汽車?yán)碚揰英文.

1、Elementary Vehicle Dynamics （汽車?yán)碚摚?Preface What can we learn from this course? The six fundamental performances of vehicle Acceleration Performance(動力性）動力性） Economical Performance （經(jīng)濟(jì)性）（經(jīng)濟(jì)性） Braking Performance（制動性）（制動性） Passing Ability（通過性）（通過性） Handling Performance(操縱穩(wěn)定性操縱穩(wěn)定性)Connering Optimal shi

2、ft point between gears（最佳 換檔時機(jī)） which are from low gear （第檔） for start-up to high gear （最高檔） 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.

3、5m)）. （用檔起步，按最佳換檔時間，逐次換至高檔，油門全開，以最大加速度行駛，全力加速至 0.8uamax所需時間，或通過某 一預(yù)定 距離所需時間） （2）The acceleration ability for high speed driving(超車加速能力) Test condition: Full engine power ; High gear（最高檔）or inferior high gear（次高檔） Evaluation indexT T is the time need to accelerate from the minimum stable speed of hig

4、h gear(最 高檔的最小穩(wěn)定車速）to 0.8Uamax or the time needed to pass through a fixed distance （400 m or mile）. (在直接檔工作時，油門全開，由該檔的最小穩(wěn)定車速全力加速至 0.8Uamax所需時間，或通過某一預(yù)定距離所需的時間） 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（檔） under good ro

5、ad condition with fully rated load（額定滿載）. i=tg EQ140 imax=28% EQ240 imax=58% =30 （2）Actual Measurement of imax 1.2 Driving Mechanics of Vehicle To analyze the balance between Total Roads（行駛阻力）and Tractive Force（驅(qū)動力驅(qū)動力）along one degree of freedom（自由度） that is longitudinal direction（縱向）. 1.Tractive Fo

6、rce（驅(qū)動力） TiiTt T gtq 0 r iiT tgtq tF 0 Ttq Torque of Engine Flying Wheel Numerical Ratio of the Transmission Numerical Ratio of the Final drive Total efficiency of driveline Torque of Driving Wheel r Tt tF 0 i g i T Tt (1)Torque of Engine Engine maybe characterized by its torque and power curve as a

7、 function of speed. Figure 1. shows typical curves for gasoline engine. Figure 1. Performance characteristics （外特性曲線） of gasoline Full performance and Full performance with all the accessories (外特性與使用外特性外特性與使用外特性) Useful formulas for Power calculation Unit: Pe (kW) ; Ttq (Nm); n(r/min)。 9549 nT tq e

8、P （2）Efficiencies of Driveline lThe 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 pr

9、oducts of the efficiencies of the individual components. l T （combined efficiency of driveline） consists of four primary parts: 離合器 變速箱 傳動軸 驅(qū)動 橋 t drivefinalshaftpropellerontransmissiclutchT （3）Tire Radius Definition: lNominal Radius（自由半徑）： the radius of tire without load （spare tire 備胎 radius). lSt

10、atic Loaded Radius（靜力半徑） ：the distance from the center of static tire to the contact point with ground under vertical load only. lRolling Radius（滾動半徑） ： the radius which is measured by S (distance passed by vehicle）and n (rolling numbers). nrS s 2 s r r r rs rr （4）Graph of Tractive Force （驅(qū)動力圖） lHow

11、 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) 1000 1 260 0 r ii n u g a a u a u 0 377. 0 ii nr u g a at uF 2）Make the graph lTwo basic formulas for making the graph: lMake the tra

12、ctive force line of each gear （given ）of the vehicle（given 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

13、 high-speed driving). 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 acce

14、leration performance. 2. Road Load force （行駛阻力） （1）Rolling Resistance Force F f（滾動阻力） 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 particles l Rolling resistance torque T f （滾動阻力偶矩） T

15、 f = F za The mechanics analysis of driven wheel with constant revolution assume Rolling Resistant Force of driven wheel （從動輪的滾動阻力） assume a/r = f （ Coefficient of rolling resistant） 滾動阻力系數(shù)滾動阻力系數(shù) conclution: under given conditions( stiff road; constant revolution speed) rTF TrF ff fx 11 11 1f F r a

16、FF zf 11 fFF zf 11 11111111 / 1111 wFfwFffwFfwF p FF xx FF f pxxf 1 1 wFp f assumed : driving force rolling resistance force of driving wheel total rolling resistance : rTrTF TTrF ftx tfx / 22 22 22 / ff FrT tt FrT/ )( 222txftx FFFFF r aF F z f 2 2 fwfFz 22 GffFFfFfFFFF zzzzfff )( 212121 f F The mec

