ASZ mit 255PS kann das sein? | Posts 16+

Jan6K wrote:

While in the 4th gear, the air resistance, which is not so easy to calculate, becomes significantly more relevant (around 150 km/h at 4000 RPM in the 4th gear).

Hi Jan,

As long as there are no strong gusts of wind, the KPower device is even suitable for measurements at maximum speed. The braking effect of air resistance is taken into account in the deceleration after disengagement, meaning that the corresponding power is "credited" back to the motor in the calculation.

This principle also works with virtually any wind speed and direction, as long as...
a) the motor reaches the final speed required for the measurement.
b) the wind is blowing steadily. Gusts, of course, will introduce curves into the diagram .

Hello!

Which specific test bench is available and which set of rollers is being used?

Can it even withstand that much tensile force?
"6 kN is already too much for typical roller sets or older testing rigs..."

Macht die Messung mal im 5. Sure, here's the translation:

"Hey!" or "What's up?"

BYE
TDI mechanics.

Hello,

Jan6K wrote:

...especially since I have no idea what a "direct" course is supposed to be. Perhaps that comes from the time when 4 courses were considered the maximum?

This design dates back to the era of longitudinally mounted engines with a driveshaft. These transmissions had an input and output shaft aligned in the same plane. Different gear ratios were achieved through gears, where one half was rigidly shrunk onto a parallel layshaft, while the other half ran on needle bearings on the input and output shafts. One pair of gears could be eliminated by connecting the input and output shafts directly with a coupling, resulting in a 1:1 gear ratio. Due to the reduced friction, wear and efficiency were optimal in this configuration. Typically, the 4th (highest) gear was used (which was the case in my BMW 02).
The vocational school teacher apparently hasn't realized that there is no direct gear (like with only two shafts) in transversely mounted front engines from Volkswagen. Some outdated beliefs persist even among experts in the automotive field.
In a dynamometer test, while a higher efficiency should theoretically result in greater power at the wheel, the lower parasitic losses would mean that the overall engine power (which is the sum of wheel power and parasitic losses) would remain the same. I completely agree with you on that point. And whether it's even possible to measure such a small difference is another question. If it only amounts to half a percent, it's certainly a significant amount, and that likely falls within the range of measurement accuracy.



Best regards, Uli.

Herr Antje wrote:

Can someone explain the consideration of "braking effect" in more detail to me?

Probably the software author himself... huhu, Rainer .

Hello,

Simply put: Total motor power equals the vehicle's acceleration power plus the vehicle's braking power (air resistance, rolling resistance, etc.).

Attention: A dragging engine is NOT part of the braking system, so shift to a lower gear or put it in neutral when coasting!

Best regards, Rainer.

Hello Rainer,

Thank you for the response. Unfortunately, I suspect that you misunderstood my question, or that I misunderstood your answer.

I understand that the vehicle's braking performance is taken into account (and how). Let me try to explain it with an example. The values are irrelevant and unrealistic, and the calculation behind it (torque) is not considered.

For example, at high speeds (160 km/h, with the 4th gear engaged, the engine speed would be 4500 rpm), air resistance generates approximately 10 kW of "braking power." At lower speeds, air resistance almost disappears, reducing the "braking power" to only 5 kW (at 70 km/h, with the 4th gear engaged, the engine speed would be 2000 rpm).

If the acceleration performance is 70 kW at 2000 rpm and 100 kW at 4500 rpm, then the following kPower values would be possible:
a) The braking power is determined as a function of speed: at 2000 rpm, the power is 70 + 5 = 75 kW; at 4500 rpm, the power is 100 + 10 = 110 kW.
b) The braking power is averaged between the beginning (160 km/h) and end (70 km/h). In this example, it's 7.5 kW (actually even higher). KPower outputs the following values: 2000 rpm = 70 + 7.5 = 77.5 kW; 4500 rpm = 100 + 7.5 = 107.5 kW.

a) would of course be correct, but probably much more difficult to program. Ulf is right in his statement.
b) Not entirely correct, but the actual difference might be within the tolerance range, as I don't know the air resistance values at different speeds. In theory, Jan6K is right: the lower the speed, the more accurate it would be. However, a question then arises whether you can log data quickly enough.

Therefore, my question is: Is the air resistance considered as a function of speed, or is it averaged out?

Regards,
Tom.

Herr Antje wrote:

Therefore, my question is: Is the air resistance considered as a function of speed, or is it averaged?

Hi Tom,

Let me preface this by saying...

The total braking force from air and rolling resistance (and potentially incline/decline) increases with speed. Therefore, the deceleration is strongest in the initial moment after disengaging the clutch (e.g., 2 m/sec²) and gradually weakens during the coasting process (e.g., 0.6 m/sec² at the end). It doesn't fundamentally matter which portion of this braking force comes from air resistance or rolling resistance.

Multiplying the roll-out delay 'a' by the vehicle mass 'm' and the currently logged velocity 'v' yields the braking power curve (P_brake = m * a * v) for the recorded driving data.
It is added to the logged acceleration power (Pzug = m * a * v) for each speed, and thus the total power curve is obtained, which is then mapped onto the motor speed in the diagram based on the logged relationship between km/h and rpm .

It is calculated according to a) .

@ulf & Rainer
Great! Thanks for the answer.