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Journal Article

External Biofidelity Evaluation of Pedestrian Leg-Form Impactors

2017-03-28
2017-01-1450
Current state-of-the-art vehicles implement pedestrian protection features that rely on pedestrian detection sensors and algorithms to trigger when impacting a pedestrian. During the development phase, the vehicle must “learn” to discriminate pedestrians from the rest of potential impacting objects. Part of the training data used in this process is often obtained in physical tests utilizing legform impactors whose external biofidelity is still to be evaluated. This study uses THUMS as a reference to assess the external biofidelity of the most commonly used impactors (Flex-PLI, PDI-1 and PDI-2). This biofidelity assessment was performed by finite element simulation measuring the bumper beam forces exerted by each surrogate on a sedan and a SUV. The bumper beam was divided in 50 mm sections to capture the force distribution in both vehicles. This study, unlike most of the pedestrian-related literature, examines different impact locations and velocities.
Journal Article

Thermal Modeling of Power Steering System Performance

2008-04-14
2008-01-1432
Power steering systems provide significant design challenges. They are detrimental to fuel economy since most require the continuous operation of a hydraulic pump. This generates heat that must be dissipated by fluid lines and heat exchangers. This paper presents a simple one-dimensional transient model for power steering components. The model accounts for the pump power, heat dissipation from fluid lines, the power steering cooler, and the influence of radiation heat from exhaust system components. The paper also shows how to use a transient thermal model of the entire system to simulate the temperatures during cyclic operation of the system. The implications to design, drive cycle simulation, and selection of components are highlighted.
Journal Article

Computer Simulation of Automotive Air Conditioning - Components, System, and Vehicle: Part 2

2008-04-14
2008-01-1433
In 1972, the first SAE paper describing the use of computer simulation as a design tool for automotive air conditioning was written by these authors. Since then, many such simulations have been used and new tools such as CFD have been applied to this problem. This paper reviews the work over that past 35 years and presents several of the improvements in the basic component and system models that have occurred. The areas where “empirical” information is required for model support and the value of CFD cabin and external air flow modeling are also discussed.
Technical Paper

The Interaction of Air Bags with Upper Extremities

1997-11-12
973324
Recently there has been a greater awareness of the increased risk of certain injuries associated with air bag deployment, especially the risks to small occupants, often women. These injuries include serious eye and upper extremity injuries and even fatalities. This study investigates the interaction of a deploying air bag with cadaveric upper extremities in a typical driving posture; testing concentrates on female occupants. The goals of this investigation are to determine the risk of upper extremity injury caused by primary contact with a deploying air bag and to elucidate the mechanisms of these upper extremity injuries. Five air bags were used that are representative of a wide range of air bag ‘aggressivities’ in the current automobile fleet. This air bag ‘aggressivity’ was quantified using the response of a dummy forearm under air bag deployment.
Technical Paper

Total Phosphorus Detection and Mapping in Catalytic Converters

2007-10-29
2007-01-4078
The poisoning of three way catalysts (TWC) by the phosphorus contained in oil formulations containing zinc dialkyldithiophosphate (ZDDP) is examined. Catalysts were exposed to various types of ZDDP and detergents under conditions that were known to reduce performance through phosphorus poisoning without the blocking of sites by formation of glazing. The presence of phosphorus was detected with energy dispersive x-ray spectroscopy (EDX). In addition to analyzing the surface concentration of the phosphorus on the washcoat, the catalyst was cross cut so phosphorus that diffused into the washcoat could be mapped. The total phosphorus in the catalyst could then be calculated. The amount of total phosphorus detected correlated well with the reduced activity of the catalyst as measured by the temperature of 50% conversion.
Technical Paper

Evaluation of 5th Percentile Female Hybrid III Thoracic Biofidelity during Out-of-Position Tests with a Driver Air Bag

