Four wheel air cycle machine

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

• shaft means disposed for rotation about a longitudinally extending axis, said shaft means having a first end portion, a second end portion, and a central portion disposed therebetween;
• a first wheel mounted to the first end portion of said shaft means for rotation therewith, said first wheel comprising a turbine rotor;
• a second wheel mounted to the second end portion of said shaft means for rotation therewith, said second wheel comprising a fan rotor;
• a third wheel mounted to the central portion of said shaft means in spaced relationship from said first wheel and from said second wheel for rotation with said shaft means, said third wheel comprising a turbine rotor;
• a fourth wheel mounted to the central portion of said shaft means in back-to-back relationship with said third wheel between said second wheel and said third wheel for rotation with said shaft means, said fourth wheel comprising a compressor rotor;
• first journal bearing means for supporting said shaft means for rotation about the axis, said first bearing means disposed about the first end portion of said shaft means between said first wheel and said third wheel;
• and
• second journal bearing means for supporting said shaft means for rotation about the axis, said second bearing means disposed about the second end portion of said shaft means between said second wheel and said fourth wheel.

In an air cycle machine for conditioning air for supply to an enclosure, of the type having a plurality of rotors coaxially mounted on a single shaft for rotation therewith, wherein the shaft is supported for rotation about a longitudinally extending axis by a plurality of journal bearings, the improvement comprising:

• a. the shaft having a first end portion, a second end portion, and a central portion disposed therebetween;
• b. a first turbine rotor fixedly mounted on a first end portion of the shaft;
• c. a fan rotor fixedly mounted on the second end portion of the shaft;
• d. a second turbine rotor fixedly mounted on the central portion of the shaft in spaced relationship from the first turbine rotor and from the fan rotor;
• e. a compressor rotor fixedly mounted on the central portion of the shaft in back-to-back relationship with the second turbine rotor between the fan rotor and the second turbine rotor, wherein the second turbine rotor and the compressor rotor each has a set of impeller blades on one side and a substantially planar surface on an opposite side without any blades, the second turbine rotor and the compressor rotor are supported for rotation by a central disc between them with piloting rims, the two planar surfaces abut the central disc on opposite sides of the disc, and the two sets of blades extend away from each other in opposite directions;
• and
• f. whereby the back-to-back relationship minimizes the overall length of the shaft and permits the shaft to be sufficiently supported for rotation by only two journal bearings, with one of the journal bearings being disposed about the first end portion of the shaft between the turbine rotors and the second journal bearing being disposed about the second end portion of the shaft between the fan and compressor rotors.