4WS System Research Articles

Strange nonchaotic attractors and bifurcation of a four-wheel-steering vehicle system with driver steering control

In this paper, a dynamical model is developed for the four-wheel-steering(4WS)vehicles, with nonlinear lateral tyre forces and quasi-periodic disturbances from the steering mechanism and quasi-periodic pavement external deformation. Initially, the stability and Hopf bifurcation of the 4WS vehicle system without disturbance are analyzed employing the central manifold theory and projection method. The effects of parameters on the stability and the types of Hopf bifurcation for the vehicle system are also discussed. It is shown that both Hopf bifurcation and degenerate Hopf bifurcation occur in the vehicle system. The critical speed decreases with increased driver’s perceptual time delay and distance from the vehicle’s center of gravity to the front axles, while it increases with the control strategy coefficient. However, the increase of the frontal visibility distance of the driver leads to an initial increase of the critical speed, decreasing afterwards. Subsequently, the strange nonchaotic dynamical behaviour of the disturbed 4WS system is investigated. Several routes and mechanisms for the birth of strange nonchaotic attractors (SNAs) are identified, including the torus doubling bifurcation, the torus fractalization, and the loss of transverse stability of a torus. Finally, the nonchaotic property is verified through the calculation of the maximum Lyapunov exponent, and the strange property is characterized using power spectra and rational approximation.

Study on Design and Fabrication of 4 Wheel Steering Mechanism

This study focuses on the design and fabrication of a four-wheeled steering (4WS) mechanism, a technology that enables all four wheels of a vehicle to turn, thus enhancing control and manoeuvrability. Four-wheel steering allows for significant improvement in a vehicle's turning circle at low speeds by enabling the rear wheels to turn in the opposite direction to the front wheels. At high speeds, this system contributes to increased stability and a reduced risk of over steer. Despite these advantages, 4WS systems are complex and expensive, which has limited their prevalence in the automotive market. The Honda Prelude, introduced in 1987, was the first car equipped with 4WS. However, the technology has not been widely adopted, largely due to driver unfamiliarity with the control dynamics at low speeds. This research aims to explore the potential benefits of 4WS and assess its future adoption prospects as technological advancements and cost reductions are realized. Through detailed analysis and experimental fabrication, this study seeks to contribute to the understanding and potential application of 4WS in modern vehicles.

Integrated control of path tracking and handling stability for autonomous ground vehicles with four-wheel steering

Accurate modelling of an autonomous ground vehicle (AGV) is challenging due to strong nonlinearity, model perturbations and external disturbances. This necessitates the design of path tracking controllers with robustness. In this paper, an integrated control strategy for path tracking and handling stability of AGVs is proposed, leveraging a four-wheel steering (4WS) system. To address the path tracking problem, a fuzzy logic-based steering strategy is developed, which enables parameter self-adjustment based on displacement error. Additionally, a reference model is employed to transform the path tracking problem into a reference signal tracking problem, ensuring the handling stability of vehicles. A sliding mode controller is designed to track the reference signal, utilizing an extended state observer to estimate and compensate for unmodeled dynamics and unknown external disturbances in real-time. Simulation results demonstrate the effectiveness of the proposed strategy in accurately tracking the desired path while maintaining the lateral stability of the vehicle. Furthermore, the strategy exhibits strong robustness against uncertainties and disturbances.

Research on automobile four-wheel steering control system based on yaw angular velocity and centroid cornering angle

In order to improve the handling stability of four-wheel steering (4WS) cars, a two-degree-of-freedom 4WS vehicle dynamics model is constructed here, and the motion differential equation of the system model is established. Based on the quadratic optimal control theory, the optimal control of 4WS system is proposed in this paper. When running at low speed and high speed, through yaw rate feedback control, state feedback control, and optimal control, the 4WS cars are controlled based on yaw rate and centroid cornering angle with MATLAB/Simulink simulation. The result indicates that 4WS control based on the optimal control can improve the displacement of the cars. And, the optimal control of 4WS proposed in this paper can eliminate centroid cornering angle completely compared with other two traditional optimal control methods. Besides, the optimal control enjoys faster response speed and no overshoot happens. In conclusion, the optimal control method proposed in the paper represents better stability, moving track and stability, thereby further enhancing the handling property of cars.

