toplessFC3Sman

iTrader: (1)

As far as I understand, all an EBC is is a little bit of logic that compares intake boost pressure to a set upper limit, and when boost reaches that, it opens the wastegate.

Thinking about this, it would be pretty simple to build a bit of digital logic to compare the boost sensor's output to some value (determined by a resistor array with a potentiometer), and when one exceeded the other, trigger a pneumatic solenoid valve to connect intake boost to the wastegate. This way it'd be adjustable, straightforward, and cheap.

Going a step farther would be to integrate this onto a PIC along with temperature sensor input (cutting boost earlier when the intake is hot) and possibly a throttle position sensor (dropped throttle = open solenoid valve).

Am i missing anything obvious here? Sound logical/doable?

coldfire

iTrader: (1)

that sounds about right. the only thing is EBCs are sometimes a little smarter and implement a control algorithm that is dependent on a few variables. getting a non-linear response, based on throttle, etc., would also be harder.
but i am pretty sure you could make something that could do at least as good of a job as a manual BC. really it can be purely electrical, no digital logic needed, for something simple. i would think automotive signals are usually quite "dirty" for digital systems, so sometimes require cleaning up.

a lot of the cost of a EBC you can buy also comes from the user interface and display.

whatever you do make sure the system design is failsafe .

i've done some of this stuff at school (more so digital logic). PM if you are wondering about something, although you might know more than me.

edit:
good info here, http://en.wikipedia.org/wiki/Boost_c..._boost_control

pengarufoo

if you could integrate road speed & rpm inputs you could approximate the gear and alter the boost curve accordingly to help keep traction in the shorter gears.

good luck if you take on the project, you have my uh... moral support or something

toplessFC3Sman

iTrader: (1)

altering the boost curve is something a bit beyond the original scope I was thinking of, but a good idea to try to implement later. I was planning on using a completely seperate boost sensor than stock, and havent put a lot of thought into the temp sensor, but by building an isolated system, hopefully that will help to quiet it down a bit.

nik

This will not work because it will blast the wastegate full open as soon as it triggers, then you will loose boost, then it will fall below the threshold again and close the wastegate fully. Likely to get some oscillations there.

Not opening the wastegate at all until desired pressure will result in extreme boost spiking.

Proper EBC has solenoid valve to adjust how much pressure the wastegate sees, in an analog not on/off fashion.

Most ebcs that people use(eg profec) are open loop and do not actually compare the manifold presssure to target boost.

arghx

iTrader: (3)

^ Apexi' AVC-R is to my knowledge the most sophisticated one. It's what I plan on running in my car. It has its own external pressure sensor, allows you to map boost in each gear, and map solenoid duty cycle. It's ******* sweet.

pengarufoo

the solenoid valve is a binary state device, it's simply driven by PWM to achieve this 'analog' behavior, his circuit can manage it.

Obviously a solenoid valve capable of continuous use without overheating will need to be used, these are readily available for this purpose...

nik

The way he was describing it was an on/off type solenoid. Solenoids meant for pwm have some kind of counter load (a spring) so that the valve can exist in varying states of opening and closing.

These also need to operate within certain bounds of frequencies, which this type of controller totally ignore. Also the boost spiking will be a serious problem.

As far as i know the avcr is an open loop controller, and a pain in the *** to tune compared to a simple cheaper profec B

pengarufoo

Theres no problem with the solenoid being "on/off type", thats the point of PWM.

from:
http://en.wikipedia.org/wiki/Boost_c..._boost_control

but this concept is far reaching, nothing EBC-specific going on here.

nik

As i am sure you know, not all solenoids are constructed the same. You even said this yoursely in that it must be rated for continuous use and not overheat. Some are meant for pwm applications and some are not. Not all solenoids are driven by PWM. Of course, now you may argue what pwm means.

Regardless of these things, the proposed system, with no concern lent to control system stability, will perform in a poor fashion compared even to a manual boost controller. How poor depends on a host of things like solenoid speed, wastegate configuration, engine, turbo, etc.

As far as i can tell, there will initially be an overshoot of the target boost level. This will be followed by a series of oscillations that may or may not converge to the desired setting. All in all, not a good idea for implementation as is.

SirCygnus

iTrader: (1)

yeah. one exists.

its from tullos tech.
its currently in beta stages and is about the size of an ipod.

its completly open sourced and you controle it via your laptop.

arghx

iTrader: (3)

http://www.apexi-usa.com/pdfInstallation/21.pdf

AVC-R has a self-learning mode to map solenoid duty cycle over different RPMs and gears. I would consider that a closed loop system.

