Permanent Magnet Rotor Cooling With Centrifugal Oil Flow
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Solution Overview
Problem
Permanent magnet rotors in electric machines face heat management challenges due to high temperatures, leading to reduced remanence and coercivity, torque output reduction, and magnetization/demagnetization issues, exacerbated by rotor geometry designs that create thermal resistance paths.
Innovation Solution
A rotor cooling assembly utilizing centrifugal force to circulate conditioned oil through radial passages within the rotor shaft and core, promoting a fluid film for enhanced heat dissipation, which absorbs heat generated by rotor core and magnet eddy current losses and circulates it out of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If rotor geometry designs are used to accommodate permanent magnets, then motor performance is improved, but thermal resistance paths are created leading to high localized temperatures
Solution Approach 1:
The patent introduces a cooling fluid (oil) as an intermediary substance that circulates through passages in the rotor shaft and core, absorbing heat from the permanent magnets and rotor core. This mediator transfers thermal energy from high-temperature zones to a heat exchanger, resolving the thermal management problem while preserving the motor's geometric design for optimal performance.
Solution Approach 2:
The patent employs a hydraulic cooling system where conditioned oil is pumped through internal passages of the rotor shaft and core. The fluid-based cooling mechanism effectively removes heat from critical components without interfering with the rotor's mechanical structure or magnetic field generation, thereby maintaining both motor performance and thermal management.
2Temperature
If centrifugal force is used to move cooling oil through radial passages, then heat dissipation is enhanced, but device complexity increases
Solution Approach 1:
The patent utilizes the rotor's own rotation to generate centrifugal force, which automatically drives the cooling oil through the radial passages without requiring external pumps or complex control systems. The rotating rotor shaft and core act as self-powered fluid transport mechanisms, enhancing heat dissipation while minimizing additional device complexity.
Solution Approach 2:
The cooling system is designed to be dynamic, leveraging the rotational motion of the rotor to create centrifugal forces that propel the cooling fluid through the passages. This dynamic approach converts the rotor's operational motion into a useful cooling function, eliminating the need for separate pumping mechanisms and reducing overall system complexity.
3Temperature
If outlet ports are restricted to promote fluid film, then heat dissipation increases, but fluid flow restriction reduces cooling capacity
Solution Approach 1:
The patent modifies the outlet port geometry to create a restricted flow configuration that promotes fluid film formation. By changing the physical parameters of the outlet ports (size, shape, positioning), the system optimizes the balance between flow volume and heat transfer efficiency, allowing sufficient cooling capacity while enhancing heat dissipation through fluid film contact with the rotor core surfaces.
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 maintains the rotor assembly at lower temperatures, increasing continuous power and torque output, enabling a wider RPM range and improving motor reliability by actively cooling the rotor during operation.
Implementation Method 1
centrifugal forces from the cylindrical motor shaft and the cylindrical rotor core move the cooling fluid through the fluid flow passage to the internal channel of the cylindrical rotor core
Implementation Method 2
Heat generated by rotor core loss and magnet eddy current loss is absorbed by the oil in both channels
Implementation Method 3
Heat generated by rotor core loss and magnet eddy current loss is absorbed by the oil in both channels
Implementation Method 4
restricting outlet ports provided on an outlet end ring, opposite the annulus end ring, allows the oil to exit the rotor core channels, but restricts enough flow that a fluid film is promoted inside the various channels, further increasing heat dissipation effectiveness
Data Source
AI summary
A rotor assembly for a permanent magnet motor, including: a rotor shaft comprising an internal cavity having an inlet and an outlet; and a rotor core disposed about the rotor shaft, comprising an internal channel having an inlet and an outlet; wherein the outlet of the internal cavity of the rotor shaft is coupled to the inlet of the internal channel of the rotor core; and wherein the internal cavity of the rotor shaft and the internal channel of the rotor core are configured to circulate a cooling fluid through the rotor shaft and the rotor core. The rotor core includes a plurality of permanent magnets adapted to interact with a stator assembly disposed about/adjacent to the rotor core.