1998-02-23
980636
This paper evaluates the biofidelity of the Hybrid III 5th percentile female dummy relative to seven small female cadavers tested as out-of-position drivers in static air bag deployment tests. In the out-of-position tests, the chest was positioned against the air bag module in an effort to recreate a worst-case loading environment for the thorax. Two pre-depowered production air bags and a prototype dual-stage air bag were evaluated. Thoracic accelerometers and chestbands were used to compare chest compression, velocity, acceleration, and Viscous Criteria. A statistical comparison of dummy and cadaver results indicate acceptable biofidelity of the Hybrid III dummy with significant differences observed only in the Viscous Criteria.
Technical Paper

Wear Mechanism in Cummins M-11 High Soot Diesel Test Engines

1998-05-04
981372
The Cummins M-11 high soot diesel engine test is a key tool in evaluating lubricants for the new PC-7 (CH-4) performance category. M-11 rocker arms and crossheads from tests with a wide range of lubricant performance were studied by surface analytical techniques. Abrasive wear by primary soot particles is supported by the predominant appearance of parallel grooves on the worn parts with their widths matching closely the primary soot particle sizes. Soot abrasive action appears to be responsible for removing the protective antiwear film and, thus, abrades against metal parts as well. Subsequent to the removal of the antiwear film, carbide particles, graphite nodules, and other wear debris are abraded, either by soot particles or sliding metal-metal contact, from the crosshead and rocker arm metal surfaces. These particles further accelerate abrasive wear. In addition to abrasive wear, fatigue wear was evident on the engine parts.
Technical Paper

The Design of Automatic Transmission Fluid to Meet the Requirements of Electronically Controlled Transmissions

1990-10-01
902151
Design changes in automatic transmissions have resulted in new requirements for automatic transmission fluids. Electronic controls, for instance, perform best with fluids having better low-temperature properties. Achievement of the target low-temperature properties can be accomplished in different ways. The advantages and disadvantages of each approach are discussed with respect to total fluid performance. Fluid performance properties examined include viscometrics, shear stability, antiwear and stability toward thermal stress and oxidation.
Technical Paper

The Effect of Shear Rate and Shear Stress on Viscosity Determinations at Low Temperatures for Engine Oils

1990-10-01
902091
The viscosity of engine lubricants was measured at multiple shear rates by a unique Scanning Brookfield apparatus. These oils included both Pumpability Reference Oils (PRO) and a selection of today's commercial multigrade oils. It was found that the viscosity of “flow-limited” oils remained constant when the shear rate decreased. Oils with “air-binding” properties exhibited an increase in viscosity with decreasing shear rate. The magnitude of a change in “slope of the temperature/viscosity profile was found to suggest the degree of air-binding character of an oil. The flow characteristics of PRO 1, 3, 9, 11, and 16 were measured at several shear stresses and temperatures in the Mini-Rotary Viscometer. The Scanning Brookfield technique and the Mini-Rotary Viscometer were found to yield similar results when the shear stress of the Mini-Rotary Viscometer was reduced from 525 to 35 Pascals.
Technical Paper

Viscous Fan Drive Model for Robust Cooling Air Flow Simulation

2007-04-16
2007-01-0595
One Dimensional models for front end air flows through the cooling system package are very useful for evaluating the effects of component and front end geometry changes. To solve such models for the air flow requires a robust iterative process that involves a number of non-linear sub-models. The cooling fan (s) constitute a major part of the difficulty, especially when they employ a viscous or “thermal” fan drive. This drive varies the torque coupling between the input and output shafts based on the radiator outlet air temperature. The coupling is achieved by viscous shear between two grooved disks and is regulated by a bimetal strip valve that varies the amount of fluid between the disks. This paper presents a mathematical model by which the input/output speed ratio may be determined as a function of the air temperature and input speed. Coefficients in the model are estimated from standard supplier performance information.
Technical Paper

