汽車理論武漢理工課件

1、1.4 Traction-Limited Acceleration and AdhesionRatio汽車行駛的驅(qū)動-附著條件和附著率1. Traction-Limited Acceleration（1）Driving Condition of Acceleration（驅(qū)動條件）= 0= 0FiFjWhen Level road:Constant speed:Ft= Ff+ FWLevel road & Constant speed:Ft = Ff+ FW + Fi + Fj d m du = F - (F+ F+ F )tfWidt1Chapter 1Acceleration Perfor

2、mance（1）Driving Condition of Acceleration（驅(qū)動條件）Ft = FfF tFfF tFf+ FW+ FW+ FW+ Fi+ Fi+ FiFor constant speed:acceleration: deceleration:（勻速）（）SoDriving Condition is2Chapter 1Acceleration PerformanceF = Ttqig i0hT ,trig ori0 orhT or Ttq orr Ft FtFf+ FW + Fi（2）Limited Condition of Acceleration（附著條件） Pre

3、suming there is adequate power from the engine, the acceleration may be limited by the friction that is F（附著力） between the tire and road for anti-skid purpose.附著力：地面對輪胎切向作用力的極限值。In this case Fis ：= Fzj j= FX maxFj輪驅(qū)動，限制車輪打滑的極限力）Where: Coefficient of adhesion（道路附著系數(shù)）,usually ranges from 0.70.8. Weigh

4、t on driving wheels（驅(qū)動輪上道路垂直反力）FZ3Chapter 1Acceleration PerformanceTt - Tf 2= F F = Fj（后rX 2jZjAverage Coefficient of Friction for Common Road4Chapter 1Acceleration PerformanceRoad Condition(路面條件)Dry Blacktop（干瀝青路面）0.70.8Wet Blacktop（濕瀝青路面）0.50.6Dry gravel road（干燥的碎石路）0.60.7Dry earth road （干土路）0.50.

5、6Wet earth road （濕土路）0.20.4Rolling snow road（滾壓后的雪路）0.20.3Tyre of Formula 1 racing car5Chapter 1Acceleration Performancedry tyre or Slick tyre干地胎Intermediate tyre中性胎wet tyre雨地胎（3）Traction-limited Acceleration (驅(qū)動附著條件-充分必要條件)6Chapter 1Acceleration PerformanceFf+ FW + Fi Ft FjQ FX 2 = Ft - Ff 2 j FZ 2

6、 Ft ( f + j)FZ 2and f j Ft j FZ 2 = FjThinking?7Chapter 1Acceleration PerformanceFi = G sin aFXmax = Fj = Gj cosaneed: Fj FiGj cosa G sin ai =100%即a = 45oneed :j1jmax 0.8 ，How could off-road vehicle climb 100% grade？越野車如何爬上100的坡道？2.（1） Define:Adhesion Ratio（附著率）= FX1C（When front wheel is the driving

7、 wheel）j1FZ1= FX2C（When rear wheel is the driving wheel）j 2FZ2Note:So C is the minimum coefficient of friction which vehicle needed to use driving adequately. (附著率是汽車充分發(fā)揮驅(qū)動力作用時要求的最低附著系數(shù)。)8Chapter 1Acceleration PerformanceFF = Fj = Fj FX 2 j CjX 2jZjZ 2Fj 2Z 2C= FXj= 驅(qū)動輪上的道路切向反力jF驅(qū)動輪上的道路垂直反力Zj9Chapte

8、r 1Acceleration Performancescceleration from standing start起步急not easy to meet the needs of limited condition which working condition?be in high gear and stepaccelerator pedal slightlystanding start on ice and snow roadhigh gear or low gear?not easy to meet the needs of limited conditionwhich road?s

9、lick road濕滑路面ice and snow road sand roadFX1 good road condition，ua ，F(xiàn)f ；Fw ；flat road，F(xiàn)i ； smooth acceleration ，F(xiàn)j 。 front wheel is the driving wheel： FX1、FZ1、C1 ，easy to meet the needs of limited condition.（2）FX（驅(qū)動輪上的道路切向反力 ）When front wheel is the driving wheel：( Fis small)jw1When rear wheel is th

