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Engine Specific Info and Questions => IDI Engine => Topic started by: regcheeseman on November 23, 2009, 05:37:26 am
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I am currently working on a VNT controller based around a micro processor.
At the moment I have the potential to monitor boost via a piezo cell, implement a multitude of rev dependent boost limits with a servo controlled VNT.
I also have a crank pickup to drive a standard revcounter and provide an engine speed signal.
I also have a throttle position sensor.
The problem I’m having right now concerns the algorithm/map/whatever, I’m measuring actual boost and then setting vane position dependant on revs and throttle position.
For example the engine is sat at 2000 rpm (the boost limit for this range is 4psi), the throttle is 75% open. Therefore I require 75% of the maximum boost and the servo should adjust to give a maximum 3psi.
I’m concerned that my original setup idea will overcomplicate the system and the power will suffer.
The more I look at this setup it seems wrong, I’m thinking that the throttle input is a redundant signal to measure and will in effect control boost by it’s original method i.e. adding fuel
So by loosing the throttle position signal… following the same example the engine is sat at 2000 rpm (the boost limit for this range is 4psi), the throttle is 75% open. But the system doesn’t care where the throttle is and adjusts the turbo to deliver a max of 4 psi
However, I’m cruising along now, engine still sat at 200 and throttle barely open at 10% but the system will have shut the vanes right down to try and get 4psi. Is this a bad thing?
If I went back to my original idea the servo vanes would be wide open as the boost limit would be 10% of 4 psi i.e 0.4psi
I’m not sure which way to go and I also notice other people working on similar systems utilise a throttle position sensor, but I have been unable to discover how and why?
So my question is this, how should the control algorithm work?
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I would think,
Assume you are aiming for a max boost around 20psi.
(Values in table expressed as vanes % closed):
Boost 0 2 4 6 8 10 12 14 16 18 20
TPS
0% 0 0 0 0 0 0 0 0 0 0 0
20% 20 20 20 20 20 20 20 20 20 10 5
40% 40 40 40 40 40 40 40 30 25 20 15
60% 60 60 60 60 60 60 60 50 40 30 20
80% 80 80 80 80 80 80 80 70 60 50 40
100% 100 100 100 100 100 100 100 90 80 70 50
That way:
-Closed throttle, vanes open for less backpressure (coast for FE).
-As you apply more throttle, the vanes close down to spool the turbo.
-As boost approaches max, you open up the vanes to get as little backpressure as possible for the boost level.
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The idle position would be controlled by a small area of the code which keeps the vanes full open no matter what when the revs are below a given threshold.
I would see the accelerator position as the most often used signal that would govern the position of the vanes, with the maximum closed position being based on RPM and with the boost pressure overriding everything to open the vanes all the way regardless of the other positions.
So to confirm, vane position will be the inverse of throttle position, unless the boost limit has been reached in which case open the vanes.
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Great help guys, thanks very much.
The term throttle was a regional thing and not meant to be a physical reference to a throttle - The 'throttle' is the name for the foot pedal inside the car. Sorry for any confusion.
My original thinking for having some 'idle' code was a throw back to the first designs for the controller which as soon as the accelerator pedal was lift off idle, would slam the vanes full shut, then open them to regulate boost. Obviously not an ideal situation.
Re the boost spikes, surely my current setup is similar to a ball/spring type boost controller where the opening pressure is considerably larger than the pressure required to keep it open. It is prone to a large amount of hysteresis in it's operation.
Thanks for the heads-up on this issue, I'll try to add a degree or proportional control to the servo response pattern.
Booneylander, thanks for the table. It sure gives my project so extra new ideas. I was aiming for a max boost level depending on revs but you have gone for a TPS controlled max vane position. I haven't really got a feedback for actual vane position in the servo, but it could be implemented.
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Been juggling a few ideas about and I'm going to start the vnt control routine by checking a rev/boost limit, providing this isn't exceeded then the vane will be set with a map similar to the one suggested.
I will have a program port on the box to allow the map to be altered in situ
Thanks for your help - I'll keep the forum posted of any developments
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Thanks for the input, I notice you are referencing throttle (pedal) position versus revs whereas the map is throttle position versus boost, can I safely assume the boost is proportional to revs?
Will the vanes being too closed produce excessive gas temps or any other obvious signs
For the original table, would you prefer the 100% pedal position to read something like.....
Boost 0 2 4 6 8 10 12 14 16 18 20 - max limit
TPS
100% 100 90 80 70 60 50 40 30 20 10 0
As for the 20psi limit, no thanks - I'm thinking more 30+ psi limit (1.6 GTD block, AAZ head, 10mm pump, 1Y inlet mani, VNT17)
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You'd have to experiment and see, I really don't think it's appropriate for us to say anything at all about how closed or not the vanes should be at some *point* (rpm/tps/boost) because the setup is so unique. The map I posted was just an "idea" of how I think you would want it to control.
Ideally, you'd need to sit on an eddy current dyno at max rpm @WOT with the vanes fully open, close them down until you hit 30psi, back them out until you just barely start to fall off 30psi, then go a tiny bit the other way again (so the wastegate is just starting to open) and record the servo position . Then 3900rpm do the same thing, 3800rpm and so on until you fall off boost (turbo can't spool even with vanes fully closed). Then fill out the rest of the map as "fractions" of that position, and depending on your taste (ie do you want to cruise at 30%TPS at 10lbs boost so that if you mash the go pedal you hit 30psi really fast, or do you want to cruise at 0psi boost at 50% TPS for fuel economy and only get on boost at higher TPS etc).
That would give you the best map for your setup. Anything else is just guesses in the dark. But I think the "logic" in the map I proposed is solid, rpm and boost are linked so not sure which is best to control for (might be rpm), you may want a 3D matrix?
