Showing papers in "Vehicle System Dynamics in 1994"
TL;DR: In this article, the authors investigated two different longitudinal control policies for automatically controlled vehicles, one is based on maintaining a constant spacing between the vehicles while the other is based upon maintaining the constant headway (or time) between successive vehicles.
Abstract: SUMMARY This paper investigates two different longitudinal control policies for automatically controlled vehicles. One is based on maintaining a constant spacing between the vehicles while the other is based upon maintaining a constant headway (or time) between successive vehicles. To avoid collisions in the platoon, controllers have to be designed to ensure string stability, i.e the spacing errors should not get amplified as they propagate upstream from vehicle to vehicle. A measure of string stability is introduced and a systematic method of designing constant spacing controllers which guarantee string stability is presented. The constant headway policy does not require inter-vehicle communication to assure string stablity. Also, since inter-vehicle communication is not required it can be used in systems with mixed automated-nonautomated vehicles, e.g for AICC (Autonomous Intelligent Cruise Control). It is shown in this paper that for all the autonomous headway control laws, the desired control torques ...
537 citations
TL;DR: In this paper, a detailed model is developed to investigate the vertical interactions between railway vehicles and tracks, in which the vehicle subsystem is modelled as a multi-body system with 10 DOF running on the track with a constant velocity, and the track substructure as an infinite Euler beam supported on a discrete-continuous elastic foundation consisting of the three layers of rail, sleeper, and ballast.
Abstract: SUMMARY A new detailed model is developed to investigate the vertical interactions between railway vehicles and tracks. The model consists of two subsystems of vehicle and track in which the vehicle subsystem is modelled as a multi-body system with 10 DOFs running on the track with a constant velocity, and the track substructure as an infinite Euler beam supported on a discrete-continuous elastic foundation consisting of the three layers of rail, sleeper, and ballast. The interface between these two subsystems is the wheel / rail interaction described by Hertzian nonlinear elastic contact theory. In order to get numerical results of such a complex system, a new simple fast integration method is adopted. And typical numerical results are compared with field measured data to verify the detailed model. Finally, the model is applied to analysing the wheel / rail dynamic interactions in high-speed rail and in heavy haul railway.
282 citations
TL;DR: In this article, the Steepest Gradient (SG) algorithm was developed and its performance was shown to be superior to that of the Clipped Optimal Solution (CLOP) solution.
Abstract: SUMMARY This paper attempts to clarify the question of what the optimal semi-active suspension is that minimizes a deterministic quadratic performance index. The optimal control law is a time-varying solution that involves three related Riccati equations. The constant Riccati solution (the so-called “clipped optimal” solution) is not optimal, although its performance is generally quite close to that of the time-varying solution. As the time-varying solution cannot be practically implemented, several constant gain sub-optimal solutions are investigated. A new semi-active algorithm, called the “steepest gradient” algorithm, is developed and its performance is shown to be superior to that of the “clipped optimal” solution.
124 citations
TL;DR: In this article, a generalized two-degree-of-freedom model incorporating nonlinearities due to shock absorber damping, linkage friction and bump stops is presented for vertical seat-suspension systems.
Abstract: SUMMARY Vertical seat-suspension systems are characterized by a generalized two- degree-of-freedom model incorporating nonlinearities due to shock absorber damping, linkage friction and bump stops. The analytical model is validated using the results obtained from laboratory tests performed under sinusoidal excitations in the 0.5-8.0 Hz frequency range. Human body models of varying complexities, derived from the mechanical impedance data, are discussed and integrated to the nonlinear seat-suspension model to derive a coupled driver- seat-suspension model. Nonlinear analytical models are expressed by their linear equivalent models using a local equivalent linearization technique based on energy similarity. The vibration attenuation performance characteristics of the seat-suspension and driver-seat-suspension models are investigated for deterministic and random cab floor excitations. The results of the study revealed that the seated human body contributes considerably to the overall ride performance.
92 citations
TL;DR: In this paper, the authors used range versus range-rate diagrams to illustrate concepts concerning the objectives of headway control, linear trajectories in the range versus rate space, and the influences of acceleration/deceleration limits on headway controller systems.
