Foil Bearing Gap Profile for Stable Shaft Floating
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Solution Overview
Problem
In foil bearings, managing the stiffness of the top foil portion is challenging, particularly at the end portions, which affects followability with shaft displacement and fluid dynamics, leading to potential degradation in the floating effect of the shaft.
Innovation Solution
The foil bearing design features foils with non-uniform gap widths between the front and rear ends, allowing for adjustable resiliency by varying the support span of intermediate foils, achieved by forming the front and rear ends with different contour shapes, such as recessed and protruding shapes, to manage stiffness and enhance followability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the front end of the foil has stiffness to maintain structural integrity, then the foil can support load, but followability with shaft displacement is degraded and fluid is pushed out from the bearing gap
Solution Approach 1:
The foil is designed with non-uniform thickness distribution, where the front end portion has a smaller thickness than the rear end portion. This creates local variation in stiffness properties - the thinner front end is more compliant and follows shaft displacement, while the thicker rear end provides sufficient structural support and load-bearing capability.
Solution Approach 2:
The thickness parameter of the foil is changed along its length to achieve different mechanical properties in different regions. By controlling the thickness gradient from front to rear, the foil achieves optimal balance between followability at the front end and structural strength at the rear end.
2Strength
If the foil thickness is increased to improve load bearing capacity, then strength is improved, but manufacturing complexity and difficulty of achieving precise thickness control increases
Solution Approach 1:
Instead of using a uniform thick foil that would be difficult to manufacture with precise thickness control, the invention uses a locally varied thickness design. The front end is made thinner while the rear end is made thicker, allowing each region to have optimal thickness for its specific function while simplifying manufacturing requirements.
3Measurement precision
If the gap width between foils is reduced to improve bearing precision, then measurement precision is improved, but manufacturing precision requirements increase significantly
Solution Approach 1:
The invention changes the thickness parameter of the foil to achieve the desired bearing gap. By making the front end thinner, the effective gap width is controlled without requiring extremely tight manufacturing tolerances on the gap itself, thus reducing manufacturing precision requirements while maintaining bearing precision.
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 stabilizes the floating effect of the shaft by improving followability with shaft displacement and thermal expansion, ensuring stable bearing performance under severe conditions.
Implementation Method 1
During rotation of the shaft, fluid films (for example, air films) are formed in bearing gaps formed between the shaft and the bearing surfaces of the foils, and the shaft is supported in a non-contact manner
Implementation Method 2
the bearing surfaces are deformable along with, for example, displacement or thermal expansion of the shaft
Implementation Method 3
the bearing surfaces are allowed to be deflected, and the bearing surfaces are deformable
Data Source
Figure 1~2
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AI summary
A foil bearing (40) includes foils (42) at a plurality of portions in a rotation direction of a shaft member (11). A top foil portion (Tf) including a bearing surface (S2) is formed in a region including a front end (421) of each of the foils (42), and a back foil portion (Bf) is formed in a region including a rear end (422) of each of the foils (42). A gap (C1) is secured between, of two of the foils adjacent to the foil (42) in a rotation direction (R) and a direction opposite to the rotation direction, the rear end (422) of the foil on the rotation direction side and the front end (421) of the foil on the side opposite to the rotation direction side. A width of the gap (C1) is set to be non-uniform in a direction (N) orthogonal to the rotation direction.