Wuhan University of Technology Undergraduate Graduation Design (Thesis)

Design (Thesis) Title: Structural design of passive cooling unit of electric vehicle power system

School: School of International Education

Specialty amp; Class: Automotive Engineering gj1604

Name: Zhou Zisen

Tutor: Tan Gangfeng

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I solemnly declare：The thesis submitted is the research result independently obtained by myself under the guidance of my tutor. Except for the contents specifically quoted in this thesis, this thesis does not include any other works that have been published or written by individuals or groups. I fully understand that the legal consequences of this statement are borne by me.

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Date: May 31, 2020

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Abstract

In this paper, the thermal network of a Toyota Prius motor is simulated by means of motor CAD software. The maximum temperature rise area and its temperature and the overall thermal loss of the motor are obtained. A passive cooling structure unit based on the heat pipe is designed, and the maximum temperature of the motor is compared in two cases with or without the passive cooling structure. The results are of great guiding significance to reduce the energy consumption of electric vehicles and improve the endurance mileage.

This paper mainly studies the passive cooling structure of motor based on heat pipe.

The results show that the motor can still work in the proper temperature range when some heat pipes fail on the general horizontal road, but on the climbing Road, some other active cooling and heat dissipation measures may be needed to ensure the driving safety.

The feature of this paper: it has high reliability and economy by using the passive phase change characteristic of heat pipe to transfer heat efficiently.

Key Words：Motor temperature rise; copper water heat pipe; passive heat dissipation; different working conditions

Contents

Chapter 1 Introduction 1

1.1 Purpose and significance 1

1.2 Research status at home and abroad 1

1.3 The basic content of the study, objectives, and plans to adopt 3

1.3.1 Research objectives 3

1.3.2 Research purpose 4

1.3.3 Technical solutions 4

1.3.4 Technical measures 4

Chapter 2 Analysis of Motor Temperature Rise 7

2.1 Numerical settings 7

2.1.1 Motor data setting 7

2.2 Numerical analysis 9

2.2.1 Temperature analysis of each area of the motor 9

2.2.2 Motor loss analysis 10

Chapter 3 Heat transfer characteristics of heat pipes 14

3.1 Analysis of heat transfer characteristics of heat pipes 14

3.1.1 Thermal resistance of the heat source to the outer wall of the evaporation section of the heat pipe 15

3.1.2 Internal thermal resistance of the heat pipe 16

3.1.3 Thermal resistance outside the condensation section 17

Chapter 4 Thermal Performance Calculation and Analysis 22

4.1 Calculation of total thermal resistance of the system 22

4.2 Calculation of motor temperature drop 23

Chapter 5 Introduction Combined with Vehicle Dynamics Analysis 25

5.1 Analysis of driving conditions 25

5.1.1 Driving at a constant speed 25

5.1.2 Driving uphill 26

5.2 Analysis of heat dissipation of drive motor 26

5.2.1 Relationship between vehicle speed and heat dissipation performance 26

5.2.2 Relationship between slope and heat dissipation performance 29

Chapter 6 Conclusion 32

Acknowledgments 34

References 35

Appendix A 37

Chapter 1 Introduction

In the context of the gradual popularization of new energy vehicles and a large number of entering the market. The design of the heat dissipation structure of electric vehicles under various working conditions becomes particularly important. Compared with ordinary fuel vehicles, electric vehicles are equipped with more electrical components and are more sensitive to temperature changes. Excessive temperature will also affect the safety, service life and economic and environmental protection of the vehicle. Therefore, designing a passive passive heat dissipation structure will greatly improve the safety and reliability of electric vehicles. Therefore, the heat pipe is used for heat dissipation in this design. The heat pipe has the advantages of small thermal resistance, small size, fast heat transfer and heat conduction. The heat pipe heat dissipation process is a linear process, and the temperature will not change stepwise. It will cause damage due to the excessive temperature difference between the radiator and the heat source. At the same time, the heat pipe heat dissipation principle is due to the phase change process of the internal working medium, so this structure does not require external energy supply and will be able to dissipate heat for the motor at any time Improve the service life and safety performance of electric vehicle motors and ensure that the motors can work in a reasonable working temperature range for a long time.

