Patent ID: 8727925

Claim:
A method of operating a drive-train, of a hybrid vehicle, comprising a drive aggregate which comprises an internal combustion engine ( 1 ), an electric machine ( 2 ), a transmission ( 3 ), and a planetary gear system ( 5 ) comprising a ring gear element ( 9 ), a sun gear element ( 10 ) and a carrier element ( 8 ), a first element of the planetary gear system ( 5 ) is fixedly coupled to an input shaft ( 11 ) of the transmission ( 3 ), a second element of the planetary gear system ( 5 ) is fixedly coupled to the electric machine ( 2 ), and a third element of the planetary gear system ( 5 ) is connectable, via a first clutch ( 6 ), to the internal combustion engine ( 1 ), and two of the three elements ( 8 , 9 , 10 ) of the planetary gear system ( 5 ) are connectable by a second clutch ( 7 ) to one another such that, when the second clutch ( 7 ) is disengaged, the drive-train operates in a first operating mode and, when the second clutch ( 7 ) is engaged, the drive-train operates in a second operating mode, the method comprising the steps of: changing from the first operating mode to the second operating mode, when the drive-train is either started up or crawling, while maintaining a traction force at a drive output ( 4 ) of the drive-train by engaging the second clutch ( 7 ) such that a transmission capacity of the first clutch ( 6 ) is reduced until the first clutch ( 6 ) operates with slip; operating the internal combustion engine ( 1 ) with speed regulation while the second clutch ( 7 ) is synchronizing; and engaging the second clutch ( 7 ) without any load.