Car transmission: Its function and types

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  • Post last modified:August 8, 2022
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There is a transmission or gearbox in every vehicle with an engine. Its task is to absorb the power of the engine and transmit it further. More precisely, it is the torque. With the help of the gearbox, the torque is transmitted to the wheels. In this article, we will explain everything about the car transmission function and types.

car transmission function

When talking about a transmission in a car, the designation first includes the gearbox housing. There are parts and gears inside that make up the actual gearbox in an impressive structure.

Why do you need a transmission?

The function of a gearbox is the transmission of torque according to the given requirement. The vehicle’s combustion engine produces only a relatively weak torque. This is especially true at low speeds. For this reason, geared motors are used in the drive technology of motor vehicles with internal combustion engines.

They help to control the engine power in the way the driver wants. The transmission connects the engine to the driveline, adapting torque and power to the load situation called for. Every car needs a minimum amount of torque to be able to start and accelerate.

The gears are also adapted to this power. The gearbox translates so much in the first gear that the engine does not stall with it and can be accelerated up to around 30 Km/h without the engine being over-revved.

How does car transmission works

The typical usable speed range is 1500-5500 (diesel) or 1500-8000 rpm (gasoline engine). Each gear requires a different transmission ratio to keep the engine speed in the range where the engine delivers optimum power.

In the first gear, the main shaft of the transmission rotates at about 25 percent of the input speed. Now you can accelerate until the car engine reaches the highest possible speed. Now you have to shift to a higher gear.

The transmission now converts the power in a different range of the higher gear. It can accelerate to a higher speed. But you can not start with this so well or not at all.

Manual or automatic transmission?

There are engines with four types of gearboxes in the car for the drive, with different structures and functions:

  • Manual transmissions
  • Automatic gearboxes
  • Automatic transmission
  • Continuously variable automatic transmissions (CVT transmissions)

Manual transmission in the car

In the manual transmission, the driving force flows from the engine through a disc clutch to the gearbox. In each gear, there is a pair of gears that transmits power to the drive train. The gear ratio of the pair of gears determines the speed and torque on the drive axle, and the gear is selected by the driver using the shift lever.

Automated manual transmission

The classic automated manual car transmission has the same mechanical design as the manual. Hydraulic or electric actuators operate the clutch and gearshift, controlled by the shift electronics. It either selects the gear independently or receives the shift command via a shift rocker. In our another article, learn what is an EGR valve, its structure and function.

Direct shift transmission

The direct shift transmission is a modern development with two mechanically independent automatic sub-transmissions. Both parts carry the gears alternately. The control electronics first engage the correct gear in the load-free line before the clutch shifts to the selected gear without interrupting the train.

This gear motor combines the advantage of uninterrupted transmission with the high efficiency of a gear transmission. Due to the more complex design, direct-shift transmissions are more expensive to manufacture and maintain.

Automatic car transmission

Automatic transmissions enable automatic gear changes without interrupting traction. The most common type of automatic transmission is the torque converter automatic transmission. Automatic transmissions eliminate the need for a mechanical clutch. Planetary gears carry the transmission ratio.

Multi-plate clutches and torque converters provide synchronization and traction interruption during start-up and shifting. The advantage of this car transmission is the almost uninterrupted power transmission, similar to a direct shift gearbox. However, the efficiency is worse and causes higher fuel consumption than the manual car transmission.

Continuously variable automatic transmission

Continuously variable automatic transmission allow infinitely variable speed and torque transmission. The change in transmission ratio is achieved by two pairs of conical pulleys connected by a chain or a connecting link.

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