Steer-by-wire Research Articles

Fault-Tolerant Control for Intelligent Electrified Vehicles Against Front Wheel Steering Angle Sensor Faults During Trajectory Tracking

Steer-by-Wire (SBW) systems are an integral and essential component of intelligent electrified vehicles and are critical to ensure safe vehicle operations. In this paper, a fault-tolerant control method for SBW is proposed to mitigate the adverse influence of front wheel steering angle sensor faults based on the Kalman filtering technique. First, a linearized vehicle model is derived based on tire characteristics and is further combined with a steering actuator model to provide the modelling foundation for estimating the front wheel steering angle. Considering multi-source noises and their significant influence on the front wheel steering angle sensor, the Butterworth filter is employed to filter out the high-frequency noises. The front wheel steering angle estimation is realized by incorporating the measurements of the yaw rate and lateral acceleration of vehicle and the current of steering motor. In particular, a dynamic threshold mechanism is adopted to activate the fault diagnosis and fault-tolerant compensation based on the residual theory. Finally, a linear time-varying model predictive controller is presented to execute the trajectory tracking task for an intelligent electrified vehicle. The effectiveness of the proposed scheme is verified under the single lane change and double lane change maneuvers during the trajectory tracking.

Coordinated control of steer‐by‐wire and brake‐by‐wire for autonomous emergency braking on split‐μ roads

Autonomous emergency braking (AEB) is an active safety technology which aims to prevent collisions by operating harsh braking. When AEB is activated on split-μ roads, the yaw moment generated by the asymmetric braking forces will lead to losing control of the vehicle. In this study, a coordinated control scheme of steer-by-wire (SBW) and brake-by-wire (BBW) is developed to solve this problem. An anti-lock braking system is achieved by a sliding mode controller. Besides, two model predictive controllers based on a 7-degree-of-freedom vehicle dynamics model are proposed for different road adhesion conditions. According to the simulation results, the proposed scheme can maintain the stability of the vehicle and achieve a satisfying braking efficiency under various friction differences between the two-side wheels. At last, the experiments are also carried out to verify the effectiveness and the real-time performance of the proposed scheme on a hardware-in-loop bench of BBW and SBW.

Super-twisting algorithm with fast super-twisting disturbance observer for steer-by-wire vehicles

The control performance of a vehicle steer-by-wire (SBW) system can be seriously affected by vagaries of tyre-road conditions and external disturbance. Aiming at the problem of fast estimating and compensating the time-varying disturbance torque acting on the front wheels under different working conditions, this article presents a super-twisting algorithm (STA) combined with fast super-twisting disturbance observer (FSTDO) control scheme. At first the SBW system is modelled according to the experiment plant. Secondly, the FSTDO is designed according to SBW system model. A fast reaching law is adopted to accelerate the sliding variable convergence rate and enhance the response speed of the observer. The FSTDO-STA controller adopts STA control in closed-loop system. The control signal is continuous, so that, the chattering could be inhibited. The stability of FSTDO error dynamics and closed-loop dynamics is proved in the sense of Lyapunov. Finally, comparative verification experiments are carried out to demonstrate the validity of FSTDO-STA. The FSTDO-STA controller can quickly estimate and compensate disturbance torque under various operating conditions. Compared with other comparative algorithms, the proposed controller has some advantages in response speed, control accuracy and robustness. And it was corroborated by the experimental results.

Active Front Steering-Based Electronic Stability Control for Steer-by-Wire Vehicles via Terminal Sliding Mode and Extreme Learning Machine

In this article, a novel active front steering (AFS) control strategy including the upper controller and the lower controller is proposed to improve the yaw stability and maneuverability for steer-by-wire (SbW) vehicles. The adaptive recursive integral terminal sliding mode (ARITSM) control is adopted in the upper controller for guaranteeing the convergence performance of both the actual sideslip angle and the yaw rate with strong robustness and fast convergence rate. Then, a fast nonsingular terminal sliding mode (FNTSM) control with extreme learning machine (ELM) estimator to estimate its equivalent control is designed in the lower controller to track the desired front wheel steering angle calculated from the upper controller for driving the sideslip angle and the yaw rate to converge ideal value. It is shown that the upper controller takes two controlled variables (vehicle sideslip angle and yaw rate) and only one control input (front steering angle) into consideration, which can obtain a better performance compared with the case of using only one of these values. Since using the ELM technique in the lower controller to estimate the equivalent control of the FNTSM, not only the dependence of SbW system dynamics can be alleviated in the process of designing controller but also the excellent steering control performance can be achieved. Comparative simulations are carried out by utilizing Carsim and Matlab software to validate the excellent performance of the proposed control strategy for different steering maneuvers.

