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Re: Conrod force/acceleration
From: Sargent Schutt <email@example.com>
>Come again? Is there not a point in time where acceleration and velocity
>are zero? I certainly think so. When there is no velocity, there is no
>acceleration. Acceleration can be zero while velocity is constant, but if
>velocity = 0, acceleration = 0; acceleration is nothing more than the rate
>of change in velocity. At TDC velocity is zero, and therefore acceleration
>is zero, too. Yet the engine is most definitely running.
At TDC, acceleration being a function of cosine of the crank angle, the
acceleration of the piston is at its highest level. Piston velocity is a
function of the sine of the crank angle, hence the highest piston speeds are
at 90 and 270 degrees (I think we can even visualize that one...). Remeber,
basic integration rules to achieve d^2S/d^2T from dS/dT, S being the
displacement of the piston from the crankshaft centre. If you want to check
the derivation of the formulae I gave as an attachment a a day or so ago,
get the two volumes of "The Internal Combustion Engine in Theory and
Practice" by Charles Fayette Taylor, it is (or was at least ten years ago)
the bible of any budding engine designer...
>Are you suggesting a perfectly parabolic acceleration curve with no zero
>point? (1) There will be a time when acceleration is zero; (2) You have
>massive acceleration/deceleration approaching/leaving TDC, as a function of
>rapid reversal of travel. You also have zero velocity, and therefore zero
>acceleration, at one micor-instant in time (at TDC).
Zero velocity happens at TDC/BDC, where the acceleration values are at their
peak numerical (positive/negative) values. If you've designed a crank that
will give you zero velocity AND zero acceleration at any one point, I'd look
up the same physician Phil was referring to a day or so ago...
Jouko "assume rigid bodies" Haapanen
Audi dealer who has now dusted all his ME books out of the closet...