Countermeasures for Impulsive Noise Character in Internal Combustion Engines

Abstract

The demand for efficient vehicle propulsion has led to downsizing of the internal combustion engines. Combined with a request for increased power output, these engines experience high peak pressures and strong pressure gradients. The downsizing strategy has been found to induce noise that has an impulsive character. This project investigates ways to counteract the transfer of this noise into the vehicle cabin. The assessment of the impulsive noise character is based on the peak to average power ratio, spectrograms and subjective listening of the vibration time history signal in the mounting points between the engine and the car. The evaluation has also been aided by an overall sound pressure level estimate. The analysis is carried out using an existing discretized model of a spark ignited four cylinder four stroke internal combustion engine. The influence of material density, material stiffness, combustion strategy and bearing clearance on the generation of impulsive noise character is investigated in a parameter study. Moreover, the possible mitigation of the noise character is investigated in a design study, where the attachments in the engine structure of one of the mounting points between the engine and the car are changed, while maintaining the position of the mounting point to the car. It is concluded that an increased crank shaft stiffness, a prolonged combustion duration and a redesigned suspension console are the three most efficient countermeasures to diminish the noise character.