What is Gearbox? Definition, Parts, Working, Types, Applications,

In this article, we will learn the basic details of gearbox along with definition, parts, how does it work, different types, applications, advantages & disadvantages. Let’s explore.

What is Gearbox & Gear Ratio? Definition

Gearbox Basics & Gear Ratio

Gearbox, as the name, defines itself as a box that contains a set of gears. The most fundamental concept of the gearbox deals with a mechanical system comprising a series of gears that can alter the speed of a motor. It reduces or increases the torque and speed of an automobile.

  • The gearbox is not a new invention; it was used back in history.
  • These devices were used in horse-powered systems, wind, and steam mills for hoisting, milling, and pumping. But gearbox also evolved with the evolution of the human mind.
  • Now modern gearboxes are used in automobile vehicles. They increase the output torque of the motor. In return, speed is reduced.

Gearbox Definition

A gearbox is a complex structure of circulating machines that can control the speed and torque of a motor. In simple words, it is a system of gears in a vehicle. It is also known as transmission due to its transmitting capacity. It varies from motor to motor depending on the overall diversity among automobiles. Gears are the part of machinery that changes the machine’s motion accordingly, and the process of changing gears is called gearing.

Gear Ratio Definition

The gear ratio can be defined as the number of gears present in a gearbox. All the gearboxes have a common feature that their gear ratio can’t be changed. It remains the same as it was during the construction of gears. The factors that affect a gearbox’s construction include output and input speed, output and input torque, efficiency, durability and strength rating, and the factors of life, service, and application.

Why Do We Need Gearbox?

There are many reasons for using a gearbox.

  • The gearbox has its unique importance in any mechanical system.
  • It is the most reliable and experimentally proven method for the transmission of power. We can’t use a direct engine to transmit the power, so we must use a gearbox for transmission.
  • It is used to transmit power, speed, and torque.
  • It is used to keep gears lubricated and away from the dust.
  • It also protects the gearing process from any mishap.
  • It helps in a clockwise and anticlockwise direction.

Main Parts of Gearbox

The gearbox is a complex structure consisting of various components with their respective functions. All the components are interdependent and work collectively. Each component with its specifications is described below:

what gearbox definition parts components working types applications
Parts of gearbox

Clutch Shaft

A Clutch shaft does the role of a driving shaft. It takes power from the main engine and redistributes this power to other shafts. It is connected with the clutch, a mechanical device that engages and disengages the power transmission. When someone engages the clutch, it also rotates the driving shaft of the vehicle.

It consists of a single gear fixed on it. It rotates with the rotation of the crankshaft of the engine at the same speed. The crankshaft is the backbone of an engine which changes the linear motion into a rotatory motion. It is also known as a driving or input shaft.

Counter Shaft

The Countershaft has a direct connection with the clutch shaft. It consists of different ratios of gears. These gears help it in connecting with the main shaft and clutch shaft. The running of the countershaft varies with engine speed depending on the number of gears attached to it.

Main Shaft

It is also known as the output shaft. It runs with the running of the vehicle. It carries the power from the countershaft with the help of aligned gears and uses that power in the motion of vehicles. Its speed varies from the countershaft. It provides the desired torque to a moving vehicle.


When a thing moves or rotates, it produces friction with surrounding parts. This friction affects the motion of an object. To counter this friction, bearings are used around the shafts. It reduces the friction by rolling motion, which decreases the consumption of energy. Both the counter and main shafts work with the support of the bearing.


Gears are circulating machines with cut teeth of different sizes. They transfer the torque and speed from one shaft to another. Transmission of torque depends on two things: the teeth of gears and the sizes of teeth. If the ratio of gear’s teeth is high, it will produce more torque. An increase in torque will lessen the speed respectively. Gears on the clutch and counter shafts move along with the shaft movement, while gears attached to the main shaft can slide in both directions.

Gear selectors

Gear selectors are mechanical devices consisting of a lever that helps in engaging and disengaging gears throughout the mechanism.

Manual Gearbox Parts

The manual gearbox consists of a variety of different minor components having special functions.

  • It consists of a clutch disc that transforms power from the engine to a manual system. The clutch pedal works on the principle of hydraulics, and it stimulates the disc on pressing.
  • To synchronize the speed, synchronizers are used for engagement between collar and gear. Another essential component of a manual system is gear. 
  • According to their functions, they have different sizes; greater gear means more torque while smaller gear means less torque and more speed.
  • Some other components are also present in this system, including the flywheel, a circular component that passes torque from the engine towards the disc, selectors fork that helps collars move above the output shaft, and the stick shift.
  • Stick shift is that outer component that we use by hand for gear switching. Collars shift the torque to output shafts by locking selection during gears switching.

Automatic Gearbox Parts

Let’s try to understand the parts of an automatic gearbox.

