Ashley L. Dunn

New Model for Simulating the Dynamics of Pneumatic Heavy Truck Brakes with Integrated Anti-Lock Control

This paper introduces a new nonlinear model for simulating the dynamics of pneumatic-over-mechanical commercial vehicle braking systems. The model employs an effective systems approach to accurately reproduce forcing functions experienced at the hubs of heavy commercial vehicles under braking. The model, which includes an on-off type ABS controller, was developed to accurately simulate the steer, drive, and trailer axle drum (or disc) brakes on modern heavy commercial vehicles. This model includes parameters for the pneumatic brake control and operating systems, a 4s/4m (four sensor, four modulator) ABS controller for the tractor, and a 2s/2m ABS controller for the trailer. The dynamics of the pneumatic control (treadle system) are also modeled. Finally, simulation results are compared to experimental data for a variety of conditions.

In-Depth Analysis of the Influence of High Torque Brakes on the Jackknife Stability of Heavy Trucks

Published NHTSA rulemaking plans propose significant reduction in the maximum stopping distance for loaded Class-VIII commercial vehicles. To attain that goal, higher torque brakes, such as air disc brakes, will appear onprime movers long before the trailer market sees significant penetration. Electronic control of the brakes on prime movers should also be expected due to their ability to significantly shorten stopping distances. The influence upon jackknife stability of having higher performance brakes on the prime mover, while keeping traditional pneumatically controlled s-cam drum brakes on the trailer, is discussed in this paper. A hybrid vehicle dynamics model was applied to investigate the jackknife stability of tractor-semitrailer rigs under several combinations of load, speed, surface coefficient, and ABS functionality. These simulations were run to simulate brake-in-turn (B.I.T.) scenarios for a tractor-semitrailer articulated vehicle which is near the maximum drive-through speed limit for various vehicle weight / surface coefficient conditions. ECBS-disc brake equipped tractors were directly compared to those having s-cam drum brakes. This study shows that the simulated presence of ECBS-disc brakes on the tractor results in no degradation of the performance of the rig, in terms of jackknife stability, while braking in a turn. Furthermore, the elaborate vehicle simulations showed significant reduction in the tractor maximum yaw rate and hitch articulation angle seen during the simulation, for those simulated vehicles equipped with disc brakes and electronically controlled braking systems (ECBS).

Brake Timing Measurements for a Tractor-Semitrailer Under Emergency Braking

The timing and associated levels of braking between initial brake pedal application and actual maximum braking at the wheels for a tractor-semitrailer are important parameters in understanding vehicle performance and response. This paper presents detailed brake timing information obtained from full scale instrumented testing of a tractor-semitrailer under various conditions of load and speed. Brake timing at steer, drive and semitrailer brake positions is analyzed for each of the tested conditions. The study further seeks to compare the full scale test data to predicted response from detailed heavy truck computer vehicle dynamics simulation models available in commercial software packages in order to validate the model’s brake timing parameters. The brake timing data was collected during several days of full scale instrumented testing of a tractor-semitrailer performed at the Transportation Research Center, in East Liberty, Ohio. Instrumented braking tests were performed at two speeds of 13.4 m/s (30 mph) and 27 m/s (60 mph) for 4 configurations including a bobtail condition, an unloaded semitrailer configuration, a half loaded semitrailer condition and a full gross vehicle weight condition. These straight-line braking tests were performed on dry concrete surfaces. In addition, brakein-turn tests and stopping tests were performed on a wet jennite surface to evaluate the vehicle response and handling for ABS and non-ABS configurations The effects of test conditions on brake timing are analyzed and are presented in this paper. The various braking configurations were simulated using detailed test parameters including brake system parameters at each wheel. Simulated vehicle kinematics were then validated against the full-scale test results and the simulation process and choices are discussed. Brake lag (delay) times and first-order model time constants are offered and discussed. The findings of this study are also compared to other testing and simulation results published in literature on this topic. INTRODUCTION Brake timing for tractor-semitrailer vehicles has been evaluated in a limited fashion in past literature aimed at either accident reconstruction or modeling using computer vehicle dynamics simulation models. In the reconstruction field, brake timing is usually identified as brake lag, or the time required for the air brakes to become fully applied. Although recognizing that wheel location has an impact on the buildup of pressure at a given axle, reconstruction analysis is usually simplified by assigning a single number meant to account for the necessary delay in obtaining full braking at all wheels. Computer simulation models on the other hand provide the ability to model braking parameters more extensively but present the opposite problem of requiring many parameters. The authors of this research wanted to offer additional and contemporary data of a real world vehicle in addition to the data already available in the public domain. The data are analyzed to provide the basis of both a simplified calculation and a more complex computer simulated analysis of tractor-semitrailer stopping performance.

Derivation and Validation of New Analytical Planar Models for Simulating Multi-Axle Articulated Vehicles

This paper discusses the derivation and validation of planar models of articulated vehicles that were developed to analyze jackknife stability on low-μ surfaces. The equations of motion are rigorously derived using Lagranges method, then linearized for use in state-space models. The models are verified using TruckSim, a popular nonlinear solid body vehicle dynamics modeling package. The TruckSim models were previously verified using extensive on-vehicle experimental data [1, 2]. A three-axle articulated model is expanded to contain five axles to avoid lumping the parameters for the drive and semitrailer tandems. Compromises inherent in using the linearized models are discussed and evaluated.

