Dual-mass flywheel
A dual-mass flywheel is a rotating mechanical device that is used to provide continuous energy in systems where the energy source is not continuous, the same way as a conventional flywheel acts, but damping any violent variation of torque or revolutions that could cause an unwanted vibration. The vibration reduction is achieved by accumulating stored energy in the two flywheel half masses over a period of time but damped by arc springs, doing that at a rate that is compatible with the energy source, and then releasing that energy at a much higher rate over a relatively short time. A compact dual-mass flywheel often includes the whole clutch, including the pressure plate and the friction disc.
History
Dual-mass flywheels were developed to address the escalation of torque and power, especially at low revs. The growing concern for the environment and the adoption of more stringent regulations have marked the development of more efficient new engines, lowering the cylinder number to 3 or even 2 cylinders, and allowing the delivery of more torque and power at low revolutions. The counterpart has been an increase in the level of vibration which traditional clutch discs are unable to absorb. This is where the dual-mass flywheels play a key role, making these mechanical developments more viable.The absorption capacity of the vibration depends on the moving parts of the DMF, these parts are subject to wear. Whenever the clutch is replaced, the DMF should be checked for wear. The two key wear characteristics are freeplay and sideplay. These should be measured to determine whether the flywheel is serviceable. The wear limit specifications can be found in vehicle or flywheel manufacturer's published documentation. Other failure modes are severely grooved/damaged clutch mating surface, grease loss, and cracking.