Differentials & Parts

In an automobile and other wheeled vehicles, a differential is a device, usually consisting of gears, for supplying equal torque to the driving wheels, even as they rotate at different speeds. more...

In some vehicles such as karts, torque is simply applied evenly to all driving wheels using a simple driveshaft. This works well enough when travelling in a straight line, but when changing direction the outer wheel needs to travel farther than the inner wheel. Hence, the simple solution results in the inner wheel spinning. For general road use, such a method would result in too much damage to both the tire and road surface. Differentials are typically composed of a gear mechanism in which a ring gear receives input power, which is transferred to two side gears by means of usually two opposing central pinion gears on a common shaft. The pinion gear(s) are mounted to a cage which is affixed to the ring gear. When the ring gear and cage rotate, the pinion gears drive the side gears; the pinion gears are free to rotate about their own axis when either of the side gears meets resistance.

In a motor vehicle, the two side gears may be used to transfer power to the left and right wheels. When the vehicle turns a corner, or one of the wheels encounters resistance, the pinion gears rotate around the side with the most resistance; this rotation drives the other side gear with additional speed.

The most basic differential described above, known as an open differential, suffers from one important problem, however. In an automobile, if one wheel begins to slip while the other maintains traction, the slipping wheel will receive most of the power. This means that if one wheel is spinning on ice while the other is still in contact with the pavement, acceleration of the driveshaft will only cause the slipping wheel to spin faster and very little power will reach the wheel with good traction. Similarly, if one wheel is lifted off the ground, nearly all the power will go to the wheel that is off the ground; not a hopeful prospect for off-road vehicles. Such a loss of traction is sometimes called "diffing out."

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