Vertical Dynamics of an Offroad Race Car (Motionsolve)

vertical dynamics of an offroad race car (MotionSolve)

( Altair MBD-conference USA )

Dirk Bordiehn, Katja Fritzsch 04.11.2009 agenda

§ Volkswagen Motorsport (history, field of action) ...... 3 § Simulation at VW-M – example RaceTouareg ...... 4 VW-M § Challenge load identification ...... 5 § MBD model ...... 7 - spring/damper ...... 8 - tire model ...... 10 § Results ...... 13 MBD simulation MBD § Summary and conclusion ...... 16

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 2 Katja Fritzsch motorsport at Volkswagen

§ VW-Motorsport GmbH (since 2004), 100% subsidiary of VWAG § CEO: Kris Nissen § 150 employees § competing in rally raid, track racing and touring car championships § 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 § Touring cars: - ADAC Volkswagen Polo cup in Germany, Polo cup in India - JettaTDI cup in USA, Scirocco cup in China, etc. § Track racing: - “24h race” at Nürburgring (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) 04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 3 Katja Fritzsch simulation at VW-M – example RaceTouareg

vehicle dynamics (MBD) aerodynamics (CFD)

suspension (FEA) intake / radiator (CFD)

chassis (FEA) engine (FEA)

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 4 Katja Fritzsch load identification

Why do we have problems to acquire representative loads? production vehicle development: § standard scenarios: regulations, - vehicle crash due to EuroNCAP: velocity v = compulsory laws barrier = compulsory based on post processing = standardized empiric studies - comfort analysis (NVH: acoustic, vibration, static) fictitious values 1. BiW eigenfrequency > ##Hz „bottom-factor“ steering wheel vibration > ##Hz § test and validation phases § risk: delayed start of production, recall campaign motorsport: § no standard scenarios: we have to - comparison to preceding model too late! - analysis of occurred damage - find reasonable and ample § no large-scale test series, we’re driving in „prototypes“. load assumptions - make robust predictions § risk: total failure, injury to persons

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 5 Katja Fritzsch load identification – simplified scenarios

The real load situation (offroad) is very complex and barely reproducible. Standard tests of production vehicles (e.g. VWs test area “Ehra”) are not applicable for this car. ⇒ own simplified test scenarios

Advantage of simplified tests: – fewer parameters in the simulation (rigid ground, only vertical dynamics) – reproducible – small local test area useable RaceTouareg on artificial hill

Important despite simplicity! Example: KickBack as accident.

accident Dakar 2005 accident CER 2008

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 6 Katja Fritzsch MBD model

The MBD-model is based on submodels: spring/damper § front axle: suspension FA, damper FA, spring FA, steering FA, power train FA § rear axle: suspension RA, damper RA, spring RA, power train RA § chassis: rigid BiW with connection to ground „tire model“ § road: profile and visualization, interaction tyre-2-road § payload: spare wheels, fuel tank (>90gal)

parameter study (not shown in this presentation)

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 7 Katja Fritzsch MBD model – spring/damper

suspension in principle:

vehicleAufbau 1 mainHelfer- a. und helper Hauptfeder spring 2 damperDämpfer mit w. Anschlag bump stop 3 gasGasdruck pressure

1 2 3

wheelRad Force [N] Force ride height

compression rebound travel [mm] velocity [mm/s]

suspension (clean) suspension (dirty)

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 8 Katja Fritzsch MBD model – spring/damper

Generation of spring function by forms (datasets)

spring parameters function is generated from the input data stiffness main spring 1 stiffness helper spring 1 3 2 stiffness main spring 2 1 stiffness helper spring 2

free length main spring 1 helper spr. coupler 2 free length helper spring 1 Force [N] free length main spring 2 1 free length helper spring 2 compression rebound block length main spring 1

block length helper spring 1 main spring travel [mm] block length main spring 2 block length helper spring 2 x preload length main spring 1 min preload length helper spring 1 coupler height main spring 2 coupler height helper spring 2

additional advantage: visual verification (spring length changes with input values) 3) transfer point 2) compr. 1) rebound

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 9 Katja Fritzsch MBD model – “tire model”

