and F of the gear sets G 3 , G 5  of the third and of the fifth forward gear are disposed in a third shift set S 3 . 
     For the manual transmission  1 . 1  of a hybrid drives  6 . 1 ,  6 . 2 ,  6 . 3  described below according to  FIGS. 1 to 3 , it is important to note that the reverse gear set R immediately axially adjacent to the gear-side end  5  of the second input shaft GE 2  and the gear set G 1  disposed axially adjacent thereto are allocated to the first input shaft GE 1 , and that the idler gears  9 ,  10  as well as the allocated gear clutches C, D of these gear sets R, G 1  are disposed on the first input shaft GE 1 . 
     Based on the double clutch transmission  1 . 0  according to  FIG. 10 , a manual transmission  1 . 1  of a hybrid drives  6 . 1  according to  FIG. 1  is thereby created such that, instead of the reverse gear set R of the reverse gear and of the allocated gear clutch C, a coupling device  7 . 1  is provided, by means of which the two input shafts GE 1 , GE 2  can be drivingly connected with one another. In the present case, the coupling device  7 . 1  comprises a shifting clutch S, disposed on the first input shaft GE 1  instead of the gear clutch C of the reverse gear, by means of which shifting clutch S, the first input shaft GE 1  can be directly coupled with the gear-side end  5  of the second input shaft GE 2 . The shifting clutch S is integrated with the gear clutch D of the gear set G 1  of the first forward gear in a common shift set S 2   a , by means of which the first input shaft GE 1  is coupled with the gear-side end  5  of the second input shaft GE 2  in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the idler gear  10  of the gear set G 1  of the first forward gear in a rotationally fixed manner in a second shift position. 
     In the hybrid drive  6 . 1  according to  FIG. 1 , the first input shaft GE 1  can be connected with the drive shaft  4  of the internal combustion engine VM on the input side by means of a first friction clutch K 1 . The second input shaft GE 2  is directly connected on the input side in a rotationally fixed manner with the rotor  8  of an electric machine, which can be operated as a motor and as a generator EM, and which is disposed coaxially above the first input shaft GE 1 . The reverse gear set R of the reverse gear present in the underlying double clutch transmission  1 . 0  is omitted entirely in the manual transmission  1 . 1 , which is possible without any problem since a reverse start and reverse-maneuvering are made possible, for example, by means of the gear set G 2  of the second forward gear in conjunction with a reverse in rotation of the electric machine EM. Accordingly, with only minor changes, the manual transmission  1 . 1  of the hybrid drive  6 . 1  according to  FIG. 1  can be derived from the double clutch transmission  1 . 0  according to  FIG. 10  in a manner that does not require additional installation space, and without substantial functional limitations, and can be manufactured in a correspondingly cost-effective manner. 
     The same manual transmission  1 . 1  of the hybrid drive  6 . 1  according to  FIG. 1  can also be derived form a known double clutch transmission  1 . 0 ′ according to  FIG. 13 , which differs from the double clutch transmission  1 . 0  according to  FIG. 10  having the same axial arrangement of the gear sets G 1  to G 5  and R in that the reverse gear set R is allocated to the second input shaft GE 2 . In this double clutch transmission  1 . 0 ′, the reverse gear set R of the reverse gear is disposed on the gear-side end of the second input shaft GE 2 , while the gear set G 1  of the first forward gear continues to be allocated to the first input shaft GE 1  and is now axially adjacent to the gear-side end of the second input shaft GE 2 . Accordingly, the idler gear  9 * and the allocated gear clutch C of the reverse gear set R are disposed on the second input shaft GE 2 , wherein the gear clutch C is a component of a separate shift set S 2   x , which has a shift position, in which the idler gear  9 * is coupled with the second input shaft GE 2 , and a neutral position, in which the idler gear  9 * is decoupled. The idler gear  10  and the allocated gear clutch D of the gear set G 1  of the first forward gear are disposed on the first input shaft GE 1 , as in the case of the double clutch transmission  1 . 0  according to  FIG. 10 . The gear clutch D is now a component of a separate shift set S 2   y , however, which has a shift position, in which the idler gear  10  is coupled with the first input shaft GE 1 , and a neutral position, in which the idler gear  10  is decoupled. 
