Starter Generator Braking Relay for Aircraft Engine Windmilling
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Solution Overview
Problem
Gas turbine engines in aircraft propulsion systems and auxiliary power units are susceptible to windmilling during various operating conditions, leading to undesirable wear and increased risk of fire due to lubricant circulation, and existing systems do not adequately address these issues.
Innovation Solution
A braking control assembly that includes a starter generator and a control relay with a switch and variable resistor, which selectively connects or isolates electrical terminals to apply a braking force to the rotational assembly, preventing windmilling by controlling the rotation speed and magnitude of the braking force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the starter generator is used to drive rotation of the rotational assembly, then the engine can be started, but the starter generator cannot provide braking force to prevent windmilling
Solution Approach 1:
The starter generator operates dynamically in two distinct modes: motor mode for engine starting and generator mode for windmilling prevention. The control relay dynamically switches between connecting the motor winding to the battery (motor mode) and connecting the motor winding terminals together (generator mode), allowing the same device to perform both functions reliably
Solution Approach 2:
The starter generator serves multiple functions: it acts as a motor to crank the engine during startup, and as a generator to provide braking force during windmilling conditions. This multi-functionality eliminates the need for separate starting and braking systems, while the control relay enables seamless transition between these opposing operational modes
2Object-affected harmful factors
If a braking force is applied to prevent windmilling, then fire risk is reduced, but the engine cannot be restarted after shutdown
Solution Approach 1:
The control relay implements periodic switching between braking mode and motor mode based on operational requirements. During normal operation, the relay maintains braking mode to prevent windmilling. When restart is required, the relay periodically switches to motor mode to provide cranking power, then returns to braking mode once rotation is established, allowing controlled restart while maintaining fire prevention
Solution Approach 2:
The control relay responds to feedback signals from the engine control unit regarding rotational speed and operational state. When windmilling is detected, the relay applies braking. When restart is commanded and rotational speed indicates successful cranking, the relay disengages braking and allows motor mode operation, enabling intelligent transition between safety and operational modes
3Force
If the switch directly connects the motor winding terminals, then a strong braking force is applied, but the braking force cannot be controlled or modulated
Solution Approach 1:
The variable resistor changes the electrical resistance parameter in the motor winding circuit to modulate the braking force. By varying resistance values, the current through the motor winding is controlled, which directly controls the magnitude of the electromagnetic braking force. This allows the system to adapt braking intensity to different operational conditions such as varying rotational speeds and windmilling severity
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
Effectively prevents windmilling and reduces the risk of fire by applying a controlled braking force to the rotational assembly, thereby mitigating wear and fire hazards during operational and inoperative conditions of the gas turbine engine.
Implementation Method 1
The starter generator is configured to selectively drive rotation of the rotational assembly
Implementation Method 2
the starter generator may be configured to resist rotation of the rotational assembly with the switch in the second contact position
Data Source
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AI summary
An assembly for a gas turbine engine of an aircraft includes a rotational assembly, a starter generator (28), and a control relay (54). The starter generator (28) is coupled with the rotational assembly and is configured to selectively drive rotation of the rotational assembly and a motor winding (64) including a first electrical terminal (65) and a second electrical terminal (66). The control relay (54) includes a switch (72) electrically connected to the first electrical terminal (65). The switch (72) is positionable in a first contact position and a second contact position, in the first contact position, the first electrical terminal (65) is electrically isolated from the second electrical terminal (66) through the switch (72). In the second contact position, the first electrical terminal (65) is electrically connected to the second electrical terminal (66) through the switch (72) such that a closed electrical circuit is formed through the motor winding (64), the first electrical terminal (65), the second electrical terminal (66), and the switch (72).