Development of the Control Strategy for an Innovative 4WD Device

The potentialities shown by controlled differentials are making the automotive industry to explore this field. While VDC systems can only guarantee a safe behaviour at limit, a controlled differential can also increase the handling performance. The system derives from a rear wheel drive architecture with a semi-active differential, to which has been added a controlled wet clutch that directly connects the front axle and the engine crankshaft. This device allows distributing the drive torque between the two axles, according to the constraints due to kinematics and thermal problems. It can be easily understood that in this device the torque distribution doesn’t depend only from the central clutch action, but also from the engaged gear. Because of that the central clutch controller has to consider the gear position too. The control algorithms development was carried on using a vehicle model which can precisely simulate the handling response, the powertrain dynamic and the actuation system behaviour. A right powertrain response required the development of a customize library in Simulink. The approach chosen to carry on this research was the one used in automotive industry nowadays: an intensive simulation campaign was executed to realize an initial controller design and tuning.