浮动杯式轴向柱塞泵

Achten1Designingtheimpossiblepump.Dr.ir.PeterA.J.Achten,InnasBVNikkelstraat154823AEBredaNetherlandsE-mail:[e-mail]::axialpistonpump,floatingcupprinciple,torquelosses,efficiencyAchten21NomenclatureadimensionbdimensioncdimensionDdiameterFforceMtorqueppressureRradiusofthepistonpitchcirclespistonstrokevvelocityznumberofpistonsbbarreltiltanglejangularbarrelpositionmfrictioncoefficientwrotationalspeedSubscriptsccylinderffrictionminminimumNnormalpPiston2OffthebeatentrackInhisbook“TheInnovator’sDilemma:WhenNewTechnologiesCauseGreatFirmstoFail”ClaytonChristensenanalysesanumberoftechnologybreakthroughsintherecenthistoryofproductdevelopment[1].Oneofthemistheappearanceofhydraulicexcavatorsinthefiftiesofthelastcentury.Inlessthanadecadethemarketofcable-actuatedexcavatorswasalmostcompletelygone,andonlyafewexcavatorproducerssurvivedthechange.Thiswastheshortinnovationeraofthehydraulicindustry.Lookingbackitishardtobelievethatfluidpowerassuchhaseverbeenadisruptivetechnology.Moreovermostpeopleworkinginthehydraulicindustryhavecompletelyforgottenaboutit(whoremembersthe‘giantBucyrus-Erie’?).Insteadofacontinuationoftheroleofinnovator,thehydraulicindustryhasfocussedonsustainingtheexistingproductsandtechnologies:toimproveincrementallytheperformanceofestablishedproductsinexistingmarkets.Yet,thispaperisnotfollowingthesameroad;thispaperisaboutaninnovation,anentirelynewconceptofhydrostaticmachines.Itiscalledthefloatingcupprinciple[2,3,4]andhasbeenintroducedforthefirsttimeinMarch2002.Thefloatingcupprincipleisadisruptivetechnologyinthemarketofhydrostaticpumpsandmotors.Itwillenablethepumpindustrytocreatenewmarketopportunitiesandtochangetherulesofthegame;atleastforthoseindustriesthatarestillopenforinnovations.Atotherindustrieshowever,thenewinnovationwillautomaticallystartofftheirimmuneresponsesystems.Intheendthenewtechnologyisamixedblessing.Itwilljeopardisetheoldproductionlines.Anditthreatenstheknow-howstatusofcurrentpumpexperts,designersandproducers.Thisisespeciallyofrelevanceforcurrentmarketleadersinthehydrostaticpumpandmotorbusiness.Theyhaveadifficultdecisiontomakefornotonlytheconceptisnewanddifferent,butitalsoinvolvesanewproductiontechnology,thatistosay,newforthehydraulicindustry.Achten3Butthereissomethingtogainhere:apumpthathasahighefficiency,extremelylowpulsationsandlownoiselevels.Ifappliedinamotorthenewprincipleimprovesthestart-upandthelowspeedbehaviour.Andduetothekindofproductiontechnologiesthenewprincipleisdesignedfor,itofferstheopportunityforfurthercostreductions.Figure1:Cut-awayviewofthefirstprototypeofafloatingcuppumpThispaperisfocussedonthehydro-mechanicalefficiencyofthenewprinciple.Mostlossesofhydrostaticmachinesarecausedbyfrictionandotherhydro-mechanicallosses.Asidefromtheenergylossesthefrictionwillalsoresultinareductionofthestartingtorque,whichisespeciallyimportantformotoroperation.3KinematicsofaxialpistonmachinesThefloatingcupprinciplebelongstothefamilyofaxialpistonmachines.Thepistonsarearrangedinacirclearoundacentralaxisandthedisplacementis(forthemostpart)realizedintheaxialdirectioni.e.paralleltotheaxisofthebarrel.Inslippertype(figure2a)andbentaxispumps(figure2b)–currentlythemostimportantmembersoftheaxialAchten4pistonfamily–thecylindersareallpartofasolidbarrel:theycanonlymovetogetherwiththebarrelintheradialdirection.Inbothpumptypes,thepistonshaveasphericaljointattheoppositeendofthepistonsealing.Asaresultthepistonscanonlytransferloadsintheaxialdirectionofthepiston.Allotherpistonloadsthatwillcreateatorqueatthesphericaljointwillhavetobetakenbythebarrel.a)slippertypeb)bentaxisFi