Patent Publication Number: US-11396929-B2

Title: Transmission for a motor vehicle, motor vehicle powertrain, and method for operating a transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is related and has right of priority to German Patent Application No. 102018215226.8 filed in the German Patent Office on Sep. 7, 2018 and is a nationalization of PCT/EP2019/071039 filed in the European Patent Office on Aug. 5, 2019, both of which are incorporated by reference in their entirety for all purposes. 
     FIELD OF THE INVENTION 
     The invention relates generally to a transmission for a motor vehicle, including an electric machine, a first input shaft, a second input shaft, an output shaft, and a first planetary gear set, a second planetary gear set, and a third planetary gear set. The planetary gear sets each include multiple elements, wherein a first shift element, a second shift element, a third shift element, a fourth shift element, a fifth shift element, and a sixth shift element are provided. A rotor of the electric machine is connected to the second input shaft. Moreover, the invention relates generally to a motor vehicle drive train, in which the transmission is utilized, and to a method for operating the transmission. 
     BACKGROUND 
     In hybrid vehicles, transmissions are known which also include, in addition to a gear set, one or multiple electric machine(s). In this case, the transmission is usually configured to be multi-stage, i.e., multiple different transmission ratios are selectable, as gears, between an input shaft and an output shaft by actuating appropriate shift elements, wherein this is preferably automatically carried out. Depending on the arrangement of the shift elements, the shift elements are clutches or brakes. The transmission is utilized in this case for suitably implementing an available tractive force of a prime mover of the motor vehicle with respect to various criteria. In this case, the gears of the transmission are mostly also utilized in interaction with the at least one electric machine for implementing purely electric driving. Frequently, the at least one electric machine can also be integrated in the transmission in order to implement various operating modes in different ways. 
     DE 10 2014 218 610 A1 describes a transmission fora hybrid vehicle, which includes, in addition to a first input shaft and an output shaft, three planetary gear sets and an electric machine. Moreover, in one variant, six shift elements are provided, via which different power paths are achieved from the first input shaft to the output shaft while implementing different gears and, in addition, different integrations of the electric machine can be configured. Here, purely electric driving can also be implemented simply by transmitting power via the electric machine. 
     SUMMARY OF THE INVENTION 
     Example aspects of the present invention provide a transmission for a motor vehicle, with which, with a compact design, different operating modes can be implemented in a suitable way. 
     According to example aspects of the invention, a transmission includes an electric machine, a first input shaft, a second input shaft, an output shaft, as well as a first planetary gear set and a second planetary gear set. The planetary gear sets include multiple elements, wherein, preferably, a first element, a second element, and a third element are associated with each of the planetary gear sets. In addition, a first shift element, a second shift element, a third shift element, a fourth shift element, and a fifth shift element are provided, via the selective actuation of which different power paths can be implemented while shifting different gears. It is particularly preferred when, from the ratio, at least three different gears can be formed between the first input shaft and the output shaft that differ in terms of ratio, wherein a rotor of the electric machine is connected to the second input shaft. 
     Within the meaning of the invention, a “shaft” is understood to be a rotatable component of the transmission, via which associated components of the transmission are rotationally fixed to each other or via which a connection of this type is established upon actuation of an appropriate shift element. The particular shaft can connect the components to each other axially or radially or also both axially and radially. The particular shaft can also be present as an intermediate piece, via which a particular component is connected, for example, radially. 
     Within the meaning of the invention, “axially” means an orientation in the direction of a longitudinal central axis, along which the planetary gear sets are arranged coaxially to one another. “Radially” is then understood to mean an orientation in the direction of the diameter of a shaft that lies on this longitudinal central axis. 
     Preferably, the output shaft of the transmission includes a tooth system, via which the output shaft is then operatively connected, in the motor vehicle drive train, to a differential gear arranged axially parallel to the output shaft. In this case, the tooth system is preferably provided at a mounting interface of the output shaft, wherein this mounting interface of the output shaft is preferably situated axially in the area of an end of the transmission, at which a mounting interface of the first input shaft is also provided, the mounting interface establishing the connection to the upstream prime mover. This type of arrangement is particularly suitable for the application in a motor vehicle with a drive train aligned transversely to the direction of travel of the motor vehicle. 
     Alternatively, an output of the transmission can also be provided, in principle, at an axial end of the transmission situated opposite to a mounting interface of the first input shaft. In this case, a mounting interface of the output shaft is then designed at an axial end of the output shaft coaxially to a mounting interface of the first input shaft, so that the input and the output of the transmission are located at opposite axial ends of the transmission. A transmission configured in this way is suitable for the application in a motor vehicle with a drive train aligned in the direction of travel of the motor vehicle. 
     The planetary gear sets are preferably arranged in the sequence first planetary gear set, second planetary gear set, and, finally, third planetary gear set axially following the mounting interface of the first input shaft. In example aspects, an alternative arrangement of the planetary gear sets can also be implemented in the axial direction, provided the connection of the elements of the planetary gear sets allows this. 
     Advantageously, the output shaft is rotationally fixed to the second element of the second planetary gear set and rotationally fixed to the third element of the first planetary gear set and is rotationally fixable to the first input shaft by the first shift element. 
     In addition, a second element of the first planetary gear set is rotationally fixed to a third element of the second planetary gear set. In addition, the first input shaft is rotationally fixable by the second shift element to the second element of the first planetary gear set and to the third element of the second planetary gear set. In addition, the first element of the second planetary gear set is fixable at a rotationally fixed component by the third shift element. 
     The first element of the first planetary gear set is fixable at the rotationally fixed component by the fourth shift element. The second input shaft can be rotationally fixed to the second element of the first planetary gear set by the fifth shift element and rotationally fixed to the first element of the first planetary gear set by the sixth shift element. 
     The first, second, fifth, and sixth shift elements are preferably clutches, which, upon actuation, each synchronize, if necessary, the particular components of the transmission joined directly to the clutches, with respect to turning motions of the particular components and, thereafter, connect the components to each other in a rotationally fixed manner. 
     The third shift element and the fourth shift element can be, in particular, brakes, which, upon actuation, fix the first element of the first planetary gear set or of the second planetary gear set, respectively, and, consequently, prevents a turning motion thereof. 
     A particular rotationally fixed connection of the rotatable components of the transmission is preferably implemented, according to example aspects of the invention, via one or also multiple intermediate shaft(s), which can also be present, in this case, as short intermediate pieces when the components are positioned in a spatially dense manner. Specifically, the components that are permanently rotationally fixed to each other can each be present either as individual components that are rotationally fixed to each other, or also as single pieces. In the second case mentioned above, the particular components and the optionally present shaft are then formed by one common component, wherein this is implemented, in particular, for the case in which the particular components are situated spatially close to one another in the transmission. 
     In the case of components of the transmission that are rotationally fixed to each other only upon actuation of a particular shift element, a connection is also preferably implemented via one or also multiple intermediate shaft(s). 
