吉林大学汽车理论汽车动力性

1、第一章汽车动力性Vehicle Performance主要研究内容: 分析受力; 建立行驶方程式; 以图、表(或编程)形式，按照评价指标，确定汽车的动力性。定义在平直良好路面上行驶时所能达到的平均行驶速度。Definition : At the good and straight and even track, the auto driving can reach at the average speed.Main contents:Analysis is subjected to the reactions;Establishing the motion equation of vehicl

2、e;With the form of the diagram, the table or the plait distance), press the vehicle tractive evaluation index, make sure the motion of the vehicle.汽车动力性Veh. Perf.第一章 汽车动力性1.1 汽车动力性评价指标1.2 汽车驱动力和行驶阻力1.3 汽车驱动力附着条件以及附着力1.4 汽车驱动力行驶阻力平衡图1.5 汽车功率平衡1.1 Traction performance evaluation index1.2 Traction forc

3、es and the resistance as vehicle driving1.3 Driving traction force , adhesive condition and its forces1.4 Balance diagram between the traction force & driving resistance1.5 Power balanceVehicle traction performance1.1 汽车动力性评价指标最大车速 umax加速时间 t最大爬坡度 imaxIndex Evaluating Vehicle Traction Performance Ma

4、ximum SpeedAcceleration TimeMaximum grade加速时间评价方法超车加速时间 Overtaking acceleration time 以最高档或次高档，以amax加速至某一高速所用的时间。原地起步加速时间 The start acceleration time 由I或II档起步，以amax，并考虑换档时间，一般用0400m或0100km/h的时间表示原地起步的加速时间。Method evaluating acceleration time 最高车速 Max Speed最高车速，是指汽车在平直的良好道路(混凝土或柏油)上所能达到的平均最高行驶车速。Max. s

5、peed, means that the vehicle drives on the straight and even and good (concrete or asphalt) roadway can reach at the average and largest speed.汽车加速过程曲线VelocityTimeDiagram of velocity vs timevehicle acceleration history 车速Gear shifting爬坡能力的评价 以满载、良好路面上的imax来表示: 商用车30或16.5； 越野汽车60或31。 轿车最高车速较大，且通常在良好的

6、市区道路行驶，其爬坡度很大。对其无这项要求。 有的国家要求汽车在常遇坡道上汽车必须保持的速度来表明其加速能力。The sloping ability evaluationSome nations request the MV on often meeting the road of slope the speed that the MV must keep to expresses that it accelerates the ability.发动机传动系离合器、变速器、分动器、传动轴、主减速器、半轴驱动轮驱动力行驶阻力滚动阻力坡度阻力加速阻力空气阻力汽车动力传递路线：发动机离合器变速器副变

7、速器传动轴主减速器差速器半轴轮边减速器车轮1.2 汽车驱动力和行驶阻力1.2 Traction forces and resistances as vehicle driving平衡1.2 汽车驱动力和行驶阻力Traction force and resistances as vehicle driving驱动力滚动阻力空气阻力加速阻力爬坡阻力驱动转矩行驶阻力发动机转矩Traction forcetraction effortdriving force图1-2 汽车驱动力MV Traction ForceNormal reactionGravitySpeedRadiusTorque部分负荷特性

8、：节气门部分开启时，转矩或功率等与转速的关系使用负荷特性曲线：即带有附件时的负荷特性，通常汽油机下降15，而柴油机下降10外特性曲线：节气门(油门)全开时，转矩或功率等与转速的关系发动机速度特性full throttle/acceleratorrpm:revolution per minute 图1-3 汽油发动机外特性Braking Power ,kWRevolution, rpmCharacteristic of engine speed at full throttleBraking Torque, .m发动机过渡工况的速度特性在过渡工况，功率和转矩均下降约5%6%。Characteri

