Gearless Mechanism--4 stroke i.c. engine

[Brian Rupnow]

I have long been fascinated with the old hit and miss engines that were 4 cycle engines, but used no gear to drive the cam shaft at half the speed of the crankshaft. I have studied on this, and they break down into two main types. The kind I can not reproduce on a manual mill is the type which had cam tracks cut into the face or periphery of a disc. Chuck Fellows did a really nice job of reproducing one of those last year. The other type, which I can reproduce on my manual machinery, is the "star wheel" type. I don't want to start another engine build right now. However, I will attempt to create one of the mechanisms, post drawings of how I made it, and build the mechanism and make a video of it operating. I might fall on my face here, but follow along if you are interested. The one I make will be sized to work on a model engine.

[Jasonb]

Brian, now that you have your DRO I wonder if it would be possible to use CAD to plot out say 360 different Y positions that could be used to plunge cut with a small milling cutter as the work is rotated 1degree at a time on a rotary table, with a bit of clean up you should be able to get the right sort of shape groove. I have something similar to make for teh coiling gear if I do my Ploughing engine and had thought that may be a way. Not unlike cam cutting but moving teh tool sideways rather than up and down.

Look forward to seeing the star wheel develope

J

[jadge]

Presumably these mechanisms were used because they were cheaper than gears at the time the full size engines were being manufactured. Can we assume that the original parts were made on manual machines, and if so, how did they do it?

Andrew

[kvom]

Very possibly use a duplicating mill that worked like a pantograph.

[Brian Rupnow]

Got to have something to mount the star wheel in----

[Myrickman]

Brian- these types of mechanisms also hold a soft spot in my mechanical interest. The one you show above is fascinating to watch on both models and full sized. The slots on the ones I've seen have been cut using a square cutter where the valve contacts. Makes fabbing it on manual machines way easier? Have you seen this one which was on the Wright bros shop stationary engine?  Don't mean to be a thread hijacker, but I thought you'd like this one and so I toss it on the pile. Very clever....  <a href="https://www.youtube.com/watch?v=M7H-wnHxxXU" target="_blank">http://www.youtube.com/watch?v=M7H-wnHxxXU</a> I saw it on a report on their early engines and had to make a mockup.. Forgot if I posted it in an older post .

[Brian Rupnow]

Myrickman--Yes, I seen that on an earlier thread, but it was never used on any engines I know of. It is however, ingenious.--Brian

[Alan Haisley]

Brian, is this similar to a Geneva mechanism?

Alan

[Brian Rupnow]

These mechanisms seem to do a lot better with a roller on the end which rides on the cam. I am assuming that this is because #1--it will be moving twice as many times in a complete cycle as a lifter which runs off a camshaft---and #2---it will be moving twice as fast, and #3--it has more mass than a standard "valve pushrod".

[Brian Rupnow]

Brian, is this similar to a Geneva mechanism?

Alan

No

[Brian Rupnow]

At this point, I have to decide whether the engine cylinder will be horizontal or vertical. The gearless mechanism will work on either, but for illustration purpose, I will use vertical. I also needed to show the exhaust valve that will be acted on (the intake valve is atmospheric)----and what better to use than the valve body/carburetor that I so recently designed for the oscillating i.c. engine.
----Now, to get into the science of how this thing works. Immediately below the stem of the exhaust valve, you will see the 4 lobed brown "star wheel". This star wheel has 4 "lobes" that will contact the bottom of the exhaust valve and lift it, if the entire gearless mechanism is lifted on a cam. It also has 4 "relieved areas" between the "lobes"  (as shown) which will NOT contact the valve stem if the star wheel gets rotated 1/8 (22.5 degrees) before it gets lifted again!! So--Stay with me--the cam is attached to the crankshaft. That means that with every single revolution of the crankshaft, that gearless mechanism will lift up on the cam lobe and then return to the "down" position--(There will be a tension spring attached to the gearless mechanism to ensure that it does return to the "down" position and stay in contact with the cam. So---as long as we are able to rotate that star wheel 1/8 of a turn every time the mechanism goes up and down then the valve will only get lifted EVERY OTHER time the gearless mechanism is lifted.--That nifty looking green ratchet wheel with 8 notches on the same shaft as the star wheel is the component which ensures this will happen.

[Alan Haisley]

The fog lifts. Thanks, Brian.

[Brian Rupnow]

Toolguy raises a very good point.--What keeps the star wheel and ratchet wheel from drifting out of the proper rotational relationship to the valve stem. I have seen it done two ways, and know of a third. The third way which I know of, is a spring loaded detent ball and eight detents in either the star wheel or the ratchet wheel. This might work fine for something that only sees occasional use and slow moving components, but it wouldn't live with something like this application.  I have seen the following method used on a model---A piece of rubber or vinyl tubing is slipped over the axle  between the ratchet wheel and the blue "fork" supporting it, and is a bit longer than the actual space provided there. This acts as a friction brake to keep the star wheel from rotational drifting out of alignment. The third way, which is used by Philip Duclos on his gearless engine design, it to have a piece of spring wire laying tight against the flat face pf an 8 sided octagonal wheel which rotates with the star and ratchet wheel.  When the star wheel and ratchet wheel and octagonal wheel rotate, the spring wire is bent away from the flat it lays against and after the 22.5 degrees of rotation another flat face is presented and the spring wire snaps into place against the flat to keep it from drifting rotationally until the next cam action turns it again. I like the Philip Duclos method best, and will investigate it farther---The only thing I don't like about it is that it begins to get very "busy" around the star wheel. If anyone out there knows of a better/different way, please step forward and tell me about it.---Brian

[Brian Rupnow]

I just found this video, which shows the action of the starwheel very clearly at 2:18 into the video.
https://www.youtube.com/watch?v=dneJKmdRbu8

[cfellows]

Here is another gearless valve mechanism...

<a href="https://www.youtube.com/watch?v=Q3xlUbMB4Jc" target="_blank">http://www.youtube.com/watch?v=Q3xlUbMB4Jc</a>

This type of horizontal shuttle and cam arrangement is pretty easy to make using a vertical milling machine...  I made something similar for a flame sucker engine a number of years ago using my vertical mill and my indexing spin jig... no CNC involved.

Chuck