Cómo funcionan los motores de válvula de manguito

Durante la Segunda Guerra Mundial, los ingenieros del régimen nazi idearon algunas de las mejores y más avanzadas armas aéreas de la época. Un avión de combate alemán, el Focke-Wulf Fw 190 , durante un tiempo superó cualquier cosa que los Aliados pudieran poner en el aire.

Afortunadamente para los Aliados, la ingeniería de su lado finalmente hizo girar el péndulo de la superioridad aérea a su favor. Un motor resistente y poco convencional del que muchas personas probablemente nunca hayan oído hablar ayudó a neutralizar al Fw 190 y al resto de la Luftwaffe. A su manera, un motor ayudó a impulsar a los aliados a la victoria [fuente: Rickard ].

El motor de válvula de manguito, que se ha utilizado tanto en automóviles como en aviones, impulsó veloces cazas británicos como el Hawker Typhoon y el Hawker Tempest. Con su potencia bruta , ayudaron a los Aliados a controlar los cielos, brindar apoyo aéreo a las fuerzas terrestres y finalmente ganar la guerra.

Pero, ¿qué es exactamente un motor de válvula de manguito y cuál es el nombre gracioso? ¿Y por qué no vemos ni escuchamos mucho sobre ellos hoy?

El motor recibe su nombre de la manga de metal de paredes delgadas que se desliza hacia arriba y hacia abajo dentro de cada cilindro durante el proceso de combustión. Por lo general, los orificios en el manguito y en el cilindro que lo contiene se alinean a intervalos predecibles para expulsar los gases de escape y aspirar aire fresco.

A pesar de su honorable historial de servicios armados, la compleja configuración de la válvula de manguito perdió frente a lo que usamos hoy en los motores de combustión interna, las válvulas de taqué. En los aviones, por supuesto, las plantas motrices impulsadas por pistones de todo tipo dieron paso en gran medida a los motores a reacción.

Pero espera, no descartes la válvula de manguito como una reliquia histórica inútil todavía.

Al menos una empresa está tratando de volver a poner en funcionamiento el venerable motor de válvula de manguito, pero con algunos giros modernos.

En las próximas páginas, echaremos un vistazo a lo que hace girar el motor de válvula de manguito. También examinaremos por qué cayó en desgracia, junto con las razones por las que se llama ahora, más de un siglo después de su invención, para servir en un tipo diferente de "lucha".

1. Tecnología de motor de válvula de manguito
2. Válvulas de manguito por vía terrestre: uso en motores de automóviles
3. Válvulas de manguito por aire: uso en motores de aviones
4. ¿Que sigue?

Al llegar como lo hizo durante el apogeo de la era industrial, el motor de válvula de manguito parece un artilugio que se sentiría como en casa en una novela steampunk . Los ingenieros de hoy en día se maravillan con su ingenio. Y cloquear en su alta complejidad.

Así que ahí, has sido advertido. En realidad, es algo muy hermoso una vez que entiendes cómo funcionan todas esas piezas juntas. Ahora arremangarse, porque estamos a punto de ensuciarnos con el funcionamiento interno de un motor de válvula de manga.

Este motor tiene tantas cosas que casi desafían la descripción. Pero lo intentaremos. Los motores de válvula de manguito, al igual que sus contrapartes de válvula de empujador, pueden venir en muchas configuraciones diferentes. Uno de esos arreglos, los motores de válvula de manguito radial que se usan en los aviones, se parecen un poco a lo que podrías obtener si un robot Rock 'Em Sock 'Em tuviera un bebé con un centinela "calamardo" de "The Matrix".

Para comprender qué es y qué hace un motor de válvulas de manguito, podría ser útil entender primero qué no es. No es, ante todo, el sistema popular con el que la mayoría de nosotros estamos familiarizados, un motor de válvula de asiento. Las válvulas de asiento son el estándar de facto en los motores de combustión interna actuales. Con ellos, las válvulas en forma de hongo bajo la tensión de los resortes se abren y cierran rítmicamente para controlar la entrada y salida de combustible, aire y gases de escape en el cilindro.