9、stic of the engine speed in transient conditionIn transient condition, power and torque all descend about 5%-6%.外负荷特性的使用和制作方法表格法（辅助插值）曲线族法数学模型法n1n2n3nnPe1Pe2Pe3PenTt1Tt2Tt3Ttnbe1be2be3benFull-load characteristic diagram methodInterpolation with tableCurvesModeling外特性及负荷特性数学描述Modeling for Full- & par

10、t-load characteristicm7 mopt5Braking Power ,kW图1-4 汽油发动机外特性及部分负荷特性Characteristic of engine speed at full and part loadengine speed, r/minBraking Torque, N.m发动机负荷特性经验公式Approximation for Full- & part-load characteristic传动系功率损失机械损失液力损失摩擦润滑油齿轮传动副间摩擦轴承摩擦。润滑油的搅动润滑油与零件表面间摩擦。传动系机械效率T Transmissions efficienc

11、yPower lossLiquid L.Mecha. L.RubLubr.传动系机械效率T Transmissions efficiency损失主要部件: Parts causing to lose 变速器和主减速器(含差速器)损失主要形式: Forms causing to lose 液力损失和机械摩擦损失 Mechanical loss & liquid loss液力损失,如搅动和磨擦。与润滑油的性能、温度、转速、油面高度等有关。46档变速器 4-6speed gearbox 0.9668档变速器 6-8speed gearbox 0.95传动轴 drive shaft 0.98离合器 C

12、lutch 0.98主减速器 differential 0.96-0.92半轴 semi-shaft 0.99汽车机械效率 MV mechanical efficiency轿车 Passenger car T=0.900.92商用车 Commercial Veh.T=0.820.85越野车(SUV) 4W drive Veh.T=0.800.85典型的传动系效率值Typical drive system efficiency某汽车变速器的机械效率Mechanical efficiency of MV gearbox轮胎半径r Tire radius自由半径 r Unloaded radius静

13、力半径 rs Static radius with load滚动半径 rr Dynamic radius with load rr= rs = r=s/(2nw)S行驶距离 trip，n 转动圈数 revolutions欧洲轮胎与轮辋委员会(ETRTO)推荐 rr= Fd/(2) F=3.05 radial F=2.99 bias德国橡胶工业协会推荐 CR=CR(1+ua/1000),mmCircumference length轮胎半径r（mm)车型规格自由静力滚动桑塔纳2000195/60R1429532685286红旗CA7228l85/70HRl431232855301奥迪100195/

14、65Rl531732915308跃进NJl0617.00-2045244306448解放CA10919.00-2050954856492东风EQl0929.R2050954766493黄河JNll8111.00-2054265177525大 小 中定义：用Ft-ua曲线图来全面地描述汽车的驱动力。若已知外特性曲线、传动系速比、传动系机械效率、车轮半径就可求计算驱动力。汽车驱动力图 MV traction force diagramDefinition:Use the Ft-ua curves to describe completely the MV traction force. If on

15、e has already known the full load characteristic curve, transmission , system efficiency and rolling radius, one can calculates the traction forces.转速速度线性变换转矩驱动力线性变换驱动力图制作 Drawing diagram of tractionSp ISp IISp IIITractionMV VelocityMV traction diagram驱动力汽车行驶阻力滚动阻力Ff :轮胎内部摩擦产生的迟滞损失。这种迟滞损失表现为阻碍车轮运动的阻

16、力偶。MV driving resistanceRolling resistance Ff: the tire inner part rub causes to loss, this kind of lose performance shows the resistance moment of the wheel motion.轮胎径向变形曲线 Tire radius deforming curveDamping loss轮胎/路面接触轮胎变形载荷迟滞损失阻力偶loadunload从动轮Driven Wheel滚动阻力系数 f rolling resistance coefficient轮胎内

