16-05-2012, 01:06 PM
You seriously need that feedback, or yes, as you say the cruising pressures are way higher, at 70mph if you have it in at a point where it spools very quick, you're talking 18-20psi inlet and 25-30psi exhaust pressure, WAY too high really, you end up having to ease off the vane stop point, in which case you may as well have a Wastegate turbo...
But essentially, that's what I've done, got a Microcontroller to read MAP, TPS and RPM - you then have a table TPS vs RPM which then you have to set up with values from scratch, but it's not that difficult, depending how fine your table is - the finer the smoother... So essentially it's a boost control and limiter all in one... I actually have two maps it can run, one for cruising and one for ragging the ass out of it, purely because of the way the injection pumps work and it not being able to know the position of the LDA - the throttle percentage isn't actually really relative to IQ, so when you're cruising you'll find it's producing too much boost, but when ragging it, you'll find that it's a bit unresponsive under trailing throttle and some transients you tend to encounter.
Then use PID control to give it a target boost pressure with MAP as your feedback... It's then a case of fudging round with the PID variables to make it not hunt and overshoot too much for all conditions - in fairness that was actually the second hardest part...
The actual hardest part was essentially rewriting and refudging a load of the firmware for the controller I am using, most solenoid valves work on 140Hz PWM, typically the controller I use wants to use 100Hz PWM, therefore the solenoid valve used to go nuts... With adjusting the internal clocks, I've got it to 137.somethingHz now, which seems fine as long as you don't use the outer edges duty cycle, or it gets very jittery/jumpy...
When I did it I was sad enough to do an adaptation/calibration function which allows you to adjust the outer edges where the the solenoid valve needs to work, it actually only needs from about 35-70% duty cycle... Also have the same thing on the throttle pedal, so it reads a value for 0% and a value for 100% and works between that, makes life so much easier!
</geekrant>
But essentially, that's what I've done, got a Microcontroller to read MAP, TPS and RPM - you then have a table TPS vs RPM which then you have to set up with values from scratch, but it's not that difficult, depending how fine your table is - the finer the smoother... So essentially it's a boost control and limiter all in one... I actually have two maps it can run, one for cruising and one for ragging the ass out of it, purely because of the way the injection pumps work and it not being able to know the position of the LDA - the throttle percentage isn't actually really relative to IQ, so when you're cruising you'll find it's producing too much boost, but when ragging it, you'll find that it's a bit unresponsive under trailing throttle and some transients you tend to encounter.
Then use PID control to give it a target boost pressure with MAP as your feedback... It's then a case of fudging round with the PID variables to make it not hunt and overshoot too much for all conditions - in fairness that was actually the second hardest part...
The actual hardest part was essentially rewriting and refudging a load of the firmware for the controller I am using, most solenoid valves work on 140Hz PWM, typically the controller I use wants to use 100Hz PWM, therefore the solenoid valve used to go nuts... With adjusting the internal clocks, I've got it to 137.somethingHz now, which seems fine as long as you don't use the outer edges duty cycle, or it gets very jittery/jumpy...
When I did it I was sad enough to do an adaptation/calibration function which allows you to adjust the outer edges where the the solenoid valve needs to work, it actually only needs from about 35-70% duty cycle... Also have the same thing on the throttle pedal, so it reads a value for 0% and a value for 100% and works between that, makes life so much easier!
</geekrant>