     A fixation takes place, in particular, by way of a rotationally fixed connection to a rotationally fixed component of the transmission, which is preferably a permanently non-rotating component, preferably a housing of the transmission, a part of such a housing, or a component rotationally fixed thereto. 
     Within the meaning of the invention, the “connection” of the rotor of the electric machine to the second input shaft of the transmission is to be understood as a connection of such a type that a constant rotational-speed dependence prevails between the rotor of the electric machine and the second input shaft. 
     Overall, a transmission according to example aspects of the invention is distinguished by a compact design, low component loads, good gearing efficiency, and low losses. 
     According to one example embodiment of the invention, selective engagement of the six shift elements results in three gears between the first input shaft and the output shaft that differ in terms of ratio. A first gear can be implemented between the first input shaft and the output shaft by actuating the second shift element and the third shift element, in which travel takes place with the simultaneous integration of a prime mover joined at the first input shaft, as well as the electric machine. Moreover, a first variant of a second gear that is effective between the first input shaft and the output shaft results by engaging the first shift element and the third shift element. In the process, travel is also implemented in each case with the simultaneous integration of the upstream prime mover as well as the electric machine. In addition, the second gear in a second variant can be implemented by actuating the first and fourth shift elements and in a third variant by actuating the first and second shift elements. 
     In addition, a third gear can be engaged between the first input shaft and the output shaft by engaging the second shift element and the fourth shift element. Additionally, the fifth or the sixth shift element is actuated in all gears. 
     If neither the fifth shift element nor the sixth shift element is actuated in the aforementioned shift conditions, travel can take place via the upstream prime mover. The electric machine can also be decoupled in this case. As a result, zero-load losses of the electric machine can be avoided. However, a shift into the first three variants of the second gear has the advantage that the electric machine is also integrated and, as a result, hybrid driving can take place. 
     Given a suitable selection of stationary transmission ratios of the planetary gear sets, a transmission ratio range which is suitable for the application in a motor vehicle is implemented as a result. In this case, gear shifts between the gears are implementable, in which only the condition of two shift elements (since the fifth or the sixth shift element always remains engaged in the hybrid mode), in each case, is always to be varied, in that one of the shift elements contributing to the preceding gear is to be disengaged and another shift element is to be engaged in order to implement the subsequent gear. As a further consequence thereof, a shift between the gears can take place very rapidly. 
     Due to the connection of the electric machine to the second input shaft of the transmission, different operating modes can also be achieved in a simple way: 
     A first gear between the second input shaft and the output shaft can be utilized for purely electric driving, wherein this first gear results by engaging the third shift element and the sixth shift element. The ratio of the first gear is shorter or less than the first internal-combustion-engine gear. 
     In addition, a second gear can be implemented between the second input shaft and the output shaft for purely electric driving. The third shift element and the fifth shift element are to be actuated in order to engage this second gear. A ratio of this second gear, which is effective between the second input shaft and the output shaft, corresponds to a ratio of the first gear between the first input shaft and the output shaft. 
     In addition, a third gear can be implemented between the second input shaft and the output shaft for purely electric driving. The fourth shift element and the fifth shift element are to be actuated in order to engage this second gear. A ratio of this third gear, which is effective between the second input shaft and the output shaft, corresponds to a ratio of the second gear between the first input shaft and the output shaft. 
     Starting from purely electric driving in the first gear, which is effective between the second input shaft and the output shaft, the upstream prime mover can then be started into the first gear, which is effective between the first input shaft and the output shaft. In addition, starting from the first electric gear or e-gear, a start can take place into the first variant of the second gear. The third shift element and the sixth shift element are engaged in each of the two gears. 
     Likewise, a start of the upstream prime mover into the first gear and into the second variant of the second gear, which is effective between the first input shaft and the output shaft, can also take place from the second gear, which is effective between the second input shaft and the output shaft, since the third shift element and the fifth shift element are engaged. 
     Likewise, a start of the upstream prime mover into the second variant and into the third gear, which is effective between the first input shaft and the output shaft, can also take place from the third gear, which is effective between the second input shaft and the output shaft, since the fourth shift element and the fifth shift element are engaged. 
     As a further operating mode, a charging operation of an electric accumulator can also be implemented, in that the second shift element and the fifth shift element are engaged and, therefore, a rotationally fixed connection between the first input shaft and the second input shaft and, therefore, also a coupling with the electric machine are established. At the same time, a force-fit connection to the output shaft is not established, and therefore the transmission is in a neutral position. Apart from a charging operation, a start of the upstream prime mover via the electric machine can also be implemented as a result. 
     Moreover, powershifts with tractive force support can be implemented: during the gearchange between the first gear, which is effective between the first input shaft and the output shaft, and the first variant of the second gear, which is effective between the first input shaft and the output shaft, the tractive force with the third shift element engaged and with the fifth or sixth shift element engaged can be supported via the electric machine, wherein the synchronization of the shift element to be engaged takes place via a closed-loop control of the rotational speed of the upstream prime mover. Alternatively, however, this can also take place by using synchronized shift elements or also by using another, separate synchronizing mechanism, such as a transmission brake or also one further electric machine, which can be operatively connected directly or indirectly to the first input shaft. If one further shift element, as a separating clutch, is also provided on the input side of the input shaft, the inertial mass of the upstream drive machine can be decoupled during the synchronization. 
     Likewise, a gearchange under load can also take place between the second variant of the second gear, which is effective between the first input shaft and the output shaft, and the third gear, which is effective between the first input shaft and the output shaft, with the fourth shift element and the fifth shift element engaged. 
     The transmission according to example aspects of the invention can also be operated in such a way that a rotational-speed reduction of the electric machine is achieved during driving. It is therefore possible to initially drive in a hybrid manner in the first variant of the second gear, in that the third shift element initially remains engaged either after a gear shift from the first gear into the second gear with torque support via the electric machine or after a start of the prime mover into the second gear. In order to now reduce a rotational speed of the electric machine in the first variant of the second gear at higher ground speeds, however, a change-over can be implemented from the first variant of the second gear into the second variant of the second gear, since the rotor of the electric machine has a lower rotational speed here than in the first variant of the second gear. This change-over takes place while preserving the tractive force via the upstream prime mover with the first shift element and the fifth shift element engaged. Initially, the load-free, third shift element is disengaged and, subsequent thereto, the load-free, fourth shift element is engaged, wherein the rotational-speed adaptation takes place via closed-loop control of the rotational speed of the electric machine. 
     A separate shift element is not necessary for decoupling the upstream prime mover, since, in the second variant of the second gear, which is effective between the first input shaft and the output shaft, the upstream prime mover can be decoupled by disengaging the first shift element. As a result, the second gear is then implemented, which is effective between the second input shaft and the output shaft. 
