Additional impact protection for electric vehicles
If an electric car is involved in a crash, the DC/DC converter for the low- voltage vehicle electrical system can pose a hazard for vehicle occupants and emergency responders if it breaks and comes into contact with live parts. For added protection, Audi has contracted Frenzelit to supply an aramid textile that covers the entire DC/DC converter in the Audi e-tron.
Roland Wegscheider, Design Power Electronics/Charging Systems at Audi, explained the requirements for the protective material: “We defined all the key properties in our specifications. At the top of the list were cut resistance, electrical insulation, temperature resistance and media resistance, e.g. against oils.”
Frenzelit has developed a protective sheath made of aramid fibres called thermoREFLEX with an additional UV and moisture-resistant coating for increased dielectric strength. The insulation resistance is ten megaohms even after being subjected to a range of weathering processes.
Aramid was the material of choice for the Audi developers from the outset. It is used in the Audi e-tron in crash sensitive areas as cable sheathing thanks to its cut resistance, so it also appeared to be a good candidate to protect the DC/DC converter.
Audi subjected the thermoREFLEX protective sheath to tests that go beyond the statutory requirements. Roland Wegscheider explained: “Our requirements for vehicle approval are high, especially when it comes to safety. We want to consider all possible eventualities and therefore go above and beyond what is legally required.”
For example, one statutory requirement is that active discharge of the high-voltage intermediate circuit must take place within five seconds in the event of a crash. First responders generally do not reach the vehicle in five seconds, and occupants do not touch any live parts within this short period either. Nevertheless, if a connection breaks at the DC/DC converter and the capacitor is not immediately discharged internally, Frenzelit’s thermoREFLEX sheathing provides additional protection by preventing contact with live parts.
The testing included a climatic shock resistance test with a temperature range of +80 to -40°C and a temperature shock test from -40 to max. plus 95°C. The requirement: No changes in tensile strength. Resistance to moisture was also tested under conditions of 40°C for over 400 hours. Since the joints represent a potential weak point, it also had to pass a seam test. The aramid protective sheathing proved to be an additional safety factor in all scenarios.