China's passenger car electric drive market ushers in a diversified competition

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In February 2017, the National Development and Reform Commission, together with the Ministry of Science and Technology, the Ministry of Industry and Information Technology, the Ministry of Finance and other relevant departments, organized and published the "Guided Catalogue of Key Products and Services for Strategic Emerging Industries (2016 Edition)" (referred to as "Catalogue"). Among them, among the products newly cultivated by new energy vehicles, the centralized motor that occupies the main position of the market, the wheel motor that has just entered the market, and the hub motor that is in the research and development stage are all listed.

At present, China's pure electric bus power system drive mode is mainly divided into two categories: centralized drive and distributed drive. At present, the domestic bus market is dominated by centralized driving, and the two types of decentralized driving methods, wheel-side drive and wheel-drive, are gradually being introduced to the market.

â–  Centralized drive is the mainstream of the current market

The pure electric bus central drive system can also be called centralized drive. This type of drive is based on the transmission system of the traditional power car. The main motor is connected to the drive axle through the drive shaft. In short, it is the power of the traditional internal combustion engine. The system is replaced with a motor-based drive system.

"Centralized drive is divided into single motor and double motor. Single motor has three types: direct drive, motor + variable/decelerator and central drive axle. The dual motor scheme has dual motor parallel + variable / speed reducer, double Motor series + variable / speed reducer program and two motors + variable / speed reducer (two motors are separated at the ends of the transmission)." Chen Youfei, deputy general manager of the pure electric business division of Suzhou Green Control Transmission Technology Co., Ltd. said that these The modes can meet the passenger car products of various specifications, and belong to the more mature drive type.

“In this case, the direct drive motor is the most widely used Solution on the pure electric bus. The system is connected to the drive axle through a drive shaft. The structure is simple, reliable and easy to maintain.” Jingjin Electric Technology Co., Ltd. The relevant person in charge of the company said that because of the high maturity of direct drive motor technology, it is more easily accepted by customers. This is also the reason why bus companies generally adopt direct drive motor solutions.

In addition, the central drive axle can be seen as an upgraded version of the centralized drive to date. It is understood that the central drive axle is to converge the motor on the drive axle. The elimination of the final reducer helps to reduce energy consumption, while the integrated design also reduces the overall weight. Currently, it is on models below 8 meters. Have certain advantages.

“However, although the centralized drive technology has a high maturity, there are also defects in the subdivision drive scheme. For example, direct drive motors have insufficient climbing performance, lack of medium and high speed performance, and are relatively heavy and costly. Higher problems." Chen Youfei pointed out.

“Evenly, in order to get the product into the market as soon as possible, the auto company will basically choose a centralized drive technology solution at the beginning.” Wang Xiaoquan, director of the Southeast New Energy Technology Office, explained in an interview with the China Auto News that the new energy bus In the early stage of marketization, the policy dividend is the main driving force. The car companies will definitely seek a simple-changing drive solution to quickly seize the market, and centralized drive technology is the best solution at that time.

â–  Decentralized drive is gradually becoming the future trend

"With the gradual deepening of pure electric vehicle technology research, the layout of its drive system has gradually evolved from a centralized drive of a single power source to a decentralized drive of multiple power sources." Head of Electric Drive System Design, Beiqi Foton Motor Co., Ltd. Wang Hailong pointed out that compared with the centralized drive, the decentralized drive eliminates the components such as the transmission, drive shaft, mechanical differential, and half shaft, and moves the motor to the wheel side, making the transmission structure simpler.

At present, the most common type of distributed drive is the wheel drive. The drive form is to arrange the drive motor beside the wheel and directly drive the wheel through the speed reduction mechanism.

According to Wang Yongtao, an engineer at the Hager Bus Technology Center, the wheel drive has a very prominent advantage. “Firstly, the wheel drive can make the vehicle drive system and the vehicle structure more compact and compact, and it is easy to achieve low floor and standing area and passenger load. At the same time, it can also reduce the center of gravity of the vehicle and improve the driving stability of the vehicle. In addition, the wheel drive system is short in power transmission chain, and can optimize driving and braking force distribution through energy management and power system control strategies to reduce energy consumption and improve vehicle fuel economy. Compared with internal combustion engines and concentrated motor-driven vehicles, Wheel-side drive technology can also greatly improve the driving dynamics of the vehicle. It can easily realize ABS, TCS and ESP functions through motor control technology. In addition, the system can improve the steering performance of the vehicle and effectively reduce it. The steering radius, even zero turning radius, greatly increases steering flexibility," he said.

