[机械模具数控自动化专业毕业设计外文文献及翻译]【期刊】行星齿轮组和自动变速器仿真设计课程-外文文献

Planetary Gear Set andAutomatic TransmissionSimulation for MachineDesign CoursesSCOTT T. DENNIS, DANIEL D. JENSENDepartment of Engineering Mechanics, U.S. Air Force Academy, Colorado Springs, Colorado 80840Received 13 November 2002; accepted 15 July 2003ABSTRACT: Due to their unique ability to provide a variety of gear ratios in a verycompact space, planetary gear systems are seen in many applications from small poweredscrew drivers to automobile automatic transmissions. The versatile planetary gear device isoften studied as part of an undergraduate mechanical engineering program. Textbook pre-sentations typically illustrate how the different planetary gear components are connected.Understanding of the operation of the planetary gear set can be enhanced using actualhardware or simulations that show how the components move relative to each other. TheDepartment of Engineering Mechanics at the United States Air Force Academy has developed acomputer simulation of the planetary gear set and the Chrysler 42LE automatic transmission.Called PG-Sim, the dynamic simulations complement a static textbook presentation. PG-Simis used in several of our courses and assessment data clearly indicates students appreciationof its visual and interactive features. In this paper, we present an overview of PG-Sim and thendescribe how the simulation courseware facilitates understanding of the planetary gearsystem. C2232003 Wiley Periodicals, Inc. Comput Appl Eng Educ 11: 144C0155, 2003; Published online in WileyInterScience (.); DOI 10.1002/cae.10045Keywords: planetary gear set; Chrysler 42LE; PG-Sim; animation; coursewareINTRODUCTIONThe planetary gear set is an ingenious device ap-parently first used by the Romans in an astronomicalcomputer about 82 BC 1. Planetary gear sets haveseen use in the American automobile since theautomobiles inception. For example, the DuryeaPower Company implemented a planetary gear setin their transmission in 1897 2. Additionally, plane-tary gears were used in the Cadillac 3-speed in 1904and in the Ford Model-T 2-speed for many yearsuntil 1927. The 1940 General Motors Hydramaticmarked the first use of a fluid coupling incombination with a 4-speed planetary, fully automatictransmission 3. The how stuff works websiteCorrespondence to S. T. Dennis ().Published by Wiley Periodicals, Inc. This article is a USGovernment work and, as such, is in the public domain in theUnited States of America.144() states the amazingpiece of gearing, the planetary gear set, is the key tothe transmission and everything else is there to helpthe planetary gear set do its thing. All automatictransmissions rely on the planetary gear set fortransfer of power and gearing 4. In addition, plan-etary gear systems are used in manyother applicationsdue to their unique ability to provide a variety of gearratios in a very compact space.The planetary gear set is studied in undergraduatedynamics and machine design courses that are usuallyrequired in mechanical engineering programs. Theautomatic transmission is an excellent example of anapplication familiar to all. Indeed, Ref. 5 presentsthe 1940 Hydramatic automatic transmission as thesingle comprehensive case study that concludes theirmachine design textbook.An understanding of the planetary gear set operationand capabilities can be enhanced using actual hard-ware that shows moving components. In addition,computer simulations can aid in visualizing theplanetary gear set motion in an automatic trans-mission where the gear components are usuallyhidden by input or reaction splines, clutch packs,etc. This paper describes a computer simulation of theChrysler 42LE automatic transmission. The simula-tion, called PG-Sim for Planetary gear simulation,was developed in the Department of EngineeringMechanics at the United States Air Force Academy.PG-Sim facilitates understanding of how both asimple planetary gear train and a compound planetarygear set work in an actual transmission. The si-mulation is used in our machine design, automotivetechnology, and dynamics courses. Only the gearingis simulated; no control systems or fluid couplingsare demonstrated. For more information on theChrysler 42LE, see the SAE paper by Berthold andRedinger 6.From a pedagogical standpoint, PG-Sim adds sig-nificantly to the learning environment. When used inconjunction with other teaching techniques, it facil-itates complete navigation of theKolb cycle7,8.Thespecific manner in which PG-Sim enhances thelearning process, as well as assessment data showingthe affect of the simulation in the classroom are in-cluded in detail below.The simulation was originally inspired by the cadetsin a senior-level design course as part of a semester-long tasking to develop a teaching demo of anautomatic transmission 9. The authors adopted theapproach suggested by the cadets. We first describethe simulation and then discuss how it facilitateslearning of the planetary gear train in an actual trans-mission design.SIMULATIONThe purpose of the simulation is to demonstrate theoperation of a simple planetary gear set and illustrateits use in an actual applicationan automatic trans-mission. There are a number of advantages of thesimulation over a textbook-only presentation. A pri-mary advantage is that PG-Sim is dynamic; it showsmoving parts. Textbooks typically present schematicsof transmissions that show how components are con-nected, not their relative motions. In addition, PG-Simis interactive, highly visual, and illustrates a real-world application. The specific pedagogical advan-tages of these features of PG-Sim are discussed inmore detail below.Figure 1 shows the user interface where audio visualinterleaved (avi) files are activated by clicking oncertain command buttons. Other command buttonsdisplay joint photographic experts group (jpeg) filesthat give explanations