Die-Cast Rotor Open Slot Geometry for Cooling and Skin Effect Loss
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Solution Overview
Problem
In rotary electric machines using die-cast rotors, the open slot design for improved cooling can lead to issues with air resistance and stress concentration on the ventilation flue, as well as excessive heat generation and losses due to current concentration caused by the skin effect.
Innovation Solution
A rotary electric machine with a rotor formed from laminated electromagnetic steel sheets and a slit-forming method that creates an open slot with a narrower circumferential width than the rotor bar, exposing the lamination surface and forming a slit groove with varying depths to enhance ventilation and reduce die-cast material on the slit walls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an open slot design is used to form a slit at the top of the rotor slot, then cooling performance is improved, but air resistance increases and stress concentration occurs on the end face
Solution Approach 1:
The patent applies local quality by making the slit width variable along its length. The slit is narrower at the top (opening) and wider at the bottom (root), creating different local characteristics that optimize both cooling and structural integrity. This gradual width change reduces stress concentration at the end face while maintaining effective cooling channels.
Solution Approach 2:
The patent changes the geometric parameter of the slit width along its length. By gradually increasing the slit width from top to bottom, the design optimizes the balance between cooling efficiency (requiring adequate slit dimensions) and mechanical strength (requiring sufficient material at the end face to reduce stress concentration and air resistance).
2Temperature
If the slit width is increased to improve ventilation, then cooling performance improves, but current concentration and heat generation increase due to skin effect
Solution Approach 1:
The patent applies local quality by creating different slit widths at different locations. The narrower top portion reduces the surface area where skin effect currents can concentrate, thereby reducing heat generation and energy losses. The wider bottom portion maintains adequate ventilation and cooling efficiency. This spatial variation in slit width optimizes both cooling and electrical performance.
Solution Approach 2:
The patent changes the slit width parameter along the radial direction to simultaneously optimize thermal and electrical performance. The gradual width increase from top to bottom ensures that the slit is narrow enough at the exposed surface to minimize skin effect losses while wide enough at the root to provide effective cooling ventilation.
3Temperature
If a vane is provided for the short-circuit ring on the axial end face to secure ventilation, then cooling performance improves, but air resistance increases and stress concentration occurs
Solution Approach 1:
The patent extracts the ventilation function from the end face by forming slits that extend from the rotor slot opening toward the end face without requiring separate vanes on the end face itself. This eliminates the need for additional end face structures that would increase air resistance and stress concentration, while still providing adequate ventilation through the slit structure.
Solution Approach 2:
The patent merges the ventilation function with the rotor slot structure itself. The slits are formed as integral parts of the rotor slot, combining the slot structure and ventilation channels into a single integrated feature, eliminating the need for separate end face vanes and their associated drawbacks.
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 improves heat dissipation characteristics of the rotor without degrading temperature performance, even with a die-cast rotor, and inhibits excessive losses due to alternating current concentration, thereby maintaining efficient operation at high frequencies.
Implementation Method 1
excessive heat generation and losses due to current concentration caused by the skin effect
Implementation Method 2
improving cooling performance and solving the heat generation problem
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
The present invention provides a rotary electric machine in which heat dissipation characteristics of the rotor are improved and temperature characteristics do not deteriorate even if a die-cast rotor is used. A rotary electric machine of the present invention comprises rotor formed of laminated electromagnetic steel sheets, and a stator placed on an outer circumference of the rotor. The rotor is a die-cast rotor to be formed so that a plurality of rotor bars is formed at a predetermined interval in a circumferential direction and a die-cast material is poured into a rotor slot extending in an axial direction. The rotor slot is an open slot in which the rotor bar is exposed from a slit formed on its outer circumference. A circumferential width of the slit is narrower than a circumferential width of the rotor bar, a side wall of the slit exposes a side surface (lamination surface) of the electromagnetic steel sheet, and the slit provides a slit groove in which a depth to an exposed part of the rotor bar is greater than a depth to a non-exposed part of the rotor bar.