Autonomous System Brake (ASB)

On UT23 (our team's 2023 race car), the goal was to develop a driverless mode also known as autonomous driving. My responsibility as the brakes lead was to make an autonomous system brake (ASB) that obeyed the Formula Student Germany rules. Such a system needs a service brake and an emergency braking system that solely relies on mechanical energy storage to actuate the brakes in case of electrical failure. For this, I designed the following system that would be placed in the rear of the car as the chassis of the car could not be change to accommodate this system in the front, close to the pedal tray. The ASB uses a servo of maximum torque 400 kg-cm which was sponsored to us. I had to use two master cylinders since independent front and rear circuits are required by the rules and the pressure in each circuit is different. Both master cylinders needed to be actuated by one servo so, a lever was connected to the fulcrum of the servo and the master cylinder rod ends would go on both sides of the servo at a calculated distance that would allow the servo to provide the required force to each master cylinder without stalling. This system is the service brake portion of the ASB designed to generate a deceleration of 0.8g on dry track conditions. The lever is also connected to a third rod end that belongs to a pneumatic actuator. The pneumatic actuator is part of a pneumatic circuit that connects a gas cartridge as the emergency mechanical energy source to the master cylinders. The gas cartridge's required volume to actuate the brakes was calculated with respect to its pressure and the available products on the market. A 12g CO2 paintball gas cartridge was a feasible choice due to its volume that allows up to 3 times actuation of the system and its non-flammable gas at room temperature. This cartridge is connected to a number of elements such as a pressure regulator, a safety valve, on/off valves, normally open solenoid valves, and a shuttle valve which leads to the pneumatic actuator that actuates the lever. Any electrical failure results in low signal and the solenoid valves open allowing the air to come through the open manual on/off valve and bleed into the pneumatic actuator. Two solenoid valves and a shuttle valve are used for redundancy. The lever itself is mounted on a dog clutch that is connected to the servo on the bottom and to the lever on top allowing the pneumatic actuator to actuate the master cylinders without back-driving and breaking the servo.

In this project, I did a lot of research on pneumatics, servo force calculations, and market research for availability of parts. As well, after designing the first draft of the CAD assembly in SolidWorks based on my calculations, I guided the members of my team to optimize the design with me. I especially delegated tasks such as redesigning the mounts for easier machinability by telling them the DFM and DFA principles and giving them suggestions and general descriptions. As well, we carried out an FEA analysis to verify the strength of the mounts that connected the system to the chassis. We are very excited to move into the manufacturing stage now and build this in real life and see it in action with the software on the car!