Thrust Magnetic Bearing Core Slits for Eddy Current Control
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Solution Overview
Problem
Thrust magnetic bearing devices experience deteriorated responsiveness in position control due to eddy currents generated around iron cores, which can bypass grooves formed inside the cores, and the machining of these grooves is challenging.
Innovation Solution
The core of the electromagnet includes a slit extending from the outer peripheral surface toward the center, effectively blocking eddy currents from bypassing and reducing their generation, while allowing for easier machining by forming the slit in specific ranges that minimize impact on the attractive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If grooves are formed inside the core to suppress eddy currents, then eddy current generation is reduced, but the machining difficulty increases and eddy currents can still bypass through the radially outer side
Solution Approach 1:
The core is segmented by forming slits that divide the continuous iron core into separated regions. These slits extend from the radially outer side toward the radially inner side, effectively blocking eddy current paths without requiring complex internal groove machining. The segmentation approach simplifies manufacturing while maintaining eddy current suppression effectiveness.
Solution Approach 2:
The harmful eddy current paths are extracted or removed by introducing slits that eliminate the continuous conductive path for eddy currents. By taking out the problematic current loops through strategic slit placement, the solution addresses the harmful effect without adding complex internal structures.
2Object-generated harmful factors
If slits are formed deeply inside the core to block eddy currents, then eddy current suppression improves, but the attractive force of the electromagnet decreases
Solution Approach 1:
Different regions of the core are treated differently: slits are formed in the radially outer region where eddy currents are most harmful, while the radially inner region near the thrust disc is kept intact to maintain strong magnetic attraction. This localized approach ensures eddy current suppression where needed without compromising the attractive force.
Solution Approach 2:
Instead of forming slits throughout the entire core depth, the solution applies partial action by limiting slits to extend only from the radially outer side toward the center, stopping before reaching the radially inner side. This partial slit formation is sufficient to block eddy currents while preserving the magnetic circuit integrity for attractive force.
3Object-generated harmful factors
If multiple slits are formed in the core, then eddy current suppression improves, but the core strength and attractive force decrease
Solution Approach 1:
The solution uses the minimum necessary number of slits (at least one) extending from the radially outer side toward the center, without forming multiple slits throughout the core. This partial approach provides sufficient eddy current suppression while maintaining core structural strength and magnetic performance.
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 adequately suppresses eddy current generation and maintains responsiveness of position control, while simplifying the machining process by focusing on the outer and inner peripheral surfaces where eddy currents are most prevalent.
Implementation Method 1
a pair of electromagnets attract a thrust disc, provided at a rotating body, to receive force in a direction along a rotation axis
Implementation Method 2
when the position of the thrust disc in the direction along the rotation axis changes, eddy currents flowing around the rotation axis are generated at iron cores covering the coils
Data Source
Figure 1~2
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AI summary
A thrust magnetic bearing device according to one aspect of the present invention includes: a thrust disc fixed to a rotating body; and a pair of electromagnets provided so as to sandwich the thrust disc and be spaced apart from the thrust disc in a direction along a rotation axis. Each of the pair of electromagnets includes: a coil wound around the rotation axis of the rotating body; and a ring-shaped core accommodating the coil. The core includes a slit which is located at at least one circumferential position of the core and extends from an outside outer peripheral surface as a starting point toward a center of the core. The slit is formed in a range including at least an inside outer peripheral surface.