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SAE TECHNICALPAPER SERIES 2004-01-1481

Analytical Design of Cockpit Modulesfor Safety and Comfort

John Z. Lin and Stephen M. PitrofDelphi Corporation

Reprinted From: Advances in Interiors and Instrument Panels(SP-1848)

2004 SAE World CongressDetroit, MichiganMarch 8-11, 2004

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2004-01-1481

Analytical Design of Cockpit Modules for Safety and Comfort

John Z. Lin and Stephen M. PitrofDelphi Cor por ation

Copyright © 2004 SAE International

ABSTRACT

This paper reviews the state of the art on analyticaldesign of cockpit modules in two most crucialperformance categories: safety and comfort. On safety,applications of finite element analysis (FEA) for achievingrobust designs that meet FMVSS 201, 208 and 214requirements and score top frontal and side NCAP star-ratings are presented. On comfort, focus is placed onNoise, Vibration and Harshness (NVH) performance.Cutting-edge analytical tools for Buzz, Squeak and Rattle(BSR) avoidance and passenger compartment noisereduction are demonstrated. Most of the analyticalresults shown in this paper are based on thedevelopment work of a real-life application program.Correlations between the analytical results and physicaltest results are included. Examples of ComputationalFluid Dynamics (CFD) analysis for climate control arealso included. At the end, the road map toward 100percent virtual prototyping and validation is presented.

INTRODUCTION

Ever-increasing market competition has drivenautomakers to produce stylish, safe and durable vehiclesat a faster-than- ever pace and reduced costs. A cockpitmodule as the “brain” of a vehicle and the major human-machine interface plays a vital role in distinguishing oneOEM from the rest of the pack. A high performancecockpit module can be defined as an integrated, cost-effective interior product that provides modernfunctionalities and styling, maximized safety, durabilityand comfort. While customers are attracted to nichestyling design and more convenience provided bytelecommunication and navigation devices as well asentertainment electronic packages, they have alsobecome increasingly educated in safety and comfortrelated performance. In a sense, what safety means toautomakers and customers is beyond Federal MotorVehicle Safety Standards (FMVSS), which determine thesalability of all vehicles marketed in U.S. It is the safetyratings such as NCAP (New Car Assessment Program)issued by NHTSA and J.D. Power Initial Quality Surveysthat set the bar for high-performance cockpit modules.

Relevant to cockpit modules, FMVSS 201 and 208regulate interior impact protection and occupant crashprotection respectively. FMVSS214 specifies

performance requirements for protection of occupants inside impact crashes. While FMVSS208 requires aimpact speed of 25 mph and unbelted anthropomorphicdummies, a NCAP test for frontal crash protectionutilizes belted dummies with 35 mph initial impact speed.The regulated impact speed for FMVSS214 is 33.5 mph.However, for side crash New Car Assessment Program,that impact speed is increased to 38.5 mph with the restof the test conditions remain the same. Figure 1 andTable1 shows the criteria for frontal and side NCAPratings, respectively. It is important to note that superiorNCAP performance does not attribute to a particularcockpit module only but the entire restraint systemincluding Driver Air-Bag (DAB), Passenger Air-Bag(PAB), collapsible steering column/wheel, lower torsoenergy absorption systems (knee bolster and glove boxassemblies) and seat belts.

Figure 1. NCAP (Frontal Impact) Rating Criteria

Table 1. Side NCAP star rating criteria (TTI –The Thoracic TraumaIndex =1/2 (GR + GLS ) where GR is the greater of the peak accelerationof either the upper or lower rib and GLS is the lower spine peakacceleration, both expressed in g’s)

S id e N C A P S ta rR a tin g T T I1 S ta r > 9 52 S ta r 8 5 -9 53 S ta r 7 2 - 8 54 S ta r 5 9 - 7 25 S ta r < 5 9

200

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30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

5-star

4-star

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30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

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30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

5-star

4-starHIC

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30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

5-star

4-star

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1000

30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

200

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1000

30 35 40 45 50 55 60 65 70C G

Chest Acceleration (g)

5-star

4-starHIC

Except seat belts, the rest of the above mentionedsubsystems belong to the cockpit module. Hence, asystematic approach in cockpit module design andoptimization is essential for NCAP performance.

