EV Rotor Magnet Retention Using Spring-Groove Cavities

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Solution Overview

Problem

Permanent magnets in electric machines shift out of their pockets due to centrifugal force and thermal expansion, leading to damage and reduced efficiency, and existing manufacturing methods for spring-groove connections are complex and costly.

Innovation Solution

Integrally manufactured permanent magnets with spring-groove connections using metal injection molding, featuring protrusions and recesses to secure the magnets in place, eliminating the need for separate mechanical machining.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If permanent magnets are arranged as far outward radially as possible on the rotor core to maximize efficiency, then the efficiency of the electric machine is improved, but the permanent magnets shift out of the pockets and into the radial gap due to centrifugal force at high speeds

Engineering Contradiction:

Improveefficiency of the electric machineVSAvoiddisplacement of permanent magnets

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent applies preliminary action by providing protrusions on the rotor core that extend into the magnetic receptacle cavities before the permanent magnets are installed. These protrusions pre-establish the mechanical constraints that will prevent centrifugal displacement during operation, allowing the magnets to be positioned as far outward as possible without risk of shifting into the radial gap

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The protrusions act as an intermediary element between the rotor core and the permanent magnets. They provide a form-fit connection that mechanically couples the magnets to the rotor core, preventing direct radial displacement while allowing the magnets to maintain their optimal outward position for maximum efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If protrusions are provided on magnetic receptacle cavities to secure permanent magnets in a form-fit manner, then displacement of permanent magnets is prevented, but the permanent magnets have to be offset in the direction of the axis of rotation away from the radial gap causing reduction in efficiency

Engineering Contradiction:

Improvesecuring of permanent magnetsVSAvoidefficiency of the electric machine

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent resolves this contradiction by changing the dimensional approach from axial offset to radial extension. Instead of offsetting magnets axially away from the gap (reducing efficiency), the protrusions extend radially into the magnetic receptacle cavities from the rotor core, providing form-fit securing while allowing magnets to remain as close as possible to the radial gap for maximum efficiency

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If recesses are provided on permanent magnets for spring-groove connection to prevent displacement, then the permanent magnets are secured against displacement in the direction of the radial gap, but the manufacture of permanent magnets becomes elaborate and costly requiring separate mechanical machining steps

Engineering Contradiction:

Improvesecuring of permanent magnetsVSAvoidmanufacture of permanent magnets

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies inversion by reversing which component carries the form-fit features. Instead of providing recesses in the permanent magnets (which are difficult to machine after sintering), the protrusions are provided on the rotor core. This allows the permanent magnets to be manufactured by simple sintering without subsequent mechanical machining, while still achieving secure form-fit connection through the protrusions extending into the magnetic receptacle cavities

Inventive Principle:

Principle #13The other way round (Inversion)

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 provides secure, cost-effective, and efficient retention of permanent magnets, enhancing the electric machine's performance by preventing displacement and maintaining proximity to the radial gap.

Implementation Method 1

the permanent magnets shift out of the respective pockets and into the radial gap due to the centrifugal force applied to them

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Implementation Method 2

the rotor core and the permanent magnets heat up during operation, wherein the different thermal expansion coefficients of the rotor core and the permanent magnet increase the risk of the permanent magnets shifting in the direction of the radial gap

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS12476501B2Rotor and electric machine of an electric vehicle

Publication Date: 2025.11.18 DR ING H C F PORSCHE AG

AI summary

A rotor of an electric machine of an electric vehicle includes a plurality of permanent magnets a rotor core, which includes a plurality of magnetic receptacle cavities, in each of which one permanent magnet is arranged. The permanent magnets are respectively connected to the rotor core via a spring-groove connection in a form-fit manner such that a displacement of the permanent magnets in a direction of an outer peripheral surface of the rotor core is blocked. The permanent magnets are each integrally manufactured by metal injection molding.