Also, for the case of being at high rpm at little or no throttle and then mashing the pedal, because the vanes are already open, and need to close down, boost will come on long before the vanes get fully closed, and you'll get into a part of the map that keeps them open appropriately, so boost shouldn't spike, as the software is way faster to respond than the servo ever could be. Not sure if I'm stating that clearly, but hopefully you'll know what I mean.
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Correct me if i am wrong but i was always under the impression that the whole purpose of the vnt was to obtain your max boost at low rpm by closing the vanes and then as exhaust flow increases with the rise in rpm the vanes open to maintain that level of boost without over boosting , by increasing the flow through the turbo by opening the vanes dose away with the need for a waste-gate .The biggest advantage off the O/E control system is that they will close the vanes {regardless of pedal position } if the boost drops due to extra load put on the engine i.e going up hill with your foot to the floor and rpm dropping .To sum it up the vnt is all about producing max boost at lowest rpm possible and maintaining it right through the rev range {without over boosting} regardless of load, its not about getting X amount psi at 20% throttle and X amount at 50% its all about creating your boost at low rpm and maintaining it without over boosting and the need for a waste-gate and that would lead me to believe that boost would be the key signal to the control not throttle position i.e if boost drops below your set parameters the vanes would close and if it exceeds your maximum parameters the vanes would open .I just wish i had the electronic s knowledge to do what your doing but i don't so i will just have to play with stone age diesels :'( hope that is of some help though
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Forgot to say on tdis the vnt is controlled by the n75 valve which is controlled by the ecu which takes it signal from the map sensor {manifold absolute pressure sensor} i don't think throttle position comes in to it for the control of the vnt so as far as i can see if you can set a max -min boost parameter e.g 16psi min 18psi max and control a n75 bleed valve to control the vane actuator you have cracked it all you need then is a vacuum supply for the n75 valve and if you achieve that i will be your first customer
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wow! Excellent ideas being kicked about!
I've been working with the values and rationilised them until I could form a simple arithmetic rule
which I further simplified with the addition of a 'tuning factor' a simple change results in a global map shift
Ignoring the minus figures which would be resolved to 0
Vane position Vp = Tp - Tf x Ba x Tp
TUNING FACTOR Tf=0.05
Ba = Boost Actual
Tp = Throttle position
Boost
TPS 0 2 4 6 8 10 12 14 16 18 20 30
0.05
0 0 0 0 0 0 0 0 0 0 0 0 0
10 10 9 8 7 6 5 4 3 2 1 0 -5
20 20 18 16 14 12 10 8 6 4 2 0 -10
30 30 27 24 21 18 15 12 9 6 3 0 -15
40 40 36 32 28 24 20 16 12 8 4 0 -20
50 50 45 40 35 30 25 20 15 10 5 0 -25
60 60 54 48 42 36 30 24 18 12 6 0 -30
70 70 63 56 49 42 35 28 21 14 7 0 -35
80 80 72 64 56 48 40 32 24 16 8 0 -40
90 90 81 72 63 54 45 36 27 18 9 0 -45
100 100 90 80 70 60 50 40 30 20 10 0 -50
What do you think? Fairly sensible figures?
I think if I add in a revs variable I'll produce a 3D map which my head/coding ability cannot cope with even if the processor could!
The revs limit variable will be applied in another section of code, it works by having five boost limits in five different rev bands, these limits are applied before the map above is even considered. Their values will overide any map values.
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damn the table looked fine in review, any way to control the way it appears?
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Yes i understand tdis take signals from maps -mafs-mats-and throttle-pots to control fueling timing and i also just realized i misread your map/ graph i thought the % was pedal position i now see where you are coming from and i realize part of what i wrote sounded like it was written in stone but it was meant more as a question than a statement and i cant get my head round the pedal/throttle potentiometer without a mass air flow meter which u obviously cant use with a mechanical pump or am i barking up the wrong tree with that :-\
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I would have thought boost pressure sensor{maps} gives you the p.s.i of a volume of air and not the actual VOLUME, a mass air flow sensor gives you the volume of air{cubic meters} before it is pressurized and a m3 of air requires the same amount of fuel added {air fuel ratio}weather at atmospheric pressure or 2 bar, to burn efficiently and yes they all play a part of producing /controlling boost /and fueling all combined with a ecu but manifold absolute pressure sensor{maps} is the only one that monitors actual boost P.S.I regardless of volume so you could end up having 10 m3 at 1500rpm and 10psi or 40 m3 at4000rpm and 10psi so the pressure is the same but volume is diffrent so the fuel requirements would be totally diffrent but the pedal positon could be the same {depending on load} with out a mafs and throttle pot and one with out the other is the bit i cant get my head round it would be like having a guard dog with no teeth?
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Sorry to jump in so late.
Since weeks I observe the actuator control pressure (vac) and boost in my TDI to tell my electronic buddy how it works. He might build the VTG controller for mine and his Benz.
It is clear for me that the throttle position (power demand) sets a certain boost level (not max. boost, until full pedal). Also lifting the foot sets the boost to a certain position and I can see the vac(= vane position) is going up (vanes are more and more closing) when speed/rpm go down. I also think that zero pedal is equal to a not zero set boost. The vac tries to keep boost low first then when actual boost is below that min boost the vane close to achieve that min boost (but rpm is not able to reach it). With this configuration the vane position is waiting for the next acceleration in the closed position.
Correct me if I am wrong or even better tell me which situation you need to "see" on my TDI to get further.
Tom
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waiting in the fully open position is the difference to the OE?
In my TDI I see full vac (vanes closed) at idle.
Has anybody a working mechanical solution? I would like to get ahead with the car while waiting for my buddy.
Tom
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I am quite sure that the vanes are at closed position at idle. Idle and vanes open will result in louder exhaust sound. The back pressure issue is solved (in my eyes) by setting a very low boost at pedal position zero.
Now coming from high boost and lifting the foot the system tries to get to this low (set-) boost and open the vanes which will give low back pressure.
In my TDI full vac is applied when I start the engine and idle. There is no need to look for low back pressure at idle and on the other hand the system is prepared for instant boost build up.
