便車窗玻璃升降器外殼沖壓模具設(shè)計(jì)（桂電子）

便車窗玻璃升降器外殼沖壓模具設(shè)計(jì)（桂電子）,便車,窗玻璃,升降,外殼,沖壓,模具設(shè)計(jì),電子 桂林電子科技大學(xué) 本科畢業(yè)設(shè)計(jì)（論文）翻譯 英文原文名Analasis of Polsation Inside Pipe and Study on Exhaust Sound Characteristics of V Type8 Cylinder Engine–Study on Optimitized Front Pipe Junction Structure 中文譯名：V8發(fā)動(dòng)機(jī)排氣管內(nèi)震動(dòng)與排氣噪聲特性的分析 與研究—關(guān)于排氣歧管最優(yōu)化連接的研究 班 級(jí) 06001102 姓 名 劉志杰 學(xué) 號(hào) 0600110218 指導(dǎo)教師 楊曉青 摘要 對(duì)V8發(fā)動(dòng)機(jī)排氣管內(nèi)震動(dòng)波傳播的研究表明，將兩排氣歧管連接到排氣總管可以改變發(fā)動(dòng)機(jī)的震動(dòng)。概而言之，管內(nèi)的震動(dòng)頻率并不總是和發(fā)動(dòng)機(jī)最初正常工作的燃燒頻率及其和聲頻率一致。因此，排氣管連接結(jié)構(gòu)的研究表明：在連接處形成一定體積可以增加發(fā)動(dòng)機(jī)主要壓力波動(dòng)向向下壓力波動(dòng)的轉(zhuǎn)換，也使得排氣噪聲更嚴(yán)重。這種現(xiàn)象是由V8發(fā)動(dòng)機(jī)兩邊汽缸無規(guī)律的燃燒和在連接處存在傳播相位差所造成的。 前言 最近，符合LEV(Low Emission Vehicle的縮寫,亦即”低污染排放車輛”之意)和ULEV(Ultra-Low Emissions Vehicle的縮寫,”超低排放車”之意)排放法規(guī)的V型發(fā)動(dòng)機(jī)在左右兩邊配備了較大的接觸應(yīng)力智能轉(zhuǎn)換器。排氣管結(jié)構(gòu)發(fā)生了實(shí)質(zhì)性的變化，排氣前管伸長與排氣總管中部相連（見圖1）。最優(yōu)化的排氣系統(tǒng)應(yīng)優(yōu)先考慮安靜性，其次是發(fā)動(dòng)機(jī)性能。 V8發(fā)動(dòng)機(jī)兩邊汽缸的燃燒在左右兩排氣前管內(nèi)引起復(fù)雜的震動(dòng)，這種排氣前管內(nèi)的震動(dòng)和四缸直列等其他類型發(fā)動(dòng)機(jī)的不同。目前尚未有關(guān)于左右排氣前管內(nèi)此類震動(dòng)共同作用效果的研究，也沒有關(guān)于這種震動(dòng)在排氣前管連接處的傳播的研究。雖然對(duì)于兩邊的震動(dòng)波在排氣前管連接處的疊加的分析已經(jīng)考慮了氣體流動(dòng)的影響，但是尚未有集中于V8發(fā)動(dòng)機(jī)各邊汽缸之間的燃燒間隔與震動(dòng)在連接處衰減的關(guān)聯(lián)性的研究。人們廣泛研究消聲器衰減技術(shù)，但是很少關(guān)注其連接結(jié)構(gòu)。然而，由于目前排氣噪聲備受關(guān)注，連接結(jié)構(gòu)的優(yōu)化就顯得必要了。 這篇論文主要是研究震動(dòng)在連接處的傳播，從而依據(jù)實(shí)驗(yàn)數(shù)據(jù)和計(jì)算，探討V8發(fā)動(dòng)機(jī)排氣前管連接的優(yōu)化方案。使用有限元法或其他類似方法計(jì)算排氣噪聲的線性頻率響應(yīng)的計(jì)算方法并不適用于邊界條件情況下以及V8整個(gè)排氣管內(nèi)的各種頻率。一方面，研究表明，用流體熱力學(xué)模型進(jìn)行聲學(xué)計(jì)算可以預(yù)知聲壓。對(duì)一維計(jì)算進(jìn)行修正后應(yīng)用于實(shí)際尺寸模型，在一維線性空間和三維非線性空間都取得了良好的效果。另一方面，目前尚無人申請(qǐng)分析機(jī)械現(xiàn)象。 本文通過直接測量管內(nèi)壓強(qiáng)和使用流體熱力學(xué)模型計(jì)算從進(jìn)氣到排氣過程的管內(nèi)壓強(qiáng)，對(duì)比測量結(jié)果和計(jì)算結(jié)果，分析V8發(fā)動(dòng)機(jī)主要由于排氣管連接處的壓力波動(dòng)引起的震動(dòng)。 具有長排氣前管的V8發(fā)動(dòng)機(jī)管內(nèi)震動(dòng)的傳播 為了滿足排放標(biāo)準(zhǔn)，排氣管外形趨向于圖1所示。 圖1.具有長前管的排氣管 排氣歧管在左右兩邊汽缸的排氣口附近相接，從而形成了左右排氣前管，并在前管上裝置大量的傳感器。然后，合成的長前管在整個(gè)排氣裝置的中間位置連接起來。圖2.顯示了發(fā)動(dòng)機(jī)在一定的轉(zhuǎn)速下穩(wěn)定運(yùn)行時(shí)，排氣管內(nèi)各部分的震動(dòng)情況。由圖可見，在工作行程和排氣行程中，排氣口處測得7個(gè)主要的最高點(diǎn)，但是在排氣前管連接處測得8個(gè)大小和間隔都相同的最高點(diǎn)。這就是說，通過連接兩排氣前管可以改變管內(nèi)傳播的震動(dòng)頻率。對(duì)于4缸直列發(fā)動(dòng)機(jī)，管內(nèi)傳播的震動(dòng)頻率和發(fā)動(dòng)機(jī)初次正常工作頻率或者合成頻率基本相同。V8發(fā)動(dòng)機(jī)的管內(nèi)震動(dòng)傳播過程與4缸直列發(fā)動(dòng)機(jī)的有本質(zhì)的不同。圖3表示的是V8發(fā)動(dòng)機(jī)各個(gè)汽缸的點(diǎn)火順序，兩邊各缸的燃燒并不是交替發(fā)生而是在曲軸轉(zhuǎn)角為180、90、180、270處間隔無規(guī)律地發(fā)生。其次，排氣前管內(nèi)各處震動(dòng)波測量的結(jié)果如圖4所示?？紤]排放要求，排氣口處的震動(dòng)波取決于從排氣門到排氣歧管連接點(diǎn)的長度和連接處的體積；一邊的氣缸內(nèi)的壓力最高點(diǎn)轉(zhuǎn)化為排氣前管的順流動(dòng)力。在排氣前管中部壓力下降但是震動(dòng)頻率不變。 但是，震動(dòng)頻率在前管連接處發(fā)生變化。也就是說在另一邊汽缸的排氣前管震動(dòng)波的影響下，頻率發(fā)生了變化，而馬上形成的波動(dòng)在連接處前后平均壓強(qiáng)、振幅是相同的。根據(jù)點(diǎn)火次序合成每一個(gè)汽缸內(nèi)的向下壓力最高點(diǎn)可以解釋這個(gè)現(xiàn)象。此外，分析兩前管的連接結(jié)構(gòu)和震動(dòng)波的傳播，目的在于研究連接結(jié)構(gòu)對(duì)排氣噪聲特性的影響。 連接結(jié)構(gòu) 對(duì)如圖5所示的兩種排氣管進(jìn)行對(duì)比，分析前管連接結(jié)構(gòu)。兩者從發(fā)動(dòng)機(jī)到消聲器的長度分別相同，區(qū)別在于聯(lián)結(jié)是在消聲器之前還是之內(nèi)。 這兩個(gè)排氣管噪聲的綜合測量結(jié)果如圖6所示。由圖可見，排氣管1的噪聲比較小。 當(dāng)發(fā)動(dòng)機(jī)轉(zhuǎn)速為2500rpm時(shí)，在對(duì)應(yīng)的曲軸轉(zhuǎn)角測量聲壓，以此探討排氣管1和排氣管2排氣聲壓的差異。 圖2.不同的管內(nèi)震動(dòng)壓力與排氣聲壓 圖3.V8發(fā)動(dòng)機(jī)的點(diǎn)火次序 圖4.