Dual Mass Flywheel - Seminar Paper

 

Introduction 

In modern light-diesel technology we are seeing much greater horsepower and torque gains sometimes coupled to better fuel economy. Dual Mass Flywheels have been used in many light-duty diesel trucks since 1987 that are fitted with a standard manual transmissions . Along with their continued use in such applications, DMFs are now also being fitted to high performance vehicles such as BMW’s and other similar luxury vehicles their primary purpose being to provide a vibration dampening action in the drive train.

The benefits of Dual Mass Flywheels

• To eliminate excessive transmission gear rattle, making driving comfortable at any speed,
• reduce gear change/shift effort, and
• increase fuel economy.

Why is a Dual Mass Flywheel needed?

Transmissions in light duty trucks diesel powered vehicles have a by default 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.

By providing a vibration dampening action that is superior to the normal dampening actions in a normal clutch arrangement the vehicle can be operated for longer periods without long term damage.

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.

Function and Operation

The function of the Dual Mass Flywheels or DMF 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 DMF was not used the torsional frequencies could damage to the transmission.

DMFs are designed to provide maximum isolation of the frequency below the engine’s operating RPM, usually between 200-400 RPM. The time that the DMF works hardest is during engine startup and shutdown.

Construction

There are two basic types of DMF The first type of dual mass flywheel, or DMF as it is more commonly known, 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.

The system is also fitted with damper springs to absorb shocks.

The second is designed with planetary gearing (planetary DMF) is designed especially for engines with stronger vibrations in the lower rpm range. Although these are primarily diesel engines, this type of DMF provides a smooth engine output comparable to that of gasoline engines.

This type provides in addition to greater driving and shifting comfort, benefits for drivers include lower fuel consumption because the idling rpm is lower.