汽车理论课件汽车理论英.ppt

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1、Elementary Vehicle Dynamics（汽车理论）PrefaceWhat can we learn from this course?The six fundamental performances of vehicleAcceleration Performance(动力性）动力性）Economical Performance（经济性）（经济性）Braking Performance（制动性）（制动性）Passing Ability（通过性）（通过性）Handling Performance(操纵稳定性操纵稳定性)Connering&Rollover Ride Perform

2、ance(行驶平顺性）行驶平顺性）Whats the aim of this courselTo find out the reasonable method to design and use vehicle according to the relationship among the parameters of structure and performance of vehicle.（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）Chapter one Acceleration Performance1.1 Evaluation Index（评价指标）1

3、.Maximum Vehicle Speed(Velocity)最高车速uauamax(km/h):（1）Definition：The maximum speed which the vehicle can get under good and flat road with rated load（额定载荷).（2）Actual Measurement of uauamax2.Acceleration Ability（加速能力）（1）The acceleration ability for starting(原地起步加速能力)Test Condition:Full engine power（油门

4、全开）;Optimal shift point between gears（最佳换档时机）which are from low gear（第档）for start-up to high gear（最高档）for fuel economy.Evaluation IndexT T is the time needed by the vehicle to accelerate from 0 to 0.8Uamax under the above test condition or the time needed to pass through a fixed distance（400 m or mi

5、le(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）The acceleration ability for high speed driving(超车加速能力)Test condition:Full engine power ;High gear（最高档）or inferior high gear（次高档）Evaluation indexTT is the time need to accelerate from the minimum stable speed of high

6、 gear(最高档的最小稳定车速）to 0.8Uamax or the time needed to pass through a fixed distance（400 m or 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）3.Maximum Gradeability of Vehicle imax（最大爬坡度）（1）Definition：The maximum grade which the vehicle can climb in the first gear（档）under good road condi

7、tion with fully rated load（额定满载）.i=tg EQ140 imax=28%EQ240 imax=58%=30（2）Actual Measurement of imax1.2 Driving Mechanics of Vehicle To analyze the balance between Total Roads（行驶阻力）and Tractive Force（驱动力驱动力）along one degree of freedom（自由度）that is longitudinal direction（纵向）.1.Tractive Force（驱动力）Torque

8、of Engine Flying Wheel Numerical Ratio of the Transmission Numerical Ratio of the Final drive Total efficiency of driveline Torque of Driving Wheel(1)Torque of Engine Engine maybe characterized by its torque and power curve as a function of speed.Figure 1.shows typical curves for gasoline engine.Fig

9、ure 1.Performance characteristics（外特性曲线）of gasolineFull performance and Full performance with all the accessories(外特性与使用外特性外特性与使用外特性)Useful formulas for Power calculationUnit:Pe(kW);Ttq(Nm);n(r/min)。（2）Efficiencies of DrivelinelThe necessity of the introduction of T:The inefficiencies due to mechani

10、cal and viscous losses in the driveline components（transmission;driveshaft;differential and axles）have not been taken into account.These act to reduce the engine torque in proportion to the products of the efficiencies of the individual components.l T（combined efficiency of driveline）consists of fou

11、r primary parts:离合器 变速箱 传动轴 驱动桥 （3）Tire RadiusDefinition:lNominal Radius（自由半径）：the radius of tire without load（spare tire 备胎 radius).lStatic Loaded Radius（静力半径）：the distance from the center of static tire to the contact point with ground under vertical load only.lRolling Radius（滚动半径）：the radius whic

12、h is measured by S(distance passed by vehicle）and n(rolling numbers).（4）Graph of Tractive Force（驱动力图）lHow to make tractive force-speed characteristics graph：1）Mathematical conversion between n（engine revolution speed)and （vehicle speed）Note:(km/h);n(r/min);r(m)2）Make the graphlTwo basic formulas for

13、 making the graph:lMake the tractive force line of each gear（given ）of the vehicle（given&given r and given ）：lMake all the curves of the vehicle figure1.2:Figure 1.2 Tractive force-speed characteristics for a manual transmission3)Conclutions from the graph of tractive force:l“Constant Engine Power”i

14、s equal to the maximum power of the engine;which is the upper limit of tractive force available,less any losses in the driveline.lThe curves illustrate visually the need to provide a number of gear ratios for operation of the vehicle(low gearing for start-up,and high gearing for high-speed driving).

