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As per available reports about 5 relevant Journals and 8 Conferences are presently dedicated exclusively to NVH and about 55 open-access articles and 30 conference proceedings are being published on NVH.
Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, harshness is a subjective quality, and is measured either via "jury" evaluations, or with analytical tools that provide results reflecting human subjective impressions. These latter tools belong to the field known as "psychoacoustics." An interior NVH deal with noise and vibration experienced by the occupants of the cabin, while exterior NVH is largely concerned with the noise radiated by the vehicle, and includes drive-by noise testing. NVH incorporate concepts from Noise, Vibration and Harshness (NVH) Engineering, Aerodynamics, Automobile Engineering, Biodiesel etc. etc.
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Scope and Importance:
NVH are one of the critical areas of operations in the automotive industry. Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, harshness is a subjective quality, and is measured either via "jury" evaluations, or with analytical tools that provide results reflecting human subjective impressions. These latter tools belong to the field known as "psychoacoustics."
An interior NVH deal with noise and vibration experienced by the occupants of the cabin, while exterior NVH is largely concerned with the noise radiated by the vehicle, and includes drive-by noise testing.
NVH is mostly engineering, but often objective measurements fail to predict or correlate well with the subjective impression on human observers. For example, although the ear's response at moderate noise levels is approximated by A-weighting, two different noises with the same A-weighted level are not necessarily equally disturbing. The field of psychoacoustics is partly concerned with this correlation.
In some cases the NVH engineer is asked to change the sound quality, by adding or subtracting particular harmonics, rather than making the vehicle quieter.
The sources of noise in a vehicle are many, including the engine, driveline, tire contact patch and road surface, brakes, and wind. Noise from cooling fans, or the HVAC, alternator, and other engine accessories is also fairly common. Many problems are generated as either vibration or noise, transmitted via a variety of paths, and then radiated acoustically into the cabin. These are classified as "structure-borne" noise. Others are generated acoustically and propagated by airborne paths. Structure-borne noise is attenuated by isolation, while airborne noise is reduced by absorption or through the use of barrier materials. Vibrations are sensed at the steering wheel, the seat, armrests, or the floor and pedals. Some problems are sensed visually - such as the vibration of the rear-view mirror or header rail on open-topped cars.
Typical instrumentation used to measure NVH includes microphones, accelerometers and force gauges, or load cells. Many NVH facilities will have semi-anechoic chambers, and rolling road dynamometers. Typically signals are recorded direct to hard disk via an analog-to-digital converter. In the past magnetic or DAT tape recorders were used. The integrity of the signal chain is very important, typically each of the instruments used are fully calibrated in a lab once per year, and any given setup is calibrated as a whole once per day. Laser scanning vibrometry is an essential tool for effective NVH optimization. The vibrational characteristics of a sample are acquired full field under operational or excited conditions. The results represent the actual vibrations. No added mass is influencing the measurement; as the sensor is light itself.
There are three principal means of improving NVH:
•Reducing the source strength, as in making a noise source quieter with a muffler, or improving the balance of a rotating mechanism
•Interrupting the noise or vibration path, with barriers (for noise) or isolators (for vibration)
•Absorption of the noise or vibration energy, as for example with foam noise absorbers, or tuned vibration dampers.
Deciding which of these (or what combination) to use in solving a particular problem is one of the challenges facing the NVH engineer. Specific methods for improving NVH include the use of tuned mass dampers, subframes, balancing, modifying the stiffness or mass of structures, retuning exhausts and intakes, modifying the characteristics of elastomeric isolators, adding sound deadening or absorbing materials, or using active noise control. In some circumstances, substantial changes in vehicle architecture may be the only way to cure some problems cost effectively.
Market Analysis:
Growth in global automotive production is likely to remain at around+4% per year in 2014 and 2015,with an increase in production in China, India, and Mexico at the expense of Europe. Production is even expected to exceed 100 million vehicles by 2017. The major component manufacturers, which are essential for auto makers, have relocated to follow production and register healthy levels of profitability.
BCG predicts that, by 2016, one-third of world demand in automobile industry will be in the four BRIC markets (Brazil, Russia, India and China). Other potentially powerful automotive markets are Iran and Indonesia.
According to a J.D. Power study, emerging markets accounted for 51% of the global light-vehicle sales in 2010. The study expects this trend to accelerate. Emerging auto markets already buy more cars than established markets.
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This page was last updated on November 25, 2024
