Design of electrical powertrain for Chalmers Formula Student with focus on 4WD versus RWD and regenerative braking

This thesis describes the design of an electric powertrain for a Formula Student race car. The main focus is the comparison of RWD versus 4WD and to investigate the possibilities to use regenerative braking and torque vectoring. 2014 will be the first time that Chalmers Formula Student team will compete with an electricly powered vehicle; this thesis gives guidelines for the design. Models of the vehicle dynamics are set up to investigate the differences between RWD and 4WD. From the longitudinal dynamics model the maximum possible acceleration is calcualted which is of great importance for a race car. This model also sets the requirements for the motors and gearings. The lateral dynamics investigates the performance of the car in cornering. The advantages in using a torque vectoring system are studied. The vertical dynamics models give data about the affect of having higher unsprung mass, which in-wheel motors will cause. From these models it is evident that major advantages can be gained by using 4WD. More traction, and thus better acceleration, is gained when the tire grip of all four wheels is used. It is also possible to implement a more powerful torque vectoring system when the driving force of all four wheels can be controlled. A torque vectoring algorithm were implemented on a RC-car to be able to evaluate the concept and control algorithms. Calculations on the regenerative braking show how much energy efficiency that can be gained. The calculations also show the large benefit of combining 4WD and regenerative braking. The most important powertrain components such as batteries, motors, gears and motor controller are investigated. Recommendations of components types and important design parameters are presented.