Are rotating masses in the flow solver too large?

Hi everyone,

The calculation tool for traction has been further expanded, including features to account for rotating masses in the engine, transmission, and tires.
This results in longer calculated ventilation times - as far as I understand it, and thank you to the person who made the update (I unfortunately deleted the original direct messages from that time).

However, I wonder if the assumed moments of inertia are not too high.
For example, when I calculate the time for my wife's standard ALH Ibiza, I get 8.47 seconds.
I measured 7.2 seconds (under mostly normal temperature conditions, etc.), which would correspond to a serial increase in performance of 15%, or 103 horsepower instead of 90.

In my Golf, without any pump tuning and with the boost box turned off, the factory-stated horsepower would be approximately 123 instead of 110.

Since my Golf, at the very least, is on par with other vehicles in the forum, this would mean that the average TDI engine not only reaches but exceeds the legally permissible power tolerance of 10%.

If that's really the case, or if, for example, the underlying calculation concept is no longer valid, meaning that some losses have been double-counted?
Reducing the overall losses would contradict the standard values of test bench runs even more than the already tight margin of 12%...

Since my Golf, at the very least, is on par with other vehicles in the forum, this would mean that the average TDI engine not only reaches but exceeds the legally permissible power tolerance of 10%.


Hello Ulf,
I used to have a Golf 3 TDI with 90 horsepower until January. It ran extremely well. My workshop foreman told me that most Golf 3 TDIs with 90 horsepower actually often have over 100 horsepower. He estimated that mine had 105-110 horsepower. It is reportedly that the insurance companies have sent warnings to Volkswagen, threatening to reclassify the vehicles.
My old car could almost always reach 195 km/h according to the speedometer, even when fully loaded, which translated to a real speed of 188 km/h (measured over a 5 km distance). Only 175 km/h was entered.
My new Golf 4, which also has 90 horsepower, accelerates much worse and has a significantly lower top speed. It runs either full or empty, with a top speed of 180-185 km/h according to the speedometer (180 km/h is the registered limit).
What bothers me the most is that VW is increasingly adapting the performance curve to resemble that of gasoline engines. This means that the characteristic, strong pull of a true diesel engine is being lost. A true retiree's car...

Regards,

Eike.

Hi Eike.

Quote:

My old car could almost always reach 195 km/h according to the speedometer, even when fully loaded, which was actually 188 km/h (measured over a 5 km distance). Only 175 km/h was entered. My new Golf 4, which also has 90 horsepower, accelerates much worse and has a significantly lower top speed. It runs either full or empty, with a top speed of max 180-185 km/h according to the speedometer (180 km/h is the registered/official speed).

Well, the fact that the newer TDIs have less power than the older ones might also be due to the better emission standards of the newer models.

My wife's Ibiza is also from 2001, is definitely not driven "sportily," and has the typical "new car" sluggish acceleration at low RPM compared to my 1997 Golf – even though you might think it's been converted to have 90 horsepower.

Despite this, the Ibiza appears to have 103 horsepower according to the updated drag coefficient calculator. When the loader is running at full speed, it produces a significant amount of power, but it reacts unpleasantly and sluggishly to small movements of the gas pedal.

Hello Ulf,

I can definitely confirm that my TDI exhibits a similar sluggishness compared to a 1Z.

Hello everyone!

I have done the update .
But the values should definitely not be too low. While the exact values may need to be adjusted individually, the ones I provided should be approximately correct.

A 1.4-liter gasoline engine from the A-Class has a moment of inertia of 1.4 kgm².
I know how much each TDI engine has, but I'm not exactly sure. However, since some things increase exponentially, I would estimate it to be slightly more than 1.9. Many factors influence this, such as... Mass balance waves can be extremely tiring.

A wheel has a moment of inertia of approximately 1 kg·m². The 3 kgm² value I provided for all four wheels is only accurate for small wheels with lightweight aluminum rims and small brake discs.

