New Engine Design

[Captain Jerry]

Hi Y'all

I'm back. The shop is decommissioned for a while longer but I have been thinking about a new project. The design has been kicking around in my head while I was away but since the battery on my laptop battery died early in the cruise, I was only able to design in my head, with a few sketches to keep it real.

Before I left, I had been knocking a few ideas around. The "Pull My Finger Engine" http://www.homemodelenginemachinist.com/index.php?topic=4291.0 was a test of the Z-Axis mechanism and will be the basis of this design. I had been thinking of building a 3 cylinder Axial engine similar to the "Weeble" engine http://www.homemodelenginemachinist.com/index.php?topic=3540.0 but I have now changed that thought. The new engine will be a four cylinder design. It could also be considered a two cylinder, double acting design since there will be two cylinders with two double headed pistons. The cylinders will lay parallel to the shaft (Axial) and will operate the spider arms through a four motion bushing in the center of each piston.

The design of this four motion bushing is the second major design problem critical to this engine ( after the z-axis bearing ) and has not yet been tested but I believe that I have the major points covered. The design is done, the execution will follow.

The third critical design element is the valve mechanism. Previous experience with rotary valves has been less than ideal. They do not seal well and they make it difficult to incorporate ball bearings. I looked at Elmer's 3-cyl radial and the valve seemed to solve these problems but I didn't like the small pin that drives the valve disk and I also didn't like the fact that this valve makes it impossible to have a double ended output shaft. I borrowed the concept and modified it fix what I thought were shortcomings. I've got the design worked out but it hasn't been built yet.

Most of the details have been worked out using Alibre' since I got back and have the use of my laptop. I am using the free version which limits assemblies to five parts so I can't post a fully assembled model. I'm not sure that I can get the partial assembly PDF to post but here's trying.

I'll post some progress pics when I make some progress but for now feel free to comment.

Jerry

View attachment Spider Plates and Cyls.pdf

 

[dsquire]

Jerry

Welcome Back. Hope the cruise was good. Too bad the computer died but more time for watching gir.. scenery.

That looks like it is going to be an interesting engine, I'll be watching.

Cheers

Don

 

[ksouers]

Jerry,
Welcome back! Hope you enjoyed your time on the 'Banks.

Interesting design, a double-weeble. Gotta see this one completed


Kevin

 

[Captain Jerry]

Enjoyed the cruise. Enjoyed the Fishing and the fish (you have to try cracked conch). Hated the weather, worst in 10 years of cruising. I got pics if anyone is interested.

Here's where I am on piston design. The narrowed sections are to reduce weight. The wrist pin fits into the round hole in the piston boss. It must be able to rotate through 40 deg. and slide approx 1/32". The rod fits into the hole in the wrist pin and must able to rotate 40 deg. and slide approx. 1/32". Piston will be brass (Maybe aluminum for weight), the wrist pin will be brass (3/8" dia.) and the rod will be polished drill rod (3/16" dia.) The oblong hole in the piston is to allow the rod to articulate through 40 degrees. This will give a stroke of 27/32" and with a bore of 5/8" the displacement will be .259 cu. in. per cylinder or just over 1 cu. in. total.

View attachment HMEM Ex View.pdf

View attachment HMEM Piston.pdf

View attachment HMEM Piston.pdf

 

[Captain Jerry]

Here is a little video of the Z-shaft action. This is a test. If it works, Ill edit this post.

http://screencast.com/t/4pIYJ7R5fSD

This is from a screen video capture using "Jing" of an Alibre assembly. This is from the free version of Alibre 11.1 which only allows 5 unique parts per assembly so the entire mechanism is not shown here. The flywheel on the end of the shaft is only to show the rotation of the shaft. The motion is a little bit jerky. Probably a combination of the animation in Alibre and the frame capture rate of Jing. It smooths out at the end so I'll work on technique and maybe able to do better.

The purpose of this video is to show the translation of reciprocal motion ( the outer ends of the rods ) to rotary motion ( the shaft and flywheel. The two outer rods will be driven by the double headed pistons and the center rod will be captured between two parallel retaining rods to prevent the Spider ring from rotating. The spider ring is mounted to the outer race of a ball bearing and the inner race is seated on the angled section of the drive shaft.

Best to all
Jerry

 

[Captain Jerry]

Hi Y'all

This is how I plan to build the eccentric operated slide valve for the new engine. I hesitate to call it a rotary valve because that makes me think of valves where the crankshaft has a hole or a flat on it that controls air/steam.

This valve uses an eccentric (red) on the shaft which moves a ring (green) around the inside of a steam chest (blue). As the ring slides freely, it uncovers ports that are connected to the air inlet (top), the exhaust (bottom) and the head end of two cylinders (side ports). As the ring moves it alternately connects each cylinder to the inlet or the exhaust. If you watch the video, when a port is blue it is intake and when it is red it is exhaust. This design eliminates air leaks around the shaft and allows the use of ball bearings.

Because the engine will be double acting, there will be a valve at each end of the engine.

http://s468.photobucket.com/albums/rr41/CaptainJerry_Albumlbum/?action=view&current=ValveVid.flv

http://screencast.com/t/XcAUHWQR

 

[vlmarshall]

Impressive valve design! :bow:

 

[bearcar1]

Thank for sharing the video explanations, I was scratching my....................head :big:.......... in an attempt to understand the principle. I just could not get my logic to encompass the notion. That plus I was thinking (?) how in the world is the man going to get the required motion to drive the cylinders. Now I see it clearly and you are a wild man sir,I would have never thought of this concept. :bow:


BC1
Jim

 

[Captain Jerry]

Hi Y'all

A change in plans!

I'm not going to build this engine yet. I think I've got the design worked out OK but bringing it to life may be more than I can take on right now. There are two new design components that I have never tried and I'm don't want to try them both at the same time. The six-way bearing in the double headed piston will be a real nightmare and I'm not sure that I am ready for that.

The rotary slide valve should be a lot easier to build but because this engine is double acting, it will take two of these valves. I'd rather start with a single acting engine that has only one valve until I get the bugs out of it.

The Z-shaft swash plate with ball bearing was used in the "Pull My Finger" engine but has not been tried in a steam/air engine.

My next engine is going to be a three cylinder axial swash plate engine with a rotary slide valve. It will use the ball joint piston/rod mechanism as in the Weeble so I don't have to face the Six-Way bearing just yet. I'll post some drawings in a little while, but right now, Pearl (the dog) is demanding some frisbee time.

Jerry

 

[Captain Jerry]

Hi Y'all

Pearl has been exercised, dinner has been eaten and now down to business. Here is a drawing of the new 3 cyl engine. I'm going to start a new thread for this engine.

Jerry