     In addition, in the case of a vehicle that is slowing down, a downshift from the second gear, which is effective between the first input shaft and the output shaft, into the first gear, which is effective between the first input shaft and the output shaft, can be prepared, in that, initially, a change-over takes place from the second variant into the first variant of the second gear and, in the process, the tractive force is preserved via the upstream prime mover with the first shift element engaged. In the first variant of the second gear, the third shift element is then engaged, which becomes necessary in order to support the tractive force via the electric machine as part of the downshift from the second gear into the first gear. 
     One further example embodiment of the invention is to provide a transmission, wherein a seventh shift element is provided, which is arranged and designed for connecting two elements of the first planetary gear set P 1  or two elements of the second planetary gear set P 2  to each other. In other words, one of the two planetary gear sets is interlocked by the seventh shift element in the actuated condition. Due to the connection of the two planetary gear sets, as a result of the interlock of the one planetary gear set, the other planetary gear set is also simultaneously interlocked. 
     The interlock preferably takes place via a rotationally fixed connection of
         the first element with the second element of the second planetary gear set,   the second element with the third element of the first planetary gear set,   the first element with the second element of the first planetary gear set, or   the second element with the third element of the second planetary gear set.       

     It is particularly preferred when an additional electric gear is implementable between the second input shaft and the output shaft by engaging the fifth shift element and the seventh shift element. 
     By the seventh shift element, a fourth electric gear is therefore implementable, which corresponds to the second hybrid gear (direct drive). The ratio of the fourth gear is situated between the ratio of the second electric gear and the ratio of the third electric gear. The fourth electric gear is then also engageable when the fifth and seventh shift elements are engaged. 
     With this preferred example embodiment, a hybrid transmission is provided, which has precisely three internal-combustion-engine gears and precisely four purely electric gears. Finely stepped electric gears have the advantage that the electric machine can be operated with high efficiency during purely electric driving at a favorable operating point. 
     As one further example design option of the invention, a further electric machine is provided, the rotor of which is connected at the first input shaft. Such an example embodiment has the advantage that further driving modes can be achieved as a result. In addition, as a result, a start of the upstream prime mover can be implemented immediately, if necessary, if the prime mover is designed as an internal combustion engine. In addition, the additional electric machine can support the upstream prime mover in the synchronization of shift elements. 
     According to one further example embodiment of the invention, the first input shaft can be connected in a rotationally fixed manner, via an eighth shift element, to a connection shaft, which, in turn, is then preferably coupled within a motor vehicle drive train to the prime mover connected upstream from the transmission. The eighth shift element can be designed, in principle, as a force-locking or also as a form-locking shift element in this case, although it is particularly preferred when the eighth shift element is a dog clutch. Via the eighth shift element, the upstream prime mover can therefore also be completely decoupled from the transmission, so that a purely electric operation is implementable in a problem-free manner. 
     In one example refinement of the invention, one or multiple shift element(s) is/are each implemented as a form-locking shift element. In this case, the particular shift element is preferably designed either as a constant-mesh shift element or as a lock-synchronizer mechanism. Form-locking shift elements have the advantage over friction-locking shift elements that lower drag losses occur in the disengaged condition, and therefore a better efficiency of the transmission can be achieved. In particular, in the transmission according to example aspects of the invention, all shift elements are implemented as form-locking shift elements, and therefore the lowest possible drag losses can be achieved. In principle, however, one shift element or multiple shift elements could also be configured as force-locking shift elements, for example, as lamellar shift elements. 
     Within the scope of example aspects of the invention, the planetary gear sets can each be a minus planetary gear set, provided it allows for a connection of the elements, wherein the first element of the particular planetary gear set is a sun gear, the second element of the particular planetary gear set is a planet carrier, and the third element of the particular planetary gear set is a ring gear. A minus planetary gear set is composed, in a way known, in principle, to a person skilled in the art, of the elements sun gear, planet carrier, and ring gear, wherein the planet carrier, rotatably mounted, guides at least one planet gear, although preferably multiple planet gears, which each individually intermesh with the sun gear as well as with the surrounding ring gear. 
     Alternatively thereto, one planetary gear set or also multiple planetary gear sets can also be a plus planetary gear set, however, provided it allows for the connection of the particular elements, wherein the first element of the particular planetary gear set is then a sun gear, the second element of the particular planetary gear set is a ring gear, and the third element of the particular planetary gear set is a planet carrier. In a plus planetary gear set as well, the elements sun gear, ring gear, and planet carrier are present, wherein the planet carrier guides at least one planet gear pair, in which one planet gear is meshed with the internal sun gear and the other planet gear is meshed with the surrounding ring gear, and the planet gears are intermeshed with each other. 
     Where permitted by a connection of the individual elements, a minus planetary gear set can be converted into a plus planetary gear set, wherein, as compared to the design as a minus planetary gear set, the ring gear connection and the planet carrier connection are to be interchanged, and a stationary transmission ratio is to be increased by one. Conversely, a plus planetary gear set could also be replaced by a minus planetary gear set, provided the connection of the elements of the transmission enables this. In this case, as compared to the plus planetary gear set, the ring gear connection and the planet carrier connection would also need to be interchanged, and a stationary transmission ratio would need to be reduced by one. Within the scope of example aspects of the invention, the three planetary gear sets are each preferably designed as a minus planetary gear set, however. 
     According to one further example embodiment of the invention, the first shift element and the second shift element are combined to form one shift element pair, with which one actuating element is associated. The first shift element, on the one hand, and the second shift element, on the other hand, can be actuated via the actuating element starting from a neutral position. This has the advantage that, due to this combination, the number of actuating elements can be reduced and, therefore, the manufacturing complexity can also be reduced. 
     Alternatively or also in addition to the aforementioned example variants, the third shift element and the fourth shift element are combined to form one shift element pair, with which one actuating element is associated. The third shift element, on the one hand, and the fourth shift element, on the other hand, can be actuated via this actuating element starting from a neutral position. As a result, the manufacturing complexity can be reduced, in that, due to the combination of the two shift elements to form one shift element pair, one actuating unit can be utilized for both shift elements. 
     Alternatively to the aforementioned example variant, the fifth shift element and the sixth shift element are combined to form one shift element pair, with which one actuating element is associated. The fifth shift element, on the one hand, and the sixth shift element, on the other hand, can be actuated via this actuating element starting from a neutral position. As a result, the manufacturing complexity can be reduced, in that, due to the combination of the two shift elements to form one shift element pair, one actuating unit can be utilized for both shift elements. 
     It is particularly preferred when all six shift elements are combined to form particular shift element pairs. In this way, advantageously, six shift elements can be actuated with only three actuators. 
     In one example variant with seven shift elements, it is preferred, in particular, when the third shift element and the seventh shift element are combined to form one shift element pair, with which one actuating element is associated, wherein, via the actuating element, the third shift element, on the one hand, and the seventh shift element, on the other hand, are actuatable from a neutral position. 
