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Technical Paper

Multi-Disciplinary Aerodynamics Analysis for Vehicles: Application of External Flow Simulations to Aerodynamics, Aeroacoustics and Thermal Management of a Pickup Truck

2007-04-16
2007-01-0100
During the design process for a vehicle, the CAD surface geometry becomes available at an early stage so that numerical assessment of aerodynamic performance may accompany the design of the vehicle's shape. Accurate prediction requires open grille models with detailed underhood and underbody geometry with a high level of detail on the upper body surface, such as moldings, trim and parting lines. These details are also needed for aeroacoustics simulations to compute wall-pressure fluctuations, and for thermal management simulations to compute underhood cooling, surface temperatures and heat exchanger effectiveness. This paper presents the results of a significant effort to capitalize on the investment required to build a detailed virtual model of a pickup truck in order to simultaneously assess performance factors for aerodynamics, aeroacoustics and thermal management.
Technical Paper

An Integrated Design and Appraisal System for Vehicle Interior Packaging

2007-04-16
2007-01-0459
Static seating bucks have long been used as the only means to subjectively appraise the vehicle interior packages in the vehicle development process. The appraisal results have traditionally been communicated back to the requesting engineers either orally or in a written format. Any design changes have to be made separately after the appraisal is completed. Further, static seating bucks lack the flexibility to accommodate design iterations during the evolution of a vehicle program. The challenge has always been on how to build a seating buck quickly enough to support the changing needs of vehicle programs, especially in the early vehicle development phases. There is always a disconnect between what the seating buck represents and what is in the latest design (CAD), since it takes weeks or months to build a seating buck and by the time it is built the design has already been evolved. There is also no direct feedback from seating buck appraisal to the design in CAD.
Technical Paper

Transient Dynamic Analysis of Suspension System for Component Fatigue Life Estimation

2007-04-16
2007-01-0638
For suspension systems, fatigue and strength simulations are accomplished mostly at the component level. However, the selection of loading conditions and replication of boundary conditions at the component level may be difficult. A system level simulation eliminates most of the discrepancy between component level and vehicle level environment yielding realistic results. Further advantage of system level simulation is that the boundary conditions are limited to suspension mounting points at body or frame and the loading is limited to wheel-end or tire patch loading. This provides for a robust set of boundary constraints that are known and repeatable, and loads that are simpler and of relatively higher accuracy. Here, the nonlinear transient dynamic behavior of a suspension system along with its frame and mounting was simulated using a multibody finite element analysis (FEA).
Technical Paper

Robust Optimization Design of the Power-train Mounting System of the Light Truck

2007-04-16
2007-01-0556
In order to improve the isolating performance of the power-train mount system of one light truck with the uncontrollable parameters of the stiffness and location, a robust optimization design problem based on the 6-DOF dynamical equation of the power-train mount system is presented in the paper. For the robust optimization design of the power-train mount system with the uncontrollable parameter variations, a deterministic, non-gradient approach for objective robust and constraint robust optimization is discussed based on the design of orthogonal experiment and Genetic Algorithm.
Technical Paper

Simulation Process to Investigate Suspension Sensitivity to Brake Judder

2007-04-16
2007-01-0590
Brake judder, which is a low frequency excitation of the suspension and thus, the body structure during low-G braking, is mainly felt at the steering wheel and throughout the vehicle structure. Brake judder is a problem that costs manufacturers millions of dollars in warranty cost and undesirable trade offs. The magnitude of judder response depends not only on the brake torque variation, but also on the suspension design character-istics. This paper discusses the judder simulation process using ADAMS software to investigate the suspension design sensitivity to the first order brake judder performance. The paper recommends “tuning knobs” to suspension designers and vehicle development engineers to resolve issues in the design and development stages. Various suspension design varia-bles including geometry and compliances as well as brake related characteristics were investigated.
Technical Paper

