Atkinson cycle

From Free net encyclopedia

Template:Thermodynamic cyclesThe Atkinson cycle engine is a type of Internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power.

The Atkinson cycle allows the intake, compression, power, and exhaust strokes of the four-stroke cycle to occur in a single turn of the crankshaft. Owing to the linkage, the expansion ratio is greater than the compression ratio, leading to greater efficiency than with engines using the alternative Otto cycle.

The Atkinson cycle may also refer to a four stroke engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This reduces the effective compression ratio and, when combined with an increased stroke and/or reduced combustion chamber volume, allows the expansion ratio to exceed the compression ratio while retaining a normal compression pressure. This is desirable for improved fuel economy because the compression ratio in a spark ignition engine is limited by the octane rating of the fuel used. A high expansion ratio delivers a longer power stroke, allowing more expansion of the combustion gases and reducing the amount of heat wasted in the exhaust. This makes for a more efficient engine.

The disadvantage of the four-stroke Atkinson cycle engine versus the more common Otto cycle engine is reduced power density. Because a smaller portion of the intake stroke is devoted to compressing the intake air, an Atkinson cycle engine does not intake as much air as would a similarly-designed and sized Otto cycle engine.

Four stroke engines of this type with this same type of intake valve motion but with forced induction (supercharging) are known as Miller cycle engines.

Multiple production vehicles use Atkinson cycle engines:

Toyota Prius hybrid electric (front-wheel-drive)

Ford Escape hybrid electric (front- and four-wheel drive)

In all of these vehicles, the lower power level of the Atkinson cycle engine is compensated for through the use of electric motors in a hybrid electric drive train. These electric motors can be used independent of, or in combination with, the Atkinson cycle engine.

External links

• Animation of Atkinson Cycle Engine Note that this animation shows the true Atkinson engine, which uses a complex linkage that allows different stroke lengths for intake/compression and power/exhaust. However, the illustration shows the engine with the linkage laid out to generate 4 equal strokes. To alter the ratio of the strokes, the rightmost pivot point (the one that is attaching the horizontal green link to the frame) should be moved downwards along the frame. This will allow more angular movement as the link rotates up, giving a longer piston stroke for power and exhaust, and less angular movement as the link rotates down, giving a shorter piston stroke for intake and compression. In fact, a sliding pivot point at that location would allow the engine to dynamically change the stroke ratios.
• Modified Atkinson Cycle Engine: alternative variable valve timing strategy increases low speed torque obtainable from Atkinson Cycle Engine.de:Atkinson-Prozess

it:Ciclo Atkinson ja:アトキンソンサイクル ru:Цикл Аткинсона sk:Atkinsonov cyklus