     By way of example, the refinements of the hybrid drive  6 . 1  according to  FIG. 1  shown in  FIG. 2  and  FIG. 3  have design features, which can be used in any combination and independent of one another in conjunction with all of the manual transmissions  1 . 1 ;  2 . 1 ,  2 . 2 ;  3 . 1 ,  3 . 2 ,  3 . 3 ,  3 . 4  described above, as well as with similarly designed manual transmissions. 
     In the embodiment of the hybrid drive  6 . 2  according to  FIG. 2 , the first input shaft GE 1  can be connected on the input side with the drive shaft  4  of the internal combustion engine VM by means of an unsynchronized dog clutch K 1 ′. A dog clutch K 1 ′ design is more cost-effective than a friction clutch K 1  and therefore possible, because this dog clutch can be synchronized by means of the electric machine EM′ when the shifting clutch S is engaged. As also illustrated by way of example in  FIG. 2 , the electric machine EM′ can also be disposed adjacent to the first input shaft GE 1  and parallel to the axis, and the rotor  8 ′ of the electric machine EM′ can be drivingly connected with the second input shaft GE 2  by means of an existing input transmission stage KE designed as a spur gear pair, which advantageously has a transmission ratio i KE  greater than one (i KE &gt;1.0). This allows for the electric machine EM′ to be designed to be less powerful, and therefore correspondingly more compact and lighter. 
     In the embodiment of the hybrid drive  6 . 3  according to  FIG. 3 , the first input shaft GE 1  is directly connected on the input side, that is, without a separator clutch K 1 , K 1 ′, with the drive shaft  4  of the internal combustion engine VM in a rotationally fixed manner, which embodies a further simplification and cost savings. The gear sets G 1 , G 3 , G 5  allocated to the first input shaft GE 1  are made unavailable thereby for purely electric vehicle operation, that is, for actuation using only the electric machine EM″. This does not present a substantial functional limitation due to the larger available speed range of an electric machine EM″ as compared to an internal combustion engine VM. As also shown by way of example in  FIG. 3 , the electric machine EM″ can also be disposed coaxially over the first input shaft GE 1 . In addition, the rotor  8 ″ of the electric machine EM″ can be drivingly connected with the second input shaft GE 2  by means of an input transmission stage KE′ designed as a planetary gear assembly, which advantageously has a transmission ratio i KE ′ greater than one (i KE ′&gt;1.0). In this case as well, the electric machine EM″ can be designed to be less powerful and accordingly, more compact as well as lighter. 
       FIG. 11  shows a diagram of a known double clutch transmission  2 . 0  from which the two embodiments of a manual transmission  2 . 1 ,  2 . 2  of a hybrid drives  6 . 4 ,  6 . 5  described below are derived. The double clutch transmission  2 . 0  is largely identical in design to the double clutch transmission  1 . 0  according to  FIG. 10 . The essential difference is in the fact that the idler gears and the gear clutches A, B, C, D of the gear sets G 2 , G 4  and R, G 1  are now each disposed on the output shaft GA, and the respective fixed gears are each disposed in a rotationally fixed manner on the allocated input shaft GE 2  or GE 1  respectively. Accordingly, the two shift sets S 1 , S 2 , in which the gear clutches A, B of the gear sets G 2 , G 4  of the second forward gear and of the fourth forward gear as well as the gear clutches C, D of the reverse gear set R of the reverse gear and of the gear set G 1  of the first forward gear are combined, are now disposed on the output shaft GA. 
     For the embodiments of a manual transmission  2 . 1 ,  2 . 2  of a hybrid drives  6 . 4 ,  6 . 5  according to  FIGS. 4 and 5  described below, it is important to note that the reverse gear set R, disposed immediately axially adjacent to the gear-side end  5  of the second input shaft GE 2  and the axial gear set G 1  disposed axially adjacent thereto, are allocated to the first input shaft GE 1 , and that the idler gears  9 ′,  10 ′ as well as the allocated gear clutches C, D of these gear sets R, G 1  are disposed on the output shaft GA. 