Robust Compressor Model for AC System Simulation

2007-04-16
2007-01-0596
Simple component models are advantageous when simulating vehicle AC systems so that overall model complexity and computation time can be minimized. These models must be robust enough to avoid instability in the iteration method used for determining the AC system operating or “balance” point. Simplicity and stability are especially important when the AC system model is coupled with a vehicle interior model for studies of transient performance because these are more computationally intensive. This paper presents a semi-empirical modeling method for compressors based on dimensionless parameters. Application to some sample compressor data is illustrated. The model equations are simple to employ and will not introduce significant stability problems when used as part of a system simulation.
Technical Paper

Critical Oil Physical Properties that Control the Fuel Economy Performance of General Motors Vehicles

1998-10-19
982503
The effect of critical physical properties of engine oils on fuel economy performance in General Motors (GM) vehicles has been measured. Reductions in an oil's high temperature high shear viscosity, boundary friction coefficient and pressure-viscosity coefficient were found to equally improve fuel economy. These same oil properties affect fuel economy measured in the Sequence VIA engine test. However, fuel economy performance in GM vehicles is more dependent on an oil's boundary friction coefficient and pressure-viscosity coefficient than that measured in the Sequence VIA engine test. New fuel economy measurement conditions have been proposed for the Sequence VIB engine test. Changes in an oil's boundary friction coefficient were found to have the same effect on fuel economy measured under these new measurement conditions as that measured in GM vehicles.
Technical Paper

Toward Requirements for a Web-based Icing Training Program for Flight Dispatchers

2003-06-16
2003-01-2151
The Icing Branch at NASA Glenn Research Center has funded an exploratory effort to identify requirements for developing a flight dispatcher-centered web-based icing training program that would be available for all airspace users. Through research and discussions with personnel at airlines, target areas were identified as influences on the requirements for the training system: 1 Flight dispatchers' icing related judgments and decision-making; 2 Certification, new hire and recurrent flight dispatcher training with respect to icing; 3 Icing related weather sources and the problems that flight dispatchers may have in their interpretation; 4 Pedagogical strategies (such as flight dispatcher-centered scenario-based approaches) for delivering flight dispatcher training content; and 5 Concerns/constraints with respect to web-based training for flight dispatchers.
Technical Paper

Constitutive Modeling of Polymers Subjected to High Strain Rates

2001-03-05
2001-01-0472
A biaxial test procedure is used to assess the constitutive properties of polymers in tension. The constitutive constants are derived for high strain rate applications such as those associated with crashworthiness studies. The test procedure is used in conjunction with a time- and strain-dependent quasi-linear viscoelastic constitutive law consisting of a Mooney-Rivlin formulation combined with Maxwell elements. The procedure is demonstrated by describing the stress vs. strain relationship of a rubber specimen subjected to a step-relaxation input. The constitutive equation is transformed from a nonlinear convolution integral to a set of first order differential equations. These equations, with the appropriate boundary conditions, are solved numerically to obtain transient stresses in two principal directions. Material constants for use in the explicit LS-Dyna non-linear finite element code are provided.
Technical Paper

Data Censoring and Parametric Distribution Assignment in the Development of Injury Risk Functions from Biochemical Data

2004-03-08
2004-01-0317
Biomechanical data are often assumed to be doubly censored. In this paper, this assumption is evaluated critically for several previously published sets of data. Injury risk functions are compared using simple logistic regression and using survival analysis with 1) the assumption of doubly censored data and 2) the assumption of right-censored (uninjured specimens) and uncensored (injured) data. It is shown that the injury risk functions that result from these differing assumptions are not similar and that some experiments will require a preliminary assessment of data censoring prior to finalizing the experimental design. Some types of data are obviously doubly censored (e.g., chest deflection as a predictor of rib fracture risk), but many types are not left censored since injury is a force-limiting phenomenon (e.g., axial force as a predictor of tibia fracture). Guidelines for determining the censoring for various types of experiment are presented.
Technical Paper

