NVH Testing & Consulting
CASE HISTORY
Case history
In this section are present some SCS experiences.
Some of this activities have been executed in SCS technical centre, others in customer sites.
Pass-By
Place: China
Period: four months in 2005
Customer: CAR producer
SCS in the year 2005 performed an acoustical study with the objective to reduce external noise “PASS BY” on new model of the car. The customer required the SCS help due the vehicle didn’t pass the parameters request from the Chinese Standard Homologation regarding the level of the noise in the Pass by test.
A team of SCS technicians executed the test on the vehicle directly in customer promises in China with the help of SCS technical centre in Italy.
The study of the vehicle showed the needs to modify some parts in the car, mainly silent part of the exhaust system, air box, and the improvement of the material used to prepare the insulation kit. A complete study was dedicated to change the configuration of air filter box.
The techinicians also modify the silent part of exhaust system.
After only for months of the job, the customer obtained the homologation for the Pass by test.
Cabin Noise
Place: China
Period: one month in 2006
Customer: CAR producer
In march 2006 SCS performed for one of the most important Chinese car maker an NVH stud to improve the cabin noise on one model.
A team of SCS technicians executed these measurements in the customer site, in China.
The analysis and elaboration of the data collected suggested 15 different improvements to decreae the level of the noise in the passenger compartment.
The most importants modification were on the insulation kit and the evaluation of the correlation vibration – noise.
Particular attention was on the study of the more suitable materials to improve the effects of acoustic insulation and to decrease the influence of some vibration source, as filter box. As a result of the improvements, the customer decides to promote in the more important cities in China a sort of competition, to show to the market that this car became the most quiet model of its category. At today, nobody could propose any other model quiter that the model with SCS improvement.
For more details, SCS invite to visit the following website:
CSP 360
Cnhan.com
Auto.sina.com.cn
Please consider that in these site is reported with SCS the name of Alipalia, that is a mistake produced from a customer: they want to mean “from ITALIA”.
Acoustic Comfort
Place: China
Period: two weeks in 2007
Customer: CAR producer
In the year 2006 a car producer requires to SCS to perform experimental tests to check the acoustic comfort in the car.
In particular SCS technicians executed acoustic tests on the open / close of the door, on the noise produced by windscreen wiper and on the insulation produced by windows sealing of the window.
The results of the tests permitted to the customer to improve the comfort on its car model and to compare this model with the most important ones of the category.
Light Truck Pass-by Noise Modelling with Boundary Elements Method
One of the first studies on automobile pass-by and internal noises, using a hybrid method involving source identification and numerical analysis, achieved through a partnership between SCS and one of major acoustic materials manufacturers, a firm which performs analysis and design, and provides solutions for automobile manufacturers. SCS was charged to perform numerical analysis and the acoustic and vibration expertise, and to manage the experimental analysis development. The objective of this study was to improve the acoustic behaviour of a light weight truck.
The important outcome of this study is that relevant solutions and improvements were investigated with a numerical model (based on the CAD model) of the van, before a prototype was available.
The project was conducted in 2 phases:
1. A complete investigation was conducted on an existing van in order to validate the hybrid method contained in Rayon Solver (I-deas component) in which the experimental part consisted of: pass-by noise, engine noise radiation and internal noise measurements.
2. The second phase was the acoustic design of the new light truck with a numerical model, by using the engine source of the existing van (the new engine was not yet available). Results were then updated when the new engine was characterized. A proper source model of the engine was derived by using an Inverse Boundary Element scheme, involving experimental data and a boundary element model of the engine, defined as a set of prescribed acceleration surfaces. Once the engine noise model has been derived, the pass-by noise is computed by using the standard Variational Boundary Element Method.
Engine Noise Modelling with Boundary Elements Method
A simplified BEA model of the engine is built using 442 Linear quadrangular elements, sufficient to perform calculation up to 1300Hz (according to a 4 elements per wavelength mesh criterion). The model is subdivided in 18 surfaces defined as prescribed acceleration pistons.
The ground is taken into account as an infinite rigid plane. At this stage, transfer functions (Hik) between measurement point pressure (i) and each panel acceleration (k) are derived by using BEA solver. Then, the equivalent engine source model is achieved by finding panel acceleration auto interspectra (Akl), which minimize the error between experimental pressure spectra (Sijexp) and those derived from the model (Sijnum).
