Experimental Study of Wire Brush Brake Noise on a Personal Car

<strong>Experimental</strong> <strong>Study</strong> <strong>of</strong> <strong>Wire</strong> <strong>Brush</strong>
<strong>Brake</strong> <strong>Noise</strong> on a Personal Car
Eskil Lindberg, Lindberg Nils-Erik Hörlin, Hörlin Peter Göransson
KTH - Royal Institute <strong>of</strong> Technology
Stockholm Stockholm, Sweden

<strong>Wire</strong> <strong>Brush</strong> <strong>Noise</strong> (Scratch <strong>Noise</strong>)
hDisc and pad surface roughness induced,
no non non-linear linear feedback
hB hBroadband db d
hLow frequency
hInterior Interior noise
2

Scope <strong>of</strong> Work
1. Preliminary study <strong>of</strong> noise phenomenon
• Understanding <strong>of</strong> the problem
• Parameter study, speed and brake pressure
2. Component measurement
• B<strong>Brake</strong> k system t vibration ib ti study t d
3. Surface roughness
• Controlled surfaces
4. Transfer path
• Correlation study y
5. … Source model
3

Preliminary <strong>Study</strong>
Monitored effect <strong>of</strong> varying
h<strong>Brake</strong> pressure
hVehicle speed
Instrumented
h<strong>Brake</strong> pad (Accelerometer)
hInterior Interior and exterior (Microphones)
4

Description <strong>of</strong> Test Rig
Tests rig
hElectrical engine driven rollers
hExternal brake pump
hSmall personal car
5

Limiting Factors <strong>of</strong> Test Rig
h<strong>Noise</strong> Masking
hTire-roller Tire roller noise
hRoller noise
hElectrical Electrical engine
hRoller mechanics
hBackground Background noise
6

Interior <strong>Noise</strong>
-Increasing Increasing <strong>Brake</strong> Pressure
65
•Increasing noise levels
with brake pressure 60
•Broadband
20 μPa
55
•Low frequency 50
Spectra will be
referred to as ether
“flat” or “oscillating”
in frequency, (fig in
slide “oscillating”)
dB re.
SPL
45
40
35
30
25
5.0 [bar]
3.3 [bar]
1.8 [bar]
00.0 0 [bar]
100 200 300 400 500 600 700 800
7
Frequency [Hz]
Roller speed, 1.3 [km/h]

SPL dB
Norrmalized
Interior and Exterior <strong>Noise</strong>
-Increasing Increasing <strong>Brake</strong> Pressure
15
10
5
0
Interior Exterior
5.0 [bar]
33.3 3 [bar] [b ]
1.8 [bar]
200 400 600 800 1000
Frequency [Hz]
SPL dB
Normalized
15
10
Roller speed, 1.3 [km/h]
•<strong>Noise</strong> <strong>Noise</strong> phenomenon present only interiorly
8
5
0
5.0 [bar]
33.3 3 [bar]
1.8 [bar]
200 400 600 800 1000
Freq Frequency enc [Hz] [H ]

Interior <strong>Noise</strong>
-Increasing Increasing <strong>Brake</strong> Pressure, Roller Speed
•Increased levels with
•<strong>Brake</strong> pressure
•Roller speed
•Curve almost parallel
for all speeds
Hz dB
100−1000H
Noormalissed
SPL
1
16
14
12
10
8
6
4
2
2.9 [km/h]
1.9 [km/h]
1.3 [km/h] /
1 dB/bar
0
0 2 4 6
<strong>Brake</strong> Pressure [bar]
9
TTotal t ll level l1001000 100-1000 HHz

Interior <strong>Noise</strong>
-Increasing Increasing Roller Speed
70
•Increased noise levels
with increased speed 65
•Fundamental shape <strong>of</strong>
spectra intact.
(“oscillating” frequency
response)
20 μPa
dB re.
SPL
60
55
50
45
40
35
30
2.9 [km/h]
1.9 [km/h]
1.3 [km/h]
25
100 200 300 400 500 600 700 800
Frequency [Hz]
10
B<strong>Brake</strong> k pressure, 5 [b [bar]
]

<strong>Brake</strong> Pad Vibrations
-Increasing Increasing brake pressure
•Increased vibration levels
with increased brake
pressure
•Fundamental shape <strong>of</strong>
spectra NOT intact
•“Flatter” frequency
response
•Peaks Peaks shifted up p in
frequency with increasing
brake pressure
s 2
1 μm/s
dB re.
Level
80
75
70
65
60
55
5.0 [bar]
3.3 [bar]
11.8 8 [bar]
0.0[bar]
100 200 300 400 500 600 700 800
11
Frequency [Hz]
RRoller ll speed, d 1.3 13[k [km/h]
/h]

<strong>Brake</strong> Pad Vibrations
-Increasing Increasing Roller Speed
•Increased vibration levels
with increased roller speed
•Fundamental shape <strong>of</strong>
spectra NOT intact
•“Flatter” Flatter frequency
response
•Peaks intact with
iincreasing i roller ll speedd
s 2
1 μm/s
dB re.
Level
90
88
86
84
82
80
78
76
74
72
NB! <strong>Brake</strong> force 70
unchanged (if
2.9 [km/h]
1.9 [km/h]
1.3 [km/h]
68
100 200 300 400 500 600 700 800
Coulomb friction)
12
Frequency [Hz]
B<strong>Brake</strong> k pressure, 5 [b [bar]
]

Conclusion
h <strong>Noise</strong> event can be reproduced in measurement
h Increased brake pressures and roller speed gives
h Increased interior noise levels
h Increased pad vibration levels
h Frequency response shape <strong>of</strong> pad vibrations change,
but fundamental shape <strong>of</strong> interior noise intact
h BBetter tt understanding d t di <strong>of</strong> f ttransfer f path th system t
13

Future Work
hComponent measurement
hRoughness influence
hResponse correlation
hTransfer path
h…Source model
14

Questions
Acknowledgment
The work has been performed within the research project "Environmental Friendly
<strong>Brake</strong>s”, <strong>Brake</strong>s , sponsored by Vinnova/Green Car program in which the participating
partners are Saab Automobile AB and KTH. The funding is gratefully
acknowledged.
15

Interior <strong>Noise</strong>
-Influence Influence <strong>of</strong> Exterior <strong>Noise</strong>
40
From measured reduction
index estimated
35
contribution <strong>of</strong> the
exterior airborne noise to 30
interior total noise 25
z dB
L
0.1−1kHz
Normali N zed SPL
20
15
10
TTotal t ll level l1001000 100-1000 HHz
5
Total inside SPL
Outside contribution to inside SPL
0
1 2 3 4 5 6 7
Roller speed [km/h]
16
B<strong>Brake</strong> k pressure, 5 [b [bar] ]