Rotary piston type internal combustion engines

Rotary piston engine comprising a casing which comprises a rotor housing having an inner wall of trochoidal configuration and a pair of side housings gas-tightly secured to the opposite sides of the rotor housing to define a trochoidal cavity therein, a substantially polygonal rotor disposed in the cavity for rotation with apex portions in sliding contact with the inner wall of the rotor housing so that working chambers of variable volume are defined in said cavity between said inner wall of the rotor housing and flanks of the rotor, intake means for introducing intake gas into one of said working chambers which is in intake stroke, exhaust means for exhausting gas from another working chamber which is in exhaust stroke, said rotor housing being applied on the inner wall thereof with pin-point type porous chromium plating mainly including discontinuous pores and having a porosity of 10 to 60 percent and a hardness of 930 to 1200 in Vicker's scale, said rotor being provided on each of the apex portions with an apex seal having a sliding surface adapted to be brought into sliding contact with the chromium plating on the inner wall of the rotor housing, said apex seal being constituted by cast-iron based material with 50 to 70 volume percent of carbides in at least in the sliding surface and having a hardness of 700 to 900 in Vicker's scale at the sliding surface.