排氣前管內(nèi)震動(dòng)波的傳播過程 圖5排氣管對(duì)比 相應(yīng)的曲軸轉(zhuǎn)角對(duì)應(yīng)的壓力波動(dòng)如圖7所示?？梢?，曲軸轉(zhuǎn)過720度，排氣管1的壓力波有8個(gè)波峰（圖8（a）所示）。但對(duì)于排氣管2，主要工作壓力波動(dòng)與的排氣壓力疊加（如圖8（b）所示），使得排氣噪聲更為嚴(yán)重。從而，人們開始分析為什么當(dāng)兩排氣前管在消聲器內(nèi)連接時(shí)會(huì)發(fā)生壓力波動(dòng)。 圖6.排氣管1、2的排氣聲壓對(duì)比（測量值） 圖7. 排氣管1、2的排氣聲壓時(shí)間相位對(duì)比（轉(zhuǎn)速為2500轉(zhuǎn)/分鐘時(shí)的測量值） 圖8.排氣管2的聲壓組成 發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力波動(dòng)的分析 測量兩排氣管內(nèi)的震動(dòng)波來分析產(chǎn)生發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力所對(duì)應(yīng)的曲軸轉(zhuǎn)角。對(duì)比結(jié)果如圖9所示。排氣管1、2在排氣門處的壓力基本相同。由此看來，連接排氣歧管對(duì)壓力波動(dòng)的影響比連接排氣前管的大。雖然在消聲器前后，排氣管1的壓力波峰間隔和幅值都基本相同，波形也相似，但是消聲器前后排氣管2的排氣震動(dòng)波卻有很大的不同，這表明了發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力波動(dòng)發(fā)生在連接處。排氣管1、2在左右排氣前管連接之前的管內(nèi)震動(dòng)對(duì)比結(jié)果分別如圖10所示。可見排氣管1在兩前管連接之前形成的震動(dòng)波和總管的基本一致，但是排氣管2卻不然。就是說，管1的兩排氣前管之間的相互影響較大，并且兩列波疊加不發(fā)生相位延遲。相比之下，管2前管之間的相互影響較小，并且兩列波疊加時(shí)波峰相位延遲。 此外，為了研究兩前管之間的相互影響，使單邊的廢氣流經(jīng)消聲器，另外一邊流經(jīng)其他出口，測量管內(nèi)的震動(dòng)情況。另外，當(dāng)兩邊廢氣均流經(jīng)消聲器時(shí)，測得進(jìn)入連接處的震動(dòng)如圖11所示。兩者相比較。 圖9.排氣管1、2內(nèi)壓力波的對(duì)比 圖10.左右兩管匯合之前的震動(dòng)對(duì)比 圖11.不同輸入時(shí)，臨匯合前的震動(dòng)對(duì)比 單邊輸入廢氣時(shí)，無規(guī)律爆燃造成的管1、2內(nèi)壓力峰值間隔取決于燃燒間隔；當(dāng)廢氣兩邊輸入時(shí)，管1、2的前管內(nèi)震動(dòng)波峰值之間間隔相同。這表明，兩前管內(nèi)的震動(dòng)波疊加且沒有發(fā)生相位延遲。另一方面，即使廢氣兩邊輸入，管2的震動(dòng)波峰之間間隔也不相同。這就表明，兩前管內(nèi)的震動(dòng)波疊加發(fā)生了相位延遲。 單邊和雙邊廢氣輸入的排氣聲壓對(duì)比如圖12所示?？梢?，雙邊輸入時(shí)排氣噪聲較小。這是由于360度曲軸轉(zhuǎn)角過程中四個(gè)汽缸分別交替在180、90、180、270度點(diǎn)火，兩邊震動(dòng)波的相位相反，在連接處疊加抵消。 圖12.兩種不同的輸入下聲壓的對(duì)比 圖12表明發(fā)動(dòng)機(jī)的向下壓力對(duì)兩列波疊加抵消情況有很大的影響。 這樣的話，把排氣管2（包括排氣管、進(jìn)氣系統(tǒng)以及發(fā)動(dòng)機(jī)主體）看作是等容一維流體動(dòng)力學(xué)模型進(jìn)行計(jì)算。經(jīng)過消聲器之后排氣壓力的計(jì)算結(jié)果和測量結(jié)果對(duì)比如圖13所示。模擬管2的發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力波動(dòng)，表明流體動(dòng)力學(xué)計(jì)算能模擬測量結(jié)果。 圖13.消聲器順流的壓力計(jì)算結(jié)果（距消聲器50mm處） 圖14.排氣管1、2聯(lián)合運(yùn)用1D和3D流體動(dòng)力學(xué)計(jì)算的速度矢量的對(duì)比 為了分析兩前管連接處內(nèi)部的流動(dòng)情況，考慮到連接結(jié)構(gòu)和消聲器內(nèi)流動(dòng)的順逆流，把一維計(jì)算的結(jié)果看作是三維模型的邊界情況，就可以計(jì)算瞬時(shí)流動(dòng)狀態(tài)。耦合一位模型和三維模型計(jì)算出來的速度矢量如圖14所示。當(dāng)排氣管1連接處的氣流不發(fā)生相位延遲順流進(jìn)入另一排氣前管時(shí)，廢氣在管2消聲器內(nèi)堆積，使得另一前管內(nèi)震動(dòng)波的傳播和流動(dòng)順流均延遲。就是說，連接處的一定容積另一前管內(nèi)震動(dòng)波的傳播和流動(dòng)順流均延遲。排氣管1在消聲器前的震動(dòng)與管2的不相同。對(duì)管1來說，兩排氣前管在消聲器之前匯合，在消聲器之前的震動(dòng)峰值之間間隔一致；但是對(duì)管2來說，兩排氣前管不在消聲器之前匯合，在消聲器之前的震動(dòng)峰值之間間隔無規(guī)律。由于震動(dòng)在空間傳播具有滯后性。間隔小的部分峰值影響下一個(gè)峰值引起一系列波峰點(diǎn)。這些波峰點(diǎn)分別聚集在兩前管內(nèi)。曲軸每旋轉(zhuǎn)360，間隔為180、90、180、270度的不同相位的燃燒周期在左右兩邊汽缸內(nèi)交替發(fā)生，在兩個(gè)旋轉(zhuǎn)周期內(nèi)引起兩組峰值，從而產(chǎn)生了發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力的波動(dòng)。 由此得出結(jié)論，經(jīng)過消聲器后發(fā)生的V8發(fā)動(dòng)機(jī)轉(zhuǎn)動(dòng)初壓力波動(dòng)是由兩邊各個(gè)汽缸之間燃燒間隔無規(guī)律和震動(dòng)在消聲器內(nèi)傳播發(fā)生相位延遲所引起的。 為了證實(shí)這一結(jié)論，前文所述的把管2（當(dāng)點(diǎn)火次序改變使得左右兩邊汽缸的燃燒間隔分別完全一致時(shí)包括進(jìn)氣系統(tǒng)以及發(fā)動(dòng)機(jī)主體）看作一維流體動(dòng)力學(xué)模型進(jìn)行計(jì)算。 廢氣流經(jīng)消聲器之后，發(fā)動(dòng)機(jī)轉(zhuǎn)動(dòng)主要壓力不存在，圖13中同一位置的壓力波計(jì)算值如圖15所示。 圖15.兩邊燃燒間隔相等是，消聲器逆流壓力的計(jì)算結(jié)果 進(jìn)入消聲器之前的排氣前管內(nèi)的壓力計(jì)算值如圖16，可見壓力峰值之間間隔相等。 圖16. 兩邊燃燒間隔相等是，臨進(jìn)入消聲器之前壓力的計(jì)算結(jié)果 以上結(jié)果表明經(jīng)過消聲器之后，消聲器前側(cè)得的間隔相等的發(fā)動(dòng)機(jī)轉(zhuǎn)動(dòng)初壓力波動(dòng)峰值消失了。因此，上述機(jī)理得證。 匯合處容積與發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力波動(dòng)的相互關(guān)系 對(duì)應(yīng)兩前管連接處不同容積，聲壓級(jí)測量結(jié)果如圖18所示。 