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Design For NVH

Design For NVH. MPD575 DFX Jonathan Weaver. Development History. Originally developed by Cohort 1 students: Jeff Dumler, Dave McCreadie, David Tao Revised by Cohort 1 students: T. Bertcher, L. Brod, P. Lee, M. Wehr

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Design For NVH

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  1. Design For NVH MPD575 DFX Jonathan Weaver

  2. Development History • Originally developed by Cohort 1 students: Jeff Dumler, Dave McCreadie, David Tao • Revised by Cohort 1 students: T. Bertcher, L. Brod, P. Lee, M. Wehr • Revised by Cohort 2 students: D. Gaines, E. Donabedian, R. Hall, E. Sheppard, J. Randazzo

  3. Design For NVH (DFNVH) • Introduction to NVH • DFNVH Heuristics • DFNVH Process Flow and Target Cascade • DFNVH Design Process Fundamentals • Key DFNVH Principles • Airborne NVH • Radiated/Shell Noise • Tube Inlet/Outlet Noise • Impactive Noise • Air Impingement Noise • Structure-Borne NVH • Wind Noise Example • 2002 Mercury Mountaineer Case Study • Summary

  4. Introduction to NVH What is NVH? • Movement is vibration, and vibration that reaches the passenger compartment in the right frequencies is noise. • The science of managing vibration frequencies in automobile design is called NVH - Noise, Vibration, and Harshness. • It is relatively easy to reduce noise and vibration by adding weight, but in an era when fuel economy demands are forcing designers to lighten the car, NVH engineers must try to make the same parts stiffer, quieter, and lighter.

  5. Introduction to NVH What is NVH? • Noise: • Typically denotes unwanted sound, hence treatments are normally to eliminate or reduce • Variations are detected by ear • Characterized by frequency, level & quality • May be Undesirable (Airborne) • May be Desirable (Powerful Sounding Engine)

  6. Introduction to NVH What is NVH? Vibration • An oscillating motion about a reference point which occurs at some frequency or set of frequencies • Motion sensed by the body (structureborne) • mainly in 0.5 Hz - 50 Hz range • Characterized by frequency, level and direction • Customer Sensitivity Locations are steering column, seat track, toe board, and mirrors (visible vibrations)

  7. Introduction to NVH What is NVH? • Harshness • Low-frequency (25 -100 Hz) vibration of the vehicle structure and/or components • Frequency range overlaps with vibration but human perception is different. • Perceived tactilely and/or audibly • Rough, grating or discordant sensation

  8. Introduction to NVH What is NVH • Airborne Noise: • Kind of sound most people think of as noise, and travels through gaseous mediums like air. • Some people classify human voice as airborne noise, but a better example is the hum of your computer, or air conditioner. • Detected by the human ear, and most likely impossible to detect with the sense of touch. • Treatment / Countermeasures: Barriers or Absorbers

  9. Introduction to NVH What is NVH? Structureborne: • Vibration that you predominately “feel”, like the deep booming bass sound from the car radio next to you at a stoplight. • These are typically low frequency vibrations that your ear may be able to hear, but you primarily “feel” • Treatment / Countermeasure: Damping or Isolation

  10. Introduction to NVH What is NVH? • Barriers: • Performs a blocking function to the path of the airborne noise. Examples: A closed door, backing on automotive carpet. • Barrier performance is strongly correlated to the openings or air gaps that exist after the barrier is employed. A partially open door is less effective barrier than a totally closed door. • Barrier performance is dependent on frequency, and is best used to treat high frequencies. • If no gaps exist when the barrier is employed, then weight becomes the dominant factor in comparing barriers.

  11. Introduction to NVH What is NVH? Barriers: Design Parameters • Location (close to source) • Material (cost/weight) • Mass per Unit Area • Number and Thickness of Layers • Number and Size of Holes

  12. Introduction to NVH What is NVH? • Absorbers: • Reduces sound by absorbing the energy of the sound waves, and dissipating it as heat. Examples: headliner, and hood insulator. • Typically, absorbers are ranked by the ability to absorb sound that otherwise would be reflected off its surface. • Good absorber designs contain complex geometries that trap sound waves, and prevent reflection back into the air. • Absorber performance varies with frequency.

