Heavy truck deceleration rates as a function of brake adjustment

Abstract: Driver braking behavior was analyzed using time-series recordings from naturalistic rear-end conflicts (116 crashes and 241 near-crashes), including events with and without visual distraction among drivers of cars, heavy trucks, and buses. A simple piecewise linear model could be successfully fitted, per event, to the observed driver decelerations, allowing a detailed elucidation of when drivers initiated braking and how they controlled it. Most notably, it was found that, across vehicle types, driver braking behavior was strongly dependent on the urgency of the given rear-end scenario's kinematics, quantified in terms of visual looming of the lead vehicle on the driver's retina. In contrast with previous suggestions of brake reaction times (BRTs) of 1.5 s or more after onset of an unexpected hazard (e.g., brake light onset), it was found here that braking could be described as typically starting less than a second after the kinematic urgency reached certain threshold levels, with even faster reactions at higher urgencies. The rate at which drivers then increased their deceleration (towards a maximum) was also highly dependent on urgency. Probability distributions are provided that quantitatively capture these various patterns of kinematics-dependent behavioral response. Possible underlying mechanisms are suggested, including looming response thresholds and neural evidence accumulation. These accounts argue that a naturalistic braking response should not be thought of as a slow reaction to some single, researcher-defined "hazard onset", but instead as a relatively fast response to the visual looming cues that build up later on in the evolving traffic scenario.

Abstract: The safe operation of vehicles on roads depends, among other things, on a properly functioning brake system. Air brake systems are widely used in commercial vehicles such as trucks, tractor-trailers, and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate the foundation brakes mounted on the axles. In this paper, a model-based diagnostic system for air brakes is presented. This diagnostic system is based on a nonlinear model for predicting the pressure transients in the brake chamber that correlates the brake chamber pressure to the treadle valve (brake application valve) plunger displacement and the pressure of the air supplied to the brake system. Leaks and "out-of-adjustment" of push rods are two prominent defects that affect the performance of the air brake system. Diagnostic schemes that will monitor the brake system for these defects will be presented and corroborated with experimental data obtained from the brake testing facility

Abstract: Continuing research in brake condition monitoring for vehicles equipped with air brakes considers the feasibility of using air pressure data to determine brake stroke, a vital parameter in determining the effectiveness of the total braking system. Recent statistics show there is an alarming number of vehicles operating with brakes that are out of adjustment even with the introduction and requirement of automatic slack adjustment in 1994. The importance of brake stroke information is thus highlighted. To address this problem, a mathematical model of an air brake chamber is developed and used to investigate parameter sensitivity. A method capable of indirectly determining brake stroke by examining air pressure data is formulated and its effectiveness is proven through simulation and testing.

Abstract: This report describes the results of experimental evaluation of longitudinal control algorithms for commercial heavy vehicles (CHVs). Given the problem of delays in the fuel and brake actuators of automated CHVs, the researchers present improved modeling of air brakes for CHVs, and novel nonlinear algorithms for the longitudinal control of CHVs without intervehicle communication. The significance of these results in terms of Intelligent Transportation Systems (ITS) deployment is that one of the major obstacles to autonomous vehicle following for CHVs has now been removed The authors also point out that adaptive cruise control can now be implemented in CHVs that are not equipped with Electronic Brake Systems.

Abstract: This report focuses on the design of longitudinal control algorithms for commercial heavy vehicles (CHVs). The algorithms use nonlinear spacing policies, backstepping control design, and aggressive prediction schemes to deal with the presence of significant delays and saturations in the fuel and brake actuators. The algorithms can also deal with delays both in the presence and in the absence of intervehicle communication. A by-product on this research is the development of two software packages, Platoon-Builder and TruckVis, for simulation and animation of CHV platoons. Additionally, another important result of this project is a new simplified framework for evaluating the longitudinal string stability properties of platoons of automated vehicles.

Abstract: This volume consists of Appendices A through G which provide detailed vehicle information and test data that supports the technical report (Volume 1)

Abstract: A number of different types of heavy duty air braked vehicles including buses, trucks, truck tractors and trailers were tested to determine their stopping capability in straight line and turning maneuvers on various types of road surfaces including ice. In addition, the braking force distributions of the vehicles were experimentally determined, several different brake proportioning systems were evaluated and the effect of initial brake temperature on stopping capability was investigated. Results of the testing indicate that stable stopping capability is primarily determined by brake force distribution. If brake force distribution is close to the normal force distribution on the axles of a vehicle, its stopping capability will be optimum; however, if brake force distribution does not match normal force distribution, premature wheel lockup and loss of control will occur before the vehicle is able to achieve full utilization of the friction forces available at the tire/road interface. Brake force distribution on most heavy duty vehicles is fixed at a level that favors the loaded condition and therefore they do not perform as well in the empty condition. In addition, many heavy duty vehicles are "underbraked" on their front steering axles under all operating conditions and would benefit even in the loaded mode if front brake force level was increased. Devices that adjust braking distribution as a vehicle's load changes appear to provide very significant gains in braking performance not only in the straight line stopping situation but also in braking and turning maneuvers.