On the Stability of a Flexible Vehicle Controlled by a Human Pilot

This paper presents a stability analysis of a vehicle flexible in the plane of yawing and being controlled by a human pilot. The vehicle is represented by a two degrees-of-freedom model and the pilot is assumed to respond to the lateral displacement and to the lateral velocity with a time delay. It is shown that in order for the pilot model to exhibit a realistic human operator behavior, driver's gain must be linearly proportional to vehicle velocity and also inversely related to frontal visibility. Moreover, application of the Hurwitz criterion indicated that flexibility of the vehicle frame has a destabilising effect on the lateral stability and reduces the stable domain of operation.     

On the Stability of a Flexible Vehicle Controlled by a Human Pilot

SUMMARY

This paper presents a stability analysis of a vehicle flexible in the plane of yawing and being controlled by a human pilot. The vehicle is represented by a two degrees-of-freedom model and the pilot is assumed to respond to the lateral displacement and to the lateral velocity with a time delay. It is shown that in order for the pilot model to exhibit a realistic human operator behavior, driver's gain must be linearly proportional to vehicle velocity and also inversely related to frontal visibility. Moreover, application of the Hurwitz criterion indicated that flexibility of the vehicle frame has a destabilising effect on the lateral stability and reduces the stable domain of operation.     

Analysis of bifurcation and stability for a tractor semi-trailer in planar motion

This paper is intended for bifurcation analysis of a nonlinear tractor semi-trailer vehicle model in planar motion and for investigating its stability under constant running conditions. Bifurcation analysis shows that bifurcation diagrams of a tractor semi-trailer are quite different from those of a single-unit vehicle. Some instability phenomena of the vehicle system such as jackknifing, sideslip, and spinning are explained by correlating them with the behaviour in the neighbourhood of unstable fixed points based on analysis of eigenvectors, phase trajectories, and status of lateral tyre force saturation. It is also found that yaw planar instability of a tractor semi-trailer is caused by lateral tyre force saturation of the tractor's rear axles and/or the trailer's axles. Moreover, the stability region in the state space is demarcated, and a stability index for evaluating size of the stability region in a feasible domain is proposed. Yaw stability under constant driving conditions is analysed by using the proposed stability index.     

Investigation into untripped rollover of light vehicles in the modified fishhook and the sine maneuvers. Part I: Vehicle modelling, roll and yaw instability

Vehicle rollovers may occur under steering-only maneuvers because of roll or yaw instability. In this paper, the modified fishhook and the sine maneuvers are used to investigate a vehicle's rollover resistance capability through simulation. A 9-degrees of freedom (DOF) vehicle model is first developed for the investigation. The vehicle model includes the roll, yaw, pitch, and bounce modes and passive independent suspensions. It is verified with the existing 3-DOF roll-yaw model. A rollover critical factor (RCF) quantifying a vehicle's rollover resistance capability is then constructed based on the static stability factor (SSF) and taking into account the influence of other key dynamic factors.

Simulation results show that the vehicle with certain parameters will rollover during the fishhook maneuver because of roll instability; however, the vehicle with increased suspension stiffness, which does not rollover during the fishhook maneuver, may exceed its rollover resistance limit because of yaw instability during the sine maneuver. Typically, rollover in the sine maneuver happens after several cycles.

It has been found that the proposed RCF well quantifies the rollover resistance capability of a vehicle for the two specified maneuvers. In general, the larger the RCF, the more kinetically stable is a vehicle. A vehicle becomes unstable when its RCF is less than zero. Detailed discussion on the effects of key vehicle system parameters and drive conditions on the RCF in the fishhook and the sine maneuver is presented in Part II of this study.     

Nonlinear PI front and rear steering control in four wheel steering vehicles

Vehicle steering dynamics show resonances, which depend on the longitudinal speed, unstable equilibrium points and limited stability regions depending on the constant steering wheel angle, longitudinal speed and car parameters.