All loads pass through the tire ⇒ tire model is very important in vehicle dynamics Unfortunately ... § MotionSolve9.0 has no tire model § external tire models can’t be linked to MS9.0 § only very few tire data is available (deformable ground?) ⇒ tire properties must be approximated by MS-basic functions

Which properties are important (in vertical dynamics) ? How can they be modeled in MS/MV9.0 ? easy to method versatility parameter importance known? use? lateral stiffness –– – RigidBody contact contact form. + radial stiffness + + + (implicit or modeled) impact form. + damping + – springs variable – friction –– – active force variable –

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 10 Katja Fritzsch MBD model – “tire model”

static simulation of radial stiffness to verify different modeling techniques

Impact-Funktion“contact” vs. Kontaktfunktionstiffness 3.50E+04 Fimp. Impact-FunktionIMPACT function Kontaktcontact H3D H3D 3.00E+04 Kontaktcontact zwei 2 cones Kegel Kontaktcontact Zylinder cylinder Steifigkeitmeasured nach stiffness Gleichnung 17 2.50E+04

2.00E+04

1.50E+04force VertikaleKraftFz [N] 1.00E+04

5.00E+03

0.00E+00 0.00E+00 1.00E+01 2.00E+01 3.00E+01 4.00E+01 5.00E+01 6.00E+01 displacementVerformung [mm]

§ rigid body contact produces unstable stiffness results § only the active IMPACT-force reproduces the target stiffness well damp. max F = k ×∆ze – c×ż STEP-function impact yu xu max.penetr.

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 11 Katja Fritzsch MBD model – “tire model”

§ IMPACT-force shows good stiffness results between two markers.

§ How to combine that with an arbitrary road profile? Fwheel ⇒ lots of local markers ! artificial hill with markers (autom. generated from points of a spline) The force on the wheel Fwheel = F 0 + F 1 + ... + F x-1 + F x-1 + F x-1 + ... + F 100 is the total of all local forces. = 0 + 0 + ... + 70% + 30% + 0 + ... + 0 With the implementation of = 100% the STEP-function only the markers near the wheel have non-zero values.

Advantage of this very simple tire model: § easy to automate (only new spline needed) § mathematical representation leads to fast and smooth results

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 12 Katja Fritzsch results – kinematic and compliance

test simulation verification: comparison of - k&c test (full vehicle) and - k&c simulation of single axle

→ close match

k&c test bench @ VW-Wolfsburg k&c simulation of a front axle

track width change camber angle change toe angle change Spurweitenänderung Vorderachse Spurwinkeländerung Vorderachse Sturzwinkeländerung Vorderachse

140 140 140 130 130 130 120 120 120 110 110 110 100 100 100 90 90 90 80 80 80 70 70 70 60 60 60 50 50 50 40 40 40 30 30 30 20 20 20

Federweg [mm] Federweg 10 10

Federweg [mm] Federweg 10 Federweg [mm] 0 0 0 -10 -10 -10 -20 -20 -20 -30 -30 -30 -40 -40 -40 wheel travel [mm] travel wheel wheel travel [mm] travel wheel -50 [mm] travel wheel -50 -50 -60 -60 -60 -70 -70 -70 -80 -80 -80 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 Spurwinkel vorne [min] track Spurweitewidth vorne [mm][mm] camber angle [mm] toeSturzwinkel angle vorne [grad] [mm] 04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 13 Katja Fritzsch results – artificial hill

front axle hits obstacle rear axle hits obstacle

pretensioning travel [mm] of rear axle

time [s]

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 14 Katja Fritzsch results – cuvette (natural depression) in reality KickBack occurs in depressions (“cuvette”), wheel travel when bump stop is active flat spot § specific velocity = bump stop too fast → energy in damper not in bump stop § specific depth travel [mm] too shallow → energy in spring not in bump stop time [s] test

bump stop active flat spot force[N] travel [mm]

displacement [mm] or velocity [mm/s] time [s] simulation 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, ż) ) 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.

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 15 Katja Fritzsch 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])

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 16 Katja Fritzsch End

thank you for your attention.

04.11.2009; Dirk Bordiehn, vertical dynamics of an offroad race car (MotionSolve) 17 Katja Fritzsch