1. 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

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

3. 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

4. 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!!!!!!

5. 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

6. 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!“

7. 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

8. 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

9. Material Identification & Classification
Testing
Static Identification
Dynamic Identification
Interpolation
Classification

10. 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

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

12. 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

13. 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 [-]

14. 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

15. 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

16. 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

17. 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

18. Thank You for Your Attention!!!!