Compared with the wheel-drive technology, the wheel drive technology, which is known as the ultimate solution for pure electric buses, brings the essence of “distributed drive” to the extreme.

“The biggest feature of the hub motor system is that the power unit, transmission and brakes are all integrated into the hub, which greatly simplifies the traditional system of the electric vehicle.” Wang Hailong emphasized that the chassis of the assembled wheel motor is much less than the traditional chassis. Parts and components will have a big advantage in terms of cost. In addition, its transmission efficiency is higher than that of centralized drive and wheel drive.

“Preliminary calculations show that the hub motor system is 13% to 16% more efficient than the centralized drive. While the wheel drive system is in principle also placed on the axle, the motor system will pass through the reduction mechanism. The efficiency loss is about 10%. The hub motor directly drives the wheels, which avoids the problem of efficiency loss.” Lu Chao, chairman of Tianhai Synchronous Group, said.

Although the advantages are obvious, the technical challenges of distributed drive technology cannot be ignored. Wang Hailong pointed out that the unsprung mass change of the wheel motor affects the smoothness and handling of the vehicle. In addition, there is still no ideal solution to solve the differential problem of wheel drive, especially in the case of high-speed cornering and road bumps. Differential control. The reliability of the hub motor and the increase in the quality of the unsprung load are more obvious. At the same time, since all components are concentrated in the hub, heat dissipation and electronic control problems are also urgently to be solved.

The high cost of distributed drive solutions is another important reason for its marketization. “Distributed drive requires at least two motors, and the cost is about three times that of the direct drive system.” Zhao Fucheng, deputy dean of Geely Automotive Powertrain Research Institute, points out the benefits and systems created by distributed drives in reducing power consumption. The cost is not equal.

â– The future market may be diversified

The industry generally believes that the new energy vehicle power system is divided into three technological development stages, the first stage is centralized drive technology, the second stage is wheel-side motor technology, and the third stage is called hub motor technology called ultimate solution.

From the current market structure, it is an indisputable fact that centralized drive technology dominates the pure electric bus market. Then, as a more advanced drive solution, decentralized drive technology will be able to come later?

"In terms of production scale and economic efficiency, centralized drive technology will be the mainstream of the pure electric bus market for a long time in the future, this time will last at least 3 to 5 years." Industry insiders said.

In this regard, Wang Xiaoquan also pointed out that the dominant position of centralized drive technology in the pure electric bus market cannot be shaken in the near future. After 2020, the subsidence of the subsidence has made the marketization of distributed drive technology more difficult.

Lu Chao is a supporter of the "subversive theory" of decentralized drive technology. He believes that the wheel drive technology will occupy a place in the pure electric bus and pure electric special vehicle market. In addition, the market opportunities brought by the combination of hub motor technology and autonomous driving will be greater.

“The BYD K9 with wheel-side drive technology can be said to be the pioneering work of the company's new energy bus field.” Xiao Haiping, the public relations director of BYD's commercial vehicle sales division, is very optimistic about the development prospects of wheel-side drive technology. In 2014, BYD equipped with wheel-side motors. After the bus was introduced in China, it has already promoted thousands of vehicles in Nanjing, Hangzhou and Shenzhen. “The operation mileage of this product in Shenzhen has exceeded 400,000 kilometers, and the quality has been unanimously recognized by users.”

It is understood that Futian Ou Hui has mass-produced 18 meters of wheel-side driven pure electric products in 2015, and Haige buses also have 12-meter wheel-drive passenger cars to export overseas. "I believe that the future of distributed drive technology will be the mainstream of the industry, and the cost will also decrease with the increase in production." Jiang Tao, chief engineer of Shanghai Futian Electric Technology Co., Ltd. said.

"It is undeniable that wheel drive and wheel drive are the development direction of new energy bus electric drive system." Wang Hailong believes that the development trend of system integration and control digital will also help the rapid spread of distributed drive technology. "However, at present In terms of distributed drive technology, technology accumulation needs to be completed as soon as possible, and it will be able to achieve a long-term growth when it comes to market opportunities."