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WOST – 2016Design Optimization and Robustness of a Passenger Car Brake RotorCAE-Braking; ZF TRW Active & Passive Safety TechnologyDr. –Ing. Stanley Baksi

ZF Friedrichshafen AG

© ZF Friedrichshafen AG, 20151

Contents

1. Background

2.

3.

4.

Motivation

Analysis and Solution

Robustness of Design

5. Conclusion

© ZF Friedrichshafen AG, 20152 CAE-Braking; ZF TRW Active & Passive Safety Technology, Presentation title11/10/2016

Background: Focus of Work

Noise and VibrationFunction / Performance

Weight / Design SpaceDesign / Appearance

Pad Wear / Dust Emission Reduced CO Emission /


Pad Wear / Dust Emission Reduced CO2 Emission / Residual Drag

Background: Brake Rotors – Performance Requirements

V

Kinetic energy : ½ m V2

gy

∆ E – Energy is dissipated through brake - rotor

Ene

rg brake - rotor

t t

Time

t0 t1

Brake system, particularly rotor is subjected to mechanical and thermal loading

Decel – ‘x’ g

Begin decel at time t0Stop decel at time t1


X % of ∆ E

Y % of ∆ E

loading

X + Y = 100% of ∆ E

Background: Thermo Mechanical Loading of Rotor

Coning

Deceleration leads to mechanical loading and material stress –critical for component durability

Thermal loading leads to thermal deflections => thermo mechanical stress. Large differential deflection may lead to BTV (Brake Torque variation ) issues


Both characteristics should be evaluated in rotor design

Motivation: Design RestrictionsFrozen Design Space

Change in design possible

Space

I iti l d i b d il bl d i did t t

Initial Design Mechanical stress over limit in initial design


Initial design based on available design space did not meet either mechanical or coning requirement

150

Motivation: Problem Statement

130

140

150

it

Coning Value

Mechanical stress

N k R di

100

110

120% of lim

i

Acceptance Limit

Neck Radius80

90

1.5 1.75 2 2.25 2.5 2.75 3 4

Neck Radius (mm)


Motivation: Best Design

How to design stiffening rib?


How to design stiffening rib? What shape would fulfill function and be robust against process variations?How to reduce mass due to addition of new feature?

Motivation: Functional and Robust

Functional component

Meet specifications under production variation

No scraps – no warranty costs

Thermal coningFulfill thermal and mechanical requirements

Acceptable rotor design

Mechanical strength

Minimum mass

All parts produced should be within specification

mechanical requirements

Maximize profitability

Robustness in production

p


Analysis: Design of Experiments

O t t P t 41

23 Input Parameters - 8 Output Parameters - 43

48 48

Sensitivity Analysis

1 2Strength i di t 1

Strength i di t 2

Sensivity Analysis: Latin Hypercube Sampling with

67 indicator 1 indicator 2

y g100 design points

All input parameters were varied continuously

5

3 4


Coning Mass

Analysis: Schematic for Stochastic Response AnalysisThermo-mechanical loading calculations

-4

Parametrizedmodel Geometry parametrization in Catia +

CADNexus3

4

s -8

aram

eter

s -

FE calculation using Ansys workbench

Sensitivity analysis using Optislang

para

met

ers

Out

put p

a

+y y g p g

inside workbench

Run time for single run ~ 1 hour

1 2

h

Inpu

t

Sensitivity Database

gstrength


Stochastic Analysis

Analysis: Results

C P 95%CoP 93% CoP 90% CoP – 95%CoP – 93% CoP – 90%

Con

ing

th in

dica

tor 1

h in

dica

tor 2

C

Stre

ng

Stre

ngt h


DoE provided an analytical model with desired level of accuracy => Optimization can be done on analytical model to save FE calculation time

Solution: Optimization

Optimization is carried out based on MoP model obtained using DoEOptimization is carried out based on MoP model obtained using DoECross check of optimized design is done by confirmation FE calculation

Optimized Design

Optimized design nominal limit to margin: Mechanical strength indicator 1: 19 %Mechanical strength indicator 2: 25 %


Coning: 27 %No significant increase in mass but improved robustness

25

Robustness: Process VariationWorst case material 25

20

15

10Freq

uenc

y

Variation in material properties: Position in casting

palette

material

130120110100

5

0

% in terms of material strength

Variation in material strength

Variation in material Variation in cooling

timeCasting process Rotor design

h ld bVariation in material strength

Variation in Geometry: T l

should be robust against all process variations

Cpk values

Specification limits

Tool wear Accuracy of

machine

Machining


Machining process

Variation in Geometrytool

Robustness: Simulation of Product RobustnessRotor design is always evaluated using

25

20

15

10Freq

uenc

y

worst case material to ensure robustness due to material properties

130120110100

10

5

0

% in terms of material strength

F

Cpk values

+

All geometric features of

+

Simulation of product robustness


geo e c ea u es orotor are parametrized ~ 26 parameters

Robustness: Prediction vs Test Results

Prediction Verification by sample testing15 % more load possible

Prediction Verification by sample testing

All parts tested achieved more than 15% than specified load

High probability of parts meeting specificationWorst case margin to limitStrength indicator 1: 15%Strength indicator 2: 22%Coning: 19%


Key driving dimensions for strength and coning characteristics identified for production control to ensure product quality

Coning: 19%

Summary

• Product requirements presented a design challenge • Detailed analysis was performed to understand key parameters drivingDetailed analysis was performed to understand key parameters driving

product performance• The product design was optimized to increase profit while meeting

i trequirements• Proposed optimized design to was analyzed to ensure robustness of

designdesign• Dimensions critical to quality were defined to ensure performance

under variation in production conditions


Thank you for your attention

© ZF Friedrichshafen AG, 201518ZF Friedrichshafen AG behält sich sämtliche Rechte an den gezeigten technischen Informationen einschließlich der Rechte zur Hinterlegung von Schutzrechtsanmeldungen und an daraus entstehenden Schutzrechten im In- und Ausland vor.ZF Friedrichshafen AG reserves all rights regarding the shown technical information including the right to file industrial property right applications and the industrial property rights resulting from these in Germany and abroad.

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