04FTM13

Superfinishing Motor Vehicle Ring andPinion Gears

by: L. Winkelmann, J. Holland and R. Nanning, REM Chemicals, Inc.

TECHNICAL PAPER

American Gear Manufacturers Association

Superfinishing Motor Vehicle Ring and Pinion Gears

Lane Winkelmann, Jerry Holland and Russell Nanning, REM Chemicals, Inc.

[The 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, themotor vehiclemarket is focusing on ”lubed for life” differentials requiring no service for the life of thevehicle. Still, differentials are prone to develop problems of one sort or another since they are used to transmita heavy torque through a right angle. Oneweak point in the differential is the ring and pinion gearset. As such,a proper break--in period is essential to attain the required service life. Break--in is an attempt to smooth thecontact surfaces of 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 damage occurs since break--in always results in stress raisers, metal debris and an extremetemperature spike. Break--in and its negative effects can be eliminated with chemically accelerated vibratoryfinishing. When this method is used to superfinish ground (AGMAQ10) or lapped (AGMAQ8) ring and piniongearsets to less than 10min.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 preserving 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 meets 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 2004

American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314

October, 2004

ISBN: 1--55589--836--X

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Superfinishing Motor Vehicle Ring and Pinion Gears

Lane Winkelmann, Jerry Holland and Russell Nanning, REM Chemicals, Inc.

Introduction

Break--In Process

Vehicular differentials are apt to develop problemsof one sort or another since they are used to trans-mit a heavy torque through a right angle. A differen-tial consists of a ring gear, pinion gear, side gears,spider gears, and bearings. See Figure 1. The spi-ral bevel or hypoid gearsets can be a weak point inthe differential since they need to withstand largesliding pressures and shock loading. Over theyears, many improvements have been made to dif-ferentials such that now many require no mainte-nance (i.e., “lubed for life”). New ring and pinion

gears are not normally ground after carburization,but rather are lapped at the factory and maintainedas a matched gearset. Lapping partially correctsthe distortion which occurs during carburization,and therefore somewhat reduces the operatingtemperature, wear and noise. It is impractical, how-ever, to perform the lapping under the same loadsas thosewhichare experiencedunder actual drivingconditions. Therefore, ring and pinion gearsetsmust always go through a “break--in” cycle, which isprofessed 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, andproper break--in results in a differ-ential lasting, 180,000 miles.

Key1 Ring2 Pinion3 Shims4 Housing5 Side gears6 Spider gears

Figure 1. Exploded view of a differential pointing out the various parts discussed in this paper.

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Break--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 during this process until a lower and rela-tively stable surface roughness is reached. Duringthe break--in cycle, it is hoped that the lubrication ofthe 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 isformed on the surface between the gear teeth. Thisfilm is referred to asHydrodynamic or Full FluidFilmLubrication, 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.As a load, however, is placedon thegearset, the hy-drodynamic layer decreases. At the same time, thetemperature rises and the viscosity of the lubricantdecreases, which further decreases the film thick-ness. As the load and/or temperature continue toincrease, the lubricant film becomes too thin to pro-vide total separation. Contact between the peak as-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 isan attempt to maintain the temperature low enoughto provideboundary lubrication until the peak asper-ities are worn away leaving the lower and relativelystable surface roughness on the contact surfaces.

In order to understand the shortcomings and mis-conceptions concerning break--in, it is worthwhile tobriefly examine what advice the experts are givingto theenduser. Althougheveryexpert hashis orherown recipe for break--in, the following is fairlytypical:

All new ring & pinion sets run hot until they are“broken in” and in some situations they can runhot enough to break down the gear oil anddam-age the gear set. Some of those situations are:

S Towing

S Tall tires

S Heavy loads

S High numeric gear ratios (4.56 & up)

