Martin Loew

Hello gentlemen,
I was referred here by a good friend of mine. It's my understanding that one of the members here use to be a member at one of our engineering discussion boards last year. I was told that he's a moderator here and that he might be able to help me with a little valve spring modeling project I'm working on right now at school. I'm guessing this person was "Injuneer"?
I need any help anyone might could offer on developing a simple modal approach for linear valve springs.
This is a new area of study for me so any insight would be most helpful. I am in the process of acquiring a few papers from the SAE but I would like to get a good head start by starting my paper this weekend. Thanks.

Martin Loew
Engineering student Rice University

Injuneer

It's not me.....

Probably meant Chuck Riddeck.... aka "Mr. Horsepower". Hopefully he will see this.

Mindgame

Buy Comp Pacalloy, PSI or Isky...... just kidding.
You'll need someone a heck of a lot smarter than I on this one.

Chuck does come to mind though.

-Mindgame

Mr. Horsepower

Hello sir,

I don't know if the member you mention is me or not but I use to frequent quite a few engineering forums before I had so many problems with this infernal piece of equipment in front of my nose. Actually, I think the problem was rooted in the ISP more than my computer.

You have a question and I'll do the best I can to answer it. I don't know of anywhere I can refer you for information on the subject but I do have a few papers that I could point you to. I will however have to find them and that's not going to be an easy task. Believe it or not... I don't know the numbers off the top of my head either.
So, I'll give you a basis and get into the subject of linear valvesprings. It's too broad a subject for one sitting so I'll just hit on the basics and you can lead me where you want to go from there. This is hardly going to give you much to work with in your modeling attempts as you will need a detailed non-linear model to predict effects of progressive springs, including coil clash. I don't know what you've read so I'll take a bit of latitude in this subject starting with the very basics. This will undoubtedly lose a few people and doesn't promise to be a "fun" read...

Anyways, as you know the spring is by no means a rigid component as it is subject to internal vibrations when excited by the valvetrain. Saying that a spring shows "wave propogation of disturbances" is a pretty accurate. This leads us to the approach that each individual infinitely small spring element is governed by the "wave equation"... a second order partial differential equation. The eigenmodes being the characteristic form of motion and forming an infinite series with increasing frequency. The 1st mode with the lowest frequency (~500Hz) is an in-phase motion of all the spring particles with the maximum amplitude in the middle of the spring. The ends of the spring are fixed, therfore the amplitude is zero at both ends. In the second mode, having about twice the frequency, the two halves of the spring move in antiphase, and so on for the higher modes. The vibrations are governed by this equation:

(a^2Y(xt))/at^2) = c^2((a^2Y(xt))/ax^2)

Y = particle displacement

c = sq rt (L^2k/m) defines the speed of wave propogation in a spring, much the same as sound traveling through air.. with "L" being the spring's length, "k" being it's stiffness and "m" of course representing the spring's active mass.
We now arrive at two boundary conditions, the spring displacement being equal to the valve displacement at the retainer end and zero at the other end or:

Y(0,t) = h(t) and Y(L,t)=0

The total force exerted on the valve by the spring including the preload due to precompression in the "installed" position Fc=kS is then given in this equation:

F = Fc+Lk(cY/cx)

Then the static case where we get a relation for the particle displacement...

Y(x) = ((L-x)/L)h

For the time dependent excitation, we take another approach to write the total solution as a sum of the static contribution plus a dynamic deviation u(x,t)

And I'll wrap it up there getting into more of this tomorrow evening. This should get you going in the right direction... we'll get into the equation governing the dynamic deviation my next trip through. Don't want to go too far at this point due to the fact that I know you're going to have some questions at this point. Hopefully not too many but I know how I was when first getting into this subject.

Hope that helps you out a bit Martin. We definitely need a better way of writing equations on this website... something quick and easy.

Fred, please send my regards to Unstable Bob... haven't seen him around for some time and his spunk is really missed around here.

Take care,
Chuck

Brady

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j/k~

Mindgame

Chuck,
You never cease to amaze me.

Martin,
I could write you a VB program if you need it. Just need to see the formulas and spend some time writing the program. A good interface would make something like this much easier to work on I'd think. Use to do afair bit of this for a former employer so no biggie.

-Mindgame

nosfed

.... and that is why I decided engineering wasn't for me. Chuck

Martin Loew

Chuck,
Thanks for all the information! I meant to get back to this last night but our school computers wouldn't allow me access. This gave me a good head start though and I'll need some time to digest the information.
One thing I am curious about if you don't mind is the calculation of spring properties, namely the method for calculating total mass of the spring? That would really give me enough information to work through the better part of this. Sorry, I don't mean to have you do any homework for me but this information seems to be hard to find. Just need a little direction. Thanx!

Martin