Electronic Boost Control

[Robert E. Yorke]

Adrian:  

You're project sounds interesting; I wish you luck in coming up with a
working product.  I myself would be interested in buying one of your
controllers if and when you get it done.  I've had my fill of faulty
pneaumatic diaphragm controllers  (What's even worse, I can't even find out
who MAKES 'em, so I can complain!).  Although completely unsophisticated
relative to the details I might provide a caveat: make sure the actual
components that are right at the turbo, will withstand the high amplitude
heat cycling.

Good Luck!


At 09:07 AM 4/3/97 EST, you wrote:
>     Hi Everyone,
>     
>     I am a new comer to this mailing list, and I'm not 100% sure that the 
>     information which I am after is applicable, but I'll tell you anyway.
>     
>     I own a 1992 Subaru Liberty (or Legacy) RS Turbo, for which I wish to 
>     add an electronic boost controller. The advantage of such a system is 
>     improved boost curve through the use of a PID control system instead 
>     of the current proportinal pnuematic bleed control system so better 
>     bottom end performance, and more accurate control of boost than the 
>     current system which due to its dependance on the flow of gases, can 
>     vary alot with temperature. Due to availability of development tools I 
>     have chosen to use a 68HC705B16 as the microcontroller for this 
>     system.
>     
>     My first query is to a power supply to produce a clean 5V from the 
>     dirty 12V supply of a running engine. Does anyone have a schematic of 
>     a typical power supply which may be used for such an application, be 
>     it switch mode, linear, or whatever? I will need to drive a 12V pulse 
>     solenoid valve, so will need sufficent curent to run driving circuitry 
>     for this valve (I expect that this will be biggest current demand on 
>     the system)
>     
>     My second query is in regards to the driving of the valve. It uses a 
>     12V coil which requires around 800mA holding current. Does anyone have 
>     any recommended methods to drive coils like this from a logic output?
>     
>     My final query is to modelling boost pressure in the manifold. In 
>     order to test (and tweak to a certain extent) my controller code off 
>     the car and avoid risk of over-boost, I would like to model manifold 
>     pressure as a function of throttle and load for my car using no boost 
>     control using C code. I have chosen to use a C compiler to develop my 
>     microcontroller code, so I could therefore test my code using such a 
>     model and allow many of the PID parameters for the controller to be 
>     optimised intially so that only minor tweaking of these parameters is 
>     required on the car. I have reasonable knowledge of how turbos work 
>     and have written my own model, however it is not fantastic, and I have 
>     no idea of the order of time constants for the turbo, and transfer 
>     functions for calculating the volume of flow of the turbo for a given 
>     exhaust flow etc. If anyone can point in the direction of anyone who 
>     might be able to help in such matters it would be greatly appreciated?
>     
>     The issues I have raised are not purely efi, but I hope that they may 
>     be relevant to this group. Also does anyone know of any information 
>     sources for DIY electronic boost control.
>     
>     Cheers,
>     
>     Adrian
>
>
>
Riverside, CA
2 '88 GTs!