1、06FTM10Fabrication, Assembly and Test of a High Ratio, UltraSafe, High Contact Ratio, Double Helical PlanetaryTransmission for Helicopter Applicationsby: F.W. Brown, M.J. Robuck, M. Kozachyn, J.R. Lawrenceand T.E. Beck, The Boeing CompanyTECHNICAL PAPERAmerican Gear Manufacturers AssociationFabricat
2、ion, Assembly and Test of a High Ratio, UltraSafe, High Contact Ratio, Double Helical PlanetaryTransmission for Helicopter ApplicationsFrederick W. Brown, Mark J. Robuck, Mark Kozachyn, John R. Lawrenceand Timothy E. Beck, The Boeing Company, Rotorcraft DivisionThe statements and opinions contained
3、herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractAn ultra-safe, high ratio planetary transmission, for application as a helicopter main rotor drive, has beendesigned, fabricated and tested under the spon
4、sorship of NRTC-RITA. The anticipated improvementsoffered by this new planetary transmission are reduced weight, reduced transmitted noise and improvedfail-safety. This paper discusses the fabrication assembly and test results for the subject planetarytransmission. Thedesignandanalysisofthistransmis
5、sionsystemhavebeendiscussedinapreviouspaperpresented at the AGMA FTM in 2004.The ultra-safe, high ratio planetary transmission design utilizes a compound planetary configuration with a17.5:1reductionratiowhichwouldreplaceaconventionaltwostagesimpleplanetarytransmission.Thenewdesignusesultra-safeprin
6、ciplessuchassplit-torquepathsandhighcombinedcontactratiogearing.Doublehelical gears in the planet/ ring meshes balance axial tooth forces so that axial bearing reactions are notrequired. The spur gear sun/planet meshes are staggered to achieve a compact spatial arrangement.Fabricationandassemblyofth
7、ecomponentsforthistransmissionarecomplicatedbytheirconfiguration. Thegrinding process for the helical gears must use small diameter wheels due to the proximity of the adjacenthelix, since most the gears in this configuration are integrated designs. Assembly procedures also requirespecial considerati
8、on because of the integrated design and helical gears. Test results are presented tosupport the goals of this project, including, concept verification, weight reduction, noise reduction anddetermination of the operating characteristics of the test transmission.Copyright 2006American Gear Manufacture
9、rs Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October, 2006ISBN: 1-55589-892-01Fabrication, Assembly and Test of a High Ratio, Ultra-Safe, High Contact Ratio,Double Helical Compound Planetary Transmission for Helicopter ApplicationsFrederick W. Brown, Mark J. Robuck, Mark
10、Kozachyn, John R. Lawrenceand Timothy E. Beck, The Boeing Company, Rotorcraft DivisionIntroductionAn ultra-safe, high ratio planetary transmission, forapplicationasahelicoptermainrotorfinaldrive,hasbeen designed, fabricated and tested under thesponsorship of National Rotorcraft TechnologyCenter - Ro
11、torcraft Industry Technology Associa-tion (NRTC/RITA). The improvements offered bythis new planetary transmission are reducedweight,reducednoiseandimprovedfail-safetyandefficiency. This paper discusses the fabrication, as-sembly and testingof theimproved planetarytrans-mission. The design and analys
12、is of thistransmissionsystem have been discussed in a pre-vious paper presented at the AGMA FTM in 20041.An existing helicopter rotor transmission planetarydrive served as the baseline for comparison to theimproved transmission design. The existing CH47system utilizes a two-stage conventional spur g
13、earplanetary design with fixed internal ring gears.Torque is supplied to the first stage sungear that,inturn,mesheswithfourplanetgears.First stageout-put is via the planet carrier that drives the secondstage sun gear. Thesecond stagesun mesheswithsix planets and the second stage carrier drives thehe
14、licopter rotor shaft to turn the helicopter main ro-tor blades. This two-stage planetary provides a re-duction ratio of 17.47-to-1.Thenewdoublehelicalplanetary(DHP) systemde-sign uses a compound planetary arrangement withinnovations such as staggered planets and highcombined contact ratio gearing in
15、 a unique configu-ration. Double helical gears in the planet/ ringmeshes balance axial tooth forces so that axialplanet bearing reactions are not required. Thespurgearsun/planet meshesare staggeredto achieveacompact spatial arrangement. The sun gear is fullyfloating. Proof-of-Concept or demonstratio
16、n test-ing of a full scale prototype DHP transmission hasrecently been completed. This testing has demon-strated successful operation of the DHP transmis-sion. Preliminary evaluation of the data recorded inthetestsuggeststhatreducedweightandimprovedefficiency have been achieved. These parameterswill
17、 be investigated in further testing.Description - Double Helical PlanetaryTo transcend thelimitations ofcurrent planetaryde-signs1,andtoinvestigateimprovedgeararrange-ments for helicopter main rotor drives, a high ratio,Ultra-Safe, high contact ratio, staggered and inter-meshed planet, double-helica