Abstract: SUMMARY This paper uses range versus range-rate diagrams to illustrate concepts concerning the objectives of headway control, linear trajectories in the range versus range-rate space, and the influences of acceleration/deceleration limits on headway control systems. Relationships illustrated in range versus range-rate diagrams are used in evaluating first, second, and higher order systems for automatically controlling headway. Ideas for comparing driver control of headway with automatic control of headway are presented.
67 citations
TL;DR: In this article, a new methodology for designing observers for automotive suspensions is proposed, which guarantees exponentially convergent state estimation for both semi-active and non-active suspensions with hydraulic actuators.
Abstract: SUMMARY This paper proposes a new methodology for designing observers for automotive suspensions. Automotive suspensions are disturbance-affected dynamic systems. Semi-active suspensions are bilinear while active suspensions with hydraulic actuators are nonlinear. The proposed methodology guarantees exponentially convergent state estimation for both these systems. It uses easily accessible and inexpensive measurements. The fact that sprung mass absolute velocity of the suspension cannot be estimated in an exponentially stable manner with such measurements is also demonstrated. Controllers using estimated states are implemented experimentally on the Berkeley Active Suspension Test Rig. Experimental results for two cases are presented : use of observer states to improve ride quality in an active suspension and use of observer states to reduce dynamic tire loading in a semi-active heavy vehicle suspension.
61 citations
TL;DR: In this paper, the conditions under which longitudinal disturbances in strings of coupled vehicles can be made to attenuate as they travel upstream are discussed, and it is shown that broadcasting the velocity and acceleration of the lead vehicle to all vehicles in die string is sufficient to eliminate the slinky effect.
Abstract: SUMMARY This paper discussed the conditions under which longitudinal disturbances in strings of coupled vehicles can be made to attenuate as they travel upstream. The “slinky” effect is defined as the condition where these disturbances are amplified, a condition that can lead to collisions among upstream vehicles. Input/output linearization is applied to linearize the spacing error to throttle dynamics. Well known linear norm relationships are then applied to investigate the “slinky” effect It is shown that broadcasting the velocity and acceleration of the lead vehicle to all vehicles in die string is sufficient to eliminate the slinky effect.
61 citations
TL;DR: In this article, three nonlinear models of a MacPherson strut wheel suspension have been studied and the most suitable model was further studied with special attention to nonlinear phenomena such as multiple solutions and subharmonics.
Abstract: SUMMARY Three nonlinear models of a MacPherson strut wheel suspension have been studied. The nonlinearities considered are due to the nonlinear geometrical effects in the mechanism, the amplitude limitation due to the bumpstop, the progressive stiffness of the bumpstop and the different damping coefficients for the shock absorber in bump and rebound. The models have been derived according to physical parameter values of. the MacPherson strut wheel suspension of the car SAAB 9.000. The most suitable model was further studied with special attention to nonlinear phenomena. For harmonic forcing the system had phenomena such as multiple solutions and subharmonics. For some parameter values the solution was very sensitive to changes in the integration tolerances in the numerical integration routine. No chaotic steady state solutions were found for the parameter values studied.
48 citations
TL;DR: In this paper, a semi-active adaptive skyhook control based on the tire load variations is proposed to improve the road holding and ride comfort of a vehicle with adjustable shock absorbers.
Abstract: SUMMARY Using adjustable shock absorbers within vehicle suspension systems, it is possible to improve ride comfort significantly when a control strategy is applied based on the so-called skyhook principle. However, the drawback is a poorly damped wheel-hop mode which makes the road holding ability worse. Using adaptive semi-active suspension control based on the tire load variations as introduced in this paper, the trade-off between road holding and ride comfort can be relaxed. Implementation of adaptive skyhook control requires the determination of a number of important and difficult to measure states of the vehicle. This can either be accomplished by several sensors and filters or by a state estimator in combination with less sensors and an internal model of the vehicle. Both methods are discussed. Finally some preliminary test results are discussed.
45 citations
TL;DR: In this paper, a flexible ring model of the tire is presented, which is able to describe the zeroth and first order vibration modes of the tyre, and residual stiffnesses are introduced to take into account the contribution of higher order modes on the total deformation of the rubber.
