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Abstract
The sporting spirit that characterises a high-performance car can be observed in certain technical solutions. The power distribution on the rear wheels is the simplest example of that. It is well known that rear-wheel drive (RWD) vehicles are more fun to drive and faster in their reactions. Unfortunately, they are also less intuitive and harder to control because of their natural oversteering behaviour. The idea of maintaining an RWD driveline in the future is not farseeing, because it would imply an excessive tyre dimension increasing to let the driver use all engine power in many cornering and low-friction conditions. The choice of adopting a part-time all-wheel drive (AWD) driveline comes from the will of enhancing the overall performance by using all the available friction every time that it is needed. It has to be kept into account that a normally aspirated motor of a sport car can supply 500–600 Hp nowadays, and that it will supply 700–800 Hp in the very near future. However, the proposed driveline has not to worsen the weight characteristics (mass and load distribution) that make an RWD vehicle better than other cars. Because of all these considerations and constraints, a new driveline system has been designed. It derives from an RWD driveline with a semi-active differential, to which has been added a controlled wet clutch that directly connects the engine to the front differential. This device allows the drive torque to be distributed between the two axles. It can be understood that in such a device, the torque distribution does not depend only on the central clutch action, but also on the engaged gear. Because of this particular layout, this system can not work in the whole gear range because of thermal problems due to kinematical reasons. So the centre clutch controller has to consider the gear position too. The control algorithms development was carried out using a vehicle model, which can precisely simulate the handling response, the powertrain dynamic, and the actuation system behaviour. Such a modelling precision required the development of a customised powertrain model library in Matlab/Simulink.