The main contribution of this paper is to show that a combined decentralized proportional active front steering control and proportional-integral active rear steering control from the yaw rate tracking error can assign the eigenvalues of the linearised single track steering dynamics, without lateral speed measurements, using a standard single track car model with nonlinear tire characteristics and a non-linear first-order reference model for the yaw rate dynamics driven by the driver steering wheel input. By choosing a suitable nonlinear reference model it is shown that the responses to driver step inputs tend to zero (or reduced) lateral speed for any value of longitudinal speed: in this case the resulting controlled vehicle static gain from driver input to yaw rate differs from the uncontrolled one at higher speed. The closed loop system shows the advantages of both active front and rear steering control: higher controllability, enlarged bandwidth for the yaw rate dynamics, suppressed resonances, new stable cornering manoeuvres, enlarged stability regions, reduced lateral speed and improved manoeuvrability; in addition comfort is improved since the phase lag between lateral acceleration and yaw rate is reduced.

For the designed control law a robustness analysis is presented with respect to system failures, driver step inputs and critical car parameters such as mass, moment of inertia and front and rear cornering stiffness coefficients. Several simulations are carried out on a higher order experimentally validated nonlinear dynamical model to confirm the analysis and to explore the robustness with respect to unmodelled dynamics.     

Closed-Loop Directional Stability of Car-Trailer Combinations in Straight-Line Motion

This work focuses on the interaction between a driver and a car-trailer combination. A model characterizing human operator behavior in regulation task is employed to study directional stability of the overall system. The vehicle-trailer model retains nonlinear cornering force and other kinematic nonlinearities. Linear stability of the straight line motion is analyzed by the application of Routh-Hurwitz criteria and stability boundaries in parameter space are constructed by setting appropriate Hurwitz determinant to zero. It is shown that two types of transition in stability are possible in the driver/car-trailer system. They correspond to one pair or two pairs of complex conjugate eigenvalues crossing the imaginary axis simultaneously. The implications in terms of resulting motions for the nonlinear system are also discussed. It is shown that stabilization of the combination can be achieved by adding a passive controller at the articulation point. Articulation damper turns out to be a more useful device for controlling trailer oscillations instability although a combination of damper and torsional spring would be a more ideal solution.     

Closed-Loop Directional Stability of Car-Trailer Combinations in Straight-Line Motion

SUMMARY

This work focuses on the interaction between a driver and a car-trailer combination. A model characterizing human operator behavior in regulation task is employed to study directional stability of the overall system. The vehicle-trailer model retains nonlinear cornering force and other kinematic nonlinearities. Linear stability of the straight line motion is analyzed by the application of Routh-Hurwitz criteria and stability boundaries in parameter space are constructed by setting appropriate Hurwitz determinant to zero. It is shown that two types of transition in stability are possible in the driver/car-trailer system. They correspond to one pair or two pairs of complex conjugate eigenvalues crossing the imaginary axis simultaneously. The implications in terms of resulting motions for the nonlinear system are also discussed. It is shown that stabilization of the combination can be achieved by adding a passive controller at the articulation point. Articulation damper turns out to be a more useful device for controlling trailer oscillations instability although a combination of damper and torsional spring would be a more ideal solution.     

Modeling Human Vehicle Driving by Model Predictive Online Optimization

A driver model is designed which relates the driver's action to his perception, driving experience, and preferences over a wide range of possible traffic situations. The basic idea behind the work is that the human uses his sensory perception and his expert knowledge to predict the vehicle's future behavior for the next few seconds (prediction model). At a certain sampling rate the vehicle's future motion is optimized using this prediction model, in order to meet certain objectives. The human tries to follow this optimal behavior using a compensatory controller. Based on this hypothesis, human vehicle driving is modeled by a hierarchical controller. A repetitive nonlinear optimization is employed to plan the vehicle's future motion (trajectory planning task), using an SQP algorithm. This is combined with a PID tracking control to minimize its deviations. The trajectory planning scheme is experimentally verified for undisturbed driving situations employing various objectives, namely ride comfort, lane keeping, and minimized speed variation. The driver model is then applied to study path planning during curve negotiation under various preferences. A highly dynamic avoidance maneuver (standardized ISO double lane change) is then simulated to investigate the overall stability of the closed loop vehicle/driver system.     

