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Dynamically-distinct precrash scenarios in rear-end collisions were identified in a recent study conducted by the Volpe National Transportation Systems Center, of the United States Department of Transportation, Research and Special Programs Administration, in conjunction with the National Highway Traffic Safety Administration (NHTSA) using NHTSA's General Estimates System (GES) crash database from 1992 through 1996. Precrash scenarios represent vehicle dynamics immediately prior to a collision. This paper provides a statistical description of the five most frequently-occurring rear-end precrash scenarios in terms of vehicle and driver characteristics, using the 1996 GES database.

Veridian, Calspan Operations is currently developing an on-vehicle threat detection system for intersection collision avoidance (ICA) as part of its ICA program with the National Highway Traffic Safety Administration. This paper briefly reviews the system design and describes recent efforts that include the development of a multi-radar collision avoidance (C/A) system. Results from in-traffic experiments utilizing two radars to simultaneously observe crossroads traffic from both directions will be presented for the first time. Warning functions were applied to the data in real time and for non-real-time signal processing. These functions warn the ICA vehicle against entering the intersection when targets are predicted to be present. This research demonstrates the feasibility of preventing many intersection collisions.

This paper summarizes the activities and results of a preliminary human factors review for the Intelligent Vehicle Initiative (IVI) Program. The objective of the project was to identify human factors work that needs to be done early in the life cycle of the IVI program to ensure safe and well-engineered vehicles. This project was comprised of two major subtasks. Subtask 1 provided for a “Preliminary IVI Human Factors Technology Workshop” to draw together the stakeholders in the IVI program and define the technologies and the human factors issues that should be considered in developing an IVI. Subtask 2 investigated the preliminary infrastructure and human factors in-vehicle requirements for alternative candidate configurations of an IVI.

The unsteady near wake of a ground vehicle body was investigated using hot wire anemometry and an unsteady pressure measurement system. A three dimensional bluff body model was used to simulate the time dependent, three dimensional near wake flow field generated by trucks, buses, and automobiles. Coherence and coherence phase were effective methods to analyze the unsteady pressure field and to relate different pressure signals. Spectral analysis of the velocity and pressure signals was used to identify periodic wake flow structures. The time averaged near wake contains a ring vortex enclosed by shear layers which start where the model boundary layer separates from the body. At the start of the shear layer, vortex shedding was measured at a dimensionless frequency, StH(shed) = 1.157. As these vortices convected along the shear layer, vortex pairing was observed which approximately halves the characteristic frequency.

Avoiding low-frequency pressure pulsations and establishing a good axial static pressure distribution are primary concerns for open jet wind tunnels. The current research was conducted to ensure the full scale Chrysler Aero-Acoustic Wind Tunnel (AAWT) design is consistent with good performance in these two areas. Experiments were conducted in two tunnels: a 1/3.6-scale closed-circuit tunnel and a 1/12-scale open-loop tunnel. Results from both are consistent, and a configuration that exhibits i) minimal pulsations for both empty test section and 15% vehicle blockage and ii) a good axial static pressure distribution has been identified for the AAWT. The results illustrate the effect of open jet length, collector geometry, and plenum geometry on pulsation levels and highlight the spatial variation of the pulsation levels within the plenum chamber. Pulsation levels were observed to increase with increasing open jet length and decreasing collector throat area.

This paper describes a system for measuring unsteady pressure at up to 256 spatial points and at frequencies up to 300 Hz. The system consists of commercially available equipment for measuring steady pressures. It is based on the use of electronically scanned pressure (ESP) sensors, 16 A/D converters, and a personal computer to control the whole system and acquire data. The signal outputs through the tubes connecting the pressure taps and the ESP sensors are compensated, as are the phase delays between the scanned signals and the gain variation. A 1/5 scale model of a sedan was used in this experiment. The passenger car model was placed in a wind tunnel equipped with a moving belt, which was operated at the same speed as the uniform flow in the wind tunnel. Pressure measurements were obtained at 252 points in a plane behind the model perpendicular to the uniform flow. Measurements were made with the belt turned on and off.

