Showing papers on "Vehicle dynamics published in 1979"

Automated vehicle guidance using discrete reference markers

Abstract: Techniques for providing steering control for an automated vehicle using discrete reference markers fixed to the road surface are investigated analytically. Either optical or magnetic approaches can be used for the sensor, which generates a measurement of the lateral offset of the vehicle path at each marker to form the basic data for steering control. Possible mechanizations of sensor and controller are outlined. Techniques for handling certain anomalous conditions, such as a missing marker, or loss of acquisition, and special maneuvers, such as u-turns and switching, are briefly discussed. A general analysis of the vehicle dynamics and the discrete control system is presented using the state variable formulation. Noise in both the sensor measurement and in the steering servo are accounted for. An optimal controller is simulated on a general purpose computer, and the resulting plots of vehicle path are presented. Parameters representing a small multipassenger tram were selected, and the simulation runs show response to an erroneous sensor measurement and acquisition following large initial path errors.

Dynamic performance of automated guideway transit vehicles with dual-axle steering

Abstract: The lateral dynamic performance of automatically guided dual and single steered axle vehicles is determined using a three-degree-of-freedom nonlinear model. Vehicle acceleration levels and tracking errors are determined for performance during curve entry, station entry, and on straight but randomly irregular guideway references. Independent dual-axle controllers, yaw dual-axle controllers, and zero-sideslip dual-axle controllers are studied in detail. Configurations for dual-axle controllers are developed, which have reduced tracking errors and either comparable or reduced acceleration levels in comparison to single-steered axle vehicles for curve and station entry maneuvers.

"Safe-approach" vehicle-follower control

Abstract: A "safe-approach" control policy is presented, which simultaneously handles close-headway vehicle following and various maneuver situations. The policy is illustrated with an example controller design and simulation evaluation.

Model-follower longitudinal control for automated guideway transit vehicles

Abstract: An approach for the design of longitudinal control systems for automated transit vehicles using the vehicle-follower control concept is presented. It is shown that the spacing policy selected for system operations generates a dynamic model for ideal vehicle response during station keeping. The longitudinal control system should force the actual vehicle response to be as close to this model response as possible. Two model-following controller designs are discussed. In one design the command from the controller is acceleration, and in the other design the command from the controller is jerk. The acceleration- and jerk-limited dynamic response of both controllers is examined by the use of describing functions and by computer simulations.

Nonlinear Analysis of Rail Vehicle Forced Lateral Response and Stability

Abstract: The method of statistical linearization is presented as a design tool for rail vehicles that is capable of including fundamental nonlinearities such as wheel profile geometry and suspension nonlinearities. The method is capable of predicting the response of the vehicle to statistical track irregularities as well as the onset of hunting. The fundamentals of the method, and efficient frequency domain numerical algorithm for stationary response, and a design example are presented. The design example illustrates the influence of wheel profile, gage, track roughness, and suspension variations on vehicle response and stability.

Vortex-Induced Asymmetric Loads on Slender Vehicles.

Abstract: : The steady and unsteady vortex-induced asymmetric loads on slender vehicles were investigated. The study reviewed pertinent two- and three-dimensional data; developed analytic means for predicting the upper limit for vortex-induced asymmetric loads; and assessed the importance of these loads to the vehicle dynamics of slender bodies of revolution. The study showed boundary layer transition to have a dominant influence on static and dynamic vortex-induced loads. The predicted upper limit for vortex-induced asymmetric loads bounds all available experimental data from subcritical to supercritical Reynolds numbers. The most powerful dynamic effect is that of the moving wall at the separation point, which has a wall-jet-like effect on the boundary layer separation and transition. Preliminary experimental results indicate that because of this effect the dynamic stability parameters due to pitching and coning can be one order of magnitude larger than those occurring in attached flow at lower angles-of-attack. A very important effect of asymmetric vortices existing at high angles-of-attack is to provide a coupling mechanism at zero sideslip between longitudinal and lateral degrees of freedom. As these cross coupling effects are very large, highly nonlinear, often discontinuous and associated with hysteresis effects, with especially large impact on the vehicle dynamics, they are of great concern to missile and aircraft designers.

A structural model of the adaptive human pilot

Abstract: A compensatory tracking model of the human pilot is offered which attempts to provide a more realistic representation of the human's signal processing structure than that which is exhibited by pilot models currently in use. Two features of the model distinguish it from other representations of the human pilot. First, proprioceptive information from the control stick or manipulator constitutes one of the major feedback paths in the model, providing feedback of vehicle output rate due to control activity. Implicit in this feedback loop is a model of the vehicle dynamics which is valid in and beyond the region of crossover. Second, error-rate information is continuously derived and independently but intermittently controlled. An output injected remnant model is offered and qualitatively justified on the basis of providing a measure of the effect of inaccuracies such as time variations in the pilot's internal model of the controlled element dynamics. The data from experimental tracking tasks involving five different controlled element dynamics and one nonideal viewing condition were matched with model generated describing functions and remnant power spectral densities.