The Control Strategy Research of 4WID Vehicles Steering-by-Wire System

Once the traditional electric vehicle was refitted with distributed drive (4wid) system, the increasing of vehicle’s unsprung mass would significantly increase the steering resistance, as a result of that, the efficiency and accuracy of the original car’s steer-by-wire (SBW) system will be reduced. In order to solve this problem, taking BAIC-EV150 for example, this paper introduced a design of SBW control strategy for 4WID vehicles, and the corresponding refitting work of real vehicle were completed. The refitted vehicle adopted dual-motor, dual-controller to coordinate control the output torque, aiming at compensating the resistance moment. Simulation and experimental results show that the controller can meet the requirements of 4WID vehicle steering, and the dual-motor steering system based on fuzzy PID control is more responsive and more accurate than the single-motor steering system which under ordinary PID control.

Adaptive Sliding Mode-Based Lateral Stability Control of Steer-by-Wire Vehicles With Experimental Validations

In this paper, a robust adaptive sliding mode (ASM) controller for improving vehicle maneuverability and lateral stability of steer-by-wire (SBW) vehicles. The proposed stability control algorithm is composed of the following three remarkable characteristics: 1) As the vehicle sideslip angle which is very useful in vehicle stability control is often unavailable or unmeasurable for practical applications, a sliding mode-based state observer is proposed to online estimate the actual sideslip angle via the yaw rate and the lateral acceleration measurements. 2) ASM lateral stability controller, as an upper level controller, is designed to calculate the corrected steering angle for driving both the yaw rate and the sideslip angle to achieve their desired values in the presence of modelling uncertainties and external disturbances. Moreover, an adaptive law is incorporated in the control law to estimate the switching gain such that the complex uncertainty bound information can be avoided. 3) The desired steering angle is realized by a lower steering controller via ASM for an SBW system. The hardware-in-the-loop simulation results demonstrate the excellent stability control performance of the proposed control for different steering maneuvers.

Fault-tolerant control of steer-by-wire systems under voltage and current sensors faults

Steer-by-wire (SBW) systems benefit from several advantages including lower weight, volume, and cost compared to counterpart electric power steering systems. However, system reliability is impacted since SBW performance is highly dependent on correct operation of several voltage, current, speed, yaw rate, and position sensors. This paper presents a new method in SBW system reliability improvement by introducing a novel fault detection, isolation, and reconstruction (FDIR) control technique. The proposed FDIR method detects if any fault is observed on voltage or current sensors and identifies the faulty sensor location. Additionally the identified faulty sensor’s output is replaced with an estimated value to allow system continuous fault-ride through operation. The SBW system equipped with proposed FDIR technique provides fault-tolerance property against up to 3 faulty voltage or current sensors. Therefore, enhanced overall reliability is obtained at no further hardware costs associated with additional sensors redundancy solutions. The proposed technique is studied using system modelling and hardware prototyping, and its effectiveness is demonstrated using simulation and experimental results.

Energy optimization strategy of vehicle DCS system based on APSO algorithm

In order to improve the reliability and safety of the steer-by-wire (SBW) system, this paper presents a vehicle dual-motor coupling-drive steer-by-wire (DCS) system. However, the introduction of dual-motor will change the energy consumption of the system. Aiming at the energy consumption problem, an energy optimization strategy is proposed to improve the economic performance of the DCS system. Then, the energy optimization model of the DCS system with minimum power consumption is established based on the required torque, the rotating speed of steering wheel and the map of motor efficiency, and the adaptive particle swarm optimization (APSO) algorithm is adopted to optimize the torque distribution coefficient. Finally, combined with Matlab/Simulink, Prescan, Carsim and steering data acquisition test bench, the co-simulation is conducted under sinusoidal condition, double-lane change condition and intelligent transportation environment. The results indicate that compared with traditional single-motor SBW system and DCS system with average torque distribution, the energy consumption of the DCS system with optimized torque distribution is reduced by more than 5.2% and 4.3% under sinusoidal condition and double-lane change condition, while the corresponding values under the intelligent transportation environment are decreased by 5.2% and 7.5% respectively, which demonstrates the effectiveness of the proposed energy optimization strategy.

