Centrifugal Pendulum DMFs
Dual Mass Flywheels (DMFs) set a new standard for drivetrain noise insulation and vibration damping when launched by LuK in 1985. A total of 63 million DMFs have since been manufactured, and one in three cars on European roads currently use DMF technology to aid comfort and reduce fuel consumption and CO2 emissions. Now pendulum-type absorbers have taken this technology a step further.
A brief history
Instead of a rigid flywheel located between the engine and the transmission, the DMF employed a flywheel split into two masses. This allowed the momentum of the primary mass on the engine side to be decoupled from the momentum of the secondary mass on the transmission side, while both remained connected to each other by means of a spring damping system.
Arc springs are at the heart of the DMF. These are significantly longer than the clutch damper springs previously used and are more efficient at insulating transmission vibration. Consequently, DMFs were able to reduce critical engine speeds to levels below idle speed, thereby ensuring reliable damping of engine vibration.
A step further
Engineers and designers at LuK have since managed to push the dampening properties of the DMF even further by incorporating aircraft engine technology into the design. Centrifugal pendulum absorbers have been in existence for decades and are used in many aircraft engines. With the integration of a number of centrifugal pendulum absorbers, the damping characteristics of the DMF have been greatly increased.
Centrifugal pendulum absorbers are mounted into the drive flange of the DMF which is subsequently attached to the secondary mass. This gives the flywheel extra inertia which is variable with engine speed, and at the low point of the rev range (where we see the most vibration) this extra inertia can adjust the amount of absorption, thus reducing the amount of vibration.
Efficient absorption of the selected vibration level, i.e. the frequency of the engine, can be achieved through the appropriate tuning of the pendulum masses. The basic vibrations are still absorbed by the DMF using a spring damper system; however the residual vibrations are taken care of by the centrifugal pendulum absorbers.
As the pendulum weights are attached to the drive plate and therefore take up no extra space, centrifugal pendulum absorber DMFs can be used wherever a standard DMF is already installed. A pendulum mass of just one kilogram is all it takes to reduce the vibration transmitted to the transmission by up to 60%.
LuK says almost 69,000 DMFs with centrifugal pendulum absorbers were fitted to new cars to the end of 2010. This new DMF design will filter through to the aftermarket over the next 3-5 years as these cars start to come out of their warranty period.