《汽车理论》课程教学课件（英文讲稿）第3章 汽车动力装置参数选择 Decisions for Engine Power and Gear Ratios 3.3 Decision for Maximum Gears Ratio（最大传动比 的选择）

3.3 Decision for maximum gears ratio-imaxgears ratio=i,igi. when gears ratio meets itsmaximum value imax=ioig, (lowest gear).because iohas alreadybeengotfrom theabovestep.Method : making the ig, selection with the constraintscaused by driving and limited conditions ofacceleration（驱动-附着条件）：

Method : making the ig1 selection with the constraints caused by driving and limited conditions of acceleration（驱动-附着条件）. gears ratio=ig·i0·ic → when gears ratio meets its maximum value imax=i0 ig1 (lowest gear). because i0 has already been got from the above step. 3.3 Decision for maximum gears ratio-imax

Fordrivingconditionofacceleration（驱动条件）Fy could be ignored because u,is very low with theIst gear.So driving condition of acceleration could besimplified into this form:F≥F,+Fthen"igrio nr ≥G(f cos αmax +sinantgmaxmax≥G(fcosαmax+sinαtmaxmax1G(f cosαmax + sin αnmaxOTqmax io - nt

Fw could be ignored because ua is very low with the 1st gear. So driving condition of acceleration could be simplified into this form: then F F F t f i   max 1 0 max max max max max cos sin cos sin tq g T t T i i F G f G f r         ≥（    ） ≥（ ） max max 1 max 0 cos sin g tq T G f r i T i        （ ） ≥ 1）For driving condition of acceleration (驱动条件)

Forlimitedconditionofacceleration（附着条件）F≤<F,=FzoΦtmaxTtqmax'iglionrL≤FzopFzoprg7tqmaxionrWhere Fzo is the weight on the drive wheels.（驱动轮上道路的垂直反力）FoprG(f cosaαmax + sin αmax-1Tagmaxionriqmax ionr

Where FZφ is the weight on the drive wheels. （驱动轮上道路的垂直反力） max max 1 0 t Z tq g T Z F F F T i i F r       ≤  ≤ max max 1 max 0 max 0 cos sin z g tq T tq T G f r F r i T i T i         （ ） ≤ ≤ 2）For limited condition of acceleration (附着条件） 1 max 0 Z g tq T F r i T i    ≤

3) forcross-countryvehicle> Because of the minimum stable vehicle speed (uamin-stableconstraintfor cross-country vehicle, we must do thefurtheradjustmenttoigl:r.nmin=0.377uamin-stableigriornmin1≥0.37791amin-stablelo

 Because of the minimum stable vehicle speed（uamin-stable） constraint for cross-country vehicle，we must do the further adjustment to ig1： min min -stable 1 0 0.377 a g r n u i i    3）for cross-country vehicle min 1 min 0 0.377 g a stable rn i u i  ≥