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 608 Posts Member #: 1106 Post Whore Hungerford, Berks |
5th Apr, 2021 at 08:40:15am
On 4th Apr, 2021 robert said:
maybe a ratio divider arm for the vnt graham,so ,say 3mm movement of the servo equals 1mm of the vnt arm ? , or just extent the vnt arm ? Yes Robert, I was considering extending the VNT arm, though I’d still need an expensive servo with high resolution to get 0.5deg increments. I have roughly calculated around 33deg of servo rotation with a 1:1 ratio between servo horn and VNT arm. Still scratching my head on this. how accurate does the vane movement actually have to be (considering the slop in the mechanism) and how fast do the vanes actually need to change? The other option , I even be to investigate further an electronic linear actuator with positional feedback. Edited by Graham T on 5th Apr, 2021. ’77 Clubman build thread
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 (2)[/url] by [url=https://www.flickr.com/photos/150672766@N03/]Rod Sugden[/url], on Fli) 5988 Posts Member #: 2024 Formally Retired Rural Suffolk |
5th Apr, 2021 at 11:35:04am
Things may well have moved on since I looked at VNT but 6 or 7 years ago they were for deisel only.
Schrödinger's cat - so which one am I ??? |
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
5th Apr, 2021 at 06:13:43pm
On 5th Apr, 2021 Rod S said:
Things may well have moved on since I looked at VNT but 6 or 7 years ago they were for deisel only. The internal bits couldn't live with the temperatures of petrol exhaust. Yes, as I understood when reading up on VNT’s. This thread covers what you are saying: VNT or Twin Scroll http://www.turbominis.co.uk/forums/index.p...id=446826&fr=25 And one of your points in that thread …it seems the average head gasket life on this forum is 1k miles. pistons maybe 2k miles, blocks not much longer when the head gasket fails and thrust bearings fail even quicker. So 100k on a production diesel seems good - my VNT lasted 65K and that was on a Ford. Can anyone destroy a VNT on a Mini before the rest of the engine ??? No evidence so far :) :) :)… So I thought: well lets see how it goes. 😊 On 5th Apr, 2021 Rod S said:
I dismantled a GT1752V - a broken one on my old Mondeo TDCi just to see how they work. Very crude. That one used a vacuum actuator (controlled by two solenoid valves on the vacuum line) but later ones had an electric servo motor controlled direct by the ECU. On the deisel engines their mode of operation seemed to be very much on/off, restrict gas flow at low RPM to increase pressure at the turbine so the boost came in at low RPM, then release the restriction at higher RPM. But, like I said, it was an early 1752V so the newer ones may be a lot more sophisticated, I split this new one to take a look at how it all works, and as you say “Very crude”. That’s really why I made the comment/ posed the question about how accurate the control needs to actually be. 
The little notch in the control ring above (at 12 and 1 o'clock) shows just how little VNT lever movement there is between fully open and fully closed vanes So far I have 2 MAP sensors monitoring MAP and exhaust pre turbine back pressure. An input in the form of a PWM signal is received from the normal boost controller output of the MS2. The input PWM % is ranged according to the desired boost range – so for example 0% being 0 boost and 100% being 304Kpa (or whatever is set as the max boost in the variables of the controller program) The Programming has the vanes closing up at tick over/ over run, so 0% PWM input, to increase gas velocity over the turbine wheel and so decrease spool time once the input PWM % increases. I also have a routine in the program whilst Input PWM % remains at 0% to open the vanes slightly if exhaust pre turbine backpressure is too high with the vanes completely closed – again a variable which can be altered to set the acceptable pre turbine backpressure. If the Input PWM is not at 0%, then the controller monitors the actual measured MAP and will open or close the vanes to get the actual MAP to match the target MAP calculated from the input PWM %. I have a “range” set here also to try to reduce any fluctuation caused by the controller missing its target (over or under) and trying to correct. So as long as the actual MAP is within X Kpa of the target, the controller will do nothing. _ I currently have this set to 3 Kpa. A PID loop calculates the servo steps to move and there is a delay in the program to allow the vane position change to take effect, before sampling MAP again. I have also added in a routine to constantly monitor the Pre turbine back pressure and if the pre turbine back pressure rises above MAP by a pre-defined ratio, then regardless of the target MAP, the controller will open the vanes in order to reduce pre turbine back pressure. My thought here is why choke the engine to make more boost which cannot be efficiently used? I have that all working using potentiometers as the MAP inputs and a pot directly connected to the servo to simulate boost change with servo movement, and a second Arduino simulating the PWM input. 
