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Development of RefinedFriction Materials
Dr. Tim Hodges
NVH Manager
Federal-Mogul Friction Products Group
Overview
Key attributes of friction material NVH strategy Principal NVH concern areas
- squeal- judder- creep-groan
Summary
Friction Materials - Key Criteria
Physical properties- compressibility- thermal conductivity
Performance- nominal friction- fade- speed/temp/pressure
sensitivity
Wear Cost Environmental Refinement
- cold/thermal judder- creep-groan- squeal- pedal feel
+……………………..
Federal-Mogul Approach to NVH
Friction Material(“Excitation”)
Brake System (“Response”)
Finite ElementModelling
Measurement of System on Noise Dynamometer
and/or Vehicle
Scanning Laser Vibrometer
Accelerometer DataAcquisition (LMS)
Noise vs Formulation (FMTL + Dev’t Centres)
Noise Measurement onDynamometer c/w knuckle
or full suspension
Core Development
ApplicationEngineering
Structured Dev’t of Quiet MaterialsTest Hardware Principal Test
Schedule(s)
Core Dev’t Noise dynamometer & standardcalliper/knuckle assembly
AK Noise
App’n Engineering
Level 1
Level 2/3
Troubleshooting
Noise dynamometer & appropriatecalliper/knuckle assembly
Schenck noise dynamometer & fullcorner assembly
“ “ “
LACT / AK noise matrix
“ “
Above + appropriateroutine to reproduceproblem condition
Final vehicleappraisal
Vehicle Customer critical test
Noise Dynamometers
Must reproduce noise from vehicle testing Full-suspension capability (front/rear axle)
Other key features: Climate control LACT & matrix-type schedules Standard objective assessment methods Low background noise required for accurate assessment Roller on some machines
NVH Problem Solving - Example 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:
mm/s Mod
0
10
20
30
40
50
60
Creep-groan
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 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
- Does not guarantee reproducible results even on dynamometer
Controlled Contact Device maintains and controls pad/disc contact in ‘off brakes’ situation
- Compensates for wear- Does not require special caliper
High Speed (“Hot”) JudderS
peed
(K
m/h
)
Frequency (Hz)
DTV measurement systems and the F-M dual wavelength pyrometer may be used together to measure the effects of hot spotting
Temp (C)700
600
500
400
300
200
Advanced NVH Modelling
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
Performance, refinement, time & cost are often conflicting compromises
Structured approach required for problem identification & solution
More analytical work required