Transcript Development of refined friction materials

Development of Refined
Friction Materials
Dr. Tim Hodges
NVH Manager
Federal-Mogul Friction Products Group
Overview
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Key attributes of friction material
NVH strategy
Principal NVH concern areas
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squeal
judder
creep-groan
Summary
Friction Materials - Key Criteria
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Physical properties
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compressibility
thermal conductivity
Performance
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nominal friction
fade
speed/temp/pressure
sensitivity
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Wear
Cost
Environmental
Refinement
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cold/thermal judder
creep-groan
squeal
pedal feel
+……………………..
Federal-Mogul Approach to NVH
Noise Measurement on
Dynamometer c/w knuckle
or full suspension
Friction Material
(“Excitation”)
Noise vs Formulation
(FMTL + Dev’t Centres)
Core Development
Finite Element
Modelling
Application
Engineering
Measurement of System
on Noise Dynamometer
and/or Vehicle
Brake System
(“Response”)
Scanning Laser
Vibrometer
Accelerometer Data
Acquisition (LMS)
Structured Dev’t of Quiet Materials
Test Hardware
Core Dev’t
Principal Test
Schedule(s)
Noise dynamometer & standard
calliper/knuckle assembly
AK Noise
Level 1
Noise dynamometer & appropriate
calliper/knuckle assembly
LACT / AK noise matrix
Level 2/3
Schenck noise dynamometer & full
corner assembly
App’n Engineering
Troubleshooting
Final vehicle
appraisal
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Vehicle
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Above + appropriate
routine to reproduce
problem condition
Customer critical test
Noise Dynamometers
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Must reproduce noise from vehicle testing
Full-suspension capability (front/rear axle)
Other key features:
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Climate control
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LACT & matrix-type schedules
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Standard objective assessment methods
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Low background noise required for accurate assessment
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Roller on some machines
NVH Problem Solving - Example
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1.8 kHz noise problem
Modal analysis shows component frequencies
not related to noise frequency
Laser vibrometer, noise dyno & vehicle used to
provide solution
Laser identifies high vibration levels on leading
edge inner pad
Solution - move inner pad clip by 1.5 mm
Subjective/objective results:
VER (LACT)
% > 70 dB
Before
4
23
After
9
1
mm/s Mod
60
50
40
30
20
10
0
Creep-groan
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Creep-groan occurs at very low speeds,
< 2rpm
Used for core development material
screening
Very low speed, high torque capability,
allows relation of  characteristics to
vibration using full-size pads
DTV Generation and Cold Judder
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DTV generation subject to a wide range of factors (Driving
style, Calliper characteristics, Friction material tribology &
compressibility)
Need to “screen” good/bad materials
Key to control of test lies in pad/disc contact
In a vehicle contact refreshed with periodic brake app’s
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Does not guarantee reproducible results even on dynamometer
Controlled Contact Device maintains and controls pad/disc
contact in ‘off brakes’ situation
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Compensates for wear
Does not require special caliper
High Speed (“Hot”) Judder
Temp (C)
Speed (Km/h)
700
600
500
400
300
200
Frequency (Hz)
DTV measurement systems and the F-M dual wavelength pyrometer may be
used together to measure the effects of hot spotting
Advanced NVH Modelling
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Need to represent system components
We have good model-experiment correlation for
system level modal analyses
We are continuing to develop our analytical
modelling methods to give us a predictive
capability
Summary
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Performance, refinement, time & cost are
often conflicting compromises
Structured approach required for problem
identification & solution
More analytical work required