An important aspect of vehicle comfort is the silence of the brake system. Especially low velocity braking maneuvers are sometimes accompanied by heavy noise occurrences. Although these noise occurrences do not affect the brake system negatively with respect to braking performance they mostly result in customer insecurity. Therefore, most OEMs invest much time and money on developing silent brake systems. The presentation will illustrate the physical reasons behind such brake noise events. Practical methods for vibration damping will be discussed as well. Different analytical approaches for early estimation of noise potentials of brake systems based on the Finite-Element-Method as well as Multi-Body-Dynamics will be presented. Finally, future steps for the investigation of brake noise occurrences by analytical methods will be offered. Speakers Daniel Scharding, Adam Opel AG

1. 1
SIMULATION METHODS TO ASSESS THE BRAKE NOISE
BEHAVIOR OF PASSENGER VEHICLE BRAKE SYSTEMS

2. 2
AGENDA ABSTRACT
INTRODUCTION
PROBLEM DEFINITION
PHYSICAL REASONS FOR BRAKE NOISE
PRACTICAL METHODS FOR BRAKE NOISE DAMPING
ANALYSIS
COMPLEX EIGENVALUE ANALYSIS
TRANSIENT ANALYSIS
DISCUSSIONS
CONCLUSIONS
Page 3
Page 4
Page 7
Page 12
Page 26
Page 28

3. 3
An important aspect of vehicle comfort is the silence of the brake system. Especially low
velocity braking maneuvers are sometimes accompanied by heavy noise occurrences.
Although these noise occurrences do not affect the brake system negatively with respect to
braking performance they mostly result in customer insecurity. Therefore, most OEMs invest
much time and money on developing silent brake systems.
The presentation will illustrate the physical reasons behind such brake noise events.
Practical methods for vibration damping will be discussed as well. Different analytical
approaches for early estimation of noise potentials of brake systems based on the Finite-
Element-Method as well as Multi-Body-Dynamics will be presented. Finally, future steps for
the investigation of brake noise occurrences by analytical methods will be offered.
ABSTRACT
Daniel Scharding,
Dr. Janko Wuchatsch,
Benjamin Leblanc,
Jens Maehler,
AUTHORS
Adam Opel AG, D-65423 Ruesselsheim,
phone: ++49 6142 7 73190, email: daniel.scharding@de.opel.com
Adam Opel AG, D-65423 Ruesselsheim,
phone: ++49 6142 7 78165, email: dr.janko.wuchatsch@de.opel.com
Altair Engineering GmbH, D-71034 Boeblingen,
phone: ++49 7031 6208 173, email: benjamin.leblanc@altair.de
Altair Engineering GmbH, D-71034 Boeblingen,
phone: ++49 7031 6208 214, email: maehler@altair.de

4. 4
INTRODUCTION

5. 5
Brake Noise is one of the most critical vehicle quality issues. Noisy
brake systems directly impact customer satisfaction negatively.
 Customer insecurity on brake performance aspects
(although performance is not affected negatively)
 The customer’s overall quality feeling is influenced negatively
 Brake noise solutions significantly drive vehicle mass in particular
cases
 Brake noise solutions drive cost with respect to the development of
quiet brake systems or in terms of warranty cost.
INTRODUCTION

6. 6
Different types of brake noise and their corresponding frequency domains [1]:
INTRODUCTION
0 100 500 1k 3-4k 10k
Frequency [Hz]
Judder
Moan
Groan
Low Frequency
Squeal
High Frequency
Squeal
TypeofOscillation
enforcedself-excited

