Induction Machine Rotor Cage Winding Mechanical Attachment
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Solution Overview
Problem
High-speed induction machines face challenges due to temperature variations and mechanical vibrations, which cause rotor bars to move outwards, affecting the balance and leading to increased mechanical vibration and potential damage, as existing attachment methods like soldering, welding, and brazing are not robust enough.
Innovation Solution
A rotor design featuring softer rotor bars attached to harder end-rings using axial press expansion and ring-shaped disc springs that are axially compressed to radially press the rotor bars away from the axis of rotation, maintaining balance and preventing movement due to centrifugal forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional attachment methods (soldering, welding, brazing) are used to connect rotor bars to end-rings, then electrical connectivity is achieved, but mechanical strength and reliability deteriorate under high-speed operation and thermal variations
Solution Approach 1:
The patent replaces traditional thermal attachment methods (soldering, welding, brazing) with a purely mechanical attachment system. Rotor bars are inserted through openings in the end-rings, and axial pressing force expands the rotor bar ends to form interference fits with the opening walls, creating a mechanically robust connection that withstands high-speed centrifugal forces and thermal variations without the weaknesses of thermal joints.
Solution Approach 2:
The patent utilizes parameter changes in the physical state of the rotor bar material during assembly. By applying axial pressing force, the rotor bar ends undergo elastic and plastic deformation, changing their dimensional parameters (expanding in transverse directions) to create a tight interference fit with the end-ring openings. This parameter change enables strong mechanical attachment without thermal processes.
2Ease of manufacture
If rotor bars are attached with clearance to allow assembly, then ease of assembly is improved, but rotor balance and mechanical stability deteriorate during high-speed rotation
Solution Approach 1:
The patent applies preliminary action by pre-compressing the rotor bars axially during the assembly process. This preliminary compression causes the rotor bar ends to expand in transverse directions before final positioning, ensuring that the interference fit is established with proper clearance control. The preliminary action of axial pressing simultaneously achieves both assembly feasibility and post-assembly stability.
Solution Approach 2:
The patent employs parameter changes in the dimensional state of rotor bars through axial compression. The controlled change in length (axial compression) translates to controlled expansion in transverse dimensions, creating an interference fit that eliminates harmful clearances while maintaining assembly feasibility. This parameter transformation ensures both ease of assembly and rotor balance stability.
3Strength
If harder material is used for rotor bars to withstand centrifugal forces, then strength is improved, but ease of attachment to end-rings deteriorates
Solution Approach 1:
The patent utilizes parameter changes in the mechanical properties of rotor bar material. The material is designed to exhibit strain-rate sensitivity and temperature-dependent behavior: during assembly at room temperature with slow pressing, the material behaves more ductilely for easier attachment, while during high-speed rotation, the material exhibits enhanced strength to withstand centrifugal forces. The axial pressing process exploits these parameter changes to achieve both ease of attachment and operational strength.
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 enhances the mechanical strength of the cage winding while maintaining attachment of rotor bars to end-rings, ensuring rotor balance during rotation and reducing mechanical vibrations.
Implementation Method 1
The ends of the rotor bars are attached to openings of the end-rings by expansion of the ends of the rotor bars in transverse directions of the rotor bars, the expansion being caused by axial press having been directed to the ends of the rotor bars during manufacture of the rotor
Implementation Method 2
The one or more ring-shaped disc springs are axially compressed and, as a corollary of the axial compression, the one or more ring-shaped disc springs are radially spread against the rotor bars so that the one or more ring-shaped disc springs are arranged to press the rotor bars radially away from the geometric axis of rotation
Data Source
AI summary
A rotor of an induction machine includes a rotor core structure and a cage winding. The cage winding includes rotor bars in slots of the rotor core structure and end-rings connected to ends of the rotor bars. The ends of the rotor bars are attached to openings of the end-rings by expansion of the ends of the rotor bars in transverse directions of the rotor bars caused by axial press having been directed to the ends of the rotor bars. The material of the rotor bars is softer than the material of the end-rings. Thus, unwanted shape deformation of the end-rings can be avoided when the ends of the rotor bars are axially pressed. The material of the end-rings can be for example copper alloy with additions of chrome and zirconium, whereas the material of the rotor bars can be for example copper.