Hybrid Propeller Shaft Seal with Tortuous Leakage Path
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Solution Overview
Problem
Existing propeller shaft seals in aircraft systems wear out and leak lubricant, causing environmental issues and customer dissatisfaction.
Innovation Solution
A seal assembly comprising an inner and outer seal element with a lip seal, airflow openings, and a tortuous pathway design to minimize leakage and contamination, featuring a circumferentially split configuration for improved serviceability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional seals are used in propeller shaft bearing systems, then the structure is simple and easy to manufacture, but the seals wear out during operation and leak lubricant
Solution Approach 1:
The seal assembly is divided into multiple functional segments: an inner seal element with knife edges that rotates with the shaft, and an outer seal assembly that includes both a labyrinth seal and a lip seal. This segmentation allows each component to perform its specific function optimally while working together to provide comprehensive sealing, thereby improving reliability without excessive complexity.
Solution Approach 2:
The inner seal element is nested within the outer seal assembly, with the inner seal's knife edges interacting with the outer seal's labyrinth structure. The lip seal is further nested within the outer seal assembly, positioned to interact with the inner seal element. This nested configuration maximizes sealing effectiveness within a compact structure.
2Reliability
If seals are installed to prevent lubricant leakage, then lubricant retention is improved, but the seals wear in operation and begin to leak
Solution Approach 1:
Different regions of the seal assembly have different sealing mechanisms tailored to local requirements. The inner seal element uses knife edges for initial sealing and protection, the outer seal uses a labyrinth structure for drag reduction and secondary sealing, and the lip seal provides tertiary sealing. Each local region is optimized for its specific function, improving overall durability.
Solution Approach 2:
The seal assembly combines multiple sealing mechanisms (labyrinth seal, lip seal, and knife edges) into a composite sealing system. This composite approach leverages the advantages of each mechanism: the labyrinth seal reduces drag and provides structural support, the lip seal offers flexible contact sealing, and the knife edges provide sharp initial sealing. Together they create a more durable system than any single mechanism alone.
3Ease of repair
If a continuous seal structure is used, then sealing effectiveness is maximized, but serviceability and replacement become difficult
Solution Approach 1:
The outer seal assembly is segmented into separable components including the outer seal housing, labyrinth seal elements, and lip seal assembly. This segmentation allows the seals to be replaced as modular units without replacing the entire bearing system, improving serviceability while maintaining effective sealing through the coordinated design of the segmented components.
Solution Approach 2:
The seal assembly is designed with pre-positioned locating features and mounting interfaces that facilitate quick installation and removal. The inner seal element is pre-configured with knife edges that automatically engage with the outer seal, and the lip seal is pre-positioned to interact with the inner seal element, allowing for rapid replacement while ensuring proper sealing geometry is maintained.
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
Reduces lubricant leakage and contamination while enhancing seal performance and service life by utilizing airflow to control seal movement and creating a tortuous path to prevent linear leakage.
Implementation Method 1
one or more airflow openings are defined in the outer seal and are configured to inject airflow into a seal cavity to urge the seal lip radially away from the seal platform during operation
Implementation Method 2
The first circumferential seal segment includes one or more circumferentially extending first segment fingers installed into one or more complimentary second segment pockets at least partially defining a tortuous pathway in an axial direction between the first seal segment and the second seal segment
Data Source
AI summary
A seal assembly of a shaft bearing system includes an inner seal element fixed to a shaft and rotatable therewith about a shaft axis, and an outer seal assembly located radially outboard of the inner seal element and rotationally fixed relative to the shaft axis. The outer seal assembly includes an outer seal interactive with the inner seal element at a plurality of knife edges of the inner seal element, and a lip seal having a seal lip interactive with the inner seal element of the inner seal element. The outer seal assembly includes a first circumferential seal segment, and a second circumferential seal segment abutting the first circumferential seal segment at a seal joint.