7. 7
PROBLEM DEFINITION

8. 8
Stick-Slip-Effect [2]
 Due to the continuous switch of the contact interface rotor/pads from
stick to slip vibration is induced
 The negative friction slope may directly yield negative damping and
hence instability
Sprag-Slip-Effect [2, 3]
 Local periodic self-locking and release of the brake system due to
geometric imperfections of single components
 Oscillation induced at constant friction coefficient
Mode Coupling [2, 4]
 The vibration modes of components match geometrically
 Resonance effects between the coupling parts can induce more energy
into the system than it can dissipate
 Geometric coupling involving sliding parts results in the change of
friction forces in the contact interface which induces frictional
vibration
PHYSICAL REASONS FOR BRAKE NOISE

9. 9
Brake Pad Geometry [5, 6]
 End chamfers/Slots: Adjustment of pad
loading, Alteration of pad modal behavior,
Prevention of mode coupling, Pad volume/life
reduction
Shim/Noise Insulator [5, 6]
 Layered composite of metal and viscoelastic
material provides damping for specific modes
on the viscoelastic layer
Interruption of transfer path
 Modification of static and dynamic stiffness of
components
 Tuned mass absorber, redistribution of the
vibration energy of the brake system,
additional damping of the brake system,
heavy and expensive solution
PRACTICAL METHODS FOR BRAKE NOISE DAMPING

10. 1 0
ANALYSIS

11. 1 1
Complex Eigenvalue Analysis (CEA)
 Objective: Prediction of brake noise occurrences by determination of
the brake system’s unstable complex modes (positive real part
negative damping)
 Consideration of steady-state braking condition (constant pressure
and constant rotational material velocity)
 CEA is the most common industrial simulation method for the
estimation of noise sensitivity of brake systems
 The capability of the CEA to predict brake noise occurrences is under
discussion due to it’s over predictive character
ANALYSIS

12. 1 2
Complex Eigenvalue Analysis - Brake Corner Model Content
ANALYSIS
 Caliper Fist w/ Piston, Guide Pins
 Adaptor Plate w/ Wheel
Bearing/Hub
 Disc, Linings, Carrier
 Linear elastic material properties
throughout
 Transversely isotropic elasticity
as pad material property

13. 1 3
Complex Eigenvalue Analysis - Structural Part
 Incorporation of nonlinear effects due to contact interactions, large
displacements and material nonlinearities [7]
1. Pressure Step
 Application of hydrostatic brake
pressure
ANALYSIS
2. Rotation Step
 Rotation of the brake disc at low
velocity (steady-state equilibrium)
generic
exponential
friction law

14. 1 4
Complex Eigenvalue Analysis - Modal Part
3. Modal Analysis of the undamped brake system
 Determination of modal subspace in order to reduce the original
equation system
4. Computation of complex eigenvalues provides the brake system’s noise
potentials in terms of unstable complex modes
ANALYSIS

15. 1 5
Transient Analysis (MotionSolve)
 Objective: Prediction of brake noise occurrences by simulation of the
brake system’s actual self-excitation.
 Consideration of transient braking event (constant pressure and
constant rotational velocity).
 The expectation is to achieve limitation of CEA results.
ANALYSIS

16. 1 6
Transient Analysis (MotionSolve)
ANALYSIS
 Brake Corner Model Content (as
flexible bodies derived from the
corresponding FE component):
 Caliper Fist w/ Guide
Pins, Piston
 Adaptor Plate with Wheel
Bearing/Hub
 Brake Disc, Linings,
Carrier

17. 1 7
Transient Analysis - Brake Corner Contact Interfaces
Rotor Normal Direction
 Pads/Rotor w/ deformable surface
 9 contact points per each pad
can interact with the deformable
surface
 The contact surface deformation is
interpolated between the markers
 The stiffness of the contact surface is
provided by the underlying flexible body
representation of the rotor
ANALYSIS

18. 1 8
Transient Analysis - Brake Corner Contact Interfaces
Rotor normal direction
 Piston/inner backing plate w/ deformable surface
 Caliper fist/outer backing plate w/ deformable surface
ANALYSIS

