Written 01/09/22 by Tom Johnson

In my second article on the regenerative braking system for our electric Formula Student car, UH27 - I will be discussing a physical implementation of the system on our vehicle.

In theory, only one physical addition to the braking system needs to be made - meaning only one component needs to be designed. I won't be covering the design of such a component here - as that falls to the braking team in the Drivetrain department.

Currently, the brake pedal is connected to two master cylinders, one for the front brakes and one for the rear brakes. The bias is adjusted by a bar on the back of the pedal. Pressing the brake pedal directly actuates the hydraulic system, causing the braking procedure to take place. Monitoring of the braking system for use in LV systems like the BSPD is done using a potentiometer, which effectively measures the brake travel.

We need to design some sort of linkage between the brake pedal and the master cylinders that allows us to prevent some initial pedal travel from actuating the hydraulic braking system. This enables us to use the potentiometer to alert the ECU and inverters that regenerative braking needs to take place. However, once the pedal has been pressed even further, signifying that the driver requires extra braking force, the physical actuation of the hydraulic braking system takes place.

One of the benefits to our motor-inverter setup is that no other major modifications need to be made. The Fischer Ti-085 motors we are using can produce 29.1Nm of torque each, which is significantly higher than the 20Nm total that our regenerative system can handle. In fact, if all four motors were working at maximum torque, we could produce over 120kW of regenerative power. For context, Tesla's regenerative braking system can only produce ~ 60kW under hard braking. Additionally, the inverters and ECU should handle such a system with no problems - so long as the software is up to scratch!