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Flat-six engine

Continental O-470-13A air-cooled aircraft engine A flat-six engine (also known as a horizontally opposed-six engine ) is a six-cylinder piston engine with three cylinders on eac...

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Continental O-470-13A air-cooled aircraft engine

A flat-six engine (also known as a horizontally opposed-six engine) is a six-cylinderpiston engine with three cylinders on each side of a central crankshaft. The most common type of flat-six engine is the boxer-six engine, where each pair of opposed cylinders moves inwards and outwards at the same time. An alternative configuration for flat engines is a 180-degree V engine, where both cylinders move to the right then the left at the same time.

The advantages of the flat-six layout are good engine balance (for reduced vibration), a low center of gravity, short length (compared with an inline-six engine) and being well suited to air-cooling. The disadvantages are a large width (which can limit the maximum steering angle when used in a front-engined car), a large intake manifold being required when a central carburetor is used, and duplication of the inlet and outlet connections for water-cooled engines.[1]

The first production flat-six engine was in the 1904 Wilson-Pilcher 18/24 HP car. The most notable use of flat-six engines is the Porsche 911 sports car, which has used flat-six engines continuously since 1963. Several other car manufacturers, including Subaru, have produced flat-six engines at times. Flat-six engines have also occasionally been used in motorcycles, and commonly in general aviation aircraft, along with the flat-four engine.

Engine balance

A boxer-style flat-six engine is able to have perfect primary and secondary balance. As in other six-cylinder engines, the overlapping of the power strokes of the different cylinders (with a firing interval of 120 degrees in a four-stroke engine) reduces the pulsating of the power delivery relative to that of similar engines with fewer cylinders.

En una configuración bóxer , un motor de seis cilindros opuestos no presenta un par de balanceo . La simetría de la disposición, en la que una bancada de tres cilindros es simétrica a la otra, implica que no existe una fuerza neta de ningún par de cilindros simétricos a lo largo del eje de movimiento de los pistones. Por lo tanto, no solo no hay un efecto alternativo primario o secundario neto, sino que tampoco existe una fuerza de giro neta (momento) que intente hacer girar el motor hacia adelante y hacia atrás sobre sus soportes. (En la práctica, el momento no es exactamente cero, ya que cada par de cilindros está ligeramente desplazado con respecto al otro; de lo contrario, chocarían en el cigüeñal). En este sentido, el motor bóxer de seis cilindros es igual que un motor bóxer de cuatro cilindros opuestos, que tampoco experimenta ningún par de balanceo. [ 2 ]

Estas características dan como resultado bajas vibraciones en los motores de seis cilindros opuestos (al igual que en los motores de seis cilindros en línea ), especialmente si se comparan con los desequilibrios presentes en los motores V6 con un ángulo de bancada de 90 grados.

Uso en aeronaves

Motor de aviación refrigerado por aire Franklin O-335 (1945-1975)

Entre los primeros motores de seis cilindros opuestos se encuentran el Franklin O-265, cuya producción comenzó en 1940, y el Lycoming O-435 , cuya producción se inició en 1942. Varios fabricantes utilizan la letra O en los códigos de sus modelos de motores de disposición plana para indicar la configuración de cilindros opuestos. El Franklin O-335 se utilizó en el helicóptero ligero Bell 47 .

Tras la Segunda Guerra Mundial, los motores planos sustituyeron en gran medida a los motores radiales, históricamente más populares, en las aeronaves pequeñas, debido a su menor coste de fabricación. Su menor superficie frontal, en comparación con un motor radial, también reduce la resistencia aerodinámica, si bien el diseño radial ofrece una mejor refrigeración.

Algunas aeronaves han utilizado motores de seis cilindros opuestos diseñados originalmente para automóviles. El motor Porsche PFM 3200 , producido entre 1985 y 1991, se basó en el motor utilizado en el automóvil deportivo Porsche 911. Varios ejemplares del avión monoplano de construcción casera Pietenpol Air Camper han utilizado el motor refrigerado por aire del automóvil compacto Chevrolet Corvair . [ 3 ] En comparación con los motores utilizados en automóviles, los motores de seis cilindros opuestos utilizados en helicópteros tienen grandes cilindradas y bajas revoluciones, lo que produce más par motor y menos potencia. [ 4 ]

A notable recent flat-six aero-engine is the 4-litre side-valveBelgianD-Motor LF39, a modular variant of the 2.7-litre flat-fourD-Motor LF26. Although the side-valve format has long been abandoned for most automotive applications because its combustion chamber is a bar to high engine rpm, the massively over-square (1.295:1) D-Motor is a very simple, low-revving, compact, reliable lightweight aero-engine (without the heavy (and bulky) complication of ohv valve-gear).[5]

Use in automobiles

Porsche

1966 Porsche 911

The flat-six engine is often associated with the Porsche 911, a rear-engined sports car which has used flat-six engines exclusively since 1963. The engines were air-cooled until 1999, when Porsche started using water-cooled engines.[6]

Other Porsche models that use flat-six engines are the 1970–1972 Porsche 914/6 (mid-engine), the 1986–1993 Porsche 959 (rear-engine), and the 1996–2021 Porsche Boxster/Cayman (mid-engine).