Eliminating Drum Brake Squeal by a Damped Iron Drum Assembly

2007-04-16
2007-01-0592
Control of drum brake squeal is difficult to accomplish. After many trials guided by CAE and previous experience, for a passenger car it was felt that changing the metallurgical characteristics of the drum would lead to improved noise performance. The chemistry of the drum casting material was altered. The carbon equivalent was modified by increasing carbon and silicon content of the castings as well as changing the other materials. The integral hub and drum assembly was tested on two different dynamometers. The results were also verified by finite element complex eigenvalue analysis. Finally the solution was validated through vehicle level testing - Los Angeles City Traffic (LACT). For the structural consideration rotary fatigue was evaluated by CAE comparison followed by test rig confirmation. The higher carbon equivalent material drums successfully eliminated the annoying squeal in customer vehicles.
Technical Paper

Sensitivity Analysis of Powertrain Cooling System Performance

2007-04-16
2007-01-0598
This paper identifies the difference in powertrain cooling system content levels using a nominal and a +3 Standard deviation maximum temperature design approach. Variation simulation analysis tools are used along with a 1-D cooling system performance model to predict resulting temperature distribution for different combinations of input variable populations. The analysis will show differential in powertrain cooling system content, mass, and impact to fuel economy for a nominal vs. +3 sigma design approach.
Technical Paper

Neat Biodiesel Fuel Engine Tests and Preliminary Modelling

2007-04-16
2007-01-0616
Engine performance and emission comparisons were made between the use of 100% soy, Canola and yellow grease derived biodiesel fuels and an ultra-low sulphur diesel fuel in the oxygen deficient regions, i.e. full or high load engine operations. Exhaust gas recirculation (EGR) was extensively applied to initiate low temperature combustion. An intake throttling valve was implemented to increase the differential pressure between the intake and exhaust in order to increase and enhance the EGR. The intake temperature, pressure, and EGR levels were modulated to improve the engine fuel efficiency and exhaust emissions. Furthermore, a preliminary ignition delay correlation under the influence of EGR was developed. Preliminary low temperature combustion modelling of the biodiesel and diesel fuels was also conducted. The research intends to achieve simultaneous reductions of nitrogen oxides and soot emissions in modern production diesel engines when biodiesel is applied.
Technical Paper

Effect of Materials Stack-ups on Fatigue Performance of DP780 and Aluminized Coated Boron Steel GMAW Lap Joint

2007-04-16
2007-01-0634
In this study, fatigue performance of Gas Metal Arc Welded (GMAW) joint for 1.5 mm uncoated DP780 and 1.0 mm and aluminized coated boron (or USIBOR) steel was investigated. Metallurgical properties of DP780 to coated boron steel dissimilar steel lap joints were evaluated using optical microscopy. Microhardness traverse, static and fatigue tests were conducted on these joints. Finite element analysis (FEA) was used to identify the stress distribution of the weld joints with different stack-ups and at same loading conditions. It was found that position of the material (top or bottom in lap joint configuration) had a significant impact on fatigue performance of the dissimilar joint. The amount of heat introduced by welding to coated boron steel is also believed to be important to the fatigue performance of the dissimilar joints. The findings in this study can be used when aluminized boron steel is involved in dissimilar steel and dissimilar thickness GMAW lap joint design.
Technical Paper

Finite Element Analyses of Fastened Joints in Automotive Engineering

2007-04-16
2007-01-1204
In this paper, the methodology of finite element analyses of fastened joints in automotive engineering applications is described in detail. The analyses cover a) the possibility of slippage of the spacer with the design/actual clamp load, and under critical operating loads; b) the strength of the fastener and other structural components comprising the joint under the maximum clamp load. The types of fastened joints, the mechanical characteristics of the joints, the relationship of clamp load to torque, the design and maximum clamp loads, the finite element model meshing and assembly, the non-linearity due to contact, the determination of gaps and stack-up, and the nonlinear material simulation and loading procedures are described. An analysis example of a fastened joint on chassis is also illustrated.
Technical Paper

