# A Systematic Review and Future Development of Automotive Classis Control Technology
## 2 Automotive Steering-By-Wire System
### Key Technologies  
(1) Fault tolerance  
The probability of faults such as open circuit of switch tubes, abnormal rotary transformer signals, and abnormal temperature sensors in the motor is high, which also has a significant impact on the system. Short circuits, open circuits, and mechanical faults in sensors have a significant impact on the system, but their occurrence frequency is not high [20; 21; 22]. Poor contact of connectors in the communication bus has a significant impact on the system and a high probability of occurrence [23].  
Figure 2: Schematic diagram of steering by wire.  
Current fault-tolerant methods can be divided into two categories from a technical perspective: one is based on hardware backup redundancy technology, and the other is based on software fault-tolerant algorithm technology. The hardware redundancy method mainly improves the fault tolerance performance of the system by providing backup for important components and vulnerable components; The software redundancy method mainly relies on the fault-tolerant algorithm of the controller to improve the redundancy of the entire system, thereby improving the fault-tolerant performance of the system [24; 25].  
Hardware backup technology and software fault-tolerant technology are highly complementary; Hardware backup technology can enhance the reliability of fault-tolerant control technology at the hardware level; Software fault-tolerant technology can reduce the space and volume requirements of the steering system caused by hardware redundancy. The future wire-controlled steering system will be a highly intelligent system with both hardware backup and fault tolerance algorithms [26; 27; 28].  
(2) Road feeling feedback  
Due to the SBW system's inability to provide the driver with inherent steering feel, there is a risk of misoperation by the driver resulting in traffic accidents. Therefore, road feeling simulation technology is required to provide the driver with feedback information from the road surface. By obtaining feedback information about the road and steering wheel through the hand feel on the steering wheel, the driver can help complete driving tasks such as turning and lane changing. The resistance torque that the driver needs to overcome when turning the steering wheel mainly includes two aspects, namely, return torque and Friction torque, while the road sense feedback torque includes return torque and Friction torque. To enable the driver to experience a realistic road feel, the essence is to control the data and information from lower-level motors and sensors through upper-level road feel motors using appropriate strategies, simulating and transferring them to the steering wheel to provide the driver with feedback torque from the road surface and steering wheel realignment torque. The methods for obtaining feedback torque of road feel include parameter fitting, sensor measurement, and dynamic model-based methods, with the third being the mainstream of current research [29; 30]. Return torque control technology is an evaluation criterion for the quality of SBW systems and the basis for active steering research. The core issue in this research is how to improve the return torque to achieve the same effect as the power steering system.  
Based on the dynamic model method, according to the vehicle dynamic response, driver steering wheel, input and other states, the vehicle dynamics model is used to estimate the tire return torque and the feedback torque to be compensated, and then calculate the expected feedback torque command [31].  
The wire-controlled steering system has the advantages of improving handling stability, improving comfort, energy conservation, and environmental protection, improving passive safety, and facilitating vehicle lightweight. However, the safety and reliability of the wire-controlled steering system have always been the core obstacles hindering its implementation.