1、04FTM13Superfinishing Motor Vehicle Ring andPinion Gearsby: L. Winkelmann, J. Holland and R. Nanning, REM Chemicals, Inc.TECHNICAL PAPERAmerican Gear Manufacturers AssociationSuperfinishing Motor Vehicle Ring and Pinion GearsLane Winkelmann, Jerry Holland and Russell Nanning, REM Chemicals, Inc.The
2、statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractToday,themotorvehiclemarketisfocusingon”lubedforlife”differentialsrequiringnoserviceforthelifeofthevehicle. Still,differ
3、entialsarepronetodevelopproblemsofonesortoranothersincetheyareusedtotransmitaheavytorquethrougharightangle. Oneweakpointinthedifferentialistheringandpiniongearset. Assuch,a proper break-in period is essential to attain the required service life. Break-in is an attempt to smooth thecontact surfaces o
4、f the gears and bearings through controlled or limited metal-to-metal contact. Theroughness of the contact surfaces is reduced during this process until a lower and relatively stable surfaceroughness is reached. The lower surface roughness is advantageous, but irreversible metallurgical andlubricant
5、 damage occurs since break-in always results in stress raisers, metal debris and an extremetemperature spike. Break-in and itsnegative effectscan beeliminated withchemically acceleratedvibratoryfinishing. Whenthismethodisusedtosuperfinishground(AGMAQ10)orlapped(AGMAQ8)ringandpiniongearsets to less t
6、han 10 min.Ra, the life of the lubricant, bearings and gears is significantly increased. Just afew years ago, this technology was considered impractical for high production volume OEM ring and piniongearsets due to lengthy processing times. This superfinishing technology also had difficulties preser
7、ving thegeometry of rough lapped gears, which required more stock removal than finely ground aerospace gears(AGMA Q12+). As a result the transmission error of these gears was increased leading to unacceptablenoise. The superfinishing technology discussed in this paper overcomes these obstacles and m
8、eets theneeds of the motor vehicle industry. Gear metrology, contact patterns, transmission error and actualperformance data for superfinished gearsets will be presented along with the superfinishing process.Copyright 2004American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexand
9、ria, Virginia, 22314October, 2004ISBN: 1-55589-836-X1Superfinishing Motor Vehicle Ring and Pinion GearsLane Winkelmann, Jerry Holland and Russell Nanning, REM Chemicals, Inc.IntroductionBreak-In ProcessVehicular differentials are apt to develop problemsof one sort or another since they are used to t
10、rans-mitaheavytorquethrougharightangle. Adifferen-tial consists of a ring gear, pinion gear, side gears,spider gears, andbearings. SeeFigure1. Thespi-ral bevel or hypoid gearsets can be a weak point inthe differential since they need to withstand largesliding pressures and shock loading. Over theyea
11、rs, many improvements have been made todif-ferentials such that now many require no mainte-nance (i.e., “lubed for life”). New ring and piniongears are not normally ground after carburization,but rather are lapped at the factory and maintainedas a matched gearset. Lapping partially correctsthe disto
12、rtion which occurs during carburization,and therefore somewhat reduces the operatingtemperature,wearandnoise. Itisimpractical,how-ever, to perform the lapping under the same loadsasthosewhichareexperiencedunderactualdrivingconditions. Therefore, ring and pinion gearsetsmust alwaysgothrougha“break-in
13、”cycle, whichisprofessed by car experts as the magic potion forpreventing future failure. As one expert puts it, im-proper break-in results in a differential lasting90,000miles,andproperbreak-inresultsinadiffer-ential lasting, 180,000 miles.Key1 Ring2 Pinion3Shims4 Housing5 Side gears6 Spider gearsF
14、igure 1. Exploded view of a differential pointing out the various parts discussed in this paper.2Break-in is an attempt to create a smooth surfaceon the contact surfaces of the gears and bearingsthrough controlled or limited metal-to-metal con-tact. The roughness of the contact surfaceschanges durin
15、g this process until a lower and rela-tively stable surface roughness is reached. Duringthebreak-incycle, it is hoped that the lubricationofthe ring and pinion gearset is maintained. In fact,this is vital to the life of the differential. During theinitial start-up of the break-in cycle, an oil film
