Rotary combustion engine of trochoid design with oil return groove

A rotary combustion engine of trochoid design. The engine includes a housing composed of a jacket having a multicurved inner jacket face and two parallel side walls and a substantially horizontally disposed eccentric shaft which extends through circular apertures in the side walls. A liquid cooled piston is rotatably mounted on the eccentric. Oil control rings are mounted on the piston end walls which coact with the side faces of the side wall. A disk is provided in at least one piston end wall with a hub which rotates with the eccentric shaft concentrically with respect to the rotational axis of the piston and extends into the aperture of the side wall. The disk and the hub are provided with sealing rings in tight sealing engagement with the piston end wall and the wall of the aperture, respectively. The sealing rings encompass an annular chamber which is limited radially outwardly by the oil control ring. A groove is provided in the lower range of the wall of the aperture which receives the hub of the disk. This groove is coupled at its lowermost point with a return line by means of a bore.