Aircraft Engine Rotary Interference Fit With Undercut Stability
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Solution Overview
Problem
Aircraft engine rotary parts experience high centrifugal loads and thermal expansion, leading to variations in interference fit and vibrations due to radial pull, which affect the assembly and operation of rotary components.
Innovation Solution
Implementing an undercut feature at the interface between rotary parts and the shaft to manage radial pull and thermal expansion, using an interference fit that allows for deflection and reduced contact area, thereby stabilizing the fit and reducing vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an interference fit is used between rotary parts and shaft to secure high-speed rotation, then the strength and reliability of the connection is improved, but the fit becomes unstable due to radial pull from centrifugal loads and thermal expansion
Solution Approach 1:
The patent introduces a deflectable region in the rotary part that allows dynamic adjustment of the interference fit. This region enables the rotary part to deflect relative to the shaft, accommodating radial pull forces from centrifugal loads and thermal expansion while maintaining reliable connection. The fit transitions from static to dynamic, allowing controlled movement that preserves connection integrity under varying operating conditions.
Solution Approach 2:
The patent changes the physical parameters of the interference fit by creating a deflectable region with specific geometric characteristics (reduced thickness or material removal). This modifies the stiffness and compliance of the connection, allowing the fit to adapt to radial forces. The parameter change enables the connection to maintain reliability while accommodating dimensional changes due to temperature and centrifugal effects.
2Object-generated harmful factors
If the interference fit is made tighter to reduce vibrations, then the vibration level is reduced, but the assembly and disassembly of rotary parts becomes more difficult
Solution Approach 1:
The patent segments the rotary part into a rigid region and a deflectable region. The rigid region maintains stable connection and reduces vibrations, while the deflectable region (with reduced thickness or material removal) provides compliance for easier assembly and disassembly. This segmentation allows the connection to have both stability for vibration reduction and compliance for manufacturing ease.
Solution Approach 2:
The patent applies local quality by creating a deflectable region with specific geometric characteristics at a particular location in the rotary part. This local modification (reduced thickness, material removal, or undercut) provides the necessary compliance for assembly while the rest of the rotary part maintains rigidity for vibration control. The local change in geometry creates different mechanical properties in different regions of the same component.
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 undercut feature stabilizes the interference fit, minimizing vibrations and facilitating assembly/disassembly of rotary parts, while accommodating thermal expansion and centrifugal forces across varying operating conditions.
Implementation Method 1
Rotors, such as compressor rotors, coupled to a shaft, or other rotary parts mounted one to another within the engine may experience such high centrifugal loads and thermal expansion
Implementation Method 2
Aircraft engine parts rotating at high speed may experience high centrifugal loads and thermal expansion in normal operating conditions
Data Source
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AI summary
A rotary assembly (30) for an aircraft engine (10) is disclosed. A shaft (20) is mounted for rotation about a central axis (11) and a rotary part (31) is mounted on the shaft (20) for common rotation therewith. The rotary part (31) has an axial end portion (32A) extending away from a center of mass (CM) of the rotary part (31), the axial end portion (32A) having a radial thickness (RD) smaller than that of the rotary part (31) at an axial location (AC) aligned with the center of mass (CM). The shaft (20) and the rotary part (31) have an interface (SR) defining an interference fit between the shaft (20) and the axial end portion (32A) of the rotary part (31). The interface (SR) is located at a distance (AL) along the central axis (11) from the center of mass (CM). An undercut (33A) is defined in the rotary part (31). The undercut (33A) extends axially from adjacent the interface (SR) towards the center of mass (CM).