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Technical Paper

A Simulation Model for Vehicle Braking Systems Fitted with ABS

Most vehicles built today are fitted with anti-lock braking systems (ABS). Accurate simulation modeling of these vehicles during braking as well as combined braking and steering maneuvers thus requires the effects of the ABS to be included. Simplified, lump parameter models are not adequate for detailed, 3-dimensional vehicle simulations that include wheel spin dynamics. This is especially true for simulating complex crash avoidance maneuvers. This paper describes a new ABS model included in the HVE simulation environment. It is a general purpose model and is available for use by any HVE-compatible vehicle simulation model. The basic operational and control characteristics for a typical ABS system are first reviewed. Then, the specific ABS model and its options as implemented in the HVE simulation environment and employed by the SIMON vehicle simulation model are described. To validate the model, pressure cycles produced by the model are compared with stated engineering requirements.
Technical Paper

Single Vehicle Wet Road Loss of Control; Effects of Tire Tread Depth and Placement

When an automobile is driven on wet roads, its tires must remove water from between the tread and road surfaces. It is well known that the ability of a tire to remove water depends heavily on tread depth, water depth and speed, as well as other factors, such as tire load, air pressure and tread design. It is less well known that tire tread depth combined with placement can have an adverse effect on vehicle handling on wet roads. This paper investigates passenger car handling on wet roads. Flat bed tire testing, three-dimensional computer simulation and skid pad experimental testing are used to determine how handling is affected by tire tread depth and front/rear position of low-tread-depth tires on the vehicle. Some skid pad test results are given, along with corresponding simulations. A literature review also is presented. Significant changes in tire-road longitudinal and lateral friction are shown to occur as speed, tread depth and water depth vary, even before hydroplaning occurs.
Technical Paper

Validation of DyMESH for Vehicle vs Barrier Collisions

A new three-dimensional collision simulation algorithm, called DyMESH (Dynamic MEchanical SHell) was recently introduced.[1]* This paper presents a validation of DyMESH for vehicle vs. barrier collisions. The derivation of the three-dimensional force vs. crush relationship was described previously.[1] Here the application of three-dimensional force vs. crush curves using the outlined methodology is shown to be effective. Nonlinear force versus crush relationships are introduced for use in DyMESH. Included are numerous DyMESH collision simulations of several types of vehicles (e.g., light and heavy passenger car and sport utility) compared directly with experimental collision test results from various types of barrier tests (e.g., full frontal, angled frontal, and offset frontal). The focus here is not on the vehicle’s change in velocity, but on the acceleration vs. time history.
Technical Paper

Integrating Design and Virtual Test Environments for Brake Component Design and Material Selection

A new, systematic approach to the design-evaluation-test product development cycle is described wherein the vehicle design and simulation environments are integrated. This methodology is applied to brake mechanical design and material selection. Time-domain computations within a vehicle dynamic simulation environment account for brake and lining geometry and material properties, actuator properties, and temperature effects. Two examples illustrate the utility of this approach by examining: the effect of varying hydraulic cylinder diameter on passing federally mandated stopping distance tests, and the effect of S-cam actuator adjustment on the performance of air brakes on a tractor-trailer. The simulation results are compared with experimental vehicle stopping distance tests to assess the validity of the simulations.
Technical Paper

An Overview of the EDSMAC4 Collision Simulation Model

The EDSMAC simulation model has been in widespread use by vehicle safety researchers since its introduction in 1985. Several papers have been published that describe the model and provide validations of its use. In 1997, the collision and vehicle dynamics models were extended significantly. The main control logic was also extended and generalized. The resulting model was named EDSMAC4. This paper describes the EDSMAC4 model with particular attention to the extensions to the original algorithms. The paper also provides a validation of the new model by direct comparison to staged collision experiments and the results from the previous EDSMAC model.
Technical Paper

An Overview of the Way EDCRASH Computes Delta-V

The two procedures, DAMAGE and OBLIQUE IMPACT, which are used by EDCRASH for computing delta-V, are described in detail. Enhancements in EDCRASH Version 4 which improve the DAMAGE method of computing delta-V are also described. The advantages and disadvantages of each method are explored, and the numerical and graphical output and use of warning messages are reviewed. In general, it was found the two methods are complimentary: The DAMAGE procedure is best-suited for the conditions in which the OBLIQUE IMPACT procedure is least-suited, and vice-versa.
Technical Paper

An Overview of the Way EDSMAC Computes Delta-V

The EDSMAC personal computer program for use by accident investigators is described. The input data requirements are reviewed. The general calculation procedures are discussed and the specific procedures for computing delta-V are explained in detail. The method, based on equalizing the force between the vehicles at all times during the impact phase, is seen to be simple in concept but extremely complex in practice. The numerical and graphical output and warning messages are reviewed. Applications of the program are illustrated. The major benefit of EDSMAC is the ability, using graphics, to provide an analytical method illustrating how an accident may, or may not, have occurred.
Technical Paper

