Vapaarullajärjestelmien

Vapaarullajärjestelmät, often translated as free-wheeling systems or freewheel mechanisms, are devices that allow a driven shaft to rotate freely in one direction while engaging and transmitting torque in the opposite direction. This unidirectional engagement is the core principle behind their operation. They are a type of clutch that automatically disengages when the driven member rotates faster than the driving member, and engages when the driving member rotates faster or is stationary.

The most common application of vapaarullajärjestelmät is found in bicycles, specifically in the rear hub, allowing riders to coast without pedaling. In this context, when the rider stops pedaling, the rear wheel continues to rotate due to inertia, and the freewheel mechanism disengages the pedal crank from the wheel. As soon as the rider starts pedaling again, the mechanism re-engages, transmitting power to the wheel.

Beyond bicycles, vapaarullajärjestelmät have various industrial and automotive applications. They are used in conveyor systems to prevent reverse motion, in certain types of engine starters to disconnect the starter motor once the engine is running, and in power transmission systems where overrunning capabilities are required. The design typically involves a set of rollers or sprags held within an outer race. When torque is applied in the driving direction, the rollers are wedged between the inner and outer races, creating a positive lock. When the driven side tries to overtake, the rollers are released, allowing free rotation.