汽车理论英文PPT课件.ppt

ElementaryVehicleDynamics 汽车理论 1 Preface Whatcanwelearnfromthiscourse 2 What stheaimofthiscourse Tofindoutthereasonablemethodtodesignandusevehicleaccordingtotherelationshipamongtheparametersofstructureandperformanceofvehicle 通过车辆结构参数与性能之间的关系 找到正确设计汽车的方法和合理使用汽车的途径 3 Chapterone AccelerationPerformance 1 1EvaluationIndex 评价指标 1 MaximumVehicleSpeed Velocity 最高车速 uamax km h 1 Definition Themaximumspeedwhichthevehiclecangetundergoodandflatroadwithratedload 额定载荷 2 ActualMeasurementofuamax 4 2 AccelerationAbility 加速能力 1 Theaccelerationabilityforstarting 原地起步加速能力 TestCondition Fullenginepower 油门全开 Optimalshiftpointbetweengears 最佳换档时机 whicharefromlowgear 第 档 forstart uptohighgear 最高档 forfueleconomy EvaluationIndex TTisthetimeneededbythevehicletoacceleratefrom0to0 8Uamaxundertheabovetestconditionorthetimeneededtopassthroughafixeddistance 400mor mile 402 5m 用 档起步 按最佳换档时间 逐次换至高档 油门全开 以最大加速度行驶 全力加速至0 8uamax所需时间 或通过某一预定距离所需时间 2 Theaccelerationabilityforhighspeeddriving 超车加速能力 Testcondition Fullenginepower Highgear 最高档 orinferiorhighgear 次高档 Evaluationindex TTisthetimeneedtoacceleratefromtheminimumstablespeedofhighgear 最高档的最小稳定车速 to0 8Uamaxorthetimeneededtopassthroughafixeddistance 400mor mile 在直接档工作时 油门全开 由该档的最小稳定车速全力加速至0 8Uamax所需时间 或通过某一预定距离所需的时间 5 3 MaximumGradeabilityofVehicle imax 最大爬坡度 1 Definition Themaximumgradewhichthevehiclecanclimbinthefirstgear 档 undergoodroadconditionwithfullyratedload 额定满载 i tg EQ140imax 28 EQ240imax 58 30 2 ActualMeasurementofimax 6 1 2DrivingMechanicsofVehicle ToanalyzethebalancebetweenTotalRoads 行驶阻力 andTractiveForce 驱动力 alongonedegreeoffreedom 自由度 thatislongitudinaldirection 纵向 1 TractiveForce 驱动力 TorqueofEngineFlyingWheel NumericalRatiooftheTransmission NumericalRatiooftheFinaldrive Totalefficiencyofdriveline TorqueofDrivingWheel 7 1 TorqueofEngine Enginemaybecharacterizedbyitstorqueandpowercurveasafunctionofspeed Figure1 showstypicalcurvesforgasolineengine Figure1 Performancecharacteristics 外特性曲线 ofgasoline 8 FullperformanceandFullperformancewithalltheaccessories 外特性与使用外特性 9 UsefulformulasforPowercalculation Unit Pe kW Ttq Nm n r min 10 2 EfficienciesofDriveline Thenecessityoftheintroductionof T Theinefficienciesduetomechanicalandviscouslossesinthedrivelinecomponents transmission driveshaft differentialandaxles havenotbeentakenintoaccount Theseacttoreducetheenginetorqueinproportiontotheproductsoftheefficienciesoftheindividualcomponents T combinedefficiencyofdriveline consistsoffourprimaryparts 离合器变速箱传动轴驱动桥 11 3 TireRadius Definition NominalRadius 自由半径 theradiusoftirewithoutload sparetire备胎radius StaticLoadedRadius 静力半径 thedistancefromthecenterofstatictiretothecontactpointwithgroundunderverticalloadonly RollingRadius 滚动半径 theradiuswhichismeasuredbyS distancepassedbyvehicle andn rollingnumbers 12 4 GraphofTractiveForce 驱动力图 Howtomaketractiveforce speedcharacteristicsgraph 1 Mathematicalconversionbetweenn enginerevolutionspeed and vehiclespeed Note km h n r min r m 13 2 Makethegraph Twobasicformulasformakingthegraph Makethetractiveforcelineofeachgear given ofthevehicle given givenrandgiven 14 Makeallthecurvesofthevehiclefigure1 2 Figure1 2Tractiveforce speedcharacteristicsforamanualtransmission 15 3 Conclutionsfromthegraphoftractiveforce