S Motorhomes

New gears are lapped at the factory but someare lappedmore than others and even with lap-ping they are still not lapped under the samepressures that driving creates. The loads gen-

erated while driving force any microscopic highspots on the gear teeth back into the surface ofthe metal. This is called ”work hardening”.Work hardening is similar to forging in the waythat it compresses the metal molecules into avery compact andhard formation. This canonlybe accomplished if the metal surfaces are lubri-cated and the temperature is not hot enough tochange the molecular structure due to the heatalone. If the temperature of the metal gets hotenough to change the molecular structure it willsoften the surface instead of hardening it. Thismay seem like a balancing act but it all happenseasily & passively as long as the oil keeps thegear cool while it is breaking in. All new gearsets require a break--in period to prevent dam-age from overheating. Usually 500 miles willbreak--in the gears but until then, you want acool rear end. The greatest damage resultswhen a new ring & pinion has been run for sev-eral miles during the first 500miles and the oil isvery hot. Any heavy use or overloading at thistime will cause irreparable damage to the gearset. So all this means keeping your rear endcool.

During “break--in” cycle, it is desirable to run thegears under light loading so that the differentialruns cool. During this period, it is hoped that themicroscopic high spots on thematinggear teethare flattened and worked back into the surfaceunder actual driving conditions causing workhardening. [1]

Break--In Misconceptions and Problems

Clearly then the differential break--in process onlyprovides a partial solution to curing the problem,and has several serious and often ignored misun-derstandings and disadvantages. First, thesegears are typically case carburized to a high hard-ness, and therefore the peak asperities cannot bework hardened to a smooth surface during run--in.Instead the peak asperities are abraded away re-sulting inmetal debris which is always found in useddifferentials upon inspection. This debris is not onlydamaging to the gears but also to thebearings. Thewind turbine industry, for example, has recom-mended a 3.0 micron filtration system for its lubri-cants since it was discovered that even 10 micronparticles causepremature gear/bearing failures. [2]If metal debris is a serious problem in filtered lu-brication systems, it is not surprising then that it iseven more problematic for systems such as differ-entials where the oil is recirculated by the ring gearand flung over all the parts without being filtered.

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Furthermore, at the microscopic level the run--inabrading process consists of micro--cutting, micro--plowing, and micro--cracking, resulting in the cre-ation of stress raisers setting the stage for future fa-tigue failure through contact fatigue.

Second, many vehicles which experience highloads at relative low gear speeds (e.g., buses, rec-reational vehicles, and off--highway equipment) areplaced in immediate service such that their differen-tials never have the luxury of going through the rec-ommended break--in process. Such vehicles oftenexperience high loading and shock loading, where-by theoperating temperature can increase to apointwhere the gear oil is non--functional as a result of itsreduced viscosity or degradation. Premature gear-set failure then occurs.

Third, break--in does little to remove the distressedmetal at the surfaceof gears. Surface stress raisersare caused by heat treatment and residual machin-ing lines, which serve as the initiation points for fu-ture wear and fatigue failure.

In spite then of all the advances in gear manufactur-ing and lubrication, there are still problems with ringand pinion failures. What is needed is a practicalway to remove the peak asperities from the gearsetwithout affecting the contact pattern such that bothfriction and damaging metal debris are reducedand/or eliminated. Thesegearsetswould requirenobreak--in and could be used immediately for highload service.

The Superfinishing Challenge

Chemically accelerated vibratory finishing, hence-forward referred to as superfinishing is routinelyused on aerospace spiral bevel gears (AGMAQ12+). Since the flanks are typically ground afterheat treatment to a 12 min. Ra, little stock needs tobe removed to superfinish such gears to a desirable3.0 min Ra final surface finish. As was previously re-ported, these superfinished gears maintain theircritical geometrical tolerances. [2] Superfinishedaerospace spiral bevel gears experience hydrody-namic or full fluid film lubrication immediately afterbeing placed in service. It is well documented thatthese gears have significantly lower wear, noise/vibration, and operating temperature as well as anincreased service life. [4] [5] [6]

Likewise, for over ten years, the motorsports indus-try has utilized superfinishing on high performancering and pinion gearsets (AGMA Q10) typically

ground to a starting 25 min. Ra. These high perfor-mance gears are superfinished to approximately10.0 min. Ra and in certain venues to as low as 1.5min. These motorsport gears have been widely rec-ognized for their enhanced durability and efficiencythroughout the industry.

