Showing papers in "Vehicle System Dynamics in 1999"

Optimal Adaptive Cruise Control with Guaranteed String Stability

Abstract: A two-level Adaptive Cruise Control (ACC) synthesis method is presented in this paper. At the upper level, desired vehicle acceleration is computed based on vehicle range and range rate measurement. At the lower (servo) level, an adaptive control algorithm is designed to ensure the vehicle follows the upper level acceleration command accurately. It is shown that the servo-level dynamics can be included in the overall design and string stability can be guaranteed. In other words, the proposed control design produces minimum negative impact on surrounding vehicles. The performance of the proposed ACC algorithm is examined by using a microscopic simulation program – ACCSIM created at the University of Michigan. The architecture and basic functions of ACCSIM are described in this paper. Simulation results under different ACC penetration rate and actuator/engine bandwidth are reported.

A fast wheel-rail forces calculation computer code

Abstract: In the simulations of rail vehicle dynamic behaviour, the computation of wheel-rail forces is repeated many times. Therefore a short calculation time is very important. A fast algorithm and computer code for the computation of wheel-rail forces under known contact geometry and creep and spin conditions is presented in the paper. The proposed method assumes ellipsoidal contact area and normal stress distribution according to Hertz. Because of the short calculation time it can be used instead of simple formulas to improve the accuracy or as a substitution of Kalker's programme FASTSIM to save the computation time. The method has been tested and used in different simulation tools with very good experience. The computer code and some test results given in the appendix allow to apply this method in the user's own computer simulation programmes. For the covering abstract see ITRD E117109.

Vehicle Dynamics Estimation Using Kalman Filters

Abstract: This paper deals with the application of stochastic state estimators in vehicle dynamics control. It is often unrealistic to assume that all vehicle states and the disturbances acting on it can be measured. System states that cannot be measured directly, can be estimated by a Kalman Filter. The idea of the Kalman filter is to implement a model of the real system in an on-board computer in parallel with the system itself. This paper will give 3 examples of this principle applied to automotive systems.

Vehicle-Track Dynamics in the Mid-Frequency Range

Abstract: During the last years railway companies have observed increasing problems with track damage like rail corrugation, deterioration of ballast or unround wheels. Since the origin of these damages is suspected in the mid-frequency dynamics, research activities in the frequency range from 50 up to 500 Hz have been initiated. The article demonstrates that in comparison to the low and high frequency range the knowledge about physical effects in the mid-frequency range is poor. Apart from a historical literature review on vehicle and track modelling, recently published methods and models are collated and problems in their mathematical treatise are mentioned. Regarding the vehicle, the paper shows the development starting with Klingel's massless wheelset model and ending with sophisticated elastic multibody system models. Concerning the track, different mathematical approaches in frequency and time domain are compared. In the mid-frequency range the pad, ballast and subsoil properties play an important role. Hence...

Slip-Angle Estimation for Vehicle Stability Control

Abstract: Recently, some direct yaw-moment control systems have been in development. Obviously, such systems need accurate slip-angle information. This paper describes a strategy of vehicle slip angle estimation. The difficulty in slip angle estimation is due to nonlinear characteristics of tyres and influence of relative slant of the road surface. To solve this difficulty, a combined method of model observer and direct integration method is proposed. In this method, two kinds of values of the side forces of the wheels are provided, i.e., direct detected values by the G-sensor and values from a tyre model. Then those values are combined appropriately which results in the combination of model observer and direct integration. A feedback algorithm, redesigned to suppress the influence of tyre model error, is applied in the observer. Considering interference of road surface and its avoidance, road slant angle is estimated and consequently vehicle model is corrected. The estimated value of the road friction coefficient ...

