Powertrain for a motor vehicle and control method thereof

Powertrain for a vehicle comprising:

• an internal combustion engine provided with a crankshaft;
• a first electric machine operating at least as a starter motor and located on a first side of the internal combustion engine facing in use towards a transmission (T) of the vehicle;
• an accessory drive comprising:
• a first pulley connected to one end of the crankshaft on a second side of the engine opposite in use to the transmission of the vehicle;
• a second electric machine located on the second side of the internal combustion engine;
• a second pulley connected to the second electric machine;
• a third pulley connected to an accessory of the internal combustion engine,
• a belt connecting the first, the second, and the third pulleys together to rotate in the same direction of rotation (R) as the crankshaft;
• and
• a tensioner acting on a span of the belt between the second pulley and the third pulley;
• and
• a control unit
• programmed to control the second electric machine so as to transmit an active torque to said second pulley during start-up of the internal combustion engine by means of the first electric machine, so as to maintain a predetermined minimum tension level in a span of the belt comprised between the first and the second pulleys in said direction of rotation.