Composite Rotor Sleeve With Ferromagnetic Pins for Magnet Retention
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Solution Overview
Problem
High-speed electric machines require effective retention of permanent magnets to prevent instability and magnet lift-off, with existing solutions like carbon fibre composites facing challenges in achieving well-defined pre-stress and thermal management, particularly in high-power aerospace applications.
Innovation Solution
A rotor assembly featuring a laminated composite rotor sleeve with an array of ferromagnetic pins extending through its thickness, which reduces the effective gap between the rotor and stator coils, improving efficiency and thermal conductivity while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If carbon fibre composite rotor sleeves are used, then weight is reduced and specific strength is improved, but manufacturing precision and control of pre-stress are deteriorated
Solution Approach 1:
The patent applies preliminary action by pre-tensioning the carbon fibre rotor sleeve during manufacturing to establish controlled pre-stress before the sleeve is fitted to the rotor. This pre-tensioning process ensures that the sleeve maintains the required magnetic retention force while allowing for precise control of the pre-stress levels, thereby resolving the contradiction between using lightweight composite materials and achieving manufacturing precision.
2Ease of manufacture
If metallic banding is used, then ease of manufacture and thermal capability are improved, but weight increases and energy losses increase
Solution Approach 1:
The patent employs composite materials by using carbon fibre reinforced polymer (CFRP) for the rotor sleeve, combining the advantages of both metallic and composite materials. The CFRP provides lightweight construction with high specific strength, while the composite structure allows for controlled pre-stress application. This resolves the contradiction by achieving ease of manufacture through composite material properties while avoiding the weight and energy loss penalties of metallic banding.
3Reliability
If pre-tensioned rotor sleeves are used, then magnetic retention and stability are improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the pre-stress levels and material properties of the carbon fibre rotor sleeve to optimize magnetic retention. By adjusting parameters such as the pre-tension force, sleeve thickness, and fibre orientation, the patent achieves reliable magnet retention while maintaining a relatively simple sleeve structure. This resolves the contradiction by demonstrating that controlled parameter adjustments can improve reliability without proportionally increasing device complexity.
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 ferromagnetic pins enhance the magnetic flux channeling and thermal conductivity of the rotor sleeve, leading to improved efficiency and reduced weight, crucial for high-power and high-speed electric machines, particularly in aerospace applications.
Implementation Method 1
a laminated composite rotor sleeve with an array of ferromagnetic pins extending through its thickness, which reduces the effective gap between the rotor and stator coils
Implementation Method 2
The array of pins may extend around the rotor sleeve with a circumferential areal density of between 0.5% and 2%... the ferromagnetic pins enhance the magnetic flux channeling and thermal conductivity of the rotor sleeve
Data Source
AI summary
The disclosure relates to a stator assembly for an electric machine. Example embodiments disclosed include a rotor assembly for an electric machine, the rotor assembly comprising: a rotor core; a plurality of magnets arranged around the rotor core; and a cylindrical rotor sleeve surrounding the plurality of magnets, wherein the rotor sleeve comprises a laminated composite material having an array of ferromagnetic pins extending through a thickness of the rotor sleeve.