# Thermal Design and Analysis of Oil-Spray-Cooled In-Wheel Motor Using a Two-Phase Computational Fluid Dynamics Method

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Oil Cooling Design

^{3}.

## 3. Analysis Method

#### 3.1. Governing Equations

#### 3.2. Two-Phase Model

_{q}is the volume fraction of q phase; S

_{q}is the mass source for q phase; m

_{qp}is the mass transferred from phase q to phase p; and m

_{pq}is the mass transferred from phase p to phase q. As for this oil-cooled e-motor, the q and p phases are defined as oil and air, respectively, and the mass-transferred term is ignored. The implicit method is used to solve the upper equations with a high-accuracy interface-tracking scheme, which is compressive in Fluent. Based on the variable α

_{q}, the free surface of the volume fraction of fluid at different times is constructed and tracked. If α

_{q}= 1, the computation cell is fully occupied by the q phase. If α

_{q}= 0, the cell is occupied by the p phase. If 0 < α

_{q}< 1, the cell consists of two phases, and there is an interface. For each cell, the sum of the volume fraction is equal to one unit.

#### 3.3. Fluid–Solid Thermal Coupling

- (1)
- Separate the solid parts of the motor from the fluid domain and identify the interfaces between the fluid and the solid.
- (2)
- Assume a suitable initial temperature, e.g., 80 °C, on all surfaces of the fluid in contact with the solid parts.
- (3)
- Use the unsteady solver to simulate the two-phase fluid domain consisting of air and oil as a VOF model in a time step 0.001 s and monitor the velocity, pressure, and temperatures at multiple locations. The flow field is considered to converge when the inlet and outlet flows in the oil circuit system reach equilibrium and when the physical quantities at multiple spatial locations remain essentially constant.
- (4)
- Extract the temperatures, 3D coordinates, and convective HTC at the center of the first boundary layer mesh of the fluid, which can be seen from Figure 5b, and then map them in the form of a field to all solid surfaces intersecting the fluid.
- (5)
- Perform the steady-state solution for the solid heat transfer simulation until convergence, then map the results for the temperature fields on all the solid surfaces in contact with fluid back to the ΔT in the solid that is less than 0.5 °C. Then, the temperature field of the fluid and solid is obtained for the given operating point.

#### 3.4. Meshing for Fluid and Solid

#### 3.5. Losses and Boundaries

^{−3}kg/(m·s), 852 kg/m

^{3}, and 2360 J/(kg·K), respectively.

## 4. Analysis Results

## 5. Testing and Validation

## 6. Conclusions

- (1)
- An oil-spray-cooled concept for IWMs is offered. The flat structure makes the oil flow design more flexible. In this paper, both end windings and rotor ends are effectively cooled by the oil from four pipes.
- (2)
- A complete geometry model without simplification is created. The combination of CFD with a two-phase VOF model and mixed timescale method was employed and proved to be accurate at predicting the temperature distribution of IWMs. The iteration procedures by mapping the temperature of the interfaces back to the fluid were implemented through programming. It could be a reference for solving similar thermal problems.
- (3)
- Although the mixed timescale method is applied, this calculation is still very time consuming to simulate the transient heat rising or other complex variable cycles under current hardware conditions. However, due to the real geometry model and high numerical calculation accuracy, it provides the possibility that some simplified thermal models seriously rely on some thermal parameters that can be calibrated on the basis of analysis results.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

