NVH Category
NVH Characteristic
Frequency (Hz)
Steady State Frequency Response
•
•
•
•
•
•
Ride
Shake
Boom
Moan
Structural Borne Noise
Air Borne Noise
<5
5 - 40
20 - 100
100 - 150
150 – 500
> 500
Transient Response
• Harshness
20 - 100
Single Degree of Freedom
Amplitude (20% Damped)
Control by
Damping
Control by
Dynamic
Stiffness
Control by
Mass
Isolation Region
Frequency (Hz)
fn
2 * fn
Dynamic Stiffness
Dynamic Stiffness:
(K - m ω2) – j C ω
K* = ---------------------------------(K - m ω2)2 + (C ω)2
Mass M
Stiffness K
Damping C
ω = 2* π*f
f is the frequency
Pure Tone
• Sound at a single frequency
• Sound Pressure
– Objective measurement
• dB
– Logarithmic of sound pressure
• dBA
– A-Weighted to adjust for ear sensitivity
Human Sensitivity
• More constant across frequency range
with velocity
• Hearing range 20 – 2000 Hz
• Depends on overall level
• Sound at one frequency may mask by
other frequencies
• Depends on age, sex and other factors
Tactile Response
Subjective-Objective
Acceleration
SR = 5
SR = 6
Frequency
Tactile Response
Subjective-Objective (2)
Velocity
SR = 5
SR = 6
Frequency
Sound Pressure Level
and A Weighting
NVH Classification
• Operating Condition
– Idle, Low Speed, Cruising, POT, WOT
• Subjective Evaluation
– Shake, Boom, Noise, Harshness
• Objective Measurement
– Sound Pressure, Acceleration
• Frequency Range
• Source
– Powertrain, Road, Exhaust
NVH Subjective Rating
No Sale
Most
Targets
NVH Objectives
• Assess vehicle responses relative to
design targets:
–Tactile responses
• Seat track
• Steering column
• Toe pan
–Acoustic responses
• Driver’s ear
• Front Passenger’s ear
• Rear passenger’s ear
Shake
•
•
•
•
•
5 – 40 Hz
Idle Shake
Isolated Road Shake
Rough Road Shake
Smooth Road Shake
– Wheel/Tire Imbalance
– Tire Force Variation
Design For Shake
• Body vertical, lateral bending and torsion
modes
• Front end bending and torsion modes
• Front floor modes
• Steering column modes
• Seat modes
• Avoid stickiness of the shock and CV
joints that causes high force input and
resonance in smooth road shake
Design For Shake (2)
• Mode separation and mode shape
management of engine bounce, roll, pitch
and yaw rigid body modes
Boom
•
•
•
•
20 - 100 Hz
Idle Boom
Isolated Road Boom
Rough Road Boom
Body Design for Boom
•
•
•
•
•
•
•
•
1st and 2nd fore-aft acoustic modes
Body 1st and 2nd order vertical bending
Front floor vertical bending
Dash panel fore-aft bending
Quarter panel bending
Fuel tank bounce
Spare tire tub bounce
Decklid, liftgate or lower back panel pumping
Structural Borne Noise
•
•
•
•
100 - 500 Hz
Powertrain Noise
Rough Road Noise
Gear Whine
Design For Noise
• Most of the vibration energy imparted to the vehicle
is below 150 Hz.
• Below 150 Hz:
– Body structure is important for controlling noise and
vibration
– Lack of structure usually results in costly design and
tooling changes
• Above 150 Hz:
– Can be resolved with relatively simple structure
modifications, such as bead patterns, or damping
treatments.
Design For Noise (2)
• Powertrain Bending Isolation
• Powertrain Bracket Isolation
Modal Chart
CHASSIS/POWERTRAIN MODES
Suspension Hop and Tramp Modes
Ride Modes
Suspension Longitudinal Modes
Powertrain Modes
0
5
10
15
Exhaust Modes
20
25
30
35
40
45
50
Hz
BODY/ACOUSTIC MODES
Body First Torsion (25Hz)
Steering Column First Vertical Bending (29Hz)
Body First Bending (22Hz)
0
5
10
15
First F/A Acoustic Modes (48Hz)
20
25
30
35
40
45
50
Hz
EXCITATION SOURCES
Inherent Excitations (General Road Spectrum, Reciprocating Unbalance, Gas Torque, etc.)
Process Variation Excitations (Engine, Driveline, Accessory, Wheel/Tire Unbalances)
First Order Wheel/Tire Unbalance (5-75MPH)
0
5
10
15
20
25
V8 Idle (500-550RPM)
Hot Cold
30
35
40
45
50
Hz
Body-in-White Targets
• Static Stiffness
– Bending
– Torsion
• Normal Modes
– Vertical bending
– Torsion
– Lateral bending
Trimmed Body Targets
• Normal Modes
– Vertical bending
– Torsion
– Lateral bending
– Front end bending
– Front end torsion
Instrument Panel/Column
Targets
• Normal Modes
– Vertical bending
– Lateral bending
Seat Targets
• Normal Modes
– On Bedplate
• Fore aft
• Lateral
– In Vehicle
• Fore aft
• Lateral
• Different row may have different target
Idle Load
Idle Torque
Pbore
mrecip
Ttotal  ( Fgas  Frecip ) * h * tan
arecip

