Vehicle interior sound quality is regarded as a major quality attribute by automobile consumers and manufacturers. Whining noise, due to its steady state and tonal nature, is easily perceived as an annoyance to normal driving comfort. The blower motor in the climate control air-handling system can be a source of whining noise, especially when the motor is located in the passenger compartment.
This paper describes a systematic case study carried out to identify the major noise generating mechanisms of a whining noise from the climate control air-handling system. The paper discusses the use of commonly available tools and techniques to resolve typical automotive NVH concerns resulting in improved sound quality. Particular measurement and analysis techniques presented include sound field mapping using acoustic intensity, resonance identification using transfer functions, three-axis spectrum analysis, and some physical modifications to the source and propagation paths. A variety of objective noise and vibration data is presented and explained. The investigation concludes the source of the whining noise as a type of brush noise. The path is identified as structureborne noise transmitted from the brush-commutator interface, through the motor support structure, to the blower assembly casing, where it is radiated from various positions as airborne noise. The recommended solution is to mount the motor so that it is vibration isolated. Data measured on an iso-mount design is presented to confirm this solution.