外文翻譯一個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的無聲空氣濾清器的虛擬設(shè)計(jì)及性能預(yù)測(cè)

1、個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的無聲空氣漉消器的虛擬設(shè)計(jì)及性能預(yù)溜一個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的無聲空氣濾清器的虛擬設(shè)計(jì)及性能預(yù)測(cè)HAO Zhi-yong, JIA Wei-xin FANG Fang(College of Mechanical and Energy Engineenng, Zhejiang Umx-crsity; Hangzhou 310027, China)(Tianjin Internal Combustion Engine Research Institute, Tianjin Umveisity, Tianjin 300072,China)E-皿山 haozy, jiawxR

2、eceived Jan. 17, 2005, revision accepted May 12,2005摘要：本文報(bào)道中采用低噪聲內(nèi)燃機(jī)進(jìn)氣系統(tǒng)開發(fā)的虛擬設(shè)計(jì)方法結(jié)介作者的研究結(jié)果。由 此產(chǎn)生的高的通過噪聲水平高于在全油門的立法目標(biāo)時(shí)，發(fā)動(dòng)機(jī)轉(zhuǎn)速為5200r/min需要邊界 元輔助設(shè)計(jì)任務(wù)，按照典型的進(jìn)氣系統(tǒng)的設(shè)計(jì)與開發(fā)過程。在最初的設(shè)計(jì)中，基于聲學(xué)理論 和要求并考慮空間發(fā)動(dòng)機(jī)室中的約束，總體積和粗糙的內(nèi)部尺寸的測(cè)定。在詳細(xì)設(shè)計(jì)階段, 確定了空氣濾清器的確切的內(nèi)部尺寸，和一個(gè)有效的方法應(yīng)用于低頻聲性能的改善。預(yù)測(cè)表 明，進(jìn)化系統(tǒng)的聲功率達(dá)到最小的進(jìn)氣系統(tǒng)噪聲降低發(fā)動(dòng)機(jī)整體噪聲。關(guān)鍵詞：虛擬設(shè)計(jì)

3、;聲學(xué)性能;沉默的空氣濾清器;邊界無法（BEM）1簡(jiǎn)介一個(gè)原函數(shù)的進(jìn)氣系統(tǒng)的主要功能是首先有效信道的新鮮空氣對(duì)發(fā)動(dòng)機(jī)進(jìn) 氣噪聲，其次是減少排放。有一些現(xiàn)有方法的發(fā)展來提高進(jìn)氣系統(tǒng)設(shè)計(jì)一個(gè)更現(xiàn) 實(shí)的方法。這些目標(biāo)包括：更有效的消聲性能，達(dá)到降低噪聲一方面口益嚴(yán)峻的 立法目標(biāo)，優(yōu)化發(fā)動(dòng)機(jī)的性能和燃油經(jīng)濟(jì)性伴隨著車輛質(zhì)量的提高。一個(gè)典型的程序，用于汽車發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的設(shè)計(jì)與開發(fā)過程中。設(shè)計(jì)過程 包括仔細(xì)調(diào)諧的匹配這些發(fā)動(dòng)機(jī)運(yùn)行和呼吸特性的影響，污染物排放優(yōu)化影響噪 聲進(jìn)氣系統(tǒng)的所有組件，性能和經(jīng)濟(jì)性。從現(xiàn)有的或符號(hào)的系統(tǒng)布局，進(jìn)行各種 性能綜合評(píng)價(jià)。這種信息可能會(huì)被適當(dāng)?shù)厥褂迷u(píng)估的各種設(shè)計(jì)目標(biāo)當(dāng)前系

