Transverse Liquid Cooled Induction Motor Rotor and Stator
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Solution Overview
Problem
High-power electric motors face challenges in efficiently managing heat generated due to increased specific power levels, which leads to inefficiencies and mechanical failures, particularly in induction motors used in electric and hybrid vehicles.
Innovation Solution
A transverse liquid cooling system is implemented in induction motors, utilizing oil as a coolant that flows through apertures in magnetic laminations to effectively transfer heat away from the rotor and stator, maintaining high specific power levels and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If speed and torque are increased to achieve higher specific power, then power output is improved, but heat generation increases by a factor of four requiring enhanced cooling
Solution Approach 1:
The cooling system is segmented into multiple independent fluid channels formed by apertures in each magnetic lamination. These channels are distributed throughout the stator and rotor cores, dividing the heat removal function into numerous small-scale pathways that collectively handle the four-fold increase in heat generation from high-speed operation
Solution Approach 2:
A liquid cooling system using fluid (coolant) is implemented to transport heat away from the motor components. The fluid flows through the transverse channels in the magnetic laminations, providing hydraulic heat removal capacity sufficient to manage the elevated thermal loads from high specific power operation
2Power
If rotor surface speed is increased to improve specific power, then power density is improved, but centrifugal stress approaches mechanical failure limits
Solution Approach 1:
The rotor core is constructed from stacked magnetic laminations rather than a solid structure. This segmentation reduces the moment of inertia and centrifugal stresses at high speeds while the fluid channels provide additional structural reinforcement and thermal management
Solution Approach 2:
The rotor operates at optimized surface speeds around 120 m/sec, a parameter selected to achieve high specific power while remaining below the centrifugal failure threshold. The lamination structure and cooling system enable operation at this critical speed parameter
3Power
If current density is increased to improve torque and specific power, then power output is improved, but conductor losses increase requiring better cooling
Solution Approach 1:
Liquid coolant flows through channels in close proximity to the stator windings and rotor conductors, providing direct thermal coupling to remove conductor losses. This hydraulic cooling system enables sustained high current densities by continuously extracting the resulting heat
Solution Approach 2:
The cooling fluid acts as an intermediary heat transfer medium between the conductors and the external environment. It absorbs heat from the high-current-density windings and transports it away, enabling the conductors to operate at elevated current densities without thermal damage
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 system enables continuous specific power levels exceeding 10 kW/kg by achieving high heat transfer rates, maintaining efficiency and preventing mechanical failures, while reducing conductor and iron losses.
Implementation Method 1
Heat is removed using a system and method of liquid cooling, termed 'transverse lamination cooling,' in which fluid (i.e., coolant) flows transversely through narrow regions formed by apertures in every other magnetic lamination
Implementation Method 2
The resulting conductor and iron specific losses are respectively on the order of 5 W/cm3 and 1 W/cm3. In order to handle these high levels of heat production, the required specific heat transfer is on the order of 0.1 W/cm3/° C.
Implementation Method 3
a rotor, the rotor having a shaft and a rotor core having a plurality of stacked magnetic laminations... and a rotary fluid coupling in fluid communication with the rotor fluid channels; wherein the rotor and the stator are configured to form a magnetic circuit including an air gap between the rotor and the stator
Implementation Method 4
The torque limit may be proportionate to the square of the gap magnetic flux density
Data Source
AI summary
An electric machine with fluid cooling. The electric machine includes a stator, the stator having a stator winding and a stator core having a plurality of stacked magnetic laminations, each of the laminations of the stator core having a plurality of apertures overlapping to form a plurality of stator fluid channels, a stator fluid channel of the plurality of stator fluid channels being not entirely axial. The electric machine further includes a rotor, the rotor having a shaft and a rotor core having a plurality of stacked magnetic laminations, each of the laminations of the rotor core having a plurality of apertures overlapping to form a plurality of rotor fluid channels, and a rotary fluid coupling in fluid communication with the rotor fluid channels. The rotor and the stator are configured to form a magnetic circuit comprising an air gap between the rotor and the stator.