The search for clean automotive propulsion system has brought to study a new hybrid system. This hybrid system allows the mechanical energy produced by the thermal engine be partly stored in battery pack and partly be sent directly to the wheels without being converted into electrical energy.
The main components of this system are: one battery pack, two electrical machine, one i.c. engine, and a three-axes planetary train.
The i.c. engine has a constant speed, so that it is possible to minimise fuel waste. The first electrical machine drives the first axis of planetary train and is connected to the driving shaft of the i.c. engine through a friction drive; the role of this electrical machine is to modulate the torque of the i.c. engine. The second electrical machine drives the second axis of the planetary train and is running at a variable speed; the role of this electrical machine is to provide the kinematic control of the vehicle. The third axis of the planetary train is connected to the transmission shaft of the vehicle. In addiction it has been stressed out that this hybrid system can work even using only the electrical supply (ZEV). Finally, the use of this hybrid system sounds to be much appropriate to drive the small city cars, which represent one of the most actual interest of car industries.