how a vgt turbo works when mechanicaly controled
 

we will use a 351VGT holste turbo for our example but all knowledge on any vgt turbo is great. i want to kow how do you mechanicaly run a vgt turbo? if you use a mechanicaly controled how do you have the vgt i feel like it would be a fixed blad and then the waist gate would let it out at a set psi. let me know thanks pictures are great!

If its a fixed blade then its not a VGT turbo, I dont know how you can run them mechanically, all the ones I know run of the PCM

Using a wastegate will choke the engine at part throttle loads. You must use a system that limits boost pressure based on engine load or throttle position.

Like this: http://mercedesforum.com/forum/diese...ne-load-49672/

Is it possible to calculated engine load based on revs versus throttle position ?

I've seen a setup on a awd talon with a 6.0 psd trubo where it was connected to the throttle with a cable and spring, which would pull it closed when you pushed the throttle down and a wastegate actuator to push it back open when it built boost and overcame the throttle spring. Who said ricers arent good for anything :p

HMMM intereasting, learning stuff every day...

If I had paint on my phone id draw it up, was at a car show a couple years back.

Thats no different and just as bad a putting a wastegate straight on the control arm. G@ssers have no comparison to diesels when talking about turbos, especially VNT/VGT turbos. A g@sser has very little airflow at part throttle because they are choked off, a diesel is always flowing lots of air even at idle.
With his system you're not controlling boost pressure, you're controlling how fast the turbo spools up to maximum pressure.

There isn't a good way to control a VGT turbo mechanically. You either end up with several "stages" of boost like my controller or you end up with little better than a traditional wastegate. You really need electronics and a programmable map.

Very good expressed.
In the Jeep Liberty the VGT is controlled by boost pressure. By adjusting the VGT vane angle is is possible to control the airflow to the turbine wheel.
In this way it is possible to have an optimized turbo spool up.

But:
Electronics are only used to adjust the airflow (and therefore the vane angle) to the turbine wheel. Even VGT turbos can still have an old style wastegate to control overboost conditions.

I may have missed them completely but I have not seen wastegates on VNT equiped TDIs and people mention that they control boost just by the vane angle.

From a map I've seen for a DIY VNT controller, there is a target boost based on rpm and throttle position.

Is the Tdi the only engine using VGT?

Diesel and throttle?:w2:

Just as info:
Variable geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R Ratio) of the turbo to be altered as conditions change.
This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds.
If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output.

By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum.
Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds.

The vanes are often controlled by a membrane actuator identical to that of a wastegate, however electric servo actuation is becoming more common. Hydraulic actuators have also been used in some applications.

I was just listing the TDI as an example I have seen. Same thing on the CRD's I've seen, no wastegate but if there are examples please list one :)

IIRC part of the VNT/VGT control algorithm in the TDI uses the injection quantity, which is read from the 3rd injector (on VP cars). So isn't the throttle position a good way of telling the injection quantity ? Add RPM to the equation and based on the turbine efficiency map you can tell how much boost you can request, to adjust the vanes.
I have a TPS on my IP, even though it's an old VE pump :)

This is just merely what I have read around, I'm not stating them as hard, indisputable facts :humm:

The "throttle" position is not enough. An easy example. You are hitting the pedal at a step uphill climb while towing a heavy trailer.
You demand power but since the load is that heavy the RPM's will not change. CPS is transmitting tghe actual rpm to the ECU compares your "throttle" position with the available air and rpm's and nothing happens because the ECU protects the engine from overfueling.
Another example is the same situation and you run out of air. A rich fuel condition would result in extremely high EGT's.

Now add extreme RPM's to the book. Old style VP' limited the fuel supply via a cenrtifugal limiter inside the VP- this is done now by counting the CPS pulses.

Let me seek for the circuitry plan, showing as an example how many inputs are interefering with the fuel supply and boost conditions.

And the TDI's are known for their huge electronic "network" of sensors and values to be obeyed.

I agree with you that throttle position alone cannot be used for VGT control, I never counted on that and that's why I mentioned it as part of the control algorithm :)

So, a bit simplified, engine load is rpm vs throttle position and you need that to control a VGT turbo ideally?

If that's the case then for an ideal control, mechanical control is out of the question and an electronic control unit is needed, which reads a requested boost map (boost vs rpm vs throttle) and adjusts the vane position so that the generated boost matches the requested boost. This is also simplified (PID loops are one big thing in matching actual boost to requested boost)

Yes, but that is reeeaaaally simplified.
You should have a look into a bosch diesel handbook to have a look at the block diagrams(I should look for it too). Sadly this book is in the 130€ range( really to much for an occasional view)

I already have that :rocking:
Really haven't had time to read it though.

Anyway, on the matter of VGT control, I will have my sensor reader ready in about a month. RPM, Intake manifold pressure, Exhaust manifold pressure, throttle position and 3 more inputs which are unused at this point. Should be a good base for starting a controller :)

i would be interested in such a controller for an LB7 duramax. seems like a VVT would be a nice upgrade for us fixed vain guys.

should be easy to find a turbo off of an LLY or LBZ and make it work on the LB7 with such a controller

Well, I'm using an Arduino so I can provide the code but after I get the sensor reading part it will take me a bit of time to collect the $$ for a VGT.

Couldn't us CR guys use the signal from the FPR to open & close the vanes? It would be something like the controller used in the duel CP3 setup. The turbo would supply air in proportion to the fuel. When the pedal is pressed and the demand for fuel is increased then the turbo vains will also open for more air.

Thats not how VGT turbos work. Opening the vanes reduces boost.

my bad, your correct. but i think the idea is still there.

For the hater, idk what his drive pressure is though, or what the spring tension is.


Sent from my U.S. Cellular Android device

Thats even worse than the others. Zero control over boost pressure. Then you have the exact same problem mentioned before, the turbo is choking the crap out of the engine's exhaust at low loads.

It also won't work on any but the first generation of VGT turbos, all now have holes drilled in the vane base to equalize pressure across it so they can use "low force" actuators.

Thats all I use and its worked perfect for 15 years.

​​​I used a two stage pressure regulator. Everything works great. The car is much more powerful, fuel economy is 25-30 percent compared to the wastegate turbine.