Validation of the EDVSM 3-Dimensional Vehicle Simulator

EDVSM is a 3-dimensional vehicle simulator developed for the HVE simulation environment. The EDVSM vehicle model was based on the original HVOSM model, developed at Calspan for the Federal Highway Administration. This paper describes the vehicle and tire models used by EDVSM. The basic model is unchanged from the original HVOSM model, however, tire-road modeling has been substantially improved by the model's integration into the HVE environment. This paper provides the details of the integration procedure. The paper also includes a validation study, comparing results between EDVSM, HVOSM and real-world handling studies. Comparison reveals the results are substantially similar. Finally, applications and limitations of the model are addressed.
Technical Paper

An Overview of the HVE Developer's Toolkit

A substantial programming effort is required to develop a human or vehicle dynamics simulator. More than half of this effort is spent designing and programming the user interface (the means by which the user supplies program input and views program output). This paper describes a pre-programmed, 3-dimensional (3-D), input/output window-type interface which may be used by developers of human and vehicle dynamics programs. By using this interface, the task of input/output programming is reduced by approximately 50 percent, while simultaneously providing a more robust interface. This paper provides a conceptual overview of the interface, as well as specific details for writing human and vehicle dynamics programs which are compatible with the interface. Structures are provided for the human, vehicle and environment models. Structures are also provided for events, interface variables, and the output data stream.
Technical Paper

An Overview of the HVE Human Model

Developers of human dynamics simulation software inherently use a mathematical/physical model to represent the human. This paper describes a pre-programmed, object-oriented human model for use in human dynamics simulations. This human model is included as part of an integrated simulation environment, called HVE (Human-Vehicle-Environment), described in previous research. The current paper first provides a general overview of the HVE user and development environments, and then provides detailed specifications for the HVE Human Model. These specifications include definitions for model parameters (supported human types and human properties, such as dimensions, inertias, joints and injury tolerances). The paper also provides detailed specifications for the HVE time-dependent human output group parameters (kinematics, joints, contacts, belts and airbags).
Technical Paper

An Overview of the HVE Vehicle Model

Developers of vehicle dynamics simulation software inherently use a mathematical/physical model to represent the vehicle. This paper describes a pre-programmed, object-oriented vehicle model for use in vehicle dynamics simulations. This vehicle model is included as part of an integrated simulation environment, called HVE (Human-Vehicle-Environment), described in previous research [1,2] *. The current paper first provides a general overview of the HVE user and development environments, and then provides detailed specifications for the HVE Vehicle Model. These specifications include definitions for model parameters (supported vehicle types; vehicle properties, such as dimensions, inertias, suspensions; tire properties, such as dimensions and inertias, mu vs slip, cornering and camber stiffnesses; driver control systems, such as engine, transmission/differential, brakes and steering; restraint systems, such as belts and airbags).
Technical Paper

Truck Brake Failure: Differences between Failure Modes for Drum and Disc Brakes

On-highway heavy trucks are fitted with air disc brakes with increasing frequency. Disc brakes and traditional air drum brakes have different adjustment and heat dissipation characteristics. These differences lead to different failure modes when overheated. This paper describes how adjustment and other in-use factors affect the general braking capability of on-highway trucks fitted with disc and drum brakes. Simulations of a loaded tractor-trailer on a long, down-hill grade are used to predict brake temperature increase over time, and how that temperature increase can result in a runaway condition. The tractor and trailer are modeled with both traditional drum brakes and new disc brakes to illustrate operational differences between the two brake types.
Technical Paper

Development of a 12-NodeThermodynamic Simulation Model of a Disc Brake Assembly

Overheated brakes on a heavy truck can lead to a loss of braking and subsequent crash. This typically occurs after prolonged braking on a downhill grade. The problem is often accompanied by improper brake adjustment, causing one or more of the actuators to reach the end of travel due to thermal expansion. Reconstruction of this type of crash requires the consideration of overheated wheel brake assemblies. A thermodynamic model of a drum-type foundation brake is included in the HVE simulation environment and has been used successfully to study this phenomenon. However, newer on-highway trucks are often fitted with disc brakes. A similar thermodynamic model for a heavy truck disc brake does not exist, making the problem described above difficult to address. This paper describes a new thermodynamic model of a disc foundation brake, such as those often fitted on newer heavy trucks.
Technical Paper

3-Dimensional Simulation of Vehicle Response to Tire Blow-outs

Sudden tire deflation, or blow-out, is sometimes cited as the cause of a crash. Safety researchers have previously attempted to study the loss of vehicle control resulting from a blow-out with some success using computer simulation. However, the simplified models used in these studies did little to expose the true transient nature of the handling problem created by a blown tire. New developments in vehicle simulation technology have made possible the detailed analysis of transient vehicle behavior during and after a blow-out. This paper presents the results of an experimental blow-out study with a comparison to computer simulations. In the experiments, a vehicle was driven under steady state conditions and a blow-out was induced at the right rear tire. Various driver steering and braking inputs were attempted, and the vehicle response was recorded. These events were then simulated using EDVSM. A comparison between experimental and simulated results is presented.