Transverse Flux Machine Stator Phase Offset Cogging Torque
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Solution Overview
Problem
Permanent magnet electric machines suffer from cogging torque, which causes noise, vibration, and premature failure due to non-zero momentary resistance at most rotational positions, leading to increased wear and vibration in systems driven by or driving these machines, and existing methods to reduce cogging torque often result in increased complexity and non-sinusoidal back EMF waveforms.
Innovation Solution
A transverse flux machine or commutated flux machine is configured with a stator comprising two sets of stator teeth with specific angular spacings, where adjacent teeth are separated by different distances, and a sixth-phase offset is applied to reduce the peak magnitude and harmonics of cogging torque, making the torque waveform more sinusoidal and improving back EMF waveform sinusoidality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional stator tooth arrangements with uniform angular spacing are used, then the structure is simple and easy to manufacture, but cogging torque causes noise, vibration, and non-sinusoidal back EMF waveforms
Solution Approach 1:
The patent applies asymmetry by introducing a phase offset between the two sets of stator teeth, where the angular positions are deliberately made non-uniform relative to each other. Specifically, the first set of stator teeth has angular positions defined by one spacing pattern while the second set uses a different spacing pattern, creating an asymmetric configuration that reduces cogging torque harmonics and produces more sinusoidal back EMF waveforms.
Solution Approach 2:
The stator is segmented into two distinct sets of stator teeth (first set and second set), each with its own angular spacing characteristics. This segmentation allows independent optimization of each set's contribution to the overall magnetic flux distribution, enabling reduction of cogging torque while maintaining manageable structural complexity through modular design.
2Object-affected harmful factors
If methods to reduce cogging torque are applied, then noise and vibration are reduced, but back EMF waveform sinusoidality may be compromised and device complexity increases
Solution Approach 1:
The patent changes the angular spacing parameters between stator teeth in a controlled manner. By defining specific angular distance relationships between adjacent teeth in the two sets (with different spacing patterns), the magnetic flux distribution is optimized to produce sinusoidal back EMF waveforms while simultaneously reducing cogging torque-induced noise and vibration.
3Ease of manufacture
If uniform angular spacing is used between all stator teeth, then manufacturing is simpler, but cogging torque harmonics increase causing more vibration and noise
Solution Approach 1:
Instead of uniform angular spacing, the patent implements asymmetric spacing between the two sets of stator teeth. The first set follows one angular spacing pattern while the second set follows a different pattern, creating deliberate asymmetry that cancels out cogging torque harmonics and reduces vibration and noise while remaining manufacturable.
Solution Approach 2:
The solution moves from a single-dimension uniform spacing approach to a two-dimensional spacing strategy, where radial and tangential positioning of the two stator tooth sets are independently optimized. This dimensional expansion allows complex harmonic cancellation while maintaining reasonable manufacturing simplicity through systematic positioning.
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 configuration significantly reduces the peak magnitude of cogging torque and harmonics, resulting in reduced noise, vibration, and increased sinusoidality of the cogging torque waveform, while maintaining a minor reduction in back EMF peak magnitude, facilitating easier control and integration into polyphase configurations.
Implementation Method 1
magnetic flux paths have sections where the flux is transverse to a rotational plane of the machine
Implementation Method 2
any of the first set of stator teeth provides a flux path to any of the second set of stator teeth, the flux path traversing at least partially around a coil
Implementation Method 3
When unenergized, the electrical machine seeks a rotational position that results in the lowest magnetic circuit reluctance (or the highest permeance)
Data Source
Figure 1A~1B
Figure 2A~3B
Figure 3C
AI summary
Electrical machines, for example transverse flux machines and/or commutated flux machines, may be configured to achieve reduced overall cogging torque via implementation of a sixth-phase offset. Individual cogging torque waveforms in the electrical machine may be evenly distributed across one-sixth of a voltage phase or other suitable spacing, resulting in a reduced magnitude and/or increased sinusoidality of the overall cogging torque waveform for the electrical machine.