Help me! piston travel question..

Does anyone know the equation for piston travel if the stroke and rod length are known?

Random I know but im applying it to homework problem. I figured GRM folk would know faster than searching all over google...

In reply to cxhb:

http://john.rushworth.com/Pics/Piston/

Uhhhh... unless I am missing something the piston travel should be equal to stoke?

Are you looking for travel or position? The center line of the crank to the journal should be 1/2 the stroke, as stoke is basically the diameter of the circle traced by the big end of the piston.

So you could find the location of the big end of the position by (1/2) x stroke x the cosine of the angle of rotation from top dead center

And from there the height of the piston would be the square root of the length of the rod squared - (1/2 x stroke x sine of angle of rotation ) ^2

So the height of the piston wrist pin relative the crank centerline would be the location of the big end relative the crank + the heigh of the piston relative the big end.

Should be like S = stroke L = rod length A = angle from top dead center

(1/2)Scos(A) + [R^2 - ((1/2)Ssin(A))^2] ^ (1/2) = height of wrist pin relative crank assuming the cylinder is directly above the crank and wrist pin offset is 0 or negligible.

I think....

RedS13Coupe wrote: Uhhhh... unless I am missing something the piston travel should be equal to stoke?

Unless something has gone horribly wrong

What is the problem ? Stroke is fixed by the crankshaft. Or are we thinking piston speed ?

What's the homework problem? Maybe that's easier.

Dan

RedS13Coupe wrote: Uhhhh... unless I am missing something the piston travel should be equal to stoke?

Or stroke x 2; as in it travels up and down once per RPM...?

Hey, this is a trick question!

I believe RedS13Coupe has what im looking for. That or I am making this more difficult than it needs to be... which I tend to do.

The question doesnt even actually have to do with the internal combustion engine. But rather can be applied directly to the same equation... and btw pin position is irrelevent in this question. Or if you must know, it is dead center on the piston.

The question asks How far does the "piston" travel if part D (the center point of the big end of the connecting rod) travels 360 degrees about pin F. Essentially, part D to F is the stroke, and a "rod" connects part D to F with the "piston". They dont actually call it a piston or a rod or anything..

Sorry if that made no sense.. hard to explain in words lol

Its just that when i first saw the problem I immediately saw what looked to be a crank, a connecting rod, and a piston.

I think we still need more info. This could easily be figured if you knew how far part D was from pin F or if you knew the circumference of part D's path.

cxhb wrote: I believe RedS13Coupe has what im looking for. That or I am making this more difficult than it needs to be... which I tend to do. The question doesnt even actually have to do with the internal combustion engine. But rather can be applied directly to the same equation... and btw pin position is irrelevent in this question. Or if you must know, it is dead center on the piston. The question asks How far does the "piston" travel if part D (the center point of the big end of the connecting rod) travels 360 degrees about pin F. Essentially, part D to F is the stroke, and a "rod" connects part D to F with the "piston". They dont actually call it a piston or a rod or anything..

oh, lol. Still kinda depends on the class. If they mean travel like "how far does it move" then in one rotation the piston moves twice the diameter of the crank. At its lowest point it is at the bottom of the circle + the height of the connecting rod, at its highest it is one diameter above that last point. So it travels up one diameter, then back down one diameter, for 2 diameters worth of travel.

If its a vector question, and the specifically mention "displacement" the answer is 0. But unless they specifically mention displacement and vectors this is probably not the case."travel" isn't really the type of word they would use when talking about displacement since displacement is just finish point - starting point and travel would normally be assumed to be the whole trip in between.

In reply to RedS13Coupe:

lol See?! I figured I may be just completely over-complicating it! my first guess was 2*stroke. My mind just kind of wandered off and started thinking about how different rod lengths have an affect on things. The TRAVEL with a long or a short connecting rod will be the same right? But the piston SPEED will be different... Is this thinking correct?

EDIT. My bad, double post.

Also, the question is not a vector problem. Just simply "how far does the thing travel?"