Robust adaptive integral terminal sliding mode control for steer-by-wire systems based on extreme learning machine

In this paper, a novel extreme-learning-machine (ELM)-based robust adaptive integral terminal sliding mode (AITSM) control strategy is developed for the precise tracking control of a steer-by-wire (SBW) system with uncertain dynamics. The proposed control not only ensures the finite-time error convergence but also effectively estimates the lumped uncertainty via a single-hidden layer feedforward network (SLFN) with ELM. Different from conventional ELM using least square optimization approach, the ELM in this work is designed to adaptively estimate the lumped uncertainty from the perspective of global stability of the closed-loop system. The stability of the closed-loop control system is proved in Lyapunov sense. Simulations are carried out to demonstrate the superior control performance of the proposed control.

Design and Analysis of Secure and Dependable Automotive CPS: A Steer-by-Wire Case Study

The next generation of automobiles (also known as cybercars) will increasingly incorporate electronic control units (ECUs) in novel automotive control applications. Recent work has demonstrated the vulnerability of modern car control systems to security attacks that directly impacts the cybercar's physical safety and dependability. In this paper, we provide an integrated approach for the design of secure and dependable automotive cyber-physical systems (CPS) using a case study: a steer-by-wire (SBW) application over controller area network (CAN). The challenge is to embed both security and dependability over CAN while ensuring that the real-time constraints of the automotive CPS are not violated. Our approach enables early design feasibility analysis of automotive CPS by embedding essential security primitives (i.e., confidentiality, integrity, and authentication) over CAN subject to the real-time constraints imposed by the desired quality of service and behavioral reliability. Our method leverages multicore ECUs for providing fault tolerance by redundant multi-threading (RMT) and also further enhances RMT for quick error detection and correction. We quantify the error resilience of our approach and evaluate the interplay of performance, fault tolerance, security, and scalability for our SBW case study.

Recent Developments in the Vehicle Steer-by-Wire System

The next generation of steering systems in the auto manufacturing industry would be steer-by-wire (SBW) in which the mechanical connection between vehicle steering wheel and tires is removed. Numerous advantages are envisaged for this modification, but there are still some under-research technical and safety-related challenges to be addressed. This article presents a thorough review on the history of vehicle steering systems first. The structure and components of the cutting edge technology SBW system are subsequently described with the advantages and disadvantages discussed in detail. The main challenges of this system, including the required motor drives equipped with advanced controllers and reliability concerns, are studied and proposed solutions presented in the literate are reviewed. Finally, a projection of the future of steering systems considering driverless vehicles with integrated steering and traction systems is briefly presented.

Control Strategy of the Vehicle's Active Steer by Wire

Zhang, Q.; Lin, W.; Wang, Y.; Wu, X., and Luo, Y., 2020. Control strategy of the vehicle's active steer by wire. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 355–360. Coconut Creek (Florida), ISSN 0749-0208.The Steer-By-Wire (SBW) system is free from the constraints of mechanical structure. Whether the system can work normally depends on the correctness of the control strategy. Therefore, this paper will study the control strategy of active steering by wire, which includes the design of ideal variable angle ratio control and active front wheel steering controller. Feed-forward control of ideal variable angle transmission ratio was determined based on constant yaw angular velocity gain. The sliding mode variable structure control theory is adopted. Based on the yaw rate deviation, the integral sliding surface is constructed, and the control strategy of equivalent and switching control is designed and active front wheel steering controller is completed. Through feedback control, the active control of the vehicle's front wheel angle is achieved, which improves the stability of the vehicle. Finally, through the typical test conditions, the designed control strategy was simulated and verified, and compared with the simulation results of uncontrolled vehicles. The results showed that the sliding mode controller of active SBW front wheel designed by yaw angular velocity feedback under the ideal variable transmission ratio can run stably under any working conditions and achieve good track following ability.