10、e driving wheel：note : F = Gdujgdt10Chapter 1Acceleration PerformanceF= F+ F+ F + G duX 2X 1wigdtFX 2= Ff 1 + Fw + Fi + FjF= F+ F+ F + G duX 1X 2wigdt= F+ F+ F + F+ G duf 2wijw1gdt FX 1 = Ff 2 + Fw + Fi + FjThe mechanics analysis of vehicle with accelerationFwFZw1G duFTZw2gdtjw1GTfwjw2Tf 2Tf 1FTx1Fx

11、 2FZ1FZ 211Chapter 1Acceleration Performance（3）FZj（驅(qū)動輪上的道路垂直反力 ）A. static part:B. dynamic part:Note: Ignore Rotational mass inertial moment12Chapter 1Acceleration PerformanceF - G du hg Zd1gdtLF G du hg Zd 2gdtLF= G (b cosa - h sin a )Zs1LgF= G (a cosa + h sin a )Zs 2Lg13Chapter 1Acceleration Perfor

12、mancePorsche 911Roadster RRrear drivingsports carrear drivingwhen acceleration FZd1$ FZd2#Thinking：Which driving mode easy to meet the needs of limitedcondition? front wheel drive or rear wheel drive?第四節(jié)汽車行駛的附著條件與汽車的附著率14Chapter 1Acceleration PerformanceAll Wheels Drive(AWD)Thinking：what is idea dri

13、ving mode? Most Roadster 雙座跑車MR第四節(jié)汽車行駛的附著條件與汽車的附著率15Chapter 1Acceleration Performanceheavy goods vehicle 重型貨車m，F(xiàn)f；not good road condition，off-road vehicle 越野車not good road condition，super car 超級跑車ua，F(xiàn)W ； Big engine displacement，F(xiàn)t 。Limousine Car 高級轎車m，F(xiàn)f；ua，big car body，F(xiàn)W ；Big engine displacement 發(fā)

14、排量，F(xiàn)t Which type vehicle fits AWD？（3）FZj（驅(qū)動輪上的道路垂直反力 ）C. lift force:Note:CLf is the coefficient of lift forcefor front;for rear.CLris the coefficient of lift forceD. the part produced by rollingthis part is very small and is ignored.torque :16Chapter 1Acceleration PerformanceF= F- F- G du hgF= F- F+

15、 G du hg Z1Zs1Zw1g dtLZ 2Zs 2Zw2g dtLF= 1CAru2Zw12LfrF= 1CAru2Zw22LrrCoefficient of lift force The height of air dam skirt(前阻風(fēng)板) and rear spoiler(后擾流板) affect CD、CLf and CLr.17Chapter 1Acceleration Performance（4）analysisa. Acceleration and uphill (front wheel drive cars):Note: q is the equivalent gr

16、ade(等效坡度) ；一定值路面上能通過的最大等效坡度 ，so the jwhich vehicle needed is big and the front drivingCj1wheel is easy to skid.18Chapter 1Acceleration Performanceq =b L1 + hgjLq = i +11 ducosa g dt+i +11 duCFiFjcosa g dt=qj1G du hgbh11 du bhgF-g i +-qZs1gdtLLL cosa g dt LLC= FX 1 =Ff 2 + Fw + Fi + Fjj1FG du hZ1F- F

17、-g Zs1Zw1g dtL（4）analysisif rear wheel drive cars:So the front driving wheel is easy to skid.19Chapter 1Acceleration Performancerear wheel driveq =a L1 - hgjLC= FX 2=Ff 1 + Fw + Fi + Fjj 2FG du hZ 2F- F+g Zs 2Zw2g dtLFi + Fj=qF+ G du hga + hg qZs2g dtLLL（4）analysisb.high speed (rear wheel driving cars):= 1ru2F