Squirrel-Cage Rotor Flexible Bar-Ring Contact at Low Speeds
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Solution Overview
Problem
The existing electric machine rotors with short-circuit cages face challenges in maintaining reliable electrical contact between the bars and short-circuit rings, particularly at low rotation speeds where centrifugal force is insufficient to ensure contact pressure, leading to potential sparking and excessive heating.
Innovation Solution
The rotor design incorporates flexible, electrically conductive strips arranged along the periphery of the end portions of the bars, which are movable around a pivot axis and distributed into sets to ensure consistent contact with both the short-circuit rings and bars, using retaining strips for mechanical and electrical connection, and a socket arrangement to enhance contact reliability across the entire periphery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rigid bars are directly connected to short-circuit rings in holes, then the structure is simple, but electrical contact reliability deteriorates at low rotation speeds due to insufficient centrifugal force
Solution Approach 1:
The patent changes the physical state and mechanical properties of the connection elements by introducing flexible conductive strips that can deform elastically. These strips transition from a relaxed state to a compressed state under centrifugal force, maintaining continuous electrical contact across the full rotation speed range. The flexibility parameter allows the strips to adapt to varying centrifugal forces, ensuring reliable contact both at low speeds (where elastic deformation maintains contact) and high speeds (where centrifugal force enhances contact pressure).
Solution Approach 2:
The patent introduces flexible conductive strips as intermediary elements between the bars and short-circuit rings. These strips act as a mediator that compensates for the insufficient centrifugal force at low rotation speeds by utilizing their own elastic properties. The strips deform to maintain contact pressure, effectively bridging the gap between the rigid bar-ring connection and the dynamic operational conditions, thereby ensuring continuous reliable electrical contact.
2Reliability
If flexible strips are arranged along the entire periphery of bar end portions, then electrical contact reliability is improved across all rotation speeds, but device complexity increases
Solution Approach 1:
The patent segments the flexible connection system into multiple identical modular units, each consisting of conductive strips arranged in sets around bar end portions. Each set contains multiple strips that can be independently configured but function collectively. This segmentation allows the complex function of maintaining peripheral contact to be achieved through repetition of simpler, standardized components, making the overall complex structure manageable and manufacturable through modular assembly.
Solution Approach 2:
The flexible conductive strips serve multiple functions simultaneously: they provide electrical conduction, maintain mechanical contact pressure through elastic deformation, accommodate varying centrifugal forces, and ensure continuous electrical connection across the entire periphery. This multi-functionality reduces the need for separate components for each function, thereby managing device complexity while achieving comprehensive electrical contact reliability.
3Force
If centrifugal force is used to ensure contact pressure, then contact force increases at high speeds, but contact pressure becomes insufficient at low speeds
Solution Approach 1:
The patent applies preliminary action by pre-configuring the flexible conductive strips in a relaxed state that inherently exerts contact force on the bars and short-circuit rings even before rotation begins or at very low speeds. The strips are positioned and tensioned during assembly to ensure initial contact pressure is maintained. This preliminary configuration ensures that electrical contact is established and maintained across the entire speed range, with centrifugal force serving to enhance rather than create the contact pressure.
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 ensures stable and reliable electrical contact between the bars and short-circuit rings across a wide range of rotor speeds, from stationary to high rotation, reducing the risk of sparking and heating issues while maintaining consistent contact pressure.
Implementation Method 1
comprising, for each conductive bar (28), a first connecting means (36) arranged between the first end portion (30) and the first short-circuit ring (24), in order to electrically connect the first end portion (30) to the first short-circuit ring (24) radially relative to the axis of rotation X-X'
Implementation Method 2
Sometimes, the free arrangement of the ends of the bars in the holes made in the short-circuit rings does not guarantee electrical contacts under all conditions of use, in particular for low rotation speeds of the rotor, where the centrifugal force is not sufficient to ensure contact pressure
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
This asynchronous motor rotor, which extends along an axis of rotation, comprises a squirrel cage. The squirrel cage is formed by the conductive bars (28) and short-circuit rings (24). The connecting means (36) between an end portion (30) of one of the conductive bars (28) and one of the short-circuit rings (24) comprise a plurality of flexible strips (50) capable of conducting electric current.