A novel IMC-FOF design for four wheel steering systems of distributed drive electric vehicles

To improve handling and stability for distributed drive electric vehicles (DDEV), the study on four wheel steering (4WS) systems can improve the vehicle driving performance through enhancing the tracking capability to desired vehicle state. Most previous controllers are either a large amount of calculation, or requires a lot of experimental data, these are relatively time-consuming and laborious. According to the front and rear wheel steering angle of DDEV can be distributed independently, a novel controller named internal model controller with fractional-order filter (IMC-FOF) for 4WS systems is proposed and studied in this paper. The IMC-FOF is designed using the internal model control theory and compared with IMC and PID controller. The influence of time constant and fractional-order parameters which is optimized using quantum genetic algorithms (QGA) on tracking ability of vehicle state are also analyzed. Using a production vehicle as an example, the simulation is performed combining Matlab/Simulink and CarSim. The comparison results indicated that the proposed controller presents performance to distribute the front and rear wheel steering angle for ensuring better tracking capability to desired vehicle state, meanwhile it possesses strong robustness.

Improving Handling Stability Performance of Four-Wheel Steering Vehicle Based on the H2/H∞ Robust Control

Considering the demand for vehicle stability control and the existence of uncertainties in the four-wheel steering (4WS) system, the mixed H2/H∞ robust control methodology of the 4WS system is proposed. Firstly, the linear 2DOF vehicle model, the nonlinear 8DOF vehicle model, the driver model, and the rear wheel electrohydraulic system model were constructed. Secondly, based on the yaw rate tracking strategy, the mixed H2/H∞ controller was designed with the optimized weighting functions to guarantee system performance, robustness, and the robust stability of the 4WS vehicle stability control system. The H∞ method was applied to minimize the effects of modeling uncertainties, sensor noise, and external disturbances on the system outputs, and the H2 method was used to ensure system performance. Finally, numerical simulations based on Matlab/Simulink and hardware-in-the-loop experiments were performed with the proposed control strategy to identify its performance. The simulation and experimental results indicate that the handling stability of the 4WS vehicle is improved by the H2/H∞ controller and that the 4WS system with the H2/H∞ controller has better handling stability and robustness than those of the H∞ controller and the proportional controller.

The effect of parallel steering of a four-wheel drive and four-wheel steer electric vehicle during spinning condition: a numerical simulation

X-by-wire technology is an advancement in automotive industry and is recognized by many countries in recent years. The in-wheel motor system is a type of drive-by-wire technology and it will be the main focused for the vehicle model in this paper. The steer-by-wire is a kind of by-wire technology in the automotive industry for the electric vehicle. [1] Steer-by-wire technology can be divided into two types which are two-wheel steering (2WS) and four-wheel steering (4WS). As we know, 2WS system is used in most of the vehicles.[2] However, the lower maneuverability will be shown in this type of vehicle during the vehicle spinning. The dynamic equation of motion was used for the simulation of vehicle movement.[3] The software of MATLAB Simulink was used to imitate that the effect of 4WD and 4WS EV during cornering.[4,5] The passive control was used in this simulation. As the result, the simulation indicated that 2WS EV is easy oversteered. After applied 4WS system, the vehicle oversteer problem was successfully solved by use parallel steering mode.

Yaw and Lateral Stability Control for Four-Wheel Steer-by-Wire System

A four-wheel steer-by-wire vehicle (FSV), which is a combination of a steer-by-wire (SBW) system and a four wheel steering (4WS) system, not only can improve vehicle safety and maneuverability, but also steering flexibility. Considering the parameters, uncertainties of vehicle speed, and tire cornering stiffness, weighted function is solved to express the uncertain system. Aiming at the multiple-input multiple-output (MIMO) system, the structured singular value $\mu $ is used to research FSV under multiple perturbations in this paper. Based on $\mu $ control strategy, $\mu $ controller is designed to track the desired sideslip angle and yaw rate. Thus, the vehicle gets better performance. Compared with SBW and 4WS systems, FSV has better state response under steering angle step input simulation experiment. The advantages of $\mu $ control compared with $H$ ∞ control on FSV have been explained in the simulation experiments. Furthermore, experiment results show that the designed controller can make the vehicle well track the reference model and improve the vehicle maneuverability.

LQR optimal control research for four-wheel steering forklift based-on state feedback

Taking the steering performance of four-wheel steering (4WS) forklift as the research object, based on two degrees of freedom (2DOF) model and three degree of freedom (3DOF) model of 4WS system, combined with the characteristics and steering requirements of forklift, the Linear Quadratic Regulator (LQR) optimization control algorithm based on state feedback is proposed, and the solution of LQR control algorithm for the 4WS forklift is presented. The simulation analyses of the steering performance of proportional control 4WS, LQR control 4WS and rear wheel steering (RWS) control are given. The simulation results show that the comprehensive effect of LQR optimal control is better, and it effectively improves the flexibility and the handling stability of 4WS forklift.

