車輛工程外文翻譯-先進(jìn)陶瓷摩擦材料在離合器中的潤(rùn)滑 【中文4260字】【PDF+中文WORD】
車輛工程外文翻譯-先進(jìn)陶瓷摩擦材料在離合器中的潤(rùn)滑?【中文4260字】【PDF+中文WORD】,中文4260字,PDF+中文WORD,車輛,工程,外文,翻譯,先進(jìn),陶瓷,摩擦,材料,離合器,中的,潤(rùn)滑,中文,4260,PDF,WORD
【中文4260字】
先進(jìn)陶瓷摩擦材料在離合器中的潤(rùn)滑
1 介紹
為了滿足越來(lái)越多關(guān)于應(yīng)用程序的需要在效率和環(huán)境影響下新動(dòng)力傳動(dòng)系統(tǒng)特別是在機(jī)動(dòng)車輛的要求。在大多數(shù)情況下，車輛的動(dòng)力傳動(dòng)傳動(dòng)系統(tǒng)采用離合器系統(tǒng)在換檔和啟動(dòng)。根據(jù)不同的動(dòng)力傳動(dòng)系統(tǒng)的概念離合器系統(tǒng)上有不同的要求。新的動(dòng)力傳動(dòng)系統(tǒng)概念根據(jù)不同的操作條件可能使用多個(gè)離合器連接和斷開(kāi)不同的發(fā)動(dòng)機(jī)及配套裝置。多片離合器系統(tǒng)，該系統(tǒng)通常在車輛的動(dòng)力傳動(dòng)系統(tǒng)，以及在工廠中使用，對(duì)功率密度和整個(gè)系統(tǒng)的[1-3]的動(dòng)態(tài)行為有很大影響。整個(gè)系統(tǒng)的安全運(yùn)行都有非常不同情況下得到保證加上提高功率密度的需求。
1.1多片離合器的潤(rùn)滑
圖1顯示了客運(yùn)車輛多盤(pán)離合器變速器使用潤(rùn)滑的多片離合器系統(tǒng)。
離合器系統(tǒng)使用兩個(gè)徑向排列的壓盤(pán)。每個(gè)壓盤(pán)由摩擦片使用有機(jī)面臨和計(jì)數(shù)板制成的鋼基材料。不同的壓盤(pán)是可位移轉(zhuǎn)換成軸向方向，但連接到內(nèi)部和外部載體成圓周方向。為了使轉(zhuǎn)矩壓盤(pán)組壓縮成軸向。由于摩擦和計(jì)數(shù)板之間的摩擦力，因此能夠傳遞轉(zhuǎn)矩。在操作過(guò)程中有通過(guò)離合器系統(tǒng)中的油流動(dòng)。這種油流是對(duì)離合器系統(tǒng)的對(duì)流冷卻，進(jìn)而為接觸摩擦影響必要的過(guò)程。供油用液壓泵送潤(rùn)滑油通過(guò)過(guò)離合器系統(tǒng)載體的內(nèi)部。在離合器系統(tǒng)中油的流動(dòng)是壓盤(pán)的轉(zhuǎn)速和摩擦片的表面上設(shè)計(jì)凹槽的離心力的影響。油通過(guò)外載體離開(kāi)離合器系統(tǒng)。
Hohn 等，[4,5]表明離合器系統(tǒng)的溫度是非常影響潤(rùn)滑離合器系統(tǒng)的耐用性。因此，類似的離合器系統(tǒng)使用不同摩擦系數(shù)的變化為準(zhǔn)則，以確定在負(fù)載循環(huán)測(cè)試摩擦接觸損傷變化。在實(shí)驗(yàn)測(cè)試的鋼板顯示溫度高3001℃。它也可以看出，離合器系統(tǒng)的最大溫度導(dǎo)致了長(zhǎng)期穩(wěn)定的性能。
實(shí)驗(yàn)以及關(guān)于計(jì)算閃光溫度由Ingram等進(jìn)行。圖[6]其結(jié)果是閃光的溫度保持在一個(gè)較低的水平?？梢缘贸鼋Y(jié)論，關(guān)于潤(rùn)滑離合器系統(tǒng)使用紙質(zhì)材料閃光溫度相比其他材料溫度上升。
圖2示出了多片式離合器系統(tǒng)的黑箱描述。在操作過(guò)程中存在一個(gè)通過(guò)系統(tǒng)邊界發(fā)送機(jī)械性能和熱功率。根據(jù)操作條件的不同機(jī)械和熱功率輸出之間的比例是變化的。機(jī)械功率和輸出之間的差值被轉(zhuǎn)換成熱，它們分別加熱離合器系統(tǒng)被傳遞到冷卻介質(zhì)(Eq. (1))
Eq.(1) 多盤(pán)離合器的熱量方程 [7]。
