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Markov Chain-based Reliability Analysis for Automotive Fail-Operational Systems

SAE International Journal of Connected and Automated Vehicles

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SAE International Journal of Transportation Safety

AUDI AG-Andre Kohn, Rolf Schneider
Infineon Technologies AG-Antonio Vilela, Udo Dannebaum
  • Journal Article
  • 2017-01-0052
Published 2017-03-28 by SAE International in United States
A main challenge when developing next generation architectures for automated driving ECUs is to guarantee reliable functionality. Today’s fail safe systems will not be able to handle electronic failures due to the missing “mechanical” fallback or the intervening driver. This means, fail operational based on redundancy is an essential part for improving the functional safety, especially in safety-related braking and steering systems. The 2-out-of-2 Diagnostic Fail Safe (2oo2DFS) system is a promising approach to realize redundancy with manageable costs. In this contribution, we evaluate the reliability of this concept for a symmetric and an asymmetric Electronic Power Steering (EPS) ECU. For this, we use a Markov chain model as a typical method for analyzing the reliability and Mean Time To Failure (MTTF) in majority redundancy approaches. As a basis, the failure rates of the used components and the microcontroller are considered. The comparison to a non-redundant system shows a significantly higher reliability and MTTF of the redundant approaches.
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Fire Suppression Modeling & Simulation Framework for Ground Vehicles

SAE International Journal of Transportation Safety

Alion Science & Technology-Steven Hodges
US Army TARDEC-Vamshi Korivi, Steven McCormick
  • Journal Article
  • 2017-01-1351
Published 2017-03-28 by SAE International in United States
The US Army Tank Automotive Research, Development and Engineering Center (TARDEC) has developed a unique physics based modeling & simulation (M&S) capability using Computational Fluid Dynamics (CFD) techniques to optimize automatic fire extinguishing system (AFES) designs and complement vehicle testing for both occupied and unoccupied spaces of military ground vehicles.The modeling techniques developed are based on reduced global kinetics for computational efficiency and are applicable to fire suppressants that are being used in Army vehicles namely, bromotrifluoromethane (Halon 1301), heptafluoropropane (HFC-227ea, trade name FM200), sodium-bicarbonate (SBC) powder, water + potassium acetate mixture, and pentafluoroethane (HFC-125, trade name, FE-25). These CFD simulations are performed using High Performance Computers (HPC) that enable the Army to assess AFES designs in a virtual world at far less cost than physical-fire tests.This methodology is applied to vehicle crew compartments for multiple scenarios using HFC227e + SBC powder which is the suppressant combination used in most US combat and tactical vehicles with crew fire protection systems. Predicted and test results match qualitatively very well for overall suppression time as well as…
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Bridging the Gap between Open Loop Tests and Statistical Validation for Highly Automated Driving

SAE International Journal of Transportation Safety

BMW AG-Alexander Koenig, Michael Gutbrod
KIT Karlsruhe Institute of Technology-Sören Hohmann, Julian Ludwig
  • Journal Article
  • 2017-01-1403
Published 2017-03-28 by SAE International in United States
Highly automated driving (HAD) is under rapid development and will be available for customers within the next years. However the evidence that HAD is at least as safe as human driving has still not been produced. The challenge is to drive hundreds of millions of test kilometers without incidents to show that statistically HAD is significantly safer. One approach is to let a HAD function run in parallel with human drivers in customer cars to utilize a fraction of the billions of kilometers driven every year. To guarantee safety, the function under test (FUT) has access to sensors but its output is not executed, which results in an open loop problem. To overcome this shortcoming, the proposed method consists of four steps to close the loop for the FUT. First, sensor data from real driving scenarios is fused in a world model and enhanced by incorporating future time steps into original measurements. Second, recorded time-shifted data is used to identify intentions of each driver of the surrounding traffic. Third, the real scene is used as…
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A Comprehensive Validation Method with Surface-Surface Comparison for Vehicle Safety Applications