For Side NCAP performance, cockpit modules play aless important role than vehicle body structures such asrockers, floor pans and doors. This is especially evidentfor passenger cars with longer wheelbases and trucksand SUV’s because the side impact barrier willcompletely miss the cross-car beam. However, forcompact and mid-sized vehicles, the cross-car structureof a cockpit module does take substantial amount ofimpact load and very often it will make a difference inLINCAP rating.

On comfort, a squeak and rattle free cockpit module isdefinitely a major contributor to customer’s satisfactionon a vehicle’s perceived quality [1][2]. According to J. D.Power’s initial quality surveys, Buzz, Squeak and Rattle(BSR) is one of the top five customer dissatisfactioncomplaints. As vehicle OEMs continue to improve theperceived quality of their products, combating BSRproblems and eventually producing BSR-free vehicleshas become increasingly crucial in the vehicledevelopment cycle. Cockpits (instrument panelassemblies) have been well known to be a majorcontributor to interior BSR noises due to their complexityin terms of the number of components, modules andconnections.

The major challenges for producing high performancecockpit modules lie in: (1) Ever-increasing demand forcost cutting (material costs and prototype costs) andfaster-to-market (reducing development cycle), and (2)The pursuit of spaciousness and sharpness (line-to-linezero gaps) in cockpit module design, resulting indramatically-reduced overall packaging space anddistance between parts. Utilizing time- and cost-effectiveanalytical tools has proven to be the only choice to meetthese challenges.

The purpose of this paper is to demonstrate the availableanalytical tools that can be utilized to help cockpitmodule suppliers to deliver high performance cockpitmodules that meet and exceed customer expectations.

The rest of this paper is organized into the followingsections. An overview of available analytical tools anddesign philosophy is outlined in the next section.Analytical design for safety will follow, which coversFMVSS related analyses and a systematic approach forfrontal crashworthiness. Analytical design for comfortincludes both traditional NVH analyses and a newtechnology for BSR prediction. SEA (Statistical EnergyAnalysis) and CFD analyses are also reviewed in thissection. SEA is a useful tool for passenger compartmentnoise reduction while CFD is the industry standardmethod for climate control related performance. At theend, conclusions will be drawn, accompanied by a roadmap to 100 percent virtual prototyping.

ANALYTICAL TOOLS AND DESIGNPHILOSOPHY

Most of the analytical tools used for cockpit modulesafety and comfort analyses are based on Finite ElementMethods (FEM), which have become increasingly robustand powerful over the years due to the advance incomputing power. The following is an inconclusive list ofindustry standard CAE software for cockpit moduleanalytical design:

Hypermesh: Direct CAD data input, meshing, post-processing, line geometry output.

NASTRAN: Linear static, natural frequency, frequencyresponse analyses (NVH, Sag, Stiffness, etc.)

LS-DYNA3D: 3D Non-linear dynamic simulations –occupant protection, crashworthiness (FMVSS201, 208,214, airbag deployments, etc.)

Nhance.BSR: Buzz, Squeak and Rattle hot spotpredictions

AutoSEA: Mid-High frequency noise transmission viaStatistic Energy Analysis

Star-CD/Fluent: CFD based HVAC Air-flow, heat transferanalysis.

The key in design and engineering of a high performancecockpit module is to apply FEA and other analytical toolsfrom concept to final production design. In the process,FEA is mostly in the leading role in meeting performancetargets while design takes the lead in packaging, toolingand GD&T. Nevertheless, FEA and Design shouldalways work side by side and converge at milestonedesign releases. Figure 2 shows schematically such adesign philosophy and process. From a programexecution viewpoint, a co-located design and FEA teamis highly desirable.

Figure 2. Schematic design philosophy for high performancecockpit module.

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ANALYTICAL DESIGN FOR SAFETY

Cockpit module - the major human-machine interfaceand the carrier of occupant protection devices suchdriver and passenger airbags and energy absorbingsteering columns – plays a vital role in safetyperformance of a vehicle. Achieving FMVSS compliancehas always been and will continue to be the foundationfor auto safety. Analyses that address the relevantstandards can provide great insights for meeting themandatory and beyond and dramatically reduce the riskof non-compliance at late stages of product developmentand the cost associated with the subsequent problem-fixes.

