Frequency-domain analysis of valvetrain dynamics
Frequency-domain analysis of valvetrain dynamics
(OP)
Hello
Anyone ever muck about with frequency-domain analysis of a valvetrain? I'm currently working on some analytical tools to help me with said analyses, and I'm wondering if there might be some pointers that someone could throw out for me, as I'm a bit green in this area. Most of my experience w/valvetrains is via time-domain simulation.
If you've looked at valvetrain vibration in the frequency domain, I'd be interested to know more about what you've done, and what parameters, etc., you typically look at. A brief description of your methods would be most appreciated.
Thanks
Isaac
Anyone ever muck about with frequency-domain analysis of a valvetrain? I'm currently working on some analytical tools to help me with said analyses, and I'm wondering if there might be some pointers that someone could throw out for me, as I'm a bit green in this area. Most of my experience w/valvetrains is via time-domain simulation.
If you've looked at valvetrain vibration in the frequency domain, I'd be interested to know more about what you've done, and what parameters, etc., you typically look at. A brief description of your methods would be most appreciated.
Thanks
Isaac





RE: Frequency-domain analysis of valvetrain dynamics
Isaac, I tried my hand at doing a vibration analysis of a crankshaft using EE tools some time ago. I was a bit clumsy at it, but got what I wanted. SPICE is one tool that is available as a freebee in lite versions. Various functions are there - Fourier to do freq/displacement conversions, etc.
I think SAE has some nice dedicated software tools but they don't seem to know the word free. $$$$
RE: Frequency-domain analysis of valvetrain dynamics
It seems to me that for some valvetrain configurations, an improvement in vibratory behavior might be achieved by redistributing inertia & stiffnesses (when constraints prevent broad changes to hardware). A perfect example - is it better to have a heavy, stiff pushrod, or a light, flexible one? The valve spring can only control so much mass, but too much flexibility is bad too (and you don't want to buckle the thing, etc). I was hoping to be able to find answers to questions like "what is the right mass&stiffness for a pushrod in this system" by looking at the mode shapes & natural frequencies. If anyone has some general pointers in that direction, I'd appreciate them.
Also, it seems to me that the appropriate way to represent the system excitation is via a fourier series expansion of the cam acceleration profile (since excitation force will be roughly proportional to the acceleration). I'd assumed that the right thing to do was "expand" the whole cycle (including the base circle), but someone suggested that I might want to look only at the portion between the start of the opening ramp and the end of the closing ramp. If someone had previously performed the analysis, perhaps he wouldn't mind sharing how he represented the excitation?