Tom
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If I might drag this back to the IDI electronic VNT controller, I've been away to bother a PIC forum regarding coding the map and seem to have a workable solution that runs on a simulator fine.
Now, I'm looking at driving the vanes directly via a large servo, when I remove the standard vac can I'm guessing that the heavy return spring will be removed also. I would like to run minus any spring load on the vane control arm. Would the action of the turbine/gas pressure tend to open the vanes?
I have a pre-start vane open/close/open routine with inbuilt tests and various fail safes built into the code.
Would you remove the vane return spring entirely or use something considerably lighter than the original?
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My Canbus controller seems to be a worm gear with no spring.
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By way of an update...long overdue....
I've been busy prototyping/developing /coding my VNT controller - the code is finished and the prototype is a bit of a mess at the moment but it's begining to show signs of life.
(http://i492.photobucket.com/albums/rr281/regcheeseman/protoboard.jpg)
That is quite an old photo and the board is pretty crowded now. I've decided to make the display of led bargraph remote from the controller and thought it would be good incorporated into the revcounter. However, there's no real way to get the board and components into the revcounter housing.
The only way I could get it to fit was to bin the revcounter internals and make a board to accomodate display and display driver bits, plus the original revcounter drive circuit which I'm already pretty familiar with, though it'll mean converting a diesel revcounter back to petrol.
(http://i492.photobucket.com/albums/rr281/regcheeseman/BOOSTL1.jpg)
I've drawn up a piccy of how the final gauge should look...in theory it could be made to fit to any mk1, with or without the VNT controller. I'm hoping to use the pumps injection sensor to drive it.
(http://i492.photobucket.com/albums/rr281/regcheeseman/ledtacho.jpg)
I had short notice on Friday of an opportunity to get the PCBs done, so rapidly transferred a half finished prototype circuit board into..
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/FILE.jpg)
Might not look much, but theres about 5 hours of design and maybe 100 hours of research and prototyping. Not even properly tested yet.....
Boards have now been produced and are currently being drilled.
No engine built yet though.
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Still trying to solve the electric pickup - mk1 speedo conundrum, but at least I've partially managed to integrate the electronic boost gauge and vnt status indicator into the standard mk1 revcounter. Still have to refit the original revcounter needle and mechanism to make it multifunction.
(http://s492.photobucket.com/albums/rr281/regcheeseman/?action=view¤t=Video0001.flv)
works too!
The solitary multicolour led is a status indicator.
Solid green - RUN mode
Solid red - calibration/configuration mode (when the boost gauge changes operation as a diagnostic guide)
Flashing red - limp mode
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Neat! Dimmable? Stage 2 should be the moving redline like the M3's, redline gets higher as oil temps come up.
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Neat! Dimmable? Stage 2 should be the moving redline like the M3's, redline gets higher as oil temps come up.
Dimmable? yep, close your eyes a bit ;)
It looks bright because my phone's camera is rubbish - the leds are on their minimum 10mA and not that bright in reality, though intensity variation/flashing etc is a possibility with the led drivers used - however space is at a premium.
It's a boost guage so not actually a redline as such, but it is used as feedback for the VNT vane servo position - the map for which varies with revs.
It would be simple to add a temperature input (it had crossed my mind early on it the project) and there are plenty of redundant inputs on the microprocessor. I was thinking to limit the map to max 50% closed vanes until a temperature threshold is reached.
I think I'll just get the mk1 circuit up and running and maybe develop it from there....
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Still trying to solve the electric pickup - mk1 speedo conundrum, but at least I've partially managed to integrate the electronic boost gauge and vnt status indicator into the standard mk1 revcounter. Still have to refit the original revcounter needle and mechanism to make it multifunction.
(http://s492.photobucket.com/albums/rr281/regcheeseman/?action=view¤t=Video0001.flv)
works too!
The solitary multicolour led is a status indicator.
Solid green - RUN mode
Solid red - calibration/configuration mode (when the boost gauge changes operation as a diagnostic guide)
Flashing red - limp mode
...oh wow, i want one!
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You get a mk1 setup going, I'll GLADLY pay for one.
VERY cool.
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Reg - in laymans terms does your box of tricks take 3 inputs?
boost
throttle position
revs?
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To sum it up the vnt is all about producing max boost at lowest rpm possible and maintaining it right through the rev range {without over boosting} regardless of load, its not about getting X amount psi at 20% throttle and X amount at 50% its all about creating your boost at low rpm and maintaining it without over boosting and the need for a waste-gate and that would lead me to believe that boost would be the key signal to the control not throttle position i.e if boost drops below your set parameters the vanes would close and if it exceeds your maximum parameters the vanes would open .
It seems you miss the point of the vane control and the point of this thread. No one is trying to make a goal of producing a certain amount of boost with a certain position of the vanes. The whole basis of the VNT control in the O/E design and what I have tried to present here is to produce the optimal amount of boost to meet the current power demands up to the limits of the engine. The purpose of the descriptions of possible maps in this thread is to approximate what vane position would be necessary at a given demand for power to produce the optimal boost pressure. The O/E design is most certainly based on pedal position. The O/E design does not produce excess boost at any opportunity. Doing so hurts fuel economy, hurts performance (yup, more boost than necessary hurts power) and causes additional unnecessary wear on the turbo. The purpose of the VNT is not to always produce max boost at low rpms, but rather to be able to when the demand is there. The control parameters I described accomplish that goal most effectively. Boost will always increase with increased load even if the vanes remain stationary except in the rare circumstance such as you mention where a hill is steep enough that rpms drop off enough that there is not enough exhaust flow to maintain that pressure. Under that circumstance, with the control parameters I described, the vanes would close proportional to the amount necessary to maintain the boost at the max just like in the O/E system. With the O/E system, if you let off the go pedal, boost is not maintained @ max. Again, I would reiterate, that to close the vanes farther than necessary for the current demand for power is counter-productive in many ways and so matching the vane position to the demand for power is the purpose of the O/E design and the most effective way to both produce maximum power under all circumstances and maximum efficiency and longevity for any given power setting.
well said Andrew, and your absolutely correct. Further, there is no way in the world that the OEM VNT controller doesnt use accelerator position for the boost control It absolutely does.
