Path tracking is the rudimentary capability and primary task for autonomous ground vehicles (AGVs). In this paper, a novel four-wheel-independent-steering (4WIS) and four-wheel-independent-drive (4WID) electric vehicle (EV) is proposed which is equipped with steer-by-wire (SBW) system. Compared with conventional front-wheel-steering (FWS) vehicles, 4WIS and 4WID EV has superior maneuverability, handing stability and path-tracking capability thanks to more actuators. Therefore, it is more suitable for a desired AGV. For path-tracking controller design, the nonlinear vehicle model with 2 degrees of freedom (DoF) is built utilizing the nonlinear Dugoff tire model. The nonlinear dynamic model of SBW system is conducted as well considering the external disturbances.
Abstract The development of an integrated controller for a 4WS/4WD electric bus is investigated. The front wheel steering angle is assumed to be controlled by the human driver. The vehicle is controlled by the rear wheel steering and the yaw moment that can be generated by the differential torque/brake control on each wheel. The high speed cornering is used as the testing scenario to validate the designed controller. Due to the highly nonlinear and the multiple-input and multiple-output nature, the control design is separated into different stages using the hierarchical layer control concept. The longitudinal speed is controlled using a PI controller together with a rule-based speed modification. The other two control inputs, namely the rear wheel steering and the DYC moment, are then designed using the state-dependent Riccati equation method. The designed controllers are evaluated using computer simulations first, and the simulations showed promising results.
Abstract Compared with the traditional front-wheel- steering (FWS) vehicles, four-wheel-independent-steering (4WIS) vehicles have better handing stability and path-tracking performance. In view of this, a novel 4WIS electric vehicle (EV) with steer-by-wire (SBW) system is proposed in this paper. As to the 4WIS EV, a linear quadratic regulator (LQR) optimal controller is designed to make the vehicle track the target path based on the linear dynamic model. Taking the effect of uncertainties in vehicle parameters into consideration, a robust controller utilizing μ synthesis approach is designed and the controller order reduction is implemented based on Hankel-Norm approximation. In order to evaluate the performance of the designed controllers, numerical simulations of two maneuvers are carried out using the nonlinear vehicle model with 9 degrees of freedom (DOF) in MATLAB/Simulink.
Design of the Linear Quadratic Control Strategy and the Closed-Loop System for the Active Four-Wheel-Steering Vehicle
Abstract In the field of active safety, the active four-wheel-steering (4WS) system seems to be an attractive alternative and an effective tool to improve the vehicles' handling stability in lane-keeping control performance. Under normal using condition, the vehicle's lateral acceleration is comparatively small, and the mathematic relationship between the small side force excitation and the small slip angle of the tire is in the linear region. Furthermore, the effects of roll, heave, and pitch motions are neglected as well as the dynamic characteristics of the tires and suspension system in this work. Therefore, the linear quadratic control (LQC) theory is used to ensure that the output of the 4WS control system can keep track of the desired yaw rate and zero-sideslip-angle response can also be realized at the same time.
The main characteristic of vehicle moving on road is related to its response to the drivers command and to environmental factors affecting the direction of motion of vehicle. The two basic problems in handling the vehicle are control of vehicle along the desired path and stabilization of the direction of motion of vehicle against external disturbances. The vehicle with best handling characteristics is the vehicle which can always be controlled by the driver. While parking the vehicle and doing sharp turnings the vehicle with two wheel steering cannot be more significant. The two wheel steering system takes large radius of turning and requires more space to take turn. Hence four wheel steering is preferable than two wheel steering systems. A multi-function four wheel steering system could improve directional stability at high speeds, sharp turning performance at low speeds, and parking performance of a vehicle.
An overview of existing and alternative forms of vehicle understeer/oversteer expressions is presented. New forms are derived consistent with conceptual extensions to the configurations of the vehicle's steering system, the driving mode - steady-state or transient, and the responses - path curvature or yaw velocity. Derivation of all understeer expressions is presented with a consistent use of the Ackermann reference case and the related “Ackermann vehicle” construct. The vehicle is otherwise represented in a traditional manner as a bicycle model operating in the linear range consistent with small angle approximations. The vehicle's steering system is assumed to be more generally configured with four-wheel steer and active or steer-by-wire actuation at both axles. The actuation is assumed to allow the introduction of significant speed sensitivity to the effective overall steering ratios.
