Method of controlling hybrid electric vehicle

A method of controlling a hybrid electric vehicle with a torque converter disposed between a motor for driving the hybrid electric vehicle and a transmission, and an engine clutch disposed between an engine and the motor, the method comprising:

• by a control unit:
• determining a driver demand torque and an output speed of the torque converter based on vehicle driving information obtained in real time while a vehicle travels;
• determining a target output torque of the torque converter from a plurality of output torques, the target output torque having a same value as the driver demand torque;
• determining a target input speed and a target input torque of the torque converter corresponding to the target output torque;
• determining, before starting the engine, the target input speed of the torque converter from the output speed of the torque converter based on preset characteristic information of the torque converter and information on the driver demand torque, the preset characteristic information including speed ratio (SR), torque ratio (TR), and capacity factor (Cf) of the torque converter;
• determining the target input speed of the torque converter as a target engine starting speed;
• and
• performing control to:
• start the engine using torque of the motor transmitted through the engine clutch when entering an engine-on mode;
• and
• once the engine has started, controlling an engine speed to the target engine starting speed,
• wherein a combination of input/output operating conditions of the torque converter corresponding to the speed ratio (SR), the torque ratio (TR), and the capacity factor (Cf) of the torque converter are obtained from the output speed of the torque converter at which the vehicle travels.