Wankel engine

Московский  государственный агроинжинерный университет  имени В.П. Горячкина 

Кафедра: Иностранного языка

Курсовая  работа

По  теме: «Wankel engine » 
 
 
 
 
 
 
 

Москва 2009 

Wankel engine

The Wankel engine is a type of internal combustion engine which uses a rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that is similar in shape to a Reuleaux triangle. This design delivers smooth high-rpm power, from a compact size. Since its introduction the engine has been commonly referred to as the rotary engine, though this name is also applied to several completely different designs.

The engine was invented by German engineer Felix Wankel. He began its development in the early 1950s at NSU Motorenwerke AG (NSU) before completing a working, running prototype in 1957. NSU then licensed the concept to companies around the world, who have continued to improve the design.

Because of their compact design, Wankel rotary engines have been installed in a variety of vehicles and devices such as automobiles including racing cars, along with aircraft, go-karts, personal water craft, chain saws, and auxiliary power units. The most extensive automotive use of the Wankel engine has been by the Japanese company Mazda.

History

In 1951, the German engineer Felix Wankel began development of the engine at NSU Motorenwerke AG, where he first conceived his rotary engine in 1954 (DKM 54, Drehkolbenmotor). The so-called KKM 57 (the Wankel rotary engine, Kreiskolbenmotor) was constructed by NSU engineer Hanns Dieter Paschke in 1957 without the knowledge of Felix Wankel, who remarked "you've turned my race horse into a plow mare".[1] The first working prototype DKM 54 was running on February 1, 1957 at the NSU research and development department Versuchsabteilung TX.[2]Considerable effort went into designing rotary engines in the 1950s and 1960s. They were of particular interest because they were smooth and quiet running, and because of the reliability resulting from their simplicity.

In the United States, in 1959 under license from NSU, Curtiss-Wright pioneered minor improvements in the basic engine design. In Britain, in the 1960s, Rolls Royce Motor Car Division at Crewe, Cheshire, pioneered a two-stage diesel version of the Wankel engine.[3]Also in Britain, Norton Motorcycles developed a Wankel rotary engine for motorcycles, based in the Sachs air cooled Wankel that powered the DKW/Hercules W-2000 motorbyke, which was included in their Commander and F1; Suzuki also made a production motorcycle with a Wankel engine, the RE-5, where they used ferrotic alloy apex seals and an NSU rotor in a successful attempt to prolong engine's life. In 1971 and 1972 Arctic Cat produced snowmobiles powered by 303 cc Wankel rotary engines manufactured by Sachs in Germany. Deere & Company designed a version that was capable of using a variety of fuels. The design was proposed as the power source for United States Marine Corps combat vehicles and other equipment in the late 1980s.[4]After occasional use in automobiles, for instance by NSU with their Ro 80 model,[5] Citroën with the M35, and GS Birotor using engines produced by Comotor, as well as abortive attempts by General Motors and Mercedes-Benz to design Wankel-engine automobiles, the most extensive automotive use of the Wankel engine has been by the Japanese company Mazda.

углAfter years of development, Mazda's first Wankel engine car was the 1967 Cosmo. The company followed with a number of Wankel ("rotary" in the company's terminology) vehicles, including a bus and a pickup truck. Customers often cited the cars' smoothness of operation. However, Mazda chose a method to comply with hydrocarbon emission standards that, while less expensive to produce, increased fuel consumption, just before a sharp rise in fuel prices. Mazda later abandoned the Wankel in most of their automotive designs, but continued using it in their RX-7 sports car until August 2002 (RX-7 importation for Canada ceased with only the 1993 year being sold. The USA ended with the 1994 model year with remaining unsold stock being carried over as the '1995' year.). The company normally used two-rotor designs, but the 1991 Eunos Cosmo used a twin-turbo three-rotor engine. In 2003, Mazda introduced the Renesis engine with the RX-8. The Renesis engine relocated the ports for exhaust and intake from the periphery of the rotary housing to the sides, allowing for larger overall ports, better airflow, and further power gains.Early Wankel engines had also side intake and exhaust ports, but the concept was abandoned because of carbon buildup in ports. The Renesis engine solved the problem by using a keystone scratching side seal. (Masaki Ohkubo et al., SAE paper 2004-01-1790) The Renesis is capable of delivering 238 hp (177 kW) with better fuel economy, reliability, and environmental friendliness than previous Mazda rotary engines,[6] all from its 1.3 L displacement.

