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This article presents an autonomous steering control scheme for articulated heavy vehicles (AHVs). Despite economic and environmental benefits in freight transportation, lateral stability is always a concern for AHVs in high-speed highway operations due to their multi-unit vehicle structures, and high centers of gravity (CGs). In addition, North American harsh winter weather makes the lateral stability even more challenging. AHVs often experience amplified lateral motions of trailing vehicle units in high-speed evasive maneuvers. AHVs represent a 7.5 times higher risk than passenger cars in highway operation. Human driver errors cause about 94% of traffic collisions. However, little attention has been paid to autonomous steering control of AHVs.

This paper presents a robust active trailer steering (ATS) controller for car-trailer combinations. ATS systems have been proposed and explored for improving the lateral stability and enhancing the path-following performance of car-trailer combinations. Most of the ATS controllers were designed using the linear quadratic regulator (LQR) technique. In the design of the LQR-based ATS controllers, it was assumed that all vehicle and operating parameters were constant. In reality, vehicle and operating parameters may vary, which may have an impact on the stability of the combination. For example, varied vehicle forward speed and trailer payload may impose negative impacts on the directional performance of the car-trailer combination. Thus, the robustness of the conventional LQR-based ATS controllers is questionable. To address this problem, we propose a gain-scheduling LQR-based ATS controller.

As the forward speed of a car increases, the safety of the vehicle and the driver becomes a more significant concern. Active aerodynamic control can effectively enhance the lateral stability of high speed vehicles over tight cornering maneuvers. A split rear wing has been proposed. By means of manipulating the attack angles for the right and/or left parts of the split rear wing, a favorable yaw moment may be achieved to ensure the lateral stability of the vehicle. However, active control of the split rear wing has not been adequately explored. This paper proposes a novel active split rear wing, which can improve the lateral stability over tight cornering maneuvers, and will not degrade the longitudinal dynamics of the vehicle. A Linear Quadratic Regulator (LQR) based controller for the active split rear wing is designed using a linear vehicle model.

In this research, active aerodynamic wings are investigated using numerical simulation in order to improve vehicle handling performance under emergency scenarios, such as tight cornering maneuvers at high speeds. Air foils are selected and analyzed to determine the basic geometric features of aerodynamic wings. Built upon the airfoil analysis, the 3-D aerodynamic wing model is developed. Then, the virtual aerodynamic wings are assembled with the 3-D vehicle model. The resulting 3-D geometry model is used for aerodynamic analysis based on numerical simulation using a computational fluid dynamics (CFD) software package. The CFD-based simulation data and the vehicle dynamic model generated are combined to study the effects of active aerodynamic wings on handling performance of high-speed vehicles. The systematic numerical simulation method and achieved results may provide design guidance for the development of active aerodynamic wings for high-speed road vehicles.

Ensuring the lateral stability and handling of a car-and-trailer combination remains one of the challenges in safety system design and development for articulated vehicles. This paper reviews the state-of-the-art approaches for car-trailer lateral stability control. A literature review covering the effects of external factors, such as aerodynamic forces, tire forces, and road & climatic conditions, is presented. To address the effects of these factors, researchers have previously investigated numerous passive and active safety control techniques. This paper intends to identify the inadequacies of the passive safety approaches and analyzes promising active-control schemes, such as active trailer steering control (ATSC), active trailer braking (ATB) and model reference adaptive controller (MRAC). A comparative study of these control strategies in terms of applicability and cost effectiveness is performed.

This paper presents nonlinear bifurcation stability analysis of articulated vehicles with active trailer differential braking (ATDB) systems. ATDB systems have been proposed to improve stability of articulated vehicle systems to prevent unstable motion modes, e.g., jack-knifing, trailer sway and rollover. Generally, behaviors of a nonlinear dynamic system may change with varying parameters; a stable equilibrium can become unstable and a periodic oscillation may occur or a new equilibrium may appear making the previous equilibrium unstable once the parameters vary. The value of a parameter, at which these changes occur, is known as “bifurcation value” and the parameter is known as the “bifurcation parameter”. Conventionally, nonlinear bifurcation analysis approach is applied to examine the nonlinear dynamic characteristics of single-unit vehicles, e.g., cars, trucks, etc.

