Aircraft Generator Rotor Stator Air Gap Control
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Solution Overview
Problem
The increasing size of electric machines in aircraft gas turbine engines due to rising electrical power demands poses challenges in packaging within limited space, and existing solutions are heavy, complex, and inefficient, with difficulties in maintaining accurate rotor-stator air gaps and engine balance.
Innovation Solution
An aircraft gas turbine engine design featuring a self-contained electric machine with separate bearings for the rotor and stator, allowing independent control of the rotor-stator air gap and flexible mounting to accommodate movement, enabling efficient packaging and minimizing loads on the electric machine bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If electric machines are installed within the annular space radially inward of a compressor (embedded generators), then packaging efficiency is improved, but maintaining accurate rotor-stator air gaps becomes difficult
Solution Approach 1:
The electric machine is segmented into independent rotor and stator components with separate bearing arrangements. The rotor has its own bearing arrangement extending between the rotor and stator, while the stator is mounted to static structure by a mount member. This segmentation allows each component to be precisely positioned and maintained independently, solving the air gap accuracy problem while maintaining compact packaging.
Solution Approach 2:
The stator mount member is designed with flexible mounting capabilities to accommodate movement between the rotor and stator during engine operation. This dynamic mounting approach allows the air gap to be maintained accurately despite thermal expansion, vibration, and engine flexing, resolving the contradiction between compact packaging and air gap precision.
2Ease of operation
If conventional packaging arrangements with bevel gears and angle drive shafts are used, then the electric machine can be mounted, but the system becomes heavy and complex
Solution Approach 1:
The complex gearing system (bevel gears and angle drive shafts) is completely removed from the electric machine mounting arrangement. Instead, the electric machine is directly integrated into the engine structure with the rotor mounted to the main engine shaft and the stator mounted to static structure, eliminating unnecessary mechanical complexity while maintaining mounting capability.
Solution Approach 2:
The electric machine bearing arrangements are merged with the engine's existing bearing systems. The rotor bearing arrangement integrates with the main engine shaft bearing, and the stator is mounted to the engine's static structure, combining multiple functions into a unified system that reduces overall complexity.
3Volume of moving object
If the electric machine is flexibly mounted to accommodate engine movement, then packaging efficiency is improved, but vibrations may affect the rotor-stator air gap
Solution Approach 1:
The stator mount member acts as an intermediary element between the static engine structure and the electric machine stator. It provides flexible mounting to accommodate engine movement while maintaining air gap stability through its designed compliance and damping characteristics, isolating the rotor-stator air gap from vibrations and structural flexing.
Solution Approach 2:
The mount member's mechanical parameters (stiffness, damping, compliance) are optimized to filter out vibrations and movements that would affect the air gap. By carefully selecting and tuning these parameters, the system achieves both flexible mounting for compact packaging and stable air gap for reliable operation.
Data Source
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AI summary
An aircraft gas turbine engine (10) comprises a main engine shaft (22, 23), a main engine shaft bearing arrangement (36, 49, 50) configured to rotatably support the main engine shaft (22, 23), and an electric machine (30) comprising a rotor (32) and a stator (34). The rotor (32) is mounted to the main engine shaft (22, 23) and is rotatably supported by a further electric machine bearing arrangement (70, 72) extending between the rotor (34) and the stator (32), and the stator (32) is mounted to static structure (38) of the gas turbine engine (10).