In 1961, the Soviet research organization of NATI, NAMI and VNIImotoprom started experimental development, and created experimental engines with different technologies.[7]Soviet automobile manufacturer AvtoVAZ also experimented with the use of Wankel engines in cars but without the benefit of a license.[8] In 1974 they created a special engine design bureau, which in 1978 designed an engine designated as VAZ-311. In 1980, the company started delivering Wankel-powered VAZ-2106s (VAZ-411 engine with two-rotors) and Ladas, mostly to security services, of which about 200 were made.[9][10] The next models were the VAZ-4132 and VAZ-415. Aviadvigatel, the Soviet aircraft engine design bureau, is known to have produced Wankel engines with electronic injection for aircraft and helicopters, though little specific information has surfaced.Although many manufacturers licensed the design, and Mercedes-Benz used it for their C111 concept car, only Mazda has produced Wankel engines in large numbers. American Motors (AMC) was so convinced "...that the rotary engine will play an important role as a powerplant for cars and trucks of the future...", according to Chairman Roy D. Chapin Jr., that the smallest U.S. automaker signed an agreement in February 1973, after a year's negotiations, to build Wankels for both passenger cars and Jeeps, as well as the right to sell any rotary engines it produces to other companies. It even designed the unique Pacer around the engine, even though by then, AMC had decided to buy the Wankel engines from GM instead of building them itself. However, GM's engines had not reached production when the Pacer was to hit the showrooms. Part of the demise of this feature was the 1973 oil crisis with rising fuel prices, and also concerns about proposed US emission standards legislation. General Motors' Wankel did not comply with those emission standards, so in 1974 the company canceled its development, although GM claimed having solved the fuel consumption problem; unfortunately, they never published the results of their research. This meant the Pacer had to be reconfigured to house AMC's venerable AMC Straight-6 engine with rear-wheel drive.

Design

In the Wankel engine, the four strokes of a typical Otto cycle occur in the space between a three-sided symmetric rotor and the inside of a housing. In the basic single-rotor Wankel engine, the oval-like epitrochoid-shaped housing surrounds a rotor which is triangular with bow-shaped flanks (often confused with a Reuleaux triangle), a three-pointed curve of constant width, but with the bulge in the middle of each side a bit more flattened. From a theoretical perspective, the chosen shape of the rotor between the fixed apexes is basically the result of a minimization of the volume of the geometric combustion chamber and a maximization of the compression ratio, respectively. Thus, the symmetric curve connecting two arbitrary apexes of the rotor is maximized in the direction of the inner housing shape with the constraint not to touch the housing at any angle of rotation (an arc is not a solution of this optimization problem).

The central drive shaft, called the eccentric shaft or E-shaft, passes through the center of the rotor and is supported by fixed bearings. The rotors ride on eccentrics (analogous to cranks) integral with the eccentric shaft (analogous to a crankshaft). The rotors both rotate around the eccentrics and make orbital revolutions around the eccentric shaft. Seals at the corners of the rotor seal against the periphery of the housing, dividing it into three moving combustion chambers. The rotation of each rotor on its own axis is caused and controlled by a pair of synchronizing gears. A fixed gear mounted on one side of the rotor housing engages a ring gear attached to the rotor and ensures the rotor moves exactly 1/3 turn for each turn of the eccentric shaft. The power output of the engine is not transmitted through the synchronizing gears. The force of gas pressure on the rotor (to a first approximation) goes directly to the center of the eccentric, part of the output shaft.

The best way to visualize the action of the engine in the animation at left is to look not at the rotor itself, but the cavity created between it and the housing. The Wankel engine is actually a variable-volume progressing-cavity system. Thus there are 3 cavities per housing, all repeating the same cycle.

As the rotor rotates and  revolves, each side of the rotor gets closer and farther from the wall of the housing, compressing and expanding the combustion chamber similarly to the strokes of a piston in a reciprocating engine. The power vector of the combustion stage goes through the center of the offset lobe.

While a four-stroke piston engine makes one combustion stroke per cylinder for every two rotations of the crankshaft , each combustion chamber in the Wankel generates one combustion stroke per each driveshaft rotation, i.e. one power stroke per rotor orbital revolution and three power strokes per rotor rotation. Thus, power output of a Wankel engine is generally higher than that of a four-stroke piston engine of similar engine displacement

Wankel engines also generally have a much higher redline than a reciprocating engine of similar power output, in part because the smoothness inherent in circular motion, but especially because they do not have highly stressed parts such as a crankshaft or connecting rods. Eccentric shafts do not have the stress-raising internal corners of crankshafts. The redline of a rotary engine is limited by wear of the synchronizing gears. Hardened steel gears are used for extended operation above 7000 or 8000 rpm. Mazda Wankel engines in auto racing are operated above 10,000 rpm. In aircraft they are used conservatively, up to 6500 or 7500 rpm. However, as gas pressure participates in seal efficiency, running a Wankel engine at high r.p.m. under no load conditions can result in the engine destruction.

