Noise Reduction in Over-molded HVAC Module Doors

1
Noise Reduction in Over-molded HVAC Module Doors
Industrial Sponsor
Goal Create a component and or system design
that will eliminate any acoustic signal audible
to automobile passengers.
Result Eliminated acoustic whistling with the
experimentally proven Tear-Drop Design.
Design Recommendation
Problem Statement
Design Requirements
Noise Reducing Tear-Drop Design
During the initial 5-15 rotation of an HVAC
by-pass temperature door from its sealed to
unsealed position, a whistling noise is generated
from air flowing between gaps created by doors
seal and HVAC housing in panel full cold mode.
? Minimal effect on housing
? Eliminate the acoustic whistle
? Available for mass production
? Size must remain within 101.6 x 50.8 x 19.0,
/- 0.2 mm
? Service life exceeds 10 years
? Ease of Manufacture
? Adaptive to existing platform
? Low Cost
? Reliable and robust
? Minimal number of parts
Stimulated Vortex Generation and Sound Radiation

• A-side seal edge receives Tear-Drop Extension.
• Total Added Volume 441.5 mm3.
• Easily Manufactured with existing Injection
  Over-molding with minimal retooling
• Inexpensive and easily mass produced.

• Housing
• High Flow Velocity
• Flow Separation
• Vortex Drift Velocity (Vd) 0.8 x FlowVelocity

A-Side By- Pass Door
Whistling Is Audible to Automobile Passengers
Why it Works
Provided by BEHR
Existing HVAC Door Module
Previous Investigation Initial investigation
focused on decreasing the air velocity between
the by-pass door and HVAC housing
HVAC Unit
Resonance Conditions for Stimulated Vortex
Generation and Sound Emission Time for a
vortex to reach Housing L/Vd
Vortex Shedding Period T5d/V Time for
pressure pulse to reach door L/c
Condition for Resonance is L/Vd5nd/V
Total time L/Vd L/c ? L/Vd
Resonance Occurs when L4nd
Airflow to Passengers
Tear-Drop Design
Existing By-Pass Door
Existing Door
A-Side

• Increased Seal Tip diameter
• Changes the conditions of resonance for
  Stimulated Generation.
• Minimizes boundary layer separation by increasing
  seal-tip radius
• Minimizes vortex formation thus resonant feedback.

Benchmark Values Vmax 28.5 m/s Vavg 10.3 m/s
Whistling
Resonant Sound Waves
Waved Design
Experimental Validation
Waved Results Vmax 28.8 m/s Vavg 10.4 m/s
B-Side
Over-molded By-Pass Temp. Door
1.Air boundary layers encounter i) Large
pressure gradient between the plenum and channel.
ii)
Door-seals small tip diameter. 1B. The turbulent
boundary layer separates from the door and forms
air vortices and sound. 2. Sound (Pulsed
Pressure) is reflected from the housing providing
a feedback mechanism to stimulate the formation
of air vortices. 3. Feedback increases the
intensity of emitted sound creating the acoustic
whistle.

• Clay Molding
• Conceptual designs were modeled by molding clay
  to the existing door platform.
• Doors were tested in HVAC under operation
  conditions producing whistling.
• Results were analyzed and the best design was
  optimized.
• Tear-Drop Design was validated by tested
  prototype (not pictured)

Clay Molded By-Pass Door
By-Pass Temperature Door Specs. Mfg. Process
Injection Over-molding Door Material Hard
Plastic Seal Material 35 Grade Sanoprene Outer
Dimensions 27 x 20 x 5 mm (length x
width x seal thickness)
Ribbed Design
Ribbed II. Results Vmax 21.8 m/s Vavg 8.9 m/s
Existing Door Platform Clay Molding
Team Members Aaron Kleinow (Industrial Advisor),
Dr. Giles Brereton (MSU Faculty Advisor), Bethany
Danielski, Andrew W. Siefert, and Matt Warner
Whistling Still Remained!