A Normalization Technique for Developing Corridors from Individual Subject Responses

2004-03-08
2004-01-0288
This paper presents a technique for developing corridors from individual subject responses contained in experimental biomechanical data sets. Force-deflection response is used as an illustrative example. The technique begins with a method for averaging human subject force-deflection responses in which curve shape characteristics are maintained and discontinuities are avoided. Individual responses sharing a common characteristic shape are averaged based upon normalized deflection values. The normalized average response is then scaled to represent the given data set using the mean peak deflection value associated with the set of experimental data. Finally, a procedure for developing a corridor around the scaled normalized average response is presented using standard deviation calculations for both force and deflection.
Technical Paper

Fundamentals of Anti-Shudder Durability: Part II - Fluid Effects

2003-10-27
2003-01-3254
Friction plate degradation and/or friction plate glazing has often been related to the loss of friction control in automatic transmissions. However, in JASO SAE No.2 and LVFA tests, friction material glazing has been found to not be a sufficient condition for the loss of anti-shudder performance or a reduction in torque capacity durability. Therefore, changes in automatic transmission fluid properties rather than changes to the friction surfaces would be expected to play a dominant role in controlling anti-shudder performance and torque capacity. Earlier theoretical studies have proposed that friction in wet clutches is a combination of boundary and hydrodynamic friction. Therefore, changes in these properties should control anti-shudder durability and torque capacity. In this paper, we confirm that boundary and thin-film friction contribute to friction measured in JASO SAE No.2 and LVFA tests.
Technical Paper

ATF Effects on Friction Stability in Slip-Controlled Torque Converter Clutches

2003-10-27
2003-01-3255
A model of an automotive powertrain equipped with a slip-controlled torque converter clutch (TCC) is presented that incorporates the clutch control system and the friction-related properties of the automatic transmission fluid (ATF) and clutch friction material. Prior research has established that stability of a slip-controlled TCC is enhanced by maintaining a positive slope of the coefficient of friction, μ, with respect to sliding speed, v. The model presented here agrees with this result, but suggests that it is neither a necessary nor sufficient condition guaranteeing stability. The model indicates that other factors affecting stability at the equilibrium sliding speed include the magnitude of μ, the engine speed, the engine torque-speed slope, the ATF pressure, and the time constants of the clutch control system. This model will aid in the development of future wet clutch systems with improved friction stability performance.
Technical Paper

Investigation of Pitting Mechanism in the FZG Pitting Test

2003-10-27
2003-01-3233
Extended gear fatigue pitting life is an essential performance requirement for today's gear oils in automotive driveline applications. One of the important industrial standard tests used to evaluate fully formulated oil's ability to extend gear pitting fatigue life is the FZG pitting test. To understand the fatigue pitting behavior in these gears we have conducted surface analyses on the FZG gears to determine fatigue modes. We have found that micro-pitting is the major fatigue mode and pitting/spalling is mostly initiated by micro-pitting in the FZG test. To help further understand how pitting and micro-pitting relate to gear oil properties and gear surface morphology, we have also carried out a statistical analysis correlating fatigue pitting life with four major physical parameters: boundary friction coefficient, oil film thickness, oil corrosiveness, and surface roughness of the gear tooth.
Technical Paper

Displacement Measurements in the Hybrid III Chest

2001-03-05
2001-01-0118
This paper presents an analysis of the displacement measurement of the Hybrid III 50th percentile male dummy chest in quasistatic and dynamic loading environments. In this dummy, the sternal chest deformation is typically characterized using a sliding chest potentiometer, originally designed to measure inward deflection in the central axis of the dummy chest. Loading environments that include other modes of deformation, such as lateral translations or rotations, can create a displacement vector that is not aligned with this sensitive axis. To demonstrate this, the dummy chest was loaded quasistatically and dynamically in a series of tests. A string potentiometer array, with the capability to monitor additional deflection modes, was used to supplement the measurement of the chest slider.
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