My current project is adapting a Garrett AVNT turbo to a gasoline passenger car application with performance in mind. The Garrett AVNT turbo is an electro-hydraulically activated VNT turbo, the pressurized oil supply from the engine is used to change the position of the vanes in the turbine housing. The spool valves(ball valve) directing the oil supply are controlled electronically by the ECU based on calculated engine load.

Here's what I have found out about the signal that actuates the variable turbine: "A pulse width modulated proportional solenoid provides infinitely variable control. Further, the design is completely self-contained with only a single electrical plug-in to the engine's ECU. As a result, all variable forces are removed from the control loop; aerodynamic loading, friction and oil pressure." -- cut/pasted from this article: http://www.findarticles.com/p/articles/mi_m0FZX/is_10_69/ai_110471904

The Garrett engineer I spoke to today told me to ask a Ford or GM dealer (they both use the same AVNT center section on their respective turbos) what kind of signal they should get  going to the turbo when they put the truck on the scope.

Maybe I can end up running it the same way I would run a fuel injector off my ECU, the ECU will think it's sending the signal to a fuel injector but really it will be going to the turbo...

Does anyone have any experience or comments about this subject?

Generally the important parmaeters with a PWM signal are voltage, current (load), and duty cycle. Frequency also comes into play, though that comes more from the duty cycle.

From my understanding the signal should be a square wave with the duty cycle representing the on time or (pulse width). So that if the on time is 10ms and the off time is 90ms, the duty cycle is 10% and the frequency is 10hz. The signal has to have engough power (current & voltage) to actuate the solenoid reliably without burning out its drive circuit, or cooking the solenoid.

Disclaimer: I am not an EE, I have a very basic understanding of PWM signals.  

It seems to me that you would want a control system similar in action to a wastegate. IE: at low RPM, WOT the VNT system should extract the maximum amount of nrg (energy) from the exaust. As the RPM's increase the VNT system should back off the blades to improve flow and keep the compressor wheel from running out of its efficient range.

This sounds really cool, imagine a boost curve that is flat from 1500-6500rpm!

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