Variable Frequency Generator Valve Assembly
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Solution Overview
Problem
Variable frequency generators in aerospace applications experience increased internal case pressure due to non-contact lift-off seals, leading to oil loss through venting, which results in an insufficient oil level over time.
Innovation Solution
A valve assembly with an oil restrictor and vent valve, utilizing a plurality of ball bearings that apply centrifugal force to bias the vent valve axially, ensuring a sealed condition during operation and controlled venting only during shutdown, preventing oil leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a non-contact lift-off seal is used to seal the generator, then sealing effectiveness is improved, but internal case pressure increases causing oil loss
Solution Approach 1:
A vent valve assembly is introduced as an intermediary component between the sealed generator interior and exterior. This valve selectively releases built-up pressure to prevent oil loss, while maintaining effective sealing during normal operation. The vent valve acts as a pressure relief mediator that opens only when necessary to maintain system balance.
Solution Approach 2:
The vent valve assembly changes its operational state based on pressure parameters. During normal operation, the valve remains closed to maintain sealing. When internal case pressure exceeds a threshold, the valve opens to release pressure, then closes again. This dynamic parameter-based control resolves the contradiction between maintaining seal integrity and preventing pressure-induced oil loss.
2Stress or pressure
If the vent valve remains open to release pressure, then case pressure is reduced, but oil leaks continuously during operation
Solution Approach 1:
The vent valve is designed as a dynamic component that automatically transitions between open and closed states based on real-time pressure conditions. During operation, the valve closes to prevent oil leakage. During shutdown, when pressure builds up, the valve opens to release pressure. This dynamic adaptability eliminates continuous oil leakage while still managing pressure effectively.
Solution Approach 2:
The vent valve assembly is designed to self-regulate pressure without external control. The valve automatically opens when pressure exceeds the threshold and closes when pressure is relieved, using the pressure differential itself as the control mechanism. This self-service capability ensures pressure management without compromising sealing or causing continuous oil loss.
3Reliability
If ball bearings are used to bias the vent valve, then sealing during operation is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical valve actuation systems with a simpler ball bearing-based mechanism. The ball bearings, positioned within the vent valve assembly, use pressure differential to automatically bias the valve closed during operation. This mechanical substitution eliminates the need for external actuators, sensors, or control systems, reducing overall device complexity while maintaining reliable sealing.
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 solution effectively maintains a sealed condition during operation and allows controlled venting during shutdown, preventing oil loss and ensuring adequate oil levels in the generator, even at high rotational speeds.
Implementation Method 1
imparting a centrifugal force on a plurality of ball bearings disposed within an annulus partially defined by an angled wall of a vent valve
Data Source
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AI summary
A valve assembly (30) for a variable frequency generator (10) includes an input shaft (12) extending about a longitudinal axis and having a bore (31) defined therein. Also included is a disconnect shaft (14) extending about the longitudinal axis and disposed in abutment with the input shaft (12). Further included is an oil restrictor disposed with the bore (31) of the input shaft (12). Yet further included is a vent valve (34) disposed within the bore (31) and in abutment with the oil restrictor, the vent valve (34) comprising an angled wall, the angled wall partially defining an annulus. Also included is a plurality of ball bearings (48) disposed within the annulus, the plurality of ball bearings (48) sliding radially outwardly away from the longitudinal axis during rotational operation of the input shaft (12) to apply a force on the angled wall of the vent valve (34) to bias the vent valve (34) axially into a sealed condition.