车辆工程外文翻译-先进陶瓷摩擦材料在离合器中的润滑 【中文4260字】【PDF+中文WORD】
车辆工程外文翻译-先进陶瓷摩擦材料在离合器中的润滑 【中文4260字】【PDF+中文WORD】,中文4260字,PDF+中文WORD,车辆,工程,外文,翻译,先进,陶瓷,摩擦,材料,离合器,中的,润滑,中文,4260,PDF,WORD
【中文4260字】
先进陶瓷摩擦材料在离合器中的润滑
1 介绍
为了满足越来越多关于应用程序的需要在效率和环境影响下新动力传动系统特别是在机动车辆的要求。在大多数情况下，车辆的动力传动传动系统采用离合器系统在换档和启动。根据不同的动力传动系统的概念离合器系统上有不同的要求。新的动力传动系统概念根据不同的操作条件可能使用多个离合器连接和断开不同的发动机及配套装置。多片离合器系统，该系统通常在车辆的动力传动系统，以及在工厂中使用，对功率密度和整个系统的[1-3]的动态行为有很大影响。整个系统的安全运行都有非常不同情况下得到保证加上提高功率密度的需求。
1.1多片离合器的润滑
图1显示了客运车辆多盘离合器变速器使用润滑的多片离合器系统。
离合器系统使用两个径向排列的压盘。每个压盘由摩擦片使用有机面临和计数板制成的钢基材料。不同的压盘是可位移转换成轴向方向，但连接到内部和外部载体成圆周方向。为了使转矩压盘组压缩成轴向。由于摩擦和计数板之间的摩擦力，因此能够传递转矩。在操作过程中有通过离合器系统中的油流动。这种油流是对离合器系统的对流冷却，进而为接触摩擦影响必要的过程。供油用液压泵送润滑油通过过离合器系统载体的内部。在离合器系统中油的流动是压盘的转速和摩擦片的表面上设计凹槽的离心力的影响。油通过外载体离开离合器系统。
Hohn 等，[4,5]表明离合器系统的温度是非常影响润滑离合器系统的耐用性。因此，类似的离合器系统使用不同摩擦系数的变化为准则，以确定在负载循环测试摩擦接触损伤变化。在实验测试的钢板显示温度高3001℃。它也可以看出，离合器系统的最大温度导致了长期稳定的性能。
实验以及关于计算闪光温度由Ingram等进行。图[6]其结果是闪光的温度保持在一个较低的水平。可以得出结论，关于润滑离合器系统使用纸质材料闪光温度相比其他材料温度上升。
图2示出了多片式离合器系统的黑箱描述。在操作过程中存在一个通过系统边界发送机械性能和热功率。根据操作条件的不同机械和热功率输出之间的比例是变化的。机械功率和输出之间的差值被转换成热，它们分别加热离合器系统被传递到冷却介质(Eq. (1))
Eq.(1) 多盘离合器的热量方程 [7]。
提高对流散热可以让离合器系统的温度降低。假设质量温度是有关功率密度最主要的影响，基于Hohn等工作。图[4,5]和Ingram等。图[6]可以看出提高一个离合器系统的负载能力可以通过提高对流冷却。散热油取决于油的分布本身受槽的方向和槽的几何形状的影响。离合器系统的温度是受油流的主要影响。关于凹凸的规模微观油流量是很重要的，例如，关于局部压力，因此，接触内的摩擦化学和摩擦物理学流程。但关于全球散热它被认为不那么重要。除了列举文献[4-6]的原因是少量的油接触的范围内相比，离合器系统的凹槽内的油量。这就是为什么宏观油流的重点是本文中的原因。通过改进的槽的几何形状实现具有增加功率密度离合器系统的设计加深关于通过离合器系统油流的知识是重要的。因此，实验研究用不同的离合器系统都进行了确定离合器系统内的油流。
Fig.1. 双离合器系统。
Fig.2. 多片离合器的方程。
Fig.3. Piv设置。
Fig.4. 相机和激光同步。
Fig.5. 矢量场的计算。
Fig.6. 以离合器系统为例做向量场的计算。
Fig.7. 多离合器试验台（图片和原理图）。
2 方法和组件
热传递是非常受通过离合器系统的油流影响。油流本身是受凹槽设计的影响非常大。在下面的一个叫做粒子图像测速方法引入到确定润滑离合器系统内的油流呈现。
2.1 粒子图像测速
为了确定流体流动的PIV法（粒子图像测速）被使用。该测试装置包括包含原油与示踪粒子，激光，对CCD-照相机（图3）的离合器系统。因为油体积的可访问性的相机和激光器的取向几乎同轴且垂直于油体积。
