Canted Electrical Machine Axis for Gas Turbine Torque Density
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Solution Overview
Problem
In aero gas turbine engines, the compactness and arrangement of components like the ancillary gearbox and electrical machine are crucial to avoid increases in nacelle size and drag, which existing designs struggle to achieve efficiently, especially with larger diameter electrical machines that require a significant step-down ratio and torque density.
Innovation Solution
The electrical machine's axis of rotation is canted with respect to the main rotational axis of the gas turbine engine, often at angles between 45° and 90°, allowing for a larger diameter to axial length ratio, which enables tighter packaging and increased torque density, potentially eliminating the need for a gearbox by incorporating a rotor gear for direct drive and optimizing the arrangement to reduce the radial footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electrical machine diameter is increased to achieve larger step-down ratio and torque density, then the torque density and step-down ratio improve, but the packaging space requirement and nacelle size increase
Solution Approach 1:
The electrical machine is oriented with its rotational axis substantially perpendicular to the main shaft axis, transitioning from a conventional parallel alignment to a perpendicular configuration. This dimensional reorientation allows the electrical machine to be positioned in the radial direction rather than extending axially, achieving high torque density while minimizing the axial packaging space required in the gas turbine engine
2Power
If the electrical machine diameter is increased to achieve larger step-down ratio, then the step-down ratio improves, but the centrifugal forces on the rotor increase
Solution Approach 1:
The patent changes the geometric parameters of the electrical machine by increasing its diameter while maintaining a high diameter-to-length ratio (at least 2.5:1). This parameter optimization allows the rotor to achieve the required step-down ratio (4:1 to 8:1) while the perpendicular orientation and compact axial length minimize the rotational speed and associated centrifugal forces on the rotor
3Power
If the electrical machine is oriented with larger diameter relative to axial length, then the torque density and step-down ratio improve, but the arrangement complexity and packaging difficulty increase
Solution Approach 1:
By orienting the electrical machine with its axis perpendicular to the main shaft and positioning it in the radial direction, the patent simplifies the overall packaging arrangement. The direct perpendicular connection eliminates the need for complex intermediate gear trains, reducing mechanical complexity while achieving the required step-down ratio through the rotor-stator magnetic coupling
Solution Approach 2:
The patent combines the electrical machine directly with the rotor assembly, integrating the magnetic coupling mechanism into the rotor structure itself. This merging of functions allows the electrical machine to serve both as the power generation component and as the step-down mechanism, eliminating separate gearbox components and simplifying the overall arrangement
Data Source
AI summary
A gas turbine engine comprising an electrical machine 30, 130, 200, 210, the electrical machine 30, 130, 200, 210 having an axis of rotation that is canted with respect to the main rotational axis of the gas turbine engine.