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Old 07-26-2007, 01:33 PM   #1
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Default closed loop boost control

For those who are running EBC, are you running closed or open loop?

I dabbled in the closed loop stuff earlier today, and it seems that it will work with a little tuning. The way it looks like it works, is you help get it there by inputting data in the duty cycle table, then give it boost targets in kpa. If the difference between the duty cycle table and target table is too large, it gives up trying closed loop and reverts to open loop.

I set all my closed loop targets to 149kpa to see if the system would work. My peak boost as derived from the duty cycle table is closer to 200kpa, so if the closed loop system would be forced to pull a lot of EBC duty cycle. That way it would be obvious to me if it worked or not.

Here is a result:



Top Graph, RPM in green, TPS in white, MAP in purple
Bottom Graph, Boost in red, and EBC duty cycle in Green

Again the boost target I gave it was 149kpa, and you can see how the MS controlled the EBC dutycyle to hit the target. This was a partial throttle pull. I don't have a WOT pull to show with the same results, as the discrepency between the duty cycle table and boost target table was so large (50kpa or 7psi), the MS gave up trying to run closed loop at WOT and reverted to open loop.

So with a little tuning, it seems that it should work. I'm hopeful that it will because that way boost control becomes stable with temperature. And boost targets will be automatically lowered with high intake temp, and with knock events.

Comments?

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Old 07-26-2007, 02:22 PM   #2
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I know my EBC works great in open loop with just duty cycle targets with little % change through the revs.

I never tried closed loop, but wanted to dabble with a toggle switch so I can run dual maps.

just gotta having a running car to do it
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Old 07-28-2007, 09:49 AM   #3
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No comments. Heh I must be the only one running boost control then, huh?

I'm going to play with this some more today, if it doesn't rain. The sky is dark right now though :/
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Old 07-28-2007, 10:39 AM   #4
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does the MS have proportional integral derivative control over boost?
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Old 07-28-2007, 10:49 AM   #5
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was that like every word you remembered from calc 101, all used in the same sentence?
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Old 07-28-2007, 11:26 AM   #6
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haha, i skipped calc 101 thanks

no it's the three words I remembered from Control Systems 101.
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Old 07-28-2007, 11:52 AM   #7
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Dick.
I took 2 semesters each AP stat and calc in highschool. Got As and Bs in all. Took both AP tests, scored 4 (out of 5) on both tests. In the end, the only math class it exempted me from was College Algebra. But I took it anyway. Easy A. Made dean's list freshman year. And then the first semester sophmore year. And then I started partying.

I have no clue what algorithyms the MS uses to determine BCDC. I tried to play with it this morning, but it's raining very lightly, so the street is super slick. Went sideways twice, break out was anything but progressive and predictible. Second time put me oncoming with an SUV. So I put it away.

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Old 07-28-2007, 01:05 PM   #8
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I was a math nerd in HS but it doesn't get you the ladies...

Smart move to wait til it's dry out. Maybe I'll go have a look for no real reason.
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Old 07-28-2007, 01:19 PM   #9
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http://forums.turbobricks.com/showthread.php?t=80599

it does have P and D it looks like.
Heres some nerding up for you:
http://en.wikipedia.org/wiki/PID_controller

Proportional: a rubber band between boost setpoint and actual boost.
Derivative: a shock absorber on that rubber band
Integral: the longer you're not at the setpoint, the harder it tries to get there.
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Old 07-28-2007, 01:59 PM   #10
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Oh PID. Yeah I understand PID control. Sorry brain fart, I saw all those big math words and didn't make the connection.

No, I don't think it does I. In fact, I think it has a function that is the opposite of I, where basically if it is too far out of bound, it simply gives up and reverts back to open loop.
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Old 07-28-2007, 02:02 PM   #11
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For those getting into boost control w/ the GM solenoid: I was at Advanced Auto Parts a little while ago. I was looking through their generic plugs and connectors looking for a COP harness. Didn't see anything for the COPs, but I did see what looked like the GM pigtails for the boost solenoid for $6. Nice little rubber crush boot and all.

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Last edited by Ben; 07-28-2007 at 02:17 PM.
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Old 07-28-2007, 02:11 PM   #12
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It does do PID, including the 'I' I believe, but it has a programmable threshold you can set so that if it gets too far away from the desired boost pressure it can 'abort mission' and failback to to open loop DC table.
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Old 07-30-2007, 01:31 PM   #13
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Is that the "closed loop kpa limit" under "boost controller parameters"?
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Old 07-30-2007, 01:50 PM   #14
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That is the value that if the boost is out of bound by, the closed loop gives up and goes to open loop. I think the minimum value it allows is 20kpa.
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Old 07-30-2007, 02:18 PM   #15
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so im not sure I understand the advantage of this closed loop boost control. Does the open loop use a static duty cycle which may mean varying levels of boost on different days or somthing? And the closed loop thingie is there to add a bit more intelligence to the boost control or what?
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Old 07-30-2007, 02:30 PM   #16
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pretty much the only difference.

One is preset DC values, the other takes readings directly from the MAP sensors and makes on the fly adjustments.

But closed loop also allows for dual tables, so a toggle switch can allow you to switch between high and low kPa targets. open loop mode doesnt seem to have dual tables.

I only ran open loop, as I only had the EBC working for a few days before I melted my pistons. I misunderstood closed loop and figured I needed to run fueling in closed loop as well, which you don't. So if it works as well as Ben says, I'll be running two tables with closed loop.
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Old 07-30-2007, 02:37 PM   #17
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Quote:
Originally Posted by akaryrye View Post
so im not sure I understand the advantage of this closed loop boost control. Does the open loop use a static duty cycle which may mean varying levels of boost on different days or somthing? And the closed loop thingie is there to add a bit more intelligence to the boost control or what?
Pretty much yes. You give it a ballpark with the duty cycle table. Then you give it an actual target with the target table. Then the MS will vary boost control duty cycle (bcdc) based on its algorthym. Not only will this compensate for temperature and altitude, but also allows MS to intelligently reduce your kpa targets with intake temp and knock. And you can set the thresholds and agressiveness of both cut features. Meaning your IC is heatsoaked and you're running 140F IAT, the MS can lower BCDC so that you are boosting 10 psi instead of 13 psi. Or whatever you set it to. Also, you're cruising around and your friend Knock comes to say hi. MS will pull some boost so Knock goes away.

I haven't tried dual EBC tables. That's kind of neat.
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Old 08-05-2007, 07:49 AM   #18
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So i went ahead and did the mod for boost control today ... got a wire hanging out ready to be hooked up to the solenoid so i should have it up and running tomorrow I hope. Once I get that out of the way, I need to get my Automatic TPS throttle body registering so i can do throttle based boost. Hoping to have that set up for my first drag event this coming wednesday. Ill probably run about 15psi for that, and running it pretty rich too (think 11:1)
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