In a Formula SAE car, as for almost all racecars, suppressing or limiting the action of the differential mechanism is the technique mostly adopted to improve the traction exiting the high lateral acceleration corners.
The common Limited Slip Differentials (LSDs) unbalance the traction torque distribution, generating as a secondary effect a yaw torque on the vehicle. If this feature is electronically controlled, these devices can be used to manage the attitude of the car.
The yaw torque introduced by an electronically controlled LSD (which can also be called SAD, “Semi-Active Differential”) could suddenly change from oversteering (i.e. pro-yaw) to understeering (i.e. anti-yaw), depending on the driving conditions. Therefore, controlling the vehicle attitude with a SAD could be challenging, and its effectiveness could be low if compared with the common torque vectoring systems, which act on the brake system of the car. In addition, unlike common ESC (“Electronic Stability Control”) systems do, a SAD can modify the vehicle attitude without limiting its traction performance, which is a crucial factor for racecars.
This paper shows the SAD designed at the University of Florence, highlighting its technical features and discussing its torque vectoring capabilities through the results of the simulation performed with a numerical vehicle model. These results show that this system is capable of improving the performance of the vehicle, in terms of both vehicle stability and traction.