Cantilevered External Rotor Motor With Isolated Rotor-Stator Gap
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Solution Overview
Problem
Aircraft electric motors face challenges in achieving high efficiency and power density while maintaining a narrow rotor/stator gap, which requires high shaft stiffness, often leading to increased weight and reduced efficiency.
Innovation Solution
The design incorporates a combination of separate propeller support, bearing coupling between the rotor and stator, and mechanical isolation to reduce forces on the rotor/stator gap, along with an improved heatsink design using a two-level structure and flexible couplers to manage axial and radial forces, and enhance torque transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If more shaft material is added to increase shaft stiffness for maintaining narrow rotor/stator gap, then the rotor/stator gap can be maintained, but the motor weight increases and specific power decreases
Solution Approach 1:
A flexible coupler is introduced as an intermediary element between the propeller shaft and the rotor. This coupler isolates the rotor/stator gap from propeller forces (radial and axial), allowing the gap to be maintained at narrow tolerances without requiring excessive shaft stiffness. The flexible coupler absorbs and isolates these forces, enabling the use of lighter shaft materials while maintaining manufacturing precision of the critical gap dimension.
2Manufacturing precision
If shaft stiffness is increased to maintain narrow rotor/stator gap, then gap stability is improved, but motor efficiency decreases
Solution Approach 1:
The flexible coupler serves as a mediator that protects the narrow rotor/stator gap from destabilizing forces generated by the propeller. By isolating the gap from radial and axial forces through this intermediary element, the system maintains gap stability without requiring increased shaft stiffness, thereby avoiding the associated efficiency losses from excessive structural mass and reduced specific power.
3Weight of moving object
If mechanical isolation is implemented to reduce forces on rotor/stator gap, then weight can be reduced, but device complexity increases
Solution Approach 1:
The flexible coupler provides mechanical isolation between the propeller and rotor, reducing forces on the rotor/stator gap and enabling weight reduction. Despite the addition of this component, the overall complexity increase is managed because the coupler is a relatively simple element that addresses multiple force components (radial and axial) simultaneously, and it enables the use of lighter shaft materials that would otherwise be required to handle these forces.
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
This approach allows for a lighter weight, high-efficiency electric motor with improved torque transmission and heat management, maintaining a narrow rotor/stator clearance while resisting axial and radial forces, thus enhancing power density and reducing unnecessary weight.
Implementation Method 1
A flexible coupler is positioned between at least one of a first portion of the rotatable shaft and a second portion of the rotatable shaft and between the stator and the frame isolating the stator and rotor from relative radial or axial force
Implementation Method 2
a first bearing assembly supports a first portion of the shaft that joins an outer surface of the shaft and an inner portion of the stator restraining relative motion between the stator and rotor to coaxial rotation
Data Source
AI summary
A high-efficiency, high specific power electric motor/generator for aircraft use provides a cantilevered external rotor removed from load thrust and vibration by an isolator and hearing set between the rotor and stator reducing material demands and weight otherwise required for stiffness to preserve close rotor/stator proximity.