Rotor Core Refrigerant Passage Design for Drag Loss Reduction
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Solution Overview
Problem
Conventional rotary electric machines experience increased drag loss due to excessive refrigerant release in the gap between the rotor and stator, which affects cooling efficiency and motor torque, while existing cooling techniques do not adequately address this issue.
Innovation Solution
A rotor design with a shaft refrigerant passage and core refrigerant passages that guide refrigerant to the gap between the rotor and stator, featuring central, inner, and outer passages, and dams to control refrigerant discharge, allowing effective cooling while minimizing drag loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a large amount of refrigerant is released into the gap between the rotor core and stator, then the cooling effect on the rotor core outer surface, stator core inner surface, and stator coil is improved, but the drag loss due to refrigerant shearing resistance increases
Solution Approach 1:
The refrigerant discharge is segmented into multiple controlled outlets distributed around the rotor core perimeter, rather than a single large discharge. This segmentation allows the refrigerant flow to be distributed and controlled, maintaining cooling effectiveness while reducing localized shearing resistance and drag loss in the gap.
Solution Approach 2:
The refrigerant discharge system incorporates adjustable control valves that dynamically regulate the refrigerant flow rate based on operating conditions. This dynamic control allows the system to optimize the balance between cooling effect and drag loss by adjusting the refrigerant quantity released into the gap according to actual thermal requirements.
2Reliability
If a magnet with high coercive force is employed to avoid demagnetization, then the reliability against demagnetization is improved, but the cost increases due to increased heavy rare earth content
Solution Approach 1:
The patent changes the thermal parameter (temperature) by implementing an active refrigerant-based cooling system that maintains the permanent magnet temperature below critical levels. This parameter change allows the use of magnets with lower coercive force and reduced heavy rare earth content, thereby lowering cost while maintaining reliability against demagnetization through temperature control.
Solution Approach 2:
The patent replaces the reliance on mechanical/material properties (high coercive force magnets) with a thermal control system (refrigerant cooling). Instead of depending on the magnet's inherent resistance to demagnetization through material selection, the system actively controls the thermal environment to prevent demagnetization, substituting material property dependence with active thermal management.
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 design effectively cools the rotor and stator while reducing drag loss by controlled refrigerant release, maintaining motor efficiency and preventing demagnetization of permanent magnets.
Implementation Method 1
a refrigerant is supplied from a shaft refrigerant passage formed inside a rotating shaft to a radially outer end of a rotor core, thereby releasing the refrigerant to a gap between the rotor core and a stator
Implementation Method 2
oil supplied from a supply oil passage formed inside a rotating shaft is discharged through a plurality of cooling oil passages formed inside a rotor core, so as to cool down a rotor
Data Source
AI summary
A rotor core includes at least one core refrigerant passage configured to release a refrigerant to a gap between the rotor core and a stator. The core refrigerant passage includes: a central refrigerant passage provided radially inside a permanent magnet so as to extend in an axial direction, the central refrigerant passage being opened on axial end surfaces of the rotor core; an inner refrigerant passage communicating the shaft refrigerant passage with the central refrigerant passage; an outer refrigerant passage communicating the central refrigerant passage with the gap; and dams provided on both axial-end sides of the central refrigerant passage relative to the outer refrigerant passage so as to project toward a radially inner side from a radially outer side in the central refrigerant passage.