870960 Interactive DesignofOff=Highway Vehicle Suspensions RichardC.Coddington Agricultural Engineering Dept. University ofIllinois Urbana,IL GeorgeP.Kalhorn JohnDeereDubuque Works JohnDeereRoad Dubuque,IA ABSTRACT Engineers fromdesign, testand analysis teamed together todevelop a suspension fortheJohnDeere 862Scraper. Thedesign engineer coordinated developmental activiti.es of theteam.Theengineering analyst helped evaluate initial design alternatives using aninteractive program topredict rideperformance. Thetestengineers instrumented ascraper tomeasure ride performance under avariety of conditions andsuggested practical changes tothemechanical andhydraulic components ofthesuspension toimproveitsperformance. Theteamapproach proved tobeacosteffective, timely approach tothedesign ofoff-highway vehicle suspensions. INTRODUCTION Afrontaxle, leading arm suspension hasbeendeveloped forthe JohnDeere 862scraper (Figure 1)and theKressAD86-35 dumptruck(Figure 2). Sinceitsintroduction in1980,this scraper hasdemonstrated thebenefits of afavorable weighttopowerratio. With recognition ofitshighproductivity, the862scraper hasincreasingly been usedforfullproduction rolesrather thanjustutility andclean-up tasks. Consequently, thehaulshavebecome longer andtheneedforasuspension moreapparent. Productivity hasoften been limited bytheoperator's reluctance to tolerate theroughriderather thanby 105horsepower. Rideconsideration targeted theneedforsometypeofvehicle suspension. TEAMAPPROACH Toaidinevaluating therelative importance ofthemanydesign parameters involved, thedesign engineer formed a teamconsisting ofanexperienced design engineer, anengineering analyst andtwo fieldtestengineers. Theintent wastoquickly andeconomically develop a suspension fortheJohnDeere 862. scraper. Thedesign engineer coordinated activities amongtheteammembers. The analyst wasresponsible todevelop an interactive program topredict ride performance andtoassist initsuse. Onetestengineer instrumented the scraper, recorded, reduced and interpreted theexperimental data. The othertestengineer conducted thetests,identified practical changes for improving rideperformance andsuggested changes tothemechanical andhydraulic components ofthesuspension system to improve itsperformance. Interact ion among theteammembers occurred ona dailybasiswithteammeetings to discuss problems, suggest solutions I evaluate alternative designs and coordinate activities among team members. MODELDEVELOPMENT Theprimary goalindeveloping a modeltopredict rideperformance ofa scraper withafrontaxlesuspension was tocome upwith auserfriendly,Downloaded from SAE International by Imperial College London, Monday, September 24, 2018interactive program toquickly andinexpensively evaluate design alternatives andtohelp"tune the design" foracceptable performance. Theanalyst identified two general sources ofexcitation causing unwanted motion ofthescraper during transport operation. Thefirstsource wasarandom excitation thatthescraper experiences onrough haulroads. The second source wasadeterministic excitation resulting fromthescraper striking abumpordepression while traveling alongthehaulroad. Thus, theanalyst created twofamilies of lumped massmodels, onetopredict the frequency response ofthescraper for random excitation andtheother to predict thetimedependent response of thescraper resulting fromstriking a bumpordepression. Models toStudyFrequency Response Theanalyst developed afamilyof fivelumped massmodels torepresent the bounce andpitchofascraper intwo dimensions. Hetransformed theequations ofmotion tothefrequency domain and specified thedisplacement spectral density oftheterrain, anapproach like thatofPershing (1).Sincetravel across therandomprofile oftheterrain excited boththefrontandreartires simultaneously, theanalyst usedan approach likethatofRobson (2)to modelthisinput. Inaddition, heused apowerlawmodelduetoVanHeusen (3) torepresent thedisplacement spectral density oftheterrain. Themodels ranged fromtwotosix degre