Hub motor application
The hub motor drive system can be flexibly arranged in the wheels of various electric vehicles to directly drive the hub to rotate. Compared with traditional centralized driving methods such as internal combustion engines and single motors, its technical advantages and characteristics in power configuration, transmission structure, handling performance, energy utilization, etc. are extremely obvious, mainly as follows:
The power control is changed from a hard connection to a soft connection, and the electronic controller can realize the stepless speed change between the hubs from zero to the maximum speed and the differential requirement between the hubs. The traditional mechanical shifting, clutch, transmission, drive shaft and mechanical differential are eliminated, which makes the drive system and the vehicle structure simple and uniform, and the available space is increased, and the transmission efficiency is improved (theoretical value is 10%).
The freedom of vehicle layout and body design is greatly increased. Taking the automobile as an example, after the bearing function of the chassis is separated from the transmission function, the bridge structure is greatly simplified, and it is easier to realize product diversification and serialization of different body shapes of the same chassis, shorten the development cycle of the new vehicle, and reduce the development cost.
The torque of each hub is independently controllable, the response is fast, the forward and reverse rotation is flexible, and the instantaneous power performance is superior, which significantly improves the driving ability to adapt to the harsh road conditions.
It is easy to realize the energy feedback of the electric brake of the hub, the electromechanical compound brake and the braking process, and it can also optimize the control and management of the efficient use of the vehicle energy, and effectively save energy.
For electric vehicles driven by hub motors, if four-wheel steering technology (4WS) is further introduced to reduce the steering radius, it is also possible to achieve zero-radius steering.
The shape of the hub motor is basically the same, most of them are flat, but the motor type, structure form and driving method are quite different, and the classification is as follows.
Classified by motor type: There are four main types of motors currently used in electric hubs, namely permanent magnet motor (PM), asynchronous motor (IM), switched reluctance motor (SRM) and transverse flux motor (TFM). Among them, permanent magnet motor is the most common application, and transverse flux motor is a kind of competitive low speed and high torque new type motor.
Classified by structure: from the main magnetic flux path, it covers all three basic forms of radial, axial, and transverse. From the perspective of the movement mode, there are also inner rotor, outer rotor and double rotor. Among them, the double rotor structure is the most innovative. The inner rotor is active and the outer rotor is driven. The two transmit power through a set of planetary gears to achieve reverse rotation, so that the speed of the magnetic field cutting conductor is the sum of the inner and outer rotor speeds. Obviously, this kind of speed superposition and the ingenious combination of mechanical linkage not only bring the relaxation space to the motor design, but also play the role of slow release load disturbance, smoothing the impact load and effectively protecting the battery.
Classified by driving method: When driving directly, the motor adopts the outer rotor structure, that is, the rotor directly drives the hub to rotate, so the rotation speed is low. Correspondingly, in the case of indirect driving, the motor is mostly an inner rotor structure, and the rotation speed is high. The deceleration is realized by the planetary gear ring gear mechanism, and the wheel hub is rotated, which is also called a deceleration drive.
Classified by rotation speed: The hub motor also has high speed and low speed, but the corresponding speed range is not clearly defined, depending on the application object. Generally, the definition of the high and low speed ranges has a relatively accurate meaning only after the driving mode is determined, that is, the direct driving generally corresponds to a low speed motor (large volume, large consumables, low power density, low noise), and indirect driving is more Corresponding to high speed motors (small size, low consumables, high power density, high noise).
The driving method of the hub motor used in the pure electric transmission car is directly driven by the outer rotor. The stator, rotor and inverter of the motor are integrated into one. It consists of 8 logical sub-motors, using a common rotor and realized by an algorithm. Independent and coordinated control of each sub-motor. This "distributed" structure reduces the power requirements for each sub-motor, so small-volume, low-cost power electronics can be used, allowing the entire motor to be integrated very compactly; with reasonable coordination of the eight sub-motors Control, the power and torque output of each sub-motor can be superimposed to achieve the strong driving force of the whole motor; at the same time, if one of the sub-motors fails, the other motors can continue to work normally without causing the car to directly anchor. .