有了这个设置两张照片是采取定额补偿ΔT（图4）。避免反射光导致颗粒和周围产生的问题，以确定速度矢量，相机配备一个带阻滤波器，它允许切割出激光的波长之间的对比度低。荧光发色粒子吸收由激光发出的光并发射光以不同的波长，可以通过摄像机看到。其结果是，反射光都没有看到由相机不过荧光发色粒子是重要的，以确定该油流的速度。
为解释的图像被划分成部分图像作为矢量计算（图5）提供了基础。该矢量被计算每个局部图像并最终结合到整个画面的矢量中。
测量数据的整个分析示于图6使用以1000rpm和1.5l/min的油流的旋转速度的润滑离合器系统的例子。采取的CCD相机各图中由16001200像素（图6，左图）。在此测试装置的每个像素代表具有长度和宽度为16毫米的离合器系统的一个矩形。为32×32像素（512×512平方毫米）的互相关矩形被取（图6，中间）。出这两个影像的生成的矢量场的矢量（图6，右图）。
2.2 多片式离合器试验台
图7示出了用于本文中所示的所有实验研究的多片式离合器试验台。测试装备了两个电动马达，以实现摩擦和计数板的旋转速度不同。离合器系统是通过内部和外部的载体整合到试验台上，并且由液压缸驱动。所呈现的实验研究都进行了使用配备有一个窗口计数板，以允许光进入摩擦接触。
2.3 多片式离合器
该多片式离合器系统由摩擦片与径向槽或划线槽。摩擦片具有80mm和108mm的外径的内径。径向槽摩擦片有1mm的深度和1.6mm宽15槽。整个沟面336 mm2和槽体积336mm3。摩擦板与交叉槽具有槽为5.5mm，1mm的宽度和0.25mm的深度的距离。这导致约1365mm2的槽表面和341mm3的槽体积。
3. 理论
散热装置的能量输送，由于温度差。有三个相关的机制：导通、对流、放射线。
这项工作中对流是重点，因为它是关于一个离合器系统内热传递的主要影响。因为散热的复杂机制是一种现象学式的计算，适用于大多数情况。方程（Eq（2））表示操作参数，所述离合器系统和离合器组件的材料特性与几何形状和油之间是相互依赖性。
可以看出，通过对流热的传递是由油的流速影响。油流，因为有两个非常重要的影响。散热系数是取决于流体中固体表面接触的边界层上。由于更加动荡的油流增加油速度影响散热系数。在另一方面，增加油的流动导致油和离合器部件之间有较短的接触时间。这可能导致一个槽不能完全充满油，将其用于热传递的生成和减少热流减小面积。因此次参数作为离合器系统的油流量和旋转速度在实验研究范围内变化，以加深有关操作期间油流速槽的填充认识。
Eq.(2) 因为热传递的对流。
图8所示出带有油的一个离合器压盘的槽，由于槽的阻力有油的内载体（1和2之间）中保留（2和3之间）。内载体由于油离心力作用导致点2处的压力。通过凹槽增加油的流量使压力越来越大。另一方面流动阻力取决于沟槽范围内的油的流量。这意味着槽的内载体范围内只是完全充满油的状态。油的保持在很大程度上取决于流动性和凹槽设计。因此，由于油保持槽的压力和流动阻力之间的平衡状态取决于槽的设计和操作条件如转速为止。
Fig.8. 完全充满了油的摩擦片与径向槽。
Fig.9. 摩擦片与径向槽，1000RPM，1.5l/min。
Fig.10. 摩擦片与径向槽，1000RPM，3l/min。
4 结论
在第一个实验中进行了使用一个摩擦片与压盘和不同油流入每一侧15 的径向凹槽。它可以看出，在1.5升/分钟（图9）油流速结果是填充了部分沟槽。随着油流速3升/分钟（图10）槽完全充满油。以3升/分钟和4.5升/分钟（图11）比较油流速，可以看出，从大约1.1米/秒油速增加的最大速度，以达2米/秒。旋转速度从1000增加到2000转导致一个接近无油的槽（图12）。
不断增长的油的流量可达9升/分钟（图13）不会导致凹槽完全充满油。为了得到完全充油的凹槽油的流量必须进一步增加。
摩擦片与交叉沟槽显示了在完全填充凹槽的条件下（图14）。提高油流量从1.5至3升/分钟导致速度的增加（图15）。值得注意的是，速度增加仅发生在径向导向槽。切向导向槽显示油速度影响的很小。
Fig.11. 摩擦片与径向槽，2000RPM，4.5l/min.
