Development of Advanced Signal Analysis Technique for Pass-by Noise Source Identification of Light Commercial Vehicle

The Auto industry, particularly goods-moving trucks, is heavily responsible for noise pollution in cities. From a noise pollution control perspective, the noise produced, which is subject to regulation (IS 3028:1998), requires immediate action. This noise is mainly contributed by various vehicle systems like engine, exhaust, intake, tires etc. Identifying the major contributing source is a challenge when the pass-by noise levels does not comply with regulatory norms. The existing methods of source identification like windowing sources or swapping sub-systems sequentially are time consuming and needs more resources. Acquiring noise data using data acquisition system at vehicle level and pass-by noise measurement location can be carried out for contribution analysis, but currently being measured by two separate data acquisition systems. There exists no process/method to synchronize the measurements in two individual data acquisition systems without external exclusive synchronising technology like telemetry. A simple and accurate signal processing method is developed for synchronizing near source data in vehicle to the external pass-by noise microphone data and identifying the source contributing to higher pass-by noise. This method is based on extracting of vehicle engine speed (rpm) from pass-by noise microphone noise colour plots using advanced signal processing tools. Once the engine speed (rpm) at which the highest pass-by noise occurs is identified, the contribution of each source in the vehicle to the measured pass-by noise level at that particular engine speed (rpm) can be determined through octave analysis and contribution analysis. This method was successfully validated by identifying transmission system as root cause of higher pass-by noise in a light commercial vehicle. This exercise provides a method to synchronize and analyse data from 2 independent data acquisition systems without any external synchronizing equipment and also proves that transmission unit contribution to pass-by noise is significant and must be monitored closely.