Load Stress in Idle: Is It Meaningless?

Hello,

My turbocharger is also building significant pressure even when it's supposed to be in bypass mode. For example, the LDA (likely a pressure sensor) shows 0.2 bar at 2000 rpm, even though there's definitely no boost pressure needed.
The corresponding logs show an actual pressure of approximately 1200 mbar, while the target pressure is approximately 1000 mbar.

What's the point of such a strategy?
To keep the turbocharger at a certain RPM in advance, so that when you accelerate fully, the pressure increase is only 2.1 bar instead of 2.3 bar?
That is, in my opinion, ridiculous .

By the way, my VTG (Variable Turbine Geometry) isn't stiff. If you look at the vane position of the logs (32% at 2000 rpm in boost), it becomes clear that this is intentional on the part of the developer.

But why

Hello Ulf,

While I don't have a technical background, I believe this is an attempt to minimize turbo lag when suddenly accelerating. Another idea would be to ensure constant lubrication of the turbocharger shaft by maintaining some degree of shaft movement.

I'm getting a meaningless 0.4 bar of boost pressure even at 4,000 RPM. I think it's to prevent that black cloud of smoke when I suddenly accelerate.

Regards,

Manuel.

Manuel Thomas wrote:

I even have 0.4 bar of meaningless boost pressure at 4,000 RPM.

I think this might help prevent the black smoke when I suddenly accelerate.
Well, according to the TDI-theory:(, a TDI engine shouldn't produce soot because, with (still) too little boost pressure, the soot reduction system should kick in...

Only in practice does } sometimes turn out differently.

Does a turbocharger not always have to generate a certain amount of pressure?
On the exhaust side, it's always immersed in the exhaust flow and is driven by it. If no pressure were built up on the intake side, it would only be running against the resistance of the bearing friction and air turbulence. Wouldn't the speed increase to an unhealthy level in that case?

While in theory, no airflow would be needed in a "push" mode, and therefore no power would be required, the turbocharger would have to restart with every throttle input. Furthermore: Would you really want to climb a steep incline at full throttle and then descend the slope in "push" mode with a super-hot turbocharger that's no longer spinning???
So, he always has to rotate, and when he rotates, he needs some kind of "braking" force.
That's how I would imagine it, at least.

joegolf wrote:

Doesn't a turbocharger always have to generate a certain amount of pressure? On the exhaust side, it is always located in the exhaust stream and is driven by it. If no pressure were built up on the intake side, it would only run against the resistance of bearing friction and air turbulence. Wouldn't the speed increase to an unhealthy level in that case?

Hm? I can't quite understand... it seems that the intake and exhaust volumetric flow rates are practically the same.
If a charger is still drawing energy to build up boost pressure, that's something akin to a perpetual motion machine .

Quote:

Furthermore: Climbing the slope with full power and then going down the slope in afterburner mode with a turbo that is extremely hot and no longer spinning???

Even a stationary engine would cool down quickly because it is constantly being flushed with cold intake air and (exhaust gases that are almost as cold) from the turbocharger.

And the oil circulation, which also provides cooling, should continue to flow even when the bearings are stationary... ?

joegolf wrote:

On the exhaust side, it is always located in the exhaust stream and is driven by it. If no pressure were built up on the intake side, it would only run against the resistance of bearing friction and air turbulence. Wouldn't the speed increase to an unhealthy level?

For this, there is a boost pressure control system using a wastegate or VTG.

ulf wrote:

The corresponding logs show an actual value of approximately 1200 mbar, while the target value is approximately 1000 mbar. Looking at the throttle response of the engine (32% at 2000 rpm in boost), it becomes clear that this is an intentional design choice by the developer.

Hello Ulf,

Before we start wildly speculating about the developer's intentions or mistakes, or about the technical circumstances:
Have you checked whether the 32% PWM duty cycle actually has a significant effect? Have you tried disconnecting the solenoid valve and seeing if the low-pressure build-up is still almost 0.2 bar?

