Rotor Magnet Resin Fixing to Prevent Thermal Gaps
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Solution Overview
Problem
In rotor manufacturing, the thermal expansion mismatch between neodymium magnets and thermoplastic resin materials can lead to gaps, reducing magnetic strength due to temperature-induced length changes, which affect the performance of rotating electric machines.
Innovation Solution
A method where neodymium magnets are oriented with their non-magnetization direction aligned with the rotor's axial direction, and the thermoplastic resin material is injected and solidified to fix the magnets, ensuring the magnet length and closing portion lengths satisfy a specific inequality to prevent gap formation by controlling thermal expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the resin material is cooled and solidified to fix the magnet, then the magnet is fixed to the rotor core, but the resin material contracts causing a gap to form between the magnet and closing portion
Solution Approach 1:
The patent applies preliminary action by pre-heating the resin material before injection. This heating is performed in advance to compensate for the subsequent contraction that will occur during cooling. The resin material is heated to a temperature higher than the magnet temperature before being injected into the magnet housing hole, so that when it cools and contracts, it maintains sufficient contact pressure with the magnet without forming gaps.
Solution Approach 2:
The patent changes the temperature parameter of the resin material to control its dimensional changes. By heating the resin material to a predetermined temperature before injection and controlling the cooling rate, the patent manages the thermal contraction of the resin. This parameter change allows the resin to maintain appropriate dimensions during different stages of the process, preventing gap formation while still providing fixing strength.
2Strength
If the closing portion deforms more than the magnet during cooling, then the magnet is fixed, but a gap forms that traps heat and increases magnet temperature
Solution Approach 1:
The patent applies preliminary action by pre-heating the resin material before injection. This heating is performed in advance to compensate for the subsequent contraction that will occur during cooling. The resin material is heated to a temperature higher than the magnet temperature before being injected into the magnet housing hole, so that when it cools and contracts, it maintains sufficient contact pressure with the magnet without forming gaps.
Solution Approach 2:
The patent converts the harmful thermal contraction of the resin material into a beneficial effect. Instead of trying to prevent contraction, the patent utilizes the contraction force to maintain contact pressure between the resin and magnet. By controlling the initial temperature and dimensions, the contraction that would normally create gaps is transformed into a mechanism that ensures continuous contact, thereby preventing heat trapping while still achieving fixation.
3Strength
If the resin material is heated to melt and fill the magnet housing hole, then the magnet is fixed, but the magnet temperature increases and length decreases
Solution Approach 1:
The patent changes the temperature parameter of both the resin material and magnet to manage their dimensional changes. The resin material is heated to a predetermined temperature higher than the magnet temperature before injection. The magnet temperature is also controlled within a specific range. These parameter changes ensure that when the resin cools and contracts, the magnet has not shrunk excessively, maintaining the inequality relationship that prevents gap formation.
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 approach prevents gap formation between the magnet and closing portion, maintaining magnetic strength and rotor performance by ensuring the magnet's expansion exceeds the closing portion's contraction, thus avoiding heat trapping and temperature increases.
Implementation Method 1
fixing the magnet to the rotor core by filling the magnet housing hole, in which the magnet is accommodated, with the resin material that is melted and solidifying the molten resin material
Implementation Method 2
The neodymium magnet has a positive coefficient of linear expansion in a magnetization direction, and has a negative coefficient of linear expansion in a non-magnetization direction orthogonal to the magnetization direction. Thus, when the lengthwise direction of the magnet coincides with the non-magnetization direction, the heat of the resin material arranged in the magnet housing hole increases the temperature of the magnet and decreases the length of the magnet.
Implementation Method 3
When the resin material is cooled, the resin material solidifies inside the magnet housing hole. In this case, the resin material contracts such that the length of the closing portion in the axial direction (hereinafter, simply referred to as the length of the closing portion) is decreased.
Data Source
AI summary
In a method for manufacturing a rotor, when “Lm” represents a length of a magnet in an axial direction before a resin material is injected into a magnet housing hole, “Lr” represents a length of a closing portion in the axial direction when the magnet is heated by the resin material in the magnet housing hole and shortened, “α” represents a negative coefficient of linear expansion of the magnet in the axial direction, “β” represents a contraction rate of the resin material, and “ΔT” represents a difference between a temperature of the magnet that is heated by the resin material in the magnet housing hole and shortened and a temperature of the magnet when the resin material is cooled and solidified, the length Lm of the magnet and the length Lr of the closing portion are set to satisfy an inequality Lm·α·ΔT≥(Lr·β)/2.