The 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.

give me figure of the Atkinson cycle engine

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Recently Atkinson cycle has been used to describe a modified Otto cycle 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 is more like a Miller cycle engine than an actual Atkinson cycle engine. The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed) but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio. Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.

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 compression stroke is devoted to compressing the intake air, an Atkinson-cycle engine does not take in 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 a supercharger to make up for the loss of power density are known as Miller cycle engines.
http://en.wikipediawiki/Atkinson_cycle
http://hybrid-vehiclehybrid-vehicle-ice.html
http://animatedenginesatkinson.shtml
Virtually all engines utilizing Atkinson cycle technology are used in conjunction with superchargers or electric motors (hybrids). This is due to detonation limited low speed maximum torque deficiencies associated with late intake valve closings utilized in conventional Atkinson Cycle Engines.

The increased light load thermal efficiencies associated with Atkinson engines using late intake valve closings are indisputable.

SAE papers 850074 (Nissan) and 930820 (Honda) document phenomena that could facilitate percent increases in maximum low speed power availability approximately equal to percent decreases in low power availability associated with conventional late close Atkinson Cycle engines.

I came across this early close Atkinson scenario totally by accident while developing variable valve event technology in conjunction with high compression ratios in the early 1980's. Unfortunately the huge increases in low speed torque were accompanied by forfeiting most of the thermal efficiency gains associated with late close Atkinson concept. Eventually I figured out how to have increased maximum low torque and maintain the increased light load thermal efficiency associated with the late close Atkinson Cycle engine. (Patent 4,961,406)

The basic concept could best be described as a Honda i-VTEC engine with a smaller low speed intake valve event and more intake valve phasing in conjunction with an Atkinson cycle expansion ratio. The reduced size intake valve event is run in the advanced position when maximum power is required and retarded when maximum thermal efficiency is desired at light load.

SAE paper 850074 and SAE paper 930820 both acknowledge that earlier than conventional intake valve closings will decrease mixture burn rates. Both papers acknowledge that mixture motion and charge temperature decrease as intake valve closings are advanced. The Honda paper acknowledges that Wide Open Throttle Volumetric Efficiently actually increases, compared to baseline, at low speeds with earlier than normal intake valve closings.

It is amazing that the auto industry did not recognize the aforementioned scenario 20 years ago as a means to capitalize on their research and let Toyota obtain the competitive edge when Toyota patented the knock control concept 20 years later (patent 6,848,422 whose validity could be questioned in light of 4,961,406 which was not even cited in Toyota's patent)


Virtually all engines utilizing Atkinson cycle technology are used in conjunction with superchargers or electric motors (hybrids). This is due to detonation limited low speed maximum torque deficiencies associated with late intake valve closings utilized in conventional Atkinson Cycle Engines.

The increased light load thermal efficiencies associated with Atkinson engines using late intake valve closings are indisputable.

SAE papers 850074 (Nissan) and 930820 (Honda) document phenomena that could facilitate percent increases in maximum low speed power availability approximately equal to percent decreases in low power availability associated with conventional late close Atkinson Cycle engines.

I came across this early close Atkinson scenario totally by accident while developing variable valve event technology in conjunction with high compression ratios in the early 1980's. Unfortunately the huge increases in low speed torque were accompanied by forfeiting most of the thermal efficiency gains associated with late close Atkinson concept. Eventually I figured out how to have increased maximum low torque and maintain the increased light load thermal efficiency associated with the late close Atkinson Cycle engine. (Patent 4,961,406)

The basic concept could best be described as a Honda i-VTEC engine with a smaller low speed intake valve event and more intake valve phasing in conjunction with an Atkinson cycle expansion ratio. The reduced size intake valve event is run in the advanced position when maximum power is required and retarded when maximum thermal efficiency is desired at light load.

SAE paper 850074 and SAE paper 930820 both acknowledge that earlier than conventional intake valve closings will decrease mixture burn rates. Both papers acknowledge that mixture motion and charge temperature decrease as intake valve closings are advanced. The Honda paper acknowledges that Wide Open Throttle Volumetric Efficiently actually increases, compared to baseline, at low speeds with earlier than normal intake valve closings.

It is amazing that the auto industry did not recognize the aforementioned scenario 20 years ago as a means to capitalize on their research and let Toyota obtain the competitive edge when Toyota patented the knock control concept 20 years later (patent 6,848,422 whose validity could be questioned in light of 4,961,406 which was not even cited in Toyota's patent)






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