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1、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 Optimal shift point between gears（最
2、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
3、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
4、.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 condition with fully
5、 rated load（额定满载）. 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
6、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.
7、 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) ; Ttq (Nm); n(r/min)。 （2）Efficiencies of Driveline lThe necessity of the introduction of T: The inefficiencies due to mechan
8、ical 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） consist
9、s of four primary parts: 离合器 变速箱 传动轴 驱 动桥 （3）Tire Radius Definition: 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
10、） ： the radius which 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）Ma
11、ke the graph lTwo basic formulas for making the graph: lMake the tractive 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 opera
12、tion of the vehicle ( low gearing for start-up, and high gearing for 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 t
13、he 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） 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 fri
14、ction of rubber particles l Rolling resistance torque T f （滚动阻力偶矩） T f = F za 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
15、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）
