How can I produce sinusoidal piston motion?

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Offline Geezer

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How can I produce sinusoidal piston motion?
« on: 10/10/2009 04:25:33 »
What is the most efficient method of generating sinusoidal motion in a piston from a rotating shaft?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #1 on: 10/10/2009 17:50:19 »
The scotch yoke would certainly be sinusoidal. Not so sure that the swashplate would be - at least not the version in the animation on Wikipedia. The rods will have to tilt if they are driving pistons. I think that would introduce some distortion.

In the Wiki animation it's not clear what is preventing the "fixed plate" (aka wobbler I believe) from rotating with the swashplate.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline LeeE

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How can I produce sinusoidal piston motion?
« Reply #2 on: 13/10/2009 22:10:18 »
Could you not do it with a cam?
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #3 on: 13/10/2009 23:25:43 »
Yes. A cam would work, but it may not be the most efficient method. If the piston loads are great, the friction between a cam and a cam-follower could be significant.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Freeman

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How can I produce sinusoidal piston motion?
« Reply #4 on: 14/10/2009 12:38:10 »
Quote from: Geezer
The rods will have to tilt if they are driving pistons. I think that would introduce some distortion.

Not really Geezer due to the fact that the piston only moves backwards and forwards the needed be any bending of the rod.That is if it is a normal inline engine

Quote from: Geezer
In the Wiki animation it's not clear what is preventing the "fixed plate" (aka wobbler I believe) from rotating with the swashplate.

That is quite easy.The swash plate and fixed plate is in essence a normal roller bearing with the fixed plate not connected to the drive shaft so it spins freely or remains stationary to act as a pump head actuator.

Hope this helps [;)].

Could you not do it with a cam?

Problem with a systems such as you proposed is how do you couple the vertical movement of the piston with rotational movement on the shaft if the cam is set up as in the example.

[See attached image]

Or do I have the idea wrong?.
Some correction will be appreciated.

Yes. A cam would work, but it may not be the most efficient method. If the piston loads are great, the friction between a cam and a cam-follower could be significant.

The question is,If the idea will even work at all based on the image I provided if it is the right one.
« Last Edit: 14/10/2009 12:41:23 by Freeman »
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Offline LeeE

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How can I produce sinusoidal piston motion?
« Reply #5 on: 14/10/2009 18:53:50 »
Yes. A cam would work, but it may not be the most efficient method. If the piston loads are great, the friction between a cam and a cam-follower could be significant.

Put a roller on the cam follower?

Quote
Problem with a systems such as you proposed is how do you couple the vertical movement of the piston with rotational movement on the shaft if the cam is set up as in the example.

Umm... I don't quite see the problem - the diagram looks fine, although I think that cam shape should be circular and simply offset for a sinusoidal track, and I'd expect guides and a return spring.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Freeman

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How can I produce sinusoidal piston motion?
« Reply #6 on: 14/10/2009 19:12:52 »
Umm... I don't quite see the problem - the diagram looks fine, although I think that cam shape should be circular and simply offset for a sinusoidal track, and I'd expect guides and a return spring.

Ok.Yes the diagram was put together for argumentative reason so finer details has been omitted [Should have put that in my previous post come to think of it].

Shoot!!.I just shot myself in the foot in my previous post.I had the idea that it be based similarly to that of a internal combustion engine where the piston drives the rotation when it is the other way around.

Hmm.Yes you are correct.The mentioned above will work fine. 
« Last Edit: 14/10/2009 19:53:45 by Freeman »
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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #7 on: 14/10/2009 19:20:06 »
Yes. A cam would work, but it may not be the most efficient method. If the piston loads are great, the friction between a cam and a cam-follower could be significant.

Put a roller on the cam follower?

Yes, but for some applications the load could be quite large. As you point out, the cam should be an eccentric circle for sinusoidal motion, so it's possible to put a rolling bearing on the outer periphery of the cam. Some sort of guide bearing would be required to provide lateral support to the pushrod, otherwise the cantilever force on the piston could be a problem.


Quote
Problem with a systems such as you proposed is how do you couple the vertical movement of the piston with rotational movement on the shaft if the cam is set up as in the example.

Umm... I don't quite see the problem - the diagram looks fine, although I think that cam shape should be circular and simply offset for a sinusoidal track, and I'd expect guides and a return spring.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Freeman

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How can I produce sinusoidal piston motion?
« Reply #8 on: 14/10/2009 20:04:12 »
Quote from: Geezer
Put a roller on the cam follower?

Yes, but for some applications the load could be quite large. As you point out, the cam should be an eccentric circle for sinusoidal motion, so it's possible to put a rolling bearing on the outer periphery of the cam. Some sort of guide bearing would be required to provide lateral support to the pushrod, otherwise the cantilever force on the piston could be a problem.

Indeed.

Just one question.What did you have in mind when you asked about this?.
Just curious. [;)]
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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #9 on: 15/10/2009 00:35:28 »
Polyphase hydrostatic torque transmission  [:)]
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline peppercorn

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How can I produce sinusoidal piston motion?
« Reply #10 on: 19/10/2009 10:55:57 »
Polyphase hydrostatic torque transmission  [:)]
can you expand on that a bit?
ie. Me no understand! - Well the polyphase bit anyway!

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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #11 on: 19/10/2009 16:11:02 »
Polyphase hydrostatic torque transmission [:)]
can you expand on that a bit?
ie. Me no understand! - Well the polyphase bit anyway!

It's a sort of hydraulic analog of polyphase (e.g. three-phase) electrical transmission. Three (or more) columns of fluid reciprocate between two "translators". The translators convert sinusoidal piston motion into rotary motion and vice-versa. 
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Offline peppercorn

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How can I produce sinusoidal piston motion?
« Reply #12 on: 20/10/2009 12:20:23 »
Quote
It's a sort of hydraulic analog of polyphase (e.g. three-phase) electrical transmission. Three (or more) columns of fluid reciprocate between two "translators". The translators convert sinusoidal piston motion into rotary motion and vice-versa. 
I see.
And this method of getting rotary motion has some advantage does it?

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Offline Geezer

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How can I produce sinusoidal piston motion?
« Reply #13 on: 21/10/2009 23:19:33 »
Quote
I see.
And this method of getting rotary motion has some advantage does it?


Certainly does. It permits almost unlimited articulation compared with mechanical drivelines (flex drives, Hook joints, CV joints etc.) Also, it's simple to disconnect and/or reverse the torque.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline peppercorn

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How can I produce sinusoidal piston motion?
« Reply #14 on: 22/10/2009 12:20:06 »
Sounds useful! Any web resource you can suggest so I might get a better understanding?