FMVSS208 – OCCUPANT CRASH PROTECTION

FMVSS208 regulates the limits of occupant headacceleration (HIC), chest acceleration and compression,femur loads, neck forces and neck injury indexes (Nij’s)in frontal crash impacts (straight and angular). Althougha full vehicle barrier simulation with dummies is theultimate solution for FMVSS208, sled simulations andknee impact simulations at cockpit subsystem levelthroughout product development stages have proven tobe very effective.

Sled

Sled simulations are typically done with LS-DYNA3D.The loading and boundary conditions are setup toduplicate the exact physical sled test. Figure 3 shows atypical sled model consisting of a deformable, clippedfront end, seat buckets and cushions, a rigid floor wherevehicle pulse is applied, driver and passenger sidedummies and a fully loaded cockpit module. The keyfactors in achieving a good correlation with the physicaltest results are: (1) Robust material constitutive modelsfor engineering plastics used for knee bolster and glovebox assemblies, (2) Element size and formulation ofenergy absorption (EA) brackets, (3) Initial positions ofdummies including knee locations and foot placements.For material models, Type 24 – Piecewise linearplasticity model provided in LS-DYNA3D actually does agood job for metals and plastics alike, provided materialfailure strain and strain rate effect is accuratelycharacterized from material tensile tests and unloadingphenomenon is not important.

(a) (b)

Figure 3 (a) A typical sled model at 0 millisecond (b) At 80 millisecond.

Figure 4 shows the correlation between the FEA resultsand physical sled test results for Femur loads, driverhead and chest accelerations.

Figure 4. Correlation between the FEA results and physical sled testresults. Note the steel EA bracket deformation was captured in thesimulation (bottom left) as compared to the post-test photo (bottomright).

As can be seen from those results, a good correlation atsled level is not unreachable. With the confidence inFEA models, sled simulations can play a central role in

the systematic analytical design process outlined later inthis section.

Cockpit-Level Knee Impact

For knee bolster, glove-box and EA bracketsdevelopments, only femur loads are of major concern.Cockpit-level knee impact simulations are goodalternatives other than sleds. They are especially usefulin early stages of subsystems design and developmentwhen all the individual subsystems are being developedin parallel.

There are two types of knee impact models, one hasonly knee forms (caps) representing dummy lower torsosand the other with entire dummy lower torsos included.Figure 5 shows both commonly used knee impactmodels. The knee forms and the pelvises of the lowertorsos are constrained to move in the longitudinaldirection only. The initial velocity is equivalent to 800Joules and 2000 Joules total kinetic energy (or 200 to500 Joules per knee), depending on the size of thedummies. The results from knee form models areaccelerations of knee forms, which are scaled to kneeloads by mass (F=ma). Generally speaking, both modelsprovide conservative results for femur loads. The lowertorso model can also be run in a “quasi-sled” way when avehicle pulse is applied to cockpit body attachments (orthe floor if it is included).

(a) (b)

Figure 5. Cockpit-level knee impact models (a) Knee -form (b) Lower -torso

Table 2 summarizes the pros and cons of the two kneeimpact models

KneeimpactModel

Pros Cons

Knee Form

Quick turnaround, easyset-up, excellent tool forcapturing the worst-casescenario: knee positions,angle variations, hardpoints

Usually over-predicts FemurLoads

LowerTorso

More realistic, goodcorrelation to sleds canbe achieved

Requires longerrun-time

Table 2. Cockpit-level knee impact model comparisons

Air-bag Deployment

Instrument panel retainers, especially those with hiddenPAB doors, are traditionally developed with prototypestatic deployment tests. The number of physical tests istypically in the range of one to two hundreds in order toaddress temperature/age effects (high, low, normal) anddifferent inflator outputs. A robust static deployment FEAmodel is of tremendous benefit from time and costreduction point of view. Such a model can provide greatinsights for the design of instrument panel retainerfeatures, PAB door tear seam patterns, skin/foamscoring depths, and for advanced airbag performance forout-of-position occupants.

Figure 6 show a simulated process of a folded PABbursting through the hidden door of an I/P retainer. Thefolding was carried out using Primer while the simulationwas done in LS-DYNA3D Version 960.

Figure 6. Simulated PAB deployment through an I/P retainer with ahidden airbag door.

