Variable-Flux Rotor Magnet Layout to Prevent Demagnetization
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Solution Overview
Problem
Existing electric machines with variable magnetic flux face challenges in preventing demagnetization of permanent magnets due to transverse fields, especially under high load conditions, which affects efficiency and torque density, particularly in applications like electric vehicles.
Innovation Solution
The use of permanently magnets of two types with different coercivity levels, along with strategically placed cavities to reduce inductance and prevent transverse fields, and controlled three-phase current application to armature coils for magnetization and demagnetization, combined with specific arrangements of magnets and cavities to enhance magnetic flux and torque density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If permanent magnets with low coercive field strength are used to achieve high torque density, then torque density is improved, but the magnets are susceptible to demagnetization by transverse fields
Solution Approach 1:
The rotor is divided into multiple magnetic poles, each containing permanent magnets arranged in specific patterns. This segmentation allows the magnetic field to be distributed and controlled across different regions, reducing the impact of transverse fields on individual magnets while maintaining high torque density through optimized pole configurations
Solution Approach 2:
Different regions of the rotor are designed with different magnet arrangements and cavity configurations. Cavities are strategically placed in specific locations to provide localized protection against transverse fields, while other regions are optimized for maximum torque production. This local differentiation allows simultaneous achievement of high torque density and magnet protection
2Force
If permanent magnets are magnetized at high load conditions to deliver high torque, then torque output is improved, but the magnets are exposed to higher risk of demagnetization
Solution Approach 1:
The rotor design incorporates pre-configured cavities and magnetic pole arrangements that create protective magnetic pathways before high-load conditions occur. These pre-designed structural features actively counteract the demagnetizing effect of transverse fields that would otherwise occur during high-torque operation, allowing the magnets to operate at full capacity without excessive demagnetization risk
3Reliability
If high coercive field strength magnets like SmCo are used to prevent demagnetization, then magnet stability is improved, but torque density and temperature resistance are reduced
Solution Approach 1:
The invention changes the operational parameters of low-coercivity magnets through optimized magnetic circuit design. By adjusting the magnetic flux distribution, pole configurations, and cavity dimensions, the effective operating point of the magnets is shifted to regions where they can operate at high torque density without exceeding their demagnetization thresholds, achieving performance comparable to or exceeding high-coercivity materials
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 solution effectively prevents demagnetization, allows for efficient operation under varying load conditions, and enables the use of low-coercivity magnets like AlNiCo for high load applications, achieving higher torque density and temperature resistance while minimizing energy losses.
Implementation Method 1
a rotor element (12) rotating about a rotational axis (R) and forming, with its radial center axis (d), a magnetic pole (P)
Implementation Method 2
the magnetization of the permanent magnets of the first type can be varied by a current pulse in the stator, which generates a magnetic force
Implementation Method 3
at least two cavities (18a, 18b), which reduce inductance along the transverse axis (q) and thus represent a first magnetic barrier
Data Source
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AI summary
The invention provides an electric machine with variable magnetic flux having a plurality of angular segments (10; 10'; 10"), each comprising: an outer stator element (11) with a plurality of armature coils (13a - 13f) wound around respective armature cores (14a - 14g); an inner rotor element (12; 12'; 12") whose radial central axis (d) forms a magnetic pole (P), with a rotor core (15; 15'; 15") rotatable about a rotational axis (R); wherein the rotor element (12; 12'; 12") comprises one or more permanent magnets (16; 16'; 16") of a first type and one or more permanent magnets (17a, 17b; 17a', 17b'; 17a", 17b") of a second type, wherein the permanent magnets (16, 17a, 17b; 16', 17a', 17b'; 16", 17a", 17b") of the first and second type are arranged symmetrically to the radial central axis (d), wherein the permanent magnets (16; 16'; 16") of the first type have a lower coercive field strength than the permanent magnets (17a, 17b;17a', 17b'; 17a", 17b") of the second type, wherein the permanent magnets (16; 16'; 16") of the first type are magnetized parallel to the radial central axis (d), wherein a magnetization (Q, Q') of the permanent magnets (17a, 17b; 17a', 17b'; 17a", 17b") of the second type has an angle to the magnetic pole (P), wherein the magnetization (Q, Q') of the permanent magnets (17a, 17b; 17a', 17b'; 17a", 17b") of the second type points towards the interior of the angular segment (10; 10'; 10"), wherein the permanent magnets (17a, 17b; 17a', 17b'; 17a", 17b") of the second type are closer to the axis of rotation (R) than the permanent magnets (16; 16'; 16") of the first type, wherein at least two cavities (18a, 18b; 18a', 18b'; 18a", 18b") are arranged on a side of the rotor core facing the stator.;