Search Results

Exhaust noise from engines is one of component noise pollution to the environment. Exhaust systems are developed to attenuate noise meeting required db (a) levels and sound quality, emissions based on environment norms. Hence this has become an important area of research and development. Most of the advances in theory of acoustic filters and exhaust mufflers have been developed in last two decades. Mufflers are important part of engine system and commonly used in exhaust system to minimize sound transmissions caused by exhaust gases. Design of mufflers is a complex function that affects noise characteristics, emission and fuel efficiency of engine. Therefore muffler design becomes more and more important for noise reduction. Traditionally, muffler design has been an iterative process by trial and error. However, the theories and science that has undergone development in recent years has given a way for an engineer to cut short number of iteration.

Commercial vehicle NVH attributes primarily focus on interior noise for driver's comfort and exterior noise for environmental legislation. Major sources for both the interior and exterior noise are power train unit, exhaust and air intake system. This paper focuses on development of Air Intake System (AIS) for better interior and exterior NVH performance for medium and heavy commercial vehicles. For air intake system, structural radiations from its panels and nozzle noise are significant contributors on overall vehicle NVH. Noise generation mechanism in air intake system occurs due to opening and closing of the valves and inlet air column oscillation by sharp pressure pulse from cylinder. Based on benchmarking, vehicle level targets have been arrived, and then cascaded to system and sub-system level targets. For air intake system, targets for nozzle noise at wide open throttle condition have been set for exterior NVH performance.

The cost incurred to make design modifications to solve NVH problems increases with maturity of design in the development process. Hence NVH issues should be addressed in the initial phase to avoid any significant changes in structure and subsequent changes in overall performance of the vehicle. Hybrid methodology with application of advanced testing and Computer Aided Engineering (CAE) tools to achieve full vehicle NVH attribute targets is nowadays a must for this reason. This paper represents a case study on low frequency NVH performance evaluation and refinement for heavy commercial vehicle truck using Hybrid Test-CAE methodology. To achieve better NVH performance, it is important to set competitive overall vehicle level NVH targets and cascade it down to system and sub-system targets. Test-CAE correlation has been carried out to validate Finite element (FE) modeling procedure and methodology.

Pass-By-Noise (PBN) requirements area an important aspect of NVH development of a commercial vehicle. The PBN on an Intermediate commercial vehicle (ICV) with refrigerator container was the subject of this study. This vehicle emitted PBN greater than accepted threshold due to its configuration. The overall approach to identify the sources and contributors for PBN was to test the vehicle in its baseline condition as well as with improvements. Near source noise measurements were performed at all potential noise contributors. A windowing technique was used to identify the potential noise sources. This Windowing technique is the exposing of each individual noise source while keeping all others shielded. This technique is reliable and quickly reveals significant noise contributors. Improvements to noise sources were reviewed for effectiveness to the overall PBN and overall recommendations were made.