load testing of gearboxes

7/27/2019 Load Testing of Gearboxes

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Fu l l -L o ad Tes t in g o fL a r g e G ea r b o x esU s in g C lo s ed -L o o pP o w e r C i r c u la t i o n

R . I B . F r o s tU n i v e r s i t y o f I N ' e w S ' o u th W a lle s . K e n s i n g t o n , A u s t r a H a

' lR . C ' r o s sJ 'o h n W e 'l s b P ly . L t d . M 'e l b o u r n e . A u s t r, a 'i i a

Summary: Thi .method of testing large gear-boxes or, indeed. any power transmission ele-ment. has numerous advantages, and offers 'thepossibility of large avings in time. energy, andplant. if the overall. situation is conducive to itsuse. This, u ual ly requires that several such unitsneed to be tested. an d that they can be conve-niently connected toeach other in such a way asto form a clo ed-loop drive train ..No power ink (a)is required. and the drive input system has onlyto m ake up power losses. The level of circulatingpower i controlled by the torque, which iapplied statjcaUy during rotation,and the drivepeed. Principles. advantage, and limitations are (b)described. together witb. recent experiences inthe only known large-scale usage of this tech-nique in Australia,

IntroductionFull-load testing of large gearboxes and otherpower tran mission modules or components hastraditionally been carried out. with 'Ille tesungdrive train arranged in .3 . schematically linear OTopen manner, a hown in fig. la o This necessi-tates the use of a power source and a power sink.or brake, each with .3 . capacity at lea t equal 10that ofthe required test further. all energywhich passes through the gearboxunder test,which can. be considerable. is wasted inlhe ink.This 13 t factosiscornpounded unumerous unitsneed to be tested, Iflhe rated power of thegearbox under test is large.and the output speedis low, the torque at the sink can be inconve-

oiently mas ive, unless further supplementarygearing is provided ..One way of doing this, ofC~lU" e, is to test two gearboxes simuttaneouslyin series, as shown in Fig. 1 . 0 . . This, however.does nothingto avoid the necessity fora largesource and sink.

I P o w e r ll 1 GearSource II I BoxUnderI ,Power Iest

I ISink

l P , o w e r l Ie ,I IPo;- ' t 'sr I II rst I S ~ : ~ d ,ource I Gear I Sink IBox I B o xUnderIUnde rTest I Test I

F ig . ~ - T he tr ad it io na l, schemal: icaJI.y o pe n a rra ng em en t o f g ear bo x te st rig s: (0)the .implesl arrangement; (b ) a tandem anangememt which tests two gearboxes im l l ll n neol is ly a nd wh ich avo id s 8.ma ss iv e to rq ue a t a l ow s pe ed al th e power sink.The above situation can be markedly im.-

proved by the use of a closed-loop arrangementof the test drive train. Such an arrangementallows the return to the test system ofthe outputpower from each gearbox under t es t, s o t ha t. no power sink is required;.' the power ource only has to provide make-

li p power equal to the sum of system losses:.'several gearboxes are 'tested simultaneously.Obviously. large savings can accrue from the

avoidance of the necessity for iii power sink and!

I R . B . F r a s 1i s S en io r L ec /u re r.S c ho o l 0 1Me c ha n ic al& . Industrial Engineer-inB. Univers i ty olNewS o ul h Wa le s,T . R . C r o s sis MalUIging Director.John Wt'/~h ,Pty. LId. infI i lelbouf"1!l !. Australia.

SEPTE,IIBERIQCTQ!lER 18111 3 5


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nom thelarge reduction m 'the required capacit.yo f th e p ow er source. Ifnumerous units need to betested, large savings in time and energy arepossible.Disadvantages or Iirmtancas on the use of

such a test method are that OOI 1 -backdr iv ing gea rboxes . suchas h igh- sa rin

worm drives, cannot. be tested in this manner; a somewhat larger floor area is required for

the test. setup; the pow er level in each gearbox. in a particu-

la r setup' win be s li gh tl y d if fe re nt due to lossesaround die drive train loop;.the method isbest suited to situations where

at least as many gearboxe need to be tested asare required to make up the drive 'train loop;

if the number 'of units to. be tested is not. anintegral multiple of die ollmber required to makeu p th e loop, some will need to undergo two teststo allow fonnation ofthe final loop at the end ofthe series of tests.While such multiple simultaneous testing is

not uncommon in Europe. it has not been used toany great extent in AllJstralia.