17、部因摩擦产生的迟滞损失表现为阻碍车轮运动的阻力偶.The damping loses caused by tire inner inter-rubs are shown as the resistance moment against wheel motion滚动阻力系数:车轮在一定条件下，滚动所需要推力Fp1与负荷W1之比，即单位重力的推力。Rolling resistance coefficient: wheel under the certain condition rolls over with the ratio of push force Fp1 to weight W1, nam

18、ely push force for the unit gravity .阻力偶一般用滚动阻力描述roll resistance moment is depicted by rolling resistance.滚动阻力无法在受力图上画出。它是一个数值,在受力图上它是切向反力。Roll resistance cant be drawn in being subjected to the reaction diagram, It is only one value. There is a longitudinal reaction in the force diagram.在实际计算时可不必考虑

19、阻力偶，而用滚动阻力描述。While computing physically need not consider the resistance pair, but use to roll resistance.试验确定法牵引法、滑行法和转鼓法经验法 通过以往试验结果归纳的经验公式滚动阻力系数的确定方法室内试验道路试验滚动阻力系数的影响因素1. 速度 ua 对 f 的影响creating a phenomenon of standing wave, heat, shed off, burst.Effect of velocity ua on resistance coefficient f.驻

20、波弹性轮胎在滚动时，胎面各部份都反复处于受力变形和恢复原形的状态。这个运动过程使轮胎的变形恢复到原状的力有弹力、胎压和离心力等。轮胎从接地受力变形，到离开地面后恢复原状，存在滞后时间。其长短与轮胎负荷、转速、工作温度和环境温度等有关。负荷大，胎面变形大; 转速高，胎面离心力大。离心力使胎面反向变形，这样胎面在正、反方向力的交替作用下造成不同胎面部位半径的波动。当轮胎行驶速度超过轮胎的挠屈变形极限速度后，此胎面波动看上去变形移动的状态恰似停止，称作驻波。常发生在胎肩与胎侧交界区。 2.轮胎结构、材料、帘线对 f 的影响也很大。子午线轮胎 f 小，天然橡胶 f 低。The tire structu

21、re, material, the influence of the lines upon the f is also very big. The meridian tire f is small, the crude rubber f is low.f 经验公式 fit for fCommercial veh.Passenger carPassenger carCommercial veh.While turning normally驱动轮受力图Forces reacting on drive wheel切向力Circumferential Force真正驱动车轮前进的力是地面切向反力FX2

22、。其在数值上等于汽车驱动力Ft与滚动阻力Ff之差驱动力与地面纵向（切向）力定义：汽车直线行驶时受到的空气阻力在汽车行驶方向上的分力。分类：压力阻力和摩擦阻力压力阻力由形状阻力、扰动阻力和诱导阻力组成。形状阻力主要与汽车的形状有关，约占58。空气阻力drag or air resistanceCD对高速汽车动力性和燃料经济性影响极大! 干扰阻力：汽车上的突出部件，如后视镜、门把手、导水槽、驱动轴、悬架导向杆等，约占14。 内循环阻力：发动机冷却系、车身通风气流等流过汽车内部形成的，占12。 诱导阻力：空气升力在水平方向的分力，占7。 摩擦阻力：9。空气阻力Fw正比于气流相对运动的动压力。Fw的影

23、响因素：CD和A。A由于乘坐空间的制约变化不大,CD变化较大。19501970年为0.40.6,1990年为0.250.40,概念车约为0.2,当前 Passat 0.28。1. 前部低 2. 过渡平滑3. 后部加扰流板4. 掠背式(舱背式)5. 底部导流、平整化，向后应逐步升高6. 整车俯视形状为腰鼓式7. 改进气流进、出口位置8. 商用车顶(侧)部安装导流罩CD降低的要点降低汽车空气阻力的基本思路Basic thought for decreasing aerodynamic drag MV坡道阻力grade resistanceRoad resistance coefficientGra