Strength Prediction and Correlation of Tow Hook Systems using Finite Element Analyses

2007-04-16
2007-01-1206
In this paper, tow hook systems and their functional objectives are briefly introduced. General analysis considerations in strength prediction of a tow hook system are described. These considerations contain nonlinear, clamping and material property simulations. Connections and loading simulation of a tow hook system model are discussed in details. A correlation example of a tow hook system is illustrated. This study shows that detailed modeling of a tow hook system is a fundamental requirement for accurate strength prediction and good correlation between finite element analysis and testing.
Technical Paper

Modeling, Validation and Dynamic Analysis of Diesel Pushrod Overhead Bridged Valve Train

2007-04-16
2007-01-1256
A bridged valve train configuration exhibits complex dynamic behavior due to the uniqueness of the special elephant foot/bridge/valve structure. Consequently, this system arrangement presents significant design challenges in system stability at high speed, high load, wear, no-follow and valve seating velocity, etc. An efficient way to gain a thorough understanding of the behavior of this type of valve train system and to drive the valve train design improvement is through the use of an effective dynamic simulation tool. In this paper, an advanced CAE tool developed by Ford Motor Company for the bridged type valve train simulations has been described. This automated CAE tool provides a complete virtual ADAMS-based simulation environment for the pushrod bridged valve train system analysis. This paper also presents the correlation and validation between the simulations and the measurements. The design analysis for the bridged valve train has been discussed briefly in this paper.
Technical Paper

Design of Vehicle Air Conditioning Systems Using Heat Load Analysis

2007-04-16
2007-01-1196
The objective of this paper is to describe a Computer Aided Engineering (CAE) model and its applications for A/C system development at early design stages. This CAE tool calculates the heat load of the vehicle passenger compartment with considerations of solar radiation, conductive/convective heat transfer through the body shell, and any passengers present in the vehicle. A data bank of 6 glass types, 9 surface finishes and 15 material properties are available to increase simulation flexibility. This heat load model can be used as a stand alone tool to calculate the steady-state thermal load of the passenger compartment under users' pre-defined conditions. When interfaced with an A/C refrigerant subsystem model, this integrated CAE tool is capable of evaluating the impacts on A/C system performance when body structures and/or operating conditions are changed.
Technical Paper

Resistance Spot Weldability of Three Metal Stack Dual Phase 600 Hot-dipped Galvanized Steel

2007-04-16
2007-01-1363
Fuel economy and federal safety regulations are driving automotive companies to use Dual Phase and other Advanced High Strength Steels (AHSS) in vehicle body structures. Joining and assembly plays a crucial role in the selection of these steels. Specifications are available for the resistance spot welding (RSW) of lower strength sheet steels, covering many aspects of the welding process from the stabilization procedure to endurance testing. Currently, specifications in the automotive industry for RSW with AHSS are limited. It is well known that welding of a thickness ratio greater than 1:2 poses a challenge. To utilize thinner gauge AHSS panels on body-in-white, welding schedules to join the thin to thick sheet steel stack-up are needed. Most of the existing published work was conducted on uncoated sheets and welded to the same thickness.
Technical Paper

Driver Airbag Linear Impactor Dynamic Testing Method and Data Analysis

2006-04-03
2006-01-1436
A sub-system test method for driver air bags has been established to quantify their dynamic restraint capability. The sub-system includes a driver airbag module as well as a steering wheel with rim supported. The test is called Driver Air Bag Linear Impactor Test – Dynamic (DABLIT-D). This test method can be used for not only A to B comparisons, but also for evaluating the performance of any DAB module design in general. A variety of impactor, pendulum and drop tower test methods are currently used at suppliers. DABLIT-D is aimed to standardize airbag testing. A DOE test series was done to determine the best test parameters. Production and prototype hardware were tested to investigate the characteristics of the sub-assemblies that provide restraint capability. A modification of the Weibull function was used to characterize the resultant data.
Technical Paper

