AdvicesWhat Is A Transmission In A Car (And Why Is It Important)?

August 19, 2021cargarage0

Understanding the different parts of your car and how they’re all working in synch to keep you on the road isn’t exactly essential knowledge for a driver to have, but it definitely makes owning a vehicle cheaper, easier and more rewarding. 

The transmission (or gearbox) is one of those many parts we all know are found somewhere in our vehicle, but might not be able to answer ten questions about its function. 

At the end of this article, we hope to give you the power to do that and have a clearer picture of exactly what’s going on inside your transmission. 

What is a transmission (and how does it work?)

Most motorists know what their transmission/gearbox is used for, but how many know how it actually works? 

In short, transmissions are quite basic parts of a car. It is mounted directly on the engine, converting the engine’s combustion power into the vital momentum that drives the car’s wheels. 

The transmission and gearbox are responsible for efficient driving. By changing gears, a driver can keep their RPM’s (revolutions per minute) low and avoid overloading the engine. This also keeps fuel consumption low, resulting in more effective and environmentally friendly driving, along with greater fuel economy for the vehicle owner. 

The transmission itself is responsible for converting both speed and momentum into power, keeping the car moving and the engine efficient. 

This is achieved through the use of gears and gear ratios that are selected either automatically by the vehicle or manually by the driver (see below for a more detailed explanation of the differences). 

If you’re an experienced driver you likely have a preference for the type of gearbox/transmission you like to use. If you’re a new driver or thinking of purchasing a new car though, this article will outline the differences to help you make an informed decision on your next purchase. 

What is a gearbox (and how does it work?)

Things can get confusing quite quickly when it comes to covering gearing components, so we’ll try to keep this section simple. 

There are many terms that gear manufacturers, as well as car engineers, designers and mechanics, will use to discuss the same thing. The gearbox itself is one of those terms, with many using ‘gearhead’ or gear reducer’ as alternative names. 

The most basic definition of a gearbox is that it is a contained gear train, mechanical unit or component consisting of a series of integrated gears within a housing. 

In short, a box full of gears. 

It functions as a system of interlocking gears, altering the torque and speed of a vehicle’s driving device. 

Each make and model of a car will have its own unique elements as manufacturers find new ways to streamline their products. However, this design has largely stayed the same for many decades and rarely varies beyond the above description. 

Types of gearbox

There are three common types of gearbox drivers should be aware of. 

Semi-automatic gearbox

In a semi-automatic gearbox (or semi-automatic transmission), the clutch is still a part of the transmission (but not the clutch pedal), while a computer maintains the gear changes automatically.

Semi-automatic gearboxes still see the clutch play an important role as part of the transmission, although not the clutch pedal. 

A computer will change gears automatically. 

How this process works will change from car to car. In some cases, the driver has no input when changing gears, letting the engine and electronics do the work for them. 

In other makes, the driver will need to inform the engine when they want the gear to go up or down, by pushing the gear lever in the direction they want. The electrics will then automatically shift gears. This actual change is made in the “actuator”. 

DSG gearbox

A DSG gearbox blends elements of manual and automatic transmissions. There is a clutch, but no clutch pedal and the function of the clutch itself is retained in a dual clutch, which provides for easy and immediate gear changes. 

Many models carry this, particularly German manufactured ones. 

DSG gearboxes can often cause maintenance issues. Gearbox oil and oil filter changes are necessary during services, as they can only last a relatively short time in comparison to manual alternatives. Aim to get this inspected every 38,000 miles to avoid wear-related dust and sediment build-up. 

Sequential gearbox

Sequential gearboxes possess a number of similarities to a manual gearbox, but with one glaring difference. 

Unlike the manual option, a sequential gearbox demands the driver cycle through each gear one at a time whether they’re moving up or down. During this process, the driver shifts gears on a pair of cogwheels. 

Unlike a manual gearbox, you can only switch gears to one that comes before or after the one you’re currently driving in. This is because gears are “in line” as opposed to the traditional H format. 

