Mechanical VNT controller systems - post what you find!

[Bean]

http://www.vwdieselparts.com/forum/viewtopic.php?f=21&t=11042

Yup - pilfering VW guys work again - but this one looks decent. Hard to do with the set up in the XD3T's - but I like in principle how it works. If it works well and it's physically possible to implement this would be the system I'd try to emulate... (So far anyway)

Rabin

[andrethx]

as i mentioned in the other thread, i saw a bunch of stuff relating to this, most of it having to do with the work of a francophone dieselhead named tintin. i think the setup he did was similar to libbypapa's (the one you link to, above)

http://forums.tdiclub.com/showthread.php?t=163748

andré

[Bean]

Thanks for the link Andre - and yes it looks very similar.

Seems like it should work quite well for a mechanical set up, problem for the XD3T's is that the injection pump is low down on the driver side, and the turbo is fairly low down on the passenger side of the engine.

I think my best bet will be an electromechanical version of this where the throttle position is translated with a stepper motor, but if I'm doing that kind of work it'd be nice to just do it right with a proper electronic controller that took throttle position and boost and engine temp into consideration so that you could map the boost curve exactly how you wanted it. (Temp so that it won't boost a cold engine.)

Rabin

[andrethx]

I think my best bet will be an electromechanical version of this where the throttle position is translated with a stepper motor, but if I'm doing that kind of work it'd be nice to just do it right with a proper electronic controller that took throttle position and boost and engine temp into consideration so that you could map the boost curve exactly how you wanted it. (Temp so that it won't boost a cold engine.)

that sounds like a lot of work! would it be easier to move the pump or the turbo? relatively speaking? especially if you are looking at changing the way the turbo mounts to the engine down the road (to facilitate use of a different turbo assembly)?

andré

[tulaweb]

that sounds like a lot of work! would it be easier to move the pump or the turbo? relatively speaking? especially if you are looking at changing the way the turbo mounts to the engine down the road (to facilitate use of a different turbo assembly)?

andré

This discussion is all somewhat over my head (fascinating anyway) but since the pump is mechanically driven on one side and the intake and exhaust manifolds are on the other side, I don't see how they could be relocated to the same side, in either direction.

[Bean]

As Dave mentions - it's not feasible to move the injection pump, and to move the turbo would be way more work and a custom exhaust manifold. Guys have done complicated linkages, but I would much rather have programmable stand alone controller to really leverage the usefulness of the VNT - or go with a small internally wastegated turbo that spools as fast as the stock turbo but still flows to support 160+ HP - and most any stock turbo of a small gas engine would do that. (I've got a TD05 off an older 1.8L Subaru that might work - but adapting to the T3 would be some work.)

Properly sized turbo with an electronic boost controller would be a close second to a VNT - the VNT would just spool quicker which is still the ideal with such a short power band. (4000 rpm redline)

[andrethx]

i see.

okay, next question -- if you are translating the throttle position, you essentially have a drive-by-wire vnt. would it make sense to just swap out the accelerator pedal assembly for a recent DBW unit? then your engine throttle and the vnt could use the same signal...i seem to recall that some of the engine swaps that i've read about on ls1tech.com have involved similar DBW retrofits...

andré

[Bean]

That'd be even harder actually. Diesels don't actually have a throttle plate like a DBW throttlebody would control, it just controls a lever on the injection pump which controls fuel flow. So you'd have to modify it to control the lever. If you set up the DBW to control that lever on the pump, you'd need an additional control circuit just for that, and then that could would still need to be interpretted by the VNT controller.

It would be easier to keep the cable control but use a TPS sensor for the shaft pivot, and then use that for the control circuit for the VNT. There was one guy that had a prmising set up using Arduino that controlled the factory Hella stepper motor on a VNT turbo - but it wasn't fully developed and offered as a DIY kit. You can read about it, and duplicate it with enough time, but not something I could do anytime soon.

http://dmn.kuulalaakeri.org/vnt-lda/

Seems like there's a few that have gotten it to work - but I want a P'nPlay solution.

EDIT: I just noticed that the site has been recently updated and it looks like it might be more doable than it used to be. Still DIY - but last I checked he wasn't updating or supporting it at all.

Rabin

[JunktionFET]

For all out simplicity, there are a some OEM parts you could use/repurpose for an entirely mechanical system:

1. XD2S EGR vacuum modulator mounted as-is on the IP, with the vacuum outlet connected to a cruise control servo/diaphragm.

2. "Wastegate actuator"-like device with its inlet connected to the pressurized side of the intake.

