Machine Wankel Inventory
Wankel was born in 1902 in Lahr in what was then the Grand Duchy of Baden in the Upper Rhine Plain of present-day southwestern Germany. He was the only son of Gerty Wankel (née Heidlauff) and Rudolf Wankel, a forest assessor. His father fell in World War I. Thereafter, the family moved to Heidelberg. He went to high schools in Donaueschingen, Heidelberg, and Weinheim, and left school without Abitur in 1921. He learned the trade of purchaser at the Carl Winter Press in Heidelberg and worked for the publishing house
until June 1926. He and some friends had already run an unofficial afterwork machine shop in a backyard shed in Heidelberg since 1924. Wankel now determined to receive unemployment benefits and to focus on the machine shop. One of his friends, who had graduated from university, gave his name and transformed the shop into an official garage for DKW and Cleveland motor bikes in 1927, where Wankel worked from time to time until his arrest in 1933.
Wankel reportedly came up with the basic idea for a new type of internal combustion gasoline engine when he was only 17 years old. In 1924, Wankel set up a small laboratory where he began the research and development of his dream engine, which would be able to attain intake, compression, combustion and exhaust, all while rotating. He brought his knowledge of rotary valves to his work with the German Aeronautical Research Establishment during World War II, and to a leading German motorcycle company, NSU Motorenwerk AG, beginning in 1951. Wankel completed his first design of a rotary-piston engine in 1954, and the first unit was tested in 1957.
In other internal-combustion engines, moving pistons did the work of getting the combustion process started; in the Wankel rotary engine, an orbiting rotor in the shape of a curved equilateral triangle served this purpose. Fewer moving parts created a smoothly performing engine that was lightweight, compact, low-cost and required fewer repairs. After NSU officially announced the completion of the Wankel rotary engine in late 1959, some 100 companies around the world rushed to propose partnerships that would get the engine inside their products. Mazda, the Japanese automaker, signed a formal contract with NSU in July 1961, after receiving approval from the Japanese government.
In an attempt to experiment with the rotary engine and perfect it for use in its vehicles, Mazda formed an RE (Rotary Engine) Research Department in 1963. The Cosmo Sport, which Mazda released in May 1967, was the planet’s first dual-rotor rotary engine car. With futuristic styling and superior performance, the Cosmo wowed car enthusiasts worldwide. Mazda began installing rotary engines in its sedans and coupes in 1968, and the vehicles hit the U.S. market in 1971. In the wake of a global oil crisis in 1973-74, Mazda continually worked on improving its rotary engines to improve fuel efficiency, and by the end of that decade its sports cars had become popular in both Europe and the United States In addition to Mazda, a number of other companies licensed the Wankel engine during the 1960s and 1970s, including Daimler-Benz, Alfa Romeo, Rolls Royce, Porsche, General Motors, Suzuki and Toyota.
Meanwhile, Wankel continued his own work with the rotary piston engine, forming his own research establishment in Lindau, Germany, in the mid-1970s. In 1986, he sold the institute for 100 million Deutschmarks (around $41 million) to Daimler Benz, maker of the Mercedes. Wankel filed a new patent as late as 1987; the following year, he died after a long illness.
Design
In the Wankel engine, the four strokes of an Otto cycle piston engine occur in the space between a three-sided symmetric rotor and the inside of a housing. In each rotor of the 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). The theoretical shape of the rotor between the fixed corners is the result of a minimization of the volume of the geometric combustion chamber and a maximization of the compression ratio, respectively. The symmetric curve connecting two arbitrary apexes of the rotor is maximized in the direction of the inner housing shape with the constraint that it not 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.[30] The rotors ride on eccentrics (analogous to crankpins) integral to 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.[30] 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 easiest 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 three cavities per housing, all repeating the same cycle. Points A and B on the rotor and E-shaft turn at different speeds—point B circles three times as often as point A does, so that one full orbit of the rotor equates to three turns of the E-shaft.
As the rotor rotates orbitally revolving, each side of the rotor is brought closer to and then away from the wall of the housing, compressing and expanding the combustion chamber like the strokes of a piston in a reciprocating piston engine. The power vector of the combustion stage goes through the center of the offset lobe.
While a four-stroke piston engine completes one combustion stroke per cylinder for every two rotations of the crankshaft (that is, one-half power stroke per crankshaft rotation per cylinder), each combustion chamber in the Wankel generates one combustion stroke per driveshaft rotation, i.e. one power stroke per rotor orbital revolution and three power strokes per rotor rotation. Thus, the power output of a Wankel engine is generally higher than that of a four-stroke piston engine of similar engine displacement in a similar state of tune; and higher than that of a four-stroke piston engine of similar physical dimensions and weight.
Wankel engines generally are able to reach much higher engine revolutions than reciprocating engines of similar power output. This is due to the smoothness inherent in circular motion, and the absence of highly stressed parts such as crankshafts, camshafts or connecting rods. Eccentric shafts do not have the stress related contours of crankshafts. The maximum revolutions of a rotary engine is limited by tooth load on 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, racing a Wankel engine at high rpm under no load conditions can destroy the engine.
National agencies that tax automobiles according to displacement and regulatory bodies in automobile racing variously consider the Wankel engine to be equivalent to a four-stroke piston engine of 1.5 to 2 times the displacement of one chamber per rotor, even though there are three chambers per rotor. Some racing series have banned the Wankel altogether, along with all other alternatives to the traditional reciprocating piston four-stroke design
