12. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 12
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
13. Single Degree of Freedom Vibration
APPLIED FORCE
F = FO sin 2 π f t
1 + (2ζ f fn ) 2
TR = FT / F =
(1 − f fn ) + (2ζ f fn )
2 2 2 2
m
Transmitted
Force
k c FT ζ = fraction of critical damping
fn = natural frequency k m
f = operating frequency
Slide 13
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
14. Vibration Isolation Principle
4
0.1
APPLIED FORCE
Transmissibility Ratio
0.15
F = FO sin 2 π f t
3
m TR = FT / F
0.25
2 k c FT Transmitted
0.375 Force
0.5
1.0
1
Isolation Region
Isolation Region
0
0 1 1.414 2 3 4 5
Frequency Ratio (f / fn) Slide 14
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
15. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 15
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
19. Structure Borne NVH Sources
Primary Consideration:
Reduce the Source first as much as
possible because whatever enters the
structure is transmitted through multiple
paths to the receiver.
Transmission through multiple paths is
more subject to variability.
Slide 19
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
20. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 20
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
21. Receiver Considerations
Subjective to Objective Conversions
Subjective NVH Ratings are typically based on a
10 Point Scale resulting from Ride Testing
Receiver Sensitivity is a Key Consideration
A 2 ≈ 1/2 A 1
Represents 1.0 Rating Change
TACTILE: 50% reduction in motion
SOUND : 6.dB reduction in sound pressure level
( long standing rule of thumb ) Slide 21
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
22. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 22
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
23. Symbolic Model of Unibody Passenger Car
8 Degrees of Freedom
2 4
8
1 3 5
6 7
Total 2178.2 Kg (4800LBS) Tires 350.3 N/mm
Mass Sprung 1996.7 Kg KF 43.8 N/mm
Unsprung 181.5 Kg (8.33% of Total) KR 63.1 N /mm
Powertrain 181.5 Kg Beam mass lumped on
grids like a beam
M2,3,4 =2 * M1,5
Slide 23
From Reference 6
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
24. 8 Degree of Freedom Vehicle NVH Model
Engine Mass
8
Engine Flexible Beam for Body
Isolator
1 2 3 4 5
Suspension
Springs
6 7
Wheels
Tires
Slide 24
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
25. 8 Degree of Freedom Vehicle NVH Model
Force Applied to Powertrain Assembly
Feng
8
1 2 3 4 5
6 7
Forces at Powertrain could represent a First Order
Rotating Imbalance
Slide 25
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
26. Engine Isolation Example
Response at M id Car
1.0000
Constant Force Load; F~A 15.9 Hz
8.5 Hz
Velocity (mm/sec)
0.1000
7.0 Hz
0.0100
0.0010
2 4
8
1 3 5
6 7
700 Min. RPM First Order Unbalance
0.0001 Operation Range of Interest
5.0 10.0 15.0 20.0
Frequency Hz
Slide 26
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
27. Concepts for Increased Isolation
“Double” isolation is the typical strategy for
further improving isolation of a given vehicle
design.
Second Level of
Isolation is at Subframe
to Body Mount
Subframe is
Intermediate Structure
Suspension Bushing is first level
Slide 27
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
29. Double Isolation Example
Vertical Response at DOF3
6.0E+00
Base Model
5.0E+00
(mm/sec)
Without Double_ISO
4.0E+00
2 4
8
1 3 5
6 7
3.0E+00
Velocity
1.414*fn
2.0E+00
1.0E+00
0.0E+00
5.0 10.0 15.0 20.0
Frequency Hz
Slide 29
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
30. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 30
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
31. Mode Management Chart
EXCITATION SOURCES
Inherent Excitations (General Road Spectrum, Reciprocating Unbalance, Gas Torque, etc.)
