Active Front Steering System Research Articles

Research on the Control Strategy of Active Front Steering System

Research on the Control Strategy of Active Front Steering System

Research on Yaw Stability Control of Active Front Steering Based on BP Neural Network PID

This paper proposes using BP neural network PID to improve the yaw stability of the vehicle with active front steering system. A dynamic model of vehicle with active front steering is built firstly, and then the BP neural network PID controller is designed in detail. The controller generates the suitable steering angle so that the vehicle follows the target value of the yaw rate. The simulation at different conditions is carried out based on the fore established model. The simulation results show the BP neural network PID controller can improve the vehicles yaw stability effectively.

H∞ control of novel active steering integrated with electric power steering function

Based on the traditional active steering system, a novel active steering system integrated with electric power steering function was introduced, which can achieve the functions of both active steering and electric power steering. In view of the interference from road random signal and sensor noise in the novel active steering system, the H∞ control model of the novel active steering system was built. With satisfying steering feel, good robust performance and steering stability being the control objectives, the H∞ controller for the novel active front steering (AFS) system was designed. The simulation results show that the novel AFS system with H∞ control strategy can attenuate the road interference quickly, and there is no resonance peak in the bode diagram. It can make the driver obtain more useful information in the low frequency range, and attenuate the road interference better in the high frequency range, thus the driver can get more satisfying road feeling. Therefore, the designed H∞ controller can synthesize the advantages of both robust performance and robust stability, and has certain contribution to the design of novel AFS system.

Study on the performance of active front steering system

The performance of a steering system equipped with active front steering (AFS) device is investigated with the consideration of AFS intervention and a proposed dynamic model. Firstly, the kinematics and dynamics of AFS are illustrated based on the mechanism of AFS with planetary gear set and a detailed dynamic model. Furthermore, a basic control on the voltage of DC motor at AFS actuator is proposed. It is realized by a proportional controller that the input is the difference of desired steering ratio and a conventional gear ratio. Finally, two numerical simulations are carried out. One is on-center handling test to demonstrate the basic characteristics of AFS. The other simulation is to demonstrate the effects of vehicle speed, frequency of steering input and AFS intervention on steering system performance. It is shown that the proposed AFS dynamic model is capable to simulate dynamic performance of AFS. The effect of AFS intervention on turning efforts at hand steering wheel is inevitable and the turning comfort is deteriorated to some extent.

Study on Mechanism of Active Front Steering Based on Harmonic Drive

The steering ratio of vehicle can be changed by attaching a angle, Changing the steering gear ratio can improve the safety in high-speed and comfort in low-speed and the vehicle steering stability. The paper introduces an active front steering system (AFS) based on harmonic drive, the composition and working principle of the system are analyzed, and the kinematic analysis of the system is researched, finally, the self-control mechanism and integrated control mechanism with other stability system are studied.

능동전륜조향장치 및 능동후륜제동장치의 통합제어기 개발

An integrated dynamic control (IDCF) with an active front steering system and an active rear braking system is proposed and developed in this study. A fuzzy logic controller is applied to calculate the desired additional steering angle and desired slip of the rear inner wheel. To validate IDCF system, an eight degree of freedom, nonlinear vehicle model and a sliding mode wheel slip controller are also designed. Various road conditions are used to test the performance. The results show that the yaw rate of IDCF vehicle followed the reference yaw rate and reduced the body slip angle, compared with uncontrolled vehicle. Thus, the IDCF vehicle had enhanced lateral stability and controllability.

English

This paper includes the modeling and simulation of active front steering (AFS) system. AFS controls the front wheel steering angle to improve the steering feel and comfort. Driver and vehicle models are used for the simulation. AFS adjusts the yaw rate in critical driving maneuvers. The driver workload is reduced and the yaw rate response is diminished by AFS. Firstly, step function is applied to the vehicle. Secondly the vehicle is examined under side wind disturbance. Vehicle with AFS and standard vehicle are tested at higher velocity and normal velocity. The simulation results show that the vehicle with AFS is more stable and shows better performance than the standard one.   Key words: Active front steering, wind disturbance, driver safety.