Synchronization and stability control of dual-motor intelligent steer-by-wire vehicle

In order to improve the safety of steer-by-wire (SBW) system, a dual-motor SBW system is proposed to enhance the fault tolerance and reliability of the system. However, the dual-motor SBW vehicle often loses its stability due to the external interference, and the asynchronous response between the dual-motor will further deteriorate the stability of the vehicle. Aiming at the existing problems, this paper proposes a hierarchical control strategy, in which the upper layer controls the vehicle stability and the lower layer controls the synchronization of the dual-motor. Firstly, the models of dual-motor SBW system and the vehicle are established. Secondly, considering the interference of lateral wind, sensor noise and the limitation of control output, a yaw rate controller is designed in the upper layer based on the mixed H2/H∞ robust control theory to improve the stability and tracking performance of the vehicle. Thirdly, a sliding mode speed synchronization control strategy is proposed in the lower layer based on the cross-coupling control structure and the sliding mode control algorithm to enhance the synchronization performance between the dual-motor. Finally, the simulation is carried out by using Carsim/Simulink and the hardware-in-the-loop experiment is conducted based on the dual-motor SBW experimental station. The simulation and experimental results verify the effectiveness of the control strategy proposed in this paper.

Actuator fault tolerant control for steer-by-wire systems

Automotive steer-by-wire (SbW) system is a safety-critical system where the safety and reliability issues must be addressed during the operation. This paper proposes a fault detection and isolation-based actuator fault tolerant control for SbW system based on model predictive control. The fault detection and isolation module uses a two-stage Kalman filtering algorithm to provide simultaneous control parameter and state estimation to detect the occurrence of actuator failure. Additionally, a model predictive controller is designed to maintain the original functionality of the SbW systems using the output of fault detection and isolation to update the fault information. We evaluate the performance of the proposed approach by numerical simulations and experiments on our SbW platform. The simulation and experimental results illustrate that our approach achieves a better steering performance than a conventional model predictive controller without fault detection and isolation and stabilise the overall SbW system in occurrence of actuator failure.

Robust Observer Based Intermittent Forces Estimation for Driver Intervention Identification

On the way to fully automated driving, Level 3 automated driving systems (ADS) seem to be a more realistic choice in the short term. Within operational design domain (ODD), although the driver is not required to monitor the vehicle all the time, it is expected that the driver is ready to intervene in the ADS whenever certain risks are encountered. Hence, timely identification of driver intervention in the vehicle lays the foundation for safe switching from the ADS to the driver. Although many researches have been conducted on driver torque estimation in the last decade, most of them are based on electric power steering (EPS) systems, therefore are not quite suitable for application in steer-by-wire (SBW) systems, which shall be the next generation's steering systems. In view of this, the SBW system parameters with uncertainties are first identified through experiments. Then, a PID controller and a robust observer considering Coulomb friction are designed and analyzed for the SBW systems, so that the system is asymptotically stable and the driver torque can be identified irrespective of parameter uncertainties and system noises. Detailed experimental results on a hardware-in-the-loop test bench verify the effectiveness of the proposed method, which shall also be implementable in a real vehicle.

Architectural design and analysis of a steer-by-wire system in view of functional safety concept

In the context of intelligent and automated vehicles, drive-by-wire (DBW) systems have aroused wide attention, both in academia and industries. Over the years, a lot of discussion has been made about the architectural design of brake-by-wire (BBW) systems. However, the architectural design of the steer-by-wire (SBW) system hasn’t been emphasized enough, especially in the context of functional safety concept. In view of this, based on the newly released version of ISO 26262:2018 as well as the technical report from National Highway Traffic Safety Administration (NHTSA), a fail-operational architecture for the SBW system is proposed in this paper, following the detailed analysis results of the concept phase as suggested in ISO 26262:2018. Further utilizing state transition diagrams and quantitative fault-tree-analysis (FTA) analysis respectively, detailed qualitative as well well as quantitative analysis results are provided, proving the safety and reliability of the proposed architecture. The aim is to provide guidance as well as some references for the SBW system design and analysis, where the essential problem is safety and reliability of the system, so that safety and reliability of automated vehicles can be guaranteed.

