Showing papers in "Vehicle System Dynamics in 2008"

MPC-based yaw and lateral stabilisation via active front steering and braking

Abstract: In this paper we propose a path following Model Predictive Control-based (MPC) scheme utilizing steering and braking. The control objective is to track a desired path for obstacle avoidance maneuver, by a combined use of braking and steering. The proposed control scheme relies on the Nonlinear MPC (NMPC) formulation we used in [1] and [2]. In this work, the NMPC formulation will be used in order to derive two different approaches. The first relies on a full tenth order vehicle model and has high computational burden. The second approach is based on a simplified bicycle model and has a lower computational complexity compared to the first. The effectiveness of the proposed approaches is demonstrated through simulations and experiments.

The use of vehicle acceleration measurements to estimate road roughness

Abstract: Road roughness is a broad term that incorporates everything from potholes and cracks to the random deviations that exist in a profile. To build a roughness index, road irregularities need to be measured first. Existing methods of gauging the roughness are based either on visual inspections or using one of a limited number of instrumented vehicles that can take physical measurements of the road irregularities. This paper proposes the collection of data from accelerometers fixed in a specific vehicle type and the use of this data to estimate the road condition. Although the estimate is approximate, accelerometers are being increasingly used by car manufacturers to improve suspension performance and the proposed method is relatively inexpensive to implement and provide road managers with constantly updated measurements of roughness. This approach is possible due to the relationship between the power spectral densities of road surface and vehicle accelerations via a transfer function. This paper shows how road profiles can be accurately classified using axle and body accelerations from a range of simulated vehicle-road dynamic scenarios.

A simplified model of wheel/rail contact mechanics for non-Hertzian problems and its application in rail vehicle dynamic simulations

Abstract: The presented model assumes semi-elliptical normal pressure distribution in the direction of rolling. The contact area is found by virtual penetration of wheel and rail. The normal pressure is calculated by satisfying contact conditions at the geometrical point of contact. The calculation is non-iterative, fast and completely reliable. It may be carried out on-line in MultiBody Systems (MBS) computer codes. The tests using the programme CONTACT by Kalker and experience from application in MBS codes show that the model is suitable for technical applications. The creep forces have been calculated with the FASTSIM algorithm, adapted for a non-elliptical contact area. Some applications in rail vehicle dynamics and wear simulation have been outlined.

Human driving data-based design of a vehicle adaptive cruise control algorithm

Abstract: This paper presents a vehicle adaptive cruise control algorithm design with human factors considerations Adaptive cruise control (ACC) systems should be acceptable to drivers In order to be acceptable to drivers, the ACC systems need to be designed based on the analysis of human driver driving behaviour Manual driving characteristics are investigated using real-world driving test data The goal of the control algorithm is to achieve naturalistic behaviour of the controlled vehicle that would feel natural to the human driver in normal driving situations and to achieve safe vehicle behaviour in severe braking situations in which large decelerations are necessary A non-dimensional warning index and inverse time-to-collision are used to evaluate driving situations A confusion matrix method based on natural driving data sets was used to tune control parameters in the proposed ACC system Using a simulation and a validated vehicle simulator, vehicle following characteristics of the controlled vehicle are compared with real-world manual driving radar sensor data It is shown that the proposed control strategy can provide with natural following performance similar to human manual driving in both high speed driving and low speed stop-and-go situations and can prevent the vehicle-to-vehicle distance from dropping to an unsafe level in a variety of driving conditions

Sideslip angle estimation using extended Kalman filter

Abstract: Vehicle sideslip angle can be estimated using either dynamic or kinematic models. The dynamic model requires vehicle parameters, which might have uncertainties due to different load conditions, vehicle motions, and road frictions. Parameter uncertainties might result in estimation errors. Thus system identifications are required to estimate those parameters online. On the other hand, the kinematic model does not require these parameters. A closed-loop estimator can be formulated to estimate the sideslip angle using the kinematic model. Since the system matrix which consists of the yaw rate is time varying, the required input vector and output contain process and measurement noises, respectively, and the disturbance input matrix contains estimated states, extended Kalman filter is used to obtain the estimation gain in this paper. CarSim is used to evaluate the proposed approach under different driving scenarios and road frictions in Matlab/Simulink. The preliminary results show promising improvement of the...

