摘 要:本设计的任务是设计一台用于轿车上的FR式的手动变速器。本设计采用中间轴式变速器，该变速器具有两个突出的优点：一是其直接档的传动效率高，磨损及噪声也最小；二是在齿轮中心距较小的情况下仍然可以获得较大的一档传动比。                  

　　　根据轿车的外形、轮距、轴距、最小离地间隙、最小转弯半径、车辆重量、满载重量以及最高车速等参数结合自己选择的适合于该轿车的发动机型号可以得出发动机的最大功率、最大扭矩、排量等重要的参数。再结合某些轿车的基本参数，选择适当的主减速比。根据上述参数，再结合汽车设计、汽车理论、机械设计等相关知识，计算出相关的变速器参数并论证设计的合理性。

　　　它功用是：①改变传动比，扩大驱动轮转矩和转速的变化范围，以适应经常变化的行驶条件，如起步、加速、上坡等，同时使发动机在有利的工况下工作；②在发动机旋转方向不变的前提下，使汽车能倒退行驶；③利用空档，中断动力传递，以使发动机能够起动、怠速，并便于发动机换档或进行动力输出。这台变速器具有五个前进档（包括一个超速档五档）和一个倒档，并通过锁环式同步器来实现换档。

关键词： 变速器；锁环式同步器；传动比；中间轴

ABSTRACT:The duty of this design is to design a FR type manual transmission used in the saloon,It’s the countershaft-type transmission gearbox.This transmission has two prominent merits: Firstly,the transmission efficiency of the direct drive keeps off high, the attrition and the noise are also slightest;Secondly ,it’s allowed to obtain in the biger gear ratio of the first gear when the center distance is smaller.

　　　According to the contour,track，wheel base，the smallest ground clearance,the smallest turning radium,the vehicles weight, the all-up weight as well as the highest speed and so on, union the choosing engine model we can obtain the important parameters of the max power,the max torque, the displacement and so on. According to the basic parameters of the certain saloon,choose the suitable final drive ratio.According to the above parameters,combining the knowledge of automobile design, automobile theory, machine design and so on, calculate the correlated parameters of the gearbox and proof the rationality of the design. 

　　　Its function is:①Changing gear ratio,expanding the torque of the driving wheel and the range of the rotational speed,to adapt the travel condition which frequently changes, like start, acceleration, climbing and so on, simultaneously causes the engine to work under the advantageous operating mode;②Under the premise of the invariable rotation, enables the automobile to travel back;③Using neutral, severances the power transmission, to make the engine start, idle, and is advantageous for the engine to shift gears or to carry on the dynamic output. This gearbox has five (including over drive—fifth gear) and a reverse gear, and through the inertial type of synchronizer to realize shift gears.

KEY WORDS: transmission; inertial type of synchronizer; gear ratio; countershaft