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The Atkinson-cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide
Atkinson's third design was named the "Utilite Engine". Atkinson's "Cycle" engine was efficient; however, its linkage was difficult to balance for high speed operation. Atkinson realized an improvement was needed to make his cycle more applicable as a higher-speed engine.
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. The Utilite operates much like a standard two-stroke except that the exhaust port is located at about the middle of the stroke.
During the expansion/power stroke, a cam-operated valve (which remains closed until the piston nears the end of the stroke) prevents pressure from escaping as the piston moves past the exhaust port. The exhaust valve is opened near the bottom of the stroke; it remains open as the piston heads back toward compression, letting fresh air charge the cylinder and exhaust escape until the port is covered by the piston.
After the exhaust port is covered the piston begins to compress the remaining air in the cylinder. A small piston fuel pump injects liquid during compression. The ignition source was likely a hot tube as in Atkinson's other engines. This design resulted in a two-stroke engine with a short compression and longer expansion stroke.
The Utilite Engine tested as even more efficient than Atkinson's previous "differential" and "cycle" designs. Very few were produced, and none are known to survive. The British patent is from 1892, #2492. No US patent for the Utilite Engine is known.
The ideal Atkinson cycle consists of:
* 1–2 Isentropic, or reversible, adiabatic compression
* 2–3 Isochoric heating (Qp)
* 3–4 Isobaric heating (Qp')
* 4–5 Isentropic expansion
* 5–6 Isochoric cooling (Qo)
* 6–1 Isobaric cooling (Qo')
In the late 20th century, the term "Atkinson cycle" began to be used to describe a modified Otto-cycle engine—in which the intake valve is held open longer than normal, allowing a reverse flow of intake air into the intake manifold. This "simulated" Atkinson cycle is most notably used in the Toyota 1NZ-FXE engine from the early Prius and the Toyota Dynamic Force engine used by many vehicles.
The effective compression ratio is reduced—for the time the air is escaping the cylinder freely rather than being compressed—but the ''expansion'' ratio is unchanged (i.e., the compression ratio is smaller than the expansion ratio). The goal of the modern Atkinson cycle is to make the pressure in the combustion chamber at the end of the power stroke equal to atmospheric pressure. When this occurs, all available energy has been obtained from the combustion process. 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.
The disadvantage of the four-stroke Atkinson-cycle engine versus the more common Otto-cycle engine is reduced power density. Due to a smaller portion of the compression stroke being 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 that use the same type of intake valve motion but using forced induction to make up for the loss of power density are known as Miller-cycle engines.
The Atkinson cycle can be used in a rotary engine. In this configuration, an increase in both power and efficiency can be achieved when compared to the Otto cycle. This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle.
Exhaust gases are expelled from the engine by compressed-air scavenging. This modification of the Atkinson cycle allows the use of alternative fuels such as diesel and hydrogen.
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. See external links below for more information.
The Sachs KC-27 Wankel engine in the Hercules W-2000 motorcycle used the Atkinson cycle. A depression capsule opens a secondary path for the incoming charge.
While a modified Otto-cycle piston engine using the Atkinson cycle provides good
Comparison of Prime Movers Suitable for USMC Expeditionary Power Sources
Oak Ridge National Laboratory
Libralato Engines
- developing a rotary Atkinson cycle engine
Rotary Atkinson cycle engine
- gives details of this engine as well as comparisons with conventional and Wankel engines
The Prius's Not So Secret Gas-Mileage Secrets
- how the Prius uses the Atkinson cycle to get better results than an Otto cycle engine
James Atkinson at Find A Grave
- personal details {{Thermodynamic cycles, state=uncollapsed Thermodynamic cycles Hybrid vehicles
efficiency
Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...
at the expense of power density.
A variation of this approach is used in some modern automobile engines. 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.
Design
Atkinson produced three different designs that had a short compression stroke and a longer expansion stroke. The first Atkinson-cycle engine, the ''differential engine'', used opposed pistons. 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. The reciprocating engine had the intake, compression, power, and exhaust strokes of the four-stroke cycle in a single turn of thecrankshaft
A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
, and was designed to avoid infringing certain patents covering Otto-cycle engines. Atkinson's third and final engine, the ''utilite engine'', operated much like any two-stroke engine.
The common thread throughout Atkinson's designs is that the engines have an expansion stroke that is longer than the compression stroke, and by this method the engine achieves greater thermal efficiency than a traditional piston engine. Atkinson's engines were produced by the British Gas Engine Company and also licensed to other overseas manufacturers.
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. In 1888, Charon filed a French patent and displayed an engine at the Paris Exhibition in 1889. The Charon gas engine (four-stroke) used a similar cycle to Miller, but without a supercharger. It is referred to as the "Charon cycle".
