Charles C. MacAdam

Understanding and Modeling the Human Driver

Summary This paper examines the role of the human driver as the primary control element within the traditional driver-vehicle system. Lateral and longitudinal control tasks such as path-following, obstacle avoidance, and headway control are examples of steering and braking activities performed by the human driver. Physical limitations as well as various attributes that make the human driver unique and help to characterize human control behavior are described. Example driver models containing such traits and that are commonly used to predict the performance of the combined driver-vehicle system in lateral and longitudinal control tasks are identified.

Measurement and Representation of the Mechanical Properties of Truck Leaf Springs

The force-vs.-deflection characteristics of truck leaf springs were investigated with respect to the influences of stroking frequency and amplitude and nominal static load on hysteretic damping and effective spring rate. Measurements were made on five currently employed leaf springs at five stroking frequencies (0.5 to 15.0 Hz) for three stroking amplitudes at two static loads. Test results indicate that the stroking frequency over the studied range has no influence on the spring rate and energy dissipation properties of truck leaf springs. Truck leaf springs are highly nonlinear devices for which the average damping force in a stroking cycle increases directly with either the stroking amplitude or nominal static load, and the effective spring rate decreases inversely with the stroking amplitude or directly with the static load. A mathematical method is presented which represents the force-vs.-deflection characteristics of truck leaf springs in a form suitable for use in the simulation (digital calculations) of vehicle dynamics.

APPLICATION OF ELEMENTARY NEURAL NETWORKS AND PREVIEW SENSORS FOR REPRESENTING DRIVER STEERING CONTROL BEHAVIOUR

SUMMARY This paper demonstrates the use of elementary neural networks for modelling and representing driver steering behaviour in path regulation control tasks. Areas of application include uses by vehicle simulation experts who need to model and represent specific instances of driver steeringcontrol behaviour, potential on-board vehicle technologies aimed at representing and tracking driver steering control behaviour over time, and use by human factors specialists interested in representing or classifying specific families of driver steering behaviour. Example applications are shown for data obtained from a driver/vehicle numerical simulation, a basic driving simulator, and an experimental on-road test vehicle equipped with a camera and sensor processing system.

Crosswind Sensitivity of Passenger Cars and the Influence of Chassis and Aerodynamic Properties on Driver Preferences

SUMMARY Results of vehicle crosswind research involving both full-scale driver-vehicle tests and associated analyses are presented. The paper focuses on experimental crosswind testing of several different vehicle configurations and a group of seven drivers. A test procedure, which utilized wind-generating fans arranged in alternating directions to provide a crosswind “gauntlet”, is introduced and described. Driver preferences for certain basic chassis and aerodynamic properties are demonstrated and linked to elementary system responses measured during the crosswind gauntlet tests. Based on these experimental findings and confirming analytical results, a two-stage vehicle design process is then recommended for predicting and analyzing the crosswind sensitivity of a particular vehicle or new design.

USING NEURAL NETWORKS TO IDENTIFY DRIVING STYLE AND HEADWAY CONTROL BEHAVIOR OF DRIVERS

SUMMARY This paper illustrates the use of neural network techniques for analyzing headway data collected from a group of 36 driving subjects during normal on-highway driving. Pattern recognition methods are used to identify different types of headway-keeping behavior exhibited by these drivers and their relative distributions. Possibilities for using neural networks to represent longitudinal control behavior of drivers are also considered and discussed.

Static Turning Analysis of Vehicles Subject to Externally Applied Forces - A Moment Arm Ratio Formulation

SUMMARY A formulation for representing the static turning response of a two-axle vehicle due to applied external or control forces is expressed in terms of a simple ratio of two distances along the vehicle longitudinal axis. The two distancescoincide with points on the vehicle at which externally applied/ control forces and their reactive inertial forces act with respect to the vehicle neutral steer point. The resulting formulation is equivalent to the rotational equilibrium equation written with respect to the neutral steer point. The method allows a simple “visual analysis” of the steady turning process by showing how key forces and associated moment arms can change with respect to one another due to vehicle modifications or different operatingconditions, thereby affecting the static turning response of the vehicle.

Tests Characterizing Performance of an Adaptive Cruise Control System

This paper describes methods for characterizing the headway control performance of adaptive cruise control (ACC) systems. The inputs to the test are the speed of the preceding vehicle. Results of the tests are based upon measurements of range, range rate, velocity transmission shift commands,, and velocity commands. Numerical performance measures are derived from these data and are used to characterize system performance quantitatively.

A Computer-Based Study of the Yaw/Roll Stability of Heavy Trucks Characterized by High Centers of Gravity.

A class of heavy truck vehicles, characterized primarily by high centers of gravity, was studied using analysis and computer simulation to identify and understand the relationship between directional and roll stability of such vehicles during steady turning maneuvers. Findings of the computer based study suggest: (1) directional instability (yaw divergence) is possible for such vehicles during steady turning while operating at elevated speeds on horizontal road surfaces, (2) yaw divergence will lead to rollover in the absence of corrective steering action and/ or reduced speed, and (3) the primary mechanism responsible for precipitating yaw divergent behavior in such vehicles is the non linear sensitivity of truck tire cornering stiffness to vertical load acting in combination with typical heavy truck fore/ aft roll stiffness distributions. In addition, the influences of roadway superelevation and driver steering control as contributors to vehicle stabilization are examined and discussed (a).

A STUDY OF THE CLOSED-LOOP DIRECTIONAL STABILITY OF VARIOUS COMMERCIAL VEHICLE CONFIGURATIONS

SUMMARY Computer analysis of the closed-loop directional stability of four common commercial vehicle configurations was performed using 1) a disturbance input technique to study low lateral acceleration driving conditions, and 2) a lane-change maneuver for studying system response at elevated lateral acceleration conditions. The results of the disturbance input calculations indicated, that under low lateral acceleration conditions, drivers of different commercial vehicle configurations should be capable of providing adequate control compensation to achieve more or less equal stability margins for most systems. Evaluation of directional stability, based upon the transient lane-change maneuver, indicated systematic reduction in system damping for all vehicles with Increased levels of lateral acceleration. The 5-axle tractor-semitrailer system exhibited the greatest level of directional damping and rollover immunity during the lane-change maneuver. The truck full-trailer was the least damped system while als...

A simple differential brake control algorithm for attenuating rearward amplification in doubles and triples combination vehicles

SUMMARY A simple brake control algorithm useful for attenuating rearward amplification tendencies in doubles and triples combination trucks is described. The basic goal was to first design, and then to demonstrate through experimental testing, an automatic brake control system that could intervene—only when needed—to help suppress unwanted trailer yaw oscillations (commonly referred to as ‘rearward amplification’) in large combination vehicles (typically doubles and triples combinations in the U.S.). The system would only be enabled for highway speed operating conditions, and if possible, so simple that the system could be provided on a trailer-by-trailer basis. That is, the proposed system, when implemented on a particular trailer within a combination vehicle train, would not have to depend upon sensor information from units ahead of it or behind it in order to function properly and yet provide significant benefit. The primary focus therefore of this work was on the development and demonstration of a so-called “trailer-only” RAMS (Rearward A mplification Suppression) system [1].