  13. Introduction to NVH What is NVH? • Absorbers: Design Parameters • Area of absorbing material (large as possible) • Type of material (cost/weight) • Thickness (package/installation)

  14. Introduction to NVH What is NVH? • Damping: • Defined as a treatment of vibration to reduce the magnitude of targeted vibrations • Damping is important because it decreases the sensitivity of the body at resonant frequencies • Vehicle Sources of Damping are: Mastics, sound deadening materials, weather-strips/seals, tuned dampers, and body/engine mounts

  15. Introduction to NVH What is NVH? • Damping: Design Parameters • Density (low as possible) • Stiffness (high as possible) • Thickness (damping increases with the square of thickness) • Free surface versus constrained layer • Constrained layer damping is more efficient than free surface damping on a weight and package basis, but is expensive, and raises assembly issues. • Note: Temperature range of interest is very important because stiffness and damping properties are very temperature sensitive

  16. Introduction to NVH What is NVH? • Isolation: • Method of detaching or separating the vibration from another system or body. • By definition: does nothing to reduce the magnitude of vibration, simply uncouples the vibration from the system you are protecting. • All isolation materials perform differently at different frequencies, and if engineered incorrectly, may make NVH problems worse instead of better.

  17. Introduction to NVH What is NVH? • Isolation by Bushings and Mounts: • Excitations are generally applied to components such as engine or road wheels. • The force to the body is the product of the mount stiffness and the mount deflection, therefore strongly dependent on the mount spring rates • Compliant (softer) mounts are usually desirable for NVH and ride, but are undesirable for handling, durability and packaging (more travel/displacement space required). • Typically, the isolation rates (body mount/engine mount stiffness) that are finally selected, is a result of the reconciliation (trade-off) of many factors.

  18. Introduction to NVHWhy Design for NVH? “NVH is overwhelmingly important to customers. You never, ever get lucky with NVH. The difference between good cars and great cars is fanatical attention to detail.” Richard Parry-Jones, 11/99

  19. Introduction to NVHWhy Design for NVH? • NVH impacts Customer Satisfaction • NVH impacts Warranty • NVH has financial impact

  20. NVH Introduction to NVHWhy Design for NVH? Corporate Leverage vs. Customer Satisfaction NVH Customer Satisfaction Needs Improvement at 3 MIS IMPROVE 9 SUSTAIN / BUILD * Overall Handling Relative Leverage 6.9 Cup holders * Exterior Styling * REVIEW MAINTAIN 5 65% 77% 85%

  21. Introduction to NVHWhy Design for NVH? NVH Can Both Dissatisfy and Delight KANO Model + Customer Satisfaction Exciting Quality (Surprise & Delight) Performance Quality (Attributes) Sound Quality TGR Harley Mustang Lexus Loudness + Degree of Achievement + Performance - Performance Dissatisfiers Basic Quality (Inhibitors) Axle Whine Wind Noise Unusual Noises TGW - Customer Satisfaction

  22. Introduction to NVHWhy Design for NVH? Summary of Customer Importance • Customers place a high value on NVH performance in vehicles • About 1/3 of all Product / QualityComplaints are NVH-related

  23. Introduction to NVHWhy Design for NVH? Summary of Customer Importance (continued) • About 1/5 of all Warranty costs are NVH-related • Dealer may spend many hours to determine source of NVH problem • Dealer may have to repair or rebuild parts that have not lost function but have become source of NVH issue. • NVH can provide both dissatisfaction and delight

  24. Design For NVH (DFNVH) • Introduction to NVH • DFNVH Heuristics • DFNVH Process Flow and Target Cascade • DFNVH Design Process Fundamentals • Key DFNVH Principles • Airborne NVH • Radiated/Shell Noise • Tube Inlet/Outlet Noise • Impactive Noise • Air Impingement Noise • Structure-Borne NVH • Wind Noise Example • 2002 Mercury Mountaineer Case Study • Summary

  25. Design For NVH Heuristics • Design the structure with good "bones" • If the NVH problem is inherent to the architecture, it will be very difficult to tune it out. • To remain competitive, determine and control the keys to the architecture from the very beginning. • Set aggressive NVH targets, select the best possible architecture from the beginning, and stick with it (additional upfront NVH resources are valuable investments that will return a high yield)