     For the second embodiment of the manual transmission  2 . 2  according to  FIG. 5 , it is also important that the idler gear  13  and the allocated gear clutch B of the gear set G 4  allocated to the second input shaft GE 2  and disposed axially adjacent to the gear-side end  5  thereof are likewise disposed on the output shaft GA. 
     Based on the double clutch transmission  2 . 0  according to  FIG. 11 , a first embodiment of a manual transmission  2 . 1  of a hybrid drives  6 . 4  according to  FIG. 4  is created such that, instead of the reverse gear set R of the reverse gear and of the allocated gear clutch C, a coupling device  7 . 2  is provided by means of which the two input shafts GE 1 , GE 2  can be drivingly connected with one another. The coupling device  7 . 2  comprises a gear step GK having an idler gear  11  rotatably mounted on the output shaft GA and a fixed gear  12  disposed on the gear-side end  5  of the second input shaft GE 2  in a rotationally fixed manner, and comprises a shifting clutch T, said gear step GK and shifting clutch T being disposed in the manual transmission  2 . 1  instead of the reverse gear set R as well as the allocated gear clutch C of the reverse gear of the underlying double clutch transmission  2 . 0  ( FIG. 11 ). 
     The shifting clutch T of the gear step GK is integrated with the gear clutch D of the gear set G 1  of the first forward gear in a common shift set S 2   b , by means of which the idler gear  10 ′ of the gear set G 1  of the first forward gear is coupled with the idler gear  11  of the gear step GK in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the output shaft GA in a rotationally fixed manner in a second shift position. 
     The effective transmission ratio i GK  of the gear step GK between the output shaft GA and the second input shaft GE 2  preferably corresponds to the transmission ratio i G1  of the gear set G 1  of the first forward gear (i GK =i G1 ), since the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is then equal to one (i K =i G1 /i GK =1) when the shifting clutch T is engaged. 
     A second embodiment of the manual transmission  2 . 2  of a hybrid drives  6 . 5  according to  FIG. 5 , derived from the double clutch transmission  2 . 0  according to  FIG. 11 , is largely identical to the manual transmission  2 . 1  according to  FIG. 4 . The essential difference is in the fact that the coupling device  7 . 3  now comprises the axially adjacent gear set G 4  of the forward gear allocated to the second input shaft GE 2  and a shifting clutch U, that is, instead of a separate gear step GK, the gear set G 4  of the fourth forward gear is also used to couple the two input shafts GE 1 , GE 2 . 
     The shifting clutch U is thereby integrated with the gear clutch D of the gear set G 1  of the first forward gear in a common shift set S 2   c , by means of which the idler gear  10 ′ of the gear set G 1  of the first forward gear is coupled with the idler gear  13  of the gear set G 4  of the fourth forward gear in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the output shaft GA in a rotationally fixed manner in a second shift position. In this case, the advantage of saving a separate gear step GK counteracts the possible disadvantage of a clutch transmission ratio i K  that is not equal to one (i K ≠1). The effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  when the shifting clutch U is engaged is obtained with the equation i K =i G1 /i G4 &gt;1 in the present embodiment of the manual transmission  2 . 2 . 
     The manual transmissions  2 . 1 ,  2 . 2  of the hybrid drives  6 . 4 ,  6 . 5  according to  FIGS. 4 and 5  are each also derived from the double clutch transmission  2 . 0  according to  FIG. 11  with minor changes in a manner that requires no additional installation space and without substantial functional limitations, and can be manufactured in a correspondingly cost-effective manner. 
     The manual transmission  2 . 1  of the hybrid drive  6 . 4  according to  FIG. 4  and the manual transmission  2 . 2  of the hybrid drive  6 . 5  according to  FIG. 5  can also be derived from a known double clutch transmission  2 . 0 ′ according to  FIG. 14 , which differs from the double clutch transmission  2 . 0  according to  FIG. 11  having the same axial arrangement of the gear sets G 1 -G 5 , R in the allocation of the reverse gear set R to the second input shaft GE 2 . In this double clutch transmission  2 . 0 ′, the reverse gear set R of the reverse gear is disposed on the gear-side end  5  of the second input shaft GE 2 , while the gear set G 1  of the first forward gear continues to be allocated to the first input shaft GE 1  and is now axially adjacent to the gear-side end of the second input shaft GE 2 . The idler gears  9 ′,  10 ′ and the gear clutches C, D of the reverse gear set R as well as of the gear set G 1  of the first forward gear continue to be disposed on the output shaft GA, and the aforementioned gear clutches C, D are likewise combined in a common shift set S 2 . 
