車輛工程外文翻譯-先進陶瓷摩擦材料在離合器中的潤滑?【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,陶瓷,摩擦,材料,離合器,中的,潤滑,中文,4260,PDF,WORD 【中文4260字】 先進陶瓷摩擦材料在離合器中的潤滑 1 介紹 為了滿足越來越多關(guān)于應用程序的需要在效率和環(huán)境影響下新動力傳動系統(tǒng)特別是在機動車輛的要求。在大多數(shù)情況下，車輛的動力傳動傳動系統(tǒng)采用離合器系統(tǒng)在換檔和啟動。根據(jù)不同的動力傳動系統(tǒng)的概念離合器系統(tǒng)上有不同的要求。新的動力傳動系統(tǒng)概念根據(jù)不同的操作條件可能使用多個離合器連接和斷開不同的發(fā)動機及配套裝置。多片離合器系統(tǒng)，該系統(tǒng)通常在車輛的動力傳動系統(tǒng)，以及在工廠中使用，對功率密度和整個系統(tǒng)的[1-3]的動態(tài)行為有很大影響。整個系統(tǒng)的安全運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多片離合器的潤滑 圖1顯示了客運車輛多盤離合器變速器使用潤滑的多片離合器系統(tǒng)。 離合器系統(tǒng)使用兩個徑向排列的壓盤。每個壓盤由摩擦片使用有機面臨和計數(shù)板制成的鋼基材料。不同的壓盤是可位移轉(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)矩壓盤組壓縮成軸向。由于摩擦和計數(shù)板之間的摩擦力，因此能夠傳遞轉(zhuǎn)矩。在操作過程中有通過離合器系統(tǒng)中的油流動。這種油流是對離合器系統(tǒng)的對流冷卻，進而為接觸摩擦影響必要的過程。供油用液壓泵送潤滑油通過過離合器系統(tǒng)載體的內(nèi)部。在離合器系統(tǒng)中油的流動是壓盤的轉(zhuǎn)速和摩擦片的表面上設計凹槽的離心力的影響。油通過外載體離開離合器系統(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)的變化為準則，以確定在負載循環(huán)測試摩擦接觸損傷變化。在實驗測試的鋼板顯示溫度高3001℃。它也可以看出，離合器系統(tǒng)的最大溫度導致了長期穩(wěn)定的性能。 實驗以及關(guān)于計算閃光溫度由Ingram等進行。圖[6]其結(jié)果是閃光的溫度保持在一個較低的水平。可以得出結(jié)論，關(guān)于潤滑離合器系統(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。在操作過程中存在一個通過系統(tǒng)邊界發(fā)送機械性能和熱功率。根據(jù)操作條件的不同機械和熱功率輸出之間的比例是變化的。機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) 多盤離合器的熱量方程 [7]。 提高對流散熱可以讓離合器系統(tǒng)的溫度降低。假設質(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]可以看出提高一個離合器系統(tǒng)的負載能力可以通過提高對流冷卻。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)的摩擦化學和摩擦物理學流程。但關(guān)于全球散熱它被認為不那么重要。除了列舉文獻[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是本文中的原因。通過改進的槽的幾何形狀實現(xiàn)具有增加功率密度離合器系統(tǒng)的設計加深關(guān)于通過離合器系統(tǒng)油流的知識是重要的。因此，實驗研究用不同的離合器系統(tǒng)都進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設置。 Fig.4. 相機和激光同步。 Fig.5. 矢量場的計算。 Fig.6. 以離合器系統(tǒng)為例做向量場的計算。 Fig.7. 多離合器試驗臺（圖片和原理圖）。 2 方法和組件 熱傳遞是非常受通過離合器系統(tǒng)的油流影響。油流本身是受凹槽設計的影響非常大。在下面的一個叫做粒子圖像測速方法引入到確定潤滑離合器系統(tǒng)內(nèi)的油流呈現(xiàn)。 2.1 粒子圖像測速 為了確定流體流動的PIV法（粒子圖像測速）被使用。該測試裝置包括包含原油與示蹤粒子，激光，對CCD-照相機（圖3）的離合器系統(tǒng)。因為油體積的可訪問性的相機和激光器的取向幾乎同軸且垂直于油體積。 有了這個設置兩張照片是采取定額補償ΔT（圖4）。避免反射光導致顆粒和周圍產(chǎn)生的問題，以確定速度矢量，相機配備一個帶阻濾波器，它允許切割出激光的波長之間的對比度低。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，可以通過攝像機看到。其結(jié)果是，反射光都沒有看到由相機不過熒光發(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算（圖5）提供了基礎。該矢量被計算每個局部圖像并最終結(jié)合到整個畫面的矢量中。 測量數(shù)據(jù)的整個分析示于圖6使用以1000rpm和1.5l/min的油流的旋轉(zhuǎn)速度的潤滑離合器系統(tǒng)的例子。采取的CCD相機各圖中由16001200像素（圖6，左圖）。在此測試裝置的每個像素代表具有長度和寬度為16毫米的離合器系統(tǒng)的一個矩形。為32×32像素（512×512平方毫米）的互相關(guān)矩形被取（圖6，中間）。出這兩個影像的生成的矢量場的矢量（圖6，右圖）。 