     According to one example embodiment of the invention, the rotor of the electric machine is rotationally fixed to the second input shaft. Alternatively, according to one example design option of the invention, the rotor is connected to the second input shaft via at least one gear stage. The electric machine can be arranged either coaxially to the planetary gear sets or so as to lie axially offset with respect thereto. In the former case, the rotor of the electric machine can either be rotationally fixed directly to the second input shaft or can be coupled thereto via one or also multiple intermediate gear stage(s), wherein the latter allows for a more favorable configuration of the electric machine with higher rotational speeds and lower torques. The at least one gear stage can be designed as a spur gear stage and/or as a planetary gear stage in this case. In the case of a coaxial arrangement of the electric machine, the two planetary gear sets can then also, more preferably, be arranged axially in the area of the electric machine as well as radially internally with respect thereto, so that the axial installation length of the transmission can be shortened. 
     If the electric machine is provided axially offset with respect to the planetary gear sets, however, a coupling takes place via one or multiple intermediate gear stage(s) and/or a flexible traction drive mechanism. The one or the multiple gear stage(s) can also be implemented individually, in this case, either as a spur gear stage or as a planetary gear stage. A flexible traction drive mechanism can be either a belt drive or a chain drive. 
     If a further electric machine is also provided, a rotor of this further electric machine can also be either rotationally fixed to the first input shaft directly or can be coupled to the first input shaft via at least one gear stage. The at least one gear stage can be a spur gear stage or a planetary gear stage or also a flexible traction drive mechanism. In addition, the further electric machine can be provided coaxially or also axially offset with respect to the first input shaft and, therefore, also to the planetary gear sets. 
     Within the scope of example aspects of the invention, a starting component can be installed upstream from the transmission, for example a hydrodynamic torque converter or a friction clutch. This starting component can then also be an integral part of the transmission and acts to configure a starting process, in that the starting component enables a slip speed between the prime mover, which is designed, in particular, as an internal combustion engine, and the first input shaft of the transmission. In this case, one of the shift elements of the transmission or the separating clutch, which may be present, can also be designed as such a starting component, in that the starting component is present as a frictional shift element. In addition, a one-way clutch with respect to the transmission housing or to another shaft can be arranged on each shaft of the transmission, in principle. 
     The transmission according to example aspects of the invention is, in particular, part of a motor vehicle drive train for a hybrid or electric vehicle and is then arranged between a prime mover of the motor vehicle, which is configured as an internal combustion engine or as an electric machine, and further components of the drive train, which are arranged downstream in the direction of power flow to driving wheels of the motor vehicle. In this case, the first input shaft of the transmission is either permanently coupled to a crankshaft of the internal combustion engine or to the rotor shaft of the electric machine in a rotationally fixed manner or can be connected thereto via an intermediate separating clutch or a starting component, wherein a torsional vibration damper can also be provided between an internal combustion engine and the transmission. On the output end, the transmission is then preferably coupled, within the motor vehicle drive train, to a differential gear of a drive axle of the motor vehicle, wherein a connection to an interaxle differential can also be present in this case, however, via which a distribution to multiple driven axles of the motor vehicle takes place. The differential gear or the interaxle differential can be arranged with the transmission in one common housing in this case. A torsional vibration damper, which is optionally present, can also be integrated into this housing. 
     Within the meaning of the invention, the expressions that two components of the transmission are “connected” or “coupled” or “are connected to each other” mean a permanent coupling of these components, and therefore said components cannot rotate independently of each other. In that respect, no shift element is provided between these components, which can be elements of the planetary gear sets and/or also shafts and/or a rotationally fixed component of the transmission. Instead, the appropriate components are coupled to each other with a constant rotational speed dependence. 
     However, if a shift element is provided between two components, these components are not permanently coupled to each other. Instead, a coupling is carried out only by actuating the intermediate shift element. In this case, an actuation of the shift element means, within the meaning of the invention, that the particular shift element is transferred into an engaged condition and, consequently, synchronizes the turning motions, if necessary, of the components connected directly thereto. In the case of an example embodiment of the particular shift element as a form-locking shift element, the components directly connected to each other in a rotationally fixed manner via the shift element rotate at the same rotational speed, while, in the case of a force-locking shift element, speed differences can exist between the components also after an actuation of the same shift element. This intentional or also unintentional condition is nevertheless referred to, within the scope of the invention, as a rotationally fixed connection of the particular components via the shift element. 
     The invention is not limited to the specified combination of features of the main claim or the claims dependent thereon. In addition, individual features can be combined with one another, provided they arise from the claims, the description of preferred embodiments of the invention which follows, or directly from the drawings. References in the claims to the drawings via the use of reference signs is not intended to limit the scope of protection of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantageous example embodiments of the invention, which are explained in the following, are represented in the drawings. Wherein: 
         FIG. 1  shows a diagrammatic view of a motor vehicle drive train; 
         FIGS. 2 and 3  each show a diagrammatic view of a transmission of the type that can be utilized in the motor vehicle drive train from  FIG. 1 ; 
         FIG. 4  shows an exemplary shift pattern for a transmission from  FIGS. 2 and 3 ; 
         FIG. 5  shows a diagrammatic view of a transmission of the type that can also be utilized in the motor vehicle drive train from  FIG. 1 ; 
         FIG. 6  shows a diagrammatic view of a transmission of the type that can also be utilized in the motor vehicle drive train from  FIG. 1 ; 
         FIGS. 7 and 8  shows an exemplary shift pattern for a transmission according to  FIG. 5 ; and 
         FIGS. 9 through 14  each show a schematic of a modification of the transmissions from  FIGS. 2 through 5  as well as  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein. 
       FIG. 1  shows a diagrammatic view of a motor vehicle drive train of a hybrid vehicle, wherein, in the motor vehicle drive train, an internal combustion engine VKM is connected to a transmission G via an intermediate torsional vibration damper TS. Connected downstream from the transmission G, on the output end thereof, is a differential gear AG, via which drive power is distributed to driving wheels DW of a drive axle of the motor vehicle. The transmission G and the torsional vibration damper TS are arranged in a common housing of the transmission G in this case, into which the differential gear AG can then also be integrated. As is also apparent in  FIG. 1 , the internal combustion engine VKM, the torsional vibration damper TS, the transmission G, and also the differential gear AG are aligned transversely to a direction of travel of the motor vehicle. 
       FIG. 2  shows a schematic of the transmission G according to a first example embodiment of the invention. As is apparent, the transmission G includes of a gear set RS and an electric machine EM 1 , which are both arranged in the housing of the transmission G. The gear set RS includes two planetary gear sets P 1  and P 2 , wherein each of the planetary gear sets P 1  and P 2  includes a first element E 11  and E 12 , respectively, a second element E 21  and E 22 , respectively, and a third element E 31  and E 32 , respectively. The first element E 11  and E 12  is formed by a sun gear of the planetary gear set P 1  and P 2 , respectively, while the second element E 21  and E 22  of the planetary gear set P 1  and P 2 , respectively, is present as a planet carrier, and the third element E 31  and E 32  of the planetary gear set P 1  and P 2 , respectively, is present as a ring gear. 