Estimation of Tire-Road Friction Using Observer Based Identifiers

Abstract: This paper presents methods for identifying the tire-road friction coefficient. The proposed methods are: an observer-based least square method and an observer/filtered-regressor-based method. These methods were designed assuming that some of the states are not available since physical parameter identification methods developed assuming that the system states are available are not attractive from a practical point of view. The observer is used to estimate signals which are difficult or expensive to measure. Using the estimated states of the system and the filtered-regressor, the parameter estimates are obtained. The proposed methods are evaluated on an eight state nonlinear vehicle/transmission simulation model with a Bakker-Pacejka's formula tire model. Vehicle tests have been performed on dry and wet roads to verify the performance of the methods. It has been shown through simulations and vehicle tests how the RPM sensors can be used with observer based identification methods to estimate the tire-road f...

A General Method for the Evaluation of Vehicle Manoeuvrability with Special Emphasis on Motorcycles

Abstract: This paper presents a novel approach to the assessment of the manoeuvrability of vehicles which is not based on the simulation of open-loop manoeuvres, nor does it rely on the modelling of the driver as a control system. Instead, the essence of the method is the solution of a two-point optimal control boundary value problem, in which a vehicle, subject to physical constraints like tyre adherence and road borders, among others, is required to go between given initial and final positions as fast as possible. The control inputs - i.e., the driver's actions - that make the vehicle move between the two states in the most efficient way are found as a part of the solution procedure and represent the actions of a sort of ideal, perfect driver. The resulting motion is called the optimal manoeuvre and, besides being the most efficient way that the given vehicle has for travelling between the two points according to the chosen optimal criterion, may be taken as a reference for meaningful comparisons with other vehic...

Roll-over prevention system for commercial vehicles - additional sensorless function of the electronic brake system

Abstract: Recent experiences have shown that even small-medium size passenger cars face an accident which has been connected with commercial vehicles so far: the roll-over. The roll-over is the most horrible accident type for truck drivers, since he/she does not have any indication before it happens, and consequently does not react properly. This article discusses some of the problems of the commercial vehicle stability in general, and offers a solution for detecting and avoiding roll-over by using the existing sensors and actuators of electronic brake system (EBS).

The Application of Roller Rigs to Railway Vehicle Dynamics

Abstract: Roller rigs have been built world-wide to research into the dynamics of railway vehicles and they have particularly been applied to the development of high-speed trains. This survey takes into consideration both full scale as well as small scale model roller rigs. Besides performance, most important experimental work and the emphasis of application, the scaling strategies of model test rigs and the differences involved in roller rig experiments are treated. Suggestions for potential future uses and developments are also given for this tool which is useful for demonstration and analysis of railway vehicle dynamic behaviour.

On the Theory of Nonlinear Dynamics and its Applications in Vehicle Systems Dynamics

Abstract: We present a brief outline of nonlinear dynamics and its applications to vehicle systems dynamics problems. The concept of a phase space is introduced in order to illustrate the dynamics of nonlinear systems in a way that is easy to perceive. Various equilibrium states are defined, and the important case of multiple equilibrium states and their dependence on a parameter is discussed. It is argued that the analysis of nonlinear dynamic problems always should start with an analysis of the equilibrium states of the full nonlinear problem whereby great care must be taken in the choice of the numerical solvers. When the equilibrium states are known certain linearizations around one chosen state may be applied carefully in order to facilitate or speed up the numerical solution of the dynamical problem. It is argued, however, that certain problems cannot be linearized. The applications of nonlinear dynamics in vehicle simulations is discussed, and it is argued that it is necessary to know the equilibrium states ...

Linear quadratic gaussian control of a quarter-car suspension

Abstract: This paper presents a method for designing linear multivariable controllers in the frequency-domain for an intelligent controlled suspension system for a quarter-car model. The design methodology uses singular value inequalities and optimal control theory. The vehicle system is augmented with additional dynamics in the form of an integrator to affect the loop shapes of the system. The measurements are assumed to be obtained in a noisy state, and the optimal control gain and the Kalman filter gain are derived using system dynamics and noise statistics. A combination of singular value analysis, eigenvalue analysis, time response, and power spectral densities of random response is used to describe the performance of the active suspension systems.

