C. Bastien*, J. Christensen*, M. Blundell *,

M. Stefuca**, N. Ravenhall***, A. Garewal***

Towards the Lightweighting of

Low Carbon Vehicle Architectures

using Topology Optimisation

EHTC 2011 - Bonn

* Coventry University, Department of Engineering and Computing, Priory Street, Coventry, CV1 5FB

** Altair Engineering Ltd., Imperial House, Holly Walk, Royal Leamington Spa,CV32 4JG

*** Jaguar Cars Ltd., Engineering Centre, Abbey Road, Coventry, CV3 4LF

Content

• Low Carbon Vehicle Technology Project (LCVTP)

Deliverables

• LCVTP Work Packages

• BIW Holistic Optimisation

– Locked Elements Density (LCED)

– Boundaries vs. Inertia Relief

• Limitations of Topology Optimisation

• Generation of front-end Crash Structure

• Floor Design Proposal

LCVTP Deliverables

• Project £19million

• Sponsor: Advantage West Midlands

• Hybrid HEV architecture

• Lightest structure possible (<200kg)

• EuroNCAP compliant

• Best in class for torsional rigidity

• Affordable for high volumes (>100,000)

– Steel baseline is assumed

• Based on Tata Beacon vehicle concept

LCVTP Work Packages

Work

Package Description Leader 1 Batteries Tata

2 Drive Motors Zytek

3 Power Electronics Warwick University

4 High Voltage Electrical Distribution Systems Tata

5 Auxiliary Power Units Ricardo

6 Vehicle Supervisory Control Ricardo

7 Lightweight Structures Coventry University

8 Vehicle Dynamics Jaguar/ LandRover

9 HVAC and System Cooling Coventry University

10 Parasitic Losses Ricardo

11 Energy Recovery and Storage Ricardo

12 Aerodynamic Performance Coventry University

13 HMI Warwick University

14 JLR Validation Vehicle Jaguar/ LandRover

15 Tata Validation Vehicle Tata

Presented Study

• 18 months of research connected with the Low Carbon

Vehicle Technology Project (LCVTP)

• Design Process used to firstly obtain a first draft for this

BIW, utilising topology optimisation, by means of Altair

HyperWorks.

• Process includes: – Drivetrain and general packaging requirements associated with a Hybrid

Electric Vehicle (HEV).

– Includes aspects such as sensitivity analysis (of the results obtained)

– in addition to HEV roof topology, including potential effects of the

recently proposed changes to the Federal Motor Vehicle Safety

Standard (FMVSS) 216.

BIW HOLISTIC OPTIMISATION

Loadcases Considered

# Load case Applied force Applied force magnitude,

EVM = 1200 kg

1 Front impact(ODB) 60 * g * EVM 707 kN

2 Pole impact 300 kN 300 kN

3 Side barrier impact 300 kN 300 kN

4 Roof crush (A-pillar) 2.5 * g * EVM 29.5 kN

5 Low speed rear impact 150 kN 150 kN

6 High speed rear impact 60 * g * EVM 707 kN

7 Torsion Unit

• Average element size: 25mm.

• 103000 nodes

• 527000 elements.

• Material: Steel (MAT1) - linear

elastic isotropic.

LoCked Elements Densities

• Elements near load

disappeared (instability)

• Solution: large loads

when connected to non-

design elements (helped

a lot) 70 iterations

• Keep areas as small as

possible in order to

maximise computation on

design volume (loads and

SPCs)

Initial Results

• Used beam sizing to

evaluate section

areas and BIW mass

(208kg)

• On target for mass

• Increase detail within

optimisation process

Floor Topology (SPC)

• Battery: 200kg

• Range extender: 110kg

• Effect of topology

• Floor topology when

using SPCs

Floor shape topology

output independent of

battery permutations !

Not logical…

Floor Topology (IR)

• Floor topology with SPC

do not make sense (IR

investigated)

• IR balances external

loading with inertial loads

and accelerations within

the structure itself.

