Patent ID: 7461443

Claim:
A method for making a permanent magnet machine comprising: attaching an inner sleeve around at least a portion of a rotor of said permanent magnet machine; the inner sleeve having a first coefficient of thermal expansion; attaching a first stub shaft to an inner sleeve first end; attaching a second stub shaft to an inner sleeve second end; fitting a magnet against said inner sleeve between said first stub shaft and said second stub shaft, the magnet having an outside diameter; axially compressing said magnet by moving said first stub shaft toward said second stub shaft, with said magnet therebetween; heating the outer sleeve, wherein the outer sleeve having an inside diameter smaller than the outer diameter of the magnet before heating; the heated outer sleeve having an inside diameter greater than the outer diameter of the magnet; fitting the heated outer sleeve around said magnet, said first stub shaft and said second stub shaft; cooling the outer sleeve to reduce its inside diameter and to apply a radially compressive force on the magnet; the outer sleeve having a second coefficient of thermal expansion different from the first coefficient of thermal expansion of the inner sleeve; and wherein the radially compressive force increases as a function of increasing ambient temperature of the machine as a result of a differential rate of thermal expansion of the inner sleeve and the outer sleeve.