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Worldwide automotive sector regulatory norms have changed and become more stringent and complex to control environmental noise and air pollution. To continue this trend, the Indian Ministry of Road Transport is going to impose new vehicle exterior pass-by noise regulatory norms IS 3028:2023 (Part2) to control urban area noise pollution. This paper studies the synthesis of M1 category vehicle driving acceleration, dominant noise source, and frequency contribution in exterior PBN level. A vehicle acceleration analysis study was carried out to achieve an optimized pass by noise (PBN) level based on the vehicle’s PMR ratio, reference, and measured test acceleration data. Based on the analysis, test gear strategy was decided to achieve a lower PBN level. This strategy involved increasing the effective final drive ratio and optimizing engine calibration, resulting in improvement with acceleration in the ith gear.

Sound signature design is gaining more importance within global auto manufacturers. ‘Sportiness’ is one of the important point to consider while designing a sound character of a car for passionate drivers and those who love aggressive driving. Nowadays automobile manufacturers are more focused in developing a typical sound signature for their cars as a ‘unique design strategy’ to attract a niche segment of the market and to define their brand image. Exhaust system is one of the major aggregate determining the sound character of ICE vehicles which in turn has the direct influence on the customer perception of the vehicle and the Brand image and also the human comfort both inside and outside the cabin. This research work focuses on novel approaches to identify frequency range and order content by a detailed study of subjective feelings based on psycho-acoustics. Sound samples of various benchmark sporty vehicles have been studied and analyzed based on sound quality parameters.

This paper addresses the "Grunt Noise" anomaly in Hydraulic Power Assisted Steering (HPAS) systems, detailing an extensive effort to resolve this disruptive issue. HPAS, while cost-efficient, faces challenges as it adapts to customer demands for reduced steering effort and enhanced handling. Intensified HPAS intervention requires components to withstand higher pressures and tighter tolerances, leading to occasional anomalies. "Grunt Noise" arises from Torsion bar (T-bar) resonance with fluid pressure pulsations. A comprehensive study identifies load conditions, transfer paths, and frequency bands, extending from vehicle to Pinion Valve assembly levels. Root cause analysis traces the issue from Steering Wheel to T-bar, validating the approach. The T-bar's twisting operation renders torsional stiffness crucial for Grunt Noise. Lower stiffness T-bar, when overpowered by liquid force, causes microsecond imprecise valve openings, leading to cavitation-induced Rack & Pinion vibrations.

Designing a Passenger vehicles suspension system is a key challenge for all OEMs because balancing buzz, squeak, and rattle (BSR) acoustic performance at low-speed driving and improving ride quality at high-speed driving conditions are bet challenging. Suspension noise deteriorates in-cab acoustic quietness and overall vehicle performance. For this reason, optimizing these noises is becoming increasingly prioritized as a key design issue throughout the development process of suspension system. This paper studies the various components of suspension system and their noises in Passenger vehicles. Based on customer voice index and drive pattern, suspension anomalous Clunking noise was identified in Passenger vehicles. This noise phenomenon was cascaded from the vehicle level to BSR rig and eventually to the suspension rig for root cause analysis.

Small commercial vehicles (SCVs) are the drivers of a major part of India’s indirect economy, providing the most efficient means of transport. With the introduction of BS-VI norms, some major overhauls have been done to the SCV models to meet BS VI norms in challenging timeline for early market entry. This forced to automotive designers towards challenge of cost competitiveness as well as refinement level to survive in this competitive market. This paper explains the systematic approach used to overcome challenges of higher tactile vibrations, higher in-cab noise because of BS VI requirement in 2 cycle engine required for small commercial vehicle. The solutions were need to be worked out without compromising the other performance attributes like total cost of ownership, fuel economy, ease of servicing and cost effectiveness.

The future of bus transit in new millennium is promising. This optimism is based on an anticipated long-term slowdown in growth of suburbs and revitalization of central cities. It reflects and escalates the public concern with traffic congestion, sprawl and pollution. This calls for double the use of public transport to address above issues. It calls for changing the mind-set of society towards public transports like buses, coaches etc. This could happen if bus design ensures right comfort, safety and TCO by ensuring refined bus transport. Hence, it is responsibility of OEMs to provide the new generation buses and coaches, which will ensure the public demands of comforts in terms of NVH refinement. This paper covers the unique approach used to convert the existing bus NVH refinement to next level as a short-term solution and with the intention of articulating NVH strategies for new generation bus development.

Noise Vibration and Harshness (NVH) refinement is one of the important parameters in modern vehicle development. In city traffic conditions, idling is an engine operating condition where a driver focuses attention more to his/her vehicle. Tactile vibration & noise levels inside the cab play an important role in all vehicles, especially those powered by diesel engines where combustion pressures are higher. They lead to discomfort & fatigue of passengers of even a low cost vehicle. Now its idle NVH is influenced mainly by vibration-isolation provided by power-train (PT) mounting design, This paper describes steps taken to improve the idle vibrations at a driver seat of a small commercial vehicle (SCV) with a 2-cylinder diesel engine of 800 cc through redesign of PT-mounting along with fine tuning of idle speed of the engine. A resonance was avoided between the first firing order at idling and PT rigid-body mode in pitching.

This paper discusses various fruitful iterations / experiments performed to reduce air flow induced noise without compromising on total air flow requirement for thermal comfort and ways to avoid heat ingress inside the bus. Also the paper discusses the devised process for noise reduction through front loading of computer aided engineering and computational fluid dynamics analysis. Air conditioning buses in light commercial vehicle (LCV) segment is growing market in India, especially for applications like staff pick-up and drop, school applications and private fleet owners. The air-conditioning system is typically mounted on bus roof top and located laterally and longitudinally at center. It is an easiest and most feasible way to package air conditioning system to cater the large passenger space (32 to 40 seats) with the conditioned air. This makes air conditioning duct design simple and commercially viable.

Production variations of a heavy duty truck for its vibrations were measured and then analyzed through an Ishikawa diagram. Noise and Control factors of the truck idle shake were indentified. The major cause was found to be piece to piece variations of its power-train (PT) rubber mounts. To overcome the same, a new nominal level of the mount stiffness was sought based on minimization of a cost function related to vibration transmissibility and fatigue damage of the mounts under dynamic loadings. Physical prototypes of such mounts were proved to minimize the variations of the driver's seat shake at idling among various trucks of the same design. These learning's are useful for design of various subsystems or components to refine the full vehicle-Noise Vibration Harshness (NVH) at the robust design level.

This paper discusses combined experimental and simulation approach used for NVH refinement of Passenger Vehicle for in-cab Boom Noise. On initial testing of Proto Vehicles a boom was identified in the speed range of 1300-1600 rpm in all the gear conditions. Investigations through measured Vibrations and Operational Deflection Analysis (ODS) identified that the rear axle had a vibration mode of the axle on the trailing arm bushes at around 43 Hz excited by the engine combustion forces. This finding was concurred by predicted full vehicle level modal and acoustic response analysis results. Based on simulation findings, conceptual change of rigid attachment between rear axle and trailing arm suppressed the vehicle boom. Using simulation approach a realistic design solution was worked out in terms of optimization of trailing arm rear bush stiffness values. Benefits of same were confirmed on the vehicle.