Implementation of Low Cost Inertial Measurement Unit (IMU) Integrated with a Global Positioning System (GPS) Receiver- A Study
This paper focuses on developing a Low Cost IMU integrated with GPS for vehicle state estimation. Knowledge of vehicle states can help design control systems which take these states as an input. Technological advancements in Micro-Electro-Mechanical Sensors (MEMS) have made accelerometers and gyroscopes economical. However, these MEMS based low cost sensors have inherent noise which accumulates with the passage of time and therefore makes their output unreliable. GPS measurements can be used to rectify the inertial sensor errors. Calibration as well as hardware implementation has been discussed in detail. Emphasis is on measurement of body slip angle. Simulations as well as actual results are being presented. Conclusion is being made on the performance of this system.
In this paper a four independent wheel-steering system and its application on the HOST prototype are presented. The prototype is a heavy duty vehicle with four wheel motors controlled by wire, so that each wheel is mechanically not-linked to the other ones and has four degrees-of-freedom. Each wheel has an electric steering actuator to move the wheels around the steering axis, which is controlled by wire. The first part of the work deals with the model determination, reducing the four degree-of-freedom system into a one degree-of-freedom system. In the second part, the relationship between the rotations of each wheel and the linear movement of the electric steering is presented. In the third part the steering ratio is calculated and a parameter to reduce the slip angle is defined. In this way a four independent wheel steering model has been developed and applied to the specific characteristics of HOST.
4 wheel Active Steer (4WAS), which controls all four steering angle, is developed first in the world. This system achieves dynamic performance with secure and invigoration feel on higher level, based on active steer technology of rear axle. This paper describes aim and necessity of all four steering control, and introduces outline and efforts of this system.
Active steering systems can help the driver to master critical driving situations. This paper presents a fuzzy logic control strategy on active steering vehicle based on a multi-body vehicle dynamic model. The multi-body vehicle dynamic model using ADAMS can accurately predict the dynamic performance of the vehicle. A new hybrid steering scheme including both active front steering (applying an additional front steering angle besides the driver input) and rear steering is presented to control both yaw velocity and sideslip angle. A set of fuzzy logic rules is designed for the active steering controller, and the fuzzy controller can adjust both sideslip angle and yaw velocity through the co-simulation between ADAMS and the Matlab fuzzy control unit with the optimized membership function. To ensure the design of high-quality fuzzy control rules, a rule optimization strategy is introduced.
Enhanced Vehicle Lateral Stability in Crosswind by Limited State Kalman Filter Four Wheel Steering System
In this work, a theoretical investigation of four-wheel steering (or shortly 4WS) system is presented using a linear model to simulate vehicle handling characteristics. This model incorporates driver';s operation. The simulation concerns the vehicle in straight running while the vehicle is subjected to side wind excitation. Limitations of measurements in practice are supporting the implementation of limited state feedback systems instead of those which are based on full state feedback information. Therefore, the well known Kalman filter algorithm is used in this work to design a practical 4WS control strategy. This practical system uses only feedback signals of lateral acceleration and front steering angle to obtain the control law. Measurement noise is taken into account and results are generated to obtain the step response of the outputs of interest.
A New Non Linear Control Strategy Basing on a Validated Model for a Vehicle Trajectory Tracking in the Presence of Faults
This paper describes the problem of vehicle trajectory tracking control in the plane (X, Y). While following this trajectory, and to test some of the extreme cases, several types of faults are produced. Some of these faults may be described by a decrease in tires inflation pressures. For that reason, an analytical model representing the comportment of the vehicle and integrating these faults is proposed. In order to use this model in the control, several validations are made by the advanced simulator VE-DYNA. As a second step of this work, the controller design is made; this controller acts on the steering angle and on the torques of the wheels. It is based on the principles of the predictive control. The controller is tested in two cases: in the normal case where the task is to follow a predefined trajectory without faults, and in the other case where the task is the same but faults described by tires pressures decrease are produced.
