Dual Mass Flywheel (DMF)

DMF with centrifugal pendulum-type absorber

For most of the engine applications, the torsional vibrations could be reduced with dual mass flywheel, assuming that comfortable driving at low engine speeds was possible. In addition to engine speed and number of cylinders, engine rotational speed irregularities greatly depend on how much torque the engine can produce at low speeds. Modern petrol and diesel engines which produce a high level of torque at a low speed cause greater torsional vibrations compared with the engines that produce less torque of the same engine speed.

These high torque engines place very high demands on the torsional vibration damping system and the engine vibrations can no longer be satisfactorily eliminated using conventional dual mass flywheels.

An innovation to efficiently eliminate two engine torsional vibrations is the dual mass flywheel with centrifugal pendulum absorbers. It is best suited for the torque characteristic and the torsional vibration behaviour of modern engines because it can reduce the lower limit of the usable speed range of the engine, which means that fuel and CO2 savings are possible.

DMF with centrifugal pendulum absorber

Image: DMF with centrifugal pendulum absorber
Credit: BMW

The centrifugal pendulum absorbers are an additional functional unit in the dual mass flywheel, which contain four pendulum masses on the secondary mass. The springs used in the primary mass absorb relevant vibrations, while the remaining engine rotational speed irregularities are effectively eliminated by the pendulum masses.

The pendulum masses are arranged at 90° intervals and amounted so that they can oscillate freely in the direction of rotation. The weight of the pendulum masses and the curved radius of the bearing track are precisely coordinated to the torsional vibration or behaviour of the engine so that they oscillate contrary to the torsional vibrations of the engine. With this opposing effect of the pendulum force, the disturbing torsional vibrations of the engine are reduced very effectively upstream of the gearbox.

At low engine speeds when the disturbing torsional vibrations are particularly high, the pendulum swings are correspondingly large and so work effectively against the torsional vibrations of the engine. With increasing engine speed the torsional vibrations of the engine become weaker and have a higher frequency. Due to the interplay a pendulum force on the curved shape of the pendulum bearing the pendulum swings also become less severe and have a higher frequency.

Dual Mass Flywheel with Centrifugal Pendulum-type Absorber

Image: DMF with centrifugal pendulum-type absorber
Credit: LuK

The counter vibrations are just smoothly to fit with the engine speed until an engine speed is reached where there are no longer any noticeable torsional vibrations. Dual mass flywheel with centrifugal pendulum absorbers cannot be differentiated from dual mass flywheel without centrifugal pendulum absorbers purely by their external appearance

With centrifugal pendulum absorber technology, engine rotational speed irregularities are eliminated more effectively than was possible with conventional dual mass flywheel. Centrifugal pendulum absorber technology is particularly effective on low consumption and high torque engines, with a low number of cylinders as these naturally run less smoothly.

Centrifugal pendulum absorber technology enables low engine speed in economic driving with high acoustic driving comfort. Centrifugal pendulum absorbers are not used instead of the dual mass flywheel but instead integrated as an additional functional unit.

The DMF with centrifugal pendulum-type absorber has been developed to further increase damping capacity at low engine speeds. Using no additional installation space, a further additional mass (the centrifugal pendulum-type absorber) has been added to the two main masses in the DMF. It consists of three or four double pendulum masses which sit on the DMF drive plate. They are suspended on two studs which move in kidney-shaped paths in the pendulum masses and in the drive plate.

Standard DMF - centrifugal pendulum-type absorber

Image: Standard DMF – centrifugal pendulum-type absorber
Credit: LuK

1 – pendulum mass

Oscillation of the pendulum masses is induced by the ignition frequency of the engine. The pendulum, however, is not directly in the power flow. As a result of inertial torque, the pendulum masses move in opposition to the initial oscillation and, in this way, act as oscillation dampers. The total weight of the pendulum mass is only one kilogram.

The result is optimum oscillation damping at high torque and low engine speed. This makes a major contribution to reducing fuel consumption and CO2 emissions.