2.2 多片式離合器試驗臺 圖7示出了用于本文中所示的所有實驗研究的多片式離合器試驗臺。測試裝備了兩個電動馬達，以實現(xiàn)摩擦和計數(shù)板的旋轉(zhuǎn)速度不同。離合器系統(tǒng)是通過內(nèi)部和外部的載體整合到試驗臺上，并且由液壓缸驅(qū)動。所呈現(xiàn)的實驗研究都進行了使用配備有一個窗口計數(shù)板，以允許光進入摩擦接觸。 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。有三個相關(guān)的機制：導通、對流、放射線。 這項工作中對流是重點，因為它是關(guān)于一個離合器系統(tǒng)內(nèi)熱傳遞的主要影響。因為散熱的復雜機制是一種現(xiàn)象學式的計算，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，通過對流熱的傳遞是由油的流速影響。油流，因為有兩個非常重要的影響。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，增加油的流動導致油和離合器部件之間有較短的接觸時間。這可能導致一個槽不能完全充滿油，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)速度在實驗研究范圍內(nèi)變化，以加深有關(guān)操作期間油流速槽的填充認識。 Eq.(2) 因為熱傳遞的對流。 圖8所示出帶有油的一個離合器壓盤的槽，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致點2處的壓力。通過凹槽增加油的流量使壓力越來越大。另一方面流動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性和凹槽設計。因此，由于油保持槽的壓力和流動阻力之間的平衡狀態(tài)取決于槽的設計和操作條件如轉(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 在第一個實驗中進行了使用一個摩擦片與壓盤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2米/秒。旋轉(zhuǎn)速度從1000增加到2000轉(zhuǎn)導致一個接近無油的槽（圖12）。 不斷增長的油的流量可達9升/分鐘（圖13）不會導致凹槽完全充滿油。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)，作為一個結(jié)果。增加油的流量與完全填充凹槽導致速度的增加（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。增加油的速度導致散熱系數(shù)的增大。另一方面在潤滑離合器系統(tǒng)的槽內(nèi)油速度高時由于連續(xù)性槽的填充減少，因此減小散熱面積。這兩種效應相互連接對有關(guān)對流冷卻的相對影響。這兩種效應都是重要的影響，問題依然存在。但必須指出，下列調(diào)查僅是本文討論的范圍內(nèi)來回答這個問題。 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)陶瓷材料的高強度，有可能增加槽區(qū)。這個系統(tǒng)允許不同溝槽填充油的速度在一個巨大的范圍。摩擦材料的變化，如進一步影響是不是本文的重點。 該系統(tǒng)采用一個外載體與油出口的耐油性。使用此測試裝置就可以實現(xiàn)完全充油槽（圖17，左進一步稱為流動阻力），以及部分填充的溝槽（圖17，右進一步稱為自由流動）。圖17示出兩個摩擦元件之間被聚焦的油填充的區(qū)域。 如圖18所示先進陶瓷多片離合器的實驗結(jié)果。兩個系統(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行在0.093 W/mm2摩擦功率與石油相同流量（每個摩擦片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)境壓力油通過內(nèi)載體。該油通過離心力加速進入徑向方向。系統(tǒng)之間的唯一區(qū)別是外載體的流動阻力。一個系統(tǒng)使用的外載一個合適的流動阻力來實現(xiàn)完全充滿油槽，如圖17左側(cè)的所謂的流動阻力。其他系統(tǒng)具有非常低的流動阻力的外載，無油流通過離合器系統(tǒng)啟動，如圖17在右邊所謂的自由流動。 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。 流動阻力系統(tǒng)：由于高流動性非常低的油的速度為徑向方向是可能的，但槽注滿油。 鋼板的溫度過程測量使用圖18所示熱電偶的滑動操作。摩擦片開始增加到70°C油的入口溫度被增加，最終達到接近平穩(wěn)的溫度。這意味著公式（1）中的時間依賴內(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定溫度可以被看作是關(guān)于散熱的指標的原因。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，通過潤滑離合器系統(tǒng)，以確定油的流量。進行的調(diào)查顯示，這取決于凹槽設計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。在實驗研究范圍內(nèi)增加凹槽的區(qū)域會使散熱增加，如圖所示。因此，顯示了先進陶瓷增加的散熱和提高潤滑的作用。 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 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