Vehicle Directional Stability Research Articles

The Relationship between Car Caster Angle and the Directional Stability of Car

Appropriate alignment parameters may maintain stability of driving and handiness of operation, and automatic returnability of the steering system when the vehicle goes on straight. The alignment parameters of wheel and the steering mechanism are very important factors on tire wear. Among these parameters, the caster angle of the car is one of the most important factors to maintain the stability of the car. Choosing a suitable caster angle will reduce the wear degree of the car and improve the safety factor. Decades of research into the relationship between vehicle stability and caster angle have been exhaustive. From a large number of experiments in the past to the development of modeling software in recent years, people can use modeling software to simulate and obtain more accurate results. It will focus on the analysis methods using several typical modeling software on the market, and finally obtain the quantitative and qualitative relationship between the vehicle directional stability and caster angle.

Direct Yaw-Moment Control Integrated With Wheel Slip Regulation for Heavy Commercial Road Vehicles

When a road vehicle is subjected to combined cornering and emergency braking, it potentially has a greater risk of wheel lock followed by loss of steerability and/or undesired yaw motion. While an Anti-lock Braking System (ABS) is mandatory in many countries to avoid wheel lock, more attention is required to its combined cornering and braking performance. This paper aims to design a Direct Yaw-Moment Controller (DYC) integrated with ABS to achieve vehicle directional stability for Heavy Commercial Road Vehicles (HCRVs). This study implements a robust reaching law-based sliding mode controller for DYC and ABS. The developed algorithm was evaluated in a Hardware-in-Loop (HiL) setup. The experimental results are compared for the integrated algorithm and standalone ABS algorithms. The proposed algorithm improved the Directional Performance Index (DPI) in the range of 29% to 84% over the open-loop behavior while maintaining vehicle stability. Moreover, it also improved the DPI in the range of 5% to 53% over standalone ABS in various emergency test cases.

Estimation of reliable vehicle dynamic model using IMU/GNSS data fusion for stability controller design

This study deals with the enhancement of reliability of vehicle dynamic model for the stability controller design by estimating the effect of uncertainties in both tire forces and vehicle dynamics. In this respect, any selected initial kinetic model of vehicle is updated at each instant by adding some complementary terms using a novel prediction approach. The proposed estimation method uses the information fusion between the inertial measurement unit (IMU) and the aided systems including the global navigation satellite system (GNSS) and the calibrated compass system. The bias of acceleration sensors and the drift of gyroscope are compensated using a novel adaptive algorithm by which the estimator weights are tuned automatically. Therefore, the vehicle longitudinal and lateral velocities together with the yaw rate are accurately estimated with a high frequency. The proposed estimation algorithm is mathematically analyzed for the stochastic stability and experimentally evaluated through real-world vehicular tests. Accordingly, a nonlinear controller for vehicle directional stability is designed based on the updated dynamic model within the CarSim software environment as a virtual vehicle experiment platform. The obtained results reveal that, the designed data fusion algorithm remarkably improves the estimation performance in the presence of system and measurement uncertainties. Also, the controller designed by the estimated vehicle dynamic model will be reliable and robust in the presence of uncertainties.

An anti-lock braking system algorithm using real-time wheel reference slip estimation and control

Knowledge of the tyre-road interface traction limit during braking of a road vehicle can drastically improve safety and ensure stable braking on varied road conditions. This study proposes an optimal reference slip algorithm that determines the road surface while the vehicle is braking, by implicitly tracking the traction limit. It presents wheel slip variance regulation as a potential approach towards reference wheel slip estimation for wheel slip regulation (WSR). The variance regulation approach computes reference wheel slip using past wheel slip estimates and regulates wheel slip variation at a set point. This variance regulation problem was solved using least-squares estimation, yielding reference slip dynamics. A 3-staged nested control architecture was developed with reference slip dynamics to yield an anti-lock braking system (ABS) algorithm consisting of a brake controller, WSR algorithm and reference slip estimation. The algorithm was experimentally corroborated in a Hardware-in-Loop setup consisting of the pneumatic brake system of a heavy commercial road vehicle, and IPG TruckMaker®, a vehicle dynamics simulation software. The proposed ABS algorithm was tested on straight roads with homogeneous surfaces, split friction surfaces, and transition friction surfaces. It ensured stable braking in all road cases, with a 7%–18% reduction in braking distance on homogeneous road surfaces compared to the same vehicle without ABS. The vehicle directional stability was retained on a split-friction surface, and the ABS algorithm was observed to adapt to sudden transitions in the road surface.

