Engine assessment @CARS24 : Sound analysis using Signal Processing & CNN
There are different types of engine related issues which are crucial while assessing a pre-owned car — abnormal sound from crankshaft, tappet cover, engine vibrations, engine misfiring and blow-by from the engine.
Multiple approaches explored around assessing these issues require sensors to make contact with engine components, like vibrometer, temperature sensor etc. However, because of extreme temperatures and exhaust gases in the engine chamber, these sensors can be quite expensive and are prone to frequent breakdowns. A rather non-intrusive way to capture engine condition is by monitoring the engine sound at idle and at 2000 RPM, we at CARS24 have been collecting this for years now and have engine sound data recorded for millions of cars.
Engine sound, when looked at in the frequency domain, shows specific dominating frequencies. These frequencies are produced by the engine’s fundamental frequency and its integral multiples (harmonics). All rotating parts in the engine contribute their own frequencies to the overall sound profile as these components interact and vibrate in time with the engine’s cycles. Thus, our hypothesis was, that if we could establish a frequency pattern under ideal conditions for different types of engines and above mentioned critical imperfections, we can categorize engines using only sound data.
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