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Technical Paper

Vehicle System Energy Analysis Methodology and Tool for Determining Vehicle Subsystem Energy Supply and Demand

2007-04-16
2007-01-0398
A greater understanding of where fuel energy is being demanded from a vehicle system standpoint is necessary for developing more fuel efficient vehicles. This paper presents an overview of the development and application of a vehicle energy analysis methodology and a MATLAB®/Simulink® based tool that uses empirical data and first principles to identify vehicle subsystem energy supply and demand. An accurate analysis requires the tool to be populated with chassis dynamometer drive cycle data as well as vehicle and component information. The tool can be used to investigate vehicle system energy requirements, prevailing fuel economy factors, and incremental hypothetical fuel saving scenarios that could not otherwise be measured due to inherent test-to-test variability.
Technical Paper

Vehicle Road Simulation Testing, Correlation and Variability

2005-04-11
2005-01-0856
In this paper, responses from a vehicle's suspension, chassis and body, are used to demonstrate a methodology to optimize physical test results. It is well known that there is a variability effect due to an increase of wheel unsprung mass (due to loads measurement fixturing), tire pressure, speed, etc. This paper quantifies loading variability due to Wheel Force Transducer (WFT) unsprung mass by using a rainflow cycle counting domain. Also, presents a proving ground-to-test correlation study and the data reduction techniques that are used in road simulation test development to identify the most nominal road load measurement. Fundamental technical information and analytical methodology useful in overall vehicle durability testing are discussed. Durability testing in a laboratory is designed to correlate fatigue damage rig to road. A Proving Ground (PG) loading history is often acquired by running an instrumented vehicle over one or more PG events with various drivers.
Technical Paper

Vehicle Powertrain Loading Simulation and Variability

2004-03-08
2004-01-1563
In this paper, loads acting on driveline components during an entire proving ground (PG) durability schedule are used to demonstrate the methodology of optimizing driveline performance reliability using both physical and computational methods. It is well known that there is an effect of driver variability on the driveline component loads. Yet, this effect has not been quantified in the past for lack of experimental data from multiple drivers and reliable data analysis methods. This paper presents the data reduction techniques that are used to identify the extreme driver performance and to extrapolate the short-term measurement to long-term data for driveline performance reliability. The driveline loading variability is made evident in the rotating moment histogram domain. This paper also introduces the concept for a simulation model to predict the driveline component loads based on a complete proving grounds schedule. A model-to-test correlation is also performed in this paper.
Technical Paper

Torque Converter CFD Engineering Part II: Performance Improvement through Core Leakage Flow and Cavitation Control

2002-03-04
2002-01-0884
The performance of a large-volume production torque converter is slightly different from those of development prototype due to the core leakage flow. The sealing gap between the stator crown and pump or turbine core of the production converter is usually larger than that of prototypes because of fabrication method and tolerances. In this work, the core leakage flow of torque converter was investigated using CFD. The core region was modeled and coupled together with other three major components of a converter. Studies show that for a particular converter the core leakage flow could result in a 3.6% stall torque ratio reduction and a 2% peak efficiency decrease. The effects of sealing gap dimensions were also studied. Computational investigations in this work indicated that the variation of input K factor with input torque level observed in dyno tests is due to the cavitation in the torque converter.
Technical Paper

Torque Converter CFD Engineering Part I: Torque Ratio and K Factor Improvement Through Stator Modifications

2002-03-04
2002-01-0883
To improve vehicle launch feeling, the powertrain torque output needs to be largely increased. Compared with modifications to engine, transmission, and axle, one of the most inexpensive ways of achieving this goal is to modify the torque converter to get a higher stall torque ratio. In other applications, in order to lower engine speed for better fuel economy, and to match with a higher output engine, a converter with higher torque capacity (lower K factor) is also often desired. In some case of small-volume production, the torque converter modifications are limited to the stator only in order to reduce the manufacturing cost. In the present study, the engineering CFD simulations were used to develop new stators for stall torque ratio and K factor improvement. The flow fields of both baseline and modified torque converters were simulated. The overall performances of the converter were calculated from the flow field data, and correlated with the dyno test data.
Technical Paper

The Effect of HIP Processing on the Properties of A356 T6 Cast Aluminum Steering Knuckles

2004-03-08
2004-01-1027
Hot Isostatic Pressing (HIP) has been routinely used to densify castings for aerospace and medical applications for over 30 years. While HIP is widely known to improve the toughness and fatigue life of castings through the healing of internal porosity, it has been perceived as too expensive for most cast aluminum alloys for automotive applications. Recent developments suggest that the cost effectiveness of certain special HIP processes should be revisited due to reductions in process cost and improvements in throughput. This paper will evaluate the Densal® II process applied to a front aluminum steering knuckle. Two casting processes representing differing levels of relative cost and quality were evaluated. The first was Alcoa's VRC/PRC process, a metal mold process with bottom fill, evacuation before fill and pressurization after fill. This is considered to be a premium quality, but higher cost casting process that is already qualified for this application.
Technical Paper

