Car Drivetrain: How it works?

For the next part of our Car Parts series, I will delve into the bare bones of a car and that is the Drivetrain! Apart from the engine, being the most essential part of the car, the drivetrain plays a really big role where it transfers the power generated from the engine to the wheels. Whether that be a Front or Rear Wheel Drive (FWD/RWD) or All Wheel Drive (AWD), the idea is the same! Some people confuse the terms drivetrain and powertrain; the only difference between the two is that the powertrain includes the engine as well as all the components that transfer the power from the engine to the wheels whereas the drivetrain doesn’t include the engine.

As I have already touched upon how an engine works in one of my previous articles linked here – Car Parts: Car Engine WorksI will only go over the drivetrain in particular and not the powertrain.

Components?

ComponentsThe Drivetrain has at least 4 different components which are essential in transferring power to the wheels

The drivetrain can easily be split into 3 different articles given the complexity of the drivetrain however for the sake of simplicity (and your time), I’ll summarize the drivetrain as simply and concisely as I can. The components of a drivetrain are the following:

  • Transmission (Gearbox)
  • Driveshaft
  • Differential
  • Axles

Each one plays an integral part in transferring the power from the engine to the wheels of the car and I’ll get into some details later in this article!

Types of Drivetrains?

DrivetrainDrivetrains refer to the system that transfers power from the engine to the wheels

You’ll hear this anywhere whether you’re a big car fan or just looking to buy a new car, but the types of drivetrains out there in normal production vehicles are quite basic and fall into the following 4 categories:

  • All-Wheel Drive (AWD)
  • Four-Wheel Drive (4WD)
  • Front-Wheel Drive (FWD)
  • Rear-Wheel Drive (RWD)

What all these different types of drivetrains refer to are where the power from the engine is allocated to and how it is sent to those wheel – i.e. Front-wheel drive drivetrains refer to the engine power being sent to the front two wheels.

You might be asking: What in the world is the difference between AWD and 4WD?. Similarly to drivetrains and powertrains, many people tend to get these two mixed up although fundamentally they are very similar. Here’s an interesting video which sums it up quite well:

An AWD drivetrain is a more casual drivetrain which sends power to all four-wheels and is heavily controlled by electronics. AWD vehicles are best equipped to handle wet or slippery roads. This type of drivetrain is often used on modern SUVs such as the Hyundai Santa Fe or Volvo XC60.

A 4WD drivetrain is more extreme and the AWD’s bigger brother. The 4WD system also sends power to all 4 wheels but the main difference is the 4WD system has a more robust and sophisticated mechanism that allows for maximum traction in extreme/offroad situations which often involve manual adjustments of the differentials (which I will get into). You will find this system on serious off-road vehicles such as the Toyota Land Cruiser or Ford F150.

Transmission or Gearbox

GearboxGearboxes/Transmissions usually come in two variants Automatic and Manual (although other variants do exist)

The first part of the drivetrain is the transmission – otherwise known as the gearbox. As I said, I could easily dedicate a whole other article on the transmission but enough of that now… The transmission transfers the torque (rotational energy) from the engine and passes it along the driveshaft (which we’ll get into next) and ensures that the power is delivered smoothly. The purpose of the transmission is to control how much power is being sent to the wheels at whatever point in time, otherwise the car would have a very limited speed range.

This is done through the different gears and their appropriate gear ratios which determine how much of the power from the engine is delivered to the wheels. As you all may know, cars have different gears which either you or the car has to shift through (depending on whether you have manual or automatic vehicle). Those gears allow for cars to travel the speeds they can now as the gears allow for a massive range of torque to be delivered to the wheels.

Driveshaft

Driveshaft DiagramThe driveshaft links the gearbox and differential along the underside of the vehicle

The driveshaft is quite an important link that has a huge purpose if the car has to allocate the power to the rear wheels (either in an AWD, 4WD or RWD). The driveshaft is a long rotating spinning tube which takes the power from the engine + transmission and transfers it to the differential (more on that later) and subsequently to the wheels. The driveshaft runs along the middle underside of the vehicle. Most driveshafts connect to the differential with a U-joint however other variants may even use two u-joints.

Differential

One of THE most essential parts of the driveshaft is the differential. It allows for the wheels to rotate at different speeds (at least that is what they are made to do). It’s the last major mechanical process on the drivetrain before the power gets to the wheels and is crucial especially in high-performance vehicles. Drawing upon the name, it’s called a differential as it allows for the wheels to spin at different speeds.

You might be wondering, why in the world would I want my wheels to spin at different speeds? Well.. the reason lies in the corners. When you’re turning let’s say into a right corner, your right wheel will have to travel a smaller distance than the left wheels given the width of the car. As such, the inner wheels travel slower than the ones outside which travel a bit faster.

There are various types of differentials out there:

  • Open Differential (Most-common)
  • Limited Slip Differential (LSD)
  • Welded Differential
  • etc…

Limited Slip DifferentialThe Limited Slip Differential (pictured) limits the loss of traction. Pictured above is the clutch based LSD

A certain type of called a Limited Slip Differential (LSD) which many performance-oriented enthusiasts go for, allows for both wheel to rotate at different speeds – but limits the difference in speed of both tyres in order to maximize traction with the road.

The logic behind this is that if a limited slip differential unit weren’t installed (making it an open differential), the power will go to the wheels with the least resistance. An example of this is if one of the wheels were to contact a patch of ice with an open differential, majority (if not all) of the power will go to the wheel over ice as it has the least resistance due to it being on a very slippery surface. This results in a complete lack in traction and thus can result in a loss of control.

Conclusion

Driveshaft UndersideDrivetrains are fundamental in getting the power to your wheels

Drivetrains are quite a tricky and complex thing to wrap your head around. It might seem simple from a bigger picture but when you get into the nitty-gritty details, the whole system becomes a whole lot more complicated. There are a variety of drivetrains, transmissions, driveshaft and differentials out there but the purpose behind remains the same: to transfer power from the engine to the wheels as efficiently and effectively as possible!

If you have any questions you might want to ask, or want more details on any more of the points then don’t hesitate to comment below!

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