     In the present case, the first planetary gear set P 1  and the second planetary gear set P 2  are each therefore present as a minus planetary gear set. The particular planet carrier thereof guides at least one planet gear in a rotatably mounted manner; the planet gear is meshed with the particular radially internal sun gear as well as with the particular radially surrounding ring gear. It is particularly preferred, however, when multiple planet gears are provided in the case of the first planetary gear set P 1  and in the case of the second planetary gear set P 2 . 
     As is apparent in  FIG. 2 , the transmission G includes a total of six shift elements in the form of a first shift element A, a second shift element B, a third shift element C, a fourth shift element D, a fifth shift element E, and a sixth shift element F. The shift elements A, B, C, D, E, and F are each designed as form-locking shift elements and are preferably present as constant-mesh shift elements. While the third shift element C and the fourth shift element D are each a brake, the remaining shift elements A, B, E, and F are clutches. 
     The first element E 11  of the first planetary gear set P 1  is fixable by the fourth shift element D at a rotationally fixed component GG, which is the transmission housing of the transmission G or a portion of this transmission housing. The first element E 12  of the second planetary gear set P 2  is fixable at the rotationally fixed component GG by the third shift element C. 
     The third element E 31  of the first planetary gear set P 1  and the second element E 22  of the second planetary gear set P 2  are connected in a rotationally fixed manner to an output shaft GWA of the transmission G. The second element E 22  of the second planetary gear set P 2  and the third element E 31  of the first planetary gear set P 1  and, therefore, also the output shaft GWA are jointly rotationally fixable to a first input shaft GW 1  of the transmission G by engaging the first shift element A. 
     A second input shaft GW 2  is rotationally fixable to the second element E 21  of the first planetary gear set P 1  by the fifth shift element E and rotationally fixable to the first element E 11  of the first planetary gear set P 1  by the sixth shift element F. 
     The second input shaft GW 2  of the transmission G is also permanently rotationally fixed to a rotor R 1  of an electric machine EM 1 , the stator S 1  of which is continuously fixed at the rotationally fixed component GG. 
     The first input shaft GW 1  as well as the output shaft GWA form a mounting interface GW 1 -A and GWA-A, respectively, wherein the mounting interface GW 1 -A in the motor vehicle drive train from  FIG. 1  is utilized for a connection at the internal combustion engine VKM, while the transmission G is connected at the mounting interface GWA-A to the downstream differential gear AG. The mounting interface GW 1 -A of the first input shaft GW 1  is formed at an axial end of the transmission G, while the mounting interface GWA-A of the output shaft GWA is situated in the area of the same axial end and, here, is aligned transversely to the mounting interface GW 1 -A of the first input shaft GW 1 . In addition, the first input shaft GW 1 , the second input shaft GW 2 , and the output shaft GWA are arranged coaxially to one another. 
     The planetary gear sets P 1  and P 2  are also situated coaxially to the input shafts GW 1  and GW 2  and the output shaft GWA, wherein the planetary gear sets P 1  and P 2  are arranged in the sequence first planetary gear set P 1  and second planetary gear set P 2  axially subsequent to the mounting interface GW 1 -A of the first input shaft GW 1 . Likewise, the electric machine EM 1  is also located coaxially to the planetary gear sets P 1  and P 2  and, therefore, also to the input shafts GW 1  and GW 2  and to the output shaft GWA, wherein the electric machine EM 1  is arranged axially spaced apart from the first planetary gear set P 1  and the second planetary gear set P 2 . 
     As is also apparent from  FIG. 2 , the first shift element A and the second shift element B are arranged axially between the first planetary gear set P 1  and the second planetary gear set P 2 , wherein, here, the second shift element B is situated axially adjacent to the first planetary gear set P 1 , followed axially by the first shift element A. 
     The third shift element C is situated axially on a side of the second planetary gear set P 2  facing away from the first planetary gear set P 1 . The fourth shift element D, the fifth shift element E, and the sixth shift element F are situated axially on a side of the first planetary gear set P 1  facing away from the second planetary gear set P 2 . 
     The first shift element A and the second shift element B are situated axially directly next to each other and radially at the same level and are combined to form one shift element pair SP 1 , in that a common actuating element is associated with the first shift element A and the second shift element B, via which the first shift element A, on the one hand, and the second shift element B, on the other hand, can be actuated from a neutral position. 
     The third shift element C and the fourth shift element D are spatially separated from each other by the shift elements A, B and are combined to form one shift element pair SP 2 , in that a common actuating element is associated with the third shift element C and the fourth shift element D, via which the third shift element C, on the one hand, and the fourth shift element D, on the other hand, can be actuated from a neutral position. 
     Likewise, the fifth shift element E and the sixth shift element F are combined to form one shift element pair SP 3 , in that a common actuating element is associated with the fifth shift element E and the sixth shift element F, via which the fifth shift element E, on the one hand, and the sixth shift element F, on the other hand, can be actuated from a neutral position. 
       FIG. 3  shows a diagrammatic view of a transmission G according to a second example design option of the invention, which can also be utilized in the motor vehicle drive train in  FIG. 1 . This design option largely corresponds to the preceding example variant according to  FIG. 2 , with the difference that the sequence of the planetary gear sets P 1 , P 2  is interchanged. As a result, the first electric machine EM 1  is now no longer located axially next to the planetary gear sets P 1  and P 2 , but rather essentially axially at the level thereof and radially surrounds the planetary gear sets P 1  and P 2 . As a result, the transmission can be designed to be axially even more compact. Otherwise, the example design option according to  FIG. 3  corresponds to the example variant according to  FIG. 2 , and therefore reference is made to the description thereof. 
       FIG. 4  shows an exemplary shift pattern for the transmission G from  FIGS. 2 and 3  in table form. As is apparent, a total of three gears  1  through  3 , which differ in terms of the ratio, are implementable between the first input shaft GW 1  and the output shaft GWA, wherein, in the columns of the shift pattern, an X indicates which of the shift elements A through F is engaged in which of the gears  1  through  3 . 
     As is apparent in  FIG. 4 , a first gear  1  is implemented between the first input shaft GW 1  and the output shaft GWA by actuating the second shift element B and the third shift element C. 
     In addition, a second gear  2  can be implemented between the first input shaft GW 1  and the output shaft GWA in a first variant  2 . 1  by actuating the first shift element A and the third shift element C, wherein the second gear can also be formed in a second variant  2 . 2  by engaging the first shift element A and the fourth shift element D, and in a third variant  2 . 3  by actuating the first shift element A and the second shift element B. 
     In addition, a third gear  3  also results between the first input shaft GW 1  and the output shaft GWA by actuating the second shift element B and the fourth shift element D. 
     In all the aforementioned gears, additionally, either the fifth shift element E or the sixth shift element F is engaged. 