Abstract: SUMMARY A flexible ring model of the tyre is presented in this paper. The natural frequencies and mode shapes of the tyre are obtained from this ring model. The vibration transmission properties of the tyre between the tyre-road contact point and the wheel axle are analysed. Based on the results of this flexible ring model, a simplified tyre model is developed, which is able to describe the zeroth and first order vibration modes of the tyre. Residual stiffnesses are introduced to take into account the contribution of higher order modes on the total deformation of the tyre. A tyre-road interface model based on the well-known brush model is also developed and integrated into the simplified tyre model. The parameters of both models are established for two different tyres. Finally some numerical results are presented.
45 citations
TL;DR: In this article, the authors investigated the dynamics of Cooperrider's bogie model with realistic wheel and rail profiles and presented the results mainly as bifurcation diagrams and found speed ranges with asymptotically stable forward motion along the track centre line, coexisting attractors, symmetric and asymmetric oscillations and chaos.
Abstract: SUMMARY We investigate the dynamics of Cooperrider's bogie model with realistic wheel and rail profiles. The results are presented mainly as bifurcation diagrams We find speed ranges with asymptotically stable forward motion along the track centre line, coexisting attractors, symmetric and asymmetric oscillations and chaos. In contrast to earlier investigations, we also find chaotic transients, which lead to derailment, before the motion might have settled down to stable motion The influence of a change in the coefficient of adhesion, the wheel base, the gauge and the cant of the rails on the bifurcation points is discussed.
TL;DR: In this article, a modified 1/4 car model is derived which allows suspension, torque and steering control to be applied to a low-order vehicle model, and a study is presented dealing with the synergism coming from the integration of such controlled systems which are designed for improving the dynamic behaviour of road vehicles.
Abstract: SUMMARY A study is presented dealing with the synergism coming from the integration of such controlled systems which are designed for improving the dynamic behaviour of road vehicles. A modified 1/4 car model is derived which allows suspension, torque and steering control to be applied to a low order vehicle model. A number of investigations, based either on complex vehicle models or on ground tests, show that important synergistic effects can be obtained from the integration of suspension, torque and steering controls. The straight running on irregular roads may take advantage from the co-operation of active suspension and four-wheel-steering systems. The braking under µ-split conditions can be improved with a proper control of ABS and rear wheel steering. The driveability of a car entering a curve with changing surface conditions could be substantially enhanced thanks to the combined exploitation of ABS and additional four wheel steering.
TL;DR: In this paper, the authors investigated the effects of vehicle and tire model order on the response of automated vehicles to an emergency step lane change using a controller based on linear vehicles and tire models.
Abstract: SUMMARY Due to increased traffic congestion and travel times, research in Advanced Vehicle Control Systems (AVCS) has focused on automated lateral and headway control. Automated vehicles are seen as a way to increase freeway capacity and vehicle speeds while reducing accidents due to human error. Recent research in automated lateral control has focused on vehicle control during low-g maneuvers. To increase safety, automated lateral controllers will need to recognize and react to emergency situations. This paper investigates the effects of vehicle and tire model order on the response of automated vehicles to an emergency step lane change using a controller based on linear vehicle and tire models. From these studies it is concluded that control strategies based solely on linear vehicle and tire models are inadequate for emergency vehicle maneuvers. A strategy is then proposed to automatically control vehicles through emergency maneuvers. Here the response of a nonlinear vehicle model is used with a linear s...
TL;DR: In this paper, a model for the numerical simulation of interaction between railway vehicles, track and supporting structure is presented, which is used to calculate forces and vibrations transmitted to the supporting structure or to the ground by the passage of a train and evaluate the safety of train running and passenger comfort.
Abstract: SUMMARY A model for the numerical simulation of interaction between railway vehicles, track and supporting structure is presented. The mathematical model is used to calculate forces and vibrations transmitted to the supporting structure or to the ground by the passage of a train and to evaluate the safety of train running and passenger comfort Some applications are reported, comparing the performances of different sorts of railroad superstructures.
TL;DR: In this article, a comprehensive ride dynamic simulation model is developed, assuming constant forward vehicle speed and non-deformable terrain profile, including dynamic track load and wheel/track-terrain interaction.
