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1、06FTM10 Fabrication, Assembly and Test of a High Ratio, Ultra Safe, High Contact Ratio, Double Helical Planetary Transmission for Helicopter Applications by: F.W. Brown, M.J. Robuck, M. Kozachyn, J.R. Lawrence and T.E. Beck, The Boeing Company TECHNICAL PAPER American Gear Manufacturers Association
2、Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:57:10 MDTNo reproduction or networking permitted without license from IHS -,-,- Fabrication, Assembly and Test of a High Ratio, Ultra Safe, High Conta
3、ct Ratio, Double Helical Planetary Transmission for Helicopter Applications Frederick W. Brown, Mark J. Robuck, Mark Kozachyn, John R. Lawrence and Timothy E. Beck, The Boeing Company, Rotorcraft Division The statements and opinions contained herein are those of the author and should not be construe
4、d as an official action or opinion of the American Gear Manufacturers Association. Abstract An ultra-safe, high ratio planetary transmission, for application as a helicopter main rotor drive, has been designed, fabricated and tested under the sponsorship of NRTC-RITA. The anticipated improvements of
5、fered by this new planetary transmission are reduced weight, reduced transmitted noise and improved fail-safety. This paper discusses the fabrication assembly and test results for the subject planetary transmission. Thedesignandanalysisofthistransmissionsystemhavebeendiscussedinapreviouspaper presen
6、ted at the AGMA FTM in 2004. The ultra-safe, high ratio planetary transmission design utilizes a compound planetary configuration with a 17.5:1reductionratiowhichwouldreplaceaconventionaltwostagesimpleplanetarytransmission.Thenew designusesultra-safeprinciplessuchassplit-torquepathsandhighcombinedco
7、ntactratiogearing.Double helical gears in the planet/ ring meshes balance axial tooth forces so that axial bearing reactions are not required. The spur gear sun/planet meshes are staggered to achieve a compact spatial arrangement. Fabricationandassemblyofthecomponentsforthistransmissionarecomplicate
8、dbytheirconfiguration. The grinding process for the helical gears must use small diameter wheels due to the proximity of the adjacent helix, since most the gears in this configuration are integrated designs. Assembly procedures also require special consideration because of the integrated design and
9、helical gears. Test results are presented to support the goals of this project, including, concept verification, weight reduction, noise reduction and determination of the operating characteristics of the test transmission. Copyright 2006 American Gear Manufacturers Association 500 Montgomery Street
10、, Suite 350 Alexandria, Virginia, 22314 October, 2006 ISBN: 1-55589-892-0 Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:57:10 MDTNo reproduction or networking permitted without license from IHS -,
11、-,- 1 Fabrication, Assembly and Test of a High Ratio, Ultra- -Safe, High Contact Ratio, Double Helical Compound Planetary Transmission for Helicopter Applications Frederick W. Brown, Mark J. Robuck, Mark Kozachyn, John R. Lawrence and Timothy E. Beck, The Boeing Company, Rotorcraft Division Introduc
12、tion An ultra-safe, high ratio planetary transmission, for applicationasahelicoptermainrotorfinaldrive,has been designed, fabricated and tested under the sponsorship of National Rotorcraft Technology Center - Rotorcraft Industry Technology Associa- tion (NRTC/RITA). The improvements offered by thisn
13、ewplanetarytransmissionarereduced weight,reducednoiseandimprovedfail-safetyand efficiency. This paper discusses the fabrication, as- sembly and testingof theimproved planetarytrans- mission.Thedesignandanalysisofthis transmission system have been discussed in a pre- vious paper presented at the AGMA
14、 FTM in 2004 1. An existing helicopter rotor transmission planetary drive served as the baseline for comparison to the improved transmission design. The existing CH47 system utilizes a two-stage conventional spur gear planetary design with fixed internal ring gears. Torque is supplied to the first s
15、tage sungear that,in turn,mesheswithfourplanetgears.First stageout- put is via the planet carrier that drives the second stage sun gear. Thesecond stagesun mesheswith six planets and the second stage carrier drives the helicopter rotor shaft to turn the helicopter main ro- tor blades. This two-stage
16、 planetary provides a re- duction ratio of 17.47-to-1. Thenewdoublehelicalplanetary(DHP) systemde- sign uses a compound planetary arrangement with innovations such as staggered planets and high combined contact ratio gearing in a unique configu- ration. Double helical gears in the planet/ ring meshe