On the other hand, ring and pinion gears used formotor vehicles (AGMA Q8) are seldom ground inthe U.S. after carburization for economic reasons,but instead are lapped and maintained as amatchedgear set. Their starting surface roughnesstypically has a 60 min. Ra in the contact area. In Eu-rope, however, ring and pinion gears are precisionground to a 30 min. Ra after carburization. By grind-ing to the final net shape, the need to keep the ringand pinion together as a matched set is eliminated.This precision grinding has recently beenintroduced to the North American market.

Until recently, superfinishing motor vehicle ring andpinion gearsets had two major problems. First,since the starting surface is much rougher than thatfor ground aerospace gears, much more stock hasto be removed to achieve a smooth surface. Sincethe stock removal was not uniform across the flank,however, therewas an increased transmissionerrorresulting in increased noise. Interestingly, the con-tact pattern did not drift after superfinishing, and socould not be used to flag changes in transmissionerror. Second, the processing time to superfinish aring and pinion gearset using chemically acceler-ated vibratory finishingwas too long for it to be com-mercially viable for high production manufacturing.

Experimental

Description of Ring and Pinion Gearset

For the majority of work in this study, Yukon DANA44 ring and pinion gearsets were used. This is avery popular and readily available gearset used invarious vehicles since its introduction in 1955. Itwas also selected since it matched an existinghousing of the single flank test rig used in this study.TheDANA 44 ringand pinionused in this study con-sists of a 46--tooth, 10--bolt hole, ring gear and a 26spline, 13--tooth pinion gear, resulting in a 3.54 gearratio. The ring gear has a diameter of 8.5 inches,and the pinion has a diameter of 1.376 inches. Thepinion offset is 1.50 in. The ring and pinions are amatched set which have been case carburized andlapped for correct contact patterns.

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Superfinishing Using Chemically AcceleratedVibratory Finishing

Details of using chemically accelerated vibratoryfinishing have been published elsewhere. [7] Thefollowing is a brief summary of the technique. Thesuperfinishing is produced in vibratory finishingbowls or tubs. An active chemistry is used in the vi-bratory machine in conjunction with high density,non--abrasive ceramic media. When introducedinto the machine, this active chemistry produces astable, soft conversion coating on the surface of themetal gears being processed. The rubbing motionacross the gears developed by the machine andmedia effectively wipes the conversion coating offthe “peaks” of the gears’ surfaces, but leaves the“valleys” untouched. No finishingoccurs whereme-dia is unable to contact or rub. The conversion coat-ing is continually re--formed and rubbed off duringthis stage producing a surface smoothing mecha-nism. This process is continued in the vibratoryma-chine until the surfaces of the gears are free of as-perities or until the surface attains the desired levelof finish. At this point, the active chemistry is rinsedfrom the part and the gears are dipped in rust pre-ventive.

Details of Processing Procedure

The Yukon DANA 44 ring and pinion gearsets werefixtured as shown in Figure 2 in an early attempt tomaintain the lapped ring and pinion together as apair. This fixture is rugged and protects the threads

on the pinion from damage, and also prevents me-dia from lodging in the tappedholes on the ring gear.Since that time, other proprietary devices havebeen designed, which have the same features, butare more applicable for handling high productionvolumes.

The gearsets used in this study wereprocessed in a3--ft3 vibratory bowl using a newly developed highspeed gear finishing process, which has a muchhigher stock removal rate than that previously avai-lable. Two different medias were used to superfin-ish the gearsets to determine the effect of mediasize and shape on the uniformity of stock removal,contact pattern and ultimately noise. Descriptionsof Media A and Media B are detailed in Figure 3.

In a previous project, Media A had been used to su-perfinish similar OEM gearsets to a 4.0 min. Ra. Al-though the operating temperature of this gearsetwas significantly reduced, the customer reportedthat superfinishing increased the noise level.Therefore, this test was designed to verify whetheror not Media A was the root cause of the problem.

