1st & 2nd order

[par1]

1.what is the first order, second order in terms of NVH?

2.In auto industry, what do you mean by " any order peak at certain frequency at certain rpm?"

could you just explain me details.

3.does this statement is correct - If vehicle is at 1000 rpm at idele means it is at 17 HZ?

Please rectify it if necessary.

 

[GregLocock]

1) Order is the frequency divided by the rotating frequency of the system. To keep track of the different rotational speeds we often append a letter, so 3E means 3 times engine rotational speed, 2W means twice wheel speed.

2) If you have a waterfall plot look up the line for a given rpm. It is asking for the highest peak along that line

3) At 1000 rpm, first order s at 17 Hz, 2nd order is at 33 Hz, 3rd order is at 50 Hz, 2.5 order is at 2.5*1000/60 Hz etc



Cheers

Greg Locock

 

[par1]

Thanks for your reply,
Could you explain me the physical significance of 1st,2nd order frequency at 1000 rpm?

 

[GregLocock]

On an engine first order is typically out of balance of the crankshaft etc.

Second order is typically caused by the non sinusoidal motion of the pistons, due to the L/r ratio, which rarely cancel internally except with straight six or boxer engines.



Cheers

Greg Locock