NVH Category NVH CharacteristicFrequency (Hz) Steady State Frequency Response Ride< 5 Shake5 - 40...
-
Upload
bertina-ramsey -
Category
Documents
-
view
225 -
download
2
Transcript of NVH Category NVH CharacteristicFrequency (Hz) Steady State Frequency Response Ride< 5 Shake5 - 40...
NVH Category
NVH Characteristic Frequency (Hz)Steady State Frequency Response• Ride < 5• Shake 5 - 40• Boom 20 - 100• Moan 100 - 150• Structural Borne Noise 150 – 500• Air Borne Noise > 500
Transient Response• Harshness 20 - 100
Single Degree of Freedom
Frequency (Hz)
Am
plit
ud
e (2
0% D
amp
ed)
Control byDynamicStiffness
Control byMass
Control byDamping
Isolation Region
2fn * fn
Dynamic Stiffness
Dynamic Stiffness:
(K - m ω2) – j C ω
K* = ----------------------------------
(K - m ω2)2 + (C ω)2
Mass M
Damping CStiffness K
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 ResponseSubjective-Objective
Acceleratio
nA
cceleration
FrequencyFrequency
SR = 6SR = 6
SR = 5SR = 5
Tactile ResponseSubjective-Objective (2)
Velo
cityV
elocity
FrequencyFrequency
SR = 6SR = 6
SR = 5SR = 5
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
MostTargetsNo Sale
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
0 5 10 15 20 25 30 35 40 45 50
CHASSIS/POWERTRAIN MODES
Ride ModesPowertrain Modes
Suspension Hop and Tramp Modes
Suspension Longitudinal ModesExhaust Modes
0 5 10 15 20 25 30 35 40 45 50
BODY/ACOUSTIC MODES
Body First Bending (22Hz)
Body First Torsion (25Hz) Steering Column First Vertical Bending (29Hz)
0 5 10 15 20 25 30 35 40 45 50
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)V8 Idle (500-550RPM)
Hot Cold
Hz
Hz
Hz
First F/A Acoustic Modes (48Hz)
Modal Chart
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
recipreciprecip amF *
borecrankboregas APPF *)(
tan**)( hFFT recipgastotal
r
h
Pbore
Pcrank
mrecip
arecip
L
Idle Torque
coscos rLh
2sin1cos LL
cossin1 2 rLh
2sin1cos
L
r sinsin
r
h
Pbore
Pcrank
mrecip
arecip
L
Piston Displacement
dt
duvw
dt
dvuw
dt
dwuv
dt
duvwdt
dv
dt
du
dt
vuddt
dunu
dt
du
dt
d
dt
ddt
d
dt
d
nn
)(
sincos
cossin
1
r
h
Pbore
Pcrank
mrecip
recip
L
Trigonometric Derivatives
222
222
2
sin
sincossin
sin
sincossin
)coscos(
rL
rr
rL
rr
dt
d
rLdt
d
dt
dhv
r
h
Pbore
Pcrank
mrecip
arecip
L
Piston Velocity
23222
224
222
22
222
)sin(
sincos
sin
2coscos
)sin
sincos(sin)(
rL
r
rL
rr
rL
r
dt
dr
dt
dva
r
h
Pbore
Pcrank
mrecip
arecip
L
Piston Acceleration
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 = mr2
– 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 ImbalanceSpeed 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 VariationSpeed 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
y = 1.7872x-0.6729
R2 = 0.6538
1
10
100
1000
0.0001 0.0010 0.0100 0.1000
Wave Number (cycles/mm)
PS
D (
mm
^2
/(c
yc
les
/mm
))