Showing papers on "Vehicle dynamics published in 1985"

General Purpose Vehicle System Dynamics Software Based on Multibody Formalisms

Abstract: SUMMARY This paper pursues two objectives: Firstly, to review the state-of-the-art of general purpose vehicle system dynamics software and secondly, to describe two representatives, the program MEDYNA and the program NEWEUL. The general modeling requirements for vehicle dynamics software, the multibody system approach and a comparative discussion of multibody software are given. The two programs NEWEUL and MEDYNA are described with respect to modeling options, computational methods, software engineering as well as their interfaces to other software. The applicability of these programs is demonstrated on two selected examples, one from road vehicle problems and the other from wheel/rail dynamics. It is concluded that general purpose software based on multibody formalisms will play the same role for mechanical systems, especially vehicle systems, as finite element methods play for elastic structures.

On the design of a vehicle longitudinal controller

Abstract: A methodology for designing an automated vehicle longitudinal controller is presented and applied to an automobile characterized by velocity-dependent dynamics. The design consists of a cascade compensator, which is selected to achieve small tracking errors, and an observer/controller compensator. The controller portion was designed to achieve a velocity-invariant response, and the observer to derive the state-feedback signals. Both compensators were realized on an eight-bit microcomputer, and the vehicle dynamics were simulated on an analog computer. The performance of the resulting system was evaluated using a large-signal, entry merging command and small-signal mainline commands. Excellent results were obtained with typical values being a maximum position error of 0.63 m during an entry maneuver and 0.15 m during a mainline maneuver; however, the designed system was sensitive to large changes in critical vehicle parameters. Thus, there is a need to modify the controller so that it can adaptively compensate for such changes. Then, the designed digital controller, with its flexibility to perform other functions and its ease of reliability enhancement, is an attractive candidate for implementation, and at the very least, indicates the type of longitudinal performance one can expect from a realistically designed controller over the speed range 0-30 m/s.

Heavy vehicle design parameters and dynamic pavement loading

Abstract: This paper presents preliminary results from ARRB project 387: "Whole Vehicle Dynamics Affecting Dynamic Pavement Loading". The aims and modelling approach of the project are described. Comparisons between model predictions and experimental data are made, showing reasonable agreement. The effects of various parameter changes, such as centre of gravity location, distribution of sprung mass, speed, roughness scale, as well as suspension stiffness and damping, are investigated. The direction for future work in this project is outlined. Model predictions indicate that whole vehicle configuration has an important effect on the level of pavement loading. It is therefore concluded that pavement-protecting guidelines for vehicle suspension selection should have regard to overall vehicle configuration. The form of calculated speed-load relationships is complicated and variable between vehicles, which indicates that the pavement damaging effect of a particular vehicle should be assessed over a speed range rather than at just one or two speeds. It is predicted that the dynamic loading level of vehicles fitted with tandem suspensions which provide only poor damping of pitch motions will be high over certain speed ranges, but that these high levels will be significantly reduced when shock-absorbers are fitted between the chassis and axles. (Author/TRRL)

Dynamics modelling of a single-link flexible robot

Abstract: The dynamics modelling of a single-link flexible robot with a rigid mass attached to the tip is addressed The flexibility is represented by lateral bending motion of the robot link The model is obtained using a Newton-Euler formulation and the natural frequencies and mode shapes are obtained using a constrained mode approach The paper models the flexibility effects as an internal disturbance torque generated by lateral bending which affects the rigid body motion The model is suitable for control system analysis and synthesis A numerical example is presented for the purpose of illustrating the calculation of natural frequencies, mode shapes, and other modal parameters based on the model developed

Analysis and simulation of rail and road vehicles with the program medyna

Abstract: SUMMARY A computer general purpose program for the analysis and design of mechanical systems is presented. A brief description of the underlying theory and of the system analysis features is given. Two representative examples in the program's main application area, vehicle dynamics, are presented in order to demonstrate its capabilities. First, the derailment behaviour of three connected freight cars is studied. As a second example, a motor car with different vehicle parameters running across road irregularities is analysed.

Aerodynamics of Road- and Rail Vehicles

Abstract: SUMMARY The technical state-of-the-art of aerodynamics of ground transportation vehicles is reviewed. Currently available theoretical calculation methods and experimental simulation techniques as well as typical results illustrating the impact of aerodynamics on vehicle performance and running characteristics are summarized and the interactions between vehicle system dynamics and aerodynamics are adressed. Correlation of theoretical and experimental data show the present potential of vehicle aerodynamics and point to fields in which further research work is necessary.

The Control of Aerodynamic Parameters Influencing Vehicle Dynamics

Abstract: An analytical model is used to compare the influence of aerodynamic parameters on vehicle dynamics at high speeds (typically 180 km/h) to the influence of other important vehicle characteristics. Typical driving conditions considered are fast highway driving, braking, and driving in a cross wind. Some experimental results are presented in addition. The results show that a low overall lift level with a positive pitch moment is desirable for good handling characteristics. They also show that observed differences of the aerodynamic data on production cars are less influential on crosswind sensitivity compared with certain other vehicle characteristics, such as center of gravity position. The control of the important aerodynamic parameters influencing vehicle dynamics, such as lift and yaw-moment coefficients, is described in some detail. The behavior of these aerodynamic parameters for low-drag cars is also discussed.