Vehicle directional stability control: a literature survey

Vehicle directional stability control: a literature survey

Concept and Preliminary Simulations of a Driver-Aid System for Transport Tasks of Articulated Vehicles with a Hydrostatic Steering System

Heavy-wheeled vehicles with articulated hydraulic steering systems are widely used in construction, road building, forestry, and agriculture, as transport units and tool-carriers because they have many unique advantages that are not available in car steering systems, based on the Ackermann principle, such as—high cross-country mobility, excellent maneuverability, and high payload and lift capacity, due to heavy axles components. One problem that limits their speed of operation and use efficiency is that they have poor directional stability. During straight movement, articulated tractors’ deviate from a straight line and permanent driver correction is required. This limits the vehicles’ speed and productivity. In this study, we describe a driver-aid system concept that would improve the directional stability of articulated vehicles. Designing such a system demands a comprehensive knowledge of the reasons for the snaking phenomenon and driver behaviors. The results of our articulated vehicle directional stability investigation are presented. On this basis, we developed models of articulated vehicles with hydraulic steering systems and driver interaction. We next added the stabilizing system to the model. A simulation demonstrated the possibility of directional stability improvement.

Probability Based Survey of Braking System: A Pareto-Optimal Approach

Active brake control systems are able to use more accurate control designs on the real-time knowledge of wheel slip such as tire braking forces and external momentums. A multi-objective Pareto type optimization approach is used to evaluate the inconsistent points of the optimization design namely those of minimizing the directional deviation while achieving maximum braking forces on wheels. Moreover, the optimal target slip values defined by the braking purposes like as shorter stopping distance and stability increment by keeping the vehicle in the straight line. This gets by the control of the longitudinal and lateral slip dynamics of each wheel concerning to the road conditions. A controller is optimally brought up by manipulating optimal control law with weights of two control inputs with mathematical and probabilistic characterization. The first-passage probability of critical response levels is used to directly control the vehicle directional stability. An impressive simulation technique based on Monte Carlo method named asymptotic sampling is applied to define the required first-passage probabilities and the Latin Hypercube sampling is used to design of experiments and to cover the design space. Afterwards, a Pareto-type optimization approach is applied to a trade-off between the inconsistent points of the optimization design. The simulation is conducted by the validated vehicle model and the results are indicated that the probability-based control design is represented as a preferable braking performance in comparison with the other systems for braking in sever conditions.

Novel Constrained Nonlinear Control of Vehicle Dynamics Using Integrated Active Torque Vectoring and Electronic Stability Control

This study deals with a new integrated control sys-tem using active torque vectoring (ATV) and electronic stability control (ESC) for enhancement of vehicle directional stability and steerability. In this system, the stabilizing yaw moment is calculated using a novel constrained nonlinear controller with both input and state constraints. The proposed controller is designed using the prediction of continuous nonlinear vehicle model. It guarantees the vehicle directional stability by restricting the side slip angle in the admissible range when the yaw rate tracks its desired response for improved steerability. The calculated yaw moment is generated as driving and braking forces by integrated ATV and ESC systems. According to the integration policy, the required yaw moment is initially generated by ATV in the rear wheels to keep the vehicle driving performance. Because of limitation of ATV, if more yaw moment is required, the ESC system applies asymmetric braking pressure to front wheels to compensate the scarcity of ATV. By the proposed strategy, the small reduction of vehicle velocity is achieved and the vehicle drivability performance is maintained. In order to determine the full capacity of ATV, the active differential dynamics is considered in this paper. Simulation studies are conducted to evaluate the efficiency of proposed constrained controller in comparing with the unconstrained controller and a conventional nonlinear model predictive controller (NMPC) developed in the recent papers using 14-DOF vehicle model. By analyzing the results, it is clear that the proposed controller is much faster and easy to solution and implementation.