16、isformedonthesurfacebetweenthegearteeth. ThisfilmisreferredtoasHydrodynamicorFullFluidFilmLubrication, which completely separates the ringfrom the pinion so that there is no metal-to-metalcontact. As the speed of the ring and pinion in-creases, the hydrodynamic layer thickens as well.Asaload,however
17、,isplacedonthegearset,thehy-drodynamic layerdecreases. At thesametime,thetemperature rises and the viscosity of the lubricantdecreases, which further decreases the film thick-ness. As the load and/or temperature continue toincrease, thelubricant film becomes toothin topro-videtotalseparation. Contac
18、tbetweenthepeakas-perities occurs, which results in higher frictionalforces and the concomitant temperature rise. Thisis referred to as the Boundary Lubrication or ThinFilm Lubrication regime. The break-in process isanattempt tomaintain thetemperature lowenoughtoprovideboundarylubricationuntilthepea
19、kasper-ities are worn away leaving the lower and relativelystable surface roughness on the contact surfaces.In order to understand the shortcomings and mis-conceptionsconcerningbreak-in,itisworthwhiletobriefly examine what advice the experts are givingtotheenduser. Althougheveryexperthashisorherown
20、recipe for break-in, the following is fairlytypical:All new ring (2)measurements of the contact patterns; and (3)single flank testing.Direct Measurement of Stock RemovalFigure 4 shows the relative stock removal normal-ized to unity across theflank of the gearsets super-finished using Media A and Med
21、ia B. From thesecharts,itisapparentthatMediaAdistortstheprofileby removing more stock from the flank of the gearnearer the tip than the root, but does not negativelyaffectthespiral. Therefore,itisexpectedthatgearssuperfinished with this media mixture will have ahigher transmission error leading to a
22、n increase innoise. On the other hand, Media B does not distortthespiralortheprofile,butremovesstockuniformlyfrom the tip to the root and across the spiral. Thesmall variations seen in theMedia B charts areduetoslightmeasurementinaccuracies. Therefore,itisexpected that the transmission error will no
23、t be in-creased. This willbeshown anddiscussed inmoredetail later.6Figure 4: Relative stock removal normalized to unity using Media A and Media B.Contact PatternsGroupIcontactpatternsweremeasuredforthefourgearsets to ensure proper alignment and position-ing. Thegearsets weretheninstalledinaDANA44hou
24、sing which had been modified for use in theLoaded Bevel Gear Test Rig at the Gear DynamicsandGear NoiseResearchLaboratoryat OhioStateUniversity. General Motors marking grease wasused to coat the gearsets. They were then rotatedby hand in both the forward and reverse directionsuntil a clear contact p
25、attern was developed on theringgear. Thecontactpatternforeachgearsetwasthenchecked todetermine if the superfinishinghadaltered or caused a contact pattern to become un-7acceptable. Though there were some very slightdeviations from the baseline contact pattern, allcontact patterns before and after su
26、perfinishingwere found to be acceptable.Group II gearsets were superfinished identically tothosetestedat theGear Dynamics and Gear NoiseResearch Laboratory. The contact patterns of be-fore and after superfinished gearsets were mea-suredat TheGleasonWorks. Again, thelaboratoryreportednochangeinthecon
27、tact patterns aftersu-perfinishing. The contact patterns are displayed inFigure 5.Figure 5. Contact patterns of Group II gearsets as determined at The Gleason Works.Single Flank TestingSingle flank transmission error testing was con-ducted on Group I gearsets at the Gear DynamicsandGear NoiseResearc
28、hLaboratoryat OhioStateUniversity. Their Loaded Bevel Gear Test Rig wasused to measure the transmission error (TE) withthe gearsets mounted in an actual differential hou-sing. This was doneinordertomeasuretheTEun-derlight loadas wellas underloadingsothat theef-fect of friction on noise/vibration cou
29、ld also bedetermined. Unfortunately, technical difficulties8were encountered such that the TE could only bemeasuredunder lightloading. Only arankingoftheTEcouldbederivedfromtheirdata. Ablindtestwasconducted such that the testing laboratory did notknow the history of the gearsets. See Table 2.Althoug
30、h variation in the test results were reportedfrom theassembly/disassembly andalignmentpro-cesses, therankings arenoteworthy andexpected.The gearset with non-uniform stock removal bysuperfinishing with Media A had the highest TE.Interestingly, gearsets No. 3 and 4 with uniformstock removal by superfi