Decomposition and State Variable Feedback Control of Elastic Robotic Systems

Abstract: Energy efficient, lightweight robot arms for space applications have considerable structural flexibility. We present in this paper an approach to control of a class of flexible robotic systems. A control law is derived which decouples the joint-angle motion from the flexible motion and, in addition, asymptotically decomposes the elastic dynamics into two subsystems. This allows the design of an elastic mode stabilizer independently based on lower order models representing structural flexibility. The closed-loop system is shown to be globally asymptotically stable and robust to uncertainty in system parameters. Simulation results show that the combination of nonlinear decoupling and elastic stabilization permits rapid, accurate tracking of large joint angle commands with well damped elastic response, in spite of space vehicle motion and payload uncertainty.

Demonstration of closed-loop trajectory control of an underwater vehicle

Abstract: The design of the closed-loop control system is a primary issue for any underwater vehicle that is not controlled manually. Precise control of all vehicle movements is particularly difficult due to the high-order, nonlinear, uncertain nature of the dynamics of underwater systems. A new control system design methodology called sliding control has been shown to deal with these difficult problems effectively. In this paper, the methodology is reviewed and results from in-water tests are described.

Effects of steering response characteristics on control performance of driver-vehicle system

Abstract: A series of closed-loop tests was conducted on a lateral motion simulator and a proving ground to find out how the driver's control performance would be affected by the steering response characteristics of the vehicle. In any existing automobile with a conventional front-wheel steering system, the yaw and lateral acceleration responses can hardly be separated from each other. During the tests, these two characteristics were set independently by using a special experimental vehicle that could steer both the front and rear wheels. This permitted us to examine separately what roles each of the two response characteristics plays in a driver-vehicle system.

Maneuverability constraints for supervisory steering control

Abstract: Real-time feedback algorithms proposed for supervisory steering control of robotic manipulators or autonomous vehicles are based on models of the system dynamics in the global coordinates of the workspace. On the other hand, the system dynamics and control limits are most easily specified in generalized coordinates directly related to the generalized degrees of freedom and torque/force inputs for the manipulator or vehicle. This paper concerns the mapping of the state and control variable constraints in the generalized coordinates into operating regions and acceleration limits in the global coordinates. The objective is to determine maneuverability constraints in the global frame which facilitate computationally tractable supervisory control algorithms while guaranteeing the feasibility of the desired controls. The paper defines the general steering control problem, describes a formal procedure for determining maneuverability constraints and discusses the application of the concepts to a two-degree-of-freedom manipulator. Several directions for future research are discussed in the concluding section.

Identification of pilot dynamics from in-flight tracking data

Abstract: Data from a representative flight task involving an F-14 'pursuer' aircraft tracking a T-38 'target' aircraft in a 3G wind-up turn and in level flight are processed using a least squares identification technique in an attempt to identify pilot/vehicle dynamics. Comparative identification results are provided by a Fourier coefficient method which requires a carefully designed and implemented input consisting of a sum of sinusoids. The least-squares results compare favorably with those obtained by the Fourier technique. An example of crossover frequency regression is discussed in the light of the conditions of one of the flight configurations.

The increase of cornering force and traction by a wheel-slip-control-system

Abstract: SUMMARY The present paper investigates some questions of safety in traffic especially vehicle dynamics under changing slippery and icy road conditions. Whereas the well introduced “Antilock-System” (ABS) is concerned with deceleration, an engine directed “Wheel-Slip-Control-System” (ASR) will increase the comfort and safety potential when accelerating. Measured and calculated results of such a system are compared to those of noncontrolled vehicles with different driveline concepts. As far as the here discussed cornering manoeuvres are concerned the active safety is comparable to that of a four wheel driven car.

The Effect of Structural Dynamics on the Strength and Behaviour of Road and Rail Vehicles

Abstract: Road and rail vehicles operate in such different ways that it is difficult to see how the same problems confront them. Road vehicles and in particular, their use in bad road or off the road condition leads to a design philosophy where all the effort has to be put into the vehicle. A rail vehicle can be regarded as part of a unified system where the design and maintenance effort put into the track can be traded against the design sophistication of the vehicle. It is surprising to find therefore in the paper, compiled separately from the two points of view, road and rail, that substantially the same problems have to be approached in a similar way to achieve satisfactory structural designs in both situations. One obvious difference is that the handling dynamics of the road vehicle depend almost entirely on the vehicle, and the limitations of structural stiffness that this necessitates is brought out in the paper. The rail vehicle, being guided, has no such limitations but in most cases it is designed with high structural stiffness, as are road vehicles, and both have to be checked for the vibrational behaviour of their structures which can cause unpleasant effects on passengers. The paper is divided into four sections, the behaviour and strength of road vehicles first and then for rail vehicles. (TRRL)

Wide bandwidth positioning systems for space and underwater vehicles

Abstract: This paper presents a method for wide bandwidth stiff position control of unmanned underwater and space vehicles. We start by arguing that the use of feedback alone may not provide an underwater or a space vehicle sufficient bandwidth with large stiffness. In other words with feedback alone the vehicle may not behave like a stiff platform in the presence of a wide frequency range of disturbances. Given this limitation, we suggest that the vehicle must be connected to environmental structures by means of cables or grabbers. These connecting cables will develop dynamic and kinematic constraints on the vehicle motion. This problem led us to develop a method that allows for control of the motion of constrained underwater or space vehicles. This method is called Impedance Control [1],[2],[3]. The frequency domain essentials of Impedance Control and a robust controller design method are given in reference [3]. We explain how, with the help of this method, a vehicle connected to a structure by means of cables can be positioned with high stiffness while at the same time the cable tensions are also under control.