Abstract: SUMMARY Ride dynamic behaviour of a typical high-speed tracked vehicle, such as a conventional military armoured personnel carrier (APC) negotiating rough off-road terrains, is studied through computer simulations and field tests. A comprehensive ride dynamic simulation model is developed, assuming constant forward vehicle speed and non-deformable terrain profile. The ride model includes dynamic track load and wheel/track-terrain interaction. Dynamic track load is modeled in view of track belt stretching and initial track tension, whereas an equivalent damper and continuous radial spring formulation is employed to model wheel/track-terrain interaction. Field testing of a APC subjected to discrete half round obstacles of various radii, a sinusoidal course, a random course, and a Belgian Pave\ is carried out for various vehicle configurations and speeds. Computer simulation results are validated against field measured results. The comparison of measured and predicted results shows generally good agreement.
TL;DR: In this paper, the authors compared the vertical dynamic behavior of a railway vehicle with flexible wheels with that of a vehicle with standard solid wheels on a railway track for high speed trains.
Abstract: SUMMARY The vertical dynamic behaviour of a railway vehicle with flexible wheels is compared to that of a vehicle with standard solid wheels. Full-scale field experiments performed on a portion of a recently built railway track for high-speed trains are reported. Flexible and solid wheels without and with wheel flats were instrumented for measurement of transient vertical wheel/rail contact forces. Accelerations and strains in the track structure were measured in parallel. The location of the instrumented wheelset in relation to the instrumented portion of the track was determined at each instant of time. Flexible wheels are shown to considerably reduce the contact forces. A linear mathematical model of the track is suggested based on a previously reported technique for solving vertical interaction problems. Track parameters determined at the test-site are used as input to die model. Numerical results show acceptable agreement with measured responses.
TL;DR: In this paper, a range of design options is considered and analysis of a specific, simple arrangement of bogie vehicle demonstrates that active guidance leads to excellent steering performance together with dynamic stability at high speeds.
Abstract: SUMMARY Railway vehicles using conventional forms of wheelset have limited performance in sharp curves, but the application of independently rotating wheels in conjunction with active guidance offers the possibility of much improved curving performance. The range of design options is considered in this paper and analysis of a specific, simple arrangement of bogie vehicle demonstrates that active guidance leads to excellent steering performance together with dynamic stability at high speeds. The mechanisms of the various modes of instability are discussed.
TL;DR: In this paper, the possibility of improving both the dynamic stability and curving performance of railway trucks through the use of semi-active control is discussed, and a realistic method of achieving this is proposed: using harder primary longitudinal stiffness on the trailing axle and using a primary yaw damper only on the leading, allows bidirectional operation by changing the damping force.
Abstract: SUMMARY The possibility of improving both the dynamic stability and curving performance of railway trucks through the use of semi-active control is discussed. According to the direction of vehicle motion, the truck parameters are switched in a longitudinally asymmetric manner. Using a method of evaluation proposed here, the stability of trucks having the same steering ability was examined using linear models. A truck equipped with independently rotating wheels on the trailing axle and with unsymmetric primary suspension has the best performance. A realistic method of achieving this is proposed: using harder primary longitudinal stiffness on the trailing axle and using a primary yaw damper only on the leading, allows bidirectional operation by changing the damping force.
TL;DR: In this article, a Variable Yaw Constraint Suspension System (VYCSS) for self-steering bogies is presented. But the model was then expanded to a full vehicle model, giving similar results.
Abstract: SUMMARY This paper outlines the development of a Variable Yaw Constraint Suspension System (VYCSS) for self-steering bogies. Using a simplified bogie model, that is two wheelsets that are connected by a shear (cross anchors) and a yaw (longitudinal springs) constraint, the basic concept of the Variable Yaw Constraint (VYC) was developed and simulated. The model was then expanded to a full vehicle model, giving similar results. The final proof was the successful prototype testing.
TL;DR: In this article, the authors used a complex nonlinear model of a driver and a vehicle during the straight line motion of the vehicle on a rough road and applied the Hooke-Jeeves method and the objective function that enabled simultaneous optimization of vertical vibrations of the driver's seat, the steering wheel and normal reactions in the contact surface of the tyre and road.
