Note: Descriptions are shown in the official language in which they were submitted.
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A MARINE PROPULSION SYSTEM
This invention relates to a marine propulsion
system. More particularly, this invention relates to a
marine propulsion system for a passenger ship.
Heretofore, it has been known to have a propulsion
system for a ship in which at least one drive shaft equipped
with a variable-pitch propellor which is directly coupled to a
low-speed two-stroke diesel engine serving as a propulsion
engine. It has also been known to provide at least two
auxiliary diesel engines for driving individual generators
in order to produce electrical energy for the ship.
As is known, the peak speed required for a
passenger ship, particularly a cruise ship, is considerably
above the maximum necessary cruising speed. Usually,
the peak speed is required only in exceptional cases. However,
the propulsion engine must be designed for the peak speed.
As a result, the propulsion engine is over-dimensioned and
makes relatively ineffective use of the installed engine
power.
On the other hand, for aafety reasons, the power for
generating the required electrical energy for the ship must
be considerably greater than necessary, for example, by
thirty percent to forty perce~t. Usually, the required
power is produced exclusively by medium-speed or high-
speed auxiliary eng~nes.
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Accordingly, it is an object of the invention
to improve the use of the total power installed on a
ship in the form of diesel engines.
It is another object of the invention to provide
an efficient marine propulsion system.
It is another objectof the invention to provide
for the efficient use of power on ~ passenger ship.
; Briefly, the invention provides a marine propulsion
system for a passenger ship which comprises at least one
drive shaft~ a variable-pitch propellor connected to the
drive shaft to be driven thereby and a low-speed two-stroke
diesel engine coupled to the drive shaft for driving the
shaft and having a crank shaft connected to the drive
shaft. In addition, the system includes at least two
generators for generating electrical energy for delivery
to an electrical system of the ship, at least two auxiliary
diesel engines each of which is connected to a respective
generator to drive the generator and an electric motor/
generator connected to and between the low-speed engine
and the electrical system to selectively transfer power
from the electrical system to the crank shaft in order to
drlve the drive shaft or deliver excess power from the two-
stroke engine o the electrical system in the form of
electrical energy.
In this manner, the propulsion engina or engines
can be designed so that, allowing for a safety margin and
using, for example, ninety percent of their maximum power~
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the engines can supply just the power required at the ~Q~
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cruising speed. This power is usually the 1:,,ir~u.~ nccc~s~r,,
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that is, the base~loa~ on the propulsion capacity. Thus,
higher speeds or propulsion powers can be taken ~rom the
redundant power reserved in the electrical system of the
ship via the motor/generator which is preferrably disposed
in series with the drive shaft and the propulsion diesel
engine.
Consequently, a propulsion system is available
for the speed range usually required and is directly coupled
to the two stroke diesel engine. The propulsion system is
particularly characterized by low fuel consumption, low
maintenance costs and the elimination of transmission losses.
" If a synchronous machine is used as the motor/
generator, it is advantageous, after reaching the
synchronous speed, for increases in propulsion power,
for example, for higher ship's speeds, to be made exclusively
by varying the pitch of the variable-pitch propellor (i.e.
screw blades).
Advantageously, if there is a certain excess of
power due to a low ship's speed, the rotation rate can be
increased to the synchronous speed of the motor/generator
without increasing the power avallable for propulsion, by
varylng the pitch of the variable-pitch propellor. The
excess power of the propulsion en~ine available at the
synchronous speed is then converted by the m~tor/generator
into electrical energy and supplied to the ship's electrical
system. The output of the generator/cliesel motors can then
be reduced and electrical energy can be generated by the
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economic two-stroke diesel engine. To this end, a low-speed
motor/generator can be directly connected to the crankshaft
of the propulsion engine~ If the dimensions of the required
electrical machines are too large, a step-down gear can
alternatively be incorporated between the propulsion engine
and the motor/generator, in which case a flexible clutch
will be provided between the gear and the propulsion engine.
