Tham khảo tài liệu 'lubrication fundamentals 2011 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | There is probably more variation in transmission design and application than in any other automotive component. For ease of discussion transmissions can be considered to be mechanical automatic semiautomatic or hydrostatic. A. Mechanical Transmissions A mechanical transmission is an arrangement of gears shafts and bearings in a closed housing such that the operator can select and engage sets of gears that give different speed ratios between the input and output shafts. In most cases a set of gears that can be engaged to drive the output shaft in the opposite direction is also included. For a constant power torque increases as speed is decreased the transmission provides a series of steps of torque multiplication. In an elementary sliding element transmission Figure one of each pair of gears is splined onto its shaft in such a way that it can be moved along it by a shift fork into and out of mesh with its mating gear. Drive is from the input shaft also called the clutch shaft through the main gear to the countershaft. The output shaft ends in a pilot bearing in the main gear which is free to revolve at a speed or in a direction different from those of the input shaft. Thus the output shaft is driven from the countershaft by whichever pair of gears is engaged or directly from the main gear if the direct drive gear is engaged with the internal gear in the main gear. Sliding element transmissions are used now only in low speed applications such as tractors. In this application the clutch must be disengaged and the vehicle must be at a complete stop before the gears can be engaged or the gear ratio changed. For other applications syncromesh or synchronized transmissions are used. In this type of transmission all gears are always in mesh except the reverse gear. One of each pair of gears is free to revolve on its shaft unless locked to it by a clutching mechanism called a synchronizer. The synchronizer which is keyed or splined to the shaft consists of a friction .
