A Victorian patent dodge now helps hybrid cars squeeze more miles from fuel
James Atkinson built odd engines in the 1880s partly to sidestep patents protecting Nikolaus Otto's four-stroke design. His real insight lay elsewhere: let the piston expand farther than it compresses. More than a century later, Toyota leaned on that trick when its first Prius went on sale in late 1997.
Atkinson's first machine, the 1882 differential engine, set two pistons facing each other in one cylinder. A toggle linkage let one sit almost still while the other came in and went back, then swapped roles, so each revolution delivered compression and power from one piston and exhaust and intake from the other. Because the power piston stayed withdrawn while gases were swapped, the valves never faced high pressure and could be simple steam-style or even reed types.
His 1887 Cycle Engine went further, using a cam, poppet valves and an over-centre arm to fit all four strokes into a single turn of the crankshaft, with intake and compression noticeably shorter than expansion and exhaust. Made in sizes up to 100 horsepower and licensed abroad, it was efficient but hard to balance at speed. The fix was the Utilite, patented in Britain in 1892: essentially a two-stroke with its exhaust port halfway down the cylinder and a cam valve holding pressure until late in the stroke. It ran up to 600 rpm and tested even better, yet very few were built and none survive.
Others chased similar ideas. Charon filed a French patent in 1888 and showed an engine in Paris in 1889; Hugo Guldner credited the firm Korting with an 1891 build based on Otto Kohler's 1887 proposal. American engineer Ralph Miller patented his version on Dec 24, 1957, and adding forced induction to recover lost power now defines a Miller-cycle engine.
Modern cars mostly fake the effect. Holding the intake valve open a little longer pushes some air back into the manifold, trimming effective compression while leaving expansion untouched, so less energy is wasted as the burnt charge leaves. The cost is weaker power for a given size, which is why the approach pairs so well with an electric motor that fills in when extra push is needed, as in Toyota's early 1NZ-FXE engine. Variable valve timing lets some engines switch between this thrifty mode and ordinary Otto running.
Source: Atkinson cycle
