Shaftless Rotor Electric Machine Cooling and Torque Ripple
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Solution Overview
Problem
Electric machines, particularly Y machines, face challenges with cooling and torque ripple due to high heat generation and cogging effects, which limit torque capacity and efficiency.
Innovation Solution
A shaftless rotor design with a large diameter and hollow rotor structure, combined with a stator housing that incorporates cooling medium circulation and optimized magnetic flux paths, reduces reluctance and enhances cooling efficiency while minimizing cogging through angled shoe and magnet gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high torque density is employed to improve power output, then power density increases, but heat generation increases leading to cooling difficulties
Solution Approach 1:
The stator is divided into multiple independent bars with discrete coils, allowing each bar to be independently cooled. The rotor is segmented into multiple permanent magnet segments arranged in circumferentially arrayed rows, enabling distributed heat management. This segmentation allows cooling channels to be positioned between bars and around rotor segments, effectively removing heat while maintaining high torque density.
Solution Approach 2:
Cooling passages are provided between the stator bars and within the rotor structure to circulate cooling medium. The hollow rotor design incorporates internal cooling channels that allow fluid flow through the rotor volume, directly removing heat from the permanent magnets and winding supports. This hydraulic cooling system enables sustained high power operation by preventing thermal buildup.
2Object-generated harmful factors
If discrete coils with magnetic separation are used to reduce cogging, then torque ripple decreases, but magnetic connection efficiency deteriorates
Solution Approach 1:
The stator bars are provided with shoes at their ends that have different magnetic properties than the bar material. The shoes are positioned to face the permanent magnets and have optimized geometry to concentrate and direct magnetic flux. This local modification at the shoe-magnet interface improves magnetic coupling efficiency while the spaces between bars maintain magnetic separation to reduce cogging. The shoes act as flux concentrators that overcome the air gap reluctance without requiring continuous magnetic paths.
3Use of energy by moving object
If high permeability core material is used to improve magnetic flux density, then magnetic connection improves, but eddy current losses increase
Solution Approach 1:
The stator is constructed from discrete bars rather than a continuous core, with coils wound on individual bars. This segmentation interrupts the eddy current paths that would otherwise form large loops in a continuous high-permeability core. Each bar acts as an independent magnetic circuit element, limiting eddy current magnitude while maintaining high flux density through the bar material itself. The shoes provide local flux concentration without creating extensive eddy current loops.
Solution Approach 2:
The stator bars are constructed from laminated or composite magnetic materials that provide high permeability for flux conduction while incorporating insulating layers to break eddy current paths. The shoes may be made from different magnetic materials optimized for flux concentration. This composite approach allows the stator to achieve high magnetic flux density where needed while minimizing eddy current losses through the use of laminated structures and strategic material selection.
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
The solution improves cooling efficiency, reduces torque ripple, and increases torque capacity by minimizing the use of permanent magnet material and optimizing magnetic flux paths, leading to more efficient and cost-effective electric machines.
Implementation Method 1
the sleeve being hollow whereby cooling medium is circulated
Implementation Method 2
A rotor is rotatably journalled in the housing. The stator bars appear to be laminated
Implementation Method 3
The rotor has two stages comprising discs provided with permanent magnets that face either end of each coil of the stator
Implementation Method 4
magnetic path at any stage of operation is: through a first coil into a first magnet on a first stage of the rotor
Implementation Method 5
the bars are preferably provided with shoes to spread the flux in the air gap and reduce the flux density therein - the air gap is of high reluctance
Data Source
AI summary
An electric machine (100) comprises a stator (112) and a rotor (114a, b) mounted for rotation about a rotor axis (120) with respect to the stator. Permanent magnets (124a, b) are carried by the rotor. The rotor has an output (190). The stator has coils (122) wound on stator bars (116) for interaction with the magnets. The rotor has two stages (114a,b) arranged one at either end of the stator bars, with two air gaps (126a,b) between the ends of the bars and the rotor stages. An annular housing (102,142a, b,146) retains and mounts the stator. A bearing (164a, b) is between the rotor and stator, the rotor being hollow around said rotor axis. There are two significant magnetic flux paths (30,30') of the motor. The first passes between adjacent coils in a circuit on a substantially circumferential plane with respect to the axis (120). A second path 30' is in an axial plane, passing around the bearing. The stator coils are spaced around the rotor axis and approach the rotor axis no closer than a first, stator radius (R1) of the stator. The bearing comprises rolling elements rolling on a surface of the rotor that is no closer to the rotor axis than a second, rotor radius (r), which rotor radius is between 60% and 90% of the stator radius.