A Nonlinear Transient CAE Method for Vehicle Shift Quality Prediction

2006-04-03
2006-01-1640
Automatic transmission gear changes are transient disturbances in a non-linear system, during which the effective ratio of the transmission is continually changing. In addition, vehicle characteristics can very strongly influence customer perception of the shift event. Further, the interface elements between the vehicle and powertrain are often crucial in determining the quality of shift feel. This paper presents a validated CAE method that employs the ADAMS software to predict the intricate dynamics of the vehicle response due to transmission shift events. First principles of the transmission modeling elements are described. Model simulation results are compared to vehicle test data. A method to quantify the customer's perception of vehicle shift quality is discussed. Model simulation results for a FWD vehicle application are also analyzed.
Technical Paper

Modal and Impact Simulations of a Tire in Time Domain

2006-04-03
2006-01-1626
Tires are a key factor determining vehicle NVH performance. Tire models are usually reduced to linear modal models in the frequency domain even though the tire behaves nonlinearly in vibration and impact performance. Improving the CAE capability of vehicle NVH prediction requires an appropriately representative tire model and finite element analysis program capable of non-linear transient analysis. In this paper a detailed tire model of solid elements has been developed. Using an explicit integration finite element program, the nonlinear effects in tire modal extractions were studied. The finite element model tire was inflated and preloaded against a flat platform with applied impulse loads to simulate the laboratory tire hammer impact tests. The tire modes in each direction were then extracted with fast Fourier transformation to compare with traditional finite element method generated modes and vehicle NVH test data.
Technical Paper

A Comparison of the Effect of E85 vs. Gasoline on Exhaust System Surface Temperatures

2007-04-16
2007-01-1392
With concerns over increasing worldwide demand for gasoline and greenhouse gases, many automotive companies are increasing their product lineup of vehicles to include flex-fuel vehicles that are capable of operating on fuel blends ranging from 100% gasoline up to a blend of 15% gasoline/85% ethanol (E85). For the purpose of this paper, data was obtained that will enable an evaluation relating to the effect the use of E85 fuel has on exhaust system surface temperatures compared to that of regular unleaded gasoline while the vehicle undergoes a typical drive cycle. Three vehicles from three different automotive manufacturers were tested. The surface of the exhaust systems was instrumented with thermocouples at specific locations to monitor temperatures from the manifold to the catalytic converter outlet. The exhaust system surface temperatures were recorded during an operation cycle that included steady vehicle speed operation; cold start and idle and wide open throttle conditions.
Technical Paper

Simultaneous Real-Time Measurements of NO and NO2 in Medium Duty Diesel Truck Exhaust

2007-04-16
2007-01-1329
The goal of the present work was to investigate the ability of the SEMTECH®-D Portable Emissions Measurement System (PEMS) to provide simultaneous, accurate, real-time (1Hz) measurements of NO and NO2 in vehicle exhaust. Extensive chassis dynamometer laboratory evaluation studies of the SEMTECH® system were conducted. The instantaneous (1Hz) NOx emissions were measured using a conventional chemiluminescence analyzer (CLA) and were compared to the sum of the instantaneous NO and NO2 measurements from the SEMTECH®-D. The sum of the NO and NO2 emissions measured by the SEMTECH® were in excellent agreement (within 95% in most cases) with the total NOx measurements from the conventional CLA. During the laboratory evaluation studies, several Federal Test Procedure (FTP) drive cycles were conducted. Examples of the NO and NO2 concentration and mass emissions measured using the SEMTECH®-D are presented along with the corresponding SEMTECH®-D detection limits.
Technical Paper

Transmission Mount Assembly Modelling for Load Simulation and Analysis

2007-04-16
2007-01-1348
Transmission mounts are usually tested as an assembly and typically only translational stiffnesses are provided. The torsional stiffness of the assembly is traditionally estimated based on experience in load simulation and analysis. This paper presents a procedure to estimate the torsional stiffness of the transmission mount assembly by using the test data. The effects of the torsional stiffness on the simulation results are also discussed.
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