VOLKSWAGEN ALTAIR Vertical Dynamics With MotionSolve 20091104 Dbo

Dirk Bordiehn, Katja Fritzsch

04.11.2009

vertical dynamics of an offroad race car (MotionSolve)

( Altair MBD-conference USA )

04.11.2009; Dirk Bordiehn,Katja Fritzsch

vertical dynamics of an offroad race car (MotionSolve) 2

agenda

Volkswagen Motorsport (history, field of action) ................................ 3

Simulation at VW-M example RaceTouareg ................................ 4

Challenge load identification .............................................................. 5

MBD model ....................................................................................... 7

- spring/damper ............................................................................... 8

- tire model ..................................................................................... 10

Results ............................................................................................ 13

Summary and conclusion ................................................................ 16

MB

D s

imula

tio

nV

W-M



motorsport at Volkswagen

rally raid:

- marathon rally world cup

- main event: Dakar Rally (Race Touareg)

- success in Dakar 2009: double victory (over all)

1st victory of a diesel powered car

Track racing:

- 24h race at Nrburgring (Scirocco)

- success in GT24 2009: place 1+3 in class 2L-turbo (SP3T)

place 1+2 in class altern.fuel. (AT)

- participation and engine supplier Formula 3 (EuroSeries,

GB-F3, ATS cup D)

Touring cars:

- ADAC Volkswagen Polo cup in Germany, Polo cup in India

- JettaTDI cup in USA, Scirocco cup in China, etc.

VW-Motorsport GmbH (since 2004), 100% subsidiary of VWAG

CEO: Kris Nissen

150 employees

competing in rally raid, track racing and touring car

championships



simulation at VW-M example RaceTouareg

suspension (FEA)

chassis (FEA)

vehicle dynamics (MBD)

intake / radiator (CFD)

engine (FEA)

aerodynamics (CFD)



load identification

Why do we have problems to acquire representative loads?

standard scenarios:

- vehicle crash due to EuroNCAP: velocity v = compulsory

barrier = compulsory

post processing = standardized

production vehicle development:

- comfort analysis (NVH: acoustic, vibration, static)

1. BiW eigenfrequency > ##Hz

steering wheel vibration > ##Hz

fictitious values

bottom-factor

motorsport:

no standard scenarios:

- comparison to preceding model

- analysis of occurred damage

risk: delayed start of production, recall campaign

no large-scale test series, were driving in prototypes.

regulations,

laws

based on

empiric studies

test and validation phases

risk: total failure, injury to persons

we have to

- find reasonable and ample

load assumptions

- make robust predictions

too late!



load identification simplified scenarios

Standard tests of production vehicles (e.g. VWs test area Ehra) are not applicable

for this car.

Important despite simplicity!

Example: KickBack as accident.

accident Dakar 2005 accident CER 2008

Advantage of simplified tests:

fewer parameters in the simulation

(rigid ground, only vertical dynamics)

reproducible

small local test area useable

own simplified test scenarios

RaceTouareg on artificial hill

The real load situation (offroad) is very complex and barely reproducible.



MBD model

chassis: rigid BiW with connection to ground

front axle: suspension FA, damper FA, spring FA, steering FA, power train FA

rear axle: suspension RA, damper RA, spring RA, power train RA

road: profile and visualization, interaction tyre-2-road

The MBD-model is based on submodels:

payload: spare wheels, fuel tank (>90gal)

spring/damper

tire model

parameter study(not shown in this presentation)



MBD model spring/damper

suspension in principle:

travel [mm]velocity [mm/s]

compression rebound

ride height

Forc

e [N

]

1 2 3

Aufbau

Rad

1

2

3

Helfer- und Hauptfeder

Dmpfer mit Anschlag

Gasdruck

wheel

vehicle

main a. helper spring

damper w. bump stop

gas pressure

suspension (clean) suspension (dirty)



stiffness main spring 1

stiffness helper spring 1

stiffness main spring 2

stiffness helper spring 2

free length main spring 1

free length helper spring 1

free length main spring 2

free length helper spring 2

block length main spring 1

block length helper spring 1

block length main spring 2

block length helper spring 2

preload length main spring 1

preload length helper spring 1

coupler height main spring 2

coupler height helper spring 2

spring parameters

travel [mm]

Fo

rce

[N

]

compression rebound

MBD model spring/damper

xmin

3) transfer point 2) compr. 1) rebound

Generation of spring function by forms (datasets)

1

additional advantage:

visual verification (spring length

changes with input values)

12

3

2

function is generated from the input data

help

er

spr.

main

spring

coupler



+

known?