19. 1 9
1 2
Transient Analysis - Brake Corner Joint Modeling
 Major difference to FE contact modeling
ANALYSIS
Clearance
Fit
Interference
Fit
# Joint Type
constrained
DOFs
kinematics
1 inline 2,3
axial displacement
spherical rotation
2 inline 2,3
axial displacement
spherical rotation
3 cylindrical 2,3,5,6
axial displacement
axial rotation
4 inline 2,3
axial displacement
spherical rotation
5 inline 2,3
axial displacement
spherical rotation
3
4 5

20. 2 0
Transient Analysis - Result
 Operational vibration of the brake corner
ANALYSIS

21. 2 1
Transient Analysis - Result
 Operational vibration of the rear axle
ANALYSIS

22. 2 2
Results
 y-velocity (out of plane) at reference points on disc
for steady-state equilibrium
ANALYSIS
1
2
3

23. 2 3
Results
 Frequency spectrum of y-velocity at reference points on disc for
steady-state equilibrium
ANALYSIS

24. 2 4
DISCUSSIONS

25. 2 5
Comparison CEA vs. Transient Analysis
 Instability Chart vs. Waterfall Diagram
DISCUSSION

26. 2 6
CONCLUSIONS

27. 2 7
CONCLUSIONS
Sketch of a future CAE process:
Initial Brake Design
(CAD)
Identification of critical
Noise Potentials
System
Stability
sufficient?
Design Update/
FE Model Update
critical
FE
Instabilities
fixed?
MBS Model Update for
Confirmation Run
NO
NO
YES
YES
Internal (Shape-) Optimization
Loop controlled by
OptiStruct/HyperStudy
Model Build
(MBS)
Transient
Analysis
Model Build
(FE)
CEA
Post-Processing:
HyperView
HyperGraph
HyperGraph3D
MotionView/
MotionSolve
HyperMesh/
OptiStruct

28. 2 8
THANKS FOR YOUR ATTENTION

29. 2 9
[1] Veitl, A., Leblanc, B.: Brake Noise Simulation using Multi-Body Simulation
Analysis, European Altair Technology Conference, Munich (2012)
[2] Ghazaly, N. M., El-Sharkawy, M., Ahmed, I.: A Review of Automotive Brake Squeal
Mechanisms, Journal of Mechanical Design and Vibration, 2013, Vol. 1, No. 1, 5 -9
[3] Breuer, B., Bill, K. H.: Bremsenhandbuch. ATZ/MTZ-Fachbuch, Springer Vieweg,
Wiesbaden (2012)
[4] Sinou, J.-J., Thouverez, F., Jezequel, L., Analysis of friction and instability by the centre
manifold theory for a non-linear sprag-slip model, Journal of Sound and Vibration 265 (2003)
527–559
[5] DiLisio, P., Parisi, R., Rieker, J., Stringham, W.: Brake Noise Resolution on the 1998
Mercedes-Benz M-Class, Proceedings of the 16th Annual SAE Brake Colloquium and
Engineering Display (P-327), San Francisco, California (1998)
[6] Shi, T. S., Dessouki, O., Warzecha, T., Chang, W. K., Jayasundera, A.:Advances in
Complex Eigenvalue Analysis for Brake Noise, Proceedings of the 2001 Noise and
Vibration Conference (NOISE2001CD), Traverse City, Michigan (2001)
[7] Bajer, A., Belsky, V., Jun Zeng, L., Combining a Nonlinear Static Analysis and
Complex Eigenvalue Extraction in Brake Squeal Simulation, 21st Annual Brake
Colloquium and Exhibition Hollywood, Florida USA (2003)
[8] Altair Engineering, Inc., HyperWorks Online Help, Copyright (c) 1993-2013
[9] Gräbner, N., Tiedemann, M., Von Wagner, U., and Hoffmann, N., Nonlinearities in
Friction Brake NVH - Experimental and Numerical Studies, SAE Technical Paper
2014-01-2511, 2014, doi:10.4271/2014-01-2511
LIST OF REFERENCES