of, for example, gear kine-matics or the Chrysler 42LE transmission, seeFigure 2. Along the bottom left of the user interfaceis the command button set that activates the simpleplanetary gear simulations. A planetary gear set iscomprised of a sun and ring gear and several planetgears. The planet gears are mounted on a carrier. Thestudent can review the laws that govern planetary setmotion, see Figure 3. The operation of a single plane-tary set is simulated once the user chooses one of thesun, ring, or carrier components for the driving orinput gear and a different component for the driven oroutput gear. The third component, by default, is theheld or fixed component. Six different combinationscan be simulated depending on the users choice forthe input and output components. Each of these sixcombinations produces a different gear ratio and de-termines if the system provides for a forward orreversegear. Figure 4 shows one of the six simulationsfor the simple planetary gear set.Along the right side of the interface are the commandbuttons that activate the 42LE automatic transmissionsimulations. The user chooses one of three radiobuttons for each of the five transmission gears.Figure 5 shows two views of one type of simulation.In Figure 5, we see a simulation of the outside of the42LE transmission that shows the five input orreaction splines. The first three splines, at left, arethe input splines and one or more turn at torqueconverter speed. That is, the input spline receivespower from the engine through the torque converterand fluid coupling. The splines are connected tocomponents of the compound planetary gear set. Thereverse spline, shown in darker grey in Figure 5, turnsat torque converter speed for reverse gear. The twoPG-SIM FOR MACHINE DESIGN COURSES 145splines at far right, allow planetary set components tobe held. Figure 5 shows the L/R (Low/Reverse)spline in dark grey to indicate that for reverse, thatspline is held. As the simulation progresses, some ofthe outer splines become translucent thus revealingthe compound planetary gear in motion within, see thebottom view of Figure 5.A second type of simulation is activated by choosingthe second radio button for any of the 42LEtransmission gears. Figure 1 shows reverse, as an ex-ample. In this simulation, the interaction of the twoplanetary gear sets of the 42LE is demonstrated. Thethird radio button for each 42LE transmission geardisplays a jpeg file that explains the gear ratio, seeFigure 6. Therefore, for each of the four forward andreverse gears of the 42LE, the user can choose twodifferent simulations (Figs. 1 and 5 show these forreverse) and an explanation of that particular gearsratio calculation (see Fig. 6).Finally, the smaller 42LE grouping of commandbuttons at the bottom of the interface gives someadditional information on the automatic transmission.The Explode command button activates a simula-tion that shows how the transmission components fittogether by showing the components disassembling.The 42LE Kinematics button provides an overviewof the transmissions kinematics and the resulting gearratios.Each of the gears for the 42LE transmissionwas modeled using AutoDesk InventorTM() and the models are based on Chryslersupplied drawings. Other components were approxi-mately modeled with Inventor using measurementsmade from the actual hardware. Assemblies of com-ponents were then imported into MSC visualNastran() for the dynamic simulations.The simulations were saved as avi files for activationusing Microsoft Visual Basic for the user interface.Figure 1 User interface. Simulation of reverse shows how planetary gear sets interact.Gears are colored to distinguish input, output, and held components.146 DENNIS AND JENSENHOW PG-SIM ENHANCES THELEARNING PROCESSA Multi-Faceted Learning EnvironmentIt is well established that different students learn indifferent manners 11,12. As previously mentioned,PG-Sim provides a learning environment that has thefollowing features: (1) dynamic, the gears move toshow their interaction, (2) highly visual, (3) inter-active, there are 25 different things the student canhavePG-Sim do, and (4) based on a real-world device,the 42LE is in current use in a number of Chryslervehicles. These different features allow students wholearn in different ways to find their niche. Felderspecifically advocates this type of learning experiencewhen he advises teaching across the spectrum oflearning styles 11. In the case of PG-Sim, studentswho learn visually, for example, have ample oppor-tunity to do so using the software. The real-worldapplication shown in PG-Sim provides increasedmotivation in certain groups of students. The inter-activity and dynamic nature of PG-Sim creates anactive learning environment that appeals to manytypes of students as well.PG-Sim in Light of the Kolb CycleThe Kolb model describes an entire cycle aroundwhich a learning experience progresses 7. The goal,therefore, is to structure learning activities that willproceed completely around this cycle, providing themaximum opportunity for full comprehension. Thismodel has been used extensively to evaluate and en-hance teaching in engineering 8,13C015. The cycle isshown in Figure 7. The Kolb model swings thependulum of learning engineering from an emphasison generalization and theory to a balance with allFigure 2 Kinematics development for simple planetary gear set. The kinematicsdevelopment taken from the course notes of Dr. Rob Redfield of the US Air ForceAcademy, and appears in Automotive Engineering Fundamentals, Stone and Ball 10.Color figure can be viewed in the online issue, which is available at .PG-SIM FOR MACHINE DESIGN COURSES 147modes of learning 16. Learning tools like inter-active, dynamic simulations are given an emphasis onequal footing with traditional modes like lecture pre-sentation of analysis and theory.In particular, PG-Sim