Method for operating a drivetrain

A method of operating a drive train of a motor vehicle for a crawling start of the motor vehicle in which the drive train comprises a hybrid drive with a combustion engine (2) and an electric motor (3);

• a clutch (4) is positioned between the combustion engine (2) and the electric motor (3);
• a transmission (5) is positioned between the hybrid drive and an output (6);
• the drive includes either a transmission internal starting element (9) or a transmission external starting element (7) along with a brake pedal (11) and an accelerator pedal (10), the method comprising the steps of:
• initiating the crawling start of the motor vehicle, with the deive train being in a starting condition in which the clutch (4), which is positioned between the combustion engine (2) and the electric motor (3), is disengaged, and the brake pedal (11) is activated and the accelerator pedal (10) is unactivated, and the combustion engine (2) of the hybrid drive is turned off;
• either bringing the starting element (7,9) to filling pressure or maintaining the filling pressure of the starting element (7, 9) either by deactivation or after deactivation of the brake pedal (11);
• immediately thereafter bringing the electric motor (3) of the hybrid drive, which is operated in a rotational speed controlled mode, to a rotational speed that is higher by a defined slippage rotational speed than a transmission side rotational speed of the transmission (5);
• further engaging the starting element (7, 9) to create torque at the output (6) for the crawling start, when the slippage is reached;
• continually operating the electric motor (3) in the rotation seed controlled mode to maintain the slippage for the crawl starting;
• and
• immediately after the filling pressure is present at the starting element (7, 9), bringing the electric motor to a rotational speed that is higher by a defined slippage rotational speed than a transmission input rotation speed of the transmission (5).

A method of operating a drive train of a motor vehicle for a crawling start of the motor vehicle in which the drive train comprises a hybrid drive with a combustion engine (2) and an electric motor (3);

• a clutch (4) is positioned between the combustion engine (2) and the electric motor (3);
• a transmission (5) is positioned between the hybrid drive and an output (6);
• the drive includes either a transmission internal starting element (9) or a transmission external starting element (7) along with a brake pedal (11) and an accelerator pedal (10), the method comprising the steps of:
• initiating the crawling start of the motor vehicle, with the drive train being in a starting condition in which the clutch (4), which is positioned between the combustion engine (2) and the electric motor (3), is disengaged, and the brake pedal (11) is activated and the accelerator pedal (10) is unactivated, and the combustion engine (2) of the hybrid drive is turned off;
• either bringing the starting element (7,9) to filling pressure or maintaining the filling pressure of the starting element (7, 9) either by deactivation or after deactivation of the brake pedal (11);
• immediately thereafter bringing the electric motor (3) of the hybrid drive, which is operated in a rotational speed controlled mode, to a rotational speed that is higher by a defined slippage rotational speed than a transmission side rotational speed of the transmission (5);
• further engaging the starting element (7, 9) to create torque at the output (6) for the crawling start, when the slippage is reached;
• continually operating the electric motor (3) in the rotation speed controlled mode to maintain the slippage for the crawl starting;
• and
• either bringing or maintaining the starting element (7, 9) to filling pressure for the electric crawling start by means of an electrically operated auxiliary hydraulic pump.