h
L

r
Pcrank
Frecip  mrecip * arecip
Fgas  (Pbore  Pcrank ) * Abore
Piston Displacement
Pbore
mrecip
h  L cos  r cos
cos   1  sin 2 
arecip

h
L
r sin 
sin  
L
L cos   L 1  sin 2 

r
Pcrank
h  L 1  sin 2   r cos 
Trigonometric Derivatives
Pbore
mrecip
recip

h
L

r
Pcrank
d sin 
d
 cos
dt
dt
d cos
d
  sin 
dt
dt
n
du
n 1 du
 nu
dt
dt
d (u  v) du dv


dt
dt dt
duvw
dw
dv
du
 uv
 uw  vw
dt
dt
dt
dt
Piston Velocity
Pbore
mrecip
arecip

h
L

r
Pcrank
dh d
v
 ( L cos  r cos )
dt dt
d 
r 2 cos sin  

 r sin   2 2 2 
dt 
L  r sin  

r cos sin  
 r sin  

2
2
2
L  r sin  

Piston Acceleration
Pbore
mrecip
dv
d 
r cos sin 
a
 (r )  (sin 
dt
dt 
L2  r 2 sin 2 
arecip

h
L

r
Pcrank
2

r
cos 2
  2  r cos 
L2  r 2 sin 2 

r 4 cos2  sin 2  


3
( L2  r 2 sin 2  ) 2 

)

Smooth Road Shake
Wheel/Tire Imbalance
Definition
• Simulation
– Shake caused by the unbalanced inertia forces
from the high speed rotation of the unbalanced
wheel in vehicle cruising
• Load
– 1.0 oz-inch (Sensitivity) unbalanced force at the
spindles
– Both vertical and fore-aft loads with vertical load
trailing fore-aft load by 90 degrees
• Applications
– Front wheel in-phase, Front wheel out-of-phase,
Rear wheel in-phase and Rear wheel out-of-phase
Wheel/Tire Imbalance
Calculation
• F = mr2
–
–
–
–
F is imbalance Force (N)
m is imbalance mass (Mg)
r is imbalance radius (mm)
 is rotation speed (rad/sec)
• F = 1.0 oz-in = 1.0 * 28.3 * 10-6 (Mg/oz) * 25.4
(mm/inch) * 4 * 2 * f2 = 0.0284 * f2 (N)
– f is frequency (cycles/sec)
Wheel/Tire Imbalance
Speed Map
• The wheel/tire speed map (frequency v.s.
vehicle speed) is dependent on the wheel/tire
size, the wheel/tire stiffness and the payload
• V = 2 * π * Tire Effective Radius * Frequency
• However, the Frequency/Vehicle Speed(MPH) is
typically around 0.2
• Based on the above assumption, the frequency
range of interest from 25 MPH to 125 MPH is
– 5 Hz to 25 Hz
Tire Force Variation Definition
• Simulation
– Shake caused by the variation of the radial stiffness of
the tires
• Load
– 1.0 lbf (Sensitivity) variation force at the spindles
– Vertical load only
• Applications
– Front wheel in-phase, Front wheel out-of-phase, Rear
wheel in-phase and Rear wheel out-of-phase
Tire Force Variation
Speed Map
• The wheel/tire speed map (frequency v.s.
vehicle speed) is dependent on the wheel/tire
size, the wheel/tire stiffness and the payload
• V = 2 * π * Tire Effective Radius * Frequency
• However, the Frequency/Vehicle Speed(MPH) is
typically around 0.2
• Based on the above assumption, the frequency
ranges of interest from 25 MPH to 125 MPH are
– First Order : 5 Hz to 25 Hz
– Second Order : 10 Hz to 50 Hz
Rough Road Noise
Spatial PSD Road Profile
• Spatial Frequency ( Cycles / mm)
– Wave number
– 1 / wavelength
• PSD Amplitude (mm^2 / (cycles / mm))
• Power Regression Analysis (Y = 1.7872 * X-0.6729)
Spacial PSD Road Profile
PSD (mm^2/(cycles/mm))
1000
100
-0.6729
10
1
0.0001
y = 1.7872x
R2 = 0.6538
0.0010
0.0100
Wave Number (cycles/mm)
0.1000