Fig.12. 摩擦片与径向槽，2000RPM，1.5l/min.
Fig.13. 摩擦片与径向槽，2000RPM，9l/min.
Fig.14. 摩擦片与交叉沟槽，2000RPM，1.5l/min的油流。
Fig.15. 摩擦片与交叉沟槽，2000RPM，3l/min的油流。
Fig.16. 使用陶瓷作为摩擦材料的多片离合器。
5 讨论
根据连续性，可以得出结论，增加油的流量与部分填充槽的主要影响填充所述的槽（图9和10）。这的结果几乎恒定的雷诺数和努塞尔数与常数的散热系数，作为一个结果。增加油的流量与完全填充凹槽导致速度的增加（图10和11）。雷诺数和努塞尔数以及散热系数都在增加。
在切向导向凹槽内显示几乎恒定的流速与产生恒定雷诺数和努塞尔数以及热传递系数作为结果（图14和15）。聚焦径向槽内交叉槽可以看到一个类似的行为在径向槽（图14和15与图10和11比较）。
如图所示（式2）对流换热传递是受散热系数和散热面积的影响。增加油的速度导致散热系数的增大。另一方面在润滑离合器系统的槽内油速度高时由于连续性槽的填充减少，因此减小散热面积。这两种效应相互连接对有关对流冷却的相对影响。这两种效应都是重要的影响，问题依然存在。但必须指出，下列调查仅是本文讨论的范围内来回答这个问题。
如图16所示出了使用陶瓷作为摩擦材料的多片式离合器系统。根据陶瓷材料的高强度，有可能增加槽区。这个系统允许不同沟槽填充油的速度在一个巨大的范围。摩擦材料的变化，如进一步影响是不是本文的重点。
该系统采用一个外载体与油出口的耐油性。使用此测试装置就可以实现完全充油槽（图17，左进一步称为流动阻力），以及部分填充的沟槽（图17，右进一步称为自由流动）。图17示出两个摩擦元件之间被聚焦的油填充的区域。
如图18所示先进陶瓷多片离合器的实验结果。两个系统都使用完全相同的部件。这两种系统都在相同的工作条件下运行在0.093 W/mm2摩擦功率与石油相同流量（每个摩擦片0.5升/分钟）和相同的旋转速度（1090转内的载体，136转外载）。在这两种系统是在环境压力油通过内载体。该油通过离心力加速进入径向方向。系统之间的唯一区别是外载体的流动阻力。一个系统使用的外载一个合适的流动阻力来实现完全充满油槽，如图17左侧的所谓的流动阻力。其他系统具有非常低的流动阻力的外载，无油流通过离合器系统启动，如图17在右边所谓的自由流动。
自由流系统：由于低流高阻油的速度是可能的。由于连续性，只有一小块体积的槽是油填充。
流动阻力系统：由于高流动性非常低的油的速度为径向方向是可能的，但槽注满油。
钢板的温度过程测量使用图18所示热电偶的滑动操作。摩擦片开始增加到70°C油的入口温度被增加，最终达到接近平稳的温度。这意味着公式（1）中的时间依赖内在能量是不相关的。其结果是，所有由摩擦产生的热量被传递到油。这就是为什么在钢板的测定温度可以被看作是关于散热的指标的原因。较高的温度意味着低效率的热传递。
Fig.17. 使用陶瓷完全充油槽的多片离合器（1ooorpm，1.5l/min）。
Fig.18. 多碟离合与陶瓷比传统的离合器系统。
6 结论
在本文中提出了一种方法，通过润滑离合器系统，以确定油的流量。进行的调查显示，这取决于凹槽设计油的分布急剧的变化。它已经表明，热散递比油的速度更受填充凹槽的影响。在实验研究范围内增加凹槽的区域会使散热增加，如图所示。因此，显示了先进陶瓷增加的散热和提高润滑的作用。
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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