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Reg, I have been following you adventures and look forward to seeing how you progress. It’s my opinion that you are on the right path to getting an efficient system working. So with this in mind I offer the following.
VNT, Variable Nozzle Turbocharger is actually another name for "Variable Geometry Turbocharger", I prefer the latter name rather than the former because it it is more precise in it's description of the function, which is to alter the "Aspect Ratio" (A.R.) in the turbine side of the Turbo. This is the primary function, control the aspect ratio of the Turbine and not to control the pressure of the Compressor, now obviously there is a pressure control component, including acting as a wastegate in limiting overboost and overspeed, but to repeat, the primary function is to alter the A.R.
With this in mind we can see clearly that by using the "Vanes" just to control pressure is wasting the potential of the technology behind the design.
So lets take a look at an example where this technology has been used to solve a sticky problem related to getting maximum performance and maximum drivability on the street. In the early '90s Nissan put twin turbos in the 300zx, V6. Now the question for Nissan was how to make a turbo work between off idle to 6-7 k redline.
At off idle the three cylinders would not produce enough volume/velocity of exhaust gas to turn a larger turbo, thus you get turbo lag. So with the VNT you can adjust the A.R., thus allowing for a smooth transition between off idle up through the full RPM/Power band.
So the bottom line is that with a variable A.R. you can have a large turbo, which at lower RPM’s, can act as a smaller turbo, virtually eliminating turbo lag. This is the genius of the design. So you might want to focus on programming the aspect ratio rather than pressures.
If you could find specs that would show the aspect ratio of the turbo you are using at different vane positions it would make the programming much easier.
Also as far as inputs are concerned, while throttle position, RPM, and Pressure are important, I would consider them a starting point. To make a true determination of the engines needs, Vehicle speed, gear shift position, and if possible Air Mass would really help to refine the A.R. settings. For example Cruising at x throttle position is different than pulling at x throttle position.
Obviously there is more to be said as far as converting A to D signals, etc. But I hope this helps a bit to see the real purpose behind the technology.
Let the Flaming begin.
Long live the Karman Vortex Sensor
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Hook up an opacity detector on the exhaust and regulate the smoke level.
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I was thinking of fitting a BPM counter to the CD unit to determine my state of mind, the car would then map it's response according to my mental state.
Blue Mule,
I have taken on board your ideas and thanks for airing them, but bear in mind, this project is on a shoestring development of an old diesel engine and unfortunately I've not got the resources of Nissan! I could in theory implement every conceivable input but also I'd like to be driving the car THIS summer.
How would you even begin to monitor AR values - are they not a function of vane position?
Reg - in laymans terms does your box of tricks take 3 inputs?
boost
throttle position
revs?
Yup! And a feedback input of vane position.
Meanwhile back with the actual design stage, not looking quite so much like a gcse project now, the VNT controller is built....almost.
(http://i492.photobucket.com/albums/rr281/regcheeseman/DSC00437.jpg)
Not shown is the servo that actually controls the turbo vanes and a pickup attached to the pump.
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Reg, the spring in the can provides x amount of resistance, there is no need to monitor the Aspect Ratio change, all you need to know is the following, full open xx aspect ratio, 50% xx aspect ratio, and full closed xx Aspect ratio. When I say AR i am reffering to the actual geometry of the turbine housing. There must be specs on this somewhere.
Anyway, I am enjoying your work and am looking forward to see how it comes out.
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Blue Mule,
Sorry but you've lost me completely now. ???
There is no spring and no can in my design.
I am monitoring servo position and therefore vane position - Is that not AR? I really don't understand it's relevance as a measurement when I have the other conditions being monitored?
At off idle the three cylinders would not produce enough volume/velocity of exhaust gas to turn a larger turbo, thus you get turbo lag. So with the VNT you can adjust the A.R., thus allowing for a smooth transition between off idle up through the full RPM/Power band.
So the bottom line is that with a variable A.R. you can have a large turbo, which at lower RPM’s, can act as a smaller turbo, virtually eliminating turbo lag. This is the genius of the design. So you might want to focus on programming the aspect ratio rather than pressures.
I had thought this is what I was doing????? In that the thing being controlled is the AR. The criteria for it's position being the throttle position/revs condition.
I.e If I'm nailing the accelerator to the floor the AR will be forced to push the boost as high as possible
I.e If I'm light on the accelerator then the AR will be relaxed
My only use for the boost measurement is to implement a limit (in fact 5 limits) - low rev boost will be severely limited as I understand too much at low revs will kill the engine?
The map is easily modified with a usb lead and laptop and all the boost limits can be reconfigured in situ with no additional equipment by pressing a button during the units start-up diagnostics check.
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I think you're totally on the right track.
Thanks for that, it's a bit to late in the day for any u-turns! Time will tell I think.....
I'll probably run the car with the servo un connected and the VNT fully open for a bit and rig up a servo position indicator just to monitor what the turbo vanes would potentially be doing. It's fine testing on the bench but until the unit is properly hooked up to an engine I'll not really know how it will work.