15、lFor maximum acceleration performance the optimum shift point between gears is the point where the line cross.lThe area between the lines for the different gears and the constant power curve is indicative of the deficiencies of（缺乏，不足）the transmission in providing maximum acceleration performance.2.R

16、oad Load force（行驶阻力）（1）Rolling Resistance Force F f（滚动阻力）l Energy losses:Due to the deflection of tires:Due to the deflection of road surface:converted into the heat within the tires caused by the friction of rubber particlesl Rolling resistance torque T f（滚动阻力偶矩）T f=F zaThe mechanics analysis of dr

17、iven wheel with constant revolution assume Rolling Resistant Force of driven wheel （从动轮的滚动阻力）assume a/r=f（Coefficient of rolling resistant）滚动阻力系数滚动阻力系数 conclution:under given conditions(stiff road;constant revolution speed)assumed:driving force rolling resistance force of driving wheel total rolling

18、 resistance :The mechanics analysis of driving wheel with constant revolutionNote:1.Rolling resistance is present from the instant the wheels begin to turn.2.The rolling resistance is the primary motionresistance force.3.For off-high way,level ground operation,the rolling resistance is the only sign

19、ificant retardation force.4.usually is equal to 0.012.（2）Aerodynamic Drag(空气阻力)Aerodynamic Drag（空气阻力）（空气阻力）Pressure Drag（压力阻力）（压力阻力）Vicious Friction（摩擦阻力）（摩擦阻力）Form Drag-形状阻力形状阻力 58%Total Protuberance Drag-干扰阻力干扰阻力 14%Total Internal Drag-内循环阻力内循环阻力 12%Induced Drag-诱导阻力诱导阻力 7%lAerodynamic forces inte

20、ract with the vehicle causing drag，lift（or down load），lateral forces，and their individual moments.lThe Aerodynamic forces produced on a vehicle arise from two sources：Note:1）Total Internal Drag comprises of air flow management of cooling system and inside ventilation of the body.（发动机冷却、车身通风）With no

21、attention to the need for air flow management,the air entering through the radiator dissipates much of its forward momentum against the vehicle components in the engine compartment before spilling out through the underside openings.The momentum exchange translates directly into increased drag.2）Bern

22、oullis Equation：P-大气压；-空气密度；C-常数 Zero underbody(车身底板)air speed produces the pressure difference Lift Force unsmoothed underbody panel Induced Friction（the projection of lift force along the longitudinal direction）（minimizing underbody drag is the use of a smooth underbody panel）3）For minimizing Form

23、 Drag we adopt the body of streamlined shape (流线形）流线形）which is usually be described as drop-like body.Calculation of Aerodynamic Forces FwSemi-empirical models：Where:Aerodynamic drag coefficient（空气阻力系数）Frontal area of the vehicle（迎风面积）Air density（空气密度）Relative Velocity（相对速度）International CD:China CD

24、 Cars 0.300.35 Cars 0.4 Vans 0.330.35 Vans 0.6 Pickup trucks 0.420.46 Pickup trucks 0.8Because of ua(km/h)；ur(m/s)；ur=ua/3.6(m/s)(no wind)So（3）Uphill Grade Resistance Force F i（坡道阻力）Define:Road Resistance（道路阻力）Define:Road Resistance Coefficient （道路阻力系数）（4）Acceleration ResistanceFj1.Translational mas

25、s inertial force（平移质量惯性力）Fj1G/g质量 du/dt加速度2.Rotational mass inertial force(moment)（回转质量惯性力or 力矩）（Tj;Fj2）(rotating components comprise of fly wheel,gear system,shafts&axles,wheels)I转动惯量 d/dt角加速度1)Inertial moment for fly wheel 2)3)4)5)6)e angular velocity of fly wheel7)w angular velocity of wheel8)Ua

26、vehicle speed9)r radius of wheel Deliver Tf to driving wheel Tfw2)Total inertial moment for wheel and rotational mass inertial force Tj；Fj23.Total Inertial Force FjAssumed:rotational mass coefficient （回转质量换算（回转质量换算系数）系数）So 3.Driving Equation（行驶方程）1)General model of driven wheel:2)General model of dr

27、iving wheel:3）General model of vehicle:Note:Fjw2 comprises of two parts:1）the rotational mass inertial force of fly wheel that is delivered into the driving wheel;2）the rotational mass inertial force of the driving wheel itself;For general model of the vehicle,Fp and Ft are considered as internal fo