Disadvantages

The most important problem considers a condition of sealants. The area of a stain of contact is very insignificant, and pressure difference very high. A consequence of it, unsoluble for engines Vankelja, contradictions are high leaks between separate chambers and, as consequence, falling of efficiency and toxicity of an exhaust.Although in two dimensions the seal system of a Wankel looks to be even simpler than that of a corresponding multi-cylinder piston engine, in three dimensions the opposite is true. As well as the rotor apex seals evident in the conceptual diagram, the rotor must also seal against the chamber ends.

Other feature of engines Wankel is its propensity to an overheat. The combustion chamber has  the form, that is at small volume at it rather big area. At temperature of burning of a working mix the basic losses of energy go through radiation. Intensity of radiation is proportional to the fourth degree of temperature, thus the ideal form of the chamber of combustion - spherical. Radiant energy not only it is useless leaves the combustion chamber, but also leads to an overheat of the working cylinder. These losses not only reduce efficiency of transformation of chemical energy in mechanical, but also cause problems with ignition of a working mix, therefore in an engine design often provide 2 candles.

Compared to four stroke piston engines, the time available for fuel to be port injected into a Wankel engine is significantly shorter, due to the way the three chambers rotate. The fuel-air mixture cannot be pre-stored as there is no intake valve. Also the Wankel engine, compared to a piston engine, has 50% longer stroke duration. The four Otto cycles last 1080° for a Wankel engine versus 720° for a four stroke reciprocating piston engine.

There are various methods of calculating the engine displacement of a Wankel; the Japanese regulations calculating displacements for engine ratings on the basis of the volume displacement of one rotor face only. This is widely accepted as the standard method of calculating the displacement of a rotary, however comparing a piston engine to a Wankel rotary using this displacement convention is flawed and results in large imbalances in specific output in favor of the Wankel motor. Many believe this is for marketing purposes on Mazda's part.

For comparison purposes between a Wankel Rotary engine and a piston engine, displacement (and thus power output) can more accurately be compared on a displacement per revolution (of the eccentric shaft) basis. This dictates that a two rotor Wankel displacing 654 cc per face will have a displacement of 1.3 liters per every rotation of the eccentric shaft and 2.6 liters after two revolutions . This is directly comparable to a 2.6-liter piston engine with an even number of cylinders in a conventional firing order which will also displace 1.3 liters through its power stroke after one revolution of the crankshaft, and 2.6 liters through its power strokes after two revolutions of the crankshaft. However, a Wankel Rotary engine is still a 4-stroke engine and pumping losses from non-power strokes still apply. But the absence of throttling valves and a 50% longer stroke duration result in a significantly lower pumping loss compared against a four stroke reciprocating piston engine. Measuring a Wankel rotary engine in this way more accurately explains its specific output numbers, as the volume of its air fuel mixture put through a complete power stroke per revolution is directly responsible for torque and thus horsepower produced.

All Mazda-made Wankel rotaries, including the new Renesis found in the RX8, burn a small quantity of oil by design; it is metered into the combustion chamber in order to preserve the apex seals. Owners must periodically add small amounts of oil, marginally increasing running costs-though it is still reasonable and comparable in some instances when compared to many reciprocating piston engines.

For the account of absence of transformation of back and forth motion in rotary, engine wankel is capable to maintain much bigger turns, but with smaller vibrations, in comparison with traditional engines. Rotorno-piston engines possess higher capacity at small volume of the chamber of combustion, the design of the engine is rather small and contains less details. The small sizes improve controllability, facilitate an optimum arrangement of transmission  and allow to make the car more spacious for the driver and passengers.

Двигатель Wankel

Двигатель Wankel - тип двигателя внутреннего сгорания, имеет круговое устроиство, чтобы преобразовать давление во вращающееся движение вместо того, чтобы использовать возвратно-поступательное  движение поршня. Его четырехтактный цикл проходит между  внутренней частью кожуха овальной-формы и ротором, который подобен  треугольнику. Это позволяет развивать высокую мощность при компактном размере. Начиная с его разработки двигатель обычно упоминался как ротационная машина, хотя это название также применено к нескольким другим проектам.

