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Faurecia: Getting to the bottom of car seat designLMS Virtual.Lab Motion impacts the design process atEuropes leading automotive seating manufacturer


2/52LMS International| [email protected] | www.lmsintl.com

Engineers at Faurecias Methods and Systems Research and Development department tackle

some of the toughest mechanism design problems and work against the product development

clock using LMS Virtual.Lab Motion simulation software to efciently develop optimal seating

mechanisms that balance safety, comfort, ergonomy, and most certainly, functionality.

Car seats, obviously the most direct

contact between people and machine,

help create an overall feel for the

vehicle and important perception

of brand value. Even as perspective

buyers sit in a car on the showroom

oor, seating systems give a rst and

lasting impression and they often

are a factor in the purchase decision.

So carmakers go all out to incorporate

a range of seating functions made toimpress including a mind-boggling array

of convenient front-seat adjustments

and controls for lower-back, shoulders,

seat height, cushion angles, back tilt

and body contour as well as retractable,

adjustable and foldable rear seats.

Buried under fabric and foam

Hidden beneath layers of cushion fabric

and foam padding are some of a vehicles

most complex mechanisms. Gears,

levers, cams, ratchets and other partsoften must operate with the precision

of a Swiss watch while being able

to lock into place instantly for crash

protection. To meet the strict technical

requirements from automakers, cost

and weight must be minimized, and seat

suppliers must work against the clock

to create workable designs that meet

platform and production requirements.

To handle this type of complex

mechanical design that typically

balances hundreds of contact and

friction points, seat engineers

typically combine manual calculations,experience with past designs, and

numerous build-and-test prototypes

to develop new seating mechanisms.

The process is time-consuming and

typically results in a workable design,

but not optimal performance due to

time and budgetary constraints.

France-based Faurecia is taking a

huge step beyond these standard

industry procedures. Europes leading

automotive seating system manufacturer

and one of the top three worldwide,the company also designs and

manufactures door panels, instrument

panels, acoustic packages and other

assemblies for major automakers

around the world. Customers include

Audi, BMW, Cadillac, Peugeot, Renault,

VW, Ford, Mercedes Benz and Toyota.

Quick, error-proof seatmechanism modeling

One recent project required kinematic

and load calculations to be performed

on a seat height adjuster mechanism

controlled by the driver/passenger using

a pump lever with a low operating torque

for easy actuation. Pressing the lever

rotates a gear set that moves the seat

up and down. A rotating ring with ngers

that engage slots on the perimeter of

the assembly serves as a clutch that

holds the gear in place after adjustment.

Inside the ring, a rotating cam moves ball

bearings that compress a set of springs,

creating a return torque that retracts the

pump lever into its original position.

The design is a compromise of threeimportant functions of the mechanism:

the fail-safe ability of the system to

stay locked into position during a crash,

the pump force needed to actuate the

Key to the successful model was LMS Virtual.Labs ability to represent non-

permanent contact between parts. In this case, the height adjuster mechanism

has 18 contact points represented between the cam, ring and bearings.


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mechanism and the return torque of the

ball-and-spring assembly of the command

device, explained R&D engineer Dr.

Tanguy Moro. In particular, the role

of friction between the bearings, cam,ring and springs is critical in providing

sufcient return torque for the lever.

In this study, a virtual model of the

mechanism was created in LMS

Virtual.Lab Motion by importing data

from CAD in this case, the CATIA

V5 system used by Faurecia design

engineers. Because of the tight CATIA

integration, data on part geometries,

assembly joints and kinematic

constraints was transferred directly into

LMS Virtual.Lab Motion with a singleclick of a button without conversion.

Modeling was quick, straightforward

and much less error-prone.

Key to the successful model was LMS

Virtual.Labs ability to represent non-

permanent contact between parts an

important feature since contact plays

a critical role in determining friction

between so many moving parts. In this

case, the height adjuster mechanism

has 18 contact points represented

between the cam, ring and bearings.

