rigid body modes
rigid body modes
(OP)
I am looking at the Engine/transmission rigid modes of the transversly mounted engine of passenger vehicle from the point of view of locating there positions.
In the mode development exercise, what mode should be priortised to be the lowest mode ie bounce or pitch and what should be the criteria for the lowest frequency ie should it be based on avoiding human sensitive frequency range or suspension modes. What should be the optimum lowest rigid mode of p/t for idle vibration/suspension/human sensitivity inputs.
The other question on how do we calculate the hop and tramp modes.
In the mode development exercise, what mode should be priortised to be the lowest mode ie bounce or pitch and what should be the criteria for the lowest frequency ie should it be based on avoiding human sensitive frequency range or suspension modes. What should be the optimum lowest rigid mode of p/t for idle vibration/suspension/human sensitivity inputs.
The other question on how do we calculate the hop and tramp modes.





RE: rigid body modes
You need to develop your modal alignment strategy based on human response, in a whole vehicle model. This will govern the interactions between engine modes and suspension modes.
Hop and tramp modes are calculated (badly) much the same way - for a hand calculation just use the unsprung mass on the tyre vertical stiffness.
That won't agree particularly well with an experiment, because both of those numbers are flaky. Best bet is to fit your target tyre to a similar vehicle and measure it on the road.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: rigid body modes
When I said bounce and pitch, which of these two are most sensitive to suspension modes . Surely if the dominant bounce is most likely to get excited in transverse layout then bounce mode should be kept lowest in order or vise versa. This is what I am not sure.
RE: rigid body modes
You can't use 12 Hz, that is too close to wheelhop
I agree it would be nice to get the bounce mode out of the 4-8 Hz region - good luck
What configuration is your engine, what is the idle speed?
I strongly suggest that you benchmark your image car. Then think about their modal strategy, what areas would you like to improve?
Sorry to be so cagey, this subject is difficult, but it is a core competency for NVH
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: rigid body modes
RE: rigid body modes
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: rigid body modes
RE: rigid body modes
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: rigid body modes