  26. Design For NVH Heuristics • Cost rules • Once the architecture is selected, it will be very costly to re-select another architecture. Therefore, any bad design will stay for a long time

  27. Design For NVH Heuristics • Don't confuse the functioning of the parts for the functioning of the system (Jerry Olivieri, 1992). • We need to follow Systems Engineering principles to design for NVH. Customers will see functions from the system, but sound designs requires our ability to develop requirements of the parts by cascading functional requirements from the system

  28. Design For NVH (DFNVH) • Introduction to NVH • DFNVH Heuristics • DFNVH Process Flow and Target Cascade • DFNVH Design Process Fundamentals • Key DFNVH Principles • Airborne NVH • Radiated/Shell Noise • Tube Inlet/Outlet Noise • Impactive Noise • Air Impingement Noise • Structure-Borne NVH • Wind Noise Example • 2002 Mercury Mountaineer Case Study • Summary

  29. DFNVH Process Flow and Target Cascade • During the early stages of a vehicle program, many design trade-offs must be made quickly without detailed information. • For example, on the basis of economics and timing, power plants (engines) which are known to be noisy are chosen. The program should realize that extra weight and cost will be required in the sound package. (Historical Data) • If a convertible is to be offered, it should be realized that a number of measures must be taken to stiffen the body in torsion, and most likely will include stiffening the rockers. (Program Assumptions)

  30. DFNVHProcess Flow and Target Cascade

  31. DFNVHProcess Flow and Target Cascade Noise Reduction Strategy: Targets are even set for the noise reduction capability of the sound package.

  32. SC KO PA SI PR J1 CP Customer Customer Wants/Needs Satisfaction Vehicle (VDS - P/T NVH etc) Confirm Define Req’s System (SDS - Force, Sensitivity,......) Subsystem (stiffness, ....) Cascade Targets Verify & Optimize & Iterate Components CDS Optimize DFNVHProcess Flow and Target Cascade Systems Engineering “V” and PD Process Timing

  33. SI Trade-Offs Flow Chart System & Sub-System Targets Force or P/F Targets Determined with Parametric Models Program Specific Wants PALS (QFD, VOC, etc.) Vehicle Assumptions Fixed SLA or McPherson Strut Suspension Functional Images for Segment - R202 Vehicle Level Target Ranges Subjective (1-10) and Objective Component End Item Targets Component Resonant Frequencies, etc. Preliminary Target Ranges Future Functional Attribute Targets Objective Target Ranges - VDS Trade-Off Loop Perform Iterations Until Assumptions Comparable PA Design Optimization CAE Optimization Hardware Development System/Sub-System Assumptions McPherson vs. SLA, etc. Requires Hardware Parametric Model Affordable Business Structure (ABS) Is Gross Architecture Feasible? Development DFNVHProcess Flow and Target Cascade

  34. DFNVHProcess Flow and Target Cascade NVH Functional Attribute Sub -Attributes Road P/T Comp. S.Q. Wind Brake S&R Pass-by Noise (Reg.)

  35. POWERTRAIN NVH ACCELERATION DECELERATION TRANSIENTS IDLE NVH CRUISE NVH STEERING NVH NVH NVH NVH TAKE-OFF ACCELERATION ENGINE START DRIVEAWAY WOT UP / SHUT OFF NVH NVH AUTOMATIC TIP-IN / TIP OUT TRANS. SHIFT NVH NVH DFNVHProcess Flow and Target Cascade Convert attribute target strategy to objective targets

  36. CUSTOMER PERCEIVED P/T NVH STRUCTURE-BORNE AIRBORNE NOISE NOISE P/T RADIATED AIRBORNE BODY ACOUSTIC MOUNT NOISE NOISE REDUCTION SENSITIVTY FORCES MOUNT DYNAMIC P/T VIBRATION STIFFNESS DFNVHProcess Flow and Target Cascade Acceleration NVH Target Cascade

  37. DFNVHProcess Flow and Target Cascade • NVH Classification Parameters • Operating Condition (idle, acceleration, cruise on a rough road, braking…) • Phenomenon (boom, shake, noise…) this is strongly affected by the frequency of the noise and vibration. • Source (powertrain, road, wind ..etc) • Classifying NVH problems provides a guidance for design, for example, low frequency problems such as shake, historically, involves major structural components such as cross members and joints.

