Electric Machine Evaporative Cooling for High Torque
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Solution Overview
Problem
Electric machines, particularly yokeless and segmented armature machines, face challenges in effective cooling, leading to heat generation limitations that restrict torque capacity, especially in high-torque applications, due to inadequate heat conduction between isolated coils.
Innovation Solution
A passive evaporative cooling system is implemented within the machine, where a sealed chamber around the stator coils contains a refrigerant with a boiling point below the stator's operating temperature but above the rotor's, allowing vapor to condense on an external heat-dissipating surface, utilizing wicking material and paddles to manage the coolant effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high torque is employed in a Y machine, then torque density is improved, but heat generation increases and cooling becomes insufficient
Solution Approach 1:
The patent employs evaporative cooling where a refrigerant undergoes phase transition from liquid to vapor within the sealed chamber, absorbing heat from the coils during evaporation. This phase change mechanism efficiently removes the excessive heat generated by high torque operation without requiring complex active cooling systems.
Solution Approach 2:
The cooling system is designed to be passive and self-sustaining, utilizing the natural evaporative cycle of the refrigerant. The system automatically regulates temperature through the phase change process without requiring external control mechanisms, making the high-torque machine self-cooling.
2Ease of manufacture
If coils are isolated from one another, then manufacturing and assembly are simplified, but heat conduction between coils is reduced
Solution Approach 1:
The patent introduces a refrigerant as an intermediary cooling medium within the sealed chamber. This refrigerant provides a thermal pathway between the isolated coils, enabling heat removal from each coil individually while maintaining their electrical and physical isolation. The refrigerant vapor circulates and condenses on the external heat-dissipating surface, efficiently conducting heat away from the coil assembly.
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 solution provides efficient heat dissipation with minimal additional equipment, reducing power loss and maintaining high torque capacity by regulating temperature through self-sustaining evaporative cooling, even in high-torque conditions.
Implementation Method 1
the cooling medium has a boiling point less than a design temperature of operation of the stator and more than design temperature of operation of the rotor housing
Implementation Method 2
allowing vapor to condense on an external heat-dissipating surface
Implementation Method 3
allowing vapor to condense on an external heat-dissipating surface
Implementation Method 4
external heat-dissipating surface accessible by a coolant
Data Source
AI summary
An electric machine comprises a rotor, preferably having permanent magnets, although other field generation means are available, and a stator. The stator has coils wound on stator bars for interaction with the magnetic field of the rotor across an air gap defined between them. The rotor comprises a housing of a chamber containing refrigerant. The rotor housing has heat dissipating fins accessible by the open environment whereby air movement relative to the housing caused at least by rotation of the rotor absorbs heat from the fins. The machine may be an axial flux machine, the coils being wound on bars that are disposed circumferentially spaced around a fixed axle of the machine forming a rotational axis of the rotor. The machine may be a wheel motor for a vehicle, wherein the wheel is mounted directly on the rotor housing.