Двигатель был  изобретен немецким инженером Феликсом Ванкель. Он начал его разработку в начале 1950-ых в NSU Motorenwerke AG (NSU) Прежде, чем закончить работу был создан опытный образец в 1957, NSU лицензировали эту концепцию по всему миру, и продолжили улучшать проект.

Из-за их компактного  проекта ротационные машины Wankel были установлены во множестве транспортных средств и устройств, таких как автомобили, включая гоночные автомобили, наряду с самолетом, картами, личным водным транспортом, цепными пилами, и вспомогательными блоками питания. Самой большой автомобильной компанией использующей двигатели Wankel была японской компанией Мазда.

История

В 1951, немецкий инженер  Феликс Ванкель начал разработку двигателя в NSU Motorenwerke AG, где он задумывал свой роторный двигатель в 1954 (DKM 54, Drehkolbenmotor). Так называемый KKM 57 (роторный двигатель Wankel, Kreiskolbenmotor) был построен инженером Hanns Дитером Paschke NSU в 1957 без Феликса Ванкеля, который отметил, что "Вы превратили мою гоночную лошадиную силу в кобылу с плугом".  первый рабочий опытный образец DKM 54 запустили 1 февраля 1957 в научно-исследовательском отделе NSU Versuchsabteilung TX.

Значительные  силы пошли на проектирование роторных двигателей в 1950-ых и 1960-ых. Они были особенно интересны, потому что они были плавны и тихие  в работе, и из-за надежности и простоты.

В Соединенных  Штатах, в 1959 согласно лицензии от NSU, Curtiss-мастер вел незначительные усовершенствования основного агрегата двигателя. В Великобритании, в 1960-ых, Rolls Royce Motor Car Division в Кру, Чешире, вело двухтактную дизельную версию двигателя Wankel.

Также в Великобритании, Norton Motorcycles разработал роторный двигатель для мотоциклов, базируемый на воздушном охлаждении, который приводил в действие DKW/Hercules W-2000 motorbyke в, который был включен и F1; Suzuki также сделал мотоцикл с двигателем Wankel, RE-5, где они использовали легированные сплавы в попытке продлить срок службы двигателя. В 1971 и 1972 "Артик Кат" произвел снегоходы, приведенные в действие 303 cc роторным двигателем, произведенные Sachs в Германии. Deere & Company проектировали двигатели, которые были способны к работе на разных топливах. Проект был предложен как источник энергии военно-морских сил Соединенных Штатов и других в конце 1980-ых.

После  использования  в автомобилях, например NSU с их Ro 80 моделью,  Citroën с M35, и GS Birotor использование двигателей, произведенных Comotor, так же были неудавшиеся попытки General Motors и Мерседес-Бенца, в проектировани автомобилей с роторным двигателем, самым обширным автомобильным использованием двигателя Wankel была японской компанией Мазда.

После нескольких лет развития первым автомобильным двигатьелем Мазды роторного типа  был Cosmo в 1967году. Компания устанавливала Wankel ("ротация" в терминологии компании) на транспортные средства такие как автобусы и пикапы. Клиенты часто говорили о плавности работы автомобилей. Однако, Мазда выбрала метод по внедрению углеводородных элементов , которые, в то время были менее дорогие, что повлияло на уменьшения топливного потребления, как раз перед резким повышением топливных цен. Позже Мазда оставила роторные двигатели в большинстве их автомобильей, но продолжила использовать его в их спортивном автомобиле RX-7 до августа 2002 (импорт RX-7 для Канады прекратился  только в 1993 году, а в США закончились в 1994 году. И выпуск с сохранением непроданного запаса, перенесенного как 1995 ). . Компания обычно использовала проекты с двумя роторами, но 1991 Eunos Cosmo использовал парно-турбо двигатель с тремя роторами. В 2003, Мазда начинала двигатель Renesis с RX-8. Двигатель Renesis перемещал порты для выхлопа и впуска от периферии ротационного кожуха к сторонам, учитывая большие полные углубления, лучший поток воздуха, и дальнейшие усиления по мощности. У двигателей Wankel были также впускные  и впускные каналы, но концепция была оставлена из-за нароста нагара в портах. Двигатель Renesis решил проблему при использовании угловатого ротора, царапающего стороны. Renesis способен развивать 238 hp (177 кВт) с лучшей экономией топлива, надежностью, и экологичностью, чем предыдущие двигатели Мазды,  при объеме в 1.3 L.

В 1961, советская  организация исследования НАТИ, НАМИ и ВНИИ начала экспериментальное  развитие, и создала экспериментальные двигатели с различными технологиями.