PROJECT ON ELECTRONIC STEERING SYSYTEM

As the four-wheel steering (4WS) system has great potentials, many researchers' attention was attracted to this technique and active research was made. As a result, passenger cars equipped with 4WS systems were put on the market a few years ago. This report tries to identify the essential elements of the 4WS technology in terms of vehicle dynamics and control techniques. Based on the findings of this investigation, the report gives a mechanism of electronically controlling the steering system depending on the variable pressure applied on it. This enhances the controlling and smoothens the operation of steering mechanism.

Stability Simulation of a Vehicle with Wheel Active Steering

This paper deals with the possibility of increasing the vehicle driving stability at a higher speed. One of the ways how to achieve higher stability is using the 4WS system. Mathematical description of vehicle general movement is a very complex task. For simulation, models which are aptly simplified are used. For the first approach, so-called single-truck vehicle model (often linear) is usually used. For the simulation, we have chosen to extend the model into a two-truck one, which includes the possibility to input more vehicle parameters. Considering the 4WS system, it is possible to use a number of potential regulations. In our simulation model, the regulation system with compound coupling was used. This type of regulation turns the rear wheels depending on the input parameters of the system (steering angle of the front wheels) and depending on the output moving quantities of the vehicle, most frequently the yaw rate. Criterion for compensation of lateral deflection centre of gravity angle is its zero value, or more precisely the zero value of its first-order derivative. Parameters and set-up of the simulation model were done in conjunction with the dSAPACE software. Reference performances of the vehicle simulation model were made through the defined manoeuvres. But the simulation results indicate that the rear-wheels steering can have a positive effect on the vehicle movement stability, especially when changing the driving direction at high speed.

OPTIMAL CONTROL STRATEGY FOR LOW SPEED AND HIGH SPEED FOUR-WHEEL-ACTIVE STEERING VEHICLE

In this work, based on the optimal control theory approach, a four-wheel-active steering (4WAS) system is proposed for low speed and high speed applications. A model following the control structure is adopted consisting of a feed-forward and feedback compensation strategy that serves as correction inputs to enhance the vehicle's dynamic behavior. The velocity dependent feed-forward control inputs are based on the driver's steering intention while the feedback control inputs are based on the vehicle's state feedback errors, being the sideslip and yaw rate of the vehicle. Numerical simulations are conducted using the Matlab/Simulink platform to evaluate the control system's performance. The performance of the 4WAS controller is tested in two designated open loop tests, being the constant steer and the lane change maneuver, to evaluate its effectiveness. A comparison with conventional passive front-wheel-steering (FWS) and conventional four-wheel-steering (4WS) systems shows the preeminent result performance of the proposed control strategy in terms of the response tracking capability and versatility of the controller to adapt to the system's speed environment. In high speed maneuvers, the improvement in terms of yaw rate tracking error in rms is evaluated and the proposed active steering system considerably beat the other two structures with 0.2% normalized error compared to the desired yaw rate response. Meanwhile, in low speed, turning radius reductions of 25% and 50% with respect to the capability of normal or typical FWS vehicles are successfully achieved.

Closed-loop design for decoupling control of a four-wheel steering vehicle

In this paper, a four–wheel–steering (4WS) system with multiple inputs is introduced. This multiple–input 4WS system provides the driver with the ability to control the sideslip motion and yaw motion of the vehicle simultaneously and independently. The decoupling control of these two independent motions is accomplished by a steering controller which translates the steering commands into the steer angles of the front and rear wheels. A method to find the inverse transfer matrix of the vehicle in a simple symbolic form is introduced to design the steering controller. By the design method introduced in this paper, the decoupling control of the sideslip and yaw motion can be achieved by three types of controllers for a stable vehicle plant without any signal fed back. The performance of the system under the variations of the vehicle parameters is also investigated via computer simulation.

Comparison of a vehicle equipped with Electronic Stability Control (ESC) to a vehicle with Four Wheel Steering (4WS)

Electronic Stability Control (ESC) and Four Wheel Steering (4WS) have been used to control the yaw rate and sideslip angle of automobiles, in order to improve stability and prevent accidents. The scope of this paper is to compare the behaviour of a vehicle equipped with no control systems, to a vehicle equipped with ESC, a vehicle equipped with 4WS and a vehicle equipped with a combination of ESC and 4WS in a series of simulated tests, using an adequate vehicle and driver model. The operating parameters of the control systems and the driver model have been optimised by using an evolution strategy. According to the results, the vehicle equipped with 4WS performed better in open-loop tests, while the vehicle equipped with ESC performed better in closed-loop tests where the vehicle is controlled by the driver model. The vehicle equipped with a combination of ESC and 4WS has achieved consistently better results in all our tests and has shown that the use of 4WS systems can augment the operation of ESC system and achieve a better safety level for future vehicles.