The challenges in airbag deployment simulations are: (1)Folding of deflated cushions with irregular configurations,(2) For soft I/P’s, the material constitutive models forskins and foams (strain-rate dependence and failurecharacterization), and (3) Robustness of early stageairbag self-contact and inflation algorithms.

Systematic Approach

As pointed out early on, sled simulations play a key rolein FMVSS 208 performance. Contributions from cockpitmodules are shown in Figure 7 – The flow chart for asystematic approach for achieving FMVSS208compliance and superior NCAP ratings.

This approach starts with full vehicle barrier (0 and +/-30degrees) simulations with a concept or carried-over bodystructure. The goal is to obtain the worst-case vehiclepulse in anticipation of an unusually stiff front end, whichcould be resulting from the attempt to improve IIHSOffset Deformable Barrier (ODB) rating. In parallel to

0 ms 5ms

7ms 14ms

0 ms 5ms

7ms 14ms

vehicle body structure development, analytical designsfor safety subsystems that belong to a cockpit moduleevolve. Virtually validated initial subsystem models willthen be integrated into a sled model (the focal point inthis systematic analytical design approach) for a systemlevel evaluation. This process will repeat over milestonedesign releases with or without prototype buildsdepending on specific OEM requirements until sufficientsafety margins are achieved. Detecting and providingcountermeasures for all kinds of variations in vehiclepulses and individual subsystems is also critical forensuring the success of analytical safety designs.

Figure 7. A systematic approach for FMVSS208 performance.

FMVSS201- INTERIOR IMPACT PROTECTION

FMVSS201 requires that the deceleration of a specifiedlinear impact head form with a 19-kilometer per hourinitial velocity shall not exceed 80 g continuously formore than 3 milliseconds, and during the impact eventinterior compartment doors such as glove box doorsshall remain closed.

From energy absorption viewpoint, there are two ways tocomply with FMVSS 201: (1) Provide sufficient clearancebetween the Class-A surface and any underlying hardpoints. Typically, this clearance ranges from 30 mm to45 mm, and (2) Engineer EA components such as foamblocks, crushable plastic ribs and steel brackets.Strategy (2) is especially challenging except for steel EAbrackets because it requires accurate material modelsfor polymeric foams and engineering plastics such asPC/ABS, TPO, SMA, etc. Once again, strain-ratedependent constitutive model with material failure iscritical in such situations. Xiao [3] provides a goodreference for selecting appropriate material models inLS-DYNA3D. Using refined elements with full integrationin the contact regions and a contact algorithm that allowscrack propagation is also important. Figure 8 shows agood correlation case - the simulated acceleration historyin comparison with the test result for a location at thepassenger center-line near the glove-box latch. Withdetailed modeling of the latch mechanisms (see theinserted picture in Figure 8), the compliance to the glove-box door closure requirement can be assessed also.

Head impact simulations are very well defined per theregulation in terms of initial and boundary conditions.However, difficulty lies in the arbitrarity of impactlocations within the specified head impact zone. How todeal with location variations becomes another majorchallenge for IP retainer designs with packaging spaceand cost constraints.

Figure 8. Simulated acceleration history in comparison with the testresult for a location at the passenger center line.

FMVSS214 – SIDE IMPACT PROTECTION

FMVSS214 specifies performance requirements forprotection of occupants in side impact crashes. The onlyrelevant part within a cockpit module is the cross-carbeam. If designed properly, a cockpit module structurecan become an integrated part of a vehicle bodystructure, especially in the hinge pillar area, and help tominimize the door intrusion. For compact and mid-sizepassenger cars, a stiff cross-car beam with high loadcarrying capacity is definitely a plus for FMVSS 214compliance and a superior Side NCAP rating. Lin andLanka detailed in [4] the analytical design process for amagnesium cockpit structure.

ANALYTICAL DESIGN FOR COMFORT

For cockpit modules, comfort means three major things:(1) Non-shaky steering columns and wheels and I/P trimcomponents during driving and/or idling, (2) Minimizedannoying noises inside the vehicle (e.g., BSR noises,HVAC blower noise, wind noise, engine noise, etc.) and(3) Efficient and effective climate control. Asdemonstrated in this section, these can be addressed viaNVH, BSR, SEA and CFD analyses.