Empirical Models for Commercial Vehicle Brake Torque from Experimental Data

This paper introduces a new series of empirical mathematical models developed to characterize brake torque generation of pneumatically actuated Class-8 vehicle brakes. The brake torque models, presented as functions of brake chamber pressure and application speed, accurately simulate steer axle, drive axle, and trailer tandem brakes, as well as air disc brakes (ADB). The contemporary data that support this research were collected using an industry standard inertia-type brake dynamometer, routinely used for verification of FMVSS 121 commercial vehicle brake standards.

Braking of commercial vehicles equipped with air-disc brakes from high speed - effects on stopping distance

Due to increased speed limits at the state level, NHTSA has pursued additional testing of heavy trucks at higher test maneuver entry speeds. Test results from three vehicles, a Class 7 school bus, a Class 8 truck tractor and a Class 8 straight-truck are presented here. Results are discussed for full treadle straight-ahead stops from 60, 70 and 75 mph. Each vehicle was tested with two different brake configurations. As expected, higher entry speeds resulted in increased stopping distances. Causes for increased stopping distances are briefly discussed. Comparisons show that vehicles in the hybrid configuration (air-disc brakes on steer axle and S-cam brakes on drive axle(s)) had superior stopping performance to the vehicles equipped with traditional S-cam brakes. The vehicles in the hybrid configuration were less susceptible to increased stopping distances from higher entry speeds. A linear regression of stopping distance versus speed reinforced the benefit of placing air-disc brakes on the vehicles. In terms of reduced deceleration levels, only the S-cam configured vehicles at LLVW were adversely affected due to increased entry speeds, whereas at GVWR both S-cam and hybrid configurations were. The truck tractor, when equipped with all S-cam brakes, consistently performed the worst of the three vehicles. Finally, it was demonstrated that the vehicles exhibited an increase, not a decrease, in braking performance throughout the stop.

The Development of a Heavy Truck ABS Model

This paper discusses the improvement of a heavy truck anti-lock brake system (ABS) model currently used by the National Highway Traffic Safety Administration (NHTSA) in conjunction with multibody vehicle dynamics software. Accurate modeling of this complex system is paramount in predicting real-world dynamics, and significant improvements in model accuracy are now possible due to recent access to ABS system data during on-track experimental testing. This paper focuses on improving an existing ABS model to accurately simulate braking under limit braking maneuvers on high and low-coefficient surfaces. To accomplish this, an ABS controller model with slip ratio and wheel acceleration thresholds was developed to handle these scenarios. The model was verified through testing of a Class VIII 6x4 straight truck. The Simulink brake system and ABS model both run simultaneously with TruckSim, with the initialization and results being acquired through Matlab. This paper provides a description of the ABS controller and TruckSim vehicle models, an analysis of the field test data, and a comparison of the simulation and field test results.

Application of the Extended Kalman Filter to a Planar Vehicle Model to Predict the Onset of Jackknife Instability

The widely used Extended Kalman Filter (EKF) is applied to a planar model of an articulated vehicle to predict jackknifing events. The states of hitch angle and hitch angle rate are estimated using a vehicle model and the available or measured states of lateral acceleration and yaw rate from the prime mover. Tuning, performance, and compromises for the EKF in this application are discussed. This application of the EKF is effective in predicting the onset of instability for an articulated vehicle under low-μ and low-load conditions. These conditions have been shown to be most likely to render heavy articulated vehicles vulnerable to jackknife instability. Options for model refinements are also presented.

Vehicle Handling and Control Following Front Ball Joint Failure

This paper describes how, following many accidents, one of the vehicles involved is found with partial or total separation of one of its wheels. In many such cases, forensic evidence on the wheel, and/or on some surface struck by the wheel, provide direct evidence that the wheel separation resulted from the impact. However, in some cases such direct evidence is not as obvious or cannot be identified. In those cases, it is often asserted that before the accident occurred one of the involved vehicles might have undergone a sudden loss of control as a result of a spontaneous partial or total wheel separation. This paper examines the response of rear wheel drive vehicles when there is a failure involving a ball joint on the front suspension as the vehicle is traveling along a roadway. The design of the front suspension is analyzed to determine the expected effects of such failure on the wheel geometry and on the interaction between the tires and the pavement. Next some case studies of accidents involving wheel loss are examined. Finally, the results of a series of tests are discussed in which ball joint failures are caused to occur as the vehicle is being driven. The effect of these failures on vehicle handling and control is described and compared with the predictions from the design analysis. Finally, the physical evidence left on the vehicle and roadway by the failures is described.

The Effects of Foundation Brake Configuration on Class-8 Tractor Dry Stopping Performance

This study compares dry stopping performance of various foundation brake systems on Class VIII truck tractors. Four configurations of foundation brakes were fitted to two modern 6x4 conventional truck tractors without modification to the control, application or antilock brake systems. The foundation brake configurations included: standard S-cam drum brakes on all six positions, high output S-cam drum and then air disc brakes on the steer axles, and air disc brakes on all six brake positions. The stopping distances from 60 mph were analyzed for all test conditions. The truck tractors were tested in two weight configurations: LLVW (i.e., bobtail) and GVWR (50,000 lb total axle weight) using an unbraked control semitrailer. Analysis of variance tests indicate statistically different stopping distance means between all foundation brake configurations, whether the results for both weight configurations were combined or analyzed separately. Combining the results for both tractors, an all disc brake configuration could yield a 20% improvement in stopping distance at GVWR over the standard all S-cam brake configuration on dry pavement, and a 16% improvement at LLVW. With hybrid disc brakes, the improvements were 12% for GVWR and 19% for LLVW. For hybrid drum brakes, the improvements were 10% for both GVWR and LLVW. Margins of compliance for the minimum stopping distances (versus a 30% reduction in current standards) are shown for each brake configuration.