Page 54 - Introduction to Marine Engineering

Diesel engines 4 i

Clutches
A clutch is a device to connect or separate a driving unit from the unit it
drives. With two engines connected to a gearbox a clutch enables one or
both engines to be run, and facilitates reversing of the engine.
The hydraulic or fluid coupling uses oil to connect the driving section
or impeller with the driven section or runner (Figure 2.25). No wear will
thus take place between these two, and the clutch operates smoothly.
The runner and impeller have pockets that face each other which are
filled with oil as they rotate. The engine driven impeller provides kinetic
energy to the oil which transmits the drive to the runner. Thrust
bearings must be provided on either side of the coupling because of the
axial thrust developed by this coupling.
A plate-type clutch consists of pressure plates and clutch plates
arranged in a clutch spider (Figure 2.26). A forward and an aft clutch
assembly are provided, and an externally mounted selector valve
assembly is the control device which hydraulically engages the desired
clutch. The forward clutch assembly is made up of the input shaft and
the forward clutch spider. The input shaft includes the forward driven
gear and, at its extreme end, a hub with the steel pressure plates of the

Circulation
vortex

Recirculating
Shrouding oil drain
cover holes

Figure 2.25 Hydraulic coupling