Valve Timing: Open/Closed - Explained

Hello, I've read all the articles about VTG, but the connections between things are still unclear.

In detail:
Please correct the following sentence/statement:

A) In which position is the VTG (Ventil-Tür-Gleichlauf) considered to be open or closed?
B) In what position are the guide vanes when the engine is running at full load/low speed/low exhaust flow?
C) Duty cycle close to 0% = Vacuum sensor fully actuated (maximum vacuum). What is the position of the guide vanes?
D) Duty cycle close to 100% = atmospheric pressure (resting state with the engine off). This is the range that occurs when the engine speed is high and the exhaust volume is large.

My interpretation:
A) In the blue position, the VTG is open, and in the red position, it is closed.
B) Regarding /Red?: Simulation of a small turbine.
C) When the duty cycle is close to 0%, the maximum vacuum pressure is applied, and the VTG (Variable Turbine Geometry) is closed. The blades are in the "red" position.
D) The guide vanes move towards the "blue" position, fully opening the turbine cross-section and simultaneously directing the exhaust flow onto the turbine wheel.


The image containing the red and blue elements is attached.


Thank you for your help.

Hello,

"Blue indicates an open setting, which results in lower boost pressure."

(Details about VTG: https://community.dieselschrauber.org/en/viewtopic.php?t=2992)

Imagine an open garden hose. Water is bubbling out of the front.
Now, use your thumb to cover the opening of the hose, leaving only a small opening free.


How quickly does the water come out, and how fast would a small water wheel spin with it?
If you cannot answer the question, try it.

Best regards, Rainer.

DrDeca wrote:

My interpretation: A) In the blue position, the VTG is open, and in the red position, it is closed. B) Regarding /Red?: Simulation of a small turbine. C) When the duty cycle is close to 0%, the maximum vacuum pressure is applied, and the VTG (Variable Turbine Geometry) is closed. The blades are in the "red" position. D) The guide vanes move towards the "blue" position, fully opening the turbine cross-section and simultaneously directing the exhaust flow onto the turbine wheel.

A and B are correct. You have switched C and D.

Key ratio 0% = no vacuum = VTG open.
Key ratio 100% = maximum vacuum = VTG closed.

Quote:

Key ratio 0% = no vacuum = VTG open. Duty cycle 100% = maximum vacuum = VTG closed

Regarding older engines, such as the AFN, my recollection is that the duty cycle is the opposite.
Without activation, the VTG (variable turbine geometry) is always open.

Autoservice wrote:

Quote: Key ratio 0% = no vacuum = VTG open. Key ratio 100% = maximum vacuum = VTG closed Regarding older engines, such as the AFN, my recollection is that the duty cycle is actually the opposite. Without activation, the VTG is always open.

Both are somehow correct.
Assuming the control current flowing through the N75 valve, 0% current indicates the "safe" position of the VTG: open, meaning no boost pressure is generated. 100% current, on the other hand, produces the maximum boost pressure.
Similarly, the software includes fields for inputting the value-added tax (VAT) information.

To deliberately confuse users, the programmers came up with a diagnostic message called "inverted key ratio," which appears in the log data depending on the application. Then, a high value means low pressure buildup, and a low value means high pressure buildup. The conversion to a percentage is simply "100 - log value."
What is actually implemented in the engine control unit (ECU) becomes apparent when the engine is running at full throttle and low RPM: in this situation, the system always requests the maximum pressure build-up. However, this maximum request is usually limited to approximately 80% (or 20%).

Let's take a look at the term "duty cycle."
The percentage indicates how often the valve is activated.
0% = no modulation = valve remains completely closed = no vacuum at the output.
100% = continuous "actuation" (permanently energized) = valve permanently open = maximum vacuum at the output.

So, how can anything happen with the VTG (voltage transient generator) at 0% duty cycle? For that to happen, the N75 would have to be configured as a normally closed switch, which is not the case, because otherwise, for example, if the coil burns out, you would have a permanently closed VTG.

Deca.

If you're already stealing Thomas's pictures , then at least read everything through.
He already explained it.

The rest will become clear, as I said, when you're going full throttle.
The older ones (as far as I know, the VWP models) have a 20% rate, while the newer ones (from the PD models onwards) are at the other end of the scale, with an 85% rate.

Greetings.
m;

PS: To further complicate things, BW and Garret sometimes mounted the can in front of the turbo and sometimes behind it, so sometimes the rod pulls it, and sometimes it pushes it.

TDI-GTI-4-Motion wrote:

So, how can anything happen with the VTG at 0% duty cycle?

By not relating the % data to the current portion of the PWM signal, but rather to the pause portion. The result is the same as the aforementioned "inverted duty cycle," which is standardly output in the MWB11 for the EDC15 (1.9l PD), for example.

The diagnostic output can also be reprogrammed to log the "correct" duty cycle. Then, at full throttle in the low RPM range, you'll see approximately 80%, and as boost pressure and RPM increase, the logged value continues to decrease, while hardware-wise, the same thing happens as with the original software.

Are you watching... AFN?

Yes, and?
The log also shows the inverted N75 key ratio.
If you add a formula column next to it with "=100-(Field)", you will see the approximate current flow in the N75 .

ulf wrote:

By not relating the % data to the duty cycle in the PWM signal, but rather to the pause percentage.

I didn't expect to be convinced to use something so unusual...

So, can we conclude that there are no general answers for questions C and D?

Regarding the shovels:

If there is a lot of exhaust gas (indicated by many red arrows), they are "dumped" to prevent the turbine from over-speeding.

When little fuel is available, one tightens the valve to ensure that even a small amount of gas is sufficient to provide a steady flow.

https://www.youtube.com/watch?v=AmASUCOYnkw#t=2m30s

m;

The animation isn't quite right.
Does the air velocity and rotational speed not normally increase when the gap between the blades becomes smaller?

https://www.youtube.com/watch?v=69B5K3OX6Pw

Yes.

Be careful...

If you interpret the red arrows as representing "the exhaust volume offered by the engine," then it makes sense again.

It will not, however, show the change in flow velocity at the VTG (Variable Turbine Geometry) blades.

"That's true again - I find the point in the first video a bit pointless, as the turbine shaft always rotates at the same speed, which contradicts any real-world application."