Modeling and Torque Split Control Strategy development of a 4WD-Hybrid Vehicle for Rally Application

The aim of this thesis work is the conversion of a Fiat Panda variant ‘1108 i.e. 4X4’ into a hybrid vehicle, for the purpose of its participation to the long-distance amateur rally, called “Panda Raid”, in the year 2020. The development process of the car’s model follows the guidelines of the V-shaped design, allowing the modeling of the entire vehicle in the Simulink environment. The starting model consist of a longitudinal driver which takes in input a velocity profile to follow and returns the commands of acceleration and braking to the vehicle (system’s plant). It includes the mapping of the real engine and the values of all the driveline’s ratios taken from the datasheets. The car dynamics is longitudinal, and it has three degrees of freedom, allowing to consider also the effect of the surface inclination on the car’s pitch. The wheels model takes account of H. B. Pacejka’s studies on the dynamics of the tires grip. The proposals of the hybrid conversion include the addition, to the original engine, of: an electric motor on the rear axle; a generator coupled to the engine on the front axle; a small battery in order to keep the vehicle lighter. Consequently, a driveline based on independent axes has been obtained. Once both the original and the hybrid model have been designed, a torque split control strategy for the motors has been found and implemented according to the results of the simulations obtained on a specific kind of path, designed to replicate the average track faced during the event in terms of rolling resistance and adhesion coefficients. The final design of the hybrid vehicle sees the electric machine on the front axle working as a generator during vehicle deceleration and regenerative mode, and as a motor (to assist the engine) during vehicle accelerations. The electric motor on the rear axle has been designed to work constantly with the thermal motor to provide a four-wheel drive traction. Furthermore, in order to obtain a uniform traction, it has been implemented a control of the motors based on the variation of the vertical loads.