• “Addition" of an extra

displacement-dependent

load to the load vector

[kadd]

• HPC Solver: 2 core

• SPC: 16.5 hours

(stiffness matrix needs

reforming each time the

BC are altered)

• IR: 1.4 hours (straight

solving)

F k u

IR

add

k 0F k u u

0 k

Comparison of Floor

Topologies

• SPC • IR

Batteries

Same void

regardless of

battery

permutations

IR result

more

logical

Sensitivity Study

• Impact angle variation

was then considered

in the topology

optimisation

• Battery Stiffness was

considered

No major changes

on the topology

results

Investigation on

FMVSS216 (Roof crush)

• Investigation of the

potential effects of the

recently proposed

changes to the Federal

Motor Vehicle Safety

Standard (FMVSS) 216

upon the BIW topology.

• Big changes

• General layout:

Optimised BIW

LIMITATIONS OF TOPOLOGY

OPTIMISATION

Limitation of linear

topology optimisation • SPC are not possible to

use for ideal component

location.

• IR can be used.

• LCED “restraints” the

optimisation

• Optimisation model

stability

• Widespread

“triangulation”

• .

• “Full” inertial / dynamic

effects not possible to

include

• Buckling modes not

captured (e.g.

longitudinals)

• Bifurcation problems

• Interpretation of results:

– Passenger cell

– Crash structure

GENERATION OF FRONT-END

CRASH STRUCTURE

Front Crash Structure

Longitudinal beams + crush cans (1), bumper

beam (2), short longitudinal beams (3),

transverse beam (4)

2 1

4

3

Front Crash Structure

• ‘g’ max: 32.9 ‘g’

• Intrusion: 526 mm

• Mass: 40.9 kg

Front Crash Structure

• Coupling crash simulations with HyperMorph and HyperStudy to investigate the influence of shape and thickness modification

• Optimization was focused on entire structure and individually on the upper transverse beam

• HyperMorph enabled defining complex shape modifications (variables)

• DOE runs generated and evaluated using HyperStudy (HyperOpt engine applied to find the optimum set of parameters)

Reduced thickness of the sheet metal components and redesigned upper transverse beam

Front Crash Structure

• Weight reduction:

3.154 kg (-7.7 %)

• Max displacement increased

from 526 mm to 539 mm

Max acceleration increased

from 32.8 ’g’ to 37.4 ’g’

• Crash pulse characteristic

remained

FLOOR DESIGN / BATTERY

CASING PROPOSAL

Battery Casing Design

• Battery load: 30’g’

Floor Proposal

• Recommended battery

position for LCVTP

minimum BIW mass

(under driver seat)

• Battery encased in cradle

secured in horse-shoe

hybrid floor (honeycomb

and metal)

LCVTP Conclusions

• A holistic method has been derived to engineer

a HEV lightweight structure using Altair

HyperWorks

• Use of LCED and IR are necessary

• Results make sense for the ‘safety cell’

• Still some limitations on areas subjected to

buckling where a bifurcation event cannot be

calculated accurately with an implicit solver

(explicit is needed)

LCVTP Next steps

• Re-develop a beam model of final proposal to

validate BIW mass and check for buckling

integrity and displacements of ‘safety cell’

• Perform detailed CAD data and base initially

section properties on beam section study

• Validate safety deliverables based on shell FEA

model

Acknowledgements

• The authors would like to thank:

– Mr. Mike Dickison, Mr. Richard Nicholson (both of Coventry

University),

– Mr. Alistair Crooks of MIRA Ltd.

– Tata Motors European Technical Centre (TMETC)

– Jaguar Land Rover (JLR)

– Warwick Manufacturing Group (WMG)

– Advantage West Midlands (AWM)

– the European Regional Development Fund (ERDF)

– and other contributors to the Low Carbon Vehicle Technology

Project (LCVTP) for supplying data and guidance to assist in the

making of this presentation.

Thank you for your attention.

...any questions?