An improved technique is described for the experimental modeling of transient cross wind gust influences on passenger vehicles. The new configuration uses a set of vertical axis shutters which open and close in a ‘Mexican wave’ fashion to scan the cross wind jet along the working section of the wind tunnel. The new arrangement dramatically increases the rate at which experiments can be performed and offers the opportunity to apply phase-averaging techniques to multiple data sets in order to reduce noise. This is a significant development as most previous test methods have suffered from poor signal to noise ratios. Experimental results are presented for transient surface pressure measurements on a simplified vehicle model which clearly demonstrate the benefits of the new technique.

A new method for processing data from time-accurate point measurements has been developed in order to investigate periodic elements of unsteady flow fields. The technique synchronizes the phase of measurements taken at different locations using a reference signal and collapses the spectral peak of interest onto a single frequency. The technique has been applied to data gathered using a time-accurate 5-hole probe behind a two dimensional body exhibiting vortex shedding. It has been possible to generate a sequence of instantaneous pressure and velocity fields which show the shedding of vorticity and total pressure loss to form a vortex street.

We have developed a rear spoiler with built-in antenna. The spoiler has two features. First, the built-in antenna does not protrude from the vehicle contour and has an improved serviceability. Second, the air flow effect provides the driver with a clearer rear view, resulting in an improved safety. This paper discusses characteristics of the rear spoiler with built-in antenna.

A 3D Navier-Stokes CFD model of a wheel located within a wheelhouse cavity has been produced. Both a stationary wheel on a fixed ground and a rotating wheel on a moving ground were considered. Extensive comparisons with the results of a wind tunnel investigation based on the same geometry are presented. These consist of three force coefficients and pressures on the internal faces of the cavity. Comparison with the experimental results gave encouraging agreement. It was found that the rotating wheel produced more drag than the stationary wheel whilst shroud drag decreased when the groundplane was moving compared to when it was stationary.

Three-dimensional time-dependent calculations are performed to investigate the compressible turbulent flow about a train passing through a single-track tunnel. The “snapper” algorithm in KIVA-3 is used to allow the train to pass through the stationary tunnel mesh. Actual train geometry is simplified considerably. The length of the train/tunnel as well as the speed of the train is considered to investigate their effects on the train-tunnel interaction. In an effort to understand the whole process of the train-tunnel aerodynamic interaction, the formation and propagation of the pressure waves, the radiation and reflection of the waves at the tunnel portals and the histories of aerodynamic forces on the train are studied. The experimental results compare well with the computational data.

Increasing design emphasis on factors such as styling, fuel reduction and soundproofing raises a number of additional problems concerning under-bonnet aerodynamics and heat exchange. Because experimental work on successive prototypes entails heavy penalties in terms of development lead-time, it is becoming more and more important to integrate simulation from the pilot study stage, as a way to minimize the number of prototypes. Fortunately, early integration of under-bonnet air-flow modelling is becoming an increasingly viable proposition, thanks to the spectacular increase in computer processing power, which stimulates the development of more efficient meshing software and facilitates the generalized implementation of CAD techniques throughout the design processes. Modelling thus emerges as a new investigatory method that enhances the design office's capabilities by enabling it to adopt a sharper design focus right from the pilot project stage.

The numerical and modeling errors in computational aerodynamics consist of several components. The errors have been shown to be large at the front in the stagnation region and in the rear in the base region, see Ramnefors et. al. (1996). This paper presents results from numerical simulations of the flow around a simplified Volvo FH truck. Experimental data have been created for comparison in the Volvo Wind-tunnel. Simulation of the flow around the truck using several turbulence models and numerical schemes are compared to experimental measurements of drag, surface pressure distribution and total pressure distribution in the wake. It was found that the numerical scheme is very important for the base pressure. Several turbulence models have been tested. The models range from simple linear eddy viscosity models, EVMs, to more complex models such as non-linear EVMs and Reynolds stress transport models. The errors are shown to be surprisingly large along the roof of the truck.

In this paper we investigate the influence of the aerodynamics of the vehicle on the performance of the washer fluid spray. A planar windshield block model with various windshield angles, as well as a “generic” passenger car shape with a fixed windshield angle, is used for the present studies. CFD simulations of the flow field and the spray trajectories are undertaken in this study. The effect of windshield angles, nozzle location and crosswind on the spray performance is presented in this paper. For very large windshield angles of around 60° (measured from the vertical plane), there is no flow separation in the hood-windshield intersection region and the spray trajectory is significantly affected by the airstream for all nozzle locations.

