MODERN TRANSMISSIONS

摘要

For many years there had only been two types of transmissions fitted to most cars and light commercial vehicles, manual and automatic. Manual transmission is relatively simple: using a dry clutch and pairs of gears at various ratios, the engine is connected to the final drive and the road wheels. Gear sets are engaged by the driver using synchronisers and a mechanical linkage. The system is both reliable and fuel efficient but is falling in popularity due to urban driving conditions. Automatic transmission traditionally uses a fluid drive (torque converter) and sets of epicyclic gears at various ratios. The engine is connected to the final drive and the road wheels. Hydraulics, controlled by electronics in modern vehicles, automatically operate wet clutches to select gear sets according to engine and road speed. The transmission is less fuel efficient than a manual transmission but it is gaining popularity due to urban driving conditions (see Figure 1).