Design of active yaw controller integrated with ABS and TCS for multi-wheeled vehicles

Prodigious improvements have been attained in active vehicle safety systems region depending on different control systems. Active yaw control is one of these systems which target the vehicle stability in case of any rapid and/or severe manoeuvre. This paper presents the design of active yaw control system for (8 × 8) multi-wheeled vehicle and its integration with other safety control systems such as anti-lock braking system (ABS) and traction control system (TCS). A simplified vehicle model 'bicycle model' is employed to predict the desired vehicle yaw behaviour depending on road condition and driving situation. TruckSim-MATLAB/Simulink vehicle model was developed to verify the proposed integrated safety control system. The developed integrated active yaw controller with ABS and TCS succeeded in improving vehicle directional stability and traction performance. Furthermore, it should be mentioned that the road friction affects the controller efficiency as it limits the available braking torque to be used by the controller.

A novel technique for optimal integration of active steering and differential braking with estimation to improve vehicle directional stability

This study deals with the enhancement of directional stability of vehicle which turns with high speeds on various road conditions using integrated active steering and differential braking systems. In this respect, the minimum usage of intentional asymmetric braking force to compensate the drawbacks of active steering control with small reduction of vehicle longitudinal speed is desired. To this aim, a new optimal multivariable controller is analytically developed for integrated steering and braking systems based on the prediction of vehicle nonlinear responses. A fuzzy programming extracted from the nonlinear phase plane analysis is also used for managing the two control inputs in various driving conditions. With the proposed fuzzy programming, the weight factors of the control inputs are automatically tuned and softly changed. In order to simulate a real-world control system, some required information about the system states and parameters which cannot be directly measured, are estimated using the Unscented Kalman Filter (UKF). Finally, simulations studies are carried out using a validated vehicle model to show the effectiveness of the proposed integrated control system in the presence of model uncertainties and estimation errors.

Gain-scheduling robust control for a tire-blow-out road vehicle

This paper presents a robust control approach to keeping directional and driving stability for a road vehicle after a tire blow-out. Considering the time-varying vehicle velocity as well as the uncertain tire characteristics, a linear parameter varying vehicle model is built. With front wheel steering angle and yaw control moment as control inputs, a gain-scheduling H∞ controller is developed to attenuate the effects of a flat tire. An optimal control allocation law is presented to perform the yaw control moment by differential braking on the other three tires. Finally, a hardware-in-the-loop testing system, composed of the veDYNA high-fidelity software program and an actual automotive hydraulic braking system, is utilized for controller validation. The results clearly demonstrate the effectiveness of the proposed coordinated controller in improving vehicle directional stability and robustness against the disturbances caused by a tire blow-out.

Fuzzy Scheduled Optimal Control of Integrated Vehicle Braking and Steering Systems

The safe hard braking of a turned vehicle requires short stopping distance while maintaining the vehicle in the path. To achieve the first aim, a wheel slip controller is designed to calculate the maximum braking force of each wheel according to the tire/road conditions. For the second aim, a new optimal multivariable controller for integrated active front steering and direct yaw moment control is analytically developed to control the vehicle directional stability directly. Since the required stabilizing external yaw moment has to be produced by reducing the maximum achievable braking forces of one side wheels, it leads to increase the stopping distance and should be kept as low as possible. In an effective way to manage the integrated control inputs, a fuzzy logic is defined to determine the weight factor of each control input in the integrated optimal control law. This logic is defined using the stability index obtained by the phase plane analysis of nonlinear vehicle model. Therefore, the proposed controller can be tuned automatically for different driving conditions. The simulation results carried out using a validated vehicle model demonstrate that the integrated control system has a better performance compared with stand-alone braking and steering systems to attain the desired purposes.