Process Variation Excitations (Engine, Driveline, Accessory, Wheel/Tire Unbalances)
0 5 10 15 20 25 30 35 40 45 50
First Order Wheel/Tire Unbalance Hz
V8 Idle
Hot - Cold
CHASSIS/POWERTRAIN MODES
Suspension Hop and Tramp Modes
Ride Modes Suspension Longitudinal Modes
Powertrain Modes Exhaust Modes
0 5 10 15 20 25 30 35 40 45 50
Hz
BODY/ACOUSTIC MODES
Body First Torsion Steering Column First Vertical Bending
Body First Bending First Acoustic Mode
0 5 10 15 20 25 30 35 40 45 50
Hz
(See Ref. 1)
Automotive Analytics LLC 2009
Slide 31
2009 SAE NVC Structure Borne Noise Workshop
32. 8 Degree of Freedom Vehicle NVH Model
Bending Mode Frequency Separation
8
1 2 3 4 5
Beam Stiffness was
adjusted to align Bending
Frequency with Suspension
6 7
Modes and then
progressively separated
back to Baseline.
Slide 32
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
34. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 34
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
35. Mount at Nodal Point
First Bending: Nodal Point Mounting Example
Front input forces Rear input forces
Locate wheel centers at node points of the first bending modeshape
to prevent excitation coming from suspension input motion.
Slide 35
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
36. Mount at Nodal Point
First Torsion: Nodal Point Mounting Examples
Side View
Rear View
Passenger sits at Engine
node point for
First Torsion.
Transmission Mount of a
3 Mount N-S P/T is near
the Torsion Node. Slide 36
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
37. Powertrain Bending Mode Nodal Mounting
1 2 3 4 5
6 7
Mount system is placed to support Powertrain at the Nodal Locations of
the First order Bending Mode.
Best compromise with Plan View nodes should also be considered.
Slide 37
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
38. 8 Degree of Freedom Vehicle NVH Model
Bending Node Alignment with Wheel Centers
Redistribute Beam Masses
8 to move Node Points to
Align with points 2 and 4
1 2 3 4 5
6 7
Slide 38
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
39. First Bending Nodal Point Alignment
Response at Mid-Car
4.0E+00
Node Shifted
4
Base Model 8
2
(m m/sec)
1 3 5
6 7
3.0E+00
2.0E+00
Velocity
1.0E+00
0.0E+00
5.0 10.0 15.0 20.0
Frequency Hz
Slide 39
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
40. Low Frequency Basics
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 40
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
41. Dynamic Absorber Concept
Auxiliary Spring-Mass-Damper
m = M / 10
x x
SDOF 2DOF
M M
YO YO
Slide 41
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
42. Powertrain Example of Dynamic Absorber
Anti-Node Identified
at end of Powerplant
k c
m
Absorber attached at anti-node acting in
the Vertical and Lateral plane.
Tuning Frequency = √ k/m
Slide 42
[Figure Courtesy of DaimlerChrysler Corporation]
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
44. Low Frequency Basics - Review
• Source-Path-Receiver Concept
• Single DOF System Vibration
• NVH Source Considerations
• Receiver Considerations
• Vibration Attenuation Strategies
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
Slide 44
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
45. Structure Borne NVH Workshop
• Introduction
• Low Frequency Basics
• Mid Frequency Basics Greg Goetchius
• Live Noise Attenuation Demo
• Real World Application Example
• Closing Remarks
Slide 45
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
46. Mid Frequency NVH Fundamentals
This looks familiar!
Frequency Range of Interest has changed to
150 Hz to 1000 Hz Slide 46
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
47. Typical NVH Pathways to the Passenger
PATHS
FOR
STRUCTURE
Noise Paths are the
BORNE
Noise Paths are the
same as Low
same as Low NVH
Frequency Region
Frequency Region Slide 47
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
48. Mid-Frequency Analysis Character
Structure Borne Noise
Airborne Noise
• Mode separation is less practical in
• Mode separation is less practical in
High modal density mid-frequency
mid-frequency
and coupling in
source, path and
• New Strategy is Effective Isolation:
• New Strategy is Effective Isolation:
receiver
Achieved by reducing energy transfer
Achieved by reducing energy transfer
locally between source and receiver at
locally between source and receiver at
key paths.
key paths.