Based on in--house process knowledge, it was an-ticipated that Media B would be less likely to alterthe gear profile. From the outset of this studythough, it was uncertain if it was possible to super-finish gears having a high starting roughness to a4.0 min. Ra without increasing the noise level.Therefore, Media B was used to process one gear-set to a 10 min. Ra, and another gearset to a 4.0 min.Ra.

Figure 2. Fixture used to superfinish and keep the lapped gearsets as a matched pair.

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Media ANon abrasive Ceramic Media

Mixture of:

S 6 mm x 10 mm tristarS 20 mm x 15 mm x 5 mm ellipse

Figure 3a. Media A

Media BNon abrasive Ceramic Media

Mixture of:

S 3 mm x 6 mm angle cut cylinders

Figure 3b. Media B

Two separate groups of gearsets were processedand analyzed. See Table 1 for details. Group I wastested at the Gear Dynamics and Gear Noise Re-search Laboratory at Ohio State University. Group

II was tested at The Gleason Works. Neither labo-ratorywas awareof theprocessing conditions or theexpected outcomes.

Table 1.

Group I Group IIGear Dynamics andGear Noise Research

Laboratory

The Gleason Works

S Lapped baseline. S Superfinished usingMedia A to a 4.0min. Ra.

S Superfinished usingMedia A to a 4.0min. Ra.

S Superfinished usingMedia B to a 10.0min. Ra.

S Superfinished usingMedia B to a 10.0min. Ra.

S Superfinished usingMedia B to a 4.0min. Ra.

S Superfinished usingMedia B to a 4.0min. Ra.

Uniformity of Stock Removal

Three different experimental methods were used todetermine the effect of superfinishing on gear ge-ometry: (1) Direct measurement of stock removalacross the flanks of the ring and pinion gearsets; (2)measurements of the contact patterns; and (3)single flank testing.

Direct Measurement of Stock Removal

Figure 4 shows the relative stock removal normal-ized to unity across the flank of the gearsets super-finished using Media A and Media B. From thesecharts, it is apparent thatMedia Adistorts theprofileby removing more stock from the flank of the gearnearer the tip than the root, but does not negativelyaffect the spiral. Therefore, it is expected that gearssuperfinished with this media mixture will have ahigher transmission error leading to an increase innoise. On the other hand, Media B does not distortthe spiral or the profile, but removes stock uniformlyfrom the tip to the root and across the spiral. Thesmall variations seen in the Media B charts are dueto slight measurement inaccuracies. Therefore, it isexpected that the transmission error will not be in-creased. This will be shown and discussed in moredetail later.

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Figure 4: Relative stock removal normalized to unity using Media A and Media B.

Contact Patterns

Group I contact patternsweremeasured for the fourgearsets to ensure proper alignment and position-ing. The gearsets were then installed in a DANA 44housing which had been modified for use in theLoaded Bevel Gear Test Rig at the Gear Dynamicsand Gear NoiseResearch Laboratory at Ohio State

University. General Motors marking grease wasused to coat the gearsets. They were then rotatedby hand in both the forward and reverse directionsuntil a clear contact pattern was developed on thering gear. The contact pattern for each gearset wasthen checked to determine if the superfinishing hadaltered or caused a contact pattern to become un-

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acceptable. Though there were some very slightdeviations from the baseline contact pattern, allcontact patterns before and after superfinishingwere found to be acceptable.Group II gearsets were superfinished identically tothose tested at the Gear Dynamics and Gear Noise

Research Laboratory. The contact patterns of be-fore and after superfinished gearsets were mea-sured at The GleasonWorks. Again, the laboratoryreported no change in the contact patterns after su-perfinishing. The contact patterns are displayed inFigure 5.

Figure 5. Contact patterns of Group II gearsets as determined at The Gleason Works.