NVH - NOISE, VIBRATION AND HARSHNESS

Eigen-value based modal analysis and frequencyanalysis have become the industry standard methods forevaluating cockpit module NVH performance. Fornatural frequency, typical OEM requirements range from30 HZ to 35 HZ for the first column mode and local I/Pmodes. For idle shake and rough load responsesmeasured at a steering column wheel rim in threedirections, the requirements vary from –20 dB to –40dB

Full Vehicle Airbags

Inflator output,cushionshape/coverageStaticDeployments

I/P

Tear seamKnee bolsterGlove boxEA’s

StaticdeploymentsKnee Impacts(Location &angle variation)

SteeringColumn

Break away loadEA characteristicsBlack Tuffy

Barrier 0 and +/- 30 deg w/Concept/Carry-over Bodystructure and target mass

Worst-case vehicle pulses

Sled Simulations0 & +/-30 deg, 5th% &50th%,Dummy position variations

Confirmation/Correlation/Certification Prototype sleds or barrier tests

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Full Vehicle Airbags

Inflator output,cushionshape/coverageStaticDeployments

I/P

Tear seamKnee bolsterGlove boxEA’s

StaticdeploymentsKnee Impacts(Location &angle variation)

SteeringColumn

Break away loadEA characteristicsBlack Tuffy

Barrier 0 and +/- 30 deg w/Concept/Carry-over Bodystructure and target mass

Worst-case vehicle pulses

Sled Simulations0 & +/-30 deg, 5th% &50th%,Dummy position variations

Confirmation/Correlation/Certification Prototype sleds or barrier tests

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over

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G/BoxLatch

Head Form

G/BoxLatch

Head Form

in terms of power spectral acceleration (referenced to1G). Kulkarni and Thyagarajan [5] provided an in-depthreview of various methods for determining steeringcolumn modes. They concluded that using the quarter-buck free vibration method, which accounts for bodyattachment stiffness, is the most physically realisticmeans without involving clutter of full vehicle modes.

The key factors affect steering column NVH performanceare:

• Natural frequencies of a stand-alone steeringcolumn on a rigid fixture. If the steeringwheel/DAB is represented by a mass-equivalenttest weight only, the first mode (usually thevertical) of the steering column shall be 10 to 15HZ above the in-vehicle, with real steering wheelrequirements (30 – 35 HZ)

• Steering column mounting stiffness provided bythe local features of a cross-car beam.

• Modal alignment to avoid overlapping amongsteering column natural frequencies andpowertrain/suspension frequencies.

Local modes of I/P components are relatively easy to fixwith stiffening ribs. HVAC modules sometimes alsopresent a challenge to cockpit module NVH performancedue to their non-structural masses but very often it canbe resolved by designing in a sufficient number ofattachments to the cross-car structure.

BSR – BUZZ, SQUEAK AND RATTLE

As mentioned previously, cockpit modules have beenwell known to be a major contributor to interior BSRnoises due to their complexity. To combat the problemand eventually produce BSR-free cockpit modules, it ishighly desirable to have a robust analytical tool and applyit at the earliest design stage as possible. Nhance.BSRdeveloped by Lohitsa Inc. appears to be such a viabletool for potential BSR locations identification. Applicationstudies with this software can be found in [6] and [7].While the turnaround time for frequency analysis basedBSR simulations is relatively short, the upfront modelingeffort is somewhat tedious in order to capture all thedesign details down to individual clips. Figure 9 shows adetailed clip FEA model for BSR study.

Typical outputs from Nhance.BSR are shown in Figures10 and 11. Figure 10 is the ranked potential rattle pointmap for a cockpit module mounted on a single shakerdriven fixture. Figure 11 shows the position-time historyof two rattle points within the contacting component pairas well as amplitude and phase spectrums. Themismatch in vibration amplitude at a certain frequencyrange is the source for rattle. In this particular case,because it is a subsystem test only, the floor ductadaptor (the lower part) was not supported by the rearfloor duct at the other end and the rattle was easilyidentified by both the simulation and the physical test.

The simulations in the study [7] correlated well with thetest results at other locations such as the center stackand the glove-box areas.

The current BSR analytical tool only focuses on thedetection of BSR regions but certainly does not addressthe complex question of how this relates to the actualsound levels related to BSR (measured in Sones by N10Zwicker Loudness). Further R&D efforts are invited inthis regard.

