On the Influence of Body-Stiffness to Vehicle Dynamics

Markus Wick, Vehicle Dynamics CAE

FORD Werke GmbH

Elmar Teipen, FORD Werke GmbH, Development Engineer, Vehicle Dynamics Methods & Tools

Subject

• Presentation of current CAE methods in Veh. Dynamics

• CAE-Methods to assess Body-Structure• Application on Component- and Vehicle-Level• Cost and Benefit of these Methods

• Examples from development work

• Body & Subframe• Local & Global Stiffnesses

CAE-Methods in Vehicle Dynamics

• General Approaches • Finite-Element-Method (FEM)

Numerical Solver for elasto- / elastoplastic problemsStructural elements: Beams, Shells, Plates, Springs , …Material Properties (Hooke, etc.)Structural elements are connected by FE-nodesSolver: e.g. MSC ©NASTRAN, ABAQUS, etcResults: Deform., Stresses, Strains, Forces, …Application: Static, Dynamic, Modal, …���� Answering the Question:

„what is the wheels’ reaction?“

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Multibody Systems (MBS)• Rigid Bodies• Connected via Springs, Damper, Joints, etc.• Mechanical principles:

• Principle of virtual work• D‘Alemberts Principle • Lagrangian equation …

• Formulation of numerical resolvable equations• Solver: e.g. MSC.ADAMS, Simpack, …• Results: Displacements, Forces, Velocities, Acceler ations, …• Application: Kinematics, Elastokinematic, Dynamic M aneuvers���� Answering the Question:

„what is the wheels’ reaction?“

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Development of Components in ChassisShort turnaround time at component & system level d evelopmentApplication: target stiffness values local & global

• Example: Front A-Arm point (pt.3) at frame• Stiffness important for steering-precision• Frame rigidly fixed to ground • Fixed in DOF 1-6• Single lat. Load [kN]• ���� Deformation [mm]• ���� Stiffness [kN/mm]• Parallel Forces (cornering)• Relative deform. (measurable)• Result: Stiffness target

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Example: Stiffness Pt3 at frame (fixed to ground)scaling: 500 x

Fy left = 1 kNFy left = 1 kN

Fy right = 1 kN

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Advantages• Simple Modeling of this Load case• Reproducible for different variants• Short simulation time• Simple Validation to rig-test

• Disadvantages• Unrealistic boundary condition• „Shortcut“ of structural elast.• Low practical relevance

• Alternative• Integration of next higher assembly: body• More Realistic modeling���� Attachment of subframe to body

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Enhancement: Stiffness Pt3 at Frame (attached to Body)

• Attachment of Frame to Body (with bushes where appl icable)• Body structure Supported to ground (at rocker)

DOF 1-6Fy links = 1 kN

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Enhancement: Stiffness Pt3 at Frame (attached to Body)

Deformationsskalierung: 500 xPt3: Fy left = 1 kN

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

CAE-Methods in Vehicle Dynamics

• Advantages• Considers local stiffness of body structure

• Disadvantages• Constraint forces at support points• Deformations at rocker• Unrealistic stiffness values

• Consequence• Demands a method for stiffness

calculation under realistic boundary conditions

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

MBS-Methods in Vehicle Dynamics

• Question: What is the wheels’ reaction?• Reproduction of vehicle kinematics & elastokinemati cs

• Modular vehicle modelEfficient assembly, concise modifications,Structured parameterization

• Calculation of Vehicle- & System characteristicsBounce, Roll motion of Front & Rear-Suspension syst ems

Influence of structural elasticities on system behav ior?Transient maneuver on full vehicle level

Stiff body (with simplified torsional spring model)Influence of structural elasticities on vehicle dyna mics?

