Atkinson cycle
While originally seen exclusively in hybrid electric applications such as the earlier-generation Toyota Prius, later hybrids and some non-hybrid vehicles now feature engines with variable valve timing, which can run in the Atkinson cycle as a part-time operating regimen, giving good economy while running in Atkinson cycle, and conventional power density when running as a conventional, Otto cycle engine.
The second and best-known design was the cycle engine, which used an over-center arm to create four piston strokes in one crankshaft revolution.
Many modern engines now use unconventional valve timing to produce the effect of a shorter compression stroke/longer power stroke.
Miller applied this technique to the four-stroke engine, so it is sometimes referred as the Atkinson/Miller cycle, US patent 2817322 dated Dec 24, 1957.
[3] Hugo Güldner argued in his 1914 book that Körting was the first firm to build a gas engine with a short compression stroke and a longer expansion phase in 1891, based on a design first proposed by Otto Köhler in 1887.
[4] Roy Fedden, at Bristol, tested an arrangement in the Bristol Jupiter IV engine in 1928, with variable retard timing allowing part of the charge to be blown back into the intake manifold, in order to have sustainable reduced operation pressures during takeoff.
[citation needed] Modern engine designers are realizing the potential fuel-efficiency improvements the Atkinson-type cycle can provide.
[8] Atkinson's "Cycle" engine was efficient; however, its linkage was difficult to balance for high speed operation.
With this new design, Atkinson was able to eliminate the linkages and make a more conventional, well balanced engine capable of operating at speeds up to 600 rpm and capable of producing power every revolution, yet he preserved all of the efficiency of his "Cycle Engine" having a proportionally short compression stroke and a longer expansion stroke.
For any given portion of air, the greater expansion ratio converts more energy from heat to useful mechanical energy—meaning the engine is more efficient.
This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle.
Disadvantages of this design include the requirement that rotor tips seal very tightly on the outer housing wall and the mechanical losses suffered through friction between rapidly oscillating parts of irregular shape.
These electric motors can be used independently of, or in combination with, the Atkinson-cycle engine, to provide the most efficient means of producing the desired power.
As of July 2018[update], many production hybrid vehicle drivetrains use Atkinson-cycle concepts—for example, in: The 1887 patent (US 367496) describes the mechanical linkages necessary to obtain all four strokes of the four-stroke cycle for a gas engine within one revolution of the crankshaft.
