3 ms·
If the wheel speed sensors drop out they put nothing on the CAN bus, not a "0 speed" message. I think it's pretty safe to assume the controller logic here has a
by Doxin 2y ago
If the wheel speed sensors drop out they put nothing on the CAN bus, not a "0 speed" message. I think it's pretty safe to assume the controller logic here has a fairly strict timeout on how often it wants to see wheel speed messages.
- Retr0id 2y agoThere is presumably still some possibility of them failing in an "always reports 0" way
- lostlogin 2y ago…Like when dismembered and spread across a bench.
- Arch-TK 2y agoIt's not unthinkable that whatever transducer takes rotation and turns it into a signal which is processed by an MCU and translated into CAN messages could get stuck producing one signal and trigger such a scenario without the car's control system needing to be on a bench.
- 0_____0 2y agoThere are some parts of engineering in safety systems where you have a single thing that could go wrong that would have serious consequences, and the result of the FMEA is that "it has to not do that".
- zardo 2y agoI don't think you'll find a wheel speed sensor without a few "outputs incorrect speed" failure modes.
- 0_____0 2y agoDetectability is one dimension of an error, and "bad wheel speed" has decent detectability I reckon - either through redundancy, grey codes, index pulse checking, bound checking. Also the issue experienced in the post wasn't an issue with a sensor per se.
- throw88888 2y agoSure, it is possible theoretically. However, most relevant regulation (IEC61508, ISO26262, DO-178X) requires that systems controlling machines in automotive, rail or aerospace have a possibility of dangerous faults lower than 10^-9 (over the expected lifespan). Many critical control systems like this are formally verified and/or extremely well-tested and have redundancy in both software and hardware.