Granted, I've never used one, but I'm sure it's harder to tune than a Profec--those are just a bunch of ***** (do they have a digital one now?). But more capabilities = longer learning curve to use properly, at least to a point. It's the same with an engine management system.

nik

The self learning mode is not true closed loop control. It is simply an open loop algorithm whose parameters can be automatically configured, during some special learning mode only. Now, if it were possible to stay in this self learning mode at all times then it could be considered a closed loop controller. A closed loop controller will be able to compensate for changes in weather, gear, etc inherently in the algorithm, without necessarily having sensors for these specific things.

The avcr is not worth the extra money in my opinion. However the gear dependent boost has good applications.

pengarufoo

try a google search for pwm solenoid driver, if for some reason the fellow asking about the diy boost controller can't piece together a pwm driver ic in the circuit himself there are places that sell them as modules ready to take a voltage level in -> duty cycle of pwm out for this.

this is all very common stuff, and suitable solenoids are all over the place.

nik

Hehe, so now we are using pwm driver ICs, a much better plan than before.

Throw in a difference amplifier to measure the difference between the target boost and the measured boost, and feed that into the voltage controlled driver IC, and you got a simple proportional closed loop boost controller. Adjusting gain on the amp will allow you to tune the system.

Of course it probably wont work very well...

pengarufoo

Hey, the original poster was already talking about throwing in a PIC...

toplessFC3Sman

iTrader: (1)

I've got a few spares laying around from another project, that seems to be what i'm leaning towards at the moment. Set up a PID algorithm on it (altho i dont know how useful the integral control would be... just for extra stability I'd think), create the PWM on the chip so a PWM driver wouldnt be necessary. Probably use a servo-controlled valve instead of the solenoid one. Modelling the system beforehand may be a bitch tho, considering things like the wastegate actuator bleed rate, response time of the intake pressure to wastegate dumping, and specifics on the valve's transient behavior arent really known.

RotaryEvolution

iTrader: (30)

the title of this thread scared me too much to read it.

a boost controller is one essential ingredient to whether your engine will live or die today, keep that in mind when trying to DIY stuff together to save money.

nik

I was actually thinking of doing the same thing(implement a PID). Like you said it wont be easy/possible to model the rest of the system, so stability calculations won't be an option. But PID is so common that there are guidelines as to what one should choose for parameters. It wouldn't be significantly more work to set up than a profec.

Another nice thing one could incorporate is some traction control, like tie in the wheel sensors from the abs and limit boost under wheelspin.

Anybody know if the megasquirt project is working on something like this?

Aaron Cake

iTrader: (1)

Long story short is that I have thought about this for years, built sample circuits, experimented with various solenoids and whatnot...What it came down to for me was that commercial boost controllers are available very cheaply, most EMS systems have boost control built in, and I didn't want to risk an engine if something failed (ie. drive MOSFET died due to unanticipated flyback loads).

My design was very simple: GM MAP sensor with a 0-5V output directly driving some PWM chip (I forget which one but I could probably look it up) that PWM'ed a solenoid based on manifold pressure...Higher MAP meant longer PWM on time which meant more wastegate opening. Stupidly simple and adding a little hysteresis to avoid oscillation would likely result in an easily workable controller...

Aaron Cake

iTrader: (1)

MSnSE has included boost control for a while now. The V3 board has a boost control output you can use to drive a MOSFET or two to run your solenoid.

classicauto

iTrader: (3)

Haltech's EBC is only $78...how cheap are the FC owner's getting now-a-days? lol

I've been thinking about getting it but the MBC Im using will leave holes in my interior when I remove it......but it works great and its in cabin so Ill use it.....

SirCygnus

iTrader: (1)

i got my ebc for ree. its the blitz unit. lol.

getting a ms to controle boost would be cool since it can calculate everything you need on the fly.

homemade doesnt necessarilly mean poor quality. home made just means it mnight have a quirk or two or non that a manufactiured piece has,

nik

I think what we are getting to here is closed loop boost control. I run a profec B in my car and it is annoying to have to retune it based on the temp differences between night and day. For a while my HIGH setting was my day, and LOW was my night. I frankly expected a bit more for the hundreds of dollars that unit cost.

Haltech EBC is not closed loop in the e6x, but is in the higher models. Of course, this requires buying a haltech.

A well designed system will have the failure modes result in wastegate boost, not ovreboost(although the originally proposed system does not satisfy this). Also there is always overboost fuel cut for emergencies.

Is the megasquirt control closed loop? If it is that would be a great starting point.

coldfire

iTrader: (1)

Nik, knows what he is talking about, ask him questions.

i should have posted that a PWM circuit of some sort would be required, but i think the original poster already knew that. i'm pretty sure even every stock solenoid used for boost control is a stepper motor type, or something requiring PWM signal.

as for MS, i believe (i read at some point in time) it supports both closed and open loop. not sure on the details. info is probably somewhere on this page:
http://megasquirt.sourceforge.net/extra/index.html

and people have actually been trying to implement boost control in a dual stage config (basic TCS) on megasquirt:
http://www.msefi.com/viewtopic.php?t=22660