Electric Motor Thermal Circuit for Accurate Internal Temperature Estimation
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Solution Overview
Problem
Existing techniques for estimating the internal temperature of electric motors cooled by liquid within the case face challenges in accuracy and calculation load, particularly when identifying heat release paths.
Innovation Solution
A thermal circuit is used to estimate internal temperature by simplifying assumptions such as symmetrical stator core and coil, uniform rotor temperature, and negligible heat transfer via air, with boundary conditions including cooling liquid temperatures before and after heat reception, and calculating heat generation and transfer quantities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detailed thermal circuit model is used to estimate internal temperature of liquid-cooled electric motors, then estimation accuracy is improved, but calculation load increases
Solution Approach 1:
The thermal circuit model is segmented into distinct thermal zones (stator core, coil, case, cooling liquid) with simplified heat transfer paths. Each segment uses aggregated thermal parameters rather than detailed spatial distributions, reducing computational complexity while preserving essential thermal behavior for accurate internal temperature estimation.
Solution Approach 2:
The model transforms complex spatial and temporal thermal parameters into simplified equivalent thermal circuits with lumped parameters. By changing the representation from continuous heat diffusion equations to discrete thermal resistance-capacitance networks, the calculation load is reduced while maintaining estimation accuracy for critical temperatures.
2Measurement precision
If heat release paths in liquid-cooled electric motors are precisely identified, then estimation accuracy is improved, but device complexity increases
Solution Approach 1:
The model extracts and isolates the dominant heat release paths (conduction through stator core, convection to cooling liquid, radiation from case) while omitting minor heat transfer mechanisms. This extraction of essential heat flow paths reduces thermal circuit complexity while preserving accuracy for the primary heat dissipation routes in liquid-cooled motors.
Solution Approach 2:
Instead of modeling heat transfer from internal components outward through multiple interfaces, the approach inverts the perspective by modeling heat absorption by cooling liquid and working backward to determine internal temperatures. This inversion simplifies the thermal circuit by reducing the number of heat release paths that must be explicitly identified and modeled.
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 approach reduces calculation load and maintains estimation accuracy, enabling precise internal temperature estimation even in liquid-cooled electric motors, while avoiding performance degradation and allowing for cost-effective output maximization using lower-grade permanent magnets.
Implementation Method 1
the coil being cooled by a first cooling liquid in the case
Implementation Method 2
a thermal circuit that regards a temperature of the first cooling liquid after heat reception from the coil as a first temperature
Implementation Method 3
heat transfer quantity calculation portion that calculates, using the thermal circuit, a heat transfer quantity of the each element
Data Source
AI summary
A device for estimating an internal temperature of an electric motor. The electric motor has a stator core extending cylindrically in a direction of an axis and around which a coil is wound, a rotor arranged rotatably around the axis, and a case that houses the stator core and the rotor, the coil being cooled by a first cooling liquid in the case. The device estimates the internal temperature by using a thermal circuit that regards a temperature of the first cooling liquid after heat reception from the coil as a first temperature equal to a temperature of the case.