This paper presents an all-wheel-drive (AWD) hybrid electric vehicle (HEV) design approach for extreme off-road applications. The paper focuses on the powertrain design, modeling, simulation, and performance analysis. Since this project focuses on a military-type application, the powertrain is designed to enhance crew survivability and provide several different modes of limp-home operation by utilizing a new vehicle topology -herein referred to as the island topology. This topology consists of designing the vehicle such that the powertrain and other equipment and subsystems surround the crew compartment to provide a high level of protection against munitions and other harmful ordnance. Thus, in the event of an external shield penetration, the crew compartment remains protected by the surrounding equipment - which serves as a secondary shield.
This paper describes the use of a designed Fuzzy Logic Control for the purpose of integrating the driver’s steering input together with the four-wheel steering system (4WS) in order to improve the vehicle’s dynamic behavior with respect to yaw rate and body sideslip angle. The control objective is to obtain zero body sideslip angle by a two-dimensional rule table, which is created based on the error and on the change in the error of sideslip angle that is to be minimized. The dynamics of the model is developed with a three-degree of freedom nonlinear vehicle model including roll dynamics. The Magic Formula is applied in order to formulate the nonlinear characteristics of the tires. A lane change and steady state cornering simulations are performed to show the effectiveness of the control on transient motion body sideslip angle and yaw rate response time behaviors. During simulations, comparisons are done with the two-wheel steered vehicle and the control techniques studied previously.
Torque Vectoring Axle and Four Wheel Steering: A Simulation Study of Two Yaw Moment Generation Mechanisms
There is increasing demand for enhancement of stability and handling performance in modern automobiles. Active yaw moment generation mechanisms are essential for implementing intelligent stability control schemes. Two mechanisms being considered here are Torque Vectoring Rear Axle and Four Wheel Steering System. Torque Vectoring Axle allows active control of wheel speed ratio and torque distribution typically through the use of wet clutch/brake system and secondary gearing. Four wheel steer systems usually have conventional steering in the front axle and an active steering system in the rear axle. The steering logic is based on improved performance in terms of turning radius at low speeds and directional stability and response at higher speeds. In this study, a lumped parameter, large amplitude, non-linear vehicle model of a rear wheel drive, high-performance vehicle is used.
This paper is supposed to address the BMW approach to the challenge of integrating chassis control systems and it highlights the major issues that have to be addressed. It points out possible solutions for scalable functional and hardware configurations for variable chassis control system combinations. A short outlook is given at possible functional benefits of an integrated structure. Finally, aspects such as components costs (e. g. for sensors and ECUs) as well as reactions on system failures and degradability have to be looked at.
In this paper, we proposed a novel integrated vehicle chassis control configuration, which is based on the combination of vehicle vertical and lateral motion controls. Focusing on the improvement of vehicle handling and riding performance, particularly the active safety under critical driving condition, the purpose of Active Suspension (AS) in the integrated system is to achieve ride comfort quality and to provide more tyre cornering ability near the cornering force saturation regions, while the effect of Four Wheel Steering (4WS) is expected to eliminate the body side slip angle and to achieve an ideal yaw rate model following.
The four wheel steer system better known as the Quadra Steer system (QS4) is a system that provides steering control of the rear wheel of long based pickups and large sport utilities. Analysis was utilized to develop Rear/Front (R/F) steering algorithm with the vehicle in it's normal mode which is characterized as vehicle at curb + 2 passengers or GVW/RGAWR on dry surface. Analysis utilized BZ3 control response simulation model to conduct this study. This dynamic model was used to evaluate key vehicle handling parameters to validate and optimize the algorithm.
