Variable Rotor Stator Alignment in Permanent Magnet Motors
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Solution Overview
Problem
Electric motors with high torque constants face inefficiencies at higher speeds due to back EMF and induced eddy currents, limiting maximum speed and increasing losses, making it desirable to vary the torque constant over the range of operation.
Innovation Solution
The design incorporates a magnetic rotor assembly with torque-generating magnets and a coil stator assembly, utilizing a lift-generating mechanism that changes the magnet engagement length with speed, reducing torque constant at higher speeds through induced eddy currents and a spring assembly to maintain efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a motor with high torque constant is used to produce high torque at low RPM, then torque output is improved, but back EMF and induced eddy currents increase at higher speeds, reducing maximum speed and efficiency
Solution Approach 1:
The patent applies the dynamics principle by making the magnet engagement length variable rather than fixed. The magnetic rotor assembly is designed to allow magnets to engage and disengage from the coil stator assembly dynamically based on rotational speed. At low speeds, more magnets are engaged to provide high torque constant, while at high speeds, fewer magnets remain engaged to reduce back EMF and rotational losses, thus adapting the motor characteristics to different operating conditions
Solution Approach 2:
The patent implements parameter changes by varying the effective magnet engagement length as a function of rotational speed. This is achieved through a mechanical design where centrifugal force or spring mechanisms cause magnets to lift off or engage with the stator at different speed thresholds, thereby changing the electromagnetic coupling parameter (torque constant) dynamically to optimize performance across the speed range
2Force
If a motor with high torque constant is used, then high torque at low RPM is achieved, but maximum speed is limited due to increased back EMF
Solution Approach 1:
The patent uses dynamics to enable the motor to transition between different operational modes. The magnetic rotor assembly incorporates a mechanism where magnets can dynamically engage or disengage from the stator based on rotational speed. This dynamic adjustment allows the motor to maintain high torque constant at low speeds while reducing it at high speeds, thereby extending the maximum achievable speed without sacrificing low-speed torque capability
3Force
If magnet engagement length is increased to maintain high torque constant, then torque output is improved, but rotational losses and back EMF increase at higher speeds
Solution Approach 1:
The patent applies segmentation by dividing the magnetic rotor assembly into multiple discrete magnets that can independently engage or disengage from the stator. This segmentation allows selective engagement of only the necessary number of magnets at any given speed, rather than having all magnets continuously engaged. At high speeds, fewer magnet segments remain engaged, reducing the total back EMF and rotational losses while still providing sufficient torque
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 approach enhances efficiency by reducing rotational losses and allowing higher speeds while maintaining high torque at lower speeds, achieving improved performance across a broader torque/speed range.
Implementation Method 1
the array of lift-generating elements and the electrically conductive region separated from each other in the axial direction by a separation distance; and wherein the bearing assembly enables the magnetic rotor assembly to rotate about the rotational axis of the hub assembly and enables the separation distance of the magnetic rotor assembly and the coil stator assembly to change in response to a lift force generated by the relative movement of the array of lift generating element and the electrically conductive region with respect to each other
Implementation Method 2
enables the separation distance of the magnetic rotor assembly and the coil stator assembly to change in response to a lift force generated by the relative movement of the array of lift generating element and the electrically conductive region
Data Source
Figure 1
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Figure 3A
AI summary
An electric motor including: a first and second subsystems, one of which is a magnetic rotor assembly and the other of which is a coil stator assembly; a hub assembly supporting the magnetic rotor assembly and the coil stator assembly and defining an axis of rotation; and a bearing assembly supporting at least one of the first and second subsystems on the hub assembly, wherein the first subsystem has an array of lift-generating elements for generating axially directed magnetic fields, the second subsystem has an electrically conductive region aligned with and opposite to the array of lift-generating elements of the first subsystem, and wherein the bearing assembly enables the magnetic rotor assembly to rotate about the rotational axis of the hub assembly and enables the separation distance of the magnetic rotor assembly from the coil stator assembly to change.