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Old 11-12-2009, 01:07 PM
GerWil GerWil is offline
Officially Welcomed to the 'Fest
Location: Vermont
 
Join Date: Dec 2006
Posts: 320
Mein Auto: 2013 335i xDrive
Quote:
Originally Posted by DSXMachina View Post
I recently attended a school on the "drive by wire" throttle control systems on all cars sold in the US. As you can imagine the main concern on everyone's mind, right after how we can make money on these things, was reliability and liability.
There are so many redundant (dual or triple) systems at both the signal and receiver end that runaway acceleration is theoretically impossible. At least two signals are generated at the pedal, one high voltage, one low voltage. These are carried by separate wires and the voltage decoded at the throttle. If the signal is whacky the system goes limp home. The throttle is also heavily safeguarded. It has a stepper motor which generates a signal every time it moves. A minicomputer compares that signal, coming from two separate sources within the throttle, with the pedal signal. Any mismatches? Limp home.
Even if all these signal matching safeguards fail, the throttle motor itself is set to fail in a closed position. Limp home. No, the motor does not have to close the throttle! If it doesn't, a spring does. Limp home.
I cut my teeth on this kind of scenario back in the runaway Audi days (simply put, drivers were hitting the accelerator and not the brake, but that almost put Audi out of business). I'm not naive, and have some ability to imagine how things can go bad. I cannot think of any possible way the current dbw systems can make a car take off when the throttle isn't pushed.

Edit: I believe that the dbw system has as many feedback loops and redundant systems at the hydraulic controls on an Airbus.
I once owned a vehicle (not BMW) with a faulty cruise control that engaged without the button being pressed. Not saying that happened here, since claim is that foot was on brake, but there can be other causes for an acceleration other than the throttle.
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2007 335xi (ED 5/10/07, Redelivery 7/12/07)
2010 335i-xdrive (ED 10/19/09, Redelivery 12/30/09)
2013 335i xDrive (ED 9/15/12), Redelivery 11/23/12) mineral grey
2014 X1 xDrive28 (ED 5/13/13), Redelivery 7/11/13)
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