But what I did not realise as previously stated was just how little movement there is on the VNT lever. And obviously it’s all simulated, so might not work at all on the car. Also am thinking about how to mount some sort of “safety” BOV to blow at 16PSI, just in case it all goes to sh!t… Edited by Graham T on 5th Apr, 2021. ’77 Clubman build thread
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 428 Posts Member #: 10128 Senior Member Dorset |
6th Apr, 2021 at 02:13:43pm
You clever bastard, had to go over the last post twice to allow my few braincells to comprehend.
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5988 Posts Member #: 2024 Formally Retired Rural Suffolk |
6th Apr, 2021 at 04:14:37pm
Well you did prove me right re. head gaskets....
Schrödinger's cat - so which one am I ??? |
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 8604 Posts Member #: 573 Formerly Axel Podland |
6th Apr, 2021 at 05:04:58pm
Have you considered adapting a 12v IACV bi-polar stepper motor? They have a short travel that should suit.
Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
6th Apr, 2021 at 05:11:56pm
On 6th Apr, 2021 e5tus said:
You clever bastard, had to go over the last post twice to allow my few braincells to comprehend. Only twice? I still keep re-reading it to make sure I have it right… e5tus said:
Great work on the roof and gutter, that's a lot of work, and looks like a very good result. A lesser man would have reached for the fuel and matches way before now! Thanks, it’s really taking shape now, except my new mask filters have still not arrive so the colour coat is still not done. And it was a close thing, except it was a can of thinners that was close at hand, not a can of fuel. But I decided I like the garage too much to burn it down. On 6th Apr, 2021 Rod S said:
Well you did prove me right re. head gaskets.... Ok, yes, very true. But luckily it was only a head gasket. Rod S said:
For protecting a VNT against overboost I would definately do it on the exhaust side, not the compressor side. If you bleed off excess air on the compressor side it will just allow all the excess exhaust gas to overspeed the turbine and destroy itself. If you feel it needs protection, something like an external wastegate (ie, to over-ride the VNT control) ??? Good point Rod. Thanks. As it happens I have a brand new external waste gate still sat in a box in the garage. I just feel the protection for overboost would be a good thing to start with. I cannot be sure how the code will work on the car and I cannot be sure of the reliability of the servo (or electronics for that matter). If I have the code all wrong or the servo fails it could be at just the wrong time and end up with a bit more than head gasket failure… ’77 Clubman build thread
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
6th Apr, 2021 at 05:34:23pm
On 6th Apr, 2021 Paul S said:
Have you considered adapting a 12v IACV bi-polar stepper motor? They have a short travel that should suit. You can get a suitable H-Bridge control board for the arduino, although you are probably already using one. That's another good option Paul. Yes I have a handful of H-bridge control boards for the Variable length runners. The only downside I can see to using an IACV is speed. I cannot remember how fast an IACV's linear movement is, but I do not recall it being that fast. Just thinking whether the speed at which the vanes can be move might affect the ability to tightly control the boost level, or even worse allow overshoot and cause spikes (oscillation??) as the controller is always playing catch up with the varying MAP. Edited by Graham T on 6th Apr, 2021. ’77 Clubman build thread
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8604 Posts Member #: 573 Formerly Axel Podland |
6th Apr, 2021 at 05:52:24pm
The Peugeot/GM ones that I use move pretty quick. Less than a second for full travel at a guess. They will fire the pintle across a room if you operate them outside of the body.
Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
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1267 Posts Member #: 831 Post Whore Montreal, Canada |
6th Apr, 2021 at 08:16:10pm
To get the best speed out of a stepper IACV, you will want to accelerate the step time for large movements. You'll need to characterize the stepper you're using for the shortest initial step time and the acceleration curve.
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
7th Apr, 2021 at 12:09:57pm
Thanks Paul and Jean.
’77 Clubman build thread
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8604 Posts Member #: 573 Formerly Axel Podland |
7th Apr, 2021 at 04:11:59pm
The software that we use for control of our CNC converted milling machine uses ramp profiles for the stepper motor drives as Jean describes. However, that involves movement of relatively heavy machine beds, vices and workpieces to within fractions of thousanths of an inch.