Impact Loads due to Wheel Flats and Shells

Abstract: A Finite Element (FE) model of vehicle-track system is employed to duplicate the experiments carried out by British Rail and CP Rail System. The theoretical results of the wheel/rail contact forces, rail-pad forces and strains in the rail showed very good correlation to the experimental data. Extensive results are compared with experimental data in the time domain for through validation of the developed model. The characteristics of the impact loads due to wheel flats and shells are investigated based on the validated FE model. The study shows that the shape and size of flat or shell, axle load, vehicle speed and rail-pad stiffness mainly affect the impact loads. Adding elastomeric shear pads on the wheelset bearing does not reduce the wheel/rail dynamic contact force but it may reduce the dynamic force on the bearing. Reducing rail-pad stiffness to a certain level on a concrete-tie track may significantly reduce the dynamic load and the force transmitted to the concrete tie.

History of stability of railway and road vehicles

Abstract: Stability of running of vehicles is one of the important design criteria of railway and road vehicles. Railway vehicle stability is based on kinematics as well as contact mechanics. It reaches back to the 19th century and had its first hey-day with the work of Carter and Rocard on stability of locomotives. A rediscovery of their knowledge, which seemed to have been forgotten, was inevitable due to increased vehicle speeds since the early Fifties. — Though investigations on road vehicle stability only began approximately in 1930 with the treatment of the shimmy phenomenon, realistic solutions were available at the same time as for railway vehicles. Besides considering historical aspects we discuss in the paper links which exist between both approaches; open questions are described.

Safe Platooning in Automated Highway Systems Part I: Safety Regions Design

Abstract: SUMMARY This paper addresses the problem of designing safe controllers for vehicle manuevering in Automated Ž. Highway Systems AHS in which traffic is organized into platoons of closely spaced vehicles. Conditions to achieve safe platooning under normal modes of operation are investigated. The notion of safety is related with the absence of collisions that exceed a given relative velocity threshold. State dependent safety regions for the platoons are designed in such a way that, whenever the state of a platoon is inside these safety regions, it is guaranteed that platoon maneuvering will be safe and follow the behavior prescribed by the finite state machines that control vehicles manuevers. It is shown that it is possible to design control laws that keep the state of the platoons inside these safety regions. The results obtained allow one to decouple the controllers for the regulation of the manuevers and the finite state machines that determine their proper sequence in AHS architectures. The overall complexity of the design and verification of the AHS as an hybrid system is therefore greatly reduced.

A Three–Dimensional Airspring Model with Friction and Orifice Damping

Abstract: This paper proposes a non-linear airspring model for general three-dimensional motions. The non-linearity stems from friction behaviour of rubber parts and from the air flow in the pipe between airbag and surge reservoir, in particular if the surge pipe is equipped with orifice damping. The model is based on superposition of elastic, friction and viscous forces. For a given preload, the model has 6 and 7 parameters for horizontal and vertical motions, respectively. Comparisons between model and measurement results show good agreement for a wide range of cases. The model represents a reasonable compromise between accuracy and computational effort and should be a suitable tool in rail vehicle dynamics analysis. For the covering abstract see ITRD E117109.

A conceptual framework for active safety in road traffic

Abstract: Starting from a short review of the classical definition of traffic safety as given by Wilfert, 1966, a novel classification scheme for Active Safety in the form of a fault tree is being derived. The discussion will consider human factors implications of the new technical potential of artificial recognition of the vehicle's traffic environment. As a typical example of driver assistance systems Adaptive Cruise Control ACC will be described.

Steady turning of two-wheeled vehicles

Abstract: When driving along a circular path, the driver of a motorcycle controls the vehicle mainly by means of steering torque. If low steering torque is necessary, the driver feels that the vehicle is manoeuvrable. In this paper, a mathematical model concerning steering torque is developed; it takes into account the actual kinematic behaviour of the vehicle and the properties of motorcycle tyres. Tyre forces act at the contact points of toroidal tyres, which are calculated according to kinematic analysis. Non-linear equations are solved using an iterative approach. Several numerical results are presented, and the influence of tyre properties and some geometrical and inertial properties of the vehicle on steering torque are discussed.