• 1. Purpose and significance

The title of this graduation project is "Design of Passive Heat Dissipation Structure Units of Electric Vehicles", which mainly chooses to study representative motors in electric vehicle power systems. The purpose is to use the phase change heat dissipation of the heat pipe to passively dissipate the electric car motor, so that the motor always works in a safe and effective temperature range, so as to ensure that the electric car motor can be within a certain range under the corresponding working conditions, and only rely on passive heat dissipation. Can work safely and effectively.

• 1. Research status at home and abroad

The design of the passive heat dissipation structure of the electric vehicle motor mainly considers three aspects. First, it analyzes the temperature rise of the motor, secondly, the selection of heat pipes of the heat dissipation structure, and finally the verification of different heat dissipation requirements due to different working conditions .

In the establishment of the motor temperature rise model, Yang Chaonan [1] introduced three current mainstream analysis methods, namely simplified formula method, equivalent thermal network method and finite element analysis method. Because the accuracy of the data obtained by the simplified formula method is low, it is generally only used in motor manufacturers and does not meet the accuracy requirements of research and design. Wang Jianbo [2] combined the design of a permanent magnet synchronous motor project, established the motor thermal analysis model and thermal resistance network diagram using the principle of equivalent thermal network method in Motor-cad, and determined the basic process of motor thermal analysis. Wang Xiaoyuan et al. [3] established an equivalent thermal network temperature field analysis model and a finite element model based on the structure of a general hub motor prototype for electric vehicles. According to the temperature rise experiment of the hub motor, the calculation results of the two methods are compared and analyzed, and the effectiveness of the equivalent thermal network analysis model and the finite element model is verified, which shows that the equivalent thermal network method and the finite element method Computational adaptability and compatibility. Zhang Qi [4] analyzed the overall temperature field of the hub motor under rated operating conditions in the ANSYS Transient Thermal module, and used the calculated heat dissipation boundary conditions to simulate the heat dissipation of the hub motor. Zhou Xiaoyan [5] and Han Xueyan [6] continued to conduct a detailed analysis of the temperature rise of permanent magnet motors based on the equivalent thermal network method.

The research on heat pipes is discussed from the aspects of the shape of the heat pipe and the working fluid. Jin Yu [7] proposed a fin-shaped gravity heat pipe, which has more heat dissipation area than the general flat heat pipe. Xie Hua [8] analyzed the influence of the shape and quantity of heat pipes on the heat dissipation performance. Wang Yishi [9] proposed to install the heat pipe on the motor housing, and analyzed the heat dissipation performance of the improved structure. Fresh scale [10] discusses the separate heat pipe, and Yu Shijie [11] makes a research on the working fluid reflow structure inside the heat pipe, and discusses the advantages and disadvantages of the sintered core structure and the groove structure. Gao Tianqi [12] studied the heat pipe heat dissipation performance under different wind speeds. Xu Chunlin [13] optimized the structure of the heat pipe and strengthened its heat dissipation performance by studying the heat dissipation of the high-power motor; Yang Youping [14] proposed a method of replacing the rotating shaft with a heat pipe in the AC inverter motor. Sun Yalong [15] designed to solve the heat dissipation problem of permanent magnet motor windings, designed to install the heat pipe on the blind hole of the chassis. Qing Qing [16] and Song Fuqiang [17], etc. conducted numerical analysis on gravity heat pipes and finned heat pipes, respectively, and obtained the relationship between gravity and flow velocity and heat transfer coefficient. Shoai Naini, Shervin [18] and others proposed a heat bus-based heat bus model; Shervin Shoai Naini [19], Wei Wu [20], and Shiping Huang [21] continued to study the cold end of the air-cooled heat pipe.