  • An automatic gearbox system consists of a torque converter. It consists of a pump, a turbine, and a stator. All three components of converter collectively in power transmission. They also ensure the continuous working of the engine even when the vehicle is stopped.
  • Another main component is the oil pump provides transmission fluids to the valve body and all other components according to their desire.
  • Planetary gears systems have a significant role in the automatic gearbox. Unlike a manual gearbox, it consists of three layers of gears of different sizes. For movement, there is a variety of gears ratio, but other gears become locked when one is working. Clutch plates are replaced with clutch packs which work automatically.
  • Oil pressure from the valve body controls the movement of the clutch pack. When they get stimulation, other clutch packs become locked to get the desired gear ratio.
  • After completing all internal processes, power is shifted to the output shaft and then to the drive shaft. Brake pads can temporarily stop the planetary gears while the oil pan is also there to accumulate excessive oil for the pump.
  • The valve body is a guiding component that delivers oil to the needed component and exerts the oil pressure accordingly. Although it’s a highly complex component, it still has its elite importance.

How Does gearbox Works?

For a better understanding of its working principle, we must know the torque and speed. Torque is a rotational force developed by a motor, while the motor rotation rate will be called its speed. Toque and speed vary with each other inversely. If one is increasing, the other will decrease, and vice versa. The gearbox takes mechanical advantage through gears which increase output torque and reduce rotations per minute. In simple terms, two different gears are attached to input and output shafts and are also engaged with each other.

Larger gear is attached to the output shaft, while the input shaft has a smaller gear. Its principle depends on one the movement of these two mating gears. The larger gear of the output shaft has slow movement compared to the smaller gear of the input shaft. The slow-motion of the bigger gear of the output shaft gives a mechanical advantage. This advantage produces more torque and lessens the speed.

Types of Gearbox

There are different types of gearboxes depending on their use and working people. It includes an automatic gearbox, manual gearbox, and epicyclic gearbox with their respective subtypes.

Manual Gearbox System

It is a simple gearbox which is further divided into three categories.

Sliding Mesh Gearbox

Spur and helical gears are used in the sliding mesh gearbox to act. Spur gear’s teeth make a parallel connection with the gear axis. They are expensive and a little bit noisy at high speed. At the same time, the helical gears’ teeth are unparalleled to the gears’ axis and make an angle with it. These gears have high loading capacity, smooth movement, and less noise.

sliding Mech Gearbox
Sliding Mech Gearbox
  • The sliding mesh system consists of a set of arranged gears connected with their respective shafts. As mentioned, sliding the splined shaft left and right with the gear lever helps change the vehicle’s gears ratio.
  • Louis-Rene and Emile Levassor, in 1894, firstly invented it. These French inventors firstly introduced the 3-sliding mesh gearbox.
  • It was the first-ever transmission system introduced in automobiles. Its gear ratio depends upon the desired gears for proper functionality.
  • Mainly they consist of three forward and one reverse gear.
  • The main shaft has four gears, while the layshaft consists of three attached gears. The gears of the main shaft and layshaft mesh with each other. That’s why it is called a mesh gearbox.

Constant Mesh Gearbox

Same as the sliding mesh gearbox, it also has three forward while one reverse speed. In these gearboxes, mesh among the gears is a continuous process. A specific form of clutch known as dog clutch is used to hold the engagements and disengagements of gears.

constant Mesh Gearbox
Constant Mesh Gearbox

These crutches select the gear ratio. Clutches can connect different gears attached to varying shafts for power transmission. They use helical gears for their transmission rather than spur gears.

  • Gears of the output shaft circulate freely while on the layshaft, gears are rigidly attached with it. If there is no power transmission among the Layshaft and output shaft gears, it means there is no movement.
  • To counter these disengagements, dog clutches are employed to connect both shafts’ gears and smooth power transmission.
  • The dog clutch is connected with the selector fork and then to the gear lever.
  • For example, if a driver pushes the gear lever, it will force the dog clutch to engage the gears of the output shaft with a layshaft. It is how power will be transmitted. An idler gear is used to reverse the vehicles.

Synchromesh Gearbox system

It is the most refined and advanced form of a constant mesh system. As the name is mentioned, it uses synchronizers for gear change instead of sliding or continuous mesh. A synchronizer is a device that brings gears together and does their frictional contact and smooth engagements.

  • The principle of the synchromesh gearbox is considered as “the gears are abraded with each other before the gear is engaged and engaged after the speed is equalized.”
  • It adds some more specifications to the mesh system. It divides the dog clutch into a synchronizer hub and shift sleeve(pinion).
  • Synchronizer hub is a gear attached to the drive shaft while the collar with sliding ability around it is shift sleeve.
  • Collars can slow down or speed up the gears with the help of friction.
  • The real purpose of this up and down is to balance speed between synchronizers hub and shift sleeve.
  • When the balance of speed is achieved, collars or pinions connect everything for smooth power transmission. This whole complex process happens in a fraction of a second.

Epicyclic Gearbox System

It is also named a planetary gearbox. It consists of two gears designed in a sequence. The center of one gear rotates around the center of the other gear. One gear is known as planet gear, while the other is known as sun gear; both are attached through a carrier. These gears are named after the solar system.

