Abstract
During the past ten years noise and vibration in the vehicle along with the engine have decreased in high proportions. As a consequence, former secondary noise sources like air-conditioning and A/C loop systems have now become the major noise and vibration sources.
The subject of this study is to analyse and reduce the A/C loop noise in a car using noise measurement in the car cabin by microphone or by acoustic head. In the engine compartment we measure the vibration of the tubes and the pressure pulsation. These measurements help us to identify the noise sources.
The main object of this study is double. The first step is to define an experimental method to detect the structural and the flow noise of the A/C loop. The second step is to apply this measurement methodology to describe our A/C loop noise and vibration.
The first methodology is based on measurements inside the car cabin and measurement in the engine compartment. The noise in the car cabin, the vibration and pressure pulsation in the engine compartment are measured at several engine RPM. The second methodology is based on test bench measurements. The test bench consists in two climatic chambers with low noise level (see figure 1). The HVAC unit is placed in the first room and the other components of the A/C loop are placed in the second room. An acoustic insulating material is placed between the two rooms. The temperature and Relative Humidity (RH) of the rooms are controlled. One microphone is placed in the first room to measure the noise of the HVAC unit. Accelerometers and pressure sensors are placed on the tubes and hoses to measure vibration and pressure pulsation. The measurements are performed at several compressor RPM.
To reduce the noise and vibration of the A/C loop we analyse each component alone. The vibration analysis of the different samples of hoses gave us the best one and the noise analysis of the evaporator, expansion valve and the compressor allowed us to choose a design to reduce the flow noise.
With the measurement methodology in the car and the measurement methodology on the test bench, the correlation between noise, vibration and pressure pulsation gave us the sources of noise and vibration. The compressor and the expansion valve are the main sources of noise and vibration. The hoses and tubes are the transmission lines of vibration and pressure pulsation. The noise and vibration are amplified by the evaporator and HVAC unit.