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Reg, I agree with Andrew that what you are designing will work to control boost, and the vehicle will no doubt be very drivable. Just to add I think you are doing an excellent job in your set up including the Tach. Please understand, my purpose is not to be critical either, it was just to point out that the real genius in this type of technology is in the drivability aspect. Also please keep in mind I am a Southerner with German born grandparents on both sides, so I tend to be a bit direct in my speech, and I don't mean to offend ;D
So if I may, allow me to illustrate. A turbocharged vehicle with a direct link to the nozzles is driving at 60 mph at 3k RPM, it encounters a large incline, like Cheddar Gorge, the engine "feels" the load and the RPM's start to drop a bit, the driver steps on the gas to add more fuel to keep the RPM's and speed of the vehicle up, also since the AR is linked directly to the throttle, the "system" makes the AR larger, this may sound great, but in reality under these conditions you need the aspect ratio on the turbine to get smaller so that the turbo will stay spooled with the lower RPM due to engine load. Now someone will jump in here and say "Blue all you have to do is downshift", yes this is true, but then you are having the same situation as a fixed AR turbo. One of the drivability aspects of a VNT is to cut down on the shifting in the manual trans and auto trans. There are other conditions of course, but I think this one is the most clear in real world application.
Now as far as the sensor situation, the RPM, Throttle, VSS, are a very good start, but think how much more you could get out of a system that uses Air Mass to help filter the other three inputs, again this is just a thought, and I am not saying it is absolutely needed to function.
As far as control, I see you have replaced the “can”. I do have a thought for future reference; you only need a vacuum solenoid and a circuit that uses a TI 555 timer to alter the duty cycle to the solenoid this would allow a very precise sizing of the AR while using the original can.
Anyway, much respect to you and your project, and I look forward to you further installments.
“Spring little cobra with all your might”
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Reg are you planning to develop a few more of these sale?
Id be very interested in it and on my 306 i already have the boost input, revs input and throttle poistion input.
The programming etc i just wouldnt have the hardware or the brain power to even begin to start making one.
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So if I may, allow me to illustrate. A turbocharged vehicle with a direct link to the nozzles is driving at 60 mph at 3k RPM, it encounters a large incline, like Cheddar Gorge, the engine "feels" the load and the RPM's start to drop a bit, the driver steps on the gas to add more fuel to keep the RPM's and speed of the vehicle up, also since the AR is linked directly to the throttle, the "system" makes the AR larger, this may sound great, but in reality under these conditions you need the aspect ratio on the turbine to get smaller so that the turbo will stay spooled with the lower RPM due to engine load.
True - but: When you add fuel (as the incline increases and you put your foot down) you are increasing exhaust gas flow aswell. Infact, by adding fuel you are able to increase exhaust gas flow by an incredibly large amount compared with the change in rpm.
In an ideal scenario, (lets take your getting to a hill example) the vanes will go wherever they need to in order to keep an optimum (caution, gasser terms here) Air Fuel Ratio. In a turbo-diesel, we need to look at it this way - for high load application, we want to keep EGT pegged to a critical value of our own choosing. This ofcourse is largely governed by the AFR at any given time. What we want to achieve ideally is to increase boost with fuelling to keep the EGT in check, up to the point of maximum torque output for whatever rpm you are at.
What consequences does this have for our controller design? We need to consider what it is the vane controller is actually doing. The controller shown in this thread uses a "map" (the matrix of numbers) that depends only upon 2 inputs. With 2 inputs, we need to choose exaclty which inputs are going to be the most useful to achieve a given outcome. We can say that we will manually tune the EGT at full load with the LDA, so clearly the best inputs should be boost pressure and rpm, as these allow: 1) a controller feedback; and 2) idle/midrange/full speed tuning capability.
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Also please keep in mind I am a Southerner with German born grandparents on both sides, so I tend to be a bit direct in my speech, and I don't mean to offend
Man, you'll have to try a whole lot harder to manage that! ;)
also since the AR is linked directly to the throttle
no, not exactly it's a function of revs and boost too - so in your scenario the vanes won't just open up and create lag
(was the 'cheddar gorge' reference purely for my benefit? - like it!)
As far as control, I see you have replaced the “can”. I do have a thought for future reference; you only need a vacuum solenoid and a circuit that uses a TI 555 timer to alter the duty cycle to the solenoid this would allow a very precise sizing of the AR while using the original can.
Why the fascination with the diaphragm can? It's a poor solution with considerable hysteresis and limited controlabilty. It would also shift the system from being electro/mechanical to pneumo/electro/mechanical - (ignoring the boost input) , this would add extra complication and potential failure modes, lots of leaky pipes, clunky solenoid valves and other stuff best avoided.
My servo position is adjustable in 256 steps - how much precision do you require in a 100(?) degree arc.
The servo also has feedback built in.
My only reservations with the servo is it's response rate, however I have the option to overclock the processor by 4x if required - currently running at 8MHz.
Reg are you planning to develop a few more of these sale?
Id be very interested in it and on my 306 i already have the boost input, revs input and throttle position input.
In keeping with this forum ethos (and my ranting about the covert nature of some peoples knowledge regarding mtdi work ;) ) I will publish everything I can, when I am happy with it.
I may consider making some more - but a system for a peugeot may have to be tailored. The input amp gains may not suit peugeot sensors....but it's merely a matter of three resistors to change.
5v pulse from pump to get revs signal.
1K - 1.5K variable on throttle position
The servo is currently from a Honda NSR250 but I may switch to a more available yamaha unit.
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Reg, OK,
As far as the can is concerned, since its already on the turbo I'm just thinking out loud that it would be one less thing to have to modify, but I know that dodge sprinters use a system that is completely electronic, so as long as your solenoid can function with the heat, then it can be very precise in its metering.
Mule Out
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I think what we are seeing here is the good old "80/20" rule... 80% of the problem can be solved with a simple 20% system... the remaining 20% finesse takes 80% more engineering. ;-)
Andrew's mechanical control has demonstrated that good drivability can be obtained using a vane controller with only two mechanical inputs: throttle position and boost. Reg is taking it to the next level by adding a third input: RPM... as well as putting electronics into the mix. Mule is talking about even more sophistication, more inputs, arguably more finesse from a control perspective
All of these designs are valid...it's up to the reader to decide when they are on the other side of the 80/20 curve... ie, when is further finesse not worth the additional time, effort, expense?? Guys happy with wastegate turbos would probably argue "too late... who needs vanes in the first place!!!" ;)
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The primary reason for chosing an electronic solution over a mechanical one was cosmetic. I'm aiming to get a 'scene' accepted engine bay with a diesel engine.
