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Optimised Rear Twist Beam Design

Altair Conference

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Gestamp Global Locations Optimized Rear Twist Beam Design

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Gestamp Chassis Products Optimization based Chassis Design

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RTB Suspension System

Rigid trailing arms/side rails with

Body Mounts

Torsion Element

Optimized Rear Twist Beam Design

Reinforcer

Image from Wikipedia

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Optimized Rear Twist Beam Design Advantages of RTB Rear Suspension

Image from a2mac1.com

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Optimized Rear Twist Beam Design

Several interlinked targets, which depend on shape, position and gauge of structural

members

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Gestamp RTB Design Process

• Initial Information

Optimized Rear Twist Beam Design

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Key Inputs Defining Basic RTB Geometry

Roll Stiffness = C/∆θ

Optimized Rear Twist Beam Design

Roll Stiffness

A measure of how much the RTB resists the rolling moment of the vehicle. Resistance provided by the torsional rigidity of the Torsion Element.

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Key Inputs Defining Basic RTB Geometry Optimized Rear Twist Beam Design

Roll Stiffness

A

A

Section Through A - A

Position (x,z)

Shape Gauge

Reinforcer Length

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Key Inputs Defining Basic RTB Geometry Optimized Rear Twist Beam Design

Roll Steer Steer angle change of rear wheels during vehicle cornering. This can be used to generate “Roll Understeer”.

Turn Direction

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Key Inputs Defining Basic RTB Geometry Optimized Rear Twist Beam Design

A

A

Section Through A - A

Position (x,z)

Shape

Roll Steer Gauge

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Key Inputs Defining Basic RTB Geometry Optimized Rear Twist Beam Design

Available Package Space

RTB Designs require minimal space, but the positioning of the fuel tank/spare wheel can influence the design.

Image from a2mac1.com

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Optimized Rear Twist Beam Design

Gestamp have worked with Altair to develop a method of quickly producing RTB concept

designs which meet K&C and package requirements.

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RTB Toolbox Optimized Rear Twist Beam Design

Optimisation

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RTB Toolbox

DOE sensitivity study

Optimized Rear Twist Beam Design

Optimisation Design Variables

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Gestamp RTB Design Process

• Initial “Trial and Error” CAD loop eliminated.

Optimized Rear Twist Beam Design

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Optimized Rear Twist Beam Design Next Design Stage: Optimisation for Antiphase Durability Target

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Target Conflict: Roll Stiffness and Antiphase Durability

There is a relationship between the Roll Stiffness and Fatigue Life for the Antiphase Durability Load Case.

Long Reinforcer Thin Gauge Torsion Element

Short Reinforcer Thick Gauge Torsion Element

Mass

Stress

z

y

Optimized Rear Twist Beam Design

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Optimized Rear Twist Beam Design

There is an optimum combination of reinforcer length and torsion element gauge

for a given Roll Stiffness and Fatigue requirement.

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Optimisation of Basic Concept Optimized Rear Twist Beam Design

VARIABLES Length and profile of reinforcer

Section Gauge

OBJECTIVE

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Optimized Rear Twist Beam Design

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Optimized Rear Twist Beam Design

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Optimised Concept Meeting K&C and Durability Requirement

Optimum Length

and shape

Optimum Gauge and

Section

Optimized Rear Twist Beam Design

Mass Minimised

A

A

Section Through A - A

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Gestamp RTB Design Process

Basic Design complete

Optimized Rear Twist Beam Design

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40mm Antiphase Rolling Load Case - Von Mises Stress (MPa)

Local Shape Optimisation for Stress Reduction Optimized Rear Twist Beam Design

Max = 295MPa

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Moveable control point defining edge shape

• Variables - xy grid co-ordinates of 7control points defining a curve.

• Constraints - Don’t move too far (within bounds of feasible design)

• Objective - minimize the maximum stress in any of the measured elements

Record stress in edge elements

Shape Optimisation for Stress Reduction Optimized Rear Twist Beam Design

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Moveable control point defining edge shape

Shape Optimisation for Stress Reduction – Iteration 1 Optimized Rear Twist Beam Design

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Shape Optimisation for Stress Reduction – Iteration 2 Optimized Rear Twist Beam Design

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Shape Optimisation for Stress Reduction – Iteration 3 Optimized Rear Twist Beam Design

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Shape Optimisation for Stress Reduction – Iteration 5 Optimized Rear Twist Beam Design

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295MPa

40mm twist loadcase - Von Mises Stress (MPa) Iteration 0

40mm twist loadcase - Von Mises Stress (MPa) Iteration 9

295MPa 255MPa

Shape Optimisation for Stress Reduction Optimized Rear Twist Beam Design

14% Stress Reduction

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Gestamp RTB Design Process

Benefit of using an Optimisation led approach

Optimized Rear Twist Beam Design

Typical RTB Design Process

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Conclusions Optimized Rear Twist Beam Design

• This design process has allowed Gestamp to react quickly and

produce competitive, low cost, low mass designs for RTB suspension systems.

• Gestamp have recognised the potential for mass reduction through optimisation of the U section design.

©2013 GESTAMP AUTOMOCIÓN

Optimised Rear Twist Beam Design

16/06/15

A Charlesworth