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Wankel engine history

The Wankel engine is a type of internal combustion engine using an eccentric 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 but with sides that are somewhat flatter.


Felix Wankel worked for a long time on this subject. He catalogued 862 pairs of possible geometrical shapes, eliminated 278 most impractical ones and examined 149 most promising concepts from 584 pairs left. He received his first patent for the engine in 1929. After WW2 Wankel returned to this concept, while working for NSU Motorenwerke AG. He began development of the engine in 1951. In 1954 DKM 54 (Drehkolbenmotor) design was prepared. The first working prototype, KKM 57 (Kreiskolbenmotor) was constructed by NSU engineer Hans Dieter Paschke in 1957 without the knowledge of Felix Wankel, who remarked "you have turned my race horse into a plow mare". DKM 54 was running on February 1, 1957 at the NSU research and development department. It produced 21 horsepower; unlike modern Wankel engines, both the rotor and the housing rotated. In 1960 NSU (the firm the inventor worked for) and the US firm Curtiss-Wright signed an agreement where NSU would concentrate on the development of low and medium powered Wankel engines and Curtiss-Wright would develop high powered Wankel Engines, including aircraft engines of which Curtiss-Wright had decades of experience designing and producing.

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. For a while, engineers faced what they called chattered marks and devil's scratches in the inner epitrochoid surface, they discovered that the origin was in the apex seals reaching a resonating vibration, and was solved by reducing the thickness and weight of apex seals. Another early problem of buildup of cracks in the stator surface was eliminated by installing the spark plugs in a separate metal piece instead of screwing it directly into the block.

Among the manufacturers signing licensing agreements to develop Wankel engines were Alfa Romeo, American Motors, Citroen, Ford, General Motors, Mercedes-Benz, Nissan, Porsche, Rolls-Royce, Suzuki, and Toyota. In the United States, in 1959 under license from NSU, Curtiss-Wright pioneered improvements in the basic engine design. In Britain, in the 1960s, Rolls Royce Motor Car Division pioneered a two-stage diesel version of the Wankel engine. Also in Britain, Norton Motorcycles developed a Wankel rotary engine for motorcycles, based on the Sachs air-cooled Wankel that powered the DKW/Hercules W-2000 motorcycle, 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 the 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 80s.

Mazda and NSU signed a study contract to develop the Wankel engine in 1961 and competed to bring the first Wankel powered automobile to market. Although Mazda produced an experimental Wankel that year, NSU was first with a Wankel automobile on sale, the sporty NSU Spider in 1964. In 1967, NSU began production of a Wankel-engined luxury car, the Ro 80. However, problems with apex seal wear led to frequent engine failure, which led to large warranty costs for NSU, and curtailed further Wankel engine development. Mazda, however, claimed to have solved the apex seal problem, and was able to run test engines at high speed for 300 hours without failure. After years of development, Mazda's first Wankel engine car was the 1967 Cosmo 110S. 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 hydrocarbonemission 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.