# A Systematic Review and Future Development of Automotive Classis Control Technology
## 4 Automotive Driving by Wire System
### Key Technologies  
(1) Efficiency improvement of permanent magnet synchronous motor  
To improve NVH performance, electric vehicle drive motors generally choose designs with multiple poles and high rotational speeds; Due to the higher rotational speed leading to higher iron loss, the loss control of ordinary silicon steel sheets in the high-frequency region is relatively weak. The loss can be reduced by reducing the thickness of silicon steel sheets [65; 66].  
The use of high-efficiency silicon steel sheets can reduce iron loss, but it is still necessary to optimize the copper loss of the motor at low speed and high torque. One method is to use a card-issuing motor. The scientific name of the card-issuing motor is Hairpin motor, which is a type of flat wire motor with winding ends similar to the card- issuing motor. The card-issuing motor has low copper consumption and high efficiency. Currently, Toyota, and Dianzhuang have adopted the card-issuing motor scheme [67].  
(2) Hub Motor Technology  
The hub motor drive system can be flexibly placed in the wheels of various electric vehicles, directly driving 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 [68].  
Hub motors are mainly divided into two types: outer rotor motors and inner rotor motors, with differences mainly reflected in the presence or absence of a reduction structure. The inner rotor hub motor and wheel edge motor converge in transmission structure, with the main difference being that the inner rotor motor is integrated with the hub, while the wheel edge motor is placed on the wheel edge [69]. The schematic diagram of the hub motor drive device is shown in Figure 4. Overall, the application of wheel hub motors has the advantages of high integration, flexible driving, and being in line with the development of intelligent vehicles and platform generalization applications [70].  
Figure 4: Schematic diagram of hub motor drive.  
Material and process innovations may break through the constraints of electromagnetic load on motor volume in hub motors. Further research and development of high-permeability, low-loss magnetic materials, low-resistivity conductive materials, high-thermal conductivity insulating materials, and low-density, high-strength structural materials can reduce motor losses and mass, improve heat transfer within the motor, and increase power/torque density in hub motors. Innovations in motor processing will achieve low-loss, lightweight, and high-cooling-efficiency designs in motors based on existing materials through different process structures. In the future, motor design will no longer be a simple electromagnetic or structural design, but a true multidisciplinary design that pushes the limits of motor performance.  
Motor controller Silicon carbide (SiC) is very suitable as a material for power semiconductors due to its strong bandgap, thermal conductivity, and insulation capabilities. It is easier to achieve low loss, high switching frequency, and high junction temperature compared to silicon (Si)-based devices, and the increase in temperature has little effect on switching loss [71]. Its good output characteristics are more suitable for traction conditions. Although the high cost is the main obstacle it faces, with the decrease in material prices and the improvement of production processes, SiC devices will reduce the cost of electronic control products in the dimensions of efficient operation, component savings, and chips [72; 73; 74; 75].