The Drive Traio. LoopThis consists of several of the limits to be

tested, coupling shafts, and three other compon ents: a m otion in put dnve,a torque application,coupling, and a torque transducer.Such a loop can be achieved in several conve-nient ways ..I ft he g ea rboxes a re p ar al le l- sh af te d,two can be coupled as shown in Fig. 2; if theyinvolve shafts at right angles, e.g., as wwth bevel

GEA .RI B O X 1 1

II

~,i~ 10....- _DRIVEIN 'PUTFig. 2 - A elo .ed- loop arrangement rorr testing two parallel-shafted gearboxessimultaneously and IJtiJizingcirculating power, thereby avoiding thenecessity fora 'p ow e r sink., 3 6 1 GEAR TECHNOLOGY

input stages, chen four can be coupled as shownin Fig, 3. For generality, and because of recentexperience with such a ' erup, the remainder ofthis article is written as relating to a setup lISshown in Fig. 3.The three additional. components referred to

above can be incorporated in an y convenientmanner or location in th e l oo p, The drive inputcan be incorporated ina coupling shaft as a 'beltor chain drive or as a separate gearbox with adouble-ended output shaft, or it can be attacheddirectly to a shan extension on one oflhe unitsunder test, If one ti s available. Alternatively. ifthe motor speed corresponds to th e sp ee d 0 1 thehigh- peed shafts, and the motor has a double-ended shaft, i t ca n be incorporated directly inone of the high-speed shaft lines, The torqueapplication coupling is a device which join ap air o f ad jac en t. shan ends and which applieequal an d opposite torques to them whiletheyare borh rotating. and in the presence of somedegree uf relative rctatian between them, It maybe thought of in practice as a hydraulic motor,supplied and drained by two lines via a rotatablehydrauli.c coupling, with :its shaft connected toone of the tw o s ha ft ends referred to above. andits body connected to the other.

The Action .o f the Test Rig'This is best described by considering tbe rig atrest while the torque application coupling isloaded by the application of hydraulic pressure.The whole drive train loop is thereby loadedtorsionally so thateach section of it. being intors.ionaI equilibrium, has equal and oppositetor1lues at its two ends: i.e., an actioa and areaction ..If the motion input :isnow started. thewhole drive train loop w:iUrotate in the directionin which it is driven. Fora particular loop 'oc-tion, the applied torque and the rotation will bein . the same direction at one end, where powerw i IIbe entering thadoop sec tion, and illoppos itedirections atthe other end, where power will be~eavinglh3!t loop section. This applies to eachloop section, so that power eirculaees continu-ously around the drive train loop in a dieecticnwhich is determined by the combinanon of thedirectioas of the drive rotation and the torqueapplication,The level of circulating power is,detennined

by the combination of the speed of the driverotation and the level of the torque application.


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where T l is the efficiency of each indiv idual F ig.], - Similar t o F i g . 2. b u t to suitfourright-angle-drive gearboxc . Power flowsgearbox. 0 th at th e to ta l p ow er [0 is given by and losses are hew n,

boxes, C learly . large avin gs io instal led cap ac-ity . tim e and energy can be realized , providedt he o v er lo ad OR som e u nits can be to le ra te d f orthe duration of the test. This overload i,ofc ou rs e. s ig ni fi ca nt ly r educ ed if P I' P2' or P 3 ca nb e a gr ee d upon as the pow er level for the test,r at he r t ha n P 4'Con sid era tio n n ee ds to b e g iv en to th e "h an d-

in g" of gearboxe an d the resulting com patibil-ily o f rotationaround the drive train loop. Re-gardle of this. how ever, it i nece arily truethat one diagonally oppo ire pa'ir of boxes w il lb e o p er ati ng i n t he c hemati caUy f orw ar d ( power -flow ) sense as ' peed reducers, bearing on theforw ard flanks of the teeth, while the otherdiagonally opposite pair are operating in thes ch em atic al ly b ack ward s en se a s s pee d in cre as -er , bearing on the rear flIanks. PD r spi ra l b ev elgearing the difference in geom etry and forcelevels betw een thesetwo ca e are lgm ficant,W hether this is seen as a problem . a in thenecessity to prove every box in every m ode, or asa ll ,o pp ortu nity w hereb y eac h o f th ese tw o. c a escan be dem on trated sim ultaneously , dependsIO nth e way in wnich test requirements are w rit-ten. A t m ost, how ever, this probl em w ould onl yi nv ol ve a re ve rs al o fro ta tio n an d/o r to rq ue in th e, r une setup once testing is under w ay ,R ecent E xperience W ith C losed-L oop T estingJohn W elsh P ly . L td. of Me lb our ne r ec en tl yupplied 2~ gearboxes, each rated at 610 kW ,\485 RPM input speed .. I7.76: \ redaction ratiowith a sp iral bevel input stage and a hel ical

W ith the exception of the Iosse due 1 1 0 th ei ne ff ic ie nc ie s l in the gearboxe power does notl ea ve th e d riv e train loop; therefore, it doe ' 1 1 1 0 1ne d to b e p ro vid ed b y th e d riv e in pu t, except torth e losses, r eg ar dl es s o f th e level ofthe circular-i ng p owe r.P ow er flow s and 1 1 0 ses are show n in F ig ..3 . If

P I is the input power to the gearbox IO n th e"downstream" sideof the drive input (in thepo wer-flow en e) and P :s is th e pow er deliveredto th e d riv e in pu t by th ea djac en t g ea rb ox o n th e"up ITeam " ide, then

T he input p ow er fraction, w hich is the ratio o finput p ow er req uired w he n 'l .Is in ga c lo ed -l oo prig to thaI . required w hen using a rig of the ty peshow n in Fig .. I , w here input pow er m ust equaltest pow er, is g iven by

