Presentation by Andrew Charlesworth, Gestamp

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

5. 4©2015 GESTAMP
Optimized Rear Twist Beam Design
Advantages of RTB Rear Suspension
Image from a2mac1.com

6. 5©2015 GESTAMP
Optimized Rear Twist Beam Design
Several interlinked targets, which depend on
shape, position and gauge of structural
members

7. 6©2015 GESTAMP
Gestamp RTB Design Process
• Initial Information
Optimized Rear Twist Beam Design

8. 7©2015 GESTAMP
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.

9. 8©2015 GESTAMP
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

10. 9©2015 GESTAMP
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

11. 10©2015 GESTAMP
Key Inputs Defining Basic RTB Geometry
Optimized Rear Twist Beam Design
A
A
Section Through
A - A
Position (x,z)
Shape
Roll Steer
Gauge

12. 11©2015 GESTAMP
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

13. 12©2015 GESTAMP
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.

14. 13©2015 GESTAMP
RTB Toolbox
Optimized Rear Twist Beam Design
Optimisation

15. 14©2015 GESTAMP
RTB Toolbox
DOE sensitivity study
Optimized Rear Twist Beam Design
Optimisation
Design Variables

16. 15©2015 GESTAMP
Gestamp RTB Design Process
• Initial “Trial and Error” CAD loop
eliminated.
Optimized Rear Twist Beam Design

17. 16©2015 GESTAMP
Optimized Rear Twist Beam Design
Next Design Stage: Optimisation for Antiphase Durability Target

18. 17©2015 GESTAMP
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

19. 18©2015 GESTAMP
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.

20. 19©2015 GESTAMP
Optimisation of Basic Concept
Optimized Rear Twist Beam Design
VARIABLES Length and profile of reinforcer
SectionGauge
OBJECTIVE

21. 20©2015 GESTAMP
Optimized Rear Twist Beam Design

22. 21©2015 GESTAMP
Optimized Rear Twist Beam Design

23. 22©2015 GESTAMP
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

24. 23©2015 GESTAMP
Gestamp RTB Design Process
Basic Design complete
Optimized Rear Twist Beam Design

25. 24©2015 GESTAMP
40mm Antiphase Rolling Load Case -
Von Mises Stress (MPa)
Local Shape Optimisation for Stress Reduction
Optimized Rear Twist Beam Design
Max = 295MPa

26. 25©2015 GESTAMP
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

27. 26©2015 GESTAMP
Moveable control point defining edge shape
Shape Optimisation for Stress Reduction – Iteration 1
Optimized Rear Twist Beam Design

28. 27©2015 GESTAMP
Shape Optimisation for Stress Reduction – Iteration 2
Optimized Rear Twist Beam Design

29. 28©2015 GESTAMP
Shape Optimisation for Stress Reduction – Iteration 3
Optimized Rear Twist Beam Design

30. 29©2015 GESTAMP
Shape Optimisation for Stress Reduction – Iteration 5
Optimized Rear Twist Beam Design

31. 30©2015 GESTAMP
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

32. 31©2015 GESTAMP
Gestamp RTB Design Process
Benefit of using an Optimisation led
approach
Optimized Rear Twist Beam Design
Typical RTB Design Process

33. 32©2015 GESTAMP
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