Sealed Permanent Magnet Machine Cooling via Dual Air-Liquid System
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Solution Overview
Problem
Permanent magnet electric machines face challenges in cooling, particularly when sealed from the outside environment, as traditional methods either result in oversized designs, inefficiencies due to coolant windage, or require complex active systems.
Innovation Solution
A sealed permanent magnet electric machine with a dual cooling system, utilizing a liquid cooling block with external coolant channels and an air cooling circuit driven by fan blades, where air flows radially outward to absorb thermal energy from the magnets and stator, then transfers heat to a water-to-air heat exchanger for external dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the machine is designed with enough excess capability to reduce magnet thermal load, then demagnetization is prevented, but the machine becomes overly physically large
Solution Approach 1:
A heat transfer fluid is introduced as an intermediary substance to carry thermal energy away from the permanent magnets. The fluid circulates through the rotor cavity, absorbing heat from the magnets and transporting it to external heat exchangers, thereby preventing demagnetization without requiring excess machine capability or size
Solution Approach 2:
The thermal management function is extracted from the machine's structural design. Instead of designing the machine with excess capability to handle thermal loads, the heat removal function is separated into an independent cooling system that circulates fluid through dedicated passages in the rotor assembly
2Reliability
If coolant is flooded into the rotor cavity to cool magnets, then demagnetization is prevented in sealed machines, but windage losses severely impact efficiency
Solution Approach 1:
The system uses a liquid cooling fluid circulated through hydraulic passages within the rotor assembly. The fluid absorbs heat from the permanent magnets through conduction and convection, then transports the thermal energy to external heat exchangers, providing effective cooling without the aerodynamic drag problems of air-based systems
Solution Approach 2:
A heat transfer fluid serves as an intermediary between the permanent magnets and the external environment. The fluid circulates through closed-loop passages, absorbing heat from the magnets and delivering it to heat exchangers mounted on the stator or externally, thereby enabling thermal management in sealed machines without direct coolant contact with the rotor airflow
3Temperature
If active cooling systems with coolant spray or circulation are used, then thermal management is improved, but lubrication and scavenge systems are required
Solution Approach 1:
The cooling function is merged with the existing rotor structure. Cooling passages are integrated into the rotor assembly, allowing the permanent magnets to be directly cooled by fluid circulating through passages in the rotor itself, eliminating the need for separate active cooling mechanisms and their associated complexity
Solution Approach 2:
The rotor assembly serves its own cooling needs through integrated passages. The fluid circulation system is simplified because the rotor structure itself provides the cooling channels, and heat is removed through the stator-mounted heat exchangers, eliminating the need for complex scavenge and lubrication systems
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
Effectively maintains the performance of permanent magnet electric machines by preventing demagnetization without the need for oversized designs or complex active cooling systems, ensuring efficient thermal management within a sealed environment.
Implementation Method 1
A liquid cooling block is located radially inboard of the stator core and substantially abuts the stator core or other stator component... Thermal energy is transferred to the coolant from the stator
Implementation Method 2
The coolant flows through the plurality of cooling channels... Thermal energy is transferred to the coolant from the stator
Implementation Method 3
one or more flow-driving devices are disposed at the rotor... Another portion of the flow of air flows past and through the stator end turns, removing thermal energy therefrom. Another portion of the flow of air flows across the plurality of permanent magnets, removing thermal energy therefrom
Implementation Method 4
The flow-driving device maintains the flow of air through the machine such that when the heat is removed in the water-to-air heat exchanger, the air circulates back to the stator end turns and the permanent magnets to absorb more thermal energy
Data Source
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AI summary
A cooling system for a sealed permanent magnet electric machine (10) includes one or more flow driving devices (40) disposed at a rotor (12) of the electric machine configured to urge an airflow across a plurality of permanent magnets (16) of the rotor and across a plurality of stator end turns (24) of the electric machine to remove thermal energy therefrom. A plurality of cooling channels (34) are located in the electric machine in thermal communication with the stator (18) configured to transfer thermal energy from the stator to a flow of fluid coolant through the plurality of cooling channels. A heat exchanger (42) is in thermal communication with the plurality of cooling channels to transfer thermal energy from the airflow to the fluid coolant.