Experimental and Numerical Methods for Optimizing the Dynamic Comfort of Seat Structures (4. VDI-Tagung Humanschwingungen, Würzburg) Dr. Karl Siebertz, M.Sc. J. Lem Ford Forschungszentrum Aachen M.Sc. A. Siefert Wölfel Beratende Ingenieure

Contents Motivation & Requirements Methods Virtual Parameter Study Experimental Virtual Parameter Study Setup Simulation Results Conclusions

Interfaces between Driver and Vehicle seat back head-rest steering wheel seat cushion Driver arm rest foot rest pedals floor gearshift From all interfaces, the seat has the highest influence, as it supports the postural stability of the driver!!! Vibration comfort is mainly influenced by the dynamic characteristics of the seat

Requirements for Seat Development Static Comfort Dynamic Comfort Ingress / Egress Driving Feel Package Crash Seat Design NVH Adjustability Flexibility Durability primary ride secondary ride force feedback sound visual feedback road feel Seat characteristics should correlate with the vehicle!!!!!!

Evaluation of Dynamic Seat Characteristics Seat Transfer Function Enhanced Evaluation Methods for Seat Transfer Function Dimensions of Perception: Occupant on seat: A1 = rms(aZ |3-10 Hz) Impulse: A2 = rms(aZ |1-30 Hz) High frequency shake: A3 = rms(aZ |11-30 Hz) Body vibration: A4 = rms(aZ |1-3 Hz) Seat Transfer Function Enhanced Evaluation Methods for Seat Transfer Function Main characteristics of STF: Resonance frequency and magnitude: Ares, fres Isolation frequency: fiso Isolation performance: Aiso qBX qBY response qS,B on seat surface excitation q0 on seat rail qCZ q0Z q0Y q0X

Influences on Seat-Transfer-Function Occupant Small woman (w05) ... Medium man (m50) Large man (m95) Design / Seat Type Foam with suspension Foam with deep pan Foam material distrib. ... 5 10 15 20 25 30 35 NOT INFLUENCEABLE INFLUENCEABLE Foam PUR-Mixture Static response curve Damping Dynamic stiffness ... Excitation: AK Freeway Highway Cobblestone Rough road track Idle running Driving speed ... TASK: „Optimize the design and the material properties in consideration of the occupant and the expectant excitations!“

Investigation Methods for Development Objective Tests Subjective Evaluations CAE Methods must be combined for optimal development Objective criteria Results must be reproducible for straight forward development Human models Information is required in early phase of development CAE methods

Virtual Investigation by CASIMIR/Automotive CAE tool for simulation of seating comfort quantities Model setup reflect real testing scenarios Seat structure: frame, joints, drives,… Unoccupied seat: + foam pads, padding, trim Occupied seat: + occupant model

Material Identification & Classification Testing Static Identification Dynamic Identification Interpolation Classification

Human Body model CASIMIR upper torso: head, neck and arms lumbar spine model back model musculature compliant body surface dynamic model of viscera buttocks model skeleton model: pelvis and legs

Simulation Typical Output Seat pressure distribution Meat-to-Metal Backset value H-point Seat-transfer-function

Experimental Testing by Using MEMOSIK® Vibration dummies are used to replace the human occupant for increasing reproducibility Technically, vibration dummies have a phenomenological setup, i.e. in case of MEMOSIK that it represents the phenomena of the ‘ Dynamic Masses’, defining the occupants influence on the STF Thereby effects out of different human must be included f05 -- f05 -- m50 -- m95 magnitude [kg] m50 frequency [Hz] m95

Application Scenarios for Seat Optimization design target magnitude [-] Evaluation of Setup Variants Testing against target corridors Definition of testing procedures for supplier for reproducible results Benchmark Testing Comparison of different seats Specification of influence factor out of vehicle and seat design on final exposition of occupant magnitude [-]

Numerical Parameter Study For focusing on influence of varied parameters the study is carried out with simplified model Variations are only carried out for the cushion Investigated parameters are: Overall thickness Thickness ratio between upper and lower layer Material combination of both layers Suspension type (rigid, middle, soft) Backrest Cushion: lower layer Cushion: upper layer For each parameter three states have been investigated The variant design was carried out by a DoE procedure A Box-Behnken test plan lead finally to 24 setups

Simulation Simulation was carried out in two steps Static Seating under gravity considering all nonlinear effects Dynamic simulation of z-excitation considering frequency depending effects Evaluation of the variants was carried out by the following quantities: Maximum pressure peak Contact area Vertical displacement of upper and lower surface Maximum amplitude of STF Average value of STF in predefined frequency ranges

Results for Dynamic Seating Comfort Strong influence of parameters can be observed on STF Difference between variants is about 0.6 resp. 25 % of the maximum value Final an principle component analysis was carried out leading to an optimal design Standardized Pareto Chart for STF Maximum Main Effects Plot for STF Maximum D C CD AB A B AC BD BC AD A B C D

Conclusion CASIMIR/Automotive was applied for virtual parameter study Influence of parameters was observed by principle component analysis Thereby optimization of seating comfort is possible for: Dynamics by tuning STF Statics by tuning seat pressure distribution and overall displacement Implementation of this procedure within seat development process would reduce number of required hardware prototypes By additional final tests with MEMOSIK and test drivers a good correlation was found enabling the combination of all three methods

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