Enhancement of vehicle braking performance on split-μ roads using optimal integrated control of steering and braking systems

Shorter stopping distance and less deviation from the straight line are two requirements of vehicle safe braking on split-µ roads. The first one is achieved by controlling the longitudinal slip of each wheel at its optimum value calculated by road conditions. However, in order to directly control the vehicle directional stability, a new multivariable controller is optimally developed for integrated active front steering (AFS) and direct yaw moment control. In an efficient way to manage two control inputs, the weights of the integrated optimal control law are online determined by fuzzy logics. These logics are defined using the stability index obtained by the phase plane analysis of nonlinear vehicle model. In this way, the required external yaw moment can be calculated for different driving conditions to only compensate the drawback of AFS for stabilising the vehicle system. The minimum usage of stabilising external yaw moment leads to the less reduction of maximum achievable braking forces of one side wheels and results the shorter stopping distance. By determination of the weighs in limit conditions, the integrated control law easily leads to the stand-alone braking control law. The simulation results carried out using a validated vehicle model demonstrate that the integrated control system has a better braking performance compared with the stand-alone braking system, reported in literature, to attain the shorter stopping distance with less lateral deviation on split-µ roads.

Robust Control of Regenerative and Hydraulic Brakes for Enhancing Directional Stability of an Electric Vehicle During Straight-Line Braking

Thanks to the actuation flexibility of their systems, electric vehicles with individual powertrains, including in-wheel and on-board motors, are a very popular research topic amongst various types of electrified powertrain architectures. The introduction of the individual electric powertrain provides great capacity for improvement of the vehicle's energy efficiency and control performance. However, it also poses tremendous challenges concerning vehicle safety, due to the complex system dynamics and cooperation mechanisms between multiactuators. For an electric vehicle with independently controlled motors, because of design and manufacturing factors, the steady-state error of each motor output torque, and the flexibilities and nonlinear backlash of left and right drivetrains, can be different. This results in asymmetrical output characteristics of electric powertrain systems on the same axle. Therefore, during a normal straight-line deceleration, an unexpected yaw moment would be generated, affecting vehicle's directional stability. In this study, a novel method of directional stability enhancement through robust control of blended braking of an electric vehicle equipped with four individual on-board motors during normal straight-line deceleration are studied. System models, including the vehicle dynamics, tire, electric powertrain, and hydraulic brake models, are developed. Mechanisms of directional instability of the electric vehicle during straight-line braking are analyzed. To further improve the electric vehicle's safety and performance, robust control algorithm of blended braking is developed using nonlinear sliding mode approach. Simulations of the proposed control strategy is carried out under straight-line braking. The results demonstrate that the developed approach is advantageous over the baseline, with respect to both the directional stability and regeneration efficiency, thus validating the feasibility and effectiveness of the controller synthesis.

Research of Three Anti-Lock Braking Control Algorithms to Enhance the Effect of Vehicle Directional Stability

Sets up a nonlinear vehicle dynamic model of eight degrees of freedom and simulates in Matlab/Simulink environment using three anti-lock braking control algorithms, which contain PID, logic threshold and sliding mode variable structure. On the basis of the work, the improving effects for vehicle directional stability, the control effects analyzing from the aspects of tire/whole vehicle parameters and the phase-plane of slid slip angel and its rate are compared and analyzed. The results show that: PID responses fastest but with larger overshoot, logic threshold has smallest fluctuations thus can be implemented more easily, sliding mode control responses slowest but can hold the slip rate more accurately.

Optimization of nonlinear control strategy for anti-lock braking system with improvement of vehicle directional stability on split-μ roads

In a hard braking on a split-μ road, the achievement of shorter stopping distance while maintaining the vehicle in the straight line are of great importance. In this paper, to achieve these conflicting aims, an optimal nonlinear algorithm based on the prediction of vehicle responses is presented to distribute the wheel braking forces properly. The base of this algorithm is reducing the maximum achievable braking forces of one side wheels, as low as possible, so that the minimum stabilizing yaw moment is produced. The optimal property of the proposed control method makes it possible to get a trade-off between the shorter stopping distance and the less deviation of the vehicle heading from the straight line. The special case of this algorithm leads to the conventional anti-lock braking system (ABS) which generates the maximum braking forces for all wheels to attain the minimum stopping distance. However, the ABS cannot control the vehicle directional stability directly. The simulation results carried out using a nonlinear 8-DOF vehicle model demonstrate that the designed control system has a suitable performance to attain the desired purposes compared with the convectional ABS.