This task is performed by using a linear least squares minimization technique. The total energy by summing all the autospectra is predicted with an error of less than 0,5dB. Local result comparison shows discrepancies less than 2dB at harmonic peaks.
Air conditioning external unit (chiller) SEA noise modelling
At the design stage of a new chiller and in order to achieve a possible noise reduction, it becomes necessary to study the emissions sources/causes and to separate the airborne radiation from the structure borne radiation (compressor vibration).
The existing CAD has been used to build a simplified SEA model from which the influence of the structure borne component have been identified. As a first result of the study, it was the inconsistency of increasing the mass of the insulation enclosure around the compressor, because the vibrational excitation would have neglected the theoretical result; in effect it was clear that a suitable damping material will give a much better noise reduction.
Noise Sources identification
Noise sources identification is an experimental process requiring high skill and suitable methodology, unless the goals is just to obtain some sort of “sound mapping” without any energetic correlation with the sound sources.
Sound intensity has been used for some time as a sources recognition tool, but in more recent year it has been proven that Holography is able to give far better results and possibilities for simulating modification to the structure or as screen material addition.
One example (figure below) is relative to the noise sources identification an classification of a diesel engine for agricultural machinery, and the subsequent simulation for investigating achievable noise reduction by modifying the engine cover.
Car Noise reduction using SEA
The goal of the project was to finalize a methodology of noise reduction possibilities by creating a specific materials data-base for SEA simulation, to be used to optimise weight of added trims during new car models development. Materials acoustic characteristics have been determined with SCS 902A materials suite and with direct measurements on car subsystem (trunk and passenger compartment) of specific characteristics, i.e. sound absorption and insulation.
The car subsystem is then analysed in terms of modal density, stiffness and damping, the latter was related to the real need of damping materials addition vs. efficiency in terms of noise reduction. Experimental data on body in white elements have been used to tune the SEA simulation model of the car, while further on, the materials data-base has been merged to the SEA model to obtain a “real” and validated development model for prototyping.
Reference List
• Quality control on seats (Lear, Johnson Controls)
• Acoustic project of commercial vehicle (Iveco, IRAN KHODRO)
• SEA modelling (Lear-FIAT, IRAN KHODRO)
• Noise source identification trough acoustic holography (Ovatex-Fiat)
• Road test to check the behaviour of tyres (Bridgestone)
• Road test to check the behaviour of exhaust system (Flexider)
• Sound power and Sound quality on agricultural machinery (Ovatex-Same, CNH, Carraro)
• Sound quality on exhaust system (Magneti Marelli)
• Research on acoustic material (Ovatex)
• Damping of acoustic material for navy industry (Fincantieri)
• Acoustic characterization on electric lift (Carraro)
• Defects determination on fuel pump (Riello)
• Study on train railroad (Ferrovie Suzzara, ATM Torino, FS)
• Beamforming system (Industrie Pinifarina)
• Noise monitoring close refinery (Infineum)
• Pass by noise test (Liebao Changfen)
• Cabin noise (Zhejiang Geely)
• Acoustic comfort (Nanjing Fiat Nanya)
• Break noise optimisation (ITT)
• Systems design and manufacturing, based on vibration and/or noise emission of:
· Air collectors (Magneti Marelli)
· Refrigerators (Electrolux)
· Washing machines (Electrolux)
· Electrical motors (Electrolux)
· Common rail injectors (Fiat Research Center)
· Security belts (TRW)
· Gearboxes (Graziano Trasmissioni, Ferrari cars, Iveco, Euroricambi, Iran Khodro)
· Seats (Lear Corporation, Johnson Control)
· Turbine blades (Ansaldo Energia)
· Gas valves (Sit la Precisa)
· Automotive electronic devices – Vibration screening test bench (Facet)
· Vibration absorbers (Integra – Fiat)
Some cients
• Fiat
• Iveco
• Ferrari
• Maserati
• Industrie Pininfarina
• Lear
• Johnson Controls
• IRAN KHODRO
• Bridgestone
• Flexider
• CNH
• Carraro
• Magneti Marelli
• ITT
• Fincantieri
• Riello
• Alstom
• Ferrovie Suzzara
• ATM Torino
• Liebao Changfen
• Zhejiang Geely
• Nanjing Fiat Nanya