HelperC
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« on: February 17, 2017, 10:37:27 AM »
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I have been doing as much reading as I can on this map. Checked the FR as well and did find some literature on this map (KFMDS).
It has to do with engine drag torque.
Can anyone put this in simpler terms and explain why changes to this map is necessary, also what values this map is displaying would be some helpful information? My best guess is torque %
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« Last Edit: February 17, 2017, 10:39:28 AM by CHRISTIANDOY »
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nyet
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« Reply #1 on: February 17, 2017, 11:20:27 AM »
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I don't see that modifying that map is necessary.
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HelperC
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« Reply #2 on: February 17, 2017, 11:24:01 AM »
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I didn't think so but I noticed it was changed along with some other maps that I didn't think needed adjustment either. Maps were KFPU, KFKHFM and KFWDKPP which were changed in a vr6 file I got my hands on. Seems like they were trying to adjust fueling with KFKHFM and KFPU in another way than LAMFA. Don't really understand the reasoning behind it.
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« Last Edit: February 17, 2017, 11:27:25 AM by CHRISTIANDOY »
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prj
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« Reply #3 on: February 17, 2017, 02:01:26 PM »
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Well they clearly had no idea what they were doing, so I recommend sending that file straight to the recycle bin and stop wasting time.
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daniel2345
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« Reply #4 on: February 18, 2017, 12:07:59 AM »
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Its the torque, the engine 'consumes' while moving (energy transfer from kinetic to heat Energy) without beeing propelled by combustion. It reflects the inner resistance.
And said already absolutely right - there is no need to change that unless you do fundamental changes to the crank drive. Like putting compressor and belt on, reducing crank weight a lot, and so on.
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prj
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« Reply #5 on: February 18, 2017, 01:11:16 PM »
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Its the torque, the engine 'consumes' while moving (energy transfer from kinetic to heat Energy) without beeing propelled by combustion. It reflects the inner resistance.
And said already absolutely right - there is no need to change that unless you do fundamental changes to the crank drive. Like putting compressor and belt on, reducing crank weight a lot, and so on.
Crank weight has no effect on friction. Nor a lighter flywheel. This map does not take reciprocating mass into account. |
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HelperC
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« Reply #6 on: February 18, 2017, 08:19:37 PM »
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Well they clearly had no idea what they were doing, so I recommend sending that file straight to the recycle bin and stop wasting time.
lol! great response. thanks prj  |
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HelperC
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« Reply #7 on: February 18, 2017, 08:20:28 PM »
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Its the torque, the engine 'consumes' while moving (energy transfer from kinetic to heat Energy) without beeing propelled by combustion. It reflects the inner resistance.
And said already absolutely right - there is no need to change that unless you do fundamental changes to the crank drive. Like putting compressor and belt on, reducing crank weight a lot, and so on.
thank you very much for your response. I was thinking that these changes were a bit odd. |
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daniel2345
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« Reply #8 on: February 20, 2017, 12:58:02 AM »
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Crank weight has no effect on friction. Nor a lighter flywheel.
This map does not take reciprocating mass into account.
It clearly have. Think about to rotating moment (inertia), which presses the piston rings against the combustion chamber wall. The more weight, the greater the moment - bigger friction. It might be a little influence compared to the whole system, but it is there. |
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prj
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« Reply #9 on: February 20, 2017, 07:14:05 AM »
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It clearly have. Think about to rotating moment (inertia), which presses the piston rings against the combustion chamber wall. The more weight, the greater the moment - bigger friction.
It might be a little influence compared to the whole system, but it is there. You are getting caught in a physics trap. 1) This map is calculated steady-state. 2) The rotating assembly is balanced to zero. Does not matter how much mass you have hanging off of the crank. 3) Crank lies on an oil journal bearing. If it were not balanced and were to move you would spin a bearing instantly. |
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« Last Edit: February 20, 2017, 07:15:37 AM by prj »
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daniel2345
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« Reply #10 on: February 20, 2017, 11:58:18 AM »
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Yes, your points make sense.
But a steady and balanced crankshaft does not say, that the piston cant move during dynamic conditions?
The Piston moves in the bore, regardless of the not axialy moving and balanced crankshaft assembly, while the force of the rotating weight moves the piston upwards and sideways.
Thatswhy the bore gets oval after long engine usage.
So there is an influence in my opinion.
But as always, there might be more than one opinion, no problem.