Damped Flywheel Clutch (DFC)

Damped Flywheel Clutch (DFC)

Image: Damped Flywheel Clutch (DFC)
Credit: LuK

When replacing the clutch and DMF, the DFC is a proven repair alternative. It consists of a pre-assembled, tuned assembly unit of DMF, clutch disc and clutch pressure plate. The preassembly of the individual components in the factory saves considerable time in the workshop, as the DFC can be mounted directly on the engine. No clutch assembly work is necessary. Frequent causes of faults, such as incorrect assembly or the combination of components from different manufacturers, are avoided.

Damped flywheel clutch (DFC) - front-rear view

Image: Damped flywheel clutch (DFC) – front-rear view
Credit: LuK

1 – clutch assembly containing clutch pressure and driven plates
2 – secondary mass with flange
3 – primary mass

DMF for Continuously Variable Transmission (CVT)

In a fully automatic gearbox, the torque converter acts, among other things, as a centrifugal oscillation damper in the drive train. CVT gearboxes, however, work without a torque converter. Therefore, the centrifugal damping is provided by a special form of the DMF.

The crucial difference from the DMF designs described above is in the design of the torque output. This does not take place via the friction surface of the secondary mass or via the flange toothing as in the double clutch damper. In the DMF for CVT gearboxes, the engine torque is directly transferred through a central hub, riveted to the flange and the secondary mass, to the form-fit gearbox input shaft.

DMF for Continously Variable Transmission (CVT)

Image: DMF for Continously Variable Transmission (CVT)
Credit: LuK

1 – hub
2 – additional mass on the secondary mass side

Planetary gear DMF

Compared to a standard dual mass flywheel, in a planetary dual mass flywheel the primary mass is connected to the secondary mass via an arc spring damper unit which also contains a planetary gear set. The planetary gear directly connected to the primary side helps to create an anti-resonance in the transfer system behaviour. Vibration excitation with frequencies close to the anti-resonance frequency are
reduced very well with the planetary gear flywheels. The planetary gear dual mass flywheel improves also the noise reduction.

DMF with planetary gear

Image: DMF with planetary gear
Credit: ZF Sachs

1 – primary mass
2 – spring
3 – planetary gear
4 – plain axial bearing
5 – plain radial bearing
6 – ring gear
7 – hole for securing pin
8 – spring cap
9 – sliding shoe
10 – cover plate to retain lubricant (grease)
11 – secondary mass

Planetary gear dual mass flywheels are mainly used for commercial vehicles applications.

To summarise, in an automotive application a dual mass flywheel has to control three basic operating modes of the engine and drivetrain:

  • transmission rattle during idle, drive and coast
  • resonance break-through during engine start and stop
  • surging associated with torque changes

Improvements in driving comfort achieved by the dual mass flywheel (DMF), together with low-cost designs resulting from goal-oriented, value analysed development, has led to the increased popularity of dual mass flywheel (DMF).

References

  • Dual Mass Flywheel with Centrifugal Pendulum-type Absorber, LuK
  • Gérémy Bourgois, Dual Mass Flywheel for Torsional Vibrations Damping – Parametric study for application in heavy vehicle, Chalmers University of Technology, 2016
  • Dr.ing. Albert Albers, Advanced Development of Dual Mass Flywheel (DMFW) Design – Noise Control for Today’s Automobiles, LuK Clutch Symposium
  • Dipl. ing. Michael Schnurr, Development of the Super-Long-Travel Dual Mass Flywheel, LuK
  • Dr. Ad Kooy, Isolation is key – The evolution of the centrifugal pendulum-type absorber not only for DMF
  • Dual Mass Flywheel – Technology, Failure Diagnosis, Special Tool, User Instruction, LuK
  • Transmission Systems – Dual Mass Flywheel, Valeo

Leave a Reply

Ad Blocker Detected

Dear user, Our website provides free and high quality content by displaying ads to our visitors. Please support us by disabling your Ad blocker for our site. Thank you!

Refresh