LO 8-11 Identify and describe the purpose, function, and types of diesel engine flywheels

1.1. Dual Mass Flywheels

Dual Mass Flywheels

Torsional vibration damping is important to drivetrain durability and reduction of noise, vibration, and harshness. A number of MD engines incorporate specialized torsional vibration damping springs into the flywheel and are called dual mass flywheels (DMFs). When connected to manual transmissions, DMFs enable the use of lighter transmissions and drivelines by minimizing torque spikes produced by torsional vibration Figure 74. Transmissions shift easier, and transmission gear rattle is virtually eliminated with DMFs.

DMFs are made from two separate sections that should be disassembled and inspected during clutch servicing. The clutch surface and ring gear are each separate halves of the flywheel. DMFs are further recognized by a series of springs located around the flywheel circumference on the engine side of the flywheel. One set of bolts (near the center hub) connects the flywheel to the crankshaft and another set of bolts holds both halves of the flywheel together Figure 75.

FIGURE 08-74: Dual mass flywheels minimize the transfer of torsional vibration to transmissions and drivelines.

FIGURE 08-75: A dual mass flywheel is constructed of two major parts. This rear section contains damping springs used to absorb torsional vibration. A flat steel clutch plate (removed) bolts to the front surface section of the flywheel.

Power is transmitted to the flywheel clutch mounting surface through a series of springs located around the circumference of the inner plate, which attaches to the crankshaft. These springs act like the damping springs of a clutch disc to reduce torsional vibration. Between the inner and outer sections of the flywheel, a friction ring permits the inner and outer parts of the flywheel to slip. This friction ring will slip only under high torque input, which prevents transmission damage from excessively high torque inputs that are caused by loading the vehicle beyond its gross vehicle weight (GVW) capacity. The friction ring is made of a material similar to brake lining and can wear out if excessive torque loads are continuously applied. If this occurs, there is a loss of torque transfer to the powertrain and the flywheel requires replacement.