Coil Unit Ferrite Core Thermal Stress Reduction
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Solution Overview
Problem
In contactless power transmission devices, the high magnetic flux density at specific regions of ferrite cores leads to thermal stress and increased magnetic energy loss due to heat generation, causing temperature gradients and inefficiencies in power transfer.
Innovation Solution
The coil unit design features ferrite cores with wider regions at the highest magnetic flux density areas to disperse heat and reduce thermal stress, with curve portions of the coil wound across virtual straight lines through their curvature centers, ensuring heat is evenly distributed and gradients are minimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the coil is wound in a rectangular shape with curve portions at corners, then the coil can be easily manufactured and assembled, but the magnetic flux density becomes concentrated at the curve portions causing thermal stress and energy loss
Solution Approach 1:
The ferrite core is designed with non-uniform thickness where the thickness is increased at curve portions and decreased at straight portions. This local variation in geometry distributes the magnetic flux density more evenly across the core, preventing concentration at curve portions while maintaining the rectangular coil structure for easy manufacturing.
Solution Approach 2:
The physical parameter of ferrite core thickness is changed locally to optimize magnetic flux distribution. By making the core thicker at curve portions and thinner at straight portions, the magnetic path length is equalized, which balances the magnetic flux density throughout the core and reduces thermal stress and energy loss.
2Ease of manufacture
If the ferrite core has uniform thickness, then the manufacturing process is simplified, but thermal stress increases due to concentrated magnetic flux density at curve portions
Solution Approach 1:
The ferrite core transitions from uniform thickness to non-uniform thickness with localized variations. The thickness is specifically increased at curve portions where magnetic flux density is naturally higher, and decreased at straight portions, creating local geometric optimization that reduces thermal stress without complicating the overall manufacturing process.
Solution Approach 2:
The solution moves from a two-dimensional planar view to a three-dimensional geometric modification by varying the thickness dimension of the ferrite core. This dimensional change allows the core to compensate for magnetic flux concentration at curve portions, distributing thermal load more evenly and reducing thermal stress.
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 reduces thermal stress by approximately 75% and minimizes magnetic energy loss while maintaining high power transmission/reception efficiency by equalizing heat distribution across the ferrite cores.
Implementation Method 1
a power transmission device that transmits electric power to a power reception device in a contactless manner, and the power reception device that receives electric power from the power transmission device in a contactless manner
Implementation Method 2
plate-shaped ferrite cores and an annular coil that is annularly wound
Implementation Method 3
the density of magnetic flux flowing through the ferrite cores is higher at the curve portion than at the straight portion. As a result, the temperature becomes high at a radial region around the region with the highest magnetic flux density
Data Source
AI summary
A coil unit includes ferrite cores; and a coil disposed to face the ferrite cores, the coil including a plurality of curve portions. Each curve portion is wound across a virtual straight line extending through a curvature center of the curve portion. The ferrite cores include curve portion ferrite cores disposed to face the curve portions, respectively. Each of the curve portion ferrite cores is provided such that a width of a region with a highest magnetic flux density is larger than a width of a region other than the region with the highest magnetic flux density, in a region that faces the coil, in a case where a length direction is defined as a direction in which the virtual straight line extends, and a width direction is defined as a direction perpendicular to the virtual straight line.