Regards,
Guste.

guste100 wrote:

Have you checked whether the 32% PWM actually has a significant impact? So, have you tried disconnecting the solenoid valve and seeing if the low-pressure (LD) still builds up to almost 0.2 bar?

I did it differently, but the result is the same:
When the vacuum pressure in the VTG sensor is lower, the boost pressure effectively returns to zero.

Hi Ulf!

I suspect two things that might be responsible for an "aggressive" VTG (Variable Transmission Gear) setting in sliding operation:

1. Increase in engine braking force (increased boost pressure = higher exhaust back pressure).
2. Reduction of oil consumption (the gap seal on the compressor side is supported by the pressure gradient).

It is also possible that the transient behavior, i.e., the response characteristics of the ATL, should be positively influenced.

Regards,
Alex.

ulf wrote:

joegolf wrote: Doesn't a turbocharger always have to generate a certain amount of pressure? On the exhaust side, it is always located in the exhaust stream and is driven by it. If no pressure were built up on the intake side, it would only run against the resistance of bearing friction and air turbulence. Wouldn't the speed increase to an unhealthy level in that case? Hm? I can't quite understand... it seems that the intake and exhaust volumetric flow rates are practically the same. If a charger is still drawing energy to build up boost pressure, that's something akin to a perpetual motion machine .

Okay, it's clear that in practice, he's still building up boost pressure during the idle phase. Either the engine is still injecting fuel during the idle phase, or the pump is being used.

Hi,

Ulf, why don't you play around with the accelerator a bit (both in a sporty/aggressive way and in a relaxed, cruising style).
I was at least surprised by what I consider to be a sensible behavior.
It seems that the MSTG is trying to determine whether the system is being used for heating or cruising.

Best regards, Rainer.

I also believe that the improved responsiveness (combined with reduced soot emissions at the end of the thrust phase) and the better sealing of the compressor are the reasons.

In motorsports, there was a time when left-foot braking became common practice with turbocharged engines. At the same time, the turbocharger was kept "spooling" by modulating the throttle. While this is only partially applicable to our tractors, I believe that maintaining a certain level of turbo boost will positively affect the responsiveness.

wolfi_b wrote:

joegolf wrote: On the exhaust side, it is always located in the exhaust stream and is driven by it. If no pressure were built up on the intake side, it would only run against the resistance of bearing friction and air turbulence. Wouldn't the speed increase to an unhealthy level? For that, there is a boost pressure regulation via wastegate or VTG.

Okay, I understand. But VTG would have to almost completely seal the exhaust side if the turbocharger is running freely on the intake side. And then the turbocharger would run at undefined speeds until it stops. Even tiny air currents might be enough to keep the turbocharger running.

Alternatively: The plain bearings are likely the most vulnerable part during the turbo's startup phase. Therefore, repeatedly stopping the turbo during operation, even under load, is probably not a good idea. Furthermore, the oil would flood the turbo through the sealing rings if it were not running.
In order for the turbocharger to operate within a useful RPM range, it needs a certain amount of back pressure (boost pressure) that can be properly regulated (by the variable turbine geometry - VTG). With a boost pressure of 0 bar, the VTG lacks any control parameter. The turbocharger's RPM is not measured. Therefore, the turbo would either accelerate until it generates boost (possibly reaching 0.2 bar) or it would simply stop.

I hope I was able to make myself understood .

Due to the plain bearings, the initial start-up of the turbocharger is likely to be the most wear-prone.

I agree. In this state, there's a mixed condition between a wave bearing and a plain bearing, and this operating condition should be avoided.

Hello,
Even in sliding mode, the engine pumps a significant amount of air, and the ATL (Anti-Lag Turbine) will never come to a complete standstill; the control range of the VTG (Variable Turbine Geometry) is simply not that wide. And in the process, it compresses the air slightly on the pressure side.
Best regards,
Günther.