各試驗(yàn)樣品的兩前管和消聲器之間的連接方式不變，改變消聲器的長度以改變匯合處的容積。如圖17所示，排氣管3的消聲器容積增加1/4 V（如圖17b）;排氣管4的消聲器容積增加1/2V（如圖17c） 圖17.對(duì)比不同連接容積的排氣管 曲軸旋轉(zhuǎn)720度，管1內(nèi)測得8個(gè)壓力峰值點(diǎn)。當(dāng)在排氣總管上增加消聲器的總?cè)莘e時(shí)，壓力幅值減小，從而產(chǎn)生兩組壓力峰值（發(fā)動(dòng)機(jī)旋轉(zhuǎn)初壓力峰值）相應(yīng)傳播到消聲器內(nèi)。 也就是說，匯合處的容積越小，經(jīng)過消聲器之后產(chǎn)生的發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力幅值越小。這表明容積越小，由于消聲器內(nèi)波的傳播延遲變小，所以引起的發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力波動(dòng)就越小。 圖18.連接處容積與發(fā)動(dòng)機(jī)主要壓力波動(dòng)的關(guān)系 （測量點(diǎn)：距排氣尾管末端0.5m處） 連接形式和連接角度的影響 對(duì)比圖19所示兩連接形狀不同的排氣管。圖19a中，兩前管連接形成一定的角度；圖19b中，兩排氣前管平行連接。 圖19. 排氣管連接形式和連接角度的對(duì)比 兩中連接方式所測得的排氣聲壓如圖20所示?？梢?，兩者并沒有什么差異。就是說，連接角度對(duì)排氣噪聲沒有什么影響。 圖20. 排氣管連接形式和連接角度的影響（測量值） 結(jié)論 借助實(shí)驗(yàn)和仿真模擬，分析排氣管內(nèi)的壓力波，結(jié)果表明： 1.有長排氣前管的V8發(fā)動(dòng)機(jī)整個(gè)排氣管內(nèi)各處震動(dòng)波頻率是不同的。兩前管連接可以改變管內(nèi)震動(dòng)波特性，并且使得兩列波相互疊加削弱。 2.V型汽缸的發(fā)動(dòng)機(jī)各汽缸之間的燃燒間隔無規(guī)律性，傳播進(jìn)入左右排氣前管的震動(dòng)波峰值間隔也無規(guī)律性。當(dāng)兩排氣前管順流匯合后進(jìn)入消聲器的排氣管中，前管內(nèi)的震動(dòng)傳播到匯合處且不發(fā)生相位延遲，并且流經(jīng)消聲器之前的震動(dòng)波峰值之間間隔一致。但是，當(dāng)兩排氣前管在消聲器內(nèi)匯合，臨進(jìn)入消聲器前的震動(dòng)峰值之間間隔無規(guī)律。由于震動(dòng)傳播在空間上發(fā)生相位延遲，間隔短的那些峰值影響下一個(gè)峰值而產(chǎn)生了一系列的波峰，這些波峰聚集在各自的排氣前管內(nèi)，從而形成了發(fā)動(dòng)機(jī)旋轉(zhuǎn)主要壓力的波動(dòng)，這一新的波動(dòng)使得排氣噪聲更為嚴(yán)重。 3.當(dāng)排氣具有長的排氣前管并且各邊汽缸之間的燃燒間隔無規(guī)律，就比如本文中提到的排氣管，震動(dòng)計(jì)算值和用流體動(dòng)力學(xué)模型表示整個(gè)進(jìn)排氣系統(tǒng)以及發(fā)動(dòng)機(jī)內(nèi)的氣流計(jì)算值可以模擬實(shí)際現(xiàn)象，也可以預(yù)測震動(dòng)和排氣噪聲。 致謝 感謝Mr.Toshiyuki Hashimoto,Kazunori Okubo 和Sumio Ogawa 有幫助的討論和指點(diǎn),也感謝Mr.Toshiyuki Hashimoto和Norihiko Konishi的實(shí)驗(yàn)工作和在理解結(jié)構(gòu)裝置上的寶貴貢獻(xiàn)。 參考資料： REFERENCES 1. Flamang,P. et al., “Experimental theoretical analysis of the flow in exhaust pipe junction”, IMechE 1989 2. Katayma, T.,et al., “An estimation of method for acoustic characteristics of muffler”, Toyota Tech., Vol.41,1991 3. Hosomi,M., et al., “Optimization of Exhaust Pipe Muffling Performance by Sound Pressure Modal Analysis”,FISITA’96.1996 4. Tanaka, T., et al., “Analysis of a Three Dimensional Sound Field by Using The Boundary Element Method”, Translation of The Japan Society of Mechanical Engineers(c), Vol.53,No.491,1987 5. Morel, T., Morel, J. and Blaser,D.A., “Fluid Dynamic and Acoustic Modeling of Concentric-Tube Resonators/Silencers”, SAE paper 910072,1991Desantes, J.M., 6. Torregrosa, A. J. et al., “Hybrid Linera/Nonlinear Method for Exhaust Noise Prediction”, SAE paper 950545,1995 7. Isshiki, Y.,Shimamoto,Y. and Wakisaka T., “Simultaneous Prediction of Pressure Losses and Acoustic Characteristics in Silencers by Numerical Simulation”, SAE paper 960637,1997 8. A.Selamet, et al., “The effect of vehicle exhaust system components on flow losses and noise in firing spark-ignition engines”, SAE paper 951260,1995 Analysis of pulsation inside pipe and study on exhaust sound Characterstics of V type 8 cylinder engine-study on Optimized front pipe junction structure ABSTRACT The research of pulsation wave propagation inside exhaust pipe in V8 engine shows that pulsation from engine was changed by joining two front pipes in entire exhaust pipe. In short ,frequency of pulsation inside the pipe is not always equal to engine explosion fitst order frequency or its harmonics.Accordingly,structure of junction has been studied,which