PURPOSE: To improve injunction strength between a ring-shaped member and a rotor main body by causing a ring-shaped member to contain C, Si, Mn and Mg at specified weight percentage respectively, and composing a pin boss part of spheroidal graphite cast iron material treated by austempering.
CONSTITUTION: A ring-shaped member 12 made of spheroidal graphite cast iron and internally chilled in a rotor main body 1 made of aluminium alloy contains C, Si, Mn, and Mg at the weight percentage of 2.6W4.0, 1.5W3.5, 0.2W1.0 and 0.005W0.8 respectively, and is expanded by heat due to a rotary piston engine being in operation. In this case, since at least the pin boss part 12a of said ring-shaped member 12 has been treated by austempering, said treated part is increased in its heat expansion, and a difference in the heat expansion due to difference in material between said ring-shaped member 12 and said rotor main body 1 is therefore reduced for the improvement of junction strength between said member 12 and said main body 1. In addition to that, a metal clearance between said member 12 and a bearing member 3 can be reduced to secure force for tightening them.
YAMAMOTO YUKIO
SATO KAZUO