An investigation into unified chassis control scheme for optimised vehicle stability and manoeuvrability

Abstract: This paper describes a unified chassis control (UCC) strategy to improve the lateral stability andmanoeuvrability of vehicles by integrating individual chassis control modules such as electronic stability control (ESC), active front steering (AFS) and continuous damping control (CDC). In order to achieve a target lateral vehicle response, an integrated AFS and four individual wheel braking controls have been used for an optimum distribution of longitudinal and lateral tyre forces the desired yaw moment for lateral stability has been designed by the sliding control method using a planar bicycle model and taking into consideration cornering stiffness uncertainties. The desired yaw moment is generated by the coordinated control of AFS and ESC. Optimal coordination of the control authority for the AFS and the ESC has been determined to minimise longitudinal deceleration. Estimated vertical tyre forces have been used for the optimum distribution of the longitudinal and lateral tyre forces. For the improved per...

Dynamic interaction between train and railway turnout – full-scale field test and validation of simulation models

Abstract: Results from an extensive field test performed in a UIC60-760-1:15 turnout on Svealandsbanan in Sweden are reported. Lateral and vertical wheel-rail contact forces were measured by a wheelset instrumented with strain gauges on the wheel discs. The test train with axle load 25 tonnes passed through the turnout in the main and diverging routes and in the facing and trailing moves. The influences of train speed and moving direction on the magnitude and the position of the maximum lateral contact force in the diverging route of the switch panel, and the influences of train speed, moving direction and route on the maximum vertical contact force in the crossing panel, are investigated. Measured contact forces are compared with calculated forces for a validation of two previously developed numerical models. The magnitude and position of the calculated maximum lateral contact forces are in good agreement with the corresponding measured values. Both measurements and numerical simulations show an increase in maximu...

Impact of inerter nonlinearities on vehicle suspension control

Abstract: This paper discusses the nonlinear properties of inerters and their impact on vehicle suspension control. The inerter was recently introduced as an ideal mechanical two-terminal element, which is a substitute for the mass element, where the applied force is proportional to the relative acceleration across the terminals. Until now, ideal inerters have been applied to vehicle, motorcycle and train suspension systems, in which significant performance improvement was achieved. However, due to the mechanical construction, some nonlinear properties of the existing mechanical models of inerters are noted. This paper investigates the inerter nonlinearities, including friction, backlash and the elastic effect, and their influence on vehicle suspension performance. A testing platform is also built to verify the nonlinear properties of the inerter model.

Improving roll stability of articulated heavy vehicles using active semi-trailer steering

Abstract: This paper discusses an optimal linear quadratic control algorithm to improve the roll stability of a tractor semi-trailer using active semi-trailer steering. The controller minimises a combination of the path-tracking deviation of the trailer rear end relative to the path of the hitch point (5th wheel) and the lateral acceleration of trailer centre of gravity (CoG). First a linear vehicle model of tractor semi-trailer is constructed. Then a ‘virtual driver’ model for trailer steering control is introduced to minimise the path-tracking deviation of trailer rear end. The lateral acceleration of trailer CoG is included as a second objective of the optimal controller so as to improve roll stability. A Kalman filter with linear vehicle model is used to estimate unknown vehicle states, needed by the controller. Simulation results show that optimal control of semi-trailer steering could improve the roll stability significantly during transient manoeuvres while keeping the path-tracking deviation of trailer rear...

