Car designers have three contradictory forces to trade-off with:
In order to calibrate correctly an engine, every NVH (Noise, Vibration, and Harshness) engineer knows that there are three forces that have to be managed and balanced each one to the others:
Engine horsepower - Fuel consumption - Engine Noise
As for Engine power or horsepower, indeed it is a key feature as main focus of the car buyer. The first thing you’ll tell your friends when buying a sporty car or even a family pick-up. However due to new EcoTech downsizing constraint, the rules has changed: engines must keep the horsepowers but with less displacement.
EcoTech? Downsizing? This is how to get the best motor efficiency and get higher horsepower and increased torque on a new 1.6l compared to the last generation at 2.0l, even adding reduce fuel consumption.
Fuel efficiency is the second force to exert. It has become a major selling argument and car-makers seek to reduce vehicle weight in order to optimized not only fuel consumption and but also CO2 emissions.
European Union legislations require that any new car registered in the EU shall not emit more than an average of 130g CO2/km by 2015, meaning an average fuel consumption of 5.6 l/100 km (gasoline) or 4.9 l/100 km (diesel).
And by 2021, this limit moves to 95 g CO2/km, meaning an average fuel consumption of 4.1 l/100 km (gasoline) or 3.6 l/100 km (diesel).
Indeed, those CO2 emission regulations impose weight optimization of cars and using passive countermeasures such as sealing and sound- absorption material must be avoided, as generating more weight therefore more fuel consumption.
Therefore the noise shall be cancelled without the use of extra weighted material.
As an example on typical European car using a 4-cylinder engine, the most predominant noise is the 2nd order harmonic of the engine rotational speed.
When the engine speed ranges from 1200 to 6000 rpm, the 2nd