07 Oct 05
I ask you this...
Does a piston in an internal combustion engine ever stop as the engine runs?
Remember, it is directly connected to a crank moving in an endless circle!
If the answer is no; then why would we argue that anything doing a similar 180 change of direction does stop before doing so?
07 Oct 05
2 edits
it passes through a point in time where its velocity is zero. It never stops, in the sense that there is always an acceleration or jerk on it.
also, keep in mind that the crank does not move at the same speed at all times, it moves faster right after the explosion in the chamber.
07 Oct 05
Originally posted by AThousandYoungQuite correct. The connecting rod between piston and crankshaft is attached so that it allows the connecting rod to sway back and forth. It's *not* rigidly attached to the piston. It's more correct to say that the piston is attached to the connecting rod, which is then attached to the crankshaft, rather than saying that the pistion is directly attached to the crankshaft. This allows the piston to stop at two points in the movement of the crankshaft, just as you said.
Even though it's attached to a moving crank, that crank at two points in time moves perpendicular to the line of motion of the piston. At those two points in time the piston stops.
08 Oct 05
1 edit
Originally posted by logicalhippoThat may be true if the engine only has one cylinder.
also, keep in mind that the crank does not move at the same speed at all times, it moves faster right after the explosion in the chamber.
What about a any other combination, 4-6cylinders, V5-12cyliners, modern engines which can electronically control the number of operating cylinders.
The piston is only at its highest velocity at the center of its stroke. Piston velocity actually slows at the top and bottom of the stroke(becasue of how its conected), but not the crank RPM's.
Of course the crank does not move at the same speed at all times.
But the rise or fall of RPM's is not because of a single combustion pushing a single piston..
The rpm of the crank, or "engine speed" keeps all pistons moving in unison, or the engine would fail. All pistons are contionuosly pushing or being pulled by the crank, So I would imagine its RPM's rise and fall very smoothly.
Any mechanics like to add their 2cents?
08 Oct 05
2 edits
Originally posted by AThousandYoungDo you mean TDC and BDC of the piston stroke? Please explain?
Even though it's attached to a moving crank, that crank at two points in time moves perpendicular to the line of motion of the piston. At those two points in time the piston stops.
How can the forece of crank move perpendicular to the piston's line?
I think that may cause a failure.
There are only a two single points opposite of each other in the revolution, where the push or pull is not parallel to the piston's line of motion.
A line of motion or any line requires two points of reference, que no?
08 Oct 05
7 edits
Originally posted by Raw760Let me add to or rephrase this. Referring to an in-line engine for simplicity.
There are only a two [b]single points opposite of each other in the revolution, where the push or pull is not parallel to the piston's line of motion.
A line of motion or any line requires two points of reference, que no?[/b]
The horizontal(perpendicular) position of the connecting point of the connection rod to the crank shaft (as it turns) *in relation* to the piston's vertical line of motion, has no affect of stopping vertical travel of the piston.
Only the vertical(parallel) position of this point (as well as the length of the connection rod) affects the pistons length of vertical travel and velocity(wait, sorry velocity depends on relation the two and TDC or BDC).
TDC and BDC are the extents of this motion.
As the connecting point revolves with the crank, there is no travel where the rod's push or pull is perpendicular to the piston's line of motion.. Not even TDC or BDC, these are single points.
A line of motion or any line still requires two points of reference, right?
And velocity is a measure of distance over time.
So the all pistons would not cease to have a measurable velocity until the engine stopped.
Anyone?...Anyone?...Bueller?
08 Oct 05
3 edits
Originally posted by AThousandYoungThe point of connection is on a circular path. It will never run perpendicular or parallel to anything.
Even though it's attached to a moving crank, that crank at two points in time moves perpendicular to the line of motion of the piston. At those two points in time the piston stops.
BECAUSE ITS DIRECTION IS CONSTANTLY CHANGING.
So long as the engine runs the piston will be pushed and be pulled in relation to this point. So it will always have a measurable velocity.
Even from TDC and BDC.
CAN YOU READ THIS PRINCESS???