Crankshaft Dynamics

[jackboot]

Problem:
I have a crankshaft, connecting rod, wrist pin and a piston.

Based on a given mass of the piston, what would the acceleration (and therefore the force) be on the wrist pin holding the piston to the connecting rod.

I realize this will vary with the crank postion (for a given rpm). I would like to write an equation and put this into EXCEL.

Please help if you can as it has been 7 or more years since I took dynamics at the University of Hard Knocks.

jackboot

 

[ivymike]

Here are some kinematic equations of motion for the piston pin.

http://www.geocities.com/compact_enthusiast1/slider_eqns.html

This doesn't take into account any dynamic behavior, and it doesn't take into account the conrod whipping effects.

 

[bhart]

jack,
Just to make sure that you are getting what you want, the acceleration of the piston alone will not get the wrist pin force for you... it will get you the inertial component of the wrist pin force (caused by the piston's mass resisting acceleration). In other words, if you multiply the piston mass by its acceleration, you are getting the difference between the force from the wrist pin and the force from the cylinder pressure (F_wristpin -F_cylinder_pressure=piston_mass*piston_acceleration). In order to get the actual force on the wrist pin you will need cylinder pressure information (or you will need to assume something about the cylinder pressure).
I hope this is useful for you,
bhart

 

[jackboot]

Thank you both.

I found the information after doing a google search and plugged the info into a EXCEL spreadsheet. I appreciate the help.

jackboot