FS Vitoria: Engineering for Reliability and Performance

Last season, the team focused on improving the efficiency of the previous year’s car, as this was the most noticeable shortcoming in the V02 version of the vehicle.

This reliability was mainly sought in the electrical and drivetrain departments, aiming for more robust electronics and replacing the treatments for the transmission gears to reduce wear during use.

The rest of the departments concentrated on gaining a better understanding of the vehicle and how different aspects affected its behavior, as well as beginning to plan an iteration of the car with significant changes, with the goal of having a worthy successor to “Bizkor” by the end of this season or the next.

The sponsorship with Eurocircuits allows us to have our PCB done in quite a fast time and not only that, but also with a great quality, which means a great reliability of the electrical part of the car, which is the most critical one.

Talking about critical systems of the car, there is a PCB which is on charge of managing all the critical signals that need to switch off the car. According to FS rulering all the EV cars have got a shutdown circuit, with give the supply of the battery contactors. In case this system is not complete armed there is no way the battery is electrically connected to the car. And in case the is an issue once the battery is connected, this PCB turns down the supply to the contactors, so they open and put the car the in a safe state again.

For that aim, there are three critical signals that are monitored with the PCB. And also is the starting point of the rest of the shutdown circuit system, with is compose of different mushrooms, interlocks and crash sensors. In case the three critical signals are okay, the following system is supply.

The critical signals are the AMS (Battery Management System), BSPD (Brake System Plausibility Device) and the IMD (Insulation Monitoring Device).
As power stages for opening the shutdown circuit by the AMS, IMD and BSPD, DPST-NO (two contacts driven with the same coil) mechanical relays are used.
One of the two contacts of the relay will be used for actuating the SDC while the other will be used for the latching circuit.

The working principle is the following one.

1. Powering on the circuit: When the circuit is powered on, the optocoupler and the SDC will be open, even if there is no fault.
2. Power-on circuit: A power-on circuit is needed to close the optocoupler for the necessary time to activate the relay coil and close the SDC.
3. Relay maintenance: After the power-on circuit finishes, one of the relay contacts allows current to flow to the coil, keeping the relay activated and the SDC closed.
4. System fault: If the fault signal turns to 0V, the N-channel MOSFET disconnects the ground of the coil, opening the relay and the shutdown circuit.
5. Reset after fault: If the fault signal returns to 5V, the relay coil will not be supplied, and the SDC will remain open until the optocoupler is closed again.
6. Reactivating the SDC: After closing the optocoupler for a few milliseconds, the SDC is closed again if the fault signal is 5V.

Power cycling set/reset circuitry: For the power stage latching circuit operation, it is necessary to activate the optocoupler to supply the relay coil when the LVS is switched on. This will be done through a system based on an RC timer and a P- channel MOSFET

So once the PCB is tested in a simulation program and verified that it working principles are fulfilled is time to send to Eurocircuits for manufacturing the PCB. The actual board photo can be seen now.

And once received the PCB, thanks to the quick manufacturing and sending processes from Eurocircuits we can assembly in our workshop. Finally, once it is assembly and a real test is done to assure that everything works correctly the PCB is ready to be installed in the car.

For more information please visit the FS Vitoria website.