Car gearbox: Definition, types, and functions explained

Have you ever wondered how your car switches gears and goes faster or slower? Well, the answer lies in a component called a gearbox, which is an essential part of a car that requires varying torque and speed to function properly. In this article, we’ll examine what is car gearbox, how it works, and the different types of gearboxes commonly found in cars.

What is a car gearbox?

A gearbox, also known as transmission, is a mechanical component that helps to transfer power from the engine to the wheels by using different gear ratios. It is usually located between the engine and the wheels, consisting of several gears, shafts and bearings. The gearbox is connected to the engine’s crankshaft through a clutch, which allows the motor and gearbox to be temporarily disengaged when changing gears. Its primary role is to churn out the right amount of power and torque to the wheels at different speeds to achieve optimal performance and mileage.

Parts of a car gearbox

Here are the primary parts of a gearbox.

• Clutch shaft: It is also known as the drive shaft that uses the force from the engine and sends the power to other parts. A clutch attaches the drive shaft to the engine and other components. When you engage the clutch, the drive shaft starts to rotate.

• Counter shaft: It is the second most prominent gearbox part and includes various gears in different sizes that can produce enough torque to propel the vehicle.

• Main shaft: It is also referred to as an output shaft. It offers mandatory torque to the vehicle. It has ridges and teeth so the gears can move smoothly.

• Bearings: It supports the rotating shafts and minimises friction.

• Gears: These transfer power from one shaft to another. The torque transferred through the gears depends on the number of ridges and teeth and the gear size.

Different types of gearboxes in cars

The primary types of car gearboxes are manual and automatic. The automatic gearbox is further classified into Torque Converter, CVT (Continuously Variable Transmission), Automatic Manual Transmission (AMT) and DCT (Dual Clutch Transmission). Here’s an overview of car transmissions.

Manual gearbox

A manual gearbox allows the driver to get complete control and choose the gears manually, operating both the gearstick and the clutch. Manual transmissions are affordable and easy to maintain compared to automatic transmissions. The manual version is a predominant gearbox option in Indian cars due to its low-cost factor and maintenance.

Automatic gearbox

An automatic gearbox is a type of gearbox that automatically shifts gears and doesn’t require manual intervention. It uses electronic sensors to monitor the vehicle’s speed and shifts gears with the help of an Electronic Control Unit (ECU).  Automatic gearboxes are more convenient and easier to use than manual transmissions but are more complex and expensive to maintain and repair. Here is an overview of different types of automatic gearboxes in cars.

• Automated Manual Transmission (AMT)

An AMT gearbox is a type of gearbox that automates the manual gearbox by employing a hydraulic to actuate the clutch pedal. It removes the manual effort of using the clutch (physically) and gears since the AMT gearbox uses electronic sensors to perform the task. The AMT gearbox in cars has revolutionised the car market in India, offering the option of affordable automatic cars. Its biggest highlight is the lower cost factor since it has fewer components compared to pure automatic gearboxes, thereby reducing the overall cost of the vehicle. 

• Torque Converter Gearbox

The Torque Converter Gearbox is an automatic gearbox that utilises fluid coupling to transfer power from the engine to the transmission. This gearbox doesn’t require a clutch pedal to shift gears like other automatic transmissions. The torque converter is one of the traditional gearboxes that has witnessed a decline in its popularity in recent times due to its low fuel efficiency and high maintenance cost.

• Continuously Variable Transmission (CVT)

A CVT gearbox is a type of automatic transmission that works via a pulley system. It uses several intricate parts to shift between a range of preset gears. The CVT system includes cones at each pulley linked through a belt and moves to increase or decrease the chain belt diameter to change gear ratios. The CVT is reliable and offers higher fuel efficiency. It is common in Japanese cars such as the Hondas, Nissans and Toyotas.