indicated that having volume at junction add edgine revolution first order component pressure fluctuation to blow-down wave component and makes exhaust sound worse.This phenomena is caused by irregular explosion interval on each bank of V8 engine and phase delay of propagation at junction. INTRODUCTION Recently,V type engines meeting the LEV and ULEV emission regulations are equippen with a large capacity catalytic converter for each of the left and right banks,and the front pipes ten to be long and join in the middle of overall length of the exhaust sustem(Fig.1)and substantial changes have been made in the exhaust pipe structure.An optimum exhaust system superior in quietness and engine performance should be considered. Irregular exploslon intervals among cylinders on each bank of the V8 engine produce pulsation with complex characteristics inside the left and right front pipes,which is different from pulsation inside front pipes in the other type of engines,for instance ,in-line 4 cylinder engine and so on.There has been no studies of the mutual effect between pulsation inside right front pipe and that inside left front pipe and no studies of propagation of pulsation at junction of the front pipes.While analysis of junction has been studied regarding flow,there has been no irregular explosion intervals among cylinders on each bank of the V8 engine. While attenuation technique with muffler has been widely studied,there has been few studies with junction.Moreover,it is necessary to optimize the junction for exhaust sound quality recently focused on. In this paper,propagation of pulsation at junction was investigated to optimize the front pipe junction of V8 engine with experiments and numerical calculation. Linear frequency response calculation of exhaust noise using finite element method or the likeis not suitable for boundary condition and variety of frequency inside entire pipe of V8 engine.On the other hand,acoustic calculation using fluid dynamics model has studied to predict sound pressure and recently improved to apply to full size model with good results in modified one dimensional calculation,In hybrid linear/three-dimensional calculationand in hybrid one-dimensional/three-dimensional calculation.On the other hand there has been no application to analyzing mechanism of phenomena. In this paper,the mechanism of engine revolution first order component pressure fluctuation caused at the front pipe junction of V8 engine exhaust pipes was analyzed by measuring pressure inside pipe and calculation with fluid dynamics model from intake to exhaust with comparison between measured and calculated results. PULSATION WAVE PROPAGATION INSIDE EXHUAT PIPE WITH LONG FRONT PIPE INSTALLED IN V TYPE 8 CYLINDER ENGINE To meet requirements of the emission regulations,the exhaust pipe tends to be of a shape shown in Fig.1. The pipes of exhaust manifold join near the exhaust port at each of the left and right banks and then forms left and right front pipes,each of which is equipped with a large capacity catalytic converter,and resultant long front pipes join in the middle of the entire exhaust pipe. Fig.2 shows the pulsation inside the pipe at each part of the exhaust pipe during steady operation at a constant engine speed.Seven major peaks were observed at the outlet of exhaust port during engine’s second rotation,while there