4、統(tǒng)的性 能，通過對(duì)其構(gòu)成要素進(jìn)行適當(dāng)修改，為系統(tǒng)優(yōu)化設(shè)計(jì)提供理論基礎(chǔ)。邊界元法廣泛應(yīng)用在進(jìn)氣和排氣系統(tǒng)的設(shè)計(jì)可以用來計(jì)算內(nèi)部，外部，或兩 個(gè)領(lǐng)域的同時(shí)，只要求的空氣濾清器可分為元素的周長(zhǎng)：和施加邊界條件的緩解 是另一個(gè)吸引。在本文中，邊界元法是用來預(yù)測(cè)的空氣濾清器的傳輸損耗和噪聲 排放。原來的進(jìn)氣系統(tǒng)設(shè)計(jì)中出現(xiàn)的水平高于在全油門和發(fā)動(dòng)機(jī)轉(zhuǎn)速在520017111m 的噪聲信號(hào)的頻譜特性的立法目標(biāo)噪聲高通連接通常是由離散的音調(diào)，對(duì)發(fā)動(dòng)機(jī) 的點(diǎn)火頻率是173赫茲對(duì)應(yīng)5200 t/niin內(nèi)聯(lián)四缸四沖程發(fā)動(dòng)機(jī)諧波相關(guān)的廣泛的 序列占主導(dǎo)地位。在許多情況下，從主源的聲能量體分布較低的頻率成分，可能 是難

5、以控制的。因此，本文提到的頻率范圍是從0到1千赫。在這個(gè)頻率范圍內(nèi)， 如灌紙對(duì)集成系統(tǒng)的聲學(xué)性能的影響是微不足道的，所以濾紙不顧。噪音是從空 氣濾清器入口噴出，與空氣濾清器系統(tǒng)出口連接到發(fā)動(dòng)機(jī)的進(jìn)氣。所以在發(fā)動(dòng)機(jī) 空氣濾清器的出入口壓力為邊界兀法的邊界條件。一個(gè)降噪通常有兩部分功能的傳統(tǒng)進(jìn)氣系統(tǒng)：空氣濾清消聲器。由于空間發(fā) 動(dòng)機(jī)室中的約束，重新設(shè)計(jì)的空氣凈化器結(jié)合清洗和沉默效果。在這項(xiàng)工作中， 一個(gè)所謂的沉默的空氣濾清器進(jìn)行了重新設(shè)計(jì)，幾何結(jié)構(gòu)確定的預(yù)測(cè)TL和邊界 元的聲功率發(fā)射。同時(shí)，為了盡量減少在較低頻率的進(jìn)氣系統(tǒng)的聲功率，旁通管 被添加到空氣輸送管。所產(chǎn)生的聲學(xué)性能分析表明，該方法最大限

6、度地減少對(duì)進(jìn) 氣系統(tǒng)噪聲降低發(fā)動(dòng)機(jī)整體噪聲的目標(biāo)是可行的。2無聲空氣濾清器的設(shè)計(jì)2.1 原裝空氣濾清器的評(píng)價(jià)這種原始的空氣濾清器的清潔設(shè)計(jì)主要關(guān)注減少噪音排放?？諝鉃V清器的出 口段是一個(gè)單位的速度振幅。計(jì)算T1時(shí)，空氣濾清器的出口部分給出了單元速度振幅模型的聲源，所有 其他的表面被建模為“聲學(xué)硬”默認(rèn)情況。出口部分的聲功率可以從公式計(jì)算。 所有后續(xù)的TL的預(yù)測(cè)具有相同的邊界條件。預(yù)測(cè)的空氣濾清器性能。在發(fā)動(dòng)機(jī)進(jìn)氣道的聲功率級(jí)是顯示圖的噪聲源信號(hào) 峰值為173赫茲的頻率諧波相關(guān)的發(fā)動(dòng)機(jī)點(diǎn)火。由于發(fā)動(dòng)機(jī)燃燒分布式低頻率從 100赫茲到800赫茲之間的聲音能量堆積太高，傳輸損耗在220赫茲到1 T赫

