Method for simultaneous control of torque from combustion engine and electric machine in a hybrid vehicle

A method for driving a vehicle having a propulsion system comprising a combustion engine including an output shaft, a gearbox including an input shaft, an electric machine comprising a stator and a rotor, a planetary gear comprising three components in the form of a sun gear, a ring gear and a planet wheel carrier;

• the output shaft of the combustion engine connected to a first one of said components of the planetary gear so that a rotation of this shaft causes rotation of this first component;
• the input shaft of the gearbox being connected to a second one of said components of the planetary gear so that a rotation of this shaft causes rotation of this second component;
• the rotor of the electric machine being connected to a third one of said components of the planetary gear so that a rotation of the rotor causes rotation of this third component;
• and
• said propulsion system further comprising a locking means movable between a locking position in which two of said three components of the planetary gear are inter-locked so that said three components thereof rotate with the same rotational speed and a releasing position in which said three components of the planetary gear are allowed to rotate with different rotational speeds;
• said method comprising the following steps:
• a) determining that the locking means shall be moved to the releasing position from the locking position,
• b) controlling the electric machine to apply a first torque corresponding to the product of a propulsion system torque requested and a transmission ratio of the planetary gear and, at the same time, controlling the combustion engine to apply a second torque corresponding to the product of the propulsion system requested torque and a value obtained by subtracting the transmission ratio of the planetary gear from 1, and
• c) moving the locking means to the releasing position when both said first torque and said second torque have been provided such that torque balance exists in the planetary gear.