I am confused with the reduced mass of the cran wwb of a crankshaft!!!

[lanka6000]

Hi,
Do anybody know the Explanation of reduced mass of the crankweb of the crank shaft which goes with the conservation of centrifugal force in a crankshft.
That means the mass of the crankshaft is mkw=mass of the journal(mz) + reduced mass of the crankweb (mwred= (mw)*(rws/r))
My question is can anybody try to explain to me why the mass of the crank web is reduced by multiplying the mass with the ration of center of gravity of the crankweb (rws) to crank radius (r).
From this expression what i understand is that the mass of the crank web has to be reduced to shere the same center of gravity with crank journal.
But i have calculated the center of gravity of the crank web and try to calculate the reduced mass,BUT THE MASS OF THE REDUCED CRANK WEB (mwred) IS HIGHER THAN THE CALCULATED MASS OF THE CRANK WEB (mw).I am confused with the increase in the mass of the reduced crank web (mwred)OR Can anyone give me the real meaning of reducing the mass of the crank web in calculaating the mass of the crank shaft?

 

[GregLocock]

I'm sorry your question contains so many errors that it is very hard to answer. Can you get your translation checked by someone who is competent in technical matters, and both languages?

I think you are confusing rotational inertia and mass.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[lanka6000]

Hellow Greglocock,
Thank you for replying to my question.I am sorry that my question is not well presented?
i try again.Here it goes:
I want to calculate the rotational mass force which is expressed by the following equation:
Frot= mrot*r*w^2

where :
mrot=rotational mass of the crank shaft throw
which is mrot=mplrot + mkw
mplrot= rotating portion of the connecting rod = 2/3*mpl
mkw = mass of the crankshaft = mz + mw*(rws/r)
mz = mass of the crank journal
mw*(rws/r)=reduced mass of the crank web because mw*rws=mwred*r (i.e the centrifugal mass force must remain the same before and after the reduction)
rws is the centroid of the crank web from the rotating axes
r is the centroid of the crank journal from the rotating axes.(crank radius)
My question is then,Since i want to calculate the rotational mass mrot,i need to calculate the parameters mention above.
I have calculated the masses,but i want to get more explanation of this expression:the centrifugal mass force must remain the same before and after the reduction).(1)why the mass of the crank web should be reduced with respect to the above euation that is mw*rws=mwred*r ? (2)Must the redused mass of the crank web be lower than the calculated mass of the crank web?

I hope the expplanation of the question sound ok.if not i will try again.
CU

 

[GregLocock]

Frot= mrot*r*w^2


OK, that is the centrifugal force, where r is the eccentricity of the mass mrot

Well, I still don't really see what you are getting at. You haven't defined all your terms.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Fabrico]

Are you talking about anything similar to what has been done to this crank?