After seeing several Lego pneumatic engines on the internet, I decided I had to give it a shot. I first built a type of steam engine after a design by C.S.Soh. But I was drawn to modeling car engines like Alex Zorko. I wanted to build a horizontally opposed engine like in a Subaru, but it was too wide and didn't look right. So then I tried a V4 engine.
|
|
This 7.3 mL engine has an ABS block, dual camshaft, silicone intake manifold, and 1.5 valves per cylinder! (Each piston has its own intake port from the pneumatic switch, while the exhaust is shared by two pistons) The camshafts are driven at the same speed as the crankshaft by the timing gears at the front. |
|
|
The bottom showing the crank shaft. Now I just need to install an oil pan... Actually I saw this view of real engines a lot last summer. I was working in quality control at an engine remanufacturing plant. I checked the conrod bearings at the last step on the line before the oil pan was mounted. |
|
|
Now with the intake manifold removed, you can see the camshafts. The valves are actuated by the same means as the window walker. |
|
|
The first version of the engine ran pretty rough. I thought it was an issue with the timing and the angle between the cylinder banks not being exactly 90 degrees. So I built the red "high performance" engine and fixed the angle problem. Unfortunately, the engine still ran rough. I guess you can't expect an engine without counterweights on the crankshaft to be terribly smooth. I have a thought to try and model what Honda did on the Insight Hybrid engine. They use the electric motor to provide counter pulses to balance the crankshaft instead of counter weights. I could hook up a motor, a rotation sensor, an RCX... |
|
|
Ahhh. Much better. The flywheel made all the difference. This baby is now as smooth as a BMW. The flywheel is geared up 3 times from the crankshaft. The air tanks helped smooth things out as well. |
|
|
Top. The intake manifold has been tidied up a bit. |
|
|
And the bottom view showing the crankshaft once again. The red engine is pretty much identical to the blue one except for the mounting of the pistons. |
|
Just in case you want to build this engine, you can download the instructions here. The steps aren't in perfect sequence, but you should be able to figure things out. The tubing is not shown but should be clear from the pictures. You will have to adjust the timing as well. You may need some of the pneumatic parts which can be found on Mark Klein's site. |
|
One more view just for the heck of it. |
What's next? I think I may try changing the gearing for the camshafts so they are exactly 180 degrees apart (it is a bit off now because of the 24t gears). This should improve the timing. Then I might try rebuilding the entire engine to incorporate conrods like in a real engine. After that, I might try using the new style double acting cylinders. That would effectively turn this engine into a V8 since there would be eight power strokes per revolution. By that time I am going to be really tired of pumping...
