How do the gears of the automobile transmission change?

The power transmission route of an automobile is: engine - clutch - transmission input shaft - transmission output shaft - -differential - half shafts - wheel hubs.

Inside the transmission, the input shaft and the output shaft are parallel, the input shaft gear and the output shaft gear are always mesh state, called the gear pair, for example, the input shaft first gear and the output shaft first gear are always mesh together, and the other gears of the gears are also the same. Each pair of gears are a gear and shaft is a rolling fit, and another gear is a spline fit, the gear change is completed by the synchronizer (synchronizer structure and principle can be Baidu), to one or two synchronizer, for example, to the left to dial the synchronizer that is engaged with the gear gear pair of gears on the engagement teeth, so that the transmission is a first gear, to the right to dial the synchronizer, and the combination of gear teeth to get out of the way, and then dial with the gear pair of gear gear gear engagement, so that it is the second gear! The synchronizer is disengaged from the first gear binding teeth, and then engaged with the engagement teeth on the second gear pair, so that the transmission is in second gear.

Rather simple, if there is a diagram, a look will understand.