Handling Analysis of a Motorcycle with Added Cambering of the Front Frame

Through linear analysis, the handling characteristics of the motorcycle with fixed control of added cambering of front frame are investigated under the variation of fixed and free controls of steering axis. The cornering responses and stability characteristics of the motorcycle are presented with the aid of the handling diagram. From numerical results for a typical motorcycle, it is found that the influence of the cambering of front frame on the cornering response of fixed steering control is opposite to that of free steering control. Moreover, the design philosophy of a so-called semi-direct steering mechanism, which cambers the front frame for cornering, is studied.     

The Influence of Structural Flexibilities on the Straight-running Stability of Motorcycles

SUMMARY

A new tyre model for studies of motorcycle lateral dynamics, and three new motorcycle models, each incorporating a different form of structural compliance, are developed. The tyre model is based on “taut string” ideas, and includes consideration of tread width and longitudinal tread rubber distortion and tread mass effects, and normal load variation. Parameter values appropriate to a typical motorcycle tyre are employed. The motorcycle models are for small lateral perturbations from straight running at constant speed, and include (a) lateral compliance of the front wheel in the front forks, (b) torsional compliance of the front forks, and (c) torsional compliance in the rear frame at the steering head about an axis perpendicular to the steering axis.

Results in the form of eigenvalues, indicating modal damping properties and natural frequencies are presented for each model. The properties of four large production machines for a range of forward speeds, and the practicable range of stiffnesses are calculated, and the implications are discussed.

It is concluded that typical levels of structural compliance in models (a) and (c) contribute significantly to the steering behaviour properties of large motorcycles, and their observed behaviour can be understood better in terms of the new results than of those existing previously. Some conclusions relating to optimal structural stiffness properties are also drawn.     

Automotive Stability and Handling Dynamics in Cornering and Braking Maneuvers

SUMMARY

Automotive steering behaviour is classified for steady-state cornering and the definitions of over-/understeer and stability/instability are well known. In this paper it is intended to apply these definitions to combined cornering and braking maneuvers i.e. to extend the criteria to quasi-steady-state conditions. This way of investigation was chosen because it gives a clear idea of the typical handling behaviour. Furthermore, the vehicle behaviour is analyzed using the cornering stiffness of the axles and front/rear cornering stiffness ratio because this is always of primary significance. The following contribution is based on a theoretical analysis considering the most important non-linear vehicle properties.

The paper deals with two groups of vehicles: single vehicles (passenger cars) and combinations (passenger car/caravan and tractor/semitrailer). In the case of combinations the effect of trailers on the towing vehicles is examined. So, careful attention is paid to the coupling forces, which alter the wheel loads and influence steerability and stability.     

Integrated Control of Active Rear Wheel Steering and Direct Yaw Moment Control

SUMMARY

An integrated control system of active rear wheel steering (4WS) and direct yaw moment control (DYC) is presented in this paper. Because of the tire nonlinearity that is mainly due to the saturation of cornering forces, vehicle handling performance is improved but limited to a certain extent only by steering control. Direct yaw moment control using braking and/or driving forces is effective not only in linear but also nonlinear ranges of tire friction circle. The proposed control system is a model matching controller which makes the vehicle follow the desired dynamic model by the state feedback of both yaw rate and side slip angle. Various computer simulations are carried out and show that vehicle handling performance is much improved by the integrated control system.     

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.     

Additional 4WS and Driver Interaction

SUMMARY

This investigation is based on a complex 4-wheel vehicle model of a passenger car that includes steering system and drive train. The tyre properties are described for all possible combined longitudinal and lateral slip values and for arbitrary friction conditions. The active part is an additional steering system of all 4 wheels, additionally to the driver's steering wheel angle input. Three control levels are used for the driver model that thereby can follow a given trajectory or avoid an obstacle.

The feedback control of the additional 4 wheel steering is based on an observer which can also have adaptive characteristics. Moreover a virtual vehicle model in a feedforward scheme can provide desired steering characteristics.

To get information for critical situations a cornering manoeuvre with sudden u-split conditions is simulated. Further a similar manoeuvre is used to evaluate the reentry in a high friction area from low friction conditions. And finally the performance of the controller is shown in a severe lane change manoeuvre.     

Study on integrated control of active front steer angle and direct yaw moment

This study proposes a control system to improve vehicle handling and stability under severe driving conditions by actively controlling the front steering angle and the distribution of braking forces on four tires. With the application of a model-matching control technique, this proposed control system makes the performance of the actual vehicle model follow that of an ideal vehicle model with consideration of nonlinearity of tire characteristics. Finally, this paper investigates the effectiveness of control system during the following conditions: braked cornering, lane change and side wind disturbance.     

双前桥转向机构优化设计方法研究

双前桥转向机构包含两个独立的转向梯形机构和双前桥间的转向联动机构—双摇臂系统。文中分析了双前桥转向机构应实现的功能、运动规律和与其它系统可能造成的运动干涉,提出了同时保证双前桥汽车车轮转向时做纯滚动和杆系干涉造成的车轮异常磨损最小的多目标优化设计方法。     

Anti-Skid Braking of a Tractor-Semitrailer Truck

ABSTRACT

This paper describes a study of anti-skid braking and the effects of such braking on the handling behavior and braking performance of a tractor-semitrailer truck. The truck, represented by a digital computer model having fourteen degrees of freedom, is taken to be in a cornering maneuver that involves braking and driver steering. Conventional braking or one of three types of anti-skid braking is used in the maneuver. The results show that the effects of anti-skid braking on the handling behavior and braking performance of the truck are beneficial. The results also show that the behavior of the wheels and the handling behavior and braking performance of the truck depend on the type of anti-skid braking used.     