SAE International Journal of Transportation Safety

Chongqing University-Junqi Yang, Zhenfei Zhan, Ling Zheng, Gang Guo
Tongji University-Changsheng Wang
  • Journal Article
  • 2017-01-0221
Published 2017-03-28 by SAE International in United States
Computer Aided Engineering (CAE) models have proven themselves to be efficient surrogates of real-world systems in automotive industries and academia. To successfully integrate the CAE models into analysis process, model validation is necessarily required to assess the models’ predictive capabilities regarding their intended usage. In the context of model validation, quantitative comparison which considers specific measurements in real-world systems and corresponding simulations serves as a principal step in the assessment process. For applications such as side impact analysis, surface deformation is frequently regarded as a critical factor to be measured for the validation of CAE models. However, recent approaches for such application are commonly based on graphical comparison, while researches on the quantitative metric for surface-surface comparison are rarely found. To deal with this problem, a validation metric, which combines the discrepancies measurements in magnitude and shape, is proposed to evaluate the inconsistence between two deformed surfaces. For magnitude error, an exploited 2-Dimensional Dynamic Time Warping (2D-DTW) method is applied to address the mismatch in surface features between two surfaces. Geometric features, say mean curvatures…
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ERRATUM: Study of Reproducibility of Pedal Tracking and Detection Response Task to Assess Driver Distraction

SAE International Journal of Transportation Safety

Honda R&D Co., Ltd.-Tatsuya Iwasa, Toshihiro Hashimoto
  • Journal Article
  • 2015-01-1388.01
Published 2015-04-14 by SAE International in United States
1. On page 111, the authors have described a method to assess driver distraction. In this method, participants maintained a white square size on a forward display by using a game gas pedal of like in car-following situation. The size of the white square is determined by calculating the distance to a virtual lead vehicle. The formulas to correct are used to explain variation of acceleration of the virtual lead vehicle. The authors inadvertently incorporated old formulas they had used previously. In the experiments discussed in the article, the corrected formulas were used. Therefore, there is no change in the results. The following from the article:
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Practical Design Considerations for Lightweight Windshield Applications

SAE International Journal of Transportation Safety

Ford Motor Company-Chester Walawender
Pittsburgh Glass Works LLC-Michael Ulizio, DeWitt Lampman, Mukesh Rustagi, Jason Skeen
  • Journal Article
  • 2017-01-1306
Published 2017-03-28 by SAE International in United States
Automotive manufacturers are requiring lightweight materials, including glazing materials to improve vehicle fuel economy mandates. Since windshields are one of the largest glazing surface areas, reducing the thickness of the glass in its construction can significantly provide weight savings opportunities. Automotive glazing design considerations must include overall glass strength, rigidity, acoustical, and solar performance, which are affected by changes of glass thicknesses. This paper will evaluate those design considerations in the lightweighting of windshield glazings.One important design consideration for the windshield position is the impact of debris from the environment. Lightweighting of glazings in this body position affects the way the construction reacts to an impact. Use of asymmetry in glass plies in a laminated construction can have a marked effect on the part’s impact performance and surface damage creation. Various lightweight glazing constructions will be analyzed, and based upon basic strength and stiffness, the probability of failure from stone impact in parts per million is predicted from a statistical model. Further testing and analysis will be done to demonstrate lifetime effects in windshield glazings…
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Application of Lateral Pole Impact Force-Displacement Data to the Reconstruction of Side Impacts with Narrow Objects

SAE International Journal of Transportation Safety

Design Research Engineering-B. Nicholas Ault, Daniel E. Toomey
  • Journal Article
  • 2017-01-1416
Published 2017-03-28 by SAE International in United States
Reconstruction of passenger vehicle accidents involving side impacts with narrow objects has traditionally been approached using side stiffness coefficients derived from moveable deformable barrier tests or regression analysis using the maximum crush in available lateral pole impact testing while accounting for vehicle test weight. Current Lateral Impact New Car Assessment Program (LINCAP) testing includes 20 mph oblique lateral pole impacts. This test program often incorporates an instrumented pole so the force between the vehicle and pole at several elevations along the vehicle - pole interface is measured. Force-Displacement (F-D) characteristics of vehicle structures were determined using the measured impact force and calculated vehicle displacement from on-board vehicle instrumentation. The absorbed vehicle energy was calculated from the F-D curves and related to the closing speed between the vehicle and the pole by the vehicle weight.The presented approach resulted in approximately a 2% underestimation of closing speed in large four-door sedans and approximately a 9 to 10% underestimation in large four-door pickup trucks. Accounting for structural restoration is important when assessing accident severity using this methodology. The…
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Analysis of Driver Kinematics and Lower Thoracic Spine Injury in World Endurance Championship Race Cars during Frontal Impacts