Fault classification method for the driving safety of electrified vehicles

A fault classification method is proposed which has been applied to an electric vehicle. Potential faults in the different subsystems that can affect the vehicle directional stability were collected in a failure mode and effect analysis. Similar driveline faults were grouped together if they resembled each other with respect to their influence on the vehicle dynamic behaviour. The faults were physically modelled in a simulation environment before they were induced in a detailed vehicle model under normal driving conditions. A special focus was placed on faults in the driveline of electric vehicles employing in-wheel motors of the permanent magnet type. Several failures caused by mechanical and other faults were analysed as well. The fault classification method consists of a controllability ranking developed according to the functional safety standard ISO 26262. The controllability of a fault was determined with three parameters covering the influence of the longitudinal, lateral and yaw motion of the vehicle. The simulation results were analysed and the faults were classified according to their controllability using the proposed method. It was shown that the controllability decreased specifically with increasing lateral acceleration and increasing speed. The results for the electric driveline faults show that this trend cannot be generalised for all the faults, as the controllability deteriorated for some faults during manoeuvres with low lateral acceleration and low speed. The proposed method is generic and can be applied to various other types of road vehicles and faults.

Control of Yaw Disturbance Using Fuzzy Logic Based Yaw Stability Controller

Yaw stability is an important consideration for the vehicle directional stability and handling behavior during emergency maneuvers. In order to maintain the desired path of the vehicle, in presence of disturbances due to cross wind, different road conditions, and tire deflections, a fuzzy logic based yaw stability controller is proposed in this paper. Proposed control system receives yaw rate error, steering angle given by the driver, and side slip angle as inputs, for calculating the additional steering angle as output, for maintaining the yaw stability of the vehicle. As the side slip angle cannot be measured directly in a vehicle, it was estimated using a model based Kalman observer. A two-degrees-of-freedom vehicle model is considered in the present work. The effect of disturbance on yaw rate and yaw rate error of the vehicle is simulated for sinusoidal, step maneuver and compared with the existing fuzzy control system which uses two inputs such as steering angle and yaw rate. The simulation results show better performance of the proposed fuzzy based yaw controller as compared with existing control system. Proposed fuzzy based yaw stability controller can be implemented in steer-by-wire system for an active front steering of a road vehicle.

A new strategy for minimum usage of external yaw moment in vehicle dynamic control system

Due to the loss of vehicle directional stability in emergency maneuvers, a new complete desired model for vehicle handling based on the linear two-degrees-of-freedom (2DOF) model and tire/road conditions is presented to be tracked by the direct yaw moment control (DYC) system. In order to maintain the vehicle actual motions, yaw rate and side-slip angle, close to the proposed desired responses without excessively large external yaw moment, a complete linear quadratic (LQ) optimal problem is formulated and its analytical solution is obtained. Here, the derived control law is evaluated and its different versions are discussed. It is shown that the side-slip tracking by DYC is more effective than the yaw rate control to stabilize vehicle motions in nonlinear regimes. Also, optimal property of the control law provides the possibility of reducing the external yaw moment as low as possible, at the cost of some admissible tracking errors. Simulation studies of vehicle handling, with and without control, have been conducted using a full nonlinear vehicle dynamic model. The results, obtained during various maneuvers, indicate that when the proposed optimal controller is engaged with the model, improvements in the handling performance through a reduced external yaw moment can be acquired.

Investigation of the dynamic characteristics of suspension parameters on a vehicle experiencing steering drift during braking

This paper presents a simulation study into the characteristics of a vehicle experiencing steering drift under straight line braking. Simulation modelling has been performed using a multi-body dynamics analysis based on a model of an actual vehicle. Front and rear suspension parameters have been modelled as rigid links joined with flexible bushes so as to assess their effect on a vehicle while braking. Suspension geometry and alignment settings, which define characteristic responses such as lateral acceleration, yaw velocity, toe, and caster angles of a vehicle in a transient manoeuvre, are primary to a vehicle's directional stability. Any symmetric inconsistencies in these settings will potentially affect a vehicle's performance. The findings from this research have increased the understanding of the causes of steering drift during braking conditions.