Squirrel-Cage Rotor Retention for Thermal Expansion and Full Bar Cross-Section
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Solution Overview
Problem
Existing squirrel-cage asynchronous rotating electric machines face reduced torque and power production due to the partial piercing of conductive bars for retaining screws, which decreases the cross-section of current passage and leads to thermal expansion issues and stress concentration, resulting in friction wear and potential screw failure.
Innovation Solution
The implementation of compacting elements with shorting discs and retaining means featuring insertion holes, blind holes, flexible elements, and Belleville washers to securely hold conductive bars along an axial direction, preventing rotation and accommodating thermal expansion while maintaining a larger cross-section for current passage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pin or retaining screw is inserted into the conductive bar to maintain it in housing, then the conductive bar is secured against rotation and axial movement, but the cross-section of passage for induced current is reduced, leading to reduced torque and power
Solution Approach 1:
The retaining means are extracted from the conductive bar itself and relocated to the shorting disc. The shorting disc now contains the insertion holes and retaining means (screws, springs, and retaining elements), completely separating the retention function from the current-carrying function of the conductive bar. This allows the full cross-section of the conductive bar to remain intact for current passage while the shorting disc provides secure retention.
2Temperature
If the conductive bar is fastened at one end rather than mid-length to allow axial expansion, then thermal expansion is accommodated, but axial forces are not compensated leading to stress concentration and potential screw shearing
Solution Approach 1:
The retaining system incorporates a spring element that provides dynamic, elastic retention. The spring can compress and extend to accommodate thermal expansion and contraction of the conductive bar while continuously applying a retaining force. This dynamic retention prevents stress concentration because the spring absorbs thermal forces through its elastic deformation rather than transmitting them to the screw fastening point.
Solution Approach 2:
The spring element acts as a cushioning element that absorbs and compensates for thermal expansion forces before they can cause stress concentration or screw failure. The spring is pre-loaded to provide continuous contact and force distribution, cushioning the system against thermal shocks and gradual expansion forces.
3Temperature
If the conductive bar is free at one end to expand axially, then thermal expansion is possible, but friction wear occurs between the free end and shorting ring
Solution Approach 1:
The harmful friction wear contact is eliminated by extracting the retention function from the end-contact method and replacing it with an internal retention mechanism. The retaining element engages with the conductive bar internally through the shorting disc, allowing axial expansion without end-to-end friction contact. The spring provides retention force without creating sliding friction at the bar ends.
4Reliability
If a larger fastening screw is used to prevent stress concentration, then screw reliability is improved, but the cross-section for current passage is further reduced
Solution Approach 1:
The fastening screw is completely relocated from the conductive bar to the shorting disc. The screw now fastens the retaining element to the shorting disc, not the conductive bar itself. This extraction allows the use of an appropriately sized screw for structural retention without any impact on the conductive bar's current-carrying cross-section, as the screw operates entirely within the shorting disc 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
This solution enhances torque and power output by maintaining conductive bars securely without reducing the current passage cross-section, mitigating thermal expansion issues and stress concentrations, thus improving the efficiency and durability of the rotor.
Implementation Method 1
the bar fastened at its centre is free to expand along axial directions on either side of the pin or of the retaining screw
Implementation Method 2
The flexible element allows to absorb the thermal expansion of the conductive bar along the axial direction
Data Source
AI summary
The rotor with a non-through shaft for a rotary electric machine comprises a cylindrical magnetic body clamped between two half-shafts, each comprising an attachment flange connected to the magnetic body, axial housings being uniformly provided in the magnetic body on at least one diameter of the magnetic body in order to house conductive bars. At least one attachment flange comprises insertion holes, each arranged facing a housing for inserting the conductive bars into the housings and the exterior diameter of the attachment flange is substantially equal to the exterior diameter of the magnetic body, the attachment flange comprising as many insertion holes as housings.