Use of Variable Reluctance Linear Motor for a Low Cost Stirling Cycle Cryocooler

Abstract

In the implementation of a compressor for a linear Stirling cryocooler, one major cost factor is the volume of magnet material required in the motor. Since the magnet material used is oftentimes the high energy-density rare earth types for size and high ambient operating temperature considerations, any reduction in the total magnet volume will result in a cost savings. The use of a variable reluctance linear motor configuration can be implemented into a compressor for a specified peak force, with a reduced amount of magnet material required. However, a variable reluctance motor has a non-linear force profile which also must be taken into account for optimal performance. This is especially critical when implementing cryocoolers which use gas bearings for long-life operation. Design data, and resulting performance for a linear free-piston Stirling-Cycle Cryocooler implemented using a variable reluctance motor are presented and compared to a conventional linear motor implementation.