higher engine orders 9-15-21

[rmmechatronics]

Hi,
We did a couple of vibration tests on a bus engine compartment (rear drive+north-south engine) to find the root cause of high level of vibrations perceived inside the bus. On the engine/transmission active and passive sides we see normal engine orders dominating (3-6-9). However, the problem inside the vehicle seem to be coming from 9-15-21 (multiples of 3) orders and on the vehicle they seem to be coherent at rear differential connection (shaft to rear axle attachment point). The number of gear teeths at pinion are totally different. How come these higher orders excite(d) the structure? What component they can be related to? This is a problem I have not experienced before.
thanks for the ideas in advance

 

[SomptingGuy]

Do you have a colormap (Campbell diagram, Waterfall, etc) of vibration across the speed range?

- Steve

 

[MikeyP]

Are the dominant orders exact integer engine orders? If yes, then they must be related to something that is directly driven by the engine (the rear differential tooth passing order would not be an integer engine order unless you were very unlucky). Direct driven components would be gears on transmission input shaft or gears/belts/chains for engine timing or running auxiliaries (alternator, air-con, pumps)

M

--
Dr Michael F Platten

 

[rmmechatronics]

ok.. they are not exact integers that is correct. However, the active side accelerations on the engine side itself is not very high for that orders. Only dominant on rear axle-shaft connection. We are now looking into bearings. If it is not the issue I can share the data.
Thanks for the answers.

 

[MikeyP]

Are the dominant orders (relative to engine speed) the same in every speed gear? If yes, then it cannot be a bearing or a gear associated with the driveline "south" of the gearbox.

M

--
Dr Michael F Platten

 

[GregLocock]

Do you see the same orders popping up in neutral?

I assume this is an I6 engine?

A campbell's plot is the most useful diagnostic as Steve says.

Not too sure how much I trust coherence with order type signals, in theory all of them should be 100% coherent with all paths.




Cheers

Greg Locock

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

 

[rmmechatronics]

Attached you can find the acceleration data from differential block .

 

[rmmechatronics]

sorry, upload option not working properly, I will try later

 

[rmmechatronics]

Here is the acceleration response from the differential connection point

 

[rmmechatronics]

This orders are calculated with regard to shaft revolution.

 

[rmmechatronics]

we have a bearing with the properties given:
dt (roller distance to roll center)
dw (roller nominal diameter)
z number of rollers
alfa angle of contact

how can we calculate dominating orders for any bearing with the properties given above. I believe we have found a link between the orders shown in the figure and the first bearing

thanks for the help

 

[rmmechatronics]

The BSP - ball spin frequency corresponds to 6.7 the first order shown the figure. The rest are harmonics of order 2.2. The only problem left is to find where this 2.2 comes from? All the orders seen on the figure is multiples of 2.2..