The dual mass flywheel, or DMF, eliminates excessive transmission gear rattle, reduces gear change/shift effort, and increases fuel economy.
There are two basic types of Dual Mass Flywheels. The first is made up of a primary and secondary flywheel with a series of torsion springs and cushions.
There is a friction ring located between the inner and outer flywheel that allows the inner and outer flywheel to slip. This feature is designed to alleviate any damage to the transmission when torque loads exceed the vehicle rating of the transmission. The friction ring is the weak spot in the system and can wear out if excessive engine torque loads are applied through it. The system also has a center support bearing that carries the load between the inner and outer flywheel, and is fitted with damper springs to absorb shocks.
The second type of DMF incorporates planetary gearing. It is designed for engines with stronger vibrations in the lower RPM range. As well as greater driving and shifting comfort, the planetary DMF provides the benefit of lower fuel consumption because the idling RPM is lower.
Dual mass flywheels are fitted to light-duty diesel trucks with standard manual transmissions and, and to higher performance luxury vehicles to dampen vibration in the drive train. This also allows vehicles to be operated for longer periods without long term damage.
Transmissions in light-duty diesel powered trucks have a heightened sensitivity to fluctuating torsional inputs. This results in a strong torsional resonance or vibration that occurs during operation of the vehicle within normal driving ranges.
The function of the dual mass flywheels is to isolate torsion crankshaft spikes created by diesel engines with high compression ratios. By eliminating the torsion spikes, the system eliminates any potential damage to the transmission gear teeth. If the dual mass flywheel was not used, the torsional frequencies could damage to the transmission.
The dual mass flywheel construction relocates the damper from the driven disc to the engine flywheel. This repositioning dampens engine torsional vibrations more than is possible with standard clutch disc dampening technology.
Dual mass flywheels are designed to provide maximum isolation of the frequency below the engine's operating RPM, usually between 200-400 RPM. They are also most effective during engine startup and shutdown.