Quote:
Originally Posted by ard
Engineering practices usually design based on 'single fault conditions': what will happen if X fails, or Y fails.
The system is not designed to accommodate failed airbags in a car that ALSO has some other electronic failure preventing sleep mode
If the airbag fails, the owner will note a sag. I will bet there is something, somehwere in the owners manual that says 'see your dealer if _______'.
In product design there are a handful of 'controls' that one can apply, which vary based on the risk of the failure. Life threatening (or car control) issues tend to have much stronger controls than others...but at the end of the day the owners manual is the place where all that ties to the driver.
Hazard analysis, risk management, Design failure mode analysis, Use analysis, etc...all try to capture failures then risks. Some of these may even look at certain cascading faults (dual fault) based on risk (ie fire, crash). These documents will run to thousands of pages and are among the most confidential of company documents.
And no, I dont think BMW engineers missed this.
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Thanks Ard for flying the BMW flag. I was looking for something a bit more conclusive than just design concepts and brand reputation.
So let me be more spcific;
Over two consecutive nights I checked mm deviation using a scan tool as well as measuring height with a tape measure. On both mornings no visible lowering of the car and mm deviation. This led me to believe that the air springs are good or the compressor is keeping them inflated throughout the night AND therefore prevented the vehicle from going into "sleep" mode.
Then I removed the fuse for the compressor, within 90mins the car was visibly at its lowest point. This lead me to beleive that either the bags were deliberatly deflated due to error code or they leaked out.
Therefore if you did not know that your airsprings were leaking, you would not know about it until the leak was big enough to overcome the compressor filling rate. By this time the compressor may have passed its normal duty cycle and failed.
What I was looking for was a fail-safe shutdown of the compressor after say three failed attempts to fill the air springs.