  38. DFNVHProcess Flow and Target Cascade

  39. DFNVHProcess Flow and Target Cascade • The customer’s experience of NVH problems involves two factors, 1) the vehicle operating conditions, such as braking or WOT, and 2) the very subjective responses such as boom, growl, and groan. • It is critical that objective and subjective ratings be correlated so the customer concerns can be directly related to objective measures. This requires subjective-objective correlation studies comparing customer ratings and objective vibration measurements.

  40. DFNVHProcess Flow and Target Cascade

  41. DFNVHProcess Flow and Target Cascade • Summary • Noise reduction targets should be set for important operating conditions such as WOT (wide open throttle). • Noise reduction targets must be set for the radiated sound from the various sources. • The sound package must be optimized for barrier transmissibility and interior absorption. • Classifying NVH problems provides guidance for design and a means to communication among engineers.

  42. Design For NVH (DFNVH) • Introduction to NVH • DFNVH Heuristics • Process Flow and Target Cascade • DFNVH Design Process Fundamentals • Key DFNVH Principles • Airborne NVH • Radiated/Shell Noise • Tube Inlet/Outlet Noise • Impactive Noise • Air Impingement Noise • Structure-Borne NVH • Wind Noise Example • 2002 Mercury Mountaineer Case Study • Summary

  43. Excitation Sensitivity Response DFNVH Process FundamentalsSource-Path-Responder Excitation Source Examples: • Engine Firing Pulses • Driveshaft Imbalance • Rough Road • Tire Imbalance • Speed Bump • Gear Meshing • Body-Shape Induced Vortices

  44. Excitation Sensitivity Response DFNVH Process FundamentalsSource-Path-Responder Sensitivity: Tendency of the path to transmit energy from the source to the responder, commonly referred to as the transfer function of the system

  45. Interior Sound Pressure STRUCTURE p (dB) V (mm/s) Vibration Velocity at Driving Point Force Input at Driving Point F (N) Interior Sound Pressure STRUCTURE p (dB) p (dB) Airborne Noise DFNVH Process FundamentalsSource-Path-Responder Example: Body Sensitivity Tactile • Point mobility (v/F) (Structural velocity induced by force) Acoustic • Airborne (p/p) (Airborne sound pressure induced by pressure waves) • Structureborne (p/F) (Airborne sound pressure induced by force)

  46. DFNVH Process FundamentalsSource-Path-Responder Body Sensitivity Demonstration Point Mobility Typical Point Mobility Spectrum for Compliant & Stiff Structures More Compliant Point Mobility (V/F) Less Compliant Frequency ( f ) 140 50

  47. Excitation Sensitivity Response Response: • Objective • (measurable) • S/W Shake • S/W Nibble • Seat Track (Triax) • Spindle Fore/Aft • Tie Rod Lateral • Subjective • (customer perception) • S/W Shake (vertical) • S/W Nibble (rotational) • Seat Track (non-specific) DFNVH Process FundamentalsSource-Path-Responder S/W = Steering Wheel

  48. Body Acoustic Attenuation (dB) Tailpipe Intake Orifice Airborne P/T NVH Airborne NVH Engine Radiated Sound Body Acoustic Attenuation (dB) Driver Right Ear (dBA) Active Engine Vibration (X, Y, Z) Mount Stiffness (N/mm) Body Acoustic Sensitivity Structure-borne P/T NVH Structure-borne NVH Active Exhaust Vibration (X, Y, Z) Mount Stiffness (N/mm) Body Acoustic Sensitivity DFNVH Process FundamentalsSource-Path-Responder Powertrain Noise Model

  49. Road Noise (P) Suspension/Frame Design Parameters NPA + + Body/Frame Sensitivity (P/F) Chassis Forces to Body (F) Sub-structuring Modal Analysis (MA) Suspension Force Isolation Tire/Wheel Forces MA Suspension/Frame Modes Tire/Road Force Transfer Function Body Modes Road Profile Body Design Parameters Tire/Wheel Modes & Design Parameters DFNVH Process FundamentalsSource-Path-Responder Road Noise Model

  50. DFNVH Process FundamentalsSource-Path-Responder Driveline Model

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