Shortcomings of hub motors
1: Increase the unsprung mass and the moment of inertia of the hub, which has an impact on the handling of the vehicle.
For a car, we can divide it into two parts: unsprung mass and sprung mass. If the unsprung mass is defined next, it refers to the mass that is not supported by the elastic elements in the suspension system, generally including wheels, springs, shock absorbers and other related components, and the sprung mass is naturally the rest of the vehicle. Quality, generally including the frame, power system, transmission, occupants, etc. Increasing the unsprung mass is extremely detrimental to comfort and handling.
For ordinary civilian vehicles, some relatively lightweight materials such as aluminum alloys are often used to make the suspended components to reduce the unsprung mass and improve the response speed of the suspension. However, the hub motor just increases the unsprung mass to a large extent, and also increases the moment of inertia of the hub, which is detrimental to the handling performance of the vehicle. However, considering that electric vehicles are mostly limited to travel rather than pursuing power performance, this is not the biggest flaw.
2: The electric braking performance is limited, and it takes a lot of electric energy to maintain the braking system.
The built-in retarder of the commercial vehicle axle adopts the principle of eddy current braking, and the braking of the hub motor can also utilize this principle.
The second point is about the impact of braking. Traditional cars are equipped with brake discs and brake calipers, but the hub motors need to use electric brakes. Simple capacity recovery is definitely not enough, and more braking is needed. There will also be power loss.
Many of today's conventional power commercial vehicles have been equipped with auxiliary reduction gears that utilize the principle of eddy current braking (ie, resistance braking), such as electric retarders used in many trucks. Due to the relationship between energy and electric vehicles, electric braking is also the first choice. However, for the vehicle driven by the hub motor, because the electric braking capacity of the hub motor system is small and cannot meet the requirements of the braking performance of the whole vehicle, additional mechanical system is required. Dynamic system, but for ordinary electric passenger cars, without the vacuum pump driven by the traditional internal combustion engine, electric vacuum pump is needed to provide brake boost, but it means more energy consumption, even if regenerative braking can recover some energy, If the effectiveness of the braking system is to be ensured, the energy consumed by the braking system is also one of the important factors affecting the cruising range of the electric vehicle.
In addition, the working environment of the hub motor is harsh, facing many influences such as water and dust, and also has high requirements in terms of sealing. In addition, how to implement the electric braking scheme and how to dissipate heat are some problems.
to sum up
Compared with the centralized power drive of the motor, the hub motor technology has great advantages. It has a more flexible layout, does not require a complicated mechanical transmission system, and has its own significant disadvantages, such as the balance between the seal and the starting current/torque. As well as the differential speed of the drive wheels during steering, etc., if the problems can be solved in engineering, the hub motor drive technology will have broad prospects in the future of new energy vehicles.
