Interior Rotor Slot Geometry for Wide-Speed Torque and Efficiency
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Solution Overview
Problem
Existing electric machines face challenges in achieving high performance metrics such as torque density, power density, efficiency, and maximum speed while reducing costs, particularly in light, small, and medium electric vehicle applications, due to issues with magnet retention, flux linkage, and limited saliency in hybrid machines, and volatile rare-earth material prices.
Innovation Solution
The design incorporates a rotor with nested semi-hexagonal slots and dual field windings (q-axis and d-axis) embedded in magnetically permeable material, allowing for increased saliency and flux linkage, reducing magnet content, and utilizing additively manufactured structural support to enhance mechanical integrity and thermal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If magnet content is increased to achieve high peak torque, then peak torque capability is improved, but core losses increase and efficiency deteriorates in low-torque regions
Solution Approach 1:
The rotor is divided into multiple independent rotor assemblies, each with its own magnets and field windings. This segmentation allows selective activation of magnet groups based on operating conditions - full magnet activation for peak torque, selective deactivation for low-torque regions to reduce core losses.
Solution Approach 2:
The patent implements dynamic control of magnet excitation through independently controllable field windings for each rotor assembly. The excitation state of magnets can be dynamically adjusted between fully excited, partially excited, and unexcited states, enabling adaptive optimization of torque production and loss reduction across different operating regions.
2Power
If magnet content is increased to achieve high power density, then power density is improved, but material cost increases due to rare-earth materials
Solution Approach 1:
The rotor system is segmented into multiple independent rotor assemblies with selective magnet placement. This allows the machine to achieve high power density when needed while using significantly less total rare-earth material compared to a conventional single-rotor design with continuous magnet coverage.
Solution Approach 2:
The patent changes the operational parameters of magnets from continuous excitation to selective excitation. By controlling the excitation state of individual rotor assemblies, the system can achieve high power density output while maintaining lower overall magnet content, thus reducing rare-earth material requirements.
3Speed
If rotor slots are configured to house field windings, then torque production over wide speed range is improved, but device complexity increases
Solution Approach 1:
The rotor is divided into multiple independent rotor assemblies that can be manufactured separately and then assembled. Each assembly contains standardized slot configurations for field windings, which simplifies individual manufacturing while the modular assembly approach manages overall system complexity.
Solution Approach 2:
Multiple rotor assemblies are nested or coupled together within the stator structure. This nested configuration allows complex torque production capabilities to be achieved through combination of simpler, standardized rotor assemblies, effectively managing device complexity through hierarchical structuring.
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 configuration enables high efficiency at low and continuous torque operating points, supports short bursts of peak torques over a wide speed range, and reduces material costs, resulting in improved peak power density and operational flexibility.
Implementation Method 1
rotor q-axis and d-axis field windings, which produce flux linkages
Implementation Method 2
allowing for increased saliency and reduced magnet content, enabling high torque production
Data Source
AI summary
Example electric machines presented herein generally include an embedded rotor slot geometry that can promote rotor q-axis flux linkage. The slot geometry can form concentric branches of magnetic material between slots that follow curvature of q-axis flux when current is flowed through rotor q-axis field windings positioned within a first portion of the slots. Current direction through rotor q-axis field windings can be aligned within a single pole and alternate in direction between poles so that q-axis flux from adjacent poles is additive along q-axes. A second portion of the slots can include rotor d-axis field windings positioned therein and configured to produce flux on the d-axis. A portion of the rotor d-axis field windings and/or rotor q-axis field windings can be replaced with magnets to achieve differing torque and efficiency profiles.