     Although the shift elements A through F are each designed as a form-locking shift element, a shift between the first gear  1  and the first variant  2 . 1  of the second gear can be implemented under load, since the third shift element C contributes thereto in each case. Here, the first electric machine EM 1  is connected either to the first element E 11  or to the second element E 21  of the first planetary gear set P 1 . 
     In addition, a shift between the second variant  2 . 2  of the second gear and the third gear  3  can be implemented under load, since the fourth shift element D contributes thereto. Here, the first electric machine EM 1  is connected to the second element E 21  of the first planetary gear set P 1 . 
     A synchronization during the gear shifts can take place in each case via an appropriate closed-loop control of the upstream internal combustion engine VKM, and therefore the particular shift element to be disengaged is disengaged without load and the shift element to be subsequently engaged can be engaged without load. 
     The transmissions G from  FIGS. 2 and 3  can also be operated in alternative operating modes with the aid of the electric machine EM 1 . Purely electric driving can take place in a first gear E 0 , which is effective between the second input shaft GW 2  and the output shaft GWA and, for the implementation of which, the third shift element C and the sixth shift element F are to be transferred into an engaged condition. As a result, with the third shift element C and the sixth shift element F engaged, the first electric machine EM 1  is directly connected to the output shaft GWA with a constant ratio. The ratio of the first gear E 0  is shorter or less than the first internal-combustion-engine gear  1 . 
     In addition, purely electric driving can take place in a second gear E 1 , which is effective between the second input shaft GW 2  and the output shaft GWA and, for the implementation of which, the third shift element C and the fifth shift element E are to be transferred into an engaged condition. With the third shift element C and the fifth shift element E engaged, the first electric machine EM 1  is connected to the output shaft GWA with a constant ratio (with the element E 12  fixed, the third element E 32  is rotatable with the second element E 12  of the second planetary gear set). 
     The ratio of the second gear E 1  corresponds here, in each case, to a ratio of the first gear  1  between the first input shaft GW 1  and the output shaft GWA. 
     In addition, a third gear E 3  can also be implemented between the second input shaft GW 2  and the output shaft GWA, for the implementation of which the fourth shift element D and the fifth shift element E are to be engaged. As a result, the electric machine EM 1  is connected to the output shaft GWA with a constant ratio (second element E 21  is rotatable with the third element E 31  while the first element E 11  of the first planetary gear set P 1  is fixed). A ratio of this third gear E 3  corresponds, in each case, to a ratio of the third gear, which is effective between the first input shaft GW 1  and the output shaft GWA. 
     Advantageously, a start of the internal combustion engine VKM into the first gear  1  and into the first variant  2 . 1  of the second gear  2  can be carried out starting from the first gear E 0 , since the third shift element C and the sixth shift element F are engaged in each of these gears. 
     Starting from the second gear E 1 , a start of the internal combustion engine VKM into the first gear  1  and into the first variant  2 . 1  of the second gear  2  can be carried out, because the third shift element C and the fifth shift element E contribute thereto. 
     Starting from the third gear E 3 , a start of the internal combustion engine VKM into the second variant  2 . 2  of the second gear and into the third gear  3  can be carried out, because the fourth and fifth shift elements D and E are engaged here. 
     Therefore, a transition from purely electric driving into driving via the internal combustion engine or into hybrid driving can be carried out rapidly. 
     If the first electric machine is to be decoupled from the first element E 11  and coupled onto the second element E 21  of the first planetary gear set P 1 , the tractive force can be maintained in the meantime with the internal combustion engine VKM. This is useful mainly in the first gear  1  or the first variant  2 . 1  of the second gear  2 , because the shift element D is not engaged there. If the shift element D as well as the shift element F would be simultaneously engaged, the first electric machine EM 1  would be braked. 
     Moreover, a charging or start function can be implemented by engaging the second shift element B and the fifth shift element E. This is the case because, in the engaged condition of the second shift element B and the fifth shift element E, the second input shaft GW 2  is directly coupled, in a rotationally fixed manner, to the first input shaft GW 1  and, therefore, also to the internal combustion engine VKM, wherein, simultaneously, there is no force-fit connection to the output shaft GWA. When the electric machine EM 1  is operated as a generator, an electric accumulator can be charged via the internal combustion engine VKM, whereas, when the electric machine EM 1  is operated as an electric motor, a start of the internal combustion engine VKM is implementable via the electric machine EM 1 . 
     In addition, a rotational-speed reduction of the electric machine EM 1  can be configured in the mechanical or hybrid mode: after a gear shift from the first gear into the second gear, with torque support via the electric machine EM 1 , or after a start of the internal combustion engine VKM into the second gear, hybrid driving results, wherein a rotationally fixed connection exists between the second input shaft GW 2  and the second element E 21 , i.e., the fifth shift element E is engaged. 
     In order to reduce the rotational speed of the electric machine EM in the second gear at higher ground speeds, a change-over can be carried out from the first variant  2 . 1  of the second gear into the second variant  2 . 2 , in which the rotor R 1  has a lower rotational speed. This change-over takes place while preserving the tractive force via the internal combustion engine VKM with the third shift element C engaged. For this purpose, the third shift element C, which is then load-free, is disengaged and the likewise load-free, fourth shift element D is engaged, wherein the rotational-speed adaptation takes place in each case via a closed-loop control of the rotational speed of the electric machine EM. 
     The advantage of utilizing the second variant  2 . 2  is that the internal combustion engine VKM, on the one hand, can be decoupled at any time by disengaging the shift element A also without an additional separating clutch K 0 , while the electric machine EM 1  drives or decelerates (recuperation) the vehicle. On the other hand, in the case of a vehicle that is slowing down, a downshift from the second gear into the first gear can be prepared, in that a change-over from the second variant  2 . 2  into the first variant  2 . 1  takes place while the internal combustion engine maintains the tractive force (the first shift element A remains engaged). In the first variant  2 . 1  of the second gear, the third shift element C is engaged, which becomes necessary in order to support the tractive force with the electric machine EM 1  during the downshift from the second gear into the first gear. 
       FIG. 5  shows a diagrammatic view of a transmission G according to a further example design option of the invention, which can also be utilized in the motor vehicle drive train in  FIG. 1 . This design option largely corresponds to the preceding example variant according to  FIG. 2 , wherein the transmission G includes an additional seventh shift element K. 
     The seventh shift element K is arranged in such a way that, in the actuated condition, the seventh shift element K interlocks the second planetary gear set P 2 . Due to the permanently fixed carrier-ring gear connection of the two planetary gear sets P 1  and P 2 , when the second planetary gear set P 2  is interlocked, the first planetary gear set P 1  is always also interlocked. 
     By the seventh shift element G, a fourth electric gear is implementable, which corresponds to the second hybrid gear (direct drive). The ratio of the fourth gear E 2  is situated between the ratio of the second electric gear E 1  and the ratio of the third electric gear E 3 . In the fourth electric gear E 2 , the seventh shift element K and the fifth shift element E are engaged. 
