Permanent Magnet Rotor Retaining Ribs for Minimal Air Gap
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Solution Overview
Problem
The existing designs for electric machine rotors with permanent magnets result in a relatively large magnetically relevant distance between the magnets and the stator, leading to poor efficiency due to the need for a significant gap and radial thickness of casings, which are also prone to damage and assembly challenges.
Innovation Solution
The use of web-shaped holding elements that cover permanent magnets on their outer surfaces, either centrally or on one side, minimizing the distance between the magnets and the stator by avoiding coverage of the edges, and employing connecting rings for secure attachment, allowing for a more efficient and robust connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal or plastic casing surrounds the permanent magnets, then the permanent magnets are secured against being lost during operation, but the magnetically relevant distance between the rotor's permanent magnets and the stator coils increases, leading to poor efficiency
Solution Approach 1:
The casing is divided into multiple individual retaining elements that are distributed around the permanent magnets. Each retaining element is a separate component that can be independently positioned and secured, allowing for localized support without requiring a continuous casing structure. This segmentation enables the magnetic field to pass through the gaps between retaining elements, reducing the overall magnetic resistance while maintaining mechanical security.
Solution Approach 2:
The retaining elements are designed with varying properties: they have a first section that contacts the permanent magnet for secure retention, and a second section that extends toward the stator but maintains controlled spacing. This local differentiation allows the structure to provide mechanical support where needed while preserving magnetic field continuity in critical areas, optimizing both security and efficiency.
2Loss of energy
If the casing is designed with minimal radial thickness, then the magnetically relevant distance is reduced, but the casing becomes highly susceptible to damage and assembly difficulties arise
Solution Approach 1:
Instead of a single thin-walled casing, the structure is divided into multiple discrete retaining elements. Each element can be independently manufactured with optimal thickness for its specific function, and the gaps between elements provide structural reinforcement while maintaining minimal overall thickness. This segmentation eliminates the weakness of continuous thin walls while achieving the goal of reduced magnetic distance.
Solution Approach 2:
The retaining elements are designed to utilize composite construction, combining materials with different properties in a single component. The elements may incorporate high-strength materials in critical load-bearing sections while using lighter materials in non-critical areas, achieving both damage resistance and minimal thickness requirements for optimal magnetic performance.
3Ease of manufacture
If web-shaped retaining clips project into external recesses of the permanent magnets, then assembly is facilitated, but the magnetically relevant distance increases due to the covering structure
Solution Approach 1:
The retaining elements are designed to engage with the permanent magnets primarily in the axial dimension rather than projecting radially inward. By utilizing the axial direction for assembly engagement and the radial direction for magnetic field passage, the design achieves easy assembly without compromising magnetic efficiency. The retaining elements connect to the magnet ends or sides, allowing radial magnetic field lines to remain unobstructed.
Data Source
Figure 1
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AI summary
A rotor (1) for an electric machine comprises a rotor shaft (2), a base body (3) that is non-rotatably connected to and surrounds the rotor shaft (2), and a plurality of permanent magnets (4) that are connected to the base body (3) externally in an annular arrangement. Furthermore, a plurality of rib-shaped retaining elements (9) are provided, each of which externally covers at least one of the permanent magnets (4) such that it covers the respective permanent magnet(s) (4) either on its outer surface exclusively in a section located centrally with respect to the circumferential direction of the rotor (1) or exclusively on one side surface of each permanent magnet (4). The retaining elements (9) should therefore not cover at least the edges of the permanent magnets (4) where the respective outer surfaces transition into one of the associated side surfaces.This makes it possible to form the smallest possible magnetically effective distance between the permanent magnets (4) of the rotor (1) and an associated stator.