提高對(duì)流散熱可以讓離合器系統(tǒng)的溫度降低。假設(shè)質(zhì)量溫度是有關(guān)功率密度最主要的影響，基于Hohn等工作。圖[4,5]和Ingram等。圖[6]可以看出提高一個(gè)離合器系統(tǒng)的負(fù)載能力可以通過(guò)提高對(duì)流冷卻。散熱油取決于油的分布本身受槽的方向和槽的幾何形狀的影響。離合器系統(tǒng)的溫度是受油流的主要影響。關(guān)于凹凸的規(guī)模微觀油流量是很重要的，例如，關(guān)于局部壓力，因此，接觸內(nèi)的摩擦化學(xué)和摩擦物理學(xué)流程。但關(guān)于全球散熱它被認(rèn)為不那么重要。除了列舉文獻(xiàn)[4-6]的原因是少量的油接觸的范圍內(nèi)相比，離合器系統(tǒng)的凹槽內(nèi)的油量。這就是為什么宏觀油流的重點(diǎn)是本文中的原因。通過(guò)改進(jìn)的槽的幾何形狀實(shí)現(xiàn)具有增加功率密度離合器系統(tǒng)的設(shè)計(jì)加深關(guān)于通過(guò)離合器系統(tǒng)油流的知識(shí)是重要的。因此，實(shí)驗(yàn)研究用不同的離合器系統(tǒng)都進(jìn)行了確定離合器系統(tǒng)內(nèi)的油流。
Fig.1. 雙離合器系統(tǒng)。
Fig.2. 多片離合器的方程。
Fig.3. Piv設(shè)置。
Fig.4. 相機(jī)和激光同步。
Fig.5. 矢量場(chǎng)的計(jì)算。
Fig.6. 以離合器系統(tǒng)為例做向量場(chǎng)的計(jì)算。
Fig.7. 多離合器試驗(yàn)臺(tái)（圖片和原理圖）。
2 方法和組件
熱傳遞是非常受通過(guò)離合器系統(tǒng)的油流影響。油流本身是受凹槽設(shè)計(jì)的影響非常大。在下面的一個(gè)叫做粒子圖像測(cè)速方法引入到確定潤(rùn)滑離合器系統(tǒng)內(nèi)的油流呈現(xiàn)。
2.1 粒子圖像測(cè)速
為了確定流體流動(dòng)的PIV法（粒子圖像測(cè)速）被使用。該測(cè)試裝置包括包含原油與示蹤粒子，激光，對(duì)CCD-照相機(jī)（圖3）的離合器系統(tǒng)。因?yàn)橛腕w積的可訪問(wèn)性的相機(jī)和激光器的取向幾乎同軸且垂直于油體積。
有了這個(gè)設(shè)置兩張照片是采取定額補(bǔ)償ΔT（圖4）。避免反射光導(dǎo)致顆粒和周圍產(chǎn)生的問(wèn)題，以確定速度矢量，相機(jī)配備一個(gè)帶阻濾波器，它允許切割出激光的波長(zhǎng)之間的對(duì)比度低。熒光發(fā)色粒子吸收由激光發(fā)出的光并發(fā)射光以不同的波長(zhǎng)，可以通過(guò)攝像機(jī)看到。其結(jié)果是，反射光都沒(méi)有看到由相機(jī)不過(guò)熒光發(fā)色粒子是重要的，以確定該油流的速度。
為解釋的圖像被劃分成部分圖像作為矢量計(jì)算（圖5）提供了基礎(chǔ)。該矢量被計(jì)算每個(gè)局部圖像并最終結(jié)合到整個(gè)畫(huà)面的矢量中。
測(cè)量數(shù)據(jù)的整個(gè)分析示于圖6使用以1000rpm和1.5l/min的油流的旋轉(zhuǎn)速度的潤(rùn)滑離合器系統(tǒng)的例子。采取的CCD相機(jī)各圖中由16001200像素（圖6，左圖）。在此測(cè)試裝置的每個(gè)像素代表具有長(zhǎng)度和寬度為16毫米的離合器系統(tǒng)的一個(gè)矩形。為32×32像素（512×512平方毫米）的互相關(guān)矩形被?。▓D6，中間）。出這兩個(gè)影像的生成的矢量場(chǎng)的矢量（圖6，右圖）。
2.2 多片式離合器試驗(yàn)臺(tái)