24、de angle 汽车行驶方程式MV motion formulaCorrelation of drive force and driving resistance隔离法：平面受力图driven tireInsulation method: force diagram with two dimensionsLongitudinal forceNormal forcetangential reactioncircumferential force从动轮受力分析 reaction analysis of the moved tireVertical forceNormal reaction从动轮受

25、力分析（续）analysis of forces on the moved tire隔离法：受力图Forces reacting on drive tireInsulation method: force diagram with two dimensions驱动轮受力分析Forces acting on the tracition tire除以r驱动轮受力分析(续)Forces on the tracitive tire加速时车身受力图Force diagram on the body while acceleration车体受力分析 forces on the body飞轮惯性矩Flywh

26、eel inertial车体受力分析 (续) forces on the body车体受力分析 (续) forces on the body车体受力分析 (续) forces pressed on the body汽车行驶方程式_总结 只是表示各个物理量之间的数量关系。 有些项并不是外力。Ft不是作用于车轮上的切向反作用力，仅为了计算方便才定义为驱动力。 滚动阻力也不是作用于汽车上的阻力，而是以滚动阻力偶矩的形式作用于车轮上。 作用在汽车上的惯性力是mdu/dt，而不是mdu/dt。飞轮惯性力矩作用在汽车的横截面上，而不作用于车轮上。 Fj 代表惯性力和惯性力矩的总效应。1.3 汽车行驶驱动-

27、附着条件及汽车附着力1.汽车行驶驱动附着条件Driving traction, adhesive condition and its forceDriving tractionadhesive condition驱动（行驶）的必要条件:Driving essential condition:the adhesive condition between the tire and ground tire shows the phenomenon of slide revolution on the road 后驱动汽车Fz2Reaction of ground on traction tire,

28、i.e. It is controlling the second condition that MV drives. generally is the necessary and full conditions that the MV drives.Rear drive MV2. 汽车附着力 MV adhesive force在硬路面上， 主要取决路面的种类和状况，也与 有关。On the hard road, it depends mainly on the category and conditions of road surface, also is relevant with the

29、 velocity路面类型 混凝土（干） 混凝土（湿）附着系数 0.70.8 0.50.6路面类型 碎石 土路（干） 土路（湿）附着系数 0.60.7 0.50.6 0.20.4L=wheel baseB=wheel track前轮驱动和后轮驱动时的地面反力对后轮取矩，得到Torque received on rear tire , givenRoad Reactions on front/rear drive tire对前轮取矩，得到Torque received on front tire, given轴距增加，重心高度小，动载荷减小。良好路面Static load on axleDyna

30、mic load on axle前轮静载荷 static load front tire 后轮静载荷static load rear tire Getting from above formulae由此得到For rear drive对于后驱动后驱动地面附着力adhesive force of rear driveFor rear drive对于前驱动前驱动地面附着力adhesive force of front driveFor 4WD(AWD)Prior conditionThen it can make use of well前轮、后轮驱动附着利用率For RWDFor FWDUtili

31、zation of MV adhesives while front or rear axle driveUsually for front drive MV , the static load of front axle larger then that of rear axle. The position of the mass center can be determined by means of weighing.附着利用率RWDFWD4WDAdhesive factorAdhesive utilizationAdhesive utilization depending on dri

32、ve type1.4 汽车驱动力-行驶阻力平衡图便可分析在附着良好的典型路面上汽车的行驶能力。即在油门全开时，汽车可能达到最大速度、加速能力和爬坡能力。汽车行驶方程式反映了汽车行驶时，驱动力和外界阻力之间的普遍情况；若已知1.4 balance Between Traction & driving MV resistanceThe driving equation shows the correlation between the traction and driving resistance when the MV drives. Ifare known, can analyze then

33、the driveability of MV on the good road to face, namely at full acceleration pedal, the MV may attain the max. speed, acceleration ability and grade ability. 驱动力与行驶阻力平衡图定义：为了清晰地描述汽车行驶时受力情况及其平衡关系，通常将平衡方程式用图解方式描述，即将驱动力Ft和常见行驶阻力 Fw 和 Ff 绘在同一张图上。1. 最高速度和部分负荷时的平衡2. uamax3. 最大爬坡度diagram of the equilibrium