Performance Enhancement of Road Vehicles Using Active Independent Front Steering (AIFS)

Technological developments in road vehicles over the last two decades have received considerable attention towards pushing the safe performance limits to their ultimate levels. Towards this goal, Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) systems have been widely investigated. AFS systems introduce corrective steering angles to conventional system in order to realize target handling response for a given speed and steering input. It is thus expected that such an action under severe maneuvers may cause one tire to reach saturation while the other tire may be capable of developing more force. This study, therefore, proposes an Active Independent Front Steering (AIFS) system capable of controlling a wheel independently. At low speeds, the proposed AIFS system will modify the steer angle with speeds while maintaining pro-ackerman geometry similar to an AFS system. In doing so, it will realize a target response defined as one provided by a neutral steer system. However, in a severe maneuver, as the inner tire approaches the saturation limit, the AIFS system controller will only increase the angle of the outer tire, effectively introducing an anti-ackerman geometry. The study is carried out using a comprehensive 4-wheel handling model with AIFS capability. A PI controller with ability to detect and control the outer wheel independently is incorporated to examine the handling performances of an understeer vehicle under a ramp-step and sinusoidal steering inputs. In general, the results demonstrate that AIFS can perform as well as AFS in realizing target response while AIFS can provide performance enhancement beyond the limits of AFS. The control approach of AIFS is also shown to be effective for split-μ condition. Language: en

Unified Chassis Control for the Improvement of Agility, Maneuverability, and Lateral Stability

This paper describes a unified chassis control (UCC) strategy for improving agility, maneuverability, and vehicle lateral stability by the integration of active front steering (AFS) and electronic stability control (ESC). The proposed UCC system consists of a supervisor, a control algorithm, and a coordinator. The supervisor determines the target yaw rate and velocity based on control modes that consist of no-control, agility-control, maneuverability-control, and lateral-stability-control modes. These control modes can be determined using indices that are dimensionless numbers to monitor a current driving situation. To achieve the target yaw rate and velocity, the control algorithm determines the desired yaw moment and longitudinal force, respectively. The desired yaw moment and longitudinal force can be generated by the coordination of the AFS and ESC systems. To consider a performance limit of the ESC system and tires, the coordination is designed using the Karush-Kuhn-Tucker (KKT) condition in an optimal manner. Closed-loop simulations with a driver-vehicle-controller system were conducted to investigate the performance of the proposed control strategy using the CarSim vehicle dynamics software and the UCC controller, which was coded using MATLAB/Simulink. Based on our simulation results, we show that the proposed UCC control algorithm improves vehicle motion with respect to agility, maneuverability, and lateral stability, compared with conventional ESC.

Experimental Verification of Active Front Steering Based on Driver-Friendly Reaction Torque Control

SUMMARY In recent years the demand for safer vehicles has increased. Active front steering (AFS) is an effective technology for stabilizing motion control after the detection of dangerous motion in a vehicle such as slip. However, if AFS intervenes excessively during the steering process, it becomes difficult to prevent interference between driver steering and AFS automatic steering. Therefore, at present vehicles are rarely equipped with AFS. This paper proposes a steering torque control method based on reaction torque estimation and variable damping control for use in a human-friendly AFS system and discusses how an experimental device was used to verify the effectiveness of this control method.

Control strategy of a novel electric power steering system integrated with active front steering function

A novel electric power steering system (EPS) integrated with active front steering (AFS) is developed. It has functions of both AFS system and EPS system with two actuator units: the AFS actuator unit and the EPS actuator unit. The AFS actuator unit controls the displacement transfer behavior of the steering system, and improves the handling stability under adverse road conditions by varying the steering ratio directly related to the speed and road conditions. The EPS actuator unit controls the force transfer behavior of the steering system, and improves the steering portability and road feel of the vehicle. Based on a dynamic model, the mixed H2/H∞ control strategy of the EPS actuator and the active steering intervention control strategy of the AFS actuator are designed. The simulation indicates that the novel EPS system with the designed control strategies has obvious advantages in vehicle handling stability and the driver’s road feel over the traditional EPS system, and extends the vehicle’s steering performance.

Vehicle Yaw Control Using an Active Front Steering System with Measurements of Lateral Tire Forces

We have proposed a design method of an active front wheel steering controller that guarantees closed-loop stability under lateral tire force saturation. The controller uses lateral tire force information to counteract destabilization caused by such saturation. The controller suppresses slip angle magnitude while lateral tire force is saturated. Numerical simulation results confirmed the effectiveness of the proposed method.

Dynamic Modeling and Steering Performance Analysis of Active Front Steering System

The kinematic models of planetary gear set and steering gear are established, based on the analysis of the transmission mechanism of angle superposition with Active Front Steering system (AFS). A controller of variable steering ratio for Active Front Steering system is designed, and virtual road tests are made in CarMaker driver-vehicle-road simulation environment. The results of simulation tests validate the controller performance and the advantage of variable steering ratio function, also show that the driving comfort is improved at low speed especially, due to the Active Front Steering system alters the steering ratio according to the driving situation.