圖7示出了用于本文中所示的所有實(shí)驗(yàn)研究的多片式離合器試驗(yàn)臺(tái)。測(cè)試裝備了兩個(gè)電動(dòng)馬達(dá)，以實(shí)現(xiàn)摩擦和計(jì)數(shù)板的旋轉(zhuǎn)速度不同。離合器系統(tǒng)是通過(guò)內(nèi)部和外部的載體整合到試驗(yàn)臺(tái)上，并且由液壓缸驅(qū)動(dòng)。所呈現(xiàn)的實(shí)驗(yàn)研究都進(jìn)行了使用配備有一個(gè)窗口計(jì)數(shù)板，以允許光進(jìn)入摩擦接觸。
2.3 多片式離合器
該多片式離合器系統(tǒng)由摩擦片與徑向槽或劃線槽。摩擦片具有80mm和108mm的外徑的內(nèi)徑。徑向槽摩擦片有1mm的深度和1.6mm寬15槽。整個(gè)溝面336 mm2和槽體積336mm3。摩擦板與交叉槽具有槽為5.5mm，1mm的寬度和0.25mm的深度的距離。這導(dǎo)致約1365mm2的槽表面和341mm3的槽體積。
3. 理論
散熱裝置的能量輸送，由于溫度差。有三個(gè)相關(guān)的機(jī)制：導(dǎo)通、對(duì)流、放射線。
這項(xiàng)工作中對(duì)流是重點(diǎn)，因?yàn)樗顷P(guān)于一個(gè)離合器系統(tǒng)內(nèi)熱傳遞的主要影響。因?yàn)樯岬膹?fù)雜機(jī)制是一種現(xiàn)象學(xué)式的計(jì)算，適用于大多數(shù)情況。方程（Eq（2））表示操作參數(shù)，所述離合器系統(tǒng)和離合器組件的材料特性與幾何形狀和油之間是相互依賴性。
可以看出，通過(guò)對(duì)流熱的傳遞是由油的流速影響。油流，因?yàn)橛袃蓚€(gè)非常重要的影響。散熱系數(shù)是取決于流體中固體表面接觸的邊界層上。由于更加動(dòng)蕩的油流增加油速度影響散熱系數(shù)。在另一方面，增加油的流動(dòng)導(dǎo)致油和離合器部件之間有較短的接觸時(shí)間。這可能導(dǎo)致一個(gè)槽不能完全充滿油，將其用于熱傳遞的生成和減少熱流減小面積。因此次參數(shù)作為離合器系統(tǒng)的油流量和旋轉(zhuǎn)速度在實(shí)驗(yàn)研究范圍內(nèi)變化，以加深有關(guān)操作期間油流速槽的填充認(rèn)識(shí)。
Eq.(2) 因?yàn)闊醾鬟f的對(duì)流。
圖8所示出帶有油的一個(gè)離合器壓盤(pán)的槽，由于槽的阻力有油的內(nèi)載體（1和2之間）中保留（2和3之間）。內(nèi)載體由于油離心力作用導(dǎo)致點(diǎn)2處的壓力。通過(guò)凹槽增加油的流量使壓力越來(lái)越大。另一方面流動(dòng)阻力取決于溝槽范圍內(nèi)的油的流量。這意味著槽的內(nèi)載體范圍內(nèi)只是完全充滿油的狀態(tài)。油的保持在很大程度上取決于流動(dòng)性和凹槽設(shè)計(jì)。因此，由于油保持槽的壓力和流動(dòng)阻力之間的平衡狀態(tài)取決于槽的設(shè)計(jì)和操作條件如轉(zhuǎn)速為止。
Fig.8. 完全充滿了油的摩擦片與徑向槽。
Fig.9. 摩擦片與徑向槽，1000RPM，1.5l/min。
Fig.10. 摩擦片與徑向槽，1000RPM，3l/min。
4 結(jié)論
在第一個(gè)實(shí)驗(yàn)中進(jìn)行了使用一個(gè)摩擦片與壓盤(pán)和不同油流入每一側(cè)15 的徑向凹槽。它可以看出，在1.5升/分鐘（圖9）油流速結(jié)果是填充了部分溝槽。隨著油流速3升/分鐘（圖10）槽完全充滿油。以3升/分鐘和4.5升/分鐘（圖11）比較油流速，可以看出，從大約1.1米/秒油速增加的最大速度，以達(dá)2米/秒。旋轉(zhuǎn)速度從1000增加到2000轉(zhuǎn)導(dǎo)致一個(gè)接近無(wú)油的槽（圖12）。
不斷增長(zhǎng)的油的流量可達(dá)9升/分鐘（圖13）不會(huì)導(dǎo)致凹槽完全充滿油。為了得到完全充油的凹槽油的流量必須進(jìn)一步增加。
摩擦片與交叉溝槽顯示了在完全填充凹槽的條件下（圖14）。提高油流量從1.5至3升/分鐘導(dǎo)致速度的增加（圖15）。值得注意的是，速度增加僅發(fā)生在徑向?qū)虿?。切向?qū)虿埏@示油速度影響的很小。
Fig.11. 摩擦片與徑向槽，2000RPM，4.5l/min.