Single Flank Testing

Single flank transmission error testing was con-ducted on Group I gearsets at the Gear Dynamicsand Gear NoiseResearch Laboratory at Ohio StateUniversity. Their Loaded Bevel Gear Test Rig was

used to measure the transmission error (TE) withthe gearsets mounted in an actual differential hou-sing. This was done in order to measure the TE un-der light load as well as under loading so that the ef-fect of friction on noise/vibration could also bedetermined. Unfortunately, technical difficulties

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were encountered such that the TE could only bemeasured under light loading. Only a ranking of theTEcould bederived from their data. A blind testwasconducted such that the testing laboratory did notknow the history of the gearsets. See Table 2.

Although variation in the test results were reportedfrom the assembly/disassembly and alignment pro-cesses, the rankings are noteworthy and expected.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 superfinishing with Media B hadthe lowest TE, and were even better than the rawlapped gear. At this time, there is no explanation forthis latter result.

In an effort to verify the previously measured noise/vibration results, TheGleasonWorksmeasured theTE on the Group II gearsets before and after super-finishingusing the552GleasonSingle FlankTester.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 increasesthe TE. On theother hand,Media Bhas proven thateven a 4.0 min. Ra can be achievedwithout any per-ceptible noise level. It is also clear that an accept-able contact pattern is no guarantee that the TEhasnot increased.

Table 2: Results of Single Flank Testing onGroup I gearsets at the Gear Dynamics and

Gear Noise Research Laboratory

Description of SurfacesTested

TransmissionError Ranking

Lowest Highest1 2 3 4

Raw Lapped Baseline 3Superfinished using MediaA to a 4.0 min. Ra.

4

Superfinished using MediaB to a 10.0 min. Ra.

2

Superfinished using MediaB to a 4.0 min. Ra.

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Figure 6. TE measurements of Group II gearsets by The Gleason Works.

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Performance Testing

Laboratory Testing:

Automotive OEM Ring and Pinion: Severalyears ago, ring and pinion gearsets were superfin-ished using Media A for an OEM automotive ap-plication to evaluate the effect of superfinishing onoperating temperature. This superfinished gearsetwas compared to a standard carburized and lappedgearset using the L--37 (ASTM D6121) Perfor-mance of Gear Lubricants at High Speed, LowTorque, Followed by Low Speed, High Torque. TheL--37 test is used by individual OEMs, the Military,and Federal Government, to measure five parame-ters that are the result of distress on gears. The re-sults are shown in Figure 7. The superfinishedgearset had a peak temperature of 124 °Cwhile thestandard gear had a peak temperature of 165 °C. Itis assumed that the slight temperature increase inthe initial phase of the testing of the superfinishedgearset is attributable to bearing break--in. The ab-sence of a large temperature spike during break--ineliminates thepossibility of any thermaldegradationof the lubrication. It is also indicative that the super-finished gearset does not generate damagingmetaldebris and will have significantly lower wearthroughout its service life. This same phenomenon

was observed a number of years ago for superfin-ished bearings by The Timken Company. [8] [9]

In a separate study [6], Sikorsky Aircraft Corpora-tion tested superfinished second stage spiral bevelgears (Q12+), third stage pinion gears and the bullgear of their S--76C+, LowNoiseTransmission toanRa of less than 4.0 min. The standard ground sur-faces of these gears have a nominal Ra of approxi-mately 15 min. The results of the standard two--hourAcceptance Test Procedure (ATP) are shown inFigure 8. This test is mandatory for all gearboxesprior to flight approval. As such, the baseline resultsshown are from three standard production gearbox-es. The superfinished gearbox was run through theATP three separate times. This is indicated by themultiple data points at the same torque loading. Itshould be noted that this test is conducted using anoil recirculation system and an external cooler. Thetemperature is measured on the outflow side.Again, it is seen that the superfinished gears had avery significant temperature drop in comparisonwith gears having the standard ground surface. Thesuperfinished gears showed no damage or wearupon final inspection. As a result of their 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.

Sump Temperature vs. Time

Figure 7. Sump Temperature (°°°°C) versus Time (seconds) for gearset with a standard lappedfinish versus a superfinished gearset.

