Page 55 - Introduction to Marine Engineering

42 Diesel engines

Forward
clutch Output
Forward spider gear
driven Forward Input wheel
gear pinion shaft

Output
shaft

Input
shaft

T
Reverse Output
driven gear Reverse
gear wheel clutch
spider
(a)
Figure 2.26 Plate-type clutch

forward clutch assembly spline-connected, i.e. free to slide. Thus when
the input shaft turns, the forward driven gear and the forward clutch
pressure plates will rotate. The forward clutch plates are positioned
between the pressure plates and are spline-connected to the forward
clutch spider or housing. This forward clutch spider forms part of the
forward pinion assembly which surrounds but does not touch the input
shaft. The construction of the reverse clutch spider is similar.
Both the forward and reverse pinions are in constant mesh with the
output gear wheel which rotates the output shaft. In the neutral position
the engine is rotating the input shaft and both driven gear wheels, but
not the output shaft. When the clutch selector valve is moved to the
ahead position, a piston assembly moves the clutch plates and pressure
plates into contact. A friction grip is created between the smooth
pressure plate and the clutch plate linings and the forward pinion
rotates. The forward pinion drives the output shaft and forward
propulsion will occur. The procedure when the selector valve is moved
to the astern position is similar but now the reverse pinion drives the
output shaft in the opposite direction.

Gearboxes

The gearing arrangement used to reduce the medium-speed engine
drive down to suitable propeller revolutions is always single reduction