Flywheel: Description and Operation
Double Mass Flywheel
Power strokes and the firing order of the engine produce speed fluctuations, which cause torsional oscillation of the entire drive train because of their irregularity.
This torsional oscillation in turn causes rattling, knocking or grinding of all loose parts with play and not in power flow (loose gear wheels, parts of synchronization, shift elements). This could lead to disturbing transmission noise, especially at low engine speed.
In order to reduce the level of transmission noise, the torsional oscillation must be reduced enough prior to passing into the transmission, that it is no longer found to be disturbing. Operation without noise is only possible when the resonance speed of the drive train is lower than the common operating speed, e.g. less than 500 rpm.
This can be accomplished by increasing the mass moment of inertia for the transmission's input shaft with help of additional flywheel mass after the torsion damper.
In order not to have to accelerate or decelerate this additional mass during shifts, a one-way clutch is in power flow behind the actual torsion damper. A double mass flywheel is produced in this manner.
Section Drawing Of Double Mass Flywheel:
1 - Primary flywheel
2 - Gear ring for reference mark sender
3 - Starter gear ring
4 - Cover plate
5 - Rubber damper
6 - Damping elements
7 - Secondary flywheel
8 - Drive plate
9 - Service-life lubricated ball bearing
10 - Circlip
11 - Plug
12 - Bolt
13 - Pressure plate housing
14 - Pressure plate
15 - Clutch slave cylinder
16 - Release fork
17 - Release bearing
18 - Transmission input shaft
19 - Crankshaft
The secondary flywheel mass. which has positive connection on transmission shaft (18) via drive plate (8) when the clutch is closed, changes the natural resonance of the drive train to very low speeds and in this manner guarantees smooth transmission operation, especially at low operating speeds.
Components
The double mass flywheel system is mounted direct on the crankshaft. The primary mass, with positive connection on the flywheel, consists of primary flywheel (1), which is fitted with gear ring (2) for the ignition's reference mark sender.
Starter gear ring (3) is also mounted on the primary flywheel. Housing (13) for the pressure plate is made of light alloy metal, while pressure plate (14) is a gray cast iron product. Housing and pressure plate belong to the secondary mass.
Mechanical stops (A) on the primary flywheel can be recognized readily. They have contact with the counterstops of secondary mass when reaching a torsion angle of approx. 30° in drive or coasting.
This image shows a partially disassembled double mass flywheel with starter gear ring (3). The starter gear ring can be replaced for repairing.
Cover plate (4) located underneath must not be removed, since there is a precisely weighed amount of silicone grease on the inside for damping of oscillation.
NOTE: It could be possible that the silicone grease settles on low points of the damping chamber after a long period of downtime or, for example, while transporting the car by railroad, depending on the operating temperature immediately before downtime. Consequently the double mass flywheel could be imbalanced during the first seconds of engine operation after starting the engine. This residual imbalance, however, will be eliminated in a short time after the silicone grease is distributed uniformly in the damping chamber.
Cover plate (4) belongs to the mass of the primary flywheel.
The actual rubber damper (5), which is mounted with the outer race on the primary flywheel, is visible underneath the cover plate. Damper is mounted from the inside on the secondary mass with twelve bolts. Torsion angles of 30° each are possible.
Eight damping elements (6) arranged in a star pattern move in silicone grease, which is not shown in this picture.
Damping elements are connected positively on the secondary mass.
The outside of secondary mass (7) bolted on the inner race of the rubber damper is the bearing surface (engine end) for clutch disc (8). Ball bearing (9), permanently lubricated and sealed on both ends, is applied to the center and guide both flywheel masses to each other. This ball bearing can be replaced after removal of circlip (10).
Drive plate (8) is completely inflexible in the circumferential direction, but does have a spring-loaded liner for soft clutching. Beral K 208/1b liner does not contain asbestos.
If a double mass flywheel has to be disassembled, plugs (11) must be removed first. Twelve bolts (12) will then be visible underneath, which are used to bolt rubber damper (5) on the secondary mass.
After removal of these bolts, primary and secondary masses can be pried apart with the help of bolts.
Plugs (11) and mounting bolts (12) must always be replaced after disassembling.
The following repairs are possible:
- Replacement of starter gear ring
- Replacement of secondary mass with mounted ball bearing (9)