車輛工程外文翻譯-先進(jìn)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(jìn),陶瓷,摩擦,材料,離合器,中的,潤滑,中文,4260,PDF,WORD 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 M,Reddyhoff T,Spikes HA.Thermal Behaviour of a Slipping Wet ClutchContact.Tribol