用不同方法进行发动机噪声源识别的研究英文
Transactions of Tianjin University
Vol.8No.3 Sep.2002 Engine Noi Source Identification with Different Methods
LI U Y ue2hui,H AO Zhi2yong,BI Feng2rong,FU Lu2hua,H AN Song2tao
(School of Mechanical Engineering,Tianjin University,Tianjin300072,China)
Abstract:Engine noi source identification is esntial for making noi reduction strategies.Predominant noi sources of engines are normally identified as some cover com ponents such as oil pan,valve cover and front gear
cover etc.The radiated noi sources of a62cylinder construction diel engine are identified with two meth2
ods—lead covering technique and surface vibration technique,and the ranking of the major cover on the basis of
acoustic power is prented in this paper.Firstly the sound power level of the cover com ponents and their
contributions to the total acoustic power are determined with lead covering method under hemi2anechoic condi2
tion.Then the vibration characteristics of the com ponents are investigated.The sound power level of various
components is predicted via the mean square area average vibration.Both results basically agree well and verify
the effectiveness of both techniques in engineering field.
K eyw ords:engine;vibration;noi source;lead covering technique
Ξ Together with the reduction of fuel consumption and exhaust pollution,noi reduction is one of the high2 est prior targets for IC engine development becau of the more and
more strict engine noi limits.Noi issue is also of rious concern to today′s engine manufactures; the subject of noi engineering is steadily included better methods for identifying and resolving this issue.
Engine noi can be classified into aerodynamic noi and surface radiated noi.In order to reduce the noi level of existing engines,modifications have to be imple2 mented on the existing ries production engines in a short time and as cheaply as possible to meet the engine noi regulations.The aerodynamic noi of air intake and exhaust systems can be reduced significantly by the u of air intake and exhaust mufflers,thus the surface radiated noi will become the predominant factor for noi reduction strategy in order to reduce the noi of engines to a tolerable level.So an exact noi source iden2 tification and analysis is necessary in order to classify the noi radiation of individual engine components and their contributions to the overall engine noi.Potentially there are a large number of possible methods,which can be ud as source location techniques,and normally most of them ud in the engine industry are:1)Lead covering or shielding technique;2)Surface vibration technique;
3)Acoustic intensity technique.
Suffice to say that all methods will give the overall results,but will differ considerably in detail and accura2 cy.Of the methods the lead covering technique is still the most reliable,although it must be undertaken under anechoic conditions,it is rather costly and time2consum2 ing.The surface vibration technique doesn′t require ane2 choic conditions but requires a large amount of data mea2 surement and calculations.Acoustic intensity technique was developed in1970′s and currently acoustic intensity techniques are popular,but the required instruments are very expensive.
1 Lead covering or shielding technique
Lead covering technique is also called partial expo2 sure technique and is a traditional noi source identifica2 tion technique for engines.It is still the most reliable,al2 though it is rather costly and time2consuming.This is simply covering the whole engine or all of the components with an acoustic high transmission loss material(usually lead).It is mounted on fiberglass wool for isolation and to prevent reverberant buildup,to give considerable no
i reduction.A component is then uncovered and the noi increa is noted.The process is repeated for each compo2 nent,the sound power level and the noi balance for the engine are calculated by the u of the noi increa val2 ue.
The engine detailed in this paper is an NA construc2 tion diel engine.An abridged engine specification is as
ΞAccepted date:2002204225.
L IU Yue2hui,born in1971,male,M,lecturer.
follows. Bore : 108mm Stroke : 105mm No.of cylinders : 6
Rated power : 92kW at 2200r/min
The surface vibration measurement is carried out un 2der hemi 2anechoic condition at Tianjin University.The noi at rated condition is measured at 4microphone posi 2tions ,i.e.at the front ,on the right side ,on the left side and above the engine.According to SAE
recommenda 2tions ,the microphone is 1m from the center of the ap 2propriate side of a virtual box ,which enclo the engine. Covers are one of the important components of en 2gines ,such as the oil pan ,the valve cover ,the front gear cover and the external surface of the muffler.The func 2tion of the covers is to enclo the working mechanisms and to retail oil or/and water.It has been shown by pre 2vious study that covers generally constitute the predomi 2nant sources of engine radiated noi and that some re 2duction of engine noi is always possible by improved cover design [1,2].So the sound power level of the four components is determined by lead covering technique in order to outline possible noi reduction strategies of this ries production.Firstly ,all the 4components are cov 2ered with lead sheet and fiberglass wool ,then the front gear cover is uncovered.The same process is repeated to the valve cover ,the oil pan and the muffler.The sound pressure level of different microphone positions is record 2ed each time when a component is uncovered and the val 2ue at each time is shown in Fig.