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Figure 8. Main gearbox oil out temperature of a Sikorsky S--76C+ Low Noise Transmission duringtheir standard ATP test.

Field Testing

Heavy Duty Ring & Pinions: Ring and pinionsused in heavy axle vehicles can often experiencepremature failures. Asmentioned earlier, gears likethese, which operate under high loads at relativelylow gear speeds, typically experience boundarylubrication during their initial operation, and do nothave the luxury of going through a proper break--inperiod. Since mid--2003, more than 200 heavy axlering andpiniongearsetswere superfinished to solvea severe micropitting problem. Superfinishing hasnow been incorporated as the final production stepfor this application. Prior to installation, the gear-sets pass their contact pattern and transmissionerror acceptance tests.

NASCAR Racing Ring & Pinions: NASCAR ringand pinions (AGMA Q10) are subjected to extremeloads and shock loading during racing. These ringand pinions are lapped after carburization typicallyresulting in a25min. Ra. Today virtually all NASCARgearsets are superfinished to a 10 min. Ra to reducewear and to gain efficiency. Two gearsets wereobtained courtesy of TEX Racing. One was onlylapped, and the other was lapped and superfin-ished. Both went through a break--in cycle on adynamometer prior to being placed in service. Thebreak--in process is still done on the superfinished

ring and pinion gearsets only because the otherdifferential components are not superfinished. Aspreviously discussed the large break--in tempera-ture spike is absent for the superfinished gearset.Each has accumulated 2,000 miles in NASCARsanctioned races in differentials containing oil recir-culation pumps, cooling, filtration and magneticparticle separator systems.

Figure 9 is the profilometer traces and surfaceroughness parameters measured on the drive sidepinion of each gearset. It is evident that the super-finishedpinionhas a superior surface in comparisonto the lappedpinion. Whereas the lappedpinionhaslarge peak asperities remaining (Rp = 104 min.), thesuperfinished gearset is much smoother (Rp = 27.6min.). Similarly, the material ratio is vastly superiorfor the superfinished pinion. As discussedpreviously, the superfinished gearset will thereforecontinue to run longer, cooler and more efficientlybecause of the reduced friction.

As an indication of the acceptance of superfinishingin the racing industry, it is reported byTEXRacingofEther, North Carolina that approximately 85% ofCup level NASCAR ring and pinions are currentlysuperfinished. [10] As such, it is common to findused superfinished ring and pinion gearsets for saleby race teams. For example, the authorspurchased four used superfinished gearsets from a

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top Winston Cup racing team’s website(www.Roushracing.com). Each set comes com-plete with the racing history and miles completedprior to removal and sale. By contactingwww.Roushracing.com, the authors found that thegearsets are typically removedafter completing onerace and practice racing before the next. These arethen sold to the general racing public for two rea-sons: First, they are an inexpensive replacement

item for theRacingTeam andsecond, because theyare still perfectly fine for further use in other racingvenues. The examples purchased by the authorsdo not show any indications of wear or micropittingand in fact, the ring and pinions that have been runfor 800+ miles appeared no different than the onesthat have only been run for 100 --120 miles. Table 3gives a summary of the history of the four gearsetspurchased by the authors.

Figure 9: Profilometer traces of the post race condition of two similar pinion gears used in NAS-CAR sanctioned events. The top profile shows a standard lapped gear that has gone through anoptimal break--in cycle and completed a nominal distance of 2,000 miles of racing. The bottomprofile is of a ring gear superfinished to an Ra of approximately 10 min. after completing a

nominal 2,000 miles of racing. Gears courtesy of TEX Racing.

Table 3: Summary of the racing history of four used superfinished gearsets purchased by theauthors from Roushracing.com.