Una válvula de manguito, por otro lado, utiliza un manguito deslizante, a veces giratorio, para controlar la cantidad de aire y combustible que se detona con cada carrera de compresión. La premisa básica de encender combustible y aire para impulsar un conjunto de pistones y hacer girar un cigüeñal es la misma que con otros motores de combustión interna.

Aquí hay otra característica distintiva de las válvulas de manguito. En los diseños en los que el manguito gira, los puertos que se cortan en él se alinean con los puertos de admisión o los puertos de escape en el cilindro, según la parte de la carrera que se esté realizando. Un pistón se mueve hacia arriba y hacia abajo dentro de cada manguito, incluso cuando el manguito se desliza hacia adelante y hacia atrás. El movimiento de la manga es impulsado por engranajes conectados al cigüeñal.

¿Todavía te rascas la cabeza sobre qué sucede exactamente? Aquí están los pasos:

Now multiply that by several cylinders and toss in a crankshaft for them to rotate, and you've got yourself a sleeve-valve engine!

If it sounds complicated, well, that's because it is. One of the main knocks against these engines was that they were so complex. It makes a bit more sense, though, when you see the entire process in action. Check out the video on this page to better visualize it.

Get Your Swirl On: Sleeve Valves and Volumetric Efficiency

So why would anyone want to monkey around with an engine this complicated? After all, they were notoriously thirsty for lubricating oil; and they didn't take kindly to impurities such as grit. The answer is that they offer the advantage of volumetric efficiency. In other words, they're much better than regular engines at getting air into and out of the combustion chamber. Also, the arrangement of the ports provide better swirl characteristics. That's engineer-ese for, they create turbulent air, causing the air and fuel mix to burn more efficiently [source: Raymond].

Indiana-born Charles Yale Knight purchased a three-wheeled Knox automobile around 1901 so that he could report and publish his farm journal in the U.S. Midwest. But he found the clatter created by the car's valves to be a serious pain in the ears. So he did what any self-respecting entrepreneur with a background in industrial machinery would do: He set out to build a better engine himself.

With a wealthy backer's support, he developed and extensively tested prototypes. By 1906, he had made enough progress to reveal his 4-cylinder, 40-horsepower "Silent Knight" car at the Chicago Auto Show.

The Knight engine featured not one, but two sleeves per cylinder, with the inner sleeve sliding within the outer. The piston, in turn, slid inside the inner sleeve. The Knight, true to its moniker, was impressively quiet. Even though the Knight engine proved superior to the loud and fragile poppet valves of its day, U.S. automakers gave it the cold shoulder, initially.

Knight and his financial benefactor L.B. Kilbourne fared considerably better overseas. After some refinements to the design, the Knight engine found its way onto Daimler cars in England (not to be confused with Daimler-Benz).

The Silent Knight was a hit, and soon other manufacturers wanted in on the sleeve valve action -- including automakers in the United States. Willys cars and light trucks, Daimler, and Mercedes-Benz, among others, employed the Knight sleeve-valve engine [source: Wells].

However, by the 1920s, sleeve valve design had advanced beyond Knight's sleeve-within-a-sleeve configuration. Single-sleeve designs, including the Burt-McCollum, were lighter, less complex and less costly to build, and therefore preferable to manufacturers. With further modification from engine manufacturers such as Bristol and Rolls-Royce, they would even take to the sky.

Harry R. Ricardo (later "Sir" Harry Ricardo), born in London in 1885, didn't wait until college to begin his engineering studies. He observed and absorbed at the knee of a local machinist as a young boy, and would go home from the machinist's shop to apply his new knowledge in building engines . He would later say:

"As a child, I was always fascinated by engines and mechanical motions generally, and above all, by the great mystery as to how such things were actually made...looking back, I think I learnt more of actual value from these early and very crude attempts at design and manufacture than from anything else" [source: University of Cambridge].

Ricardo, in his working engineer adulthood, was an incurable overachiever. In addition to tweaking the engines on tanks that helped break the stalemate of World War I, he led ground-breaking research into assigning octane ratings to different grades of fuel.

Perhaps his most notable contribution in the World War II years was his work on making the sleeve-valve engine better.

