[Abstract] Car is one of the main means of transport in modern society. The automobile is one of the main conveyance tools of the modern societies. the automobile power originates from the internal-combustion reciprocating engine, but its torque and the rotational speed range of variation is extremely small, but the complex use environment, needs the automobile the force of traction and the automobile speed in an greater scope change. Therefore， transmission in the car with a transmission. By changing the transmission ratio, making the driving wheel torque and speed are constantly changing to meet the driving requirements. By setting the reverse, the car can go forward or backward, while the gap can be terminated by the transmission of power, realized exchange between the stalls, but also to protect the gears from shock. The design for the SLS sedan fourth gear transmission, which has four forward gears, one reverse, its velocity ratio is in turn: I =2.92; II =1.81; III =1.12; IV =0.7; The reverse gear is 2.38. The transmission is a class of two axis gear transmission, the input shaft to install the four forward gears and one reverse gear; output shaft installation is the four forward gears and one reverse driven gear, reverse gear shaft installation A double-Gear, it avoids interference between the gears. Installed on the three synchronizers unified output shaft, through the synchronizer, can shift, reverse and neutral, to meet the driving requirements.
