Gears and the transmission system

A car has a whole box full of gears – the gearbox – sitting between the crankshaft and the drive shaft. A car engine makes power in a fairly violent way by harnessing the energy locked in gasoline. It works efficiently only when the pistons in the cylinders are pumping up and down at high speeds – about 10-20 times a second. Even when the car is simply idling by the roadside, the pistons still need to push up and down roughly 1000 times a minute or the engine will cut out. Actually, it takes a massive of force to get a car moving from a standstill and an engine that tries to go at top speed, won’t generate enough force to do it. That’s why cars need gearboxes. In effect, the gearbox is reducing the speed of the engine greatly but increasing its force in the same proportion to get the car moving. Once the car’s going, the driver switches to a higher gear. More of the engine’s power switches to making speed - and the car goes faster.

The gearbox assists in variation of torque produced by the engine in accordance with the driving conditions. A large torque is required at the start of the vehicle and a low torque at higher speeds. It helps in smooth running of the vehicle at different speed since variation a torque induces.

The mechanism that transmits engine to the rear wheel or to the front wheel is known as a transmission system. Several kinds of transmission are employed on auto vehicles. These can be classified as follows:

1) Manual shifted transmission is the simplest and most inexpensive transmission for car drivers. The design of MST incorporates: a single-plate dry clutch as the power take-up element and for interrupting the power flow during gear changes; gears mounted on two shafts, positive clutches as shifting elements actuated via a synchronizer assembly. The main features are: high efficiency, compact, light design, economical construction, absence of comfortable operation (clutch pedal, manual gear changing), driver-dependent shifting strategy, interruption of tractive force during gear shifting.

2) Automated shift transmission (AST) helps to simplify transmission operation and increase economic operation. The AST is made possible by electronic clutch management, supplemented by two servomotors (selecting and shifting motors) for selection and shifting. Thanks to the electric-motor-driven actuators of the AST concept, it is possible at little expense to achieve automation of the transmission complete with the associated increase in convenience. AST is characterized by the following features: basic design as for manual transmission, actuation of clutch and gear change by actuators (pneumatic, hydraulic or electric-motor-driven) and electronic control. The main features are: compact design, adaptation to existing transmission possible, more competitively priced than AT or CVT, simple operation, suitable shifting strategies for achieving optimum fuel consumption and best consumption figures, interruption of tractive force during gear shifting.

3) Dual-clutch transmission (DCT) is seen as the further development of the AST. They operate without interruption of tractive force, a major drawback of the AST. The DCT’s main benefit lies in its lower fuel consumption compared with AST. The design of dual-clutch transmission is characterized by the following features: basic design as for manual transmissions, gear mounted on three shafts, two clutches, actuation of clutch and shifting elements via transmission-shift control and actuators. The main features of the DCT are: similar levels of convenience to an automatic transmission, high efficiency, no interruption of tractive force during gear shifting, skipping of a gear possible, takes up more space than an AST, high bearing forces, solid construction.

4) Automatic transmission (AT) perform power take-up, select the gear ratios, and carry out the gearshifts themselves. A hydrodynamic converter acts as the power take-up element. The AT is installed on the four-shaft planetary –gear set that is the basis of many automatic speed transmissions.

5) Nowadays the other kind of transmission is constantly becoming popular. That is continuously variable transmission - CVT. CVT is an “infinite speed” transmission which can change steplessly through an infinite number of effective gear ratios between maximum and minimum values. Unlike traditional automatic transmissions, continuously variable transmissions don't have a gearbox with a set number of gears, which means they don't have interlocking toothed wheels. The CVT will gradually replace the conventional automatic transmission due to its high fuel efficiency and smooth gear shift.