Air Cycle Machine Seal Land Radial Clearance Design
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Solution Overview
Problem
Existing seals in air cycle machines fail to effectively manage air leakage between the shaft and housing, particularly in high-pressure applications, leading to inefficiencies in air compression and expansion processes.
Innovation Solution
A seal design featuring a polyimide material with a specific ratio of outer to inner diameter and tapered surfaces is used, which engages knife edges on the shaft to create a controlled radial clearance, allowing for controlled air leakage while maintaining the integrity of the air cycle machine's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If existing seal designs are used, then the seal structure is simple and easy to manufacture, but air leakage between the shaft and housing is not effectively controlled
Solution Approach 1:
The seal land is provided with a specific radial clearance (0.004-0.006 inch) that is optimized for air leakage control, while the tapered surface (15-30 degrees) provides localized geometric optimization. This local quality enhancement at critical areas allows effective air leakage management without requiring complete redesign of the entire seal structure.
Solution Approach 2:
The invention specifies precise parameter ranges: radial clearance of 0.004-0.006 inch, tapered angle of 15-30 degrees, and polyimide material properties. These parameter optimizations enable the seal to achieve effective air leakage control while maintaining manufacturability through standard machining tolerances and material availability.
2Productivity
If a tight seal is used to prevent air leakage, then air compression and expansion efficiency improves, but the seal may fail to accommodate shaft movement and wear
Solution Approach 1:
The invention converts the potentially harmful effect of air leakage into a beneficial controlled clearance system. The radial clearance of 0.004-0.006 inch allows minimal controlled air passage that lubricates the seal interface, reducing friction and wear while maintaining sufficient sealing effectiveness for high-pressure applications.
Solution Approach 2:
The tapered surface geometry (15-30 degrees) and radial clearance design allow the seal to dynamically adapt to shaft movement and rotation. The geometry enables the seal to maintain contact with the knife edges while accommodating operational dynamics, ensuring both sealing effectiveness and durability under varying operating conditions.
3Loss of energy
If the seal radial clearance is reduced to minimize air leakage, then compression efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention specifies a radial clearance range of 0.004-0.006 inch, which balances air leakage control with manufacturability. This parameter optimization achieves effective sealing without requiring ultra-precise manufacturing tolerances, making the seal practical for production while maintaining performance.
Solution Approach 2:
The tapered surface geometry (15-30 degrees) provides localized geometric control that compensates for variations in radial clearance. This local geometric optimization ensures consistent sealing performance across production batches even with normal manufacturing tolerances, reducing the stringency of precision requirements.
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 seal design effectively reduces air leakage, optimizing the air compression and expansion processes by providing a precise radial clearance, thereby enhancing the efficiency and reliability of the air cycle machine's operation.
Implementation Method 1
A radial clearance between the seal land and the knife edges is nominally 0.006 inch in one example
Implementation Method 2
a tapered surface extending at an angle relative to the outer diameter from the lateral side to the seal land, the tapered surface facing the large end
Data Source
AI summary
An air cycle machine includes a bearing housing with a shaft bore. A rotor shaft is arranged in the shaft bore and includes knife edges extending from the rotor shaft. A seal engages the shaft bore and includes an outer diameter and an inner diameter providing a seal land axially aligned with the knife edges. A radial clearance between the seal land and the knife edges is nominally 0.006 inch. The inner diameter is arranged between lateral sides of the seal that define a width. In one example, a tapered surface extending at an angle relative to the outer diameter from the lateral side to the seal land, the tapered surface facing the large end. The outer diameter to the inner diameter provides a first ratio of 1.25-1.28, and the inner diameter to the width provides a second ratio of 4.33-5.58.