Emergency steering control of autonomous vehicle for collision avoidance and stabilisation

ABSTRACT

Collision avoidance and stabilisation are two of the most crucial concerns when an autonomous vehicle finds itself in emergency situations, which usually occur in a short time horizon and require large actuator inputs, together with highly nonlinear tyre cornering response. In order to avoid collision while stabilising autonomous vehicle under dynamic driving situations at handling limits, this paper proposes a novel emergency steering control strategy based on hierarchical control architecture consisting of decision-making layer and motion control layer. In decision-making layer, a dynamic threat assessment model continuously evaluates the risk associated with collision and destabilisation, and a path planner based on kinematics and dynamics of vehicle system determines a collision-free path when it suddenly encounters emergency scenarios. In motion control layer, a lateral motion controller considering nonlinearity of tyre cornering response and unknown external disturbance is designed using tyre lateral force estimation-based backstepping sliding-mode control to track a collision-free path, and to ensure the robustness and stability of the closed-loop system. Both simulation and experiment results show that the proposed control scheme can effectively perform an emergency collision avoidance manoeuvre while maintaining the stability of autonomous vehicle in different running conditions.     

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.     

The Influence of Structural Flexibilities on the Straight-running Stability of Motorcycles

A new tyre model for studies of motorcycle lateral dynamics, and three new motorcycle models, each incorporating a different form of structural compliance, are developed. The tyre model is based on “taut string” ideas, and includes consideration of tread width and longitudinal tread rubber distortion and tread mass effects, and normal load variation. Parameter values appropriate to a typical motorcycle tyre are employed. The motorcycle models are for small lateral perturbations from straight running at constant speed, and include (a) lateral compliance of the front wheel in the front forks, (b) torsional compliance of the front forks, and (c) torsional compliance in the rear frame at the steering head about an axis perpendicular to the steering axis.

Results in the form of eigenvalues, indicating modal damping properties and natural frequencies are presented for each model. The properties of four large production machines for a range of forward speeds, and the practicable range of stiffnesses are calculated, and the implications are discussed.

It is concluded that typical levels of structural compliance in models (a) and (c) contribute significantly to the steering behaviour properties of large motorcycles, and their observed behaviour can be understood better in terms of the new results than of those existing previously. Some conclusions relating to optimal structural stiffness properties are also drawn.     

四轮转向汽车自适应模型跟踪控制研究

使用单点预瞄驾驶员模型，针对确定性汽车模型探讨了４ＷＳ汽车在单移线行驶过程中后轮的最优转向控制规律。通过引入状态反馈，改善了整车的转向特性，将实际汽车的前后轮胎侧刚度及外界干扰视为有界的不确定性参数，采用自适应模型跟踪变结构控制方法，使得不确定的实际汽车模型能够很好地跟踪确定的最优理论模型，仿真结果表明该方法的可行性，控制系统能够有效地克服参数摄动及外界干扰对系统稳定性的影响。     

System identification and attitude control of motorcycle by computer-aided dynamics analysis

System identification of the motorcycle model constructed by computer-aided dynamics analysis is introduced to design a control system for attitude stabilization of the motorcycle. The identified model can be reduced to the coupled mode system between the roll and the front steering. The front-steering control system using the roll angle is designed by H_∞ control theory, based on the reduced-order model and the full-order model, respectively. It is verified from simulation results that the motorcycle attitude against disturbance is stabilized by the H_∞ controller, and that the reduced-order controller exhibits efficient stabilization performance in comparison with the full-order controller.     

主动前轮转向客车的操纵稳定性仿真分析

建立某大型客车的含侧向、横摆及侧倾三自由度动力学模型,通过方向盘角阶跃转向仿真结果和试验数据的比较,验证了仿真分析的准确性。采用横摆角速度跟踪主动前轮转向控制策略,结合比例积分控制方法,在考虑作动器动态特性和前轮转角饱和特性的基础上,对主动前轮转向控制前后的车辆进行直线行驶下的侧向风扰动和湿滑路面急转弯情况下的仿真对比分析。结果表明,主动前轮转向控制后的车辆其操纵稳定性和行车安全性都有较大的提高。     

A Variable Free Control Characteristic Vehicle

A variable characteristic car (VCC) has been developed at Melbourne University for driverlvehicle handling research. The vehicle is unusual in that it has facilities for varying both its fixed control and free control dynamic characteristics over wide ranges. In this paper the servo systems used to effect these changes are described. The calibration methods used to relate the vehicle response characteristics to the variable servo settings are detailed. Sample calibration results are given for the fixed control parameters steering ratio, yaw response time and stability factor. Calibration of the free control parameters is also described and results are given for the steering torque gradient, and the time-to-peak and percentage overshoot of the steering wheel motion in response to a step input of torque.     

String tyre model for evaluating steering agility performance using tyre cornering force and lateral static characteristics

The cornering force and lateral static characteristics of a tyre are fundamental factors that describe the steering feel for handling performance. However, it is difficult to justify the contribution of each factor when the tyre’s cornering motion is evaluated through subjective assessment. Currently, the relaxation length of Pacejka’s tyre model is close to describing these tyre motions. Therefore, this paper proposes a string tyre model based on the relaxation length in order to represent the steering performance. The proposed method provides a more accurate modelling of the steering agility performance. Therefore, it is possible to use this model to predict the steering response performance, and this is validated through comparison with a real relaxation length.     

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.