What is the name of the device that allows a car's driving wheels to turn at different speeds when cornering?

Differential

http://auto.howstuffworks.com/differential.htm

The differential has three jobs:

*To aim the engine power at the wheels
*To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
*To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)

Why You Need a Differential

Car wheels spin at different speeds, especially when turning. Each wheel travels a different distance through the turn, and the inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the distance traveled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.

[Added text from the reference link - McG]

In an automobile and other wheeled vehicles, the differential allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them.

https://en.wikipedia.org/wiki/Differential_%28mechanical_device%29