Every thing that could be relocated has been, wiring hidden, holes plated etc - to fit a bunch of cables, pulleys, levers and spring would ruin the look.
The servo will be remote mounted in the car (well away from heat) and two discreet bowden cables through the bulkhead/firewall directly to a pulley on the turbo.
Incorporating the boost gauge into the factory rev counter was also important in maintaining the 'look'
It's always my ethos that 'Form follows function' but having both is a bonus...
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Libbybapa,
I'm really impressed that you seem to know better than me how my system operates! Having mentally converted the systems operation into a set of variables and then translating those variables into a variety of voltages and then translated those voltages into PWM values of frequency and duty cycle - I've actually forgotten what the design was supposed to do in the first place!
Now I've got to final testing, I've had to go back over the original scribbles and posts on here to jog my memory!
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Neat! Dimmable?
I've finally managed to get some code loaded (test routine) into the processor and now bacause it is running from a PWM signal from the processor the display actually increases in intensity as the boost increases!
Way cool 8)
Oh yeah, it wasn't just a fluke - I meant that to happen honest!
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Very awsome project !!! Do you have an EGT to at least see how hot your turbine wheel it getting, if not an input to V2 of your project ?
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It seems like any further inputs would actually be redundant. Reg is already measuring air mass in that it is a function of rpms and boost. He's already got servo position which is in turn A/R. I can't see how VSS would be worth measuring as RPMs are already measured (do the vanes care what gear you're in?).
Might be worth something if you are programming for reduced output in lower gears to save you made of glass transmission?
Turbine speed would be a handy input from a diagnostic standpoint, but not easy to implement on our R&D buget.
I like where this is going:)
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Are the gearboxes that weak then? I knew the clutch was weak but the 020 seems to take some abuse, I'll be running the cable change 02A TDI box anyway.
Tonight I've been thinking of whacking a shift light in, it would require a small circuit board to be added and a little bit of code, but would be user configurable at startup - as are the boost limit settings - you just have to hit a button within 5 seconds of turning the ignition on to enter the config mode or the unit continues into normal mode.
I was thinking of putting the shift light into the revcounter but it may be too crowded so add it as a remote output switched 12v line.
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On an IDI, I don't really think so, but the ALH TDI with an auto sure seems to do some funny stuff in an attempt to preserve itself. A lot of Honda products, you can't manually select 1st gear...
More of an issue with engine converted vehicles, running slicks, etc
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The VNT controller servo is now responding to servo feedback and throttle position.
(http://s492.photobucket.com/albums/rr281/regcheeseman/?action=view¤t=P1010937.flv)
As a fair few people have suggested it, I've written the code in for a shift light.
Meanwhile, back in the workshop, the proper engineering carries on....
Front end, my IC fun wasn't completely wasted. ;) Shame about the dog poo bags!
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Maystatus002.jpg)
One manky gearbox tidied up
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Engineandgearboxinpaint002.jpg)
Block well on the way (WAITING FOR GIRDLE!!!!!)
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Engineandgearboxinpaint001.jpg)
Marked up the manifolds for some port matching and a bit of flow work.
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Engineandgearboxinpaint004.jpg)
Finally - toys. mmmmwahahahahahahahahahahaha :)
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Engineandgearboxinpaint005.jpg)
1Y/AAZ head, 1Y manifold, MK4 VNT turbo, MLS gasket, ARP studs
I've been painting more bits this evening and putting a few bits together, then I got the carbide burrs out and the hacksaw and ruined my manifold....
(http://i492.photobucket.com/albums/rr281/regcheeseman/P1010936.jpg)
Don't worry all will be fine!
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IDK if the mani is as tough as the D24 that I ported, but if so good job. The 1.6L TD intake was like butter compared to the D24. Looks great keep up the good work.
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Started to attack my ports with a carbide burr in a drill (gave up on the die grinder and the dremel)
Was taking ages, then I found a milling cutter and whacked that in the drill - that sorted it!
Then I got a abrasive disc in my grinder and sorted that inlet manifold out - just have to get the holes welded up.
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/enginebits002.jpg)
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Updates??? :D
Brendan
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I think BlueMule might have been confused, Turbos are load dependent not RPM dependent.
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not a massive amount to update really, but the project has changed a lot, I've tested the mark one PCB as far as it will go and to be honest am not happy.
Mark two has been designed and coded and now I'm on mk 3 using different technology to improve the inputs and the speed. I've ditched the complex config mode and implemented a shift light.
I've lost the multi stage boost limits and switched to a simpler single 'power factor' which shifts the boost map up or down.
This streamlines the code with no detrimental effect on functionality
I've also designed the adaptor to run the mk1 speedo from an electronic gearbox pick-up
Meanwhile the car got painted, the paint reacted, was stripped and is ready for re-painting.
Oh and I also swapped my daily from a ford to a VW - and then modified that.
When I get some real usable results or pictures, you will know!
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Reg,
Besides the controller, can you give off a parts list of the turbo, actuator and the like?
I'm just looking at going turbo and I'm going to go straight for this!
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The turbo is a BV?39 I think - from a mk4 golf
The actuator is a power valve assembly from an NSR 250 - with custom made fitting at the turbo end, actuation is remote via bowden (http://en.wikipedia.org/wiki/Bowden_cable)cables
TPS sensor is just a quality potentiometer attached to the accelerator pedal
The system I'm designing should have enough adjustability to work with any VNT.
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And the prize for the most over engineered throttle position sensor......
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Throttlepositionsensor002.jpg)
I originally stuck the sensor on the throttle pedal shaft but only got 30 degrees of rotation which would give poor resolution so I messed around with cogs and gears and the found a drive mech from a drug infusion pump going for scrap.
transfers the 30 degrees to nearly the 270 of the sensor - the rest is compensated for by electronic wizardy.
