Induction Motor End Rings with Prestressed Collars
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Solution Overview
Problem
Die-cast induction motors face rotor end ring deformation and potential cracking due to centrifugal stresses at high operational speeds, leading to contact with the stator inner wall, which compromises motor performance and reliability.
Innovation Solution
The implementation of collar-reinforced end rings with a prestressed condition, using stainless steel collars in a press or shrink fit configuration around aluminum or copper end rings, maintains compressive stress and constant diameter, reducing tensile stresses and hoop stress, thereby enhancing rotor stability at high rotational speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotor operates at high rotational speeds, then the power output and productivity are improved, but the end rings experience centrifugal stresses causing deformation and potential cracking
Solution Approach 1:
The collar is pre-installed on the end ring in a prestressed condition before the rotor operates at high speeds. This preliminary application of compressive stress counteracts the centrifugal tensile stresses that will occur during high-speed rotation, preventing deformation and cracking of the end ring
Solution Approach 2:
The invention combines the end ring material (aluminum or copper) with a collar material (stainless steel or other high-strength material) to create a composite structure. The collar provides the necessary mechanical strength to withstand centrifugal forces while the end ring maintains its electrical and thermal properties
2Reliability
If collars are added to reinforce end rings, then the reliability and stability are improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The rotor structure is segmented into distinct components: the end ring and the collar. This segmentation allows each component to be manufactured separately with optimized properties, then assembled together. The collar is fitted onto the end ring to provide reinforcement without requiring a complete redesign of the entire rotor structure
Solution Approach 2:
The collar is installed in a prestressed condition, changing the stress state parameters of the end ring from tensile (during operation) to compressive (during installation). This parameter change allows the end ring to withstand high-speed rotation without deformation while maintaining a relatively simple structural design
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 design allows induction motors to operate at higher rotational speeds without end ring deformation, improving reliability and extending the lifespan of the motor by containing centrifugal forces and stresses, particularly relevant for electric vehicle applications.
Implementation Method 1
each of the plurality of collars has an interference fit with a corresponding one of the plurality of end rings to establish the prestressed condition
Implementation Method 2
The prestressed condition is configured to maintain a compressive stress in the plurality of end rings at a maximum-designed rotational speed of the rotor
Implementation Method 3
The plurality of conductors applies a centrifugal force to the plurality of end rings while the rotor is rotating
Data Source
AI summary
An induction motor includes a stator and a rotor. The stator is configured to generate a rotating magnetic field. The rotor is disposed inside the stator, separated from the stator by an air gap, and is configured to rotate around an axis in response to the rotating magnetic field. The rotor includes a rotor core, multiple end rings, and multiple collars. The end rings are attached at opposite ends of the rotor core. Each end ring has one of multiple regions disposed outside the air gap. Each region has an outer surface. The collars are attached in a prestressed condition around the outer surface of each region. The prestressed condition is configured to maintain a compressive stress in the end rings at a maximum-designed rotational speed of the rotor.