Fluid Dynamic Bearing Oil Buffer for Cavitation and Stiffness
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Solution Overview
Problem
Conventional fluid dynamic bearing apparatuses face issues with radial stiffness reduction and air bubble formation due to reduced axial dimensions, leading to potential leakage and tilting of rotating components, especially under external shocks or vibrations.
Innovation Solution
The design incorporates a thrust washer with a cylindrical portion and a flat plate portion, featuring a pumping groove system that communicates with an oil buffer to dissolve air bubbles and maintain lubrication, enhancing radial and axial support while preventing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the axial dimension of the shaft is reduced to make the fluid dynamic bearing apparatus thinner, then the size and thickness are reduced, but the length of the radial dynamic pressure bearing portion is reduced causing a reduction in radial stiffness
Solution Approach 1:
The invention introduces a new radial dimension for the dynamic pressure bearing portion by making the shaft have a larger diameter at its radially outer portion compared to its radially inner portion. This dimensional change in the radial direction compensates for the reduced axial length, maintaining sufficient radial stiffness while achieving a thinner overall apparatus.
Solution Approach 2:
The shaft is designed with non-uniform cross-sectional properties, where the radially outer portion has a larger diameter than the radially inner portion. This local variation in geometric quality allows the bearing portion to maintain high radial stiffness where needed while keeping the overall axial dimension reduced.
2Length of moving object
If the axial dimension of the shaft is reduced, then the apparatus is thinner, but an external force such as shock may cause the rotating member or shaft to tilt
Solution Approach 1:
By increasing the radial diameter of the shaft at the bearing portion, the invention adds radial dimensional strength to compensate for reduced axial dimension. This enhances the shaft's resistance to external shocks and prevents tilting of rotating members while maintaining a thin overall profile.
Solution Approach 2:
The enlarged radial diameter of the shaft creates a built-in structural cushion that resists external shocks before they can cause tilting. This preventive design feature ensures reliability under shock conditions without requiring additional active control mechanisms.
3Strength
If a substantially cup-shaped member is adopted to maintain a sufficient length of the radial dynamic pressure bearing portion, then radial stiffness is maintained, but the lubricating oil held in the minute gap may come under negative pressure causing air bubble generation
Solution Approach 1:
The invention changes the geometric parameters of the shaft, specifically making the diameter at the radially outer portion larger than at the radially inner portion. This parameter modification allows the dynamic pressure bearing to function effectively with a smaller axial gap, preventing negative pressure conditions that would cause air bubble generation while maintaining radial stiffness.
4Adaptability or versatility
If vibration is applied to the fluid dynamic bearing apparatus, then the axial dimension of the radially extending gap changes, but this causes air bubbles to be generated in the bearing fluid due to cavitation
Solution Approach 1:
By modifying the shaft diameter parameters (larger at radially outer portion, smaller at radially inner portion), the invention creates a more stable gap geometry that is less susceptible to vibration-induced cavitation. This parameter optimization prevents air bubble generation even when the apparatus experiences vibrations during transportation or operation.
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 improves the perpendicularity of the thrust portion and prevents oil leakage by dissolving air bubbles within the lubricating oil, ensuring stable operation and reduced errors in disk rotation.
Implementation Method 1
dynamic pressure grooves provided in each of the radial dynamic pressure bearing portion and the thrust dynamic pressure bearing portion produce a pumping action to induce a fluid dynamic pressure on the lubricating oil filling a minute gap
Implementation Method 2
the lubricating oil held in a minute gap between a lower surface of the rotating member including the sleeve and an upper surface of the substantially cup-shaped member, which is opposite to the lower surface of the rotating member, may come under negative pressure
Data Source
AI summary
In a fluid dynamic bearing apparatus, an oil buffer is defined between a thrust gap and a pumping gap. The oil buffer has an axial dimension greater than that of the thrust gap, and/or has a radial dimension greater than that of the pumping gap. An air bubble generated in the thrust gap due to cavitation, for example, when a fluid dynamic bearing apparatus experiences a vibration can be dissolved in lubricating oil provided within the oil buffer. This prevents leakage of the lubricating oil due to the air bubble residing in the fluid dynamic bearing apparatus.