reinforces three parts of thecycle: (1) Active experimentation, (2) Abstract hypo-thesis and conceptualization, and (3) Reflective obser-vation. PG-Sim enhances Active experimentationsimply by allowing the student to play with thedifferent simulations available. In many cases it hasbeen shown that students will spend significant timeusing multimedia content when they will not use thetext 17. The Abstract hypothesis and conceptuali-zation category is facilitated by providing detail onthe analysis of the gear ratios. Although this materialis most likely also included in the textbook, its in-clusion in the PG-Sim reinforces the link betweentheory and the real-world situation illustrated in thesimulations. The Reflective observation sectionfrom the Kolb cycle can be engaged by asking thestudents more abstract questions regarding details ofthe 42LE. An example might be to ask them how thetwo separate planetary gear systems in the 42LE areattached to each other and why that particular attach-ment was chosen by the Chrysler engineers. TheConcrete Experience section in the Kolb cycle is notdirectly addressed by PG-Sim. However, this fourth,and completing part can be engaged if a physicalplanetary set is made available for the students tomanipulate. Construction of a simple planetary set isnotatall complicated. Asan alternate,one canbe seenin a number of relatively inexpensive products like asmall power screw driver (see Fig. 8). In addition, inorder to further enhance this Concrete Experiencearea, it is possible to take the CAD files for the actual42LE and create physical models using rapid proto-typing technology. Figure 9 shows polyester 42LEparts we have fabricated using the rapid prototypingfacilities at the US Air Force Academy. Alternatively,a salvaged 42LE transmission can be purchased; localFigure 3 Laws of planetary gear set motion. Color figure can be viewed in the onlineissue, which is available at .148 DENNIS AND JENSENsalvage yards were asking from $90 for one youremove from the car, to $750 off the shelf.PG-Sim Use in EngineeringMechanics ClassesWe have used PG-Sim in three of our courses:Dynamics, Machine design, and Automotive technol-ogy. In all three classes, both professors and studentshave indicated that the simulation has been verybeneficial. In dynamics, PG-Sim fits well in thesection of the course devoted to relative motion. Arelative motion based derivation of the gear ratiosis given in Figure 2. In machine design, the use ofPG-Sim accompanies the material on gear trains.Most machine design texts have a specific sectiondevoted to planetary systems and the PG-Sim materialcan be used in conjunction with this text section. Inour automotivetechnology course, the PG-Sim is usedto provide details on the technology underlying theautomatic transmission.Assessment of PG-SimWe have assessed the PG-Sim software in two man-ners. First, we have asked professors that have usedthe simulation their opinion of the product. Second,we have surveyed the students who have used PG-Simto gain their perspective. The feedback from profes-sors has been very positive. They have commentedthat the software is very well constructed, easy touse and is a very helpful tool to enhance the learn-ing environment. In addition, we have received anumber ofideas on how to effectively use the softwareincluding combining the software with hands-onexercises using the actual transmission and using thesoftware to validate homework solutions.The student assessment data comes from a two-partsurvey which was given to 42 students who used thesoftware in the spring of 2002. The first part of thesurvey asks a series of seven short answer questions.The second part asks for numerical ratings in ninecategories.Figure 4 Simple planetary gear set simulation. Components are colored to distinguishinput, output, and held components. Color figure can be viewed in the online issue, whichis available at .PG-SIM FOR MACHINE DESIGN COURSES 149Figure 5 Simulation of reverse. Splines shaded dark gray indicate a component that is theinput from torque converter or a held component. Top figure shows initial outside view ofrotating splines. Bottom figure gives see through view revealing rotating inside planetarygear set components. Color figure can be viewed in the online issue, which is available .150 DENNIS AND JENSENWritten Feedback from Students. Table 1 belowshows the seven short answer survey questions.The dominant response to the first question was thatthe visualization was the most helpful. This was alsothe feedback given in response to question no. 6. Arepresentative response from a student reads, itmakes more sensewhenyou actually see the planetarygears in motion. Another student commented thatthe animations were what made the entire systemreal, such a stimulant really makes you want to jumpin and learn the material even further. Many studentscontextualized their response by adding that the inter-activity, exploded views, and color coding were es-pecially helpful. Three themes appeared in the studentresponses to question no. 2. The most common res-ponse was that the three radio buttons on the rightcolumn should be identified. This was also the mostcommon response to question 4 regarding navigationissues. Secondly, a few students requested that someinformation on thetorquetransferandvelocitiesof thegears be made available. Finally, a small number ofstudents requested that additional functionality beadded so that gear sizes could be changed. In futureadditions, we plan to incorporate the first two sug-gestions, i.e., identify the radio buttons and includeinformation on torque. The third suggestion, allow-ing students to change gear sizes, requires significanteffort and we believe is therefore not currentlyjustified.In the meantime, some additional help avenues wereadded to directly address the students concerns.Explanati