It is becoming increasingly important to reduce the noise generated by heavy duty vehicle engines in order to increase ride comfort and comply with the acoustic limitations set by regulations.
This paper describes the work done to reduce the noise generated by a heavy duty diesel engine. Here is a presentation of the methodology, which features both experimental and calculation aspects.
The calculation step represents the main work with deep analysis and knowledge of the main mechanisms generating noise. Indeed, if the most radiating structure can be globally localized with sufficient accuracy, it is often not obvious to know which internal mechanical excitation generates high acoustic levels. This is particularly true when high acoustic levels are measured in a broad frequency band.
In this paper, the contribution of the internal mechanical excitation is simulated for broadband emission from the timing front case. Particular attention is paid concerning the use of validated excitation data. The structure is modelled using the Finite Element method (FEM), and the judgement criterion is based on calculated acoustic dimensions using the Boundary Element Method (BEM).
When the structural model and the excitations are validated, a sensitivity study is conducted by modifying the structure and excitations. The main influent parameters for noise can thus be found. It is to be pointed out that a low cost modification to the generation of excitation improves the acoustic behaviour of the timing front case in a significant way. An experiment with a prototype solution demonstrates a satisfactory correlation between measured and calculated noise reduction. The solution allows a 1 dBA reduction of the acoustic power radiated by the complete engine at maximum power condition.