These and other objects and advantages of the
invention will become more apparent from the following
detailed description taken in conjunction with the accompanying
drawings wherein:
Fig. 1 illustrates a schematic diagram of a marine
propulsion system in accorda~ce with the invention.
Fig. 2 illustrates a modified connection between
a motor/generator and a two-stroke engine of the propulsion
system; and
Fig. 3 graphically illustrates the required
propulsion power versus the ship's speed and the speed of the
propulsion engine crank shaft.
Referring to FlgO 1, the marine propulsion system
is constructed for use in a passenger ship, such as a
cruise ship. As shown, the system includes a pair of
drive shafts 1, each of which is connected to a variable-
pitch propellor or screw 2 ~or driving of the propellor
2. In addition, a low-speed two stroke diesel engine 3 is
coupled to each drive sha~t l in order to drive the
respective drive shafts 1. Alternatively~ instead of using
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two shafts 1 there may, of course, be only one shaft or
more than two shafts. The low-speed two-stroke diesel
engine also has a crank shaft 9 connected to the drive
shaft 1 in known manner.
The propulsion system also has a plurality of
generators 5, for example four or more generators, which
are provided for generating electrical energy for delivery
to an electrical system 4 of the ship. This electrical
system is symbolically illustrated a~ a busbar. Each
generator 5 i5 driven by a separate auxiliary diesel engine
6, for example a medium-speed or high-speed four stroke
engine. The capacity installed in these engines 6 is so
large that the electrical energy requirement can be covered
many times, for example, by a factor of 1.25 to 1.5.
As shown, a pair of electric motor/generators 7
are connected to and between the electrical system 4 and a
crank shaft 9 of a respective diesel engine 3. As indicated
in Fig. 1, the connection of a motor/generator 7 to a crank
shaft 9 may be via a step-down gear 8 and a flexible clutch
lO which serves to mechanically separate the motor/generator
7 from the crank shaft 9. Alterna~ively, as show~ in Fig. 2,
each motor/generator may be directly coupled to the cranX
shaft 9 of an engine 3.
~he low-speed diesel engines 3 are designed to
maintain the maximum required cruising speed when using
about ninety percent of their maximum power~ This power
coxresponds to the point 11 shown to the left the graph
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of Fig. 3. The speed range A of the ship is therefore
covered by the propulsion engines alone. Advantageously,
the power can be adjusted, for example, by varying the
speed of rotation. Between the points 11 and 12 5hown in
Fig. 3, the power required for a speed range B cannot be
covered by the diesel engines 3 alone. In this range, the
motor/generators7 are also connected as engines to the
respective crank shafts 9.
As shown to the right in Fig. 3, the propulsion
power at point 11 is assigned to a crank shaft speed at a
point 13 which coincides (see Fig. 2) or corresponds (see
Fig. 1) with the synchronous speed ns of the motor/generator
7.
The conventional speed regulating system of the
diesel engines 3 is designed so that even after a further
increase in power, the synchronous speed of rotation is
kept constant with any increase in the required power being
accounted for in known manner by varyi~ the pitch of the
propellors 2 In this manner, the power required for
20~^? maximum ship speed 12 is reached at the point 14 indicated
in Fig. 3. The required power C is thus taken from the
electric motor/generators 7 or the ship's elsctrical system 4.
As previously explained, i there are considerable
differences in efficiency bet~een the two-stroke and four-
stroke engines 3, 4 at low ship's speeds, at points 15 or 16
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in Fig. 3, the power can be adjusted by regulating the
propellors instead of the speed of rotation and the
speed of rotation can simultaneously be increased from
nl to nS The power reserve then available from the
two~stroke diesel engines 3 in the range D is supplied by
motor/generators 7 as electrical energy to the ship's
electrical system 4.
As indicated in Fig. 1, each motor/generator 7
and respective low-speed engine 3 are disposed in series
relative to a drive shaft 1.
The invention thus provides a relatively efficient
marine propulsion system in which the power required to move
a ship at peak speed can be taken, in part, from the
electrical system of the ship. In like manner, the reserve
power provided by the diesel engines of the propulsion
system can be used in the electrical system of the ship.
