Rotor Short-Circuit Cage Rectangular Bar Prestress
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Solution Overview
Problem
The existing rotor design for asynchronous motors, with round bars and circular holes, fails to ensure consistent electrical and mechanical contacts and results in low engine power due to limited copper material utilization.
Innovation Solution
The rotor design incorporates a short-circuit cage with rectangular bars and crowns, where the connecting means provide radial prestress to ensure secure contact and high copper mass utilization, using a method that involves heating and shrinking the crowns to create a radial play for assembly and maintaining contact under rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If round bars with circular holes are used in the short-circuit cage, then the assembly is simple, but the copper material filling is low and engine power is reduced
Solution Approach 1:
The patent applies asymmetry by transitioning from circular to rectangular cross-sections for both bars and holes. This asymmetric change allows better space utilization within the rotor volume, increasing copper material filling from the inefficient circular arrangement to the more compact rectangular arrangement, thereby increasing engine power while maintaining manufacturability through standardized rectangular components.
Solution Approach 2:
The patent changes the geometric parameters of the short-circuit cage components from circular dimensions (diameter) to rectangular dimensions (width and height). This parameter transformation enables more efficient packing of copper material within the available rotor space, directly increasing the copper filling factor and consequently the engine power output.
2Ease of manufacture
If round bars with circular holes are used in the short-circuit cage, then the manufacturing process is simple, but the electrical and mechanical contact reliability is insufficient
Solution Approach 1:
The rectangular cross-section provides asymmetric contact surfaces that ensure stable electrical and mechanical contact. The flat surfaces of rectangular bars against rectangular holes create defined contact areas, preventing the instability and potential loss of contact that occurs with circular sections, thereby improving reliability while maintaining manufacturing simplicity through standardized rectangular forms.
Solution Approach 2:
Changing from circular to rectangular geometry transforms the contact interface from a point or line contact to a surface contact. This parameter change increases the contact area and distributes mechanical and electrical stresses more uniformly, ensuring reliable contact under all operating conditions while using simple rectangular components that are easy to manufacture.
3Power
If rectangular bars and crowns are used with prestress, then copper material filling and power density increase, but the assembly process becomes more complex
Solution Approach 1:
The patent applies preliminary action by pre-stressing the rectangular bars and crowns during assembly. The components are designed with built-in prestress mechanisms that create initial contact pressure and secure the rectangular bars within the rectangular holes before operation. This preliminary action ensures reliable electrical and mechanical contact from the start, maintaining high copper filling and power density while simplifying the overall assembly process through pre-engineered stress distribution.
Solution Approach 2:
The rectangular geometry enables precise control of assembly parameters such as fit tolerance and contact pressure. The straight edges and flat surfaces of rectangular components allow for more accurate alignment and positioning compared to circular sections, facilitating easier assembly despite the increased power density. The prestress mechanism leverages the rectangular form to distribute forces uniformly, reducing assembly complexity.
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 reliable electrical contact and increased power density by allowing axial expansion of bars and utilizing a larger copper mass within a given volume, while being easy to manufacture and maintain.
Implementation Method 1
expand the short-circuit ring by heating it; threading the expanded short-circuit ring on the or each end part associated with this short-circuit ring; allow the short-circuit ring to shrink while allowing it to cool
Implementation Method 2
allow the short-circuit ring to shrink while allowing it to cool; the prestress of the end part being created during the shrinkage of the short-circuit crown
Data Source
Figure 1
Figure 2~3
Figure 4~7
AI summary
The rotor has a short-circuit cage comprising a bar (20) with an end part (24) that is connected to a short-circuit crown (16) by a connection unit (30), where the unit is a complementary connection unit that retains the part relative to the crown in a retaining direction (S) extended radially relative to a rotation axis. The unit pre-stresses the part in a pre-stressed direction (P) having a radial component relative to the axis when the rotor does not rotate around the axis, where the pre-stressed direction is directed radially relative to the axis and opposed to the retaining direction. An independent claim is also included for a method for manufacturing a rotor.