Stamping and Crush Performance of Dual Phase Steel

2001-10-16
2001-01-3074
Traditionally, high-strength low-alloy (HSLA) steel is used for automotive vehicle weight reduction in the North American automotive industry. Dual phase (DP) high strength steel has gained great attention because it provides a combination of high strength and good formability. The main advantage of DP steel is the high ratio of tensile strength to yield strength, which provides more flexibility in stamping and higher energy absorption in a component crush event. This study compares the performances of DP and HSLA steel grades in stamping processes and component crush events, as shown in a typical automotive unibody inner rail. Simulation results show that DP steel offers more uniform strain distribution, improved formability, and better crush performance than conventional HSLA steel.
Technical Paper

Simulating the Die Gap Effect on Springback Behavior in Stamping Processes

2000-03-06
2000-01-1111
The springback behavior might be different due to different gap clearances between die and punch. A study using FEA simulation is done to investigate the die gap effect. A 3D brick element and an explicit-implicit method are employed to investigate a few simple problems. A draw form, a crash form with an upper pad and a flange form are investigated separately. Numisheet’93 2D draw bending springback problem is also investigated using an explicit dynamic code. Comparisons between springback simulation results on several different die gaps are illustrated. The Kirchhoff assumption of C° shell element and the Mindlin/Love assumption of thin shell element are also examined on different cases. A case study then is performed on a rail type panel. Conclusions and recommendations for future studies are summarized.
Technical Paper

Reliability-Based Fatigue Strength Testing by the Staircase Method

2004-03-08
2004-01-1288
The staircase fatigue testing method is a recognized method for determining the fatigue limit of powertrain components. The purpose of this paper is to improve upon existing standards by adding common practices that will ensure a higher degree of statistical accuracy in the data. This includes specifying appropriate sample sizes, stress increments and initial load conditions, as well as making suggestions for appropriate methods of analyzing the data. Two methods (Dixon and Mood method and probit analysis method) are selected and compared in terms of relative percent difference on four parameters (mean, standard deviation, B10 fatigue strength and B50 fatigue strength). The staircase data are obtained by simulations from normal and lognormal fatigue limit distributions.
Technical Paper

Proactive Ergonomic Verification Through Human Biodynamic Modeling and Digital Simulation

1999-09-28
1999-01-3371
An extensive digital simulation study on lift devices that interact with human operators in DaimlerChrysler automotive assembly plants has been initiated and deployed. This digital mock-up of human-machine workcells is to scientifically evaluate and further certify a number of typical commercial lift devices that are served in car-assembly operations. The entire model is based on human biomechanical Jacobian relationship, as a fundamental kinematic structure, to predict human body instantaneous joint-torque distribution when the human is working with a certain payload. The developed modeling and simulation system will play a pivotal role in proactive ergonomic prediction, verification and digital certification in car advance manufacturing engineering processes.
Technical Paper

Prediction of Draw Bead Coefficient of Friction Using Surface Temperature

2002-03-04
2002-01-1059
Sheet metal stamping involves a system of complex tribological (friction, lubrication, and wear), heat transfer, and material strain interactions. Accurate coefficient of friction, strain, and lubrication regime data is required to allow proper modeling of the various sheet stamping processes. In addition, non-intrusive means of monitoring the coefficient of friction in production stamping operations would be of assistance for efficiently maintaining proper stamping quality and to indicate when adjustments to the various stamping parameters, including maintenance, would be advantageous. One of the key sub-systems of the sheet metal stamping process is the draw bead. This paper presents an investigation of the tribology of the draw bead using a Draw Bead Simulator (DBS) Machine and automotive zinc-coated sheet steels. The investigation and findings include: 1) A new, non-intrusive method of measuring the surface temperature of the sheet steel as it passes through the draw bead.
Technical Paper

Optimization of Accessory Drive System of the V6 Engine Using Computer Simulation and Dynamic Measurements

2005-05-16
2005-01-2458
At the initial accessory drive system design stage, a model was created using commercial CAE software to predict the dynamic response of the pulleys, tensioner motion and pulley slip. In a typical 6 cylinder automotive accessory drive systems, the first system torsional mode is near the engine idle speed. The combination of these two events could generate numerous undesirable noise and vibration effects in the system. Data acquisition on a firing engine with a powertrain dynamometer confirmed the computer model's results. Correlations are then developed and established based on results between the firing engine to the CAE model to increase confidence in the generated model. Further system optimization through design modifications are used to tune the system to minimize the overall system dynamics.
Technical Paper

