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#15
by
tomnik
on 29 Nov, 2009 08:54
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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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#16
by
regcheeseman
on 01 Dec, 2009 07:26
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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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#17
by
745 turbogreasel
on 01 Dec, 2009 16:24
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My Canbus controller seems to be a worm gear with no spring.
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#18
by
regcheeseman
on 31 Mar, 2010 09:41
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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.
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.
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.
I had short notice on Friday of an opportunity to get the PCBs done, so rapidly transferred a half finished prototype circuit board into..
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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#19
by
regcheeseman
on 20 Apr, 2010 18:45
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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.
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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#20
by
blackdogvan
on 20 Apr, 2010 19:16
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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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#21
by
regcheeseman
on 21 Apr, 2010 07:47
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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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#22
by
Rabbit on Roids
on 21 Apr, 2010 11:48
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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.
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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#23
by
monomer
on 21 Apr, 2010 19:58
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You get a mk1 setup going, I'll GLADLY pay for one.
VERY cool.
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#24
by
anto
on 22 Apr, 2010 08:28
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Reg - in laymans terms does your box of tricks take 3 inputs?
boost
throttle position
revs?
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#25
by
gldgti
on 23 Apr, 2010 05:31
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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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#26
by
BlueMule
on 24 Apr, 2010 12:07
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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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#27
by
fatmobile
on 24 Apr, 2010 22:55
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Hook up an opacity detector on the exhaust and regulate the smoke level.
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#28
by
regcheeseman
on 26 Apr, 2010 08:28
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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.
Not shown is the servo that actually controls the turbo vanes and a pickup attached to the pump.
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#29
by
BlueMule
on 26 Apr, 2010 14:32
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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.