7、茲 的頻率范圍內(nèi)是如此之低，噪聲排放不能最小化，所以一個(gè)沉默的空氣濾清器具 有較高的TL 200赫茲到1赫茲的要求。2.2 無聲空氣濾清器的初步設(shè)計(jì)如果有足夠的空間，一個(gè)復(fù)雜的結(jié)構(gòu)，可以被分配到降低進(jìn)氣噪聲排放。因 此我們必須充分利用有限的空間。在這項(xiàng)工作中用CAD軟件或Pio/E進(jìn)行包絡(luò) 發(fā)動(dòng)機(jī)室中的其他汽車部件的剩余空間。然后從籠罩空間獲得的總體積所需的空 氣濾清器。下一步是選擇合適的消聲器單元和它們的尺寸。考慮空氣凈化效果， 必須滿足兩個(gè)要求：（1）空氣流量應(yīng)等于或超過原通量值；（2）過濾面積不能降 解。在這要求的基礎(chǔ)上，對(duì)消聲器單元理論初步確定開采布局?？諝鉃V清器是由 兩塊隔板分隔成三

8、個(gè)膨脹室，右擋板的中間有個(gè)洞，左擋板有四個(gè)孔的四角，濾 紙放在中間膨脹室的中心。因?yàn)檫@空氣濾清器的復(fù)雜性，孔的直徑大于原來的。 第二個(gè)要求是在第一擋板孔的直徑和長(zhǎng)度的二室，讓過濾面積等于原來的，然后 第二膨脹室的長(zhǎng)度可以確定。所以空氣濾清器的幾何結(jié)構(gòu)是由兩個(gè)變量確定的。整體的聲學(xué)行為是三室的所有組成元件的行為總和。為了提供連續(xù)衰減譜寬 的帶寬，在他們個(gè)人的貢獻(xiàn)衰減最小不應(yīng)同時(shí)發(fā)生。為了調(diào)查三室個(gè)人的聲學(xué)性 能，綜合空氣濾清器被分成三個(gè)部分，其中之一是擴(kuò)張室消聲器單元，只是在兩 擋板的位置。邊界元法的運(yùn)行進(jìn)行計(jì)算的三個(gè)個(gè)體的聲學(xué)性能。第一室具有高和 連續(xù)在300-1000赫茲頻段的衰減，并在40

9、0-800赫茲的頻率范圍的第：腔室具 有高衰減的聲學(xué)性能梢微比第一個(gè)更糟。第三室性能最差，但在約230赫茲的頻 率，其中第一和第二室的最小衰減，它具有更高的衰減，從而為第一和第二部分 提供的補(bǔ)償效果。同時(shí)，在更高的頻率，第三部分可能是良好的聲學(xué)性能，這是 在這個(gè)圖中沒有說明。請(qǐng)注意，這種單一的部分還介紹了之間存在不確定性，聲 相互作用，即使他們的個(gè)人表現(xiàn)，可以適當(dāng)?shù)卮砘蚪?。明確的單一部分的聲 學(xué)性能的初始設(shè)計(jì)提供了重要的信息。在某些領(lǐng)域的變化，集成系統(tǒng)在獲得最佳 的聲學(xué)性能的詳細(xì)設(shè)計(jì)的邊界元法計(jì)算。在最初的設(shè)計(jì)，外部幾何尺寸已確定，并且已用粗糙的尺寸單位選擇消聲器。 在擋板的位置和四個(gè)孔的

