Tasauspyörästö

Tasauspyörästö, often referred to as a differential, is a gear train that allows an automobile's driven wheels to rotate at different speeds. This is crucial when a vehicle turns. During a turn, the outer wheel travels a longer distance than the inner wheel, and thus must rotate faster. If both wheels were locked to the same axle speed, this difference in speed would cause tire scrub, strain on the drivetrain, and difficulty in steering.

The basic open differential consists of a set of bevel gears mounted on a carrier. The carrier is driven by the engine through the driveshaft and pinion. As the carrier rotates, it turns a set of spider gears, which are meshed with two side gears. Each side gear is connected to one of the drive axles. When the vehicle travels in a straight line, the spider gears do not rotate on their own axes, and both side gears, and thus both wheels, rotate at the same speed.

When a turn is initiated, the resistance to rotation of the outer wheel is less than that of the inner wheel. This causes the spider gears to rotate on their axes, allowing the side gears (and wheels) to turn at different speeds. While an open differential is simple and effective, it has a drawback: if one wheel loses traction (e.g., on ice), all the engine's power can be sent to that spinning wheel, leaving the vehicle stuck. This limitation led to the development of limited-slip differentials and locking differentials.