Planet gears move around the sun gear as the real planets revolve around the sun. In this type of automatic transmission system, there is no need to put pressure on the clutch.

  • A ring gear is an external gear assembling all the planetary gears in it. The sun gear is fixed while planetary gears revolve around it and make an epicyclic curve.
  • Planet gears are in continuous mesh with both the ring and sun gears. They not only rotate around their axis but also around the sun like our solar system.
  • The carrier which unites all the planetary gears revives the output and transfers it to an output shaft.
  • Fixation of all the ring, sun, and planetary gears work collectively for a sole purpose. The purpose of fixation is to obtain desired torque and speed.

Automatic Gearbox system

As the name is mentioned, this type of gearbox auto-fixes gears, engagements, and time. The driver has only one role in selecting vehicle conditions, either neutral, forward, or reverse. There is no need for clutch and gear level to change the gear. There are two types of automatic gearbox

Hydramatic gearbox

It was first introduced in 1939 for automobiles. It consists of the fluid coupling and three planetary gears. They collectively make three forward and one reverse speed. There is no clutch for engagement and disengagement from the engine.

  • The vehicle is controlled through only a speed accelerator and brake.
  • A fluid flywheel is used for gear transmissions. It operates hydraulically and uses fluid coupling for a gear’s ratio.
  • It reduces the torque of the engine by using the throttle and centrifugal governor.

Torque Converter Gearbox

Torque converter does the same function that the clutch does in the manual gearbox system. In this type of gearbox system, a flywheel from the engine unites with the torque converter. The flywheel rotates the entire torque converter with the same speed as the engine.

Torque converter takes advantage of the centrifugal force and throws the oil out of it. It works like an oil pump. Fluid from inside of the converter casing spreads throughout the turbine. The turbine absorbs this fluid and starts rotation. It is directly attached to the output shaft.

  • When the rational output speed is low, the converter increases the torque production.
  • Epicyclic planetary gears, torque converter, and fluid coupling make a unity.
  • They work collectively with each other. It is present in the automatic gearbox system.

Applications of Gearbox

Gearboxes are a set of gears that alter the speed and torque, which depends on the gear ratio. The size and shape of gear teeth are significant in machines’ efficiency, speed, and torque.

Many gearboxes have different functions according to their structures. Various forms of gears encased in gearboxes with their applications are discussed below;

  • Bevel gearboxes have spiral and straight teeth shapes. These gearboxes are used in power plants, steel plants, and automobiles.
  • Spur gears make parallel angles, which are used in speed controllers, packaging, and power plants.
  • Worm gears can handle high shock loads. They haven’t any noise while running and they need to be cost-free in case of maintenance.
  • These gearboxes are used in elevators, mining, escalators, and presses.
  • Another form of gearboxes that works on the principle of the solar system is called planetary gears. They have a wide range of applications in different types of machinery, especially in lifts and cranes.
  • Other smooth and quiet helical gears are also employed. They are used in cutters, oil industries, and elevators.

Advantages of gearbox

  • Gearboxes have a mechanical advantage, and they use this advantage to increase the torque and reduce the race. This advantage is obtained through the slow rotation of output shafts as compared to input shafts.
  • They have a constant transmission rate without interruption and have high working stability compared to any other alternative. Because the design provides high input energy, which seems impossible from any other gear arrangements.
  • Required speed can be obtained by adjusting the gears ratio in a box.
  • It consists of a variety of gears with their specification. Drivers have complete control over the procedure as they can do the predictive transmission. There is less risk due to almost zero electronic processes.
  • They have a large transmission rate and high bearing ability. It has very high reliability and stability.
  • The gearbox comprises a complex structure. All the components of the gearbox work collectively in a very precise and safe manner.
  • They are effortless to maintain and have low maintenance costs due to fewer parasitic losses. Oils are used, which are cheaper as compared to other fluids.
  • They are very lightweight and have a very high-power density. The efficiency can be increased by adding more gears to it. It depends on how much time a machine takes to transfer the energy from one shaft to another.
  • They have a long lifespan with high-duty applications.
  • Another craziest benefit of the gearboxes is they can’t be stolen.

Disadvantages of Gearbox

  • They produce noise and vibrations while running fast.
  • They need lubrication for their proper movement.
  • Manual gearboxes involve the constant role of the driver throughout the movement. It causes fatigue and restlessness to the drivers. It also needs extra care and use of the hand and makes driving a multitasking process.
  • The construction and design of automatic gearboxes are very complicated and complex in design. Sometimes it happens that desired torque is not produced through the automated gearbox system. It also isn’t much fun as compared to manual because it does not involve the driver much. In a manual system, you can change gears whenever you want, while it changes according to a condition in an automatic system.


The gearbox contains a gear train that has a pattern of gears. These gears do teamwork and alter the torque and speed of the types of machinery they are fitted. The gears vary from each other in their teeth shapes, working principles, and uses. While choosing the gearbox, make sure that you have enough knowledge of gearboxes and their specific roles.

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