LMS International| [email protected] | www.lmsintl.com

Modeling these contacts in LMS

Virtual.Lab Motion lets seat engineers

accurately predict normal and tangential

forces on these components.

Finding the counter-intuitive solution

Using optimization capabilities within

LMS Virtual.Lab, a series of design of

experiment (DOE) simulations were

then automatically performed on the

mechanism model based on boundary

conditions and constraints entered

by Dr. Moro. By automatically running

simulations and comparing results for a

set of numerous different combinations

of mechanism design parameters particularly friction coefcients between

the various parts the software

performed a sensitivity analysis

identifying the variables with the greatest

impact on mechanism performance

and the trade-offs necessary for an

optimal design. Results were mapped

on a response surface plot to visualize

the inuence of these design variables.

The sensitivity analysis showed that the

coefcients of friction between the cam,

the bearings and the ring are not the

main parameters which determine the

return torque of the assembly and the

retraction of the pump lever. The LMS

Virtual.Lab sensitivity analysis found a

solution that was not intuitively obviousand totally different from what the

design engineers expected, noted Dr.

Moro. By focusing on bearing friction,

they were barking up the wrong tree.

Using LMS Virtual.Labto blend CAE and test

On another project, LMS Virtual.

Lab simulation was used to study the

backrest fold-down capability to increase

rear-vehicle storage capacity. Dynamic

simulations were also used to study thereal-life behavior of the car seat under

actual passenger seating conditions.

Currently under development, this

Easy Break function relies on springs

at the lever joints to help actuate the

seat with minimal applied pressure.

The springs must provide enough

torque to overcome friction and easily

fold down the seat without imposing

an impact danger to a child or pet,

said Dr. Moro. The system absolutely

must provide interference-free motion

The design of seating mechanisms can be signicantly improved and

performed much more efciently using LMS Virtual Lab Motion.

Dr. Tanguy Moro, Fauricia, R&D engineer

LMS Virtual.Lab analyzed the kinematic motion of the backrest and related loads as well as a range of spring torques. This determined relative

movements and loading due to contact and friction between different mechanism parts, especially between the backrest fabric and seat cushion.


4/54LMS International| [email protected] | www.lmsintl.com

with a high level of control throughout

the entire fold-down process.

LMS Virtual.Lab analyzed the kinematic

motion of the backrest and related loads

as well as a range of spring torques.

A critical aspect of the simulation wasdetermining relative movements and

loading due to contact and friction

between different mechanism parts,

especially between the backrest

fabric and seat cushion. Frictional

losses in such areas were determined

empirically and integrated into the

unied virtual model using LMS Virtual.

Lab for blending actual test and CAE

representations. In this way, the study

determined an optimal spring torque,

which was validated by experimental

tests on a hardware prototype.

1-2-3 model templatefor future designs

More broadly, this fold-down function

will hopefully be the basis for a generic

backrest model used by designers for

numerous future seating systems. With

this model, designers simply enter key

parameters into a simulation template

instead of recreating models from scratch

each time. This template workow is

possible thanks to LMS Virtual.Lab

Motions ability to automate repeated

processes with macros written in VBA

(Visual Basic for Applications) scripting

for parameterized models. Result post-

processing would also be automated; as

would the optimization of mechanism

designs according to target requirements.

Simulation and optimization based

on LMS Virtual.Lab would have a

tremendous impact on automotive

seating system development and a

deep understanding of the complex

mechanical behavior of these systems,

said Dr. Moro. The design of seatingmechanisms can be signicantly

improved and performed much more

efciently using LMS Virtual.Lab Motion.

More importantly, designs developed in

virtual space can be optimized beyond

the capability of manual processes.

From a business perspective, the

implications are staggering, allowing a

supplier to increase project throughput

and respond to automaker orders

much faster with better products

than was ever before possible.


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APC Fauricia 2009