Rotary piston engines

Claim 1

Rotary piston engine comprising a casing which includes a rotor housing having a trochoidal inner wall and a pair of side housings secured to the opposite sides of the rotor housing to define a cavity therein, and a substantially polygonal rotor disposed in said cavity for rotation with apex portions in sliding engagement with the inner wall of the rotor housing, said rotor being provided at each apex portion with an apex seal of iron-based material which includes 50 to 75% in volume of carbide at least in a sliding surface which is adapted to be brought into sliding engagement with the inner wall of the rotor housing, said apex seal having a hardness of 700 to 900 in Vickers' scale at the sliding surface, said rotor housing including a base which is made of an iron-based material having a hardness of not less than 105 in Vickers' scale and provided at its inner wall with a chromium-plated layer having a hardness not less than 850 in Vickers' scale, the hardness of the rotor housing base and that of the chromium-plated layer being in a region defined in a chart having an ordinate representing the hardness of the rotor housing base and an abscissa representing the hardness of the chromium-plated layer by a line connecting a first point which corresponds to the base hardness of 180 and the plated layer hardness of 850 and a second point which corresponds to the base hardness of 125 and the plated layer hardness of 950, and also by a further line connecting said second point and a third point which corresponds to the base hardness of 105 and the chromium plated layer hardness of 1200, all in Vickers' scale, said region being at a side of the lines wherein the values of the hardness are greater than those on the lines.