Purists will pooh-pooh the Atkinson cycle engine of today, with nary a vibrating link in sight. As a matter of fact, if you put a modern Atkinson cycle engine next to a modern Otto cycle engine, you wouldn't be able to see any difference. "There's nothing in [the Prius] engine that's not in the regular engine," according to David Lee at the University of Toyota. (It's not a university you can attend unless you're a Toyota employee needing to know about the latest and greatest rolling out to the dealerships. Sorry.)
What Atkinson had to achieve with crankshaft placement we now can do with variable valve timing, a far cheaper and easier solution. Remember that in Atkinson's original, the intake valves would close early to keep out some of the air-fuel mixture. Nowadays, the intake valve is held open a little too long, so that when the piston moves up for the compression stroke, a little of the gas-air mixture can escape. Each method has the same end: the compression ratio is lower. In engineer-speak, the modern method is known as "livic" -- late intake valve closure. Then the spark plug does its thing -- sparking -- and the piston takes advantage of the combustion with a full power stroke down the cylinder. And then the exhaust stroke does its clean-up job.
More than that has changed in 120-plus years. In the quest for increased efficiency, new materials have been developed. Lighter-weight pistons, rings, and valves springs, for instance, reduce friction and the overall weight of the car. Hauling less weight around takes less energy. Using a dual-overhead cam engine, as Ford does in its Fusion and other hybrids, makes it even easier to control the process.
And again, clever reader, you probably noticed that the modern version of this engine produces less power, just like its predecessor. Too true. As Lee noted, "This engine would struggle in a regular car."
But you know where it doesn't struggle? In a hybrid drivetrain.