So, overall, the value is probably even higher.

Okay, now let's talk about the discrepancies in the values: Yes, every engine has more power than what's stated in the registration document. I was recently at BMW in Steyr and learned quite a few things there. For example, the engine maps are specifically determined for each individual engine. (There was a post about whether it's beneficial to fine-tune the engine control unit for each individual engine... this confirms that it is.)
For this reason, the engines with an untuned engine control unit are very closely spaced (from the factory), and they all have more power than what is officially certified. My question about whether they were exceeding the 10% threshold was dismissed with a smile (yes, of course).

If a pull test reveals 20% more power, it doesn't necessarily mean there's 20% more maximum power output. The dyno test, therefore, indicates the average additional torque at 2000-4000 RPM.

I still find the test very useful and I would like to congratulate Ulf again. Perhaps the wheel diameter is still a bit too large. I'm consistently measuring smaller values (vertically, because the wheel is being compressed, which results in R_dynamic).
Then you have to put in the effort and type everything in carefully, and run several tests. And calculate an average over multiple times (and not exclude the bad times ).

And the device used at BMW to calculate/simulate such times is so complex that even the qualified engineers there cannot fully understand it, they admitted.
Greetings.

Hi Ernst

How does the moment of inertia change in different gears?
The engine, along with the "transmission input," is always accelerated from 2000 to 4000 rpm, but the transmission output and the wheels rotate at different speeds depending on the gear selected.
Could we incorporate a speed-dependent correction to further improve its performance?

For individual tuning of the engine control units for each engine: whenever this is done, problems may arise when replacing engine computers. If you obtain a used unit that was originally paired with an engine that differs "significantly" from your own engine, the performance characteristics will also be different.

And what about a replacement device from the brand's distributor? Is this programmed using "standard calibration maps," or does the Vehicle Identification Number (VIN) need to be provided when ordering, so that the original data set of the customer's vehicle can be "customized" again?

And finally: Why are the engines "deliberately" made more powerful than what's stated on paper? So that it's not so noticeable how heavy and sluggish today's cars are, fundamentally?

During my tour at BMW, they explained that each characteristic curve in the engine plant is determined and then sent via a data connection to the automotive plant, where it is stored along with the engine's identification number. Okay, I believe that replacement control units will then receive this specific calibration data again, and providing the number is no problem.
I'm not sure if it's the same with VW, but I once heard from a workshop that they wanted to know the exact number and then sent it in, in the case of an engine control unit issue.

Why would someone increase the performance beyond what's specified? Who else would drive a BMW? And, as you said, the new VWs are also quite heavy.

@Gear Test: Just change the gear ratios... and the moment of inertia will adjust. Besides mass, diameter, and the gear ratio where each mass is located, there are no other dependencies. I only need the wheel diameter because force and weight are calculated there. So, it works in every gear.

Of course, the most important thing comes last: Changing the speed value from 50 to 49 reduces the time by three tenths... That's too much, especially when you look at the tire's variation range, and the actual dynamic tire radius is even smaller. And the speedometer inaccuracy as well...
I actually only need the speed for the air resistance calculation; otherwise, couldn't I determine the calculation and measurement based solely on the rotational speed? However, the speed is included in the traction calculation, which certainly doesn't make the error any smaller.
I'll think about how to modify the calculation to minimize inaccuracies. Only the process of thinking takes me a little .

There's nothing more that can be improved. I have to say that you did an extremely good job with the calculation, and the wheel diameter is already the dynamic one. (Respect)

Okay, assuming you have relatively new tires.
and a section of road that has a truly 0% gradient.
and that results in a 15% increase in performance...
I suppose then you have them too.

Unfortunately, I don't have it with me, but the measured value is quite close to the calculated value.
Greetings.

Hi Ernst,

Quote:

Change the gear ratios... and the moment of inertia will adjust accordingly

.