汽车驾驶员模型的研究现状及发展趋势

汽车驾驶员模型是汽车交通安全、智能交通系统、汽车自动驾驶和车辆巡航等技术的基础研究内容和关键环节之一。按照汽车驾驶员模型的研究方向及应用,将驾驶员模型分为基于人—车—环境闭环系统汽车操纵稳定性的驾驶员模型、基于智能交通系统的驾驶员行为模型和基于交通安全的驾驶员疲劳模型等类型,综述了上述各类汽车驾驶员模型的研究现状,对各类驾驶员模型存在的不足进行了分析论述,并展望了汽车驾驶员模型的发展方向及趋势。     

Characterization of Dynamic Vehicle Stability Using Two Models of the Human Pilot Behaviour

This article deals with a study of the stability of the vehicle/pilot system for two different models of human operator behaviour. These models, are the outcome of various.approximations of the precision model for single loop compensatory situations. The vehicle is represented with two degrees of freedom and the pilot is assumed to respond to the lateral displacement and to the lateral velocity with a time delay. The properties of these resulting systems are presented and it is observed that, for any given forward visibility, a critical velocity defines a domain of controllability from a domain of uncontrollability. Furthermore this critical velocity is shown independant of the vehicle/ pilot parameters and may be considered as a possible vehicle safety criterion.     

Modeling Human Vehicle Driving by Model Predictive Online Optimization

A driver model is designed which relates the driver's action to his perception, driving experience, and preferences over a wide range of possible traffic situations. The basic idea behind the work is that the human uses his sensory perception and his expert knowledge to predict the vehicle's future behavior for the next few seconds (prediction model). At a certain sampling rate the vehicle's future motion is optimized using this prediction model, in order to meet certain objectives. The human tries to follow this optimal behavior using a compensatory controller. Based on this hypothesis, human vehicle driving is modeled by a hierarchical controller. A repetitive nonlinear optimization is employed to plan the vehicle's future motion (trajectory planning task), using an SQP algorithm. This is combined with a PID tracking control to minimize its deviations. The trajectory planning scheme is experimentally verified for undisturbed driving situations employing various objectives, namely ride comfort, lane keeping, and minimized speed variation. The driver model is then applied to study path planning during curve negotiation under various preferences. A highly dynamic avoidance maneuver (standardized ISO double lane change) is then simulated to investigate the overall stability of the closed loop vehicle/driver system.     

跟驰过程中驾驶员认知结构模型的建立

在道路交通4要素中(人、车、路、环境),人以其主动性和智慧性起着支配作用,是其中的主体要素。基于认知心理学的有关知识,论文采用因子分析法对五轮仪实验系统观测到的车辆跟驰数据进行分析,确定了对车辆跟驰信息提取过程有独立作用的4个因素,相应地将驾驶员认知过程划分为4个阶段,建立了车辆跟驰过程的驾驶员认知结构模型。为驾驶行为研究和车辆跟驰模型的建立提供了理论基础。     

The characteristic velocity stability indicator for passenger cars

Driver assistance systems have received increased attention as market demands have pushed for improved automotive safety. These systems are designed to aid the driver by preventing any unstable or unpredictable vehicle behaviour. One global indicator for stability and driving conditions could help to manage the control algorithms and driver warning subroutines. Another problem which could be solved by a precise driving situation indicator is evaluating new vehicles during test drives. After a short introduction to a linear lateral vehicle model, an analytical approach for an online calculation of different driving conditions (i.e., stability, understeering, oversteering, and neutralsteering) is given. A characteristic velocity stability indicator is defined, which allows online computation of the present driving condition. Results are then checked against real measurements of a test vehicle.     

Development of a Strategy Model of the Driver in Lane Keeping

Based on vehicle constraints and known human operator characteristics, a strategy model was postulated for describing behavior in the lane keeping task. This model includes nonlinear thresholds operating on vehicle yaw and lateral translation, random input sources to account for spurious driver activity, and smoothing to account for driver response lag. The output of the model is steering wheel position

To determine model parameters and model suitability in describing driver behavior, recordings were made for driver-subjects performing a lane-keeping task in a moving base driving simulator having a computer generated display. A procedure involving both analytic and experimental techniques was then developed for determining the model parameters of each driver

Statistical comparisons and visual inspections made between driver-vehicle and model-vehicle time histories indicate a high degree of correspondence. Models such as these show promise in obtaining a better understanding of driver behavior and driver-vehicle response by incorporating nonlinear elements in the driver model.     

