Aircraft Generator Disconnect Using Hydraulic Hold and Spring Release
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Solution Overview
Problem
Existing disconnect devices for aircraft engine generators face challenges such as insufficient actuating force, sensitivity to manufacturing tolerances, short service life, and inability to operate at zero speed, leading to unreliable disconnection in critical failure scenarios.
Innovation Solution
A fail-safe hydraulic disconnect device utilizing a spring-based disconnect biasing means and a fluid cavity that maintains the drive transfer means in a connected configuration with pressurized fluid, switching to a disconnected configuration upon pressure loss, ensuring reliable disconnection even in failure situations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If mechanical power is extracted from the rotating drive shaft to operate the disconnect mechanism, then very high actuating forces and rapid disconnection are achieved, but very accurate tolerances are required and the device becomes unreliable in the event of rotor bearing failure
Solution Approach 1:
The patent replaces the mechanical power extraction system with a hydraulic actuation system. Instead of using mechanical components to generate disconnect force, the invention uses hydraulic pressure from the engine's oil cooling system to actuate the disconnect mechanism, eliminating the need for mechanical power extraction and its associated tolerance and reliability issues.
Solution Approach 2:
The invention directly applies hydraulic pressure from the engine's oil cooling system to provide the axial force required for disconnection. The hydraulic actuator converts hydraulic pressure into mechanical force to move the drive transfer means axially, providing high actuating force without the reliability problems of mechanical power extraction systems.
2Reliability
If a large actuator and mechanical advantage generating mechanism are used, then a more robust assembly process and higher reliability are achieved, but the axial force produced is limited and may not be sufficient to guarantee disconnection
Solution Approach 1:
The invention uses hydraulic pressure from the engine's oil cooling system to generate high axial force through a hydraulic actuator. This hydraulic system provides both the robustness and reliability of a well-assembled mechanical system while delivering the high axial force (up to 5 kN) necessary to guarantee disconnection in all failure scenarios.
3Force
If hydraulic pressure from the oil cooling system is used to provide axial force, then very high disconnecting forces are achieved, but the method does not work in the event of a failure in the oil cooling system
Solution Approach 1:
The invention pre-charges the hydraulic accumulator with nitrogen gas during assembly, storing potential energy in advance. This preliminary action ensures that when hydraulic pressure is needed for disconnection, the accumulator can immediately provide the necessary force without relying on the oil cooling system being functional at the moment of failure.
Solution Approach 2:
The hydraulic accumulator acts as an intermediary between the hydraulic system and the disconnect mechanism. It stores hydraulic fluid under pressure and can deliver it independently of the oil cooling system's operational status, providing a backup mechanism that ensures disconnection capability even when the primary hydraulic system fails.
4Reliability
If the disconnect device requires the generator shaft to be turning at low speed or uses an additional layshaft, then disconnection can be achieved, but the power to weight ratio of the generator is reduced
Solution Approach 1:
The invention extracts and eliminates the additional layshaft component from the disconnect mechanism. By using a hydraulic actuator that can be integrated into the existing drive shaft structure, the design removes unnecessary mechanical components, reducing weight while maintaining the ability to achieve disconnection without requiring low-speed operation.
5Ease of manufacture
If the disconnect device is tested without being removed from the aircraft, then regular testing can be performed, but the generator and engine must be turning at minimum idle speed
Solution Approach 1:
The hydraulic accumulator is pre-charged with nitrogen gas during the assembly process, allowing the disconnect mechanism to be tested and verified without requiring the engine to be running. This self-service feature enables testing at zero speed by using the pre-stored hydraulic pressure to actuate the disconnect mechanism, eliminating the need for idle-speed operation during testing.
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 provides a reliable and high-force disconnection mechanism that operates at zero speed, overcoming limitations of existing devices by ensuring disconnection in all circumstances with a compact and robust design.
Implementation Method 1
a spring-based disconnect biasing means
Implementation Method 2
provision of a pressurised fluid in the fluid cavity biases the drive transfer means toward, and can retain the drive transfer means in, the connected configuration
Data Source
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AI summary
The present invention relates to a generator drive disconnect device, of a generator arranged to be driven by an aircraft engine. The disconnect device comprises: a drive transfer means (1) having a first, connected configuration, and a second, disconnected configuration; a disconnect biasing means (200), configured to bias the drive transfer means to the disconnected configuration; and a fluid cavity (300), configured such that provision of a pressurised fluid in the fluid cavity biases the drive transfer means to the connected configuration.