Development of an e-LSD Control Strategy Considering the Evolution of the Friction Torque with the Wear Depth

The Electro actuated Limited Slip Differential (e-LSD) can help increasing the dynamic features of the vehicle, but to implement a well designed control logic it is necessary a deep knowledge of the actual friction torque built up by the differential clutch. This work presents the development of such a control law that takes into account the wear depth progression. To carry out this task, an alternative method has been used to study the clutch discs engagement depending on the wear rate.The method takes advantages from a mixed approach with a numerical and an experimental part. Using a general purpose block-on-ring test bench, the tribologic analyses were performed following the ASTM G77 standard; thus, the friction coefficient has been investigated in the contact between discs with molybdenum treatment and steel alloy discs, as well as its variation depending on the wear rate. The results were input in a numerical algorithm aimed at evaluating the friction torque of the clutch as a function of the pressure and the wear depth. The results, besides providing useful hints for the clutch design, were used to numerically assess the differential effects on a vehicle equipped with it. To accomplish this goal, a technique generally known as SiL - Software in the Loop was applied to multibody analyses. The paper is aimed at comparing the vehicle behavior using three different devices (open, self-locking and e-LSD) and performing standard (ISO) manoeuvers. The outcomes prove the advantages of the e-LSD in terms of handling, lateral dynamics and traction in comparison with the other solutions.