Tie the actuating rods from the cruise servo and "wastegate actuator" together and to the VNT vanes.

The connection would be such that applying maximum boost pressure to the "wastegate actuator" OR full vacuum to the cruise servo would "Open" the VNT vanes

The EGR vacuum modulator applies full vacuum with the throttle at idle, and the vacuum progressively drops to nothing as the throttle opens. It is adjustable, but in its stock form I believe it drops to nothing around half throttle.

[andrethx]

okay, next noob question: is it necessary to use an actuating rod, or could one use something (relatively) flexible like a throttle cable to "tie" the vnt vanes to the lever on the injection pump?

i assume this is something you've considered and rejected, i'm just wondering why...

andré

[JunktionFET]

A cable would work as well, and it might be the only way to do it so that the actuating devices can be remote.

Of course there's more to it than just a connection between the pump's throttle lever at the VNT vanes. You need to somehow incorporate actual boost pressure as well so that it can be regulated. But at any rate, a cable somewhere in the mix is perfectly acceptable and likely unavoidable.

[andrethx]

interesting, it wasn't clear to me why one needed two inputs to control the position of the vnt vanes...i think i'm starting to understand now.

here's another design based on tintin's work...this guy uses a cable and a rotating cam...

andré

[Bean]

For all out simplicity, there are a some OEM parts you could use/repurpose for an entirely mechanical system:

1. XD2S EGR vacuum modulator mounted as-is on the IP, with the vacuum outlet connected to a cruise control servo/diaphragm.

2. "Wastegate actuator"-like device with its inlet connected to the pressurized side of the intake.

Tie the actuating rods from the cruise servo and "wastegate actuator" together and to the VNT vanes.

The connection would be such that applying maximum boost pressure to the "wastegate actuator" OR full vacuum to the cruise servo would "Open" the VNT vanes

The EGR vacuum modulator applies full vacuum with the throttle at idle, and the vacuum progressively drops to nothing as the throttle opens. It is adjustable, but in its stock form I believe it drops to nothing around half throttle.

I've thought a lot about this set up and concluded that this could be the best idea yet in combination with a control cable (IE push pull) link to the throttle shaft. I had no idea how the EGR modulator works, but now that I know - and visualizing how this could possibly work and I'm thinking it might work great.

Just going to run down how I imagine this working to get some feedback:

The biggest thing I can see is that you would still need a direct connection to the vanes from the throttle lever so that at from a dead stop if you floored it - the EGR modulator vacuum would go to 0 and the vanes would return to their open position and no boost would build.

1. At rest / engine off - the vanes would be in the open position.
   
2. At start up / idle the vacuum pump would be running and through the EGR modulator it would apply full vacuum to the cruise control servo closing the vanes (Fastest spool position)
   
3. At partial throttle or easy application of throttle, as the throttle lever moves the vacuum levels drop off at the same time that the boost starts building.
   
4. As boost starts to peak the wastegate actuator starts to open the vanes which then reduces / controls boost levels to whatever the wastegate actuator is set too.
   
5. Direct cable connection would allow rapid throttle without the vacuum dropping off and opening the vanes too soon.
   

So there would be three mechanical analogue controls.:

1. Direct connection from throttle to vane control - through a tension spring.
   
2. Cruise servo and EGR modulator to have the vanes closed for fastest throttle response - as vacuum drops the mechanical connection to the throttle keeps them closed.
   
3. As boost approaches the wastegates threshold - it starts to close the vanes which opens the vanes and modulates boost to the wastegate actuator setting.
   

Does that sound right? Or did I miss something?

Rabin

[JunktionFET]

Ah, I was thinking kind of the opposite operation, wherein the vanes would be normally closed (i.e. no vacuum and no boost pressure - fully closed vanes).

However, at idle the high vacuum from the modulator would open the vanes. As the throttle goes from idle to near halfway, vacuum progressively fades away, thus closing the vanes, giving maximum boost potential.

Boost pressure would then act to re-open the vanes once maximum pressure is reached. Also, immediately releasing the throttle would put the modulator back into full vacuum, thus re-opening the vanes fully.

[Bean]

Taking advantage of the VNT I figured it would be best to have the vanes closed at idle since that will build boost the fastest... I think the way you describe would work essentially like a regular turbo, and have more of linear boost curve...

Not sure if the way I suggest would be too aggressive and build boost too fast. but the big thing would be to ensure that the system was fast acting. Been looking at pneumatic controllers / cylinders instead of using existing components, and I think if done right a single push pull pneumatic cylinder with some basic switches could do the job nicely.

Rabin