18、l compound epicyclicgear system concept was developed. The im-proved transmission is configured as a single stagecompound planetary with an axially staggered, in-termeshed,spurgearinputmeshanddoublehelicaloutput mesh with an overall ratio of 17.5-to-1. Thisratio is approximately equivalent to the ex
19、istingbaseline transmission, which has a two-stage sim-ple planetary system described above. The DHPgearsweresizedforthesamepowerandspeedop-erating conditions as the baseline design, 4500 HPat 225 RPM (output). The core DHP transmissionconfiguration is shown in Figure 1.Theuniquefeaturesofthisplanet
20、arysystemaretheuse of double helical gears for the final mesh andthe axially staggered, intermeshed spur gear con-figuration, which permits theuse ofsix planetsrath-er than three, for greater power density. The overallspatial arrangement is slightly larger than the base-line two-stage planetary syst
21、em; however theweight of the system is less.A capacity limiting factor of the simple planetary ar-rangement is the number of planets that can be ac-commodated within the internal ring gear diameter.Notethatthesun-planetmeshinacompoundplan-etary is not restricted to fit within the internal ringgear d
22、iameter. This means that the sun-planet en-velopemayberadiallylargerthaninasimpleplane-tary design. With the compound planetary,“staggering” the planets can circumvent anotherlimitation and substantially increase capacity. In a2Figure 1. Compound planetary transmission configuration(with and without
23、 ring gear installed)staggeredarrangement,the sungear islengthenedto allow it to mesh with staggered planetary gears.This nearly doubles the number of planet gearswhich can fit within the compound planetary, result-ing in significantly higher capacityand powerdensi-ty for a given gearbox envelope. A
24、 fully floating sungeardesignwasusedtoaidinuniformload-sharingamong the planet gears.Theuseofdoublehelicalgearsinacompoundplan-etary arrangement is another unique feature of thisdrive. Double helical gears are used extensively inheavy industry like mill drives. One benefit of thedouble helical arran
25、gement is increased total con-tact ratio due to the action of the helix angles in thedoublehelicalgears.Theincreasedcontactratiore-sults in higher mesh load capacity and reducesmesh-generated noise. Since the thrust loads de-veloped on each helix within the double helical gearare oriented in opposin
26、g directions, the net axialload from a double helical mesh is zero. This per-mits a simpler support bearing arrangement wherelarge axial load capacity is not required.ComponentweightsfortheDHPconfigurationweredetermined and compared with the existing base-line planetary. A weight saving of 90 lbs wa
27、s identi-fied for the DHP when compared to the baselinetwo-stage simple planetary components as shownin Table 1. This is a 12.7% weight reduction for theDHPcomponentscomparedtothebaselinedesign.Thisrepresentsasubstantialimprovementinpowerdensity which is due only to the DHP configuration,independent
28、 of other technology improvements. Itshould be noted that the incorporation of technolo-giestoimprovegeartoothloadcapacitywouldhaveadditive effects on the power density improve-ments. Weight reduction technologies applied tonon-gear components, such as ceramic rolling ele-ments in the planet and sha
29、ft support bearings,would also further reduce the weight. It should alsobenotedthattheweightcomparisonisbasedontheweightoftheprototypetestcomponents.Thesetestcomponents were not fully optimized for minimumweight due to the limited scope and budget of thisproject.Itmaybepossible,withadditionaloptimiz
30、a-tion effort, to further increase the weight reductionrealized with the DHP design.Table 1. Weight comparison of baseline and DHP design planetary componentsDesign Baseline Planetary DHPWeight of planetary components 708 lb 618 lbWeight reduction for DHP design - - 90 lbPercent weight reduction for
31、 DHP design - - 12.7 %3Gearbox FabricationFabrication of the components for the prototypeDHP gearbox involved many challenges. All mainpowergearswerefabricatedusingaerospaceprac-tice. Gears were fabricated from aerospace quality9310 alloy steel. Gear teeth were carburized, hard-ened and ground. Stan
32、dard aerospace post-grind-ing processes, such as shotpeening and NDTinspections, were employed. Gear teeth weremanufactured to tolerances equivalent to AGMAQuality 12, with tip and root modifications appropri-ate for the expected load conditions. Other techni-cal challenges encountered with the fabr
33、ication ofthe gearbox components included:Complexity of the one piece planet carrier/ shaftcomponent required significant amount of machin-ingtime ona relativelylarge component.Innovativefixtures and machining processes were required toproduce this part. The existing baseline transmis-sion uses an i
