5 Types of Automotive Differentials Explained
Posted by Auto Surgeons on
Last week we looked at the meaning of differential in cars and how they work. This week we'll guide you through everything you need to know on the types of automotive differentials. We will start with the simplest type of differential, called an open differential.
Open Differential
What It Does
Splits engine torque into two outputs, each of which is able to rotate at a different speed.
Shortcomings
When one tire loses traction, the opposing tire also experiences a torque reduction. In the worst case, your car is stuck with one wheel freely spinning while the tire with better traction can’t deliver enough torque to budge the vehicle. Modern traction-control systems compensate by applying the brakes (and thus a reaction torque) to the slipping wheel. That said, a more sophisticated diff is generally quicker-acting and more effective than this type.
Found In
Anything without the pretense of performance or off-road ability—family sedans, crossovers, minivans, economy cars, etc.
Locking Differential
What It Does
With the diff locked, the connected wheels always spin at equal speeds. In sand, mud, and snow, a locked differential ensures that torque continues to flow to the wheel with higher traction.
Shortcomings
Behaves like an open differential when not locked. Locking the diff on a high-grip surface such as dry pavement makes it difficult to turn the vehicle and can grenade the drive-line.
Found In
Jeep Wrangler, Mercedes-Benz G-class, Ram 2500 Power Wagon; optional on most full-size trucks.
Limited-slip Differential
What It Does
A limited-slip differential marries the concepts of open and locked diffs, working like an open differential the majority of the time, then automatically beginning to lock as slip occurs. Lock-up can be achieved via a viscous fluid, a clutch pack, or a complex geartrain.
Shortcomings
Purely mechanical limited-slip diffs are reactive. That is, they don’t begin to lock up until after wheelslip has occurred.
Found In
Nissan 370Z with Sport package (viscous), Mazda MX-5 Miata (clutch type), Scion FR-S/Subaru BRZ (helical gears).
Electronically Controlled Limited-slip Differential
What It Does
An electronically controlled clutch pack offers rheostatlike control between open and fully locked behaviors, with adjustments made hundreds of times per second. For example, if the computer determines there’s too much oversteer during cornering, it can dial in more lockup to stabilize the car.
Shortcomings
As with a conventional limited-slip diff, torque is biased toward the slower wheel.
Found In
BMW M3 and M4, Cadillac ATS-V and CTS-V, Chevrolet Corvette with Z51 package, Ferrari 488GTB.
Torque-vectoring Differential
What It Does
Using additional geartrains to overdrive the half-shafts, torque-vectoring differentials fine-tune the torque delivered to each drive wheel. This produces a yaw moment that can slow or quicken the car’s rotation in a corner. Still confused? Read the damn story.
Shortcomings
Torque-vectoring differentials are heavy, complex, and expensive, and inflict a slight fuel-economy penalty.
Found In
Audi S4, S5, and S6; BMW X5 M and X6 M; Lexus RC F.
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(Credit to: www.caranddriver.com - ERIC TINGWALL, auto.howstuffworks.com - KARIM NICE)