     The fourth electric gear is then also engageable when the seventh shift element K and the sixth shift element F are engaged. 
     With this preferred example embodiment, a hybrid transmission is provided, which has precisely three internal-combustion-engine gears and precisely four purely electric gears. Finely stepped electric gears have the advantage that the electric machine can be operated with high efficiency during purely electric driving at a favorable operating point. 
     Not represented, but possible, is an interlock also via the rotationally fixed connection of
         the second element E 21  with the third element E 31  of the first planetary gear set P 1 ,   the first element E 11  with the second element E 21  of the first planetary gear set P 1 , or   the second element E 22  with the third element E 32  of the second planetary gear set P 2 .       

     In the example embodiment according to  FIG. 5 , the first shift element A and the second shift element B are combined to form a first shift element pair SP 1 . The third shift element C and the seventh shift element G are combined to form a second shift element pair SP 2 . The fifth shift element E and the sixth shift element F are combined to form a third shift element pair SP 3 . For the rest, the example variant according to  FIG. 5  corresponds to the example design option according to  FIG. 2 , and therefore reference is made to the description thereof. 
     Moreover,  FIG. 6  shows a schematic of a transmission G according to a further example embodiment of the invention, of the type which can also be utilized in the motor vehicle drive train in  FIG. 1 . This example embodiment essentially corresponds to the example variant according to  FIG. 2 , wherein, in contrast thereto, the first input shaft GW 1  can now be rotationally fixed, at the mounting interface GW 1 -A via an eighth shift element K 0 , to a connection shaft AN, which is then connected to the upstream internal combustion engine VKM in the motor vehicle drive train. The eighth shift element K 0  is configured as a form-locking shift element and, particularly preferably, is present as a constant-mesh shift element. Moreover, a further electric machine EM 2  is also provided, the rotor R 2  of which is rotationally fixed to the first input shaft GW 1 , while a stator S 2  of the further electric machine EM 2  is fixed at the rotationally fixed component GG. The rotor R 2  is connected at the first input shaft GW 1  axially between the eighth shift element K 0  and the first planetary gear set P 1 . For the rest, the example variant according to  FIG. 6  corresponds to the example design option according to  FIG. 2 , and therefore reference is made to the description thereof. 
     In  FIGS. 7 and 8 , different conditions of the motor vehicle drive train from  FIG. 1 , with utilization of the transmission G from  FIG. 6 , are represented in table form, wherein these different conditions are achieved via different integrations of the two electric machines EM 1  and EM 2  as well as the internal combustion engine VKM. 
     First, purely electric driving by a single electric machine and disengaged shift element K 0  is described with reference to  FIG. 7 . 
     If the shift element E or F is engaged, purely electric driving is possible with only one electric machine, as follows. 
     In the first gear E 0 , purely electric driving takes place via the first electric machine EM 1 , in that the first gear E 0  is implemented in the transmission G in the way described above with respect to  FIG. 4 . 
     In the second gear E 1 , purely electric driving takes place via the first electric machine EM 1 , in that the second gear E 1  is implemented in the transmission G in the way described above with respect to  FIG. 4 . 
     In the fourth gear E 3 , purely electric driving also takes place via the first electric machine EM 1 , in that the fourth gear E 3  is implemented in the way described above with respect to  FIG. 4 . 
     The third gear E 2  can be driven by the second electric machine, in that the first shift element A and the fifth shift element E are engaged in the transmission G. 
     Second, alternative purely electric driving with decoupled first electric machine EM 1  and disengaged shift element K 0  is described. 
     If neither the fifth shift element E nor the sixth shift element F is engaged, purely electric driving is possible with only the second electric machine EM 2 , as follows. 
     In the second gear E 1 , purely electric driving is implemented, in that the second and third shift elements B and C are engaged in the transmission G. 
     In a first variant E 2 . 1  of the second electric gear, purely electric driving is implemented, in that the first and third shift elements A and C are engaged in the transmission G. 
     In a second variant E 2 . 2  of the second electric gear, purely electric driving is implemented, in that the first and fourth shift elements A and D are engaged in the transmission G. 
     In a third variant E 2 . 3  of the second electric gear, purely electric driving is implemented, in that the first and second shift elements A and B are engaged in the transmission G. 
     The third gear E 3  can be driven, in that the second shift element B and the fourth shift element D are engaged in the transmission G. 
     Third, purely electric driving by both electric machines and disengaged shift element K 0  is described with reference to  FIG. 8 . 
     The same gear steps or variants can be implemented as described in  FIG. 4 , wherein these can now be driven purely electrically. The hybrid driving and the purely internal combustion engine-driving are not represented in  FIG. 8 . For the rest, reference is made to the comments presented with respect to  FIG. 4 . 
     The advantages of two electric machines can be summarized as follows:
         purely electric powershift, since the second electric machine EM 2 , with disengaged shift element K 0 , performs the functions of the internal combustion engine;   the second electric machine EM 2 , with disengaged shift element K 0 , can be utilized for synchronization, while the first electric machine EM 1  supports the tractive force;   a greater total electrical power is implementable with disengaged shift element K 0 ;   a greater range is possible with a hybrid operation;   the internal combustion engine VKM can be started by the second electric machine EM 2 ;   the second electric machine EM 2  can synchronize the shift element K 0     a battery-independent serial operation is possible; and   the second electric machine EM 2  can be used as a generator, the first electric machine EM 1  can be used as a motor.       

     Finally,  FIGS. 9 through 14  show modifications of the example transmissions G from  FIGS. 2, 3, 5  as well as  FIG. 6 . These modifications relate to alternative possibilities for integrating the electric machine EM 1 , although the example modifications can also be utilized, in a similar way, for the further electric machine EM 2  in the transmissions G according to  FIG. 6 . 
     In  FIG. 9 , for example, the electric machine EM 1  is not located coaxially to the particular gear set RS (not represented in greater detail here) of the transmission G, but rather is arranged axially offset with respect thereto. A connection takes place via a spur gear stage SRS, which is composed of a first spur gear SR 1  and a second spur gear SR 2 . The first spur gear SR 1  is connected at the second input shaft GW 2  in a rotationally fixed manner on the side of the particular gear set RS. The spur gear SR 1  then meshes with the spur gear SR 2 , which is located on an input shaft EW of the electric machine EM 1  in a rotationally fixed manner. Within the electric machine EM 1 , the input shaft EW establishes the connection at the rotor (not represented further in this case) of the electric machine EM 1 . 
