Composite Rotor Sleeve for Magnet Containment Under Centrifugal Load
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-power electric machines, particularly those used in aircraft, securely affixing permanent magnets to the rotor core is challenging due to incompatible materials and high centrifugal forces, leading to safety issues and reduced power density from increased rotor-stator distance and weight concerns of conventional rotor banding systems.
Innovation Solution
A rotor sleeve composed of an inner layer of wound filaments with a low modulus of elasticity and an outer layer with a higher modulus, pre-stressed to resist centrifugal forces, is used to securely contain the magnets, with the inner layer made from materials like glass fibers and the outer layer from carbon or ceramic fibers, arranged at specific angles to optimize strength and reduce thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional rotor banding system is used to contain permanent magnets, then the magnets are securely contained under centrifugal forces, but the rotor-stator distance increases and power density decreases
Solution Approach 1:
The rotor banding uses a composite structure with an inner layer of glass fibre filaments and an outer layer of carbon fibre filaments. The glass fibre inner layer provides flexibility and stress distribution, while the carbon fibre outer layer provides high stiffness and strength. This composite material approach achieves effective magnet containment with a thinner banding structure, reducing the rotor-stator distance and improving power density.
Solution Approach 2:
Different layers of the rotor banding have different material properties optimized for their specific functions. The inner layer uses glass fibre with lower modulus for flexibility and stress distribution, while the outer layer uses carbon fibre with higher modulus for stiffness and strength. This local differentiation of material quality allows the banding to achieve effective containment with reduced thickness.
2Power
If the rotor sleeve thickness is reduced to increase power density, then the air gap decreases and power density increases, but the ability to resist centrifugal forces is compromised
Solution Approach 1:
The multi-layer composite structure combines materials with different mechanical properties to achieve high strength-to-thickness ratio. The glass fibre inner layer and carbon fibre outer layer work together to provide the necessary centrifugal force resistance in a thinner configuration, enabling reduced sleeve thickness while maintaining strength.
Solution Approach 2:
The rotor banding is pre-stressed during installation to apply initial compressive forces on the permanent magnets. This preliminary action creates a pre-load that helps counteract centrifugal forces during operation, allowing the banding to be thinner while still providing adequate containment under high-speed rotation.
3Reliability
If high pre-stress is applied to the rotor sleeve to improve magnet containment, then the containment effectiveness increases, but the sleeve material requirements and manufacturing complexity increase
Solution Approach 1:
The composite structure of glass fibre and carbon fibre layers is designed to distribute and manage pre-stress effectively. The glass fibre inner layer provides stress distribution and flexibility, while the carbon fibre outer layer provides high stiffness to maintain the pre-stress state. This material combination facilitates the application of high pre-stress while managing manufacturing complexity through standardized composite fabrication processes.
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 solution effectively contains the magnets under high centrifugal forces, reducing the rotor sleeve thickness, weight, and increasing power density by allowing higher pre-stress levels, resulting in a stronger, lighter design that enhances torque transmission and reduces the air gap between the rotor and stator.
Implementation Method 1
high centrifugal forces which act to drive the magnets radially outwards
Implementation Method 2
an inner layer of wound filaments comprising a first material having a first modulus of elasticity
Implementation Method 3
an outer layer of wound filaments wound around the inner layer, the outer layer comprising a second material having a second modulus of elasticity higher than the first modulus
Implementation Method 4
The inner and/or outer layer of wound filaments may comprise pre-stressed filaments. The outer layer of wound filaments may be pre-stressed to a stress of greater than 1000 MPa
Implementation Method 5
resistant to centrifugal forces in use, thereby providing effective containment of the rotor
Data Source
AI summary
A rotor sleeve (46) for a rotor (29) of an electric machine (28), the rotor sleeve (46) comprising:an inner layer (52) of wound filaments (56) comprising a first material having a first modulus of elasticity; andan outer layer (54) of wound filaments (60) wound around the inner layer (52),the outer layer (54) comprising a second material having a second modulus of elasticity higher than the first modulus.