In-wheel Motor Cogging Torque Reduction via 32-Magnet Fractional Slot Design
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Solution Overview
Problem
Conventional in-wheel motors face challenges in reducing cogging torque, which leads to vibration and heat generation issues, particularly in direct drive systems where large torque is required, and existing configurations either fail to minimize cogging torque effectively or complicate the winding process.
Innovation Solution
An in-wheel motor of an outer-rotor type with a surface permanent magnet rotor and a stator having 32 permanent magnets and 24 slots, where each magnet has chamfers to prevent magnetic flux concentration, and wedge-shaped protrusions for precise alignment, satisfying the expression 920≦Mw3×Tw3×Ri2×SinMa8×1100≦932 to achieve reduced cogging torque without complicating the winding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the number of permanent magnets is increased to reduce cogging torque, then the LCM increases and cogging torque decreases, but the GCD decreases making windings more complex and heat generation more severe
Solution Approach 1:
The patent changes the numerical parameters of the motor structure by setting the number of permanent magnets to 32 and the number of slots to 24, achieving an optimal balance where the LCM is sufficiently large to reduce cogging torque while the GCD remains adequate to maintain manageable winding complexity and prevent excessive heat generation
2Object-affected harmful factors
If the number of permanent magnets is increased to reduce cogging torque, then vibration is reduced, but the current in windings increases causing excessive heat generation
Solution Approach 1:
The patent optimizes the numerical parameters by setting 32 permanent magnets and 24 slots, which provides a sufficient LCM to reduce cogging torque and vibration while maintaining an adequate GCD to keep the current in windings at acceptable levels, thereby preventing excessive heat generation
3Force
If the slot space is reduced to increase magnetic flux density, then torque increases, but the manufacturing of coils becomes difficult and heat dissipation is impaired
Solution Approach 1:
The patent optimizes the slot space parameters by setting 24 slots with appropriate dimensions, maintaining sufficient space for coil manufacturing and heat dissipation while achieving adequate torque output through the optimized combination of 32 permanent magnets and 24 slots
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 effectively reduces cogging torque, inhibits excessive heat generation, and facilitates easy motor control by maintaining a sufficient slot space, making it suitable for in-wheel motor applications without manufacturing difficulties.
Implementation Method 1
the electric motor rotates with magnets disposed in a rotor and teeth with windings of a stator attracting and repelling each other alternately
Implementation Method 2
each of the permanent magnets has chamfers on each of the ends so that a magnetic flux cannot concentrate
Data Source
AI summary
An in-wheel motor, comprising: a rotor (14) of a surface permanent magnet type, wherein a plurality of permanent magnets (15) are fixed along an inner circumferential surface of the rotor; wedge-shaped protrusions (42) for fixing the permanent magnets (15) on the rotor (14); and a stator (30) disposed inside the rotor (14), wherein teeth (35) and slots (36) are alternately formed on an outer circumferential portion of the stator; wherein the number of the permanent magnets (15) is 32, and the number of the slots 36 is 24; wherein each of the permanent magnets (15) has chamfers (43) on each of the ends so that a magnetic flux cannot concentrate, and is convex toward the stator (30), in a cross-section perpendicular to a rotary axis of the rotor (14).