Fig.12. 摩擦片與徑向槽，2000RPM，1.5l/min.
Fig.13. 摩擦片與徑向槽，2000RPM，9l/min.
Fig.14. 摩擦片與交叉溝槽，2000RPM，1.5l/min的油流。
Fig.15. 摩擦片與交叉溝槽，2000RPM，3l/min的油流。
Fig.16. 使用陶瓷作為摩擦材料的多片離合器。
5 討論
根據(jù)連續(xù)性，可以得出結(jié)論，增加油的流量與部分填充槽的主要影響填充所述的槽（圖9和10）。這的結(jié)果幾乎恒定的雷諾數(shù)和努塞爾數(shù)與常數(shù)的散熱系數(shù)，作為一個(gè)結(jié)果。增加油的流量與完全填充凹槽導(dǎo)致速度的增加（圖10和11）。雷諾數(shù)和努塞爾數(shù)以及散熱系數(shù)都在增加。
在切向?qū)虬疾蹆?nèi)顯示幾乎恒定的流速與產(chǎn)生恒定雷諾數(shù)和努塞爾數(shù)以及熱傳遞系數(shù)作為結(jié)果（圖14和15）。聚焦徑向槽內(nèi)交叉槽可以看到一個(gè)類似的行為在徑向槽（圖14和15與圖10和11比較）。
如圖所示（式2）對(duì)流換熱傳遞是受散熱系數(shù)和散熱面積的影響。增加油的速度導(dǎo)致散熱系數(shù)的增大。另一方面在潤(rùn)滑離合器系統(tǒng)的槽內(nèi)油速度高時(shí)由于連續(xù)性槽的填充減少，因此減小散熱面積。這兩種效應(yīng)相互連接對(duì)有關(guān)對(duì)流冷卻的相對(duì)影響。這兩種效應(yīng)都是重要的影響，問(wèn)題依然存在。但必須指出，下列調(diào)查僅是本文討論的范圍內(nèi)來(lái)回答這個(gè)問(wèn)題。
如圖16所示出了使用陶瓷作為摩擦材料的多片式離合器系統(tǒng)。根據(jù)陶瓷材料的高強(qiáng)度，有可能增加槽區(qū)。這個(gè)系統(tǒng)允許不同溝槽填充油的速度在一個(gè)巨大的范圍。摩擦材料的變化，如進(jìn)一步影響是不是本文的重點(diǎn)。
該系統(tǒng)采用一個(gè)外載體與油出口的耐油性。使用此測(cè)試裝置就可以實(shí)現(xiàn)完全充油槽（圖17，左進(jìn)一步稱為流動(dòng)阻力），以及部分填充的溝槽（圖17，右進(jìn)一步稱為自由流動(dòng)）。圖17示出兩個(gè)摩擦元件之間被聚焦的油填充的區(qū)域。
如圖18所示先進(jìn)陶瓷多片離合器的實(shí)驗(yàn)結(jié)果。兩個(gè)系統(tǒng)都使用完全相同的部件。這兩種系統(tǒng)都在相同的工作條件下運(yùn)行在0.093 W/mm2摩擦功率與石油相同流量（每個(gè)摩擦片0.5升/分鐘）和相同的旋轉(zhuǎn)速度（1090轉(zhuǎn)內(nèi)的載體，136轉(zhuǎn)外載）。在這兩種系統(tǒng)是在環(huán)境壓力油通過(guò)內(nèi)載體。該油通過(guò)離心力加速進(jìn)入徑向方向。系統(tǒng)之間的唯一區(qū)別是外載體的流動(dòng)阻力。一個(gè)系統(tǒng)使用的外載一個(gè)合適的流動(dòng)阻力來(lái)實(shí)現(xiàn)完全充滿油槽，如圖17左側(cè)的所謂的流動(dòng)阻力。其他系統(tǒng)具有非常低的流動(dòng)阻力的外載，無(wú)油流通過(guò)離合器系統(tǒng)啟動(dòng)，如圖17在右邊所謂的自由流動(dòng)。
自由流系統(tǒng)：由于低流高阻油的速度是可能的。由于連續(xù)性，只有一小塊體積的槽是油填充。
流動(dòng)阻力系統(tǒng)：由于高流動(dòng)性非常低的油的速度為徑向方向是可能的，但槽注滿油。
鋼板的溫度過(guò)程測(cè)量使用圖18所示熱電偶的滑動(dòng)操作。摩擦片開(kāi)始增加到70°C油的入口溫度被增加，最終達(dá)到接近平穩(wěn)的溫度。這意味著公式（1）中的時(shí)間依賴內(nèi)在能量是不相關(guān)的。其結(jié)果是，所有由摩擦產(chǎn)生的熱量被傳遞到油。這就是為什么在鋼板的測(cè)定溫度可以被看作是關(guān)于散熱的指標(biāo)的原因。較高的溫度意味著低效率的熱傳遞。
Fig.17. 使用陶瓷完全充油槽的多片離合器（1ooorpm，1.5l/min）。
Fig.18. 多碟離合與陶瓷比傳統(tǒng)的離合器系統(tǒng)。
6 結(jié)論
在本文中提出了一種方法，通過(guò)潤(rùn)滑離合器系統(tǒng)，以確定油的流量。進(jìn)行的調(diào)查顯示，這取決于凹槽設(shè)計(jì)油的分布急劇的變化。它已經(jīng)表明，熱散遞比油的速度更受填充凹槽的影響。在實(shí)驗(yàn)研究范圍內(nèi)增加凹槽的區(qū)域會(huì)使散熱增加，如圖所示。因此，顯示了先進(jìn)陶瓷增加的散熱和提高潤(rùn)滑的作用。
Advanced ceramics as friction material in lubricated clutch systemsJohannes Bernhardtn,Albert Albers,Sascha OttIPEKInstitute of Product Engineering,Karlsruhe Institute of Technology(KIT),Germanya r t i c l e i n f oArticle history:Received 4 August 2011Received in revised form30 July 2012Accepted 1 August 2012Available online 18 August 2012Keywords:Advanced ceramicsLubricated multi-disc clutchOil flowParticle image velocimetrya b s t r a c tThe trend in development of mobility systems is very much influenced by the need of reducing CO2emission.For this reason it is important to increase power density and efficiency of vehicles powertrainby improving single powertrain components as well as developing completely new powertrainconcepts.Shiftable clutches are influencing the dynamic behaviour as well as the energy efficiency ofthe powertrain due to complex interaction within the system.Power density is very much influencedby the tribological contact of clutch systems which is very important concerning fulfilling systemsfunctionality.The paper focuses experimental investigations of lubricated clutch systems.New experimentalmethods to determine the oil flow within the tribological contact are presented.Based on these resultsthe potential concerning increasing power density and the methods and tools to support developmentof tribological systems based on advanced ceramics will be discussed.&2012 Elsevier Ltd.All rights reserved.1.IntroductionTo fulfil increasing demands concerning efficiency and environ-mental impact new powertrain systems especially in motor vehicleapplications are required.In most cases the powertrain of vehiclesuses clutch systems to enable gearshift and start-up.Depending onthe powertrain concept there are different requirements on clutchsystems.New powertrain concepts are maybe using more than oneclutch to connect and disconnect different engines and ancillaryunits depending on the operating condition.Multi-disc clutchsystems,which are often used in the powertrain of vehicles as wellas in industrial plants,have a high impact on power density anddynamic behaviour of the whole system 13.A safe operation ofthe whole system has to be guaranteed under strongly varyingconditions combined with the need of increasing