       FIG. 12  shows a diagram of a known double clutch transmission  3 . 0  from which the two embodiments of a manual transmission  3 . 1 ,  3 . 2  of a hybrid drives  6 . 6 ,  6 . 7  described below are derived. The double clutch transmission  3 . 0  has two coaxial input shafts GE 1 , GE 2  and a common output shaft GA. The first input shaft GE 1  is centrally disposed within the second input shaft GE 2 , which is designed as a hollow shaft. Both input shafts GE 1 , GE 2  can be connected on the input side with the drive shaft  4  of an internal combustion engine VM in each case by means of an allocated friction clutch K 1 , K 2 . On the output side, both input shafts GE 1 , GE 2  can each be drivingly connected with a first countershaft VG 1  and a second countershaft VG 2  by means of multiple selectively shiftable gear sets R, G 2 , G 4 , G 6  or G 1 , G 3 , G 5 , G 7  respectively, said countershafts being drivingly connected with the output shaft GA in each case by means of an output constant AK 1 , AK 2 . 
     In the present case, the reverse gear set R of the reverse gear and the gear sets G 2 , G 4 , G 6  of the even numbered forward gears are allocated to the first input shaft GE 1 , said gear sets being disposed in a common radial plane each using a common fixed gear. The reverse gear set R of the reverse gear comprises an idler gear  14  disposed on the second countershaft VG 2  and the gear set G 2  of the second forward gear disposed in the same radial plane between the first input shaft GE 1  and the first countershaft VG 1 . The gear sets G 1 , G 3 , G 5 , G 7  of the odd numbered forward gears are allocated to the second input shaft GE 2 , said gear sets being disposed in pairs in a common radial plane and each using a common fixed gear. 
     The idler gears and the gear clutches A to H of the gear sets R, G 2 , G 4 , G 6  or G 1 , G 3 , G 5 , G 7  respectively are each disposed on one of the two countershafts VG 1 , VG 2 , while the respective fixed gears are each disposed in a rotationally fixed manner in each case on the allocated input shaft GE 1 , GE 2 . The gear clutches A to H are each combined in pairs in a common shift set S 1 , S 2 , S 3 , S 4 . Thus the gear clutches A, B of the gear sets G 3 , G 7  of the third and of the seventh forward gear are disposed in a first shift set S 1 , the gear clutches C, D of the reverse gear set R of the reverse gear and of the gear set G 6  of the sixth forward gear are disposed in a second shift set S 2 , the gear clutches E, F of the gear sets G 1 , G 5  of the first and of the fifth forward gear are disposed in a third shift set S 3 , and the gear clutches G, H of the gear sets G 2 , G 4  of the second and of the fourth forward gear are disposed in a fourth shift set S 4 . 
     For the embodiments of a manual transmission  3 . 1 ,  3 . 2  of a hybrid drives  6 . 6 ,  6 . 7  according to  FIGS. 6 and 7  described below, it is important to note that the reverse gear set R disposed immediately axially adjacent to the gear-side end  5  of the second input shaft GE 2  and the axial gear set G 6  disposed axially adjacent thereto are allocated to the first input shaft GE 1 , and that the idler gears  14 ,  15  as well as the allocated gear clutches C, D of these gear sets R, G 6  are disposed on the second countershaft VG 2 . For the second embodiment of the manual transmission  3 . 2  according to  FIG. 7 , it is also important that the idler gear  18  and the allocated gear clutch B of the gear set G 7  allocated to the second input shaft GE 2  and disposed on the gear-side end  5  thereof are likewise disposed on the second countershaft VG 2 . 