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And the prize for the most over engineered throttle position sensor......
(http://i492.photobucket.com/albums/rr281/regcheeseman/Golf%20in%20progress/Throttlepositionsensor002.jpg)
I originally stuck the sensor on the throttle pedal shaft but only got 30 degrees of rotation which would give poor resolution so I messed around with cogs and gears and the found a drive mech from a drug infusion pump going for scrap.
transfers the 30 degrees to nearly the 270 of the sensor - the rest is compensated for by electronic wizardy.
That is sooooo cool.
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Hi,
regcheeseman, will your VNT controller be available to buy (as a complete set or parts and code)?
Did you get it to a final version?
Tom
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I'm intending to make five boards, four to sell, I will also bundle notes, schematics, PCB artwork, parts listings, Microprocessor code etc into a package for free.
I'm not quite at that stage yet. The second revision of the board was taken to the developers last week.
(http://i492.photobucket.com/albums/rr281/regcheeseman/cheeseVNTboardsmall.jpg)
Hopefully have it working properly in the new year.
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Do you have a bird? you have way too much time on your hands...
:P
Well done so far, smart arse...
:-*
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These two PCBs are around the same size as an EDC15 ECU. Maybe a bit over engineered for the simple job it is going to do? ;)
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I would want you to sell these eventhough I don't have a VNT yet. I think I love you a little...no homo
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Do you have a bird? you have way too much time on your hands...
;D - No bird......... no time what with having a wife, two young kids, house and full time job. Most of the PCB prototype work I do in my lunchtimes.
These two PCBs are around the same size as an EDC15 ECU. Maybe a bit over engineered for the simple job it is going to do?
The image is not actual size, I'm dealing with large packages (not SMD devices) on a single sided board. The lower board is the display/boost gauge
The circuit drives the display / shift light / rev counter AND controls the VNT servo.
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am I right considering the controller as 2 parts:
PID and pwm generator?
If so a LED dimmer could be the the pwm part.
I ordered such a thing that outputs a pwm 140 Hz, 12 V, adjustable with a poti.
With that I should be able to move either the stepper motor or via solenoid the vac.
Now the PID only has to "operate" the poti.
Is there any kind of PID available that could do this?
Or does it make no sense to split the complete unit like that?
I am not an electronic, just want to get my Benz running after the mechanical installation of a VTG.
Tom
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The 28X2 micro processor has two PWM outputs built in it also has several analogue IN lines and configurable digital inputs/outputs
a quad op amp looks after the pressure input from boost sensor
throttle position is measured via pot
vnt is controlled via servo motor driven by motor driver chip - positional feedback is via pot
An engine speed signal is taken from pump tranducer and via a freq/voltage convertor LM2917 to give an analogue value for revs.
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so what is needed to complete the controller?
The code only?
Are the mentioned hard ware components proved and tested and available?
I don't want to sound silly, just try to learn where you are and how I can give input.
(not personally me but buddies who know more about electronics than i do)
Tom
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I appreciate the offer of help, but electronics is my profession, The hardware is all prototyped and bench tested, the code written and working. There were a few problems with input signal levels and op-amps but these are now all resolved.
I've improved the design to incorporate new features and increase processing speed.
The only thing that's holding up the completion of the project is life in general - if you could send your buddies round to re-plumb my central heating, finish the house extension, cook the meals, wash-up etc it would be much appreciated ;)
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I discovered that I needed a buffer stage on an output to drive revcounter, a spare buffer was available on the board but to use it required re-working half of the design, 6 hours later I have yet another print and it's a bit smaller. Main board is 110mm x 50mm
(http://i492.photobucket.com/albums/rr281/regcheeseman/Alllayerssmall.jpg)
Hopefully it will be produced fairly quick and I'll have a working version
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My project is just about complete, all sensors are returning required values, the servo driver is responding as expected = I just need to implement a new map and would like to bounce my ideas about on here....
I have a number of variables sampled
Tp = Throttle position 0=accelerator not pressed 255=pedal mashed into carpet
Ba = Boost actual 0=no boost 255=max boost (circuit currently built such that max boost is 30 psi)
Revs =Engine speed 0 = 0rpm 255 = 7300rpm (again this max depends on circuit configuration)
I need to manipulate these variable to give a desired vane position Vp
If I simplify the setup considerably and make each variable a binary value I get this
Tp Ba Revs Vp
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 1
1 0 1 1
1 1 0 0
1 1 1 0
Therefore Vp = Tp AND (not)Ba
It would appear that the revs value is redundant, however I think the over-simplification has caused this and I see the actual value of VP being a function of Revs value - providing the basic Tp AND (not)Ba is adhered to.
If the variables are taken back to 0-255 analogue variable, (not)Ba would be (255-Ba) then the basic equation would be
Vp = Tp - (255-Ba) All values over 255 = 255 and any negatives would be 0
If I bring revs back in, we get
Vp = (Tp - (255-Ba)) - revs
And tuning factor Tf could be introduced to shift the performance up or down
Vp = Tf x ((Tp - (255-Ba)) - revs)
Does this sound feasible? any ideas?
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I love how I don't understand 90% of the jargon being used in this thread, but nonetheless I approve! Good luck bringing this to fruition.
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I love how I don't understand 90% of the jargon being used in this thread, but nonetheless I approve! Good luck bringing this to fruition.
x2 on not understanding half this thread..
but i know i want one when they are done.. 8)
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At the best of times I've only got 80% comprehension of the thread. ;D
Been working with the MAP, it seems that the oversimplification of the map may well be right - convertuing it from 2D to 3D when you add in a REVs variable, actually has very little influence on the map profile.
The replacement of the REV variable with a fixed Tuning factor, serves pretty much the same purpose - and is much quicker through the processor.
So the only thing driven by rev signal is the shift light, I'm tempted to rip it out of the final circuit board.
I'd build a seperate revcounter driver with shift light - that would hook straight up to any four cylinder petrol revcounter.