31、nishing with Media B hadthe lowest TE, and were even better than the rawlappedgear. Atthistime,thereisnoexplanationforthis latter result.Inaneffort toverify thepreviously measurednoise/vibrationresults,TheGleasonWorksmeasuredtheTE ontheGroupII gearsets beforeandaftersuper-finishingusingthe552Gleason
32、SingleFlankTester.The changes in transmission error (TE Before Su-perfinishing TE After Superfinishing) is shown inthe last chart of Figure 6.It is apparent that Media A significantly increasestheTE. Ontheotherhand,MediaBhasproventhatevena4.0min. Racanbeachievedwithout anyper-ceptible noise level. I
33、t is also clear that an accept-ablecontactpatternisnoguaranteethattheTEhasnot increased.Table 2: Results of Single Flank Testing onGroup I gearsets at the Gear Dynamics andGear Noise Research LaboratoryDescription of SurfacesTestedTransmissionError RankingLowest Highest1234Raw Lapped Baseline 3Super
34、finished using MediaAtoa4.0min. Ra.4Superfinished using MediaB to a 10.0 min. Ra.2Superfinished using MediaBtoa4.0min. Ra.1Figure 6. TE measurements of Group II gearsets by The Gleason Works.9Performance TestingLaboratory Testing:Automotive OEM Ring and Pinion: Severalyears ago, ring and pinion gear
35、sets were superfin-ished using Media A for an OEM automotive ap-plication to evaluate the effect of superfinishing onoperating temperature. This superfinished gearsetwas comparedtoastandardcarburizedandlappedgearset using the L-37 (ASTM D6121) Perfor-mance of Gear Lubricants at High Speed, LowTorque
36、, Followedby LowSpeed, HighTorque. TheL-37 test is used by individual OEMs, the Military,and FederalGovernment, tomeasure fiveparame-ters that aretheresult of distress on gears. There-sults are shown in Figure 7. The superfinishedgearset hadapeak temperatureof 124 Cwhilethestandardgear hadapeak temp
37、eratureof 165 C. Itis assumed that the slight temperature increase inthe initial phase of the testing of the superfinishedgearset is attributable tobearing break-in. Theab-sence of a large temperature spike duringbreak-ineliminatesthepossibilityofanythermaldegradationofthelubrication. It isalsoindic
38、ativethat thesuper-finishedgearsetdoesnotgeneratedamagingmetaldebris and will have significantly lower wearthroughout its servicelife. This samephenomenonwas observed a number of years ago for superfin-ished bearings by The Timken Company. 8 9In a separate study 6, Sikorsky Aircraft Corpora-tion tes
39、ted superfinished second stage spiral bevelgears (Q12+), third stage pinion gears and the bullgearoftheirS-76C+,LowNoiseTransmissiontoanRaof less than 4.0 min. The standard ground sur-faces of these gears have a nominal Raof approxi-mately15min. Theresultsofthestandardtwo-hourAcceptance Test Procedu
40、re (ATP) are shown inFigure 8. This test is mandatory for all gearboxespriortoflightapproval. Assuch,thebaselineresultsshownarefromthreestandardproductiongearbox-es. Thesuperfinishedgearbox wasrunthroughtheATP three separate times. This is indicated by themultiple data points at the same torque load
41、ing. Itshouldbenotedthat this test is conducted usinganoilrecirculationsystemandanexternalcooler. Thetemperature is measured on the outflow side.Again, it is seen that the superfinished gears had avery significant temperature drop in comparisonwithgearshavingthestandardgroundsurface. Thesuperfinishe
42、d gears showed no damage or wearuponfinalinspection. As aresult oftheir testing,Si-korsky has licensed this flight certified superfinish-ing technology. This data is presented here to ex-emplify that even ground spiral bevel or hypoidgearsets can realize huge performance benefitsfrom superfinishing.
43、Sump Temperature vs. TimeFigure 7. Sump Temperature (C) versus Time (seconds) for gearset with a standard lappedfinish versus a superfinished gearset.10Figure 8. Main gearbox oil out temperature of a Sikorsky S-76C+ Low Noise Transmission duringtheir standard ATP test.Field TestingHeavy Duty Ring Pr
44、oc. ATLE/ASME, Tribology Conference, Maui,HI, 1994.9. Bearing Surfaces with Isotropic Finish, F. Ha-shimoto, R. Zhou, K. Howlett, US Patent Number5,503,481, 993, Assigned to REM Chemicals, Inc.,1999.10. Roger Chilton (2004), TEX Racing, 2268 US220, Ether, North Carolina, .11. ChassisDynoTest,B.Bolles,CircleTrackMag-azine, December, 2003.
