How a differential works and its types

Following the presentation and road test of the new SEAT Ibiza SC Cupra, many people have asked me what a differential is or how it works. In a quick and simple way, we could summarise an entire article by saying that a differential is nothing more than a mechanical part that distributes engine torque between the driven wheels, allowing one of them to turn at a different speed from the other.

A differential is somewhat more complex, even without considering the variety that exists today, from mechanical to electronic. Over the next few paragraphs, at Highmotor, we will try to explain the variety of differentials we can find, along with their different operating principles.

Taking as a base a vehicle with drive on a single axle, whether rear or front, we can find everything from an open differential to an electronic one, passing through limited-slip differentials, Torsen units or electronic limited-slip systems.

When we drive in a straight line, that is, both wheels cover the same distance, the differential, made up of several gears, keeps the latter at the same speed. When entering a corner, the outer wheel, which bears the car’s weight, covers more distance than the inner one. This is why the differential exists. This mechanism, as we have said before, distributes the engine’s power between the wheels, allowing them to travel at different speeds.

Below we look at the types of differentials, together with how they work:

OPEN Differential

The vast majority of road cars, without being sports cars, use the well-known open differentials. In these, when cornering, the outer wheel (which is loaded and bears much of the vehicle’s weight) receives little engine power, because the differential sends most of it to the inner wheel, which has less grip, due to the ease with which it can reach it.

Under normal conditions this is not a problem, but when driving fast, whether on a track or on a winding road, the inner wheel, if we have no traction and stability control, can end up spinning out of control, causing wheelspin or loss of grip, with the consequences that entails.

LIMITED-SLIP or LSD Differential

To solve the problems caused by an open differential, the so-called Limited-Slip Differential or LSD was invented. Its operation, like the others, centres on corners. On entering one, when the outer wheel is loaded and the inner wheel starts receiving too much engine torque, the limited-slip differential, as its name suggests, locks up, sending power to the wheel with more weight on it, improving traction and preventing the inner wheel from spinning out of control.

In this way, the speed through corners increases notably. True sports cars use this kind of differential, although in recent years electronic differentials have become fashionable, mainly because they are easy to control by computer.

TORSEN Differential

Between the two types explained above are the well-known Torsen-type differentials. These take their name from an acronym for Torque Sensing. They offer an important advantage over the other systems.

It is not exactly a limited-slip differential, since it cannot be locked completely; instead, it sends torque to the wheel that can best transfer it to the ground. Compared with a limited-slip differential, the Torsen prevents one wheel from slipping, supplying only what that wheel can put down on the ground and diverting the excess to the other.

This type, besides being used on a single axle, can also be used in four-wheel-drive vehicles in a central position, transferring different amounts of torque from one axle to the other depending on the resistance received from one or the other.

Tomorrow we will continue studying the different types of differentials. I hope you enjoyed it as much as I enjoyed writing it.

Photography | Automotive mechanic