17、s balance axial tooth forces so that axial planet bearing reactions are not required. Thespur gearsun/planet meshesare staggeredto achievea compact spatial arrangement. The sun gear is fully floating. Proof-of-Concept or demonstration test- ing of a full scale prototype DHP transmission has recently
18、 been completed. This testing has demon- strated successful operation of the DHP transmis- sion. Preliminary evaluation of the data recorded in thetestsuggeststhatreducedweightandimproved efficiency have been achieved. These parameters will be investigated in further testing. Description - - Double
19、Helical Planetary To 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-helical compound epicyclic gear system concept was develop
20、ed.The im- proved transmission is configured as a single stage compound planetary with an axially staggered, in- termeshed,spurgearinputmeshanddoublehelical output mesh with an overall ratio of 17.5-to-1. This ratio is approximately equivalent to the existing baseline transmission, which has a two-s
21、tage sim- ple planetary system described above. The DHP gearsweresizedforthesamepowerandspeedop- erating conditions as the baseline design, 4500 HP at 225 RPM (output). The core DHP transmission configuration is shown in Figure 1. Theuniquefeaturesofthisplanetarysystemarethe use of double helical ge
22、ars for the final mesh and the axially staggered, intermeshed spur gear con- figuration, which permits theuse ofsix planetsrath- er than three, for greater power density. The overall spatial arrangement is slightly larger than the base- line two-stage planetary system; however the weight of the syst
23、em 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 ring gear diameter. This means that th
24、e sun-planet en- velopemayberadiallylargerthaninasimpleplane- tarydesign.Withthecompoundplanetary, “staggering” the planets can circumvent another limitation and substantially increase capacity. In a Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=B
25、oeing Co/5910770001 Not for Resale, 07/25/2008 02:57:10 MDTNo reproduction or networking permitted without license from IHS -,-,- 2 Figure 1. Compound planetary transmission configuration (with and without ring gear installed) staggeredarrangement,the sungear islengthened to allow it to mesh with st
26、aggered planetary gears. This nearly doubles the number of planet gears which can fit within the compound planetary, result- ing in significantly higher capacityand powerdensi- ty for a given gearbox envelope. A fully floating sun geardesignwasusedtoaidinuniformload-sharing among the planet gears. T
27、heuseofdoublehelicalgearsinacompoundplan- etary arrangement is another unique feature of this drive. Double helical gears are used extensively in heavy industry like mill drives. One benefit of the double helical arrangement is increased total con- tact ratio due to the action of the helix angles in
28、 the doublehelicalgears.Theincreasedcontactratiore- sults in higher mesh load capacity and reduces mesh-generated noise. Since the thrust loads de- veloped on each helix within the double helical gear are oriented in opposing directions, the net axial load from a double helical mesh is zero. This pe
29、r- mits a simpler support bearing arrangement where large axial load capacity is not required. ComponentweightsfortheDHPconfigurationwere determined and compared with the existing base- line planetary. A weight saving of 90 lbs was identi- fied for the DHP when compared to the baseline two-stage sim
30、ple planetary components as shown in Table 1. This is a 12.7% weight reduction for the DHPcomponentscomparedtothebaselinedesign. Thisrepresentsasubstantialimprovementinpower density which is due only to the DHP configuration, independent of other technology improvements. It should be noted that the
31、incorporation of technolo- giestoimprovegeartoothloadcapacitywouldhave additive effects on the power density improve- ments. Weight reduction technologies applied to non-gear components, such as ceramic rolling ele- ments in the planet and shaft support bearings, would also further reduce the weight
32、. It should also benotedthattheweightcomparisonisbasedonthe weightoftheprototypetestcomponents.Thesetest components were not fully optimized for minimum weight due to the limited scope and budget of this project.Itmaybepossible,withadditionaloptimiza- tion effort, to further increase the weight redu
33、ction realized with the DHP design. Table 1.Weight comparison of baseline and DHP design planetary components DesignBaseline PlanetaryDHP Weight of planetary components708 lb618 lb Weight reduction for DHP design-90 lb Percent weight reduction for DHP design-12.7 % Copyright American Gear Manufactur
