Volvo D11 series, Installation Manual

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Torsional vibrations
Torsional vibrations occur due to forces on the crank-
shaft caused by the piston and connecting rod during
the power stroke. These forces tend to deflect the
crankshaft, including angular displacement of the
shaft.
•
The frequency is the time rate of torsional vibra-
tions
•
The amplitude is the angular displacement due to
torsional vibrations.
•
The critical speed is the speed at which the ampli-
tude of the vibrations in a shaft are maximum and
could result in stresses that exceed the safe limit
of the material.
•
Torsional vibrations may also be caused by torque
vibrations at the propeller.
Torsional vibration approvals
The object of a Torsional Vibration Calculation (TVC)
is to locate the critical speed points and to ensure
that these critical speeds are outside the operating
range of the engine.
Disregarding the torsional compatibility of the engine
and driven equipment may fracture the crankshaft
and flywheel bolts and overheat the vibration damper.
Since compatibility of the installation is the system
designer’s responsibility; it is also his responsibility to
obtain the theoretical torsional vibration analysis.
Volvo Penta standard propulsion packages would
generally not require TVCs unless front end PTO is
utilised. TVCs are recommended for all heavy duty
commercial applications. In classified installations, a
TVC must be performed.
Torsional analysis data
Volvo Penta will do a torsional analysis on receipt of
the necessary details from the customer. The follow-
ing technical data is required to perform a torsional
analysis:
A. Operating speed ranges. Lowest speed to highest
speed.
B. Maximum power output.
C. Detailed drawing of rotating components.
D. Inertia of rotating components and location of
masses.
E. A general layout drawing is needed for more com-
plicated installations.
For the purpose of TVCs, most drive line manufactur-
ers provide shaft drawings, with moment of inertia
and their position on the shaft diameters.
Torsional vibrations and TVC calculations