Towards the Lightweighting of Low Carbon Vehicle Architectures using Topology Optimisation
Towards the Lightweighting of Low Carbon Vehicle Architectures using Topology Optimisation EHTC 2011 - Bonn C. Bastien*, J. Christensen*, M. Blundell *, M. Stefuca**, N. Ravenhall***, A. Garewal**** 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 WorkPackage 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.
Loadcases Considered • Average element size: 25mm. • 103000 nodes • 527000 elements. • Material: Steel (MAT1) - linear elastic isotropic. Applied force magnitude, # Load case Applied force 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
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 • Floor topology when• Range extender: 110kg using SPCs• Effect of topology Floor shape topology output independent of battery permutations ! Not logical…
Floor Topology (IR)• Floor topology with SPC F k u do not make sense (IR k 0 investigated) F k IR u u• IR balances external 0 k add loading with inertial loads and accelerations within • HPC Solver: 2 core the structure itself. • SPC: 16.5 hours• “Addition" of an extra (stiffness matrix needs displacement-dependent reforming each time the load to the load vector BC are altered) [kadd] • IR: 1.4 hours (straight solving)
Comparison of FloorTopologies• SPC • IR Batteries Same void IR result regardless of more battery logical permutations
Sensitivity Study• Impact angle variation • Battery Stiffness was was then considered considered in the topology optimisation No major changes on the topology results
Investigation onFMVSS216 (Roof crush)• Investigation of the • Big changes potential effects of the recently proposed • General layout: changes to the Federal Motor Vehicle Safety Standard (FMVSS) 216 upon the BIW topology.
Limitation of lineartopology optimisation• SPC are not possible to • “Full” inertial / dynamic use for ideal component effects not possible to location. include• IR can be used. • Buckling modes not• LCED “restraints” the captured (e.g. optimisation longitudinals)• Optimisation model • Bifurcation problems stability • Interpretation of results:• Widespread – Passenger cell “triangulation” – Crash structure• .
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 Proposal• Recommended battery • Battery encased in cradle position for LCVTP secured in horse-shoe minimum BIW mass hybrid floor (honeycomb (under driver seat) 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.
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