1. Development of Refined Friction Materials
Dr. Tim Hodges
NVH Manager
Federal-Mogul Friction Products Group

2. Overview Key attributes of friction material NVH strategy
Principal NVH concern areas
squeal
judder
creep-groan
Summary

3. 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
+……………………..

4. Federal-Mogul Approach to NVH
Noise vs Formulation
(FMTL + Dev’t Centres)
Noise Measurement on
Dynamometer c/w knuckle
or full suspension
Friction Material
(“Excitation”)
Core Development
Finite Element
Modelling
Application
Engineering
Measurement of System
on Noise Dynamometer
and/or Vehicle
Scanning Laser
Vibrometer
Accelerometer Data
Acquisition (LMS)
Brake System
(“Response”)

5. Structured Dev’t of Quiet Materials

6. 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

7. 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 60 50 40 30 20 10

8. 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

9. 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

10. High Speed (“Hot”) Judder
Temp (C)
700
600
500
400
300
200
Speed (Km/h)
Frequency (Hz)
DTV measurement systems and the F-M dual wavelength pyrometer may be used together to measure the effects of hot spotting

11. 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

12. Summary
Performance, refinement, time & cost are often conflicting compromises
Structured approach required for problem identification & solution
More analytical work required