Segmented Foil Bearing Assembly for Compressor Vibration Damping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Centrifugal compressors using foil bearing assemblies face challenges with sub-synchronous vibrations, which reduce the operating envelope, and existing solutions like oil-based or magnetic bearings are either incompatible with certain refrigerants or complex in design.
Innovation Solution
A foil bearing system with an outer and 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 to reduce cross-coupling and sub-synchronous vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a foil bearing assembly is used in a centrifugal compressor, then the compressor is compatible with all refrigerant compositions and can use lighter-weight driveshaft materials, but the compressor becomes prone to sub-synchronous vibrations that reduce the operating envelope
Solution Approach 1:
The inner foil assembly is divided into multiple separate inner foil pads (first inner foil pad, second inner foil pad, third inner foil pad) spaced circumferentially around the driveshaft. Each pad is independently positioned and can move axially within its housing, creating a segmented structure that disrupts the fluid film and reduces cross-coupled stiffness, thereby mitigating sub-synchronous vibrations while maintaining refrigerant compatibility
2Ease of operation
If oil-based lubricant is used in compressor bearings, then friction is reduced, but the lubricant is incompatible with certain refrigerant compositions
Solution Approach 1:
The patent replaces oil-based lubrication with a hydrodynamic foil bearing system that uses the refrigerant gas itself as the lubricating medium. The compliant inner foil pads generate a hydrodynamic fluid film that supports the driveshaft and reduces friction without requiring any lubricant, making the system compatible with all refrigerant compositions including HFCs and hydrocarbons
3Ease of operation
If magnetic bearings are used to levitate the driveshaft, then friction is eliminated, but the design becomes complex and driveshaft material choices are limited to ferromagnetic materials
Solution Approach 1:
The patent replaces complex magnetic bearing systems with a simpler hydrodynamic foil bearing system. The inner foil pads, when rotated by the driveshaft, generate a hydrodynamic pressure field that levitates the driveshaft without contact, eliminating friction without requiring magnets, power electronics, or ferromagnetic materials, thereby reducing design complexity and expanding material choices
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 by improving damping and reducing cross-coupled stiffness, enhancing the operational stability and efficiency of centrifugal compressors.
Implementation Method 1
Foil bearings are well-suited for the high-speed operating environment typical of centrifugal compressors, are compatible with all refrigerant compositions, and may be used with a wider variety of driveshaft materials
Implementation Method 2
The segmented foil bearing design effectively reduces sub-synchronous vibrations by improving damping and reducing cross-coupled stiffness
Data Source
Figure 1
Figure 2
Figure 3
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.