Cryogenic Refrigerator Drive Shaft Structure for Lower Displacer Torque
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Solution Overview
Problem
Cryogenic refrigerators face challenges in reducing the torque required to drive the displacer without increasing the size of the structure, particularly when used for high-cooling-capacity applications like high-temperature superconducting equipment, as the pressure adjustment in the assist space may not sufficiently suppress the required driving torque.
Innovation Solution
The design incorporates a compressor with a return end and suction end that selectively connects to an expansion space, a housing with an assist space, a cylinder, and a displacer that undergoes reciprocating motion, utilizing a drive shaft with different cross-sectional areas for the upper and lower parts, which are sealed and supported by respective seal members, to optimize the assist force and reduce motor load torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the pressure in the assist space is adjusted to reduce driving torque, then the torque required to drive the displacer is reduced, but the structure size increases
Solution Approach 1:
The drive shaft is divided into two distinct parts: a first shaft part with a first cross-sectional area and a second shaft part with a second cross-sectional area. This segmentation allows different portions of the drive shaft to experience different assist forces from the assist space pressure, optimizing torque reduction while maintaining a compact structure without requiring overall size increases.
Solution Approach 2:
The drive shaft exhibits local quality variation through its two different shaft parts with different cross-sectional areas. The first shaft part (with larger area) experiences greater assist force from the assist space pressure than the second shaft part (with smaller area), allowing targeted torque reduction at specific locations along the drive shaft while maintaining structural integrity and compact dimensions.
2Force
If a single cross-sectional area drive shaft is used, then the structure is simpler, but the torque reduction effectiveness is insufficient
Solution Approach 1:
The drive shaft is segmented into two parts with different cross-sectional areas to optimize torque reduction effectiveness. This segmentation creates varying assist force distribution along the drive shaft, improving torque reduction performance while adding only minimal structural complexity compared to a uniform shaft design.
Solution Approach 2:
The drive shaft incorporates local quality variation through different cross-sectional areas at different positions. This allows the shaft to be optimized for torque reduction at specific locations (where larger cross-sectional area provides greater assist force) while maintaining simpler geometry in other regions, achieving effective torque reduction with controlled complexity.
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 configuration effectively reduces the torque required to drive the displacer, preventing large motor load torque from being applied, even with significant pressure loss through the regenerator material, without increasing the refrigerator's size or power consumption.
Implementation Method 1
the pressure within a space (or assist space) formed at a tip end part of the drive shaft and the housing are adjusted
Implementation Method 2
optimize the assist force and reduce motor load torque
Implementation Method 3
the first shaft part that is sealed and supported by a first seal member, and a second shaft part that is sealed and supported by a second seal member
Data Source
AI summary
A cryogenic refrigerator includes a compressor having a return end and a suction end that selectively connects to an expansion space, a housing having an assist space that communicates to the return end, a cylinder having one end connected to the housing and another end connected to the expansion space, a displacer that undergoes a reciprocating motion inside the cylinder, and tolerates flow of a working gas to and from the expansion space, and a drive shaft that is accommodated within the housing and drives the displacer. The drive shaft includes first and second parts having different cross sectional areas, sealed and supported by first and second seals, respectively. An end of the first part opposes the housing to form the assist space, and an end of the second part connects to the displacer.