- Chakraborty, S.; Kumar, N.M.; Jayakumar, A.; Dash, S.K.; Elangovan, D. Selected Aspects of Sustainable Mobility Reveals Implementable Approaches and Conceivable Actions. Sustainability
**2021**, 13, 12918. [Google Scholar] [CrossRef] - Krings, A.; Monissen, C. Review and Trends in Electric Traction Motors for Battery Electric and Hybrid Vehicles. In Proceedings of the 2020 International Conference on Electrical Machines (ICEM), Gothenburg, Sweden, 23–26 August 2020; pp. 1807–1813. [Google Scholar] [CrossRef]
- Matteo, M.; Marcus, A.; Arent, D.; Bazilian, M.; Cazzola, P.; Dede, E.M.; Farrell, J.; Gearhart, C.; Greene, D.; Jenn, A. The rise of electric vehicles—2020 status and future expectations. Prog. Energy
**2021**, 3, 022002. [Google Scholar] [CrossRef] - Ning, X.; Chen, M.; Zhou, Z.; Shu, Y.; Xiong, W.; Cao, Y.; Shang, X.; Wang, Z. Thermal Analysis of Automobile Drive Axles by the Thermal Network Method. World Electr. Veh. J.
**2022**, 13, 75. [Google Scholar] [CrossRef] - Jneid, M.; Harth, P.; Ficzere, P. In-wheel-motor electric vehicles and their associated drivetrains. Int. J. Traffic Transp. Eng.
**2020**, 10, 415–431. [Google Scholar] - Deepak, K.; Frikha, M.A.; Benômar, Y.; El Baghdadi, M.; Hegazy, O. In-Wheel Motor Drive Systems for Electric Vehicles: State of the Art, Challenges, and Future Trends. Energies
**2023**, 16, 3121. [Google Scholar] [CrossRef] - Chang, X.; Zhang, H.; Yan, S.; Hu, S.; Meng, Y. Analysis and Roll Prevention Control for Distributed Drive Electric Vehicles. World Electr. Veh. J.
**2022**, 13, 210. [Google Scholar] [CrossRef] - Gronwald, P.O.; Kern, T.A. Traction motor cooling systems: A literature review and comparative study. IEEE Trans. Transp. Electrif.
**2021**, 7, 2892–2913. [Google Scholar] [CrossRef] - Bourgault, A.J.; Roy, P.; Ghosh, E.; Kar, N.C. A Survey of Different Cooling Methods for Traction Motor Application. In Proceedings of the 2019 IEEE Canadian Conference of Electrical and Computer Engineering (CCECE), Edmonton, AB, Canada, 5–8 May 2019; pp. 1–4. [Google Scholar]
- Gai, Y.; Kimiabeigi, M.; Chong, Y.C.; Widmer, J.D.; Deng, X.; Popescu, M.; Goss, J.; Staton, D.A.; Steven, A. Cooling of Automotive Traction Motors: Schemes, Examples, and Computation Methods. IEEE Trans. Ind. Electron.
**2019**, 66, 1681–1692. [Google Scholar] [CrossRef] [Green Version] - Chai, F.; Tang, Y.; Pei, Y.; Liang, P.; Gao, H. Temperature Field Accurate Modeling and Cooling Performance Evaluation of Direct-Drive Outer-Rotor Air-Cooling In-Wheel Motor. Energies
**2016**, 9, 818. [Google Scholar] [CrossRef] [Green Version] - Bae, J.C.; Cho, H.R.; Yadav, S.; Kim, S.C. Cooling Effect of Water Channel with Vortex Generators on In-Wheel Driving Motors in Electric Vehicles. Energies
**2022**, 15, 722. [Google Scholar] [CrossRef] - Xue, H.; Tan, D.; Liu, S.; Yuan, M.; Zhao, C. Research on the Electromagnetic-Heat-Flow Coupled Modeling and Analysis for In-Wheel Motor. World Electr. Veh. J.
**2020**, 11, 29. [Google Scholar] [CrossRef] [Green Version] - Karnavas, Y.L.; Chasiotis, I.D.; Peponakis, E.L. Cooling System Design and Thermal Analysis of an Electric Vehicle’s In-Wheel PMSM. In Proceedings of the 2016 XXII International Conference on Electrical Machines (ICEM), Lausanne, Switzerland, 4–7 September 2016; pp. 1439–1445. [Google Scholar]
- Chen, Q.; Dai, G.; Liu, H. Volume of Fluid Model for Turbulence Numerical Simulation of Stepped Spill way Overflow. J. Hydraul. Eng.
**2002**, 128, 683–688. [Google Scholar] [CrossRef] - Srinivasan, C.; Yang, X.; Schlautman, J.; Wang, D.; Gangaraj, S. Conjugate Heat Transfer CFD Analysis of an Oil Cooled Automotive Electrical Motor. SAE Int. J. Adv. Curr. Pract. Mobil.
**2020**, 2, 1741–1753. [Google Scholar] [CrossRef] - ISO/TR 14179-1; Gears—Thermal Capacity—Part 1: Rating Gear Drives with Thermal Equilibrium at 95 °C sump Temperature. ISO Copyright Office: Geneva, Switzerland, 2001.
- Menter Florian, R. Two-equation eddy-viscosity turbulence models for engineering applications. AIAA J.
**1994**, 32, 1598–1605. [Google Scholar] [CrossRef] [Green Version] - Jungreuthmayer, C.; Bauml, T.; Winter, O.; Ganchev, M.; Kapeller, H.; Haumer, A.; Kral, C. A Detailed Heat and Fluid Flow Analysis of an Internal Permanent Magnet Synchronous Machine by Means of Computational Fluid Dynamics. IEEE Trans. Ind. Electron.
**2012**, 59, 4568–4578. [Google Scholar] [CrossRef] - Yin, Y.; Li, H.; Xiang, X. Oil Friction Loss Evaluation of Oil-Immersed Cooling In-Wheel Motor Based on Improved Analytical Method and VOF Model. World Electr. Veh. J.
**2021**, 12, 164. [Google Scholar] [CrossRef]