power density.1.1.Lubricated multi-disc clutchFig.1 shows a lubricated multi-disc clutch system used in dualclutch transmissions of passenger vehicles.The clutch system uses two radial arranged disc sets.Each discset consists of friction plates using organic facing and counterplates made out of steel based material.The different discs aredisplaceable into axial direction but connected to the inner andouter carrier into circumferential direction.To enable torquetransmission the disc set is compressed into axial direction.Dueto friction forces between friction and counter plates it is possibleto transmit torque.During operation there is an oil flow throughthe clutch system.This oil flow is necessary for convection coolingof the clutch system and furthermore for influencing tribologicalprocesses within contact.Oil supply is realised using a hydraulicpump delivering the lubricant via the inner carrier of the clutchsystem.Within the clutch system oil flow is mainly influenced bycentrifugal forces due to the rotational speed of the discs and thedesign of the grooves on the surface of the friction plates.The oilleaves the clutch system via the outer carrier.H ohn et al.4,5 show that temperature of the clutch system isvery much influencing the durability of lubricated clutch systems.Therefore similar clutch systems are tested with varying load cycleusing change of coefficient of friction as a criterion to determinedamage of the tribological contact during load cycle.During experi-mental testing the steel plates show temperatures of up to 300 1C.Italso can be seen that limiting the maximum temperature of theclutch system leads to stable long term performance.Experimental as well as calculations concerning flash tem-peratures are carried out by Ingram et al.6.The result is thatflash temperatures remain on a low level.It can be concluded thatconcerning lubricated clutch systems using paper based materialsflash temperatures are from minor relevance compared toincrease of mass temperature.Fig.2 shows a black-box description of a multi-disc clutchsystem.During operation there is a mechanical and thermalpower transmitted through the systems boundary.Dependingon the operating conditions the proportion between mechanicaland thermal power output is varying.Contents lists available at SciVerse ScienceDirectjournal homepage: International0301-679X/$-see front matter&2012 Elsevier Ltd.All rights reserved.http:/dx.doi.org/10.1016/j.triboint.2012.08.002nCorresponding author.E-mail addresses:johannes.bernhardtkit.edu(J.Bernhardt),albert.alberskit.edu(A.Albers).Tribology International 59(2013)267272The difference between mechanical power in-and output isbeing transformed into heat which heats up the clutch systemrespectively is transferred to the cooling medium(Eq.(1)Pmech,in?Pmech,out?Ptherm,outdQclutchdtPmech,in?Pmech,outdQclutchdtPtherm,out1Eq.(1)is the energy equation multi-disc clutch 7.Improved convection cooling leads to a reduced temperaturelevel of the clutch system.Due to the assumption that masstemperature is the main influence concerning power density,based on the work of H ohn et al.4,5 and Ingram et al.6,it canbe seen that load capacity of a clutch system can be increased byimproving convection cooling.The heat transfer to the oil is depending on oil distributionwithin the system which is itself influenced by groove orientationand groove geometry.The mass temperature of the clutch systemis mainly influenced by the macroscopic oil flow.The microscopicoil flow on the scale of asperities is important,for example,concerning local pressure and therefore the tribochemical andtribophysical processes within the contact.But concerning globalheat transfer it is assumed to be less important.Besides the citedwork 46 the reason is the small amount of oil within thecontact compared to the oil volume within the grooves of theclutch system.That is the reason why macroscopic oil flow isfocused within this paper.To realise clutch systems with increased power density byimproved groove designs it is important to deepen the knowledgeconcerning oil flow through clutch systems.Therefore experi-mental investigations with different clutch systems are carriedout to determine the oil flow within the clutch system.2.Methods and componentsHeat transfer is very much influenced by oil flow through theclutch system.Oil flow itself is influenced by groove design verymuch.In the following a