Hugo Güldner
Carl Hugo Güldner (18 July 1866 – 12 March 1926) was a German engineer and inventor. He is best known for inventing the two-stroke diesel engine, and the Valve_timing#Valve_overlap, valve overlap in internal combustion engines.
Life and car ...
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
Otto Köhler (25 June 1903 – 1 April 1976) was a German operatic baritone and voice teacher.
Life
Born in Neu-Isenburg, Köhler, like his cousin, the tenor Franz Völker, first completed an apprenticeship at Disconto-Bank in Frankfurt, where ...
in 1887. This engine also had an engine-load dependent valve train which increased the intake and compression stroke with increasing engine load. On the other hand, the compression was decreasing at low and medium loads, which ultimately reduced the efficiency.
Roy Fedden at Bristol tested an arrangement in the Bristol Jupiter
The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turn ...
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.
Modern engine designers are realizing the potential fuel-efficiency improvements the Atkinson-type cycle can provide.
Atkinson "Differential Engine"
The first implementation of the Atkinson cycle was in 1882; unlike later versions, it was arranged as an opposed piston engine, the Atkinson differential engine. In this, a single crankshaft was connected to two opposed pistons through a toggle-jointed linkage that had a nonlinearity; for half a revolution, one piston remained almost stationary while the other approached it and returned, and then for the next half revolution, the second-mentioned piston was almost stationary while the first approached and returned. Thus, in each revolution, one piston provided a compression stroke and a power stroke, and then the other piston provided an exhaust stroke and a charging stroke. As the power piston remained withdrawn during exhaust and charging, it was practical to provide exhaust and charging using valves behind a port that was covered during the compression stroke and the power stroke, and so the valves did not need to resist high pressure and could be of the simpler sort used in many steam engines, or even reed valves.Atkinson "Cycle Engine"
The next engine designed by Atkinson in 1887 was named the "Cycle Engine" This engine used poppet valves, a cam, and an over-center arm to produce four piston strokes for every revolution of the crankshaft. The intake and compression strokes were significantly shorter than the expansion and exhaust strokes. The "Cycle" engines were produced and sold for several years by the British Engine Company. Atkinson also licensed production to other manufacturers. Sizes ranged from a few up to 100 horsepower.Atkinson "Utilite Engine"
Atkinson's third design was named the "Utilite Engine". Atkinson's "Cycle" engine was efficient; however, its linkage was difficult to balance for high speed operation. Atkinson realized an improvement was needed to make his cycle more applicable as a higher-speed engine.
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. The Utilite operates much like a standard two-stroke except that the exhaust port is located at about the middle of the stroke.
During the expansion/power stroke, a cam-operated valve (which remains closed until the piston nears the end of the stroke) prevents pressure from escaping as the piston moves past the exhaust port. The exhaust valve is opened near the bottom of the stroke; it remains open as the piston heads back toward compression, letting fresh air charge the cylinder and exhaust escape until the port is covered by the piston.
After the exhaust port is covered the piston begins to compress the remaining air in the cylinder. A small piston fuel pump injects liquid during compression. The ignition source was likely a hot tube as in Atkinson's other engines. This design resulted in a two-stroke engine with a short compression and longer expansion stroke.
The Utilite Engine tested as even more efficient than Atkinson's previous "differential" and "cycle" designs. Very few were produced, and none are known to survive. The British patent is from 1892, #2492. No US patent for the Utilite Engine is known.
Ideal thermodynamic cycle
The ideal Atkinson cycle consists of:
* 1–2 Isentropic, or reversible, adiabatic compression
* 2–3 Isochoric heating (Qp)
* 3–4 Isobaric heating (Qp')
* 4–5 Isentropic expansion
* 5–6 Isochoric cooling (Qo)
* 6–1 Isobaric cooling (Qo')
Modern Atkinson-cycle engines
In the late 20th century, the term "Atkinson cycle" began to be used to describe a modified Otto-cycle engine—in which the intake valve is held open longer than normal, allowing a reverse flow of intake air into the intake manifold. This "simulated" Atkinson cycle is most notably used in the Toyota 1NZ-FXE engine from the early Prius and the Toyota Dynamic Force engine used by many vehicles.
The effective compression ratio is reduced—for the time the air is escaping the cylinder freely rather than being compressed—but the ''expansion'' ratio is unchanged (i.e., the compression ratio is smaller than the expansion ratio). The goal of the modern Atkinson cycle is to make the pressure in the combustion chamber at the end of the power stroke equal to atmospheric pressure. When this occurs, all available energy has been obtained from the combustion process. 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.
The disadvantage of the four-stroke Atkinson-cycle engine versus the more common Otto-cycle engine is reduced power density. Due to a smaller portion of the compression stroke being 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 that use the same type of intake valve motion but using forced induction to make up for the loss of power density are known as Miller-cycle engines.