Ricardo theorized in the 1920s that a sleeve-valve airplane engine could generate greater horsepower than a comparable tappet-valved engine because it could generate a higher compression ratio.

It so turned out that by 1941, British aircraft including the mainstay Supermarine Spitfire fighter plane, were taking a pounding from Germany's superior Focke-Wulf Fw 190 . The Fw 190s also launched ground attack raids on Allied installations with near-impunity, since nothing could catch them at low altitude after they dropped their bombs.

The sleeve valve-engined Hawker Typhoon, entering service in 1942, changed that. Propelled by a 2,180-horsepower Napier Sabre engine, the "Tiffy's" extra get-up-and-go meant it could not only shoot down quick Luftwaffe interlopers, but it could carry bombs as well. Later in the war, bomb- and rocket-equipped Typhoons would prove pivotal in supporting Allied ground forces as they tightened the noose on the Nazis and ended the war in Europe [source: Rickard].

Despite the sleeve-valve engine's exemplary military record, the writing was on the wall: jet engines would dominate commercial and military aviation from the postwar years forward.

The legacy of Knight, Ricardo and others would not completely go away -- engine enthusiasts would memorialize the sleeve-valve engine with home-built models and on Web sites in the decades to follow. Some flying model planes use miniature sleeve-valve engines. And it's conceivable the technology could experience a resurgence in some of the world's largest and fastest-growing automotive markets.

So, was the sleeve-valve engine an evolutionary dead end, as far as the advance of internal combustion ?

Let's put it this way. Just like Hollywood likes to recycle old concepts and put a fresh spin on them when it's running low on new ideas, so does the auto industry. Electric cars , you may recall, were a big deal before (ironically) the electric starter made internal combustion cars highly practical. Electrics pretty much vanished from mainstream motoring until environmental concerns brought them back from the grave near the turn of the century.

And so, similarly, could the case be unfolding with the slumbering sleeve-valve engine. As the saying goes, "what's old is new again."

San Carlos, Calif.-based Pinnacle Technologies is counting on pent-up demand for clean, cheap transportation in Asia to snap up its modern interpretation of the sleeve valve. A new engine is based on what the company describes as a four-stroke, spark-ignited (SI), opposed-piston, sleeve-valve architecture.

Pinnacle founder Monty Cleeves says his patented engine can yield a 30- to 50-percent efficiency improvement over current internal combustion engines [source: Pinnacle Engines].

"This engine technology provides the fuel economy and CO2 emissions of a hybrid at a price that the whole world can afford," Cleeves said in a company-issued statement

Pinnacle says it isn't worried about electric vehicles making its technology obsolete any time soon. Instead, it believes there's a big opportunity to serve rapidly growing markets such as India and China. They and other developing countries want to curb greenhouse gas emissions while improving their citizens' standard of living, through motor vehicle ownership. Since electric vehicles and hybrids still carry a significant price premium, Pinnacle says its re-envisioned sleeve-valve is a good "bridge technology" until electrics become more affordable for everyone.

Pinnacle, which has received several million dollars in venture capital, said it was pursuing a licensing agreement with an Asian auto manufacturer and it expected production to begin in 2013.

Author's Note: How Sleeve-valve Engines Work

As a big military aircraft geek, I had heard of sleeve-valve engines prior to this assignment. But that was about the extent of it. Given their footnote-in-history status, I had always thought of them merely in the abstract. Unlike a poppet valve engine that you can study in your own driveway, these "sleeve-valve things" were to me just a forgotten, if quaint, technology, like steam locomotives. So when I tapped the power of the Interwebs to see them in action, I was instantly struck with both awe and admiration. How did folks 100 years ago figure out all the necessary angles, tolerances, weight balances and more to bring these incredibly complex machines to life? The fact that entrepreneurs today are looking to breathe new life into the concept speaks volumes about those original pioneers' genius and vision. One could argue that the original, twentieth-century sleeve-valve engines were "over-engineered" -- that is, they were too complicated for their own good. Or it could simply be that, lacking the advances in materials science and the precision of computer-aided design that we enjoy today, they were merely ahead of their time.

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