method called particle image velocime-try is introduced to determine the oil flow within a lubricatedclutch system is presented.2.1.Particle image velocimetryTo determine the fluid flow the PIV-method(particle imagevelocimetry)is used.The test setup consists of the clutch systemincluding the oil with tracer particles,the laser,the CCD-camera(Fig.3).Because of accessibility of the oil volume the camera andthe laser are oriented almost coaxial and orthogonal to the oilvolume.With this setup two pictures are taken with a defined offsetDt(Fig.4).To avoid reflexions that lead to low contrast betweenparticles and the surrounding resulting in problems to determinevelocity vectors,the camera is equipped with a band eliminationfilter that allows cutting out the wavelength of the laser.Thefluorescent particles absorb the light emitted by the laser andemit light at a different wavelength that can be seen by thecamera.The result is that reflexions are not seen by the camerabut the fluorescent particles that are important to determine thevelocity of the oil flow.For interpretation the pictures are divided into partial picturesas a basis for vector calculation(Fig.5).The vectors are calculatedfor each partial picture and finally combined to the vector field ofthe whole picture.The whole analysis of the measured data is shown in Fig.6using the example of a lubricated clutch system at a rotationalspeed of 1000 rpm and an oil flow of 1.5 l/min.Each figure takenFig.1.Dual clutch system.Fig.2.Energy equation of multi-disc clutch system.Fig.3.PIV setup.Fig.5.Vector field calculation.Fig.4.Camera and laser synchronisation.J.Bernhardt et al./Tribology International 59(2013)267272268by the CCD-camera consists of 1600?1200 pixels(Fig.6,left).Inthis test setup each pixel represents a rectangle of the clutchsystem with length and width of 16mm.For cross correlationrectangles of 32?32 pixels(512?512mm2)are taken(Fig.6,middle).Out of these two pictures vectors of the vector field aregenerated(Fig.6,right).2.2.Multi-disc clutch test rigFig.7 shows the multi-disc clutch test rig that is used for allthe experimental investigations shown in this paper.The test righas two electric motors to realise different rotational speeds offriction and counter plates.The clutch system is integrated intothe test rig via inner and outer carrier and is actuated by ahydraulic cylinder.The presented experimental investigations arecarried out using a counter plate equipped with a window toallow optical access to the tribological contact.2.3.Multi-disc clutchThe multi-disc clutch system consists of friction plates withradial grooves or crossed grooves.The friction plates have aninner diameter of 80 mm and an outer diameter of 108 mm.Theradial grooved friction plate has 15 grooves of 1 mm depth and1.6 mm width.The whole groove surface is 336 mm2and thegroove volume is 336 mm3.The friction plates with crossedgrooves have grooves with a distance of 5.5 mm,a width of1 mm and a depth of 0.25 mm.This results in a groove surface ofabout 1365 mm2and a groove volume of 341 mm3.3.TheoryHeat transfer means transport of energy due to a difference intemperature.There are three relevant mechanisms:?conduction?convection?radiationWithin this work convection is focused because it is the maininfluence concerning heat transfer within a clutch system.Because of the complex mechanisms of heat transfer a phenom-enological type of calculation is suitable in most cases.Theequations(Eq.(2)show interdependencies between operatingparameters,geometry of the clutch system and material proper-ties of the clutch components and the oil.DPtherm fa,A,DT 2a heat transfer coefficientA heat transfer areaDT temperature differenceNualcharl,Nu fRe,Prlchar characteristic lengthRe rcnc flow velocityPr nrcPll heat conduction coefficientallcharNuRe,Prr density fluida flchar,c,l,r,cP,ncP spec:heat of fluidn kin:viscosityEq.