Design and implementation of autonomous braking system for Formula Student Driverless application

To achieve the autonomous drive, a vehicle must be able to do the perception of the environment, to elaborate the signals for the path planning and to perform the dynamic manoeuvres without any human intervention. For the perception part, the main sensors that are used are the radar, the lidar, the stereo camera and the ultrasonic sensors. For the path planning on the autonomous vehicles some dedicated hardware is present in order to elaborate the information coming from each sensor and to control properly the vehicle dynamics. For what concerns the dynamic manoeuvres, the development of systems that can properly reproduce human’s inputs to such as the steering action and the pedals pushing are necessary. An Autonomous Braking System will be the object of this thesis. Its function is useful both for autonomous vehicles and traditional ones, since it is able to increase the safety when the human intervention cannot be performed. This kind of device can be implemented in different ways, such as through electric motors that directly move the pedal or with pumps that rise the oil pressure inside the braking lines. This device will be developed on the Formula Student prototype SC19D. The aim of this vehicle is to participate to Formula Student Driverless, a competition in which each team is composed by engineering students with the aim to design and build a fully autonomous vehicle. The Autonomous braking System developed in this thesis will be an adaptation of an already existing traditional brake pedal, equipped with two independent master cylinders and a balance bar, needed to make the partition of the brake effort between the front and the rear axle. The layout of the system will be composed by a servomotor that, through a pulley, actuates with metal cable directly on the top of the brake pedal. After a short introduction in the first chapter, in which will be exposed the context about the autonomous drive and the formula student competitions, two models of the brake system will be developed. The first one will be a bidimensional model collapsed on the midplane, obtained by physical and geometrical considerations, that represent the brake pedal and the master cylinders. This model will be very simplified but useful to perform a rough sizing of the servomotor. Then, a parametric multibody 3d model will be carried out on MATLAB® Simulink. In this one the two master cylinders, the balance bar, the servomotor and the pulley with the metal cable will be modelled. From the results obtained by the simulations of the multibody model, some lookup tables will be realized to directly link the servomotor PWM control signal to the oil pressure inside the brake lines. Moreover, a PID controller will be designed to realize a closed loop control on the oil pressure and to reduce the errors. The chapter 4 “Mechanical Implementation” will be dedicated to the design of the mechanical parts. In that section a more detailed design of the main mechanical components will be analysed. In the end, there will be an experimental campaign done directly on the vehicle. This will lead to important results to validate the architecture, the models and the control of the system.