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Electric Drive Wheel Hub Motor Technology

Release time:2021/10/28

Electric drive, intelligent network connection, and low-carbon travel have become the main direction of the transformation and transformation of the global automobile industry, and electric drive ranks first. Distributed drive in-wheel motor technology is the ultimate solution for electric vehicle drive. Prior to this, the in-wheel motor technology, as a "proactive, leading and exploratory major technology, can become an important basic technology for the future product technology upgrade of new energy vehicles and the promotion of industrial development."

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Compared with the central motor, the in-wheel motor eliminates the gearbox, transmission shaft and mechanical differential. With distributed drive and linear control, it can fully meet the needs of future automobile travel for safer, greener, more convenient, and more enjoyable.


First, non-contact transmission can achieve zero maintenance costs, and zero failures for millions of kilometers, which is more reliable.

The second is that the line control power has a 10 times faster response time than the traditional power, which solves the delay problem of the smart car system and is more safe.

Third, there is a huge potential for intelligent applications in driving, braking, energy recovery, differential steering, and data acquisition.

The fourth is that the transmission efficiency and energy recovery efficiency of 30% higher than the central motor and the lightweight body can not only reduce the overall cost, but also minimize carbon emissions. It is an important measure for the automotive industry to achieve the "dual carbon" goal.


To make the in-wheel motor technology truly become the ultimate driving solution for electric vehicles, especially electric passenger vehicles, there are still technical problems to be overcome.


China has the prerequisites to take the lead in the industrialization of in-wheel motors, and has the prerequisite to fully control the key core technologies of in-wheel motors, and also has the following three factors.


As an inevitable new energy vehicle production and sales country, China has provided huge development space for the industrialization of in-wheel motors. China's new energy vehicle production and sales have ranked globally for six consecutive years. As of the end of May 2021, China's new energy vehicle population is about 5.8 million, accounting for 50% of the global total of new energy vehicles. It is estimated that the production and sales growth rate of electric vehicles will remain above 40% in the next five years. By 2025, the proportion of new vehicles will exceed 20%, or reach a higher level. In the next 15 years, under the new development pattern of "dual cycle", the auto industry will continue to evolve towards electrification, connectivity, and intelligence. This is a "chase" for global auto companies to race against time.


The double carbon goal will further accelerate the industrialization process of in-wheel motors. Under this rigid constraint, Chinese auto companies must accelerate their transition to green and low-carbon development in order to ensure that the auto industry achieves its dual-carbon goals. As a carbon reduction tool, the in-wheel motor technology is bound to usher in unprecedented opportunities for industrialization.


The desire for survival of traditional Chinese car companies and the desire to make stars of new car-making forces will become a huge thrust for the industrialization of in-wheel motors. At present, the problem of high manufacturing cost of in-wheel motors can be solved through the simultaneous progress of localization, industrialization, and large-scale; the problem of insufficient research and development capabilities of power electronic architecture and intelligent control system applications of in-wheel motors by OEMs can be achieved through large-scale collaborations between industry, university, research, and application. The establishment of an industrial chain innovation alliance to solve the problem of insufficient publicity and guidance for the early application of in-wheel motors by the market, national policy support is the best public opinion guide.

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Functions and advantages of in-wheel motors


1. The function of the hub motor


a. Carrying and driving


Bearing and driving is a necessary function of the in-wheel motor. The load bearing is realized by relying on the axle bearing to realize the centering of the rotation and the stator. The wheel rim of the vehicle is connected to the suspension axle housing through the axle bearing instead of the stator and rotor to carry the road shock absorber and load. The driving method is that the outer rotor is directly connected to the rim to achieve the purpose of direct driving.


b. Electronic differential speed control


Electronic differential control is also one of the functions of the in-wheel motor. The realization method is front-wheel steering, which is completed by ordinary steering gear; the required slip of the rear wheels is completed by the electronic differential; the turning radius is determined by the angle of the front-wheel steering gear, and the rear-wheel slip is determined by the turning radius and wheelbase of the vehicle. Calculate the slip of the rear wheels from the angle of rotation of the front-wheel steering gear. The steering machine can also be an electronic steering. Even if the differential speed of the rear wheel cannot be strictly, the inner wheel should be changed from "active" to "slave" by disconnecting the motor or connecting a compensation resistor in series in the loop.


c. Braking energy recovery


The function of the in-wheel motor is also the recovery of braking energy. During the braking process of an electric vehicle, the kinetic energy of the vehicle is transferred to the motor through the wheels, thereby driving the motor to travel. At this time, the motor is working in the power generation state, charging the energy storage device, that is, the battery or super capacitor, and converting the braking energy into the energy and storing it in the energy storage device to realize energy regeneration. At the same time, the resistance torque generated by the motor acts on the wheels to generate a braking torque, which plays a role in deceleration and braking. Motor cooling There are two cooling methods for in-wheel motors, air cooling and water cooling. Air cooling, using a structure conducive to gas circulation to cool the in-wheel motor, such as a built-in cooling fan: water cooling, set up a special cooling liquid channel, and cool the in-wheel motor by exchanging with the liquid.

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2. The advantage of the in-wheel motor is that there is no restriction of complex transmission structure, which reduces the difficulty and cost of new car development, mainly in the following aspects:


a. The hub motor can directly control the speed of each wheel, so the differential that is necessary on the general car is not needed. This can reduce the turning radius and simplify the structure of the car, making the car look more like four Each wheel comes with a box, so you can get more space in the car.


b. With the reduction of the transmission mechanism and the reduction of the transmission distance, the transmission efficiency will be higher.


c. Without the limitation of complicated transmission structure, it can realize a variety of complicated driving modes, whether it is front-drive, rear-drive or four-wheel drive. At the same time, the in-wheel motor can realize differential steering similar to tracked vehicles through the different speeds of the left and right wheels, or even reverse rotation, which greatly reduces the turning radius of the vehicle. Under special circumstances, it can almost achieve in-situ steering, which is very valuable for special vehicles.


d. Because the in-wheel motor is highly integrated, it is easy to realize modularization, reducing the difficulty and cost of new car development.

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