Lateral dynamics of a railway vehicle in tangent track and curve: tests and simulation

Abstract: A mathematical model for the simulation in time domain of the dynamic behaviour of a railway vehicle running in tangent track and curve is presented in the paper. The main features of the model, with particular emphasis on the subject of wheel-rail contact, are described, and some comparisons with experimental data coming from line tests are presented. The topics of wheel rail contact modelling and of defining a suitable, frequency dependent model for the anti-yaw dampers appear from these comparisons to be critical in order to obtain satisfactory results. For the covering abstract see ITRD E117109.

Vehicle models for rts applications

Abstract: A vehicle system dynamics model is presented that captures the essential braking and handling behavior of a passenger car and runs faster than real-time on a 1998 Pentium 233 MHz laptop computer The simulation code was generated with the AutoSim multibody code generator and linked with C functions that communicate with braking hardware to create a real-time simulation (RTS) with hardware in the loop (HITL) Techniques are described that were used to allow the simulation program to work with HITL The model (without controller) was also integrated with the Simulink environment to provide a design tool for control engineers

Semiactive Suspension Design with an Optimal Gain Switching Target

Abstract: The paper presents a two-phase design technique for semiactive suspensions. In the first phase, we use a procedure proposed by Yoshida et al. to compute a target active control law that can be implemented by Optimal Gain Switching. This control law is such that the force generated by the suspension system is bounded within a set U. In the second phase, we approximate this target by controlling the damper coefficient of the semiactive suspension. We also compute the region of the state space in which the force generated by the semiactive suspension is still within the set U. The results of several simulations show that the use of a semiactive suspension leads to minimal loss with respect to optimal performance of an active suspension.

Development of an Active Control Engine Mount System

Abstract: In an attempt to reduce idling vibration and booming noise in automobile engines, the authors have developed an engine mounting system we call the ACM(Active Control engine Mount) system. Comprisin...

Optimising a Car Chassis

Abstract: This paper presents a method to optimise a car chassis fitted either with passive or active suspensions Provided that a full vehicle model is available for accurate simulations of many different driving situations (J-turn, lane-change, power-on/power-off on even/rough, dry/wet roads), the method allows to tune the parameters of the chassis system (suspension elastokinematics, stiffnesses, dampings, actuator gains, tyre pressures) in order to achieve the desired dynamic behaviour of the car in all of the considered driving situations According with the Global Approximation approach, the original physical car model is substituted by another purely numerical mathematical model (backpropagating Artificial Neural Network) This reduces the simulation time dramatically and enables the optimisation process to come to successful results The computation of the Pareto-optimal set is performed by using Genetic Algorithms The method is validated by optimising the parameters of the suspension system of an actua

Wheel Slip Control in Traction Control System for Vehicle Stability

Abstract: Traction control systems are used to prevent wheel slippage and to maximize traction forces. This paper proposes a new scheme to enhance vehicle lateral stability with a traction control system during cornering and lane changes. This scheme controls wheel slip during cornering by varying the slip ratio as a function of the slip angle. It assumes that a traction control system with the engine throttle angle is used. The scheme is dynamically simulated with a model of front-wheel-driven passenger vehicles. Simulation results show that the proposed scheme is robust and superior to a conventional one, which is based upon fixed slip ratios, during cornering and lane changes.

Wheelset control strategies for a two-axle railway vehicle

Abstract: This paper studies actively controlled wheelsets for railway vehicles and explores the potential benefits from actively stabilisation and steering the wheelsets of a railway vehicle via a mechatronic approach. Two models are developed in the study for a two-axle railway vehicle, one with solid axles and the other with independently rotating wheelsets. A number of control schemes including optimal controllers, intuitively formulated controllers as well as modal control approaches, are proposed. Both curving performance and ride quality of the vehicle are assessed for all control schemes. For the covering abstract see ITRD E117109.

