Rotor Core Protrusions for Torque Stability
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Solution Overview
Problem
Existing fastening methods for rotor cores in rotating electric machines, such as keyways, knurling, and press-fitting, lead to torque variations and deformation due to backlashes and high press-fit stress, affecting the machine's performance and air gap consistency.
Innovation Solution
A rotor design with a hollow cylindrical core featuring non-contacting recesses and contacting protrusions, where press-fit stress is distributed only among protrusions, and absorbed by through-holes, preventing core deformation and maintaining a consistent air gap, along with a cooling oil passage system for effective cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If keys are used to fasten the rotor core to the rotating shaft, then the rotor core can be securely attached, but circumferential backlashes occur between the keys and keyway walls causing torque variation
Solution Approach 1:
The patent removes the traditional key fastening structure and replaces it with a press-fit design where the rotor core is directly pressed onto the rotating shaft. This eliminates the key and keyway interface that causes circumferential backlashes, thereby resolving the torque stability issue while maintaining secure attachment through distributed press-fit stress.
Solution Approach 2:
The patent introduces localized protrusions on the rotor core that concentrate the press-fit stress at specific contact points with the rotating shaft. This local quality approach allows secure fastening through focused stress regions while avoiding the backlash problems of key-based fastening systems.
2Strength
If knurling process is performed on contact surfaces, then the rotor core can be fastened to the rotating shaft, but backlashes are created between contact surfaces due to centrifugal force differences causing torque variation
Solution Approach 1:
The patent eliminates the knurling process and traditional contact surface fastening methods. Instead, it uses a press-fit design with protrusions that create interference fit between the rotor core and rotating shaft, avoiding the backlash issues that arise from knurled surfaces under centrifugal loading.
3Reliability
If press-fitting is performed with zero interference at maximum speed, then torque variation is reduced, but high press-fit stress is induced during assembly causing rotor core deformation
Solution Approach 1:
The patent introduces protrusions that localize the press-fit stress to specific contact regions. This allows the use of a larger interference fit during assembly (improving manufacturing precision and preventing deformation) while the protrusion geometry ensures that operational stress is properly distributed, maintaining torque stability at high speeds.
Solution Approach 2:
The rotor core is segmented with multiple protrusions distributed around its circumference. This segmentation distributes the press-fit stress across multiple contact points, preventing localized deformation during assembly while maintaining the zero-backlash condition during operation.
4Strength
If interference between rotor core and rotating shaft is increased, then fastening strength is improved, but press-fit stress during assembly increases causing rotor core deformation
Solution Approach 1:
The patent uses protrusions to create localized high-stress contact regions that provide strong fastening. The protrusion geometry concentrates the interference fit stress at specific points, achieving high fastening strength without requiring uniformly high interference across the entire contact surface, thereby preventing overall rotor core deformation.
Solution Approach 2:
The contact interface is segmented into multiple discrete protrusion contact points. This allows the interference fit to be applied at these specific locations, providing strong fastening strength while distributing the stress to prevent deformation of the overall rotor core structure.
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 design effectively distributes press-fit stress, prevents rotor core deformation, maintains a consistent air gap, and enhances cooling efficiency, thereby improving torque stability and performance.
Implementation Method 1
during the process of press-fitting the rotating shaft into the center hole of the rotor core, the press-fit stress induced in the rotor core is distributed only among the contacting protrusions
Implementation Method 2
for each of the contacting protrusions, the displacement of the contacting protrusion caused by the press-fit stress can be absorbed by the corresponding through-hole located radially outside the contacting protrusion
Implementation Method 3
a cooling oil passage system for effective cooling
Data Source
AI summary
A rotor includes a hollow cylindrical rotor core that has a center hole, in which a rotating shaft is to be press-fitted, and a plurality of magnet-receiving holes in which a plurality of permanent magnets are respectively received. In a radially inner surface of the rotor core defining the center hole, there are formed a plurality of non-contacting recesses and a plurality of contacting protrusions alternately in the circumferential direction of the rotor core. Each of the non-contacting recesses is recessed radially outward so as not to be in contact with the rotating shaft. Each of the contacting protrusions protrudes radially inward so as to be in pressed contact with the rotating shaft. The rotor core further has a plurality of through-holes each of which penetrates the rotor core in the axial direction of the rotor core and is located radially outside a corresponding one of the contacting protrusions.