     Based on the double clutch transmission  3 . 0  according to  FIG. 12 , a first embodiment of a manual transmission  3 . 1  of a hybrid drives  6 . 6  according to  FIG. 6  is thereby created such that, instead of the reverse gear set R of the reverse gear and the allocated gear clutch C, a coupling device  7 . 4  is provided, by means of which the two input shafts GE 1 , GE 2  can be drivingly connected with one another. The coupling device  7 . 4  according to  FIG. 6  comprises a gear step GK′ with an idler gear  16  rotatably mounted on the second countershaft VG 2  and with a fixed gear  17  disposed on the gear-side end  5  of the second input shaft GE 2  in a rotationally fixed manner, and with a shifting clutch V, which is disposed in the manual transmission  3 . 1  instead of the reverse gear set R and the allocated gear clutch C of the reverse gear of the underlying double clutch transmission  3 . 0  ( FIG. 12 ). 
     The shifting clutch V of the gear step GK′ is integrated with the gear clutch D of the gear set G 6  of the sixth forward gear in a common shift set S 2   d , by means of which the idler gear  15  of the gear set G 6  of the sixth forward gear is coupled with the idler gear  16  of the gear step GK′ in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the second countershaft VG 2  in a rotationally fixed manner in a second shift position. 
     The effective transmission ratio i GK ′ of the gear step GK′ between the second countershaft VG 2  and the second input shaft GE 2  preferably corresponds to the transmission ratio i G6  of the gear set G 6  of the sixth forward gear (i GK ′=i G6 ), since the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is then equal to one (i K =i G6 /i GK ′=1) when the shifting clutch V is engaged. 
     A second embodiment of the manual transmission  3 . 2  of a hybrid drives  6 . 7  according to  FIG. 7 , derived from the double clutch transmission  3 . 0  according to  FIG. 12 , is largely identical to the manual transmission  3 . 1  according to  FIG. 6 . The essential difference is in the fact that the coupling device  7 . 5  now comprises the axially adjacent gear set G 7  of the seventh forward gear allocated to the second input shaft GE 2  and a shifting clutch W, that is, that instead of a separate gear step GK′, the gear set G 7  of the seventh forward gear is also used to couple the input shafts GE 1 , GE 2 . 
     The shifting clutch W is integrated with the gear clutch D of the gear set G 6  of the sixth forward gear in a common shift set S 2   e , by means of which the idler gear  15  of the gear set G 6  of the sixth forward gear is coupled with the idler gear  18  of the gear set G 7  of the seventh forward gear in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the second countershaft VG 2  in a rotationally fixed manner in a second shift position. The advantage of eliminating a separate gear step GK′ counteracts the possible disadvantage of a clutch transmission ratio i K  that is not equal to one (i K ≠1). The effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  when the shifting clutch W is engaged is obtained with the equation i K =i G6 /i G7 &gt;1 in the present embodiment of the manual transmission  3 . 2 . 
     The manual transmissions  3 . 1 ,  3 . 2  of the hybrid drives  6 . 6 ,  6 . 7  according to  FIGS. 6 and 7 , which are also designed according to the basic principle of the invention, are also each derived from double clutch transmission  3 . 0  according to  FIG. 12  with minimal changes in a manner that does not require additional installation space and without substantial functional limitations, and can be manufactured in a cost-effective manner. 
     In a similar manner to that with the double clutch transmission  3 . 0  according to  FIG. 12 , two embodiments of a manual transmission  3 . 3 ,  3 . 4  of a hybrid drives  6 . 8 ,  6 . 9  described below can be derived from the known double clutch transmission  3 . 0 ′ according to  FIG. 15 . The double clutch transmission  3 . 0 ′ according to  FIG. 15  is largely identical in design to the double clutch transmission  3 . 0  according to  FIG. 12 . It differs therefrom however in an axial arrangement of the gear sets G 1  to G 7  and R. Accordingly, the gear sets G 1 , G 3 , G 5 , G 7  of the odd numbered forward gears are now allocated to the first input shaft GE 1 , and the gear sets G 2 , G 4 , G 6 , R of the even numbered forward gears as well as of the reverse gear are allocated to the second input shaft GE 2 . 
