I have re-read the section you mention (I was first introduced to the rattler a long time ago) and this is what it says…
“Answer: There are fluid type and stock type or elastomer dampers. Newest to the market is the Rattler� absorber. The first two units have been readily available to the automotive market for many years and in fact were the only types available. The fluid type and elastomer type devices are dampers and tend to reduce vibration by > using friction to dissipate energy> . The Rattler, an absorber, is a device that absorbs and controls vibration by using internal rollers that automatically offsets the twisting forces that cause vibration.”
It cleary says that the elastomer type reduces vibration by using friction to dissipate energy. This is incorrect, whereas a fluid type damper does dissipate energy by heat caused by friction (and is usually finned to aid cooling) an elastomer type asborber only dissipates a small amount of energy via heat and this is not by design but is a loss associated with its relatively low efficiency.
The majority of the energy absorbed is put back into the crankset during the latent non excitation phase, just as it is with the rattler. In this application the elastomer acts just like a spring, storing energy on extension (excitation of the crank) and releasing it when latent.
This is entirely consistent with the explanation given in my post earlier in this thread.
"Often, the vibration attenuating devices on the free end of an engine crankshaft are incorrectly referred to as “DAMPERS”. In most cases, they are ABSORBERS. (That’s not semantics. A damper dissipates energy, typically as heat. An absorber alternately stores and releases energy to counteract vibration).
The elastomeric (“metal-ring-on-rubber-spring”) devices used by the automotive industry are ABSORBERS which are tuned to counteract vibration at the frequency where the particular engine generates its worst torsional excitation."
Generically both devices smooth or dampen the uneven torque loadings on the crank which is why they are lazily called ‘dampers’ since this term adequately describes their function and precludes the need to distinguish between them. However their modes of operation are very different and the means by which they achieve their functions is distinct.
Dampers operate by only reducing the peak torque loading, whereas absorbers reduce the peak torque as well as ‘reducing’ the torque trough by returning energy to the system at this point in the cycle. The weight of the ring and its moment of inertia determines pretty much the rev range at which the ‘absorber’ operates. A damper will pretty much operate at any point in the rev range.
A ‘damper’ will soak up some of the torque peak energy (typically 4 or 5 times the average torque) and this will be shed as heat, an absorber will soak up some of the energy and return it to the crankset as the crank decellerates.
The elastomer type absorber is dual mass with the outer heavy ring attached to the pulley with a rubber/elastomer bond, as the crank accelerates the outer ring is left behind since it is attached elastically, as the crank decellerates the outer ring catches up and momentarily overtakes the crank returning most of its energy.
This is common with dual mass flywhels which can eliminate rollover noise at idle in the same way.
The rattler achieves this by leaving behind the steel rollers during the acceleration/excitation phase, these catch up on the latent or decelleration phase and return their energy in a similar way to an elastomer damper.
Add your name to the list of people incorrectly referring to absorbers as dampers.
dva’s efforts at timpony
Although percussive it’s hardly timpony, campanology would be a better analagy.
Dave