Response
Absorption
+
Local Stiffness Mass
+ +
Global Stiffness Damping Sealing
“Low” “Mid” “High”
~ 150 Hz ~ 1000 Hz
Log Frequency ~ 10,000 Hz
Slide 48
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
49. Mid-Frequency Analysis Character
Control Measures for Mid Frequency Concerns
Effective Isolation
Attenuation along Key Noise Paths
Slide 49
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
50. Mid-Frequency Analysis Character
Control Measures for Mid Frequency Concerns
Effective Isolation
Attenuation along Key Noise Paths
Slide 50
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
51. Isolation Effectiveness
Classical SDOF: Rigid
Source and Receiver
“Real Structure”
Flexible (Mobile)
1.0 Source and
Receiver
Transmissibility Ratio
Isolation Region
Isolation Region f/fn
1.0 1.414 10.0
Effectiveness deviates from the classical development as resonances
occur in the receiver structure and in the foundation of the source.
Slide 51
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
52. Mobility
• Mobility is the ratio of velocity response at the excitation point on structure
where point force is applied
Velocity
Mobility =
Force
• Mobility, related to Admittance, characterizes Dynamic Stiffness of
the structure at load application point
Frequency * Displacement
Mobility =
Force
Frequency
=
Dynamic Stiffness
Slide 52
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
53. Isolation
• The isolation effectiveness can be quantified by a theoretical model based on
analysis of mobilities of receiver, isolator and source
• Transmissibility ratio is used to objectively define measure of isolation
Force from source with isolator
TR =
Force from source without isolator
V Receiver Vr
V Receiver Vr
V Fr
Fr Fs =
Yi + Y r + Y s F ir
V ir
Fs
Vs Isolator V is
Source
F is
V
F s= Fs
Yr +Ys Vs
Source
Slide 53
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
54. Isolation
Force from source with an isolator Receiver Vm
TR =
Force from source without an isolator
Fm
TR = ( Y r + Y s ) / ( Y i + Y r + Y s ) F im
V im
Isolator V if
Y r : Receiver mobility
F if
Y i : Isolator mobility
Y s : Source mobility Ff
Vf
Source
• For Effective Isolation (Low TR) the Isolator
Mobility must exceed the sum of the Source and
Receiver Mobilities.
Recall that Y ∝1
K Slide 54
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
55. Designing Noise Paths
1 1 1 1 1
TR = ( + ) / ( + + )
K body K source K body K iso K source
K source
K body K iso
K iso 1.0 5.0 20.0
1.0 0.67 0.55 0.51
5.0 0.55 0.29 0.20
20.0 0.51 0.20 0.09
Generic targets:
body to bushing stiffness ratio of at least 5.0
source to bushing stiffness ratio of at least 20.0
Slide 55
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
56. Body-to-Bushing Stiffness Ratio
Relationship to Transmissibility
0.6
For a source ratio of 20
Transmissibility Ratio TR
0.5
0.4
Target Min. = 5
0.3 gives TR = .20
0.2
0.1
0
1 2 3 4 5 6 7 8 9 10
Stiffness Ratio; K body / K iso
Slide 56
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
57. Mid-Frequency Analysis Character
Control Measures for Mid Frequency Concerns
Effective Isolation
Attenuation along Key Noise Paths
Slide 57
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
58. Identifying Key NVH Paths
Key NVH paths are identified by Transfer Path Analysis (TPA)
Tactile
Tactile Acoustic
Acoustic
Transfer
Transfer Transfer
Transfer
Fi Break the system at the
points where the forces
enter the body (Receiver)
Operating loads Operating loads