ConstantEnginePower isequaltothemaximumpoweroftheengine whichistheupperlimitoftractiveforceavailable lessanylossesinthedriveline Thecurvesillustratevisuallytheneedtoprovideanumberofgearratiosforoperationofthevehicle lowgearingforstart up andhighgearingforhigh speeddriving Formaximumaccelerationperformancetheoptimumshiftpointbetweengearsisthepointwherethelinecross Theareabetweenthelinesforthedifferentgearsandtheconstantpowercurveisindicativeofthedeficienciesof 缺乏 不足 thetransmissioninprovidingmaximumaccelerationperformance 16 2 RoadLoadforce 行驶阻力 1 RollingResistanceForce Ff 滚动阻力 Energylosses Duetothedeflectionoftires Duetothedeflectionofroadsurface convertedintotheheatwithinthetirescausedbythefrictionofrubberparticlesRollingresistancetorque Tf 滚动阻力偶矩 Tf Fz a 17 Themechanicsanalysisofdrivenwheelwithconstantrevolution assume RollingResistantForceofdrivenwheel 从动轮的滚动阻力 assumea r f Coefficientofrollingresistant 滚动阻力系数 conclution undergivenconditions stiffroad constantrevolutionspeed 18 assumed drivingforce rollingresistanceforceofdrivingwheeltotalrollingresistance Themechanicsanalysisofdrivingwheelwithconstantrevolution 19 Note 1 Rollingresistanceispresentfromtheinstantthewheelsbegintoturn 2 Therollingresistanceistheprimarymotionresistanceforce 3 Foroff highway levelgroundoperation therollingresistanceistheonlysignificantretardationforce 4 usuallyisequalto0 012 20 2 AerodynamicDrag 空气阻力 Aerodynamicforcesinteractwiththevehiclecausingdrag lift ordownload lateralforces andtheirindividualmoments TheAerodynamicforcesproducedonavehiclearisefromtwosources Note 1 TotalInternalDragcomprisesofairflowmanagementofcoolingsystemandinsideventilationofthebody 发动机冷却 车身通风 Withnoattentiontotheneedforairflowmanagement theairenteringthroughtheradiatordissipatesmuchofitsforwardmomentumagainstthevehiclecomponentsintheenginecompartmentbeforespillingoutthroughtheundersideopenings Themomentumexchangetranslatesdirectlyintoincreaseddrag 21 2020 3 19 22 2 Bernoulli sEquation P 大气压 空气密度 C 常数Zerounderbody 车身底板 airspeedproducesthepressuredifferenceLiftForceunsmoothedunderbodypanelInducedFriction theprojectionofliftforcealongthelongitudinaldirection minimizingunderbodydragistheuseofasmoothunderbodypanel 3 ForminimizingFormDragweadoptthebodyofstreamlinedshape 流线形 whichisusuallybedescribedasdrop likebody 23 CalculationofAerodynamicForces FwSemi empiricalmodels Where Aerodynamicdragcoefficient 空气阻力系数 Frontalareaofthevehicle 迎风面积 Airdensity 空气密度 RelativeVelocity 相对速度 InternationalCD ChinaCDCars0 30 0 35Cars0 4Vans0 33 0 35Vans0 6Pickuptrucks0 42 0 46Pickuptrucks0 8Becauseofua km h ur m s ur ua 3 6 m s nowind So 24 3 UphillGradeResistanceForce Fi 坡道阻力 Define RoadResistance 道路阻力 Define RoadResistanceCoefficient 道路阻力系数 25 4 AccelerationResistance Fj 1 Translationalmassinertialforce 平移质量惯性力 Fj1G g 质量du dt 加速度2 Rotationalmassinertialforce moment 回转质量惯性力or力矩 Tj Fj2 rotatingcomponentscompriseofflywheel gearsystem shafts axles wheels I 转动惯量d dt 角加速度Inertialmomentforflywheel e angularvelocityofflywheel w angularvelocityofwheelUa vehiclespeedr radiusofwheel 26 DeliverTftodrivingwheel Tfw2 Totalinertialmomentforwheelandrotationalmassinertialforce Tj Fj23 TotalInertialForce FjAssumed rotationalmasscoefficient 回转质量换算系数 