were eight peaks at the junction having a uniform interval between peaks and an equal peak level.That is,the frequency of the pulsation wave propagated inside the pipe was changed by joining two front pipes.In the case of the most genersl in-line 4 cylinder engine,the frequency of the pulsation wave inside the pipe is almost equal to engine explosion first order frequency or its harmonic frequencies at each of the exhaust pipe. There is an essential difference in the pulsation propagating process inside the pipe between the V type 8 cylinder engine and in-line 4 cylinder engine.Fig.3 shows the order of explosion in each cylinder of the V type 8 cylinder engine,where explosion does not occur alternately but at irregular intervals of crank angles of 180,90,180 and 270 degrees on each bank. Next,results of measurement of the pulsation wave at each part inside the front pipe are shown in Fig.4.Considering exhaust requirements,the pulsation wave at the exhaust port outlet was detemined by the length from exhaust port toexhaust maniflod junction and the volume of the junction,and pressure peaks existed according ti the interval of explosions on the bank,which were transmitted to the downstream of the front pipe.The pressure decreased in the middle of the front pipek while the frequency of the pulsation wave remained unchanged.However,the frequency changed near the juntion of the front pipeslm.That is,the frequency changed under the effect of the pulsation wave from the front pipe of the other bank.The wave froms immediately before and after the junction(l,m)were almost equal,at almost the same magnitude under the effect of the opposite bank,and the perssure levels were equal.This can be explained by combining peaks of the blow-dowm pressure from each cylinder according to the order of explosion.In addition,the junction structure of two front pipes and the pulsation wave propagation were analtzed.The purpose of the junction on the exhaust sound characteristics. STRUCTURE OF JUNCTION Two exhaust pipes shown in Fig.5 were compared to analyze the junction structure of two front pipe.The length from engine to muffler was equal for both,but the difference between them is whether two front pipes joined before the muffler or inside the muddler. Fig.6 shows the measured results of the exhaust sound overall from the two exhaust systems,where exhaust pipe 1 shows a smaller level. To resesrch the difference of sound pressure between exhaust pipe 1 and exhaust pipe 2,sound pressure at engine speed 2500rpm in relation to the casnk angle was mensured. The wave form of the pressure wave in relation to the crank angle is shown in Fig.7. There are eight peaks during crank gngle 720 degrees in case of exhaust pipe 1,while in the case of exhaust pipe 2,engine revolution first order component pressure fluctuation shown as Fig.8(b) is added to exhaust blow-down component shown as Fig.8(a) and make exhaust noise worse.Next,the mechanism for why engine revolution first order componment pressure fluctuation occurs in the case of the two front pipes joining inside the muffler was analyzed. ANALYSIS OF ENGINE REVOLUTION FIRST ORDER PRESSURE FLUCTUATION The pulsation wave inside two exhaust pipes were measured to research the location of engine revolution first order pressure fluctuation occurrence. The compared results are shown in Fig.9. The pressure