Pauter & Carrillo rods

[Pisobiker]

Originally posted by 91_S2
Hi Marco,

You are way outta my league but I am curious. How does the length affect max acceleration? I am not getting this

ciao buddy,

Rich

Hi Rich,

don't want to become too theoretycal. Will try to tell in practical terms:

PISTON "up and down" travel vs. time is not only a simple sinusiod, but is the combination of it + the "up and down" contribution of CONROD BIG END through the conrod lenght.

Think of the "triangles" the CONROD describes each cranck ° (triangles given by "crank center to rod small end center" + "rod small end center to rod big end center" + the horizontal connection between the two).

When crank is at 0° (piston at TDC) conrod contribution to the piston hight is maximum (because rod is perfectly vertical).
Then, while crank angles go to 90° conrod contribution to piston hight decreses.

this means that the piston (while crank supposedly rotates at constant speed) needs to ACCELERATE more than the sinusoidal motion of the crankshaft to keep up with him.
This further acceleration will then be higher the shorter the conrod (because it's vertical lenght change will be greater).

Past the 90° conrod will then INCREASE it's contribution to piston hight thus SLOWING it down compared to the sinusoidal motion.

Same thing (but reversed) while going from BDC to TDC.

This shows that at TDC piston reaches it's maximum acceleration given by the sum of synusidal contribution of crank + "triangular" contribution of conrod which will be lower the longer the conrod.


Marco

[91_S2]

Professer!

OK. I understand how you are thinking. I will have a look at the geometries and it should become clear.

Thanks.

Rich

[Pisobiker]

My explaination is probably not so clear (sorry) so here is a quick drowing to help show what I meant:

[Pisobiker]

Above drawing shows that:


Given at TDC piston is reversing its dyrection (from upwards to downwards), so its velocity (thus acceleration)=zero;

A) Piston going to 90° of crankshaft not only has to accelerate for the sinusoidal vertical travel forced by crankshaft rotation, but also of the “shortening” vertical contribution of conrod, which is grater the shorter the conrod.

B) Same thing going from 270° to TDC where conrod “forces” piston to accelerate more than the sinusoidal travel to compensate for its increasing vertical contribution.

THEN Piston will have max acceleration at TDC when it reverses direction and where effects of conrod’s position will be maximum.

All this to say that in a high rev engine, where inertial forces (which are proportional to mass and accelerations of it) become very rilevant on conrod / pin / bearings stresses, using longer conrods help reducing max acceleration thus max stresses.


Hope this helps.


Marco

[Jeffer]

I'm def. in for a nice set of carillo or pauters. If it contributes to the price