Set RaceLocation

MilesCompleted

Ratio Series Car # DateArchived

1 Dover 510 4.44 Winston Cup 99 10--23--03TB

2 NazarathRichmond

651531

4.71 Busch GrandNational

60 Not Available

3 Indy 565 3.75 Winston Cup 6 2--28--02 TB4 Talladega

Daytona63222472

3.10 Winston Cup 99 2--2--04

1 Used for practice, testing and/or qualifying.2 Used for the last race at Talladega and the first of the year practicing at Daytona

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A recent paper presented at the 2003 SAEPerformance Racing Industry (PRI) Conferenceand later published by Circle Track Magazine [11]documented the increased efficiency of a highperformance differential containing a superfinishedring and pinion gearset. The test specimens usedwere a standard quick change differential withstandard bearings and seals, and a quick changedifferential with low friction bearings, seals andsuperfinished ring and pinion gears known as a“Tiger” in the racing industry. This study used aDynojet Model 248 chassis dynamometer (as usedto monitor NASCAR Winston Cup cars) and aNASCAR Late Model with a 350 cubic inch enginerunning a two barrel carburetor. For this test, thedynamometer was used to measure thehorsepower as the RPM climbed and also thehorsepower during the coast--down. The goal wasto measure the maximum horsepower output of theengine on run--up in fourth gear and then theamount of resistance at two speed intervals, 85 and100 mph while the car was coasting. The run wasstopped after coasting down to 80mph. The resultsshowed an average gain of 14.25horsepower andareduction in parasitic friction losses through the rear

end by 50 percent at 85 mph and 52 percent at 100mph. These testing results are shown in Table 4.

Production Ready

Processing Times

Gearsets with two different starting surface rough-nesses were superfinished using Media B in a 3--ft3

vibratory bowl using a newly developed high speedgear finishing process, which has a much higherstock removal rate than that used for the aerospaceindustry where only small amounts of stock removalis necessary. The first gearset tested had a starting54 min. Ra and is representative of a typical carbu-rized and lapped gearset, while the second gearsethad a starting 35 min. Ra and would be similar to thesurface roughness recently advertised by a largeOEM which supplies ground ring and pinions to themotor vehicle industry. See Table 5 for the superfin-ishing process time and the final Ra achieved at thecontact area of the teeth. It was found that bothgearsets can be superfinished in less than 30 min-utes to a point where considerable performancebenefits will be realized.

Table 4: Results of chassis dynamometer testing of standard and low friction (superfinished)quick change differentials in a NASCAR Late Model car. [11]

Standard Quick ChangeBearings and Seals

Low Friction Bearings and Sealswith Polished Surfaces

Run #1 Run #2 Run #3 Run #4 Run #5 Run #1 Run #2 Run #3 Run #4 Run #5Max. HP 286.5 284.4 282.3 285.3 280.9 296.8 297.16 296.80 299.80 300.10Coast @85 MPH

N/A N/A 17.5 16.5 16.1 9.60 8.56 8.13 8.00 7.70

Coast @100 MPH

N/A N/A 24.0 25.5 22.3 13.40 11.66 10.97 10.67 10.40

Averages: Standard

Max. HP = 283.8885 MPH Coast = 16.70 HP

100 MPH Coast = 23.93 HP

Averages: Low Friction

Max. HP = 298.1385 MPH Coast = 8.40 HP

100 MPH Coast = 11.42 HPGains:

Maximum Horsepower = +14.25 (represents a 5% gain in HP)85 MPH Coastdown = (--) 8.30 HP (represents a 50% Reduction)

100 MPH Coastdown = (--) 12.51 HP (represents a 52% Reduction)

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Table 5: Times required to superfinish gear-sets with different starting surface roughnessusing Media B and the newly developed high

speed gear finishing process.

Starting Ra(min)

Final Ra(min.)

ProcessingTime

(minutes)54

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7. SuperfinishingGears ---- TheState of theArt,G.Sroka, L. Winkelmann, Gear Technology, Novem-ber/December, 2003.

8. A NewRolling Contact Surface andNo--Run--inPerformance Bearings, Zhou R.S., Hashimoto, F.;Proc. 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, www.texracing.com.

11. ChassisDynoTest, B. Bolles, Circle TrackMag-azine, December, 2003.