For the map, you have two possibilitys when changing crank weight drastically:
1) leave it untouched
2) change it
I have a lot better experience with number 2 when calibrating such race engines.
But again, for a drilled crank pulley or lightweight flywheel in Street car usually no change is needed.
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prj
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« Reply #11 on: February 21, 2017, 03:31:05 AM »
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Yes, your points make sense.
But a steady and balanced crankshaft does not say, that the piston cant move during dynamic conditions?
The Piston moves in the bore, regardless of the not axialy moving and balanced crankshaft assembly, while the force of the rotating weight moves the piston upwards and sideways. Crank weight is mostly irrelevant for friction. Weight is important in dynamic acceleration and deceleration. KFMDS is a steady state map. Basic physics. End of story. Heavier crank to ECU is like driving slightly more uphill. Lighter crank is like driving slightly less uphill. Meaning in driving conditions and ECU cal this is nearly completely irrelevant. Piston side-to-side movement and forces are mostly based on bore/stroke, their ratio and RPM. All other factors are small. Weight of the piston/rod affects bearing and pin wear. As for heavier or lighter crank - it's 99% the same like having a lighter or heavier flywheel on it. KFMDS should never need changing even if you change the rotating mass weight significantly. What needs changing is the idle PID, the rev limiter control, fuel cutoff targets and so on. If you modified KFMDS you did it wrong. Anpassung von KFMDS: KFMDS stell das Schelppmoment des Motors dar und wird im ungefeuerten Betrieb des Motors auf einem
Schlepp-Prüfstand ermittelt. Der Motor muß dabei warm sein (80C mindestens als Öltemperatur).
Für verschiedene Drehzahl und Lastpunkte wird das Drehmoment ermittelt, das für das Schleppen des
unbefeuerten Motor notwendig ist. Dieses Kennfeld wird bei der Grundparametreierung des Motors
am Motorenfrüfstand bereits ermittelt. |
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« Last Edit: February 21, 2017, 03:42:03 AM by prj »
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daniel2345
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« Reply #12 on: February 21, 2017, 06:15:44 AM »
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I was often at the desk of the 'motorprüfstand' (engine dyno) when such maps are filled with data.
Steady state is irrelevant here, its just an info on how the data can be aquired. You target a given load / rpm point, torque is measured. It changes with crank weight, thats just what i observed in some years with all that. During run time values are interpolated between stady measured points. So it goes into every calculation in dynamic conditions also.
I can give you a small example of the change. An Engine on such a dyno. Old Flywheel: torque of around 12, fits current application roughly. New flywheel, same point: 13.5. It is a difference of 12.5% - not irrelevant for me. In fact small.
So saying changing the map is wrong is some kind 'small' minded in my opinion.
But ok - people can think what they want. Two opinions on the table. Topic is done for me now. Everything more said is turning around the same thing over and over again.
Best regards
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prj
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« Reply #13 on: February 21, 2017, 10:06:02 AM »
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How about putting a single scientific fact on the table, rather than "I saw, I was". If flywheel and crank weight affected friction torque, all OEM's would run superlight flywheels and cranks to reduce fuel consumption. Fact of the matter is, they don't and physics agree with me. This map is steady state friction torque, nothing more, nothing less. The mass of the crank is irrelevant. If you measured differences in steady state with mass of the crank (or a different flywheel) that means there was something else different - viscosity of the oil, bearing clearance, ring gap and so on. Simply by increasing weight of a rotating component balanced to zero absolutely nothing changes in friction torque. Once you are in steady state it still takes the same amount of force to keep it spinning. You could argue that gravity has an effect on the friction coefficient of the oil film, but this is negligible. Steady state is irrelevant here, its just an info on how the data can be aquired. You target a given load / rpm point, torque is measured. It changes with crank weight, thats just what i observed in some years with all that. Actually it is extremely relevant. If it is not settled in steady state then the results are useless, as the results simply are the product of how quickly you accelerate or decelerate the crankshaft. |
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« Last Edit: February 21, 2017, 10:18:29 AM by prj »
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nyet
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« Reply #14 on: February 21, 2017, 11:56:15 AM »
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Steady state is irrelevant here
Basic physics: increasing/decreasing angular velocity - mass steady state - friction So saying changing the map is wrong is some kind 'small' minded in my opinion.
Changing the map is not needed. |
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« Last Edit: February 21, 2017, 11:58:04 AM by nyet »
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