| Message |
When windows craps out, and it has happened before - but very rarely, the boost system and air/fuel control will go into a fail-safe mode that I have already developed. The wastegates will be controlled to open at 9PSI, thereby limiting boost at that point, and the airflow meter information will be instantaneously re-routed directly to the ECU. Basically, the car will take on stock TT parameters in the event something goes amuck. The wastegate function is completely mechanical though - basically a pseudo-manual boost controller. The airflow meter information is a little more complicated - but simply put, it is a relay that is controlled by the computer, but it is more than "just a relay". When the computer is on and the boost control system is operating, a signal is fed to a controller that allows the computer to intercept the airflow meter information before it gets to the ECU. Additioanlly, it connects the analog output from the acquisition board directly to the ECU. The acquisition board is responsible for adjusting the airflow meter information and feeding the adjusted value to the ECU. In the event that the system hangs, or the power supply overheats (causing system power loss), the fail-safe device no longer receives the appropriate signal, thereby re-looping the airflow meter directly to the ECU, and the vehicle operating "normally". -OR- at least - without fail. The fail-safe device I have built is simply a programmable interrupt controller (PIC) that interfaces via a serial port. There is no mechanical relay, only electronic, and it has a response time of 2us. (microseconds) The ECU will see it as a slight aberration in the signal as this happens, but nothing that will affect engine performance. It will eventually be used the same way with ignition timing - but thats a little way down the road. (no pun intended) :-D
My CarPuter Headquarters:
http://ashleypowers.homepage.com
agpowers@bellsouth.net
 |
 |