Attitude Stability of a Pseudorate Jet-Controlled Flexible Spacecraft

Abstract: The small-angle stability of a single-axis spacecraft attitude control system incorporating a nonlinear pseudorate controller, jet actuator, flexible vehicle dynamics, and a loop time delay is analyzed. The dynamics include a low-frequency rigid vehicle mode and a highly underdamped flexible mode that has its modal frequency outside the rigid vehicle control system bandwidth. The single input sinusoidal describing function for the pseudorate controller is derived and used to determine the effect of the controller on each mode individually. A stable limit cycle for the rigid vehicle mode response is predicted. The flexible mode response is predicted to be stable, unstable, or to exhibit a stable limit cycle, depending on the loop time delay and the flexible mode frequency and damping. Simulation results verify the integrity and interpretation of analytically predicted stability conditions.

Automated control of guideway transit vehicles

Abstract: The control of vehicles for ground transport is an important element of automated people mover systems. An overview of the system control structure is presented, and attention is focused on individual vehicle longitudinal and lateral control. A longitudinal and lateral control system which utilizes a fixed guideway reference system has been designed, tested, and developed. The fixed guideway reference system is comprised of guideway-mounted measurement markers and an inductive communication link which provides the means for vehicle state error measurement and control. Vehicle status information and longitudinal commands are transmitted to/from the wayside via the inductive link. In addition, measurements of the electromagnetic field surrounding the communication link are used to obtain estimates of vehicle lateral position error with respect to a prescribed path. These vehicle state error measurements are processed by an on-board vehicle computer, and the proper longitudinal and lateral control commands are generated and applied to the appropriate control equipment to effect the necessary longitudinal and lateral control responses. Preliminary conclusions from this on-going study are as follows: 1. Using the approach described, specific vehicle dynamics data can be used to provide a good estimate of potential wire following lateral control performance. 2. Lateral paths requiring vehicle yaw acceleration provide the most severe input to a wire-following vehicle. 3. Good longitudinal control accuracy and ride comfort are inversely related. Although analytical predictions of longitudinal control accuracy are useful, final control parameter value selection requires actual hardware testing to select a level of accuracy consistent with ride comfort requirements.

Programmable digital vehicle control system

Abstract: The programmable digital vehicle control system or PDVCS is based upon the Intel 8080A microprocessor and is designed to replace the hardwired discrete components traditionally used in the on-board control of automated rapid transit vehicles. Although designed specifically for the advanced group rapid transit (AGRT) system under development by the Boeing Company, with funding by the Department of Transportation, the PDVCS can easily be adapted for use in any automated transit system. A breadboard PDVCS has been programmed to perform the basic AGRT longitudinal control system functions, including closed-loop emergency braking, and has been subjected to closed-loop laboratory testing. Prototype tachometers and a seventh-order nonlinear analog computer simulation of motor, brake, and vehicle dynamics were used to close the control loop for test purposes; command scenarios were input manually. The test results demonstrate the feasibility of microcomputers in on-board vehicle control and show their capability to meet the performance requirements associated with a short headway (3 s) system.

Vehicle-guideway interaction problems

Abstract: This article discusses three general methods for studying vehicle-guideway interaction problems: the moving force approximation, the massless guideway approximation, and the moving approximation. The trolley problem at the Sandia Laboratories, which falls in the category of a moving mass problem is also summarized.

Moped Directional Dynamics and Handling Qualities

Abstract: Analytical results describing moped lateral-directional response properties are presented. Design characteristics of four example mopeds related to directional handling are presented and compared with sample motorcycle properties. Resultant moped dynamics are quantified and compared. Using a nominal moped example, the sensitivity of the vehicle dynamics to operations and design variables, such as speed, loading and tire properties, is shown. Implications for rider/moped handling are reviewed.

The influence of vehicle aerodynamic and control response characteristics on driver-vehicle performance

Abstract: The effects of changes in understeer, control sensitivity, and location of the lateral aerodynamic center of pressure (c.p.) of a typical passenger car on the driver's opinion and on the performance of the driver-vehicle system were studied in a moving-base driving simulator. Twelve subjects with no prior experience on the simulator and no special driving skills performed regulation tasks in the presence of both random and step wind gusts.

Bus roll over accident simulation

Abstract: The paper describes the theoretical simulation of roll over accidents. A brief account of the findings of accident investigation into bus roll overs is given. This shows that most actual rolls occur with lateral vehicle motion. The simulation starts with a vehicle dynamics program which reconstructs manoeuvres necessary to simulated until the structure impacts the ground plane. When the roof structure impacts the ground a structural collapse program (CRASHD) is used to obtain the deformation history of the vehicle structure.

Influence of Antiskid Systems on Vehicle Directional Dynamics

Abstract: The results presented demonstrate the influence of longitudinal tire slip and load transfer during braking on steering behavior of cars in terms of parameters which have been found to be important for the function of the driver/vehicle control loop. This is followed by a description of an antiskid system and a comparison of directional properties during braking with conventional brake system and with antiskid. The importance of appropriate selection of slip levels during adaptation of antiskid systems to a given vehicle is pointed out.

Development of the N-Type Runflat Tire and Its Evaluation in Vehicle Dynamics

Abstract: Judging from the viewpoint of automotive safety and more space by eliminating a spare tire, the development of the run-flat tires is important. Many problems relating to weight increase and usability had to be solved in the course of the development of such tires. The "N" type run-flat tire, described in this paper, has a simple structure with reinforced side walls and additional beads to fit the rim flanges. Though this tire system brought about a small amount of weight increase, it needs no special part, therefore the conventional road wheels, air valves and tire changers may be used. Passenger cars equipped with these tires have been tested, with particular attention being paid to vehicle dynamics, such as steering and stability. It appears that such tires are safe even for driving on expressways when they are flat.