**Figure 1.**Main cooling system for electric-drive motor: (

**a**) oil-submerge-cooled for EA motor; (

**b**) oil-spray-cooled for EA motor; (

**c**) oil-spray-cooled for IWM.

**Figure 6.**Mesh for solid: (

**a**) one concentrated coil; (

**b**) zoomed-in view of intensified prism layers.

**Figure 7.**Oil pressure at inlet and oil-wetted area fraction on the surfaces of the winding and stator carrier.

**Figure 8.**Typical moments during the change in phase oil volume fraction: (

**a**) start of partial spraying; (

**b**) start of full spraying; (

**c**) start of accumulation; (

**d**) start of equilibrium.

Oil Pipe | Pipe 1 | Pipe 2 | Pipe 3 | Pipe 4 |
---|---|---|---|---|

Nozzle diameter (mm) | 1.5 | 1.5 | 1.56 | 1.6 |

Oil flow rate (L/min) | 1.516 | 1.483 | 1.494 | 1.507 |

Part Description | Thermal Conductivity (W/m·k) | Specific Heat Capacity (J/kg·K) | Equivalent Density (kg/m ^{3}) |
---|---|---|---|

Stator carrier | 43 | 465 | 7850 |

Stator core | 21/21/4.43 | 460 | 7650 |

Rotor core | 21/21/4.43 | 460 | 7650 |

Rotor magnet | 7.5 | 460 | 7500 |

Slot copper wire | 2/5.5/314 | 460 | 7296 |

Slot insulation | 0.25 | 1180 | 1990 |

Slot varnish | 0.2 | 1700 | 1400 |

Busbar copper | 390 | 385 | 8920 |

Busbar carrier | 0.25 | 1180 | 1990 |

Part | Loss (W) | Part | Loss (W) |
---|---|---|---|

Stator teeth | 88 | Rotor core | 21 |

Stator yoke | 59 | Windage and friction | 15 |

Cooper wire | 926 | Magnet | 3.6 |

Part Description | T1 | T2 | T3 | T4 |
---|---|---|---|---|

Simulated (°C) | 122.5 | 129.3 | 126.3 | 122 |

Measured (°C) | 122 | 128 | 123 | 120 |

Error (%) | 0.41 | 1.02 | 2.68 | 1.67 |

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |

© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Huang, C.; Xiong, L.; Hu, L.; Gong, Y.
Thermal Design and Analysis of Oil-Spray-Cooled In-Wheel Motor Using a Two-Phase Computational Fluid Dynamics Method. *World Electr. Veh. J.* **2023**, *14*, 184.
https://doi.org/10.3390/wevj14070184

**AMA Style**

Huang C, Xiong L, Hu L, Gong Y.
Thermal Design and Analysis of Oil-Spray-Cooled In-Wheel Motor Using a Two-Phase Computational Fluid Dynamics Method. *World Electric Vehicle Journal*. 2023; 14(7):184.
https://doi.org/10.3390/wevj14070184

**Chicago/Turabian Style**

Huang, Chao, Lu Xiong, Liang Hu, and Yu Gong.
2023. "Thermal Design and Analysis of Oil-Spray-Cooled In-Wheel Motor Using a Two-Phase Computational Fluid Dynamics Method" *World Electric Vehicle Journal* 14, no. 7: 184.
https://doi.org/10.3390/wevj14070184