34、 between drive force and driving resistanceDefinition: For describing the automobile to drive clearly be subjected to the reaction and its balance relations, usually draw equilibrium equation to illustrate the way to carry on the description, ie draw the drive force Ft and the driving resistance Fw

35、and Ff in the same diagram.1. max speed and force balance for part load (see next page)2.uamax3. max grade climbing汽车驱动力行驶阻力平衡图FtSpeed, ua (km/h)equilibrium between drive force and driving resistancedrive force2. 加速能力，可用aj评价,， 但不方便，常用加速时间或加速距离来评价。加速度倒数：Acceleration reciprocalAcceleration timeAcceler

36、ation travel汽车加速度速度图Speed, ua,km/hDiagram of acceleration vs velocity MV ua is different from uAcceleration aj,m/s2加速度倒数曲线图1/ajua,Diagram of acceleration reciprocalacceleration reciprocaltSpeed, km/h将驱动力、滚动阻力和空气阻力计算出，就可按公式计算加速度及其倒数，从而求得加速时间或者加速距离。After computing drive force, roll resistance and air

37、resistances, it can be computed the acceleration and its reciprocal according to the formula and get the acceleration time or travel.手工计算时一般忽略原地起步过程的离合器打滑过程，即假设在最初时刻，汽车已具备起步换档所需的最低车速。换档时刻的确定：若I-II加速度曲线相交，规定在交点处换档；若I-II的加速度曲线不相交，则规定在发动机最高转速处换档；换档时间一般忽略不计（正态分布t=0.2-0.4s)。计算加速时间的用途：确定汽车加速能力；传动系匹配情况；合理选

38、择发动机的排量。注意NoticeGenerally when handicraft computes, at first ,the slide of clutch at the start process is neglected, then the assumption is in the first time, the MV has already had the lowest speed that start need when shift gear.Time of shift gear to determine: If the gear 1st- 2nd acceleration cu

39、rves is intersected, then shift gear 1st to 2nd; If the acceleration curves of the gear 1st and 2nd is not intersected, then at max engine speed shift the gear 1st to 2nd; neglect shift gear spending time. (normal distribution t=0.2-0.4 s)Use of computing acceleration time: to determine MV accelerat

40、ion ability, trade-off power-train; reasonably choose displacement of the engine.3. 利用驱动力行驶阻力平衡图确定汽车爬坡能力Its prior condition is a road surface good, except overcoming the Fw+ Ff ,all drive force is used for overcoming a grade resistance, namely.Diagram of equilibrium of drive force - driving resistan

41、ce to determine grade ability of MV其前提条件是路面良好，汽车克服Fw+Ff后的全部力都用于克服坡道阻力，即坡度通常用i表示i represents grade usuallyMV gradient iSpeed, km/himax is max sloping gradient for 1st gear.i0max is max sloping gradient for top gear.Objective: decreasing the number of shift on normal slope, which makes the speed of MV

42、 slowly down. 二、动力特性图评价汽车动力性unit drive force to evaluate MV tractive performanceNormalized drive forcedrive factorCharacteristic of normalized drive force and its use汽车动力特性图及其用途To solve imax ,let While MV acceleration, the road must be flatness. i.e.1.5 汽车功率平衡 MV power balance 汽车在行驶时驱动力与阻力平衡 发动机输出功率也与行驶阻力功率平衡定义：用纵坐标表示功率，横坐标表示车速，将发动机功率与经常遇到的阻力功率对车速的关系绘制在直角坐标图上，就得到功率平衡图。The traction and resistance balances when the MV drivesThe engine power output also balances with the driving resistance power. Definition: let vertical coordinate as the power, horizontal coordinate as MV speed, draw diag