A rotary engine has fewer parts than a four stroke cylinder engine. While the Rotary engine has four parts (housing, two rotors and an eccentric shaft) the cylinder engine requires almost ten times that ammount of parts to accomplish the same job. Some of the parts that are found only on cylinder engines are: Cams, valves, valve springs, cam gears pistons and connecting rods.
The main parts of the rotary engine are: Housing, shaft and rotor.
Cutaway of a modern Mazda rotary engine.
Housing
The housing contains all other parts of the motor making the rotary engine very compact in size.
The housing is epitrochoid in shape.
Designed to keep all three tips of rotors in contact with housing at all times.
Housing creates three separate volumes of gas at any time during rotation.
Housing is designed with four parts specifically dedicated to one of the following : Intake, compression, combustion and exhaust.
Rotor
Rotor supercedes the pistons engine's reciprocating piston.
The rotor has three convexing faces each acting like a piston.
Metal blade at apex of each face forms seals of the combiston chamber.
teeth at the center of the rotor connected to output shaft.
Output Shaft
Output shaft has lobes mounted offset from the centerline of the shaft. Rotors are mounted on these lobes.
Each lobe acts as a cranckshaft on the piston engine.
When the rotor follows the surface of the housing it creates torque on the lobes making the output shaft rotate.
Intake and Exhaust Port
Ports are created in the housing eliminating valves, camshafts, cams, lifter rods and timing belts.
Rotary engines have 4 or 6 ports for intake and exhaust.
6 port rotary engines use one extra intake port per rotor used only at higher RPM's.