Abstract: SUMMARY Spatial random vibrations of a vehicle that arise during driving represent an important factor in functioning of a dynamic system: Driver - Vehicle - Environment. They carry certain information for driver and also cause fatigue of driver and passenger. This is the reason why the tendency is towards the minimization of vibratory loads, what in practice can be achieved by optimization of characteristics of elasto - damping elements of a vehicle. In this paper for optimization of elasto - damping elements of a vehicle we used a complex nonlinear model of a driver and a vehicle during the straight - line motion of the vehicle on a rough road. Optimization was performed by application of the Hooke - Jeeves method and by use of outside penalty functions as well as the objective function that enabled simultaneous optimization of vertical vibrations of the driver's seat, vibrations of the steering wheel, and normal reactions in the contact surface of the tyre and road. The optimization was performed with ...
TL;DR: In this article, an adaptive control scheme for electronic throttle that achieves good tracking of arbitrary constant speed commands in the presence of unknown disturbances is proposed, which is based on a simplified linear vehicle model derived from a validated nonlinear one.
Abstract: SUMMARY Electronic throttle control is an important part of every advanced vehicle control system. In this paper we design an adaptive control scheme for electronic throttle that achieves good tracking of arbitrary constant speed commands in the presence of unknown disturbances. The design is based on a simplified linear vehicle model which is derived from a validated nonlinear one. The designed control scheme is simulated using the validated full order nonlinear vehicle model and tested on an actual vehicle. The simulation and vehicle test results are included in this paper to show the performance of the controller. Due to the learning capability of the adaptive control scheme, changes in the vehicle dynamics do not affect the performance of the controller in any significant manner.
TL;DR: In this article, a simple linear model of the vehicle is used to investigate three strategies for active roll control, and the strategies are then implemented on the validated nonlinear model and validated handling tests performed on an articulated vehicle.
Abstract: SUMMARY This paper describes an investigation of active roll control of heavy road vehicles. Results from handling tests performed on an articulated vehicle are used to validate a nonlinear simulation of the vehicle. A simple linear model of the vehicle is used to investigate three strategies for active roll control. The strategies are then implemented on the validated nonlinear model.
TL;DR: The architecture of the PATH vehicle lateral control system is presented in this paper, where two main modules are an intelligent reference/sensing system, and an Frequency-Shaped-Linear-Quadratic/preview control algorithm.
Abstract: SUMMARY The architecture of the PATH vehicle lateral control system is presented in this paper. The two main modules are an intelligent reference/sensing system, and an Frequency-Shaped-Linear-Quadratic/preview control algorithm. The whole lateral control system was formerly evaluated on a two-door test vehicle. It was transplanted to a four-door vehicle which is considerably different from the older two-door test vehicle in dynamic characteristics. The objective of this study is to investigate the reusability of our control system.
TL;DR: In this paper, the effects of braking force distribution on a vehicle's lateral and longitudinal directions were investigated. And the authors found that controlling the lateral distribution of the braking force on both the front and rear wheels achieves the two effects mentioned above.
Abstract: Studies were made on the effects of braking force distribution, on a vehicle's lateral and longitudinal directions. The studies were made on distribution on non-linear regions, under combined high lateral acceleration and deceleration conditions, using the value of the yaw moment versus the side slip angle. Consequently, a method for obtaining optimum braking force distribution was found. Controlling the lateral distribution of the braking force on the front wheels was found to be effective for the improvement of vehicle stability, while that on the rear wheels was found to be effective for extending the limit of vehicle motion. Therefore, controlling the lateral distribution of the braking force on both the front and rear wheels achieves the two effects mentioned above. Simulation tests were carried out to confirm these effects in terms of turning performance and controllability to avoiding obstacles in emergency situations. (A) For the covering abstract see IRRD 864807.
TL;DR: In this paper, a continuous look-ahead preview control scheme (a control strategy in which the road input is sensed before it reaches to the vehicle) is developed and applied to the well known quarter car model.
Abstract: SUMMARY In this paper a continuous look-ahead preview control scheme (a control strategy in which the road input is sensed before it reaches to the vehicle) is developed and applied to the well known quarter car model. The results of this study showed that the active system with preview control reduces dramatically the body acceleration and the dynamic tyre load when compared with an optimised system that does not use preview information. These substantial improvements are obtained when both systems consume the same working space. In comparison with other preview control methods, it is shown that the strategy developed in this work gives a lower overall performance index and the control law presented here is easier to realise in practice.
TL;DR: In this paper, a non-linear control algorithm is proposed in order to enhance the driveability of two-wheel-drive automobiles fitted with a traction control system, and numerical computations show that the active safety of such automobiles could be considerably enhanced with respect to that of conventional ones.