28、rces,so there is no Fp and Ft on the graph.Ft and Ff are the result of assumption,so there is neither Ft nor Ff on the graph.1.3 Traction-Limited Acceleration（1）Driving Condition of AccelerationWhen Level road:Constant speed:Level road&Constant speed:For constant speed:（匀速）acceleration:（加速）decelerat

29、ion:（减速）So Driving Condition（驱动条件）is（2）Limited Condition of Acceleration （附着条件）Presuming there is adequate power from the engine,the acceleration may be limited by the friction that is between the tire and road for anti-skid purpose.In this case is：（限制车轮打滑的极限力）Where:Coefficient of friction （道路附着系数）W

30、eight on drive wheels（驱动车轮上道路垂直反力）（3）Traction-limited Acceleration（驱动附着条件）（4）Traction Limits(maximum tractive force)（最大牵引力）Clew:Independent front drive axle (maximum tractive force for front drive axle)Independent rear drive axle (maximum tractive force for rear drive axle)1）by(equilibrium of static

31、 equilibrium)(求矩)2）when:For rear drive axle(rear-wheel-drive cars):Also in the case of front drive axle(front-wheel-drive cars):In the case of four-wheel-drive cars:5）percentage of utilization of maximum tractive force （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:Maximum tractive force of front-wh

32、eel-drive cars Maximum tractive force of rear-wheel-drive cars Maximum tractive force of four-wheel-drive carsFor front-wheel-drive cars:rear-wheel-drive cars:four-wheel-drive cars:Graph of ：Note:increase leads to decrease in the case of fron-wheel-drive;is the percentage of utilization of cars weig

33、ht on the drive axle；Forward longitudinal weight transfer and increase in the case of front-wheel-drive car；（质心偏移）For cars the load on the front(drive)axle is usually higher than the load on the rear axle；（前部轴荷后部轴荷）1.4 Tractive Force&Driving ResistanceSpeed Characteristics （驱动力-行驶阻力平衡图）From Drivng E

34、quation:when level road&constant speed To (Driving Resistance comprises of and )Analyze:Acceleration Performance of the vehicle through Tractive Force&Driving Resistance-Speed Characteristics.（1）Maximum Vehicle Speed(Velocity)(km/h):So is the corresponding x-coordinate of the cross point of the driv

35、ing resistance curve and the tractive force curve of the fourth(high-speed)gear.（2）Maximum Gradeability of Vehicle The maximum uphill grade resistance force which the vehicle could overcome F i（坡道阻力）（3）Acceleration AbilityEstimate：The acceleration ability of the vehicle at any speed(ua1).the tractiv

36、e force which the vehicle need to drive with constant speed(ua1).the maximum tractive force which could be used to accelerate at this speed(ua)Conclusion:l The acceleration ability changes with the change of gear.l Higher gear leads to lower acceleration ability.l Changing the position of pedal make

37、 the constant speed drive possible because the tractive force-speed curve would move up and down vertically with the change of injection system.(the force-speed curves shown above is the upper limit ones of the vehicle)1.5 Dynamic Character of Vehicle（汽车的动力特性）In order to make the analysis of dynamic

38、 performance simpler,we use another group of characteristic curves which comprise the Dynamic Characteristic Graph（动力特性图）（动力特性图）of the vehicle.Method:(The right side of the equation concerns the grade ability and acceleration ability only,it has nothing to do with the mass of the vehicleG/g)Definiti

39、on:So:where:Ddynamic factor（动力因数）road resistance coefficient（道路阻力系数）Note:D=f when:constant speed du/dt=0 level road =0 f=0.012 under the most situation f0.02 when ua50 km/h where f0=0.012 ua fAnalyze：（1）Maximum Vehicle Speed(Velocity)(km/h):So is the corresponding x-coordinate of the cross point of

40、f curve and D curve of the fourth (high-speed)gear.（2）Maximum Gradeability of Vehicle So when climbing the soft grade(坡度小坡度小)because cos=1,sintgi,D=f+i when climbing the big grade（坡度大）（坡度大）because （3）Acceleration ability：driving on the level road So How to calculate T which is the evaluation index o

41、f acceleration ability?1.6 Power Equilibrium1.Equation of Power Equilibrium：2.How to make the Graph of Power Equilibrium:because:(功率平衡图）功率平衡图）abreverse supply of power(后备功率)1.is the corresponding x-coordinate of the cross point of the resistance power curve and the full power curve of the fourth(high-speed)gear.2.The reverse supply of power changes with the change of gear.-Higher gear leads to lower reverse supply of power and acceleration ability.3.-The maximum difference between the resistance power curve from the full power curve of the first(-speed)gear