Impact of engine firing torsional excitation on Powertrain Bending

[lhuang8]

when considering powertrain bending frequency target. Does engine fundamental firing order play a whole lot in the game?
I did some research on papers and saw lots of ujoint (driveline 2nd) and imbalance but didn't find much engine torsional vs. powertrain bending. If any, I saw consider the firing order on idle speed. Should engine torsional being considered when setting up powertrain bending target frequency?
Will converter damper help on this? typically converter damper helps on torsional vibration. didn't find much article talking about reducing torsional induced powertrain bending. any inputs?

Thanks!

 

[GregLocock]

What do you mean by firing order? On an I6 153624, or 3E?

On a traditional layout car increasing the bending stiffness of the powertrain does offer significant NVH benefits, the other option is a tuned mass damper on the back of the gearbox. Or both.

Stiffening the powertrain is an uphill battle, typically as a bodge you add a frame around the sump back to the bellhousing. An alternative is a structural sump. I don't remember the converter having much effect on all this but never say never.

Cheers

Greg Locock


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[lhuang8]

Hi Greg,
Thanks for replying. I was talking about 3rd order of inline 6 or 2nd order of inline 4 etc.
Does engine torsional needs to be considered for deciding powertrain bending frequency target?
Say the max engine speed is 3600 rpm for inline 6, should powertrain bending frequency target consider 3600/60*3=180 Hz? so when designing housing and stiffening powertrain higher than 180 Hz.
If so, since the purpose of input damper or coupling is to isolate/damp out the engine torsional vibration to the gear box and driveline, does it also provide the benefit of reducing powertrain bending response due to the engine torsional vibration.
Thanks again.

 

[GregLocock]

Ah, I see what's happening. You are referring to the forces into the crankshaft as torsional, that's not the usual terminology. It's not wrong just diferent.

So, should you set your bending frequency target above maximum firing frequency? Yes, and by a significant margin.

"If so, since the purpose of input damper or coupling is to isolate/damp out the engine torsional vibration to the gear box and driveline, does it also provide the benefit of reducing powertrain bending response due to the engine torsional vibration."

Are you referring to the isolators in the flex plate or clutch, or the harmonic damper in the front pulley?

Cheers

Greg Locock


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[lhuang8]

yes, I think the standard margin is sqrt(2) times whatever the frequency is?
I was referring to isolator between engine flywheel and transmission input. so like a torque converter clutch damper. or a coupling after engine flywheel.
Thanks,

 

[GregLocock]

They are usually tuned to suppress gear rattle.

Cheers

Greg Locock


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[lhuang8]

Thanks for replying Greg. A little off the topic here, are there any conferences that you recommended for NVH ? especially for automotive industry.

Thanks,

 

[GregLocock]

I used to get the proceedings from Internoise, that seemed pretty good. The SAE one would probably be OK. Sadly the tendency to obfuscate the actual measurements means that papers are less informative than they should be. I'm not even slightly current on NVH, I haven't done any for 16 years!

Cheers

Greg Locock


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