Stepped Bearing With Variable Interference Fit
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Solution Overview
Problem
Gas turbine engine bearings face challenges in maintaining contact pressure due to extreme temperature gradients, which can lead to thermal expansion and unwanted vibrations, as existing designs fail to accommodate varying thermal conditions effectively.
Innovation Solution
A bearing assembly with a cylindrical outer shell featuring first and second annular outer lands of different diameters, providing an interference fit with a bearing housing to maintain contact pressure, and a method of installation that includes connection members to secure the assembly within the housing, ensuring proper placement and accommodating thermal gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bearing is placed within a housing wall to support rotational movement, then the bearing allows relative motion between shaft and components, but thermal expansion from extreme temperature gradients causes the bearing to dislodge from the housing
Solution Approach 1:
The bearing shell is designed with different interference fit characteristics at different locations to accommodate thermal expansion. The first portion (proximal to combustor) and second portion (proximal to compressor) have different interference fit values, allowing each location to adapt to its specific thermal conditions while maintaining overall bearing retention
Solution Approach 2:
The interference fit parameter is varied along the bearing shell to compensate for thermal expansion. By changing the interference fit value from the first portion to the second portion, the design accounts for temperature gradients and prevents bearing dislodge
2Ease of manufacture
If a uniform interference fit is used between bearing shell and housing, then manufacturing is simplified, but thermal expansion causes loss of contact pressure and bearing dislodgment
Solution Approach 1:
Instead of a uniform interference fit, the design implements location-specific interference fit values. The first portion has a first interference fit value and the second portion has a second interference fit value, optimizing contact pressure maintenance at each location while accounting for thermal effects
3Adaptability or versatility
If the bearing shell expands thermally, then the bearing accommodates temperature changes, but the bearing loses contact with the housing and develops vibrations
Solution Approach 1:
The interference fit parameter is modified along the bearing shell length to prevent vibration. By having different interference fit values at different portions, the design maintains sufficient contact pressure even when thermal expansion occurs, preventing the bearing from loosening and generating subsynchronous vibrations
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 bearing assembly maintains a minimum of 2,000 pounds of contact pressure, preventing dislodgment and subsynchronous vibrations, even under thermal gradients, thereby enhancing the operational stability and longevity of gas turbine engines.
Implementation Method 1
Bearings located within GTEs often undergo extreme temperature gradients which may cause thermal expansion of at least a portion of the bearing itself, the component within the GTE adjacent to the bearing, or both.
Implementation Method 2
The first outer land diameter may be greater than the second outer land diameter and a different degree of an interference fit exists between the first outer surface and the housing, and the second outer surface and the housing to accommodate a thermal gradient across the outer bearing shell.
Data Source
AI summary
A bearing assembly having a cylindrical outer bearing shell. The outer bearing shell including a first annular outer land, a second annular outer land, and a recess therebetween. The outer bearing shell further including a first positioning bore having a first bore diameter and a second positioning bore having a second bore diameter. The second bore diameter may be smaller than the first bore diameter. A diameter of the first annular outer land may be larger than a diameter of the second annular outer land.