Continuing The Legacy Of Felix Wankel | Part Two

How The Rotary Engine Works

The rotary engine functions in a way that is fundamentally different from conventional internal combustion engines. The piston is in fact a rotor that spins in the centre of a housing that is shaped like an oval pinched slightly in the middle. The rotor has a set of internal gear teeth cut into the centre of one side. These teeth mate with a gear that is fixed to the housing. This gear mating determines the path and direction the rotor takes through the housing.

The eccentric shaft is turned by the rotors in a way similar to a handle turning a winch. With every 360-degree turn of the rotor, the output shaft turns three times. The rotor itself is triangular shaped, and its three points are in constant contact with the housing wall through an apex seal. The shape of the housing ensures that the rotor’s centre point forms a closed circle with every complete turn. The three flanks of the rotor combined with the inner surface of the housing form three working chambers, whose volume constantly changes during a single turn of the rotor. This architecture makes a traditional crankshaft and valves unnecessary. The only moving parts are the rotary piston itself and the eccentric shaft. These characteristics mean that a rotary engine is lighter and more compact than a traditional reciprocating engine.

While a normal four-cycle piston engine needs four cycles to facilitate two turns of the crankshaft, rotary engines achieve all four cycles with only one turn of the rotor. The rotor itself produces the power of the rotary engine and applies it to the eccentric shaft, which fulfils a function comparable to the crankshaft of a traditional piston engine.

The Unique Characteristics of a Rotary Engine

Rotary engines with more than a single rotor are characterised by their extreme operating smoothness and low vibration. With a twin-rotor engine the lobes of the eccentric shaft are placed 180 degrees in relation to each other, which ensures an almost perfect balance of mass. A twin-rotor engine operates more smoothly than a six-cylinder piston engine with hardly any vibrations at all. The rotary engine is also characterised by its uncomplicated architecture, with a minimum of components, which means less weight and a compact size. The extremely compact size of Mazda RX-8’s rotary engine allowed engineers to place it more towards the centre of the vehicle, in a front-midship layout, which meant a 50/50 weight distribution over the front and rear axle. This guarantees excellent handling characteristics.

continues... | Part Three
Published 21 June 2003 Melanie Carter

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