So 27 3 DrivingEquation 行驶方程 1 Generalmodelofdrivenwheel 2 Generalmodelofdrivingwheel 28 3 Generalmodelofvehicle Note Fjw2comprisesoftwoparts 1 therotationalmassinertialforceofflywheelthatisdeliveredintothedrivingwheel 2 therotationalmassinertialforceofthedrivingwheelitself Forgeneralmodelofthevehicle FpandFtareconsideredasinternalforces sothereisnoFpandFtonthegraph FtandFfaretheresultofassumption sothereisneitherFtnorFfonthegraph 29 1 3Traction LimitedAcceleration 1 DrivingConditionofAccelerationWhenLevelroad Constantspeed Levelroad Constantspeed Forconstantspeed 匀速 acceleration 加速 deceleration 减速 SoDrivingCondition 驱动条件 is 30 2 LimitedConditionofAcceleration 附着条件 Presumingthereisadequatepowerfromtheengine theaccelerationmaybelimitedbythefrictionthatisbetweenthetireandroadforanti skidpurpose Inthiscaseis 限制车轮打滑的极限力 Where Coefficientoffriction 道路附着系数 Weightondrivewheels 驱动车轮上道路垂直反力 usuallyrangesfrom0 7 0 8 3 Traction limitedAcceleration 驱动附着条件 31 4 TractionLimits maximumtractiveforce 最大牵引力 Clew Independentfrontdriveaxle maximumtractiveforceforfrontdriveaxle Independentreardriveaxle maximumtractiveforceforreardriveaxle 1 by equilibriumofstaticequilibrium 求矩 2 when 32 Forreardriveaxle rear wheel drivecars Alsointhecaseoffrontdriveaxle front wheel drivecars Inthecaseoffour wheel drivecars 33 5 percentageofutilizationofmaximumtractiveforce 附着利用率 Definition 汽车附着力 全轮驱动汽车附着力 附着利用率 Where Maximumtractiveforceoffront wheel drivecarsMaximumtractiveforceofrear wheel drivecarsMaximumtractiveforceoffour wheel drivecarsForfront wheel drivecars rear wheel drivecars four wheel drivecars 34 Graphof Note increaseleadstodecreaseinthecaseoffron wheel drive isthepercentageofutilizationofcars weightonthedriveaxle Forwardlongitudinalweighttransfer andincreaseinthecaseoffront wheel drivecar 质心偏移 Forcarstheloadonthefront drive axleisusuallyhigherthantheloadontherearaxle 前部轴荷 后部轴荷 35 1 4TractiveForce DrivingResistance SpeedCharacteristics 驱动力 行驶阻力平衡图 FromDrivngEquation whenlevelroad constantspeedTo DrivingResistancecomprisesofand Analyze AccelerationPerformanceofthevehiclethroughTractiveForce DrivingResistance SpeedCharacteristics 1 MaximumVehicleSpeed Velocity km h Soisthecorrespondingx coordinateofthecrosspointofthedrivingresistancecurveandthetractiveforcecurveofthefourth high speed gear 36 2 MaximumGradeabilityofVehicle Themaximumuphillgraderesistanceforcewhichthevehiclecouldovercome Fi 坡道阻力 3 AccelerationAbilityEstimate Theaccelerationabilityofthevehicleatanyspeed ua1 thetractiveforcewhichthevehicleneedtodrivewithconstantspeed ua1 themaximumtractiveforcewhichcouldbeusedtoaccelerateatthisspeed ua Conclusion Theaccelerationabilitychangeswiththechangeofgear Highergearleadstoloweraccelerationability Changingthepositionofpedalmaketheconstantspeeddrivepossiblebecausethetractiveforce speedcurvewouldmoveupanddownverticallywiththechangeofinjectionsystem theforce speedcurvesshownaboveistheupperlimitonesofthevehicle 37 1 5DynamicCharacterofVehicle 汽车的动力特性 Inordertomaketheanalysisofdynamicperformancesimpler weuseanothergroupofcharacteristiccurveswhichcomprisetheDynamicCharacteristicGraph 动力特性图 ofthevehicle Method Therightsideoftheequationconcernsthegradeabilityandaccelerationabilityonly ithasnothing