Air cycle machine with heat isolation having back-to-back turbine and compressor rotors

An air cycle machine for conditioning air for supply to an enclosure, said air cycle machine comprising:

• shaft means supported for rotation about a longitudinally extending axis;
• a compressor wheel mounted to said shaft means for rotation therewith for compressing air delivered thereto;
• a turbine wheel mounted to said shaft means for expanding compressed air from said compressor wheel thereby extracting energy to drive said shaft means in rotation about the axis, said turbine wheel and said compressor wheel disposed in back-to-back relationship;
• a turbine inlet duct circumscribing said turbine wheel for directing a flow of relatively cooler air into said turbine wheel to be expanded in said turbine wheel;
• a compressor outlet duct circumscribing said compressor wheel for discharging a flow of relatively warmer air passing out of said compressor wheel;
• said turbine wheel and said turbine inlet duct defining a turbine circuit and said compressor wheel and said compressor outlet defining a compressor circuit;
• means for thermally isolating said turbine circuit from said compressor circuit for retarding heat transfer from the relatively warmer air traversing said compressor circuit to the relatively cooler air traversing said turbine circuit;
• said thermally isolating means including a thermally insulating plate extending radially substantially the extent of said turbine circuit and said compressor circuit;
• and
• said shaft means including a shaft sleeve supporting said turbine wheel and said compressor wheel being fabricated from material having a lower heat conductivity than the material of said turbine wheel and said compressor wheel.