基于驾驶员跟车习惯的报警/避撞算法研究

在驾驶员实车实验的基础上,研究跟车工况中的驾驶员行为特性和习惯,建立驾驶员跟随车距模型,并结合对车辆制动过程的分析,研究分别基于驾驶员制动行为特性和驾驶员跟随车距模型的报警/避撞算法,通过改变算法的参数值,可使算法得到的报警/避撞时机符合不同驾驶员的驾驶习惯。利用实验数据对算法进行离线检验,验证该算法在报警/避撞系统中的适用性。     

融合预瞄与势场栅格法的紧急避撞驾驶人模型

紧急避障工况下的驾驶人操作具有响应快且动作幅值较大的特点，传统预瞄驾驶人模型已不能适应紧急避障工况的需求，故考虑实际避撞场景开发相应的驾驶人模型就显得尤为必要。针对此种状况，基于驾驶模拟器，结合紧急避撞工况实际驾驶人操纵数据，提出了一种融合预瞄与势场栅格法的紧急避撞驾驶人模型。首先针对紧急避撞工况下车辆运动特点，建立车辆横、纵向耦合非线性动力学模型，并给出其状态空间方程描述；其次，离线仿真分析紧急避撞系统特征，并结合线性二次型最优控制，建立最优曲率预瞄+跟踪误差反馈驾驶人模型；再者，基于紧急避撞工况下真实驾驶人经验转向行为数据，开发基于势场栅格法的驾驶人模型，为进一步提高驾驶人模型对避障行驶工况的适应性，将基于势场栅格法的驾驶人模型与最优曲率预瞄+跟踪误差反馈驾驶人模型进行融合，并基于Sigmoid函数实现两者输出的权重分配；最后，针对所提出的融合预瞄与势场栅格法的驾驶人模型，开展基于避撞台架的驾驶人在环仿真试验以及实车试验。研究结果表明：在紧急避撞工况下，对比最优曲率预瞄+跟踪误差反馈驾驶人模型，融合预瞄与势场栅格法的驾驶人模型输出的转向动作与实际驾驶人行为较为接近，可在保证避障安全性的前提下，兼顾避障路径跟踪精度与车辆行驶的稳定性。     

基于侧向稳定性的圆曲线路段设计指标研究

车辆在附着系数较小的圆曲线路段转向时,轮胎会处于非线性区内工作,此时基于线性理论的侧向稳定性分析方法会产生较大误差.建立6自由度非线性车辆系统模型,分析其处于非线性域与线性域下不同的特性状态,得到不同车速、路面附着系数下使车辆系统处于临界状态的圆曲线路段半径、超高设计指标.对线性域与非线性域内的车辆系统分别采用基于线性...     

An Advanced Steering System with Active Kinesthetic Feedback for Handling Qualities Improvement

SUMMARY

Advanced Steering System with artificial steering wheel torque-active kinesthetic information feedback for improving handling qualities is discussed. Fundamentally the structure of the system may be considered to another form of model following control. In this system, a driver always remains in the control loop and receives steering control information which give him/her a direct hint to steer a steering wheel. This system works as a stability and control augmentation system of the vehicle to improve the vehicle handling qualities both in compensatory and pursuit control task, and is expected to reduce driver's workload. Effects of this system are analyzed in terms of man-machine system characteristics. Identification of driver dynamics was carried out to find why such improvement could be achieved. Availability of the proposed system is verified by analysis, simulator and proving ground tests.     

The characteristic velocity stability indicator for passenger cars

Driver assistance systems have received increased attention as market demands have pushed for improved automotive safety. These systems are designed to aid the driver by preventing any unstable or unpredictable vehicle behaviour. One global indicator for stability and driving conditions could help to manage the control algorithms and driver warning subroutines. Another problem which could be solved by a precise driving situation indicator is evaluating new vehicles during test drives. After a short introduction to a linear lateral vehicle model, an analytical approach for an online calculation of different driving conditions (i.e., stability, understeering, oversteering, and neutralsteering) is given. A characteristic velocity stability indicator is defined, which allows online computation of the present driving condition. Results are then checked against real measurements of a test vehicle.     

Stability Analysis of the Human Controlled Vehicle Moving Along a Curved Path

A method to study handling characteristics of a vehicle moving along a curved path is presented. A simple bicycle model and a feedback controller with proportional gain are used to simulate the vehicle and the driver. The lateral stability of the vehicle/driver system is analyzed by using the root locus method and numerical integration in the time domain. The effect of the curvature on the system stability is discussed in detail. A new suggestion is made for the look ahead distance to calculate the preview lateral error of the vehicle with respect to the center of the road. Interesting results are shown for some important parameters such as the gain factor, the vehicle speed and the curvature of the path. Possible extensions of the method to more general cases and other applications are discussed.