Abstract: SUMMARY Referring to road vehicles, the problem of traction force distribution between the wheels of a driving axle is investigated. Particular attention is devoted to front-wheel-drive automobiles but the main conclusions of this study can be extended easyly to other vehicles. The basic features and related limitations pertaining to mechanical systems for traction control are studied. Possible arrangements of non-conventional differentials for traction control are presented, discussed and classified in terms of left/right torque split ratio and efficiency. A non-linear control algorithm is proposed in order to enhance the driveability of two-wheel-drive automobiles fitted with a traction control system. Numerical computations show that the active safety of such automobiles could be considerably enhanced, with respect to that of conventional ones.
TL;DR: In this paper, a one-dimensional corrugated surface is modelled as a periodic, differentiable function of the distance traversed, and three criteria of corrugation growth are developed.
Abstract: SUMMARY The paper consists of three parts 1.Description of a One-Dimensional Corrugated Surface The surface is modelled as a periodic, differentiable function of the distance traversed. Three criteria of corrugation growth are developed 2. The Frequency Response of Wheel and Rail A linear relationship is assumed between the Fourier transforms of the displacement difference of wheel and rail, and the contact force. The constant of proportionality is the frequency response which is shown to have three important properties. The actual frequency response is approximated by the sum of three functions having these properties 3. Numerical Results Wear is taken proportional to frictional work, which is calculated by a contact mechanical code (CONTACT or FASTSIM). The surface is taken sinusoidal; 11 wave lengths have been investigated, varying from 10 to 200 mm. It is shown that a quasisteady rolling contact code (FASTSIM) may be used to obstain the results, which comes down to the statement that the used frequenc...
TL;DR: In this paper, the dynamic vertical interaction between a moving rigid wheel and a flexible railway track is investigated using an extended state-space vector approach in conjunction with a complex modal superposition for the track.
Abstract: SUMMARY The dynamic vertical interaction between a moving rigid wheel and a flexible railway track is investigated. A round and smooth wheel tread and an initially straight and noncorrugated rail surface are assumed in the present optimization study. A symmetric linear three-dimensional beam structure model of a finite portion of the track is suggested including rail, pads, sleepers and ballast with spatially nonproportional damping. The full interaction problem is numerically solved by use of an extended state-space vector approach in conjunction with a complex modal superposition for the track. Transient bending stresses in sleepers and rail are calculated. The influence of seven selected track parameters on the dynamic behaviour of the track is investigated. A two-level fractional factorial design method is used in the search for a combination of numerical levels of these parameters making the maximum bending stresses a minimum.
TL;DR: The concept of autonomous lateral control or auto-tracking is introduced, which allows us to use only line-of-sight sensor information to effect vehicle control and the possibilities of using this method for lane change purposes in an automated highway system are examined.
Abstract: SUMMARY Lateral control of vehicles in IVHS requires the installation of on-board sensors as well as the installation of roadway hardware such as cables, magnets, etc. Existing control approaches in PATH require road curvature and vehicle lateral position (with respect to the center of the lane) information. Hence these approaches rely on roadway sensors to obtain relative lateral position. These methods will necessitate infrastructural changes to the highway. This paper introduces the concept of autonomous lateral control or auto-tracking. The method allows us to use only line-of-sight sensor information to effect vehicle control. We present a detailed vehicle model. Controllers have been proposed to demonstrate the effectiveness of the proposed auto-tracking scheme. We also examine the possibilities of using this method for lane change purposes in an automated highway system.
TL;DR: In this paper, a vehicle model that can be used for simulation tests in the field of AVCS studies is presented. But this model contains the non-linear elements of the engine, the torque converter, the automatic gear shift and the tire.
Abstract: SUMMARY This paper initially introduces a vehicle model that can be utilized for simulation tests in the field of AVCS studies. This model contains the non-linear elements of the engine, the torque converter, the automatic gear shift and the tire. The vehicle model has 3 degrees of freedom and it can be used for multiple vehicle simulations in AVCS as well as in ATIMS. This paper applies the model to the study and analysis of vehicle “platooning” for automated driving. In this paper, it is shown that platooning can be realized both longitudinally and laterally by the application of the sliding control.