Curve control: Why your car's differential lock is so important

By DPA | 20 November 2020


BERLIN: You might not have woken up this morning thinking "I want to learn what a differential lock does."

But hear us out, because this key part of your car is what helps your wheels from spinning out on slippery corners, while reducing tyre wear and tear.

To understand what a differential lock is, first we need to take a step back and explain what a differential gear is. You don't know what it is?

Yes, you do, because you can find it in every car. It has nothing to do with changing gears, but is there to help you turn corners comfortably, in a way that is gentle on the tyres.

Basically, a gear mechanism like this serves to split the power: It divides the power from an input shaft, such as a cardan shaft, to two output shafts and compensates for any differences in speed. “Without a differential gear, there would be increased tyre slip on the inside of the wheel and the wheel would spin,” explains Denny Weiser from the Dekra vehicle inspection company.

However, in certain situations the differential gear's properties can get rather disruptive. For example, in cold weather, when one wheel is on a frozen puddle and the other wheel is on rough asphalt. The wheel on the ice has hardly any grip because it's so slippery, and when you step on the accelerator it immediately spins crazily while the other wheel holds still. Power is not transferred, making it impossible to start up.

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The same applies when starting up in rough terrain or with a powerful sports car. "In a situation like this, a limited-slip differential can help," says Weiser.

This can temporarily - or if desired permanently - block the distribution, partially or completely. With the example of the ice, this would mean that a certain percentage of the power always gets transferred to the wheel that's on the asphalt. Starting up is then possible again.

According to Denny Weiser from Dekra, there are purely mechanical, pneumatic-mechanical, hydraulic-mechanical and electro-mechanical versions of the limited-slip differential. The blocking can have either variable and load or speed-dependent values, as well as fixed ones.

The simplest type is a fixed value lock triggered manually by the driver. So-called friction clutches distribute the torque at a fixed percentage between the two output shafts.

Load-dependent differential locks, on the other hand, only do their job when there is a difference in torque between the output shafts; speed-dependent locks, like the electronic version, only start doing their job when there is a certain difference in speed.

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