In contrast to manual transmission, according to which the driver must operate the gear lever himself (or herself) and engage the chosen suitable gear, automatic transmission selects the gear ratio from motor speed to drive speed without the driver‘s intervention. As a result, operating the clutch and changing gears become unnecessary with a vehicle with automatic transmission, and driving turns into an easier task. That is also the reason why so many car drivers decide to go for an automatic transmission vehicle, despite the higher acquisition costs: particularly commuters for work reasons benefit from not having to change gears manually in typical stop-and-start traffic situations; yet, even drivers who do not use the car much, and therefore are not too conversant with clutch operating, can feel more confident as they can devote all their concentration to the traffic itself.
The four main designs of automatic gears
There are four main designs, out of which the most widely known is the automatic torque converter transmission. In this type, a torque converter replaces the clutch when starting up the car. The torque converter ensures a wear-free starting up and manoeuvring. Another somewhat lighter and cheaper design is the automatic gearbox. In this type of design, the gears are not engaged by the driver, as it happens with normal manual gears, but they are instead operated by means of either electro-hydraulics or mechanics controlled by a computer; thus, the need for a clutch pedal is rendered unnecessary. The relatively light weight and the high efficiency level of this design make its use advantageous for sports cars and smaller vehicles. A third design type, called “double clutch transmission”, was originally devised for use in motorsport, although it has –meanwhile– become a customary feature of several different types of motor vehicle. It consists of two separate independent transmissions, which are responsible respectively for even and for odd gears. The transmission control system can work out, from the current driving condition, which gear should be engaged next, so that a faster and smoother switching over from one sub-transmission to the other may take place. Both fuel consumption and driving comfort are, thus, optimised. The fourth design type is represented by the continuously variable transmission, known as CVT, which provides the ideal transmission ratio for the engine. This means that, when accelerating, the engine always works with a speed, which is just right in order to bring about the best performance. This way, speed is adjusted without any manual gear shifting at all, a factor, which makes for extra comfort when driving in city traffic, and also avoids wasting fuel during overland trips. Nevertheless, the acceleration phase becomes longer at higher speed.
The gear selector in automatic transmission systems
P = Parking mode. The engine starts, when the selector is on P and the brakes are applied.
R = Reverse gear. As soon as the brakes are released, the vehicle moves backwards.
N = Neutral, idle mode. The vehicle can be pushed.
D = Drive. As soon as the brakes are released, the car starts.
1 = 1st gear, manual shifting.
2 = The car switches between 1st and 2nd gear manually.
3 = The car switches between 1st and 3rd gear manually.
S = Sport mode. The engine runs at higher speed.
E = Economy. Shifting into high gear at lower speed.