SMA Torque Tube Motor for Continuous Rotor Bow Mitigation
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Solution Overview
Problem
Aircraft gas turbine engines experience rotor shaft bowing due to uneven cooling after shutdown, leading to potential engine damage and vibrations, which existing methods struggle to mitigate efficiently, especially in scenarios where power is limited or unavailable, causing departure delays and increased costs.
Innovation Solution
A motor assembly using cooperatively connected torque tubes made from shape memory alloys (SMAs) that generate continuous torque by changing shape in response to heat, connected to the rotor shaft to reduce or prevent thermal bowing, with a ratcheting mechanism ensuring continuous torque output and efficient operation without the need for constant power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional power sources (batteries, APU, facility power) are used to power the ETM, then the rotor shaft can be turned to reduce thermal bowing, but the system becomes dependent on external power sources which may not be available, increasing complexity and reducing reliability
Solution Approach 1:
The SMA torque tubes generate mechanical work autonomously by utilizing the temperature difference between the hot rotor shaft and the cooler environment. The shape memory alloy material inherently converts thermal energy into mechanical torque without requiring external power sources, control systems, or complex infrastructure, enabling the ETM to function independently in any operational scenario.
Solution Approach 2:
The patent replaces conventional electromechanical motor systems with a thermomechanical system based on shape memory alloy. Instead of using electrical motors that require power supply infrastructure, the SMA torque tubes directly convert thermal energy into rotational mechanical work through phase transformation, eliminating the need for complex electrical power systems.
2Adaptability or versatility
If lithium-ion or nickel-cadmium batteries are used to power the ETM, then the engine can be turned without external power, but the batteries have high failure rates and flammability concerns in the extreme engine environment
Solution Approach 1:
The patent eliminates vulnerable electrical battery systems by employing shape memory alloy torque tubes that convert thermal energy directly into mechanical work. This thermomechanical approach removes all electrical components from the ETM system, eliminating battery failure modes and flammability risks while maintaining operational independence.
Solution Approach 2:
The SMA torque tubes autonomously generate torque by exploiting the natural temperature gradient between the hot rotor shaft and ambient environment. The system requires no external power supply, control electronics, or vulnerable energy storage devices, as the shape memory effect inherently converts available thermal energy into useful mechanical rotation.
3Object-affected harmful factors
If the engine is motored at low RPM after starting to straighten the rotor shaft, then thermal bowing can be reduced, but departure delays occur and operational costs increase
Solution Approach 1:
The SMA torque tubes are heated periodically or sequentially to generate torque pulses that rotate the rotor shaft. By controlling the heating cycles of multiple torque tubes, the system achieves continuous rotation at optimal speeds to straighten the rotor shaft quickly, minimizing the time the engine remains stationary and reducing departure delays.
Solution Approach 2:
The system dynamically adjusts the heating parameters of the SMA torque tubes to optimize rotation speed. By controlling the temperature and heating rate of the shape memory alloy, the ETM can achieve higher rotational speeds compared to conventional low-RPM motoring, thereby reducing the time required to eliminate thermal bowing and allowing earlier departure.
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 SMA motor effectively reduces rotor shaft bowing, preventing engine damage and vibrations, while being lightweight and power-efficient, reducing departure delays and operational costs by allowing for autonomous rotor straightening without relying on external power sources.
Implementation Method 1
A motor assembly using cooperatively connected torque tubes made from shape memory alloys (SMAs) that generate continuous torque by changing shape in response to heat
Implementation Method 2
with a ratcheting mechanism ensuring continuous torque output and efficient operation
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
An engine turning "clock work" motor including two shape memory alloy (SMA) torque tube actuators, ratcheting mechanisms, and gearing. The gearing communicates the SMA torque tube actuators with a common gear that applies torque to a shaft, so that while one torque tube is heated and applying torque, the other torque tube is relaxed (using a cooling mechanism). The ratchet prevents the relaxing torque tube from applying torque in the incorrect direction.