Rotor Cooling Flow Path Bypassing Air Gap
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Solution Overview
Problem
Conventional cooling techniques for electrical machine rotors and stators fail to effectively reduce friction and windage losses caused by cooling oil flowing in the air gap between the rotor and stator, limiting efficiency.
Innovation Solution
An electric machine rotor assembly with a flow path that extends from an inner rotor body through o-rings and end plate passages, bypassing the air gap by using wedges with unequal flow areas and banjo bolts, directing coolant radially through the rotor core and into a stationary volute, which leads to a sump, ensuring close proximity to windings without entering the air gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling oil is placed close to copper windings for effective cooling, then cooling efficiency is improved, but friction and windage losses increase due to oil flowing in the air gap
Solution Approach 1:
The rotor assembly is segmented into distinct functional zones: an inner rotor body containing the flow path, a rotor core with air gap, and end plates with passages. This segmentation allows the cooling system to be isolated from the air gap while maintaining proximity to windings for effective heat transfer.
Solution Approach 2:
The flow path is nested within the inner rotor body, which rotates with the rotor core. The o-rings create sealed chambers that contain the cooling oil within the rotating assembly, preventing it from entering the air gap while maintaining close thermal contact with the windings.
2Temperature
If cooling oil flows in the air gap between rotor and stator, then cooling coverage is improved, but friction and windage losses increase
Solution Approach 1:
The harmful element (cooling oil in the air gap) is extracted from the system. The flow path is designed to bypass the air gap entirely, with the inner rotor body and its sealed passages containing the cooling oil away from the rotor-stator interface where friction occurs.
Solution Approach 2:
The end plates with their curved passages act as intermediaries, transferring cooling oil from the inner rotor body to the rotor core regions adjacent to windings without the oil directly contacting the air gap. The o-rings serve as sealing intermediaries to maintain this isolation.
3Loss of energy
If a flow path bypasses the air gap completely, then friction and windage losses are minimized, but cooling proximity to windings must be maintained
Solution Approach 1:
Different regions of the rotor assembly have different functional qualities: the inner rotor body provides sealed containment for cooling oil, the end plates provide directed flow paths with curved passages, and the flow path regions are positioned locally adjacent to windings to provide targeted cooling without oil entering the air gap.
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 achieves superior cooling efficiency by maintaining coolant flow close to windings while completely avoiding the rotor/stator air gap, thereby minimizing friction and windage losses.
Implementation Method 1
an axially spaced pair of o-rings sealing between the inner rotor body and the rotor core
Implementation Method 2
porting the coolant axially through wedges in proximity to windings
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An electric machine rotor assembly includes a rotor core (102) defining a rotor axis (A). Windings (106) are seated in the rotor core. A plurality of wedges (108) circumferentially spaced apart around the rotor core relative to the rotor axis. Each rotor core extends axially and separates between two respective portions of the windings. A supply end plate (110) is mounted at a first axial end (112) of the rotor core. A return end plate (114) is mounted at a second axial end (116) of the rotor core opposite the first axial end. A flow path (118) for coolant fluid extends through the supply end plate into the wedges, through the wedges and into the return end plate, and through the return end plate.