820909 Bus,Truckand Transmissionsfor VehicleElectronic Controls Off-Highway Kenneth B.HarmonandKeithD.Struthers DetroitDieselAllison DivisionofGeneralMotorsCorp, Indianapolis. IN Abstract Mostbus,truckandoff-highway vehicleauto­ matictransmissions todayhavehydraulic controls similartothetypeusedonautomobile transmis­ sions.Becausethenumberoftransmission appli­ cationsisincreasing rapidly andcustomer demands forimproved vehicleperformance, greaterdurabil­ ityandbetterreliability aregrowing, present hydraulic controls arebeingpushedtotheircapa­ city.Overalltransmission performance canbeim­ provedbyreplacing hydraulic controls withelec­ trohydraulic controls whichincorporate microcom­ puter-based electronics forintelligence, butcon­ tinuetoemployhydraulics forpowertoapplythe clutches inthetransmission. Important benefits available withamicrocom­ puter-based controls systeminclude: shiftpoint optimization, improved shiftpointaccuracy, transmission-application customization, mechanical linkageelimination, improved fueleconomy, and overallpowertrain optimization.effectively reducedvehicleoperating costsand increased vehicleavailability. Since1978,OOA hasbeendeve10pin9 newmicrocomputer-based elec­ troniccontrols toprovideacosteffective system forthesmalleron-highway transmission applica­ tions.Although thisnewsystemisbeingde­ velopedforinitialintroduction totheon-highway market,itwillsubsequently beutilized inthe off-highway marketresulting inreducedsystem costsforthelargeroff-highway vehicles. Be­ causeoftheveryadaptable natureofthenew microcomputer-based system,ithasbeennamedthe Universal Electronic Control (UEC)System. SYSTEMDESIGN Akeystepinthedevelopment ofelectronic controlsystemsistheidentification ofsystem designrequirements. Oneofthemajordesignre­ quirements imposed ontheUECwasthatitmustbe adaptable forusewiththecomplete OOAhauling transmission productlineshowninFigure1. AUTOMATIC TRANSMISSIONS HAVEBEENAVAILABLE for application tobuses,heavy-duty trucksandoff­ highwayvehicles foranumberofyears.Untilre­ cently,mostofthesetransmissions haveutilized hydraulic controls similartothetypeusedon automatic automobile transmissions. Thesehy­ drauliccontrols haveprovided andcontinue to provideexcellent performance. However, theyhave limitations whichdictatetheneedtodevelop new controls. Rapidexpansion ofdifferent transmis­ sionapplications, customer demandsforoptimum vehicle andfueleconomyperformance, increased durability andreliability andanticipated Govern­ mentrequirements arepushingthesecontrols to theircapacity, requiring thattheybespecially calibrated forthevariousapplications. Availability oflowcost,microcomputer-based electronics offerstheopportunity toreplace thesehydraulic controls withelectrohydrau1ic controls resulting inimproved fueleconomy, en­ hancedperformance, unexcelled vocational adapt­ ability, increased customer satisfaction, anda numberofmanufacturing benefits. Electronic transmission controls arenotnew. Inthelate1960's,DetroitDieselAllison (OOA) Division ofGeneralMotorsCorporation introduced automatic discrete component, open-loop electronic transmission controls forheavy-duty off-highway vehicles suchasearthmovers,largedeeppitmin­ ingtrucks, andoilfieldrigs.ThesecontrolsFig.1 -Commercial HeavyDuty Automatic Transmissions Included inthehaulin9transmission product lineareafulllineofhydrokinetic transmissions withcapabilities from235HPto1350HP.On­ highwayvocational coverage ofthisproductline includes schoolbuses,citybuses,intercity buses,pickupanddelivery trucks,garbagetrucks, dumptrucks,firetrucks,utilityvehicles and manyotherspecialized vehicles. Off-highway vocational coverage includes farmtractors, log­ gingvehicles, minin9dumptrucks,giantearth- 147Downloaded from SAE International by North Carolina State Univ, Tuesday, September 18, 2018moversaswellasmanyotherlargeoff-highway vehicles. Ingeneral, eachoftheseapplications resulted inspecific controlsystemlogicand modingrequirements, andcollectively, theydic­ tat