Linear Motor Core Topologies for Force Ripple Reduction
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Solution Overview
Problem
Existing transportation systems face challenges in achieving high speed, high efficiency, and high-power density while propelling a payload or vehicle along a track using a propulsion motor, and guiding or levitating the motor relative to the track.
Innovation Solution
The system employs homopolar linear synchronous motors with ferromagnetic cores shaped to provide increasing magnetic permeance or decreasing magnetic reluctance from the ends towards the center, along with stepped armature coils and strategically designed track segments to reduce force ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional propulsion motors are used to achieve high speed and high efficiency, then propulsion performance is improved, but force ripple increases causing mechanical stress and reduced reliability
Solution Approach 1:
The patent applies local quality by varying the geometry of specific ferromagnetic cores (particularly end cores) to have different cross-sectional areas compared to intermediate cores. This local geometric modification creates a gradient in magnetic permeance that specifically targets force ripple reduction at critical locations without altering the overall motor structure or sacrificing propulsion speed performance.
Solution Approach 2:
The patent employs asymmetry by designing end ferromagnetic cores with different geometries from intermediate cores and from each other. The asymmetric configuration of end cores with reduced cross-sectional areas creates a deliberate imbalance in magnetic path characteristics that compensates for force ripple caused by the finite length of the motor, thereby reducing mechanical stress while maintaining high-speed operation.
2Power
If propulsion motor power density is increased to achieve higher power output, then power density is improved, but force ripple and mechanical stress increase
Solution Approach 1:
The patent applies local quality by modifying the geometry of end ferromagnetic cores to have different cross-sectional areas compared to intermediate cores. This localized geometric variation creates a gradient in magnetic permeance that specifically addresses force ripple at critical locations, enabling higher power density operation without proportionally increasing mechanical stress on the motor structure.
3Ease of manufacture
If ferromagnetic cores with uniform geometry are used, then manufacturing is simplified, but force ripple increases due to end effects
Solution Approach 1:
The patent applies local quality by specifying that end ferromagnetic cores have different cross-sectional areas from intermediate cores. This local geometric differentiation creates the necessary magnetic permeance gradient to reduce force ripple caused by end effects, while the overall manufacturing process remains relatively simple as it only requires modifying specific cores rather than the entire assembly.
Solution Approach 2:
The patent applies segmentation by dividing the ferromagnetic core structure into distinct types: end cores with reduced cross-sectional areas and intermediate cores with standard geometry. This segmentation allows each type of core to be optimized for its specific function, with end cores managing force ripple and intermediate cores providing consistent magnetic pathways, thereby reducing overall force ripple while maintaining manufacturing feasibility.
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 propulsion force distribution, reduces force ripple, and improves overall system efficiency, enabling higher speeds and power densities while minimizing mechanical stress on the propulsion motor.
Implementation Method 1
ferromagnetic cores arranged along a movement axis of the propulsion motor, the ferromagnetic cores including one or more end ferromagnetic cores located at an end of the movement axis, the one or more end ferromagnetic cores shaped to provide one or more of increasing magnetic permeance or decreasing magnetic reluctance from the end of the movement axis towards a center of the propulsion motor and/or the movement axis
Data Source
AI summary
Various topologies to reduce force ripple for propulsion motors are provided. A propulsion motor comprises: ferro-magnetic cores arranged along a movement axis, the ferromagnetic cores including one or more end ferromagnetic cores located at an end of the movement axis, the one or more end ferromagnetic cores shaped to provide one or more of increasing magnetic permeance or decreasing magnetic reluctance from the end of the movement axis towards a center of the movement axis; armature coils located around the ferromagnetic cores; and at least one field coil around one or more of the armature coils and the ferromagnetic cores.