10、第二隔板半徑可以改變，以達(dá)到更好的聲學(xué)性能。2.3 噪聲排放預(yù)測(cè)直到現(xiàn)在，我們已經(jīng)完成了總體設(shè)計(jì)的無聲空氣濾清器。為了與原來的做一 個(gè)比較，的噪聲輻射進(jìn)行了預(yù)測(cè)。為了驗(yàn)證設(shè)計(jì)的空氣濾清器的實(shí)用性能，在5200轉(zhuǎn)/分鐘在發(fā)動(dòng)機(jī)試驗(yàn)臺(tái)作 為原始和重新設(shè)計(jì)的空氣濾清器邊界條件或噪聲源在全油門和發(fā)動(dòng)機(jī)轉(zhuǎn)速的測(cè) 量是在發(fā)動(dòng)機(jī)進(jìn)氣道的聲壓，進(jìn)而預(yù)測(cè)噪聲排放進(jìn)空氣濾清器。測(cè)量聲壓時(shí)，空氣濾清器和發(fā)動(dòng)機(jī)的噪音屏蔽掉。此外，由于在發(fā)動(dòng)機(jī)的進(jìn) 氣端口測(cè)量壓力引起的噪聲信號(hào)的空氣流的影響和誘導(dǎo)麥克風(fēng)干擾，惡化的發(fā)動(dòng) 機(jī)性能的困難，麥克風(fēng)的測(cè)量定位在200亳米到進(jìn)氣端口。邊界條件施加在空氣 濾清器系統(tǒng)出口處應(yīng)在測(cè)量位

11、置上面提到的基于聲學(xué)理論從噪聲信號(hào)中提取的。在進(jìn)氣道軸的點(diǎn)P的聲壓與最高的相比，在相同的距離其他點(diǎn)的入口段中 心。2.4 盡減少額外聲功率的方法在使用以前的布局的一個(gè)潛在的問題是在173赫茲的聲音從空氣濾清器的 進(jìn)氣發(fā)射功率水平，頻率不為其他頻段的低?？罩妹娣e在管道連接空氣濾清器與 發(fā)動(dòng)機(jī)的進(jìn)氣口表明其他一些可能的空氣清潔系統(tǒng)的改進(jìn)。本文采用旁路管來實(shí) 現(xiàn)這一目標(biāo)。提高TL在大約173赫茲的頻率為目標(biāo)確定尺寸LD = 980毫米。比較預(yù)測(cè) 的聲學(xué)性能上的布局與管和柔性分流管的布局現(xiàn)狀沒有改變。旁路管道布置的聲 學(xué)性能顯著提高在大約173赫茲的頻率和519赫茲的頻率的三倍，大致對(duì)應(yīng)半波 長(zhǎng)，預(yù)計(jì)

12、旁路管道布置TL輕度上升?？梢钥闯?，無輔助空氣凈化器在173赫茲是最高的聲功率級(jí)，而旁路管空氣 凈化器在這個(gè)頻率大大降低?？偮暪β仕綇?到1赫，為無旁路管空氣清潔 器110.2分貝，并為旁路管空氣清潔器105分貝。請(qǐng)注意，引擎聲功率級(jí)不從實(shí)驗(yàn)檢測(cè)進(jìn)氣系統(tǒng)噪聲112.2分貝和無聲的旁通 管的空氣清潔器105分貝，所以重新設(shè)計(jì)的無聲空氣濾清器切實(shí)降低發(fā)動(dòng)機(jī)整體 噪聲為最小的進(jìn)氣系統(tǒng)噪聲。3結(jié)論本文報(bào)道了一個(gè)邊界元法的輔助設(shè)計(jì)無聲空氣濾清器。在最初的設(shè)計(jì)中，基 于聲學(xué)理論和要求并考慮空間約束，進(jìn)行空氣濾清器總體積、空氣濾清器的粗糙 的內(nèi)部尺寸的測(cè)定。之后，一個(gè)有效的方法應(yīng)用到173赫茲的頻率的聲學(xué)