     For the embodiments of a manual transmission  3 . 3 ,  3 . 4  of a hybrid drives  6 . 8 ,  6 . 9  according to  FIGS. 8 and 9  described below, it is important to note that the reverse gear set R, disposed immediately adjacent to the gear-side end  5  of the second input shaft GE 2 , and the gear set G 6  of the sixth forward gear, disposed axially adjacent thereto, are allocated to the second input shaft GE 2 , and that the idler gears  14 ,  15 , as well as the allocated gear clutches C, D of these gear sets R, G 6 , are disposed on the second countershaft VG 2 . 
     For the second embodiment of the manual transmission  3 . 4  according to  FIG. 9 , it is also important that the idler gear  18  and the allocated gear clutch B of the gear set G 7  of the seventh forward gear allocated to the first input shaft GE 1  and disposed axially adjacent to the gear-side end  5  of the second input shaft GE 2  are likewise disposed on the second countershaft VG 2 . 
     Based on the double clutch transmission  3 . 0 ′ according to  FIG. 15 , a first embodiment of a manual transmission  3 . 3  of a hybrid drives  6 . 8  according to  FIG. 8  is thereby created in accordance with the principle of the invention, such that, instead of the reverse gear set R of the reverse gear and the allocated gear clutch C, a coupling device  7 . 6  is provided, by means of which the two input shafts GE 1 , GE 2  can be drivingly connected with one another. The coupling device  7 . 6  comprises a gear step GK* with an idler gear  16 ′ rotatably mounted on the second countershaft VG 2  and with a fixed gear  17 ′ disposed on the first input shaft GE 1  axially adjacent to the gear-side end  5  of the second input shaft GE 2  in a rotationally fixed manner, and also comprises a shifting clutch X, said gear step GK* shifting clutch X being disposed in the manual transmission  3 . 3 , instead of the reverse gear set R and the allocated gear clutch C of the reverse gear of the underlying double clutch transmission  3 . 0 ′. 
     The shifting clutch X of the gear step GK* is integrated with the gear clutch D of the gear set G 6  of the sixth forward gear in a common shift set S 2   f , by means of which the idler gear  15  of the gear set G 6  of the sixth forward gear is coupled with the idler gear  16 ′ of the gear step GK* in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is connected with the second countershaft VG 2  in a rotationally fixed manner in a second shift position. 
     The effective transmission ratio i GK * of the gear step GK* between the second countershaft VG 2  and the second input shaft GE 2  preferably corresponds to the transmission ratio i G6  of the gear set G 6  of the sixth forward gear (i GK *=i G6 ), since the effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  is then equal to one (i K =i G6 /i GK *=1) when the shifting clutch X is engaged. 
     A second embodiment of the manual transmission  3 . 4  of a hybrid drives  6 . 9  according to  FIG. 9  derived from the double clutch transmission  3 . 0 ′ according to  FIG. 15  is largely identical to the manual transmission  3 . 3  according to  FIG. 8 . The essential difference is in the fact that the coupling device  7 . 7  now comprises the gear set G 7  of the seventh forward gear axially adjacent to the gear-side end  5  of the second input shaft GE 2  allocated to the first input shaft GE 1 , and a shifting clutch Y, that is, instead of a separate gear step GK*, the gear set G 7  of the seventh forward gear is also used to couple the two input shafts GE 1 , GE 2 . 
     The shifting clutch Y is integrated with the gear clutch D of the gear set G 6  of the sixth forward gear in a common shift set S 2   g , by means of which the idler gear  15  of the gear set G 6  of the sixth forward gear is coupled with the idler gear  18  of the gear set G 7  of the seventh forward gear in a rotationally fixed manner in a first shift position, is decoupled in a neutral position, and is coupled with the second countershaft VG 2  in a rotationally fixed manner in a second shift position. 
     The advantage of saving a separate gear step GK* counteracts the possible disadvantage of a clutch transmission ratio i K  that is not equal to one (i K ≠1). The effective clutch transmission ratio i K  between the first input shaft GE 1  and the second input shaft GE 2  when the shifting clutch Y is engaged is obtained with the equation i K =i G7 /i G6 &lt;1 in the present embodiment of the manual transmission  3 . 4 . 
