Permanent Magnet Rotor Cooling via Turbulent Refrigerant Flow

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Solution Overview

Problem

Conventional permanent magnet embedded rotary electric machines have a low cooling effect due to the lack of direct refrigerant application to the permanent magnet, making it difficult to increase output, especially in applications like electric power steering.

Innovation Solution

A rotor iron core with stacked magnetic material sheets and magnet accommodation holes allows direct refrigerant passage under the permanent magnets, with protrusions in the refrigerant passage to transition the refrigerant flow from laminar to turbulent, enhancing heat dissipation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a refrigerant flow passage is provided in a rotor iron core composed of stacked magnetic material sheets, then the cooling effect is improved, but the permanent magnet cannot be directly cooled by the refrigerant

Engineering Contradiction:

Improvecooling effectVSAvoidcooling structure

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The rotor iron core is segmented into stacked magnetic material sheets with magnet accommodation holes, allowing the refrigerant flow passage to be divided into multiple segments that can directly contact the permanent magnet surfaces, thereby improving cooling effectiveness without requiring a completely new cooling structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The refrigerant flow passage is nested within the rotor iron core structure, with the passage formed inside the stacked magnetic material sheets. The permanent magnet is positioned within the magnet accommodation hole, and the refrigerant passage directly contacts the permanent magnet, creating a nested configuration where the cooling system is integrated within the rotor structure

Inventive Principle:

Principle #7Nested doll (Nesting)

2Temperature

If a refrigerant passage is formed between the rotor iron core and the permanent magnet, then direct cooling of the permanent magnet is achieved, but the refrigerant flow transitions from laminar to turbulent

Engineering Contradiction:

Improvepermanent magnet coolingVSAvoidtemperature boundary layer

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

Protrusions are provided on the permanent magnet surface to create mechanical disturbances in the refrigerant flow, causing the flow to transition from laminar to turbulent. This turbulent flow prevents the formation of temperature boundary layers, thereby improving heat dissipation from the permanent magnet

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The surface geometry of the permanent magnet is changed by adding protrusions, which alters the flow parameters of the refrigerant. This geometric modification causes the refrigerant flow to transition from laminar to turbulent regime, enhancing convective heat transfer and preventing boundary layer formation

Inventive Principle:

Principle #35Parameter changes

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 direct refrigerant cooling and turbulent flow effectively prevent temperature boundary layers near the permanent magnets, significantly improving the cooling effect and output of the electric machine.

Implementation Method 1

a refrigerant passage for passing a refrigerant therethrough is formed, in a shaft direction of the rotor iron core, between the rotor iron core and a portion of the permanent magnet corresponding to a radially inner side

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

a refrigerant is caused to collide with protrusions in the refrigerant passage, so that flow of the refrigerant shifts from laminar flow to turbulent flow

Methodology Applied

Scientific EffectConvection: Convection

Implementation Method 3

flow of the refrigerant shifts from laminar flow to turbulent flow, whereby occurrence of a temperature boundary layer in the vicinity of the permanent magnet can be effectively prevented

Methodology Applied

Scientific EffectTurbulent flow: Turbulence

Implementation Method 4

flow of the refrigerant shifts from laminar flow to turbulent flow

Methodology Applied

Scientific EffectLaminar flow: Laminar Flow

Data Source

PatentUS9570950B2Permanent magnet embedded rotary electric machine

Publication Date: 2017.02.14 MITSUBISHI ELECTRIC MOBILITY CORP

AI summary

A permanent magnet embedded rotary electric machine includes: permanent magnets 23 respectively accommodated in the magnet accommodation holes 25. In the magnet accommodation hole 25, a portion of each permanent magnet 23 corresponding to the radially outer side of the rotor iron core 21 is fixed to the rotor iron core 21, and a refrigerant passage 27 is formed, in a shaft direction of the rotor iron core 21, between the rotor iron core 21 and a portion of the permanent magnet 23 corresponding to the radially inner side of the rotor iron core 21. Protrusions 28 are provided, perpendicularly to a passing direction of a refrigerant, on an exposed portion 21a of the rotor iron core 21 in the refrigerant passage 27.