Integrated vehicle chassis control based on direct yaw moment, active steering and active stabiliser

Abstract: In order to coordinate steering, braking/traction and active stabiliser, an integrated vehicle chassis controller is proposed. The controller is realised via a main/servo-loop structure: in the main-loop, stabilising forces/moments are first calculated using robust sliding mode controller; then in the servo-loop, the stabilising forces/moments are optimally distributed to tyre control inputs, i.e. active steering and wheel torques. To reduce body roll angle and assist to track the desired yaw rate, active stabilisers are further integrated. Through open-loop and closed-loop simulations using Matlab/Simulink® and MSC CarSim®, it is verified that the controller can significantly improve vehicle handling performances and ride in comfort in the meantime.

Heavy duty vehicle rollover detection and active roll control

Abstract: This paper presents the results of a comprehensive study on heavy-duty vehicle (HDV) roll stability improvement technology. The proposed rollover threat warning system uses the real-time dynamic model-based time-to-rollover (TTR) metric as a basis for online rollover detections. Its feasibility for implementation in a HDV rollover threat detection system is demonstrated through vehicle dynamic simulation studies. The research on the development of a rollover threat detection system is further enhanced in combination with an active roll control system using active suspension mechanism to improve heavy-duty trucks’ roll stability both in the static cornering and in emergency maneuvers. It has been demonstrated that the roll stability of typical heavy-duty trucks has been largely improved by the proposed active safety monitoring and control system.

Numerical and experimental approach for the evaluation of severe longitudinal dynamics of heavy freight trains

Abstract: The paper presents an analysis of heavy freight train dynamics carried out both from a numerical and experimental point of view. A numerical procedure has been developed to investigate the dynamics of heavy freight trains; the proposed methodology combines a new numerical model designed for the longitudinal dynamics of the whole trainset called TSDyn (TrainSet Dynamics simulator) with a multi-body code named MoNSTram (Modular Non-Stationary TRAMcar dynamics simulator) originally developed to analyse the dynamics of modular tramcars and used for a more detailed investigation of the response of a trainset segment. On-line tests have been carried out aiming at acquiring data both for the validation of the simulation code and for the characterisation of buffers’ response. A numerical analysis is eventually presented to show the effect of trainset composition on running safety.

Experimental evaluation of observers for tire–road forces, sideslip angle and wheel cornering stiffness

Abstract: This paper proposes a new estimation process to estimate tire–road forces, sideslip angle and wheel cornering stiffness. This method uses measurements from currently–available standard sensors. The estimation process is separated into two blocks: the first block contains an observer whose principal role is to calculate tire–road forces without a descriptive force model, while in the second block an observer estimates sideslip angle and cornering stiffness with an adaptive tire-force model. The different observers are based on an Extended Kalman Filter method. Concerning the vehicle model, for observability reasons, the rear longitudinal forces are neglected relative to the front longitudinal forces. The estimation process was applied and compared to real experimental data, notably wheel force measurements. Experimental results show the accuracy and potential of the estimation process, and a limitation in the estimation of the cornering stiffness.

Electro-mechanical suspension system considering energy consumption and vehicle manoeuvre

Abstract: In this paper, the performance of the electro-mechanical suspension is discussed on the energy consumption, vibration isolation, and vehicle manoeuvrability. On the basis of the formulation of electro-mechanical suspension, the energy consumption and vibration isolation are discussed through the contour maps with the sprung and unsprung mass velocity feedback gain axes. From the numerical simulation and experimental results, the contour maps for the evaluation of the performance with feedback gain axes are proposed, and on these maps, the abilities of vibration isolation and manoeuvrability are evaluated. On the energy consumption, the regeneration region exists, and the velocity feedback gain of unsprung mass should be considered for regeneration and energy saving. Moreover, Gain settings for improving each vehicle performance are proposed and verified by shaker tests. From simulation and experimental results, it is demonstrated that the proposed active suspension system is able to solve the compatibilit...