Fatigue Analysis for Axle Differential Cases

2006-04-03
2006-01-0779
The recent trends of increasing driveline torque and use of traction control devices call for increasingly higher durability capacity from driveline components. Bench and vehicle durability tests are often used to validate designs, but they are not cost-effective and take months to complete. Traditional finite element analysis (FEA) procedures have been used effectively in the re-design of driveline components to reduce stress, and occasionally, to predict fatigue life. But in the case of certain rotating components, such as the Axle Differential Case, where the component sees large stress/strain fluctuations within the course of one complete rotation, even under constant input torque, historical fatigue analysis (when conducted) yields very conservative results. The axle differential case tends to be one of the weakest links in the rear axle assembly. Therefore, there is a crucial need for analytical methods to more accurately predict fatigue life to reduce testing time and cost.
Technical Paper

Effect of Forming Strain on Fatigue Performance of a Mild Automotive Steel

2001-03-05
2001-01-0083
The effect of forming strains on the fatigue behavior of an automotive mild steel, interstitial free steel, was studied after being prestrained by balanced biaxial stretch and plane strain. In the long life region, higher than 5×105 reversals, prestrain improves fatigue resistance. In the short life region, prestrain reduces fatigue resistance. At even shorter fatigue lives, the detrimental effect of prestrain diminishes. For plane strains, the fatigue behavior is anisotropic. In the direction perpendicular to the major strain, the steel exhibits much better fatigue resistance than in the direction parallel to the major strain.
Technical Paper

Data-Based Models for Spine Acceleration Response of the Side Impact Dummy

1999-10-10
99SC07
The response of the spine acceleration to rib and pelvis acceleration input of the side impact dummy (SID) is modeled using system identification methods. The basis for the modeling is a simplified representation of the SID by a 3-mass, 2-spring system. Based on this spring-mass representation, two types of response models are established. The first is a "gray-box" type with rib/pelvis-spine relationship modeled by Auto Regression with eXogeneous (or eXtra) input (ARX) type system models. The structure of these models is partially based on the spring-mass simplified representation, hence the notion "gray- box." The parameters of these models are identified through linear regression from test data. The second type of models is noted "physical model" here, since it is strictly a state- space form of the equation of motion of the simple spring-mass representation.
Technical Paper

Calculating Partial Contribution Using Component Sensitivity Values: A Different Approach to Transfer Path Analysis

1999-05-17
1999-01-1693
Transfer Path Analysis (TPA) is a widely used methodology in Noise, Vibration and Harshness (NVH) analysis of motor vehicles. Either it is used to design a vehicle from scratch or it is applied to root cause an existing NVH problem, TPA can be a useful tool. TPA analysis is closely related to the concept of partial contribution. The very basic assumption in TPA is that the summation of all partial contributions from different paths constitutes the total response (which could be either tactile or acoustic). Another popular concept in NVH analysis of vehicles is the component sensitivity. Component sensitivity is a measure of how much the response changes due to a change in one of the components of the system, i.e., the thickness of a panel or elastic rate of an engine mount. Sensitivity rates are more popular among CAE/Simulation community, simply because they are reasonably easy to calculate using mathematical models.
Technical Paper

Advances in Thixomolding Magnesium Alloys Part II

2003-03-03
2003-01-0181
Thixomolding (1) is a relatively new process in which the metallic slurry is injected into a die cavity tool at semi-solid or liquid temperatures to form near net-shape products from the solid feedstock. As part of on-going research into Thixomolding technology, this study continues the work of a previous study, that concentrated on magnesium alloys AZ91D and AM60B. The test samples were made with high, low and zero percent fraction solid. The test results of the thixomolded samples of the various percent fraction solid are compared to conventional high pressure die casting samples and there is a discussion of the why the Thixomolding process produces superior properties. In addition, a comprehensive corrosion resistance study was completed utilizing uncoated corrosion plates in an salt spray environment (ASTM B117).
Technical Paper

Achieving Acceptable Cp and Cpk Values in Sheetmetal Stampings

1999-09-28
1999-01-3193
Detail parts are approved during several different phases of the prototype build cycle. There is much pressure at all stages to meet strategic body quality targets. Parts stamped for assembly must meet a process capability requirement of Cpk>1.33. For final PSO (process sign off), as called out in the PPAP (Production Part Approval Process) manual, the requirement can be increased to meeting a Cpk>1.67. During the 2000 Neon part approval process, the PPAP requirements provided the guideline necessary for consistent buy-offs. However, on some critical parts the Cpk requirement made part approvals difficult to accomplish. Occasionally this caused resources to be focused in the wrong place. This paper will discuss how a requirement of Cpk>1.33 can make part approvals more difficult to achieve and change the entire application of a tolerance.
Technical Paper

A Springback Study on Three Rail Type Panels

1999-09-28
1999-01-3196
A springback study on three rail type panels is summarized. Numisheet'96 S-rail, A/S P rail II and a Daimlerchrysler rail are presented with experiment data and FEA simulation predictions. The details of the measurement on experiment samples and simulation models are illustrated. The comparison between the experiment data and the simulation results from four different softwares is made on separate cases. The correlation between experiment data and simulation results is analyzed.
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