13、性能的 改善。邊界元法的聲學(xué)工程設(shè)計(jì)使用幫助迅速增加。本文的研究結(jié)果為無聲空氣濾 清器的工程應(yīng)用指南。流量的影響在本研究中并沒有考慮。雖然平均流將不會(huì)對(duì)聲學(xué)性能影響顯 著，這可能對(duì)空氣凈化性能的影響和濾紙的影響被忽略，盡管它可能會(huì)影響在高 頻率的空氣濾清器聲學(xué)性能。未來的研究應(yīng)包括在高頻率上的空氣凈化和過濾紙 上的聲學(xué)性能影響的流動(dòng)的影響。5一個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的無聲空氣灌消器的虛擬設(shè)計(jì)及性能預(yù)測(cè)參考文獻(xiàn)1 Bilau chuk, S.，F(xiàn)yfe, K.R., 2003. Companson and iniplementation of the vanous numerical meth

14、ods used for calculating transmission Loss m alencer systemsJ. Applied Acoustics, 64 903-916.2 Davies, P.O.A.L., 1996. Piston engine intake and exhaust system designJ. Journal of Sound and Vibration,190 677-712.3 Wu, T.W, Cheng, C YR, Tao, Z,，2003. Boundary dement analysis of packed silencers with p

15、rotective cloth and embedded thin surfacesJ. Journal of Sound and Vibration,261 1-15.6個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣系統(tǒng)的無聲空氣漉清器的虛擬設(shè)計(jì)及性能預(yù)測(cè)Virtual design and performance prediction of a silencing aircleaner used in an LC. engine intake systemHAO Zhi-yong, JIA Wei-xui FANG Fang(College of Mechanical and Energy Engineering,

16、 Zhejiang University; Hangzhou 310027, China)(Tianjin Internal Combustion Engine Research Institute, Tianjin Univeisity, Tianjin 300072,China)E-mail: haozy, jKHvxReceived Jan. 17, 2005, revision accepted May 12,2005Abstract： This paper reports results of the authors* studies on the virtual design me

17、thod used in the development of low noise intake system of I.C. engine. The resulting high pass-by noise at level above the legislative target at full throttle when engine speed was around 5200 r/mn necessitated a BEM-aided redesign task following the typical process of design and development of an

18、intake system During the miUal design, based on the acoustic theory and the requirements and considenng the constraint of space in rhe engine compartment, total volume and rough mteraal dimensions were determined. During the detailed design, the exact internal dimensions of the air cleaner were dete

19、nmned, and an effective method was applied to improve the acoustic perfwmance at low frequency. The predicted sound power of the intake system indicated that the objective of reduang the overall engine noise by nMnunizing intake system noise 3as achieved.Key words: Virtual design, Acoustic perfonmnc

20、e, Silencing air cleaner, Bouiidarv element method (BEM)INTRODUCTIONThe primary function of an The primary function or an intake system is firstly to efficiently channel fresh air to the engine, and secondly to numiiuze intake noise emissions. There are a number of current approaches for developing

21、a more realistic method to improve intake system design. The objectives include more effective silenang performance to meet increasingly severe legislative targets for reduced noise on the one hand, with optimized engine perfornxmce and fuel economy accompanied by improvements in vehicle quality on

22、the other handA typical procedure followed dunng the design and development of an intake system for a vehicle engine is shown. The design process includes a careful tuning of all components of the intake system that influence noise emission with optimized matching of these to the engine 7一個(gè)用于內(nèi)燃發(fā)動(dòng)機(jī)進(jìn)氣

23、系統(tǒng)的無聲空氣灌消器的虛擬設(shè)計(jì)及性能預(yù)測(cè)operational and breathing charactensues influenang pollutant emission, perfomnnce and economy. Starting with an existing or notational system Layout, an integrated assessment of the various performances is performed. This infonmtion may then be used appropriately to assess curren

24、t system performance in terms of the various design objectives, to provide rational basis for systeimtic optimization of the design by implementing appropriate modifications to its constituent elements.The BEM widely used in the design of intake and exhaust system can be used to compute the interior

25、, exterior, or both fields simultaneously and only requires that the perimeter of the air cleaner be divided into elements,and the ease in imposing the boundary condition is another attractioa In this paper BEM is used to predict the air cleaner's transmission loss and noise emission.The redesig

