Thrust Foil Bearing Expansion Geometry for Load Capacity Retention
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Solution Overview
Problem
Thrust foil bearings face a challenge in maintaining load capacity due to radial bending of the top foil on the downstream side, where high fluid pressure leads to increased bending, making it difficult to further increase pressure and maintain appropriate taper angles.
Innovation Solution
The thrust foil bearing incorporates an expansion portion on the top foil with a decreasing width in the virtual straight line direction, supported by the back foil on the most downstream side, which includes a single peak on the outer peripheral side, enhancing radial bending rigidity and suppressing radial bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the top foil is thickened to reduce bending, then radial bending is reduced, but tilt deformation in the circumferential direction is hindered
Solution Approach 1:
The top foil is designed with non-uniform thickness, featuring a thickened portion at the downstream end where radial bending resistance is needed, and a thinner portion at the upstream end where flexibility is required. This local variation in thickness allows the foil to exhibit different mechanical properties at different locations, resolving the contradiction between needing radial stiffness and circumferential flexibility.
Solution Approach 2:
The invention addresses the two-dimensional contradiction by introducing a thickness dimension variation across the top foil. By making the thickness non-uniform in the radial direction, the design simultaneously achieves radial bending resistance (through increased thickness at downstream end) and circumferential flexibility (through reduced thickness at upstream end), effectively resolving the contradiction that cannot be solved by uniform thickness alone.
2Strength
If the top foil is thickened to suppress radial bending, then load capacity increases, but tilt deformation is hindered making it difficult to form appropriate taper angle
Solution Approach 1:
The top foil incorporates a thickened portion specifically at the downstream end where radial bending suppression is critical for load capacity, while maintaining thinner sections where tilt deformation and taper angle formation are necessary. This localized thickness variation allows the bearing to achieve both radial stability and proper taper geometry without compromising manufacturing precision.
3Strength
If pressure of fluid lubricating film is increased to improve load capacity, then bearing load capacity increases, but radial bending on downstream end side increases making further pressure increase difficult
Solution Approach 1:
The top foil is designed with a thickened portion at the downstream end where high fluid pressure acts, providing localized radial stiffness to suppress bending deformation. This allows the bearing to operate at higher fluid pressures for improved load capacity without suffering from excessive radial bending that would otherwise limit further pressure increases.
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 suppresses radial bending of the top foil, maintaining a strong fluid lubricating film and improving the bearing's load capacity by distributing pressure and maintaining non-contact with the thrust collar even at high loads.
Implementation Method 1
air is introduced between the top foil pieces and the thrust collar due to rotation of the thrust collar. This air forms a wedge-shaped fluid lubricating film between the top foil piece and the thrust collar
Implementation Method 2
the top foil includes an expansion portion in which a width of the expansion portion in a virtual straight line direction in which a virtual straight line extends decreases in a direction orthogonal to the virtual straight line
Data Source
AI summary
A thrust foil bearing of the present disclosure includes a base plate which includes an insertion hole through which a rotation shaft is inserted, a back foil which is disposed around the insertion hole and supported by the base plate, and a top foil which is supported by the back foil, wherein the top foil includes an expansion portion in which a width of the expansion portion in a virtual straight line direction in which a virtual straight line extends decreases in a direction orthogonal to the virtual straight line, the virtual straight line being supported by the back foil on a most downstream side in a rotation direction of the shaft.