An energy-saving strategy for steering-motors of steer-by-wire vehicles

In a steering process, the steering-motor of a steer-by-wire (SBW) vehicle consumes energy. To facilitate energy efficiency analyses, the steeringmotor energy consumption is split into two parts, which correspond to varied and constant steering-wheel angle operating condition, respectively. The former condition is a vehicle operational manoeuvre, in which steering-wheel angle varies continuously, whereas the latter is a constant-radius circular-curve negotiation, in which steering-wheel angle maintains constant. Analysing the relation of steering-wheel angle with a road curvature, we propose an energysaving strategy for steering-motors of SBW vehicles. The energy-saving strategy is featured with a concept, a hydro-mechanical locking device, and an SBW controller for the steering-motor unit. The feasibility and effectiveness of the energy-saving strategy is demonstrated using closed-loop simulations. To implement the closed-loop simulation, we combine the driver, vehicle, and curved road models generated in CarSim software with the steering-motor model and the SBW controller developed in Matlab/Simulink.

Adaptive Sliding Mode Control of Rack Position Tracking System for Steer-by-Wire Vehicles

This paper describes adaptive sliding mode control of a steer-by-wire (SBW) system to guarantee rack position tracking performance in various driving situations. The proposed control algorithm was developed using only motor position sensors (MPS) without information on tire/road friction. A stiffness parameter adaptation law was designed to compensate for disturbances in the SBW rack system. It is demonstrated that the proposed adaptation algorithm provides good tracking performance without using an additional gain tuning approach under various road conditions. Moreover, in the proposed algorithm, a dynamic stiffness model has been developed to improve rack position tracking performance under a zero vehicle speed scenario. In a dynamic stiffness model, the stiffness center is not fixed but changes depending on the actual rack position. In the event than an SBW vehicle is parking, it is important to ensure rack position tracking performance at low and zero vehicle speeds. Computer simulations and vehicle tests were performed under various driving situations to test the performance of the proposed control algorithm. The results demonstrate that the proposed control algorithm ensures tracking performance on dry asphalt and wet road conditions, as well as at zero vehicle speed.

Research on synchronous control strategy of steer-by-wire system with dual steering actuator motors

Steer-by-wire (SBW) system with dual steering actuator motors is a novel and potential type of steering system by means of hardware fault tolerant redundancy to enhance the driving safety. The basic control strategy "road feel feedback and steering angle control" has been carried out. Aiming at the non-synchronous appearance of dual steering actuator motors, dual-motor synchronous control employing differential negative feedback method has been proposed to reduce the adverse influence of "servo fight" non-synchronous issue. In addition, considering the existence of unavoidable backlash impact, dual-motor anti-backlash control adopting variable bias compensation current method has been developed to abate the negative effect caused by backlash factors for SBW system, so that the precision of steering implementation for SBW system can be enhanced. The results of simulations and hardware-in-loop experiments are analysed and then the conclusion has been drawn that the proposed control strategy is effective and feasible.

Four-Wheel Differential Steering Control of IWM Driven EVs

This paper aims to realize the four-wheel differential steering function of an in-wheel motor (IWM) driven electric vehicle (EV) with a steer-by-wire (SBW) system. The dynamic models of four-wheel differential steering vehicle (4WDSV) and four-wheel steering vehicle (4WSV) are established, and a front-wheel steering vehicle (2WSV) with the neutral steering characteristics and a drop filter of the sideslip angle is employed as the reference model to provide the ideal yaw rate and sideslip angle. According to the reference model, the decoupling and fractional PI λ D μ controllers are designed for the 4WSV to obtain the standard inputs, i.e., the front and rear wheel steering angles, which is finally drawn as the MAP. Furthermore, the sliding mode controller (SMC) and torque distributor are designed to control the 4WDSV to have the same yaw rate as the 4WSV, whose inputs are consulted from the MAP drawn in advance according to the vehicle speed. The simulation results of several vehicle models with/without the controller of two working conditions (reverse and in phase steering) are presented, which indicates that the proposed decoupling and fractional PI λ D μ controller for the 4WSV is effective to obtain its standard inputs, and the proposed SMC and torque distributor for the 4WDSV ensure that it has the same yaw rate as the 4WSV, as well as the good robustness.