NOISE & VIBRATION SOLUTIONS

AUTOMOTIVE

Transmission Shift Engagement Clunk

Problem: Automotive OEMs are continually challenged to meet consumer demands for vehicles that are quieter and smoother. In response to this demand, several OEM customers have asked Roush to address transmission shift engagement “clunk.” This annoying noise and vibration is caused by impact occurring in a vehicle powertrain when the transmission is shifted between Park, Reverse and Drive.

Solution: Roush mounted accelerometers on each of the rotating shafts in the powertrain system to identify the source of the noise and vibration. The resultant data, when viewed alongside microphone data, pinpointed the source. A rear differential bracket was functioning as a speaker, allowing a high frequency metallic sound to become very noticeable. Several innovative treatments were applied to the bracket to effectively damp the annoying noise and vibration. These treatments included:

- Constrained layer application
- Mastic
- Added stiffeners

Result: Through the application of advanced experimental and analytical technologies and innovative treatments, Roush quickly addressed and resolved this critical quality issue.


Powerplant Noise Source Identification

Problem: The popular off-road vehicle market presents unique demands: engineer a vehicle that’s tough enough to take a beating from rough terrain, powerful enough to climb steep grades, yet quiet enough to provide an appealing rider environment and comply with stringent passby noise requirements. An off-road recreational vehicle manufacturer looked to Roush to address this complex issue.

Solution: We determined that the critical objective was to identify the major powerplant noise at full load and cruise. The powerplant (engine with clutch/CVT, full intake and exhaust) was installed in one of our hemi-anechoic dynamometer cells. We then performed a masking study at full and partial load conditions. While evaluating with sound pressure, we determined that the major sources of powerplant noise were the clutch and engine body at partial load and the clutch, exhaust shell and engine body at full load.

Results: Sound power measurements on these key components indicated, for example, that the muffler was the main noise source at lower frequency for the exhaust, and the expansion chamber was the primary source above 1500 Hz. Having identified these key components, we are now working with the manufacturer to design and implement production-feasible improvements.