Edited by Paul S on 7th Apr, 2021. Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
7th Apr, 2021 at 06:26:15pm
On 7th Apr, 2021 Paul S said:
…Biggest step change will be a sudden closure of the throttle when the vanes will need to open up to slow the turbine. However, the sudden drop in exhaust gas pressure at the same time will probably have more of an impact, allowing for a slower opening of the vanes… Not being argumentative here, just trying to understand better before I break something on the car… A sudden throttle closure would predominately indicate a gear change? In which case I am thinking we want to keep turbine speed up ready for the next plant of the foot on the throttle, in a hope to build boost back up as soon as possible. This would mean closing the vanes, rather than opening them. As you point out a sharp throttle closure would reduce exhaust gas flow pretty quickly and also the sudden vacuum in the plenum would aid the DV to open to waste any “excess” boost still being produced by the compressor, hence keeping everything in balance and not destroying the turbo. Then when the throttle opens again, the vanes are already closed up, keeping exhaust gas velocity high over the turbine and aiding spool? At least thats the logic I was working on - which you have just totally blown out of the water 
Edited to add missing sentence: This would mean closing the vanes, rather than opening them. Edited by Graham T on 8th Apr, 2021. ’77 Clubman build thread
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8604 Posts Member #: 573 Formerly Axel Podland |
7th Apr, 2021 at 08:07:59pm
Agree on the gear change going up the gears. How about when you need to brake or go down the gears?
Edited by Paul S on 7th Apr, 2021. Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
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 7265 Posts Member #: 1268 The Boom Boom speaker Police! Essex |
8th Apr, 2021 at 09:06:39am
Great stuff. I really loved the VNT on Joe’s car (about a decade ago). In the 13's at last!.. Just |
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
8th Apr, 2021 at 12:13:22pm
On 7th Apr, 2021 Paul S said:
Agree on the gear change going up the gears. How about when you need to brake or go down the gears? Edit: Actually thinking about the transient conditions with a conventional turbo with a waste gate, when the throttle is closed, the waste gate slams shut sending all gas flow through the turbine. No issues with that so I don't actually see a problem if the servo or stepper takes a little longer to close. Thanks Paul, that helps to clear it up a little in my mind. On 8th Apr, 2021 theoneeyedlizard said:
Great stuff. I really loved the VNT on Joe’s car (about a decade ago). Yeah, Actually I have to give Joe big thanks for taking the time to talk through his experience of the VNT with me and give me some guidance and ideas. ’77 Clubman build thread
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 6745 Posts Member #: 828 Post Whore uranus |
8th Apr, 2021 at 01:37:50pm
throttle shut = negligible gas flow . ? Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM |
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
4th May, 2021 at 08:03:53am
It feels like that last few weeks I have made very little progress.
’77 Clubman build thread
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 855 Posts Member #: 951 Post Whore Bromsgrove |
4th May, 2021 at 12:30:28pm
Those wheels are perfect as they are 'Where does the engine go?' |
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428 Posts Member #: 10128 Senior Member Dorset |
4th May, 2021 at 03:08:44pm
Fantastic up-cycling of excess decking for the spray rack. I'll show this to my wife to bolster my argument for keeping my collection of scraps in the shed! |
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
7th Jun, 2022 at 12:50:57pm
Well, 1 year and 1 month later I have finally managed to feel well enough to get back in the garage. (crap year!!)
’77 Clubman build thread
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6745 Posts Member #: 828 Post Whore uranus |
7th Jun, 2022 at 07:49:11pm
well yay on the progress , and pooh on the housing ! Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM |
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 2629 Posts Member #: 1246 Post Whore Lowestoft, Suffolk. |
7th Jun, 2022 at 10:00:26pm
So glad to see some progress Graham, hopefully you manage to keep it up.
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608 Posts Member #: 1106 Post Whore Hungerford, Berks |
13th Jun, 2022 at 01:35:01pm
On 7th Jun, 2022 robert said:
well yay on the progress , and pooh on the housing ! Yes, Oh pooh – or slightly stronger. But I have sourced another. On 7th Jun, 2022 shane said:
So glad to see some progress Graham, hopefully you manage to keep it up. Shane Cheers Shane, I am a year behind schedule now which is annoying, but flat out back at it now. Only a small update for today. Managed to get the front subframe in colour now, so that can hide out of the way for a short while 
First attempt on painting the door furniture went slightly wrong. I am not sure why, but apparently I bought satin black. Sold as 40° Matt black. I don’t like it. So I have ordered another kit, this time 2° matt. The only place I could find that sells matt black epoxy lacquer is in France, it has been shipped but I am now waiting on it clearing customs. And finally, some nice glossy green bits… 
’77 Clubman build thread
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428 Posts Member #: 10128 Senior Member Dorset |
14th Jun, 2022 at 08:40:24am
Looking great Graham. Annoying about the Matt/Satin mixup, colours are so personal it can really make a difference. |
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