Assembly of FEM-Body and MBS-Full vehicle Model

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

FEM-Body in MBS-Vehicle Model

• Cost(Windows-Workstation Dell Precision 650, 2x 3.06 GH z Intel Xeon, 4 GB RAM, 300 GB Hard disc)

• Pre-Processing BodyDecision on TB / BIPModifications (Interface / Masses)

• Solver: MSC.NASTRAN (ADAMSMNF)Calculation Time 4-35h (dep. on model size)MNF-File: ca 100KB – 8GB (dep. on details)

• Solver: ADAMS/ChassisCalculation time: factor 5-30

• Post-Processing:Numerical- and memory intensive graphics

• Benefit• Vehicle responses to variations on local & global s tiffness variations

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on K&C-Rig

• Prototype test: wheel movement under enforced load• 3 variants

• Proto 1 (stiff Body)• Proto 2 (flex. Body)• Proto 3 (flex. Body – stiffened)

• Investigations on:• Deformation Animation• Veh. Dyn. Metrics

Roll/Bounce motionToe ComplianceCamber ComplianceWheelcentre-Displ.

• Influence on additional PartsTop mount (tower) brace, Tunnel brace …

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on K&C-Rig

• scaling: 250 x

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on K&C-Rig

• scaling: 250 x

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on K&C-Rig

•

Fro

nt S

uspe

nsio

nR

ear

Sus

pens

ion

Camber Compliance

���� Differences in Body-Structure of Prototypes measurable on virtual K&C-Rig

Inital � Rigid : - 11,1 %

Initial � Modified: -1,5 %

Initial � Rigid : - 4,0 %

Initial � Modified: - 1,8 %

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on Maneuver

• 4 Variants (all flexible)• 1) Proto 1 initial setup (Reference)

Flex BodyFlex Frames (Front & Rear)

• 2) Proto 2 (Modified with initial weight)Brackets at BodyWeight neutral ���� + stiffness only

• 3) Proto 2 (Modified)Additional weight of structure���� + weight

• 4) Proto 2 (Modified rigid)Rigid Body with brackets���� stiffness → ∞ (borderline case)ADAMS Standard

• Example: Step Steer• 100 Km/h• 45 Deg. SWA-Step (left turn)

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on Maneuver

• Modal Coordinates in Time Domain

Curve: Lateral Acceleration Straight: Accelerate / Brake

A

C

B D

A

B

C

D

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on Maneuver

• Example: Step Steer (left turn)• Open loop maneuver• Proto 1 (grey) → Proto 2 (green)

Same mass and distribution

• ResultsLess deformation on rear endLess under steer

(Steady state turning radius -2m)Increased slip-angle

(Peak +3.9% Steady state +3.7%)Increased lateral acceleration

(Peak & Steady state +1.1%)Increased yaw-rate

(Peak +2.0% Steady state +1.1%)���� different cam track (Open-Loop-Maneuver)���� influence of Body-stiffness

apparent on Vehicle-level

scaling: 250 x

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Influence of Body flexibility on Maneuver

• Example: Closed Loop Maneuver• Lap ADAMS/Driver controller• ADAMS Driveline Model included• Flex. Body and Frames

930 m

115 m

Length: 3.125 mWidthmax.: 10 mWidth min.: 2 m

scaling: 250 x

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Summary

• Enabler to evaluate the contribution of the body st ructure to Veh. Dynamic metrics.

• Modal participation• Body-side changes are observable in response• Combination with ADAMS/Driver and Driveline Model

possible• Methodology is not standardized but currently under

development• Cost / Benefit balance• Further potential to optimize Routines (MSC/Nastran ->

MSC/Adams coupling)• Recommended implementation in the vehicle developme nt

cycle• Major program gateways/milestones• Specific effect investigations: Body-Modifications

(Convertible), accessories (tower brace)

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Outlook & Potential

• Analysis of Body and Sub-frame interaction• Purpose: target setting for Body and subframe

• Correlation to other attribute stiffness targets• Body torsion- bending-stiffness , Equivalent

stiffness, inertia relief

• Improved evaluation of the effect of local stiffening measures• ADAMS parts to simulate principal bracings (w/o

elasticity)• Tower brace• Body braces (tunnel, front-end, …)

• Racing applications

Summary

Maneuver

K&C-Rig

MKS

FEM

Introduction

Q&A

Questions & Answers

Contact Details

EMEA05-041On the Influence of Body-Stiffness to Vehicle

Dynamics

Markus WickFORD Werke GmbHVehicle Dynamics CAEmwick@ford.com

Increasing Stiffness

Increasing Stiffness

Weight Influence

Increasing Stiffness

Increasing Stiffness

• Side Slip Angle increases with stiffness

• No observable effect of additional mass

Incr. Stiffness