A short circuit in the vehicle electrical system. This is a scenario for which solutions must be found for autonomous driving. An electronic isolating element, as developed by scientists at Fraunhofer IZM, could prevent a total failure.
With regard to autonomous driving, there are still various unanswered questions: Can an automatic system also react reliably in an emergency and what happens if it breaks down due to a spreading short circuit?
In current on-board network architectures of highly and fully automated vehicles, it is common practice to delimit the affected area by an overload protection. This design, however, results in the affected component being switched off completely in the event of a fault. For high- and fully automated driving, such a procedure is only possible if all components and the on-board network are redundant, i.e. duplicated. This approach is expensive, especially in the case of the vehicle electrical system, and it also takes up space and weight.
In order to ensure highly reliable safety while driving even without a second on-board power supply system, researchers at Fraunhofer IZM in the HiBord project, together with partners from industry and the Fraunhofer Institute for Integrated Systems and Device Technology IISB, have therefore developed a disconnecting element that switches off the faulty component of the on-board power supply system and still guarantees the supply of safety-relevant components.
What sounds like a savings approach is a significant improvement for autonomous driving in terms of safety. Phillip Arnold, a research associate at Fraunhofer IZM, explains: »With the current systems, undervoltage during driving can lead to an abrupt and uncontrolled failure of the entire electronics, including the steering and braking systems. Especially at high speeds, this is an intolerable risk. Thanks to our new module, part of the on-board network continues to function and the fully automated car still has enough time to drive the passengers to a safe area, for example to a hard shoulder or parking lot«.
The newly developed isolating element has 16 MOSFET switches and can easily conduct up to 180 A. If this threshold value is exceeded, for example in the event of a short circuit, the electrical switch opens and disconnects the current. Since the MOSFET switches can even handle loads of up to 300 A, they are operated far below their load limit and thus have a significantly longer service life than previous solutions.
During tests, the researchers created artificial short circuits. The results show that the electronic module can reliably insulate up to a current of 700 A without the short circuit spreading. The switching speed also has clear advantages over the conventional principle: While a conventional fuse needs about 20 ms to trip, the isolating element detects a fault within 10 µs and trips within 300 µs. This makes it over 60 times faster than current fuse systems.
The finished module has already been successfully tested in an electric BMW i3 demonstrator and is designed so that it can be used in principle in any electric vehicle. As a failure protection for unexpected electronic events, it represents a groundbreaking step towards the safe and reliable realization of autonomous driving.