What is a transmission?

Transmission is one of the automobile systems having various units and details in its composition. Their main task is to transfer force from the motor to the drive axle. However, this is only a superficial idea of a modern car transmission; in fact, it requires more detailed study.

Attention, please. The transmission system not only transfers torque (CM) from the engine to the wheels of the car, but also influences the direction of rotation and frequency, and controls the force distribution between the axles.

Transmission types

To date, 4 types of transmissions have been used in the automotive industry:

Manual gearbox

Manual gearbox
Manual gearbox

The most famous and oldest is the MACP or manual gearbox. In this transmission, rotation is transmitted through the operation of gears, which are manually controlled by the driver.


The strong points of the gearbox are rather high efficiency, good fuel economy, simplicity of construction and reliability, inexpensive maintenance. As for disadvantages, it is low driving comfort – modern motorists do not like to “pull” the handle every time. Today it is uncomfortable, given the degree of congestion of urban roads and a large number of traffic lights.


Despite the technical archaic, MKPU still remains the leader among other types of transmissions installed on cars today. Experts explain this arrangement by the low budget for the production of manual transmissions.

The principle of “mechanics” is implemented in conjunction with the clutch. The unit allows you to temporarily separate the power unit from the transmission, which allows you to quickly change gears without damaging the box and engine. The clutch is adjusted by the driver from the interior by pressing the pedal with his foot.

It consists of gears and shaft axles. Today, the majority of gears with a plait tooth are used. They are less noisy and sturdy, have a maximum service life. Special attention should be paid to synchronizers, which allow you to do without double squeezing.

A robotic transmission

A robotic transmission
A robotic transmission

A “robot” or robotic transmission differs from “mechanics” in the way it is controlled by electronics, not the driver. Although the “robot” is able to operate in semi-automatic mode, when the motorist himself shifts the steps using the selector or steering paddles.

Robotic transmission

The plus of the robotic box is the comfort of operation – no need to pull the lever every time. As for the disadvantage, the main one is the delay in switching, observed by many car owners. There are other known disadvantages – lack of smooth running and sharp jerks.

It is interesting. Concerned with a lot of shortcomings of the robotic gearbox, modern engineers have come up with an effective way out. Nowadays, the “robot” is synchronized with 2 clutches, which allows faster shifting of steps. This option is called a selective gearbox.

Automatic gearbox

Automatic gearbox
Automatic gearbox

“Automatic” or automatic gearbox is second most popular after the MACP. It is a complex transmission, consisting of many elements, including sensors. The automatic transmission works not with the clutch, but with a torque converter.

The principle of operation of the “automatic machine” is similar to that of a “robot” in that switching steps is possible both manually and without the help of the driver. However, the automatic transmission does not have a typical disadvantage of a robotic gearbox – sharp jerks during gear change.

The disadvantage of the automatic gearbox is rightly called high cost. It is not definitely economical for a car owner – it uses a lot of oil. This, along with the fact that the repair of “automatic machine” costs a lot of money.

There are 2 types of automatic transmissions: with hydraulics and electronics.

Hydraulic automatic machine is considered the simplest box, working together with the turbines of working fluid.
Electronic automatic transmission – a modernized version of the hydraulic automat, allowing you to choose modes Sport, Econom and Winter.

Stepless transmission

Stepless transmission
Stepless transmission

A variator is a box that has no switching steps. That’s what it’s called – a stepless gearbox. Transmission of CM in such a transmission is carried out by a chain or a belt, and the gear ratio is regulated by the pulley.

The basic advantages of a variator: increase in a resource of the automotor, smoothness of a course and complete absence of jerks at movement. As for disadvantages, it is slow acceleration and expensive service.

Transmission units of the car

Transmission can otherwise be called a set of certain mechanisms and units. In addition to the gearbox, these include: clutch, main gear, differential and cardan.