Control of four wheel steering using independent actuators

In four wheel steering (4WS) system the steering angles in each wheel must follow Ackermann steering geometry in order to eliminate the lateral slippage of the wheels. In agricultural vehicles, the steering actuators are typically hydraulic cylinders. In pure four wheel steering with two degrees of freedom and without additional constraints, a straight forward way is to install one actuator with a position sensor per wheel to realize Ackermann principle. In agricultural robot studies four wheel steering is a common kinematic structure. In this paper, modeling and control of steering in a 4WS remote controlled tractor is studied. The tractor is equipped with four asymmetric cylinders that steer each wheel, without any additional mechanical rods. The hydraulic system consists of one variable displacement pump and four proportional directional valves with load sensing function. The system model is split into subsystems and the overall model contains both dead-time delay, first order dynamics, static nonlinearities, temperature dependency and combined saturation. Besides modeling and analysis, the paper presents a control design that compensates nonlinearities but also takes care of saturation while compensating the dynamics. The objective in control is synchronous motion in the position control of the steering angles of all wheels. The results show controller performance in single wheel motion without saturation and overall controller performance under saturated pump flow.

능동전륜조향장치를 채택한 사륜조향차량의 횡방향 안정성 강화에 대한 연구

This study is to propose and develop an integrated dynamics control system to improve and enhance the lateral stability and handling performance. To achieve this target, we integrate an AFS and a 4WS systems with a fuzzy logic controller. The IDCS determines active additional steering angle of front wheel and controls the steering angle of rear wheel. The results show that the IDCS improves the lateral stability and controllability on dry asphalt and snow paved road when double lane change and step steering inputs are applied. Yaw rate of the IDCS vehicle tracks reference yaw rate very well and body slip angle is reduced about by 50%. Response time of the IDCS vehicle is also decreased.

Comparison of lateral rear force between two and four wheel steering in a vehicle with steer by wire system

One kind of steering systems in vehicles is Steering by Wire (SBW). Control and stability of this method are important issues. In fact the SBW system is very suitable for Four Wheel Steering systems. In this paper the SBW used for Four Wheel Steering system to take result. The effect of 4ws on turning is shown. When a 4ws system turns at low speed, the rear Wheels steer in the opposite direction as the front wheels, so that the maneuverability and parking of the system increases. At higher speed the rear wheels steer in the same direction as the front wheels, so that more stability and less lateral rear force are resulted. In this paper, a bicycle model is used for dynamic modeling for testing the stability and controllability. This model is built with the assumption theorem. Steer by wire is used for steering the rear and front wheels. The lateral rear force is estimated with a Hall Effect sensor.

Comparing rear wheel steering and rear active differential approaches to vehicle yaw control

A comparison between two different approaches to vehicle stability control is carried out, employing a robust non-parametric technique in the controller design. In particular, an enhanced internal model control strategy, together with a feedforward action and a suitably generated reference map, is employed for the control of a vehicle equipped either with a rear wheel steering (RWS) system or with a rear active differential (RAD) device. The uncertainty arising from the wide range of operating conditions is described by an additive model set employed in the controller design. Extensive steady state and transient tests simulated with an accurate 14 degrees of freedom nonlinear model of the considered vehicle show that both systems are able to improve handling and safety in normal driving conditions. RAD devices can make the vehicle reach higher lateral acceleration values but they achieve only slight stability improvements against oversteer. On the other hand, 4WS systems can greatly improve both vehicle safety and manoeuvrability in all driving situations, making this device an interesting and powerful stability system.

Mathematical Theory of Autodriver for Autonomous Vehicles

Introducing an independent four-wheel-steering (4WS) system, we are able to design an autodriver to keep an autonomous vehicle on a given road. The kinematic condition of steering can be used to set the steer angles such that the kinematic center of rotation be at any desired point. The road and tire characteristics, along with the dynamics of a moving vehicle cause the vehicle to turn about an actual point that is not necessarily at the road curvature center. The position of the dynamic turning center can be controlled by adjusting the steer angles such that it coincides with the road curvature center. Such a vehicle will move on the desired road autonomously.

Hybrid state-feedback sliding-mode controller using fuzzy logic for four-wheel-steering vehicles

This paper presents a fuzzy controller for high-speed four-wheel-steering (4WS) vehicles based on the state-feedback and the sliding-mode control methods. In the proposed fuzzy controller, the consequent part of the fuzzy IF-THEN rules consists of either a sliding-mode controller or a state-feedback controller. Also, it will be proved that, if every fuzzy rule is stable in the sense of Lyapunov for a general Lyapunov function, defined for the whole system, then the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed method for handling improvement of the 4WS systems will be demonstrated by simulations using a nonlinear vehicle model. The simulation results show that the proposed control method can enhance the dynamic response of the 4WS vehicles by reducing the transient response time and improving vehicle stability as compared to the sliding-mode and the fuzzy sliding-mode control methods.