A four wheel steer control logic is described. A first control logic release, obtained during previous research activity, is based only on feed forward (F.F.) but is here upgraded merging closed loop control (C.L.). Integration between F.F. and C.L. is described. Rear steering electromechanical actuator frequency response is analyzed, in order to consider its not ideal behaviour during control logic design. Several simulation are performed to qualitatively evaluate the error committed considering an ideal actuator during the control logic design. Specific manoeuvres are chosen to investigate about active system influence on vehicle handling; a 14 degrees of freedom vehicle model is validated in order to compare simulation results with experimental data.
Through a single track model, correspondence between typical frequency analysis coefficients and test driver's opinion developed after experimental tests has been stated. Benchmark analysis of several vehicles, considered significant, has been carried out as well as a sensitivity analysis of vehicle behavior depending on passive design parameters, such as vehicle sideslip stiffness and tyre relaxation length. It led to the definition of the different transfer function capable of describing passive vehicle linear behavior; vehicle performance limits, due to unbridgeable physical phenomenon, has been also considered. 4WS vehicle chance to overcome these limits has been investigated, depending on rear steering control logic complexity. Vehicle frequency response has been then analyzed for different longitudinal velocity, introducing thus the concept of “natural vehicle”. The design of a four wheel steer system control logic, based only on feed forward, is described.
This paper presents a new steering controller for cars equipped with 4-wheel steer-by-wire. The controller commands the front and rear steering angles with the objective of tracking reference sideslip and yaw rate signals describing the desired car lateral dynamics. In addition, the controller automatically rejects any disturbances in sideslip and yaw rate caused, for example, by μ-split braking manoeuvres or lateral wind gusts. The structure of the controller is based on a simplified model of the lateral dynamics of 4-wheel steering cars. This structure allows an originally complex multivariable control design problem to be broken down into two simpler single-input, single-output (SISO) control design problems by means of the Individual Channel Design (ICD) methodology. Within the proposed structure, individual sideslip and yaw rate controllers, valid for varying vehicle speed, can be designed using classical linear control design techniques.
An algorithm was developed for a speed-dependent four-wheel steering system for a Formula SAE car. A linear bicycle model was implemented using the MATLAB and SIMULINK software packages. Various control laws were investigated for the rear steer angle with the objective of reducing the sideslip angle. A full 3D model of the vehicle incorporating weight transfer and tire non-linearity was then developed using the DADS software. An algorithm developed using the linear model with the aim of reducing vehicle sideslip angle was implemented in the nonlinear model. It is shown that this algorithm can improve the dynamic performance for both high-speed and low-speed maneuvers.
Four-wheel-steering Control Strategy and its Integration with Vehicle Dynamics Control and Active Roll Control
The paper presents a 4-wheel-steering (4WS) control strategy devoted to reduce the turn diameter for small longitudinal speed values and to obtain a yaw rate damping effect in dynamic manoeuvres. Moreover, the 4WS active system conceived produces compensation both for lateral wind and road irregularities. The main results obtained through a functional vehicle model are presented. 4WS was integrated with a Vehicle Dynamics Control (VDC), which was improved for turn while braking manoeuvres. The results due to integration were very good, with a reduction of both systems interventions. Finally, a VDC-4WS-Active Roll Control (ARC) integration was tried, based on only one reference body yaw rate for all the active systems. The main results obtained are presented and discussed.
Purpose of this work is to investigate, through a virtual analysis in multi body environment, how to use a four wheel steering system (4WS) to improve vehicle handling and comfort performance. Working only on rear axle, the idea is to define a suspension layout that maximizes the comfort using the mechanical approach, while the handling performance is demanded to the active system. The vehicle used for the theoretical study is an Alfa Romeo 166 3.0 V6. The standard vehicle has been mechanically modified by changing the original rear suspension, a multilink geometry, with a Mc-Pherson layout designed to maximize longitudinal comfort performances. Then an active system, which controls rear steering angles, has been integrated in the rear axle in order to maximize handling performance.