(2)is the heat transfer because of convection.Fig.6.Clutch system as example for vector field calculation.Fig.7.Multi-disc clutch test rig(picture and schematic).J.Bernhardt et al./Tribology International 59(2013)267272269It can be seen that heat transfer by convection is influenced byvelocity of the oil flow.Oil flow has a very important influencebecause of two aspects.Heat transfer coefficient is depending onthe boundary layer of the fluid contacting the solid surface.Increasing oil velocity influences heat transfer coefficient due toa more turbulent oil flow.On the other hand increasing oil flowresults in a shorter contact time between oil and clutch compo-nents.This could result in a groove not completely filled with oilwhich means decreasing area for heat transfer and a resultingreduced heat flow.Therefore parameters as oil flow and rotationalspeed of the clutch system are varied within the experimentalinvestigations to deepen the knowledge concerning oil velocityand filling of the grooves during operation.Fig.8 shows a clutch disc with oil flow through the grooves.Due to flow resistance of the grooves(between points 2 and 3)there is oil retained within the inner carrier(between points1 and 2).Centrifugal force acting on the oil within the innercarrier results into a pressure at point 2.Increasing pressuremeans increasing oil flow through the grooves.Flow resistance onthe other hand is depending on oil flow within the grooves.Thismeans that grooves are only completely filled with oil retainingwithin the inner carrier.Oil retaining depends very much on flowresistance and groove design.Therefore an equilibrium statebetween flow resistance of the grooves and pressure because ofoil retaining is reached depending on groove design and operatingconditions such as rotational speed.4.ResultsThe first experiment carried out using a friction plate with 15radial grooves on each side of the friction plate with different oilflows.It can be seen that an oil flow of 1.5 l/min(Fig.9)results ina partially filled groove.With increasing oil flow grooves arecompletely filled with oil at 3 l/min(Fig.10).Comparing oilvelocity at 3 l/min and 4.5 l/min(Fig.11)it can be seen thatmaximum velocity of oil increases from about 1.1 m/s to up to2 m/s.Increasing rotational speed from 1000 to 2000 rpm leads to anearly oil free groove(Fig.12).Increasing oil flow up to 9 l/min(Fig.13)does not result in completely oil filled grooves.To getcompletely oil filled grooves a further increase in oil flow isnecessary.Friction plates with crossed grooves show under the sameconditions(Fig.14)completely filled grooves.Increasing oil flowfrom 1.5 to 3 l/min leads to increased velocity(Fig.15).It isremarkable that velocity increase takes place only in radialoriented grooves.Tangential oriented grooves show only littlechange in oil velocity.Fig.8.Friction disc with radial grooves,completely filled with oil.Fig.9.Friction plate with radial grooves,1000 rpm,1.5 l/min.Fig.10.Friction plate with radial grooves,1000 rpm,3 l/min.Fig.11.Friction plate with radial grooves,1000 rpm,4.5 l/min.J.Bernhardt et al./Tribology International 59(2013)2672722705.DiscussionBased on continuity it can be concluded that increasing oilflow with partially filled grooves influences mainly filling of thegrooves(Figs.9 and 10).This results in nearly constant Reynolds-and Nusselt-number and constant heat transfer coefficient,a,as aconsequence.Increasing oil flow with completely filled grooveslead to increase of velocity(Figs.10 and 11).Reynolds-andNusselt-number as well as heat transfer coefficient are increasing.Crossed grooves show within tangential oriented groovesnearly constant flow velocity with resulting constant Reynolds-and Nusselt-number and constant heat transfer coefficient as aconsequence(Figs.14 and 15).Focusing radial grooves withincrossed groove pattern it can be seen a similar behaviour as inradial grooves(Figs.14 and 15 compared with Figs.10 and 11).As shown(Eq.2)convective heat transfer is influenced by heattransfer coefficient and heat transferring area.Increased oilvelocity leads to high heat transfer coefficient.On the other handhigh oil velocity within the grooves of a lubricated clutch systemtends to reduced filling of the grooves due to continuity andtherefore a reduced heat transferring area.Both effects areconnected to each other with an opposed influence concerningconvection cooling.The question concerning importance of botheffects remains.It has to be said that the following investigationonly is discussed within this paper to answer this question.Fig.16 shows a multi-disc clutch system using ceramics as afriction material.According to the high strength of the ceramicFig.12.friction plate with radial grooves,2000 rpm,1,5 l/min.Fig.13.Friction plate with radial grooves,2000 rpm,9 l/min.Fig.14.Friction plate with crossed grooves,2000 rpm,1.5 l/min oil flow.Fig.15.Friciton plate with corssed grooves,2000 rpm,3 