Figure 9. A detailed clip model for BSR study

Figure 10 Critical Rattle Points (Sine Sweep Load)

Figure 11 Floor Duct and Adaptor Outlet – Random Load

SEA – STATISTICAL ENERGY ANALYSIS

SEA is an analytical tool complementary to FEA and BEA(Boundary Element Analysis) for high frequency

structure-borne or air-borne (acoustic) noisetransmission and attenuation [8-10]. From a noisereduction point of view, cockpit module serves as asound barrier between the engine compartment and thepassenger compartment. Figure 12 shows schematicallythe test set-up for a typical sound transmission loss (TL)measurement [11]. Energy absorption characteristics(damping) and leakages of a cockpit module are ofimportance for producing a “quiet” car. AutoSEA byVibro-Acoustic Sciences is one of the most popularsoftware applications in the market and has been provento be effective for vibro-acoustic engineering. Figure 13shows the correlation between experimental andAutoSEA sound transmission loss results [11].

SEA models identify critical noise paths and provideseffective design solutions. Therefore, it can be used tooptimize vibro-acoustical performance and to minimizedevelopment costs by selecting the best designconfiguration and material [11]. Typical SEA applications

for cockpit modules include sealing design at the front ofdash and windshield interface and acoustic foammaterial/size selection and placement within a cockpitmodule.

Figure 12. Schematic of the test set-up for a typical soundtransmission loss (TL) measurement [11].

Figure 13. Correlation between experimental and AutoSEA soundtransmission loss results [11].

CLIMATE CONTROL

Providing a comfortable thermal environment in thepassenger compartment of a vehicle is the ultimate goalof HVAC systems. High performance cockpit moduleswithout high performance HVAC systems are simply notsatisfactory. For most passenger cars, HVAC systems(modules and ducts) are integrated into cockpit modulesthrough attachments to the cross-car structure. Somecockpit module designs even turn HVAC ducts into loadcarrying structures replacing the cross-car beam [12, 13].

Analytical design for climate control is based on CFDanalysis, which can be used to address a variety offluid/air flow and heat transfer related engineeringconcerns. For HVAC performance, CFD can be used forduct and outlet design development and optimization,HVAC airflow and thermal mixing development, andblower performance optimization for noise reduction.Figure 14 shows a CFD airflow distribution within aHVAC system.

Figure 14. CFD airflow velocity magnitude contour of a HVAC system(Courtesy Delphi Harrison Thermal Systems)

Aiming at developing high performance HVAC systemsfor the ultimate comfort feeling of occupants in a fullvehicle environment, Delphi Harrison Thermal Systemshas developed a strategy of Virtual Thermal ComfortEngineering and the necessary analytical toolsassociated with it [14]. This virtual tool set provides thecapability of predicting occupant thermal comfort tosupport automotive climate control systems. Figure 15shows the CFD result of airflow distribution inside theentire passenger compartment. Note that models of thehuman thermal regulatory system (“thermal dummies”)are included in the analysis. The comfort model has theability to predict local thermal comfort level of anoccupant in a highly non-uniform thermal environment asa function of air temperature, surrounding surfacetemperatures, air velocity, humidity, direct solar flux, aswell as the level of activity and clothing type of eachindividual. Use of Virtual Thermal Comfort Engineering(VTCE) will allow for exploration of different climate

Source Room(reverberate room)

Receiver Room(anechoic room)

100 dBwhite noise measured

noise

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control strategies as they relate to human thermalcomfort in a quick and inexpensive manner.

Figure 15. Passenger compartment CFD result at outside air mode(Courtesy Delphi Harrison Thermal Systems)

CONCLUSION

A variety of analytical tools that can be used to efficientlydesign and develop high performance cockpit modulesat reduced time and cost are available. These toolshave become mature enough so that when utilized byexperienced users with good physics and engineeringsenses they can simulate the physical reality.

Over the years, analysis and physical prototyping hasbeen co-existing. Although it is not very clear whether ornot this co-existence product development model reallysaves development time and cost because thedevelopment cycle is pretty much controlled by long-leadprototype items, a big push for 100% virtual prototypingand validation is definitely the key for a higher level ofcompetitiveness in terms of faster-to-market and cost-reduction for OEM’s and suppliers alike.