at the outlet of exhaust port was almost equal between two exhaust pipes. This seemed to be because the effect of reflected wave from exhaust manifold junction on the pressure at the outlet of exhaust port was larger than that from front pipe junction. While exhaust pipe 1 showed peaks at an equal interval and almost the same level immediately before the muffler and similar pulsation. After the muffler, exhaust pulsation before and after the muffler of exhaust pipe 2 was considerably different, indicating that engine revolution first order pressure fluctuation occurred at the junction.. Fig.10 shows comparison of the inside pipe pulsation immediately before the junction between left and right front pipe in the case of exhaust pipe 1 and 2, repectively.While the pulsation wave from of both front pipe immediately before the junction were different in exhanst pipe 2.That is,while the mutual effect between both front pipes was large with exhaust pipeq 1 and pulsation of one front pipe progagated into the other front pipe occurred with delay. Further, to study the mutual effect between both front pipes,the exhaust gas was input from single bank (left bank)in the cindition engine firing and right bank routed to other exit and comparison of pulsation was made with case the exhaust gas input from two banks,and the measured front pipe pulsation wave form immediately before the junction is shown in Fig.11. In the case of an input from single bank,irregular interval between explosions in the bank poduce pressure peaks existing according to the interval of explosion with either exhuast pipe 1 or exhuast pipe 2.While,in the case of an input from both banks,peaks of front pipe pulsation wave from existed at equal interval with exhuast pipe 1,indicateing that pulsation from the other front pipe propagated without phase delay.On the other hand,even in the case of an input from both banks,peaks of pulsation did not exist at equal interval with exhuast pipe 2, indicateing that pulsation from the other front pipe propagated with phase delay, Compariton of exhaust sound pressure between an input from a single bank and that from both banks is shown in Fig.12,An input from both banks presented smaller exhaust sound,This was because a cycle of explosions at interval of 180,90,180 and 270 degrees was repeated in the eft and right banks at a phase difference of 360 degrees of tbe crank angle to make pulsation in the recerse phase ,to be canceked at the junction. This indicated that the phenomenon was largely effected by the blow-down pressure from the engine. At this, one dimensional fluid dynamics calculation using finite volume approach(5) was conducted as to a model of exhaust pipe 2 including not only the wxhaust pipe but the intake system and main body of the engine. The munerical result of pressuerd rusults,where engine revolution first order pressure fluctuatone occurring in wxhaust pipe 2 is sumulated,indicating that fluid dynamics calculation can simulate the measuerd phenomena. To study flow at junction of two front pipes,the result of one-dimensional calculation was input as a boundary condition to the three-dimensional model concerning the junction to the upstream and downstream of the muffler,and the transient flow was calculated.The velocity vector calculated by coupling one dimensional model and three dimensional model is show