NVH orders

[trisha26]

Does anyone know what the 5.45th order is?

 

[GregLocock]

What sort of machine?

Does it track operating speed perfectly?

Is it measurable at more than one location?

What resolution do you have?

What slew rate are you using?

Can you post a Campbell's diagram (contour plot)?

What is the typical operating speed of the machine (in rpm)?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rob768]

a 5.45 order is generated by a puls with a frequency of 5.45 the running speed. The term "order" refers, to the referring speed (usually the running or driving speed of an installation or plant). Usually, this are even numbers, unless through a combination of gears you have shafts with differents speeds.
An example: a six cilinder 4-stroke engine (one combustion cylce per two revolutions) generates a 3rd order (and harmonics).

 

[Tmoose]

With ball and roller bearings the discreet ball/inner race/outer race "defect" frequencies are often wacky non integers of running speed.

 

[GregLocock]

Agreed. But I was hinting that maybe it was say 5.5th order, which is a perfectly feasible thing to find on a 6 cylinder internal combustion engine, for example.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rob768]

Tmoose, your right, i was thinking in the line of diesels and gearboxes.
In fact, 5.45th order could well be a bearing. I think SKF has a calculator for bearing frequencies on their site.

 

[Rob45]

In automotive NVH problems, you can find something oddball like 5.45-order vibration when the source is e.g. a belt-driven accessory turning some multiple of crankshaft speed.
For example, suppose you had a 5-blade fan driven at 1.09 x crank speed. It could produce a 5.45-order noise.