Other manufacturers

1904 Wilson-Pilcher engine
2007–2019 Subaru EZ36 engine

The first car to use a flat-six engine was the 1904–1907 Wilson-Pilcher 18/24 HP,[7] which used an engine based on a flat-four engine with two cylinders added. The Wilson-Pilcher was a front-engined car with the crankshaft in-line with the chassis and the cylinders between the chassis rails. Reports on this car quote it as being "remarkably silent and smooth running" and "almost total absence of vibration".[8]

Two American manufacturers briefly produced cars with flat-six engines—the 1948 Tucker 48 (water-cooled, based on the Franklin O-335) and the 1960–1969 Chevrolet Corvair (air-cooled).[9] Both are rear-engined cars with rear-wheel drive. Chevrolet produced over 1.8 million Corvairs of various types and utilized a turbocharger on some models; one of the first uses of a turbocharger on a mass-produced automobile.

Japanese manufacturer Subaru produced water-cooled flat-6 engines from 1988–1996 and 2000–2019.[10] Their first flat-6 engine, the Subaru ER27, was added to the model range of the Subaru XT coupe. In 1991, the Subaru EG33 engine was used in the Subaru Alcyone SVX, the replacement for the Subaru XT.[11] Following a hiatus of flat-6 engine production for four years, the Subaru EZ30 engine was introduced in the 2000 Subaru Legacy/Outback. The Subaru EZ36 engine was introduced in 2007 and was produced until 2019. All engines were used in front-engine cars with all-wheel drive, plus the XT and Alcyone SVX were also available with front-wheel drive.

Use in motorcycles

1997–2004 Honda Valkyrie engine

Most motorcycles use engines with four or fewer cylinders, however the Honda Gold Wing touring motorcycle has used a water-cooled flat-six engine since 1988.[12] Initially, the engine had a displacement of 1.5 L (92 cu in), until it was enlarged to 1.8 L (110 cu in) in 2001.[13]:208

The Honda Valkyrie F6C (1997–2003) was a cruiser based on the GL1500 Gold Wing.[13]:198,218 The limited edition 2004 Valkyrie Rune was based on the GL1800.[13]:218,220

See also

References

  1. ↑Nunney, M J (2007). Light and Heavy Vehicle Technology. Butterworth-Heinemann. p. 13. ISBN 978-0-7506-8037-0. Retrieved 24 September 2019.
  2. ↑"The Physics of: Engine Cylinder-Bank Angles". www.caranddriver.com. Retrieved 9 September 2019.
  3. ↑"Pietenpol Official Pietenpol Air Camper Family Website". community.pressenter.net. Pietenpol Aircraft Company. Archived from the original on April 23, 2017. Retrieved May 6, 2017. As the years passed, Bernard Pietenpol taught himself how to repair televisions and radios. By 1960, Chevrolet introduced the six cylinder air-cooled Chevrolet Corvair. This would be the last engine Bernard would experiment with in powering his Air Camper. In 1966 Bernard completed his first Corvair powered Air Camper, then another in 1970 which was dubbed "the Last Original".
  4. ↑"The Lycoming O-540 Engine and Why We Use It". www.hieldsaviation.co.uk. 18 November 2015. Archived from the original on 19 September 2019. Retrieved 10 September 2019.
  5. ↑Note: A low-revving engine is eminently suitable to drive a propeller, which is typically most effective at about 2,000 rpm. If a valve in a side-valve engine should stick open, it cannot hit the piston and cause engine failure; the engine will continue with just that cylinder inoperative. This is an important safety feature for aero-engines.
  6. ↑"Flat Sixy: The Evolution of Porsche 911 Engine Size, Technology, and Output in the U.S."www.caranddriver.com. 13 December 2013. Retrieved 21 September 2019.
  7. ↑"7 Flat-Six-Powered Vehicles That Aren't Porsches". www.carthrottle.com. Retrieved 21 September 2019.
  8. ↑"The Wilson-Pilcher Petrol Cars", The Automotor Journal, April 16th, 1904, pp. 463-468
  9. ↑"Corvair History". www.corvair.org. Archived from the original on 22 June 2014.
  10. ↑"Flat-6 Club: 1993 Subaru Impreza w/ Legacy 6-Cyl". www.dailyturismo.com. Archived from the original on 21 September 2019. Retrieved 21 September 2019.
  11. ↑"Subaru history in the USA: the models, the changes". www.cars101.com. Retrieved 23 September 2019.
  12. ↑"Touring". www.honda.com. Retrieved 23 September 2019.
  13. 123Mitchel, Doug (2005). Honda Motorcycles: Everything You Need to Know About Every Honda Motorcycle Ever Built. Krause Publications. ISBN 9780873499668.