SAE International Journal of Transportation Safety

Toyota Motor Corp.-Tadasuke Katsuhara, Yoshiki Takahira, Shigeki Hayashi, Yuichi Kitagawa, Tsuyoshi Yasuki
  • Journal Article
  • 2017-01-1432
Published 2017-03-28 by SAE International in United States
This study used finite element (FE) simulations to analyze the injury mechanisms of driver spine fracture during frontal crashes in the World Endurance Championship (WEC) series and possible countermeasures are suggested to help reduce spine fracture risk. This FE model incorporated the Total Human Model for Safety (THUMS) scaled to a driver, a model of the detailed racecar cockpit and a model of the seat/restraint systems. A frontal impact deceleration pulse was applied to the cockpit model. In the simulation, the driver chest moved forward under the shoulder belt and the pelvis was restrained by the crotch belt and the leg hump. The simulation predicted spine fracture at T11 and T12. It was found that a combination of axial compression force and bending moment at the spine caused the fractures. The axial compression force and bending moment were generated by the shoulder belt down force as the driver’s chest moved forward. The axial compression force at the spine was also induced by the forces from the crotch belt and the leg hump. Based on these…
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Crush Energy and Stiffness in Side Impacts

SAE International Journal of Transportation Safety

Donald E. Struble
Exponent, Inc.-John D. Struble
  • Journal Article
  • 2017-01-1415
Published 2017-03-28 by SAE International in United States
Crash tests of vehicles by striking deformable barriers are specified by Government programs such as FMVSS 214, FMVSS 301 and the Side Impact New Car Assessment Program (SINCAP). Such tests result in both crash partners absorbing crush energy and moving after separation. Compared with studying fixed rigid barrier crash tests, the analysis of the energy-absorbing behavior of the vehicle side (or rear) structure is much more involved. Described in this paper is a methodology by which analysts can use such crash tests to determine the side structure stiffness characteristics for the specific struck vehicle. Such vehicle-specific information allows the calculation of the crush energy for the particular side-struck vehicle during an actual collision – a key step in the reconstruction of that crash.Based on fundamental principles of physics and engineering, this methodology provides transparency in the calculation of side structure stiffness parameters for the particular vehicle of interest. Additionally, sample calculations are presented. Utilizing widely available computational tools and publicly available test data, the method was applied to a representative sample of recent-model vehicles.The results…
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Vapour Space Flammability Measurements of High Ethanol (“E85”) and Low Ethanol (“E10”) Winter Automotive Fuels: Effects of Fuel Composition and Vapour Pressure

SAE International Journal of Transportation Safety

Nexum Engine R&D-David Gardiner
  • Journal Article
  • 2017-01-1352
Published 2017-03-28 by SAE International in United States
This paper presents an experimental study of the vapour space flammability of Fuel Ethanol (a high-ethanol fuel for Flexible Fuel Vehicles, commonly known as “E85”) and gasoline containing up to 10% ethanol (commonly known as “E10”). The seasonal minimum vapour pressure limits in specifications for automotive spark ignition fuels are intended, in part, to minimize the formation of flammable mixtures in the headspace of vehicle fuel tanks. This is particularly important at subzero temperatures, where the headspace mixture may not be rich enough to prevent combustion in the presence of an ignition source such as a faulty electrical fuel pump. In the current study, the upper temperature limits of flammability were measured for field samples of “E85” and “E10”, and a series of laboratory-prepared blends of denatured ethanol, Before Oxygenate Blending (BOB) gasoline, and n-butane. The paper compares the measured flammability limits with the ambient temperatures of the field sampling locations, documents the relationship between vapour space flammability and vapour pressure, and discusses the requirements for achieving gasoline-like flammability performance at high ethanol levels.
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