Texto  Motor Wankel

Texto sobre o motor Wankel.

Motor Rotativo Wankel

A rotary-piston internal-combustion engine developed in Germany is radically different in structure from conventional reciprocating piston engines. The engine was conceived by Felix Wankel,a specialist in the design of sealing devices, and experimental units were built and tested by a German firm beginning in 1956. Instead of pistons that move up and down in cylinders, the Wankel engine has an equilateral triangular orbiting rotor (see Figure 1B). The rotor turns in a closed chamber and the three apexes of the rotor maintain a continuous sliding contact with the curved inner surface of the casing. The curve-sided rotor forms three crescent-shaped chambers between its sides and the curved wall of the casing. The volumes of the chambers vary with the rotor motion. Maximum volume is attained in each chamber when the side of the rotor forming it is parallel with the minor diameter of the casing, and the volume is reduced to a minimum when the rotor side is parallel with the major diameter. Shallow pockets recessed in the flank of the rotor control the shape of the combustion chambers and establish the compression ratio of the engine. In turning about its central axis the rotor must follow a circular orbit about the geometric centre of the casing. The necessary orbiting rotation is attained by means of a central bore in the rotor in which an internal gear is fitted to mesh with a stationary pinion fixed immovably to the centre of the casing. The rotor is guided by fitting its central bore to an eccentric formed on the output shaft that passes through the centre of the stationary pinion. This eccentric also harnesses the rotor to the shaft so that torque is applied when gas pressure is exerted against the rotor flanks as the fuel and air charges burn. A 3-to-1 gear ratio causes the output shaft to turn three times as fast as the rotor turns about the eccentric. Each quarter turn of the rotor completes an expansion or a compression, permitting intake, compression, expansion, and exhaust to be accomplished during one turn of the rotor. The only moving parts are the rotor and the output shaft. The fuel mixture is supplied by a carburetor and enters the combustion chambers through an intake port in one of the end plates of the casing. An exhaust port is formed in one of the flattened sides of the casing wall and a spark plug is located in a pocket communicating with the chambers through a small throat in the opposite side of the casing wall. The rotor and its gears and bearings are lubricated and cooled by oil circulating through the hollow rotor. The apex vanes are lubricated by a small amount of oil added to the fuel in proportions as low as 1 to 200. Water is circulated through cooling jackets in the casing, the entrance to which is located adjacent to the spark plug where the temperature tends to be highest. Maintaining pressure-tight joints by suitable seals at the apexes and on the end faces of the rotor is a major design problem. Radial sliding vanes are fitted in slots at the three apex edges and kept in contact with the casing by expander springs. The end faces of the rotor are sealed by arc-shaped segmental rings fitted in grooves close to the curved edges of the rotor and pressed against the casing by flat springs. The major advantages of the Wankel engine are its small space requirements and low weight per horsepower, smooth and vibrationless operation, quiet operation, and low manufacturing costs resulting from mechanical simplicity. The absence of inertial forces from reciprocating parts and the elimination of spring-closed poppet valves permit operation at much higher speed than is practical for reciprocating piston engines, an advantage because shaft speed must be high for optimum performance. The induction of fresh fuel mixture and exhaust are more effective because the ports are opened and closed more rapidly than with poppet valves, and gas flow through them is almost continuous. Heat transfer and the resulting cooling requirement are low because the jacketed surface is small. Fuel economy is at least as good as that of conventional gasoline engines, providing knock-free combustion with a wider range of permissible fuels. Lower weight and a lower centre of gravity make it much safer in an automobile in the event of a collision. There are approximately one third as many parts in a Wankel engine as in a typical six-cylinder automobile engine.

Figure 1 - Certain types of gasoline engines.

Wankel, Felix

(b. Aug. 13, 1902, Lahr, Ger.--d. Oct. 9, 1988, Lindau, W.Ger.)

German engineer and inventor of the Wankel rotary engine. The Wankel engine is distinguished by the presence of an orbiting rotor in the shape of a curved equilateral triangle that does the work done by the moving pistons in other internal-combustion engines. Advantages of the Wankel engine include light weight, few moving parts, compactness, low initial cost, fewer repairs, and relatively smooth performance. Wankel, originally a sealing specialist, carried out development work on rotary valves between 1936 and 1945 with the German Aeronautical Research Establishment DVL. In 1951 he began working in Lindau with the research department of the NSU Motorenwerk AG, based at Neckarsulm. He completed his first design of a rotary-piston engine in 1954, and the first unit was tested in 1957. Mazda, a Japanese automobile company, produced and developed the Wankel engine, introducing it to the American market in 1971. During the next few years, poor fuel economy and a world oil crisis discouraged buyers, but the engine was constantly improved, and by the end of the decade the company's sports cars were being enthusiastically received in Europe and the United States. Wankel became director of his own research establishment at Lindau, where he continued to investigate the fundamental problems and future applications of the rotary-piston engine.

Mazda Motor Corporation

Formerly (1927-84) TOYO KOGYO COMPANY, Japanese automotive manufacturer, maker of Mazda passenger cars, trucks, and buses. The company is affiliated with the Sumitomo group. It is headquartered at Hiroshima. Founded in 1920 as a cork plant, the company acquired its Toyo Kogyo name in 1927. In 1931 it began manufacturing its first vehicles, a line of three-wheel trucks, producing some 200,000 in the next 25 years. During World War II, it provided the Japanese armed forces with these trucks as well as with rifles. The company's factory survived the atomic bombing of Hiroshima because it lay shielded behind a hill. The company entered the passenger-car market in 1960 with the production of a coupe model; two years later, sedans and station wagons came on line, and in 1964 it introduced a line of cars that were marketed in the United States. In 1967 the company committed itself to producing automobiles with the rotary-piston Wankel engine. By the early 1970s, more than half of all Mazdas were equipped with the new engine. The major drawback of the Wankel engine, however, was its relatively poor fuel efficiency. With the rise in the price of gasoline in the 1970s, sales of Mazdas dropped sharply. Since then the company gradually has regained its fortunes. By reducing its work force through attrition, greatly improving productivity, and turning to conventional, more fuel-efficient engines for its cars, the company has become one of the largest automobile manufacturers in Japan. In 1981 it brought out a more fuel-efficient Wankel engine for some of its models. Also important to its recovery has been its relationship with the Ford Motor Company. Mazda supplies axles for Ford and ships a ready-to-assemble car that Ford markets. The company also manufactures rock drills, machine tools, and gauge blocks. The company changed its name from Toyo Kogyo Company to Mazda Motor Corporation in 1984.


Source: Encyclopedia Britannica