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OVI46 (Automotive) (OP)
23 Apr 03 13:34
Could anybody please help?

I am using the Bosh Automotive Hand book to calculate the necessary mass for a 4 cylinder engine.
I calculated the Oscillating mass, using the sum of the piston mass and 1/3of the Conecting rod mass.
I calculated the Rotating mass using the crank mass plus 2/3 of the connecting rod mass,
then as the book says I calculate the 2nd order free forces of inertia as being
4*mo*r*w^2*lambda*cos(2alpha)

What now?
I need 2 balance shafts rotating opposite directions at double the crank speed.
But what is the excentric mass ?
radomir (Aeronautics)
24 Apr 03 19:42
Have a look at this:

http://autozine.kyul.net/technical_school/engine/smooth2.htm

It might be of some help
radomir (Aeronautics)
27 Apr 03 17:39
The site I gave you is rather basic but from those schematic views it is obvious how excentric masses should be determined.

Their centrifugal forces should counterbalance the maximum 2nd order free forces (in Top and Bottom DCs) you have already calculated.

Centrifugal force of rotating excentric mass is:  Fc = m*r*w^2

where:
    m  is amount of excentric mass (the both masses in this case)
    r  is distance between axis of rotation (balance shaft axis) and CG of excentric mass
    w  is angular speed of balance shafts

In your case variables (unknown) are m and r so you may play with those quantities (having in mind limiting factors, space for sure) to equalize the Fc with the max 2nd order free  force.
 

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