Using an op amp take the output from the MAP sensor as one input with the other input set from a pot connected to one of the handy 4.98V reference sources floating about - like the MAP sensor supply so that you could get the op amp to switch its output at a preset MAP voltage - eg. 4.1V == 17PSI. This would be connected to the factory wastegate control solenoid.

Then you would have a system which left the solenoid open until target boost was reached and would then close it increasing pressure on the wastegate actuator, opening the wastegate and then hopefully rocking the boost closely around your target.

Is the idea is workable, and it does seem pretty simple and I could've missed something like - how quick can the wastegate control solenoid cycle and would an op amp's output oscillate too quickly - I hope that it would not because it wouldn't switch off again until the wastegate diaphragm had pressure, the wastegate opened and the boost dropped - hardly instantaneous in solenoid terms?

Idea could be fixed for part throttle full boost problem by having another op amp connected again to a reference/pot and TPS output. This could switch between two setups as above - one for part throttle (say below 3/4) where it would use a lower boost target or even the FBC, and switching to the other boost target solenoid controller for WOT.

This setup would have the advantage of using the factory config and solenoid, and could sit next to the ECU. It should give even less wastegate creep than a MBC?

Any ideas welcome.

http://www.force8.demon.co.uk/impreza/bcontrol.htm looking at this page it seems that the solenoid is controlled by pulse width modulation in the OEM setup at about 14 times a second and it also seems that many controllers are designed with some anticipation involved to avoid overshoot of turbo boost.

Also posted on I-club so they can laugh as well!

Abbreviations if not obvious:
MAP = manifold pressure sensor
TPS = throttle position sensor
FBC = factory boost controller
WOT = wide open throttle


[Edited by john banks - 11/25/2001 12:55:44 PM]

 

John
I think you`ve bamboozled everyone!

[Edited by JohnD - 11/25/2001 3:55:59 PM]

 

http://www.i-club.com/forums/showthr...5&goto=newpost

One of the I-club guys has been thinking along similar lines...

 

Can't help you much, apart from the op-amp oscillation question...you should be able to build some hysteresis into the switching point quite easily, just to prevent crossover rattle.

But judging buy your post you probably knew that anyway..

Justin

 

What op amp were you thinking of John ? It will almost certainly not have enough current capability to activate the solenoid directly.

---john---

 

Would use a power transistor (with a protective diode if necessary) or a solenoid driver.

But before any of this I am going to fiddle with a relief valve set at 10psi with a needle valve to replace the restrictor as per the reports on I-club of the least spiking MBC with good part throttle behaviour.