26、n of the original intake system arises in connection with a high pass-by noise with level above the legislative target at full throttle with engine speed around 5200 r/rnm. The spectral characteristics of the noise signal are normally dominated by an extensive sequence of discrete tones that are lia

27、rnionically related to the engine firing frequency which is 173 Hz corresponding to 5200 r/nun and the inline 4-cyknder 4-stroke engine. In anny instances the bulk of the acoustic energy from the primary source is distnbuted among the lower frequency* components that may be difficult to control. Thu

28、s frequency range this paper referred to is from 0 to 1 kHz. In this frequency range, as the uifluence of filter paper on acoustic perfonimice of integrated system is trivial, so filter paper is disregarded. The noise is emitted from the inlet of the air cleaner, and die outlet of the air cleaner sy

29、stem connects to the inlet of the engine. So the pressure at the inlet of the engine or the outlet of rhe air cleaner is the boundary condition for the BEM.Traditional intake system with a function of noise reduction normally has two parts air deaner and silencer. Due to the constraint of space in t

30、he engine compartment, the redesigned air cleaner combines the effect of cleaning and sdenang. In this work, a so-called silenang air cleaner was redesigned, geometrical strucnire deteranned by predicted TL and sound pove【 emission by BEM. Also, in order to minimize the sound power of rhe intake sys

31、tem at low frequency, a bypass pipe was added to the air-channeling pipe. Analysis of the resulting acoustic perfonmnee showed tint the method is feasible for the goal of educing the overall engine noise by mnimizing the intake system noiseDESIGN OF THE SILENCING AIR CLEANEROriginal air cleaner eval

32、uationThis onginal air cleaner of mainly cleaning design paying little attention to iniiunnzing noise emission is its BEM meshDuring calculation of TL, the outlet section of the air cleaner is given a unit veloaty amplitude to model a sound source, all other surfaces are modeled as "acousticall

33、y hard*' by default . The sound power of the outlet section can be calculated from the formula. All the subsequent TL predictions have the same boundary condRioaThe predicted air cleaner performance is shown The sound po er level at the engine intake port is shown . The peaks of the noise source

34、 signal are harniomcally related to the engine firing frequency of 173 Hz. As the bulk of the acoustic energy from the engine combustion distributed among the low frequencies from 100 Hz to 800 Hz is too high the transmission Loss at the frequency range of 220 Hz to 1 kHz is so low that the noise em

35、ission cannot be mimmized, so a silencing air cleaner with a higher TL at 200 Hz to 1 kHz is required.Initial design of the silencing air cleanerIf there is sufficient space, a complex structure can be assigned to minimize the intake noise emission. So we must make good use of the limited space. In

36、this work CAD software Pro/E was used to envelop the rest of the space of the other automotive components m the engine compartment. Then the total air deaner volume required is obtamed from rhe enveloped space. The next step is to choose appcopnate silencer units and their dimensions. Considering di

37、e effect of air deaiung, two requirements must be satisfied (1) The air flux should equal to or exceed the value of original flux, (2) The filtering area must not be degraded. Based on the requirements and the theory of the silencer units, an initial layout was deter- mined. The air cleaner is separ

38、ated into three expansion chambers by two baffles, the nghr baffle has a hole in the middle, and the Left baffle has four holes at its four comers respectively The filter paper is placed at the center of the middle expansion chamber. The diameter of the hole in rhe right baffle is detemuned by the f

39、irst requiremenr, because of the complexity of this air cleaner, the diameter of the hole is bigger than the cnginal one. The second requirement relates to the diameter of the hole in the first baffle and the length of the second chamber, after letung the filtering area be equal to the original one,

40、 then the length of rhe second expansion chaniber can be determined. So the geometncal structure of the air cleaner is set by two variables.The overall acousuc behavior is a sumimtion of the behavior of all constituent components of the tliree chambers. In order to provide a wide bandwidth of contin

