With the development of pure electric vehicle motor technology, the design concept of traditional fuel vehicles and the layout of pure electric drive have been misaligned, and the disadvantages of low transmission efficiency and complex control of centralized drive have gradually become prominent. Compared with the centralized drive, the distributed drive eliminates transmission components such as clutches, transmissions, transmission shafts, and differentials, and installs the motor directly near the drive wheels to independently drive the wheels, which is more conducive to system integration. Lightweight and modular design, while saving cost and space, has the advantages of high response speed, high control accuracy, and good information transmission. It is the main direction of electric vehicle drive system technology. There are usually two ways of in-wheel motor drive: in-wheel motor and in-wheel motor. The so-called wheel side motor means that each driving wheel is driven by a separate motor, but the motor is not integrated in the wheel, but connected to the wheel through a transmission. The advantage of the wheel-side motor drive axle is that it no longer transmits through long half-shaft components, and abandons traditional mechanical components such as clutches and transmission systems, which simplifies the mechanical transmission structure and reduces its own weight. At the same time, the dynamic response of the wheel control has been improved. Evolution from centralized drive to distributed drive In the distributed drive, the wheel motor is usually installed on the frame together with the fixed speed reducer. The output shaft of the reducer is connected to the wheel directly or through the short semi-shaft to drive the wheel. The hub motor connects the power, transmission and braking device Integrating them into the inside of the wheel saves space and improves attention. Wheel motor and hub motor installation layout Picture above (left): ZF AVE130 wheel-side electric drive axleAbove (right): protean hub motor The first to have a systematic understanding of distributed motors is actually the Audi e-tron S drive motor structure. It is the first brand to use three-motor architecture and electric torque distribution on the BEV platform for mass production. The dual-motor e-axle platform assembled on the rear axle, the model is ATA250. The scientific name of ATA250 is called electrical decoupling. In fact, this is the official statement that the two rear axle wheels are controlled by a motor respectively. Among them, ATA250 is a veritable rear axle distributed wheel motor drive. The motors of the ATA250 series are driven by distributed control. Two motors on both sides control the half shaft on one side respectively. If you look carefully, a set of reduction devices are arranged on both sides. This set of reduction devices is mainly composed of planetary gear reducers. . At the same time, there is a set of inverters on each side to convert the DC power of the battery pack into AC power. Therefore, since the traditional mechanical differential has been cancelled, there is a higher challenge in the precise control of the output wheel speeds on both sides. APA250: parallel shaft 250Nm AKA320: coaxial 320Nm APA320: large motor, parallel shaft output, 320Nm ATA250: small motor, dual motor coaxial, 500Nm. This point is actually different from Acura's SH-AWD system, because Acura's SH-AWD is developed on the traditional fuel vehicle platform. The motor is not distributed from the power domain controller, but according to CAN bus communication. The engine power domain of Acura has a higher right to speak to the SH-AWD of the rear axle, but even so, Acura's SH-AWD can give people a very good "track sense". Immediate driving experience. BYD Yi Sifang's wheel-side motor is accelerating, and the wheel-side motor is expected to usher in new opportunities. On January 5, 2022, BYD looked up to the off-road vehicle U8 and the supercar U9. BYD's innovative distributed electric drive system platform "Easy Square" was unveiled, among which the maximum output power of four wheel-side motors reached 220kW~240kW, and the maximum torque reached 320N. m~420N·m, the maximum speed reaches 20500rpm, as the power source can realize the vector control of the size and direction of the driving force independently of each other, and realize diversified coordination through the central computing platform + domain controller, so as to realize the original angle of the vehicle Ground rotation, emergency flotation and precise skid control. We expect that with the mass production of models equipped with the "Easy Square" platform, wheel motors are expected to usher in new opportunities. Picture above (left): BYD Yisifang electric drive assembly systemPicture above (right): Independent control of BYD Yisifang motor Where is the challenge of BYD's looking up series? The author believes that the challenge of BYD's Yangwang series lies in the gap between the unit price of new car products and the price range of models that the brand has cultivated before. As for the technical level of the product, looking up at the series of electric drive assemblies, BYD has many years of accumulation in manufacturing, research and development, and design. The miniaturization of electric drive assemblies is not a big challenge for this company. . In addition, the new product is said to have added a deep wading function. The wading sealing ability of this electric drive system must exceed the so-called "IP67" level of traditional electric vehicles.
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