Optical position detection to measure tyre carcass deflections

Abstract: Active safety systems would benefit from tyre force and friction potential information. Different sensor concepts, including, among others, the EU–funded Apollo–project developed tyre sensor based on optical position detection, are being studied. The sensor can measure tyre carcass deflections with respect to the rim. The carcass deflections can be used to calculate tyre forces and they may be exploited in the estimation of friction potential. The waveforms of the sensor signal are illustrated. The vertical and lateral force estimations are presented with unavoidable compensation parts. The tyre sensor measurements were compared to the measurement–vehicle results and good correlations achieved. Continuing activities are concerned with the estimation of friction potential and the detection of aquaplaning.

Model-based condition monitoring at the wheel–rail interface

Abstract: The dynamics of a rail vehicle is driven by the interaction between the wheel and rail. Any change to, for example, the shape of the wheel–rail profile or the contact adhesion conditions will change the response of the vehicle. The condition monitoring challenge is to interpret these changes into useful condition information. This paper presents the ongoing research into model-based condition monitoring at the wheel–rail interface applied to two applications: (i) wheel–rail profile estimation; and (ii) low adhesion detection. The wheel–rail profile estimation was carried out on a linearised simulation model that included a nonlinear conicity function. This function could be successfully estimated by also estimating the lateral track irregularities and giving the Kalman Filter self-updating information about the shape of the conicity function. The low adhesion detection was carried out on a complex nonlinear half vehicle model that included saturating contact force equations. The contact forces could be es...

Robust LPV– ∞ control for active suspensions with performance adaptation in view of global chassis control

Abstract: This paper presents a new methodology for suspension control in view of global chassis control, developed in particular to guarantee greater driving safety and comfort. The control of the suspension subsystem allows the vehicle road holding (safety) and passenger comfort to be improved, but not at the same time. In order to reach them for every driving situation, an ‘adaptive’ two-degrees-of-freedom controller for active suspensions is proposed. This control architecture is ‘open’ and could be linked and aggregated to many other controllers of vehicle dynamics. This control strategy ensures, on the one hand, the robustness in performances with respect to parameter uncertainties and, on the other hand, the trade-off between road holding and comfort. The proposed design is based on the LPV/ ∞ theory. Robust stability and performances are analysed within the μ-analysis framework.

Differential wear and plastic deformation as causes of squat at track local stiffness change combined with other track short defects

Abstract: Squats have become a major problem in the track of many railways. In the quest for the root causes of squats, it is observed that they are occasionally found at locations of track stiffness changes such as at fish-plated insulated joints and at switches and crossings. Obviously, there should be other factors in the track, which, together with the stiffness change, have played important roles otherwise there will be squats at all such locations. A validated hybrid multibody-finite element model of vehicle–track vertical interaction is extended to simulate the frictional dynamic rolling contact at a fish-plated insulated joint in order to identify such factors. Elastic–plastic rail material property is taken into account. It is found that it is track short defect in the preload condition of the bolts and the contact between the fishplates and the rail head, which together with the stiffness change, causes large normal and longitudinal contact force variation at the fishplate end so that differential wear an...

Interaction of vehicle and steering system regarding on-centre handling

Abstract: For the on-centre handling behaviour of vehicles the steering system is absolutely important. To investigate the interaction of the vehicle and steering system a validated, especially tailored simulation model was developed. Some meaningful vehicle and steering system parameters are altered to show the influence on steering wheel torque, steering feel and understeer. The results underline the importance of an accurate steering system model. Identified measures to improve the centre feel and steering response were a stiffer torsion bar, a higher cornering stiffness or a lower overall steering ratio. The steering response, however, suffers when the centre feel is improved by a higher trail. The steering rack friction reduces mainly the steering response while the steering column friction decreases the centre feel whereas a stiffer torsion bar lessens the understeer tendency.

