Of all the inventions of mankind, the wheel stands out as the most important. Man could move faster than ever before, and he could move heavy loads over long distances. There is a joke in automotive circles. The man who invented the wheel did not accomplish much. It was the man who invented the other three wheels who was the genius. The wheel, however, as a stand-alone invention, great as it was, provided only locomotion. It was the invention of gears, later incorporated into a gearbox, that really moved man. We are familiar with the gearbox in cars. The earlier gearboxes had three speeds, later four, and today the norm is a five-speed gearbox. In many cases the fourth and fifth gears are overdrive.
This simply means that while maintaining the speed of the vehicle, the engine rpm is reduced. This improves fuel efficiency, and an engine running at a lower rpm will have less wear and tear. The manual transmission features a number of gears mated to a gear selector lever. On automobiles the driver could select any gear, for forward speeds or reverse. A change from this was the sequential gearbox, as found on mobikes.
In this case you can select only the next gear ratio up or down, i.e. if you are in third, you can go up to four and five, or down to two and one. From three you cannot go to five or drop to one. The change must be in sequence — 1-2-3-4-5 or 5-4-3-2-1. The first manual gear transmission is credited to Louis-René Panhard and Emile Levassor. This would be some time in the late 19th century.
They offered multiple gear ratios and, most importantly, a reverse. It was a simple matter for the driver to depress the clutch, move the gear selector lever, and move off. However, the real wizardry was in the gearbox, which sat below the floorboards mated to the engine via the clutch. The gears were mounted on shafts, and engaging the required gear ratio meant sliding them on their shafts, courtesy, the gear shift lever.
The term shifting gears originates here. Today, irrespective of the type of gearbox, the phrase shifting gear is still used. Changing gear was a cumbersome and carefully executed operation. It could not be done at high speed. It meant moving into neutral, dropping engine rpm and moving into the next gear, usually up. Shifting into a lower gear was well nigh impossible.
The next important invention was the synchronised gearbox. As the name implies, all the gears are in sync. The gears are always in mesh and rotating, but only one gear on one shaft can rotate freely, and be locked to the drive shaft. This is the gear ratio the car is running in. Since all the gears are in constant mesh, the gear change is swift and smooth, and hardly noticed.
It was great for long drives but as traffic built up in the cities, and the phrase "stop-and-go" traffic was invented, constant changing of gears demanded pumping the clutch hundreds of times while commuting. It was tiring, and fatigue set in before you even got to the office. Along came a new invention — automatic transmission, also just auto or A/T. Today when you go shopping for a car, the A/T against the car’s name indicates automatic transmission. The A/T automatically changes gear ratios as the car moves off and picks up speed.
This frees the driver from pumping the clutch and shifting gears. It provides a relaxed drive. The driver only has to manipulate the accelerator and brake. There is no clutch with an automatic gearbox. In no way does it hinder the transfer of power of the engine to the wheels. There is no loss of performance. To say it won't climb steep hills is a complete fallacy. The A/T will automatically drop into low gear when you press on the accelerator while going uphill. The selector lever can be on the steering column, the floor or even the dashboard in a series of push buttons. Wherever placed, it reads P-R-N-D-L. The function is the same.
The letters stand for park, reverse, neutral, drive, low. At rest the car is in P for park. The hand brake must be on. P is one setting when the engine can be started. The hand brake is important because while parked on inclines, it takes the pressure off the park pin mechanism, and thus increases the life of the transmission. The car must come to a complete stop before engaging P. To move into D and driving off, the foot brake must be depressed. These are safety measures and electronically controlled. If you don't follow these procedures, the car won't move. The A/T was considered to be the best option there was. This has also been improved on.
It is the continuously variable transmission (CVT). It is what the Kinetic Honda scooter runs on, as do some models of the Audi, Nissan and Honda City. Most A/T cars have a set gear ratio. CVT offer a step-less range of gear ratios which are different from the conventional A/T. It is entirely possible that the days of the A/T are numbered. The CVT is the way to go.