For cockpit module virtual validation, it is the author’sbelief that 100% virtual prototyping and validation isfeasible in the near future, with the helps from basicresearch and development on material and joint propertycharacterization and best practices in design. The majorhurdles towards 100% virtual prototyping and validationas discussed throughout this paper are:

1. Robustness and accuracy of material constitutivemodels for engineering plastics and polymeric foamsunder high strain-rate and large deformations.

2. Early stage airbag inflation modeling and robust self-contact algorithms.

3. Modeling techniques of joints (mechanical fasteners,welds, clips, snaps, etc.) that present the short-termand long-term behaviors

4. Vast amount of computing resources to investigatethe effects of geometrical, spacial, and materialvariations.

5. Simulating long-term durability (e.g., creep and warpunder solar exposure).

ACKNOWLEDGMENTS

The author would like to give thanks to colleagues atDelphi – Mohamad El-Essawi, Ramesh Gummalla, andSwami Natarajan, and Triet Cam of General Motors fortheir support, and to Delphi Modular Cockpit EngineeringGlobal Manager Joe Bertucci and Program ManagerPam Greenwald for their encouragement in writing thispaper. Special thanks to Dr. Lee Zhang and Dr. LinjieHuang for their permission to use the pictures in SEAand CFD sections.

REFERENCES

1. Farokh Kavarana and Benny Rediers, “Squeak andRattle – State of the Art and Beyond”, SAE paper1999-01-1728, Noise and Vibration Conference,Traverse City, Mi, May 17-20, 1999.

2. Robert S. Brines, Lesley G. Weiss and Edward L.Peterson, “ The Application of Direct Body ExcitationToward Developing a Full Vehicel Objective Squeakand Rattle Metric”, SAE paper 2001-01-1554.

3. Xinran Xiao, “Plastic Material Modeling for FMVSS201 Simulation”, SAE paper 2002-01-0385.

4. John Z. Lin and Suresh Lanka, “Development of aDie-Cast Magnesium AM60B Modular CockpitCross-car Beam for FMVSS 214 Compliance andLINCAP Rating”, SAE Paper 04ANNUAL-81, inpreparation.

5. Kumar B. Kulkarni and Rai S. Thyagarajan, “Effectsof Body Attachment compliance on steering columnin-vehicle modes”, SAE paper 2000-01-2692.

6. Naganarayana B P, Shankar S, Bhattachar V S,Brines R S and Rao S, “N-hance: Software foridentification of critical BSR locations in automotiveassemblies using finite element models”, #03NVC-283, Noise & Vibration Conference, SAE-2003, May5-8, Grand Traverse Resort, Traverse City, MI, USA,2003.

7. Mohamed El-Essawi, John Z. Lin, Gary Sobek, B. P.Naganarayana and S. Shanka, “ AnalyticalPredictions and Correlation with Physical Tests forPotential Buzz, Squeak, and Rattle Regions in aCockpit Assembly”, SAE Paper 04AC-102.

8. M. J. Croker, et al., “ Sound Transmission UsingStatistical Energy Analysis”, J. of Sound Vib., Vol.9,pp469-486, 1969.

9. S. M. Clifton, et al., “AutoSEA User Guide”, Vibro-Acoustic Sciences Publication.

10. B. Cimerman, et al., “Incorporating Layered AcousticTrim Materials in Body Structural-Acoustic Models”,Proc. SAE 1995 Noise & Vibration Conf., 951307,1995, pp 611-616.

11. Lijian (Lee) Zhang & Denis Blanchet, “ModelingVibro-Acoustical Behavior of Cockpit Module UsingStatistical Energy Analysis Method”, Proceedings ofInter-Noise 2002.

12. Luis Lorenzo, Scott Burr, Dave Chapman and MickHeckert, “ Evolution of Plastic IP TechnologyTechnical Feasibility of Integrated Modular IPSystem”, SAE Technical Paper 980435.

13. Todd Kovacic, Suresh Lanka and Matthew Marks, “Development of an Integrated Structural HVACInstrument Panel Cockpit System”, SAE TechnicalPaper 2002-01-0309.

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CONTACT

John Z. Lin and Stephen M. Pitrof are currently seniorproduct engineers at Delphi Safety & Interiors,specializing in virtual validation of Cockpit/InstrumentPanel Systems. For additional information, pleasecontact them via email: john.z.lin@delphi.com orstephen.m.pitrof@delphi.com