The phase-plane analysis technique has become a powerful tool for analyzing lateral stability of single-unit vehicles. Articulated vehicles, such as car-trailer combinations, consist of multiple vehicle units. Multi-unit vehicles exhibit unique dynamic features compared against single-unit vehicles. For example, a car-trailer may exhibit one of the three unstable motion modes, i.e., jack-knifing, trailer sway and rollover. Considering the distinguished configurations and dynamic features of articulated vehicles, it is questionable whether the phase-plane analysis method based on single-unit vehicles is applicable for analyzing the lateral stability of multi-unit vehicles. In order to address the problem, case studies are conducted to test the effectiveness of the phase-plane method for analyzing the lateral stability of a car-trailer combination, which is represented by a nonlinear vehicle model generated using the CarSim software package.

This paper proposes a model reference adaptive control (MRAC) strategy for active trailer steering (ATS) in order to improve the lateral stability of articulated heavy vehicles (AHVs). Optimal controllers based on the Linear Quadratic Regulator (LQR) technique have been explored to enhance the lateral stability of AHVs; these controllers are designed under the assumption that the vehicle model parameters and operating conditions are given and they remain as constants. However, in reality, the vehicle system parameters and operating conditions may vary. To address the variable payloads of trailer(s), the controller based on MRAC technique is adopted. A three degrees of freedom (DOF) linear yaw-plane tractor-semitrailer model is generated to design the control law. The reference model is also developed using the linear yaw-plane model with the LQR technique. The effectiveness of the MRAC controller is demonstrated using numerical simulations under an emulated single lane-change maneuver.

To date, various control strategies based on linear vehicle models have been researched and developed for improving lateral stability of car-trailer (CT) systems. Is a linear-model-based controller applicable to active safety systems for CT systems under emergency operating conditions, such as an evasive maneuver at high lateral accelerations? In order to answer the question, the applicability of an active trailer differential braking (ATDB) controller designed using a linear CT model is tested and evaluated, while the controller being applied to a CT system represented by a linear and a nonlinear CT model. The current research leads to the following insightful findings: the ATDB controller designed using the linear model can effectively improve the lateral stability of CT systems under regular evasive maneuvers at low lateral accelerations, but the controller is not applicable to CT active safety systems under emergency evasive maneuvers at high lateral accelerations.

The paper examines typical vehicle dynamics models used for the design of car-trailer active safety systems, including active trailer braking and steering. A linear 3 degree-of-freedom (DOF), a nonlinear 4 DOF and a nonlinear 6 DOF car-trailer model are generated. Then, these models are compared with a car-trailer model developed with the commercial software package, CarSim. The benchmark investigation of the car-trailer models is carried out through examining numerical simulation results obtained in two emulated tests, i.e., a single lane-change and a Fishhook maneuver. In the vehicle modeling, a mathematical model of a tire with flexible sidewalls is included to account for transient tire forces. Steady-state aerodynamic forces are included in these models. The deviation of the model dynamic responses, e.g., the variation of the articulation angle between the car and trailer, is discussed.

This paper presents the design of airfoil and briefly introduces a real physical prototype for an actively controlled wing to improve high speed vehicle safety. Conventionally, active safety systems of road vehicles, including active steering and differential braking, mainly manipulate the tire/road forces to enhance the lateral stability of vehicles. However, this active safety technology is hindered by the saturation of tire/road forces at high lateral accelerations and on icy slippery roads. In contrast, the use of controlled aerodynamic forces has received little attention. In this paper, the actively controlled wing is proposed to manipulate the negative lift force (downforce) to enhance handling capabilities of vehicles at high speeds.

This paper presents a preliminary investigation of the closed-loop driver/articulated vehicle directional dynamics using numerical simulation. To date, a lot of attention has been focused on investigating the closed-loop directional dynamics of driver/single-unit vehicle systems. Little effort has been paid to examining the closed-loop directional dynamics of driver/articulated vehicle systems. Compared with single-unit passenger cars, multi-unit articulated vehicles have unique directional dynamic characteristics. Generally, a driver's behavior for an articulated vehicle is different from that for a passenger car. To investigate the impact of driver behavior on articulated vehicle directional dynamics, three driver models based on dynamic responses of tractor, trailer and combined tractor/trailer, respectively, have been developed.

