Needle bearing load calculation

[adrag]

I am trying to design a full compliment needle bearing for the wrist pin of a prototype two stroke engine. I'm using Timken's catalog located at:

http://timken.dirxion.com/Main.asp

On page C326, Timken gives bearing load rating equations for dynamic and static applications. I have put together a spreadsheet using these equations to determine dynamic load ratings but I am having trouble with the static load rating equation. It may be a misprint, but the equation has "cos" with nothing following it. According to the website, the equations come from ISO 76 and other standards. Could somebody double check the equation, or post the correct equation for me?

Also, since the needles will be seeing limited oscillation motion, should I calculate the load rating based on static or dynamic equations? The equations for dynamic load rating are giving me a rather low rating. I would need a very large wrist pin diameter just to carry the load and I haven't even applied a safety factor yet!

The cylinder bore is 68mm and I'm assuming a 2000 psi peak combustion pressure so I'm getting a wrist pin load of 11,260lbs. Thanks

Al

 

[MikeHalloran]

Wow, that loads S L O W.
Must be hosted on a pig of a server,
or badly coded.

Can you post an image of the page in question?


My limited experience suggests that you may need to accept a finite life in order to get the bearing size into the range you might expect.




Mike Halloran
Pembroke Pines, FL, USA

 

[BobM3]

I see "cos([α])" and "cos([α])=1". I don't see any "cos" with missing operands on that page.

 

[dinjin]

They have the modified equation below and since the
cos and i are equal to 1, you can use the modified equation.
With limited oscillation, you may experience a lot of fretting. How limied is this oscillation? Timken provides free consultation.

 

[adrag]

I posted a picture of the catalog. It is the static load rating equation. The rod will only swing though an angle of 35 degrees so which equation should I be using to calculate bearing load capacity?

Al

 

[MikeHalloran]

They sure used a crappy font for an equation. The minus symbol looks like a flyspeck.
And the first 'cos' lacks an argument.


It should say somewhere in the fine print that fretting is less of an issue when the tracks of individual needles overlap.

Mike Halloran
Pembroke Pines, FL, USA

 

[adrag]

Mike,

Are you referring to running two rows of needle bearings? Also, does anyone have the correct equation pls?

Al

 

[dinjin]

Adrag,

The equation is ok except that both should read
cos alpha. Since alpha is zero, cos alpha equals
1 in both cases.
Sorry that I did not read far enough in my last post.
35 degrees oscillation is probably enough to keep the roller greased or lubed at the high point.

 

[MikeHalloran]

No, I'm not referring to two rows of needles.

Let me phrase it another way:
If the oscillation is large enough so that each needle makes more than one complete revolution, fretting should not be an issue.

I.e., 35 degrees should be okay.
35 milliradians would be of concern.

Mike Halloran
Pembroke Pines, FL, USA