5 ms·

I have a question: exactly what causes the piston to come back after the intake/power stroke? Let me write what I guess I have understood - 1. The intake strok

by tmptmp 11y ago

I have a question: exactly what causes the piston to come back after the intake/power stroke? Let me write what I guess I have understood - 1. The intake stroke piston movement may be considered to be caused by gravity and/or atmospheric pressure 2. The power stroke piston movement may be considered to be caused by gravity and/or atmospheric pressure and/or the expansion due to explosion all taken together Correct me if I am wrong. But what baffles me is this: what causes the piston movement during the compression stroke and exhaust stroke? Any expert here to enlighten me on this? edit: typo

6x9equals42 11y ago
Momentum from the flywheel/flexplate keeps it spinning
- acranox 11y ago
  The flexplate has very little mass to provide momentum. The fact that the flexplate is bolted to the (heavier) torque converter is what's really going to provide the momentum.
imakesnowflakes 11y ago
Not an expert, but I always assumed that it was caused by the rotational inertia of the Flywheel[1]. [1] https://en.wikipedia.org/wiki/Flywheel https://en.wikipedia.org/wiki/Flywheel
jayflux 11y ago
There's usually more than 1 piston on the crankshaft. So while one is coming up, the power for that is coming from another going down
delinka 11y ago
If you can find a pull-start gas engine lawn mower, you can learn lots from it. These things generally have a single piston. The pull string that you use to start it gets it moving in the right direction, and once it starts running on its own, it's momentum that brings it back around for another go. Also keep in mind that this single piston engine is two-stroke and not four as in the article. Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cycling back around. The more pistons you have, the more there are firing between each revolution of a given piston (and thus overcoming resistance and supplementing that momentum) and thus the more power available to drive the vehicle.
- shocks 11y ago
  Yup, two stroke model engines from cars/planes are also great for learning. Pull start, cheap, easy to disassemble, and you'll need to learn about tuning too - which is another whole load of fun!
- dbloom 11y ago
  This is a great explanation. I'd add one small clarification: > Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cycling back around The firing of other pistons helps, but really, momentum alone is sufficient. There are tons of single-cylinder, 4 stroke motorcycle, scooter, and off-highway engines out there.
mcguire 11y ago
None of the intake, compression, power, or exhaust strokes have anything to do with gravity or atmospheric pressure. Initially, a secondary motor causes the rotating components to rotate, which causes the pistons to move in the cylinder. Later, either inertia or the power stroke from another cylinder maintains the rotation. The piston movement itself is caused by the piston arm, which is offset from the axis of the crank shaft.
mikestew 11y ago
The kinetic energy of the flywheel keeps things moving when burning gases aren't moving the pistons. The evidence of this is demonstrated on the two flavors of the motorcycle I own. One version (BMW R1200GS Adventure) has a heavier flywheel than the other (non-Adventure). I've ridden both. With the light flywheel it's easier to kill it pulling from a dead stop because there isn't as much mass to overcome the lack of subtlety in my clutch hand. On the Adventure version that I own, sloppy clutch work that often comes with trying to get a 600 lb. "dirt bike" out of a mud hole is ignored by the more massive flywheel. Even when the cylinders are barely able to fire because I'm one sniff of clutch away from killing the engine, the bigger flywheel will keep things turning for a wee bit longer before I kill it and fall over in the mud. As for the answers parallel to mine that say it's the mass of the other pistons, the mass of a piston is trivial in comparison to that of the flywheel. Even lawn mowers mentioned in one example have flywheels (at least the ones I owned always did). The mass of a tiny lawn mower piston is going to have a hard time against the relatively large mass of a lawn mower blade with no flywheel. To speak to your two points: 1. My motorcycle's pistons lie on their sides, gravity has no practical effect. 2. Power stroke movement is caused by the expansion of burning gases, period. All other factors, such as flywheel inertia, contribute relatively minimally.

by tmptmp 11y ago

6x9equals42 11y ago

Momentum from the flywheel/flexplate keeps it spinning

acranox 11y ago
The flexplate has very little mass to provide momentum. The fact that the flexplate is bolted to the (heavier) torque converter is what's really going to provide the momentum.

imakesnowflakes 11y ago

Not an expert, but I always assumed that it was caused by the rotational inertia of the Flywheel[1]. [1] https://en.wikipedia.org/wiki/Flywheel https://en.wikipedia.org/wiki/Flywheel

jayflux 11y ago

There's usually more than 1 piston on the crankshaft. So while one is coming up, the power for that is coming from another going down

delinka 11y ago

If you can find a pull-start gas engine lawn mower, you can learn lots from it. These things generally have a single piston. The pull string that you use to start it gets it moving in the right direction, and once it starts running on its own, it's momentum that brings it back around for another go. Also keep in mind that this single piston engine is two-stroke and not four as in the article. Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cycling back around. The more pistons you have, the more there are firing between each revolution of a given piston (and thus overcoming resistance and supplementing that momentum) and thus the more power available to drive the vehicle.

shocks 11y ago
Yup, two stroke model engines from cars/planes are also great for learning. Pull start, cheap, easy to disassemble, and you'll need to learn about tuning too - which is another whole load of fun!
dbloom 11y ago
This is a great explanation. I'd add one small clarification: > Back to four stroke engines: Momentum and the firing of other pistons keeps the whole thing cycling back around The firing of other pistons helps, but really, momentum alone is sufficient. There are tons of single-cylinder, 4 stroke motorcycle, scooter, and off-highway engines out there.

mcguire 11y ago

None of the intake, compression, power, or exhaust strokes have anything to do with gravity or atmospheric pressure. Initially, a secondary motor causes the rotating components to rotate, which causes the pistons to move in the cylinder. Later, either inertia or the power stroke from another cylinder maintains the rotation. The piston movement itself is caused by the piston arm, which is offset from the axis of the crank shaft.

mikestew 11y ago

The kinetic energy of the flywheel keeps things moving when burning gases aren't moving the pistons. The evidence of this is demonstrated on the two flavors of the motorcycle I own. One version (BMW R1200GS Adventure) has a heavier flywheel than the other (non-Adventure). I've ridden both. With the light flywheel it's easier to kill it pulling from a dead stop because there isn't as much mass to overcome the lack of subtlety in my clutch hand. On the Adventure version that I own, sloppy clutch work that often comes with trying to get a 600 lb. "dirt bike" out of a mud hole is ignored by the more massive flywheel. Even when the cylinders are barely able to fire because I'm one sniff of clutch away from killing the engine, the bigger flywheel will keep things turning for a wee bit longer before I kill it and fall over in the mud. As for the answers parallel to mine that say it's the mass of the other pistons, the mass of a piston is trivial in comparison to that of the flywheel. Even lawn mowers mentioned in one example have flywheels (at least the ones I owned always did). The mass of a tiny lawn mower piston is going to have a hard time against the relatively large mass of a lawn mower blade with no flywheel. To speak to your two points: 1. My motorcycle's pistons lie on their sides, gravity has no practical effect. 2. Power stroke movement is caused by the expansion of burning gases, period. All other factors, such as flywheel inertia, contribute relatively minimally.