Patent ID: 7341439

Claim:
A scroll fluid machine comprising: a driving shaft having an eccentric axial portion at one end; a fixed scroll having a fixed wrap; and an orbiting scroll having an orbiting wrap and rotatably mounted around the eccentric axial portion of the driving shaft to form a compression chamber between the fixed and the orbiting wraps, the orbiting scroll being revolved by the driving shaft to reduce a volume of the compression chamber towards a center of the orbiting scroll thereby compressing a gas sucked from an outer circumference of the fixed scroll to discharge the gas through an outlet close to the center, and an adiabatic expansion chamber being formed between an innermost winding portion of the fixed wrap and the eccentric axial portion of the driving shaft: wherein the adiabatic expansion chamber is greater in volume than an innermost compression chamber; and a projection is formed on an inner circumferential surface of an innermost winding portion of the fixed wrap, an inner end of the orbiting wrap coming in sliding contact with the projection thereby preventing compressed gas from flowing back to the compression chamber.