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THEORETICAL ANALYSIS AND DES IGN/CALCULATION FORMULAE FOR  HYDRAULIC IMPACT MECHANISM

摘要撰写人 : TsingHua
浏览次数 : 39  词语: 300   出版日期: 三月 30, 1995
THEORETICALANALYSISANDDESIGN/CALCULATION FOR MULAEFOR HYDRAULICIMPACTMECHANISMHe;Qinghua (DepartmentofMechanicalEngineering,CentralS outhUniversityofTechnology,Changsha410083)A bstract:Theperiodofthepistonmotionofhydraul icimpactmechanismwasdividedintothreestages. andanon-dimensionalparameter-theaccelaratio nratioβwasalsogeneralized.Andthenaseriesoff ormulaedescribingthemechanicsandthekinetics ofthepistonwerederived,whichProvidedanewapp roachfordesigningandstudyingthehydraulicmec hanismandnewtheoreticalbasesforfurtherresea rch.Keywords:hydraulicimpactmechanism;accel erationratio;unretrievedoil1INTRODUCTIONThe vitalworkingmechanismofallhydraulicdrillors plittersistheimpactmechanismconsistingofare ciprocatelymovingpiston.Inordertoimprovethe performanceoftheimpactmechanismandsearchana ccuratemethodforitsdesignandanalysis,itisof greatimportancetostudythemotionlawofthepist on.Althoughitiswellknownthattheperiodofthep istonmotioncanbedividedapproximatelyintothr eestages,i.e.thereturnacceleration,theretur ndecelerationandtheimpactacceleration,itisi mpossibletodescribethemwithaprecisemathemat icsmodelonaccountofthecomplexityoftheactual motionofthepiston.UPtonowmanymechaniciansus edalinearmodeltoanalyzethemotionofthepiston ,supposingthepressedoilissuppliedataconstan tpressureandthepistonisacceleratedevenly.In additionbeingequalinvaluesthereturndecelera tionandtheimpactaccelerationwereconsideredt obethesame.Andthussomesimpleformulaedescrib ingtherelationshipamongthemotionparameterso fthepistonunderanidealworkingconditionwered erived.Inthispaper,athree-stagedanalysismet hodwasputforward.Consideringinnegligibledif ferencesexistbetweentheaccelerationvaluesof thereturnandimpactstagesunderactualworkingc ondition,andsotheaccelerationsofthethreesta gesneedtobeconsideredrespectively.Foraccura cyandapplicabilitysomefactorsareadded.2PARA METERSDESCRIBINGHYDRAULICIMPACTMECHANISMPer formanceparametersincludeimpactefficiencyf, impactenergyEi,totalefficiencyη,volumeeffic iencyηvandmechanismefficiencyηm.Structuralp arametersincludemassofthepiston,mp,areasoft hepiston’sfront-andrear-chamberAf,Arandgas- chargedvolumeoftheaccumulatorVa.Workingpara metersincludeinputoilpressurePin,inputoilfl owQin,leakingoilflowQ1.featurespeedsofthepi stonincludingtheimpactspeeduimandmaximumspe edduringthereturnaccelerationurm,pistonstro keSpincludingreturnaccelerationstrokeSrandr eturndecelerationstrokeSd,periodofpistonmot ionTincludingreturnaccelerationtimetr,retur ndecelerationtimetdandimpacttimeti,Received 1994,Oct15pistonaccelerationsincludingretur naccelerationar,returndecelerationadandimpa ctaccelerationai,gas-chargedpressureoftheac cumulatorpa,oil-chargedvolumeVriandoil-disc hargedvolumeVroduringthereturnacceleration, oil-chargedvolumeViandoil-dischargedvolumeV oduringthereturndecelerationandtheimpact.Th erearetwokindsofvalve-controlledhydraulicim pactmechanismswidelyusedaroundtheworld.Oneh asaconstant-pressurizedfront-chamber,andthe oilpressureintherear-chamberchangesalternat ively.Theotherhasnoconstant-pressurizedcham ber,theoilpressuresinboththefront-chamberan dtherear-chamberchangeingalternatively.Here afterthesetwokindsofvalve-controlledhydraul icimpactmechanismsareabbreviatedtoRCandDCre spectively.3THEANALYSISOFTHEPISTONKINEMATIC SDuringthereturndecelerationstagethesealres istance,theadhesiveresistance,thehydraulicl ockingresistance,thedecelerationresistance, causedbytheoilpressureactinthesamedirection .Whileduringtheimpactaccelerationthesealres istance,theadhesiveresistanceandthehydrauli clockingresistanceactintheoppositedirection oftheoilpressurewhichleadsthepistontoaccele rate.Sotheabsolutevalueoftheaccelerationdur ingthespeed-downislargerthanthatduringthesp eed-up.Forconvenience,twonon-dimensionalpar ametersareintroduced.Oneistheaccelerationra tioβ(β=ar/ai),andtheotherisβ1(β1=a1/ad).Int hecaseofthefrequencyfandtheimpactenergyEibe inggiven,theimpactvelocityuim,theimpactoilp ressurePinandβbeingproperlychosen,andthepausetimeafterimpactingbeingneglected,aseriesofformulaedescribingthekinematicsrelationshipofthepistoncanthusbederived.Whereψspandψur

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