Total Acoustic Response is summation of partial responses
over all noise paths
Pt = Σ paths [Pi ] = Σ paths [ (P/F) i * Fi ]
Slide 58
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
59. Designing Noise Paths
Acoustic Transfer (P/F)i
Acoustic Transfer (P/F)i
P/V
V/F P/F
(Kbody)
F F F F
F F Fi F
Operating loads create
Forces (Fi) into body at
All noise paths
Pt = Σ paths [Pi ] = Σ paths [ Fi * (P/F) i ]
= Σ paths [ Fi * (P/V) i * (V/F)i]
Measurement Parameters Generic Targets
P/F Acoustic Sensitivity 50 - 60 dBL/N
V/F Structural Point Mobility 0.2 to 0.3
(Receiver Side) mm/sec/N Slide 59
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
60. “Downstream” Effects: Body Panels
Recall for Acoustic Response Pt
Pt = Σ paths [Pi ] = Σ paths [ Fi * (P/V) i * (V/F)i]
(P/V)i ! “Downstream” (Body Panel) System Dynamics: Three Main Effects:
1. Panel Damping
Increased Damping
3. Panel Acoustic Contribution
2. Panel Stiffness
Increased Stiffness
Slide 60
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
61. Generic Noise Path Targets
Primary: Minimize the Source Force
< 1.0 N
K body K source
> 5.0 > 20.0
K iso K iso
Structural
Mobility < 0.2 to 0.3 mm/sec/N
Acoustic 50 - 60
<
Sensitivity dBL/N
Panel Damping Loss Factor
> .10
Slide 61
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
62. Final Remarks on Mid Frequency Analysis
• Effective isolation at dominant noise paths is critical
• Reduced mobilities at body & source and softened
bushing are key for effective isolation
• Mode Separation remains a valid strategy as modes
in the source structure start to participate
• Other means of dealing with high levels of response
(Tuned dampers, damping treatments, isolator
placement at nodal locations) are also effective
Slide 62
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
78. SAE 2009 NVH Conference
Structure Borne NVH Workshop
Thank You for Your Time!
Q&A
Slide 78
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
79. Structure Borne NVH References
Primary References (Workshop Basis: 4 Papers)
1. A. E. Duncan, et. al., “Understanding NVH Basics”, IBEC, 1996
2. A. E. Duncan, et. al., “MSC/NVH_Manager Helps Chrysler Make
Quieter Vibration-free Vehicles”, Chrysler PR Article, March 1998.
3. B. Dong, et. al., “Process to Achieve NVH Goals: Subsystem
Targets via ‘Digital Prototype’ Simulations”, SAE 1999-01-1692,
NVH Conference Proceedings, May 1999.
4. S. D. Gogate, et. al., “’Digital Prototype’ Simulations to Achieve
Vehicle Level NVH Targets in the Presence of Uncertainties’”,
SAE 2001-01-1529, NVH Conference Proceedings, May 2001
Structure Borne NVH Workshop - on Internet
At SAE www.sae.org/events/nvc/specialevents.htm
WS + Refs. at www.AutoAnalytics.com/papers.html Slide 79
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop
80. Structure Borne NVH References
Supplemental Reference Recommendations
5. T.D. Gillespie, Fundamentals of Vehicle Dynamics, SAE 1992
(Also see SAE Video Lectures Series, same topic and author)
6. D. E. Cole, Elementary Vehicle Dynamics, Dept. of Mechanical
Engineering, University of Michigan, Ann Arbor, Michigan, Sept.
1972
7. J. Y. Wong, Theory of Ground Vehicles, John Wiley & Sons, New
York, 1978
8. N. Takata, et.al. (1986), “An Analysis of Ride Harshness” Int.
Journal of Vehicle Design, Special Issue on Vehicle Safety, pp.
291-303.
9. T. Ushijima, et.al. “Objective Harshness Evaluation” SAE Paper
No. 951374, (1995).
Slide 80
Automotive Analytics LLC 2009 2009 SAE NVC Structure Borne Noise Workshop