Arriving as it did during the height of the Industrial Age, the sleeve-valve engine looks like a contraption that would be right at home in a steampunk novel. Modern-day engineers marvel at its cleverness. And cluck-cluck at its high complexity.
So there, you've been warned. Actually, it's a pretty beautiful thing once you understand how all those pieces work together. Now roll up your sleeves, because we're about to get down and dirty with the inner workings of a sleeve-valve engine.
This engine has so much going on that it almost defies description. But we'll try. Sleeve-valve engines, like their tappet valve counterparts, can come in many different configurations. One such arrangement, the radial sleeve-valve engines used on airplanes, look a bit like what you might get if a Rock 'Em Sock 'Em Robot had a baby with a "squiddie" sentinel from "The Matrix."
To understand what a sleeve-valve engine is and does, it might help to first understand what it is not. It is not, first and foremost, the popular system with which most of us are familiar, a poppet valve engine. Poppet valves are the de facto standard on today's internal combustion engines. With them, mushroom-shaped valves under the tension of springs open and close rhythmically to control the entry and exit of fuel, air and waste exhaust gases in the cylinder.
A sleeve valve, on the other hand, uses a sliding, sometimes rotating sleeve to control how much air and fuel get detonated with each compression stroke. The basic premise of igniting fuel and air to drive a set of pistons and turn a crankshaft is the same as it is with other internal-combustion engines.
Here's another distinct feature of sleeve valves. On designs where the sleeve rotates, ports that are cut into it align with either intake ports or exhaust ports in the cylinder, depending on what part of the stroke is taking place. A piston moves up and down within each sleeve, even as the sleeve is sliding back and forth. The sleeve motion is driven by gears connected to the crankshaft.
Scratching your head still on what, exactly, takes place? Here are the steps:
- Compression stroke: the piston approaches top-dead-center, all of the cylinder's ports are closed, and the spark plug fires and ignites the fuel/air mix
- Combustion stroke: ignition forces the piston back down into the cylinder; as the piston goes to bottom-dead-center, the liner (or sleeve) shifts to align its cutout openings with the cylinder's exhaust ports
- Exhaust stroke: exhaust gas is expelled as the piston comes back up; the exhaust ports close
- Intake stroke: the sleeve rotates the other way, exposing the air intake ports; the piston descends, drawing in fresh air; the sleeve shifts to close off the intake port for the next firing stroke and then the entire process repeats
Now multiply that by several cylinders and toss in a crankshaft for them to rotate, and you've got yourself a sleeve-valve engine!
If it sounds complicated, well, that's because it is. One of the main knocks against these engines was that they were so complex. It makes a bit more sense, though, when you see the entire process in action. Check out the video on this page to better visualize it.