Clutch disc

By influencing the clutch when the car stops, the driver does not have to jam the engine – neutral speed is activated and the box is disconnected from the engine. While driving, the clutch again combines the rotating engine and the box.

The main task of the clutch is to connect and disconnect the gearbox to the engine, making it as smooth as possible. The unit is located between the power unit and the gearbox.

In the vehicle transmission, the clutch acts as a conductor. It is it that transmits the gain from object to object. It is controlled by a driver sitting at the wheel of the car. By means of a pedal, it acts on the drive unit, and therefore the force is transferred.

There are 3 types of drive, although in the automotive industry only two types are used: mechanical and hydraulic. Electrohydraulic drive is not so common.

Clutch disc
Clutch disc

Clutch disc

The clutch consists of a number of functional elements:

  • the disks, which are closely linked to each other;
  • the flywheel connected to the basket – one of the strongest elements that can withstand heavy loads;
  • shutdown fork that unlocks the discs when the pedal is pressed;
  • the primary shaft of the box, to which the KM is transmitted.

It is accepted to distinguish “dry” and “wet” clutch.

  1. The first type transfers the force directly between the motor disk and the gearbox, thanks to the friction forces. It is often installed on SUVs equipped with all-wheel drive.
  2. The “wet” clutch uses torque converter oil. The fluid is between both discs. This option is more reliable, but it costs more than the usual clutch.

Main gear

Main gear
Main gear

This device is designed to transmit the CM directly to the drive axle. It consists of a unit consisting of a semi-axis, a slave and a drive pinion, a semi-axis pinion and a satellite pinion.

The main task of the main gear is to increase the CM of the power unit and reduce the speed of the drive wheels. On front-drive vehicles, this unit is located in the gearbox next to the differential, and on rear-drive cars – in the axle crankcase.

It is common to distinguish between a single gear and a double, which is often found on trucks with an increased gear ratio.


It is intended for transmission, modification and distribution of CM. One of the structural elements of the transmission. It is located depending on the vehicle drive:

  • in the crankcase – rear drive;
  • in a gearbox – front drive;
  • in the dispensing – all-wheel drive.

The structural feature of the differential is a planetary gearbox. And depending on a gearing, it is accepted to distinguish:

  • bevel gear differential, used as an inter-wheel gear differential;
  • a spur gear differential, which is placed between the axles of all-wheel drive vehicles;
  • worm – a universal variant, used both between wheels and between the axles.

The differential consists of:

  • a housing or cup that accepts the CM from the main gear;
  • a slave gear rigidly fixed to the housing;
  • axles with rotating satellites;
  • gear wheel.

Cardan gear

The cardan consists of shafts, intermediate support, hinges and splines, and a clutch.

  1. The rear shaft of the cardan is equipped with 2 hinges, which allow you to smoothly transfer the CM from the gearbox to the main gear when driving on bumps.
    Hinges with crossbones allow to transfer KM at an angle.
  2. Splits are designed to dampen the vibrations of the car body.
  3. The cardan is one of the most important components. If the gear is not adjusted correctly, there are difficulties in the work of the transmission: unpleasant noise, vibrations and other malfunctions.

Vehicle Transmission Destination

Vehicle Transmission Destination
Vehicle Transmission Destination

Thus, the purpose of transmission is to connect the engine with the driving axle of the car, to transfer the CM and redistribute it between the wheels, as well as to change and direct the rotation.

Attention. Due to the transmission operation the internal combustion engine power is transformed into useful rotating moment. The vehicle easily starts from a place and goes further at a certain speed.

Main symptoms of transmission malfunction:

  • clutch pedal hitting or jamming;
  • the appearance of noise in the clutch area;
  • the presence of jerks at start;
  • vehicle slippage;
  • transmission fluid leakage.

Purpose of the vehicle transmission

In order for the transmission to perform its functions as efficiently as possible, it is recommended to maintain it regularly and to identify and correct faults in a timely manner.