34、ers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:57:10 MDTNo reproduction or networking permitted without license from IHS -,-,- 3 Gearbox Fabrication Fabrication of the components for the prototype DHP gearbox involved many challeng
35、es. All main powergearswerefabricatedusingaerospaceprac- tice. Gears were fabricated from aerospace quality 9310 alloy steel. Gear teeth were carburized, hard- ened and ground. Standard aerospace post-grind- ing processes, such as shotpeening and NDT inspections, were employed. Gear teeth were manuf
36、actured to tolerances equivalent to AGMA Quality 12, with tip and root modifications appropri- ate for the expected load conditions. Other techni- cal challenges encountered with the fabrication of the gearbox components included: Complexity of the one piece planet carrier/ shaft component required
37、significant amount of machin- ingtime ona relativelylarge component.Innovative fixtures and machining processes were required to produce this part. The existing baseline transmis- sion uses an integral rotor shaft / planet carrier, and therefore, a similar design approach was selected for the DHP de
38、sign. This part could be designed as a two-piece splined assembly thereby avoiding some of the complexity associated with the one- piece design. Grinding operations were complicated by the double helical configuration, as expected, and the spacebetweenopposinghelicesonthedoubleheli- cal gears limite
39、d grinding wheel size and tool life. The aisle width between the helices on the internal ring gear was 0.6 inch and between the helices on theplanetitwas0.55inch.Forfinalgrindingofthese gears, 1.9 inch diameter aluminum oxide wheels were selected, as illustrated in Figure 2. The grind- ing wheel was
40、 mounted ona beltdriven spindleand it was noted that this was not the ideal solution for grinding thesecomponents ina productionenviron- ment. Improvementscanbemadetothisapproach, including more robust tooling, larger spacing be- tween opposing helices, or possibly as an alterna- tive, joined or wel
41、ded helical gears Greater than anticipated distortions during carbu- rization and heat treatment required additional stock removal from ring gear. Alternate heat treat methods, development of specific (for the applica- tion) quench process tooling, heat treatment simu- lationandanalysis,areafewappro
42、achesthatcould be utilized to deal more effectively with this issue in future products. Figure 2. Grinding wheel clearance for staggered double helical tooth arrangement Manufacturingtolerancesandstructuraldeflections of the gears and shafts can have a significant effect on the effective load sharin
43、g among planet gears. Accordingly, an additional tolerance requirement was established for the angular indexing relation- ship of the planet gear teeth. This index tolerance controlled the location of the planet spur gear teeth relative to a datum established by the helical gear teeth. The tolerance
44、 allotted for gear tooth indexing was considered very tight by the fabricators. Addi- tionally, the long and short planet shafts were de- signed to have the same torsional “wind-up” under load so that the gear teeth wouldshare loadequally between the long and short planets. Photographs of some parts
45、 during fabrication are shown in Figures 3 though 5. Figure3. Sungearsearlyinfabricationprocess Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/25/2008 02:57:10 MDTNo reproduction or networking permitted witho
46、ut license from IHS -,-,- 4 Figure 4. Compound planet gear Figure 5. Double- -helical internal ring gear Gearbox Assembly Testing was to be conducted in a back-to-back ar- rangement, therefore requiring two DHP transmis- sions, one designated as the test transmission the other designated as the slav
47、e. As the major components were completed, thepro- cess of assembling the two prototype DHP trans- missions was initiated. Installation of the tapered roller bearings onto the carriershaft wascompleted first. The carrier and bearing assembly was then installed into the welded structure which support
48、ed the transmissions. The tapered bearings were shimmed to obtain the proper setting. Once proper shim size was established, the carrier shaft was re- moved so the planet gears could be installed with the ring gear. Figure 6. Carriers with tapered bearings installed A key concern with the DHP transm
49、ission was the assembly procedure for the staggered compound planets.Toaddresstheseconcerns,adetailedCAD model of the components was used to simulate the assemblysequenceandeliminatepotentialinterfer- ences. The study of the assembly sequence was important for this project since the sun gear, planet gears and mating rin