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Battery Powertrain Design - QFR 2020

10.03.20 · Engineering News

3rd Year Mechanical Engineer Ciaran McNicholl discusses the battery powertrain on the new all-electric 2020 Formula Student car with QFR Team Leader Rachel MacNeill.

 

Rachel: So this year we’re transitioning to electric and we have a 3rd year design team dedicated to designing electric power train. So Ciaran can you tell us what you have been doing with the project so far?

Ciaran: We took the QFR 19 chassis as a basis to start off with, took measurements of the size available for the engine and went with this for trying to size up our accumulator. Obviously taking into account that the motor would sit at the back within the chassis as well. This gave us the basis to start on a CAD model to try and incorporate some sort of size measurements for what we had available to us. We then looked about at how we were going to create this capacitive battery, keeping in mind the endurance event and the acceleration event to try and find the balance between obviously energy storage against power required to accelerate the car as quick as possible. We done this using MATLAB script which then gave us figures and requirements from our battery. We then went about spec’ing the batteries that would fulfil these requirements. Which tuned out to be 18 650 cells, cylindric cells, mainly due to safety reasons over quick cells, which can quite easily enter thermal runaway which would basically result in a fire.

Rachel: So, how is the chassis shape going to change now that you have the accumulator so near the engine?

Ciaran: So due to the engine being taken out and an electric vehicle power train being added, obviously we no longer require the fuel tank, so due to the fuel tank going we can now move the fire wall closer to the seat, giving us a lot more space available here. The cross member cylinder can be raised up slightly to accommodate for more height due to the BMS and all those other requirements within the accumulator, so that gives us a little more space as well. Obviously the QFR 19 chassis was actually shortened to be optimised for the R6 engine. This can be lengthened back, so obviously then we have more space for a motor at the back. Then once we have these lengths, we can then start to look at the width. So due to these high voltages, high currents, we have huge conduit wire which will be carrying up to 500 volts, 200 amps. So, these obviously require a lot of space as well due to bend radius – because we are using 35mm squared wire, which is quite thick wire. So once we get these singles in we can then look at cooling. Which was one of the biggest problems with this year’s accumulator, was trying to find spacing for the cooling. Because it is quite big, we were trying to push it out wide, because we were struggling lengthways. Which then means if the cooling is coming in the side, we need quite a lot of space to turn the duck from the side pod round into the accumulator.

Rachel: So obviously you have only had 9 months to do this project, but in future years is there anything you think they would do differently or add in that you haven’t had time to do?

Ciaran: I think that in general, quick cells may be the way to go forward – weight saving and stuff like that. I think that in general in future we will go down the quick cell route.

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