# Comparison of Commonly Used Cooling Concepts for Electrical Machines in Automotive Applications

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## Abstract

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## 1. Introduction

- Stator jacket cooling (blue) with water ethylene glycol (WEG) or oil
- Rotor shaft cooling (magenta) with WEG or oil
- Interior end winding cooling (green) with oil

## 2. Thermal Model for Electrical Machines

## 3. Validation of the Reference Machine

## 4. Comparison of Cooling Concepts for the Reference Machine

## 5. Comparison of Different Machine Lengths

## 6. Rotor Sensitivity Study

- Coolant volume flow rate and distribution;
- Magnet temperature limit;
- Magnet thermal contact resistance;
- Rotor iron losses;
- Coolant inlet temperature;
- Thermal conductivity of the rotor and the magnets;
- Shaft thermal contact resistance;
- Air gap heat transfer.

## 7. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Illustration of shaft cooling, end winding cooling and stator jacket cooling in a permanent magnet synchronous machine (adopted from [5]).

**Figure 2.**Schematic representation of the relative peak power and continuous power of a permanent magnet synchronous machine along with the theoretical limits if only stator windings or magnets were to be taken into account.

**Figure 3.**Electrical machines for different applications in full electrical vehicles and hybrid electrical vehicles [19].

**Figure 4.**Simplified lumped parameter thermal model with resistances between the active components and the cooling medium for a PMSM.

**Figure 6.**Validation of the thermal model with test bench data: (

**a**) comparison of simulated heat flows for different volume flow rates for the WEG and oil-cooling jacket with results of the cooling jacket test bench and (

**b**) comparison of simulated continuous torques for the water-cooling jacket and the rotor cooling jacket with results of the electric machine test bench.

**Figure 7.**Continuous power as a function of machine speed for different oil volume flow rates in the rotor shaft (OS), the stator jacket (OJ) and the end winding cooling (OEW) for the reference machine at a constant inlet temperature.

**Figure 8.**Comparison of the continuous power as a function of machine speed for water and oil cooling at different volume flow rates in the rotor shaft (WS/OS), the stator jacket (WJ/OJ) and the end winding cooling (OEW).

**Figure 9.**Comparison between of the relative continuous power of three different cooling topologies for different machine lengths: (

**a**) ${L}_{\mathrm{EM}}=0.5\cdot {L}_{\mathrm{ref}}$, 100 kW performance category, (

**b**) ${L}_{\mathrm{EM}}={L}_{\mathrm{ref}}$, 200 kW performance category and (

**c**) ${L}_{\mathrm{EM}}=1.5\cdot {L}_{\mathrm{ref}}$, 300 kW performance category. Topologies have the same overall volume flow rate but different distributions between water/oil stator jacket (WS/OJ), shaft (WS/OS) and end winding cooling (OEW).

**Figure 10.**Schematic illustration of the cross-section of the electrical machine and of the parameters that influence the thermal performance of the rotor.

**Figure 11.**Sensitivity analysis of multiple parameters that effect the thermal performance of the rotor, namely the coolant inlet temperature, the magnet temperature limit, the contact resistance at the magnet surfaces and the iron losses in the rotor with constant volume flow rates in the oil stator jacket (OJ), oil shaft (OS) and oil end winding cooling (OEW).

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**MDPI and ACS Style**

Lehmann, R.; Künzler, M.; Moullion, M.; Gauterin, F.
Comparison of Commonly Used Cooling Concepts for Electrical Machines in Automotive Applications. *Machines* **2022**, *10*, 442.
https://doi.org/10.3390/machines10060442

**AMA Style**

Lehmann R, Künzler M, Moullion M, Gauterin F.
Comparison of Commonly Used Cooling Concepts for Electrical Machines in Automotive Applications. *Machines*. 2022; 10(6):442.
https://doi.org/10.3390/machines10060442

**Chicago/Turabian Style**

Lehmann, Robert, Moritz Künzler, Matthias Moullion, and Frank Gauterin.
2022. "Comparison of Commonly Used Cooling Concepts for Electrical Machines in Automotive Applications" *Machines* 10, no. 6: 442.
https://doi.org/10.3390/machines10060442