The rotor is mounted in an oval-shaped housing. The housing is made of aluminum alloy, but the curved surface has hard chromium plating. This surface has to put up with the wear and tear of the rotor sliding against it as it turns in the housing.
There are usually two spark plugs fixed to the housing which enable combustion to occur.
The rotor housing also has an exhaust port to expel burnt gases. It has cooling passages for water to circulate.
The rotor has three apexes which have seals to seal between the rotor and the rotor housing. This prevents premature wear as the apex seals and housing are in continuous contact.
Side seals seal between the rotor and side housing.
The combustion chamber is formed by hollows in the flanks of the rotor. These hollows are sometimes called bathtubs.
Front and rear housings, or side housings, are bolted to each side of the rotor housing. If it is a two-rotor engine there is an intermediate housing between the two rotors.
An internal gear in each rotor meshes with a corresponding stationary gear in the front housing and rear housings.
When combustion occurs, the meshing of the teeth forces the rotor to walk around the stationary gear. This combines with the eccentric shaft to make the rotor follow the curved surface of the housing, and it gives the rotor planetary motion.
The rotor is attached to an eccentric shaft at points called rotor journals. This shaft is like a crankshaft in a piston engine but with the journals off-center.
Because the rotor is off-center, the force applied to the shaft is off-center too. The whole shaft is supported by main journals, so the final output is smooth rotary motion.
