From the current trend of the times and national policy can be seen，new Energy vehicle is the main trend of current automobile development. For the new energy vehicle, because the motor itself has a very high speed and torque output range, so the role of the gearbox began to be replaced by the reducer. Among them, the planetary gear has the advantages of good coaxiality, small mass, small volume, large transmission ratio, large carrying capacity, stable transmission and high transmission efficiency, which meet the requirements of the automobile. At home and abroad, there are many researches on the planetary gear reducer, but most of them are single-stage planetary gear reducer, and the research on double-stage planetary gear reducer is very few. In addition, the single-stage reducer has some disadvantages such as high requirements for driving and low efficiency of electric drive assembly. Therefore, this graduation project carries out the research on the double-stage planetary gear reducer, studies its structure design method, and puts forward the strength checking calculation method It is valuable to improve the transmission performance of two-stage planetary gear reducer and promote its application in new energy vehicles. In this paper, first of all, the performance parameters of the automobile are analyzed, then the data needed for the design of the reducer are converted, and then the structural types of the two-stage planetary gear reducer and its components are analyzed To determine the structural design scheme of the two-stage planetary gear reducer and its components, and to analyze and check the design calculation of the two-stage planetary gear reducer and its components, finally, the Assembly drawing and the main parts drawing of the two-stage planetary gear reducer are drawn.
Key Words: New Energy Vehicle; Planetary Gear; two-stage reducer
Chapter One Introduction 1
1.1 Research background 1
1.2 Research Status at Home and Abroad 3
1.2.1 Research status of China 3
1.2.2 Research Status of Abroad 5
1.3 Overview of the research 6
1.3.1 Main research contents 6
1.3.2 Summary of each paragraph 7
Chapter Two Establishment of the Overall Scheme of Planetary Gear Reducer 8
2.1Basic condition and definition of planetary gear transmission 8
2.2Selection of planetary gear trains 9
2.3Tooth fitting calculation 10
2.4Primary calculation of main parameters of gear 10
2.4.1 Calculate module M of high speed gear 11
2.4.2 Calculate gear module M of low speed stage 11
2.5Calculation of meshing parameters 12
2.5.1 Calculation of meshing parameters of high-speed stage 12
2.5.2 Calculation of meshing parameters of low-speed stage 12
2.6Calculation of geometric size 13
2.6.1High-speed stage 13
2.6.2Low-speed stage 14
2.7Checking calculation of assembly condition 14
2.7.1Adjacency condition 14
2.7.2 Concentric condition 15
2.7.3Installation conditions 15
2.8Calculation of transmission efficiency 15
2.9Checking the strength of gear transmission 18
2.9.1Fatigue strength check of high-speed gear 18
(2)B-C gear pair： 21
2.9.2Fatigue strength check of low-speed gear 23
Chapter Three Axle 28
3.1Input axle 28
3.2 Output axle 29
3.3 Check and analysis of drive shaft 29
3.4 Planetary terminal 31
Chapter Four Other Structure 33
4.1Internal gear 33
4.2Planetary gear design 33
4.3Design of rotating arm 34
4.4 Design of box body 35
4.5 Deep groove ball bearings 36
4.6Flat key 37
Chapter Five Summary and Outlook 39
5.1 Full text summary 39
5.2 Innovations in this article 39
5.3Research outlook 39
Chapter One Introduction
1.1 Research background
The automobile industry is a very important part of the world today, and the traditional automobile industry has been on the road of new intelligence and new energy after years of development. Now, with its oil shortage, environmental pollution, climate warming and other problems, each country began to launch a new development strategy to maintain the sustainable development of the automobile industry and real-time response to the international situation, improve their competitiveness, therefore, the new energy automobile becomes the 21st Century Automobile Industry Development Main Hot spot. Foreign Development, the first electric vehicle produced in the United States, and the American Electric Vehicles Alliance also proposed by 2040 a clear new energy vehicle development goals and action plans. Japan exempted new energy vehicles from a variety of taxes a decade ago. Germany says renewables will account for 47% of its energy by 2020. 
In february this year, the Ministry of Industry and Information Technology organized the launch of the compilation of the new energy automobile industry development plan (2021-2035) , which showed that The new top-level planning route is to vigorously develop fuel-cell vehicles and subsidize charging stubs.
Meanwhile, Wan Gangye, vice-chairman of the National Committee of the Chinese People's Political Consultative Conference, said, "the future of new energy vehicles is fuel cell vehicles. "
The China charging alliance predicts that 480,000 private charging piles will be added in 2019, and 120,000 public charging piles will be added. By the end of 2019, the total number of charging infrastructure will reach about 1.4 million units, and the charging industry will enjoy explosive growth.
Thus, as a new generation of automotive engineers, the study of new energy vehicles is a major trend.
And the study of new energy vehicles, speed reducer can be said to be one of the very worthy research direction.
Because in the traditional automobile, the gearbox and the engine may say is the automobile most important two parts, is also closely related, is indispensable  . However, for new energy vehicles, because the motor itself has a very high speed and torque output range, so the role of the gearbox began to be replaced by the reducer.
If the electric vehicle is driven by the motor directly instead of the reducer, then the motor is required to have the characteristics of low speed and high torque, and the motor speed is proportional to the power when the Torque is certain, and the speed of the drive motor with the same power is lower The bigger the weight and volume of the motor, the bigger the size and weight of the motor, and the output power curve may not meet the requirements of the vehicle. At the same time, the motor reducer solution can also reduce the overall weight and manufacturing cost of the drive system. For example, the scheme of "motor reducer rear axle" and "motor rear axle" , the overall weight of the scheme with reducer than the scheme without reducer not only the overall weight of at least 100 kg less, the cost of more than 10,000 yuan.
But if the electric vehicle does not have the reducer, the output to the wheel torque is too small, it is difficult to meet the climbing and other needs of large torque. And daily use, most of the time is in flat road driving, if the selection of large torque motor, the price will be extremely high, the car cost-effective down.