Design of Active Front Steering (AFS) system with QFT control

This paper investigates a control strategy of active front wheel steering based on quantitative feedback theory (QFT). By incorporating feedback from yaw rate sensor into active steering system, the control system improves the dynamic responses of the vehicle. A multi degree-of-freedom nonlinear vehicle model is co-simulated with MATLAB Simulink and ADAMS/CAR. The performance of the control system is evaluated under various emergency manoeuvres and road conditions. The results show that the designed robust control algorithm has good control performance and can efficiently improve the handing qualities and stability characteristics.

Vehicle Yaw Control Using an Active Front Steering System with Measurements of Lateral Tire Forces

We propose a design method of an active front wheel steering controller that guarantees closed-loop stability under the lateral tire forces saturation. The proposed controller utilizes the information on the lateral tire forces to counteract the destabilizing effects caused by the lateral tire force saturation. The controller can suppress the magnitude of the slip angle while the lateral tire forces are in the saturated region. The effectiveness of the proposed method is shown through numerical simulation results.

Development of an active front steering (AFS) system with QFT control

This paper investigates an active front steering control strategy based on quantitative feedback theory (QFT). By incorporating feedback from a yaw rate sensor into the active steering system, the control system improves the dynamic response of the vehicle. The steering response of a vehicle generally depends upon uncertain quantities like mass, velocity, and road conditions. Thus, QFT is used to design a controller with robust performance. A multi-degree-of-freedom nonlinear model is co-simulated here by MATLAB Simulink and ADAMS/CAR. The performance of the control system is evaluated under various emergency maneuvers and road conditions. The result shows that the designed robust control system has good control performance and can efficiently improve handing qualities and stability characteristics.

Design synthesis of mechatronic vehicles with coordinated control systems

A mechatronic vehicle with a coordinated control system is optimised using a multilevel design synthesis (MDS) approach. The design problem of the vehicle is decomposed into a number of smaller and more manageable tasks that can be executed concurrently. Accordingly, the vehicle models are divided into various system and subsystem models that are used for design evaluations at different levels. These decomposed models retain the corresponding mechanical and control properties. To coordinate the various design criteria and find good trade-off solutions, a multilevel optimisation formulation and a direct search algorithm are introduced. The efficacy and feasibility of the MDS approach is demonstrated through the optimisation of a vehicle with a coordinated active front steering and active roll moment control system. With this MDS approach, the interactions among design problems at different levels are well exposed and can be fully investigated for optimal designs.

Modelling and simulation of an active front steering system using Lagrangian dynamics

Modelling and simulation provide effective methods for analysing the dynamic characteristics of an Active Front Steering (AFS) system. However, most of the existing research on AFS fails to address the detailed dynamic behaviour of the system. In this paper, a mathematical model of our developed double-motor AFS system has been built using Lagrangian dynamics. The model was further simulated using MATLAB and validated in field test. The results indicate that the model is capable of satisfactorily representing the dynamic responses of the developed AFS system. This work contributes to further understanding and control of the AFS system.

Linear time‐varying model predictive control and its application to active steering systems: Stability analysis and experimental validation

AbstractA model predictive control (MPC) approach for controlling an active front steering (AFS) system in an autonomous vehicle is presented. At each time step a trajectory is assumed to be known over a finite horizon, and an MPC controller computes the front steering angle in order to best follow the desired trajectory on slippery roads at the highest possible entry speed. We start from the results presented in (Int. J. Veh. Auton. Syst. 2005; 3(2–4):265–291; IEEE Trans. Contr. Syst. Technol. 2007; 15(3)) and formulate the MPC problem based on successive online linearization of the nonlinear vehicle model (linear time‐varying (LTV) MPC). We present a sufficient stability condition for such LTV MPC scheme. The condition is derived for a general class of nonlinear discrete time systems and results into an additional convex constraint to be included in the LTV MPC design.For the AFS control problem, we compare the proposed LTV MPC scheme with the LTV MPC scheme in (IEEE Trans. Contr. Syst. Technol. 2007; 15(3)) where stability has been enforced with an ad hoc constraint. Simulation and experimental tests up to 17 m/s on icy roads show the effectiveness of the LTV MPC formulation. Copyright © 2007 John Wiley & Sons, Ltd.

Predictive Active Steering Control for Autonomous Vehicle Systems

In this paper, a model predictive control (MPC) approach for controlling an active front steering system in an autonomous vehicle is presented. At each time step, a trajectory is assumed to be known over a finite horizon, and an MPC controller computes the front steering angle in order to follow the trajectory on slippery roads at the highest possible entry speed. We present two approaches with different computational complexities. In the first approach, we formulate the MPC problem by using a nonlinear vehicle model. The second approach is based on successive online linearization of the vehicle model. Discussions on computational complexity and performance of the two schemes are presented. The effectiveness of the proposed MPC formulation is demonstrated by simulation and experimental tests up to 21 m/s on icy roads