Permanent Magnet Rotor Assembly with Interference Fit Preload
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Solution Overview
Problem
High-speed permanent magnet rotors face challenges in maintaining magnet attachment due to high centrifugal forces, requiring a stronger preload than traditional bonding methods can provide, and thin sleeves may be damaged by excessive axial pressure during insertion.
Innovation Solution
A permanent magnet rotor assembly with a cylindrical magnet housing made of magnetic material and a preloaded retaining sleeve using a resultant interference fit formula (IF2=−ØY+√((ØY+IF1)^2+ØY^2−ØX^2)) to ensure precise preload application, allowing for a metallic or composite sleeve and enabling easier manufacturing and assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin retaining sleeve is used to hold magnets at high speed, then the centrifugal force can be resisted, but the sleeve may be destroyed or deformed under very high axial pressure during press insertion
Solution Approach 1:
A magnet housing is introduced as an intermediary component between the shaft and the retaining sleeve. The housing receives the interference fit from the shaft, while the sleeve is then installed around the magnets within the housing. This mediator distributes the mechanical stress and prevents direct transmission of excessive axial pressure to the thin sleeve during assembly.
Solution Approach 2:
The magnet housing is pre-installed on the shaft with the interference fit before the retaining sleeve is installed. This preliminary action creates a prepared structure that can safely receive the sleeve without subjecting it to damaging axial pressures during the insertion process.
2Reliability
If a high interference fit is applied to preload the retaining sleeve, then the magnets can be held securely at high speed, but the sleeve may be damaged during insertion
Solution Approach 1:
The assembly process is segmented into distinct steps: first installing the magnet housing with interference fit, then installing the retaining sleeve around the magnets. This segmentation allows the high interference fit to be applied to the housing (which can withstand it) rather than directly to the thin sleeve, making the process feasible for serial manufacturing.
Solution Approach 2:
The magnet housing serves as a mediator that absorbs the high interference fit stresses during assembly. By installing the sleeve after the housing is in place, the sleeve avoids exposure to the damaging axial pressures that would occur if it were installed directly onto the shaft with interference fit.
3Ease of manufacture
If thermal expansion is used to achieve sliding fit clearance, then assembly is easier, but the clearance is insufficient for the high interference required in high-speed motors
Solution Approach 1:
The magnet housing acts as an intermediary that receives the high interference fit from the shaft. This allows the design to use interference fit (providing necessary preload for high-speed operation) without requiring the thin retaining sleeve to directly withstand the insertion forces, thus resolving the conflict between assembly ease and retention reliability.
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 provides a precise and reliable preload without damaging the sleeve, facilitating high-speed motor operation, reducing manufacturing complexity and costs, and enabling easier in-situ magnetization and assembly, thus enhancing performance and efficiency.
Implementation Method 1
the retaining cylindrical sleeve is preloaded by a resultant interference fit IF2 which is defined by the following formula: IF2=−ØY+√{square root over (((ØY+IF1)^2+ØY^2−ØX^2))}
Implementation Method 2
IF1 is a primary interference fit between an external diameter of said cylindrically shaped shaft and said internal diameter of所述 cylindrical magnet housing
Data Source
AI summary
A permanent magnet rotor assembly includes a cylindrically shaped shaft having an outer surface, a plurality of permanent magnets constituting portions of annular segments and an outer retaining cylindrical sleeve surrounding the plurality of permanent magnets. The assembly further includes a cylindrical magnet housing mounted on the cylindrically shaped shaft for supporting the plurality of permanent magnets. The cylindrical magnet housing is formed of a magnetic material. The retaining cylindrical sleeve is preloaded by a resultant interference fit IF2 defined by the following formula IF2=−ØY+√{square root over (((ØY+IF1)^2+ØY^2−ØX^2))}, where ΦY is an external diameter of the plurality of permanent magnets, ΦX is an internal diameter of the cylindrical magnet housing, and IF1 is a primary interference fit between an external diameter of the cylindrically shaped shaft and the internal diameter of the cylindrical magnet housing.