     The manual transmissions  3 . 3 ,  3 . 4  of the hybrid drives  6 . 8 ,  6 . 9  according to  FIGS. 8 and 9  are also each derived from the double clutch transmission  3 . 0 ′ according to  FIG. 15  with minor changes in a manner that requires no additional installation space and without substantial functional limitations, and can be manufactured in a correspondingly cost-effective manner. 
     REFERENCE CHARACTERS 
     
         
           1 . 0  double clutch transmission 
           1 . 0 ′ double clutch transmission 
           1 . 1  manual transmission 
           2 . 0  double clutch transmission 
           2 . 0 ′ double clutch transmission 
           2 . 1  manual transmission 
           2 . 2  manual transmission 
           3 . 0  double clutch transmission 
           3 . 0 ′ double clutch transmission 
           3 . 1  manual transmission 
           3 . 2  manual transmission 
           3 . 3  manual transmission 
           3 . 4  manual transmission 
           4  drive shaft of a VM (internal combustion engine) 
           5  gear-side end of GE 2   
           6 . 1  hybrid drive 
           6 . 2  hybrid drive 
           6 . 3  hybrid drive 
           6 . 4  hybrid drive 
           6 . 5  hybrid drive 
           6 . 6  hybrid drive 
           6 . 7  hybrid drive 
           6 . 8  hybrid drive 
           6 . 9  hybrid drive 
           7 . 1  coupling device 
           7 . 2  coupling device 
           7 . 3  coupling device 
           7 . 4  coupling device 
           7 . 5  coupling device 
           7 . 6  coupling device 
           7 . 7  coupling device 
           8  rotor of an EM (electric machine) 
           8 ′ rotor of an EM′ (electric machine) 
           8 ″ rotor of an EM″ (electric machine) 
           9 ,  9 ′,  9 * idler gear of R 
           10 ,  10 ′ idler gear of G 1   
           11  idler gear of GK 
           12  fixed gear of GK 
           13  idler gear of G 4   
           14  idler gear of R 
           15  idler gear of G 6   
           16  idler gear of GK′ 
           16 ′ idler gear of GK* 
           17  fixed gear of GK′ 
           17 ′ fixed gear of GK* 
           18  idler gear of G 
         A gear clutch of G 2  and G 3   
         AK 1  first output constant 
         AK 2  second output constant 
         B gear clutch of G 4  and G 7   
         C gear clutch of R 
         D gear clutch of G 1  and G 6   
         E gear clutch of G 3  and G 1   
         EM electric machine 
         EM′ electric machine 
         EM″ electric machine 
         F gear clutch of G 5  and G 5   
         G gear clutch of G 2   
         G 1 -G 7  gear sets of the forward gears 
         GA output shaft 
         GE 1  first input shaft 
         GE 2  second input shaft 
         GK gear step 
         GK′ gear step 
         GK* gear step 
         H gear clutch of G 4   
         i G1  transmission ratio of G 1   
         i G4  transmission ratio of G 4   
         i G6  transmission ratio of G 6   
         i G7  transmission ratio of G 7   
         i GK  transmission ratio of GK 
         i GK ′ transmission ratio of GK′ 
         i GK * transmission ratio of GK* 
         i K  clutch transmission ratio 
         i KE  transmission ratio of KE 
         i KE ′ transmission ratio of KE′ 
         K 1  first friction clutch, separator clutch 
         K 1 ′ dog clutch, separator clutch 
         K 2  second friction clutch 
         KE input transmission stage 
         KE′ input transmission stage 
         R reverse gear set of the reverse gear 
         S shifting clutch 
         S 1 -S 4  shift sets 
         S 2   a  shift set 
         S 2   b  shift set 
         S 2   c  shift set 
         S 2   d  shift set 
         S 2   e  shift set 
         S 2   f  shift set 
         S 2   g  shift set 
         S 2   x  shift set 
         S 2   y  shift set 
         T shifting clutch 
         U shifting clutch 
         V shifting clutch 
         VG 1  first countershaft 
         VG 2  second countershaft 
         VM internal combustion engine 
         W shifting clutch 
         X shifting clutch 
         Y shifting clutch