Design For NVH

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 : D. Gaines, E. Donabedian, R. Hall, E. Sheppard, J. Randazzo, J. Torres, B. Dhruna, J. Stevens, D. Kammerzell *

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? • Vibration is movement, and vibration that reaches the passenger compartment at the right frequency is noise. • The science of managing the vibration frequencies in automobile design is called NVH - Noise, Vibration, and Harshness. • It is relatively easy to reduce noise and vibration by adding weight thereby changing the natural frequency, 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 implemented to eliminate or reduce it • 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 (structure-borne) • mainly in 0.5 Hz - 50 Hz range • Characterized by frequency, magnitude 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 the vibration frequencies but human perception of it is different. • Perceived tactilely and/or audibly • Rough, grating or discordant sensation • Unpleasant *

8. Introduction to NVH What is NVH Airborne Noise: • Sound most people interpret as noise, and travelsthrough gaseous mediums like air. • Some people classify human voice as airborne noise, a better example is the hum of your computer, or an airconditioner. • Detected by the human ear and most likely impossible to detect with the sense of touch. • Treatment/Countermeasures: Elimination of the source if possible; Barriers or Absorbers if not. *

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 automotivecarpet. • Barrier performance is strongly correlated to the openings or air gaps that exist after the barrier is installed. A partially open door is a 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, Direction and Thickness of Layers • Number and Size of Holes Note: Active Noise Cancellation (ANC) is a recent method discussed in this DFX. For airborne noise it can work between 30 and 1000 Hz to change the noise heard. ANC units offset unwanted sound by emitting opposing frequencies that “cancel” the unwanted sound. ANC technology is available in cars like the Lincoln MKS, Honda Odyssey, and Infiniti Q50 *

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 • Absorbers are ranked by the ability to absorb sound that otherwise would be reflected off its surface • Good absorber design contains 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 and location specific added mass *

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 or by 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 NVH How is NVH Measured? One of the challenges of measuring and analyzing powertrain NVH is the large range in the absolute levels of sounds and vibrations that occur. Measurement and analysis require observation of small (low-level) signals in the presence of large (high-level) signals. This is required due to the capability of the human ear to process signals at a wide range of levels.

19. Introduction to NVH How is NVH Measured? Amplitude Scales: The ratio between the largest and smallest signals that we can analyze is the dynamic range. Using a linear amplitude measurement scale limits our ability to display a wide dynamic range simultaneously as shown on Graph A. However, as shown on Graph B of the same sound, a logarithmic amplitude scale compresses large amplitude signals and expands small ones so that we can display a wide dynamic range simultaneously for analysis. This is why we use the logarithmic decibel (dB) scale to measure sounds and vibrations

20. Introduction to NVH How is NVH Measured? Amplitude Scales: The decibel (dB) is a logarithmic representation of an amplitude ratio. It is 20 times the base 10 logarithm of the ratio of the measured amplitude to a reference. In the case of sound, the units of measure are pressure and the reference is typically the threshold of hearing. On the dB scale, 0 dB approximately corresponds to the normal threshold of human hearing and 140 dB approximately corresponds to the threshold of pain. Each 1 dB step approximately represents the smallest change in sound level that normal human hearing can detect 50% of the time. The table compares dB levels for various sounds at 1 meter and 10 meters. To become more familiar with dB levels.

21. Introduction to NVH How is NVH Measured? Amplitude Scales: The formula for calculating sound pressure level (SPL) in decibel (dB) is: Adding decibel (dB): Because the dB scale is a logarithmic ratio, we cannot add dB levels directly. To add two dB values, we must apply the rules of logarithms as follows:

22. 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 *

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

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

25. 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 *

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

27. NVH: Cost & Weight Considerations • Often times, cost and weight targets prevent avoidance of NVH issues An example is a 2-pc driveshaft, which is less expensive, lighter, and has fewer joints than a 3-pc driveshaft, but has boom at a certain RPM. The 3-pc driveshaft does not demonstrate the boom. What do you do??? • NVH countermeasures CAN work harmoniously within the system as long as they are DESIGNED INTO the system from the beginning. How do I go about doing it? • Get management buy-in. Costs for NVH countermeasures are never put into programs early enough. This needs to change to ensure success. • Run CAE early, using the best simulations available. Determine the frequency range and driving mode. Trust your CAE. • Develop NVH countermeasures and make sure they are on the first phase of prototype vehicles (NOT the last) • In this case, a torsional damper on the rear of the driveshaft solves the issue, but interferes with the fuel tank • Since packaging studies were run early, the fuel tank was modified prior to hard tooling to provide clearance for the damper. • Result • A well-packaged driveshaft which is lighter, less expensive, and more durable than the alternate design, which fully satisfies all customer and corporate requirements. Heuristic: NVH is always a late guest to the party. Plan countermeasures ahead to ensure you have enough energy, time and tools to entertain your guest!

28. Introduction to NVHWhy Design for NVH? • About 1/5 of all Warranty costs are NVH-related • Dealers may spend many hours to determine source of NVH problem • Dealers 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 *

29. 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 *

30. 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) *

31. 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 *

32. Design For NVH Heuristics • Don't confuse the functioning of the parts with 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 vehicle designs require the ability to develop requirements for the parts by cascading functional requirements from the system. *

33. 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 *

34. 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) *

35. DFNVHProcess Flow and Target Cascade *

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

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

38. DFNVHProcess Flow and Target Cascade 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 MacPherson 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 *

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

40. DFNVHProcess Flow and Target Cascade Convert attribute target strategy to objective targets 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 *

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

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

43. DFNVHProcess Flow and Target Cascade

44. 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. *

45. DFNVHProcess Flow and Target Cascade *

46. 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 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. • NVH from audio system interaction is also important with pulse width modulated signals for loads that couple with audio speakers. *

47. 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 *

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

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

50. 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) • Structure-borne (p/F) (Airborne sound pressure / induced by force) 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 *