The gearbox converts the torque transmitted from the engine in magnitude and direction. This is necessary to ensure optimal speed and flotation of the vehicle, as well as for the most economical operation of the engine and reversing of the vehicle. In addition, the gearbox separates the engine and transmission when the vehicle is stopped and parked, and when it coasts with the engine running.
Cars are equipped with 4- or 5-speed gearboxes. The gearbox parts are housed in the crankcase, which is bolted to the rear of the engine.
Torque from the engine through the clutch is transmitted to the input shaft of the gearbox. The transmission output shaft transmits torque through the propeller shaft to the rear final drive. The gears of the input and output shafts of the gearbox are in constant engagement with the gears of the intermediate shaft. The gear is switched on by moving the sliding sleeve of the synchronizer, as a result of which the gear is rigidly connected to the shaft.
Gear shifting is carried out by a lever mounted on the floor of the car and a gear selection mechanism.
The gear selector moves the corresponding fork, which in turn moves the synchronizer sliding sleeve, causing the gear to be rigidly connected to the synchronizer hub. Since the synchronizer hub is mounted on the splines of the output shaft, a rigid connection between the hub and the gear ensures that torque is transmitted from the gear to the output shaft. The synchronizer consists of blocking rings, spring-loaded crackers, a hub and a sliding clutch.