Formula SAE Electric team of Sapienza University of Rome

INTRODUCTION

Fast Charge is the Formula SAE Electric team of Sapienza University of Rome. The team was born in 2012 from the heritage of TUSCIA Reparto Corse and thanks to the collaboration and support of ENEL, SCIRE, CTL and ENEA. After a crowded stage of recruiting in October, for the current season a team of more than 40 young students was founded focusing its design activity on the optimization of powertrain and rolling chassis, in order to obtain a lightweight full electric racing car. A careful design of the storage system has been performed, combining a sizing strategy tailored on endurance real data with an optimized cooling system. The main specs for this competition season are made up of: optimized steel tube chassis, single YASA DD500 electric motor with SEVCON Evolution 5 drive, EP 6.3Ah lithium-ion cells with ABS case, air cooling system with electronic management, aluminum wheel groups, limited slip differential, data logging system with thermocouples on all cells, a complete set of sensors for car vehicle dynamics and last but not least carbon fiber bodywork and a complete

aerodynamic kitfor an overall car weight of 240 kg, 80 kW@300V and 1500 Nm@wheels.

DESIGN PHILOSOPHY

The philosophy behind the Fast Charge project involves the design and implementation of a reliable, light, powerful, easy to drive car with a low cost of construction and maintenance, reducing the environmental impact. Team name is inspired to the fast recharge technologies of the future: one of the waysto make electric cars a solid answer to mobility’s questions.

Developing the project, an extensive use of CAE software was made, for the mechanical design and for the tuning of the powertrain. Thanks to the support of ANSYS and Fluent, The MathWorks, Adams Car, a complete dynamic, electric and thermal model of the car and its main components has been realized and the whole design has been driven by the simulation results. What is our goal? Our job wants to contain weight, to optimize handling, to control energy and temperatures inside the storage system, to have good performances, to control the maximum delivered torque in order to avoid wheel slip in acceleration.

ELECTRONICS

The design of the car electronic equipment is based, first, on the compliance with the FSAE rules. On the car, several electronic devices are present, classified as programmable and not programmable devices. The goal of this year is to develop a reliable architecture with high and easy expansion perspective which could be resilient at many secondary faults and could permit the external live monitoring of the entire car system.

System Overview

The programmable electronic system manages the inverter which control the electric motor, realizes the safety procedures for plausibility checks, controls the Accumulator Isolation Relays, controls the traction state and the racing performances and communicates with the box with a radio bridge. All these responsibilities are decoupled in many electronic devices wich are explicitly designed to accomplish the proper task and can easily modified without affecting the entire modular architecture. The on-boardcommunication relies on two CAN bus, one is for the acquiring of the measurements of the analog sensors and in the more critical second bus found place the inverter, the AMS and the control unit. To locate the electronic devices in the car the boxing strategy is completely redesigned by the team using the additive manufacturing process to prototype and develop the solutions.

VCU

The functional operations of the vehicle are controlled by the Control Unit based on a CORTEX M3. The board is a gateway among two CAN bus and a radio communication. It read the pedals value via CAN bus with analog redundancies to be fault tolerant on them which are criticals and drives the inverter through another CAN bus. Between the VCU and the vehicle there is an analog isolation stage board. It provides the current to close the AIRs, monitors the Shutdown Circuit and has all the transceivers needed for the serial communications.

VDIM

The VDIM is based on a Texas Instrument F2837xS board with two CAN lines, Simulink support and high mathematics capabilities. The main task of this board is the traction control of the car:it acquires the signals of the sensors and calculates the dinamic state of the vehicle and how many of the torque request are need to cut signaling this value to the VCU. It prevents undesired slips of the tires. CAN bus. In order to ease the acquiring and the preprocessing load of sensors value on the VCU and VDIM, to simplify the wiring in the vehicle and to enhance the development perspective, a CAN bus is placed to link all the sensors and user interfaces. A custom board developed by the team, based on an ARM CORTEX M4, with high communications capability, manage and elaborate the informations in a harsh racing environment. With the introduction of such redundancy of calculation capability, the overall safety level of the signals system is increased.