Automatic Gearboxes Explained

Automatic gearboxes provide a wide range of output speeds by allowing the engine to operate within a narrow range of speeds. These gearboxes make use of a device named planetary gear set to achieve automation. For achieving different speeds gear ratio needs to be changed. Without proper gear ration engine screams out and wears out finally, making your vehicle dysfunctional. While manual gearboxes make use of different sets of gears to achieve different gear ratios, the automatic ones produce different gear ratios by using the same set of gears.

How do automatic gearboxes work?


Present day gearboxes in cars and 4×4 vehicles that work automatically consist of epicyclical gear train. The epicyclical gear train consists of four to five gear rings such as a sun gear, a ring gear and two to three planetary gear. While sun gear and ring gear work as central and outermost gears respectively, the planetary gears revolve in between these two. The transmission of gears is achieved through fluid drive. The whole concept is called torque conversion.

Transmission and speed

To achieve a speed increase the central ring is locked, planetary rings are driven and the output is taken from the outer ring. To achieve a decrease in speed, the outer ring is locked and the central gear is driven. As above the planetary rings are driven in the same way. To achieve a speed in reverse the power input is fed to the central gear, the external gear is driven and the planetary rings are locked. A direct drive without change in speed is achieved through locking of central gear and external gear. The whole unit works as one to achieve a single direction of rotation. Most of gearboxes have three forward speeds and they make use two sets of planetary gears. The whole locking mechanism is achieved through hydraulic pressure by operating multi-plate clutches. For changing down top acceleration knockdown mechanism is used.

How automatic gearboxes are different from manual ones?

You need to shift the gears as per the speed in manual gearboxes, while in automatic ones; you don’t need to change gears. In manual gearboxes, a driver has to give inputs constantly. In automatic ones, all the functions occur without any input from the driver. The mechanism utilized by manual gearboxes is easy in comparison to the automatic ones. Any auto mechanic can detect problems with the manual gearboxes. But for automatic gearboxes you need to go to specialised mechanics.

What problems you may have with automatic gears?

Delay of response

Delay of response is a transmission based problem that arise at times when you are about to shift in to drive and you feel a delay in gear engage.

Buzzing noise

You can hear a humming sound during gear transmission with gearboxes that work automatically.

Leakage of automatic transmission fluid

Automatic transmission fluid is the life-blood of the gearboxes as it works as a lubricant. Transmission of gear system breaks down with the leakage of this fluid.

Burning smell

Overheating of transmission fluid may cause your breaking system breakdown.

Gear slipping

It is a common problem in which transmission fails and the gear system goes back to neutral.

Dragging clutch, neutral transmission noise and many other problems are there related to automatic gearboxes.

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