Rotary Atkinson-cycle engine
The Atkinson cycle can be used in a rotary engine. In this configuration, an increase in both power and efficiency can be achieved when compared to the Otto cycle. This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle.
Exhaust gases are expelled from the engine by compressed-air scavenging. This modification of the Atkinson cycle allows the use of alternative fuels such as diesel and hydrogen.
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. See external links below for more information.
The Sachs KC-27 Wankel engine in the Hercules W-2000 motorcycle used the Atkinson cycle. A depression capsule opens a secondary path for the incoming charge.
Vehicles using Atkinson-cycle engines
While a modified Otto-cycle piston engine using the Atkinson cycle provides good fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...
, it is at the expense of a lower power-per-displacement as compared to a traditional four-stroke engine. If demand for more power is intermittent, the power of the engine can be supplemented by an electric motor during times when more power is needed. This forms the basis of an Atkinson cycle-based hybrid electric drivetrain. 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. This drive-train first entered production in late 1997 in the first-generation Toyota Prius.
, many production hybrid vehicle drivetrain
Hybrid vehicle drivetrains transmit power to the driving wheels for hybrid vehicles. A hybrid vehicle has multiple forms of motive power.
Hybrids come in many configurations. For example, a hybrid may receive its energy by burning gasoline, but s ...
s use Atkinson-cycle concepts—for example, in:
* Chevrolet Volt
* Chrysler Pacifica (front-wheel drive) plug-in hybrid model minivan
* Ford C-Max (front-wheel drive / US market) hybrid and plug-in hybrid models
* Ford Escape/ Mercury Mariner/Mazda Tribute
The (''Code J14'') is a compact SUV made by Japanese automaker Mazda from 2000 to 2011. It was jointly developed with Ford Motor Company and based on the front-wheel drive Mazda 626 platform, which was in turn the basis for the similar Fo ...
electric (front- and four-wheel drive) with a compression ratio of 12.4:1
* Ford Fusion Hybrid/ Mercury Milan Hybrid/ Lincoln MKZ Hybrid electric (front-wheel drive) with a compression ratio of 12.3:1
* Ford Maverick
* Honda Accord Plug-in Hybrid
* Honda Accord Hybrid (front-wheel drive)
*Honda Clarity Plug-In Hybrid
The Honda Clarity is a nameplate used by Honda on alternative fuel vehicles. It was initially used only on hydrogen fuel-cell electric vehicles such as the 2008 Honda FCX Clarity, but in 2017 the nameplate was expanded to include the battery-e ...
* Honda Insight (front-wheel drive)
* Honda Fit (front-wheel drive) some of the 3rd generation engines switch between Atkinson and Otto cycles.
*Hyundai Sonata Hybrid
The Hyundai Sonata is a mid-size car that has been manufactured by Hyundai Motor Company, Hyundai since 1985. The first generation Sonata, which was introduced in 1985, was a Facelift (automotive), facelifted Hyundai Stellar with an engine upgrad ...
(front-wheel drive)
* Hyundai Elantra Atkinson-cycle models
* Hyundai Grandeur hybrid (front-wheel drive)
* Hyundai Ioniq hybrid, plug-in hybrid (front-wheel drive)
* Hyundai Palisade 3.8 L Lambda II V6 GDi
*Infiniti M35h
The Infiniti M is a line of mid-size luxury (executive) cars from the Infiniti luxury division of Nissan. From 2013 (model year 2014) on it has been marketed as the Infiniti Q70, reflecting the company's new naming scheme.
The first iteration wa ...
hybrid (rear-wheel drive)
* Kia Forte 147 hp 2.0 petrol only (front-wheel drive)
* Kia Niro hybrid, plug-in hybrid (front-wheel drive)
*Kia Optima Hybrid
The Kia K5, formerly known as the Kia Optima, is a mid-size car manufactured by Kia since 2000 and marketed globally through various nameplates. First generation cars were mostly marketed as the Optima, although the Kia Magentis name was used i ...
Kia K5 hybrid 500h (front-wheel drive) with a compression ratio of 13:1
* Kia Cadenza Hybrid Kia K7 hybrid 700h (front-wheel drive)
*Kia Telluride
The Kia Telluride is a mid-size crossover SUV with three-row seating manufactured and marketed by Kia since 2019. Positioned above the smaller Sorento, the Telluride was previewed as a concept car in 2016, with the production model debuting in the ...
3.8 L Lambda II V6 GDi
*Kia Seltos
The Kia Seltos ( ko, 기아 셀토스) is a subcompact crossover SUV manufactured by Kia. Introduced in mid-2019, the Seltos is positioned between the smaller Stonic, Soul, or Sonet and the larger Sportage in Kia's global SUV lineup.
The Seltos ...
