Electric Machine Stator Bars and Shoes for Torque Ripple Reduction
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Solution Overview
Problem
Electric machines, particularly Y machines, face challenges with cooling and torque ripple due to heat generation and cogging effects, which limit torque density and efficiency.
Innovation Solution
The design incorporates a stator with coils wound on stator bars and a rotor with permanent magnets, featuring high-reluctance shoe and magnet gaps angled to each other, and a stator housing with a cooling medium to manage heat and reduce cogging, using soft-iron particles and composite materials to optimize magnetic flux and reluctance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high torque density is achieved in a Y machine, then power output is improved, but heat generation increases causing cooling difficulties
Solution Approach 1:
The stator is divided into discrete bars with individual coils, and the rotor is segmented into separate magnet stages. This segmentation allows for distributed heat generation and multiple cooling pathways, enabling better thermal management while maintaining high torque density through optimized magnetic circuits in each segment.
Solution Approach 2:
A dedicated cooling system with cooling channels and cooling medium acts as an intermediary between the heat-generating coils and the environment. The cooling medium circulates through channels positioned to efficiently remove heat from the coils without directly contacting the permanent magnets, thus managing temperature while preserving torque density.
2Ease of manufacture
If discrete coils are used for magnetic separation, then manufacturing simplicity is improved, but torque ripple increases due to cogging effects
Solution Approach 1:
The numbers of permanent magnets on the rotor and coils on the stator are deliberately made different, creating an asymmetric configuration. This asymmetry disrupts the alignment of magnetic cogs between rotor magnets and stator coils, reducing the periodic cogging effects that cause torque ripple, while the discrete coil structure remains simple to manufacture.
3Power
If high permeability core is used to develop strong magnetic field, then magnetic flux density is improved, but eddy currents increase causing energy loss
Solution Approach 1:
Instead of using expensive, complex laminated structures, the patent employs discrete stator bars with coils that are electrically isolated from each other. These bars act as short-lived magnetic paths that carry the necessary flux density for strong magnetic fields, while their discrete, isolated nature prevents large-scale eddy current loops, reducing energy loss without requiring expensive laminated materials.
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 enhances cooling efficiency, reduces torque ripple, and maintains high torque density by minimizing heat transfer to magnets and optimizing magnetic flux paths, thereby improving the machine's operational capacity and efficiency.
Implementation Method 1
heat generated in the coils at high torques
Implementation Method 2
cooling medium to manage heat
Implementation Method 3
permanent magnets to cooperate with the coils across an air gap... magnetic field being developed through the coils
Implementation Method 4
magnetic flux through the bars with said magnets
Implementation Method 5
high-reluctance shoe and magnet gaps... adjacent shoes facing the same stage of the rotor have a high-reluctance shoe gap between them, and adjacent magnets on each stage of the rotor have a high-reluctance magnet gap between them
Data Source
AI summary
An electric machine (10; 100) comprises a rotor (14) having permanent magnets (24) and a stator (12) having coils (22) wound on stator bars (16) for interaction with the magnets across an air gap (26a, b) defined between them. The rotor has two stages (14a, b) arranged one at either end of the bars. The bars have a shoe (18a, 8) at each end of each bar that links magnetic flux through the bars with said magnets on each stage. Adjacent shoes facing the same stage of the rotor have a high-reluctance shoe gap (27) between them; adjacent magnets on each stage of the rotor have a high-reluctance magnet gap (25) between them; and the shoe and magnet gaps (25, 27) are angled with respect to each other such that they engage progressively as the rotor rotates. Alternatively, the shoes facing each stage are in a ring of connected shoes such that the magnets experience a continuous reluctance that is at least 90% constant as a function of rotor position. The bars (16) and shoes (18) are formed separately from one another and at least a part of each is formed by moulding soft-iron particles so that the particles have a short dimension that is arranged transverse a reluctance-plane. The bars and shoes are assembled so that the reluctance-plane of the bar is parallel a longitudinal axis (16a) of the bar and said reluctance-plane of the shoe is transverse said longitudinal axis.