Segmented Inner Foil Bearing Assembly for Sub-Synchronous Vibration
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Solution Overview
Problem
Centrifugal compressors using foil bearing assemblies face challenges with sub-synchronous vibrations, which reduce the operating envelope, and existing lubricant compositions are incompatible with some refrigerants, limiting the choice of driveshaft materials and increasing complexity.
Innovation Solution
A bearing system with a foil bearing assembly comprising an outer foil assembly, an inner foil assembly, and a bump foil assembly, where the inner foil pads are welded to the outer foil assembly and extend circumferentially, providing a segmented design that disrupts the swirling fluid film and reduces cross-coupling, and the bearing housing includes locking features to maintain the foil bearing assembly at a fixed rotational position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If oil or alternative compositions are used as lubricant in compressor bearings, then friction between the bearing and driveshaft is reduced, but compatibility issues arise with certain refrigerant compositions
Solution Approach 1:
The patent removes the lubricant from the bearing system entirely, extracting the harmful element that caused incompatibility issues with certain refrigerants. The foil bearing operates without lubricant, eliminating the friction reduction benefit that came with lubricant compatibility problems.
2Loss of energy
If magnetic bearings are used to levitate the driveshaft, then friction is eliminated and refrigerant compatibility is improved, but device complexity and weight increase significantly
Solution Approach 1:
The patent employs a simpler, less expensive foil bearing structure that, while not eliminating friction entirely like magnetic bearings, provides a practical balance between complexity and performance. The foil bearing is a straightforward mechanical structure without the complex magnet assemblies, control systems, and ferromagnetic material requirements of magnetic bearings.
3Ease of manufacture
If a unitary inner foil assembly is used, then manufacturing is simplified, but sub-synchronous vibrations increase and operating envelope is reduced
Solution Approach 1:
The patent divides the inner foil assembly into multiple segmented pads rather than using a single unitary structure. This segmentation disrupts the continuous fluid film path, reducing cross-coupling stiffness and thereby mitigating sub-synchronous vibrations while maintaining manufacturing feasibility through modular assembly.
4Ease of operation
If foil bearing assembly is allowed to rotate freely, then operational flexibility is improved, but fixed rotational position is required to maintain proper alignment with locking features
Solution Approach 1:
The patent incorporates bearing retention features and locking mechanisms that pre-establish the correct rotational position of the foil bearing assembly within the bearing housing. This preliminary positioning ensures proper alignment before operation begins, maintaining manufacturing precision while allowing the bearing to function effectively.
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
The segmented foil bearing design effectively reduces sub-synchronous vibrations and allows for the use of lighter-weight materials, improving damping characteristics and operational efficiency while being compatible with all refrigerant compositions.
Implementation Method 1
support the driveshaft on a fluid layer formed between the driveshaft and the foil elements
Implementation Method 2
disrupts the swirling fluid film and reduces cross-coupling
Implementation Method 3
a foil bearing that includes compliant foil elements that surround the driveshaft and support the driveshaft on a fluid layer
Implementation Method 4
The bearing retention feature is cooperatively engaged with the at least one bearing assembly locking feature to maintain the foil bearing assembly within the bearing housing at a fixed rotational position
Data Source
AI summary
A bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve that defines a cylindrical bore and includes at least one bearing assembly locking feature, and a mounting structure. The foil bearing assembly includes an outer foil assembly, an inner foil assembly, and a bump foil assembly positioned between the outer foil assembly and the inner foil assembly. The outer foil assembly includes at least one outer foil pad that extends circumferentially from a first end including a bearing retention feature to a second end. The bearing retention feature is cooperatively engaged with the at least one bearing assembly locking feature. The inner foil assembly includes a plurality of circumferentially-spaced inner foil pads. Each inner foil pad extends circumferentially from a tab to a free end. At least one inner foil pad is welded to the outer foil assembly along the tab.