High Frequency Railway Vehicle-Track Dynamics Through Flexible Rotating Wheelsets

Abstract: Some railway problems, such as the corrugation of rails or the impact caused by a wheelflat, are associated with a vehicle–track coupled dynamic phenomenon. Models for the analysis of these problems must account for the structural vibrations of the track components (rails and sleepers), but the most adequate approach for the wheelset has not been sufficiently investigated until present. The wheelset can be considered as an undeformable solid, as an elastic structure where the rotation effects are neglected, or as a rotating flexible solid. In order to fill this gap, this article presents a methodology to use the structural vibrations of a rotating wheelset in high-frequency railway dynamics analyses. The model makes use of Eulerian modal coordinates, a formulation that provides very low computational cost. The method is applied in this article to a wheelflat impact calculation and a vehicle running on a corrugated track. The results show the importance of the more realistic model in the simulations, mainl...

Effect of curved track support failure on vehicle derailment

Abstract: In order to investigate the effect of curved track support failure on railway vehicle derailment, a coupled vehicle–track dynamic model is put forward. In the model, the vehicle and the structure under rails are, respectively, modelled as a multi-body system, and the rail is modelled with a Timoshenko beam rested on the discrete sleepers. The lateral, vertical, and torsional deformations of the beam are taken into account. The model also considers the effect of the discrete support by sleepers on the coupling dynamics of the vehicle and track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the calculation of the coupled vehicle and track dynamics, the normal forces of the wheels/rails are calculated using the Hertzian contact theory and their creep forces are determined with the nonlinear creep theory by Shen et al [Z.Y. Shen, J.K. Hedrick, and J.A. Elkins, A comparison of alternative creep-force models for rail vehicle d...

Real-time multiple-model estimation of centre of gravity position in automotive vehicles

Abstract: In this paper, we present a methodology based on multiple models and switching for real-time estimation of centre of gravity (CG) position in automotive vehicles. The method utilises well-known simple linear vehicle models for lateral and roll dynamics and assumes the availability of standard stock automotive sensors. We illustrate the technique with numerical simulations as well as with measured sensor data from an sport utility vehicle. We also compare our estimation results with traditional linear least-squares estimators to show the efficacy of our technique. Finally, we give a simple application example for implementing the idea in automotive vehicles as a switch for rollover controller activation.

Analytical dynamic tire model

Abstract: Modeling of tire friction is one of the central problems for vehicle control systems design. LuGre-type dynamic tire model has been proposed and well discussed in previous studies, because it offers a compact form of dynamic model that is convenient in advanced control studies. It has been successfully used in tire slip control design and vehicle state estimation problems. In this article, a concept of time-constrained Stribeck effect is introduced to interpret the mechanism of the LuGre friction model in predicting tire friction characteristics. A modified two-dimensional (2D) dynamic LuGre friction model is introduced to make it compatible with the governing theorem in the steady state. An analytical 2D modified LuGre-type dynamic tire model is developed, in which some fundamental limitations of classical LuGre models are eliminated. The main modifications involve a change in the structure of the 2D LuGre friction model, introduction of load-dependent parameters in 1D and 2D tire models, and a changed s...

Short wavelength rail corrugation and non-steady-state contact mechanics

Abstract: J. J. Kalker has been the first to consider non-steady-state or transient contact mechanics. Based on Kalker the second author developed a linear contact model for the non-steady-state rolling contact of a wheel running over slightly corrugated rails. The theoretical investigations are concentrated on linear, non-steady-state contact mechanics superimposed to a nonlinear reference state. The reference state is given by the running behaviour of a wheelset due to traction, curving or hunting. For the linear, non-steady-state analysis Kalker's theory has to be modified to predict wear rates in dependency of the corrugation wavelengths. As a result corrugations are only amplified in the range between 2 and 10 cm. Therefore, non-steady-state contact mechanics and wear are responsible for a wavelength fixing mechanism. Structural mechanics of the rail indicate that wavelength in this range is predominantly amplified.

