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NVH refinement of a vehicle with light weight structure[1] focusing on fuel efficiency is a challenging task. Resonance between the air volume of the cabin and revolving engine excitation generates booming. This booming noise affects the annoyance of sound quality in the cabin. Engine torque variation, penetration of air intake and exhaust system, and tire unbalance caused by engine auxiliary resonance are the most influential sources for high speed booming. This paper describes the booming noise level reduction between 100-200 Hz during high RPM driving conditions in one of the passenger cars. Detailed CAE iterations and testing has been done to identify the root cause of the booming noise. By considering the cost vs NVH performance trade off, the optimized NVH countermeasure has been chosen and validated. Modal analysis, operational deflection shapes, Input point inertance and Noise transfer function techniques have been used for root-cause analysis and counter measure proposal.

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.

In the automotive industry several attributes needs to be considered for the development of a new vehicle which are important for the customer, such as vehicle dynamics, driveability, fuel consumption, emissions, durability and NVH among many others. Sometimes these characteristics are conflicting and often need is to create a robust trade-off where the design space is sufficient to fit all of them in a vehicle that rhymes with the brand image and is appealing to the intended customer. Automobile manufacturers try to meet the requirements with respect to quality and comfort and often, emotional, aspects supercede the previous objective, pragmatic demands. The satisfaction of the demands by the customers concerning comfort, driving pleasure, design appears dominant and functionality criteria sometimes takes a back seat. NVH is considered to be one of the key buy in factor among the above mentioned attributes.

Driver fatigue is one among the important factors for accidents, causing loss of precious life and property. Apart from long driving hours, driver fatigue can be due to poor ride quality, cabin noise, high vibration levels and poor ergonomics. In last few years, there has been enough emphasis to improve the noise and vibration comfort of commercial vehicles, which is governed by vibration levels at tactile points such as steering wheel, gear lever, pedal and seat. Steering wheel vibration is an important element which driver uses to express about the vehicle vibration quality. Design of steering system is driven by ergonomics, packaging, durability, safety, vibration & ride and handling requirements. This paper discusses about methodology of steering assembly development for Noise Vibration and Harshness (NVH) performance of commercial vehicle.

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.