Self-cooled Rotor with Segmented Internal Channels
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Solution Overview
Problem
High-speed permanent magnet electric machines face challenges in cooling due to mechanical and electrical losses, which lead to temperature gradients and increased friction losses, and existing cooling methods require external pumping sources, increasing complexity and cost.
Innovation Solution
A rotor design with axial and radial channels that create a dual cooling action, allowing cooling fluid to circulate internally and through the rotor-stator gap, utilizing the rotor's rotation to generate a pumping action and minimize external pumping needs, with separate channels for mechanical and electrical loss cooling to optimize flow rates and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air is forced through the radial gap between rotor sleeve and stator bore for cooling, then cooling effectiveness is improved, but friction losses increase
Solution Approach 1:
The cooling system is segmented into two independent circuits: an internal cooling circuit with channels through the rotor core and magnets, and an external cooling circuit through the radial air gap. This segmentation allows separate optimization of each circuit - the internal circuit cools heat sources directly with minimal flow, while the external circuit handles heat dissipation with larger flow, resolving the contradiction between cooling effectiveness and friction losses.
Solution Approach 2:
Different regions of the rotor are provided with different cooling characteristics. The internal channels provide localized cooling directly at heat generation points (magnets and core), while the external radial gap provides distributed cooling across the rotor surface. This local quality differentiation allows optimal cooling performance without excessive friction losses in the radial gap.
2Power
If the rotor length is increased, then power output is improved, but pressure gradient and temperature gradient increase
Solution Approach 1:
The rotor is segmented axially with multiple inlet and outlet positions for the cooling channels. This segmentation creates multiple shorter cooling paths in parallel, reducing the effective length each cooling air stream must traverse. Consequently, pressure and temperature gradients are reduced while maintaining the ability to cool longer rotors with higher power output.
Solution Approach 2:
The cooling system transitions from a purely axial cooling approach to a multi-dimensional cooling architecture with radial channels providing cross-flow cooling. This dimensional change creates additional cooling pathways that reduce the axial temperature gradient, allowing longer rotors to be cooled effectively without excessive temperature differences from end to end.
3Loss of energy
If carbon fibre sleeve is used for retaining magnets, then electrical losses are minimized, but thermal insulation increases making cooling difficult
Solution Approach 1:
The thermal management system is segmented into internal conduction cooling (through the rotor core and magnets via integrated channels) and external convection cooling (through the radial air gap). This segmentation allows the carbon fibre sleeve to perform its primary function of electrical loss reduction while the segmented cooling system handles thermal removal through alternative pathways, primarily conduction through the rotor structure and convection in the radial gap.
Solution Approach 2:
The cooling channels act as thermal intermediaries, providing dedicated pathways for heat transfer from the magnets and rotor core to the cooling air. These intermediary channels bypass the thermal insulation barrier of the carbon fibre sleeve, allowing effective heat removal while maintaining the sleeve's electrical loss reduction function.
4Productivity
If external pumping sources are added for cooling, then cooling flow rate is improved, but system complexity and cost increase
Solution Approach 1:
The rotor design utilizes its own rotation to generate the cooling airflow through the radial gap, eliminating the need for external pumping sources. The rotational motion of the rotor itself serves the dual function of generating electromagnetic power and driving the cooling airflow, thereby reducing system complexity and cost while maintaining effective cooling flow rates.
Solution Approach 2:
The cooling system merges with the rotor structure itself, using the rotor's rotation and geometry to generate cooling airflow. The radial channels and rotor geometry work together to convert rotational motion into directed cooling airflow, combining the power generation and cooling functions into a single integrated system rather than separate components.
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 design achieves efficient cooling with reduced pressure and temperature gradients, minimizing friction losses and eliminating the need for external pumps, while optimizing cooling for both internal and surface heat sources, enhancing the performance and efficiency of the electric machine.
Implementation Method 1
the pressure ratio required to move sufficient cooling air through the radial air gap needs to be generated from an external source such as a cooling fan or by virtue of other means
Implementation Method 2
cooling of the magnet material and any pole spacers that sit between the magnets, as these will also be subject to heat build up due to electrical losses
Implementation Method 3
forcing air to flow through the small radial gap between the outer diameter of the rotor sleeve and the bore of the stator
Data Source
AI summary
A self-cooled rotor for an electrical machine being internally provided with a cooling channel to carrying cooling fluid. The machine includes a further channel for carrying cooling fluid in proximity to a magnetic field generating means for cooling it, the two passages being connected to each other within the machine.