MBD model tire model

+ +radial stiffness

+

importance

friction

damping

lateral stiffness

parameter

All loads pass through the tire

tire model is very important in vehicle dynamics

tire properties must be approximated by MS-basic functions

Unfortunately ...

MotionSolve9.0 has no tire model

external tire models cant be linked to MS9.0

only very few tire data is available (deformable ground?)

Which properties are important (in vertical dynamics) ?

How can they be modeled in MS/MV9.0 ?

+impact form.

variable

variable

contact form.

versatility

active force

springs

+RigidBody contact

(implicit or modeled)

easy to

use?method



Impact-Funktion vs. Kontaktfunktion

0.00E+00

5.00E+03

1.00E+04

1.50E+04

2.00E+04

2.50E+04

3.00E+04

3.50E+04

0.00E+00 1.00E+01 2.00E+01 3.00E+01 4.00E+01 5.00E+01 6.00E+01

Verformung [mm]

Ve

rtik

ale

Kra

ft F

z [N

]

Impact-Funktion

Kontakt H3D

Kontakt zwei Kegel

Kontakt Zylinder

Steifigkeit nach Gleichnung 17

forc

e

displacement

IMPACT function

contact H3D

contact 2 cones

contact cylinder

measured stiffness

contact stiffness


static simulation of radial stiffness to verify different modeling techniques

Fimpact = kze c

rigid body contact produces unstable stiffness results

only the active IMPACT-force reproduces the target stiffness well

Fimp.

xu max.penetr.

damp.max

yu

STEP-function




Fwheel = F0 + F1 + ... + Fx-1 + Fx-1 + Fx-1 + ... + F100

= 0 + 0 + ... + 70% + 30% + 0 + ... + 0

= 100%

IMPACT-force shows good stiffness results between two markers.

How to combine that with an arbitrary road profile?

lots of local markers !

The force on the wheel

is the total of all local forces.

With the implementation of

the STEP-function only the

markers near the wheel have

non-zero values.

artificial hill with markers

(autom. generated from points of a spline)

Advantage of this very simple tire model:

easy to automate (only new spline needed)

mathematical representation leads to fast and smooth results

Fwheel



results kinematic and compliance

k&c test bench @ VW-Wolfsburg

Spurweitennderung Vorderachse

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30

Spurweite vorne [mm]

Fed

erw

eg

[m

m]

track width change

track width [mm]

wh

ee

l tr

ave

l [m

m]

Spurwinkelnderung Vorderachse

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10

Spurwinkel vorne [min]

Fed

erw

eg

[m

m]

camber angle change

camber angle [mm]

wh

ee

l tr

ave

l [m

m]

Sturzwinkelnderung Vorderachse

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

Sturzwinkel vorne [grad]

Fe

de

rwe

g [

mm

]

toe angle change

toe angle [mm]

wh

ee

l tr

ave

l [m

m]

verification:

comparison of

- k&c test (full vehicle) and

- k&c simulation of single axle

k&c simulation of a front axle

test simulation

close match



results artificial hill

pretensioning

of rear axle

front axle

hits obstacle

rear axle

hits obstacle

trav

el[m

m]

time [s]



results cuvette (natural depression)

in reality KickBack occurs in depressions (cuvette),

when bump stop is active

specific velocity

too fast energy in damper not in bump stop

specific depth

too shallow energy in spring not in bump stop

Simulations of several sculptured cuvettes show promising flat spots in wheel travel,

but car jumps too high, too long and too soon.

Reason is, that the real bump stop has both, elastic and damping properties ( FBS,test = f(z, ) )

it absorbs energy.

The bump stop in the simulation is only stiffness (FBS,sim = f(z) ) and stores energy.

Bump stop characteristics are very important, but they are unfortunately not known.

bump stop active

simulation

flat spot

displacement [mm] or velocity [mm/s]

forc

e [N

]

time [s]

travel[m

m]

wheel travel

flat spot= bump stop

testtime [s]

travel[m

m]



summary and conclusion

the pilot project vertical vehicle dynamics with MotionSolve is based on a simplified scenario:

simple car (no bushings ...)

very simple tire model

only vertical dynamics

very few real data available

almost no experience

with these premises all targets are met:

model setup within HyperWorks (mainly MotionView, a bit HyperMesh)

user-friendly data input with forms

fast and stable simulations with MotionSolve

close match of test and simulation data

better understanding of effect of payload on KickBack (not shown)

very successful project !

next steps:

integration of a more sophisticated tire model (partner product FTire?)

transverse dynamics (tire, driver, power train, bump stop)

flex bodies (all parts are available as FE-models [Optistruct])



End

thank you for your attention.

VOLKSWAGEN ALTAIR Vertical Dynamics With MotionSolve 20091104 Dbo

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