In the late 1950's a German engineer called Felix Wankel designed a revolutionary rotary engine.
The basic principles of the four stroke combustion engine had remained virtually unchanged since its invention in the 1880's. The standard engine involved the pistons being driven up and down by the combustion stroke known as `reciprocal' movement which then had to be converted into a rotary movement by the crankshaft before being able to `drive' the gearbox.
Felix Wankel's design replaced the traditional oblong cylinder with a round one, and the piston became a triangular disc which would rotate inside the now round cylinder. Each side of the disc is slightly curved allowing a small gap between the walls of the cylinder and the piston. This allows some room for the moving and expanding gases on two of its curved sides. All four strokes of the traditional engine are present (ie. induction, compression, combustion and exhaust); on one complete revolution there are three power strokes compared to one for the basic engine. This gives the Wankel engine the advantage of being smaller and lighter than a conventional engine in that one rotor is equivalent to three cylinders, two rotors are equivalent to six cylinders and so on.
The rotary piston has only two moving parts, the rotor and the output shaft. It does not require piston rods, a crankshaft or complicated valve timing gears although it still requires spark plugs and a carburettor.
NSU and Mazda cars have recognised the possibilities of this engine and were the first to fit rotary engines to some of their models.
