How a Differential Works
All cars that require good road handling and are more than just a small beginners toy will use differentials. Every single full sized car you have ever travelled in has them, and they are a key device in many areas of mechanical movement.
The differential was first legally patented in 1827 by a French watchmaker for use in automobiles, although the original idea came much earlier and the very original inventor is unclear and lost to history.
The idea was born from a simple issue with seemingly no solution. A vehicle travels around a bend or anywhere apart from a perfectly straight line - the result is that the outside wheel is travelling a slightly further distance than the wheel on the inside and therefore rotating a bit quicker. If the wheels are on a solid shaft and directly linked to each other then this obviously cannot happen so either the shaft will break due to stress, or one of the wheels must slip causing huge wear and tear and friction.
This is where the differential is a simple but ingenious solution. An axel with a differential on it can allow the shaft to be driven by the motor/engine in exactly the same way, but the two ends of the shaft can also rotate at a different speed. The diff contains small diff gears, or spider gears as they are also called that allow for the different rotational speeds. You can even stop one end of the shaft completely which will then transfer 100% of the drive to the other end of the shaft via the spider gears. This means no excess stress on the shaft and no slip for the wheels and tyres.
Different Kinds of Differential
The job of the differential is to send the power from the motor or engine to each wheel. Different types of diffs do this in different ways.
The four types of differential we will compare are:
- Open
- Locking
- Limited Slip
- Torque-Vectoring
Open Diff
Found in most regular cars, this is the most basic kind. It effectively splits the power of the engine in half and sends it to each wheel separately meaning each wheel is free to turn at a different speed in relation to each other if the car turns a corner.
Locking Diff
You will find this kind of diff in off-road vehicles and also drift cars.
The type in drift cars is more commonly called a welded diff meaning that the ability to split the engine's power to each wheel is deliberately stopped permanently so that all power is sent to both wheels at all time. While this is not great due to previously mentioned issues with drivetrain stress, I think we can all agree that in a drift car the wheels are meant to have some slip! Of course this is usually on the rear axle.
The locking diff in an off road car like a Land Rover will have a switchable locking system meaning it can be turned from normal to locked and back again from behind the wheel. This is used when the car gets stuck.
Picture the car going over very uneven ground. If one of the front wheels and one of the back wheels are off the ground at the same time, then when you apply power the two wheels off the ground will spin and the car is stuck due to all the drive being wasted on just those two wheels. The locking mechanism can then be engaged to transfer the engine's power directly to every wheel meaning the car can drive the wheels that are in contact with the ground and hopefully get itself unstuck.
Limited Slip Diff
This kind of differential is a little more complicated - it can behave like an open diff and a locking diff at the same time. It will operate basically the same as an open diff for the majority of the time. It will only begin to lock up when it detects one wheel losing traction (spinning faster than the other). This should aid traction to the road surface.
Picture the car doing a hard launch. If it has an open differential and breaks traction, then the one wheel will spin up and the other one will have power actually taken away from it - overall this will equate to a slow take off. The car next to it with a limited slip diff will break traction as well, but the diff will immediately transfer more power/drive to the opposite wheel rather than wasting it on the wheel that has broken traction. These diffs unsurprisingly are very popular in high performance cars.
Torque Vectoring Diff
This kind of diff takes the job of a limited slip diff and improves on it with the help of computer control. While the limited slip diff’s mechanical method is simple and effective most of the time, it really is no match for electronically controlled vectoring which can sense traction loss, and send the exact amount of power exactly where it needs to go in a fraction of a second. Cars with this technology will have excellent grip in all conditions even on the driving limit.
