SOCIETY OFAUTOMOTIVE ENGINEERS, INC. TwoPennsylvania Plaza, NewYork, N.Y.10001 AnAutomatic Transmission forOff-Highway Vehicles J.W.Schmidt and K.B.Harmon Detroit Diesel Allison Division ofGeneral Motors Corporation Earthmoving Industry ConferenceCentral Illinois Section Peoria, Illinois April2-4, 1973730442 Downloaded from SAE International by Imperial College London, Monday, August 20, 2018730442 AnAutomatic Transmission forOff-Highway Vehicles J.W.Schmidt and K.B.Harmon Detroit Diesel Allison Division ofGeneral Motors Corporation Twenty-five years ago Detroit Diesel Allison pioneered thepowershift transmission. Since that time, Allison transmissions have become widely accepted bytheindustry forboth onand off highway equipment. Inoff-highway equipment these transmissions serve thefollowing industries: Earthmoving Mining Lumbering Material Handling OilField Construction Field experience hasshown, however, that there isastrong need inoff-highway vehicles to: ABSTRACT Thecontinuing improvement anddevelopment of off-highway working vehicles hasdemanded cor responding continuing advancements intransmis sion technology. Asaresult Detroit Diesel Allison willintroduce, in1973, theAllison CLBT 750fully automatic transmission for service inthe off highway market of20to35-ton trucks and 15to20 yard scrapers. The CLBT 750transmission was designed asa five-speed unit with automatic shift modes forse cond through fifth ranges. Design activity onthe transmission included development ofahydrauliccontrols system which would provide optimum shif ting forallconditions ofengine andvehicle speeds andloads while ensuring that those shifts, both up and down, aresmooth, positive, and safe. The design activity also included development ofa minimum size, high capacity, highly responsive retarder toensure safe descent ofsteep grades. Inaddition tothe engineering, logic, design techniques, anddevelopment testing described in thepaper, theauthor outlines, ingeneral, an engineering approach tosuccessful new product design. Downloaded from SAE International by Imperial College London, Monday, August 20, 20182 Minimize required driver training, Eliminate inadvertent driver abuse ofthe power train, Reduce operator fatigue byincreased ease of operation. The Allison approach tofulfilling these needs liesinthedevelopment offully automatic shifting transmissions. For example, in1972 weagain pioneered with theautomatic electronic shift con trol, anoptional feature which when added tothe Allison DP8961 power shift transmission (used in trucks ofthe800to1000-horsepower class) per mitted ittoachieve theoptimum infully automatic operation. Now in1973 Detroit Diesel Allison is preparing togointoproduction with theCLBT 750 transmission. TheCLBT 750byvirtue ofbeing ful lyautomatic inthetopfour of itsfiveranges solves within itself theproblems ofminimizing driver training, eliminating driver abuse, and reducing driver fatigue. The design anddevelopment ofthe CLBT 750isthesubject ofthispaper. INPUT RATINGS The CLBT 750 was designed foroff-highway applications, described bythefollowing twobasic classes ofequipment: Trucks-20 to35tons Scrapers-15 to20yards This automatic transmission israted tothepower level ofengines serving these classes ofvehicles, namely: InputTorque 1100 lb.ft. Engine Governed Speed 2500 rpm InputHorsepower 400 These ratings areforthenetinstalled engines. TRANSMISSION DESIGN The CLBT 750transmission, Fig. 2,isafive forward speed transmission with torque converter andlockup clutch with onereverse gearrange. Shift modes 1,2,2-3, 2-4, and 2-5,permit optimum con trolunder allconditions byallowing thedriver to hold inanyrange. However, inmost instances, the 2-5position provides adequate drive control. Manual selection tolimit thetoprange foreither speed control orincreased braking can beac complished without danger ofover-speeding the drive train. This isachieved with adown shift in hibitor system which prevents shifts tomanually selected low