l/min oil flow.Fig.16.Multi-disc clutch using ceramics as friction material.J.Bernhardt et al./Tribology International 59(2013)267272271material it is possible to increase groove area.This system allowsvarying groove filling and oil velocity in a huge range.Furtherinfluences of a variation of the friction material such as localprocesses within contact are not in focus of this paper.The system uses an outer carrier with variable oil resistance ofthe oil outlet.Using this test setup it is possible to realisecompletely oil filled grooves(Fig.17,leftfurther called flowresistance)as well as partially filled grooves(Fig.17,rightfurther called free flow).Each of the pictures in Fig.17 shows theoil filled area between two friction elements is focused.Fig.18 shows experimental results of the multi-disc clutchwith advanced ceramics.Both systems use completely identicalcomponents.Both systems are running under the same operatingconditions at 0.093 W/mm2of friction power with the same oilflow(0.5 l/min per friction plate)and the same rotational speeds(1090 rpm inner carrier,136 rpm outer carrier).In Both systemsoil is feeded through the inner carrier with ambient pressure.The oil is accelerated into radial direction by centrifugal force.Theonly difference between the systems is the flow resistance ofthe outer carrier.One system uses a suitable flow resistance at theouter carrier to realise completely oil filled grooves as shown inFig.17 on the left sidecalled flow resistance.The other systemhas a very low flow resistance at the outer carrier that free oilflow through the clutch system is enabled as shown in Fig.17 onthe rightcalled free flow.System with free flow:Due to low flow resistance high oilvelocity is possible.Because of continuity only a small volume ofthe grooves is oil filled.System with flow resistance:Due to high flow resistance verylow oil velocity into radial direction is possible,but grooves arecompletely filled with oil.The temperatures of the steel plates are measured duringsliding operation using thermocouples shown in Fig.18.Startingat the oil inlet temperature of 70 1C the temperatures of thefriction plates increase and finally reach a nearly stationarytemperature.This means that the time dependent component ofinner energy in Eq.(1)is not relevant.The consequence is that allthe heat generated by friction is transferred to the oil.That is thereason why the measured temperature of the steel plates can beseen as an indicator concerning heat transfer.Higher temperaturemeans less efficient heat transfer.The increase in temperature of the system with flow resistanceis about 55 K.The system with free flow shows an increase intemperature of about 140 K.This means that the system withcompletely filled grooves has about 2.5 times higher heat transfer.This means that the effect of heat transferring area seems to bedominant compared to heat transfer coefficient.6.ConclusionWithin this paper a method to determine the oil flow throughlubricated clutch systems is presented.Investigations carried outshow that depending on the groove design oil distribution variesdramatically.It has been shown that heat transfer is moreinfluenced by filling of the grooves than by oil velocity.Theincreased groove area allows increased heat transfer as shownwithin experimental investigations.Therefore advanced ceramicsshow potential to increase heat transfer and improve powerdensity of lubricated clutch systems due to high strength andthe resulting possibility of groove design.References1 Abbassi M.Steigerung des Antriebsstrangkomforts im Kfz durch elektro-nischesKupplungsmanagement.ATZAutomobiltechnischeZeitschrift1999;101:11826.2 Bach H.Systematische Suche und schwingungstechnische Absch atzung neuerWirkprinzipien f ur alternative Drehschwingungsentkopplungssysteme imPKW-Antriebsstrang.VDI-Berichte Number 1749 2003:6988.3 McGrath M,M uller B,Maucher E,Marathe B,Bailey G.Der Drehmoment-wandler.LuK Kolloquium 2002;4:2131.4 H ohn,B R,Pflaum,H.;H ammerl,B.:A new calculation method for loadcarrying capacity of wet running multi-clutches in application with variableload,In:4th World Congress on Gearing and Power Transmission Paris.16./18.03.1999,p.126577.5 H ohn B-R,Pflaum H,H ammerl B.Ermittlung der Leistungsgrenzen olgek uhlterLamellenkupplungen anhand von Temperaturkriterien.VDI-Berichte Number1323 1997:50725.6 Ingram 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