The document discusses the optimization of rear twist beam (RTB) designs for vehicle suspensions. It describes Gestamp's process of using optimization software to design RTBs that meet requirements for roll stiffness, roll steer, durability, packaging space, and mass. The process eliminates initial trial and error CAD work. It then focuses on optimizing the reinforcer length, torsion element gauge, and local edge shapes to minimize stress and mass while satisfying the rollover and fatigue targets. The optimized design process allows Gestamp to quickly develop competitive low-cost, low-mass RTB designs.

1. 16/6/15
Optimised Rear Twist Beam Design
Altair Conference

2. 1©2015 GESTAMP
Gestamp Global Locations
Optimized Rear Twist Beam Design

3. 2©2015 GESTAMP
Gestamp Chassis Products
Optimization based Chassis Design

4. 3©2015 GESTAMP
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
SectionGauge
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.

34. ©2013 GESTAMP AUTOMOCIÓN
Optimised Rear Twist Beam Design
16/06/15
A Charlesworth