Actually, *building blocks amazement*... I hadn't really understood yet.
Respect!

Quote:

Change the value for the speed from 50 to 49, and the time will be reduced by 3 tenths... That is too much.

I don't think so, or rather, I think the reasoning is correct, because, for example, with an increasing initial velocity...
- Does the longer gear ratio reduce the tractive force?
- The range of speeds at which the vehicle can travel increases, meaning the car stores more kinetic energy, which the engine must initially provide.
- Furthermore, the level of air resistance also increases.

Even based on my intuition, the sum of all effects for approximately 0.3 seconds with a 1 km/h starting difference is "good" .
. . . also: how long is 0.3 seconds

Quote:

I actually only need the speed for the air resistance; otherwise, couldn't I perform the calculation and measurement based solely on the rotational speed? In the traction force calculation, the speed is included, which certainly doesn't make the error smaller.

The pulling force is inversely proportional to the speed, because of the relationship F x v = power, which is generated by the motor (simplified, without considering losses, etc.). You probably won't be able to accurately calculate the speed in this case.
By linking with the starting speed (at 2000 rpm), I avoid having to calculate the traction separately using the respective gear ratio and rolling radius from the speed calculator sheet.
What do people do when they don't know their gear ratios? I wanted to make the computer accessible to them as well, even if only through their built-in speed estimator.

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So, if you have relatively new tires and you find a track that has absolutely 0% incline, and you then achieve a 15% increase in performance... I would guess that you have them.

Interestingly, the difference between new and old tires is almost negligible. The high, new tread patterns are compressed and worn down so much during rolling that the larger outer diameter of the new tires is only minimally noticeable compared to worn-out tires.
I've measured it multiple times... Peanuts compared to the permissible tolerances of the new tires.

Let me explain the effect of the tires by saying that the different circumference also changes the axle ratio!

Docter wrote:

Let's explain the effect of the tires by saying that the different circumference also changes the axle ratio!

How is that supposed to work? Does grinding down the tire lugs change the number of teeth on the pinion and/or ring gear?

The rolling circumference is simply a component of the overall translation, but instead of being expressed as a ratio of tooth numbers, it's expressed as a ratio of distance and revolutions.

No, but the radius of the wheel is included in the axle ratio calculation. If the radius gets smaller, the overall ratio becomes shorter; if it gets larger, the ratio becomes longer.

Translation primarily has nothing to do with the number of teeth, but rather it's simply a conversion from input speed to output speed, and similarly for distance, etc.

Hi Doc.

Quote:

Translation primarily has nothing to do with the number of teeth, but rather it's simply the conversion from input speed to output speed, and similarly for distance, etc.

Okay, regarding "input speed to output speed," I don't see a place for the distance traveled, because the ratio is most directly determined by the number of teeth in gear pairs.

The wheel radius, or... The distance or circumference becomes necessary for calculation only when there is no longer a defined interlocking (i.e., tire --> road surface).

As a gear ratio , I have always only known the tooth ratio between the pinion and the ring gear (as x : y or the result of the division), but I have never seen a specification of "soundsoviel meters per revolution."

There's also a gear ratio or angle of displacement, which is what a lever essentially does.

about...

Imagine the wheel is worn out and has a radius of 0.9 meters.

A torque of 100 Nm is acting on the wheel, and the force that is accelerating you is now 111 N.

Now, with a new radius of 1 meter, and a torque of 100 Nm, the resulting force is 100 N. The rotational speeds also change in the same proportion, so it is indeed a translation .

Hi Doc,

Of course, the rolling radius is part of the overall translation (and therefore also affects the pulling force), as I mentioned earlier.

I came across the term "axle ratio" in connection with the wheel radius.
For me, the axle ratio is currently only defined as the ratio of the number of teeth between the pinion gear and the ring gear, regardless of the size of the driven tire.

Do you have any technical literature or similar resources that define the (dynamic) wheel radius as part of the axle ratio?