4P . . I -1 1f = mpul =- (3)p P 1 ' \ 34

w here P 4, w hich is the low est inp ut pow er level[0a ny g earb ox in th e [001'. is taken robe thea gree d p ow er l ev el f or 'th e tes t. T his a gree men tcould be m ade differently . of course. in w hichcase, f w ill be d efined d ifferently . b ut this willpmake l it tl e d if fe re nc e tD f .pT he in pu t e ne rg y fra ctio n :f or t estin g a s erie s o fgear boxe in this w ay , rather than a in Fig, 1 , isg iven by

f 1 ~ 1 1 4f = = .. . .: : : : - - (4)E - c - 3N Nilw here N is the num ber of gearbox units testeds ima lto ne ou sl y . .In t he s it ua ti on c on si de re d h er e.N=4.S im ilarly . th e overload factor on G earb ox I, in

order to achieve P 4 into G earbox 4, is given by

F ig ,4 h ow s \l a\l .1 eso f fpi fE ' and Fo fm a rangeof T \ w hich is realistic t:or a l arge range of gear-

(5)

P ' + (1- '1) P 'l OSS2 2

Pi- (1-11) PLoss! 1

SE P T E !. IBE RIO cr e B E R 1991 3 7


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1 . . 15 ,,..---""""T----,~----,.---.------,I , 0 5I I

F~g.4 - Variation of energy fraction fE ' power fraction fp' and overload factorFo far a ra ng e o f e ff ic ie nc y . :1 f I l . for th e se tu p sh ow n in Fig. 3 .output stage, for coal conveyor drives. These

were te ted four-at-a-time in an arrangementsimilar to that shown in Fig. 3, at 50% of fullload and then at HXJ% of full load, in each caseuntil temperature equilibrium was reachedand thereafter to allow noise measurementsto be taken.Drive input. was vi a a multiple V-belt drive

of the appropriate ratio from an inductionmotor rated at 220 kWal 960. RPM. onto oneof the high-speed shafts connecting the gear-boxes ..This haft also contained the torqueapplication coupling, which was a propri-etary item, model VM2-4000-100 fromGlyco in Germany. It provided two activehydraulic chambers. in each direction to fa-cilitate tile production of a large torque froma compact design, and thereby provided atotal relative rotation of on I.)! 'WO. The elas-tic torsional deflection around the drive !rainloop at 1 . 15% of futl-Iead torque, 9

E, was

calculated to be approximately 31.so of rela-tive rotation at the adjacent shaft ends wherethe torque application coupling was to belocated and tile backlash in the gearing, ,(JSL'was estimated to be approximately 5 . 5" at thisloeation. For loading in both direction, thisrequired a total relative rotation of the torque Acknowledgemen't: Th.is aniele was originallyapplication coupling of presented at The }n.r/jlmiO'n 0 '1 Engineers ..AUSlrQ-

1 . 3 I--~-.,...j-~'r-I~--+--""""""---il 0.3I~ ~~~

1 . 2 I----II---~---"'rl"'-'---t__--t- 02

L- ~L- ~L- ~L- ~~~o1 091 . 096

1 )098

appro imarely 31.5" for angular assemblyof the flanges of this coupling, which. it wasanticipated, would be assembled last in thedrive train loop with its mating flanges onthe adjacent coupl ing shaft ends. In tile event,however, it was found that the torque trans-ducer had sufficient holes in its flanges toallow convenient final closure and connec-tion 'of the drive train loop at its flanges.with the torque application coupling ini-tiaUy set .0 that it had approximately 7 S O t l ofits stroke available il l 'Ihe reqaired directionof testing.The Lebow 1641- lOOK torque transducer

was located il l the other high-speed shaft.In eachinstance of testing, the motor

driving the rig was tarted while the torqueapplication coupling was ubject to a smallrequired minimum pressure of approximately5 bar. This gave rise to the necessity toovercome some degree of initial stiction inthe lightly torsionally pre-loaded rig. Thiwas nota real problem, however, and oncethe rig broke the stiction and started to move,it ran very freely. The.hydraulic pressure tothe torque application coupling was thenprogressively increa ed, thereby increasingthe circulating power Ievel, the losses. lindthe motor load, until the required readingwas achieved en the torque meter. Thi read-ing of course, had to be calculated specifi-cally in view of the pcsition 1 . 1 1 Ihe drivetrain loop occupied by the torque transducer.The rig was then run as required for thetesting procedure. In all cases the rig be-haved in a stable manner and the testingproceeded without problems.

ConcilUlsi.onSlmaltaneous res ting of mulltiple gearboxesusing a elosed-looptest rig arramgementis a veryconvenient and co t-effective testing methodwhere the conditions favoring such a method. asoutlined in the introduction. are satisfied. Onsuch occasions. (he authors recommend con sid-eration of this method. I.

lia, Filth Intemattona! Conference 0/1 Manufac-(6 ) turing Engineering, July 1113, 1990.

W,ollongong, NSW, Australia. Reprinted withwhich was within its range and which left permission., 3 8 , GEAR TECHNOLQGV

load testing of gearboxes

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