Compared with traditional motors, why are advanced in-wheel motor electric vehicles not equipped on a large scale?

With the expansion of the new energy vehicle market, more and more automobile manufacturers are engaged in motor research and development. At present, the most mainstream motors are placed on the front internal combustion engine or rear axle of traditional cars, and the layout is the same as that of traditional cars. But in many concept electric vehicles, we will see the word hub motor, which is installed on the hub and directly drives the wheels. As a new research direction, although many manufacturers have been committed to this, we still haven't seen large-scale equipment. So what's the difference between hub motor and traditional motor?

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

Take asynchronous hub motor as an example, it is mainly composed of stator, rotor and accessories. Stator core is generally made of silicon steel sheet with insulating layer, which is used to place stator winding. Stator windings are distributed at the same angle on the center of the circle, that is, they each form an angle of 120 degrees. The coils on the winding are wound according to certain rules, and the stator winding is electrified to generate a rotating magnetic field. At this time, the rotating magnetic field has relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor produces induced electromotive force and induced current, and the rotor conductor is acted by electromagnetic force in the magnetic field to form electromagnetic torque, which drives the rotor to rotate. Generally speaking, it is the process of converting electric energy of current into mechanical energy. I believe many people have played four-wheel drive when they were young. The motor driving the four-wheel drive 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, electric motors are actually simpler and easier to control.

In fact, the principle of hub motor is no different from that of traditional motor, but the structure is more complicated, that is to say, there are fewer coils and the magnetic field is not as strong as that of traditional motor, so the output power is relatively small. In addition, there are two kinds of hub motors: internal rotating motor and external rotating motor, in which the rotor of external rotating motor is located inside the stator, just like traditional motor. The rotor of the external rotating electric machine is located outside the stator and rotates around the stator. Hub motor integrates power device, transmission device and braking device into hub, so the mechanical part of electric vehicle is greatly simplified.

2. What are the advantages and disadvantages of hub motor compared with traditional motor?

As mentioned above, due to the limited hub diameter and tire width, the maximum volume of hub motor is not as good as that of traditional motor, and the output power is difficult to meet the standard. So at present, many in-wheel motors are only used on two-wheeled electric vehicles. Compared with traditional motors, in-wheel motors actually have many remarkable advantages. First of all, this design has no transmission loss, because there is no transmission rod from the engine to the wheel, so the efficiency is very high. In addition, the hub motor can reverse the rotation speed of the left and right wheels at different speeds, thus realizing differential steering similar to that of a tracked vehicle, greatly reducing the turning radius of the vehicle, and almost realizing in-situ steering under special circumstances, that is, tank steering. In terms of loading space, hub motor vehicles also have advantages, and they can have large suitcases in front and back.

There are too many advantages. Why is it difficult to see in reality that besides power, cost is also a part of restricting development? Because the hub needs to integrate the brake system, the integration is more difficult than the traditional motor, and the heat dissipation of the brake system is also a very important part. Although the motor does not need much air to dissipate heat, it will occupy most of the volume, making it more difficult to dissipate heat, and there are hidden dangers in braking safety.

Secondly, the service life is more expensive than the traditional motor placed in the middle of the vehicle. The motor in the machine room will have multiple protective layers, so there will be no wind and sun exposure, and the stone dust on the road will not affect the motor. Because the hub motor is exposed, its service life is short and it often needs maintenance. These are the problems that need to be solved urgently for in-wheel motors.

Detective's point of view: In our daily life, it is difficult to see mass-produced cars equipped with hub motors at present, but with the development of electric vehicles, I believe such electric vehicles will appear in the near future. However, due to obvious shortcomings, although there is a new breakthrough in handling, maintenance is the biggest problem, so it is not recommended to choose such a vehicle.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.