     In the case of the example modification according to  FIG. 10  as well, the electric machine EM 1  is located axially offset with respect to the particular gear set RS of the particular transmission G. In contrast to the preceding example variant according to  FIG. 10 , a connection is not established in this case via a spur gear stage SRS, however, but rather via a flexible traction drive mechanism ZT. This flexible traction drive mechanism ZT can be configured as a belt drive or also a chain drive. The flexible traction drive mechanism ZT is then connected at the second input shaft GW 2  on the side of the particular gear set RS. Via the flexible traction drive mechanism ZT, a coupling to an input shaft EW of the electric machine EM 1  is then established. Within the electric machine EM 1 , the input shaft EW establishes a connection at the rotor of the electric machine. 
     In the case of the example modification according to  FIG. 11 , an integration of the electric machine EM 1 , which is located axially offset with respect to the particular gear set RS, is implemented via a planetary gear stage PS and a spur gear stage SRS. The planetary gear stage PS is connected downstream from the gear set RS, wherein, on the output end of the planetary gear stage PS, the spur gear stage SRS is then provided, via which the connection to the electric machine EM 1  is established. The planetary gear stage PS includes a ring gear HO, a planet carrier PT, and a sun gear SO, wherein the planet carrier PT guides, in a rotatably mounted manner, at least one planet gear PR, which is meshed with the sun gear SO as well as with the ring gear HO. 
     In the present case, the planet carrier PT is connected at the second input shaft GW 2  in a rotationally fixed manner on the side of the gear set RS from  FIGS. 2, 3, 5  as well as  FIG. 6 . By comparison, the ring gear HO is permanently fixed at the rotationally fixed component GG, while the sun gear SO is rotationally fixed to a first spur gear SR 1  of the spur gear stage SRS. The first spur gear SR 1  then intermeshes with a second spur gear SR 2  of the spur gear stage SRS, which is provided, in a rotationally fixed manner, on an input shaft EW of the electric machine EM 1 . In this case, the electric machine EM 1  is therefore connected by the gear set RS via two gear stages. 
     In the case of the example modification from  FIG. 12  as well, an integration of the electric machine EM 1  is implemented by the gear set RS via a planetary gear stage PS and a spur gear stage SRS. The modification largely corresponds to the example variant according to  FIG. 12 , with the difference that, with respect to the planetary gear stage PS, the sun gear SO is now fixed at the rotationally fixed component GG, while the ring gear HO is rotationally fixed to the first spur gear SR 1  of the spur gear stage SRS. Specifically, the ring gear HO and the first spur gear SR 1  are preferably designed as one piece, in that the ring gear HO is equipped, at an outer circumference, with a tooth system. For the rest, the example modification according to  FIG. 12  corresponds to the example variant according to  FIG. 11 , and therefore reference is made to the description thereof. 
     Moreover,  FIG. 13  shows one further example modification of the transmissions G from  FIGS. 2, 3, 5  as well as  FIG. 6 , wherein, in this case as well, an integration of the electric machine EM 1  is implemented via a spur gear stage SRS and a planetary gear stage PS. In contrast to the preceding example variant according to  FIG. 12 , the gear set RS is initially followed here by the spur gear stage SRS, while the planetary gear stage PS is provided in the power flow between the spur gear stage SRS and the electric machine EM 1 . The planetary gear stage PS also includes, once again, the elements ring gear HO, planet carrier PT, and sun gear SO, wherein the planet carrier PT guides, in a rotatably mounted manner, multiple planet gears PR 1  and PR 2 , each of which is meshed with the sun gear SO as well as with the ring gear HO. 
     As is apparent in  FIG. 13 , a first spur gear SR 1  of the spur gear stage SRS is connected in a rotationally fixed manner on the side of the gear stage RS of the transmissions G from  FIGS. 2, 3, 5  as well as  6 , wherein this connection is completed at the second input shaft GW 2 . The first spur gear SR 1  then intermeshes with a second spur gear SR 2  of the spur gear stage SRS, which is rotationally fixed to the planet carrier PT of the planetary gear stage PS. The ring gear HO is permanently fixed at the rotationally fixed component GG, while the sun gear SO is provided, in a rotationally fixed manner, on an input shaft EW of the electric machine EM 1 . 
     Finally,  FIG. 14  shows one further example modification of the transmissions G from  FIGS. 2, 3, 5  as well as  FIG. 6 , wherein this example modification essentially corresponds to the preceding example variant according to  FIG. 10 . The only difference is that the sun gear SO of the planetary gear stage PS is now permanently fixed at the rotationally fixed component GG, while the ring gear HO of the planetary gear stage PS is rotationally fixed to the input shaft EW of the electric machine EM 1 . For the rest, the example modification according to  FIG. 14  corresponds to the example variant according to  FIG. 13 , and therefore reference is made to the description thereof. 
     Using example embodiments of the invention, a transmission having a compact design and good efficiency can be implemented. 
     Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. In the claims, reference characters corresponding to elements recited in the detailed description and the drawings may be recited. Such reference characters are enclosed within parentheses and are provided as an aid for reference to example embodiments described in the detailed description and the drawings. Such reference characters are provided for convenience only and have no effect on the scope of the claims. In particular, such reference characters are not intended to limit the claims to the particular example embodiments described in the detailed description and the drawings. 
     REFERENCE CHARACTERS 
     
         
         G transmission 
         RS gear set 
         GG rotationally fixed component 
         P 1  first planetary gear set 
         E 11  first element of the first planetary gear set 
         E 21  second element of the first planetary gear set 
         E 31  third element of the first planetary gear set 
         P 2  second planetary gear set 
         E 12  first element of the second planetary gear set 
         E 22  second element of the second planetary gear set 
         E 32  third element of the second planetary gear set 
         A first shift element 
         B second shift element 
         C third shift element 
         D fourth shift element 
         E fifth shift element 
         F sixth shift element 
         K seventh shift element 
         K 0  eighth shift element 
         SP 1  shift element pair 
         SP 2  shift element pair 
         SP 3  shift element pair 
           1  first gear 
           2 . 1  second gear 
           2 . 2  second gear 
           2 . 3  second gear 
           2 . 4  second gear 
           2 . 5  second gear 
           3  third gear 
         E 0  first gear 
         E 1  second gear 
         E 3  third gear 
         E 2  fourth gear 
         V 1  first gear 
         V 2 . 1  second gear 
         V 2 . 2  second gear 
         V 2 . 3  second gear 
         V 3  third gear 
         GW 1  first input shaft 
         GW 1 -A mounting interface 
         GW 2  second input shaft 
         GWA output shaft 
         GWA-A mounting interface 
         AN connection shaft 
         EM 1  electric machine 
         S 1  stator 
         R 1  rotor 
         EM 2  electric machine 
         S 2  stator 
         R 2  rotor 
         SRS spur gear stage 
         SR 1  spur gear 
         SR 2  spur gear 
         PS planetary gear stage 
         HO ring gear 
         PT planet carrier 
         PR planet gear 
         PR 1  planet gear 
         PR 2  planet gear 
         SO sun gear 
         ZT flexible traction drive mechanism 
         VKM internal combustion engine 
         TS torsional vibration damper 
         AG differential gear 
         DW driving wheels