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FINISHED! ;D
Finally got it sorted and fully operational.
For those that dont know it's a circuit devised to control my VNT turbo using a servo motor, basically the servo motor opens and shuts the vanes on the VNT turbo, affecting it's gas flow geometry
The linear pot in the forground is in effect the accelerator position and the syringe is replicating boost pressure - peaking at 28 psi
The revcounter has the boost gauge incorporated as a bank of LEDS, and also a status light (partially obscured by white wire)
(http://i492.photobucket.com/albums/rr281/regcheeseman/th_MOV00556.jpg) (http://s492.photobucket.com/albums/rr281/regcheeseman/?action=view¤t=MOV00556.mp4)
So what happens in the video? I reach over and switch the power on, the servo unit cycles shut then open to check for stuck vanes, when this is complete, the status light changes to green and the unit is in it's run mode.
Any input from the accelerator is monitored and responded with respect to existing boost pressure, the nature of this response is tailored by a tuning factor entered in the program code.
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Congratutation! :D Must be so exciting to see the fruit of your labor working as envisioned. Will you be needing guinea pigs?
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Wow thats awsome. I want to see a vidoe of that thing in action. You must be pretty excited, its been a long time in the running.
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That is a thing of beauty.
I have a devils advocate moment-
Don't the OEMs limit boost off idle/low vehicle speed to protect the motor from crushing force at low oil pressure, and save the teeth on 1st gear?
And some of my related interests-
Braking mode, high boost off throttle
Maybe this can be accomplished by interrupting the TPS circuit.
Launch mode, spool up before you hit the gas ;D
Maybe I'm over the edge...
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OH thanks for that, just when I thought I'd got it finished ;)
Not sure what you mean by braking mode off throttle - what response do you need in what instance?
Launch mode would be easy enough, the circuit had a pushbutton circuit, you could set a launch mode that cancels when the TPS or REVS input gives a certain value or you could just interrupt the TPS signal as you suggest to force the turbo to spool.
Don't the OEMs limit boost off idle/low vehicle speed to protect the motor from crushing force at low oil pressure, and save the teeth on 1st gear?
I'm hoping the map will allow for this to some extent, and my inbuilt mechanical sensibility will stop me going stupid in first gear....hopefully.
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I'm a fan of the get a bigger tranny, axle, whatever approach.
Braking mode ideally, you hit a momentary pushbutton to trigger it, and it closes the vanes to work as an exhaust brake, but opens them up at a light touch of the accelerator.
at a basic level, use the same strategy as any other exhaust brake
more advanced, you tap an up/down button to set desired speed.
From new Dmax literature...
A new feature on Duramax-equipped models is an exhaust brake system. This driver-selectable feature uses the turbine control of the variable geometry turbocharger and the compression of the engine to generate backpressure, slowing the vehicle without applying the brakes. It is a smart system integrated with the cruise control feature and varies the braking to account for the grade and vehicle load.
The exhaust brake system allows for virtually effortless driving and towing, with seamless and quiet operation. It also helps prolong brake life and prevents overheating the brakes on long, downhill grades.
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Not sure about the exhaust brake at all ???
Using a turbine as a brake seems to make little sense to me, but then using brakes at all is something I tend to avoid generally.
Adding both features would be very easy regardless.
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Not sure about the exhaust brake at all ???
Using a turbine as a brake seems to make little sense to me, but then using brakes at all is something I tend to avoid generally.
Adding both features would be very easy regardless.
The scenario;
You are coming down out of the sierras with a carload of treasures.
Coasting in 3rd gear, you are holding 66 MPH at 4000 RPM, 0 fuel is being injected, vanes full open(TPS=0). An upcoming turn recommends 45 MPH.
-you could press the service brake and smoke up some pad, but neither of us likes that.
-grab 2nd?
-Raise the boost to 14 PSI, now you compress lots more air in the compression stroke, and substantially increase exhaust back pressure. There is still no fuel injected, so the increased work the engine is doing can only slow it down. It is almost like you did shift to 2nd, you are slowed to 55 and make the corner without having touched the brake.
Rounding the bend, you come upon a truck in the slow lane belching smoke as he takes a run at the next uphill, what so you want to do?
a)Keeping fields green for the bunnies is important, you leave the brake on till you match speed 2' off the back of the trailer, and draft his sorry ass up the hill.
b)WOT Demons get the best of you, but since you are already pushing 1 bar, there is not a puff of smoke as you go to full fuel, and without hesitation leap past the evil rolling highway blockade.
(http://gypsyjournal.net/blog/wp-content/uploads/2010/07/Interstate80acrossSierras2.jpg)
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or option 3...
ignore the 45 sign posted as that's for pussies and take it at the 66mph you are already at.
;)
I understand the scenario, and the beauty of a micro controlled system is that with the simple inclusion of
if pushbutton = 1 then let Vp=255
end if
into the main routine then your wish is granted,
or you could have
if pushbutton = 1 and Tp<10 then let Vp=255
end if
It basically says that if the pushbutton is pressed and there is no throttle input (Tp) (or very little) then the desired vane position (Vp) is 255 i.e. closed
The servo motor which positions the turbo vanes has a feedback variable Sp (servo position) . The servo motor is contantly driven to make Sp = VP (wthin a small tolerance)
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Now that is cool!! ::).
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nice one reg
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Congrats! Can't wait to hear how it works in the car.
I think the OEM keeps the vanes open while at idle to keep the restrictions as low as possible. So when you hit the throttle to go, there will inherently be a bit of a pause while the vanes close. I'd think this would be enough of a delay in boost.
Now launch control, I like that idea. :D
Brendan
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when do we get to buy kits/finished products? i really want one of these bad boys!
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when do we get to buy kits/finished products? i really want one of these bad boys!
ditto
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Any news on these bad boys? It's been over a year... And i just bought a vnt :)
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DITTO
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here
http://dmn.kuulalaakeri.org/vnt-lda/