汽车理论-英文

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,11/7/2009,#,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,Elementary Vehicle Dynamics （汽车理论）,Preface,What can we learn from this course?,The six fundamental performances of vehicle,Acceleration Performance(,动力性）,Economical Performance,（经济性）,Braking Performance,（制动性）,Passing Ability,（通过性）,Handling Performance(,操纵稳定性,)Connering&Rollover,Ride Performance(,行驶平顺性）,Whats the aim of this course,To 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 Performance,1.1 Evaluation Index,（评价指标）,1.Maximum Vehicle Speed (Velocity),最高车速,ua,max,(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,ua,max,2. 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 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,）,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 indexT,T,is the time need to accelerate from the minimum stable speed of high 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,i,max,（最大爬坡度）,（,1,）,Definition,：,The maximum grade which the vehicle can climb in the,first gear,（,档）,under good road condition with,fully rated load,（额定满载）,.,i=tg,EQ140,i,max,=,28%,EQ240,i,max,=,58% =30,（,2,）,Actual Measurement of,i,max,1.2 Driving Mechanics of Vehicle,To,analyze the balance between Total Roads,（行驶阻力）,and,Tractive Force,（,驱动力,）,along one degree of freedom,（自由度）,that is longitudinal direction,（纵向）,.,1.Tractive Force,（驱动力）, Torque 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.,Figure 1. Performance characteristics,（外特性曲线）,of gasoline,Full performance and,Full performance with all the accessories,(,外特性与使用外特性,),Useful formulas for Power calculation,Unit,:,Pe,(kW) ;,T,tq,(Nm);,n,(r/min),。,（,2,）,Efficiencies of Driveline,The necessity of the introduction of,T,:,The inefficiencies due to,mechanical 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.,T,（,combined efficiency of driveline,）,consists,of four primary parts:,离合器 变速箱 传动轴 驱动桥,（,3,）,Tire Radius,Definition:,Nominal Radius,（自由半径）,：,the radius of tire without load,（,spare tire,备胎,radius).,Static Loaded Radius,（静力半径）,：,the distance from the center of static,tire to the,contact point with ground under vertical load only.,Rolling Radius,（滚动半径）,：,the radius which is measured by,S,(distance,passed by vehicle,）,and,n,(rolling numbers).,（,4,）,Graph of Tractive Force,（驱动力图）,How 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 graph,Two basic formulas for making the graph:,Make the tractive force line of each gear,（,given,）,of the vehicle,（,given & given r and given,）：,Make all the curves of the vehicle,figure1.2,:,Figure 1.2 Tractive force-speed characteristics for a manual transmission,3)Conclutions from the graph of tractive force:,“Constant Engine Power” is equal to the maximum power of the engine; which is the upper limit of tractive force available, less any losses in the driveline.,The 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).,For maximum acceleration performance the optimum shift point between gears is the point where the line cross.,The 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. Road Load force,（行驶阻力）,（,1,）,Rolling Resistance Force F,f,（滚动阻力）,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 particles,Rolling resistance torque T,f,（滚动阻力偶矩）,T,f,= F,z,a,The mechanics analysis of driven 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,conclution: under given conditions( stiff road; constant,revolution speed),assumed : ,driving force,rolling resistance force of driving wheel,total rolling resistance :,The mechanics analysis of driving,wheel with constant revolution,Note:,1.Rolling resistance is present from the instant the,wheels begin to turn.,2.The rolling resistance is the primary motion,resistance force.,3.For off-high way, level ground operation, the rolling,resistance is the only significant retardation force.,4. usually is equal to 0.012.,（,2,）,Aerodynamic Drag(,空气阻力,),Aerodynamic Drag,（空气阻力）,Pressure Drag,（压力阻力）,Vicious Friction,（摩擦阻力）,Form Drag-,形状阻力,58%,Total Protuberance Drag-,干扰阻力,14%,Total Internal Drag-,内循环阻力,12%,Induced Drag-,诱导阻力,7%,Aerodynamic forces interact with the vehicle causing drag,，,lift,（,or down load,），,lateral forces,，,and their individual moments.,The 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 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,）,Bernoullis 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 Drag we adopt the body of,streamlined shape,(,流线形）,which is usually be described as drop-like body.,Calculation of Aerodynamic Forces Fw,Semi-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 C,D,: China C,D,Cars 0.300.35 Cars 0.4,Vans 0.330.35 Vans 0.6,Pickup trucks 0.420.46 Pickup trucks 0.8,Because of u,a,(km/h),；,u,r,(m/s),；,u,r,=u,a,/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 ResistanceF,j,1.Translational mass,inertial force,（平移质量惯性力）,F,j1,G/g,质量,du/dt,加速度,2.Rotational mass,inertial force (moment),（回转质量惯性力,or,力矩）,（,T,j,; F,j2,）,(rotating components comprise of,fly wheel, gear system, shafts&axles,wheels,),I,转动惯量,d/dt,角加速度,Inertial moment for fly wheel,e angular velocity of fly wheel,w angular velocity of wheel,Ua vehicle speed,r radius of wheel,Deliver T,f,to,driving wheel, T,fw,2) Total inertial moment for wheel and rotational mass inertial force,T,j,；,F,j2,3. Total Inertial Force ,F,j,Assumed : rotational mass coefficient,（回转质量换算系数）,So,3.Driving Equation,（行驶方程）,1)General model of driven wheel:,2) General model of driving wheel:,3,）,General model of vehicle:,Note: F,jw2,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 ,F,p,and F,t,are considered as internal forces ,so,there is no F,p,and F,t,on the graph.,F,t,and F,f,are the result of assumption , so there is neither F,t,nor F,f,on the graph.,1.3 Traction-Limited Acceleration,（,1,）,Driving Condition of Acceleration,When,Level road,:,Constant speed:,Level road & Constant speed:,For,constant speed:,（匀速）,acceleration:, （加速）,deceleration:,（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）,Weight 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 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-wheel-drive cars,Maximum tractive force of rear-wheel-drive cars,Maximum tractive force of four-wheel-drive cars,For,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 weight 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 Equation:,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 driving 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 Ability,Estimate,：,T,he,acceleration ability of the vehicle at any speed(,u,a1,).,the tractive force which the vehicle need to drive with constant speed (u,a1,).,the maximum tractive force which could be used to accelerate at this speed (u,a,),Conclusion:,The acceleration ability changes with the change of gear.,Higher,gear leads to,lower,acceleration ability.,Changing the position of pedal make 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 performance,simpler ,we use another group of,characteristic curves which comprise the Dynamic Characteristic Graph,（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,),Definition:,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 f,0,=0.012,ua f,Analyze,：,（,1,）,Maximum Vehicle Speed (Velocity),(km/h):,So,is the corresponding x-coordinate,of the cross point of,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,),because,cos=1,sintgi,D=f+i,when climbing the big grade,（坡度大）,because,（,3,）,Acceleration ability,：,driving on the level road,So,How to calculate,T,which is the evaluation index of acceleration ability ?,1.6 Power Equilibrium,1.Equation of Power Equilibrium,：,2. How to make the,Graph of Power Equilibrium,:,because,:,(,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 re,sistance power curve from the full power curve of the first (-speed) gear,