Marine Installation Manual
2021-08
6-14
6 Engine Dynamics
6.4 Torsional vibration
X72DF
Figure 6
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9 Vibration dampers (spring type and viscous type)
6.4.2
PTO/PTI systems effect on torsional vibration
A propulsion plant may include a main engine-driven generator (PTO, power
take-off), a shaft-line connected electric motor (PTI, power take-in), or both.
These elements are connected to the engine or shafting by clutches, gears, shafts
and/or elastic couplings (see
-
ments).
Installations with PTO or PTI require special attention in the early stages of a
project. These systems may cause torsional vibrations and alignment challenges.
Risk of instable
engine speed
For many PTO /PTI systems that use elastic couplings, the lowest torsional nat
-
ural frequency can be problematic if it is below approximately 1.5 Hz. Here, there
is a risk of engine speed instability where the engine constantly adjusts its speed
to compensate the rotating vibration; this must be considered and compensated
for in the engine speed control system.
Installation of MFD
In addition, such PTO /PTI systems are very sensitive to misfiring as varying
firing loads can cause inadmissible torsional vibrations. To protect the elastic
couplings and gears from any misfiring, a misfiring detection device (MFD) must
be installed. This indicates either partial or total misfiring, allowing for appro
-
priate countermeasures (e.g. speed reduction, de-clutching of PTO /PTI branch)
to be applied automatically, protecting the PTO /PTI components.
For additional consideration about PTO /PTI application refer to section
, and for support regarding system layout, please contact WinGD.
SM-0095
Cover
Inertia ring
Casing
Silicone fluid
Springs
Intermediate parts
Lube oil supply
Viscous type
Spring type