34、ntegral rotor shaft / planet carrier, andtherefore, a similar design approach was selectedfor the DHP design. This part could be designed asa two-piece splined assembly thereby avoidingsome of the complexity associated with the one-piece design.Grinding operations were complicated by thedouble helic
35、al configuration, as expected, and thespacebetweenopposinghelicesonthedoubleheli-cal gears limited grinding wheel size and tool life.The aisle width between the helices on the internalring gear was 0.6 inch and between the helices ontheplanetitwas0.55inch.Forfinalgrindingofthesegears, 1.9 inch diame
36、ter aluminum oxide wheelswere selected, as illustrated in Figure 2. The grind-ing wheel was mounted ona beltdriven spindleandit was noted that this was not the ideal solution forgrinding thesecomponents ina productionenviron-ment. Improvementscanbemadetothisapproach,including more robust tooling, la
37、rger spacing be-tween opposing helices, or possibly as an alterna-tive, joined or welded helical gearsGreater than anticipated distortions during carbu-rization and heat treatment required additionalstock removal from ring gear. Alternate heat treatmethods, development of specific (for the applica-t
38、ion) quench process tooling, heat treatment simu-lationandanalysis,areafewapproachesthatcouldbe utilized to deal more effectively with this issue infuture products.Figure 2. Grinding wheel clearance forstaggered double helical tooth arrangementManufacturingtolerancesandstructuraldeflectionsof the ge
39、ars and shafts can have a significant effecton the effective load sharing among planet gears.Accordingly, an additional tolerance requirementwas established for the angular indexing relation-ship of the planet gear teeth. This index tolerancecontrolled the location of the planet spur gear teethrelat
40、ive to a datum established by the helical gearteeth. The tolerance allotted for gear tooth indexingwas considered very tight by the fabricators. Addi-tionally, the long and short planet shafts were de-signed to have the same torsional “wind-up” underload so that the gear teeth wouldshare loadequally
41、between the long and short planets.Photographs of some parts during fabrication areshown in Figures 3 though 5.Figure3. Sungearsearlyinfabricationprocess4Figure 4. Compound planet gearFigure 5. Double-helical internal ring gearGearbox AssemblyTesting was to be conducted in a back-to-back ar-rangemen
42、t, therefore requiring two DHP transmis-sions, one designated as the test transmission theother designated as the slave.As the major components were completed, thepro-cess of assembling the two prototype DHP trans-missions was initiated. Installation of the taperedroller bearings onto the carriersha
43、ft wascompletedfirst. The carrier and bearing assembly was theninstalled into the welded structure which supportedthe transmissions. The tapered bearings wereshimmed to obtain the proper setting. Once propershim size was established, the carrier shaft was re-moved so the planet gears could be instal
44、led withthe ring gear.Figure 6. Carriers with tapered bearingsinstalledA key concern with the DHP transmission was theassembly procedure for the staggered compoundplanets.Toaddresstheseconcerns,adetailedCADmodel of the components was used to simulate theassemblysequenceandeliminatepotentialinterfer-
45、ences. The study of the assembly sequence wasimportant for this project since the sun gear, planetgears and mating ring gear are all of single partconstructionInitially,thesuppositionwasthattheringgearwouldneed to be a two-piece design inorder toassemblethe gearbox, because of the double helical gea
46、r ar-rangement.Asequencewasdevisedthatallowsas-sembly of the gearbox with one-piece ring gearconstruction. The result is reduced weight and few-er dynamically loaded joints, which are often prob-lematic with instances of fretting and wear. Figure7includes frames from the assembly study showingsequen
47、tial installation steps for a long planet gear.CAD modeling proved that the components couldbe assembled prior to building hardware.Figure 7. Assembly sequence study showing installation of long planet5The assembly sequence was verified with actualDHP transmission components. Installation of theplan
48、ets into the carrier and double helical internalring gear was accomplished without difficulty. Fig-ure 8 shows the planets installed into carrier and in-ternal ring gear.Figure 8. Planets installed into ring gearThe planet gear and ring gear sub-assembly werethen installed back into the welded suppo
49、rt struc-ture.Asecondgearboxwasassembledinthesamemanner. The covers were not installed in order toverify fit and function, as seen in Figure 9. Oncethesun shaft and the instrumented coupling (shownwith bubble wrap) were installed, and alignmentmarks made for reassembly at the Ohio State Uni-versity test facility, the gearbox housing coverswere installed, as shown in Figure 10.Figure 9. Gearboxes assembled into the testarrangement (housing covers not installed)TestingThe DHP transmission system was successfullyrun in a “proof-of-concept”
