Halbach External Rotor Molding for Tight Air Gaps
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Solution Overview
Problem
Existing external rotors for electric drive systems, particularly in vehicle cooling devices, are costly, complex to produce, and suffer from imprecision leading to larger air gaps and reduced torque due to non-uniform glue distribution and variable magnet heights, necessitating broader spacing tolerances.
Innovation Solution
A single-piece external rotor made of a plastic-magnetic material, magnetized with a Halbach array, is injection-molded to ensure high precision and reduced air gaps, enhancing magnetic efficiency and torque transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional metal cup with manual gluing of permanent magnets is used, then the rotor can be produced with mechanical machining, but the production cost increases and manufacturing precision deteriorates
Solution Approach 1:
The patent merges the metal cup structure and permanent magnets into a single integrated component by injecting molten metal into a mold containing the magnets. This eliminates the separate gluing process and mechanical machining steps, simultaneously simplifying manufacture and improving dimensional precision through direct casting.
Solution Approach 2:
The patent replaces the mechanical gluing process with a thermal casting process. Instead of manually or automatically gluing magnets to the metal cup, molten metal is injected directly into the mold cavity containing the magnets, allowing the metal to solidify and form a unified structure. This substitution eliminates the complexity of mechanical assembly and achieves superior dimensional accuracy.
2Productivity
If manual or automatic gluing of permanent magnets is used, then the rotor can be assembled, but the production cost increases and glue distribution uniformity deteriorates
Solution Approach 1:
The patent replaces the mechanical gluing system with a thermal casting system. Molten metal is injected under pressure into the mold cavity containing the permanent magnets, allowing the metal to flow around and bond with the magnets uniformly as it solidifies. This eliminates the non-uniform glue distribution problem inherent in manual or automatic gluing processes.
Solution Approach 2:
The patent changes the physical state of the bonding material from solid glue to liquid molten metal. By controlling the temperature and injection pressure parameters, the molten metal achieves uniform distribution and complete filling of the mold cavity, ensuring consistent bonding between the metal cup and permanent magnets throughout the entire structure.
3Ease of manufacture
If broader spacing tolerances are used to accommodate imprecision, then the rotor can be manufactured more easily, but the air gap increases and torque performance deteriorates
Solution Approach 1:
The patent uses hydraulic pressure to inject molten metal into the mold cavity. This high-pressure injection ensures complete filling of the mold and achieves precise dimensional control of the rotor components, minimizing air gaps without requiring broader tolerances. The hydraulic system provides consistent pressure distribution for uniform solidification and tight tolerances.
Solution Approach 2:
The patent controls the temperature and pressure parameters of the molten metal injection process to achieve precise dimensional control. By optimizing these parameters, the rotor is manufactured with tight tolerances that minimize air gaps between components, thereby maximizing torque delivery while maintaining ease of manufacture through the casting process.
4Device complexity
If bigger air gaps are left between stator and rotor, then the spacing tolerances are simplified, but the magnetic flux passage is resisted and torque delivery deteriorates
Solution Approach 1:
The patent employs high-pressure hydraulic injection to achieve precise dimensional control of the rotor components. This ensures minimal and uniform air gaps between the stator and rotor, reducing magnetic flux resistance and energy losses. The hydraulic system maintains consistent pressure during injection and solidification, guaranteeing tight tolerances without increasing device complexity.
Solution Approach 2:
The patent optimizes the temperature and pressure parameters of the molten metal injection process to achieve minimal air gaps. By carefully controlling these parameters, the rotor is formed with precise dimensions that minimize the distance between stator and rotor surfaces, thereby reducing magnetic flux resistance and improving energy efficiency while maintaining simple tolerance specifications.
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 solution results in a simpler, cheaper, and more efficient rotor production with improved torque performance and reduced air gaps, optimizing magnetic circuit efficiency.
Implementation Method 1
The hollow cylinder and the circular plate are made as one piece from the same material consisting essentially of at least 80% by weight of a ferromagnetic metal, which can be magnetized in a permanent manner, and a remaining percentage of a plastic binder. The hollow cylinder is magnetized so as to provide a Halbach array of permanent magnets which produces a permanent magnetic field
Implementation Method 2
a ferromagnetic metal, which can be magnetized in a permanent manner
Data Source
Figure 1~3b
Figure 4~5
Figure 6~8
AI summary
External rotor for electric drive systems, in particular for an electric motor, comprising: - a body comprising a hollow cylinder (110) extending around a longitudinal axis and closed by a circular plate (130) at one of its two bases, wherein said body is formed as a single moulded piece of plastic-magnetic material consisting essentially of a plastic binder and at least 50% by weight of a ferromagnetic metal which can be permanently magnetized, and wherein at least the hollow cylinder is magnetized with a Halbach magnetization which produces a permanent magnetic field of the rotor which has at least two magnetic poles in the internal volume of the internal cylinder and is substantially zero on the outside thereof.