In-wheel motors vs. traditional motors: why advanced in-wheel motor electric vehicles are not widely used

With the expansion of the new energy vehicle market, more and more automakers are investing in the research and development of electric motors. Currently, the most mainstream motor is placed in the position of the front internal combustion engine of a traditional car or on the rear axle. The layout is no different from that of a traditional car, but in many concept electric cars, we will see the term hub motor, which is installed on the hub of the wheel and directly drives the wheel. As a new research direction, although many manufacturers are already committed to this, we still have not seen large-scale equipment. So what is the difference between hub motors and traditional motors, and what are their advantages and disadvantages? Today, our car selection detective will analyze it in detail.

1. Is the principle of the hub motor the same as that of the traditional motor?

Taking the asynchronous hub motor as an example, it is mainly composed of a stator, a rotor and additional parts. The stator core is generally made of silicon steel sheets with an insulating layer, which is used to place the stator winding. The stator winding is distributed at the center of the circle at the same angle, that is, each at an angle of 120 degrees. The coils on the windings are wound according to a certain rule, and the stator winding flows through the current to generate a rotating magnetic field. At this time, the rotating magnetic field and the rotor conductor have a relative cutting motion. According to the principle of electromagnetic induction, the rotor conductor generates an induced electromotive force and an induced current. The rotor conductor is affected by the electromagnetic force in the magnetic field, forming an electromagnetic torque, which drives the rotor to rotate. In layman's terms, it is the process of converting the electrical energy of the current into mechanical energy. I believe that many people have played with four-wheel drive cars when they were young, and the motor that drives the four-wheel drive car is a small motor, but the two magnets inside are permanent magnets, and the AC motor needs electricity to generate a magnetic field. Compared with internal combustion engines, motors are actually simpler and easier to control.

The principle of the hub motor is actually the same as that of the traditional motor, but the structure is more compact, which means that there are fewer coils and the magnetic field is not as strong as the motor with the traditional position arrangement, so the output power is relatively small. In addition, there are two types of hub motors: internal rotation motors and external rotation motors. The rotor of the external rotation motor is located inside the stator, just like a traditional motor. The rotor of the external rotation motor is located outside the stator and rotates around the stator. The hub motor integrates the power unit, transmission device and brake device into the wheel hub, so the mechanical part of the electric vehicle is greatly simplified.

2.What are the advantages and disadvantages of hub motors compared to traditional motors?

就像上面所说，由于轮毂的直径和轮胎的宽度有限，因此轮毂电机的最大体积不如传统电机，输出功率也很难达到标准，因此目前许多轮毂电机只在两轮骑行电动车上使用。相比传统电机，轮毂电机其实有许多非常显著的优点，首先这种设计没有传输损失，因为没有传动杆从发动机到车轮，所以效率非常高。此外，轮毂电机可以通过左右车轮的不同转速反转，实现类似履带式车辆的差动转向，大大减小车辆的转弯半径，在特殊情况下几乎可以实现原地转向，也就是常说的坦克转弯。在装载空间上，轮毂电机车辆也占有优势，前后都可以拥有宽大的行李箱。

With so many advantages, why are they so hard to see in reality? In addition to the power factor, cost is also a constraint on development. Since the brake system needs to be integrated into the wheel hub, the integration difficulty is higher than that of traditional motors. The heat dissipation of the brake system is also a very important part. Although the motor does not require too much air for heat dissipation, it will occupy most of the volume, making heat dissipation more difficult and posing a safety hazard to braking.

Secondly, its lifespan is also longer than that of traditional motors placed in the middle of the vehicle. The motors in the cabin will have multiple layers of protection and will not be exposed to wind and sun, and the stones and dust on the road will not affect the motors. Since the hub motors are exposed to the outside, they have a short lifespan and often require repairs and maintenance. These are problems that need to be solved urgently for hub motors.

Car Selection Detective’s opinion: In daily life, it is difficult for us to see mass-produced cars equipped with hub motors. But with the development of electric vehicles, I believe that such electric vehicles will appear in the near future. However, due to their obvious shortcomings, although there are new breakthroughs in control, maintenance is the biggest problem. Therefore, we do not recommend choosing this type of model.