What’s the advantage of doing this? This method allows for faster shifting to the next gear to improve acceleration, which is why you’ll find a sequential gearbox in most racing cars. 

What is a clutch (and how does it work?)

The clutch is the kind of car part you don’t think about until something goes wrong. 

In short, though, the clutch transfers the rotational power from the engine to the wheels in a manual vehicle. It does this by connecting two rotating shafts. It is a vital part of a car’s working machinery. 

To ensure a car can both change speed and come to a complete stop without turning off the engine, the driver needs to temporarily break the connection between the engine and the wheels. 

A clutch has two main parts: the clutch plate and the flywheel. If your foot isn’t pressed down on the clutch pedal, a set of springs will keep a pressure plate pushed against the clutch plate. The pressure from these springs also pushes the clutch plate up against the flywheel, connecting the engine to the shaft and allowing for the transfer of motion to the wheels, making both turn at the same time.

When you push your foot down on the clutch pedal, you press down on the release, allowing a series of springs and pins to pull the pressure plate away from the clutch plate. This breaks the connection between the rotating engine and wheels, allowing the wheels to continue to spin but this time under their own momentum. 

This design allows drivers to disengage the wheels fully from the engine in order to change gear, giving drivers a greater sense of control over the speed of their car. 

Manual gear vs automatic transmission

Whether you drive a manual or an automatic is a matter of preference, but it’s helpful for drivers to get a sense of how both options operate. 

A car with manual transmission features:

  • 5 or 6 forward gears
  • 1 reverse gear

The driver can change between these manually. While automatic transmissions, as the name suggests, perform these necessary changes automatically as you drive. 

Automatic cars have, historically, been a rarity on UK roads, with the vast majority of drivers prefer manual options. However, this seems to have changed in recent years, with automatic vehicles seeing a 70.5% upturn

The benefits of automatic cars over those with manual transmission are quite simple: driving ease. 

Automatics are generally more comfortable, accessible and easier to drive. However, manual cars do provide a greater sense of control and grip on the road, which many car owners enjoy and have become accustomed to. 

Automatic transmission: how it works

So, we know the benefits of driving automatic over manual, but what’s the science behind how this system works? 

Automatic gearboxes are designed so that in the centre of the gears there sits a large cogwheel, also known as the sun gears, which transmits the power from the engine. Around the cogwheel are a series of smaller gears, known as planetary gears. These come in many different sizes and can be interconnected or separated. Encircling them is a second large cogwheel, which transmits the power from the planet gears, in turn, transferring it to the wheels. 

Hear shifts occur as a fluid transition between the various planet gears, making driving a smoother and quieter experience than if you were to disengage and engage the clutch through manual gear changes. 

There are alternative forms of automatic transmissions, such as the Ford Power Shift and the Continuous Variable Transmission gearbox. These can provide a better grip or smoother ride respectively. 

These automatic gearboxes can be more prone to direct damage and wear and tear over time in comparison to manual transmissions, so it’s worth arranging regular services and inspections to assess their condition. They should be fully cleaned before this, primarily of wear-related contaminants within the gear oil. 

Active Shift Control

First developed exclusively for Hyundai vehicles, Active Shift Control is an improved version of the transmission for hybrid cars. 

The advantage of the Active Shift Control system is that it shifts to the electric motor at times when an ordinary petrol car would consume the highest volume of fuel, such as during start-up and acceleration. 

That’s not all though. Active Shift Control also provides vehicles with greater gearshift and gearbox durability, whilst also improving the acceleration. 

This is achieved through the optimisation of momentum and the transfer of power to the wheels by streamlining the gear shift speed. The sensor in the electric motor detected the revolutions in the gearbox, synchronising with it. This way, energy losses are avoided by up to 30% due to a smoother gear shift, with the electric motor keeping the gear’s revolutions consistently high throughout the shifting process.


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