in Fig. 14. While the flow at the junction of exhaust pipe 1 entered the other front pipe and downstream without delay,exhaust gases were accumulated at the muffler of exhaust pipe 2,delaying propagation to the other front pipe and the downstream.That is,a capacity at the junction caused a delay in propagation to the other front pipe and downstream.Pulsation of exhaust pipe 1 differed from that of exhaust pipe 2 immediately before the muffler.In the case of exhaust pipe 1,the two front pipes had been joined before the muffler and peaks of pulsation before the muffler were observed at equal intervals,while in the case of exhaust pipe 2,two front pipes were not joined before the muffler and peaks of pulsation before the muffler were observed at irregular intervals.As pulsation propagates at volume with delay,some peaks which exist at short interval effected the next peak to generate one group of peaks and peaks gathered at each of the two front pipes.A cycle of explosions at intervals of 180,90,180 and 270 degrees was repeated in the left and right banks at a phase difference of 360 degrees of the crank angle,resulting in two groups of peak in two revolutions of the engine,which generated engine revolution first order component pressure fluctuation. As a conclusion ,engine revolution first order component pressure fluctuation appearing after muffler is caused by irregular explosion intervals among cylinders on each bank of V 8 engine and propagation of pulsation at muffler with delay. To verify this,previously mentioned one-dimensional fluid dynamics calculation was conducted as to a model of exhaust pipe 2 including intake and main body of the engine to have explosions at a uniform interval on the left and right bank respectively. The calculated result of pressure wave form after muffler at same place as Fig. 13 is shown in Fig.15,where engine revolution first order component did not exist. Fig.16shows the calculated result of pressure wave form inside the front pipe immediately before the muffler where pressure peaks exist at equal interval. These results indicate that engine revolution first order component pressure fluctuation appearing after muffler does not exist with the pressure peak immediately before the muffler with equal explosion interval and the mechanism above mentioned was verified to be true. RELATIONSHIP BETWEEN CAPACITY OF JUNCTION AND ENGINE REVOLUTION FIRST ORDER COMPONENT PRESSURE FLUCTUATION The measured result of sound level pressure with various capacities of two front pipes junction is shown in figs 18. The connection between two front pipes and muffler are unchanged among the specimens, and the muffler length was changed to change the capacity of the junction. Muffler of 1/4V volume was installed in Exhaust pipe 3 shown as fig 17(b), Muffler of 1/2V volume was installed in Exhaust pipe 4 shown asfig 17(c). Eight peaks exist during crank angle 270 degrees in exhaust pipe 1. While increasing total capacity of muffler in entire exhaust pipe makes sound pressure a amplitude of exhaust pipe smaller, two group of peaks (engine revolution first order component peak) were generated in proportion to capacity of junction. That is, the smaller capacity of junction, the smaller the amplitude of a engine revolution first order component produced after junction. This indicates that a smaller capacity at junction