2.0L (front-wheel drive)
*Lexus CT 200h
The is a hybrid electric vehicle, hybrid electric automobile produced by Lexus, a luxury division of Toyota, as a Luxury vehicle#Premium compact, premium compact hatchback. The CT, consisting of a single model called the CT 200h is a luxury hybr ...
(front-wheel drive)
*Lexus ES 300h
The is a series of mid-size executive cars marketed since 1989 by Lexus, the luxury division of Toyota, across multiple generations, each offering V6 engines and a front-engine, front-wheel-drive layout. The first five generations of the ES used ...
(front-wheel drive)
* Lexus GS 450h hybrid electric (rear-wheel drive) with a compression ratio of 13:1
* Lexus RC F (rear-wheel drive)
*Lexus GS F
The is an executive car sold by Lexus, the premium division (business), division of Toyota. The same car had been launched in 1991 as the Toyota Aristo in Japan. For non-Japanese markets, it was released as the Lexus GS in February 1993. It cont ...
(rear-wheel drive)
*Lexus HS 250h
The Lexus HS (Japanese: レクサス・HS, ''Rekusasu HS'') is a dedicated hybrid vehicle introduced by Lexus as a new compact executive car sedan in 2009. Built on the Toyota New MC platform, it is classified as a compact under Japanese regu ...
(front-wheel drive)
*Lexus IS 200t
The is a compact executive car sold by Lexus, a luxury division of Toyota since 1999. The IS was originally sold under the nameplate in Japan from 1998 (the word ''Altezza'' is Italian for 'height' or 'highness'). The IS was introduced as an e ...
(2016)
* Lexus NX hybrid electric (four-wheel drive)
* Lexus RX 450h hybrid electric (four-wheel drive)
* Lexus UX hybrid electric (four-wheel drive)
* Lexus LC (rear-wheel drive)
*Mazda Mazda6
The Mazda6 (known as the Mazda Atenza in Japan and China, derived from the Italian '' attenzione'') is a mid-size sedan produced by Mazda since 2002, replacing the long-produced Capella/626.
The Mazda6 was marketed as the first example of the co ...
(2013 for the 2014 model year)
* Mercedes ML450 Hybrid (four-wheel drive) electric
* Mercedes S400 Blue Hybrid (rear-wheel drive) electric
*Mitsubishi Outlander PHEV
The is a mid-size
crossover SUV manufactured by Japanese
automaker Mitsubishi Motors. It was originally known as the when it was introduced in Japan in 2001.
The original Airtrek name was chosen to "describe the vehicle's ability to transpo ...
(2018 for the 2019 model year, plug-in hybrid four-wheel drive)
* Subaru Crosstrek Hybrid (2018 for the 2019 model year, all-wheel drive)
* Toyota Camry Hybrid electric (front-wheel drive) with a compression ratio of 12.5:1
* Toyota Avalon Hybrid (front wheel drive)
* Toyota Highlander Hybrid (2011 and newer)
* Toyota Prius hybrid electric (front-wheel drive) with a (purely geometric) compression ratio of 13.0:1
* Toyota Yaris Hybrid (front-wheel drive) with a compression ratio of 13.4:1
* Toyota Auris Hybrid (front-wheel drive)
*Toyota Tacoma
The Toyota Tacoma is a pickup truck manufactured by the Japanese automobile manufacturer Toyota since 1995. The first-generation Tacoma (model years 1995 through 2004) was classified as a compact pickup. The second generation (model years 2005 t ...
V6 (beginning in 2015 for the 2016 model year)
*Toyota RAV4 Hybrid
The is a compact crossover SUV produced by the Japanese automobile manufacturer Toyota. Considered the first ever compact crossover SUV, it made its debut in Japan and Europe in 1994, and in North America in 1995, being launched in January 19 ...
(beginning in 2015 for the 2016 model year)
* Toyota Sienna (2016 for the 2017 model year, hybrid beginning for 2021 model year)
* Toyota Venza (hybrid beginning for 2021 model year)
* Toyota C-HR Hybrid (2016 - present)
* Toyota Yaris Cross Hybrid (2021 - present)
Patents
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. There is also a reference to an 1886 Atkinson patent (US 336505), which describes an opposed-piston gas engine. The British patent for the "Utilite'" is from 1892 (#2492).See also
* History of the internal combustion engine * Variable valve timing * Variable valve liftReferences
External links
Comparison of Prime Movers Suitable for USMC Expeditionary Power Sources
Oak Ridge National Laboratory
Libralato Engines
- developing a rotary Atkinson cycle engine
Rotary Atkinson cycle engine
- gives details of this engine as well as comparisons with conventional and Wankel engines
The Prius's Not So Secret Gas-Mileage Secrets
- how the Prius uses the Atkinson cycle to get better results than an Otto cycle engine
James Atkinson at Find A Grave
- personal details {{Thermodynamic cycles, state=uncollapsed Thermodynamic cycles Hybrid vehicles