A drive unit for a hybrid vehicle is known from DE 10 2006 059 591 A1, whereas the drive unit comprises a drive assembly with an internal combustion engine and an electric motor and a transmission for shifting between the drive assembly and an output. The transmission is designed as a dual-clutch transmission and includes several sub-transmissions. Through a planetary transmission, the electric motor of the drive assembly of the drive unit is coupled to an input shaft of a first sub-transmission and an input shaft of a second sub-transmission shifted in parallel to the first sub-transmission. Through a frictional-locking separating clutch, the internal combustion engine is able to be coupled to the input shaft of the first sub-transmission and, if the separating clutch is locked, is directly coupled to the input shaft of one of the sub-transmissions. For all-electric driving when the internal combustion engine is decoupled, with this drive unit in both sub-transmissions, one gear is engaged, whereas the separating clutch is open.
An additional drive unit for a hybrid vehicle is known from DE 10 2010 061 824 A1, whereas the drive unit of DE 10 2010 061 824 A1 is distinguished from the drive unit of DE 10 2006 059 591 A1 by the fact that a positive-locking bypass shift element is also present, which works together with the planetary transmission in such a manner that, with a locked bypass shift element, there is a torque-proof connection between the electric motor, the input shaft of the first sub-transmission, and the input shaft of the second sub-transmission, while, with an open bypass shift element, this connection between the electric motor and the two input shafts of the two sub-transmissions does not exist. With this drive unit, there can be all-electric driving in three different manners, that is, if, in both sub-transmissions, one gear is engaged and the separating clutch and the bypass shift element are both open, or if the bypass shift element is locked, the separating clutch is open, and in the first or second sub-transmission, one gear is engaged in the other sub-transmission is in neutral.
Both drive units known from DE 10 2006 059 591 A1 and DE 10 2010 061 824 A1 have the disadvantage that, for the coupling of the internal combustion engine coming out of all-electric driving, only one gear is available for the internal combustion engine.
Therefore, the need exists for a method for operating a drive unit for a hybrid vehicle, with which, for the coupling of the internal combustion engine coming out of all-electric driving, several gears are available for the internal combustion engine.