1.1 Purpose and significance

The drive axle is the mechanism at the end of the drive train that changes the speed and torque from the transmission and transmits them to the drive wheels. In addition, the drive axle is also subjected to vertical forces, longitudinal and lateral forces acting on the road surface and the frame or body, as well as braking torque and reaction forces. A common drive axle is generally composed of a final drive, a differential, a half shaft, and a axle housing, and the electric drive axle is powered by a motor, and a motor is arranged on a conventional drive axle to achieve an electric drive.

With the continuous development of the automobile industry and the continuous improvement of technology, it brings great convenience to human beings and brings about three major problems of energy, safety and environmental protection. In order to effectively alleviate the problem of energy and environmental pollution, the transition of automobiles from traditional fuel vehicles to electric vehicles is an inevitable choice in history. In June 2012, the “Energy Conservation and New Energy Vehicle Industry Development Plan (2012-2020)” issued by the State Council emphasized that the technical route for the development of new energy vehicles is based on pure electric drive as the main strategy for the development of new energy vehicles and the transformation of the automobile industry. Orientation, the current focus is to promote the industrialization of pure electric vehicles and plug-in hybrid vehicles, promote the popularization of non-plug-in hybrid vehicles, energy-saving internal combustion engines, and improve the overall technical level of China's automobile industry.

The development of the drive axle is extremely important for electric vehicles. The performance of the drive axle will directly reflect the rationality of the vehicle design. In the design and manufacture process of the drive axle, it is necessary to ensure that the quality of the drive axle cannot be too large, otherwise it will not only increase the production cost, but also reduce the economical efficiency of the vehicle.In recent years, advanced modern design methods such as computer-aided design, computer-aided engineering, and finite element analysis methods have entered the automotive industry, which can effectively shorten the design cycle, reduce production costs, and improve the reliability and economy of the electric drive axle.

1.2 Research Status at Home and Abroad

The domestic research on electric drive axles is relatively late compared to foreign countries. The research on new electric drive axles is based on the standard of traditional drive axles .

The electric drive system is the core component of the electric vehicle, and its technical level directly limits the overall performance of the electric vehicle. For the source of the driving torque applied by the driving wheel, the driving mode adopted by the electric vehicle can be generally divided into two types: a concentrated driving and a wheel independent driving. The centralized drive uses a power source to reduce the speed through the transmission and the reducer (or only through the reducer). Finally, the differential torque is distributed to the left and right drive axles approximately equally through the differential. The front wheel drive and the rear wheel can be used. Drive or four-wheel drive form. It is used as a traditional drive in fuel vehicles and most electric vehicles. In addition, there are wheel independent drives. Wheel independent drive refers to driving a single wheel with multiple power sources, which can be divided into two-wheel independent drive and four-wheel independent drive ^[1] . In this design, the electric drive axle is a centralized drive.

There are also designs and experiments on electric drive axles in China, such as "Design and Test of Electric Drive Axles for Pure Electric Vehicles". After determining the basic performance requirements of the design objects, from the mechanical structure of the electric drive axle and the drive controller system. Designed. Based on the analysis and determination of the arrangement of the motor and the drive axle, the design of the electric drive axle is carried out, which mainly includes the components such as the half shaft, the final drive, the differential and the axle housing. According to the three typical working conditions analysis methods of automobile operation, the basic parameters of each component are determined by theoretical calculation; the virtual prototype of electric drive axle is established in CATIA; the strength and fatigue check of each component are combined with finite element analysis method ^{[ 2]} .

The research of electric drive axles is not limited to the new structural design. The electric drive axles need the same lightweight design as the traditional drive axles. At present, the main lightweight ideas are the application of high-strength, lightweight materials and the adoption of a more compact new structure. to fulfill. For the axle portion of the drive axle, the cast-type axle housing is used to replace the original stamped-welded axle housing, which reduces the thickness of the overall shell. The key force position on the axle shell is optimized and partially strengthened, and the overall weight reduction is finally realized. For the main reducer housing, cast aluminum alloy is used instead of the original cast iron material. Since the density of cast aluminum is about one-third the density of cast iron, the weight of the part can be greatly reduced. For the improvement of the structure of the wheel part, the more compact arrangement is adopted, and the original bearing type is replaced by the hub bearing unit, which shortens the axial dimension of the hub and reduces the weight ^[3] .

At present, the researches on electric drive axles in China are mainly the analysis or improvement of existing structures. Compared with foreign countries, there are still some gaps. The development of foreign electric vehicles is earlier than domestic and has many years of history and more innovative technologies.