• Dual Clutch Transmission (DCT)

The DCT employs two clutches to shift gears, offering optimum performance. It uses two separate clutches for odd and even gear sets, reducing gear shift lag. This allows for quicker and smoother gear shifts compared to traditional gearboxes. While one of the clutches is engaged, offering the required power, the other pre-selects the next gear, allowing for faster transitions. DCTs are popular among high-performance and sports cars. However, it is fast becoming one of the most preferred in the mass-market car segment. Brands such as Volkswagen, Skoda, Audi and more are offering DCT in their Indian car portfolio.

Functions of the car gearbox

Here are some of the functions of the car gearbox.

• Change gear ratio: The gearbox changes gear ratio to match driving conditions. It allows the driver to manually change the gear ratio as per the speed and road conditions.

• Transfer power to the wheels: The gearbox transfers the required amount of power from the engine to the wheels at different speeds. This allows for optimising fuel efficiency and performance.

• Control the speed: It controls the car's speed by allowing the driver to slow down or speed up the car by selecting the appropriate gear.

• Offers torque: It multiplies the engine's torque output to offer more power to the wheels, enabling the vehicle to drive through steep inclines.

How does a car gearbox work?

The gearbox in a car works by transferring power from the engine to drive the wheels by employing a set of gears that can be shifted to change the speed and torque. The gears are arranged in different patterns to offer different speeds while maintaining the engine performance. A car gearbox is controlled by a lever or an electronic selector inside the vehicle, and the driver physically selects the desired gear. In a manual transmission-equipped car, the driver must shift the gears physically by moving the lever or the selector. In contrast, in an automatic transmission-equipped vehicle, the gearbox employs electronic sensors to change gears based on the car’s speed and load.

Advantages and disadvantages of manual gearbox

Here are some of the merits and demerits of manual transmissions.

Advantages

• Driver has complete control over the gears

• Costs lesser than automatic gearboxes

• Low maintenance

• Good mileage

Disadvantages

• Can be annoying in heavy traffic

• Precise control over steep inclines can be challenging for some drivers

• New drivers can find it difficult to learn

• Hands and feet can hurt

Advantages and disadvantages of automatic gearbox

Here are some of the merits and demerits of automatic transmissions.

Advantages

• Easy to drive in heavy traffic

• Gearshift is quick and smooth

• Comfortable for drivers

• Have similar mileage to manual gearbox cars

Disadvantages

• Slightly expensive compared to manual gearbox cars

• Expensive to repair

• May not be suited for off-road driving

• Can be heavier than a manual gearbox

Interesting facts about car gearboxes

Here are some interesting facts about car gearboxes.

• The first mass-produced automatic gearboxes were back in the 1930s. General Motors (GM) introduced the HydraMatic gearbox in their Cadillac and Oldsmobile models.

• Manual gearboxes no longer always offer high mileage. Automatic gearboxes offer similar, if not better, fuel efficiency.

• There are several types of automatic gearboxes.

• The manual gearbox is still cheaper than an automatic gearbox.

Frequently asked questions

FAQs

Are the terms gearbox and transmission the same thing?

Commonly, both terms are used interchangeably. However, in a real sense, transmission means the whole drivetrain process, which includes the gearbox.

What is the clutch used for?

The clutch engages and disengages the engine from sending power to the wheels.

Which car gearbox is better?

The choice depends on factors such as budget, performance, familiarity, etc. Opt for the automatic gearbox-equipped car if you are unfamiliar with using the manual gearbox.

Which type of car gearbox offers more mileage?

Traditionally, manual gearboxes have been more fuel efficient than automatic gearboxes, especially when compared to Torque Converter Gearboxes. However, automatic gearboxes have evolved and offer similar mileage to manual gearboxes.

Which car insurance policy is better?

Opt for the Comprehensive Car Insurance Policy for wider coverage. It offers coverage against third-party liabilities and damages to the insured vehicle. It also provides coverage against theft. You also have the option to include add-ons to enhance the coverage.

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Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. It is based on industry experience and several secondary sources on the internet, and is subject to changes. Please go through the applicable policy wordings for updated ACKO-centric content, and before making any insurance-related decisions.