An automotive vehicle steering is achieved not only by means of hand steering wheel (SW) but also by varying actual valued of the angular velocity and sense of rotation of all the electromechanical/mechanoelectrical (E-M/M-E) steered, motorized and/or generatorized wheels (SM&GW) for all-wheel driven (AWD) × all-wheel steered (AWS) automotive vehicles. The betterment tri-mode hybrid steer-by-wire (SBW) AWS diversion automotive high-tech has made significant progress during the 1990s. An evolutionary factor behind this has been the increasing requirements or an active safety as well as ride comfort and handling (RC&H) of automotive vehicles. A major contribution to this progress is the introduction and fast growing application rate of electrically powered and mechatronically controlled rack-and-pinion (R&P) steering gears.
A dual steering control, where steering angle of both rear and front wheels are controlled independently, and single rear steering control of a 4WS vehicle is studied. In this regard, a Time Delay Controller (here after called TDC) is proposed. The TDC performance is compared with the LQR optimal control method. Control schemes are based on the yaw and lateral velocity reference model following. A 3DOF linear vehicle model comprising yaw, lateral and roll motions is used to design the control laws. The time delay controller is a model reference tracker that estimates disturbances such as side wind, road irregularities and actual model nonlinearities, and considers them into the linear controller model. Simulations based on steady state cornering and lane change maneuvers are presented. To establish the sufficient level of model complexity, a 3-DOF nonlinear simulation model comprising yaw, lateral and roll motions with CALSPAN tire coefficients is used.
This paper discusses about a LQR controller as optimal regulator, which is suited for state variable regulation and tracking as a full state feed back controller, Zero side slip (ZSS) and zero yaw rate (ZYR) compensators. ZSS and ZYR are controllers that force the linear system to regulate the steady state response of side slip state variable (have linear relation with lateral velocity) and yaw rate state variable respectively in linear model. As dynamic models, a 2 DOF linear handling model with yaw rate and lateral velocity variables is used as controller model, and a 3 DOF nonlinear model with yaw rate, lateral velocity and roll variables and CALSPAN tire coefficients is proposed for simulations.
Control schemes and strategies of a 4WS vehicle are studied, where schemes are single and dual steering and strategies are zero side slip (ZSS), zero yaw rate (ZYR) and model reference tracking. While Single steering scheme controls only the front steering angle of vehicle, dual steering controls both rear and front steering angles independently. A special model reference tracker, which smoothes vehicle transient response and yields the same steady state yaw behavior as 2WS vehicle, is finally proposed. The dynamic models are a 2DOF linear handling model for controller and a 3DOF nonlinear handling model with CALSPAN tire coefficients for simulation. Simulation results show that while dual steering scheme can effectively control yaw rate and lateral velocity references, single steering scheme is not able to track both of the mentioned variables. It is also shown that the proposed reference is able to improve the handling properties of vehicle.
Sport Utility Vehicles (SUV) and light duty trucks have gained in popularity for the last several years and the demand for more car-like behavior has increased, accordingly. Two areas for potential improvement are vehicle stability and maneuverability while parking. 4WS (4 wheel steering system) is known as an effective solution to stability and low speed maneuverability. In this paper, we identify a new systematic design method of two degree of freedom vehicle state feedback control algorithm that can improve vehicle stability, and show its control effects for a SUV with trailer towing. Low speed maneuvering is improved when the rear tires are steered in negative phase relative to the front tires. However with a large rear steer angle at low speed, the vehicle's rear overhang tracks a wider swing-out path than a 2WS vehicle. For this concern, we propose a new swing-out reduction control algorithm.
Turning at high speed, doing sharp turning at low speed, and doing parking are three critical motions of a vehicle needed to be considered. This research studied dynamic characteristics of a multi-function four-wheel steering system that could improve directional stability of vehicles on turning at high speed, minimize radius of turning of vehicles while doing sharp turning at low speed, and reduce spaces needed on parking motion. Four methods were used to study dynamics characteristics of a multi-function four-wheel steering system. Those four methods were method of constant yaw rate, method of equal side slip angle, method of zero side slip, and method of negative side slip or controlling side slip angle. The results of the study show that the method of zero side slip is the best method to determine rear wheel angle needed for a vehicle doing parking motion in order to minimize radius of turn.