Air Core Stator Windings Thermal Management for High Specific Power
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Solution Overview
Problem
Current electric machines fail to achieve high specific power capability per weight while sustaining it for extended durations due to heat generation and thermal management limitations, which restricts their practical applications in vehicles and industrial use.
Innovation Solution
A high specific power electric machine design featuring a rotor with permanent magnets, air core stator windings bonded to a slotless ferromagnetic stator backiron, and a two-phase fluid cooling system that efficiently transfers heat from the windings to a remote condenser, minimizing thermal resistance and maximizing power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If air core electric machines are designed for highest power density, then power capability per weight is improved, but heat generation increases and thermal management becomes unsustainable for extended periods
Solution Approach 1:
The patent extracts the thermal management function from the traditional integrated motor design by implementing a separate, remote cooling system. The cooling system is decoupled from the motor housing, allowing the motor to maintain high power density while thermal management handles heat removal independently through remote radiators and fluid circulation pathways.
Solution Approach 2:
The patent introduces a two-phase fluid as an intermediary heat transfer medium between the windings and the remote environment. This fluid circulates through channels in the motor housing, absorbing heat from the windings and transporting it to remote radiators, enabling efficient thermal management without direct mechanical connection between cooling components and motor structure.
2Duration of action of moving object
If thermal management systems are added to sustain high power operation, then duration of high power capability is improved, but system weight and complexity increase
Solution Approach 1:
The motor housing serves multiple functions: it provides structural support for the motor, acts as a thermal conduit for heat removal, and serves as a flow path for the two-phase cooling fluid. This multi-functionality eliminates the need for separate cooling housings or additional thermal management structures, reducing overall system complexity while enabling sustained high power operation.
Solution Approach 2:
The cooling system utilizes the motor's own housing and structural components as heat transfer pathways, rather than requiring entirely separate cooling infrastructure. The housing itself becomes part of the thermal management system, self-serving the dual purpose of structural support and heat removal, thereby minimizing added complexity.
3Loss of energy
If conventional cooling systems are used, then heat removal is achieved, but thermal resistance from windings to cooling medium is too high to sustain high specific power
Solution Approach 1:
The patent replaces conventional single-phase liquid cooling with a two-phase heat transfer system. The phase change mechanism provides dramatically higher heat transfer coefficients, enabling efficient heat removal from the windings without requiring complex high-flow-rate pumping systems or large heat exchanger surfaces, thus achieving superior heat removal with simpler mechanics.
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 achieves a sustained specific power capability of over 17.4 kW/kg, twice that of current machines, with reduced temperature increases and increased efficiency, enabling extended high-power operation without the need for additional thermal management systems.
Implementation Method 1
The evaporator transfers heat from the stator backiron to the fluid through phase change energy of the fluid
Implementation Method 2
the fluid is passively circulated to the condenser where the phase change energy is released remotely by convection of heat to ambient air
Implementation Method 3
The rotor comprises permanent magnets that generate magnetic flux across the magnetic airgap and through air core stator windings
Implementation Method 4
the fluid is passively circulated to the condenser where the phase change energy is released remotely
Data Source
AI summary
An electric machine for converting between electrical and rotary mechanical energy includes a rotor that is journalled to rotate about an axis of rotation, and an adjacent stator that magnetically exerts torque upon the rotor across a magnetic airgap in response to applied electric power to air core stator windings that are bonded in thermal contact to a slotless ferromagnetic stator backiron forming the stator surface facing the magnetic airgap, the rotor has a surface that is opposed to, and spaced apart from, the corresponding surface on the stator, the rotor surface and the stator surface define the airgap therebetween. The rotor has permanent magnets that generate magnetic flux across the magnetic airgap and through the air core stator windings. The air core windings are cooled by a physical loop having an evaporator, a remote located condenser and connected by two fluid flow lines filled with two phase fluid comprising liquid and gas both traveling in the same direction around the physical loop. The evaporator is constructed as an annulus co-annular with the rotor and located in thermal contact with the stator backiron and in thermal conduction indirectly with heat across the bond of the air core stator windings and through the stator backiron as heat is generated from the application of electric power; The evaporator transfers heat from the stator backiron to the fluid through phase change energy of the fluid, and the fluid is passively circulated to the condenser where the phase change energy is released remotely by convection of heat to ambient air, wherein the condenser is located at a higher elevation than the stator and the evaporator has two internal parallel fluid paths located on opposite diametral sides of the stator.