41、uous attenuation 叩ectru1nl the attenuation minimum in their individual contnbutions should not occur simultaneouslv In Jorder to investigate rhe individual acoustic perfofinance of the three chambers, the integrated air cleaner was separated into three parts, one of which is a silencer unit of expan

42、sion chamber just at the place of the two baffles. BEM run was performed to calculate the individual acoustic perfoiLiimce of the three chambers. The first chamber has lugh and continuous attenuation at die frequency" band 比 300-1000 Hz, and the acoustic performance of the second chamber which

43、has higli attenuation at the frequency range of 400-800 Hz is a shade worse than that of the first one. The rlurd chamber has the worst performance, but at the frequency- of about 230 Hz, where the first and the second chamber have minimal attenuation it has higher attenuation, thus providing compen

44、sation effect for the first aod second parts. Also, at higher frequency, the third pan possibly represents good acoustic performance, which is not illustrated in this figure.Note that the acoustic interactions that exist between such single parts also introduced unccnainties, even when their individ

45、ual perfonmnee can be appropnately represented or modeled. Clear understanding of the acoustic performance of the single part gives significant inforimtion for initial design . The integiated system with changes in some areas is calculated by the method of BEM in rhe detailed design to gain the best

46、 acoustic performance.In the initial design, the external geometncal dimension is decided, and silencer unit with a rough dimension is chosen. While the position of the baffles and the radius of the four holes in the second baffle can be varied to achieve better acoustic perfomnnce.Noise emission pr

47、edictionUntil noxx; we have accomplished total design of the silencing air deaner. In order to make a companson with the onginal, prediction of the noise emission was earned out.To verity the practical perfomunce of the redesigned air cleaner, the sound pressure at the engine intake port was measure

48、d at full throttle with engine speeds at 5200 r/min at engine test bed as die boundary condition or noise source of the original and the redesigned air cleaner, then predicting the noise emission from the inlet of the air cleaner.When measuiing this sound pressure, the air cleaner was removed, and t

49、he engme noise was shielded off. In addition, due to the difficulties in measunng the pressure at the engine intake pon be- cause of the air flow influence on noise signals and the induced microphone disturbance that detenorate the engine performance, rhe measurement Location of the microphone was a

50、t the place 200 min to the intake port, and at 45 to the nonnal of the intake port section . The boundary condition applied at the outlet of the air cleaner system should be extracted from the noise signals at the measurement Location mentioned above based on acoustic theorvThe sound pressure of the

51、 point P0 at die axis of the intake port ls the maximum compared to the other points with the same distance to the center of the intake pon section O.EXTRA METHOD TO MINIMIZE SOUND POWEROne potential problem in using the previous layout is that at the frequency" of 173 Hz die Level of sound poe

52、r emitted from air cleaners inlet is nor as low as that of other frequency bands. The vacant space around the pipe connecting the air cleaner and the engine intake port suggests some other possible improvements of the air cleaner system This paper uses a bypass pipe to achieve this goal.Increasing o

53、f TL at frequency of around 173 Hz being the goal detemuncs that dimension Ld=980 nim. Compare the predicted acoustic performance between the previous layout with no change on pipe and the present layout with flexible bypass pipe. The acousttc performance of the bypass pipe layout improved draimtica

54、lLy at frequency of around 173 Hz, and at frequency of 519 Hz, corresponding roughly to thrice of half wavelength, the TL of bypass pipe layout increased Lightly, as expected.The resulung sound power level is illustrated . It can be seen that sound poA'er Level of the without-accessory air cleaner at 173 Hz is the highest, while that of the uith-bypass-pipe air cleaner ar this frequency is greatly decreased. The overall sound pove【level from 0 to 1 kHz, for the without-bypass-pipe air cleaner is 110.2 dB, and for the with-bypass-pipe air cleaner is 105.0 dB.Note that