The differential of cars it’s a mechanical device which, by means of a series of gears, distributes the same torque value to the driving wheels regardless of their rotation speed which can be different, as when cornering, between the inner and outer wheel.
When there is no differential
Some vehicles, such as karts, are without differential: the drive wheels are integral with the axle and turn at the same speed even when cornering. If this solution does not create problems on the straight, obvious difficulties are generated in the curve, when the inner wheel travels less road than the outer one. This causes very strong friction, which results in poor handling on tight mixed roads and abnormal tire wear. But let’s go in order and gradually deepen this new notion of automotive technology present in the transmission.
How the differential works
Let’s find out now how the differential works present in the transmission of cars. The differentialallows the two-wheel drive when cornering to turn at a different speed from each other. Almost all cars on the road are equipped with an “open” differential.
In essence, this device, through a series of gears, sends the same torque value to the driving wheels regardless of their rotation speed which can be different, as in curves, between the internal and external wheel.
Differential operation diagram in the bathroom of oil
Differential how it is done
The differential is generically constituted by a satellite cage to which two axes are bound. Two satellites are installed on the latter, in engagement with two planetary gears (bevel gears) integral with the half shafts.
In this way the transmits to the wheels an equal number of revolutions in straight lines, while in curves the internal wheel can decrease revolutions and transfer them to the external one.
Free differential
How free is it? Since the torque value is proportional to the resistance (or grip) present, it follows that the amount of torque transmitted derives from the drive wheel with less grip between the two. If a wheel slips, the torque directed to the one with the most traction is automatically reduced. And this is the limit of the free differential o open: in practice, when one wheel loses grip, the other no longer discharges power.
On a front-wheel drive this results in a loss of traction resulting in understeer “power.
Examples of torque transfer and traction with free mechanical differential
Differentials can also be “Lockable” like the one mounted on the Peugeot 308 GTbut of self-locking differential we advise you to read the following study HERE.
How the differential works
A full article on free differential and self-locking and locking differentials was covered in the magazine PROCESS 240 July 2019.
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