17、hanics 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 retar

18、dation force. 4. usually is equal to 0.012. f （2）Aerodynamic Drag(空氣阻力) Aerodynamic Drag （空氣阻力）（空氣阻力） Pressure Drag（壓力阻力）（壓力阻力） Vicious Friction（摩擦阻力）（摩擦阻力） Form Drag-形狀阻力形狀阻力 58% Total Protuberance Drag-干擾阻力干擾阻力 14% Total Internal Drag-內(nèi)循環(huán)阻力內(nèi)循環(huán)阻力 12% Induced Drag-誘導(dǎo)阻力誘導(dǎo)阻力 7% lAerodynamic forces int

19、eract 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.（發(fā)動機(jī)冷卻、車身通風(fēng)） W

20、ith 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 dr

21、ag. 2）Bernoullis Equation： P -大氣壓； -空氣密度；C-常數(shù) Zero underbody(車身底板) 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）F

22、or minimizing Form Drag we adopt the body of streamlined shape ( 流線形）流線形） which is usually be described as drop-like body. CvP 2 2 1 Calculation of Aerodynamic Forces Fw Semi-empirical models： Where: Aerodynamic drag coefficient（空氣阻力系數(shù)） Frontal area of the vehicle（迎風(fēng)面積） Air density （空氣密度） Relative V

23、elocity（相對速度） International CD: China CD 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 ua (km/h) ；ur(m/s)；ur=ua/3.6 (m/s) (no wind) So ACuF Drw 2 2 1 r D u A C wvr uuu 15.21/ 2 aDw AuCF （3）Uphill Grade Resistance Force F i（坡道阻力） Define: Road Resist

24、ance （道路阻力） Define: Road Resistance Coefficient （道路阻力系數(shù)） if FFF iGGFitansin F sin)( 21 GfFFF zz sincosGfG iffsincos )(ifG GiGf （4）Acceleration ResistanceFj 1.Translational mass inertial force （平移質(zhì)量慣性力）Fj1 G/g質(zhì)量 du/dt加速度 2.Rotational mass inertial force (moment) （回轉(zhuǎn)質(zhì)量慣性力or 力矩）（Tj; Fj2） (rotating comp

25、onents comprise of fly wheel, gear system, shafts 2） the rotational mass inertial force of the driving wheel itself ; For general model of the vehicle ,Fp and Ft are considered as internal forces ,so there is no Fp and Ft on the graph. Ft and Ff are the result of assumption , so there is neither Ft

26、nor Ff on the graph. jwift jwjwwfft wjwfjwft wxx FFFFF dt du g G FFFGFFF dt du g G FGFFFFF dt du g G FGFF )(sin)( sin sin 2121 1122 12 1.3 Traction-Limited Acceleration （1）Driving Condition of Acceleration When Level road: Constant speed: Level road is the percentage of utilization of cars weight on

27、 the drive axle； Forward longitudinal weight transfer and increase in the case of front-wheel- drive car； （質(zhì)心偏移） For cars the load on the front (drive) axle is usually higher than the load on the rear axle； （前部軸荷后部軸荷） C 1 F 1 F C C 1.4 Tractive Force & Driving ResistanceSpeed Characteristics （驅(qū)動力-行駛

28、阻力平衡圖） 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-coordina

29、te of the cross point of the driving resistance curve and the tractive force curve of the fourth (high-speed) gear. jwift FFFFF wft FFF maxa u maxa u f F w F 0 0 max i j a F F u 0 0 377.0 ii nr u r iiT F g a Tgtq t wf FF （2）Maximum Gradeability of Vehicle The maximum uphill grade resistance force wh

30、ich the vehicle could overcome F i（坡道阻力） （3）Acceleration Ability Estimate ： The acceleration ability of the vehicle at any speed(ua1). the tractive 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) Conclus

31、ion: 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 the constant speed drive possible because the tractive force-speed curve would move up and down vertically with the change of injection system. (t

32、he force-speed curves shown above is the upper limit ones of the vehicle) maxmax sinGAB )( maxmax tgi AB EF FG u a1 dt du g G Fj dt du wf FF 1.5 Dynamic Character of Vehicle （汽車的動力特性） In order to make the analysis of dynamic performance simpler ,we use another group of characteristic curves which co

33、mprise the Dynamic Characteristic Graph （動力特性圖）（動力特性圖）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 （動力因數(shù)） road resistance coefficient （道路

34、阻力系數(shù)） 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 f dt du g f G FF FFFFF FFFFF wt jifwt wifjt sincos D G FF wt dt du g D 0 377. 0 ii nr u G FF D g a wt )50(01. 01 0 a uff fhkmua/50 Analyze： （1）Maximum Vehicle Speed (V

35、elocity) (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 (坡度小坡度小) because cos=1, sintgi, D=f+i when climbing the big grade （坡度大）（坡度大） because maxa u 0 0 max dt du ua maxa u )( maxmax tgi sincos0 max fD dt du 0 max dt du maxmax 2 2 max 2 max max max