Stepped Permanent Magnet Assembly for Low-Cogging Axial Flux Motors
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Solution Overview
Problem
Axial flux machines used in door drives experience cogging forces and vibrations due to magnetic interference, leading to reduced efficiency and increased noise, which existing measures like bevelling of magnetic edges have not adequately addressed.
Innovation Solution
The design of permanent magnets with step-shaped side surfaces featuring varying helix angles and a ratio of step width to step height that increases from the inner to the outer surface, along with non-continuous surfaces and circumferential displacement, reduces cogging torques by altering the magnetic field interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If permanent magnets with conventional trapezoidal base and constant helix angle are used, then the machine structure is simple and easy to manufacture, but cogging torques and vibrations are high leading to reduced efficiency and increased noise
Solution Approach 1:
The patent applies local quality by varying the helix angle along the height of the permanent magnet. Instead of using a constant helix angle throughout, the magnetic edges are designed with different helix angles at different positions (inner surface versus outer surface), allowing each local region to contribute differently to reducing cogging torques while maintaining overall machine performance
Solution Approach 2:
The patent introduces a new dimensional aspect by adding stepped profiles to the side surfaces of permanent magnets. This creates multiple levels or stages in the magnetic edge geometry, transforming the conventional single-surface design into a multi-level structure that effectively reduces cogging torques through altered magnetic field distribution
2Object-generated harmful factors
If permanent magnets with stepped side surfaces and varying helix angles are used, then cogging torques are significantly reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the side surface of each permanent magnet into multiple stepped levels. Each step represents a distinct geometric feature with its own helix angle, allowing the complex magnetic edge profile to be broken down into manageable segments that can be manufactured using standard processes while achieving the desired cogging torque reduction
3Object-generated harmful factors
If the ratio of step width to step height increases from inner to outer surface, then cogging torques are further reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent employs asymmetry by designing the stepped profile such that the ratio of step width to step height varies systematically from the inner surface to the outer surface of the permanent magnet. This asymmetric distribution of geometric parameters creates an optimized magnetic field pattern that reduces cogging torques while the variation follows a controlled gradient that manages manufacturing precision requirements
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 significantly reduces cogging torques and moments, enhancing the operational efficiency and reducing noise and vibration in axial flux machines, particularly in door drive applications.
Implementation Method 1
the magnetic flux flows through the permanent magnet arrangement and the coil arrangement axially to the rotational axis of the motor
Implementation Method 2
magnetic field lines running between the north pole and the south pole within the respective permanent magnet run parallel to the machine axis
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a permanent magnet arrangement (1) for use as a rotor or stator of an axial flux machine, in particular an axial flux machine of a door drive. The permanent magnet arrangement (1) comprises several permanent magnets (3) arranged in a ring around a machine axis (2) and each magnetized in an axial direction parallel to the central axis (2). Adjacent permanent magnets (3) have oppositely oriented polarizations. Each permanent magnet (3) extends from an inner surface (6) of the permanent magnet (3) facing the machine axis (2) to an outer surface (7) of the permanent magnet (3). Each permanent magnet (3) has a first side surface (9) and a second side surface (10) opposite the first side surface (9). The two side surfaces (9, 10) connect the inner surface (6) and the outer surface (7).The first side surface (9) of each permanent magnet (3) is oriented towards the second side surface (10) of an immediately adjacent permanent magnet (3). Each first side surface (9) has a stepped profile from the inner surface (6) to the outer surface (7).