Vehicle simulators are often used for vehicle system development and driver behaviour study. The target of this study is to design and evaluate an Active Trailer Steering (ATS) system for a Long Combination Vehicle (LCV) with mutiple trailers using a real-time vehicle simulator. A linear yaw-plane LCV model is generated to derive an optimal ATS controller. Then, the controller is reconstructed in LabVIEW and integrated with a vehicle model for a B-train double from TruckSim. The Driver-Software-in-the-Loop (DSIL) real-time simulations are conducted with the vehicle simulator. The DSIL real-time simulations indicate that the ATS controller can effectively improve the LCV's low-speed maneuverability and high-speed stability under the test maneuvers of a low-speed 90-degree turn and a high-speed single-lane change, respectively.

An optimal preview controller is designed for active trailer steering (ATS) systems to improve high-speed stability of articulated heavy vehicles (AHVs). AHVs' unstable motion modes, including jack-knifing and rollover, are the leading course of highway accidents. To prevent these unstable motion modes, the optimal controller, namely the compound lateral position deviation preview (CLPDP) controller, is proposed to control the steering of the front and rear axle wheels of the trailing unit of a truck/full-trailer combination. The corrective steering angle of the trailer front axle wheels is determined using the preview information of the lateral position deviation of the trajectory of the axle center from that of the truck front axle center. In turn, the steering angle of the trailer rear axle wheels is calculated considering the lateral position deviation of the trajectory of the axle center from that of the trailer front axle.

This paper examines the performance of different active control strategies for improving lateral stability of car-trailer systems using numerical simulations. For car-trailer systems, three typical unstable motion modes, including trailer swing, jack-knifing and roll-over, have been identified. These unstable motion modes represent potentially hazardous situations. The effects of passive mechanical vehicle parameters on the stability of car-trailer systems have been well addressed. For a given car-trailer system, some of these passive parameters, e.g., the center of gravity of the trailer, are greatly varied under different operating conditions. Thus, lateral stability cannot be guaranteed by selecting a specific passive parameter set. To address this problem, various active control techniques have been proposed to improve handling and stability of car-trailer systems. Feasible control methods involve active trailer steering control (ATSC) and active trailer braking (ATB).

This paper presents an integrated design method for active trailer steering (ATS) systems of articulated heavy vehicles (AHVs). Of all contradictory design goals of AHVs, two of them, i.e. path-following at low speeds and lateral stability at high speeds, may be the most fundamental and important, which have been bothering vehicle designers and researchers. To tackle this problem, a new design synthesis approach is proposed: with design optimization techniques, the active design variables of ATS systems and passive design variables of trailers can be optimized simultaneously; the ATS controller derived from this approach has two operational modes, one for improving lateral stability at high speeds and the other for enhancing path-following at low speeds. To demonstrate the effectiveness of the proposed approach, it is applied to the design of an ATS system for an AHV with a tractor and a full trailer.

Under intensive braking, such as continuous down-hill braking, high temperatures could be generated in automotive brake disks. The heat dissipation and thermal performance of vented brake discs strongly depends on the aerodynamic characteristics of the air flow through the rotor passages and the geometry configurations of brake discs. In this paper, commercial software GAMBIT is used for geometrical modeling and automatic mesh generating for brake rotors. Then, a computational fluid dynamic package, FLUENT, is employed to simulate the turbulent motions of air flow through the vented discs. Through the numerical simulations, the design criteria regarding the heat transfer rate and air flow rate of the discs are predicted. To optimize the 2-D and 3-D geometrical configurations of the brake discs, commercial software iSIGHT is used to integrate the geometrical modeling with GAMBIT and numerical simulations based on CFD software FLUENT.

This paper outlines the state-of-the-art of approaches for automated design synthesis of ground vehicle suspensions. Conventionally, design synthesis of suspensions has been based on trial and error approaches, where designers iteratively change the values of design variables and reanalyze until acceptable performance criteria are achieved. This is time-consuming and tedious. With stringent requirements for vehicles, design synthesis undergoes fundamental changes. This puts much attention on the potentials of an automated process. This process is based on the following techniques: effective modelling and simulation methods, realistic formulation approaches, and appropriately selected optimization algorithms. These techniques are reviewed and an automated design synthesis methodology is briefly introduced.