A railway vehicle multibody model for real-time applications

Abstract: Hardware in the loop (HIL) techniques are widely used for fast prototyping of control systems, electronic and mechatronic devices. In the railway field, several mechatronic on board subsystems are often tested and calibrated following the HIL approach. The accuracy of HIL tests depends on how the simulated virtual environment approximates the physical conditions. As the computational power available on real-time hardware grows, the demand for more complex and realistic models of railway vehicles for real-time application increases. In past research activities, the authors worked on the implementation of simplified real-time models for several applications and in particular for an HIL test rig devoted to the type approval of wheel slide protection systems. The activity has then been focused on the development of a three-dimensional model of the dynamics of a railway vehicle for more complex applications. The paper summarises the features and the results of the study.

A stochastic quarter-car model for dynamic analysis of vehicles with uncertain parameters

Abstract: A quarter-car model is used to investigate the vibration response of cars with uncertainty under random road input excitations in this paper. The sprung mass, unsprung mass, suspension damping, suspension stiffness, and tyre stiffness are considered as random variables. The road irregularity is considered a Gaussian random process and modelled by means of a simple exponential power spectral density. The power spectral density, mean value, standard deviation, and variation coefficient of the vehicle's natural frequencies and mode shapes are obtained by using the Monte Carlo simulation method. The computational expressions for the numerical characteristics of the mean square value of the vehicle's random response in the frequency domain are developed by means of the random variable's functional moment method. The influences of the randomness of the vehicle's parameters on the vehicle's dynamic response are investigated in detail using a practical example, and some useful conclusions are obtained.

Comparison of wheel-rail contact codes for railway vehicle simulation: an introduction to the Manchester Contact Benchmark and initial results

Abstract: A new benchmark is being undertaken to assess the impact of wheel-rail contact modelling assumptions on the simulation of railway vehicle dynamics. The benchmark is split into two distinct simulation cases: the first, Case A, using a single wheelset to pinpoint the differences between the contact models and the second, Case B, using a simplified railway vehicle to assess the effect of the different contact models on the simulation of vehicle behaviour. After an open discussion of the Case A specification, the initial call for contributions was made in November 2006. The discussion of simulation Case B specifications was opened in April 2007 and to date is ongoing. This paper briefly introduces the new Manchester Contact Benchmark and presents some of the initial findings from simulation Case A.

Anticollision system PRORETA with automatic braking and steering

Abstract: Methods and experimental results of a collision-avoidance, driver-assistance system are described with automatic object detection, trajectory prediction, and track following, with controlled braking and steering. The objects are detected by a fusion of Light Detection and Ranging (LIDAR) scanning and video camera pictures that show the location, size and speed of objects in front of the car. A desired trajectory is calculated depending on the distance, the width of a swerving action and differential speed. For the trajectory control, different control methods were designed and tested experimentally, such as velocity-dependent linear feedback and feedforward control, nonlinear asymptotic output tracking and nonlinear flatness-based control, using extended one-track models with vehicle state estimation for the sideslip angle and cornering stiffness. Automatic braking is realised with an electrohydraulic brake and automatic steering with an active front steering. Various control systems are compared by simul...

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

Abstract: 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 rollove...

Stochastic analysis of dynamic interaction between train and railway turnout

Abstract: The performance of a railway turnout (switch and crossing) is influenced by a large number of input parameters of the complex train–turnout system. To reach a robust design that performs well for different traffic situations, random distributions (scatter) of these inputs need to be accounted for in the design process. Stochastic analysis methods are integrated with a simulation model of the dynamic interaction between train and turnout. For a given nominal layout of the turnout, using design of experiments methodology and a two-level fractional factorial screening design, four parameters (axle load, wheel–rail friction coefficient, and wheel and rail profiles) are identified to be the most significant. These parameters are further investigated using a three-level full factorial design and stochastic analysis. The random distributions of transverse wheel profile and set of transverse rail profiles along the switch panel are accounted for by the Karhunen–Loeve expansion technique. The influence of the rand...