Gearbox vs transmission
A gearbox is precisely what it sounds like: a box of gears. A transmission, on the other hand, is a more comprehensive term that refers to all the devices that increase or decrease the turning power supplied by an engine to the wheels. Essentially, it is an intermediary between the engine and the wheels.
A transmission is composed of two integral assemblies: a coupling assembly and a gearbox.
How do transmissions work?
An engine has several parts that perform linear (straight-line) or rotary motion when fuel is burnt. One such part is the crankshaft. It is connected to various parts of the engine and is responsible for the transmission of the energy of combustion to motion. As fuel burns in an engine, the crankshaft rotates to produce turning force or torque, which is then transferred to the wheels. However, the torque produced by an engine is seldom enough, for example, to get a car moving from a standstill, or on a slope.
Therefore, torque modulation is needed. The transmission, as stated earlier, is an intermediary device between the engine and the wheels, and effectively serves this function. Torque modulation is achieved by selecting appropriately sized gears from those available in the gearbox. Apart from torque modulation, gearboxes also enable drive reversal; in other words, appropriate gearing allows wheels to move in reverse, rather than solely moving forward.
The selection of gears isn’t possible when the engine is connected to the wheels, which is why a coupling/decoupling device is needed. A coupling device can be mechanical (a clutch in manual gearboxes) or hydraulic (a torque converter in automatic gearboxes) in nature. When disengaged, it disconnects the engine and the wheels, allowing an appropriate gear to be selected.Upon selection of the gear, the clutch pedal is released to engage the clutch, thereby transmitting the required torque to the wheels.