Bearing Stack Retainer With Preload Control for Concentric Shafts
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Solution Overview
Problem
In gas turbine engines, independently moving concentric rotating shafts require robust bearing systems to maintain concentricity and operational longevity, and without proper preload, issues like false brinelling and inadequate lubrication can arise, necessitating effective preload solutions for ball bearings.
Innovation Solution
A bearing stack retainer with castellations and an oil retaining dam is used to secure the bearing stack in place, along with a preload disc applying pressure to the ball bearing race, ensuring consistent preload and lubrication for the bearing stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If preload force is applied to ball bearings to maintain robustness and prevent false brinelling, then bearing reliability is improved, but device complexity increases due to the need for additional preload generation mechanisms
Solution Approach 1:
The bearing stack retainer is combined with multiple functions: it retains the bearing stack in position, generates preload force through its interaction with the outer shaft, and provides lubrication flow pathways. This integration eliminates the need for separate preload generation mechanisms, reducing overall device complexity while maintaining bearing reliability
Solution Approach 2:
The bearing stack retainer serves multiple purposes simultaneously: it acts as a positioning element for the bearing stack, a preload generation device through its castellated structure interaction with the outer shaft, and a lubrication distribution component. This multi-functionality resolves the contradiction by achieving reliable bearing operation without adding dedicated complex preload mechanisms
2Duration of action of stationary object
If bearing stack is preloaded to ensure operational longevity and prevent false brinelling, then bearing life is extended, but manufacturing precision requirements increase to ensure proper preload distribution
Solution Approach 1:
The castellated structure on both the bearing stack retainer and outer shaft creates localized contact points that naturally distribute preload force across multiple discrete locations. This localised approach to preload application ensures uniform preload distribution without requiring extremely high manufacturing precision across the entire bearing stack assembly
Solution Approach 2:
The bearing stack retainer is designed with built-in preload generation capability through its castellated structure, which automatically applies preload force when the outer shaft rotates. This preliminary design feature ensures proper preload is established during normal operation without requiring complex post-assembly adjustments or extremely tight manufacturing tolerances
3Manufacturing precision
If bearing stack retainer is used to maintain preload and position bearing stack, then bearing alignment is improved, but device complexity increases due to additional retaining components
Solution Approach 1:
The bearing stack retainer combines positioning and preload generation functions into a single integrated component. The castellated structure simultaneously retains the bearing stack axially and generates preload through its interaction with the outer shaft, eliminating the need for separate positioning and preload devices
Solution Approach 2:
The bearing stack retainer is designed as a multi-functional component that performs axial retention, radial positioning, and preload generation all through its castellated structure. This universal design achieves proper bearing alignment without requiring multiple separate retaining components, thus not increasing overall device complexity
Data Source
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AI summary
An arrangement of concentric, independently rotating shafts (21, 26) for a rotating gear train system is disclosed. The arrangement may include an inner shaft (21), the inner shaft (21) operatively coupled to a rotating element, and an outer shaft (26), the outer shaft (26) concentric with the inner shaft (21) and arranged radially outward from the inner shaft (21). The arrangement may further include a first bearing stack (32), the first bearing stack (32) arranged radially outward from the inner shaft (21) and including at least one preloaded ball bearing (40) and a second bearing stack (36), the second bearing stack (36) arranged radially outward from the outer shaft (26) and comprising at least one ball bearing. The arrangement may include a bearing stack retainer (50), the bearing stack retainer (50) mating with the first and second bearing stacks (32, 36) to hold the first and second bearing stacks (32, 36) in position with respect to the inner and outer shafts (21, 26) and the bearing stack retainer (50) coupled with and rotating with the outer shaft (26).