Analysis of Vibro-Acoustic Propagation Generated by an Automotive Refrigeration System

Air conditioning systems are being increasingly applied in the Brazilian automotive industry becoming indispensable rather than an optional item for car buyers, who are constantly seeking out more comfort. Conversely, the application of these systems in motor vehicles involve the use of compressors which operate at high pressures, making them important sources of vibration and unwanted noise in the cabin of the vehicle, thus causing vibratory discomfort and noise annoyance. Despite the major technological developments in automotive air conditioning systems, there is still a shortage of engineering research conducted in the field of vibration and noise originated in these particular systems. The present study is aimed at investigating and characterizing experimentally the vibration and acoustic propagation in the interior of a vehicle, generated by the compressor of the air conditioning system. In order to allow correlation between noise and vibration, measurements were taken over time using the acquisition system LMS SCADAS, in two conditions: increasing rotation in the engine and stabilized rotation at the highest noise level. The data collected was processed and analyzed using different methodologies in time and frequency domain using the LMS software Test.Lab v.12A. The results show that the noise emitted by the air conditioning system is related to the operating rotational speed of the compressor and the H6 and H12 harmonics are the most emissive inside the cabin. Moreover, the results indicate that the vibration propagation happens primarily via the condenser. Therefore, a quieter system can be produced by a close cooperation between car vehicle and compressor.