Estimation of the non-linear suspension tyre cornering forces from experimental road test data.

Abstract: The paper discusses the application to real data of an identification procedure based on an Extended Kalman Filter, for estimating the equivalent non-linear suspension tyre cornering forces of a road vehicle from a single standard manoeuvre. In particular, both the steady-state and the dynamic handling characteristics can be evaluated.

Observer Design for Semi-Active Suspension Control

Abstract: This paper presents an observer for automotive semi-active suspension control. Automotive suspensions are disturbance affected dynamic systems and semi-active suspensions can be represented as a bilinear model. An observer for semi-active suspensions is formulated such that the estimation error is independent of unknown external disturbance. The proposed observer uses easily accessible measurements such as accelerations and guarantees exponentially convergent state estimation for suspension deflections and velocities. Absolute sprung mass and unsprung mass velocities can be estimated using the proposed observer. Simulations and experimental rig tests show that all states of a semi-active suspension can be estimated only with acceleration measurements. The estimated states are used to improve ride quality in a semi-active suspension.

Track Settlement Prediction Using Computer Simulation Tools

Abstract: A project is being carried out at Manchester Metropolitan University to examine the effects of different vehicles on track deterioration and consequent maintenance costs. A number of track settlement models have been investigated including those published by Prof. Sato in Japan and a model based on laboratory experiments at the Technical University of Munich. The MEDYNA simulation package has been used to generate the equations of motion for the vehicles being studied and time stepping integration routines used to predict motions and forces as required. The ADAMS/Rail package has also been used to assist with the visualisation of the models and the predicted behaviour. Inputs to the model were made at each wheelset. These were either idealised discrete events such as dipped rail joints or measured values from real sections of track. The results are presented here for three vehicles with different types of suspension and for two of the track settlement models. All of the settlement models used predict that the suspension characteristics have a large effect on the rate of track deterioration. The general trends in predicted track settlement rate agree between the two settlement models but there are also some very significant variations in the relative rates for some cases.

Control of wheel slip ratio using sliding mode controller with pulse width modulation

Abstract: For the control of anti-lock brake system (ABS), a longitudinal four-wheel vehicle model with brake actuator is described and a sliding mode controller with pulse width modulation (PWM) method has been developed for passenger vehicles. In our research, we introduce actuator dynamics of solenoid-solenoid valve type in system equation and derive the sliding mode control input theoretically. We propose using PWM method to compensate for the discrete nature of actuator dynamics by duty control. The effectiveness of the proposed control algorithms was confirmed by vehicle test on an in-door test bench that was specially constructed for the purpose concerned.

On the design and development of a magneto-rheological mount

Abstract: This paper evaluates the performance of a Magneto-Rheological (MR) mount. The mount incorporates MR fluid in a conventional fluid mount to open and close an inertia track between the fluid chambers of the mount. It is shown that such switching of the inertia track improves the mount's isolation effect by eliminating the large transmissibility peak that commonly exists at frequencies larger than the notch frequency for conventional fluid mounts. The switching frequencies of the MR mount are evaluated based on the parameters of the mount. A simple control scheme for switching the mount between the open and closed states is proposed, and the performance of the controlled mount is compared with conventional mounts. A sensitivity analysis is conducted to evaluate the effect of parameter errors in estimating the switching frequencies and mount performance. The results show that the switching frequencies can be accurately determined from mount parameters that are easily measured or estimated.

Worst-case vehicle evaluation methodology : examples on truck rollover/jackknifing and active yaw control systems

Abstract: SUMMARY A worst-case vehicle evaluation methodology is presented in this paper. This evaluation method identifies worst-case excitation signals so that the vehicle performance under extreme conditions can be assessed. Two case study examples are presented to illustrate the design procedure and potential benefits of this method: the rollover and jackknifing of an articulated truck, and the evaluation of an active yaw control system. In both cases, the worst-case method was able to produce unstable results at very modest steering/braking levels.