Cryogenic Refrigerator Motor Shielding Against External Magnetic Fields
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Solution Overview
Problem
Cryogenic refrigerators used for cooling superconducting coils face reduced motor torque due to external magnetic fields generated by the coils, affecting the operation of the refrigerator.
Innovation Solution
A cryogenic refrigerator design that includes a motor with a magnetic path to guide external magnetic fields, isolating the back yoke from these fields by using a magnetic member outside the stator, which is hermetically housed within the casing, thereby reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the motor is placed near the superconducting coil to cool it, then the cooling efficiency is improved, but the motor torque is reduced due to external magnetic field interference
Solution Approach 1:
A magnetic member is introduced as an intermediary component between the external magnetic field source (superconducting coil) and the motor. This magnetic member creates a dedicated magnetic path that guides external magnetic field lines away from the motor's back yoke, thereby protecting the motor torque while allowing the motor to remain in close proximity to the superconducting coil for efficient cooling.
Solution Approach 2:
The magnetic path is segmented into distinct regions: the magnetic member located radially outward from the back yoke creates a separate magnetic pathway that handles external magnetic field lines, while the back yoke maintains its original function for the motor's internal magnetic field. This segmentation allows the two magnetic field systems to coexist without interference.
2Object-affected harmful factors
If the magnetic member is placed radially outward from the back yoke, then the external magnetic field interference is reduced, but the device complexity increases
Solution Approach 1:
The magnetic member serves multiple functions simultaneously: it acts as a magnetic path for external magnetic field lines, provides structural support within the motor assembly, and helps define the radial spacing between the back yoke and external environment. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
3Object-affected harmful factors
If the magnetic member is spaced apart from the back yoke, then the magnetic path for external fields is established, but the volume of the motor increases
Solution Approach 1:
The magnetic member is positioned only in the specific radial region where external magnetic field lines penetrate the motor structure. Rather than uniformly increasing the motor volume in all directions, the magnetic member is strategically placed only where needed for magnetic field management, thereby minimizing the overall volume increase while achieving effective magnetic shielding.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces the influence of external magnetic fields on the motor, improving the operational torque and performance of the refrigerator by blocking external magnetic interference and enhancing the coefficient of performance.
Implementation Method 1
a magnetic member that acts as a magnetic path of an external magnetic field generated outside of the casing
Data Source
AI summary
In a cryogenic refrigerator, a valve switches between a flow passage of a low-pressure refrigerant gas and a flow passage of a high-pressure refrigerant gas. A motor drives the valve. The motor includes a rotor and a stator, the rotor located radially inward of the stator. A casing hermetically houses the rotor and the stator. The stator includes a back yoke and a magnetic member that acts as a magnetic path of an external magnetic field generated outside of the casing, the magnetic member located radially outward of and spaced apart from the back yoke. The magnetic member is hermetically housed in the casing.