Testing of an OHC valve train with hydraulic lash adjuster in which the valve displacements, velocities and accelerations were measured and analyzed in both time and frequency domains, coupled with analysis of the frequency content of the valve acceleration function and its ramps, show that traditional designs of the opening and closing ramps used on some IC engine valve cams can exacerbate vibration in the follower system causing higher levels of spring surge and noise. Suggestions are made for improvement to the design of the beginning and ending transitions of valve motion which can potentially reduce dynamic oscillation and vibration in the follower train.

Various advanced ignition systems have been investigated in order to evaluate their efficiency to initiate combustion of highly diluted mixtures in SI-Engines (lean burn and EGR concepts). Experiments have been performed on a single-cylinder engine on basis of a modern 4 valve passenger-car engine. Several levels of tumble flow were provided by means of different intake port configurations. The flame initiation mechanisms of the ignition systems were analyzed with cylinder pressure indication, mass fraction burned calculation and optical investigation of the flow field near the spark plug and the flame kernel. The study shows that transistorized coil ignition systems lead to better flame initiation of lean mixtures than capacitive-discharge ignition systems. Among a variety of standard spark plugs only a plug with thin electrodes and extended gap improves lean operation in comparison to the production J-plug. Surface-gap spark plugs lead to a reduced lean limit.

“Module” is a recent trend in Automotive Industry and many kinds of module products were exhibited at the '98 SAE International Congress & Exposition. Returnless fuel pump module is being developed to enable the vehicle to meet lower emissions requirements. Returnless fuel pump module integrates Fuel pump, Fuel filter and Pressure regulator. One characteristic of this module is to make the fuel filter of plastic and to hold it by a plastic bracket for weight reduction. Also, a returnless fuel delivery system uses a plastic fuel tube in place of a rubber hose. Here, design consideration of static electricity was needed. In general, the charged object is grounded. However, we have derived the unique idea to decrease the static electricity of the fuel filter with a non-conductive plastic case and plastic tube without taking the static charge to ground by reducing the generating charge.

This paper presents a computer model for simulating dynamic responses inside an injector of an automotive fuel rail system. The injector contains a filter at the top, a coil spring in the middle, and a needle and orifices at the bottom. The equations of motion for unsteady one-dimensional flow are derived for the fluid flowing through the injector. The needle motion is described by a second order ordinary differential equation. The forces exerted on the needle include the magnetic force that controls the opening and closing of the injector and the coil spring force. To account for the loss of kinetic energy, we define two loss factors Ka and Kb. The former describes the loss of kinetic energy as fluid enters the injector through the filter at the top, and the latter depicts that as fluid is ejected into a large chamber through the passage between the needle and the needle seat and across four orifices at the bottom of the injector.

In SI engines with port injection system, the injected fuel spray adheres surely on the port wall and the inlet valve, consequently, the spray-wall interaction process leads to the generation of unburned hydrocarbons and uncontrollable mixture formation. This paper deals with the fuel mixture preparation process including basic research on characteristics of the wall-wetted fuel film on a flat wall inside a constant volume vessel. In the experiments, iso-octane mixed with biacetyl as a tracer dopant was injected through a pintle type injector against a flat glass wall under the ambient conditions of atmospheric pressure and room temperature. The thickness of the adhered fuel film on the wall was quantitatively measured by using laser induced fluorescence (LIF) technique, which provides 2-D distribution information with high special resolution as a function of the injection duration, the impingement distance from the injector to the wall, and the impingement angle against the wall.

From the view of suppressing the global warming and environmental pollution, responding to the regulation of fuel consumption and exhaust gases along with lengthening the maintenance interval, are becoming more demanded. The development of a high-performance, long life spark plug has become essential in response to these demands. While improve performance (high ignitability and low required voltage), the discharge part of the spark plug needs to be reduced in size. But, in the past this has been difficult because of the limitations of platinum alloys in terms of wear. It has been difficult to achieve both smaller discharge parts and longer life. To dramatically improve wear resistance, we researched materials that are both resistant to oxidation and have a high melting point. This research resulted in our development of a new iridium alloy. Through this development we have been able to produce an iridium spark plug that surpasses the conventional platinum technology.