caused less engine revolution first order component fluctuation due to less delay in pulsation propagation at junction. Effect of shape and angle of junction Comparison was made between in the shape of the junction of two front pipe among figs 19 (a) and (b). Fig 19(a) is the case two front pipes join with same angle, (b) is the case front pipes join in parallel. Fig 20 shows the measured result of exhaust sound pressure. Almost no difference was observed in exhaust sound. That is , the angle of junction and the separation of junction did not have much effect on the exhaust sound Conclusion Analysis of pressure waves inside the exhaust pipe using experiments and simulations revealed the following 1. the pulsation wave frequency inside the pipe is different in the entire exhaust pipe with long front pipes of 8V engine. The characteristics of the pulsation wave inside the pipe are changed due to joining, and the two front pipes dissipate each other 2 .the V type 8 sylinder engine has irregular explosion intervals among sylinders on each bank and pulsation with irrigation interval peaks propagate into left and right front pipe. In the exhaust pipe where the two pipes join upstream of the muffler, pulsation inside front pipes propagate into junction without phase delay and pulsation peaks immediately before the muffler exist at equal interval. While, in exhaust pipe in which the two front pipes join at muffler. Pipe in which the two front pipes join at muffler, pulsation peaks immediately before the muffler exist at irregular intervals. As pulsation propagates at volume with delay, some peaks which exist at short interval effected the next peak to generate one group of peaks and peaks gathered at each of the two front pipes, which generated an engine revolution first order component pressure fluctuation. This new engine revolution first order component pressure fluctuation generated at muffler makes exhaust sound worse. 3. In the case an exhaust pipe has long front pipes and explosion intervals among cylinders on each bank of engine are irregular, such as the one described in this paper, the calculated results of pulsation and flow using fluid dynamic model representing the entire intake system, engine and exhaust system can simulate actual phenomena and suitable to predict pulsation and exhaust noise. ACKNOWLEDGMENTS The acthors thank Mr. Toshiyuki Hashimoto, Kazunori Okubo and Sumio Ogawa gor their helpful discussion and useful indication, and also thank Mr. Toyoharu Yoshitake and Norihiko Konishi for their work in the Lab and valuable contribution towards understanding the mechanism. REFERENCES Flamang, P. et al. “Experimental theoretical analysis of the floe in exhaust pipe junction”, IMeche 1989 Katayama, T., et al., “An estimation of method for acoustic characteristics of muffler”, Toyota Tech., vol. 41,1991 Hosomi, M., et al., “Optimization of Exhaust Pipe Muffling Performance by Sound Pressure Modal Analysis”, FISIYTA 96,1996 Tanaka, T., et al., “Analysis of a Three Dimensional Sound Field by Using The Boundary Element Method”, Transaction of The Japan Society of Mechanical Engineers(c),vol.53,No.491,1987 Morel, T., Morel, J. and Blaser, D. A., “Flhid Dynamic and Acoustic Modeling of Concentric-Tude Resonators/Silencers”, SAE paper 910072, 1991 Desantes,. J. 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